A partir de medidas isotérmicas e isobáricas de susceptibilidade magnética diferencial, determinamos o diagrama de fases magnéticas do metamagneto Ni(NO3)2.2H2O, para pressões hidrostáticas de até cerca de 11 kbar. Determinamos o campo de transição à temperatura nula Hc(0,P) e à temperatura de Néel, ambos apresentando um crescimento aproximadamente linear com P. A partir de efeitos de desmagnetização, pudemos determinar o ponto de união das linhas de primeira e segunda ordem de cada diagrama, e para P=0 pudemos caracterizá-lo com um ponto tricrítico, com temperatura tricrítica Tt=3.70K. Observamos ainda a existência de uma transição metamagnética induzida por pressão para valores do intervalo de 0 a 8 kbar. Usando a Aproximação de Campo Médio num modelo elástico aproximado para metamagnetos com S=1, pudemos obter expressões para TN(P) e Hc(0,P), ambas apresentando uma dependência linear em P, em bom acordo com os dados experimentais. Usando este modelo obtivemos também uma expressão analítica para Tt(P). Uma vez que TN(P), Hc(0,P) e Tt(P) dependem dos parâmetros de \"exchange\", pudemos determinar a dependência de tais parâmetros com a pressão. Também através deste modelo simples, pudemos compreender que a transição metamagnética induzida por pressão está provavelmente associada a uma forte dependência do campo cristalino com a pressão / From isothermical and isobaric differential magnetic susceptibility measurements we have determined the magnetic phase diagram of the metamagnetic system Ni(NO3)2.2H2O, for several hydrostatic pressures up to 11 kbar. The zero temperature transition field Hc(0,P) and the Néel temperature TN(P) were determined, both increasing almost linearly with P. From demagnetizing effects we were able to determine the joint point of the first and second order lines of each diagram, which for P=0 is a tricritical point, with tricritical temperature Tt=3.70K. We also observed a pressure induced metamagnetic transition in the range from 0 to 8 kbar. Using Mean Field Theory in an approximated elastic S=1 metamagnetic model, we could obtain expressions for TN(P) and Hc(0,P), both showing linear dependence on P, in agreement with experimental data. We could also obtain, using this model, an analytical expression for Tt(P). Once TN(P), Hc(0,P) and Tt(P) are dependent on the exchange parameters, we cou1d obtain the pressure dependence of these parameters. From this simple model we could understand that the pressure induced metamagnetic transition is probably associated with a strong variation of the crystalline field with pressure

Atualmente, existe uma grande demanda por materiais caracterizados por um balanço adequado de propriedades, para aplicações estruturais em altas temperaturas. Superligas de última geração a base de níquel podem ser usadas sob carregamento em temperaturas próximas a 1150 ºC, mas informações indicam que materiais constituídos de microestruturas multifásicas apresentam maior potencial para estas aplicações, dentre os quais, os que contêm fase(s) intermetálica(s) em equilíbrio com um metal ou liga refratária. Na última década foram avaliados pelo Grupo Diagrama de Fases e Termodinâmica Computacional da Escola de Engenharia de Lorena os sistemas ternários metal refratário (molibdênio, nióbio, tântalo, vanádio, titânio, zircônio)-silício-boro, com o objetivo de serem determinadas as relações de fases em altas temperaturas e de ser desenvolvido um banco de dados termodinâmicos. Com o estudo experimental do sistema háfnio-silício- boro na seção isotérmica a 1600 ºC e sua Projeção Liquidus, na região rica em Háfnio, completa-se este ciclo de trabalhos. Saliente-se que o estudo deste sistema ternário exigiu a revisão dos sistemas binários háfnio-silício e háfnio-boro, através de sua avaliação experimental. Foram