Surface Diffusion Processes and Dendritic Growth in the Electrodeposition of Silver from Molten Halides

Abstract

Studies of the rise time of the cathodic overpotential during galvanostatic pulsing of silver electrodes in molten AgC1-LiC1-KC1 mixtures at 450°C show that the mechanism of electrodeposition from fused salts includes a step for surface diffusion of adatoms from point of deposition to growth sites on the metal surface. The concentration of adatoms on the surface at equilibrium and the surface diffusion rate have been determined and are compared to those found in aqueous electrolyte solutions at 25°C The formation of dendritic deposits of silver is found to occur only when a concentration gradient equivalent to 4 mv polarization is produced. Destruction of this gradient through the use of a high concentration of silver chloride and convection reduces the concentration polarization and leads to the formation of coherent deposits. Studies of the dendrites produced by electrodeposition show that they all contain two parallel twin planes and indicate that nucleation and growth in these dendrites occur by the twin plane re-entrant edge mechanism previously shown to occur in the growth of germanium dendrites from the supercooled liquid. © 1966, The Electrochemical Society, Inc. All rights reserved.