The implementation of energy storage systems in the current electrical grid will increase the grid's reliability and e ciency. Room temperature sodium batteries are seen as potential technology, especially to assist renewable energy generation sources. Currently, suggested negative electrode materials, however, are still not satisfactory for practical use in terms of fabrication costs, gravimetric /volumetric energy densities, cyclability, and irreversible capacity losses occur at the rst cycle. The literature describes various strategies that enhance the specific capacity and/or the cyclability of negative electrode materials but all involve increasing the fabrication costs due to the chosen synthesis or the complexity of the electrode's design. Furthermore, strategies, that reduce the irreversible capacity loss at first cycle, are not discussed. In this present experimental research work, presodiating bulk metallic negative electrode materials prior to cycling, prepared via a simple, cheap and easy-to-scaleup synthesis route, is introduced as a new strategy to improve the cyclability and to effectively reduce the first cycle irreversible capacity loss. Electrochemical and structural experiments were carried out to investigate sodiumtin-antimony powders. Presodiating mechanically bulk Sn-Sb negative electrode materials e ectively reduces the irreversible capacity loss at first cycle and enhances the specific capacity when compared to the non-presodiated powder, while the proper choice of electrode composite and electrolyte formulation improves the cycle life of the electrodes. The enhancement of the electrochemical properties of the presodiated NaSnSb powder, composed of the ternary phase Na5Sb3Sn and an unknown ternary phase crystallising in a hexagonal setting P6, is associated with the stabilisation of the SnSb as desodiation product. Presodiating bulk SnSb negative electrode material is a viable strategy to reduce the first cycle irreversible capacity loss, alleviating the volume changes. With an optimised system, this approach may be extended to other negative electrode materials, reducing the fabrication costs of high capacity negative electrode materials for room temperature sodium batteries. Presodiated NaSnSb negative electrode material may be combined with non-sodiated positive electrode material, such as sulphur to develop competitive room temperature sodium-sulphur batteries. / Die Implementierung von Energiespeichersystemen im bereits bestehenden Stromnetz ist eine der Lösungen, um die Zuverlässigkeit und die Effizienz des Netzes zu nutzen. Raumtemperatur Natrium-Batterien gelten als erfolgsversprechende Technologie insbesondere zur Unterstützung erneuerbarer Energieerzeugungsquellen. Jedoch sind die naheliegenden negativen Elektrodenmaterialien für eine praktische Anwendung hinsichtlich Herstellungskosten, gravimetrischer oder volumetrischer Energiedichte, Zyklenfestigkeit und irreversiblen Kapazitätsverlusten im ersten Zyklus noch nicht zufriedenstellend. Die Literatur beschreibt verschiedene Strategien, die die spezifische Kapazität und / oder die Zyklenfestigkeit von negativen Elektrodenmaterialien verbessern. Diese führen jedoch alle zu einer Erhöhung der Herstellungskosten aufgrund der gewählten Synthese oder des Designs der komplexierten Elektrode. Darüber hinaus werden Strategien zur Reduzierung des irreversiblen Kapazitätsverlusts im ersten Zyklus nicht erörtert. Diese experimentelle Forschungsarbeit präsentiert mit Natrium angereicherte metallische negative Elektrodenmaterialien vor der Wechselbeanspruchung/dem periodischen Durchlaufen, die durch einen schlichten, billigen und einfach zu skalierenden Syntheseweg hergestellt wurden, als eine neue Strategie zur Verbesserung der Zyklenfestigkeit und zur wirksamen Verringerung des irreversiblen Kapazitätsverlusts im ersten Zyklus. Elektrochemische und strukturelle Experimente wurden durchgeführt, um mit Natrium angereichertes