<p>Electropolishing is a commonly used method of mitigating surface roughness and yielding a polished appearance. One of the first described and most studied of electropolishing systems is the anodization of copper in phosphoric acid. Under normal conditions this reduces copper surface roughness substantially; however deviating from optimal electropolishing conditions can promote the development of semi-ordered surface roughness. Anodizing copper substrates in 98-100% H₃PO₄ solutions generated feature heights ranging from 0.5 - 2µm and surface area increases in excess of 30% were obtained. The samples demonstrated a macroscopic optical dullness characteristic of this type of surface roughening. Investigations as to their applicability in surface enhanced Raman spectroscopy and electron field emission were conducted. And while their formation mechanism is still speculated on, it is believed that oxygen evolution and subsequent bubble formation plays a key role. Electrochemical and microscopic imaging techniques were the primary methodologies used to probe the optical dulling phenomenon. With data obtained from experiments utilizing these techniques and others a qualitative mechanism is proposed.</p> / Master of Science (MSc)

Made available in DSpace on 2017-07-24T19:22:00Z (GMT). No. of bitstreams: 1 Andres Felipe M Cardenas.pdf: 5280325 bytes, checksum: 04a1911a6a06b35dcfc2a254330c8113 (MD5) Previous issue date: 2016-05-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This study evaluated the effect of application the different pHs (0.5, 1 and 2) of meta-phosphoric acid 40% (MPA) with ortho-phosphoric acid 37% (OPA) in different application times with three laboratory studies in vitro. For all experiments, the teeth were distributed into 12 experimental conditions according to the combination of independent variables: acid [37% orthophosphoric acid (OPA), 40% metaphosphoric acid (MPA) pH - 0.5, 1 and 2] and application time [7, 15 and 30 seconds]. For experiment 1, the acids were applied on 72 human molars for microtensile bond strength (μTBS), and nanoleakage (NL). After acid conditioning the adhesive system was applied (Ambar) and restoration in composite resin was performed. Then, the teeth were sectioned to obtain specimens and tested immediately. The Etching Pattern (PC) was evaluated after acid application in dentin. For experiment 2, 93 human molars were used. After acid application in dentin, the adhesive system was applied and composite resin restoration was made. They were then sectioned, half sticks were tested immediately and the other half after 6 months of storage in water for μTBS and NL analysis. The analysis of chemical composition was performed by micro-Raman spectrometry. For experiment 3, 60 human molars were distributed according to the similar independent variables as the experiment 1 and 2. The enamel surfaces were stored in water (37 °C / 24 h) and tested for (μSBS). The PC and qualitative analysis composition of chemical enamel by micro-Raman test was evaluated. For the experiment 1 and 3, acid vs time of application the μTBS and NL data were submitted to 2-way ANOVA and Tukey's test (α = 0.05). For the experiment 2, acid vs application time vs storage time the μTBS data and NL were submitted to 3-way ANOVA and Tukey's test (α = 0.05). For experiment 1, MPA pH 0.5 showed μTBS similar to OPA, independent of the application time (p> 0.05) and statistically higher NL was observed for OPA compared with MPA (p <0, 03). For experiment 2, a significant decrease μTBS value was observed only OPA after 6 months (p = 0.001) and higher values of NL were found when compared to MPA (p = 0.003). For the experiment 3, OPA and MPA pH 0.5 produced statistically higher μSBS when compared to MPA pH 1 and 2 independent of the application times (p <0.001). The MPA acid is an alternative agent for the simultaneous conditioning of enamel and dentin, increasing the μTBS, reducing the NL immediate and after 6 months of storage when compared to the conventional ortho-phosphoric acid. The sum of the properties evaluated, MPA pH 0.5 showed high μSBS, showing be promissory. / O objetivo desse trabalho foi avaliar o efeito de diferentes pHs (0,5, 1 e 2) do ácido metafosfórico 40% (AMF) com o ácido ortofosfórico 37% (AOF) sob diferentes tempos de aplicação por meio de três estudos laboratoriais in vitro. Em cada estudo, os dentes foram distribuídos aleatoriamente em 12 condições de acordo com a combinação das variáveis independentes: Ácido [ácido ortofosfórico a 37% (AOF), ácido metafosfórico a 40% (AMF) pH - 0,5, 1 e 2] e tempos de aplicação [7, 15 e 30 s]. Para o experimento 1, os ácidos foram utilizadas e aplicados sobre 72 molares para resistência de união (RU) e nanoinfiltração (NI). Após condicionamento ácido aplicou-se o sistema adesivo (Ambar) e realizou-se a restauração em resina composta (Opallis). Depois de 24 h foram seccionados e testados. O padrão de condicionamento (PC) foi avaliado após aplicação dos ácidos em dentina. Para o experimento 2, foram utilizados 93 molares, após aplicação dos ácidos em dentina, aplicou-se o sistema adesivo e a restauração em resina composta. Logo após, foram seccionados e metade dos palitos foram testados imediatamente e a outra metade após 6 meses de armazenamento em água para análise da RU e NI. A análise da composição química foi realizada por espectroscopia micro-Raman. Para o experimento 3, 60 molares foram utilizados e distribuídos em função das variáveis já citadas. As superfícies de esmaltes foram armazenadas em água (37 °C / 24 h) e testadas para resistência de união no esmalte por microcisalhamento. O PC e análise de composição da química qualitativa do esmalte por teste micro-Raman foram avaliados. Para o experimento 1 e 3, ácido vs tempo de aplicação os dados de RU e NI foram submetidos a ANOVA 2 fatores e teste de Tukey (α = 0,05). Para o experimento 2, ácido vs tempos de aplicação vs tempo de armazenamento os dados de RU e NI foram submetidos a ANOVA 3 fatores e teste de Tukey (α = 0,05). Para o experimento 1, o AMF pH 0,5 mostrou RU significativamente semelhante ao AOF, independentemente do tempo de aplicação (p>0,05) e uma NI estatisticamente mais elevada foi observada para AOF em comparação com AMF, (p<0,03). Para o experimento 2, diminuições significativas nos valores de RU foram observados somente para AOF após 6 meses (p = 0,001) e valores de NI mais elevados foram encontrados quando comparado com AMF (p = 0,003). Para o experimento 3, o AOF e AMF pH 0,5 produziram valores RU estatisticamente mais elevados, quando comparados com AMF pH 1 e 2 independentemente dos tempos de aplicação (p<0,001). O AMF é um ácido que pode ser utilizado simultaneamente em esmalte e dentina, demonstrando uma alta RU, diminuição da nanoinfiltração imediata e após 6 meses de armazenamento quando comparado com o AOF. No somatório das propriedades avaliadas, o pH 0,5 apresentou alta RU em esmalte em relação ao AOF, mostrando-se promissor.

