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Ribeiro, Rafael Parra. "Efeito do tratamento de oxidação a plasma na produção de uma bicamada SiOx/SiOxCyHz". Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152465.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Devido às suas propriedades mecânicas, soldabilidade e baixo custo, o aço carbono é um material amplamente utilizado nos mais diversos setores. Entretanto, o aço carbono é facilmente oxidado quando exposto ao ambiente. Para evitar esse problema, alguns trabalhos sugerem o desenvolvimento de revestimentos protetivos utilizando técnicas de deposição a plasma baseadas no composto hexametildisiloxano, HMDSO. A partir deste composto podese obter desde estruturas organosilicones até as inorgânicas pela alteração dos parâmetros de deposição. Revestimentos tipo óxido de silício são mais resistentes à corrosão que os organosilicones, porém sua estabilidade física é menor. Com o objetivo de associar as propriedades favoráveis de ambos os tipos de revestimentos, investigou-se, no presente trabalho, a possibilidade de revestir o aço carbono com sistemas bicamadas SiOx/SiOxCyHz através da combinação de metodologia de deposição e oxidação em plasmas de baixa pressão. Para tanto, filmes do tipo SiOxCyHz foram depositados a plasma de mistura de HMDSO (70%), O2 (20%) e Ar (10%) excitado por radiofrequência (150 W). A pressão total da atmosfera de deposição foi de 20 Pa. Os filmes foram depositados por 30 min e, posteriormente, expostos a plasmas de O2 (3,3 Pa, 10-300 W, 60 min) com o objetivo de criar uma camada superficial inorgânica. Foram investigados os efeitos da potência de excitação do plasma de O2 na espessura de camada, estrutura química e composição elementar das amostras. Avaliou-se também o efeito da potência do plasma de oxidação nas propriedades de barreira do revestimento depositado sobre aço carbono. Filmes como-depositados foram caracterizados como organosilicones. A exposição ao plasma de oxigênio foi observada remover hidrogênio, carbono e grupos metil da estrutura transformando-a em óxido de silício, sendo, todavia, o grau de conversão e a espessura da camada convertida fortemente dependentes da potência do plasma de oxidação. A resistência do sistema preparado sobre o aço carbono à corrosão foi observada depender da espessura final da camada e também da conectividade da estrutura convertida em sílica mais que do grau de conversão. A condição de tratamento eleita como ótima neste trabalho foi a conduzida com 50 W de potência por criar uma camada superficial inorgânica fina, compacta, com uma estrutura superficial similar a da sílica além de preservar a espessura do filme e aumentar as propriedades de barreira do sistema.
Due to its mechanical properties, welding and low cost, carbon steel is a material widely used in several sectors. However, carbon steel is easily oxidized when exposed to the environment. To avoid this problem, some work suggests the development of protective coating using plasma deposition techniques based on the compound hexamethyldisiloxane, HMDSO. From this compound it is possible to obtain from organosilicones structures to inorganic by changing the parameters of deposition. Silicon oxide type coatings are more resistant to corrosion than organosilicones, but their physical stability is lower. With the objective of associating the favorable properties of both types of coatings, the present work investigated the possibility of coating the carbon steel with SiOx/SiOxCyHz bilayer systems through the combination of deposition and oxidation methodology in low pressure plasmas. For that, SiOxCyHz films were deposited in a mixture plasma of HMDSO (70%), O2 (20%) and Ar (10%) excited by radiofrequency (150 W). The total pressure of the atmosphere of deposition was 20 Pa. The films were deposited for 30 min and subsequently exposed to O2 plasmas (3.3 Pa, 10-300 W, 60 min) to create an inorganic surface layer. The effects of the excitation power of the O2 plasma on the layer thickness, chemical structure and elemental composition of the samples were investigated. The effect of the oxidation plasma power was also evaluated in the barrier properties of the coating deposited on carbon steel. As-deposited films were characterized as organosilicones. Exposure to oxygen plasma was observed to remove hydrogen, carbon and methyl groups from the structure transforming it into a silicon oxide, however, the degree of conversion and the thickness of the converted layer is strongly dependent on the power of the oxidation plasma. The corrosion resistance of the system prepared on carbon steel was observed to depend on the final thickness of the layer and also on the connectivity of the structure converted to silica rather than the degree of conversion. The treatment condition chosen as optimal in this work was the one conducted with 50 W of power by creating a thin, compact, inorganic surface layer with a silica-like surface structure in addition to preserving the film thickness and increasing the barrier properties of the system.
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Queiroz, José Renato Cavalcanti de [UNESP]. "Filmes de SiOx crescidos em substrato de zircônia tetragonal policristalina estabilizada por ítria: influência na durabilidade da adesão a cimentos resinosos". Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/105537.
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Este estudo comparou o efeito de filmes à base de Si depositados pela técnica reactive magnetron sputtering com o uso do jateamento de partículas de alumina e a aplicação de primer na adesão de cimentos resinoso a superfície de zircônia. Blocos de zirconia (N=300) (4,5×4,5)mm foram sinterizados e regularizados com lixas de SiC (1200), sonicamente limpos com água destilada por 10 min e randomicamente divididos em 30 grupos (n=10) de acordo com 3 parâmetros: 1- cimento resinoso (Panavia/Kuraray; Multilink/Ivoclar; RelyX U100/3M); 2- tratamento de superfície (sem tratamentocontrole, Metal/Zirconia Primer, jateamento com partículas + Metal/Zirconia Primer, Filme A + Monobond S; Filme B + Monobond S); 3- termociclagem (TC). Parâmetros de rugosidade da superfície (Ra, Rz, Sdr) foram avaliados por Microscopia de Interferência e Microscopia Eletrônica de Varredura (MEV). Cilindros de cimento resinoso foram construídos (Ø: 2,4 mm; altura: 2 mm) sobre a superfície de zirconia. O ensaio de resistência adesiva ao cisalhamento foi realizado no momento inicial (24 h) e após a termociclagem (5o- 55oC, 6.000 ciclos) utilizando máquina de ensaio universal (1 mm/min). As superfícies fraturadas foram analisadas por microscopia ótica (30×) e MEV (100× e 2000×) para categorizar o modo de falha. Adicionais blocos de zirconia (15×15)mm confeccionados para análises por Espectroscopia por Retroespalhamento de Rutheford (RBS), e Trabalho de Adesão (WA) após os tratamentos de superfície. Os dados foram estatisticamente analisados por Anova 3-fatores e 11 teste Tukey (5%). Fotomicrografias revelaram microdefeitos nos filmes. Os resultados de Wa mostraram que os filmes melhoraram a molhabilidade da superfície. As análises por RBS mostraram que a concentração elementar dos filmes...
This study compared the effect of si-based nanofilm deposition using reactive magnetron sputtering to application of air-abrasion (alumina particles) and zirconia primers on the adhesion of resin cements to zirconia. Zirconia (Nblocks=300) (4.5 mm × 3.5 mm × 4.5 mm) were sintered, ground finished to 1200 SiC paper and cleaned ultrasonically in distilled water for 10 min. The blocks were randomly divided into 30 groups (n=10) according to 3 testing parameters: 1- Resin Cements (Panavia/Kuraray; Multilink/Ivoclar; RelyX U100/3M); 2- Surface conditioning (no conditioning-control, Metal/Zirconia Primer, air-abrasion + Metal/Zirconia Primer, Sibased film A + Monobond S; Si-based film B + Monobond S); 3- Aging (with and without). Surface roughness parameters (Ra, Rz, Sdr) before and after surface conditioning were evaluated using interference microscopy (IM). Rutheford Backscattering Spectroscopy (RBS), Scanning Electron Microscopy (SEM), and Work of Adhesion (WA) analyses were performed after surface treatments. Resin cements were incrementally built up (Ø: 2.4 mm; height: 4 mm) on the zirconia surfaces. Bonded specimens were then thermocycled (5o-55oC, 6,000 cycles). Shear bond strength (SBS) was performed using the Universal Testing Machine (1 mm/min). After fracture, the surfaces were analyzed using an optical microscopy (30 ×), SEM (100 × and 2000 ×) to categorize the failure modes. The data were statistically evaluated using 3-way ANOVA and Tukey's test (5%). Scanning Electron Microscopy showed micro defects on Si-based nanofilms surface. The result to Wa showed that surface coated with Si-based nanofilms improved wetability when compared to the other surface treatments. RBS analysis showed that was produced films with different chemical elemental concentration. While air-abraded... (Complete abstract click electronic access below)
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Queiroz, José Renato Cavalcanti de. "Filmes de SiOx crescidos em substrato de zircônia tetragonal policristalina estabilizada por ítria : influência na durabilidade da adesão a cimentos resinosos /". São José dos Campos : [s.n.], 2011. http://hdl.handle.net/11449/105537.
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Orientador: Lafayette Nogueira JúniorCoorientador: Marcos Massi
Banca: Luiz Felipe Valandro
Banca: Argemiro Soares da Silva Sobrinho
Banca: Rodrigo Othavio de Assunção e Souza
Banca: Marco Cícero Bottino
Resumo: Este estudo comparou o efeito de filmes à base de Si depositados pela técnica reactive magnetron sputtering com o uso do jateamento de partículas de alumina e a aplicação de primer na adesão de cimentos resinoso a superfície de zircônia. Blocos de zirconia (N=300) (4,5×4,5)mm foram sinterizados e regularizados com lixas de SiC (1200), sonicamente limpos com água destilada por 10 min e randomicamente divididos em 30 grupos (n=10) de acordo com 3 parâmetros: 1- cimento resinoso (Panavia/Kuraray; Multilink/Ivoclar; RelyX U100/3M); 2- tratamento de superfície (sem tratamentocontrole, Metal/Zirconia Primer, jateamento com partículas + Metal/Zirconia Primer, Filme A + Monobond S; Filme B + Monobond S); 3- termociclagem (TC). Parâmetros de rugosidade da superfície (Ra, Rz, Sdr) foram avaliados por Microscopia de Interferência e Microscopia Eletrônica de Varredura (MEV). Cilindros de cimento resinoso foram construídos (Ø: 2,4 mm; altura: 2 mm) sobre a superfície de zirconia. O ensaio de resistência adesiva ao cisalhamento foi realizado no momento inicial (24 h) e após a termociclagem (5o- 55oC, 6.000 ciclos) utilizando máquina de ensaio universal (1 mm/min). As superfícies fraturadas foram analisadas por microscopia ótica (30×) e MEV (100× e 2000×) para categorizar o modo de falha. Adicionais blocos de zirconia (15×15)mm confeccionados para análises por Espectroscopia por Retroespalhamento de Rutheford (RBS), e Trabalho de Adesão (WA) após os tratamentos de superfície. Os dados foram estatisticamente analisados por Anova 3-fatores e 11 teste Tukey (5%). Fotomicrografias revelaram microdefeitos nos filmes. Os resultados de Wa mostraram que os filmes melhoraram a molhabilidade da superfície. As análises por RBS mostraram que a concentração elementar dos filmes... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This study compared the effect of si-based nanofilm deposition using reactive magnetron sputtering to application of air-abrasion (alumina particles) and zirconia primers on the adhesion of resin cements to zirconia. Zirconia (Nblocks=300) (4.5 mm × 3.5 mm × 4.5 mm) were sintered, ground finished to 1200 SiC paper and cleaned ultrasonically in distilled water for 10 min. The blocks were randomly divided into 30 groups (n=10) according to 3 testing parameters: 1- Resin Cements (Panavia/Kuraray; Multilink/Ivoclar; RelyX U100/3M); 2- Surface conditioning (no conditioning-control, Metal/Zirconia Primer, air-abrasion + Metal/Zirconia Primer, Sibased film A + Monobond S; Si-based film B + Monobond S); 3- Aging (with and without). Surface roughness parameters (Ra, Rz, Sdr) before and after surface conditioning were evaluated using interference microscopy (IM). Rutheford Backscattering Spectroscopy (RBS), Scanning Electron Microscopy (SEM), and Work of Adhesion (WA) analyses were performed after surface treatments. Resin cements were incrementally built up (Ø: 2.4 mm; height: 4 mm) on the zirconia surfaces. Bonded specimens were then thermocycled (5o-55oC, 6,000 cycles). Shear bond strength (SBS) was performed using the Universal Testing Machine (1 mm/min). After fracture, the surfaces were analyzed using an optical microscopy (30 ×), SEM (100 × and 2000 ×) to categorize the failure modes. The data were statistically evaluated using 3-way ANOVA and Tukey's test (5%). Scanning Electron Microscopy showed micro defects on Si-based nanofilms surface. The result to Wa showed that surface coated with Si-based nanofilms improved wetability when compared to the other surface treatments. RBS analysis showed that was produced films with different chemical elemental concentration. While air-abraded... (Complete abstract click electronic access below)
Doutor
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Dresch, Mauro André. "Aplicação de catalisadores PtSn/C e membranas Nafion-SiO2 em células a combustível de etanol direto em elevadas temperaturas". Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-06102014-102906/.