Zinn-Antimon-Pulver zu untersuchen. Die mechanischen mit Natrium angereichertes Sn-Sb-negativen Elektrodenmaterialien verringert effektiv den irreversiblen Kapazitätsverlust im ersten Zyklus und erhöht die spezische Kapazität im Vergleich zu dem ohne Natrium angereicherte Pulver, während die richtige Wahl der Elektrodenzusammensetzung und der Elektrolytformulierung die Lebenszyklus der Elektroden verbessert. Die Verbesserung der elektrochemischen Eigenschaften des mit Natrium angereicherten NaSnSb-Pulvers, bestehend aus der ternären Phase Na5Sb3Sn und einer unbekannten ternären Phase, die in einer hexagonalen Aufbau P6 kristallisiert, ist mit der Stabilisierung des Enddesodiationsproduktes beim periodischen Zyklus verbunden, wobei das intermetallische SnSb nach Rekristallisation vorliegt. Mit Natrium angereicherte SnSb negativen Elektrodenmaterialien sind eine tragfähige Strategie zur Verringerung des irreversiblen Kapazitätsverlustes im ersten Zyklus, die Volumenänderungen abschwächen. Mit einem optimierten System kann dieser Ansatz auf andere negative Elektrodenmaterialien erweitert werden um die Herstellungskosten von negativen Elektrodenmaterialien mit hoher Kapazität für Raumtemperatur-Natrium-Batterien zu verringern. Mit Natrium angereichertes NaSnSb-negatives Elektrodenmaterial kann mit nicht mit Natrium versetztem positivem Elektrodenmaterial wie Schwefel kombiniert werden, um realisierbare Raumtemperatur Natrium-Schwefel-Batterien zu entwickeln.

The implementation of energy storage systems in the current electrical grid will increase the grid's reliability and e ciency. Room temperature sodium batteries are seen as potential technology, especially to assist renewable energy generation sources. Currently, suggested negative electrode materials, however, are still not satisfactory for practical use in terms of fabrication costs, gravimetric /volumetric energy densities, cyclability, and irreversible capacity losses occur at the rst cycle. The literature describes various strategies that enhance the specific capacity and/or the cyclability of negative electrode materials but all involve increasing the fabrication costs due to the chosen synthesis or the complexity of the electrode's design. Furthermore, strategies, that reduce the irreversible capacity loss at first cycle, are not discussed. In this present experimental research work, presodiating bulk metallic negative electrode materials prior to cycling, prepared via a simple, cheap and easy-to-scaleup synthesis route, is introduced as a new strategy to improve the cyclability and to effectively reduce the first cycle irreversible capacity loss. Electrochemical and structural experiments were carried out to investigate sodiumtin-antimony powders. Presodiating mechanically bulk Sn-Sb negative electrode materials e ectively reduces the irreversible capacity loss at first cycle and enhances the specific capacity when compared to the non-presodiated powder, while the proper choice of electrode composite and electrolyte formulation improves the cycle life of the electrodes. The enhancement of the electrochemical properties of the presodiated NaSnSb powder, composed of the ternary phase Na5Sb3Sn and an unknown ternary phase crystallising in a hexagonal setting P6, is associated with the stabilisation of the SnSb as desodiation product. Presodiating bulk SnSb negative electrode material is a viable strategy to reduce the first cycle irreversible capacity loss, alleviating the volume changes. With an optimised system, this approach may be extended to other negative electrode materials, reducing the fabrication costs of high capacity negative electrode materials for room temperature sodium batteries. Presodiated NaSnSb negative electrode material may be combined with non-sodiated positive electrode material, such as sulphur to develop competitive room temperature sodium-sulphur batteries. / Die Implementierung von Energiespeichersystemen im bereits