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Dipartimento di Ingegneria "Enzo Ferrari"

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2021 - Electrodeposition of Cu on PEDOT for a Hybrid Solid-State Electronic Device [Articolo su rivista]
Vizza, Martina; Pappaianni, Giulio; Giurlani, Walter; Stefani, Andrea; Giovanardi, Roberto; Innocenti, Massimo; Fontanesi, Claudio

Conductive polymers are nowadays attracting great attention for their peculiar mechanical, electrical and optical proprieties. In particular, PEDOT can be used in a wide range of innovative applications, from electroluminescent devices to photovoltaics. In this work, the electrochemical deposition of 3,4 ethylenedioxythiophene (EDOT) was performed on various substrates (ITO, thin films of gold and palladium on silicon wafers) by means of both potentiostatic and potentiodynamic techniques. This was intended to further expand the applications of electrochemically deposited PEDOT, particularly regarding the preparation of thin films in tight contact with electrode surfaces. This allows one to obtain systems prone to be used as electrodes in stacked devices. Chronoamperometric experiments were performed to study the nucleation and growth process of PEDOT. SEM, ESEM and AFM analysis allowed the characterization of the morphology of the polymeric films obtained. Raman and visible spectroscopy confirmed the high-quality of the coatings on the different substrates. Then, the PEDOT films were used as the base material for the further electrodeposition of a copper layer. In this way, a hybrid electronic device was obtained, by using electrochemical methods only. The high conductivity and ohmic behavior of the device were confirmed over a wide range of frequencies with electrical impedance spectroscopy analysis.

2021 - Influence of magnetic field on the electrodeposition and capacitive performances of MnO2 [Articolo su rivista]
Girimonte, A.; Stefani, A.; Innocenti, M.; Fontanesi, C.; Giovanardi, R.

This study focuses on the influence of an applied external magnetic field on the elec-trodeposition process and capacitive performances of MnO2, as pseudo-capacitive active material for supercapacitors electrodes. MnO2 was electrochemically deposited on Si/Au substrates in the presence and in the absence of a 0.5 T magnet, and its capacitive performance was tested via electrochemical characterization. The samples obtained in the presence of the magnetic field show a positive influence on the deposition process: the increase in deposition efficiency leads to more compact and uniform MnO2 coatings, with a decrease in capacitance values for the samples produced with the magnetic field.

2021 - Latent fingermarks and electrochemistry: possibilities for development and aging studies [Capitolo/Saggio]
Rosa, Roberto; Mugoni, Consuelo; Bononi, Massimiliano; Giovanardi, Roberto

2021 - Synthesis and characterization of (68-x) CuO – xV2O5 – 32TeO2 (x = 0–68 mol%) and (35-x) CuO – xV2O5 – 65TeO2 (x = 0–35 mol%) glasses: Conduction mechanism, structure and EPR study [Articolo su rivista]
Mugoni, C.; Rosa, R.; Giovanardi, R.; Affatigato, M.; Gualtieri, M. L.; Siligardi, C.; Andronenko, S. I.; Misra, S. K.

In this work, two series of glasses, i.e. (68-x) CuO – xV2O5 – 32TeO2 (x = 0–68 mol%, Te32 series) and (35-x) CuO – xV2O5 – 65TeO2 (x = 0–35 mol%, Te65 series), were synthesized by the melt-quenching method and subjected to physical, thermal and electrical characterization. Their vitreous nature was confirmed by X-Ray diffraction and differential scanning calorimetry, while their structural units were determined by Raman spectroscopy. CuO substitution by V2O5 led to a decrease in density and glass-transition temperature, together with a conductivity increase. Conduction mechanism was interpreted as mainly due to small polaron hopping from the lower (V4+) to the higher (V5+) vanadium valence states. Te32 glasses, possessing the highest electronic conductivities (ranging from 2 E−4 to 5 E−7 Ω−1 cm−1), were investigated by the Electron Paramagnetic Resonance technique, in order to more deeply analyze their structure-conductivity correlation. Particularly, the observed signals were determined to consist in a superposition of a first line due to paramagnetic Cu2+ ions and a second line due to exchange-coupled CuO clusters. Differences in the spectra were determined between samples with higher (i.e. 20-30 mol%) Cu2+ concentrations and samples with lower Cu2+ concentrations, suggesting they are located in different local environments. Finally, it was found that the Cu2+ ions are not involved in the process of electron transfer.

2020 - Corrosion resistance of commonly used plumbing materials for water distribution systems exposed to disinfection treatments [Articolo su rivista]

In this study, the corrosion resistance of commonly used plumbing materials was evaluated when three disinfection treatments were applied in hot water distribution systems. In particular copper, brass, stainless steel and galvanised steel were tested in environments containing monochloramine, chlorine dioxide and hydrogen peroxide disinfectants under real field conditions for a long period of time (1 year), in order to evaluate the effect of free corrosion on the metal specimens; chlorinated polyvinylchloride (CPVC) was tested in the same environments in order to evaluate the degradation of the mechanical properties of plastic specimens. The results obtained enabled us to rank the metallic materials corrosion resistance against disinfectants in decreasing order, as follows: stainless steel, copper and copper-based alloys, galvanised steel. CPVC samples proved to be extremely stable in all of the disinfectants investigated, maintaining the same compression behaviour of the pipes aged with untreated water after 12 months of exposure

2020 - Spin dependent electrochemistry: Focus on chiral vs achiral charge transmission through 2D SAMs adsorbed on gold [Articolo su rivista]
Innocenti, Massimo; Passaponti, Maurizio; Giurlani, Walter; Giacomino, Agnese; Pasquali, Luca; Giovanardi, Roberto; Fontanesi, Claudio

The efficiency of charge transmission in chiral compared to achiral molecular systems, of structurally related compounds, is probed via cyclic voltammetry measurements. For such a purpose five different thiols have been selected two achiral (i.e. 3-mercaptopropionic acid (MPA) and 8-mercapto-1-octanol (M8O)) and three chiral (i.e. L- and D-cysteine (Lcys, Dcys) and D-penicillamine (Dpen)). These compounds are used to form 2D self-assembled monolayers (SAM) on gold. Cyclic voltammetry (CV) measurements, by using the potassium hexacyanoferrate(III)/potassium hexacyanoferrate(II) redox couple (Fe3Fe2), are exploited to probe the charge transfer ability of the electrode|SAM|solution interface. In particular, MPA, Lcys and Dpen compounds are se- lected due to their quite similar structural and geometrical characteristics (virtually the same molecular length and terminal groups). M8O is a longer SAM forming thiol, which was selected as a reference blocking electrode compound. The comparison of the cyclic voltammetry data shows that a better ability in the charge transmission is obtained when chiral SAM are used; namely in the case of L-cysteine and D-penicillamine. This result can be related to the spin filtering ability of chiral compounds: chiral induced spin selectivity (CISS) effect. As rational- ized on the basis of theoretical values of optical rotation (OR), calculated at the CAMB3LYP/6-31G(d,p) level of the theory.

