The adsorption of hydrogen on the three main faces (100), (111), and (110) of platinum single crystal electrodes has been studied in 8N H2SO4 at different temperatures with the voltage sweep method. As on polycrystalline platinum electrodes, hydrogen adsorbs on each of the faces in two distinctly different binding states which present themselves as two pronounced maxima in the current‐voltage sweep curves. There are indications for a third binding state giving rise to a third, less pronounced maximum. The potentials at which the maxima occur are essentially the same for polycrystalline and for each of the three single crystal electrodes. However, the relative heights of the maxima are different in each case. The adsorption isotherms and the heats of adsorption are also notably different on the three faces. Under the usual assumption of one hydrogen atom adsorbed per platinum surface atom, initial roughness factors of 1.0–1.9 result which increase to 1.9–2.4 during the experiments. The results suggest that, in fact, each of the crystal faces exposes more than one crystal plane. The left pronounced maximum is assigned to a (110) plane, the right pronounced maximum to a (100) plane, and the third small maximum to a (111) plane. Different proportions of these planes determine the different shape of the curves obtained on the different nominal faces and on polycrystalline electrodes.

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X-ray radiography coupled with high resolution optical densitometry, as well as optical and scanning electron microscopy, was employedto study the effect of pivotal zinc deposition parameters on thezinc morphology within a porous C foam electrode. Deposition was carried out in zinc-bromine and zinc-zinc cells with circulating electrolyte. Results on the effects of flow rate, substrate thickness, current density, and electrolyte composition on zinc distribution in the substrate and on its surface are described. This study has shown that in the absence of organic inhibitors, very nonuniform zinc deposition occurs within the porous electrode. This zinc deposition corresponds to the nonuniform primary current distribution dominated by ohmic resistance. This study has led to the conclusions that high electrolyte flow rates, moderate current densities, and thick foams all aid in producing increasingly uniform zinc deposits. The most beneficial effects on the zinc morphology, however, were obtained by adding to the electrolyte a dendrite inhibitor-solubilizer combination consisting of certain fluorosurfactants and butyrolactone.

A m ( c r a m roc 75 121 295-5Oi (1992) The electrical conductivity of high-purity single-crystal alumina is determined in a temperature range from 400" to 1300°C. By applying an advanced fully guarded threeterminal measurement technique, reliable conductivity measurements are performed to as low as R-'*cm-'. Gas and surface conduction are measured separately and shown to be negligible. High-purity sapphire exhibits a conductivity of W' ocm-' at 400"C, two characteristic activation energies of 0.4 and 4.8 eV with increasing temperature, and a conductivity of 3 X lo-' W'-cm-' at 1300°C. The fraction of the current carried by ions is determined by electron probe analysis of the electrodes following a 640-h transference test at 1200°C with 4 kV/cm field applied. Only 0.3% of the current at 1200°C is carried by ions. A mathematical model of electrical conduction in sapphire is developed which describes sapphire as a wide-bandgap semiconductor, doped with one dominant donor and one dominant acceptor. The observed conductivity is well described by the model over the entire temperature range from 400" to 1300°C. [

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