Evaluation of thermodynamic parameters for hydrogen in the storage device ST-90®

Abstract

The thermodynamic parameters such as partial molar enthalpy (Δ H H), partial molar entropy (Δ S H), and partial molar excess entropy (Δ S E H) of the dissolved hydrogen in the hydrogen storage unit ST-90 ® containing 18.6 kg of misch metal based AB 5 alloy are evaluated based on the calculation of Sieverts constant and from Clausius–Clapeyron equation. The partial molar enthalpy at infinite dilution (Δ H 0 H) and the partial molar excess entropy at infinite dilution (Δ S E,0 H) have been obtained from the dependence of and on the hydrogen concentration. The nature of metal-hydrogen and hydrogen interactions are also evaluated for the three single phases namely α, β and γ. The hydrogen–hydrogen interaction is attractive in the α phase and repulsive in the β and γ phases. For the mixed phases α+ β and β+ γ, it is very difficult to predict the nature of the interactions either as attractive or repulsive.