This thesis seeks to examine both permeability measurement and material characterisation of Continuous Filament Mat (CFM) glass fibre reinforcements. As an alternative to fabrics, which generally provide higher in-place properties, CFMs are often employed as low cost, 'lofty' (high uncompressed thickness, and therefore good specific flexural stiffness), easy to process reinforcements for Resin Transfer Moulded (RTM) parts. Within this project, investigation of permeability measurement has involved the development of two (radial and linear) liquid flow permeability techniques to provide a reliable and robust data set for a specific CFM (Unifilo U813-300). Then two novel (radial and linear) airflow techniques were developed for the measurement of CFMs, these providing comparative results with the liquid flow measurements. The benefits of airflow versus liquid flow include cleaner, lower pressured flow using a fluid that may be produced by compressor rather than stored, therefore having significant benefits for both laboratory and industrial measurements of permeability. Material characterisation is necessary to analytically investigate reinforcement materials, as permeability has a non-linear relationship with overall porosity. Permeability is therefore considered as a function of pore distribution, which encompasses the two scales of intra and inter fibre-bundle flow. Two areas have been investigated, these involving permeability measurement and microstructure characterisation. Comparative permeability measurements of a second CFM (Unifilo U850-300), consisting of a different arrangement of fibre bundle sizes, were undertaken using the 1D airflow method, and inter-laminar flow was investigated using the radial airflow method. These resulted in a permeability ratio of between 0.54 and 0.64 (U813/U850) across a 0.1 to 0.3 fibre volume fraction range for the two CFMs, and no significant inter-laminar pore space effect. Microstructural characterisation initiated with image analysis of electron micrographs, providing measurement of fibre diameters and intra-bundle porosity. Kozeny-Carman modelling then showed the permeability of intra-bundle areas to be insignificant resulting in a focus on inter-bundle flow. Although limited by assumptions made for various material parameters, semi-empirical models to provide inter-bundle porosity and fibre bundle geometries were developed. Relation with permeability was then achieved through calculating hydraulic radius and mean hydraulic radius and provision of a range of Kozeny constants (0.55 to 6.17) and coefficients to replace the Kozeny constant, which provide upper and lower bounds for the remaining factors of permeability. The overall future industrial benefits for material engineers rely on the addressing of these limitations for quantifying geometries, so as to provide clarity of the relationship between controllable material parameters and permeability. Towards this goal, suggestions of further work here investigate employing micro-CT imaging and the use of 3D modelling that have the

Some transition metal carbides and borides are ultra-high temperature ceramic compounds that have application in the nuclear and aerospace industries. The existing thermodynamic assessments of the systems containing the hafnium and zirconium carbides and borides were examined, along with all available experimental and theoretical data. One of the challenges of thermodynamic modelling is in accurately describing the point defects in ordered compounds. In the transition metal carbides and borides, vacancies and substitutional defects are common and play a significant role in determining the material behaviour. Hafnium and zirconium are very difficult to separate, and as such there is always some level of contamination in these compounds. Despite this, there is very limited quantitative information available about the effect that this contamination has on the properties of the material. Using first principles calculations of substitutional point defects in UHTC compounds, the CALPHAD modelling in existing thermodynamic assessments of the ternary boron-hafnium-zirconium and carbon-hafnium-zirconium systems was considered and areas for improvement were identified using the first principles insights. Hafnium and zirconium carbide have a wide range of stoichiometry facilitated by carbon vacancies. Developments to first principles techniques have allowed calculations of properties such as the vacancy formation energy that should be considered in thermodynamic assessment, but are currently not explicitly considered in the modelling. Using the carbon-zirconium system as an example, a method was developed by which the vacancy formation energy and vacancy-vacancy interaction energies can be considered directly in an existing CALPHAD optimisation without losing any of the information already encoded within it. This was applied to a thermodynamic assessment in the literature and to a new assessment of the carbon-zirconium system that was performed incorporating new experimental insights.

