No / Small-angle neutron scattering measurements on a series of monodisperse linear entangled polystyrene melts in nonlinear flow through an abrupt 4:1 contraction have been made. Clear signatures of melt deformation and subsequent relaxation can be observed in the scattering patterns, which were taken along the centerline. These data are compared with the predictions of a recently derived molecular theory. Two levels of molecular theory are used: a detailed equation describing the evolution of molecular structure over all length scales relevant to the scattering data and a simplified version of the model, which is suitable for finite element computations. The velocity field for the complex melt flow is computed using the simplified model and scattering predictions are made by feeding these flow histories into the detailed model. The modeling quantitatively captures the full scattering intensity patterns over a broad range of data with independent variation of position within the contraction geometry, bulk flow rate and melt molecular weight. The study provides a strong, quantitative validation of current theoretical ideas concerning the microscopic dynamics of entangled polymers which builds upon existing comparisons with nonlinear mechanical stress data. Furthermore, we are able to confirm the appreciable length scale dependence of relaxation in polymer melts and highlight some wider implications of this phenomenon.

Neste trabalho tivemos como objetivo sintetizar e caracterizar os ortossilicatos de elementos alcalino-terrosos com destaque para o Sr2SiO4, uma matriz hospedeira para íons dopantes como o cádmio II e o európio III, resultando em materiais com propriedades luminescentes. Outro objetivo é reduzir a temperatura de síntese pelos métodos aqui empregados em relação aos métodos convencionais descritos na literatura. Tanto a matriz quanto os sistemas dopados foram caracterizados por meio da difratometria de raios x, análise de área superficial e tamanho de poros, microscopia eletrônica de varredura e de transmissão. Os métodos empregados neste trabalho foram basicamente o da metátese e o do sal fundido, sendo que o método da metátese foi conduzido por sol-gel (utilizando-se sílica comercial e TEOS) e por precipitação em atmosfera ambiente e em atmosfera de nitrogênio. Já no método do sal fundido utilizamos duas temperaturas de síntese, 600 e 750ºC. A 750ºC foi utilizada uma mistura equimolar de cloreto de sódio e cloreto de potássio juntamente com nitrato de estrôncio e sílica mesoestruturada na proporção molar de 2:1. A 600ºC foi utilizada somente a mistura de nitrato de estrôncio e sílica mesoestruturada também na proporção molar de 2:1. Nestas duas formas de se conduzir a síntese por sal fundido utilizamos nitrato de sódio (proporção molar de Na/Si = 0,1) a fim de se facilitar a quebra das pontes de oxigênio da sílica e verificar a influência desse reagente sobre o produto final. Já o Ca2SiO4 e o Ba2SiO4 foram sintetizados apenas a 600ºC bem como as dopagens do Sr2SiO4 (1% em mol). Os resultados mostram uma densificação do produto em relação à sílica e a obtenção de nanofibras de silicatos obtidos pelo método do sal fundido. Já no método da metátese obtivemos carbonato de estrôncio e outros tipos de silicatos. / In this work our objective was to synthesize and characterize orthosilicates of alkaline-earth elements with emphasis on Sr2SiO4. This is a silicate host matrix for doping with ions such as cadmium II and europium III, resulting in materials with luminescent properties. Another objective is to reduce the synthesis temperature using the methods employed here when compared to conventional methods described the literature. Both the matrix and the doped systems were well characterized by X-ray diffraction, surface area and pore size distribution, scanning and transmission electron microscopy. The methods employed in this study were basically the metathesis and the molten salt; the metathesis method was conducted by sol-gel (using a commercial silica and tetraethyl orthosilicate TEOS) and precipitation in air and nitrogen atmospheres. In the molten salt method, two synthesis temperatures were used: 600 and 750ºC. At 750°C an equimolar mixture of sodium chloride and potassium chloride with strontium nitrate was used in addition to mesostructured silica in the molar ratio of 2:1. At 600°C only a mixture of strontium nitrate and mesostructured silica was used, also in the molar ratio of 2:1. In these two pathways, sodium nitrate (molar ratio Na/Si = 0.1) was used in order to facilitate the breakup of the silica oxygen bridges and its influence on the final product was also studied. Furthermore, Ca2SiO4 and Ba2SiO4 were synthesized only at 600ºC and the doping of Sr2SiO4 (1 mol %) was also carried out only at 600°C. The results show a densification of the product compared to the silica precursor and the formation of silicate nanofibers by the molten salt method. In the metathesis method we obtained strontium carbonate and other types of silicates.

