Development of polyaniline-polypyrrole composite coatings on steel by aqueous electrochemical process

Polyaniline-polypyrrole composite coatings were formed on low carbon steel using oxalic acid as electrolyte by a potentiostatic method under aqueous c onditions. A passive layer of iron (II) oxalate is deposited on the steel s urface prior to the formation of composite coatings. The electrochemical pr ocess shows three distinct regimes - formation of passive layer, dissolutio n of passive layer and formation of polymeric composite coatings. These thr ee regimes have been studied in depth using spectroscopic techniques and el ectron microscopy. Quantitative analysis of the current-time transient (I-t ) curves show that the nucleation and growth of the passive layer occur by three-dimensional (3D) instantaneous nucleation and that of the composite c oatings occur by 3D progressive nucleation. It has also been shown that the morphology of the composite coatings depends upon the electrochemical depo sition parameters. (C) 2001 Published by Elsevier Science Ltd.