Brampton, David (2010)
M.Res. thesis, University of Birmingham.
It has been shown that lithium borohydride can be destabilized with magnesium hydride additions for the purpose of reversibly hydrogen. In reactive composites of these hydrides alternative chemical pathways become available for dehydrogenation, which can modify both the thermodynamics and kinetics of the hydrogen sorption reactions. To try and clarify the reaction process mechanically milled samples have been studied, and the different desorption products assessed. Analysis of samples during desorption, recombination and cycling were performed using high pressure differential scanning calorimetry (HP-DSC) to calculate the enthalpies of the reactions. Thermogravimetric analysis (TGA) was also carried out in conjunction with mass spectrometry to determine the amount of hydrogen evolved. Samples were analysed using X-ray diffraction and FTIR at various stages during cycling to try and identify any reaction products present. When dehydrogenated these mixed hydride systems release hydrogen in two stages, firstly from MgH2 (275 - 350°C) then secondly from LiBH4 (315 - 450°C). The desorption temperature was found to increase with increasing amounts of LiBH4. No MgB2 or LiH was detected in the desorption products of samples dehydrogenated up to 450°C under 3 bar of flowing Ar but evidence for a Li – Mg phase was detected.
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