Influence of Alloying on the Nature of Passive Films and Their Breakdown

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This research examines factors leading to breakdown of protective passive films on metals. Sophisticated experimental methods are used to follow the effects of hydrogen and chloride anions in film deterioration. Neutron reflectivity studies are carried out on mirror-smooth alloy surfaces of iron and iron-chromium alloys to determine how hydrogen is distributed in the passive films and the manner of breakdown of passivity in the films. EXAFS (Extended X- ray Absorption Fine Structure) analysis in conjunction with a photocathode proportional counter detector is used to determine the presence of damaging anions in the passive film surface. The effect of chromium content in iron alloys on passive film properties relevant to film breakdown is studied by anodic polarization in buffered borate solutions. These data are incorporated into a model of the passive film breakdown process. %%% The passivity of non-noble metals and their alloys is the basis for the successful application of metallic materials in technologies where they are exposed to aqueous environments. The special film that forms on the surfaces of metals, the passive film, enables them to resist corrosion failure. Detailed knowledge is needed on how alloying constituents affect the structure, composition, and electronic properties of passive films to improve the corrosion resistance of metal alloys.