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Polycrystalline nickel-base superalloys have found extensive application throughout the aerospace, petrochemical and power generation sectors, due to their exceptional balance of high temperature mechanical properties, thermal stability and oxidation resistance. Extensive alloy development has produced a diverse class of alloys suited to a wide range of operating conditions. This work details research performed to develop new low-cost polycrystalline Ni-base superalloys, intended for intermediate temperature and loading environments. There is currently significant industrial demand for alloys of this type, that offer improved thermal stability and mechanical properties compared to current commercial alloys such as Inconel 718 and ATI 718Plus, whilst retaining good amenability to deformation processing and joining operations. The important properties required of polycrystalline Ni-base superalloys are discussed alongside an initial comparison of current commercially available materials and a potential class of candidate alloys suitable for further development. Compositional modifications were made to these alloys in order to improve their thermal stability and reduce their cost. Characterisation was performed after a standard ageing heat treatment, and after long term thermal exposure at 700˚C, revealing significantly improved resistance to precipitation of the δ phase in these alloys compared to Inconel 718. Despite this, comparable measurements of the hardness values indicated similar mechanical strength. The oxidation resistance of the candidate alloys was also assessed through 1000~hour exposures in air at 700˚C and 800˚C. The alloys were found to be chromia forming, with internal oxidation of Al forming a discontinuous subscale. Significant microstructural degradation was observed at 800˚C due to the formation of the δ phase, with the differences in oxidation behaviour rationalised using Wagnerian diffusional analyses. So that further investigation of fundamental alloy behaviour could be performed, industrial quantities of three candidate alloys were produced. The initial characterisation of these materials is described, including a detailed study of the ageing response after a controlled solution heat treatment performed using a quenching dilatometer. The observed precipitate coarsening was well described using classic models, and was correlated to the hardening response by comparison to the contributions from strong- and weak-pair dislocation coupling. The deformation behaviour of small-scale thermomechanical compression specimens of the preferred candidate alloy was studied under both sub- and super-solvus forging operations. Subsequent microstructural examination was used to assess the extent of recrystallisation, and characterise the microstructural evolution that took place during deformation. In the supersolvus trials, fully recrystallised microstructures were obtained, with partially recrystallised microstructures evident in the sub-solvus trials. These results, combined with the flow curve data were used to specify large-scale forging of the industrially produced compacts. In an exploratory study of the weldability of these alloys, electron beam welding was used to produce autogenous bead-on-plate welds using three different welding conditions. All the welds produced were fully penetrating, with no deleterious defects characterised in any of the conditions studied. Using scanning electron microscopy and large area hardness contour mapping, the effects of a post-weld heat treatment on the as-welded microstructure were assessed. The restoration of mechanical properties across the weld cross-section was successfully correlated with the local distribution of precipitates within the fusion zone after heat treatment. The results indicated that the alloys were amenable to joining via this process. The research described details the development of new low-cost polycrystalline Ni-base superalloys from initial compositional design, through to industrial production, including detailed studies of the phase equilibria, thermal stability, microstructural evolution and oxidation resistance. In addition to demonstrating superior microstructural stability compared to current commercial alloys, the alloys developed appear to be readily formed via conventional deformation processing routes, and can be joined without producing defects using electron beam welding. With additional work to verify the detailed mechanical response of the alloys produced, it is hoped that they will find industrial application in the near future.

This project aims to develop a mechanistic understanding of the oxidation and simultaneous carburisation in type 316H austenitic stainless steel under Advanced Gas-cooled Reactor (AGR) service conditions, and subsequently their impact on the creep mechanics at 550 °C of pre-carburised creep specimens. Sections of the boiler pipework in the AGRs are fabricated from type 316H austenitic stainless steel and are exposed to high temperatures (480-650 °C) and pressurised (4.14 MPa) gaseous primary coolant mixture of CO₂/CO. The remaining life of these boiler components is restricted by their tolerance to creep and resistance to environmental degradation mechanisms i.e. oxidation and carburisation. In this project, two 316H austenitic stainless steel casts, differing in the Mn content, were first exposed to simulated AGR service conditions at 550 or 600 °C, inducing the simultaneous formation of oxide and carburised layers. The results revealed a limited amount of atomic carbon in solid solution within the austenite lattice, whereas the excess carbon precipitates as M23C6 carbides. The local diffusion of substitutional solutes (i.e. Cr) is the rate-controlling step for carburisation. Furthermore, the creep behaviour at 550 °C of the pre-carburised specimens was influenced by the cracking of embrittled, carburised grain boundaries and by the modified local material properties of the near-surface carburised layer. The formation of ferrite grains in the carburised layer was also detected, with the ferrite fraction increasing with creep strain, indicative of a strain relief mechanism locally. This work contributes to further the understanding of environment-creep interactions required for structural assessment procedures for AGRs and future Gen IV fission reactors.

In this thesis, the advanced spectroscopic techniques of atomic force microscopy - infrared (AFM-IR) spectroscopy and sum-frequency generation (SFG) spectroscopy are explored in detail for their innate ability to unravel the complexities of biological interfaces. The benefits of both techniques are demonstrated through applications to a variety of different interfaces, ranging from whole cells and aggregates (red blood cells and hair fibres) to artificial mimics (hydrogels) and thin molecular films (phospholipid monolayers). Specifically, the lateral chemical resolution and surface sensitivity of AFM-IR are used to chemically characterise the constituent components of biologically relevant systems below the diffraction limit whilst correlating these measurements to the nanoscale physical properties of the surface, such as topography, friction, and adhesion, that are accessible through traditional AFM. Similarly, the inherent surface specificity and sub-monolayer sensitivity of SFG is utilised, along with its ability to elucidate chemical structure and conformation, to probe oxidation in cell membranes, both in whole cells and monolayer mimics, thereby yielding a much deeper understanding of the oxidation mechanism due to reactive oxygen species (ROS) in physiological systems. Furthermore, some limitations and challenges associated with the use of these techniques in biologically relevant systems are identified, characterised and discussed, along with potential ways to circumvent them or minimise their impact in such investigations. Specifically, the inability of AFM-IR to probe thick substrates under aqueous conditions is discussed due to the relevance to studying many biological systems under physiological conditions. A novel method of sample preparation is proposed to maintain pseudo-aqueous conditions for the substrate whilst avoiding the limitations associated with AFM-IR measurement. Additionally, the common application of SFG to study surfactant monolayers at the air-water interface, particularly phospholipids due to them modelling cell membranes, is critically assessed for some inherent issues. The first example of which is associated with the inherent fluidity of the monolayer that makes it highly susceptible to local heating from the necessarily large incident fields. The effects of this local heating are thoroughly investigated and modelled, leading to conclusions about how to minimise this disruption in future investigations. Finally, SFG simulations are then used to quantitatively assess the validity of a common assumption associated with SFG investigations of phospholipids, namely that both alkyl chains yield the same spectral contributions despite having different orientational distributions.

Advanced technology fuels (ATFs) are key in the drive to improve the overall performance and safety in the nuclear industry. The intermetallic uranium silicide phases are of significant interest to the nuclear fuel cycle, with three of the stoichiometric phases, U₃Si, U₃Si₂, and U₃Si₅ being highlighted as ATFs. These phases have the potential to offer higher thermal conductivities and uranium densities when compared to the widely used UO₂. For these phases to be implemented into the nuclear fuel cycle, the understanding of these materials must be extended across the entire uranium-silicon phase diagram. This will highlight how inclusions of secondary phases that may form as a result of the bulk fabrication process could alter the behaviour of the main fuel compound. Thin films provide idealised samples that are well suited for single parameter investigations. Epitaxial U₃Si, U₃Si₅, α−USi₂, and USi₃, alongside poly-crystalline U₃Si₂ have been engineered for the first time using DC magnetron sputtering, allowing for novel measurements to be conducted on these materials. Characterisation of these phases using x-ray diffraction and x-ray photoelectron spectroscopy have provided information about the structural and chemical nature of each compound. X-ray photoelectron spectroscopy provided a unique insight into the chemical bonding and stoichiometry of each uranium silicide phase, presenting the metallic nature of these compounds, alongside their unique U:Si ratios using the U-4f and Si-2s core levels. Thin films also provide excellent samples upon which surface sensitive investigations can be conducted. Here, the ambient surface oxidation in air of each compound is presented, from which the results indicated the preferential oxidation of uranium sites, allowing for the formation of silicon-rich phases within the native oxide. The aqueous corrosion of uranium silicides within H₂O and H₂O₂ is also considered. These experiments provided further understanding of the preferential oxidation model, with indication that this mechanism applies to uranium silicides within aqueous environments. Finally, the implications of the results collected from each uranium silicide phase regarding its application as a nuclear fuel candidate are considered.

The inclusion of Cₛₚ³-F bonds into bioactive compounds has a broad range of benefits. This, along with general synthetic routes, will be discussed in chapter one. The difluoroalkyl functionality has garnered recent attention due its ability to adopt a gauche conformation in solution. However, current syntheses are limited to the difluorination of electron deficient alkenes. Therefore, the development of a novel electrochemical vicinal difluorination of alkenes will be discussed in chapter two. This approach utilises electrochemistry to enable access to new substrate classes in a sustainable and scalable manner. Two methods will be presented: an "in-cell" method for the difluorination of electron poor alkenes, and an "ex-cell" method for the difluorination of electron rich alkenes. Fluorofunctionalisation of unactivated alkenes is an interesting problem because it poses significant diastereo- and regioselective problems. Hence, the chlorofluorination of alkenes has only ever been completed with anti-diastereoselectivity. Thus, the development of a diastereodivergent chlorofluorination of alkenes will be discussed in chapter three. Both syn- and anti-methods had good functional group tolerance. Afterwards mechanistic investigations were conducted to propose the origins of the elegant diastereoselectivity swap and regioselectivity.

This thesis investigates the influence of the crystallographic orientation of the UO2 on the oxidation process and phase transition into U3O8. The samples were prepared by DC magnetron sputtering and a new sputtering system was constructed. A new method to produce poly-epitaxial columns of UO2 with controlled grain size was developed and used. X-ray characterisation of single crystal epitaxial thin films revealed the best long range order for the (001) orientated samples. The truly polycrystalline character of the poly-epitaxial thin films, without preferred orientation, was demonstrated by x-ray diffraction and electron backscatter diffraction. Utilising these idealised systems, fundamental studies have been conducted to explore the oxidation behaviour of uranium dioxide. The in-situ oxidation studies performed on poly-epitaxial UO2 revealed a fastest oxidation rate for (001) orientation, in contradiction to the literature data. This discovery was further investigated using single crystal samples. In situ High Temperature- Environmental Scanning Electron Microscopy observations showed disintegration of the UO2 structure after phase transition to U3O8, for the (111) and (110) oriented single crystal, while there was no loss of integrity for the initially (001) oriented structure. Additionally, in-situ X-ray diffraction studies revealed an epitaxial relationship between the (130) plane of U3O8, rotated 45°, on the (001) plane of UO2. This was identified as a topotactical phase transition, with sigmoidal nucleation and growth kinetics. In conclusion, this thesis has discovered a new epitaxial relationship between the (001) plane of UO2 and (130) plane of U3O8. This match was also attributed to the faster oxidation rate observed for (001) oriented grains in polycrystalline systems, as possibly lower energy is required for phase transition in this oxidation route. This new insight into the oxidation process of the most common nuclear fuel can help improve the efficiency, reliability and safety throughout the nuclear fuel cycle, and might potentially apply to other oxide systems.

