The Effect of Lead Ions on the Dissolution and Deposition Characteristics of a Zinc Single Crystal in 6N KOH

Dissolution of the basal plane of single crystal zinc and deposition of zinc on the same material in alkaline solutions in the presence of 10 −4 M lead ion, has been studied using in situ microscopy and the scanning electron microscope (SEM). It was found that in the presence of lead ions, most of the surface was protected against dissolution when polarized as much as 100 mV positive to the rest potential. Dissolution occurs initially in the form of a limited number of hexagonal etch pits that grow in size and number with time. The pits appear to correspond to sites of macroscopic crystalline imperfection. In the absence of Pb ions, deposition of Zn on the basal plane of a zinc crystal tends toward epitaxial growth at low overpotentials. In the presence of Pb ions, at both high and low overpotentials, Zn deposition tends to initiate mainly at the few sites not protected by the microscopically smooth Pb film. At high overpotentials, growth tends to be cylindrical and microcrystalline, rather than dendritic. It is shown that, under the present conditions, no increase in the cathodic current is to be expected with increase of time.