Thermodynamic Analysis of ZrB ₂ –SiC Oxidation: Formation of a SiC‐Depleted Region

Abstract

A thermodynamic model was developed to explain the formation of a SiC‐depleted layer during ZrB 2 –SiC oxidation in air at 1500°C. The proposed model suggests that a structure consisting of (1) a silica‐rich layer, (2) a Zr‐rich oxidized layer, and (3) a SiC‐depleted zirconium diboride layer is thermodynamically stable. The SiC‐depleted layer developed due to active oxidation of SiC. The oxygen partial pressure in the SiC‐depleted layer was calculated to lie between 4.0 × 10 −14 and 1.8 × 10 −11 Pa. Even though SiC underwent active oxidation, the overall process was consistent with passive oxidation and the formation of a protective surface layer.