Corrosion protection by multilayered conducting polymer coatings

Multilayered coatings, consisting of combinations of the conducting polymers polyaniline (Pani) and polypyrrole (Ppy), were galvanostatically deposited on to both carbon steel and stainless steel. Potentiodynamic polarisation was used to assess the ability of these copolymers to provide an effective barrier to corrosion in chloride environments. For carbon steel the performance of these multilayered coatings on carbon steel were not sufficiently better than for single Pani coatings to justify their more complicated deposition procedures. However, in the case of stainless steels the new multilayered coatings proved to be significantly better than previously reported single Pani coatings, especially at protecting against pitting corrosion. It was found that the degree of protection was a function of the deposition order of the copolymer, with films consisting of a Pani layer over the top of a Ppy layer yielding the best results. Scanning electronic microscopy observations and adhesion measurements, along with the electrochemical data suggested that the ability of a conducting polymer film to act as electronic and chemical barriers were more important in providing corrosion protection than its ability to act as a physical barrier. (C) 2002 Elsevier Science Ltd. All rights reserved.