Self-Generating High-Temperature Oxidation-Resistant Glass-Ceramic Coatings for C-C Composites Using UHTCs

Carbon-carbon (C-C) composites are ideal for use as aerospace vehicle structural materials; however, they lack high-temperature oxidation resistance requiring environmental barrier coatings for application. Ultra high-temperature ceramics (UHTCs) form oxides that inhibit oxygen diffusion at high temperature are candidate thermal protection system materials at temperatures >1600 degrees C. Oxidation protection for C-C composites can be achieved by duplicating the self-generating oxide chemistry of bulk UHTCs formed by a composite effect upon oxidation of ZrB2-SiC composite fillers. Dynamic Nonequilibrium Thermogravimetric Analysis (DNE-TGA) is used to evaluate oxidation in situ mass changes, isothermally at 1600 degrees C. Pure SiC-based fillers are ineffective at protecting C-C from oxidation, whereas ZrB2-SiC filled C-C composites retain up to 90% initial mass. B2O3 in SiO2 scale reduces initial viscosity of self-generating coating, allowing oxide layer to spread across C-C surface, forming a protective oxide layer. Formation of a ZrO2-SiO2 glass-ceramic coating on C-C composite is believed to be responsible for enhanced oxidation protection. The glass-ceramic coating compares to bulk monolithic ZrB2-SiC ceramic oxide scale formed during DNE-TGA where a comparable glass-ceramic chemistry and surface layer forms, limiting oxygen diffusion.