Neste trabalho tivemos como objetivo sintetizar e caracterizar os ortossilicatos de elementos alcalino-terrosos com destaque para o Sr2SiO4, uma matriz hospedeira para íons dopantes como o cádmio II e o európio III, resultando em materiais com propriedades luminescentes. Outro objetivo é reduzir a temperatura de síntese pelos métodos aqui empregados em relação aos métodos convencionais descritos na literatura. Tanto a matriz quanto os sistemas dopados foram caracterizados por meio da difratometria de raios x, análise de área superficial e tamanho de poros, microscopia eletrônica de varredura e de transmissão. Os métodos empregados neste trabalho foram basicamente o da metátese e o do sal fundido, sendo que o método da metátese foi conduzido por sol-gel (utilizando-se sílica comercial e TEOS) e por precipitação em atmosfera ambiente e em atmosfera de nitrogênio. Já no método do sal fundido utilizamos duas temperaturas de síntese, 600 e 750ºC. A 750ºC foi utilizada uma mistura equimolar de cloreto de sódio e cloreto de potássio juntamente com nitrato de estrôncio e sílica mesoestruturada na proporção molar de 2:1. A 600ºC foi utilizada somente a mistura de nitrato de estrôncio e sílica mesoestruturada também na proporção molar de 2:1. Nestas duas formas de se conduzir a síntese por sal fundido utilizamos nitrato de sódio (proporção molar de Na/Si = 0,1) a fim de se facilitar a quebra das pontes de oxigênio da sílica e verificar a influência desse reagente sobre o produto final. Já o Ca2SiO4 e o Ba2SiO4 foram sintetizados apenas a 600ºC bem como as dopagens do Sr2SiO4 (1% em mol). Os resultados mostram uma densificação do produto em relação à sílica e a obtenção de nanofibras de silicatos obtidos pelo método do sal fundido. Já no método da metátese obtivemos carbonato de estrôncio e outros tipos de silicatos. / In this work our objective was to synthesize and characterize orthosilicates of alkaline-earth elements with emphasis on Sr2SiO4. This is a silicate host matrix for doping with ions such as cadmium II and europium III, resulting in materials with luminescent properties. Another objective is to reduce the synthesis temperature using the methods employed here when compared to conventional methods described the literature. Both the matrix and the doped systems were well characterized by X-ray diffraction, surface area and pore size distribution, scanning and transmission electron microscopy. The methods employed in this study were basically the metathesis and the molten salt; the metathesis method was conducted by sol-gel (using a commercial silica and tetraethyl orthosilicate TEOS) and precipitation in air and nitrogen atmospheres. In the molten salt method, two synthesis temperatures were used: 600 and 750ºC. At 750°C an equimolar mixture of sodium chloride and potassium chloride with strontium nitrate was used in addition to mesostructured silica in the molar ratio of 2:1. At 600°C only a mixture of strontium nitrate and mesostructured silica was used, also in the molar ratio of 2:1. In these two pathways, sodium nitrate (molar ratio Na/Si = 0.1) was used in order to facilitate the breakup of the silica oxygen bridges and its influence on the final product was also studied. Furthermore, Ca2SiO4 and Ba2SiO4 were synthesized only at 600ºC and the doping of Sr2SiO4 (1 mol %) was also carried out only at 600°C. The results show a densification of the product compared to the silica precursor and the formation of silicate nanofibers by the molten salt method. In the metathesis method we obtained strontium carbonate and other types of silicates.