utilizadas no trabalho matérias-primas de elevada pureza (háfnio - mínimo de 99,8%, silício - mínimo de 99,998% e boro - mínimo de 99,5%). A metodologia experimental envolveu basicamente as seguintes etapas: (i) produção das ligas em forno a arco; (ii) tratamento térmico das ligas na temperatura de 1600 ºC; (iii) caracterização por difração de raios-X, microscopia eletrônica de varredura das ligas no estado bruto de fusão e tratadas termicamente e espectroscopia de energia dispersiva. Como resultado do estudo observou-se: (i) no sistema binário háfnio-silício a reação eutética L _HfSS + Hf2Si, na região rica em háfnio, as reações peritéticas L + Hf5Si3 Hf2Si, L + Hf3Si2 Hf5Si3, L + Hf3Si2 Hf5Si4, L + Hf5Si4 HfSi, L + HfSi HfSi2, a transformação congruente L Hf3Si2, e a reação eutética L SiSS + HfSi2, na região rica em silício, a estabilidade das fases intermediárias Hf2Si, Hf5Si3, Hf3Si2, Hf5Si4 a 1600 ºC, e a estabilidade de HfSi e HfSi2 a 1200 ºC, o que sugere alterações significativas em relação ao diagrama de fases atualmente aceito pela literatura; (ii) no sistema binário háfnio-boro a reação eutética L _HfSS + HfB, na região rica em háfnio, a reação peritética L + HfB2 HfB, a transformação congruente L HfB2 e a reação eutética L B-RhomSS + HfB2, na região rica em boro, e a estabilidade das fases intermediárias HfB e HfB2 a 1600 ºC, o que está de acordo com o diagrama de fases atualmente aceito pela literatura; (iii) no sistema ternário háfnio-silício-boro na região rica em háfnio, na projeção Liquidus, verificou-se as reações L _HfSS + Hf2Si + HfB, L HfB + Hf2Si, L HfB2 + Hf2Si, L HfB2 + Hf5Si3, L HfB2 + Hf3Si2, L HfB2 + Hf5Si4, L HfB2 + HfSi, L _HfSS + Hf2Si, L _HfSS + HfB, L + Hf5Si3 Hf2Si, L + Hf3Si2 Hf5Si3, L + Hf3Si2 Hf5Si4, L + Hf5Si4 HfSi e L + HfB2 HfB e na seção isotérmica a 1600 ºC, verificou-se a estabilidade das fases _HfSS, Hf2Si, Hf5Si3, Hf3Si2, Hf5Si4, HfSi, HfSi2, HfB e HfB2, e a existência dos campos trifásicos _HfSS + HfB + Hf2Si, HfB2 + HfB + Hf2Si, HfB2 + Hf2Si + Hf5Si3, HfB2 + Hf5Si3 + Hf3Si2, HfB2 + Hf3Si2 + Hf5Si4, HfB2 + Hf5Si4 + HfSi e HfB2 + HfSi + HfSi2. / Nowadays, there is a big demand for materials for structural applications at high temperatures. These materials must present a good properties balance. The last generation of the nickel-base superalloys can be used at temperatures close to 1150oC. However, information available so far shows that multiphase microstructure materials are potentially better for such application. Among these materials, the Group of Phase Diagrams and Computational thermodynamics in the Escola de Engenharia de Lorena has chosen those systems, which contains intermetallic(s) phase(s) in equilibrium with refractory metal or alloy for evaluation. Recently we have evaluated the phase stability at high temperature in the refractory metal (molybdenum, niobium, tantalum, vanadium, titanium, zirconium)- silicon-boron system, aiming at the development of a thermodynamic data base. The experimental study of the isothermal section at 1600 ºC and the Liquidus projection of the hafnium-silicon-boron system completes this cycle of works. The study of this ternary system demanded the revision of the hafnium-silicon and hafnium-boron binary systems, through its experimental evaluation. Alloys had been produced with blades of hafnium (minimum 99.8%), silicon (minimum 99.998%) and boron (minimum 99.5%), in the voltaic arc furnace under argon atmosphere, and heat treated at 1600 ºC under argon atmosphere. The phases had been identified by X-ray diffraction and contrast in backscattered electron imaging mode and spectroscopy of dispersive energy. The study determined: (i) in the binary system hafnium-boron the eutectic reaction L _HfSS + HfB, in the rich region of hafnium, the peritectic