bestehenden Stromnetz ist eine der Lösungen, um die Zuverlässigkeit und die Effizienz des Netzes zu nutzen. Raumtemperatur Natrium-Batterien gelten als erfolgsversprechende Technologie insbesondere zur Unterstützung erneuerbarer Energieerzeugungsquellen. Jedoch sind die naheliegenden negativen Elektrodenmaterialien für eine praktische Anwendung hinsichtlich Herstellungskosten, gravimetrischer oder volumetrischer Energiedichte, Zyklenfestigkeit und irreversiblen Kapazitätsverlusten im ersten Zyklus noch nicht zufriedenstellend. Die Literatur beschreibt verschiedene Strategien, die die spezifische Kapazität und / oder die Zyklenfestigkeit von negativen Elektrodenmaterialien verbessern. Diese führen jedoch alle zu einer Erhöhung der Herstellungskosten aufgrund der gewählten Synthese oder des Designs der komplexierten Elektrode. Darüber hinaus werden Strategien zur Reduzierung des irreversiblen Kapazitätsverlusts im ersten Zyklus nicht erörtert. Diese experimentelle Forschungsarbeit präsentiert mit Natrium angereicherte metallische negative Elektrodenmaterialien vor der Wechselbeanspruchung/dem periodischen Durchlaufen, die durch einen schlichten, billigen und einfach zu skalierenden Syntheseweg hergestellt wurden, als eine neue Strategie zur Verbesserung der Zyklenfestigkeit und zur wirksamen Verringerung des irreversiblen Kapazitätsverlusts im ersten Zyklus. Elektrochemische und strukturelle Experimente wurden durchgeführt, um mit Natrium angereichertes Zinn-Antimon-Pulver zu untersuchen. Die mechanischen mit Natrium angereichertes Sn-Sb-negativen Elektrodenmaterialien verringert effektiv den irreversiblen Kapazitätsverlust im ersten Zyklus und erhöht die spezische Kapazität im Vergleich zu dem ohne Natrium angereicherte Pulver, während die richtige Wahl der Elektrodenzusammensetzung und der Elektrolytformulierung die Lebenszyklus der Elektroden verbessert. Die Verbesserung der elektrochemischen Eigenschaften des mit Natrium angereicherten NaSnSb-Pulvers, bestehend aus der ternären Phase Na5Sb3Sn und einer unbekannten ternären Phase, die in einer hexagonalen Aufbau P6 kristallisiert, ist mit der Stabilisierung des Enddesodiationsproduktes beim periodischen Zyklus verbunden, wobei das intermetallische SnSb nach Rekristallisation vorliegt. Mit Natrium angereicherte SnSb negativen Elektrodenmaterialien sind eine tragfähige Strategie zur Verringerung des irreversiblen Kapazitätsverlustes im ersten Zyklus, die Volumenänderungen abschwächen. Mit einem optimierten System kann dieser Ansatz auf andere negative Elektrodenmaterialien erweitert werden um die Herstellungskosten von negativen Elektrodenmaterialien mit hoher Kapazität für Raumtemperatur-Natrium-Batterien zu verringern. Mit Natrium angereichertes NaSnSb-negatives Elektrodenmaterial kann mit nicht mit Natrium versetztem positivem Elektrodenmaterial wie Schwefel kombiniert werden, um realisierbare Raumtemperatur Natrium-Schwefel-Batterien zu entwickeln.

Die vorliegende Arbeit liefert einen Beitrag zum Verständnis der komplexen Wechselwirkungen zwischen Nanopartikeln und Polymeren in dünnen Schichtsystemen. Dazu wurden in einem geeignetem Modellsystem drei verschiedene Einflussparameter auf die Nanopartikelverteilung im Polymer und zwischen einer hydrophilen und einer hydrophoben Grenzfläche analysiert. Für eine erste Abschätzung der Verträglichkeit der einzelnen Komponenten wurden Wechselwirkungsparameter, binäre und ternäre Phasendiagramme ermittelt. Die experimentelle Charakterisierung der Nanopartikelverteilung erfolgte mittels Rasterkraftmikroskopie, Rasterelektronenmikroskopie und Transmissionselektronenmikroskopie. Die erhaltenen Ergebnisse wurden mit denen der theoretischen Vorbetrachtungen verglichen um herauszufinden, ob Vorhersagen zur Nanopartikelverteilung in einem Polymer möglich sind. In dieser Arbeit konnte gezeigt werden, dass die Nanopartikelverteilung im Polymer mit den untersuchten Parametern gezielt beeinflusst werden kann.

