Biocorrosion Behavior of Titanium Oxide/Butoxide-Coated Stainless Steel

Stainless steel coated with multilayers of Ti oxide/butoxide was prepared via a layer-by-layer sol-gel deposition process. The successful buildup of the Ti oxide/butoxide coatings was ascertained by X-ray photoelectron spectroscopy and static water contact angle measurements. The differences in corrosion behavior between the Ti oxide/butoxide-coated and the uncoated coupons in a simulated seawater-based modified Baar's medium inoculated with Desulfovibrio desulfuricans under anaerobic conditions were investigated by electrochemical analyses, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Electrochemical analyses and SEM results revealed that the pristine, the hydroxylated, and the nitric acid-passivated coupons were all vulnerable to biocorrosion due to localized breakdown of the passive film under synergistic attack of Desulfovibrio desulfuricans and biogenic sulfide ions, leading to destructive pitting and crevice corrosion. However, the Ti oxide/butoxide-coated coupons exhibited desirable resistance in the biocorrosion environment and the coating remained relatively stable throughout the exposure period. EDX analysis revealed that the bioactive properties of the Ti oxide/butoxide coating arose from the concomitant deposition of calcium and phosphorous compounds. The increase in resistance of the Ti oxide/butoxide coatings with time was correlated with the increase in nucleation of calcium apatite in electrochemical studies.