Self-propagating high temperature-synthesis of Si3N4: role of ammonium salt addition

This paper presents results of combustion synthesis (SHS) of Si3N4 from silicon powders under nitrogen pressure (Pnitrogen=10 MPa). The role of different additives, such as NH4Cl, NH4F, NH4CO2NH2, (NH4)2 C2O4H2O, NH3 CO3H+NH2COONH4, on Si3N4 synthesis has been examined. Density and microstructural variations have been studied too. The product as synthesised presents two very different types of morphologies; (1) agglomerated form of α-Si3N4 and β-Si3N4, and (2) irregular formations with presence of oxynitrides and other phases.