Transport modes were determined from examinations of morphology for electrochemical oxidation and reduction within electrodes consisting of beds of silver spheres 37.2 μm in diameter in 1NnormalKCl and subjected to 5.0 mA cm−2 applied current density. Oxidation proceeded via silver dissolution, probably at dislocation sites, followed by diffusion and, then, deposition of normalAgCl in characteristic, bulbed mounds which grow together to form layers of approximately uniform thickness. normalAgCl film thickness, for the case of partially covered underlying silver, was about 3500Aå and distance from silver dissolution pits to normalAgCl deposition sites was found to be increased from 4,000 to 40.000Aå as the local transfer current density became larger within the sphere bed. Reduction of anodically formed normalAgCl on partially covered silver proceeded by an opposite path: solution and diffusion of normalAgCl , and deposition of silver on preferred sites of surrounding bare silver surface.

Elementary processes for the reduction of thin films of silver chloride on silver have been investigated using rotating disk techniques. Experiments were carried out in i, 2, and 4N solutions of KCI. The effective diffusion coefficients of the prevalent species of silver ion in 2 and 4N KCl are about 1.42 and 0.31 X 10 -5 em2/sec, respectively. Reduction of thin AgCl films on Ag can be carried out at high rates, 100-200 mA/cm 2 at 300 mV overpotential, two orders of magnitude higher than that for the reduction of dissolved AgCI from bulk solution at 2000 rpm. A linear i ----l] relationship and its independence of the state of charge suggest that liquid phase transport occurs, possibly followed by a rate controlling process of surface diffusion.The silver/silver chloride electrode is an example of the class of battery electrodes which consists of a dispersed, sparingly soluble reactant within a continuous, conductive matrix. Electrodes of this class have a structure which is repeatedly encountered in practical batteries. Recent theoretical studies (1, 2) have indicated that a great variety of current density distributions may exist in such systems, e.g., exhibiting maxima and/or minima in the discharge profile, depending on local conditions governing mass and charge transfer. Identification and evaluation of local conditions during electrode charge or discharge are consequently necessary not only for more accurate assessment of electrode behavior in terms of the developing theory, founded on firm experimental bases and corresponding closely to reality, but also to help ascertain conditions of the recently predicted current distributions. The present work on the reaction paths of reduction at silver/silver chloride electrodes was accordingly undertaken to provide information that may be of use in interpreting behavior of electrodes in this important class. Summary of Reaction PathsSparingly soluble reactants.--In general, the proc-

The discharge reaction taking place within the confinement of an experimental analog, simulating porous electrode behavior, is examined in terms of the solution-precipitation path for the Zn-KOH system. A scanning electron microscopic (SEM) investigation, combined with an analytical treatment of a simplified model of nucleation and growth processes, provided a connection between the shape of individual crystaUites and the form of the duplex oxide film. It was shown that the coupling between the growth kinetics and local transport is instrumental in the development of observed morphologies.

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