A systematic study of the crystallization of terthiophene, chosen as a model compound, has been carried out using the thermal gradient technique. We have observed that nucleation and growth can be decoupled for organic semiconductors (OSC) crystallizing from the melt in a temperature gradient and that these conditions lead to the generation of highly textured thin films with uniaxial in-plane alignment. Furthermore, adequate gradient conditions allow the selective growth of a single polymorphic form of terthiophene. The last results obtained on terthiophene concern the orientation of the unit cell with the reciprocal vector c* normal to the substrate and the alignment of the [100] and [-100] directions parallel to the gradient direction. It is hypothesized that the geometry of the system and the temperature profile induce a preferential fast growth direction perpendicular to the gradient direction.<p>In order to validate these results, we embarked on an exploratory study of the crystallization of a set of organic semiconductors, carefully selected based on rational arguments, to evaluate the potential of the thermal gradient process as well as the required parameters for an OSC to perform adequately in this treatment. As in the case of terthiophene, nucleation and growth can be decoupled for the other organic semiconductors depending on their rate of growth. Furthermore, we have been able to reproduce on another polymorphic compound the selective growth of a single polymorphic form by applying adequate gradient conditions. We have also observed that compounds tend to orient preferentially along one of their major morphological planes parallel to the substrate, indicating a heterogeneous nucleation mechanism. A careful comparison between the different samples allowed us to confirm and complete our growth mechanism proposition. Based on the undercooling, maximal growth rate, primary and secondary nucleation rates of the compound, geometry of the system and adequate gradient parameters, a preferential alignment of the crystals along the thermal gradient direction can be achieved. Finally, we showed through this investigation and careful comparison that 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene possesses all the characteristics to be an excellent material candidate for the thermal gradient processing: low primary nucleation rate, moderate undercooling, high growth rate, platelet-like crystal growth morphology and liquid crystal phase allowing preorganization of the compound before crystallization and processing on single substrates without dewetting. Moreover, this compound is currently one of the best solution processable organic semiconductors.<p>We then investigated the directional crystallization of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene directly from its liquid crystal phase as a function of thermal gradient parameters (magnitude of the gradient, sample velocity) and film thicknesses in thin film geometry (spin-coated films). Again, decoupling of the nucleation and growth has been observed for crystallization processed directly from the liquid crystal phase leading to the generation of highly textured films presenting uniaxial in-plane alignments of the crystallites. Moreover, secondary nucleation spots highlighted by POM in the alignment region give a clue to elucidate the alignment mechanism. The unit cell orients with the reciprocal vector c* normal to the substrate. Moreover, POM observation tends to indicate systematic thermal cracks orientations for higher rates of displacement (25 μm.s-1) as well as a reduction of the number of domains present in the sample, suggesting a preferential alignment of the crystallites at higher rates of displacement. All our results indicate that an optimum of the quality of the aligned film is reached for thermal gradient conditions of 120 °C - 90 °C - 25 μm.s-1. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

There has been substantial market demand for a portable Gas Chromatography (GC) system. Throughout the years, much progress has been made on fabricating a micro system that works as well as a benchtop system. Unfortunately, even though many substrates, channel types, channel widths, temperature control systems, and interface solutions have been attempted, existing versions of the micro-GC still fall short of the ideal. This thesis presents the design, fabrication, and testing of a silicon based micro-GC column that presents a solution for interfacing and heating of the chip. A polyimide resin is used to create a durable high temperature low thermal mass interface with the chip, while a silk screen method is demonstrated for easy printing of heaters. Chromatogram results are shown in both Temperature Program and Thermal Gradient runs.

