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Nguyen, Ty, and ty nguyen@csiro au. "Preparation, Characterisation and Cell Testing of Gadolinium Doped Cerium Electrolyte Thin Films for Solid Oxide Fuel Cell Applications." RMIT University. Electrical and Computer Engineering, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20081030.110755.
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Solid Oxide Fuel Cells (SOFCs) are devices that directly convert chemical energy into electrical energy, without proceeding through a Carnot combustion cycle. These devices are based on the usage of solid oxide electrolytes operating at relatively elevated temperatures. Two major hurdles must be overcome in order to decrease the operating temperatures of practical SOFCs. The first relates to reducing ohmic losses within solid electrolytes. The second relates to the need for developing high performance electrodes since electrolyte reaction rates at both anode and cathode are affected detrimentally as operating temperatures fall. This PhD project has focussed on addressing the first hurdle in two innovative ways: 1. the implementation of solid electrolytes with higher ionic conductivity than zirconia, 2. the development of very thin film electrolytes as thick as 5Ým. Several thin films with novel electrode-electrolyte structures were fabricated and evaluated in order to demonstrate the viability of low temperature SOFC operations. Development of such thin films was innovative and challenging to achieve. The approach taken in this work involved fabricating a dense and thin gadolinia doped ceria (10GDC - Gd 10wt%, Ce 90wt%) oxide electrolyte. 10GDC is an electrolyte exhibiting higher conductivities than conventional materials during low temperature operations. A research contribution of this PhD was the demonstration of the deposition of 10GDC thin films using RF magnetron sputtering for the first time. 10GDC thin film electrolytes with thickness in a range between 0.1 to 5Ým were fabricated on 10 yttrium stabilised zirconium (10YSZ) substrates by using a RF magnetron sputterer. The primary parameters controlling 10GDC thin film deposition using this method were explored in order to identify optimal conditions. The fabricated films were subsequently analysed for their morphology, composition and stoichiometry using a variety of methods, including Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectrometry (EDS), optical microscopy, X-ray Photoelectron Spectroscopy (XPS), and X-ray Diffraction (XRD). A preliminary test was conducted in order to examine the function of 10GDC thin film electrolytes together with the cathode and anode substrates at intermediate temperatures (700oC). A complete planar single cell was designed and assembled for this purpose. However, when fully assembled and tested, the cell failed to generate any voltage or current. Consequently, the remainder of the PhD work was focused on systematically exploring the factors contributing to the assembled fuel cell failure. As fabrication failure analysis is seldom reported in the scientific literature, this analysis represents a significant scientific contribution. This analysis proceeded in a series of steps that involved several different methods, including SEM, red dye analysis, surface morphology and cross section analysis of the cell. It was found that pinholes and cracks were present during the fuel cell operating test. Cathode delamination was also found to have occurred during the test operation. This was determined to be due to thermal expansion mismatch between the cathode substrate and the 10GDC electrolyte thin film. A series of suggestions for future research are presented in the conclusion of this work.
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Cooper, C. S. "Computational modelling of yttrium stabilised zirconia in catalysis." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1431123/.
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This thesis employs a range of computational modelling techniques to explore the structure, properties and catalytic activity of yttrium stabilised zirconia (YSZ) with a focus on its functions as a catalyst in methane reforming by partial oxidation. The surface and bulk properties of the material are explored, including the use of an exhaustive search of all possible defect configurations at a low yttrium loading in a bulk and a surface system allowing conclusions to be drawn about the relationship between defect configurations and stability. One significant property of YSZ materials is their ability to become oxygen ionic conductors at high temperatures, which is crucial to their use in solid oxide fuel cells and may be significant in catalytic applications. This thesis presents results of calculations designed to explore the effects of surfaces and defects on the ionic conductivity of YSZ materials, presenting evidence that oxygen conduction may be significantly enhanced at the surfaces of the material. Calculations using electronic structure techniques are carried out to examine the catalytic properties of YSZ. Initially potential surface active sites are characterised. The surface model is then shown to strongly adsorb and activate molecular oxygen, carbon dioxide and water from the gas phase. The energetics and electron movements in these surface interactions are described. These results provide the basis for investigations of reforming reactions in subsequent chapters and will be of interest in investigations of other catalytic processes over YSZ materials. A novel mechanism of methane C-H bond activation is reported over YSZ, activated by the presence of an adsorbed partially reduced O2 species. The mechanism is investigated in detail, including the use of two electronic structure techniques to allow mechanistic details to be proposed and activation energy estimated. It may be that this mechanism is more generally applicable to oxidative C – H bond activation over many metal oxide materials.
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McClellan, Kenneth James. "Structure/property relations in yttrium oxide-stabilized cubic zirconium oxide single crystals." Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1061395556.
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Holz, Laura Isabel Vilas. "Yttria-stabilized Zirconia with beige colour." Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/21874.
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Mestrado em Engenharia de MateriaisA Zircónia é um cerâmico avançado que se tem destacado como um material versátil e promissor, apresentando uma combinação interessante de propriedades térmicas, elétricas, óticas e mecânicas, pouco comuns nos materiais cerâmicos, sendo por isso utilizada em diversas aplicações. A empresa INNOVNANO produz pós de Zircónia com diferentes características e atualmente tem clientes interessados em cerâmicos à base de Zircónia estabilizada com ítria de coloração bege com propriedades mecânicas específicas. Assim, o trabalho realizado neste estágio pretendeu desenvolver um material que cumpra os requisitos solicitados, tendo como referência uma amostra cedida por um cliente da INNOVNANO cuja cor se pretendia reproduzir, mas cuja composição e processamento eram desconhecidos. Deste modo, o trabalho teve início com a caracterização da amostra de referência através de Microscopia Eletrónica de Varrimento, Difração de raios X, espectroscopia de Raman, Fotoluminescência e Refletância Difusa de modo a permitir compreender o mecanismo de coloração, o qual mostrou ser baseado em defeitos estruturais, desenvolvidos em condições redutoras. A introdução de defeitos extrínsecos pela dopagem com óxido de ferro (Fe2O3) na matriz da Zircónia estabilizada com 2 mol % de ítria (2YSZ) foi a alternativa selecionada para a reprodução da cor solicitada. As amostras foram estudadas do ponto de vista microestrutural, estrutural e ótico. A dopagem com óxido de ferro revelou ser um mecanismo de coloração adequado, reprodutível e irreversível, permitindo o desenvolvimento de um material cromaticamente estável no que concerne à sua utilização em diferentes condições de processamento, tais como diferentes atmosferas e intervalos de temperatura. A estabilidade da cor foi confirmada com tratamentos térmicos em atmosferas oxidantes e redutoras. O efeito da adição do dopante nas propriedades mecânicas da Zircónia foi estudado, avaliando-se a tenacidade à fratura (KIC), a dureza de Vickers (HV10) e a resistência à flexão (σflexural) em amostras com elevado teor de Zircónia tetragonal ( >92 %) e com elevada densidade relativa ( >96%). Os materiais desenvolvidos preenchem os requisitos previamente definidos pela INNOVNANO, tendo-se observado, contudo, um ligeiro decréscimo da tenacidade à fratura com a adição de dopante. Já a dureza Vickers e a resistência à flexão não foram significativamente afetadas pela adição de Fe2O3.
