Synthesis of high purity, alpha phase silicon nitride powder

A method for preparing high purity, alpha silicon nitride powder which comprises the steps of:

• a. reacting high purity, liquid silicon tetrachloride with anhydrous ammonia gas in dry deoxygenated benzene or dry normal hexane at a temperature in the range of about -10.degree.C to 5.degree.C, the mole ratio of silicon tetrachloride to ammonia gas being about 1 to 6, thereby forming a precipitate of a mixture of silicon diimide and ammonium chloride;
• b. removing deoxygenated benzene or normal hexane from the mixture;
• c. recovering the resulting dried mixture of silicon diimide and ammonium chloride, the mixture being in finely divided form;
• d. heating the mixture of silicon diimide and ammonium chloride under a vacuum or in an inert atmosphere to a temperature in the range of about 1200.degree. to 1350.degree.C;
• and
• e. maintaining the mixture at a temperature in said range for a period of about 2 to 8 hours, thereby converting the mixture to a product consisting of alpha silicon nitride.