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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Avaliação de propriedades de artefatos à base de borracha natural / Evaluation of the properties of articles based on natural rubber

Janaina Dallas Caroline Bárbara di Kássia Fonseca da Silva 18 June 2007 (has links)
A combinação de excelentes propriedades mecânicas aliadas à biocompatibilidade torna a borracha natural um material amplamente empregado na fabricação de artefatos voltados à saúde, tais como bicos de chupetas e de mamadeiras, e luvas cirúrgicas e de procedimentos não-cirúrgicos. Esses artefatos são processados a partir de látices de poli(cis-isopreno) extraído de seringueiras. Entretanto, o grande número de insaturações presentes na cadeia polimérica, mesmo após a vulcanização, resulta em uma baixa resistência desse material ao envelhecimento, causado principalmente pela associação de fatores como temperatura, oxigênio, ozônio e radiação. Outro inconveniente associado à aplicação da borracha natural é a presença de proteínas no látex, com potencial alergênico, podendo promover reações fisiológicas em alguns usuários. Por esse motivo artefatos comerciais à base de material sintético também são encontrados no mercado. Esses artefatos também não são isentos dos processos naturais de desgaste e decomposição. Esta Dissertação teve como objetivo realizar um estudo comparativo de propriedades dos produtos comerciais à base de borracha natural e à base de material sintético (bicos de chupeta e de mamadeiras e luvas) de diferentes fabricantes, como adquiridos e após sofrerem envelhecimento acelerado. O estudo foi feito empregando-se as técnicas de espectroscopia na região do infravermelho com transformada de Fourier (FTIR) e termogravimetria (TG). Uma avaliação mecânica com métodos padronizados foi também realizada / By combining the excellent mechanical properties as well as biocompatibility, natural rubber is a suitable material to be applied in the manufacture of commercial articles as pacifiers, nursing bottles and gloves. Those products are processed from lattices of poly(cis-isoprene) extracted from rubber-trees. Nevertheless, the expressive amount of insaturations present along the polymeric chains, even after the vulcanization process, leads to degradation mainly caused by an association of factors as heat, oxygen, ozone and radiation. Another inconvenience in the application of natural rubber is the presence of some proteins in the latex, which causes allergic problems in a few usuaries. Thus synthetic materials are also employed in the production of such articles that are not free from degradation problems as well. The objective of this Dissertation was to carry out a comparative study of some properties of commercial products (nipples, of pacifiers and nursing bottles, and gloves) from different manufacturers. The materials were characterized, as received and after being submitted to accelerated degradation, by infrared spectroscopy (FTIR) and thermogravimetry (TG). Some mechanical properties were also evaluated by employing standard methods
42

Modificação da sílica propiletilenodiamina com formaldeído, estudo do equilíbrio e da cinética de adsorção dos íons cádmio, chumbo e cromato / Modification of silica propiletilenodiamina with formaldehyde - a study of equilibrium and the kinetics of adsorption of cadmium, lead and chromate ions.

