Nanostructured metal films were electrodeposited through the hexagonal lyotropic liquid crystalline phase (HI). The mesoporous structure consists of porous channels (a few nm in diameter) arranged in an hexagonal array. These mesoporous metal films exhibit high surface areas supplied by the concave surface within the pores. The properties of these mesoporous materials have been investigated to gain an insight on the mesoporous structure. Cyclic voltammetry in acid of HI mesoporous Pt is similar to polycrystalline Pt made up of low index Pt facets. However CO stripping voltammetry shows differences between the HI mesoporous Pt and polished Pt electrodes. The CO stripping voltammogram for the HI mesoporous Pt electrode exhibits a CO oxidation pre-wave and CO oxidation at lower overpotentials. These differences result from the presence of trough sites corresponding to the intersection of two pore walls within the mesoporous structure. The adsorption of foreign atoms Bi and Ge on HI mesoporousPt was investigated to identify the different crystalline Pt facets. The features of the voltammetric profiles recorded in acid revealed the absence of large (111) domains and the presence of (100) terraces sites. CO stripping voltammetry for HI mesoporous Pt modified with Bi suggests the presence of a CO-Bi mixed ad layer. However, the absence of the aforementioned pre-wave was attributed to the adsorption of Bi on the trough sites thus causing inefficiency in oxygen transfer for CO oxidation. In contrast, the significant pre-wave observed for HI mesoporous Pt-Ge leads to an enhancement for CO oxidation. HI mesoporous metal films grown on microelectrodes show good stability of the measurement of hydrogen peroxide. HI mesoporous Rh with a variety of film thicknesses was extensively studied over a wide range of hydrogen peroxide concentrations. A kinetic model is proposed to describe the diffusion of hydrogen peroxide and the surface reaction in the pore. The accessibility of the ionic liquid BMIM-PF6 in the pores was investigated to assess the performance of mesoporous electrodes in supercapacitors. HI mesoporous Pt of diverse pore size and polished Pt electrodes were characterised in 1 M sulphuric acid and then tested in BMIM-PF6. The double layer capacitances were higher for the HI mesoporous Pt films thanks to their internal surface area leading to the confirmation that the ionic liquid penetrates into the pores. The analysis of electrochemical impedance spectroscopy shows that the results fit a transmission line model and provides useful parameters for the characterisation of the nanostructured Pt film in BMIM-PF6. 11.

In this EngD thesis the phenomenon of sustained macroscopic deflected crack growth (SMDCG) during fatigue in Nickel based Superalloys is discussed, also referred to as ‘teardrop’ cracking in previous work. In a corner notched bend (CNB) specimen a fatigue crack usually grows in a quarter-circular plane perpendicular to the stress axis, the SMDCG however exhibits considerable deflection from this plane at the free surfaces, so that a central planar region is enclosed by large shear terraces (thus forming the ‘teardrop’). This is difficult to characterise in terms of component lifing (both in terms of crack path and crack growth rates), and this thesis aims to further understanding of the underlying mechanisms and to develop assessment methodologies for lifing of such cracks in aeroengine components. The SMDCG effect has been observed under externally applied mode I loading in Udimet 720Li with relatively fine grain sizes of 6-18μm, which are candidate materials for aero engine turbine discs. CNB and single edge bend notch bend (SENB) fatigue tests have been carried out on cast and wrought and powder metallurgy variants of Udimet 720Li and SMDCG was observed at 300°C in air and at 300, 600 and 650°C in vacuum. A consistent measure of the onset of deflection has been defined; this is the crack tip stress intensity factor range K at which the sustained deflection from the free surface exceeds the expected shear lip area, which is estimated as the distance of the monotonic plane stress plastic zone size from the free surface. This has been used to characterise samples from other research programmes and aeroengine components from rigtests, that have shown some form of deflected crack growth, to assess whether they exhibit SMDCG or whether the apparent deflection was caused by the expected plane stress region, or other factors such as tunnelling due to creep effects or complex overall loading conditions. Fracture surfaces exhibiting SMDCG have been studied via SEM and the fractographic analysis shows a competition between local shear crack growth and mode I crack growth occurs in both the macroscopically deflected and planar regions. This indicates that the macroscopic deflection is triggered by the stress state at the free surface. Further detailed analysis of the deflected crack tip with focussed ion beam (FIB) serial sectioning combined with EBSD analysis has allowed a detailed 3D reconstruction of the crack tip interaction with local microstructure. This, together with TEM foils extracted via FIB in the same region, have confirmed that the SMDCG in these systems is not linked to any local texture effects or surface microstructural differences. Lifetime predictions for the CNB samples have been carried out based on Paris law coefficients from the SENB tests, and showed shorter lifetimes than the actual samples with deflected crack growth. Whilst this could be partially due to unaccounted for initiation effects, it could also indicate that significant extrinsic shielding caused by the deflected crack growth may actually increase fatigue lifetimes. To assess the driving force evolving during SMDCG, an Alicona Infinite Focus profilometre has been used to map the complex 3D crack shapes, from where tilt angles could be measured to define a mixed mode plane stress SENB test, with the aim of replicating the stress state that had given rise to the locally deflected shear growth and to explicitly measure crack growth behaviour in the deflected regions. However this was not achieved with this test set-up, as the achievable ΔKeff was not high enough to trigger the deflection throughout the sample. As a result the 3D map was next used to define Finite Element model to assess the local crack tip stress state of the complex deflected crack path. Crack driving forces that have been identified at the point the deflected crack path becomes self-sustaining, could be used in a lifing model to predict crack paths in aeroengine components, together with the measured onset of deflection.

