Journal of the Less Common Metals (J Less Common Met)

Publisher: Elsevier

Current impact factor: 2.73

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Website Journal of the Less-Common Metals website
Other titles Journal of the less-common metals, Journal of the less common metals
ISSN 0022-5088
OCLC 1782919
Material type Periodical, Internet resource
Document type Journal / Magazine / Newspaper, Internet Resource

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Elsevier

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    • Publisher last reviewed on 03/06/2015
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Publications in this journal

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    [Show abstract] [Hide abstract]
    ABSTRACT: The problem of bonding in actinide solids has been approached through the establishment of semi-theoretical correlations between thermodynamic and structural properties and the degree of participation to the bond of the different electronic orbitals of the actinide atom. The first part of the chapter is devoted to an analysis of these correlations, as well as to the presentation of the most important experimental results. In a second part the following stage of development is reviewed, i.e. the introduction of more quantitative theories mostly based on bond structure calculations. These theories are given a thermodynamic form (equation of states at zero temperature), and explain the typical behaviour of such ground state properties as cohesive energies, atomic volumes, and bulk moduli across the series. They employ in their simplest form the Friedel model extended from the d- to the 5 f-itinerant state. The Mott transition (between plutonium and americium metals) finds a good justification within this frame. In actinide binary compounds an equation of state can also be developed on the same lines. The difference in electronegativity of the actinide and the non-actinide element plays an important role, determining the degree of mixing between the actinide orbitals (5 f and 6 d) and the orbitals of the ligand. A mixture of metallic, ionic and covalent bond is then encountered. In the chapter, two classes of actinide compounds are reviewed: NaCl-structure pnictides or chalcogenides, and oxides. In oxides a large departure from the stoichiometric composition is usually met. The importance of this phenomenon, also for the understanding of the oxide bond, is highlighted at the end of the chapter.
    Preview · Chapter · Aug 2007
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    ABSTRACT: A combination of anion exchange separation, electrolytic extraction, floating zone refining and dry hydrogen treatment was used to purify cobalt. The effectiveness of each purification process was confirmed by measurements of the residual resistivity ratio (RRR) and activation analyses. Proton activation analysis revealed that all the main metallic impurities except iron were effectively removed by a combination of these processes. The effective removal of oxygen, nitrogen and carbon by dry hydrogen treatment was confirmed by activation analyses using 3He ion beams, proton beams and γ rays. It was found that the rate-controlling step in the decarburization process was a surface reaction. The maximum RRR obtained for the purified specimen was 334, which is higher than previously reported values.
    No preview · Article · Jan 2002 · Journal of the Less Common Metals
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    ABSTRACT: The PtGaAs solid state equilibrium phase diagram was determined at 600 °C with the use of X-ray powder diffraction, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). No ternary PtGaAs phases were found and limited solid solubility was measured in the constituent binary PtGa and PtAs compounds. GaAs, PtGa and PtAs2 form a region of three-phase equilibrium which dominates the GaAs side of the phase diagram. The phase diagram is in agreement with previous observations that PtGa and PtAs2 are the stable phases when platinum thin films are reacted to completion on GaAs.
    No preview · Article · Jan 1993 · Journal of the Less Common Metals
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    ABSTRACT: The electrochemical behaviour of hexavalent uranium is reported in various organic solvents at room temperature and also in hexamethylphosphoramide, dimethylsulphone, sulpholane between 310 and 400 K. The reduction of UO22+ proceeds in two steps, leading to tetravalent uranium. Depending on the solvent acidity, the tetravalent species is either soluble or precipitates as UO2(cr). Numerous additional kinetic phenomena are evidenced in all the reactions.Special attention is paid to the deposition of UO2(cr) in macroscopic quantities.
    No preview · Article · Jul 1992 · Journal of the Less Common Metals
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    ABSTRACT: V-20Ti samples heat treated in an H2 atmosphere at about 1000 mbar for differenttimes were inspected by transmission electron microscopy for the occurrence of hydrides. Hydriding between 500 and 600°C leads to thin plates of a b.c.t. hydride presumably identical to the ε phase in the work of Hagi et al. Hydriding between 650 and 700°C produces a b.c.c. hydride with a unit cell approximately 7% larger than that of the matrix. This hydride is richer in titanium than the matrix and may be identified as Hagi et al.'s β phase. Hydriding at 750°C did not produce any hydrides or phase separation. Thus, to avoid embrittlement problems, one has to proceed with caution when annealing V−20Ti alloys in H2 gas in the intermediate temperature range. We also expect hydride precipitation when V−20Ti is exposed to atomic hydrogen, as will occur in a fusion device. Contrary to thermodynamic considerations, long-term annealing of FeTi in H2 does not result in TiH2 precipitation.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: Properties of a novel hydrogen storage alloy system, Mg-Zn-Ni (Mg:Zn=7:3), were investigated by pressure-composition isotherm measurements, thermogravimetry-differential thermal analysis and X-ray powder diffraction. Mg7Zn3 has a low melting point, near 600 K, but the hydriding reaction proceeds at more than 620 K. At least a part of the alloy melted during hydrogenation. The hydride formed was MgH2 and no new hydride phases have been observed. Addition of nickel to the Mg-Zn alloy improved the reaction kinetics.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: It is very important to control continuously the hydrogen equilibrium pressureP-temperature T characteristics of hydrogen storage alloys to have them applicable in a wide range of temperatures. The relation between the alloy phases and the P-C-T characteristics was determined for C14 (MgZn2) type Laves phase alloys based on Ti(Zr)Mn2 by changing the alloy composition.The P-C-T characteristics, hysteresis and plateau pressure were changedsubstantially by suchtituting zirconium for titanium in the A site and other elements such as chromium, copper or nickel in the B site. In this case, the crystal lattice constants and hydrogen equilibrium pressure were changed more effectively by substituting zirconium for titanium in the A site. The range of equilibrium pressures covered was from 10 to 108 Pa at 20°C (this corresponds to the range from −50°C to +250°C at 1.013×105 Pa). The equilibrium pressure changes particularly markedly for lattice constants a=(4.84–5.05)×10−10 m and c=(7.94–8.28)×10−10m.These results show that the C14-type Laves phase alloys with excellent flatnessof the plateau pressure and small hysteresis, are applicable in these ranges of temperatures and pressures for hydrogen storage.We have confirmed these results by fabricating a prototype heat pump with ahydrogen storage alloy that utilizes high temperature waste heat.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals

