Corrosion Protection Evaluation of Mild Steel Painted Surface by Electrochemical Impedance Spectroscopy

This study focuses on the evaluation of corrosion protection performance of zinc based epoxy paint on the chemically treated mild steel surface in artificial sea water by Electrochemical Impedance Spectroscopy (EIS). EIS and Open Circuit Potential (O.C.P) measurements of the rusted surface prior to chemical treatment were also studied to make a comparison with the corrosion behavior of the applied paint film. The electrochemical behavior of painted surface was estimated by EIS parameters that contained paint film resistance, paint film capacitance and double layer capacitance. On the basis of calculation using EIS spectrums it was observed that pore resistance (Rpore) decreased with the appearance of doubled layer capacitance (Cdl) due to the electrolyte penetration through the film. This was further confirmed by the decrease of polarization resistance (Rp) and OCP towards more negative value was also the indicator of the deterioration of paint film protectiveness.