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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.
21

Development of low-cost high efficiency electrode materials by electrodeposition for li-ion battery applications

Lak, Gyorgy B. January 2014 (has links)
Global demand for energy continues to rise dramatically and will do so into the foreseeable future. Energy storage technologies, such as Li-ion batteries, are considered the most promising for electric vehicles and renewable energy systems operating on intermittent energy sources such as wind and solar power. An in-depth introduction on secondary electrochemical energy storage technologies is presented with a special emphasis on the development of novel and effective improvements needed for existing Li-ion battery systems. The critical review of the relevant papers is focusing initially on Li -ion battery technology and its parameters followed by a detailed consideration of the electrode materials. Special focus is given to the anode materials, where tin-based alloy electrodes, prepared by electrodeposition and other methods, are described and discussed. Employing a range of different techniques based on electrode position, a number of novel binary and ternary alloys, namely SnCo, SnNi, SnFe, SnCoFe and SnNiFe, with a range of different compositions, structures and surface morphologies have been produced and tested in a model Li -ion cell as anodes to derive a Li-ion battery for improved future battery application. These results are discussed in detail and compared with results reported in relevant literature papers. The main focus was on the deposit performance as a negative electrode for Li-ion battery application. Their compositions, structures, phases and morphologies are given detailed consideration in relation to electrode performance. A key aspect reported is the investigation of these alloys with a view to identifying alloys with an appropriate Sn content, microstructure and surface morphology which indicate potential as a Li-ion electrode material. For each alloy system initially Hull cell and modified Hull cell experimentation was conducted to establish the boundary of the plating system in terms of quality of deposits and inform further in-depth experimentation and testing. A range of electrolyte combinations were initially studied to achieve suitable electrolytes operating under constant potential and pulse current deposition. The best performing SnCo alloy deposit as an electrode material was obtained by pulse plating at 100mA/cm2 with t on=O.Ols t off=0.49s resulting in a deposit which provided an initial 820mAh/g discharge capacity and a retained capacity after the 10th cycle of 420mAh/g. The SnNi system results indicate that constant potential deposition led to a retainable and stable discharge capacity of 765mAh/g over 10 lithiation-delithiation cycles. However, the theoretical capacity of this sample is 920mAh/g, which means that 17% of the theoretical capacity is inactive. The best SnFe deposit results indicate that constant potential deposition from a gluconate based electrolyte provided a maximum retainable discharge capacity of 500mAh/g after 10 lithiation-delithiation cycle. The best performing SnCoFe deposit as an electrode was obtained by pulse plating at 59mA/cm2 with t on=O.Ols t off=0.49s and it delivered an initial 550mAh/g discharge capacity with the retained capacity after the 10th cycle being 300mAh/g. A SnNiFe solid solution ternary system was electrode posited by pulse plating techniques at lOOmA/cm2 with ton=O.Ols toff=O.19s delivered an initial 700mAh/g discharge capacity which is only 3% less than the predicted theoretical capacity for the Sn content with retention of its capacity after the 10th cycle. This is the most promising result obtained within the framework of this study. It was also demonstrated that increasing the substrate roughness prior to deposition leads to a desirable large surface area per unit volume and thus supports the theoretical capacity of the samples being achieved. This result ultimately proved that a large surface area per unit volume morphology is the key factor to improve the Sn alloys cycle life and discharge capacity performance. The previously mentioned results are generally better than the conventional carbon discharge capacity (250-400mAh/g), and all of these alloys have a distinct potential for development as new electrode materials for Li-ion battery application.
22

A study of flame inhibition by non-flammable gaseous diluents

Cox, N. W. January 1975 (has links)
No description available.
23

Characterisation and molecular modelling of selected benzoxazines and their polymers

