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Phenol and its compounds are highly toxic even in low concentration, and have become the subject of intense research during the last two decades. Effluents from industries such as oil refining, paper milling, olive oil extraction, wood processing, coal gasification and textiles and resin manufacturing and agro-industrial wastes discharge phenols at levels much higher than the toxic levels set for this compound. Advanced Oxidation Processes (AOPs) such as UV, UV-TiO2, UV-H2O2, O3 and UV-O3 have become popular in recent years as efficient treatment methods for recalcitrant compounds like phenol. The effect of microwave (MW) and combined MW-UV treatment on degradation of phenol was studied in aqueous solution in the presence and absence of TiO2 under controlled temperature conditions. It was found that the efficiency of MW and MW-UV processes for the degradation of phenol was less than 10% after 120 minutes of treatment. However, the efficiencies of MW-TiO2 (hydrothermal) and MW-TiO2 (sol-gel) were slightly more than those of the above processes at 12 to 15% after 120 minutes, which might be due to adsorption of the phenol on the surface of TiO2 particles. It also was observed that MW-UV-TiO2 was superior to any other process studied for the degradation of phenol. At natural pH, the degradation efficiency of MW-UV-TiO2 (HT) on 1500 ppm of phenol in water was 23%, and for MW-UV-TiO2 (SG) it was 20%. Hence, it can be concluded that the catalyst (TiO2) prepared by the hydrothermal (HT) method had better catalytic activity than TiO2 prepared by the sol-gel (SG) method, which might be due to its structural and optical characteristics. Of the two developed reactors which are MW and a combined MW-UV reactor, MW-UV combined with TiO2 could be used for most successful degradation of phenol.

The nature of chalcogenides as electrets is virtually an unexplored arena. Electrets now exist in a variety of forms such as the electroelectret, thermal electret, photoelectret, radioelectret and magnetelectrets. An investigation of selenium as a dielectric is employed using the method necessary for the preparation of thermal electrets. The effect of the various parameters such as charging time, charging temperature and sample dimensions are investigated and observed. From these observations a conclusion can be made to the type of preferred orientation taking place in the material; be it dipole orientation, ion transfer or carrier displacement.

Electromagnetic heating (EMH) processes are being increasingly used in the industrial and domestic sectors, yet they receive relatively little attention in the thermal engineering domain. Time-temperature characteristics in EMH are qualitatively different from those in conventional heating techniques due to the additional parameters (viz dielectric properties of the material, size and shape of the product and process frequency). From a unified theory perspective, a multi-purpose model has been developed in order to obtain the heating characteristics for an arbitrary processing situation. Theoretical analyses of various EMH processes in materials of various regular geometries and a range of physical properties have been undertaken. Despite the wide spread usage of microwave energy in the food engineering sector. few understand microwaves and their interactions with foods. Much of the published research is largely focussed from the view point of an electrical engineer and aimed at the oven designer. However, trial-and-error methods are usually employed when developing microwavable food products and when using microwave ovens. The presented thesis is focussed from the view-point of the thermal engineer and aimed primarily at food developers and end users. The multi-purpose model was then modified specifically for simulating the heating of food materials in a microwave oven. The validity of the commonly made assumptions was investigated; in particular the variation of dielectriC properties during the heating processes and their likely influence on the model's predictions. Experimental data available in the literature were compiled and analysed to form a set of equations for predicting the dielectric properties of various food materials. Also available correlations for thermal properties were evaluated for a selected set of experimental data of different food materials. Analyses were undertaken to demonstrate and evaluate the effects of various parameters on the heating characteristics of different food materials commonly heated/cooked in microwave ovens. A qualitative comparison of model predictions and experimental measurements is provided to validate the physical basis of the model. Findings from the model lead to a better understanding of the interactions between foods and microwaves.

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The use of bioenergy has been increasing due to efforts in fossil fuels replacement. Modern bioenergy technologies aim for high efficiency and low pollution levels, which increases the need for methods for the on-line characterization of biofuels. Dielectric methods have been identified as useful for the sensing of solid biofuels because they allow for rapid, nonhazardous, nondestructive, and bulk determination of material properties. The dielectric properties describe the interaction between the material and the electromagnetic waves. Dielectric properties are intrinsic of the materials and can therefore be used for the development of prediction models that can be applied regardless of the measurement technique. The study of the dielectric properties is also important as it improves the understanding of the dielectric behavior of the materials. This thesis focuses on the dielectric properties of solid biofuels and their use in the characterization of these materials. The work presented includes the development of new methods permitting the determination of the dielectric properties of solid biofuels with large particle size (waveguide method), broadband measurement of the dielectric properties (coaxial-line probe), and the use of a previously developed method for the accurate determination of the dielectric properties (free-space method). The results includes the dielectric properties of solid biofuels and their dependence on parameters such as frequency, moisture, density, and temperature. This thesis also presents semi-theoretical models for the determination of moisture content, which obtained a RMSEP of 4% for moisture contents between 34 and 67%, and an empirical model that resulted in a RMSEC of 0.3% for moisture contents between 4 and 13%. Finally, this thesis includes measurements of the influence of salt content on the dielectric properties and a discussion of its use for estimation of the ash content of solid biofuels. 

