Now showing 1 - 10 of 14
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    Thermodynamics and stability of dissolved hydrogen in pd rich binary Pd1-xZx and ternary Pd1-x-yZxZy′ solid solution alloys
    (01-01-1998)
    The relative chemical potential of the dissolved hydrogen (Δμ0H) and the partial pair interaction free energies, gPH↔Z, and (gPH↔Z/Z)average respectively, in Pd based Pd1 - xZx-H and Pd1 - x - yZxZ′y-H systems are correlated to the stability of the dissolved hydrogen in the octahedral interstitial sites by classifying the Pd1 - xZx alloys based on the "effective valence, ns" of the substitutional metals. From the dependence of Δμ0H on the lattice constant of the alloy, (a0)alloy, and of gPH↔Z ((gPH↔Z/Z′)average) on the ionic diameter of the substituent metal, dZ, ((dZ/Z′)average) for systems Pd1 - xZx-H (Pd1 - x - yZxZ′y-H), the exceptional behavior of the binary "expanded" alloys Pd1 - xZx (Z = Nb, Ta and Pt), the binary "contracted" Pd1 - xZx alloys (Z = Ti and Li) and the ternary "contracted" alloys Pd0.903Er0.078Cu0.019 and Pd1 - 2xAgxNix towards hydrogen absorption is explained. © 1998 International Association for Hydrogen Energy.
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    Hydrogen Solubility and Thermodynamics of Hydrogen Absorption in Palladium-rich Binary Pd1-xZx and Ternary Pd1-x-yZXZ'y Solid Solution Alloys
    (01-01-1997)
    Weiss, Alarich
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    Rajalakshmi, Nataraja
    A review is given of the effects of alloying Pd with a substitutional metal (Z) on the hydrogen solubility and the thermodynamics of hydrogen absorption at infinite dilution. A large volume of thermodynamic data on Pd1-xZx-H systems have been analysed by classifying the binary Pd1-xZx alloys based on the effective valency of the substitutional metal, which results in the finding that the interaction energy EZ⊗H is a more dominant factor than the size rh of the octahedral interstitial hole in determining the hydrogen solubility. Recent years have witnessed hydrogen solubility studies on ternary Pd1-x-yZxZ′y alloys, which are discussed. The effect of alloying of Pd with a substitutional metal Z on the plateau pressure PäL-ß is also presented. Ein überblick wird gegeben über die Einflüsse der Legierung von Pd mit einem Substitu-tionsmetall (Z) auf die LöUslichkeit und die Thermodynamik der Absorption von Wasser-stoff bei unendlicher Verdünnung. Eine großZe Menge thermodynamischer Daten von Pd1-xZx-H-Systemen wurde analysiert durch Klassifizierung der binäUren Pd1-xZx-Legierungen aufgrund der effektiven Wertigkeit des Substitutionsmetalls, was zu dem Ergebnis führte, daßZ die Wechselwirkungsenergie Ez-h die WasserstofflöUslichkeit stäUrker beeinflußt als die GröUße rh der oktaedrischen Zwischengitterplätze. Diskutiert werden auch Untersuchungen der Wasserstoff-LöUslichkeit in ternäUren Legierungen, Pd1-x-yZxZ'y, die in den letzten Jahren durchgeführt wurden. Auch wird der Effekt aufgezeigt, den die Legierung von Pd mit einem Substitutionsmetall Z auf den Plateaudruck PäL-ß ausübt. © 1997, R. Oldenbourg Verlag, München. All rights reserved.
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    Electron paramagnetic resonance study of X-irradiated tri-coordinated copper(I) complexes
    (01-03-1999)
    X-irradiation of single crystals of several tri-coordinated Cu(I) monomer and dimer complexes studied by EPR revealed that Cu(I) monomer complexes form Cu(II) complexes while X-irradiation of the Cu(I) dimer complexes has no such effect. The formation of Cu(II) complexes is attributed to the addition of a radiogenic atom on the Cu(I) precursor. The absence of any structural changes due to the X-irradiation of the Cu(I) dimer complexes is discussed based on the electronic structure of these complexes.
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    An NQR study of inclusion compounds formed between small chlorine-containing molecules and bis(N-alkylimidazolidine-2-thione)Cu(I) halide complexes
    (01-01-1996)
    Zhao, Ya Nan
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    Lucken, Edwin A.C.
