Effect of nucleation mode on the morphology and texture of electrodeposited zinc

The effect of temperature, pH and current density on the morphology and texture of electrodeposited zinc on mechanically polished steel was studied. The electrodeposited zinc had mostly basal (0 0 0 2) and low angle planes (1014, 1013, 1012) parallel to the surface. At pH 2, increasing overvoltage (i.e., increasing current density or decreasing temperature) reduced the percentage of basal plane and increased the percentage of low angle planes parallel to the substrate surface. Increasing overvoltage decreased the zinc crystal size. At pH 4, increasing current density increased the percentage of both basal and low angle planes parallel to the surface, but increased the zinc crystal size. This variation of behaviour at pH 4 was explained by a change in nucleation mode due to hydroxide adsorption. The nucleation mode was determined by comparing dimensionless (i/i(m))(2) vs (t/t(m)) potentiostatic current-time transient graphs with models for instantaneous and progressive nucleation. It was shown that at pH 2, instantaneous nucleation was predominant, whereas at pH 4, it was close to progressive.