abstract: Encapsulant is a key packaging component of photovoltaic (PV) modules, which protects the solar cell from physical, environmental and electrical damages. Ethylene-vinyl acetate (EVA) is one of the major encapsulant materials used in the PV industry. This work focuses on indoor accelerated ultraviolet (UV) stress testing and characterization to investigate the EVA discoloration and delamination in PV modules by using various non-destructive characterization techniques, including current-voltage (IV) measurements, UV fluorescence (UVf) and colorimetry measurements. Mini-modules with glass/EVA/cell/EVA/backsheet construction were fabricated in the laboratory with two types of EVA, UV-cut EVA (UVC) and UV-pass EVA (UVP). The accelerated UV testing was performed in a UV chamber equipped with UV lights at an ambient temperature of 50°C, little or no humidity and total UV dosage of 400 kWh/m2. The mini-modules were maintained at three different temperatures through UV light heating by placing different thickness of thermal insulation sheets over the backsheet. Also, prior to thermal insulation sheet placement, the backsheet and laminate edges were fully covered with aluminum tape to prevent oxygen diffusion into the module and hence the photobleaching reaction. The characterization results showed that mini-modules with UV-cut EVA suffered from discoloration while the modules with UV-pass EVA suffered from delamination. UVf imaging technique has the capability to identify the discoloration region in the UVC modules in the very early stage when the discoloration is not visible to the naked eyes, whereas Isc measurement is unable to measure the performance loss until the color becomes visibly darker. YI also provides the direct evidence of yellowing in the encapsulant. As expected, the extent of degradation due to discoloration increases with the increase in module temperature. The Isc loss is dictated by both the regions – discolored area at the center and non-discolored area at the cell edges, whereas the YI is only determined at the discolored region due to low probe area. This led to the limited correlation between Isc and YI in UVC modules. In case of UVP modules, UV radiation has caused an adverse impact on the interfacial adhesion between the EVA and solar cell, which was detected from UVf images and severe Isc loss. No change in YI confirms that the reason for Isc loss is not due to yellowing but the delamination. Further, the activation energy of encapsulant discoloration was estimated by using Arrhenius model on two types of data, %Isc drop and ΔYI. The Ea determined from the change in YI data for the EVA encapsulant discoloration reaction without the influence of oxygen and humidity is 0.61 eV. Based on the activation energy determined in this work and hourly weather data of any site, the degradation rate for the encaspulant browning mode can be estimated. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2018

