Kyocera Corporation

Tomohiro Iwaida

Shoji Kohsaka

Kenichi Tajima

Takehiro Oda

Sentaro Yamamoto

Koichi Tanaka

Hideki Uchimura

A sintered product of silicon nitride containing not smaller than 70 mol % of a .beta.-silicon nitride as well as an element of the Group 3a at least including Lu of periodic table and impurity oxygen, wherein when the content of the element of the Group 3a of periodic table and the content of the impurity oxygen are, respectively, expressed being reckoned as the amount of an oxide of the element of the Group 3a of periodic table (RE.sub.2 O.sub.3) and as the amount of SiO.sub.2 of impurity oxygen, their total amount is from 2 to 30 mol %, the molar ratio (SiO.sub.2 /RE.sub.2 O.sub.3) of the amount of the element of the Group 3a of periodic table reckoned as the oxide (RE.sub.2 O.sub.3) thereof to the amount of impurity oxygen reckoned as SiO.sub.2 is from 1.6 to 10, and the intergranular phase of the sintered product chiefly comprises a crystal phase consisting of the element of the Group 3a of periodic table, silicon and oxygen and a process for producing the same. The sintered product has a large strength from room temperature through up to high temperatures and maintains excellent resistance against oxidation even at high temperatures, and exhibits excellent resistance against creeping and excellent breaking toughness.

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Kokubu, Japan

Tomohiro Iwaida