Electrochemical impedance spectroscopy (EIS) was employed to study the properties of a stand-alone industrial coating Chemlok 205® primer used in rubber/metal-bonded composites in water. The impedance behavior was observed between systems exposed in aerated and de-aerated systems. The coating properties were interpreted through Nyquist and Bode's EIS plots. Equivalent electrical circuit models derived from the spectra were employed to describe the degradation process of the coatings. Data obtained showed that coating samples exposed under aerated water experienced a significant drop in impedance followed by the development of a corrosion cell. Data from the Nyquist and Bode's plots were used to model the electrical equivalent circuits that described the overall coating degradation process. The degradation process for the aerated system can be represented by three different equivalent electrical circuits, indicating a reduction of the coating impedance against the exposure time. This was, however, not the case for the de-aerated coating system, which was found to have been able to maintain high coating impedance values and good adhesion throughout the duration of the experiment. A comparison on the change in the coating capacitance and pore resistance of the Chemlok 205 primer between the aerated and de-aerated water systems indicated that dissolved oxygen significantly contributed to the adhesion failure of the coating. A Fourier transform infrared spectroscopy analysis conducted after alkaline exposure to represent the coating in alkaline medium when subjected to cathodic polarization confirmed the chemical degradation of the primer caused by hydroxide attack. The analysis shows a natural reaction of the acidic phenolic group within the primer, with the basic hydroxide ions resulting in the formation of a phenolic salt or phenoxides.

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