Electrochemical synthesis and characterization of polypyrrole and substituted polypyrrole coatings on steel substrates

This research work focuses on electrochemical synthesis and characterization of polypyrrole and substituted polypyrrole coatings on steel substrates. The purpose of this research work is to explore the possibility of using aqueous electropolymerized polymers for corrosion protection of steel. Our results show that polypyrrole and poly(N-methylpyrrole) coatings have been successfully formed on low carbon steel substrates from aqueous oxalate solutions by electrochemical method. Electrochemical processing parameters were found to have a significant effect on the formation process of the coatings. In acidic solutions, an induction period was shown before the electropolymerization took place. Passivation of the steel substrate at the end of the induction period was due to the deposition of an FeC2O4·2H2O coating, which was composed of a monolayer of closely packed small crystals. Our results also show that iron(II) oxalate formed during the induction period decomposed again during the initial part of the electropolymerization stage. However, the decomposition reaction was followed by the electrodeposition of polypyrrole on the steel surface. The steel substrates were uniformly covered by the electrodeposited polypyrrole and poly(N-methylpyrrole) coatings. The rate of electropolymerization of pyrrole increased with the applied current density and initial pyrrole concentration, but the applied current density had a more significant effect on the rate of electropolymerization than the initial monomer concentration. The current efficiency for the electropolymerization of pyrrole was all below 100%. The current efficiency seemed to have a weak dependence on the applied current density. The monomer concentration had a relatively more significant effect on the current efficiency. The surface chemistry, surface free energies and surface topography of the electrodeposited polypyrrole and poly(N-methylpyrrole) coatings are all favorable for the application of strongly adherent topcoatings. The adhesion and corrosion performance of polypyrrole and poly(N-methylpyrrole) coatings were influenced by electrochemical processing parameters. Polypyrrole coatings showed better adhesion and corrosion performance than poly(N-methylpyrrole) coatings. Electrodeposited polypyrrole appears to be a good candidate to be used as corrosion inhibiting coatings.