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 Cristina LEONELLI Professore Ordinario presso: Dipartimento di Ingegneria "Enzo Ferrari"

## Pubblicazioni

- METHOD AND APPARATUS FOR NEUTRALIZING THE BACTERIAL CONTENT IN HOSPITAL WASTE OR OTHER SPECIAL WASTE, SO AS TO BE ABLE TO DISPOSE OF SAID WASTE AS ORDINARY WASTE [Brevetto]
L., SALDA LUCIANO; A., Cappi; Leonelli, Cristina; Veronesi, Paolo
abstract

The invention relates to a method characterized by the sequence of at least the following working steps: introducing an accumulated mass of waste which has been suitably shredded into a plurality of composite, pressure-resistant, treatment chambers which are screened with respect to the exterior and provided with windows which are arranged suitably staggered with respect to each other and distributed at least along the height of the said accumulated mass and are connected to respective waveguides linked up to magnetrons and are such that the microwaves produced by the latter are forced to strike said waste; preparing each said composite chamber, for treatment of the associated accumulated mass of internal waste, with appropriate moisture, pressure and temperature values and with suitable cycle times, preferably with implementation of a prior step involving internal depressuhsation of this composite chamber, which is filled, closed and ready for the sterilisation cycle; activation of the magnetrons of the said composite chamber and rotation of the associated accumulated mass of internal waste in relation to the said magnetrons which remain in a static position, so to obtain the uniformly distributed sterilisation of the said accumulated mass of waste, also using low-power magnetrons; releasing the pressure and the vapours from the said composite chamber so as to be able to open it safely and discharge from said chamber the sterilised waste.

- Plasma generator [Brevetto]
Veronesi, Paolo; Leonelli, Cristina; M., Garuti
abstract

A plasma generator (1) comprising a main duct (10) for a gas to be ionised (20), a waveguide (50) for electromagnetic radiation (30), and at least one supporting element (60) on which the waveguide (50) and main duct (10) are mounted; a first portion (51) of the waveguide (50) extends transversely of the supporting element (60) in a first region (61a) facing a first surface (61) of the supporting element. A second portion (52) of the waveguide (50) intersects the duct (10) for interaction between the gas (20) and the radiation (30) and for plasma generation (40); the duct (10) expends transversely of the supporting element (60) in the first region (61a).

- Plasma generator with a slot antenna [Brevetto]
Veronesi, Paolo; Leonelli, Cristina; M., Garuti
abstract

A plasma generator comprising a propagation chamber (10) propagating an electromagnetic radiation, and a plasma-generating chamber (20) associated with the propagation chamber (10); said propagation chamber (10) has a passage region (12) of increasing width on moving away from the entrance region (11) for insertion of the electromagnetic radiation into the propagation chamber (10). The passage region (12) enables an at least partial passage of the electromagnetic radiation towards the plasma-generating chamber (20).

- Procedimento di inertizzazione di amianti mediante applicazioni di microonde [Brevetto]
Leonelli, Cristina; Pellacani, Gian Carlo; Siligardi, Cristina; G., Gherardi; G., Marucci
abstract

Il brevetto descrive un metodo per poter riscaldare in un forno a microonde diverse pezzature di amianto o materiali contenenti amianto. Il riscaldamento a microonde, trasferendo energia sotto forma del campo elelttromagnetico, riesce a riscaldare in breve tempo l'amianto che è un noto isolante termico. A seguito del riscaldamento il minerale fibroso degrada in un materiale assolutamente innocuo attuando così l'auspicata inertizzazione ed azzerando la tossicità del prodotto iniziale. Il brevetto riporta dati sperimentali eseguiti presso i laboratori attrezzati dell'ENEA. Si riporta anche l'idea di avere applicatori aperti in grado di realizzare l'inertizzaizone su superfici piane di amianto o di materiali conteneti amianto, come ad esempio l'Eternit.

2021 - Alkali activation of metallurgical slags: Reactivity, chemical behavior, and environmental assessment [Articolo su rivista]
Lancellotti, I.; Piccolo, F.; Traven, K.; Cesnovar, M.; Ducman, V.; Leonelli, C.
abstract

Alkali-activated materials (AAMs) represent a promising alternative to conventional building materials and ceramics. Being produced in large amounts as aluminosilicate-rich secondary products, such as slags, they can be utilized for the formulation of AAMs. Slags are partially crystalline metallurgical residues produced during the high temperature separation of metallic and non-metallic materials in the steelmaking processes. In the present study, the electric arc furnace carbon or stainless steel slag (EAF) and secondary metallurgical slag such as ladle furnace basic slag (LS) were used as precursors in an alkali-activation process. EAF slag, with its amorphous fraction of about 56%, presented higher contents of soluble Si and Al species with respect to ladle slag R (35%). However, both are suitable to produce AAM. The leaching behavior shows that all the release values are below the regulation limit. All the bivalent ions (Ba, Cd, Cu, Ni, Pb, and Zn) are well immobilized in a geopolymeric matrix, while amphoteric elements, such as As and Cr, show a slight increase of release with respect to the corresponding slag in alkaline and aqueous environments. In particular, for Sb and As of AAM, release still remains below the regulation limits, while Mo presents an increase of leaching values that slightly exceeds the limit for landfill non-dangerous waste.

2021 - Effect of Combined Metakaolin and Basalt Powder Additions to Laterite-Based Geopolymers Activated by Rice Husk Ash (RHA)/NaOH Solution [Articolo su rivista]
Venyite, P.; Makone, E. C.; Kaze, R. C.; Nana, A.; Nemaleu, J. G. D.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

The present study deals with the use of locally prepared rice husk ash (RHA)-based sodium silicate for alkaline activation of laterites (uncalcined (LNW) and calcined (LCA)). RHA-based activator (SSR) was prepared by adding as-collected RHA to 6&nbsp;M NaOH at a solid/liquid mass ratio of 0.56. The various proportions of metakaolin (MK) and basalt powder (BA) influenced the final properties of the geopolymer products. After 28&nbsp;days of curing at room temperature, XRD, SEM and FT-IR analyses were used to study the evolution phases. Uncalcined laterite-based formulations showed their highest compressive strength at 29.86&nbsp;MPa with 20&nbsp;wt.% of MK, whereas calcined ones showed the most elevated strength at 47.02&nbsp;MPa, with the addition of 25&nbsp;wt.% MK. Further additions above these thresholds tend to reduce strength and increase setting time. Substitution of calcined laterite with basalt powder permitted to control the porosity of samples at low values with the consequent reduction of strength. In general, the water absorption and apparent porosity decrease with addition of metakaolin in raw laterite-based formulations and relatively decrease with addition of basalt powder in calcined laterite-based formulations, while bulk density remains relatively constant. The locally produced RHA-based alkaline activator is efficient for laterite geopolymerization, resulting in products with robust mechanical and physical properties capable of fostering application in quality housing.

2021 - Innovative porous ceramic matrices from inorganic polymer composites (IPCs): Microstructure and mechanical properties [Articolo su rivista]
Nana, A.; Cyriaque Kaze, R.; Salman Alomayri, T.; Suliman Assaedi, H.; Nemaleu Deutou, J. G.; Ngoune, J.; Kouamo Tchakoute, H.; Kamseu, E.; Leonelli, C.
abstract

The thermal performance of pegmatite-based geopolymer composites is investigated. Dense and compact matrix was prepared replacing metakaolin with pegmatite in the range of 70–85 wt% and activate with sodium hydroxide/sodium silicate solution in 1:1 vol ratio. The products of geopolymerization, cured at room temperature for 28 days, were heated at 100, 200, 400, 600, 800, 900, 1000 and 1100 °C with 2 h soaking time. The high values of flexural strength (46–51 MPa) were observed at 1000 °C as the consequences of low porosity (173 mm3/g) and water absorption (4.50–5.62%). The increase of the vitrification at 1100 °C enhanced the liquid phase and develop porosities responsible for reduction of strength. The mechanical properties, microstructural evolution and pore size distribution were found to be influenced by the amount of fine powder of pegmatite (solid solution).

2021 - Microwave Processing of PET Using Solid-State Microwave Generators [Articolo su rivista]
Veronesi, P.; Colombini, E.; Salvatori, D.; Catauro, M.; Leonelli, C.
abstract

The present study addresses the possibility of using a frequency-controllable microwave source, that is, a solid-state microwave generator, to rapidly and efficiently heat PET. Based on dielectric properties measurement of PET, numerical simulation has been used to model dedicated microwave applicators, suitable for the rapid reheating of PET granules or preforms. Numerical simulation, validated by experimental activity, demonstrates that using the proper frequency change as PET is being processed allows to maximize heating efficiency or homogeneity. Two examples of microwave applicators, one for small-scale and the other for large-scale production are presented, specially addressing the effect of using different metals for the modeling and construction of the microwave cavity.

2021 - Particle size-related limitations of persistent phosphors based on the doped Y3Al2Ga3O12 system [Articolo su rivista]
Boiko, V.; Dai, Z.; Markowska, M.; Leonelli, C.; Mortalo, C.; Armetta, F.; Ursi, F.; Nasillo, G.; Saladino, M. L.; Hreniak, D.
abstract

Co-doped Ce3+, Cr3+ and Pr3+ yttrium–aluminium–gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100&nbsp;°C show the optimal persistent luminescence and nano-particle size.

2020 - Alkali activated materials using pumice from the Aeolian Islands (Sicily, Italy) and their potentiality for cultural heritage applications: Preliminary study [Articolo su rivista]
Occhipinti, R.; Stroscio, A.; Finocchiaro, C.; Fugazzotto, M.; Leonelli, C.; Jose Lo Faro, M.; Megna, B.; Barone, G.; Mazzoleni, P.
abstract

In this paper, the potentialities of pumice-based geopolymers have been explored with the aim to evaluate their use as restoration materials. In particular, the behaviour of Aeolian pumice during alkali activation process, either alone or in binary mixtures with metakaolin, has been assessed using sodium hydroxide and sodium silicate activators. Hardened products were characterized by: X-ray diffraction; infrared spectroscopy; thermo gravimetry and electron microscopy. Furthermore, Hg-intrusion porosimetry, water absorption, compressive strength and colorimetric measurements were carried out in order to define the technical features of the produced geopolymers. The results reveal that Aeolian pumice mixed with small quantities (20–30 wt%) of metakaolin is suitable for the formation of lightweight geopolymers which exhibit an accessible porosity up to 30%, water absorption of about 18.0%, and satisfactory 28-day compressive strength up to 12 MPa. These values indicate good breathability and adaptability to the substrates of the proposed formulations. Final products display a homogeneous and compact amorphous matrix, and their colour mimic the original stones, highlighting their potential role in Cultural Heritage preservation.

2020 - Artificial neural networks test for the prediction of chemical stability of pyroclastic deposits-based AAMs and comparison with conventional mathematical approach (MLR) [Articolo su rivista]
Finocchiaro, Claudio; Barone, Germana; Mazzoleni, Paolo; Sgarlata, Caterina; Lancellotti, Isabella; Leonelli, Cristina; Romagnoli, Marcello
abstract

Abstract: The investigation on the reticulation degree of volcanic alkali-activated materials, AAMs, were experimentally determined in terms of chemico-physical properties: weight loss after leaching test in water, ionic conductivity and pH of the leachate and compressive strength. Artificial neural network (ANN) was successfully applied to predict the chemical stability of volcanic alkali-activated materials. Nine input data per each chemico-physical parameter were used to train each ANN. The training series of specific volcanic precursors were tested also for the other one. Excellent correlations between experimental and calculated data of the same precursor type were found reaching values around one. The evidence of strong effect on chemical stability of the alkaline activator SiO2/Na2O molar ratio as well as the Si/Al ratio of precursor mixtures on the reticulation degree of ghiara-based formulation with respect to volcanic ash-based materials is presented. It must be noted that such effect was much less pronounced on the compressive strength values, appearing more insensitive the molar ratio of the alkaline activator. The comparison of the ANN results with more conventional multiple linear regression (MLR) testifies the higher prediction performance of the first method. MLRs results, less significant, are useful to confirm the powerful capacity of ANNs to identify the more suitable formulation using a set of experimental AAMs. This study, as few others, on the correlation between chemical stability and compressive strength of AAMs provide a great contribution in the direction of durability and in-life mechanical performance of these class of materials. Graphic abstract: [Figure not available: see fulltext.].

2020 - Characterization and performance evaluation of laterite based geopolymer binder cured at different temperatures [Articolo su rivista]
Rodrigue Kaze, C.; Ninla Lemougna, P.; Alomayri, T.; Assaedi, H.; Adesina, A.; Kumar Das, S.; Lecomte-Nana, G. -L.; Kamseu, E.; Chinje Melo, U.; Leonelli, C.
abstract

This paper presents the results of experimental evaluation of curing conditions on the microstructure and performance of geopolymer binders developed from iron-rich laterite soils. Two calcined iron-rich laterites namely LB600 and LY600 were used as solid precursors in the preparation of geopolymer binders. The geopolymer samples were cured at 20, 60 and 80 °C. FTIR, XRD, EDS and DTA/TG were used to evaluate the microstructural properties of the prepared products. The performance of the binder was evaluated in terms of the compressive strengths, water absorption, porosity, bulk density and thermal conductivity. The findings from this study showed that the dissolution of the calcined laterites in 8 M NaOH increased the dissolution of Al, Si and Fe elements with increasing temperature from 20 to 80 °C. This higher dissolution of the monomers further resulted to an increase in the compressive strength of the binders at 7 and 28 days. It was also found out that curing the geopolymer in the dry state resulted in higher compressive strength at all ages compared to those cured in the wet and wet-dry state. Drying shrinkage evaluation of the geopolymer samples cured between 60 and 80 °C exhibited a lower linear shrinkage due to a high degree of geopolymerization. Microstructural investigation of the geopolymer samples cured at 80 °C showed a heterogeneous compact and dense structure resulting from high polycondensation. This densified microstructure also induced an increase in the thermal conductivity from 0.65 to 0.90 W/mK and 0.75 to 0.91 W/mK for LB600 and LY600, respectively. Nonetheless, both geopolymer binders made of LB600 and LY600 laterite powders performed well in dry, wet and wet-dry conditions, and can be used for various construction applications especially in the precast industry.

2020 - Construction and demolition waste (Cdw) valorization in alkali activated bricks [Capitolo/Saggio]
Lancellotti, Isabella; Vezzali, Vittorio; Barbieri, Luisa; Leonelli, Cristina; Grillenzoni, Andrea
abstract

2020 - Dependence of the geopolymerization process and end-products to the nature of solid precursors: Challenge of the sustainability [Articolo su rivista]
Kamseu, Elie; Alzari, Valeria; Nuvoli, Daniele; Sanna, Davide; Lancellotti, Isabella; Mariani, Alberto; Leonelli, Cristina
abstract

This review retrieves the determinant role of the solid precursor on the definition, chemistry, processing and applications of geopolymers. It is demonstrated that the process, the alkaline solution, the curing conditions as well as the orientation of the end-products in term of performance and potential application are governed by the intrinsic nature and characteristics of the aluminosilicate precursors. In particular, the amorphous fraction and the available Al and Si cations governs the geopolymerization. Solid precursors with relatively large amount of amorphous phase are easily activated with standard alkaline solution (6–8 M) leading to the formation of a gel, designated as cement or binder. Al-rich gels are efficient for the design of high strength concretes or composites. Solid precursors with low amorphous fraction need relatively high concentrated alkaline solution (&gt;8 M), particularly aluminosilicates with crystalline habitus such as fly ash, volcanic ash, feldspars, granites, nepheline, etc. In these cases, both the dissolution and the curing steps require temperature above ambient. The pastes produced are dominated by non-reacted or incongruently dissolved particles more addressed for mortars and precast. When high concentrated alkaline solution is used, some additions of Si-rich or Al-rich reactive materials are needed to stabilize the extra alkali present within the matrix: steam or long-term curing are, therefore, required. Regarding the curing conditions, the temperature and relative humidity to be applied are directly linked to the nature of the solid precursor. This paper should be viewed as a significant contribution for the understanding and classification of geopolymer cement and composites as well as the science and technology of the geopolymers.

2020 - Effect of frequency on MW assisted sintering: 2.45 GHz versus 5.8 GHz [Articolo su rivista]
Gil-Flores, L.; Salvador, M. D.; Penaranda-Foix, F. L.; Fernandez, A.; Suarez, M.; Rosa, R.; Veronesi, P.; Leonelli, C.; Borrell, A.
abstract

Innovative non-conventional approaches, such as microwave sintering, are being developed as a method for sintering a variety of materials which shown advantages over conventional sintering procedures. This work involves an investigation of the microwave sintering of an ATZ composite with two different microwave applicators and frequency generators: 2.45 GHz and 5.8 GHz. Zirconia doped with ceria and toughened with alumina (10Ce-TZP/Al2O3) is the composite used in this study. The samples were sintered by microwave in air at 1200 and 1300 °C with 10 min of dwell time at 2.45 and 5.8 GHz in order to evaluate their effects on sintering, using an optimized experimental configuration. In addition, the mechanical properties of MW-sintered samples were compared with those obtained for the same composites sintered by the conventional method (1500 °C/120 min), such as relative density, hardness and fracture toughness.

2020 - Effect of isopropanol co-product on the long-term stability of TiO2 nanoparticle suspensions produced by microwave-assisted synthesis [Articolo su rivista]
Paradisi, E.; Rosa, R.; Baldi, G.; Dami, V.; Cioni, A.; Lorenzi, G.; Leonelli, C.
abstract

In this paper we evaluate the effect of isopropanol arising from the reagent Ti(O-iPr)4 on the long-term stability of nanoparticle size of TiO2 produced during a microwave assisted sol-gel synthesis. Different configurations of microwave apparatus have been considered: the synthesis was carried out both in vessel or flask, and both performing or not isopropanol distillation through a modified microwave apparatus. Results revealed that isopropanol distillation after a short reaction time provided suspensions with slightly smaller particle size, that also show longer stability over time, especially for syntheses carried out at certain temperatures. Reactions performed distilling isopropanol from vessel and flasks showed comparable results, superior to the corresponding suspensions obtained without distilling isopropanol. This study is intended to provide a useful contribution to those applications where the need for stable TiO2 suspensions is critical.

2020 - Effect of the crystallisation time and metal oxide pigments on translucency and the mechanical and physical properties of mica glass-ceramics [Articolo su rivista]
Srichumpong, T.; Angkulpipat, S.; Prasertwong, S.; Thongpun, N.; Teanchai, C.; Veronesi, P.; Suputtamongkol, K.; Leonelli, C.; Heness, G.; Chaysuwan, D.
abstract

Mica glass-ceramics tend to be opaque making them less desirable, from an aesthetic point of view, for dental materials. This research focuses on the development of a mica glass-ceramic for use as a restorative dental material with improved translucency. A ceria-based pigment and a zircon-based pigment consisting of Pr-ZrSiO4 and Fe-ZrSiO4 were added to glass-ceramic and the effect on translucency, phase development and morphology, strength, thermal expansion and chemical solubility were studied. The addition had no effect on the level of crystallinity obtained, the morphology of the crystals formed or the strength. The use of the pigments allowed for the control of the translucency and values of the translucency parameter similar to natural teeth were produced. The characteristic strength values and chemical solubility obtained to make these materials acceptable as dental ceramics type II class 2, for single-unit anterior or posterior prostheses adhesively cemented, according to ISO 6872.

2020 - FT-IR characterization of antimicrobial hybrid materials through sol-gel synthesis [Articolo su rivista]
Catauro, M.; Piccolella, S.; Leonelli, C.
abstract

Silica/polycaprolactone and titania/polycaprolactone hybrid organic/inorganic amorphous composites were prepared via a sol-gel method starting from a multi-element solution containing tetramethyl orthosilicate (TMOS) or titanium butoxide (TBT), polycaprolactone (PCL), water and methylethylketone (MEK). The molecular structure of the crosslinked network was based on the presence of the hydrogen bonds between organic/inorganic elements as confirmed by Fourier Transform Infra-Red (FT-IR) analysis. In particular, the structure of crosslinked network was realized by hydrogen bonds between the X-OH (X = Si or Ti) group (H donator) in the sol-gel intermediate species and ester groups (H-acceptors) in the repeating units of the polymer. The morphology of the hybrid materials; pore size distribution, elemental homogeneity and surface features, was studied by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and by atomic force microscopy (AFM). The bioactivity of the synthesized hybrid materials was confirmed by observing the formation of a layer of hydroxyapatite (HAP) on the surface of the samples soaked in a simulated body fluid. The antimicrobial behavior of synthetized hybrids was also assessed against Escherichia coli bacteria. In conclusion, the prepared hybrid materials are proposed for use as future bone implants.

2020 - FT-IR study of early stages of alkali activated materials based on pyroclastic deposits (Mt. Etna, Sicily, Italy) using two different alkaline solutions [Articolo su rivista]
Finocchiaro, C.; Barone, G.; Mazzoleni, P.; Leonelli, C.; Gharzouni, A.; Rossignol, S.
abstract

The huge availability of volcanic deposits in Mt. Etna volcano and the wide use of volcanic materials as aggregates in local architecture encouraged us to apply them in alkaline environment to produce geopolymeric binders to restore historical buildings of Mt. Etna area. Two clusters of samples for each volcanic precursor (volcanic ash and ghiara paleo-soil) were produced, using 10 and 20% wt. of metakaolin and two different alkaline solutions based on sodium and potassium respectively. A comparative study was made in relation to activators used, focusing on evaluation of polycondensation step (in ATR); chemical and structural characterization (FT-IR); TGA analysis, qualitative XRD analysis and mechanical compressive test after 7 and 21 curing days. ATR results confirmed the occurrence of geopolymerization for all samples; FT-IR analysis showed a higher content of carbonates in potassium-samples, decreasing at increasing of metakaolin content. A low weight lost was recorded in consolidated samples, as well as a partial dissolution of volcanic phases. Higher mechanical compressive strengths for K-samples, reaching 89 MPa as highest value after 21 days, differently to sodium-samples (51 MPa) were recorded, reflecting the porosity of the different specimens.

2020 - Ferrisilicates formation during the geopolymerization of natural Fe-rich aluminosilicate precursors [Articolo su rivista]
Kamseu, E.; Kaze, C. R.; Fekoua, J. N. N.; Melo, U. C.; Rossignol, S.; Leonelli, C.
abstract

The progressive addition of the reactive silica from rice husk ash (10–50 wt%) changes the phases evolution and the microstructure of the laterites based geopolymer composites. It was found that the presence of soluble silica enhanced the formation of Si–(A)-OH–Fe bonds and changed considerably the FTIR and XRD patterns of the products: polysialates, ferrosialates and ferrisilicates were present into the matrices. The solid/liquid ratio and the curing cycle influenced the pore network, the bulk density, the total pore areas, and the final microstructure. The relative low viscous paste that is maintained at ambient temperature for 1–2 h before curing at 90 °C gave better cohesion and low porosity resulting to the high concentration of strongest (Fe–O–Si) bonds compared to pastes cured directly after preparation or those with high viscosity. While polysialates and ferrosilicates are hindered in the case of quite treatment at 80 °C due to the rapid evaporation of water, polysialates, ferrosialates and polynuclear ferrisilicates complexes are formed at room temperature and polynuclear complexes can growth to more crystalline phases with the increase of the temperature. Ferrisilicates integrated the interlayers of the matrix improving the geopolymerization with significant modification of the microstructure. Those newly formed phases are promising components for the development of eco-friendly and sustainable high strength composites, porous matrices for filtration, heavy metal removal/immobilization, membranes for catalysis and template for new carbone replicate.

2020 - Mechanical Properties and Microstructure of a Metakaolin-Based Inorganic Polymer Mortar Reinforced with Quartz Sand [Articolo su rivista]
Nana, A.; Alomayri, T. S.; Venyite, P.; Kaze, R. C.; Assaedi, H. S.; Nobouassia, C. B.; Sontia, J. V. M.; Ngoune, J.; Kamseu, E.; Leonelli, C.
abstract

The synthesis, mechanical behaviour, and microstructure of metakaolin-based geopolymer mortar reinforced with quartz sand are presented in this investigation. Fine sand (quartz sand) aggregate were added in different proportions of 50, 60, 70 or 80&nbsp;wt.% to prepare the fresh metakaolin-based geopolymer paste. The geopolymer mortar was achieved by a mixture of geopolymer paste and river sand in the ratio 2:5 by mass. The mixture of sodium hydroxide solution (10&nbsp;M) and sodium silicate solution (Na2SiO3) in a volume ratio of 2:3 was used as an alkaline activator. All the specimens were cured at room temperature and tested after 28&nbsp;days of curing. The investigations on microstructure and physical properties indicated a significant reduction of the open pores and interconnection of micro and meso cracks in the structure network with increase in the amount of quartz sand. As a consequence, the samples show a good mechanical strength principally with the addition of 60&nbsp;wt.% of quartz sand to binder with values of 8 and 66&nbsp;MPa for flexural strength and compressive strength, respectively.

2020 - Meta-halloysite to improve compactness in iron-rich laterite-based alkali activated materials [Articolo su rivista]
Kaze, C. R.; Venyite, P.; Nana, A.; Juvenal, D. N.; Tchakoute, H. K.; Rahier, H.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

In this paper, the results of the experimental investigation were used to understand the effect of fine meta-halloysite on the reactivity, mechanical and microstructural properties of laterite-based geopolymers. Laterite was replaced by 0, 20, 30 and 50 wt% of meta-halloysite in order to improve the physico-chemical performance. Meta-halloysite was prepared by calcination of natural halloysite at 600 °C. The moduli (molar ratio SiO2/Na2O) of the activating solutions were 1.04, 0.92, and 0.75 with H2O/Na2O = 9.78, 10.45 and 12.04, respectively. The results indicated that calcined laterite has a high specific surface area (43.00 ± 0.12 m2/g), notwithstanding a high average particle size (d50 = 45.20 μm) compared to meta-halloysite with a smaller average particle size (d50 = 8.40 μm) and a specific surface (29.80 ± 0.16 m2/g). The compressive strength of geopolymers increased upon the addition of meta-halloysite from 12 MPa to 45 MPa at 28 days. While the setting time and water absorption decrease with increase in the of meta-halloysite content as well as with increase in Si/Al, Si/Fe, Al/Fe and Na/Al molar ratios used in the synthesis of geopolymers. The use of fine meta-halloysite resulted in better efficiency and improved mechanical performance of synthesized products.

2020 - Microstructural and mechanical properties of poly(sialate-siloxo) networks obtained using metakaolins from kaolin and halloysite as aluminosilicate sources: A comparative study [Articolo su rivista]
Tchakoute, H. K.; Melele, S. J. K.; Djamen, A. T.; Kaze, C. R.; Kamseu, E.; Nanseu, C. N. P.; Leonelli, C.; Ruscher, C. H.
abstract

This work focuses on the comparison between the mechanical and microstructural properties of poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin. Poly(sialate-siloxo) networks were prepared using three metakaolins as aluminosilicate sources. Sodium waterglass from rice husk ash and commercial sodium waterglass were used as chemical reagents. The obtained results showed that metakaolins from kaolins have plate shapes with coarse particle sizes whereas the one from halloysite has a spherical morphology and smaller particle sizes. The IR spectra of poly(sialate-siloxo) networks from calcined halloysite indicate the higher value of the wavenumber of the main band. The XRD patterns of all poly(sialate-siloxo) networks show the broad hump structure with higher intensity between 18 and 40°(2θ). The XRD patterns of poly(sialate-siloxo) networks show the band of the unreacted metakaolin at about 20.45°(2θ). This band is more pronounced on the XRD patterns of geopolymer cements from calcined halloysite. The obtained poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin have a compact, homogenous and denser microstructures. The compressive strength values of the poly(sialate-siloxo) networks using calcined kaolin are ranging from 58.43 to 66.52 MPa whereas those using calcined halloysite are between 72.29 and 88.50 MPa. The compressive strength values of poly(sialate-siloxo) networks using calcined halloysite are higher compared to those from calcined kaolin. The higher compressive strength values of the geopolymer cements from calcined halloysite could be attributed to the fine and spherical particle sizes of calcined halloysite. This implies that the shape and the fine particle sizes of the raw materials influence the properties of the poly(sialate-siloxo) networks. Metakaolin from halloysite can be used as an aluminosilicate source for producing poly(sialate-siloxo) network with higher mechanical properties.

2020 - Microstructure and physico-chemical transformation of some common woods from Cameroon during drying [Articolo su rivista]
Nouemsi Soubgui, E.; Tene Fongang, R. T.; Kamseu, E.; Oum Lissouck, R.; Andreola, F.; Boubakar, L.; Rossignol, S.; Leonelli, C.
abstract

The influence of drying on the microstructure, physical and chemical properties of some tropical wood species has been investigated using thermogravimetric analysis, differential scanning calorimetric (DSC), FTIR-ATR spectroscopy, mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) analysis. Eleven tropical species were used in this study. Results showed that the common Cameroonian wood species can be grouped into three classes: Ga (lightwood) with cross-linking fibers having high volume of macropores, density in the range 0.2–0.4&nbsp;g&nbsp;cm−3 and high lignin content; Gb (medium dense) with unidirectional fibers packing, density around 0.6&nbsp;g&nbsp;cm−3 and Gc group showing high densification of unidirectional fibers and low porosity justifying the density &gt; 0.8&nbsp;g&nbsp;cm−3. Both the Gb an Gc groups have less significant lignin content. A relatively high rate of drying for Ga with respect to low drying rate for Gc was observed in direct relation with their porosity of ~ 72 Vol% and ~ 36 Vol%, respectively. LTF and WG showed similar cumulative pore volume (0.44&nbsp;mL&nbsp;g−1) with different pore size distribution: 28% and 22% of macropores, 39% and 60% of mesopores and 33% and 18% micropores, respectively. Thermal analysis revealed that lightwoods have the highest amounts of residues and lower thermal stability of chemical components than dense woods. It has been found that the degradation process of hemicellulose, cellulose and lignin occurs mainly at about 200–300&nbsp;°C, 300–350&nbsp;°C and 350–500&nbsp;°C, respectively. The group Ga with low drying rate, a low cycle of reproduction, a high volume of porosity together with large pore sizes appeared promising candidates for the design of ecological, environmental and sustainable management policy of wood transformation in developing countries and even worldwide.

2020 - Microwave assisted sintering of Na-β’’-Al2O3 in single mode cavities: Insights in the use of 2450 MHz frequency and preliminary experiments at 5800 MHz [Articolo su rivista]
Mortalo, C.; Rosa, R.; Veronesi, P.; Fasolin, S.; Zin, V.; Deambrosis, S. M.; Miorin, E.; Dimitrakis, G.; Fabrizio, M.; Leonelli, C.
abstract

Microwave assisted sintering of Na-β’’-Al2O3 in single mode cavities was accurately investigated. The use of single mode cavity allowed monitoring the parameters affecting the sintering process, like the forward power, together with the temperature evolution, making possible to perform energy efficiency and specific energy consumption evaluations. Experiments have been performed at the frequency of 2450 MHz, but preliminary results are also reported using the higher frequency of 5800 MHz, in order to investigate its effect on important parameters like the power density distribution as well as the penetration depth, which are responsible of the resulting heating rate and sintering outcome. Dielectric properties of the powders were measured as a function of temperature in order to partially predict and support the understanding of their experimental heating behaviour. Furthermore, dielectric properties provide the fundamental information needed for the multiphysics numerical simulation, performed with the aim to reach insights into the power density evolution in the specimen as sintering proceeds.

2020 - Potentiality of the Use of Pyroclastic Volcanic Residues in the Production of Alkali Activated Material [Articolo su rivista]
Barone, Germana; Finocchiaro, Claudio; Lancellotti, Isabella; Leonelli, Cristina; Mazzoleni, Paolo; Sgarlata, Caterina; Stroscio, Antonio
abstract

Volcanic rocks have been used for building activity by the inhabitants of important cities located on the slopes of Mt. Etna, Italy. In this paper, the potential use of volcanic residues (code 20 03 03—“Municipal waste” residues from road cleaning in the European Waste Catalogue (EWC)) for the production of alkali activated material, especially devoted to the restoration of buildings belonging to the Baroque Sicilian architecture, was investigated. In particular, large volcanic pyroclastic deposits of recent eruptions considered waste materials were studied and a volcanic paleo-soil, locally named ghiara, widely used for mortars and plaster production in XVII–XVIII century with good pozzolanic features, was also considered. Both volcanic materials were activated using different mixtures of NaOH and Na2SiO3. Furthermore, formulations with different amount of metakaolin addition (10–25 wt%) were prepared due to low reactivity of volcanic materials and to allow the activation at room temperature. X ray diffraction revealed the formation of small quantities of zeolites as a result of the alkali activation process. The mechanical-physical results evidenced that the mechanical strength is strongly dependent on the metakaolin amount (10–38 MPa); accessible porosity average 25% and an average pore diameter of 0.06 µm; water absorption range 9–15%, eluates conductivity in the range 20–350 µS/m. These results confirm the occurring of alkali activation and the good potential for these pyroclastic wastes for valorization in the restoration field.

2020 - Preliminary Thermal Investigations of Calcium Antimonate Opacified White Glass Tesserae [Articolo su rivista]
Boschetti, Cristina; Leonelli, Cristina; Rosa, Roberto; Romagnoli, Marcello; Valero Tévar, Miguel Ángel; Schibille, Nadine
abstract

Calcium antimonate (in the hexagonal or cubic form) dispersed in the glass matrix is an artificially synthesized phase commonly documented as opacifier for white glasses during the Roman period. Glasses of this type occasionally contain variable amounts of lead oxide. There is no consensus about the origin and role of the lead component in white glasses, whether it was functional to modify the workability of the glass and/or to help the precipitation of the particles, or whether it was an unintentional pollutant introduced with the raw materials. A group of lead and lead-free white mosaic tesserae from the fourth-century CE villa of Noheda in Spain were analyzed by differential scanning calorimetry (DSC) and high temperature X-ray diffraction (HTXRD) to evaluate the impact of variable amounts of lead oxide in the precipitation of calcium antimonate on the viscosity of the glass. The analyzed glasses show thermal events that have been related to the composition of the glass via multicomponent linear regression model. CaSb2O6 and Ca2Sb2O7 formed in the glass during the cooling phase and the glass was not reheated. Lead oxide influences the thermal behavior of the glass, lowering the onset temperatures of all the events, implying a more cost-effective production process. We propose that lead was added intentionally or that lead-bearing raw materials were selected specifically by the ancient glass artisans

2020 - Preparation of low-cost nano and microcomposites from chicken eggshell, nano-silica and rice husk ash and their utilisations as additives for producing geopolymer cements [Articolo su rivista]
Tchakoute, H. K.; Tchinda Mabah, D. E.; Henning Ruscher, C.; Kamseu, E.; Andreola, F.; Bignozzi, M. C.; Leonelli, C.
abstract

This work aims to prepare low-cost nanocomposite and microcomposite with lower molar ratio CaO/SiO2 (0.4). Nano-silica, rice husk ash and calcined chicken eggshell have been used as silica and calcium sources. Metakaolin has been separately replaced by 0, 10 and 20 wt% of each composite in order to study their behavior on the properties of geopolymers. The hardener used is sodium waterglass from rice husk ash. The surface area of nano-silica and rice husk ash was 54.40 and 4.08 m2/g, respectively. The cumulative volumes of the control geopolymer, the ones containing 10 wt% of microcomposite and nanocomposite are 119.71, 89.92 and 110.49 mm3/g, respectively. The compressive strength of the control specimen is around 64.02 MPa. The one using 10 wt% of microcomposite was 68.97 MPa. It drops to 42.88 MPa when metakaolin was replaced by 20 wt % of microcomposite. Whereas the one using 10 wt% of nanocomposite was 30.03 MPa and it decreases to 26.05 MPa when metakaolin was substituted by 20 wt% of nanocomposite. It can be concluded that 10 wt% of microcomposite could be mixed to metakaolin for strength development and nanocomposite does not recommend to use as an additive for producing high strength of geopolymer cements.

2020 - Production of Porous Poly(phospho-siloxo) Networks for Thermal Insulations Using Low-Value Calcium-Rich Wastes as Pore-Forming Agents [Articolo su rivista]
Tchakoute, H. K.; Bewa, C. N.; Kesseng, N. A.; Ruscher, C. H.; Kamseu, E.; Andreola, F.; Ali, B. N.; Leonelli, C.
abstract

Abstract: This study focuses on the preparation of porous poly(phospho-siloxo) networks for thermal insulation applications using commercial calcium carbonate and calcium-rich wastes such as oyster shell, snail shell and eggshell powders as pore-forming agents. The control and porous poly(phospho-siloxo) networks were prepared by adding phosphoric acid (4&nbsp;M) as a chemical ingredient to metakaolin containing 0 and 15 wt% of each foaming agents. The final products were monitored using the X-ray diffractometry, infrared spectroscopy, apparent density, absolute density, thermal conductivity, optical microscopy, scanning electron microscopy and mercury intrusion porosimetry. The results show that the thermal conductivity of the control and porous poly(phospho-siloxo) network from commercial calcium carbonate are 0.35 and 0.20&nbsp;W/mK, respectively. They were higher compared to those from snail shell (0.17&nbsp;W/mK), eggshell (0.15&nbsp;W/mK) and oyster shell (0.14&nbsp;W/mK). The cumulative pore volumes are 211.4, 365.5, 380.6, 389.7 and 393.3 mm3/g for the control and porous specimens from chicken eggshell, commercial calcium carbonate, snail shell and oyster shell powders, respectively. Their total porosity measured by mercury intrusion porosimeter are 30.9, 45.5, 46.0, 45.9 and 45.4%, respectively, whereas those calculated with apparent and true density measured by pycnometer are 34.48, 45.25, 52.74, 50.84 and 52.60%, respectively. The concentrated pore size diameter of the porous sample from eggshell is highest compared to the others. It can be seen that the total porosities measured by mercury intrusion porosimeter of porous specimens are nearly the same trend as well as the thermal conductivity. It was found that the low-value calcium-rich wastes could be used for producing porous poly(phospho-siloxos) networks which could be utilized for thermal insulation applications. Graphic Abstract: [Figure not available: see fulltext.].

2020 - The coordination core and charge of chromium in Metakaolin-geopolymers as revealed by X-Ray absorption spectroscopy [Articolo su rivista]
Giorgetti, Marco; Berrettoni, Mario; Aquilanti, Giuliana; Boldrini, Giacomo; Lancellotti, Isabella; Leonelli, Cristina
abstract

Geopolymers obtained by mixing metakaolin powder with tannery wastewater and NaOH pellets are proposed as 3D aluminosilicate network to chemically entrap Cr(III) species. X-ray Absorption Spectroscopy studies show the absence of toxic Cr(VI). The analysis of EXAFS also reveals a Cr(III) first coordination shell formed by 6 oxygens and a second shell of 7/8 Al or Si atoms, indicating strong bonding with the aluminosilicate network.

2020 - Thermal and microbiological performance of metakaolin-based geopolymers cement with waste glass [Articolo su rivista]
Catauro, M.; Dal Poggetto, G.; Sgarlata, C.; Vecchio Ciprioti, S.; Pacifico, S.; Leonelli, C.
abstract

In this paper, we investigated the behavior of the metakaolin-based geopolymeric matrix incorporated with waste glass. Pure metakaolin and mixtures obtained by adding different percentages (30, 40, and 50 wt%) of waste glass were consolidated via alkali activation at 50 °C. Infrared spectroscopy was able to reveal the formation of bonds in the mixtures between the clay and the glass in the geopolymeric matrix. Leaching tests were carried out to evaluate the eventual release of toxic metals, while cytotoxicity and antibacterial tests completed the environmental evaluation of the final consolidated products that showed how the mechanical performance were improved by adding different amount of waste glass under compression in the range of 18–39 MPa. Simultaneous thermogravimetry/differential thermal analysis (TG/DTA) experiments showed that about 20 wt% of water was retained in all the samples and released up to 500 K, while lower amount of water was removed by dehydroxylation in the two glass-rich mixtures because of the lower degree of reticulation i.e. lower number of hydroxyl groups underwent to condensation.

2020 - Tribology, mechanical properties and coloration of a mica glass-ceramic [Articolo su rivista]
Prasertwong, S.; Angkulpipat, S.; Srichumpong, T.; Suputtamongkol, K.; Thanachayanont, C.; Sola, R.; Heness, G.; Leonelli, C.; Chaysuwan, D.
abstract

The research employed pigments, Fe2O3 and CeO2, into the glass frit for adjustable mechanical properties and coloration. Disc samples were prepared to determine microstructures and mechanical properties in terms of tribology and nano-indentation hardness as well as biaxial flexural strength. The glass system presented the crystalline phases, by XRD, of phlogopite Ca-mica, fluorapatite, stishovite, anorthite and strontium apatite. Furthermore, SEM micrographs revealed rod-like microstructures and parent glass phase in all specimens 1) GC, 2) GC + 1wt% CeO2, 3) GC + 0.1wt% Fe2O3 and 4) GC + 1wt% CeO2 + 0.1wt% Fe2O3. For the tribology test, specimens were tested by a pin-on-disc tribometer with 10 N load and 1,000 wear cycles. The obtained values of wear rate and friction coefficient of GCF were better than those of others. The nanoindentation hardness results showed that GC exhibited 3.2 GPa which lower than those of GCC, GCF and GCCF, respectively. The addition of pigments affected reddish yellow color. After crystallization, the contrast ratio is around 0.72 for GC and decreases to 58-75% for the mica glass-ceramics that contain the pigments. The values of biaxial flexural strength of all were acceptable (≥100 MPa) according to ISO 6872:2015.

2019 - Comparison of shear bond strengths between a mica-based glass-ceramic and human dentin using three different resin cements [Articolo su rivista]
Srichumpong, T.; Suputtamongkol, K.; Thongpun, N.; Phokhinchatchanan, P.; Angkulpipat, S.; Prasertwong, S.; Bolelli, G.; Veronesi, P.; Leonelli, C.; Heness, G.; Chaysuwan, D.
abstract

Three resin cements, RelyX™ Ultimate, Panavia F2.0 and RelyX™ U200, were evaluated for their bond strengths between a mica glass-ceramic and human dentin. This research shows that a self-etch dental cement resin system, Panavia F2.0 provided the best bond strength. The glass-ceramic was produced and phases analysed. Biaxial flexural strength and hardness were measured and found to be comparable to that of human enamel and dentin. Bond strength was measured before and after thermocycling. Thermocycling was found to reduce the bond strength. Thermocycling reduced the shear bond strengths of all adhesives by 50–60%. The two-way ANOVA test was used to analyse the data (p = 0.05). Failure modes were analysed, showing failure predominately at the cement/glass-ceramic and dentin/resin cement interfaces. Failure modes changed after thermocycling. The resin cement bond between the dentin and mica glass-ceramics interfaces was examined for failure by optical microscopy (OM) and scanning electron microscopy (SEM).

2019 - Design of low cost semi-crystalline calcium silicate from biomass for the improvement of the mechanical and microstructural properties of metakaolin-based geopolymer cements [Articolo su rivista]
Tchinda Mabah, D. E.; Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Elimbi, A.; Leonelli, C.
abstract

The main objective of this work is to use low-value SiO2 and CaO-rich wastes like rice husk ash and chicken eggshell powders, respectively for producing semi-crystalline calcium silicate with molar ratio CaO/SiO2 equal to 0.4. The prepared valuable semi-crystalline calcium silicate was used as an additive for a replacement level of metakaolin (0, 1, 3, 5, 7 and 10% by mass). The resulting powders were used to synthesize geopolymer cements using hardener obtained by mixing commercial sodium silicate, sodium hydroxide and distilled water. The final products were characterized by compressive strengths, apparent density, X-ray diffractometry, infrared spectroscopy, scanning electron and optical microscope observations. The results show that the compressive strengths of geopolymer cements were between 33.25 and 51.38 MPa. They increase when metakaolin was replaced by 5, 7 and 10% of semi-crystalline calcium silicate, but no significant change was observed on the strengths of geopolymer cements content 0, 1, 3 and 5% of semi-crystalline calcium silicate. The micrograph images of the selected geopolymer cements were homogeneous and compact and the one from 10% of semi-crystalline calcium silicate shows a coarse microstructure. It was found that the low-value silica and calcium-rich wastes such as rice husk ash and eggshell can be used to prepare semi-crystalline calcium silicate. The obtained product could be used as a low-cost additive to enhance the microstructural and mechanical properties of poly(sialate-siloxo) network.

2019 - Improving insulation in metakaolin based geopolymer: Effects of metabauxite and metatalc [Articolo su rivista]
Zenabou, Ngouloure N. M.; Benoit-Ali, Nait; Zekeng, S.; Rossignol, S.; Melo, U. C.; Tchamba, A. B.; Kamseu, E.; Leonelli, C.
abstract

To improve the thermal stability of porous geopolymers, metabauxite and metatalc were used as partial replacement of metakaolin. The results of optical microscopy, Scanning Electron Microscopy (SEM), thermal sintering, mercury intrusion porosimetry (MIP) and hot disk investigations, were used to establish the effective stability of the porous composites up to 800 °C. At 1000 °C, the metabauxite based composites showed microcracks into the larger pores and small microcracks into the matrix as the results of residual poorly bounded Alumina oligomers. Metatalc based porous composites showed microcracks only inside larger pores. Those microcracks can be eliminated with the optimization of the mix-design. Despite those microcracks, the specimens maintained their integrity and stability. Above 800 °C it can be seem that the thermal conductivity of the matrices with only metakaolin increases more rapidly compared to matrices containing metatalc or metabauxite. The combination of high volume of porosity (60–65%), low thermal conductivity (̴ 0.30 W/m/K) and good thermal stability gives to porous refractory geopolymers a large scale of intrinsic properties that can be positively exploited in the field of incinerators, anti flames, kilns and building constructions.

2019 - In vitro surface reaction in SBF of a non-crystalline aluminosilicate (geopolymer) material [Articolo su rivista]
Tippayasam, C.; Sutikulsombat, S.; Kamseu, E.; Rosa, R.; Thavorniti, P.; Chindaprasirt, P.; Leonelli, C.; Heness, G.; Chaysuwan, D.
abstract

Geopolymer is a non-crystalline material based on aluminosilicate reaction exhibiting ceramic-like properties. It showed the possibility to use geopolymer as biomaterials by soaking in SBF solution to induct carbonate apatite onto the surface of samples. Carbonate apatite possesses good biocompatibility and bioactivity. The aims of this research were to study the geopolymer synthesis as a biomaterial to replace bones and the effects of Ca/P ratio on bioactivity properties of metakaolin-based geopolymers. For in vitro bioactivity test, the samples were soaked in SBF to study the influence of Ca(OH) 2 contents on the surface reaction. The 14, 28, and 90&nbsp;day-soaked sample surfaces were investigated using SEM, XRD, and FTIR characterization. The compressive strength of samples was also tested. The SEM micrographs revealed that the increase of Ca/P ratio resulted in the increase of the carbonate apatite on sample surfaces. FTIR results confirmed that the formation of Ca 10 (PO 4 ) 3 (CO 3 ) 3 (OH) 2 was investigated.

2019 - Influence of the curing temperature on the properties of poly(phospho-ferro-siloxo) networks from laterite [Articolo su rivista]
Bewa, Christelle N.; Tchakouté, Hervé K.; Rüscher, Claus H.; Kamseu, Elie; Leonelli, Cristina
abstract

2019 - Influence of the molar ratios CaO/SiO2 contained in the sustainable microcomposites on the mechanical and microstructural properties of (Ca, Na)-poly(sialate-siloxo) networks [Articolo su rivista]
T. Mabah D., E.; K. Tchakoute, H.; Fotio, D.; Ruscher, C. H.; Kamseu, E.; Bignozzi, M. C.; Leonelli, C.
abstract

The sustainable microcomposites with different molar ratios CaO/SiO2 such as 0, 0.4, 0.6, 0.8, 1.0 and 1.2 were prepared using calcined brown chicken eggshell, rice husk ash and distilled water. 10 wt% of each microcomposite was used to substitute metakaolin and the obtained calcium aluminosilicate materials were used for investigating the effects of the molar ratios CaO/SiO2 in the microcomposites on the physical, mechanical and microstructural properties of (Ca, Na)-poly (sialate-siloxo) networks. Commercial sodium waterglass and sodium waterglass from rice husk ash with a molar ratio SiO2/Na2O kept constant at 1.6 were used as chemical ingredients. Each (Ca, Na)-poly (sialate-siloxo) network was obtained by mixing each calcium aluminosilicate material with each hardener. The final products were characterized by infrared spectroscopy and X-ray diffractometry. The determination of the apparent density, compressive strength and scanning electron microscopy analysis were done. The results show that the compressive strength values of geopolymer cements using hardener from rice husk ash and microcomposites containing the molar ratios CaO/SiO2 equal to 0, 0.4, 0.6, 0.8, 1.0 and 1.2 are 64.01, 67.97, 66.15, 65.09, 60.73 and 49.40 MPa, respectively. Whereas, those from commercial sodium waterglass are 64.75, 69.03, 64.64, 56.73, 36.47 and 28.30 MPa, respectively. It was found that the most convenient molar ratio CaO/SiO2 in the structure of microcomposite required for producing (Ca, Na)-poly (sialate-siloxo) networks with higher mechanical properties is around 0.4.

2019 - Low temperature degradation behaviour of 10Ce-TZP/Al2O3 bioceramics obtained by microwave sintering technology [Relazione in Atti di Convegno]
Gil, L.; Salvador, M. D.; Penaranda-Foix, F. L.; Rosa, R.; Veronesi, P.; Leonelli, C.; Borrell, A.
abstract

Zirconia is one of the most used ceramics, especially for biomedical applications, due to its exceptional mechanical properties. However, it is commonly known that its properties can be diminished owing to a low temperature degradation (LTD). This phenomenon consists on a spontaneous phase transformation, from tetragonal to monoclinic, under certain conditions, which is accelerated when the samples are exposed under high levels of humidity at a temperature range between 20-300 ºC. In addition to the fact that the monoclinic phase presents worse mechanical properties than the tetragonal one, there is a volume change of 4% between phases that gives rise to defects in the material as microcracks. Due to this reason, zirconia prostheses failed catastrophically inside the human body between 1999 and 2001 (1). Previous researches reveal that Al2O3 addition suppress the propagation of phase transformation (2). Thus, the aim of the present work is to study the hydrothermal ageing of zirconia doped with ceria and toughened with alumina (10Ce-TZP/Al2O3) composite, which has been sintered by microwave employing two different frequencies: 2.45 and 5.8 GHz. Microwave heating technology is based on the absorption of electromagnetic radiation by the material, which allows the sample to be heated. So far, most microwave heating equipments use 2.45 GHz; accordingly, the novelty of this study is to employ a frequency of 5.8 GHz and to investigate its effect on LTD. LTD is carried out in an autoclaved in steam at 120 ºC and 1.2 bar, because these conditions accelerate the hydrothermal aging process (3). In order to characterize the degraded samples, micro-Raman spectroscopy, AFM, nanoindentation technique and electronic microscopy have been performed. References 1. Norton, M. R., Yarlagadda, R., Anderson, G. H. J. Bone Joint Surg. Br., 2002, 84–B, 631–635. 2. Fabbri, P., Piconi, C., Burresi, E., Magnani, G., Mazzanti, F., Mingazzini, C. Dent. Mater., 2014. 3. Presenda, Á., Salvador, M. D., Moreno, R., Borrell, A. J. Am. Ceram. Soc., 2015, 98, 3680–3689.

2019 - Microstructural and mechanical properties of (Ca, Na)-poly(sialate-siloxo) from metakaolin as aluminosilicate and calcium silicate from precipitated silica and calcined chicken eggshell [Articolo su rivista]
Tchuente, F. M.; Tchakoute, H. K.; Banenzoue, C.; Ruscher, C. H.; Kamseu, E.; Andreola, F.; Leonelli, C.
abstract

The aim of this work is to investigate the influence of the amorphous calcium silicate on the microstructural, physical and mechanical properties of (Ca, Na)-poly(sialate-siloxo) networks. The calcium silicate with molar ratio CaO/SiO 2 equal to 1.0 was prepared from the precipitated silica and calcined chicken eggshell. The X-ray patterns and infrared spectra of the synthesized calcium silicate indicate that it mainly constitutes of the amorphous calcium silicate hydrate. The X-ray patterns of geopolymer cements indicate that the prepared amorphous calcium silicate hydrate does not include in the network. The compressive strengths of the geopolymer mortars decrease from 28.92 to 12.03 MPa with increasing the replacement level of metakaolin (from 0 to 25% by mass). Whereas, the values of the apparent densities increase with increasing the replacement level of metakaolin. It seems that the amorphous calcium silicate hydrate in the structure of calcium silicate affects negatively the mechanical properties of the (Ca, Na)-poly(sialate-siloxo) network. The heterogeneous structure of geopolymer mortars containing 25% of calcium silicate could be related to the higher calcium content and the amorphous structure of calcium silicate hydrate. It was typically found that in the absence of significant levels of dissolved calcium, the precursors such as silicate and aluminate condense to form (Ca, Na)-poly(sialate-siloxo) networks. This implies the homogenous structure and the higher values of the compressive strengths of geopolymer mortars containing 0, 5, 10 and 15% of calcium silicate. Whereas those from the replacement level of metakaolin by 20 or 25% of calcium silicate contain significant levels of dissolved calcium and amorphous calcium silicate hydrate in their structure which hinder the formation of the precursors and therefore impede the formation of the (Ca, Na)-poly(sialate-siloxo) networks.

2019 - Microstructure and mechanical properties of 5.8 GHz microwave-sintered ZrO2/Al2O3 ceramics [Articolo su rivista]
Gil-Flores, L.; Salvador, M. D.; Penaranda-Foix, F. L.; Fernandez, A.; Suarez, M.; Rosa, R.; Veronesi, P.; Leonelli, C.; Borrell, A.
abstract

Aim of the present study is to sinter zirconia nanocomposite powders doped with ceria and toughened with alumina (10Ce-TZP/Al2O3) by non-conventional means, i.e. microwave sintering technology. The sintering effects of various microwave applicators and frequency generators were evaluated using an optimised experimental set-up. The microwave-sintered samples were compared with the composites sintered by the conventional method. The mechanical properties of the ceramic composites were evaluated by their hardness, fracture toughness and Young's modulus. Likewise, their density and microstructure were analysed.

