CORROSION PROTECTION OF MILD-STEEL BY COATINGS CONTAINING POLYANILINE

The anti-corrosion performance of polyaniline coated mild steel sample s exposed to artificial brine and dilute hydrochloric acid environment s was evaluated. Samples of mild steel (UNS G10100) coated with polyan iline deposited from solution, and overcoated with an epoxy barrier pa int, when scratched to expose precise areas of bare metal, exhibited c orrosion rates in aqueous 3.5% NaCl solutions 2 times less, and in 0.1 N HCl solutions, 100 times less than observed on identical samples co ated with epoxy paint alone. Mechanistic information, and quantitative corrosion rates were obtained by Tafel Extrapolation, Potentiodynamic Polarization, Galvanic Coupling and Electrochemical Impedance Spectro scopic techniques. These studies, in conjunction with surface analysis by ESCA and Auger techniques, indicate that the corrosion protection, even for exposed bare steel areas, occurs by the formation of passiva ting iron oxide (gamma-Fe2O3 and Fe3O4) surface layers. The formation of these specific oxide layers occurs when the polyaniline is galvanic ally coupled to the steel. This is evident by the fact that the dimens ions of the exposed bare steel area that can be protected in a scratch can be large, but are limited in each corrosion environment.