No description available.

The work presented has the ultimate aim to increase dynamic mechanical properties by improvements in density and optimisation of microstructure of ultra high carbon PM steels by careful selection of processes, i.e. mixing, binding, alloying, heating profile and intelligent heat treatment. ThermoCalc modelling was employed to predict liquid phase amounts for two different powder grades, Astaloy 85Mo or Astaloy CrL with additive elements such as (0.4-0.6wt%)Si, (1.2-1.4wt%)C and (1-1.5wt%)Mn, in the sintering temperature range 1285-1300ºC and such powder mixes were pressed and liquid phase sintered. In high-C steels carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat-treated. To assist the breaking up of these continuous carbide networks, 0.4-0.6% silicon, in the form of silicon carbide, was added. The water gas shift reaction (C + H2O = CO + H2, start from ~500ºC) and Boudouard reaction (from ~500ºC complete ~930ºC) form CO gas in the early part of sintering and can lead to large porosity, which lowers mechanical properties. With the use of careful powder drying, low dew point atmospheres and optimisation of heating profiles, densities in excess of 7.70g/cm3 were attained. The brittle microstructure, containing carbide networks and free of cracks, is transformed by intelligent heat treatment to a tougher one of ferrite plus sub-micron spheroidised carbides. This gives the potential for production of components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains of up to 16 % were attained. Forging experiments were subsequently carried out for spheroidised specimens of Fe-0.85Mo+06Si+1.4C, for different strain rates of 10-3, 10-2, 10-1 and 1sec-1 and heated in argon to 700ºC, density ~7.8g/cm3 and 769 MPa yield strength were obtained.

La connaissance des propriétés thermodynamiques et des diagrammes de phases des composés fluorés est indispensable pour le dimensionnement et l'optimisation des systèmes thermodynamiques. Les applications sont nombreuses : réfrigération, récupération de chaleur (ORC), pompe à chaleur, climatisation automobile. Du fait des contraintes environnementales (la F-gaz pour l'UE) liées au fait que les fluides actuellement utilisés doivent être inoffensifs vis-à-vis de la couche d'ozone mais aussi posséder un pouvoir de réchauffement climatique bas (GWP CO2=1, valeur de référence), les chimistes doivent développer de nouvelles molécules qui répondent à ce nouveau cahier des charges. Actuellement, ils ont mis au point des fluides de la famille des HFO dont le plus célèbre est le HFO1234yf. Son GWP est faible (4) tout comme celui de ses principaux isomères, le HFO1234ze et le HFO1234zd. Si le fluide pur ne convient, des mélanges (blends) doivent être élaborés. Si le fluide pur ne convient pas pour les applications souhaitées, des mélanges doivent être élaborés.L'objectif de cette thèse est d'étudier plusieurs HFOs en corps purs et en mélanges et de développer/comparer des modèles thermodynamiques permettant de prédire les diagrammes de phases et les densités de ces fluides. Ces modèles doivent pouvoir être transposables vers l'industrie. Le CTP dispose de plusieurs équipements permettant d'acquérir des données expérimentales. Le densimètre à tube vibrant sera utilisé pour acquérir des données de masse volumique, et une cellule d'équilibre entre phase (technique statique-analytique) pour acquérir des données d'équilibre liquide vapeur. Les équations d'état cubiques seront utilisées pour le traitement des données. Une nouvelle équation d'état plus précise pour la prédiction des masses volumiques sera présentée. Une comparaison en termes de description des diagrammes de phases et des propriétés volumétriques sera également effectuée. / The knowledge of the thermodynamic properties and phase diagrams of fluorinated compounds is essential for the design and optimization of thermodynamic systems. There are many applications: refrigeration, organic Rankine cycle (ORC), heat pump, and air conditioning systems. Due to the environmental constraints (F-gaz for the EU) related to the fact that the fluids being used must be harmless to the ozone layer, but also with a low global warming potential (GWP CO2 = 1 reference value), the chemists must develop new molecules responding to these constraints. Today, they have developed fluids called HFOs whose most famous is the HFO1234yf, with a low GWP (4), along with his isomers HFO1234ze and HFO1234zd. If the pure fluid is not suitable for the applications, blends should be developed instead. The objective of these theses is to study several HFOs, in pure compounds and mixtures and develop / compare thermodynamic models in order to predict the phase diagram and density of these fluids. These models should be transferable to industry. The CTP has several equipments to acquire experimental data. The vibrating-tube densimeter will be used to acquire density data, and equilibrium cell (static-analytic method) to acquire liquid-vapor equilibrium data. The cubic equations of state will be used for data treatment. A new equation of state more accurate for density prediction will be presented. A comparison in terms of phase diagrams and density prediction will be carried out.

