This work has investigated structural and compositional changes in LiBH\(_4\), Mg(BH\(_4\))\(_2\), Ca(BH\(_4\))\(_2\), LiBH\(_4\)-Ca(BH\(_4\))\(_2\), MgH\(_2\)-B-TiX (TiX = Ti, TiH\(_2\) or TiCl\(_3\)), and hydrided Li-Mg alloy during heating. The crystal and vibrational structures of these borohydrides/composites were characterized using lab-based X-ray diffraction (XRD) and Raman spectroscopy, with particular attention to the frequency/width changes of Raman vibrations of different polymorphs of borohydrides. The thermal stability and decomposition pathway of the borohydrides was studied mainly using differential scanning calorimetry and thermogravimetric analysis, XRD and Raman measurements, whilst the gaseous products during heating were monitored using a mass spectrometry. Hydrogen is the main decomposition gaseous product from all of these compounds, but in some cases a very small amount of diborane release was also detected. These studies suggest that the thermal decomposition of the metal borohydrides occurs via a wide range of reaction pathways, often in several steps, which may involve simultaneous competing reactions. This can include the formation of stable borane intermediates/by-products which largely preclude the possibility of reversibility. Furthermore, the role of diborane in the decomposition and formation of borohydrides, was later studied by heating metal borohydrides (or hydrides) to various temperatures in a gaseous diborane-hydrogen atmosphere; and different types of borane products were observed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636849 |
| Date | January 2015 |
| Creators | Guo, Sheng |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.bham.ac.uk//id/eprint/5674/ |
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