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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.
31

Interferometric measurement of local mass transfer rates to an impinging jet by non-photographic holography

Gholizadeh, Nasreddin January 1992 (has links)
The purpose of this research work was to employ the optical technique of real time holographic interferometry to measure local mass transfer rates from a flat surface, coated with silicone rubber polymer swollen with a liquid swelling agent of known physical properties, into an impinging air stream in various specified flow conditions. A proprietary holocamera was to be employed to make the required holograms during the work. The first part of the experimental work was concerned with the clarification of the situation regarding the vapour pressure of a widely used swelling agent (ethyl salicylate). Paterson et al [28] have claimed that previous vapour pressure values of ethyl salicylate measured and reported by Kapur and Macleod [27] and subsequently widely used by other workers, are in fact higher by about 25&37 than the true values as carefully redetermined by them. On the other hand the vapour pressure values of Kapur and Macleod give mass transfer coefficients in impinging laminar jet experiments in close agreement with theoretical expectation. Laminar impinging air-jet experiments were to be carried out to calibrate the technique of measurement; mass transfer rates of chemically different materials from a flat polymer-coated surface into a submerged impinging isothermal air-jet were to be measured, and the results were to be used to test the related theory. Finally, it was intended to extend the mass transfer measurements to turbulent air jets, using a suitable swelling agent. Laminar mass transfer experiments were carried out at room temperature for two nozzles; a plain tube and a contoured nozzle, using three suitable swelling agents (ethyl salicylate, 1-methyl naphthalene and n-tetradecane) under various dynamic conditions involving variation of nozzle-to place spacing in the range z/d = 0.26-20.0 and Reynolds number in the range Re = 700-1,810.
32

Nucleation in polymorphic systems

Towler, Christopher January 2004 (has links)
No description available.
33

Ionisation and excitation in pulse radiolysis of organic systems

Roberts, John Pugh January 1968 (has links)
No description available.
34

Adsorption at the interface between two fluids, with special reference to the adsorption of certain dyes at liquid-liquid interfaces

Addison, Cyril Clifford January 1936 (has links)
No description available.
35

Physical properties of free radicals

Richards, J. R. January 1953 (has links)
For more than twenty years it has been recognised that the free aliphatic radicals play an important part in many reactions. A large amount of experimental work has been done, principally on vapour phase reactions, where their presence is much more easily detected. The major types of reaction in which they occur are now known, and there is general agreement on the mechanisms by which they are formed and react to yield the final products. A not inconsiderable amount of information has also been gained about the energetics of these processes.
36

The application of radioactive tracer techniques in the elucidation of the mechanism of chemical reactions

Walton, Alan January 1956 (has links)
Isotopic Exchange reactions may be broadly classified into two main types, homogeneous and heterogeneous (1). In the homogeneous-exchange reaction the reactants are uniformly distributed in the same phase and the only change taking place in the system, during the reaction, is the distribution of the different isotopes. In heterogeneous exchange reactions, on the other hand, the reactants exist in different phases. In this thesis, attention has been confined to an exchange reaction of the latter type, the exchanging atoms being the hydrogen atoms in a hydrocarbon and those in tritiated water. In the case of exchange between hydrogen isotopes (2) the reactions may be divided into four classes according to the state of the bonding of the hydrogen atoms.
37

Clustering for 2D chemical structures

Chu, Chia-Wei January 2011 (has links)
The clustering of chemical structures is important and widely used in several areas of chemoinformatics. A little-discussed aspect of clustering is standardization, it ensures all descriptors in a chemical representation make a comparable contribution to the measurement of similarity. The initial study compares the effectiveness of seven different standardization procedures that have been suggested previously, the results were also compared with unstandardized datasets. It was found that no one standardization method offered consistently the best performance. Comparative studies of clustering effectiveness are helpful in providing suitability and guidelines of different methods. In order to examine the suitability of different clustering methods for the application in chemoinformatics, especially those had not previously been applied to chemoinformatics, the second piece of study carries out an effectiveness comparison of nine clustering methods. However, the result revealed that it is unlikely that a single clustering method can provide consistently the best partition under all circumstances. Consensus clustering is a technique to combine multiple input partitions of the same set of objects to achieve a single clustering that is expected to provide a more robust and more generally effective representation of the partitions that are submitted. The third piece of study reports the use of seven different consensus clustering methods which had not previously been used on sets of chemical compounds represented by 2D fingerprints. Their effectiveness was compared with some traditional clustering methods discussed in the second study. It was observed that no consistently best consensus clustering method was found.
38

