Effect of the anode to cathode surface area ratio on the concentration distribution near the solid-liquid interface

Xu Guangye - Iwai Kazuhikoi

Faculty of Engineering, Hokkaido University, Division of Materials Science and Engineering, Kita 13, Nishi 8, Kita-ku, Sapporo, 060-8628, Japan

Abstract
For the solid-liquid chemical reaction, the mass transfer near the solid-liquid interface is often the rate determining step, such as in an electroplating process and in a high temperature process. To enhance the chemical reaction, traditional methods reduce the concentration boundary layer thickness formed near the solid-liquid interface by exciting a macro-scale flow in the bulk region. However, traditional methods have limitation in reducing the concentration boundary layer, because the concentration boundary layer exists in the velocity boundary layer. This means that the excitation of flow in the concentration boundary layer is important. Based on this concept, direct imposition of a force near the solid-liquid interface by superimposing the magnetic field and current has been proposed. By this means, the flow can be directly excited in the concentration boundary layer. In the past research, a Cu anodic electrode was dissolved in a Cu²⁺ aqueous solution, and the increase of the Cu²⁺ concentration decreased under the imposition of a time-varying force compared to that without the time-varying force imposition just above the centre of the anode. In this experiment, the uniformity of the solute concentration distribution under the time-varying force imposition with a different anode to cathode surface area ratio was investigated. As a result, the uniformity of the Cu²⁺ concentration distribution increased, and the average Cu²⁺ concentration in the vicinity of the anode surface decreased by increasing the anode to cathode surface area ratio. Tables 2, Figs 3, Refs 13.