Hydrogen absorption–desorption properties of Mg–Ca–V BCC alloy prepared by mechanical alloying

Mg2CaV3 ternary alloy was prepared by the mechanical alloying (MA) of CaMg2 Laves phase alloy and V. A structural analysis performed using X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning TEM (STEM) showed that the prepared Mg2CaV3 alloy consisted of nanocrystalline grains with a body-centered cubic (BCC) structure. After the alloy had been activated by milling it with graphite, it absorbed up to 3.3 wt.% hydrogen at 25 °C. The alloy maintained its BCC structure even after hydrogenation although the crystal lattice of the alloy expanded. This structural change during hydrogen absorption is quite different from that of typical V-based BCC alloys. The Mg2CaV3 alloy did not desorb hydrogen at 25 °C; this process began at around 270 °C under an argon pressure of 0.1 MPa. We also found that the hydrogen desorption occurred together with the formation of Mg and CaH2 caused by the partial decomposition of the hydrogenated alloy.