Although the airbath oven is a reliable heating method for gas chromatography (GC), resistive heating is needed for higher analytical throughput and on-site chemical analysis because of size, heating rate and power requirements. In the last thirty years, a variety of resistive heating methods were developed and implemented for both benchtop and portable GC systems. Although fast heating rates and low power consumption have been achieved, losses in column efficiency and resolution, complex construction processes and difficulties experienced in recovering damaged columns have also become problematic for routine use of resistively heated columns. To solve these problems, a new resistively heated column technique, which uses metal columns and self-insulated heating wires, was developed for capillary gas chromatography. With this method, the total thermal mass was significantly less than in commercial column assemblies. Temperature-programming using resistive heating was at least 10 times faster than with a conventional oven, while only consuming 1—5% of the power that an oven would use. Cooling a column from 350 °C to 25 °C with an air fan only required 1.5 min. Losses in column efficiency and peak capacity were negligible when compared to oven heating. The major trade-off was slightly worse run-to-run retention time deviations, which were still acceptable for most GC analyses. The resistively heated column bundle is highly suitable for fast GC separations and portable GC instruments. Fabrication technologies for microelectromechanical systems (MEMS) allow miniaturization of conventional benchtop GC to portable, microfabricated GC (µGC) devices, which have great potential for on-site chemical analysis and remote sensing. The separation performance of µGC systems, however, has not been on par with conventional GC. Column efficiency, peak symmetry and resolution are often compromised by column defects and non-ideal injections. The relatively low performance of µGC devices has impeded their further commercialization and broader application. This problem can be resolved by incorporating thermal gradient GC (TGGC) into microcolumns. Negative thermal gradients reduce the on-column peak width when compared to temperature-programmed GC (TPGC) separations. This unique focusing effect can overcome many of the shortcomings inherent in µGC analyses. In this dissertation research, the separation performance of µGC columns was improved by using thermal gradient heating with simple set-ups. The analysis time was ~20% shorter for TGGC separations than for TPGC when wide injections were performed. Up to 50% reduction in peak tailing was observed for polar analytes, which significantly improved their resolution. The signal-to-noise ratios (S/N) of late-eluting peaks were increased by 3 to 4 fold. These results indicate that TGGC is a useful tool for bridging the performance gap between µGC and benchtop GC.

In order to make gas chromatography (GC) more widely accessible, considerable effort has been made in developing miniaturized GC systems. Thermal gradient gas chromatograpy (TGGC), one of the heating methods used in GC, has recieved attention over the years due to it's ability to enhance analyte focusing. The present work seeks to develop high performance miniaturized GC systems by combining miniaturized GC technology with thermal gradient control methods, creating miniaturized thermal gradient gas chromatography (µTGGC) systems. To aid in this development a thermal control system was developed and shown to successfully control various µTGGC systems. DAQ functionality was also included which allowed for the recording of temperature and power data for use in modeling applications. Thermal models of the various µTGGC systems were developed and validated against the recorded experiemental data. Thermal models were also used to aid in decisions required for the development of new µTGGC system designs. The results from the thermal models were then used to calibrate and validate a stochastic GC transport model. This transport model was then used to evaluate the effect of thermal gradient shape on GC separation performance.

Approved for public release, distribution is unlimited / The Monterey Bay sea breeze varies because of the influence of features such as inversions, clouds, synopticscale flow, and topography. The sea breeze is important because it impacts fire weather, air pollution, agriculture, and aviation operations, among other things. Analyses are conducted using a multi-quadric based program, which incorporates aircraft data, surface observations, and profiler data, to investigate the Monterey Bay sea breeze during 01-31 August 2003. Factors including inversions, cloud cover, amount of heating, distribution of heating, synoptic-scale flow, and topography are studied to determine their influence on the sea breeze. Six days are selected that best illustrate the factors that influence the structure of the Monterey Bay sea breeze. Results show that offs hore flow weakened the strength of the sea breeze and decreased the depth. A cooling trend in surface temperatures at the end of August also weakened the strength of the sea breezes and decreased the depth. Clouds are present during this period, which influenced the amount of heating, and consequently, the sea breeze response. The presence of a marine layer weakened the thermal gradient that in turn, weakened the sea breeze circulation. / Lieutenant Junior Grade, United States Naval Reserve

