Adsorption behavior and synergistic mechanism of a cationic inhibitor and KI on the galvanic electrode

The synergistic effect between KI and imidazoline derivative as a cationic inhibitor for inhibiting galvanic corrosion has been investigated by using electrochemical methods, atomic force microscopy and Fourier transform infrared (FTIR) spectroscopy. A galvanic electrode was prepared by coupling N80 carbon steel and S31803 stainless steel, and all experiments were performed in NaCl solution in the presence or absence of imidazoline derivative (MAD) and KI. Zero charge potential experiments reveal carbon steel and stainless steel carry positive and negative excess charges in NaCl solution, respectively, and stainless steel carries negative excess charge in NaCl solution with KI. Polarization curves and galvanic current measurements suggest that, for the galvanic corrosion, both MAD and KI are mainly cathodic type inhibitors, and a synergistic effect exists between KI and MAD. FTIR and AFM were used to analyze the inhibitor film formed on the surface of the electrodes. Results show that in the presence of KI, compared with that in the absence of KI, the inhibitor film on the anode of galvanic electrodes (GE) is more compact, and the adsorbability of the inhibitor on the surface of carbon steel is strengthened. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from electrochemical measurements, AFM and FTIR. It is found that the anion I− can change the distribution of excess charge on the surface of galvanic electrode, thus helps the inhibitor to adsorb on both the cathodic area and the anodic area.