Physical significance of impedance equivalent circuit elements and protective mechanisms of zinc-rich coatings

In this study, impedance ratios (modulus and real and imaginary parts) are introduced to study the effect of varying the operating conditions of zinc-rich coatings (ZRCs) and zinc powders on the electrochemical impedance spectra of both. The physical significance of the components in the equivalent circuit of the ZRC impedance spectrum is analysed based on the impedance and open circuit potential. The results show that the high-frequency and low-frequency impedances of ZRCs are the contact impedance between zinc powders ( Z m ) and the zinc powder corrosion reaction impedance ( Z corr ), respectively. Finally, the role of OH − , the zinc powder corrosion mechanism and the formation mechanism of the corrosion product layer on the outer surface of the coating were discussed. The above-mentioned mechanism indicates that the effect of corrosion products in filling the pores of the coating is weak, which denies the traditional zinc-rich coatings’ shielding effect. The experimental and analytical methods used in this study provide a new approach to the interpretation of the physical meaning of equivalent circuit elements.