A range of new mixed metal carboxylate ((M(O2CR)n) glasses has been prepared. Typically, Mn+ = alkali metals, alkaline earth metals, Zn2+, Pb2+, Sn2+, Co2+ and Cu2+. R increases from CH3 to C7H15 and higher. The alkyl chain can also be branched or aromatic. The properties of these glasses are affected by both the metal cations and carboxylate anions. Densities range from 1.2 to 2.7 g cm-3 and refractive indices from 1.4 to 1.6. Transparency has been shown to extend from 250 to 1400 nm. The carboxylate mixtures could be maintained in the molten state, at temperatures ranging from 100-200°C for prolonged periods without decomposition. Glass transition temperatures have been determined; these generally extended from 30°C up to 60°C. The melts were excellent solvents for a wide range of organic compounds. These dissolved in the carboxylate melts with no appreciable decomposition. The melts could then be quenched to give monolithic glass matrices. By choosing specifically designed organic compounds, the glasses have potential application for photochromism, electrochromism and non-linear optics. Investigation of the solubility of the glasses in water indicated the dependence on cation combination and chain length of the carboxylate ion. These investigations were made to explore the use of the glasses as host media for the release of agrochemical and other compounds with biological activity. It has been shown that Culex quinquefasciatus gives a positive ovipositional response to pheromone that is released from doped glasses over an extended time period. An investigation of the glass structure and the environment it provides for guest materials was undertaken using selected analyses. The structures of zinc carboxylates were determined by X-ray crystallography to provide information pertinent to the nature of the coordination of zinc in these glasses. Organotin compounds were dissolved in carboxylate glasses and studied by 119Sn NMR and Mossbauer spectroscopy. Anion exchange reactions readily occurred in the melts; there was also evidence of Sn-C bond cleavage with certain species. The potential of using Mossbauer spectroscopy as a probe into the glass "structure" is discussed.

TiO2 is widely considered as a promising photocatalyst to degrade various organic pollutants in water, and to harvest sunlight renewable energy application. However, the efficiency of the photocatalytic reaction using TiO2 is not high due to its wide band-gap (3.22 eV, corresponding to the wavelength of 385 nm), which corresponds to the lower end of the wavelengths of solar light. The aim of this project is to use a continuous hydrothermal flow synthesis (CHFS) technique and other post-treatment methods to synthesize and tailor nano-TiO2 and TiO2-related photocatalysts for improved photoactivity. It was demonstrated that the rapid crystallising environment in a CHFS system resulted in the anatase phase of TiO2 (ca. 5 nm) with a high surface area and a high crystallinity. The CHFS system provides a flexible route of doping TiO2 at the atomic level (lattice doping) either to decrease the band-gap or to introduce intra-band gap states, which allow activation by visible-light. The structures of the resulting nanocatalysts were investigated using powder X-ray diffraction (XRD) and Raman spectroscopy. The quantity and chemical nature of the catalyst surface were determined by X-ray photoelectron spectroscopy (XPS). Morphologies of the products were characterized by Transmission Electron Spectroscopy (TEM) and Scanning Electron Spectroscopy (SEM). Band-gap energy was determined by UV-Vis spectrophotometry. A TiO2-CeO2 composite catalyst was successfully synthesized by CHFS. A stable solid-solution was indentified, which leads to a totally different optical property (i.e. with a narrow band-gap) when mixed with a methylene blue (MB) dye solution. All the composites materials show improved photodecolourisation rates. Novel 2D sodium titanate nano-sheets (ca. 400×500 nm) were developed with a high concentration of NaOH into the reactor. This material exhibits the highest photocatalytic efficiency amongst all materials being tested in this project. Several post-treatment methods were also adopted to further modify the CHFS-prepared nano-TiO2 samples. By heat-treating nano-TiO2 powder in air, the crystallinity of the sample was increased. By exposing the nano-TiO2 to ammonia atmosphere at a range of temperatures, products ranging from N-doped anatase TiO2 to phase-pure titanium nitride (TiN) were successfully obtained. N-doped TiO2 materials showed significant red-shift in band-gap. Surface modification of TiO2 in vanadium salt leads to a high surface absorbability and photo-oxidising power. Among all the modified samples, some of them indeed exhibited improved photocatalytic activity over the unmodified nano-TiO2. Moreover, the microwave dielectric properties of selected TiO2 samples (metal ion lattice doped) were also examined using sintered TiO2 discs. The results suggest that a useful dielectric resonator material can be achieved by introduction of certain dopants in combination with a spark plasma sintering (SPS) method.

