Dans le cadre du développement du démonstrateur de réacteur de IVème Génération ASTRID (Advanced Sodium Fast Reactor for Industrial Demonstration), une sonde potentiométrique permettant de réaliser une mesure spécifique et précise de l’oxygène dissous dans le sodium, redondante et diversifiée par rapport à l’indicateur de bouchage, est en voie d’élaboration. Celle-ci inclut une céramique électrolyte, la thorine yttriée, qui en constitue un élément essentiel. Ce travail de thèse a donc consisté à évaluer les propriétés d’un tel électrolyte solide, dont sa conduction ionique et sa durabilité en sodium, en fonction de paramètres microstructuraux afin d’en optimiser les conditions d’élaboration.La première partie de ce travail de thèse a porté sur la préparation d’échantillons frittés d’oxydes mixtes Th1-xYxO2-x/2 (0,01 ≤ x ≥ 0,22) de microstructures variées. Après co-précipitation oxalique des cations, les précurseurs ainsi que les oxydes résultant de leur conversion ont fait l’objet de caractérisations structurale, morphologique ou chimique poussées. Par la suite, l’étape de densification conduisant à l’élaboration de cartes de frittage a consisté à maîtriser la microstructure des céramiques et ainsi répondre aux contraintes fixées par l’application visée (densité élevée, faible taille de grains). En outre, les propriétés de conduction des échantillons ont été évaluées par spectroscopie d’impédance. Un maximum de conductivité a été relevé pour des teneurs d’yttrium comprises entre 8 et 15 mol.%.Les céramiques préparées ont ensuite été testées dans le sodium liquide à 500°C pendant plusieurs centaines d’heures. Dans les conditions expérimentales retenues, alors qu’aucun signe de corrosion n’a été observé à la surface des matériaux, les fractographies ont mis en évidence deux faciès de rupture différents indiquant une pénétration du sodium aux joints de grains. Des mesures par spectroscopie d’impédance après corrosion ont en outre montré une réponse différente du signal électrique, notamment au niveau des phénomènes de blocages. Par ailleurs, l’ajout volontaire d’impuretés a été réalisée au sein de certaines céramiques (Al, Zr et Si jusqu’à 1 mass.% ). Alors que de telles impuretés n’entraînent que de légères modifications microstructurales (diminution de la taille de grains), un effet délétère a pu être constaté quant à la tenue au sodium lors de l’incorporation de silicium ou de fortes teneurs de zirconium. / In the field of the development of a fourth generation nuclear reactor demonstrator, ASTRID (Advanced Sodium Fast Reactor for Industrial Demonstration), an electrochemical sensor, allowing accurate and specific measurement of dissolved oxygen in liquid sodium, is currently under development. One critical point of this device is the solid electrolyte, such as yttrium-doped thoria. Several properties of the solid electrolyte such as ionic conductivity and resistance to sodium corrosion were analyzed as a function of microstructure, in order to optimize the conditions of elaboration.First, sintered Th1-xYxO2-x/2 (0,01 ≤ x ≥ 0,22) ceramics showing various microstructures were prepared. In this aim, the starting oxalate precursors as well as the final oxides obtained after conversion were thoroughly characterized from structural, microstructural and chemical points of view. Furthermore, densification of the oxide samples was investigated to build sintering maps (average grain size vs. relative density). They further led to determine the optimal sintering conditions required to address the specifications of the electrolyte ceramic. In addition, electric properties of the ceramics were characterized by impedance spectroscopy. The results obtained showed the existence of a maximum of conductivity between 8 and 15 mol.% of yttrium incorporation rate.Thus, the compatibility of the ceramic with liquid sodium was undertaken at 500°C during several hundred hours. For experimental conditions considered, no sign of corrosion was evidenced at the surface of the samples while fracture of the pellets showed two different habits (trans- and intergranular) indicating a penetration of sodium through the grain boundaries. Post-mortem electric characterization revealed significant variation of the conductivity, especially concerning grain boundary contributions.Finally, similar experiments were developed on samples incorporating impurities on purpose (Al, Zr and Si up to 1 mass.%). While the incorporation of such impurities only causes slight microstructural change, a significant deleterious role on the resistance to liquid sodium was noted for silicium and high zirconium contents (1 mass.%).

