Paolo VERONESI - personale UniMoRe

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Paolo VERONESI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

Pubblicazioni

- FORNO A MICROONDE PER DISTRIBUTORE AUTOMATICO [Brevetto]
M., Garuti; Veronesi, Paolo
abstract

Forno a microonde con porte scorrevoli idoneo per l’installazione all’interno di un distributore automatico, in grado di portare alla temperatura edibile una confezione da 250 g di cibo surgelato in 60 secondi. Il forno è dotato di due generatori di microonde, progettati e posizionati in modo opportuno da non danneggiarsi né disturbarsi a vicenda, che erogano contemporaneamente nella stessa cavità la potenza necessaria per eseguire il ciclo in tempo ridotto.

- 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).

2023 - Fluid–Structure Interaction of a thin cylindrical shell filled with a non-Newtonian fluid [Articolo su rivista]
Zippo, A.; Iarriccio, G.; Bergamini, L.; Colombini, E.; Veronesi, P.; Pellicano, F.
abstract

This paper presents the results of an extensive experimental campaign on the dynamic interactions between an elastic structure and a non-Newtonian fluid. The structure consists of a thin circular cylindrical shell, with the bottom end clamped to a shaking table, and the top end carrying a heavy mass. The fluid is a mixture of water and cornstarch, also known as oobleck. The system dynamics has been analyzed in the presence of different fluid levels (i.e., empty, partially, and full-filled). The experimental modal analysis has been carried out to identify the modal properties of the system. High energy tests have been performed by means of a seismic excitation consisting in a stepped sine sweep, spanning the forcing frequency within the neighborhoods where strong resonance phenomena take place. Different excitation amplitudes have been considered in order to induce phase transitions in the fluid, and the onset of complex dynamics has been detected using Fourier spectra and bifurcation diagrams of the Poincaré maps: when the fluid–solid transition occurs, the entangled non-Newtonian fluid rheology results in a complex dynamic scenario where period-doubling cascades, quasiperiodic and chaotic responses can be observed.

2023 - High-Throughput Nanoindentation Mapping of aMicrosegregated CoCrFeNi Multi-Principal Element Alloy(MPEA): Challenges and Limitations [Articolo su rivista]
Gualtieri, Eva Magdalena; Colombini, Elena; Testa, Veronica; Bolelli, Giovanni; Giovanardi, Roberto; Veronesi, Paolo
abstract

2023 - Improvement in Wear Resistance of Grade 37 Titanium by Microwave Plasma Oxy-Carburizing [Articolo su rivista]
Veronesi, P.; Balestri, A.; Colombini, E.
abstract

Grade 37 titanium is widely used in racing applications thanks to its oxidation resistance up to 650 °C, but it suffers from poor wear and fretting resistance, especially at high temperature. In this paper, different surface modification techniques, namely, carburizing, coating by PVD-ZrO2 and a novel microwave plasma oxy-carburizing treatment, are investigated in terms of hardness, wear resistance and scratch hardness, compared to the untreated substrate. Numerical simulation allowed optimization of the design of the microwave plasma source, which operated at 2.45 GHz at atmospheric pressure. The proposed microwave plasma oxy-carburizing treatment is localized and can serve to improve the tribological properties of selected regions of the sample; compared to untreated Grade 37 titanium, the oxy-carburized layer presents a decrease in the wear rate at 450 °C against alumina of 54% and an increase in scratch hardness of more than three times.

2023 - Influence of Different Filler Metals on the Mechanical and Microstructural Characteristics of Arc-Welded Joints Made of Dissimilar Titanium Alloys [Articolo su rivista]
Gaiani, S.; Gozzi, M.; Ferrari, E.; Menozzi, A.; Lassinantti Gualtieri, M.; Colombini, E.; Veronesi, P.
abstract

In the motorsport industry, the choice of material for manufacturing the heat resistant components often falls on titanium alloys. In most cases, the production flow for this kind of part involves CNC machining and subsequent assembly by welding process, to other parts obtained by cold plastic forming and possibly made using different titanium alloys. Hence, the alloying element-content in the joint area can be extremely heterogeneous and variable point-by-point. To investigate this topic further, dissimilar welding of the alpha/beta alloy Ti6Al4V and of the oxidation-resistant alpha alloy KS-Ti 1.2 ASN-EX was made by GTAW technology and using different filler metals. Chemical and mechanical properties of the welds were investigated by XRD, SEM-EDS, microhardness maps, and tensile and bending tests. Results show that, despite the different alloying elements present in the two filler wires investigated, static properties of the welds are similar. Results also show that the local V/Al content ratio affects the microhardness as it is responsible for the creation of supersaturated alpha phases during the cooling of the weld beads.

2023 - Pulsed Current Effect on the Hard Anodizing of an AlSi10Mg Aluminum Alloy Obtained via Additive Manufacturing [Articolo su rivista]
Dallari, E.; Bononi, M.; Pola, A.; Tocci, M.; Veronesi, P.; Giovanardi, R.
abstract

The hard anodizing treatments of cast Al-Si alloys are notoriously difficult. Indeed, their microstructural features hinder the growth of a uniform, compact, and defect-free anodic oxide. In this paper, AlSi10Mg samples, produced via Gravity Casting (GC) and Additive Manufacturing, i.e., Laser Powder Bed Fusion (L-PBF), were hard anodized in a sulfuric acid bath, in order to verify how the particular microstructure obtained via L-PBF affects the thickness, hardness, compactness, and defectiveness of the anodic oxide. Moreover, for the first time, Pulsed Direct Current (PDC) procedures were used to perform the hard anodizing treatments on additively manufactured AlSi10Mg alloy. Several combinations of temperature and electrical parameters, i.e., current density, frequency, and Duty Cycle, were tested. The anodized samples were characterized through optical microscopy analysis, Scanning Electron Microscopy (SEM) analysis, and accelerated corrosion tests, i.e., Potentiodynamic Polarization (POL) and Electrochemical Impedance Spectroscopy (EIS) measurements. The PDC procedures allowed improvement of the compromise between evenness, compactness, and defectiveness. Among the attempted PDC procedures, a specific combination of electrical parameters and temperature allowed the best results to be obtained, i.e., the highest hardness and the lowest volumetric expansion values without compromising the oxide quality rating and the corrosion resistance behavior. However, none of the attempted PCD strategies allowed the hardness values obtained on samples produced via GC to be reached.

2023 - Recycling Of Spent Powders From Additive Manufacturing Processing Of Inconel 625 For The Synthesis Of Cocrfenimoxnb0.4x (X=0-0.1) Multi-Principal Element Alloys (Mpeas) By Spark Plasma Sintering (SPS) Of Mechanically Alloyed Powders [Relazione in Atti di Convegno]
Veronesi, P.; Gualtieri, M. L.; Feltrin, A. C.; Akhtar, F.; Colombini, E.
abstract

Sieve residues from the powder recycling stream in Laser powder bed fusion (L-PBF) processing of Inconel 625 are currently disposed of as hazardous waste, which conflicts with circular economy thinking. Here, the synthesis of metal matrix composites (MMCs) based on carbide- and oxide-strengthening phases finely dispersed in a Multi-Principal Element Alloy (MPEA) matrix was explored as a recycling option for these powders. In particular, mixtures of virgin metal powders and a spent Inconel 625 powder were mechanical alloyed and consolidated by Spark Plasma Sintering (SPS). The process control agent (PCA, ethanol) used during mechanical alloying acted as a source for C and O in the subsequent crystallization of nano-sized carbides and oxides during sintering. By carefully controlling the powder mixture composition, MPEA matrices with different contents of Nb and Mo in the face-centered cubic structure were obtained, as revealed by X-ray Powder diffraction. The bulk samples were further characterized by Scanning Electron Microscopy (SEM) and preliminary mechanical analyses using instrumented indentation. The results showed that spent powder of Inconel 625 was a valuable source of 4d transition metals for the synthesis of MMCs based on a MPEA matrix with enhanced solid solution strengthening and finely dispersed ceramic phases.

2023 - Recycling Of Spent Powders From Laser Powder Bed Fusion Processing Of Inconel 625 For The Mechanical Synthesis Of Cocrfenimoxnb0.4x (X=0-0.1) Multi-Principal Element Alloys (Mpeas) [Relazione in Atti di Convegno]
Colombini, E.; Gualtieri, M. L.; Paggetti, S.; Veronesi, P.
abstract

2023 - Synthesis of Multi-Principal Element Alloys by a Conventional Powder Metallurgy Process [Relazione in Atti di Convegno]
Valsecchi, G.; Colombini, E.; Gualtieri, M. L.; Mortalo, C.; Deambrosis, S. M.; Montagner, F.; Zin, V.; Miorin, E.; Fabrizio, M.; Veronesi, P.
abstract

The development of tailored microstructures of Multi-principal element alloys (MPEAs) is currently a hot topic in physical metallurgy. The most targeted systems are equimolar alloys composed of 3d transition metals including the so-called Cantor alloy (i.e. CoCrFeMnNi) and derivatives such as CoCrFeNi and CoCrFeNiAlx. Powder metallurgy is a promising route for this purpose and include manufacturing techniques such as hot pressing of mechanically activated or prealloyed powders or the less popular press-sinter route of mixed powders. In this work, cold pressing followed by fast vacuum sintering (1h) at various temperatures (Tmax =1100-1300 °C) of mixed powders of CoCrFeNi and CoCrFeNiAl0.4 were explored for the synthesis of structurally and chemically homogeneous alloys. This approach is promising for the synthesis of bulk alloys of higher purity with respect to hot pressing of mechanically prealloyed powders. Microstructural investigations were performed by X-ray Powder diffraction (XRPD) and Scanning electron microscopy (SEM). It will be shown that the reactive sintering kinetics of the investigated systems require a Tmax of 1200 °C for effective alloying at the short holding time employed for CoCrFeNi. Instead, 1300 °C is needed for CoCrFeNiAl0.4.

2022 - A Multi-Physic Modelling Insight into the Differences between Microwave and Conventional Heating for the Synthesis of TiO2 Nanoparticles [Articolo su rivista]
Poppi, G.; Colombini, E.; Salvatori, D.; Balestri, A.; Baldi, G.; Leonelli, C.; Veronesi, P.
abstract

Microwave-assisted synthesis of nanoparticles usually leads to a smaller and more uni-formly distributed particle size compared to conventional heating (e.g., oil bath). Numerical simulation can help to obtain a better insight into the process in terms of temperature distribution or to evidence existing different temperature profiles and heating rates between the two techniques. In this paper multi-physics numerical simulation is used to investigate the continuous flow synthesis of titanium oxide nanoparticles starting from alkoxide precursors. Temperature-dependent permit-tivity of reactants has been measured, including the effects of permanence at the maximum synthesis temperature. A temperature homogeneity index has been defined to compare microwave and conventional heating. Results show that when using microwave heating at 2450 MHz, in the inves-tigated conditions, a much higher temperature homogeneity of the reactants is reached. Moreover, reactants experience different heating rates, depending on their position inside the microwave ap-plicator, while this is almost negligible in the case of conventional heating.

2022 - A method for yield and cycle time improvements in Al alloy casting with enhanced conductivity steel for die construction [Articolo su rivista]
Vergnano, A.; Salvati, E.; Magistrelli, A.; Brambilla, E.; Veronesi, P.; Leali, F.
abstract

A die for Al alloy casting must be designed to achieve the expected quality levels. Moreover, the casting unit cost must be regarded as the objective function to be minimised It can be expressed as a function of the quantity of materials and energy to be used, cycle time and equipment investment. This work compares the performance of the die with inserts manufactured using the usual 1.2343 steel with that of the innovative 1.2383. The latter is considered due to its enhanced thermal conductivity, despite being more expensive. Simulation experiments are designed to evaluate different die layouts. The quality design solutions are evaluated against the cost objective function in order to identify the optimal die choice. A case study on gravity die casting (GDC) of an AlSi7Mg0.3 engine head shows faster solidification dynamics when using 1.2383 instead of 1.2343 steel. This reduces the feeder volume, thus increasing the production yield and speeding up the cycle time with a leverage effect. The higher investment cost for the inserts is rapidly returned thanks to the reduction in variable costs. The Return On Investment (ROI) with the improved die in the new solution is short compared with the life of the die.

2022 - In-house synthesis of CoCrFeNi ingots using an electric furnace [Articolo su rivista]
Colombini, E.; Lassinantti Gualtieri, M.; Mortalo, C.; Deambrosis, S. M.; Veronesi, P.
abstract

Bulk Multi-Principal Element Alloys (MPEAs) are generally synthesized by casting, a process needing specific equipment. Here, a standard laboratory electric furnace was used to synthesize bulk CoCrFeNi by melting of prealloyed powders followed by natural cooling. The use of prealloyed powders guaranteed atomic-level mixing. In accordance with the literature, the resulting ingot had a face-centered cubic structure. A typical dendritic-interdendritic microstructure was obtained which was explained by partitioning during solidification and grain boundary wetting phenomenon. Post-annealing treatment improved chemical homogeneity without crystallographic phase change. This work shows the feasibility of melt-aided synthesis of CoCrFeNi HEA under static conditions using a conventional laboratory furnace.

2022 - Powder Metallurgy Route for the Synthesis of Multiprincipal Element Alloys Sputtering Targets [Articolo su rivista]
Colombini, E.; Lassinantti Gualtieri, M.; Mortalo, C.; Deambrosis, S. M.; Montagner, F.; Zin, V.; Miorin, E.; Valsecchi, G.; Fabrizio, M.; Veronesi, P.
abstract

Sputter deposition of multiprincipal element alloys (MPEAs) is a relatively new field of research with high functional potential. The multicomponent design space is immense and practically unexplored. An important obstacle for academic research of such sputtered films is the availability of single-alloy targets and technical difficulties in using cosputtering of multiple metal targets or powder targets. This article focuses on the development of a simple powder metallurgy route, including cold uniaxial pressing of powder mixtures followed by pressureless sintering, for the preparation of targets made of two common base alloys forming simple solid solutions, i.e., FeNiCrCo and FeNiCrMn. In addition, targets of the former one containing 10 at% Al are also prepared. The sintered pellets are composed of randomly oriented crystallites with face-centered cubic structures and an optimum chemical homogeneity. Oxide inclusions and residual porosity, inherent to consolidation and sintering of metal precursors, are observed and possible solutions to overcome these challenging problems are discussed. Nevertheless, encouraging results from preliminary deposition tests of FeNiCrCoAl0.4 using both direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) are presented.

