Effect of heat treatment on microstructure and oxidation resistance of SiO2-B4C-glass coating on alumina-carbon refractories

To improve oxidation resistance of alumina-carbon refractories, SiO2-B4C-glass composite coating was prepared by slurry brushing method. The coated sample was heat treated in argon atmosphere to improve compactness and oxidation resistance of the coating. Effects of heat treatment temperature and time on microstructure and oxidation resistance of the coating were studied. Results showed that after heat treatment at 800 degrees C, borosilicate glass powder in the coating melted into glass phase, which could fill holes and cracks of the coating. As heat treatment temperature increased to 900 degrees C, viscosity of the glass phase decreased, resulting in the better selfhealing ability and oxidation resistance of the coating. When heat treatment time increased to 1.5 h, some glass phases flowed away from the coating surface due to its large fluidity, so oxidation resistance of the coating decreased. When heat treatment temperature was too high (1000 degrees C), B2O3 in the glass powder was eutectic with SiO2, more glass phase with larger fluidity generated, which leaded to that thickness and oxidation resistance of the coating both decreased. After heat treatment at 900 degrees C for 0.5 h, microstructure of the coating was smooth and compact, leading to its good oxidation resistance. Weight loss of the coated sample was only -1.041 % after oxidation at 800 degrees C for 80 h.