Hydrodynamic effects on the macromorphology of electrodeposited zinc and flow visualization: The rotating disk electrode

Abstract

The macromorphological features of electrodeposited zinc on a rotating disk electrode (RDE) that result from hydrodynamic flow conditions have been investigated using acidic chloride solutions (mainly 1.0 M ZnCl 2 +HCl) for the current density range 0.2 mA cm −2 to 3 A cm −2 and particularly between 10 and 30 mA cm −2. All the complex hydrodynamic characteristics of the reattaching flow and the presence of streamwise-directed counter-rotating Taylor vortices originating from the stagnation point have been clearly outlined and marked by the macromorphology of three-dimensional relief imprints. The macromorphological features of relief spirals in zinc electrodeposition represent mainly the competition between the flow- and electric-field strength and depend on the average current density, the rotation speed, the time of deposition, the ionic zinc content, the electrolyte composition, the pH value and the local hydrodynamic flow pattern. The time sequences at constant average current density and rotation speed afford the visual photoimprints of the secondary convection development near the RDE with all the characteristics of a stable Taylor vortex system envisaged by almost perfect relief equiangular (logarithmic) spirals in the electrodeposit. The macromorphological imprints of electrodeposited zinc within a certain current density range can be employed for both the instantaneous and the cumulative (time sequence of photoimprints) electrochemical visualization method. A survey of the existing knowledge and past explanations for corrugated electrodeposit growth is also presented.