La fusion sélective par laser est un procédé de la technologie de fabrication rapide de plus en plus utilisé dans l’industrie automobile, aéronautique, médicale, etc. Selon le principe de la fabrication rapide, la pièce est fabriquée couche par couche en fusionnant et soudant les particules fines par laser. Actuellement, les principaux matériaux utilisés sont les métaux métalliques ou les polymères. Le faible ou modeste point de fusion de ces matériaux conduit à une mise en œuvre par laser relativement facile. Cependant, en raison de leur point de fusion élevé, de la forte résistance à haute température et de la faible conductivité thermique, l’utilisation de matériaux céramiques est limitée dans la technologie de fusion laser sélective. Cette étude explore la fusion laser sélective de zircone stabilisée par yttrine avec un laser à fibre de longueur d’onde d’environ 1 µm. L’influence de différentes puissances de laser et de différentes vitesses de balayage sur la microstructure et la déformation de l’échantillon a été étudiée, et la densité relative et la microdureté ont été mesurées. Notamment, l’effet de différentes températures de préchauffage sur la microstructure sera étudié. En même temps, la structure cristalline céramique et la transformation des phases pendant le procédé de prototypage rapide ont été analysées. Les résultats expérimentaux montrent qu’il est possible de fondre complètement de la poudre YSZ avec un laser à fibre NIR, et avec l’optimisation des paramètres de fabrication, la densité relative de l’échantillon peut atteindre 91 %. Il est inévitable de voir se former des fissures et des pores dans les pièces fabriquées du fait de l’hétérogénéité de la distribution de l’énergie du laser. Cette distribution de l’énergie peut être améliorée grâce à l’optimisation des paramètres ; les longueurs de fissure peuvent être contrôlées et maîtrisées par un préchauffage du lit de poudre. Notamment, à haute température (1500°C, 2000°C et 2500°C) de préchauffage, la fissure verticale continue devient désordonnée et courte. Une transformation de la structure monoclinique et cubique en structure tétragonale s’est produite pendant le processus de fabrication. / Selective laser melting is a rapid manufacturing process coming from the rapid prototyping technology, which is widely used in the automotive, aeronautical, medical industry etc. According to the principle of rapid manufacturing, the piece is manufactured layer by layer through the laser sintering or melting the fine powder. Currently, the main powder materials used are metal or polymer materials. The low melting point of these materials facilitates the melting process. However, duo to the high melting point, strong strength at high temperature and low thermal conductivity the application of ceramic materials is limited in the technology of selective laser melting. In this study, selective laser melting of the ceramic yttria stabilized zirconia by a 1μm wavelength fiber laser was explored. The influence of different laser powers and different scanning velocities on the microstructure and the deformation were analyzed, then the micro-hardness and relative density were measured. In particular, the effect of different preheat temperatures on microstructure was investigated. At the same time, the crystal structure and phase transformation during the fabrication were analyzed. Experimental results show that YSZ powder can be completely melted by the near IR fiber laser. With the optimization of the manufacturing parameters, the relative density of sample could reach 91 %. The forming of cracks and pores in the manufactured parts is rarely avoid due to the heterogeneity of distribution of energy. The energy distribution could be improved by optimizing the parameters and the crack lengths can be controlled by preheating the powder bed. In particular, the high temperature (1500 ℃, 2000 ℃ and 2500 ℃) lead the continuous vertical crack becomes messy and short. The transformation of monoclinic and cubic crystal to tetragonal crystal can be observed during the fabrication.

