Cushman, Darby & Cushman
Silicon nitride sintered body and process for preparation thereof
 A silicon nitride sintered body comprised of 1.5 to 3.0% by weight of Y.sub.2 O.sub.3, 0.1 to 1.0% by weight of Al.sub.2 O.sub.3 and 96 to 98.4% by weight of Si.sub.3 N.sub.4 wherein the Y.sub.2 O.sub.3 /Al.sub.2 O.sub.3 weight ratio is at least 2.5, and having a density of at least 3.0 g/cm.sup.3, exhibits a high oxidation resistance and a high strength at a high temperature. This silicon nitride sintered body is prepared by sintering a powdery mixture consisting essentially of 1.5 to 3.0% by weight of Y.sub.2 O.sub.3 powder, 0.1 to 1.0% by weight of Al.sub.2 O.sub.3 powder, and 96 to 98.4% by weight of Si.sub.3 N.sub.4 powder, the Y.sub.2 O.sub.3 /Al.sub.2 O.sub.3 weight ratio being at least 2.5, the oxygen content in the Si.sub.3 N.sub.4 powder being less than 2.0% by weight and the total metallic impurity content in the Si.sub.3 N.sub.4 being less than 200 ppm, at a temperature of 1,850.degree. to 2,000.degree. C. in a non-oxidizing atmosphere. 
Tosoh Corporation
C C
C04B C04B
inventional inventional
Yoshihiro Toshihiko Toshiyuki
Matsumoto Arakawa Mori