2019 - Microstructure and mechanical, physical and structural properties of sustainable lightweight metakaolin-based geopolymer cements and mortars employing rice husk [Articolo su rivista]
Riyap, H. I.; Bewa, C. N.; Banenzoue, C.; Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Bignozzi, M. C.; Leonelli, C.
abstract

This work focuses on an in-depth investigation of the formation of pores in the structure of lightweight geopolymer cements and mortars using rice husk as a foaming agent. The hardener used in this study was sodium waterglass. Metakaolin was replaced by 0, 10, 20, 30 and 40 % by mass of husk and the obtained powders were used to produce lightweight geopolymer cements and mortars. The formation of pores in the lightweight geopolymer cements was monitored using X-ray diffractometry and infrared spectroscopy while those in the mortars were assessed using apparent density and compressive strength measurements, mercury intrusion porosimetry and optical and scanning electron microscopy. The values for the compressive strength and apparent density were in the ranges of 28.92–0.75&nbsp;MPa and 1.88–1.70&nbsp;g/cm 3 , respectively. The results indicated that the values for the compressive strength and apparent density of geopolymer mortars decreased while those of the cumulative pore volume increased with increases in the metakaolin replacement level. Stereomicroscopic and scanning electron microscopic images showed the presence of rice husk and fibres of rice husk, respectively, in the networks. It was found that rice husk can be used as a foaming agent for producing sustainable lightweight geopolymer mortars.

2019 - Mild and efficient synthesis of secondary aromatic amines by one-pot stepwise reductive amination of arylaldehydes with nitroarenes promoted by reusable nickel nanoparticles [Articolo su rivista]
Fiore, A. M.; Romanazzi, G.; Dell'Anna, M. M.; Latronico, M.; Leonelli, C.; Mali, M.; Rizzuti, A.; Mastrorilli, P.
abstract

The one-pot stepwise reductive amination of arylaldehydes with nitroarenes is described, using reusable nickel nanoparticles (Ni-pol) as catalyst and NaBH4 as mild, inexpensive, and safe reducing agent. The proposed catalytic system holds several advantages such as the use of a non-precious and earth-abundant metal, the facile separation of the catalyst from the reaction mixture by centrifugation, excellent stability towards air and moisture, very mild reaction conditions, good recyclability, broad substrate scope with good to excellent yields, and easy scalability (up to 1.0 g). FESEM analyses indicate that the active species are cubic nanocrystals of Ni in the average cross section value of 35 nm with a quite narrow (25–45 nm) and monomodal distribution, which becomes bimodal with the recycling reactions but without agglomeration.

2019 - On the versatility and distinctiveness in the use of microwave energy for the ignition of low exothermic Ni–Ti intermetallics combustion synthesis [Articolo su rivista]
Rosa, R.; Trombi, L.; Casagrande, A.; Cugini, F.; Leonelli, C.; Veronesi, P.
abstract

Microwave energy has been employed in the present work in order to reach ignition of the combustion synthesis in the binary Ni–Ti system without the need of any separate additional pre-heating step. Indeed, the latter is known to be necessary with more conventional ignition strategies, due to the low exothermic character of the reaction between elemental Ni and Ti powders. On the opposite, the unique microwaves heating mechanism allows directly transferring electromagnetic energy in the reactive specimen that absorbs and transforms it into the heat necessary to reach ignition of the exothermic reaction. According to the electromagnetic field distribution inside the microwave single mode applicator employed, it was possible to realize both Thermal Explosion (TE) and Self-propagating High-temperature Synthesis (SHS) ways of combustion. Moreover, the use of a single mode applicator also allowed separately investigating the effect of electric and magnetic fields strengths, at the 2450 MHz microwave frequency, on the combustion characteristics. This significantly affected the microstructure as well as the phase evolution in the synthesized products.

2019 - Room-temperature alkaline activation of feldspathic solid solutions: Development of high strength geopolymers [Articolo su rivista]
Nana, A.; Ngoune, J.; Kaze, R. C.; Boubakar, L.; Tchounang, S. K.; Tchakoute, H. K.; Kamseu, E.; Leonelli, C.
abstract

Amorphous fraction, grains defects and the incongruent dissolution of solid solutions (pegmatite, trachyte, and granite) were used to design high strength geopolymer composites with crystalline content in the range of ∼70–85%. The geochemical history of the natural solid solutions affects the dissolution and polycondensation/geopolymerization. These solid solutions were altered with 15, 20, 25 and 30% of metakaolin and activated with alkaline solution. Experimental results (phase evolution, three-point flexural strength, microstructure, mercury intrusion porosimetry and water absorption) indicated that polycondensation/polymerization is enhanced in trachyte, granite and pegmatite based specimens, compared to sand, due to the increase in N-A-S-H secondary phases. The amorphous/crystalline ratio of the solid precursors were used to understand the role of dissolved and undissolved fraction into the strength development of geopolymer composites. It was concluded that high strength geopolymer composites of chemico-mechanical equilibrium can be achieved with solid solutions having reduced fraction of pores volume and pore-size.

2019 - Structural evolution of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ composite MPEC membrane by in-situ synchrotron XRD analyses [Articolo su rivista]
Mortalo, C.; Santoru, A.; Pistidda, C.; Rebollo, E.; Boaro, M.; Leonelli, C.; Fabrizio, M.
abstract

Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered very promising materials for H2 separation at T &gt; 600 °C. Among these, BaCe0.65Zr0.2Y0.15O3-δ-Ce0.85Gd0.15O2-δ (BCZ20Y15-GDC15) composite combine an acceptable H2 flux and good chemical stability under CO2- and H2S-containing atmospheres. However, a clear understanding of its crystal structure, phase stability and mechanical stability under real working conditions could not yet be obtained. In this work, its structural evolution was investigated from room temperature to 800 °C by in-situ synchrotron XRD analyses under dry and wet H2. No chemical interaction between the BCZ20Y15 and GDC15 phases occurred in the composite, thus demontrating its excellent chemical stability under operating conditions. However, some phase transitions were observed for the BCZ20Y15 phase, under both dry and wet H2: i.e., it showed an orthorhombic Imma structure from room temperature to 100 °C, trigonal R-3c up to 700 °C and cubic Pm-3m up to 800 °C. On the other hand, the GDC15 phase did not display any phase transition, remaining in a cubic Fm-3m structure under all tested conditions. Moreover, a synergistic effect of the BCZ20Y15 and GDC15 phases in the volume expansion of the composite was revealed: indeed, BCZ20Y15 and GDC15 lattice expansion rates tend to approach each other in the composite under reducing conditions. This synergistic effect is very important for the mechanical performances of BCZ20Y15-GDC15 composite. The similar expansion rate observed for BCZ20Y15 and GDC15 may reduce the strain and prevent failure of this ceramic membrane under operating conditions.

2019 - Welcome letter from the AMPERE President [Abstract in Atti di Convegno]
Leonelli, C.
abstract

Preface for the Book of Proceedings of the 17th International Conference on Microwave and High Frequency Heating-AMPERE 2019, Valencia; Spain; 9 September 2019 through 12 September 2019;

2018 - Development of Thai lignite fly ash and metakaolin for pervious geopolymer concrete [Relazione in Atti di Convegno]
Sutikulsombat, Sarochapat; Srichumpong, Thapanee; Boonanunwong, Phachongkit; Tippayasam, Chayanee; Leonelli, Cristina; Chindaprasirt, Prinya; Chaysuwan, Duangrudee
abstract

The study was to use Thai lignite fly ash and metakaolin to produce geopolymer paste as binder material in pervious concrete. The proper ratio of fly ash to metakaolin were varied as 100:0, 70:30, and 50:50. Alkali solution to pozzolan (L/P) ratios viz., 0.5, 0.6 and 0.8 by weight were prepared. The mechanical and characterization of pervious geopolymer concrete (PGC) were carried out. The results presented that the particle of fly ash was sphere with smooth surface, while metakaolin was partly agglomerated and irregular shaped. The increase of fly ash in the ratio of fly ash to metakaolin affected the lower requirement of volume of alkali solution. The compressive strength and of pervious geopolymer concrete at 28 days were 3.7-5.4 MPa. The void ratio and water permeability were 28.5-30.7% and 1.9-2.1 cm/sec, respectively. Therefore, geopolymer paste from fly ash and metakaolin could be used for pervious concrete with satisfied properties according to standard of ACI 522R-10.

2018 - Development of geopolymer mortar from metakaolin blended with agricultural and industrial wastes [Relazione in Atti di Convegno]
Tippayasam, Chayanee; Suttikulsombat, Sarochapat; Paramee, Jamjuree; Leonelli, Cristina; Chaysuwan, Duangrudee
abstract

Geopolymer is greener alternative cement produced from the reaction of pozzolans and strong alkali solutions. Generally, the cement industry is one of largest producers of CO2 that caused global warming. For geopolymer mortar usage, Portland cement is not utilized at all. In this research, geopolymer mortars were prepared by mixing fly ash with metakaolin and various wastes (bagasse ash and rice husk ash) varied as 80:20, 50:50 and 20:80, 15M NaOH, Na2SiO3 and sand. The influence of various parameters such as metakaolin to ashes ratios and pozzolans to alkali ratios on engineering properties of metakaolin blended wastes geopolymer mortar were studied. Compressive strength tests were carried out on 25 x 25 x 25 mm3 cube geopolymer mortar specimens at 7, 14, 21, 28 and 91 air curing days. Physical and chemical properties were also investigated at the same times. The test results revealed that the highest compressive strength was 80% fly ash - 20% metakaolin geopolymer mortar. When the curing times increases, the compressive strength of geopolymer mortar also increases. The mixing of fly ash and bagasse ash/rice husk ash presented lower compressive strength but higher water absorption and porosity. For FTIR results, the geopolymer chain such as the H-O-H, Si-OH and Al-O-Si were found. Moreover, the geopolymer mortar could easily plastered on the wall.

2018 - Effect of silicate modulus on the setting, mechanical strength and microstructure of iron-rich aluminosilicate (laterite) based-geopolymer cured at room temperature [Articolo su rivista]
Kaze, C. R.; Djobo, J. N. Y.; Nana, A.; Tchakoute, H. K.; Kamseu, E.; Melo, U. C.; Leonelli, C.; Rahier, H.
abstract

This paper studies the alkali activation of iron-rich aluminosilicates (laterites). Three activating alkaline solutions were prepared from sodium hydroxide solution (8, 10 and 12 M) with sodium silicate (Na2SiO3) in order to obtain the sodium silicate solutions with moduli of SiO2/Na2O equal to 0.75, 0.92 and 1.04; H2O/Na2O = 9.78, 10.45 and 12.04. The effects of above-defined solutions on the setting time, physical and microstructural properties of geopolymer binders from calcined laterite (600 °C), containing metakaolinite, as the sole binder at room temperature are reported and discussed. A laterite from Eloumden and one from Odza were used. The synthesized products were labelled GPEL(i=1.04, 0.92 and 0.75) and GPOD(i=1.04, 0.92 and 0.75) series. The dry compressive strength measured after 7 and 28 days were 4–10 and 10–18 MPa, respectively. It was typically found that the geopolymer paste from sodium hydroxide with molar concentration 12 M and the molar ratio SiO2/Na2O of the silicate solution equal to 0.75 produced the highest compressive strength (~ 18 MPa). These samples also have a denser matrix. The dry bulk densities of both series increased with the decrease of silica moduli and were in the range 2.31–2.43 and 2.32–2.52 g/cm3 and the water absorptions were in the range of 8.21–11.40% and 7.23–13.03% for geopolymers GPEL and GPOD series, respectively. The setting time decreased with increasing molarity of NaOH solutions. The physicochemical properties and the mineralogy of both iron-rich aluminosilicates were influenced by the silicate modulus of activating solutions and the best compositions were achieved with characteristic SiO2/Na2O = 0.75 and H2O/Na2O = 9.78.

2018 - Investigation of the relationship between the condensed structure and the chemically bonded water content in the poly(sialate-siloxo) network [Articolo su rivista]
Melele, Sorelle J. K.; Tchakouté, Hervé K.; Banenzoué, Charles; Kamseu, Elie; Rüscher, Claus H.; Andreola, Fernanda; Leonelli, Cristina
abstract

The main objective of this work was to investigate the relationship between the condensed structure and the chemically bonded water content in the metakaolin-based geopolymer network. The kaolin used in this work as an aluminosilicate source was transformed to metakaolin by calcination at 700 °C. The powder of the waste glass and the silica fume were used as silica sources for the synthesis of the hardeners, dissolving with caustic soda solution. The obtained hardeners were characterized by infrared spectroscopy and MAS-NMR 29Si. The metakaolin and the hardeners were used for producing geopolymers cements. The synthesized products were characterized by X-ray diffractometry, infrared spectroscopy, mercury intrusion porosimetry, scanning electron microscopy, MAS-NMR 29Si and 27Al, thermal analyses (TG and DSC) and compressive strength. The results show that the compressive strength of geopolymer cements using hardener from silica fume and the one from waste glass are 61.93 and 25.51 MPa, respectively. The microstructure (SEM observations) of geopolymer cements obtained using hardener from silica fume is homogeneous, compact and dense with an average pore diameter around 13 nm. Whereas, the one obtained using hardener from waste glass are heterogeneous and contains larger pores (with average pore diameter around 168 nm). MAS-NMR 29Si and 27Al results show that the specimen obtained using hardener from the silica fume contains more aluminum in four-fold coordination in its network than the ones using hardener from waste glass. This indicates a higher degree of crosslinking of poly(sialate-siloxo) chains which could lead to a smaller pore sizes and a higher water uptake in the structure of the sample. The amount of chemically bonded water contained in the network of geopolymer cements using hardeners from waste glass and silica fume were 6.82 and 11.23%, respectively, as determined from weight loss in the range 100–300 °C. All these results indicate that the higher content of chemically bonded water in the network of geopolymer cement obtained using hardener from silica fume is related to the much smaller average pore size diameter and the hydrophilic character of aluminum, which reveals obviously better mechanical and microstructural properties of the specimen. This could indicate here a higher degree of condensation using silica fume based hardener for geopolymerization.

2018 - Microstructure and engineering properties of Fe2O3(FeO)-Al2O3-SiO2 based geopolymer composites [Articolo su rivista]
Kaze, R. C.; Beleuk a Moungam, L. M.; Cannio, M.; Rosa, R.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

The objective of this study is to develop low cost, eco-friendly and sustainable building materials by applying the technology of mineral polymerization (geopolymerization) process on naturally abundant iron-rich aluminosilicate (laterite) materials. Iron-rich aluminosilicates based-geopolymer composites containing 10 to 40 wt% of rice husk ash (RHA) were cured at room temperature and at 90 °C. This paper examines the phase transformation, microstructural and mechanical changes that occur in the geopolymer composites when fine aggregates of quartz sand are added. Experimental results indicate good polycondensation and more cohesion resulting in high strength due to the better dissolution of RHA that provides soluble reactive silica to equilibrate the Si/Al and Si/Fe molar ratios. Ferro-sialates, Fe(Al)–S–H, were identified at the room temperature in addition to polysialates, S–A-N–H, phases. The flexural strength of resultant composites increases from 10 to 12 MPa for room temperature curing to ∼40 MPa when the composites were cured at about 90 °C as from the intensive formation of ferrisilicates. The formation of ferri-silicates that changed the flexural strength and microstructure seem to play significant role in the engineering properties of laterites based geopolymer composites making them promising candidates for applications as pavements, roads and building construction.

2018 - Moisture Control Capacity of Geopolymer Composites: Correlation of the Bulk Composition–Pore Network with the Absorption–Desorption Behavior [Articolo su rivista]
Kamseu, E.; Mohamed, H.; Sofack, J. C.; Chaysuwan, Duangrudee; Tchakoute, H. K.; Djobo, J. N. Y.; Rossignol, S.; Leonelli, C.
abstract

Abstract: Porous composites with the principal class of porosity in the range of those presented in the literature as ideal for the moisture control capacity of building environment are described. In the course of the design of the matrices, micrometric pores are introduced to give to the pore systems a bi- or multimodal characters with the aim of improving the phases percolation during the course of desorption and make the moisture accumulation–desorption behavior of the porous composites essentially function of weather and environment. The porous composites present size of pores in the range 0.001-1μm for the gel pores and peak centered at 10μm for the micrometric pores which insure the matrices efficiency in moisture control capacity and durability. The results of cycles of moisture absorption–desorption in the course of various seasons of the year permit to identify the activities of gel pores meanly efficient in the extreme environment: absorption when the temperature is under 11∘C; relative humidity is >60% and desorption when the temperature is above 18∘C. At ambient conditions, the pores more active are micrometric pores, while gel pores enter in activity only in the extreme environment conditions. The proposed porous geopolymer composites appeared promising candidates for the management of the moisture while improving the thermal insulation of residential building particularly in the regions with important fluctuation of weather. The use of geopolymerization process for the production of those porous composites, the choice of recycling industrial and municipal inorganic wastes appears ideal solution, environmentally friendly, eco-efficient and sustainable for the design of newly materials for the moisture control capacity in building environment. Graphical Abstract: [Figure not available: see fulltext.].

2018 - Polymer supported Nickel nanoparticles as recyclable catalyst for the reduction of nitroarenes to anilines in aqueous medium [Articolo su rivista]
Romanazzi, Giuseppe; Fiore, Ambra Maria; Mali, Matilda; Rizzuti, Antonino; Leonelli, Cristina; Nacci, Angelo; Mastrorilli, Piero; Dell'Anna, Maria Michela
abstract

Polymer supported nickel nanoparticles, generated by calcination under nitrogen of a Ni(II) containing polyacrylamide, catalyzed the hydrogenation of nitroarenes to anilines in aqueous medium at room temperature in the presence of NaBH4. The protocol generally favored the formation of the desired aniline as single product in high yields with short reaction times and proved to be highly selective in the hydrogenation of halonitrobenzene to haloaniline, avoiding the formation of hydro-dehalogenated side-products. The catalyst displayed excellent recyclability over at least five cycles (which is not trivial for nickel nanoparticle based catalysts used in water) and no leaching of metal into solution occurred, that made the overall system eco-friendly and economic. STEM analyses revealed that the thermally formed Ni nanoparticles turned into cubic nanotwins under reaction conditions, which remained almost unchanged with the re-cycles.

2018 - Role of ɣ-Al2O3 on the mechanical and microstructural properties of metakaolin-based geopolymer cements [Articolo su rivista]
Tchakouté, Hervé K.; Kamseu, Elie; Banenzoué, Charles; Rüscher, Claus H.; Andreola, Fernanda; Tchamo, Claudia C. L.; Leonelli, Cristina
abstract

The main target of this work is to investigate the influence of ɣ-Al2O3 on the properties of metakaolin-based geopolymer cements. The kaolin used as starting material for producing geopolymer cements contains approximately 28 and 64% of gibbsite and kaolinite, respectively. This kaolin was transformed to metakaolins by calcination at 500, 550, 600, 650, and 700 °C for 1 h. Gibbsite contained in kaolin was transformed to γ-Al2O3 during the calcination process. The hardener was obtained by mixing commercial sodium silicate and sodium hydroxide solution (10 M) with a mass ratio sodium silicate/sodium hydroxide equal to 1.6:1. Geopolymer cements, GMK-500, GMK-550, GMK-600, GMK-650, and GMK-700, were obtained using the prepared hardener with a mass ratio hardener/metakaolin equal to 0.87:1. It could be seen that the specific surface area of metakaolins decreases with increasing the calcination temperature of kaolin owing to the formation of the particles of γ-Al2O3. The compressive strengths 18.21/29.14/36.61/36.51 increase in the course GMK-550/GMK-600/GMK-650/GMK-700. The X-ray patterns and micrograph images of geopolymer cements, GMK-600, GMK-650, and GMK-700, indicate the presence of γ-Al2O3 in their structure. It was typically found that γ-Al2O3 remains largely unaffected during the geopolymerisation, and therefore could act as an inert filler and reinforce the structure of geopolymer cements. [Figure not available: see fulltext.].

2018 - Synthesis and properties of inorganic polymers (geopolymers) derived from Cameroon-meta-halloysite [Articolo su rivista]
Kaze, C. R.; Tchakoute, H. K.; Mbakop, T. T.; Mache, J. R.; Kamseu, E.; Melo, U. C.; Leonelli, C.; Rahier, H.
abstract

Cameroonian Balengou clay has been characterized as precursor for inorganic polymer (geopolymer) binder. The lowest possible calcination temperature for this halloysite type clay was found to be 600 °C to convert it into meta-halloysite (MH), which is reactive enough for geopolymerization. This implies an energy saving compared to the 800 °C, previously reported in literature. The inorganic polymer has been produced using sodium hydroxide or sodium silicate solutions. A maximum dry compressive strength of 27.5 MPa after 28 days was obtained with a sodium silicate solution [Na2O·1.25SiO2·9.76H2O] resulting in a material with composition: Na2O·3.78SiO2·7.22Al2O3·9.76H2O. This inorganic polymer was amorphous according to XRD, showed a compact microstructure (scanning electron microscopy), with lower values of water absorption, porosity, and higher density. In addition the same composition showed better resistance to 5% sulfuric/hydrochloric solution than the ones made with higher and lower ratio of Na/Al. Meta-halloysite based geopolymers had a 20–30% reduction in strength after immersion in 5% sulfuric/hydrochloric acids for 7 days and even up to 62.5% after 28 days, due to the depolymerisation process of the geopolymer network. The results obtained demonstrated the suitability of Cameroonian meta-halloysite for geopolymer synthesis at room temperature.

2018 - The effects of synthesized calcium phosphate compounds on the mechanical and microstructural properties of metakaolin-based geopolymer cements [Articolo su rivista]
Tchakouté, Hervé K.; Fotio, Daniel; Rüscher, Claus H.; Kamseu, Elie; Djobo, Jean N. Y.; Bignozzi, Maria C.; Leonelli, Cristina
abstract

Dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HAP) were prepared from oyster shell powder and phosphoric acid solution as raw materials using sol-gel process in order to study the influence of calcium phosphate compounds on the mechanical and microstructural properties of metakaolin-based geopolymer cements. The synthesized DCPD and HAP with molar ratio Ca/P equal to 1.00 and 1.65, respectively, were used as additives for replacement of metakaolin (0, 2, 4, 6, 8 and 10 wt%) and the resulting powders were used for producing geopolymer cements. The compressive strengths of geopolymer cements containing DCPD were in the range 40–48 MPa with increasing DCPD content, but when 10 wt% was used, the strength fell to 26 MPa. Similar results were obtained for HAP addition with a decrease of the compressive strength at 8 wt%. The ESEM images of geopolymers containing 4–10 wt% of HAP showed some non-reacted or partially reacted particles that do not well connect to the matrix. Samples of geopolymer with 4–8 wt% of DCPD present a lower number of unreacted particles and the matrix appeared denser than that of the control geopolymer cements. The use of calcium phosphate compounds such as brushite and hydroxyapatite led to the overall improvement in compressive strength and contribute to the densification of the structure of geopolymer cements. On the other hand, the addition of 4% of HAP and 10% of DCPD resulted in a large amount of hydroxyapatite and brushite, respectively in the systems. The matrix appear less dense indicating that a fraction of calcium phosphate addition at the aforementioned level was excessive.

2018 - Water resistance and thermal behavior of metakaolin-phosphate-based geopolymer cements [Articolo su rivista]
Nobouassia Bewa, C.; Tchakoute, H. K.; Fotio, D.; Ruscher, C. H.; Kamseu, E.; Leonelli, C.
abstract

The main target of this work was to investigate the thermal behavior and water resistance of geopolymer cement made from metakaolin as an aluminosilicate source using phosphoric acid solution (10&nbsp;M) as a hardener. The obtained geopolymer cements were cured at room temperature for 28&nbsp;days, the one part was treated at 200°C, 400°C, 600°C, 800°C and 1000°C, and the others were soaked in water for 28&nbsp;days. The geopolymer cements were characterized by microstructural properties using X-ray diffractometry, infrared spectroscopy, microstructure, physical property based on water resistance and thermo-mechanical properties (thermal analysis, compressive strength). The results show that the compressive strength of the unheated geopolymer cement was 87.96&nbsp;MPa. The ones soaked in water revealed a strength of 40.71&nbsp;MPa. This indicates that the specimens soaked in water lose about 54% of their strengths. The X-ray patterns of heated geopolymer cements showed the formation of crystalline phases even at relatively low temperatures. It was typically found that the compressive strength of metakaolin-phosphate-based geopolymer cements decreases due to the hydrolysis of Si-O-P bonds in the presence of water.

2017 - A new multi principal element alloy synthesized by microwave powder metallurgy technique [Relazione in Atti di Convegno]
Colombini, E.; Rosa, R.; Poletti, M. G.; Battezzati, L.; Casagrande, A.; Veronesi, P.; Leonelli, C.
abstract

Multi principal element alloys (MPEAs), consisting of five or more alloying elements at near equiatomic concentrations and forming bcc and/or fcc solid solution phase, were recently developed. According to the literature research, the synthetic route to produce MPEAs should guarantee short alloying time, efficient cooling and capability to operate in controlled atmosphere. Such conditions can be achieved using high frequency electromagnetic fields, like in microwave heating. Microwave assisted combustion synthesis of pure metal powders mixtures as reactants has already been used during the last decade by the authors to prepare intermetallics, functionally-graded materials, and recently to produce multi-principle alloys. Moreover the addition of SiC in these alloys increases the mechanical properties and oxidation resistance at high temperature, as demonstrated in a recent paper by the authors. In this work a new MPEA (Al15Mn20Fe25Co15Ni25) was prepared with and without the addition of SiC, using powder metallurgy route and exploiting microwave as way of generating heat inside the precursors and hence to start the reactive sintering. Results show that direct microwave heating at 2450 MHz of the powder precursors leads to the ignition conditions, with an evident exothermal event ascribable to the mixing enthalpy, and then self-sustaining of the synthesis occurs. The temperature and duration of the microwave-assisted process resulted much lower than other conventional powder metallurgy routes, but at the cost of a higher residual porosity. Sample characterization confirmed that the powder metallurgy approach is suitable to retain the shape of the load imparted during forming by uniaxial pressing.

2017 - Addition of WEEE glass to metakaolin based geopolymeric binder: a cytotoxicity study [Articolo su rivista]
Catauro, Michelina; Lancellotti, Isabella; Leonelli, Cristina
abstract

Waste Electrical and Electronic Equipment (WEEE) types of glass, including Cathode Ray Tube (CRT) glass, are now separately collected in European Union 28 (EU28) zone. Due to the high level of Pb and Ba in their compositions, this type of waste finds its way to the disposal. In the present research, a geopolymer matrix based on metakaolin is used to blend in fine powder panel and funnel glass from personal computer (PC) and television (TV) monitors. Such waste glass, which cannot be directed to glass melting furnaces, is safely incorporated into a geopolymer matrix. The consolidation of the geopolymeric matrix containing the waste glass was followed by pH and conductibility up to 28 days of curing. Scanning electron microscope equipped with energy dispersive spectroscopy (SEM/EDS) was used to obtain information on the microstructure of the consolidated products. Cytotoxicity tests helped the environmental evaluation of these materials.

2017 - Design of ceramic filters using Clay/Sawdust composites: Effect of pore network on the hydraulic permeability [Articolo su rivista]
Youmoue, Martine; Fongang, R. T. Téné; Sofack, J. C.; Kamseu, Elie; Melo, U. Chinje; Tonle, Ignas K.; Leonelli, Cristina; Rossignol, Sylvie
abstract

Clay based ceramic composite materials with hydraulic permeability were elaborated using sawdust as porogent agent. Their mechanical, morphological, microstructural and pore network properties were investigated. Mixtures in various ratios of two kaolinite clay minerals, Ba (highly plastic) and Va (sand-rich) constitute the five ceramic matrixes studied (CM1, CM2, CM3, CM4 and CM5). Due to their high flexural strength, CM3 and CM4 received 0%, 5%, 10% and 15% sawdust before firing, to improve the porosity of the final matrixes. Results revealed that 900–1000 °C is the range of temperature necessary to get good sintering and flexural strength (≥2 MPa). A typical clay-sawdust based materials (parallepipedic bricks) present porosity ≥40 vol% and 1.5 g/cm3 density. Characterizations such as FTIR, SEM, MIP and flow permeability of ceramic candles were performed. A Hydraulic permeability of ~10 mDarcy was obtained and the mean pore diameter varies from 0.05 to 0.1 µm, in agreement with the microstructure exhibited by the ceramic candles. In the presence of sawdust, pores with size up to 10 µm were observed, justifying the increase of flowing permeability. The elaborated matrixes are promising candidates for microfiltration.

2017 - Development of microwave-assisted sintering of Portland cement raw meal [Articolo su rivista]
Kaewwichit, Praphatsorn; Junsomboon, Jaroon; Chakartnarodom, Parinya; Tippayasam, Chayanee; Srichumpong, Thapanee; Thavorniti, Parjaree; Leonelli, Cristina; Chaysuwan, Duangrudee
abstract

Typically, using a rotary furnace as a heat generator, a temperature of approximately 1450 °C and a time of 60 min is needed to produce clinker requiring large amounts of energy. Recently, a method of sintering Portland cement by microwave furnace has been developed with the aim to reduce this high consumption of energy in the conventional cement production. In this work, cement raw meal was calcined by a microwave furnace operating at 2.45 GHz with 900 W at 1150 °C at several periods of time but was not completely successful in terms of clinker formation. Therefore, an electric furnace was used at 1300 °C and 1350 °C for 30 min to further heat the material. Chemical compositions of the formed clinker, characterized by XRD, presented C3S, C2S, C3A and C4AF as the main constituents confirming a clinker similar to those of clinker produced by rotary kiln or conventional technique. Loss on ignition and insoluble residue of the resultant clinker were analyzed by chemical analysis and the results were found to pass ASTM C-114. It was found that the raw meal sintering process using a microwave furnace followed by transfer to an electric furnace could reduce not only the temperature by at least 100 °C but also the processing time of the clinker. In addition, there is no grinding cost for clinker preparation in this process. This processing of clinker would decrease energy consumption and carbon dioxide emission to the atmosphere, a major cause of global warming.

2017 - Electrochemical impedance spectroscopy: A deeper and quantitative insight into the fingermarks physical modifications over time [Articolo su rivista]
Rosa, Roberto; Giovanardi, Roberto; Bozza, Andrea; Veronesi, Paolo; Leonelli, Cristina
abstract

The present work is focused on a novel approach for the study and quantification of some of the physical changes to which a fingermark deposited on non-porous substrates is subjected as its ageing proceeds. Particularly, electrochemical impedance spectroscopy (EIS) technique has been applied for the first time in order to monitor the electrochemical behaviour of the system constituted by the fingermark residue and the underlying substrate. The impedance spectra proved to be significantly affected by the presence of the mark residue as well as by its ageing process. Opportune fitting operations performed on the experimental data allowed obtaining quantitative electrochemical parameters used to reach useful information on the fingermarks ageing mechanism as well as to calculate the fingermark ageing curves from which fundamental information could be potentially extrapolated.

2017 - Energy Efficiency in the Microwave-Assisted Solid-State Synthesis of Cobalt Aluminate Pigment [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; Bondioli, Federica
abstract

Due to their rapid, selective, and volumetric heating, microwaves have been widely used in the past to enhance solid-state reactions as well as the synthesis of ceramic pigments. The aim of this work is to present a case study involving the preparation of blue CoAl2O4 pigment using different microwave applicators and generator frequencies, showing the advantages which can derive from a properly designed microwave reactor for the solid-state synthesis of such pigment. The results show that, when using a properly designed microwave applicator, the specific energy consumption can be significantly lowered compared to conventional heating techniques. Consistently with the data on the dielectric properties of precursors found in literature, the microwave processing of cobalt oxide and aluminum hydroxide mixtures resulted more favorable at 2.45 GHz than at 5.8 GHz microwave frequency.

2017 - Geopolymerization as cold-consolidation techniques for hazardous and non-hazardous wastes [Relazione in Atti di Convegno]
Leonelli, Cristina; Kamseu, Elie; Lancellotti, Isabella; Barbieri, Luisa
abstract

Many interesting studies on the utilization of wastes produced in different human activities (urban, agricultural and industrial) have been carried out with the goals to reduce, to recycle, to reuse or to recovery: the R4 strategy. Many of these waste contains high amount of silicoaluminates, making them suitable for alkali activation to become one of the most promising binders for the future. Other type of wastes, even if hazardous, such as incinerator fly ash, electric arc furnace dust, lead smelting slag, etc. can be easily added as minor components to the geopolymer matrix for being immobilized as either cations or anions or both.

2017 - Influence of the molar concentration of phosphoric acid solution on the properties of metakaolin-phosphate-based geopolymer cements [Articolo su rivista]
Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Andreola, F.; Leonelli, C.
abstract

Six different phosphoric acid solutions with molar concentrations 4, 6, 8, 10, 12 and 14&nbsp;M were prepared by dilution of commercial phosphoric acid in distilled water. The obtained phosphoric acid solutions were used for producing metakaolin-phosphate-based geopolymer cements. These geopolymer cements were obtained by adding each fresh prepared phosphoric acid solution to metakaolin with a mass ratio phosphoric acid solution/metakaolin&nbsp;=&nbsp;0.80. It was observed in the infrared spectra of phosphoric acid solutions 8, 10, 12 and 14&nbsp;M, the absorption bands at 875–879 and 949–972&nbsp;cm−&nbsp;1 which are assigned to H2PO4−. The SEM images of geopolymer cements exhibit the presence of berlinite (AlPO4) which is dispersed in the matrix and contributes to enhancing the strength, whereas the geopolymer cements from phosphoric acid solution with 14&nbsp;M are heterogeneous microstructures. The compressive strength of phosphate-based geopolymer cements was between 36.4 and 93.8&nbsp;MPa; it increased with increasing the concentration of phosphoric acid solutions up to 10&nbsp;M. It can be concluded that the most convenient concentration of phosphoric acid solution required for producing phosphate-based geopolymer cements with good mechanical properties is around 10&nbsp;M.

2017 - Microwave energy application to combustion synthesis: A comprehensive review of recent advancements and most promising perspectives [Articolo su rivista]
Rosa, R.; Trombi, L.; Veronesi, P.; Leonelli, C.
abstract

Microwave heating fundamentally differs from other heating techniques as the consequence of its unique characteristic of being based on the electromagnetic energy transfer from the microwaves source to the interacting material, which according to its electric, dielectric, and magnetic properties can convert the absorbed energy into heat. This peculiar heating mechanism is at the basis of plenty of unquestionable advantages that were reported during the last three decades in most of the different branches of chemistry as well as materials science, thus including also combustion synthesis. After a brief overview of the microwave heating fundamentals as well as of the different components constituting the scientific microwave applicators, all the most significant and recent advancements in the use of microwaves as energy source in both solid-state as well as solution combustion synthesis processes will be comprehensively reviewed, highlighting the unique opportunities arising from the coupling of these two energy efficient techniques. Moreover the possible employment of less conventional frequencies as well as the use of new-generation solid state generators will be critically discussed also in the framework of scaling-up and microwave reactor design considerations.

2017 - Microwave processing of high entropy alloys: A powder metallurgy approach [Relazione in Atti di Convegno]
Veronesi, P.; Rosa, R.; Colombini, E.; Leonelli, C.; Garuti, M.
abstract

Microwaves at the ISM frequency of 2450 and 5800 MHz have been exploited to prepare FeCoNiCrAl-family high entropy alloys by direct heating of pressed mixtures of metal powders. The aim of this work is to explore a new microwave assisted near-net-shape technology, using powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies (defects formation) or solid state ones (time demanding). Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the compound. Microwave processing, exploited both for the ignition and sustaining of such reactions, has been compared to reactive sintering in laboratory furnace and mechanical alloying in a planetary ball milling. Results demonstrate that microwave required the shortest time and lowest energy consumption, thus it is promising time- and cost-saving synthetic route.

2017 - Microwave processing of high entropy alloys: A powder metallurgy approach [Articolo su rivista]
Veronesi, Paolo; Colombini, Elena; Rosa, Roberto; Leonelli, Cristina; Garuti, Marco
abstract

Microwaves at the ISM frequency of 2450 and 5800 MHz have been exploited to prepare FeCoNiCrAl-family high entropy alloys by direct heating of pressed mixtures of metal powders. The aim of this work is to explore a new microwave assisted near-net-shape technology, using powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies (defects formation) or solid state ones (time demanding). Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the compound. Microwave processing, exploited both for the ignition and sustaining of such reactions, has been compared to reactive sintering in laboratory furnace and mechanical alloying in a planetary ball milling. Results demonstrate that microwave required the shortest time and lowest energy consumption, thus it is promising time- and cost-saving synthetic route.

2017 - New ceramic materials from MSWI bottom ash obtained by an innovative microwave-assisted sintering process [Articolo su rivista]
Taurino, Rosa; Karamanov, Alexander; Rosa, Roberto; Karamanova, E.; Barbieri, Luisa; Atanasova Vladimirova, S.; Avdeev, G.; Leonelli, Cristina
abstract

Preliminary results on the production of new ceramic bricks by an innovative microwave-assisted sintering process employing MSWI bottom ashes are reported. Microwave heating technique was compared with a conventional thermal treatment with the aims to: (1) study the influence of heat treatment method on the crystallization behavior and on the microstructure of obtained samples; (2) define the crystallization evolution in microwave field; (3) gain an insight into the physical properties of the new samples. Higher crystallinity and new crystal phases were observed in the samples prepared by microwave heating, where precipitation of new sodium rich crystal phases was observed, together with quartz and anorthite, formed in the conventionally prepared samples. The possibility to obtain novel bricks with huge waste amount, in a very short thermal cycle and at relatively low temperatures was demonstrated with significant reductions in the energy demand for their production. Finally, the samples obtained by microwave-assisted sintering are characterized by improved mechanical properties.

2017 - Process Intensification by Experimental Design Application to Microwave-Assisted Extraction of Phenolic Compounds from Juglans regia L. [Articolo su rivista]
Rosa, Roberto; Tassi, Lorenzo; Orteca, Giulia; Saladini, Monica; Villa, Carla; Veronesi, Paolo; Leonelli, Cristina; Ferrari, Erika
abstract

Microwave-assisted extraction was applied to Juglans regia L. fresh male flowers and unripe walnut seeds to evaluate the total phenolic contents of the extracts as well as the percentage of water-soluble polyphenols. The research was planned using the Design of Experiments technique to investigate the role on the extraction efficiency of different parameters, such as temperature, time and number of microwave heating cycles, together with their possible interactions. Optimization was achieved by applying a Response Surface Methodology comprising a three-factor, two-level, full-factorial Face-Centred Central Composite Design. The two input variables with a significant effect on the recovery of phenols from fresh male flowers were the extraction temperature and the number of microwave cycles. In the case of unripe walnut seeds, a linear two-factor interaction model was selected, with significant interactions occurring between temperature and time, and time and number of microwave cycles. The best experimental conditions were as follows: 100 °C, 6 min, three microwave heating cycles and 22.7 ± 0.2 mg gallic acid equivalent (GAE)/g (total phenolic content, PC); energy consumption calculations suggested slightly different conditions: 60 °C, 30 min, three microwave heating cycles and 20.7 ± 0.3 mg GAE/g (TPC).

2017 - Special Issue AMPERE 15-Foreword [Abstract in Rivista]
Leonelli, C.
abstract

Dear Reader, This Special Issue has been dedicated to collect the most interesting and innovative works presented at the 15th edition of AMPERE EUROPE (Association for Microwave Power in Europe for Research and Education) biennial meeting: the International Conference on Microwave and High Frequency Heating (AMPERE 2015) here at the Cracow University of Technology, Krakow, Poland. AMPERE, is an "European" non-profit association devoted to the promotion of microwave and radio frequency heating techniques for research and industrial applications, every two year select one of its research groups to host the event. This time the Polish research group of Professor Dariusz Bogdal, here at the Cracow University of Technology, in Kraków, Poland, was selected. The conference has been successfully organised from 14th to 17th September 2015 and it was confirmed to take the aspect of an excellent international meeting with participants coming from all over the world, underlining once more the world-wide interest on this topic from part of academics, industrialists, and consultants. The high number of plenary and key-note lectures, jointly with oral and poster presentations, allowed the attendees to report on the novelties in the field of microwave and radio frequency applications and increase the interest of you all in this still evolving research fields. This Special Issue will furnish the scientists of the world with an excellent reference book. I trust also that this will be an impetus to stimulate further study and research in all these areas. AMPERE is thankful to all authors for their contributions and to the Guest Editors for their excellent job. Cristina Leonelli AMPERE President

2017 - Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming [Articolo su rivista]
Kamseu, Elie; Beleuk à. Moungam, L. M.; Cannio, Maria; Billong, Ndigui; Chaysuwan, Duangrudee; Melo, U. Chinje; Leonelli, Cristina
abstract

Rice husk ash (RHA), a by-product from the rice industry, was used as principal source of amorphous silica for the production of sodium silicate solution (MR ∼ 3) used for the replacement of standard commercial sodium silicate in the mix-design of metakaolin based geopolymer composites. Three initial concentrations of NaOH were considered (8, 10 and 12 M) with the aim to investigate on the optimum dissolution and formation of silica oligomers capable to act as binder during the geopolymerization. Results (FT-IR and XRD) showed that RHA-NaOH sodium silicate solutions have characteristics similar to that of standard commercial sodium silicate and the residual carbonates present in the viscous pastes can be monitored during the preparation of geopolymers using the mix-design. Combined 25 vol% standard sodium silicate solution with ∼75 vol% of RHA-NaOH based sodium silicate solution conducted to good polycondensation, densification, high flexural strength (∼8 MPa) and low porosity similar to that of the standard matrix of metakaolin based composites. The new approach is found promising for the significant reduction of the Global Warming Potential of Geopolymers.

2017 - The corrosion of kaolinite by iron minerals and the effects on geopolymerization [Articolo su rivista]
Kaze, R. C; Beleuk à. Moungam, L. M.; Fonkwe Djouka, M. L.; Nana, A.; Kamseu, Elie; Chinje Melo, U. F.; Leonelli, Cristina
abstract

Iron-rich aluminosilicates with disordered structure (laterites) due to the corrosion of kaolinite by iron minerals were investigated as solid precursors for geopolymerization. The particle size distribution, B.E.T surface area, thermal activation, and chemical and mineralogical compositions were used to evaluate the reactivity of iron-rich laterites (35 wt.% of Fe2O3-FeO). The raw materials in the temperature range between 25 and 500 °C showed geopolymerization behaviour similar to that of metakaolin. At temperatures higher than 500 °C, the coarsening of particles and the decrease of B.E.T surface area correspond to an initial sintering of laterites explaining the poor polycondensation/geopolymerization and the decrease of strength of the final products. The increase of the temperature of calcination of raw laterites between 25 and 500 °C corresponds to a reduction of the setting time of geopolymer products. However, this variation of temperature did not significantly affect the flexural strength that remained between ~ 4 and ~ 6 MPa, confirming the possibility to produce sustainable matrices, with more energy saving, using highly corroded laterites.

2017 - The influence of gibbsite in kaolin and the formation of berlinite on the properties of metakaolin-phosphate-based geopolymer cements [Articolo su rivista]
Tchakoute, H. K.; Ruscher, C. H.; Kamseu, E.; Djobo, J. N. Y.; Leonelli, C.
abstract

Two different kaolins (Kao1, Kao2) containing about 11 and 28% of gibbsite were applied for producing metakaolin-phosphate-based geopolymer cements. These kaolins were transformed to metakaolins by calcination them at 700 °C. Gibbsite contained in these kaolins were transformed to γ-Al2O3 during the calcination. The hardener used in this work was a phosphoric acid solution with molar concentration 10 M. It could be observed that the compressive strength of metakaolin-phosphate-based geopolymer cements (54.41/36.01 MPa) decreases in the course GMK1/GMK2. The both geopolymer cements indicate the formation of berlinite which is well dispersed in GMK1 and therefore reinforced the structure of the specimen. The micrograph images of phosphate-based geopolymer cements GMK2 is heterogeneous while the one of the GMK1 is homogeneous and more compact microstructure. The higher content of gibbsite in Kao2 affects negatively the mechanical and microstructural properties of metakaolin-phosphate-based geopolymer cements.

2017 - Thermal Behavior of Metakaolin-Based Geopolymer Cements Using Sodium Waterglass from Rice Husk Ash and Waste Glass as Alternative Activators [Articolo su rivista]
Tchakouté, Hervé K.; Rüscher, Claus H.; Kong, Sakeo; Kamseu, Elie; Leonelli, Cristina
abstract

The aim of this work was to study the thermal behavior of metakaolin-based geopolymer cements using sodium waterglass (NWG) from rice husk ash and waste glass as alternative alkaline activators. Metakaolin-based geopolymer cements were obtained by adding freshly prepared NWG and metakaolin. The geopolymer cements obtained using sodium waterglass from rice husk ash and the one obtained with sodium waterglass from the waste glass were treated at room temperature for 28 days and then heated at 200, 400, 600 and 800 °C. The results show that the metakaolin-based geopolymer cements lose their compressive strength from room temperature to 400 °C. At 600 °C, the compressive strength of geopolymer cements increases relative up to 200 and 400 °C. At 800 °C, the reduction of compressive strength of geopolymer cements is assigned to the total evaporation of the rest of structural water. However, it is higher than that measured at ambient temperature for geopolymer cement obtained using the sodium waterglass from waste glass but lower for the sample obtained with sodium waterglass from rice husk ash. The total mass loss of geopolymer cements obtained with sodium waterglass from rice husk ash and one obtained with sodium waterglass from waste glass are about 12.57 and 15.04 %, respectively. This suggests that geopolymer cement obtained using sodium waterglass from waste glass are more condensed geopolymer structure indicating that it could a very suitable material for fire resistant application. The results indicate that NWG from rice husk ash and waste glass could be served as suitable alternative activators for producing metakaolin-based geopolymer cements with high-temperature performance.

2017 - Utilization of sodium waterglass from sugar cane bagasse ash as a new alternative hardener for producing metakaolin-based geopolymer cement [Articolo su rivista]
Tchakoute, H. K.; Ruscher, C. H.; Hinsch, M.; Djobo, J. N. Y.; Kamseu, E.; Leonelli, C.
abstract

Sugar cane bagasse ash from SOSUCAM company in Cameroon was used to synthesize sodium waterglass as a new alternative hardener. The new hardener was used to prepare metakaolin-based geopolymer cements. The compressive strength of the resulting geopolymer cement cured at room temperature for 28&nbsp;days was 32.9&nbsp;MPa. Samples soaked for 28 days in water in parallel experiments revealed a strength of 31.4&nbsp;MPa. This shows that exposure of water does not lead to any weakening. The value of water absorption was 7.1% in the water-soaked cements, indicating the presence of fewer pores and voids than in the dry cements. However, in SEM micrographs, the microstructure of geopolymer cement appears rather homogeneous and compact without any change by water soaking. It can thus be concluded that sodium waterglass from sugar cane bagasse ash can be used as an alternative hardener or reactive ingredient for producing geopolymer cement with a high degree of cross-linking geopolymer framework. The use of this low-value silica-rich waste for producing sodium waterglass results in environmental benefits including a significant reduction of CO2 emission and energy consumption compared to the production of commercial sodium waterglass.

2017 - Valorization of wastes, “end of waste” and by-products using hot and cold techniques [Capitolo/Saggio]
Barbieri, L.; Andreola, F.; Taurino, R.; Ponzoni, C.; Manfredini, T.; Leonelli, C.; Lancellotti, I.
abstract

The Framework Directive 2008/98/EC, implemented in Italy by Legislative Decree no. 205/2010, in addition to reporting specific criteria and targets, gave the impression of a new cultural attitude that offers the combination of sustainable use of resources coupled with sustainable management of waste. The adoption of the best available technologies for processing and valorization respects first of all the proximity of the production of the waste. The final aim is the increase of recycling practice to reduce the pressure on the demand for raw materials with a double effect: reuse valuable materials, that would otherwise end up as waste, and reduce energy consumption and emissions of greenhouse gases in the process of extraction and machining. By 2020, we must manage waste as a resource through those instruments and actions that will affect the diffusion of wastes separated collection, promotion of efficient and of high-quality recycling. Contemporary we will assist to the development of markets for the new raw materials obtained by waste recovery and energy recovery limited to the non-recyclable materials regardless of the decrease in per capita and the removal of illegal shipments as well as the landfill.

2016 - Comparison of metakaolin-based geopolymer cements from commercial sodium waterglass and sodium waterglass from rice husk ash [Articolo su rivista]
Tchakouté, Hervé K.; Rüscher, Claus H.; Kong, Sakeo; Kamseu, Elie; Leonelli, Cristina
abstract

Abstract: Three sodium waterglass (NWG) such as commercial NWG (S1), NWG from pure rice husk ash (S2) and NWG from raw rice husk ash (S3) were applied for producing geopolymer cements using metakaolin (MK) as aluminosilicate source. Geopolymers (Geo1, Geo2 and Geo3) were prepared using each NWG with the molar ratios SiO2/Na2O and H2O/Na2O kept constant at 1.5 and 12, respectively. It could be observed that the water absorption of Geo1, Geo2 and Geo3 is 7, 9 and 13.2 % and the mass loss is 15.8, 14.7 and 12.4 %, respectively. Their compressive strength at 20 days (37.5/34.3/29.6 MPa) and 28 days (43.3/40.3/33.2 MPa) increases with increasing the aging and decreases in the course Geo1/Geo2/Geo3. Their average pore radius (6/8/20 nm) and cumulative pore volumes (155/205/245 mm3/g) increase in the course Geo1/Geo2/Geo3. It is discussed that the presence of phosphate known as corrosion inhibitors in raw rice husk ash hinders the dissolution of SiO2. It entails the formation of NaH2PO4 in S3 which reduces the soluble Si atoms. Therefore, less amount of metakaolin could be dissolved leaving thus a higher amount of unreacted metakaolin particles in Geo3. The reacted volumes and compositions of the geopolymers are different in the three cases, too. A content of approximately 20, 25 and 35 % of unreacted metakaolin was proved for Geo1, Geo2 and Geo3, respectively. Graphical Abstract: [Figure not available: see fulltext.]

2016 - Cradle to the grave Life Cycle Assessment of microwave assisted vs. conventional extraction for the obtainment of highly pure curcumin [Abstract in Atti di Convegno]
Rosa, Roberto; Zerazion, Elisabetta; Ferrari, Erika; Veronesi, Paolo; Leonelli, Cristina; Saladini, Monica; Ferrari, Anna Maria
abstract

Microwave assisted extraction of natural compounds is widely recognized as one of the most promising green extraction techniques, even if comprehensive comparisons with more conventional procedures are surprisingly scarce, being on the other hand limited to mere considerations concerning extraction time and yield. In this work, “cradle to the grave” environmental assessments of microwave assisted compared to conventional Soxhlet-based extraction procedures will be presented, for the particular case of curcumin molecule, extracted from Curcuma longa L., in view of its important antioxidant, anti-inflammatory and anticancer properties. The Life Cycle Assessment (LCA) methodology was applied, since it allows evaluating the environmental consequences associated with all the stages of the extraction process, thus including the crop production of the Indian plant, the subsequent production of the dried rhizomes, their commercialization, their transport, all the energy consumptions needed, the necessary laboratory facilities and their maintenance, together with the chemicals needed and their disposal treatments. The study was then completed by also comparing the obtained results with those of a particular synthetic strategy of curcumin, in order to establish the most environmentally friendly production procedure of this fundamental phytochemical.

2016 - Design of inorganic polymer mortar from ferricalsialic and calsialic slags for indoor humidity control [Articolo su rivista]
Kamseu, Elie; Lancellotti, Isabella; Sglavo, Vincenzo M.; Modolo, Luca; Leonelli, Cristina
abstract

Amorphous silica and alumina of metakaolin are used to adjust the bulk composition of black (BSS) and white (WSS) steel slag to prepare alkali-activated (AAS) mortars consolidated at room temperature. The mix-design also includes also the addition of semi-crystalline matrix of river sand to the metakaolin/steel powders. The results showed that high strength of the steel slag/metakaolin mortars can be achieved with the geopolymerization process which was particularly affected by the metallic iron present into the steel slag. The corrosion of the Fe particles was found to be responsible for porosity in the range between 0.1 and 10 μm. This class of porosity dominated (~31 vol %) the pore network of B compared to W samples (~16 vol %). However, W series remained with the higher cumulative pore volume (0.18 mL/g) compared to B series, with 0.12 mL/g. The maximum flexural strength was 6.89 and 8.51 MPa for the W and B series, respectively. The fracture surface ESEM observations of AAS showed large grains covered with the matrix assuming the good adhesion bonds between the gel-like geopolymer structure mixed with alkali activated steel slag and the residual unreacted portion. The correlation between the metallic iron/Fe oxides content, the pore network development, the strength and microstructure suggested the steel slag's significant action into the strengthening mechanism of consolidated products. These products also showed an interesting adsorption/desorption behavior that suggested their use as coating material to maintain the stability of the indoor relative humidity.

2016 - Geopolymer binders from metakaolin using sodium waterglass from waste glass and rice husk ash as alternative activators: A comparative study [Articolo su rivista]
Tchakouté, Hervé K.; Rüscher, Claus H.; Kong, Sakeo; Kamseu, Elie; Leonelli, Cristina
abstract

Rice husk and waste glass from sources in Cameroon were used for producing sodium waterglass (NWG) solution denoted S1 and S2 respectively as alternative activators to prepare metakaolin-based geopolymer binder. Metakaolin-based geopolymer binders (G1, G2) were obtained using freshly prepared NWG with a mass ratio NWG/MK = 0.83. The IR spectra of S1, S2 using ATR and KBr methods show the presence of SiQ0, SiQ1, SiQ2 units, and S1 contained also SiQ3 and SiQ4 units. The mechanical testing, environmental scanning electron microscopy, mercury intrusion porosimetry, X-ray diffractometry, infrared spectroscopy, amount of binders and thermogravimetric analysis are investigated to study the properties of the geopolymer binders. The results show that the compressive strength values of geopolymer G2 (22.9, 27.6, 32.6, 36 and 39.7 MPa) are higher than that of G1 (17.7, 19.1, 21.2, 29.9 and 32.8 MPa) at 7, 14, 21, 28 and 56 days respectively. The microstructure of G2 is more compact with fewer unreacted metakaolin particles. It can be concluded that sodium waterglass from waste glass and rice husk ash are suitable alternative activators for the production of metakaolin-based geopolymers. In addition, they constitute a better ecological choice when compared to commercial sodium silicate from melting process.

2016 - Glass coloring and recycling in late antiquity: A new case study from Aquileia (Italy) [Articolo su rivista]
Boschetti, C.; Mantovani, V.; Leonelli, C.
abstract

Aquileia is widely cited as a major Roman glassworking center, but this assumption is based on scarce archaeological evidence and supported by only a few indicators of production, mainly found out of archaeological context. This article discusses problems relating to the glass industry in Aquileia, presenting a new group of indicators of production, excavated in 2014, that includes fragments of a melting chamber, cullet, mosaic tesserae, and one glassworking tool. This new discovery, interpreted as a fourth-century context of glass coloring and recycling, is the first evidence of colored glass working ever investigated stratigraphically at Aquileia, and it adds new data to the complex picture of the structure of the Late Antique glass industry in the Roman town. The authors analyzed 15 glass samples by ESEM-EDS, demonstrating that glasses were recycled both by mixing mosaic tesserae with colorless glass and by re-melting or softening mosaic tesserae.

