Measurements of expansion of LaNi5 compacted powder during hydrogen absorption/desorption cycles and their influences on the reactor wall

Abstract

The volume expansion, which occurs during the storage of hydrogen by metal hydrides, is a phenomenon linked to the lattice swelling or structural transition some samples. An experimental study realized out in order to characterize the progressive swelling and shrinking observed during the hydrogen absorption and desorption cycles by the compacted LaNi5 powder. The sample LaNi5 compacted has been submitted to 30 hydrogen absorption/desorption cycles, at the same cooling temperature equal 40 °C, under pressure 0.2 bar for the description state and 6 bars for absorption. As expected, the experimental results clearly indicate that the cyclic hydrogenation causes pellet volume changes, i.e. an almost reversible swelling/shrinking in the radial direction. However, this phenomenon can generate major mechanical stresses on the cell containing the pellet. The deformations react on the tank wall tantamount to the initial pressure of hydrogen. The values of the amplitude of the displacement increase progressively up to the 30th cycle, then, the phenomenon is stabilized up to 35 cycles, and this is explained that the relaxation of the metal limited the radial expansion.