In order to increase the efficiency and economic viability of solid oxide fuel cells (SOFCs), new materials for the cathode, anode, and electrolyte of the cells must be found. SOFCs have a ceramic electrolyte, which is commonly made of fully stabilized zirconia. Due to increased material degradation rates at elevated temperatures ( ~ 1000°C) of current SOFCs, materials for the manufacture of intermediate temperature SOFCs, which operate in the range of 700-800°C, are currently under study. In this study, the manufacturing process for scandia-ceria stabilized zirconia powder (1 0mol¾ Sc2O3, lmol¾ CeO2, 89mol% ZrO2), from Daiichi Kigenso Kagaku Kogyo (DKKK) is developed, including tape casting and sintering procedures to result in pellets of high enough quality to produce single button cells. It is found that a slip prepared with about 44 wt% zirconia powder and increased proportions of solvents, dispersant, binder and plasticizers produces a favorable viscosity of about 7 40cP after deairing, and will produce tapes that are reasonably smooth and of stable thickness. Since the single cell will be structurally based upon this electrolyte material, the physical properties of the pellets are important, in addition to the electrochemical properties of the constituent materials. Tapes cast at 500µm, at 50% feed rate with a 50°C drying temperature, laminated and sintered at 1500°C on setter plates will produce flat, smooth, stiff pellets for the production of single buttons for use as the electrolyte. Cathode (50-50 mixture of La0.6Sr0_4Fe0_8Co0.2O3 + 20mol% Gd2O3 80mol% CeO2) and Anode (35 wt% DKKK powder, 65 wt% NiO) materials were hand-painted on to either side of the electrolyte and sintered to create a complete SOFC cell consisting of cathode, electrolyte, and anode.

Scandia doped zirconia has been considered a candidate for electrolyte material in intermediate temperature Solid Oxide Fuel Cells (SOFCs) due to its high ionic conductivity, chemical stability and good electrochemical performance. The aim of this study is to determine the mechanical properties of SCZ, ie. zirconia (ZrO₂) doped with Scandia (Sc₂O₃) and small amount of ceria (CeO₂) that are important for reliability and durability of the components manufactured from SCZ. The SCZ was prepared from powder by uniaxiall cold pressing at subsequent sintering at 1550 ºC for 4 hours. The density and porosity of the sintered samples was measured following the ASTM Standard C20-00 for alcohol immersion method. A pure cubic phase of SCZ sample was identified by X-ray diffraction (XRD) at room temperature. Quantitative compositional analyses for Zr, Sc, Ce, Hf and Ti were carried out on a Cameca SX50 electron microprobe with wavelength-dispersive spectroscopy (WDS) and energy-dispersive spectroscopy (EDS). Scanning Electron Microscopy (SEM) images were acquired using both secondary electron (SE) and back-scattered electron (BSE) detectors. WDS and EDS analysis also revealed that Zr, Sc, Ce, Hf and Ti are relatively homogeneously distributed in the structure. The average grain size of sintered SCZ samples was measured to be 4 μm. Thermal expansion at different temperatures for the SCZ ceramic was determined using Thermal Mechanical Analyzer, and the instantaneous Coefficient of Thermal Expansion (CTE) was found to be 8.726х10⁻⁶ 1/°C in the in 25-400 °C temperature range. CTE increases monotonically with temperature above 400 ºC to 1.16х10⁻⁵ at 890 °C, most likely as a result of thermo-chemical expansion due to an increase in oxygen vacancy concentration. Room temperature Vickers hardens of 12.5 GPa was measured at loads of 1000 g, while indentation fracture toughness was found to vary from 2.25 to 4.29 MPa m¹⁄², depending on the methodology that was used to calculate fracture toughness from the length of the median corner cracks. Elastic moduli, namely Young and shear moduli were determined using Resonance Ultrasound Spectroscopy (RUS). It was found that elastic moduli decreases with temperature in non-linear manner, with significant drop in the 300-600 °C temperature range, the same temperature range in which loss modulus determined by Dynamic Mechanical Analyzer exhibits frequency dependant peaks. The high loss modulus and significant drop in elastic moduli in that temperature regime is attributed to the relaxation of doping cation-oxygen vacancies clusters. The flexural strength in 4-point bending was measured at room temperature, 400 °C, 600 °C and 800 °C. and the results were analyzed using Weibull statistics. It was found that flexural strength changes with temperature in a sigmoidal way, with the minimum strength at around 600 °C. Non-linear decrease in strength with temperature can be traced back to the changes in elastic moduli that are caused predominately by relaxation of oxygen vacancies.

