[en] Nickel powder was coated with aluminum nitrate solution to increase the thermal stability of a porous nickel support and control the nickel content in the Pd-Cu-Ni ternary alloyed membrane. Raw nickel powder and alumina coated nickel powder were uniaxialy pressed by home made press with metal cylindrical mold. Though the used nickel powder prepared by pulsed wire evaporation (PWE) method has a good thermal stability, the porous nickel support was too much sintered and the pores of porous nickel support was plugged at high temperature (over 800 .deg. C) making it not suitable for the porous support of a palladium based composite membrane. In order to overcome this problem, the nickel powder was coated by alumina and alumina modified porous nickel support resists up to 1000 .deg. C without pore destruction. Furthermore, the compositions of Pd-Cu-Ni ternary alloy membrane prepared by magnetron sputtering and Cu-reflow could be controlled by not only Cu-reflow temperature but also alumina coating amount. SEM analysis and mercury porosimeter analysis evidenced that the alumina coated on the surface of nickel powder interrupted nickel sintering

No abstract available

[en] The decrease of the ¹⁵¹Eu isomer shift on hydrogenation of a dilute EuPd (2,5 at % Eu) alloy is discussed in terms of the volume effect on the charge density at the nucleus

[en] Membrane catalysts are considered made of palladium alloys which are highly active in the processes of hydrogenation, dehydrogenation, hydrodealkylation, and dehydrocyclization. In the process of cyclohexane dehydrogenation, an alloy of palladium with 5% of nickel is more active than palladium and an alloy with 10% of nickel is less active than palladium. With increasing content of ruthenium in an alloy with palladium from 1 to 10%, catalytic activity towards the same reaction has a maximum corresponding to an alloy with 8.36% of ruthenium. An alloy of palladium with 6% of ruthenium is more penetrable for hydrogen than palladium. Alloys containing from 6 to 9% of ruthenium have improved mechanical properties as compared with palladium which makes it possible to decrease the thickness of the membrane catalysts without a strength loss at high temperatures. Palladium-ruthenium and palladium-rhodium alloys are active catalysts in transforming normal paraffins into aromatic hydrocabons. Unlike many other catalysts, palladium-based alloys are more active after rapid cooling down from'700 deg C

[en] The specific heat of PdDy alloys between 1.2 and 20 K in external fields ranging from 0 to 20 kOe was measured. The data are analyzed with respect to the crystal field splitting CFS of the Dy-ion in a cubic symmetry. Previously, different crystal field level schemes had been proposed for this system based upon the interpretation of EPR, magnetization and specific heat measurements. The application of a straightforward CFS analysis still shows systematic deviations from our experimental data. Some different CFS possibilities are presented here, which, when combined with a weak internal field, form a reasonable description for the specific heat data

[en] A possibility of hydrogenation of a single double bond in cyclopentadiene in the presence of membrane catalysts penetrated only by hydrogen is elucidated. The hydrogenation was studied for palladium-ruthenium (4.36 and 9.78 mass %Ru) and palladium-rhodium (2.0 and 5.0 %Rh) alloys. The Pd-Rh (5%) alloy was less active: it provided hydrogenation only above 106 deg, and even at 240 deg the quantity of unreacted cyclopentadiene was 28%. Selectivity, however, exceeds 0.96%. The experimental activation energies of hydrogenation of cyclopentadiene into cyclopentene were 9 and 5 kcal/mole for palladium-ruthenium and palladium-rhodium alloys respectively. The membrane palladium alloy catalysts investigated provide high selectivity of cyclopentadiene-to-cyclopentene conversion avoiding elevated hydrogen pressure and temperature, as well as the use of poisons as in the case of other catalysts. High selectivity may be explained by hydrogen entering the hydrogenation zone through the membrane catalyst. One may thus preset a hydrogen superficial concentration

No abstract available

[en] Short note

[en] Hydrogen permeation through metallic membranes is an industrial process used for purification purposes. Palladium-based alloys are generally used as permeation materials at operating temperatures above the critical value so that the metal-H system remains monophasic and that diffusion proceeds at sufficient rate. In state of the art systems, metallic membranes with typical thickness of a few tens of microns are used and rate limitation are generally attributed to atomic H transport by diffusion. Because of cost considerations, it is necessary to reduce the thickness of these membranes. In the micron thick range, surface contributions are expected to become rate determining, or at least to play an increasing role. Further, when the membrane is used on the exit side of a gas reformer to directly extract hydrogen, corrosion problems are expected to occur on the upstream side of the membrane. For all these reasons, there is a need to separately measure surface and bulk (diffusion) rate contributions to the overall permeation flux. A new experimental equipment has been specifically designed for this purpose. This setup can be operated in two different modes: for sorption or permeation experiments. In a typical sorption experiment, the metallic membrane is disposed in the reaction chamber and hydrogen is allowed to react from both side of the surface. This procedure allows the separate measurement of surface absorption and desorption resistances associated with the chemisorption step. In a typical permeation experiment, the membrane is mounted between two volume chambers, a pressurized hydrogen source reservoir and an empty sink reservoir. Initially, a difference of pressure is set between the two reservoirs. When the valve of the source tank is opened, H₂(g) flows to the membrane and permeation proceeds until pressure reaches an equilibrium value. In both experimental configurations, gas pressure transients are synchronously sampled all along the experiment. Impedances of the sorbing (permeating) membrane materials are then calculated using the theory of linear and time-invariant systems, by numerically Fourier-transforming the discretely sampled pressure signals. Using appropriate initial and boundary conditions, it is shown that the rate constants of the two major steps of the sorption (permeation) mechanisms can be separately accessed, i.e. surface resistances related to hydrogen dissociation (upstream side) and recombination (downstream side) processes, and bulk diffusion impedance. This experimental equipment and this treatment procedure therefore provide a new tool for analyzing the dynamics of hydrogen permeation across metallic membranes. This tool can be used for diagnosis purposes and for optimizing the structure and composition of permeation membranes. Results obtained with Pd and Pd₇₇Ag₂₃ foils are presented and discussed. (authors)

[en] The concentration of hydrogen in a fluid mixture is controlled to a desired concentration by flowing the fluid through one chamber of a diffusion cell separated into two chambers by a hydrogen permeable membrane. A gradient of hydrogen partial pressure is maintained across the membrane to cause diffusion of hydrogen through the membrane to maintain the concentration of hydrogen in the fluid mixture at the predetermined level. The invention has particular utility for the purpose of injecting into and/or separating hydrogen from the reactor coolant of a nuclear reactor system