M.Sc. / The 11B/10B stable isotope ratio in wine- and provenance soil samples of four South African wine regions was determined by means of quadrupole inductively coupled plasma mass spectrometry (ICP-MS). The data obtained was combined with multi-element results for the same samples. Discriminant analysis and ANOVA statistics were utilized to create a footprint of wines compared to their provenance soil. The results showed that the stable boron isotope ratio was a distinguishable characteristic in wine and soil samples for the Stellenbosch, Robertson, Swartland, and Walker Bay wine regions. The potential improvement of precision and accuracy was investigated specifically for ICP-QMS (quadrupole mass spectrometry) analysis of boron isotope ratios. Sample preparation methods for the matrices used in this work were developed and applied. The influence of the matrix components was investigated. Ion exchange separation procedures were developed for the separation of total B from the wine and soil matrices. Results were treated mathematically to minimize mass bias effects. It was found that combined matrix effects and TDS (total dissolved solids) deposition did have a pronounced effect on the 11B/10B isotope ratios of the samples. The possibility of boron isotope fractionation was investigated in vine plants. Hydroponic experiments were set up with test plants of two cultivars. A 10B enriched nutrient solution or growth solution with natural 11B/10B ratio was supplied to the plants during alternating periods of 5 weeks each. New growth leaves were harvested once every week during each of these time periods. All samples were carefully prepared and analyzed to determine the relationship of the 11B/10B ratio in the leaves compared to that of the supplied nutrient solution. It was observed that the 11B/10B isotope ratio of the growth solution had an influence on the 11B/10B stable isotope ratio in new growth leaves of vine plants.

Cette thèse présente la réactivité de diènes polyfonctionnalisés incorporant un atome de bore (diènes borylés) en présence de composés de type nitroso. La première partie est une étude de la réactivité des diènes borylés en présence de dérivés arylnitroso. Le produit formé ainsi que l'efficacité de la réaction est dépendant de la substitution sur l'atome de bore ainsi que du solvant utilisé pour la réaction. Suivant les conditions employées, la formation de composés avec différentes structures; pyrroles, oxazines substitués par un atome de bore, ou nitrones a été obtenue. Une stratégie one-pot a ensuite été développée pour la synthèse d'oxazolines utilisant la formation des nitrones en tant qu'intermédiaire. Des investigations théoriques et pratiques concernant le mécanisme de la formation du pyrrole ont été réalisées. La séquence expliquant la synthèse de cette structure est basée sur la cascade suivante; cycloaddition régiosélective (Nitroso Diels-Alder)/réarrangement/élimination du borate. La formation des composés de type nitrone n'a pas été totalement explicité. Des recherches sont actuellement en cours dans le but d'obtenir plus de détails sur le mécanisme mis en jeu. La deuxième partie de l'étude est orientée sur la réactivité des diènes borylés en présence de dérivés carbonylnitroso. Au contraire des dérivés arylnitroso, la nature du composé carbonylnitroso joue un rôle majeur sur la réactivité. Si le même type de réactivité engendrant la formation de pyrroles et d'oxazines substitués par un atome de bore a été observé dans certains cas, l'utilisation d'un composé carbonylnitroso étant assez pauvre en électrons génère la formation du produit issu d'une réaction nitroso-ène. Ce produit, issu de la réaction nitrosoène, a été utilisé comme intermédiaire clé pour la synthèse de différents produits polycycliques. Une séquence one-pot, multicomposants, Diels-Alder/allylboration a été optimisée donnant différentes structures suivant le dienophile et l'aldehyde employé. Dans le but de diversifier la chimie du produit résultant de la réaction nitroso-ène, une autre séquence a été mise au point utilisant la synthèse des pyrroles. Une voie multi-étape a permis la synthèse de nouvelles structures bicycliques incorporant une oxazine et un pyrrole. / This thesis presents the reactivity of dienylboronated compounds towards arylnitroso and carbonylnitroso derivatives and its use in the synthesis of heterocyclic and polycyclics compounds. The first study focused on the reactivity of dienylboronate compounds with arylnitroso derivatives resulting in pyrrole or furan products. The outcome and efficiency of the reaction is related to the boron on the dienyl moiety and the solvent used. Using the certain conditions, pyrroles, boronated MIDA ester oxazines or nitrones could be obtained. A one-pot strategy was then applied to synthesise oxazoline derivatives using nitrones as an intermediate. Theoretical, as well as experimental, work has supported that the formation of the pyrrole was obtained by a regioselective nitroso Diels-Alder reaction/rearrangement/borate elimination cascade process. Details on the nitrone formation have not been clarified, but further investigations are on-going. Secondly, attention was focused on the reactivity of dienylboronate compounds with carbonylnitroso derivatives. Contrary to the arylnitroso species, the nature of the carbonylnitroso had a dramatic impact on reactivity. On the one hand, similar reactivity towards the formation of pyrroles and boronated MIDA ester oxazines was observed, however, by employing a higher electron-deficient carbonylnitroso species, the product resulting from a nitroso-ene reaction was obtained. Ene-product was used as the key intermediate for the synthesis of different polycyclic compounds. A multicomponent, one-pot, Diels-Alder/allylboration procedure was optimised to yield various structures depending on the nature of the dienophile and the aldehyde. To diversify the chemistry of the ene-product another sequence was designed using the pyrrole synthesis. A multi-step pathway was optimised to afford novel fused bicylic oxazine-pyrrole products.

