Water vapor effects on the oxidation resistance of modified potassium silicate coating at high temperature

An inorganic potassium silicate coating with pigments of alumina, aluminum phosphate, NiCrAlY and copper chromite black was prepared on CB2 stainless steel. Oxidation behavior in either ambient air or O2+H2O mixture at 630 °C for 2000 h was comparatively studied, and the coating exhibited excellent resistance under both test conditions. The water vapor considerably accelerated the oxidation of the uncoated CB2 steel, as the hydroxide, the main constituent of the coating, had a negligible evaporation rate at test temperature, while it had a limited effect on the coated sample. Meanwhile, the existence of coating may prolong or eliminate the incubation period in the O2+H2O mixture at 630 °C. After oxidation, the coating matrix is in an amorphous state and fillers as alumina and copper chromite black are stable in the coating. Leucite (KAlSi2O6) formed by Al from NiCrAlY and potassium silicate in the coatings was detected after tests either in O2 or O2+H2O mixture.