A study on the N-, S- and Cl-modified nano-TiO2 coatings for corrosion protection of stainless steel

Nano-titania coatings doped with anions of nitrogen, sulfur and chlorine have been supplied on the surface of 316L stainless steel by a sol–gel process and dip-coating technique. The measurements of XRD, SEM, ATR-IR, Raman and XPS were carried out to characterize the chemical composition and structure for the prepared samples. The corrosion performances of the coating in 0.5 M NaCl were evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. According to the measurements of EIS and electrochemical polarization, the N-modified TiO2 nano-coatings show a highest corrosion resistance among the prepared coatings. It is revealed, from the SEM, XRD and Raman characterizations, that the surface of N-modified TiO2 nano-coatings are more compact and uniform, relatively well-crystallized and able to act as an optimal barrier layer to metallic substrates. The XPS analysis confirms the presence of low concentration of N element in two forms, atomic β-N (interstitial state) and chemisorbed γ-N2 on the surface of TiO2 nano-coatings. It is suggested that the addition of nitrogen is beneficial to improve the compact structure and enhance the hydrophobic property.