| 摘要 |
PURPOSE: To attain dense sintering and to improve high-temp. strength and oxidation resistance by compacting a powdery mixture of silicon nitride powder with ytterbium oxide powder and aluminum oxide powder, firing the resultant compact in an atmosphere of gaseous nitrogen and cooling it under specified conditions. CONSTITUTION: A powdery mixture is prepd. by mixing 70-97wt.% silicon nitride powder with 2-30wt.% ytterbium oxide powder and 0.1-5.0wt.% aluminum oxide powder so that the weight ratio of ytterbium oxide to aluminum oxide is regulated to >=10. The mixture is compacted and fired at 1,700-2,100 deg.C in an atmosphere of gaseous nitrogen under <=10kg/cm<2> pressure and the resultant compact is cooled to 900-940 deg.C at >=20 deg.C/min rate, held for >=5min, heated to 1,150-1,350 deg.C and held for 4-8hr to obtain the objective silicon nitride sintered compact in which the grain boundary parts among silicon nitride grains are made of microcrystals of ytterbium silicon oxynitride as a stable crystal phase. |
