O principal programa de pesquisa do Grupo de Diagrama de Fases e Termodinâmica Computacional do LOM/EEL-USP é o estudo de estabilidade de fases em ligas dos sistemas MR-Si-B (MR = Metal Refratário), os quais apresentam um interesse crescente na área de ligas com potencial para aplicações em altas temperaturas. Destes estudos, este Grupo está construindo uma base de informações termodinâmicas com a finalidade de extrapolá-las para sistemas de ordem superior. Diversos sistemas já foram ou estão sendo estudados. Dando continuidade a este programa, os objetivos principais deste trabalho são a avaliação experimental de pontos críticos do sistema Cr-Si-B na região rica em Cr e a modelagem termodinâmica completa do sistema. Foram utilizadas informações da projeção liquidus de Chad (2008) e realizadas medidas experimentais para a determinação das composições das fases em diversas relações de equilíbrio a 1200 ºC, ambas na região rica em Cr. As amostras foram produzidas por fusão em forno a arco, a partir de pedaços de Cr, Si e B de alta pureza; tratadas termicamente a 1200oC por 200 horas e caracterizadas via difração de raios X e MEV/Microssonda eletrônica. Nessa condição de preparação das amostras, não houve dificuldade em se alcançar o equilíbrio termodinâmico. De uma forma geral, as relações de fases a 1200oC de Chad (2008) são confirmadas no presente trabalho. Não foi verificada através de medida por análise térmica diferencial até a temperatura de 1550oC a transformação polimórfica ?Cr5Si3 _ ?Cr5Si3, que segundo Chang (1968) ocorre a 1505oC. Nenhuma modelagem termodinâmica para este sistema ternário é encontrada na literatura. Para a otimização do sistema ternário foram utilizados os coeficientes de Coughanowr, Ansara e Lukas (1998) para o binário Cr-Si; os coeficientes de Campbell e Kattner (2002) para o binário Cr-B e os coeficientes de Fries e Lukas (1998) para o binário Si-B. Foram usados dois modelos para as fases T1 e T2 para descrever suas solubilidades de B e Si, respectivamente. O modelo adotado para a fase ?Cr5Si3 (T1) foi o de solução com três sub-redes (Cr)4(Cr)1(Si,B)3 e o modelo adotado para a fase Cr5B3 (T2) foi o de solução com três sub-redes (Cr)5(B,Si)2(B)1. Estes dois modelos estão compatíveis com aqueles adotados para outros sistemas MR-Si e MR-Si-B. Para a fase CrSS (BCC_A2), o modelo escolhido para permitir a solubilidade de B e/ou Si foi o substitucional para o Si e o intersticial para o B, resultando em uma descrição com duas sub-redes (Cr,Si)1(B,Va)3. A adoção destes modelos compatíveis com otimizações já desenvolvidas e publicadas é importante para permitir o desenvolvimento de uma base de dados multicomponentes MRSi- B que possibilitará previsões confiáveis para as relações de fases em sistemas de ordem superior. A otimização atual reproduziu bem a seção isotérmica a 1200oC e a projeção liquidus do sistema Cr-Si-B na região rica em Cr. / Currently, the main research program of the Phase Diagram and Computational Thermodynamics Group of LOM/EEL-USP is the study of phase stability in MR-Si- B ternary systems (MR = Refractory Metal), which presents an increasing interest in the area of alloys with potential for applications at high temperatures. These research activities include the development of a thermodynamic database to evaluate systems of higher order. Several systems have already been studied. In a continuation of this program, the main objectives of this work are the experimental evaluation of the Cr-Si-B ternary system in the Cr-rich region and the thermodynamic modeling of the complete system. Experimental data from the liquidus projection of Chad (2008) were used and experimental measurements were performed to determine the compositions of various phases in equilibrium at 1200°C, both in the Cr-rich region. The samples were produced by arcmelting high-purity pieces of Cr, Si and B, followed by heat treatment at 1200oC for 200 hours. The samples were characterized by X-ray diffraction and SEM/WDS microanalysis. With this