Patent ID: 7510785

Claim:
A corrosion-resistant silicon nitride ceramics in which a surface corrosion-resistant layer composed mainly of zirconium oxide stabilized by an element of the group 3a of the periodic table is laminated via an intermediate layer on a ceramic substrate composed mainly of silicon nitride, wherein the intermediate layer comprises a stress relaxing layer and a crack extension preventing layer that are laminated in this order on the ceramic substrate, and that satisfy the following relational expressions (II) and (III): Î± 3 <Î± 2 (II) Î± 3 <Î± 4 (III) wherein Î± 2 is the thermal expansion coefficient of the stress relaxing layer; Î± 3 is the thermal expansion coefficient of the crack extension preventing layer; and Î± 4 is the thermal expansion coefficient of the surface corrosion-resistant layer.