2016 - Microwave assisted synthesis of Si-modified Mn25FexNi25Cu(50−x) high entropy alloys [Articolo su rivista]
Veronesi, Paolo; Colombini, Elena; Rosa, Roberto; Leonelli, Cristina; Rosi, Fabrizio
abstract

Rapid microwave heating at 2450 MHz of metallic powders mixtures compacts was performed under Ar flux in a single mode applicator in order to produce Si-modified Mn25FexNi25Cu(50−x), (x=25, 30, 35, 40) high entropy alloys. Microwave heating was conducted in presence of a SiC auxiliary absorber, so that the compacts are subjected to both direct heating by microwave absorption and indirect heating by the auxiliary absorber. Due to the extremely rapid processing times, including the cooling stage, depletion of the most oxygen-reactive elements was moderate, considering the not perfectly protective atmosphere used. FCC solid solutions have been obtained and the role of Si is discussed as a microstructure modifier and as increaser of the microhardness.

2016 - Microwave ignition of the combustion synthesis of aluminides and field-related effects [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Casagrande, Angelo; Leonelli, Cristina
abstract

Combustion synthesis of aluminide intermetallics starting from reactive powders mixtures comprising a ferromagnetic component (Fe, Co and Ni) has been performed by igniting the exothermic reactions in a microwave single mode applicator, in order to investigate possible effects related to the positioning of the reactive sample into the region of predominant electric or magnetic field. In addition to an increase of the reproducibility of the experiments and the possibility to avoid electric arcs generation, the ignition of the combustion reactions in predominant magnetic field allowed to significantly reduce the ignition times, with a global reduction of the power required to synthesize the intermetallics. This implies that the amount of the reactive volume under ignition conditions is reduced proportionally, thus moving from thermal explosion towards Self-propagating High-temperature Synthesis mode of combustion. Moreover, in the case of Fe-Al system, the disposition of the load into the region of predominant magnetic field increased the yield of the desired intermetallic compound, to the detriment of α-Fe(Al) solid solution co-product. Furthermore, the possibility to continue to furnish energy to the reactive Fe + Al sample after combustion synthesis ignition has been proven for both configurations. Results show that in case of exposure to the predominant magnetic field, the sample cooling rate resulted lower, hence the permanence at high temperatures after synthesis could be proficiently exploited to increase adhesion to an underlying substrate, in case combustion synthesis technique is used to obtain intermetallic-based coatings.

2016 - Microwave-assisted extraction of phytochemicals [Abstract in Atti di Convegno]
Rosa, Roberto; Zerazion, Elisabetta; Ferrari, Erika; Veronesi, Paolo; Villa, Carla; Saladini, Monica; Ferrari, Anna Maria; Leonelli, Cristina
abstract

Several epidemiological studies highlighted the importance of a diet based on fruits and vegetables, for a significant reduction in the risk of several human health diseases [1]. Therefore, the extraction of the so-called dietary phytochemicals started gaining an extraordinary research interest from both academia and industries, to the detriment of their synthesis, particularly when the concepts and principles of Green Extraction [2] and Process Intensification [3] are considered, in order to pursue a sustainable development. Among the green extraction techniques, the application of microwave energy is surely to be considered one of the most appealing ones, mainly as a direct consequence of its unique heating mechanism. According to the nature of the plant matrix as well as of the phytochemical compounds of interest, microwaves can be applied in a plenty of variants. Aim of the present work is to display some of our recent results obtained by microwave assisted extraction (MAE) of phenolic compounds from Juglans regia L., Cinnamomum Zeylanicum and Curcuma longa L. [4], highlighting the advantages, when any, over more conventional extraction procedures as well as over the chemical synthesis of those molecules, also in terms of energy consumptions as well as environmental assessments of these different approaches.

2016 - Mosaic tesserae from Italy and the production of Mediterranean coloured glass (4rd century BCE-4th century CE). Part I: Chemical composition and technology [Articolo su rivista]
Boschetti, Cristina; Henderson, Julian; Evans, Jane; Leonelli, Cristina
abstract

Roman highly coloured glass is well represented amongst mosaic tesserae, occasionally found in Italy from the middle of the 2nd century BCE and commonly used from the early 1st century CE. SEM-EDS microstructural and chemical analysis has revealed colouring elements and opacifiers. Chemical analysis has identified both natron and plant ash glasses, the former fitting five compositional types of ancient natron glass (Levantine I and II, HIMT, Wadi Natrun and Egypt II) and of Roman colourless glass. The apparent Levantine and Egyptian provenance for the 'raw glasses' (once the colourants and opacifiers were removed) is discussed critically in the light of Nd and Sr isotopic results in part II.

2016 - Phytochemical compounds or their synthetic counterparts? A detailed comparison of the quantitative environmental assessment for the synthesis and extraction of curcumin [Articolo su rivista]
Zerazion, Elisabetta; Rosa, Roberto; Ferrari, Erika; Veronesi, Paolo; Leonelli, Cristina; Saladini, Monica; Ferrari, Anna Maria
abstract

Natural compounds represent an extremely wide category to be exploited, in order to develop new pharmaceutical strategies. In this framework, the number of in vitro, in vivo and clinical trials investigating the therapeutic potential of curcumin is exponentially increasing, due to its antioxidant, anti-inflammatory and anticancer properties. The possibility to obtain this molecule by both chemical synthesis and extraction from natural sources makes the environmental assessments of these alternative production processes of paramount importance from a green chemistry perspective, with the aim, for both industries and academia, to pursue a more sustainable development. The present work reports detailed and quantitative environmental assessments of three different curcumin production strategies: synthesis, conventional Soxhlet-based extraction (CE) and microwave-assisted extraction (MAE). The chemical synthesis of curcumin, as recently optimized by the authors, has been firstly evaluated by using the EATOS software followed by a complete “cradle to the grave” study, realized by applying the Life Cycle Assessment (LCA) methodology. The life cycles of CE and MAE were then similarly assessed, considering also the cultivation of Curcuma longa L., the production of the dried rhizomes as well as their commercialization, in order to firstly investigate the widely claimed green character of MAE with respect to more conventional extraction procedures. Secondly, the results related to the two different extraction strategies were compared to those obtained by the chemical synthesis of curcumin, with the aim to determine its greenest preparation procedure among those investigated. This work represents the first example of an environmental assessment comparison between different production strategies of curcumin, thus smoothing the way towards the highly desirable establishment of environmentally friendly rankings, comprising all the existing alternatives to the chemical synthesis of a target chemical compound.

2016 - Potassium alkali concentration and heat treatment affected metakaolin-based geopolymer [Articolo su rivista]
Tippayasam, Chayanee; Balyore, Pongpob; Thavorniti, Parjaree; Kamseu, Elie; Leonelli, Cristina; Chindaprasirt, Prinya; Chaysuwan, Duangrudee
abstract

Geopolymers prepared using KOH and K2SiO3 alkali solution instead of the more common NaOH and Na2SiO3 are reported. The influence of KOH concentration, curing temperature and heat treatment on the properties of metakaolin-based geopolymers were studied. The KOH concentrations were varied at 6, 8, 10, 20, 30 and 40 M, the K2SiO3/KOH ratios used were 1 and 1.5 and curing temperatures of 40 °C and 60 °C for 24 h were applied. Results showed that geopolymer with 10 M KOH, cured at 40 °C, 24 h and heat treated at 550 °C gave the highest compressive strength at 28 days. The heat treatment process caused the porosity of geopolymer increased because water was eliminated from the geopolymer structure by the applied heat, therefore, the density decreased whereas the water absorption and the porosity of geopolymer specimens increased. The microstructure of heat-treated specimens showed more mature geopolymer matrix than that of non heat-treated ones leading to higher compressive strength in the former geopolymers and had ceramic-like property.

2016 - Production of cement blocks and new ceramic materials with high content of glass waste [Relazione in Atti di Convegno]
Andreola, Nora Maria; Lancellotti, Isabella; Taurino, Rosa; Leonelli, Cristina; Barbieri, Luisa
abstract

Virgin inorganic raw materials can be partially replaced by glass waste in order to reduce the environmental impact being its recycling a significant problem for municipalities worldwide. In Italy in 2013, approximately 1, 600, 000 tons of container glass have been collected but it has not been possible to recycle all of them in the glass melting process. The valorization, reuse and reclamation of glass waste as raw material in new cement and ceramic products are here proposed with the aim to convert it from an environmental and economic burden to a profitable, added-value resource in the formulation of new mixes. Several parameters, such as grinding, forming, firing, etc. have been studied and optimized to transform glass waste in an alternative raw material for hot and cold consolidation processes. Chemical, physical and mechanical properties of products have proved that there are new and real possibilities to use high amounts of glass waste for fired items (up to 80wt%) and for cold cement mixes (up to 75wt%).

2016 - Recycling of industrial wastes in ceramic manufacturing: State of art and glass case studies [Articolo su rivista]
Andreola, Nora Maria; Barbieri, Luisa; Lancellotti, Isabella; Leonelli, Cristina; Manfredini, Tiziano
abstract

Nowadays, ceramic tile are manufactured at zero emissions permitting to recycle all by-products and part of residues derived from depuration treatments (exhausted lime, glazing sludge and polishing sludge). In addition to this environmentally friendly tendency, in the last years an increasing number of scientific studies demonstrated the feasibility to use alternative raw materials in substitution of different component of the ternary clay-feldspar-quartz system. In the first part of the paper is reported the state of the art of industrial waste recycling in the ceramic sector, with the focus on review studies related to both ceramic tiles and bricks..In the second part of the work are reported two case studies conducted by the authors with the aim to formulate ceramic bodies using alternative raw materials. New tailored compositions were obtained replacing clays, flux and/or inert compounds (higher than 60. wt%) by scraps from packaging waste glass in tiles, and cathode ray tube glasses and packaging waste glass up to 20. wt% in the brick compositions.

2016 - Self-compacting geopolymer concretes: Effects of addition of aluminosilicate-rich fines [Articolo su rivista]
Kamseu, Elie; Ponzoni, Chiara; Tippayasam, Chayanee; Taurino, Rosa; Chaysuwan, Duangrudee; Sglavo, Vincenzo M.; Thavorniti, Parjaree; Leonelli, Cristina
abstract

The presence of alunimosilicate based fine aggregates (2.5 to 7.5 wt%) effectively acted to densify the microstructure of the interfacial zone with a reduction of pore threshold and mean pore size jointly with change on the fracture mode of the Self-Compacting (SC) geopolymer concretes. From the results, pumice and recycled glass with amorphous structure improved the bi-axial four-point flexural strength from 5 to 8 MPa while semi-crystalline feldspar sludge (nepheline syenite) reached 11 MPa. The formation of additional geopolymer gels were responsible for the strengthening mechanism. The specimens with amorphous fines showed the tendency to delay the desorption in the laboratory conditions indicating the need for a very long curing time for the final consolidation. The semi-crystalline fines -nepheline syenite- appeared appropriate for the design of self-compacting geopolymer concretes due to their bulk composition, capacity to enhance densification and strength with low deformation rate, in a short range of curing together with a high rate of desorption, all important parameters for the prediction of the durability of concretes.

2016 - Stabilization and thermal conductivity of aqueous magnetite nanofluid from continuous flows hydrothermal microwave synthesis [Articolo su rivista]
Cannio, Maria; Ponzoni, Chiara; Gualtieri, Magdalena Lassinantti; Lugli, Eleonora; Leonelli, Cristina; Romagnoli, Marcello
abstract

Magnetite, Fe3O4, nanoparticles, synthesized by hydrothermal microwave assisted technique in continuous flow, are characterized by X-ray diffraction, FTIR and TEM. The suspension stabilization of the nanoparticles dispersed in aqueous media is evaluated by the zeta potential trend and particle size distribution. The effect of the pH, the addition of a phosphate based dispersant and the sonication time on the suspension stabilization are investigated in detail. Moreover, once identified the most stable nanofluid, its thermal properties are measured to evaluate its possible application as heat transfer fluid. The preliminary results indicate a significant enhancement of magnetite water based nanofluid thermal conductivity with respect to water (up to 25%) and conventional water based fluid.

2016 - The role of kyanite in the improvement in the crystallization and densification of the high strength mullite matrix: Phase evolution and sintering behaviour [Articolo su rivista]
Deutou, J. G. N.; Mohamed, Hawa; Nzeukou, N. A.; Kamseu, Elie; Melo, U. C.; Beda, T.; Leonelli, Cristina
abstract

Fine particles of kyanite were used as reinforcement in mullite matrix composite. Mix of metakaolin and meta-alumina (calcined bauxite) received different fraction of fine kyanite particles: 37.5, 42.5 and 50 mass%. The objectives were to improve the crystallization of kaolin-based mullite matrix reducing the amorphous content and the grain growth. Packing process and densification were enhanced, leading to the action of kyanite at low temperature (<1250 °C) as phase separator and nucleation sites for the transformation of metakaolin to acicular mullite. At high temperature (>1350 °C), the kyanite particles are decomposed to mullite still without glassy phase and the metastable alumina presented in the mix reacts with amorphous silica to produce additional mullite. The sintering behaviour, the thermal expansion behaviour of ~0.5 % between 200 and 1000 °C and the coefficient of the thermal expansion of 5.92, 5.15 and 6.92 × 10−6/°C for KY3, KY4 and KY5, respectively, between 200 and 1000 °C, and their decrease at higher temperature demonstrated the optimum refractoriness of the mullite matrix composites developed.

2016 - Valutazione ambientale comparativa di alcune strategie sintetiche di nanoparticelle di TiO2 [Abstract in Atti di Convegno]
Rosa, Roberto; Pini, Martina; Neri, Paolo; Corradi, Anna; Leonelli, Cristina; Ferrari, Anna Maria
abstract

Il convegno si svolge presso le sale di Palazzo Garzolini di Toppo Wassermann, sede della Scuola Superiore dell’Università di Udine, che racchiude tre secoli di storia, arte, cultura e un futuro dedicato ai giovani e alla conoscenza. Tale evento nasce come occasione per favorire il confronto e lo scambio di esperienze tra i partecipanti sia per quanto attiene i recenti risultati della attività di ricerca scientifica che per questioni inerenti la specifica didattica orientata alle Tecnologie Chimiche per l’Ingegneria.I lavori del convegno, i cui atti saranno pubblicati esclusivamente in formato elettronico, sono articolati in forma di conferenze plenarie, comunicazioni orali e conferenze da parte di giovani ricercatori a cui vengono conferiti i premi AICIng per le migliori Tesi di Dottorato. In particolare, tali premi hanno lo scopo di dare riconoscimento ai risultati di giovani talenti e stimolarli verso una carriera nella ricerca più innovativa. Non mancherà una articolata sessione poster che, assieme ai vari eventi sociali, consentirà la più ampia interazione tra i partecipanti. Il tema della Tavola Rotonda di quest’anno sarà “Ricerca di base, ricerca applicata e trasferimento tecnologico” sul quale interverranno il Magnifico Rettore dell’Ateneo di Udine, prof. Alberto De Toni, il prof. Marco Gilli, Magnifico Rettore del Politecnico di Torino, la prof. Silvia Licoccia, collega AICIng e delegata alla Ricerca dell’Università di Roma Tor Vergata, e il dott. Emilio Sassone Corsi, AD di Management Innovation, Roma.

2015 - A polymer supported palladium(II) β-ketoesterate complex as active and recyclable pre-catalyst for selective reduction of quinolines in water with sodium borohydride [Articolo su rivista]
Dell'Anna, Maria Michela; Romanazzi, Giuseppe; Intini, Simona; Rizzuti, Antonino; Leonelli, Cristina; Piccinni, Alberto Ferruccio; Mastrorilli, Piero
abstract

A polymer supported palladium catalyst, obtained by copolymerization of Pd(AAEMA)<inf>2</inf> [AAEMA<sup>-</sup> = deprotonated form of 2-(acetoacetoxy) ethyl methacrylate] with ethyl methacrylate (co-monomer) and ethylene glycol dimethacrylate (cross-linker), exhibited excellent activity and selectivity for the hydrogenation of quinolines to 1,2,3,4-tetrahydroquinolines in the presence of NaBH<inf>4</inf> as hydrogen donor in water. Both the activity and selectivity could be maintained for at least seven reaction runs. No metal leaching into solution occurred during recycles. TEM analyzes carried out on the catalyst showed that the active species were supported palladium nanoparticles having a mean size of 3 nm, which did not aggregate with the recycles.

2015 - Chromium liquid waste inertization in an inorganic alkali activated matrix: Leaching and NMR multinuclear approach [Articolo su rivista]
Ponzoni, Chiara; Lancellotti, Isabella; Barbieri, Luisa; Spinella, Alberto; Saladino, Maria Luisa; Martino, Delia Chillura; Caponetti, Eugenio; Armetta, Francesco; Leonelli, Cristina
abstract

A class of inorganic binders, also known as geopolymers, can be obtained by alkali activation of alumi-nosilicate powders at room temperature. The process is affected by many parameters (curing time, curingtemperature, relative humidity etc.) and leads to a resistant matrix usable for inertization of hazardouswaste. In this study an industrial liquid waste containing a high amount of chromium (≈2.3 wt%) in theform of metalorganic salts is inertized into a metakaolin based geopolymer matrix. One of the innova-tive aspects is the exploitation of the water contained in the waste for the geopolymerization process.This avoided any drying treatment, a common step in the management of liquid hazardous waste. Theevolution of the process - from the precursor dissolution to the final geopolymer matrix hardening - ofdifferent geopolymers containing a waste amount ranging from 3 to 20% wt and their capability to iner-tize chromium cations were studied by: i) the leaching tests, according to the EN 12,457 regulation, atdifferent curing times (15, 28, 90 and 540 days) monitoring releases of chromium ions (Cr(III) and Cr(VI))and the cations constituting the aluminosilicate matrix (Na, Si, Al); ii) the humidity variation for differentcuring times (15 and 540 days); iii) SEM characterization at different curing times (28 and 540 days);iv) the trend of the solution conductivity and pH during the leaching test; v) the characterization of theshort-range ordering in terms of T O T bonds (where T is Al or Si) by29Si and27Al solid state magic-anglespinning nuclear magnetic resonance (ss MAS NMR) for geopolymers containing high amounts of waste(10–20% wt). The results show the formation of a stable matrix after only 15 days independently on thewaste amount introduced; the longer curing times increase the matrices stabilities and their ability toimmobilize chromium cations. The maximum amount of waste that can be inertized is around 10 wt%after a curing time of 28 days.

2015 - Cleaner production of the lightweight insulating composites: Microstructure, pore network and thermal conductivity [Articolo su rivista]
Fongang, R. T. Tene; Pemndje, J.; Lemougna, P. N.; Melo, U. Chinje; Nanseu, C. P.; Nait Ali, B.; Kamseu, Elie; Leonelli, Cristina
abstract

Inorganic polymer cement paste was used as cleaner binder for the design of lightweight matrices as insulating envelopes and panels in building and construction industries. Sponge-like structure with a homogeneously distributed pore network, low density and low thermal conductivity permitted to classify the geopolymer-wood fiber composites promising clean insulating materials. Matrices with the density ∼0.79 g/cm<sup>3</sup>, bi-axial four-point flexural strength of ∼4 MPa presented thermal conductivity between 0.2 and 0.3 W/(m K). The possibility of substituting the sodium silicate with rice ash-NaOH system and the efficiency of the matrices to constitute an effective tortuous road for the thermal gradient improved the sustainability and quality of this new class of products. The pores network and the microstructure approximated by a spatial periodic geometry suggested a "macro transport" mechanism to explain the movement of heat across the matrix of light geopolymer composite.

2015 - Cold-setting refractory composites from cordierite and mullite-cordierite design with geopolymer paste as binder: Thermal behavior and phase evolution [Articolo su rivista]
Djangang, Chantale N; Tealdi, Cristina; Cattaneo, Alice S.; Mustarelli, Piercarlo; Kamseu, Elie; Leonelli, Cristina
abstract

Cordierite and mullite-cordierite based geopolymer binders were prepared as refractory bonds to embed coarse kyanite aggregates. Alkali activation was used to consolidate the refractory at room temperature and generate a reactive interface between the matrix and the aggregates. The flexural strength at room temperature of consolidated materials was 11 MPa without kyanite addition, whilst it reached 28 MPa when kyanite was added. The latter showed thermal expansion near to zero up to 500 °C, followed by an expansion of ∼0.5% up to 1000 °C, then a decrease between 1000 and 1050 °C, concluding with a constant value of expansion <0.5% up to 1250 °C. The increase in expansion was found to be linked to the transformation of the geopolymer into ceramic bond with the formation of crystalline phases, while the decrease was apparently related to the liquid phase sintering. The stability of mullite, cordierite and leucite formed up to 1250 °C was responsible for the constant expansion observed up to this temperature. The mechanical properties, the phase evolution and the thermal behavior of the K2O-MgO-Al2O3-SiO2 bonds, together with the refractory behavior of kyanite aggregates, were found suitable for the design of sustainable cold-setting refractory composites.

2015 - Cumulative pore volume, pore size distribution and phases percolation in porous inorganic polymer composites: Relation microstructure and effective thermal conductivity [Articolo su rivista]
Kamseu, Elie; Ngouloure, Zénabou N. M.; Ali, Benoît Nait; Zekeng, S.; Melo, U. C.; Rossignol, S.; Leonelli, Cristina
abstract

Rice hush (R) and volcanic (P) ashes, two recycled natural wastes were used for their high amorphous silica to improve the homogeneity and structure composition of inorganic polymer pastes before the expansion with aluminum powder. The fine powders were found to be appropriate in enhancing the geopolymerization and expansion conducting to lightweight structure with pore size and pore distribution linked to the viscosity, the concentration of blowing agent, and the crystalline nature of the waste. From the Stereo optical microscope, environmental scanning microscope and the mercury intrusion porosimetry used for the characterization, it appeared that in the interval of complete percolation of the skeleton, there exists correlation between the viscosity, expansion, roundness of pores, pores size distribution. The interpretation of the microstructure of porous geopolymer in this interval allows the description of their effective thermal conductivity with the Maxwell-Eucken model and the novel effective medium theory proposed recently.

2015 - Dielectric and magnetic measurements of iron-based materials and their variations at high temperature [Relazione in Atti di Convegno]
Catala Civera, Josã; Veronesi, Paolo; Rosa, Roberto; Toso, Omar; De Appollonia, Marco; Llorens, Gabriel; Leonelli, Cristina
abstract

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2015 - Ecosustainable Development of Novel Bio-inorganic Hybrid Materials as UV Protection Systems for Potential Cosmetic Applications [Articolo su rivista]
Villa, Carla; Lacapra, Chiara; Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina
abstract

A new organoclay, bio-inorganic hybrid material, was successfully prepared following the "green chemistry" principles, exploiting microwave irradiation (as an alternative energetic source) in both the solvent-free synthesis of the organic filler (UVB filter) and in its hydrothermal intercalation in a sodium Bentonite clay (renewable natural inorganic source at low temperature). The organic filler is a benzylidene camphor derivative with the same cationic moiety as the well- known UV filter camphor benzalkonium methosulfate. The aim of the research was the ecosustainable development of a new UV protection model, suitable for use in cosmetic and pharmaceutical products, with potential advantages of stability, efficiency and safety compared to the commercially available UVB sunscreens. The organically modified clay was thoroughly investigated using X-ray diffraction (XRD), infrared spectroscopy (IR), thermo gravimetric analysis and differential thermal analysis (DTA). Results confirmed the complete intercalation of the organic filler in the interlayer region of the smectite clay, leading to a new bio-inorganic hybrid material with potential for cosmetic and pharmaceutical applications in the UV protection field, as confirmed by preliminary photochemical studies. This work represents the first example in the use of Na-Bentonite cationic clay (usually employed as rheological additive) as hosting agent of the synthesized quaternary UVB filter, as well as in the complete MW-assisted preparation of the organoclay, starting from the synthesis of the organic UV sunscreen to its hydrothermal intercalation.

2015 - Geopolymers: An option for the valorization of incinerator bottom ash derived “end of waste” [Articolo su rivista]
Lancellotti, Isabella; Cannio, Maria; Bollino, Flavia; Catauro, Michelina; Barbieri, Luisa; Leonelli, Cristina
abstract

In the present paper, bottom ashes from urban waste incineration wer used as sole source material to develop geopolymers activated with alkali solution. This study intends to gather basic structural data on the synthesized materials at fixed curing times (3 h;1, 4, 5, 7, 30 days; 20 months) by X-ray (XRD) and Fourier Transform Infrared (FTIR) analysis. Curing time affects both crystalline phase transformation and the geopolymeric gel structure. The XRD results showed the starting of geopolymerization, due to the alkali activation, already within the first 3 hof curing. New phases such as hydrated sodium carbonate and gismondine, confirming the progressive ash reactivity, appeared after 4 h and 1 day of curing respectively. Finally, after approximately 30 days curing at room temperature, the condensation process and, consequently, the formation of a stable 3D gel of aluminosilicate network occurred. FTIR showed a 40 cm_1 displacement of the band at 980cm_1 during the first hours of the geopolymer formation confirming the formation of the geopolymeric network also from a matrix without metakaolin. Furthermore Scanning Electron Microscopy (SEM–EDS) analyses were performed to assess morphological characteristics and to evaluate the presence of unreacted aluminosilicate particles in the obtained geopolymers.

2015 - Handbook of Alkali-Activated Cements, Mortars and Concretes [Monografia/Trattato scientifico]
Pacheco Torgal, F; Labrincha, J. A.; Leonelli, Cristina; Palomo, A.; Chindaprasirt, P.
abstract

This book provides an updated state-of-the-art review on new developments in alkali-activation. The main binder of concrete, Portland cement, represents almost 80% of the total CO2 emissions of concrete which are about 6 to 7% of the Planet's total CO2 emissions. This is particularly serious in the current context of climate change and it could get even worse because the demand for Portland cement is expected to increase by almost 200% by 2050 from 2010 levels, reaching 6000 million tons/year. Alkali-activated binders represent an alternative to Portland cement having higher durability and a lower CO2 footprint. Reviews the chemistry, mix design, manufacture and properties of alkali-activated cement-based concrete binders. Considers performance in adverse environmental conditions. Offers equal emphasis on the science behind the technology and its use in civil engineering.

2015 - Influence of fine aggregates on the microstructure, porosity and chemico-mechanical stability of inorganic polymer concretes [Articolo su rivista]
Kamseu, Elie; Ponzoni, Chiara; Tippayasam, Chayanee; Taurino, Rosa; Chaysuwan, Duangrudee; Bignozzi, Maria Chiara; Barbieri, Luisa; Leonelli, Cristina
abstract

This work investigates the effects of the structure, the bulk chemical composition and amount of the aluminosilicate fines on the strength development, pore refinement, water permeability, moisture control capacity and the microstructure of inorganic polymer concretes (IPC). The amorphous fines, one from pumice and another from recycled glass, presented sponge-like microstructure with tortuous pore network that maintained the presence of fine capillary pores while semi-crystalline feldspar sludge, the third type of fine aggregates used for this study, showed more dense and compact microstructure that explain the higher strength enhancement. Both amorphous and semicrystalline fines contributed to decrease the porosity, improve the strength and microstructure. However, based on the moisture control capacity and the durability indicators, the fine aggregate derived from semicrystalline feldspar was found to be more appropriate and efficient for the development of IPC at short time scale of curing. Pumice fine aggregate was found to be effective only with a long term curing.

2015 - Inorganic syntheses assisted by microwave heating [Articolo su rivista]
Leonelli, C.; Komarneni, S.
abstract

2015 - Microstructural study of microwave sintered zirconia for dental applications [Articolo su rivista]
Monaco, C; Prete, F.; Leonelli, Cristina; Esposito, L.; Tucci, A.
abstract

Conventional sintering techniques for zirconia-based materials, which are commonly used in dental reconstruction, may not provide uniform heating, with the consequent generation of microstructural flaws in the final component. A sintering system using microwave heating may represent a viable alternative. The purpose of this study was to compare the dimensional variation and physical and microstructural characteristics of commercial zirconia (Y-TZP), used as a dental restoration material, sintered in conventional and microwave furnaces. A physicalmineralogical-microstructural characterisation was carried out to evaluate the level of densification and the presence of flaws in the sintered specimens. Use of the microwave systems allowed the length of the sintering cycle to be reduced to a few minutes, compared with the several hours necessary with a 'traditional' heating system. Additionally, the maximum temperature used to reach the required density decreased from 1450-1480 °C with the electric furnace to 1200 °C in the microwave furnace. An important clinical implication is that the reduced sintering time could allow the introduction of zirconia in chair-side treatments, if used as a monolithic material.

2015 - Microwave Reactors for Chemical Synthesis and Biofuels Preparation [Capitolo/Saggio]
Leonelli, Cristina; Veronesi, Paolo
abstract

Microwave reactors are among the most novel thermochemical technologies to treat biomass and improve process sustainability. The microwave-assisted process offers several advantages over the traditional ones in terms of uniform internal heating of heterogeneous low-thermal conductivity loads, ease of control, saving of time and heat energy for properly designed or selected reactors. The geometries and the functioning principles of microwave reactors commonly adopted for chemical synthesis and biofuels are discussed in this chapter. Temperature monitoring , output microwave power control and product enhancement are critical to obtain process efficiency with microwave reactors.

2015 - Microwave-Assisted Preparation of High Entropy Alloys [Articolo su rivista]
Veronesi, Paolo; Rosa, Roberto; Colombini, Elena; Leonelli, Cristina; Veronesi, Paolo
abstract

Microwaves at the ISM (Industrial, Scientific and Medical, reserved internationally) frequency of 2450 or 5800 MHz have been used to prepare FeCoNiCuAl, FeCrNiTiAl and FeCoCrNiAl2.5 high entropy alloys by direct heating of pressed mixtures of metal powders. The aim of this work is to explore a new microwave-assisted near-net-shape technology, using a powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies (defects formation) or solid state ones (time demanding). High entropy alloy compositions have been selected so as to comprise at least one ferromagnetic element and one highly reactive couple, like Ni-Al, Ti-Al, Co-Al or Fe-Al. Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the load. Microwaves have been applied both for the ignition and sustaining of such reactions, showing that by the proposed technique, it is possible to control the cooling rate of the newly-synthesized high entropy alloys. Results showed also that microwave heating in predominant magnetic field regions of the microwave applicator is more effective at controlling the cooling rate. The herein proposed microwave-assisted powder metallurgy approach is suitable to retain the shape of the load imparted during forming by uniaxial pressing. The homogeneity of the prepared high entropy alloys in all cases was good, without the dendritic segregation typical of arc melting, even if some partially-unreacted powders were detected in the samples.

2015 - Microwave-assisted preparation of sodium-silicate solutions from perlite [Articolo su rivista]
Bagramyan, V. V; Sarkisyan, A. A.; Ponzoni, Chiara; Rosa, Roberto; Leonelli, Cristina
abstract

Systematic studies on the preparation of sodium-silicate solutions of different compositions via the hydrothermal-microwave treatment of perlite with an NaOH solution were performed. The effect of various factors on the degree of SiO2 recovery and the reaction rate was studied. The application of microwave energy was established to intensify the process of hydrothermal treatment compared to conventional heating.

2015 - Physical-mechanical properties of new green building materials based on glass waste [Articolo su rivista]
Taurino, Rosa; Andreola, Nora Maria; Leonelli, Cristina; Manfredini, Tiziano; Gastaldi, Paolo; Barbieri, Luisa
abstract

Recently several innovative suggestions on how industrial wastes can be utilised in new products have been presented in literature, e.g. as filler or additives in concrete, incorporated in ceramic materials to produce glass-ceramics and pavement construction. In this work, metallurgical materials from secondary aluminium scrap processing and glass waste derived from treatments of packaging and fluorescent lamps were considered for fabrication of new ceramic materials using powder technology and sintering process. The effect of composition and heat treatment temperature, on the sintering process and then final properties, were evaluated. The results showed that, with the proper firing temperature, lightweight ceramic materials containing high amount of glass waste and an innovative product resulting from the processing of secondary aluminum (ArgAlum) can be produced. The low water absorption (< 1%), low density (< 2 g/cm3) and the good flexural strength (16-20 MPa) associated to relatively low sintering temperatures obtained with the addition of ArgAlum can be considered as promising initial results to obtain new green building materials.

2015 - Recycled natural wastes in metakaolin based porous geopolymers for insulating applications [Articolo su rivista]
Ngouloure, Zénabou N. M.; Nait Ali, Benoît; Zekeng, S.; Kamseu, Elie; Melo, U. C.; Smith, D.; Leonelli, Cristina
abstract

The effectiveness of two amorphous silica based wastes, rice husk ash and volcanic ash powders, used to act as structural reinforcement and partial replacement of metakaolin in porous matrices for thermal isolation was assessed. Both wastes produced colloidal phase that contributed to improve the reactivity and homogeneity of the matrices enhancing the mechanical strength. Rounded pores were obtained in relation with significant reduction of the interpore partitions under controlled addition of the blowing agent. The bulk thermal conductivity decreased from 0.6 to less than 0.15 W m-1 K-1 with the increase of the concentration of blowing agent. The final matrix presented pore size distribution and pore connectivity that allows analytical description and prediction of their effective thermal conductivity.Results demonstrated that clear relations can be established among the viscosity of the pastes, chemical composition, amount of blowing agent and the volume expansion/pore size distribution.

2015 - Recycling of aluminum and titanium chips by microwave augmented SHS [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Colombini, Elena; Lancellotti, Isabella; Giovanardi, Roberto; Leonelli, Cristina; Montecchia, L.; Cavatorta, G.
abstract

Recycling of titanium and aluminium chips to manufacture wear and corrosion-resistant intermetallic-based coatings is achieved by microwave assisted Self Propagating High Temperature Synthesis (SHS). A multi-physics model implementing both reaction kinetic and microwave heating and heat transfer has been developed in order to optimize the synthesis condition. Numerical simulation allowed to investigate the preferable applicator geometry and to quantify the excess heat generated, which could be useful to promote further reactions with an iron-based substrate, thus realizing intermetallic-coated steel-based products.

2015 - Resin-immobilized palladium nanoparticle catalysts for organic reactions in aqueous media: Morphological aspects [Articolo su rivista]
Mastrorilli, Piero; Dell'Anna, Maria M.; Rizzuti, Antonino; Mali, Matilda; Zapparoli, Mauro; Leonelli, Cristina
abstract

An insight into the nano- and micro-structural morphology of a polymer supported Pd catalyst employed in different catalytic reactions under green conditions is reported. The pre-catalyst was obtained by copolymerization of the metal-containing monomer Pd(AAEMA)2 [AAEMA = deprotonated form of 2-(acetoacetoxy) ethyl methacrylate] with ethyl methacrylate as co-monomer, and ethylene glycol dimethacrylate as cross-linker. This material was used in water for the Suzuki-Miyaura cross-coupling of aryl bromides, and for the reduction of nitroarenes and quinolines using NaBH4 or H2, as reductants. TEM analyses showed that in all cases the pristine Pd(II) species were reduced in situ to Pd(0), which formed metal nanoparticles (NPs, the real active species). The dependence of their average size (2-10 nm) and morphology on different parameters (temperature, reducing agent, presence of a phase transfer agent) is discussed. TEM and micro-IR analyses showed that the polymeric support retained its porosity and stability for several catalytic cycles in all reactions and Pd NPs did not aggregate after reuse. The metal nanoparticle distribution throughout the polymer matrix after several recycles provided precious information about the catalytic mechanism, which was truly heterogeneous in the hydrogenation reactions and of the so-called "release and catch" type in the Suzuki coupling.

2015 - Rheology parameters of alkali-activated geopolymeric concrete binders [Capitolo/Saggio]
Leonelli, Cristina; Romagnoli, Marcello
abstract

Industrially . a material has a practical interest if a shape. however complex. can be produced quickly and at low cost. Given the characteristics of the geopolymeric fresh pastes , colloidal dispersions featuring temporary structural stability prior to the polymerization process, some forming methods are eligible as best suitable for this purpose. As already mentioned above, the scientific and technical literature is unfortunately not very rich in examples on this topic in relation to the geopolymeric systems. For such a reason, in this section we briefly describe not only the most commonly used forming methods, but also those of potential applicaiton that have only received a limited and quick reference: casting, extrusion, double-diaphragm forming, compression molding, injection molding, hand lay-up, rotational molding, shaping by 3D printer. In some cases it has been possible to trace only a brief reference about the experimentation without any additional information on the actual efficiency of the forming technique. Nevertheless, the techniques which are presented in the following are all potentially usable dependently on the characteristics of the geopolymer paste before consolidation which have to match the parameters requested by each single forming processes.

2015 - Solution combustion synthesis of La1-xSrxFe1-yCuyO3±w (x=0, 0.2; Y=0, 0.2) perovskite nanoparticles: Conventional vs. microwaves ignition [Articolo su rivista]
Rosa, Roberto; Ponzoni, Chiara; Veronesi, Paolo; Natali Sora, Isabella; Felice, Valeria; Leonelli, Cristina
abstract

La1-xSrxFe1-yCuyO3±w (x=0, 0.2; y=0, 0.2) nanoparticles have been prepared by solution combustion synthesis exploiting both conventional and microwave heating in the ignition of the self-sustaining reactions. Interaction of microwaves with the reaction mixture allowed significant reduction of the ignition time according to the dielectric properties of the precursor gels, which have been measured at room temperature in the 0.5-3 GHz frequency range. Both the ignition strategies led to the preparation of crystalline single-phase products without affecting particles morphology. The ignition technique influenced only the average particles size with those prepared by microwaves-ignition, possessing typically larger dimension, as a probable consequence of the higher temperatures reached due to microwave absorbing products. Perfectly crystallised nanoparticles were obtained after combustion syntheses and calcination at 600 °C for 3 h in the particle size range between 20 and 80 nm dependently upon the heating source and the dopant level.

2015 - Stabilization of bismuth ferrite suspensions in aqueous medium with sodium polyacrylate characterized by different molecular weights [Articolo su rivista]
Ponzoni, Chiara; Cannio, Maria; Rosa, Roberto; Leonelli, Cristina
abstract

Electrostatic stabilization of bismuth ferrite BiFeO3 (BFO) single phase micronized particles suspended for the first time in aqueous medium, using sodium polyacrylate (Na-PAA) as suspending agent, was investigated to form homogeneous films through electrophoretic deposition technique. The dispersion efficiency was evaluated in terms of the zeta potential trend as a function of pH and sediment percentage, employing a fast and easy spectrophotometric method. All the tests were performed using three suspending agents characterized by the same polyacrylate functional group (-COONa) but with different molecular weights (Na-PAA Mw = 2100, 5100, and 20 000). The effect of BFO particles concentration (wt%), suspending agent concentration (wt%), suspending agent molecular weight and sonication time have been evaluated. The results showed that for all the experiments carried out the electrostatic stabilization of the BFO micronized particles in aqueous medium is accomplished in high basic pH range (8.5-9 or 9-11) depending on the molecular weight of the polyacrylate additive.

2015 - Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore evolution, mechanical strength and microstructure [Articolo su rivista]
Kamseu, Elie; Djangang, Chantale; Veronesi, Paolo; Andreola, Nora Maria; Melo, Uphie Chinje; Sglavo, Vincenzo Mario; Leonelli, Cristina
abstract

Two K2O-MgO-Al2O3-SiO2 based geopolymer gels with bulk chemical composition corresponding to cordierite (Co) and 1:1 mullite-cordierite (MuCo) were successfully transformed to crystalline bonds in high temperature service of cold-setting made refractory concretes. Kyanite aggregates changed the flexural strength of the gels from11 to 28 MPa due to the development of good adhesive bonds. Under thermal cycles, up to 1250 °C, the cumulative pore volume remained at 0.09 mL/g, as fromthe absence of important densification/shrinkage. However, the behavior of the cumulative pore volume curves changed from that of a matrix with a wide range of distribution of pore sizes to that, of matrix, consisting of relatively coarse grains. The latter exhibits a rise at 10 μm as void spaces created around the contact points among the coarse kyanite grains and that at 0.054 μm as poreswithin the crystalline phases (cordierite, kalsilite, leucite,mullite, enstatite) formed. Themicrostructural observations confirmed the transformation of gel pores (size around 0.01 μm) to interparticle and intergranular pores due to the crystallization. The flexural strength of refractory concretes increased from28MPa to 40MPa in agreement with the increase in the elastic modulus from 9 to 30 GPa. The crystallization was enhanced by the MgO content (being important in Co compared to MuCo) and the kyanite concentration as particles of kyanite effectively acted as phase separation and nucleation sites

2015 - Ultrafast microwave hydrothermal synthesis and characterization of Bi1-xLaxFeO3 micronized particles [Articolo su rivista]
Ponzoni, Chiara; Cannio, Maria; Boccaccini, D. N.; Bahl, C. R. H.; Agersted, K.; Leonelli, Cristina
abstract

In this work a microwave assisted hydrothermal method is applied to successfully synthesize lanthanum doped bismuth ferrites (BLFO, Bi1-xLaxFeO3 where x = 0, 0.15, 0.30 and 0.45). The growth mechanism of the Bi1-xLaxFeO3 crystallites is discussed in detail. The existence of the single-phase perovskite structure for all the doped samples is confirmed by the X-ray powder diffraction patterns. A peak shift, observed at lower angle with increasing La doping concentration, indicates that the BiFeO3 lattice is doped. The results of TG/DTA show a shift in the transition temperature from 805 °C to 815 °C as function of the La-doping for all the doped powders. At higher levels of La doping, i.e. x = 0.30 and 0.45, significant weight losses occur above 860 °C suggesting a change in the physical and chemical properties. Finally, magnetic measurements are carried out at room temperature for pure BiFeO3 and Bi0.85La0.15FeO3. The results indicate that the materials are both weakly ferromagnetic, with no significant hysteresis in the curves.

2015 - Use of alkali-activated concrete binders for toxic waste immobilization [Capitolo/Saggio]
Lancellotti, Isabella; Barbieri, Luisa; Leonelli, Cristina
abstract

The increasingly urgent need for the use of industrial inorganic waste as raw material for new materials poses geopolymers as an alternative to the traditional Portland cement /concrete. These alkali activated materials can, in fact, be considered a resource in a sustainable waste management as it is possible to formulate them starting from waste, mostly aluminosilicates, not dangerous. Nevertheless it is also possible to design and use alumina and silica bearing wastes as matrices for inertization of hazardous compounds which might be contained in the waste itself or that can be added on with the purpose to reach solidification/stabilization. In this sense we can define the geopolymerization of waste materials the technique that combines the alkaline activation of the aluminosilicatic and/or phosphatic component to act as matrix and the dissolution/activation/hydrolization of the surface of the particles of waste. The surface reactivity is in fact responsible for the bond that is formed between the waste particles and the aluminosilicatic matrix immobilizing the heavy metal ions. The nature of the waste, in terms of mineralogy, alumina and silica contents, particle size, surface area and morphology, significantly affect the reactivity of the waste itself. Single heavy metals cations as well as more complex hazardous wastes of industrial or urban origin have been successfully treated with the geopolymeration technique over the past few years.

2015 - Valorization of inorganic waste, end of waste and by-product for ceramics [Capitolo/Saggio]
Barbieri, Luisa; Andreola, Nora Maria; Taurino, Rosa; Lancellotti, Isabella; Leonelli, Cristina
abstract

Recycling and re-use of waste are economically attractive options for public and private actors due to widespread separate collection and the development of functional markets for secondary raw materials. The ceramic sector is particularly sensitive to this setting through re-entry into the production cycle of all by-products and partially amounts of residues derived from depuration treatment process. Besides, thanks to academic and industrial research results, there is the tendency to see different inorganic wastes, “end of wastes” and by-products as new good candidates. In the present work, two case studies, one describing ceramics with high amount of glass waste and one ceramics with different kind of wastes, end-of-wastes and by-products, are reported with a commented list of technological and environmental benefits.

2015 - Wastes materials in geopolymers [Relazione in Atti di Convegno]
Lancellotti, I.; Ponzoni, C.; Barbieri, L.; Leonelli, C.
abstract

A promising process, often indicated as geopolymerization, describes the formation of an aluminosilicate amorphous matrix where Ca is absent or contained in low amount. Geopolymers are obtained from an aluminosilicate powder activated by alkaline solutions and the synthesis process involves three separate stages: dissolution, condensation and polymerization. Sodium silicate is used for the activation of many kinds of aluminosilicate precursors and hazardous wastes. In the present work, three case studies of solid and liquid, hazardous and non-hazardous wastes added in geopolymers will be presented. The results show the versatility of this technique and the possibility to obtain geopolymers from aluminosilicate-based waste and to immobilize their hazardous ions.

2014 - A sustainable approach for the geopolymerization of natural iron-rich aluminosilicate materials [Articolo su rivista]
Obonyo, Esther A.; Kamseu, Elie; Lemougna, Patrick N.; Tchamba, Arlin B.; Melo, Uphie C.; Leonelli, Cristina
abstract

Two iron-rich clayey materials (L1 and L2, with the main difference being the level of iron accumulation) have been studied for their suitability as solid precursors for inorganic polymer composites. L1, with the lower iron content, was calcined at 700°C for 4 h and used as replacement, in the range of 15-35 wt%, for both raw laterites in the formulations of geopolymeric composites. The different mixtures were activated with a highly concentrated alkaline solution containing sodium hydroxide and sodium silicate. River sand with semi-crystalline structure was added to form semi-dry pastes which were pressed to appropriate shape. X-ray diffraction, Infrared spectroscopy, Scanning Electron Microscopy and Mercury Intrusion Porosimetry results demonstrated the effectiveness of the calcined fraction of L1 to act as nucleation sites and extend the geopolymerization to the matrix composites. A highly compact matrix with low porosity and good stability in water, together with a strength comparable to that of standard concretes was obtained allowing for conclusions to be made on the quality of laterites as promising solid precursor for sustainable, environmentally-friendly, and cost-efficient structural materials. © 2014 by the authors.

2014 - Binder chemistry – Low-calcium alkali-activated materials [Capitolo/Saggio]
Provis, John L.; Fernández Jiménez, Ana; Kamseu, Elie; Leonelli, Cristina; Palomo, Angel
abstract

Early developments in the developments of low-calcium (including calcium-free) alkali-activated binders were led by the work of Davidovits in France, as noted in Chap. 2. These materials were initially envisaged as a fire-resistant replacement for organic polymeric materials, with identification of potential applications as a possible binder for concrete production following relatively soon afterwards [1]. However, developments in the area of concrete production soon led back to more calcium-rich systems, including the hybrid Pyrament binders, leaving work based on the use of low-calcium systems predominantly aimed at high-temperature applications and other scenarios where the ceramic-like nature of clay-derived alkali-activated pastes was beneficial. Early work in this area was conducted with an almost solely commercial focus, meaning that little scientific information was made available with the exception of a conference proceedings volume [2], several scattered publications in other conferences, and an initial journal publication [3]. Academic research into the alkaline activation of metakaolin to form a binder material led to initial publications in the early 1990s [4, 5], and the first description of the formation of a strong and durable binder by alkaline activation of fly ash was published by Wastiels et al. [6-8]. With ongoing developments in fly ash activation, which offers more favourable rheology than is observed in clay-based binders, interest in low-calcium AAM concrete production was reignited, and work since that time in industry and academia has led to the development of a number of different approaches to this problem. A review of the binder chemistry of low-calcium AAM binder systems published in 2007 [9] has since received more than 350 citations in the scientific literature, indicating the high current level of interest in understanding and utilisation of these types of gels.

2014 - Calibration and use of the heating microscope for indirect evaluation of the viscosity and meltability of archeological glasses [Articolo su rivista]
Montanari, F.; Miselli, P.; Leonelli, C.; Boschetti, C.; Henderson, J.; Baraldi, P.
abstract

The heating microscope is a widely used instrument in many industrial applications, especially in the ceramic field, to obtain information on the sintering behavior and, indirectly, on the viscosity curve of glass. It is therefore important for the study of glass technology. Usually, heating microscopes work by taking images of the sample outline, during a preset thermal cycle, which define five characteristic temperatures corresponding to particular shapes of the specimen. The first two characteristic temperatures can also be extracted from the sintering curves provided by the instrument. In agreement with three published models, the five temperatures are associated with five viscosity values, producing the two best-fitting plots (Log10(η) - T). In this work, the heating microscope was calibrated using a glass with known properties, to determine the most reliable model, so that it can be applied successfully in the field of archeological science. The selected methodologies were used to analyze two opacified Roman mosaic glass tesserae excavated in Pompeii, previously characterized chemically. A Pompeiian transparent glass, sampled from a large block of base (raw) glass, and its experimental reproduction were also studied. Finally, the relationship between the opacifiers and the thermal behavior of base glass was investigated. © 2013 The American Ceramic Society and Wiley Periodicals, Inc.

2014 - Crystallization of some modified fluor-miserite Kx(Ca,Ce)5xSi8O22F2 glasses [Articolo su rivista]
Hamzawya, Esmat; Ferrari, Anna Maria; Leonelli, Cristina
abstract

Fluorine-rich miserite glass compositions with variable K2O to CaO ratios, Kx(Ca5.5x,Ce0.5)Si8O21.5F3 where x ¼ 1, 2 or 3, have been investigated in term of crystallization path and Ce3þ substitution. For sake of comparison a second series without ceria was also prepared: KxCa6.5xSi8O21.5F3. Xonotlite, tokkoite, fluorite and cristobalite were developed in all crystallized glasses; however, miserite was only identified in Ce-containing samples. Increase of K2O/CaO ratio, in Ce-free sample, enhanced the formation of tokkoite, and reduced the contents of xonotlite and fluorite. On the other hand, in Ce-containing samples, an increase of K2O/CaO ratio promotes the formation of miserite crystals. Quantitative Rietveld analyses assessed the presence of Ce3þ cations in miserite structure. The microstructure of Ce-free glasseceramics was relatively coarse in the form of interlocked flakes and rods; however, it became unpronounced in the sample of highest K2O/CaO ratio. In Ce-containing glass-ceramics, irregular nanosized grains were spread in cryptocrystalline groundmass, whose fineness increased with increasing K2O/CaO ratio. The CTE values of the parent glasses and their glasseceramics varied from 10.31 to 11.05 and from 7.52 to 9.84 106 C1 respectively with lower values for Ce-free glass-ceramics. Density and micro hardness values were also measured.

2014 - Development of Thai fly ash blended with rice husk ash geopolymers [Relazione in Atti di Convegno]
Chaysuwan, D.; Tippayasam, C.; Keawpapasson, P.; Thavorniti, P.; Panyathanmaporn, T.; Jiemsirilers, S.; Leonelli, C.
abstract

Fly ash (FA) presented in the research is one of the by-products from combustion processes of lignite in electricity plants in Thailand. Generally, FA is exploited to mix with Portland cement to improve the mechanical properties of cement paste or mortar. In addition, FA is also claimed as an active pozzolanic material to synthesize geopolymers. The rice husk is used as fuel in rice mills and converted to ash called rice husk ash (RHA). The RHA in the research contains approximately 85%-90% amorphous silica. RHA was chosen to blend with FA producing geopolymers to retard hardening time and develop good results of compressive strength of geopolymers. The mixed proportion of FA to RHA was prepared by variation as five ratios of 0:100, 20:80, 50:50, 80:20 and 100:0 by weight. Sodium hydroxide of 8 Molar (8M NaOH) and sodium silicate (Na2SiO3) solution was used as alkali activators by mass ratio of Na2SiO3: NaOH at 3:2. The suitable Si/Al molar ratio, the Na/Al molar ratio, pH and conductivity of experiment were studied and characterized. Finally, the specimens were investigated for compressive strength at 7, 14, 21 and 28 day ages and flexural strength and microstructures at 7 days of age.

2014 - Direct energy supply to the reaction mixture during microwave-assisted hydrothermal and combustion synthesis of inorganic materials [Articolo su rivista]
Rosa, R.; Ponzoni, C.; Leonelli, C.
abstract

The use of microwaves to perform inorganic synthesis allows the direct transfer of electromagnetic energy inside the reaction mixture, independently of the temperature manifested therein. The conversion of microwave (MW) radiation into heat is useful in overcoming the activation energy barriers associated with chemical transformations, but the use of microwaves can be further extended to higher temperatures, thus creating unusual high-energy environments. In devising synthetic methodologies to engineered nanomaterials, hydrothermal synthesis and solution combustion synthesis can be used as reference systems to illustrate effects related to microwave irradiation. In the first case, energy is transferred to the entire reaction volume, causing a homogeneous temperature rise within a closed vessel in a few minutes, hence assuring uniform crystal growth at the nanometer scale. In the second case, strong exothermic combustion syntheses can benefit from the application of microwaves to convey energy to the reaction not only during the ignition step, but also while it is occurring and even after its completion. In both approaches, however, the direct interaction of microwaves with the reaction mixture can lead to practically gradient-less heating profiles, on the basis of which the main observed characteristics and properties of the aforementioned reactions and products can be explained.

2014 - Dispersing hydrophilic nanoparticles in hydrophobic polymers: HDPE/ZnO nanocomposites by a novel template-based approach [Articolo su rivista]
de Luna, M. Salzano; Galizia, M.; Wojnarowicz, J.; Rosa, Roberto; Lojkowski, W.; Leonelli, Cristina; Acierno, D.; Filippone, G.
abstract

The efficiency of a novel template-based approach for the dispersion of hydrophilic nanoparticles within hydrophobic polymer matrices is investigated. The procedure envisages the permeation of a well dispersed nanoparticle suspension inside a micro-porous matrix, obtained through selective extraction of a sacrificial phase from a finely interpenetrated co-continuous polymer blend. Specifically, a blend of high density polyethylene (HDPE) and polyethylene oxide (PEO) at 50/50 wt% is prepared by melt mixing. The addition of small amounts of organo-clay promotes the necessary refinement of the blend morphology. Once removed the PEO, the micro-porous HDPE matrix is dipped in a colloidal suspension of zinc oxide nanoparticles which exhibits low interfacial tension with HDPE. A system prepared by traditional melt mixing is used as reference. Melt- and solid-state viscoelastic measurements reveal a good quality of the filler dispersion despite the uneven distribution on micro-scale. The latter can be capitalized to minimize the filler content to attain a certain improvement of the material properties or to design nano-structured polymer composites. © BME-PT.

