Evaluation of a high resistance paint coating with EIS measurements: Effect of high AC perturbations

Electrochemical impedance spectroscopy (EIS) was used to evaluate a high resistance paint coating immersed in 10% sodium chloride solution. Although this method was valuable in evaluating this type of coating there were many fluctuations in measured data at low AC perturbations. In this work the role of high AC perturbation to fit EIS data of high resistance coating with equivalent electrical circuit (EEC) was studied. EIS measurements showed that these fluctuations could be reduced by high AC perturbation. The impedance plots showed best fitting at 400 mV AC perturbation at the initial time of immersion and at 100 mV AC perturbation after 90 days of immersion. The coating resistance and coating capacitance were extracted from the Bode and Nyquist plots during the period of 90 days of immersion.