Determinar o conteúdo dos lipídeos presentes nos tecidos animais nem sempre resulta em uma resposta com precisão, devido á pouca disponibilidade de métodos adequados para a extração e determinação quantitativa destes lipídeos. A extração de lipídeos de matrizes complexas, como o pescado, por meio dos métodos tradicionais de Bligh & Dyer e Folch normalmente utilizam solventes com elevada toxicidade, cujos resíduos podem gerar um elevado impacto ambiental. A chamada segurança química está diretamente ligada à qualidade de vida e alerta para as questões de controle e prevenção dos efeitos adversos dos solventes ao ser humano e ao ambiente, compreendendo desde a extração, uso e descarte desses e seus resíduos. Portanto, o objetivo deste trabalho foi estudar as condições de extração de lipídeos totais de resíduos do processamento de tilápias, visando à proposição de um método alternativo que garanta uma eficiência tão satisfatória quanto as obtidas pelos métodos tradicionais de extração. Ademais, foi desenvolvido um método de extração mais seguro ao ambiente utilizando solventes menos tóxicos que os propostos pelo método de Bligh &Dyer, por meio da aplicação experimental de um diagrama de fases hexano- etanol- água. Após a identificação da melhor combinação de solventes, os extratos obtidos com hexano- etanol apresentaram rendimento eficiente em lipídeos totais e capacidade de extrair os componentes lipídicos polares e apolares das amostras analisadas. O melhor aproveitamento dos lipídeos a serem extraídos da matriz resíduos de peixes na proporção em massa de solvente hexano: etanol: água, foram da solução 1 (1: 7: 1,375) para a carcaça, da solução 2 (1: 2,5: 1,1875) para a cabeça e da solução 4 (4: 1: 4,375) para as vísceras totalizando 14,13%, 14,69 e 47,63% de teor de lipídeos, respectivamente. Logo, ao buscar sistemas de solventes alternativos ao clorofórmio - metanol, para extrair lipídeos de resíduos do processamento de tilápias, foi possível identificar as melhores proporções de hexano: etanol: água como substituição do método tradicional proposto por Bligh & Dyer (1959). / The total lipid content of animal tissues is not always accurately measured due to the lack of adequate methods for lipid extraction and quantitative determination of tissue fat. The extraction of lipids from complex matrices, such as fish, using the traditional methods proposed by Bligh &Dyer and Folch usually, employs solvents with high toxicity, whose residues can generate a high environmental impact. The chemical safety concern nowadays is directly linked to quality of life involving control and prevention of adverse effects of solvents to humans and the environment, ranging from the extraction, use and disposal of these and their residues. Moreover, the procedures of sample preparation, the sample: solvent ratio, the proportion of solvents applied, and the order of addition of solvents during the experiment are not standardized in these methods. Therefore, the present study aimed to assess the extraction conditions of total lipids from fish processing residues, and thus propose a standardized method which ensures a maximum efficiency in lipid extraction. Furthermore, a more environmental-friendly oil extraction method using less toxic solvents than those proposed by the Bligh & Dyer method (i.e. using the hexane-ethanol-water phase diagram) was developed. After identifying the best combination of solvents, the extracts obtained with hexane- ethanol showed effective yield on total lipids and the ability to extract the polar lipid components and nonpolar of the samples. The best use of lipids to be extracted from fish waste matrix, were the solution 1 (1: 7: 1,375) for the carcass of solution 2 (1: 2,5: 1,1875) for the head and the solution 4 (4: 1: 4,375) for the viscera totaling 14,13%, 14,69% and 47,63%(4: 1: 4,375) respectively. Therefore, to seek alternative solvent systems chloroform - methanol to extract lipids of tilapia processing waste, it was possible to identify the best proportions of hexane: ethanol: water as replacing the traditional method proposed by Bligh & Dyer (1959).

