Study of high-frequency impedance of zinc-rich coatings

Abstract

In this paper, three types of impedance spectra were investigated, i.e., impedance spectra of two zinc powders (new and old) and five coatings (two different thicknesses of epoxy zinc-rich coatings (EZRCs), an ethyl silicate zinc-rich coating, an epoxy coating and an autodeposition coating) in 3.5 wt.% NaCl solution, dry film impedance spectra of two coatings (the thicker EZRC and autodeposition coating) and their impedance spectra in a 0.003 M LiCl–methanol solution. The results show that the resistive part of the high-frequency impedance of the ZRCs at the early stage of immersion is the contact resistance ( Rm) between the zinc powders, and the capacitive part is the parallel connection of the contact capacitance ( Cm) and the film capacitance ( Cc) of the binder. The coupling of the two capacitors results in a deviation of the measured Pm from the true Pm, where Pm is the Cm-dependent dispersion coefficient