Microwaves are commonly used for a number of solid state reactions, including sintering of ceramics, drying of materials and ionic substitution reactions. It is for such solid state processes that some of the most interesting effects are observed; yet these are presently amongst the most poorly understood. Diffraction is arguably the most incisive technique for the probing of solid state processes. To observe specific effects of microwave radiation it is necessary to perform <i>in-situ</i> diffraction experiments. Here we detail microwave applicators, modified for such a purpose. Simple phenomena, such as thermal expansion and phase transitions were observed for diverse materials (aspirin, silver iodide, β-alumina and barium titanate) under the influence of microwave heating. Furthermore, the use of w-situ diffraction as a method of temperature measurement is investigated. Some of these materials show unexpected effects when heated with microwaves, including anomalously large thermal expansion, the lowering of the phase transition temperature and a reduction in atomic displacement parameters. A consistent model has been proposed to explain these effects in terms of interactions of the electric field with a low-energy transverse optic phonon mode. The model only applies to materials possessing such a mode and no anomalous effects are observed otherwise. Barium titanate is a seemingly more complicated material and a strong electron-phonon interaction, resulting in local ordering may account for further anomalies. Another application of microwaves is the synthesis of nanoparticles using a microwave-induced plasma. This is an established technique, yet its application is limited to species with a volatile precursor. Here we extend the technique and design apparatus for use with a precursor in an aerosol, allowing the use of non-volatile, cheap precursor compounds.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:661190 |
| Date | January 2005 |
| Creators | Robb, Graeme R. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11895 |
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