Zirconia is a very versatile advanced ceramic that offers an interesting combination of thermal, chemical, electrical, mechanical and optical properties which are uncommon to find in ceramic materials and therefore is used in several applications. INNOVNANO is one of the main Zirconia powders suppliers in the market with potential clients for beige YSZ ceramics with specific mechanical properties. Thus, the work performed during this internship aimed to develop a material that meets the requested requirements, having as reference a sample provided by an INNOVNANO’s client which colour was intended to be reproduced but which composition and processing were unknown. In this way, the work began with reference material characterization through Scanning Electron Microscopy, X-ray Diffraction, Raman Spectroscopy, Photoluminescence and Diffuse Reflectance in order to understand the colouring mechanism, which was shown to be based on structural defects developed under reducing conditions. The introduction of extrinsic defects by doping with iron oxide (Fe2O3) in the matrix of 2 mol % yttria-stabilized Zirconia (2YSZ) was the alternative selected for the reproduction of the requested colour. The samples were studied from the microstructural, structural and optical point of view. Doping with iron oxide has proved to be a suitable, reproducible and irreversible colouring mechanism allowing the development of a chromatically stable material with respect to its use in different processing conditions such as different atmospheres and temperature ranges. Colour stability was proved by thermal treatments in oxidizing and reducing atmospheres. The effect of dopant addition on the mechanical properties of Zirconia was studied by evaluating the fracture toughness (KIC), Vickers hardness (HV10) and flexural strength (σflexural) in samples with high tetragonal Zirconia content (> 92%) and high relative density (> 96%). The developed material fulfils the requirements previously defined by INNOVNANO, but a slight decrease of the fracture toughness with the addition of dopant was observed while Vickers hardness and flexural strength were not significantly affected by the addition of Fe2O3.
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Sondhi, Anchal. "Investigations in the Mechanism of Carbothermal Reduction of Yttria Stabilized Zirconia for Ultra-high Temperature Ceramics Application and Its Influence on Yttria Contained in It." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500159/.
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Zirconium carbide (ZrC) is a high modulus ceramic with an ultra-high melting temperature and, consequently, is capable of withstanding extreme environments. Carbon-carbon composites (CCCs) are important structural materials in future hypersonic aircraft; however, these materials may be susceptible to degradation when exposed to elevated temperatures during extreme velocities. At speeds of exceeding Mach 5, intense heating of leading edges of the aircraft triggers rapid oxidation of carbon in CCCs resulting in degradation of the structure and probable failure. Environmental/thermal barrier coatings (EBC/TBC) are employed to protect airfoil structures from extreme conditions. Yttria stabilized zirconia (YSZ) is a well-known EBC/TBC material currently used to protect metallic turbine blades and other aerospace structures. In this work, 3 mol% YSZ has been studied as a potential EBC/TBC on CCCs. However, YSZ is an oxygen conductor and may not sufficiently slow the oxidation of the underlying CCC. Under appropriate conditions, ZrC can form at the interface between CCC and YSZ. Because ZrC is a poor oxygen ion conductor in addition to its stability at high temperatures, it can reduce the oxygen transport to the CCC and thus increase the service lifetime of the structure. This dissertation investigates the thermodynamics and kinetics of the YSZ/ZrC/CCC system and the resulting structural changes across multiple size scales. A series of experiments were conducted to understand the mechanisms and species involved in the carbothermal reduction of ZrO2 to form ZrC. 3 mol% YSZ and graphite powders were uniaxially pressed into pellets and reacted in a graphite (C) furnace. Rietveld x-ray diffraction phase quantification determined that greater fractions of ZrC were formed when carbon was the majority mobile species. These results were validated by modeling the process thermochemically and were confirmed with additional experiments. Measurements were conducted to examine the effect of carbothermal reduction on the bond lengths in YSZ and ZrC. Subsequent extended x-ray absorption fine structure (EXAFS) measurements and calculations showed Zr-O, Zr-C and Zr-Zr bond lengths to be unchanged after carbothermal reduction. Energy dispersive spectroscopy (EDS) line scan and mapping were carried out on carbothermaly reduced 3 mol% YSZ and 10 mol% YSZ powders. Results revealed Y2O3 stabilizer forming agglomerates with a very low solubility in ZrC.
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Kilo, Martin, and Robert A. Jackson. "Oxygen transport and association in yttria stabilised zirconia." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195369.
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Kilo, Martin, and Robert A. Jackson. "Oxygen transport and association in yttria stabilised zirconia." Diffusion fundamentals 2 (2005) 23, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14353.
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Wei, Chiao-Chien. "Yttria stabilised zirconia (YSZ) membranes and their applications." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4345.
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1 Abstract The development of ceramic hollow-fibre membranes has gradually grown in the past decade. This specific geometry which has a high surface area per unit volume can dramatically increase the efficiency of separation processes and can be adapted to a variety of industrial applications. In addition, ceramic membranes are well known for their superior chemical and thermal stability which allows them to operate at high temperatures and/or in chemically harsh environments. Nevertheless, the main challenge for their industrial application is their insufficient mechanical strength. Yttria-stabilized zirconia (YSZ) is selected as a membrane material in this study. This is because the material has superior mechanical strength and it is relatively cheaper than other ceramic materials. The ionic conducting property of YSZ material is also a benefit when it is used in electrochemical applications. Porous and dense YSZ hollow-fibre membranes have been developed in the study using a combined phase inversion and sintering process. Different membrane morphologies, surface properties, mechanical strength and porosity could be achieved by controlling the YSZ content and sintering temperature. The developed YSZ hollow-fibre membranes with porous or dense structures show great potential for a variety of applications. Porous YSZ hollow-fibre membranes can be used as membrane contactors in aqueous media or for fluid separations in harsh environments, which most polymeric membranes cannot withstand. For the application of membrane contactors in aqueous media, the nature of the YSZ membranes must be modified from hydrophilic to hydrophobic in order to keep them non-wetted during the aqueous contacting processes. A robust and hydrophobic YSZ hollow-fibre membrane was developed by introducing a pretreatment technique, followed by a grafting procedure. The hydrophobic YSZ membrane was found to be thermally stable up to 270 °C and chemically stable in hexane for 100 h. This membrane was then applied to the absorption of carbon dioxide from a high concentration aqueous ethanolamine solution. The results demonstrated the high efficiency of the ceramic hollow-fibre membrane contactor compared to traditional devices. Dense YSZ hollow-fibre membranes with outer diameters of 1.28 mm have been used as an electrolyte support in a solid oxide fuel cell. The YSZ electrolyte-supported SOFC was prepared at relatively lower sintering temperatures and shorter sintering durations. The YSZ-based hollow fibre SOFC demonstrated its ionic stability in a redox environment and mechanical stability at temperatures up to 800 °C. The results also demonstrated its electrochemical performance at high temperature. In summary, this thesis focuses on the development of YSZ hollow-fibre membranes from the initial step of fabricating the membrane to the final step of their potential application. Different structures of YSZ hollow-fibre membranes were studied, discussed and their potential performance was compared to the achievements of others in order to gain more understanding and information on the use of the membranes for practical applications.
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Clifton, Andrew Charles. "Novel processing of nanostructured yttria-stabilized zirconia." abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1438928.