  • No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: The hydrogen absorption characteristics of TiMn1.25Cr0.25 alloy were studied by means of X-ray photoelectron spectroscopy, X-ray diffraction and oxygen poisoning. The capacity for hydrogen absorption is increased and the slope of the plateau is decreased effectively by annealing the alloy at 1000–1200°C. Enrichment of manganese in the surface layer (approximately 100 ) of the alloy appears to give good hydrogen absorption activity and improved resistivity to oxygen poisoning. The capability for hydrogen absorption of the poisoned alloy can be restored by treatment at 300°C with 10 atm H2.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: Experimental uncertainty is greatly affected by temperature changes caused by the exothermic and endothermic characteristics of metal hydride reactions. However, it is not difficult to perform experiments under thermodynamically consistent conditions if an adequate experimental technique is used with a reactor which is highly thermally responsive. Thermal equilibrium between the reacting bed and the heat exchange medium must be reached as quickly as possible. It is important to optimize the experimental set-up with respect to mass and heat balance. The volume to mass relationship determines the experimental consistency and has a significant effect on the apparent reaction rate.In this paper the experimental procedures required to obtain thermodynamically consistent data are discussed.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: A column packed with pellets of copper-plated LaNi4.25Al0.75 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.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: The electrochemical capacities and the durabilities during galvanostatic charge-discharge cycling of misch metal—nickel-based metal hydride electrodes and the effects of copper plating on their performance have been investigated. The morphology of the electrode surface and the oxygen profile within the copper plating layer were examined by scanning electron microscopy and X-ray photoelectron spectroscopy. It is found that the MlNi3.45 (CoMnTi)1.55 (MI=misch metal) electrode has good overall characteristics and copper plating on the hydride powder is effective, to some extent, in improving the durability of the electrode.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: Flow of hydrogen isotopes in a metal hydride chromatographic column is calculated by a one-dimensional finite difference method. Published data for gas flow in packed columns are used to define the gas flow; and equilibrium pressure isotherms are used to define the distribution between the solid and gas phases. Solid phase loadings show that concentrations move as a wave front on absorption, but remain more uniform on desorption.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: Changes in the crystal structure and isothermal sorption kinetics of the hydride-formingalloy TiFe0.8Ni0.2 were investigated after prolonged cyclic sorption. The changes were followed by X-ray diffraction, reaction rate and pressure-composition-temperature (P-C-T) measurements, of samples after various numbers of cycles, up to 65000. After 65000 sorption cycles, a decrease of 16% in the hydrogen absorption capacity was detected. Residual, trapped hydride was indicated, the amount of which increased as the cycling advanced. Overall isothermal reaction rate measurements were interpreted by assuming a first-order rate law. The decomposition rates of TiFe0.8Ni0.2H after cycling were found to be lower than those obtained for non-cycled (activated only) alloy. The changes found in the kinetics and in the X-ray diffraction pattern of the alloy are discussed. A relationship between the reacted fraction α and f(P), the pressure function, was established for closed measuring systems.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: A study was done to compare the absorption and desorption kinetics of a series of LaNi4.5T0.5 hydrides (T=Fe, Co or Cu) with those of LaNi5−H. Measurements were done under essentially isothermal and isobaric conditions. Experiments were also designed so that the ratio of the equilibrium plateau pressure to the opposing pressure was the same in all cases. It was found that, under identical reaction conditions, partial substitution of the lanthanum in LaNi5 with copper, cobalt or iron generally decreases desorption rates. Among the LaNi4.5T0.5 hydrides desorption rates decreased in the following order: T=Ni>Cu>Co>Fe. Since this is the same order as the plateau pressures in these materials, it appears that in alloys having similar crystallographic and electronic properties, the reaction rate is inversely proportional to hydride stability. The absorption experiments differed in that LaNi5 absorbed hydrogen slower than any of the ternary alloys. This anomalous behavior indicates that absorption proceeds by a different mechanism than does desorption and that the presence of copper, cobalt or iron may be altering the rate-limiting process.