Aguiar, Franklin Pessoa 01 November 2009 (has links)
Made available in DSpace on 2015-05-14T13:21:48Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1997340 bytes, checksum: d9de6932e705d57a480fc922a17f1ba4 (MD5) Previous issue date: 2009-11-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work, modified silica gel with the group aminopropiletanoimina was used as retention capacity for the ions cadmium, lead and cromate. The tests were accomplished in aqueous solutions under different conditions of pH, in constant temperature of 298±1 K. The number of mol of the organic chain anchored to the matrix was 0,97mmol /g. The analysis of the curves TG, for the degradation interval between 0,12 and 0,4, shows certain constancy of the value of the activation energy with the increase of the value of the conversion degree, however, the comparison of the activation energies calculated by the method of FWO and by the method of Coats-Redfern shows different results for all the models of simple mechanisms, for that, it is believed that the process in such area conversion doesn't happen through a simple mechanism, but through a complex process where more than one mechanism is acting in the dynamics of the degradation reaction. Based in the number of mols of cadmium, lead and cromate adsorbed, it can settle down the following order: cadmium > cromate > lead. The analysis of the kinetics of the reaction for the three ions shows that the processes of adsorption follow a kinetic law of speed of pseudo-second order with the constants of speed cadmium > lead > cromate. The balance of the process of adsorption is not described by the same model of adsorption; the lead and the cromate are described reasonably well by Langmuir, but for the cadmium it was not found any model to describe the behavior of the process of adsorption satisfactorily. / Neste trabalho, sílica gel modificada com o grupo aminopropiletanoimina foi utilizada como adsorvente para os íons cádmio, chumbo e cromato. Os testes foram realizados em soluções aquosas sob diferentes condições de pH em temperatura constante de 298±1 K. O número de mol da cadeia orgânica ancorada à matriz foi de 0,97mmol /g. A análise das curvas TG, para o intervalo de degradação entre 0,12 e 0,4, mostra certa constância do valor da energia de ativação com o aumento do valor do grau de conversão, entretanto, a comparação das energias de ativação calculadas pelo método de FWO e pelo método de Coats-Redfern mostra resultados diferentes para todos os modelos de mecanismos simples, por isso, acredita-se que o processo em tal região de conversão não ocorre a través de um mecanismo simples, mas sim, através de um processo complexo onde mais de um mecanismo está atuando na dinâmica da reação de degradação. Com base no número de moles de cádmio, chumbo e cromato adsorvidos pode-se estabelecer a seguinte ordem: cádmio > cromato > chumbo. A análise da cinética da reação para os três íons mostra que os processos de adsorção seguem uma lei cinética de velocidade de pseudo-segunda ordem com as constantes de velocidade de cádmio > chumbo > cromato. O equilíbrio do processo de adsorção não é descrito pelo mesmo modelo de adsorção; o chumbo e o cromato são descritos razoavelmente bem pelo Langmuir, mas, para o cádmio não foi encontrado nenhum modelo que descrevesse o comportamento do processo de adsorção satisfatoriamente.
43

Estudo dos efeitos da radiação gama no polietileno linear de baixa densidade (PELBD) injetado / Study of effects gamma radiation linear low density polyetilene (LLDPE) injected

OLIVEIRA, ANA C.F. de 10 November 2014 (has links)
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2014-11-10T11:49:28Z No. of bitstreams: 0 / Made available in DSpace on 2014-11-10T11:49:28Z (GMT). No. of bitstreams: 0 / O uso do método de esterilização por radiação gama ajuda na redução da contaminação microbiológica. O polietileno linear de baixa densidade (PELBD) é um polímero de cadeias lineares e ramificações curtas. Neste trabalho o PELBD injetado foi irradiado por uma fonte de 60Co com 2000 kCi de atividade, na presença de ar, em doses de 5, 10, 20, 50 ou 100 kGy e taxas de dose de cerca de 5 kGy.h-1 em temperatura ambiente (25 ºC). Após a irradiação, foi necessário submeter as amostras a um tratamento térmico em uma estufa por 60 min a 100 ºC para a recombinação e aniquilação dos radicais residuais. Na sequência as amostras injetadas foram irradiadas e caracterizadas para identificar os efeitos de degradação térmica, cisão e reticulação em cada dose. Verificou-se uma degradação térmica da resina ao passar pelo processo de modelagem por injeção confirmada pela análise de FTIR. Os PELBD injetados irradiados nas doses de 5, 10 ou 20 kGy tiveram maior tendência a cisão do que aqueles nas doses de 50 ou 100 kGy, nos quais predominou a reticulação. Desta forma determinaram-se os efeitos da irradiação e do processo nos PELBD moldados por injeção. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
44

Estudo de degradação a baixa temperatura de cerâmicas Y-TZP/Al2O3 sintetizadas por coprecipitação / Low temperature degradation study of Y-TZP/Al2O3 ceramics synthesized by coprecipitation

