The mechanisms of combustion and continuous reactions during mechanical alloying

Some materials exhibit a combustion event during mechanical alloying, which results in the rapid transformation of reactants into products, while othe rs show a slow transformation of reactants into products, In this paper, th e continuous W + C --> WC reaction is compared to the Ti + C --> TiC combus tion reaction. Rietveld refinement of X-ray diffraction patterns is used to show that these particular reactions proceed through different pathways, d etermined by crystallographic factors of the reactants. When a crystallogra phic relationship exists between the reactants and the products, such as th at between W and WC, the product forms slowly over a period of time. In con trast, insertion of C into the Ti structure is associated with atomic rearr angements within the crowded lattice planes and the subsequent catastrophic failure of the reactant lattices results in combustion to form TiC. (C) 20 01 Academic Press.