preparation procedure, no difficulty was found to bring the samples to the thermodynamic equilibrium condition. In general, the phase relations at 1200oC proposed by Chad (2008) were confirmed in this study. The polymorphic transformation ?Cr5Si3 _ ?Cr5Si3, which according to Chang (1968) occurs at 1505oC, has not been verified by differential thermal analysis experiments performed until 1550oC. No thermodynamic modeling for this ternary system was found in the literature. The binary coefficients of Coughanowr, Ansara and Lukas (1998) for the Cr-Si, Campbell and Kattner (2002) for the Cr-B and Fries and Lukas (1998) for the Si-B were used in the optimization of the ternary system. Two models for T1 and T2 phases were used to describe their B and Si solubilities, respectively. The model adopted for ?Cr5Si3 (T1) was the solution with three sublattices (Cr)4(Cr)1(Si,B)3 and for Cr5B3 (T2) was the solution with three sublattices (Cr)5(B,Si)2(B)1. These two models were consistent with those adopted in other RM-Si and RM-Si-B systems. For the phase CrSS, the substitutional and interstitial models were used to describe the solubility of Si and B in the BCC structure, respectively, resulting in a solution with two sublattices (Cr,Si)1(B,Va)3. These models are compatible with other previously published optimizations. This is important to enable the development of a multicomponent MR-Si-B database, which will enable reliable predictions for the phase relations in higher-order systems. The Cr-rich region of the isothermal section at 1200oC and of the liquidus projection are well reproduced by the coefficients of the present optimization.

Computer simulations of the growth of binary alloy thin films in two and three dimensions were performed using an extension of the Solid on Solid model. Snapshots for a range of interactions and diffusion rates are presented and critically compared to experiment. A wide variety of distinct phases is identified and their growth conditions analyzed. These findings are summarized in a phase diagram. In addition, a fractal analysis of the domains is performed. It is found that for negative interactions the islands are two-dimensional, while for positive interactions, regardless of diffusion rate, a fractal dimension of 1.78 is obtained. / by Mark R. Bouwens. / Thesis (Ph.D.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

O principal programa de pesquisa do Grupo de Diagrama de Fases e Termodinâmica Computacional do LOM/EEL-USP é o estudo de estabilidade de fases em ligas dos sistemas MR-Si-B (MR = Metal Refratário), os quais apresentam um interesse crescente na área de ligas com potencial para aplicações em altas temperaturas. Destes estudos, este Grupo está construindo uma base de informações termodinâmicas com a finalidade de extrapolá-las para sistemas de ordem superior. Diversos sistemas já foram ou estão sendo estudados. Dando continuidade a este programa, os objetivos principais deste trabalho são a avaliação experimental de pontos críticos do sistema Cr-Si-B na região rica em Cr e a modelagem termodinâmica completa do sistema. Foram utilizadas informações da projeção liquidus de Chad (2008) e realizadas medidas experimentais para a determinação das composições das fases em diversas relações de equilíbrio a 1200 ºC, ambas na região rica em Cr. As amostras foram produzidas por fusão em forno a arco, a partir de pedaços de Cr, Si e B de alta pureza; tratadas termicamente a 1200oC por 200 horas e caracterizadas via difração de raios X e MEV/Microssonda eletrônica. Nessa condição de preparação das amostras, não houve dificuldade em se alcançar o equilíbrio termodinâmico. De uma forma geral, as relações de fases a 1200oC de Chad (2008) são confirmadas no presente trabalho. Não foi verificada através de medida por análise térmica diferencial até a temperatura de 1550oC a transformação polimórfica ?Cr5Si3 _ ?Cr5Si3, que segundo Chang (1968) ocorre a 1505oC. Nenhuma modelagem termodinâmica para este sistema ternário é encontrada na