    Twenty-five inclusion complexes formed by bis(N-alkylimidazolidine-2-thione)cuprous halides with the small, chlorine-containing guest molecules CCl4, CHCl3, CH2CA2, CH3CCl3 or C2H2Cl2, have been prepared. Their 63Cu and 35Cl NQR spectra have been measured over the temperature range 77-300 K. For the corresponding bromides the 79Br and/or 81Br spectra have also been investigated. The studies reveal the number and symmetry of different inclusion site. The onset of rapid reorientation of the guest molecules is indicated by the fading out of their NQR signals between 77 and 300 K, whereas the resonances from the host molecules usually persist throughout this temperature range. However, as evidenced by discontinuities in the temperature-dependence of the NQR frequencies of the hosts, sixteen of the complexes show one or more phase-changes in this temperature-range.
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    Hydrogen absorption characteristics in the Tb1-xZrxFe3 (x=0.1, 0.2, 0.3) system
    (30-06-1999)
    Sivakumar, R.
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    Rama Rao, K. V.S.
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    Anton, H.
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    Schmidt, P. C.
    The hydrogen absorption pressure-composition-isotherms of the PuNi3 type rhombohedral Tb1-xZrxFe3 (x=0.1, 0.2, 0.3) alloys are investigated by Sievert's apparatus, in the temperature and pressure ranges 75≤T(°C)≤150 and 0.1≤P(bar)≤25, respectively, with a view to study the dependence of hydrogen solubility and the plateau pressure on Zr content. The P-C isotherms show the presence of a single plateau region in the temperature and pressure ranges studied and it is found that the plateau pressure at any given temperature increases with increase of Zr content along with a reduction in the hydrogen capacity. The absorption of hydrogen is accompanied by a maximum of 17.4% expansion in the unit cell volume of the host material without any change in PuNi3 type structure as evidenced by the X-ray diffraction studies on the alloy-hydrides. The presence of single and two phase regions as seen in the P-C isotherms are confirmed from the powder X-ray diffractogram of the alloy-hydrides with appropriate hydrogen concentration. The powder X-ray diffractograms on the alloy-hydrides with maximum hydrogen concentration further show the absence of hydrogen induced amorphization (H1A) upon hydrogenation.
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    Electrochemical investigation of YxZr1-x,Mnm,FenCopV oCrq(m+n+o+p+q=2) electrode for Ni-MH battery application
    (22-08-1999)
    Rajalakshmi, N.
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    Dhathathreyan, K. S.
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    The AB2 type Laves phase hydrogen absorbing alloys are being investigated as suitable electrode materials for Ni-MH batteries, because of their higher electrochemical capacity. The electrochemical properties like electrode potential, reversible electrochemical capacity and diffusion coefficient as a function of state of charge in the YxZr1-x MnmFenCopVoCr q(m+n+o+p+q=2) electrodes were investigated in an alkaline solution. The reversible electrochemical capacity of the electrode was found to be in excess of 450 mAh/g and hydrogen concentration was estimated as 3.5 hydrogens/formula unit. The process that occur in the electrode during charge and discharge, has been studied by Cyclic Voltammogram(CV) experiments, carried out at different sweep rates. It was found that at low sweep rates, the hydrogen concentration on the surface increases due to longer polarisation and the hydrogen concentration approaches a value which favours a metal hydride formation. The diffusion coefficients were also evaluated with respect to state of charge. The results will be presented in the paper.
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    Oxidation of a tricoordinated CuI complex to a tetracoordinated CuII species. A single-EPR study
    (01-12-1995)
    Palivan, Cornelia
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    Berclaz, Théo
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    Geoffroy, Michel
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    Bernardinelli, Gérald
    Bis(N-methylimidazolidinethi-2-one)copper(I) chloride has been synthesized and its crystal structure determined. X-Irradiation of a single crystal of this compound leads to the formation of a CuII complex which was studied by EPR: it was shown that this species results from the addition of a radiogenic Cl atom on the CuI precursor. The structural changes induced by this reaction are revealed by the g-tensor and by the hyperfine tensors of one copper and two chlorine nuclei. The structure of this S2Cl2Cu type complex was compared with other sulfur- or chlorine-containing CuII complexes.