Os métodos de primeiros princípios dentro da Teoria do Funcional Densidade têm se desenvolvido bastante, devido aos avanços computacionais ocorridos nas últimas décadas. Por outro lado, a Termodinâmica e a Mecânica Estatística têm representado um papel importante na compreenssão da Física de Materiais, em especial no estudo dos materiais intermetálicos ordenados. A aliança entre estas duas abordagens têm se tornado cada vez mais factível, uma vez que os cálculos de estrutura eletrônica de primeiros princípios são hoje capazes de proporcionar resultados extremamente precisos para energias de formação de compostos estequiométricos. É dentro deste contexto que neste trabalho investigamos o diagrama de fases composição-temperatura do sistema Fe-Al-Mo, na estrutura cúbica de corpo centrado utilizando o método Full-Potential Linear Augmented Plane Wave (FP-LAPW) aliado ao Método Variacional de Clusters (CVM) na aproximação do tetraedro irregular. Através do método FP-LAPW determinamos a energia total de configurações cristalinas do sistema Fe-Mo-Al cúbico de corpo centrado. Estes valores são utilizados como parâmetros de entrada do CVM para determinação do potencial termodinâmico do sistema em suas diferentes fases e os correspondentes equilíbrio entre estas fases em função da composição e da temperatura, ou seja, o diagrama de fases do sistema. Embora o Fe-Al tenha grande interesse tecnológico, o seu comportamento magnético é bastante complicado e normalmente mal descrito pelos métodos de cálculos usuais. Este trabalho procura enfrentar este problema com ferramentas \"estados de arte\" e apontam para as limitações inerentes ao procedimento geral aqui utilizado. / First-principles methods within the framework of Density Functional Theory, have been developed sufficiently, due to the computational advances occurrences in the last decades. On the other hand, the Thermodynamics and the Statistical Mechanics have represented an important role in the understanding of the Physics of Materials, in special in the study to ordered intermetallic compounds. The alliance between these two approaches has become each more feasible with the time due to the fact that electronic structure calculations of first principles are today to provide almost exact results for the formations energies of stoichiometric compounds. It is inside of this context that in this work we investigate the composition-temperature phases diagram of the Fe-Al-Mo system, in the body centered cubic structure (BCC), using the Full-Potential Liner Augmented Plane Wave (FP-LAPW) method allied to the Cluster Variation Method (CVM) in the irregular tetrahedron approximation. Through the FP-LAPW method we determined the total energy of crystalline configurations of BCC Fe-Mo-Al system. These values are used as input parameters of the CVM for the determination of the thermodynamic potential of the system in its different phases and corresponding to the equilibria between these phases as a function of the composition and the temperature, that is the phase diagram of the system. Although the Fe-Al has great technological interest, its magnetic behavior is complicated and badly described by the methods used in the actual ab-initio calculations. This work faces this problem with state-of-art tools and points to the inherent limitations of the general procedure used here.