Un concept innovant de réacteurs nucléaires à sels fondus, le Thorium Molten Salt Reactor (TMSR), a été défini au LPSC Grenoble. Le présent mémoire porte sur les études, optimisations et caractérisations réalisées sur les configurations en spectre rapide de ce concept, appelées ‘TMSR non modérés' ou TMSR-NM, très prometteuses. Le cœur est un simple cylindre dans lequel circule un sel fluore contenant du LiF et le combustible. Nos études portent sur les caractéristiques de ces réacteurs en termes de sûreté, inventaire fissile, retraitement chimique, production de déchets et capacité de régénération et de déploiement. Un tel réacteur présente maints avantages intrinsèques permettant un fonctionnement simple et sûr en cycle du combustible Thorium, ainsi que l'utilisation de divers éléments fissiles au démarrage tels l'233U, 235U ou les transuraniens issus des réacteurs actuels. Ceci permettrait une transition optimisée vers le cycle Thorium tout en fermant le cycle actuel.

Among the obstacles for the commercialization of the MoltenCarbonate Fuel Cell (MCFC), the dissolution of thestate-of-the-art lithiated NiO cathode is considered as aprimary lifetime limiting constraint. Development ofalternative cathode materials is considered as a main strategyfor solving the cathode dissolution problem. LiFeO2and LiCoO2had earlier been reported as the most promisingalternative materials; however, they could not satisfactorilysubstitute the lithiated NiO. On the other hand, ternarycompositions of LiFeO2, LiCoO2and NiO are expected to combine some desirableproperties of each component. The aim of this work was todevelop alternative cathode materials for MCFC in the LiFeO2-LiCoO2-NiO ternary system. It was carried out byinvestigating electronic conductivity of the materials, firstin the form of bulk pellets and then in ex-situ sinteredporous-gas-diffusion cathodes, and evaluating theirelectrochemical performance by short-time laboratory-scale celloperations. Materials in the LiFeO2-NiO binary system and five ternary sub-systems,each with a constant molar ratio of LiFeO2:NiO while varying LiCoO2content, were studied. Powders withcharacteristics appropriate for MCFC cathode fabrication couldbe obtained by the Pechini method. The particle size of LiFeO2-LiCoO2-NiO powders considerably depends on thecalcination temperature and the material composition. Theelectrical conductivity study reveals the ability of preparingLiFeO2-LiCoO2-NiO materials with adequate electricalconductivity for MCFC cathode application. A bimodal pore structure, appropriate for the MCFC cathode,could be achieved in sintered cathodes prepared usingporeformers and sub-micron size powder. Further, this studyindicates the nature of the compromise to be made between theelectrical conductivity, phase purity, pore structure andporosity in optimization of cathodes for MCFC application. Cellperformance comparable to that expected for the cathode in acommercial MCFC could be achieved with cathodes prepared from20 mole% LiFeO2- 20 mole% LiCoO2- 60 mole% NiO ternary composition. It shows aniR-corrected polarization of 62 mV and a iR-drop of 46 mV at acurrent density of 160 mAcm-2at 650 °C. Altogether, this study revealsthe possibility of preparing LiFeO2-LiCoO2-NiO cathode materials suitable for MCFCapplication. Keywords: molten carbonate fuel cell (MCFC), MCFC cathode,LiFeO2-LiCoO2-NiO ternary compositions, electrical conductivity,porous gas diffusion electrodes, polarization, electrochemicalperformance, post-cell characterization.

