Accelerated tests, a necessary complement of electrochemical assays to evaluate anti-corrosive coatings

Abstract

Corrosion processes of painted metals may be monitored by accelerated and/or electrochemical assays. There is certain relationship between both types of test. Particularly, when using paint coatings with high barrier effect (R > 108 Ω cm2) and low dielectric capacity (C < 10−9 F cm−2), a good anti-corrosion performance was accomplished and results from both types of tests match. Once corrosion has started, a charge transfer resistance value > 106 Ω cm2 ensures kinetic inhibition of the corrosion process. The question arises when the values of the above-mentioned parameters differ from those and a realistic approach to the coating useful service life is needed. In this paper, it was demonstrated that, in such cases, accelerated and electrochemical assays complement each other. Accelerated tests are related to coating durability while electrochemical ones provide information about the degradation mechanism. To carry out this investigation, three anti-corrosive paints containing ecological pigments were prepared and their protective behavior evaluated in the salt spray chamber and by electrochemical impedance spectroscopy (EIS).