Application of electrochemical impedance spectroscopy technology to evaluate passivation performance of film forming and adsorption types corrosion inhibitors

Electrochemical impedance spectroscopy (EIS) technology is a mature quantitative method used to accelerate the evaluation of the corrosion resistance of protective coatings. In a short test time, an EIS measurement is highly reliable in predicting the long-term performance of the coating. This study used EIS technology to assess the adsorption processes and the performance of film-forming corrosion inhibitors on metal surfaces. Sodium hexametaphosphate and sodium borosilicate controlled-release inhibitors were selected to determine the effect and efficiency of the Adsorption Type Inhibitor (ATI) and Film-Forming Type Inhibitor (FFTI) on the substrate. EIS integrated with a three electrodes configuration system was employed at room temperature with an addition of each type of inhibitor for 30 days and measured daily throughout the immersion time. EIS data analysis provided information on the different parameters viz. charge transfer resistance, double layer capacitance, phase angle and relaxation time. SEM further confirmed the surface morphology of the metal. The Nyquist impedance spectra result shows that the capacitance arc radius of FFTI is greater than ATI while the control group has the smallest. The results of Bode impedance show that the surface resistance of FFTI is the highest, followed by ATI and the control group. These findings give a theoretical foundation for using EIS technology to evaluate the corrosion inhibitor & rsquo;s passivation performance.