Chater, Philip A (2010)
Ph.D. thesis, University of Birmingham.
The first examples of a new class of mixed anion complex hydride have been synthesised and characterised. The structures of three amide-borohydride complex hydrides of lithium and sodium, Li\(_4\)BH\(_4\)(NH\(_2\))\(_3\), Li\(_2\)BH\(_4\)NH\(_2\) and Na\(_2\)BH\(_4\)NH\(_2\), have been solved by powder diffraction methods and characterised by infrared and Raman spectroscopy. The thermal decomposition of these hydrogen rich materials was investigated and hydrogen was observed as the major gaseous product in all cases. Ammonia was observed as a minor product with the amount of ammonia release dependent on the sample composition and experimental set-up. Powder diffraction was used to identify the solid decomposition products and decomposition pathways are proposed. Two competing decomposition pathways, one forming metal hydride and boron nitride, the other forming metal nitridoborate, were identified for the lithium system and suggested for the sodium system. \(In\)-\(situ\) and \(ex\)-\(situ\) powder diffraction, differential scanning calorimetry and temperature programmed desorption were used to investigate the lithium amide-borohydride system in detail and a phase diagram was proposed. The reactions of metal hydrides with Li\(_4\)BH\(_4\)(NH\(_2\))\(_3\) were tested and were found to reduce the amount of ammonia released. A reversible hydrogen storage reaction was observed upon reaction with magnesium hydride, which was investigated with gravimetric methods and \(ex\)-\(situ\) powder diffraction to elucidate the reaction pathway.
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