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Este trabalho teve como objetivo a combinação de ânodos e eletrólitos otimizados, para a formação de células a combustível de etanol direto (DEFC), operantes em elevadas temperaturas (130 ºC). Como materiais de ânodo, foram produzidos eletrocatalisadores baseados em PtSn/C, com diversas razões atômicas Pt:Sn, preparados pelo método do poliol modificado, essa metodologia possibilita a produção de eletrocatalisadores auto-organizados com estreita distribuição de tamanhos de partículas e elevado grau de liga. Os eletrocatalisadores foram caracterizados por DRX e stripping de CO. Os resultados mostraram que esses materiais apresentaram elevado grau de liga e Eonset de oxidação de CO em potenciais menores do que os materiais comerciais. Como eletrólito, foram sintetizados híbridos Nafion-SiO2 com a incorporação do óxido diretamente nos agregados iônicos de diversos tipos de membranas Nafion. Os parâmetros de síntese, tais como o solvente em meio solgel, a espessura da membrana, e a concentração do precursor de sílica foram avaliados em termos do percentual de sílica incorporada e da estabilidade mecânica do híbrido. Por fim, ânodos e eletrólitos otimizados foram avaliados em DEFCs nas temperaturas de 80 e 130 ºC. Os resultados mostraram um significativo incremento no desempenho de polarização (122 mW cm-2), resultado da aceleração na taxa de oxidação de etanol devido ao material de ânodo otimizado e do aumento de temperatura de operação, uma vez que o uso de eletrólitos híbridos possibilita o aumento da temperatura sem perdas de condutividade. Nesse sentido, a combinação de eletrodos e eletrólitos otimizados é uma alternativa promissora para o desenvolvimento de tais dispositivos.This work has as objective to evaluate anodes and electrolytes in direct ethanol fuel cells (DEFC) operating at high temperature (130 ºC). As anode materials, electrocatalysts based on PtSn/C were prepared by Modified Polyol Method with various Pt:Sn atomic ratios. Such methodology promotes selforganized electrocatalysts production with narrow particle size distribution and high alloying degree. The eletrocatalysts were characterized by XRD, and CO stripping. The results showed that these materials presented high alloying degree and Eonset CO oxidation at lower potential as commercial materials. As electrolyte, Nafion-SiO2 hybrids were synthesized by sol-gel reaction, by the incorporation of oxide directly into the ionic aggregates of various kinds of Nafion membranes. The synthesis parameter, such sol-gel solvent, membrane thickness and silicon precursor concentration were studied in terms of silica incorporation degree and hybrid mechanical stability. Finally, the optimized anodes and electrolytes were evaluated in DEFC operating at 80 130 ºC temperature range. The results showed a significant improvement of the DEFC performance (122 mW cm-2), resulted from the acceleration of ethanol oxidation reaction rate due to anode material optimization and high temperature operation once the use of hybrids possibilities the increase of temperature without a significant conductivity loses. In this sense, the combination of optimized electrodes and electrolytes are a promising alternative for the development of these devices.
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Dresch, Mauro André. "Síntese e caracterizção eletroquímica de membranas híbridas Nafion-SIO2 para a aplicação como eletrólito polimérico em células a combustível tipo PEM". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-26092011-141218/.
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Neste trabalho foi estudado o efeito dos parâmetros de síntese na resposta de polarização de híbridos Nafion-SiO2 como eletrólitos em células a combustível poliméricas (PEMFC) em elevadas temperaturas (até 130 °C). A fase inorgânica foi adicionada à matriz polimérica com o objetivo de aumentar a retenção de água na membrana em elevadas temperaturas (acima de 100 °C); melhorar as propriedades mecânicas do Nafion e favorecer cineticamente as reações eletródicas. As membranas foram preparadas a partir da incorporação in-situ de sílica em membranas comerciais de Nafion por rota sol-gel acompanhada de catálise ácida. Os parâmetros de síntese, tais como: concentração do catalisador ácido, natureza do solvente, temperatura e tempo de reação e concentração do precursor de silício (Tetraetil-Ortosilicato TEOS) foram avaliados em função do grau de incorporação e resposta de polarização. Os híbridos Nafion-SiO2 foram física e quimicamente caracterizados por gravimetria, termogravimetria (TG), microscopia eletrônica de varredura e espectroscopia de energia dispersiva de raios X (MEV-EDX), espectroscopia de impedância eletroquímica (EIS) e espalhamento de raios X em baixos ângulos (SAXS). Por fim, os híbridos sintetizados foram avaliados diretamente como eletrólitos em células PEM unitárias alimentadas com hidrogênio (H2) e oxigênio (O2) no intervalo de temperatura de 80 ºC a 130 ºC e a 130 ºC em condições de umidade relativa reduzida (75 e 50%). Resumidamente, o desempenho dos híbridos se mostrou fortemente dependente dos parâmetros de síntese, principalmente, o tipo de álcool utilizado e concentração inicial de TEOS.In this work, the effect of sol-gel synthesis parameters on the preparation and polarization response of Nafion-SiO2 hybrids as electrolytes for proton exchange membrane fuel cells (PEMFC) operating at high temperatures (130 oC) was evaluated. The inorganic phase was incorporated in a Nafion matrix with the following purposes: to improve the Nafion water uptake at high temperatures (> 100 oC); to increase the mechanical strength of Nafion and; to accelerate the electrode reactions. The hybrids were prepared by an in-situ incorporation of silica into commercial Nafion membranes using an acid-catalyzed sol-gel route. The effects of synthesis parameters, such as catalyst concentration, sol-gel solvent, temperature and time of both hydrolysis and condensation reactions, and silicon precursor concentration (Tetraethylorthosilicate TEOS), were evaluated as a function on the incorporation degree and polarization response. Nafion-SiO2 hybrids were characterized by gravimetry, thermogravimetric analysis (TGA), scanning electron microscopy and X-ray dispersive energy (SEM-EDS), electrochemical impedance spectroscopy (EIS), and X-ray small angle scattering (SAXS). The hybrids were tested as electrolyte in single H2/O2 fuel cells in the temperature range of 80 130 oC and at 130 oC and reduced relative humidity (75% and 50%). Summarily, the hybrid performance showed to be strongly dependent on the synthesis parameters, mainly, the type of alcohol and the TEOS concentration.
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Vecchi, Pierpaolo. "Caratterizzazione elettrica e spettroscopia superficiale di film sottili a base di silicio". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16338/.
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Questa tesi presenta la misura di proprietà elettriche e ottiche di film sottili a base di Si, in particolare ossinitruri di silicio (a-SiOxNy) e ossidi di silicio (a-SiOx) sub-stechiometrici.
Questi materiali trovano applicazione nelle celle solari ad eterogiunzione in Si con due funzioni: strato passivante e contatto elettrico. Il silicio amorfo idrogenato, sia intrinseco che drogato, utilizzato finora per buffer layer ed emettitore, presenta assorbimento parassita della luce, ma l'introduzione di carbonio, azoto e/o ossigeno amplia il bandgap del materiale e ostacola la fotogenerazione di cariche. I campioni depositati con PECVD, con tutti i flussi costanti e variando quelli di N2O e CO2, hanno proprietà ottiche ed elettriche migliori del Si amorfo.
Sono state depositate due serie con silano e CO2 per a-SiOx, silano e N2O per a-SiOxNy. In altre due serie è stato aggiunto anche diborano, per ottenere silicio drogato boro.
Sono state effettuate misure di corrente-tensione su campioni depositati su vetro borosilicato (per eliminare la componente spuria del substrato nella misura della resistività) e misure di surface photovoltage (SPV) su campioni depositati su c-Si drogato boro per individuare bandgap dei materiali e qualità dell’interfaccia layer-substrato.
È risultato che i campioni con boro hanno conduttività maggiore dei rispettivi campioni intrinseci, ma non ad alte concentrazioni di azoto e ossigeno, che causano aumento del disordine reticolare e ostacolano l’attivazione del drogante.
Il carbonio, invece, introdotto nel materiale solo per alti
flussi di CO2, agisce probabilmente come drogante e
promuove l’aumento della conducibilità elettrica.
Le misure SPV hanno individuato il bandgap del silicio amorfo intorno a 1.8 eV. È stato inoltre possibile vedere transizioni energetiche dovute ad altre fasi presenti nel materiale. Indagando un diverso range di energia è stato possibile studiare la qualità dell’interfaccia con il substrato.
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McConkie, Thomas O. "Curious Growth of a Buried SiO2 Layer". BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3755.
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Initial investigation of Moxtek wire grid polarizers composed of Al and coated with SiO2 - SiX - SiO2 (where SiX is used to indicate a Si rich layer whose complete composition is not to be disclosed for proprietary reasons) showed a growth of 3x in the inner (closest to Al) SiO2 layer after baking. Upon removing the X and varying rib composition and layering composition and geometries in 12 sets of before and after samples, no obvious growth was observed. Even baking the original unbaked sample yielded no growth. Our data suggest that the initial conclusion of buried oxide growth was flawed and that the observed changes in optical properties upon baking are either very sensitive to layer thicknesses (smaller than we can confidently observe) or due to some other mechanism. Here we present our sample preparation and analysis using the Focused Ion Beam (FIB), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive Xray Spectroscopy (EDXS).
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Quiroga, Jean-Manuel. "Étude des propriétés optiques de multicouches a-Si:H/a-SiO2". Grenoble 1, 1998. http://www.theses.fr/1998GRE10124.
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L'etude porte sur les proprietes optiques de puits nanometriques multiples a-si:h/a-sio#2 elabores par pecvd (he+sih#4+o#2). Les caracteristiques des materiaux de reference sont determinees par diverses techniques de spectroscopie optique. Nous montrons la necessite de simuler les spectres en tenant compte des reflexions multiples afin d'eviter des erreurs importantes sur la valeur du coefficient d'absorption. Des mesures in situ de la teneur en oxygene dans le plasma nous ont permis de determiner une procedure de depot des multicouches reduisant la largeur des interfaces. La modulation de la composition chimique dans l'epaisseur est observee par des mesures de met, de rayons x et de spectrometrie infrarouge. La simulation des spectres de transmission infrarouge de la multicouche consideree comme un milieu effectif montre que l'interface a-sio#2/a-si:h est la plus large. La variation de l'epaisseur des motifs pour des series de multicouches de largeur de puits (d#a#-#s#i#:#h) ou de barriere constante permet d'elaborer des profils-modele de la composition d'oxygene en epaisseur x(d) en tenant compte de la reduction de la couche de silice et de l'oxydation de celle du silicium amorphe par le plasma lors du depot des couches ulterieures. Nous presentons enfin les mesures d'absorption et de photoluminescence des multicouches. La reduction de la largeur du puits conduit a une augmentation apparente du gap (e#g) mais une analyse plus fine s'appuyant sur le modele physico-chimique montre que la valeur apparente de e#g ne correspond pas a la separation minimale entre les bandes de valence et de conduction. Une emission de lumiere visible a l'il a temperature ambiante est observee pour des largeurs de puits nominales inferieures a 20a. Contrairement aux predictions du modele de confinement quantique, la position du pic de photoluminescence est independante de d#a#-#s#i#:#h. Nous concluons que la presence de sous-oxydes au fond du puits est a l'origine de l'emission observee.