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    Hydrogen solubility and thermodynamics of hydrogen absorption in palladium rich binary Pd1 - XHox (x=0.05 and 0.08) solid solution alloys
    (22-06-1997)
    Nirupama, C. V.
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    Sunita,
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    The hydrogen solubility and the thermodynamic parameters for absorption of hydrogen in Pd1 - xHox (x=0.05 and 0.08) solid solution alloys have been determined from the pressure-composition isotherms in the ranges 473≤T/K≤873 and 0≤P/mbar≤900 using a pressure reduction method. The results are compared with those of the previously determined Pd1 - xREx (RE=Er, Dy, Y, Gd, Sm; x=0.05 and 0.08) solid solution alloys. The partial molar enthalpy of solution of hydrogen at infinite dilution (ΔHoH) becomes more exothermic with increase of xHo and the partial molar excess entropy of hydrogen solution at infinite dilution (ΔSE,oH) decreases with increase of Ho content. The relative chemical potential of dissolved hydrogen at infinite dilution (ΔμoH) decreases with increase of xHo indicating that the stability of dissolved hydrogen increases with increase of xHo. The Pd1 - xHox-H systems fall on the correlation between the ionic diameter (dRE) of the substituent RE metals when in solution in Pd and ΔHoH for the Pd1 - xREx-H (RE=Er, Dy, Y, Gd, Sm; x=0.05 and 0.075) systems confirming that the effective valance of Ho is 3 when dissolved in the host Pd lattice.
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    Hydrogen absorption and kinetic studies in Zr0.2Ho0.8Fe2
    (01-11-1996)
    Kesavan, T. R.
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    Rama Rao, K. V.S.
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    Das, T. P.
    The hydrogen absorption and the kinetics of hydrogen absorption are studied on the C15 type Laves phase pseudo-binary alloy Zr0.2Ho0.8Fe2 in the temperature and pressure ranges RT ≤ T ≤ 150 °C (RT = room temperature) and 0 ≤ P ≤ 70 bar respectively. The maximum hydrogen concentration of 8.1 hydrogen atoms per formula unit is attained at the equilibrium pressure of 67 bar at RT, which is the highest value observed so far in Zr-based C15 Laves phase alloys. From the dependence of thermodynamics of dissolved hydrogen on the hydrogen concentration, the two-phase region in the isotherm corresponding to the equilibrium pressure of about 67 bar at RT is identified as the γ-phase region. This is further confirmed through the X-ray powder diffractogram of the hydrogenated samples on the two-phase regions and from the kinetics of hydrogen absorption. The relative partial molar enthalpy (ΔH̄H) and entropy (AS̄H) of hydrogen at infinite dilution are found to be in the ranges -(3-13) kJ (mol H)-1 and -(14-33) J K-1 (mol H)-1 respectively. The unit cell volume expansion (ΔV/V) upto 26% is found at the maximum hydrogen concentration at RT without change in its cubic Laves phase structure. The average activation energies (Ea) in the (α + β) and β phases are found to be 24 kJ mol-1 and 2 kJ mol-1 respectively.
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    Hydrogen solubility and thermodynamics of dissolved hydrogen in Pd1-xTbx (x = 0.05 and 0.08) solid solution alloys
    (01-01-1997)
    Narayanan, S. Shankara
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    The hydrogen absorption and the thermodynamics of dissolved hydrogen in Pd1-xTbjr (x = 0.05 and 0.08) solid solution alloys have been determined from the pressure-composition-temperature relation in the ranges 5≤P/mbar≤1000 and 473≤T/K≤873 using a pressure reduction method. The hydrogen solubility is found to increase with increase of xTb. The partial molar enthalpy of hydrogen solution at infinite dilution (ΔHHo) the partial molar excess entropy of dissolved hydrogen at infinite dilution (ΔSHE,o) decrease with increase of terbium content. The chemical potential of dissolved hydrogen at infinite dilution (ΔHHo) decreases with increase of x-n, indicating that the stability of dissolved hydrogen increases with increase of xTb. The Pd1-xTbx-H systems fall on the correlation between the ionic diameter (dRE) of the substitutent RE metals when in solution in Pd and the exothermicity of hydrogen absorption for the Pd1-xREx-H (RE = Er, Ho, Dy, Y, Gd and Sm; x - 0.05 and 0.075) systems. © WILEY-VCH Verlag GmbH, 1997.