Submitted by LUIS CARLOS RIOS QUIROGA null (lcriosq@gmail.com) on 2016-12-12T00:09:20Z No. of bitstreams: 1 Tese Luis Carlos Rios 2016.pdf: 5350341 bytes, checksum: 21d3aaff1b9c7c11beb35ad9586d6956 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-13T12:02:23Z (GMT) No. of bitstreams: 1 quiroga_lcr_dr_guara.pdf: 5350341 bytes, checksum: 21d3aaff1b9c7c11beb35ad9586d6956 (MD5) / Made available in DSpace on 2016-12-13T12:02:23Z (GMT). No. of bitstreams: 1 quiroga_lcr_dr_guara.pdf: 5350341 bytes, checksum: 21d3aaff1b9c7c11beb35ad9586d6956 (MD5) Previous issue date: 2016-11-29 / Asociación Universitaria Iberoamericana de Postgrado (AIUP) / A aplicação do etanol como combustível ou como aditivo misturado à gasolina é muito importante para a maioria dos países que procuram reduzir a dependência dos combustíveis fósseis e mitigar os gases de efeito estufa. O uso cada vez maior de misturas de etanol e gasolina torna cada vez mais relevante o conhecimento de suas propriedades físicas e químicas, de forma a favorecer uma melhor compreensão do efeito do teor de etanol na mistura com a gasolina no desempenho do motor. Esta tese tem por objetivo avaliar se existe, ou não, uma relação entre a energia de ativação da mistura de etanol e gasolina, obtida pelas técnicas de análise térmica, e a energia útil obtida em testes de motor. Foram utilizadas diferentes percentagem de etanol na mistura de etanol-gasolina denominadas por E0 (gasolina pura), E5 (5% v/v etanol), E10, E15, E20, E25, E30, E50 e E75. O estudo cinético foi realizado em um sistema simultâneo TG (termogravimetria) e DTA (análise térmica diferencial) com a metodologia para ensaios não isotérmicos para obter a energia de ativação. Alem de utilizar a análise do sinergismo, entre os componentes das misturas, como ferramenta para avaliar o efeito do teor de etanol na mistura com a gasolina. A energia útil dos combustíveis foi obtida nos testes de dinamômetro no motor monocilíndrico padrão de ciclo Otto com seis taxas de compressão diferentes. Na análise dos dados verificou-se que existe sinergismo nas misturas com teor de etanol entre 5% e 30%. Estas misturas também foram as que apresentaram melhores resultados na potência, para taxas de compressão entre 6:1 a 7:1. Os resultados da análise térmica mostram que as misturas com baixo conteúdo de etanol (até 30%) apresentam maior volatilidade e, possivelmente, esta é característica que melhora a combustão nos motores de ciclo Otto. / The use of ethanol as fuel or as an additive blended with gasoline is very important for most countries which aim to reduce the heavy dependence on fossil fuels and mitigate greenhouse gases emission. An increased use of ethanol and gasoline blends has placed great relevance on acquiring knowledge about their physical and chemical properties. Thus, knowledge of such properties favors a better understanding of the effect of the percentage of ethanol/gasoline blends on engine performance. This thesis aims to assess whether there is or not a relationship between the activation energy of the mixture of ethanol and gasoline, obtained by thermal analysis techniques, and the useful energy obtained in engine tests. They used different percentage of ethanol in the ethanol-gasoline blends denoted by E0 (pure gas), E5 (5% v/v ethanol), E10, E15, E20, E25, E30, E50 and E75. A kinetic study has been conducted through a simultaneous TG (thermogravimetry) and DTA (differential thermal analysis) by following the methodology of non-isothermal tests to obtain the activation energies of the tested mixtures. Was used the synergism analyze, between the components of the mixtures, as a tool to evaluate the effect of ethanol content in the gasoline mixture. The useful energy fuel was obtained by dynamometer tests to Otto cycle single cylinder standard engine with six different compression rates. In the data analysis was found that synergism exists in mixtures with ethanol content between 5% to 30%. These mixtures also showed the best power results for compression ratios of 6:1 to 7:1. The thermal analysis results showed that mixtures with low ethanol content (to 30%) exhibit higher volatility and, possibly, this characteristic improves combustion in Otto cycle engines.

A diminuição nos custos de fabricação das SOFC e também a flexibilização do combustível utilizado em seu abastecimento são obstáculos que, uma vez transpostos, podem possibilitar a utilização em larga escala das SOFC. A melhoria no desempenho dos componentes das SOFC pode fazer esse dispositivo trabalhar em temperaturas mais baixas, facilitando a operação do dispositivo e aumentando sua vida útil. Nesse sentido, é útil o desenvolvimento de métodos de fabricação simples e de baixo custo de componentes de SOFC, que atualmente são obtidos na forma de filmes finos cerâmicos. Assim, é proposto o desenvolvimento de uma nova técnica baseada na reação de combustão para síntese de pós e a aerografia, no intuito de, por via úmida, obter filmes finos porosos de composições cerâmicas. Foram realizadas deposições de manganitas de lantânio dopadas com estrôncio e cromo (LSM e LSCM) e óxido de cério dopado com lantânio (LCO) sobre substratos de zircônia estabilizada com ítria (YSZ) e de aço AISI 430, com o propósito de verificar a viabilidade do método de combustão de solução aspergida (CSA) proposto neste trabalho. Embora vários dos filmes fabricados tenham ficado descontínuos ou com uma quantidade excessiva de trincas, alguns resultados foram satisfatórios. Alguns filmes de LSM depositados sobre YSZ apresentaram tamanho de grão reduzido, da ordem de algumas dezenas de nanômetros, e uma porosidade fina e interconectada que levou o material a apresentar um bom desempenho eletroquímico, visando sua aplicação como cátodo de SOFC. A partir das suas propriedades eletroquímicas e, principalmente, pela energia de ativação dos processos do eletrodo, verificou-se que a microestrutura conferida pelo método de CSA proporcionou uma melhoria no desempenho da LSM. Os filmes de LSM obtidos nesse trabalho apresentaram energias de ativação inferiores a 1,26 eV, enquanto na literatura são encontrados valores mais altos para meia-células semelhantes. / Lowering fabrication costs of SOFC’s and also their fuel flexibility are obstacles that, once transposed, can make possible the mass utilization of such devices. The improvement on the performance of SOFC’s components can allow these devices to work in lower temperatures, facilitating their operation and increasing their lifespan. In this sense, is very useful the development of simple and cheap fabrication techniques of SOFC’s components, which are nowadays obtained in the form of thin ceramic films. Thus, the development of a new fabrication method is proposed, based on the solution combustion synthesis reaction and airbrush painting, in order to obtain, by a wet chemical route, thin and porous ceramic films. Depositions of strontium and cobalt doped lanthanum manganites (LSM and LSCM) and lanthanum doped cerium oxide (LCO) were carried out over yttria-stabilized zirconia (YSZ) and AISI 430 steel with the intent of verifying the viability of the Airbrushed Solution Combustion (ASC) method, proposed in this work. Although several films fabricated by ASC were discontinuous or excessively cracked, some results were satisfactory. Some LSM films deposited over YSZ showed reduced grain size, in the order of tens of nanometers, and a fine interconnected porosity, which led the material to present good electrochemical performance, aiming its application as a SOFC’s cathode. From their electrochemical properties and, mainly, through activation energy of the electrode processes, it was seeing that the microstructure acquired with the ASC method enhanced the overall performance of LSM. The LSM films obtained in this work showed activation energies below 1,26 eV, while in the literature the values are higher than this for similar half-cells.

