New methods for the study of organic coatings by EIS - New insights into attached and free films

Organic coatings are widely used for the protection of structures against m arine corrosion. Based on long-term service experience, their thickness rea ches often as high as several hundreds of micrometers. However, for primer coatings, where the barrier effect is believed to play a minor protective p urpose, the surface preparation and the nature of the substrate seem to pla y an important role. Experiments have been performed on free standing and supported coatings and the comparison showed considerable differences. It is postulated that the adhesion mechanisms provide an important part of the protection afforded by the coating. The insertion of a conducting probe inside the coating allowe d separating the impedance of the inner part of the coating in contact with the substrate from that of the enter part in contact with the solution. In formation on the influence of the adhesion on the protection was then evide nced. A gold electrode, deposited on the surface of the inner half-layer of the coating, was used as a potential probe to perform electrochemical impe dance measurements. The first results presented in this paper show a clear difference between the behaviour of these two parts of the coating. (C) 200 1 Elsevier Science B.V. All rights reserved.