2014 - Effect of Thai Kaolin on properties of agricultural ash blended geopolymers [Articolo su rivista]
Tippayasam, Chayanee; Keawpapasson, Pimpawee; Thavorniti, Parjaree; Panyathanmaporn, Thammarat; Leonelli, Cristina; Chaysuwan, Duangrudee
abstract

Geopolymer has been developed as an alternative material to Portland cement. It is based on the polymerization of alkali activators and oxides of silicon and aluminium from pozzolans. Pozzolans are materials mainly SiO 2 and/or Al2O3 which reacts with NaOH and Na2SiO3 to generate a three dimentional aluminosilicate structure. The clean and fine kaolin from south of Thailand transforms into metakaolin at 550-600 C, as determined by DTA. In this research, kaolin was heated at 600 C, 700 C and 800 C for 2 and 6 h to optimize its transformation into metakaolin as pozzolans for geopolymers preparation. Additionally, the as-received kaolin was exploited also as a pozzolan for geopolymers in order to reduce heat energy consumption. However, it was found that kaolin alone did not display sufficient pozzolanic behavior to form geopolymer at 7 days of age unless specimens were slightly warm cured. Therefore, it was blended with more active pozzolans such as bagasse ash and rice husk ash. Finally, the results of compressive strength and microstructures were investigated and discussed. © 2013 Published by Elsevier Ltd.

2014 - Glass-ceramic foams from borosilicate glass waste [Articolo su rivista]
Taurino, Rosa; Lancellotti, Isabella; Barbieri, Luisa; Leonelli, Cristina
abstract

In this study, we reported the studies on a glass-ceramic foam with wollastonite and cristobalite micrometric crystals prepared by sintering a borosilicate glass waste with organic binder as foaming agent. The waste glass, coming from the dismantling of washing machine, was characterized by high CaO content and low-temperature sinterability. The effect of the temperature on the sinter-crystallization ability of the borosilicate glass waste was followed with thermal analysis, heating microscopy, and electron scanning microscopy (ESEM) observations. Additionally, the effect of temperature on the evolution of crystalline phases and density variation was monitored with XRD and density measurements. The softening started at 800°C and crystallization at 845°C to be completed at 900°C with a linear expansion of 38-40% in the range 850-900°C. Wollastonite and cristobalite were identified as crystalline phases in variable proportions dependently upon temperature. No crack evidence was found at high ESEM magnification even though cristobalite crystals were present. The final products showed a total porosity around 78-79% and an apparent density of about 0.5 g/cm3, in line with common porous closed-cell glass foams used for thermal insulation. © 2014 The American Ceramic Society and Wiley Periodicals, Inc.

2014 - High-energy-low-temperature technologies for the synthesis of nanoparticles: Microwaves and high pressure [Articolo su rivista]
Lojkowski, W.; Leonelli, C.; Chudoba, T.; Wojnarowicz, J.; Majcher, A.; Mazurkiewicz, A.
abstract

Microwave Solvothermal Synthesis (MSS) is a chemical technology, where apart from possible effects of microwaves on the chemical reaction paths, microwave heating allows the precise planning of a time-temperature schedule, as well as to achieve high super-saturation of the reagents uniformly in the reactor vessel. Thus, MSS is suitable for production of nanoparticles with small grain size distribution and a high degree of crystallinity. A further advantage of the technology is a much lower synthesis temperature than for gas phase, plasma or sol-gel technologies. New reactors have been developed to exploit these advantages of the MSS technology of nanoparticles synthesis and to scale up the production rate. Reactor design and realization has been shown to be decisive and critical for the control of the MSS technology. Examples of oxidic and phosphatic nanoparticles synthesis have been reported.

2014 - Incinerator Bottom Ash and Ladle Slag for Geopolymers Preparation [Articolo su rivista]
Lancellotti, Isabella; Ponzoni, Chiara; Maria Chiara, Bignozzi; Barbieri, Luisa; Leonelli, Cristina
abstract

Ladle slag (LS) and urban incineration bottom ash (BA) are two types of non hazardous inorganic wastes which do not contain significant amounts of pollutants such as heavy metals and organics. Nowadays they are necessarily disposed of with little attention placed for re-use or recycling. Considering their chemical composition, rich in silica and alumina with substantial levels of lime and iron oxides, these residues can be suitable for generating new alkali activated materials. A safe reuse of these residues in high percentages (60–70 wt%) is presented in this study for mortar production. The final room-temperature consolidated materials, also known as geopolymers, have been characterized in terms of thermogravimetric analysis, morphology, porosity, and crystalline phases evolution. When incinerator BA is used, the morphology of the resulting geopolymer is very close to that of pure metakaolinic pastes, whereas for LS based geopolymers calcium presence promotes the formation of calcium–aluminate–silicate–hydrate phase. This investigation also demonstrated that the content of reactive fraction of BA is of primary importance to assess its possible use in alkaline activation process.

2014 - Mechanical and dynamic-mechanical behavior and morphology of polystyrene/perovskite composites: Effects of filler size [Articolo su rivista]
Russo, Pietro; Acierno, Domenico; Rosa, Roberto; Leonelli, Cristina; Corradi, Anna; Rizzuti, Antonino
abstract

Composites based on a commercial grade polystyrene (PS) resin containing non commercial perovskite particles were prepared by melt mixing and analyzed in terms of mechanical properties, dynamic-mechanical behavior and morphology. In particular, with the aim to study the influence of the filler size on the ultimate properties of PS based composites micro- and nano-sized perovskite La0.5Sr0.5MnO3 crystal particles, synthesized by using an efficient and rapid microwave-assisted hydrothermal route, were considered.Measurements of flexural parameters such as modulus and strength by static tests and storage modulus and damping factor by dynamic-mechanical evaluations showed better performance for nanofilled systems with respect to the ones containing micro particles, with the same filler content.Mechanical evidences were explained also by morphological observations from which a different level of filler dispersion seems to be obtained with the organization of perovskite nanosized crystals in superstructures able to support viscoelastic results. © 2012 Elsevier B.V.

2014 - Metakaolin-based inorganic polymer composite: Effects of fine aggregate composition and structure on porosity evolution, microstructure and mechanical properties [Articolo su rivista]
Kamseu, E.; Cannio, M.; Obonyo, E. A.; Tobias, F.; Bignozzi, M. C.; Sglavo, V. M.; Leonelli, C.
abstract

2014 - Metakaolin-based porous geopolymer with aluminium powder [Relazione in Atti di Convegno]
Keawpapasson, P.; Tippayasam, C.; Ruangjan, S.; Thavorniti, P.; Panyathanmaporn, T.; Fontaine, A.; Leonelli, C.; Chaysuwan, D.
abstract

Porous concretes such as aerated and lightweight concretes are commonly used in construction fields. Lightweight construction materials are used to reduce either the weight or the budget of building structures. Aluminium (Al) powder was utilized to create bubbles in porous structure and giving information for porous geopolymer production. It was introduced by adding 0.05-1% Al-powder as the initiated materials of geopolymers to react with water in those materials and promote hydrogen gas inside specimens. The research, therefore, focused on the synthesis of porous geopolymer by metakaolin as a pozzolan and mixed with alkali solution consisting of 8M NaOH and Na2SiO 3 as well as Al-powder as a foaming agent. The highly porous geopolymers were produced with various Al-powders as 0%, 0.2%, 0.4%, 0.6% 0.8% and 1% by weight. After 7, 14 and 28 days age, the specimens were tested the mechanical properties, such as compressive strength. The water absorption, apparent porosity and bulk density were analyzed at 28 days age. The synthesis of metakaolin-based porous geopolymers with Al-powder presented good results. It showed that Al-powder content affected to degree of porosity of geopolymers and 0.2% Al-powder was the optimal Al-powder content for the porous geopolymer. © (2014) Trans Tech Publications, Switzerland.

2014 - Polymer supported palladium nanocrystals as efficient and recyclable catalyst for the reduction of nitroarenes to anilines under mild conditions in water [Articolo su rivista]
Dell'Anna, Maria Michela; Intini, Simona; Romanazzi, Giuseppe; Rizzuti, Antonino; Leonelli, Cristina; Piccinni, Ferruccio; Mastrorilli, Piero
abstract

Polymer supported palladium nanoparticles, generated in situ by Pd(II) reduction under reaction conditions, catalyzed the hydrogenation of nitroarenes to anilines with high efficiency in water at room temperature in the presence of NaBH4. The protocol proved to be highly selective and generally favored the formation of the desired aniline as single product in high yields with short reaction times. TEM analyses revealed that the size distribution of the formed Pd nanocrystals was regulated by the reductant agent. In details, when 1 atm H2 was used as the nitroarene reductant, the in situ generated polymer supported palladium nanoparticles were crystallites with diameters ranging from 6 to 10 nm. On the contrary, when the reaction was carried out in the presence of NaBH4 in water under N2 or air, the formation of Pd nanocrystallites was observed as well, but this time they were smaller (mean size diameter ca. 3 nm) and catalytically more active compared to the palladium nanoparticles formed under 1 atm H2 in the absence of NaBH4. The catalyst displayed excellent recyclability over twelve cycles and no leaching of metal into solution occurred, which made the overall system eco-friendly and economic.

2014 - Reaction sintering and microstructural evolution in metakaolin-metastable alumina composites [Articolo su rivista]
Djangang, Chantale Njiomou; Tchamba, Arlin Bruno; Kamseu, Elie; Melo, Uphie Chinje; Elimbi, Antoine; Ferrari, Anna Maria; Leonelli, Cristina
abstract

Fine needles of mullite grains were obtained successfully in a compact and low porous matrix using solid state sintering. We treated high-grade kaolin and sand-rich kaolin at 750 °C to amorphous metakaolins, and bauxite at 1,000 °C to metastable alumina. By designing a stochiometric composition of mullite, each amorphous metakaolin was added to metastable alumina. Fine grains of mullite with almost complete crystallization were obtained from 1,350 °C in a case of amorphous metakaolin from high-grade kaolin and at 1,550 °C in the other case where amorphous metakaolin is from sand-rich kaolin. The difference in the temperatures of mullitization was linked to the late dissolution of silica from the cristobalite and quartz phases which were still present in the sand-rich metakaolin sample at 1,350 °C. The use of metastable alumina and metakaolin instead of kaolin to design the mullite matrix allows the increase in number of mullite nucleation sites. This results to high densification and crystallization, fine grain size, and high mechanical properties of the final matrix. © 2014 Akadémiai Kiadó, Budapest, Hungary.

2014 - Valutazione ambientale della sintesi della curcumina tramite parametri quantitativi di green metrics [Abstract in Atti di Convegno]
Zerazion, Elisabetta; Rosa, Roberto; Ferrari, Erika; Leonelli, Cristina; Corradi, Anna; Ferrari, Anna Maria
abstract

La curcumina [(1E,6E)-1,7-Bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] è un composto fenolico presente nei rizomi della pianta Curcuma longa L. Essa, così come numerosi suoi derivati, possiede interessanti proprietà antiossidanti, antiinfiammatorie e antitumorali [1]. Per questo motivo la sintesi chimica dei diversi curcuminoidi risulta fondamentale allo scopo di realizzare un accurato studio di tutte le possibili relazioni esistenti tra struttura e proprietà. Lo scopo di questo lavoro è quello di presentare una dettagliata valutazione ambientale del processo sintetico della curcumina così come messo a punto da alcuni degli autori [2]. Infatti, ultimamente accanto ai tradizionali parametri che accompagnano una sintesi chimica (come resa, tempo di reazione, etc.) sta acquisendo sempre maggiore importanza l’utilizzo dei cosiddetti parametri di green metrics, allo scopo di promuovere uno sviluppo sempre più sostenibile, permettendo al chimico organico di scegliere la strategia sintetica meno impattante sull’ambiente e sulla salute umana [3,4]. L’approccio seguito ha previsto l’utilizzo del software EATOS (Environmental Assessment Tool for Organic Synthesis [5,6]) e di uno studio tramite metodologia LCA (Life Cycle Assessment) [7]. Al contrario del software EATOS (che è limitato alla sola valutazione delle sostanze chimiche coinvolte nella sintesi e nel work-up) l’analisi LCA permette di prendere in considerazione numerose altre categorie potenzialmente impattanti quali i consumi energetici, quelli dovuti al trasporto delle materie prime, agli imballaggi delle sostanze utilizzate, e molti altri, permettendo di realizzare una valutazione dell’intero ciclo di vita del processo “dalla culla alla tomba”. I risultati ottenuti permetteranno anche un successivo paragone con il processo estrattivo, così come con le sintesi e le estrazioni che prevedano l’utilizzo di tecniche non convenzionali, come ad esempio il riscaldamento dielettrico a microonde.

2013 - A review on combustion synthesis intensification by means of microwave energy [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina
abstract

Combustion synthesis (CS) is a materials manufacturing technique, which gained increased attention by both academia and industries, due to its intrinsic energy saving characteristics and high purity of the products. Energy requirements for CS are limited to the ignition step, since the desired products are obtained by using the heat generated by exothermic reactions occurring between the reactants.CS has been here addressed from a process intensification perspective, since CS characteristics perfectly fit into several process intensification definitions, aims and approaches.Particular attention has been dedicated to the use of microwaves as energy source for CS, and the benefits deriving from the combination of these two techniques have been reviewed. The doubtless better energy transfer efficiency of microwaves, with respect to conventional heating techniques, arising from the direct interaction of the electromagnetic energy with the reactants, contributes to further intensify both solid state and solution CS processes.Moreover, microwaves peculiarities, such as their selective and volumetric nature, together with their energy transfer nature, open new attractive opportunities for CS in different fields of materials science, like joining and advanced protective coatings. Innovative strategies of microwaves-ignited and/or sustained CS for the process intensification of advanced materials manufacturing are proposed as well.

2013 - Alkali activation processes for incinerator residues management [Articolo su rivista]
Lancellotti, Isabella; Ponzoni, Chiara; Barbieri, Luisa; Leonelli, Cristina
abstract

Incinerator bottom ash (BA) is produced in large amount worldwide and in Italy, where 5.1 millions tons of municipal solid residues have been incinerated in 2010, corresponding to 1.2–1.5 millions tons of produced bottom ash. This residue has been used in the present study for producing dense geopolymers containing high percentage (50–70 wt%) of ash. The amount of potentially reactive aluminosilicate fraction in the ash has been determined by means of test in NaOH. The final properties of geopolymers prepared with or without taking into account this reactive fraction have been compared. The results showed that due to the presence of both amorphous and crystalline fractions with a different degree of reactivity, the incinerator BA geopolymers exhibit significant differences in terms of Si/Al ratio and microstructure when reactive fraction is considered.

2013 - Application of heating microscopy on sintering and melting behaviour of natural sands of archaeological interest [Articolo su rivista]
Montanari, F.; Boschetti, C.; Miselli, P.; Hanuskova, M.; Baraldi, P.; Leonelli, C.
abstract

In antiquity, beach sand was one of the main raw materials for glass-making and for the production of other vitreous materials, like Egyptian blue and faience. During the 1st century AD, glass and pigments manufacturing industry was active along the Gulf of Naples, Italy, where we sampled four littoral sands. Samples were analyzed with different techniques: chemical analysis was performed by means of X-Ray Fluorescence (XRF) and mineralogical analyses with X-Ray Powder Diffraction (XRPD) and Raman Spectroscopy. The complete sintering to melting thermal behaviour of the four sands was studied by heating microscopy or hot-stage microscope (HSM) equipped with an high resolution camera capable to collect sample profile during heating. The effect of the grain size on the sintering curves, which were automatically elaborated by specimen profile transformation, was also investigated. Finally, some deductions about the granulometry effect and the presence of alkaline and alkaline-earth oxides on sintering and melting behaviour were drawn. All the four sands were found suitable for highly sintered manufacts rather than glasses, to reach complete amorphous materials the addition of fluxes was necessary.

2013 - Crystal formation in modified fluor-miserite Kx(Ca, Ce)5-xSi8O22F2 glasses [Abstract in Atti di Convegno]
Hamzawy, Ezmat; Ferrari, Anna Maria; Leonelli, Cristina
abstract

Different ratios of K2O/CaO were investigated in a Kx(Ca,Ce)5-xSi8O22F2 fluor-miserite glass composition to find their effect on crystallization process. Xonotlite, tokkoite, fluorite and cristobalite were developed in all crystallized glasses; however, miserite was only identified in Ce-containing samples. Increase of K2O/CaO ratio, in Ce-free sample, enhanced the formation of tokkoite K2Ca4Si7O17(OH,F)2, and reduced the contents of xonotlite Ca6Si6O17(OH,F)2 and fluorite CaF2. Rietveld evaluation on XRD spectra allowed the quantification of phase percentages. On the other hand, in Ce-containing samples, an increase of K2O/CaO ratio promotes the formation of miserite crystallized with or without cerium in the structure. The cerium containing miserite lattice parameter were also evaluated. The microstructure of Ce-free glass–ceramics was relatively coarse and characterized by presence interlocked flakes, rods; however, it became unpronounced in the sample of highest K2O/CaO ratio. In Ce-containing glass-ceramics, irregular fine growths were spread as nano–size in cryptocrystalline groundmass, such fineness increase with increasing K2O/CaO ratio. The CTE values of the present glasses and the corresponding glass-ceramics varied from 10.305 to 11.053 and from 7.524 to 9.840 x 10-6 °C-1 respectively. The CTE of Ce-free glass-ceramics was lower than Ce-containing ones. Densities of the glass-ceramic samples varied from 2.652 to 2.856 g/cm3 and the samples containing miserite show larger densities.

2013 - Effect of low-temperature high-pressure sintering on BiFeO3 density, electrical magnetic and structural properties [Articolo su rivista]
Ponzoni, C.; Cannio, M.; Rosa, R.; Chudoba, T.; Pietrzykowka, E.; Buscaglia, V.; Finocchio, E.; Nanni, P.; Lojkowski, W.; Leonelli, C.
abstract

Single-phase multiferroic BiFeO3 (BFO) powders were prepared by hydrothermal microwave synthesis and dense BiFeO3 ceramics were fabricated for the first time by the low-temperature high-pressure (LTHP) sintering technique. Effect of sintering temperature ranging from 400 to 800 °C (3 min and 10 min) and pressure of 3-8 GPa on structural, microstructural, electric and magnetic properties were investigated through X-ray diffraction, scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), density and magnetic measurements. The results highlighted that LTHP sintering method, thanks to the high pressure involved, requires lower temperature and shorter time than other techniques, avoiding BiFeO3 phase degradation. SEM images show that for short experimental time (t = 3 min) the average grain size of the sintered samples was approximately the same size of raw powder. Extending the sintering time up to 10 min the grain growth phenomena occurred. Moreover the results indicate that the best obtained density value was around 98% of theoretical density. The dielectric behavior of BiFeO3 ceramics was not significantly influenced by the LTHP sintering conditions. Magnetic measurements showed that ceramic BiFeO 3 is weakly ferromagnetic at room temperature. © 2013 Taylor &amp; Francis.

2013 - Electrophoretic deposition of multiferroic BiFeO3 sub-micrometric particles from stabilized suspensions [Articolo su rivista]
Ponzoni, Chiara; Rosa, Roberto; Cannio, Maria; Buscaglia, Vincenzo; Finocchio, Elisabetta; Nanni, Paolo; Leonelli, Cristina
abstract

The electrophoretic deposition (EPD) was applied to BiFeO3 (BFO) powders, one of the most interesting multiferroic compounds characterized by simultaneous magnetic and ferroelectric activity, to form homogeneous films. The preparation and characterization of stable BFO colloidal suspensions in aqueous, organic and mixed solvents were investigated by zeta potential measurements at room temperature in the presence of surfactants. BFO thin films were then deposited on steel substrates from stabilized BFO suspensions, by adjusting the preparative parameters to optimize the film quality. The compositional, morphological and electrical characteristics of the obtained BFO films, together with thickness measurements, were studied using SEM, XRD, AFM, EIS and optical surface profilometer. EPD method applied to BFO stable suspensions produced homogeneous thickness BFO films, free from pinholes and cracks, that were successively sintered and characterized also in terms of photocatalytic response.

2013 - Field-related effects in the microwave ignited synthesis of aluminides [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Leonelli, Cristina
abstract

Microwave ignited combustion synthesis can be used to achieve complete conversion of reactants and to obtain products with unique microstructures. However, this synthetic route suffers from usually poor reproducibility due to the possible electromagnetic field distribution-related ignition mechanisms. Ignition can occur by the direct heating of the reactants, or by their indirect heating by the use of microwave co-absorbers or due to the possible occurrence of breakdown phenomena. In this work, the effects of microwave ignition in regions of predominant electric or magnetic field is investigated in case of mixtures of powdered metal reactants, one of which is aluminium and the remaining is of ferromagnetic nature. These reactions, when a high heating rate is applied, are usually preceded by the formation of liquid aluminium, which then reacts with the other elements to form the intermetallics. The aim of the work is to improve the process reproducibility and to propose new strategies to optimise the synthesis of high purity aluminide intermetallics. Significant differences between ignition in predominant E or H field were experimentally observed, suggesting that the electromagnetic field-related effects could be proficiently exploited to control the kinetic and the microstructure of the final products.

2013 - Geopolymers: A new and smart way for a sustainable development [Articolo su rivista]
Benito, P.; Leonelli, C.; Medri, V.; Vaccari, A.
abstract

2013 - INERTIZATION OF CHROMIUM LIQUID WASTE IN INORGANIC POLYMERS VIA ALKALI ACTIVATION OF METAKAOLIN [Articolo su rivista]
LANCELLOTTI, Isabella; PONZONI, Chiara; BARBIERI, Luisa; LEONELLI, Cristina
abstract

In the present work, a hazardous waste deriving from the colouring process of ceramic tiles surfaces was immobilized in geopolymeric inorganic matrix. This waste is in liquid homogeneous form composed prevalently of aqueous solutions of metals compounds which develop colours during the firing cycle. The colorant solution contains Fe, Mo, Mn, Co, Cr, depending on the final colour, together with mineralisers and complexes. One of the innovative aspects of this research is the exploitation of water content of the waste and the absence of the drying step, the latter being a common step in the management of liquid hazardous wastes.

2013 - Induration of laterites in tropical areas: Assessment for potential structural applications [Articolo su rivista]
Kamseu, E.; Nzeukou, A.; Lemougna, P.; Billong, N.; Melo, U. C.; Leonelli, C.
abstract

Indurated lateritic blocks (yellow-brown and red) were collected from two deposits in Yaounde, Cameroon for investigation as structural building and construction materials. Dimensioned blocks were characterized using XRD, DTA/TGA, mechanical compression, water absorption and porosity tests, and examination by optical and electron microscope. Water absorption values, pore size distribution and cumulative pore volume were used to compare indurated laterites with fired day-based bricks. Atmospheric exposure of the test specimens resulted in progressive strengthening of the matrix and transformation of yellow areas to a browner colour. This confirms other observations in the literature which describe induration as the transformation of goethite to hematite with red matrix as the end step and most stable laterite form. Presence of larger size pores and significant pore-to-surface area ratio negatively affect the material's compressive strength. However, due to stability in water, blocks with significant phase distribution and amorphous interlinking are suitable as structural building and construction materials.

2013 - Influence of the drying treatment on the performance of V-Nb mixed oxides catalysts synthesised via sol-gel [Articolo su rivista]
Catauro, M.; Bollino, F.; Papale, F.; Leonelli, C.
abstract

Mixed oxides NbVO5 amorphous catalysts have been synthesised by means of the sol-gel technique using different vanadium oxide to water ratios and gel drying treatments: in particular air-drying at room temperature and microwave heating have been adopted. Successively, the dried materials were calcinated up to 550 C in flowing air. Brunauer-Emmett-Teller (BET) surface area analysis showed that this parameter depends on drying method and on the thermal treatment. Differential thermal analysis (DTA) proved that the crystallisation process of the NbVO5 powders occurred at lower temperature when microwave drying was used. An increase of crystallinity was also recorded by X-ray diffraction (XRD) analysis for samples prepared using a high V/H 2O ratio and dried by microwave heating. These samples also show high reducibility and surface acidity, as demonstrated by temperature programmed reduction (TPR) and temperature programmed desorption (TPD) techniques respectively. An improvement of the catalytic performances for the gel dried by microwave heating in the oxidative dehydrogenation of ethane at 550 C has been observed. © 2013 Elsevier Ltd. All rights reserved.

2013 - Inorganic polymers from alkali activation of metakaolin: Effect of setting and curing on structure [Articolo su rivista]
Lancellotti, Isabella; Michelina, Catauro; Ponzoni, Chiara; Flavia, Bollino; Leonelli, Cristina
abstract

Geopolymers, obtained by chemical reaction between aluminosilicate oxides and silicates under highly alkaline conditions, are studied in this paper. The proposed mechanism of geopolymer setting and hardening or curing consists of a dissolution, a transportation or an orientation, as well as a polycondensation step. The aim of this paper is to investigate the influence of the curing time and temperature, the relative humidity and the reagents temperature on the geopolymerization process in order to obtain a resistant matrix usable for inertization of hazardous wastes. The evolution of the process from the precursors dissolution to final geopolymer matrix hardening has been followed by FTIR spectroscopy, X-ray diffractometry, SEM/EDS and leaching tests. The results show the significant influence of both curing temperature in the curing stage and of the mould materials on the matrix stability. The easy-to-run preparation procedure for a chemically stable metakaolin geopolymer individuated can be summarized as reagents setting and curing at room temperature and material mould which permits moisture level around 40%.

2013 - Microwave assisted combustion synthesis in the system Ti-Si-C for the joining of SiC: Experimental and numerical simulation results [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; S., Han; V., Casalegno; M., Salvo; Colombini, Elena; Leonelli, Cristina; M., Ferraris
abstract

Microwaves at 2.45GHz have been applied to ignite the combustion synthesis of compacted Ti-Si-C powders mixtures, having 1:1:1 atomic ratio, in order to join SiC-based components. A mixture of different refractory phases such as TiC and TiSi2 were obtained. Depending on the synthesis conditions, no residual silicon in the joint was detected, suggesting the suitability of the here proposed experimental joining approach for nuclear plants and high temperature applications. A simplified model was developed with the aim of obtaining a deeper understanding of the here proposed rapid, almost pressure-less and localized heating joining method. Experimental and numerical simulation results demonstrate that joining of SiC can be rapidly obtained with minimization of heat affected zones in the SiC substrates. Maximum apparent shear strength values of the joints ranged from 9.9 to 45.1MPa, depending on the process conditions.

2013 - Microwave selective thermal development of latent fingerprints on porous surfaces: Potentialities of the method and preliminary experimental results [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina
abstract

The thermal development of latent fingerprints on paper surfaces is a simple, safe, and chemicals-free method, based on the faster heating of the substrate underlying the print residue. Microwave heating is proposed for the first time for the development of latent fingerprints on cellulose-based substrate, in order to add to the thermal development mechanism the further characteristic of being able to heat the fingerprint residues to a different extent with respect to the substrate, due to the intrinsic difference in their dielectric properties. Numerical simulation was performed to confirm and highlight the selectivity of microwaves, and preliminary experimental results point out the great potentialities of this technique, which allowed developing both latent sebaceous-rich and latent eccrine-rich fingerprints on different porous surfaces, in less than 30 sec time with an applied output power of 500 W. Microwaves demonstrated more effectiveness in the development of eccrine-rich residues, aged up to 12 weeks

2013 - Microwave-assisted melt reaction method for the intercalation of carboxylic acid anions into layered double hydroxides [Articolo su rivista]
Rosa, R.; Leonelli, C.; Villa, C.; Priarone, G.
abstract

Carboxylic acid anions intercalated layered double hydroxides are currently gaining increasing interest due to their potential applications in pharmaceutical field for controlled drug release in novel tunable drug delivery systems. In this work different aliphatic carboxylic acid anions were intercalated into the interlayers of commercial as well as synthetically prepared layered double hydroxides, through a novel microwave mediated melt reaction approach. The volumetric nature of microwave dielectric heating was exploited in order to rapidly heat the intimate mixture of the lamellar inorganic precursor and the appropriate organic acid, at the melting temperature of the particular monoor dicarboxylic acid used, reaching the intercalation in approximately two hours treatment.

2013 - Mix-design and characterization of alkali activated materials based on metakaolin and ladle slag [Articolo su rivista]
Maria Chiara, Bignozzi; Stefania, Manzi; Lancellotti, Isabella; Kamseu, Elie; Barbieri, Luisa; Leonelli, Cristina
abstract

Recycling industrial waste to produce newmaterials is a driving path to promote a sustainable development. Alkali activation can be a very effective tool to reach this goal especially when the starting material can be carbon fly ash and blast furnace slag instead of calcined natural clays such as metakaolin. With the aim to further increase the type ofwaste to be used as precursor and to promote a new recycling route, alkali activated materials based on partial substitution of metakaolin with ladle slag, deriving from the refining process of steel produced by arc electric furnace technology, are reported. In particular, being ladle slag rich in Ca-containing crystalline phases, its effect on the consolidation process has been investigated by means ofmicrostructure analysis carried out with XRD, SEM and MIP techniques. The results show that ladle slag are activated by alkaline solutions and participate in gels formation. Indeed, an optimization in terms of ladle slag content (60–80 wt.%) and the coexistence of different types of gels (3D aluminosilicate, C-S-H and Ca-rich aluminosilicate) have been envisaged.

2013 - Optimization of BFO microwave-hydrothermal synthesis: Influence of process parameters [Articolo su rivista]
Ponzoni, Chiara; Rosa, Roberto; Cannio, Maria; Buscaglia, Vincenzo; Finocchio, Elisabetta; Nanni, Paolo; Leonelli, Cristina
abstract

Multiferroic materials exhibiting ferromagnetic and ferroelectric properties in a certain temperature range are acquiring interest in information storage and sensors applications. Facile microwave hydrothermal synthesis route was optimized for the preparation of BiFeO3 (BFO) pure-phase. Influence of process parameters (i.e. precursor ratio, mineralizer concentration, temperature, time) on phase formation, particle size distribution and morphology was investigated in detail. The BFO powders were characterized by XRD, ESEM and TEM. Single phase BFO was formed using KOH, 8 M at 200 °C, 30 min and KOH, 10 M at 180 °C, 30 min; the presence of Na 2CO3, acting as electron donor, allowed the reaction to be performed at lower KOH concentrations and temperatures, 6 and 8 M at 180 °C in 30 min. Particles' morphology evolution with concentration and temperature without Na2CO3 followed the sequence: spherical, lamellar, lamellar semi-cubic, cubic; while with Na2CO3 addition the evolution was: lamellar semi-cubic, cubic and prismatic truncated octahedron shape. © 2012 Elsevier B.V. All rights reserved.

2013 - Porcelain stoneware with pegmatite and nepheline syenite solid solutions: Pore size distribution and descriptive microstructure [Articolo su rivista]
Kamseu, E.; Bakop, T.; Djangang, C.; Melo, U. C.; Hanuskova, M.; Leonelli, C.
abstract

Investigations correlating the pore size distribution-cumulative pore volume to the microstructure are used to compare the efficiency of two solid solutions of pegmatite and nepheline syenite as fluxing agents for the design of porcelainized stoneware. Particularly the fusibility of the two solid solutions was modified by adjusting the CaO content of the bodies. As results, the pegmatite based flux produced an extended viscous phase capable on embedding the crystalline phases and close open porosity as from 1175°C. Conversely, the bodies with nepheline syenite remained relatively porous up to 1225°C although the similar results of the mechanical strength at this temperature. The investigations on microstructure, pores size distribution and cumulative pore volume indicated almost complete reduction of the open pores in the pegmatite based bodies and the development of a band of closed pores ranged between 0.080 and 0.9μm showing P series as a more compact structure. For the nepheline syenite based bodies, the incomplete reduction of the open pores and the relative absence of the band of pores between 0.080 and 0.9μm were ascribed to the difference in fusibility and the viscosity of the glassy phases. These differences were interpreted in term of the differential action of CaO in Na2O-Al2O3-SiO2 and K2O-Al2O3-SiO2 on the amount and viscosity of the liquid phase formed already described in the literature. © 2013 Elsevier Ltd.

2013 - Single step combustion synthesis of β-NiAl-coated γ-TiAl by microwave ignition and subsequent annealing [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; A., Casagrande
abstract

β-NiAl-coated γ-TiAl-based alloys were synthesised following a single combustion synthesis step in a mono mode microwave applicator operating at 2.45. GHz under a moderate pressure of 0.15. MPa, allowing the simultaneous synthesis and forming of the required shape. Two reactive cylindrical specimens composed respectively of substrate (Ti. +. Al, 50:50. at.%) and coating (Ni. +. Al, 50:50. at.%) powder mixtures were positioned in the region of maximum electric field strength of the microwave applicator. The high exothermicity of the reactions involved, together with the application of pressure, allowed synthesising in a self-propagating regime the new intermetallic phases and to promote a good adhesion between them, due to the formation of complex reaction interface belonging to the Ni-Al-Ti system. A subsequent isothermal annealing treatment at 1230. °C led to the obtainment of the desired homogeneous γ-TiAl structure into the substrate without affecting the single β-NiAl phase constituting the coating. The anomalous presence of annealing twins was observed and explained considering the different states in which combustion synthesis of aluminides in the Ni. +. Al, Ti. +. Al and Ni. +. Al. +. Ti systems occurs

2013 - Sintering behaviors of two porcelainized stoneware compositions using pegmatite and nepheline syenite minerals [Articolo su rivista]
Tchakounte Bakop, T.; Tene Fongang, R. T.; Melo, U. C.; Kamseu, E.; Miselli, P.; Leonelli, C.
abstract

Semi-vitreous bodies, with flexural strength of ~78 MPa and water absorption of ~0.4 % for the optimal maturated specimens, were successfully prepared with solid solutions of pegmatite and nepheline syenite, respectively, for the full dense (P) and relatively porous composition (G). Despite the similarity on the bulk chemical composition of the two formulations, it was found that their thermal behaviors were significantly affected by the action of CaO on the flux system considered leading to earlier vitrification of P specimens with high flexural strength as from 1,175 C. Conversely, the flexural strength of G specimens increases progressively with soaking time and temperature development up to 1,225 C. The positive action of 5 mass% of CaO in the vitrification range of pegmatite solution, the relative low temperature of maturation of the semi-vitreous matrices, and the results of water absorption allow us to describe the formulations studied to offer promising potential in the production of sustainable and low-cost porcelainized stoneware. The high strength of P at relatively low temperature could be explained by the matrix-strengthening theory, while the extent of crystallization of G could be ascribed to the mullite theory. © 2013 Akadémiai Kiadó, Budapest, Hungary.

2013 - Solution Combustion Synthesis of perovskite oxides: Comparison between MWs and conventional ignition [Abstract in Atti di Convegno]
Rosa, R.; Ponzoni, C.; Veronesi, P.; Natali Sora, I.; Felice, V.; Leonelli, C.
abstract

Solution Combustion Synthesis is a nanomaterials preparation technique which is significantly energy- and time-efficient, being the energy required limited to the ignition step and being the reaction time greatly reduced as a consequence of the explosive nature of the exothermic process. Aim of this work is to present a detailed comparison between conventionally-ignited and microwavesignited solution combustion synthesis of LaFeO3 nanopowders, being this oxide at the basis of La1-xSrxFe1-yCuyO3-w perovskite materials, which represent a promising class of oxides to be exploited as the cathode in solid oxide fuel cells (SOFCs). The effects of the different ignition conditions on synthesis parameters and on nanoparticles size and morphology have been investigated in detail.

2013 - Suzuki-Miyaura coupling under air in water promoted by polymer supported palladium nanoparticles [Articolo su rivista]
Dell'Anna, Maria Michela; Mali, Matilda; Mastrorilli, Piero; Rizzuti, Antonino; Ponzoni, Chiara; Leonelli, Cristina
abstract

Suzuki couplings of aryl bromides were efficiently performed by a polymer supported palladium catalyst under air in water at 100°C without additives. In the case of activated aryl chlorides the reactions proceeded smoothly in the presence of a suitable phase transfer agent. The catalyst was active and recyclable for at least five times. Atomic absorption analyses revealed that the metal content in the polymeric support did not significantly decrease with the cycles while inductively coupled plasma analyses revealed that the palladium amount both in the mother liquors and in the organic products after reactions was lower than 500 ppb. The activity of the mother liquors has been investigated in detail. A transmission electron microscopy study of the supported catalyst before, during and after duty is also described. © 2012 Elsevier B.V.

2012 - A lifetime prediction method based on Cumulative Flaw Length Theory [Articolo su rivista]
Boccaccini, Dino Norberto; Maioli, Marco; Cannio, Maria; I., Dlouhy; Romagnoli, Marcello; Leonelli, Cristina; A. R., Boccaccini
abstract

Ultrasonic pulse velocity testing (UPVT) was carried out to perform non-destructive quality control of refractory plates. Used in conjunction with fracture mechanics, ultrasonic velocity measurements have proved a powerful technique for detecting, positioning and sizing internal voids and cracks in the samples, originated from the manufacturing process. Two cordierite-mullite refractory compositions exhibiting different microstructure and crack propagation behaviour were characterized through their lifetime during which they were subjected to thermal shock loading. In this paper, a new statistical method is proposed which allows to estimate the lifetime when the stress state that will be applied in service (loading) and the scattering of the ultrasonic velocity data in the as-received state are known. Since this lifetime prediction method is based on a non-destructive technique, it could be implemented into a code in an automatic quality control device for continuous lifetime estimation. The correlation between crack propagation behaviour and thermal shock resistance is discussed and semi-empirical models were developed to predict the service life of refractory plates from the measured values of ultrasonic velocities on as-received samples.

2012 - Bulk composition and microstructure dependence of effective thermal conductivity of porous inorganic polymer cements [Articolo su rivista]
Kamseu, Elie; B., Nait Ali; M. C., Bignozzi; Leonelli, Cristina; S., Rossignol; D. S., Smith
abstract

Experimental results and theoretical models are used to assess the effective thermal conductivity of porous inorganic polymer cements, often indicated as geopolymers, with porosity between 30 and 70 vol.%. It is shown that the bulk chemical composition affects the microstructure (grains size, pores size, spatial arrangement of pores, homogeneity, micro cracks, bleeding channels) with consequently the heat flow behaviour through the porous matrix. In particular, introduction of controlled fine pores in a homogeneous matrix of inorganic polymer cements results in an increase of pore volume and improvement of the thermal insulation. The variation of the effective thermal conductivity with the total porosity was found to be consistent with analytical models described by Maxwell–Eucken and Landauer.

2012 - Combination of electrophoretic deposition and microwave-ignited combustion synthesis for the preparation of ceramic coated intermetallic-based materials [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Michelazzi, Marco; Leonelli, Cristina; A. R., Boccaccini
abstract

Electrophoretic deposition (EPD) was used to deposit sub-micrometric ZrO2 particles on metallic powder compacts belonging to the systems Ni + Al and Ti + Al, which were used as deposition electrodes in the EPD cell. After EPD, combustion synthesis (CS) of such reactive electrodes was ignited in a microwave single-mode applicator, operating at a frequency of 2.45 GHz, in order to obtain in a single step the synthesis of the desired intermetallic phase (substrate) and the sintering of the previously deposited ceramic particles (or coating). Experimental results demonstrate that the excess heat released during the formation of nickel and titanium aluminides by CS can be exploited not only to self-sustain and self-propagate the reaction front along the substrate, but also to rapidly sinter the coating obtained by EPD. The innovative procedure here proposed is a promising strategy in order to obtain, in a single step, high temperature intermetallic-based materials, protected by well adhered ceramic coatings.

2012 - Correlation between microstructural evolution and mechanical properties of a-quartz and alumina reinforced K-geopolymers during high temperature treatments [Articolo su rivista]
Kamseu, E.; Catania, V.; Djangang, C.; Sglavo, V. M.; Leonelli, C.
abstract

Geopolymer material based K 2O-Al 2O 3-SiO 2 systems were investigated for high temperature applications. High viscous geopolymer paste was prepared using standard grade metakaolin dissolved in potassium hydroxide/potassium silicate solution (volume ratio, 1 : 1). The alkalinity of the solution was predetermined to optimise the dissolution of amorphous aluminosilicate. Quartz sand and alumina (25, 50 and 75 wt-%) were successively introduced as filler to form refractory concretes. RGPS4, RGPS2 and RGPS34 for sand and RGPA4, RGPA2 and RGPA34 for alumina were produced. The samples obtained were cured in sealed plastic containers for 7 days at room temperature before sintering at 200, 800, 1000, 1100 and 1200°C. The heating rate was 5°C min -1, and the dwelling time at peak temperature completes the sintering time to 4 h. Unvaried mechanical strength, up to 800°C, was observed: ~25 MPa for biaxial and ~20 MPa for uniaxial four-point bending strengths. This behaviour was ascribed to the maintenance of the structure of the geopolymer materials within the temperature interval considered. Above this temperature, all the samples presented significant densification; the most important increase in mechanical strength was ~65 and ~60 MPa respectively for biaxial and uniaxial four-point bending strengths. This was accompanied by a decrease in porosity. The dense structures observed at 1000-1100°C were affected by a further increase in temperature. Microcracks, vitrification and deformation appeared at 1200°C, which can be considered as detrimental to the mechanical properties. The mechanical properties and the microstructural evolution were found to be influenced by the amount of fillers added. Si and Al rich geopolymer concretes were found promising for the development of potential thermoresistant materials through the cold process. © 2012 Institute of Materials, Minerals and Mining.

2012 - Insulating behavior of metakaolin-based geopolymer materials assess with heat flux meter and laser flash techniques [Articolo su rivista]
Kamseu, Elie; B., Ceron; H., Tobias; Leonelli, Cristina; M. C., Bignozzi; Muscio, Alberto; Libbra, Antonio
abstract

Thermo physical behavior of metakaolin-based geopolymer materials was investigated. Five compositions of geopolymers were prepared with Si/Al from 1.23 to 2.42 using mix of sodium and potassium hydroxide (~7.5 M) as well as sodium silicate as activator. The products obtained were characterized after complete curing to constant weight at room temperature. The thermal diffusivity (2.5-4.5 × 10-7m2/s) and thermal conductivity (0.30-0.59 W/m K) were compared to that of existing insulating structural materials. The correlation between the thermal conductivity and parameters as porosity, pore size distribution, matrix strengthening, and microstructure was complex to define. However, the structure of the geopolymer matrix, typical porous amorphous network force conduction heat flux to travel through very tortuous routes consisting of a multiple of neighboring polysialate particles.

2012 - L’IMPIEGO DEL MICROSCOPIO OTTICO PER LA VALUTAZIONE DELLA VISCOSITA’ DI VETRI ANTICHI. [Relazione in Atti di Convegno]
F., Montanari; C., Boschetti; Baraldi, Pietro; Leonelli, Cristina
abstract

La determinazione della viscosità è un fattore di fondamentale importanza per lo studio della tecnologia dei vetri antichi, ma tale valutazione implica grandi quantitativi di vetro, che spesso non sono disponibili in ambito archeometrico. In questo articolo presentiamo un metodo per determinare indirettamente la viscosità, attraverso l‟analisi al microscopio ottico riscaldante.L‟analisi viene effettuata su qualche milligrammo di vetro in polvere, che viene sottoposto a un ciclo di riscaldamento reimpostato, mentre lo strumento raccoglie immagini del profilo del campione. Dall‟andamento del profilo del campione in sinterizzazione è possibile ricavare alti punti di viscosità caratteristici del rammollimento. Il lavoro propone un confronto tra due vetri Pompeiani colorati ed opacizzati ed un vetro trasparente riprodotto in laboratorio.

2012 - Mechanical and biological characterization of geopolymers for potential application as biomaterials [Articolo su rivista]
M., Catauro; F., Bollino; I., Kansal; Kamseu, Elie; Lancellotti, Isabella; Leonelli, Cristina
abstract

In this study three different geopolymer compositions have been investigated and characterized as potential biomaterials. Two geopolymer formulations are mainly composed of metakaolin, with some silica additions so that to reach Si/Al = 2.10 molar ratio, the third one contains a reduced amount of metakaolin and it is constitutes mainly of silica gel with composition: H24AlK7Si31O79 with Si/Al = 31. While in the first two formulations the powders were added of NaOH and sodium silicate in different percentages as activator and ligand, respectively, in the third one two different KOH addition methods (separately or jointly with potassium silicate solution) were performed. Room temperature consolidation was followed by thermal activation of composition Si/Al=31 at 60°C for 150 min and at 500°C for 180 min. The work presents exhaustive microstructural characterization (FT-IR, SEM/EDS, XRD) jointly with compression resistance tests and bioactivity studies on pressed powders of the two geopolymers. The materials were composed of amorphous aluminosilicates and a limited amount of zeolitic phases, found on the top surface. The compressive strength of the first two compositions was higher than 15 MPa and flexural strength around 2 MPa after 2 days of curing at room temperature. Compressive strength tests were carried out on Si/Al = 31 geopolymer on both activated sample series and demonstrated that when added separately the activator leads to more fragile specimens (0.90 MPa vs 1.95 MPa). To authors knowledge the effect of geopolymer preparation on mechanical properties of thermally activated Si/Al = 31 formulation has never been proved before. The bioactivity was successfully tested with the soaking of the samples in a simulated body fluid (SBF) for 3 weeks. The formation of a layer of hydroxyapatite on the surface of the materials was shown both by SEM micrograph and EDS analysis.

2012 - Microwave Processing of Ceramic and Ceramic Matrix Composites [Capitolo/Saggio]
Leonelli, Cristina; Veronesi, Paolo
abstract

Principles of Dielectric Heating Microwave Applicators Microwave Processing of Ceramics and Composites Advantages/Disadvantages of Microwave Processing of Ceramics and Composites Concluding Remarks: Scale-Up and Industrial Perspectives

2012 - Microwave ignited combustion synthesis as a joining technique for dissimilar materials [Articolo su rivista]
Rosa, Roberto; Colombini, Elena; Veronesi, Paolo; Poli, Giorgio; Leonelli, Cristina
abstract

Microwave energy has been exploited to ignite combustion synthesis (CS) reactions of properly designed powders mixtures, in order to rapidly reach the joining between different kinds of materials, including metals (Titanium and Inconel) and ceramics (SiC). Beside the great advantage offered by CS itself, i.e., rapid and highly localized heat generation, the microwaves selectivity in being absorbed by micrometric metallic powders and not by bulk metallic components represents a further intriguing aspect in advanced materials joining applications, namely the possibility to avoid the exposition to high temperatures of the entire substrates to be joined. Moreover, in case of microwaves absorbing substrates, the competitive microwaves absorption by both substrates and powdered joining material, leads to the possibility of adhesion, interdiffusion and chemical bonding enhancements. In this study, both experimental and numerical simulation results are used to highlight the great potentialities of microwave ignited CS in the joining of advanced materials.

2012 - Microwave ignited combustion synthesis as a joining technique for dissimilar materials: Modeling and experimental results [Articolo su rivista]
Colombini, Elena; Rosa, Roberto; Veronesi, Paolo; M., Cavallini; Poli, Giorgio; Leonelli, Cristina
abstract

Microwave energy has been applied to ignite the combustion synthesis (CS) in Ni + Al (50: 50 at %) powder mixtures in order to join dissimilar materials, in particular high-temperature metals. A numerical simulation was performed in order to obtain the data otherwise difficult to be experimentally measured and to develop a simplified predictive model of microwave ignited and sustained CS in metal powder compacts for joining applications. Experimental and numerical simulation results demonstrate that joining can be rapidly obtained by microwave ignition of the combustion synthesis characterized by a minimum extension of heat affected zones in the joined substrates.

2012 - Microwave-Assisted Extraction: An Introduction to Dielectric Heating [Capitolo/Saggio]
Leonelli, Cristina; Veronesi, Paolo; Cravotto, Giancarlo
abstract

Low environmental impact and high efficiency in chemical processing and manufacturing can be attained with the use of “light” instead of conductive heating. At microwave (MW) frequencies (300 MHz–300 GHz), the electromagnetic field can be dissipated by matter in the form of heat via polarization mechanisms, magnetic interactions, and ionic conduction. The conversion is extremely rapid, and heat is volumetrically diffused into the solvents, leading to an incredibly fast temperature increase that can speed up extraction processes in a way no other technique can match. In closed systems, microwave-assisted extraction can be performed at higher temperatures, and extraction times can be reduced drastically. In fact, enhanced plant matrix swelling increases the diffusion rate and promotes faster extraction kinetics. However, the user must take into account that the temperature distribution in a solvent exposed to microwave radiation is strictly dependent on the electromagnetic field distribution in the reactor, on the dielectric properties of the material, and on the presence of mass transport phenomena such as natural convection and stirring. Shorter extraction times and shorter cooling times usually avoid material degradation and afford high-quality extracts.

2012 - Ni-Al-Ti coatings obtained by microwave assisted combustion synthesis [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Poli, Giorgio; Leonelli, Cristina; Corradi, Anna; A., Casagrande; I., Boromei
abstract

Microwaves at 2·45 GHz have been used to ignite the self-propagating high temperature synthesis of Ni and Al powder mixtures (50:50 at-%) to produce a duplex intermetallic coating on Ti substrates. Owing to the high β-NiAl synthesis reaction enthalpy and the energy provided by the electromagnetic field, the newly formed aluminide is in the liquid phase. Thus, it can react with the underlying Ti substrate, forming a ternary eutectic at the interface, belonging to the Ni‐Al‐Ti system. The peculiar interlocking microstructure of such ternary layer is responsible for an increase in toughness and hardness compared to the parent NiAl coating. Moreover, the ternary layer’s oxidation resistance was tested, showing the possibility of replacing the functionality of hard and brittle NiAl, but limitedly up to 750°C. This can be ascribed to the relatively low Al content in the ternary layer, which hinders the formation of a continuous and protective Al2O3 scale. For this reason, the increase in Al content, or the addition of further elements such as Cr or Si, in the starting powder mixture, helps improve the oxidation resistance of the complex intermetallic coating at the interface, up to the tested temperature of 900°C.

2012 - Pair distribution function analysis and Mössbauer study of defects in microwave-hydrothermal LiFePO 4 [Articolo su rivista]
Bini, Marcella; Ferrari, Stefania; Capsoni, Doretta; Mustarelli, Piercarlo; Spina, Gabriele; Giallo, Franco Del; Lantieri, Marco; Leonelli, Cristina; Rizzuti, Antonino; Massarotti, Vincenzo
abstract

Olivine-type LiFePO 4 is nowadays one of the most important cathode materials of choice for high-energy lithium ion batteries. Its intrinsic defectivity, and chiefly the so-called lithium iron anti-site, is one of the most critical issues when envisaging electrochemical applications. This paper reports a combined diffractometric (Synchrotron Radiation XRD with Rietveld and PDF analyses) and spectroscopic (Mössbauer) approach able to give a thorough characterization of the material defectivity. Such analytical procedure has been applied to a sample prepared following an innovative microwave-assisted hydrothermal synthesis route that, in a few minutes, allowed us to obtain a well crystallized material. PDF analysis, which is applied for the first time to this type of battery material, reveals the presence of disorder possibly due to Li/Fe exchange or to a local symmetry lowering. A 5% amount of iron on the lithium site has been detected both by PDF as well as by Mössbauer spectroscopy, which revealed a small percentage of Fe 3+ on the regular sites. © 2012 The Royal Society of Chemistry.

2012 - Rheology of geopolymer by DOE approach [Articolo su rivista]
Romagnoli, Marcello; Leonelli, Cristina; Elie, Kamse; Magdalena Lassinantti, Gualtieri
abstract

The effects of solid/liquid content, temperature, curing time and deflocculant concentration on some fundamental rheological parameters of metakaolin-based geopolymer suspensions activated by NaOH were studied by statistical DOE approach. Solid content appears to be the most important parameter among the studied ones. As well known, it has an influence both on viscosity, shear behaviour and yield stress. Instead the additive, an industrial grade sodium polyacrilate, has demonstrated to have a poor effect on the viscosity and yield stress. In synergy with curing time, temperature showed a different effect with respect to its classic rheological influence. In countertrend, increasing the temperature resulted in an increased viscosity due to acceleration of the geopolymerisation reactions.Rheological parameters have proven to be very sensitive to chemical changes in the studied system. In combination with DOE methodology, it is a potent tool for monitoring the microstructural evolution of geopolymers during curing.

2012 - The effects of carboxylic acids on the aqueous dispersion and electrophoretic deposition of ZrO2 [Articolo su rivista]
Hanaor, Dorian; Michelazzi, Marco; Leonelli, Cristina; Sorrell, Charles C.
abstract

The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO2 with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO2 suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO2 surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability. © 2011 Elsevier Ltd.

2012 - Ultrafine magnetite nanopowder: Synthesis, characterization, and preliminary use as filler of polymethylmethacrylate nanocomposites [Articolo su rivista]
Russo, P.; Acierno, D.; Palomba, M.; Carotenuto, G.; Rosa, R.; Rizzuti, A.; Leonelli, C.
abstract

Magnetite (Fe 3O 4) nanoparticles prepared by microwave-assisted hydrothermal synthesis have been characterized in terms of morphological and structural features. Electron micrographs collected in both scanning (SEM) and transmission (TEM) modes and evaluations of X-ray powder diffraction (XRD) patterns have indicated the achievement of a monodispersed crystallite structure with particles having an average size around 1520 nm. Structural investigations by Micro-Raman spectroscopy highlighted the obtainment of magnetite nanocrystals with a partial surface oxidation to maghemite (γ-Fe 3O 4). Preliminary attention has been also paid to the use of these magnetite nanoparticles as filler for a commercial polymethylmethacrylate resin. Hybrid formulations containing up to 3 wt of nanoparticles were prepared by melt blending and characterized by calorimetric and thermogravimetric tests. For sake of comparison, same formulations containing commercial Fe 3O 4 nanoparticles are also reported. Calorimetric characterization indicates an increase of both glass transition temperature and thermal stability of the nanocomposite systems when loaded with the synthesized magnetite nanoparticles rather then loaded with the same amount of commercial Fe 3O 4. This first observation represents just one aspect of the promising potentiality offered by the novel magnetic nanoparticles when mixed with PMMA. © 2012 Pietro Russo et al.

2011 - Advancing the use of secondary inputs in geopolymer binders for sustainable cementitious composites: A review [Articolo su rivista]
Obonyo, E.; Kamseu, E.; Melo, U. C.; Leonelli, C.
abstract

Because of concerns over the construction industry's heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of "green" binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems. © 2011 by the authors.