MATSUI, JEFERSON M. 17 November 2017 (has links)
Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2017-11-17T17:43:50Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-17T17:43:50Z (GMT). No. of bitstreams: 0 / A zircônia tetragonal estabilizada por ítria (Y-TZP) têm sido utilizada na área odontológica para próteses livres de metais devido à estética associada ao alto desempenho mecânico. Porém, a presença de ambiente úmido pode causar a transformação acelerada da fase tetragonal para monoclínica e consequente falha catastrófica deste material, processo este conhecido como degradação a baixa temperatura ou envelhecimento. A cinética desta transformação é função da composição química da cerâmica e sua microestrutura. Tendo em vista que métodos químicos permitem a síntese de pós cerâmicos à base de zircônia de dimensões nanométricas, cuja microestrutura da cerâmica sinterizada é constituída por grãos submicrométricos quimicamente homogêneos, e que a presença de alumina é indicada para evitar a degradação de fases da zircônia, o objetivo deste estudo foi verificar a degradação a baixa temperatura e ambiente úmido de cerâmicas de zircônia estabilizada com 3 mol% de ítria (Y-TZP) e do compósito Y-TZP/Al2O3, proveniente de pós sintetizados pela rota de coprecipitação. A concentração de alumina na Y-TZP foi estudada na faixa de 0,05 a 20% em massa. A eficiência do processo desenvolvido foi verificada pela avaliação das características físicas dos pós obtidos (granulometria, área de superfície específica, estado de aglomeração e estrutura cristalina). As amostras cerâmicas foram prensadas, sinterizadas e avaliadas quanto à densidade aparente e microestrutura. Após a caracterização inicial das cerâmicas a degradação das amostras foi estudada in vitro em reator hidrotérmico pressurizado a 150°C. As amostras (n=4) foram submetidas à análise de difração de raios X de acordo com o tempo de envelhecimento, acompanhando a curva cinética de transformação de fase. A porcentagem de cada fase cristalina foi determinada pelo Método de Rietveld. A relação entre o tempo de envelhecimento e a concentração de fase monoclínica foi determinada pela equação de Avrami modificada por Kolmogorow (Johnson-Mehl- Avrami-Kolmogorow JMAK). Após envelhecimento a 150°C por 70 horas, todas as amostras contendo alumina apresentaram menor concentração de fase monoclínica, comparativamente à cerâmica Y-TZP, que apresentou 66,5% dessa fase. Menores porcentagens de fase monoclínica após o envelhecimento hidrotérmico foram obtidas com a adição de 10 e 20% em massa de alumina na matriz de zircônia, sendo esses valores 59,1 e 52,9%, respectivamente. Deve-se considerar, no entanto, que a diminuição da degradação total é consequência da menor porcentagem de zircônia na matriz em função da adição de alumina. Neste contexto, o efeito benéfico da adição de alumina ocorre apenas no início do envelhecimento. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
45

Comparison on the thermal degradation kinetics and mechanism of hides before and after formaldehyde-tanning

Hu, Yadi, Luo, Lan, Liu, Jie, Wang, Fang, Zhu, Haolin, Tang, Keyong 28 June 2019 (has links)
Content: The thermal degradation kinetics of hides before and after being tanned with formaldehyde were investigated using thermalgravimetric analysis (TGA) at four different heating rates of 5, 10, 20, 30 K/min. Such model-free methods as Flynn-Wall-Ozawa and Friedman as well as model-fitting method of Criado were employed to determine the thermal degradation active energy and degradation mechanism. Based on the Flynn-Wall-Ozawa and Friedman methods, the average active energy (Ea) of formaldehyde-tanned leather was 223.1 kJ/mol and 230.7 kJ/mol respectively. Results from general master curves showed diffusion processes in the thermal degradation of formaldehyde-tanned leather. Neither the thermal degradation activation energy nor the degradation mechanism is affected by the formaldehyde tanning. Nevertheless, the results by thermalgravimetric analyzer coupled with Fourier transform infrared spectrometry (TG-FTIR) indicated difference in the relative amounts of evolved products. According to the 3D-FTIR analysis, the dominant components of evolved gas for both untanned and tanned hides are CO2, CH4, H2O, NH3 along with small amount of HNCO. However, after formaldehyde tanning, both the evolved NH3 by the decomposition of free –NH2 groups and peptide –NH– groups from different amino acids in collagen and CH4 by the cleavage of -CH3 and -CH2- increase. Take-Away: 1. The theraml degradtion mechanism of hides before and after formaldehyde-tanning is eatablished in our paper. 2. The main degradation pathway of hides before and after formaldehyde-tanning is discussed with the help of TG-FTIR analysis.
46