reaction L + HfB2 HfB, the congruent transformation L HfB2 and the eutectic reaction L B-Rhom + HfB2, in the rich region of boron, and the stability of the intermediate phases HfB and HfB2 at 1600 ºC, what is in agreement to the currently accepted diagram; (ii) in the binary system hafnium-silicon the eutectic reaction L _HfSS + Hf2Si, in the rich region of hafnium, the peritectic reactions L + Hf5Si3 Hf2Si, L + Hf3Si2 Hf5Si3, L + Hf3Si2 Hf5Si4, L + Hf5Si4 HfSi and L + HfSi HfSi2, the congruent transformation L Hf3Si2, and the eutectic reaction L SiSS + HfSi2, in the rich region of silicon, the stability of the intermediate phases Hf2Si, Hf5Si3, Hf3Si2, Hf5Si4 at 1600 ºC, and the stability of HfSi and HfSi2 at 1200 ºC, what suggests significant alterations in relation to the currently accepted diagram; (iii) in the ternary system hafnium-silicon-boron, in the rich region in hafnium, in the Liquidus projection, the reactions L _HfSS + Hf2Si + HfB, L HfB + Hf2Si, L HfB2 + Hf2Si, L HfB2 + Hf5Si3, L HfB2 + Hf3Si2, L HfB2 + Hf5Si4, L HfB2 + HfSi, L _HfSS + Hf2Si, L _HfSS + HfB, L + Hf5Si3 Hf2Si, L + Hf3Si2 Hf5Si3, L + Hf3Si2 Hf5Si4, L + Hf5Si4 HfSi e L + HfB2 HfB and in the isothermal section at 1600 ºC, the stability of the phases _HfSS, Hf2Si, Hf5Si3, Hf3Si2, Hf5Si4, HfSi, HfSi2, HfB and HfB2, and the threephase fields _HfSS + HfB + Hf2Si, HfB2 + HfB + Hf2Si, HfB2 + Hf2Si + Hf5Si3, HfB2 + Hf5Si3 + Hf3Si2, HfB2 + Hf3Si2 + Hf5Si4, HfB2 + Hf5Si4 + HfSi and HfB2 + HfSi + HfSi2.

O fosfeto de manganês, MnP, é um composto rico em fases magnéticas, exibindo uma variedade de transições de fase. Essas transições e a estrutura das fases magnéticas têm sido objetos de muitas investigações experimentais nas últimas duas décadas. Com o campo externo aplicado ao longo dos eixos intermediário e duro (eixos b e a, respectivamente) foram estudadas as geometrias das fronteiras nos pontos onde as fases moduladas se encontram com a fase ferromagnética no diagrama de fase Temperatura vs. Campo Magnético. Este estudo, realizado por meio de medidas de suscetibilidade magnética, visa esclarecer se as fronteiras das fases encontram-se formando um ângulo ou não, pois isto pode ser um indicativo da natureza desses pontos \"triplos\". Na situação em que o campo é aplicado ao longo do eixo intermediário, mostramos que a forma com que as três fronteiras se encontram é consistente com a atribuição feita anteriormente a esse ponto, isto é, trata-se de um ponto triplo ordinário no qual as três fronteiras de fase são de primeira ordem. Para a configuração em que o campo é aplicado ao longo do eixo duro, os resultados obtidos para o diagrama de fase, na região onde as duas fases moduladas e a fase ferromagnética se encontram, são consistentes com a existência de um ponto crítico terminal de uma linha de transições de segunda ordem separando as fases moduladas. / Manganese phosphide is a rich compound in magnetic phases and exhibits a variety of phase transitions which have been the subject of many experimental investigations for more than a decade. With the external magnetic field H applied along the b and a axes (intermediate and hard axis, respectively) the geometry of the boundaries in the points where the modulated phases meet with ferromagnetic phase in the phase diagram T x H were studied. Measurements of magnetic susceptibility were realized to elucidate if the phase boundaries meet at an angle or not thus indicating the nature of these triple points. For the case of H applied along the intermediate axis it is shown that the shape in which the phase boundaries meet is consistent with the geometry of an ordinary triple point. With H parallel to the a axis the results are consistent with the existence of critical end point in which the modulated phases boundary close.