2021 - Laser welding with wobbling system of dissimilar nickel superalloys for applications in the aeronautical field [Articolo su rivista]
Rigon, R.; Roana, G.; Gonzo, A.; Casadei, F.; Lusvarghi, L.; Veronesi, P.
abstract

Laser welding process applied to dissimilar nickel superalloys can lead to cracking and embrittlement phenomena. A recent development, called laser welding with “wobbling” technique, allows heat input optimization and has been selected as the most promising solution to prevent defects in aerospace components. A preliminary study was performed comparing conventional TIG, laser and recent laser “wobbling” applied to representative weld specimen characterized from mechanical, microstructural and metallurgical point of view. The results were also assessed with reference to the applicable specifications, which define quality levels of the welds in terms of surface and volumetric defects admissible for aeronautical application. The welding parameters were optimized for the joint studied following an experimental test plan. The improvements achieved with the optimized welding process and “wobbling” technology were finally evaluated on a real application case that was ready for the industrialization phase. At the same time, an automatic welding system was developed with a vision system, dimensional control in real time and multiple robots able to cooperate to obtain the welding of the components, managing all the phases starting from gripping, positioning, spot welding and gas protection. Automation performance has been analyzed to understand its influence on the welding process, the parameters have in fact been optimized so that the entire production cycle is robust and the results of the welding checks are consistent with those of the qualification.

2021 - MICROWAVE SINTERING OF SODIUM-β -ALUMINA: EXPERIMENTAL AND NUMERICAL SIMULATION RESULTS [Relazione in Atti di Convegno]
Rosa, R.; Mortalo, C.; Veronesi, P.; Fasolin, S.; Zin, V.; Deambrosis, S. M.; Miorin, E.; Dimitrakis, G.; Fabrizio, M.; Leonelli, C.
abstract

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 - NEW APPLICATORS FOR THE PROJECT SIMPLIFY: SONICATION AND MICROWAVE PROCESSING OF MATERIAL FEEDSTOCK [Relazione in Atti di Convegno]
Veronesi, P.; Colombini, E.; Poppi, G.; Rosa, R.; Dami, V.; Cioni, A.; Lorenzi, G.; Baldi, G.; Leonelli, C.
abstract

2021 - Simulation and experimental validation of Secondary Dendrite Arm Spacing for AlSi7Mg0.3 chassis parts in Low Pressure Die Casting [Relazione in Atti di Convegno]
Vergnano, Alberto; Bergamini, Umberto; Bianchi, Daniele; Veronesi, Paolo; Spagnolo, Roberto; Leali, Francesco
abstract

The structural properties of cast aluminum parts are strongly affected by the solidification in the production process. The solidification dynamics determines the Secondary Dendrite Arm Spacing (SDAS), directly affecting the structural strength of the alloy. Simulation techniques enable the integrated design of chassis parts and their production equipment. However, in order to effectively predict the SDAS formation, the simulation models need to be investigated and calibrated. The present research investigates the SDAS formation models and identifies a robust relation to be used in Design by Simulation phases for AlSi7Mg0.3 parts.

2021 - Susceptor-assisted fast microwave sintering of TiN reinforced SiAlON composites in a single mode cavity [Articolo su rivista]
Canarslan, O. S.; Koroglu, L.; Ayas, E.; Canarslan, N. S.; Kara, A.; Veronesi, P.
abstract

In the present study, 17 wt % TiN reinforced α-β SiAlON composites were sintered at low temperature by susceptor-assisted microwave heating. The effect of TiN addition on dielectrical properties of starting powders, as well as the influence of sintering temperature on phase evolution, microstructure development and mechanical properties of α/β-SiAlON-TiN composites were investigated. The obtained results showed that TiN addition increased the microwave absorbing properties which is reflected in the peak sintering temperature. Thus, the α:β ratio decreased and mechanical properties were improved, especially the fracture toughness of the composites. Furthermore, an estimate of energy consumption during microwave assisted sintering at the laboratory scale is presented. As a result, the highest values for relative density (97.1%), Vickers hardness (13.35 ± 0.47 GPa), and fracture toughness (7.52 ± 0.54 MPa m1/2) were obtained by microwave sintering for 30 min at 1300 °C.

2021 - The effect of zr addition on melting temperature, microstructure, recrystallization and mechanical properties of a cantor high entropy alloy [Articolo su rivista]
Campari, E. G.; Casagrande, A.; Colombini, E.; Gualtieri, M. L.; Veronesi, P.
abstract

The effect of Zr addition on the melting temperature of the CoCrFeMnNi High Entropy Alloy (HEA), known as the “Cantor’s Alloy”, is investigated, together with its micro-structure, mechanical properties and thermomechanical recrystallization process. The base and Zr-modified alloys are obtained by vacuum induction melting of mechanically pre-alloyed powders. Raw materials are then cold rolled and annealed. recrystallization occurred during the heat treatment of the cold-rolled HEA. The alloys are characterized by X-ray diffraction, electron microscopy, thermal analyses, mechanical spectroscopy and indentation measures. The main advantages of Zr addition are: (1) a fast vacuum induction melting process; (2) the lower melting temperature, due to Zr eutectics formation with all the Cantor’s alloy elements; (3) the good chemical alloy homogeneity; and (4) the mechanical properties improvement of re-crystallized grains with a coherent structure. The crystallographic lattice of both alloys results in FCC. The Zr-modified HEA presents a higher recrystallization temperature and smaller grain size after recrystallization with respect to the Cantor’s alloy, with precipitation of a coherent second phase, which enhances the alloy hardness and strength.

2021 - Use of combustion synthesis/self-propagating high-temperature synthesis (SHS) for the joining of similar/dissimilar materials [Capitolo/Saggio]
Rosa, Roberto; Veronesi, Paolo; Leonelli, Cristina
abstract

2020 - A novel microwave and induction heating applicator for metal making: Design and testing [Articolo su rivista]
Colombini, E.; Papalia, K.; Barozzi, S.; Perugi, F.; Veronesi, P.
abstract

The use of microwave heating in primary metallurgy is gaining an increasing interest due to the possibility to selectively process ores and to volumetrically heat large amounts of low-thermal conductivity minerals. In this paper the study, development and testing of a new applicator combining the use of microwave and induction heating for rapid reduction of metal containing oxides is described. Numerical simulation was used in order to achieve the proper control over heat generation, considering the use of microwave solid state generators. A prototype, with a capacity up to 5 liters of standard input feed but with the predisposition for continuous processing has been designed, built and tested on reference loads like iron oxide powders and pellets. Results on the microwave heating part of the applicator indicate that it allows to efficiently and rapidly process these kinds of loads, which change from dielectric to conductors as reduction proceeds. The use of variable frequency solid state microwave generators allows to maximize energy efficiency and to controllably change the heating pattern inside the load.

2020 - A simple test method for measurement of the interface thermal resistance of coated and uncoated metal surfaces [Relazione in Atti di Convegno]
Pedrazzi, Simone; Vergnano, A.; Allesina, G.; Veronesi, Paolo; Leali, F.; Tartarini, P.; Muscio, A.
abstract

Dies for metal casting must often be coated internally to minimize interaction between the surface of the steel die and the melt metal during pouring and solidification. However, the added coating increases the thermal interface resistance during the cooling process and can thus extend the process duration. For example, numerical predictions and experimental results are matched if the interface resistance is even quintupled in the presence of usual interface coating, compared to the uncoated mold. In order to have a reasonable estimate of the interface thermal resistance, an easy to use measurement approach has been tested. This consists of contacting a cold and a hot samples of metals with known thermal properties, one at ambient temperature and the other one much hotter. The temperatures of the two samples, assumed to be uniform in each sample, are measured by thermocouples, and the interface resistance is retrieved from the time evolution pattern of those temperatures during the thermal transient that follows the instant in which the samples have been contacted.

2020 - A study on PVD coatings for reduction of friction and wear of swashplate axial piston pumps and motors [Relazione in Atti di Convegno]
Sola, R; Veronesi, P; Zardin, B; Borghi, M
abstract

Swashplate axial piston pumps and motors are widely used under severe conditions because of their capability to operate at high pressure values and various ranges of speeds, maintaining a good efficiency. In some operating conditions however, the machine efficiency may be relatively low because of insufficient lubrication and this causes rapid wear and high friction losses. PVD coatings may help in reducing the friction thus having a positive impact on the machine efficiency. For this reason, pin on disk testing were conducted to investigate the friction and wear behavior of different PVD coatings on various metallic substrates. A copper and tin alloy coated with PA-CVD DLC, a carburized 17NiCrMo7 with a PVD DLC coating and a nitrided 41CrAlMo7 PVD coated with TiCN were studied. Results of tribological testing, carried out at 0.2 and 0.5 m/s as sliding speed and 5000, 10000 and 20000 rounds as ending conditions, showed that wear and friction had been reduced; moreover, microstructure features were analyzed for understanding underlying mechanism and to allow selecting the most suitable coating for the application on the swashplate axial piston machine.

2020 - Cryogenic turning of the Ti6Al4V alloy [Articolo su rivista]
Sola, R.; Veronesi, P.
abstract

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 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 - 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 - On the effect of steel substrate alloying elements on the in-situ formation of intermediate thermal diffusion barrier layers [Articolo su rivista]
Rosa, R.; Veronesi, P.; Casagrande, A.
abstract

The aim of this work was to evaluate the feasibility of a hot-dipping aluminizing process, for the simultaneous production of an iron aluminide coating, a protective alumina topcoat layer and an intermediate thermal diffusion barrier layer, at the aluminide coating/steel substrate interface, the latter being thought in order to limit the detrimental depletion of Al content in the coating layer as a consequence of its inward diffusion towards the substrate. Indeed, the steel substrates were opportunely selected for their high weight percentages of alloying elements (namely Ni, Cr, Mn and Co) potentially able to diffuse from the substrate and react with the inward diffusing Al at the temperatures employed in the coating preparation, thus forming transition metal aluminides able to stop Al depletion, thus potentially prolong the lifetime of iron aluminide coatings in service. The effective in-situ growth of this intermetallic thermal diffusion layer was found to be strictly dependent on several factors, including the enthalpy of formation of the alloying-element aluminides, together with the atomic percentages of the selected alloying element in the steel substrate as well as its diffusion rate. The obtained results, can be considered an important contribution to the selection criteria of iron aluminides-coated steel substrates, to be employed in burdensome scenarios at high temperatures.

2020 - Rapid microwave synthesis of magnetocaloric Ni–Mn–Sn Heusler compounds [Articolo su rivista]
Trombi, L.; Cugini, F.; Rosa, R.; Amade, N. S.; Chicco, S.; Solzi, M.; Veronesi, P.
abstract

The magnetocaloric Ni50Mn25Sn25 Heusler compound was prepared via ultra-fast and sustainable microwave synthesis, by using the two ways hybrid microwave heating method. The structural, microstructural, magnetic and magnetocaloric properties of the prepared specimen are presented. The functional features of the synthetized sample result comparable with compounds obtained with other high-temperature preparation techniques that require larger amount of energy. The proposed time and energy-efficient preparation method could promote the development of large mass production routes of multifunctional huge-potential Heusler compounds, exploitable as active materials in thermomagnetic energy conversion machines and in other technological applications.

2019 - Coating of Titanium Substrates with ZrO2 and ZrO2-SiO2 Composites by Sol-Gel Synthesis for Biomedical Applications: Structural Characterization, Mechanical and Corrosive Behavior [Articolo su rivista]
Catauro, Michelina; Barrino, Federico; Bononi, Massimiliano; Colombini, Elena; Giovanardi, Roberto; Veronesi, Paolo; Tranquillo, Elisabetta
abstract

The use of metallic materials as implants presents some major drawbacks, such as their harmful effects on the living organism, especially those induced by corrosion. To overcome this problem, the implant surface of titanium implants can be improved using a coating of bioactive and biocompatible materials. The aim of this work is the synthesis of SiO2/ZrO2 composites with different percentages of zirconia matrix (20, 33 and 50 wt.%), by the sol-gel method to coat commercial Grade 4 titanium disks using a dip coater. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy was used to evaluate the interactions between the inorganic matrices. Furthermore, the mechanical properties and corrosive behavior of the SiO2/ZrO2 coatings were evaluated as a function of the ZrO2 content. The bioactive properties of the substrate coated with different composites were evaluated using simulated body fluid (SBF). The antibacterial activity was tested against gram-negative and gram-positive Escherichia coli and Enterococcus faecalis, respectively, to assess the release of toxic products from the different composites and to evaluate the possibility of using them in the biomedical field.

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 - E-LCA of Two Microwave Absorbers Obtained from Slag of Copper Primary Production [Articolo su rivista]
Zerazion, Elisabetta; Pini, M.; Mugoni, C.; Siligardi, C.; Veronesi, P.; Ferrari, A. M.
abstract

Purpose: This research investigates the environmental performance of two products obtained using slag derived from copper primary production (copper slag, CS). The first is a tile produced as a traditional stoneware ceramic plate (CS tile) and the second product is a glass–ceramic sample obtained by melt quenching method (CS bulk sample). The products are intended for use in industrial plants as auxiliary heating elements aimed at absorbing microwave. Methods: The environmental assessment was carried out using LCA methodology, and the obtained outcomes were compared to the results calculated for a traditional tile containing silicon carbide (SiC tile). Results: The analyses show that the innovative products have an environmental load of 74% for the CS tile and 54% for the CS bulk sample lower than the environmental impact calculated for the traditional SiC-based material tile. The latter presents a high environmental load due to the incidence on the total impact of the raw materials production. In fact, LCA analysis proves that copper slag production has an impact of 96% lower with respect to the SiC production. Conclusions: This study identifies a possible waste reduction strategy in accordance with the European end-of-waste criteria, but these results should be supported by a site analysis in order to provide an appropriate context for decision making.

2019 - Effect of the T6 heat treatment on corrosion behavior of additive manufactured and gravity cast AlSi10Mg alloy [Articolo su rivista]
Girelli, L.; Tocci, M.; Conte, M.; Giovanardi, R.; Veronesi, P.; Gelfi, M.; Pola, A.
abstract

This study investigates the corrosion behavior of AlSi10Mg alloy produced by additive manufacturing and gravity casting before and after T6 heat treatment. Electrochemical tests showed that the additive manufactured material in as-produced condition exhibits high corrosion resistance, due to the very fine microstructure, while immersion test allowed to identify an exfoliation-like corrosion phenomenon, which caused a significant mass loss. In this case, T6 heat treatment was beneficial for corrosion resistance since the related change in microstructure led to a less detrimental corrosion mechanism. Therefore, the T6 heat treatment resulted necessary to use additive manufactured AlSi10Mg components in aggressive chloride-bearing environments.

