Abstract
In sodium chloride, proton irradiation resulted in a increase in the pitting potential of stainless steel (0.425 vs saturated calomel electrode). In addition, the passive region of the polarization curve during irradiation was associated with a drop in metastable pitting activity by a factor of 100. Mott–Schottky experiments in pH 1.6 found that irradiation was associated with an increase in oxygen vacancy concentration ( vs ). However, electrochemical impedance spectroscopy experiments found that the Warburg coefficient increased during irradiation ( vs ). An increase in film impedance was also observed. Given that σ is inversely proportional to , one would expect that an increase in would result in a decrease in σ. This apparent dichotomy, an increase in oxygen vacancies in the space charge region at the film/solution interface and a corresponding increase in σ, can be explained if the film is composed of inner Cr-rich p-type and outer Fe-rich n-type semiconducting layers. It is proposed that changes in the inner Cr-rich layer of the oxide are responsible for the observed increase in pitting potential during irradiation.
Published Version
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