literatura. Para a otimização do sistema ternário foram utilizados os coeficientes de Coughanowr, Ansara e Lukas (1998) para o binário Cr-Si; os coeficientes de Campbell e Kattner (2002) para o binário Cr-B e os coeficientes de Fries e Lukas (1998) para o binário Si-B. Foram usados dois modelos para as fases T1 e T2 para descrever suas solubilidades de B e Si, respectivamente. O modelo adotado para a fase ?Cr5Si3 (T1) foi o de solução com três sub-redes (Cr)4(Cr)1(Si,B)3 e o modelo adotado para a fase Cr5B3 (T2) foi o de solução com três sub-redes (Cr)5(B,Si)2(B)1. Estes dois modelos estão compatíveis com aqueles adotados para outros sistemas MR-Si e MR-Si-B. Para a fase CrSS (BCC_A2), o modelo escolhido para permitir a solubilidade de B e/ou Si foi o substitucional para o Si e o intersticial para o B, resultando em uma descrição com duas sub-redes (Cr,Si)1(B,Va)3. A adoção destes modelos compatíveis com otimizações já desenvolvidas e publicadas é importante para permitir o desenvolvimento de uma base de dados multicomponentes MRSi- B que possibilitará previsões confiáveis para as relações de fases em sistemas de ordem superior. A otimização atual reproduziu bem a seção isotérmica a 1200oC e a projeção liquidus do sistema Cr-Si-B na região rica em Cr. / Currently, the main research program of the Phase Diagram and Computational Thermodynamics Group of LOM/EEL-USP is the study of phase stability in MR-Si- B ternary systems (MR = Refractory Metal), which presents an increasing interest in the area of alloys with potential for applications at high temperatures. These research activities include the development of a thermodynamic database to evaluate systems of higher order. Several systems have already been studied. In a continuation of this program, the main objectives of this work are the experimental evaluation of the Cr-Si-B ternary system in the Cr-rich region and the thermodynamic modeling of the complete system. Experimental data from the liquidus projection of Chad (2008) were used and experimental measurements were performed to determine the compositions of various phases in equilibrium at 1200°C, both in the Cr-rich region. The samples were produced by arcmelting high-purity pieces of Cr, Si and B, followed by heat treatment at 1200oC for 200 hours. The samples were characterized by X-ray diffraction and SEM/WDS microanalysis. With this preparation procedure, no difficulty was found to bring the samples to the thermodynamic equilibrium condition. In general, the phase relations at 1200oC proposed by Chad (2008) were confirmed in this study. The polymorphic transformation ?Cr5Si3 _ ?Cr5Si3, which according to Chang (1968) occurs at 1505oC, has not been verified by differential thermal analysis experiments performed until 1550oC. No thermodynamic modeling for this ternary system was found in the literature. The binary coefficients of Coughanowr, Ansara and Lukas (1998) for the Cr-Si, Campbell and Kattner (2002) for the Cr-B and Fries and Lukas (1998) for the Si-B were used in the optimization of the ternary system. Two models for T1 and T2 phases were used to describe their B and Si solubilities, respectively. The model adopted for ?Cr5Si3 (T1) was the solution with three sublattices (Cr)4(Cr)1(Si,B)3 and for Cr5B3 (T2) was the solution with three sublattices (Cr)5(B,Si)2(B)1. These two models were consistent with those adopted in other RM-Si and RM-Si-B systems. For the phase CrSS, the substitutional and interstitial models were used to describe the solubility of Si and B in the BCC structure, respectively, resulting in a solution with two sublattices (Cr,Si)1(B,Va)3. These models are compatible with other previously published optimizations. This is important to enable the development of a multicomponent MR-Si-B database, which will enable reliable predictions for the phase relations in higher-order systems. The Cr-rich region of the isothermal section at 1200oC and of the liquidus projection are well reproduced by the coefficients of the present optimization.