In the last decade new materials appeared that are candidates to be used as an electrolyte in a Solid Oxide Fuel Cell, SOFC. Some materials show high ionic conductivity but lack in important properties, such as mechanical stability or chemical compatibility with other materials in the fuel cell. Scandia Stabilised Zirconia, SSZ, became a possibility when the scandia price dropped with the opening of the Chinese and Russian markets. In the starting system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2), scandia is introduced to improve conductivity and stabilise the cubic phase; yttria is introduced to fully stabilise the cubic phase and ceria to enhance conductivity lost with the introduction of yttria. The aim of this project is to develop a reliable new method to produce quality ceramics that are not strongly composition dependent, then to prepare a range of compositions and compare intrinsic properties without having to be concerned that poor sintering dominates conduction properties. This project can be divided in two sections, the first section the powder production method, the characteristics of the powders and its final products are in focus. In the second section the relation between electric characteristics and microstructure of the material is reported. In the first section, the effect of different compositions of the system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2) is studied, in terms of structure, phase and microstructure. The nature, size and shape of the powders are discussed, and their effect on the final product. The sol-gel and combustion method gives the formation of hard agglomerates (shells), during the combustion, a wide range of grain sizes, between less than 1µm and 200 µm, and the formation of grains with non spherical shape. In this project, the sol-gel and combustion process and solid state method are also compared. In the second section of this project, AC Impedance measurements, as a function of temperature, oxygen partial pressure and time are discussed. The Arrhenius plot for all compositions shows two regions (high and low temperature) and the change of region occurs at 580 °C. At low temperatures there is a slight difference between compositions but this difference is less at high temperatures. The obtained ionic conductivity, at 350 °C, varies from 3.84×10⁻⁶ to 5.53×10⁻⁵ S/cm; at 700 °C, ionic conductivity from 0.013 to 0.044 S/cm. At low temperatures, the activation energy associated with bulk process is generally lower than grain boundary process; for example, the composition Ce₀.₁Y₀.₁Sc₀.₆Zr₃.₂O₇.₆₅ has an activation energy, for the bulk process, of 1.05 eV and an activation energy, for the grain boundary process, of 1.17 eV. For compositions with higher ceria content, activation energy, for bulk and grain boundary, have similar values. The AC impedance as function of oxygen partial pressure show that the amount of ceria introduced as an effect on the conductivity at low oxygen partial pressure. For the sample with no ceria in its composition, Y₀.₂Sc₀.₆Zr₃.₂O₇.₆₀, the conductivity does not vary significantly as the oxygen partial pressure is decreased; for oxygen partial of 0.21 atm, conductivity is 0.018 S/cm and when oxygen partial pressure is approximately 10⁻²⁴ atm conductivity is 0.018 S/cm. For the sample with a higher content of ceria, Ce₀.₁₂Y₀.₀₈Sc₀.₆Zr₃.₂O₇.₆₆, there is a decrease in conductivity while oxygen partial pressure decreases; and there is also the appearance of a semi-circle for lower oxygen partial pressures. For oxygen partial pressure approximately 0.21 atm, conductivity is 0.019 S/cm, but when oxygen partial pressure is decreased to 10⁻²⁴ atm conductivity decreases to 0.011 S/cm. AC impedance measurements as a function of annealing time at 600 °C were performed. Total conductivity is fairly stable, for all compositions, until 1800 hours but after this time, conductivity slowly decreases. Some compositions show a second semi-circle in the AC impedance spectra, either from the beginning, time equals 0 hours, or after some working hours. Here, the changes in conduction and conduction processes with time are discussed.

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.

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.

