Conducting Polymers and Corrosion: Polyaniline on Steel

Abstract

Polyaniline-coated steel panels were studied by electrochemical impedance spectroscopy (EIS) and electrochemical noise methods (ENM). EIS data for the polyaniline sample was obtained for increasing time of immersion. An increase in charge-transfer resistance (Rct) with immersion time was observed. ENM data showed that active electrochemical changes occurred during the early stages of immersion. The mean current from ENM exhibited a rather large oscillatory behavior during early stages of immersion, and the mean potential from ENM displayed a tendency toward positive values. Noise resistance (Rn) values also showed initial oscillatory fluctuations, with values that reflected a poor barrier property for polyaniline coating. Tafel plots showed a lower corrosion rate and a more noble corrosion potential for the polyaniline-coated sample as compared to a bare steel sample. Electrochemical data confirmed that significant interactions between the polyaniline and steel occurred during the first 5 days of immersion, but that a continuing interaction occurred throughout the entire immersion period. EIS of a polyaniline/epoxy two-coated system on steel also was carried out. Performance of the polyaniline/epoxy system was superior to that of bare steel coated with epoxy alone.