STATISTICAL MODEL FOR THE BETA ZIRCONIUM HYDRIDES
It appears reasonable to consider the hydrogen as bonded covalently to zirconium in the zirconium hydrides. After consideration of the known structure of ZrH/sub 2/, the hypothesis is made that the nonstoichiometric beta (bcc) Zr-H phases have four symmetrical (tetrahedral) hydrogen sites on each face of the unit cell, with simultaneous occupancy restricted to pairs not closer than the shortest H -- H distance in ZrH/sub 2/. The complex configurational problem is solved for all concentrations by developing a simple process of building up the lattice, after making tests of the amount of detail required for accurate solutions in one and two dimensions. The total entropy, when decreased by the corresponding configurational entropy, corresponds to values of the hydrogen vibration frequency averaging 1440 cm/sup -1/ and showing no consistert trend with temperature or with a fourfold change in hydrogen concentration. A semiempirical energy model is constructed by irtroducing the hypothesis that zirconium bonded to no hydrogen is abnormally stable, and the two energy parameters are derived from the experimental data. The agreement with the curves derived from thermodynamic data is fairly good for the partial molal entropy and energy of hydrogen, and excellent for the hydrogen equilibrium pressures. Alternative models, however, are not eliminated unambiguously. (auth)
- Research Organization:
- National Bureau of Standards, Washington, D.C.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-18-019959
- OSTI ID:
- 4020429
- Journal Information:
- Journal of Chemical Physics (U.S.), Journal Name: Journal of Chemical Physics (U.S.) Vol. Vol: 40; ISSN JCPSA
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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