Thermal degradation of PFAS in solid matter / Termisk nedbrytning av PFAS i fast materia

Al-Badri, Tuqa January 2024 (has links)
Per- och Polyfluorerade alkylsubstanser (PFAS) är syntetiskt framställda organiska föreningar som har använts i stor utsträckning i konsument- och industriprodukter. PFAS-substanser besitter attraktiva egenskaper såsom resistans mot väta, fett, fläckar och är dessutom värmetåliga. De används i bland annat brandskum, smink, vattentäta kläder med ”andas-funktion”, möbler och non- stickstekpannor. Den senaste forskningen har dock visat att PFAS utgör en fara för levande organismer och miljön. Vissa PFAS-substanser har klassats som persistenta, bioackumulativa och toxisk (PBT), samt väldigt persistenta och väldigt bioaccumulativa (vPvB).Existerande forskning har fokuserat på beteendet hos PFAS i olika miljöer. Dock finns det en kunskapslucka när det gäller hur dessa PFAS-substanser beter sig under termiska behandlingsprocesser, samt förbränningsgraden i kommersiella förbränningsanläggningar vid temperaturerna 850–950 °C. I detta projekt undersöks därför nedbrytningsgraden av PFAS genom förbränning samt bildning av potentiellt farliga biprodukter efter förbränning. För att genomföra denna studie skulle förbränning av PFAS-haltigt avloppsslam i en pilotskalig bubblande fluidiserad bädd (BFB) genomföras. På grund av hinder utfördes experimenten i stället i en konventionell och simpel laboratorieugn. Dessutom genomfördes en litteraturstudie för att undersöka bildandet av potentiellt farliga biprodukter efter förbränning av PFAS. Denna studie har visat att termisk behandling genom förbränning är en effektiv metod för att behandla PFAS i avloppsslam med reduktion under kvantifieringsgränserna. Undersökning av potentiellt farliga biprodukter baserat på litteraturstudier har visat att kortkedjiga PFCAs var mest förekommande i aska, vätska och gasformiga rester efter termisk behandling. Några undersökningar tyder på att termisk behandling av PFAS-haltigt material möjligen resulterar i ozonnedbrytande ämnen. Utifrån den genomförde litteraturstudien i detta projekt saknas starka bevis för att kunna påstå att det bildas ozonnedbrytande ämnen under förbränning av PFAS. / Per- and polyfluoroalkyl substances (PFAS) are man-made organic compound widely used in consumer and industrial products. They exhibit attractive properties such as resistance to water, heat, and grease. Therefore, PFAS are used in fire foam, non-stick pans, water-resistant clothes, make-up, and furniture. Recent studies have revealed that PFAS substances can be harmful to humans, animals, and the environment. Some PFAS substances have, therefore, been classified as persistent, bioaccumulative, and toxic (PBT), and very persistent and very bioaccumulative (vPvB). This means that PFAS resists degradation, accumulates in living organisms and biota, and inherits toxic effects. In previous and current research, the focus has been on the behavior of PFAS in different environmental settings. However, there is a gap in research on how these PFAS substances behave during thermal treatment processes in commercial facilities at temperatures of 850-950 °C and how effective the thermal degradation is. This project investigates the effectivity of thermal degradation via combustion and the fate of PFAS post-combustion, focusing on the formation of potentially hazardous by-products. Therefore, the combustion of PFAS-containing sewage sludge in a bench- scale bubbling fluidized bed (BFB) was to be conducted to fulfill the objective of this study. Due to hindrances, the experiments were performed in a conventional furnace furnace instead. Also, a literature study was conducted to investigate the fate of PFAS after combustion. From this study, it was concluded that thermal treatment via combustion at temperatures 850 and 950 °C is an effective method to degrade PFAS in sewage sludge. Also, the literature study investigation revealed that persistent short-chain PFCAs were most abundant in the ash, liquid, and gaseous residues after thermal treatment. A few investigations indicate that thermal treatment of PFAS-containing matter possibly results in ozone-depleting compounds. Based on the conducted literature study, there is a lack of strong evidence that supports the claim of the formation of ozone- depleting compounds during combustion of PFAS.
47

