Teses / dissertações: "Contenu en carbone"

1

Haan, Denis. "Teneurs en monoxyde de carbone de l'air contenu dans la glace de l'Antarctique et du Groenland". Phd thesis, Université Joseph Fourier (Grenoble), 1996. http://tel.archives-ouvertes.fr/tel-00754243.

Texto completo da fonte

Resumo:

Le monoxyde de carbone (CO) est présent à l'état de trace dans l'atmosphère, il participe à de nombreuses réactions chimiques qui affectent la composition atmosphérique et le climat. Dans le cadre de cette étude, une méthode expérimentale a été mise au point pour extraire le gaz piégé dans la glace ancienne et analyser sa concentration en CO. L'extraction du gaz par fusion et regel de l'échantillon de glace apparaît comme étant la méthode la mieux adaptée à l'étude du CO contenu dans la glace. Des tests "blanc" réalisés à partir de glace artificielle montrent que cette méthode est efficace (pas de contamination en CO détectable) à condition de nettoyer préalablement la surface de l'échantillon. Il reste à déterminer dans quelle mesure ces observations faites sur la glace artificielle peuvent être extrapolées à la glace naturelle. Il semble que ce soit le cas pour la glace antarctique dont le comportement au cours d'un cycle de fusion-regel est similaire à celui de la glace artificielle. Par contre, le cas de la glace du Groenland paraît plus complexe, car elle semble induire, dans certaines sections de carotte, une contamination supplémentaire liée vraisemblablement à des processus in situ de production de CO. La méthode d'extraction par fusion-regel a été appliquée à un nombre important d'échantillons provenant de carottes antarctiques et groenlandaises. Pour la première fois, une interprétation en terme de signal atmosphérique a pu être apportée pour des échantillons couvrant les deux derniers siècles. Ainsi, l'analyse des carottes Eurocore (Groenland) et D47 (Antarctique) nous a pennis de retracer l'évolution au cours de la période 1850-1950 de la concentration en CO aux hautes latitudes. Une augmentation d'environ 20% des teneurs en CO apparaît, au cours de cette période, dans l'hémisphère nord, en phase avec l'évolution des sources anthropiques de CO telles que la combustion du charbon et la consommation des carburants liquides. Au cours de la période 1850-1916, l'Antarctique se caractérise, en revanche, par une relative stabilité des teneurs en CO qui suggère que les hautes latitudes sud sont restées influencées, pendant au moins la première partie de l'ère industrielle, par la prédominance de sources naturelles de CO. A partir d'un scénario d'évolution des sources, nous avons montré que ces résultats présentent des implications importantes dans la compréhension du cycle atmosphérique du CO. Ils suggèrent en effet que des sources anthropiques de CO doivent déjà être prises en compte pour la période pré-industrielle, ce qui constitue une contrainte importante pour les modèles. En marge de ces résultats, l'étude de la partie basse de la carotte Eurocore suggère la possiblité d'interactions physico-chimiques au sein de la glace pouvant modifier le signal atmosphérique originel. Le profil de concentration en CO, présente en effet dans cette partie de la carotte, une variabilité importante qui ne peut pas être a priori expliquée par la modification des sources et des puits de CO. L'existence de mécanismes d'oxydation de la matière organique contenue dans la glace pourrait être à l'origine des variations observées sur ces niveaux. La similitude du profil de CO avec celui du CO2 dans cette partie de la carotte semble confirmer cette hypothèse.

Estilos ABNT, Harvard, Vancouver, APA, etc.

2

Baril, Benjamin. "Contenu en carbone du panic érigé et du sol amendé avec du biochar et une inoculation microbienne". Thesis, Université Laval, 2013. http://www.theses.ulaval.ca/2013/29830/29830.pdf.

Texto completo da fonte

Resumo:

L’utilisation du panic érigé amendé avec du biochar et/ou inoculé avec des rhizobactéries, pour produire de l’énergie, pourrait permettre de réduire les gaz à effets de serre. Afin d’évaluer les effets de ces amendements sur le contenu en carbone (C) de la plante et du sol, un essai a été mis en place sur un loam sableux à St-Augustin-de-Desmaures, selon un plan en tiroirs répété 3 fois avec en parcelles principales, un traitement de biochar de 10 Mg MS ha-1 et un traitement sans biochar, et en sous-parcelles, 3 doses d’azote ( 0, 25, 50 kg ha-1) et 2 traitements d’inoculation bactérienne. L’apport d’engrais minéral azoté a augmenté significativement le rendement en biomasse aérienne et en C lors de la 2e année de croissance. Le biochar et l’inoculation n’ont eu aucun effet sur la biomasse aérienne du panic et un effet marginal sur la biomasse racinaire. Aucun effet significatif n'a été observé sur le contenu en C du sol.
The use of switchgrass (Panicum virgatum L.) amended with biochar and/or rhizobacteria to produce energy, could potentially be a solution to reduce greenhouse gases and contribute to increase carbon (C) sequestration in soil. In this experiment, switchgrass was treated with biochar and N-fixing and P-solubilising bacteria in a split-plot experimental design. To assess the C dynamics in switchgrass production, the experiment was established on a sandy loam in St-Augustin-de-Desmaures near Quebec. A biochar treatment of 10 Mg of dry matter per hectare and treatments without biochar has been used as main plots, while three nitrogen rates (0, 25 and 50 kg ha-1) and treatments of bacterial inoculation were installed as sub-plots. The mineral nitrogen fertilizer significantly increased the aboveground biomass yield and C after two years of growth. A small positive effect of biochar (p=0,08) increase root C. Soil C was not affected by any treatment after two years of growth.

Estilos ABNT, Harvard, Vancouver, APA, etc.

3

RIVET, SEBASTIEN. "Extraction avec le dioxyde de carbone supercritique et en presence d'un agent complexant du cation uranyle contenu dans les solutions de retraitement". Paris 6, 1998. http://www.theses.fr/1998PA066609.

Texto completo da fonte

Resumo:

L'extraction en phase supercritique a l'echelle analytique connait depuis quelques annees un essor considerable. En effet, cette technique de traitement de l'echantillon possede de nombreux avantages parmi lesquels on peut citer le plus important a savoir sa selectivite. Elle permet d'eviter pratiquement l'utilisation de solvants liquides organiques dont l'usage est de plus en plus reglemente. Elle ne genere pas ou peu d'effluents liquides dont le cout de stockage, d'incineration, ou de recyclage est eleve. L'objectif de ce travail de these etait de mettre au point une methode d'extraction et d'analyse de l'uranium generant pas ou peu d'effluents liquides. Celui-ci a ete atteint. Le dioxyde de carbone supercritique etant un fluide peu polaire, il ne permet pas de solubiliser des composes ioniques comme les cations metalliques. En consequence, la formation de complexes organometalliques neutres, peu polaires est obligatoire afin d'en autoriser l'extraction par le dioxyde de carbone supercritique. Depuis le debut de cette etude, une dizaine de travaux relatifs a l'extraction en phase supercritique de cations metalliques tels que l'uranium et les lanthanides presents dans la solution de dissolution du combustible nucleaire use, ont ete publies. Cependant, les complexants utilises presentent l'inconvenient majeur de contenir des atomes de soufre, soit des atomes d'halogenes ou des atomes de phosphore ; ils ne sont donc pas aisement incinerables, ce qui oblige l'entreposage des effluents. Ce sont les raisons pour lesquelles nous avons choisi comme complexant de l'uranium la 2,6-diacetylpyridine bis (benzoylhydrazone) compose uniquement d'atomes de carbone, d'hydrogene, d'azote, et d'oxygene, ce qui le rend integralement incinerable. Nous avons d'abord nuclearise l'extracteur en phase dioxyde de carbone supercritique, rendant ainsi possible l'utilisation d'un radionucleide tel que l'uranium. Nous avons pu ainsi demontrer la faisabilite de l'extraction du cation uranyle en phase dioxyde de carbone supercritique en presence du complexant 2,6-diacetylpyridine bis (benzoylhydrazone). La non superposition des spectres uv-visible du complexe d'uranium et du complexant nous a permis de coupler l'extraction en phase dioxyde de carbone supercritique a la spectrophotometrie uv-visible. En effet, le positionnement d'un detecteur uv-visible en aval de la cellule d'extraction mais en amont du regulateur de pression, a permis de suivre en temps reel le processus d'extraction, et de demontrer qu'il existe une relation de linearite entre l'aire du profil d'extraction et la quantite d'uranium extraite. Ce couplage a permis d'obtenir en ligne la quantification de l'uranium dans les effluents radioactifs. Pour comprendre et optimiser le processus d'extraction de l'uranium en phase dioxyde de carbone supercritique, nous avons choisi d'utiliser la methode des plans d'experiences. Deux plans d'experiences (plans fractionnaires 2 7 4 principal et complementaire) nous ont permis de cerner en seize essais (repetes deux ou trois fois), les parametres gouvernant le rendement de l'extraction de l'uranium : la pression, le pourcentage volumique de methanol, le debit du co 2 liquide, la duree de l'extraction dynamique et l'exces molaire de complexant. Les quatre premiers facteurs cites ont un effet positif sur l'extraction du cation uranyle. L'influence significative et negative du facteur exces molaire de complexant sur le rendement de l'extraction de l'uranium prouve que lorsque une trop grande fraction de ce complexant est dissoute dans le fluide, celle-ci gene la solubilisation du complexe d'uranium. On a donc montre ici que le facteur limitant l'extraction de l'uranium depose sur une matrice inerte (sable de mer, ou terre diatomee) est la solubilite du complexe d'uranium dans le fluide. Ces parametres ont ete optimises a l'aide d'un autre plan d'experiences. La pression a ete remplacee par la masse volumique. Les valeurs optimales des parametres etudies (une masse volumique de 0,95 g/cm 3, un pourcentage volumique de methanol (v/v) de 3%, un debit de co 2 de 1,5 ml/min, une duree de l'extraction dynamique raisonnable de 30 minutes, un exces molaire de complexant de i) permettent d'aboutir a un rendement de l'extraction de 87,6% pour 20 g d'uranium en ne generant un volume d'effluent liquide aussi faible que 1,3 ml pour chaque extraction. Ce rendement peut paraitre insuffisant mais en se referant aux resultats du paragraphe 3. 1 page 97 qui montrent des extractions quantitatives pour des quantites d'uranium inferieures a 15 g, on peut donc raisonnablement admettre que les conditions optimales permettront, elles aussi, d'extraire des quantites d'uranium inferieures ou egales a 15 g. Il faut mentionner que nous n'avons pas recupere le complexe d'uranium extrait mais, comme cela a ete deja demontre la mise en uvre de phase stationnaire de grandes surfaces specifiques (>1000 m 2. G 1) permet de recuperer quantitativement des solutes de natures varies avec des teneurs en solvant polaire dans le co 2 aussi grandes que 10 a 20%.

Estilos ABNT, Harvard, Vancouver, APA, etc.

4

Lhardy, Fanny. "Role of Southern Ocean sea ice on deep ocean circulation and carbon cycle at the Last Glacial Maximum". Electronic Thesis or Diss., université Paris-Saclay, 2021. http://www.theses.fr/2021UPASJ013.

Texto completo da fonte

Resumo:

La période froide du Dernier Maximum Glaciaire était caractérisée, en regard de notre climat moderne, par une couverture de glace de mer australe accrue, une circulation profonde Atlantique moins profonde et une plus faible concentration en CO2 dans l’atmosphère. Ces différences sont bien connues grâce aux observations indirectes mais difficiles à représenter dans les simulations issues des modèles de climat. En effet, ces modèles simulent fréquemment une concentration en CO2 atmosphérique trop élevée, une circulation océanique trop profonde dans l’Atlantique et une banquise présentant une distribution trop circulaire dans l’océan austral ainsi qu’une étendue hivernale et une amplitude saisonnière trop faibles. Ces désaccords modèle-données observés au Dernier Maximum Glaciaire remettent en cause la représentation numérique de certains processus climatiques essentiels. Plusieurs études soulignent le rôle majeur de la glace de mer australe sur la capacité de stockage de carbone de l’océan et la circulation océanique profonde. Je me suis donc focalisée sur cette région pour mieux com-prendre les processus associés à ce stockage. Grâce aux simulations réalisées avec le modèle système terre iLOVECLIM, j’ai pu démontrer que les incertitudes liées à la représentation des calottes polaires ont un impact limité sur les variables examinées ici. En revanche, d’autres choix de conditions aux limites (affectant le volume de l’océan, l’ajustement de l’alcalinité) peuvent entraîner des modifications importantes du contenu total en carbone de l’océan. Je montre également que l’utilisation d’une paramétrisation simple de la plongée des saumures résultant de la formation de glace de mer permet d’améliorer significativement la simulation de la glace de mer australe, de la circulation océanique profonde et de la concentration en CO2 atmosphérique. Un ensemble de simulations incluant l’impact de différentes paramétrisations océaniques est utilisé pour montrer que la circulation océanique très profonde simulée par notre modèle ne peut être attribuée à une glace de mer australe insuffisante. En revanche, les processus de convection dans l’océan austral semblent clefs pour améliorer à la fois la glace de mer australe, la circulation océanique profonde et la concentration en CO2 atmosphérique auDernier Maximum Glaciaire
Compared to the present-day climate, the cold period of the Last Glacial Maximum was characterized by an expanded sea-ice cover in the Southern Ocean, a shoaled Atlantic deep ocean circulation and a lower atmospheric CO2 concentration. These changes are well-documented by indirect observations but difficult to represent in simulations of climate models. Indeed, these models tend to simulate a too high atmospheric CO2 concentration, a too deep Atlantic deep ocean circulation, and a sea-ice cover with a too circular distribution in the Southern Ocean and a too small winter extent and seasonal amplitude. The model-data discrepancies observed at the Last Glacial Maximum call into question the model representation of some important climate processes. Several studies have underlined the crucial role of the Southern Ocean sea ice on ocean carbon storage capacity and deep circulation. I have therefore focussed on this region to improve our understanding of the processes associated with this storage. Thanks to simulations performed with the Earth System Model iLOVECLIM, I have demonstrated thatthe uncertainties related to ice sheet reconstructions have a limited impact on the variables examined in this study. In contrast, other choices of boundary conditions (influencing the ocean volume and alkalinity adjustment) can yield large changes of carbon sequestration in the ocean. I also show that a simple parameterization of the sinking of brines consequent to sea-ice formation significantly improves the simulated Southern Ocean sea ice, deep ocean circulation and atmospheric CO2 concentration. A set of simulations including the effects of diverse ocean parameterizations is used to show that the too deep ocean circulation simulated by our model cannot be attributed to an insufficient sea-ice cover, whereas convection processes in the Southern Ocean seem crucial to improve both the Southern Ocean sea ice, the deep ocean circulation and the atmospheric CO2 concentration at the Last Glacial Maximum

Estilos ABNT, Harvard, Vancouver, APA, etc.

5

Ahvar, Shohreh. "Resource allocation in cloud and Content Delivery Network (CDN)". Thesis, Evry, Institut national des télécommunications, 2018. http://www.theses.fr/2018TELE0011.

Texto completo da fonte

Resumo:

L’objectif de cette thèse est de présenter de nouveaux algorithmes de répartition des ressources sous la forme de machines virtuelles (VMs) et fonction de réseau virtuel (VNFs) dans les Clouds et réseaux de diffusion de contenu (CDNs). La thèse comprend deux principales parties: la première se concentre sur la rentabilité des Clouds distribués, et développe ensuite les raisons d’optimiser les coûts ainsi que les émissions de carbone. Cette partie comprend quatre contributions. La première contribution est une étude de l’état de l’art sur la répartition des coûts et des émissions de carbone dans les environnements de clouds distribués. La deuxième contribution propose une méthode d’allocation des ressources, appelée NACER, pour les clouds distribués. La troisième contribution présente une méthode de placement VM efficace en termes de coûts et de carbone (appelée CACEV) pour les clouds distribués verts. Pour obtenir une meilleure performance, la quatrième contribution propose une méthode dynamique de placement VM (D-CACEV) pour les clouds distribués. La deuxième partie propose des algorithmes de placement de VNFs dans les Clouds et réseaux de CDNs pour optimiser les coûts. Cette partie comprend cinq contributions. Une étude de l’état de l’art sur les solutions proposées est le but de la première contribition. La deuxième contribution propose une méthode d’allocation des ressources, appelée CCVP, pour le provisionnement de service réseau dans les clouds et réseaux de ISP. La troisième contribution implémente le résultat de l’algorithme CCVP dans une plateforme réelle. La quatrième contribution considère l’effet de la permutation de VNFs dans les chaîne de services et la cinquième contribution explique le placement de VNFs pour les services à valeur ajoutée dans les CDNs
High energy costs and carbon emissions are two significant problems in distributed computing domain, such as distributed clouds and Content Delivery Networks (CDNs). Resource allocation methods (e.g., in form of Virtual Machine (VM) or Virtual Network Function (VNF) placement algorithms) have a direct effect on cost, carbon emission and Quality of Service (QoS). This thesis includes three related parts. First, it targets the problem of resource allocation (i.e., in the form of network aware VM placement algorithms) for distributed clouds and proposes cost and carbon emission efficient resource allocation algorithms for green distributed clouds. Due to the similarity of the network-aware VM placement problem in distributed clouds with a VNF placement problem, the second part of the thesis, getting experience from the first part, proposes a new cost efficient resource allocation algorithm (i.e., VNF placement) for network service provision in data centers and Internet Service Provider (ISP) network. Finally, the last part of the thesis presents new cost efficient resource allocation algorithms (i.e., VNF placement) for value-added service provisioning in NFV-based CDNs

Estilos ABNT, Harvard, Vancouver, APA, etc.