The room temperature sol-gel processing technique was employed for the first time in the present work to fabricate the novel binary compound of the calcia-alumina (C12A7) system consisting of calcium oxide (CaO) and aluminium oxide (Al2O3) in a 12:7 ratio. The highest level of homogeneity and transparency of the C12A7 solution in ethanol was achieved by optimizing pH values, reaction dynamics and modified precursor structures. Studies were performed on this binary oxide in both thin film and powder forms. By using High Temperature X-Ray Diffraction (HTXRD) and Simultaneous Thermal Analyzer (STA), phase transformations in C12A7 powder were examined in situ under continuous heat treatment from room temperature to 1200°C. The samples were found to be amorphous at room temperature. As the temperature was increased, crystallisation was completed at 1100°C. The purity of C12A7 and the removal of redundant chemical by-products were confirmed by independent Fourier Transform InfraRed (FTIR) and Raman Spectroscopic measurements. C12A7 thin films were spin coated on single crystal MgO <100> substrates and the effect of heat treatment on crystallinity were investigated using XRD. Initial signs of the crystallisation of C12A7 thin film were observed at 800˚C and the complete crystallisation was achieved on heat treatment at 1100°C for 3 hours. Optical absorption spectroscopy measurements were made in the UV-Visible region and experimental data were analyzed to evaluate the dependence of the band structure of C12A7 crystalline phase on annealing temperature.

Ceramic materials have considerable attraction for use in applications where the service temperatures are high and where fire performance and non-combustibility are important. Unfortunately most monolithic ceramic materials are extremely brittle which limits their use for structural applications. The development of fibre and particulate reinforced ceramic composites provides a route to achieving increased toughness in the materials, although this is often at the expense of ultimate strengths and/or the process-ability of the materials. Many reinforcing fibres used with ceramics are inherently expensive and manufacturing routes to produce fibre reinforced materials can involve high processing temperatures and are consequently expensive. A key goal of this research therefore is to develop a new type of ceramic matrix composites that combine toughness, strength and process-ability to provide a cost effective structural material. The research described in this thesis has been concerned with the development and characterisation of a series of ceramic compounds that can be moulded at modest temperatures( 130-160" C) and pressures in a manufacturing system that replicates dough moulding compounds (DMC) as used for polymeric matrix composites. The conventional polyester matrix of polymeric DMC has been replaced by a soluble inorganic system which is compounded with fibres, fillers and hardening agents to produce a paste-like or doughy substance The handle-ability of the material is determined by the viscosity of the matrix and the type or amount of fillers and additives present. The research has involved a careful set of experiments in which the formulation of the ceramic DMC has been systematically varied in order to achieve an optimum viscosity for storage and handling together with a further series of experiments studying the hardening and cure of the compounds. The mechanical properties of the compounds have been measured and additional formulation changes have been introduced to maintain desirable processing characteristics while improving mechanical properties, and in particular the impact resistance using instrumented falling weight impact machines. Finally the fire properties of the compounds have been studied using cone calorimetry and indicative furnace testing. The structure of the compound has been studied throughout the programme with various microscopic techniques and thermal analysis systems used to characterise the materials, their dispersion and changes that occurred during processing and after high temperature exposure. The final result of the programme has been the identification of a range of material formulations that can provide a tough moulding compound, capable of high temperature service use, that possesses useful structural properties and which can be processed cheaply at modest temperatures using low cost materials.