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Pietrowski, Marek J., Souza Roger A. De, Umberto Anselmi-Tamburini, Sangtae Kim, Zuhair A. Munir, and Manfred Martin. "Oxygen diffusion in nanocrystalline yttria-stabilized zirconia." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186906.
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Xia, X. "Computational modelling study of yttria-stabilized zirconia." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20483/.
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Interatomic potential and quantum mechanical simulation techniques have been applied to both the bulk and surfaces of yttrium-stabilized cubic zirconia (YSZ) with special reference to its role in partial oxidation reaction at high temperature. The stabilities of pure ZrO2 phases and surfaces have been examined. The bulk structures of low pressure phases are reproduced with the observed order of stability: monoclinic > tetragonal > cubic zirconia. The relative stability of plane cubic ZrO2 surfaces is predicted to be (111)c > (110)c > (100)c > (310)c. In addition, the stability of topological surfaces is found to be reduced with the coordination number of Zr ions at the topological sites in the order: plane > step > kink > corner. The dispersion of defects in YSZ systems has been studied, considering both the dopant content and surface segregation. In the bulk, the yttrium dopants tend to form a pair with two yttrium atoms close to each other and preferentially occupying the 1st or 2nd nearest neighbour (NN) sites to the compensating oxygen vacancy. At the surface, yttrium segregates to the top layers (up to 4-5 Å) of the dominant (111) surface of YSZ. The composition of the outermost surface of YSZ is predicted to be independent of Y bulk concentration and reach a maximum Y/Zr ratio of 1:1. In relation to catalytic oxidation, the interaction between oxygen molecules and the (111) surfaces of pure c-ZrO2 and YSZ have been investigated using quantum-mechanical DFT-GGA methods. The adsorption states of oxygen and the pathways for dissociation have been indentified on the plane and stepped (111) surfaces. In general, the creation of oxygen vacancies by yttrium doping provides an active site for oxygen adsorption. In addition, the low-coordinated Zr cations on the YSZ surfaces can attract strongly reduced oxygen species and the most stable adsorption state of oxygen is adopted to achieve a higher bond saturation of the neighbouring Zr site.
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Pietrowski, Marek J., Souza Roger A. De, Umberto Anselmi-Tamburini, Sangtae Kim, Zuhair A. Munir, and Manfred Martin. "Oxygen diffusion in nanocrystalline yttria-stabilized zirconia." Diffusion fundamentals 12 (2010) 54, 2010. https://ul.qucosa.de/id/qucosa%3A13890.
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Santa, Cruz Hernán. "Processing and properties of macroporous nanocrystalline yttria stabilised zirconia ceramics." Berlin dissertation.de, 2009. http://d-nb.info/993571190/04.
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Marinis, Aristotelis. "Fracture toughness of yttrium stabilized zirconia sintered in conventional and microwave ovens." Thesis, University of Iowa, 2011. https://ir.uiowa.edu/etd/1017.
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Chaba, Pudumo Jimmy. "Computer simulation studies of fastion yttria-stabilised cubic zirconia." Thesis, University of Limpopo, 1999. http://hdl.handle.net/10386/2076.
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Asadikiya, Mohammad. "Thermodynamic Investigation of Yttria-Stabilized Zirconia (YSZ) System." FIU Digital Commons, 2017. https://digitalcommons.fiu.edu/etd/3550.
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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.
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Davis, Andrew Scott. "Temperature Induced Deflection of Yttria Stabilized Zirconia Membranes." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1338369600.
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Zhang, Qingyin. "Molecular simulation of transport in Yttria stabilized-zirconia and silica nanopore." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557686.
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Burke, Darren. "Low temperature degradation of yttria stabilised tetragonal zirconia polycrystals (TZP's)." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287662.
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Zhang, Qingyin, and 張慶印. "Molecular simulation of transport in Yttria stabilized-zirconia and silica nanopore." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557686.
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Stollberg, David Walter. "Nanoindentation of YSZ-alumina ceramic thin films grown by combustion chemical vapor deposition." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/43977.
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Combustion chemical vapor deposition (combustion CVD) is a thin film deposition process that uses a flame created by the ignition of an aerosol containing precursors dissolved in a flammable solvent. Combustion CVD is a relatively new technique for creating thin film oxide coatings. Combustion CVD has been successfully used to deposit high quality thin oxide films for potential applications such as thermal barrier coatings, dielectric thin films, composite interlayer coatings, etc. The present work involved developing the optimum parameters for deposition of thin films of yttria-stabilized zirconia (YSZ), alumina (Al₂O₃), and YSZ-alumina composites followed by a determination of the mechanical properties of the films (measured using nanoindentation) as a function of composition. The optimized parameters for deposition of YSZ, alumina, and YSZ-alumina composites onto single crystal a-plane alumina involved using an organic liquid as the flammable solvent and Y 2-ethylhexanoate, Zr 2-ethylhexanoate and Al acetylacetonate as the metal precursors at a 0.002 M concentration delivered at 4 ml/min at flame temperatures of 155 ℃ and substrate temperatures of 105 ℃. The resulting films were grown with deposition rates of ~ 1.5 μm/hr. Measurement of the mechanical properties (hardness, elastic modulus and fracture toughness) of the films was performed using a mechanical properties microprobe called the Nanoindenter®. In order to obtain valid results from nanoindentation, the combustion CVD films were optimized for minimum surface roughness and grown to a thickness of approximately 0.8 μm. With the penetration depth of the indenter at approximately 150 nm, the 800 nm thickness of the film made influences of the substrate on the measurements negligible. The hardnesses and elastic moduli of the YSZ-alumina films did not vary with the composition of the film. The fracture toughness, however, did show a dependence on the composition. It was found that second phase particles of alumina grown into a YSZ matrix increased the fracture toughness of the films (on average, 1.76 MPa• m⁰.⁵ for 100% YSZ to 2.49 MPa• m⁰.⁵ for 70 mol% YSZ/30 mol% alumina). Similarly, second phase particles of YSZ grown into an alumina matrix also increased the fracture toughness (on average, 2.20 MPa• m⁰.⁵ for 100% alumina to 2.45 MPa• m⁰.⁵ for 37.2 mol% YSZ/62.8 mol% alumina). Modeling of the fracture toughness of the YSZ-alumina films was successfully achieved by using the following toughening mechanisms: crack deflection from the second phase particles, grain bridging around the particles, and residual stress from the CTE mismatch between the film and the substrate and between the second phase particles and the matrix of the film.
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Primdahl, Søren. "Nickel/Yttria-stabilised zirconia cermet anodes for solid oxide fuel cells." Enschede : University of Twente [Host], 1999. http://doc.utwente.nl/58232.
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Zhang, Wenzhong. "Yttria stabilised zirconia pH sensor development for high temperature aqueous environments." Thesis, University of Newcastle Upon Tyne, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402271.
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Kim, Jong Min. "Electrochemical Promotion of Gold Nanoparticles Supported on Yttria-Stabilized Zirconia." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20435.
