Can reduced size of metals induce hydrogen absorption: ZrAl₂ case

The hydrogen absorption ability of the non-absorbing Al-rich ZrAl ₂ compound was examined after reducing its particles-size to the nanometer regime. The hydrogen abstinence of bulk ZrAl₂ has been previously related to its excessive elastic shear stiffening. The particle size of ZrAl₂ was reduced by attrition milling and cryomilling. The minimal average particle size was estimated from powder X-ray diffraction analysis to be in the range of 10-20 nm. The hydrogen absorption of the milled compounds was measured in different hydrogenation systems at hydrogen pressures between ∼6 MPa and ∼2 GPa. In all the cases the hydrogen absorption was negligible. In addition, there was a reduction of the hydrogen absorption capacity of nanosized Zr(Al_0.5Co_0.5)₂ as compared to the corresponding bulk compound at the same conditions. We suggest, in view of our and other results, that no significant improvement of the thermodynamics (unlike the kinetics) of the hydrogen absorption can be achieved via the nanoparticle avenue.