This thesis concerns the development of the first BINOL phosphoric acid (BPA) catalysed enantioselective N-acyliminium cyclisation reactions and their incorporation into domino sequences that allow for the construction of architecturally complex enantioenriched polycycles in a single step from easily accessible starting materials. More specifically, this thesis deals with the discovery of a BPA-catalysed enantioselective N-acyliminium cyclisation cascade of enol lactones and tryptamines. Its extension to a doubly catalysed process involving gold(I) to cycloisomerise alkynoic acids and a BPA to effect the enantioselective N-acyliminium cyclisation is presented. In addition, the exploitation of this method in highly diastereo- and enantioselective N-acyliminium cyclisations of oxoacids and tryptamines and in a site isolated base-catalysed Michael addition / acid-catalysed N-acyliminium cyclisation cascade is described. A study on the proposed mechanism and model for the origin of enantioselectivity is discussed, based on experimental data and a computational study. As a separate part of our programme, the development of a new class of stronger Brønsted acids, chiral benzenesulphonic acids, is described. The optimisation of the synthetic routes as well as the synthesis of a library of acids is presented and their assessment in precedented reactions is discussed.

The research presented in this thesis was carried out as part of a collaboration between the groups of Dr Tanja van Mourik at the School of Chemistry, University of St Andrews and Professor Jonathan Tennyson at the Department of Physics and Astronomy at University College London. This thesis presents State-Averaged Complete Active Space Self Consistent Field (SA-CASSCF) calculations on nucleic acid bases, deoxyribose and phosphoric acid H₃PO₄). In the case of uracil, for comparison, Multireference Configuration Interaction calculations were also performed. The SA-CASSCF orbitals were subsequently used in R-matrix electron scattering calculations using the close-coupling model. Of major importance for obtaining accurate SA-CASSCF results is the choice of the active space and the number of calculated states. Properties such as the electronic energy, number of configurations, excitation energy and dipole moment were considered in the choice of active space. Electron-collision calculations were performed on two of the most stable isomers of phosphoric acid, a weakly dipolar form with all OH groups pointing up and a strongly dipolar form where one OH group points down. A broad shape resonance at about 7 eV was found for both isomers. Ten-state close-coupling calculations suggest the presence of narrow, Feshbach resonances in a similar energy region. Elastic and electronically inelastic cross sections were calculated for both isomers. The R-matrix calculations on uracil were done by the group from UCL. R-matrix calculations are currently being done on guanine. Scattering calculations on the other DNA bases will be performed in the near future.