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The feasibility of highly dispersed gold nanocatalyst supported on yttria-stabilized zirconia (YSZ) for the model reactions of C2H4 and CO oxidation is demonstrated for the first time. Gold nanoparticles are synthesized on YSZ powder by chemical reduction of the precursor salt in the mixture of ethanol, water and polyvinylpyrrolidone (PVP). Resulting metal loading of the catalysts are 1 wt.% with average particle sizes ranging from 6 to 9 nm. Results of CO and C2H4 oxidation display catalytic activity at 65 0C and 25 0C for CO and C2H4 oxidation, respectively. The catalytic properties of the catalysts are different due to their average particle size. Electrochemical Promotion of Catalysis (EPOC) of C2H4 oxidation is demonstrated. Application of constant potential difference between two electrodes in the bipolar electrochemical cell led to increase in C2H4 conversion. A proposed mechanism explains the bipolar EPOC phenomenon through formation of O2- flux across the electrochemical cell, resulting in the change of Work Function of gold nanoparticles placed in between the electrodes and is electronically isolated.
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Peters, Travis L. "Solid-State Yttria-Stabilized Zirconia Electrochemical Sensors for Extreme Environments." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563457578931313.
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Brown, Philip D. "Yttria stabilized zirconia buffered silicon: substrates for YBCO microwave applications." FIU Digital Commons, 1998. http://digitalcommons.fiu.edu/etd/1878.
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The use Yttria-Stabilized Zirconia (YSZ) as a buffer layer for YBa2Cu3O7-x (YBCO) thin films on (100) silicon (Si) substrates is investigated. YSZ was grown using on-axis pulsed D.C. (PDC) and R.F. magnetron sputtering from a 99.9% pure YSZ target [(Y2O3)0.08(ZrO2)0.92]. Sputtering was carried out in Argon/Oxygen atmosphere at total pressures ranging from 6 to 320 mTorr containing 0.1 to 10% Oxygen. Substrate temperatures were varied from 300° C to 900° C. (111), (100) and mixed (100) and (111) oriented YSZ films were produced with thickness of 50 to 200 nm. YBCO films, 200 nm thick, were then grown by pulsed-laser deposition in an atmosphere of 0.5 Torr 02 at 750° C. The critical temperature (TC(R=0)) of the films produced was 75 K - 81K. A "T" resonator design was patterned on the YBCO/YSZ/Si structure and tested. Results show a band-reject response centered at 3.872 GHz with a quality factor of 20,000.
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Verdon, Christopher. "Development and characterization of yttria stabilized zirconia doped with erbia." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/53996.
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Zirconia ceramics have high thermal resistance, chemical inertness and irradiation stability. One application where zirconia composites may find use is in supercritical water nuclear reactors (SCWR), which are expected to have improved thermal efficiency in comparison to current nuclear reactors. Zirconia ceramics may be useful as insulator materials in SCWR pressure tubes where high thermal resistance, chemical stability, irradiation resistance and supercritical water (SCW) degradation resistance are necessary. Additionally, some preliminary tests have found that specific zirconia composites, such as yttria stabilized zirconia (YSZ) outperform pure zirconia in SCW environments.
YSZ is a commonly used zirconia composite, and has an excellent thermal resistance and chemical inertness. Due to the presence of yttrium, the high temperature brittle failure caused by the tetragonal to monoclinic crystal structure transformation frequently observed in zirconia is avoided. However, currently available YSZ does not fully satisfy the SCW degradation targets for a SCWR, thus motivating research into the possibility of doping YSZ to further improve YSZ’s SCW degradation resistance.
One possible dopant is erbium oxide (erbia), a rare earth oxide that is used as a technical ceramic and has been studied for use in nuclear applications due to its ability to absorb neutrons. Erbia has not been studied in depth as a dopant in the zirconia system or in YSZ. Thus, this research was conducted in order to determine the effect of erbia doping on the densification, hardness, grain size, crystal lattice parameter and SCW degradation resistance of YSZ.
Erbia-YSZ composites of 8mol% YSZ with 5, 10 and 15mol% erbia were fabricated by spark plasma sintering (SPS), a novel powder metallurgy process that is known to produce high density composites, at 1200, 1300 and 1400°C with 30 and 60MPa pressures for 5min. Densification during SPS was characterized based on ram position during sintering. Grain size analysis of the as-sintered composites was performed on fractured surfaces. A preliminary study of the SCW degradation resistance of the erbia-YSZ composites was conducted by exposing them to SCW for 2.5h in pressure vessels.
The results suggest that erbia-YSZ composites with >95% theoretical density (TD) were successfully fabricated using SPS. Erbia doping into YSZ was found to inhibit densification, but promoted grain growth and resulted in crystal lattice expansion. Additionally, weight loss during SCW degradation revealed that erbia doping improved the SCW degradation resistance of YSZ, but additional work is necessary to further improve the degradation resistance to meet SCWR targets.Applied Science, Faculty of
Engineering, School of (Okanagan)
Graduate
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Hohls, Adrian Christian. "Investigation into phase transformation of Yttria stabilized zirconia femoral heads." Diss., University of Pretoria, 2010. http://hdl.handle.net/2263/26215.
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27 Retrieved Yttria Stabilised Tetragonal Zirconia (Y-TZP) femoral heads were studied for the occurrence of tetragonal to monoclinic phase transformation and the effects that such transformation has on the bearing surface. The mean monoclinic percentage found is 53.6% with 25 of the samples having transformed more than 20%. This finding nullifies earlier predictions that it would take 25 to 30 years to transform to a monoclinic content of 30 to 40% inside the human body (Chevalier, Drouin&Calés 1997). It was however shown that Hot Isostatic Pressed (HIP’ed) Y-TZP femoral heads have a better, though still not adequate, resistance to phase transformation in the human body than non-HIP’ed femoral heads. Results of various investigations show that this transformation degrades the surface condition of the femoral heads, which in turn increases wear and subsequently decreases the survival rate of the prosthesis due to a greater risk of aseptic loosening. It is postulated that a great contributing factor to the phase transformation is increased temperatures inside the bearing couple, due to inadequate lubrication between the two bearing surfaces. Tetragonal to monoclinic phase transformation and its associated effects renders Y-TZP femoral heads less attractive for hip replacements.Dissertation (MEng)--University of Pretoria, 2010.
Mechanical and Aeronautical Engineering
unrestricted
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Gibson, Iain R. "The characterisation and electrical properties of novel 8 mol% yttria-stabilised zirconias." Thesis, University of Aberdeen, 1995. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU527983.
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The powder characteristics of the following 8 mol% yttria-stabilised zirconia samples were studied: Tioxide yttria-coated zirconia (coated-YSZ), Tioxide co-milled YSZ, Tosoh co-precipitated YSZ and A YSZ prepared in-house by a conventional solid state route. Co-milled YSZ powders containing 3-11 mol% yttria were also studied. The phase assemblage of as-received and reacted powders was investigated by XRD. As-received co-precipitated YSZ was cubic single phase. All other as-received powders consisted of a mixture of yttria and monoclinic zirconia. The phase evolution of the samples between 1000 and 1500° was studied. The coated and co-milled YSZ were cubic single phase only after reaction at 1300°. The rate at which the different powders reached equilibrium on heating decreased in the sequence: coated-YSZ > co-milled YSZ>YSZ prepared in-house. This difference in reactivity is discussed in terms of the yttria distribution in the as-received powder. A detailed study of the yttria-zirconia reaction in coated-YSZ was made. A model was devised to describe the counter-diffraction of yttria from the external coating and the zirconia. TEM analysis of a partially-reacted coated-YSZ sample showed that some grains contained to tetragonal inner core surrounded by a cubic outer shell. The kinetics of the yttria-zirconia reaction were studied: an activation energy of 470-555 kJmol-1 was determined, which was attributed to cation counter-diffusion. The formation of the metastable t'-phase in YSZ samples was studied. On rapid-cooling, cubic YSZ solid solutions containing between 3 and 7.7 mol% yttria transformed to the t'-phase: for compositions greater than 7.7 mol% the cubic solid solutions were retained to room temperature.
