The crystallization behavior of bisphenol-A polycarbonate (BAPC) was studied, focusing on the initial stage of crystallization and the secondary stage of crystallization. Bisphenol-A polycarbonate was the polymer chosen for this study because of its slow crystallization rate. With slow crystallization kinetics, the polymer morphology does not change when quenched below its glass transition temperature, enabling the study of different stages of crystallization through the frozen morphology. The study of the initial stages of crystallization pertained to crystallization times prior to the growth of detectable crystallinity. This study employed BAPC because of the long induction period, a direct result of the slow crystallization kinetics. During the induction period of polycarbonate crystallized at 190°C there was no evidence of polymer chain ordering that was seen in literature for other polymers. The length of the induction period determined by differential scanning calorimetry and wide-angle X-ray diffraction varied by over 6 hours because differential scanning calorimetry can detect a smaller amount of crystallinity than wide-angle X-ray diffraction. Signs of pre-ordering in the literature could be a result of experimental sensitivity. The study of the secondary crystallization dealt with the isothermal lamellar thickening of BAPC crystals during annealing, after crystallization for an extended period of time. Small-angle X-ray scattering and differential scanning calorimetry experiments were performed on bisphenol-A polycarbonate samples crystallized near 190°C for 8 days and annealed at either 223°C or 228°C for various times. The Gibbs-Thomson relationship, which can be defined using the experiments mentioned, yielded two thermodynamic constants, the equilibrium melting temperature and the surface free energy. Including data from literature in the determination of the constants, the equilibrium melting temperature and surface free energy of BAPC is 303°C and 36.6mJ/m2, respectively. Comparing the lamellar thickness measurements by small-angle X-ray diffraction with direct measurements by microscopy was difficult because the morphology of the polymer was not easily seen in the bulk using atomic force microscopy or scanning electron microscopy. Etching the sample was the most promising technique for future investigations of revealing the bulk morphology for direct lamellar thickness measurements. Crystallizing thin films of polycarbonate on calcite substrates allowed the measurement of lamellar thickness using scanning electron microscopy because the lamellae grow epitaxially to the substrate. The measurement of the long spacing in thin film samples was comparable to that of bulk samples. / Master of Science

AgÃncia Nacional do PetrÃleo / Biodiesel à definido como sendo uma mistura de Ãsteres alquÃlicos obtido a partir de uma reaÃÃo de transesterificaÃÃo de um triglicerÃdeo (Ãleo vegetal ou gordura animal) com um Ãlcool de cadeia curta, normalmente metanol ou etanol na presenÃa de catalisadores bÃsicos. Entretanto, biodieseis derivados de matÃrias-primas que possuam Ãcidos graxos insaturados em sua estrutura terÃo uma menor estabilidade oxidativa. Este fato pode comprometer a armazenagem e a sua utilizaÃÃo como combustÃvel, no entanto sua baixa estabilidade pode ser superada pela utilizaÃÃo de aditivos. Neste trabalho, realizou-se um estudo cinÃtico da reaÃÃo de oxidaÃÃo para as amostras de biodiesel de Ãleo de mamona e de Ãleo de soja em funÃÃo da temperatura e pressÃo de oxigÃnio puro a 700 kPa. Os ensaios cinÃticos foram realizados nas temperaturas de 100, 120 e 140ÂC com paradas de tempo prÃ-determinadas, como tambÃm foram avaliadas a eficiÃncia de alguns aditivos antioxidantes sintÃticos (BHA, PG, TBHQ e DBPC). O presente estudo foi realizado segundo o mÃtodo ASTM 7545, onde todas as amostras aditivadas e nÃo aditivadas foram submetidas a um ensaio de oxidaÃÃo acelerado sob pressÃo de oxigÃnio puro a 700 kPa e temperatura de 140ÂC. O grau de oxidaÃÃo foi acompanhado pelo Ãndice de Acidez Total (IAT), Viscosidade CinemÃtica a 40 ÂC e Massa EspecÃfica a 20 ÂC. Os resultados obtidos mostraram que o aumento da temperatura exerceu um efeito preponderante sobre o nÃvel de oxidaÃÃo das amostras com a evoluÃÃo destas propriedades. Os resultados obtidos tambÃm mostraram que os antioxidantes sintÃticos aumentaram significantemente a estabilidade oxidadativa das amostras de biodiesel estudadas. Para as amostras de biodiesel de mamona aditivadas com o antioxidante DBPC sua estabilidade aumentou em atà 6 vezes, enquanto as amostras aditivadas com o antioxidante TBHQ obtiveram comportamentos semelhantes ao DBPC, porÃm amostras aditivadas na maior concentraÃÃo (5000 ppm) deste aditivo obtiveram perÃodos de induÃÃo menores. O antioxidante BHA apresentou uma atividade mÃxima para concentraÃÃo de 2000 ppm, enquanto o antioxidante PG apresentou melhor desempenho para amostras aditivadas a partir de 3000 ppm. O antioxidante TBHQ aumentou a estabilidade oxidativa do biodiesel de soja 2 vezes, enquanto o antioxidante PG apresentou melhor atividade para o nÃvel de aditivaÃÃo de 1000 ppm e esta mesma atividade sà pode ser evidenciada para o BHA com amostras aditivadas acima de 2000 ppm. / Biodiesel is defined as a mixture of alkyl esters obtained by the transesterification reaction of triglycerides such as vegetable oil or animal fat with a short-chained alcohol, usually methanol or ethanol in presence of basic catalysts. However, biodiesel obtained from raw materials which have unsaturated fatty acids in their composition may show less oxidative stability. This fact may jeopardize its storage and use as fuel, but its low stability may be increased by the addition of additives. In this work, a kinetic study of the oxidation reaction of biodiesel samples from castor oil and soybean oil was carried out at different temperatures and pure oxygen pressure of 700 kPa. Kinetic studies were carried out at temperatures of 100, 120 and 140ÂC with preset stops, as well as the efficiencies of some synthetic antioxidant additives (BHA, PG, TBHQ, DBPC) were evaluated. This study was made according to method ASTM 7545. This method is consisted by submitting samples with and without additives to an oxidation test at 140ÂC and pure oxygen pressure of 700 kPa. The oxidation degree was monitored by Total Acid Number, Kinematic Viscosity at 40ÂC and Density at 20ÂC as parameters. The results showed that temperature increase has a significant effect on oxidation degree of the samples. The results also showed that synthetic antioxidants increased significantly the oxidative stability of the evaluated biodiesel samples. The antioxidant DBPC increased oxidative stability of biodiesel from castor oil by around 6 times. Samples with additive TBHQ showed similar behavior, but samples with higher concentration of DBPC (5000 ppm) showed smaller induction periods. BHAâs antioxidant maximum activity was obtained at concentration of 2000 ppm. The best performance of antioxidant PG was at concentration of 3000 ppm. Antioxidant TBHQ increased oxidative stability of biodiesel from soybean oil by 2 times, while PG showed best activity for the concentration of 1000 ppm and the same level of activity was reached for BHA for concentrations above 2000 ppm.

