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US 5,691,261 AGranted
Silicon nitride ceramic
AssigneeNGK Insulators, Ltd.
InventorsAkira Takahashi, Masaaki Masuda, Keiichiro Watanabe
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AssigneeNGK Insulators, Ltd.
InventorsAkira Takahashi, Masaaki Masuda, Keiichiro Watanabe
Estimating the term…
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.
A silicon nitride ceramic comprising silicon nitride and a rare earth compound, wherein the ratio of (1) the transverse rupture strength, at room temperature, of a fired surface used as a tensile surface to (2) the transverse rupture strength, at room temperature, of a 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 0.83 or more and wherein pores on the fired surface each have a size of 50 .mu.m.times.50 .mu.m or smaller.
A silicon nitride ceramic consisting essentially of silicon nitride and a rare earth compound, wherein the ratio of (1) the transverse rupture strength, at room temperature, of a fired surface used as a tensile surface to (2) the transverse rupture strength, at room temperature, of a 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 0.83 or more and wherein pores on the fired surface each have a size of 50 .mu.m.times.50 .mu.m or smaller.
Dependencies are inferred from the claim text.