Scandate cathode under various processing stages: scandia nano-powder, tungsten scandia mix powder, sintered and impregnated pellets, were characterized with techniques that included electron microscopy, EDS, XPS, and work function measurements. The size and shape uniformity of nano-scale scandia particles changed from round to square and polyhedron during heat treatment. Reduction in size and improvement in size uniformity as heat treating temperature increased were observed. When determining the highest Sc coverage, three assessment methods were used and with their combined results, it was concluded that set VII had the highest Sc at%. In the sintered pellets, it was observed with SEM that more initial scandia coverage in the mix powder sets corresponded to a larger number of scandia particles distributed over the tungsten surface. The structure of the cross section made on pellet surface was porous which was expected in any functional cathode. Kelvin probe measurements revealed that work function values of sintered pellets were similar and decreased by approximately 0.6 eV after the impregnation. A cross section on the impregnated pellet surface revealed that the pores that existed in sintered pellets were gone and filled with impregnated materials that emerged to the surface during impregnation.

This master thesis studies debates on historical theory in Sweden ́s two main historical journals, Historisk tidskrift and Scandia, during the last fifty years. The study investigates discussions of epistemological questions, the purposes of historical writing, and the influence of postmodernism. The theoretical approach and methodology used is inspired by the American pragmatist philosopher Richard Rorty. In a concluding chapter Rorty’s writings are used to confront the study’s results. The purpose of this is to highlight certain problems from the investigation. It is argued that the vocabulary used by the Swedish historians is an effect of the correspondence theory of truth, and that a pragmatic approach to the study of history could help history break free from that unfortunate vocabulary.

Estudos recentes demonstram que o sistema cerâmico zircônia-escândia-céria (ScCeSZ) apresenta-se promissor para aplicações como eletrólito sólido em células a combustível de óxido sólido de temperaturas intermediárias de operação (600 a 800 °C). Neste trabalho, foi realizada a sinterização convencional, de duas etapas e assistida por campo elétrico do ZrO2 contendo 10% em mol de Sc2O3 e 1% em mol de CeO2 comercializado pela Fuel Cell Materials visando melhorar a densificação com reduzido tamanho médio de grãos. A condutividade elétrica de amostras densas de ScCeSZ sinterizadas pelos diferentes métodos foi investigada por espectroscopia de impedância. Diferentes condições de sinterização foram analisadas. A taxa de retração dos compactos é máxima a 1180 °C, determinada pela análise de dilatometria. Foi confirmado por difração de raios X que a adição de céria à zircônia-escândia promove a estabilização da fase cúbica à temperatura ambiente. No entanto, dependendo das condições de sinterização pode haver a formação de fases secundárias, as quais foram detectadas por difração de raios X e espectroscopia Raman. A sinterização assistida por campo elétrico promoveu a formação das fases cúbica e tetragonal. Considerando os métodos convencional e de duas etapas, para a obtenção do material cúbico monofásico é necessária uma seleção cuidadosa das condições de sinterização. Os valores de condutividade elétrica estão de acordo com as condutividades do ScCeSZ reportadas na literatura. / Recent reports show that scandia-and ceria-doped zirconia (ScCeSZ) is a promising material for application as solid electrolyte in solid oxide fuel cells operating at intermediate temperatures (600 - 800 °C). In this work, ZrO2 containing 10 mol% Sc2O3 and 1 mol% CeO2 commercial powder (Fuel Cell Materials) was used to investigate the densification along with the mean grain size in specimens sintered by different methods: conventional, two-step sintering and electric field assisted sintering. The electrical conductivity of dense sintered specimens was studied by impedance spectroscopy. The linear shrinkage was followed by dilatometry. The maximum shrinkage rate of powder compacts was obtained at 1180 ºC. X-ray diffraction experiments revealed that ceria stabilizes the cubic phase of scandia-doped zirconia at room temperature. However, secondary phases (rhombohedric and tetragonal) were detected by both X-ray diffraction and Raman spectroscopy depending on the sintering conditions. The field assisted sintering method resulted in specimens with cubic and tetragonal phases. In the case of conventional and two-step sintering methods, a careful selection of the temperatures and sintering times is essential to obtain a cubic single-phase material. Values of the electrical conductivity of ScCeSZ are in general agreement with those reported in the literature.

