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Titanium production is a long and complicated process. What we often consider to be the standard method of primary titanium production (the Kroll process), involves many complex steps both before and after to make a useful product from titanium ore. Thus new methods of titanium production, especially electrochemical processes, which can utilize less-processed feedstocks have the potential to be both cheaper and less energy intensive than current titanium production processes. This project is investigating the use of lower-grade titanium ores with the electrochemical MER process for making titanium via a molten salt process. The experimental work carried out has investigated making the MER process feedstock (titanium oxycarbide) with natural titanium ores|such as rutile and ilmenite|and new ways of using the MER electrochemical reactor to \upgrade" titanium ores or the titanium oxycarbide feedstock. It is feasible to use the existing MER electrochemical reactor to both purify the titanium oxycarbide feedstock and produce titanium metal.

This Thesis describes the synthesis and characterisation of titanium hydrazido(2-) and alkylidene hydrazido(2-) complexes and their reactivity towards unsaturated molecules. Exploration of the bonding in titanium hydrazido(2-) and alkylidene hydrazido(2-) complexes is performed through structural and computational studies. Chapter 1 introduces current Group 4 hydrazido chemistry in comparison to Group 4 imido and mid/late metal hydrazido examples. Current Group 4 alkylidene hydrazido chemistry is also described. Chapter 2 describes the synthesis, bonding and the novel reaction chemistry of titanium hydrazido(2-) half-sandwich complexes. Novel reactivity at the Ti=N, bond is presented with the mechanisms of some of these transformations probed by Density Functional Theory (DFT) calculations. Chapter 3 describes the novel reaction chemistry of Cp*Ti{MeC(Nipr)2} (NNMe2) in comparison to its imido and diphenyl hydrazido analogues. Novel reactivity at both Ti=N, and Na-N~ bonds is presented with the mechanisms of some of these transformations probed by Density Functional Theory (DFT) calculations. Chapter 4 describes the synthesis and characterisation of a new titanium alkylidene hydrazido(2-) complex. The bonding of the alkylidene hydrazido(2-) ligand is explored through structural and computational studies. Novel reactivity at Ti=N, and Na-N~ bonds is presented. Chapter 5 presents full experimental procedures and characterising data for the new complexes reported. CD Appendix contains .cif files for all new crystallographically characterised complexes described.

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.

University of Macau / Faculty of Science and Technology. / Department of Electromechanical Engineering

by Leung Yat-chor, Calvin. / Includes bibliographical references / Thesis (M.Ph.)--Chinese University of Hong Kong, 1984

Ti6Al4V is the most commonly used of the titanium alloys and is known for its high strength to weight ratio and superb corrosion resistance compared to conventional steels. Ti6Al4V is used in applications in the aerospace, biomedical, automotive, power generation and oil and gas fields. Laser metal deposition (LMD) is an additive manufacturing (AM) platform used to build 3-D metal shapes. LMD is one of the most researched topics within the laser processing field currently and is advancing continuously. The rapid growth in the AM field is driven by market demands to reduce manufacturing costs, shorter lead times and an increasing demand for customized products. One of the major challenges facing the production of Ti6Al4V components using LMD is the high resultant residual stresses, limiting build size due to delamination or distortion. At the commencement of this study, little data pertaining to the residual stress build up in larger LMD components was available. This research was conducted to create an understanding of the relationship between build height and surface residual stresses and how they influence the dimensional stability of a part. Additionally, the relationship between build height and static mechanical properties was analysed. The effects of laser power, scanning speed and powder mass flow rate on the deposition layer were evaluated. The number of defects and the deposition build height were evaluated to determine the optimum process parameters for multi-layer components. An increase in laser power resulted in an increase in build height for the parameter window selected for the study. Similarly, an increase in build height was observed with an increase in powder mass flow rate, while an increase in scanning speed resulted in a decrease in build height. As laser power and scanning speed had inverse effects on the build height, heat input was evaluated to determine the optimum combination of the 2 parameters. Multilayer samples were produced with a laser power setting of 1900 W, a scanning speed of 0.01 m/s and a powder mass flow rate of 8 g/min. Fully dense components were produced with no notable defects. These components were analysed to reveal the relationship between build height and surface residual stresses and showed that the minimum residual stress observed in a component was related to an actual height from the base and was not affected by the build height of the sample. Maximum residual stresses were observed closest to the base of the cylinder and the stresses were larger in larger samples for both hoop and longitudinal surface residual stress. The micro-hardness of the samples increased as build height increased. The tensile strength remained within constant range between 1080 MPa and 1050 MPa for all samples successfully tested. Brittle failures were observed on the upper sections of the larger samples, attributed to the high micro-hardness observed in these areas. The study successfully evaluated the relationship between build height and surface residual stresses as well as build height and static mechanical properties thereby increasing the knowledge within this field.