2019 - Evaluation of the usage-induced degradation of Genius and Reciproc nickel–titanium reciprocating instruments [Articolo su rivista]
Generali, Luigi; Borghi, Alessia; Lusvarghi, Luca; Bolelli, Giovanni; Veronesi, Paolo; Vecchi, Andrea; Consolo, Ugo; Becce, Carlo; Bertoldi, Carlo; Sassatelli, Paolo
abstract

The aim of this study was to characterize the main features and the usage-induced degradation of the Genius file after four severely curved root canal instrumentations and to compare their properties to the Reciproc files. Brand new and ex vivo used files were analysed by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), X-ray diffraction (XRD), optical metallography, and nano-indentation to disclose their morphological, chemical, mechanical, thermal, and phase composition features. Nano-indentation data were statistically analysed using the Student’s t test for normal distribution or the Kolmogorov–Smirnov test for not-normal distributions. SEM analysis showed the presence of micro-cracks near the tip on both files after ex vivo usage test. EDS analysis confirmed that both files are manufactured from an almost equiatomic NiTi alloy. DSC analysis revealed that the transition temperature of the Genius is below 20 °C, while that of the Reciproc is above 20 °C. XRD analysis of Genius files identified cubic B2 austenite with minor peaks of residual monoclinic B19 martensite, while the contemporaneous presence of martensite, austenite and hexagonal R-phase was observed in the Reciproc files. Significant differences in nanohardness and modulus of elasticity (P <.05) were observed in both Genius and Reciproc files before and after use. The collected results showed that both instruments can be safely used as single-use files.

2019 - High entropy alloy manufactured by SLM: characterization and development [Articolo su rivista]
Garzoni, A; Colombini, E; Giovanardi, R; Veronesi, P; Casagrande, A; Todaro, I
abstract

The aim of this study was to investigate an alternative manufacturing process to produce a High Entropy Alloy (HEA) starting from mechanically prealloyed powders, compared to the arc and induction melting. In this work the microstructural developments of the equimolar CoCrFeMnNi high entropy alloy processed by SLM were studied. The influence of process parameters and powders properties on the microstructure was characterized. X-ray diffraction and SEM-EDS semi-compositive investigations carried out on the HEA revealed a single crystalline structure (FCC). Preliminary evaluations of the mechanical properties showed higher microhardness values compared to the same alloy produced with conventional manufacturing processes, due to the finer microstructure morphology, the high dislocation density near subgrain and the precipitation of fine particles.

2019 - Improving Durability of Titanium for Biomedical Use by Composite Ceramic Coatings [Capitolo/Saggio]
Tranquillo, Elisabetta; Bononi, Massimiliano; Colombini, Elena; Giovanardi, Roberto; Veronesi, Paolo; Barrino, Federico; Catauro, Michelina
abstract

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 - 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 - Microwave sintering of SiAlON ceramics with TiN addition [Articolo su rivista]
Canarslan, O. S.; Rosa, R.; Koroglu, L.; Ayas, E.; Kara, A.; Veronesi, P.
abstract

α-β SiAlON/TiN composites with nominal composition of α:= β25:75 were fabricated by microwave sintering. The effect of titanium nitride addition on the phases, microstructure, microwave absorption ability and mechanical properties (Vickers hardness and fracture toughness) of the SiAlON-based composites were studied. Finite Difference Time Domain (FDTD) software was used for the numerical simulation in order to assess the most suitable experimental setup. Sintering trials were performed in a single mode microwave furnace operating at 2.45 GHz and a power output of 660W, for a reaction time of 30 min. SiC blocks were used as a susceptor to accelerate the microwave processing by hybrid heating, with reduced heat losses from the surface of the material of the α- βSiAlON/TiN composites. The optimum comprehensive mechanical properties, corresponding to a relative density of 96%, Vickers hardness of 12.98 ± 1.81 GPa and Vickers indentation fracture toughness of 5.52 ± 0.71 MPa.m1/2 were obtained at 850°C when the content of TiN was 5 wt.%.

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.

2018 - Al, cu and zr addition to high entropy alloys: The effect on recrystallization temperature [Relazione in Atti di Convegno]
Colombini, Elena; Garzoni, Andrea; Giovanardi, Roberto; Veronesi, Paolo; Casagrande, Angelo
abstract

The equimolar Cr, Mn, Fe, Co and Ni alloy, first produced in 2004, was unexpectedly found to be single-phase. Consequently, a new concept of materials was developed: high entropy alloys (HEA) forming a single solid-solution with a near equiatomic composition of the constituting elements. In this study, an equimolar CoCrFeMnNi HEA was modified by the addition of 5 at% of either Al, Cu or Zr. The cold-rolled alloys were annealed for 30 minutes at high temperature to investigate the recrystallization kinetics. The evolution of the grain boundary and the grain size were investigated, from the as-cast to the recrystallized state. Results show that the recrystallized single phase FCC structures exhibits different twin grains density, grain size and recrystallization temperatures as a function of the at.% of modifier alloying elements added. In comparison to the equimolar CoCrFeMnNi, the addition of modifier elements increases significantly the recrystallization temperature after cold deformation. The sluggish diffusion (typical of HEA alloys), the presence of a solute in solid solution as well as the low twin boundary energy are responsible for the lower driving force for recrystallization.

2018 - From Field to Shelf: How Microwave-Assisted Extraction Techniques Foster an Integrated Green Approach [Capitolo/Saggio]
Rosa, Roberto; Ferrari, Erika; Veronesi, Paolo
abstract

Microwave-assisted extraction of organic compounds from vegetal matrixes is a relatively young ield of research. The exceptional results achievable at the laboratory scale by microwave-assisted extraction, like shorter extraction times, lower average temperatures, reduction of organic solvents use, higher yields and selectivity, as well as energy and cost saving, are not always accompanied by a successful scale up. Nevertheless, microwave-assisted techniques of extraction have been multiplying during last decades. In this framework, a deeper knowledge of microwave applicator design criteria is mandatory. This chapter starts from the basis of microwave heating and the relevant material properties involved in a successful microwave-assisted extraction application, to continue with a short overview on how such properties can be measured and used to optimize the experimental setup or a possible scale up of the process under investigation. A comprehensive review of recent applications of microwave-assisted extraction, applied to vegetal matrixes, is presented next. The chapter ends reviewing duplex treatments of vegetal matrixes for extraction purposes, where microwave heating is coupled to other techniques, like ultrasounds, and indicating new paths, where the recent advent of new microwave solid-state generators has led to beter process control and higher yields and energy efficiency.

2018 - High entropy alloys obtained by field assisted powder metallurgy route: SPS and microwave heating [Articolo su rivista]
Colombini, E.; Rosa, R.; Trombi, L.; Zadra, M.; Casagrande, A.; Veronesi, P.
abstract

The aim of this work was to investigate the field assisted powder metallurgy route for producing HEAs at equimolar composition, i.e. FeCoNiCrAl, starting from metal powders. Both mixed, mechanically activated and mechanically alloyed powders have been used. The powders obtained by mechanical alloying were synthesized only by SPS, whereas the remaining ones were sintered by SPS or microwave heating. The investigated field assisted sintering techniques allowed an extremely short alloying time, high energy density on the load and negligible contamination by the surrounding environment. Both the conducted sintering-synthesis technology resulted not definitive to produce chemical homogeneity and to obtain a single stable structure. Thus a subsequently heat treatment was required. The post heat treatment, indeed, led to a single crystalline structure (FCC) and the material was fully recrystallized. After heat treatment samples are isomorphic: they exhibit two different phases with the same FCC cell, but different chemical composition, in detail Fe-Cr richer and Al-Ni richer. SPS-ed samples present a reduced porosity, while microwave processed ones are much more porous and this is reflected in the mechanical properties.

2018 - Influence of a post-tempering cryogenic treatment on the toughness of the AISI M2 steel [Abstract in Atti di Convegno]
Sola, R.; Veronesi, P.; Giovanardi, R.; Merlin, M.; Garagnani, G. L.; Soffritti, C.; Morri, A.; Parigi, G.
abstract

A deep cryogenic treatment, carried out after quenching, can improve several mechanical properties of many metallic materials, but there are few reports on the effect of post-tempering deep cryogenic treatments on steels. The main aim of the present research work is the study of the effects of a post-tempering cryogenic treatment on microstructural and mechanical properties of the AISI M2 tool steel. In particular, the results of impact strength, fracture toughness, scratch test and microhardness show that the microstructural changes, induced by the post-tempering cryogenic treatment, promote a relief of residual stresses and a little improvement of mechanical properties, except for the hardness. Microstructural analysis performed by means of Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), equipped with an Energy Dispersive X-ray Spectroscopy (EDS) microprobe, confirmed the precipitation of small and homogeneously dispersed secondary carbides. The induced precipitation of fine and homogeneously dispersed sub-micrometric carbides does not alter hardness but reduces residual stresses and increase fracture toughness. Finally, scratch test proved to be an alternative simple technique to determine fracture toughness of cryogenically treated steels.

2018 - Nitriding of stainless steels: Combined plasma-gaseous process [Articolo su rivista]
Giovanardi, R.; Veronesi, P.; Sola, R.; Borg, L.; Parigi, G.
abstract

In this work a combined process for the nitriding of stainless steels was developed, applying a first plasma nitriding treatment, which acts as an "activator" of the surface, then followed by a gaseous nitriding step, to increase the diffusion of the nitrogen and therefore the penetration of the treatment. The substrates for the process are two different stainless steels, AISI 304 and AISI 422, subjected to the single treatment of plasma nitriding (NP) and to the combined treatment of plasma nitriding followed by gaseous nitriding (NPNZ). The samples obtained were characterized (and compared with the two non-treated materials, NT) by cross-section micro-hardness profiles, metallographic analysis (SEM), wear tests (pin-on-disk tribometer) and accelerated corrosion tests (polarizations in acidic environment, H2SO4, and neutral saline, NaCl). The results obtained confirm that the combined treatment (NPNZ) is able to significantly increase the hardening depths, without excessively compromising the corrosion resistance in chlorides of the tested steels.

2018 - SPS-assisted Synthesis of SICp reinforced high entropy alloys: reactivity of SIC and effects of pre-mechanical alloying and post-annealing treatment [Articolo su rivista]
Colombini, E.; Lassinantti Gualtieri, M.; Rosa, R.; Tarterini, F.; Zadra, M.; Casagrande, A.; Veronesi, P.
abstract

In this work a traditional high entropy alloy (FeCoNiCrAl) was reinforced by uniformly distributed reactive silicon carbide (SiC) particles by a powder metallurgy synthetic route, using as precursors simply mixed powders or mechanically prealloyed ones. The reactive sintering produced a single isomorphic BCC structure. The sample microstructure resulted equiassic, more homogenous in samples based on prealloyed powders. The instability of SiC in the presence of metal precursors resulted in the formation of more stable carbides and silicides, as well as in carbon diffusion in the high entropy alloy matrix and partially unreacted SiC particles. The formation of these newly formed fine precipitates, as well as the presence of residual SiC were useful to increase the hardness of the alloy.

2017 - A Novel Duplex Treatment of C20 Steel Combining Low-Pressure Carburizing and Laser Quenching [Articolo su rivista]
Sola, R.; Veronesi, P.; Giovanardi, R.; Parigi, G.
abstract

The aim of this experimental study is to improve hardness layer thickness and wear resistance through laser quenching. Laser quenching treatment is used as a part of duplex treatments to improve the thickness and hardness of surface layers of steels. This duplex treatment allow to reach a very high hardening depth, improving wear resistance and load bearing capacity. In present study the surface properties of a low carbon steel treated by low-pressure carburizing prior to a laser quenching process are investigated. Results demonstrate that laser quenching is an effective means of improving wear resistance of low-pressure carburized layer and the improvement is significantly affected by increase of hardened layer thickness.

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 - A novel method for fracture toughness evaluation of tool steels with post-tempering cryogenic treatment [Articolo su rivista]
Sola, Ramona; Giovanardi, Roberto; Parigi, Giovanni; Veronesi, Paolo
abstract

Cryogenic treatments are usually carried out immediately after quenching, but their use can be extended to post tempering in order to improve their fracture toughness. This research paper focuses on the influence of post-tempering cryogenic treatment on the microstructure and mechanical properties of tempered AISI M2, AISI D2, and X105CrCoMo18 steels. The aforementioned steels have been analysed after tempering and tempering + cryogenic treatment with scanning electron microscopy, X-ray diffraction for residual stress measurements, and micro-and nano-indentation to determine Young’s modulus and plasticity factor measurement. Besides the improvement of toughness, a further aim of the present work is the investigation of the pertinence of a novel technique for characterizing the fracture toughness via scratch experiments on cryogenically-treated steels. Results show that the application of post-tempering cryogenic treatment on AISI M2, AISI D2, and X105CrCoMo18 steels induce precipitation of fine and homogeneously dispersed sub-micrometric carbides which do not alter hardness and Young’s modulus values, but reduce residual stresses and increase fracture toughness. Finally, scratch test proved to be an alternative simple technique to determine the fracture toughness of cryogenically treated steels.

