| 摘要 |
PURPOSE:To obtain the title sintered compact improved in high-temperature strength and oxidation resistance by heat treatment of a specific Si3N4 sintered compact in a non-oxidative atmosphere containing SiO to effect depositing silicate glass. CONSTITUTION:A mixture comprising (A) 85-99mol% of Si3N4, (B) 0.5-15mol% of an oxide (RE2O3) of group IIIa element and (C) such an amount of SiO2 as to be 0.5-14.5mol% whose oxygenic content is obtained by subtracting the oxygen quantity stoichiometrically bound as RE2O3 from the total amount of oxygen in sintered compact, is formed and then calcined at 1600-2000 deg.C in a non-oxidative atmosphere into a sintered compact made up of (1) Si3N4 crystal phase and a grain boundary phase consisting of glass phase at least composed of Si3N4, RE2O3 and SiO2 and/or crystal phase. Then, this sintered compact is heat-treated at 1300-1900 deg.C in a non-oxidative atmosphere containing SiO to effect depositing silicate glass on the surface layer of the sintered compact and also depositing the surface layer of 1-100mum thickness having the contents of both oxygen and silicon higher than those in the inside. |
