A QUANTITATIVE STUDY OF GRAVITY-INDUCED CONVECTION IN 2-DIMENSIONAL PARALLEL ELECTRODEPOSITION CELLS

Even in thin horizontal cells, electrodeposition of tree-like metal ag gregates is accompanied by a gravity-induced fluid flow at the electro des. This flow has been calculated and the resulting map of the salt c oncentration has been deduced. Two extreme flow regimes are found: at shorter times, fluids with different densities behave as immiscible li quids and the extent of the perturbed zone near the electrode is found to vary with time as t(4/5). For longer times, fluid motion is suffic iently slow that diffusion tends to equalize the concentrations vertic ally (i.e. along the direction normal to the cell). In this regime, th e extent of the perturbed zone varies as t(1/2). These two types of be haviour account quantitatively for experimental measurements on Cu ele ctrodeposition in copper sulphate electrolytes.