Fundando-se em argumentos de equilíbrio e estabilidade termodinâmica, a solubilidade de soluto em um solvente é definida pelo limiar de existência da mistura como sistema homogêneo. De fato, entende-se tal grandeza sobre a coexistência de fases. A noção de solubilidade apresentada é desenvolvida através de modelos simples, que incluem resultados na rede bem como a extensão do modelo de van der Waals ao caso de duas componentes. Desta extrai-se uma condição genérica à observação de mínimos na solubilidade incidente sobre a topologia de seu diagrama de fases e de evidente correspondência física. / Concerning the equilibrium and stability in thermodynamics, the solubility of solute in a solvent is defined as the threshold of the mixture existing as a homogeneous system. Indeed, such quantity meets its meaning when understood on the coexistence surface. The idea of solubility presented is developed following the discussion of simple models, including results on the lattice as well as the van der Waals model extended to include two components. From these results we extract a general condition which connects the occurence of a minimum in solubility to the topological structure of the phase diagram.

L'épuisement des ressources d'origine pétrochimique conduit à la recherche de matières premières renouvelables pour l'élaboration des membranes. La gélatine, un biopolymère abondant, sous produit de l'industrie agroalimentaire, représente grâce à ses propriétés filmogènes un candidat de choix pour l'élaboration de membranes “vertes”. L'objectif de cette thèse est l'élaboration de membranes à base de gélatine et l'étude de l'impact de la structure du matériau sur les propriétés mécaniques, thermiques, de résistance à l'eau et de transfert gazeux. Pour cela les mécanismes d'élaboration par TIG-Dry cast process ont d'abord été formalisés par l'établissement du diagramme de phase du système gélatine/eau. Puis des réticulants alternatifs au glutaraldéhyde, toxique, ont été examinés pour augmenter la résistance à l'eau de la gélatine hydrosoluble. L'acide férulique et le téréphthalaldéhyde se sont montrés les plus prometteurs et complémentaires suivant les applications visées. Les films de gélatine se sont révélés barrières aux gaz à cause de la forte cristallinité induite par la renaturation des triples hélices. L'ajout d'un élastomère de la famille des polyéther amines a permis d'augmenter drastiquement les coefficients de perméabilité du CO2 de 1,4 à 250 Barrer. L'influence de la température et de l'humidité relative des flux gazeux sur les perméabilités a également été étudiée. / Petroleum based raw materials shortage leads to investigate renewable raw materials for membrane elaboration. Gelatin, an abundant, industrial by-product is a biosourced polymer with filmogenic properties which makes it an educated choice for “green” membrane production. This thesis work aims at developing gelatin based membrane and studying the influence of the material structure on mechanical and thermal properties, water resistance and gas transport properties. Thus, the elaboration mechanisms by TIG/Dry-cast process were studied in details by establishing the phase diagram of the gelatin/water system. To improve the water resistance of the hydrosoluble gelatin, crosslinking is necessary. Alternative cross-linkers were tested to replace the glutaraldehyde, classified as toxic. Ferulic acid and terephthalaldehyde were promising and showed complementary characteristics. The high crystallinity level of gelatin films, related to their renaturation level, led to rather gas barrier properties. By adding an elastomer, polyetheramine, the permeability to CO2 increased from 1.4 to an outstanding 250 Barrer. The influence of the temperature and relative humidity of the gas flux on permeability was also studied.

