No description available.

In this thesis, we use rst principles density functional theory (DFT) to study the energetics, structural and electronic properties of hydrogenated and lithiated bilayer graphene material systems. The newly developed four variants of the non-local van der Waals (vdW) exchange-correlation functionals (vdW-DF, vdW-DF2, vdW-DF C09x and vdW-DF2 C09x) are employed to explore all the possible con gurations of hydrogen adsorption at 50% and 100% coverage on a 1 1 unit cell. The results obtained are also compared with the GGA PBE functional. For 50% hydrogen coverage, 16 unique con gurations are identi ed in the unrelaxed state. Formation energy analysis reveals six possible energetically favourable con gurations with three low-energy competing con gurations. It is found that the properties of hydrogenated bilayer graphene greatly depend on the hydrogen con guration. For instance, the formation of a hydrogen dimer within the layers decouples the structure, whereas the dimer formation outside surfaces does not have a signi cant in uence on the van der Waals forces; thus the bilayers remain coupled. In this coupled con guration, the vdW-DF C09x functional predicts the lowest formation energy and shortest interlayer separation, whereas the GGA PBE functional gives the highest formation energy and largest interlayer distance. The reasons behind the variation of these functionals are discussed. Two of the three low-energy competing con gurations exhibit semimetallic behaviour, whereas the remaining con guration is a wide band gap material. The wide band gap structure is found to undergo a hydrogen-induced spontaneous phase transformation from hexagonal to tetrahedral (diamond-like) geometry. We conclude that this wide band gap con guration represents a viable template for synthesizing nanodiamonds from graphene by hydrogenation. At 100% coverage, ten unique hydrogen con gurations are identi ed from a 1 1 unit cell. All exchange-correlation functionals predict nine of the structures to have negative formation energies. From these nine structures, three low-energy competing structures are noted and found to be wide band gap semiconductors, whereas the other con gurations exhibit either a semimetallic or metallic character. Although a 1 1 unit-cell is able to present a clear picture for the interaction between hydrogen and graphene, our results reveal that it limits the occurrence of other interesting physics. The cell size was increased to 2 1, to identify other low-energy con gurations that are not possible in a 1 1 cell. The identi ed con gurations have shown physically interesting hydrogen arrangements such as chair-like, zigzag-like and boat-like con gurations. Furthermore, our results reveal that hydrogenation reduces the elastic properties of the pristine structures. We further perform a systematic investigation of the e ects of lithium (Li) on AA and AB stacking sequences of bilayer graphene. Two Li atoms are considered to examine the e ects of the Li-Li interaction on bilayer graphene, and a total of 12 unique con gurations for AB and 9 for AA stackings are identi ed. The vdW-DF consistently predicts the highest formation energies, whereas vdW-DF2 C09x gives the lowest. Unlike in the case of the pristine structures, it is noted that for lithiated bilayer graphene, GGA PBE gives comparable results to the other functionals. One of the Li intercalated con gurations undergoes a spontaneous translation from the AB to AA stacking, and is found to be the most energetically stable con guration. We therefore conclude that Li favours the AA stacking, and that con guration represents a feasible template for experimentally synthesizing and characterizing a Li-based anode material. We noticed that all identi ed Li con gurations exhibit metallic behaviour. Lastly, we found that the intercalated Li dimer weakly interacts with the graphene layers, whereas the intercalated isolated Li atom exhibits strong interaction. / Thesis (PhD)--University of Pretoria, 2014. / gm2014 / Physics / unrestricted

No description available.

The synthesis of 2,4-disubstituted pyrimidine derivatives is described. The synthetic route involved the addition reaction of lithiated intermediates, mostly heterocycles, to position 4 of 2-chloropyrimidine to give a dihydropyrimidine intermediate which was oxidized back to a pyrimidine. This was followed by nucleophilic aromatic substitution with various amines of the chlorine in the position 2. A number of compounds were prepared which showed binding towards various serotonin receptors in preliminary biological evaluation.