6

Ahvar, Shohreh. "Resource allocation in cloud and Content Delivery Network (CDN)". Electronic Thesis or Diss., Evry, Institut national des télécommunications, 2018. http://www.theses.fr/2018TELE0011.

Texto completo da fonte

Resumo:

L’objectif de cette thèse est de présenter de nouveaux algorithmes de répartition des ressources sous la forme de machines virtuelles (VMs) et fonction de réseau virtuel (VNFs) dans les Clouds et réseaux de diffusion de contenu (CDNs). La thèse comprend deux principales parties: la première se concentre sur la rentabilité des Clouds distribués, et développe ensuite les raisons d’optimiser les coûts ainsi que les émissions de carbone. Cette partie comprend quatre contributions. La première contribution est une étude de l’état de l’art sur la répartition des coûts et des émissions de carbone dans les environnements de clouds distribués. La deuxième contribution propose une méthode d’allocation des ressources, appelée NACER, pour les clouds distribués. La troisième contribution présente une méthode de placement VM efficace en termes de coûts et de carbone (appelée CACEV) pour les clouds distribués verts. Pour obtenir une meilleure performance, la quatrième contribution propose une méthode dynamique de placement VM (D-CACEV) pour les clouds distribués. La deuxième partie propose des algorithmes de placement de VNFs dans les Clouds et réseaux de CDNs pour optimiser les coûts. Cette partie comprend cinq contributions. Une étude de l’état de l’art sur les solutions proposées est le but de la première contribition. La deuxième contribution propose une méthode d’allocation des ressources, appelée CCVP, pour le provisionnement de service réseau dans les clouds et réseaux de ISP. La troisième contribution implémente le résultat de l’algorithme CCVP dans une plateforme réelle. La quatrième contribution considère l’effet de la permutation de VNFs dans les chaîne de services et la cinquième contribution explique le placement de VNFs pour les services à valeur ajoutée dans les CDNs
High energy costs and carbon emissions are two significant problems in distributed computing domain, such as distributed clouds and Content Delivery Networks (CDNs). Resource allocation methods (e.g., in form of Virtual Machine (VM) or Virtual Network Function (VNF) placement algorithms) have a direct effect on cost, carbon emission and Quality of Service (QoS). This thesis includes three related parts. First, it targets the problem of resource allocation (i.e., in the form of network aware VM placement algorithms) for distributed clouds and proposes cost and carbon emission efficient resource allocation algorithms for green distributed clouds. Due to the similarity of the network-aware VM placement problem in distributed clouds with a VNF placement problem, the second part of the thesis, getting experience from the first part, proposes a new cost efficient resource allocation algorithm (i.e., VNF placement) for network service provision in data centers and Internet Service Provider (ISP) network. Finally, the last part of the thesis presents new cost efficient resource allocation algorithms (i.e., VNF placement) for value-added service provisioning in NFV-based CDNs

Estilos ABNT, Harvard, Vancouver, APA, etc.

7

Nye, Michael Brandon. "Understanding business participation in UK emissions trading : accounting for content, context and carbon". Thesis, University of Cambridge, 2006. https://www.repository.cam.ac.uk/handle/1810/252013.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

8

Zehnder, Thomas. "Deposition of silicon carbide and amorphous carbon films by pulsed laser deposition /". Bern : [s.n.], 1995. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

9

Hashimoto, Maurício Maia Braga [UNESP]. "Caracterização microestrutural de um aço baixo carbono e baixos teores de elementos de ligas com estrutura contento ferrita acicular". Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/94408.

Texto completo da fonte

Resumo:

Made available in DSpace on 2014-06-11T19:27:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-02Bitstream added on 2014-06-13T20:16:09Z : No. of bitstreams: 1 hashimoto_mmb_me_guara.pdf: 4222707 bytes, checksum: 27f8c8d0ab8e7954c8e4ec0d9dcc1c48 (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A ferrita acicular é um desenvolvimento recente do conceito dos aços HSLA e envolve nucleação da ferrita a partir de partículas não metálicas, de forma intragranular e heterogênea. O mecanismo de transformação da ferrita acicular é semelhante à formação da bainita, diferenciando-se basicamente no local onde cada constituinte se nucleia e a aparência da microestrutura. A presença de carbonitretos precipitados e a microestrutura acicular desorganizada tende a desviar a propagação de trincas e aumentar tenacidade do material. Desta forma, os aços com microestrutura de ferrita acicular têm sido apontados como ótimos candidatos para aplicações em tubulações de óleo e gás em condições ambientais e operacionais severas. Este trabalho investiga os constituintes de um aço baixo carbono e baixos teores de elementos de ligas com contendo microestrutura de ferrita acicular, obtida através de tratamento de crescimento de grãos e, posteriormente, submetido a diversas rotas de tratamento isotérmico. A caracterização microestrutural foi obtida através de microscopia óptica e processamento metalográfico com o reagente Nital. Avaliou-se, também, o comportamento da resistência à tração do material antes e após os ciclos de tratamento térmico. Os resultados obtidos revelam a possibilidade de se obter estruturas multifásicas contendo grandes frações de ferrita acicular, promovendo excelente combinação das propriedades mecânicas de resistência e ductilidade
The acicular ferrite is a recent development of HSLA steels and involves a ferrite nucleation from non-metallic particles, as intragranular and heterogeneous mode. The acicular ferrite transformation mechanism is similar to bainite, differing primarily in where each constituent initiates nucleates and appearance of the microstructure. The presence of carbonitriding precipitated and disorganized acicular microstructure tends to deflect the crack propagation and increase toughness of the material. Thus, steels with acicular ferrite microstructure have been considered good candidates for applications in oil pipes and gas in several environmental and operational conditions. This work investigates the constituents of a low carbon steel and low concentration of alloys with microstructures containing acicular ferrite, obtained by grain growth treatment and, subsequently, subject to various route of isothermal treatments. The microstructural characterization was obtained by optical microscopy and metallographic processing with Nital reagent. We evaluated also the behavior of the tensile strength of the material before and after the heat treatment cycles. The results show the possibility of obtaining multiphase structures containing large fractions of acicular ferrite, promoting excellent combination of mechanical properties of strength and ductility

Estilos ABNT, Harvard, Vancouver, APA, etc.

10

Sel, Kivanc. "The Effects Of Carbon Content On The Properties Of Plasma Deposited Amorphous Silicon Carbide Thin Films". Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608292/index.pdf.

Texto completo da fonte

Resumo:

The structure and the energy band gap of hydrogenated amorphous silicon carbide are theoretically revised. In the light of defect pool model, density of states distribution is investigated for various regions of mobility gap. The films are deposited by plasma enhanced chemical vapor deposition system with various gas concentrations at two different, lower (30 mW/cm2) and higher (90 mW/cm2), radio frequency power densities. The elemental composition of hydrogenated amorphous silicon carbide films and relative composition of existing bond types are analyzed by x-ray photoelectron spectroscopy measurements. The thicknesses, deposition rates, refractive indices and optical band gaps of the films are determined by ultraviolet visible transmittance measurements. Uniformity of the deposited films is analyzed along the radial direction of the bottom electrode of the plasma enhanced chemical vapor deposition reactor. The molecular vibration characteristics of the films are reviewed and analyzed by Fourier transform infrared spectroscopy measurements. Electrical characteristics of the films are analyzed by dc conductivity measurements. Conduction mechanisms, such as extended state, nearest neighbor and variable range hopping in tail states are revised. The hopping conductivities are analyzed by considering the density of states distribution in various regions of mobility gap. The experimentally measured activation energies for the films of high carbon content are too low to be interpreted as the difference between Fermi level and relevant band edge. This anomaly has been successfully removed by introducing hopping conduction across localized tail states of the relevant band. In other words, the second contribution lowers the mobility edge towards the Fermi level.

Estilos ABNT, Harvard, Vancouver, APA, etc.

11

Silva, Robson Marcel da. "Estudo de uma metodologia para estimar a quantidade de carbono em amostras de solo utilizando espectroscopia de emissão óptica com plasma induzido por laser (LIBS)". Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/75/75132/tde-25082009-094505/.

Texto completo da fonte

Resumo:

Os solos representam um importante componente no ciclo biogeoquímico do carbono, armazenado cerca de quatro vezes mais carbono que a biomassa vegetal e quase três vezes mais que a atmosfera. Além disso, a quantidade de carbono está diretamente ligada a capacidade de retenção de água, fertilidade entre outras propriedades. Assim, a quantificação de carbono do solo em condições de campo é um tema importante para estudos do ciclo de carbono relacionado às mudanças climáticas globais. Atualmente, espectroscopia de emissão óptica com plasma induzido por laser (LIBS) pode ser usada para análise elementar qualitativa sem tratamento prévio das amostras e os resultados são obtidos rapidamente. Novas tecnologias ópticas tornaram possível sistema LIBS portáteis e, agora, a grande expectativa é o desenvolvimento de métodos que possibilitam medições quantitativas com sistemas LIBS. LIBS é uma técnica espectroanalítica que emprega a microamostragem por ablação com laser e subseqüente excitação dos átomos presentes no microplasma induzido durante a ablação. Sendo assim, o presente projeto de pesquisa visou desenvolver uma metodologia para quantificar carbono em amostras intactas de solo e avaliar o desempenho de sistemas LIBS portáteis para análises em campo. Trinta e seis amostras de solo da região do Cerrado brasileiro (Argissolo Vermelho Distrófico Latossólico) foram utilizadas. Para avaliar o efeito de heterogeneidade, trabalhou-se com as amostras moídas criogenicamente e não moídas. Com o intuito de estudar uma melhor forma para estimar a quantidade de carbono no solo, quatro metodologias diferentes foram empregadas utilizando o sistema LIBS de bancada e apenas uma metodologia para o sistema LIBS portátil. Para ambos os sistemas LIBS foi necessário inicialmente fazer correções no sinal de fundo dos espectros obtidos. A linha de emissão do carbono em 193,03 nm foi utilizada, pois esta não apresenta interferência da linha de emissão do elemento ferro. A técnica de análise térmica (combustão seca) conhecida como TOC (Total Organic Carbon) foi utilizada como referência para calibrar os sistemas. Utilizando o sistema LIBS de bancada, foram criados modelos com base em regressão linear simples e crescimento exponencial para estimar a quantidade de carbono nas amostras. Para o sistema LIBS portátil foram utilizados modelos com base em regressão linear simples e regressão linear múltipla. A melhor metodologia empregada para o sistema LIBS de bancada foi utilizando a energia máxima do laser (50 mJ) e o maior acúmulo de tiros (10 tiros) e o modelo de regressão linear simples apresentou um melhor ajuste. Não houve diferença entre os dados obtidos com as amostras moídas e não moídas. Para o sistema LIBS portátil a análise de regressão linear múltipla apresentou um melhor resultado, selecionando a melhor variável para o modelo. Sendo assim, conclui-se que sistemas LIBS são ferramentas úteis para se realizar estimativas quantitativas, podendo ser usados para a construção de inventários de carbono no solo, que são importantes para áreas ambientais com o foco em seqüestro de carbono, mudanças climáticas globais, avaliação do manejo de solos e o efeito da aplicação de águas residuárias em solos.
Soils are an important component in the biogeochemical cycle of carbon, storing about four times more carbon that biomass plants and nearly three times more than the atmosphere. Moreover, the carbon content is directly related on the capacity of water retention, fertility, among others properties. Thus, soil carbon quantification in field conditions is an important challenge related to carbon cycle and global climate changes. Nowadays, Laser Induced Breakdown Spectroscopy (LIBS) has beeb applied to qualitative elemental analyses without previous treatment of samples and the results are obtained quickly. New optical technologies made possible portable LIBS systems and now, the great expectation is the development of methods that make possible quantitative analysis with LIBS. LIBS is a technique that employs a sampling by laser ablation and subsequent excitation of atoms present in induced microplasma during the ablation. The goal of this research was the development of methodology to estimate carbon in soil samples and evaluate the performance of portable LIBS systems for analysis in the field. Thirty six soil samples of Brazilian Cerrado region (Argisoil) were used. To evaluate the effect of heterogeneity, it was used samples that were grounding in a cryogenic ground and samples if not grounded. In order to study a better way to estimate the carbon content in the soil, four different methodologies were employed using the bench LIBS system and only one methodology for the portable LIBS system. For both LIBS systems was needed to do corrections in the background of obtained spectra. The carbon line at 193.03 nm was used because it does not present an interference of iron. The technique of thermal analysis known as TOC (Total Organic Carbon) was used as reference to calibrate the systems. Using the bench LIBS system have been adjusted models based on simple linear regression and exponential growth to estimate the carbon content in the samples. For portable LIBS system were used models based on simple linear regression and multiple linear regression. The best methodology used to the bench LIBS system was using the maximum of laser energy (50 mJ) and the largest shots count (10 shots count) and simple linear regression model showed a better fit. There was no difference between the data obtained from the grounded and not grounded samples. For the portable LIBS system multiple linear regression showed a better result because was select the best variable. Thus, it appears that LIBS systems are useful tools to perform quantitative estimates and could be used to build inventories of carbon in the soil that are important to environmental areas with the focus on carbon sequestration, global climate change, assessment the management of soils and the effect of wastewater into the soil.

Estilos ABNT, Harvard, Vancouver, APA, etc.

12

Hashimoto, Maurício Maia Braga. "Caracterização microestrutural de um aço baixo carbono e baixos teores de elementos de ligas com estrutura contento ferrita acicular /". Guaratinguetá : [s.n.], 2010. http://hdl.handle.net/11449/94408.

Texto completo da fonte

Resumo:

Orientador: Marcelo dos Santos Pereira
Banca: Antonio Jorge Abdalla
Banca: Cristina de Carvalho Ares Elisei
Resumo: A ferrita acicular é um desenvolvimento recente do conceito dos aços HSLA e envolve nucleação da ferrita a partir de partículas não metálicas, de forma intragranular e heterogênea. O mecanismo de transformação da ferrita acicular é semelhante à formação da bainita, diferenciando-se basicamente no local onde cada constituinte se nucleia e a aparência da microestrutura. A presença de carbonitretos precipitados e a microestrutura acicular desorganizada tende a desviar a propagação de trincas e aumentar tenacidade do material. Desta forma, os aços com microestrutura de ferrita acicular têm sido apontados como ótimos candidatos para aplicações em tubulações de óleo e gás em condições ambientais e operacionais severas. Este trabalho investiga os constituintes de um aço baixo carbono e baixos teores de elementos de ligas com contendo microestrutura de ferrita acicular, obtida através de tratamento de crescimento de grãos e, posteriormente, submetido a diversas rotas de tratamento isotérmico. A caracterização microestrutural foi obtida através de microscopia óptica e processamento metalográfico com o reagente Nital. Avaliou-se, também, o comportamento da resistência à tração do material antes e após os ciclos de tratamento térmico. Os resultados obtidos revelam a possibilidade de se obter estruturas multifásicas contendo grandes frações de ferrita acicular, promovendo excelente combinação das propriedades mecânicas de resistência e ductilidade
Abstract: The acicular ferrite is a recent development of HSLA steels and involves a ferrite nucleation from non-metallic particles, as intragranular and heterogeneous mode. The acicular ferrite transformation mechanism is similar to bainite, differing primarily in where each constituent initiates nucleates and appearance of the microstructure. The presence of carbonitriding precipitated and disorganized acicular microstructure tends to deflect the crack propagation and increase toughness of the material. Thus, steels with acicular ferrite microstructure have been considered good candidates for applications in oil pipes and gas in several environmental and operational conditions. This work investigates the constituents of a low carbon steel and low concentration of alloys with microstructures containing acicular ferrite, obtained by grain growth treatment and, subsequently, subject to various route of isothermal treatments. The microstructural characterization was obtained by optical microscopy and metallographic processing with Nital reagent. We evaluated also the behavior of the tensile strength of the material before and after the heat treatment cycles. The results show the possibility of obtaining multiphase structures containing large fractions of acicular ferrite, promoting excellent combination of mechanical properties of strength and ductility
Mestre

Estilos ABNT, Harvard, Vancouver, APA, etc.

13

Durigan, Bruna [UNESP]. "Desenvolvimento de sensor baseado em eletrodo modificado com nanotubos de carbono contendo pentacianonitrosilferratos de metais para determinação de antioxidantes em microemulsão de biodiesel". Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/110694.

