PURPOSE: To produce a sintered compact, reduced in deteriorating actions on high-temperature characteristics due to cationic impurities such as Al, Ca, Fe and Mg and excellent in high-pressure strength and creep resistance characteristics at a low cost.
CONSTITUTION: This sintered compact is obtained by sintering a compact, containing silicon nitride as a principal component, a group IIIa element oxide (RE2O3) of the Periodic Table and silicon oxide (SiO2), composed at ≤2 molar ratio expressed by SiO2/RE2O3 and further containing 10-10000ppm cationic impurities of Al, Fe, Ca and Mg at 1700-2000°C temperature in an atmosphere containing nitrogen for ≥3hr and then annealing the resultant sintered compact from the sintering temperature to 800°C at ≤15°C/hr rate. The resultant sintered compact contains silicon nitride as a principal crystal phase, at least one crystal phase, containing a group IIIa element of the Periodic Table and selected from apatite, YAM and wollastonite in the grain boundary thereof and a part or all of the cationic impurities converted into a solid solution in the crystal phase of the grain boundary thereof.
TANAKA KOICHI
MATSUNOSAKO HITOSHI
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