The effect of the thermal properties of alumina and CBN abrasives on workpiece temperatures in grinding was investigated. A review of the literature revealed a lack of knowledge of the thermal properties of CBN limiting the accuracy of theoretical predictions of the heat conduction in CBN grinding. A grain contact analysis was developed to predict the energy partitioning between the workpiece and wheel. The analysis takes into account two dimensional transient heat transfer in the grain and maintains temperature compatibility at the grain wear flatworkpiece interface. The proportion of the total grinding energy entering the workpiece, termed the partition ratio, was estimated by correlating measured temperature distributions with theoretical distributions. The partition ratios when grinding with CBN were substantially lower than grinding with alumina wheels for a range of ferrous materials. The lower partition ratios with CBN grinding were attributed to the higher thermal conductivity of the CBN abrasive. The effective thermal conductivity of alumina and CBN grains were quantified by correlating the theoretical partitioning model with the measured results. The effective thermal conductivity of CBN was found to be considerably lower than the reported theoretical value albeit much higher than the effective thermal conductivity of alumina. A model to predict the background temperature in grinding was proposed based on the experimental findings. The thermal model takes into account a triangular heat flux distribution in the grinding zone, the real length of contact and experimentally validated grain thermal properties. The input parameters to the thermal model were specified. To avoid temper colours on the workpiece surface the maximum background temperature must not exceed 450 to 500deg. C. for commonly used ferrous materials.

