A passivation mechanism of doped polyaniline on 410 stainless steel in deaerated H2SO4 solution

To investigate the role of polyaniline (PANI) in the corrosion protection of stainless steel (SS) in oxygen-deficient acidic solution, a separate doped PANI film electrode on a glass substrate was prepared and the test solution (1 M H2SO4) was purged with high-purity N2 until dissolved oxygen level decreased more than two orders of magnitude. In this deaerated 1 M H2SO4 solution, the galvanic coupling interaction between the separate PANI film electrode and 410 SS was studied. Results reveal that the separate PANI film can passivate the 410 SS steadily for a long period of time. A variety of experimental methods including potentiodynamic measurement, potentiostatic (current–time) examination and X-ray photoelectron spectroscopy (XPS) are used to explore the mechanism by which the separate PANI film passivated the galvanic coupling SS in the deaerated sulfuric solution. These studies show that passivation is achieved because PANI film provides a large critical current at the early stage of coupling and a persistent passive current by its electrochemical dedoping/re-doping equilibrium activity with the acidic environment at the subsequent stage of coupling.