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The objective of this research project was to investigate the effect of microwave treatment on the conversion of pyrite in coal in order to enhance its magnetic properties and to aid subsequent desulphurisation by magnetic separation. Key areas of this investigation include:- a review of the fundamental theoretical aspects of heating in an applied microwave field, a detailed literature survey of the potential applications of microwave heating to aid coal desulphurisation, a study of the transformation mechanisms of pyrite by microwave and conventional heating methods, a comprehensive review of the influence of heterogeneity on the dielectric properties of coals and the effect of high power microwave heating on the decomposition of pyrite in a high sulphur coal. A detailed survey of the literature has shown that although a significant amount of work has been reported on the microwave heating of coal, little information is available which examines the mechanism through which different coals heat in an applied microwave field. A study is therefore presented in this thesis which quantifies, for the first time, the structural ordering of carbon in a range of coals of various ranks and the relationship with their dielectric properties. The results show a clear relationship between the structural ordering of carbon in coal and dielectric loss factor. Essentially, as the structural ordering increases, the level of free charge (per unit volume) increases together with electron mobility which results in an increase in dielectric loss factor. The transformation of pyrite to form the more magnetic pyrrhotite and other related decomposition products by conventional radiant heating has been the focus of much research. However, little attention has been given to the effect of microwave heating on the mechanisms of pyrite transformation in inert and oxygen-containing atmospheres. The study presented in this thesis investigates the effect of temperature, particle size and heat treatment time to establish how these affect the transformation process and the subsequent nature of the final product. This study showed that exposure of pyrite to both conventional and microwave heating methods enhanced its magnetic properties as a result phase alterations at the particle surface. Conventionally heated pyrite samples showed the highest magnetic susceptibility increases, speculated to be due difficulties surrounding the temperature control and measurement of the microwave heated samples. From a review of the literature in this field of research and by SEM observations made for each sample test in this work a general pyrite transformation model as a result of microwave exposure is proposed. The effect of microwave radiation on the conversion of in-situ coal derived pyrite was also investigated. The study presented here extends previous work by others by assessing quantitatively the influence of higher applied microwave power levels on the conversion of pyrite in coal. Samples of run-of-mine high pyritic sulphur content (~12%wt) Kentucky coal were microwave pre-treated at varying exposure times using 8kW and 15kW of microwave power operating at a frequency of 2.45GHz. This work included initial material characterisation which consisted of TGA, optical microscopy and dielectric property measurement, followed by SEM/EDAX characterisation of both microwave treated and untreated sample specimens. This is the first time that microwave treated coal, embedded in a carnauba wax mounting medium, has been observed by this method with focus on the thermal alterations of the pyrite phase. It was demonstrated that with sufficient power and residence time, the conversion of pyrite to the more magnetic pyrrhotite is achievable using microwave irradiation. The amount of pyrrhotite formed as a result of microwave exposure varies with microwave residence time and forward power level. Comparisons of change in the iron sulphide species in the coal was made between microwave treated and untreated material. Using a multimode microwave cavity it was found that significant amounts of pyrrhotite were formed in 20s when using 15kW of microwave power. Treatment at lower power levels in this type of cavity was found to be less effective. The overall effect of treatment on the coal proximate character was minimal.

Direct measurement techniques for the investigation of electrical processes in solid dielectrics are reviewed and their respective strengths and weaknesses are discussed, particularly the complementary nature of thermally stimulated current measurements. The successful design and construction of a new Thermally Stimulated Discharge Current (TSDC) Spectrometer at the University of Southampton is presented and its correct function validated with experimental measurements of the well known and often characterized synthetic polymers low density polyethylene (LDPE) and polyethylene terephtalate (PET). Results were found to correspond well to published data. First TSDC observations of filled and oil impregnated papers are presented. The second aspect of this work is the investigation of natural polymer insulation materials,specifically paper for oil-paper insulation systems. For the first time, electrical insulation papers with filler contents up to 50% were investigated. Bentonite and talcum were compared as filler materials and found to have negative and positive effects respectively. The superior electrical strength of a talcum filled kraft paper was verified, and a series of constructive modifications was undertaken to further maximise its electrical strength at comparable or improved dielectric performance. An increase in electrical breakdown strength of 20% to 30% has been observed, but the substitution of such great amounts of fiber with fillers also lead to a reduction in mechanical strength of the paper. Further trials with chemical additives were conducted to counteract this effect and polyvinyl alcohol and starch were found to enhance the paper strength. Additional trials also comprised sizing agents, guar gum and wet strength agents. Uncharged or slightly charged chemical additives provided best results with regard to dielectric performance. The significance of the trialled paper modifications is judged in light of statistical analysis.

In analysis of electric field interactions with dielectrics, higher order moments and dielectrophoretic force terms are commonly ignored in what has become known as the dipole approximation. The very few multipolar studies in the literature have either confined analysis to spherical particles or modelled non-spherical particles as spheres of similar dimensions. A major obstacle in analysing the significance of higher order moments has been the limitedness of multipole moment determination techniques. Analytic derivations for higher order moments are only available for spherical particles. This work addresses this roadblock and presents a hybrid numerical-analytical method for determination of the first three effective moments of particles of any shape subjected to electric fields of arbitrary geometry. Results of applying this method for determining higher order dielectrophoretic force terms have been verified by comparison against total force calculations using the Maxwell stress tensor method, known for its mathematical rigorousness in accounting for all interaction between an applied electric field and subject dielectric(s). It is shown that the dipole approximation is particularly unreliable for non-spherical particles, importantly comprising the vast majority of bioparticles. It is shown that higher order terms can constitute up to half the dielectrophoretic force on dielectric particles in suspension. With the current trend toward micro- and nano-electrode geometries used for single particle analysis, and a consequent increase in the number of instances where invoking the dipole approximation can be highly inaccurate, this work offers a computationally inexpensive and verifiably accurate means for determining higher order moments and dielectrophoretic forces.

Ion irradiation has been investigated as a route for the preparation of mechanically stable and highly durable cross linked sulphonated PEEK for fuel cell application. The formation of cross linking was confirmed by solvent extraction using the well known Charlsby–Pinner equation. The DSC results indicated that the cross links retard the crystallization, but no changes were observed in the mechanism of crystallization. The thermal kinetic data for irradiated PEEK quantitatively suggest that these films still have sufficient thermal stability for long term applications as fuel cell membranes. Analysis of the dielectric response by Cole-Cole, Havrilak and Negami and Williams and Watts equations indicated that the dipole relaxation was broadened and becoming more asymmetric with cross link density. The sulphonation of the cross linked PEEK in concentrated sulphuric acid indicated that the rate of reaction decreased with cross linking density and was consistent with diffusion control kinetics. Increasing cross link density resulted in more bound water in the equilibrated membranes and the nano-structure present was comparable to that of Nafion. Cross linking improved the chemical stability of PEMs in particular in methanol solution.The measurement of power output and energy efficiency suggested that the cross linked PEMs produced are promising candidates to replace Nafion membranes but more information are required, in particular on their long term stability under fuel cell operating conditions.