Hassan, Wan Aminah Wan January 2014 (has links)
This work covers a number of aspects of the thermal properties of empirical and molecular modelling with one chapter of literature survey and four chapters of result and discussion analysis. Chapter One presents a survey of the literature associated with the development of high performance polymers, of which polybenzoxazines are an example. Chapter Two introduces the materials which were supplied by Huntsman Corporation, Basel (i.e. Arald'ite MT 35600 and Araldite MT 35700). The purity of the samples was analysed in order to get an initial impression of the materials as any impurity in the sample may affect the mechanism of reaction and could influence the thermal properties. Chapter Three explains the thermal characteristics of a telechelic PEK benzoxazine by utilising a molecular modelling approach. The backbone of PEK consisting of five mOll0mers was replicated to have twelve chains in a one cubic cell of Periodic Boundary Conditions. The PEK was then crosslinked and the percentage of crosslinking was subsequently compared with several others of different percentages of crosslinking. Eight atomistic models were generated; 0-0, 58-14, 58-21, 67-31, 83-35, 92-40,100-45, and 100- 54. Chapter Four reports the results of incorporating bisphenol A into Araldite MT 35600 at four different loadings. Empirical data for these blends (i.e. containing 0 wt%, 5 wt%, 15 wt%, and 25 wt%) were generated in-house, whilst a blend containing 35 wt% bisphenol A was incorporated into the molecular modelling study. Spectroscopic and thermal analyses were carried out to obtain the structural features and thermal properties of the materials. A molecular modelling study to predict the thermal properties of the blends was undertaken and the results were compared with the empirical data and corresponded closely. The final Chapter (Five) discusses a new application of the QSPR approach, which relates selected properties to chemical structures. Three case studies were investigated with the best linear equations produced, where the coefficients of determination were close to 1. This approach is still new in the field and therefore refinement work is needed in order to optimise the model. University
24

Neutron reflectometry and ellipsometry applied to atmospheric night-time oxidation

Sebastiani, Federica January 2014 (has links)
The fate of atmospheric aerosol is currently attracting increased attention from the scientific community because its impact on the Earth's radiative balance and on cloud formation is still largely unknown. To understand the ageing process of aerosol it is helpful to investigate heterogeneous reactions occurring between organic surface films and gas-phase oxidants. While most studies have focused on the abundant daytime oxidants 0 3 and OH, during the night-time the OH concentration is very low and the concentration of the more potent NO:! becomes significant. In this thesis insoluble organic monolayers at a planar air-water interface were used as proxies for films on atmospheric aerosol, and the surface excess kinetics were monitored in situ using a combination of neutron reflectometry (NIt) and ellipsometry. A range of compounds were chosen to allow a study of the effects on the reaction kinetics and product formation of the chain length, type of headgroup and degree of unsaturation on the organic molecule as well as the type of oxidant. To allow the work to be performed several key developments were carried out: a refined method for NR data analysis, the commissioning of a dedicated new miniature sample chamber, rigorous calibration of the oxidant concentrations and development of a kinetic model. The limitations of ellipsometry as a substitute for NIt for the study of pure syst.ems were explored, yet its potential to provide complementary information about product formation was demonstrated. Six reactions of pure organic monolayers revealed that the degree of unsaturation of the chain was by far the biggest factor for the reaction rate, although other differences were also systematically examined. Two binary mixtures were investigated showing that the reaction rate is consistently lower in mixed films, which may help to explain discrepancies in the literature between laboratory studies and field measurements.
25

Novel chiral ionic liquids

Foreiter, M. B. January 2014 (has links)
Chiral ionic liquids have been present in the literature for more than a decade. The development of original chiral systems of ions is currently far more difficult than ever before. The path of innovation in this topic, however, should not be focussed exclusively on the introduction of chirality into the ionic liquid structure, but should go beyond, towards further functionalisation of these species. The combination of chirality and a functional moiety has been the starting point for the present work. Here, a focus was on creation of chiral ionic liquids possessing distinct functional groups: a strong hydrogen-bonding thiourea group was selected. Consequently, a series of novel chiral thiouronium salts were synthesised. The chirality was sourced in cheap, but structurally robust, chiral amines: (S)-1- phenylethylamine and (+)-dehydroabietylamine. Because the thiourea moiety can be functionalised at five different sites, a wide range of thiouronium and thiourea-functionalised ionic liquids could be prepared and analysed, and the influence coming from their structural diversity explored. The crucial point for the project was a confirmation of rotameric behaviour in these new thiouronium systems. Here, the hindered rotation has been examined by NMR spectroscopy, and compared with literature findings. The key message concludes that, in the thiouronium system, the C-S rotation predominates when placed in a highly polar solvent; then the syn syn conformation dominates. When, on the other hand, the constraints of the surroundings are eliminated, the syn-anti form is energetically preferable. Here, the rotamerism of the thiouronium cation in a neat liquid form was examined for the first time. Finally, these novel chiral compounds have found applications based on molecular recognition by the thiourea moiety. The discrimination of chiral oxoanions by these salts using NMR spectroscopy has been successful. A strong, double hydrogen-bonded connection between the chiral thiouronium moiety and the oxoanion proved to be a key point, generating results a competitive with the literature results. Following this approach, the separation capabilities of thiouronium systems were also explored, given that they can be effective agents for oxoanion extractions. This work demonstrated that a careful design of functional molecules is scientifically significant, and can have a great impact on their applications.
26

