Comparative study of two equivalent circuit models for electrochemical impedance spectroscopy analysis of epoxy zinc-rich coatings

In this paper, the impedance spectra of an epoxy zinc-rich coating (ZRC) and its free film immersed in 3.5% NaCl solution are investigated, the fitting error and model parameter trends of series and nested equivalent circuit fits are compared, and the differences in the high-frequency components of the ZRC and the epoxy coatings are analyzed. The results show that the high-frequency impedance of ZRC is the contact impedance between the zinc powders (Zm) rather than the film impedance (Zf). The corrosion reaction of the ZRCs is controlled by the diffusion of oxygen. For ZRCs, the series equivalent circuits are more reasonable compared to the nested equivalent circuit. Based on the series equivalent circuit, the variation law of the equivalent circuit elements (resistors, capacitors and dispersion coefficient) and the correlation of these elements with low-frequency impedance modulus (|Z|0.01Hz) and open circuit potential (OCP) are investigated in this paper.