2017 - An introduction to dielectric heating [Capitolo/Saggio]
Veronesi, P.
abstract

2017 - Effetto del trattamento preliminare sulle proprietà dell'acciaio AISI M2 sottoposto a trattamento criogenico [Articolo su rivista]
Sola, R.; Veronesi, P.; Giovanardi, R.; Forti, A.; Parigi, G.
abstract

Cryogenic treatment is widely used to enhance mechanical and physical properties of tool steels, hot work steels and high carbon steels. The application of cryogenic treatment on cutting tools improves wear resistance, hardness, dimensional stability, cutting tool durability, tool life and it reduces tool consumption, leading to a general production cost reduction. These benefits are achieved by deep cryogenic treatment because it decreases retained austenite content and it promotes the precipitation of fine carbides uniformly dispersed in martensite matrix. Retained austenite is a soft and unstable phase that reduces steel hardness and could be converted into martensite in working conditions and under stress, forming brittle (not tempered) martensite, with an increase of volume of 4%, inducing local stresses. Cryogenic treatment, by transforming retained austenite to martensite, improves dimensional stability. In addition to the transformation of retained austenite to martensite, secondary and fine carbides are formed in the structure, increasing mechanical properties, toughness and wear resistance. Cryogenic treatment generate an high internal stress state due to thermal stresses and transformation of martensite into austenite. Furthermore, thermal stresses increase the number of structural defects and the martensite, carbon-supersaturated, becomes unstable. Carbon atoms move towards the new structural defects created, martensite is decomposed and carbide precipitation takes place during the warming up phase to room temperature, producing a reduction of residual stress and resulting in an homogeneously dispersed network of tiny carbides. the greatest improvement in properties is obtained by carrying out the deep cryogenic treatment between quenching and tempering. However, in case of tool steels, an improvement can be obtained even performing cryogenic treatment at the end of the usual heat treatment cycle, i.e. to treat the finished tools. This last solution is more flexible than the previous one and can extend the use of the treatment to many practical applications. Cryogenic treatment barely changes the tensile mechanical properties and hardness of tool steel and hot work steel. But it is worth noting that cryogenic treatment notably improved fracture toughness of such steels because a fine, homogeneously dispersed carbide precipitation and a tougher martensite matrix are formed (with lower carbon content). In this framework, toughness measurement is an important tool to assess the effectiveness of the cryogenic treatment on such steels, but standard methods require careful sample preparation and dedicated equipment, while a simpler technique could be easily adopted as a quality control tool, as an alternative to ASTM E399 e BS 5447 standard method. Akono et al. in [14,15] proposed an alternative novel technique to measure the fracture toughness by scratch testing. Hence, aim of the current study is to investigate the effect of post-tempering cryogenic treatment on the microstructure and mechanical properties of AISI M2 steel. The samples were treated with two different cycles before cryogenic treatment: 1. quenching, cooling at-80°C, three tempering; 2. quenching, three tempering. All the samples were cryogenically cooled for 4h, 12h and 24 h to investigate also the influence of the time at-196°C. The results of microstructure, wear tests, X-ray diffraction, instrumented microhardness and scratch tests shows that posttempering cryogenic treatment promotes the precipitation of fine and homogeneously dispersed carbides, improves wear resistance and fracture toughness, without decreasing hardness. Also the heat treatment cycle before cryogenic cooling influences the wear and mechanical properties of the steel.

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 - Laser hardening of steel sintered parts [Relazione in Atti di Convegno]
Veronesi, P.; Sola, R.; Colombini, E.; Giovanardi, R.; Parigi, G.
abstract

The possibility of applying rapid and localized laser hardening to near-net shape parts, like the ones deriving from powder metallurgy (P/M) is investigated, demonstrating that even low alloyed steels (Fe + 2% Cu + 0,7% C) can be successfully heat treated with minimal or no dimensional variations. Laser hardening conditions have been selected on the basis of the results of the previous research, carried out by means of an Nd-YAG high power system [1]. To avoid some carbon loss, observed on previous activities, the samples have been protected by neutral atmosphere. The microstructural features of the laser hardened steels have been analyzed by optical microscopy, whereas the surface micro-geometry has been characterized by scanning electron microscope. Hardened depth (HD), hardened width (HW) and hardened area (HA) have been measured as well. As expected, the micro-hardness profiles present a sharp drop at low distance from the hardened surface. The typical splitting between hardened zone and heat-Affected zone (HAZ), well known from laser hardened fully dense steels, has been observed also on low-Alloy sintered steels. The use of a protective atmosphere has been helpful to control surface decarburization and to prevent oxidation. The research confirm that Laser transformation Hardening (LTH) is a suitable hardening process of P/M components, through the action of a scanning laser beam. The short heating time and the modest volume fraction structurally modified can contribute to avoid part distortion, in comparison with other hardening methods.

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 [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 - 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

2017 - Microwave-assisted preparation of multi principal element alloys by powder metallurgy approach [Relazione in Atti di Convegno]
Colombini, E.; Borromei, I.; Trombi, L.; Casagrande, A.; Veronesi, P.
abstract

According to literature, the synthetic route to produce High entropy alloys (HEAs) 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 microwave heating. In this work FeCoNiCrAl and FeCoNiCuAl, both equiatomic and reinforced by the 10% wt. of SiC were prepared by microwave assisted techniques. Results show that direct microwave heating of the powder precursors occurs, until the ignition conditions are reached. The temperature and duration of the microwave-assisted process result 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. The homogeneity of the samples resulted in being good in all cases, without the dendritic segregation typically occurring by liquid phase processing. © 2017 European Powder Metallurgy Association (EPMA)

2017 - Modification of Ti6Al4V implant surfaces by biocompatible TiO2/PCL hybrid layers prepared via sol-gel dip coating: Structural characterization, mechanical and corrosion behavior [Articolo su rivista]
Catauro, Michelina; Bollino, Flavia; Giovanardi, Roberto; Veronesi, Paolo
abstract

Surface modification of metallic implants is a promising strategy to improve tissue tolerance, osseointegration and corrosion resistance of them. In the present work, bioactive and biocompatible organic-inorganic hybrid coatings were prepared using a sol-gel dip coating route. They consist of an inorganic TiO2 matrix in which different percentages of poly(ε-caprolactone) (PCL), a biodegradable and biocompatible polymer, were incorporated. The coatings were used to modify the surface of Ti6Al4V substrates in order to improve their wear and corrosion resistance. The chemical structure of the coatings was analyzed by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. Coating microstructure, mechanical properties and ability to inhibit the corrosion of the substrates were evaluated as a function of the PCL amount. Scanning electron microscopy (SEM) showed that the polymer allows to obtain crack-free coatings, but when high percentages were added uncoated areas appear. Nano-indentation tests revealed that, as expected, surface hardness and elastic modulus decrease as the percentage of polymeric matrix increases, but scratch testing demonstrated that the coatings are effective in preventing scratching of the underlying metallic substrate, at least for PCL contents up to 20 wt%. The electrochemical tests (polarization curves acquired in order to evaluate the corrosion resistance) allowed to asses that the coatings have a significant effect in term of corrosion potential (Ecorr) but they do not significantly affect the passivation process that titanium undergoes in contact with the test solution used (modified Dulbecco's phosphate-buffered saline or DPBS).

2017 - Numerical Simulation and Experimental Validation of MIG Welding of T-Joints of Thin Aluminum Plates for Top Class Vehicles [Articolo su rivista]
Bonazzi, Enrico; Colombini, Elena; Panari, Davide; Vergnano, Alberto; Leali, Francesco; Veronesi, Paolo
abstract

The integration of experiments with numerical simulations can efficiently support a quick evaluation of the welded joint. In this work, the MIG welding operation on aluminum T-joint thin plate has been studied by the integration of both simulation and experiments. The aim of the paper is to enlarge the global database, to promote the use of thin aluminum sheets in automotive body industries and to provide new data. Since the welding of aluminum thin plates is difficult to control due to high speed of the heat source and high heat flows during heating and cooling, a simulation model could be considered an effective design tool to predict the real phenomena. This integrated approach enables new evaluation possibilities on MIG-welded thin aluminum T-joints, as correspondence between the extension of the microstructural zones and the simulation parameters, material hardness, transient 3D temperature distribution on the surface and inside the material, stresses, strains, and deformations. The results of the mechanical simulations are comparable with the experimental measurements along the welding path, especially considering the variability of the process. The results could well predict the welding-induced distortion, which together with local heating during welding must be anticipated and subsequently minimized and counterbalance.

2017 - Optimization of laser welding of dissimilar corrosion resistant alloys [Relazione in Atti di Convegno]
Cavallini, Michele; Veronesi, Paolo; Lusvarghi, Luca; Colombini, Elenca; Giovanardi, Roberto; Rigon, Lorenzo
abstract

The use of multi-materials components has the benefit of coupling each material's benefit where it is needed, thus achieving, for instance, heat, wear and corrosion resistance. Joining of dissimilar metals is a challenging task due to the large differences in properties. In this framework, the use of (Quasi Continuous Wave (QCW) Fiber Lasers) proved to be effective in multi-materials components assembly thanks to the high power density but low energy-input. In this paper the laser welding of dissimilar materials, namely stellite and stainless steel, is investigated and optimized in terms of corrosion resistance, comparing the results to conventional brazing joining. Results demonstrate that the optimized laser welding conditions, with the use of a proper filler material, lead to the obtainment of defect-free joints, with minimum alteration of the base materials.

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).

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 - Laser hardening of low-alloyed PM steels [Abstract in Atti di Convegno]
Bocchini, G. F.; Colombini, E.; Mannini, A.; Parigi, G.; Poli, G.; Sola, R.; Veronesi, P.
abstract

The good results obtained by laser-hardening of high-strength P/M steels drove to extend the research to low-alloy material (Fe-Cu-C; 6,6 g/cm3 density). Process conditions have been selected on the basis of previous results. To avoid carbon loss, observed on previous tests, the samples have been also protect-ed, by neutral atmosphere, during any critical step. The microstructural features of the laser hardened Cu-C P/M steels have been analyzed by LOM, whereas the surface micro-geometry has been characterized by SEM. Hardened depth (HD), hardened width (HW) and hardened area (HA) have been measured. As expected, the micro-hardness profiles present a sharp drop at low distance from the hardened surface. The typical splitting between hardened zone and heat-affected zone (HAZ), well known from laser hard-ened fully dense steels, has been observed also on low-alloy sintered steels. The addition of a protective atmosphere has been helpful to control decarburization of thin surface layers or surface oxidation. The re-search confirm that Laser transformation Hardening (LTH) is a suitable process to get hard, wear resistant surface, or defined spots on P/M components. The short heating time and the modest volume fraction structurally modified can contribute to avoid part distortion, in comparison with induction hardening. The possibility of very selective and precise hardening treatment has been confirmed. The results of the re-search open new possibilities to widen the use of high-property P/M parts, based on low-alloy materials, for wear-resistant and high precision applications.

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 - 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 - Sintesi assistita da microonde per ottenere leghe ad alta entropia a diverso tenore di alluminio [Articolo su rivista]
Colombini, Elena; Rosa, Roberto; Trombi, Lorenzo; Veronesi, Paolo
abstract

In questo studio si è analizzato l’effetto della variazione del contenuto di alluminio nella sintesi e microstruttura della lega ad alta entropia di composizione: FeCoNiCrAlx, dove x può assumere i valori x=1,1.5,2,3. Il ruolo atteso dell’alluminio durane la sintesi è di creare una fase liquida che acceleri le reazioni, che altrimenti avverrebbero unicamente allo stato solido, mentre i rimanenti elementi comprendono almeno un elemento ferromagnetico per migliorare l’assorbimento delle microonde durante la sintesi. Dalle caratterizzazioni effettuate si evince che all’aumentare del contenuto di alluminio si ottengono leghe composizionalmente più omogenee, una promozione della struttura cristallina CCC e l’aumento della durezza media. La lega equimolare FeCoNiCrAl è stata poi confrontata con la lega FeCoNiCuAl. Dalla diffrazione è possibile vedere la tendenza della lega di sposarsi verso una struttura cristallina CFC, grazie alla presenza di rame.

2016 - Tempra laser di acciai sinterizzati basso-legati [Articolo su rivista]
Bocchini, G. F.; Colombini, Elena; Mannini, A.; Parigi, G.; Poli, Giorgio; Sola, Ramona; Veronesi, Paolo
abstract

An experimental investigation with 4 kW diodes laser system was carried out to study the effects of laser hardening process parameters on properties of P/M steels, based on prealloyed and diffusion-bonded powders. Eight different process parameters have been applied to optimize the process afterwards they have been set to two different compositions. The independent variables investigated have been: surface temperature, T, and laser travel speed (mm/min). The microstructural features of the laser hardened P/M steels were analyzed using LOM and the surface morphology has been characterized by SEM. Hardened depth both via hardness test and via optical measures were evaluated as well and used as responses for the ANOVA of the experimental data gathered. This work reveals the possibility to apply a selective and precise hardening treatment, like Laser Transformation hardening (LHT), to high-property P/M steel parts. Thanks to ANOVA analysis the correlation between energy density (ED) and optical dimension of treated zone has been identified. By increasing temperature and speed the density energy ED decreases, indeed at high temperature and speed the heated zone is larger. At the same speed, a temperature increase leads to a surface hardness decrease. A similar value of hardness depth (about 0.8 mm) has been detected by means of hardness profiles. The result has been strengthened by scratch test. The parabolic zone presents a very fine martensitic structure on the top of laser trail, and bainite microstructure on transition zone, as literature related. The transition zone between the laser affected zone and the base metal exhibits a micro hardness gradient. It is also possible to notice some Cu diffusion from outer to inner zone. By comparison among LHT specimens and sintering-hardened and stress-relieved one, (characterized by similar chemical compositions) penetration depth and hardness values appear similar. Transformation Hardening (LTH) is a suitable process for producing hard surface, on defined spots of P/M components, through the action of a scanning laser beam. The short heating time enables to decrease part distortion and surface oxidation, in comparison with sinter hardened. The possibility of very selective and precise hardening treatment seems to open new possibilities to widen the use of high-property P/M parts, based on advanced design, for demanding applications.

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

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 - Effect of deep cryogenic treatment on the properties of AISI M2 steel [Relazione in Atti di Convegno]
Sola, Ramona; Poli, Giorgio; Defanti, Silvio; Veronesi, Paolo; Parigi, Giovanni
abstract

Deep cryogenic treatment is a special kind of bulk hardening heat treatment performed on a big variety of tool and carburized steels, to improve mechanical properties and wear resistance. The mai reason for this is the complete transformation from austenite into martensite plus the formation of submicrometric carbides dispersed in the tempered martensitic structure. The greatest improvement in properties is obtained by carrying out the deep cryogenic treatment between quenching and tempering. However, a significant improvement can be obtained even by treating the tools at the end of the usual heat treatment cycle, i.e. the finished tools. This last solution is more flexible than the other one and can extend the use of the treatment to many practical applications. In order to check the potential of deep cryogenic treatment on the performance of the finished products, an investigation was carried out on the AISI M2 high speed steel quenched, tempered and deep cryogenically treated. The findings shows that the cryogenic treatment promotes the precipitation of submicrometric carbides, that increment wear resistance and nano-hardness and decrease residual stresses.

