High-temperature oxidation behavior of CVD-SiC ceramic coating in wet oxygen and structural evolution of oxidation product: Experiment and first-principle calculations

SiC ceramics and SiC ceramic coatings on carbon/carbon (C/C) composites were prepared by chemical vapor deposition (CVD) method to investigate their oxidation behaviors in wet oxygen at 1773 K. The experimental results demonstrated that water vapor could increase the oxidation rate of SiC, and promote the crystallization of SiO2. By the Raman and infrared spectroscopic analyses, the existence of Si-OH vibration modes in the oxide scales indicated that the reaction between water vapor and silica could occur at high temperatures. Besides, first-principle molecular dynamics (FPMD) simulations and the static calculations based on density functional theory (DFT) also confirmed the occurrence of the reaction and illustrated that the reaction was caused by the co-effect of O and H atoms from the water, resulting in the breakage of the Si-O bonds in silica. After oxidation for 30 h, the weight loss of CVD-SiC coated C/C samples in wet oxygen reduced to 3.47%, which was ascribed to that the formation of abundant oxide scale acted as an effective oxidation barrier by healing cracks on SiC coatings. However, the crystallization and structural variation of the oxide scale might be harmful to the long-term oxidation in the condition of high-speed gaseous scour.