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

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 -  Corrosion and mechanical properties of age-hardened UNS N06625 forged bars for oil and gas applications [Articolo su rivista]
Febbrari, A.; Gelfi, M.; Giovanardi, R.; Montesano, L.; Pola, A.; Montani, R.; Veronesi, C.; Cavagnola, M.

UNS N06625 is a well-known nickel-base superalloy generally used in annealed condition due to its excellent corrosion resistance in the most severe environments containing sulfides and chlorides at high pressure and temperature. In general, the most efficient way to increase the alloy strength is by cold working, but obviously, this cannot be applied in case of large forgings. Actually, looking at its chemical composition, UNS N06625 can be considered an age-hardenable material, whose mechanical strength can be improved by promoting the second phase γ″ precipitation in the matrix. The aim of this paper was to assess the achievable mechanical properties and corrosion resistance of UNS N06625 forged bars in age-hardened condition with respect to the annealed one, to understand the feasibility of this not conventional heat treatment for the industrial application.

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.

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

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

2019 - Influence of heat treatments and disinfection treatments on corrosion resistance and food-grade of martensitic stainless steels [Articolo su rivista]
Giovanardi, R.; Bononi, M.; Parigi, G.; Tulli, R.

The aim of this work is to evaluate how the application of heat treatments (quenching and tempering) affect the corrosion resistance and food-grade of three different martensitic stainless steels: AISI420B, AISI440C and BÖHLER M340. For each steel three different heat treatments were applied and the samples obtained were characterized by accelerated corrosion tests, leach tests (according to DM 21/03/1973) and HV1 surface microhardness tests. The results obtained confirm that, for all the steels tested, the quenching followed by tempering at low temperature treatment guarantees compliance with the limits set by the DM in terms of leaching, allowing to obtain an excellent compromise between mechanical properties and corrosion resistance. However, M340 steel results as the best in terms of corrosion resistance and food-grade.

2019 - Influence of surface roughness anda build position on the corrosion resistance of AISI316L stainless steel obtained via v SML [Articolo su rivista]
Conte, M.; Gelsomini, C.; Franci, R.; Giovanardi, R.

The use of selective laser melting (SLM) technology to produce stainless steel near-net-shape components for industrial applications is definitely increasing. Despite the presence in literature of different studies that evaluate the corrosion resistance of AISI316L samples/components obtained via SLM, all them apply a controlled polishing (usually obtaining high finishing) in order to relate the corrosion resistance to the microstructure of the alloy. In this work different AISI 316L samples realized through SLM were characterized in as built condition (without polishing) and after polishing to a controlled surface roughness, in order to assess: i) the influence that surface polishing have on corrosion resistance of AISI 316L SLM components and ii) the influence that the building position (i.e. the position of the sample inside the SLM building chamber) have on microstructure, porosity and corrosion resistance. The results obtained not only show that the surface polishing is mandatory to obtain interesting corrosion resistance (i.e. to obtain a correct passivation of the surface) but that in polished condition the samples obtained via SLM have higher pitting resistance than those obtained by cold rolling; furthermore, the pitting potential of the SLM samples is strongly affected by the building position inside the SLM chamber.

2019 - Vantaggi e svantaggi di diversi biocidi nel controllo della contaminazione da Legionella in ospedale [Abstract in Atti di Convegno]
Marchesi, I.; Bargellini, A.; Paduano, S.; Frezza, G.; Mansi, A.; Giovanardi, R.; Vecchi, E.; Borella, Paola

Introduzione. Per il controllo della contaminazione idrica da Legionella, vengono proposti vari sistemi di disinfezione che richiedono una valutazione non solo dell’efficacia ma anche dei possibili effetti collaterali. Obiettivo dello studio è valutare l'efficacia nel lungo periodo di diversi trattamenti adottati in strutture sanitarie in termini di riduzione della contaminazione, presenza di legionelle vitali ma non coltivabili (VBNC), formazione di sottoprodotti tossici ed i possibili effetti corrosivi. Materiali e Metodi. Lo studio è stato condotto in strutture sanitarie del territorio modenese nelle quali sono attivi programmi di sorveglianza e controllo della legionellosi secondo le raccomandazioni delle linee guida regionali. Tali programmi prevedono l’adozione di sistemi di disinfezione in continuo (biossido di cloro, monoclorammina, perossido di idrogeno) ed il monitoraggio periodico della contaminazione degli impianti idrosanitari. Legionella spp. è stata quantificata tramite coltura (metodo ISO 11731:2017) ed identificata a livello di specie e sierogruppo. Per oltre 150 campioni, i risultati ottenuti con il metodo colturale sono stati confrontati con quelli ottenuti con la qPCR convenzionale ed il metodo EMA-qPCR che consente di rilevare l’eventuale presenza di legionelle VBNC. La concentrazione dei biocidi ed altri parametri chimico-fisici dell’acqua quali temperatura, pH, cloriti, clorati, ammonio, nitriti, nitrati, N-nitrosammine, e trialometani sono stati misurati con metodi standard. Per valutare l’eventuale effetto corrosivo dei biocidi, supporti di polivinilcloruro clorurato (PVC-C) contenenti provini di materiali utilizzati per le tubazioni/rubinetterie (rame, ottone, acciaio zincato e acciaio inossidabile) sono stati collegati al ricircolo di tre reti trattate in continuo con disinfettanti e di una non trattata. Dopo tre, sei e dodici mesi di esposizione, la corrosione dei provini metallici è stata valutata in termini di perdita di peso, mentre i supporti in PVC-C sono stati sottoposti a schiacciamento per valutarne la resistenza meccanica all’esposizione ad acqua trattata. Risultati. La monoclorammina ha dimostrato una maggiore efficacia nel controllo della contaminazione rispetto a biossido di cloro e perossido di idrogeno. Con i trattamenti a base di cloro, i punti positivi sono risultati contaminati da L. pneumophila sierogruppo 1, mentre col perossido erano prevalenti altre specie/sierogruppi. Nelle acque trattate con i biocidi allo studio non sono state rilevate legionelle VBNC. La formazione di cloriti e clorati è stata associata all’uso di biossido di cloro, mentre con la monoclorammina non sono stati osservati fenomeni di nitrificazione né formazione di nitrosammine. Tutti i biocidi hanno causato effetti corrosivi, anche se per i metalli testati la velocità di corrosione era entro 0,50 mm/anno, valore considerato soddisfacente per le reti idriche. Il PVC-C ha mantenuto inalterate le sue caratteristiche meccaniche anche in presenza dei disinfettanti. Conclusioni. La disinfezione chimica in continuo si conferma efficace nel ridurre ma non eradicare le legionelle dagli impianti evitando anche la presenza di cellule vitali ma non coltivabili potenzialmente infettive. Ogni metodo ha dei limiti in termini di aggressività, tossicità e selezione di ceppi, che devono essere attentamente valutati al momento della scelta del disinfettante da adottare.

