Mild steel protection with epoxy top coated polypyrrole and polyaniline in 3.5% NaCl

In this study, the corrosion behaviours of mild steel (MS) samples coated with single epoxy polyamine (MS/E), epoxy polyamine top-coated polypyrrole (MS/PPy/E) and polyaniline (MS/PANI/E) were investigated in 3.5% NaCl solution of pH 8. For this purpose, electrochemical impedance spectroscopy (EIS) and polarisation resistance measurements were utilized when the centres of the electrode surfaces were scratched. It was found that the PPy film reduced the corrosion protection efficiency of the epoxy coating when it was used as the primary film under the epoxy layer. The primary PANI coating was shown to improve significantly the protection efficiency of the epoxy coating against mild steel corrosion. This was related to its healing effect on surface passivation against attack by a corrosive environment along a defect.