Dans le cadre des opérations de perçage, les billettes en acier subissent un réchauffage de la température ambiante à une température d’environ 1250°C. Au cours de ce réchauffage, le gradient de température dans les billettes entraîne la détérioration de la santé axiale de celles-ci et est à l’origine de l’apparition de défauts sur le tube formé. Une méthodologie d’analyse des mécanismes à l’origine de ces défauts a été mise en place. Elle se base sur la caractérisation de la santé axiale par essais rhéologiques permettant d’établir des indicateurs de ductilité et par des examens métallurgiques identifiant les défauts internes.L'étude de la sollicitation thermomécanique induite par le réchauffage du produit est analysée à l’aide de simulations numériques par éléments finis et les zones de sollicitations critiques associées au procédé sont identifiées. La caractérisation des anomalies observées sur les billettes est ensuite faite à partir d’essais de fissuration et de simulations numériques X-FeM. L’implémentation d’un critère de rupture en contrainte dans la simulation du cycle de chauffe a permis de définir les valeurs de gradient thermique limite et les courbes de chauffe optimales. Les analyses montrent que les conditions de chauffe en début de cycle thermique ont une forte influence sur la santé axiale des billettes. Les résultats de ces travaux conduisent à des solutions concrètes pour l’amélioration de la productivité. / As part of the piercing operations, billets undergo a reheating process from room temperature to a temperature of about 1250°C. During this heating, the thermal gradient in the billet leads to a deterioration of the axial health and is responsible of the initiation ofdefects on the formed tube.A methodology for the analysis of the mechanisms at the origin of these defects has been established. It is based on first, the characterization of the axial health with hot rheological tests to establish some indicators of ductility and second, on metallurgical analyses to identify the internal defects.Then finite element simulations have been performed to study the thermo-mechanical loadings induced by heating. Critical solicitation zones of the product during the processes have been identified.Finally a characterization of the observed defects into the billets has been led coupling cracks growth tests and X-FeM numerical simulations. The implementation of the experimental stress failure criterion, in the simulation of the heating cycle allows to obtain good values of thermal gradient boundary curves and leads to optimal heating curves.The analysis shows that the conditions at the beginning of the reheating process have a strong influence on the axial health of the billets. The results of these studies lead to friendly industrial solutions for improving productivity.

Les aubes de turbine haute pression en superalliage monocristallin sont refroidies, à la fois par un réseau de canaux internes, ainsi que par des perforations débouchantes. Soumises à des cycles thermo-mécaniques complexes, elles subissent des endommagements de type fatigue, fluage et oxydation. Pour valider les chaînes de prévision de durée de vie en conditions réelles d'utilisation, il a été nécessaire d’étudier des configurations d’essais technologiques reproduisant les conditions d'un cycle moteur en laboratoire. Pour cela, une installation d'essai de fatigue à gradient thermique de paroi est développée. Le gradient thermique est généré par chauffage de la surface externe et refroidissement interne par une circulation d’air. L’installation a ainsi permis la réalisation d'essais selon une complexité croissante, allant de l’essai isotherme jusqu'au cycle thermo-mécanique complexe, sur éprouvette tubulaire lisse ou multi-perforée. Afin d’analyser finement ces essais, deux méthodes de mesures sont étudiées. La méthode du potentiel électrique pour la détection et le suivi de fissure appliquée à des géométries complexes et la corrélation d’images, dont l’utilisation est étendue à la haute température. Le point-clé de la modélisation de ces essais est l'estimation du champ thermique. L'impossibilité de le mesurer sur éprouvette, a conduit à le déterminer numériquement, notamment par des simulations couplées aéro-thermiques. La chaîne de prévision de durée de vie intégrant l'aspect non-local, a ainsi pu être confrontée aux mesures expérimentales en termes de réponse mécanique, localisation de l'endommagement et durée de vie à amorçage. / Monocrystalline high pressure turbine blades are booth cooled by an internal channel network and side-wall crossing holes. As they undergo complex thermo-mechanical cycles they suffer fatigue, creep and oxidation damages. In order to validate lifetime prediction chain under real conditions of use, the study of technological test configurations reproducing turbine cycle conditions was necessary. For that, a thermal gradient mechanical fatigue facility is developed. Thermal gradient is generated through an external surface heating and an internal air cooling. As a result, tests could be conducted following a growing complexity on smooth and multi-perforated tubular specimens going from isothermal test up to thermo-mechanical complex cycle. The need of in-depth analysis of these tests led to the study of two measurement methods. The electrical potential drop method for crack detection and crack following applied to complex shapes and digital image correlation which use was extended to high temperatures. Simulation key issue is the thermal field estimation. Measurement complexity led us to numerically determine it by various methods including aero-thermal coupled calculations. Finally lifetime prediction chain including non-local coverage was confronted with experimental measurements in terms of mechanical response, damage localisation and crack initiation lifetime.