In this project, the ferroelectric materials Pr2Ti2O7, La2Ti2O7, Sr2Nb2O7, La2-xCexTi2O7 (x=0.15, 0.25, 0.35), Nd2-xCexTi2O7 (x=0.05, 0.25, 0.5, 0.75) and Sr2-xBaxNb2O7 (x=0.1, 0.2, 0.3, 0.4, 0.5) were investigated. They have a provskite-like layered structure (PLS), and are well known for their super-high Curie points (>1200 ˚C). Their ceramics were fabricated using Spark Plasma Sintering. For Pr2Ti2O7, single phase, dense and textured ceramics were prepared. The Curie point is greater than 1560 °C which is the highest known Curie Point so far for ferroelectric materials. Pr2Ti2O7 was shown for the first time to be ferroelectric because it showed piezoelectric activity after poling. For the La2-xCexTi2O7 solid solution system, the ferroelectric and dielectric properties of cerium (Ce) substituted La2Ti2O7 (LTO) were investigated. The solubility limit of Ce in La2-xCexTi2O7 was found to be between 0.35 and 0.5 supported by XRD results. The a-, b- and c-axes of the unit cell decrease with increasing Ce substitution. The Curie points (Tc) of La2-xCexTi2O7 (x=0, 0.15, 0.25, 0.35) also decreases. The dielectric constant and loss increase with increasing Ce substitution. Electrical resistivity decreases due to Ce substitution. Cerium can increase the d33 of La2Ti2O7. The highest d33 was 3.9 ± 0.1pC/N for La1.85Ce0.15Ti2O7. In the Nd2-xCexTi2O7 system, the cell volume increases from Nd2Ti2O7 to Nd1.25Ce0.75Ti2O7 and the Curie point (Tc) decreases with Ce increase. For the Sr2-xBaxNb2O7 solid solution system, the effect of Ba substitution on the structure and ferroelectric properties of Sr2-xBaxNb2O7 (x<1.0) was investigated. The a-, b-, c- axes and cell volume increase with Ba addition because Ba2+ is a relatively large ion. A atomic displace move model was developed to explain the spontaneous lattice strain, spontaneous polarization and Curie point change in the orthorhombic phase (Cmc21) with increasing Ba substitution. The critical point of Sr2-xBaxNb2O7 solid solution (x < 0.6) was determined by XRD and was supported by the XPS spectra of Ba 2p and O 1s. Textured ceramics of Sr2-xBaxNb2O7 compounds were prepared using the spark plasma sintering technique and the piezoelectric activity can be improved by Ba substitution, which increases the domain switch mobility. The highest d33 was measured as 3.6±0.1pC/N for Sr1.8Ba0.2Nb2O7. The thermal depoling behaviors of La2Ti2O7, and Sr2Nb2O7 were investigated due to their relatively high d33 piezoelectric constant and high Curie point. Both of them have a high resistance to thermal depoling, especially La2Ti2O7. Ginzburg - Landau theory was used to explain their behavior. The electric resistivity degradation of Sr2Nb2O7 was studied at different temperatures, and it was found to be stable below 800 °C.

An electrodeposited gamma-manganese dioxide has been studied by thermal analysis in vacuum, oxygen and water vapour environments between room temperature and 450°C. Water was the predominant desorption product and five types have been identified. Textural changes occuring as a result of dehydration were monitored by nitrogen adsorption at liquid nitrogen temperature and the isotherms obtained analysed by the as method. A micropore network was generated on outgassing above 160°C due to elimination of hydroxyl groups from the oxide lattice. The products obtained by partial chemical reduction of gamma-manganese dioxide have been characterised by X-ray diffraction and magnetic measurements and their thermal behaviour investigated. The microporosity revealed on outgassing was evaluated by nonane adsorption and the results compared with those obtained from nitrogen adsorption data. The thermal decomposition of gamma- and alpha-MnOOH has been studied in vacuum and at low oxygen pressures (10 Torr). In vacuum, gamma-MnOOH decomposed below 400°C to a mixture of Mn5O8, alpha-Mn3O4 and water. Above this temperature Mn5O8 was converted to alpha-Mn3O4 as a result of oxygen removal. The vacuum dehydration of alpha-MnOOH led to a new modification of manganese sesquioxide (Mn2O3) isostructural with corundum (alpha-A12O3). In oxygen both oxyhydroxides decomposed to beta-MnO2. gamma-MnOOH transformed directly to beta-MnO2 whilst alpha-MnOOH appeared to proceed via Mn2O3. The existence of two new oxides of manganese, namely Mn7O12 and Mn7O10 has been established by thermal measurements and chemical analysis.