Nos últimos anos o principal desafio da humanidade foi a substituição total ou parcial dos combustíveis fósseis que são responsáveis pelas mudanças climáticas e contribuem para a formação dos gases do efeito estufa. Como alternativa, os combustíveis renováveis - denominados biocombustíveis - têm se tornado uma alternativa viável. Este trabalho investigou o comportamento térmico e a energia de ativação de dois biocombustíveis (farnesano e biodiesel de soja) e suas misturas com diesel fóssil. Além disso, foram feitos estudos comparativos de comportamento térmico e energia de ativação entre todos os combustíveis. Os estudos foram feitos empregando-se análise termogravimétrica (TGA) sob atmosfera de ar sintético. As condições experimentais para os testes termogravimétricos foram: massa das amostras de 4,0 ± 0,5 mg, razões de aquecimento de 5, 10, 15, 20 e 25ºC min-1 e faixa de temperatura entre 30ºC e 400ºC. Outras técnicas, tais como calorimetria, Calorimetria Exploratória Diferencial (DSC - \"Differential Scanning Calorimetry\") e testes em motor diesel OM 926 LA CONAMA P7/EURO 5 também foram aplicadas para se avaliar o comportamento térmico destes combustíveis. Os valores de poder calorífico superior (PCS) para o farnesano, diesel fóssil e biodiesel são 46,9 MJ/kg, 45,3 MJ/kg e 39,7 MJ/kg, respectivamente. Os experimentos no motor diesel mostraram uma economia de 3% para o farnesano e um consumo de 14,25 % para o biodiesel em relação ao diesel fóssil. Em média, os valores de energia de ativação para os combustíveis puros encontrados neste estudo foram de 82,20 ± 3,38 kJ mol-1, 86,61 ± 8,48 kJ mol-1 e 96,61 ± 3,74 kJ mol-1 para farnesano, diesel fóssil e biodiesel de soja, respectivamente. Como a energia de ativação está diretamente relacionada com o atraso de ignição e, consequentemente, ao processo de combustão, o farnesano apresentou uma melhor qualidade de combustão em relação ao biodiesel de soja. Por meio das emissões obtidas nos testes European Stationary Cycle test (ESC) com a utilização do motor diesel foi possível obter correlações lineares entre energia de ativação e as emissões de óxidos de nitrogênio (NOx) e hidrocarbonetos (HC) e correlações polinomiais entre energia de ativação e as emissões de monóxido de carbono (CO), dióxido de carbono (CO2) e material particulado (MP). A adição de biodiesel de soja ao diesel provocou um aumento das emissões tanto para o NOx quanto para o HC em até 21,29% e 19,31%, respectivamente, e queda nas emissões de CO, CO2 e MP em até 33,44%, 2,44% e 47,37%, respectivamente. Por outro lado, a adição de farnesano ao diesel proporcionou uma diminuição de todas as emissões, ou seja, 11,22 %, 15,67%, 15,09%, 4,66% e 6,14% para NOx, HC, CO, CO2 e MP, respectivamente. A partir dos resultados obtidos neste estudo é possível entender o comportamento dos combustíveis durante suas respectivas queimas tendo como base as suas energias de ativação. / In recent years, the main challenge of the humanity was the total or partial replacement of fossil fuels, which are responsible for both the climate changes and the production of greenhouse gases. As an alternative, renewable fuels - named biofuels - have become viable. This study investigated the thermal behavior and the activation energy of two biofuels (farnesane and soybean biodiesel) and their mixture with fossil fuel. In addition, the thermal behavior of the biofuels and their mixtures with fossil fuel were compared with pure fossil diesel. Experiments were performed applying thermogravimetric analysis (TGA) under synthetic air atmosphere and other conditions such as, sample mass of 4,0 ± 0,5 mg, heating ratios of 5, 10, 15, 20 and 25 °C min-1 and temperature range between 30ºC and 400°C. In addition, calorimetry, differential scanning calorimetry (DSC) and experiments in a diesel engine OM 926 LA CONAMA P7 / EURO 5 were applied. Calorific value (CV) of the farnesane, biodiesel and fossil diesel are 46.9 MJ kg-1, 45.3 MJ kg-1 and 39.7 MJ kg-1, respectively. Experiments in the engine showed a fuel saving of 3% for farnesane and an increase consumption of 14.24 % for biodiesel, compared to fossil diesel. On average, the values of activation energy for pure fuels determined in this study were 82.20 ± 3.38 kJ mol-1, 86.61 ± 8.48 kJ mol-1 and 96.61 ± 3.74 kJ mol-1 for farnesane, fossil diesel and soybean biodiesel, respectively. As the activation energy is directly related to the ignition delay and hence the combustion process, it was observed that farnesane presented a better quality of combustion in comparison to the biodiesel. By means of the emissions obtained by the European Stationary Cycle test (ESC) in the diesel engine, it was possible to observe linear correlations between activation energy for both nitrogen oxide (NOx) and hydrocarbon (HC) emissions, and polynomial correlations between activation energy and carbon monoxide (CO), carbon dioxide (CO2) and particulate matter (PM) emissions. The addition of soybean biodiesel to the diesel promoted an increase of both NOx and HC emissions in 1.29% and 19.31%, respectively and a decrease of 33.44%, 2.44% and 47.37% for CO, CO2 and PM emissions, respectively. On the other hand, the addition of farnesane to the fossil diesel, a reduction in all emissions were observed, i.e, 11.22%, 16.67%, 15.09%, 4.66%, 6.14%. of NOx, HC, CO, CO2 and PM, respectively. From the results obtained in this study, it is possible to understand the behavior and the emissions of the fuels produced during their burning based on their activation energies.