Semiconductor photocatalysis degrades phenolic pollutants to carbon dioxide and water, but the mechanisms of this potentially attractive method of environmental remediation remain unclear. This study aimed to elucidate the primary molecular events by HPLC analysis of the initial products of degradation in water or aqueous acetonitrile. The position of substituents relative to the hydroxyl group were found to influence the reaction rate and also primary oxidation steps, and hence the intermediate profile. 2,6- Dialkylated phenols reacted fastest and showed high conversion to dehydrodimeric products as a prelude to degradation. In contrast, 3,5-dialkylated phenols and 4-tertbutylphenol reacted more slowly and appeared to degrade directly to small polar compounds with little accumulation of primary carbocyclic intermediates. The rate of photocatalytic degradation of two isomeric dibromohydroxybenzonitriles was also influenced by substitution pattern. 3,5-Dibromo-2-hydroxybenzonitrile, however, is itself photolabile in daylight giving 3-bromo-2,5-dihydroxybenzonitrile in aqueous solution. The analogous reaction does not occur for 3,5-dibromo-4-hydroxybenzonitrile, the difference in behaviour being attributed to differences in the electronic spectra of the two compounds. The mechanism of photocatalysis appears to be influenced by the orientation of the substrate on the catalyst surface. For the alkyl phenols, particularly those with tert-butyl substitution, minimisation of disturbance to the polar network of the solvent directs the more hydrophobic parts of the molecule towards the oxidising surface of the catalyst. In addition, this effect encourages clustering of molecules with the subsequent formation of aggregated products. While part of the behaviour observed may be attributable to the presence of acetonitrile in the solvent, the hydrophobic profile of a substrate undergoing heterogeneous photocatalytic oxidation in water would seem to be a significant determinant of the molecular pathway selected in the first phase of its degradation.