Thesis (M. Tech. Engineering: Electrical)--Vaal University of Technology / Fuel cells are electrochemical devices that convert chemical energy of a fuel cell into electricity at high efficiency without combustion. They are viewed as viable power sources for many applications including automobiles, distributed power generation and portable electronics. This dissertation presents the design and development of a phosphoric acid fuel cell. It deals with the experimental studies on phosphoric acid fuel cells and possible integration in replacing the conventional sources of electrical energy in stand-by power supply systems, particularly for use in the telecommunications industry. The design of a DC-DC converter system is also incorporated into the system. The first objective was to establish performance parameters and past studies on phosphoric acid fuel cells and this research revealed that parameters that affect the system's performance include: reactant gas pressures, mass flow rates as well as the operating temperature. Mathematical models in the literature were studied and verified against the simulation models acquired. The second objective was to design and assemble a single cell in order to analyze the cell's performances as well as the operating parameters in order to obtain a model for predicting and simulating the performance of larger fuel cell stacks. The next objective was to analyse from a set of design equations and construct a small DC-DC converter. The converter was used to boost a small fuel cell voltage and regulate it at a higher voltage level. Finally, the performance characteristics of the developed fuel cell, mathematical and simulation models were evaluated and compared. Simulation results for the models and the converter showing a regulated output voltage are presented. Some recommendations for improved system performance and for further studies are suggested.

Sabe-se que o flúor causa alterações químicas e celulares no osso, dependendo da dosagem e do tempo de exposição a esse elemento. Já foi demonstrado que alterações clínicas importantes, como a osteoporose, osteopetrose e esclerose óssea, podem ser geradas pela ingestão de flúor. Sabe-se que o flúor pode guiar os osteoblastos ao crescimento, sob doses e tempos de exposição específicos. A sensibilidade dos tecidos mineralizados ao fluoreto responde a mecanismos genéticos inerentes a cada população. Dentro de uma mesma espécie, diferentes linhagens apresentam um comportamento distinto frente a esse fármaco. Durante várias décadas, os estudos com fluoretos resumiram-se ao fluoreto de sódio, amplamente utilizado na prevenção das cáries dentárias. Recentemente, outras fontes de fluoretos como TiF4 e SnF2 têm sido buscadas, com intuito de potencializar as vantagens desse elemento. Porém não existem estudos ainda sobre o efeito do AlF3 sobre o tecido ósseo até a presente data. Desse modo, achamos oportuno investigar seu papel, quando administrado a células ósseas e para tal, investigamos a viabilidade e padrão de atividade das fosfatases desse sal (AlF3) quando administrado às células da linhagem pré-osteblástica MC3T3, em comparação ao NaF. Além disso, sabendo que diferentes células apresentam comportamento distinto ao tratamento com fluoretos, estudamos o papel do NaF quando administrado a duas linhagens celulares de camundongos com densidades ósseas distintas e com diferentes susceptibilidades ao fluoreto: C3H/HeJ e C57BL/6J (C3H e C57, alta e baixa densidades ósseas, respectivamente). As células também foram avaliadas quanto à viabilidade celular e ao perfil das fosfatases. Todos os resultados foram submetidos à Análise de Variância a três critérios e nos permitiu identificar que entre os sais de fluoreto, apenas o NaF promoveu alterações na viabilidade celular das células MC3T3. O AlF3 não exerceu influência na atividade da fosfatase alcalina quando consideramos as células pré-osteoblásticas, no entanto, o efeito desse fluoreto sobre a atividade das fosfatases ácidas totais e ácida resistente ao tartarato ocorre de modo dicotômico. Quando consideramos uma população celular heterogênea, coletada de calvária, como foi o caso das linhagens C3H e C57, verificamos que o NaF interferiu tanto sobre a proliferação, quanto a atividade das fosfatases de modo bastante distinto para ambas linhagens celulares. Assim concluimos que o NaF é capaz de exercer efeitos mais diversificados em diferentes tipos celulares, alterando viabilidade celular e atividade de enzimas; em contrapartida, o AlF3 produz efeitos mais especifícos e delimitados em pré-osteoblastos. / It is well known that fluoride causes chemical and cellular alteration on bone tissue, depending on the dosage and time of exposure to this element. Several studies have been conducted to show that some bone diseases, such as osteoporosis, osteopetrosis and esclerosis, can occur as a consequence of the excessive fluoride uptake. Fluoride can lead osteoblast to proliferate, under certain conditions as time and dosage. The same way, excessive dosages of fluoride can alter protein activity in osteoblasts, by changing the expression of retated genes. Sensitivity of mineralized tissues to fluoride depends on a genetic background inherent to each population. Within the same specie, different lineages present distint behavior to the ingestion of this íon. Over several decades, many researches focused on the study of NaF as the only source of fluoride, once it is wide spread used to the prevention of dental caries. More recently, different sources of fluoride have been assessed, like TiF4 e SnF2</sub, with the main aim to enhance biochemical and physical benefits of this element. Despite of this, none of these formulations have been tested to evaluate their effect on the bone tissue. Thus, we believe it is advisable to investigate viability and phosphatases activities of pre-osteoblast MC3T3 cells treated with Aluminium fluoride, compared to NaF treatments. Besides this, facing the knowledge that different cell lines have distinct behavior when treated with fluoride, we used two inbred strains of mice with distint mineral bone densities, C3H/HeJ (C3H, high bone density) and C57BL/6J (C57, low bone density), to assess the viability and phosphatases activities after the treatment with NaF. Overall results were tested by 3 way- Anova. AlF3 did not exibit influence over on alkaline phosphatase when pre-osteoblast cells are considered, but the effect of this fluoride salt on the activity of total and tartarate resistant acid phosphatases ocurrs on a dicotomic way. When we consider a mixed cell population, collected from calvária as for the C3H and C57 assays, NaF did interfered as with the proliferation rate as phosphatase activities on a very distinct fashion between the two lineages. Thus, it is possible to conclude that NaF is able to exert variable effects in different cell types and enzyme activities; on the other hand, AlF3 effects are more specific and surrounded in pre-osteblastic cells.