Bismuth layer structure ferroelectrics (BLSFs) have attracted intensive investigation for the potential use in nonvolatile ferroelectric random access memory (NvRAM/FeRAM) and high temperature piezoelectric devices. In this thesis, there are three kinds of Bi-layered structure ferroelectric ceramics materials prepared by solid-state reaction methods. Investigations have been made on the crystal structure, surface morphology, and dielectric properties of these ferroelectric materials. In the chapter3 of this thesis, ferroelectric materials are SrBi2Ta2O9-based ceramics. One of the materials is SrBi2Ta2O9 composition with excess x wt% Bi2O3 (x=0, 2, and 4). Even 1280oC is used as the sintering temperature of stoichiometric SrBi2Ta2O9 composition, the X-ray diffraction patterns will show that the SrBi2Ta2O9 phase is coexisted with the raw material of Ta2O5 and the secondary phases of SrBi2O4 and BiTaO4. For SrBi2Ta2O9 composition with excess 2wt%- or 4wt%-Bi2O3-doped and sintered at 1040oC, the Ta2O5, SrBi2O4, and BiTaO4 phases are eliminated and only the SrBi2Ta2O9 phase is observed in the X-ray diffraction patterns. The other of SrBi2Ta2O9-based ceramics was doped with V2O5. V2O5 is used to substitute Ta2O5 of the SrBi2Ta2O9 ceramics to form SrBi2Ta2-xVxO9 composition, where x=0.1, 0.2, 0.3, and 0.4. For all SrBi2Ta2-xVxO9 composition, the crystal intensities of the (00l) planes (l =6, 8, 10, 12, and 14) increase with the increase of sintering temperature and saturate at 1050oC-sintered ceramics, and the increase in the crystal intensities of the (008) and (0010) planes are more obvious. For the same sintering temperature, the crystal intensities of the (00l) planes increase with the increase of V2O5 content and saturate at SrBi2Ta1.7V0.3O9 ceramics. In the chapter4, ferroelectric materials are SrBi4Ti4O15-based ceramics. One of the materials is (Sr1-xBax)Bi4Ti4O15 (x=0, 005, 0.1, 0.15, and 0.02), and BaO is used to substitute SrO. Dielectric properties were investigated in the temperature of 25oC~ 805oC at 1MHz. It is found that Curie temperatures are shifted to higher temperature as the BaO content increased. For (Sr1-xBax)Bi4Ti4O15 ceramics sintered at 1150oC, the Curie temperature for x=0, 0.05, 0.1, 0.15, and 0.2 are 645oC, 665oC, 705oC, 725oC, and 745oC, respectively. The other is non-stoichiometric compositions SrBi4Ti4O15+x Bi2O3, (x= -0.04, -0.02, 0, 0.02, and 0.04). From the observations of SEM, the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics reveal a two-phased grain growth, the bar-typed and the irregularly disk-typed grains coexist; The other ceramics will reveal the irregularly disk-typed grains. From the X-ray diffraction patterns, Bi2Ti2O7 and SrTiO3 phases are observed in the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics. Except the SrBi3.96Ti4O14.94 ceramics, the other ceramics have revealed an unapparent splitting peak in the (119) plane. In the chapter5, ferroelectric materials are (Na0.5Bi0.5)TiO3-BaTiO3-based ceramics. The 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 (x= 0, 1, 2, and 3) ceramics were fabricated by two different processes. The first process is that (Na0.5Bi0.5)TiO3 and BaTiO3 composition was calcined at 850oC and 1100oC, respectly, and then the calcined (Na0.5Bi0.5)TiO3 and BaTiO3 powders were mixed in according to 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions. The second process was that the raw materials were mixed in accordance to the 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions and then calcined at 900oC. The sintering process was carried out in air for 2h from 1120oC to 1240oC. As the sintering temperatures are higher than 1160oC, the maximum dielectric constants of ceramics made by the second method are higher than those of ceramics by the first method, and the maximum dielectric constant of this ceramics will reveal in the x =1 ceramics. Both ceramics reveal a broaden dielectric constant-temperature curves. The other is (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3 compositions, where x= 0.03, 0.05, and 0.07, formatted by two different methods given above. The dielectric-temperature curves of (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3-based ceramics are almost unchanged as the measured frequency changed from 10 kHz to 1MHz.

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