Combustion synthesis of transition metal nitrides

Abstract

Owing to the high heats of reaction between refractory metals and nitrogen, refractory metal nitrides can be synthesized within seconds via self-propagating high-temperature synthesis (SHS) reactions. The combustion reactions utilize pelletized or loosely packed metal systems, and are initiated by an external heat source. The high initial porosity of loosely packed powders guarantees the completion of reaction and the achievement of high yield under relatively low nitrogen pressures. The reaction product is a very fine powder which can be easily densified.

Detailed experimental studies on these gas-solid combustion reactions reveal the dependence of combustion and propagation characteristics, like front propagation velocity, combustion temperature and degree of conversion, on operating parameters like nitrogen pressure, particle size and morphology of the reactant metal and dilution of the gas and solid phases. From these studies the optimum synthesis conditions for a variety of nitrides are determined and information about the mechanisms of several gas-solid combustion reactions is obtained. With the aid of combustion theory, the apparent values of activation energy for several nitridation reactions are calculated from measured combustion characteristics.