Conducting polymers and corrosion: Polyaniline on steel

Polyaniline-coated steel panels were studied by electrochemical impedance s pectroscopy (EIS) and electrochemical noise methods (ENM). EIS data for the polyaniline sample was obtained for increasing time of immersion, An incre ase in charge-transfer resistance (R-n) with immersion time was observed. E NM data showed that active electrochemical changes occurred during the earl y stages of Immersion. The mean current from ENM exhibited a rather large o scillatory behavior during early stages of immersion, and the mean potentia l from ENM displayed a tendency toward positive values. Noise resistance (R -n) values also showed initial oscilatory fluctuations, with values that re flected a poor barrier property for polyaniline coating. Tafel plots showed a lower corrosion rate and a more noble corrosion potential for the polyan iline-coated sample as compared to a bare steel sample. Electrochemical dat a confirmed that significant interactions between the polyaniline and steel occurred during the first 5 days of immersion, but that a continuing inter action occurred throughout the entire immersion period. EIS of a polyanilin e/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 ep oxy alone.