INVESTIGATION OF HYDRIDING PROPERTIES OF LANI4.8SN0.2, LANI4.27SN0.24 AND LA0.9GD0.1NI5 AFTER THERMAL CYCLING AND AGING

Thermal degradation studies were conducted on hydrides formed by Sn and Gd substituted LaNi5 compounds. Static room temperature pressure-composition isotherms were measured after 10, 1500 and 10 000 cycles and after thermal aging to evaluate changes in the properties. The hydrogen absorption properties of La0.9Gd0.1Ni5 seriously degraded in both prolonged thermal cycling and aging tests but the LaNi4.8Sn0.2 and LaNi4.27Sn0.24 hydrides were virtually unaffected. In the case of La0.9Gd0.1Ni5 the lattice microstrains were significantly larger and the domain sizes smaller as compared with those of LaNi4.8Sn0.2 after thermal cycling, but the majority of the strains were accumulated during the first 10 activation cycles. After 10 000 cycles the hydride of la0.9Gd0.1Ni5 becomes either amorphous or microcrystalline, whereas the hydride of LaNi4.8Sn0.2 is well crystallized.