2011 - Anodic aqueous electrophoretic deposition of titanium dioxide using carboxylic acids as dispersing agents [Articolo su rivista]
Hanaor, D.; Michelazzi, Marco; Veronesi, Paolo; Leonelli, Cristina; Romagnoli, Marcello; Sorrell, C.
abstract

The dispersion of anatase phase TiO2 powder in aqueous suspensions was investigated by zeta-potential and agglomerate size analysis. The iso-electric point (IEP) of anatase was determined to be at pH 2.8 using monoprotic acids for pH adjustment. In comparison, it was found that the use of carboxylic acids, citric and oxalic, caused a decrease in zeta-potential through the adsorption of negatively charged groups to the particle surfaces. The use of these reagents was shown to enable effective anodic electrophoretic deposition (EPD) of TiO2 onto graphite substrates at low pH levels with a decreased level of bubble damage in comparison with anodic EPD from basic suspensions. The results obtained demonstrate that the IEP of TiO2 varies with the type of reagent used for pH adjustment. The low pH level of the IEP and the ability to decrease the zeta-potential through the use of carboxylic acids suggest that the anodic EPD of anatase is more readily facilitated than cathodic EPD

2011 - Continuous microwave plasma processing of cold drawn steel wire rod [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Leonelli, Cristina; Cavatorta, Giovanni
abstract

Surface modification of cold drawn steel wire rod has been performed using a set of microwave plasma torches operating at 2.45 GHz, 3 kW maximum power, with the aim to modify the wire surface morphology and chemical composition prior to hot dip coating with Znbased alloys. The effect of varying the carrier gas type and flux is investigated experimentally and by numerical simulation. Adhesion of the zinc-based coating after plasma treatment, compared to untreated samples, as well as corrosion resistance, resulted improved, however treatment reproducibility can be still considered poor.

2011 - Dynamic-mechanical behavior and morphology of polystyrene/perovskite composites: Effects of filler size [Relazione in Atti di Convegno]
Russo, P.; Acierno, D.; Corradi, A.; Leonelli, C.
abstract

Composites based on a commercial grade polystyrene resin containing 5 wt% of non commercial perovskite particles were prepared by melt blending and analyzed in terms of dynamic-mechanical behavior and morphology. In particular, micro- and nanosized perovskites La0,5Sr0,5MnO 3, synthesized by using an innovative microwave-assisted hydrothermal route, were considered. Flexural dynamic-mechanical evaluations in terms of storage modulus showed better performance for nanofilled systems with respect to ones containing micro particles: evidence explained also in terms of different reinforcing mechanisms normally occurring with variation of filler size and temperature. Finally, preliminary morphological observations emphasized the achievement of a satisfactory level of filler dispersion for micro composite formulations. © 2011 Published by Elsevier Ltd.

2011 - Energy transfer in microwave assisted Combustion Synthesis of inorganic compounds [Relazione in Atti di Convegno]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina; Corradi, Anna Bonamartini
abstract

In this work microwaves (MWs) were used to ignite and sustain, the Combustion Synthesis (CS) of micrometric metallic powders in order to obtain thick intermetallic coatings as well as joining between advanced materials. MW heating possess the peculiarity to transfer energy, and not heat directly, to the reactive powders, thus it becomes possible to continue to provide energy to the reactive specimen during and after the CS, thus controlling the heating and the cooling behaviour at the reaction front. Investigations concerning the separate effect of positioning the sample in predominant electric field or magnetic field will be presented as well.

2011 - Evolution of fired clay products: From origin to sustainable building ceramics [Articolo su rivista]
Kamseu, E.; Leonelli, C.; Obonyo, E.
abstract

Nowadays, the design of building and construction materials should be straightly linked to the environmental context of industrial development and the many regulations and constraints linked to energy, ecosystems, geography and communities. In one word, building materials today have to be sustainable. In this paper, the authors turn back to the history of structural clay products and described their evolution and the factors that have affected the evolution of their products.

2011 - Highly homogeneous Al2O3-ZrO2 nanopowder via microwave-assisted hydro- and solvothermal synthesis [Articolo su rivista]
Prete, Francesca; Rizzuti, Antonino; Esposito, Leonardo; Tucci, Antonella; Leonelli, Cristina
abstract

Zirconia-doped alumina nanometric powder (5 mol%) was prepared by means of microwave hydro- and solvothermal syntheses, with the use of either bi-distilled water or diethylenic glycol as solvents, respectively. The as-obtained products were thermal treated at different temperatures (400°, 450°, and 500°C) to study the phase evolution. The experimental method allows synthesis of carbon-coated zirconia-dispersed alumina nanopowders with excellent characteristics, such as very fine size, high homogeneity, no phase separation, and narrow size distribution. © 2011 The American Ceramic Society.

2011 - Microwave ignited combustion synthesis of metal and intermetallic matrix composites [Relazione in Atti di Convegno]
Rosa, Roberto; Sola, Ramona; Colombini, Elena; Veronesi, Paolo; Leonelli, Cristina
abstract

Aim of this work is to present the results concerning the application of microwave assisted combustion synthesis (MACS) approach in the production of different kind of cermets and intermetallic matrix composite (IMC). Combustion synthesis allows taking advantages from the heat generated from exothermic reactions, which can derive from the synthesis of the intermetallic matrix, of the reinforcement, or both. Microwaves were used to ignite such combustion reactions exploiting their heating selectivity. The use of a single mode applicator allowed also investigating any "specific" microwave effects ascribable to separate electric and magnetic fields.

2011 - Microwave-mediated preparation of bio-inorganic hybrid materials for cosmetic and pharmaceutical applications [Relazione in Atti di Convegno]
Villa, C.; Priarone, G.; Rosa, R.; Leonelli, C.
abstract

Due to their peculiar structure, layered nanomaterials, such as layered double hydroxides (LDHs, anionic clays) represent an interesting pathway to develop new multitasking hybrid materials. For biological, pharmaceutical and cosmetic purposes, LDHs can act as both reservoirs as well as carriers for organic bioactive hosts. In this study we present the preparation of organo-LDH using several Microwave (MW) - mediated intercalation procedures. MW activation was used both for the preparation of LDHs and for their subsequent hydrothermal intercalation. All the reactions were carried out using scientific single mode microwave applicators. Operative conditions and comparative results with the conventional methods will be reported.

2011 - Microwaves assisted hydrothermal synthesis of sub-micrometric BiFeO 3 particles [Relazione in Atti di Convegno]
Ponzoni, Chiara; Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina; Buscaglia, Maria Teresa; Buscaglia, Vincenzo; Finocchio, Elisabetta; Nanni, Paolo
abstract

Microwave assisted hydrothermal synthesis is widely recognized to enhance powders crystallinity leading to a narrower particle size distribution compared to conventional hydrothermal approach. The synthesis of complex oxide systems still remains a challenge due to the multiplicity of oxidation states, morphologies and phases. Multiferroic materials, since exhibit magnetic and ferroelectric order in the same temperature range, are gaining increasing interest in information storage and sensors applications. The preparation of the well-known multiferroic BiFeO3, following a microwave hydrothermal approach, has been investigated in this work. The optimization of the experimental conditions (salt precursors, mineralizer concentration, temperature, time, etc.), is presented and discussed in terms of particles size distribution, phase purity and product morphology.

2011 - Microwaves-mediated preparation of organoclays as organic-/bio-inorganic hybrid materials [Articolo su rivista]
Villa, C.; Rosa, R.; Corradi, A.; Leonelli, C.
abstract

An innovative approach in the field of nanomaterials is to develop modern and mild synthetic protocols that enable controlled and integrated organization of specific functional organic and biological building blocks. In this context, research on the preparation of clay-based organic-inorganic hybrid materials, i.e. organoclays, has received considerable attention because these lamellar materials not only possess highly ordered structure in 2D, but also provide interesting chemical intercalation and surface properties. As a result entrapment and orientation of various functional guest molecules into layered inorganic solids, has been well exploited. At present there is a great deal of interest in the rational design of hybrid organic-/bio-inorganic composites on the nanometer to micrometer length scales. These hybrids encompass highly selective recognition properties associated with organic and biological species, combined with catalytic, optical, and electronic properties of the inorganic lamellar framework. This paper presents an overview of microwave application in different preparation steps of organophilic clays, their modification and their addition to polymeric matrices. Particular attention has been given to the microwave-mediated hydrothermal technique, as innovative and eco-friendly protocol for the intercalation of different kinds of organic hosts into the interlayer of clay minerals. The few pioneering complete microwave-mediated preparation procedures, exploiting advantages of dielectric heating in both the synthesis of the organic host molecule and the intercalation in the clay structure, have been also highlighted. © 2011 Bentham Science Publishers Ltd.

2011 - One-pot synthesis of aniline derivatives from nitroarenes under mild conditions promoted by a recyclable polymer-supported palladium catalyst [Articolo su rivista]
Dell'Anna, Maria Michela; Mastrorilli, Piero; Rizzuti, Antonino; Leonelli, Cristina
abstract

This work describes the one-pot direct reductive amination of carbonyl compounds with nitroarenes promoted by a polymer supported palladium catalyst, in the presence of molecular hydrogen as the reductant. This methodology is applicable, with slight differences, to both aliphatic and aromatic aldehydes. The operational simplicity, the mild reaction conditions, the high yields and the good recyclability of the supported catalyst are major advantages of this method. TEM observations of the catalyst showed that the active species are palladium nanoparticles having a size distribution centered at 5 nm within the polymeric support. © 2011 Elsevier B.V.

2011 - Polysialate matrixes from Al-rich and Si-rich metakaolins: Polycondensation and physico-chemical properties [Articolo su rivista]
Kamseu, E.; Leonelli, C.; Chinje Melo, U. F.; Perera, D.; Lemougna, P. N.
abstract

Two metakaolins from Al-rich and Si-rich kaolinitic clays were used to design polysialate matrices with different Si/Al and NaK/Al ratios. The aim was to investigate the influence of oligomers formed during dissolution and hydrolysis on the polycondensation and transformation to hard and stable matrices. Products of geopolymerization of the different matrices were subjected to mechanical testing considering various loading configurations. The geopolymer matrices showed compressive strength from 51 ± 5 MPa (Si/Al=1.23) to 61 ± 2 MPa (Si/Al = 2.42) and bi-axial four-point strength from 11 ± 2 MPa to 16 ± 1.1 MPa respectively. These results were consistent with density, leaching ability and microstructure. It is proposed that the mechanical properties and the stability of the products of reactions can be discussed as the important parameters for the evaluation of the quality of geopolymer matrices. Moreover, polycondensation and the final performance of the product are greatly influenced by the unreacted crystalline or semi-crystalline phases that act as fillers and contribute to increased stability and mechanical properties. A good geopolymer material resulting from our study will be defined as an amorphous matrix of polysialates in which various unreacted or partly reacted crystalline phases are embedded. It is suggested that Si-rich metakaolin will present the more hardening and stable matrix with shorter setting time leading to small pores and an enhanced interlocked microstructure.

2011 - Prismatic applicator for continuous microwave-assisted synthesis of metallic nanoparticles [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Leonelli, Cristina; Cappi, A.; Barzanti, A.; Baldi, G.
abstract

Metallic (Ag, Au, Cu) nanoparticles suspensions are gaining an increasing interest in medical applications. Among the existing synthetic routes available, microwave processing allows to better control particle size and to achieve high purity of the products. The large scale production of nanoparticles requires the development of industrially-viable processes, preferably conducted using a "green chemistry" approach, at ambient pressure and relatively low temperature. Based on a recently developed microwave-assisted process in aqueous solution, a new dedicated continuous-flow reactor, made of two twin prismatic applicators has been designed, optimized and tested. It can produce up to 1000 liters/day of metal nanoparticles colloidal suspension

2011 - The Liquidus Temperature of Nuclear Waste Glasses;an International Round-Robin Study [Articolo su rivista]
B., Riley; P., Hrma; J., Vienna; M., Schweiger; C., Rodriguez; J., Cum; J., Lang; J., Marra; F., Johnson; D., Peeler; Leonelli, Cristina; Ferrari, Anna Maria; Lancellotti, Isabella; J. L., Dussossoy; R., Hand; J., Schofield; A., Connelly; R., Short; M., Harrison
abstract

Eight institutions from four countries participated in a round-robin study to determine the precision and bias of a liquidustemperature (TL) procedure for waste glasses being adopted by ASTM International as ASTM C 1720-11. The participantsof the round-robin study were asked to measure three different glasses with one or a combination of the following TLmeasurement methods: a gradient temperature (GT) method, a uniform temperature (UT) method, and/or a crystal fractionextrapolation (CF) method. The TL values reported by different institutions are generally consistent. The precision of TLmeasurements with each method was evaluated and is presented herein. The round-robin glasses were all previously studied atPacific Northwest National Laboratory and included ARG-1 (Glass A), Zr-9 (Glass B), and AmCm2-19 (Glass C), with measuredTL values spanning the temperature range of 960–1240°C. A precision (i.e., standard deviation) for TL has beenobtained from the data, even though the data were not acquired for all three glasses using all three methods from each participatingorganization. Also, the article provides a brief overview and the importance of the TL measurement.

2011 - The effects of firing conditions on the properties of electrophoretically deposited titanium dioxide films on graphite substrates [Articolo su rivista]
D., Hanaor; M., Michelazzi; J., Chenu; Leonelli, Cristina; C. C., Sorrell
abstract

Thick anatase films were fabricated on graphite substrates using a method of anodic aqueous electrophoretic-deposition using oxalic acid as a dispersant. Thick films were subsequently fired in air and in nitrogen at a range of temperatures. The morphology and phase composition were assessed and the photocatalytic performance was examined by the inactivation of Escherichia coli in water. It was found that the transformation of anatase to rutile is enhanced by the presence of a graphite substrate through reduction effects. The use of a nitrogen atmosphere allows higher firing temperatures, results in less cracking of the films and yields superior bactericidal performance in comparison with firing in air. The beneficial effects of a nitrogen firing atmosphere on the photocatalytic performance of the material are likely to be a result of the diffusion of nitrogen and carbon into the TiO2 lattice and the consequent creation of new valence band states.

2010 - Alkali-silica glassy matrixes (AGM ) as replacement for feldspar in conventional porcelain compositions [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Boccaccini, Dino Norberto; Veronesi, Paolo; V. M., Sglavo; U. C., Melo; D., Njopwouo
abstract

The effect of alkali-silica glassy matrixes (AGM), as replacement for feldspar, on the microstructure, physical properties and mechanical strength of conventional porcelain has been studied. AGM with chemical composition similar to feldspars has been prepared to introduced alkali-ions (Na+ and K+) in porcelain compositions. It has been found that the replacement of feldspar by AGM ameliorates the mechanical properties of the material. The improvements are attributed to sharp changes in the microstructure as result of a reduction of glassy phase and increase in crystalline mullite amount. AGM were found to be promising candidates as substitutes for feldspar in conventional porcelain.

2010 - Chemical and biological characterization of geopolymers for potential application as hard tissue prostheses [Relazione in Atti di Convegno]
Michelina, Catauro; Flavia, Bollino; Lancellotti, Isabella; Kamseu, Elie; Leonelli, Cristina
abstract

In this study different geopolymers have been investigated and characterized as potential biomaterials. The work presents exhaustive FT-IR, SEM/EDS and X-ray diffraction studies of twogeopolymer formulations, where water content, water to solid content and curing conditions have been varied during mixing stage, maintaining constant the ratios among Na-Al-Si. The amorphous matrix is typical of sodium aluminosilicates, as shown by the FT-IR spectra. The presence of zeolitic phases has been observed by XRD at the surface of the material while the main matrix was characterized by amorphous aluminosilicate phases. The compressive strength of all the compositions was higher than 50 MPa. In order to study their bioactivity, samples of the studied materials were soaked in a simulated body fluid (SBF). The bioactivity of the synthesized geopolymers was shown by the formation of a layer of hydroxyapatite on the surface of thematerials by using the SEM.

2010 - Chemical stability of geopolymers containing municipal solid waste incinerator fly ash [Articolo su rivista]
Lancellotti, Isabella; Kamseu, Elie; Michelazzi, Marco; Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina
abstract

Municipal solid waste incinerators every year produce tons of fly ashes which, differently from coal fly ashes, contain large amounts of toxic substances (heavy metals, dioxins, furans). The stabilization/solidification (S/S) technology known as geopolymerization is proposed with the purpose to bond physicallyand chemically incinerator fly ashes (IFA) in a solid matrix, in order to reduce pollutant mobility. The chemical stability of geopolymers with Si/Al ratio of 1.8–1.9 and Na/Al ratio of 1.0, synthesized by alkali activation of metakaolin and the addition of 20 wt% of two different kinds of IFA, is presented. The concentration of the alkaline solution, water to solid ratio and curing process have been optimized. The room temperature consolidation of IFA containing geopolymers has been tested for leachability in water for 1 day, accordingly to EN 12457 regulation and extended to 7 days to increase the water attack on solid granules. Leachable metals in the test solution, determined by ICP_AES, fall within limit values set by regulation for non-dangerous waste landfill disposal. Geopolymeric matrix evolution with leaching time has been also evaluated in terms of pH and electrical conductivity increase in solution.

2010 - Enhanced thermal stability in K2O-metakaolin-based geopolymer concretes by Al2O3 and SiO2 fillers addition [Articolo su rivista]
E., Kamseu; A., Rizzuti; Leonelli, Cristina; D., Perera
abstract

Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O-Al2O3-SiO 2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the range 0.1 μm to 1 mm) and fine powder alumina (grain size in the range 0.1-100 μm). The consolidated samples were characterized before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25-900 °C was less than 3%, reduced with respect to the most diffused potassium or sodium based geopolymer systems, which generally records a >5% shrinkage. The maximum shrinkage of the basic geopolymer composition was recorded at 1000 °C with a 17% shrinkage which is reduced to 12% by alumina addition. The temperature of maximum densification was shifted from 1000 °C to 1150 or 1200 °C by adding 75 wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to the importance of liquid phase. The geopolymer formulations developed in this study appeared as promising candidates for high-temperature applications: refractory, fire resistant or insulating materials.

2010 - Forming silver conductive thick films by microwave heating [Articolo su rivista]
Hwang, S.; Veronesi, Paolo; Leonelli, Cristina; Kim, H.
abstract

This study investigated a microwave-assisted processing route for the synthesis of conductive thick films on dielectric substrates starting from silver (Ag) and a glass frit powder mixture paste. A single mode microwave (2.45 GHz) applicator was used to reduce the processing time and improve the energy efficiency compared with conventional heating. The microstructures of the Ag-based conductive thick films that were fired using conventional and microwave heating were observed. After 300 s of microwave treatment, the shrinkage of the microwave-fired Ag conductive thick films was similar to the conventionally processed films at 580°C for 30 min. The results suggested that the drastic reduction of the substrate temperature and the rapid processing time were significant advantages because both helped to minimize the Ag diffusion into the glass, thus reducing the unwanted yellowing phenomena.

2010 - Geopolymers sintering by optical dilatometry [Relazione in Atti di Convegno]
Kamseu, E.; Leonelli, C.; Perera, D. S.
abstract

2010 - Materie prime di origine naturale nel processo di geopolimerizzazione [Articolo su rivista]
Leonelli, Cristina; Kamseu, Elie; Valentina, Medri; Samanta, Fabbri
abstract

Geopolymers are inorganic materials prepared via a room temperature treatment (25-120°C) with alkali activation. The main applications of these materials is in the field of building materials, recycle and inertization of waste, restoration. The production and final product is optimised by a careful selection of starting materials, i.e. aluminosilicate powders. In this paper are presented aluminosilicates from natural source, as an example kaolin, clays or volcanic ash. Metakaolin is the most reactive due to its amorphous structure and aluminium coordination; its reactivity is also influenced by its mineralogical origin, morphology of grains, and calcinations method. Volcanic ash present lower reactivity and the better consolidation temperature to obtain mechanically strong materials appears to be around 400°C.

2010 - Microwave (MW)-assisted combustion synthesis of micrometric metallic powders for the preparation of intermetallic-based materials [Relazione in Atti di Convegno]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina; Corradi, A. B.
abstract

Due to the interesting combination of lightweight and high refractoriness, Al-based intermetallic compounds are candidate materials for high temperature applications like turbochargers and exhaust valves. Microwaves (MW) at the frequency of 2.45 GHz were used to ignite the combustion synthesis of elemental micrometric powder mixtures belonging to Fe-Al, Co-Al and Ni-Al systems. The use of a single mode MW applicator allowed undertaking for the first time a comparative investigation concerning the effects of positioning the samples in predominant electric or magnetic field during synthesis. Moreover the effect of microwave irradiation exposure time, after ignition of the highly exothermic reactions, has been investigated as well.

2010 - Microwave Assisted Combustion Synthesis of Non-equilibrium Intermetallic Compounds [Articolo su rivista]
VERONESI, Paolo; ROSA, Roberto; COLOMBINI, Elena; LEONELLI, Cristina; POLI, Giorgio; Angelo, Casagrande
abstract

A simplified model of the microwave-assisted combustion synthesis of Ni and Al metal powders to form the NiAl intermetallic on titanium and steel substrates is presented. The simulation couples an electro-thermal model with a chemical model, accounting for local heat generation due to the highly exothermic nature of the reactions between the powders.Numerical results, validated by experimental values, show that the capability of microwaves to convey energy, and not heat, can be used to alter the temperature profiles during and after the combustion synthesis, leading to unique intermetallic microstructures. This phenomenon is ascribed to the extended existence of high temperature liquid intermetallic phases, which react with the metallic substrates at the interface. Moreover, microwave heating selectivity allows to maintain the bulk of the substrate metallic materials to a much lower temperature, compared to combustion synthesis in conventionally heated furnaces, thus reducing possible unwanted transformations like phase change or oxidation.

2010 - Microwave and ultrasonic processing: Now a realistic option for industry [Articolo su rivista]
Leonelli, Cristina; Timothy J., Mason
abstract

Environmentally friendlier preparations of chemical compounds and organic or inorganic materials are generally accompanied by the concept of saving resources by optimizing reaction conditions and/or introducing new process technologies. The use of ionic liquids and a solvent-free approach are among these technologies, but in terms of the minimisation of energy and optimization of reaction control both microwave and ultrasound irradiation have now proved to be real options. This review starts from the basic considerations on the separate interaction of microwaves and ultrasound with matter and goes on to explore some laboratory and industrial applications of each type of activation. It is also possible to enhance the effects of high frequency electromagnetic fields, typical of microwaves, or the cavitational energy associated with sonochemistry by combining them with other extreme conditions such as plasmas, high pressure and UV. Finally the simultaneous use of microwaves and ultrasound in a single reactor is described. This novel mixing of technologies has been implemented in order to combine the effects of enhanced energy with improved matter transportation.

2010 - Microwave rapid debinding and sintering of MIM/CIM parts [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; Denti, Lucia; Gatto, Andrea
abstract

Thermal debinding of parts obtained by Metal Injection Moulding (MIM) or Ceramic Injection Moulding (CIM) can benefit from the rapid, volumetric and selective microwave-assisted heating, having the organic binder or the metallic powders to preferentially absorb microwaves. This is particularly useful when dealing with ceramic powders having low thermal conductivity, but also more conductive materials can be treated faster if the maximum temperature difference inside each part is kept low. Microwave assisted debinding and sintering of MIM/CIM parts, made of stainless steel and alumina, has been optimized by means of numerical simulation, in order to determine the most favorable load configuration, in terms of heat generation homogeneity and energy efficiency. Rapid microwave-assisted debinding, in the optimized loading conditions, was experimentally achieved, with time reduction from 6 to 8 times, compared to conventional processes. Moreover, in case of MIM, pre-sintering of the brown part occurred, despite the temperature lower than 600Â°C. The occurrence of this beneficial phenomenon, which improves the brown part mechanical properties, has been ascribed to the electromagnetic field concentration which takes place in the space between the conductive particles, thus promoting rapid binder removal and neck formation.

2010 - Microwave technique applied to the hydrothermal synthesis and sintering of calcia stabilized zirconia nanoparticles [Articolo su rivista]
Rizzuti, A.; Corradi, A.; Leonelli, C.; Rosa, R.; Pielaszek, R.; Lojkowski, W.
abstract

This study is focused on the synthesis of zirconia nanopowders stabilized by 6%mol calcia prepared under hydrothermal conditions using microwave technology. Sodium hydroxide-based hydrolysis of zirconyl chloride solution containing calcium nitrate followed by microwave irradiation at the temperature of 220 °C for 30 min was sufficient to obtain white powders of crystalline calcia stabilized zirconia. By means of X-ray diffraction and transmission electron microscopy, it was shown that tetragonal zirconia nanocrystallites with a size of ca 7 nm and diameter/standard deviation ratio of 0.10 were formed. The effects of the [Ca2+] and [NaOH] as well as temperature and time of microwave irradiation on the density and specific surface area were evaluated. Sintering test of the tetragonal nanopowders at 1,300 °C in air was performed in a monomode microwave applicator. The sample was sintered to the density of 95% and the grain size, analyzed by field emission scanning electron microscopy, was in the range from 90 to 170 nm. © 2009 Springer Science+Business Media B.V.

2010 - Optimization of microwave-assisted rapid debinding of CIM parts in multimode applications [Relazione in Atti di Convegno]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina
abstract

Microwave (MW) heating selectivity was exploited in this work for the rapid thermal debinding of parts obtained by Ceramic Injection Moulding (CIM). Since the organic binder preferentially absorbs microwaves with respect to ceramic powders, heat can be efficiently transferred to the green parts, despite their low thermal conductivity which renders conventional heating techniques less effective. However, one of the major drawbacks of microwave-assisted processes is the lack of reproducibility of the results, and of non-adequate experimental conditions and procedures which can lead to misleading conclusions on the effective yield of the process. A rational approach to overcome this problem, consisting in numerical simulation coupled to Design of Experiments (DoE) technique was used. In this way it has been possible to optimize the MW-assisted thermal debinding of ring-shaped CIM parts in multi-mode applicators operating at 2.45 GHz, reducing processing times from the original 80-140 hours (depending on the shape and dimensions of the samples) by conventional heating to 6 hours by dielectric heating.

2010 - The pO-Index and R Ratio Gap Methods for the Assessment of Corrosion Risk in Refractory Materials in Contact with Glass Melts [Articolo su rivista]
Boccaccini, D. N.; Cannio, Maria; Romagnoli, Marcello; Veronesi, Paolo; Leonelli, Cristina; Boccaccini, ALDO ROBERTO
abstract

Corrosion of refractories used in glass melting technology is a complex phenomenon involving chemical wear (corrosion) and physical/mechanical wear (such as erosion and abrasion) processes as well as thermal shock and spalling. Besides the complexity in the hydrodynamics of a molten silicate bath with which refractory materials are in contact, refractories are polycrystalline heterogeneous materials containing a relatively high porosity. Pores are centers for accelerated corrosion, spalling, and penetration by the hot liquid. In this work, a corrosion study of aluminosilicate refractory crucibles by chromium and calcium oxides during the melting of Cr-containing soda lime glasses as a function of temperature (1400°–1500°C) and glass basicity has been performed. The features and mechanism of the corrosion process were compared and analyzed as a function of glass acidobasicity (pO-index) and of the ratio of network-dwelling cations to A13+ cations (R). The advantage of the pO-index and ΔR gap methods to assess refractory corrosion risk as a function of the acidobasicity differential between the refractory glassy phase and the glass melt was demonstrated. The change of the concentrations of glass constituents was monitored by ICP analysis of glass samples and correlated to the observed extent of corrosion. The crystalline composition and microstructure of the refractory materials before and after being corroded were studied by XRD analyses and SEM. Cr-doped corundum was found to be the main crystalline phase in the refractory microstructure and other mixed phases with chromium and aluminum and/or silica, which formed at the boundary layer (interface) between the glasses and the aluminosilicate refractory, were identified. The results provide a useful guide to the selection of refractory materials for application in glass and glass–ceramic manufacture in terms of their corrosion risk.

2010 - Transformation of polysialate matrixes from Al-rich and Si-rich metakaolins: Polycondensation and physico-chemical properties [Relazione in Atti di Convegno]
Kamseu, E.; Leonelli, C.
abstract

Two metakaolins from Al-rich and Si-rich kaolinitic clays were used to design polysialate matrices with different Si/Al and NaK/Al ratios. The aim was to investigate the influence of oligomers formed during dissolution and hydrolysis on the polycondensation and transformation to hard and stable matrices. Products of geopolymerization of the different matrices were subjected to mechanical testing considering various loading configurations. The geopolymer matrices showed compressive strength from 51 ± 5 MPa (Si/Al = 1.23) to 61 ± 2 MPa (Si/Al = 2.42) and bi-axial four-point strength from 11 ± 2 MPa to 16 ± 1.1 MPa respectively. These results obtained were consistent with density, leaching ability, and microstructure. It is proposed that the mechanical properties and the stability of the products of reactions can be discussed as the important parameters for the evaluation of geopolymer matrices. Moreover, polycondensation and the final performance of the product are greatly influenced by the unreacted crystalline or semi-crystalline phases that act as fillers and contribute to increase the stability and mechanical properties.

2009 - A statistical approach for the assessment of reliability in ceramic materials from ultrasonic velocity measurement: Cumulative Flaw Length Theory [Articolo su rivista]
Boccaccini, Dino Norberto; Maioli, Marco; Cannio, Maria; Romagnoli, Marcello; Veronesi, Paolo; Leonelli, Cristina; A. R., Boccaccini
abstract

A primary objective of statistical fracture approach is to predict the probability of failure of a component for an arbitrary stress state when the failure statistics are known. This study introduces the fundamentals and application of a new approach to characterize the mechanical behaviour of high temperature ceramic materials, including refractory materials, by coupling non-destructive methods, in particular ultrasonic velocity measurement, and the Batdorf statistical fracture theory. A new approach, termed Cumulative Flaw Length Theory (CFLT), has been developed for the case of macroscopically homogeneous isotropic materials containing randomly oriented microcracks uniformly distributed in a location subjected to non-uniform multiaxial stresses. A function representing the number of cracks per unit volume is estimated based on the histograms of ultrasonic velocity measurements. This function is used without additional assumptions to determine the probability of fracture under an arbitrary stress condition. Two different cordierite-mullite high temperature ceramic materials were characterized under the assumptions of this theory to provide experimental evidence to support the model.

2009 - Alkali-ions diffusion, mullite formation, and crystals dissolution during sintering of porcelain bodies: Microstructural approach [Articolo su rivista]
Leonelli, C.; Kamseu, E.; Boccaccini, D. N.; Sglavo, V. M.; Pellacani, G. C.
abstract

The effect of alkali-silicate glassy matrix as replacement for feldspar in soft and hard porcelain compositions was studied. SEM and X-ray diffraction analysis were used to evidence phase evolution. For each composition, the influence of soaking time was evaluated. The difference in chemical composition (amount of alkali and alumina) between the two types of porcelain studied influenced the final microstructure: density, pore size and shape, and mullite content. Quartz dissolution was more important in soft porcelain where the mullitization was limited by the low amount of alumina compared to hard porcelain. Replacing the feldspar by alkali-silicate glassy matrices with similar chemical composition, the amount of secondary mullite and mechanical properties increased in both soft and hard compositions.

2009 - Complete, efficient and "green" microwave assisted preparation of organoclays: Synthesis of the organic fillers and their intercalation procedure [Abstract in Atti di Convegno]
Villa, C.; Rosa, R.; Mariani, E.; Veronesi, P.; Leonelli, C.; Corradi, A.
abstract

Organoclays are organic-inorganic hybrid systems, which find a wide range of application in several industrial fields. In pursuing a Green Chemistry approach to synthetic routes coupling microwave (MW) activation to chemical processes, in this work we focused our research efforts on the MW assisted preparation of new organoclays interesting for peculiar cosmetic and pharmaceutical applications. MW heating was successfully applied to both the solventless synthetic protocol of the appropriate organic fillers (quaternary ammonium salts) and to their hydrothermal intercalation in a smectite clay structure. The organic compounds were obtained in excellent yield under mild conditions and their complete intercalation was fast achieved as confirmed by powder X-ray diffraction (XRD). Advantages of the microwave-mediated procedure over conventional preparative pathways in terms of "greenness" and the potential applications of the investigated systems are reported.

2009 - Descriptive microstructure and fracture surface observations of fired volcanic ash [Abstract in Atti di Convegno]
Leonelli, C.; Kamseu, E.; Melo, U. C.; Corradi, A.; Pellacani, G. C.
abstract

Crystals of the pyroxene group (diopside, augite and enstatite, hedenbergite), series of crystals with the general formula: (MgxFe1-x)2SiO4 having various geometry, identified as spinel (and olivine), and plagioclase crystals from anorthite to anorthoclase that grow together in mass having thin parallel groves embedded in a complex matrix together with calcium alumina silicate grains were found to be the descriptive microstructure of fired volcanic ash. Quartz grains were rarely present as confirmed by dilatometry analysis, XRD, SEM and DTA. The presence of dendrites continuously growing to pyroxene crystals indicated the precipitation/crystallization of these crystals from matrix and regions of glass concentration enhance by ions diffusion. Rings of Ti-rich iron micro-crystals observed around spinel (and olivine) suggested the probable nucleating role of these micro-crystals for the precipitation/crystallization phenomenon. The various type of crystals formed, the difference in their geometry and size and their interlocking mechanism results in a contiguous and dense structure with relevant characteristics at relative low temperature (1125-1150°C) confirm volcanic ash as promising alternative raw materials for vitrified ceramic products. It was concluded that controlled precipitation/crystallization of raw volcanic ash results on microstructure similar to that of glass-ceramic materials. The observation of fracture surface allowed comparison of fracture mechanics of volcanic ash ceramic to that of conventional vitrified ceramics. © 2009 Woodhead Publishing Limited.

2009 - Descriptive microstructure and fracture surface observations of fired volcanic ash [Articolo su rivista]
Leonelli, C.; Kamseu, E.; Melo, U. C.; Corradi, A.; Pellacani, G. C.
abstract

Crystals of the pyroxene group (diopside, augite and enstatite, hedenbergite), series of crystals with the general formula (Mg x Fe1-x )2SiO4 having various geometry, identified as spinel (and olivine), and plagioclase crystals from anorthite to anorthoclase that grow together in mass having thin parallel groves embedded in a complex matrix together with calcium alumina silicate grains were found to be the descriptive microstructure of fired volcanic ash. Quartz grains were rarely present as confirmed by dilatometry analysis, XRD, SEM and DTA. The presence of dendrites continuously growing to pyroxene crystals indicated the precipitation/crystallization of these crystals from matrix and regions of glass concentration enhance by ions diffusion. Rings of Ti-rich iron micro-crystals observed around spinel (and olivine) suggested the probable nucleating role of these micro-crystals for the precipitation/crystallization phenomenon. The various types of crystals formed, the difference in their geometry and size and their interlocking mechanism result in a contiguous and dense structure with relevant characteristics at relative low temperature (1125-1150 °C) confirming volcanic ash as a promising alternative raw material for vitrified ceramic products. It was concluded that controlled precipitation/crystallization of raw volcanic ash results on microstructure similar to that of glass-ceramic materials. The observation of fracture surface allowed comparison of fracture mechanics of volcanic ash ceramic to that of conventional vitrified ceramics. © 2009 Springer Science+Business Media, LLC.

2009 - Early evidences of vitreous materials in Roman mosaics from Italy: An archaeological and archaeometric integrated study [Articolo su rivista]
Boschetti, Cristina; Leonelli, Cristina; Michele, Macchiarola; Veronesi, Paolo; Corradi, Anna; Cinzia, Sada
abstract

This work displays the lines of a project about vitreous materials used in Roman Republican Age opus vermiculatum mosaics from Italy. This mosaic technique, originated in Egypt and Greece during the Hellenistic Age, testifies the fist evidences of vitreous materials used in mosaics: faience and glasses. The use of these materials in vermiculata mosaics from Italy was almost unknown when this research was started, so it was necessary to map and characterize the whole mosaic production. After a survey operated by a portable digital microscope, a reduced number of samples were collected to perform a laboratory characterization (OM, SEM–EDS, XRD). Data have been completed by an isotope ratio characterization (SIMS) to investigate the glasses raw materials provenance.

2009 - Investigation of volcanic ash based geopolymers as potential building materials [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Perera, D. S.; Melo, U. C.; Lemougna, P. N.
abstract

Volcanic ash powders from Etna (Italy) and Cameroon were used as the principal source of aluminosilicate to produce geopolymers with the potential for making building products. The volcanic ash was ball milled and reacted with concentrated alkaline solutions for polymerisation and subsequent curing at 75-400 °C for 12-48 h. It was found that the gel was more viscous than a similar gel formed from metakaolin. Geopolymers made from both ashes had bulk densities of 1.7-2.0 g/cm3 and water absorption values of 20-25 %. Their compressive strength values were 25-35 MPa and the bi-axial four-point flexura! strength values ranged from 14-20 MPa. These values increased by 20 % when cured for 21 d after 90 d storage. It was also found that by curing at 200-400 °C the mechanical properties increased. Scanning electron micrographs showed that with thermal curing microcrystalline phases were present along with undissolved crystalline phases. These phases remained bound to the matrix and acted as a filler for strengthening the materials. The Ca, Mg and Fe present as impurities in the volcanic ash formed some of these crystalline phases and did not form any deleterious hydroxide or carbonate phases.

2009 - MANUFACTURING METHOD OF PLASMA DISPLAY USING THE QUICK FIRING [Brevetto]
Kim, HYUNG SUN; Leonelli, Cristina; Veronesi, Paolo; Hwang, SEONG JIN
abstract

A manufacturing method of a plasma display is provided to perform a self heating operation by absorbing a microwave through a silver metal powder and a glass frit in plastic process. In a manufacturing method of a plasma display, a microwave device is comprised of a microwave generating unit, a microwave absorption part, a microwave formation controller, a sample holder, and a microwave reflection control part. A microwave generated in a microwave generating unit is controlled by the microwave formation controller. Microwave is irradiated on the sample inserted into the sample holder in order to perform the plastic process. The microwave reflection control part minimizes the reflected microwave. The reflection microwave absorption part absorbs the reflected microwave.

2009 - Microstuctural evolution during thermal treatment of three kaolinitic clays from Cameroon [Articolo su rivista]
Kamseu, E.; Braccini, S.; Corradi, A.; Leonelli, C.
abstract

The paper examines the influence of Al2O3/SiO 2 ratio, bulk chemical composition and temperature in mullite nucleation and growth from kaolinitic clays. Samples from NTAMUKA (TAN), Mayouom (MAY) and Wabane (WAB), region of high hills of West-Cameroon, undergo series of phase changes during sintering between 1000 and 1500°C. Phases transformation included: amorphous SiO2 and Al2O 3 as result of breakdown of kaolin above 700°C, nuclei of mullite that growth with temperature development to fine and then large grains at high temperature. The microstructure of the sintered products consisted on the elongated secondary mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative amount of liquid film for MAY and WAB. The morphology of mullite grains in TAN was more different being larger cuboid grains aggregated to form together with cristobalite a compact microstructure. The formation of TiO2 crystals and then Ti-Al (tialite: Al2TiO5) crystals influenced the microstructure of MAY and WAB. The microstructure at high temperature of the three kaolinitic clays indicated their suitability for dense refractory and fine ceramic applications. © 2009 Institute of Materials, Minerals and Mining.

2009 - Microwave Rapid Sintering of Nanostructured Stainless Steel Metal Powders [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; Bassoli, Elena; Denti, Lucia; Gatto, Andrea
abstract

Nanostructured AISI430 stainless steel powders, obtained by high energy milling have been uniaxially pressed in order to obtain 8 mm diameter cylindrical compacts. Microwave sintering of the green compacts has been performed in a single mode microwave applicator, at 2.45 GHz. Maximum sintering temperature of each sample, monitored using a sapphire optical fibre, was varied in the 1000-1200°C range, with heating rates in the 20-30 K/s range, applying 1200 W of microwave forward power. Dense nanostructured samples, with less than 1% porosity were obtained, presenting small local variation of Cr content in proximity of the necking region. Rapid microwave sintering helps maintaining the nanostructure, despite a non homogenous densification due to the uneven electromagnetic field distribution in the single-mode applicator

2009 - Microwave assisted combustion synthesis and compaction of intermetallic-based functionally graded materials: numerical simulation and experimental results [Articolo su rivista]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina; Corradi, Anna
abstract

compaction of intermetallics-based functionally graded materials (FGMs) is presented. Numerical simulation was used to investigate the temperature distribution in the reacting powders, before, during and after combustion synthesis occurred, showing that microwaves are capable of continuing to convey energy to the reactants and products, despite an adverse temperature gradient. Examples of the application of Microwave Assisted Combustion Synthesis (MACS) are reported, involving principally neat intermetallic based FGMs, belonging to the system CoAl-NiAl, both as freestanding and coatings on titanium grade 5 alloy. Some other preliminary results on the reliability of the here proposed experimental approach to the synthesis of freestanding samples based on intermetallic-matrix ceramic particles reinforced FGMs, are presented

2009 - Microwave assisted synthesis of new β-diketo derivatives ligands [Relazione in Atti di Convegno]
Ferrari, Erika; Lazzari, Sandra; Pignedoli, Francesca; Saladini, Monica; O., Verna; Corradi, Anna; Leonelli, Cristina; Rosa, Roberto; Veronesi, Paolo
abstract

The metal complexes of β-diketo derivatives and especially those of acetylacetone are well known and have been extensively studied. To improve the chelating ability of this molecule, we have introduced a further coordinative group. The designed compounds, which include a carboxylic group and the β-diketo moiety, are promising candidates as new metal ligands for pharmaceutical applications. Classical synthetic strategy for the obtainment of these adducts requires a two step procedure consisting first in the SN2 reaction of methylenic group and second deprotection of ester derivatives in order to set the carboxylic function free. Concerning the first step, traditional approach requires long reaction times and long work up procedures that lead to very poor product yields. Microwave (MW) irradiation at 2.45 GHz in closed vessels was exploited in this first synthetic step to take advantages from rapid heating rates thanks to the intrinsic volumetric and selectivity nature of MW heating. Results in terms of reaction times and yields as well as possible future developments, will be discussed.

2009 - Microwave ignited combustion synthesis of intermetallic-based functionally graded materials [Relazione in Atti di Convegno]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina; Corradi, A. B.
abstract

Combustion synthesis (CS) of different functionally graded materials (FGMs) based on intermetallic alloys were ignited by 2.45 GHz frequency microwaves, in order to obtain candidate materials for high temperature structural and coating applications. Combining CS with a moderate pressure, to promote porosity reduction, it was possible to obtain both freestanding samples and hard coatings on non-ferrous alloys substrates. The high temperature generated due to the high exothermicity of CS, and the selective microwave absorption by the reacting species, led to the formation of complex binary and ternary compounds and microstructures, at the interface between the reacted powders and the substrate, presenting, in some cases, an increased micro-hardness value with respect to parent materials.

2009 - Microwave pyrolizer oven design [Abstract in Atti di Convegno]
Garuti, M.; Balocchi, P.; Botti, C.; Veronesi, P.; Leonelli, C.
abstract

The present work describes the steps to design a pyrolizer oven that uses microwave to produce a low-cost activated carbon starting from waste tyres. A viability test on using microwave to transform waste rubber into carbon black was done using a small chamber that could be filled with 100 grams of rubber, treated with 500 W of microwave power: the result gave the start to the design of a lab scale oven that could be easily scaled up in case of success of the entire process. The cavity should be able to accept a minimum of 10 kg of waste rubber: as the process time was estimated near 10 minutes, the hour capacity was 60 kg (that roughly corresponds to twelve tyres processed per hour). The oven shape was a steel cylinder with diameter and length of 400 and 1400 mm respectively, with a total microwave power of 12 kW. Using an EM simulation tool (Concerto) it has been possible to evaluate the best input configuration of the 4 microwave generators, to optimize the port dimensions, to design a rectangular to cylindrical transitions, as well as the double quartz and Teflon window necessary to withstand the high temperature and pressure inside the oven-vessel.

2009 - Microwave sintering of glass-frit containing silver powders [Relazione in Atti di Convegno]
Hwang, Seongjin; Kim, Hyungsun; Veronesi, Paolo; Leonelli, Cristina
abstract

Microwaves at 2.45 GHz frequency have been used to selectively sinter Ag-based mixtures of milled glass frits and Ag powders on a glass substrate. The powders, deposited by screen printing, present much higher microwave absorption than the underlying glass, hence they are preferentially heated. Microwave heating selectivity allows maintaining almost unaltered the glass substrate, thus minimizing unwanted Ag diffusion into the glass. The effect of sintering variables, like microwave forward power and processing time are investigated in terms of Ag diffusion and dimensional changes, with respect to conventional sintering.

2009 - Microwave-assisted consolidation of coatings obtained by electrophoretic deposition (EPD) [Abstract in Atti di Convegno]
Veronesi, P.; Leonelli, C.; Corradi, A. B.; Poli, G.; Romagnoli, M.; Giovanardi, R.; Rosa, R.; Cannio, M.; Michelazzi, M.; Rizzuti, A.; Boccaccini, A. R.
abstract

Electrophoretic deposition (EPD) is an electrochemical method attracting increasing interest as a material processing technique. In the first step of EPD an electric field is applied between two electrodes and charged particles suspended in a suitable liquid move toward the oppositely charged electrode; in the second step the particles accumulate at the deposition electrode and create a relatively compact and homogeneous film, which, however, requires a further consolidation step in order to fully develop satisfactory mechanical properties. In the present work, EPD conditions have been varied in order to control the initial porosity of the deposits of nano- and sub-micrometric zirconia powders, applying an innovative "zerointegral" approach. Microwave heating was then applied to rapidly sinter the deposited powders, trying to minimize grain growth. EPD and microwave heating allow to influence the final product properties and thus its end use like thermal barrier coating or for tribological applications.

2009 - Misure di conducibilità termica di materiali refrattari mediante un apparato a piastra calda con anello di guardia [Articolo su rivista]
Boccaccini, Dino Norberto; Cannio, Maria; Veronesi, Paolo; Leonelli, Cristina; Muscio, Alberto
abstract

La conoscenza della conducibilità termica di prodotti ceramici sta assumendo importanza fondamentale per l’ottimizzazione dell’isolamento termico degli edifici in relazione alle problematiche connesse al risparmio energetico. Oggi esistono tecniche veloci, precise ed efficaci per la stima della conducibilità di materiali edilizi. Tuttavia per ottenere misure accurate di tale proprietà è opportuno scegliere il metodo di misura corretto in funzione dell’intervallo di conducibilità termica del materiale e della sua geometria. Nella realizzazione di un apparato a piastra calda con anello di guardia, nato dalla collaborazione tra DIMeC e DIMA, è stata seguita la norma ASTM C177-97. In particolare in questo lavoro viene mostrata la relazione tra conducibilità termica, densità e temperature di utilizzo di materiali refrattari cordierite-mullite.

2009 - Modelling of microwave assisted combustion synthesis applied to the joining of high temperature ceramics [Abstract in Atti di Convegno]
Rosa, R.; Veronesi, P.; Leonelli, C.; Corradi, A. B.; Salvo, M.; Casalegno, V.; Shaohua, H.; Ferraris, M.
abstract

Microwave (MW) irradiation at 2.45 GHz is a rapid and efficient way to ignite different kind of highly exothermic reactions involving powder mixtures, leading to the so-called combustion synthesis reactions. In the present work this technique was exploited to promote the rapid joining of high temperature ceramic materials composites, in a single mode applicator, applying a moderate pressure during the process. A multi-physics simplified model of the joining process between two SiC-based elements with the continuous application of microwaves was developed to study the effects on the combustion synthesis of powder mixtures preparation, microwave forward power and sample arrangement inside the applicator.

2009 - Processing fly ash from coal burning power station in a variable radiofrequency field [Relazione in Atti di Convegno]
Barbieri, L.; Lancellotti, I.; Andreola, F.; Cotradi, A.; Leonelli, C.; La Robina, M.
abstract

Experiments with fly ash obtained from a coal-burning power station in NSW, Australia, were conducted in the cold crucible facility at ANSTO using a 30kW variable frequency generator. The generator was configured as a standard Hartley oscillator with the tank capacitor able to vary from 110 pF to 4100 pF giving a frequency span of 5MHz to 18MHz. The applicator consisted of a coil with a water cooled base and top plate that formed an LC resonant cavity, which coupled to the RF generator by a single turn coil. A dark glass, confined inside the applicator, was formed by applying a high frequency electromagnetic field between two copper plates through a sample of fly ash. The temperatures reached were in excess of 1000 °C causing the powder to fuse into glass in a very brief period of a few minutes. The purpose of this experiment was to verify if dielectric and/or induction heating could melt the fly ash in a more rapid manner than conventional (resistive/joule) heating.

2009 - Sintesi assistita da microonde del pigmento CoAl2O4 [Articolo su rivista]
Veronesi, Paolo; Bondioli, Federica; Leonelli, Cristina
abstract

La sintesi del pigmento blu CoAl2O4 è stata condotta impiegando il riscaldamento a microonde alla frequenza di 2.45 GHz, utilizzando differenti applicatori (forni). I risultati della sperimentazione mostrano una grande variabilità della resa e del rendimento del processo assistito da microonde dipendentemente dal tipo di forno impiegato e dalla presenza di eventuali materiali ausiliari assorbitori di microonde. L’impiego di applicatori di microonde a modo singolo ha permesso di ottenere il pigmento in condizioni ottimali in tempi inferiori ai 2 minuti, con un consumo energetico specifico misurato di 15 kJ/g. La caratterizzazione mineralogica, colorimetrica e applicativa del pigmento entro impasto per gres porcellanato ha fornito risultati analoghi al pigmento di fabbricazione industriale o ottenuto per calcinazione in forno convenzionale. I risultati ottenuti dimostrano come l’opportuna scelta di applicatore di microonde e materiali di supporto sia fondamentale per massimizzare resa e rendimento del processo.

2009 - Structural Characterization of Zirconia Nanoparticles Prepared by Microwave- Hydrothermal Synthesis [Articolo su rivista]
Rizzuti, Antonino; Leonelli, Cristina; Corradi, Anna; E., Caponetti; D., Chillura Martino; G., Nasillo; M. L., Saladino
abstract

Nanocrystalline zirconia powders have been prepared by microwave-hydrothermal synthesis starting from aqueous solution of ZrOCl2 - 8H2O. Results of investigations on the aqueous suspension stability of the washed zirconia nanopowders by dynamic light scattering showed that the suspension, constituted by superaggregates of nanoparticles (131+/-10 nm), was stable up to 15 days. Nanopowders were investigated by means of transmission electron microscopy and small angle x-ray scattering measurements which proved that the zirconia nanopowder is constituted by small primary nanoparticles of ca. 8 nm that agglomerate forming bigger aggregates of50+/-1 nm.

2009 - Use of noncontact dilatometry for the assessment of the sintering kinetics during mullitization of three kaolinitic clays from Cameroon [Articolo su rivista]
Kamseu, Elie; Rizzuti, Antonino; Miselli, Paola; Veronesi, Paolo; Leonelli, Cristina
abstract

Noncontact dilatometry, compared to differential scanning calorimetry (DSC), was used together with scanning electron microscopy and densification behavior studies to investigate the parameters that govern the kinetics of transformation of kaolin to mullite during sintering.Three kaolinitc clays from Cameroon, with different SiO2/Al2O3 molar ratio, were examined. The temperatures of mullite nucleation were 973, 979, and 984 deg C at 5 deg C/min heating rate, respectively, for values of SiO2/Al2O3 molar ratio equal to 4.22, 2.22, and 2.08. At 20 deg C/min heating rate, the temperatures are shifted to higher values, 992, 997, and 1,001 deg C. The mullitization phenomenon, which includes a first step of nucleation and a second one of crystal growth, presented activation energy in the range of 650–730 kJ/mol, depending on the nature of the sample investigated. These values, obtained by noncontact dilatometer measurements, were comparable to those obtained by means of DSC and are in agreement with literature values. The difference in sintering kinetics for the three kaolinitic clays could explain the different morphologies obtained for the mullite grains.

2009 - “Microwave Rapid Sintering of Nanostructured Stainless Steel Metal Powders”,, Vol. 3, , Denmark, 2009, 143-148, ISBN [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; Bassoli, Elena; Denti, Lucia; Gatto, Andrea
abstract

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2008 - Assessment of viscoelastic crack bridging toughening in refractory materials [Articolo su rivista]
Boccaccini, Dino Norberto; Cannio, Maria; T. D., Volkov Husoviæ; I., Dlouhy; Romagnoli, Marcello; Veronesi, Paolo; Leonelli, Cristina
abstract

Viscoelastic bridges can be formed in refractory ceramics while cooling from high temperatures. Such bridges can shield crack tips, thus reducingthe effective crack tip stress intensity factors leading to higher resistance to creep and thermal shock. The extent to which the crack tip stress intensityis reduced can be estimated from fracture mechanics models that include experimental measurement of crack bridging and microstructuralparameters. In this paper a novel approach is proposed for the assessment of the effective crack bridging toughening from combining destructiveand non-destructive test methods. Fracture toughness values were determined applying chevron notched specimen technique and surface damage ofthe specimen was monitored by image analysis. Different cordierite–mullite compositions characterized by different microstructure morphologiesand crack propagation behaviour were investigated. A brief discussion about the correlation between thermo-mechanical properties, microstructure,crack propagation behaviour and thermal shock resistance is presented. Moreover, an empirical model able to determine the presence andeffectiveness of the viscoelastic crack bridging ligaments acting in the microstructure under thermal shock conditions and their degradation withincreasing thermal shock cycles from parameters measured at room temperature is presented.

2008 - Bi-axial four points flexural and compressive strength of geopolymer materials based Na2O-K2O-Al2O 3-SiO2 systems [Relazione in Atti di Convegno]
Leonelli, C.; Kamseu, E.; Sglavo, V. M.
abstract

Bi-axial four point flexural and compressive strength tests were used for the assessment of mechanical properties of geopolymer material-based, calcined kaolin and kaolinitic clays. Various activating solutions which consist in the mixture of potassium and sodium hydroxide, water and sodium silicate were designed and tested. Six specimens, over a wide number of investigated compositions, were selected with SiO2/Al2O3 varying from 1:1 to 3:1, The compositions 1:1 and 2:1 were obtained by using two different grades of kaolin as raw materials (standard and sand-rich), while the 3:1 was obtained by adding required amounts of silica to either kaolin or kaolinitic clay, All the samples were prepared by slip casting, using density (≈1,5 g/cm3) as indicator of the optimum viscosity for shaping geopolymer pastes, and cured at room temperature for different periods. The bi-axial four points flexural strength values vary from 13 to 21 MPa while the compressive strength vary from 45 to 67 MPa, being essentially influenced by curing time, SiO2/Al2O3 and K 2O/Na2O/H2O ratios, Increasing the SiO 2/Al2O3 ratio from 1:1 to 3:1, the mechanical properties increase but longer setting and curing times were required, Low SiO2/Al2O3 ratio results the appearance of micro cracks and deformations during curing. The flexural and compressive behaviour of the specimens studied were directly correlated to the porosity, density and the final product microstructure. The chemical behaviour of the six compositions is discussed with respect to basic dissolution-hydrolysis- polycondensation processes that occur in Na2O-K2O-Al 2O3-SiO2 systems.