The aqueous environment : lessons from small molecules

Dougan, Lorna January 2005 (has links)
An extensive series of neutron diffraction experiments combined with Empirical Structural Refinement Analysis (EPSR) has shown that mixtures of methanol and water exhibit extended structures in solution despite the components being fully miscible in all proportions. Of particular interest is a concentration region (methanol model fraction between 0.27 and 0.54) where methanol and water appear to form separate, percolating networks. This is the concentration range where many transport properties and thermodynamic excess functions reach extremal values. The observed concentration dependence of several of these material properties of the solution may therefore have a structural origin. Molecular segregation in methanol-water mixtures is studied across a wide concentration range as a function of temperature and pressure. Cluster distributions obtained from both neutron diffraction point to significantly enhanced segregation as the mixtures are cooled or compressed. The observed behaviour is consistent with an approach to an upper critical solution point. Such a point would appear to be “hidden” below the freezing line, thereby precluding observation of the two-fluid region. Finally, it is shown that the negative excess entropy of mixing characteristic of aqueous lower alcohols can be understood quantitatively in terms of molecular-scale segregation of the components. A simple model is presented and used to understand the behaviour of methanol-water solutions under extreme conditions using molecular clustering data from neutron diffraction and obviates the need to invoke other restructuring concepts which, though well-known, are unsupported by recent experiments.
39

Development of non-noble catalysts for hydrogen and oxygen evolution in alkaline polymer electrolyte membrane electrolysis

Watkins, Luke January 2013 (has links)
Hydrogen is seen as the ‘energy carrier of the future’ due to the element’s relative abundance, the formation of water as opposed to the green house gases when utilised as a fuel in fuel cells, and the ability to be produced by electrolysers powered from renewable energy sources such as wind, water and sunlight. The development of hydrogen production through electrolysis is hindered by the high costs associated with the technology, specifically the ion exchange membranes and electrocatalysts that are employed in the membrane electrode assemblies used in polymer electrolyte electrolysers. This research focused on the development of non-noble catalysts suitable for hydrogen and oxygen evolution in alkaline electrolysis. Synthesis of NiO was achieved through thermal decomposition, chemical bath deposition and solution growth techniques. A mixed metal oxide, NiCo2O4, was synthesized through thermal decomposition of metal nitrate salts. Cyclic voltammetry and steady state electrochemical experiments on the electrodes were conducted in an electrochemical half cell electrolyser. A thin film of pure NiO was formed onto a titanium substrate through chemical bath deposition followed by thermal decomposition. The performance of the electrode at 1.73 V, relative to the mass of the catalyst loading, produced 0.25 A cm-2 mg-1 in 1 M NaOH at 25°C (IrO2 produced 0.44 A cm-2 mg-1 in the same electrolyser). The electrode’s performance is attributed to the nanoporous structure of the catalyst film (20 – 200 nm pore diameters), which was formed from the chemical bath deposition method used to prepare the catalyst films. Unfortunately this procedure has a limited film thicknesses so higher loadings could not be achieved. Higher loadings of other non-noble electrocatalysts were made possible with addition of a PVDF binder to the catalyst film. Physical analysis through XRD was performed on the most promising catalysts for the oxygen evolution reaction to confirm their composition. A blend of α-Ni(OH)2 and 4Ni(OH)2•NiOOH•xH2O formed through the chemical bath deposition technique produced higher current densities (104 mA cm-2 at 0.8 V vs. Hg/HgO) than another non-noble metal catalyst, NiCo2O4 (97 mA cm-2) II in 1 M NaOH at 25°C. An alkaline polymer electrolyser free from noble metals was developed with a membrane electrode assembly that utilised a partially fluorinated membrane, a PVBC/PVC ionomer in the catalyst layers, 1.0 mg NiMoO4 cm-2 in the cathode and 0.7 mg NiCo2O4 cm-2 in the anode. It produced 0.4 A cm-2 in 1 M KOH at 25° at a potential of 1.9 V.
40

Structural studies of ionic liquids and their use in synthesis

Pringle, Jennifer M. January 2001 (has links)
Ionic liquids represent a new type of solvent with a range of advantageous properties such as a large liquid range and negligible vapour pressure. This investigation is concerned with ionic liquids containing the imidazolium cation and reports both utilisation of these ionic liquids in new synthetic reactions and also investigations into the relationship between the structure and physical properties of these compounds by synthesis of a range of new imidazolium-based ionic liquids. The fluorination of organic and inorganic compounds in the 1-butyl-3-methyl imidazolium hexafluorophosphate ionic liquid was investigated, utilising calcium fluoride as the fluorinating agent. The asymmetric hydrogenation of prochiral ketones by both homogeneous and heterogeneous hydrogenation was investigated using the chiral ionic liquid 1-butyl-3-methyl imidazolium lactate. Investigations into the relationship between the structure and physical properties of imidazolium ionic liquids were performed by changing the cation or anion of the compound to synthesise a range of new ionic liquids. Changes to the cation of the ionic liquid were effected by substitution of the acidic proton at the 2-position of the imidazole ring by methyl and phenyl groups. Methylation at this position results in an unexpected increase in melting point. The crystal structures of 1-butyl-3-methyl imidazolium chloride and 1-butyl-2,3-dimethyl imidazolium chloride are reported and analysis of the extent of hydrogen bonding within these structures used to explain this phenomenon. The effect of changing the anion of the ionic liquid was investigated and the crystal structures of 1-butyl-3-methyl imidazolium bromide, 1-butyl-2,3-dimethyl imidazolium hexafluorophosphate, 1-butyl-2,3-dimethyl imidazolium tetrafluoroborate and 1-butyl-2-phenyl-3-methyl imidazolium hexafluorophosphate are reported.

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