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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.

Ni-based superalloys are used for high-temperature components of gas turbines in both industrial and aerospace applications due to their ability to maintain dimensional stability under conditions of high stress and strain. The oxidation resistance of these alloys often dictates their service lifetime. This study focuses on the isothermal oxidation behaviour of three nickel-based superalloys; namely, polycrystalline cast IN738LC, single-crystal N5 and a ternary Ni-Fe-Cr (TAS) powder metallurgy alloy. The isothermal oxidation tests were conducted at 900°C in the static air up to 1000h and the specific aspects studied were the oxidation behaviour of these chromia-forming and alumina-forming alloys that are used extensively in industry. In particular, the behaviour of oxide scale growth and subsurface changes were analysed in detail using various techniques such as SEM, EDS and AFM. From the isothermal oxidation kinetics, the oxidation rate constant, kp was calculated for each alloy and found to be; kp = 2.79 x 10-6 mg2.cm-4.s-1 for IN738LC, kp = 1.42 x 10-7 mg2.cm-4.s-1 for N5 and kp = 1.64 x 10-7 mg2.cm-4.s-1 for TAS. Based on a microstructural analysis, IN738LC exhibited a continuous dense outer scale of Cr2O3 and discontinuous inner scale of Al2O3, whereas N5 and TAS showed a dense outer scale of Al2O3 alone. The results suggested that the N5 and PM-TAS alloys are more oxidation resistant than the IN738LC under these conditions. / October 2016

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.

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.

This thesis presents the design and analysis of photo-electro catalytic oxidation technology for its potential use in water treatment applications. Doping titanium dioxide can effectively improve oxidative reactions. Using minute reactor design adjustments, such as electrolysis, the bases of degrading soluble organic compounds can be improved within the reactor. Applications of doping and secondary catalysis are effective in increasing the process of photoactivity within the catalytic reactor, theoretically increasing the production of sacrificial electron acceptors. Higher degradation's were accomplished using doped chromium titanium dioxide photocatalyst, which degraded significantly larger amounts of organics compared with pure titanium dioxide. Techniques used to accomplish the increased photo-reactivity were doping chromium (III) ion into titanium dioxide crystal lattices and silver ions into the photocatalytic coat. Degradation curves were determined by total organic carbon and the chemical oxygen demand. Calculations of the final rate constants show that lighter molar concentrations have higher rates of degradation.

A kinetic study on polycrystalline platinum (Pt) in sulphuric acid is presented. An electrochemical kinetic mechanism of Pt oxide reduction and surface oxide structures are proposed. The reduction reaction was studied by cyclic voltammetry (CV) and various potential programs that combine sweep and hold periods by an assembled analog instrumentation. The reduction peak was studied under three surface conditions: same oxide coverage θ and same potential E, different θ and same E, and same θ but different E, to determine the influence of θ and E on the peak potential and peak shape. The double-layer charge measured previously by dynamic electrochemical impedance spectroscopy (dEIS) was used to correct the CV baseline. Differential-equation-based models as a function of θ and E were investigated to simulate the oxide reduction and oxidation, and estimate kinetic parameters. A simple mechanism combining desorption and multi-layer growth mechanisms showed good fit with both the spread-out oxidation peak and the sharp reduction peak. A microscopic surface oxide growth model was proposed to explain the surface oxides reduction mechanism. / Graduate

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Abstract Biological oxidation of methane is and important constraint on the emission of this gas from areas, such as landfills to the atmosphere. We studied the effect of covering soils on methane emission in landfill assimilation. Microbial evaluation was done on virgin soil and later on soils used as covering material. This soil was later treated differently to see different effects that has on methane emission. Treatments applied were addition of compost in soil, moistured soil with methanotroph culture instead of water. Although methane was produced from the landfill, it was not as documented between 45 and 50%. We got between 6 and 18% production. In all the soils tested the uncultivated soil had the minimal emission as it emitted 0% methane. Sand, however, had some oxidation effect. The problem was that it is porous therefore gas migration is not restricted. This shows that the oxidative bacteria are available naturally is soils, but gets abandoned as the conditions favours their growth. The treatments done to soils had little effect as methane oxidation was not influenced or altered. This can be liked into in details. There have been some good observations in the assimilated landfill. As the landfill was not controlled the pH dropped and this in return produced more hydrogen as compared to methane. With all the altered gas balance produced the leachate changed.