L'introduction de nouveaux moyens de production d'énergie sur le marché dépend en partie de leur compétitivité. Le développement à bas coût d'un procédé de réalisation de cellules de piles à combustible à oxyde solide (SOFC), sujet de cette étude, s'inscrit dans une telle dynamique. Dans le cahier des charges défini au préalable, ont été fixés la méthode de mise en forme, -le coulage en bande-, ainsi que les matériaux, -la zircone yttriée, le nickel et le manganite de lanthane dopé au strontium-.<br />Afin de baisser les coûts de production, et tout en prenant en compte le respect de l'environnement, le procédé développé utilise un solvant de barbotine aqueux. En utilisant le système développé lors d'une précédente étude, on obtient séparément les électrodes et l'électrolyte. L'utilisation dans la présente étude de supports de séchage hydrophiles, permet d'assembler les trois couches crues pour former une cellule élémentaire avec le maximum de continuité interfaciale. Un travail réalisé au niveau de la microstructure de l'anode, afin de symétriser les déformations de la cellule lors de sa mise en oeuvre, a permis de limiter le comportement mécanique différentiel des couches, ce qui a renforcé la tenue au frittage des cellules.<br />Afin d'interpréter les performances électriques faibles des cellules et leur rapide dégradation au cours du temps, des études en microscopie en transmission, sur échantillons préparés par FIB, et en spectroscopie d'impédance ont été menées. Il est apparu que deux phases isolantes apparaissaient à la cathode aux interfaces LSM/YSZ en raison d'une température de co-frittage trop élevée. De plus, on a mis en évidence une agglomération rapide des grains de nickel lors du fonctionnement, entraînant une perte locale ou globale de la percolation du réseau de nickel. Ce dernier problème a été résolu en augmentant au préalable la taille des grains d'oxyde de nickel (de 0,5 μm à 3 μm) afin de stabiliser la microstructure. Le problème de la réactivité aux interfaces LSM/YSZ a, quant à lui, été abordé de deux façons différentes; on a dans en premier lieu tenté d'abaisser la température de frittage en utilisant une nanopoudre de zircone, et dans un second lieu de remplacer la zircone par la cérine dopé du gadolinium (CGO) pour l'électrolyte. Cependant, l'utilisation d'une nanopoudre de zircone n'a pas permis d'abaisser la température de frittage en préservant la densité de l'électrolyte, et la cérine substituée à la zircone dans la barbotine de cathode a généré des instabilités mécaniques qui n'ont pas pu être résolu.<br />Le procédé développé permet cependant d'obtenir une excellente interface anode/électrolyte, au contraire d'autres procédés et malgré des différences de propriétés mécaniques importantes. Il apparaît donc pérenne pour l'utilisation d'autres matériaux ne présentant pas de réactivité aux interfaces.

La connaissance des vitesses de diffusion du plomb dans la monazite est indispensable pour comprendre les anomalies des âges U-Th-Pb de ce minéral, qui est un des plus utilisés en géochronologie après le zircon. <br />Des expériences de diffusion ont été faites dans des monocristaux de NdPO4 et des polycristaux de Nd0.66Ca0.17Th0.17PO4 à partir de couches minces de Nd0.66Pb0.17Th0.17PO4, pour étudier les échanges Pb2+ + Th4+ 2 Nd3+ et Pb2+ Ca2+. Les recuits de diffusion ont été effectués entre 1200 et 1500°C, à pression ambiante, pour des durées comprises entre une heure et un mois. Les profils de diffusion ont été analysés en MET et en RBS. <br />Les diffusivités extraites pour l'échange Pb2+ + Th4+ 2 Nd3+ suivent une loi d'Arrhenius de paramètres E = 509 ± 24 kJ mol-1 et log D0 (m2 s-1) = -3.41 ± 0.77. Les données préliminaires pour l'échange Pb2+ Ca2+ concordent avec ce résultat. <br />L'extrapolation de nos données aux températures crustales donne de très faibles diffusivités. Par exemple, le temps nécessaire pour qu'un grain de monazite de 50 µm perde tout son plomb à 800°C est supérieur à l'âge de la Terre. <br />De ces résultats et d'autres évidences de la littérature, nous concluons que la plupart des perturbations des âges U-Th-Pb des monazites ne peut pas être attribuée à la diffusion du plomb à l'état solide, mais plus vraisemblablement à des interactions avec des fluides

A challenge exists for understanding the origin of color for structurally colored, 3-dimensional bioorganic nanostructures, such as the scales of butterflies, beetles, and moths. Complex, hierarchical structures found within such scales create the overall scale appearance. The controlled alteration of color through material deposition and the addition of new optical functionalities to such structures are other areas of scientific interest. This dissertation addresses these challenges with a first-of-its-kind, systematic isolation (deconstruction) of scale component nanostructures, followed by evaluation of optical property/structure correlations. The additive deposition (constructive alteration) of emissive materials to structurally-colored templates complements this deconstructive approach towards understanding the origin of color in butterfly scales. Discoveries made through this work may help advance the bioinspired design of synthetic optical structures and subsequent color control through the addition of multilayered, emissive optical components.

