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.

This thesis explores the picosecond dynamics of aqueous solvent and the low frequency modes of biomolecular systems. These dynamics are probed with a combination of experimental THz spectroscopy and theoretical models from molecular dynamic simulations. The dynamics of the water are first measured in a polar liquid concentration series, with an attenuated total reflectance method to reduce absorption from the highly absorbing solvent. Reverse micelle systems are also investigated using a transmission method to reduce the non-essential bulk water around the sugar trehalose. The THz spectrum and molecular dynamic simulations of both these experiments show increasingly sterically hindered waters in the presence of a perturbed hydrogen bond network. Classical computational models of condensed phased water do not reproduce a broad spectral feature at 200 cm-l (6 THz). A region associated with the bending and stretching motions of hydrogen bonding. Three methods of explicit polarisation are tested on classical water models to improve modelling of this bending and stretching dynamic, but each method fails to replicate a 200 cm-l peak. It was concluded quantum mechanical effects of the hydrogen bond are not adequately accounted for, which may significantly impact the 200 cm-l frequency region. The low frequency modes of proteins are also investigated using the Gprotein coupled receptor bovine rhodopsin . Rhodopsin is activated by light illumination, which causes a conformational shift in the protein structure. This was detected as a change in the proteins low frequency dynamics that were stabilised by the presence of membrane. Normal mode analysis of the inactive and active bovine rhodopsin crystal structure confirmed these results. Furthermore, part of this thesis explores a novel THz spectrometer design, based on the principles of polarisation modulation infrared reflection absorption spectroscopy. This spectrometer has advantages over traditional methods, principally being able to perform real time referencing without the need of a separate optical path.

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This thesis is partly concerned with investigating news ways of applying microwaves in a chemical synthesis; it is also concerned with the mechanism of such processes, including microwave-assisted diffusion, structural changes induced by microwave fields and the effect of pressure on microwave-driven reactions. In some cases we also studied the mechanism of reactions driven by more traditional sources of heat. A novel microwave reactor was designed and constructed to enable us to perform mechanistic studies of the hydrothermal synthesis of iron oxide particles by small angle neutron scattering (SANS); this was performed in parallel with small angle X-ray scattering (SAXS) and EXAFS on samples heated conventionally. SANS measurements showed that after an initial burst of nucleation, particles of 50 Å mean diameter were formed in the first 30 minutes, evolving to a final size of 100 Å after 7.5 hours. The SAXS measurements reported a burst in particle growth as the sample was heated above 50-60°C, producing particles up to 250-300 Å in diameter. However, wide-angle X-ray scattering data showed that the latter samples did not exhibit any Bragg scattering, implying that they had no medium-long range crystalline order when suspended in the growth medium. EXAFS data revealed the presence of very small particles of haematite in solution, which seems to add weight to the hypothesis that haematite particles are produced first through the growth of small particles which then aggregate to larger clusters. Studies were also performed of the microwave-assisted diffusion of cations into channelled iron and manganese oxides, and showed that the choice of experimental conditions -particularly the nature of the host material - have a significant effect upon the final product. In several cases, microwave heating accelerated diffusion and could also lead to novel routes to insertion compounds. Further studies on the influence of microwave heating on the structure and dynamics of materials involved the construction of further pieces of apparatus to perform in situ diffraction during microwave irradiation. Neutron diffraction was performed on aspirin to probe proton disorder, and high-resolution powder X-ray diffraction was conducted on the fast-ion conductor beta alumina to look at thermal excitation of the relatively mobile sodium ions during microwave heating. In both cases we demonstrated that the sample could be heated and studied <i>in situ, </i>and structural changes were revealed through changes in the Debye-Waller factors of particular atoms in both materials. The experiments on aspirin indicated that the sample had been subjected to a localised heating effect.

Using a 35 Gc/sec spectrometer, E.P.R. linewidths have been measured in a number of synthetic ruby specimens grown by various means. In addition, measurements of both linewidth and relaxation time have been made on a number of specimens of calcium tungstate doped with neodymiura. Using a mathematical treatment of the second moment, the homogeneously broadened ruby line has been resolved into concentration-dependent and concentration-independent components. The observed constant nature of the former suggests that the effective concentration of paramagnetic centres is not indicative of the true chemical concentration. Analysis of the inhomogeneous ruby line results in broadening components representative of axial misorientation and strain, A moderate correlation is obtained between misorientation figures derived from x-ray and e.p.r. measurements, and a similar correlation exists between strain and spin-lattice relaxation times. There appear to be no significant differences between the various types of flame-fusion material available. Preliminary analysis suggests that the homogeneous line in calcium tungstate owes its width to processes similar to those occuring in ruby, but strain does not appear to be predominant in the inhomogeneous broadening. Relaxation times in this material exhibit concentration and orientation dependence and a temperature dependence has been fitted empirically in the Direct and Raman regions.

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No description available.

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No description available.