2008 - Crystallization of aragonite particles from solution under microwave irradiation [Articolo su rivista]
Rizzuti, Antonino; Leonelli, Cristina
abstract

The effect of intense electromagnetic fields, generated inside a multimode microwave applicators, on the crystallization of calcium carbonate polymorphs starting from calcium bicarbonate solutions has been investigated. The identification and quantitative analysis of the calcium carbonate polymorphs has been made by X-ray diffraction using Rietveld-Reference Intensity Ratio (RIR) method. Scanning Electron Microscopy analysis has also been performed to study the morphology of calcium carbonate samples. Crystallization tests have been conducted at atmospheric pressure while adjusting microwave power to maintain solution temperature between 80 °C and 90 °C. For the sake of comparison, calcium carbonate powders have also been prepared using conventional heating either in a oven or on a hot plate with a magnetic stirrer. The experiments conducted using microwave radiation gave in a high percentage yield of aragonite (99%) which has been favoured by increasing microwave exposure times. Low microwave exposure times, on the other hand, favours vaterite formation which crystallized in an unusual flower-like morphology. © 2008 Elsevier B.V. All rights reserved.

2008 - Enhanced reactive NiAl coatings by microwave assisted SHS [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; A., Casagrande
abstract

Purpose – The paper aims to focus on microwave (2.45 GHz) assisted SHS (MA-SHS) preparation ofNiAl intermetallic coatings on titanium substrates conducted in single mode applicator in order topromote the formation of a complex Ni-Al-Ti interface. This enhances the NiAl coating adhesion to thesubstrate and presents high hardness, toughness and the capability of stopping the fracturepropagation.Design/methodology/approach – Numerical modelling, coupling electromagnetic and heattransfer, allowed to demonstrate that the interface cooling rate can be controlled immediately afterSHS using microwaves, benefiting from the possibility of conveying energy to the newly formedintermetallic compounds, despite an adverse temperature gradient which would negatively affectconventional heating techniques, based exclusively on heat transfer. Experimental validation of themodelling results confirmed that by altering the synthesis conditions (load geometry, microwavepower, auxiliary microwave absorbers) the thickness of the Ni-Al-Ti layer can be controlled.Findings – The growth of the interface layer can be ascribed to the formation of a liquid phase(ternary eutectic) which progressively consumes NiAl and Ti from the substrate. In case of MA-SHS,the liquid phase presence can be prolonged during cooling, thus explaining the formation of the thickinterface layer.Practical implications – Microwave selective heating can be used to initiate the SHS withoutaffecting the metallic substrate, which is only heated locally by the reaction products, thus preservingits properties.Originality/value – Coupling numerical simulation

2008 - Glass-working evidences at Dürres, Albania: An archaeological and archaeometric study [Articolo su rivista]
Boschetti, C.; Leonelli, C.; Corradi, A.; Iacumin, P.; Martini, M.; Sibilia, E.; Santoro, S.; Sassi, B.
abstract

For the first time an archaeological and archaeometric work presents the discovery of glass-working evidences in the area of Dürres Roman Amphitheatre in Albania. Glasses, coming from a layer dating back to the 11th century A.D., have been object of an archaeometric characterization to determinate the chemical composition. Moreover the oxygen isotope ratio has been calculated to hypothesize the provenance of the sands used to melt the glass. Bricks and charcoals, elements linked to the kiln structure, were analyzed by thermoluminescence and radiocarbon respectively. © 2008 Elsevier Masson SAS. All rights reserved.

2008 - Improvement of the surface properties of polycarbonate by organic-inorganic hybrid coatings [Articolo su rivista]
Fabbri, Paola; Leonelli, Cristina; Messori, Massimo; Pilati, Francesco; Toselli, M; Veronesi, Paolo; MORLAT THERIAS, S; Rivaton, A; Gardette, J. L.
abstract

Organic-inorganic hybrids (ceramers) were prepared through the sol-gel process with opportune alkoxysilane-terminated polymer chains as the organic phase and tetraethoxysilane as the inorganic network precursor. The consolidation process, used to reach a high degree of crosslinking between the two phases, was carried out with either conventional oven heating or microwave irradiation. High conversion degrees were obtained with both treatments even when microwave postcuring turned out to be much faster than conventional heating (5-10 s vs 40 min). Scratch-test and photooxidation investigations showed a significant improvement in scratch, yellowing, and photodegradation resistance for coated polycarbonate.

2008 - Microwave assisted debinding and sintering of nanostructured metal powders: modeling and experimental results [Abstract in Atti di Convegno]
Leonelli, Cristina; Veronesi, Paolo; Denti, Lucia; Gatto, Andrea
abstract

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2008 - Microwave assisted sintering of green metal parts [Articolo su rivista]
Leonelli, Cristina; Veronesi, Paolo; Denti, Lucia; Gatto, Andrea; L., Iuliano
abstract

Microwave processing has gained worldwide acceptance as a novel method for heating and sintering a variety of materials, as it offers specific advantages in terms of speed, energy efficiency, process simplicity, finer microstructures, and lower environmental hazards.Microwave assisted post-treatment of green metal parts (AISI 420 metal powder with 2–3 wt% polymeric binder) proved to be a new method, suitable for near-net-shape and net-shape manufacturing.Green parts exposed to high intensity microwave fields, using either single mode or multimode microwave applicators operating at 2.45 GHz ISM frequency, were investigated in terms of densification behaviour, microstructure and joining micromechanism. The results, in terms of microstructure and shape retention are comparable to the conventional heating ones, reported in literature, but they have been obtained in much shorter time.

2008 - Microwave rapid debinding and sintering of mim/cim parts [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; Denti, Lucia; Gatto, Andrea
abstract

Microwave assisted thermal debinding of parts obtained by Metal Injection Moulding (MIM) or Ceramic Injection Moulding (CIM) could benefit from the heating selectivity, having the organic binder to preferentially absorb microwaves, thus accelerating the conventional process, which has to rely on heating by conduction. This is particularly useful when dealing with ceramic powders having low thermal conductivity, but also more conductive materials can be treated faster if the maximum temperature difference inside each part is kept low.Once the organic binder is removed, microwaves at 2.45 GHz can be used to rapidly sinter the obtained brown parts, minimizing grain growth.In this work, microwave assisted debinding and sintering of MIM/CIM parts, made of stainless steel, alumina and titania is studied, using numerical simulation to investigate the presence of localised effects ascribable to the electromagnetic field distribution in the powder compacts.

2008 - Mullitization behaviour during thermal treatment of three kaolinitic clays from Cameroon: Densificaron, sintering kinetics and microstructure [Articolo su rivista]
Leonelli, C.; Kamseu, E.; Melo, U. C.; Corradi, A.; Pellacani, G. C.
abstract

Three kaolinitic clays from Cameroon were studied for their mullitization behaviour. The three clayey materials were from Ntamuka (TAN), Mayouom (MAY) and Wabane (WAB), all situated in the hills of western Cameroon. X-ray diffraction and thermal, dilatometric and SEM-EDS analyses were used to follow up the phase evolution, sintering kinetics and microstructure of the three materials as a function of temperature (1000-1500°C). Fine powders of each sample were pressed and treated in the above temperature range with the goal to correlate the phase evolution with densificaron parameters (shrinkage, porosity, density and mechanical strength). The nucleation of mullite and the increase of peak intensities were directly correlated to continuous densification and reduction of open porosity as observed under the SEM, The mullitization peak temperatures at 5°C/min were 973°C, 979.1°C, and 983.6°C respectively for TAN, MAY and WAB and - in the same order but at 20°C/min 992.1°C, 997.4°C and 1001.2°C. The mullitization phenomenon, which includes a first step of nucleation and a second of crystal growth, shows an activation energy that varies depending on the nature of sample investigated: the values ranged from 650 to 730 kJ/mol. The microstructure of the sintered products consisted on the elongated secondary mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative amount of glassy phase for MAY and WAB. The morphology of mullite grains in TAN was more different being laiger cuboid grains aggregated with cristobalite to form a compact microstructure. The formation of TiO2 crystals and then Ti-Al (tialite: Al2TiO5) crystals influenced the microstructure of MAY and WAB.

2008 - Prediction of service life of cordierite-mullite refractory materials by non-destructive methods [Relazione in Atti di Convegno]
Boccaccini, Dino Norberto; Kamseu, Elie; Volkov Husoviæ, T. D.; Cannio, Maria; Romagnoli, Marcello; Veronesi, Paolo; Dlouhy, I.; Boccaccini, A. R.; Leonelli, Cristina
abstract

Ultrasonic pulse velocity testing was used to perform non-destructive quality control of refractory plates used as substrates in fast firing of porcelain whitewares. The measurement of the ultrasonic velocity was used to asses the presence of internal voids or cracks originated from the manufacturing procedure. Image analysis was used to predict thermal stability of the refractory materials. Two cordierite-mullite compositions were investigated that are characterized by different microstructure morphologies and crack propagation behaviour. A brief discussion about the correlation between microstructure, crack propagation behaviour and thermal shock resistance is presented. Moreover, empirical models were developed to predict the service life of refractory plates from measured values of ultrasonic velocities in plates in the as-received state.

2008 - Service life prediction for refractory materials [Articolo su rivista]
D. N., Boccaccini; M., Cannio; T. D., Volkov Husoviae; E., Kamseu; Romagnoli, Marcello; Veronesi, Paolo; Leonelli, Cristina; I., Dlouhy; A. R., Boccaccini; A., R.
abstract

Ultrasonic pulse velocity testing and image analysis were used to predict the thermal stability of cordierite–mullite refractories. Two compositions used as substrates in fast firing of porcelain whiteware, characterized by different microstructure and crack propagation behavior, were investigated. Fracture strength and fracture toughness values were obtained from three point bending test and chevron notched specimen technique, respectively. The measurement of the ultrasonic velocity was used to assess the material degradation with increasing number of thermal-shock cycles and specimen damage was monitored using image analysis to obtain further evidence of material degradation. The correlation between thermo-mechanical properties, ultrasonic velocity, microstructure, crack-propagation behavior and thermal-shock resistance was discussed. A remarkable similarity was found between the variation of ultrasonic velocity (when measured through the length of the refractory plates) and fracture strength with number of thermal shock cycles. On the other hand, the development of surface microcracking, as monitored by image analysis, is in good agreement with the variation of K IC with the number of thermal-shock cycles. The variation of the $$\frac{d\sigma_{\rm f}}{dE_{\rm dyn}}$$ ratio with number of thermal-shock cycles shows the highest gradient of the investigated trends and it is proposed as a promising parameter to differentiate refractory materials regarding their different thermal shock behavior. Service life prediction models for refractory plates, from measured values of ultrasonic velocity and surface damage analysis, were proposed and validated.

2008 - Sintering behaviour, microstructure and mechanical properties of low-quartz content vitrified ceramics using volcanic ash [Articolo su rivista]
Kamseu, Elie; Boccaccini, Dino Norberto; Sola, Antonella; Rizzuti, Antonino; Leonelli, Cristina; U., CHINJE MELO; N., Billong
abstract

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2008 - Synthesis of zirconia nanoparticles in a continuous-flow microwave reactor [Articolo su rivista]
F., Bondioli; A., Bonamartini Corradi; Ferrari, Anna Maria; Leonelli, Cristina
abstract

Monodispersed zirconia colloidal spherical nanoparticles were synthesized from the hydrolysis and condensation of Tetra-n-propylzirconate (TPZ) by using a continuous microwave synthesis process. The flow rate was varied from 50 to 100 ml/min in order to establish the optimum conditions required to obtain unagglomerated zirconia nanopowders. The results were compared with those obtained in batch systems. In particular as the flow rate is decreased from 100 to 50 ml/min the particle became spherical with a mean particle size of about 100 nm.

2007 - Bending Strength and Elastic Modulus of Porcelain Compositions under Various Specimen Loading Configurations [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; V. M., Sglavo; Boccaccini, Dino Norberto; Veronesi, Paolo; Pellacani, Gian Carlo; D., Njopwouoc
abstract

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2007 - Caratterizzazione archeometrica dei mosaici del ninfeo della domus del Centenario [Capitolo/Saggio]
Boschetti, Cristina; Corradi, Anna; B., Fabbri; Leonelli, Cristina; M., Macchiarola; A., Ruffini; S., Santoro; M., Speranza; Veronesi, Paolo
abstract

Vitreous tesserae from several wall mosaics in Pompii (Italy) dating around the 1st century AD have been investigated using on-site optical microscopy to sample the most relevant materials, glass, glass-cereamics, faiences. The use of complementary micro-destructive analytical techniques, such as scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), and X-ray powder diffraction (XRPD) allowed to define the nature of formers, fluxes, chromophores and opacifying compounds and to determine the type of raw materials employed for their introduction. The results gave an idnication of the glass technology used in the roman period.

2007 - Ceramic technology and sustainable development [Articolo su rivista]
Lee, ; William, E; Boccaccini, ; Aldo, R; Labrincha, ; Joao, A; Leonelli, Cristina; Drummond, ; Charles, H; Iii, Cheeseman; Christopher, R.
abstract

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2007 - Characterisation of porcelain compositions using two china clays from Cameroon [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Boccaccini, Dino Norberto; Veronesi, Paolo; Miselli, Paola; Pellacani, Gian Carlo; U., CHINJE MELO
abstract

Mayouom and Ntamuka china clays, from Cameroon were used to produce porcelain bodies. Two soft porcelain formulations: PSI (withMayouom) and PSII (with Ntamuka) and one hard porcelain, PH (with both Mayouom and Ntamuka) were prepared.The maximum density and flexural resistance for these formulations were obtained at 1200 8C for PSI, 1225 8C for PSII and 1350 8C for PH.Their properties and values were, respectively, density (2.42, 2.58 and 2.59 g/cm3), water absorption (0.15, 0.15 and 0.02%), porosity (4.3, 5.3 and4.2%) and flexural strength (148, 148 and 160 MPa). In addition to varying amounts of liquid phase, the soft porcelain formulations containedmullite and quartz crystals while the hard porcelains contained quartz and more intense mullite peaks. At 1250 8C PSI and PSII presented a selfglazingphenomenon which gave significant brightness and high aesthetic quality. PH with lower alkali (especially Na+) did not self-glaze even at1400 8C. Considering the soft porcelain formulations, the higher amounts of TiO2 (0.83%) and Fe2O3 (0.31%) in PSI (with Mayoum clay) resultedin a higher sintering effect at lower temperatures, giving lower water absorption and higher resistance. Both Mayouom and Ntamuka china clayswere found to be suitable raw materials for the production of porcelain stoneware tiles. Ntamuka could also be used for the manufacture of optimalquality whitewares.

2007 - Characterization of thermal shock damage in cordierite-mullite refractory materials by non-destructive methods. [Articolo su rivista]
D. N., Boccaccini; E., Kamseu; T. D., Volkov Husovic; M., Cannio; Romagnoli, Marcello; Veronesi, Paolo; Leonelli, Cristina; I., Dlouhy; A. R., Boccaccini
abstract

Ultrasonic pulse velocity testing and image anal. were used to predict thermal stability of refractories. Two cordierite-mullite compns. used as substrates in fast firing of porcelain whiteware characterized by different microstructure morphologies and crack propagation behavior were investigated. The measurement of the ultrasonic velocity was used to assess the material degrdn. with increasing thermal shock cycles and specimen damage was monitored using image anal. and further results of material degrdn. were obtained. A brief discussion about the correlation between thermomech. properties, microstructure, crack propagation behavior and thermal shock resistance is presented. Moreover, empirical models are developed to predict thermomech. properties from ultrasonic velocity and surface damage measurements. Then, service life prediction models of refractory plates from measured values of ultrasonic velocities in plates in the as-received state are presented.

2007 - Crystallisation and substitutions of fluor-magnesio-richterite (Li,Na,K)2Mg6Si8O22F2 glasses [Articolo su rivista]
Hamzawy, E. M. A.; Leonelli, C.
abstract

The effect of Li+ and K+ substitutions for Na + on the crystallisation of the fluor-magnesio-richterite, Na 2Mg6Si8O22F2, glasses was investigated. Transparent colourless glasses were obtained in all cases except when sodium was fully substituted by Li when cristobalite crystals where found in the melt. XRD measurements showed the presence of fluor-magnesio-richterite, proto-amphibole,fluorophlogopite, taeinolite, enstatite, forsterite, lithium disilicate and cristobalite in the samples crystallised in the 600-1000°C temperature range. The coefficient of thermal expansion values of the glass-ceramic samples were in the range 98-116×10-7°C -1 (20-500°C) depending on the composition: fluoramphibole giving relatively higher values while enstatite and fluormica gave relatively lower values. The glass-ceramics had medium densities of 2.794-2.925 g/cm3. SEM images showed homogeneous microstructures of interlocked fibrous and flake-like crystals in a cryptocrystalline groundmass.

2007 - Current and potential contribution of cramic technology achiving sustainable development [Relazione in Atti di Convegno]
W. E., Lee; A. R., Boccaccini; J. A., Labrincha; Leonelli, Cristina; C. H., DRUMMOND III; C. R., Cheeseman
abstract

The role of ceramics technology in sustainable development is discussed. Ceramics technology is contributing to the remediation and cleanup of pollution and has an important role in developing new reuse and recycling options for many wastes. These waste materials are used in high-volume applications in low-technology materials used in road construction, roof tile, cements and concretes, and house brick applications in which they can contribute significant savings in energy consumption. Their use will be extended where economics or legislative drives are present. There will be increasing use of wastes as aggregate in bound and unbound civil engineering applications. In addition, cost-effective vitrification technologies will evolve for particularly problematic hazardous wastes, which will make them inert and beneficially reusable based on plasma or cold-crucible melting technologies.

2007 - Determination of thermal shock resistance in refractory materials by ultrasonic pulse velocity measurement [Articolo su rivista]
D. N., Boccaccini; Romagnoli, Marcello; E., Kamseu; Veronesi, Paolo; Leonelli, Cristina; Pellacani, Gian Carlo
abstract

Thermal shock resistance of refractory materials is one of the most important parameters in refractory material characterization since it determines their performance in many applications. Ultrasonic pulse velocity testing was used for non-destructive quantification of thermal shock damage in refractory plates used as support for the firing of porcelain articles. When refractory materials are subjected to the industrial thermal cycles crack nucleation and propagation occurs resulting in loss of strength and material degradation. The formation of cracks decreases the velocity of ultrasonic pulses travelling in the refractory because it depends on the density and elastic properties of the material. Therefore measuring either of these properties can directly monitor the development of thermal shock damage level. Young's modulus of representative samples was calculated using measured values of ultrasonic velocities obtained by ultrasonic pulse velocity technique. Results were compared with industrial statistical data of thermal shock behaviour of the investigated materials. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable non-destructive characterisation of thermal shock damage was demonstrated in this investigation. (c) 2006 Elsevier Ltd. All rights reserved.

2007 - Dielectric characterization of La1-xAgxMnO3+δ (x = 0; 0.2) perovskites in the frequency range 200MHz-3GHz [Relazione in Atti di Convegno]
Kaddouri, A.; Rizzuti, A.; Veronesi, P.; Leonelli, C.
abstract

La1-xAgxMnO3+δ (x = 0; 0.2) perovskites have been prepared using a microwaves process (MWhyd) by comparing the heating time and reaction temperature with the same factor under conventional thermal process (CHhyd). Experiments have been conducted using hydrothermal method at medium pressure (T = 200°C, P = 2.06 MPa.) followed by a conventional treatment of the precursor at 700°C (10h). While MWhyd and CHhyd powders exhibited the same XRD patterns indexed as pure perovskite structure, their physico-chemical properties were found to be strongly influenced by the preparation method. La1-xAgxMnO3+δ perovskites were characterised using x-ray diffraction (XRD), BET sorption, temperature programmed reduction-mass spectrometry (TPR-MS), x-ray photoelectron spectroscopy (XPS), and dielectric measurements in the frequency range 200 MHz-3GHz.

2007 - Letter from the Guest Editor [Articolo su rivista]
Leonelli, C.
abstract

2007 - MICROWAVE HEATING OF FLY ASH FROM MUNICIPAL WASTE INCINERATOR [Articolo su rivista]
Kováčová, Milota; Čuvanová, Silvia; Lovás, Michal; Jakabský, Štefan; Leonelli, Cristina; Veronesi, Paolo; Boccaccini, Dino Norberto
abstract

The paper is aimed to the research of microwave heating of the fly ash from municipal waste incinerator in Košice. Before heating, two kind of fly ashes (from filter and cyclon) were analysed by XPS method. The samples were heated in single mode furnace. The microwave heating was focused, the local melting of the samples was confirmed. The evolution of the gases was followed during heating.

2007 - Main development directions in the application of microwave irradiation to the synthesis of nanopowders [Articolo su rivista]
Leonelli, Cristina; Lojkowski, W.
abstract

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2007 - Microwave enhancement of the early stages of sintering of metallic powder compacts and metal-containing composites [Capitolo/Saggio]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio
abstract

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2007 - Microwave-assisted hydrothermal synthesis as a rapid route towards manganite preparation. [Relazione in Atti di Convegno]
Leonelli, Cristina; Rizzuti, Antonino; M., Viviani; P., Nanni; Corradi, Anna
abstract

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2007 - New "Green" approaches to the synthesis of pyrazole derivatives. [Articolo su rivista]
Corradi, Anna; Leonelli, Cristina; Rizzuti, Antonino; Rosa, Roberto; Veronesi, Paolo; Grandi, Romano; S., Baldassari; C., Villa
abstract

A novel approach to the synthesis of pyrazole derivatives from tosylhydrazones of alpha,beta-unsaturated carbonyl compounds possessing a beta-hydrogen is proposed, exploiting microwave (MW) activation coupled with solvent free reaction conditions. The cycloaddition was studied on three ketones (trans-4-phenyl-3-buten-2-one, beta-ionone and trans-chalcone). The corresponding 3,5-disubstituted-1H-pyrazoles were obtained in high yields and after short reaction times. In order to simplify and point out the green chemistry features of the method, a further improvement was achieved under the same catalytic conditions with a "one pot" synthesis of these heterocyclic compounds, starting directly from their carbonyl precursors via tosylhydrazones generated in situ. For an exhaustive study, the dielectric properties of the solid reaction mixtures were also measured, in order to obtain input data for the numerical simulation of their heating behaviour in the single mode MW cavity which was used for experimental work. In order to supply a valid methodology and tool for measuring the environmental impact, a comparative study between the synthetic route proposed and the classical synthetic route has been carried out.

2007 - Non-Incineration Microwave Assisted Sterilization of Medical Waste [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; U., Moscato; A., Cappi; O., Figurelli
abstract

A non-incineration method for sterilizing hospital infectious wastes has been studied and realized. A small apparatus operating at 2.45 GHz and at a power of 3 kW was designed to optimize power transfer from the electromagnetic field to the infectious materials, which have been previously shredded and moisture-corrected. The high pressure reached in the reactor, 7 atm, was enough to ensure complete sterilization in just a few minutes for a batch of several hundred grams of waste. Sterilization efficacy during microwave irradiation was also optimized with a new procedure using thermal, microbiological and water vapour sensors in a single test.

2007 - Non-contact dilatometry of hard and soft porcelain compositions [Articolo su rivista]
Kamseu, Elie; Leonelli, Cristina; Boccaccini, Dino Norberto
abstract

Two different porcelain compositions were studied: a soft and a hard one. DTA, optical non-contact dilatometry and DSC were used to evaluate the thermal behaviour of the porcelain compositions with the aim to master the suitable thermal cycle for each. Results were interpreted on the basis of mineralogy and microstructure: the amorphous phase, abundant in soft porcelain, plays an important role on thermal expansion (8·10–6 K–1 for soft and 6·10–6 K–1 for hard at 1000°C). Thermal expansion behaviour as function of firing time was also studied. Non-contact dilatometry characterisation of porcelain bodies enable to master the suitable thermal cycle for the sintering.

2007 - Numerical simulation of an industrial microwave assisted filter dryer: Criticality assessment and optimization [Articolo su rivista]
Leonelli, C.; Veronesi, P.; Grisoni, F.
abstract

Industrial-scale filter dryers, equipped with one or more microwave input ports, have been modelled with the aim of detecting existing criticalities, proposing possible solutions and optimizing the overall system efficiency and treatment homogeneity. Three different loading conditions have been simulated, namely the empty applicator, the applicator partially loaded by both a high-loss and low loss load whose dielectric properties correspond to the one measured on real products. Modeling results allowed for the implementation of improvements to the original design such as the insertion of a waveguide transition and a properly designed pressure window, modification of the microwave inlet's position and orientation, alteration of the nozzles' geometry and distribution, and changing of the cleaning metallic torus dimensions and position. Experimental testing on representative loads, as well as in production sites, allowed for the confirmation of the validity of the implemented improvements, thus showing how numerical simulation can assist the designer in removing critical features and improving equipment performances when moving from conventional heating to hybrid microwave-assisted processing.

2007 - Numerical simulation of an industrial microwave assisted filter dryer: criticality assessment and optimisation [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; F., Grisoni
abstract

Industrial-scale filter dryers, equipped with one or more microwave input ports, have been modelled with the aim of detecting existing criticalities, proposing possible solutions and optimizing the overall system efficiency and treatment homogeneity. Three different loading conditions have been simulated, namely the empty applicator, the applicator partially loaded by both a high-loss and low loss load whose dielectric properties correspond to the one measured on real products. Modeling results allowed for the implementation of improvements to the original design such as the insertion of a wave guide transition and a properly designed pressure window, modification of the microwave inlet's position and orientation, alteration of the nozzles' geometry and distribution, and changing of the cleaning metallic torus dimensions and position. Experimental testing on representative loads, as well as in production sites, allowed for the confirmation of the validity of the implemented improvements, thus showing how numerical simulation can assist the designer in removing critical features and improving equipment performances when moving from conventional heating to hybrid microwave-assisted processing.

2007 - Pre-Sintered MIM Brown Parts Obtained by Microwave-Assisted Binder Remova [Relazione in Atti di Convegno]
Veronesi, Paolo; D., Belviso; Denti, Lucia; Gatto, Andrea; Leonelli, Cristina
abstract

Microwave assisted thermal debinding of parts obtained by Metal InjectionMoulding (MIM) was studied using Design of Experiment techniques to reducethe number of virtual experiments needed to gather information regardingbinder removal. The optimization, in terms of speed, heating homogeneityand energy efficiency of the early stages of this process in an existing2-feeds multimode applicator operating at 2.45 GHz has been reached withnumerical simulation used to perform the virtual experiments. The obtainedmodel was used to determine the optimum debinding conditions, which wereexperimentally tested in a laboratory multimode applicator. Samplecharacterization, before and after sintering, in terms of strength andfinal density, with respect to an equivalent industrial production, wasused to assess the optimized process. A process time reduction of morethan 6 times was achieved. In case of MIM parts made of 430L steel,material not prone to high temperature oxidation, the preferentialmicrowave absorption by the metallic powders resulted also in apre-sintering treatment which improves the brown parts strength and favorstheir handling during the subsequent sintering stage.

2007 - Pre-sintered mim brown parts obtained by rapid microwave-assisted binder removal [Relazione in Atti di Convegno]
Veronesi, P.; Belviso, D.; Denti, L.; Gatto, A.; Leonelli, C.
abstract

Microwave assisted thermal debinding of parts obtained by Metal Injection Moulding (MIM) was studied using Design of Experiment techniques to reduce the number of virtual experiments needed to gather information regarding binder removal. The optimization, in terms of speed, heating homogeneity and energy efficiency of the early stages of this process in an existing 2-feeds multimode applicator operating at 2.45 GHz has been reached with numerical simulation used to perform the virtual experiments. The obtained model was used to determine the optimum debinding conditions, which were experimentally tested in a laboratory multimode applicator. Sample characterization, before and after sintering, in terms of strength and final density, with respect to an equivalent industrial production, was used to assess the optimized process. A process time reduction of more than 6 times was achieved. In case of MIM parts made of 430L steel, material not prone to high temperature oxidation, the preferential microwave absorption by the metallic powders resulted also in a pre-sintering treatment which improves the brown parts strength and favors their handling during the subsequent sintering stage.

2007 - Preparation of Nd:YAG Nanopowder in a Confined Environment [Articolo su rivista]
CAPONETTI, Eugenio; CHILLURA MARTINO, Delia; SALADINO, MAria Luisa; LEONELLI, Cristina
abstract

Nanopowder of yttrium aluminum garnet (YAG, Y3Al5O12) doped with neodymium ions (Nd:YAG) was prepared in the water/cetyltrimethylammonium bromide/1-butanol/n-heptane system. Aluminum, yttrium, and neodymium nitrates were used as starting materials, and ammonia was used as a precipitating agent. Coprecipitate hydroxide precursors where thermally treated at 900 °C to achieve the garnet phase. The starting system with and without reactants was characterized by means of the small-angle neutron scattering technique. The system, without reactants, is constituted by a bicontinuous structure laying near the borderline with the lamellar phase region. The introductionof nitrates stabilizes the bicontinuous structure, while the presence of ammonia induces a transformation from thebicontinuous phase to a lamellar phase. Nd:YAG nanopowder was characterized by wide-angle X-ray scattering, transmission electron microscopy, gas adsorption, and photoluminescence spectroscopy. By comparison with a sample prepared by the conventional coprecipitation method, the obtained Nd:YAG nanopowder is constituted by smaller crystalline nanoparticles showing a lower tendency to agglomerate. In addition, the nanoparticles present a welldefined spherical shape. Photoluminescence spectroscopy confirms that the doping Nd3+ ions substitute Y3+ ions in the YAG crystalline lattice. The Nd3+ lifetime value, obtained from the luminescence decay curves, was 286 ( 10 microseconds, higher than the single-crystal value (255 microseconds) and much higher than the nanopowder value obtained by the conventional coprecipitation method (75 microseconds).

2007 - Quality control and thermal shock damage characterization of high-temperature ceramics by ultrasonic pulse velocity testing [Articolo su rivista]
Boccaccini, Dino Norberto; Romagnoli, Marcello; Veronesi, Paolo; Cannio, Maria; Leonelli, Cristina; Pellacani, Gian Carlo; T. V., Husovic; A. R., Boccaccini
abstract

Ultrasonic pulse velocity testing was carried out to perform nondestructive quality control of refractory plates used as substrates in fast firing of porcelain whiteware. Two cordierite-mullite refractory compositions characterized by different microstructure morphologies and crack propagation behavior were investigated after a number of industrial thermal cycles. Ultrasonic velocity measurements were used to determine the presence of internal voids/cracks in the samples, originating from the manufacturing procedure. A brief discussion about the correlation between microstructure, crack propagation behavior, and thermal shock resistance is presented. Empirical models were developed to predict the service life of refractory plates from measured values of ultrasonic velocities on as-received samples.

2007 - Recycling of microwave inertised asbestos containing waste in refractory materials [Articolo su rivista]
Boccaccini, Dino Norberto; Leonelli, Cristina; Rivasi, Maria Rosa; Romagnoli, Marcello; Veronesi, Paolo; Pellacani, Gian Carlo; A. R., Boccaccini
abstract

Asbestos is a health hazard and its removal a priority for pollution prevention. Asbestos containing wastes (ACW) can be transformed into inert silicate phases by means of microwave irradiation. The aim of this investigation was to recycle microwave inertised ACW in mullite-cordierite refractory materials. A MgO-rich talc was replaced by inertised asbestos keeping approximately equal oxide composition of the raw materials. No significant variations of water absorption, linear shrinkage and Young's modulus but a higher occurrence of cordierite phase with the change of raw material was found. This can be considered an important technological result. (c) 2006 Elsevier Ltd. All rights reserved.

2007 - Simulazione numerica ed evidenza sperimentale della accelerata formazione di colli durante le fasi iniziali della sinterizzazione assistita da microonde di polveri metalliche [Articolo su rivista]
Leonelli, Cristina; Poli, Giorgio; Veronesi, Paolo
abstract

Coupling numerical simulation of the electromagnetic field during sintering of metallic powder compacts and metal-containing composites with the experimental results, it has been possible to demonstrate the existence of a microwave enhancement of the early stages of sintering, in particular the necks formation. The main phenomena involved resulted to be the electromagnetic field concentration in the regions among the conductive particles, as well as direct microwave absorption within the skin depth of the metal particles. This local concentration of the electric field, occurring exactly in the regions of necks formation, can have intensity higher than the dielectric strength of the medium, thus favouring breakdown phenomena, leading to arcing and local plasma formation, which trigger more efficient mass transport mechanisms during sintering. Three different cases has been numerically simulated and experimentally tested, in order to study the effects of particles dimension and shape: sintering of micrometric steel and brass spheres, sintering of millimetric pure metals and brass spheres, sintering of glass matrix composites reinforced with metal fibres.

2007 - Studies of rapid microwave sintering of green parts [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Denti, Lucia; Gatto, Andrea; L., Iuliano
abstract

This paper regards the application of microwave for the sintering of green parts produced by selective laser sintering (SLS). Heating tests were performed on 420L stainless steel cylindrical (20 mm diameter; 20 mm height). The parameters of the electromagnetic field distribution during microwave sintering of the specimens were optimized for the heating treatments. The dates obtained from preliminary tests were used to carry out further heating treatments. This paper shows the possibility of achieving rapid consolidation in single mode and multimode applicators operating at 2.45 GHz, in less than 20 minutes. This phenomenon is confirmed by a micro-scale numerical modelling of the distribution of the electromagnetic field around the metal particles that evidence a favourable necking stage promoted by local electric field concentration among the spherical particles. The consolidated parts, however, depending on the microwave heating conditions, can present sensitisation due to the formation of chromium carbides, favoured by the C abundance provided by the decomposing organic binder.

2007 - The design and optimization of a new microwave plasma source by numerical simulation [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio; M., Garuti
abstract

Abstract The aim of the work is to design a new compact microwave plasma source with a homogeneous circumferential distribution of the electric field intensity. The software for electromagnetic field simulation combined with design-of-experiments techniques was used to design and optimize the source geometry in terms of energy efficiency and field homogeneity. The basic assumption is that plasma can be described by an equivalent dielectric load. Two relatively simple microwave waveguide plasma sources have been simulated to study the effect of impedance-matching devices on the energy efficiency of the whole system. A microwave waveguide plasma source based on the WR340 waveguide geometry has been assembled to validate the model experimentally. A completely new compact plasma source, which is a toroidal waveguide and an innovative 'self-adapting' coupling slot, has been numerically simulated, designed and built. Preliminary tests confirmed the existence of a sufficiently homogeneous five-lobe distribution of the electric field.

2007 - Thermal shock behavior of mullite-cordierite refractory materials [Articolo su rivista]
Boccaccini, Dino Norberto; Leonelli, Cristina; Romagnoli, Marcello; Pellacani, Gian Carlo; Veronesi, Paolo; I., Dlouhy; A. R., Boccaccini
abstract

The characterisation of thermal shock damage in cordierite–mullite refractory plates used as substrates in fast firing of porcelain whiteware has been investigated. Two different refractory compositions (termed REFO and CONC), characterised by different silica to alumina ratios, were studied. Thermal shock damage was induced in as received samples by water quenching tests from 1250degC. Thermal and mechanical properties were measured at room temperature by means of standard techniques and then the thermal shock resistance parameter R was calculated. The fracture toughness of selected samples was measured before and after thermal shock by the chevron notched specimen technique. The reliability of this technique for evaluation of small differences in fracture toughness after a given number of thermal shock cycles was investigated.The suitability of KIc measurements by the chevron notched specimen technique to characterise the development of thermal shock damage in refractory materials was proved in this investigation.

2007 - UNATEORIA STATISTICA PER VALUTARE L’AFFIDABILITÀ DI MATERIALI CERAMICI BASATA SU MISURE DI VELOCITÀ ULTRASONICA: CUMULATIVE FLAW LENGTH THEORY [Relazione in Atti di Convegno]
Boccaccini, Dino Norberto; Maioli, Marco; Cannio, Maria; Veronesi, Paolo; Romagnoli, Marcello; Leonelli, Cristina
abstract

Uno dei principali obiettivi della teoria statistica della frattura è prevedere la probabilità di rottura per uno stress arbitrario, quando è nota la statistica di rottura. E’ stata sviluppata una nuova teoria “Cumulative Flaw Lenght Theory(CFLT)” per il caso di materiali omogenei isotropici a livello macroscopico contenenti microcricche con orientazioni random distribuite uniformemente sotto stress poliassiali. La funzione rappresentante il numero di cricche per unità di volume è basata su istogrammi relativi a misure di velocità ultrasoniche. Questa funzione è usata senza ulteriori assunzioni per determinare la probabilità di rottura in condizioni arbitrarie di stress. Questa teoria può essere facilmente incorporata in un modello a elementi finiti per prevedere la probabilità di rottura di una struttura sottoposta a stress. Inoltre il confronto della teoria con programmi esistenti usati per prevedere la probabilità di rottura di materiali ceramici e che sono basati su parametri determinati mediante prove distruttive, ad es. three point bending strenght, sottolinea il vantaggio di previsionibasate su tecniche non distruttive. Questo fatto ne permette l’impiego non solo in fase di design, ma anche per il monitoraggio dell’aumento di probabilità di rottura durante la vita in servizio. Una certa varietà di fratture introdotte durante le fasi iniziali dei metodi tradizionali di processo può portare a una affidabilità non accettabile dei materiali ceramici impiegati ad alta temperatura. Le impurezze presenti nelle materie prime (polveri, leganti..) e agglomerati formati durante il processo di formatura delle polveri sono esempi di difetti che influenzano la resistenza. Tali fratture non solo limitano la resistenza dei materiali ma incrementano lo scattering dei dati portando a affidabilità bassa (basso modulo di Weibull). La Cumulative Flaw Lenght Theory permette di valutare la funzione densità delle cricche e la probabilità di rottura a partire da dati di misura di velocità a ultrasuoni in materiali ceramici. Un nuovo metodo statistico è proposto che, basato su risultati ottenuti dalla CFLT per i campioni come ricevuti permette di valutare il vita in servizio quando il materiale è sottoposto a stress. Due diversi ceramici refrattari a base di cordierite mullite sono stati caratterizzati nell’assunzione che la teoria fosse validata in campo sperimentale. I modelli empirici di vita in servizio sono stati ottenuti considerando il numero di cicli termici sostenuti/sopportati da un numero di campioni. La buona correlazione ottenuta tra le curve teoriche e le curve ottenute con dati sperimentali mette in risalto la validità del metodo proposto.

2007 - Volcanic ash as alternative raw materials for traditional vitrified ceramic products [Articolo su rivista]
Leonelli, Cristina; Kamseu, Elie; Boccaccini, Dino Norberto; Melo, U. C.; Rizzuti, Antonino; Billong, N.; Misselli, P.
abstract

Investigation on the use of volcanic ash as 100% raw materials for traditional vitrified ceramic products is reported. X-ray diffraction (XRD), thermogravimetric-thermal differential analyses (DTA-TGA) and chemical analysis were used to characterise raw samples. Fired specimens were used to evaluate their ceramic properties. Volcanic ash contains essentially classical traditional ceramic oxides, plagioclase, pyroxene and olivine as principal minerals. In the temperature range 1100-1150°C, they present dense structure, low open porosity, without isolated quartz grains. The fired materials properties were found to be in agreement with those of stoneware class BI referring to standard ISO 13006 (i.e. the water absorption values were <1.5%). The presence of a sufficiently extended glassy phase capable of embedding crystalline phases developed during sintering allows comparison of the microstructure of fired volcanic ash with that of traditional porcelain or stoneware. © 2007 Institute of Materials, Minerals and Mining.

2006 - AMORPHOUS GERMANIUM (II) SULPHIDE PARTICLES OBTAINED BY MICROWAVE ASSISTED DECOMPOSITION OF GERMANIUM (IV) DISULFIDE [Articolo su rivista]
E., Bonometti; M., Castiglioni; P., MICHELIN LAUSAROT; Leonelli, Cristina; Bondioli, Federica; Pellacani, Gian Carlo; A. A., Barba
abstract

Microwave assisted decomposition of germanium(IV) sulphide has been used to obtain, by sublimation in He current, amorphous particles of germanium(II) sulphide in the 0.1-3.0 microns range. The adopted technique is reported in details as well as the full physical-chemical characterisation of the product (XRD, TEM, Raman, MS and dielectric properties).

2006 - Amorphous germanium(li) sulfide particles obtained by microwave assisted decomposition of germanium (IV) sulfide [Articolo su rivista]
Bonometti, E.; Castiglioni, M.; Lausarot, P. M.; Leonelli, C.; Bondioli, F.; Pellacani, G. C.; Barba, A. A.
abstract

The preparation of small, amorphous, and metastable Germanium sulfide GeS particles by using microwave assisted sublimation is discussed. The vitreous GeS2 is formed with the help of rapid quenching of liquid GeS 2. An equilibrium has also been used to calculate the standard molar enthalpy of the formation for GeS2 and for the chemical transport of Ge. The germanium sulfide was prepared using wet chemistry and characterized by its Raman spectrum for checking purity. The particle sizes observed in the experiment are smaller where the sublimation of GeS is carried in Air flow. The increase of the flow rate of the carrier gas leads to a more rapid removal of the particles from the hot subliming system preventing particles agglomeration. The transmission electron microscopy observations indicate the formation of spherical particles that have diameter in the 10-20 nm range.

2006 - Ancient glass deterioration in mosaics of Pompeii [Relazione in Atti di Convegno]
Corrradi, A.; Leonelli, Cristina; Veronesi, Paolo; Fabbri, B.; Macchiarola, M.; Ruffini, A.; Boschetti, Cristina; Santoro, S.
abstract

The aim of the present project is to evaluate the deterioration degree of ancient glass surface used as mosaic materials (tesserae) in Pompeii's 'ninfei a scala'. Specimens come from the fountain in the 'Domus del Centenario' (Pompeii, IX, 8), built starting from the 1st century AD and have been studied within a broader project on the Domus involving archaeologists, engineers, geologists, chemists and materials scientists. Using data from both non-destructive analyses (OM, XRD, SEM-EDS, UV-VIS) and those which requiring few milligrams of specimens (DTA-TGA, ICP-AES), a complete database of the tesserae based on classification by colour, materials characterisation and evaluation of their deterioration has been constructed. After characterisation, specimens were replaced in their original position in the mosaic using suitable mortars. One of the glassy tesserae that was analysed for surface deterioration-gave interesting results. The glass, coloured opaque red from Cu 2O micrometric crystallisation, turned green at the surface as a result of copper and lead leaching out and depositing as carbonate and sulphate salts. The glass production technology appeared to be very similar to that found in Nimrud (North Iraq) during the 8th century BC, the glass showing a similar chemical composition and deterioration. The identification of colour variations makes it possible to correctly read the decoration system and the archaeometric analysis will help to identify the site and production technique of materials.

2006 - Application of Microwave to Glaze and Ceramic Industry [Capitolo/Saggio]
Leonelli, Cristina; Siligardi, Cristina; Veronesi, Paolo; Corradi, Anna
abstract

Glaze sintering and crystallization processes; synthesis of ceramic pigments by solid state reactivity; and wax burnout in advanced ceramic pieces was investigated together with addition of polishing sludge to porcelain stoneware body are some of the themes developed recently at Modena University in the field of industrial ceramics.

2006 - Effect of pressure on synthesis of Pr-doped zirconia powders produced by microwave-driven hydrothermal reaction [Articolo su rivista]
A., Opalinska; Leonelli, Cristina; W., Lojkowski; R., Pielaszek; E., Grzanka; T., Chudoba; H., Matysiak; T., Wejrzanowski; K. J., Kurzydlowski
abstract

A high-pressure microwave reactor was used to study the hydrothermal synthesis of zirconia powders doped with 1 mol % Pr.The synthesis was performed in the pressure range from 2 to 8MPa corresponding to a temperature range from 215◦C to 305◦C.This technology permits a synthesis of nanopowders in short time not limited by thermal inertia of the vessel. Microwave heatingpermits to avoid contact of the reactants with heating elements, and is thus particularly well suited for synthesis of dopednanopowders in high purity conditions. A mixture of ZrO2 particles with tetragonal and monoclinic crystalline phases, about15nm in size, was obtained. The p/T threshold of about 5-6MPa/265–280◦C was necessary to obtain good quality of zirconiapowder. A new method for quantitative description of grain-size distribution was applied, which is based on analysis of the finestructure of the X-ray diffraction line profiles. It permitted to follow separately the effect of synthesis conditions on the grain-size distribution of the monoclinic and tetragonal phases.

2006 - Evaluation of thermal shock damage in refractory materials by ultrasonic pulse velocity testing [Relazione in Atti di Convegno]
Leonelli, Cristina; Romagnoli, Marcello; Kamseu, Elie; Boccaccini, Dino Norberto; Veronesi, Paolo
abstract

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2006 - Fracture behaviour of refractory ceramics after cyclic thermal shock [Articolo su rivista]
Z., Chlup; Boccaccini, Dino Norberto; Leonelli, Cristina; Romagnoli, Marcello; A. R., Boccaccini
abstract

Two commercially available refractory ceramic materials primary used as substrates for fast firing of porcelain stoneware were investigated. The first one, commercially known as CONC, contains cordierite and mullite in the ratio 50:50. The REFO refractory composite material with coarser microstructure compared to CONC has a cordierite-to-mullite ratio of 50:45 and the balance is filled by quartz. Both materials were exposed to water-quench tests from 1250 degrees C, applying various numbers of thermal cycles (shocks). Subsequently the fracture toughness was evaluated on both as-received and shocked samples using the Chevron notched specimen technique. The results were analysed with respect to the microstructure damage caused by the thermal loading. Scanning electron microscopy was used to analyse both microstructure and fracture surfaces in samples with different thermal loading history.

2006 - MICROWAVE THERMAL INERTISATION OF ASBESTOS CONTAINING WASTE AND ITS RECYCLING IN TRADITIONAL CERAMICS [Articolo su rivista]
Leonelli, Cristina; Veronesi, Paolo; Boccaccini, Dino Norberto; Rivasi, Maria Rosa; Barbieri, Luisa; Andreola, Nora Maria; Lancellotti, Isabella; Rabitti, Daniela; Pellacani, Gian Carlo
abstract

Asbestos was widely used as a building material prior to the 1970´s. It is well known that asbestos is a health hazard and its progressive elimination is a priority for pollution prevention. Asbestos can be transformed to non-hazardous silicate phases by microwave thermal treatment. The aim of this investigation is to describe the microwave inertization process of asbestos containing waste (ACW) and its recycling in porcelain stoneware tiles, porous single-fired wall tiles and ceramic bricks following industrial manufacture procedure. Inertised asbestos powder was added in the percentages of 1, 3, and 5 wt.% to commercially available compositions and then fired following industrial thermal cycles. Water absorption and linear shrinkage of the obtained industrial products do not present significant variations with additions up to 5 wt.% of microwave inertised ACW.

2006 - Preliminary Studies of the Rapid Microwave Sintering of Green Parts Made of 420L Stainless Steel [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Denti, Lucia; Gatto, Andrea; L., Iuliano
abstract

Electromagnetic field distribution during microwave sintering ofmetal compacts, obtained by MIM or SLS was performed, evidencing afavourable necking stage promoted by local electric field concentrationamong the spherical particles. Microwave heating tests on 420L stainlesssteel cylindrical (20 mm diameter; 20 mm height) green parts obtained bySLS showed the possibility of achieving rapid sintering in single modeand multimode applicators operating at 2.45 GHz, in less than 20 minutes.The sintered parts, however, depending on the microwave heatingconditions, can present sensitisation due to the formation of chromiumcarbides, favoured by the C abundance provided by the decomposing organicbinder. This phenomenon constitutes a lower limit to the overall sinteringtime of the examined SLS green parts, which can be overcome only alteringthe sintering atmosphere or performing a preliminar de-binding step

2006 - Study of thermal conductivity in refractory materials by means of a Guarded Hot Plate Apparatus", Milan, Italy, 11-15 December 2006, Abstract Book, p. 108 (2006). [Abstract in Atti di Convegno]
D. N., Boccaccini; Veronesi, Paolo; Muscio, Alberto; Leonelli, Cristina
abstract

.

2006 - Synthesis of Silica Nanoparticles in a Continuous-Flow Microwave Reactor [Articolo su rivista]
A., Corradi; F., Bondioli; Ferrari, Anna Maria; B., Focher; Leonelli, Cristina
abstract

Monodispersed silica colloidal spherical nanoparticles were synthesized from the hydrolysis and condensation of tetraethylorthosilicate (TEOS) by using a continuous microwave synthesis process. The flow rate was varied from 43 to 101mL/min in order to establish the optimum conditions required to obtain unagglomerated silica nanopowders. The results were compared with those obtained in batch systems.In particular the mean particle diameter became smaller than 50 nm as the residence time was decreased by increasing the flow rate to 101mL/min.

2005 - A novel cylindrical microwave plasma source [Abstract in Atti di Convegno]
Garuti, M.; Balocchi, P.; Botti, C.; Veronesi, P.; Leonelli, C.; Rettighieri, L.; Balestrazzi, A.; Valeri, S.
abstract

Microwave activated plasma shows advantages on obtaining high-density coatings with advanced mechanical properties, since these kinds of plasma allow to activate precursor molecules with high binding energy. We have developed a novel pulsed microwave plasma source, whose shape allows to obtain a large toroidal plasma emission zone, with a constant emission rate on the whole circumference of the emitting source. This design allows the deposition on relatively large and oddshaped samples. Plasma can be active on a large pressure range (10-2 /10 Torr), with a base pressure of 10-6 Torr to ensure a good purity for mechanical coatings. The microwave source was designed in order to fit on any kind of vacuum system equipped with a ISO standard 200 mm flange, regardless on the mounting direction. The pulsed microwave source uses a solid state power supply able to pulse the magnetron up to 8 kW peak, with a square waveform having excellent dynamic characteristic.

2005 - Ancient glass deterioration in mosaics of Pompeii [Articolo su rivista]
Corradi, Anna; Leonelli, Cristina; Veronesi, Paolo; B., Fabbri; M., Macchiarola; A., Ruffini; C., Boschetti; S., Santoro
abstract

The aim of the present project is to evaluate the deterioration degree of ancient glass surface used as mosaic materials (tesserae) in Pompeii's 'ninfei a scala'. Specimens come from the fountain in the 'Domus del Centenario' (Pompeii, IX, 8), built starting from the 1st century AD and have been studied within a broader project on the Domus involving archaeologists, engineers, geologists, chemists and materials scientists. Using data from both non-destructive analyses (OM, XRD, SEW-EDS and UV-VIS) and those requiring few milligrams of specimens (DTA-TGA and ICP-AES), a complete database of the tesserae based on classification by colour, materials characterisation and evaluation of their deterioration have been constructed. After characterisation, specimens were replaced in their original position in the mosaic using suitable mortars. One of the glassy tesserae that was analysed for surface deterioration gave interesting results. The glass, coloured opaque red from Cu2O micrometric crystallisation, turned green on the surface as a result of copper and lead leaching out and depositing as carbonate and sulphate salts. The glass production technology appeared to be very similar to that found in Nimrud (north Iraq) during the 8th century BC, the glass showing a similar chemical composition and deterioration. The identification of colour variations makes it possible to correctly read the decoration system and the archaeometric analysis will help to identify the site and production technique of materials.

2005 - Crystallisation of cu-containing K-fluor-richterite (KNaCa(Mg,Cu)(5)Si8O22F2 glasses [Articolo su rivista]
Hamzawy, Ema; Leonelli, Cristina
abstract

Gradual substitutions of Cu for Mg in K-fluor-richterite glass-ceramics were investigated. Crystallisation of Cu free or Cu containing glasses gave K-fluor-richterite, enstatite, diopside forsterite, rodderite, tenorite, cuprite, fluorite and crystalline silica. Colour changes in the crystallised glasses, from blue to orange or dark brown with increasing copper indicates change of either valency or the position of copper in the glass-ceramic structure. Although the base and low Cu containing glass-ceramic samples had ultrafine microstructures, the high Cu containing ones had pronounced crystals in a cryptocrystalline matrix. Rounded long crystals were thought to be K-fluor-richterite whilst euhedral crystals were thought to be Cu oxide phases. EDS analysis showsed a gradual replacement of Cu2+ for Mg2+ in addition to, Cu+ and Ca2+ for Na+ in the crystallised K-fluor-richterite phase. The coefficient of thermal expansion was low in base or low Cu content glasses and was high in high Cu content ones. The coefficients of thermal expansion of the corresponding glass-ceramic samples were higher than their parent glasses. The Vicker's microhardness values of the glass-ceramic samples are higher than those of the corresponding glasses. The Vicker's microhardness values decrease as the Cu content increases in the glasses or as the Cu oxide phases increase in the glass-ceramic samples. The densities of both glass and glass-ceramic increase with increasing the Cu content or Cu oxide phases, respectively.

2005 - Determination of thermal shock resistance in refractories by Ultrasonic Pulse Velocity Measurement [Articolo su rivista]
Romagnoli, Marcello; Leonelli, Cristina; D., Boccaccini
abstract

Thermal shock resistance of refractory materials is one of the most important parameters in refractory material characterization since it determines their performance in many applications. Ultrasonic pulse velocity testing was used for non-destructive quantification of thermal shock damage in refractory plates used as support for the firing of porcelain articles. When refractory materials are subjected to the industrial thermal cycles crack nucleation and propagation occurs resulting in loss of strength and material degradation. The formation of cracks decreases the velocity of ultrasonic pulses travelling in the refractory because it depends on the density and elastic properties of the material. Therefore measuring either of these properties can directly monitor the development of thermal shock damage level. Young's modulus of representative samples was calculated using measured values of ultrasonic velocities obtained by ultrasonic pulse velocity technique. Results were compared with industrial statistical data of thermal shock behaviour of the investigated materials. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable non-destructive characterisation of thermal shock damage was demonstrated in this investigation.

2005 - Investigation on the stability of dispertions of zirconia nanoparticles prepared by microwavehydrothermal synthesis [Abstract in Atti di Convegno]
Corradi, A.; Leonelli, C.; Rizzuti, A.; Veronesi, P.; Caponetti, E.; Martino, D. C.; Saladino, M. L.
abstract

Difficulties in reproducing the performances of nanoparticles dispersions are obstructive for the progress of the nanotechnology. A plausible reason for this variability is the lack of the control of the stability as well as the dimensions of the nanoparticles in the dispersions. In this work we report results of investigations on the stability of zirconia nanoparticles in aqueous medium, monitoring nanoparticles sizes by means of Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS). Nanocrystalline zirconia powders, prepared by microwave-hydrothermal synthesis, were determined to be 6-8 nm in size by TEM observations. By using DLS technique the as-prepared dispersions without any further manipulation, i.e. washing, filtering, and so on, resulted in polidispersed aggregates, constituted by the primary zirconia nanoparticles with an average diameter of 1.3 ± 0.1 mm. After eliminating sodium chloride from the synthesis solution, the nanoparticles rearrangement in a more stable suspension was found.

