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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Partial melting and phase relations in metapelitic granulites

Carrington, Damian Peter January 1993 (has links)
The cornerstone of the thesis is the set of sixty four experiments carried out on three synthetic, mineral-mix, KFMASH (K<SUB>2</SUB>O-FeO-MgO-Al<SUB>2</SUB>O<SUB>3</SUB>-SiO<SUB>2</SUB>-H<SUB>2</SUB>O) compositions, with bulk X<SUB>Mg</SUB>'s of 0.62, 0.74 and 0.86. Magnesian compositions are used so that univariant equilibria, many of which do not act on iron-rich compositions, can be constrained. The experiments were conducted in the pressure-temperature range 5-12.5 kilobars and 840-1000°C. The assemblages stable in this range were subsets of garnet-cordierite-biotite-osumilite-orthopyroxene-sillimanite-K-feldspar-quartz-melt. The results of the experiments represent a close approach to equilibrium and several key reactions were reversed. The results are used to derive a petrogenetic grid of KFMASH univariant reactions and pseudosections for each of the bulk compositions. In the KFMASH system, the position of reactions on the grid does not depend on the rock bulk composition or the activity of water. This provides an excellent, fixed reference for consideration of lower crustal processes and mineral assemblages. In particular, the fundamental granulite-facies KFMASH invariant point, which involves the BDMR's and the reaction separating garnet-cordierite and orthopyroxene-sillimanite-quartz assemblages, has been positioned between 890-910°C, 8.7-9.5kb. The current and previous data on BDMR's are accounted for by a simple model in which the melting interval is inversely proportional to the bulk X<SUB>Mg</SUB> and its absolute position in temperature is controlled by the concentration of titanium and fluorine in biotite. The reaction separating garnet-cordierite and orthopyroxene-sillimanite-quartz assemblages has been constrained to run from 900°C, 8.8kb to 1000°C, 7.8kb. This is at lower pressure than previous estimates as it accounts for vapour-undersaturation in cordierite and the fact that melt must be produced when cordierite breaks down. Osumilite has a large stability field at temperatures above approximately 900°C and is likely to be more common than is currently thought.
42

DNA-based routes to metal, inorganic and polymer nanowires

Mohamed, Hasan Daw Ashtawi January 2013 (has links)
This thesis describes the preparation and characterization of conductive nanowires. The synthesis of the nanowires was achieved using a DNA-templating strategy. The chemical identity of the nanowires was characterized using FTIR, XPS and XRD, while the structural character, electronic properties and magnetic behavior were probed using AFM, EFM and MFM, respectively. The formation of Fe3O4 nanowires involved initial association of Fe²+ and Fe³+ ions to the DNA, and subsequent co-precipitation of the Fe3O4 material, upon addition of NaOH. Chemical characterization confirmed the formation of Fe3O4 within the product material. AFM data revealed one-dimensional (1-D) nanostructures with diameters up to 30 nm, whilst EFM and MFM showed that the nanowire structures are electrically conducting and exhibit magnetic behaviour. The preparation of Fe and Rh nanowires, respectively, was achieved by DNA-templating approach in conjunction with either chemical or electrochemical reduction. Chemical characterization confirmed a metal/oxide core/shell structure. AFM data showed 1-D nanostructures with granular character, and diameters up to 26 nm for Fe and 31 and 23 nm for Rh, respectively. The structures were confirmed to be electrically conducting and to display magnetic behaviour as indicated by EFM and MFM, respectively. Finally, DNA-templating of 2,6-diaminopurine-propyl-2,5 bis-dithenyl pyrrole and thymine-propyl-pyrrole by chemical oxidation using FeCl3 yielded supramolecular polymers. FTIR and XPS studies confirmed the presence and interaction of the component polymer chains. The DNA/CPs nanowires showed smooth and uniform structures with diameters up to 25 and 35 nm, and they were found to be electrically conducting. The attempted formation of larger structures based on the base pair hydrogen bonding between the two types of nanowires was investigated by AFM studies. However, reliable evidence for larger structures formation based on this specific interaction was not found.
43

