Chemical stability of silicon nitride and oxynitride powders

Abstract

1. A study of the reactions of silicon nitride and oxynitride with acids, mixtures of acids, and alkali metal hydroxides (solutions and melts) has shown that silicon oxynitride is less stable as a chemical compound than silicon nitride. 2. In phosphoric acid, silicon oxynitride decomposes with the formation of the soluble silicyl metaphosphate and ammonium phosphates. On heating, the soluble silicyl metaphosphate is precipitated out of a phosphoric acid solution as a sparingly soluble compound of composition Si3(PO4)4. The addition of tripotassium phosphate to phosphoric acid accelerates the decomposition of silicon oxynitride. 3. A study was made of the reactions of silicon oxynitride and nitride with aqueous solutions of sodium hydroxide. It was established that 1% sodium hydroxide solution decomposes silicon oxynitride at a constant rate, but has no effect upon silicon nitride.