Electrodeposition mechanism, adhesion and corrosion performance of polypyrrole and poly(N-methylpyrrole) coatings on steel substrates

Polypyrrole and poly(N-methylpyrrole) coatings have been successfully elect rodeposited on steel substrates from aqueous oxalate solutions. In acidic s olutions, the electrodeposition process was characterized by three distinct stages. In this work the electrodeposition process was first investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and FTIR tec hniques. The adhesion and corrosion performance of the electrodeposited coa tings were then evaluated by single lap shear tests and tafel tests, respec tively. Our results reveal that deposition of FeC2O4. 2H(2)O crystal layer first established the passivation of steel at the end of the first two stag es, but the formed FeC2O4. 2H(2)O passive layer is subsequently decomposed followed by electropolymerization of pyrrole. Our results also show that el ectrochemical process parameters had significant effects on the adhesion an d corrosion performance of the electroposited polypyrrole and poly(N-methyl pyrrole) coatings. Polypyrrole coatings exhibited better adhesion and corro sion performance than poly(N-methylpyrrole) coatings. (C) 2000 Published by Elsevier Science S.A.