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 - Nitriding and post-oxidation treatments on 17-4PH stainless steel: optimization of the process to preserve high corrosion resistance [Articolo su rivista]
Giovanardi, R.; Poli, G.; Veronesi, P.; Parigi, G.; Raffaelli, N.
abstract

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 - 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 - Tempra laser di acciai sinterizzati omogenei o disomogenei [Laser hardening of homogeneous and inhomogeneous p/m steels] [Articolo su rivista]
Colombini, Elena; Bocchini, G. F.; Parigi, G.; Sola, Ramona; Veronesi, Paolo; Poli, Giorgio
abstract

An experimental investigation with 4 kW diodes laser system was carried out to study the effects of laser hardening process parameters on properties of P/M steels, based on prealloyed and diffusion-bonded powders. Eight different process parameters have been applied to optimize the process afterwards they have been set to two different compositions. The independent variables investigated have been: surface temperature, T, and laser travel speed (mm/min). The microstructural features of the laser hardened P/M steels were analyzed using LOM and the surface morphology has been characterized by SEM. Hardened depth both via hardness test and via optical measures were evaluated as well and used as responses for the ANOVA of the experimental data gathered. This work reveals the possibility to apply a selective and precise hardening treatment, like Laser Transformation hardening (LHT), to high-property P/M steel parts. Thanks to ANOVA analysis the correlation between energy; density (ED) and optical dimension of treated zone has been identified. By increasing temperature and speed the density energy ED decreases, indeed at high temperature and speed the heated zone is larger. At the same speed, a temperature increase leads to a surface hardness decrease. A similar value of hardness depth (about 0.8 mm) has been detected by means of hardness profiles. The result has been strengthened by scratch test. The parabolic zone presents a very fine martensitic structure on the top of laser trail, and bainite microstructure on transition zone, as literature related. The transition zone between the laser affected zone and the base metal exhibits a micro hardness gradient. It is also possible to notice some Cu diffusion from outer to inner zone. By comparison among LHT specimens and sintering-hardened and stress-relieved one, (characterized by similar chemical compositions) penetration depth and hardness values appear similar. Transformation Hardening (LTH) is a suitable process for producing hard surface, on defined spots of P/M components, through the action of a scanning laser beam. The short heating time enables to decrease part distortion and surface oxidation, in comparison with sinter hardened. The possibility of very selective and precise hardening treatment seems to open new possibilities to widen the use of high-property P/M parts, based on advanced design, for demanding applications.

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 - Trattamenti termochimici di nitrurazione e post-ossidazione su acciai 17-4PH: ottimizzazione dei parametri di processo per massimizzare la resistenza a corrosione [Articolo su rivista]
Giovanardi, Roberto; Poli, Giorgio; Veronesi, Paolo; Parigi, G.; Raffaelli, N.
abstract

L’acciaio inossidabile 17-4PH viene solitamente trattato termicamente per incrementarne le proprietà meccaniche. Per migliorare ulteriormente la resistenza ad usura di tale acciaio è possibile sottoporlo a trattamenti termochimici, quali ad esempio la nitrurazione. Trattandosi di un acciaio inossidabile, in grado di presentare allo stato di fornitura una notevole resistenza a corrosione conferita dall’elevato contenuto di cromo presente in lega, viene spontaneo chiedersi se e quanto i trattamenti termici e termochimici possano influenzare questa proprietà. Lo scopo del presente lavoro è quello di valutare come l’applicazione di trattamenti termici e termochimici, solitamente impiegati per incrementare proprietà meccaniche e anti-usura, influiscano sulla resistenza a corrosione dell’acciaio e di intervenire sulle variabili di processo degli stessi (oppure mediante trattamenti successivi quali la post-ossidazione) al fine di individuare le condizioni di trattamento ottimali per preservare una discreta resistenza a corrosione. A tale scopo sono state eseguite prove di corrosione accelerata, mediante acquisizione di curve di polarizzazione in cella elettrochimica, su provini sottoposti a diverse combinazioni di trattamenti termici e termochimici (invecchiamento H1025, nitrurazione, post-ossidazione) eseguiti in diverse combinazioni di tempi e temperature. Oltre alla caratterizzazione elettrochimica i provini sono stati sottoposti a prove di microdurezza HV superficiale ed in sezione, per valutare l’effettiva efficacia dei trattamenti applicati in termini di proprietà meccaniche ed antiusura. Nonostante i migliori risultati in termini di incremento della durezza superficiale e di profondità di indurimento siano stati raggiunti con trattamenti che compromettono notevolmente la resistenza a corrosione dell’acciaio, il lavoro svolto ha permesso di individuare ed ottimizzare sequenze di trattamenti che permettono di preservare quasi completamente la resistenza a corrosione dell’acciaio, pur incrementando la durezza superficiale fino a valori di oltre 850HV

2014 - Corrosion behavior and mechanical properties of bioactive sol-gel coatings on titanium implants [Articolo su rivista]
Catauro, M; Bollino, F.; Papale, F.; Giovanardi, Roberto; Veronesi, Paolo
abstract

Organic-inorganic hybrid coatings based on zirconia and poly (ε-caprolactone) (PCL) were prepared by means of sol-gel dip-coating technique and used to coat titanium grade 4 implants (Ti-4) in order to improve their wear and corrosion resistance. The coating chemical composition has been analysed by ATR-FTIR. The influence of the PCL amount has been investigated on the microstructure, mechanical properties of the coatings and their ability to inhibit the corrosion of titanium. SEM analysis has shown that all coatings have a nanostructured nature and that the films with high PCL content are crack-free. Mechanical properties of the coatings have been studied using scratch and nano-indentation tests. The results have shown that the Young's modulus of the coatings decreases in presence of large amounts of the organic phase, and that PCL content affects also the adhesion of the coatings to the underlying Ti-4 substrate. However, the presence of cracks on the PCL-free coatings affects severely the mechanical response of the samples at high loads. The electrochemical behavior and corrosion resistance of the coated and uncoated substrate has been investigated by polarization tests. The results have shown that both the coatings with or without PCL don't affect significantly the already excellent passivation properties of titanium.

2014 - Effects of Surface Morphology on the Wear and Corrosion Resistance of Post-Treated Nitrided and Nitrocarburized 42CrMo4 Steel [Articolo su rivista]
Sola, Ramona; Poli, Giorgio; Veronesi, Paolo; Giovanardi, Roberto
abstract

The surface of alloyed carbon steel was subjected to thermochemical modification by nitrocarburizing and nitriding with or without postoxidation in order to improve its mechanical properties, corrosion, and wear resistance. Treated samples were characterized by testing their basic properties (compound layer thickness, nitriding, nitrocarburizing depth, and surface hardness) according to standards. Detailed estimation of the modified metal surface was performed by additional testing: X-ray diffraction, microstructure, surface roughness and topography, and wear and corrosion resistance. The surface layer obtained after nitrocarburizing treatment consists mainly of ε-Fe2-3(N,C) and γ'-Fe4(N,C); similarly, the nitrided surface is formed by ε-Fe2-3N and γ'-Fe4N iron nitrides. The surface layer after postoxidation contains additionally Fe3O4. The results obtained show that nitrocarburization, nitridation, and postoxidation result in better mechanical, wear, and corrosion resistance of 42CrMo4 steel, and postoxidized sample properties are influenced by surface morphology.

2014 - Influence of PCL on mechanical properties and bioactivity of ZrO 2-based hybrid coatings synthesized by sol-gel dip coating technique [Articolo su rivista]
Catauro, Michelina; Bollino, Flavia; Veronesi, Paolo; Lamanna, Giuseppe
abstract

The biological properties of medical implants can be enhanced through surface modifications such as to provide a firm attachment of the implant. In this study, organic-inorganic hybrid coatings have been synthesized via sol-gel dip coating. They consist of an inorganic ZrO2 matrix in which different amounts of poly(ε-caprolactone) have been entrapped to improve the mechanical properties of the films. The influence of the PCL amount on the microstructural, biological and mechanical properties of the coating has been investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses have shown that the hybrids used for the coating are homogenous and totally amorphous materials; Fourier transform infrared spectroscopy (FT-IR) has demonstrated that hydrogen bonds arise between the organic and inorganic phases. SEM and atomic force microscopy (AFM) have highlighted the nanostructured nature of the film. SEM and EDS analyses, after soaking the samples in a simulated body fluid (SBF), have pointed out the apatite formation on the coating surface, which proves the bone-bonding ability of the nanocomposite bioactive films. Scratch and nano-indentation tests have shown that the coating hardness, stiffness and Young's modulus decrease in the presence of large amounts of the organic phase.

2014 - Influence of process parameters and alloying type on properties of laser quenched PM-steels [Relazione in Atti di Convegno]
Colombini, Elena; Bocchini, G. F.; Parigi, G.; Sola, Ramona; Veronesi, Paolo; Poli, Giorgio
abstract

Different alloyed PM steels have been laser quenched in industrial equipment laser diodes (4 kW, controlled by material surface temperature). The aim of this work is to investigate their responses to different process condition and different alloying metals, i.e. Cu, Ni, Mo, Cr and C. Furthermore the microstructure of hardened layer, heat affected zone (HAZ) and bulk zone Pre-alloyed, diffusion bonded and hybrid raw materials have been used. Design of Experiments has been the approach for evaluating the effect of treatment parameters (i.e temperature, spot size and speed) and to develop predictive models, correlating such parameters to hardening depth and scratch hardness number. Results demonstrated which valuable properties could be achieved, even through relatively low alloying. The promising results are encouraging since they allow to forecast a possible positive combination of high local hardness and wear resistance of high precision PM part.

2014 - Laser Quenching of Ionic Nitrided Steel: Effect of Process Parameters on Microstructure and Optimization [Articolo su rivista]
Colombini, Elena; Sola, Ramona; Parigi, GIAN BATTISTA; Veronesi, Paolo; Poli, Giorgio
abstract

The surface properties of 40CrMnMo7 steel have been increased by ionic nitriding thermo chemical treatment followed by laser quenching. Nitriding treatment increases the wear resistance and decreases the wear coefficient, guaranteeing an uniform, though shallow, hardening depth. Combining nitriding with laser quenching has been shown to increase of the hardening depth, while retaining the advantages obtained by the first treatment. In this work the effect of laser quenching parameters on microstructure and mechanical properties of 40CrMnMo7 steel have been investigated and predictive models developed suitable for further optimization of the process. DoE has been exploited to reduce the number of experiments and for evaluating by statistic methods the optimized process parameters.

2014 - Laser hardening of homogeneous or not-homogeneous PM steels [Relazione in Atti di Convegno]
Bocchini, G. F.; Colombini, Elena; Parigi, G; Sola, Ramona; Veronesi, Paolo; Poli, Giorgio
abstract

An experimental investigation with 4 kW diodes laser system was carried out to study the effects of laser hardening process parameters on properties of P/M steels, based on prealloyed, admixed or diffusion-bonded powders. The surface temperature of treated zone has been measured by pyrometer (to avoid local melting or surface damaging) and the travel speed on scanning the surface of test samples has been an investigated variable. A special attention has been given to specimen clamping, to avoid any misalignment with the beam movement. The independent variables investigated have been: surface temperature, T, travel speed (mm/min). The microstructural features of the laser hardened P/M steels were analyzed using LOM and the surface morphology has been characterized by SEM. Hardened depth (HD), hardened width (HW) and overall cross-sectional hardened area (HA) were measured as well and used as responses for the ANOVA of the experimental data gathered. The microhardness profiles present a sharp drop at low distance from the hardened surface. The typical splitting between hardened zone and heat-affected zone (HAZ), well known from laser hardened fully dense steels, holds also for P/M (porous) steels. The research showed that Laser Transformation Hardening (LTH) is a suitable process for producing hard, wear resistant surface, on defined spots of P/M components, through the action of a scanning laser beam. The short heating time enables to decrease part distortion and surface oxidation, in comparison with induction hardening. The possibility of very selective and precise hardening treatment seems to open new possibilities to widen the use of high-property P/M parts, based on advanced design, for demanding applications.

2014 - Microwave processing of capsule-less powdered beverages [Relazione in Atti di Convegno]
Veronesi, Paolo; Colombini, Elena; Garuti, M.; Botti, C.
abstract

Microwave rapid and selective heating is successfully applied to produce freestanding capsule-less doses of powdered beans or leaves for hot beverages preparation. 1 or 3-person doses, suitable for use in conventional hot beverage preparation machines are obtained in less than 5 seconds, without any additives except for water. Microwaves at 2.45 GHz are applied to allow shape retention and surface hardening of the pressed powders, thanks to the rapid steam generation. Load is contained inside a PTFE-lined applicator presenting micro-holes on two sides, to control vapor outlet. The use of rapidly generated steam, preferentially on the outer layers of the load, leads to weak bonding of the powders, without affecting the final taste of the brewed beverage. Modeling of the temperature- and moisture-dependent dielectric properties is used to optimize the applicator geometry, so that the outer layers of the pressed powders are preferentially heated, thus creating a rigid 'shell' hosting the remaining pressed powders.

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 - Design and optimization of a multi-port applicator for microwave assisted foaming [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Garuti, Marco; Botti, Claudio; Balocchi, Paolo
abstract

The use of numerical simulation to design a microwave applicator dedicated to foaming is presented. During foaming, the load characteristics change, both in terms of permittivity, thermal properties and size and shape. The use of a growth law able to describe size and characteristics variations of the load as microwave heating proceeds allowed to determine the most suitable microwave source arrangement able to provide both good energy efficiency and heat generation homogeneity. Load shape variations are neglected, assuming that expansion occurs with shape retention. Despite its simplified nature, the model allows to compare different scenarios of microwave applicator geometry, showing the advantages of the multi-physics approach adopted. The designed applicator was built and tested, showing the feasibility at the industrial scale of rapid microwave foaming of starch based products of complex shape.

2013 - Effect of quenching method on the wear and corrosion resistance of stainless steel AISI 420 (TYPE 30Kh13) [Articolo su rivista]
Sola, Ramona; Giovanardi, Roberto; Veronesi, Paolo; Poli, Giorgio
abstract

The effect of different kinds of quenching, i.e., laser, vacuum, and induction ones, on the mechanical properties and wear and corrosion resistances of stainless steel AISI 420 is studied. It is shown that all the three kinds of heat treatment raise considerably the wear resistance of the steel due to growth in the hardness. Laser and vacuum quenching also increases the corrosion resistance. After induction quenching the resistance to corrosion is lower than in untreated steel.