Hydroxyapatite (HA) has received wide attention in orthopedics, due to its biocompatibility and osseointegration ability. Despite these advantages, the brittle nature and low fracture toughness of HA often results in rapid wear and premature fracture of implant. Hence, there is a need to improve the fracture toughness and wear resistance of HA without compromising its biocompatibility. The aim of the current research is to explore the potential of nanotubes as reinforcement to HA for orthopedic implants. HA- 4 wt.% carbon nanotube (CNT) composites and coatings are synthesized by spark plasma sintering and plasma spraying respectively, and investigated for their mechanical, tribological and biological behavior. CNT reinforcement improves the fracture toughness (>90%) and wear resistance (>66%) of HA for coating and free standing composites. CNTs have demonstrated a positive influence on the proliferation, differentiation and matrix mineralization activities of osteoblasts, during in-vitro biocompatibility studies. In-vivo exposure of HA-CNT coated titanium implant in animal model (rat) shows excellent histocompatibility and neobone integration on the implant surface. The improved osseointegration due to presence of CNTs in HA is quantified by the adhesion strength measurement of single osteoblast using nano-scratch technique. Considering the ongoing debate about cytotoxicity of CNTs in the literature, the present study also suggests boron nitride nanotube (BNNT) as an alternative reinforcement. BNNT with the similar elastic modulus and strength as CNT, were added to HA. The resulting composite having 4 wt.% BNNTs improved the fracture toughness (~85%) and wear resistance (~75%) of HA in the similar range as HA-CNT composites. BNNTs were found to be non-cytotoxic for osteoblasts and macrophages. In-vitro evaluation shows positive role of BNNT in osteoblast proliferation and viability. Apatite formability of BNNT surface in ~4 days establishes its osseointegration ability.

The results of a solid-state 11B NMR study of a series of boronic acids, boronic esters, and boronic acid catechol cyclic esters with aromatic substituents are reported in this thesis. Boron-11 electric field gradient (EFG) and chemical shift (CS) tensors obtained from analyses of spectra acquired in magnetic fields of 9.4 T and 21.1 T are demonstrated to be useful for gaining insight into the molecular and electronic structure about the boron nucleus. It can be concluded that when adequate electronic variation is present in the compounds being studied, Ω is generally the most characteristic boron NMR parameter of the molecular and electronic environment for boronic acids and esters. Importantly, these data are only reliably accessible in ultrahigh magnetic fields. The experimental span values result from a delicate interplay of several competing factors, including hydrogen bonding, the value of the dihedral angle, and the type of aromatic ring system present.