2005 - Mechanical performance and fracture behaviour of glass-matrix composites reinforced with molybdenum particles [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina; Manfredini, Tiziano; Montorsi, Monia; Veronesi, Paolo; E. J., Minay; A. R., Boccaccini
abstract

A borosilicate glass-matrix composite has been fabricated by addition of molybdenum particles in various volume fractions. In order to systematically investigate the effect of metallic particulate reinforcement on the overall composite mechanical behaviour, a FEM based numerical model was prepared. The study focused on the global elastic and fracture response of the composites. By studying crack propagation patterns, toughening mechanisms such as crack deflection and load transfer were detected, thus enabling to assess the influence of second phase volume fraction on composite fracture toughness. Microscopy observations of fracture surfaces were performed to support the numerical results. © 2005 Elsevier Ltd. All rights reserved.

2005 - Microstructural investigations in cordierite-mullite refractories [Articolo su rivista]
Boccaccini, Dino Norberto; Leonelli, Cristina; Rivasi, Maria Rosa; Romagnoli, Marcello; A. R., Boccaccini
abstract

The influence of the mineralogical composition and phase distribution on crack initiation and propagation in cordierite-mullite refractory plates used as substrates in fast firing of porcelain whiteware is investigated. Two different refractory compositions (termed REFO and CONC), characterised by different silica to alumina ratios, were studied. Propagation of cracks introduced by Vickers´ indentations was observed by scanning electron microscopy. Chemical analysis by EDS was used for phase identification together with X-ray diffraction analysis. Microstructural features and crack propagation behaviour were correlated and used to draw conclusions on the behaviour of the two different refractory compositions under thermal shock. It was found that the presence of alpha-quartz crystals and favourable residual stress field are responsible for room temperature fracture toughness in REFO samples. The CONC material contains a larger amount of residual glassy phase than REFO material, which should lead to better high-temperature mechanical properties and higher thermal shock resistance, as the glass phase may close (heal) propagating cracks.

2005 - Microwave assisted reactive sintering of intermetallic coatings on Titanium [Relazione in Atti di Convegno]
A., Casagrande; G. P., Cammarota; Leonelli, Cristina; Poli, Giorgio; Veronesi, Paolo
abstract

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2005 - Microwave assisted sterilization of hospital waste [Relazione in Atti di Convegno]
Veronesi, P.; Leonelli, C.; Moscato, U.; Cappi, A.
abstract

2005 - Microwave-hydrothermal synthesis and hyperfine characterization of praseodymium-doped nanometric zirconia powders [Articolo su rivista]
F., Bondioli; Leonelli, Cristina; Manfredini, Tiziano; Ferrari, Anna Maria; M. C., Caracoche; P. C., Rivas; A. M., Rodriguez
abstract

This work focuses on the microwave-assisted hydrothermal synthesis of praseodymium-doped zirconia and on the subsequent evaluation of the effect of synthesis conditions on powder properties. Pure and 10 mol% Pr-doped zirconia samples have been analyzed by X-ray diffraction (XRD) and the perturbed angular correlations hyperfine technique, which probes the nearest environments of zirconium ions. At atomic scale, as determined from perturbed angular correlation data, the XRD amorphous fraction of the as-obtained powders exhibits a tetragonal-like structure. The pure powder becomes partially stabilized and the doped powder is a substitutional solid solution of praseodymium in tetragonal zirconia.

2005 - Ni-aluminide coatings on titanium by microwave assisted reactive sintering [Relazione in Atti di Convegno]
A., Casagrande; G. P., Cammarota; Leonelli, Cristina; Poli, Giorgio; Veronesi, Paolo
abstract

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2005 - Non-Conventional Curing of Organic-Inorganic Hybrids [Articolo su rivista]
Leonelli, Cristina; Messori, Massimo; Pilati, Francesco; Veronesi, Paolo
abstract

Infrared and microwave curing of organic-inorganic hybrid materials was studied, in order to achieve the maximum conversion without detrimental effects due to the overheating or to the long-time permanence at high temperature. Partially cured poly(ethylene oxide)/silica hybrids were prepared by hydrolysis and subsequent condensation of precursors for 30 minutes isothermal heat treatment at 70°C. The conversion after the preliminary treatment is still low and requires an additional heating to complete the reaction. Three different thermal treatments were investigated: conventional heating, infrared heating and microwave heating. DSC characterisation of the obtained samples evidenced a drastic reduction of the treatment time when microwaves were used, requiring only a few seconds, compared to the hours-lasting conventional treatments.

2005 - Proceedings of the 10th Intl. Conference on Microwave and HF Heating [Monografia/Trattato scientifico]
Leonelli, Cristina; Veronesi, Paolo
abstract

The 10th International Conference on Microwave and Radiofrequency heating will be heldin the Faculty of Engineering of the University of Modena and Reggio Emilia from Sept. 12to 15, 2005. This biannual event has proved once more to be effectively internationalhosting more than 150 participants coming from 40 countries all over the world.It has been an honour for me and the whole Local Organizing Committee to organize forthe second time in its history this AMPERE meeting in Italy. AMPERE Europe sees in thistenth edition a memorable event not only from the scientific (more than 140 contributions)and technical (more than 10 sponsors and exhibitors) point of views, but also for the bigsuccess of gathering scientists from around the world in this pleasant region, EmiliaRomagna, where Modena stands out for its strong industrial environment.

2005 - REFRACTORIES CONTAINING INERTISED ASBESTOS AS RAW MATERIAL [Articolo su rivista]
Leonelli, Cristina; Boccaccini, Dino Norberto; Rivasi, Maria Rosa; Romagnoli, Marcello; Veronesi, Paolo; Pellacani, Gian Carlo; A. R., Boccaccini
abstract

It is well known that asbestos is a health hazard and its progressive elimination is a priority for pollution prevention. Asbestos can be transformed into non hazardous silicate phases by means of thermal treatments. This investigation describes the recycling of microwave inertised asbestos in refractory materials of both alumina-mullite and mullite-cordierite compositions. The increase of cordierite content found in samples containing inertised asbestos should lead to an improvement in thermal shock behaviour of the refractory materials. In the case of mullite-cordierite refractories, it was found that inertised asbestos can be used as raw material to replace the currently used MgO-rich talc. No significant variation of the Young’s modulus of samples made with inertised asbestos compared to the commercial based composition was found, indicating that inertised asbestos containing refractories should behave similarly to commercial refractory materials in terms of mechanical properties.

2005 - Simplification of several types of reactions with using of alternative energy forms [Relazione in Atti di Convegno]
Nuchter, M.; Ondruschka, B.; Schneider, F.; Grandi, R.; Leonelli, C.; Rosa, R.
abstract

2005 - Sintering of metal fibre reinforced glass matrix composites using microwave radiation [Articolo su rivista]
Ej, Minay; Ar, Boccaccini; Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina
abstract

The application of microwave radiation to sinter a chopped metal fibre reinforced glass matrix composite without the use of a susceptor material to preheat the powder compact has been demonstrated. The system considered was a soda borosilicate glass powder requiring a relatively low sintering temperature, mixed with 2 or 10 vol.-% Hastelloy X fibres. Single mode microwave heating was performed using radiation of 2.45 GHz in an applicator operating in the TE103 mode. Samples could be sintered in less than 5 min. Samples heated in the maximum of the electric field showed increased pore shrinkage in comparison with samples sintered in the maximum of the magnetic field. The present work demonstrates that metallic additions may be used to eliminate the requirement of a susceptor material (usually SiC) to heat powder glass samples in a short time to a temperature at which it would be able to couple with the microwaves in order for sintering to occur.

2005 - The anorthite-diopside system: Structural and devitrification study. Part II: Crystallinity analysis by the Rietveld-RIR method [Articolo su rivista]
Barbieri, Luisa; Bondioli, Federica; Lancellotti, Isabella; Leonelli, Cristina; Montorsi, Monia; Ferrari, Anna Maria; Miselli, Paola
abstract

Abstract:The crystallization behavior of 10 binary glasses belonging to the CaO–MgO–Al2O3–SiO2 quaternary system and two glasses corresponding to anorthite and diopside composition was investigated by X-ray diffraction, thermal, and thermomechanical analyses, and scanning electron microscopy. Particular emphasis is laid on the quantitative X-ray diffraction analysis by the Rietveld–reference intensity ratio combined procedure, which seems to be a useful tool to obtain time–temperature–transformation diagrams. Results showed that to obtain glass–ceramics with a significant crystalline phase presence, it is necessary to treat samples at 1000°C for 4 h or at 1100°C for 1 h.

2005 - Thermal shock resistance of cordierite-mullite refractory composites [Relazione in Atti di Convegno]
Zden, ; K., Chlup; Ivo, Dlouhy; A. R., Boccaccini; Boccaccini, Dino Norberto; Leonelli, Cristina; Romagnoli, Marcello
abstract

The design of composite materials leads to the development of multi-component systems where each constituent has a specific function in the material, from technological and/or application points of view. Examples of such composite systems are the cordierite-mullite refractory materials investigated in this contribution. Two different commercially available compositions were selected for evaluation of the influence of microstructure on fracture behaviour under thermal shock conditions. The materials were exposed to water-quench tests from 1250 degrees C and subsequently the fracture toughness was evaluated using the chevron notched specimen technique. The results were compared to those obtained on as-received materials. Microstructural damage was also studied applying fractographic techniques with the aim to gain knowledge on the thermal shock damage mechanisms acting in the materials.

2004 - Chapter 13. Microwave-Driven Hydrothermal Synthesis of Oxide Nanopowders for Applications in Optoelectronics [Capitolo/Saggio]
W., Lojkowsky; A., Opalinska; T., Strachowski; A., Prez; S., Gierlotka; E., Grzanka; B., Palosz; W., Strek; D., Hreniak; L., Grigorjeva; D., Millers; F., Bondioli; Leonelli, Cristina; E., Reszke
abstract

The microwave driven hydrothermal synthesis permits to precisely control the reaction times for this and thus also the grain size of the resulting nanocrystalline powders. An increase of pressure leads to powders with less hydroxide groups comparing to low temperature/pressure synthesis routes. Thus the combination of the two techniques permits to best exploit their advantages: high temperature of the process and fast heating and cooling, in high purity conditions. On the example of ZrO2 doped with Pr it is seen that the luminescence centers in nanocrystalline powders may have a different structure than for bulk materials. Pr3+ ions which would not be stable in a bulk material, are stable on the surface of the powder particles, and influence both their growth rate and luminescence properties. Interaction of the excited states with surfaces leads to very short luminescence decay rates, in the range of 10 nm, which in addition can be controlled by varying the grain size. This opens perspectives for new scintillating materials with short and controlled relaxation times. The nano-powders can be sintered using high pressure techniques and the grain size an be preserved in the nanometer range. The sintered YAG:Nd ceramics displays similar luminescence spectra as single crystals.

2004 - Characterisation of CaO-ZrO2-SiO2 glasses by MAS-NMR and molecular dynamics [Articolo su rivista]
Barbieri, Luisa; Cannillo, Valeria; Leonelli, Cristina; Montorsi, Monia; Siligardi, Cristina; P., Mustarelli
abstract

In this work a wide series of compositions, belonging to the CZS ternary system, are analysed. The linear expansion coefficient of the glass materials is experimentally determined and the results are interpreted by comparison with the structural information derived by molecular dynamics simulations and by Si-29-MAS-NMR. The analysis of the alpha values indicate that, while the ZrO2 acts as network former in these glasses, CaO shows network modifier behaviour producing a decrease of the network complexity. The characterisation of the short and intermediate range structure, obtained by the MD and Si-29-MAS-NMR analysis, allows one to define the relationships between the structure modifications induced by the different oxides, and the physical properties of the glasses experimentally observed.

2004 - Control of pore size by metallic fibres in glass matrix composite foams produced by microwave heating [Articolo su rivista]
Ej, Minay; Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina; Ar, Boccaccini
abstract

The application of microwave radiation as the heating source for the fabrication of glass foams reinforced with metallic fibres has been investigated. A soda-borosilicate glass powder was chosen for the matrix. The metal fibres were Hastelloy X fibres in volume concentration of 0, 2 and 10%. The fibre diameter was 8 pm and length was 100 mum. The microwave heating process was carried out in a self constructed over-moded microwave applicator operating at the 2.45 GHz ISM frequency. The glass foamed during processing leading to greater than 50 vol.% of spherical pores. The samples were characterised in terms of pore size and distribution, density, metal fibre distribution and interface characteristics. Adding stainless steel fibres to the glass composite prevented the glass from fracturing during processing and resulted in a more even distribution of finer pores. It is proposed that porosity formed during microwave heating as a consequence of localised glass matrix overheating in correspondence with the presence of metal fibres, caused by the preferential microwave absorption exhibited by the Hastelloy X fibres themselves and by the micro-regions of the matrix heated well above the glass softening temperature.

2004 - Crystallization, microstructure and expansivity of spodumenenepheline glasses [Articolo su rivista]
Hamzawy, Ema; Leonelli, Cristina
abstract

The crystallization of some glasses within the binary spodumene(LiAlSi2O6)-nepheline(NaAlSiO4) system with and without TiO2 has been investigated using X-ray diffraction analysis, scanning electron microscopy and coefficient of thermal expansion (CTE) measurements. The crystalline phases developed were beta-spodumene, beta-eucryptite, LAS(Li(2)Al(2)Si(2)Og), nepheline, carnegieite, quartz and cristobalite. Crystallization of TiO2-free glasses was relatively dependent on the nominal ratio and the heat treatments as well, however, the lithium aluminosilicate phases were usually dominant. TiO2 catalyzed the aluminosilicate phases and precluded the crystallization of silica phases. Inversion of nepheline into carnegieite took place at higher temperatures in TiO2-free samples, however, carnegieite was also developed in small amounts in TiO2 containing samples. On the other hand, the beta-eucryptite resisted the entire inversion into beta-spodumene even at higher temperatures (up to 1100 degreesC). Glass-ceramics of heterogeneous microstructures were obtained. The CTE values of the glasses investigated decrease from 101 to 86 (.) 10(-7) K-1 (20 to 500 degreesC) with increase in the Li2O/Na2O ratio, and those of the corresponding glass-ceramics decrease from 96 to -24 (.) 10-7 K-1 (20 to 500 degreesC) with increase in the crystallization of beta-eucryptite and/or beta-spodumene.

2004 - Esperienze preliminari di fusione di metalli mediante MWaH, riscaldamento a microonde [Articolo su rivista]
Veronesi, Paolo; Poli, Giorgio; Leonelli, Cristina
abstract

A new microwave single-mode applicator was designed,modelled and developed, operating at the ISM frequencyof 2.45 GHz . Using a microwave power of300W, it was possible to melt in a crucible 30-50g of metalmicrospheres, made of commercial Cu and belonging to theP-CuZn20 alloy (P-OT80 brass). The complete melting ofthe load took place in times variable from 30 to 120 s, dependingon the load mass, without preliminary heating.The visual analysis of some of the obtained samples evidencesthe still existing experimental uncertainties, leading tooverheating or non complete melting of the load. The microstructure in the proximity of the surfacein contact with the crucible presented some evidencesof chemical interaction between the melt and the crucible itself,made of SiC.

2004 - Experimental and computer simulation study of glasses belonging to diopside-anorthite system [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Lancellotti, Isabella; Leonelli, Cristina; Montorsi, Monia
abstract

The glasses belonging to the CaO-MgO-Al2O3-SiO2 quaternary system are materials largely used in industrial applications by virtue of their melting and devitrifible properties. A systematic study of several compositions falling in the anorthite (CaO-Al(2)O(3)2SiO(2))-diopside (CaO-MgO-2SiO(2)) system has been carried out by means of thermal and physical measurements in order to obtain the relationships between the structure and the properties of the glasses. The experimental evidence has been compared to molecular dynamic simulation results. Attention has been devoted to the definition of the structural role in the glass formulation played by Al3+ and Mg2+ which can behave as network formers or modifiers depending on their coordination number in the structure.

2004 - Glass matrix composites with lead zirconate titanate particles processed by microwave heating [Relazione in Atti di Convegno]
Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina; E. J., Minay; A. R., Boccaccini
abstract

The possibility of toughening glass and ceramics by addition of a piezoelectric particulate secondary phase is the focus of current research. It is hypothesised that stress concentrations at the tip of an advancing crack can re-orient piezoelectric domains within the reinforcement in the direction of the stress field around the crack, thus dissipating energy which contribute to fracture toughness increment of the composite. Previous work has focussed on producing glass/piezoelectric inclusion composites by conventional sintering. This process is accompanied by extended porosity formation, as well as Pb depletion in the PZT phase. In several cases, the long processing times required to fully sinter the glass matrix lead to glass-PZT reactions and to loosing the stoichiometry of the PZT inclusions. In this study, the novel production of new glass matrix composites reinforced with piezoelectric inclusions by using microwave heating was investigated. Specifically, lead-zirconate-titanate (PZT) particles in lead silicate and borosilicate glass matrices were considered. Mixtures of glass and PZT powders were prepared and used to fabricate powder compacts by uniaxial cold-pressing. In order to achieve densification, the compacts were subsequently heated in a single mode applicator, connected to a generator operating at the 2.45 GHz ISM frequency. T

2004 - In vitro evaluation of zirconia nanopowders [Capitolo/Saggio]
S., Braccini; Leonelli, Cristina; Lusvardi, Gigliola; Malavasi, Gianluca; Menabue, Ledi
abstract

ZrO2 is used for a long time as biomaterial. Nanopowders of ZrO2 are prepared via a microwave assisted hydrothermal synthesis and morphological studies carried out by TEM. The powders are tested in vitro and this test does not alter the dimension of the particles.

2004 - Microwave assisted burn-out of organic compounds in ceramic systems [Relazione in Atti di Convegno]
Leonelli, Cristina; Pellacani, Gian Carlo; Siligardi, Cristina; Veronesi, Paolo
abstract

Ceramic materials containing organic compounds, as a result of a manufacturing process or coming from an unwanted pollution, can be efficiently beat-treated using microwaves rapid, volumetric and selective heating. Electromagnetic field modelling of microwave-matter interactions inside the microwave applicator helped choosing the best experimental conditions, leading to fast cycles and to the maximisation of energy transfer from the microwave source to the load. The debinding process of Al2O3, ZrO2 and TiO2 components and the complete recovery of Al2O3 millimetric spheres has been performed by microwave heating, allowing a drastic manufacturing time reduction. Microwaves, proved to be a powerful tool to speed up the hear treatment of the aforementioned ceramic systems containing significant percentages of organic compounds, which present a strong and preferential coupling to microwaves at low temperature.

2004 - Microwave processing of glass [Articolo su rivista]
Leonelli, Cristina; Siligardi, Cristina; Veronesi, Paolo
abstract

Microwaves at the ISM frequency of 2.45 GHz have been applied to heat the molten salt bath used for ion exchange. A commercial soda-lime silicate has been used in order to investigate the processing time and the exchange depth resulting from the microwave assisted treatment, compared to the conventional one. Provided the molten salt, having an high electrical conductivity, does not shield the glass sample from microwave exposure, there is evidence of an increased ion mobility under microwave irradiation. In particular, this is confirmed by the higher calculated diffusion coefficient and by the increased potassium concentration in the exchanged layers.

2004 - New flax yarn cross-linked with citric acid by thermal treatment or by microwave irradiation [Relazione in Atti di Convegno]
G., Gastaldi; E., Vismara; M., Comoli; G., Torri; Leonelli, Cristina; Veronesi, Paolo; G., Rondi; S., Maini
abstract

Industrial flax yarn can be successfully cross-linked with citric acid by thermal treatment or by microwave irradiation. Both the methods were applied to an industrial yarn, exactly as it is produced and commercialized. Treatments were run on 100-200 g of yarn spinned on polypropylene cones, i.e. common industrial textile supports. The proposed cross-linking of flax cellulose with citric acid affords a new cross-linked flax yarn, ready to produce new materials of industrial applications, in relationship to the introduced cross-linkage. The new yarn maintains the morphology of the fiber and the textile potentiality of the flax itself and moreover it can be further modified, due to the presence of the citric acid functional group. The bond between cellulose and citric acid is an ester bond, of general interest for polysaccharides. Nevertheless, this bond is critical for the textiles, as it can be broken by high temperature and hydrolyzed in basic media, typical of washing operations. In this context, esterification with polycarboxylic acids like citric acid was found to afford cross-linked cellulose more resistant to heating and basic media.

2004 - Porous glasses with controlled porosity: Processing and modelling of mechanical properties [Relazione in Atti di Convegno]
A. R., BOCCACCINI; CANNILLO, Valeria; LEONELLI, Cristina; VERONESI, Paolo
abstract

Porous glass specimens containing designed spheroidal porosity are used as model materials to test the prediction capability of theoretical and numerical approaches for the Young's modulus of porous materials. In particular, a finite element model called OOF, which converts a real microstructural image into a 2-D finite element mesh, has been adopted in order to assess the effect of porosity and pore structure on the Young's modulus.

2004 - Processing of novel glass matrix composites by microwave heating [Articolo su rivista]
Ej, Minay; Ar, Boccaccini; Veronesi, Paolo; Cannillo, Valeria; Leonelli, Cristina
abstract

The application of microwave radiation as the heating source for the processing of glass matrix composites containing metallic particles has been investigated. A borosilicate glass powder was chosen for the matrix. The metal inclusions investigated were molybdenum, tungsten, aluminium. titanium. nickel and iron particles in volume concentration of 10%. The average particle size of primary metallic particles varied between 2 and 50 mum. The microwave heating process was carried out in a self-constructed multimode microwave applicator operating at the 2.45 GHz ISM frequency. For comparison, samples were also made by conventional powder technology and sintering. The microwave- and conventionally-processed samples were characterised in terms of: particle distribution, density and glass/metal particle interfacial characteristics. The microwave-processed samples had densities up to 96% of that of the conventionally-processed samples and were obtained in significantly shorter times (7 min versus similar to7 h). In case of glass/Mo composites, a recently developed computational model based on the OOF finite element code was used in order to calculate the residual thermal stresses in the samples.

2004 - Reactivity of tosylhydrazones under microwave irradiation in solvent-free environment [Articolo su rivista]
Grandi, Romano; Corradi, Anna; Leonelli, Cristina; Siligardi, Cristina; Veronesi, Paolo
abstract

The results of the interaction of microwave irradiation (multimode, 2.45 GHz, 100-600 W power) on tosylhydrazones, T.I., interesting intermediates in many organic reactions, were presented. T.I. were supported on silica, silica gel and alumina powders. Different inorganic salts (K2CO3,Fe(NO3)(3).9H(2)O) were added to the reaction mixture. The results obtained, starting from a range of different T.I., were investigated by means of mass spectrometry and (HNMR)-H-1 in order to understand the role of microwave irradiation and presence of inorganic additives on the reaction pathway and yields.

2004 - The electromagnetic field modelling as a tool in the microwave heating feasibility studies [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; Rivasi, Maria Rosa; Pellacani, Gian Carlo
abstract

The electromagnetic field modeling of a loaded microwaveapplicator can help in choosing the proper conditions tosuccessfully organize feasibility studies, allowing savings oftime and money, which are usually wasted during “blindfold”tests. As a matter of fact, when microwave heating of materialsis performed, the pronounced nonhomogeneity of the fielddistribution in multi-mode applicators can produce contradictoryexperimental results, leading to erroneous conclusions regardingthe main variables controlling the process. This is particularlytrue considering the microwave heat treatment of low thermalconductivity materials. Two different applications in the ceramicfield, comparing the results of “blindfold” and modeling-aidedexperimental conditions, are presented: de-binding of technicalceramics and asbestos inertization and/or vitrification. Thanksto a better knowledge of the electromagnetic field in theapplicators, it has been possible to succeed in applicationsthat, at a first glance, did not seem promising at all.

2004 - “Fusione assistita da microonde di materiali metallici” [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Poli, Giorgio
abstract

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2004 - “Microwave assisted sintering of electrical discharge wire cutting scraps” [Relazione in Atti di Convegno]
Leonelli, Cristina; Poli, Giorgio; Veronesi, Paolo
abstract

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2003 - Comparison of various solvent media efficiency in the grinding of a frit containing zirconium oxide [Articolo su rivista]
Andreola, Nora Maria; Mc, D'Arrigo; Leonelli, Cristina; Siligardi, Cristina; Pellacani, Gian Carlo
abstract

In the present work thermal and chemical properties of a glass-ceramic frit containing zirconium oxide are evaluated after milling in various polar and nonpolar solvents. Particle-size distribution is one of the main variables investigated to evaluate the efficiency of several solvents. Milling in various solvents does not affect the thermal properties of the glass while the presence of polar groups in the solvent molecule increases the cation release from the glass.

2003 - Computational simulations for the assessment of the mechanical properties of glass with controlled porosity [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina; Manfredini, Tiziano; Montorsi, Monia; Ar, Boccaccini
abstract

Porous glass with closed controlled porosity is used as a model system in order to numerically assess the effect of pores on the macroscopic mechanical and fracture behavior of brittle solids. A computational code called OOF, which converts digitalized two-dimensional (2-D) images of materials microstructures into finite element meshes, is adopted, so that the effect of 2-D microstructural features (e. g. pore size and shape) on the global mechanical response of the material can be determined. Firstly, microstructures of porous glass bodies containing isolated pores were considered. These specimens were numerically investigated in terms of fracture initiation and propagation: the numerical model predicted that larger pores initiate fracture, in agreement with experimental results. Then, the effect of porosity on the elastic and fracture properties was thoroughly investigated by means of model two-dimensional microstructures consisting of selected area fractions of pores (equivalent to pore volume fractions in three dimensions) and with prescribed pore shape, orientation and dimensions. In particular, the effect of pore dimension and shape was studied, finding that the critical stress for crack initiation scales with pore dimension and aspect ratio, i.e. oblate and larger pores oriented perpendicularly to the stress direction cause a higher reduction of strength of the specimen. Finally, several 2-D microstructures characterized by different values of area fraction of pores of the same shape were investigated, in order to determine the variation of elastic properties and the fracture response of porous glasses with pore content. The study confirms the suitability of the 2-D OOF code to investigate the mechanical and fracture behavior of porous materials. Issues regarding the limitation of the model due to its 2-D character are also discussed where appropriate.

2003 - Effect of V2O5 addition on the crystallisation of glasses belonging to the CaO-ZrO2-SiO2 system [Articolo su rivista]
Ferrari, Anna Maria; Leonelli, Cristina; Pellacani, Gian Carlo; Siligardi, Cristina
abstract

The crystallisation of CaO-ZrO2-SiO2 glasses doped with V2O5 (0.1-5 mol%) has been investigated in terms of microstructure and thermal parameters. Results indicate that crystallisation is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 2 mol% of doping oxide. As detected from differential thermal analysis curves, glass transition temperature and crystallisation temperature, are strongly dependent upon V2O5 content varying from 0.0 to 2.0 mol%, while the crystallisation activation energy values decrease with a parabolic trend from B-glass (0.0 mol% V2O5 content, 495 +/- 7) to V-0.7 (0.7 mol% V2O5 content, 420 +/- 6) composition, increasing again to 442 +/- 5 kJ/mol K with higher amount of V2O5. The microstructure of the glass-ceramic materials clearly showed a marked dependence upon the amount of V2O5, also due to the presence of phase separation for content higher than 0.7 mol%. Wollastonite, CaO . SiO2 and a calcia-zirconia-silicate, 2CaO . 4SiO(2) . ZrO2, are the main crystalline phases whose ratio slightly varies with vanadium oxide content. The glass ceramics obtained from the studied materials are greenish and bluish coloured, so it is possible to use the studied glasses as coloured frits for tile glazes. (C) 2003 Elsevier Science B.V. All rights reserved.

2003 - Experimental and MD simulations study of CaO-ZrO2-SiO2 glasses [Articolo su rivista]
Barbieri, Luisa; Cannillo, Valeria; Leonelli, Cristina; Montorsi, Monia; P., Mustarelli; Siligardi, Cristina
abstract

Glasses belonging to the CaO-ZrO2-SiO2 ternary system were prepared by melting raw materials at 1600°C. Several properties of the glassy materials, such as density and thermal behavior, were experimentallydetermined, and the results were interpreted by comparison with the structural information derived frommolecular dynamics simulations and from 29Si-MAS NMR. A detailed analysis of the short- and intermediaterangestructure was performed to define the role played by the different atoms present in the glass formulationand to correlate the structural modifications to the macroscopic properties of this class of glasses.

2003 - In vitro bioactivity testing of ZrO2 nanopowders prepared by MW-assisted hydrothermal synthesis [Capitolo/Saggio]
Bondioli, Federica; Braccini, Silvia; Leonelli, Cristina; Pellacani, Gian Carlo; Lusvardi, Gigliola; Malavasi, Gianluca
abstract

Zirconia nanopowders obtaneid by hydrothermal synthesis were tested in vitro at 60°C for 30 days.Elemental analysis,XRD,SEM,TEM techniques were used for this study.Crystallinity and phase identification was performed before and after in vitro test

2003 - Microwave assisted drying of water-based paints for wood [Abstract in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; G., De Marchi; U., De Marchi
abstract

A pilot plant for the microwave assisted drying of water-based paints for wood was designed, based on modelling results, and built. By choosing the proper combination of hot air and microwave power, it was possible to dry paints in times of an order of magnitude shorter than conventional drying. The microwave assisted drying is able to express its capabilities at its maximum when operating on UV-paints deposited at the highest surface density, while the strong interaction between microwaves and the glue used to produce plywoods may represent a limit of the proposed system

2003 - Microwave assisted sintering of SLS green metal parts [Relazione in Atti di Convegno]
Veronesi, Paolo; Leonelli, Cristina; Bassoli, Elena; Gatto, Andrea; L., Iuliano
abstract

Microwave assisted post-treatment of selective laser sintered green metal parts proved to be a new, fast and efficient way to densify complex-shaped elements, suitable for near-net-shape and net-shape manufacturing. Electromagnetic field modelling on pressed samples of RapidSteel 2.0 helped in choosing the proper experimental set up, using either single mode or overmoded microwave applicators operating at 2.45 GHz ISM frequency. LaserForm SLS green parts were exposed to high intensity microwave fields, using different lining configurations. Samples were characterized in terms of densification behaviour and microstructure: SEM observation of fracture and lapped surfaces allowed to analyse failure mechanisms and sintering degree.

2003 - Microwave-hydrothermal synthesis of nanocrystalline Pr-doped zirconia powders at pressures up to 8 MPa [Articolo su rivista]
F., Bondioli; Ferrari, Anna Maria; S., Braccini; Leonelli, Cristina; Gc, Pellacani; A., Opalinska; T., Chudoba; E., Grzanka; B., Palosz; W., Lojkowski
abstract

Nanocrystalline praseodymium doped zirconia powders were produced using a microwave driven hydrothermal process under pressures up to 8 GPa. The aim of the work was to evaluate the effect of synthesis conditions on the phase composition and grain size of nanopowders of zirconia with Pr in solid solutions having Pr contents of: 0, 0.5, 1, 5 and 10 mol %.

2003 - Morphological characterization of poly(phenylacetylene) nanospheres prepared by homogeneous and heterogeneous catalysis [Articolo su rivista]
P., Mastrorilli; C. F., Nobile; G. P., Suranna; Corradi, Anna; Leonelli, Cristina; Veronesi, Paolo
abstract

Scanning electron microscopy characterization of the materials obtained by homogeneous and heterogeneous catalytic polymerization of phenylacetylene is described. The catalysts used are beta-dioxygenato rhodium(I) complexes. The effects of the reaction medium, presence of a cocatalyst and the type of catalysis (homogeneous or heterogeneous) on the morphology of the polymers obtained have been studied and discussed. Using a supported complex at 0 degreesC, nanoparticles with a diameter distribution as narrow as 30 to 70 nm were obtained. Polymer nanopowders were found to be unaffected by ageing. Copyright

2003 - Numerical modelling of the fracture behaviour of a glass matrix composite reinforced with alumina platelets [Articolo su rivista]
Cannillo, Valeria; Pellacani, Gian Carlo; Leonelli, Cristina; Ar, Boccaccini
abstract

In this work the fracture behaviour of a composite material constituted by a borosilicate glass matrix reinforced with Al2O3 platelets is studied by means of a numerical model. This material, which was experimentally investigated in a previous paper, is characterised by the presence of thermal residual stresses that arise upon cooling from the processing temperature due to the thermal expansion coefficients mismatch between the matrix and the reinforcements. A numerical model based on finite element simulations of realistic composite microstructures was adopted for the present material. The crack propagation was studied using finite elements coupled with selected failure criteria (Griffith and Weibull approaches) implemented inside the elements. Computational determination of crack propagation during failure is compared with previously obtained experimental data and microscopy images of platelet-crack interactions, showing that the model provides results in good agreement with the experimental observations. (C) 2002 Elsevier Science Ltd. All rights reserved.

2003 - Substitution of boron for silicon in K-fluor-richterite glass ceramics [Articolo su rivista]
Hamzawy, Ema; Leonelli, Cristina; Pellacani, Gian Carlo
abstract

Substitution of B3+ for Si4+ in the K-fluor-richterite KNaCaMg5Si8O22F2 structure is presented through study of the crystallisation behaviour of glasses containing up to 36-55 wt% B2O3 (B/Si=4.00 at%) upon different heat treatment regimes. Gradual additions of boron lower the melting temperatures and strong v affect nucleation and crystallisation temperatures. The effect of boron replacement on the type of crystallising phases was manifested by DTA, XRD and EDAX. A single K-fluor-richterite fluor phase resulted in crystallisation of glasses with 17.34 wt% B2O3 (B/Si=0.80 at%). For greater boron contents (>4B per formula unit), borate mineral phase crystallised, namely suanite Mg2B2O5 in addition to fluorite CaF2 and fluorphlogopite KMg2.5Si4O10F2. In the case of maximum substitution (8B per formula unit, i.e. B/Si=4.00 at%) suanite becomes the main phase, K-fluor-richterite disappears, with fluorphlogopite in addition to fluorite. Incorporation of boron in the crystalline K-fluor-richterite changes the unit cell parameters. In comparison with the pre-reported unit cell constant of B free K-fluor-richterite relative decrease in the a, b and c axes with increase the P angle are detected in B containing K-fluor-richterite. A gradual increase in crystal growth rate takes place in the monoclinic K-fluor-richterite phase with increasing boron content. The boron rich sample shows microstructures of interlocked fluormica flakes.

2003 - Synthesis and characterization of cerium-doped glasses and in vitro evaluation of bioactivity [Articolo su rivista]
Leonelli, Cristina; Lusvardi, Gigliola; Malavasi, Gianluca; Menabue, Ledi; Tonelli, M.
abstract

The results of preparation, characterization and in vitro bioactivity evaluation of phosphosilicate glasses based on Bioglass(R) 45S5 (SiO2 45; Na2O 24.5; CaO 24.5; P2O5 6 wt%) doped during melting with (1.5-13.5 wt%) cerium dioxide (CeO2), has been reported. The choice of cerium was related to its low toxicity associated with bacteriostatic properties; cerium-doped bioactive glasses could be useful when implantation concerns local infected areas. The maximum value that permitted forming a homogeneous glass was 13.5 wt% and enabled us to get a better insight into CeO2 effect on the chemical behaviour of glasses. The as-quenched glasses were characterized by means of magnetic and spectroscopic measurements that revealed the prevailing presence of cerium (III). The bioactivity of the glasses was tested by soaking them in a simulated body fluid at 37 degreesC, under continuous stirring. ICP measurements were carried out for ion concentration determinations and the solution/glass interface was investigated by scanning electron microscopy equipped with energy dispersive analyzer (SEM/EDS technique) to check morphological modifications; the solids were investigated by means of X-ray powder diffraction and IR techniques. The results indicated that at low cerium content the glass degradation and repolymerization gave rise to an internal silicon-based layer and an external calcium-phosphate-based layer formed on the glass surface; high cerium content retards the glass degradation and gave rise to ceriumphosphate layer instead of calcium one. The cerium was never found in solution. For the reacted glasses, in the external layer, at 10% and 13.5% CeO2 contents the molar ratio Ca/P were approximate to1 and 0.8 respectively and the molar ratio Ce/P was approximate to0.3 in both cases. On the surface of the glasses with the highest cerium content it could distinguish new regular aggregates mainly formed by cerium and phosphate (Ce/Papproximate to3.5, Ca/Papproximate to0.6). In the cerium-free glass and with low cerium content (1.5 wt%) the calculated Ca/P ratio was 1.67, as calculated for pure hydroxyapatite. At low cerium content (BG-1.5 Cc) the glass behaviour was strictly similar to that of Bioglass(R) 45S5. (C) 2003 Elsevier Science B.V. All rights reserved.

2003 - The effect of ZrO2 in 30K2O-70SiO2 glass: a comparison with 30Li2O-70SiO2 [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Lancellotti, Isabella; Leonelli, Cristina; Siligardi, Cristina
abstract

The influence of the introduction of ZrO2 in concentrations of up to 5 mol% into a 30K(2)O-70SiO(2) base glass composition has been investigated with the aid of differential thermal analysis (DTA), FT-IR spectroscopy, as well as chemical durability tests (pH, conductivity and AES-Inductively Coupled Plasma measurements) and refraction index determination. Several differences have been found by comparison with similar compositions belonging to the Li2OZrO2SiO2 system. The higher ionic radius and the lower field strength of K+ with respect to Li+ is responsible for higher stability towards crystallisation and lower chemical durability. Moreover, even though Zr4+ increases glass polymerisation (higher glass transition temperature, chemical durability and refraction index), the presence of high water content as highlighted by spectroscopy measurements, seems to weaken the glass structure.

2003 - The influence of microwave drying on properties of sol-gel synthetised V-Nb catalysts [Articolo su rivista]
M., Catauro; F., DE GAETANO; G., Lasorella; L., Lisi; G., Ruoppolo; Leonelli, Cristina; A., Marotta
abstract

The sol-gel bulk products requires an homogenous water/solvent evaporation to avoid fracture formation. Microwave heating has been ptoved to be an efficient heating process to remove solvent and solvet plus water content from a sol during the transition to gel. The heating treatment did not lead to degradation of the product which was a peculiar composition used in catalyses.

2003 - Unique microstructure of glass-metal composites obtained by microwave assisted heat-treatments [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; Pellacani, Gian Carlo; Ar, Boccaccini
abstract

The present study deals with the computer-aided simulation of the microwave heating of metal/glass composites in single mode applicator and the rapid densification of borosilicate glass matrix composites containing molybdenum particle inclusions. The selective and penetrating microwave heating led to a layered porous structure of the samples. They consisted of a highly porous core containing spherical pores and a relatively dense outer shell. Pores in the central region were formed in the molten glass phase due to gas evolution and entrapment. The outer region of the sample remained at lower temperature and it sintered by viscous flow with minimal distortion.

2002 - ADDITIVE PROPERTIES IN CAO-MGO-AL2O3-SIO2 GLASSES BELONGING TO DIOPSIDE-ANORTHITE PHASE DIAGRAM [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Lancellotti, Isabella; Leonelli, Cristina; Siligardi, Cristina
abstract

A systematic study of 10 glasses belonging to the system diopside-anorthite has been carried out. An interpretation of the structure of theese glasses has been sought by means of thermal, thermophysical and physical measurements.

2002 - CORRELATION BETWEEN STRUCTURE AND PROPERTIES IN NEW GLASSES CONTAINING ZrO2 [Articolo su rivista]
Lancellotti, Isabella; Leonelli, Cristina; Montorsi, Monia; Pellacani, Gian Carlo; Siligardi, Cristina; C., Meneghini
abstract

In this work several complementary techniques have been employed to carefully characterise the structure of CaO–ZrO2–SiO2 glasses as a function of Zr content. The research started from the basic binary system 40CaO.60SiO2 (wt%) to which 5, 10, 15 and 20 wt% ZrO2 has been added.Chemical and physical characterisation has been performed using classical techniques such as thermal analyses (differential thermal analysis and dilatometery) and water chemical resistance. Deeper insight on the intimate structure of the glasses has been achieved through molecular dynamics simulations and x-ray absorption spectroscopy. All results have been combined in order to accurately describe the role played by the different oxides in determining the properties of the glass. Particular carehas been devoted to the role of zirconia.

2002 - CaO-ZrO2-SiO2 glass-frit addition to porcelainized stoneware: enhancement of tiles colouring capabilities [Articolo su rivista]
Siligardi, Cristina; Veronesi, Paolo; Leonelli, Cristina; D., SETTEMBRE BLUNDO; G., Baldi; E., Generali
abstract

Porcelainized stoneware tiles have experienced many aesthetic improvements in the last few years, occasionally accompanied by some depletion of surface properties. The introduction of 5–10 mass-% of an easily devitrifiable glass frit leads to a significant increase in the white index of the ceramic body, simultaneously allowing a better exploitation of pastel hues colouring additives in bulk coloured porcelainized stoneware tiles. Optimum sintering temperature, densification, and water absorption of compositions with glass-frit addition are comparable to large-scale production porcelainized stoneware tiles. Moreover, when ceramic tiles are fired according to the typical industrial fast-firing cycle of 60 min up to 1200 °C, the flexural strength, indicated by the modulus of rupture measured values, benefits from glass-frit addition.

2002 - Evolution of macropores in a glass-ceramic under microwave and conventional sintering [Articolo su rivista]
Mc, D'Arrigo; Siligardi, Cristina; Leonelli, Cristina; Jy, So; Hs, Kim
abstract

Densification and microstructural evolution of a CaO-ZrO2-SiO2 glass powder were studied during heating in order to produce a glass-ceramic material. Microwave (2.45 GHz) and conventional heating were used for different soaking times and temperatures. Macropores, as visible from the last stage of glass sintering, were monitored as a function of temperature by SEM microscopy and image elaboration. The porosity as a results of micropores has proved to be negligible. Other important densification parameters, such as initial powder size distribution and green pellet density, which would have affected macropores evolution were kept constant. Microwave prepared samples have been compared to conventionally treated ones. The effect of microwaves was to speed up the sintering process, but did not affect the crystallization evolution of glass-ceramic materials differently when compared to the conventional sintering.

2002 - GLASS FORMATION AND DEVITRIFICATION IN THE K2O-ZRO2-SIO2 SYSTEM [Articolo su rivista]
Barbieri, Luisa; Lancellotti, Isabella; Leonelli, Cristina; Pellacani, Gian Carlo; Siligardi, Cristina
abstract

The influence of the introduction of ZrO2 up to 5 mol% into a 30K2O-70SiO2 base glass composition has been investigated with the aid of differential thermal analysis (DTA), FT-IR spectroscopy, as well as chemical durability tests (pH, conductivity and AES-Inductively Coupled Plasma measurements) and refraction index determination. Several differences have been carried out by comparison with similar compositions belonging to the Li2O-ZrO2-SiO2 system. The higher ionic radius and the lower field strength of K+ with respect to Li+ are responsible for higher stability towards crystallisation and lower chemical durability. Moreover, even though Zr4+ increases glass polymerisation (higher glass transition temperature, chemical durability and refraction index), the presence of high water content as highlighted by spectroscopy measurements, seams to weaken glass structure.

2002 - Glass formation and devitrification in the K2O-ZrO2-SiO2 system [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Lancellotti, Isabella; Leonelli, Cristina; Siligardi, Cristina; C., Tomasi; P., Mustarelli; Pellacani, Gian Carlo
abstract

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2002 - Importancia do Controle da velocidade de resfriamento na Obtencao de Vidrados Vitro-Cristalinos [Articolo su rivista]
Quinteiro, Eduardo; Boschi, Anselmo Ortega; Sanches Arantes, Flavio Josè; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina
abstract

Industrial compositons of glass-ceramics used for tile glazes have been investigated with reference to the cooling rate.

2002 - Microwave and conventional hydrothermal synthesis of zirconia doped powders [Abstract in Atti di Convegno]
Bondioli, Federica; Leonelli, Cristina; Siligardi, Cristina; Pellacani, Gian Carlo; S., Komarneni
abstract

Hydrothermal synthesis of powders is a very attractive process to directly prepare submicrometer- and nanometer-sized crystalline powders because of reduced contamination and low synthesis temperature. The application of microwave radiation during the process enhances the reaction kinetics by 1-2 orders of magnitude. Nanosized Pr-doped zirconium oxide powders were prepared by adding NaOH to a zirconyl chloride aqueous solution under microwave-hydrothermal conditions. The properties of the powders produced are compared with those of powders obtained by conventional hydrothermal synthesis

2002 - Microwave assisited sintering of powder mixtures of glass and tungsten particles [Articolo su rivista]
Veronesi, Paolo; Leonelli, Cristina; Pellacani, Gian Carlo; V., Fiumara; Aa, Barba; M., D'Amore
abstract

In this paper, the microwave assisted sintering behaviour of mixtures of glass microspheres and tungsten particles having a diameter in the range of the metal's skin depth at 2.45 GHz is investigated. The microstructure of the sintered samples is discussed as far as dielectric properties of the powders, heating rate and maximum sintering temperature are concerned.

2002 - Microwave technology applications in the synthesis of ceramic pigments [Relazione in Atti di Convegno]
Pellacani, Gian Carlo; Bondioli, Federica; Leonelli, Cristina; Siligardi, Cristina; Veronesi, Paolo; Manfredini, Tiziano
abstract

Long before chemists began altering this word, humans were interested in coloring their painting and their bodies as well as any objects they happened to make. Color is an economical way of creating new intereste in an existing product and is also the mosti immediately noticeable and least-expensive element in decoration. Thus, color is a primary tool in product development and marketing, especially in the ceramic tile industry, where product always becomes part of a general color scheme. This word resumes the experimental word done in the last few years by the CerMIC (Ceramic Investigation Center) at the University of Modena (Italy) regarding the application of the microwave technology to the synthesis of inorganic pigments. The choice has been done trying to reproduce in MW some of the most diffused and interesting crystalline structures capable of inducing coloration in ceramic tile body and coating, that is to say capable of thermal and chemical stability in the glazes or in the body at temperatures as high as 1250 degreesC for short period of times, (5-10 min), in order to evaluated the possible benefic effects of microwave heating treatments in this field.

2002 - Molecular Dynamics Study of Zirconia Containing Glasses [Articolo su rivista]
Montorsi, Monia; Menziani, Maria Cristina; Leonelli, Cristina; J., Du; A. N., Cormack
abstract

Molecular Dynamics Study of Zirconia Containing Glasses

2002 - Numerical models for thermal residual stresses in Al2O3 platelets/borosilicate glass matrix composites [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina; A. R., Boccaccini
abstract

In this paper, we model and numerically study thermal residual stresses in a borosilicate glass reinforced with Al2O3 platelets. This composite material was experimentally characterized in a previous work, The aim of this paper is to investigate further the thermal residual stresses in these composites that are responsible for toughening and to assess the variation or the thermal residual stresses with platelets content. A numerical model based on finite element simulations of the given microstructures is used. Computational tests are compared both with previously obtained experimental data and with simplified theoretical equations. The model provides consistent results which are in agreement with experimental measurements, Moreover. the numerical approach presented here is able to take into account the effect of particle shape on residual thermal stresses. which could not be computed easily by theoretical equations.

2002 - Porous molybdenum particle reinforced glass matrix composites fabricated by microwave processing [Relazione in Atti di Convegno]
Ar, Boccaccini; Veronesi, Paolo; Siligardi, Cristina; Leonelli, Cristina
abstract

Microwave-assisted densification was used to fabricate porous borosilicate glass matrix composites containing spherical porosity and molybdenum particle inclusions. The inverse thermal gradient typical of microwave heating and the presence of Mo particles led to the development of a layered porous structure of the compacts, consisting of a highly porous core and a relatively dense outer shell. Such a layered porosity was not obtained in glass compacts without Mo particles.

2002 - Preliminary experiments of in situ atomic force microscopy observation of hydroxyapatite formation on bioactive glass surface [Articolo su rivista]
Leonelli, Cristina; Lusvardi, Gigliola; Menabue, Ledi; Tonelli, Massimo
abstract

This paper demonstrates the use of atomic force microscopy (AFM) to image the bioactivity of phosphate glasses that are well-known to react rapidly in simulated body fluid. The present study demonstrates that the hydroxyapatite (HAP) crystalline layer found via AFM in the examined samples coincides with that identified using scanning electron microscopy. Moreover, the effect of a notorious bacteriostatic cation-tetravalent cerium, Ce(IV)-on the kinetics of the HAP layer is investigated in CeO2-doped bioactive glasses.

2002 - Vanadium doping in CaO-ZrO2-SiO2 glasses [Articolo su rivista]
Siligardi, Cristina; Ferrari, Anna Maria; Leonelli, Cristina; S., Bruni
abstract

Structural and colour changes induced by increasing amounts of vanadium oxide. V2O5, are presented for a near formulation of glass with composition 37CaO, 6ZrO(2), 57SiO(2) (mol%). Property changes were evaluated by measuring density, chemical durability and microhardness of glasses with increasing amount of vanadium oxide. Vanadium oxide imparts to tire glass a light green colour, not dissimilar to that from chromium, at low content, while at higher concentration the colour changes to dark brown. Spectroscopic technique, VIS-NIR and ESR were rued to identify tire chromophore centres in terms of vanadium oxidation state and coordination which there subsequently correlated to property changes. Experimental evidence is reported for an equilibrium between two species. V5+-tetrahedral and V4+ tetragonally distorted octahedral.

2001 - A simple approach for determining the in situ fracture toughness of ceramic platelets used in composite materials by numerical simulations [Articolo su rivista]
Cannillo, Valeria; Corradi, Anna; Leonelli, Cristina; Ar, Boccaccini
abstract

The present study is an example of thedetermination of an intrinsic value of fracture toughnessof embedded particles in a rigid matrix, by meansof a parametric study using the microstructural FEM code OOFand the validation by comparison with experimentalobservations.

2001 - Applicazioni del riscaldamento a microonde in campo ceramico III – Dispositivi [Articolo su rivista]
Veronesi, Paolo; M., Franchini; Leonelli, Cristina
abstract

During last decade industrial microwave application found many and new branches of interest,especially as far as rapid, volumetric and selective heating processes are concerned. This interest isdue to peculiar operating conditions which can not be achieved by conventional heating transfertechniques. However, at the moment industrial microwave heating is still pioneering, presentingfew and remunerative large scale plants surrounded by a constellation of pilot plants andlaboratory scale furnaces used to perform research and development studies.

2001 - Herstellung von glassmatrix-verbundwerkstoffen mit kontrollierter porositat durch mikrowellen erwarmung [Capitolo/Saggio]
Boccaccini, A. R.; Jana, C.; Veronesi, Paolo; Leonelli, Cristina
abstract

n.d.

2001 - Influence of small additions of Al2O3 on the properties of the Na2O center dot 3SiO(2) glass [Articolo su rivista]
Leonelli, Cristina; Lusvardi, Gigliola; Montorsi, Monia; Menziani, Maria Cristina; Menabue, Ledi; P., Mustarelli; L., Linati
abstract

Changes in the structural properties of sodium alumine-silicate glasses of general formula Na2O . xAl(2)O(3). (3-x)SiO2 were investigated as a function of Al2O3 concentration. The experimental evidences provided by density, elastic modulus, glass chemical resistance measures, Si-29 and Al-27 MAS NMR investigations were complemented by molecular dynamics simulations. While neither of the experimental techniques or computational investigation utilized in this study were able to furnish unequivocable responses for the rationalization of the measured properties of sodium alumine-silicate glasses, the synergistic application of experimental and computational techniques showed that the anomalies observed in bulk properties like density and elastic modulus find their origin in medium-range structural features.

2001 - La tecnologia a microonde applicata ai fanghi di levigatura del gres porcellanato [Articolo su rivista]
Siligardi, Cristina; Leonelli, Cristina; Veronesi, Paolo
abstract

The possibility of reusing the sludges derived from porcelain stoneware tiles polishing to produce ceramic products microwave thermal treatments is investigated. A 980 W, 2.45 GHz, multimode commercial microwave furnace with SiC susceptor was used in this study. This heating technique lead to develop of ceramic products as belonging to BIII class according to the EN 87.

2001 - Micromechanics principles applied to fracture propagation in porcelain stoneware tiles [Relazione in Atti di Convegno]
Leonelli, Cristina; F., Bondioli; Veronesi, Paolo; Cannillo, Valeria; Romagnoli, Marcello; Manfredini, Tiziano
abstract

The possibility of discussing the mech. properties of porcelain stoneware tiles with a scientific approach typically used in the investigation of the composite materials is studied. A thorough microstructural investigation was conducted to det. if the addn. of selected low-cost minerals would improve mech. properties. The minerals tested were quartz, mullite, and kyanite. Uniaxially pressed samples were submitted to the same industrial firing schedule and tested according to European tile stds. before further microstructural anal.

2001 - Microwave industrial applications in the ceramic field [Articolo su rivista]
Veronesi, Paolo; Siligardi, Cristina; M., Franchini; Leonelli, Cristina
abstract

The industrial applications of microwaves in the ceramics field are described. Microwaves greatly contribute to heat transfer in large formed shapes, speed up the entire manufacturing process, and offer the possibility of creating novel microstructures. Uses include the synthesis of ultrafine powders; drying; debinding; slip casting; sol-gel process; joining; sintering; CVD; and coating. It is shown that microwaves offer the possibility of very fast manufacturing cycles, lower production costs, decreased power consumption, obtaining new products or improving the quality of existing ones, and increasing the efficiency and productivity of processes. Most of the benefits of microwaves are derived, however, only after careful experimental laboratory work, and preliminary cost-benefit analysis is always uncertain due to the difficulties inherent in extrapolating to the industrial scale. The use of hybrid systems can help in this respect. The advantages of a well-designed microwave system are noted. 17 refs.

2001 - Microwave processing of glass matrix composites containing controlled isolated porosity [Articolo su rivista]
Ar, Boccaccini; Veronesi, Paolo; Leonelli, Cristina
abstract

Porous glass matrix composites containing well-defined spherical porosity were fabricated employing microwave-assisted densification of powder compacts. The inverse thermal gradient typical of microwave heating was used to obtain a high concentration of spherical pores in the central region of the sample and a relatively dense outer shell. Pores in the central region were formed in the molten glass phase exploiting gas evolution and entrapment. The outer region, being at a lower temperature, was sintered by viscous flow. Minimal distortion of the part occurred. The diameter of the pores showed a wide size distribution, i.e. between similar to5 and similar to 50 mum. In comparison to other methods described in the literature for the fabrication of hermetic porous materials, i.e. using hot-pressing, the present approach is advantageous due to high heating rates of microwave heating resulting in saving of time and energy. Moreover, parts of complex shape may be fabricated by this technique. (C) 2001 Elsevier Science Ltd. All rights reserved.