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 - 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 - Plastic behaviour and cristallographic texture of alpha titanium alloys for heat resistant applications [Anisotropia ed orientamento cristallografico preferenziale di leghe di titanio alfa per impieghi a caldo] [Articolo su rivista]
Gaiani, Silvia; Colombini, Elena; Veronesi, Paolo; Poli, Giorgio; I., Pribošič
abstract

As known, metallic materials presenting HCP crystallographic structure show a marked anisotropic behavior during plastic deformation, especially deep drawing. This attitude is due to the intrinsic asymmetry of hexagonal crystal lattice and is also depending on the c/a ratio of the cell itself. In addition to this aspect, also the tendency of materials such as titanium, magnesium and zirconium, to give rise to a preferential crystallographic orientation (texture) during the rolling phases needs to be taken into account. The most important aspects which contribute to texture formation are: nature and quantity of the alloying elements, reduction ratio during rolling, and heat treatments made on the alloys. Subject of present study are two alpha titanium alloys, specifically developed for heat resistant applications. Despite being quite similar in terms of chemical composition, oxidation resistance and field of application, these two alloys exhibit dissimilar plastic deformation mechanisms. The feature which makes the use of these materials very demanding on an industrial scale is the modification of their plastics properties, in particular plastic strain ratio (R-value), during the deformation progress. On the aforementioned alpha titanium alloys, a complete microstructural and mechanical characterization has been performed analyzing the material according to different orientation, whit the main purpose of identifying the trend of R-value toward strain. In addition to that, a study of the original texture of the two alloys has been made using different measuring methods (X-Ray diffraction, Electron Back-Scattering Diffraction). The purpose of this activity is finding a correlation between the macroscopic behavior of the alloys during deformation and their crystallographic orientation on microstructural scale, for better understanding the specific role played by the individual sliding systems and their spatial orientation on the plastic properties of the materials.

2013 - Recycling of alpha-titanium technological scrap for exhaust system parts manufacturing [Articolo su rivista]
Veronesi, Paolo; S., Gaiani; Colombini, Elena; Poli, Giorgio; R., Tisu
abstract

n this paper, five different titanium alpha alloys obtained by investment casting, and recycled titanium scrap which originated from other technological operations have been studied in order to investigate their basic properties and to determine the industrial feasibility of the manufacturing of recycled titanium exhaust system parts on an industrial scale. Chemical analysis after a first and a second melting step, a complete mechanical characterization and oxidation resistance test at different temperatures have been performed. The direct influence of the alloying elements, like Si and Al, on the oxidation resistance of titanium at high temperature has been studied, in order to identify the best blended alloy for investment casting applications. An important aspect which has also been evaluated is the increase of oxygen content after remelting of the blend alloys and its impact on the mechanical properties. Results show that it is possible to use the identified blend alloys to obtain cast components suitable for applications requiring exposure at a temperature up to 700 C, and for the Si-richer blends, up to 800 C

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 - 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.

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 - Corrosion resistance improvement of nitrocarburised and post-oxidised steels by oil impregnation [Articolo su rivista]
Giovanardi, Roberto; Poli, Giorgio; Sola, Ramona; Veronesi, Paolo
abstract

Nitrocarburising is a well known process developed to improve superficial hardness and wear resistance of steels; a subsequent post-oxidation step is often useful to enhance the corrosion resistance. In this work, an additional step was evaluated: nitrocarburised and post-oxidised parts were impregnated in lubricant oil in order to improve their wear and corrosion resistance. The effectiveness of this new treatment, in terms of corrosion resistance, was assessed for two steels, 20MnCr5 and 42CrMo4, using two different oils. The results obtained from corrosion tests show that the impregnation treatment increases the corrosion resistance, in both acidic and chlorurated media.

2012 - Effect of surface finishing and post-oxidation atmosphere on the properties of 41CrAlMo7 nitrided steel | [Effetto dell'atmosfera di post-ossidazione e della finitura superficiale sull'acciaio 41CrAlMo7 nitrurato] [Articolo su rivista]
Sola, Ramona; Poli, Giorgio; Veronesi, Paolo; Giovanardi, Roberto; S., Mamei; A., Zanotti
abstract

Notoriamente la nitrurazione è un trattamento termochimico di indurimento superficiale sviluppato allo scopo di migliorare le resistenze a usura e a fatica di leghe ferrose. I componenti così trattati soffrono solitamente di una carenza nella resistenza a corrosione. Un obiettivo tecnologicamente importante è lo sviluppo di nuovi trattamenti post-nitrurazione per ottenere simultaneamente buone proprietà estetiche, meccaniche, tribologiche e di resistenza a corrosione. Mediante una analisi sistematica basata sull’uso di numerose tecniche sperimentali in questo lavoro di ricerca sono state approfondite le conoscenze sullo stato superficiale indotto dalla nitrurazione dalla successiva post-ossidazione eseguita in tre diverse atmosfere (protossido di azoto, anidride carbonica e aria) sull’acciaio 41CrAlMo7 fornito in quattro differenti finiture superficiali (lappata, rettificata, tornita e pallinata) al fine di quantificarne gli effetti sui parametri tribologici e sulla resistenza a corrosione.

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 - Rapid microwave sintering of protective ZrO2 coatings on reactive metal powder compacts [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Colombini, Elena
abstract

Electrophoretic deposition was used to create protective coatings of sub-micrometric ZrO2 particles on substrates made of conductive powders mixture (Ni+Al). In order to achieve the required mechanical properties, such coating requires a sintering stage. However, the rapid microwave sintering of thin zirconia layers usually requires some form of pre-heating or auxiliary heating of the material, in order to increase its loss factor. In this study, the heat released by the exothermal reactions of combustion synthesis occurring in the powders compact, is used to concurrently synthesize high-temperature rated aluminides and pre-heat and sinter the overlaying zirconia coating. Finite elements numerical simulation, fully coupling electromagnetic, heat transfer and chemical reactions application modes is used to investigate the temperature profile and power density distribution during the microwave sintering process, Experimental results show that the concurrent synthesis allows to form a thin alumina-based bond coat, which is expected to increase the high temperature resistance of the zirconia-coated aluminides.

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 - 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 - Functionally graded materials obtained by combustion synthesis techniques: A review [Capitolo/Saggio]
Rosa, Roberto; Veronesi, Paolo
abstract

Among the large number of different techniques to produce Functionally Graded Materials (FGMs), Combustion Synthesis (CS) is gaining an increasing interest due to the possibility of achieving high-purity products in short processing times (typically of the order of few seconds or less), and with low energy consumption (limited to the ignition step), as well as low cost of the manufacturing equipment required. CS exploits high exothermic reactions between reactants, which, after reaching the ignition temperature, start to form the desired products and the reaction becomes self-sustaining, not requiring any other external energy contribution. Depending on the way of ignition, combustion synthesis can be conducted in the Self-propagating High-temperature Synthesis (SHS) mode or in the Thermal Explosion (TE) mode. In the SHS mode, the reaction is ignited at one end of the reactive sample and it self-propagates in the form of a combustion wave at very high velocities. In the TE mode (also known as reactive sintering or volume combustion synthesis) the whole volume of the sample is heated uniformly in a controlled manner until reaction takes place essentially simultaneously throughout the volume. The use of CS in FGMs manufacturing can benefit from the fast kinetics involved, allowing to create non equilibrium structures or to lead to products less prone to homogenization, thus preserving the gradient structure imparted during the forming step. Among the wide variety of possible ignition techniques, which will be discussed in the present review, recent results obtained by microwave (MW) irradiation will be presented, discussing the advantages of such a heating technique in FGMs manufacturing. MWs, in fact, can enhance the previously mentioned advantages due to their peculiarities of rapid, volumetric and selective heating, the latter particularly relevant when dealing with multi-phase systems. Â© 2012 by Nova Science Publishers, Inc. All rights reserved.

2011 - Improvement of wear and corrosion resistance of ferrous alloys by post-nitrocarburizing treatments [Articolo su rivista]
Sola, Ramona; Giovanardi, Roberto; Veronesi, Paolo; Poli, Giorgio
abstract

Gas nitrocarburizing and post-oxidation treatments were performed on 42CrMo4 and 20MnCr5 steels, G30 and GS600 cast irons, to improve wear and corrosion resistance. In both materials the thickness of the compounds layer, mainly composed by epsilon- and gamma’- phase, resulted about 15-20 micron and the measured diffusion layer was about 150 micron thick. A subsequent oxidizing step, followed by impregnation with a two different lubricating oils was performed in order to further enhance corrosion resistance. Wear resistance against alumina was measured using a ball-on-disk tribometer and the corrosion characteristics of the samples were studied using salt spray test in accordance with ASTM B117. Experimental results show that the nitrocarburizing treatment improves significantly the wear resistance of the steels but not the wear resistance of the studied cast irons. The steels present almost the same tribological behaviour, ascribable to the formation of similar compounds, while cast irons present different wear resistance due to their chemical composition and the graphite morphology. The application of nitrocarburizing alone does not significantly improve corrosion resistance and it may even promote localized corrosion. The subsequent post-oxidation step leads to a slight decrease of the corrosion rate, because it partially seals the porous nitrocarburized layer. The final oil impregnation step resulted much more effective in further decreasing the corrosion rate and this final treatment in some cases improves also the wear resistance.

2011 - Influence of different quenching technique on wear and corrosion resistance of AISI 420 stainless steel [Relazione in Atti di Convegno]
Sola, Ramona; Giovanardi, Roberto; Veronesi, Paolo; Poli, Giorgio; Parigi, G.
abstract

Food industry requires materials with high corrosion resistance, chemical stability, pore-free surfaces , impact resistance and thermal stress resistance. In many structural applications, food industry requires steels not only with the ability to be easily cleaned and healthy but also with high mechanical properties. In this work high performance AISI420 stainless steels were developed, improving bulk mechanical proprieties and surface characteristics such wear and corrosion resistance, the latter by different quenching techniques: laser quenching, induction quenching and vacuum quenching. Metallurgical characterization, tribological characterization, corrosion tests (polarization tests in H2SO4, Na2SO4 and NaCl solutions) have been used on treated and untreated AISI 420 steel. Results demonstrated that as expected all the three quenching techniques, due to the increase of surface hardness, highly improve wear resistance. Laser quenched and vacuum quenched samples present the best wear resistance, accompanied by a good corrosion resistance in all the solutions and conditions tested, while the induction quenching decreases the corrosion resistance even with respect to untreated material.

2011 - Microwave ignited Combustion synthesis of intermetallic compounds, modelling and experimental results [Articolo su rivista]
Colombini, Elena; Rosa, Roberto; Veronesi, Paolo; Casagrande, A.
abstract

The process of Combustion synthesis (CS) is based on the highly exothermic reaction by reactants, which, if properly ignited, spontaneously turn into products. The aim of this work is to study the CS of β-NiAl formed starting from Ni and Al (1:1 at. %) powders activated by microwaves at 2.45 GHz. Numerical simulation is used to obtain data otherwise difficult to be measured experimentally and to develop a predictive model of microwave ignited and sustained CS of metal powder compacts. The simulation couples an electro-thermal model with a chemical model, required to study the exothermic reaction between powders. A simplify model was obtained and validated, neglecting volume changes, to study compositional and temperature change and reaction kinetics during the CS. It allowed to demonstrate how microwave application, during and after, synthesis could control the cooling rate of products and hence the microstructure of the newly formed intermetallics.

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 - 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 - On the boron addition to beta-NiAl intermetallic obtained by microwaves ignited combustion synthesis [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Poli, Giorgio; Casagrande, Angelo
abstract

Aim of the present work is to accurately investigate the effect of Boron addition on the microstructure and mechanical properties of Î²-NiAl intermetallic phase obtained by microwave initiated and sustained combustion synthesis (CS). In this work the rapidness, selectivity and volumetric nature of microwaves (MWs) at the frequency of 2.45 GHz were exploited to ignite the combustion synthesis of precursor powder mixtures, leading to the preparation of free-standing Î²-NiAl intermetallic specimens presenting different boron amounts. Micro-alloying with B is known to contribute to improve the ductility and enhancing room temperature toughness of aluminides, while larger boron amounts significantly increase the yield strength and hardness. Since literature results are sometimes contradictory, particularly as far as the CS manufacturing process is concerned, an accurate investigation on the possible mechanisms which can be responsible for the above mentioned improvements, has been carried out, demonstrating that boron addition is effective in decreasing the intrinsic brittleness and improving the ductility of Î²-NiAl intermetallic phase, already starting form 50 ppm concentration.

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

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 - Comparison - By nanoindentation - Among PM steels obtained from diffusion-bonded powders (nominally equivalent) [Relazione in Atti di Convegno]
Bocchini, G. F.; Poli, Giorgio; Sola, Ramona; Veronesi, Paolo
abstract

In principle, powdered raw materials, produced by a given process and having equal chemical com-position, are supposed to be equivalent. In previous research works, the differences among response to sintering behaviour have been investigated on P/M steels based on four diffusionbonded powders (Fe + Ni + Cu + Mo), with atomized iron base, at the same alloy contents. Two levels of carbon (0.3 and 0.6 wt%) and two sintering conditions have been investigated, in industrial manufacturing conditions. However the comparison of dimensional changes, carbon content, and hardness reveals only modest differences. The comparison of microhardness distribution, fractal analysis, pore features, microstructure patterns show some clear differences, sometimes not univocal. The previously achieved results show that the claimed equivalence is not adequately and completely confirmed by closer and more complete comparative evaluation of experimental data. Only accurate analyses of microhardness and microstructure distributions seem powerful tools to rate, with modest sensitivity, the real similarity of the so claimed equivalent ironbase powders. Clearer differences have been shown by dilatometric analysis. To verify these observed differences, nanoindentation tests have been carried out. Each material has been characterized by nanoindentation measurement, for any process condition. The measured values, plotted on normal distribution graphs, only partially confirm the differences revealed by dilatometry. Some different ranking of diffusion level results from nanoindentation. This recently developed method, suitable to characterize very small volumes of material, appears suitable to find even minor differences among materials that could appear equivalent if evaluated by simpler and easier test methods.

2010 - Effect of Si and Cr content on the high temperature oxidation resistance of aluminide coatings on Ti obtained by microwave assisted SHS of metallic powders mixture [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Poli, Giorgio; Casagrande, A.; Boromei, I.
abstract

High temperature oxidation protection of alpha-titanium alloys is a fundamental aspect to be improved when applying such materials in demanding environments like in the case of high-performance exhaust systems. Protective Ni-Aluminide coatings produced by microwave assisted self-propagating high-temperature synthesis (SHS) of Ni and Al powder mixtures on Ti substrates are a promising route towards the improvement of hightemperature wear and oxidation resistance. As a matter of fact, the newly formed Ti-Ni-Al ternary compound at the Ti- interface (15 wt% of Al), results protective like pure NiAl, but only up to 750 Â°C. At 900 Â°C the lack of protective enough oxides does not hinder the growth of non-protective TiO2. In this study, the improvement of the 900Â°C oxidation resistance of the Ti-Ni-Al layer by powder metallurgy route is investigated, adding Si or Cr to the protective intermetallic coating and using microwave assisted SHS to minimize the extension of heat affected zones generated in the substrate when applying the coating.