[pt] CARACTERIZAÇÃO MORFOLÓGICA, QUÍMICA E TÉRMICA DE SUCATA ELETRÔNICA VISANDO DEFINIR UMA ROTA PARA RECUPERAÇÃO DE MATERIAIS / [en] MORPHOLOGICAL, CHEMICAL AND THERMIC CHARACTERIZATION OF EWASTE IN ORDER TO DEFINE A ROUTE FOR MATERIALS RECOVERY

JULIANA SANTOS SETTE DE OLIVEIRA 09 February 2021 (has links)
[pt] O crescimento da produção de resíduos sólidos devido a evolução tecnológica, principalmente nos países em desenvolvimento, vem apresentando-se de maneira acelerada. Esta evolução acarreta na produção de novos produtos eletrônicos mais atualizados e, cada vez mais sofisticados quanto à composição química, com novas funcionalidades, tornando os antigos dispositivos obsoletos. O consumo exarcebado destes novos produtos contribui para um problema que ganha cada vez mais relevância no cenário mundial, o acúmulo de lixo eletrônico de origem urbana. O presente estudo contemplará como matéria prima amostras de placas de circuito impresso de computadores, conhecidas como PCIs, que são um padrão de barramentos, destinado a conectar periféricos à placa-mãe. Tendo em vista que nestes resíduos os teores de metais são tipicamente superiores àqueles de reservas naturais, torna-se interessante buscar rotas que viabilizem a reciclagem desses resíduos com a concomitante recuperação de constituintes de interesse ou concentração de precursores em distintos grupos para a posterior recuperação de metais. Nesta abordagem, foram realizadas análises termogravimétricas para acompanhar as melhores condições de processo e caracterização do material e produtos através de MEV/EDS. Assim, este material, tipicamente constituído por material orgânico (ex: plásticos como PVC) e constituintes inorgânicos (ex: metais e ligas metálicas), será submetido a um processamento térmico em forno tubular a 350 graus C em atmosfera inerte, seguido de etapas de concentração. A partir de 300 graus C a perda de massa se mantém constante, em torno de 30 por cento, e nas seguintes etapas aplicadas, 15 por cento da amostra total em constituintes metálicos com alto valor agregado, no caso Cu, Ni e Au, podem seguir para recuperação. / [en] The production of solid residues due to technological development has been increasing fast, mainly in developing countries. This growth leads to the manufacture of improved electronic products with varied functions, which not only are better versions of the old ones but also more sophisticated in their chemical compounds. The excessive consumption of the new devices contributes to an issue which has been increasing internationally: the accumulation of electronic waste. The raw material used in this study are samples of computer printed circuit boards (PCBs), which are a bus pattern that connects peripherals to the motherboard. Since the metal content in these residues are typically more elevated than in the ones located in natural reserves, it is interesting to find ways to recycle those residues while recovering components of interest or precursor concentrations in distinct groups for later metal recovery. Thermogravimetric analysis were performed on this approach in order to observe the best conditions of the process and the characterization of material and products was through SEM/EDS. Thus, this material, typically composed by organic material (such as plastic or PVC) and inorganic constituents (such as metals and alloys), undergoes a thermal processing in tubular furnace at 350 C degrees in inert atmosphere, followed by the concentration steps. The mass loss is constant from 300 C degrees on, around 30 percent. In the following steps, 15 percent of the total sample presents metallic components with high added value, such as Cu, Ni and Au, may be recovered.
48

Modélisation et simulation d’un étage haute température pour la purification d’un gaz chargé en goudrons et en particules carbonées par assistance plasma / Modeling and design of a high-temperature chamber fed by plasma torch for removal of tars and carbonaceous particles