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

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 - Hard anodizing of AA2011-T3 Al-Cu-Pb-Bi free-cutting alloy: improvement of the process parameters [Articolo su rivista]
Bononi, Massimiliano; Giovanardi, Roberto

The free-cutting Al-Cu-Pb-Bi alloy AA2011-T3 has been anodized in a traditional sulphuric bath with the aim of producing hard and uniform oxides of technological interest. H2SO4 concentration, electrolyte temperature, Al3+ concentration and current density have been modified. The effect of each process parameter has been evaluated through Potential-vs-time plot, coating hardness, coating thickness, volumetric expansion-ratio and coating defectiveness. SEM analysis has shown that Bi-based intermetallics are the main responsible for the severe defective state. Higher H2SO4 concentration and higher current density have improved coating hardness and defectiveness, however potentiodynamic polarizations have revealed that they do not enhance corrosion resistance.

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.

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.

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 - Pulizia in linea del filo metallico su impianti di trafilatura ad alta velocità: Innovazione, ecologia e performance [Articolo su rivista]
Orlando, G.; Giovanardi, R.; Trombi, L.

Nei processi di trafilatura il filo metallico subisce una sequenza di passaggi forzati attraverso matrici (filiere), di diametro decrescente, che ne riducono progressivamente la sezione fino al valore desiderato. Per assicurare il passaggio attraverso le filiere, riducendo quanto più possibile l’attrito, è necessaria una lubrificazione, ottenuta tramite l’utilizzo di diverse sostanze chimiche: si passa da emulsioni acqua/olio per lubrificazione liquida, a stearati di sodio e/o calcio o polimeri per lubrificazione solida. Tali lubrificanti devono formare un film sottile, omogeneo e ben adeso al filo, ma devono poter essere rimossi al termine dei processi di riduzione di sezione se si desidera ottenere un filo superficialmente pulito e pronto per eventuali successivi trattamenti galvanici, termici o di rivestimento superficiale di vario genere. In questo articolo verrà analizzata una tecnica innovativa per la pulizia del filo, in linea con l’impianto di trafilatura, applicabile sia a monte del processo (pulizia/decapaggio della vergella) sia a valle (pulizia finale prebobinatura). La tecnica in esame, basata su un processo elettrochimico, può essere integrata su linee già esistenti e va a sostituire le vasche chimiche o ad ultrasuoni di pulizia post-trafilatura, facendo uso di elettroliti a minor impatto ambientale rispetto ai tradizionali liquidi per sgrassaggio acido e alcalino.

2018 - Spin-dependent electrochemistry: Enantio-selectivity driven by chiral-induced spin selectivity effect [Articolo su rivista]
Gazzotti, Mirko; Arnaboldi, Serena; Grecchi, Sara; Giovanardi, Roberto; Cannio, Maria; Pasquali, Luca; Giacomino, Agnese; Abollino, Ornella; Fontanesi, Claudio

Spin-Dependent Electrochemistry (SDE) is a new paradigm in electrochemistry where the electrochemical response of a chiral electrode|solution interface is studied as a function of spin-polarized current. In this work, the SDE concept is further developed exploring the use of the “chiral imprinting” concept, which is implemented in two different, complementary, ways i) a chiral compound in bulk solution to obtain chiral-induced spin selectivity effect at the ferromagnetic (FM) electrode surface ii) conversely, a chiral-ferromagnetic (CFM) hybrid working electrode is produced: nickel is electrochemically co-deposited with a chiral compound, L-ta or D-(−)-tartaric acid, which is added to the electrodeposition bath; this allows to obtain a chiral co-deposited nickel-tartaric acid (Ni-LTA or Ni-DTA) working electrode. As a further innovation, the ferromagnetic working electrode is prepared by direct Ni electrodeposition on the north, or south, pole of a permanent magnet. The electrochemical response of these two chiral imprinted systems is studied by comparing cyclic voltammetry (CV) curves. The latter are recorded in the potential range relevant to the Ni(III)/Ni(II) electrochemical equilibrium, and also in the presence of glucose in bulk solution. An impressive variation in peak potentials is found when comparing CVs recorded on the north, versus south, pole of the magnet (in particular, when the co-deposited CFM working electrode is used). These results are properly rationalized within the Chiral-Induced Spin Selectivity (CISS) effect.

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.

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 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

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 - Corrosive effect on various pipe materials following different treatments for Legionella spp control in hospital water systems [Abstract in Atti di Convegno]
Marchesi, I; Paduano, S; Giovanardi, R; Bonomi, Marco; Sircana, L; Vecchi, E; Bargellini, A; Borella, P.

The aim of this study is to verify the long term corrosive effect of three disinfection procedures on different commonly used plumbing materials, in hospital water networks

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.

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

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 - Hard anodizing of AA2099-T8 aluminum‑lithium‑copper alloy: Influence of electric cycle, electrolytic bath composition and temperature [Articolo su rivista]
Bononi, Massimiliano; Conte, Manuela; Giovanardi, Roberto; Bozza, Andrea

AA2099-T8 samples have been hard anodized in a traditional sulphuric bath with the aim of studying the influence of i) electrolyte temperature, ii) Al3+ concentration and iii) different electric cycles in direct current, multi-step direct current and pulsed current (both completely anodic cycles and with cathodic "off" pulses). Anodic oxide thickness, volumetric expansion ratio (Vox/VAl), mean hardness (HV0.05), faradic efficiency and defective state have been analyzed. As temperature decreases, the oxide hardness increases but defectiveness steeply worsens; similarly a middle compromise of Al3+ concentration ensures the best performances. Regimes of high current, from one side, and of low current and current transient, from the other side, strongly affect oxide defective state introducing different types of flaws; an appropriate balance is crucial for a performing non-defected oxide. High current induces the occurrence of parasitic reactions which produce rough and defected Al/ox interface. Low current and current transient induce diffused cracking and detachments of coating fragments which decrease corrosion resistance as shown by potentiodynamic polarization tests. Li-based intermetallics play a crucial role in the last mentioned flaw-creation phenomena since they produce inhomogeneities in electric field distribution and contribute to create unstable oxide structures.

2017 - Laser hardening of steel sintered parts [Relazione in Atti di Convegno]
Veronesi, P.; Sola, R.; Colombini, E.; Giovanardi, R.; Parigi, G.

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 - 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

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 - 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

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.