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 - Guest editor's message [Breve Introduzione]
Veronesi, P.
abstract

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 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.

2010 - Microwaves & metals [Breve Introduzione]
Veronesi, Paolo
abstract

2010 - Ni-Al-Ti coatings obtained by microwave assisted SHS: Oxidation behaviour in the 750-900 °C range [Articolo su rivista]
Boromei, I.; Casagrande, A.; Tarterini, F.; Poli, Giorgio; Veronesi, Paolo; Rosa, Roberto
abstract

Microwaves have been used to ignite the Self-propagating High-temperature Synthesis (SHS) of Ni and Al powder mixtures to produce a duplex intermetallic coating on Ti substrates. Due to the high exothermic nature of the reaction, the newly formed NiAl is in the liquid phase and can react with the underlying Ti to form a tough ternary intermediate layer, belonging to the Ti-Ni-Al system, in a one step process. Aim of this work is to assess the high-temperature performances of the Ti-Ni-Al layer, compared to NiAl coating and Ti. Experimental results demonstrate that the ternary layer presents oxidation resistance comparable to NiAl up to 750 °C. In this condition, the thick Ti-Ni-Al layer could replace the functionality of hard and brittle NiAl coatings. At 900 °C, instead, NiAl oxidation resistance results higher, and this can be ascribed to the relatively low Al content in the studied ternary compound, which hinders the formation of a continuous and protective scale

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 - Wear and corrosion resistance modification of nitrided and nitrocarburized steeels | [Modifica della resistenza a usura e a corrosione di acciai nitrurati e nitrocarburati] [Articolo su rivista]
Sola, Ramona; Poli, Giorgio; Giovanardi, Roberto; Veronesi, Paolo; Calzolari, C.; Zanotti, A.
abstract

Nitriding and nitrocarburizing induce surface chemical modification that are influenced by alloying element present in steels [1]. Nitriding treatment forms this layers sequence: a. the more external one, named white layer, formed by e-Fe2-3N e y'-Fe4N nitrides, b. the underlying diffusion layer in which nitrides of alloying element precipitates at grain boundary. The simultaneous presence of active carbon and nitrogen during nitrocarburizing treatment forms an external compound layer, composed by e-Fe2-3(N,C) and Y'-Fe4(N,C) carbonitrides laying on diffusion layer. The use of thermochemical treatments to enhance fatigue and wear resistance performances of highly stressed mechanical components is well known and established [2-5]. However it's technologically interesting post-nitriding and post-nitrocarburizing treatment development to guarantee good aesthetic and mechanical properties and high wear and corrosion resistance. Post-oxidation treatment, already studied in years [6-12], causes: a. nitrides and carbonitrides partial decomposition; b. Fe3O 4 growth on the surface; c. partial surface microporosity closure. Remaining open porosity, filled with lubricant oil (impregnation), could further increase wear and corrosion resistance. Aim of the work is the characterization and optimisation of post-treatments on nitrided and nitrocarburized 41CrAlMo7 and X37CrMoV5-1 steels, in order to improve corrosion resistance and to reduce wear during dry sliding against counterparts. In this study, two kinds of post-treatments have been performed after gaseous nitriding and nitrocarburizing: a) oxidation, b) oxidation and oil impregnation using two different oil in water emulsions (10wt% and 30wt% oil). The morphological features of the post-treated surface have been characterized using scanning electron microscopy and surface roughness measurements, in order to evaluate the surface morphology influence on wear and corrosion resistance. In can be concluded that, in the applied experimental conditions: 1. in both steels, nitrocarburizing a compound layer 11-16 m thick forms, constant in whole material, while nitriding a white layer, 9-10 (xm thick; 2. in both steels, the nitrided diffusion layer is thicker than nitrocarburized one and therefore nitriding allows higher total and effective hardening depth; 3. after the treatments of Tab. II, 41CrAlMo7 shows higher diffusion layer, while X37CrMoV5-1 achieved higher surface hardness than other steel. For this reason X37CrMoV5-1 presents lower wear rate; 4. nitrocarburizing and nitriding originate surfaces with very different morphology: nitrided surface is smooth, regular with a low porosity, while after nitrocarburizing the surface presents higher roughness parameters and abundant open microporosity; 5. oxidation forms Fe 3O4 on both nitrided and nitrocarburized samples. The oxide surface morphology is influenced by the substrate chemical composition and mainly by the surface morphology of the treated substrate: on the nitrocarburized sample the oxide is smooth, non porous and well adhered to the substrate; on nitrided substrate the oxide presents higher roughness value and a high porosity content. As a consequence, oxidation promotes an improvement of wear and corrosion resistance when performed on nitrocarburized substrate, but it has a detrimental effect on corrosion and wear resistance when it is performed after nitriding; 6. nitriding and nitrocarburizing promote an significant improvement of wear resistance, and nitrided steels exhibits the highest wear resistance. All the nitriding post-treatments decrease wear resistance; 7. nitriding and nitrocarburizing promote a significant corrosion resistance increment, oxidation has positive effects only after nitriding, because of post-oxidized surface morphology; 8. oil impregnation effect on wear resistance is moderate, but it is decisive on corrosion resistance, because the oil acts as an insulating.

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 - 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 - Densification and coarsening of laser sintered green parts by microwave technique [Relazione in Atti di Convegno]
Veronesi, Paolo; Gatto, Andrea; L., Iuliano
abstract

Microwave sintering of SLS green parts made of 420L stainless steel has been performed applying microwaves at the frequency of 2.45 GHz. The use of single mode and multi-mode microwave furnaces allowed to find the most suitable sintering conditions in absence of auxiliary microwave absorbers. In case the electric field intensity reaches a threshold value, able to trigger breakdown phenomena, sintering is rapidly achieved, but at the cost of homogeneity and process controllability. A lower electric field intensity allows, instead, to achieve complete sintering of the green parts in 10 to 20 minutes time, which results considerably shorter than current state of the art conventional sintering of SLS green parts. Comparison between mi-crowave and conventionally sintered parts showed that the final product present a similar microstructure, with the presence of Cr-rich regions whose extension is a function of the microwave processing time

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 - Electrophoretic deposition of PEEK-nano alumina composite coatings on stainless steel [Articolo su rivista]
Ilaria, Corni; Nico, Neumann; Saa, Novak; Katja, König; Veronesi, Paolo; Qizhi, Chen; MARY P., Ryan; ALDO R., Boccaccini
abstract

Polyetheretherketone (PEEK)-Al2O3 composite coatings have been successfully deposited on 316L stainlesssteel substrates by electrophoretic deposition (EPD) from ethanolic suspensions containing nanosize aluminaand micrometric PEEK particles. Uniform composite coatings containing between 20 and 70 wt.% of PEEKhave been obtained. An electrostatic interaction between the two kinds of particles has been confirmed byzeta potential and TEM analysis. The EPD yield increased with deposition time and difference of potentialapplied following a logarithmic trend. Reproducible PEEK-alumina coatings were deposited. A heat treatmentat 343 °C for 30 min with a heating rate 10 °C min−1 was needed to increase the adhesion substrate-coating.EPD can be considered a convenient low cost method to produce PEEK-Al2O3 composite films on metallicsubstrates. Scratch test analysis and hardness measurements showed that the deposited coatings were toorich in alumina and that a lower amount of alumina would be enough to satisfactorily increase themechanical properties. The corrosion resistance of the coatings in chlorine environment was tested. It wasshown that PEEK-alumina composite coatings performed better than pure PEEK films and exhibited asignificant increase in the pitting potential compared to uncoated stainless steel substrate.

2009 - Enhancing the scratch resistance of polycarbonate with poly(ethylene oxide)-silica hybrid coatings [Articolo su rivista]
Fabbri, Paola; Messori, Massimo; M., Toselli; Veronesi, Paolo; J., Rocha; Pilati, Francesco
abstract

Scratch-resistant coatings for bisphenol-A polycarbonate sheets were obtained by the sol–gel synthesis of an organic–inorganic hybrid system based on poly(ethylene oxide) and silica. The organic–inorganic hybrids were thermally cured into hard transparent coatings by using conventional and microwave (MW) ovens. Both techniques proved to be equally efficient in promoting the system’s crosslinking, as evaluated by 29Si MAS-NMR. The MW-assisted curing, however, was much faster. Photoelasticity analysis showed that MW-assisted curing causes localized overheating of the samples, inducing a state of residual plane stresses that bring about dimensional instability of the coated material. Instrumented scratch tests for the coated samples revealed an increase of 1 order of magnitude in the minimal load at which a scratch track appears on the sample surface. However, the friction coefficient values for samples with thermally cured coatings were lower than those produced by MW-assisted curing.

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 - Materials selection criteria for the weight reduction of high performance sports car [Articolo su rivista]
Veronesi, Paolo; Pivetti, A; Baldini, Andrea; Loiacono, M; Poli, Giorgio
abstract

For high-performance luxury cars, the first element of competitiveness isgiven by the dynamic performances. Thus, weight reduction is becoming increasinglyimportant, also in the framework of the introduction of more andmore restrictive regulations on emissions. Designers are currently focusingon maximizing the power/weight ratio, and the proper material selectionbecomes mandatory. This paper describes the weight reduction achievable onthe suspension system of a Lamborghini Murcielago, showing that the useof high strength low alloy steels as well as titanium and aluminum alloysallows to reduce weight of selected components of more than 30%.Three different components of the suspension system have been analyzed:the front lower arm (fig. 1), the front suspension spring (Table II) and theanti-roll bar (fig. 5). According to the method proposed by M.F. Ashby [2],the design requirements have been translated into a series of constraints,objectives and free variables, leading to the definition of material indexes(equations 1-8) to be used to rank the materials in order to identify the mostsuitable ones. Ranking was accomplished using the CES (Cambridge EngineeringSelector, Granta-design) software, which allows to create selectioncharts like the ones shown in Fig. 2, 3, 4, 6. Those diagrams help the designerto select graphically the candidate materials for the application, which, forthe studied cases, resulted to be:- Low alloy steels or aluminum alloys (Table II) for the front lower arm- Titanium or spring steel(fig. 1), for the front suspension spring- Aluminum alloy for the anti-roll barDimensioning of the components on the basis of the selected materials ispresented as well, demonstrating that a proper materials selection procedureallows to significantly decrease the weight of the studied components withrespect to the current solutions.

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 - Ni–Al–Ti coatings obtained by microwave assisted SHS: Effect of annealing on microstructural and mechanical properties [Articolo su rivista]
G. P., Cammarota; A., Casagrande; Poli, Giorgio; Veronesi, Paolo
abstract

Microwaves at 2.45 GHz have been used to ignite the self-propagating hightemperaturesynthesis (SHS) in a Ni and Al powder mixture to produce NiAl coatingson Ti. The temperature of the reacting powders, owing to the exothermic nature ofthe reaction and to the energy provided by the high frequency electromagnetic field,reaches the melting temperature of NiAl. The newly formed NiAl, in the liquid phase,reacts with the underlying Ti and rapidly forms at the interface a ternary eutecticbelonging to the Ni-Al-Ti system. During cooling, the formed transient liquid eutecticlayer at the Ti/NiAl interface originates an intermediate layer presenting aninterlocking network, which constitutes an in-situ reinforcement phase. In this studyit is shown that the thickness of the interface layer can be altered by annealing at temperature higher than the ternary eutectic temperature (904°C), in a few minutestime. Experimental results demonstrated also that, due to its peculiar microstructure,the intermediate layer is tougher and harder than the parent NiAl coating.

2009 - Oxidation behavior resistance of a duplex NiAl/Ti-Ni-Al coating by microwave assisted SHS on Ti substrate [Abstract in Atti di Convegno]
Boromei, I.; Poli, G.; Veronesi, P.; Rosa, R.
abstract

Microwaves have been used to ignite the Self-propagating-High-temperature Synthesis (SHS) of Ni and Al powder mixtures to produce a duplex intermetallic coating on Ti substrates. Due to the high exothermic nature of the reaction, the newly formed NiAl is in the liquid phase and can react with the underlying Ti to form a tough ternary intermediate layer in a one step process. The obtained thick intermediate layer, Ti-Ni-Al ternary compound, with improved mechanical properties could replace the functionality of hard and brittle NiAl aluminide coatings in service. Moreover, the thickness of the intermediate layer, presenting an interlocking microstructure, can be controllably altered, up to 500μm, by annealing at 950°C for times ranging in the 3-20 minutes. The present work intends to assess the high temperature performances of the Ti-Ni-Al ternary coating, compared to pure Ti, Ti-6Al-4V and NiAl. In particular, cyclic oxidation response in the 750-900°C range and wear resistance at 750°C, measured using a ball-on-disk tribometer, were evaluated. The tendency for scale spallation, adherence and oxidation rates for NiAl and Ni-Al-Ti intermediate layer was evaluated as well.

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 - The Actuality of the Ancient Metallurgy: from the XIX Century Cast Iron to the New Anti-Wear Systems [Capitolo/Saggio]
Veronesi, Paolo; Belviso, Daniela; Poli, Giorgio; Sidoli, Luigi; Acierno, D; Damore, A; Caputo, D; Cioffi, R
abstract

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

2009 - “Oxidation Behavior Resistance of a Duplex NiAl/Ti-Ni-Al Coating by Microwave Assisted SHS on Ti Substrate”, Vol 3, , Denmark, 2009, 161-166, ISBN [Relazione in Atti di Convegno]
I., Boromei; A., Casagrande; Poli, Giorgio; Veronesi, Paolo; Rosa, Roberto
abstract

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 - Development of post-oxidation treatments to improve wear and corrosion resistance [Articolo su rivista]
Sola, Ramona; Giovanardi, Roberto; Veronesi, Paolo; Poli, Giorgio; S., Masini; A., Zanotti
abstract

Gas nitrocarburizing and post-oxidation treatments were performed on 42CrMo4 steel and GS600 cast iron, to improve wear and corrosion resistance. In both materials the compounds layer after nitrocarburizing, mainly composed by ε-Fe2-3(N,C) and γ′- Fe4N phase. First the oxidizing step, a subsequent impregnation with two different lubricating oils was performed in order to further enhance corrosion resistance. Wear resistance was measured using a ball-on-disk tribometer with Al 2O3 and 100Cr6 counterpart and the corrosion resistance of the samples was studied using salt spray test in accordance with ASTM B117 and electrochemical cell. Experimental results show that the nitrocarburizing treatment improves significantly the wear resistance of the steel but not the wear resistance of the studied cast irons. The application of nitrocarburizing alone does not significantly improve corrosion resistance and it may even promote localized corrosion. The subsequent postoxidation step leads to a slight decrease of the corrosion rate, because it partially seals the porous nitrocarburized layer. The final oil impregnation step resulted much more effective in further decreasing the corrosion rate by one order of magnitude.