Neste trabalho, realizou-se o estudo que permitiu a otimização termodinâmica das seções binárias pertencentes ao diagrama de fase ternário do sistema LiF-GdF3-LuF3, para tanto o programa FactSage foi empregado na simulação computacional. Assim, o comportamento de fusão das misturas destes compostos foi elucidado, o que representa uma contribuição inovadora para o conhecimento das propriedades físicas e químicas destes materiais. Em particular, determinou-se a faixa de composições nas quais as soluções sólidas de LiGdxLu1-xF4 e GdxLu1-xF3 podem ser obtidas diretamente da fase líquida. Neste trabalho as três secções binárias, LiF-GdF3, LiF-LuF3 e GdF3-LuF3 foram reavaliadas experimentalmente utilizando a calorimetria exploratória diferencial para a obtenção de dados mais precisos de temperatura versus composição, uma vez que foi possível minimizar a contaminação das amostras com compostos de oxigênio. A capacidade calorífica e outros dados calorimétricos foram também determinados experimentalmente e comparados com os existentes na literatura. Os termos da energia livre de Gibbs de excesso para as fases representadas como soluções, os quais descrevem os efeitos de interação não ideal entre os dois fluoretos nestas fases, foram expressos com sucesso pela modelo polinomial Redlich-Kister. Finalmente, o caminho de solidificação no diagrama de fase ternário LiF-GdF3-LuF3 pôde ser extrapolado de acordo com o formalismo de Kohler-Toop. Assim, pela primeira vez, a interação ternária entre os compostos LiF, GdF3 e LuF3 foi determinada. / In this work, it was carried out the study that allowed the thermodynamic optimization of the binary sections belonging to the ternary phase diagram of the LiF-GdF3-LuF3 system, for this purpose the FactSage software was used in the computational simulation. Thus, the melting behavior of the mixture of these compounds has been elucidated, which represents an innovative contribution to the knowledge of the physical and chemical properties of these materials. In particular, it was determined the composition ranges in which the solid solutions of LiGdxLu1-xF4 and GdxLu1-xF3 can be obtained directly from the liquid phase. In this work the three binary sections, LiF-GdF3, LiF-LuF3 and GdF3-LuF3, were evaluated using differential scanning calorimetry to obtain more accurate data of temperature versus composition, since it was possible to minimize the contamination of the samples due to oxygen compounds. The heat capacity and other calorimetric data were experimentally determined and compared with those cited in the literature. The terms of the Gibbs free excess energy for the solution phases, which describe the non ideal interaction effects between the two fluorides at these phases, were expressed by the Redlich-Kister polynomial model. Finally, the solidification path in the ternary phase diagram LiF-GdF3-LuF3 could be extrapolated according to the Kohler-Toop formalism. Thus, for the first time, the interaction between the ternary compounds LiF, GdF3 and LuF3 was determined.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by David Malcolm Kundrat. / Sc.D.

L’obtention de substrats „cyto-favorables”, aptes à soutenir la régénération tissulaire, impose l’utilisation de biomatériaux qui portent des domaines de reconnaissance cellulaire, comme par exemple les scléroprotéines et certains polysaccharides. La membrane des cellules spécifiques aux tissus conjonctifs dispose de mécanismes qui facilitent l’ancrage aux substrats solides ou à l’état de gel où se retrouvent des macromolécules ou des fibrilles de (atelo) collagène, associées ou non à l’acide hyaluronique. On peut générer de tels substrats par des techniques de rassemblement moléculaire spontané ordonné (tout comme dans le cas de la restructuration du collagène quasi-natif pour former des fibrilles), ou induite physico-chimiquement ensuite stabilisé morphologiquement (tout comme dans le cas de la préparation des hydrogels mixtes, atelocollagène–hyaluronate de sodium, diversement réticulés ensuite transformés en cryo- ou vitri-gels). Dans le cadre de la thèse, nous étudions les moyens d’obtention et de purification des précurseurs bio-macromoléculaires nécessaires, par la suite, à l’obtention de substrats „cyto-favorables”, ainsi que leurs modalités de génération et de caractérisation. Les méthodes de restructuration auxquelles on en appelle sont de nature physico-chimique (la co-précipitation contrôlée dans des mélanges binaires et ternaires d’atelocollagène et d’hyaluronate de sodium), ou chimique (la réticulation par des ponts moléculaires à longueur minimale). On a étudié les possibilités de mélanger de l’atelocollagène (aK) avec deux types de polysaccharides, le hyaluronate de sodium (NaHyal) et le gellane. On a établi des formulations et les procédures optimales pour obtenir des hydrogels avec des caractéristiques rhéologiques contrôlables, et avec la réactivité et la morphologie capables de permettre la fixation et la prolifération des fibroblastes. On constate que les hydrogels et cryogels obtenus à partir des mélanges 5:1 aK:NaHyal réticulés avec du 1,4-butanediol diglycidyl éther ont des propriétés rhéologiques qui permettent leurs manipulation dans les conditions des techniques de culture cellulaire. Ils ne