EIS measurement on atmospheric exposure induced degradation of a pre-engineered passive coating on tinplate surface

Abstract

Understanding the atmospheric exposure induced degradation of passive coating is of substantial importance in gaining information regarding degradation behavior of the coating itself and its protection effect to underlying substrate. In this work, the structural evolution of a pre-engineered passive Cr2O3 coating on tinplate under atmospheric exposure conditions has been interpretated based on EIS responses to structural evolution of the passive coating. Results indicate that the EIS data interpretation by graphical method can accurately provide parameters of coating thickness δ and CPE parameter n that are associated with structural evolution and corrosion resistance of the passive coating. Following the evolutions in δ and n, two degradation patterns be determined. The first relates an initial degradation in outer layer under high humidity condition and then the failure of inner layer. The second relates an initially moderate but then an excessive growth in the inner layer under high temperature condition, which results in a structural heterogeneity in the inner layer and thus the degradation in corrosion resistance. Such evolutions correspond well to the result by SIMS characterizations. Therefore, EIS measurement can provide an accurate and detailed evaluation on degradation behavior of a passive coating under atmospheric exposure conditions, and it is believed to have a great potential in industrial practice.