No description available.

Les travaux présentés dans ce manuscrit, sont basés sur l'étude de l'auto-organisation de la matière à l'échelle nanométrique. A cette échelle, les énergies de surfaces jouent un rôle prépondérant dans cette organisation. Pour comprendre au mieux ses mécanismes nous avons étudié plusieurs types de structures à base de Silicium et de Germanium. Nous avons expérimentalement étudié la croissance cristalline ou amorphe sur différents types de substrats (amorphe : SiO2 et cristallins Si ou SOI). Certain de ces substrats furent nano-structurés en utilisant un faisceau d'ions focalisés de type Gallium ou Or-Silicium. De plus nous avons pu utiliser des surfaces différentes telle que le TiO2 ou le Silicium poreux, afin d'étudier l'organisation de la matière sur des pores de petites tailles (inférieurs à 50nm).

The understanding of multiphase flow properties is essential for the exploitation of hydrocarbon reserves in a reservoir; these properties in turn are dependent on the geometric properties and connectivity of the pore space. The determination of the pore size distribution in carbonate reservoirs remains challenging; carbonates exhibit complex pore structures comprising length scales from nanometers to several centimeters. A major challenge to the accurate evaluation of these reservoirs is accounting for pore scale heterogeneity on multiple scales. This is the topic of this thesis. Conventionally, this micron scale information is achieved either by building stochastic models using 2D images or by combining log and laboratory data to classify pore types and their behaviour. None of these capture the true 3D connectivity vital for flow characterisation. We present here an approach to build realistic 3D network models across a range of scales to improve property estimation through employment of X-ray micro-Computed Tomography (μCT) and Focussed Ion Beam Tomography (FIBT). The submicron, or microporous, regions are delineated through a differential imaging technique undertaken on x-ray CT providing a qualitative description of microporosity. Various 3-Phase segmentation methods are then applied for quantitative characterisation of those regions utilising the attenuation coefficient values from the 3D tomographic images. X-ray micro-CT is resolution limited and can not resolve the detailed geometrical features of the submicron pores. FIB tomography is used to image the 3D pore structure of submicron pores down to a scale of tens of nanometers. We describe the experimental development and subsequent image processing including issues and difficulties resolved at various stages. The developed methodology is implemented on cores from producing wackstone and grainstone reservoirs. Pore network models are generated to characterise the 3D interconnectivity of pores. We perform the simulations of petrophysical properties (permeability and formation resistivity) directly on the submicron scale image data. Simulated drainage capillary pressure curves are matched with the experimental data. We also present some preliminary results for the integration of multiscale pore information to build dual-scale network models. The integration of multiscale data allows one to select appropriate effective medium theories to incorporate sub-micron structure into property calculations at macro scale giving a more realistic estimation of properties.

High chromium ferritic steels such as Grade 91 and Grade 92 are extensively used in the power plant industry. Components made from these types of steels, including headers, steam pipes and tubes, are required to provide reliable service at high pressures (20-30 MPa) and temperatures (550-610°C) for several decades. However, in order to further improve the thermal efficiency of the power plant, the future operation temperature for the ferritic steels needs to be elevated to 650°C. Therefore, the current research project focuses on the examination of recently developed MarBN type steels (Martensitic steel strengthened by Boron and Nitrides) and four Grade 92 derivatives in order to evaluate their suitability for 650°C application, and also to assess their creep strength from a microstructural point of view.

The presence of residual stresses in engineering components may significantly affect damage evolution and progression towards failure. Correct evaluation of residual stress is of crucial importance for assessing mechanical components, predicting response and ensuring reliability. For example, when failure occurs due to cyclic loading, the underlying damage begins at the nano-, and then micro-scale. It is clear that improving engineering reliability at the micro-scale requires the ability to evaluate residual stress and mechanical properties at the appropriate scale. The key objective of the thesis is to advance the understanding and practice of residual stress evaluation at the micro-scale, and to examine the implications and applications that follow. Significant effort was devoted to the evaluation of two aspects of the relatively novel FIB-DIC micro-ring-core experimental technique: assessing the effects of Ga-ion damage and the quantification of uncertainty in stress evaluation due to unknown crystal orientation. FIB-DIC micro-ring-core milling was then used alongside with synchrotron XRD to study residual stress effects on fatigue crack growth propagation rate following the occurrence of overload or underload. The effects of the two principal mechanisms of crack retardation following an overload, residual stress and crack closure, were separated by testing samples at different loading ratios. Whilst, the acceleration after an underload was studied using validated non-linear FEM analyses. Conceptual focus was placed on the macro-micro-nano residual stress decomposition into Type I, II &amp; III according to scale and, detailed examination was conducted experimentally and numerically. In the context of shot-peening surface treatment, residual stresses were modelled using a novel eigenstrain-based modelling procedure for arbitrarily shaped components. Furthermore, a fine scale characterisation was performed of the recast layer produced by EDM, with particular attention paid to the residual stress. The investigations presented in this thesis open new perspectives for the assessment of material reliability. Improved failure prediction models will be elaborated based on the insights obtained in the present study.

