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

Abstract

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.