Thesis (Ph. D.)--School of Chemistry, Faculty of Science, University of Sydney, 2003. / Bibliography: leaves 117-121.

Thesis (Ph. D.)--University of Sydney, 2003. / Title from title screen (viewed Apr. 28, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Chemistry, Faculty of Science. Degree awarded 2003; thesis submitted 2002. Includes bibliography. Also available in print form.

Thesis (Ph.D.)--University of Melbourne, The School of Chemistry, 2010. / Typescript. Includes bibliographical references.

Structural and electronic effects in hydrocarbon reactions over metal oxides have been examined by comparing the reactions of methyl (-CH₃) and methylene (=CH₂) fragments on three different oxide single crystal surfaces: α-Cr₂O₃(101̅2), α-Cr₂O₃(0001), and α-Fe₂O₃(101̅2). The intermediates have been generated through the decomposition of halogenated hydrocarbons. The primary reactions of methyl and methylene over α-Cr₂O₃ are methyl dehydrogenation to methylene, and methylene coupling (C-C bond formation) to ethylene (CH₂=CH₂). The different surface geometric structures of α-Cr₂O₃(101̅2) and (0001) lead to an increase in the activation barrier for methylene surface migration, a critical step in the coupling reaction, of 5.9 kcal/mol over the (0001) surface. For methyl dehydrogenation, differences in the local site pair (cation/anion) geometry and the proximity of surface lattice oxygen to the methyl group do not result in a significant difference in the barrier for dehydrogenation, suggesting that the surface anions play a minor role in the dehydrogenation of methyl on these surfaces. Electronic differences in the Fe³⁺ (𝑑⁵) and Cr³⁺ (𝑑³) cations on structurally-similar α-Cr₂O₃(101̅2) and α-Fe₂O₃(101̅2) surfaces lead to major differences in reaction selectivity. α-Cr₂O₃(101̅2) is nonreducible under the reaction conditions of this study, but α-Fe₂O₃(101̅2) is highly reducible due to the difference in the d electron configuration. Hydrocarbons are formed over α-Cr₂O₃(101̅2), but nonselective oxidation products (CO₂, CO, H₂O) are formed over the stoichiometric α-Fe₂O₃(101̅2) surface along with surface reduction. Reduction of the α-Fe₂O₃(101̅2) leads to a shift in the product selectivity towards formaldehyde (CH₂O) and ethylene. For the limited number of systems examined in this study, examples of geometric structure sensitive (methylene coupling) and structure insensitive (methyl dehydrogenation) reactions have been found on α-Cr₂O₃, and electronic effects are observed for the reactions on α-Cr₂O₃(101̅2) and α-Fe₂O₃. For the structure sensitive reaction, the differences in surface geometry impact the reactions kinetics over Cr₂O₃ but not the types of products formed, while the electronic differences give rise to dramatic changes in the selectivity associated with the very different products formed over α-Cr₂O₃(101̅2) and α-Fe₂O₃(101̅2). / Ph. D.

The present work investigates the tribological properties of solid particles as lubricant additives in lubricants. Two types of solid particles, Ceria nanoparticles (CeO2) and Zinc borate ultrafine powders (ZB UFPs), were used as the lubricant additives in this study. The friction and wear behaviours of these lubricant additives in different base lubricants were identified. With an appropriate application of these solid lubricant additives, the friction reduction and wear resistance properties of the lubricant have been successfully improved. Without assistance of surfactant or surface modification, the two types of solid particles behave very differently. Evident performance was observed that pure ZB UFPs were capable of considerably reducing the friction coefficient of sunflower oil and liquid paraffin when they were used as a lubricant additive without further treatment. On the contrary, CeO2 nanoparticles did not show noticeable contribution to friction reduction when they were used as the only additive in water. Only when surfactant Sorbitan monostearate was employed to enhance the dispersibility of CeO2 nanoparticles in water, the application of this additive was capable of reducing friction coefficient of the water based lubricant effectively. Surface modification of the solid particles was carried out to improve the dispersibility of these particles in base lubricants. Oleic acid (OA) and Hexadecyltrimethoxysilane (HDTMOS) were selected as the modification agents. Modified CeO2 nanoparticles and ZB UFPs revealed outstanding wear resistance property. An improvement of up to 15 times was identified although this improvement on wear resistance, in this case, was often companied by a rise in friction coefficient. Tribo-films generated by tribo-chemical reaction were observed on most of the worn surfaces and the formation of this tribo-film appeared to have played an important role in the friction and wear behaviours of a system. A tenacious tribo-film with good surface coverage was only generated on the worn surface when HDTMOS modified solid particles were used as lubricant additives. The mechanical properties and elemental composition of the tribo-film were studied with nano-indentation and energy-dispersive X-ray spectroscopy (EDS). Finally, based on the experimental evidence, different functionalities of CeO2 nanoparticles and ZB UFPs as solid lubricant additives were recognized.