The decomposition of chloroform at 510˚C was investigated in a continuous flow system, using nitrogen as the carrier gas. The main products of the reaction were hydrogen chloride, tetrachloroethylene, pentachloroethane and hexachloroethane; hydrogen and chlorine could not be detected. Neither the addition of a radical initiator (azobisisobutyroni trile) nor an inhibitor (phenol) affected the breakdown, and so we have rejected the idea that the main reaction mechanism is of a radical nature. From the results obtained by varying the surface to volume ratio of the reactor, the reaction appeared to be catalysed by the surface of the reactor, but pretreating the tube by steaming, soaking in water or EDTA solution did not affect the pyrolysis. The reaction appeared to be virtually unaltered when a tube made from very pure silica was used. Kinetic investigations showed that the reaction was first order with respect to chloroform, and exhibited an induction period. Carrying out the reaction in a carbonised tube resulted in a faster reaction, and an increase in the induction period. To account for the results obtained, a mechanism is suggested which involves the formation of a carbon polymer on the silica reactor. Chloroform could then be adsorbed onto the polymer where reaction could occur. In a carbonised tube a graphite-like carbon structure may begin to take over as the catalyst. The alkaline hydrolysis of chloroform was studied in aqueous 1,4-dioxane (32 % w/v), at 360C. The rate of disappearance of chloroform was followed by gas-liquid chromatography, whilst the sodium hydroxide concentration was determined by titration with dilute hydrochloric acid. The reaction was second order overall, first order with respect to each of the reactants. Data obtained at 25˚C, 31˚C, 36˚C and 41˚C was used to determine the activation parameters. Increasing the concentration of dioxane in the solvent decreased the reaction rate. The reaction showed a definite negative salt effect, sodium chloride exhibiting a greater effect than potassium nitrate. The reaction between deuterochloroform and sodium deuteroxide in deuterium oxide/dioxane was faster than the reaction in the corresponding proton system. Application of the Yagil approach suggested that the transition state is associated with seven water molecules. This led us to suggest an alternative mechanism for the reaction, involving nucleophilic attack by water on the trichloromethyl anion, formed by loss of a proton from chloroform. In order to apply the Yagil criterion the hydration number of diolane had to be determined; a value of 2.25 was obtained.