As firearms continuously become more sophisticated, there have been commensurate efforts to optimize the ballistic performance of armours, with ceramic materials currently at the forefront of such studies. These efforts have focused on improving processing and microstructural design with reinforcements using dispersion particles, carbon nanotubes (CNT) and boron nitride nanotubes (BNNT). In most studies, ballistic testing has been used to identify parameters affecting the performance. The research documented here focuses on: (1) the investigation of two commercial ceramics, namely silicon carbide (SiC) and zirconia toughened alumina (ZTA). The primary material properties evaluated for the characterization included: hardness, fracture toughness, flexural strength and Young’s modulus. Other properties investigated included the microstructure, porosity/density, and mode of failure or fracture. (2) Ballistic depth of penetration (DOP) testing for six candidate ceramic armour systems including three monolithic ceramics (Al2O3, SiC and B4C) and three nanotube toughened ceramic composites (Al2O3-BNNT, Al2O3-single walled CNT and SiC-BNNT). SiC showed a hardness of 2413 HV, which is far beyond the requirements for armour ceramic. In contrast, ZTA barely met the hardness requirement of 1500 HV, but showed improved toughness of 4.90 MPa m1/2 beyond values reported for monolithic alumina. SiC and ZTA showed that microstructural design improves fracture toughness but processing introduces defects that can substantially reduce other armour related properties such as the strength. The results of the Charpy and drop tower impact tests are in agreement with indentation fracture toughness results suggesting a great degree of reliability of this cost efficient method. The addition of nanotubes produced an increase in toughness and a decrease in hardness in the ceramics, which resulted in an overall drop in performance during ballistic depth of penetration (DOP) tests. A microstructure-quasi-static mechanical properties-ballistic performance relationship was established which led to the development of a novel ballistic performance index and a new DOP model. The proposed ballistic performance index yielded a ranking, which agrees better with experimental observations than the currently published indices. The developed semi-empirical model suggests that the ballistic performance of ceramics is improved with increased fracture toughness, reduced flaw size and higher density.

In the past few years, led by graphene, a large variety of two dimensional (2D) materials have been discovered to exhibit astonishing properties. By assembling 2D materials with different designs, we are able to construct novel artificial van der Waals (vdW) heterostructures to explore new fundamental physics and potential applications for future technology. This thesis describes several novel vdW heterostructures and their fundamental properties. At the beginning, the basic properties of some 2D materials and assembled vdW heterostructures are introduced, together with the fabrication procedure and transport measurement setups. Then the graphene based capacitors on hBN (hexagonal Boron Nitride) substrate are studied, where quantum capacitance measurements are applied to determine the density of states and many body effects. Meanwhile, quantum capacitance measurement is also used to search for alternative substrates to hBN which allow graphene to exhibit micrometer-scale ballistic transport. We found that graphene placed on top of MoS2 and TaS2 show comparable mobilities up to 60,000cm2/Vs. After that, the graphene/hBN superlattices are studied. With a Hall bar structure based on the superlattices, we find that new Dirac minibands appear away from the main Dirac cone with pronounced peaks in the resistivity and are accompanied by reversal of the Hall effects. With the capacitive structure based on the superlattices, quantum capacitance measurement is used to directly probe the density states in the graphene/hBN superlattices, and we observe a clear replica spectrum, the Hofstadter-butterfly fan diagram, together with the suppression of quantum Hall Ferromagnetism. In the final part, we report on the existence of the valley current in the graphene/hBN superlattice structure. The topological current originating from graphene’s two valleys flows in opposite directions due to the broken inversion symmetry in the graphene/hBN superlattice, meaning an open band gap in graphene.

Cubic boron nitride (cBN) synthesis has gained lot of interest during the past decade as it offers outstanding physical and chemical properties like high hardness, high wear resistance, and chemical inertness. Despite of their excellent properties, every application of cBN is hindered by high compressive stresses and poor adhesion. The cost of equipment is also high in almost all the techniques used so far. This thesis deals with the synthesis of cubic phase of boron nitride on Si (100) wafers using electron beam evaporator, a low cost equipment that is capable of depositing films with reduced stresses. Using this process, need of ion beam employed in ion beam assisted processes can be eliminated thus reducing the surface damage and enhancing the film adhesion. Four sets of samples have been deposited by varying substrate temperature and the deposition time. scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) techniques have been used to determine the structure and composition of the films deposited. X-ray diffraction (XRD) was performed on one of the samples to determine the thickness of the film deposited for the given deposition rate. Several samples showed dendrites being formed as a stage of film formation. It was found that deposition at substrate temperature of 400oC and for a period of one hour yielded high quality cubic boron nitride films.

