A theoretical analysis of the impedance of polymer-coated steel was performed to identify parameters for assessing coating performance in a short time without rigorous analysis of data from electrochemical impedance spectroscopy. Results of the analysis applied to nine coating systems suggested the breakpoint frequency (fb), the frequency fmin of the phase-angle minimum observed at high frequencies (Φmin), and the ratio of the impedance recorded at Wo frequencies could be used for this purpose. Analysis also showed fb and fmin depended on the delaminated area (Ad) and the coating resistivity (p), while Φmin and the ratio fb/fmin depended only on Ad. Recording of fb, fmin, and Φmin allowed determination of coating damage and, therefore, was recommended for the design of a commercial device for field testing of the remaining lifetime of protective coatings.

Subject
Water uptake, Primers, Electrochemical impedance spectroscopy, Zinc rich coatings, Protective coatings, Coatings, Sodium chloride, Impedance, Coating degradation, Delamination, Alkyds, Coating systems, Enamels
Keywords:
delamination, exposure tests, impedance spectra, polymer coatings, steel, water uptake
NACE International
1993
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