Os motores a jato são componentes importantes e complexos de engenharia cuja eficiência e desempenho estão diretamente ligados à temperatura de operação na câmara de combustão, ou seja, quanto maior a temperatura dos gases nesta região, maior a eficiência global do processo, resultando em economia de combustível e maior potência. A superliga aeronáutica a base de níquel é o material atualmente utilizado nestes componentes mais críticos das turbinas, mas o seu desenvolvimento está chegando cada vez mais próximo do limite e, por isso, existe uma demanda de materiais que possam substituí-las. Os materiais constituídos de microestruturas multifásicas, como as ligas MR-Si-B (MR= Metal Refratário) apresentam potencial para a substituição das superligas nestas aplicações. Estudos recentes no sistema Ta-Si-B identificaram a existência de uma fase ainda não catalogada, denominada φ. No entanto, a sua estrutura cristalina permanece indefinida devido à dificuldade em se obter uma amostra com grande fração volumétrica de φ. A substituição do silício por germânio nesse sistema pode aumentar o campo de estabilidade de φ possibilitando assim, a obtenção de uma amostra através da qual a estrutura cristalina dessa fase possa ser determinada. Entretanto, para o estudo do ternário Ta-Ge-B, é importante o conhecimento dos binários que o compõem (Ta-Ge, Ta-B, Ge-B) e não foi encontrada na literatura uma proposta para o diagrama binário Ta-Ge nem informações suficientes para construí-lo. Este trabalho, portanto, tem como objetivo propor um diagrama de fases para o sistema Ta-Ge, e investigar a possível existência da fase φ no sistema ternário Ta-Ge-B. Para isto foram confeccionadas amostras, a partir de matérias primas (tântalo, germânio e boro) de alta pureza, em toda a extensão composicional do sistema Ta-Ge e na região rica em tântalo do sistema Ta-Ge-B. As amostras, em seu estado bruto de fusão bem como após tratamentos térmicos, foram caracterizadas por microscopia eletrônica de varredura (MEV), microanálise eletrônica por energia dispersiva (EDS) e difratometria de raios X (DRX). Com os resultados obtidos neste trabalho foi proposto um diagrama para o sistema Ta-Ge. A temperatura do eutético na região rica em Ta (2444°C) foi medida através de pirometria ótica. Devido a dificuldades encontradas em fundir a arco amostras com altos teores de Ge, novos experimentos serão necessários para melhor determinar esta região do diagrama de fases. Os resultados obtidos nas amostras ternárias sugerem que a fase ternária φ é estável no sistema Ta-Ge-B. / Jet engines are important and complex engineering devices, whose efficiency and performance are directly related to the operating temperature of the combustion chamber, the higher the gas temperature in this region, the greater the overall efficiency of the process, resulting in economy of fuel and more efficiency. Ni-based superalloys are currently used in the most critical jet engine components. Their development is coming close to a temperature limit and, therefore, there is a demand for new materials to replace them. Materials with multiphase microstructures, such as MR-Si-B alloys (MR = Refractory Metal), have a good potential for substituting superalloys in these applications. Recent studies in the Ta-Si-B system shows the stability of a phase φ whose crystal structure remains unknown due to the difficulty in obtaining a sample with large volume fraction of φ. The substitution of silicon by germanium in this system may increase the stability of φ, enabling the production of a sample by which the crystal structure of this phase can be determined. The study of the Ta-Ge-B ternary system requires the knowledge of the phase relations on its limiting binaries. However, there is no Ta-Ge phase diagram available in the literature, nor enough experimental information to propose one. Therefore, the present work aims at the experimental investigation of the phase relations on the Ta-Ge system, and of the stability of phase φ on the Ta-rich region of the Ta-Ge-B ternary system. Samples were prepared by arc melting high purity materials (tantalum, germanium and boron) under Ti-gettered argon. Their microstructures, in the as cast state as well as after heat treatments were characterized by scanning electron microscopy (SEM), energy dispersive electron probe microanalysis (EDS) and X-ray diffraction (XRD). A Ta-Ge binary phase diagram is proposed based on the results of the present work. The temperature of the Ta-rich eutetic (2444°C) was measured by optical pirometry. Due to the difficulty of arc melting samples with high Germanium contents, further investigation is still necessary for this region of the phase diagram. The results for the ternary samples suggest the stability of the φ phase in the Ta-Ge-B system.

