Silicon nitride ceramic

Details Silicon nitride ceramic Silicon nitride ceramic

1996-01-22

1997-11-25

Group, Karl

Compositions: ceramic

Ceramic compositions

Refractory

501 98, C04B 35587

Patent

active

056912617

ABSTRACT:
A silicon nitride ceramic possessing 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 room temperature, of the fired surface used as a tensile surface to the transverse rupture strength, at room temperature, of the worked surface used as a tensile surface subjected to working so as to have a 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 a 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 which satisfies the formula 0.05.ltoreq..beta./.alpha.+.beta..ltoreq.0.50, in which .alpha. 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 with 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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