Abstract: In a Very High Temperature Reactor (VHTR), the components of the next generational hydrogen production reactor, core and reflector are surrounded by graphite supports. Graphite materials, despite their excellent physical properties, oxidize easily above 500°C. For this reason, to prevent oxidation, a silicon carbide coating is often used. Among the physical vapor deposition methods, electron-beam coating easily develops cracks on the coating layer by thermal shock after application, forming a graphite oxidation path. In order to heal the cracks caused by thermal shock in the coating layer, this study adjusted the hydrogen ratio via. the Chemical Vapor Deposition (CVD) method and caused vapor distribution of SiC on specimens with cracks to heal. With a higher hydrogen ratio, the H2 dilution effect is intensified. This causes an enhancement in the crystallizability which changes the round-shaped microstructure into a faceted microstructure. Further, the higher the hydrogen ratio, the denser the microstructure becomes which causes higher oxidation resistivity as well. Consequently, this study found that the anti-oxidation effect was sharply increased when the healing of coating layer cracks occurred at the hydrogen ratio of 200 via. the CVD method.
Y. Kim and T. Chae, 2018. Relationship Between Microstructure and Oxidation Resistivity of SiC Coating Layer. Journal of Engineering and Applied Sciences, 13: 7916-7920.