SILICON NITRIDE CERAMIC PART AND ITS PRODUCTION

PROBLEM TO BE SOLVED: To obtain silicon nitride ceramic parts having excellent mechanical strength by normal pressure sintering method by forming a silicon oxide film on the surface of a silicon nitride sintered body containing aluminum nitride. SOLUTION: A silicon nitride green body with aluminum nitride added is sintered in an oxygen-contg. atmosphere (air) under normal pressure. The silicon nitride ceramic sintered compact obtd. by normal pressure sintering is cut into a specified form and heat-treated at a temp. lower than the sintering temp. of the silicon nitride ceramic sintered compact, lower than about 1100 deg.C at which oxidation of the sintered compact hardly proceeds, and higher than about 800 deg.C which is the softening point of yttrium oxide, aluminum oxide or the like as a glass phase, for 1 to 24 hours. Thereby, microscopic sharp notches produced by cutting are rounded by the heat treatment and an oxide film having submicron thickness and comprising silicon oxide is formed on the surface of the obtd. silicon nitride ceramic part to protect the surface.