Abstract
ZrSi2-SiC/SiC coating was prepared on the surface of high temperature gas-cooled reactor (HTR) matrix graphite spheres by two-step pack cementation and sintering process. The microstructure, oxidation resistance and thermal shock resistance properties of the as-prepared coatings with different original powder mixtures were investigated. Results show that dense microstructure of the ZrSi2-SiC/SiC coating and continuous ZrSiO4-SiO2-ZrO2 glass phase generated during the oxidation process were the key factors for the outstanding thermal properties. When the mole ratio of Zr:Si:C reaches 1:7:3 in the second pack cementation powders, the coated graphite spheres have optimum oxidation resistant ability. The weight gain is only 0.6wt% after 15 times thermal shock tests and 0.12wt% after isothermal oxidation test at 1500°C for 20h in air. The oxidation resistant mechanism of the coating was also discussed. The dense inner SiC layer and the outer glass layer generated during the oxidation process could protect the ZrSi2-SiC/SiC coating from further oxidation.
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