MCrAlY bond coatings typically used in thermal barrier coatings (TBC) systems for gas-turbine engines are studied in this thesis, with special focus on microstructural, topographical and oxidation behaviour. The effect of bond coat/thermal barrier coating (BC/TBC) interface topography on the lifetime of air-plasma sprayed (APS) TBCs has been comprehensively investigated in the present work. A quantitative description of the interface topography was achieved by utilising multiple surface texture parameters obtained from confocal microscopy, including a newly formulated parameter, denominated as total thresholded summit area, Ssth. Thermal cycling fatigue (TCF) testing showed a clear correlation between the TBC lifetime and the interface topography, especially for the newly proposed Ssth parameter. The topographical and microstructural analysis revealed that deposition of a TBC over tortuous BC topographies leads to a highly curved TBC splat morphology that influences the crack path configuration. Microindentation and three-point bending conducted on as-deposited and heat-treated specimens have showed that the aforementioned microstructural changes lead to a reduced local and global elastic moduli. These features were later associated with more beneficial fracture mechanics behaviours and higher TCF lifetimes. A modified four-point bending experiment is subsequently conducted on air-plasma sprayed (APS) TBC to gain further insight into the impact of bond coat (BC) topography tortuosity on the TBC fracture mechanics. The degree of BC tortuosity was quantified by the Ssth metric and was found to influence the crack path configuration, critical energy release rate (Gc) and crack propagation velocity (Vprop). Specimens with higher BC interface tortuosity and more compliant TBC microstructures ere associated with reduced strain energy release rates (Gc≤79.9 J.m⁻²) and crack propagation velocities (Vprop≤0.9 mm.s⁻¹). These observations seem to indicate that TBC failure is primarily governed by the degree of inter-splat cohesion and intra-splat segmentation, although the topography-induced inter-splat tortuosity still had a relevant impact on fracture mechanics. These findings suggest that despite TBC systems with higher tortuosity specimens and more compliant microstructures tending to show a premature propensity for crack nucleation, the lower strain energy release rates observed induce a slower crack propagation rate and may delay failure. The correlation observed with the lifetime of analogous thermally cycled specimens tested herein seemed to confirm this, as more compliant TBC microstructures were correlated with longer TBC lifetimes. The oxidation behaviour of CoNiCrAlY coatings deposited by high velocity oxygen fuel are studied via a combination of correlative microscopy and spectroscopy techniques. The dual-phase BC microstructure was found to promote a site-specific oxidation behaviour that had significant implications in the formation and composition of the oxide scale during the early stages. Oxide growth over the β-phase grains was faster due to accelerated diffusion of cations along the γ/β grain boundaries. It was found that this effect was more prominent in smaller grains with reduced γ/β grain boundary distance (0.8 ≤x_PB ≤ 1.2 μm), as the resulting interaction between fluxes resulted in the undesirable nucleation of mixed oxide formations in the outer scale. The evolution of the oxide scale with oxidation time further revealed that the outer scale undergoes a notable thermo-chemical transformation via outward diffusion of non-Al cations across the inner scale. The high residual stresses and premature failure suggest that the outer scale has an adverse effect on the durability of the oxide scale. Furthermore, the incorporation of large quantities of Cr in the oxide scale (~4 at.%) and subsequent segregation to the outer scale is detrimental for the early oxidation behaviour, overall stress state and durability.

Methane is an abundant earth resource important for the energy sector. The development of better catalysts for the complete combustion of methane and the discovery of new catalysts that can directly oxidise methane to methanol are of great scientific importance. The total oxidation of methane to CO2 is considered for amorphous surface palladium oxide. A partially oxidised palladium surface is found to have both metal-like and oxide-like character. This peculiar characteristic is found to be important for increased reactivity, with dehydrogenation steps having enhanced activity on metal areas and oxidation steps having enhanced activity on oxide areas of the surface. These findings allow the further development of catalysts that stabilise the metal and oxide phase together, improving catalyst efficiency. The mechanism for the direct oxidation of methane to methanol is investigated for a Rh@ZSM-5 catalyst. The effect of molecules coordinating to the single atom centre on the reaction mechanism is explored. CO has a considerable effect as a ligand, explaining the experimental requirement for CO to have a trace presence in the system. Despite water also being required experimentally, a minimal ligand effect is found. However, water is found to be crucial as a hydrogen source for a key elementary step in the reaction. The similarity of the chemistry of single atom heterogeneous systems and homogeneous systems is discussed. These findings show the possibility of modulating ligand effects in heterogeneous catalysts. The increased reactivity of methanol against methane is investigated for a variety of fcc metals. It is found that methanol as a reactant is consistently more reactive for C-H activation, C-O coupling, and C-OH coupling. As methane and methanol have different affinities for water, the effect of an aqueous environment on the conversion-selectivity limit is considered. Water is found to not have an asymmetric effect on the reactivity of methane and methanol, mirroring the findings of the gas phase calculations. However, a C-OH mechanism is promoted in the aqueous phase, which would have a considerable effect on the selectivity on the production of methanol from methane, by minimising the formation of other oxygenates. This explains a long held mystery of why water promotes the selectivity of the methane to methanol process across many systems. The failure of palladium, a total oxidation catalyst, for the methane to methanol process is characterised and explained with a total combustion microkinetic model. A streamlined microkinetic model is designed that can accurately describe the methane to methanol formation. Excess dehydrogenation of methane is the main route of selectivity loss. Single atom alloys are then considered as a potential opportunity for a selective methane to methanol catalyst class. 64 surfaces are considered as potential catalysts, with 7 found to be indicative of being effective methane to methanol catalysts. These are then modelled for their activity and selectivity towards methanol production. One modelled catalyst has remarkably improved selectivity and activity over palladium, allowing future experimental trials which are focused on the best and most promising catalysts.

During operation within an Advance Gas Cooled Reactor (AGR) 9Cr-1Mo steel is subjected to high temperature CO2 rich gas. This leads to complex interactions taking place between the CO2 and the steel. The steel is subjected to simultaneous carburisation and oxidation changing both the chemistry and the physical properties of the steel. Experimental samples were exposed on behalf of EDF Energy to better understand the processes taking place and to better understand the factors which affect time to breakaway oxidation taking place. A range of microscopy techniques have been used to study experimental samples exposed to samples aged using accelerated exposure conditions including Scanning Electron Microscopy SEM), Focused Ion Beam Microscopy (FIB) and Transmission Electron Microscopy (TEM) to better understand the corrosion processes taking place under these conditions. Carburisation of the substrate takes place with carbides forming preferentially along grain boundaries or martensitic laths depending on substrate microstate. These carbides increase in complexity with exposure time with the carbide distribution favouring higher C containing carbides at later exposures (M7C3 vs M23C6). The increase in carbide volume throughout the spinel is associated with the internal oxidation characteristics of the steel, the porosity of the oxide scale and is linked with breakaway oxidation. Some of these substrate carbides have been shown to resist oxidation at the main oxidation front through the growth of a Cr rich shell, this allows the carbide to remain within the spinel for potentially thousands of hours. The porosity across the oxide scale changes with exposure time, and a mechanism of porosity development has been linked with the substrate carbide distribution and frequency. The oxidation behaviour of the steel has been shown to be dependent on both microstructure and carbide distribution, with both the internal oxidation zone and spinel oxide showing evidence of the prior microstructure and carbide distribution. Breakaway samples have been shown to have a thinner internally oxidised regions relative to the pre-breakaway samples. Predictions for time to breakaway have been made based off the growth rate of the IOZ across the fin tips and extrapolated to lower temperatures using the Arrhenius Equation and activation energy calculated from the fin tips. These predictions take the geometry of the fins into account, important as breakaway is always observed to initiate at the fin tips and not the main body.

The contents of this thesis are concerned with the industrial manufacturing process of glass mineral wool insulation. The process converts the molten glass into a wool product by a spinning the glass at high temperatures using a critical spinner component. The component, manufactured from the cobalt-based superalloy RM4, is exposed to a complex environment of stresses, temperatures and oxidising/corrosive substances leading to its rapid degradation. The work in this thesis seeks to understand the individual contributions each of these environmental factors have on the microstructure and physical properties of RM4, whilst proposing additional processing steps to improve the performance of the component. The results from this thesis show that the microstructure of the RM4 spinner component contains a continuous skeletal network of chromium-based carbide phases throughout the microstructure of the alloy. The carbide network was vulnerable to selective oxidation and corrosion processes, critically leading to severe internal oxidation and chromium depletion by a volatilisation mechanism. To reduce the continuity of the carbide network, and thereby protecting the alloy from excess chromium depletion, a solution heat treatment regime was applied to redistribute the carbide network. Although these heat treatments proved unsuccessful in increasing the oxidation resistance of RM4, the heat treatment regime was effective at reducing the internal oxidation experienced in the Stellite-21 alloy. This was principally due to the lower carbon content of Stellite-21, avoiding the supersaturation issues RM4’s matrix phase exhibits during the heat treatment. However, the two-step heat treatment regime was found to produce a more stable distribution of precipitated carbides at high temperatures in the RM4 alloy. In large-scale spinner trials performed by Knauf Insulation, the heat-treated spinners were found to possess a superior creep resistance compared to the as-cast spinners. Consequently, Knauf Insulation are now in the preliminary steps of incorporating this heat treatment to the spinner manufacturing process, potentially increasing the service life, and thus the yield of the glass mineral wool produced. Investigations into the effects of refractory element additions into cobalt-based superalloys was performed on the Mar M-509 alloy, where it was found that higher concentrations of tantalum and titanium favoured the formation of script-like MC carbides. Since stable script-like carbides have been associated with enhanced creep resistance, these results are encouraging for the development of creep resistant and oxidation resistant cobalt-based superalloys for glass mineral wool production applications. The final package of work within this thesis focuses on the effects of trace amounts of antimony contamination on the mechanical and creep properties of RM4. At high concentrations, antimony was found to decrease the creep life of the alloy, particularly at higher stresses, although the specific mechanism leading to this degradation remains elusive. However, atom probe data has suggested that additional deleterious elements that are commonly found in the processing environment, particularly phosphorus, may segregate to the grain boundaries during service exposure, embrittling the alloy and accelerating creep.

Gold as an element, has been known for tens of thousands of years, though only recently has the chemistry of gold complexes emerged as an important field for synthetic organic chemistry research. One significant challenge when investigating the chemistry of gold complexes is the oxidation of gold(I) to gold(III), gold(I) having a very high oxidation potential. This thesis comprises an investigation of gold through a homogeneous oxidative arylation of arenes using arylsilanes. Chapter 2 examines the nature of ligands on gold through a gold catalysed arylation reaction and the application of this to synthesise chiral biaryls. The investigation realises that strongly coordinating L type ligands inhibit catalyst turnover and discovers that transient, enantiopure, chiral additives have no effect on the distribution of enantiomers of the chiral biaryl. Chapter 3 explores new, inorganic oxidants for the oxidation of gold(I) to gold(III) and investigates aryl iodide cocatalysts for gold catalysed arylation. It is discovered that periodic acid allows turnover of the gold catalyst and produces a biaryl product from an arylsilanes substrate. Through MALDI-MS, gold is also discovered to react with acetonitrile in the presence of periodic acid, in a novel oxidative reaction for gold, to form a gold(I) cyanide polymer. In Chapter 4, NMR kinetics and stoichiometric experiments are utilised in the investigation of mechanistic details of periodic acid as an oxidant for gold catalysed direct arylation. The six-electron reduction pathway for periodic acid to an iodonium species and the mechanism of formation of aryl iodide from the starting arylsilane is probed. Iodonium is proposed to be the intermediate that forms the aryl iodide byproduct. Further evidence for a reactive iodonium species is found using a chemospecific, nucleophilic trap that prevents the non-productive iodination of aryl silane. A substrate scope of the new arylation conditions using the trap is assessed and the reaction was found to tolerate substrates that generated 5 membered rings. This thesis aims to establish new conditions for gold catalysed arylation of arenes using arylsilanes and describes interactions of oxyiodine species with arylsilanes, nitrile solvents and gold.

A significant number of stainless steel components within the boilers of the UK AGR plants are subjected to oxidation, carburisation and other changes in the underlying microstructure of the material during operation. This results from exposure to the pressurised CO2-based primary circuit coolant at temperatures from about 500 to 650oC. It is believed that there is a synergistic relationship between the pressurised CO2 coolant environment and creep-fatigue initiation and cracking. Devising and implementing an evaluation methodology to account for oxidation and carburisation to enable conservative lifetime assessments is essential to manage plant lifetime. Therefore, the development of a new and fundamental understanding of environmentally assisted degradation and failure mechanisms is required. It has been postulated that the mechanism underlying the initiation of cracks is carburisation associated with the presence of a duplex oxide layer. In this study, the material-environment interaction for Type 316H stainless steel under simulated AGR conditions has been investigated to increase the understanding of the combined effects of stress, strain and surface preparation, for example, on oxidation and cracking behaviour. Experimental data are presented which show that the presence of an ultrafine grained layer induced by surface grinding promotes the formation of a thin and protective oxide scale. Conversely, the removal of the surface deformed layer by chemical polishing using an oxide dispersion polishing solution (OPS), leads to the formation of a much ticker duplex oxide that protrudes along the grain boundaries. Furthermore, an increased surface hardness due to carburisation has been observed for the polished surface only, suggesting that carburisation occurs at an early stage on a chemically polished (OPS) surface. In fact, the elevated hardness was observed only at regions associated with creep deformation. It is found that when the substrate is plastically deformed and under the effect of active stress, the thin oxide on the work hardened (abraded) surface can be disrupted, resulting in similar oxidation behaviour to a chemically polished surface but with a better resistance to carbon ingress.

