Hydrogenation Entropies of the ZrMn2+y System
Hydrogenation of Mn-containing intermetallics leads to striking changes in magnetic properties. For example, Th6Mn23 is a Pauli paramagnetic but becomes ferrimagnetic upon hydrogenation. Vapor pressure studies of ZrMn2+y hydrides. have suggested unusual ΔH and ΔS values for hydrogen release. The values are about 40 and 50%, respectively, lower than the corresponding values for the paradigm hydride material LaNi5H6. The unusual thermodynamics could originate with either a large magnetic contribution or irreversibility for the system. Recent calorimetric measurements indicate that irreversibility is the major factor. Entropies of absorbed hydrogen derived from the calorimetric results are about 17 J/K g.atom of H, which is in good agreement with the computed values, 18.3 J/K g. atom H.
KeywordsConfigurational Entropy Hydrogen Release Hydrogen Storage Material Hydrogen Capacity Vibrational Contribution
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