Corrosion protection of low carbon steel with polyaniline: passivation or inhibition?

The mechanism by which polyaniline-containing coating formulations afford corrosion protection towards carbon steel has been investigated using potentiodynamic polarization techniques. Polyaniline-containing coatings were found to reduce corrosion rates in 0.1 mol dm(-3) NaCl by approximately a factor of 2. More importantly, however, the data reveals that anodic protection of carbon steel in such media cannot explain the effect, as no evidence of an active-passive transition is observed upon anodic polarization; at sufficiently high potential the steel simply reaches a state of rapid diffusion-limited dissolution, Overall, the results of our kinetic study suggest protection stems from an inhibitory rather than a passivating effect. A mechanism is proposed which assigns the effect to inhibition by dopant ions released upon reduction of the polyaniline emeraldine salt to its non-conducting leuco counterpart. (C) 2003 Elsevier B.V. All rights reserved.