Papers by Author: Bruno DeBenedetti

Abstract: Nanostructured Mg2Ni, Fe-doped and Ti-doped Mg2Ni alloys for hydrogen storage applications have been produced by means of Mechanically Activated Self-propagating High temperature Synthesis (MASHS). Different molar compositions of Fe and Ti (0.1; 0.3 and 0.5) have been studied in order to determine their influence in the hydrogen sorption properties. Different Mg-Ni based alloys have been tested in order to study their hydrogen sorption behavior. The hydrogenation was carried out in a Pressflow Gas Controller. Subsequently, the dehydrogenation process was conducted by means of a Differential Scanning Calorimetry (DSC) equipped with an H2 detector of the purged gas. The MASHS method has been demonstrated to be effective for the obtainment of nanostructured pure and doped Mg2Ni intermetallics. In addition, the materials produced showed hydrogen storage capacities superior to 4wt%, especially in the case of Fe-doped Mg2Ni and a slight reduction of desorption temperature was reached with Ti-doped Mg2Ni. Finally, the activation energy of the dehydrogenation process was evaluated and Ti-doped sample exhibited the lower activation energy value. Obtained results are promising for technological applications of Mg-based alloys.

Abstract: Magnetron sputtering is a powerful process for the production of thin films and coatings employed for the surface modification of tools and engineering components in various industrial sectors. Nanostructured coatings for multifunctional applications were deposited by means of magnetron sputtering by adjusting the experimental parameters in order to tailor the chemistry, the microstructure and the morphology of the coatings. Among the several systems that were investigated, TiC–TiB2 for wear applications were successfully tested. TiC–TiB2 coatings were deposited on a hardmetal WC–Co substrate in an unbalanced DC magnetron sputtering system starting from composite targets fabricated by the Self-propagating High-temperature Synthesis (SHS) consolidation method, involving the material synthesis and densification in one step. The results, showing the achievement of nanostructured films with thickness ranging between 1 and 2 µm, are here presented. The properties evaluated on the developed films (hardness, adhesion, friction coefficient and volumetric wear) are promising for the improvement of wear-resistant applications.

Abstract: Nanostructured semiconductor metal oxides have played a central role in the gas sensing research field, because of their high sensitivity, selectivity and low response time. Among all the processes, developed for the synthesis of nanostructured metal oxides, gel combustion seems to be the most promising route due to low-cost precursors and simplicity of the process. It combines chemical gelation and combustion, involving the formation of a gel from an acqueous solution and an exothermic redox reaction, yielding to very porous and softly agglomerated nanopowders. In this work, nanostructured tin oxide, SnO2, and titanium oxide, TiO2, have been synthesized through gel combustion. Powders showed nanometric particle size and high specific surface area. The so-obtained TiO2 and SnO2 nanopowders have been used as sensitive element of resistive λ sensor and ethanol sensor respectively, realized depositing films of nanopowders dispersed in water onto alumina substrates provided with Pt contacts and heater. TiO2-based sensors showed at high temperature good response, fast response time, linearity in a wide range of O2 concentration and long-term stability. SnO2-based sensors have shown high sensitivity to low concentrations of ethanol at moderate temperature.

Abstract: The aim of this work is the preparation and study of the mechanisms of structure formation of dense ceramics based on the TiC–TiB2–MeO system obtained by pressure–assisted Self-propagating High-temperature Synthesis. SHS systems were selected on the basis of thermodynamic analysis as suitable to realise regimes of synthesis with formation of liquid phase allowing a full densification. It was observed that at the adiabatic temperature the liquid phase formed in the SHS products consists of either melted oxides or eutectic TiC–TiB2. The results of microstructural observations and mechanical characterization confirm that the metal oxides effectively promote the densification of the final products and the grain refinement of the SHSproduced ceramic materials.

Abstract: The aim of this work is the achievement of nanostructured TiC–TiB2 powders through a metastability approach based on the Self–propagating High–temperature Synthesis (SHS) process followed by quench to obtain highly metastable powder agglomerates. An optimisation of the reaction stoichiometry was carried out in order to obtain products with approximately eutectic composition (i.e. 67%mol TiC – 33%mol TiB2). An optimized amount of sodium borate was used as gasifying additive to produce dispersed nanostructured powder agglomerates. The metastability of the nanocomposite powders obtained through the (SHS+quench) route was evaluated by annealing. The morphological evolution of the powders after thermal treatment yielded a recrystallisation with limited grain growth of the nanostructured TiC–TiB2 phases and demonstrated the metastability of the products obtained by the (SHS+quench) route.

Abstract: Non-oxide ceramic nanostructured powders are synthesized through metastable transformation processing based on the Self-propagating High-temperature Synthesis (SHS) process followed by quenching. Binary systems like the investigated TiC–TiB2, when quenched from the liquid state give rise to metastable structures capable of being converted into a stable, fine-grained (nanocomposite) microstructure upon recrystallization by medium temperature treatments. A necessary condition is that the combustion temperature of the SHS reaction is higher than the eutectic temperature. A previous optimisation of the reaction stoichiometry was carried out to obtain SHS products with composition approximately equal to the eutectic (i.e. 67%mol TiC0,7 – 33%mol TiB2), according to the reaction: 6Ti + B4C + 1.8C → 4TiC0.7 + 2TiB2. In this work, different amounts of sodium borate (borax) were used in order to determine the optimum amount of additive to produce nanostructured TiC0.7–TiB2 composites. The morphological evolution of the powders after thermal treatment yielding re–crystallized structures demonstrates the metastability of the SHS–quench products. Therefore, the metastability process based on SHS– quench represents an extremely attractive route suitable for the achievement of nanocomposites.

Abstract: The use of magnesium and its alloys is limited by their high susceptibility to corrosion, that may be attributed to the presence of critical impurities and the high chemical reactivity of the magnesium itself. Such characteristic justifies the great interest of performing coating technologies for the protection of magnesium parts by using environmentally friendly and cheap processes, with particular relevance in the framework of the European context. While magnesium technologies are rapidly taking advantages of the research results obtained during the last years, some more efforts are necessary to evaluate the impacts of its production on the environment and on the use of existing energy resources. Following this main lines, the paper presents some results obtained in NANOMAG (“Development of Innovative Nanocomposite Coatings for Magnesium Casting Protection” – Growth Programme n. 40548), a research project sponsored by the European Commission in which magnesium and its coating processes are evaluated taking into account also their environmental performances with a life-cycle approach.