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Andrade, Gessie Maria Silva de. "Oxidação parcial de metano a compostos oxigenados (HCHO e CH3OH) sobre catalizadores oxidos MoOx/MgO-SiO2 e VOx-SiO2". [s.n.], 2003. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267468.
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Orientador: Gustavo Paim ValençaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: A utilização cada vez maior do gás natural como combustível deve-se ao aumento da demanda de energia nos países em crescimento acompanhado da disponibilidade crescente das reservas de gás em relação às de petróleo, o que pode tomá-Io uma fonte de energia de grande importância neste século XXI. O metano é o componente presente em maior quantidade no gás natural, constituindo mais de 90% da fração dos hidrocarbonetos. Um dos processos mais utilizados para funcionalização das moléculas de hidrocarbonetos, tais como o metano, é a oxidação parcial. Desta forma, no presente estudo foi realizada a oxidação parcial do metano a compostos oxigenados (HCHO e CH30H) a pressão atmosférica utilizando catalisadores de óxidos redutíveis de MoOx/MgO-Si02 e VOx/MgO-Si02 com a finalidade de investigar a influência da introdução de MgO no suporte dos catalisadores e da concentração superficial de Mo+n e V+n na atividade e seletividade destes catalisadores, assim como o efeito da razão CH4:O2 na cinética desta reação. Os óxidos mistos de MgO- Si02 foram preparados em razões atômicas preestabelecidas (Mg:Si = 1:0, 3:1,2:1, 1:1, 1:3, 1:2 e 0:1), secos e calcinados a 400 K por 12 horas e 1050 K por 5 horas, respectivamente. O método para a introdução da fase ativa Mo ou V nos suportes foi a impregnação incipiente, obedecendo-se seis diferentes percentagens em peso de Mo+6 ou V+5 nos sólidos finais: 0,1%, 1,67%, 2,2 %, 3,25%, 4,82%, 6,4%, os quais foram caracterizados por difração de raios-X, adsorção de N2 e adsorção seletiva de O2. Os principais produtos observados para a reação em estudo foram HCHO, CO, CO2, sendo que HCHO e CH30H (produtos de oxidação parcial) foram favorecidos por altas razões molares de CH4:O2. A formação de CH3OH foi observada em teores moderados de óxidos metálicos (0:l[Mg:Si]/0,I%Mo e 0:1[Mg:Si]/3,25%Mo), os quais apresentaram consideráveis seletividades para esse produto (32% e 18%, respectivamente). Os resultados obtidos para as constantes de velocidade demonstraram que para baixas conversões, a seletividade para HCHO se aproxima de 100%, enquanto a seletividade para CO2 se manteve em valores baixos, próximos de zero, mostrando que em condições diferenciais (conversão de CH4 < 10%) a velocidade de formação de HCHO é maior que a velocidade de formação de CO2
Abstract: Methane is the major component of natural gas, often present as more than 90% of the gas. Current1y it is primarily used as a fuel. In the chemical industry it is used in the production of synthesis gas, hydrogen, and in the manufacture of the halogen derivatives of methane, acetylene, hydrogen cyanide, technical carbon, and many other products. The direct conversion of methane to formaldehyde and methanol in a single catalytic step in sufficient1y high yield would give rise to new opportunities in the conversion of natural gas to other useful fuels and chemicals. Both the homogeneous and heterogeneous processes have been studied under various conditions although progress toward obtaining a yield that would make such a process industrially viable has been very slow. The majority of these studies have involved metal oxide catalysts. In this work, the selective oxidation of methane to oxygenated compounds (HCHO e CH3OH) at atmospheric pressure was studied on MoOxfMgO-SiO2 and VOx/MgO-SiO2. The mixed oxides of magnesia and silica were prepared in different atom ratios (Mg:Si = 1:0, 3:1,2:1, 1:1, 1:3, 1:2 or 0:1), dried at 400 K for 12 h and calcined at 1050 K for 5 h. The active phase, Mo (H24Mo7N6O24) or V (H4NO3 V), was added to the supports by the incipient wetness method. The percentages of Mo or V added to the mixed oxides were 0,1%, 1,67%,2,2%,3,25%,4,82% or 6,4%. The solids were characterized by X-ray diffraction, BET surface area and oxygen chemisorption. The objective of the present work was to study the influence of the introduction of MgO in the supports, of the amount of Mo and V on the surface of the supports and of the CH4:O2 molar ratios. Both supported Mo and V oxides were active in the conversion of methane to C1-oxygenates and Cox. The main products of the oxidation reaction were HCHO, CO and CO2. The partial oxidation products (HCHO, CH30H) were favored by high CH4:O2 molar ratios and formaldehyde was the first oxidation product, which was further oxidized to CO. The vanadium oxide catalysts were more active than the molybdenum oxide catalysts in conversion of methane. However, the higher reaction rate also resulted in a further oxidation of HCHO to CO
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
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Soares, Liliana do Amaral. "Cu/SiO2 : catalisador reciclável para a síntese one pot de triazóis". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/97958.
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A procura por novas tecnologias tem movido a ciência em todos seus setores. Na química um campo tecnológico que tem sido muito procurado nos últimos tempos é o dos compostos miméticos de produtos naturais. A busca de métodos simples e eficientes de síntese veio ao encontro desta busca com a click chemistry e sua cicloadição 1,3-dipolar catalisada por cobre, com a qual é possível a síntese de 1,2,3-triazóis-1,4-dissubtituídos de forma rápida e eficiente. Neste trabalho foi produzido um novo catalisador de cobre através do método sol-gel denominado Cu-sílica e testado o mesmo na cicloadição 1,3-dipolar frente a diferentes substratos e fontes de energia. Quando utilizados brometos de benzila em sistema one pot multicomponete obtivemos rendimentos de até 95% em sistema com fonte de calor após 12 horas de reação ou irradiação por microondas durante 10 minutos. Com o uso de ácidos borônicos azida e acetinelos como substrato chegamos a rendimentos de 91% com aquecimento e um tempo reacional de 48 horas a 50º C, outras fontes de energia não lograram êxito para este substrato. Finalmente foi desenvolveida uma metodologia one pot para síntese dos 1,2,3-triazóis a partir de álcoois, esta consiste de um sistema em 2 etapas reacionais que englobam três tranformações em 25 horas de reação com rendimento de 60%.The search for new technologies has inspired the science in all areas of chemistry and one of the most studied research fields lays on the search for natural product's mimetics. A good example, among different efforts for simple and efficient new methods of synthesis, is the click chemistry and its Cu catalysed 1,3-dipolar cycloaddition, once this reaction permits quick acess to 1,4-disubstituted-1,2,3-triazoles. In this work we synthesized a copper catalyst through the sol-gel methodology, so called Cu-silica and tested it in the 1,3-cycloaddition reaction, using different starting materials and energy sources. At first we applied this catalyst in a multicomponent reaction in which benzyl bromides, sodium azide and different acetylenes and the reaction was heated for 12 hours or 10 minutes under microwave irradiation (50W), providing the 1,2,3-triazoles with 95% of yield. Further we changed the benzyl halides for boronic acids; we didn’t have success using non-classical heating systems (microwave or ultrasound), however under traditional heating at 50º C for 48 hours we got the product in 91% yield. Finally we developed a new one-pot metodology to obtain 1,2,3-triazoles from alchools. This procedure consists in a two-step continuous system embracing three transformations wihtin 25 hours with an overall yield of 60%.
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Ray, Samuel L. "Evaluation of a High School Sheltered Instruction Observation Protocol (SIOP) Implementation". DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/848.
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Many school systems across the USA have implemented sheltered instruction observation protocol (SIOP) strategies to help their English language learners (ELLs) master core content while they learn English. Most studies have reported positive results from using SIOP strategies with ELLs. Elementary and middle school studies were available, but studies of SIOP implementation in a comprehensive high school were lacking. This action research project was initiated by teacher leaders (department chairs) and the school principal. It included a year of combined SIOP training and implementation. After the first academic year of utilizing SIOP school-wide, an anonymous electronic survey was used to collect information on teacher implementation, the teachers' perceptions of students' success, and teacher plans for future use of the SIOP model.
This study was implemented in a comprehensive high school in the Rocky Mountain region. The research questions were: To what degree, do teachers having received in-service training in SIOP, report implementing the various components of the program in their daily instruction? After one school year of implementing the SIOP model, what are teachers' perceptions regarding the effectiveness of using the SIOP model with students? How does SIOP need (number of ELLs per class), class size, years of teaching experience, teaching subject, or prior English as a second language (ESL) training relate to a teacher's perception of SIOP effectiveness scale? Is the level of implementation related to the teacher's perceptions of effectiveness? Do teachers plan to use the SIOP model in the future?
Teachers reported a high degree of implementing SIOP strategies. They perceived the strategies improved student learning in most cases. There was no statistically significant relationship found between the degree of SIOP implementation and perceptions of the effectiveness of SIOP. Correlational analyses indicated that SIOP need (number or ELLS per class), class size, years of teaching experience, teaching subject, and prior ESL training did not affect the degree of implementation or perceptions of the effectiveness of the SIOP model in this comprehensive high school.
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Li, Bin, i 李斌. "A study of integrated semiconductor thin-film sensors on sio2/si substrate". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B30446752.
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Li, Bin. "A study of integrated semiconductor thin-film sensors on sio2/si substrate". Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23000995.
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Feltrin, Jucilene. "Estabilização a elevadas temperaturas da fase anatase com partículas submicrométricas de SiO2". reponame:Repositório Institucional da UFSC, 2012. http://repositorio.ufsc.br/xmlui/handle/123456789/100746.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2012Made available in DSpace on 2013-06-25T22:14:09Z (GMT). No. of bitstreams: 1 315030.pdf: 3432223 bytes, checksum: 84054f849bb4c014ae9bc3dca9e31665 (MD5)
Este estudo descreve rotas desenvolvidas para obter a estabilidade da fase anatase em temperaturas acima de 900oC, através da mistura via seco de titânia e estabilizantes (quartzo e sílica amorfa), prensagem e tratamento térmico em condições industriais típicas da cerâmica de revestimento. A avaliação das fases obtidas após tratamento térmico foi realizada por difração de raios-X e por microscopia eletrônica de varredura. Em termos de processamento, as composições que revelaram maior estabilidade da fase anatase foram aquelas em que se utilizou uma titânia com maior tamanho de partícula e com dopante quartzo. Após a avaliação dos resultados foram estudados os possíveis mecanismos de formação da fase anatase e como estes foram afetados pela adição dos dopantes. Por fim, propõe-se uma rota para a estabilização da fase anatase a partir das características da titânia, dopantes e tratamento térmico. A obtenção da fase anatase em revestimentos cerâmicos é promissora e está sendo amplamente estudada por diversos pesquisadores devido à propriedade fotocatalítica deste material, capaz de degradar uma grande variedade de poluentes orgânicos tóxicos em substâncias menos inofensivas.
