Thermodynamic analysis of ZrB2-SiC oxidation: Formation of a SiC-depleted region

A thermodynamic model was developed to explain the formation of a SiC-depleted layer during ZrB2-SiC oxidation in air at 1500 degrees 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 x 10(-14) and 1.8 x 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.