O fosfeto de manganês, MnP, é um composto rico em fases magnéticas, exibindo uma variedade de transições de fase. Essas transições e a estrutura das fases magnéticas têm sido objetos de muitas investigações experimentais nas últimas duas décadas. Com o campo externo aplicado ao longo dos eixos intermediário e duro (eixos b e a, respectivamente) foram estudadas as geometrias das fronteiras nos pontos onde as fases moduladas se encontram com a fase ferromagnética no diagrama de fase Temperatura vs. Campo Magnético. Este estudo, realizado por meio de medidas de suscetibilidade magnética, visa esclarecer se as fronteiras das fases encontram-se formando um ângulo ou não, pois isto pode ser um indicativo da natureza desses pontos \"triplos\". Na situação em que o campo é aplicado ao longo do eixo intermediário, mostramos que a forma com que as três fronteiras se encontram é consistente com a atribuição feita anteriormente a esse ponto, isto é, trata-se de um ponto triplo ordinário no qual as três fronteiras de fase são de primeira ordem. Para a configuração em que o campo é aplicado ao longo do eixo duro, os resultados obtidos para o diagrama de fase, na região onde as duas fases moduladas e a fase ferromagnética se encontram, são consistentes com a existência de um ponto crítico terminal de uma linha de transições de segunda ordem separando as fases moduladas. / Manganese phosphide is a rich compound in magnetic phases and exhibits a variety of phase transitions which have been the subject of many experimental investigations for more than a decade. With the external magnetic field H applied along the b and a axes (intermediate and hard axis, respectively) the geometry of the boundaries in the points where the modulated phases meet with ferromagnetic phase in the phase diagram T x H were studied. Measurements of magnetic susceptibility were realized to elucidate if the phase boundaries meet at an angle or not thus indicating the nature of these triple points. For the case of H applied along the intermediate axis it is shown that the shape in which the phase boundaries meet is consistent with the geometry of an ordinary triple point. With H parallel to the a axis the results are consistent with the existence of critical end point in which the modulated phases boundary close.

>Magister Scientiae - MSc / Solar cells offer SA an additional energy source. While Si cells are abundantly available they are not at an optimal efficiency and the cost is still high. One technology that can enhance their performance is SiNW. However, material properties such as the diameter, porosity and length determine their effectiveness during application to solar cell technology. One method of growing SiNW uses Sn catalysts on a Si substrate. As the properties of the Sn nanoparticle govern the properties of the SiNW, this thesis investigates their formation and properties by depositing a Sn layer on a Si wafer and then subjecting it to different temperatures, during process the layer forms into nanoparticles. At each temperature the morphology, composition and crystallinity will be determined using XPS, SEM, TEM and EDS. Thus, in Chapter 1 there is an overview, Chapter 2 deals with techniques used in this study, Chapter 3 will give the quantitative and qualitative results on the XPS analysis and Chapter 4 will illustrate the structural behaviour of the annealed Sn film samples.

