Papers by Author: Roberto Tomasi

Abstract: The increased interest in nanostructured materials is due to improvements in the mechanical properties presented for these materials. Significant increases in properties such as hardness, wear resistance and in some cases, strength and toughness of nanostructured ceramics have been reported, compared to conventional ceramics. High-energy milling can lead to selfsustaining reactions in a variety of systems. In this study, reactive high-energy milling was used to synthesis niobium carbide (NbC) nanoparticles. The reaction products were de-agglomerated and mixed with commercial ultra-fine alumina powder to produce alumina matrix nanocomposites with 5vol% of nanometric NbC. Alumina/NbC nanocomposite produced using powder obtained by reactive present good microstructural characteristic, high densities, good hardness and higher toughness. What makes this material an interesting alternative for production of ceramic cutting tools.

Abstract: One possible route for the production of nanometric powders is the reactive high-energy milling. For a variety of systems of highly exothermic reactions, the milling can lead to self-sustaining reactions, with the reaction being observed after an induction or ignition time, which produces a temperature increase in the reactants. In this work, WC powder was obtained by reactive high energy-milling, performed in a SPEX 8000 shaker/mill. During milling the highly exothermic displacement reaction of reduction of the WO3 by Mg was performed in presence of carbon to produce WC and MgO. The material to ball mass ratio was fixed in 4:1 and the ignition time of the reaction was determined. In order to characterize the transformations from reactant powders to reaction products, the milling was stopped at given times before, immediately after and after the reaction; the powders obtained were characterized by X-ray diffraction, scanning electron microscopy and specific surface area. Depending on the amount of carbon, W and the W2C were also observed as reaction products. The complete formation of WC was achieved with addition of an excess of carbon.