Tokyo Shibaura Denki Kabushiki Kaisha

Kabushiki Kaisha Toshiba

Tokyo Shibaura Electric Co., Ltd.

Motoo Seimiya

Katsutoshi Nishida

Satoshi Yamaguchi

Hiroshi Endo

Masaru Hayashi

Tsutomu Yamashita

Shigeo Iiri

Isamu Koseki

High-purity molybdenum or tungsten powder can be produced by a process comprising (a) decomposing a powder or an oxide powder of molybdenum or tungsten with hydrogen peroxide water; (b) bringing the resulting aqueous solution of molybdenum or tungsten into contact with a cation exchange resin; (c) concentrating the aqueous solution; and (d) reducing a concentrated solid material. By omitting reducing step (d), one can obtain high-purity molybdenum or tungsten oxide powders. Because the Mo and W powders and MoO.sub.3 and WO.sub.3 powders prepared by this invention are of an extremely high purity, they are useful as materials for targets of VLSI elements.

Methods for preparing high-purity molybdenum or tungsten powder and

A method of producing silicon nitride which comprises heating wet process white carbon in the presence of a carbon source and a source of nitrogen.

Method of preparing silicon nitride

A method of producing silicon carbide which comprises heating wet process white carbon in the presence of a carbon source.

Method of preparing silicon carbide

A method of producing silicon carbide which comprises heating silica in a gas atmosphere comprising hydrocarbon gas and hydrogen gas.

A method of producing silicon nitride which comprises heating silica in a gas atmosphere comprising hydrocarbon gas, ammonia gas and hydrogen gas.

A method for preparing tungsten materials in which tungsten powder obtained by reducing tungsten oxides having doping agents added thereto is washed first with hydrochloric acid having a concentration of not lower than 4% by weight and then with hydrofluoric acid having a concentration of not lower than 3% by weight, and thereafter dried. The above-mentioned washing steps may be carried out at a time by using a mixture of such hydrochloric acid and hydrofluoric acid as specified above. Articles formed by treating tungsten materials obtained by the above-mentioned process are subjected to only a low high temperature deformation.

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Yokosuka, Japan

Motoo Seimiya