Parametric study on the electrochemical impedance Spectroscopy of organic-coated steels in hydrochloric acid solutions

Electrochemical impedance technique was used to study the corrosion resistance of polymer-coated steels in hydrochloric acid solutions. The mechanism of the degradation process of the coating can be described using a Randles-type equivalent circuit model with the inclusion of Warburg diffusion impedance. The impedance parameters: coating resistance R-po, coating capacitance C-c, charge transfer resistance R-ct and double layer capacitance C-dl of the metal/coating interface, and the Warburg coefficient sigma were calculated using a nonlinear least-square minimization scheme. The time dependency of impedance parameters was compared to the method of breakpoint frequency. It was found that the delamination of the metal/coating interface is more associated with the charge transfer resistance than the coating resistance. Open circuit potential measurement is indicative of the corrosion status of the coating.