Ni-based superalloys currently in-service as aero-engine turbine discs are operating at the limit of their high-temperature capability. Next-generation turbine disc superalloys must be capable of sustaining the higher operating temperatures (approaching 800°C) and stresses required for greater thermal efficiency, whilst maintaining mechanical integrity and excellent oxidation resistance. Studies on the emerging γ'-strengthened Co-based superalloys based on the Co-Al-W and Co-Al-Mo-Nb/Ta systems have been successful in mitigating the respective drawbacks of high mass density and low γ' solvus temperature by incorporation of Ni, Ti or Cr. However, systematic investigation of the fundamental quinary system, Ni-Co-Al-Ti-Cr, is essential to provide a baseline against which to compare the influence of higher-order alloying with elements, such as W, that potentially confer superior high-temperature properties. To this end, seven γ'-strengthened model superalloys of composition (Ni,Co)75Al5Ti5Cr15 (at.%) were fabricated, aged at 800°C for 1000 hours, and the effect of increasing Co:Ni ratio on their resultant microstructural characteristics and critical properties was determined. For alloys of Co content 0, 9, 19, 28, 38, 47 and 56 at.%, γ' solvus temperature decreased with increasing Co:Ni ratio, whilst alloy mass density remained fairly constant across the alloy series at ~8.1 g.cm-3. Atom probe tomography (APT) was used to determine the elemental partitioning behaviour and γ' volume fraction for each of the seven alloys, denoted 0Co, 9Co, 19Co, 28Co, 38Co, 47Co and 56Co. From APT, a non-monotonic trend in Ti, Al and Cr partitioning was observed as Co:Ni ratio increased, with a transition at ~19 at.% Co. From neutron diffraction analysis, the γ-γ' lattice misfits of alloys 0-47Co were found to be positive at all test temperatures (ambient, 400, 600, 700 and 800°C) and the magnitude of lattice misfit increased as Co content increased from 0-38 at.%. Lattice misfit values decreased with increasing temperature, the lowest values being obtained for 800°C. Crucially, this study also investigated the effect of a systematic increase in Co:Ni ratio on oxidation performance of γ-γʹ alloys of composition (Ni,Co)75Al5Ti5Cr15 (at.%). The seven model superalloys (0Co, 9Co, 19Co, 28Co, 38Co, 47Co and 56Co) underwent isothermal oxidation in air at 800°C using both thermogravimetric analysis (100 hours) and box-furnace exposure (1000 hours). X-ray diffraction was carried out to identify surface oxide phases present. Scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS) and secondary ion mass spectrometry were performed to map elemental distribution and to provide precise chemical analysis of any thin surface oxide layers present. Following 1000 hours oxidation at 800°C, the 28Co, 38Co and 47Co alloys were observed to exhibit a flat, compact, well-defined external scale and Cr2O3 layer with minimal oxygen ingress, together with a distinct Al2O3 sub-scale. This work represents the first detailed systematic study on the fundamental quinary Ni-Co-Al-Ti-Cr alloy system describing the effect of variation in Co:Ni ratio on the evolution of surface oxides and on the partitioning of elements to γ and γ' phases and associated lattice misfit.

In modern gas turbine engines, leakage of gas from the flow path reduces the efficiency of the engine. This leakage is currently ameliorated in the high-pressure turbine by using shrouded turbine blades, which give a high sealing efficiency. However, the shroud is manufactured from the same superalloy as the blade, which has a high density of 8.70 g cm−3 and hence limits the creep life of the turbine blade. Shroudless blades can be adopted to combat the issue of excessive creep. To achieve a suitable seal with a shroudless blade, the blade can be tipped with an abrasive system that cuts into an abradable liner on the static counter face. This should allow low clearance to be maintained during service. Currently, such systems for high-temperature use are composed of cubic boron nitride (cBN) abrasive particles embedded in a NiCoCrAlY anchor phase. Previous work has shown that at the operating temperatures achieved in the high-pressure turbine, the NiCoCrAlY is unable to retain the embedded cBN particles under abrasion. A new anchor phase system based on the intermetallic NiAl, strengthened with a reinforcing Laves phase, NiTaAl, has been identified as a possible replacement material with sufficient strength at high temperatures. In addition to high strength at the required temperatures, anchor phase materials must have sufficient oxidation resistance to maintain seals for the operational lifetime of the engine. Compatibility between the anchor phase and the underlying CMSX-4 turbine blade is also essential, as interdiffusion occurs over the lifetime of the blade. These two requirements, and preliminary wear behaviour, were investigated for the Ni-Al-Ta ternary system. The isothermal oxidation behaviour of a series of Ni-Al-Ta alloys with varying tantalum content was studied at 1100 °C using static oxidation testing and thermogravimetric analysis. A layer of Al2O3 is found to form on samples containing up to 20 at.% tantalum with parabolic oxidation behaviour observed for these alloys. At higher tantalum contents, parabolic oxidation behaviour is initially observed, which then transitions into a rapidly increasing rate of oxidation. Ni-Al-Ta/CMSX-4 diffusion couples were investigated experimentally and computationally. After heat treatment at 1100 °C, the NiTaAl Laves phase in the anchor phase had transformed to Ni2TaAl Heusler phase, and topologically close-packed phase precipitation was observed in the CMSX-4. A CALPHAD-based model, using Thermo-Calc and DICTRA, developed for this system was able to predict the concentration profiles across the diffusion couple at 1000 °C. However, the model predictions were poor at higher temperatures due to the limited diffusion data available for the intermetallic phases. The wear behaviour of a Ni-Al-Ta alloy was studied up to 1100 °C using a pin-on-disc abrasion rig. The Laves phase showed a layer of plastic deformation at the highest test temperatures. Preliminary attempts to deposit cBN in the new anchor phase material indicated that some cBN may be retained after abrasion. Careful consideration must be given to any future manufacturing method for the coating, to maximise cBN retention and minimise reaction with the material.

The long chain omega-3 polyunsaturated fatty acids (LC3PUFA) in human diets are mainly derived from oily fish and fish oil based supplements. Currently, the consumption of oily fish in the UK is far below the recommended level. LC3PUFA's non-fish sources such as algal oil with DHA (docosahexaenoic acid) are particularly important for vegetarians, non-fish eaters, and pregnant women. In previous work, high DHA vegetative algal oil load 50% w/w was successfully used to develop an oil-in-water nanoemulsion system suitable for functional food enrichment. The aims of this study included to investigate the effect of selected emulsifiers on oil-in-water nanoemulsions of algal oil prepared using ultrasonic technology. To improve the stability and digestibility of nanoemulsions within an In vitro digestion model. To examine the oxidation stability of nanoemulsions of algal oil and bulk algal oil with composition and droplet size changes during a 5 weeks storage trial at a temperature of 4 °C, 20 °C and 40 °C respectively. To evaluate sensory properties and consumer acceptability of food products with the incorporation of resulted nanoemulsion and find out possible relationship between the sensory profile of foods and the characteristics of added nanoemulsion. Nanoemulsion of LC3PUFA algal oil was developed with selected 6% w/w emulsifiers, including Lecithin (LN), Tween 40 (TN), Tween 60, equal ratio of Tween 40 and lecithin (LTN), 50% w/w Algal oil and 44%w/w water using a homogenizer and ultrasound processor. The results show that the nanoemulsion has been stabilised with selected emulsifiers (LN, TN & LTN) and the smallest droplet size of nanoemulsion was obtained using the combination of lecithin and Tween 40 at ratio 50:50. The In vitro digestion experiments were conducted with a model of fed state gastric and duodenal digestion using method of Lin et al (2014). The results show that the omega-3 oil nanoemulsion (LE/TW 50:50) were stable over 60 min in the gastric phase, in contrast omega-3 nanoemulsion (LE 100%) was destabilised at the gastric phase in 60 min, in which the droplet size diameter was significantly larger than at the beginning of gastric phase (P ≤ 0.05). The droplet size, fatty composition and oxidised compounds were measured to compare bulk algal oil and nanoemulsions stabilised with lecithin (LN) and Tween 40 (TN) solely and in combination (LTN) over a storage period of 5 weeks at temperatures of 4, 20 and 40°C. The results show the droplet size of nanoemulsions had no significant changes for samples stored at tested temperatures over 5 weeks storage. There were no significant differences in DHA composition within the weeks and temperatures used. For the GCHS analysed results, the increase in temperature to 40 ºC and storage time had a significant effect on the development of propanal for all samples (P≤0.05). Nanoemulsions prepared with lecithin alone had significantly higher development of propanal in week 1 at both 40 ºC and 20 ºC (P≤0.05). Lecithin (sole and combination with Tween 40) had more significant increases in oxidised volatiles at 40°C, which may be due to the instability of linoleic acid found in lecithin molecules which located in the outer layer of the oil droplets. There were no significant increase in oxidised compounds from the beginning to the end of storage for all tested samples stored at 4 °C. The sensory testing was also conducted on white sauce incorporated with omega-3 nanoemulsions with selected emulsifiers and bulk algal oil. The results show that the sensory attributes and overall acceptability of foods enriched with omega-3 nanoemulsion were statistically significantly lower than that of control sample (P≤ 0.05). Overall, the smallest droplet size of nanoemulsion was achieved with combination of lecithin and Tween 40 at a ratio of 50:50 by using ultrasonic processor. The stability and digestibility of nanoemulsion with the combination of lecithin and Tween 40 was improved in an In vitro digestion approach. A storage period of 5 weeks and temperature have no significant effect on the droplet size of tested nanoemulsion samples. However, there is a significant increase of the oxidised volatiles at 40 °C for all samples. Sensory testing show the white sauce with nanoemulsion has a stronger fishy taste and less overall liking than with bulk oil, indicating the smaller drop size is more ready to spread and reach the sensors of the mouth.

Mitochondrial membrane potential (ΔΨm) in cells is a critical biological parameter that is related to diseases such as cancer through biological processes including metabolism, oxidative stress and apoptosis. Studying ΔΨm in normal and diseased states is limited by significant challenges associated with the current state-of-the-art methods for measurement, particularly fluorescent dyes, which are often toxic and photobleaching. The aim of this work was to develop electrical and chemical sensing methods to enable sensitive detection of changes in ΔΨm in single cells. Fluorescent Nitrogen Vacancy Centres (NVCs) in nanodiamond were identified as potential sensors of electric field that could be applied in living cells to directly measure ΔΨm. Furthermore, Raman spectroscopy was identified as a label-free chemical sensing technique that could be used to reveal the location and chemical composition of the mitochondria in cells. To achieve the aim of detecting changes in ΔΨm using these two methods, complementary NVC and Raman measurements in live cells were needed. Initially, a specialised microscope was designed, built and validated to enable dual measurement of both NVC fluorescence and Raman spectroscopic signals simultaneously. Next, protocols and analysis techniques were developed for live cell Raman microscopy using a commercial reference instrument. An investigation of the impact of nanodiamonds as nanoparticles for biological sensing within live breast cancer cells, including surface modification by oxidation, was then conducted. By developing both techniques together, this project leverages the complementary advantages of long time course measurement, common laser excitation, the observation of nanodiamonds via Raman signal, with live single cell interrogation. The thesis concludes with an outlook on the future development needed to utilise NVCs and Raman spectroscopy in the measurement of cellular ΔΨm. Achieving this goal in future will provide new biological understanding of ΔΨm in normal and disease states, allowing us to follow over time changes in ΔΨm in response to biological processes such as apoptosis in single cancer cells.

