Barrier effect of zinc-rich coatings and evolutionary law of equivalent circuit elements of coatings.

• The evolution of EIS of zinc-rich coatings is explained in detail. • The corrosion product layer causes the shielding effect of zinc-rich coatings. • Semi-logarithmic relationships suggest that t1/2 axis is useful for impedance studies. • Linear correlations help in designing equivalent circuits (EE). • Linear correlations help in elucidating the physical meaning of EE components. This paper focuses on elucidating the variation rules of equivalent circuit elements of electrochemical impedance spectra (EIS) of two different thicknesses of epoxy zinc-rich coatings (EZRCs) and silicate ethyl zinc-rich coatings (ZRCs). The correlation between the circuit elements and the low-frequency impedance modulus (|Z| 0.01 Hz) and the open-circuit potential (OCP) is investigated, and an explanation of the barrier effect and the evolution law of corrosion potential (E corr) is given. The results show that there is a linear or piecewise linear relationship between the logarithm of |Z| 0.01 Hz and the circuit elements with a square root of time (t1/2), and the piecewise linear relationship between the OCP and t1/2. Further, there is a large amount of linear correlation between circuit elements. The semi-logarithmic linear relationship suggests that the square root axis can be a conventional choice for coating impedance studies. Linear correlations help in designing equivalent circuits and elucidating the physical significance of components in equivalent circuits. The barrier effect of ZRCs mainly refers to the blocking effect of the corrosion product layer on the outer surface of the coating. The barrier effect of ZRCs can be neglected. Designing equivalent circuits: location of circuit elements and current assignments, fitting accuracy, trends in model parameters, linear correlation of elements. [Display omitted] [ABSTRACT FROM AUTHOR]