Hydrodynamic effects of hydrophilic ‘Alconox’ surfactant on the macromorphology of electrodeposited zinc and flow visualization

Abstract

The macromorphological properties of electrodeposited zinc that result from hydrodynamic flow conditions on a rotating-disk electrode (RDE) and along a flat plate electrode (FPE) embedded in a channel flow cell (the mutual effects of the flow and electric fields and the interfacial tension change imposed by the adsorption of a moderately strong commercial (Alconox) surfactant) have been investigated using acidic zinc chloride solutions in the current density range 10–50 mA cm −2. All the complex hydrodynamic characteristics of the re-attaching flow and the presence of streamwise-directed counter-rotating Taylor vortices behind the stagnation point and separation, together with stabilized stream features in an admixture of Liqui-Nox surfactant, are clearly delineated by the macromorphology of three-dimensional relief imprints. The macromorphological properties of relief striations in zinc electrodeposition mainly represent the competition between teh flow and electric fields and depend on the average current density, the rotation speed (RDE) and/or the linear flow velocity (FPE), the time of deposition, the ionic zinc content, the electrolyte composition, the pH value, the hydrodynamic flow pattern and the hydrodynamic effects of surfactants. The last of these is reflected in both the stabilization of systematic disturbances and perturbations within the boundary layer, and the interfacial surface tension traction (the flow-field throw). The macromorphological imprints of electrodeposited zinc within a certain current density range could be employed for both the instantaneous and cumulative (time sequence of photoimprints) electrochemical visualization method. The hydrodynamic effect of Alconox surfactant has been compared with contributions from stronger (DuPont fluorosurfactant) and weaker (glycerol) surface-active agents, as well as with the macromorphological features obtained in surfactant-free zinc chloride solutions under the same electrodeposition conditions. The hydrophilic wetting effect of Liqui-Nox surfactant on the macromorphology of zinc deposits is emphasized.