The thesis reviews the historical development of stress analysis for the solution of stress functionsin the neighbourhood of cracks or flaws. The analysis assumes the material is a brittle continuum obeying the laws of linear elasticity. The influence of material structure on such analysis is considered both from the experimental and the theoretical point of view. For the experimental investigation, clay ceramics based on Kaolinite are used to provide a range of different coarse polyphase structures in the form of test pieces suitable for fracture testing in a three point bend rig. The values of the fracture stress OF, the critical stress intensity Kic and the modulus of elasticity E obtained in this way, are found to follow similar trends and to vary with the clay formulation. Scanning electron microscopy has been employed to study the intrinsic structure of the material. It is found that the measured values, not only of Kic and E, but also OF can be related to the structure. Thus in these materials, OF is not random flaw controlled and OF, Kic and E are all material influenced parameters. The validity of applying the stress equations to structured materials is shown to depend on the stress field at the crack tip being of the same form for both OF and Kic determinations. It is argued that in the case of quasi brittle materials, this is ensured by the plastic zone at the crack tip. In the case of the brittle ceramic materials investigated here, it is shown that similarity of stress at the crack tip is produced by subcritical crack growth. With subcritical crack growth, a physical significance can be attributed to derived variables such as the equivalent elastic crack, and the material dependence of OF can be explained.

The present work was carried out to determine the effect of different factors on the sintering of alumina using volume shrinkage as the sintering criteria, and to examine the mechanism of sintering over the temperature range 1200°C to 1950°C. Up to 1450°C this work agrees with the accepted theory of sintering by volume diffusion (shrinkage proportional to time to the power of two fifths), whereas, above 1450°C this work was found to differ from. the present-day theories of other workers, by giving a time relationship of a one fifth power. An explanation has been formulated using the concept of an exponential rise in the equilibrium concentration of vacancies present in the crystal lattice affecting the concentration gradient of defects from the particle junctions to the surface. The effect of preferring at temperatures below that at which sintering begins has been known empirically for some years, The present work explains this behaviour by considering the diffusion of atoms along the surface of the particles to give the formation of necks prior to shrinkage. Sintering from 1770°C to 1950°C was performed in vacuo and the temperature range was extended below 1770°C to 1600°C to compare the results with those obtained in air. The disparity observed has been explained on the basis of evaporation of high-energy areas giving a lower driving force for sintering and subsequent lowering of the shrinkage values compared with sintering in air A comparative examination of the effect of particle size and shape indicates the importance of the initial particle size as a control of the degree of sintering, The effect of additions of 1%, 5%, 10% liquid using sodium silicate as a liquid former, shows that an appreciable amount of liquid is not necessary for liquid-phase sintering, and that for the solution-precipitation stage only enough liquid need be present to form a lens at the particle junctions, With 1% liquid addition no liquid-phase sintering occurs, but enhanced solid state sintering is observed due to formation of b-alumina Na2O 11 A1203.

