Ube Industries, Inc.

Tetsuo Nakayasu

Tetsuo Yamada

Yasuhiko Kohtoku

Takeshi Yamao

Takuji Takahashi

Atsuhiko Tanaka

A silicon nitride powder which provides a water-based slurry with a low viscosity and a high powder concentration. The silicon nitride powder has a specific surface area of 6 to 25 m.sup.2 /g, a number of coarse particles of coarse primary particles, agglomerated particles and/or fused particles, and having a size of 3 to 50 .mu.m, of not more than 1000 per 1 cm.sup.3 of the powder, a number of foreign metallic particles, having a size of more than 20 .mu.m, of not more than 3 per 1 cm.sup.3 of the powder, and a number of foreign metallic particles, having a size of 10 to 20 .mu.m, of not more than 15 per 1 cm.sup.3 of the powder.

Silicon nitride powder

A SiAlON-based sintered body having a high mechanical strength and fracture toughness, as well as an excellent oxidation resistance, is provided. The SiAlON-based sintered body comprises 5 to 50% by weight of a first crystal phase of RE.alpha.-SiAlON represented by RE.sub.x (Si, Al).sub.12 (O, N).sub.16, where RE stands for at least one modifying rare earth element selected from the group consisting of Ho, Er, Tm, Yb and Lu and x has a value of 0&lt;x.ltoreq.2, 30 to 90% by weight of a second crystal phase of .beta.-SiAlON represented by Si.sub.6-z Al.sub.z O.sub.z N.sub.8-z (0&lt;z.ltoreq.4.2), and 1 to 50% by weight of a third crystal phase containing at least one rare earth element RE selected from the group consisting of Ho, Er, Tm, Yb and Lu, optionally together with 1 to 20% by weight of a crystal phase of .alpha.-silicon nitride.

Sialon-based sintered body and process for producing same

A fine particulate .alpha.-Sialon powder with a narrow particle size distribution, thus having an excellent sinterability, can be produced by using as the starting materials (a) amorphous silicon nitride, (b) metallic aluminum or aluminum nitride, and (c) an oxide of a metal which can be incorporated in the interstices of .alpha.-Sialon lattice or a metal compound capable of forming such a metal oxide upon thermal decomposition, and optionally, (d) an oxygen-containing compound of alumina or silicon, followed by heat treatment of the resultant mixture.

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Ube, Japan

Tetsuo Nakayasu