Texto completo da fonte

Resumo:

Made available in DSpace on 2014-11-10T11:09:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-06Bitstream added on 2014-11-10T11:57:26Z : No. of bitstreams: 1 000780459_20150825.pdf: 1277929 bytes, checksum: 3ace37183e6574c78d5e47a230e8a520 (MD5) Bitstreams deleted on 2015-08-28T16:08:59Z: 000780459_20150825.pdf,. Added 1 bitstream(s) on 2015-08-28T16:10:01Z : No. of bitstreams: 1 000780459.pdf: 3381394 bytes, checksum: 32e28f8a45200bdd370ceeea8533b655 (MD5)
No Brasil e no mundo a busca por combustíveis alternativos tornou-se cada vez mais importante e o biodiesel é considerado um combustível totalmente viável quando comparado aos combustíveis fosseis, devido a sua baixa emissão de gases causadores do efeito estufa. Porem sua baixa estabilidade à oxidação reflete diretamente em sua qualidade, assim antioxidantes sintéticos constituem os principais compostos que têm sido utilizados na preservação de biodiesel contra esses processos oxidativos. A determinação destes compostos normalmente emprega técnicas sofisticadas que requerem altos custos. Uma alternativa viável para sua determinação é a utilização de técnicas eletroanáliticas, por alcançarem baixos limites de detecção e menor custo, a utilização de eletrodos quimicamente modificados apresentam grande potencial para ampliar o campo de utilização da técnica voltamétrica, por proporcionar uma maior seletividade e sensibilidade. Neste trabalho é apresentado a determinação do antioxidante TBHQ e BHT em microemulsão de biodiesel utilizando um eletrodo de carbono vítreo modificado com nanotubos de carbono contendo pentacianonitrosilferrado de níquel e de cobre. De acordo com os resultados, foi observado que o antioxidante TBHQ sofre um processo de oxidação no potencial de 53 mV vs (Ag/AgCl) em meio de eletrólito suporte, quando comparado com o potencial obtido em eletrodo de carbono vítreo é notável o ganho provocado pela modificação, devido a uma diminuição de potencial de 130 mV e um ganho de três vezes em valor de corrente. A microemulsão utilizada foi a de composição biodiesel (composição 6% de biodiesel, 21% de eletrólito suporte contendo NaCl 0,5 mol L-1, em tampão fosfato 0,05 mol L-1 pH 7,0 e 73% de propanol). O estudo de concentração do TBHQ, utilizando técnica de redissolução adsortiva módulo varredura cíclica, apresentou linearidade na faixa de concentração de TBHQ de 5,0x10-7 a...
In Brazil and in the world to search for alternative fuels has become increasingly important and biodiesel is considered a totally viable fuel compared to fossil fuels, due to their low emission of gases causing the greenhouse effect. However, its low oxidation stability is directly reflected in their quality, so synthetic antioxidants are the main compounds that have been used in the preservation of biodiesel against such oxidative processes. The determination of these compounds usually employs sophisticated techniques that require high costs. A viable alternative for their determination is the use of electroanalytical techniques for achieving low detection limits and lower cost, the use of chemically modified electrodes have great potential to expand the application range of the voltammetric technique, by providing greater selectivity and sensitivity. This paper presents the determination of the antioxidant BHT and TBHQ microemulsion biodiesel using a modified carbon nanotubes glass carbon electrode containing pentacianonitrosilferrado nickel and copper. According to the results , it was observed that the antioxidant TBHQ undergoes an oxidation potential in 53 mV vs (Ag/AgCl) in the middle of electrolyte compared with the potential obtained at a glassy carbon electrode is caused notable gain the modification due to a reduction potential of 130 mV and a gain value of three times of current. The microemulsion used was the biodiesel composition (composition 6% biodiesel with 21% NaCl electrolyte containing 0.5 mol L-1 in phosphate buffer 0.05 mol L-1 pH 7.0 and 73 % propanol ) . The study of concentration of TBHQ, using adsorptive stripping voltammetry technique module cyclical scan showed linearity in the concentration range of TBHQ 5.0x10-7 to 3.7x10-5 mol L-1 with a LOD of 4.1x10-7 in electrolyte support and 1.1x10-4 to 9.8x10-3 mol L-1 with a LOD of 8.4x10-5 mol L- 1 in microemulsion biodiesel, using the electrode NiPCNF-MWCNTs/GCE ...

Estilos ABNT, Harvard, Vancouver, APA, etc.

14

Durigan, Bruna. "Desenvolvimento de sensor baseado em eletrodo modificado com nanotubos de carbono contendo pentacianonitrosilferratos de metais para determinação de antioxidantes em microemulsão de biodiesel /". Araraquara, 2014. http://hdl.handle.net/11449/110694.

Texto completo da fonte

Resumo:

Orientador: Nelson Ramos Stradiotto
Banca: Luiz Henrique Mazo
Banca: Mauro Bertotti
Resumo: No Brasil e no mundo a busca por combustíveis alternativos tornou-se cada vez mais importante e o biodiesel é considerado um combustível totalmente viável quando comparado aos combustíveis fosseis, devido a sua baixa emissão de gases causadores do efeito estufa. Porem sua baixa estabilidade à oxidação reflete diretamente em sua qualidade, assim antioxidantes sintéticos constituem os principais compostos que têm sido utilizados na preservação de biodiesel contra esses processos oxidativos. A determinação destes compostos normalmente emprega técnicas sofisticadas que requerem altos custos. Uma alternativa viável para sua determinação é a utilização de técnicas eletroanáliticas, por alcançarem baixos limites de detecção e menor custo, a utilização de eletrodos quimicamente modificados apresentam grande potencial para ampliar o campo de utilização da técnica voltamétrica, por proporcionar uma maior seletividade e sensibilidade. Neste trabalho é apresentado a determinação do antioxidante TBHQ e BHT em microemulsão de biodiesel utilizando um eletrodo de carbono vítreo modificado com nanotubos de carbono contendo pentacianonitrosilferrado de níquel e de cobre. De acordo com os resultados, foi observado que o antioxidante TBHQ sofre um processo de oxidação no potencial de 53 mV vs (Ag/AgCl) em meio de eletrólito suporte, quando comparado com o potencial obtido em eletrodo de carbono vítreo é notável o ganho provocado pela modificação, devido a uma diminuição de potencial de 130 mV e um ganho de três vezes em valor de corrente. A microemulsão utilizada foi a de composição biodiesel (composição 6% de biodiesel, 21% de eletrólito suporte contendo NaCl 0,5 mol L-1, em tampão fosfato 0,05 mol L-1 pH 7,0 e 73% de propanol). O estudo de concentração do TBHQ, utilizando técnica de redissolução adsortiva módulo varredura cíclica, apresentou linearidade na faixa de concentração de TBHQ de 5,0x10-7 a...
Abstract: In Brazil and in the world to search for alternative fuels has become increasingly important and biodiesel is considered a totally viable fuel compared to fossil fuels, due to their low emission of gases causing the greenhouse effect. However, its low oxidation stability is directly reflected in their quality, so synthetic antioxidants are the main compounds that have been used in the preservation of biodiesel against such oxidative processes. The determination of these compounds usually employs sophisticated techniques that require high costs. A viable alternative for their determination is the use of electroanalytical techniques for achieving low detection limits and lower cost, the use of chemically modified electrodes have great potential to expand the application range of the voltammetric technique, by providing greater selectivity and sensitivity. This paper presents the determination of the antioxidant BHT and TBHQ microemulsion biodiesel using a modified carbon nanotubes glass carbon electrode containing pentacianonitrosilferrado nickel and copper. According to the results , it was observed that the antioxidant TBHQ undergoes an oxidation potential in 53 mV vs (Ag/AgCl) in the middle of electrolyte compared with the potential obtained at a glassy carbon electrode is caused notable gain the modification due to a reduction potential of 130 mV and a gain value of three times of current. The microemulsion used was the biodiesel composition (composition 6% biodiesel with 21% NaCl electrolyte containing 0.5 mol L-1 in phosphate buffer 0.05 mol L-1 pH 7.0 and 73 % propanol ) . The study of concentration of TBHQ, using adsorptive stripping voltammetry technique module cyclical scan showed linearity in the concentration range of TBHQ 5.0x10-7 to 3.7x10-5 mol L-1 with a LOD of 4.1x10-7 in electrolyte support and 1.1x10-4 to 9.8x10-3 mol L-1 with a LOD of 8.4x10-5 mol L- 1 in microemulsion biodiesel, using the electrode NiPCNF-MWCNTs/GCE ...
Mestre

Estilos ABNT, Harvard, Vancouver, APA, etc.

15

Grimaud, Richard. "Modélisation du comportement non linéaire d'un composite carbone-carbone 3D". Ecully, Ecole centrale de Lyon, 1992. http://www.theses.fr/1992ECDL0039.

Texto completo da fonte

Resumo:

Ce travail concerne la modélisation du comportement des matériaux composites tridirectionnels au-delà du domaine linéaire. On interprète cette non-linéarité par une diminution de la rigidité élastique et par l'apparition de déformations résiduelles. On propose alors plusieurs modèles couplant élasticité, plasticité et endommagement qui permettent de reconstituer le comportement mécanique moyen. Nous disposons pour illustrer ces modèles des résultats d'essais de traction hors axes avec décharges élastiques et mesures des déformations transversales d'un composite carbone-carbone. L’intérêt de ce type d'essai est qu'il induit dans les directions d'orthotropie des contraintes de cisaillement. Après quelques généralités sur les matériaux composites tridirectionnels nous développons les bases thermodynamiques et phénoménologiques qui nous ont servi à mettre en place nos modèles. Nous insisterons tout particulièrement sur la description de l'endommagement. Nous présentons ensuite nos deux modèles de comportement (découplé et couple) dans le cadre général des matériaux standards généralisés. Nous terminons enfin par l'identification et à la validation de ces lois sur des essais fournis par la société européenne de propulsion de bordeaux (S. E. P. )

Estilos ABNT, Harvard, Vancouver, APA, etc.

16

Johnson, Brian James. "The carbon-13 content of atmospheric formaldehyde". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184320.

Texto completo da fonte

Resumo:

A measurement of the stable carbon isotopic composition of atmospheric formaldehyde was undertaken as a means of testing current photochemical theories. Sulfito surfaces were shown to meet the stringent analytical requirements of the project; an extensive characterization of these surfaces was performed for the first time. Models were developed to describe the chemical evolution of the surfaces during sampling. It was established that potassium salts have more favorable properties for an atmospheric collection system than do sodium salts. Considerable selectivity in collection was also demonstrated. A highly selective multistep procedure for the isolation and chemical oxidation of collected formaldehyde was developed expressly for this project. A previously unreported combination of reagents, HgCl₂ and AgClO₄, was used in the final reaction step of the procedure. Through the use of synthetic samples, the method was shown to be isotopically reproducible and highly chemically selective. The first data for the carbon-13 content of atmospheric formaldehyde have been obtained, with an observed mean value of δ¹³C = -17‰. This value is enriched in carbon-13 over the known atmospheric sources of formaldehyde; isotopic fractionation in the atmosphere is therefore indicated. It is believed that fractionation due to photolysis can account for the observed effect.

Estilos ABNT, Harvard, Vancouver, APA, etc.

17

Lucas, Antoine. "Dispersion et Filage continu par coagulation de nanotubes de carbone". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2009. http://tel.archives-ouvertes.fr/tel-00585478.

Texto completo da fonte

Resumo:

Cette thèse rapporte l'étude d'un procédé original de filage continu par coagulation de nanotubes de carbone afin d'obtenir une fibre composite aux propriétés balistiques remarquables. Elle s'intéresse à la caractérisation des fonctions chimiques de surface, de la morphologie et des dimensions des nanotubes aux différentes étapes du procédé. Y sont détaillées une étude quantitative des effets et cinétiques de scission des nanotubes par les ultrasons. Elle présente de plus des travaux relatifs au développement d'une ligne continue de filage des nanotubes de carbone en voie solvant. Des méthodes originales de caractérisation mécanique in-situ de fibre gel sont proposées, permettant notamment un meilleur contrôle des paramètres physicochimiques liés au procédé. Nous espérons que les résultats obtenus participeront à une meilleure compréhension des effets des traitements utilisés pour l'obtention de dispersion homogène de nanotubes de carbone et à un développement des procédés continus de filage textile.

Estilos ABNT, Harvard, Vancouver, APA, etc.

18

Pailhes, Jérôme. "Comportement mécanique sous sollicitations multi-axiales d'un composite carbone-carbone". Bordeaux 1, 1999. http://www.theses.fr/1999BOR12152.

Texto completo da fonte

Resumo:

Les performances thermomécaniques des composites carbone/carbone permettent leur utilisation thermostructurale. Afin de dimensionner correctement les structures, il est nécessaire de connaître le comportement mécanique du composite sous des sollicitations multiaxiales. Un appareillage spécifique de sollicitations multiaxiales de type traction-cisaillement a été conçu et réalisé lors de ce travail. On a déterminé le comportement mécanique et les différents mécanismes d'endommagement de traction ou de compression dans les axes et hors axes d'orthotropie du matériau. Le modèle utilisé pour rendre compte de cet endommagement est fondé sur la mécanique des milieux continus endommageables, les déformations anélastiques induites par l'endommagement étant traitées par la théorie de la plasticité. Les observations au microscope des modes d'endommagement de la matrice conduisent à la formulation d'hypothèses simplificatrices physiquement acceptables. Le modèle a été identifié à l'aide des essais de traction et de compression dans les axes de symétrie du matériau. Les essais de traction/cisaillement ont permis de compléter l'étude du comportement du matériau et de valider la loi de comportement mécanique sous sollicitations multiaxiales proposée.

Estilos ABNT, Harvard, Vancouver, APA, etc.

19

Pailhes, Jérôme. "Comportement mécanique sous sollicitations multi-axiales d'un composite carbone-carbone". Bordeaux 1, 1999. http://www.theses.fr/1999BOR10667.

Texto completo da fonte

Resumo:

Les performances thermomécaniques des composites carbone/carbone permettent leur utilisation thermostructurale. Afin de dimensionner correctement les structures, il est nécessaire de connaître le comportement mécanique du composite sous des sollicitations multiaxiales. Un appareillage spécifique de sollicitations multiaxiales de type traction-cisaillement a été conçu et réalisé lors de ce travail. On a déterminé le comportement mécanique et les différents mécanismes d'endommagement de traction ou de compression dans les axes et hors axes d'orthotropie du matériau. Le modèle utilisé pour rendre compte de cet endommagement est fondé sur la mécanique des milieux continus endommageables, les déformations anélastiques induites par l'endommagement étant traitées par la théorie de la plasticité. Les observations au microscope des modes d'endommagement de la matrice conduisent à la formulation d'hypothèses simplificatrices physiquement acceptables. Le modèle a été identifié à l'aide des essais de traction et de compression dans les axes de symétrie du matériau. Les essais de traction/cisaillement ont permis de compléter l'étude du comportement du matériau et de valider la loi de comportement mécanique sous sollicitations multiaxiales proposée.

Estilos ABNT, Harvard, Vancouver, APA, etc.

20

Laurent, Fabrice. "Croissance de nanotubes de carbone sur des fibres de carbone : application aux matériaux composites". Thesis, Mulhouse, 2016. http://www.theses.fr/2016MULH7632/document.

Texto completo da fonte

Resumo:

Le travail présenté dans ce mémoire de thèse s’est inscrit dans le cadre du développement de la technologie flamme oxyacétylénique pour la synthèse de nanotubes de carbone (NTC) au Laboratoire de Physique et Mécanique Textile. La simplicité et l’originalité de ce procédé en font un candidat très sérieux pour envisager la mise en œuvre d’un pilote industriel pour la production de fibres de renforcement multidimensionnelles, notamment composées de fibres de carbone sur lesquelles ont cru de nanotubes de carbone. Ce travail a consisté à :- Réaliser une étude bibliographique sur les procédés de croissance de NTC,- Etablir la preuve de concept de la croissance des nanotubes sur des fibres,- Concevoir et réaliser un dispositif assurant une bonne maîtrise de la croissance,- Mettre au point le procédé de croissance sur des fibres,- Identifier les principaux paramètres influençant la qualité et la quantité des nanotubes,- Caractériser les nanotubes obtenus,- Faire croître ces nanotubes sur des fibres de carbone,- Intégrer des nouveaux matériaux multidimensionnels dans des matrices afin de réaliser des matériaux composites structurels,- Caractériser ces matériaux,- Décrire les mécanismes de croissance dans la flamme.Notre effort a porté sur le traitement des fibres avant exposition à la flamme et à évaluer les conditions de croissance des NTC en faisant varier notamment, la température d’exposition des fibres et la qualité des catalyseurs de croissance. Après synthèse des NTC sur les fibres de carbone et leur caractérisation nous avons réalisé des matériaux composites. Nous avons mesuré que les NTC améliorent significativement le module d’Young des composites mais altèrent sensiblement la contrainte à la rupture. Les propriétés électriques longitudinales et transversales sont améliorées d’un facteur 8 et 5 respectivement. Nous avons proposé des mécanismes de croissance des NTC. Ces mécanismes sont directement en relation avec propriétés physiques et chimiques des particules de catalyseur
The research presented in this work aims to develop the oxyacetylene flame method for the Carbon Nanotubes (CNT) synthesis at the Laboratory of Physics and Mechanics of Textiles. The simplicity and the degree of innovation of this process make of it a serious candidate for manufacturing a pilot in order to produce new kind of tridimensional material made of CNT having grew on carbon fibres. This work consisted of:- Make a bibliographic study,- Establish a proof of concept of the growth of CNT,- Design and manufacture a device allowing process control,- Setup the process of growth on the fibres,- Identify the main parameters influencing CNT quality and quantity,- Characterize CNT,- Assume the CNT growth on carbon fibers,- Integrate these multidimensional materials into an organic matrix to realize structural composite materials,- Characterize these materials,- Describe and explain the growth mechanism in the flame.First, we focused our work on the fibres chemical treatment before flame exposition to evaluate the NTC growth conditions by varying notably, the fibres exposition temperature and the quality of the catalysts. After, the NTC syntheses on carbon fibres (CF) was done. The multidimensional product was characterized par various examinations and analyses. Composite materials were molded with epoxy resin to evaluate mechanical properties of NTC-FC. Young’s modulus was increased and tensile strength at break decreased. Transverse and longitudinal electrical properties were increased by 500 to 800 % respectively. Finally, we proposed NTC growth mechanisms. They are directly linked to the chemical and physical catalyst particles properties

Estilos ABNT, Harvard, Vancouver, APA, etc.

