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 t he ranges RT less than or equal to T/degrees C less than or equal to 1 50 and 0 less than or equal to P/bar less than or equal to 50. At RT a nd at an equilibrium pressure of about 40 bar the maximum hydrogen con centration is found to be 5.5 hydrogen atoms per formula unit. The rel ative 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), respec tively. 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 cor responding to the (beta + gamma) phase is seen at 40 bar at RT. The ki netics 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).