Synergism between rare earth cerium(IV) ion and vanillin on the corrosion of steel in H2SO4 solution : Weight loss, electrochemical, UV-vis, FTIR, XPS, and AFM approaches

Abstract The synergism between rare earth cerium(IV) ion and vanillin (4-hydroxy-3-methoxy-benzaldehyde) on the corrosion of cold rolled steel (CRS) in 1.0 M H 2 SO 4 solution at five temperatures ranging from 20 to 60 °C was first studied by weight loss and potentiodynamic polarization methods. The inhibited solutions were analyzed by ultraviolet and visible spectrophotometer (UV–vis). The adsorbed film of CRS surface containing optimum doses of the blends Ce 4+ –vanillin was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). The results revealed that vanillin had a moderate inhibitive effect, and the inhibition efficiency (IE) increased with the vanillin concentration. The adsorption of vanillin obeyed Temkin adsorption isotherm. Polarization curves showed that vanillin was a mixed-type inhibitor in sulfuric acid, while prominently inhibited the cathodic reaction. For the cerium(IV) ion, it had a negligible effect, and the maximum IE was only about 20%. However, incorporation of Ce 4+ with vanillin improved significantly the inhibition performance. The IE for Ce 4+ in combination with vanillin was higher than the summation of IE for single Ce 4+ and single vanillin, which was synergism in nature. A high inhibition efficiency, 98% was obtained by a mixture of 25–200 mg l −1 vanillin and 300–475 mg l −1 Ce 4+ . UV–vis showed that the new complex of Ce 4+ –vanillin was formed in 1.0 M H 2 SO 4 for Ce 4+ combination with vanillin. Polarization studies showed that the complex of Ce 4+ –vanillin acted as a mixed-type inhibitor, which drastically inhibits both anodic and cathodic reactions. FTIR and XPS revealed that a protective film formed in the presence of both vanillin and Ce 4+ was composed of cerium oxide and the complex of Ce 4+ –vanillin. The synergism between Ce 4+ and vanillin could also be evidenced by AFM images. Depending on the results, the synergism mechanism was discussed from the viewpoint of adsorption theory.