21

Boeira, Carla Daniela. "Comparação entre diferentes intercamadas contendo silício para adesão de filmes de DLC sobre substrato de aço AISI 4140". reponame:Repositório Institucional da UCS, 2016. https://repositorio.ucs.br/handle/11338/1758.

Texto completo da fonte

Resumo:

Estudos de filmes de carbono tipo diamante (Diamond like-carbon – DLC), com elevado apelo acadêmico, são desenvolvidos a mais de quatro décadas. Entretanto, nos dias de hoje, o interesse industrial em suas propriedades, como alta resistência ao desgaste e ultra baixo coeficiente de atrito, impulsionou o desenvolvimento de diferentes aplicações em larga escala para diversas áreas. No entanto, essas aplicações são restritas pela baixa adesão deste material sobre ligas de aço. Uma alternativa para a solução deste problema é a deposição de uma camada intermédia contendo silício. Porém, existem poucos trabalhos metódicos da dependência de parâmetros-chave como a temperatura e tempo de processo no uso de precursores líquidos contendo silício tais como tetrametilsilano (TMS), hexametildissiloxano (HMDSO) e tetraetilortossilicato (TEOS). Neste trabalho, foram depositados diferentes intercamadas usando estes três diferentes precursores sobre substrato de aço AISI 4140, a fim de melhorar a adesão do filme DLC. Os tratamentos foram realizados em um equipamento tipo PECVD com confinamento electrostático e fonte bipolar DC pulsada. As amostras foram caracterizadas por meio de FEG-SEM, EDS, GD-OES, RAMAN e testes nanoscratch. As análises de FEG-SEM revelaram uma dependência na espessura da intercamada com a temperatura de deposição, semelhante em todas as amostras estudadas. As análises de EDS e GD-OES identificaram e quantificaram a variação de intensidades dos elementos que evidenciam a estrutura DLC/intercamada/substrato. As análises de GD-OES permitiram identificar a variação da concentração dos elementos presentes na intercamada para cada precursor utilizado. Corroborando com esses resultados, os testes de nanoesclerometria linear evidenciaram a delaminação do DLC em diferentes cargas, indicando a influência da concentração de elementos sobre a adesão do filme. A carga crítica de delaminação para filmes DLC depositados sobre intercamadas depositadas por HMDSO a 300 °C é superior a 500 mN (limite do equipamento). Finalmente, a carga crítica para o TMS a 300 °C é 313,8 mN e para TEOS a 300 °C é 306 mN, onde a concentração dos elementos oxigênio e silício presentes na intercamada prejudicaram a adesão do filme de DLC. A intercamada depositada pelo precursor HMDSO aponta para a maior quantidade de C, consequentemente o maior número de ligações C–C promove uma melhor adesão do filme de DLC à temperatura de 300 oC.
Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2017-03-06T17:12:00Z No. of bitstreams: 1 Dissertacao Carla Daniela Boeira.pdf: 1949458 bytes, checksum: d142b48ae2df8185c3733b95fbf49c34 (MD5)
Made available in DSpace on 2017-03-06T17:12:00Z (GMT). No. of bitstreams: 1 Dissertacao Carla Daniela Boeira.pdf: 1949458 bytes, checksum: d142b48ae2df8185c3733b95fbf49c34 (MD5) Previous issue date: 2017-03-06
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES.
Diamond-like carbon (DLC) films research has a high academic appeal, is being developed for more than four decades. Nowadays, the industrial needs in their properties, such as high wear resistance and superlow friction coefficient, boosted the development of different applications in large scales and many fields [1]. However such applications are restricted by the low adhesion of this material on steel. An alternative for solving this problem is the deposition of a silicon-containing interlayer [2]. However, there are few methodical studies of dependence on key parameters such as temperature and process use of silicon-containing liquid precursors such as tetramethylsilane (TMS), hexamethyldisiloxane (HMDSO) and tetraethoxysilane (TEOS). In this work, different interlayer were deposited by using these three precursors on AISI 4140 steel substrates in order improve the DLC film adhesion. The treatments were done in bipolar pulsed-DC PECVD equipment with electrostatic confinement. The samples were characterizes in details by means of FEG-SEM, EDS, GD-OES and nanoscratch tests. On the one hand, FEG-SEM images revealed an interlayers thickness dependence on deposition temperature, which is quite similar in the all samples. On the other hand, EDS and GDOES analysis identified and quantified intensities variation of iron, silicon, hydrogen, oxygen and carbon intensities that are elements responsible for the structure DLC/interlayer/substrate. The GD-OES analyzes allowed to identify the variation of concentration the elements present in the interlayer for each precursor used. Corroborating these results, linear nanoscratch tests showed delamination to DLC in different loads, indicating the influence of concentration to elements on the adhesion of the film. The critical delamination load for DLC films deposited on interlayers deposited by HMDSO at 300 °C is greater than 500 mN (equipment limit). Finally, the critical load for TMS at 300 °C is 313.8 mN and for TEOS at 300°C is 306 mN, where the concentration of the oxygen and silicon elements present in the interlayer impaired adhesion of the DLC film. The interlayer deposited by the precursor HMDSO points to the greater amount of C, consequently the greater number of C–C bonds promotes better adhesion of the DLC film to a temperature of 300 °C.

Estilos ABNT, Harvard, Vancouver, APA, etc.

22

Vignal, Thomas. "Développement d’électrodes utilisant un PCE déposé sur VACNT/Al selon un procédé continu et leur utilisation dans des pseudosupercondensateurs". Thesis, Cergy-Pontoise, 2019. http://www.theses.fr/2019CERG1044.

Texto completo da fonte

Resumo:

Les travaux réalisés ont porté sur l’élaboration d’électrodes composites à base de polymère conducteur électronique déposé électrochimiquement sur des tapis de nanotubes de carbone verticalement alignés sur substrat d’aluminium (VACNT/Al). Ces nouveaux tapis VACNT/Al ont une densité de nanotube très élevée (10^11 - 10^12 CNT/cm²) et proposent une architecture nanométrique très intéressante pour l’élaboration d’électrode dans des dispositifs de stockage d’énergie de type supercondensateur. Le dépôt de polymère sur ces électrodes permet d’augmenter l’énergie spécifique des supercondensateurs. De plus, ces travaux ont aussi été dédiés à l’élaboration d’un procédé de dépôt en continu en vue d’une montée en échelle des synthèses du composite. Dans une première partie, les matériaux utilisés dans les électrodes composites ont été caractérisés individuellement. Ainsi, des dépôts en milieu liquide ionique des polymères poly(3-méthylthiophène) (P3MT) et polypyrrole (PPy) à la surface d’électrodes planes ont été réalisés et, des tapis VACNT ont été caractérisés. La deuxième partie de ce travail a été consacrée à l’optimisation de la synthèse électrochimique par une méthode chronoampérométrique pulsée en milieu liquide ionique.de nanocomposites P3MT/VACNT/Al avec des proportions massiques de P3MT dans l’électrode variant de 10 à 90 %. Ces composites ont par la suite été utilisés en tant qu’électrodes dans des supercondensateurs symétrique et asymétrique sous forme de pile-bouton permettant des énergies et puissances spécifiques de 52 Wh/kg et 12 kW/kg, respectivement. Dans la troisième partie, un procédé de dépôts du P3MT sur un tapis en mouvement a été mis au point pour étudier l’élaboration en continu d’électrodes composites et permettre la préparation d’électrodes de plus grande dimension, 80 cm² dans cette étude. Ces composites ont montré des capacitances spécifiques équivalentes aux composites obtenus avec des dépôts statiques. De plus, les bandes de 80 cm2 ont été utilisées pour la réalisation de supercondensateurs de type zig-zag symétrique et asymétrique et ont aussi montré des énergies et puissance spécifiques très similaire à celles des piles bouton. Dans une dernière partie, un transfert de méthode a été réalisé pour la synthèse de composite PPy/VACNT, en statique puis en procédé continu
The work carried out focused on the development of composite electrodes by electrochemically deposition of conductive polymer onto carbon nanotube vertically aligned on aluminum substrate (VACNT/Al). These new VACNT / Al have a very high nanotube density (10^11 - 10^12 CNT/cm²) and offer a very interesting nanometric architecture for the elaboration of electrodes in energy storage devices as supercapacitor. The deposition of polymer on these electrodes allows the increase of the supercapacitors’ specific energies. In addition, this work has also been dedicated to the development of a continuous deposition process for scaling syntheses of the composite. In a first part, the materials used in the composite electrodes have been characterized individually. Thus, ionic liquid medium deposits of poly (3-methylthiophene) (P3MT) and polypyrrole (PPy) polymers at the surface of planar electrodes were made and VACNT were characterized. The second part of this work was devoted to the optimization of electrochemical synthesis by a pulsed chronoamperometric method in ionic liquid medium. P3MT/VACNT/Al nanocomposites with mass proportions of P3MT in the electrode ranging from 10 to 90%. These composites have subsequently been used as electrodes in symmetric and asymmetric supercapacitors in coin-cell devices allowing specifics energies and powers of 52 Wh/kg and 12 kW/kg, respectively. In the third part, a P3MT deposition process onto moving VACNT was developed to study the continuous elaboration of composite electrodes and to allow the preparation of larger electrodes, 80 cm² in this study. These composites showed specific capacitances equivalent to the composites obtained with static deposits. In addition, the 80 cm2 strips were used for the realization of symmetric and asymmetric zig-zag supercapacitors and also showed specific energies and power very similar to those of coin-cells. In a last part, a transfer of method was realized for the synthesis of composite PPy / VACNT, in static then continuous process

Estilos ABNT, Harvard, Vancouver, APA, etc.

23

Warchal, Andrzej. "Study of the influence of additives (antioxidants) on the thermomechanical properties of carbon-bonded refractory composites". Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0050.

Texto completo da fonte

Resumo:

Les réfractaires alumine-carbone sont largement utilisés dans la coulée continue de l'acier. Ils sont responsables du contrôle du flux d'acier et de sa protection contre l'oxydation. Cependant, pour améliorer leur propre résistance à l'oxydation, plusieurs additifs tels que des carbures, des métaux, des composés à bas point de fusion et des frittes de verre sont ajoutés en tant qu'antioxydants. Dans cette étude, l'influence de ces additifs, ainsi que des conditions de cuisson, sur les propriétés liées à la résistance aux chocs thermiques des matériaux réfractaires à matrice carbonée a été étudiée. Des matériaux modèles, ayant une composition simplifiée par rapport aux matériaux industriels, ont été étudiés pour faciliter la compréhension des interactions entre les différents constituants du composite. Le comportement des matériaux réticulés (avant cuisson) et cuits a été étudié. La première partie de l'étude a montré que les antioxydants peuvent modifier les propriétés du réfractaire par différents mécanismes : cristallisation de la liaison carbone (B4C), guérison des microfissures (borax et fritte de verre) et formation de nouvelles phases (Al-Si). Cependant, puisque les additifs métalliques sont les antioxydants les plus largement utilisés dans les produits de Vesuvius, la deuxième partie de l'étude a porté sur leur impact (Al-Si,Al-Mg et Al) sur les propriétés clés influençant la résistance aux chocs thermiques. En plus, l'impact des conditions de cuisson (température et atmosphère) a également été étudié. Il a été prouvé que tous les antioxydants métalliques réagissent avec d'autres constituants pour former de nouvelles phases qui à la fois rigidifient le réfractaire et augmentent sa valeur du coefficient de dilatation thermique. Malheureusement, un tel comportement entraîne une détérioration de la résistance aux chocs thermiques. De plus, il s'est avéré que l'atmosphère de cuisson a une influence négligeable sur la réactivité des additifs et donc sur les propriétés finales du réfractaire. Ainsi, la température de cuisson est le paramètre qui a l'impact le plus important sur l'évolution réfractaire. Tous les résultats obtenus facilitent le choix des antioxydants et des conditions de cuisson pour obtenir les propriétés souhaitées du réfractaire
Alumina-carbon refractories are widely used in the continuous casting of steel. They are responsible for the steel flow control and its protection against oxidation. However, to improve their own oxidation resistance, several additives such as carbides, metals, low melting point compounds and glass frits are added as antioxidants. In this study, the influence of these additives, as well as firing conditions, on the properties related to the thermal shock resistance of carbon-bonded refractories was studied. Model materials, having simplified composition compared to the real industrial ones, were investigated tofacilitate the comprehension of interactions between different constituents of the composite. Behavior of both cured (before firing) and fired materials was studied. The first part of the study proved that antioxidants may modify the properties of the refractory through different mechanisms: crystallization of the carbon bond (B4C), microcracks healing (anhydrous borax and glass frit) and formation of new phases (Al-Si). However, since the metallic additives are the most widely used antioxidants in Vesuvius' products, the second part of the study was focused on their (Al-Si, Al-Mg and Al) impact on the key properties influencing the thermal shock resistance. What is more, the impact of firing conditions (temperature and atmosphere) was also investigated. It was proved that all metallic antioxidants react with other constituents to form new phases which both rigidify the refractory and increase its value of the coefficient of thermal expansion. Unfortunately, such behavior results in worsening of the thermal shock resistance. Moreover, it turned out that the firing atmosphere has a negligible influence on the additives reactivity and thus the final properties of the refractory. Thus, firing temperature is the parameter that has the most important impact on the refractory evolution. All the obtained results facilitate the choice of antioxidants and firing condition to obtain desired properties of the refractory

Estilos ABNT, Harvard, Vancouver, APA, etc.

24

Whiffen, Leonie. "Arbuscular mycorrhizal fungi and carbon sequestration in soil". Thesis, The University of Sydney, 2007. https://hdl.handle.net/2123/28114.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

25

Waiser, Travis Heath. "In situ characterization of soil properties using visible near-infrared diffuse reflectance spectroscopy". Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/5915.

Texto completo da fonte

Resumo:

Diffuse reflectance spectroscopy (DRS) is a rapid proximal-sensing method that is being used more and more in laboratory settings to measure soil properties. Diffuse reflectance spectroscopy research that has been completed in laboratories shows promising results, but very little has been reported on how DRS will work in a field setting on soils scanned in situ. Seventy-two soil cores were obtained from six fields in Erath and Comanche County, Texas. Each soil core was scanned with a visible near-infrared (VNIR) spectrometer with a spectral range of 350-2500 nm in four different combinations of moisture content and pre-treatment: field-moist in situ, air-dried in situ, field-moist smeared in situ, and air-dried ground. Water potential was measured for the field-moist in situ scans. The VNIR spectra were used to predict total and fine clay content, water potential, organic C, and inorganic C of the soil using partial least squares (PLS) regression. The PLS model was validated with data 30% of the original soil cores that were randomly selected and not used in the calibration model. The root mean squared deviation (RMSD) of the air-dry ground samples were within the in situ RMSD and comparable to literature values for each soil property. The validation data set had a total clay content root mean squared deviation (RMSD) of 61 g kg-1 and 41 g kg-1 for the field-moist and air-dried in situ cores, respectively. The organic C validation data set had a RMSD of 5.8 g kg-1 and 4.6 g kg-1 for the field-moist and air-dried in situ cores, respectively. The RMSD values for inorganic C were 10.1 g kg-1 and 8.3 g kg-1 for the field moist and air-dried in situ scans, respectively. Smearing the samples increased the uncertainty of the predictions for clay content, organic C, and inorganic C. Water potential did not improve model predictions, nor did it correlate with the VNIR spectra; r2-values were below 0.31. These results show that DRS is an acceptable technique to measure selected soil properties in-situ at varying water contents and from different parent materials.

Estilos ABNT, Harvard, Vancouver, APA, etc.

26

Veyrat, Alain. "Procédé électrochimique de traitement en continu de fibres de carbone par greffage d'amines ou de groupements aryls substitués". Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL055N.

Texto completo da fonte

Resumo:

L’objectif de cette étude est la conception et la réalisation d'un dispositif pilote de traitement de surface de fibres de carbone. Le traitement consiste en une oxydation électrochimique dans un milieu acétonitrile qui aboutit au greffage de fonctions aminées à la surface des fibres. Cet apport d'azote améliore fortement l'adhésion entre les fibres et les résines époxydes dans les matériaux composites. Le phénomène, mis en évidence par voltamétrie, est caractérisé par des analyses de surface ESCA. La cinétique du greffage de l'éthylènediamine a été étudiée sur des électrodes de fibres fixes en faisant varier leur longueur et le potentiel d'électrode appliqué. Les mesures d'intensité ont montré le rôle prépondérant de l'amine dans l'oxydation ainsi que la décroissance de l'activité le long de l'électrode. Les performances du greffage dans un dispositif ou la mèche de fibres circule dans divers bains ont été évaluées suivant trois modes de fonctionnement de la cellule électrochimique: contrôle du potentiel d'électrode, de la tension de cellule ou de la distribution de courant dans la cellule. La quantité d'azote fixée sur les fibres dépend principalement de la vitesse de défilement du fil dans la cellule. Une quantité importante de fibres traitées à la triéthylènetétramine a été produite, afin de préciser l'apport du traitement aminant au niveau des propriétés mécaniques des composites. Les résultats sont comparés avec ceux issus d'un autre procédé de traitement électrochimique, conduisant également à un apport d'azote en surface des fibres après la réduction de sels de diazonium en milieu acide

Estilos ABNT, Harvard, Vancouver, APA, etc.

