Combustion synthesis of Si3N4 powder

A combustion synthesis (SHS) process has been developed for the synthesis of Si3N4 powder under low nitrogen pressures. Si and NaN3 powders were used as the reactants, and NH4Cl powder was added as a catalytic agent. These powders were mixed and pressed into a cylindrical compact. The compact was wrapped up with an igniting agent (i.e., Ti + C), and the synthesis reaction was triggered by the combustion of the igniting agent. Addition of NH4Cl was found necessary for the combustion synthesis reaction under low nitrogen pressures (<1.2 MPa). The product as synthesized is mostly in the form of agglomerated fine particles (0.1-1 mu m in diameter) and is composed mainly of alpha-phase and a minor amount of beta-phase. Effects of various experimental parameters (N-2 pressure, NaN3, NH4Cl, and Si3N4 contents) on the product conversion and the combustion temperature were investigated. A possible reaction mechanism was proposed that explains the effects of the experimental parameters on the synthesis reaction.