Tracer Experiments on the Exchange Equilibrium of Tritium between Hydrogen Gas and the Hydrogen‐Storage Material TiMn1.5‐Hydride

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Abstract
The equilibrium distribution of3H between hydrogen gas and the intermetallic hydrogen storage material Ti0.4Mn0.6Hn, being in equilibrium with the light hydrogen, was determined by tracer experiments in the α‐phase region and in the temperature range from 23°C. to –60°C. The equilibrium separation factors follow the relationshipThe values of the separation factors show up an enrichment of tritium in the solid solution, whereas in the PdHn‐system the opposite observations are made. It is shown that the isotope distribution at higher hydrogen contents is not only determined by energy differences of vibrational states. but may also be influenced by non‐idealities within the solid solution. From the non‐idealities calculated in case of P‐PdH” together with the equilibrium separation factor measured in the P‐phase, a local mode energy of the interstitial hydrogen ofis derived ‐ For Ti0.4Mn0.6Hnin the α‐phase region a value about twice as highturns out, which we confirmed by neutron scattering experiments. From these results H is concluded to occupy interstitial tetrahedral holes in Tio,Mno”H, . ‐ From hydrogen sorption isotherms at low equilibrium pressures, measured in addition to the exchange experiments with a‐Tio,Mno,6H” contributions from “surface hydrogen” are deduced. These contributions are not reflected by the values of the separation factor because of the vibrational frequencies of “surface hydrogen” are similar to those of H in tetrahedral holes. With systems, however, dissolving hydrogen in octahedral positions (as e.g. PdH,), an inversion of the isotope effect is observed going from “bulk”‐ to “surface hydrogen”.

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