PTFE, an effective additive on the combustion synthesis of silicon nitride

Combustion synthesis (CS) of Si3N4 with the addition of polytetrafluoroethylene (PTFE) was carried out at a relatively low N2 pressure of 2 MPa. It was found that the additive PTFE promoted the nitridation of Si. The α-Si3N4 contents in the periphery of the combustion-synthesized products showed great dependence on the contents of PTFE added in the reactants, which reached 77.7 wt.% with 4 wt.% PTFE addition. The residual silicon in the center of the combustion-synthesized products could be completely nitrided by further heat treatment at 1300 °C for 1 h in N2. The temperature difference between the center and the edge of the samples was responsible for the discrepancy in both phase composition and morphology of the products.