One critical safety issue of Zirconium (Zr) alloy cladding in light water reactors (LWRs) is its severe degradation due to the rapid oxidation of cladding upon exposure to high-temperature water vapour in a loss-of-coolant accident (LOCA) scenario. In this thesis, new designs of protective coatings on Zr alloy against water vapour oxidation are proposed and studied. In addition, a new protective coating on Ti alloy against high temperature air oxidation for aerospace application is also investigated. Zirconium nitride (ZrN) coating has been deposited on Zr alloy and comparison of the oxidation behaviour of ZrN coating in water vapour and air at high temperature has been investigated. The parabolic rate constant of ZrN oxidizing in water vapour environment at 600 degree celsius is approximately 100 times faster than that in air, due to the larger pores and greater number of cracks that are formed across zirconium oxide (ZrO2) layer formed during the water vapour oxidation process than during the air oxidation process. A bilayer-structure ZrO2 with tetragonal ZrO2 near the ZrN/ZrO2 interface and monoclinic ZrO2 approaching the outer ZrO2 surface are formed in both cases. Oxidation behaviour of zirconium nitride (ZrN), titanium nitride (TiN), titanium silicon nitride (TiSiN) and silicon aluminium nitride (SiAlN) coatings in high temperature water vapour environment has been studied and compared. The oxidation resistance of designed four nitride coatings in water vapour follows the order: SiAlN > TiSiN > TiN > ZrN. The SiAlN coating with a relative thick Mo interlayer (750nm) can provide excellent protection for Zr alloy and even no oxide forms on coating upon exposure to water vapour at 1000 degree celsius for 1 h. This is due to the good oxidation resistance of amorphous SiAlN coating and the synergetic effects of Mo interlayer on adhesion, spallation resistance and phase stability of SiAlN coating on Zr alloy at high temperature. The Mo interlayer not only improves spallation resistance of SiAlN coating owing to relaxation of thermal mismatch, but also mitigates the crystallization of amorphous SiAlN. Oxidation behaviour of a NiCrAl bulk alloy and a thermally sprayed NiCrAl coating (with the same composition as that of the NiCrAl bulk alloy) on a Zr alloy in water vapour at high temperature (900-1200 degree celsius) has been investigated. The NiCrAl bulk alloy exhibits good oxidation resistance by forming a slow-growing, protective alumina scale on the surface. However, a non-protective ZrO2 scale forms on the NiCrAl coating surface at temperatures above 1000 degree celsius due to the severe interdiffusion between the NiCrAl coating and Zr alloy. With the addition of the WC-CoCr interlayer, the outward diffusion of Zr is prevented and the NiCrAl coating provides excellent protection for the Zr alloy against water vapour oxidation at 1200 degree celsius. A multilayer nitride coating with self-bonding and adaptive deformability on the Ti and its alloy has been propose and studied. The multilayer nitride coating on titanium and its alloy is designed by magnetron sputtering a SiAlN coating (1.2 um thick) with molybdenum (Mo) interlayer, followed by cyclic oxidation at 800 degree celsius. Interdiffusion and interaction during cyclic oxidation between the Ti and SiAlN layers lead to the formation of a TiN0.26 interlayer which shows remarkably adaptive deformability via mechanical twinning, and thereby largely alleviating the thermal mismatch strain between the coating and substrate. Such adaptive deformability plus excellent bonding strength equip this coating system with excellent thermal cycling life. For instance, no cracking, spallation and oxidation of the coating are observed after hundreds of hours of cyclic oxidation in air at 800 degree celsius.

Primary Water Stress Corrosion Cracking (PWSCC) of Ni-base alloys, such as Alloy 600 and Alloy 690, still remains one of the main issues in Nuclear Power Systems (NPPs). The Internal Oxidation model has been proposed by Scott and Le Calvar to develop a mechanistic understanding of the early stages of PWSCC and more recent advanced characterizations have consolidated this model. Preferential intergranular Oxide (PIO) have been observed to penetrate along High Angle Grain Boundaries (HAGBs) that exhibits local Diffusion-Induced Grain Boundary Migration (DIGM). However, the role of these 'precursor events' (namely PIO and DIGM) in the early stages of PWSCC is still unclear and the role of GB migration on crack initiation has never been clarified. In this study, oxidation experiments were performed in a low pressure superheated H2-steam system that is capable of accelerating the oxidation kinetics of Ni-base Alloys. The capability of the H2-steam system to reproduce the correct Electrochemical Corrosion Potential (EcP) with respect to the Ni/NiO transition was assessed by in-situ electrochemical measurements with a Y2O3-ZrO2 solid state reference electrode. The environmental conditions reproducing the Ni/NiO transition were identified between 372 °C and 480 °C and confirmed the possibility to use the superheated H2-steam as surrogate environment to perform oxidation experiments in conditions that are relevant to PWR primary water. Solution annealed (SA) Alloy 600 samples with an OPS surface finishing were exposed to H2-steam at 480 °C at different oxidizing conditions to clarify the role of PIO/DIGM and local microchemical segregation during the early stages of PWSCC. Advanced electron microscopy techniques showed that the PIO was more susceptible to occur under reducing conditions, whereas DIGM occurred independently from the environment. These results suggest that DIGM is a not sufficient condition for the occurrence of PIO and subsequent SCC initiation. Furthermore, it was found that SCC initiation occurred in correspondence of the intergranular oxide that developed along a migrated grain boundary and displayed a local Al/Ti rich oxide. It was postulated that the local Al and Ti enrichment can create incoherent surfaces along the migrated GB and provide an accelerating factor for the inward oxygen diffusion. Evidence of the occurrence of DIGM and minor segregation was also found in Alloy 690 TT and SA after exposure to H2-steam at 480 °C under reducing conditions. However, the material underwent DIGM but not to PIO. It is probable that the high Cr content induced the formation of a dense and protective external Cr- rich oxide that inhibited the PIO despite providing the driving force for the occurrence of DIGM; therefore, these results show that also for the Alloy 690, the DIGM can be considered as a secondary (e.g. accelerating) and not sufficient phenomena for the occurrence of PIO. Therefore, the early stages of SCC of Ni base Alloys cannot be explained only as the result of one single dominant phenomenon but due to the synergistic interactions between Al/Ti oxide and DIGM which are accelerating factors for the development of PIO which fracture upon the effect of applied stress if chemical and environmental conditions can lead to the film instability.

Defects in the functional oxides play an important role in electronic devices like metal oxide semiconductor field effect transistors (MOSFETs) and resistive random-access memories (ReRAMs). The continuous scaling of CMOS has brought the Si MOSFET to its physical technology limit and the replacement of Si channel with Ge channel is required. However, the performance of Ge MOSFETs suffers from Ge/oxide interface quality and reliability problems, which originates from the charge traps and defect states in the oxide or at the Ge/oxide interface. The sub-oxide layers composed of GeII states at the Ge/GeO2 interface seems unavoidable with normal passivation methods like hydrogen treatment, which has poor electrical properties and is related to the reliability problem. On the other hand, ReRAM works by formation and rupture of O vacancy conducting filaments, while how this process happens in atomic scale remains unclear. In this thesis, density functional theory is applied to investigate the defect behaviours in oxides to address existing issues in these electronic devices. In chapter 3, the amorphous atomic structure of doped GeO2 and Ge/GeO2 interface networks are investigated to explain the improved MOSFET reliability observed in experiments. The reliability improvement has been attributed to the passivation of valence alternation pair (VAP) type O deficiency defects by doped rare earth metals. In chapter 4, the oxidation mechanism of GeO2 is investigated by transition state simulation of the intrinsic defect diffusion in the network. It is proposed that GeO2 is oxidized from the Ge substrate through lattice O interstitial diffusion, which is different from SiO2 which is oxidized by O2 molecule diffusion. This new mechanism fully explains the strange isotope tracer experimental results in the literature. In chapter 5, the Fermi level pinning effect is explored for metal semiconductor electrical contacts in Ge MOSFETs. It is found that germanides show much weaker Fermi level pinning than normal metal on top of Ge, which is well explained by the interfacial dangling bond states. These results are important to tune Schottky barrier heights (SBHs) for n-type contacts on Ge for use on Ge high mobility substrates in future CMOS devices. In chapter 6, we investigate the surface and subsurface O vacancy defects in three kinds of stable TiO2 surfaces. The low formation energy under O poor conditions and the +2 charge state being the most stable O vacancy are beneficial to the formation and rupture of conducting filament in ReRAM, which makes TiO2 a good candidate for ReRAM materials. In chapter 7, we investigate hydrogen behaviour in amorphous ZnO. It is found that hydrogen exists as hydrogen pairs trapped at oxygen vacancies and forms Zn-H bonds. This is different from that in c-ZnO, where H acts as shallow donors. The O vacancy/2H complex defect has got defect states in the lower gap region, which is proposed to be the origin of the negative bias light induced stress instability.

The Warburg effect describes the survival advantage of cancer cells in that they can proliferate under low oxygen/hypoxic conditions via a less efficient pathway known as glycolysis. It has not yet been documented at which point, in an oxygen gradient, phenotypic changes occur. Measuring the intracellular redox potential (IRP) and its impact on cellular dynamics would provide greater insight into how disruption of redox homeostasis caused by changes in oxygen concentration leads to aberrant cell signalling and diseases such as cancer. Current techniques in measuring IRP include redox-sensitive fluorescent proteins such as roGFP which is glutathione-specific. Measuring the concentration of one redox couple is, however, not an accurate representation of IRP as it does not necessarily inform about the state of other redox couples. Furthermore, fluorescent biosensors can suffer from photobleaching and may interact with other oxidants. The IRP was measured, in this work, using our newly developed novel-class of surface enhanced Raman scattering nanoparticles which can quantitatively measure the redox potential of cells in vitro. A 'homemade' device was created to keep the cells under fixed pO2 whilst obtaining measurements. The IRP was correlated with the transcriptomic and downstream metabolic profiles of MCF7 breast cancer cells, under perturbed pO2, using 1H NMR spectroscopy (NMR), mass spectrometry (MS) and RNA-sequencing. Discriminatory metabolites were all associated with energy and glucose metabolism. Discriminatory microRNAs were all affiliated with the hallmarks of cancer; the regulation of some is controlled by transcription factors containing redox-sensitive motifs in their DNA binding domains. Multivariate analysis techniques were used to analyse the different data streams in a holistic way that allows the correlation of redox potential, metabolism and transcription.

This thesis consists of three studies which use atomic-resolution aberration-corrected TEM techniques to investigate the structure and composition of air-sensitive crystals. The first two studies investigate the oxidation of graphene-encapsulated 2D crystals, black phosphorus (BP) and NbSe2. Recent graphene-encapsulation techniques are performed in a glovebox environment, protecting thin (few-layered to monolayer) stacks of these crystals from instantaneously degrading from oxidation. Such protection allows for some of the first detailed structural and compositional studies of these crystals in pristine condition. BP is investigated specifically with a focus on electron beam damage, which can be utilised to sculpt stable features for applications in electronic devices. Intrinsic atomic defects in NbSe2 are identified with atomicresolution imaging, geometric phase analysis (GPA) and compared to density functional theory (DFT) calculations. Point defects such as vacancies and substitutional dopants are identified and play a crucial role in the overall electronic properties of the material. The final study investigates the nucleation and growth of aluminium oxide islands using atomicresolution in-situ environmental TEM (ETEM). Electron beam sputtering is used to remove initial self-healing oxide layers and oxygen is then introduced into the ETEM chamber allowing for the growth of metal oxides at room temperatures to be observed dynamically. Oxidation is studied with respect to oxygen pressure and crystallographic orientation of the aluminium. The study reveals atomic-scale insights into the oxidation mechanism which were previously elusive to bulk spectroscopy and surface science techniques.