This study aimed to investigate adaptation challenges of novice teachers in induction period, to analyze the variables influencing their adaptation, and to assess pre-service and in-service training in terms of preparing them for induction into teaching. Through a questionnaire, the data were collected from 465 novice teachers teaching in randomly selected 8 provinces of Turkey. The general results revealed that novice teachers had job-related concerns a little more often than the social concerns. The four most frequent adaptation challenges appeared as (1) workload, (2) social status and identity, (3) supervisor, and (4) classroom management challenges. Novice Teachers&rsquo / adaptation challenges differed in relation to age, subject area, university, faculty, practice teaching, existence of a mentor teacher in pre-service years, school type, grade level, amount of in-service training, and love of teaching profession. More than half of the participants perceived their pre-service and in-service training insufficient.

This diploma thesis is focused on issues concerning the stability of selected vegetable oils which are used in cosmetic industry. The stability of eight oils without additives were determined by a differential scanning calorimeter. In the first phase, the temperatures of oil degradation were determined for different rates of heating, i.e. nonisothermal stabilities. They were consequetly used to calculate isothermal stabilities alias induction periods. The calculation of induction periods was completed by using integral isoconversional methods, which applied four different temperature functions. One of the temperature functions corresponded to Arrhenius equation while the others to non-Arrhenius functions. The confrontation of induction periods under standart conditions showed that an optimal temperature function to calculate oil stabilities is one of the non-Arrhenius functions in exponential form. We can state that all oils are degraded by similar, if not the same, mechanism. The specified stabilities, in periods of months, have proved the importance of using stabilizers and other additives in the commercial and technological use of vegetable oils.

The Diploma thesis focuses on the drop-out of beginning teachers. Theoretical part elaborates on the phenomenon of drop-out, it describes the reasons why the beginning teachers leave and why they are the group of teachers which is the most threatened by drop-out. Furthermore, this part describes problems that beginning teachers have to deal with and the most frequent reasons for leaving the profession, their rate and consequences of drop-out. The end of the theoretical part presents options and suggestions that would help solve this problem. The empirical part of the thesis is realized by an on-line questionnaire and in-depth interviews. The research focuses on four main aspects: 1 - the motivation to study the teaching and to practise it, 2 - the main reasons for new teachers to leave, 3 - the possibilities to prevent drop-out and 4 - whether the respondents continue to work with children or not. Last but not least, the research focuses on the possibilities that would help respondents to stay in the profession. The results of the research confirm the reasons for quiting as described by literature. The qualitative description of the reasons for drop-outs provides a deeper understanding of how they interact in an institutional, interactive and cultural level. KEYWORDS Induction period, teacher...