2016 - Dimensional changes in automotive Pouch Li-Ion Cells: A Combined Thermo-Mechanical/electrochemical study [Articolo su rivista]
Gibellini, Erica; Lanciotti, Claudio; Giovanardi, Roberto; Bononi, Massimiliano; Davolio, Giovanni; Marchetti, Andrea; Fontanesi, Claudio

In this work it is proposed an integrated measurement system able to measure simultaneously mechanical properties, dimensional variations and Young modulus, of a pouch lithium-ion battery under operative conditions. At the same time, the designed integrated system allows also the measurement of both electrochemical main quantities (current and potentials) and temperature distribution. The complex testing capabilities system was implemented in an owner-lab-made apparatus. Experimental data collected both under normal operational conditions, as well as on abused batteries, allow to establish safer operational limits and to determine proper operation conditions to prevent the battery malfunctioning.

2016 - Environmentally friendly processes for the recovery of gold fromwaste electrical and electronic equipment (WEEE): A review [Capitolo/Saggio]
Lancellotti, I.; Giovanardi, R.; Bursi, E.; Barbieri, L.

The recovery of gold from waste is more attracting with respect to other metals. Base on the data of World Gold Council, the request for gold had an increasing trend during the last decade. Gold is commonly extracted from mines by mercury amalgamation and more refined techniques such as, cyanidization, flotation and smelting. These are processes which have high impact on the environment, for example, mercury is a common by-product; beside from mercury amalgam based processes, which are obsolete. In the last years many efforts were made in order to design alternative environmentally acceptable procedures. Besides the obtainment of gold from ores, nowadays it is particularly important the extraction of gold from secondary sources such as electronic and electric waste (WEEE). By considering the great amount of precious metals contained in electronic devices, the recovery process of such waste seems economically sustainable and recovery of precious metals, including gold from e-waste, is necessary in order to save the natural raw materials. Hydrometallurgical process has been exploited more often than the pyro-metallurgical process. The basic hydrometallurgy processing steps include extraction, concentration/purification, and recovery. The extraction consists of acid or alkaline leaching attacks of material containing gold. In the Chapter many leachants are reported belonging to two families: chloride and sulfur-based.

2016 - Preparation of an aqueous graphitic ink for thermal drop-on-demand inkjet printing [Articolo su rivista]
Romagnoli, Marcello; Gualtieri, Eva Magdalena; Cannio, Maria; Barbieri, Francesco; Giovanardi, Roberto

A graphitic ink for thermal DOD inkjet printing was developed. Challenges to be met were related to the small size of the getting nozzle (20 μm), demanding high dispersion stability of submicron particles, as well as to the physical requirements of the printer. In addition, solvents potentially hazardous to human health were excluded a priori. These necessities led to the development of a ternary aqueous solvent system based on 2-propanol and monoethylene glycol, offering an environmental-friendly alternative to conventional graphene solvents. In addition, high flexibility in terms of physical properties (e.g. surface tension, viscosity, density) important for jetting is obtained. Size reduction and exfoliation, accomplished by wet-grinding of graphite in the presence of a surfactant, were followed by laser diffraction and XRD line broadening analyses, respectively. The separated graphitic colloids used for preparation of inks were composed of ca 30 layers of AB–stacked graphene flakes, as determined by line broadening analyses (XRD data). Jetting of an ink with a solid content of 0.3 mg/mL gave a thickness increase of ca. 25 nm/pass, as determined by FESEM. Electrical characterization evidenced the need to remove residual organic molecules to regain the electrical properties of the graphitic particles.

2016 - Pulsed current effect on hard anodizing process of 2024-T3 aluminium alloy [Articolo su rivista]
Bononi, Massimiliano; Giovanardi, Roberto; Bozza, Andrea; Mattioli, Paolo

This work focused on studying the effects of different electrical parameters on the hard anodizing process (in sulphuric acid bath) of AA 2024-T3, an important heat treated aluminium alloy which has several engineering applications in aerospace, motorsport and automotive fields due to its significant combination of high mechanical properties and low density. Hard anodizing treatment is here crucial for increasing both corrosion and abrasion resistance, but the presence of typical intermetallic precipitates makes the obtainment of a performing non-defective oxide difficult. Different anodizing procedures in direct current (DC), multistep direct current (MSDC), pulsed current (PC) (slow square pulse mode) and their appropriate combination (DC&PC) were studied aiming at obtaining the optimal mechanical properties/thickness/defectiveness compromise. DC and MSDC results showed good hardness values while their optical microscopy characterization indicated a poor defectiveness state; PC modality induced a moderate loss in mechanical performances in all the different duty cycles experimented, while an extremely low defected oxide was obtained with a duty cycle of 50%. Proper merge of a soft and long initial DC current step followed by a suitable balanced final stage in PC allowed to obtain an interesting combination of significant hardness (> 340 HV) in parallel with a good oxide defectiveness state.

2016 - Pulsed current hard anodizing of heat treated aluminum alloys: Frequency and current amplitude influence [Articolo su rivista]
Bononi, Massimiliano; Giovanardi, Roberto; Bozza, Andrea

Pulsed current hard anodizing procedures have been applied to the widely used heat treated aluminum alloys AA2024-T3, AA6082-T6 and AA7075-T6. The influence of frequency and of current amplitude on anodic oxide thickness, hardness, defectiveness, volumetric expansion ratio and on process faradic efficiency has been studied. Higher frequencies generate a decrease in coating electric resistance and in general they are less effective in order to overcome typical critical issues arising in alloys difficult to be anodized. In AA2024-T3 and AA6082-T6 higher frequencies led to slight increase in thickness, decrease in compactness and faradic efficiency while hardness remained almost constant or a bit higher. With higher frequencies in AA2024-T3 defective state significantly got worse, in AA6082-T6 it improved. In AA7075-T6 an almost frequency independent behavior occurred. The highest wave amplitude with a slightly cathodic “off” current (reverse pulse) allowed to obtain greater thickness, hardness and compactness while other current amplitudes did not show significant influence on properties analyzed; a very low, but still anodic, “off” current however induced slight hardness decreases.

2015 - Electrochemical marking for instant permanent decoration of stainless steel surfaces [Relazione in Atti di Convegno]
Orlando, G.; Giovanardi, R.