27

Hsieh, Jang-Hsing. "Hydrogen embrittlement of cold worked plain carbon steel". Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/12016.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

28

Yang, Xiaoshuang. "Synthesis of aligned carbon nanotube arrays and fabrication of carbon nanotube structures for gas and water separation". Thesis, The University of Sydney, 2013. https://hdl.handle.net/2123/29250.

Texto completo da fonte

Resumo:

The purpose of this project is to optimise the synthesis of aligned carbon nanotube (CNT) arrays and explore the application of porous CNT structures in the gas and water separation. Aligned CNT arrays and CNT buckypapers are the main two types of porous CNT structures used as separation membranes. In this project, aligned multi-walled CNTs were synthesised by supported-catalyst and floating-catalyst chemical vapour deposition (CVD). In the supported-catalyst CVD, H2 pre-treatment was found to be a critical factor affecting the CNT growth. CNT array height and alignment was strongly dependent on the duration of H2 pre-treatment, with optimal height and alignment achieved using 10-15 minutes pre-treatment. Small angle X-ray scattering was used to quantify the alignment, distribution, and size of the CNTs in arrays produced from varying pre-treatment times and the results correlated with microscopy measurements. Compared to the supported-catalyst CVD, the floating-ferrocene CVD is promising due to its low cost and facile fabrication process, as well as its scalability. A two-step floating-ferocene CVD, was developed to prepare aligned CNT arrays. The effect of ferrocene loading on the size and distribution of Fe catalysts, as well as the morphology, diameter, and height of the CNT arrays, was investigated. CO2, as a weak oxidant, was introduced into the floating-ferrocene CVD to improve the growth of aligned CNT arrays. The CO2-assisted floating-ferrocene CVD method facilitates the well-controlled growth of aligned CNT arrays, where the quality of the aligned CNT arrays was significantly improved in the presence of CO2, as demonstrated by improved height, alignment and purity. A novel vacuum extraction process was employed to release the as-prepared CNT array from the Si wafer after water etching at 750 °C. The resulting free-standing CNT arrays were applied as membranes for gas permeation test (H2, N2, and CO2), showing much faster gas transport than that calculated theoretically. Alignment of the CNT arrays plays an important role in the gas permeation through the aligned CNT arrays. Compared to the theoretical calculation, the gas diffusion across the well-aligned CNT arrays was enhanced by a factor of ~ 45, which is significantly more than that across the poorlyaligned CNT arrays, with an enhancement factor of~ 8. Multi-walled CNT buckypaper was fabricated by a facile, surfactant-free assembly process. The permeation of different gases through the as-prepared buckypaper was investigated. The gas permeance is 2~3 times higher than the theoretical permeance, with ideal H2 selectivities to Ar, C2H4, and CO2, of 4.20, 3.62, and 4.59, respectively. The buckypaper was also used in water treatment as a filter membrane for removal of natural organic matters (NOM). Humic acid (HA) was used as a model NOM. Purification of the CNTs introduced carboxylic and hydroxylic functional groups that improved the rejection of HA through the buckypaper. The buckypaper prepared from purified CNTs exhibited excellent rejection of HA(> 93%). Overall, in the supported-catalyst CVD, the synthesis of aligned CNT arrays was optimised by H2 pre-treatment. In the floating-ferrocene CVD, the height, alignment, diameter and other properties of the aligned CNT arrays were firstly controlled by the addition of CO2. New methods were employed to prepare free-standing CNT arrays and buckypapers as membranes. The effect of alignment was firstly investigated by using free-standing arrays with different alignment in gas separation experiments. Buckypaper was used in a new field, NOM removal, and showed excellent performance.

Estilos ABNT, Harvard, Vancouver, APA, etc.

29

Lôbo, Ivon Pinheiro. "Desenvolvimento de método cromatográfico para quantificação de alquil ésteres em amostras de biodiesel". Instituto de Química, 2010. http://repositorio.ufba.br/ri/handle/ri/20289.

Texto completo da fonte

Resumo:

Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2016-09-08T14:22:01Z No. of bitstreams: 1 Tese de Doutorado - Ivon P. Lôbo.pdf: 3344901 bytes, checksum: 7e73b89d7c92c4df99ab47eb630bca7c (MD5)
Approved for entry into archive by Vanessa Reis (vanessa.jamile@ufba.br) on 2016-09-08T14:40:02Z (GMT) No. of bitstreams: 1 Tese de Doutorado - Ivon P. Lôbo.pdf: 3344901 bytes, checksum: 7e73b89d7c92c4df99ab47eb630bca7c (MD5)
Made available in DSpace on 2016-09-08T14:40:02Z (GMT). No. of bitstreams: 1 Tese de Doutorado - Ivon P. Lôbo.pdf: 3344901 bytes, checksum: 7e73b89d7c92c4df99ab47eb630bca7c (MD5)
Dentre os parâmetros estabelecidos para garantia da qualidade do biodiesel, o teor de ésteres destaca-se por refletir a pureza do biocombustível a ser misturado ao diesel mineral. Com esse objetivo, é preconizado pela Resolução 07/08 da ANP o método cromatográfico EN ISO 14103, que se baseia na comparação da área total dos picos dos ésteres com a área relativa ao padrão heptadecanoato de metila (C17:0-Me). Este método apresenta inconvenientes como o alto custo do padrão C17:0-Me e a sua aplicabilidade na quantificação de ésteres com cadeia carbônica com menos de 16 carbonos. Essa limitação é decorrente da maior deficiência de carbono para os ésteres de cadeia curta, resultando em respostas diferenciadas no FID. Outro ponto que deve ser destacado é que o C17:0-Me poderá estar presente em biodieseis de diferentes óleos e gorduras e poderá acarretar em erros de quantificação. Neste trabalho, foram propostos Fatores de Correção Split (FRS), baseados na razão entre a proporção de carbonos ativos na molécula do éster e na sua resposta relativa no GC FID. O propósito desses fatores é corrigir as respostas no FID para ésteres com cadeia menor que 16 carbonos e a discriminação das massas dos ésteres mais pesados, no momento da injeção split. Os FRS mostraram uma correlação linear com as respectivas massas molares, permitindo assim realizar previsão dos FRS dos ésteres do biodiesel, a partir dos FRS de três padrões adicionados a amostra. Os padrões internos empregados foram C12:0-Et, C14:0-Et e C18:1-Et nas análises de biodieseis metílicos e C12:0-Me, C14:0-Me e C18:0-Me para os biodieseis etílicos. Utilizando FRS para a análise de uma amostra sintética simulando o biodiesel de babaçu, onde estavam presentes ésteres de cadeia curta em concentrações significativas, os erros de previsão (EP%) foram respectivamente 1,4; 2,7; 1,4; 2,2; e 3,2%, para os ésteres C6:0-Et, C8:0-Et, C10:0-Et, C12:0-Et, C14:0-Et; contra 24,4; 13,5, 6,2; 2,4 e 2,0% para os mesmos ésteres determinados via padrão C17:0-Me. Para amostras reais de biodieseis de dendê, soja e pinhão manso, onde os ésteres mais leves estão presentes em concentrações não superiores a 1%, os resultados das análises realizadas através dos FRSPreditos e via padrão C17:0-Me não apresentaram diferenças significativas, conforme a avaliação do método de referência EN ISO 14103. Mesmo utilizando uma quantidade maior de padrões internos, o método proposto apresenta um custo mais baixo que o método oficial, permitindo inclusive a quantificação de C17:0-Me que possa vir está presente na amostra do biodiesel. O método mostrou-se confiável, sendo aplicável a análise de biodieseis metílico e etílicos de óleos e gorduras, onde a concentração de ésteres com cadeia carbônica menor que C16 não seja superior a 1%.
Among the parameters set for quality assurance of biodiesel, the ester content stands out because it reflects the purity of the biofuel to be blended with mineral diesel. With this objective, it is recommended by Resolution 07/08 of the ANP the chromatographic method EN ISO 14 103, which is based on a comparison of the total area of the peaks of the esters with the area on the standard methyl heptadecanoate (C17:0-Me). This method has drawbacks such as high cost of the standard C17:0-Me and its applicability in the quantification of esters with chains with less than 16 carbons. This limitation is due to higher carbon deficiency for short chain esters, resulting in differential responses on the FID. Another point to be stressed is that the C17:0-Me may be present in biodiesel of different oils and fats and can cause errors in measurement. In this work, split response factors (SRF) have been proposed, based on the ratio between the proportion of active carbons in the ester molecule and its response on the GC FID. The purpose of these factors is the correct answers to the FID chain esters with less than 16 carbons and discrimination of the masses of heavier esters, during the split injection. The SRF showed a linear correlation with their molecular weights, thus allowing prediction of SRF held the esters of biodiesel, from the FRS three patterns added to the sample. The internal standards used were C12 :0- Et, Et and C14 :0-C18 :1-Et in the analysis of methyl biodiesels and C12 :0-Me, Me, and C14 :0-C18 :0-Me for ethyl biodiesels. Using SRF to the analysis of a sample simulating synthetic biodiesel from babassu, where were these short chain esters in high concentrations, the prediction errors (PE%) were respectively 1.4, 2.7, 1.4, 2.2 , and 3.2% for C6 :0-Et ester, C8 :0-Et, C10 :0-Et, Et :0-C12, C14 :0-Et, against 24.4, 13.5, 6 , 2, 2.4 and 2.0% for the same esters determined via standard C17 :0-Me. For samples of palm, soybean and jatropha biodieseis, where the lighter esters are present in concentrations not exceeding 1%, the results of analysis performed by SRF predicted and by standard route C17:0-Me showed no significant differences, as evaluation of the reference method EN ISO 14 103. Even using a larger amount of internal standards, the proposed method has a lower cost than the official method, permitting a quantification of C17 :0-Me which may present in the sample of biodiesel. This method was reliable and applicable to analysis of methyl and ethyl esters oils and fats, where the concentration of esters with carbon chain less that C16 is not more than 1%.

Estilos ABNT, Harvard, Vancouver, APA, etc.

30

Tomiello, Stevan Scussel. "Diferentes dopagens e intercamadas contendo silício: otimização da adesão de revestimentos de a-C:H sobre aço". reponame:Repositório Institucional da UCS, 2018. https://repositorio.ucs.br/11338/4160.

Texto completo da fonte

Resumo:

O carbono tipo diamante (DLC) é um material de revestimento que alia alta resistência ao desgaste e baixo coeficiente de atrito. Devido a essas propriedades, o DLC pode ser aplicado em peças metálicas para facilitar a conformação em ferramentas de dobra e ainda para a diminuição de perdas por atrito em componentes de motores. Porém, limitações como a baixa adesão e a complexidade da técnica de deposição restringem sua utilização. Diversas estudos propõem alternativas para a otimização do filme, como a inclusão de intercamadas, dopagens ou a aplicação de diferentes parâmetros e processos de deposição, porém não há um consenso na bibliografia de qual opção ou combinação traz o melhor resultado, especialmente visando uma aplicação industrial de baixo custo. Nesse contexto, a proposta deste trabalho é realizar um estudo sistemático de diferentes arquiteturas filme/intercamada utilizando um composto a base de silício para a formação da intercamada e da zona de dopagem e, após encontrar a melhor combinação em termos de adesão, pesquisar o efeito da tensão nessa combinação específica. A técnica de deposição química a vapor assistida por plasma pulsado utilizando confinamento eletrostático foi utilizada para aplicar o revestimento e as diferentes arquiteturas sobre o aço AISI O1 e AISI 4140. As dopagens e intercamadas foram produzidas a partir de hexametildisiloxano, previamente vaporizado, que permite a formação do filme e das diferentes arquiteturas num processo único e simples. A qualidade superficial dos filmes foi avaliada por microscopia ótica, enquanto a estrutura físico-química foi analisada por microscopia eletrônica de varredura e espectroscopia de emissão óptica por descarga luminescente. Por fim, as propriedades mecânicas e tribológicas do filme foram avaliadas por medições de nanodureza e por testes de nanoesclerometria linear, respectivamente. Os resultados mostram que as diferentes arquiteturas de dopagem do DLC com silício promovem uma piora nas propriedades do filme, com o aumento nos defeitos superficiais e a diminuição da dureza e da carga crítica para sua delaminação. A combinação de DLC e uma única intercamada contendo silício apresenta-se como a melhor opção para aplicações tribológicas. Por outro lado, uma maior tensão elétrica no plasma de formação da intercamada de silício aumenta a carga crítica de delaminação e minimiza os defeitos nas bordas das amostras. O conhecimento gerado viabilizou a obtenção de um revestimento para aplicações industriais em grande escala e baixo custo de produção.
Diamond-like carbon (DLC) coatings combine high wear resistance and low friction coefficient. Due to these properties, DLC can be applied on metal parts to facilitate the conformation process in bending tools and also for the reduction of friction losses in engine components. However, limitations as low adhesion and the technical complexity of the deposition process as a whole reduce its use. Several studies show alternatives to the optimization of the film, as the use of interlayers, doping and/or the application of different etching gases and deposition process parameters. However, there is a consensus in the bibliography that an combination of the above alternatives should bring the best result, especially for a low-cost industrial application. In this context, the aim of this study is to carry out a systematic study of different architectures of the film/interlayer system using precursors containing silicon for the formation of interlayer/doping zone to reach the best system in terms of DCL integrity and adhesion. The technique of deposition by pulsed direct current plasma enhanced chemical vapor deposition assisted by electrostatic confinament was used to apply the coating and different architectures on the AISI O1 and AISI 4140 steels. The interlayers were produced from hexamethyldisiloxane with silicon acting also as dopant in carbon film under different conditions, allowing the film formation in a single simple process. The surface integrity of the films was evaluated by optical microscopy, while the physical and chemical structure was analyzed by scanning electron microscopy and glow discharge optical emission spectroscopy. Finally, mechanical and tribological properties of the film were evaluated by nanohardness and nanoscratch measurements, respectively. The results show that different doping architectures of DLC with silicon promote detrimental properties in the DLC, with the increase in the surface defects and the decrease of hardness and critical load for delamination. Moreover, the combination of DLC plus a single silicon-containing interlayer is the best option to optimize the tribological properties. On the other hand, a higher applied plasma voltage in the silicon interlayer deposition guarantees high critical loads for DLC delamination and low density of defects without delamination events at the sample edges. This knowledge made possible to obtain DLC coatings for industrial applications in large scale and low cost of production.

Estilos ABNT, Harvard, Vancouver, APA, etc.

31

Cemin, Felipe. "Físico-química de adesão de filmes de DLC sobre aço AISI 4140 utilizando intercamadas contendo silício". reponame:Repositório Institucional da UCS, 2015. https://repositorio.ucs.br/handle/11338/987.

Texto completo da fonte

Resumo:

O carbono tipo diamante (DLC) é um material de revestimento que tem atraído grande interesse devido às propriedades de alta resistência ao desgaste e baixo coeficiente de atrito. Intercamadas contendo silício são amplamente utilizadas para melhorar a adesão do DLC em ligas ferrosas, embora o fenômeno que gera a adesão ainda não seja bem entendido. Neste contexto, o objetivo desse estudo é compreender claramente os fenômenos físico-químicos e as ligações químicas que são responsáveis pela adesão de filmes de DLC sobre aços, utilizando intercamadas contendo silício produzidas em diferentes condições de processamento. Os filmes foram depositados sobre o aço AISI 4140 por deposição química a vapor assistida por plasma pulsado de corrente contínua utilizando confinamento eletrostático. As intercamadas foram produzidas a partir de tetrametilsilano em diferentes tempos e temperaturas de deposição, e o filme de DLC foi subsequentemente depositado sobre as intercamadas a partir de acetileno, utilizando-se as mesmas condições experimentais para todas as amostras. A estrutura físico-química dos filmes produzidos foi avaliada por microscopia eletrônica de varredura, espectroscopia de Raios X por dispersão em energia, espectroscopia de emissão óptica por descarga luminescente e espectroscopia Raman. As ligações químicas nas interfaces do sistema aço/intercamada/DLC foram avaliadas por espectroscopia de fotoelétrons excitados por Raios X. Por fim, a carga crítica para delaminação dos filmes foi medida por testes de nanoesclerometria linear. Os resultados mostraram que a espessura e a estrutura química das intercamadas são dependentes do tempo e da temperatura de deposição, mas a temperatura foi estabelecida como o parâmetro chave de controle da cinética de reação e de crescimento da intercamada. A intercamada é estruturada como um carbeto de silício amorfo hidrogenado com formação preferencial de ligações Si–C em temperaturas de deposição a partir de 300°C. Para as amostras com intercamada depositada a partir dessa temperatura de transição, a adesão dos filmes de DLC é alcançada, sem delaminação espontânea. A melhora na adesão está associada com as ligações químicas formadas nas interfaces. Enquanto as ligações C–C e Si–C são formadas na interface intercamada/DLC, ligações Si–Fe são formadas na interface aço/intercamada. A presença de hidrogênio e oxigênio residual na estrutura da intercamada prejudica a adesão dos filmes de DLC.
Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-08-24T15:55:55Z No. of bitstreams: 1 Dissertacao Felipe Cemin.pdf: 4353174 bytes, checksum: 9667e1c8437438cfcf3fc9f8860b0fa6 (MD5)
Made available in DSpace on 2015-08-24T15:55:56Z (GMT). No. of bitstreams: 1 Dissertacao Felipe Cemin.pdf: 4353174 bytes, checksum: 9667e1c8437438cfcf3fc9f8860b0fa6 (MD5)
Conselho Nacional de Desenvolvimento Científico e Tecnológico.
Diamond-like carbon (DLC) is a thin film material that has attracted much attention due to its properties as high wear resistance and super-low friction coefficient. Although silicon-based intermediate layers are employed to enhance the adherence of DLC films on ferrous alloys, the role of such buffer layers is not yet understood in chemical terms. In this context, the aim of this study is to clearly understand the physical-chemical phenomena and chemical bonding guaranteeing the DLC adhesion on ferrous alloys using Si-based interlayers deposited by different process conditions. The films were deposited on AISI 4140 steel by pulsed direct current plasma enhanced chemical vapor deposition assisted by electrostatic confinement. The interlayers were grown from tetramethylsilane at different deposition temperatures and times and the DLC thin film was grown from acetylene with the same experimental conditions for all samples. The physical-chemical structure of the bi-layers produced was evaluated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, glow discharge optical emission spectroscopy and Raman spectroscopy. The local chemical bonds at the interfaces of the steel/interlayer/DLC structure were evaluated by X-ray photoelectron spectroscopy. Finally, the critical loads for thin films delamination were measured by nanoscratch testing. The results show that the interlayer thickness and structure are dependent on both deposition time and temperature, but the temperature was established as being the key parameter controlling the reaction kinetic and the interlayer growth. The interlayer is structured as a hydrogenated amorphous silicon carbide alloy with enhanced formation of Si–C bonds at deposition temperatures ≥ 300°C. At such transition temperature of interlayer deposition, adhesion of DLC is reached, with no spontaneous delamination. The improved adhesion is associated with the nature of chemical bonds formed in the interfaces. Whereas C–C and C–Si bonds are formed on the interlayer/DLC interface, the steel/interlayer interface is constituted by Si–Fe bonds. The presence of hydrogen and residual oxygen in the interlayer structure degrades the adhesion of DLC thin films.

