Magnesium alanate - a material for reversible hydrogen storage?

Magnesium alanate was synthesized in a metathesis reaction of magnesium chloride and sodium alanate followed by purification. The material obtained was sufficiently pure and it was investigated by X-ray diffraction (XRD) and by thermogravimetry (TG) and mass spectrometry (MS) of the evolved gas, respectively. Thermal analysis showed a decomposition with a release of hydrogen proceeding in two major steps. Measured in vacuum, the peak decomposition temperature of the first step was found to be 163 degreesC and the residue at 200 degreesC consisted of MgH2 and Al which continues to release hydrogen and transforms into an Al3Mg2/Al mixture at higher temperatures. In the first decomposition step 6.6 wt.% of hydrogen was released. To enhance the kinetics of the decomposition, magnesium alanate was doped with a titanium based promoter and ball milled for up to 100 min, resulting in a significantly reduced peak decomposition temperature. First results on determining thermodynamic properties indicate equilibrium desorption pressures in the range of AB(5) compounds. In total, the promising properties determined so far have inspired further investigations on the thermodynamics, kinetics and reabsorption properties of the compound. (C) 2002 Elsevier B.V. All rights reserved.