The aim of this work is to study the electrochemical marking process that allows to obtain technical and decorative graphical effects on stainless steel by the controlled growth of protective oxides and to develop new electrolytes able to increase even more the technical and aesthetic result on different stainless steels series. The advantages of the electrochemical marking are: i) the possibility to obtain decorations with greater mechanical and chemical resistance compared to those obtained by screen printing and laser processes; ii) high process speed (few seconds); iii) the absence of heat input to the treated surface, unwelcome phenomenon that, in the case of laser marking, may lead to the deformation of the artifacts in particular on low sheet thicknesses or when realizing big logos; iv) high graphical definition; v) ecology: no solvents, acids or dangerous compounds needed; vi) low power consumption: possibility to use portable battery powered units. In particular, the aim of this work is to characterize the oxides obtained by electrochemical decoration on EN 1.4301/AISI 304 austenitic stainless steel in terms of corrosion resistance (by polarization curves), chemical composition (by Raman spectroscopy) and color (CIE Lab visible spectroscopy). The results obtained from the characterization were then used to formulate new compositions of the electrolyte that allow to improve the process (more black) but especially to create a specific electrolyte to treat different series of stainless steels, such as ferritic (e.g.: AISI 430) and austenitic manganese (e.g.: AISI 202) . This oxide presents a compact structure capable of giving excellent corrosion resistance and grows improving the chromium oxide naturally present on the surface of stainless steel. The black color of the marking oxide also guarantees excellent results from the aesthetic point of view, providing a high contrast with the stainless surface, not only on standard applications (company logo, data plates, codes, etc.) but also on large surface decorations for design and architecture purposes.

2015 - Instant ecological pickling on stainless steel welds and innovative surface passivation [Relazione in Atti di Convegno]
Orlando, G.; Giovanardi, R.

The aim of this work is to improve the innovative process for pickling and passivating stainless steel welds and surfaces in order to obtain complete removal of non-protective oxides and to restore the passivation. The treatment, based on an electrochemical principle, uses specific electrolytes and patented electrodes: the advantage is to increase the corrosion resistance, working speed (instant process) and surface appearance on stainless steel, avoiding the traditional pickling solutions (which usually contain high concentrations of strong and toxic acids). Different solutions were prepared using low concentrations of weak organic acids, e.g. citric, oxalic, sulphamic, gluconic and lactic, up to the new neutral (pH 7, acid free) solution used to gain high passivation on stainless steel surfaces. This aspect is very important to reduce the hazardousness of the solution compared to the pure phosphoric acid (standard solution) and moreover to the traditional pickling acids. The best solutions in terms of aesthetic result were tested in terms of corrosion resistance (free and accelerated) XPS analysis, on TIG and MIG samples. A S.E.M. analysis is used to show the influence of the carbon fiber effect depending on the technology used (transformer vs inverter) and electrolyte. A number of real field application is presented, both manual and custom/automation.

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.

2015 - Pulsed current effect on hard anodizing process of 7075-T6 aluminium alloy [Articolo su rivista]
Bozza, Andrea; Giovanardi, Roberto; Manfredini, Tiziano; Mattioli, Paolo

The aim of this work is to study the influence of pulsed current on hard anodizing process (in sulphuric acid bath) of AA 7075-T6, a commercial heat treated aluminium alloy widely used in several innovative and strategic mechanical sectors (military, automotive, aerospace, etc).Exploiting different pulsed current procedures (slow square pulse mode), combining different duty cycles and current levels it was possible to obtain thick and hard anodic oxides with a good interfacial adhesion. The optical microscopy characterization shows that the use of pulsed current minimizes the growth of defects at the oxide/alloy interface caused by the presence of intermetallic precipitates characteristic of AA 7075-T6. Moreover nano-indentation profiles, evaluated along the coatings cross section, highlight the oxide hardness increase of the samples obtained employing pulsed current cycles (PC) compared to those obtained with standard direct current process (DC) or multistep direct current procedures (MSDC).

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.

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 - 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.

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

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 - Effect of temperature on pulsed current chromium electrodeposition from Cr(III) aqueous solutions [Articolo su rivista]
Giovanardi, R; Bozza, A

Chromium electrodeposition is widely used industrially to obtain protective coatings with high corrosion resistance combined with other important properties such as high hardness and wear resistance (hard chromium plating) or high surface finishing (decorative chromium plating).In recent years, much attention was given to finding alternative electroplating methods that could achieve similar coatings without the use of hexavalent chromium, given the known toxicity of its compounds. Ideally the deposition of metallic chromium from trivalent chromium acqueous solutions represent the easier strategy to obtain such coatings without the use of hazardous solutions; unfortunatelly a lot of complications concerning the chemistry of trivalent chromium in acqueous solution make this way very difficult to pursue. In this work some deposition strategies have been developed, obtaining; on carbon steel substrate, metallic chromium coatings with good properties (high adhesion to the substrate, micro-hardness, surface finishing) starting from aqueous solutions of Cr (III) and formic acid. The developed strategies are based on the use of pulsed current (and optimization of its process parameters, such as duty cycle, period and magnitude of current applied) and low temperatures.

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

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.

2013 - An Empiric Approach to State of Charge Assessment and Range Estimation of an Electric Vehicle [Relazione in Atti di Convegno]
Giovanni, Davolio; Giovanardi, Roberto; Claudio, Lanciotti

The diffusion of electric vehicles depends on a multiplicity of reasons, technical, economic, and at the end, there is also the driver's range anxiety, the fear don't reaching the recharging plug. An aid to overtaking this fear can be done by knowing the battery state of charge; the driver needs an electrochemical gauge indicating, in real time, the remaining fraction of vehicle range. The electrochemical behavior of large capacity Li-ion cell has been studied during the operation on an electric car, recording intensiodynamic polarization curves at different points of the run test. Some characteristic features in the curves of the cell tested, have been found and related to the run distance. The series of polarization curves related to a discharge cycle characterize the behavior of a cell, with respect to the power deliverable and the effective voltage plateau in the experimented dynamic regime. The plot of cell voltage interpolated at zero current (ZCV) vs. distance also characterizes a cell in order to accomplish a gauge of state of charge; the attempts have done better results than the open circuit voltage (OCV) method. The "electrochemical gauge" warns in real time how long range is remaining.

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

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.

2012 - Corrosion resistance improvement of nitrocarburised and post-oxidised steels by oil impregnation [Articolo su rivista]
Giovanardi, Roberto; Poli, Giorgio; Sola, Ramona; Veronesi, Paolo

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 - Decapaggio elettrochimico di saldature su acciaio inox [Articolo su rivista]
Giovanardi, Roberto; Orlando, Gianpaolo

Lo scenario del trattamento delle saldature su inox si è ampliato grazie all ’introduzione di metodi di decapaggio elettrochimici, cioèprocessi innovativi che combinano l’azione chimica tipica deldecapaggio a quella elettrochimica.

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

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 - Electrochemical method for pickling and passivation of austenitic steel welds [Articolo su rivista]
Giovanardi, Roberto; Poli, Giorgio; Pasquali, Luca; Montecchi, Monica; L., Filippetti; G., Orlando

The aim of this work is to develop an innovative process for pickling and passivating tungsten inert gas welds on austenitic stainless steel in order to obtain complete removal of non-protective oxides and to passivate the metal surface. In particular, the treatment intends to increase both corrosion resistance and surface appearance of the steel without making use of traditional pickling solutions (which usually contain high concentrations of strong acids). The treatment, based on an electrochemical approach, uses specific electrolytes, and to evaluate their effect in terms of corrosion resistance and surface finish, different solutions were prepared and tested using low concentrations of weak organic acids, e.g. citric, oxalic, sulphamic, gluconic and lactic acids. This aspect is very important to reduce the hazardousness of the solution compared to the traditional pickling acids.

