Effect of Alumina Content on the Oxidation of Hot-Pressed Silicon Carbide

The oxidation behavior at 1370°C of dense SiC, hot-pressed with the aid of Al₂O₃, has been investigated as a function of Al₂O₃ content. Increasing amounts of the Al₂O₃ hot-pressing aid increased the oxidation rate. Observations of the oxide surface show that a glassy phase (indicating formation of a liquid at the oxidation temperature) containing Si, Al, Fe, and K forms over the residual Al₂O₃ in the hot-pressed material. It is suggested that the oxygen transport through an impure aluminosilicate liquid is faster than that through a pure SiO₂ scale, thus causing an increased oxidation rate.