Combined effects of molar ratio and ball milling energy on the phase transformations and mechanical dehydrogenation in the lithium amide-magnesium hydride (LiNH2 + nMgH2)(n=0.5-2.0) nanocomposites

The phase transformations occurring as a function of the ball milling energy injected into the hydride system (LiNH2 + nMgH(2)), having molar ratios n = 0.5-2.0, have been thoroughly studied. The milling energy in a magneto-mill is estimated by a semi-empirical method. Xray diffraction (XRD) and Fourier Transform Infrared (FT-IR) measurements show that for the molar ratios n < 1.0 three new phases such as LiH, amorphous Mg(NH2)(2) (a-Mg(NH2)(2)) and Li2Mg(NH)(2) are formed during ball milling depending on the injected quantity of milling energy. Hydrogen is not released during milling when the LiH and a-Mg(NH2)(2) hydrides are being formed whereas the formation of the Li2Mg(NH())2 hydride phase is always accompanied by a profound release of hydrogen. For the molar ratios n >= 1.0, at a low level of injected milling energy, the hydride phases formed are LiH and a-Mg(NH2)(2). The latter reacts with MgH2 during further milling to form the new phase MgNH whose formation is also accompanied by a profound release of hydrogen. Based on the experimental data we established an approximate hydride phase-injected milling energy diagram for various levels of injected milling energy and the molar ratios. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.