Papers by Author: Dario Vallauri

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Authors: Dario Vallauri, Isabel M. Martins, Fabio A. Deorsola, Ignazio Amato, Francisco Delmas, Manuela Oliveira
Authors: Dario Vallauri, Y. López, Bruno DeBenedetti, Ignazio Amato
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.
Authors: Isabel C. Atías Adrián, Dario Vallauri, Z. Zhang, A. Chrysanthou, Bruno DeBenedetti, Ignazio Amato
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.
Authors: Vladimir A. Shcherbakov, Anton V. Phitev, N.V. Sachkova, Fabio A. Deorsola, Dario Vallauri, Bruno DeBenedetti
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.
Authors: M. Pidria, E. Merlone, M. Rostagno, L. Tabone, F. Bechis, Dario Vallauri, Fabio A. Deorsola, Ignazio Amato, M.A. Rodríguez
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