Model building methodology for complex reaction systems

Zhang, Wenling January 2004 (has links)
The complexity of chemical reaction processes and the short market window of some chemical products mean that detailed model building can often not be justified. With little knowledge of chemistry, this work aims to provide a new methodology for model building of chemical reaction systems with minimum experimental measurements, for the purpose of reactor design and optimisation. Most often reactor designs are scaled from experimental measurements, especially for the manufacture of fine and speciality chemicals. Yet, without a model of the reaction system, major opportunities can be missed in the design and optimisation of the reactor. When models are developed for a reaction system in the laboratory, they are often inappropriate for reactor design and optimisation. In the first part of this thesis, the reaction scheme that best describes the production of a given chemical and suitable kinetic equations are obtained simultaneously using optimisation. A hybrid optimisation method is used to deal with this large problem where more than one model fits the same experimental data within a certain confidence level. Stochastic optimisation methods provide multiple solutions that are rival models for model discrimination. An NLP method improves model precision from the stochastic optimisation in the narrowed search space. A strategy for reaction scheme construction is used to generate all reactions from the reacting species and to provide plausible reaction schemes during optimisation. These reaction schemes are screened simultaneously with kinetic models to fit the most appropriate reaction scheme and kinetic model from the rival models. Optimal experiments then need to be designed to discriminate among rival models. The experimental design exploits the potential for mixing, as well as temperature and concentration effects to discriminate between models through the reactor superstructure. The oleic acid epoxidation reaction is used to demonstrate the methodology. For refinery heterogeneous catalytic reactions, due to the complex nature of catalysis, a large number of rival models pose difficulties for model building and discrimination. In the rest of the thesis, three-level kinetic study method is developed for model building to reduce the model complexity by separating diffusion effects from kinetic equations. In addition, catalyst characterisation is used to assist model discrimination. There are a large number of techniques available to connect catalyst properties, catalyst activities with model performance with different capabilities and limitations. However, not all of these will be useful in a given application. A classification of those techniques specified for hydrodesulphurisation (HDS) processes provides guidance for selecting suitable techniques to yield the most information with accuracy, speed, and economy. Furthermore, plausible ways for model discrimination and model improvement for thiophene and diesel HDS are explored, including operating condition, feedstock and catalyst effects.
44

Advanced materials for lithium batteries and electrochemical capacitors

Haj Hassan, Nooshin L. January 2009 (has links)
This thesis describes research carried out in the area of materials electrochemistry. The general goal was to develop and test advanced materials that might improve the performance of real-world electrochemical systems. Particular systems of interest were lithium thionyl chloride batteries, lithium sulphur batteries, and carbon-based electrochemical capacitors. Developments are reported in all three cases. Materials electrochemistry is an interdisciplinary field that investigates the relationship between the structure, properties, processing and electrochemical performance of novel materials. These may be electrodes, solutions, or combinations of both. Besides conventional electrochemical measurements, materials electrochemistry also includes elements of process development and engineering. In the present work, much effort was expended on the formulation, mixing, extrusion and curing of particulate carbon electrodes. In particular, numerous large-scale screening programs were carried out to examine the effects of multiple independent variables on battery performance. Although this required much effort to set up, the payoff was that it allowed improved processing parameters, and materials of advanced performance to be determined with a high level of confidence. Considerable effort was also expended on the development of apparatus for handling air-sensitive battery solvents, such as thionyl chloride. Amongst the achievements of the present work are: (i) the successful reformulation of the manufacturing solvent for commercial lithium battery electrodes, to halve the quantity of isopropyl alcohol used. In the future this will allow the manufacturing process to continue within UKIEU regulations. (ii) The improvement of the mechanical strength and electrochemical capacity of thick-film carbon electrodes by adding conducting carbon fibre. (iii) The development of an easy-to-implement test that accurately predicts the performance of lithium thionyl chloride battery electrodes. (iv) The development of a novel electrolyte solution for lithium sulphur batteries (using a sulfolane/ethylene carbonate mixture). (v) The discovery that this solution can be gelled with PVDF, and finally (vi) the discovery that some carbon blacks out-perform activated carbon in thick-film electrodes for electrochemical capacitors.
45

Kinetic studies on some first order gas phase reactions having high frequency factors

Clark, Douglas January 1955 (has links)
This thesis is concerned with a study of some of those first order, gas reactions which proceed with high frequency factors. A list of such reactions is drawn up and attempts to explain the high values in some cases are mentioned. An investigation, by the "toluene carrier", technique of the rates of decomposition of seven organic compounds. hexafluoroazomethane, acetophenone, trifluoroacetophenone, acetone, trifluoroacetone, benzophenone and dibenzyl ketone, is described, and the results of the investigation are prsented. Four of these compounds were found to decompose with high frequency factors. Pritchard's explanation of the k1netics or decomposition of the mercury alkyls 1s dealt with in deta1l, and the theory is extended, with success to explain the high frequency factors in the decompositions of diacetyl, benzyl, acetophenone, benzophenone and di-tert-butyl perox1de.
46

Some reactions of hydrazine and of amide radicals

Davis, P. January 1951 (has links)
No description available.
47

Spontaneous, proton- and electrophile- catalysed hydrolysis of 1,5- anhydrocellobiitol : models for the reduction of cellulose degree of polymerisation in papermaking fibres