Asymmetric synthesis and catalysis is one of the leading research areas in chemistry society, for its versatility and efficiency in obtaining chiral molecules that found the vast majority in natural active compounds and synthetic drugs. Developing asymmetric catalytic methodology is at the frontier in both industrial and academic research laboratories. Enantioselective organocatalysis has emerged as a powerful synthetic tool that is complementary to metal-catalyzed transformations. The development of chiral phosphoric acid and metal phosphate as catalysts has been a breakthrough in recent years. Chiral phosphoric acids have been shown to be powerful catalysts in many organic transformations. Moreover, chiral metal phosphates, which formed by simply replacing the proton in phosphoric acid with metals, have introduced new catalytic activations and broaden the scope of phosphoric acids. This thesis details new highly enantioselective chiral phosphoric acid-catalyzed Pinacol rearrangement and robust alkaline phosphates catalytic system, which utilizes novel carbonyl activation. The Pinacol rearrangement has long been known to be difficult to control in terms of regioselectivity and stereoselectivity. The initial studies found that indolyl-diol compounds can be treated with chiral phosphoric acids to afford the Pinacol rearrangement with high regio- and enantioselectivity. Over 16 chiral phosphoric acids were screened, and it was found an H8-BINOL-phosphoric acid variant with 1-naphthyl groups at 3 and 3' position was the excellent catalyst. This asymmetric transformation is tolerant toward variety of substituents both on the indole ring and migrating groups. During the study, it was found that different ways to generate the catalyst had critical effect on this catalytic transformation. Only those phosphoric acids washed with HCl after column chromatography afforded the rearrangement products with high enantioselectivity. And those without treating with HCl were found contaminated by alkaline metals. These "contamination" catalysts were also found active with carbonyl activations. A highly enantioselective catalytic hetero-Diels-Alder reaction of alpha-keto esters has been developed with chiral alkaline metal phosphates. A calcium 1-naphthyl-BINOL phosphate was found to be the optimum catalyst. A large range of alpha-keto esters as well as isatins can be applied in this alkaline phosphates catalytic system with high efficiency and selectivity. The structure of the catalyst is detailed for the first time by X-ray crystal structure analysis. A proposed Transition state model is provided based on the catalyst crystal structure and Raman spectroscopy analysis. This methodology was further developed with an asymmetric Mukaiyama-Michael addition of beta,gamma-unsaturated alpha-keto ester. The best catalyst was found to be a magnesium chiral phosphate. And the transformation was found capable of tolerating a wide variety of beta,gamma-unsaturated alpha-keto esters.