Les biaryles à chiralité axiale sont des structures privilégiées qui ont un rôle important en chimie. On les trouve dans de nombreux produits naturels biologiquement actifs, en tant que ligands chiraux en catalyse asymétrique ou encore en science des matériaux. Le but est de développer une méthode permettant de contrôler la chiralité axiale de biaryles en l’absence de métaux de transition en utilisant le couplage ARYNE. Une première approche consiste en un dédoublement atropo-diastéréosélectif dans lequel l’agent de dédoublement chiral est un sulfoxyde qui est introduit en position ortho d’un précurseur biarylique issu d’un couplage ARYNE. Basée sur la déracémisation et sur la fonctionnalisation ultérieure régio- et chimiosélective des deux parties aromatiques du biaryle énantiopur obtenu, elle permet d’accéder à une large famille de biaryles. Une seconde approche consiste à effectuer un couplage ARYNE atropo-diastéréosélectif en introduisant un auxiliaire de chiralité (sulfoxydes, oxazolines, diéthers) sur l’un des partenaires de couplage. Les biaryles ainsi obtenus peuvent être fonctionnalisés afin de synthétiser des ligands chiraux. / Biaryls are privileged structures which have an important role in chemistry. We can find them in several biologically active natural products, in asymmetric catalysis as ligands or in material sciences. The aim is to develop a methodology allowing the control of the axial chirality without transition metal using the ARYNE coupling. The first approach consists in an atropo-diastereoselective resolution in which the chiral solving agent is a sulfoxide introduced in ortho position of the biarylic precursor arising from the ARYNE coupling. Based on the deracemization and on the subsequent regio- and chemioselective functionalization of the two aromatic parts of the enantiopur biaryl obtained, it allows to access to a large family of biarylic compounds. A second approach consists in making an atropo-diastereoselective ARYNE coupling introducing a chiral auxiliary (sulfoxides, oxazolines, diethers) on one of the coupling partners. The biaryl compounds obtained could be functionalized in order to synthesize chiral ligands.