2012 - Functionalization of glassy carbon surface by means of aliphatic and aromatic amino acids. An experimental and theoretical integrated approach [Articolo su rivista]
Vanossi, Davide; Benassi, Rois; Parenti, Francesca; Tassinari, Francesco; Giovanardi, Roberto; Florini, Nicola; De Renzi, Valentina; Arnaud, Gaelle Francoise; Fontanesi, Claudio

Glassy Carbon (GC) electrode surfaces are functionalized through electrochemical assisted grafting, in oxidation regime, of six amino acids (AA): -Alanine (-Ala), L-Aspartic acid (Asp), 11-aminoundecanoic acid (UA), 4-Aminobenzoic acid (PABA), 4-(4-Amino-phenyl)-butyric acid (PFB), 3-(4-Amino-phenyl)-propionic acid (PFP). Thus, a GC/AA interface is produced featuring carboxylic groups facing the solution. Electrochemical (cyclic voltammetry and electrochemical impedance spectroscopy) and XPS techniques are used to experimentally characterize the grafting process and the surface state. The theoretical results are compared with the experimental evidence to determine, at a molecular level, the overall grafting mechanism. Ionization Potentials, Standard Oxidation Potentials, HOMO and electron spin distributions are calculated at the CCD/6-31G* level of the theory. The comparison of experimental and theoretical data suggests that the main electroactive species is the “zwitterionic” form for the three aliphatic amino acids, while the amino acids featuring the amino group bound to the phenyl aromatic moiety show a different behaviour. The comparison between experimental and theoretical results suggests that both the neutral and zwitterionic forms are present in the acetonitrile solution in the case of 4-(4-Amino-phenyl)-butyric acid (PFB) and 3-(4-Amino-phenyl)-propionic acid.

2012 - WEEE: No waste anymore but secondary raw material [Capitolo/Saggio]
Andreola, Nora Maria; Barbieri, Luisa; Cannio, Maria; Giovanardi, Roberto; Lancellotti, Isabella; Pozzi, Paolo; Soragni, Ercole

The management of Waste Electrical and Electronic Equipment (WEEE) is a topic of great interest, now being an integral part of the Italian D.Lgs. 151/2005. In order to protract life cycle of this waste, composed by glass, polymers and metals, a great effort is done to develop separation, reclamation, recycling and recovery techniques. This study reports the results achieved on the characterization of different materials constituting TV sets and computers, low environmental impact techniques of extraction and recovery of precious metals from electronic circuitry and the use of glassy components as secondary raw material in the ceramic field instead of virgin compounds.

2011 - Adsorption of organic compounds at the aluminium oxide/aqueous solution interface during the aluminium anodizing process [Articolo su rivista]
Giovanardi, Roberto; Fontanesi, Claudio; W., Dallabarba

The paper reports a systematic study concerning the role played by different organic compounds (glycolic acid, oxalic acid, glycerol) on the electrochemical oxidation process of aluminium in sulphuric acid solution. The result of the experiment as a whole provides a clear indication of the deep influence exerted by the three selected organic compounds on the aluminium oxide structure, leading to the formation of a more compact oxide layer. Electrochemical impedance spectroscopy results appear of particular interest; they are discussed in the light of a model proposed by Bojinov. The relevant parameters, half-jump distance a and cross-capture section S, are found consistently related to variations in the oxide structure (porosity). This gives a sounder basis to the physically correct nature of the assumptions underlying the Bojinov model, also suggesting that organic compounds are adsorbed at the aluminium oxide/aqueous solution interface.

2011 - Chromium electrodeposition from Cr(III) aqueous solutions [Articolo su rivista]
Giovanardi, Roberto; Orlando, Gianpaolo

The aim of this work is to study an alternative plating process to obtain chromium coatings through electrodeposition from baths containing trivalent chromium, as aqueous solutions of Cr (III) are significantly less dangerous, in terms of human health and environmental impact, as compared to the traditional Cr (VI) baths employed for this purpose. In order to overcome problems regarding the reduction of Cr (III) in aqueous solution, two approaches were followed: i) the possibility of co-depositing chromium along with a second metal, which could help the process of discharge of Cr3+ on the substrate; ii) the use of a specific ligand for the Cr3+ ion, which can generate easily reducible complexes at the metal–solution interphase. Both approaches led to interesting results: in particular, the co-deposition enabled us to obtain NiCr alloy with a high percentage of chromium, and the deposition using specific complexing agents allowed optimal bath compositions to be developed both for decorative and hard chromium plating.

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

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.

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 - Testing the Performance of High Capacity Li-Ion Batteries [Relazione in Atti di Convegno]
Giovanni, Davolio; Giovanardi, Roberto; Claudio, Lanciotti

This work aims at collecting data on the electrochemical behavior of high capacity cells of different chemistries in operative conditions. The final target is to define the most suitable battery for a given kind of usage, in our case neighborhood Electric Vehicle. Four different cells were tested: Li-ion type with Lithium Iron Phosphate cathode (LiFe), Li-ion type with Ni-Mn oxides (LiMn) and two different Li-ion Polymer (LiP) cells. The results obtained during field test show that the LiP cells exhibit lower dynamic polarization resistance with respect to both LiFe and LiMn ones and that the maximum power of LiP cells, in particular at low temperature conditions, is higher. The results suggest this method for a quick comparison (during field application) of different types of high capacity cells and for giving an index about the state of health of a cell.

2010 - A new environmentally friendly process for the recovery of gold from electronic waste [Articolo su rivista]
Barbieri, Luisa; Giovanardi, Roberto; Lancellotti, Isabella; Michelazzi, Marco

A new method for the recovery of preciousmetals, in particular gold, from electronic waste is proposed.This work focused on the research of an easilyrenewable etching agent, in order to make an environmentallyfriendly process possible. Two well knownhydrometallurgical etching agents, FeCl3 and CuCl2, wereevaluated in terms of efficiency and kinetics, testingsolutions with different concentration of etchant andhydrochloric acid. The recovery of spent etching solutionswas evaluated: promising results were found in the case ofCuCl2, which can be completely restored by oxidation ofthe cuprous chloride formed during the etching usingatmospheric oxygen.