Abstract : This study describes routes developed to obtain the anatase phase stability at temperatures above 900oC, by blending via dried and titania stabilizers (quartz and amorphous silica), pressing and heat treatment in typical industry conditions of ceramic coating. The evaluation of the phase obtained after heat treatment was carried out by X-ray diffraction and scanning electron microscopy. In terms of processing, the compositions that showed increased stability of anatase, were those which used a titania with higher particle size and with dopant quartz. After the evaluation of the results, we studied the possible mechanisms formation of the anatase phase and how they were affected by the addition of dopants. Finally, a route is proposed for stabilizing the anatase phase from the characteristics of titania, doping and thermal treatment. The anatase phase coatings are being extensively studied by many researchers due to photocatalytic property of the material, capable of degrading a variety of toxic organic pollutants into less harmless substances.
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Kramerová, Nina. "Vliv mineralizátorů na slinování a fázové transformace v soustavě Li2O-Al2O3-SiO2". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-216638.
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This work is focused on Li ceramics and glass-ceramics with low thermal expansion. Composition of these material is based on mineralogical composition of ?-spodumene – Li2O•Al2O3•4SiO2. Sol-gel route of preparation was used for preparation of the material. Sol-gel route is profitable because of production of high purity and controlled grain size powder. Lower sintering temperature, higher degree of homogeneity and shorter time of heat treatment in comparison with traditional approach belong among other advantages of sol-gel route of preparation. Influence of Li+ substitution for K+, which has similar atomic radius, is assessed in this work. These ions are localized in the interstitial position of spodumene structure and are able to maintain the charge balance. Li+ ions were substituted with K+ in the amount of 0; 0,5; 1; 2; 5 and 10 wt. % in view of Li+ weight. In the next step influence of adding mineralizer was specified in the material modified this way. The effect of adding mineralizer on phase transformation and heat treatment tendency was considered. K+ were added to the mixture in the form of potash. Due to this addition forming of orthoclase phase next to spodumene, eucryptit and SiO2 (ss) was detected. Decrease in melting temperature and ability of melt to crystallize were consequence of orthoclase forming. No crystallization appears, when more than 1 wt.% of K+ was added.
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Thyssen, Vivian Vazquez. "Catalisadores Ni/MgO-SiO2 aplicados na reação de reforma a vapor de glicerol". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-29062016-162740/.
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Catalisadores de Ni (10% em massa) suportado em matrizes mistas MgO-SiO2 foram aplicados na reação de reforma a vapor de glicerol. Os efeitos do teor de MgO como aditivo e do método de preparação foram avaliados frente às propriedades físico-químicas e texturais dos materiais; assim como à atividade, seletividade, estabilidade e formação de carbono na reforma a vapor do glicerol. Os catalisadores foram preparados com diferentes teores mássicos de MgO (10%, 30% e 50%) sobre SiO2 comercial, utilizando processo via seca (mistura física) e via úmida (impregnação sequencial com diferentes solventes: água, etanol e acetona). Foram utilizadas as técnicas de caracterização de espectroscopia de energia dispersiva de raios X, fisissorção de nitrogênio, difratometria de raios X, termogravimetria, difratometria de raios X in situ com O2, redução a temperatura programada com H2, difratometria de raios X in situ com H2, dessorção a temperatura programada com H2 e microscopia eletrônica de varredura. Foi observado que o Ni(II) interage de forma variada com os suportes com diferentes teores de MgO, e que a polaridade do solvente de impregnação utilizado no processo de preparação influencia as propriedades dos catalisadores. A fim de verificar a atividade, seletividade e deposição de carbono; os catalisadores foram testados na reação de reforma a vapor de glicerol a 600oC, por um período de 5h e razão molar água:glicerol de 12:1. Após as reações, os catalisadores foram novamente submetidos às análises de termogravimetria, difratometria de raios X e microscopia eletrônica de varredura, visando a caracterização dos depósitos de carbono obtidos durante o processo catalítico. Os catalisadores de matrizes mistas se mostraram ativos e apresentaram seletividades similares para os produtos gasosos CH4, CO e CO2, além de um alto rendimento em H2. Observou-se que a adição de MgO no suporte, aumentou a dispersão do Ni(II) no material, que por sua vez, influenciou na quantidade de carbono depositado ao longo da reação. A polaridade do solvente de impregnação também teve influência na dispersão metálica, sendo que, quanto menor a polaridade do solvente, maior foi a dispersão obtida no catalisador, e menor a deposição de carbono na reação. O material que apresentou o melhor desempenho catalítico frente ao rendimento de H2 e à deposição de carbono, foi o catalisador preparado com 30% de MgO com etanol como solvente de impregnação.Ni catalysts (10wt%) supported on MgO-SiO2 were assessed in glycerol steam reforming reaction. The effects of MgO as additive and preparation method were evaluated on physico-chemical and textural materials properties; as their activity, selectivity, stability and carbon formation in glycerol steam reforming. The catalysts were prepared with different amounts of MgO (10wt%, 30wt% and 50wt%) on commercial SiO2 by dry process (physical mixture) and wet process (sequential impregnation with water, ethanol and acetone as solvents). Samples were characterized by energy dispersive X-ray spectroscopy, nitrogen physisorption, X-ray diffraction, thermogravimetry, in situ X-ray diffraction with O2, temperature programmed reduction with H2, in situ X-ray diffraction with H2, temperature programmed desorption with H2 and scanning electron microscopy. It was observed that the Ni(II) interacts differently with supports with different MgO content, and the polarity of impregnation solvent used in preparation process influences on catalysts properties. In order to evaluated the activity, selectivity and carbon deposition, the catalysts were tested in glycerol steam reforming reaction at 600oC for 5h and water:glycerol molar ratio of 12:1. After reaction, carbon deposits obtained during the catalytic process were characterized by thermogravimetry, X-ray diffraction and scanning electron microscopy. Mixed matrices catalysts were active in glycerol steam reforming and showed similar selectivity for the gaseous products (H2, CH4, CO and CO2), with a high H2 yield. It was observed that the addition of MgO increased Ni(II) dispersion on material, which influenced on the quantity of carbon deposited during reaction. Polarity of impregnation solvent had also influence on metallic dispersion, and smaller the solvent polarity, higher the dispersion obtained in the catalyst, and lower the carbon deposition on reaction. The material that showed the best catalytic performance in H2 yield and carbon deposition, was the catalyst prepared with 30wt% of MgO with ethanol as impregnation solvent.
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Nezval, David. "Výpočty interakce systému grafen/SiO2 s adsorbovanými atomy a molekulami pomocí DFT metod". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231953.
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This master's thesis studies the electronic properties changes of graphene caused by substrate SiO2, adsorbed molecules of water and atoms of gallium. There are tested different geometrical configurations of these systems and consequently calculated band structures to derive the changes of the electronic properties: the doping effect and band gap opening of graphene layer.
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Sanjon, Elvira Prisca [Verfasser], Barbara Akademischer Betreuer] Drossel i Michael [Akademischer Betreuer] [Vogel. "A molecular dynamics investigation of tetrahedral liquids and aqueous solutions in bulk (SiO2 ) and confinements (SiO2, H2O, water-octanol mixtures) / Elvira Prisca Sanjon ; Barbara Drossel, Michael Vogel". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1173899154/34.
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Sanjon, Elvira Prisca Verfasser], Barbara [Akademischer Betreuer] Drossel i Michael [Akademischer Betreuer] [Vogel. "A molecular dynamics investigation of tetrahedral liquids and aqueous solutions in bulk (SiO2 ) and confinements (SiO2, H2O, water-octanol mixtures) / Elvira Prisca Sanjon ; Barbara Drossel, Michael Vogel". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1173899154/34.
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Krishnamoorthy, Soumya. "Development of a ZnO/SiO₂/Si high sensitivity interleukin-6 biosensor". College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6702.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Santos, Daniele Cristina Almeida Hummel Pimenta. "Obtenção e caracterização de materiais dopados SiO2-CdSe a partir de sonogeis de silica". [s.n.], 1994. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265224.
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Orientador: Iris Concepcion Linares de TorrianiTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: O processo de obtenção de materiais pela via sol-gel tem-se mostrado muito interessante na obtenção de novos materiais como atesta o grande número de trabalhos desenvolvidos na última década. A possibilidade de obter materiais sólidos monolíticos assim como pós, filmes e fibras a partir de uma mistura no estado líquido à temperatura ambiente através de reações de agregação e polimerização é particularmente interessante. A fácil manipulação da composição química precursora permite criar materiais compósitos com propriedades ópticas, eletrônicas, químicas, mecânicas especiais para aplicações em alta tecnologia. Em particular, os materiais compostos de uma matriz vítrea com inclusão de nanocristais semicondutores apresentam propriedades ópticas não-lineares e são considerados de grande importância tecnológica em aplicações estratégicas, como comunicação e processamento de informações. Neste trabalho apresentamos os resultados da obtenção de materiais compostos por partículas semicondutoras imersas numa matriz ele sílica gel. As matrizes hospedeiras foram preparadas por hidrólise do tetraetilortosilicato (TEOS) com adição de nitrato de cádmio. Como agente controlador da cinética ele secagem (drying control chemical additive -DCCA) foram usadas a formamida e a N-N-dimetilformamida. O processo de preparação incluiu a aplicação de doses pré-determinadas de ultrasom de alta potência. As matrizes foram caracterizadas através de técnicas de análise térmica (ADT e ATG), adsorção de gases (BET), picnometria de mercúrio, microscopia eletrônica de varredura (SEM) e espalhamento de raios X a baixos ângulos (SAXS). A impregnação do "sonogel" seco com uma solução de KSeCN realizada em condições de vácuo, permitiu a formação de nanocristais de seleneto de cádmio (CdSe) e melhorou as propriedades mecânicas da matriz. Xerogéis vermelhos e transparentes foram obtidos e caracterizados por espectroscopia óptica de absorção, microscopia eletrônica por transmissão (TEM) e SAXS. Os resultados desses estudos levam a propor um modelo estrutural para estes materiais consistente em uma matriz porosa contendo nanocristais de seleneto de cádmio, apresentando uma distribuição de tamanhos bimodal que depende da concentração de selênio na solução usada para a difusão líquida. O deslocamento das bandas de absorção óptica para grandes energias ("blue shift") revela o confinamento quântico nos nanocristais de seleneto de cádmio
Abstract: The sol-gel process has proved to be extremely interesting in the production of new materiaIs. This is clearly indicated by the great number of publications in this area in the last decade. The possibility of obtaining monolithic solid materials and also powders, films and fibers from a liquid mixture of components at room temperature via aggregation and polymerization reactions is particularly interesting. The easy way in which chemical composition can be modified allows the preparation of composite materiais with specific optical, electronic, chemicalor mechanical properties designed for special applications in modern tecnology. In particular, materiaIs consisting in a vitreous matrix with embedded nanocrystals of semiconductor compounds are known to present non-linear optical properties wich makes them very important in strategic technological applications, such as communications and data processing. In this work we present the results of the preparation of materials consisting of semiconducting nanoparticles embedded in a silica gel matrix. The host matrices were prepared by hydrolysis of tretaethylortosilicate (TEOS) with the addition of cadmium nitrate. Two different additives were used as a drying control agent (DCCA) : formamide and N-Ndimethylformamide. The preparation process included the use of pre-determined doses of high power ultrasound. The matrices were characterized by thermal analyses (TGA and DTA), gas adsorption techniques (BET), mercury picnometry, scanning electron microscopy (SEM) and small angle X ray scattering (SAXS). The impregnation of the dry "sonogels" using a KSeCN solution under vacuum, led to the formation of CdSe nanocrystals and improved the mechanical properties of the matrix. Typically red, transparent xerogels were obtained and characterized by optical absorption spectroscopy, transmission electron microscopy (TEM), and SAXS. The results of this study lead to propose a structural model for these materials, consisting of a porous matrix containing CdSe nanocrystals with a bimodal size distribution that depends on the selenium content in the solution used for the liquid diffusion. The shift in the optical absorption band towards higher energies (blue shift) revcals the quantum confinement in the nanosized particles of cadmium selenide
Doutorado
Doutor em Engenharia Mecânica
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Taghi, Khani Arefeh. "Characterization of growth of GaAs on Si/SiO2 via a thin layer of perovskite". Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11433/.
