Preparation of submicron silicon nitride powders via self-propagating high-temperature synthesis

Nitridation of commercial ferrosilicon via self-propagating high-temperature synthesis is described. The nitrogen pressure is shown to influence the conversion and the combustion rate of the alloy. Dilution of the starting alloy with the final product or an ammonium salt influences the nitrogen content of the nitrided material. The high nitrogen content of the reaction products made it possible to isolate a sufficient amount of silicon nitride with a particle size of 0.43 μm by acid enrichment in an HCl solution. The microstructure of silicon nitride prepared under different conditions is studied by electron microscopy. Electron diffraction results indicate that the final product contains, in addition to the well-known α and β phases (hexagonal structure), tetragonal and orthorhombic Si ₃N ₄ polymorphs.