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Joomun, Nazim Ibne. "Oxygen transport in yttria-stabilised zirconia and zinc oxide under microwave heating." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542944.
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Kanellopoulos, Panayotis. "Control of the properties of yttria-stabilised zirconia (Y-TZP) during manufacturing." Thesis, University of Sunderland, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443637.
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Parkes, Michael. "Ab initio modeling of yttria stabilised zirconia for solid oxide fuel cells." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/25541.
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Fuel cells are electrochemical devices that convert chemical fuels directly into electricity, heat, and waste products with higher efficiencies than many conventional combustion technologies. Fuel cells have already found applications in automotive and domestic applications, where their high efficiencies offer potential reductions in CO2 emissions as well as energy savings. A promising technology is the solid oxide fuel cell (SOFC), which typically runs at temperatures between 500 - 1000C, and can convert hydrogen rich gases, such as methane, directly into heat and electricity. This thesis presents work on developing improved atomistic models of yttria stabilised zirconia (YSZ), which is used as a catalyst support and electrolyte material in a solid oxide fuel cell. The catalyst, YSZ, and a gas phase containing fuel molecules, meet at the anode to form the anode triple phase boundary (TPB) in an SOFC. The anode TPB is the site at which fuel molecules undergo electrochemical oxidation, a process that releases electrons and waste products. Unfortunately the anode is susceptible to poisoning and damage through detrimental chemical reactions which can lead to carbon deposition and sulphur poisoning. A long term aim for the field of SOFC catalysis is to understand these reactions and design improved catalysts which are resistant to contamination processes. However, to date, the detailed mechanisms involved in these reactions have not been established; even the mechanism for the oxidation of hydrogen at the anode TPB is fiercely debated. For these reasons, there is interest in developing atomistic models of the anode TPB to investigate the thermodynamics of possible reaction paths. Modeling the anode TPB is dependant on many factors including: materials, surface structure, interfaces, distribution of local defects. A detailed knowledge of the YSZ surface chemistry is currently inhibited by a poor understanding of the distribution and local atomistic structure of the dopant Y3+ ions and oxygen vacancies in the bulk crystal and at the surfaces. In this thesis, a comprehensive search for low energy defect structures using a combined classical modeling and density functional theory (DFT) approach is used to identify the low energy defect structures of 3.2mol% YSZ. 3.2mol% YSZ is chosen as the limit of low dopant concentration and as a simple system to investigate, avoiding the the combinatorial complexity of higher dopant concentrations and defect-defect interactions. Through analysis of energetics computed using; the best available empirical potential model, point charges, DFT, and local strain energy estimated in the harmonic approximation, we examine the main chemical and physical interactions that determine the low energy structures. It is found that the empirical potential model reproduces a general trend of increasing DFT energetics across a series of locally strain relaxed structures, but is unreliable both as it predicts some incorrect low energy structures, and because it finds some meta-stable structures to be unstable. A better predictor of low energy defect structures is the total electrostatic energy of a simple point charge model calculated at the unrelaxed geometries of the defects. In addition, the strain relaxation energy is substantial, and is estimated effectively in the harmonic approximation to the imaginary phonon modes of cubic zirconia (c-ZrO2), but it is not a determining factor for the relative stabilities of low energy defect structures. These results allow us to propose a simple method for identifying low energy YSZ defect structures. The findings from the studies of bulk 3.2mol% YSZ are used to establish the low energy structures of a 3.2mol% YSZ (111) surface model. After initially demonstrating that a slab model, much larger than that used in previous DFT studies is required to obtain a converged surface energy, the energetic preference for yttrium to segregate to the (111) surface is investigated. After establishing that yttrium indeed segregates to the (111) surface, we compute the DFT energies of 20 low energy symmetry inequivalent surface structures, and identify the preferential defect configurations and surface chemistry sites. In addition, the DFT energy of the low energy NN structure proposed by Reaxff modeling is computed. It is shown that this structures is significantly higher in energy than our minimum energy structure, which has NNN geometry. This highlights the need for large scale DFT calculations in understanding the YSZ (111) surface structure. Having obtained atomistic structures for the surface reaction sites, water dissociation onto the lowest energy YSZ (111) surface is investigated. It is shown that it is preferable for water to associatively adsorb to the YSZ surface, and this is optimal when water adsorbs to the yttrium site. Dissociative adsorption of water is only possible over zirconium sites with the process generally being endothermic. Some exothermic paths for dissociative adsorption exist, however there are large energy barriers to the process. Associative adsorbtion to the surface yttrium site is the global minimum of the system, and yttrium sites appear to act as a trap for water molecules. Finally, the methodology developed in previous sections is used to investigate the 6.7mol% YSZ system, which is closer to the Y2O3 dopant concentration used in most commercial SOFCs (8 - 10 mol%). It is found that, whereas the electrostatic energy of the unrelaxed structures calculated using a point charge model was a good predictor of the likely low energy 3.2mol% defect structures, it is a poor predictor of the likely low energy 6.7mol% defect structures. In addition, while it was found that the best available Born-Mayer-Huggins potential model recreated general trends in DFT energies at 3.2mol%, it completely fails to reproduce DFT energy differences at 6.7mol%. In the absence of an easy to calculate, reliable predictor of the likely low energy DFT defect structures, we correlate the formation energies of the structures to simple geometric parameters. We perform an exhaustive search on 2857 symmetry inequivalent structures, characterising every structure in terms of intuitive quantities, such as: vacancy - vacancy separation, the average vacancy - Y3+ interatomic separation, the average Y3+ - Y3+ interatomic speration, the surface area occupied by the defect cluster, and the volume of the defect cluster. It is possible to explain the electrostatic formation energies of the defects in terms of intuitive attractive and repulsive forces and to find weak trends between the geometric descriptors and the final relaxed DFT energies, however, without an extensive database of fully relaxed DFT energies, it is hard to determine the statistical meaning of these results. This result highlights the combinatorial complexity of the 6.7mol% system and establishes the need for further large scale DFT calculations on the 6.7 mol% system.
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Yang, Fan. "Electrical and thermal properties of yttria-stabilised zirconia (YSZ)- based ceramic materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/electrical-and-thermal-properties-of-yttriastabilised-zirconia-ysz-based-ceramic-materials(82568afe-ffcb-4a38-9166-e5de83337763).html.
