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Due to the fast kinetics observed at ambient temperatures, LaNi 5 was subjected to<br />
further analysis as a candidate material for hydrogen recovery from H 2 :He mixtures. The<br />
effects of the addition of aluminum by ball milling, as well as varying the preparation<br />
parameters, have been investigated and the results are presented in the following sections.<br />
3.2. Aluminum in LaNi 5<br />
3.2.1. Interaction With Pure Hydrogen<br />
The effect of partial substitution of nickel by aluminum in LaNi 5 for the purpose<br />
of altering the hydriding properties has been subject of many previous studies. From the<br />
macro perspective, lower H 2 pressure was needed to achieve the same H/M ratio as LaNi 5<br />
alone. This observation is explained from the effect of Al on the crystal lattice expansion<br />
upon hydriding, which is a limiting factor to the process. Aluminum addition is reported<br />
to decrease the extent of expansion by decreasing the dislocation density and vacancy<br />
concentration upon hydriding. It also increases the lattice constants, resulting in more<br />
hydrogen being absorbed [58].<br />
In the previous studies, LaNi 5-x Al x samples were reported to be prepared by arc<br />
melting the stoichiometric amounts of the components followed by size reduction by ball<br />
milling. In this study, aluminum was added to LaNi 5 via ball milling. Therefore, the Al<br />
content is presented as mole percentages, varying between approximately 0.9 and 33.3 %<br />
of the total number of atoms in LaNi 5 Al x .<br />
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