Evaluation of thick industrial coating films by EIS and EN

Three industrial coating systems have been tested: a waterborne system; a zinc inorganic primer coated with epoxy and polyurethane topcoat; and a urethane elastomer. The samples were exposed in a salt fog chamber in accordance with the ASTM B 117-90 standard for 3000 h and were removed for evaluation following various exposure times. After each exposure period, the samples were inspected visually according to both ASTM D 714 (blistering) and ASTM D 610 (rust), after which electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) analyses were carried out. Electrochemical noise provides an alternative means for the study of the protective properties of polymeric coatings, allowing corrosion to be monitored under thick coatings, even when the coatings appear to remain in good condition, and serving as a powerful tool for the study of industrial coatings.