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Electrical and thermal conductivities of the yttria-stabilised zirconia/alumina (YSZ/Al2O3) composites and the yttria-zirconia-ceria (YSZ-CeO2) solid solutions are studied in this thesis. The electrical conductivity of the YSZ/Al2O3 composites decreases with an increase in the volume fraction of Al2O3 and exhibits typical percolation behaviour. The electrical conductivity of the YSZ/Al2O3 interface is higher than that of the YSZ grain boundary, but lower than that of the YSZ grains. The thermal conductivity of the YSZ/Al2O3 composites increases with an increase in the Al2O3 volume fraction, and it can be fitted well to the Maxwell theoretical model, which indicates the absence of obvious interfacial thermal resistances in the composites. The low interfacial thermal resistance of the YSZ/Al2O3 interface is due to the 'clean' and coherent nature of the YSZ/Al2O3 interface, along with the small difference between the elastic properties of YSZ and Al2O3. The electrical conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions has a 'V-shape' variation as a function of the mole ratio of CeO2 (x). In the ZrO2-rich region (x < 0.5), CeO2 doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO2-rich region (x > 0.5), the increase of x increases the lattice parameter, which enlarges the free channel for oxygen vacancy migration. A comparison of the YSZ-CeO2 solid solutions with the YSZ-HfO2 series indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions.The thermal conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions also has a 'V-shape' variation as a function of the mole ratio of CeO2 (x), which indicates an incorporation of Zr4+ and Ce4+ can effectively decrease the thermal conductivity of the end members YSZ and yttria-doped ceria (YDC). In the ZrO2-rich region (0 ≤ x ≤ 0.5), the thermal conductivity is almost temperature independent; in the CeO2-rich region (0.5 ≤ x ≤ 1), it decreases obviously with increasing temperature. By calculating the phonon scattering coefficients, it is concluded that the composition dependence of the thermal conductivity in the ternary solid solutions is dominated by the mass difference between Zr and Ce at the cation sites, whereas the temperature dependence is determined by the order/disorder of oxygen vacancies at the anion sites.
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AMARANTE, JOSE EDUARDO VASCONCELLOS. "CHARACTERIZATION OF THE MECHANICAL PROPERTIES OF YTTRIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTALS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36354@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORPROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE DOUTORADO SANDUÍCHE NO EXTERIOR
Materiais à base de zircônia apresentam excelentes propriedades mecânicas, estabilidade química e dimensional, tenacidade, juntamente com um módulo de Young na mesma ordem de grandeza de ligas de aço inoxidável. Devido à essas características, a zircônia tem sido utilizada em uma ampla gama de aplicações, incluindo a fabricação de peças protéticas. As modificações na composição da zircônia e o desenvolvimento do CAD-CAM (computer assisted design) fizeram com que as próteses à base de zircônia se tornassem um procedimento clinico frequentemente realizado na atual Odontologia restauradora. Blocos pré-sinterizados de zircônia, fabricados industrialmente, homogêneos e com falhas mínimas são usinados em um ambiente industrial controlado para receberem a forma desejada. Após a usinagem, as peças em zircônia são sinterizadas para promover sua densificação final. Este processo reduz os possíveis defeitos criados por etapas laboratoriais manuais e intermediárias na confecção de restaurações dentárias. O objetivo deste estudo foi avaliar o efeito da degradação hidrotérmica e do jateamento com óxido de alumínio nas propriedades mecânicas de três tipos de zircônia tetragonal policristalina estabilizada por ítria (ZTPI). Três tipos de zircônias contendo diferentes concentrações de ítria e grau de translucidez foram utilizadas: ZTPI com 5,2 por cento mol (Prettau Anterior Super-Translúcida da Zirkonzahn), ZTPI com 3 por cento mol de Y2O3 (VIPI Block Zirconn) e ZTPI com 3 por cento mol de Y2O3 com translucidez melhorada (VIPI Block Zirconn Translucent). Todas indicadas para uso em próteses odontológicas monolíticas. 15 corpos de prova de cada zircônia testada foram sinterizados e divididos em três grupos de acordo com otratamento de superfície e processo de degradação. No Grupo I as zircônias sofreram jateamento com óxido de alumino. No grupo II as zircônias foram lixadas e polidas. No grupo III as zircônias foram lixadas, polidas, recuperadas e degradadas em reator hidrotérmico por 5 horas a 134 graus Celsius e 2 bar. Para a caracterização microestrutural foram realizados ensaios de difração de raios-X, espectrometria Raman, densidade relativa, microdureza Vickers, rugosidade superficial e análise de tamanho médio de grão por MEV. Os resultados mostraram que a densidade de todos os grupos ficou acima de 99 por cento e que a degradação promoveu a transformação de fase monoclínica e afetou os valores de resistência à flexão. No entanto, a indicação clínica das cerâmicas não foi alterada. O tamanho médio de grão ficou entre 0,367 e 0,621 micrômetros. A dureza e tenacidade à fratura do material não sofreram alterações em função do teor de ítria ou das fases cristalinas presentes. A degradação não afetou de forma significativa os valores de rugosidade, porém, o jateamento com óxido de alumínio não só afetou os valores de flexão como alterou a indicação clínica de cerâmicas utilizadas neste trabalho.
Zirconia-based materials present excellent mechanical properties, tenacity, chemical, and dimensional stability as well as their Young modulus is similar to stainless steel alloys. Due to these characteristics, zirconia has been largely applied in the fabrication of dental prostheses. Modifications in the zirconia composition and the development of CAD-CAM systems has allowed zirconia-based restorations to become a common clinical procedure in current dentistry. Fully sintered and homogeneous blocks from industry are machined at controlled environments seeking to obtain the desired geometry of the restorations. After the machining process, the restorations are sintered to improve their density. This process reduces the failures caused by manual and laboratorial manipulations during fabrication procedure. The aim of this study is to evaluate the effect of hydrothermal aging and sandblasting with aluminum oxide on the mechanical properties of three Yttria-containing tetragonal zirconia polycrystalline (Y-TZP). Three types of Y-TZP, containing different yttria dioxide, were used in the study: Y-TZP with 5,2 per cent mol Y2O3 (Prettau Anterior Super-Translúcida da Zirkonzahn), Y-TZP with 3 per cent mol de Y2O3 (VIPI Block Zirconn) and Y-TZP with 3 per cent mol Y2O3 and optimized translucency (VIPI Block Zirconn Translucent). All the zirconias are indicated for being used as monolithic restorations. 15 specimens from each zirconia tested were sintered and distributed to three groups according to the surface treatment and the aging process. In the group I, the specimens were sandblasted with aluminum oxide particles. For the group II, the zirconia specimens were abraded and polished. In the group III, the specimens were abraded, polished, recovered and aged in a reactor controller for 5 hours at 134 degrees Celsius and 2 bar. The characterization of the zirconia microstructure has been carried out by means of: X-ray diffraction, relative density, Raman spectroscopy, Vickers microhardness, superficial roughness. In addition, the average grain size analysis by scanning electron microscopy were made. The results show that the relative density values were above 99 per cent, and that the hydrothermal aging causes monoclinic phase transformation and affects flexural strength values. However, the clinical indications of materials did not change. The average grain size was between 0.367 and 0.621. The microhardness and tenacity values of materials did not change by yttria concentration or crystallographic phases. The roughness values were not significantly affected by the hydrothermal aging. On the other hand, the flexural strength values were affected by sandblasting process and clinical indication of ceramics tested was changed.
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Xu, Hui. "Fabrication of yttria-stabilized-zirconia (YSZ) coatings by electrophoretic deposition (EPD)." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/fabrication-of-yttriastabilizedzirconia-ysz-coatings-by-electrophoretic-deposition-epd(db294fcd-90d1-459a-939c-c6a9c13e5e9f).html.
