The anodic oxidation of platinum in is studied by using open‐circuit transients to determine Tafel slopes and by following film growth optically with an ellipsometer. The Tafel slope values are found to be proportional to the film thicknesses measured with the ellipsometer. This result is interpreted in terms of an ionic conduction model in which the overpotential appears across the anodic oxide film, and the logarithm of the ionic current density is proportional to the field in the oxide. The results are compared with the results of similar measurements on iron and tantalum. Although platinum, iron, and tantalum have quite different chemical properties, and their oxides span a thickness range from a monolayer to several thousand angstroms, it is concluded that the same basic process is responsible for the anodic oxidation of the three metals.
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Ord et al. (1971) studied this question.