X / A combined experimental and computational investigation of the deformation behavior of pure magnesium single crystal at the micron length scale has been carried out. Employing the recently exploited method of microcompression testing, uniaxial microcompression experiments have been performed on magnesium single crystals with [0001], [2-1-12], [10-11], [11-20] and [10-10] compression axes. The advantage of the microcompression method over conventional mechanical testing techniques is the ability to localize a single crystalline volume which is characterizable after deformation. The stress-strain relations resulting from microcompression experiments are presented and discussed in terms of orientation dependent slip activity, twinning mechanisms and an anisotropic size effect. Such a mechanistic picture of the deformation behavior is revealed through SEM, EBSD and TEM characterization of the deformation structures, and further supported by 3D discrete dislocation dynamics simulations. The [0001], [2-1-12], and [10-11] compression axes results show dislocation plasticity. Specifically, the deformation due to [0001] compression is governed by pyramidal slip and displays significant hardening and massive unstable shear at stresses above 500MPa. In the case of the two orientations with compression along an axis 45 degrees to the basal plane, unsurpringly it is found that basal slip dominates the deformation. In contrast, compression along the [11-20] and [10-10] directions show deformation twinning in addition to dislocation plasticity. In the case of compression along [11-20], the twinning leads to easy basal slip, while the twin resultant during compression along [10-10] does not lead to easy basal slip. In all cases, a size effect in the stress-strain behavior is observed; the flow stress increases with decreasing column diameter. Furthermore, the extent of the size effect is shown to depend strongly on the number of active slip systems; compression along the [0001] axis is associated with 12 slips systems and displays a saturation of the size effect at a diameter of 10μm, while the other orientations still show a significant size effect at this diameter. The experimental evidence of an orientation-dependent deformation behavior in flow stress has been investigated by 3D discrete dislocation dynamics simulations. Here, the code TRIDIS was modified for hcp structure and c/a ratio of Mg. By matching the simulation results to experimental results, some proper constitutive material parameters such as initial dislocation density, dislocation source length, the critical resolved shear stress were suggested. For the case of [0001] and [2-1-12] orientation, dislocation feature in the pillar during the deformation was exhibited and strain burst was discussed.

Submitted by Alane dos Santos Viana (alane.viana@ucsal.br) on 2016-09-27T15:23:01Z No. of bitstreams: 1 DISSERTACAOEDMILSONPEREIRA.pdf: 1577353 bytes, checksum: 7bfed032c0997013e1726320e7e41cbf (MD5) / Approved for entry into archive by Maria Emília Carvalho Ribeiro (maria.ribeiro@ucsal.br) on 2016-09-30T20:52:46Z (GMT) No. of bitstreams: 1 DISSERTACAOEDMILSONPEREIRA.pdf: 1577353 bytes, checksum: 7bfed032c0997013e1726320e7e41cbf (MD5) / Made available in DSpace on 2016-09-30T20:52:46Z (GMT). No. of bitstreams: 1 DISSERTACAOEDMILSONPEREIRA.pdf: 1577353 bytes, checksum: 7bfed032c0997013e1726320e7e41cbf (MD5) Previous issue date: 2013-03-27 / O Programa Universidade para Todos (ProUni) surgiu como política pública que garante o ingresso e permanência de jovens sem recursos em universidades particulares. O Programa nasceu por iniciativa do Governo Federal e sua implantação se deu em diferentes faculdades, universidades e centros universitários do Brasil, a partir de 2005. Estuda-se o caso dos alunos egressos beneficiados do Centro Universitário Estácio/FIB, de Salvador. Como amostragem, foram entrevistados os alunos que foram beneficiados com o ProUni em 2005, grande parte formados a partir de 2008 e que já integram o mercado de trabalho. Alguns apontaram o Programa como benéfico, outros apontaram algumas poucas deficiências e, dentre eles, outros apontaram seu êxito econômico e social. / The University For All Program (ProUni) emerged as a public policy which guarantees the entry and permanence of the young people without resources in private universities. The Program was born because of Federal Government initiative and its implementation took place in different colleges and universities of Brazil, since 2005. We study the case of the graduated students who have benefited in the "Centro Universitário Estácio/FIB", in Salvador, Bahia, Brazil. As sampling, it were interviewed the students who were benefited with the ProUni in 2005, the most part graduated as from 2008 and which already in the market job. Some interviewees have pointed the Program as benefic and others have pointed some deficiencies and, among them, others have pointed their economic and social success.