Baty, John William January 2004 (has links)
In this project, the kinetics of the spontaneous, proton- and electrophile-catalysed hydrolyses of the Cl-Ol bond in the cellulose model compound 1,5-anhydrocellobiitol were measured at various temperatures (125.0-220.0°C). Sealed capillary tubes containing the substrate (and catalyst where applicable) in various buffer solutions were opened after various exposures and analysed with HPLC-RI or HPAE-PAD. For the spontaneous, specific-acid-cata1ysed and AlIII-catalysed hydrolyses, apparent first-order rate constants and activation energies were calculated, showing the relative significance of these reactions at ambient temperatures. Efficient e1ectrophilic catalysis by AlIII over H+ catalysis of the hydrolysis of the model was demonstrated, with important implications for the degradation of "rosin-alum" sized paper and other papers containing AlIII. The loss of cellulose DP as a function of time was modelled under several conditions using the af Ekenstam equation. The loss of cellulose DP under kraft pulping conditions was shown to be due significantly to the spontaneous hydrolysis mechanism. A simple equation was derived for expressing the specific rate constant as a function of pH for the hydrolysis of cellulose (modelled with 1,5-anhydrocellobiitol). This equation is applicable from very acidic conditions to -pH 12.3.
48

Effects of spin-orbit coupling and many-body interactions on the electronic structure of Sr₂RuO₄

Rozbicki, Emil Jerzy January 2011 (has links)
The aim of the project is to investigate the effects of spin-orbit coupling and many-body interactions on the band structure of the single-layered strontium ruthenate Sr₂RuO₄. This material belongs to the large family of strongly correlated electron systems in which electron-electron interaction plays a crucial role in determining the macroscopic properties. The experimental method used for this purpose is Angular Resolved Photoemission Spectroscopy (ARPES), which probes the single-particle spectral function and allows direct measurements of the quasi-particle band structure. The analysis is based on comparison of experimental data with electronic structure calculations. Typical methods for the band structure calculations including density functional theory (DFT) in the local density approximation (LDA) and tight-binding calculations (TB) are one-electron approximations and do not give insight into many-body interactions. However, comparing the measured band structures with calculated ones allows estimating the strength of the interactions in the considered system. In Chapter 1 the earlier work on Sr₂RuO₄, which is relevant to this project is presented. This chapter is an introduction to the data analysis and discussion of the results. In Chapter 2 we describe the experimental setup, theoretical principles of the measurement and summarize important improvements made during this project. In Chapter 3 we give a brief introduction into density functional theory and describe methods used within DFT to calculate the band structure. We further give a brief description of a tight binding model for Sr₂RuO₄. The bulk of this chapter is devoted to present the e ects of spin-orbit coupling on the band structure of Sr₂RuO₄. In particular, we use a tight binding model to simulate the anisotropy of the Zeeman splitting found experimentally. In Chapter 4 we present the ARPES results, their analysis and discussion. A particular focus is placed on the discussion of the surface layer Fermi surface topology and on the discovery of strong momentum dependance of the mass renormalization factors of the bulk β and γ bands.
49

Structure and energy relationships in ice and crystalline hydrates

Tribello, Gareth Aneurin January 2007 (has links)
Computer simulations of the various phases of ice have been carried out using potential methods and density functional theory. Plane wave DFT and subsequent Wannier transformations of the Kohn-Sham orbitals were used to obtain highly localised orbitals, which were treated as molecular orbitals in the calculation of molecular multipoles. Using these multipoles it has been shown that the energy differences, calculated using DFT, between different proton topologies of ice VII and Ih are reproduced when the interaction electrostatic potential energy is calculated up to terms in (1/r6) and thus that the driving force for proton ordering is electro static. Armed with this knowledge, successful blind predictions, which have been experimentally verified, of the proton ordered forms of ice V and XII (ices XIII and XIV respectively) have been made using plane wave DFT. The recently developed TIP6P potential has been modified so as to reproduce the correct structure for ice XI, the proton ordered form of ice Ih, and to reproduce the DFT energy differences between different hydrogen bonding topologies. Total energy calculations, using this potential, show that the surface energy depends strongly on the hydrogen bond topology exposed at the surface. In particular surfaces on which under-coordinated protons are clustered have high energies. Monte Carlo calculations have shown that the hydrogen bond topology adopted by ice, both at the surface and in the bulk, depends on the temperature. A comparison of the structures that are possible to make out of silica and ice has been undertaken in the hope that new ice and silica phases can be identified. This comparison is possible because both silica and water form the backbones of 4-connected nets. DFT calculations have shown that the energy maps of the various four connected nets are very similar for both structures, with any differences arising because of the greater flexibility of the O-Si-O angle in silica. Furthermore, this analysis has highlighted a number of potential new ice phases and led to the proposal of a synthetic route to a new clathrate based on the zeolite framework SGT.
50

A permittivity-study of polystyrene latex suspensions

Williams, I. M. January 1973 (has links)
No description available.

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