One critical safety issue with tri-structure isotropic (TRISO) fuel of high temperature reactors (HTRs) is the high release fraction of the fission product (FP) silver (Ag) through the intact silicon carbide (SiC) coating. Aside from Ag release, chemical attack of another fission product, pallidum (Pd), on the SiC coating is of particular interest, as Pd has a direct impact on the migration of other fission products, including Ag, through the SiC layer, the major diffusion barrier in coated fuel. A number of studies on Ag migration in SiC have been performed in both, in-pile and out-pile studies, with various mechanisms proposed. However, Ag release does not appear to be simply controlled by one existing diffusion mechanism. To have a thorough understanding of how the metallic fission products Pd and Ag behave and migrate in SiC, reaction couples Ag-SiC, Pd-SiC and PdAg-SiC were annealed from 1100°C to 1400°C to simulate the FPs-SiC interaction at the regular operation temperature of TRISO particles. Both thermodynamics and experimental work suggested that the chemical composition of FPs directly influences their migration in SiC. Liquid Ag (Si) alloy dissolved SiC in a limited way but this dissolution cannot effectively help Ag migrate through SiC below 1400°C due to the insufficient driving force for activating 'reaction-recrystallization' migration. Pd penetrated easily into SiC leaving SiC severely dissolved. FP clusters containing Pd, Ag and possibly Si can penetrate SiC with SiC remaining intact via reaction-recrystallization when the composition of clusters (atomic Pd:Ag) was in a specific range. Here, it is proposed to modify the metallic cluster's composition by adding extra Si to relieve the chemical dissolution of SiC. Initial experimental work confirmed the potential of this proposal, which could be useful in mitigating Ag release in TRISO fuel. Oxidation experiments were carried out on the SiC coating of three compositions (stoichiometric SiC and coatings with co-deposited Si or C) in both air (1200°C, 1600°C) and steam (1200°C). Silica morphology and growth kinetics suggested that the SiC coating with co-deposited Si oxidized faster than stoichiometric or C co-deposited SiC coating in air, but a slower oxidation in the steam was observed. In addition, this work suggested that production of CO gaseous group at amorphous silica/crystalline silica interface might be responsible for initial pores birth in silica, which had a great impact on silica growth kinetics afterwards, especially in steam. This interpreted the low oxidation rate of Si co-deposited SiC coating in steam due to the limited contribution of CO gases from Si, compared with other two coatings.

Primary water stress corrosion cracking (SCC) of metals in pressurized water reactors (PWRs) is known to be one of the most challenging and cost intensive modes of failure in the nuclear industry. Even though it is known that cracking in Ni-base alloys proceeds mainly intergranular (IG), the initiation and propagation of cracks in ductile metals are not yet understood and a much-desired accurate prediction of SCC related failure seems unobtainable. In this thesis, a combination of microcantilever fracture experiments, scanning electron- (SEM) and transmission electron microscopy (TEM) techniques was employed to study and compare the failure of oxidized grain boundaries of Ni-base Alloy 600 with high and low intergranular carbide coverage and different sample history. A new technique for lifting-out whole cantilevers after testing and for performing 3D focussed ion beam sequencing (3D FIB-SEM) while preserving a thin central region of the cantilever for further TEM sample preparation was developed and is presented. In lieu with recent efforts of the main project sponsor Électricité de France (EDF) to build a predictive model for IGSCC based on localized/microscopic information, one of the main objectives was the extraction of the stress at failure of individual oxidized GBs. Supported by finite element simulations, microcantilever fracture tests revealed that surface oxides on top of individual GBs have the capability to alter the mechanical response by delaying/suppressing the onset of failure. An overestimation of the failure stress (> 230 MPa) was observed, proving that the presence of the surface oxide on top of the test structures cannot be neglected. The failure stress on both samples, tested without influence of the surface oxide, was found to cover a range of 300 - 600 MPa, which agreed well with finite element simulations of the tests and further demonstrates the reliability of the obtained data. The second objective was to gain a better understanding of the observed fracture behaviour and the role of local microstructure. Using the gathered microscopy data, it was found that the crack clearly favours a progression along the IG oxide-metal interface in the presence of carbide precipitates. Electron energy loss spectroscopy (EELS) revealed that the observed crack path can be linked to compositional and density variations of the IG oxide. In the presence of carbides the oxide was layered. An oxide close to the stoichiometry of chromia was located at the original GB and next to the carbides. Next to this Cr-rich oxide, Fe-rich mixed spinel oxides of varying composition and density were found. An explanation for density variations based on the possible formation of defective spinel oxides of the type A2+B3+2O4, due to an unavailability of certain cation species is presented. No clear interface preference was observed in the absence of precipitation, where the IG oxide was found to be thin and often incomplete with Cr-richer oxides preferentially located at the original GB. While these observations were consistent on both samples (high and low carbide coverage), bigger void-like defects were located at the Fe-richer oxide-metal interface of the cold worked sample with high IG carbide precipitation only. These weak spots seemed to be the preferred path for crack propagation on this sample. The sample with low intergranular carbide coverage showed no obvious porosities at this interface but a Cr- depleted region was seen. Introducing a multi-faceted investigation strategy, supported by finite element simulations, the presented thesis provides the most accurate determination of the failure stress of oxidized GBs on Alloy 600 to date and and adds new valuable insights to our understanding of IGSCC and the future prediction of SCC related failures.

Aerosols and their indirect contribution to the Earth's climate remains a poorly understood field. The indirect effect of aerosols on the climate refers to aerosol ability to form cloud condensation nuclei (CCN) and affect cloud properties. Naturally forming, thin organic films exist on the surface of atmospheric aerosols and have the ability to influence aerosol behaviour. Given the oxidative nature of the atmosphere, thin organic films on the surface of aerosols are readily oxidised which will impact on CCN formation and the properties of cloud droplets, affecting the Earth's climate indirectly. The purpose of this thesis was to investigate the oxidation of atmospherically relevant thin films at the air water interface using the complementary techniques of optical trapping and neutron and X-ray reflectometry, to determine whether such reactions are important in the atmosphere. An optical trapping technique was developed to coat individual solid silica beads with a thin film of oleic acid and characterise both the size and wavelength dependent refractive index of the core silica aerosol and the oleic acid coating using white light Mie scattering. The size of the core aerosol and coating thickness were determined to a precision of ± 0.5 nm and 1 nm respectively. The oxidation of monolayer organic films of atmospheric proxies at the air-water interface was studied using neutron reflectometry and the common atmospheric oxidants, O3, •OH, NO3•, SO4•−. These studies provided insight into the oxidation mechanism of the film as well as film persistence and thickness. Furthermore, the oxidation of monolayer films was also found to be independent of the viscosity and ionic strength of the solution that the film was present on. X-ray reflectivity studies were carried out on the oxidation of monolayer organic films extracted from real atmospheric aerosol and sea-water samples at the air-water interface. The films were found to be inert to gaseous ozone indicating a lack of unsaturated material in atmospheric samples and that oxidation by gaseous ozone may not be important in the atmosphere.

In their attempts to understand the unwritten past of human technology and progression, archaeologists have borrowed aspects of the natural sciences to answer big questions. In one such pursuit, fundamental aspects of the sciences have been employed towards the chemical compositional analysis of copper-based artifacts, often to simply classify which is bronze, brass, or pure copper, and to explain why they are significant in limited space and time. This thesis takes the variety of identified metal types and compositions from these analyses and builds the beginnings of an ambitious thermodynamic model based on the accepted premise of consistent and widespread recycling of ancient metals over time. Following the laws of thermodynamics, in systems at equilibrium, the model predicts the outcome of metal losses over the course of ancient pyrometallurgical processes from molten systems through both volatilization and oxidation using rigorous and established mathematics and theory. Elemental loss likelihoods are modeled for all binary copper-based metals, using activity coefficients, and ternary copper and zinc-based systems, with the excess Gibbs free energy, respectively. The calculations are performed using custom-written software designed to account for hundreds of thousands of compositional permutations after the method described by Redlich and Kister (1948). The results of these calculations are given as activity (binary) and isoactivity (ternary) contour lines. Quantified tables for the oxidation and volatilization of elements from a copper melt at 1200 ºC and 1 atm are also given as rough indicators of element loss in ancient pyrometallurgical systems. A proof of concept of the models viability is also provided for binary Cu-M and ternary Cu-M-Zn (M = Ag, As, Au, Bi, Co, Fe, Ni, Pb, Sb, Sn, Zn), Cu-Sn-Pb, and Cu-Sb-As systems from the Late Bronze Age to post-medieval periods in Britain, which is based on several substantial artifact chemical datasets. For each ternary system, the interaction parameters used for higher-order calculations from the fitted behavior of each contributing binary systems are provided. Comparison of the calculated models to available experimental system assessments, and to published archaeological chemical datasets, show that in both respects the proposed modeling of ancient copper-based metal losses works. And given the near ubiquity of ancient metal use around the world, the consistency in metal production and recycling technology, and the chemical analyses available, this preliminary model can be applied virtually anywhere the technology for smelting and recycling existed. In addition to loss modeling, this thesis has the additional offshoots of predicting ancient furnace conditions based on the calculated behavior of interacting metals, and of the controlling thermodynamic factors in the ancient calamine process.

The first part of this thesis describes my research towards the valorisation of lignin. Due to environmental and political pressures, there has been a drive to start the transition from a fossil fuel based economy to a renewable based one. This will require the development of novel routes to renewable chemicals, one source of which may be the biopolymer lignin. Through the synthesis of advanced lignin model compounds, the chemistry of real lignin is explored. This work culminates in the development of a novel method for the depolymerisation of real lignin to simple mixtures of aromatic chemicals that could be useful building blocks for the chemical industry. One of the key steps in this process is the oxidation of the β-O-4 linkages in lignin using catalytic amounts of DDQ and molecular oxygen as the terminal oxidant. The second part of this thesis details the first synthesis of melohenine B and O-ethyl-14-epimelohenine B, two medium sized ring containing natural products. The key step in the synthesis of these natural products was the photo-sensitised oxidative cleavage of an indolic substrate by molecular oxygen. Additionally, the use of residual dipolar coupling (RDC) analysis for the conformational analysis of these molecules in solution has been explored. Finally, the absolute configurational assignment of the natural products was established and their biological activities investigated.

Catalysis has an effect on almost every aspect of our lives. They are used to help grow the food we eat, clean the water we drink and produce the fuels our civilisation is so dependent upon. Homogeneous catalysts, those in the same phase as the reaction medium, are highly selective as a result of their tuneable nature, for example through changes to ligands in a metal complex. However, their separation from the reaction medium can become a problematic, costly, non-green issue, overcome through the use of heterogeneous catalysts which can be removed and recycled by simple separation techniques such as filtering and sedimentation. A major limitation on understanding the behaviour of heterogeneous catalysts is the presence of different active sites due to different exposed crystal surface, concentration of defects and morphological variations. With such considerations, the first section of this thesis focuses on the synthesis of discrete and well-defined nanostructured materials (ceria and titanate) using a single-step hydrothermal method. Nanostructured ceria with different morphologies (particles, rods and cubes), present a high oxygen storage capacity and thermal stability. Their oxidation catalytic activity was assessed using CO oxidation as a model reaction as a function of their physical and chemical properties, tuned by morphological control at the nanoscale. An inverse relationship is observed between crystallite size and rates of reaction normalised per surface area. Smaller crystallites present a constrained geometry resulting in a higher concentration of defects, highly active catalytically due to their unsatisfied coordination and high surface energy. The surface to bulk oxygen ratio generally increased as the surface area increased, however, ceria nanorods present a higher surface oxygen content than that which would be predicted according to their surface area, likely due to the selective exposure of the (110) and (100) dominating crystal surfaces presenting more facile oxygen atoms in their surface. Additionally a relationship between surface to bulk oxygen ratios and activation energies was also ascribed to the more facile nature of oxygen atoms on these surfaces and their more readily formed oxygen vacancies as a result. This activity is as a result of the formation of oxygen vacancies being the rate-controlling step. The thermal stability of nanostructured ceria (particles, rods and cubes) was also studied to investigate their performance under cyclic high temperature applications. For this, the materials were pre-treated at 1000 °C under different atmospheres (inert, oxidative and reducing). In all cases, the materials sinter, consequently resulting in a dramatic decrease in surface area. Interestingly, their catalytic activity per surface area towards CO oxidation, seems to be maintained, although those materials pre-treated under inert and oxidising atmospheres became inactive in consecutive catalytic runs. However, nanostructured ceria pre-treated at 1000 °C under hydrogen appeared to maintain its activity per surface area. The presence of hydrogen during thermal treatment does not only facilitate the removal of surface oxygen, but also the bulk oxygen, resulting in a rearrangement of the structure that facilitates its catalytic stability. Titanate nanotubes were shown to be inactive for CO oxidation and thus were used in the second part of this thesis as a support for platinum nanoparticles to study the effect of the structure and metal-support interaction on the resulting catalytic activity. The study focuses on the effect of different loading methods (ion exchange and incipient wetness impregnation) of platinum nanoparticles on the resulting metal particle size, dispersion, metal-support interaction and consequently their resulting catalytic activity. Ion exchange consistently resulted in smaller nanoparticles with a lower dispersion of sizes and more active catalyst, both in terms of turnover frequency values and activation energy, compared with incipient wetness impregnation. The catalytic activity of the platinum supported on titanate nanotubes increases as the metal particle size decreases to a size value (between 1 and 2.5 nm) below which a dramatic decrease in activity is observed. Despite initial differences in catalytic activity between the different catalysts, it was observed that after initial reactions to 400 °C, the activation energy was independent of metal loading weight and was instead inherent of the loading method, suggesting the presence of similar active sites.

