Effect of mechanical grinding under argon and hydrogen atmospheres on structural and hydriding properties of LaNi5

Effect of mechanical grinding (MG) under argon and hydrogen atmospheres on structural and hydriding properties were investigated in detail. In MG-LaNi5 under argon atmosphere, the grain size reaches similar to 20 nm for MG times of 60 min and almost remains unchanged for more longer MG times. The pressure-composition isotherm (P-C) in LaNi5 at room temperature indicates an enhancement of hydrogen solubility, a lowering of plateau pressure and a narrowing of width of plateau by MG like FeTi but not Mg2Ni. On the other hand, in reactive MG (RMG)-LaNi5 under hydrogen atmosphere, a nanocrystallized LaNi5H0.15 and amorphous phases coexist within 180 min of grinding time. For RMG times longer than 180 min, the nanostructured LaNi5H0.15 phase disappears and the remaining amorphous-LaNi5Hx dissociates into nano-Ni + LaNiyHz (y<5). The P-C isotherm indicates no-plateau in the LaNi5 produced by RMG longer than 60 min and the hydriding properties become worse and worse with increasing RMG times. From these results, we conclude that the hydriding properties could not be improved by structural modifications in the system containing metals with strong affinity for hydrogen like rare earth metals.