Ionic Mass‐Transfer Rates Associated with Natural Convection along a Plane Vertical Anode Measured by Two‐Wavelength Holographic Interferometry

Abstract

Two‐wavelength holographic interferometry was applied to measure simultaneously the concentration profiles of and ions near a plane vertical anode placed in an unstirred 0.05 M ‐1.85 M aqueous solution. The measurement was carried out at a low current density, under which a uniform current density distribution along the vertical anode was assured. The measured concentration profiles were similar to those arising from cathodic natural convection, when the difference in the flow direction was taken into account. As long as the electrode surface is flat and no precipitation of copper sulfate is observed, a nondimensional cathodic correlation based on boundary layer theory can be reasonably applied to anodic natural convection. Moreover, the addition of excess resulted in a larger concentration gradient of ion at the anode surface, which compensated for the negligible contribution of migration to the ionic mass‐transfer rate.