No description available.

Im Rahmen dieser Dissertation wurden Experimente zur Wechselwirkung von schnellen Atomen mit Oberflächen von Oxidkristallen, Metallkristallen und ultradünnen Oxidfilmen auf Metalloberflächen durchgeführt und modellhaft beschreiben. Die Experimente wurden im Regime der streifenden Streuung für Energien im keV-Bereich durchgeführt. Diese Streugeometrie bietet den Vorteil einer außerordentlich hohen Oberflächensensitivität und somit die Möglichkeit, die kristallographischen Eigenschaften der obersten Atomlage zu untersuchen. Darüber hinaus wurden Experimente zur Bestimmung des Energieverlustes der an den verschiedenen Oberflächen gestreuten Projektile und zur, durch diese Projektile induzierten, Elektronenemission durchgeführt. Die Anregungsenergie für die Elektronenemission und Exzitonen wurde an der Alumina/NiAl(110)- und der SiO2/Mo(112)- Oberfläche für die Streuung von He bestimmt. Durch die Bestimmung der Anzahl von emittierten Elektronen in Abhängigkeit des azimutalen Winkels konnten die Strukturen von obersten Lagen von Adsorbaten mit der Methode der Ionenstrahltriangulation bestimmt werden. / In the framework of the present dissertation the interactions of fast atoms with surfaces of bulk oxides, metals and thin films on metals were studied. The experiments were performed in the regime of grazing incidence of atoms with energies of some keV. The advantage of this scattering geometry is the high surface sensibility and thus the possibility to determine the crystallographic and electronic characteristics of the topmost surface layer. In addition to these experiments, the energy loss and the electron emission induced by scattered projectiles was investigated. The energy for electron emission and exciton excitation on Alumina/NiAl(110) and SiO2/Mo(112) are determined. By detection of the number of projectile induced emitted electrons as function of azimuthal angle for the rotation of the target surface, the geometrical structure of atoms forming the topmost layer of different adsorbate films on metal surfaces where determined via ion beam triangulation.

Metal oxide reactions at metal oxide surfaces or at metal-metal oxide interfaces are of exceptional significance in areas such as catalysis, micro- and nanoelectronics, chemical sensors, and catalysis. Such reactions are frequently complicated by the presence of high electric fields and/or H2O-containing environments. The focus of this research was to understand (1) the iron oxide growth mechanism on Fe(111) at 300 K and 500 K together with the effect of high electric fields on these iron oxide films, and (2) the growth of alumina films on two faces of Ni3Al single crystal and the interaction of the resulting films with water vapor under non-UHV conditions. These studies were conducted with AES, LEED, and STM. XPS was also employed in the second study. Oxidation of Fe(111) at 300 K resulted in the formation of Fe2O3 and Fe3O4. The substrate is uniformly covered with an oxide film with relatively small oxide islands, i.e. 5-15 nm in width. At 500 K, Fe3O4 is the predominant oxide phase formed, and the growth of oxide is not uniform, but occurs as large islands (100 - 300 nm in width) interspersed with patches of uncovered substrate. Under the stress of STM induced high electric fields, dielectric breakdown of the iron oxide films formed at 300 K occurs at a critical bias voltage of 3.8 ± 0.5 V at varying field strengths. No reproducible result was obtained from the high field stress studies of the iron oxide formed at 500 K. Ni3Al(110) and Ni3Al(111) were oxidized at 900 K and 300 K, respectively. Annealing at 1100 K was required to order the alumina films in both cases. The results demonstrate that the structure of the 7 Å alumina films on Ni3Al(110) is k-like, which is in good agreement with the DFT calculations. Al2O3/Ni3Al(111) (γ'-phase) and Al2O3/Ni3Al(110) (κ-phase) films undergo drastic reorganization and reconstruction, and the eventual loss of all long-range order upon exposure to H2O pressure > 10-5 Torr. Al2O3/Ni3Al(110) film is significantly more sensitive to H2O vapor than the Al2O3/Ni3Al(111) film, and this may be due to the incommensurate nature of the oxide/Ni3Al(110) interface. STM measurements indicate that this effect is pressure- rather than exposure- dependent, and that the oxide instability is initiated at the oxide surface, rather than at the oxide/metal interface. The effect is not associated with formation of a surface hydroxide, yet is specific to H2O (similar O2 exposures have no effect).

No description available.