The Potentiostatic Method as Applied to the Anodic Oxidation of the Valve Metals, and the Field Dependence of the Tafel Slope for Aluminum

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Abstract
The potentiostatic method for determining the steady‐state parameters for anodic oxidation of the valve metals is examined in relation to present models for the conduction properties of the oxides. It is shown that despite the fact that potentiostatic conditions correspond to nonsteady‐state conditions, the steady‐state field coefficient (reciprocal Tafel slope) may be determined accurately, and relatively easily, from such measurements. Data for aluminum are presented in illustration and found to be in accord with an equation of the form , where is the current density, the field strength, and α, γ, and δ positive constants for isothermal conditions. The values of γ and δ obtained are in good agreement with values obtained previously using a method in which steady‐state conditions were maintained during measurement. The agreement lends further support for the inclusion of the term in in the conduction equation.

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