Environmental and regulatory constraints on the global energy market are driving the need to improve conventional power generation methods to meet commitments made to reduce carbon emissions set out in the Kyoto Protocol. To maintain security of supply and ensure competitive energy prices, fossil fuels will play a vital role in the energy market over the next century, however, in order to comply with regulations it is necessary to improve on current conventional power generation technologies. Improvements in security of supply and environmentally deleterious emissions can be realised via increases in plant efficiency. A major route to achieving a considerable increase in efficiency in conventional coal fired power station is via elevating the operating conditions of the working steam to benefit from enhanced thermal cycle efficiencies. It has been proposed that increasing the operating steam parameters from the current typical levels of ~540°C/~190 bar to ~700°C/~300 bar could lead to an increase in plant efficiency of up to 15%. The major challenges to increasing steam parameters need to be met by advanced materials. Increasing the steam temperature and pressure to the suggested levels would push traditional materials beyond their acceptable oxidation and creep resistances. One strategy to accommodate the proposed steam conditions is to substitute traditional steel based materials at key regions of the steam cycle for alternative nickel-based superalloys.

In the present study, efforts have been made to produce protective surface layers in order to improve the tribological, electrochemical and tribo-electrochemical response of titanium. In order to achieve this, two different techniques were employed: 1) thermal oxidation (TO) and 2) pack carburisation with oxygen diffusion (PC). Thermal oxidation of commercially pure titanium (CP-Ti) was undertaken at a temperature of 625 °C for durations of 5, 20 and 72 h. This results in a multi-layered structure comprising a titanium dioxide layer (rutile) atop of an α-titanium oxygen diffusion zone (α-Ti(O)). Initial attempts have also been made to improve the frictional behaviour of the oxide layer, using a prior surface mechanical attrition treatment (SMAT) and controlled slow cooling after oxidation. The results demonstrate that these prior and post treatments have a positive effect on the tribological performance of the oxide layer. Electrochemical and tribo-electrochemical characterisation was also carried out in a 0.9% NaCl solution. Electrochemical tests provided evidence that oxygen content in the upper part of the oxygen diffusion zone (depths < 5 μm from the surface) helps to accelerate passive film formation and thus improve the corrosion resistance of CP-Ti. Tribo-electrochemical testing of TO-Ti was carried out against an alumina counter face under various anodic and cathodic potentials. It is shown that the rutile oxide layer offers low friction and improved wear resistance. An unusual anodic protection behaviour for the oxide film has also been observed. When the TO-Ti is polarised anodically during sliding, the durability of the oxide layer is prolonged, resulting in low friction and much reduced material loss. In the present work a new pack carburising surface treatment method has been developed, whereby oxygen diffusion and carburisation of CP-Ti were undertaken concurrently. Optimisation of the process showed that a temperature of 925 °C for 20 h resulted in a multilayer structure comprising of a titanium carbide (TiC) network layer atop of a relatively thick α-Ti(O) diffusion zone. Tribological testing demonstrated that the new surface treatment can significantly enhance the tribological properties of titanium, in terms of much reduced friction (μ ≈ 0.2), improved wear resistance and enhanced load bearing capacity. Electrochemical corrosion testing also showed the PC-Ti retained the favourable corrosion characteristics of CP-Ti. Tribocorrosive testing revealed an improved tribological response when compared with that of untreated CP-Ti.

The present work has been produced as part of an on-going collaboration between the University of Manchester and Amec, with the primary aim of furthering mechanistic understanding of corrosion processes in zirconium alloys out-of-reactor. Zirconium alloys are used as cladding material for nuclear fuel pellets, and correct understanding of the corrosion process in autoclave is essential to predicting material behaviour in-reactor. This EngD thesis is composed of five proposed papers that investigate observations and hypotheses under the theme of mechanical degradation in oxides formed on zirconium alloys in autoclave. First investigations concern observed stress relaxation in zirconium oxide. Finite element analysis is used to capture mechanical aspects of the corrosion process and apply this to stress behaviour determined previously using synchrotron x-ray diffraction. The results indicate that a mechanism other than creep or hydrogen induced lattice strain must be present to account for the observed stress relaxation. One such potential mechanism is crack formation; statistical analysis of scanning electron microscopy images has been used to identify a link between the development of roughness at the metal-oxide interface, crack formation in the oxide and transition points or acceleration in the corrosion kinetics. Parameters such as the median radius of curvature and profile slope (Rdq) have been applied, as these parameters do not require the definition of a periodic wavelength or amplitude. These and other parameters are related to information in literature to indicate that for samples of Zircaloy-4 and ZIRLOTM, which go through transition, the interface roughness changes in a way that would increase localised stress concentrations. The third material is an experimental low tin alloy, which under the same oxidation conditions, and during the same time period, does not appear to go through transition and does not develop an interface roughness in the same way. A critical assessment of finite element analysis applied to oxidising non-planar interfaces shows the significant limitations in the existing mechanism for representing oxidation expansion and stress formation. Autoclave oxidation experiments of artificially roughened samples of Zircaloy-4 were carried out to further understand the impact of out-of-plane stress generation. The results indicate a divergence based on surface roughness after ~86 days oxidation. SEM examination of images in cross section highlighted accelerated oxidation above surface roughness peaks, and an increased crack area in rougher samples. Finally, finite element analysis of the tetragonal to monoclinic phase transformation showed that biaxial compressive stress relaxation, or the tri-axial tensile stress associated with an advancing crack tip, could reduce the transformation strain energy and destabilise the tetragonal phase. The volumetric expansion and shear strain associated with the phase transformation produces stress in the surrounding oxide sufficient to generate nano-scale cracks perpendicular to the metal-oxide interface. This would allow fast ingress routes for oxygen containing species, and therefore acceleration in the corrosion kinetics.

Aluminum based reactive nanomaterials have extensive applications in many fields including solid propellants, pyrotechnics, and catalytic reactions. One recent example is the novel concept of using nanostructured energetic particles for energy storage where the controlled exothermic reaction is the key to control the energy release process. It is of primary interest to understand the thermodynamics, kinetics, morphological and structural properties of these particles during the exothermic reaction. While the physiochemical properties of the monometallic powders are determined only by their size, the properties of bimetallic nanoalloys can be also engineered by their constituent compositions. This thesis conducts a systematic experimental investigation of the oxidation, ignition, and combustion of nano aluminum particles (nAl) and nanoalloys such as nanoscale aluminium-copper (n-AlCu) and aluminium-zinc (n-AlZn). The oxidation experiments are conducted by a TGA/DSC system with detailed characterisation of particles before and after the experiments by scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Nanosizer, Brunauer–Emmett–Teller (BET), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffractionmetry (XRD). In the TGA/DSC analysis, nanomaterials are oxidized either at constant temperature or under different heating rates in the controlled atmosphere of air or nitrogen. A unique early ignition reaction is observed at the high heating rates for nAl and n-AlCu, which is associated with the effect of polymorphic phase transformation of the alumina shell and the early melting of the aluminum core. Different to the conventional shrink-core concept, hollow structures, i.e. nanoholes, in the central regions of nAl are observed and a phenomenal model is proposed. The comparison of the thermal-chemical characteristics of different nanomaterials reveals some unique 5 features related to nano-alloys such as increased reactivity. A preliminary combustion experiment on feeding nanoparticles in a methane stream is performed with a Bunsen burner setup, where the burning characteristics of different nanoparticles are analysed.

The main aim of this work is to study the bonding behaviour of Al alloys as a function of temperature, time and processing conditions from a perspective of oxidation so as to gain a comprehensive knowledge of the oxidation issues during processing and to design better bonding approaches for different alloy systems. Two major parts of work have been carried out during the study: (a) the use of a stacking approach and a double pouring approach to potentially join two Al alloys and their effectiveness are assessed; and (b) a precise investigation of the oxidation mechanisms for Al-Cu and Al-Mg alloys using a combination of theoretical analysis and experimental characterization. The project started with the use of a stacking approach to try to bond two stacked Al alloys. The stacked sample can be viewed as a bi-metal which has an oxide bi-film layer at the bond interface. It was found that the bi-film layer was a physical barrier preventing direct metallic bonding. How this bi-film layer evolves during the bonding process was then investigated. The work then moved on to investigate the oxidation mechanisms of Al-Cu alloys and Al-Mg alloys in greater detail. The thermodynamics, kinetics of oxidation, chemistry and morphology of the oxide scale were particularly studied. Briefly speaking, in the case of the Al-Cu-O2 system, the oxidation proceeds in the order of amorphous γ-Al2O3 - to - crystalline γ-Al2O3 - to - α-Al2O3; in the case of the Al-Mg-O2 system, the oxidation proceeds as amorphous γ-Al2O3 to MgO to MgAl2O4 and the morphology of the oxide scale develops from a protective layer to a porously structured composite layer. A double pouring approach was finally developed to bond Al and Al-5Cu but the method has still not been perfected due to the formation of bi-film defects along the bond interface. Induction melting, squeeze casting, and extrusion bonding were therefore studied as an attempt to reduce the harmful effect of bi-film defects. Although all of the approaches exhibit some limitations, they have potential for future development.

A need has been established in industry and academic publications to link an engine's maintenance costs throughout its operational life to its design as well as its operations and operating conditions. The established correlations between engine operation, design and maintenance costs highlight the value of establishing a satisfactory measure of the relative damage due to different operating conditions (operational severity). The methodology developed in this research enables the exploration of the causal, physics-based relationships underlying the statistical correlations in the public domain and identifies areas for further investigation. This thesis describes a physics-based approach to exploring the interactions, for commercial aircraft, of engine design, operation and through life maintenance costs. Applying the "virtual-workshop" workscoping concept to model engine maintenance throughout the operating life captures the maintenance requirements at each shop visit and the impact of a given shop visit on the timing and requirements for subsequent visits. Comparisons can thus be made between the cost implications of alternative operating regimes, flight profiles and maintenance strategies, taking into account engine design, age, operation and severity. The workscoping model developed operates within a physics-based methodology developed collaboratively within the research group which encompasses engine performance, lifing and operational severity modelling. The tool-set of coupled models used in this research additionally includes the workscoping maintenance cost model developed and implements a simplified 3D turbine blade geometry, new lifing models and an additional lifing mechanism (Thermo-mechanical fatigue (TMF)). Case studies presented model the effects of different outside air temperatures, reduced thrust operations (derate), flight durations and maintenance decisions. The use of operational severity and exhaust gas temperature margin deterioration as physics based cost drivers, while commonly accepted, limit the comparability of the results to other engine-aircraft pairs as the definition of operational severity, its derivation and application vary widely. The use of a single operation severity per mission based on high pressure turbine blade life does not permit the maintenance to vary with the prevalent lifing mechanism type (cyclic/steady state).

Identification methods for the analysis of indigo dye within textiles have been compiled in multiple studies. Though few examples demonstrate chemical analysis and phase separation as a technique that can assist in the identity of the dyestuff. The inclusion of nontechnical methods, techniques that require little knowledge of chemistry and can be completed without the assistance of high-tech machinery, can contribute toward these efforts. The goal of this thesis was to provide a simple testing procedure where eight historic textile samples dating from the mid-eighteenth to the mid-nineteenth centuries were subjected to chemical analysis and phase separation to determine the presence of indigo for The Charleston Museum. A reducing solution of 1.25 g sodium hydroxide, 1.25 g sodium dithionite, and 25 mL deionized water was combined and introduced into Eppendorf tubes containing the historic samples to facilitate a chemical reaction. The tubes were added to a water bath at 40 C for 2-3 minutes to assist in the reaction, an observable color change that could be recorded as part of phase 1. Phase 2 consisted of adding ethyl acetate following chemical analysis to bring about phase separation, where the internal components would separate and result in two layers. Provided phase separation occurred, the top layer was extracted, and the color was noted. Findings suggest that these methods are relatively effective in determining the identity of indigo dyestuffs within historic textiles since six out of the eight samples tested were found to be positive for indigo. The data recorded in this thesis can be used to assist future museum professionals, and conservators when examining historic textiles and determining best methods of indigoid dye analysis.