This thesis addresses the development, evaluation and modelling of an anti-segregation system ("AS-System") for.use in larger silos handling alumina in the aluminium smelting industry. This work is unlike much of what has gone before because it is much more grounded in the technical and economic consequences of segregation for a particular manufacturing process. Segregation of particulates, i.e. separation of components due to differences in properties such as size, density etc., has an extensive literature going back as far as 1915, but this focuses mainly on the segregation process itself and largely ignores the context and the consequences. The consequence of segregation is loss of homogeneity; the impact that has on any given process, is generally not addressed very deeply. Surveying the literature on segregation, and studying the total processes of aluminium production, creates a basis for understanding the importance of segregation for aluminium production, as well as the importance of powder technology in general for this industry. A method for quantification of segregation in this production process, based on sampling, has been established. This was intended to give the fundamental information necessary for measuring the extent of the problem and the degree of improvement achieved. By placing sampling points along the logistic chain for the alumina, and by sampling these points for a long enough period, information about the influence of the various handling steps on the bulk solids can be identified. Segregation by particle size is the main type of influence, although the work has shown that attrition is another. Standardised statistical expressions have been used for analysing the bottlenecks of the logistic loops, and study of the results has led to a useful way of expressing the level of segregation, the change of segregation level in a handling step (silo filling and discharge), and improvements in this change. The degree of segregation when handling alumina has proven to be quite considerable in terms of effects on the production process. The effects on the efficiency of the aluminium smelting process, and the environment, have both been evaluated. Variations in the alumina due to segregation have been found to correlate with both dust concentration in the smelter pot room, and anode effects (an unwanted upset in the smelting process). An economical evaluation of an investment in anti segregation systems has been made. This evaluation has shown significant economic consequences, clearly justifying both the investigations of segregation, and the implementation of anti segregation measures. To remedy the effects of air current segregation in the aluminium industry, a complete Anti Segregation System (AS-System) based around Anti Segregation Tubes (AST) utilising a special inlet configuration has been developed. In a number of full size installations, this solution has proved itself capable of handling the variations and transients of process conditions which occur in the industry, with a large operational capacity range, due to the special inlet configuration. The effect of the full scale installed anti segregation systems have been measured, and compared to other systems. The AS-System clearly demonstrated a homogenising effect no matter how low the ingoing variations in particle size were. Other commercial systems which have been evaluated have turned out to be no more than Segregation Effect Damping Systems, since they only seem to reduce the segregation effect after it has happened, instead of trying to eliminate the problem by directly attacking the segregation mechanism itself which is what the AS-System does. A new scaled down test rig for the AS-System was developed, consisting of three ASTs fed from a central distributor. To test the potential effect of the AS-System, to determine its efficiency in countering segregation, tests with repeated filling and emptying of a scale silo were carried out. The results clearly showed that the AS-System very much reduced segregation, compared to conventional filling, even in a small-scale silo. Improved models have been developed for the function of the AST and these have been verified against measurements from the new test rig. The early version of the test rig for the AST used only one centre-mounted tube, with one pressure measurement in the top of the tube. The first models were based on the assumption of the pressure being linear, and assumed full dispersion of the falling material inside the tube; and calibrated from the single pressure measurement inside at the top of the tube. Although this simple model calculated very conservative values of the negative pressure, the model was used for the initial development and design of the AST, and later the ASSystem (Anti Segregation System). A second model was derived, where the material velocity was calculated based on free fall. This model was also based on the idea of full dispersion, but was in better agreement with measured values during further tests, which showed a considerable deviation from the original assumption of a linear pressure distribution once intermediate pressure measurements were available. When using the multi-phase-flow-simulation-program-code FLUENT to simulate the pressure distribution of the AST, the results were quite disappointing, however the FLUENT program was able to identify an initial positive pressure generated by the flow from the inlet box to the tube. Implementing this initial pressure into the simple non-linear model above, both the trend and values correspond quite well with the measured values. A single particle drag model was tried, but dismissed after calculating the maximum possible capacity for known tubes and finding the predictions to be unrealistically low. A new approach was introduced, modelling the fall of the powder in a continuous layer along the inner wall of the tube on one side, creating skin drag along the surface between the falling solid powder and the air. The length of the tube and the width of the chosen AST profile define this surface. This approach assumes that the powder falls like a layer along the tube wall. Previous theory for pressure drop in pneumatic conveying inspired this approach, but it had not previously been used for gravity flow in vertical tubes, and as a result the novel Solid Surface Body Drag Model (SSBDM) was developed. This analytical model gives very good correspondence with the measured data for the pressure distribution inside the AST, yet is extremely simple to use. When comparing the model with measured data, the SSBDM was able to predict the pressure distribution within the error boundaries of the test measurements. A method for design of the AST was derived from the SSBDM, using a dimensionless parameter function determined for the pressure drop model. The models giving the design indicate that the capacity is more than proportional to the cross sectional area of a chosen tube profile, which is in agreement with observations. The model suggests that the capacity is proportional to the cross sectional area in the power of 1.25. This model allowed the study of the effect of tube shape, which revealed that a square profile for the AST does not seem to be the optimum design; rather, a rectangular profile should be chosen for maximum capacity. The model suggests that the capacity is proportional to the width of the side of the tube along which the powder layer is falling, but proportional to the perpendicular side in a rectangular profile in the power of 1.5. The model gives an equation for pressure drop which can also be utilised to place the first valve on the tube. It also shows that for high capacities, and large silos, a system consisting of several ASTs should be chosen (AS-System). Predictions from the model have been tested against the measured capacities of full scale installed systems and give good agreement. Overall, the AS-System has been shown to be cost-effective in reducing segregation; results measured from the full scale installations show a homogenising factor (reduction in variation of the material being handled) of 1-1.5. As a result of these verifications and the simplicity of the model presented in this thesis, the plant engineer can confidently design a system which will function correctly and make a positive, predictable improvement in the homogeneity of the alumina in his plant.