2010 - Functionalisation of ceramic tile surface by soluble salts addition: part II. Titanium and Silver addition [Articolo su rivista]
Bondioli, Federica; Dinelli, Martina; Giovanardi, Roberto; Manfredini, Tiziano

The aim of this study was to assess surface functionalization of industrial ceramic tiles through the addition of soluble salts to improve mechanicalproperties (scratch and wear resistance) and conductivity, while preserving the aesthetic aspects of the finished product. This objective was pursuedthrough the application of different solutions of titanium and silver with a potential for transformation into titania and silver nanoparticles during thesintering of the material. The solutions, in different concentrations, were applied (300 g/m2) to unglazed green tiles by air brushing. The resultingproducts were polished and characterized in terms of microstructural, surface micromechanical, and technological properties based on the UNIEN ISO reference standards. The electrical conductivity deriving from the presence of titania and silver was also established with specific tests.The results were found to correlate with the results obtained from the addition of zirconium solutions as reported in part I of the paper.

2010 - Microstructural Characterisation and Electrical Properties of Multiwalled Carbon Nanotube/Glass-Ceramic Nanocomposites [Articolo su rivista]
Giovanardi, Roberto; Montorsi, Monia; Ori, Guido; . J., Cho; T., Subhani; A. R., Boccaccini; Siligardi, Cristina

We report on an improved processing method for fabricating multiwalled carbon nanotubes/glass-ceramic nanocomposites based on vanadium doped silicate glass matrices. Starting from the design of a stable aqueous dispersion of CNTs, achieved using a cationic surfactant, the interaction of CNTs with glass particles in suspension was improved using a co-solvent that provided access to nanocomposites exhibiting high quality CNT distribution in the matrix, which was confirmed by detailed micro/nano-structural and morphological characterisation. Considering that very few studies have focused on the functional properties of CNT/glass composites, in the present investigation the electrical resistivity of CNT/glass composites was measured and it was demonstrated that higher electrical conductivity values were obtained compared to previous similar materials fabricated by conventional powder processing.

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.

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 - 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.

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.

2008 - A comparison between corrosion resistances of some HVOF-sprayed metal alloy coatings [Articolo su rivista]
G., Bolelli; Lusvarghi, Luca; Giovanardi, Roberto

This study compares the corrosion resistance of one Co–based alloy coating, namely Co–28Mo–17Cr–3Si (similar to Tribaloy-800), four Ni-based alloy coatings, namely Ni–17Cr–4Fe–4Si–3.5B–1C (Diamalloy-2001), Ni–20Cr–10W–9Mo–4Cu–1C–1B–1Fe (Diamalloy-4006), Ni–22Cr–9Mo–4Nb–5Fe (similar to Inconel-625), Ni–32Mo–16Cr–3Si–2Co (similar to Tribaloy-700), and a (WC-12Co)–33Ni–9Cr–3.5Fe–2Si–2B–0.5C cermet–Ni alloy blend coating. They were produced by liquid-fuelled HVOF spraying onto AISI1040 steel plates. Electrolytic hard chrome (EHC) plating was characterised as a reference material, to verify whether some HVOF coatings are suitable as an EHC replacement. The microstructure of the coatings was examined by SEM and XRD. Electrochemical polarization tests and free corrosion tests were performed in 0.1 M HCl aqueous solution; the corrodkote test (ASTM B380-97R02) was also performed, to rank coatings qualitatively.The lowest corrosion current densities (Icorr) were recorded for EHC and Tribaloy-700. The latter coating contained few secondary phases and little porosity; the damage was mainly due to corrosion activation along lamellae boundaries. Diamalloy-2001 exhibited the highest Icorr and was significantly damaged after the polarization test, as its multi-phase microstructure had triggered severe galvanic corrosion. During free corrosion in 0.1 M HCl, Tribaloy-700 and Diamalloy-4006 retained rather stable polarization resistance (Rp), whereas the Rp of EHC decreased significantly. Tribaloy-700 survived 40 h of corrodkote test with no apparent damage and EHC underwent limited pitting corrosion. All other coatings had visible corrosion. The Inconel-625 coating failed to protect the substrate after 20 h of testing, due to inadequate processing conditions.

Fontanesi, Claudio; Giovanardi, Roberto; Cannio, Maria; E., Soragni

This work presents a study of a hard chromiumplating process using low concentration H2CrO4 baths. Inparticular, the effect of different values of CrO3/H2SO4 ratioon coating properties such as adhesion, hardness, surfaceroughness, apparent density and microstructure were considered.To increase the solution conductivity, avoiding longdeposition times and low throwing power typical of dilutesolutions, the behaviour of various inorganic compoundswas investigated. Specifically, the compounds suitable forobtaining brighter coatings with lower surface roughnessvalues than those obtained using Fink’s solutions wereNa2SO4 and Al2(SO4)3 9 18H2O. A bath composition wasidentified, with a limited use of Cr(VI) in a solution able toproduce coatings with a better surface roughness than thoseof conventional industrial baths.

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

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 - Electrochemical comparison between corrosion resistance of some thermally sprayed coatings [Articolo su rivista]
Bolelli, Giovanni; Cannillo, Valeria; Giovanardi, Roberto; Lusvarghi, Luca

Electrochemical polarisation and impedance spectroscopy tests in0.1 M HCl and 0.1 M H2SO4 solutions were performed on HVOF-sprayedcermet coatings (WC–17% Co, WC–10% Co–4% Cr) and AtmosphericPlasma-Sprayed (APS) ceramics (Al2O3, Al2O3–13 wt%TiO2, Cr2O3) with APSbond coat (Ni–Co–Cr–Al–Y). Reference tests were also performed on hardchrome electroplating. Plasma-sprayed coatings offer limited substrateprotection owing to interconnected porosity, although the bond coat promotessome forms of passivation in H2SO4. HVOF-sprayed cermets possess goodcorrosion resistance in both environments. Chrome electroplating showscomparatively better corrosion resistance in H2SO4, but worse in HCl.

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


2008 - Recovery of precious metals from electronic scraps [Relazione in Atti di Convegno]
Andreola, Nora Maria; Barbieri, Luisa; Giovanardi, Roberto; Lancellotti, Isabella; Soragni, Ercole

Recovery of precious metals (PMs) is a present topic, as they are used almost in every electronicelectric device. Gold is the second PM in order of consumption (following silver) and it is almost ubiquitary in electronics where it mainly finds application to produce bonding wires in integrated circuits and as a coating for contacts and connectors. Given this, discontinued electronic and, with a minor role, electric devices may represent a primary source of PMs as gold mines or jewelery wastes. At present the recovery of gold from such waste is generally accomplished by two strategies: by oxidative thermal treatment followed by metallurgical or chemical processes or by cyanide chemical etching; both techniques do not represent the optimum as the first one deserves a great amount of energy and non-combustible pollutant slag and fumes are produced, while the second procedure comports the use of a highly pollutant agent as cyanide. The aim of this work is the characterization of different electronics scraps to evaluate the gold concentration, and the selective recovery of this metal using enviromentally-friendly techniques. In particular, a new process was developed in order to overcome such environmental and efficiency issues. The process reaches the goal of detach the gold film from the substrate by selective leaching of the supporting metal.