From many years YSZ is used as the top coat material for TBC's, as it has good phase stability up to 1200°C, higher fracture toughness, lower thermal conductivity, erosion resistance & higher coefficient of thermal expansion. But, it has a drawbacks at high temperature such as sintering and transformation of phases. For this reason new ceramic materials with pyrochlores crystal structure such as Gd2Zr2O7 are being considered as it has high melting points, phase stability, lower thermal conductivity and CMAS resistance. But it has low fracture toughness when compared to YSZ. In order to take advantage of low thermal conductivity and high thermal stability of gadolinium zirconate and avoiding the drawbacks of low coefficient of thermal expansion and low toughness using YSZ, a double/multi-layer coatings approach is being used. Therefore, multi-layer TBCs are sprayed and compared with single layer coating in this work. These coatings are processed by suspension plasma spraying. For single layer coating YSZ is used, for double layer coating YSZ as the intermediate coating and Gd2Zr2O7 as the top coat is used. Additionally, a triple layer coating system comprising YSZ, Gd2Zr2O7 and dense Gd2Zr2O7 as top coat is also sprayed. The as sprayed coatings are characterized for microstructure analysis using optical microscope and scanning electron microscope (SEM), elemental analysis of TGO using Energy-Dispersive Spectrometer (EDS). XRD analysis was done to identify various phases in the coating. Porosity analysis using Archimedes principle was carried out. Thermal cyclic fatigue (TCF) test of the sprayed coatings was carried out at 1100°C. Failure analysis of the TCF specimens was carried out using SEM/EDS. TCF results showed that the triple layer coatings (dense Gd2Zr2O7/Gd2Zr2O7/YSZ) had higher thermal cyclic fatigue life and lower TGO thickness when compared to single layer (YSZ) and double layer (Gd2Zr2O7/YSZ) TBCs.

In this thesis a tool to be used in experimental design for batch processes is presented. Specifically, this method is to aid in the development of a process model. Currently, experimental design methods are either empirical in nature which need very little understanding of the underlying phenomena and without the objective of more fundamental understanding of the process. Other methods are model based which assume the model is correct and attempt to better define the model parameters or discriminate between models. This new paradigm for experimental design allows for process optimization and process model development to occur simultaneously. The methodology specifically evaluates multiple models as a check to evaluate whether the models are capturing the trend in the experimental data. A new tool for experimental design developed here is called the grid algorithm which is designed to constrain the experimental region to potential optimal points of the user defined objective function for the process. It accomplishes this by using the confidence interval on the objective function value. The objective function value is calculated using the model prediction of the best performing model among a set of models at the predicted optimal point. This new experimental design methodology is tested first on simulated data. The first simulation fits a model to data generated by the modified Himmelblau function (MHF). The second simulation fits multiple models to data generated to simulate a film growth process. In both simulations the grid algorithm leads to improved prediction at the optimal point and better sampling of the region around the optimal point. This experimental design method was then applied to an actual chemical vapor deposition system. The films were analyzed using atomic force microscopy (AFM) to find the resulting film roughness. The methodology was then applied to design experiments using models to predict roughness. The resulting experiments were designed in a region constrained by the grid algorithm and were close to the predicted optimum of the process. We found that the roughness of a thin film depended on the substrate temperature but also showed a relationship to the nucleation density of the thin film.

The effect of dental technical tools on the phase composition and roughness of 3/4/5 yttria-stabilized tetragonal zirconia polycrystalline (3y-/4y-/5y-TZP) for application in prosthetic dentistry was investigated. Additionally, the X-ray diffraction methods of Garvie-Nicholson and Rietveld were compared in a dental restoration context. Seven plates from two manufacturers, each fabricated from commercially available zirconia (3/4/5 mol%) for application as dental restorative material, were stressed by different dental technical tools used for grinding and polishing, as well as by chewing simulation and thermocycling. All specimens were examined via laser microscopy (surface roughness) and X-ray diffraction (DIN EN ISO 13356 and the Rietveld method). As a result, the monoclinic phase fraction was halved by grinding for the 3y-TZP and transformed entirely into one of the tetragonal phases by polishing/chewing for all specimens. The tetragonal phase t is preferred for an yttria content of 3 mol% and phase t″ for 5 mol%. Mechanical stress, such as polishing or grinding, does not trigger low-temperature degradation (LTD), but it fosters a phase transformation from monoclinic to tetragonal under certain conditions. This may increase the translucency and deteriorate the mechanical properties to some extent.