Roman military equipment has traditionally been studied from a typological perspective based on a linear concept of change. Whilst Roman alloys have been analysed scientifically and general studies on them have been published, analysis of military equipment has been scarce and mostly secluded as part of excavation reports of individual sites. Scientific analysis though, can provide independent ways of studying military equipment. It can answer questions about production and distribution of the raw materials and finished objects and is capable of informing on reasons for technological choices (the intention of obtaining determinate colours, for example), and identification of military units. A total of 216 copper-alloy military objects from the British sites of South Cadbury Castle, Ham Hill, Usk, Carlisle, Chester and Kingsholm, and the German site of Kalkriese were selected for obtaining metallurgical characterisation: chemical analysis at major, minor and trace element level and microstructural analysis to obtain fabrication history and identifying any plating. The analytical techniques employed were atomic absorption spectrometry (AAS), scanning electron microscopy with energy dispersive x-ray spectrometry (SEM-EDS), optical microscopy and multivariate statistics methods such as principal component analysis (PCA), discriminant analysis (DA) and multivariate analysis of variance (MANOVA). The aim of the project was to characterise the chemical and physical make-up of Roman military copper-alloy metalwork from the 1st century AD, with especial interest in the immediate post-conquest period. The results of the analysis show a difference between the Roman military equipment from British sites and the equipment from Kalkriese, based on trace element patterns. This difference can be explained by a large input of material into Britain that had been made in the years before AD43 in preparation for the conquest. Contrary to recent scholarship, and based on compositional and microstructural evidence, some lorica segmentata brass fittings seem to have been centrally produced. Primary brass and specific gunmetal compositions seem to be associated with the military and probably chosen primarily for their appearance and resemblance to gold, rather than for their mechanical properties. The possibility of mechanised production of brass is explored based on the brass ingot from Sheepen.

The introduction of ceramic matrix composites (CMCs) for structural applications in the hot section of a gas turbine provides many potential benefits over conventional alloy materials, including facilitating elevated operating temperatures. The development of an oxide-oxide CMC composed of commercially available Nextel 720 (3M) fibres within a porous alumina matrix was presented. A simple, low cost processing method involving slurry impregnation and subsequent consolidation and densification was developed, facilitating the production of dried pre-impregnated fabric (‘pre-preg’) that can be stored in ambient conditions. Detailed investigation into the effect of three types of PVA binder, the effect of 0-20wt% additions of an alumina precursor (ACH), the influence of a bimodal particle distribution and the effect of sintering at temperatures between 1100 and 1300°C on processing and mechanical properties was completed in order to optimise the material. The optimised composite material, composed of Nextel 720 fibres within a submicron alumina particle matrix with 10wt% ACH sintered at 1200°C, exhibited mean flexural strength >205MPa, short beam shear strength >12MPa and tensile strength >146MPa. These results were comparable to similar oxide CMCs previously reported, validating this material.