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Wafers of silicon (Si) are the standard material for deposition of thin layers used for all electronic devices; however, Si has an indirect band-gap and is thus not very efficient for optical applications. Gallium arsenide (GaAs) is much more expensive than Si, but due to its direct band-gap it is widely used for light-emitting and laser diodes. One approach towards an integrated optoelectronics with high efficiency is to grow GaAs on Si. Due to lattice mismatch, direct epitaxy of GaAs on Si leads to strain and so to dislocations and other defects detrimental to high-quality thin layers. There are various approaches for epitaxy of GaAs on Si, and this project investigates one of them. The purpose of this research has been investigating and characterizing the growth of GaAs on Si via thin layers of perovskites on top of native silicon oxide. The idea that motivated this study was a allegation by Motorola in 2001, aiming at commercialising this route for high frequency wireless and opto-electronic devices. Pulsed laser deposition (PLD) of thin layers of perovskite materials (SrTiO3 and BaTiO3) on Si(001) substrates via layers of native oxide was performed at the Technische Universität Darmstadt, Germany. The wafers then have been sent back to the University of Sheffield. The as-grown materials have been investigated using different techniques such as atomic force microscopy (AFM), scanning transmission electron microscopy (STEM) and ellipsometry. Then they have been annealed and over-grown at the National Centre for III-V Technologies at the University of Sheffield using a combined molecular beam epitaxy (MBE)-scanning tunnelling microscopy (STM) system with built-in reflection high energy electron diffraction (RHEED). The over-grown specimens have finally again been investigated using AFM, TEM, STEM and energy dispersive X-ray spectroscopy (EDXs) techniques. Here, particular emphasis has been on correlating quantitatively surface topology measurements by AFM with interface roughness measurements on cross-sectioned samples in STEM. The aim of this study was to find a way to over-grow silicon substrates with GaAs with low dislocation density, however, the perovskite layers and the subsequent GaAs never grew epitaxially but always remained poly-crystalline. This has been attributed to a lack of surface reconstruction of the perovskite layers when annealed under vacuum conditions, as confirmed by in-situ RHEED. Other studies have used sulphide buffer layer or a relaxed buffer layer of BaxSr1−xTiO3 to guarantee the perovskite thin layer to grow epitaxially. The over-growth of GaAs also has been done with the presence of oxygen to prevent the perovskite to evaporate.
23
Bohnlein, Ivy Briana 1974. "Wounded Knee in 1891 and 1973: Prophets, protest, and a century of Sioux resistance". Thesis, The University of Arizona, 1998. http://hdl.handle.net/10150/278658.
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Wounded Knee has been the site of two significant encounters between the United States and the Sioux nation: the massacre at Wounded Knee in 1891, and the takeover of Wounded Knee Village in 1973. These encounters are related to each other by more than location: both were the result of Sioux participation in a national movement. In the 1880s, that movement was the Ghost Dance, though Sioux involvement was characterized by a uniquely hostile approach. A century later, the Sioux of Pine Ridge reservation formed an alliance with the national American Indian Movement that resulted in a seventy-one day armed siege at Wounded Knee. During both time periods, similar historical factors, external forces, and internal conflicts resulted in the Sioux taking part in these movements, but the unique character of their resistance was shaped by internalized values and a cultural model which favored an aggressive response to perceived threats.
24
Dong, Tianqi. "A study of infrared femtosecond laser irradiation on monolayer graphene on SiO2/Si substrate". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275642.
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Graphene is a single hexagonal atomic carbon layer. Since its discovery, graphene is emerging as an exciting and promising new material to impact various areas of fundamental research and technology. It has potentially useful electrical properties for device applications such as graphene photodetectors and graphene-based sensors. This thesis focuses on the femtosecond laser processing of graphene from both scientific and industrial points of view. Started from the manufacturing process, a new manufacturing route for graphene devices based on a femtosecond laser system is explored. In this thesis, the graphene ablation threshold was determined in the range of 100 mJ/cm2. In this deposited fluence range, selective removal of graphene was achieved using femtosecond laser processing with little damage to the SiO2 /Si substrate. This finding supports the feasibility of direct patterning of graphene for silicon-substrate field effect transistors (FETs) as the gate dielectric, silicon dioxide is only negligibly removed (2~10 nm) and no damage occurs to the silicon. Beyond the selective removal of graphene, the effects of exposing femtosecond laser pulses on a monolayer of graphene deposited on a SiO2/Si substrate is also studied under subthreshold irradiation conditions. It has been demonstrated that a femtosecond laser can induce defects on exposure. The dependence of the D, G, and 2D Raman spectrum lines on various laser pulse energies was evaluated using Raman Spectroscopy. The I (D)/I (G) ratio was seen to increase with increasing laser energy. The increase in the D’ (intravalley phonon and defect scattering) peak at 1620 cm-1 appeared as defective graphene. These findings provide an opportunity for tuning graphene properties locally by applying femtosecond laser pulses. Applications might include p-n junctions, and the graphene doping process. To explore the power absorption process in graphene and the SiO2/Si substrate, a theoretical model was developed based on the transfer-matrix method. The results revealed that the most significant absorption was in the silicon substrate. The light reflection form each layer was considered. The model shows the temperature oscillations are more significant in the silicon layer compared to the silicon dioxide which can provide a theoretical rationale for the swelling effect observed in the experiments. This model can assist in the choice of laser parameters chosen for future laser systems used in the production of graphene devices.
25
Williams, Michael Shawn. "An Investigation of Internalizing Social-Emotional Characteristics in a Sample of Lakota Sioux Children". DigitalCommons@USU, 1997. https://digitalcommons.usu.edu/etd/6306.
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It has only been recently that research in childhood psychopathology has focused
on a group of disorders referred to as internalizing disorders. Internalizing disorders can
include such problems as depression. anxiety, social withdrawal, and somatic complaints.
Even though research has begun to focus on internalizing disorders with majority
children. there has been very little research conducted on ethnic minority children, Native
American children in particular.
The present study involved obtaining a Native American sample and determining
their internalizing symptomology utilizing the Internalizing Symptom Scale for Children
(ISSC), the Reynolds Child Depression Scale (RCDS), and the State Trait Anxiety
Inventory for Children (ST AIC). The study sample was compared to a matched
normative sample from the ISSC database. Statistical procedures included bivariate
correlations, analysis of variance (ANOV A), and discriminant function analysis.
Correlations between the ISSC and the two comparison measures (RCDS and ST AIC)
were in the expected direction and of moderate to strong magnitude. The total
internalizing symptoms scores of the Native American (Lakota Sioux) sample were
similar to those of a matched comparison group from the ISSC national normative database.
However, the study sample evidenced a unique pattern of responses on the ISSC
subscales, reporting lower rates of both internalizing distress and positive affect. Teacher
nominations of potential "internalizers" proved to be a poor predictor of their self-reported
symptoms. Implications of this study for clinical practice and future research
directions in this area are discussed.
26
Kalinová, Helena. "Vliv mineralizátorů na šířku intervalu slinování a fázové transformace v soustavě Li2O-Al2O3-SiO2". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2008. http://www.nusl.cz/ntk/nusl-216345.
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Course of synthesis of Li2O – Al2O3 – SiO2 (LAS) ceramic via sol – gel process made precursor was investigated. Powder precursor containing LAS components in molar ratio 1:1:4 were prepared by polycondensation technique in aqueous medium using lithium chloride (LiCl), hydrated aluminium nitrate (Al(NO3)39H2O) and silica sol (tosil), respectively. Heated sol was transformed into gel. The resulting gel was dried at temperature 105 °C and xerogel was next calcinated at 750°C. Further was evaluated influence of sintering additives (MgO, ZnO, Ca5(PO4)3OH) on the length of sintering interval. All of them have been stabilized spodumene in the solid solution. The properties of ceramic body prepared by sintering of precursor and grinded Li2CO2, Al2O3 a SiO2 powders were compared. Simultaneous thermogravimety and differential thermal analysis (TG-DTA), X-ray diffractions and heating microscopy were used to study sintering process of LAS ceramic.
27
Godinho, Vanda. "Synthesis and characterization of magnetron sputtered thin films of the Ti-Al-Si-N(O) system". Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209969.
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The aim of this Thesis was on one side to contribute to a better understanding of the phases formed in the TiAlSiN(O) system and the influence of impurities on their properties. On the other side it was also aimed in the Thesis to individually study the phases forming the nanocomposite. In each chapter the individual conclusions from that particular chapter are presented, a summary of the most relevant conclusions and achievements is listed below.
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Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
28
Ribeiro, Renata Uema. "Nanopartículas de Co suportadas em SiO2 : síntese, caracterização e propriedades catalíticas para a reforma a vapor do etanol". Universidade Federal de São Carlos, 2007. https://repositorio.ufscar.br/handle/ufscar/3982.
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Previous issue date: 2007-03-16Universidade Federal de Sao Carlos
Colloidal Co Nanoparticles (Co-NPs) were used to prepare supported Co catalysts. The Co- NPs were obtained by thermal decomposition of the precursor Co2(CO)8 in the presence of oleic acid and trioctylphosphine oxide (TOPO), in an inert atmosphere (Ar). The Co- NPs/SiO2 were obtained by impregnation of a colloidal suspension of nanoparticles on the support no-porous SiO2. The effect of the solvent (ethanol and methanol) used in the step of precipitation of the particles, and by tuning the oleic acid/precursor ratio in the catalytic properties for the steam reforming of ethanol were investigated. The catalysts were characterized by Specific Superficial Area (SBET) and Fourier Transform Infrared Spectroscopy of the CO adsorbed (FTIR-CO). By tuning the oleic acid/precursor ratio it was possible to obtain particles sizes in the 2 and 17nm range. The results of FTIR-CO showed that the samples present the band of CO lineally adsorbed in the same position independent of the synthesis conditions, suggesting similar electronic density of the sites of Co. The results of adsorption of H2 and CO suggest that the fraction of acessible sites of Co so much to H2, as to CO, depends on the particles sizes and the residual oleic acid . Then with the increase of the particles sizes, there is a maximum of accessible sites of Co. For the same particle size, it is obtained an increase of the number of accessible sites of Co, using methanol as solvent for precipitation, suggesting smaller recovering. The catalysts prepared with Co-NPs present profiles of similar catalytic activity for the steam reforming of ethanol. Starting from reaction data a mechanism was proposed: in low temperatures, the molecule of ethanol adsorbs in the catalyst surface and it suffers dehydrogenation producing acetaldehyde. The increase of the temperature favors the formation of species CH4 and CO, suggesting the crack of the C-C bond of acetaldehyde for the formation of these products. The activity for the reforming reactions on the Co-NPs/SiO2 begins in approximately 350ºC, suggesting that the activation of the water occurs in this temperature. Therefore it is suggested the oxidation of adsorbed species CHx and CO for the formation of the products CO e CO2, respectively, occurred in temperatures above 350ºC. The catalytic activity depends on the fraction of accessible sites of Co. The reactions results demonstrate that the catalysts prepared with methanol presented higher catalytic activity for the reforming reaction, possibly due to the presence of a larger number of accessible sites of Co.
