HYDROGEN ABSORPTION STUDIES IN ZR0.4HO0.6FE2

Hydrogen absorption isotherms and kinetics were studied for the pseudo binary Zr0.4HO0.6Fe2 alloy belonging to the C15-type Laves phase in the ranges RT less than or equal to T/degrees C less than or equal to 150 and 0 less than or equal to P/bar less than or equal to 50. At RT and at an equilibrium pressure of about 40 bar the maximum hydrogen concentration is found to be 5.5 hydrogen atoms per formula unit. The relative partial molar enthalpy (Delta $($) over bar$$ H-H) and entropy (Delta $($) over bar$$ S-H) Of hydrogen solution are found to be in the ranges - (8-10) kJ (mol H)(-1) and -(13-37) J K-1 (mol H)(-1), respectively. An expansion in the unit cell volume (Delta V/V) up to 26% is observed for the maximum hydrogen concentration without any change in its cubic Laves phase structure. In the P-C-T isotherms, a plateau corresponding to the (beta + gamma) phase is seen at 40 bar at RT. The kinetics data are fitted to a first order rate equation. These data fit into different straight lines corresponding to the alpha and (alpha + beta) phases. The activation energy (E(a)) in the (alpha + beta) phase is found to be 19 kJ (mol)(-1).