SiC/SiO₂ Coating on Matrix Graphite Spheres of HTR Fuel Element Produced by a Two-Step Pack Cementation/High-Temperature Oxidation Process

Graphite is one of the most important material for the reactor core and fuel elements of high temperature gas-cooled reactor (HTR). Improving the oxidation resistance of graphite is very essential for the research of new fuel elements and the development of HTR. In this study, a gradient SiC layer of 500~700 μm was prepared on matrix graphite spheres by a two-step pack cementation, and the outer SiO2 layer prepared by the high-temperature oxidation process. The phases, microstructure, bonding strength and oxidation resistance of SiC/SiO2 coated matrix graphite spheres were investigated. The SiC/SiO2 coated matrix graphite spheres were carried on rapid thermal shocking tests from 1773 K to room temperature for 50 times without any cracks. The SiC/SiO2 coated matrix graphite spheres exhibits excellent anti-oxidation properties. No obvious weight loss was found after isothermal oxidation in air at 1273 K for 50 h and the weight gain was less than 1% at 1773 K in air for 50 h due to the oxidation of SiC layer.