PURPOSE: To obtain a silicon nitride sintered ceramic excellent in corrosion resistance and oxidation resistance by heating a mixture of boron and/or boride and silicon in a nitrogen-contg. atmosphere to form a boron and/or boride-contg. silicon oxide on the surface layer.
CONSTITUTION: Firstly, a mixture of (A) 10 pts.wt. of boron and/or boride (e.g. boron carbide) ≤200μm in mean particle diameter and (B) 90 pts.wt. of silicon ≤50μm in mean particle diameter (e.g. silicon powder) is incorporated with (C) 9 pts.wt. of a molding auxiliary (e.g. a thermoplastic resin) followed by injection molding to produce a form. Thence, this form is heated to remove the resinous components such as the auxiliary, and heated stepwise to a temperature not higher than the melting point of silicon by taking a long time in a nitrogen gas (or mixed with a carbonizing gas like CO gas, ammonia, hydrogen, argon, helium, etc.) atmosphere to obtain the objective sintered compact. The objective sintered compact can also be produced by heating the above form at a temperature not higher than the melting point of silicon followed by raising the temperature to a level above the melting point of silicon (namely, two-step heating).
YASUTOMI YOSHIYUKI
SOFUE MASAHISA