Electrochemical reactivity in ionic liquid media

Marley, Eunan January 2014 (has links)
In our work, a number of reaction processes were investigated, using ionic liquids (ILs), or ionic liquid-based salts, as either the solvent or reactant. In chapter 3, the active form of TEMPO, the oxoammonium cation (T+), was used to synthesise T+ -bis(trifluoromethylsulfonyl)imide (NTf2) and T+trifluoromethanesulfonate (triflate) salts. These salts were used to investigate the mediated oxidation of primary alcohols. It was found that the oxidation process proceeded more rapidly for methanol than for the other two alcohols investigated. A significant drop in T+ current occurred when only base was added to the cell, with a multistep reaction process likely to be involved. The use of a solid DOWEX resin as base was also briefly investigated. In chapter 4, the electrocarboxylation of a number of benzophenone derivatives was investigated. For all investigated compounds, the carboxylation process proceeded via a ECE / DISPl mechanism. It has been found that the variation of the carboxylation reaction kinetics can be predicted based on the nature of the functional groups present on the benzene rings. Electron donating groups increased the rate of carboxylation, while electron withdrawing groups decreased the rate of carboxylation. The electrocarboxylation in I -butyl-lmethylpyrrolidinium bis-(trifluoromethane sulfonyl)imide [Bmpy][NTfz] were 2 orders of magnitude slower than those reported in DMF. In chapter 5, CO2 reduction in [Bmpy][NTfz] was briefly investigated at a number of electrode types (glassy carbon, platinum, palladium, gold, indium) using cyclic voltammetry. CO2 reduction was observed at all 5 electrodes, where it was found that Au and especially In act as electrocatalysts. The mediated reduction of COz in [Bmpy] [NTfz] was then attempted using methyl benzoate and dimethyl phthalate. Investigation of the electrochemistry of the two compounds in IL suggests that ion pairing causes an increase in the rate of dimerization over carboxylation, preventing the ester from acting as a redox mediator.
27

Development of an in-situ spatially resolved technique to investigate catalysts in a plug flow reactor

Touitou, Jamal January 2014 (has links)
This thesis presents, in detail, all the steps of the development of a new in-situ spatially resolved method to probe gas phase concentrations and temperature with minimum invasiveness. From the literature review, it was noted that no techniques developed to date were designed to investigate packed powdered catalyst beds which simultaneously obtain the gas concentrations and the temperature profile. Within this thesis, details of the development of a prototype and further optimisation of a spatial resolution technique for packed powdered catalyst beds were disclosed. The technique was designed to have negligible impact on the packed powdered catalyst bed with the use of the smallest equipment available. Significantly, a number of validation tests of the spatially resolved technique were conducted and the results proved that the technique was working under different experimental conditions. The results of these validation tests highlighted the improvements of the optimised spatial resolution system, which provided twice as many sampling points as the prototype, as well as the additional benefit of simultaneous temperature recording. Additionally, the invasiveness of the spatially resolved technique was investigated using Computational Fluid Dynamics (CFD); more precisely the sampling capillary was found to have negligible impact on the packed catalyst bed during the experiment. Furthermore, the results obtained experimentally have been compared with simulations using a micro kinetic model. The results obtained showed that a hybrid model (simulated concentrations and experimental temperature) allowed a more accurate picture of the phenomena occurring in the packed catalyst bed which was one of the initial aims of the development of the spatially resolved technique.
28

