Synthesis of high purity, alpha phase silicon nitride powder

摘要

A method is provided for preparing alpha silicon nitride powder in which very high purity, liquid silicon tetrachloride is reacted with an excess of ammonia gas in dry deoxygenated benzene or normal hexane at about 0°C, yielding a precipitate of silicon diimide and ammonium chloride. After removal of the benzene or n-hexane from the precipitate, the mixture of silicon diimide and ammonium chloride powder is heated under a vacuum from room temperature to a temperature in the range of 1200° to 1350°C and maintained at the latter temperature for a period of about 2 to 8 hours. The product obtained is a high purity, submicron, alpha phase silicon nitride powder which is eminently suitable for the fabrication of dense, high strength, creep resistant and thermal shock resistant bodies for use in high performance gas turbine engines and in radome applications.