The SRV test rig was used to evaluate the friction and wear properties of a lubricant in a laboratory setup. Normally, the coefficient of friction and the amount of wear that occurred are measured while the wear scar surface is also evaluated. Special attention was paid to factors that affect the repeatability. The test fluid was subjected to a friction and wear test on the SRV test rig in order to determine what factors affect the repeatability of the coefficient of friction, the amount of wear that occurred and the wear scar appearance. The test fluid used was based on rapeseed oil and white mineral oil. The fluid also contained an extreme pressure additive in the form of sulphurised ester. This was also compared for the same test fluid with dispersed hexagonal-boron nitride (h-BN) nanoparticles. The standard test method as described by ASTM D 6425, was used as test method. Instead of the standard temperature, the block temperature was increased to 100 °C in order to simulate harsher operating environments. The load was set at 200 N It was found that:  The rapid load increase from 50 to 200 N at the end of the running-in period (as described in the standard test method) caused poor repeatability. The test was modified with a more gradual load application for the duration of the running-in period (30 N/min), which resulted in improvement in the repeatability of the tests conducted.  The moisture content in the atmosphere also affected the repeatability of the friction and wear tests. This was most likely due to the formation of a corrosion layer that involves water and by keeping the relative humidity constant, a further improvement in the repeatability was observed. The addition of the h-BN nanoparticles resulted in an improvement of the repeatability of the coefficient of friction (COF), wear scar surface (WSS) and wear scar volume (WSV), since the wear scar surfaces indicated that the particles remove the corrosion layers. This could have led to more consistent wear surfaces for the duration of the test.  The particles also influenced the corrosion layer formation. For both fluids, Raman spectroscopy indicated that greigite (Fe3S4) and goethite (α-FeOOH) were found on the surface, while additional corrosion products were found on the wear scar surface for the test fluid with dispersed particles. These compounds were melanterite (FeSO4.7H2O) and rozenite (FeSO4.4H2O). All these corrosion products were most likely formed due to the reaction of iron from the specimens with sulphurised esters in the test fluid. / Dissertation (MEng)--University of Pretoria, 2015. / tm2015 / Chemical Engineering / MEng / Unrestricted

Made available in DSpace on 2016-01-26T18:56:23Z (GMT). No. of bitstreams: 1 Dissertacao.pdf: 308272 bytes, checksum: 7df0ae05e2e184b04647e81dec8c55af (MD5) Previous issue date: 2010-08-10 / Expressive part of the peanut (Arachis hypogaea) in São Paulo State has cultivated for rotation in condemned areas of sugar cane that need to be reformed, and those areas frequently have presented low micronutrients levels and low basis saturation in soil. The objective of this work was to quantify the production and the yield components of the peanut crop fertilized with lime and gypsum applied in sowing combined with boron manure by leaf spray. The experiment was carried out from December 2007 to April 2008, on a dystroferric Hapludox, medium texture, in Guararapes, SP, Brazil. A randomized complete blocks design, with four replicates, and split plots, was used. The plots were composed by absence of Ca font (control), dolomite limestone with 0,5, 1 and 2 Mg ha-1 and gypsum with 0,5, 1 and 2 Mg ha-1, applied on sowing time of the peanut crop. The subplots were composed by levels boron with 0, 0,5, 1 and 2 kg ha-1 applied by leaf spray in initial flowering stage of the plants. The peanut crop presented expressive response to boron manuring, and the largest grains and pods productivities were obtain with 1 kg ha-1 of B. Fertilizations only Ca fonts applied in peanut sowing didn´t increase productivity and yield components. Combinations between Ca fonts applied in crop sowing and boron manuring by leaf spray favored the net yield of grains after peel off. / Grande parte do amendoim do Estado de São Paulo é cultivada em áreas de reforma de canavial, nas quais é comum o solo apresentar baixos teores de micronutrientes e de saturação por bases. O objetivo do trabalho foi avaliar a produtividade e rendimento do amendoim fertilizado com calcário e gesso na instalação da lavoura, combinados com adubação boratada foliar, em área de renovação de canavial. O experimento foi conduzido de dezembro de 2007 a abril de 2008 em um Latossolo vermelho distroférrico de textura média, em Guararapes-SP. O delineamento experimental foi em blocos completos e parcelas sub-divididas, em que nas parcelas foram a ausência de fonte de Ca na instalação da lavoura, 0,5, 1,0 e 2,0 t ha-1 de calcário dolomítico, e 0,5, 1,0 e 2,0 t ha-1 de gesso agrícola, e nas sub-parcelas 0, 0,5, 1 e 2 kg ha-1 de B foliar. O amendoim foi responsivo à adubação boratada, sendo as maiores produtividades de vagens e de grãos, assim como o máximo rendimento de grãos, alcançados com 1 kg ha-1 de B. A fertilização somente com fonte de Ca na semeadura do amendoim não incrementou a produção e rendimento de grãos. A combinação entre fontes de Ca na instalação da cultura e B foliar favorece o rendimento de grãos do amendoim após o descascamento.