Made available in DSpace on 2014-12-17T14:07:19Z (GMT). No. of bitstreams: 1 NierllyKAMG.pdf: 1438330 bytes, checksum: d5fc2399ebd1b5a6e21ea3718fff6716 (MD5) Previous issue date: 2007-03-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The heat transfer between plasma and a solid occurs mostly due the radiation and the collision of the particles on the material surface, heating the material from the surface to the bulk. The thermal gradient inside the sample depends of the rate of particles collisions and thermal conductivity of the solid. In order to study that effect, samples of AISI M35 steel, with 9,5 mm X 3,0 mm (diameter X thickness) were quenched in resistive furnace and tempereds in plasma using the plane configuration and hollow cathode, working with pressures of 4 and 10 mbar respectively. Analyzing the samples microstructure and measuring the hardness along the transversal profile, it was possible to associate the tempered temperature evaluating indirectly the thermal profile. This relation was obtained by microstructural analyzes and through the hardness curve x tempered sample temperature in resistive furnace, using temperatures of 500, 550, 600, 650 and 700?C. The microstructural characterization of the samples was obtained by the scanning electron microscopy, optic microscopy and X-ray diffraction. It was verified that all samples treated in plasma presented a superficial layer, denominated affected shelling zone, wich was not present in the samples treated in resistive furnace. Moreover, the samples that presented larger thermal gradient were treated in hollow cathode with pressure of 4 mbar / A transfer?ncia de calor entre o plasma e um s?lido ocorre principalmente atrav?s da radia??o e colis?o das part?culas sobre a superf?cie do material, o que faz com que o aquecimento do material aconte?a da superf?cie para seu interior. Dependendo da taxa de colis?es das part?culas e da condutividade t?rmica do s?lido, haver? gradientes t?rmicos no interior das amostras. A fim de estudar esse efeito, amostras de a?o AISI M35, com 9,5 mm X 3,0 mm (di?metro X espessura) foram temperadas em forno resistivo e revenidas em plasma, nas configura??es c?todo planar e c?todo oco, com press?es de trabalho de 4 e 10 mbar, para ambas as configura??es. Analisando a microestrutura das amostras e medindo as durezas ao longo do perfil transversal pode-se associar ? temperatura de revenido avaliando indiretamente o perfil t?rmico. Essa rela??o foi obtida atrav?s de an?lise microestrutural e da curva dureza x temperatura de amostras revenidas em forno resistivo, utilizando temperaturas de 500, 550, 600, 650 e 700?C. A caracteriza??o microestrutural das amostras foi realizada atrav?s da microscopia eletr?nica de varredura (MEV), microscopia ?ptica (MO) e difra??o de raios-X (DRX). Verificou-se que todas as amostras tratadas em plasma apresentaram uma camada superficial, denominada de zona afetada por bombardeamento, que n?o se encontra presente nas amostras tratadas em forno resistivo. Al?m disso, verificou-se que as amostras que apresentaram maior gradiente t?rmico foram as tratadas em c?todo oco com press?o de 4 mbar

Ce travail se situé dans la perspective d'un contrôle de la structure de solidification des alliages métalliques sous l'effet de la convection naturelle et forcée afin d'améliorer à terme la maîtrise des microstructures de solidification grâce à un brassage électromagnétique efficace permettant d'avoir une homogénéisation du bain liquide qui par la suite peut améliorer la microstructure finale de l'alliage. La possibilité retenue dans ce travail est de réaliser ce brassage sans contact avec la solution liquide (alliage sous fusion) et sans pollution par d'autres éléments en utilisant un brassage par la force de Lorentz. L'objet de la thèse comporte une étude théorique à la fois expérimentale basée sur une installation expérimentale particulièrement documentée et instrumentée, développée au laboratoire SIMAP/EPM à Grenoble, nommée AFRODITE. Ce dispositif expérimental permet de fournir des données de quantitatives et qualitatives sur le processus de solidification des alliages métalliques. Ces données sont nécessaires à la contribution aux études menées sur la solidification des alliages métallique et enrichir la base des donnée des modèles numériques développés pour prédire les défauts liés à la solidification. L'alliage choisi dans notre travail est l'étain-plomb, vue sa basse température de fusion. Les expériences envisagées visent à étudier l'effet de deux modes de configuration dynamique sur la solidification de l'alliage Sn-Pb: la convection thermosolutale avec la variation de deux paramètres essentiels (la vitesse de refroidissement et la différence de température expérimentale) et la convection forcée par l'utilisation de plusieurs modes de brassage électromagnétique. Cette étude s'intéresse en particulier à la caractérisation des macrostructures et les défauts liés à la macroségrégation. L'originalité de l'étude vise à mesurer in situ les températures instantanées. Ceci nous a permis d'évaluer l'évolution du transfert thermique due à la convection naturelle/forcée, ainsi que leurs influence sur le processus de la solidification sous différents aspects. L'analyse post-mortem de l'alliage métallique, fournit la structure de solidification et la distribution des ségrégations à différentes échelles (mésoscopique et macroscopique). / This work is situated in the context of control of the solidification of metallic alloys structure under the effect of natural and forced convection to enhance control of solidification microstructures term through effective electromagnetic stirring to have a homogenizing the liquid which may subsequently improve the final microstructure of the alloy. The possibility considered in this work is to achieve this stirring without contacting the liquid solution (alloy in fusion) and pollution by other elements using a patch by the Lorentz force. The purpose of the thesis consists both a theoretical and experimental study based on an experimental setup particularly documented and instrumented developed / EPM SIMAP laboratory in Grenoble, named AFRODITE. The experimental device used to provide quantitative and qualitative data on the process of solidification of metallic alloys. These data are necessary for the contribution to studies on the solidification of metallic alloys and enrich the data base developed numerical models to predict defects related to solidification. The alloy selected from our work is tin-lead, for its low melting temperature. The proposed experiments are designed to study the effect of two types of dynamic configuration on the solidification of Sn-Pb alloy: the thermosolutal convection with the variation of two essential parameters (cooling rate and the difference in experimental temperature) and forced convection by the use of several modes of electromagnetic stirring. This study is particularly interested in the characterization of macrostructures and defects related to macrosegregation. The originality of this study is to measure in situ instantaneous temperatures. This allowed us to assess the evolution of the heat transfer due to natural / forced convection and their influence on the process of solidification in different aspects. The post-mortem analysis of the metal alloy provides the solidification structure and distribution of segregation at different scales (mesoscopic and macroscopic).