Demarthon, Romain 25 January 2013 (has links)
Afin de répondre aux besoins croissants en énergie primaire, le groupe Europlasma a développé le procédé CHO-Power permettant de valoriser énergétiquement un mélange de refus de tri d’ordures ménagères et de résidus de biomasse. L’une des particularités de ce procédé est l’utilisation d’un réacteur de dégradation thermique des goudrons et des particules solides fines par assistance plasma. L’objectif de cette étude de mieux appréhender les mécanismes réactionnels mis en jeu lors de l’épuration thermique du gaz. Dans cette optique, un réacteur pilote a été dimensionné puis construit sur la plate-forme de Recherche et Développement d’Europlasma. Il a été ensuite nécessaire de modifier le schéma réactionnel permettant la modélisation numérique de la dégradation des goudrons. Ce schéma réactionnel, couplé à l’utilisation d’un logiciel de mécanique des fluides numérique, permet de représenter les processus couplés (chimie, aéraulique, transferts thermiques) se déroulant au sein du réacteur. Deux modifications importantes ont été alors apportées au modèle cinétique simplifié jusque-là utilisé : la modélisation d’une phase discrète réactive permettant de prendre en compte la gazéification des particules de résidus carbonés et l’ajout de nouvelles voies réactionnelles afin de mieux modéliser la formation des particules de suie et de ses précurseurs. À terme, la comparaison des valeurs expérimentales à celle issues de la modélisation numérique permettra de valider ou non le schéma réactionnel dans sa globalité. / In order to contest to the high world demand for primary energy, the Europlasma group developed a new process, called CHO-Power, to enhance the thermochemical potential of a mixture of urban waste and biomass residues. One of the characteristics of this process is the use of a high temperature reactor assisted by a plasma torch for tar and soots thermal cracking. The aim of this study to improve the knowledge of the global reaction mechanism involved during the thermal treatment of gas. In this context, a pilot plant reactor was designed and built on the Europlasma Research and Development Center. During this work, the reaction pathway used to represent tars cracking at high temperature has been enhanced. Coupled to a computational fluid Dynamics Software, allow simulating the complex processes occurring within the reactor (aeraulics, reaction, and heat transfer). Two major changes were made to the simplified kinetic model previously used: the modeling of a discrete and reactive phase to take into account the possible particle gasification of carbonaceous residues and the addition of new reaction pathways to enhance the modeling of the formation of soot and its precursors. The comparison between the experimental and numerical values will validate or not the global reaction scheme and will give important information about the next evolution of the tar degradation scheme.
49

Modélisation, élaboration et caractérisation de cellules photovoltaïques à base de silicium cristallin pour des applications sous concentration / Modelisation, fabrication and characterisation of silicon based solar cell for application under concentrated sunlight

Guillo Lohan, Benoit 26 November 2018 (has links)
Les performances électriques des cellules photovoltaïques à base de silicium sont fortement dégradées lorsque leur température augmente. Cette problématique, pourtant bien connue, n’est pas suffisamment prise en considération dans l’industrie du photovoltaïque. Pour parer à cette dégradation, deux voies d’améliorations peuvent être explorées : diminuer la température de fonctionnement des cellules ou réduire leurs coefficients de dégradation en température. Cette étude est d’autant plus importante pour les applications sous concentrations, un éclairement élevé favorisant l’échauffement des cellules. Pour les facteurs de concentration élevés, l’utilisation de systèmes de refroidissement actifs réduit drastiquement la température de fonctionnement. Pour les faibles éclairements, le refroidissement passif est préféré, bien moins coûteux en énergie. Ce travail de thèse est focalisé sur l’étude du comportement thermo-électrique des cellules sous faible concentration du rayonnement incident. Un banc de caractérisation innovant développé dans cette thèse a rendu possible la quantification des variations de la température de la cellule avec la tension de polarisation sous différents facteurs de concentration. Avec l’augmentation de la polarisation, une évolution du facteur d’émission thermique est observée du fait des variations de la concentration de porteurs de charge minoritaires. Le refroidissement radiatif est minimal au courant de court-circuit et est maximal à la tension de circuit ouvert : la température atteinte au point de court-circuit est supérieure à celle atteinte en circuit ouvert. Pour une cellule donnée, sous un éclairement de 3 soleils, un écart de température de 6.2 °C a pu être mesuré entre ces deux points. La fabrication de cellules avec des propriétés différentes nous a permis de confirmer l’importance du dopage de la base et de l’architecture sur l’augmentation du refroidissement radiatif avec la polarisation. De plus, la comparaison du comportement thermo-électrique des cellules de type de dopages différents a mis en avant de plus faibles coefficients de dégradation en température de la tension en circuit ouvert pour les cellules ayant un substrat de type n. Par exemple, pour une température de et sous un éclairement de 1 soleil, un coefficient de dégradation en température du Voc de −0.45% %·°C-1 a été mesuré sur une cellule de type n contre −0.49%·°C-1 pour une cellule de type p. / The electrical performances of silicon based solar cells strongly degrade when increasing their temperature. However, such a well-known issue is too scarcely considered in the phovoltaic industry. To prevent the degradation of silicon based solar cells, two ways of improvement can be explored : one can either decrease the cells’ functionning temperature or either reduce the temperature degradation coefficient. As light intensity tends to favor cell heating, the study is even more important under concentrated sunlight. Regarding high light intensities, active cooling systems can be used to drastically reduce the cell temperature. For low light intensities, passive cooling systems, such as radiative cooling, are more energetically savy. The thesis aims at studying the electro-thermal behavior of cells under low light intensities. An innovative experimental set-up has been developped during this thesis to quantify the variation of the cell temperature with the applied bias voltage. When increasing the bias, an evolution of the cell emissivity is observed because of a variation of the minorities carrier concentration. The radiative cooling is at its lowest at the short circuit current and peaks its highest value at the open circuit voltage : as a result, the reached temperature is higher at the short circuit current than at the open circuit voltage. For a given solar cell, under 3 suns, a temperature shift of 6.2 °C was measured between these two points. The control of the fabrication process gives the opportunity to analyse the influence of the base doping and cell architecture on the evolution of the radiative cooling with the applied bias. Furthermore, the comparison between the electro-thermal behaviors of solar cells, which are related to their type of doping, has shown a lower thermal degradation coefficient of the open circuit voltage for n-type based dope solar cells. For example, at 60°C and under 1 sun, we measured a thermal degradation coefficient BVoc = −0.45% %·°C-1 for a n type solar cell whereas the p type solar cell recorded BVoc = −0.49% %·°C-1.
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Thermal Characterization Of Homopolymers, Copolymers And Metal Functional Copolymers Of Vinylpyridines

