Evaluation of thermodynamic parameters for hydrogen in the storage device ST-90 (R)

The thermodynamic parameters such as partial molar enthalpy (Delta H-H), pa rtial molar entropy (Delta S-H), and partial molar excess entropy (Delta S- H(E)) of the dissolved hydrogen in the hydrogen storage unit ST-90(R) conta ining 18.6 kg of misch metal based AB(5) alloy are evaluated based on the c alculation of Sievert's constant and from Clausius-Clapeyron equation. The partial molar enthalpy at infinite dilution (Delta H-H(0)) and the partial molar excess entropy at infinite dilution (Delta S-H(E.0)) have been obtain ed from the dependence of and on the hydrogen concentration. The nature of metal-hydrogen and hydrogen interactions are also evaluated for the three s ingle phases namely alpha, beta and gamma. The hydrogen-hydrogen interactio n is attractive in the alpha phase and repulsive in the beta and gamma phas es. For the mixed phases alpha + beta and beta + gamma, it is very difficul t to predict the nature of the interactions either as attractive or repulsi ve. (C) 1999 International Association for Hydrogen Energy. Published by El sevier Science Ltd. All rights reserved.