SiBCN-precursor-derived gradient oxidation protective ceramic coating for C/C composites

This paper reports a gradient anti-oxidation ceramic coating for carbon/carbon (C/C) composites, which was prepared via dip-coating the mixed slurry of polyborosilazane (denoted as PSNB, a polymer precursor for SiBCN ceramics), ZrB2 and SiC powders, followed by pyrolysis and low-temperature densification process. By controlling of the solid content of PSNB based slurry, a crack-free coating with thickness of approximately 200 mu m was achieved with only one coating-pyrolysis cycle. The micro-morphology, elemental composition and distribution, crystalline phase, anti-oxidation property, as well as anti-oxidation mechanism of the coating were investigated. The coated C/C composite showed excellent oxidation resistance with no obvious weight change after oxidation at 900 degrees C for 5 h and only 0.06% weight loss after oxidation at 1500 degrees C for 30 min. The formed dense ZrO2-B2O3 layer affords the low-temperature oxidation protection, while the ZrO2-SiO2 layer formed above 930 degrees C endows the coating with high-temperature anti-oxidation property. Besides, the gradient coating possessed superior thermal-shocking resistance with no large-area peeling off or detachment of coating from C/C composite after 12 cycles-air quenching from 1500 degrees C to room temperature.