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, SiO2–B4C-glass composite coating was prepared by slurry brushing method on the surface of refractories. Effect of SiO2 content on the oxidation resistance of the coating was studied. Oxidation resistance mechanism and failure reason of the SiO2–B4C-glass coating were discussed. Results showed that introducing SiO2 could increase viscosity activation energy and elevate the glass layer's viscosity at high temperature. With the increase of SiO2 content, the glass viscosity at high temperature gradually increased. When SiO2 content was too low, the glass exhibited smaller viscosity and larger fluidity, so the glass layer was easy to be washed away. When SiO2 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 SiO2 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.