Ngk Spark Plug Company, Limited

Kouji Funaki

Masaya Ito

Katsura Matsubara

Hiroki Watanabe

A silicon nitride sintered material containing a silicon nitride component and silicon carbide having an average particle size of 1 &#x3bc;m or less in an amount of at least 1 mass % and less than 4 mass %, based on 100 mass % of the silicon nitride component. The carbide is dispersed in the silicon nitride component, and the silicon nitride sintered material has a thermal expansion coefficient of at least 3.7 ppm/&#xb0; C. between room temperature and 1,000&#xb0; C. The silicon nitride component contains a rare earth element in an amount of 15-25 mass % as reduced to a certain oxide thereof and Cr in an amount of 5-10 mass % as reduced to a certain oxide thereof, and a crystalline phase is present in intergrain regions of the sintered material.

Silicon nitride sintered material and production process thereof

A silicon nitride sintered material containing silicon nitride, a Group 4 through 6 element, a rare earth element, and silicon carbide, characterized in that the amount of the rare earth element as reduced to a certain oxide thereof is 5.7-10.3 mol %; the ratio by mol of subtraction remainder oxygen amount calculated in relation to the oxygen contained in the sintered material, the remainder oxygen amount being expressed in terms of silicon dioxide, to the amount of oxygen contained in the sintered material is at least 0.50 and less than 0.70; a four-component crystalline phase of rare earth element-silicon-oxygen-nitrogen is not present; and the thermal expansion coefficient is at least 3.7 ppm/&deg; C. between room temperature and 1,000&deg; C.

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Gifu, Japan

Kouji Funaki