Kyocera Corporation

Makoto Yoshida

Kiyoshi Yokoyama

Kazunori Koga

Kazumi Osamura

Shoji Kousaka

Tatsumi Maeda

Masafumi Matsunaka

Akito Horiuchi

Disclosed is a silicon nitride sintered body comprising 85 to 99 mole % of .beta.-Si.sub.3 N.sub.4, 1 to 5 mole % as the oxide (M.sub.2 O.sub.3) of at least one compound of an element (M) selected from the group consisting of Sc, Vb, Er, Ho and Dy and less than 10 mole % of excessive oxygen (O.sub.2) based on the three components, wherein the excessive oxygen/M.sub.2 O.sub.3 molar ratio is lower than 2.

Silicon nitride sintered body and process for preparation thereof

Disclosed is a silicon nitride sintered body comprising 85 to 99 mol % of .beta.-Si.sub.3 N.sub.4, 1 to 5 mol % as the oxide (M.sub.2 O.sub.3) of at least one compound of an element (M) selected from the group consisting of Sc, Vb, Er, Ho and Dy and less than 10 mol % of excessive oxygen (O.sub.2) based on the three components, wherein the excessive oxygen/M.sub.2 O.sub.3 molar ratio is lower than 2.

Disclosed is a process for the preparation of a silicon nitride sintered body, which comprises steps of (i) molding a composition comprising (a) 87 to 98% by weight of silicon nitride and (b) 2 to 13% by weight of a sintering aid comprising an oxide or nitride of aluminum or an element of the group IIIa of the Periodic Table and an inorganic oxide capable of forming a liquid phase component having a melting point lower than that of silicon nitride, the inorganic oxide being present in an amount of 1 to 7% by weight based on the composition, (ii) sintering the molded body in a nitrogen atmosphere at a temperature forming a liquid phase containing said liquid phase component having a low melting point, and (iii) heat-treating the resulting sintered body in a nitrogen atmosphere at a temperature higher than the sintering temperature to volatilize the liquid phase component having a low melting point from the liquid phase. In the obtained sintered body, the oxygen content in the surface layer is controlled below 3% by weight, and the flexural strength at 1300.degree. C. of the surface layer is higher than that of the inner portion.

When a composite nitride obtained by nitriding a fine powder of an alloy comprising metallic silicon and a metal of the group IIIa of the Periodic Table is sintered, a highly homogeneous silicon nitride sintered body having a high strength can be obtained. This fine powder of the alloy and this composite nitride exert a function of promoting sintering of Si.sub.3 N.sub.4.

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Kokubu, Japan

Makoto Yoshida