Electrochemical Interfacial Phenomena under Microgravity: Part 2. Numerical Analysis of the Rate of Ionic Mass Transfer Accompanying Anodic Copper Dissolution

The anodic dissolution phenomena of copper, under microgravity in a drop shaft, was compared to that in terrestrial experiments. A 0.1 M CuSO(4-1) M H2SO4 solution layer was confined to a shallow (200-(mo)m-thick) and horizontally installed electrolytic cell. Relatively higher constant current densities were applied for visualization within 8 seconds of electrolysis duration. Fluid flows were induced in the decelerated zone of the drop shaft and in the terrestrial experiment. The interference-fringe pattern, which accompanied the copper dissolution, was measured in situ with a common path-type microscopic interferometer. Numerical analysis was used to compare the development of the interference-fringe pattern in both environments. Two boundary conditions at the anode surface were employed: a constant current density with any degree of supersaturation and a solubility limit at the surface. The calculated surface concentration was used to discuss the transient variation of measured anode overpotential. A larger degree of supersaturation, before the anodic overpotential started to increase, which was probably caused by CuSO4 precipitates followed by a kind of passivation film formation, was calculated under a microgravity environment. The drop-shaft facility provides a good opportunity to study the electrochemical interfacial phenomena which are necessary to precisely design the micromachining or microfabrication processing.