2008 - Electroless Ni coatings for the improvement of wear resistance of bearings for lightweight rotary gear pumps [Articolo su rivista]
Veronesi, Paolo; Sola, Ramona; Poli, Giorgio
abstract

The possibility of improving the performances of current aluminiumalloys in the bearings region of lightweight external gear pumps has beeninvestigated. Two different electroless Ni-based coatings, one containing highpercentages of P (10–14%) and the other modified with the addition of 25 wt%PTFE micrometric spheres, deposited on 2011 Al alloy, were characterisedby scratch test and ball-on-disc tests. Comparison with an antifrictionSn-containing Al-alloy was performed. The PTFE-containing coating presentsthe lowest wear rate and friction against steel. However, the presence of PTFEspheres and the hardness mismatch with the substrate tends to favour tensilecracking of the coating.

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 - High strength brown parts produced by fast microwave-assisted debinding [Relazione in Atti di Convegno]
Veronesi, Paolo; Denti, Lucia; Colombini, L.
abstract

The binder removal from 430L-steel MIM parts was performed in a two-step procedure using chemical and thermal debinding. During the first step, almost 80% of the binder is removed and a porous structure is created, which then favours the subsequent step. The second step was performed in a multi-mode microwave applicator, at 2.45 GHz ISM frequency. Numerical simulation allowed to optimise the microwave applicator loading conditions, in terms of heating homogeneity and efficiency. Experimental validation confirmed that using microwaves it is possible to reduce conventional debinding times by a factor of 3, and that the resulting brown parts possess a 4 times higher compressive strength. This phenomenon can be ascribed to local over-heating of the regions surrounding neighbouring metal particles, triggered by the high frequency electric field. This promotes the formation of necks among the particles, leading to pre-sintering, despite the overall measured samples temperature, which never exceeded 600Â°C.

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

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 - Nuovi trattamenti post-nitrocarburazione per la contemporanea funzionalizzazione tribologica e anticorrosiva [Relazione in Atti di Convegno]
R., Sola; Giovanardi, Roberto; Veronesi, Paolo; Poli, Giorgio; S., Masini; A., Zanotti
abstract

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 - Tough and wear resistant Ni-Al based thick intermetallic coatings on titanium Obtained by microwave assisted SHS [Abstract in Atti di Convegno]
Veronesi, P.; Rosa, R.; Poli, G.; Casagrande, A.; Cammarota, G. P.
abstract

Microwaves at 2.45 GHz have been used to ignite the Self propagating High temperature Synthesis (SHS) of Ni and Al powder mixtures to produce NiAl and a complex Ni-Al-Ti intermediate layer on titanium. The use of microwaves allows to selectively convey energy to the reacting powders, even during and after SHS, thus prolonging the existence of liquid phases and promoting the formation of a well adhered interface between titanium and the newly formed NiAl. The intermediate layer, belonging to the Ni-Al-Ti system, presents an interlocking microstructure, which provides increased mechanical properties with respect to the parent polycrystalline NiAl. Wear resistance of the complex Ni-Al-Ti layer was measured in dry-sliding against alumina using a ball-on-disk tribometer. Micro-hardness, elastic modulus, and scratch resistance (constant load, single- and multi-pass) were also measured, showing that the Ni-Al-Ti layer presents increased performances with respect to polycrystalline NiAl obtained by microwave assisted SHS.

2008 - “Tough and wear resistant Ni- Al based thick intermetallic coatings on titanium obtained by microwave assisted combustion synthesis”, , vol.3, Mannheim, Germany, 71-76, 2008, ISBN: [Relazione in Atti di Convegno]
Veronesi, Paolo; Rosa, Roberto; Poli, Giorgio; A., Casagrande; G. P., Cammarota
abstract

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

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 - 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 - 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 - La scelta dei materiali nella progettazione industriale [Traduzione di Libro]
Fabbri, Paola; Giovanardi, Roberto; Veronesi, Paolo
abstract

La nostra era, a forte connotazione tecnologica piuttosto che scientifica, pretende dai materiali prestazioni sempre più elevate e contemporaneamente richiede una maggiore affidabilità alle macchine, alle strutture ed ai prodotti finiti, soprattutto quando questi ultimi sono il risultato di progetti ad alto livello. Le due esigenze sono antitetiche, ed il risultato del loro forzato sincretismo è inevitabilmente una drastica riduzione del divario fra reale resistenza dei materiali e sollecitazioni in esercizio, e, di conseguenza, una continua riduzione dei margini di sicurezza. Il "progettista" si trova quindi a dover lottare contro difficoltà sempre più grosse per garantire la qualità dei suoi prodotti. Con queste premesse è evidente che progettista ed “esperto dei materiali” (quasi mai alle due figure culturali corrisponde la stessa persona fisica) devono unire le loro conoscenze, ognuno contribuendo, per quanto gli compete, alla corretta realizzazione di progetti ad alta tecnologia, l’uno favorendo il lavoro dell'altro. Pena per una mancata collaborazione, il rischio di far affondare un cargo di idee validissime nel bicchiere d'acqua dell'ignoranza. Ne consegue che, se calate nella realtà attuale, le classiche figure del progettista e dell'esperto di materiali subiscono una modifica sostanziale. Al primo, infatti, si richiede sempre più spesso di uscire dalla logica dell'economia ed accettare una scelta dei materiali impostata su basi scientifiche. Al secondo, invece, sono imposte precise direttrici di ricerca, tese alla messa a punto di materiali sempre più resistenti (sia modificando lo stato di lega, sia inventando nuovi trattamenti e nuovi materiali), all'approfondimento delle conoscenze in quei campi che tendono ad individuare le vere doti di resistenza dei materiali, alla definizione di metodologie che permettano di fare la migliore scelta fra tutti i materiali attualmente disponibili. Quanto fin qui detto, è doverosa premessa per presentare questo, che è sì un libro sui materiali, ma non solo. E’ bene ricordare, infatti, che oltre che un sostantivo, materiale è anche un aggettivo: un aggettivo importante perché permette di distinguere fra i diversi tipi di beni di cui l’uomo, per bontà divina o propria, può disporre. Ma i beni materiali non sono disgiunti dai beni morali, ed in questo testo, più che nei precedenti, Ashby si è dedicato alla ricerca di una soluzione per questa fondamentale equazione. Il buon uso dei materiali (sost.) è, per la nostra generazione, un problema morale, che passa attraverso il risparmio delle risorse naturali, la minimizzazione dell’impatto ambientale dovuto alle attività umane e la corretta distribuzione dei benefici materiali (agg.) che da tali attività derivano. Alla presentazione (e si potrebbe dire alla divulgazione) di tali problematiche Ashby dedica l’ultima parte di questo libro, approfondendone i diversi aspetti più che nelle edizioni precedenti. Ciò costituisce una importante novità per chi, come me, si è avvicinato alla procedura di scelta dei materiali suggerita da Ashby fin dalle prime pubblicazioni (i più vecchi diagrammi di scelta sono del 1988, come suggerisce il numerino posto accanto al nome dell’autore). A quei tempi, per un operatore della didattica, l’esame dei testi di Ashby era guidato dalla curiosità e dalla necessità di trovare nuovi metodi di insegnamento che meglio si adattassero alle esigenze degli studenti di ingegneria. Il materiale non doveva più essere un dato di fatto, un semplice accessorio utile per realizzare progetti: doveva acquistare il giusto rilievo ed entrare di diritto fra le variabili in grado di condizionare il successo delle idee progettuali. Oggi si può dire che, almeno parzialmente, questo obiettivo è stato raggiunto: una buona parte del mondo industriale è consapevole dell’importanza della individuazione del materiale più idoneo a soddisfare

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 - 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 - 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 - 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 - On the microstructures of NiAl to titanium and NiAl to carbon steel joints obtained by microwave assisted SHS [Relazione in Atti di Convegno]
Cammarota, G. P.; Casagrande, A.; Veronesi, Paolo; Poli, Giorgio
abstract

Microwaves at 2.45 GHz can ignite the self-propagating high-temperature synthesis (SHS) in a 50 at% Ni and Al powder mixture to produce NiAl coating on Ti and carbon steel substrates. During microwave assisted SHS, the temperature of the compacted reacting powders, owing to the exothermic nature of the reaction, reaches the melting temperature of NiAl. Moreover, microwaves are able to convey energy to the system even during and after SHS occurred, a condition which can not be achieved by conventional heating methods, relying on heat transfer. In this study, microwave heating was used to extend the temporary presence of a molten intermetallic phase. This allowed the formation of reaction layers belonging to the Ni-Al-Fe and Ni- Al-Ti systems, at t he interface between the newly formed NiAl and the metallic substrates, achieving chemical bonding. This process involved different metallurgical phenomena such as melting, dissolution, diffusion and different solidification routes. The chemical effects, the phase transformations, the resulting interface microstructures were examined.

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 - 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 - Unique microstructure of intermetallics obtained by microwave enhanced SHS [Relazione in Atti di Convegno]
Veronesi, Paolo; Poli, Giorgio; A., Casagrande
abstract

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 - 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

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 - Microwave-assisted combustion synthesis of NiAl intermetallics in a single mode applicator: Modeling and optimisation [Articolo su rivista]
Poli, Giorgio; R., Sola; Veronesi, Paolo
abstract

The microwave-assisted combustion synthesis of NiAl intermetallics in a single mode applicator has been simulated numerically and performed with the aim of achieving the highest yields, energy efficiency and process reproducibility. The electromagnetic field modeling of the microwave system allowed to chose the proper experimental set-up and the materials more suitable for the application, minimising the reflected power and the risks of arcing. In all the experimental conditions tested, conversions of 3-5 g 1: 1 atomic ratio Ni and Al powder compacts into NiAl ranged from 98.7% to 100%, requiring from 30 to 180 s with power from 500 to 1500 W. The optimisation procedure allowed to determine and quantify the effects of the main process variables on the ignition time, the NiAl yields and the specific energy consumption, leading to a fast, reproducible and cost-effective process of microwave-assisted combustion synthesis of NiAl intermetallics. (c) 2006 Elsevier B.V. All rights reserved.

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 - Sinterizzazione a microonde di polveri sferiche da lavorazioni industriali [Articolo su rivista]
Veronesi, Paolo; S., Ferrari; Poli, Giorgio
abstract

Microwave sintering in air of spherical powders generated during EDWC (Electrical Discharge Wire Cutting) has been studied. The main objective of the investigations is to determine if, with respect to conventional heating systems, microwave assisted heating can produce variations of the thermo-chemistry and kinetic of the chemical-physical phenomena occurring at the solid state during sintering.The powders used are made mainly by Cu/Zn and Fe/Cr/Ni micro spheres. The microwave applicator is a single mode TE10n , fed by a magnetron operating at 2.45 GHz. Microwave sintering resulted enhanced with respect to conventional heating. As a matter of fact, the highest densification occurred at temperature 100-200°C lower than conventional furnace. Moreover, the microstructure of the microwave sintered samples is completely different, presenting lower oxidation and retention of spherical metallic inclusions. These phenomena can be explained considering that the electromagnetic field is concentrated in proximity of the regions of necking.

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 - Waste treatment under microwave irradiation [Relazione in Atti di Convegno]
Corradi, Anna; Lusvarghi, Luca; Rivasi, Maria Rosa; Siligardi, Cristina; Veronesi, Paolo; Marucci, G.; Annibali, M.; Ragazzo, G.
abstract

Waste treatments to induce stabilization or recovery of waste materials is an important part of modern research efforts. Microwave processing has proved to be a powerful tool to convey energy exactly where it is needed by the process, as well as to allow operation in peculiar environments, even in remote-controlled modality. The present work is a summary of three years of joint research between Modena's University and ENEA investigation regarding microwave assisted thermal treatments lead on wastes of different nature, performed at the 2.45 GHz ISM frequency. The heat-treatments regarded the inertisation and vitrification of asbestos and the stabilization in a glassy matrix of a multi-oxide mixture simulating nuclear waste. Either single-mode or multi-mode applicators were used during the preliminary tests, and hybrid heating was exploited, if necessary. In some cases, additives ensuring a better microwave coupling were used to improve the process speed or the overall yield. Â© Springer-Verlag Berlin Heidelberg 2006.

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 - 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 - 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

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

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

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 - 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.

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 - 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 - 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 - 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]
Boccaccini, A. R.; Cannillo, V.; Leonelli, C.; Veronesi, P.
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 - Sinterizzazione a microonde di polveri sferiche da lavorazioni industriali [Relazione in Atti di Convegno]
Veronesi, Paolo; S., Ferrari; Poli, Giorgio
abstract

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

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

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 irradiation of asbestos containing materials [Abstract in Atti di Convegno]
Corradi, A.; Siligardi, C.; Veronesi, P.; Marucci, G.; Annibali, M.; Ragazzo, G.
abstract

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 - 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 - 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 - 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 - 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.

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 - Enhancing the mechanical properties of porcelain stoneware tiles: a microstructural approach [Articolo su rivista]
Leonelli, C.; Bondioli, F.; Veronesi, Paolo; Romagnoli, Marcello; Manfredini, Tiziano; Pellacani, Gian Carlo; Cannillo, Valeria
abstract

This paper focuses on the complexities of the microstructure and phase development in porcelain stoneware tiles produced following industrial fast single firing cycles. A microstructural investigation was conducted to determine if the addition of selected low cost minerals would improve mechanical properties. The minerals tested were quartz, mullite and kyanite. Uniaxially pressed samples were submitted to the same industrial firing schedule and tested according to the European tile standards before further microstructural analysis. All the requirements specified in UNI EN normative concerning BIa class tiles were fulfilled; moreover, mullite and kyanite added formulations showed sensible increases in mechanical properties, especially as far as flexural strength and abrasion resistance are concerned.

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

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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 - 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

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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

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

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2000 - Characterization of microwave inertized asbestos containing materials [Capitolo/Saggio]
Marucci, G.; Annibali, M.; Carboni, G.; Gherardi, G.; Ragazzo, G.; Siligardi, Cristina; Veronesi, Paolo; Lusvarghi, Luca; Rivasi, M. R.
abstract

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Università degli studi di Modena e Reggio Emilia

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