Microstructure and oxidation behaviors of dense mullite‑silicon carbide‑silicon coating for graphite fabricated by dipping-pyrolysis and reactive infiltration

A new-designed mullite-SiC-Si coating with dense structure for protecting graphite materials was prepared by dipping-pyrolysis combined with reactive infiltration. The phase synthesis, microstructure and anti-oxidation property of the fabricated mullite-SiC-Si coating were studied. Results demonstrated that the as-prepared coating exhibited excellent low and high temperature oxidation resistance, after isothermal oxidation at 900 °C and 1600 °C for 752 h and 550 h, respectively, the mass gains were 0.1% and 0.99%, respectively. The excellent anti-oxidation performance was ascribed to the dense structure of coating and the formed glassy oxide layer on the coating surface. The oxidation process of mullite-SiC-Si coating was controlled by the diffusion of oxygen, and the as-prepared coating after oxidation was composed of oxide layer and dense mullite-SiC-Si layer. In contrast to SiC-Si coating, the high temperature stability of mullite-SiC-Si coating was greatly improved.