A comprehensive study of domain switching process in different ferroelastic and ferroelastic/ferroelectric perovskite structured ceramics has been performed. The effects of thermal fluctuations on domain switching dynamics were investigated in the ferroelastic and in the ferroelectric case under static and dynamic electric and mechanical conditions. In the ferroelastic case, domain switching behaviour was investigated for different compositions, using different types of mechanical tests. Compression tests were carried out to characterize the ferroelastic properties, such as coercive stress, hysteresis loop and irreversible strain. Creep experiments were performed to study the domain switching time dependence at different stress levels. Domain switching kinetics during creep was characterized by implementing a rate model, based on thermal activation rate theory, which allowed the activation volume to be estimated. A Rayleigh-type analysis was performed to study the effects of stress amplitude, loading rate, temperature and composition on ferroelastic switching. Rayleigh-type relationships were proposed to fit the results and the rate model developed was applied to quantify the effect of the loading rate on the Rayleigh loops. Alternative methodologies were developed to assess the effects of rate and temperature on the coercive stress, providing original sets of data. A further application of the rate model provided an estimation of the activation parameters (volume and enthalpy). In PZT 5A at the coercive field the activation volume was calculated to be 2.44 nm3, with a reasonable consistency with the value obtained from creep tests (7.49 nm3). In the ferroelectric case, domain switching was studied by generating P-E and butterfly hysteresis loops and by analysing creep-relaxation curves. In creep experiments, the polarization and the strain were measured simultaneously, during the application of a constant electric field. An insight into the evolution of domain structure and on domain switching mechanisms was gained, highlighting analogies and differences with the ferroelastic case. Experiments at different frequencies, allowed the activation volume to be estimated at the coercive field (77 nm3). The relatively large value indicates small rate dependence and suggests a domain structure with broad and mobile domain walls, being the preferred sites for the nucleation.

The conventional materials discovery is a kind of empirical (“trial and error”) science that of handling one sample at a time in the processes of synthesis and characterization. However, combinatorial methodologies present the possibility of a vastly increased rate of discovery of novel materials which will require a great deal of conventional laboratory work. The work presented in this thesis, involved the practice of a conceptual framework of combinatorial research on BaTiO3-based positive temperature coefficient resistor (PTCR) materials. Those including (i) fabrication of green BaTiO3 base discs via high-throughput dip-pen printing method. Preparation and formulation of BaTiO3 inks (selection of dispersant and binder/volume fraction) were studied. The shape of drying residues and the morphogenesis control of droplet drying were discussed. (ii) investigation of a fast droplet-doping method, which induced the dopant precursor solution infiltrating into the porous BT base disc. Various characterization methods were used to examine the dopant distribution in the body of disc. (iii) devising a high-throughput electrical measurement system including an integrated unit of temperature control and automatic measurement operation, and an arrayed multichannel jig. (iv) synthesis of donor-doped BaTiO3 libraries, which involved lanthanum, erbium, yttrium as donor elements and manganese as an acceptor dopant element respectively. Their temperature dependant resistivities were also explored. The work successfully developed an integrated tool including high-throughput synthesis of a large batch of libraries and high-throughput electrical property measurement for combinatorial research on BaTiO3-based PTCR ceramics. The Abstract ii combinatorial method, thus validated, has the potential to deliver dopant-doped BTbased PTCR libraries rapidly with a very wide range of dopant mixtures and concentrations for electrical property measurement and deserves to be applied to other low level dopant ceramic systems. These approaches are novel and paving the way for other new materials selection and materials research.

The increasing availability of nanopowders and nanotubes combined with new processing techniques is enabling the development of new multifunctional materials. Carbon Nanotubes (CNTs) are one of the recently discovered allotropic forms of carbon. They have exceptional mechanical, electrical and thermal properties. The application of CNTs in the reinforcement of ceramic nanocomposites has not yet been fully investigated and is the subject of this study. Alumina is the main matrix used in this study. CNTs need to be de-agglomerated and homogeneously distributed in ceramic nanocomposites. Dimethylformamide (DMF) produces fine and stable CNT and alumina dispersions. All nanocomposites were sintered by Spark Plasma Sintering (SPS). Nanocomposites prepared using DMF dispersions showed better dispersions, higher electrical conductivity and mechanical properties as compared to those prepared using ethanol dispersions. The addition of CNTs or Carbon Black (CB) to alumina significantly aids its densification. The CNTs produce significant grain growth retardation. CNTs were found to be well preserved in alumina after being SPSed up to 1900 oC. Structural preservation of CNTs in ceramic nanocomposites depends on the nature of ceramic and SPS processing conditions. The electrical conductivity of alumina – CNT nanocomposites is four times higher as compared to alumina – CB nanocomposites due to the fibrous nature and high aspect ratio of CNTs. Alumina coated CNTs were used for better interfacial adhesion with the matrix. Oxidative resistance of CNTs was increased by coating them with alumina and by decreasing the grain boundary area in alumina – CNT nanocomposites. Coated and uncoated CNTs showed higher mechanical reinforcement in alumina nanocomposite as compared to CB. The future for ceramic – CNT nanocomposites is very bright, especially for applications associated with the electrical and thermal properties. Apart from a good understanding of nanocomposites, the commercial development of CNT based technologies heavily relies on the availability and price of CNTs.

