W.-K. Lu, R. Elsenbaumer, B. Wessling

Corrosion protection of mild steel by coatings containing Polyaniline

(corrosion rate measurements and XPS analysis of the passive layer)

Synth. Met. 71 (1995), 2163 - 2166

The anti-corrosion performance of polyaniline* exposed to artificial brine and dilute hydrochloric acid environments was evaluated. Samples of mild steel (UNS G 10100) coated with polyaniline from dispersion, and overcoated with an epoxy barrier paint, when scratched to expose precise areas of bare metal, exhibited corrosion 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 with epoxy paint alone. Mechanisatic information, and quantitative corrosion rates were obtained by Tafel extrapolation, Potentiodynamic Polarization, Galvanic Coupling and Electrochemical Impedance Spectroscopic 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 passivating iron oxide (-Fe2O3 and Fe3O4) surface layers. The formation of these specific oxide layers occurs when polyaniline is galvanically coupled to the steel. This is evident by the fact, that the dimensions of the exposed bare steel area that can be protected in a scratch can be large, but are limited in each corrosion environment.

XPS analysis of passive iron oxide layers form
in the presence of doped polyaniline

*found by B. Wessling, Adv. Mater. 6 (1994), 226

further informations:
the passivation mechanism of polyaniline on metals is revealed
industrial applications