Deposition of protein fibers with a characteristic cross-β sheet structure is the molecular marker associated with human disorders ranging from Alzheimer's disease to type II diabetes and spongiform encephalopathy. Given the large number of non-disease related proteins and peptides that have been shown to form amyloid fibrils in vitro, it has been suggested that amyloid fibril formation represents a generic protein phase transition. In the last two decades it has become clear that the same protein/peptide can assemble into distinct morphologically and structurally amyloid aggregates depending on the solution conditions. Moreover, recent studies have shown that the early stage, oligomeric amyloid assemblies are the main culprit in vivo. We have investigated the amyloid assemblies formed under denaturing conditions for Hen Egg White Lysozyme (HewL) whose human homologue is directly implicated in hereditary non-neuropathic systemic amyloidosis. Our early investigations showed that HewL can aggregate via at least two distinct assembly pathways depending on solution ionic strength at fixed pH, temperature, and protein concentration. By combining Dynamic Light Scattering (DLS), Static Light Scattering (SLS) and Atomic Force Microscopy (AFM) we showed that at low ionic strength, the pathway is characterized by the nucleation and growth of long (several micron), rigid fibrils (RF) via monomers assembly. A second, high ionic strength pathway is characterized by the rapid assembly of monomers into globular oligomers that further polymerize into curvilinear fibrils (aO/CF). At NaCl concentrations above 400 mM, aggregation resulted in precipitate formation. Next, we used Foureir Transform Infrared spectroscopy (FTIR) and an amyloid-specific dye, Thioflavin T (ThT), to show that both RF and (a)O/CF are amyloidogenic species, but they have detectable structural differences. Moreover, we have determined that each assembly pathway has unique SLS, DLS, FTIR and ThT response signatures that help determine the assembly type prior to AFM imaging of aggregates. Taking advantage of the morphological, structural and kinetic signatures for the two distinct HewL amyloid aggregates I mapped out their amyloid aggregates phase diagram spanning over two orders of magnitude in protein concentration and from 50 to 800 mM NaCl in ionic strength. This is the most complete phase diagram for amyloid aggregates of a given protein up to date. The phase diagram has three distinct regions delineated by sharp boundaries. The RF- aO/CF was called Critical Oligomer Concentration, and we commonly refer to “above the COC” as the region were aO/CF are kinetically favored.. In the region of low salt/high protein concentrations, RF were the only amyloid species to nucleate and grow. As both salt and protein concentrations increase, aO/CF become the kinetically favored species, and RF nucleate and grow after several days of incubation. At high protein and high salt concentrations, aO/CF form very fast and eventually lose solubility forming a precipitate (Ppt). Cross-seeding experiments showed that RF is the thermodynamically stable aggregate phase, while the O/CF are the metastable species. Finally, we used the phase diagram to design experiments that would allow us to reveal the RF nucleation mechanism in presence of aO/CF. RF nucleation above the COC can undergo either via internal restructuring of aO/CF (NCC) or through a random coalescence of monomers into a nucleus (NP). The experimental results obtained so far strongly indicate that RF nucleate via NP mechanism both below and above the COC.

X-ray diffraction from protein crystals remains the most reliable way to determine the molecular structure of proteins, and how this structure relates to biological function. However, we still lack the ability to predict solution conditions that support the nucleation and growth of high-quality protein crystals for X-ray diffraction studies. The overall goal of this thesis is two-fold: (a) determine the nucleation behavior and solubilities for lysozyme crystals with two distinct crystal structures (orthorhombic vs. tetragonal) and (b) investigate whether these changes in crystal habit and crystal solubility correlate with any discontinuities in the liquid-liquid phase boundary of lysozyme that occurs under the same solution conditions. We measured lysozyme crystal solubility by nucleating and subsequently dissolving very small lysozyme crystals in highly supersaturated solutions. The presence of crystals in our samples is detected and monitored by measuring the light scattered off the micron-sized crystals. These "turbidity measurements" are repeated across a range of protein concentrations, for pH 4.6 and 5.6, thereby yielding the crystal solubility boundary. Changes in crystal structure are assessed at the end of the experiments by microscopic inspection of the distinct crystal habits. Attractive protein interactions in solution also induce liquid-liquid phase separation. Similar to the crystal solubility measurement, we use the turbidity increase associated with liquid-liquid phase separation to map out this phase boundary. Since both crystal formation and liquid-liquid phase separation are driven by attractive protein interactions, we investigated whether the dramatic changes in crystal solubility associated with different protein crystal structures lead to any discernable “discontinuities” in the liquid-liquid phase boundaries.

No description available.