Ngk Spark Plug Company, Limited

Tomohisa Kito

Katsuhisa Yabuta

Masakazu Watanabe

Yoshinori Hattori

Silicon-nitride-based sintered body is produced by a primary sintering; applying a paste-like coating, in which a surface-homogenizing agent is at least one kind of inorganic constituents selected from the group consisting of C, Bn, AlN and Si.sub.3 N.sub.4 provided that C is present at least 5% by weight of the inorganic constituents, on a primary sintered body; and subsequently performing a secondary sintering under a pressure higher than that at the primary sintering.

Method of producing silicon-nitride-based sintered body

A turbine rotor having a ceramic turbine wheel having an improved resistance to cracking and breaking. The turbine wheel is made of a ceramic material having pores formed therein with a maximum diameter of 20 .mu.m distributed in the blade portion of the wheel at a porosity of 2 to 10 vol. %. Preferably, the volume porosity of the pores is gradually decreased from the blade surface to the interior of the blade portions.

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Konan, Japan

Tomohisa Kito