Nanopartículas coloidais de Co (Co-NPs) foram utilizadas na preparação de catalisadores de Co suportados. As Co-NPs foram obtidas por decomposição térmica do precursor octacarbonil dicobalto (Co2(CO)8), na presença de ácido oléico e óxido de trioctilfosfina (TOPO), sob atmosfera inerte (Ar). Os catalisadores Co-NPs/SiO2 foram obtidos por impregnação de uma suspensão coloidal de nanopartículas sobre o suporte. O efeito do solvente (etanol e metanol) utilizado na etapa de precipitação das partículas, e a variação da razão ácido oléico/precursor nas propriedades catalíticas para a reforma a vapor do etanol foram investigados. Os catalisadores foram caracterizados por meio de Área Superficial Específica (SBET) e Espectroscopia de Reflectância Difusa na Região do Infravermelho com Transformada de Fourier do CO adsorvido (FTIR-CO). Variando-se a razão ácido oléico/precursor foi possível obter uma faixa de tamanho de partículas entre 2 e 17nm. Os resultados de FTIR-CO revelaram que as amostras apresentam a banda do CO linearmente adsorvido na mesma posição independente das condições de síntese, sugerindo similar densidade eletrônica dos sítios de Co. Os resultados de quimissorção de H2 e CO sugerem que a fração de sítios de Co acessíveis tanto ao H2, como ao CO, dependem do tamanho das partículas e do ácido oléico residual. Assim, com o aumento do tamanho das partículas, têmse um máximo de sítios de Co acessíveis. Para um mesmo tamanho de partícula obtém-se um aumento do número de sítios de Co acessíveis, quando se utiliza metanol como solvente de precipitação das partículas, sugerindo menor recobrimento pelo ácido oléico. Os catalisadores preparados com Co-NPs apresentam perfis de atividade catalítica semelhante para a reação de reforma a vapor do etanol. A partir de dados de reação um mecanismo foi proposto: em temperaturas baixas a molécula de etanol adsorve na superfície do catalisador e sofre desidrogenação, produzindo acetaldeído. O aumento da temperatura favorece o aparecimento de espécies CH4 e CO, sugerindo a quebra da ligação C-C do acetaldeído para a formação destes produtos. A atividade para as reações de reforma sobre os Co-NPs/SiO2 inicia-se em aproximadamente 350ºC, sugerindo que a ativação da água ocorre nesta faixa de temperatura. Com isso, sugere-se que a oxidação de espécies adsorvidas CHx e CO para a formação dos produtos CO e CO2, respectivamente, ocorra em temperaturas acima de 350ºC. A atividade catalítica depende da fração de sítios de Co acessíveis. Desta forma, os resultados obtidos mostram que o catalisador preparado com metanol apresentou maior atividade catalítica para a reação de reforma, possivelmente devido à presença de um número maior de sítios do Co acessíveis.
29
Vršecký, Michal. "Studium mechanizmu koroze žáruvzdorných materiálů v soustavě SiO2-Al2O3 taveninami a struskami s vysokým obsahem alkálií a vanadu". Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2008. http://www.nusl.cz/ntk/nusl-216208.
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In this diploma thesis was analysed layer of corroded material created on refractory lining of reactors for mazut gasification. Samples of corroded material were analysed for SiO2, Al2O3, ZrO2, Fe2O3 a TiO2. Corroded material was further analysed by x-ray and IR spectroscopy to acquire more precise data about chemical composition. This thesis studies the exact effect of microstructure on static corrosion kinetics in system SiO2-Al2O3.
30
Richter, Laura. "A VLBI polarisation study of 43 GHZ SiO masers towards VY CMA /". Link to this resource, 2005. http://eprints.ru.ac.za/784/.
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Richter, Laura. "A VLBI polarisation study of 43 GHZ SiO masers towards VY CMA". Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005284.
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This thesis reports the calibration, imaging and analysis of one epoch of VLBI observations of the v (italics) = J (italics) = 1-0 transition of SiO towards VY CMa. Full polarisation information was recorded, allowing high resolution synthesis maps of each of the four Stokes parameters to be produced. A total of 81 maser components were extracted from the total intensity map, each approximately 1 mas in size. The emission spans approximately 100 x 80 mas in right ascension and declination and is concentrated to the east. The maser component positions were fitted to a ring of radius ~ 3.2R₊ (italics), or 7.2 x 1O¹⁴ cm for a stellar distance of 1.5 kpc. If the stellar position is assumed to be the centre of this ring then almost all of the maser components fall within the inner dust shell radius, which is at ~ 5R (italics)ϰ All of the maser components fall between 1.5R (italics)ϰ and 6R (italics)ϰ. A velocity gradient with position angle was observed in the sparsely filled western region of the maser ring. If interpreted as evidence of shell rotation, this gradient implies a rotational velocity of v (italics) rot (subscirpt) sin i (italics) = 18 km.s⁻¹. The fractional circular and linear polarisations of the maser spots were derived from the Stokes parameter maps. The mean fractional circular polarisation of the masers components was ~ 2 percent and the median fractional linear polarisation was ~ 6 percent, with many spots displaying over ~ 30 percent linear polarisation. The mean circular polarisation implies a magnetic field of ~ 4 G in the SiO maser region if the polarisation is due to Zeeman splitting. Two maser components display a rotation of linear polarisation position angle with velocity, possibly implying a connection between the magnetic field and the velocity field variations in the region of these components.
32
Yazhenskikh, Elena. "Development of a new database for thermodynamic modelling of the system Na2O-K2O-Al2O3-SiO2". [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=977928454.
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Waechtler, Thomas, Nina Roth, Robert Mothes, Steffen Schulze, Stefan E. Schulz, Thomas Gessner, Heinrich Lang i Michael Hietschold. "Copper Oxide ALD from a Cu(I) -Diketonate: Detailed Growth Studies on SiO2 and TaN". Universitätsbibliothek Chemnitz, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200901741.
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The atomic layer deposition (ALD) of copper oxide
films from [(nBu3P)2Cu(acac)]
and wet oxygen on SiO2 and TaN has
been studied in detail by spectroscopic
ellipsometry and atomic force microscopy.
The results suggest island growth on SiO2,
along with a strong variation of the optical
properties of the films in the early stages of
the growth and signs of quantum confinement,
typical for nanocrystals. In addition, differences
both in growth behavior and film properties
appear on dry and wet thermal SiO2.
Electron diffraction together with transmission
electron microscopy shows that nanocrystalline
Cu2O with crystallites < 5 nm is
formed, while upon prolonged electron
irradiation the films decompose and metallic
copper crystallites of approximately 10 nm
precipitate. On TaN, the films grow in a
linear, layer-by-layer manner, reproducing the
initial substrate roughness. Saturated growth
obtained at 120°C on TaN as well as dry and
wet
SiO2 indicates well-established ALD
growth regimes.
© 2009 The Electrochemical Society. All rights reserved.
34
Hanif, Raza. "Microfabrication of Plasmonic Biosensors in CYTOP Integrating a Thin SiO2 Diffusion and Etch-barrier Layer". Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19880.
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A novel process for the fabrication of Long Range Surface Plasmon Polariton (LRSPP) waveguide based biosensors is presented herein. The structure of the biosensor is comprised of Au stripe waveguide devices embedded in thick CYTOP claddings with a SiO2 solvent diffusion barrier and etch-stop layer. The SiO2 layer is introduced to improve the end quality of Au waveguide structures, which previously deformed during the deposit of the upper cladding process and to limit the over-etching of CYTOP to create micro-fluidic channels. The E-beam evaporation method is adapted to deposit a thin SiO2 on the bottom cladding of CYTOP. A new micro-fluidic design pattern is introduced. Micro-fluidic channels were created on selective Au waveguides through O2 plasma etching. The presented data and figures are refractive index measurements of different materials, thickness measurements, microscope images, and AFM images. Optical power cutback measurements were performed on fully CYTOP-cladded symmetric LRSPP waveguides. The end-fire coupling method was used to excite LRSPP modes with cleaved polarization maintaining (PM) fibre. The measured mode power attenuation (MPA) was 6.7 dB/mm after using index-matched liquid at input and output fibre-waveguide interfaces. The results were compared with the theoretical calculations and simulations. Poor coupling efficiency and scattering due to the SiO2 are suspected for off-target measurements.
35
Baganha, César Chiesorin. "Considerações sobre a origem da emissão luminosa de Nanocristais de Si em Matriz de SiO2". reponame:Repositório Institucional da UFPR, 2010. http://hdl.handle.net/1884/23720.
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Resumo: Sistemas nanoestruturados de Si tem sido alvo de intensos estudos e discussões no meio científico devido às suas propriedades eletrônicas e ópticas, as quais produzem luminescência no visível, iferentes das apresentadas pelo Si bulk. O presente trabalho traz considerações a respeito de tal luminescência e visa contribuir com as discussões a respeito de sua origem apresentando um estudo detalhado da emissão luminosa de nanocristais Si obtidos pela técnica de implantação iônica de íons de silício (Si+) em matriz de dióxido de silício (SiO2). Utilizando diferentes técnicas ópticas (fotoluminescência em função da temperatura, fotoluminescência resolvida no tempo e excitação de fotoluminescência), um modelo de confinamento esférico e um modelo semi-empírico proposto por Varshni em 1967 para a variação de gap do Si bulk, comparamos os aspectos observados experimentalmente para as emissões envolvidas na luminescência com o comportamento esperado para recombinações banda-a-banda (estados sob confinamento) do nosso sistema. Para nanocristais de diâmetro iguais de 3 nm (diâmetro obtido por microscopia de transmissão de elétrons para nossa amostra) os modelos teóricos descrevem com razoável precisão a energia de
luminescência em função da temperatura observada para a emissão mais intensa em maiores energias do espectro de fotoluminescência a baixas temperaturas e as energias dos estados excitados identificados pela técnica de excitação de luminescência. No entanto para altas temperaturas, a dependência da luminescência com a temperatura parece indicar a presença simultânea de estados de superfície emitindo nessa mesma região do espectro. As demais emissões presentes no espectro de fotoluminescência (emissões com energias menores) parecem seguir o padrão de confinamento quanto à evolução do gap com o tamanho de nanopartícula, porém seus comportamentos com a temperatura não nos levam a uma comprovação de emissão via estados confinados, tampouco via estados de superfície, até o momento. Com isso as emissões nessa região do espectro ainda precisam de uma análise mais profunda e cuidadosa para a comprovação dos mecanismos envolvidos em suas bandas. Os resultados aqui apresentados nos permitem sugerir um modelo de emissão luminosa que é dominado pelos efeitos de confinamento quântico a baixas temperaturas, mas que aponta para um eventual domínio de recombinações através de estados ocalizados para temperaturas altas, próximas e superiores à ambiente. Nossa hipótese é que, para estas nanopartículas obtidas através de implantação iônica, os mecanismos de recombinação por estados onfinados e por estados de superfície coexistem, sendo que a importância de cada um depende crucialmente da temperatura.
36
Clavel, Rojo Luis. "Respuesta ósea a la vitrocerámica del sistema CaSiO3 SiO2 Ca3(PO4). Estudio experimental “in vivo”". Doctoral thesis, Universidad de Murcia, 2011. http://hdl.handle.net/10803/83365.
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Se presenta un estudio “in vivo”, en conejos Nueza Zelanda, de una vitrocerámica del sistema CaSiO3-[CaSiO3 - Ca3(Si3O9)]-SiO2-Ca3(PO4). Se realizaron defectos óseos epifisarios de 6 x 4´5 mm donde se implantaron cilindros del material a estudio. Los animales se distribuyeron de forma aleatoria en 5 grupos de estudio según el tiempo de implantación previo al sacrifico. Cada muestra se analizó mediante estudio radiológico, histológico y de microscopia electrónica. Los resultados obtenidos demuestran que el material obtenido se puede consideran como una buena alternativa a los sustitutos óseos sintéticos en defectos óseos.