In this study production and characterization of activated carbon from an agricultural waste, pistachio-nut shells, was investigated. To determine optimum production conditions by chemical activation method, effect of tempreature (300, 500, 700 and 900 oC) and effect of impregnation ratio (1:1, 2:1 and 3:1 as activation agent:sample) were investigated by applying two different methods (raw material activation and char activation) and with two different activation agents (phosphoric acid and potassium hydroxide). To produce activated carbon, all the impregnated samples were heated to the final activation temperature under a continuous nitrogen flow (100 cm3/min) and at a heating rate of 10 oC/min and were held at that temperature for 1 hour. Pore structures of activated carbons were determined by N2 adsorption and micro-mesopore analysis was made by &ldquo / Non-local Density Functional Theory&rdquo / and &ldquo / Monte Carlo Simulation&rdquo / method (NLDFT-Monte Carlo Simulation Method). BET surface areas of produced activated carbons were found from N2 adsorption data in the relative pressure range of 0.01 to 0.15. BET surface areas of phosphoric acid activated carbons by raw material activation method were found between 880 and 1640 m2/g. The highest value of the BET surface area was obtained in the case of the activated carbon which was produced with an impregnation ratio of 3/1 (g H3PO4/g raw material), at an activation temperature of 500 oC. The repeatibility was also investigated on phosphoric acid activated carbons which were produced with conventional raw matererial activation method. Results showed that, both the BET surface area values and pore size distributions were consistent among themselves. On the other hand char activation experiments with phosphoric acid produced activated carbons having lower BET surface areas than the ones obtained with raw material activation method by creating mesoporous structure. When the same char activation method was tried with potassium hydroxide, it was concluded that elevated temperatures could help in producing activated carbons with high BET surface areas by creating microporous structure. Results also showed that properties of activated carbon such as ash content, slurry pH value, true density, elemental composition, methylene blue number and surface morphology were strongly affected by both production conditions and production method, as pore structure was affected considerably.

Die Nutzung von Kraftstoffen auf der Basis von Biodiesel erlaubt es, konventionelle, etablierte Antriebstechniken mit Nachhaltigkeit zu kombinieren. Daher kann in den nächsten Jahren mit einer weiteren weltweiten Steigerung der Biodieselproduktion gerechnet werden. Damit verbunden ist jedoch auch ein Anstieg der anfallenden Menge an Glycerol, das bei der Herstellung von Biodiesel als Koppelprodukt entsteht. Da traditionelle Märkte für Glycerol kaum mehr Wachstum zeigen, müssen neue Wege zur effizienten Verwertung von Glycerol gefunden werden. Die vorliegende Arbeit beschäftigt sich mit der heterogen-katalysierten Umsetzung von Glycerol zu Acrolein. Unter Verwendung von ZSM-5-Katalysatorproben mit unterschiedlichem Si/Al-Verhältnis und phosphorsäure-modifizierten Katalysatorproben konnte die Existenz von Synergieeffekten zwischen den texturellen, strukturellen und aciden Eigenschaften in der heterogen-katalysierten Glyceroldehydratisierung zu Gunsten der Acroleinselektivität eindeutig nachgewiesen werden. Eine selektive Umsetzung von Glycerol zu Acrolein wird daher an solchen Katalysatorproben ermöglicht, die ausgewogene texturelle, strukturelle und acide Eigenschaften aufweisen.

Magister Scientiae - MSc (Chemistry) / The anode catalyst is one of the important parts of the direct alcohol fuel cell (DAFC); it is responsible for the alcohol oxidation reaction (AOR) takes place at the anode side. Pd has been reported to have good alcohol oxidation reactions and good stability in alkaline solution. Better stability and activity has been reported for Pd alloyed catalysts when compared to Pd. Choosing a suitable alcohol also has an effect on the activity and stability of the catalyst. This study investigates the best catalyst with better AOR and the best stability and also looks at the better alcohol to use between glycerol and ethanol for the five in-house catalysts (20% Pd, PdNi, PdNiO, PdMn3O4 and PdMn3O4NiO on multi walled carbon nanotubes) using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectrometry (EIS) and chronoamperometry. HR-TEM and XRD techniques were used to determine the particle size and average particle size, respectively while EDS used to determine elemental composition and ICP was used to determine catalyst loading. It was observed from LSV that PdNiO was the most active catalyst for both ethanol and glycerol oxidation, and it was the most stable in ethanol while PdMn3O4 proved to be the most stable catalyst in glycerol observed using chronoamperometry. The best alcohol in this study was reported to be glycerol having given the highest current densities for all the inhouse catalysts compared to ethanol observed using LSV. From XRD and HR-TEM studies, particle sizes were in the range of 0.97 and 2.69 nm for XRD 3.44 and 7.20 nm for HR-TEM with a little agglomeration for PdMn3O4 and PdMn3O4NiO.