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Yttria stabilized zirconia (YSZ) coatings were produced from a YSZ suspension in acetylacetone (ACAC) using electrophoretic deposition (EPD) and then consolidated via the natural drying and isothermal sintering with the constraint of the metal substrates. Before EPD, the operational pH of the suspension was adjusted by addition of acetic acid or organic bases. The effect of suspension pH on the deposition of EPD coatings was studied with respect to the suspension stability, coating density and microstructure both for a mono-sized system and micro-nano binary systems. The constrained drying process of the deposits was examined via the measurement of the critical cracking thickness (CCT). The sinterability of coatings was evaluated by micro-hardness and microstructure. For a mono-sized (0.26μm) suspension, results showed that the zeta potential had a high positive value on both sides of the isoelectric point (IEP). This probably resulted from the adsorption of base molecules triethanolamine (TEA), detected by fourier transform infrared spectroscopy. Three alkalis with different molecular structure were compared and the effect of their molecule length on the interparticle repulsion was discussed. Accordingly, the double layer thickness of the particles can be estimated. Based on this, particle interactions were estimated for different pH suspensions. The reduced particle coagulation increased the packing density of the EPD coatings from 38 % at pH 7.4 to 53 % at pH 8.4. Therefore, subsequent sintering of coatings was promoted. After sintering at 1200 °C, coatings made in pH 8.4 suspensions obtained a much higher hardness and had fewer big pores than coatings fabricated in pH 7.4 suspensions. The CCT of the latter is slightly higher than the former which might be ascribed to its particle network structure. In a binary suspension composed of the coarse (1μm) and fine (with average size of 100 nm or 10 nm, content varied in 0-30 wt. % to the powder mixture) YSZ powders, interactions between different species can be tuned by the zeta potential of individual component. Binary particles can be well dispersed at pH 4 when both of the coarse and fine powders reached their highest zeta potentials. Heterocoagulation occurred between them to form a haloing structure with fine powders covered on the coarse particle surfaces when they exhibited zeta potentials of the opposite sign at pH 8.6. Particle interactions were estimated and the microstructures of the binary coatings were examined to discuss how the different fine particle sizes influenced the particle packing after EPD. At pH 4, there existed a “stability window” for the 10 nm fines at 10 wt. % whereas no noticeable the border of the window can be observed for 100 nm fines within the measuring range. 10 nm and 100 nm fine powders gave similar overall densities of binary EPD coatings which were independent of the fine powder content. For heterocoagulation coatings made at pH 8.6, although the adsorption of fine particles reduce the agglomeration of coarse powder, the low zeta potential of the halos led to a loose structure of the “skeleton” ( the packing of the coarse powder) in the final binary coatings. 10 nm fine powders was observed to give a higher CCT and denser particle packing than 100 nm fine powders especially in a pre-saturated heterocoagulated binary coatings at 20 wt. % fine powder content. In order to further improve the sintering of the EPD coatings at low temperature sintering, a layer of CuO was applied on the coarse powder surface. With the addition of 30 wt. % fine powders, the hardness of EPD coatings after sintering 2 hours at 1150°C increased from 6 to 61 Vickers. With the presence of CuO, the hardness values were enhanced by 2.5-4.25 times. The density measurements indicated that the CuO layer not only served as a sintering aid, the CuO layer also helped with the binary particle packing particularly in the heterocoagulation condition because of the stronger particle interactions between the fine powders and CuO modified coarse powders. It seems that CuO had no significant impact on the cracking resistance of the binary coatings during drying, however t-m phase transformation was observed during sintering possibly due to the liquid phase induce by CuO.
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Poulin, Carl. "Heck-Mizoroki reaction using palladium and nickel on yttria stabilized zirconia." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/28018.
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This work was composed of studies analysing the capacity of Pd-YSZ and Ni-YSZ as a heterogeneous catalyst for the Heck-Mizoroki reaction. Following an optimization, mechanistic studies were undertaken with Pd-YSZ. P-XRD measurements showed a decrease in the amount of metal present in the catalyst after a cycle of Heck reaction. Also, two triple phase test were done. Using a resin supported reactant, it was showed that palladium leaches into solution and reacts through a homogeneous cycle. Also, the contribution of true heterogeneous surface catalysis was examined by means of a thiol-based palladium scavenger that neutralised homogeneous catalysis. While it is impossible to completely dismiss true surface catalysis, the negative result showed that surface catalysis did not contribute significantly to the overall reactivity.
Reactions showed reactivity up to 770'000 TON with mesoporous 5% Pd-YSZ calcinated to 600°C.
Using the self-assembly and the co-precipitation method, Ni-YSZ catalysts of 1%, 5% and 10% were synthesized and calcinated to 400°C, 600°C and 950°C. Catalyst characterization through p-XRD, physisorption and chemisorption allowed knowledge of the crystallite size surface area and metallic surface area. A structure-reactivity relationship study showed a limited effect in the ability of high surface area and low particle sizes to accelerate catalysis.
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Bridget, Tshamano Matamela. "Synthesis & characterization of yttria stabilised zirconia (YSZ) hollow fibre support for Pd based membrane." Thesis, University of the Western Cape, 2013. http://hdl.handle.net/11394/3832.
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Inorganic based membranes which have a symmetric/asymmetric structure have been
produced using an immersion induced phase inversion and sintering method. An organic binder solution (dope) containing yttria-stabilised zirconium (YSZ) particles is spun through a triple orifice spinneret to form a hollow fibre precursor, which is then sintered at elevated temperatures to form a ceramic support. The phase inversion process for the formation of hollow fibre membranes was studied in order to produce the best morphological structure/support for palladium based membranes. The spinning parameters, particle size, non-solvent concentration, internal coagulant as well as the calcination temperature were investigated in order to determine the optimum values. Sintering temperature was also investigated, which would yield a sponge-like structure with an optimized permeability, while retaining a smooth outer surface. The supports produced by phase inversion were characterized in terms of dimension by mercury porosimetry, compressed air permeability, Surface Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The morphology of the produced ceramic support showed either dense or porous characteristics governed by the dynamics of the phase inversion process. The particle size of YSZ was examined in order to decrease the amount of agglomerates in the spinning suspension. Zetasizer tests indicated that at 15 minutes, the ultrasonic bath effectively homogenised the YSZ particles and prohibited soft agglomerates from reforming in the spinning suspension. In this study, an increase in air gap had no noticeable effect on the finger like voids but it had a considerable effect on both the inner diameter (ID) and outer diameter (OD) of the green fibres, while an increase in bore liquid flow rate and extrusion pressure promoted viscous fingering and significant effect on the ID and OD of the fibres, respectively. There was a decrease in porosity and permeability with increasing sintering temperature, addition of water concentration in the spinning suspension and varying Nmethylpyrrolidone
(NMP) aqueous solution of the internal coagulant. The amount of YSZ added to the starting suspension influenced the properties of the support structure. Viscous
deformation was observed for dope with lower particle loading thus resulted in the formation of cracks and defects during sintering.>Magister Scientiae - MSc
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Askestad, Inga. "Ceramic Thermal Barrier Coatings of Yttria Stabilized Zirconia Made by Spray Pyrolysis." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16324.
