Studies of the impedance models and water transport behaviors of cathodically polarized coating

Cathodic protection (CP) is usually combined with organic coatings to protect metallic structures exposed to seawater. However, the application of CP would enhance coating failure, such as cathodic delamination. To date, there has been few works characterizing the impedance models and water transport behaviors of cathodically polarized coating. In the present article, the analyses of impedance models and water uptake processes of chlorinated rubber coating subjected to various levels of cathodic protection were studied during coatings aging process by electrochemical impedance spectroscopy (EIS).Four distinguished electrical equivalent circuits (EEC) were used to fit the EIS plots of coatings without CP, while only two were employed for samples with CP. Since no corrosion was expected to take place at the metal/coating interface for sample which was polarized cathodically. Coating capacitance was used to investigate the sorption characteristic of water in coating since the increase of Cc was associated with water penetration into the coating. Compared with the sample without CP, those coating systems under CP have a smaller water diffusion coefficient and a further water uptake process after the saturation period.

► The studies was prepared as a preliminary groundwork for a more accurate designing of CP current during coatings aging periods.
► Four distinguishing impedance models were used to fit the sample spectra without CP. However, for samples with CP, only two models were employed to fit the EIS data.
► A “two-stage sorption” for water in coatings without CP was observed from the time dependence of coating capacitance. The water diffusion coefficient of samples with CP was smaller than the sample without CP.