Research has been undertaken to develop new yttria slurry systems for use in mould face coats for investment casting TiAl alloy, solving the pre-gelation problems of commercial yttria slurry systems to increase slurry life. Meanwhile, the new face coats should also have excellent sintering properties, chemical inertness, surface finish and be easy to prepare. The processes of developing the new slurry started with the filler powder investigation by adding different sintering additives into the yttria powder to achieve good sintering properties. Then the best filler powder candidates were selected to make the slurry. Finally, the new face coat slurries were used to make the shell face coat and the chemical inertness of those shells were investigated through the sessile drop and investment casting. In the research, the filler powder and face coat sintering properties were quantified through density, dilatometer testing, X-ray diffraction (XRD) and microstructural change at different testing temperatures. The interaction of different face coat systems and the metal were identified using hardness tests, sessile drop contact angle and the microstructural change at the metal/shell interface. In this research, three water-based binder face coat systems containing YF\(_3\), Y\(_2\)O\(_3\)+0.5wt% Al\(_2\)O\(_3\)+ 0.5 wt% ZrO\(_2\) (YAZ), and B\(_2\)O\(_3\) additives were found to have similar or even better sintering properties compared to a commercial face coat. Meanwhile, they had long life.

Two different Pt-aluminised bond coats, with varying thicknesses and Pt-contents were examined, regarding the in uence of bond coat phases on the oxide growth. This was done in a series of short term (3, 7 and 10 minutes) oxidation experiments at 1100°C. These clearly showed different types of oxide growing on Ni3Al and NiAl phases in the low Pt specimens. It could also be shown that the transition from NiAl to Ni3Al already occurs at these early stages of oxidation. On the high Pt specimens the same types of oxide are growing on Ni3Al and PtAl2. In addition, the high Pt specimens were examined after longer times at temperature (up to 100 hours), to gain information on the bond coat phase transformations happening at high platinum contents. It could be shown that the chromium content plays an important role with regards to phase stability fields in the ternary Ni-Al-Pt diagram. Oxidation kinetics on these samples show that the oxide is not growing at a parabolic rate, but is characterized by a time exponent of 0.145, which may be attributed to a theta to alpha a transformation in the oxide.

Investigations into micro-slot milling of high carbon, high chromium hardened AISI D2 cold work tool steel using 0.5mm diameter coated (TiAlN) tungsten carbide end mills were carried out. Performance was assessed in terms of tool life/tool wear, surface roughness, cutting forces, burr formation, slot geometry accuracy and workpiece surface integrity. The influence of operating parameters (cutting speed, feed rate and depth of cut) on tool life, surface roughness, burr width and cutting forces was evaluated using full factorial experiment design. Analysis of results included main effects plot and calculation of percentage contribution ratios (PCR) for each of the primary variable factors and their interactions were assessed via analysis of variance (ANOVA). The test array was further extended to allow for implementation of Response Surface Methodology (RSM) analysis in order to optimise tool life and surface roughness. Dual-response (cutting speed and feed rate) contours of metal removal rate and tool life/surface roughness were generated from the respective model equations. These were further developed to identify combinations of cutting speed and feed per tooth for the best tool life/surface roughness at specific metal removal rates. Finally, the impact of coatings and tool geometry on tool life and workpiece surface roughness was investigated.

Modern cobalt-chromium (CoCr) alloy compositions, for hip implants, were developed to resist the issues of wear and corrosion; however they still succumb to degradation. While the literature is vast, there is still a lack of understanding of the variability in implant-metal derivatives generated, and the effect such products can have on biological components other than just cells. In this thesis the effect of Co ions on type I collagen (main component of the extracellular matrix) was investigated. The conformation of the triple-helix was maintained, however the time taken for fibril formation to complete increased with Co concentration. In addition, with increasing Co, the collagen matrix became more heterogeneous and cellular attachment and proliferation was reduced. It is likely that Co ions are interacting with a C-O (hydroxyl) group. An overlooked population of degradation products was also investigated. They were found to be highly dependent upon the local environment. Media composition resulted in changes to the morphology, while pH directed the initiation of precipitation. A pH < 5 resulted in no observed pellet. In addition, the presence of Co ions in the media resulted in a change of Cr speciation. Finally, an approach is presented for sub-micron (600nm) x-ray absorption near edge spectroscopy (XANES) mapping of ex vivo tissue. Sub-micron XANES maps contained at least 4 spectra, determined through principal component analysis and clustering. A 5x5 pixel region was averaged for comparison to the 3μm beam approach. Both spectra contained similar features representative of chromium phosphate suggesting that XANES with a micron-sized beam (standard approach) cannot represent the full chemical variability present within the tissue.