Electrodeposition mechanism of polypyrrole coatings on steel substrates from aqueous oxalate solutions

Polypyrrole coatings have been successfully electrodeposited on steel subst rates from aqueous oxalate solutions. In acidic solutions, the electrodepos ition process was characterized by three distinct stages. In this work the electrodeposition mechanism in acidic solutions was investigated by scannin g electron microscopy (SEM), X-ray diffraction (XRD) and reflection-absorpt ion infrared spectroscopy (RAIR). Our results reveal that deposition of a t hin layer of FeC2O4. 2H(2)O crystal layer first established the passivation of the steel substrate at the end of the second stage, but the FeC2O4. 2H( 2)O formed was subsequently decomposed in the initial part of the third sta ge and electropolymerization of pyrrole occurred directly on the steel surf ace. The proposed electrodeposition mechanism is also consistent with the r esults of lap shear tests. (C) 2000 Elsevier Science Ltd. All rights reserv ed.