Dans le cadre de la vitrification des déchets nucléaires de haute activité à vie longue, un nouveau procédé a été mis en service à l’usine de La Hague en 2010 : le procédé creuset froid. Dans ce procédé, des gradients thermiques apparaissent au sein du bain de verre. Celui-ci forme une couche solide au contact de la paroi froide, appelée « auto-creuset ». Dans cette zone, le verre est soumis à des températures où il peut potentiellement cristalliser. L’objectif de ce travail était de déterminer la microstructure de cet auto-creuset en précisant les zones de cristallisation. Parallèlement, il s’agissait d’évaluer l’impact du gradient thermique sur la cristallisation des verres considérés. La cristallisation de deux verres d’intérêt nucléaire a donc été étudiée à l’aide d’une méthode basée sur l’analyse d’images MEB en conditions de traitements isotherme et sous gradient thermique. Les analyses en isotherme mettent en évidence la cristallisation de cristaux d’apatite (660°C-900°C) et de powellite (630°C-900°C) et permettent de quantifier cette cristallisation (vitesses de croissance et de nucléation, fraction cristallisée) qui reste très limitée (< 3%). La comparaison des résultats issus de ces deux types d’expérimentations montre que le gradient thermique n’a pas d’impact mesurable sur les cristallisations observées. Afin de compléter les analyses surfaciques de la cristallisation, des mesures par microtomographie in et ex situ ont été réalisées à l’ESRF sur la ligne ID19. Cette étude a permis de suivre la cristallisation d’apatites dans un verre simplifié et de confirmer la fiabilité de la méthode de quantification de la cristallisation basée sur l’analyse d’images 2D. / In the context of the vitrification of high level nuclear waste, a new industrial process has been launched in 2010 at the La Hague factory: The skull melting process. This setup applies thermal gradients to the melt, which leads to the formation of a solid layer of glass: the “self-crucible”. The question would be to know whether these thermal gradients have an impact or not on the crystallization behaviour of the considered glasses in the self crucible. In order to answer that question, the crystallization of two glass compositions of nuclear interest has been investigated with an image analysis based method in isothermal and thermal gradient heat treatments conditions. The isothermals experiments allow for the quantification (growth speed, nucleation, crystallized fraction) of the crystallization of apatites (660°C-900°C) and powellites (630°C- 900°C). The comparison of the results obtained through these two types of experimentations allows us to conclude that there is no impact of the thermal gradient on the crystallization of the studied glass compositions. In order to complete the image analysis study (based on surfaces), in and ex situ microtomography experiments have been performed at ESRF (Grenoble) on the ID10 beamline. This study allowed us to follow the crystallization of apatites in a simplified glass and to confirm the reliability of the image analysis method based on the analysis of surfaces.