Process for production of a silicon nitride ceramic

Details Process for production of a silicon nitride ceramic Process for production of a silicon nitride ceramic

1997-08-01

1998-09-08

Group, Karl

Compositions: ceramic

Ceramic compositions

Refractory

264676, 264683, C04B 35587

Patent

active

058045210

ABSTRACT:
A silicon nitride ceramic of the present invention possesses excellent strength of the surface, including a silicon nitride and a rare earth oxide compound and being characterized in that the ratio of the transverse rupture strength, at a room temperature, of the fired surface used as a tensile surface to the transverse rupture strength, at a room temperature, of the worked surface used as a tensile surface subjected to the working so as to have the surface roughness of R.sub.MAX 0.8 .mu.m or less is 0.7 or more, and the strength ratio is satisfied even when any portion besides the fired surface is utilized as the tensile surface to be worked to have the surface roughness of R.sub.MAX 0.8 .mu.m or less. The present invention also provides a process for producing a silicon nitride ceramic including the steps of: (1) mixing .alpha.-Si.sub.3 N.sub.4 powder and .beta.-Si.sub.3 N.sub.4 powder to obtain a raw material powder so as to satisfy the formula indicated by 0.05.ltoreq..beta./.alpha.+.beta..ltoreq.0.50, in which a refers to the weight of .alpha.-Si.sub.3 N.sub.4 powder and .beta. refers to the weight of .beta.-Si.sub.3 N.sub.4 powder; (2) mixing at least one sintering aid to the raw material powder; (3) forming the powder mixture to give a compact; and (4) firing the compact at a temperature ranging from 1800.degree. to 2000.degree. C. under a nitrogen atmosphere having an atmospheric pressure of at least 1 atm.

REFERENCES:
patent: 4904624 (1990-02-01), Yeckley
patent: 5017531 (1991-05-01), Ukai et al.
patent: 5118644 (1992-06-01), Watanabe et al.
patent: 5171723 (1992-12-01), Moriguchi et al.
patent: 5229046 (1993-07-01), Watanabe et al.

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