Evaluation of polyaniline films containing traces of dispersed platinum for protection of stainless steel against corrosion

We demonstrate the ability of a polyaniline film, into which highly dispers ed platinum microparticles were introduced at a fairly low level (ca. 25 mu g cm(-2)), to protect stainless steel (containing 15.86% Cr) against corro sion in strong acid solution (2 M H2SO4) We show that the electrocatalytic reduction of oxygen (from air) on the platinized polyaniline film can be co upled to the self-passivation of steel, i.e. to the anodic formation of a p assive layer composed of the oxides or oxyhydroxides of iron/chromium. The reduction of O-2 at dispersed platinum microcenters, is apparently fast eno ugh to replenish the polyaniline charge consumed by the oxidation of stainl ess steel, and to poise the steel's potential at about 0.4 V vs SCE. Conseq uently, the corrosion potential of stainless steel is stabilized within the passive range, and the rate of its dissolution is minimized. Also a low ov erpotential for the reduction of protons seems to facilitate the active-to- passive transition of stainless steel. (C) 1999 Elsevier Science Ltd. All r ights reserved.