Preparation of the hydrides Mg₂FeH₆ and Mg₂CoH₅ by mechanical alloying followed by sintering

Mg₂CoH₅ and Mg₂FeH₆ were prepared by mechanical alloying (MA) and followed by sintering under mild conditions. The effect of milling atmosphere on the end products was also studied. The mixtures 2Mg+Fe and 2Mg+Co were milled in a planetary ball mill under hydrogen and argon atmospheres. After milling, the mixtures were sintered at 623 K for 1 day under 50 bars of hydrogen. X-ray powder diffraction analysis was used not only for identification of phases formed but also for crystal structural refinement and mass fraction calculation using the Rietveld method. We found that, under the above sintering conditions, the hydrides Mg₂FeH₆ and Mg₂CoH₅ were produced only in samples that were milled prior to sintering. For 2Mg+Fe mixture, milling under hydrogen prior to sintering produced 84% Mg₂FeH₆ in the product excluding oxide. The mixture 2Mg+Co was milled and sintered producing MgH₂ and Mg₂CoH₅, but the mass fraction of Mg₂CoH₅ was independent of the milling atmosphere.