Oxidation behavior of different La₂O₃-content modified SiC ceramic at 1700 °C

Silicon carbide (SiC) ceramic specimens doped with different contents of La₂O₃ were prepared by hot pressing process to investigate the influence of La₂O₃ content on their anti-oxidation performance at 1700 °C. The result of the isothermal oxidation test reveals that La₂O₃-doped SiC ceramic showed better anti-oxidation performance than pure SiC ceramic, and the anti-oxidation performance of La₂O₃-doped SiC ceramic decreased as the content of La₂O₃ increased. Mulliken population analysis based on first-principle calculation indicates that the strength of Si–O bond was enhanced by adding a small amount of La dopant (~5 wt%) into SiO₂, which is favorable to the thermal stability of the oxide scales. The coexistence of SiO₂ and La₂Si₂O₇ under a certain ratio makes the glass layer have proper viscosity to form a compact and smooth protective layer, thus leading to a better anti-oxidation performance at 1700 °C. However, the SiC ceramic doped with excessive La₂O₃ (10–15 wt%) showed poor anti-oxidation performance owing to the defective glass layer and the destruction of SiO₂ structure. This work is beneficial to select which La₂O₃ content is suitable for the anti-oxidation SiC ceramic coating at 1700 °C.