TRANSIENT DIFFUSION AND MIGRATION TO A DISK ELECTRODE

A coordinate transformation is implemented that greatly facilitates the numerical solution of the equations describing transient ionic diffusion and migration to a disk electrode. The transformed coordinates are a modified form of the classical oblate spheroidal coordinates; singularities arising at the electrode edge are removed, and the infinite model space is collapsed down to a finite rectangle. The resulting savings in storage and execution time make it feasible to do numerical calculations that were previously difficult and computationally expensive. We have applied the coordinate transformation to model transient, two-dimensional transport to a disk surface during the deposition of a metallic film. We focus our discussion on the current distribution (which determines the film thickness and uniformity of coverage), the effect of inert electrolyte, and the influence of the disk size with regard to obtaining accurate rate-constant information.