Yttrium silicate oxidation protective coating for SiC coated carbon/carbon composites

Four kinds of yttrium silicate oxidation protective coatings SiO2·Y2O3, 1.5SiO2·Y2O3, 1.5SiO2·Y2O3/SiO2·Y2O3 and 2SiO2·Y2O3/1.5SiO2·Y2O3/SiO2·Y2O3 were prepared by plasma spray on the surface of SiC pre-coated carbon/carbon composites. The structures of the coatings were characterized by XRD, SEM and EDS analyses. It was shown that the gradied 2SiO2·Y2O3/1.5SiO2·Y2O3/SiO2·Y2O3 multi-layer coating had better high-temperature oxidation resistance. It could protect carbon/carbon composites from oxidation at 1773 K in air for 73 h with a weight loss of less than 2%. The oxidation activation energy of the coated carbon/carbon composites is 87.3 kJ/mol, and the oxidation process in C/C substrates with a multi-layer coating was controlled by the rate of oxygen diffusion through the holes in the coating.