A range of soda-lime-silica glasses based on the composition 16% Na2O, 10% CaO and 74% SiO2 have been prepared with hydroxyl ion contents which varied from 59 to 780 ppm. The hydroxyl ion contents were determined using transmission Infra-red spectroscopy. The mechanical strength properties were investigated using the constant moment, double cantilever beam arrangement for fracture mechanics studies, and under atmospheres of 1% and 60% relative humidity. Four point bend studies under liquid nitrogen, and at room temperature were carried out using a number of different loading rates. In addition extensive Hertzian fracture and Vickers hardness testing has been carried out. The results of these experiments were analysed in terms of a continuum model of mechanical strength based on fracture mechanics concepts. The fracture mechanics experiments indicated that fracture toughness increased slightly with increasing hydroxyl ion content. Under Stage I subcritical slow crack growth at 60% relative humidity, crack velocities were greater in high hydroxyl ion content glasses than in low hydroxyl ion content glasses. In addition the effects of hydroxyl ion content on the low temperature viscosity, D.C. conductivity and elastic moduli, have been investigated. The viscosity was observed to decrease with increasing hydroxyl ion content, as did the activation energy for viscous flow. The D.C. conductivity decreased with increasing hydroxyl ion content. The mechanical strength results were interpreted in terms of stress-corrosion behaviour, influenced by alkali ion diffusion to the crack tip.

The recycling of a foundry ceramic waste from investment casting has been investigated. The waste was reduced in size by fly pressing and disc milling to d50 < 20 μm and cleaned by magnetic separation and acid leaching. The powder contained zircon, alumina and amorphous silica with 37, 38 and 24 wt. % (ZrSiO4: Al2O3: SiO2) respectively. Two products were targeted: zirconia toughened mullite (ZTM) ceramics produced with an addition of alumina and zircon based pigments developed by the removal of alumina and reaction with colourant ions. With an addition of 23.5 wt. % Al2O3, a ZTM containing 30 wt. % zirconia and 70 wt. % mullite exhibiting strength, hardness, thermal shock resistance and toughness commensurate with data reported in the literature were developed. Milling in isopropanol, dry pressing and sintering at 1600 ℃ for two hours optimised the properties. The transition to ZTM appeared to be through an intermediate glassy phase and limited by the dissociation of ZrSiO4. It was estimated that 70 % of the ZrO2 was transformable tetragonal without the addition of Y2O3. With Y2O3 non-transformable tetragonal ZrO2 was produced. It was shown that a clean zircon powder free of Al2O3 was generated by reaction with K2S2O7. Dissociation-synthesis and direct-synthesis routes were used to produce pigment. It was found that higher reaction temperature and the introduction of flux can significantly increase yellowness. The yellow produced from waste materials performed as well as those from commercial grade feeds.

The main aim of this project was to develop a durable ceramic wasteform by HIPing Cs-exchanged crystalline silicotitanate (CST) used for nuclear waste clean-up. The sodium form (Na-CST) and niobium substituted sodium form (Na-Nb/CST) CST were hydrothermally synthesised and characterised. The synthesised CSTs and a commercial CST containing material, IONSIV®, were subjected to ion exchange studies and then the crystal phases present after HIPing were investigated. Cs-IONSIV® was thermally decomposed and converted to two major Cs-containing phases, Cs2TiNb6O18 and Cs2ZrSi6O15, and a series of other phases. Additionally the effect of metal addition on phase formation under HIP conditions was explored. The microstructure and phase assemblage of HIPed Cs-IONSIV® samples as a function of Cs content were examined using XRD, XRF, SEM and TEM/EDX. To understand the Cs bonding environment in these Cs-containing phases, structural characterisation was undertaken using Rietveld analysis of synchrotron X-ray powder diffraction data and neutron diffraction data. The potential of these phases for hosting Cs+ and its decay product Ba2+ was also studied. This thesis is also concerned with determining the aqueous durability of these HIPed samples by carrying out MCC-1 and PCT-B leach tests. These show very low Cs leach rates and the promise of safe long-term immobilisation of Cs from CSTs as well as suggesting these phases are more leach resistant than hollandite - the material targeted for Cs sequestration in Synroc.