Unsupported PtRu alloy powders of a wide range of compositions were prepared at low temperatures by carefully adjusting the preparation procedure. PtRu alloys of essentially the same surface, nominal and bulk composition, were formed up to ca. 46 atom % Ru content. Adsorbed CO stripping voltammetry and CH 3 OH oxidation characteristics, namely, i-V curves and pseudo-steadystate current density values recorded at constant potentials, were the same as reported for corresponding bulk alloys, suggesting that the electrocatalytic activities of the powders can be compared to bulk alloys. CH 3 OH oxidation activities obtained for PtRu alloy, Pt, and Ru powders showed the PtRu alloy of 70:30 atom % Pt:Ru composition to exhibit the highest activity independent of the temperature and potential tested ͑0.3 and 0.4 V vs. a reversible hydrogen electrode͒. The experimental pseudo-steady-state current density values for the CH 3 OH oxidation reaction were found to show the same dependence on Ru content as theoretical values calculated assuming that an assembly of three neighboring Pt and one Ru site are involved in the oxidation of a CH 3 OH molecule.

Crystals of the three Bi-based cuprates of general formula Bi2Sr2Ca, -&Cu"O~with n 1, 2, and 3 have been isolated and their structural and physical properties investigated. The structures are similar, diR'ering only in the number of Cu02-Ca-Cu02 slabs packed along the c axis. The insertion of one and two slabs increases c from 24.6 to 30.6 and 37.1 A. Transmission electron microscopy shows there are stacking faults within the crystals in agreement with our x-ray data and its analysis. Resistivity, ac susceptibility, and dc magnetization measurements demonstrate superconductivity in the n 1, 2, and 3 phases at 10, 85, and 110 K, respectively. The observed transition temperatures and the stacking fault densities are dependent upon sample processing, in particular, the annealing temperatures and cooling rates. The transition temperature is, within the accuracy of our chemical titration, independent of the average copper valency that was determined to be 2.15+'0.03 for each of the three compounds.

Superconducting critical transitions with an onset at 112 K and zero resistance at 107 K are obtained within the Bi-Sr-Ca-Cu-0 system. The synthesis and formation of the 110-K superconducting phase using the 85-K material as a precursor is explained. The 110-K phase grows from the 85-K phase such that the resulting faceted crystal (a pseudomorph)

Effect of particle size on the flocculation behaviour of ultra-fine clays in salt solutions Kotlyar, L. S.; Sparks, B. D.; LePage, Y.; Woods, J. R.

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