Combustion Synthesis of α―Si3N4 Powder Using AC as Additive

Combustion synthesis (CS) of high content of α―Si3N4 powders was carried out using Si and Si3N4 powders as reactants with the addition of diazenedicarboxamide (AC) at a relatively low N2 pressure of 3 MPa. The phase compositions and microstructure of products were characterized by XRD and SEM. Effects of AC contents on the phase compositions and Si3N4 particles morphology were studied. In addition, the reaction mechanisms were discussed. The results indicated that the additive AC promoted the nitridation of Si. The α―Si3N4 contents in the combustion―synthesized products showed great dependence on the contents of AC added in the reactants, which reached 85.2wt% adding with 24wt% AC. Meanwhile, impurities such as SiC, Si2N2O could be found in the final products when more than 12wt% AC agent was added. Poor dispersibility of Si3N4 particles would be more serious with increasing AC contents in the reactants. N2, CO and NH3 produced by decomposition of AC leaded to a change of compact porosity, thermal convection and mass transfer processes, which was responsible for the increasing contents of α―Si3N4 and the discrepancy morphology of the products.