Sorption Properties of Iron–Magnesium and Nickel–Magnesium Mg2FeH6 and Mg2NiH4 Hydrides

Abstract

Based on molecular-kinetic representations, theory of hydrogen absorption-desorption processes in binary Mg–Fe and Mg–Ni alloys is developed. Free energies of hydrides of these alloys are calculated. Equations of their thermodynamically equilibrium state determining the P–T–c diagrams are derived. A temperature dependence of the desorbed hydrogen concentration is established. A maximal desorption temperature is estimated. The state diagrams determining the concentration dependence of the maximal desorption temperature are constructed. Isopleths and isotherms of hydrogen solubility in the alloys are calculated. The possibility of manifestation of the hysteresis effect in hydrogen solubility isotherms is revealed and the decrease of the width and length of a hysteresis loop with increasing temperature is demonstrated together with the influence of the magnesium hydrate MgH₂ in Mg₂FeH₆ samples and running of chemical reactions on the behavior of the isotherms and the occurrence of bends and jumps in them. All established functional dependences of the sorption properties of the examined alloys are compared with experimental data available from the literature.