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|Title:||Hydrogen absorption characteristics in Zr0.2Ho0.8CoFe|
Rama Rao, K.V.S.
Crystal atomic structure
Pressure composition isotherms
|Citation:||Journal of Alloys and Compounds, 268(Feb.), 10-15|
|Abstract:||Hydrogen absorption studies have been carried out on the Zr0.2Ho0.8CoFe alloy which has the C15 cubic Laves phase structure. The data were collected in the temperature and pressure ranges 27�T(�C)�150 and 0.05�P(bar)�45 respectively. A maximum hydrogen concentration of 9 hydrogen atoms per formula unit at 43 bar at RT is observed. The P-C isotherms show two plateau regions which are identified as the (�+?) and (?+?) phases. These are confirmed from the variation of thermodynamic parameters as the function of hydrogen concentration and from the powder X-ray diffractograms of the samples taken at different hydrogen concentrations. The relative partial molar enthalpy (?H?H) and entropy (?S?H) of hydrogen are found to be in the ranges - (1-8) kJ (mol H)-1 and - (13-22) J K-1 (mol H)-1, respectively. The unit cell volume expansion (?V/V) up to 22% is found at the maximum hydrogen concentration at RT without a change in its crystal structure. The powder X-ray diffractogram of Zr0.2Ho0.8CoFeH9 does not indicate the occurrence of hydrogen induced amorphization (HIA) unlike the case of Zr0.2Ho0.8Co2H3 even though the atomic size ratio (RA/RB) of Zr0.2Ho0.8CoFe is more than the critical value estimated for the formation of an amorphous state upon hydrogenation. ? 1998 Elsevier Science S.A.|
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