37
Šimíková, Michaela. "Selektivní růst kovových materiálů". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2009. http://www.nusl.cz/ntk/nusl-228773.
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The diploma thesis deals with selective growth of cobalt thin films on lattices created by focused ion beam on Si(111) substrates with thin film of silicon dioxide. Further, the growth and morphology of iron thin films growing on Si/SiO2 substrate without modification was studied. In the last part, thin film of a-C:H, influence of preparation parameters on their growth and ratio of sp2 and sp3 bonds, was investigated. For analysis of those films XPS, AFM, and SEM metods were used.
38
Silva, Mariane Capellari Leite da. "Caracterização físico-química de SiC sintetizado pelo processo Acheson a partir de diferentes fontes de SiO2". Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-06052015-165740/.
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Atualmente, há uma forte demanda por cerâmicas como materiais estruturais para substituição de metais e ligas de elevada dureza e para uso em ambientes hostis. Dentre as famílias das cerâmicas estruturais, o SiC se destaca devido ao seu conjunto de propriedades: alta resistência à oxidação/corrosão, elevada resistência à abrasão, elevada condutividade térmica, baixa massa específica, elevada dureza, boa resistência ao choque térmico e manutenção da maioria destas propriedades em temperaturas elevadas. O processo Acheson se caracteriza, industrialmente, como o principal processo de síntese do SiC, consistindo em dois eletrodos sólidos, conectados a pó de grafite compactado, circundados por uma mistura de sílica e coque, em que o aquecimento é realizado eletricamente entre temperaturas de 2200 a 2600 oC [SOMIYA, 1991]. A formação do SiC é dependente da pressão parcial dos gases, da temperatura, do tamanho de grão dos reagentes, das propriedades individuais de cada grão, assim como da área de contato e do grau de mistura entre SiO2 e C [LINDSTAD, 2002]. O SiC produzido pelo processo Acheson contém impurezas como Al, Fe, Ti, Na, provindas da matéria-prima, que durante a síntese têm seu comportamento influenciado pela variação de temperatura. Partículas metálicas ou carbetos dessas impurezas estão distribuídos na matriz de SiC, sendo encontrados à medida que a temperatura diminui, com exceção do Al que se encontra em solução sólida com o SiC, substituindo os átomos de Si na rede cristalina [WEIMER, 1997]. Os objetivos deste trabalho se concentraram na caracterização e avaliação da influência da matéria-prima e das condições de processo no SiC obtido pelo processo Acheson. Podendo-se observar, através das análises químicas, mineralógicas e microestruturais, que a distribuição das impurezas, ao longo da secção transversal do SiC, é independente da matéria-prima precursora, sendo que estas se concentram nas regiões mais distantes do núcleo de grafite, porém seus teores são superiores para o SiC sintetizado a partir de uma matéria-prima menos pura, as quais ainda apresentaram temperatura de início do processo de oxidação do SiC pelo menos 50 oC menor, quando comparado ao SiC sinterizados a partir de matérias-primas com maior grau de pureza.Currently, there is a strong demand for ceramics as structural materials to replace metals and alloys with high hardness for use in hostile environments. Among structural ceramics families, silicon carbide stands out due to its unique properties combination: high corrosion/oxidation resistance, high abrasion resistance, low density, high hardness, high thermal conductivity, good thermal shock resistance and maintenance of the majority of these properties at elevated temperatures. The Acheson process is industrially the main synthesis process of silicon carbide, consisting of two solid electrodes connected to compacted graphite powder, surrounded by a mixture of silica and petroleum coke, wherein the heating is performed electrically between 2200 to 2600 oC [SOMIYA, 1991]. The formation of SiC depends on the partial pressure of gases, temperature, reactants grain size, the properties of each individual grain as well as the contact area and the degree of mixing between SiO2 and C [LIDSTAD, 2002]. The SiC produced by the Acheson process contains impurities from the raw materials, such as Al, Fe, Ti and Na, which during the synthesis are influenced by the temperature gradient. Metal or carbides particles of these impurities are distributed in SiC matrix, being found as the temperature decreases, with exception of Al that forms solid solution with SiC by replacing the Si atoms in the crystal lattice [WEIMER, 1997]. The objectives of this work was the characterization and evaluation of the influence of raw materials and process conditions on the behavior of silicon carbide synthesized by Acheson process. It was observed, through chemical, mineralogical and microstructural analyzes, that the distribution of impurities along the cross section of synthesized SiC is independent of the raw material precursor, and these are concentrated in the most distant regions of the graphite core, but its contents are superior to SiC synthesized from a less pure raw material, which also showed a change in the beginning of the SiC oxidation process, at least 50 ° C lower, than the synthesized SiC from raw material with higher purity.
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Bertram, Rodney L. "Sheltered Instruction: A Case Study of Three High School English Teachers' Experiences with the SIOP Model". Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc67959/.
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The purpose of this study was to determine the current status of secondary teachers' implementation of the sheltered instruction operational protocol (SIOP) model and its effect on Hispanic English language learners' (ELL) English language proficiency and academic achievement. In addition, this study sought to determine whether teachers perceive the SIOP model as an effective tool for instruction of high school ELL students to increase English language content and English language proficiency. This study employed qualitative and quantitative methodologies. Data were collected from four sources: Hispanic ELLs' English language proficiency scores, students' English Language Arts scores, an oral interview with participating teachers and teacher observations. Each teacher was observed at four points during the school year with the SIOP instrument. Quantitative data on student achievement were collected employing a pre-experimental, one-group pretest-post-test design. Qualitative data were collected using a time-series design. Findings revealed that on the two student assessment measures there were increases in English proficiency and English language arts achievement among the Hispanic ELLs. On the assessment of English language proficiency, the students of the teacher with the highest level of SIOP implementation made the highest gains; the students of the teacher with the second highest SIOP implementation level made the second highest gains; and students of the teacher with the lowest level of SIOP implementation made the smallest gains. These findings suggest that the higher the level of SIOP implementation, the greater the student academic achievement gains. The gains in academic achievement attributed to the proper implementation of the SIOP model can have an extensive impact on English language learners who have not previously experienced academic success. Teacher participants perceived the SIOP model as effective for delivery of content through sheltered instruction lessons for high school ELLs. The teachers agreed that the SIOP model's components provided a consistent structure for planning and delivery of their sheltered lessons.
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Johnson, Norman C. "Assessing Cognitive Abilities in a Sample of Sioux Children Utilizing Traditional and Nonverbal Measures of Intelligence". DigitalCommons@USU, 2006. https://digitalcommons.usu.edu/etd/6238.
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The disproportionate number of American Indian students receiving special education services indicates an ongoing need for research leading to improved assessment and placement practices with this population. Standardized tests are most often used to screen and select students for special education services. However, not all intelligence tests have been normed for use with all populations, especially where minority groups have been concerned.
While the merits of traditional intelligence tests must not be discounted, the emergence of new tests and assessment measures is encouraging, particularly for the assessment of American Indian students. A natural next step is to consider a traditional measure of intelligence, a more "culture fair" measure of intelligence, and behavioral indicators in the assessment of children to determine their utility with minority, in this case American Indian students. Thus, the present study investigated the Wechsler Intelligence Scale for Children-Fourth Edition and the Test of Nonverbal Intelligence-Third Edition as measures of intelligence for American Indian children receiving special education services, gifted and talented services, and those attending regular education classes. The current study also examined whether two psychosocial variables, academic achievement and behavioral incidents, were predictive of group membership. The sample for this study consisted of 90 American Indian children from the Lake Traverse Indian Reservation in northeastern South Dakota.
The results indicated that there were differences in how American Indian students performed on the various measures of intelligence. Youths in the special education group tended to have more severe behavioral incidents than the other two groups. Youths in the gifted group were more likely to have exceptional achievement than individuals in the other two groups. Examining the means on the six measures of intelligence for the three groups indicated that gifted students had the highest scores, followed by regular education students, and then special education students.
Academic achievement and behavioral incidents differentiated between the three groups in the expected manner. Therefore, teachers and administrators should be mindful of the fact that the three groups of students do not differ solely in terms of intelligence.
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RICHARD, GONZALEZ DE LINARES BENEDICTE. "Contribution a l'etude d'un procede d'imagerie radiologique utilisant le photoconducteur a memoire bi : :(12)sio::(20)". Paris 6, 1987. http://www.theses.fr/1987PA066095.
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Souza, André Machado Ribeiro de. "A influência da morfologia do MgO nas propriedades catalíticas do SiO2/MgO para a formação de 1,3-Butadieno a partir de etanol". Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/8013.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Ethanol has been largely studied in the past few decades as a substitute to fossil fuels in the synthesis of a large variety of chemicals. 1,3-Butadiene, one of these compounds, is an important chemical intermediate and also a monomer for some polymers such as synthetic rubbers. It is mainly produced as a by-product from naphtha steam cracking, which has ethylene as the major product. As crude oil prices have been fluctuating in the latest years and with the discovery of shale gas in the US, a promising source for ethylene, there is an urgency for developing alternative routes to produce 1,3-Butadiene. Several studies have been carried since the 1940s trying to create viable processes and using many different catalysts, indicating MgO/SiO2 - with or without the addition of transition metals - as being the most promising one. However, there is still a lot of missing information on how does the interaction between silica and magnesia affect the yields and selectivity. In the present work it was studied how the morphology of the MgO affects the interaction with the SiO2 to generate active sites. The MgO with different morfologies were synthesized and then wet-kneaded with SiO2 to provide catalysts with different MgO/SiO2 ratio. The samples were calcined and catalytic tests were carried out. X-Ray Diffraction, Temperature Programmed Desorption of CO2 and Scanning Electron Microscopy were also performed on the catalysts. The obtained micrographs for the oxides confirmed the successful preparation of different morphologies, and the results for catalytic tests showed that there is some influence from the morphology over conversion and selectivity of SiO2/MgO. For the MgO morphologies at the temperature of 425 oC, ethanol conversions between 11.7% and 21.9% were obtained for different samples, with selectivities for butadiene between 5.6% and 30.4%. For SiO2/MgO catalysts, in the same temperature, different yields were obtained for distinct morphologies and Mg:Si ratios. For 3:1 catalysts, yields between 21.5% and 34.3% were observed, while for 7:1 catalysts the yields vary from 18.5% to 35.4%. Catalytic properties could not be clearly correlated to the TPD-CO2 and specific surface area, indicating that they are dependant on a complex set of factors, among them the accessibility of the surface for the SiO 2 contact. Variation of the silica content for all morphologies showed that the SiO2/MgO ratio is extremely important for the preparation of active and selective catalysts for the production of 1,3-butadiene.
