Lifetime prediction of waterborne acrylic paints with the AC-DC-AC method

In this study an accelerated method for the evaluation of painted metals is proposed. Specifically, the proposed method has been applied in a study of the process of degradation of two water-based paints applied to a carbon steel surface. The technique is based on the application of cycles combining measurement of electrochemical impedance spectra, cathodic polarisation steps, and recording of the evolution of the corrosion potential of the system in function of time. The results obtained from this method are compared with those obtained from studying the evolution of the impedance spectra of both systems in function of the time of immersion, for periods of immersion of the order of 200 days. The results obtained indicate that the method proposed does not introduce alternations in the degradation mechanism of the paints studied. Moreover, it gives a considerable reduction of the time required for tests, since it is possible simulate, in hours, degradation processes that normally take place over hundreds of days. Lastly, the method has been demonstrated to have sufficient sensitivity to detect changes in the protective properties of the systems studied. (C) 2003 Elsevier B.V. All rights reserved.