Elmaci, Aysegul 01 September 2008 (has links) (PDF)
Although, the use of vinyl pyridine polymers, especially as matrices for nanoparticle synthesis, is growing considerably, the knowledge of thermal degradation behavior is still missing in the literature. In this study, thermal degradation characteristics of the homopolymers / poly(4-vinylpyridine), P4VP, and poly(2-vinylpyridine), P2VP, the diblock copolymers / polystyrene-blockpoly( 2-vinylpyridine), (PS-b-P2VP) and polystyrene-block-poly(4-vinylpyridine), (PS-b-P4VP), and the metal functional vinyl polymers / cobalt-polystyrene-blockpoly( 2-vinylpyridine) and cobalt-polystyrene-block-poly(4-vinylpyridine) were investigated by direct pyrolysis mass spectrometry. The effects of the position of the nitrogen in the pyridine ring, composition and molecular weight of diblock copolymer and coordination of the metal to the pyridine ring of the copolymer on thermal behavior were also investigated. The results showed that unlike most of the vinyl polymers that decompose via depolymerization, P2VP degrades through opposing reaction pathways / depolymerization, proton transfer to N atom in the pyridine ring yielding unsaturated linkages on the polymer backbone that decompose slightly at higher temperatures and loss of pyridine units. On the other hand the thermally less stable P4VP decomposition follows v depolymerization in accordance to general expectations. Another finding was the independent decomposition of both components of the diblock polymers, (PS-b- P2VP) and (PS-b-P4VP). Thermal degradation occurs in two main steps, the thermally less stable P2VP or P4VP chains degrade in the first step and in the second step decomposition of PS takes place. It was also concluded that upon coordination of metal, thermal stability of both P2VP and P4VP increases significantly. For metal functional diblock copolymers thermal degradation of chains coordinated to Co metal through N in the pyridine ring occurred in three steps / cleavage of pyridine coordinated to Co, coupling and H-transfer reactions yielding unsaturated and/or crosslinked structure and decomposition of these thermally more stable unsaturated and/or crosslinked blocks. TEM imaging of the metal functional block copolymers along with the results of the pyrolysis mass spectrometry pointed out that PS-b-P2VP polymer is a better and more effective matrix for nanoparticle synthesis.

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