Estilos ABNT, Harvard, Vancouver, APA, etc.

32

Lagier, Thomas. "Convertisseurs continu-continu pour les réseaux d'électricité à courant continu". Thesis, Toulouse, INPT, 2016. http://www.theses.fr/2016INPT0084.

Texto completo da fonte

Resumo:

Les évènements climatiques de ces dernières années ont encouragé de nombreux pays à augmenter la part des énergies renouvelables et non génératrices de gaz à effets de serre. Cependant, pour faciliter leur intégration à grande échelle, le besoin d’un super réseau européen se fait sentir. Ce nouveau réseau, principalement basé sur du courant continu sous haute tension (HVDC) nécessitera l’utilisation de convertisseurs DC-DC. Par conséquent, ce mémoire propose et étudie des topologies basées sur l’association de convertisseurs DC-DC élémentaires isolés. Il est organisé en une introduction, 3 chapitres et une conclusion. Dans l’introduction, un état de l’art est réalisé sur les technologies actuellement mises en oeuvre dans les applications HVDC. Le contexte de l’étude, lié au développement des réseaux DC interconnectés et maillés est ensuite développé. Dans le premier chapitre, des solutions basées sur l’association de convertisseurs DC DC élémentaires isolés sont étudiées puis comparées en termes de dimensionnement des éléments réactifs et de rendement. Cette étude nous a permis de sélectionner trois topologies pour la suite de notre travail. Dans le deuxième chapitre, nous évoquons tout d’abord les différentes problématiques pouvant apparaitre lors de la mise en oeuvre des solutions proposées. Dans un second temps, en prenant une ferme éolienne offshore comme cas d’application, les solutions proposées sont comparées en termes de pertes et de nombre de composants avec une topologie basée sur une association de convertisseurs modulaires multiniveaux (MMC) utilisés dans les réseaux HVDC. Le troisième chapitre présente l’étude et la mise en oeuvre de deux prototypes de convertisseur DC-DC isolés, d’une puissance de 100 kW et fonctionnant sous une tension de 1,2 kV. Ces prototypes ont permis de valider expérimentalement les performances des topologies étudiées dans le premier chapitre. Finalement, la dernière partie propose une conclusion des travaux présentés dans cette thèse. Ces travaux nous ont permis de montrer que les solutions proposées présentent un intérêt pour le cas d’application sélectionné
The catastrophic environmental effects seen in the last couple of decades have encouraged many countries to increase the proportion of C02-free energy from renewable sources. However, for the easier integration of these energies on a large scale, the need of a European SuperGrid has emerged. This new grid, mainly based on High-Voltage- Direct-Current (HVDC) will require the use of DC-DC converters. Therefore, this manuscript proposes and studies topologies based on the association of isolated elementary DC-DC converters. It is organized in one introduction, 3 chapters and one conclusion. In the introduction, a state-of-the-art of the technologies currently used in HVDC applications is proposed. The context of the study, linked to development of the meshed DC grids, is developed afterwards. In the first chapter, solutions based on the association of elementary isolated DC-DC converters are studied and then compared in terms of reactive components sizing and efficiency. This study permitted the selection of three topologies for the rest of our work. In the second chapter, we mention the issues which may appear during the implementation of the solution. Then, by taking an offshore wind farm as application case, the solution is compared, in terms of loss and component number, with a topology based on the association of Modular Multilevel Converters (MMC) currently used in HVDC grids. The third chapter presents the study and the implementation of two 100 kW DC-DC converter prototypes, operating at 1.2 kV. These prototypes allowed the experimental validation of the performances of the topologies studied in the first chapter. Finally, the last part proposes a conclusion of the work achieved in this thesis. This work allowed it to be shown that the proposed solutions are interesting for the selected application case

Estilos ABNT, Harvard, Vancouver, APA, etc.

33

Houillon, Nicolas. "La dynamique du carbone inorganique dans le continuum sol-épikarst-cavité du site de la Grotte de Lascaux (Dordogne, France) : apports des monitorings hydrogéochimique et microclimatique continus pour l’étude de l’aérologie et le développement d’une méthode de simulation des processus calco-carboniques aux parois". Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0441/document.

Texto completo da fonte

Resumo:

Depuis son invention en 1940 mais surtout consécutivement à sa fermeture au public en 1963, la conservation de la Grotte de Lascaux se base entre autres sur la compréhension de ses interactions avec le massif karstique environnant et notamment les processus siégeant dans l’épikarst et la zone de transmission superficielle. Ces travaux de thèse se sont donc attachés à comprendre la dynamique du CO2 dans le continuum sol-épikarst-cavité afin d’en évaluer les potentiels impacts sur la conservation des parois. Nous bénéficions à Lascaux d’une fenêtre d’observation sur les écoulements provenant de l’épikarst sus-jacent dans le SAS 1 de la cavité, mais aussi d’une instrumentation conséquente. Elle permet l’acquisition de nombreuses séries de données temporelles des paramètres microclimatiques ainsi que des teneurs en CO2 de l’air en différents points de la cavité ou encore du débit de l’émergence épikarstique depuis le début des années 2000.Une première partie de l’étude est consacrée à la caractérisation de la dynamique du CO2 dans le contexte d’un épikarst sous couverture pédologique. A cette fin, une parcelle expérimentale est instrumentée afin d’effectuer un suivi des paramètres hydroclimatiques et des teneurs en CO2 à différentes profondeurs. Des périodes de recharge (accumulation) et de vidange (émanations vers l’atmosphère) du CO2 de l’épikarst superficiel sont démontrées tout comme la constitution d’un stock de CO2 peu variable dans l’épikarst subsuperficiel. La compréhension de ces différents mécanismes aboutit à un schéma général de la dynamique du CO2 dans l’épikarst.Cette dynamique est étudiée dans la Grotte de Lascaux au cours d’une seconde partie à partir des séries temporelles des paramètres microclimatiques et des teneurs en CO2, mais aussi du signal isotopique en 13C. Il est alors démontré que les flux de CO2 entrant dans la cavité proviennent de trois origines distinctes : l’atmosphère (entrée), l’épikarst superficiel (Galerie Mondmilch et Salles Ensablées) et le massif (éboulis du Puits du Sorcier). Parallèlement, deux régimes aérologiques responsables de la répartition spatio-temporelle des teneurs en CO2 dans la cavité sont observés : stratification et thermoconvections. Ils sont les principaux responsables de la dynamique du CO2 dans la Grotte de Lascaux du fait des faibles échanges entre cette dernière et l’atmosphère comparativement à d’autres cavités karstiques de la région. Enfin, l’impact du dispositif du pompage de l’air sur l’aérologie et la dynamique du CO2 dans la Grotte de Lascaux est évalué. La comparaison de ces dynamiques avec et sans extraction de l’air de la cavité conduit à la création de schémas conceptuels de la dynamique du CO2 dans la Grotte Lascaux.L’étude des conditions d’écoulement dans l’épikarst de la Grotte de Lascaux, troisième partie de ces travaux, a été effectuée à partir d’un suivi en continu des débits, paramètres physico-chimiques et de la fluorescence naturelle de l’eau. L’analyse des séries temporelles de ces traceurs naturels conduit caractériser de façon détaillée les conditions d’écoulement et notamment l’importance de la teneur en eau de l’épikarst sur la taille zone d’alimentation et les types d’eau arrivant à l’exutoire. Parallèlement, l’impact de ces conditions d’écoulement sur les équilibres calco-carboniques des eaux arrivant dans la cavité est analysé.Enfin, les connaissances acquises sont appliquées pour déterminer l’impact potentiel en continu des eaux (condensation et exfiltration) présentes aux parois ornées de la cavité. A cette fin, une méthodologie d’estimation de la masse de calcite potentiellement précipitée par les eaux d’exfiltration et dissoute par les eaux de condensation basée sur des simulations hydrogéochimiques est développée. Son application à la paroi gauche de la Salle de la Taureaux en contextes de pompage et naturel conduit à l’évaluation de l’impact potentiel du pompage mais aussi de l’aérologie de la cavité sur la conservation des parois
Since its invention in 1940 but especially as a result of its closure to the public in 1963, the preservation of the Cave of Lascaux bases itself among others on the understanding of its interactions with the surrounding karstic massif in particular the processes sitting in the épikarst and the zone of superficial transmission. That is why this thesis research attempted to understand the dynamics of the CO2 in the continuum soil-epikarst-cave to estimate the potential impacts on the preservation of walls. We benefit in Lascaux of an observation window on the flows resulting from the epikarst known emergence in the SAS 1 of the cavity, but also the consequent instrumentation. It allows the acquisition of numerous time series data of the microclimatic parameters, carbon dioxide partial pressures at different points of the cave and the discharge of the epikarstic emergence since the beginning of the century.A first part of the study is dedicated to the characterization of the dynamics of the CO2 in the context of an epikarst under soil cover. To this end, an experimental parcel is instrumented to follow the hydroclimatic parameters and the contents in PCO2 at various depths. Periods of recharge (accumulation) and draining (emanations towards the atmosphere) of the superficial epikarst CO2 are highlighted when the constitution of a low variable CO2 stock is observed in the subsuperficiel epikarst. The understanding of these various mechanisms ends in a conceptual scheme of the CO2 dynamics in the epikarst.In a second part, this dynamic is studied in the Cave of Lascaux from the temporal series of the microclimatic parameters and the contents in CO2, but also the δ13CCO2. It is then demonstrated that the flows of CO2 entering the cavity result from three different origins: the atmosphere (entrance), the superficial epikarst (Mondmilch Gallery and Silted-up Rooms) and the massif (screw of the Shaft of the Sorcerer). At the same time, two aerological regimes responsible for the spatiotemporal distribution of the PCO2 in the cavity are observed: stratification and thermoconvection. They are the main mechanisms responsible for the dynamics of the CO2 in the Cave of Lascaux because of the low exchanges with the atmosphere. Finally, the impact of the pumping of the air on the aerology and the dynamics of the CO2. The comparison of these dynamics with and without extraction of the air of the cavity leads to the creation of conceptual schemes of the dynamics of the CO2 in the Cave Lascaux.The study of the flowing conditions in the epikarst of the Cave of Lascaux, the third part of these works, was made from a continuous monitoring of the discharge, physico-chemical parameters and the natural fluorescence of the water. The analysis of the temporal series of these natural tracers leads to characterize in a detailed way the flowing conditions and the importance of the moisture content of the epikarst on the size of the recharge area and the types of water arriving at the emergence. In parallel, the impact of these conditions on the calco-carbonic balances of waters arriving in the cavity is analyzed.Finally, the acquired knowledge are applied to determine the potential continuous impact of the waters (condensation and exfiltration) present at the adorned walls of the cave. To this end, a methodology of estimation of the mass of calcite potentially precipitated by exfiltration and dissolved by condensation based on hydrogeochemical simulations is developed. Its application to the left wall of the Hall of the Bulls with and without pumping leads to the evaluation of the potential impact of this device but also the aerology of the cavity on the preservation of walls

Estilos ABNT, Harvard, Vancouver, APA, etc.

34

Li, Chi-ho, e 李志豪. "Synthesis of photosensitizing diblock copolymers for functionalizationof carbon nanotubes and their applications". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47869379.

Texto completo da fonte

Resumo:

Block copolymers containing pendant pyrene, terpyridine and poly(3- hexylthiophene) moieties with different block ratios and chain lengths were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The block copolymers obtained had narrow molecular weight distribution. The applications of these polymers for non-covalent functionalization of carbon nanotubes and in photovoltaic devices were studied. The molecular weight distribution and block sizes of the block copolymers could be controlled quite well. The polydispersities measured were below 1.25. The block copolymers could be functionalized on the surface of CNTs. The functionalized CNTs had an improved dispersing ability and a maximum dispersing ability of 0.30 mgmL-1 in DMF was achieved. The photosensitizing properties of an individual functionalized CNT were studied by conductive atomic force microscopy. In the presence of the photosensitizing unit, the photocurrent was measured to be 6.4 nAμW-1 at 580 nm. This suggests the role of metal complexes in the photosensitizing process in the block copolymer. Poly(3-hexylthiophene)-block-pendant pyrene copolymers were synthesized by Grignard metathesis and RAFT polymerization. Different loadings of the block copolymers functionalized CNT were employed as the electron accepting materials in bulk heterojunction photovoltaic devices. A maximum power conversion efficiency of 0.77 × 10-3 % was achieved for the poly(3- hexylthiophene): 0.5% polymer functionalized CNT devices. The poor efficiency was attributed to the low CNT loadings that limited the electron transport in the devices. The poly(3-hexylthiophene)-block-pendant pyrene copolymer were employed as compatibilizer for poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction photovoltaic devices. With the addition of 20 % of the block copolymer, a maximum power conversion efficiency of 1.62 % could be achieved. The long term stability of the encapsulated photovoltaic devices was studied. There was more than 30 % reduction in the degradation of performance after 30 days when the block copolymer was added as compatibilizer. These results suggested the role of the block copolymer compatibilizers in improving both the photovoltaic performances and stability of the devices. Differential scanning calorimetry results suggested that the improved photovoltaic performances may be attributed to the enhanced compatibility between poly(3- hexylthiophene) and PCBM.
published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy

Estilos ABNT, Harvard, Vancouver, APA, etc.

35

Fanni, Saman. "Void content computation using optical microscopy for carbon fiber composites". Thesis, KTH, Hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-285602.

Texto completo da fonte

Resumo:

Three different void content calculation techniques using optical microscopy werecompared in multiple-user trials. The three methods studied comprised of a selection,thresholding, and semi-automatic machine learning method. The techniques wereapplied to micrographs of three carbon fiber-epoxy composite plates manufacturedin-house, where one plate had reduced void content by means of debulking priorto curing. The users performed the techniques on the sets of micrographs and thestandard deviation between the users void content results were measured.The advantages of the three methods were discussed and their practical applications wereproposed. The trials showed agreement between users on what are voids and not as well asshowing that uncertainties in void content are specimen-specific and not attributed todifferent users or methods applied. All three methods showed satisfying precision incalculating void content compared to void content quality levels provided by literature.It was found that thresholding, which is the current standard method of void contentcalculation using microscopy, inhabits an unscientific bias which compromises the legitimacyof the method. The study formulates a manual selection-based method usingedge-detection selection tools intended to benchmark void content in images, as wellas proposing a route to the automation of void content analysis using microscopy.
Tre olika beräkningstekniker för kavitetshalter med hjälp av mikroskopi jämfördes genom fleranvändar-tester. De tre metoderna innefattade en selektions-metod, tröskelvärdesmetod, och en övervakad maskininlärningsmetod. Metoderna applicerades på mikrografer av tre kolfiber-epoxi kompositplattor tillverkade internt, varav en platta hade reducerad kavitetshalt genom en avbulkningsprocess innan härdning. Användarna genomförde metoderna på mikrograferna och standardavvikelsen mellan användarnas resulterande kavitetshalter mättes. För- och nackdelarna hos de tre metoderna diskuterades och deras praktiska applikationer föreslogs. Testerna visade en överensstämmelse mellan användare om vad som omfattar kaviteter och inte, samt en påvisning på att osäkerheter kring kavitetshalter är provbitberoende och inte användar- eller metodberoende. Alla tre metoder uppvisade en tillfredsställande precision i kavitethaltsberäkning jämfört med kvalitetsnivåer av kavitethalter erhållna från litteratur. Det konstaterades att tröskelvärdesmetoden, vilket är nuvarande standardmetoden för kavitethaltsberäkning med mikroskopi, innehar en bias som sätter validiteten av metoden i fråga. Studien formulerar även en manuell selektions-metod som använder selektions-verktyg för randdetektering, ämnad för att hitta referensvärden för kavitetshalter. Förslag ges även kring tillvägagångssättet till att uppnå automatiserade metoder för kavitethaltsberäkning.