Les piles à combustible Solid Oxide Fuel Cell sont des systèmes de production d’électricité. Une cellule élémentaire est un multicouche constitué de matériaux céramiques et de métal. Elles sont très sensibles aux contraintes mécaniques générées lors des cycles thermiques et d’oxydo-réduction, limitant leur durée de vie.Ce travail a porté sur la détermination expérimentale des contraintes résiduelles dans des cellules SOFC à anode support en fonction des sollicitations du système. Parallèlement à des mesures in-situ en température, une approche multi-échelles a été développée pour évaluer les hétérogénéités de contraintes dans l’électrolyte liées à la forte anisotropie élastique de la zircone yttriée qui le constitue. Différentes techniques ont été mise en œuvre afin de couvrir les 3 ordres de contraintes. Les mesures à l’échelle macroscopique ont été effectuées par diffraction de rayons X de laboratoire (méthode des sin²(Ψ)). La microdiffraction de rayonnement synchrotron en mode faisceau blanc et monochromatique a permis, après un important travail d’amélioration du protocole de mesure et d’analyse, de déterminer les tenseurs complets de contraintes et déformations grain à grain dans l’électrolyte. Les déformations intra-granulaires ont été évaluées par une technique d’EBSD.Les résultats obtenus ont permis d’analyser les mécanismes principaux qui régissent les évolutions de contraintes dans l’électrolyte. Des hétérogénéités de contraintes entre grains liées à leurs orientations cristallographiques ont été mises en évidence. Au-delà du problème des SOFC, les techniques mises en œuvre ouvrent la voie aux validations expérimentales des modèles mécaniques poly-cristallins. / The Solid Oxide Fuel Cells (SOFC) are high-performance electrochemical devices for energy conversion. A single cell is composed of layers made of different ceramic materials and metal. The mechanical integrity of the cell is a major issue during its lifetime. Damage of the cells is mainly due to the high operating temperature, the “redox” behavior of the anode and the brittleness of the involved materials. In this work, residual stresses in the electrolyte of a planar anode-supported SOFC have been experimentally measured for different treatments of the cell. In situ analysis at various temperatures has been performed. A multi-scale approach has been developed to study the expected strain-stress heterogeneities in the electrolyte due to the strong elastic anisotropy of the involved material (yttria-stabilized zirconia). Different techniques have been used to determinate stresses at the 3 different orders. Macroscopic stresses were studied using the Sin2 method on a laboratory X-ray goniometer. The complete strain and stress tensors of individual grains in the electrolyte have been determinate, after various improvements in the technique, by combining the diffraction of white and monochromatic micro beams produced by synchrotron source. Strain variation into grains has been evaluated using EBSD.This study has identified the main phenomena that control the stresses variation in the electrolyte layer. Stresses heterogeneities from grain to grain have been found and linked to the crystallographic orientation. Beyond SOFC’s considerations, the techniques that have been developed should permit an experimental validation of mechanical modeling to polycrystalline materials.

Foram efetuados experimentos de sinterização em cerâmica policristalina de ZrO2: 3 mol% Y2O3 (3YSZ) por três métodos: aquecimento seguindo o perfil temperatura ambiente 1400 °C temperatura ambiente (sinterização convencional), aquecimento a partir da temperatura ambiente até 1000-1100 °C sob aplicação de campo elétrico AC (sinterização dinâmica assistida por campo elétrico), e aquecimento até 1000-1100 °C para aplicação do campo elétrico AC (sinterização isotérmica assistida por campo elétrico). O último método foi aplicado em amostras sob diferentes condições (amostras a verde, amostras a verde compactadas isostaticamente com diferentes pressões, amostras pré-sinterizadas a 1400 °C) e diferentes condições experimentais (diferentes frequências do campo elétrico AC, campo elétrico DC, diferentes limites de densidade de corrente, aplicação de carga simultaneamente à aplicação do campo elétrico). Todas as amostras de 3YSZ sinterizadas, além de terem a densidade aparente determinada, tiveram a superfície observada em microscópio eletrônico de varredura para avaliação do tamanho médio de grão e distribuição do tamanho de grão (em alguns casos, ao longo da superfície, do centro para a borda). Além disso, análises de espectroscopia de impedância foram feitas para avaliar a contribuição intergranular (principalmente contorno de grão) e intragranular (grãos) para a resistividade elétrica. A ideia principal foi coletar dados sobre sinterização assistida por campo elétrico, procurando entender o mecanismo atuando no método de sinterização, conhecido por produzir peças cerâmicas densas em temperaturas menores do que as usadas em sinterização convencional, em tempos curtos, e com inibição do crescimento de grão. Os resultados principais mostram que: 1) o nível de retração depende da frequência do campo elétrico AC, 2) quanto maior a porosidade, maior o efeito do campo elétrico, 3) quanto maior o valor da densidade de corrente, maior a densificação, até um determinado limite a partir do qual a amostra é danificada, 4) o pulso de corrente elétrica flui preferencialmente pela região intergranular, e 5) amostras submetidas a sinterização assistida por campo elétrico mostraram aumento da condutividade do contorno de grão. Um mecanismo para a sinterização assistida por campo elétrico é proposto, baseado em que 1) aquecimento Joule é o efeito principal, 2) a corrente elétrica, que surge como resultado da aplicação do campo elétrico, flui pela região intergranular, 3) o aquecimento Joule difunde as espécies químicas depletadas nas interfaces de volta aos grãos, aumentando a concentração de defeitos, levando ao aumento da condutividade do grão, e 4) o aquecimento Joule é responsável por diminuir a barreira potencial na região de carga espacial, inibindo o bloqueio dos íons de oxigênio nos contornos de grão. / Experiments on sintering ZrO2: 3 mol% Y2O3 polycrystalline ceramics (Y-TZP, hereafter 3YSZ) were carried out by three methods: heating following the room temperature-1400°C-room temperature profile (conventional sintering), heating from room temperature to 1000-1100°C under an applied AC electric field (dynamic electric field-assisted sintering), and heating to 1000-1100°C for application of an AC electric field (isothermal electric field-assisted sintering). The last method was performed under different specimen conditions (green pellets, green pellets isostatically pressed with different loads, pellets pre-sintered at 1400°C) and different experimental conditions (different frequencies of the AC electric field, DC electric fields, different limitation of the electric current densities, applying loads simultaneously to application of the electric field). All 3YSZ sintered samples, besides having their apparent densities determined, had their surfaces observed in a scanning electron microscope to evaluate average grain size and distribution of grain sizes (some, along the surface from the center to the border). Moreover, impedance spectroscopy analyses were carried out to evaluate the intergranular (mainly grain boundary) and intragranular (bulk) contributions to the electrical resistivity. The primary idea was to collect data on electric field-assisted sintering looking for understanding the mechanisms behind that sintering method, known to produce dense ceramic pieces at temperatures lower than those used in conventional sintering, in short times and inhibiting grain growth. The main results show that 1) the shrinkage level depends on the AC frequency, 2) the larger the porosity the higher the electric field effect, 3) higher current densities promotes higher densification up to a limit that could damage the sample, 4) the electric current pulse follows preferentially the intergranular instead of the bulk pathway, and 5) electric field-assisted sintered specimens show enhanced grain boundary conductivity. A mechanism for the electric field-assisted sintering is proposed based on that 1) Joule heating is the primary event, 2) the electric current, as a result of the electric field, follows the intergranular pathway, 3) Joule heating diffuses chemical species depleted at the interfaces back to the bulk, increasing the defect concentration, leading to the enhancement of the bulk conductivity, and 4) that same Joule heating is responsible for the decrease of the potential barrier at the space charge region, inhibiting the blocking of oxide ions at the grain boundaries.

