Abstract: This invention provides a method for manufacturing said sintered body, comprising preparing a starting material by adding 10 to 1,000 wt. parts of metal silicon powder to 100 wt. parts of mixed powder composed of 20 to 80 wt. % silica powder and 80 to 20 wt. % aluminium powder and mixing said powders thoroughly, further adding, if required, a refractory fine powder of alumina, silicon nitride, aluminium nitride, .beta.'-sialon, aluminium nitride polytype sialon, or silicon carbide, molding the resultant mixture into a green compact, and then sintering said green compact in a nitrogeneous nonoxidative gas atmosphere at a temperature of 1,200.degree. to 1,550.degree. C. This invention further provides a compact sintered body which will be prepared by the above mentioned method.

Abstract: A process for preparing silicon nitride powder having a high .alpha.-phase content which comprises the steps of (a) providing a blended powder material composed of silica powder and amorphous carbon powder having an oil absorption of not less than 100 ml/100g, the weight ratio of the carbon powder to the silica powder being not less than 0.5, and then (b) nitriding and burning the blended powder material by heating in at a temperature of from 1300.degree. to 1700.degree. C while feeding a nitrogen-containing, non-oxidizing gas. The product obtained by this process is suitable as a raw material for the manufacture of high-density and high-strength sintered articles of silicon nitride.