This thesis is focused on the mechanisms for corrosion andhydriding of Zircaloy. Special attention is paid tomicrostructural characterisation by cross sectionaltransmission electron microscopy of the oxide layer formed.Three main topics have been treated in this work: (i)Pre-transition oxides were investigated with the purpose ofevaluating if it is possible to predict post-transitionbehaviour of different alloys. (ii) The reason for the commonlyobserved accelerated corrosion of Zircaloy in the presence oflithium hydroxide was investigated by studying the phasetransformation of differently stabilised zirconium oxides andby corrosion studies. (iii) Pre-hydrided Zircaloy-2 was studiedto investigate the influence of hydrogen on the oxidationbehaviour. Characterisation of pre-transition oxides formed onzirconium alloys, has been accomplished with the aim ofdetermining if there are any differences in the properties(morphology, pores, cracks and phases) of the oxide layersformed which might explain the differences in corrosionbehaviour later in life. Four Zircaloy-2 versions and oneZircaloy-4 version were tested in an autoclave at 288° Cfor 20h and 168h and at 360˚C for 96h. Based on thecharacterisation of pre-transition oxide layers only small orno differences were found between the different alloycompositions, thus it is not possible to predict long-timecorrosion behaviour by studying pre-transition oxides. However,large differences were found between the two test temperatures.The higher oxidation temperature results in increased oxidationrates and larger oxide grains, the columnar grains are a factorof 3-4 longer, and the equiaxed grains have an almost doubledmaximum diameter. The fraction of columnar grains andtetragonal phase also increases with temperature. The reasonfor the difference in morphology between the two temperaturesis not fully understood, but the results show that acceleratedtesting at elevated temperatures may be a questionableapproach. One of the Zircaloy-2 samples was also anodicallyoxidised. The oxide layer formed only contains equiaxed grainsand phase analysis shows both monoclinic and tetragonal phasesare present. Oxidation tests of Zircaloy-2 and Zircaloy-4 in water andlithiated water at 360 ° C show that the pre-transitionoxidation rate is not affected by the presence of LiOH, but thetransition occurs earlier and the post-transition oxidationrate is increased. The oxidation rate correlates with thedensity of cracks in the oxide layer and the morphology of theoxide grains. The oxides formed have a layered structure andfor samples oxidised in LiOH solution the inner protectivelayer is thin. The effect of LiOH is suggested to be the resultof partial dissolution of the oxide and subsequentincorporation of lithium ions during adissolution-precipitation process. Newly formed oxide isprobably more hydrous, and the grain boundaries areparticularly liable to dissolution. The increased concentrationof LiOH within cracks and pores could reach the detrimentallevels necessary for dissolution. This is supported by theinsensitivity in the pre-transition region to both thecompositions of the alloy and to the environment. The alloycomposition influences the microstructure of the oxide layer,and thereby the resistance to accelerated corrosion rate inlithiated water. The hydrogen pickup ratio follows the weightgain, not the oxidation rate, up to the second transition. Whenthe protective oxide layer is degraded the hydrogen pickupratio increases markedly. To evaluate if hydrogen is a cause for or a consequence ofaccelerated corrosion, pre-transition oxidation tests ofZircaloy-2 have been performed with hydrogen present in threedifferent states: i) Hydrogen in solid solution in thezirconium alloy, corresponding to the initial oxidation priorto precipitation of hydrides. ii) Uniformly distributedhydrides simulating a situation in whish hydrides starts toprecipitate and iii) Massive surface hydride claimed to be themain cause of accelerated oxidation. Based on the resultsobtained, it is concluded that the oxidation of massivezirconium hydride resembles the oxidation of zirconium metal.This fact clearly shows that accelerated oxidation of zirconiumalloys cannot be due solely to the presence of a massivehydride layer, but also requires a combined effect offorexample interfacial roughness and hydride precipitation. <b>Keywords:</b>Zircaloy, Zirconium alloys, Oxidation, Oxidelayer, Pre-Transition, Hydriding, Pre-Hydrided, Hydrides,Lithium Hydroxide (LiOH), Lithiated Water, Dissolution, CrossSectional TEM

The synthesis of a series of 2-chloropyrimidine derivatives is described. The synthesis began with a nucleophilic addition of lithiated heterocyclic molecules to the 4 position of 2-chloropyrimidine to give dihydropyrimidine intermediates. The intermediates were oxidized to the pyrimidine ring using the DDQ method. This was followed by an addition-elimination reaction of an amine to the 2-chloropyrimidine derivative. The structure and properties of the final compounds were analyzed by melting point, combustion analysis, and 13C-NMR and 1H-NMR spectroscopy. Biological activities in vitro of the synthesized compounds as antagonists of the 5-HT2a and 5-HT7 receptors were determined by an independent laboratory.