Smältkarbonatbränslecellen (MCFC) är en högtemperaturbränslecell för stationära applikationer. Den har samma höga totalverkningsgrad som konventionella kraftvärme-anläggningar, men kan byggas i mindre moduler (från 250 kWe). De små modulerna och den bränsleflexibilitet (naturgas, biogas, etanol, diesel) som MCFC har, gör den intressant för exempelvis industrier med organiska restprodukter och höga krav på tillförlitlighet. Den höga temperaturen och närvaron av en saltsmälta gör dock materialdegradering till en viktig faktor för forskning och utveckling inom området. För även om de fälttester som nyligen gjorts har visat på att vissa av degraderingsprocesserna är mindre allvarliga än förväntat, finns fortfarande ett behov av utveckling för att sänka kostnaderna och förlänga livstiden. I första delen av detta arbete undersöktes material för olika delar av cellen inom ramarna för EU-projektet IRMATECH. Materialen ansågs vara interessanta alternativ till de nuvarande materialen på grund av deras lägre kostnad och/eller bättre prestanda. Två alternativa anodströmtilledarmaterial undersöktes. För anodströmtilledaren är korrosionen och den elektriska resistansen av det eventuella oxidlagret nyckelparametrar. Dessa parametrar undersöktes och utvärderades. Fastän de båda alternativa materialen hade oxidlager med låg resistans, fanns indikationer på korrosionsprocesser som kan äventyra materialets långtidsstabilitet. För katodmaterialet, NiO, har upplösningen varit problemet. De upplösta nickeljonerna fälls ut i elektrolyten och bildar dendriter som kan kortsluta cellen. Därför undersöktes nickelupplösningen hos tre alternativa katodmaterial. Det mest lovande materialet, en nickeloxid-katod dopad med magnesium och järn testades i en singelcell för att studera elektrokemisk prestanda, morfologi och områden där nickelutfällning skett. Resultaten visade att prestandan var jämförbar med NiO, men att den mekaniska stabiliteten måste undersökas ytterligare. I ”wet-seal”-området är det rostfria stålet belagt med ett aluminiumskikt för att skydda det från den mycket korrosiva miljön. Tillverkningsprocesserna för dessa aluminiumbeläggningar har hittills varit dyra och komplexa. Därför utvärderades en alternativ tillverkningsprocess. Beläggningen, studerad i både reducerande och oxiderande miljö visade en tendens till att spricka och därmed exponera det underliggande rostfria stålet. Detta berodde troligtvis på en manuell beläggningsprocess som resulterade i ett inhomogent ytskikt. I den andra delen av arbetet föreslogs en alternativ tillverkningsmetod, baserad på nyligen publicerade resultat där man elektrodeponerat aluminium från jonvätskor. Dessa har ett större katodiskt fönster än vatten och möjliggör därför elektrodeponering av elektropositiva material. För att göra processen industrivänlig provades ett alternativ till den vanligen använda aluminiumtrikloriden. Det visade sig dock att påverkan av miljön på stabiliteten hos jonvätskan behövde undersökas innan några material kunde tillverkas. Vatten i kombination med syre visade sig ha en stor inverkan på den katodiska strömtätheten. I frånvaro av dessa komponenter var jonvätskan mycket stabil. / The Molten Carbonate Fuel Cell (MCFC) is a high temperature fuel cell for stationary applications. It has the same high over-all efficiency (90%) as traditional combined heat and power plants, but MCFC can be built in small modules (from 250 kWe). The small modules in combination with fuel flexibility (natural gas, biogas, ethanol, diesel) makes MCFC an interesting alternative for industries with organic waste and high demands for reliability. The high temperature (650 °C) and the presence of molten salt result however in material degradation. Corrosion and dissolution of the materials used have been the challenge for MCFC. Although long-term field trials have shown that some of the material problems are not as severe as first believed, further material development is necessary to decrease the cost and prolong the life-time. In the first part of this work, materials for different parts of the cell were tested within the EU project IRMATECH. The materials were interesting alternatives to the state-of-the-art materials due to their lower cost and/or better performance. Two alternative anode current collector materials were tested. For the anode current collector the corrosion and electrical resistance of the possible oxide layer are key parameters. These parameters were investigated and evaluated. Although both the materials showed a low resistance, there were indications of corrosion processes which could affect the life-time of the material. For the cathode material, NiO, the dissolution of the material has been a problem. The dissolved nickel ions precipitate in the electrolyte and form conductive nickel dendrites that eventually short-circuit the cell. Therefore, the nickel dissolution of three alternative cathode materials was tested. The most promising material, a NiO doped with magnesium and iron, was tested in a single cell to study the electrical performance, the morphology after operation and the area where nickel had precipitated. The results showed that the performance was comparable to NiO, but it is necessary to investigate the mechanical strength of the material further. In the wet-seal area, the stainless steel is coated with an aluminium coating to protect the material from a severe corrosion environment. The production of aluminium coatings has so far been expensive and complex and an alternative coating process was evaluated. The alternative coating, tested in both reducing and oxidising environments showed a tendency to crack and expose the stainless steel to the corrosive environment. This was suggested being due to the manual coating process that resulted in inhomogeneous coatings. In the second part, an alternative process to coat the wet-seal was suggested, based on recently published results where aluminium had been electrodeposited from ionic liquids. These solvents have a wider electrochemical window than water, and electropositive materials can therefore be deposited. To make the coating process suitable for industrial applications, an alternative to the commonly used AlCl3 was tested. It was shown however, that the influence of the environment had to be investigated before any materials could be produced. The environment, especially water in combination with oxygen was shown to influence the cathodic current density. In absence of these components, the ionic liquid was shown to be very stable. / QC 20100906

