| 摘要 |
PURPOSE:To improve the strength by incorporating SiN as a main component and a group IIIa element in The periodic Table and holding a specific composition in a burnt molded body containing SiO2 or the like to keep fracture toughness on the polished mirror surface. CONSTITUTION:The molded body is obtained by incorporating the oxide (RE2O3) of group IIIa element in The Periodic Table or RE2O3 and SiO2 into SiN. Next, by sintering the molded body under a N2 containing atmosphere at 1600-2000 deg.C, a sintered body, (a) mainly containing SiN, (b) containing group IIIa element (RE) in The Periodic Table and oxygen and (c) satisfying I1<2.3, I2<1.9, -0.3<=I1-I2<=0.4 when the mol ratio SiO2/RE2O3 of the excess oxygen expressed in terms of SiO2 to Re expressed in terms of oxide (RE2O3) in the surface part of the sintered compact is I1 and the mol ratio in the center parts of the sintered compact is I2, is obtained. And a silicon nitride sintered compact >=5.5 MPa.m<1/2> in fracture toughness (K1c) of the mirror surface is produced by 0.06 mm-polishing the surface of the sintered compact. |