This thesis describes the synthesis and reactivity studies of the actinyl dications [AnO2]2+ in a variety of oxidation states. Chapter one introduces the importance of the chemistry of actinyl cations in nuclear technology and in the environment, and in particular the chemistry of uranyl dication, which is very stable in the higher oxidation state and considered to be chemically-inert. In Chapter two, on the synthesis of the new macrocyclic Pacman complex [UO2(S)(H2L)] is reported and its reactivity with differing amounts of lithium bases evaluated, so providing insight into the single electron reduction of the uranyl dication. Chapter three is focused on the reactions of the lithiated complexes generated in Chapter two towards acid and silyl sources to obtain complexes in which the oxogroup is further functionalised and to provide mechanistic insight into uranyl immobilisation. Chapter four evaluates the reactivity of the uranyl(VI) Pacman complex [UO2(S)(H2L)] with [Zn{N(SiMe3)2}Cl] to obtain another routes to form the complex [(Me3SiO)UO(THF)(ZnCl)2(L)] and the reactivity with different sources of potassium base, and provides a comparison to the analogues Li-base reactions described in Chapter two. The reactivity of the potassiated and lithiated complexes towards a variety of transition metals are described. Chapter five contains a summary and conclusions on this work. Chapter six presents full experimental details and analytical data.

Aims: LDL oxidation plays an important role in the initiation and progression of atherosclerosis. HDL impedes oxidation, glycation and glycoxidation in vitro and there is evidence to suggest paraoxonase-1 (PON1) plays an important role in this. 1. In patients with dyslipidaemia treated with statins, I assessed the relationship of serum PON1 activity with in vitro HDL antioxidant capacity, susceptibility of LDL to oxidation and the protection offered by HDL. 2. I studied the effect of the presence and severity of obstructive sleep apnoea (OSA) in morbidly obese patients on HDL anti-oxidant and anti-inflammatory functions. 3. I investigated the influence of extended release niacin/ laropiprant (ERN/LRP) versus placebo in patients who had persistent dyslipidaemia despite receiving high doses of potent statins. I assessed the effect of ERN/LRP on mediators of vascular inflammation and HDL's in vitro anti-oxidant function. Methods: 1. LDL isolated from dyslipidemic patients was incubated with and without HDL, in the presence of Cu2+. Similarly isolated HDL was incubated alone. Lipid peroxides (LPO) generated over 3 hours were measured. Patients were divided into 2 groups based on median serum PON1 activity. 2. 41 morbidly obese patients were divided into two groups based on the presence or absence of OSA ("OSA" and "no OSA" group) or on severity of OSA (high or low apnoea-hypoapnoea index (AHI) groups). I studied HDL's ability to protect itself from in vitro oxidation and measured serum PON1 activity, tumor necrosis factor alpha (TNFalpha) and intercellular adhesion molecule 1 (ICAM1). 3. This was a randomised double blind cross over trial, where I studied the effect of ERN/LRP compared to placebo in 27 patients who had high LDL-C inspite of maximum tolerated doses of statins. I measured lipid profile, apolipoproteins, cholesteryl ester transport protein (CETP) activity, paraoxonase 1 activity (PON1), oxidised LDL (oxLDL) and related mediators of vascular inflammation. I also examined the capacity of HDL to protect LDL from in vitro oxidation. Results and conclusion: 1. In statin treated dyslipidemic patients the capacity of HDL to protect itself and LDL from oxidation in vitro is significantly better in individuals with higher serum PON1 activity. 2. The capacity of HDL to protect itself from in vitro oxidation in morbidly obese patients is reduced with onset and severity of OSA. The differences in TNFalpha and ICAM1 levels may suggest endothelial dysfunction due to OSA. Oxidative damage of PON1 attributable to OSA could be a mechanism for HDL and endothelial dysfunction. 3. Treatment with ERN/LRP resulted in a significant improvement in HDL-C but did not affect HDL's in vitro anti-oxidant function in patients who had persistent dyslipidaemia despite high doses of potent statins. For the first time I have shown that ERN/LRP reduces mediators of vascular inflammation.

An advanced concept high temperature reactor (HTR) design has been proposed - The ‘U-Battery’, which utilises a unique sealed coolant loop, and is intended to operate with minimal human oversight. In order to reduce the need for moving parts within the design, CO2 has been selected as a candidate coolant, potentially allowing a naturally circulated system. HTR fuel is held within a semi-graphitic fuel-matrix material, and this has not previously been tested within a CO2 environment. Graphite in CO2 is subject to two oxidation reactions, one thermally driven and one radiolytically. As such, the oxidation performance of fuel-matrix material has been tested within CO2 at both high temperatures and under ionising radiation within a sealed-system. Performance has been compared to that of the Gilsocarbon and NBG-18 nuclear graphite grades. Gilsocarbon is the primary graphite grade used within the currently operating AGR fleet within the UK, and as such is known to have acceptable oxidation performance under reactor conditions. NBG-18 is a modern graphite grade, and is a candidate material for use within the U-Battery. Virgin characterisation of all materials was performed, including measurements of bulk mass and volume, skeletal volumes and surface areas. High-resolution optical microscopy has also been performed and pore size distributions inferred from digital image analysis. All results were seen to agree well with literature values, and the variation between samples has been quanti- fied and found to be < 10% between samples of Gilsocarbon, and < 4% for samples of fuel-matrix and NBG-18. Thermal performance of fuel-matrix material was observed between 600 °C – 1200 °C and seen to be broadly comparable to that of the nuclear graphite grades tested. NBG-18 showed surprisingly poor performance at 600°C, with an oxidation rate of 3×10−4%/min, approximately ten times faster than Gilsocarbon in similar conditions, and three times faster than fuel-matrix material. The radiolytic oxidation performance of fuel-matrix material and NBG-18 has been observed by irradiating sealed quartz ampoules. Ampoules were pressurised with CO2 prior to irradiation, and the pressure after 30 days of irradiation was measured and seen to fall by 50%. Radiolytic oxidation, and the subsequent radiolysis of the reaction product, CO, was seen to cause significant carbonaceous deposition on the internal surfaces of the ampoule and throughout the samples. Due to the short irradiation times available in the present study, an investigation of the microporosity within irradiated samples has been carried out, using nitrogen adsorption and small-angle neutron scattering (SANS). Pore size distributions produced from SANS show the closure of microporosity within NBG-18, most likely as a result of low-temperature neutron irradiation.As a result of this work, CO2 is no longer a candidate coolant for use with the U-Battery design, due to the rapid deposition observed following irradiation.

In this thesis, we study arylsilane oxidation from both a synthetic and a mechanistic perspective. Building upon previous work within our group, we demonstrate in an early chapter that arylhydrosilanes are surprisingly reactive to oxidation. This disproves the previous assumptions of the Tamao oxidation and provides new insights into the mechanism of the reaction. Furthermore, we find that the best substrates for oxidation are arylmethoxysilanes, and we describe rapid and efficient syntheses for these compounds. A further chapter addresses applications of arylsilane oxidation to natural product synthesis, protecting group chemistry and cycloadditions. By collecting concentration profiles of the oxidation of various arylsilanes, we reveal a rapid equilibration between arylmethoxysilanes and arylsilanols. By comparison, phenol formation (especially from silanol) is often slow. The rate of oxidation turns out to be highly sensitive to both the concentration of the oxidising agent and the substituents of the aromatic ring. In the final chapter we discuss in detail the consequences of these observations for the mechanism of arylsilane oxidation.

Stress corrosion cracking of a 14 wt% Cr martensitic stainless steel, with commercial names PH-15Cr5Ni, FV520B or X4CrNiCuMo15-5, used for the manufacture of low pressure turbine blades, has been studied with the intention of gaining a better understanding of the processes involved, how they occur and why. Industrially this is very important as stress corrosion cracking is considered to be a delayed failure process, whereby microscopic cracks can potentially propagate through a metal undetected until catastrophic failure occurs. The aim of this work is to establish links between crack length and external factors, such as exposure time, in order to devise a method of dating stress corrosion cracks and therefore predicting their possible occurrence in-service.

Cloud droplets in the atmosphere have an organic component which has been shown to form a monolayer film at the air-water interface of the cloud droplet and the atmosphere. The process by which a cloud droplet film will oxidise and the persistence or loss of an oxidised organic film from the air-liquid interface of a cloud droplet is not well quantified. To determine the surface properties of a cloud droplet film during atmospheric oxidation a measurement of a kinetic variable, the concentration of material comprising an organic film, during reaction with atmospheric radicals was required. The coupling of a Langmuir trough with a neutron reflectometer allows the measurement of the surface coverage of a monolayer in unison with measurement of the monolayer surface pressure. The technique of coupling a Langmuir trough with neutron reflectometry is used extensively for research into the properties of surfactants for industrial and medicinal use. This thesis builds on the work of King et al., (2009) and King et al., (2010), whom produced the first neutron reflectivity measurements of atmospheric proxy monolayers reacting with ozone. This is the first thesis detailing the neutron reflectometry measurement from an atmospheric perspective. Measurements were taken of representative fatty acid molecules which have atmospheric relevance (stearic acid, oleic acid and methyl oleate) as well as measurements of phospholipid molecules which are potential parent species for the fatty acids found in atmospheric waters (I ,2-dipalmitoyl-sn-glycero-3-phosphocholine). The mono layers were reacted with aqueous phase OH radical and with gas-phase ozone to assess the kinetics of the oxidation of the monolayers at the air-water interface.

Currently the mammalian endoplasmic reticulum (ER) is known to contain at least 20 different protein disulphide isomerase (PDI) family members. The oxidoreductases in the PDI family are thought to catalyse the formation and rearrangement of disulphide bonds in newly synthesised proteins. The focus of this work was to characterise two of the PDI family members: PDI and ERp46. In vitro translation reactions of major histocompatibility complex (MHC), β1-integrin (β1-I), haemagglutinin (HA), procollagen α1(III) and preprolaction (pPL) were carried out in untreated or PDI-depleted cells. The depletion of PDI decreased the rate of folding of MHC and β1-I and also prevented the oligomerisation of HA, suggesting a role for PDI in folding these putative substrates. However, when PDI was depleted neither the folding of pPL or HA was affected, implying that they may not be substrates for PDI. To determine the role of ERp46 in the cell, a substrate-trapping approach was used. Here substrates interacting with ERp46 were trapped as mixed disulphides isolated by immunoprecipitation, separated by 2D SDS-PAGE and identified by mass spectrometry. It was demonstrated that ERp46 forms mixed disulphides with at least 23 proteins, including heavily secreted proteins such as laminins, integrins and collagens. In particular, interactions with Ero1, Prx IV, EDEM3 and ERAP2 were found and confirmed by immunoprecipitation of radiolabelled in vitro translated protein. Notably nine of these clients of ERp46 have previously been identified as substrates of ERp57 (Jessop, Watkins et al. 2009). This would support the hypothesis that several different oxidoreductases, working in concert, are required to fold certain substrate proteins. Also, it was confirmed that Prx IV and Ero1 each form a mixed disulphide with PDI. These results highlight the importance of PDI family members in recruiting co-factors to substrates. Additionally, the over-expression of ERp46 led to increased cell survival following DTT treatment, yet after depletion of ERp46, cells were less able to grow, perhaps suggesting a role for ERp46 in maintaining ER redox homeostasis and cell survival. This suggestion was supported by the finding that ERp46 is able to catalyse the reduction of Prx IV in the presence of glutathione. These results suggest that Prx IV provides a novel mechanism for the transfer of disulphide bonds to nascent proteins in the ER via PDI family members such as ERp46 and PDI.