Fluctuations in protein structure are vital to function. This contrasts the dominating structure-function paradigm, which connects the well-defined three-dimensional protein structure to its function. However, catalysis is observed in disordered enzymes, which lack a defined structure. Disordered proteins are involved in molecular recognition events as well. The aim of this Thesis is to describe the structural changes occuring in protein structure and to investigate the mechanism of molecular recognition. Protein architecture is classified in a hierarchical manner, that is, it is categorized into primary, secondary, and tertiary levels. One of the major questions in biology today is how proteins fold into a defined three-dimensional structure. Some protein folding models, like the framework model, suggest that the secondary structure, like α-helices, is formed before the tertiary structure. This Thesis raises two questions: First, are structural fluctuations that occur in the protein related to the folding of the protein structure? Second, is the hierarchic classification of the protein architecture useful to describe said structural fluctuations? Kinetic studies of protein folding show that important dynamical processes of the folding occur on the microsecond timescale, which is why time-resolved fluorescence spectroscopy was chosen as the principal method for studying structural fluctuations in the peptides. Time-resolved fluorescence spectroscopy offers a number of experimental advantages and is useful for characterizing typical structural elements of the peptides on the sub-microsecond timescale. By observing the fluorescence lifetime distribution of the fluorescent probe, which is a part of the hydrophobic core of a four-helix bundle, it is shown that the hydrophobic core changes hydration state, from a completely dehydrated to a partly hydrated hydrophobic core. These fluctuations are related to the tertiary structure of the four-helix bundle and constitute structural transitions between the completely folded four-helix bundle and the molten globule version. Equilibrium unfolding of the four-helix bundle, using chemical denaturants or increased temperature, shows that the tertiary structure unfolds before the secondary structure, via the molten globule state, which suggests a hierarchic folding mechanism of the four-helix bundle. Fluctuations of a 12 amino acid long helical segment, without tertiary structure, involve a conformational search of different helical organizations of the backbone. Binding and recognition of a helix-loop-helix to carbonic anhydrase occurs through a partly folded intermediate before the final tertiary and bimolecular structure is formed between the two biomolecules. This confirms the latest established theory of recognition that the binding and the folding processes are coupled for the binding molecules.

Technological advances results in the fact that quite a large number of electronic equipment interacts with its environment leading to the malfunction of the devices. This brings about the necessity of using proper electromagnetic (EM) wave absorbers/shields to avoid such interactions. In order to absorb EM waves in a large frequency band from several MHz to GHz, barium hexaferrite (BaHF) ceramics which are produced as textured ceramics as well as in multilayered form can be used. Textured ceramics are processed by tape casting using templated grain growth (TGG) phenomenon. In order to obtain textured ceramics, BaHF powders and platelets are required as raw materials in such a way that during sintering small size powders are directioned by large platelet surfaces. In this study, ferrite powders were synthesized by mixed oxide technique while the platelets were produced by both molten salt synthesis (MSS) and reactive templated grain growth (RTGG) methods. In the case of platelet synthesis by MSS, effects of calcination temperature and time as well as type and composition of the flux on the formation and morphology of platelets were investigated based on the XRD and SEM results. Studies have shown that KCl flux led to the formation of sharper platelet morphology, while NaCl resulted in more round shapes. However, extent of BaHF formation in the case of NaCl was higher when compared to KCl flux due to its higher wettability characteristic, and hence faster interaction with the raw materials. Since the aspect ratio of the synthesized platelets was only ca. 2-4, these platelets were not efficient for further TGG studies. Alternatively, BiFeO3 (BiF) particles having ~30-40 &mu / m average size were synthesized as seed crystals for the synthesis of BaHF platelets by RTGG method. After the washing of these platelets with dilute HNO3, pure BaHF powders and platelets were directed by tape casting which was followed by sintering using TGG phenomenon. Degree of achieved texturing in the processed ceramics was studied using Rietveld analysis, pole figure measurement and electron backscattered diffraction (EBSD).