Estilos ABNT, Harvard, Vancouver, APA, etc.

36

Brandão, Sirlaine Diniz Ferreira. "Influência da funcionalização com grupos contendo oxigênio na dispersão de nanotubos de carbono de parede única em solventes do tipo amida". CNEN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, 2010. http://www.bdtd.cdtn.br//tde_busca/arquivo.php?codArquivo=256.

Texto completo da fonte

Resumo:

Nenhuma
Desde que as singulares propriedades mecânicas e condutoras dos nanotubos de carbono (NCs) estão associadas a tubos individuais isolados, a dispersão e estabilização de seus feixes em diferentes líquidos são de extrema importância em estudos fundamentais e aplicados. Solventes do tipo amida são atualmente considerados os melhores candidatos, dentre os solventes orgânicos, à dispersão quantitativa dos feixes de nanotubos, sendo que a funcionalização das paredes dos tubos favorece essa dispersão em determinados meios. Amostras brutas de nanotubos de carbono são compostas por feixes contendo até centenas de tubos com distribuição em diâmetro, comprimento, quiralidade e caráter eletrônico, unidos por interações de van der Waals. Para a dispersão desses feixes, o potencial atrativo entre os tubos deve ser balanceado por um potencial repulsivo. Assim, o custo energético das interações nanotubosolvente, que depende fortemente da composição química da superfície dos tubos e das propriedades dielétricas do meio, precisa ser entendido. Teorias de solubilidade têm sido recentemente aplicadas no entendimento dos sistemas nanotubo-solvente. Nelas, a dispersão é favorecida quando os parâmetros de solubilidade do soluto e do solvente têm valores próximos. Nos parâmetros de Hansen, contribuições de energias dispersivas (dd), dipolares (dp) e de ligação de hidrogênio (dh) são consideradas nas interações intermoleculares. O parâmetro de Flory-Huggins (χ) estima a diferença de interação entre o soluto e o solvente, podendo ser expresso em termos dos parâmetros de Hansen. Neste trabalho, apresentamos um estudo sistemático da dispersão de nanotubos de carbono de parede única, como preparados e funcionalizados com grupos ácidos contendo oxigênio, em solventes do tipo amida. As interações nanotubos-solvente foram analisadas em termos dos parâmetros de solubilidade de Hansen e de Flory-Huggins. Por refluxo em solução de HNO3 diluída, quantidades similares (~ 0,3 mmol/g C) de grupos ácidos carboxílicos e hidroxílicos foram covalentemente introduzidos à superfície dos tubos, sem criar defeitos adicionais ou destruir tubos de diâmetros menores. Os materiais de partida e funcionalizado foram amplamente caracterizados por termogravimetria, microscopia eletrônica de varredura e transmissão, titulação potenciométrica e espectroscopias por dispersão de energia, Raman, na região do infravermelho e de fotoelétrons excitados por raios X. As dispersões obtidas por sonificação/centrifugação dos NCs, antes e após funcionalização, em N-metilpirrolidona (NMP), N,N-dimetilformamida (DMF), N,N-dimetilacetamida (DMA), Ndodecilpirrolidona (N12P) e ciclohexilpirrolidona (CHP) foram caracterizadas por espectroscopia de absorção óptica na região do ultravioleta-visível (UV-Vis). Em estudo de absorbância em função da concentração, foram estimados os limites de dispersão e os coeficientes de absorção dos nanotubos de carbono em cada solvente. A presença dos grupos funcionais aumentou a dispersabilidade dos tubos em NMP, DMF e DMA, mas diminuiu em N12P e CHP. Os coeficientes de absorção, entretanto, diminuíram para todos os solventes após oxidação, refletindo a diminuição da probabilidade da transição p-p* com a funcionalização e a interação com o solvente. Os parâmetros de solubilidade de Hansen e de interação de Flory-Huggins foram calculados para as amostras antes e após funcionalização, permitindo uma análise termodinamicamente quantitativa das interações intermoleculares nos sistemas estudados. Os valores dos parâmetros de Hansen obtidos para a amostra bruta foram dD = 18,0 MPa1/2, dP = 7,4 MPa1/2 e dH = 6,8 MPa1/2, enquanto aqueles para a amostra funcionalizada foram dD = 17,4 MPa1/2, dP = 12,0 MPa1/2 e dH = 9,2 MPa1/2. Em comparação com valores tabelados para os solventes, o parâmetro de energia dispersiva mostrou-se dominante na dispersão dos tubos não-funcionalizados, enquanto interações dipolares e ligações de hidrogênio exerceram uma maior influência na dispersão dos tubos funcionalizados com grupos oxigenados ácidos. Os parâmetros de interação de Flory-Huggins estimados mostraram que os sistemas com maior afinidade foram a amostra bruta dispersa no solvente CHP e a amostra funcionalizada dispersa nos solventes NMP, DMA e DMF.

Estilos ABNT, Harvard, Vancouver, APA, etc.

37

Camel, Valérie. "Extraction par le dioxyde de carbone supercritique de polluants contenus dans des solides". Paris 6, 1994. http://www.theses.fr/1994PA066335.

Texto completo da fonte

Resumo:

L'extraction par les fluides supercritiques a ete utilisee dans le but de determiner avec precision des traces de polluants contenus dans des sols. Ce memoire s'articule autour de trois parties. Tout d'abord, apres un bref rappel des proprietes des fluides supercritiques, le critere de choix d'un fluide en extraction est expose, ainsi qu'une methode rapide d'estimation du parametre de solubilite. Puis, le principe de l'extraction et son modele theorique sont decrits. Les differents modes de couplage avec les principales techniques d'analyse et d'identification sont egalement detailles. Ensuite, les resultats experimentaux obtenus sont exposes. Dans un premier temps, nous avons etudie l'efficacite de la collection des extraits. Puis, nous avons realise une etude exhaustive des parametres regissant l'extraction pour un solute test, un phosphonate, depose sur une matrice inerte afin de limiter au maximum les interactions solute-matrice. Nous avons mis en evidence le role du solvant de depot, l'influence de la pression et de la temperature, l'importance d'un controle du debit et de la vitesse lineaire dans la cellule. Finalement, nous avons pollue artificiellement des sols et etudie l'importance des interactions solute-matrice selon la nature du solute et de la matrice. Les solutes sont plus difficilement extraits de certaines matrices (le taux de carbone et la surface specifique jouant un role tres important). D'autre part, certains composes sont facilement extraits, meme sur des sols vieillis, alors que d'autres sont tres retenus. Dans ce cas, nous avons mis en evidence l'importance d'une elevation de la temperature d'extraction, celle-ci permettant de favoriser la desorption des molecules de solute fixees sur les sites actifs de la matrice. L'ajout de modificateur polaire au fluide supercritique donne egalement de meilleurs rendements d'extraction, mais peut conduire a l'elution des composes extraits lors d'un piegeage sur un support solide

Estilos ABNT, Harvard, Vancouver, APA, etc.

38

Douarche, Nathalie. "Optimisation de l'architecture et de la nature des constituants pour la tenue en service des composites carbone-carbone pour application de freinage". Lyon, INSA, 2000. http://www.theses.fr/2000ISAL0072.

Texto completo da fonte

Resumo:

Lors de leur utilisation, les freins carbone sont fortement sollicités mécaniquement et thermiquement. Le comportement mécanique du matériau composite stratifié C/C 2,5 D a été étudié à partir des essais de traction et compression (parallèlement et perpendiculairement à la stratification), ainsi que de cisaillement inter-laminaire (essai de torsion) et de cisaillement trans-laminaire (essai Iosipescu). Pour chacun de ces essais, un scénario d'endommagement a été proposé. L'influence de différents paramètres (densité, histoire thermique, oxydation sous air à basse température (T = 550 °C)) sur les propriétés mécaniques du composite a été quantifiée. Les caractéristiques mécaniques du matériau diminuent si la densité décroît et si le degré d'oxydation augmente. Il a été mis en évidence que la zone interfaciale fibre / matrice joue un rôle privilégié dans le comportement mécanique du matériau et sa sensibilité à l'oxydation. Un traitement thermique haute température réalisé en phase finale du processus d'élaboration d'une part, tend à diminuer les performances mécaniques du matériau, et, d'autre part, à le rendre moins sensible à l'oxydation. Enfin, nous avons montré qu'un suivi de la dégradation du matériau par oxydation en cours de vie est possible par évaluation non destructive. Trois techniques d'END ont été étudiées : la tomographie X, les ultrasons et les courants de Foucault
Under use conditions, carbon brakes are strongly mechanically and thermally loaded. The typical mechanical behaviour of the 2. 5 D laminated carbon-carbon composite was studied. The mechanical characterisation was made by in plane tensile test, through-thickness compression test, interlaminar shear (torsion test) and translaminar shear (Iosipescu test) tests. For each test, a sequence of damage was proposed. The effect of various parameters (specific gravity, thermal history, under air low temperature oxidation (T = 550 °C) on composite mechanical properties were quantified. The material mechanical properties decrease with decreasing density and increasing oxidation degree. It was highlighted that the bond between fibers and matrix takes a privileged part in the material mechanical behaviour and in the material oxidation sensitivity. A high temperature thermal treatment performed at the end of the process elaboration stage caused, on the one hand, a reduction of the composite mechanical properties and, on the other hand a reduction of its oxidation sensitivity. Finally, we showed that it is possible to follow-up the material oxidation degradation during brake life cycle. Three non destructive evaluation techniques were studied: The X-ray tomography, the ultrasonic and the Eddy current

Estilos ABNT, Harvard, Vancouver, APA, etc.

39

Dalva, Moshe. "Pathways, patterns and dynamics of dissolved organic carbon in a temperate forested swamp catchment". Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59625.

Texto completo da fonte

Resumo:

Inputs of DOC in precipitation were low and increased with the passage of rainfall through different canopies. Throughfall, stemflow, leachates from A horizons and litterfall were identified as sources of DOC, while B and C horizons in upland areas provide a sink. Throughfall and stemflow displayed high temporal variability in DOC concentrations, while soil leachates and peat waters exhibited strong seasonal patterns. DOC concentrations in throughfall, stemflow and A horizons were highest in the predominantly coniferous site. In the fall, DOC concentrations from A horizons in the deciduous site were significantly higher than those from the coniferous site.
Factors influencing DOC in peat waters are: (1) peat thermal regime, (2) water chemistry, and (3) water table position. Large storms ($>$30 mm precipitation) appear to be the primary factor influencing exports of DOC in streamflow, particularly following dry antecedant soil moisture conditions. Slow rates of water movement through compact deep peats ($>$60 cm depth) and adsorption of DOC in B and C horizons of this catchment obstruct exports of DOC, which over the 5.5 month study period, were minimal in comparison to inputs.

Estilos ABNT, Harvard, Vancouver, APA, etc.

40

Iwaki, Leonardo Eidi Okamoto. "Influência dos polieletrólitos na resposta eletroquímica de filmes automontados contendo nanotubos de carbono para aplicação em nanomedicina". Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-19072011-223117/.

Texto completo da fonte

Resumo:

Nanotubos de Carbono (Carbon Nanotubes - CNTs) são nanoestruturas de carbono na forma de tubos cilíndricos que apresentam excelentes propriedades ópticas, elétricas, térmicas e mecânicas. A imobilização dos CNTs em conjunto com polieletrólitos condutores e naturais na forma de filmes ultrafinos, utilizando a técnica automontagem, apresenta uma nova alternativa para o desenvolvimento de nanocompósitos aplicados em dispositivos sensores e biossensores. Neste trabalho de mestrado foram construídos e estudados filmes automontados contendo CNTs funcionalizados com grupos ácidos carboxílicos e imobilizados com os polieletrólitos polianilina (PANI) e quitosana (QUIT). Também foram fabricados para comparação filmes de PANI e poliestireno sulfonado (PSS). O crescimento dos filmes de PANI/CNT e PANI/PSS revelou um crescimento linear com o número de bicamadas, conforme mostraram as medidas de espectroscopia UV-Vis e voltametria cíclica (CV), enquanto que para o filme de QUIT/CNT, as medidas de microbalança de cristal de quartzo (QCM) mostraram um crescimento exponencial. Análises de espectroscopias Raman e infravermelho com transformada de Fourier (FTIR) indicaram alterações nas bandas características dos filmes, comparadas com seus materiais precursores, indicando interação entre os componentes nas multicamadas dos filmes. Análises morfológicas obtidas por AFM mostraram um aumento da rugosidade com o aumento do número de bicamadas. O mapeamento Raman revelou que os filmes contendo CNTs apresentaram maior heterogeneidade química na superfície do que aos filmes somente com polieletrólitos. Foi observada uma queda na resistividade dos filmes, com o aumento do número de bicamadas, sendo esta, mais acentuada com a presença dos CNTs. Os eletrodos contendo os filmes automontados apresentaram alta estabilidade eletroquímica, a presença dos CNTs aumentou a intensidade das correntes de pico e tornou os sistemas mais reversíveis. Os eletrodos que se mostraram mais sensíveis à detecção de peróxido de hidrogênio foram selecionados para imobilização da enzima Glicose Oxidase (GOx). Foram investigados os seguintes sistemas biossensores: (PANI/CNT)7, (PANI/PSS)1 e (QUIT/CNT)5 apresentando na mesma ordem: valores de sensibilidades de 190 nA/(mmol/L), 36 nA/(mmol/L) e 220 nA/(mmol/L); Limite de detecção de 2,2 µmol/L, 67,5 µmol/L e 8,5 µmol/L, e valores deconstante de Michealis-Menten(\'K IND.M\'POT.APP\' ) de 2,2 µmol/L, 67,5 µmol/L e 8,5 µmol/L. Os resultados indicam que a utilização dos CNTs é bastante promissora para fabricação de dispositivos biossensores para aplicação em Nanomedicina, e além disso, a escolha dos componentes para formação dos nanocompósitos exerce grande influência no desempenho do dispositivo.
Carbon Nanotubes (CNTs) are cylindrical carbon nanostructures exhibiting excellent electrical, thermal, optical and mechanical properties. The immobilization of CNTs in nanostructured thin films in conjunction with polymers using the Layer-by-Layer (LbL) technique provides a new alternative for development of nanocomposites to be used as sensors and biosensors. In this study we report the fabrication of LbL films containing CNTs functionalized with carboxylic acid immobilized in conjunction with polyaniline (PANI) or chitosan (QUIT). Films comprising PANI and sulfonated polystyrene (PSS) were also produced for comparison. Film growth was monitored by UV-Vis spectroscopy, cyclic voltammetry (CV) and quartz crystal microbalance (QCM) and the results showed a linear increase with the number of bilayers in PANI films, and an exponential growth for QUIT/CNT films. FTIR and Raman analyses revealed changes in the bands of nanocomposites compared to their precursor materials, indicating the interactions between the components in the multilayers. Morphological analysis of the films obtained by atomic force microscopy (AFM) showed that the roughness of the films increased with the number of bilayers. Raman mapping showed that the presence of CNTs generated a high heterogeneity in film surface in comparison to a films formed only by polyelectrolytes. Electrical resistivity of the films decrease upon increasing the number of bilayers, especially for CNTs-containing films. Furthermore, electrodes containing LbL films exhibited high electrochemical stability, in which the presence of CNTs increased the intensity of response signal. The electrodes that exhibited best performance toward hydrogen peroxide detection were employed for immobilization of glucose oxidase (GOx) and used as glucose biosensors. The systems (PANI/CNT)7, (PANI/PSS) 1 and (QUIT/CNT)5 exhibited a sensitivity of 190 nA/(mmol/L), 36 nA/(mmol/L) and 220 nA/(mmol/L), respectively. The detection limit was estimated at 2.2 mmol/L, 67.5 mmol/L and 8,5 mmol/L, whereas the Michaelis-Menten constant ( \'K IND.M\'POT.APP\') values was found to be 2.2 mmol/L, 67.5 mmol/L and 8.5 mmol/L, respectively, to the three systems employed. The results indicated that the use of CNTs in Layer-by-layer thin films is promising for use as biosensors. Furhtermore, we showed that the choice of the polyelectrolyte is a crucial parameter to tailor specific, high performance sensors.

Estilos ABNT, Harvard, Vancouver, APA, etc.

41

Voirin, Thibaut. "Etude du comportement mécanique et de l’endommagement des composites C/C à basses et hautes températures". Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI008.

