The interface electrochemical and chemical mechanism of a low alloy steel in a 3.5% NaCl solution containing Ce3+-based inhibitor

The interface electrochemical and chemical mechanism of the low alloy steel in a 3.5% NaCl solution containing the Ce3+-based inhibitor was investigated by the electrochemical techniques in conjunction with the surface analysis technologies. It was shown that the Ce(3+-)based inhibitor was an anodic inhibitor with more than 90.0% inhibitory efficiency. The net-shaped inhibiting film with 200 to 500-nm greyish balls was observed on the specimen surface. During the corrosion reaction occurred on the surface of the low alloy steel, the hydrolysis reaction of P3O105- and the disproportionation reaction of Ce3+ ions simultaneously occurred, too, resulting in the formation of the net-shaped inhibiting film with nano-scale greyish ball-type products, which contained Ce element and had an obvious effect on the electrochemical process of the low alloy steel in a 3.5% NaCl solution containing the Ce3+-based inhibitor. Therefore, the EIS spectra of the low alloy steel in a 3.5% NaCl solution containing the Ce3+-based inhibitor were composed of a capacitive loop at a high-frequency region and an inductive impedance loop at a low-frequency region. The charge-transfer resistance (R-t) increased with the immersion elapsed time, indicating that the inhibition efficiency of the Ce3+-based inhibitor increased with immersion elapsed time. The calculated data based on the fitted electrochemical parameters showed the partial coverage of the inhibitor. This was further revealed by the analysis of electrochemical kinetics that the inductive impedance (L) loop at a low frequency region resulted from the localized absorption of the Ce3+-based inhibitor on the surface of the low alloy steel in a 3.5% NaCl solution. It was also verified by micro-morphologies.