On the Morphology of Zinc Electrodeposition from Alkaline Solutions

The morphology of zinc electrodeposition was investigated from alkaline zincate solutions on single grains of known orientation in polycrystalline zinc electrodes under potentiostatic control. The effect of overpotential, solution composition, and substrate orientation were examined. The deposition morphology was observed with a scanning electron microscope. It was found possible to disrupt the deposition repeatedly for microscopic observation, and then continue deposition. At low overpotential (50 mV) epitaxial layer type growth was observed; the width of the macrosteps increased linearly with time. A theory explaining the linear step widening is proposed, which can also account for the observed effect of substrate orientation. At 100 mV, "boulders" were observed, not all of which were epitaxial with the substrate. They are suggested to be originated by nucleation. The boulder density per cm 2 is first sharply increasing, then slowly decreasing with time. A statistical calculation for this is given, based on the model that large boulders consume the smaller ones. With further deposition a small fraction ( ca. 0.1%) of the boulders develop into dendrites, their number being limited by the available total current. Experiments were carried out to differentiate between over‐potential and current control of morphology; overpotential was found to be the critical variable.