Cost effective combustion synthesis of silicon nitride

The feasibility of mechanical activation (MA)-assisted combustion synthesis (CS) of Si3N4 was demonstrated by using Si/NH4Cl as reactants under a nitrogen pressure of 2 MPa. MA treatment significantly enhances the reactivity of Si powders, which effectively promotes the nitridation of silicon. The NH4Cl had the same effect as Si3N4 diluent in preventing extensive melting of Si within the combustion wave zone. Full nitridation of Si was achieved at diluent levels as low as 5 wt%. Si3N4 powders with α-phase contents of up to 90.6 wt% were obtained. The temperature gradient induced by heat release through radiation was responsible for discrepancies in the phase composition and morphologies of the as-synthesized product at different locations.