Leung Cheuk-wan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (Chinese) --- p.ii / Acknowledgement --- p.iii / Table of Contents --- p.v / Lists of Tables --- p.ix / Lists of Figures --- p.x / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- TiO2 Photocatalysis --- p.1 / Chapter 1.1.1 --- Mechanisms of TiO2 Photocatalysis --- p.1 / Chapter 1.2 --- Visible Light Photocatalyst --- p.4 / Chapter 1.2.1 --- Preparation of Visible Light Ti02 Photocatalysts --- p.5 / Chapter 1.2.1.1 --- Dye Sensitization --- p.5 / Chapter 1.2.1.2 --- Metal Doping --- p.6 / Chapter 1.2.1.3 --- Coupling of Semiconductors --- p.6 / Chapter 1.2.1.4 --- Nonmetal Doping --- p.7 / Chapter 1.3 --- Enhanced TiO2 Photocatalytic Activity under UV Light --- p.8 / Chapter 1.3.1 --- Preparation of TiO2 Photocatalyst with Enhanced Activity in UV Light --- p.8 / Chapter 1.3.1.1 --- Loading of Metal --- p.8 / Chapter 1.3.1.2 --- Impurity Co-doping --- p.9 / Chapter 1.3.1.3 --- Morphological Control --- p.10 / Chapter 1.3.1.4 --- Increasing Surface Area --- p.10 / Chapter 1.4 --- Summary --- p.11 / Chapter 1.6 --- Aim of This Research and its Significance --- p.12 / Chapter 1.7 --- References --- p.13 / Chapter Chapter 2 --- Preparation of N-doped TiO2 with Enhanced Surface Area: A Detailed Characterization and Mechanism --- p.19 / Chapter 2.1 --- Introduction --- p.19 / Chapter 2.2 --- Experimental --- p.21 / Chapter 2.2.1 --- Materials and Catalyst Preparation --- p.21 / Chapter 2.2.2 --- Characterization --- p.21 / Chapter 2.2.3 --- Photocatalytic Activity --- p.23 / Chapter 2.3 --- Results and Discussion --- p.24 / Chapter 2.3.1 --- XRD Analysis --- p.24 / Chapter 2.3.2 --- UV-Vis Absorption Spectroscopy and Bandgap Energies --- p.27 / Chapter 2.3.3 --- N2 Sorption Analysis --- p.29 / Chapter 2.3.4 --- SEM Analysis --- p.33 / Chapter 2.3.5 --- TEM Analysis --- p.35 / Chapter 2.3.6 --- FT-IR Spectroscopy --- p.36 / Chapter 2.3.7 --- Raman Spectroscopy --- p.39 / Chapter 2.3.8 --- XPS Studies --- p.44 / Chapter 2.3.9 --- PL Measurements --- p.49 / Chapter 2.3.10 --- Photocatalytic Activity Measurements --- p.50 / Chapter 2.3.11 --- Advantages of Using Urea as a N-doping Source --- p.54 / Chapter 2.3.12 --- Mechanisms for N-doping --- p.56 / Chapter 2.4 --- Conclusions --- p.58 / Chapter 2.5 --- References --- p.59 / Chapter Chapter 3 --- Preparation of Nanoporous Interstitial B-doped TiCO2 with Enhanced Photocatalytic Activity --- p.63 / Chapter 3.1 --- Introduction --- p.63 / Chapter 3.2 --- Experimental --- p.65 / Chapter 3.2.1 --- Materials and Catalyst Preparation --- p.65 / Chapter 3.2.2 --- Characterization --- p.66 / Chapter 3.2.3 --- Photocatalytic Activity --- p.67 / Chapter 3.3 --- Results and Discussion --- p.68 / Chapter 3.3.1 --- XRD Analysis --- p.68 / Chapter 3.3.2 --- UV-Vis Absorption Spectroscopy and Bandgap Energies --- p.71 / Chapter 3.3.3 --- N2 Sorption Analysis --- p.73 / Chapter 3.3.4 --- SEM and TEM --- p.76 / Chapter 3.3.5 --- FT-IR Spectroscopy --- p.80 / Chapter 3.3.6 --- Raman Spectroscopy --- p.82 / Chapter 3.3.7 --- PL Measurements --- p.84 / Chapter 3.3.8 --- XPS Studies --- p.85 / Chapter 3.3.9 --- Photocatalytic Activity Measurements --- p.89 / Chapter 3.3.10 --- State and Form of Boron in TiO2 Lattice and its Effects --- p.91 / Chapter 3.4 --- Conclusions --- p.93 / Chapter 3.5 --- References --- p.94 / Chapter Chapter 4 --- Conclusions --- p.97

Anodised titanium dioxide (titania, TiO2) nanotubes have been widely studied over the last few years, following the discovery in 1999 of nanoporous TiO2 films prepared via anodisation in aqueous solution containing small quantities of hydrofluoric acid. The synthesis of nanotubular titania by anodisation, a relatively simple and low cost technique, represents a motivation for scientists, considering the impact that such a material could have on a variety of applications, including gas-sensing, biomedical, photocatalysis, and photovoltaics. This research project has focused on the optimisation of the growth process of anodic titania nanotubes, both in an aqueous (NaF/Na2SO4) and an organic (Glycerol/NaF) electrolyte containing fluorine ions. Reproducibility and the ability to generate anodic films having a thickness of several micrometers are fundamental steps to be achieved before investigating any possible application of the nanotubes. To characterise the anodic specimens and build upon the general lack of information on the growth mechanism, a comprehensive study of the different stages of the process has been performed, using Scanning and Transmission Electronic Microscopy (SEM and TEM). Among the questions to be addressed in this thesis, is to establish whether the anodic film undergoes a transition from pores to tubes or develops a tubular morphology from the beginning of its growth. Additional characterisation of the anodisation process includes the study of current-time curves, and chemical composition analysis of the anodic layers using X-ray Photo-Electron Spectroscopy (XPS). The thermal stability of the nanotubes and structural/morphological changes as a result of heat treatment at different temperatures were also studied, again using SEM, TEM, XPS and Raman spectroscopy. The final part of the thesis is dedicated to preliminary work on the use of anodised TiO2 nanotubes in Dye Sensitized Solar Cells (DSSCs), along with suggestions for future works and general conclusions.