Comparison of the Corrosion Protection of Mild Steel by Polypyrrole-Phosphate and Polypyrrole-Tungstenate Coatings

The electrodeposition of polypyrrole-phosphate (PPy-P) and polypyrrole-tungstenate (PPy-W) on mild steel (MS) were achieved in an oxalic acid medium with cyclic voltammetry techniques. Adherent and homogeneous PPy-P and PPy-W films were obtained. The corrosion behavior of mild steel with phosphate (PPy-P) and tungstenate (PPy-W) composite coatings in 3.5% NaCl solutions were investigated through a potentiodynamic polarization technique, open-circuit potential-time curves, and electrochemical impedance spectroscopy (EIS). On the basis of a physical model for corrosion of mild steel composites, Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy-W coatings could provide much better protection than the PPy-P and polypyrrole coatings. The effects of the phosphate and tungstenate process parameters on the morphology and structure of the passive films were investigated by scanning electron microscopy and electron dispersion X-ray analyses. The results reveal that the PPy-P and PPy-W coated electrodes offered a noticeable enhancement in protection against corrosion processes. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 2733-2741 ,2008