Combustion synthesis of Si₃N₄ powder using sodium azide and ammonium halide as additives

The effects of sodium azide used as solid nitrogen source and ammonium halide used as active diluent on the combustion synthesis of Si₃N₄ powder were investigated through analyzing the combustion temperature profiles and the phase composition of the combustion products, The research results show that the endothermic decomposition of these two kinds of additives can increase the porosity of the reactants and thus improve the nitrogen permeability. The additives can also provide interior nitrogen source and act as catalysts of Si-N reaction that facilitates the combustion reaction of silicon in nitrogen atmosphere, The addition of sodium azide and ammonium halide can effectively lower the combustion temperature and maintain the combustion reaction at a relatively low temperature which is in favor of the formation of α-Si₃N₄. Appropriate addition of sodium azide and ammonium halide can promote the nitridation of silicon and increase the α-content in the combustion products.