Method for producing high-density silicon nitride sintered product

Abstract

A shaped body of silicon nitride enjoying high density, ample shrinkage, and outstanding mechanical strength is produced in a desired pattern by a method of preparing a shaped body comprising Si particles and a compound capable of remaining as SiC or C in the form of film on the surface of the Si particles in a non-oxidative atmosphere at a temperature in the range of 900.degree. to 1,400.degree. C., subjecting the shaped body to sintering and shrinkage of not less than 1% in an atmosphere of inert gas at a temperature exceeding 900.degree. C., and not exceeding the softening point of Si, and subsequently subjecting the resultant sintered shaped body to nitriding in a nitriding atmosphere at a pressure exceeding atmospheric pressure and at a temperature in the range of 1,200.degree. to 1,500.degree. C. In another aspect of the present invention, a method for producing a silicon nitride sintered product entails preparing a molded body by adding, to powdery silicon grains, a compound that decomposes under heating to produce H.sub.2 or hydrocarbon compounds such as CH.sub.4 and C.sub.2 H.sub.6 in a temperature range from 500.degree. C. to 1200.degree. C., subjecting the molded body to a heat treatment in a gas atmosphere of a nitriding gas and/or an inert gas, and then chemically converting silicon into silicon nitride in a nitriding gas at a temperature higher than 1200.degree. C.