A multi-layered SiC coating to protect graphite spheres from high temperature oxidation in static air

Abstract A multi-layered SiC coating was prepared on graphite spheres to improve its antioxidant performance. The oxidation behaviour of the coating prepared on graphite sphere in static air was studied systematically for the first time. As an antioxidant layer, the dense block layer is effective in protecting the internal transition layer and refined grain layer from oxidation in static air at 1773 K. An amorphous SiO2 layer developing on the surface acts as a protective shell, while some carbon particles developed at the interface of oxide layer and SiC coating. As for the oxidation process of the SiC coated graphite sphere, it is comprised of three stages. Stage I (0−6 h) is characterized by a rapid weight gain, which follows a linear model, and the passive oxidation of SiC occurs in this stage. Stage II (6−50 h) is characterized by a slow weight gain, which follows the parabolic oxidation model. Stage III (50−200 h) is characterized by an invariable weight gain of merely 0.52%, which is accompanied with the interface reaction of SiC and the self-healing of oxide layer.