The stability of SiC coating and SiO2/SiC multilayer on the surface of graphite for HTGRs at normal service condition

The stability of SiC coating in helium with a low concentration of O2, CO2, and H2O is a key factor for their application in improvement of oxidation resistance of graphite for high temperature gas-cooled reactors (HTGRs). Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC is partial pressure of active gas in helium; the critical temperature of passive oxidation for SiC increases with the partial pressure of O2, CO2, and H2O, SiC is prone to undergo active oxidation in He–CO2 and He–H2O system. SiO2/SiC multilayer coating can improve the oxidation resistance of graphite at higher temperature than SiC coating does under normal operation condition for HTGRs.