Made available in DSpace on 2016-01-26T18:56:29Z (GMT). No. of bitstreams: 1 Wellington Eduardo Xavier Guerra.pdf: 517213 bytes, checksum: e4312a4c04b742d7d293d503e16d7494 (MD5) Previous issue date: 2013-12-13 / In the western region of São Paulo state the cultivation of brassica plants it is commonly indicated B application at planting, because of the lack of information about this element in its type of soil. The objective of this study was to observe the reaction of B dosages in the culture of canola (Brassica napus L. var. oleifera) in Red Sandy Latosol in the Western São Paulo state. The experimental design was a completely randomized type, under a factorial 2 x 4 with 4 replications (two cultivars and four dosages of B). It was evaluated two different cultivars: Hyola 401 and Hyola 76. The concentration of Boron (0,0, 0,5, 1,0 and 2,0 kg B ha-1), was calculated by using boric acid - PA reagent, applied directly to the soil. The biometric parameters analyzed involved: plant height, stem diameter, shoot dry mass, root dry mass, number of branches, production of seeds per plant, seeds moisture content, 1000 grain weight, germination, seed oil content and accumulation of nutrients. All of them were subjected to the analysis of variance by F test, and comparison of means by Tukey test at 5% significance, and polynomial regression analysis through statistical programs. The results indicated that the culture of canola responded doses of B in the parameters of grain weight plant-1, root dry mass and oil percentage to grow Hyola 76. The Hyola 401 had the highest percentage of germination with 0,5 kg B ha-1. But Hyola 76 showed higher germination percentage than Hyola 401. Ratings among the cultivars Hyola 76 had a better performance in all biometric parameters regarding Hyola 401. / Na região oeste do estado de São Paulo para plantas do grupo das brássicas é indicada aplicação de B no plantio, em virtude da carência de informações sobre aplicação de B no solo. O objetivo do trabalho foi avaliar a resposta da cultura da canola (Brassica napus L. var. oleifera) à doses de B em Latossolo Vermelho Arenoso na região oeste paulista. O delineamento experimental adotado foi o delineamento inteiramente casualizados, em esquema fatorial 2 x 4 com 4 repetições (dois cultivares e quatro doses de B), avaliando dois cultivares, Hyola 401 e a Hyola 76. As doses de Boro em forma de ácido bórico P.A foram de (0,0, 0,5, 1,0 e 2,0 kg B ha-1) aplicados no solo. Os parâmetros biométricos analisados foi a altura da planta, diâmetro do caule, massa seca da parte aérea, massa seca da raiz, número de ramificações, massa de sementes por plantas, massa de mil grãos, germinação, teor de óleo e acúmulo de nutrientes. Os dados foram submetidos à análise de variância pelo teste F, comparação das médias pelo de Tukey a 5% de probabilidade e também á análise de regressão polimonial por meio de programa estatístico. Os resultados indicaram que a cultura da canola respondeu as doses de B nos parâmetros de massa de grão planta-1, massa seca da raíz e na porcentagem de óleo para o cultivar Hyola 76. A Hyola 401 apresentou a maior porcentagem de germinação com 0,5 kg B ha-1. Mas a Hyola 76 apresentou maior porcentagem de germinação que a Hyola 401. Nas avaliações entre os cultivares a Hyola 76 teve um melhor desempenho em todos os parâmetros biométricos em relação à Hyola 401.