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Several metal hydrides were shown to act as chromatographic media for hydrogen isotopes. The procedure was to equilibrate a column of hydride with flowing hydrogen, inject a small quantity of tritium tracer, and observe its elution behavior. Characteristic retention times were found. From these and the extent of widening of the tritium band, the heights equivalent to a theoretical plate could be calculated. Values of around 1 cm were obtained. The following are the metals whose hydrides were studied, together with the temperature ranges in which chromatographic behavior was observed: vanadium, 0 to 70°C; zirconium, 500 to 600°C; LaNi5, -78 to +30°C; Mg2Ni, 300 to 375°C; palladium, 0 to 70°C. A dual-temperature isotope separation process based on hydride chromatography was demonstrated. In this, a column was caused to cycle between two temperatures while being supplied with a constant stream of tritium-traced hydrogen. Each half-cycle was continued until ''breakthrough, '' i.e., until the tritium concentration in the effluent was the same as that in the feed. Up to that point, the effluent was enriched or depleted in tritium, by up to 20%.
Studying the interactions between heavy hydrogen isotopes and hydride forming metals or intermetallic compounds (IMC) is of importance for both fundamental and applied sciences. These systems offer, for example, the possibility of technical hydrogen isotope separation due to their considerable isotope effects. In addition, quite a lot of problems of hydrogen recovery, hydrogen purification, and tritium storage can be solved. This review deals with theoretical aspects of the interaction of heavy hydrogen isotopes with metals and IMC, and contains detailed information on phase and isotopic equilibrium and of the kinetics of isotope exchange in systems with hydride phases. Numerical data and results from theoretical and experimental studies are presented as well.
Hydrogen isotope exchange kinetics of Pd/k was tested in laboratory scale columns to help troubleshoot the HT-TCAP performance problem. The main objective was to evaluate the effects of old and new Pd/k, column diameter, and metal foam on hydrogen isotope exchange efficiency. This efficiency affects the separation performance of the TCAP column. Three kinds of columns were used in the tests: (1) 3/4 inch pipe, 6 inch long, U-shape column. This column was used because it was readily available due to a completed PDRD project. This group of tests compared new Pd/k and old Pd/k, and produced a bake-out recipe for new Pd/k. (2) 3-ft long columns of various diameters: 3/4 inch, 1.25 inch and 2 inch with and without foam (aluminum and copper). This group of tests compared the effect of diameter, foam and Pd/k on staging performance. (3) The Jacobs coil, an existing 20-ft coil filled with Al foam identical to HT-TCAP. This group of tests was to see how a plant-type column performed. The following methods and computer programs were developed to help evaluate the test data: (1) An equation and a visual basic program for calculating response curves to step changes in inert feed concentration. (2) A finite difference method and a visual basic program for calculating response curves to step changes in hydrogen isotope concentration. (3) A finite difference method and a visual basic program for calculating response curves to pulse changes in hydrogen isotope concentration. The pulse response test and calculation were found most useful for comparing the isotope exchange performance of Pd/k packed columns. Increasing column diameter from 1.25 inch to 2 inch reduced the number of equilibrium stages by about 40 percent. Aluminum foam and copper foam did not reduce the number of stages. The new Pd/k required much more bake-out and absorption/desorption cycles before it could reach the same exchange kinetics as the old Pd/k.
A column packed with pellets of copper plated LaNi{sub 4.25}Al{sub 0.75} has been evaluated for its separation efficiency using a displacement method. Deuterium breakthrough curves were produced experimentally and compared with those calculated with a stage model. The height equivalent to a theoretical plate was attained and its dependence on temperature and gas flow rate was established. 6 refs., 4 figs.
Porous solids such as activated alumina, silica and molecular sieves generally contain significant amounts of hydrogen atoms in the form of H2O or OH even at high temperature and low humidity environment. A significant amount of this hydrogen is available for reversible isotopic exchange. This exchange reaction is slow under normal conditions and does not render itself to practical applications. But if the exchange kinetics is improved this reaction has the potential to be used for tritium removal from gas streams or for hydrogen isotopic separation. The use of catalysts to improve the exchange kinetics between hydrogen isotope in the gas phase and that in the solid phase was investigated. Granules of alumina, silica and molecular sieve were coated with platinum or palladium as the catalyst. The granules were packed in a 2-cm diameter column for isotope exchange tests. Gas streams containing different concentrations of deuterium in nitrogen or argon were fed through the protium saturated column. Isotope concentration in column effluent was monitored to generate isotope break-through curves. The curves were analyzed to produce information on the kinetics and capacity of the material. The results showed that all materials tested provided some extent of isotope exchange but some were superior both in kinetics and capacity. This paper will present the test results.
This report describes the Spherical Particle Exchange Model (SPEM), which simulates exchange of one hydrogen isotope by another hydrogen isotope in a spherical metal hydride particle. This is one of the fundamental physical processes during isotope exchange in a bed of spherical metal particles and is thus one of the key components in any comprehensive physics-based model of exchange. There are two important physical processes in the model. One is the entropy of mixing between the two isotopes; the entropy of mixing is increased by having both isotopes randomly placed at interstitial sites on the lattice and thus impedes the exchange process. The other physical process is the elastic interaction between isotope atoms on the lattice. The elastic interaction is the cause for [beta]-phase formation and is independent of the isotope species. In this report the coupled diffusion equations for two isotopes in the [beta]-phase hydride are solved. A key concept is that the diffusion of one isotope depends not only on its concentration gradient, but also on the concentration gradient of the other isotope. Diffusion rate constants and the chemical potentials for deuterium and hydrogen in the [beta]-phase hydride are reviewed because these quantities are essential for an accurate model of the diffusion process. Finally, a summary of some of the predictions from the SPEM model are provided.
This is the very first book that offers an up-to-date and comprehensive overview on deuteride. It not only includes the concept, existing forms, key characteristics, but also reviews the preparation and characterization technologies and the latest research developments of deuteride. The special properties such as the nuclear properties, isotropic and neutron effect, poisonousness, radioactivity, volume expansion are systematically discussed to build up the sound understanding of the materials. In particular, this work reviews a number of commercial and scientific uses of the materials including nuclear reactors, NMR spectroscopy and medicines. Researchers and industrial professionals in medicine, chemistry, biochemistry, environmental sciences and defense sciences will benefit from this work.