Pitting Resistance of Nano-Structured Sol-Gel Alumina Coatings in Chloride Containing Acidic Environment

Sol–gel coatings were applied on AISI 304L stainless steel and their pitting resistance was evaluated in different concentrations of chloride ions in 0.01 M H2SO4 solution. AFM and XRD analyses of the coated surface confirmed the presence of nano structured α-alumina phase in the coating. Anodic polarisation indicated a considerable shift of pitting potential of the substrate in the noble direction after applying coatings. The SEM micrographs of the polarised specimens revealed the presence of relatively less number of pits on the coated surface. EIS analysis demonstrated the occurrence of diffusion process at the coating/metal interfaces in chloride ions presence.