| 摘要 |
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 Rmax 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 Rmax 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 -Si3N4 powder and beta -Si3N4 powder to obtain a raw material powder which satisfies the formula 0.05</= beta / alpha + beta </=0.50, in which alpha refers to the weight of alpha -Si3N4 powder and beta refers to the weight of beta -Si3N4 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 DEG to 2000 DEG C. under a nitrogen atmosphere having an atmospheric pressure of at least 1 atm.
|