2007 - La scelta dei materiali nella progettazione industriale [Traduzione di Libro]
Fabbri, Paola; Giovanardi, Roberto; Veronesi, Paolo

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

2006 - Corrosion resistance of HVOF-sprayed coatings for hard chrome replacement [Articolo su rivista]
Bolelli, Giovanni; Giovanardi, Roberto; Lusvarghi, Luca; Manfredini, Tiziano

HVOF-sprayed coatings (WC-17Co, WC-10Co-4Cr, Co-28Mo-17Cr-3Si) and electrolytic hard chrome (EHC) coatings corrosion resistances have been compared through electrochemical polarization tests (0.1 N HCl, 0.1 N HNO3) and Corrodkote test. EHC coatings passivate in HNO3, but undergo pitting corrosion in HCl and in Corrodkote test too. HVOF coatings do not passivate, but possess more noble corrosion potentials. Both in HNO3 and HCl, they undergo more generalized corrosion, with similar i(corr); crevice corrosion along splat boundaries is sometimes detected after the HCl test. Their i(corr) in 0.1 N HCl solution is lower than in several of EHC coatings. No visible damage in the HVOF coatings has occurred after the Corrodkote test. (c) 2006 Elsevier Ltd. All rights reserved.

2005 - Modelling of the initial stages of the electropolymerization mechanism of o-phenylenediamine [Articolo su rivista]
G., Camurri G; P., Ferrarini; Giovanardi, Roberto; Benassi, Rois; Fontanesi, Claudio

A detailed mechanism is proposed concerning the initial stages (up to the formation of the dimer) of the electropolymerization of ortho-phenylenediamine (oPD) to yield the polymer (PPD). Cyclic voltammetry measurements have been performed aiming to single out the effect of pH and to determine the number of exchanged electrons. The experimental evidence has been modelled considering 10 possible monomers (as obtained from the combination of oxidation and protonation/deprotonation reactions) involved in nine reactions to produce five different dimer species. Such a modelistic picture developed starting from the experimental findings, collected both in this paper and as found in the literature, is tightly compared with theoretical calculations. In particular, both E-0 values and thermodynamic quantities (Delta U, Delta H and Delta G variations), relating to the reaction path leading to the formation of the dimer, have been determined at the ab initio level of the theory (molecular structures relevant to transient complex species and transition states, as well as reaction free energy variations and activation energies were calculated too).

2005 - On the electroreduction of Cr(VI) aqueous solutions on iron and copper cathodes [Articolo su rivista]
Giovanardi, Roberto; E., Soragni; Fontanesi, Claudio; DE RENZI, Valentina; DEL PENNINO, Umberto; M. L., Foresti

The electroreductive behaviour of CrO3 +H2SO4 aqueous solution is studied on poly-crystalline iron and copper cathodes. Theelectrochemical results have been also compared with XPS, AFM and SEM findings collected ‘‘ex situ’’ on emersed electrodes andan electrochemical mechanism featuring adsorbed Cr(IV) and Cr(III) species is proposed. In the case of iron a main role is played bythe passive state of the electrodic surface caused by the presence of a protective mixed iron/chromium oxide layer and by its electrochemicaldissolution. This passive to active transition of the electrodic surface and the occurrence of an irreversible reductivecurrent peak, in a potential range where the deposition of metallic chromium does not yet occur, suggests that the electrodic surfaceplays an active role in the electrochemical process. A major difference is found between Fe and Cu cathodes, concerning the kineticmechanism of formation of adsorbed species.

2004 - On the 2D phase transition of adenine adsorbed at the Mercury/ethylene glycol solution interface [Articolo su rivista]
Fontanesi, Claudio; L., Benedetti; Giovanardi, Roberto; G., Camurri; P., Ferrarini

The liquid like → solid like 2D phase transition of adenine adsorbed at the Hg/ethylene glycol solution interface is here studied. Equilibrium aspects are effectively rationalized by using a model which was originally developed in the case of the 2D phase transition of adenine adsorbed at the Hg/aqueous solution interface [1,2]. In this work, the attention is mainly focused on the validation of the model itself in the case of a solvent different from water. The results obtained in the two different solvents are then compared in terms of structural (orientation of the adsorbate at the interface) and related thermodynamic (liquid like → solid like 2D standard entropy variation) properties. It is also found thatthe kinetics of formation of the 2D solid like phase follows a nucleation and growth mechanism, again in close similarity with the results obtained in water.

2003 - Temperature Effect on the 2D phase transition kinetics of adenine adsorbed at the Hg electrode/aqueous solution interface [Articolo su rivista]
Fontanesi, Claudio; R., Andreoli; L., Benedetti; Giovanardi, Roberto

The kinetics of the liquid-like → solid-like 2D phase transition of adenine adsorbed at the Hg/aqueous solution interface is studied. Attention is focused on the effect of temperature on the rate of phase change; an increase in temperature is found to cause a decrease of transition rate.

2002 - Computational electrochemistry. Ab-initio calculation of solvent effect in the multiple electroreduction of polypyridinic compounds [Articolo su rivista]
Fontanesi, Claudio; Benassi, Rois; Giovanardi, Roberto; Marcaccio, M; Paolucci, F; Roffia, S.

The electrochemical multiple reduction of a series of polypyridinic compounds, yielding mono, di and trianionic species is theoretically studied. Calculated electron affinity values were used to obtain molecular-structure/reactivity relationships, the latter reflected by the experimental half-wave electroreduction potentials. Gas-phase electron affinity data vs. half-wave potentials produced satisfactory linear correlations, but separated for each successive electron transfer step (i.e. a linear relationship for the first electron transfer, yield of the monoanion, neatly separated from the one concerning the second electron transfer, yield of the dianionic species). The theoretical approach was pushed further, also including solvent effects. This was done by means of two methods based on the continuum solvation model: the Onsager cavity (SCRF) and the more sophisticated SM5.42R solvation models. In particular, the latter is able to group in a single correlation the potentials referring to the first, second and third electron transfer.

2000 - On the Frumkin interaction parameter in the adsorption of aromatics on mercury in ethylene glycol [Articolo su rivista]
Fontanesi, Claudio; L., Benedetti; Giovanardi, Roberto

The Frumkin interaction parameter (AF) for the adsorption of a small series of aromatic compounds on mercury from ethylene glycol (EG) is accounted for in value and mainly in sign (always positive) using the dispersion energy contribution (εd) due to the mutual interaction among adsorbing aromatics molecules and that regarding EG molecules leaving the surface. A successful result is anyway obtained when the change of conformation of EG from the cis one in the adsorbed state to the cis-OH in the bulk phase (i.e., a conformation featuring an intramolecular OH bond) is considered.