Mechanochemical transformations in Li(Na)AlH4-Li(Na)NH2 systems

Mechanochemical transformations of tetrahydroaluminates and amides of lithium and sodium have been investigated using gas volumetric analysis, X-ray powder diffraction, solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy. In a transformation of LiAlH4 and LiNH2 taken in an 1:1 molar ratio, the amount of released hydrogen (6.6 wt.% after 30 min ball milling) was higher than in any known one pot mechanochemical process involving a hydrogen-containing solid. A total of 4.3 wt.% of hydrogen is released by the NaAlH4-NaNH2 system after 60 min ball milling; and 5.2 wt.% H2 is released when LiAlH4 and NaNH2 or NaAlH4 and LiNH2 are ball milled for 90 min and 120 min, respectively. All transformations proceed at room temperature. The mechanism of the overall transformation MAlH4(s) + MNH2(s) → 2MH(s) + AlN(s) + 2H2(g) was identified based on detailed spectroscopic analysis of the intermediate (M3AlH6) and final products of the ball milling process.