Ceramic armour must offer protection against armour piercing threats at low weight and affordable cost. As a possible means of improving armour, a range of SiC-B4C composites have been produced and characterised. The degree of contact between the two phases has been quantified and shown to have a strong effect on the densification and microstructure in these materials. This understanding has enabled independent variation of microstructural parameters which are normally interrelated. These were; porosity, SiC:B4C mass ratio, B4C distribution in a SiC matrix and SiC grain size distribution. To assess effects of each of these parameters on ballistic performance V50 testing was carried out, using 7.62 mm armour piercing rounds. The amount of porosity is shown to have a slight effect on V50 and a marked effect on scatter in V50. The pore size distribution is also shown to be important; across a range of pairs of materials with similar total pore volumes but differing pore size distributions, larger pores consistently give lower V50. SiC:B4C mass ratio does not seem to greatly affect V50, potentially allowing application specific cost/weight balances at constant protection level. B4C distribution has a strong effect. In general, for B4C features with diameters ranging from 1 m to 100 m, the coarser features performed better. Using coarse B4C particles in a SiC matrix, a V50 of approximately 980 ± 20 m s-1 at a density of 3.00 g cm-3 was achieved reproducibly. This material is preferred due to a combination of relatively lower cost, reduced density and repeatability. Knoop indentation has been used to derive possible merit indices which could potentially be used to rank ballistic materials. These includes analysis of failure probability of indents and the indentation size effect. A preliminary study indicates ballistic impacts may affect SiC polytype composition.

Glass-to-metal seals are used in a wide range of components. The nature of the interfaces between the constituents is often crucial to the performance of the seal and thus the aim of this study was to characterise the various interfaces in a novel seal made from a strontium boroaluminate glass-ceramic and the alloys Ti-6Al-4V and Kovar (Fe-29Ni-17Co). A titanium boride was found, by STEM, EELS and WDX, to have formed at the glass-ceramic to Ti-6Al-4V interface and to be bonded to both the metal on one side and the glass-ceramic on the other, in contrast to the classic view of glass to metal interfaces where bonding is thought to be promoted through metal dissolving into the glass / glass-ceramic. To establish bonding at the other interface, it was necessary to grow an oxide layer on the Kovar, by heating in air at 700 °C or 800 °C for 10 minutes. The oxide grown at both temperatures was shown (by XPS, XRD, SEM, EDX, STEM and Raman) to have the same composition, with the only significant difference being thickness (2.1 +/- 0.6) µm and (4.0 +/- 0.2) µm thick, for the oxides grown at 700 °C and 800 °C respectively. However, the oxide was found to be much more complex than was indicated by prior literature, comprising four layers. The top layer of the oxide was (Fe,Co)_3O_4, with an Fe_2O_3 layer beneath it. Below these layers were a further two layers of (Fe,Co,Ni)_3O_4. When heated to 800 °C, to simulate the sealing conditions, the oxide was changed to an Fe_3O_4 layer with metallic cobalt and nickel inclusions. Bonding was shown, by SEM and STEM, to occur between the oxidised Kovar and the glass-ceramic, as a result of dissolution of iron from the oxide into the glass. Although the interfaces were not definitively optimised, the seals produced were satisfactory and hermetic.

Glass is an inexpensive and readily available material making it an indispensable element in the many fields of science and technology. This thesis describes three methods of manipulating the optical and structural properties of glass and nanocomposite glass for varying applications. These are: thermal poling of glass, electric field assisted dissolution of glass embedded with silver nanoparticles and the irradiation of glass embedded with silver nanoparticles. Each method will be adapted to present novel and widely applicable approaches to the modification of glass. Thermal poling of glass will be used to create diffractive optical elements (DOEs) in soda-lime float glass. Thermal poling of glass results in a change to the glass structure, by using an electrode with a periodic pattern the glass was selectively restructured creating an effective DOE. The parameters of the process, namely applied voltage and temperature, were investigated for their part in the efficiency of the resultant DOE. A second method for the fabrication of DOEs will use electric field assisted dissolution (EFAD) of glass embedded with spherical silver nanoparticles. This process leads to the dissolution of silver nanoparticle into the surrounding glass. By selecting a mesh electrode with a periodic pattern an effective DOE was fabricated by selectively dissolving the silver nanoparticles in contact with the electrode. As with thermal poling, the voltage and temperature of the process will be investigated in order to produce more efficient DOEs. Glass with embedded spherical silver nanoparticles was irradiated using a nanosecond (36 ns) pulsed laser at 532 nm. Laser irradiation led to the formation of a thin surface film containing uniformly distributed nanoparticles - with an increase in the overall average nanoparticle size. The influence of the applied number of laser pulses on the optical and structural properties of such a recipient nanocomposite was investigated.

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