Supported ionic liquid catalysis

Hall, L. S. I. January 2014 (has links)
Over the last few years interest in supported ionic liquid (IL) catalysis has been growing. This is due to the increased selectivity and catalytic activity obtained in IL based systems compared with molecular solvents coupled with the advantages of solid catalyst in terms of separation. In this thesis, the effect of supported ionic liquid catalysis will be examined for various different reactions including the hydrogenation of citral and cinnamaldehyde, the Diels-Alder, Mukaiyama aldol and carbonyl-ene reactions. Solid catalyst ionic liquid layers (SCILL) catalysts and Ionic polymers (IP) were used for the hydrogenation of citral and cinnamaldehyde. Overall a Pd/Ab03 with and without an IL produced significantly higher selectivities and conversions compared with a Pd/C catalyst. The IP catalysts were shown to greatly increase the selectivity. The IP synthesised from the commercial Amberlite 910, produced the best results for both substrates achieving high selectivities up to 99%.
29

Formation, properties and functionalization of polyelectrolyte/ nucleotide coacervate droplets

Che Hak, Cik Rohaida January 2013 (has links)
The central themes of this thesis are the spontaneous formation of polymer/nucleotide complex coacervate droplets and self-assembly of a fatty acid membrane on the surface of such droplets, along with the characterization of the droplets with and without membrane. The spontaneous formation of poly-diallydimethylammonium chloride (polycationic) and adenosine 5'triphosphate (anionic) (PDDA/ATP) coacervate droplets was studied using changes in turbidity and (-potentials. The droplets' formation was determined at critical concentration for coacervation (CCC) when approximately 60 % PDDA fixed charges were neutralized by ATP binding. The CCC was dependent on PDDA concentrations, ionic strengths and PDDA molecular weight. DLS measurement showed complexation prior to droplet formation, suggesting that droplets were formed via nucleation and growth mechanism. At CCC droplets had net positive surface charges, were spherical and polydisperse under optical microscope and kinetically stable to coalescence and thermally stable up to 85°C. Conversely, at complete charge neutralization droplets were non-charged and unstable to coalescence and sedimentation. The dynamic properties and structure of coacervate phase were measured with rheological experiments. The transparent, condensed coacervate phase possessed liquid-like viscoelastic properties which was highly dependent on PDDA-ATP interactions: the stronger the interactions, the more viscous the phase. Viscoelastic behaviour was attributed to the present of ATP bound to PDDA chain, which formed a highly interconnected chain. The structure of coacervates was identified as heterogeneous domains, composed of a mixture of elastic-like component embedded into liquid-like domains, which displayed pronounced liquid-like behaviour. Surface tension measurements exposed that the coacervate phase was less polarised than water. Contact angle measurements presented the hydrophilicity of coacervate phase with the structure of coacervate was composed of ATP-rich at the surface and PDDA-rich at the interior and for charged droplets. Given these properties, coacervate demonstrated compartmentalization within the droplets' interior. The self-assembly of a fatty acid membrane was performed on the surface of coacervate droplets by a simple addition of negatively-charged fatty acid molecules into positively-charged droplets. The membrane assembly occurred at the surface of droplets at a specific molar ratio of oleate:PDDA:ATP as monitored via(-potentials and fluorescence microscopy using BODIPY FL C16- tagged fatty acid fluorescence. Multichannel confocal imaging then showed oleate membrane was at the surface while kiton red pre-stained droplets remained stable inside the membrane, thus confirming that the membrane was encapsulated by the droplets. The mechanism of membrane assembly was driven by an increase in thermodynamic for bilayer formation at the droplets' surface. The membrane was highly net negative charges and was multi-lamellar bilayer. The viscosity (FUM) was higher at the membrane than in coacervate region. The membrane was stable at higher ionic strength while coacervate was destroyed, which induced t he oleic acid vesicle fusion and growth. The membrane encapsulation showed marked changes in the sequestration properties than uncoated droplets, indicating that the semi-permeability of the membrane-coated droplets was evident.
30

The measurement of some ionic equilibria in protium oxide-deuterium oxide solvent mixtures

Gordon, Iain Nisbet January 1970 (has links)
No description available.

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