The passive oxide film that forms on the surface of 3D printed 316 L stainless (AM-SS) under acidic (pH 1) and oxidizing conditions is studied. Particular emphasis is placed on its charge transport characteristics. The electrochemical behavior of the passive oxide film in the presence of various total Fe (FeII + FeIII species with a FeII/FeIII ratio of one) concentrations (from 100 to 800 ppm) was investigated due to its extended stability and large breakdown potential (0.85 V vs SCE). The passive film formed in the acidic electrolyte was mainly composed of chromium oxide as confirmed from an X-ray photoelectron spectroscopy depth profile analysis. The n-type semiconductor behavior at potential <0.6 V vs SCE and low flat band potential compared to OCP of AM-SS confirmed the formation of a passive oxide film. It is concluded that within OCP< E<0.6 (vs SCE), FeIII species reduced on the n-type oxide film and the adsorbed layer was enriched with FeII species. Further charge transport through the adsorbed layer was controlled by the diffusion of FeIII species. For E>0.6 V vs SCE, increases in the acceptor concentration and transformation of the oxide film into a p-type semi-conductor facilitated the oxidation of FeII species at the oxide/electrolyte interface.
|Journal||Journal of physical chemistry. C|
|State||Published - 2020|