Nesse trabalho foi proposto investigar a estabilidade de fases do sistema zircônia-escândia (ScSZ) por meio do estudo termodinâmico de nanopartículas, na faixa de 0 a 20% em mol de Sc2O3, e a partir da introdução de um segundo aditivo (Dy2O3 e Nb2O5) ao ZrO2 contendo 10% em mol de Sc2O3 (10ScSZ). A estabilidade de fases do ScSZ foi avaliada com base em dados termodinâmicos determinados pelas técnicas de microcalorimetria de adsorção de água e calorimetria de dissolução à alta temperatura. As soluções sólidas foram sintetizadas pelo método de coprecipitação de hidróxidos. Dados termodinâmicos foram determinados para as formas polimórficas encontradas (monoclínica, tetragonal, cúbica, romboédrica β e γ) por difração de raios X no ScSZ. Esse trabalho resultou no diagrama de fases em nanoescala de tamanho de partícula-composição. Os efeitos produzidos pela introdução de aditivos na matriz de 10ScSZ foram investigados visando obter a possível estabilização da estrutura cúbica (c) e a supressão da transformação de fase c-β, característica do sistema binário. As composições foram sintetizadas por coprecipitação de hidróxidos e por reações em estado sólido para fins comparativos. Os materiais foram sinterizados convencionalmente e por sinterização assistida por campo elétrico. A estabilização completa da fase cúbica ocorreu a partir de teores molares de 1% de Dy2O3 e 0,5% de Nb2O5. O menor teor de Nb2O5 necessário para a estabilização da fase foi atribuído à provável formação da fase líquida durante a sinterização e ao menor tamanho do íon Nb5+. Os resultados de difratometria de raios X em alta temperatura e análise térmica mostraram que houve supressão da transição c-β. As amostras contendo 0,5% mol de Nb2O5 apresentaram valores de condutividade iônica similares aos do 10ScSZ sem aditivos em uma ampla faixa de temperatura com elevada estabilidade em um período de 170 h a 600 °C. / In this work, the phase stability of scandia-zirconia (ScSZ) system was investigated by the thermodynamic study of nanoparticles, within the range of 0 to 20 mol% Sc2O3, and by codoping of ZrO2-10 mol% Sc2O3 (10ScSZ) with Dy2O3 and Nb2O5. The phase stability of ScSZ was evaluated based on thermodynamic data collected by water adsorption microcalorimetry and high temperature oxide melt solution. Nanostructured zirconia-scandia solid solutions were synthesized by coprecipitaion method. Thermodynamic data were determined for ScSZ polymorphs (monoclinic, tetragonal, cubic, rhombohedral β and γ) found by X-ray diffraction. This systemic work resulted in an unprecedented phase diagram at the nanoscale of particle size-composition. The effects of additives on 10ScSZ were investigated aiming to stabilize the cubic (c) structure at room temperature and to suppress the characteristic cubic-rhombohedral β phase transformation. Compositions were prepared by coprecipitation and solid state reaction. Materials were sintered by conventional and spark plasma sintering. Full stabilization of the cubic phase was attained by 1 mol% Dy2O3 and 0.5 mol% Nb2O5 additions. The smallest Nb2O5 content required for cubic phase stabilization was attributed to liquid phase formation during sintering and to small ionic radius of Nb5+. Results of high temperature X-ray diffraction and thermal analysis show suppression of the c-β transformation. Samples containing 0.5 mol% Nb2O5 show total ionic conductivity similar to 10ScSZ without additives within a broad temperature range with high stability during 170 h at 600 °C.