Investigation of the thermochemical transformations in the LiAlH(4)-LiNH(2) system

The thermal transformations in the lithium alanate-amide system consisting of lithium aluminum hydride (LiAlH(4)) and lithium amide (LiNH(2)), mixed in a 1:1 M ratio, were investigated using the pressure-composition-temperature analysis, solid-state nuclear magnetic resonance, X-ray powder diffraction, and residual gas analysis. Below 250 degrees C, the alanate decomposes into Al, LiH and H(2), through the formation of Li(3)AlH(6), whereas the amide remains largely intact. The release of gaseous hydrogen corresponds to approximately 5 wt%. Above 250 degrees C, additional 4 wt% of hydrogen is produced through solidstate reactions among LiNH(2), LiH and metallic Al, through the formation of intermetallic Li-Al binary alloy and an unidentified intermediate. The overall reaction of the thermochemical transformation of the LiAlH(4) LiNH2 mixture results in the production of Li(3)AlN(2), metallic Al, LiH and the release of 9 wt% of gaseous hydrogen. The reaction mechanism of the thermal decomposition is different from one identified earlier during mechanical treatment of the same system. Rehydrogenation of the thermally-decomposed products of LiAlH(4)-LiNH(2) mixture using high hydrogen pressure (180 bar) and heating (275 degrees C) yields LiNH(2) and amorphous aluminum nitride (AlN). Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.