présentent pas de cytotoxicité et ils assurent la viabilité cellulaire dans les milieux de culture standards. La morphologie des cryogels obtenus montre une macro-porosité qui dépend de la formulation des mélanges et peu la technique d'obtention. La présence de gellane dans les mélanges conduit à une séparation de phases, même à faible concentration, soulignant la diversité des caractéristiques de substrats. / Obtaining "cyto-favourable" substrates able to support tissue regeneration leads to use biomaterials holding cellular recognition domains, as scleroproteins and some polysaccharides as examples. Cellules membranes specific to conjunctive tissues have mechanisms making easier the anchoring to solid or gel substrates where macromolecules or fibrils of (aceto)collagen, associated or not to hyaluronic acid, are found. Such substrates may be generated using spontaneous molecular gathering (as in native collagen restructuration to fibrils), or physico-chemically induced (as the preparation of mixed hydrogels then transformed in cryo- or vitri-gels). In this thesis, were studied the obtaining and purification of bio-macromolecular presursors necessary to obtaining "cyto-favourable" substrates, and the procedures to generate and characterize them. Used restructuration methods are of physico-chemical nature (controlled co-precipitation in binary and ternary mixtures of acetocollagen and sodium hyaluronate) or chemical one (crosslinking).The mixture of acetocolagen (aK) with two polysaccharides, sodium hyaluronate (NaHyal) and gellan were investigated. Formulations and optimal conditions were established to obtain hydrogels with controlled rheological characteristics, and reactivity and morphology able to allow fibroplast fixation and proliferation. Hydrogels and cryogels prepared from 5:1 aK:NaHyal crosslinked with 1,4-butanediol diglycidyl ether were defined as the best materials we have prepared. They do not show any cytotoxicity and they ensure the cellular viability within standard cellule culture media. The cryogel morphology shows macro-porosity depending on the formulation but a few on the obtaining process. The presence of gellan in the mixtures leads to a phase separation, even at low concentration.

Neste trabalho, realizou-se o estudo que permitiu a otimização termodinâmica das seções binárias pertencentes ao diagrama de fase ternário do sistema LiF-GdF3-LuF3, para tanto o programa FactSage foi empregado na simulação computacional. Assim, o comportamento de fusão das misturas destes compostos foi elucidado, o que representa uma contribuição inovadora para o conhecimento das propriedades físicas e químicas destes materiais. Em particular, determinou-se a faixa de composições nas quais as soluções sólidas de LiGdxLu1-xF4 e GdxLu1-xF3 podem ser obtidas diretamente da fase líquida. Neste trabalho as três secções binárias, LiF-GdF3, LiF-LuF3 e GdF3-LuF3 foram reavaliadas experimentalmente utilizando a calorimetria exploratória diferencial para a obtenção de dados mais precisos de temperatura versus composição, uma vez que foi possível minimizar a contaminação das amostras com compostos de oxigênio. A capacidade calorífica e outros dados calorimétricos foram também determinados experimentalmente e comparados com os existentes na literatura. Os termos da energia livre de Gibbs de excesso para as fases representadas como soluções, os quais descrevem os efeitos de interação não ideal entre os dois fluoretos nestas fases, foram expressos com sucesso pela modelo polinomial Redlich-Kister. Finalmente, o caminho de solidificação no diagrama de fase ternário LiF-GdF3-LuF3 pôde ser extrapolado de acordo com o formalismo de Kohler-Toop. Assim, pela primeira vez, a interação ternária entre os compostos LiF, GdF3 e LuF3 foi determinada. / In this work, it was carried out the study that allowed the thermodynamic optimization of the binary sections belonging to the ternary phase diagram of the LiF-GdF3-LuF3 system, for this purpose the FactSage software was used in the computational simulation. Thus, the melting behavior of the mixture of these compounds has been elucidated, which represents an innovative contribution to the knowledge of the physical and chemical properties of these materials. In particular, it was determined the composition ranges in which the solid solutions of LiGdxLu1-xF4 and GdxLu1-xF3 can be obtained directly from the liquid phase. In this work the three binary sections, LiF-GdF3, LiF-LuF3 and GdF3-LuF3, were evaluated using differential scanning calorimetry to obtain more accurate data of temperature versus composition, since it was possible to minimize the contamination of the samples due to oxygen compounds. The heat capacity and other calorimetric data were experimentally determined and compared with those cited in the literature. The terms of the Gibbs free excess energy for the solution phases, which describe the non ideal interaction effects between the two fluorides at these phases, were expressed by the Redlich-Kister polynomial model. Finally, the solidification path in the ternary phase diagram LiF-GdF3-LuF3 could be extrapolated according to the Kohler-Toop formalism. Thus, for the first time, the interaction between the ternary compounds LiF, GdF3 and LuF3 was determined.