Please read the abstract in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / PhD / Unrestricted

In vivo, la fusion membranaire ne doit pas avoir lieu spontanément. C’est pourquoi ce processus présente une barrière énergétique conséquente qui est surmontée grâce à l'action de multiples protéines. Même si la fusion biologique est très complexe, son résultat est la coalescence des deux bicouches lipidiques qui forment la matrice des membranes impliquées. L'énergie nécessaire à la perturbation de l'arrangement en bicouche lors de leur fusion doit donc être semblable à celle intervenant dans la fusion biologique. Dans le but d'estimer l’énergie d’activation de la fusion biologique, nous avons établi un protocole expérimental permettant de déterminer l’énergie d’activation et le facteur d’Arrhenius de la réaction, grâce à la loi d’Arrhenius. Les surfaces relatives occupées par la tête polaire et les queues hydrophobes d’un lipide lui confèrent une courbure préférentielle, dite courbure spontanée. En étudiant des membranes présentant des compositions lipidiques diverses, j’ai montré qu’une inadéquation entre la courbure de la membrane et la courbure spontanée du lipide affectait à la fois le facteur d’Arrhenius et l’énergie d’activation. Une courbure plus négative génère plus de défauts à la surface de la membrane « plate », ce qui augmente la fréquence de la nucléation de la fusion et accroît le facteur d’Arrhenius. Au cours du processus de fusion, la géométrie des membranes est modifiée et celle-ci présente de régions de fortes courbures. Une inadéquation entre la courbure spontanée du lipide et celle qu’il devrait adopter pour que la fusion soit accomplie peut inhiber la fusion et donc faire augmenter l’énergie d’activation. / In vivo, membrane fusion must not occur spontaneously. Thus, membrane fusion requires a large activation energy that is overcome through the action of multiple proteins. Even though biological fusion is very complex, it results in the coalescence of both lipid bilayers that constitute the cores of the involved membranes. Therefore, the activation energy that is necessary to disrupt the leaflet arrangement during lipid bilayer fusion should be similar to that of in vivo membrane fusion. In order to approach biological membrane fusion’s activation energy, we developed an experimental protocol which allows determining the activation energy and the Arrhenius factor of the reaction, thanks to Arrhenius’ law. The relative areas occupied by the polar head and hydrophobic tails of a lipid confers to it a preferential curvature, called spontaneous curvature. Investigating membranes with several lipid compositions, I found that a mismatch between the membrane curvature and the spontaneous curvature of the lipid affects both the Arrhenius factor and the activation energy. A more negative curvature generates more hydrophobic defects in the “flat” membrane which leads to an increase in the frequency of fusion nucleation, i.e. a larger Arrhenius factor. During the fusion process, membrane shapes are modified and adopt large positive and negative curvatures, each leaflet having opposite curvatures. A mismatch between the spontaneous curvature of the lipid and the one it should adopt in order for fusion to proceed can inhibit the process of fusion, i.e increase its activation energy.