<p>This thesis is focused on the mechanisms for corrosion andhydriding of Zircaloy. Special attention is paid tomicrostructural characterisation by cross sectionaltransmission electron microscopy of the oxide layer formed.Three main topics have been treated in this work: (i)Pre-transition oxides were investigated with the purpose ofevaluating if it is possible to predict post-transitionbehaviour of different alloys. (ii) The reason for the commonlyobserved accelerated corrosion of Zircaloy in the presence oflithium hydroxide was investigated by studying the phasetransformation of differently stabilised zirconium oxides andby corrosion studies. (iii) Pre-hydrided Zircaloy-2 was studiedto investigate the influence of hydrogen on the oxidationbehaviour.</p><p>Characterisation of pre-transition oxides formed onzirconium alloys, has been accomplished with the aim ofdetermining if there are any differences in the properties(morphology, pores, cracks and phases) of the oxide layersformed which might explain the differences in corrosionbehaviour later in life. Four Zircaloy-2 versions and oneZircaloy-4 version were tested in an autoclave at 288° Cfor 20h and 168h and at 360˚C for 96h. Based on thecharacterisation of pre-transition oxide layers only small orno differences were found between the different alloycompositions, thus it is not possible to predict long-timecorrosion behaviour by studying pre-transition oxides. However,large differences were found between the two test temperatures.The higher oxidation temperature results in increased oxidationrates and larger oxide grains, the columnar grains are a factorof 3-4 longer, and the equiaxed grains have an almost doubledmaximum diameter. The fraction of columnar grains andtetragonal phase also increases with temperature. The reasonfor the difference in morphology between the two temperaturesis not fully understood, but the results show that acceleratedtesting at elevated temperatures may be a questionableapproach. One of the Zircaloy-2 samples was also anodicallyoxidised. The oxide layer formed only contains equiaxed grainsand phase analysis shows both monoclinic and tetragonal phasesare present.</p><p>Oxidation tests of Zircaloy-2 and Zircaloy-4 in water andlithiated water at 360 ° C show that the pre-transitionoxidation rate is not affected by the presence of LiOH, but thetransition occurs earlier and the post-transition oxidationrate is increased. The oxidation rate correlates with thedensity of cracks in the oxide layer and the morphology of theoxide grains. The oxides formed have a layered structure andfor samples oxidised in LiOH solution the inner protectivelayer is thin. The effect of LiOH is suggested to be the resultof partial dissolution of the oxide and subsequentincorporation of lithium ions during adissolution-precipitation process. Newly formed oxide isprobably more hydrous, and the grain boundaries areparticularly liable to dissolution. The increased concentrationof LiOH within cracks and pores could reach the detrimentallevels necessary for dissolution. This is supported by theinsensitivity in the pre-transition region to both thecompositions of the alloy and to the environment. The alloycomposition influences the microstructure of the oxide layer,and thereby the resistance to accelerated corrosion rate inlithiated water. The hydrogen pickup ratio follows the weightgain, not the oxidation rate, up to the second transition. Whenthe protective oxide layer is degraded the hydrogen pickupratio increases markedly.</p><p>To evaluate if hydrogen is a cause for or a consequence ofaccelerated corrosion, pre-transition oxidation tests ofZircaloy-2 have been performed with hydrogen present in threedifferent states: i) Hydrogen in solid solution in thezirconium alloy, corresponding to the initial oxidation priorto precipitation of hydrides. ii) Uniformly distributedhydrides simulating a situation in whish hydrides starts toprecipitate and iii) Massive surface hydride claimed to be themain cause of accelerated oxidation. Based on the resultsobtained, it is concluded that the oxidation of massivezirconium hydride resembles the oxidation of zirconium metal.This fact clearly shows that accelerated oxidation of zirconiumalloys cannot be due solely to the presence of a massivehydride layer, but also requires a combined effect offorexample interfacial roughness and hydride precipitation.</p><p><b>Keywords:</b>Zircaloy, Zirconium alloys, Oxidation, Oxidelayer, Pre-Transition, Hydriding, Pre-Hydrided, Hydrides,Lithium Hydroxide (LiOH), Lithiated Water, Dissolution, CrossSectional TEM</p>