Texto completo da fonte

Resumo:

Les matériaux composites Carbone/Carbone sont utilisés dans l’industrie aéronautique ainsi que dans l’aérospatial du fait de leurs excellentes propriétés thermomécaniques, de la température ambiante jusqu’à de très hautes températures (< 3000°C). Cependant l’évolution de ces propriétés à hautes températures est peu connue, notamment sous des sollicitations de type freinage auxquelles ces composites peuvent être soumis pour des applications aéronautiques ou dans les sports mécaniques.L’objectif de ce travail était donc d’étudier le comportement mécanique d’un composite C/C stratifié sous des sollicitations mécaniques pouvant intervenir dans une situation de freinage. Ainsi, la compression et le cisaillement ont été particulièrement étudiés, afin de déterminer l’évolution des mécanismes d’endommagement en fonction de la température sous ces modes de chargement. Afin de mener à bien cette étude, plusieurs aspects expérimentaux ont été abordés, tels que la géométrie et la taille des éprouvettes, de même que les difficultés de mesures liées à la réalisation des essais mécaniques à hautes températures. C’est ainsi que des essais originaux de cisaillement interlaminaire à chaud ont pu être réalisés. Parallèlement à ces essais, la microstructure du matériau a été étudiée in-situ et post-mortem par une analyse multi-échelle (à l’échelle des strates, des torons et au niveau des fibres à l’intérieur des torons). L’évolution des propriétés mécaniques a été mise en relation avec les observations microstructurales pour les différents modes de chargement étudiés (compression « Z », compression « XY » et cisaillement interlaminaire), afin de proposer des scenarii d’endommagement du matériau en fonction de la température. Grâce à cette approche, le rôle majeur des dilatations thermiques différentielles des torons sur le frettage des aiguilletages a pu être mis en évidence pour des températures allant jusqu’à 1500°C. Pour des températures supérieures, des effets de plasticité ont été identifiés
Carbon/Carbon composites are used in aeronautics and space industries for their excellent thermomechanical properties, from room temperature to very high temperatures (up to 3000°C). Nevertheless, these properties and their evolution at elevated temperatures are not known well enough, specifically for braking-like solicitations such as plane braking or motorsport braking.The main objectives of this work was to study the mechanical behavior of this composite under mechanical solicitations that may occur during a braking situation. Thereby, compressive and shear behavior were studied in particular, in order to determine the evolution of the damage mechanisms depending on the temperature for these loading modes. In order to lead this study successfully, various experimental aspects have been approached, such as sample geometry, as well as measurements issues due to the mechanical testing at high temperatures. This is how original mechanical testing of the interlaminar shear behavior have been performed. Concurrently with these tests, the material microstructure has been studied in-situ and post-mortem with a multi-scale approach (at ply level, at yarn level and at fiber level inside the strands). The evolution of the mechanical properties has been linked to the microstructure evolution for the different loading modes (Z-compression, XY-compression and interlaminar shear) in order to propose damage scenario of the material as a function of the temperature. This approach allowed us to understand the major role of the thermal differential dilatations of the yarn on the shrinking of the needles for temperatures up to 1500°C. For temperatures higher than 1500°C, plasticity effects have been identified

Estilos ABNT, Harvard, Vancouver, APA, etc.

42

Paula, Mirian Michelle Machado de 1988. "Análise da resposta pró-inflamatória de macrófagos cultivados em substratos contendo nanotubos de carbono de parede múltipla (MWCNTs)". [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/310738.

Texto completo da fonte

Resumo:

Orientadores: Marcus Alexandre Finzi Corat, Anderson de Oliveira Lobo
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas
Made available in DSpace on 2018-08-26T10:38:02Z (GMT). No. of bitstreams: 1 Paula_MirianMichelleMachadode_M.pdf: 2407271 bytes, checksum: 8f5ae942d781fb23b3d817baa3c8a868 (MD5) Previous issue date: 2014
Resumo: As promessas da utilização de nanotubos de carbono (CNTs) para fins biomédicos se esbarram em algumas dificuldades. Muitos estudos de nanotoxicologia foram realizados analisando propriedades destes materiais em causar injúrias no tecido vivo. Apesar das evidências da citotoxicidade dos CNTs, existe também um grande número de publicações de estudos de biomateriais baseados em CNTs que suportam sua biocompatibilidade. Segundo Lobo et al, 2009 (1), os nanotubos de carbono de parede múltipla (MWCNT) foram suficientes para obter biocompatibilidade. As estruturas de VAMWCNT alinhados revelaram que um ínfimo contato entre as estruturas das células e a nanotopografia é decisivo para garantir a bioatividade e eficiência no crescimento e espalhamento celular sem produzir efeitos citotóxicos. Resultados do nosso grupo mostrou características da adesão celular em substrato contendo VAMWCNT alinhado através da análise de proteínas envolvidas no mecanismo de adesão, assim como, estudo comparativo de preferência de substrato para proliferação e viabilidade celular onde verificou-se um melhoramento de adesão e espalhamento celular de acordo com o substrato de VAMWCNT utilizado, com ou sem tratamento de funcionalização a plasma de oxigênio. No entanto os substratos de VAMWCNT, apesar de atóxico, parecem provocar mudanças no comportamento celular principalmente no primeiro contato e durante o processo de adesão das células ao substrato. Neste estudo verificou-se que os substratos com VAMWCNT-O promoveram respostas pró-inflamatórias comparado ao controle. Os substratos com tratamento a plasma de oxigênio mostraram promover um maior estimulo celular dos macrófagos quanto a expressão de interleucina 6 além disso, verificou uma correlação entre os substratos hidrofílicos em maior produção de citocinas com o aumento de migração celular de células mononucleares da medula óssea in vivo. Mostrando, assim, que estes substratos podem acarretar uma melhora na estimulação do recrutamento celular e que podem favorecer o processo regenerativo de um tecido lesionado. Estes resultados demonstram um potencial do uso deste biomaterial na medicina regenerativa no futuro
Abstract: The promise of the use of carbon nanotubes (CNTs) for biomedical purposes faces some difficulties. Many studies of nanotechnology has been realized by analyzing the properties of these materials causing tissue injury in vivo. Despite evidence of cytotoxicity of CNTs, there are also a large number of published studies of biomaterials based on CNTs that support the idea of their biocompatibility. According to Lobo et al, 2009 (1), carbon nanotube multi-wall (MWCNT) showed biocompatibility. Vertically aligned VAMWCNT revealed that the contact between the structures of the cells and nanotopography is crucial to ensure bioactivity, cell growing and cell spreading, avoiding cytotoxic effects. Results from our group have showed cell adhesion on substrate containing VAMWCNT, as well as, variability of cell adhesion and spreading according to wet-ability features after oxygen plasma treatment (VAMWCNT-O) and density of the VAMWCNT substrate. However, VAMWCNT-O substrates, although nontoxic, seem to cause changes in cell behavior in the first contact and during the process of cell adhesion to the substrate. To better understand the behavior of cells on the substrates of VAMWCNT-O, in the present study, we analyzed the properties of macrophages to trigger inflammatory response in contact with substrates containing CNTs correlating it with mononuclear bone marrow cells migration. It was found that substrates with carbon nanotubes promoted pro-inflammatory responses compared to the control. The substrates after oxygen plasma treatment showed higher stimulation of macrophages as expression of interleukin 6 and SDF-1. They showed direct correlation with increasing bone marrow cell migration in vitro and in vivo. These substrates leaded to an improvement to cell recruitment and stimulation, which might support the process of regenerating an injured tissue by using them in regenerative medicine
Mestrado
Clinica Medica
Mestra em Clínica Médica

Estilos ABNT, Harvard, Vancouver, APA, etc.

43

Meier, Jackie N. "Effects of lignosulfonate in combination with urea on soil carbon and nitrogen dynamics". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56658.

Texto completo da fonte

Resumo:

Lignosulfonate (LS), a by-product of the pulp and paper industry, may have the potential to increase fertilizer N availability by acting as a urease and nitrification inhibitor. Four consecutive laboratory studies were conducted to evaluate the behavior of LS in agricultural soils. The effects of various types and rates of LS on soil respiration and soil N dynamics were determined. Effects of LS in combination with fertilizers on microbial activity and N dynamics were measured. Due to the high water solubility of LS a leaching column study was conducted to determine the potential leaching of LS.
Higher rates (20% w/w) of LS initially inhibited microbial activity. Generally LS was relatively resistant to degradation by soil microorganisms and small proportions of added LS-C ($<$2.1%) were leached from the soil columns, but leaching was a function of soil and moisture regime. Recovery of added mineral LS-N from soil treated with LS was low ($<$41%). Mineral N recovered from LS plus fertilizer amended soil was higher than recovery from corresponding fertilizer treatments. Lignosulfonate reduced urea hydrolysis and the proportion of added N volatilized as NH$ sb3$-N from a LS plus urea treatment. The mineral N pool from LS plus fertilizer treated soils had significantly lower NO$ sb3$-N concentrations than corresponding fertilizer treatments. Nitrification inhibition was believed to have been due to high fertilizer concentrations. At reduced urea and LS concentrations, LS decreased NO$ sb3$-N recovery in one of four soil types. However, reduced recovery may not have been from nitrification inhibition but possibly from denitrification or chemical reactions between N and phenolics from LS.

Estilos ABNT, Harvard, Vancouver, APA, etc.

44

Dreshaj, Merita. "Study of paleodiet from the context of the rotunde church in Bribirska Glavica, Croatia". Master's thesis, Universidade de Évora, 2017. http://hdl.handle.net/10174/24484.

Texto completo da fonte

Resumo:

This work focuses on the study of paleodiet of selected burials and fauna from Bribirska Glavica, Croatia via stable isotopes of carbon and nitrogen. Carbon stable isotopes in bone collagen can distinguish between two types of plants (C3 and C4) whilst nitrogen isotopic composition gives an estimation of the trophic levels and the amount of protein consumed. The results are compared to several factors such as the burial context, health, time period, social status, trauma, sex and age. An attempt was made to understand the impact of these factors on stable isotopic values and, hence, the choice of diet, contextualising the results within known historical and archaeological data. This research is compared to the study done on the area of Ravni Kotari, geographical area where Bribirska Glavica is situated, extending the paleo-dietary data range to Late Medieval period in the hinterland of Dalmatia; RESUMO: (Estudo da dieta paleo no context da “rotunda” igreja em Bribirska Glavica, Croácia) O presente trabalho foca-se no estudo em paleodieta, realizado em ossos humanos e animais selecionados de um sitio arqueológico em Bribirska Glavica (Croácia), através do estudo dos seus isótopos estáveis de carbono e nitrogénio. Os isótopos estáveis de carbono presentes no colagénio dos ossos permite distinguir entre 2 tipos de plantas (C3 e C4) ao passo que a composição isotópica de nitrogénio fornece uma estimativa dos níveis tróficos e na quantidade de proteína consumida. Os resultados têm em consideração diversos fatores tais como o próprio contexto funerário, a saúde dos indivíduos, o período de tempo, o estatuto social, trauma, sexo e idade. Uma tentativa para a compreensão do impacto destes fatores nos valores dos isótopos estáveis e a escolha da própria dieta foi realizada, contextualizando desta forma os resultados obtidos com dados históricos e arqueológicos já conhecidos. Os resultados obtidos neste trabalho de investigação são ainda comparados com um estudo prévio realizado na área de Ravni Kotari, área geográfica onde se situa Bribirska Glavica, estendendo desta forma o intervalo de dados em paleodieta até ao período medieval tardio na região da Dalmácia.

Estilos ABNT, Harvard, Vancouver, APA, etc.

45

Piper, Allison. "Root Length Affects Soluble Carbon and Phosphorus in a Rotational Cropping System". Fogler Library, University of Maine, 2005. http://www.library.umaine.edu/theses/pdf/PiperA2005.pdf.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

46

Yates, Paul David. "The content and stable isotopic composition of carbon in spherical micrometeorites". Thesis, Open University, 1992. http://oro.open.ac.uk/54849/.

Texto completo da fonte

Resumo:

Micrometeorites are extraterrestrial bodies that have survived atmospheric entry to be found on Earth as grains <1mm in diameter. Of the annual flux of extraterrestrial material to the Earth ca.99% is supplied by the micrometeorites. The lifetime of the micrometeroids in the interplanetary medium in extremely ephemeral, but their population is maintained largely by ejection of particles from cometary nuclei and from collisional debris from the asteroid belt. As such, the micrometeorites are of fundemental importance to cosmogony, because they may provide the only means, at present, to directly study cometary material, and sample a far less biased cross section of the asteroid belt than conventional meteorites. A static gas source mass spectrometer for carbon isotope measurements built in the Planetary Sciences Unit has been tested and shown capable of routinely analysing ca.1 nanogram of carbon (as carbon dioxide) to precisions of ca.±1%o. To enable this gain in sensitivity to be exploited, a sample preparation and carbon dioxide extraction system has been devised that typically imparts a total of less than 20 nanograms of extraneous carbon contamination to the samples. An advantage of the mass spectrometer is its ability to make accurate isotopic abundance measurements of the blank contribution for the purpose of making corrections to the analytical data. The instrument and inlet system has been applied to studies of micrometeorites > 200∝m in diameter. A procedure has been developed involving three analytical techniques (chemical/petrographic, X-ray diffraction and stable carbon isotope). Carbon isotopic analyses of multiple-sample aliquots of deep-sea, and individual Greenland and Antarctic micrometeorites has enabled the identification of components that are similar to those within the stony chondritic meteorites. More specifically, components have been revealed that may indicate a generic connection to primitive chondrites. Carbon isotopic characterisation of acid-resistant residues prepared from micrometeorite-rich Greenland cryoconite suggested that the micrometeorites contain pre-solar dust grains of silicon carbide, graphite and diamond. which provides an additional indication of the primitive nature of some micrometeorites. Experiments to produce micrometeorite analogues by pulse-heating microgram-sized samples of whole-rock meteorites showed that indigenous carbonaceous species can survive pulse-heating above their normal combustion temperatures. The overall conclusion of the investigation is that the flux of > 200∝m micrometeorites is dominated by a steroidal material and that the atmospheric entry heating process is poorly understood.

Estilos ABNT, Harvard, Vancouver, APA, etc.

47

Schuwey, Dominique. "Equilibre du monoxyde de carbone dans le sang du cordon ombilical humain /". Bern, 1991. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

48

Wolford, Ian Mark. "Quantifying Amorphous Content of Commercially Available Silicon Carbide Fibers". Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1472054006.

Texto completo da fonte

Estilos ABNT, Harvard, Vancouver, APA, etc.

49

Mercader, C. "Filage continu de fibres de nanotubes de carbone : de la solidification aux propriétés finales". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2010. http://tel.archives-ouvertes.fr/tel-00583812.

Texto completo da fonte

Resumo:

Ce travail de thèse concerne l'étude du filage et des propriétés de fibres composites à base de nanotubes de carbone. Les propriétés mécaniques des fibres en cours de solidification et en mouvement dans un bain de coagulation sont évaluées afin d'étudier l'influence de différents paramètres physico-chimiques impliqués dans leur fabrication. Ces fibres, combinant des propriétés mécaniques et électriques prometteuses, peuvent être obtenues de façon continue grâce au développement d'un nouveau procédé de filage. Elles présentent de plus un effet original de mémoire de température dont l'origine est étudiée dans cette thèse. Ces fibres sont potentiellement utiles pour diverses applications: des matériaux à haute absorption d'énergie mécanique à des textiles conducteurs fonctionnels.

Estilos ABNT, Harvard, Vancouver, APA, etc.

50

Marion, Ronan. "Catalyse supportée en flux continu utilisant des feutres de carbone de grande surface spécifique". Rennes 1, 2011. http://www.theses.fr/2011REN1S130.

Texto completo da fonte

Resumo:

Ce travail porte sur la synthèse de nouveaux complexes de cuivre et de ruthénium à base de ligands tripodaux pour une application en catalyse supportée en flux. Ces catalyseurs ont été testés dans des réactions d’oxydation. Une famille de ligands N-tripodaux facilement fonctionnalisable a été préparée pour déterminer l’influence de certains paramètres tels que l’encombrement stérique, la basicité ou encore l’effet inductif des substituants sur l’activité catalytique. En outre, ces ligands possèdent un bras fonctionnalisé qui sert de point d’accroche lors de l’immobilisation des complexes. Les complexes de cuivre ont fait l’objet d’une étude en catalyse homogène puis en catalyse supportée en flux dans une réaction d’oxydation de catéchols pour étudier l’influence de l’immobilisation des complexes sur leur activité catalytique. Après avoir mis en avant les facteurs déterminants en milieu homogène avec ces complexes mononucléaires, un procédé de greffage covalent sur feutre de graphite a été mis au point. Par réduction électrochimique de sels de diazonium, nous avons pu obtenir un greffage homogène et rapide et insérer les complexes avec des concentrations volumiques de l’ordre de 10-8 mol. Cm-3. Une étude en catalyse supportée en flux a ensuite été réalisée montrant de meilleures activités catalytiques par rapport au milieu homogène. Des études concernant la stabilité ainsi que l’influence de la nature et de la longueur de la chaîne d’accroche ont également été effectuées. Une étude préliminaire sur les catalyseurs de ruthénium a conduit à la synthèse d’un nouveau complexe à partir d’un ligand N-tripodal
This work is about the synthesis of new copper and ruthenium complexes containing tripodal ligands for application in continuous flow catalysis. These catalysts have been tested in oxidation reactions. A family of N-tripodal ligands has been prepared to determine the influence of several parameters on the catalytic activity such as steric effects, basicity or electronic effects of the substituants. Moreover, these ligands have a functionalized arm, which will be to attach the complexes onto the support. Copper complexes have been tested in homogeneous catalysis and then in continuous flow catalysis in a catechol oxidation reaction to study the influence of their immobilization on their catalytic activity. Once the determining factors in homogeneous medium were identified, a covalent grafting process on graphite felt has been set up. By electrochemical reduction of diazonium salts, a homogeneous and fast functionalization of the graphite felt has been achieved, allowing the chemical attachment of the complexes with volume concentrations around 10-8 mol. Cm-3. Then, continuous flow catalysis has been realized showing better catalytic activities than in homogeneous medium. Studies about the stability and the influence of the chain nature and length have also been performed. A preliminary study on ruthenium catalysts provided the synthesis of a new complex containing a N-tripodal ligand

Estilos ABNT, Harvard, Vancouver, APA, etc.

Teses / dissertações sobre o tema "Contenu en carbone"

Crie uma referência precisa em APA, MLA, Chicago, Harvard, e outros estilos