Foram efetuados experimentos de sinterização em cerâmica policristalina de ZrO2: 3 mol% Y2O3 (3YSZ) por três métodos: aquecimento seguindo o perfil temperatura ambiente 1400 °C temperatura ambiente (sinterização convencional), aquecimento a partir da temperatura ambiente até 1000-1100 °C sob aplicação de campo elétrico AC (sinterização dinâmica assistida por campo elétrico), e aquecimento até 1000-1100 °C para aplicação do campo elétrico AC (sinterização isotérmica assistida por campo elétrico). O último método foi aplicado em amostras sob diferentes condições (amostras a verde, amostras a verde compactadas isostaticamente com diferentes pressões, amostras pré-sinterizadas a 1400 °C) e diferentes condições experimentais (diferentes frequências do campo elétrico AC, campo elétrico DC, diferentes limites de densidade de corrente, aplicação de carga simultaneamente à aplicação do campo elétrico). Todas as amostras de 3YSZ sinterizadas, além de terem a densidade aparente determinada, tiveram a superfície observada em microscópio eletrônico de varredura para avaliação do tamanho médio de grão e distribuição do tamanho de grão (em alguns casos, ao longo da superfície, do centro para a borda). Além disso, análises de espectroscopia de impedância foram feitas para avaliar a contribuição intergranular (principalmente contorno de grão) e intragranular (grãos) para a resistividade elétrica. A ideia principal foi coletar dados sobre sinterização assistida por campo elétrico, procurando entender o mecanismo atuando no método de sinterização, conhecido por produzir peças cerâmicas densas em temperaturas menores do que as usadas em sinterização convencional, em tempos curtos, e com inibição do crescimento de grão. Os resultados principais mostram que: 1) o nível de retração depende da frequência do campo elétrico AC, 2) quanto maior a porosidade, maior o efeito do campo elétrico, 3) quanto maior o valor da densidade de corrente, maior a densificação, até um determinado limite a partir do qual a amostra é danificada, 4) o pulso de corrente elétrica flui preferencialmente pela região intergranular, e 5) amostras submetidas a sinterização assistida por campo elétrico mostraram aumento da condutividade do contorno de grão. Um mecanismo para a sinterização assistida por campo elétrico é proposto, baseado em que 1) aquecimento Joule é o efeito principal, 2) a corrente elétrica, que surge como resultado da aplicação do campo elétrico, flui pela região intergranular, 3) o aquecimento Joule difunde as espécies químicas depletadas nas interfaces de volta aos grãos, aumentando a concentração de defeitos, levando ao aumento da condutividade do grão, e 4) o aquecimento Joule é responsável por diminuir a barreira potencial na região de carga espacial, inibindo o bloqueio dos íons de oxigênio nos contornos de grão. / Experiments on sintering ZrO2: 3 mol% Y2O3 polycrystalline ceramics (Y-TZP, hereafter 3YSZ) were carried out by three methods: heating following the room temperature-1400°C-room temperature profile (conventional sintering), heating from room temperature to 1000-1100°C under an applied AC electric field (dynamic electric field-assisted sintering), and heating to 1000-1100°C for application of an AC electric field (isothermal electric field-assisted sintering). The last method was performed under different specimen conditions (green pellets, green pellets isostatically pressed with different loads, pellets pre-sintered at 1400°C) and different experimental conditions (different frequencies of the AC electric field, DC electric fields, different limitation of the electric current densities, applying loads simultaneously to application of the electric field). All 3YSZ sintered samples, besides having their apparent densities determined, had their surfaces observed in a scanning electron microscope to evaluate average grain size and distribution of grain sizes (some, along the surface from the center to the border). Moreover, impedance spectroscopy analyses were carried out to evaluate the intergranular (mainly grain boundary) and intragranular (bulk) contributions to the electrical resistivity. The primary idea was to collect data on electric field-assisted sintering looking for understanding the mechanisms behind that sintering method, known to produce dense ceramic pieces at temperatures lower than those used in conventional sintering, in short times and inhibiting grain growth. The main results show that 1) the shrinkage level depends on the AC frequency, 2) the larger the porosity the higher the electric field effect, 3) higher current densities promotes higher densification up to a limit that could damage the sample, 4) the electric current pulse follows preferentially the intergranular instead of the bulk pathway, and 5) electric field-assisted sintered specimens show enhanced grain boundary conductivity. A mechanism for the electric field-assisted sintering is proposed based on that 1) Joule heating is the primary event, 2) the electric current, as a result of the electric field, follows the intergranular pathway, 3) Joule heating diffuses chemical species depleted at the interfaces back to the bulk, increasing the defect concentration, leading to the enhancement of the bulk conductivity, and 4) that same Joule heating is responsible for the decrease of the potential barrier at the space charge region, inhibiting the blocking of oxide ions at the grain boundaries.