Austenitic stainless steels are frequently used in the cooling circuits of nuclear reactors. It has been found that cold-worked 304 stainless steels can be particularly susceptible to stress corrosion cracking at the operating conditions of such reactors. Despite more than 130 years of research underlying mechanisms are still not properly understood. For this reason, the effects of cold-work and applied stress on the oxidation behaviour of 304SS have been studied in this thesis. A set of samples with/without prior cold-work, and with/without stress applied during oxidation, were oxidized in autoclaves under simulated pressurised water reactor primary circuit conditions. Atom-probe tomography and analytical transmission electron microscopy were used to investigate the local chemistry and microstructure in the different samples tested. Regions containing grain boundaries, deformation bands, and matrix material in contact with the environment, were extracted from the coupon specimens with a focused ion beam machine. Cross-sections of crack tips were studied with secondary ion mass spectrometry and electron backscatter diffraction. The compositions of oxides grown along the surface and the different microstructural features were analysed. Fe-rich spinels were found at the surface and Cr-rich spinels were observed along fast diffusion paths. Ni-enrichment was found at the metal/oxide interfaces and a Ni-rich phase was detected in precipitates ahead of grain boundary oxides. Li was observed in all oxidised regions and B segregation, originating from impurities in the alloy, was observed in grain boundaries and crack tip oxides. Cavities and hydrogen associated with Ni-rich regions were found ahead of the bulk Cr-rich oxide in some of the samples. The implications of these findings for the understanding of SCC mechanisms are discussed. It is suggested that Ni precipitation as well as the presence of deformation bands may play an important role in controlling SCC susceptibility in 304 stainless steel. A modification of the film-rupture model including internal oxidation and fast diffusion along H-stabilised vacancies in strain fields at the crack front is proposed.

Silica functionalised with PAMAM dendrimer chains has been investigated as a support for anchoring chiral salen complexes in both an axial and covalent fashion. It was found that using a high dendrimer chain density resulted in very low enantioselectivity in the epoxidation of styrene, 1-methyl-1-cyclohexene and α-methylstyrene. Through a thorough series of tests the poor performance was attributed to both interactions with the surface and with neighbouring dendrimer chains. It was found that the system could be improved by decreasing the dendrimer chain density and pacifying the surface by capping the remaining surface hydroxyl groups on the silica. This resulted in the epoxidation of α-methylstyrene with a considerably improved enantioselectivity. Dendritically functionalised silica and silica coated magnetic nanoparticles were also investigated as supports for the immobilisation of an achiral salen complex. High epoxide selectivity was achieved with α-pinene and 1-methyl-1-cyclohexene, while more moderate selectivity was achieved with cyclohexene and limonene as substrates. The heterogeneous catalysts could generally be used 3 times with no apparent loss in activity or selectivity. Both enantiomers of α-pinene and limonene were used to investigate immobilised chiral salen complexes. Results indicate that the diastereomeric excess produced is independent of the configuration or presence of stereogenic centres in the complex. Instead the stereoselectivity appears to be controlled by the nature of the substrate alone. These results call into question the use of such substrates for the investigation of immobilised chiral salen complexes.

When speciality chemicals are manufactured within the pharmaceutical industry, they are often produced in stirred batch/semi-batch reactors. A ‘methodology’ was explored, to help with the development of continuous fixed-bed catalytic reactors for this sector. This was tested on two different types of model reactions: (a) In the first, the viability of producing tertiary amines via ‘borrowing hydrogen’ was explored, and the reaction of morpholine and benzyl alcohol was studied, on Ru and Pt catalysts. This provided an opportunity for an early involvement in small-scale batch testing of catalysts, and then experiments were performed with the catalyst supported on granules in a packed bed (i.d. = 7 mm, length = 300 mm). Although it was shown that continuous processing is viable, and that high conversions (e.g. 73 to 98%, at 150 ºC) could be achieved, unfortunately further work was necessary to identify a more robust catalyst system, before moving on to pilot-scale trials. (b) In the second, the partial oxidation of benzyl alcohol to benzaldehyde was studied, using a Pt catalyst on a carbon support. This proved to be successful, and the reaction was finally demonstrated at pilot-scale. Carbon monoliths were used as catalyst supports (monolith o.d. = 19 mm; length = 50 mm long; square 0.7 mm x 0.7 mm channels; catalyst loading 2.5 and 2.7 wt% Pt). With a liquid flow of 1 L h-1 and a reactant concentration of ~1 mol L-1, operating at 110 ºC, conversion ranged from 80 to 90% and selectivity from 65 to 99%. The catalyst system was tested for 160 h of operation, and retained its performance. While testing the 2nd reaction, a pilot-scale reactor was also developed, which could be used for a variety of novel reactions. The design was flexible and it was easy to insert and remove the catalytic monoliths.

The aims of this work were two-fold - to enhance the 'latent functionality' of a silicon centre by expanding the range of functionalisation reactions available to such compounds, and to develop novel silicon-tethered transformations in order to increase the utility of this attractive synthetic strategy. 1. Aryle Silane Oxidation. Building upon the earlier work of Tamao and co-workers, we have developed a mild, functional group-tolerant oxidation of arylsilanes, allowing a wide range of phenols to be readily accessed. One key insight uncovered during this work was the observation that this oxidation could be acheived with sub-stoichiometric quantities of a fluoride promoter, thus allowing several TBS-protected substrates to be oxidised without any concomitant loss of the protecting group. 2. Silicon-Tethering Methodology. In order to utilise our recently acquired expertise in the field of alkoxy arylsilane synthesis, we sought to develop a novel silicon-tethered iron-catalysed biaryl coupling. Unfortunately, despite our considerable efforts, this methodology was found to suffer from reproducibility issues, and thus our attentions subsequently turned to silicon-tethered palladium- and platinum-catalysed processes. These investigations proved to be more fruitful, with the palladium-catalysed methodology affording a small range of silicon-tethered products. Finally, a novel platinum-catalysed hydro-silylation/electrocyclisation cascade was also developed, allowing a substituted arene to be accessed from a dienyne precursor.

The synthesis of pure tris(6-hydroxymethyl-2-pyridylmethyl)amine (H₃L₁₁) is reported for the first time. New complexes of H₃L₁₁ with copper(II), manganese(II) and iron(III) have been characterised by X-ray crystallography. Linear [Fe₃(L₁₁)₂](ClO₄)₃ reveals the tightest Fe-O-Fe angle (87.6°) and shortest Fe...Fe distance (2.834 Å) presently found for a weakly antiferromagnetically-coupled high spin alkoxide-bridged polyiron(III) system. H₃L₁₁ provides a route to various hydrophobic peralkylated TPA ligand derivatives for creating a hydrophobic pocket for the assembly of iron catalysts for the novel 1-hydroxylation of n-alkanes. New 6-py substituted TPA ligands containing methyl (L₁₅) and n-octyl (L₁₆) ether linkages were synthesised via alkylation. Two further novel 6-py substituted ligands were synthesized incorporating n-hexyl substituents on one (L₂₁) and two (L₂₂) of the py moieties. Here a urea spacer group was used to promote hydrogen–bond assisted heterolytic O-O cleavage (generation of the potent FeV=O oxidant) within the hydroxoperoxoiron(III) precursor. High spin [FeII(L)(CH₃CN)[subscript(x)]](CF₃SO₃)₂ complexes (x = 0–2, L = L₁₅,₁₆,₂₁,₂₂) were characterised in solution by ¹H NMR. The structure of [Fe(L₂₂)](CF₃SO₃)₂ reveals a distorted iron(II) centre bound to four N atoms and two urea carbonyls. Iron(II) complexes of H₃L₁₁, L₁₅,₁₆,₂₁,₂₂ and tris(6-Br)-TPA (L₂₄), were investigated for catalysis of the oxygenation of cyclohexane by H₂O₂. Reaction of the iron(II) complexes with H₂O₂ and [superscript(t)]BuOOH was followed by time-resolved EPR and UV-VIS spectrophotometry. A correlation between the observed catalytic activity and the nature of the FeIII(L)-OOR intermediates generated is apparent. A convenient ‘one-pot’ synthesis of benzene-1,3,5-triamido-tris(l-histidine methyl ester) is reported along with attempts at preparing N,N’-bis(pyridylmethyl)-1,3- diaminopropane-2-carboxylic acid (L₂₅), a new water soluble pyridine-amine ligand. The final demetallation step resulted in ligand hydrolysis to the novel amino acid; 1,3-diaminopropane- 2-carboxylic acid which was characterised as its HCl salt by X-ray crystallography.

This research work studies the influence of zinc on surface treatments such as mechanical polishing, anodic alkaline etching, alkaline etching and electropolishing. Solid-solution binary alloys containing 0.6, 1.0 and 1.9at.%Zn were investigated using scanning and transmission electron microscopies and ion beam analysis. Initially, the near-surface composition of the surface pretreated aluminium alloys were determined using Rutherford backscattering spectroscopy (RBS), medium energy ion scattering (MEIS) and glow discharge optical spectroscopy (GDOES). Subsequently, the surface morphologies of the pretreated specimens were characterized by secondary electron microscopy (SEM) and atomic force microscopy (AFM). Further related work was undertaken on the effect of the employed surface treatments on the anodic behaviour of aluminium-zinc alloys. A final analysis was carried out on the influence of grain orientation on zinc enrichment and surface morphologies of aluminium-zinc alloys developed during alkaline etching.The results reveal that surface pretreatments of aluminium-zinc alloys lead to zinc enrichment at the alloy/film interface. The number of zinc atoms contained in the enriched layer depends upon the employed surface pretreatment and the alloy composition. Surface pretreatments influence the topography of Al-Zn alloys. In particular, for electropolishing, alkaline etching and anodic alkaline etching, the resultant surface morphologies were associated with the oxidation-dissolution-precipitation mechanisms occurring at the alloy/film interface and at the film/solution interface. Anodizing of Al-Zn alloys shows that the anodic films growth on Al-Zn alloys in rolled condition and after surface treatment becomes detached from the substrate independently of the surface treatment employed, although detachment of the anodic film occur earlier on surface pre-treated Al-Zn alloys that developed zinc enrichment. The final studies correlated the mechanisms of oxidation and dissolution with the grain orientation. The result revealed that the (111) grain dissolves faster than other grains, while the higher number of zinc enriched atoms were measured on the (001) grain.

This thesis describes the catalytic asymmetric epoxidation of olefins mediated by chiral iminum salts. The first chapter introduces some of the most novel and effective catalytic asymmetric methods for preparing chiral oxiranes. The second chapter is divided into three sections. The first section of chapter two is dedicated to our efforts to develop new aqueous oxidative conditions using both hydrogen peroxide and sodium hypochlorite as efficient, green oxidants that remove the temperature boundaries observed with the use of Oxone® as the stoichiometric oxidant. A wider range of available temperatures was examined allowing optimization of both oxidative systems. Ethereal hydrogen peroxide was observed to mediate asymmetric epoxidation within an acetonitrile monophasic co-solvent system giving enantioselectivities of up to 56%. When sodium hypochlorite was used in a biphasic solvent system in conjunction with dichloromethane; it was observed to mediate oxidation of the substrate alkenes in up to 71% ee. The second and third sections of chapter two are dedicated to our efforts to synthesize chiral iminium salts as catalysts for asymmetric epoxidation based on a biphenyl azepinium salt catalyst structure. From previous work within the Page group, the asymmetric synthesis and subsequent defined stereochemistry of a chiral carbon atom α to the iminium nitrogen atom was shown to have significant effect on the enantiocontrol of epoxidation using the iminium salt catalyst. Work was completed on biphenyl azepinium salt catalysts, inserting an alkyl or aryl Grignard reagent into the iminium bond using a pre-defined dioxane unit as a chiral auxiliary. Oxidation of the subsequent azepine gave a single diastereoisomerically pure azepinium salt. The methyl analogue of this sub-family of azepinium catalysts has been shown to give up to 81% ee for epoxidation of 1-phenylcyclohexene, furthermore, the binaphthalene azepinium salt with an additional methyl group was also synthesized and was shown to give up to 93% for epoxidation of 1-phenylcyclohexene. Continuation of the substitution α to the nitrogen atom gave rise to an interesting tetracyclic (biphenyl) azepinum salt catalyst. Construction of an asymmetric oxazolidine ring unit encapsulating the azepinium nitrogen and one of the methylene carbon atoms was achieved. In doing so two chiral centres α to the nitrogen atom were generated. The azepinium chiral carbon atom was populated by an addition methyl group with variation in the substitution on the oxazolidine chiral carbon atom. The benzyl analogue of this sub-family of tetracyclic azepinium catalysts has shown to give up to 79% ee for epoxidation 1-phenylcyclohexene. The third chapter is the experimental section and is dedicated to the methods of synthesis and characterization of the compounds mentioned in the previous chapter. X-ray reports regarding the crystallographic analysis of the structures presented in chapter two are provided in appendix A. Appendix B contains the analytical spectra for the determination of enantiomeric excess of the epoxides.