Estudos recentes demonstram que o sistema cerâmico zircônia-escândia-céria (ScCeSZ) apresenta-se promissor para aplicações como eletrólito sólido em células a combustível de óxido sólido de temperaturas intermediárias de operação (600 a 800 °C). Neste trabalho, foi realizada a sinterização convencional, de duas etapas e assistida por campo elétrico do ZrO2 contendo 10% em mol de Sc2O3 e 1% em mol de CeO2 comercializado pela Fuel Cell Materials visando melhorar a densificação com reduzido tamanho médio de grãos. A condutividade elétrica de amostras densas de ScCeSZ sinterizadas pelos diferentes métodos foi investigada por espectroscopia de impedância. Diferentes condições de sinterização foram analisadas. A taxa de retração dos compactos é máxima a 1180 °C, determinada pela análise de dilatometria. Foi confirmado por difração de raios X que a adição de céria à zircônia-escândia promove a estabilização da fase cúbica à temperatura ambiente. No entanto, dependendo das condições de sinterização pode haver a formação de fases secundárias, as quais foram detectadas por difração de raios X e espectroscopia Raman. A sinterização assistida por campo elétrico promoveu a formação das fases cúbica e tetragonal. Considerando os métodos convencional e de duas etapas, para a obtenção do material cúbico monofásico é necessária uma seleção cuidadosa das condições de sinterização. Os valores de condutividade elétrica estão de acordo com as condutividades do ScCeSZ reportadas na literatura. / Recent reports show that scandia-and ceria-doped zirconia (ScCeSZ) is a promising material for application as solid electrolyte in solid oxide fuel cells operating at intermediate temperatures (600 - 800 °C). In this work, ZrO2 containing 10 mol% Sc2O3 and 1 mol% CeO2 commercial powder (Fuel Cell Materials) was used to investigate the densification along with the mean grain size in specimens sintered by different methods: conventional, two-step sintering and electric field assisted sintering. The electrical conductivity of dense sintered specimens was studied by impedance spectroscopy. The linear shrinkage was followed by dilatometry. The maximum shrinkage rate of powder compacts was obtained at 1180 ºC. X-ray diffraction experiments revealed that ceria stabilizes the cubic phase of scandia-doped zirconia at room temperature. However, secondary phases (rhombohedric and tetragonal) were detected by both X-ray diffraction and Raman spectroscopy depending on the sintering conditions. The field assisted sintering method resulted in specimens with cubic and tetragonal phases. In the case of conventional and two-step sintering methods, a careful selection of the temperatures and sintering times is essential to obtain a cubic single-phase material. Values of the electrical conductivity of ScCeSZ are in general agreement with those reported in the literature.

Mesoscale optical phenomena occur when light interacts with a number of different types of materials, such as biological and chemical systems and fabricated nanostructures. As a framework, mesoscale optics unifies the interpretations of the interaction of light with complex media when the outcome depends significantly upon the scale of the interaction. Most importantly, it guides the process of designing an optical sensing technique by focusing on the nature and amount of information that can be extracted from a measurement. Different aspects of mesoscale optics are addressed in this dissertation which led to the solution of a number of problems in complex media. Dynamical and structural information from complex fluids—such as colloidal suspensions and biological fluids—was obtained by controlling the size of the interaction volume with low coherence interferometry. With this information, material properties such as particle sizes, optical transport coefficients, and viscoelastic characteristics of polymer solutions and blood were determined in natural, realistic conditions that are inaccessible to conventional techniques. The same framework also enabled the development of new, scale-dependent models for several important physical and biological systems. These models were then used to explain the results of some unique measurements. For example, the transport of light in disordered photonic lattices was interpreted as a scale-dependent, diffusive process to explain the anomalous behavior of photon path length distributions through these complex structures. In addition, it was demonstrated how specialized optical measurements and models at the mesoscale enable solutions to fundamental problems in cell biology. Specifically, it was found for the first time that the nature of cell motility changes markedly with the curvature of the substrate that the cells iv move on. This particular work addresses increasingly important questions concerning the nature of cellular responses to external forces and the mechanical properties of their local environment. Besides sensing of properties and modeling behaviors of complex systems, mesoscale optics encompasses the control of material systems as a result of the light-matter interaction. Specific modifications to a material’s structure can occur due to not only an exchange of energy between radiation and a material, but also due to a transfer of momentum. Based on the mechanical action of multiply scattered light on colloidal particles, an optically-controlled active medium that did not require specially tailored particles was demonstrated for the first time. The coupling between the particles and the random electromagnetic field affords new possibilities for controlling mesoscale systems and observing nonequilibrium thermodynamic phenomena