2001 - Microwave-hydrothermal synthesis of nanocrystalline zirconia powders [Articolo su rivista]
F., Bondioli; Ferrari, Anna Maria; Leonelli, Cristina; Siligardi, Cristina; Gc, Pellacani
abstract

Nanosized zirconium oxide (ZrO2) powders were prepared by adding NaOH to a zirconyl chloride aqueous solution under microwave-hydrothermal conditions. The obtained results showed that the tetragonal polymorph increased with increasing NaOH concentration in the starting solution and reached the maximum value by using 1M ZrOCl2. The microwave-assisted hydrothermal synthesis is expected to be able to process continuously, and may lead to energy savings because of rapid heating to temperature and increased kinetics of crystallization. This method is very simple and can lead to powders with desirable characteristics such as very fine size, narrow size distribution, and good chemical homogeneity.

2001 - Modeling and simulations at microscopical scale in materials science and engineering: a review [Articolo su rivista]
Cannillo, Valeria; Leonelli, Cristina
abstract

Review of the modeling and simulations techniques at microscopical scale in materials science and engineering

2001 - New tile glaze families based on glass ceramic systems [Articolo su rivista]
Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina
abstract

The paper reports the study of different glass ceramics system used into ceramic glazes.

2001 - Porcelain stoneware as a composite material: identification of strengthening and toughnening mechanisms [Articolo su rivista]
Leonelli, Cristina; Veronesi, Paolo; Cannillo, Valeria; Pellacani, Gian Carlo; A. R., Boccaccini
abstract

Porcelain stoneware is studied using the principles usually applied for composite materials

2001 - Synthesis of Oxide Pigment Powders by Microwave Treatments [Capitolo/Saggio]
Leonelli, Cristina; Bondioli, F.; Siligardi, Cristina; Veronesi, Paolo; Corradi, A.
abstract

n.d.

2001 - Synthesis of oxide pigments powders by microwave treatments [Relazione in Atti di Convegno]
Corradi, Anna; Leonelli, Cristina; Bondioli, Federica; Siligardi, Cristina; Veronesi, Paolo; Pellacani, Gian Carlo
abstract

In this paper the authors report the use of microwave technology to synthesize inorganic pigment to color traditional ceramic material

2001 - The application of microwaves in the synthesis of Ce0.9Pr0.1O2 nanostructured powders [Articolo su rivista]
Bondioli, Federica; Ferrari, Anna Maria; Leonelli, Cristina; Siligardi, Cristina; Hart, Neil A.; Evans, Nigel G.
abstract

In this work Ce0.9Pr0.1O2 powders were synthesised by the co-precipitation method starting from the solution of cation nitrates. The possible use of microwave technology in both drying and calcination steps was evaluated. XRD analysis, dielectric properties measurements, and colour characterisation were used in order to determine the microwave benefits.

2001 - “Applicazione di pigmenti fosfatici ottenuti mediante trattamento termico convenzionale e microonde” [Articolo su rivista]
Ferrari, Anna Maria; Bondioli, Federica; Leonelli, Cristina; Siligardi, Cristina
abstract

Alcuni fosfati metallici contenenti nichel, cobalto o rame sono stati sintetizzati calcinando sia per via convenzionale sia mediante trattamento a microonde, i relativi alchilfosfonati. le polveri dei pigmenti ottenuti sono state caratterizzate con diverse tecniche quali XRD, DTA, spettroscopie IR e UV-Vis con misure di colore. Particolare attenzone è stata rivolta all'applicabilità di questi composti nella colorazione di materiali ceramici.

2000 - Bulk crystallization of glasses belonging to the calcia-zirconia-silica system by microwave energy [Articolo su rivista]
Siligardi, Cristina; Mc, D'Arrigo; Leonelli, Cristina; Pellacani, Gian Carlo; Te, Cross
abstract

This paper reports results that show the effect of microwave absorption on the bulk crystallization of two glasses in the CaO-ZrO2SiO2 system. The glass samples were de vitrified using either microwave or conventional heating, to compare the results obtained from the two different techniques. Remarkably different crystallization paths were observed, depending mostly on the composition of the glass. This observation was especially true when microwave heating was used, where the dielectric losses observed in silicate glasses are related to the ZrO2 content. X-ray diffraction analysis was performed on the powdered samples, to determine the crystalline phases present. The microstructure and microanalysis results of these glass-ceramic compositions are presented and are related to the different ZrO2 contents.

2000 - CERAMIC OXIDE (MEO2) SOLID SOLUTIONS OBTAINED BY MECHANICAL ALLOYING [Capitolo/Saggio]
F., Bondioli; Veronesi, Paolo; Leonelli, Cristina
abstract

N.D.

2000 - Colour development during devitrification in Li2O-ZnO-Al2O3SiO2 glasses under conventional and microwave heating [Articolo su rivista]
Siligardi, Cristina; Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina; M., De Sanctis; A., Lazzeri
abstract

The paper examines the effects of a series of heat treatments on the appearance and microstructure of Li2O-ZnO-Al2O2-SiO2 glasses with varying ZnO/Li2O. The base glasses coloured yellowish, become violet at temperatures between 700-800 degrees C. The glass remains transparent and the obtained colour is stable during cooling. When heated at temperatures >800 degrees C the samples become opaque violet and finally opaque white at 900 degrees C. The effect of the heat treatment on the physical and chemical properties of these materials is explained on the basis of changes in composition and morphology of the residual amorphous and crystalline phases. Electron microscopic observations individuated an initial glass nucleation induced by phase separation, which occurs at lower temperatures, followed at intermediate temperatures by the crystallisation of beta-quartz (ss) which at higher temperatures converts to beta-spodumene as shown by x-ray diffraction and thermal analysis. Mie light scattering as a consequence of phase separation have been proved to be responsible for bulk glass colouring. Besides microwave irradiation effects on the crystalline phases evolution has been explained on the basis of ionic diffusion.

2000 - Crystallization of (Na2O-MgO)-CaO-Al2O3-SiO2 glassy systems formulated from waste products [Articolo su rivista]
Barbieri, Luisa; Ferrari, Anna Maria; Lancellotti, Isabella; Leonelli, Cristina; Rincon, J. M. A.; M., Romero
abstract

Aluminosilicate and silicate glass-ceramics were obtained from controlled devitrification of CaO-Al2O3-SiO2 glassy systems starting from Spanish and Italian coal fly ash or Italian municipal incinerator slag mixed with other byproducts, such as glass cullet and dolomite, The nucleation mechanism and the crystallization kinetics were investigated by thermal, diffractometric, and microstructural measurements. Moreover, the experimentally observed devitrification and the identification of the crystalline phases formed were compared with the indications derived from Ginsberg, Raschin-Tschetveritkov, and Lebedeva diagrams used for petrological glass-ceramics. All the glasses showed a good crystallization tendency with the formation of dendritic pyroxene and acicular wollastonite together with feldspar and iron spinels starting from the surface. The activation energy values for crystallization ranging from 472 to 832 kJ.mol(-1) were found to be close to those typical for aluminosilicate glasses; moreover, the possibility to vitrify and devitrify up to 100 wt% of slag and up to 40-50 wt% of ash mixed with glass cullet and dolomite makes the vitrification treatment a suitable disposal procedure.

2000 - Densification of glass powders belonging to the CaO-ZrO2-SiO2 system by microwave heating [Articolo su rivista]
Siligardi, Cristina; Leonelli, Cristina; F., Bondioli; Corradi, Anna; Pellacani, Gian Carlo
abstract

Densification and microstructural changes of two glassy compositions belonging to the wollastonite and zirconia stability fields in the ternary CaO-ZrO2-SiO2 system were studied in a 2.45 GHz multimode microwave cavity. The effect of microwaves is to lower the sintering and devitrification temperature with stronger influence for high zirconia content composition. Correlation was found between dielectric properties and heating rate, showing lower interaction temperature for high zirconia content composition which starts to absorb microwave energy at about 400 degrees C compared to 800 degrees C for the low-zirconia one. Sintering and crystallization processes evolved in complex ways during heat treatment so that the two final glass-ceramic materials exhibit different microstructures, crystalline phases and mechanical properties. (C) 2000 Elsevier Science Ltd. All rights reserved.

2000 - Effect of silicon carbide whisker reinforcement on the CaO-ZrO2-SiO2 glass-ceramic system [Articolo su rivista]
Barbieri, Luisa; M. C., D’Arrigo; Leonelli, Cristina; Siligardi, Cristina; Pellacani, Gian Carlo; C. C., Sorrell; M., Hoffman; S., Moricca
abstract

An industrial frit formulated in the new CaO-ZrO2--SiO2 glass-ceramic system was studied as a matrix for whisker reinforced composites. The frit was ball milled in acetone and wt ultrasonically mixed with 5, 10, 20 and 30 vol.-% SiC whiskers in order to overcome whisker agglomeration and obtain intimate mixing of the two phases. The samples were hot pressed at 14 MPa in graphite dies, using a N-2 atmosphere, for 2 h at 1280 degreesC. In order to investigate the effect of whiskers as a reinforcement, flexural strength as well as crack configuration and propagation were taken into consideration. Whisker orientation perpendicular to the hot pressing direction was found by SEM observation, and no carbon layer at the whisker/matrix interface was detected by EPMA. Further characterisation of the specimens involved physical (density, elastic modulus) and microstructural properties (XRD, SEM, TEM). The result of glass devitrification was inter-locked wollastonite crystals. BCT/436.

2000 - I materiali vetroceramici: struttura, proprietà ed applicazioni. Parte II: aspetti applicativi [Articolo su rivista]
Manfredini, Tiziano; Leonelli, Cristina
abstract

L'articolo riporta le principali proprietà e le applicazioni dei materiali vetroceramici

2000 - Microwave technology applied to the recycling of fine stoneware tiles polishing sludge compared to conventional firing [Articolo su rivista]
Andreola, Nora Maria; Leonelli, Cristina; Siligardi, Cristina; C., Leonelli; Corradi, Anna
abstract

Microwave technology was a useful heating process when applied to the recycling of fine stoneware tiles polishing sludge. The manufact processed were characterized by low porosity, much lower than that registered for the same formulation heated with conventional firing.The different microstructure has been explained by considering the selective heating phenomenon generated by microwave irradiation: the SiC particles could heat much faster that the aluminosilicate matrix so that to melt the surroundings with a sort of encapsulation process.Conventional heating lead to SiC reaction with oxygen promoting its conversion in CO2 thus creating large pores.

2000 - Molecular dynamics simulations of alumina addition in sodium silicate glasses [Articolo su rivista]
Montorsi, Monia; Menziani, Maria Cristina; Leonelli, Cristina; Pellacani, Gian Carlo; A. N., Cormack
abstract

Molecular dynamics simulations of alumina containing silicate glasses have been performed in order to determine the influence of that ion on the final properties of the glasses. In particular, short- and mid-range structures were analyzed in terms of the distribution of non bridging oxygen, bridging oxygen, three bridging oxygen species in the glasses, along with the coordination number distribution (cn) and qn species distribution. The results support the hypothesis that the observed changes in the property of the glasses could be directly related to the coordination preferences of the Al ion.

2000 - Non-conventional synthesis of praeseodymiun-doped ceria by flux method [Articolo su rivista]
Bondioli, Federica; Corradi, Anna; Manfredini, Tiziano; Leonelli, Cristina; R., Bertoncello
abstract

The synthesis of Ce1-xPrxO2 solid solutions by three different methods (flux method, coprecipitation, and solid-state reactivity) has been investigated to establish optimal preparation conditions. The system studied was chosen because of its thermal and chemical properties and because of its utility as red and orange ceramic pigments. The results obtained showed that the Ce1-xPrxO2 solid solution can be achieved using all three preparation techniques. The three synthesis methodssflux, coprecipitation, and solid-state reactions vary with regard to both the time and temperature used in the heat treatments, and the characteristics of the powders obtained (purity, morphology, granularity). In the preparation of powders by the flux method, the use of molten salts ensures a notable acceleration of the reaction kinetics. We found that the eutectic NaOH-KOH is particularly effective. The samples obtained exhibited a clearly spherical shape together with a considerable fineness. This nonconventional technique thus enables the synthesis of extremely homogeneous compounds that are especially suitable in industrial application such as pigments used in decorative ceramic materials. The solid solutions obtained are, indeed, able to develop an intense red coloring, especially these with a Pr content of 5 mol %.

2000 - Reaction Mechanism in Alumina/Chromia (Al2O3/Cr2O3) Solid Solutions Obtained by Co-Precipitation [Articolo su rivista]
Bondioli, Federica; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; L., Linati; P., Mustarelli
abstract

The aim of this work is to study the structural characteristics and properties of the solid solution (Al,Cr)(2)O-3. XRD analysis, Al-27 MAS-NMR measurements, and microstructural characterization were used to determine the relationship between color and crystallochemical properties of the compounds formed, In particular, to determine more accurately the mechanism of solid solution formation above the miscibility gap of the system, the marker technique was used. In order to define the behavior of the system for temperatures below the miscibility gap at 1 bar pressure, the composition Al2O3:Cr2O3 1:1 was studied with high-temperature XRD.

2000 - Sintering behavior of glass-ceramic frits [Articolo su rivista]
Siligardi, Cristina; Leonelli, Cristina; Mc, D'Arrigo
abstract

Combining DTA and HEMA data may provide a simple and quick method for describing the sintering/crystallization process for different glass compositions

2000 - Study of the reactivity of zircon pigments in glass matrix [Relazione in Atti di Convegno]
Bondioli, Federica; Leonelli, Cristina; Manfredini, Tiziano; Wc, Lacourse
abstract

In this paper the authors report the reactivity of 3 different zircon-based pigments in ceramic glaze studied by an optical microscopy.

2000 - Techniques used to determine porosity [Articolo su rivista]
Andreola, Nora Maria; Leonelli, Cristina; Romagnoli, Marcello; Miselli, Paola
abstract

A comparison is made of the principal techniques (mercury porosimetry, helium pycnometry, image analysis and water absorption) that are used to measure porosity

2000 - Tecniche a confronto per la determinazione della porosità. Parte II [Articolo su rivista]
Andreola, Nora Maria; Leonelli, Cristina; Romagnoli, Marcello; P., Miselli
abstract

Viene presentata I'applicazione delle tecniche presentate nella parte I a sei prodotti ceramici con diverse proprietà. Ogni tecnica utilizzata infatti risulta idonea per determinate classi di materiali; pertanto la scelta del procedimento di analisi viene fatta a seconda del tipo di risultato che si vuole ottenere. Lo scopo di tale lavoro e quello di evidenziare i vantaggi e gli svantaggi di ognuna a seconda del materiale sottoposto ad analisi.

2000 - The sodium-alumino silicate glasses: a molecular dynamic study [Articolo su rivista]
Montorsi, Monia; Menziani, Maria Cristina; Leonelli, Cristina; A. N., Cormack
abstract

Alumino silicate glasses (NAS) represent an interesting class of materials expecially in virtue of their final physical and chemical properties. Several models have been proposed to interpret the macroscopical behaviour of these ternary systems and in the last years computer simulations have been also largely used as useful complementary tools for the NAS glass structure characterisation.In this work we present the comparison between experimental and theoretical data obtained for a large range of compositions (R= Al/Na from 0.0064 up to 2) of alumina containing glasses.

2000 - Transparent glass-ceramics obtained during cooling [Articolo su rivista]
Siligardi, Cristina; Leonelli, Cristina; Pellacani, Gian Carlo; Wc, Lacourse; P., Mustarelli; C., Tomasi
abstract

This paper examines the microstructure of glass-ceramics obtained during cooling melts of different compositions in the ternary Li2O-Al2O3-SiO2 system. The effects of MgO, ZnO, and TiO2 additions revealed necessary to attain the crystallisation during cooling. The microstructure of the transparent glass-ceramics, once obtained with a 15-min soak in the temperature range of 700-800 degreesC, is stable at room temperature. An interesting colour change has been noted during the treatment and TEM investigations confirmed that such coloration is produced by phase separation. The crystalline phase evolved are mixed titanates of Mg and Zn which develop from the phase separated glass, soon after T-g, and grow to form the nucleation centres for other crystalline phases. The evolution from phase separated glass to glass-ceramic has been followed by modulated DSC and NMR spectroscopies.

1999 - Influence of some transition metal cations on the properties of BaO-containing glasses and glass-ceramics [Articolo su rivista]
Barbieri, Luisa; S., Bruni; F., Cariati; Leonelli, Cristina; Pellacani, Gian Carlo; Siligardi, Cristina; U., Russo
abstract

Copper, iron, and manganese oxides were added separately to melts of BaO-MgO-Al2O3-SiO2 glasses up to a maximum of 5 mol%, than devetrified at 100 degrees C for 1 h. The transition cations acted as fluxes on the glass properties by reducing the temperature of glass transition and the exothermic crystallization peak temperature. The activation energy for crystallization was slightly reduced, remaining in the feldspatic phase range. The effects on other properties, such as hardness and toughness, were evaluated in terms of indentation tests and related toation field strength and heating treatment. The presence of copper and manganese oxides inhibited the formation of hexacelsian crystals in the glass-ceramics, thus avoiding dangerous dimensional stress due to phase transformation. The complex evolution of the remaining crystalline phases is discussed in light of XRD, FT-IR, and SEM observations.

1999 - Microstructure at the interface solution/bioactive glass cerium and silver addition in bioactive phosphosilicate glasses [Articolo su rivista]
Leonelli, Cristina; Lusvardi, Gigliola; Menabue, Ledi
abstract

Phosphosilicate glasses added with silver and cerium are studied in order to verify their bioactivity; the study is carried out in vitro and the results indicated that these glass are potentially bioglasses.

1999 - Nanosized CeO2 powders obtained by flux method [Articolo su rivista]
Bondioli, Federica; Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano
abstract

Cerium(IV) oxide (CeO2) powders were prepared by the flux method, adding cerium ammonium nitrate ((NH4)(2)Ce(NO3)(6)) to an eutectic mixture of molten salts, followed by washing and drying. To evaluate the effect of the molten salts on the powders, three different fluxes were used: KOH/NaOH, NaNO3/KNO3, and LiCl/KCl eutectic mixtures. The temperature and the stoichiometry of each reaction were determined by thermogravimetric analysis. Specific surface area analysis (BET), transmission electron microscopy (TEM), and X-ray techniques were used to study the morphology and particle size distribution of the solid products. Results showed the presence, in the reaction products, of homogeneously sized and shaped particles of a single nanosized CeO2 phase. The powder obtained with chlorides out of molten salts had the finer particle size distribution, with a very narrow dimensional range of 20-10

1999 - Studio di sinterizzazione di polveri di fritte vetro-ceramiche [Articolo su rivista]
Siligardi, Cristina; Leonelli, Cristina; G., Baldi; E., Generali
abstract

Lo scopo del lavoro è quello di poter prevedere il meccanismo di sinterizzazione di polveri vetrose durante il riscaldamento che porta alla formazione di materiali vetroceramici. Tale studio è stato eseguito sulla base dei dati ottenuti dall'analisi termica differenziale e dal microscopio riscaldante

1998 - Characterisation of the surface conductivity of glassy materials by means of impedance spectroscopy measurements [Articolo su rivista]
Fontanesi, C.; Leonelli, C.; Manfredini, T.; Siligardi, C.; Pellacani, G. C.
abstract

Abstract The phenomenon of tin dioxide doping by antimony, Sb(V), atoms in semiconductive glazes is discussed. In particular, the impedance spectra of the glaze surface at room temperature were experimentally determined, and the results were analysed in terms of equivalent circuits. The parameters resulting from the fitting procedure were related to the SnO2/Sb(V) relative content, the SnO2/Sb (V) percentage in the glaze, and the microstructure as observed by SEM. It is proposed that the addition of SnO2 and Sb2O3 to a common glaze for ceramic tile results in a semiconductive continuous phase, whose electrical characteristics fulfil the antistatic floor regulation, as far as surface conductivity is concerned. As a whole the obtained results suggest that the thermal cycle used in fast firing technology is capable to promote the oxidation of Sb2O3 to Sb2O4, resulting in a sufficient amount of Sb(V) capable of generating a semiconductive behaviour of the SnO2 crystalline phase dispersed in the glaze. © 1998 Elsevier Science Limited. All rights reserved.

1998 - Colouring effects of synthetic inorganic cobalt-pigments in fast-fired porcelainized stoneware tiles [Articolo su rivista]
Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; Miselli, P; Monari, G; Pellacani, Gian Carlo
abstract

The paper reports a laboratory and industrial study on the rationalization of using synthetic cobalt oxide, aluminate and silicate pigments (0.5-4.0 wt%) for colouring porcelainized stoneware tiles. The addition of pigments to the base body in amounts up to about 1-2 wt% does not appreciably modify microstructure, nature and amount of phases of the fired tiles; while higher amounts, promoting liquid-phase formation, favour the sintering and can cause swelling of compact samples. On the basis of the results, inorganic cobalt-pigments seem very appropriate to produce coloured porcelainized stoneware tiles, but the better results are obtained by using CoO.AI(2)O(3). By controlling type and amount of pigment, it is possible to tailor different blue shades conferring to the product particularly interesting aesthetic effects.

1998 - Microwave synthesis of Al2O3-Cr2O3(ss) ceramic pigments [Articolo su rivista]
Bondioli, Federica; Corradi, Anna; Ferrari, Anna Maria; Leonelli, Cristina; Siligardi, Cristina; Manfredini, Tiziano; Ng, Evans
abstract

A pink ceramic pigment belonging to the Al2O3/Cr2O3 oxide system was successfully obtained by drying and firing microwave treatments starting from inorganic coprecipitated hydroxide gets. Compared with rite pigments obtained by conventional industrial ceramic methods, the introduction of microwave treatment can lead to a more continuous and efficient process consuming a small fraction of the energy and time of conventional treatment.

1998 - Microwave-hydrothermal synthesis of nanophase ferrites [Articolo su rivista]
S., Komarneni; Mc, D'Arrigo; Leonelli, Cristina; Pellacani, Gian Carlo; H., Katsuki
abstract

This paper reports the synthesis of technologically important ferrites such as ZnFe2O4, NiFe2O4, MnFe2O4, and CoFe2O4 by using novel microwave-hydrothermal processing. Nanophase ferrites with high surface areas, in the range of 72-247 m(2)/g, have been synthesized in a matter of a few minutes at temperatures as low as 164 degrees C. The rapid synthesis of nanophase ferrites via an acceleration of reaction rates under microwave-hydrothermal conditions is expected to lead to energy savings.

1998 - Properties of glasses belonging to the Li2O-ZrO2-SiO2 system [Articolo su rivista]
APN de, Oliveira; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; G., Ramis; M., Trombetta; G., Busca
abstract

The behaviour and some physical, chemical and thermal properties of Li2O-SiO2 glasses with ZrO2 additions (in the form of ZrSiO4) of up to 13.00 mol% in the as-quenched state were investigated with the aid of x-ray diffraction (XRD), FT-IR spectroscopy, thermal expansion, microhardness and density measurements as well as chemical durability measurements. Transparent glasses prepared by the addition of ZrO2 up to about 11.00 mol% were obtained. For successive addition of ZrO2 and decreasing Li2O/SiO2 ratio, the expansion coefficients revealed decreasing values from 12.60x10(-6) to 8.69x10(-6)degrees C-1. The glass transition and softening point temperatures of the glasses showed a reverse behaviour. By increasing the ZrO2 content in the base glasses the hardness and density values increased. However, while hardness increases even with the decrease of the Li2O/SiO2 ratio the density showed a contrary behaviour, i.e. it increased with the ZrO2 content but decreased when the Li2O/SiO2 ratio decreased, with the highest values of 6.73 GPa and 2.71 g/cm(3), respectively. On the other hand, the chemical durability, in the case of 30Li(2)O.70SiO(2) base glass, decreased with time in water solution and increased with ZrO2 content tending to be almost constant for ZrO2 contents higher than 4.76 mol% at 60 min and 6.98 mol% in the time range from 5 to 30 min, respectively.

1998 - Sintering and crystallization of a glass powder in the Li 2O-ZrO2-SiO2 system [Articolo su rivista]
A. P., Novaes De Oliveira; Manfredini, Tiziano; Barbieri, Luisa; Leonelli, Cristina; Pellacani, Gian Carlo
abstract

Sintering and crystallization of a 23.12 mol% Li2O, 11.10 mol% ZrO2, 65.78 mol% SiO2 glass powder was investigated. By means of thermal shrinkage measurements, sintering was found to start at about 650°C and completed in a very short temperature interval (ΔT ≈ 100°C) in less than 30 min. Crystallization took place just after completion of sintering and was almost complete at about 900°C in 20 min. Secondary porosity prevailed over the primary porosity during the crystallization stage. The glass powder compacts first crystallized into lithium metasilicate (Li2SiO3), which transformed into lithium disilicate (Li2Si2O5), zircon (ZrSiO4), and tridymite (SiO2) after the crystallization process was essentially complete. The microstructure was characterized by fine crystals uniformly distributed and arbitrarily oriented throughout the residual glass phase.

1998 - Syntheses of Fe2O3/silica red inorganic inclusion pigments for ceramic applications [Articolo su rivista]
F., Bondioli; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano
abstract

The work focuses on the syntheses of red inorganic ceramic pigments by inclusion of hematite in a fumed silica matrix. Leaching tests in boiling solutions of concentrated (36 wt%) hydrochloric acid demonstrated that, starting from mixtures of fumed silica and synthetic goethite, the occlusion of hematite occurs by calcination at 1150-1200 degrees C for 2-4 h. Better results were obtained by using fumed silica having surface area ranging from 300 to 400 m(2)/g. A continuos change in colour was measured by comparing L-a-b values of the calcined samples and more information were obtained by the Kubelka-Munk absorption function. Because its chemical and thermal stability, the obtained heteromorphic pigment may be considered a suitable red pigment for ceramic manufacturing by fast firing cycles.

1997 - Alignment of silicon carbide whiskers in polymer matrix [Articolo su rivista]
Chen, Lf; Leonelli, Cristina
abstract

Polyacrylonitrile (PAN) loaded with up to 70% by weight of silicon carbide whiskers has been used as a model system to demonstrate the potential of whisker alignment by a technique similar to the conventional fibre spinning. Continuous fibres containing high percentages of whiskers can be readily produced using a laboratory scale conventional wet-spinning apparatus. Excellent whisker alignment along the fibre axes was found even for the as-extruded filaments without drawing. However, an improved alignment was obtained through optimizing whisker loading and by drawing the as-spun fibres. Drawing tends to improve the fibre mechanical properties considerably, rendering them easily handable or even useful as a ''composite fibre'' reinforcement in their own right. Although whisker alignment generally gets better with drawing, over-stretching leads to irregular fibre diameters. Preliminary experiments show that after some minor modifications, this technique may be applied to fabricate whisker reinforced ceramic composites.

1997 - Chromite as a Pigment for Fast-Fired Porcelain Tiles [Relazione in Atti di Convegno]
Bondioli, Federica; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano
abstract

In this paper the authors report the main characteristic of inorganic pigment used to color industrial ceramic materials

1997 - Conventional and Microwave Preparation of the Al2O3/Cr2O3 (ss) pink pigment [Relazione in Atti di Convegno]
Bondioli, Federica; Ferrari, Anna Maria; Leonelli, Cristina; Siligardi, Cristina; Manfredini, Tiziano
abstract

In this paper the authors report an unconventional synthesis to obtain the pink pigment Alumina/Chromia.

1997 - Effect of TiO2 addition on the properties of complex aluminosilicate glasses and glass-ceramics [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina; Siligardi, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo
abstract

The nucleating effect of titania during glass crystallization has been studied in a complex glassy system where some particular oxides, such as ZnO and MgO, which present chemical and thermodynamic affinity for titanium have been added. Such additions tend to produce phase separation in the glass and leads to titanate phases formation in the glass-ceramic. Moreover, the presence of lithia has a promoting effect on both mechanisms because the lowered viscosity increases cation diffusion. Various thermal, microscopic, and diffractometric techniques have been used to investigate the amorphous and the crystalline phase.

1997 - Feasibility of using cordierite class-ceramics as tile glazes [Articolo su rivista]
Ferrari, Anna Maria; Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina; Corradi, Anna
abstract

Basic principles of fabricating tile glazes based on cordieritic glass-ceramics are explained. Glass compositions from the MgO-Al2O3SiO2 three-component phase diagram have been melted with and without the nucleating agent TiO2. Additionally, a sodium borosilicate glass that is commonly used in the the glaze industry has been wet milled, together with the previous compositions, to produce a coating slip. Studies are focused on the role of the nucleating agent and glassy formulation in the crystallization of the glass-ceramic system using differential thermal analysis, X-ray diffractometry, and scanning electron microscopy. When added to a borosilicate glass, only one composition is capable of crystallizing cordierite under a fast-firing cycle used for ''monoporosa'' production. The porosity of the glaze layer is sufficiently low and the crystal size is small to ensure good mechanical and chemical properties, The presence of cordierite crystals in the glaze should enhance abrasion and acid resistance, in comparison to a traditional matte glaze that contains mostly enstatite or diopside crystals.

1997 - Glass-ceramic as tile glazes [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano
abstract

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1997 - Nucleation and crystallization of a lithium aluminosilicate glass [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina; Corradi, Anna; P., Mustarelli; C., Tomasi
abstract

An aluminosilicate glass of composition 61SiO(2) . 6Al(2)O(3) . 10MgO . 6ZnO . 12Li(2)O . 5TiO(2) (mol%) has been prepared by a melting process and investigated as far as crystallization is concerned. Glass-ceramic is easily obtained because glass shows a high tendency to crystallize starting from 700 degrees C. The crystalline phases evolve with temperature, showing the aluminosilicates to be the main phase up to 1050 degrees C, followed by metasilicates and silicates, some of which have lower melting points. The titanates of Mg and Zn develop from the phase-separated glass, soon after T-g, and grow to form nucleation centers for the other crystalline phases. The evolution from phase-separated glass to glass-ceramic has been followed by many thermal, diffractometric, spectroscopic, and microscopic techniques.

1997 - Processing of a silicon-carbide-whisker-reinforced glass-ceramic composite by microwave heating [Articolo su rivista]
L., Chen; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina
abstract

A calcium magnesium aluminosilicate-based glass that contained 10 wt% of silicon carbide whiskers (SiCw) as reinforcement was prepared by tape casting, followed by sintering either in a conventional furnace or in a microwave oven. The results were consistent with retardation of glass sintering through whisker bridging. The glass, by itself, was sintered to almost-full density at 750 degrees C for 4 h by conventional furnace sintering; the best sintered composite, with an estimated density of similar to 90%, was obtained at 800 degrees C with a dwell time of 4 h. Sintering at a temperature of >800 degrees C did not improve the densification but rather resulted in severe whisker oxidation. A reduced densification rate was observed for the samples that were sintered in nitrogen. By contrast, in the microwave oven, almost-full density for the glass and similar to 95% of the theoretical density for the composite were obtainable at 850 degrees C for 15 min, which represented a reduction of similar to 10 h of the total processing time and a reduced SiCw oxidation.

1997 - Relationship between microstructure and mechanical properties in fully vitrified stoneware [Articolo su rivista]
Barbieri, Luisa; L., Bonfatti; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; D., SETTEMBRE BLUNDO
abstract

Fully vitrified stoneware tiles are very important low-porosity products obtained by high-sintering of unglazed ceramic bodies and used for exterior applications and as frost-resistant materials. The dense microstructure of thp fired tiles is characterized by strongly interlocked crystals of quartz and mullite embedded in an amorphous glassy phase. Vickers microhardness (4.94-6.09 GPa), Young's modulus (68.7-73.6 GPa) and abrasion resistance (1.48-1.84 g/30x30 tile) of industrial fully vitrified stoneware tiles were measured and well represent the mechanical properties of the tiles. The microstructure is responsible for the peculiar abrasion resistance and hardness, and correlations among these mechanical properties and microstructure are discussed.

1996 - Alumina-chopped fibres as reinforcements for glass-ceramic materials [Articolo su rivista]
Leonelli, C.; Manfredini, T.; Pellacani, G. C.; Blundo, D. S.
abstract

The paper reports a preliminary study about alumina short fibres (20 mass-%) and particulate reinforced glass-ceramic matrix composites. The fabrication techniques used are: a) preparation of pellet containing randomly distributed fibres and particulate, by wet mixing, cold pressing and sintering of the dried powders; b) tape casting. The nature of the matrix was investigated in order to obtain good interfacial properties; a new calcium and magnesium aluminosilicate (CMAS) glass ceramic formulation is proposed. The sintering behaviour of composites was studied at different temperatures, ranging from 800 to 1000°C, using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The evaluation of linear shrinkage and density was sufficient to define the best sintering conditions, while SEM and XRD indicated the nature of matrix/fibre interface's.

1996 - Densification and properties of CMAS glass-ceramic prepared from compacts of pressed powders and of tape cast powder multilayers [Articolo su rivista]
Leonelli, Cristina; Barbieri, Luisa; Manfredini, Tiziano; D. S., Blundo; Siligardi, Cristina; Corradi, Anna
abstract

Calcia magnesia alumina silica (CMAS) glass ceramics containing anorthite, diopside, and barium feldspars as crystalline phases have been fabricated by uniaxial pressing of tape cast glass powder multilayers. The sinterability of the parent glass was investigated from observations of the densification process and the extent of crystallisation determined by changes in the microstructure and mechanical properties of sintered compacts which were prepared below 1100 degrees C. The results showed that glass ceramics produced by tape casting had a higher density and lower porosity than those obtained by uniaxial pressing of loose powders. The tape cast material also showed superior mechanical properties, characterised by Vickers microhardness and elastic modulus, and achieved a higher degree of crystallinity at a temperature 100 K lower than for the pressed powder samples. The low porosity (0.5-1.0%), Vickers hardness (700 HV (25 g)), and elastic modulus (125 GN m(-2)) indicate that the sintering of multilayer tape cast glass powder is a viable method for producing glass ceramics.

1996 - Electrical properties and microstructure of glass-ceramic materials from CaO-MgO-Al2O3-SiO2 system [Articolo su rivista]
Saccani, A; Sandrolini, F; Leonelli, Cristina; Manfredini, Tiziano
abstract

The electrical (volume conductivity) and dielectric (loss factor and dielectric constant) properties of glass-ceramics belonging to the CaO-MgO-Al2O3-SiO2 system have been studied, as a function of microstructure, in their glassy and ceramized forms on samples obtained as bulk materials or sintered powders. A possible application of these materials as substrates for electronic devices can be envisaged, on account of their low conductivities (<10(-14) Scm(-1) up to 250 degrees C), loss factor and permittivity values.

1996 - Modifications on bulk crystallization of glasses belonging to M2O-CaO-SiO2-ZrO2 system in a 2.45 GHz microwave field [Relazione in Atti di Convegno]
Siligardi, C.; Leonelli, C.; Fang, Y.; Agrawal, D.
abstract

The potential for microwave processing of a single phase material is often limited due to the dependence of dielectric losses upon the chemical bonding and temperature of the material. We will present results showing the effect of microwave absorption on bulk crystallization of glasses belonging to M2O-CaO-SiO2-ZrO2 system (where M = Li, Na, K). The glass samples were devitrified using both microwave and conventional heating. The effect of Li+, Na+, K+ on crystallization is quite remarkable and is a function of ion size. This is true especially in the microwave heating where the important dielectric losses observed in silicate glasses are related to the motion of alkali cations throughout the glass matrix. X-ray diffraction analysis was performed on the powdered samples to determine crystalline phases. Results of microstructure and microanalysis on these glass-ceramic samples will also be presented.

1996 - Physical properties of quenched glasses in the Li2O-ZrO2-SiO2 system [Articolo su rivista]
AP NOVAES DE, Oliveira; Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo
abstract

The behavior and some physical and thermal properties of a 30Li(2)O-70SiO(2) base glass composition with addition of ZrSiO4 in the as quenched state was investigated with the aid of X-ray diffraction (XRD), differential thermal analysis (DTA), thermal expansion and microhardness measurements, as well as density measurements. Transparent glasses prepared by the addition of ZrSiO4 up to 10.30 mol% were obtained, ZrSiO4 was found to decrease the expansion coefficient of the investigated glasses from 11.0 x 10(-6) to 7.96 x 10(-6)degrees C-1. The glass transition and softening point temperatures of the glasses showed a reverse behavior. On the other hand, both hardness and density increased for successive increases of the ZrSiO4 amounts, with the highest values of 6.3 GPa and 2.65 g/cm(3), respectively.

1996 - Quantitative determination of pyrite in, ceramic clay raw materials by DTA [Articolo su rivista]
Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano; Pennisi, L; Romagnoli, Marcello
abstract

The thermal oxidative decomposition in air of 0-1.5 wt% of pyrite added to two traditional powdered clays was investigated by non-isothermal DTA. It emerged that the first step of the exothermic oxidation of pyrite, in the 350-500 degrees C range, partly overlapped the endothermic dehydroxylation of clay minerals, centred at 590 degrees C, and the result was dependent on the pyrite contents. Based on the values of the area of the oxidative peak and of the corresponding oxidation heat, it is possible to calculate quantitatively the amount of pyrite present in the industrial clay bodies and therefore to inform the technicians of the factories so they can avoid the negative effects of reducing reactions that could occur during firing of ceramic raw materials.

1996 - Technological and product requirements for fast firing glass-ceramic glazes [Relazione in Atti di Convegno]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano
abstract

In the ceramic tile industry, the change in firing technology from traditional double firing to the faster single firing process has involved different formulations and compositions of the glazes based on new types of glasses. In consideration of their peculiar physicomechanical and chemical properties, glass-ceramics seem to be suitable for obtaining good floor tile glazes. These innovative materials have enabled the formulation of ceramic glazes to be produced on an industrial scale, and recently some industrial formulations that were based on the classic Li2O-Al2O3-SiO2, CaO-MgO-SiO2, and MgO-Al2O3-SiO2 systems and were compatible with the body properties have found practical application as tile glazes for fast firing technologies. This resulted in finished ceramic floor tile products having enhanced abrasion and wear resistance with improved mechanical properties. Both traditional and innovative firing technologies can be used.

1996 - The effect of the addition of ZrSiO4 on the crystallization of 30Li(2)O/70SiO(2) powdered glass [Articolo su rivista]
A. P., NOVAES DE OLIVEIRA; Corradi, Anna; Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano
abstract

The effects of the addition of ZrSiO4 to 30Li(2)O/70SiO(2) powdered glass on its crystallization behaviour were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Transparent glasses with a ZrSiO4 content of up to 10.30 mol% were obtained. Li2Si2O5 and/or ZrSiO4, Li2Si2O5 and tridymite were crystallized after appropriate heat treatments. Kinetics parameters for surface crystallization were estimated from the DTA curves. The crystallization was completed in the 590-907 degrees C temperature range for activation energy values between 460.5 and 715.9 kJ mol(-1). The resulting materials are potential candidates for useful sintered glass-ceramics with a wide number of applications.

1995 - Correlazioni fra proprietà microstrutturali e meccaniche nel gres porcellanato [Articolo su rivista]
Barbieri, Luisa; L., Bonfatti; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; D., SETTEMBRE BLUNDO
abstract

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1995 - Effects of nucleating agents on diopside crystallization in new glass-ceramics for tile-glaze application [Articolo su rivista]
G., Baldi; Pellacani, Gian Carlo; Leonelli, Cristina; Manfredini, Tiziano; E., Generali; Siligardi, Cristina
abstract

The effect of crystallization produced by addition of TiO2, ZrO2 and P2O5 oxides to glass-ceramic of the system CaO-MgO-SiO2 was studied using structural and thermal techniques. The devitrification process was independent of thermal treatment. X-ray diffraction studies performed on the glass-ceramic system indicated that diopside crystalline phase was more thermodynamically favourable than other phases. The effect of the nucleating agent depends on its nature: TiO2 decreased the activation energy while P2O5 and ZrO2 did not. SEM analysis of the doped glass-ceramics showed randomly distributed crystals with significant dimensional variations from those of the undoped system. All these formulations, showing a high crystallization rate, and a fast heating rate, can be used as tile glazes and/or tile-glaze components.

1995 - Glass ceramics belonging to the CaO-SiO2-ZrO2 system as tile glaze components [Relazione in Atti di Convegno]
G., Baldi; L., Frassinelli; E., Generali; Leonelli, Cristina; Manfredini, Tiziano; G. C., Pellacani; Siligardi, Cristina; C., Svicher
abstract

In order to verify the possibility of using new glass-ceramic materials as tile glaze coatings, the devitrification process of a formulation belonging to the wollastonite stability field of the CaO-ZrO2-SiO2 system was investigated by DTA, XRD and SEM techniques.

1995 - Glass ceramics belongings to the CaO-SiO2-ZrO2 system as tiles glazes components [Articolo su rivista]
Baldi di, G.; Barbieri, L.; Frassinelli, L.; Generali, E.; Leonelli, C.; Manfredini, T.; Pellacani, G. C.; Siligardi, C.; Svicher, E. C.
abstract

In order to verify the possibility to use new glass ceramic materials as glazes for floor tiles, the devetrification process of a formulation belonging to the wollastonite stability field in the CaO-SiO2-ZrO2 system was investigated by DTA, XRD and SEM techniques. The investigated system shows a high tendency toward crystallisation, that brings to the separation, also at very high heating/cooling speed, of CaO·SiO2 (wollastonite) and 2CaO·ZrO2·4SiO2 (calcium and zirconium silicate) as main crystalline phases. Industrial tests demonstrate how the formulation can be used as prevalent component in the tile glaze preparation.

1995 - MgO-CaO-Al2O3-SiO2 glassy and glass-ceramic systems: the effect of substitution of CoO or NiO in place of MgO or CaO [Articolo su rivista]
Barbieri, Luisa; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; S., Bruni; F., Cariati
abstract

Nickel and cobalt were separately incorporated in MgO-CaO-Al2O3-SiO2 glasses Their effect on the crystallisation phenomenon of the amorphous materials into a glass ceramic was investigated by means of thermal analysis and x-ray powder diffraction. These two transition cations decrease the crystal growth of anorthite and diopside and nickel produces forsterite formation. The ionic state and the coordination geometry of Ni and Co ions in the vitreous and the devitrified states have been characterised by means of electronic spectroscopy. Divalent ions were observed for nickel and cobalt in both the glasses and the glass ceramics; in the glasses both Ni2+ and Co2+ are in tetrahedral symmetry, while in glass ceramics the symmetry is predominantly octahedral. Colour changes from glass to glass ceramics correlated well with the cations coordination. The atomic distribution of Ni and Co in the glass ceramics obtained by x-ray fluorescence dispersion spectroscopy complement the information about their coordination environment, the first being present in some crystalline areas and the second being mostly segregated in the residual glass at the grain boundary of crystalline zones.

1995 - Microindentation test as parameter for evaluating the sintering and interface properties of SiC-Whiskers reinforced CMAS glass-ceramic composites [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; D., SETTEMBRE BLUNDO; Siligardi, Cristina
abstract

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1995 - Pigmenti inorganici sintetici contenenti cobalto per la colorazione del gres porcellanato [Articolo su rivista]
Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; Miselli, Paola; Monari, G.; Pellacani, G. C.
abstract

L'articolo riporta uno studio sulla possibilità di utilizzare ossido, alluminato e silicato di cobalto per colorare piastrelle di gres porcellanato. L'aggiunta dei pigmenti all'impasto base ne aumenta il ritiro lineare causando in alcuni casi il rigonfiamento delle piastrelle. Controllando la quantità e il tipo di pigmento è possibile realizzare diverse sfumature di blu e ottenere maggiore brillantezza.

1995 - Study of barium feldspar polymorphism as a function of temperature and calcium content [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo
abstract

A family of new glass-ceramic materials, of the general formula (25-x)CaO.xBaO.yMgO. zAl(2)O(3).5OSiO(2), where x=1, 2, 5, 10, 15, 20, 25, y=20 or 14 and z=5 or 11 (mol%), has been prepared by melting raw materials in two parent glasses and performing heat treatments. The systematic substitution of BaO for CaO in the base glasses allows the effect of feldspars' isomorphism and polymorphism to be studied in a series of glass-ceramics where the structural environment around the bivalent cations, Ca2+ and Ba2+, is systematically altered. Ba2+ has a large effect on the glass transition temperature and dilatometric softening point, causing a decrease with increasing BaO. The crystalline phases have been identified and found to be dependent on the preparation conditions, which are the BaO and Al2O3 contents, the heating rate and the soaking temperature adopted for the crystallization treatments. The infrared spectroscopy technique helped to identify the different polymorphs of barium feldspar, that were not clearly distinguishable by X-ray powder diffractometry due to preferred orientations. The kinetic parameters for the formation of the different crystals have also been determined and correlated with their thermal stability resumed in the well-known time-temperature-transformation curves.

1995 - THE MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF SINTERED CELSIAN AND STRONTIUM-CELSIAN GLASS-CERAMICS [Articolo su rivista]
Barbieri, Luisa; Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano; Romagnoli, Marcello; Siligardi, Cristina
abstract

In this paper the capability of surface nucleated barium and strontium feldspars glass-ceramics of being sintered was investigated by means of density and porosity measurements, X-ray diffraction measurements, microscopic observations and indentation testing and the results compared with those recorded on the corresponding bulk crystallized samples. The densification degree, higher than 95% of the theoretical density, and the favoured formation of thermally stable crystalline phases, such as celsian and Sr-celsian, with respect to those which present non-linear thermal expansion, hexacelsian, make sintering very useful for the production of low porosity, less than 3 vol%, materials. The microhardness values (470-780 Kg/mm2) and elastic modulus (57-115 GPa) of the sintered glass-ceramics, together with the refractoriness of the developed phases make these systems particularly suitable for structural applications.

1994 - Influence of mica coating on interfacial debonding of a SiC fibers reinforced glass-ceramic [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; D., SETTEMBRE BLUNDO; S., Meriani; O., Sbaizero
abstract

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1994 - Influenza del rivestimento di mica su fibre SiC sul distacco interfacciale in vetroceramici compositi [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; D., SETTEMBRE BLUNDO; S., Meriani; O., Sbaizero
abstract

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1994 - SINTERING BEHAVIOR OF TAPE-CAST CMAS GLASS-CERAMIC REINFORCED WITH ALUMINA CHOPPED FIBERS [Articolo su rivista]
Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; Blundo, Ds
abstract

The sintering behaviour of CMA S glass-ceramic and CMAS glass-ceramic/alumina chopped fibre (20 wt%) composites was studied at different temperatures, ranging. from 800 to 1000-degrees-C, using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and porosimetry investigations. The evaluation of linear shrinkage, density and porosity were sufficient to define the best sintering conditions, while SEM and XRD allowed the nature of the matrix/fibre interface to be studied.

1994 - Solubility, reactivity and nucleation effect of Cr2O3 in the CaO-MgO-Al2O3-SiO2 glassy system [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; Siligardi, Cristina; E., Tondello; R., Bertoncello
abstract

The effect of Cr2O3 on some anorthite-diopside glass-ceramics has been investigated up to amounts of 5 mol%. The solubility in the glassy compositions analysed is total for the oxide, but for amounts higher than 0.5 mol%, an insoluble spinel form, MgCr2O4, precipitates. Ultraviolet-visible spectroscopy has proved to be the most sensitive technique to the presence of Cr(III) in a crystalline spinel site, followed by X-ray diffraction and scanning electron microscopy observations. Electron spin resonance and X-ray photoelectron spectroscopy techniques excluded any oxidation state, other than Cr3+. The influence:of the transition cation on glass nucleation is that of an increasing bulk effect with chromium, and thus chromium-spinel, content. The magnesium content affects spinel formation, while heat treatments up to 1100 degrees C do not. The spinel formation influences the anorthite-diopside ratio in the glass-ceramic, with a large favour towards the pyroxene.

1994 - Structural studies on RO-MgO-Al2O3-SiO2 (R=Ca, Sr or Ba) glassy systems by density measurements [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina
abstract

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1994 - Vetroceramici appartenenti al sistema CaO-SiO2-ZrO2 come componenti di smalti per piastrelle [Articolo su rivista]
G., Baldi; Barbieri, Luisa; L., Frassinelli; E., Generali; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; Siligardi, Cristina; C., Svicher
abstract

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1993 - Caratterizzazione delle proprietà meccaniche di materiali ceramici e vetrosi sottoposti a prove di durezza Vickers e Knoop. 1a parte: Approccio teorico [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; D., SETTEMBRE BLUNDO
abstract

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1993 - Colouring inorganic oxides in MgO-CaO-Al2O3-SiO2 glass-ceramic systems [Articolo su rivista]
Barbieri, Luisa; C. L., Bianchi; S., Bruni; F., Cariati; Leonelli, Cristina; Manfredini, Tiziano; M., Paganelli; Pellacani, Gian Carlo; U., Russo
abstract

Glasses in the system MgO-CaO-Al2O3-SiO2, in which CuO, Fe2O3 and MnO were substituted for CaO, were prepared and crystallized in absence of nucleating agents. Surface nucleation dominated for all compositions, and was followed by growth of only anorthite and diopside. The relative amount of each crystal was influenced by the chemical composition and the nature of the transition metal cation. Cu and Mn segregated at the grain boundary during crystallization and Fe did not. Changes in the coordination symmetry and oxidation states of the transition metal ions in the glassy and glass-ceramic phases are as follows: Cu(II) is sixfold coordinated with regularly octahedral symmetry in glass and distorted in glass-ceramic, while the ratio Cu(II)/Cu(I) is decreased from 5 to 2 during crystallization. Fe(III) is fourfold coordinated with a symmetry C2v and Fe(II) is present, more in the glass-ceramic than in the glass, with an octahedral symmetry. Mn(II) is in cubic site symmetry with a rhombic distortion, more visible in the glass; Mn(III) is sixfold coordinated with octahedral symmetry in a constant ratio (Mn(III): Mn(II) is 2:1) during crystallization.

1993 - Determinazione della microdurezza Vickers e Knoop di materiali ceramici smaltati e tipo gres porcellanato. 2a parte [Articolo su rivista]
Barbieri, Luisa; Ferrari, Anna Maria; Leonelli, Cristina; Manfredini, Tiziano; D., SETTEMBRE BLUNDO
abstract

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1993 - EFFECT OF FORMING PRESSURE ON THE REACTIVITY AND MICROSTRUCTURE OF ZIRCON POWDER COMPACTS [Articolo su rivista]
Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina
abstract

Preliminary results of a study on the effects of the forming pressure on the reactivity, sintering and microstructure of very fine natural zircon powder compacts. The effects of compaction pressure on the green densities and sintered densities are also discussed. The relationship between the density and the compaction pressure governs the mechanism that occurs in the consolidation process. The investigation has demonstrated changing the compaction pressure in the range 45-180MPa does not influence the onset temperature of sintering of powdered zircon (1150-1170 °C) but does influence the apparent density of the green compacts and consequently the porosity of the sintered specimens. Low relative density values were obtained in these sintering conditions.

1993 - Fiber, whisker and particulate reinforced new glass-ceramic matrix for innovative composites [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Pellacani, Gian Carlo; D., SETTEMBRE BLUNDO
abstract

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1993 - INFLUENCE OF VISCOSITY ON THE CRYSTALLIZATION OF SOME ANORTHITE DIOPSIDE GLASS PRECURSORS [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Siligardi, Cristina
abstract

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1993 - Non-isothermal kinetic equations applied to crystallization of glasses [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; Romagnoli, Marcello; Pellacani, Gian Carlo; Siligardi, Cristina
abstract

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1993 - Preparation end properties of fast-fired porcelain tiles containing natural chromite [Articolo su rivista]
Corradi, Anna; Leonelli, Cristina; Manfredini, Tiziano; Pozzi, Paolo; Romagnoli, Marcello
abstract

Natural magnesium iron chromite can be used as a pigment for coloring high-sintered porcelain tiles. However, it is important to control the amount, firing time and temperature, and size distribution of the chromite powders to produce different color shades of the fired tiles from gray to black.

1992 - Kinetic study of surface nucleated MgO-CaO-Al2O3-SiO2 glasses [Articolo su rivista]
Barbieri, Luisa; Leonelli, Cristina; Manfredini, Tiziano; M., Paganelli; Pellacani, Gian Carlo
abstract

The paper investigated, by means of thermal analysis measurements. the validity of three different methods for the evaluation of the activation energy of crystallization for surface nucleated glasses belonging to the MgO-CaO-Al2O3-SiO2 system, separating anorthite and diopside crystals. The values obtained from Kissinger equation of the activation energy for crystallization are comparable with those obtained by other authors for similar glassy systems, 90 to 150 kcal/mol. The results of the kinetic analysis using single-crystallization-peak method should be corrected taking into account the dimensionality of crystal growth.

1992 - Microstructure and thermal properties in the RO-MgO-Al2O3-SiO2 (R=Ca, Sr, Ba, Zn) glass-ceramic systems [Articolo su rivista]
BARBIERI, Luisa; LEONELLI, Cristina; MANFREDINI, Tiziano; M., PAGANELLI; PELLACANI, Gian Carlo
abstract

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1991 - CRYSTALLIZATION OF SOME ANORTHITE DIOPSIDE GLASS PRECURSORS [Articolo su rivista]
Leonelli, Cristina; Manfredini, Tiziano; Paganelli, M; Pozzi, Paolo; Pellacani, Gian Carlo
abstract

Anorthite and diopside have been obtained from complete devitrification of glasses belonging to the quaternary system MgO-CaO-Al2O3-SiO2. Microstructure, the natural trend of the nucleation mechanism and kinetic studies on the crystallization phenomenon have been investigated by means of optical and electron microscopies, thermal and thermomechanical techniques and X-ray powder diffractometry. All the glasses investigated show a complete crystallization starting from a simple surface nucleation process. The activation energy for the crystallization process proved to be higher than that for viscous flow, leading to an important aspect modification in the sample during ceramization. Thermal stability and physical properties of both glass and glass-ceramic materials have been tested, suggesting the possible use of these materials in industrial application.

1991 - LI2O-SIO2-AL2O3-MEIIO GLASS-CERAMIC SYSTEMS FOR TILE GLAZE APPLICATIONS [Articolo su rivista]
Leonelli, Cristina; Manfredini, Tiziano; Paganelli, M.; Pellacani, Gian Carlo; Albaro, J. L. A.; Navarro, J. E. E.; Orts, M. J.; Bruni, S.; Cariati, F.
abstract

In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2O-Al2O3-SiO2 glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, developing a very close network of interlocked crystals of synthetic beta-spodumene-silica solid solutions (LiAlSi4O10). The results of this research are expected to establish the conditions under which these glass-ceramic systems can be practically used as tile glazes.