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.

Offshore wind farm structures may have the potential to affect marine navigation and communication systems by reflecting radar signals. With ever increasing size of wind turbines it is necessary to better understand the influence of radar signals on wind turbine blades in order to minimise the radar reflecting potential. One possible way of reducing radar reflection is to use radar absorbing materials. In this thesis, epoxy composite materials reinforced with five different types of nano-size additives: carbon nanotubes (CNTs), carbon blacks (CBs), silver, tungsten carbide and titanium oxide are manufactured and tested to investigated their potential as wind turbine blade material that absorb radar signals. Nanoadditives/epoxy composites with additives content ranging from 0.05-1 wt. % were fabricated by a simple cast moulding process. The nanoadditives were dispersed in the epoxy resin by sonication method. The degree of nanoadditives dispersion was observed by examining the surface of the composite materials using scanning electron microscope (SEM). Complex permittivity of the nanoadditives/epoxy composites was studied using a free wave transmittance only method at a frequency range of 6.5-10.5 GHz. The effect of the percolation threshold of the direct current conductivity on the composite permittivity was analysed and discussion. In order to get a better insight in the importance of the results they were compared to existing models (Maxwell- Garnett, Bruggeman, Bottcher, Lichtenecker and Lichtenecker-Rother). A new model based rule of mixtures is developed to predict the complex permittivity of the composite. A model of wind turbine rotor blade made of the nanoadditives/epoxy composite was developed using Comsol-multiphysics software. The data obtained from the experimental work was inputted in to the model to generate result of backscattered energy verses composite permittivity as a function of nanoadditives content. A decrease in backscattered energy was noticed with increasing nanoadditives content. The results demonstrate that radar reflecting signals will be significantly reduced by incorporating nanoadditives in the composite materials.

Gas sensors based on different principles have been developed for the applications of environmental monitoring, industrial processing, aerospace and the human body. Carbon nanotubes (CNTs) demonstrate a detectable electrical properties change upon gas molecules absorption. This has been extensively studied and used in chemiresistors and chemical field-effect transistors. Simultaneous response to different types of gases was reported. The aim of this study is to develop a new type of gas sensor by replacing the gate metal of a field-effect capacitor with a carbon nanotubes network. This novel sensor will combine resistivity measurements with potentiometric measurements, which should ideally lead to increased functionality and selectivity. The substrates (Al/Si/SiO2/Si3N4 or Al/Si/SiO2/Si3N4/LaF3) were fabricated with two gate electrode structures (interdigitated and two-line). CNTs in different solvents were drop or spray coated on to the substrates. Platinum coating on the CNTs was also introduced. The resistive measurements indicated an increase in the resistance of CNTs networks with increased oxygen concentration, and a decrease in the resistance of CNTs networks with increased hydrogen concentration with humidity interference. Evenly distributed CNTs film was achieved by spray coating which allowed the use of CNTs network as gate materials for potentiometric measurements. The potentiometric measurements suggested that the C-V curve shifted towards a lower voltage with an increased hydrogen concentration, and a higher voltage with an increased oxygen concentration. However, the response time was too long for practical applications. Pt deposition significantly improved the hydrogen response rate. A voltage shift of -450 mV with an equilibration time of 2 minutes was achieved when the hydrogen concentration increased from 1 to 100%. The C-V curve shifted by 500 mV with increased oxygen concentration (1-100%).

The aim of this project was two-fold. Firstly to provide an understanding of the behaviour of SMC when subjected to drop weight impact and secondly to investigate the effect of a surface layer of a metallic material (stainless steel, aluminium, brass and copper) and a layer of Ionomer on the impact behaviour of SMC. Tensile, flexural, compression, shear, charpy and drop weight impact tests were carried out on SMC (Sheet Moulding Compound). The response of SMC and various combinations of SMC and metal sheet (stainless steel, aluminium, brass and copper) and SMC with a layer of Ionomer to impact load have been assessed using an Instrumented Falling Weight Impact test machine. Slow indentation tests and a variety of destructive and non-destructive test techniques were used to monitor the initiation and propagation of damage and relate them to the major features of typical force-time curves obtained during impact. The deformation of the metallic layer was compared under impact and slow test and a calibration curve was produced. By using the calibration curve the energy absorbed by SMC and SMC as a layer in SMC+metal laminate was compared and results were related to stiffness and ductility of the metallic layer. The energy absorbed by the SMC-metal laminates were analysed and the energy absorbed by each constituents was determined. The effect of impact damage on tensile and compressive residual strength was assessed by conducting tension and compression test on the damaged specimens. Finally, a number of simple models and fInite element technique were used to predict the impact response of SMC and SMCmetal laminates to impact. The results of the research programme indicated a strong macrocomposite effect resulting in greatly improved energy absorbing capabilities for SMC. The indications were that a metal layer was required that would be stiff, thereby putting the SMC into compression and also ductile in order to support extensive deformation in the SMC whereby microcracking could accumulate.

