Effects of diazenedicarboxamide additive on the content of α-Si3N4 synthesized by combustion method

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. Effects of diazenedicarboxamide contents on the phase compositions and Si3N4 particle morphologies were studied. In addition, the reaction mechanisms were discussed. The results indicated that the additive diazenedicarboxamide promoted the nitridation of Si. The α-Si3N4 content in the combustion-synthesized products showed great dependence on the additive contents, which reached 85.21 wt% with 24 wt% diazenedicarboxamide added. N2, CO and NH3 produced by the decomposition of diazenedicarboxamide leaded to a change of compact porosity and the formation of micro-pores in the reactive area, which was responsible for the increasing contents of α-Si3N4 and the discrepancy morphology of the products.