The Open-Circuit Transient Method of Analyzing Overpotential in Anodic Oxidation

The open-circuit technique and its application to studies of overpotential in anodic oxidation are described in detail. The digital circuitry which is used to record transients under program control can be operated either by a mini-computer or a microprocessor. Transients are written on magnetic tape for recall by analysis programs written in BASIC. Three approaches to data analysis are described and their advantages and disadvantages discussed. The anodic oxidation of tantalum in sulfuric acid is chosen to illustrate application of the technique both to facilitate comparison with results obtained by other techniques, and to illustrate how a nonlinear dependence of log (i) on E affects open-circuit analysis. A procedure for second-order analysis which accounts for log(i) -E curvature through an effective-field model is described, and the significance of differences between first-and second-order results is discussed.