Isotropic polymers lack sufficient strength and stiffness for many engineering applications. In order to improve these properties polymers can be filled with structural reinforcements such as glass or natural fibres. However, current major trends focus on simple monocomponent systems in an effort to reduce costs and increase recyclability. Composite systems, by definition, must employ at least two phases with different material properties. With the introduction of careful processing routes, it has been proven possible to create a fibrous, two phase composite, in which both are polypropylene. Polypropylene can be melt spun and solid state drawn to give oriented tapes, and moduli of -15GPa and tensile strengths of -550MPa can be achieved. These tapes can then be oriented into sheets, either in the form of woven fabrics or unidirectional layers. These sheets form the reinforcing phase of a single polymer composite material. Such single polymer composites based on polyolefins can be produced by using a separate matrix impregnation route, but these are limited by relatively low volume fractions of reinforcement. Previous work executed at the University of Leeds showed that polymer fibres can be welded together by selective melting of the fibre exterior, but this method is limited by a small temperature processing window. By using polypropylene tapes co-extruded with a copolymer skin, it has been shown that such tapes can be welded together at temperatures far below the melting temperature of the tapes, thus ensuring that thermal relaxation of the highly oriented polymer does not occur. The temperature processing window can be widened further by constraining fibres during heating. The optimisation of the drawing and structure of these tapes, together with an investigation of the static and dynamic mechanical properties, impact resistance and interfacial properties of composites formed from these tapes, are investigated in this thesis

In the construction industry, prepainted metal strip is a widely used material for fagade and roofs of building intended for commercial used. The physical properties of modem coatings are outstanding, however one big problem that remains and which affects the overall coatings performance is dirt pick up. Firstly the effect of weathering induced chemical composition change was evaluated using photo-acoustic infrared spectroscopy (PA-FTIR), and X-ray photoelectron spectroscopy (XPS). The results shown that photo-oxidation processes occurs via Norrish type I and type 11 reaction at several sites on the polymer backbone, with the ester linkage and the melamine crosslinkage being the more reactive. Secondly aluminosilicates have been found to be the main source of soiling with organic pollutants also responsible but to a minor extent, the presence of such dirt was confirmed by XPS analyses. Unusual peak shape was observed on the carbon narrow scans with low binding photoelectron emitted. Finally Polymer/organically modified layered silicates (PLS) nanocomposites are a new class of filled polymer with ultrafine phase dimension. They improve considerably the physical properties of the coating while reducing dirt pick up. The best results were obtained when the insitu intercalative method was used. However the implication of the onium salts is obscure and the relation between the nanocomposite structure and its properties is not well understood.

Porous scaffold materials have been widely used in biological tissue engineering. It is known that fluid flow in porous media significantly increases the supply of oxygen and other nutrients to cells seeded in the porous material, and speeds up the clearance of metabolic end products. Local shear stress distribution is a function of media flow rate, viscosity and the porous scaffold micro-structure. This research project aims to investigate fluid movement in porous structures by using a lattice Boltzmann method. This new numerical method models the fluid as a collection of identical particles with collision and propagation procedures, and has been shown as an alternative and efficient numerical solver of Navier-Stokes equations, in particular for flows in complex geometries. The numerical scheme is verified using flow in a two-dimensional channel, as well as in three-dimensional ducts with constant shapes, where analytical solutions are available. 2D porous structures originated from micro-CT images are then used to study the flow and wall shear stress distribution. One of the advantages of the lattice Boltzmann method is that the shear stress can be computed directly from the local distribution function and has the same accuracy with the velocity profile. Fluid patterns and wall shear stress distribution in 3D porous structures, which 6 are reconstructed from the micro-tomographic slices, have been investigated under different flow rates, viscosity and geometrical structures. Results from this project demonstrate that lattice Boltzmann method is suitable for flow modelling in scaffold materials. It provides detailed information on localized velocity and stress distributions, which can be used to improve the design of the scaffold for cell and tissue engineering.

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.

Composites are normally composed of two distinct phases: reinforcement and matrix. In recent years, a new class of “self-reinforced” polymer composites or “all-polymer” composites, which are based on similar or identical materials for both reinforcement and matrix have generated increasing interests in both academia and industries due to their advantages in terms of processing, interfacial properties and recyclability. Current research trend in this field is to investigate the potential possibilities of all-polymer composites based on high-performance polymer fibres. In this thesis, all-poly(ethylene terephthalate) composites (Part 1) and all-aramid composites (Part 2) were prepared. In Part 1, Chapter 3 describes the melt spinning and drawing of poly(ethylene terephthalate) (PET) into highly oriented fibres, with moduli of 20GPa and tensile strengths of 925MPa. The effects of spinning and drawing conditions on the mechanical properties of PET fibres were studied. In the following Chapters 4 and 5, all-PET composites were prepared from 1) hot compaction of bi-component multifilament PET yarns; and 2) a film stacking technique, i.e. combining PET tapes unidirectionally with copolyester adhesive films in an alternating “brick-wall” layer-by-layer structure. The effects of processing conditions on mechanical properties were investigated. In Part 2 Chapter 7, all-aramid composites were prepared by a selective surface dissolution method where aramid fibres were partially dissolved to form a matrix phase to bond remaining fibres together into composites. The structure, morphology and mechanical properties were characterized by X-ray diffraction, scanning electronic microscopy, dynamic mechanical analysis and tensile testing. Compared to traditional aramid/epoxy composites, these all-aramid composites show significantly high mechanical properties, even at elevated temperatures. In Chapter 8, the effects of processing conditions on various properties of all-aramid composites were studied and an optimum condition was found. By replacing high concentration sulphuric acid as a solvent, a mild mixed solvent was used to dissolve aramid fibre surfaces in Chapter 9. In this way, all-aramid composites with prolonged immersion times were prepared and characterized. Potential future work including all-PET composites from post-consumer PET waste, microstructural characterization of all-aramid composites and woven all-aramid composites are discussed in Chapter 10.