In this study, mainly two sets of experiments were carried out to obtain a better understanding of the tendency of the alkaline zinc electrode to passivate. Either photomicrographs of the electrode surface were taken in‐situ at different potentials during an anodic voltage sweep or the two components of the electrode impedance were measured with a small signal of superimposed 1000 Hz A.C. The course of the passivation was found to depend strongly on the convective conditions in the electrolyte near the zinc electrode. The conditions for the formation of two different types of solid films have been defined and their effects on the current‐potential curve have been determined. Type I film is white, loose, and flocculent. It forms in the absence of convection by precipitation from a supersaturated layer of zincate near the surface. When the conditions for supersaturation are largely removed by stirring, the formation of the type II film can be observed. The latter is more compact and appears to form directly at the surface rather than by precipitation. Its color can range from light gray to black depending on the potential and time of formation. The type II film is considered responsible for the transition from the active to the passive state of zinc in alkaline solution.

Mechanical relaxation measurements are used extensively to obtain information on the diffusion rate of interstitial solute atoms in body-centered cubic metals. Such studies have been stimulated by a model, developed by J. L. Snoek, which yielded a relationship between a relaxation time, an experimental parameter, and the diffusion coefficient of the solute atom. Although Snoek's model was confirmed very well for solid solutions of carbon or nitrogen in α-iron, a number of anomalies were observed when relaxation studies were extended to the group V transition metals. An extensive experimental study has been made of the factors that influence relaxation times. The anomalous behavior of the group VA metals can be accommodated within the framework of Snoek's model by taking account of the specific nature of solid solutions based on these metals. Diffusion data obtained by a variety of relaxation techniques are presented for oxygen, nitrogen, and carbon in vanadium, niobium (columbium), and tantalum. These data are in agreement with those obtained by the more conventional concentration gradient techniques in the few instances where such information is available. The pattern of activation energies suggest that lattice strain considerations alone are insufficient to explain the activation process involved in interstitial diffusion.

The duplex structure of anodic films formed in concentrated KOH solutions with convection nearly absent--a hydrodynamic condition present near a hattery plate in proximity to a separator--has been confirmed on high-purity polycrystalline zinc and to a more limited extent on some polycrystalline zinc alloys as well Previously, the use of a very slow potential scan with simultaneous microscopic observation of single-crystal zinc electrodes showed that a precipitated coating of ZnO particles (type I film) overlies a more coherent film also of ZnO (type II). The experimental conditions required for following stages in the formation of the precipitated film, the one most difficult to observe, are defined more explicitly in this paper. Evidence is presented that the type II film serves as a catalyst for hydrogen evolution at potentials anodic to the zinc/zinc oxide equilibrium value. Hydrogen bubbles, whose formation is so catalyzed, can mechanically dislodge overlying passivating film to cause reactivation of the electrode. The presence of complex tin or lead anions at concentrations about 10-3M (molar) in KOH solutions gives rise to very smooth, almost imperceptible, films of metallic tin or lead over the zinc electrode surface. Such films are made visible, though, during zinc dissolution as they rumple and eventually gather into a wad after being undercut. These foreign metal films inhibit the dissolution of zinc to an extent that depends on the particular complex anion, its concentration, and exposure time to the zinc surface. Lead films can be made sufficiently inhibitive that zinc dissolution is reduced 'to such a rate that very little precipitation of ZnO occurs.

When a zinc anode in a strongly alkaline electrolyte is observed under a microscope, two different films can be noted under appropriate conditions. Although both have been identified as zinc oxide, type I is white and forms by precipitation from a supersaturated layer of electrolyte covering the electrode. Type II , on the other hand, seems to form directly on the electrode surface. Its color can range from light gray to black. During dissolution of the type II film, entities appear which resemble spiderwebs under the microscope. These so‐called cobwebs seem to form by the gathering together of the darkening agent in this film. They are mainly zinc, are electronically conducting, and can be oxidized. Cobwebs appear to have a relationship to the hydrogen evolution that occurs at potentials anodic to the zinc rest potential. They are important, in addition, because during subsequent electrodeposition they accelerate the formation of spongy zinc at low cathodic potentials and of dendritic zinc at higher ones.

A procedure is described in this paper for distinguishing in the measured electrical properties of polycrystalline ~-alumina, the separate contributions of the grain boundaries and of the crystal, i.e., the grain interiors. This separation is brought about through the use of a model for these properties. Certain quantitative consequences of the model are developed and compared with experimental results. For most sintered ~-alumina ceramic, the electrical properties are determined more by the characteristics of the grain boundaries than by those of the interior of the grains.Polycrystalline E-alumina is used in electrochemical devices to circumvent the deleterious high anisotropy in the electrical and mechanical properties of single crystals. Use of the polycrystalline ceramic does require, however, consideration of the effects of grain boundaries. A procedure is described here for distinguishing in the measured electrical properties of the ceramic, the separate contributions of the grain boundaries and of the crystal, i.e., the interior of the grains. This separation is brought about through the use of a model for the electrical properties of p-alumina. Certain quantitative consequences of this model are developed and compared with experimental results. Previous WorkThe conductivity both of /%alumina :single crystals and of polycrystalline ceramic has already received very considerable attention (1-15). Weber and Kummer reported that E-alumina exhibits high ionic conductivity, but no electronic conductivity (1). The ionic conductivity is due to the high mobility of sodium ions in planes perpendicular to the c-axis of the hexagonal structure. However, there is no conductivity parallel to the c-axis. They reported singlecrystal specific resistivity values of 30 and 3.5 ohm-cm at room temperature and 300~ respectively. Comparable values for polycrystalline ceramic prepared from single-crystal material was 25,0 and 18 ohm-cm. They attributed the difference to interface resistivity between the crystals of the polycrystalline material. The activation energy associated with the resistivity of single crystals was given as 3.8 kcal/mole (2).Imai and Harata, on observing that the activation energy associated with conduction in sintered /~-alumina was considerably larger than for single crystals, concluded that the conductivity of ceramic is governed by grain boundary conduction (4).Jones and Miles found that the Arrhenius ~olot curved significantly below 200~ (5). Another activated process with a higher activation energy controlled the conductivity at lower temperatures. These authors speculated that this process was grain boundary contact resistance.Whittingham and Huggins measured the conductivity of a single crys,tal from --150~ to 820~ (8).They found plots of log ~T to be linear in 1/T over this entire temperature interval. The conductivity was found to be 72 ohm-cm at 25~ The activation energy was 3.79 kcal/mole. They reported the conductivity to be sensitive to the presence of moisture below 5,0~ Imai and Harata repo...