Investigations of the mechanism of corrosion inhibition by polyaniline - Polyaniline-coated stainless steel in sulfuric acid solution

The objective of this work was to elucidate the mechanism by which polyanil ine (PANI) films passivate stainless steel surfaces in highly corrosive H2S O4 solution. A Variety of experimental methods, including measurements of t he open-circuit potential, Auger depth profiling, and the scanning referenc e electrode technique (SRET), was used. These studies have shown that passi vation is achieved because the oxidized and protically doped emeraldine-sal t form of PANI holds the potential of the underlying stainless steel electr ode in the passive region. Because of this electrostatic mechanism of corro sion inhibition, the entire stainless steel surface does not have to be coa ted with PANI in order to achieve passivation. Auger depth profiling experi ments show that, in analogy to the case of a bare stainless steel surface w hose potential is potentiostatically maintained in the passive region, the stainless steel surface beneath the PANI film is enriched in Cr after expos ure to the H2SO4 solution. Finally, SRET was used to explore passivation of the stainless steel in regions exposed to solution by pinholes intentional ly cut through the PANI film. SRET shows that the PANI film surrounding the pinhole can heal the stainless steel in the pinhole region. (C) 2001 The E lectrochemical Society. All rights reserved.