COUPLING OF DRIFT, DIFFUSION, AND ELECTROCONVECTION, IN THE VICINITY OF GROWING ELECTRODEPOSITS

We propose a theoretical approach to the problem of electroconvection in the vicinity of electrodeposits which are growing in quasi-two-dime nsional cells. Charges at the tips of the branches are expected to ind uce a convective motion of the solution. We show theoretically that, i n the steady state, pairs of contrarotative vortices must be expected between neighboring branches. The concentration map is explicitly deri ved in the limit where diffusion is negligible, as compared to drift a nd convection. A more realistic concentration map is computed numerica lly in the case of nonnegligible diffusion. We compare the theoretical predictions to experimental observations of the growth of copper depo sits from a solution of copper sulphate. We show that both the convect ive vortices and the concentration gradient are very well described by the theoretical model. Hence the simple theoretical approach that we present gives a good understanding of the intricate problem of the ele ctroconvective, diffusive, and drift motion of the ions. To our knowle dge, an electrodeposition model which incorporates these three aspects has not been published previously.