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.

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.

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<p>Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water. Fine crystals are produced by crystallization of the substance, and the crystals are agglomerated by introduction of an immiscible liquid called the bridging liquid. The concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature are found to have a significant influence on the physico-mechanical properties of the product. The product particle characterization includes the particle size distribution, morphology and mechanical strength.</p><p>Many of the solvents such as chloroform, toluene, pentane, heptane, cyclo hexane, diethyl ether and ethyl acetate were used as bridging liquids. Among the selected solvents ethyl acetate and di ethyl ether could not form the spherical agglomerates. Characteristics of the particles are changing with the bridging liquid used. Range of the operation for spherical agglomeration is very narrow and was shown that only at certain conditions the spherical agglomerates are produced. Increased amount of bridging liquid, decrease in feeding rate and temperature causes the particle size to increase. Particle morphology depends on the bridging liquid used, amount of bridging liquid and the temperature. Particles look completely spherical from the experiments where toluene is used as bridging liquid. </p><p>The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10N load cell. For single particle compression an approximate estimation of the true stress is presented. Compression characteristics for single agglomerates are compared with data on particle bed compression. Low elastic recovery and high compressibility of the single particles and of bed of particles reveals that the spherical agglomerates prepared in this work have a plastic behavior which is expected to be favorable for direct tabletting. Some of the stress–strain curves are J-shaped with no clear fracturing of the particles, and are well correlated by an exponential–polynomial equation. </p>

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The Mo-Ni-Re system is one of the important subsystems of the Ni based superalloys engineered for use in high temperature applications. Considering the contradictions among previously reported information, the present study was devoted to the complete experimental determination of the phase equilibria in the Mo-Ni-Re system, structural characterization of its intermetallic phases and thermodynamic modeling of the system with the help of the CALPHAD method. The experimental investigation of phase equilibria was carried out with the help of equilibrated alloys and phase diagrams of the Ni-Re and Mo-Ni-Re system (at 1200°C and 1600°C) were proposed. In comparison with previous investigations, the Ni-Re phase diagram determined during the present study showed significant difference in terms of homogeneity domains, freezing ranges and peritectic reaction temperature. The 1200°C isothermal section of the Mo-Ni-Re system proposed during the present study showed large extension of the Mo-Re σ phase and Mo-Ni δ phase in the ternary region. In addition, presence of two previously unknown ternary phases was also observed. The isothermal section of the Mo-Ni-Re system at 1600°C also showed large extension of σ phase in the ternary region whereas extension of the Mo-Re χ phase in both isothermal sections was restricted to narrow composition range. The presence of the ternary phases observed in the 1200°C isothermal was not evidenced in 1600°C isothermal section. On the other hand, partial investigations of phase boundaries in the Mo-Ni and Mo-Re binary systems and determination of liquidus projection of the Mo-Ni-Re system was also carried out. The liquidus projection of the Mo-Ni-Re system proposed during present study also showed largely extended primary crystallization fields of the Mo-Re σ phase and Re solid solution in the ternary region. Since isothermal sections of the Mo-Ni-Re system showed largely extended homogeneity domain of σ, structural characterization of the Mo-Ni-Re σ with particular emphasis on determination of site occupancy trends as a function of composition was carried out by combined Rietveld refinement of the X-ray and neutron diffraction data. The experimental results gathered during the present study along with the information available in the literature were used as input for thermodynamic modeling of the Mo-Ni-Re system. The thermodynamic description of the Mo-Re system was taken from literature whereas thermodynamic modeling of the Mo-Ni, Ni-Re and Mo-Ni-Re system was carried out during the present study with the help of the CALHAD method.Keywords: Mo-Ni; Mo-Re; Ni-Re; Mo-Ni-Re; phase diagram; isothermal section; structural characterization; thermodynamic modeling; CALPHAD method