Toshiba Ceramics Co., Ltd.

Isao Imai

Kouichi Sueyoshi

Toshitsugu Ishii

Toshiyuki Hirao

Akira Sano

Toshihiro Indou

Toshitsuga Ishii

Hisahiro Teranishi

Castable refractory for a slide gate plate is mainly formed of alumina raw material and amorphous carbon raw material of 2 to 15 wt %, and contains silicon carbide and/or boron carbide, the total content thereof being equal to 0.5 to 10 wt % (the content of boron carbide is equal to or less than 3 wt %, and when the content of boron carbide is less than 0.5 wt %, silicon carbide is set to 3 wt % or more), 2 to 10 wt % magnesia of 1 mm or less in particle size, 0.2 to 3 wt % silica fine powder of 5 micrometers or less in particle size, and 0.1 to 5 wt % salt of condensate of formalin and aromatic sulfonate.

Castable refractory for slide gate

A mixture of silica powder and carbon powder is heated in a mixture of NH.sub.3 gas and C.sub.m H.sub.n gas. Only silica powder may be heated in a mixture of NH.sub.3 gas and C.sub.m H.sub.n gas.

Method for making silicon nitride powder

Silica powder or a mixture of silica powder and silicon nitride whisker is heated at a temperature ranging from 800.degree. C. to 1,700.degree. C. in a gas mixture of ammonia gas (NH.sub.3) and hydrocarbon gas (C.sub.m H.sub.n) so as to produce silicon nitride whisker. The gas mixture flows at the rate of 10 mm/sec or less. The NH.sub.3 /CH.sub.4 ratio of the ammonia to the hydrocarbon, expressed as CH.sub.4, ranges from 0.5:1 to 2000:1 by volume. The silica powder is preferably mixed with at least one of six catalysts: transition metals; alkali metals; alkaline earth metals; halides of transition metals; halides of alkali metals; and alkaline earth metals. One mol part of the silica powder is mixed with 0.001-1.0 mol part of the catalyst.

Process for making silicon nitride whisker

Metal nitride powder is prepared by heating a mixture substantially containing powder of a metal oxide or a metal hydroxide in a mixed gas of ammonia gas (NH.sub.3) and a hydrocarbon gas (CmHn) at a temperature ranging from 1300.degree. C. to 1,600.degree. C., in which the mixed gas has a ratio of ammonia gas (NH.sub.3) to hydrocarbon gas (CmHn) translated into CH.sub.4, ranging from 10 (NH.sub.3) to 1.0 (CH.sub.4) to 2,000 (NH.sub.3) to 1 (CH.sub.4), by volume. The metal nitride powder contains lesser amounts of oxygen and carbon.

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Nagoya, Japan

Isao Imai