Made available in DSpace on 2016-08-19T12:56:36Z (GMT). No. of bitstreams: 1 MIRELA GHISI.pdf: 1324849 bytes, checksum: 5d9ca5c5a49c366f3bf4959e2e942a14 (MD5) Previous issue date: 2011-05-16 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The metals content in biodiesel is directly related with the raw material used and also with the utilized biodiesel production method. In this work, an evaluation of the main metals present in biodiesel samples from different sources was done. The qualitative analysis of the metal content was assessed using the Inductively Coupled Plasma Mass Spectrometry technique after sample digestion in microwave oven. The main metals identified in the analyzed biodiesel samples were Al, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn. Metals like Ag, As, Ba, Cd, Co, Tl and V have not significant presence in the samples. Among these, Cu and Fe were selected due to their relevance and importance in oxidative process of biodiesel, to the development of an analytical methodology to be used in the determination by Electrothermal Atomic Absorption Spectrometry, and also evaluate the effect of these metals over the oxidative stability of the soy biodiesel. The samples were prepared with tetramethylammonium hydroxide (TMAH), and the pyrolysis and atomization temperatures were optimized pyrolysis and atomization curves. The high pyrolysis temperature adopted, 1000 oC, certainly minimized potential interferences, but calibration had to be carried out with aqueous standard solutions in the presence of the TMAH. The detection limits in the sample (3s, n=10), were quite low 15 ng g-1 and 24 ng g-1 for Cu and Fe, respectively. Seven biodiesel samples, produced from different raw materials, including vegetable seed, waste frying oil and animal fat were analyzed. Accuracy was validated by applying the recovery test (recoveries from 105% to 120%) and through comparison with the obtained results by High Resolution Continuum Source Electrothermal Atomic Absorption Spectrometry. The precision, expressed by the relative standard deviation, was better than 3% for Cu and than 7% for Fe. Copper could be quantified in two and Fe in three of the seven samples. The biodiesel sample from fodder turnip was especially rich in the analytes in comparison to the other samples. The influence of metals Cu and Fe on soy biodiesel oxidative stability was evaluated by Rancimat method through induction period, according with the Standard EN 14112. The metals Cu2+ and Fe3+ were added to the biodiesel samples in the form of theirs salts, and different storage times of the samples were evaluated. Due to the catalytic behaviour of these metals, the oxidative stability of the samples was affected, even under low metal concentrations. Compared to Cu2+, the effect over the biodiesel stability was higher when Fe3+ was added. / A presença de metais no biodiesel está diretamente relacionada com a matéria-prima utilizada e também com o processo utilizado para a obtenção do biodiesel. Neste trabalho realizou-se uma avaliação dos principais metais presentes em amostras de biodiesel provenientes de diferentes fontes. A análise semi-quantitativa nas amostras de biodiesel foi realizada utilizando a técnica de Espectrometria de Massa com Plasma Indutivamente Acoplado após a digestão das amostras em micro-ondas. Os principais metais identificados nas amostras de biodiesel analisadas são Al, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr e Zn. Metais como Ag, As, Ba, Cd, Co, Tl e V não estão presentes em concentrações significativas nessas amostras. Em função de sua relevância e importância em processos oxidativos do biodiesel, selecionou-se Cu e Fe para o desenvolvimento de uma metodologia analítica para a determinação destes por Espectrometria de Absorção Atômica com Atomização Eletrotérmica e também a avaliação do efeito destes metais sobre a estabilidade oxidativa do biodiesel de soja. As amostras foram preparadas com hidróxido de tetrametilamônio (TMAH), e as temperaturas de pirólise e atomização foram otimizadas através de curvas de pirólise e atomização. A alta temperatura de pirólise adotada, 1000 oC, certamente ajudou a minimizar possíveis interferências; porém, a calibração teve de ser realizada com padrões aquosos na presença de TMAH. Os limites de detecção (3s, n = 10), na amostra, foram baixos, 15 ng g-1 e 24 ng g-1 para Cu e Fe, respectivamente. Sete amostras de biodiesel, produzidas de diferentes matérias-primas, incluindo óleos vegetais, óleo de fritura e gordura animal foram analisadas. A exatidão foi avaliada através do teste de recuperação (recuperações de 105% a 120%) e através da comparação com os resultados obtidos por Espectrometria de Absorção Atômica de Alta Resolução com Fonte Contínua e Atomização Eletrotérmica. A precisão, expressa pelo desvio padrão relativo foi melhor que 3% para Cu e que 7% para Fe. Cobre pôde ser quantificado em duas e Fe em três das sete amostras. A amostra de biodiesel proveniente do nabo forrageiro era especialmente rica nos analitos comparada às outras amostras. A influência dos metais Cu e Fe sobre a estabilidade oxidativa do biodiesel de soja foi avaliada pelo método Rancimat através do período de indução, de acordo com a Norma EN 14112. Os metais Cu2+ e Fe3+ foram adicionados nas amostras de biodiesel na forma de seus sais, e foram avaliados diferentes tempos de armazenamento das amostras. Devido ao efeito catalítico destes metais, a estabilidade oxidativa das amostras analisadas foi reduzida mesmo na presença de baixas concentrações dos metais. O efeito do Fe3+ sobre a estabilidade do biodiesel foi significativamente maior quando comparado ao Cu2+.

Целью выпускной квалификационной работы является разработка нового потенциометрического подхода к исследованию антирадикальных свойств соединений с учетом кинетических особенностей взаимодействия антиоксидантов с пероксильными радикалами. В работе рассмотрены причины возникновения окислительного стресса, система антиоксидантной защиты и существующие методы исследования антиоксидантных/антирадикальных свойств соединений. Разработан новый потенциометрический подход к исследованию антирадикальных свойств соединений, учитывающий кинетические особенности реакции антиоксидантов с генерируемыми пероксильными радикалами. Предложенным способом оценена константа взаимодействия с пероксильными радикалами (k3) растворов индивидуальных антиоксидантов «быстрого» и «медленного» действия. Предложен новый потенциометрический способ исследования антирадикальных свойств соединений, заключающийся в расчете площади над кривой кинетической зависимости Exp(∆E). Предложенным способом рассчитаны площади SАРЕ для «быстрых» и «медленных» антиоксидантов, в том числе с особенностью кинетики превращения. / The aim of the final qualifying work is to develop a new potentiometric approach to the study of the antiradical properties of compounds, taking into account the kinetic features of the interaction of antioxidants with peroxyl radicals. The paper considers the causes of oxidative stress, the system of antioxidant protection and existing methods for studying the antioxidant/antiradical properties of compounds. A new potentiometric approach to the study of the antiradical properties of compounds has been developed, taking into account the kinetic features of the reaction of antioxidants with generated peroxyl radicals. The proposed method estimates the constant of interaction with peroxyl radicals (k3) of solutions of individual antioxidants of "fast" and "slow" action. A new potentiometric method for studying the antiradical properties of compounds is proposed, which consists in calculating the area above the kinetic dependence curve Exp(∆E). By the proposed method, the SARE areas for "fast" and "slow" antioxidants are calculated, including those with a feature of the kinetics of transformation.