Electrodeposition of ring-substituted polyanilines on Fe surfaces from aqueous oxalic acid solutions and corrosion protection of Fe

The electrochemical polymerization of several ring-substituted anilines namely of o-toluidine (o-Tol), m-toluidine (m-Tol), o-anisidine (o-Anis) and o-chloroaniline (o-ClAn) was carried out on passivated Fe surfaces. Thin polymeric films were deposited by cyclic voltammetry, potentiostatic or galvanostatic techniques on the Fe-disc electrode from aqueous oxalic acid solutions. Well-defined cyclic voltammograms showing the electroactivity and growth of polymers were observed during each potential cycle. The electrochemical response and the surface morphology of the deposited polymeric films of substituted polyanilines were characterized in comparison with the non-substituted polyaniline films on Fe. Adherent and relatively stable polymeric films were obtained for o-Tol, m-Tol and o-Anis. These films show protective properties against corrosion of Fe in sulfuric acid solutions stabilizing the Fe passive state. Their anti-corrosion behavior, although slightly poorer than that of the non-substituted polyaniline, bears strong similarities with that of the polyaniline. A less conductive polymer with a very poor stability and protective ability against the corrosion of Fe was obtained for o-ClAn.