Made available in DSpace on 2017-07-21T20:42:43Z (GMT). No. of bitstreams: 1 LENA, Eleomar.pdf: 3273064 bytes, checksum: d7d21ed4ddfa4969702a9c497ccaccc4 (MD5) Previous issue date: 2012-08-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work studied the influence of oxidizing atmospheres of calcination and sintering temperature on the electrical properties, densification and grain size of yttria doped with 4.5 mol% zirconia synthesized by a sol-gel process followed by calcination at 600 ºC/2h in O2 and air. Used for uniaxial pressing with pressures between 150 MPa and 1.6 GPa. Sintered by Two Step Sintering (TSS): 1550 °C / 5 min and 1200, 1300, 1400 °C, remaining at these temperatures for 2 and 10 hours. Characterized by X-ray diffraction, apparent density,scanning electron microscopy, impedance spectroscopy. The density measurements were above 94% of theoretical density and grain size between 304 and 477 nm, activation energies of 0.68 and 0.90 eV. The TSS was formed in sintering and grain submicrométicos prevented their excessive growth during the final sintering.The calcination atmosphere had little influence on the values of density and porosity, but caused changes in crystallite size and influenced the values of conductivity / Neste trabalho foram estudadas as influência de atmosferas oxidadante de calcinação nas propriedades elétricas das temperaturas de sinterização, densificação e tamanho de grão em compactos de zirconia dopada com 4,5% em moles de oxido de itrio sintetizado por processo sol-gel seguido de calcinação a 600 °C/2h ao ar e O2. Compactados uniaxialmente com pressoes entre 150 MPa e 1,6 GPa. Sinterizados pelo processo Two Step Sintering (TSS): 155 °C/5 min e 1200, 1300 e 1400 °C, permanescendo por 2 e 10 horas. Caracterizados por difração de raios X, densidade aparente, microscopia eletronica de varredura e espectrocopia de impedancia. As As medições de densidade foram acima de 94% da densidade teórica e tamanho de grão entre 304 e 477 nm, as energias de activação de 0,68 e 0,90 eV. A TSS foi formou na sinterização grãos submicrométicos e impediu seu crescimento excessivo durante o final de sintering. A atmosfera calcinação teve pouca influência sobre os valores de densidade e porosidade, causando mudanças no tamanho de cristalito e influenciando os valores de condutividade Neste trabalho foram estudadas as influência de atmosferas oxidadante de calcinação nas propriedades elétricas das temperaturas de sinterização, densificação e tamanho de grão em compactos de zirconia dopada com 4,5% em moles de oxido de itrio sintetizado por processo sol-gel seguido de calcinação a 600 °C/2h ao ar e O2. Compactados uniaxialmente com pressoes entre 150 MPa e 1,6 GPa. Sinterizados pelo processo Two Step Sintering (TSS): 155 °C/5 min e 1200, 1300 e 1400 °C, permanescendo por 2 e 10 horas. Caracterizados por difração de raios X, densidade aparente, microscopia eletronica de varredura e espectrocopia de impedancia. As As medições de densidade foram acima de 94% da densidade teórica e tamanho de grão entre 304 e 477 nm, as energias de activação de 0,68 e 0,90 eV. A TSS foi formou na sinterização grãos submicrométicos e impediu seu crescimento excessivo durante o final de sintering. A atmosfera calcinação teve pouca influência sobre os valores de densidade e porosidade, causando mudanças no tamanho de cristalito e influenciando os valores de condutividade

The yttria-stabilized zirconia (YSZ) system has been extensively studied because of its critical applications, like solid oxide fuel cells (SOFCs), oxygen sensors, and jet engines. However, there are still important questions that need to be answered and significant thermodynamic information that needs to be provided for this system. There is no predictive tool for the ionic conductivity of the cubic-YSZ (c-YSZ), as an electrolyte in SOFCs. In addition, no quantitative diagram is available regarding the oxygen ion mobility in c-YSZ, which is highly effective on its ionic conductivity. Moreover, there is no applicable phase stability diagram for the nano-YSZ, which is applied in oxygen sensors. Phase diagrams are critical tools to design new applications of materials. Furthermore, even after extensive studies on the thermodynamic database of the YSZ system, the zirconia-rich side of the system shows considerable uncertainties regarding the phase equilibria, which can make the application designs unreliable. During this dissertation, the CALPHAD (CALculation of PHase Diagrams) approach was applied to provide a predictive diagram for the ionic conductivity of the c-YSZ system. The oxygen ion mobility, activation energy, and pre-exponential factor were also predicted. In addition, the CALPHAD approach was utilized to predict the Gibbs energy of bulk YSZ at different temperatures. The surface energy of each polymorph was then added to the predicted Gibbs energy of bulk YSZ to obtain the total Gibbs energy of nano-YSZ. Therefore, a 3-D phase stability diagram for the nano-YSZ system was provided, by which the stability range of each polymorph versus temperature and particle size are presented. Re-assessment of the thermodynamic database of the YSZ system was done by applying the CALPHAD approach. All of the available thermochemical and phase equilibria data were evaluated carefully and the most reliable ones were selected for the Gibbs energy optimization process. The results calculated by the optimized thermodynamic database showed good agreement with the selected experimental data, particularly on the zirconia-rich side of the system.