Recently the computational speed and the functions of the numerical methods are advancing rapidly. It is the future trend that using the computational fluid dynamics (CFD) to perform simulation for making up the experimental deficiency, reducing the risk, improving the quality of the product, and saving the cost of research and development. A two-dimensional simulation was employed to study the melt/air and melt/solid interface shapes of the miniature molten zone formed in the laser-heated pedestal growth (LHPG) system. Using non-orthogonal body-fitting grid system with control-volume finite difference method, the interface shape can be determined both efficiently and accurately. During stable growth, the dependence of the molten-zone length and shape on the heating CO2 laser is examined in detail under both the maximum and the minimum allowed powers with various growth speeds. The effect of gravity for the miniature molten zone is also simulated, which reveals the possibility for a horizontally oriented LHPG system. Such a horizontal system is good for the growth of long crystal fibers. After comparing with the shape of the molten zone in terms of the experiment and the analysis of the simulation shown as above. Heat transfer and fluid flow in the LHPG system are analyzed near the deformed interfaces. The global thermal distributions of the crystal fiber, the melt, and the source rod are described by temperature and its axial gradient within length of ~10 mm. As compared with the growth of bulk crystal of several centimeters in dimension, natural convection drops six orders in magnitude due to smaller melt volume; therefore, conduction rather than convection determines the temperature distribution in the molten zone. Moreover, thermocapillary convection rather than mass-transfer convection becomes dominant. The symmetry and mass flow rate of double eddy pattern are significantly influenced by the molten-zone shape due to the diameter reduction and the large surface-tension-temperature coefficient in the order of 10-4~10-3. According to the analysis shown as above, the results could be further extended for the analysis of the concentration profile and study of horizontal growth.

<p>Among the obstacles for the commercialization of the MoltenCarbonate Fuel Cell (MCFC), the dissolution of thestate-of-the-art lithiated NiO cathode is considered as aprimary lifetime limiting constraint. Development ofalternative cathode materials is considered as a main strategyfor solving the cathode dissolution problem. LiFeO₂and LiCoO₂had earlier been reported as the most promisingalternative materials; however, they could not satisfactorilysubstitute the lithiated NiO. On the other hand, ternarycompositions of LiFeO₂, LiCoO₂and NiO are expected to combine some desirableproperties of each component. The aim of this work was todevelop alternative cathode materials for MCFC in the LiFeO₂-LiCoO₂-NiO ternary system. It was carried out byinvestigating electronic conductivity of the materials, firstin the form of bulk pellets and then in ex-situ sinteredporous-gas-diffusion cathodes, and evaluating theirelectrochemical performance by short-time laboratory-scale celloperations.</p><p>Materials in the LiFeO₂-NiO binary system and five ternary sub-systems,each with a constant molar ratio of LiFeO₂:NiO while varying LiCoO₂content, were studied. Powders withcharacteristics appropriate for MCFC cathode fabrication couldbe obtained by the Pechini method. The particle size of LiFeO₂-LiCoO₂-NiO powders considerably depends on thecalcination temperature and the material composition. Theelectrical conductivity study reveals the ability of preparingLiFeO₂-LiCoO₂-NiO materials with adequate electricalconductivity for MCFC cathode application.</p><p>A bimodal pore structure, appropriate for the MCFC cathode,could be achieved in sintered cathodes prepared usingporeformers and sub-micron size powder. Further, this studyindicates the nature of the compromise to be made between theelectrical conductivity, phase purity, pore structure andporosity in optimization of cathodes for MCFC application. Cellperformance comparable to that expected for the cathode in acommercial MCFC could be achieved with cathodes prepared from20 mole% LiFeO₂- 20 mole% LiCoO₂- 60 mole% NiO ternary composition. It shows aniR-corrected polarization of 62 mV and a iR-drop of 46 mV at acurrent density of 160 mAcm^-2at 650 °C. Altogether, this study revealsthe possibility of preparing LiFeO₂-LiCoO₂-NiO cathode materials suitable for MCFCapplication.</p><p>Keywords: molten carbonate fuel cell (MCFC), MCFC cathode,LiFeO₂-LiCoO₂-NiO ternary compositions, electrical conductivity,porous gas diffusion electrodes, polarization, electrochemicalperformance, post-cell characterization.</p>