O etanol vem sendo largamente estudado, recentemente, como um substituto aos combustíveis fósseis na síntese de diversos produtos industriais. O 1,3-Butadieno (BD), um destes compostos, é um importante intermediário químico e monômero para alguns polímeros e borrachas sintéticas. BD atualmente é produzido principalmente como um subproduto do craqueamento a vapor do nafta, que tem o etileno como principal produto. Flutuações no preço do petróleo e a descoberta de grandes reservas de shale gas nos Estados Unidos fazem com que haja uma necessidade de busca de rotas alternativas para a produção do BD. Muitos estudos vêm sendo realizados desde os anos 1940, utilizando diferentes catalisadores, indicando o MgO/SiO2 - com ou sem a adição de metais de transição - como o mais promissor. No entanto, ainda falta informação sobre a forma como a interação entre a sílica e a magnésia afeta os resultados da reação. No presente trabalho foi verificada a influência que a morfologia do MgO tem sobre a interação com SiO2 para formação de sítios ativos. As amostras de MgO com diferentes morfologias foram sintetizadas e, então, adicionadas de sílica para gerar os catalisadores com diferentes razões MgO/SiO2. Após calcinação, testes reacionais foram realizados. As amostras de MgO e SiO2 /MgO foram caracterizadas por Difração de Raios-X, Dessorção a Temperatura Programada de CO 2 (TPD-CO2) e Microscopia Eletrônica de Varredura (MEV). As imagens de MEV dos óxidos permitiram confirmar a síntese das diferentes morfologias de MgO, e resultados para testes de atividade catalítica mostram uma influência da morfologia na atividade e seletividade do SiO2/MgO. Para os MgO, em uma temperatura de 425 oC, foram obtidas conversões entre 11.7% e 21.9% para diferentes morfologias, com seletividades para BD entre 5.6% e 30.4%. Para os catalisadores SiO2/MgO, na mesma temperatura, foram obtidos rendimentos variáveis com a morfologia e com o teor Mg:Si. Para os catalisadores 3:1, foram observados rendimentos entre 21.5% e 34.3%, enquanto que para os catalisadores 7:1 puderam ser observados rendimentos variando entre 18.5% e 35.4%. As propriedades catalíticas não puderam ser claramente correlacionadas com os dados de TPD-CO2 e área superficial específica, evidenciando que estas são dependentes de um complexo conjunto de fatores, dentre eles a acessibilidade da superfície para o contato com o SiO2 . A variação do teor de sílica mostra que a razão SiO 2/MgO é extremamente importante para obtenção de catalisadores ativos e seletivos para formação do 1,3-butadieno.
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Lian, Cheng-Wei, i 連承偉. "A Buried Silicon Nanocrystal Based High Gain Coefficient SiO2/SiOX/SiO2 Strip-Loaded Waveguide Amplifier on the Si Substrate". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/39948804785714057250.
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碩士國立臺灣大學
光電工程學研究所
96
In this thesis, we simulate the SiO2/SiOX/SiO2/Quartz-substrate strip-loaded waveguide and the SiO2/SiOX/SiO2/Si-substrate strip-loaded waveguide. The Effective-Index Method (EIM), the Beam Propagation Method (BPM), and the Finite Element Method (FEM) are used to simulate the waveguide structure. Subsequently, we fabricate these two type waveguides and measure the optical gain and loss coefficients by fitting the one dimensional amplifier equation of the Variable Stripe Length (VSL) method. We observe that the Si-rich SiOX strip-loaded waveguide with silicon (Si) nanocrystal contributed amplified spontaneous emission (ASE) at 750-850 nm with the associated spectral linewidth of 140 nm is characterized. The ASE spectrum is red-shifted 6 nm to PL spectrum because of mode guiding. The peak wavelength of ASE spectrum is blue shift with longer pumping length. Because of the longer pumping length, the mode guiding is stronger and the peak wavelength becomes stable. The optical gain and loss coefficients of the SiO2/SiOX/SiO2/Quartz-substrate strip-loaded waveguide are 70 and 5 cm-1, respectively. The optical gain and loss coefficients of the SiO2/SiOX/SiO2/Si-substrate strip-loaded waveguide are 106.7 and 21 cm-1, respectively. The optical loss coefficient of the Si-substrate device is larger than the Quartz-substrate device which is due to the optical mode leakage to Si substrate. The optical net modal gain coefficient of Si-substrate device is larger than Quartz-substrate device which is due to the better mode confinement. The small-signal amplification of up to 11.73 dB for 795 nm small laser signal under He-Cd laser pumping of 43.7 mW at the wavelength of 325 nm is obtained from the SiO2/SiOX/SiO2/Si-substrate strip-loaded waveguide amplifier with a length of 1 cm.
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Lian, Cheng-Wei. "A Buried Silicon Nanocrystal Based High Gain Coefficient SiO2/SiOX/SiO2 Strip-Loaded Waveguide Amplifier on the Si Substrate". 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-3007200823324700.
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Wu, Ming-Shing, i 吳銘興. "A-SiOx Thin Film Growth in Magnetron Plasma System". Thesis, 1993. http://ndltd.ncl.edu.tw/handle/26585093717171697201.
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Wu, Bing-Chien, i 吳秉謙. "A Study of Photodetectors Based on AZO/SiOx/n-Si Heterojunction Structure". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/08015171370439565657.
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Liu, Li-Hao, i 劉力豪. "Study of Laser Annealing of a-Si/a-SiOx Multi-layer by Raman Scattering". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/12322213673272379151.
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碩士國立臺灣海洋大學
光電科學研究所
93
Abstract: This research used a continuous wave Argon ion laser for annealing an a-Si/a-SiOx multi-layer sample and measured Raman spectrum at the same spot with reduced laser power. By subtracting amorphous silicon contribution to laser annealed multilayer’s Raman spectrum，the microcrystalline silicon’s Raman signature can be obtained. The evolution of microcrystalline silicon’s Raman peak position and width with the accumulated laser exposure was analyzed to deduce the growth process of microcrystalline silicon nanoparticles.
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Chang, Ming-Chieh, i 張民杰. "Study of SiOx Dielectric Film with Hydrogen Content for a-IGZO-TFT Device". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/08695751884636984221.
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碩士國立交通大學
平面顯示技術碩士學位學程
100
Nowadays, poly-silicon and amorphous-silicon generally have been used for active layer of TFT (Thin Film Transistor) device technology of TFT LCD (Liquid Crystal Display). Poly-silicon-TFT has high field-effect mobility of over 100Vs/cm2, but it has disadvantage of high running cost and bad processing uniformity. Moreover, amorphous silicon has lower process cost for less process steps, but its field-effect mobility is less than 1Vs/cm2. Recently, a-IGZO TFTs (amorphous Indium Gallium Zinc Oxide Thin Film Transistor) have attracted considerable attentions for their superior electrical properties including great field-effect mobility from 10Vs/cm2 to 20Vs/cm2, sub-threshold swing, and high on/off current ratio. Furthermore, a-IGZO film, which is deposited at low temperature with an amorphous phase, exhibits good uniformity and can be fabricated on plastic substrates for flexible electronic or AMOLED (Active Matrix Organic Light Emitting Display) driving TFT. This thesis discussed SiOx dielectric film with low hydrogen content for a-IGZO-TFTs. If hydrogen content of SiOx film was high, a-IGZO film will be transformed from semiconductor to conductor in the application of TFT device. It is important that hydrogen content of SiOx film is reduced when SiOx film is deposited. Therefore, hydrogen ion generated by SiH4 must be reduced when deposited SiOx film. The proposed process of a-IGZO-TFT utilized low hydrogen contents SiOx film as etching stop layer and passivation layer to produce top gate and bottom gate transistor components. Experimental results showed that a-IGZO film exhibit intrinsic semiconductor characteristic, which is main claim of the dissertation.
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Ho, Chia-chi, i 何家齊. "Cooper Gate Electrode Fabrication and SiOx Gate Dielectric Properties on a-Si:H TFTs Electrical Characterization". Thesis, 1996. http://ndltd.ncl.edu.tw/handle/07587454817268626490.
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碩士國立交通大學
材料科學與工程研究所
84
In this thesis we used low resistivity Cu/TiW double layered gate metal fabrication a-Si:H THT.Using low resistivity Cu metal as gate can effectively reduce RC delay in gate line and at the same time prevent the production of hillocks and whisker.In this way,Cu/TiW gate utilizes a complete chemical wet etching process.While Cu etched by various ratio of CH3COOH and Al etchant,we find that CH3COOH 70~80% buffer Aletchant have a uniform etching morphology,small side etch distance and excellent taper shape.The TFT with Cu/TiW double-layered gate metal provides good electrical performance,such as the small threshold voltage(1.2V),low subthreshold swing(0.24V/dec.) and high mobility (0.8cm^2/V.s). SiH4-N2O based and TEOS-O2 based oxide are fabricated in a-Si:H TFT as gate dielectric to investigate the oxide gate dielectric properties on the a-Si:H TFT performance.We find that PE-TEOS oxide have better step coverage than silane-based oxide and the surface of PE-TEOS oxideis more smooth.The breakdown strength for TEOS oxide is 8.5 MV/cm and 8 MV/cm for silane-based oxide.The value have high enough for TFT device.Both have been used a TFTs gate dielectric,and the best electrical performance is Vth about 5V, S=0.4 V/dec.,and ufe=0.6cm^2/V.s.The TFTs electrical performance with silane-based oxide are improved accompanying with oxide properties that with fewer hydrogen related bonds and rigid structure.The Vth shift decrease with the oxide gate insulator that with fewer hydrogenrelated bonds.But the subthreshold swing shift shows an inverted tendency that may resulting from the interface bonding structure related to O atoms induced weak silicon bond structure.The TFTs electrical performance with TEOS-based oxide gate insulator have similar result that oxide with complete Si-O bonding has better performance.But the oxide deposited under high power will producing a large amount of fixed charge trap in oxide by plasmadamage and resulting in high threshold voltage. SiNx TFTs with CA a-Si:H and H2 plasma treatment SiNx surface TFTs have been prepare.CA a-Si:H TFTs have many interface layers in a-Si:H and more interface states are build up resulting in decrease in ufe and increase in S.When gate bias is applied,the S will reach a saturation value and ufe will increase.The reson still not clear,maybe cause by the release of the strain in a-Si:H.from breaking weak bonds for H2 plasma treatment SiNx surface TFT when gate bias is performed both S and mobility decrease.Because the plasma damage the interface,an unstable interface is produced.All the sample have worse electrical properties than conventional SiNx TFTs.The instablity in oxide gate dielectric a-Si:H THT mainly come from the trap defect centers in oxide and state creation at or near the interface.
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Lu, Chi-Chang, i 呂其璋. "Silicon Oxide (SiOx) Film Deposition Using Radio-Frequency Atmospheric-Pressure Plasma Jet With a Spiral Electrode". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/71087727569830978254.
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碩士國立交通大學
機械工程學系
98
Thin film deposition of silicon oxide (SiOx) using a radio-frequency (13.56 MHz) coaxial argon atmospheric-pressure plasma jet (RF-APPJ) has been investigated experimentally in this thesis. A stable, arc-free swirling APPJ was produced with a spiral powered electrode covered by a quartz tube, which makes the addition of oxygen (up to 10%) possible without extinguishing the discharge. This APPJ was employed to deposit silicon oxide thin films using a precursor, hexamethyldisiloxane (HMDSO), diluted in an argon carrier gas, into the post-discharge region. Test conditions included variations of treatment passes, input power (35-50 W), treatment distances (3-7.5 mm), oxygen additions (0-10%), and substrate temperatures (25-300 oC). Results show that deposition rate increased with increasing treatment passes, input power, oxygen addition and decreased with increasing substrate temperatures and treatment distances. The variation of oxygen addition and substrate temperature greatly affected the properties of silicon oxide thin films. The deposition rate of the silicon oxide thin film was 37.5 nm/min using pure argon plasma with 50 W RF power, 300 oC substrate temperature and 5 mm treatment distance. When oxygen addition increases to 0.8%, the deposition rate increases to 275 nm/min. However, oxygen addition is more than 2%, highly porous, particle-like structure was formed. FTIR and XPS measurements show that quantity of carbon atoms, the degree of porosity and deposition rate in the film decrease with increasing substrate temperature. However, the hardness of the film surface increases with increasing substrate temperature. In summary, we have successfully deposited and characterized the silicon oxide films formed in the post-discharge region of a RF-APPJ using argon mixed with oxygen. Recommendations for the future study are also outlined at the end of the thesis.