Effect of SiO2 content on the oxidation resistance of SiO2–B4C-glass coating for alumina–carbon refractories

To improve the oxidation resistance of alumina–carbon refractories, SiO 2 –B 4 C-glass composite coating was prepared by slurry brushing method on the surface of refractories. Effect of SiO 2 content on the oxidation resistance of the coating was studied. Oxidation resistance mechanism and failure reason of the SiO 2 –B 4 C-glass coating were discussed. Results showed that introducing SiO 2 could increase viscosity activation energy and elevate the glass layer's viscosity at high temperature. With the increase of SiO 2 content, the glass viscosity at high temperature gradually increased. When SiO 2 content was too low, the glass exhibited smaller viscosity and larger fluidity, so the glass layer was easy to be washed away. When SiO 2 content was too high, the glass phase with high viscosity and low fluidity could not uniformly cover on the surface of alumina–carbon refractories. The composite coating with SiO 2 content of 55 wt% exhibited excellent oxidation resistance, which could effectively protect alumina–carbon refractories at 800 °C for 100 h with weight loss of only −1.721%. Excellent oxidation resistance of the coating mainly depended on the glass layer with good self-healing ability. With the extension of oxidation time, the coating thickness decreased, leading to the relatively poor self-healing ability and reduced weight gain rate of the coating.