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: A technique for using organic materials to improve the sorption properties of magnesium-based hydrogen-storage materials has been studied. A technique of metal vaporization into an organic matrix at 77 K is effective as a modification method. Small solvated magnesium particles formed by clustering in low temperature tetrahydrofuran (THF) matrices are exceptionally active for hydrogen absorption. The conditions of metal vaporization significantly affect the characteristics of magnesium particles (Mg−THF) obtained. The organic matrix in which the magnesium atoms are dispersed and in which crystal growth proceeds has a pronounced effect on the size and hydriding character of the particles formed. Modification by metal atoms vaporizing into organic matrices allows the formation of thermally stable and active solvated magnesium. The hydriding of the magnesium is controlled by initial surface reaction with subsequent diffusion of hydrogen through the growing hydride phase. An Mg−Ni sample obtained when magnesium and nickel metals are successively vaporized into THF matrices is much more active than magnesium alone.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: The properties of four hydride-forming materials have been investigated to determinetheir applicability for use in a process to separate hydrogen isotopes from inert gases. These materials are Zr0.8Ti0.2Ni, Zr0.65Ti0.35Co, NdCo3 and ErFe2. The properties investigated while surveying these materials include ease of activation, isotherm characteristics, kinetics, cycling stability and oxygen stability. The results of the survey indicate NdCo3 to be the hydride former of choice for use in the inert gas separation process. It is the most easily activated and has the most favorable isotherm characteristics (the largest usable capacity, flat plateaux, small hysteresis and negligible heel) as well as the fastest absorption kinetics of the materials tested. NdCo3 also has good cycling and oxygen stability.As with most intermetallic alloys, NdCo3 decrepitates into a fine powder after only a few sorption cycles in hydrogen and therefore must be consolidated in order to be used in the fixed bed absorber envisioned for the inert gas separation process. Consolidation was achieved through support of the NdCo3 in a sinter-bonded aluminum matrix. Stable compacts of NdCo3 have been made consisting of 40 wt.% Al in NdCo3 pellets, pressed at 186 MPa and sintered under vacuum for 2 h at 450°C. These compacts retained the full absorptive capacity of NdCo3 and remained 99 wt.% intact after 15 sorption cycles in hydrogen.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: Deuterium depth distributions were measured in Zr-2.5wt.% Nb pressure tube material which had been oxidized in air or in D2O steam. Oxidation in air at 400°C of deuterided samples resulted in the formation of a sub-oxide peak in the deuterium distribution. In addition to this feature, the present study shows that a very low deuterium atomic fraction is present in the oxide, 0.0001 deuterium per zirconium atom, and sometimes deuterium depletion is also observed beneath the sub-oxide peak. Oxidation in D2O steam at 490°C resulted in deuterium distributions which depend strongly on the specific corrosion conditions. The deuterium depth profiles and their relation to the interfacial region are discussed.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: An experimental programme is described which is performed in the framework of a tritium technology task for the Next European Torus (NET). The aim is to investigate the applicability of commercial gas purifiers for the removal of gaseous impurities such as N2, CO, and CO2 from a helium-hydrogen or a helium-tritium gas stream. In addition, it is intended to recover chemically bound hydrogen isotopes by decomposition of hydrocarbons, ammonia and water.Experimental results obtained in the PEGASUS facility are reported for the sorption of CH4 by three non-uranium getters as a function of temperature and gas flow rate, the enhancement of CH4 sorption efficiency by continuous removal of hydrogen, and cosorption behaviour of CO, N2 and CH4 in the presence of hydrogen.Gettering of CO and N2 was found to be much more effective than that of CH4. At temperatures above 200°C, an increasing tendency for the reaction 2H2+CO→CH4+1/2O2 was found to occur during the passage of the gas through the getter. This reaction can be suppressed by using two getters in series: the first is operated at about 250°C to remove O2, H2O, CO and CO2, and the second at 400°C or more for the removal of residual amounts of these species as well as for the removal of N2 and CH4.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals
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    ABSTRACT: We have recently developed the laser-Raman technique as a means of unambiguouslymeasuring the partial pressures of all possible hydrogen isotopes in the gas phase. Using this technique we have investigated the hydrogen-deuterium solid-phase exchange in a number of metal hydrides. Note that the exchange process we are discussing is a complete conversion of a metal hydride to the deuteride and back by successive reaction with first hydrogen and then deuterium. This report presents detailed data for isotopic exchange in the palladium hydride system over the temperature range from 26 to −100°C at a pressure of 7 atm. First-order kinetic rate constants and activation energies are summarized for the forward (hydride to deuteride) and reverse (deuteride to hydride) exchange processes. In addition, we have found that small amounts (100 p.p.m.) of impurities in the exchange gases considerably slow the exchange kinetics with the effect increasing down the series CH4, CO2, H2O and CO.
    No preview · Article · Dec 1991 · Journal of the Less Common Metals