Content: Graphene oxide (GO) is one of the most interesting nanomaterials in recent years. In order to explore its potential application in leather making process, a study on evaluating the effects of GO on the thermal stability and decomposition kinetics of bovine hide powders (HP) was performed by thermogravimetry. It was shown that the GO-doped hide powders (GO-HP) exhibit better thermal stability than those of raw hide powders. The kinetic and mechanism analysis of the decomposition stage used an integrated procedure involving model-free methods and universal master-plots method. Various methods were employed to calculate the activation energy of the fibers, including the Flynn-Wall-Ozawa (FWO), Modified Kissinger-Akahira-Sunose (MKAS) and Friedman methods. The activation energy values of GO-HP and raw hide powder were found to be 240.5 and 184.7 kJ/mol, respectively. Comparison of the experimental and theoretical master plots of various reaction mechanisms showed that when the conversion values are below 0.5, the most probable decomposition mechanism for HP and GO-HP is D1. Above 0.5, the decomposition mechanisms of HP and GO-HP are most probably described by A3 and R3 models, respectively. Take-Away: Graphene oxide (GO) doped hide powders (GO-HP) exhibit better thermal stability than those of raw hide powders. The activation energy values of GO-HP and raw hide powder were found to be 240.5 and 184.7 kJ/mol, respectively.

This work deals with persepective environmentally friendly electroinsulating liquids. Important properties of currently used electroinsulating liquids are listed. Physical nature of viscosity of liquids and its temperature dependance are described and methods of its measuring are listed. Also temperature dependance of density is described from physical point of view. Measurement of density and of temperature dependance of viscosity of chosen vegetable and mineral oils was performed. On the basis of this measurement was calulated the activation energy of these samples. Two methods of dynamic viscosity measurement were used for some samples.

In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.

This study determines the activation energy parameters for the hydrolysis of acetic anhydride in water/tetrahydrofuran solutions. These values are needed for studies to quantify the effect of the bulk electrostatic environment solvent-solute interactions on the hydrolysis reaction rate. Hydrolysis of an acetic anhydride with water or under basic conditions yields acetic acid. The current study is based on simple hydrolysis of acetic anhydride which produces acetic acid decreasing the pH over time. Simple hydrolysis is monitored by measuring pH versus time at temperatures ranging from 20.0 to 35.0 oC and mole fraction of water ranging from 0.75 to 1.00. Measuring pH over time has advantages over other methods such as conductivity, UV-vis spectroscopy, temperature scanning, FTIR, calorimeter as it is simple, inexpensive and reproducible. Experimental results were used to determine activation enthalpy and entropy for hydrolysis of acetic anhydride using tetrahydrofuran as the co-solvent. These values were determined using the Eyring rate equation under iso-mole fraction and isothermal conditions. Analysis was performed to determine if the activation enthalpy and entropy are temperature dependent. Eyring plots are expected to be linear for iso-mole fractions and isothermal conditions of tetrahydrofuran.