Neste trabalho estudamos o efeito da temperatura T e do campo magnético externo H sobre o modelo de Ising de spin 1/2 com interações competitivas J1 e J2 = -pJ1 entre primeiros e segundos vizinhos, respectivamente, numa direção axial (modelo ANNNI), e o efeito do campo de anisotropia cristalina D sobre o estado fundamental de um modelo ANNNI de spin maior que 1/2. No primeiro modelo levantamos os diagramas de fases p-T e H-T na aproximação de campo médio. Nestes diagramas encontramos diversos tipos de transições de fases tais como transições quase-contínuas e transições singular-contínuas. Encontramos também evidências da existência de pontos ípsilon () e pontos superdegenerados até então só encontrados nos diagramas de fases do estado fundamental de modelos do tipo Frenkel-Kontorova. No segundo modelo levantamos os diagramas p-D a T=0 para os dez primeiros valores de spin S. Estudamos a evolução das fronteiras de fases e de pontos de encontro de mais que duas fases sobre estas fronteiras conforme S é variado. Constatamos que as diferenças entre diagramas com S inteiro e diagramas com S semi-inteiro tendem a desaparecer com o crescimento de S. / In this work we studied the effect of the temperature T and external magnetic field H on the spin 1/2 lsing model with competing interactions J1 and J2 = -pJ1 between the first- and second-neighbors, respectively, along an axial direction (ANNNl model), and the effect of the crystal field anisotropy D on the ground state of the ANNNl model with spins greater than 1/2. In the first model we built the p-T and H-T phase diagrams in the mean-field approximation. In these phase diagrams we found various types of phase transitions such as quasi-continuous and singular-continuous phase transitions. We also found evidences for the upsilon point (1) and superdegenerate points, which have previously been found only on the groundstate phase diagrams of Frenkel-I<ontorova type models.

Expansive soils are treated with anhydrous or hydrated lime. The use of calcium-based stabilizers such as calcium oxide (lime) in sulfate-bearing clay soils has historically led to distress due to the formation of an expansive mineral called ettringite and possibly another such mineral, thaumasite. Predicting the precipitation of these minerals is a complex problem related not only to soil composition but also construction methods, availability of water, ion migration, and whether the expansive mineral growth can be accommodated by the void structure in the surrounding soil. In trying to control the damage associated with such occurrences, engineers have attempted to determine a threshold value of soluble sulfates, a quantity that is relatively easy and quick to measure, at which significant ettringite growth and, therefore, structural distress occurs. Unfortunately, experience alone and “rules-of-thumb” based on experience are not sufficient to deal with this complex issue. This thesis describes how thermodynamic geochemical models of lime-treated soil can be used as a first step toward establishing problematic threshold levels of soluble sulfates for a specific soil. A foundation for the model development is presented, and two different soils are compared to illustrate their very different sensitivities to ettringite growth upon the addition of hydrated lime. Various soil series along the route of SH 130 between Austin and San Antonio have been identified to contain soluble sulfate that may pose a problem for soil stabilization using lime and cement. Since the model predicts ettringite growth based upon site-specific properties, this thesis also shows how the model can be used to assess the potential amelioration effects of soluble silica. Research was conducted at the Texas Transportation Institute to develop a methodology for identifying areas which are susceptible for ettringite formation. The proposed methodology uses a magnetometer to quickly screen large areas for high sulfate. Application of GIS to identify ettringite formation using soils, topographical, and geological maps is also illustrated in this thesis.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (p. [148]-178).