EIS characterisation of new zinc-rich powder coatings

A zinc-rich powder coating, applied onto steel substrate, was studied using electrochemical impedance spectroscopy (EIS). Before immersion when coating is dry, EIS spectra revealed that the percolation threshold was reached. Then, an equivalent circuit including a transmission line was applied to model electrochemical response. In this model, which considers isolated and semi-isolated zinc particles within the binder, it was found that both phases were equally distributed in the coating.When specimens were immersed in a 3% NaCl solution, free corrosion potential Ecorr and EIS measurements were regularly performed. The electrochemical response was different from that observed with liquid or other zinc-rich powder formulations. It was proposed that the low porosity of the coating was the main factor contributing to a non-homogenous electrolyte penetration. Therefore, the previous model was modified to take into account all these contributions.