Mass spectrometry (MS) has become a widely used technique for the characterization of a wide range of substances in diverse fields. The selection of appropriate ionization techniques, source parameters, charge carriers based on the analyte’s polarity is essential in MS as only the ions are detected. When using a soft ionization technique, single stage-MS at best provides only chemical composition; thus, tandem MS is needed to determine structural information and dissociation pathways. This dissertation focuses on the characterization of various small molecules and ions using different ionization techniques, charge carriers, and collision-induced dissociation (CID). In Chapter II, commercially available ionic liquid (IL) cations, specifically imidazolium-based IL cations with different side-chain chemistries, were characterized by CID-MS. The imidazolium-based IL cations have diverse dissociations pathways depending on the nature of the side chain (aliphatic or aromatic) or the functional groups (allyl, vinyl, alcohol, methoxy, nitro) present on the side chain. Additionally, it was observed that some IL cations undergo thermal degradation under normal operating temperatures of electrospray ~275 °C. A variety of experimental and complementary computational chemistry results are presented. In Chapter III, cis-3-hydroxyproline (c3hPro) and cis-4-hydroxyproline (c4hPro) isomers were differentiated upon lithiation using CID-MS. The CID-MS of [c4hPro+Li]+ produces three primary fragmentation pathways, namely the neutral losses of H2O, CO, and CO2; whereas CID-MS of [c3hPro+Li]+ produces only loss of CO2 in this same region. These observations may have analytical utility, and in this work, the experimental observations were explored with thermodynamic and transition state calculations to better understand the processes. In Chapter IV, the accurate mass of synthetic monomers including PAH perfluorocycloalkene monomers and their precursors were measured and reported with a publication-quality mass accuracy using atmospheric pressure chemical ionization (APCI)-MS. Additionally, the effect of solution flow rate, ionization mode, source parameters (such as vaporization temperature, dry gas temperature and dry gas flow rate, nebulizer gas pressure), acidification, and different solvent systems on APCI-MS signal intensity were studied.

Le développement à grande échelle des microbatteries pour des applications diverses comme l’alimentation de secours de certains composants électroniques dans les téléphones portables nécessite une compatibilité avec le procédé de solder-reflow employé dans le domaine de la microélectronique. Dans ce contexte, cette étude porte sur la mise au point d’un nouveau procédé de réalisation de couches minces d’oxysulfures de titane lithiés (LixTiOySz) pour une utilisation en tant qu’électrode positive dans une microbatterie Li-ion. Tout d’abord ce travail a débuté par la synthèse et la caractérisation de plusieurs compositions de sulfures de titane lithiés à l’état massif par réaction en solution de TiS2 ou TiS3 avec le n-butyllithium mais aussi par réaction à l’état solide à haute température entre les précurseurs TiS2, Li2S et Ti. Par la suite, des couches minces de LixTiOySz ont été déposées par pulvérisation cathodique radiofréquence à effet magnétron de cibles réalisées à partir des matériaux lithiés à l’état massif. La composition chimique de ces dépôts dépend de celle de la cible utilisée ce qui permet d’obtenir des couches plus ou moins riches en lithium et en soufre. En revanche, elles sont toutes très mal cristallisées, denses et elles ne présentent pas de structuration particulière. Enfin, les caractérisations électrochimiques des dépôts de LixTiOySz, à la fois en électrolyte liquide et solide, ont permis de mettre en évidence une corrélation entre leur composition chimique et leur comportement électrochimique. Globalement, ces dernières sont performantes, compatibles avec le solder-reflow et donc tout à fait intéressante pour l’application. / Large-scale development of microbatteries for various applications such as back-up power sources for cell phone electronic components needs suitability with reflowing process that is often used in microelectronic. Here we report on the development of a new realization process to produce lithiated titanium oxysulfides (LixTiOySz) thin films for use as positive electrode in Li-ion microbatteries. First of all, this work began with synthesis and characterization of several lithiated titanium sulfides compounds prepared by reaction between TiS2 or TiS3 with n-butyllithium but also by solid state reaction at high temperature between TiS2, Li2S and Ti. Then, LixTiOySz thin films were sputtered by magnetron effect radio-frequency sputtering from targets made of lithiated materials previously synthesized. The chemical composition of those films depends on the target one and allows obtaining thin films with different lithium and sulfur contents. In contrast, they are all amorphous, dense and they don’t have a morphological structuration. Finally, electrochemical characterizations of thin films, both in liquid and solid electrolyte, have highlighted a correlation between their chemical composition and their electrochemical behavior. Taken as a whole, LixTiOySz thin films are powerful, suitable with reflowing process and thus very interesting for the application.