Abstract: Processes for the production of a silicon nitride sintered body are disclosed. One process comprises molding a mixed powder of 100 parts by weight of metallic silicon with a maximum particle size of 20 .mu.m or less and 0.2 to 2 parts by weight (calculated as chromium oxide) of a chromium component and, thereafter, reaction sintering the mold in a nitrogen gas or in a non-oxidizing atmosphere containing nitrogen gas at a temperature of 1,300.degree. to 1,500.degree. C. This invention provides further process which comprises molding a mixed powder of 100 parts by weight of metallic silicon with a maximum particle size of 20 .mu.m or less, 0.2 to 1 part by weight (calculated as chromium oxide) of a chromium component, and further 10 to 20 parts by weight of an oxide component of one or more of the oxides of yttrium, lanthanum, cerium, gadolinium, and erbium, reaction sintering the above-prepared mold, and thereafter, hot pressing the reaction sintered body.

Abstract: A sintered silicon nitride products and processes for the fabrication thereof are described, wherein the product comprises from 60 to 98.9% by weight of silicon nitride, from 0.1 to 15% by weight of one or more chromium components selected from metal chromium, chromium oxide, and chromium nitride, and from 1 to 25% by weight of one or more oxides selected from oxides of rare earth elements, scandium oxide, yttrium oxide, aluminum oxide, zirconium oxide and silicon dioxide.