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A thermal barrier coating (TBC) is used as thermal protection of metallic components exposed to hot gas streams in e.g. gas turbine engines. Due to a high thermal expansion coefficient, low thermal conductivity, chemical- and thermal stability, yttria stabilized zirconia (YSZ) is the most widely used material for TBCs today. In the work presented in this master thesis an aqueous nitrate precursor solution was prepared and deposited on stainless steel substrates by spray pyrolysis to produce 8YSZ coatings (8 mol% of Y2O3 in ZrO2). The precursor solution concentration and deposition parameters, including set-point temperature and volume sprayed, were optimized to produce continuous and crack-free green coatings.The deposited green coatings were characterized by scanning electron microscopy, thermogravimetry and Fourier transform infrared spectroscopy to study the influence of substrate temperature on the microstructure of the green coatings. A substantial change in microstructure was observed for the green coatings in a certain temperature range indicating that a minimum deposition temperature was necessary to obtain crack-free green coatings.Heat treatment was necessary to decompose the nitrate species in the deposited film. During heat treatment, vertical cracks were introduced into the coatings due to the nitrate decomposition. The cracking behavior of the coatings was studied for different drying times and conditions, and it was found that the crack propagation can be controlled to obtain the preferred size and geometry of the cracks. Due to built-up stresses in the coating, which can exceed the fracture toughness of the material, it was found that there was a maximum film thickness achievable before spallation of the coating for a given precursor solution. Therefore, the possibility of spraying multi-layered coatings was investigated. The introduction of a second layer showed that it was possible to double the thickness of the coating.
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Roa, Baerga Victor Orlando. "Laser shockwave sintering of micro and nanoscale powders of yttria-stabilized zirconia." [Ames, Iowa : Iowa State University], 2010. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1476342.
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Predith, Ashley P. (Ashley Page). "Computational studies of cation and anion ordering in cubic yttria stabilized zirconia." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36208.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 127-137).
The investigation of ordering and phase stability in the ZrO2-Y203 system involves two sets of calculations. The first set of calculations uses the cluster expansion method. A guide to the practical implementation of the cluster expansion outlines methods for defining a goal and choosing structures and clusters that best model the system of interest. The cluster expansion of the yttria stabilized zirconia system considers 447 configurations across the ZrO2-Y203 composition range. The effective cluster interaction for pair clusters show electrostatic repulsion between anions and little interaction between cations. Triplet anion terms largely modify the energy contributions of the pair terms. Separate cluster expansions using structures at single compositions show that cation clusters become more important at high yttria composition. The cluster expansion led to the discovery of three previously unidentified ordered ground state structures at 25, 29, and 33 % Y on the cubic fluorite lattice. The ground state with 33 % Y is stable with respect to the calculated energies of monoclinic ZrO2 and the Y4Zr3012 ground state. The ground states have the common ordering feature of yttrium and vacancies in [1 1 2] chains, and Monte Carlo simulations show that vacancy ordering upon cooling is contingent on cation ordering.
(cont.) The second set of calculations consider three driving forces for order: ionic relaxation, vacancy arrangements, and differences in Zr and cation dopant radii. Bond valence sums of fully relaxed and anion relaxed structures are nearly equal at all compositions. In supercells of ZrO2, the vacancy arrangement of the ground state with 25 % Y is more stable than arrangements maximizing the distance between vacancies or aligning vacancies in [1 1 1]. Comparing the YSZ ground state with structures of the same configuration with scandium replacing yttrium shows different stable phases on the convex hull between cubic ZrO2 and the dopant M203 phase. The change in the stability of the configurations may be a result of cation radius sizes. The factors suggest that the driving forces of phase stability depend on composition.
by Ashley P. Predith.
Ph.D.
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Gouldstone, Andrew. "Electrochemical vapor deposition of a graded titanium oxide-yttria stabilized zirconia layer." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39612.
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Guo, Fangwei. "Electrophoretic deposition of yttria-stabilized zirconia for application in thermal barrier coatings." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/electrophoretic-deposition-of-yttriastabilized-zirconia-for-application-in-thermal-barrier-coatings(05f66a54-9ab3-4d18-8378-6e02a3895dfc).html.
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Electrophoretic deposition (EPD) has been used to produce the yttria-stabilized zirconia (YSZ) coatings on metal substrates. Sintering of YSZ with and without doping has been carried out at 1150 °C for 2hrs. The properties of these coatings have been examined in light of thermal barrier applications. For EPD, the green density increases with an initial increase in the HCl concentration and the EPD time. This suggests that particle packing was influenced by a time dependent re-arrangement, in addition to the initial suspension dispersion state. The green density peaks at a electrical conductivity of around 10×10-4 S/m achieved by an 0.5 mM HCl addition for the 20 g/l suspensions with the EPD time of around 8 ~10 minute. For sintered coatings, the HCl concentration had a marked effect on the neck size to grain size ratio of the 8 mol% yttria-stabilized zirconia (8YSZ) coatings. The presence of ZrCl4 and ZrOCl2, and a high concentration of oxygen vacancies at the grain boundaries are believed to promote neck growth in the early stage of sintering at 1150 °C. During sintering of 3 mol% and 8 mol% yttria-stabilized zirconia (3YSZ and 8YSZ) at 1150 ºC for 2hrs, the densification rate substantially increased with a small amount of Fe2O3 addition (0.5 mol%) to the 3YSZ/8YSZ deposits. A more pronounced graingrowth was present in the Fe2O3 doped 8YSZ deposits. The increased Zr4+ diffusion coefficient is mainly responsible to the rapid densification rate of the Fe2O3 doped 3YSZ/8YSZ deposits. A small grain growth observed in the Fe2O3 doped 3YSZ deposits is attributed to the Fe3+ segregation at grain boundary. A small amount of CeO2 doping was found to substantially inhibit the densification rate of the doped 3YSZ deposits with a minor grain growth. Fe2O3 doping reduced the thermal conductivities of 3YSZ/8YSZ. It is found that Rayleigh-type phonon scattering due to the mass difference alone is inadequate to explain the thermal conductivity of Fe2O3 doped YSZ systems. The lattice strain effects due to the ionic radius difference could more effectively reduce thermal conductivity of the Fe2O3-doped 3YSZ. A decrease in the growth rate of the TGO scale with the increasing Fe2O3 additions was observed for the oxidized FeCrAlY metal substrates with the Fe2O3-doped 3YSZ coating, which was found to be attributed to the early formation of the stable and dense α-Al2O3 phase due to the presence of Fe3+ ions.
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Kennerknecht, Tobias [Verfasser]. "Fatigue of Micro Molded Materials - Aluminum Bronze and Yttria Stabilized Zirconia / Tobias Kennerknecht." Karlsruhe : KIT Scientific Publishing, 2014. http://www.ksp.kit.edu.
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Waldbillig, David. "Aqueous suspension plasma spraying of yttria stabilized zirconia solid oxide fuel cell electrolytes." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/27910.
Full textAbstract:
In order to meet increasing world energy demand in a sustainable manner, clean and
efficient new energy technologies need to be developed. Fuel cells have been proposed as a potential energy conversion technology to help facilitate this transition to cleaner energy. Solid oxide fuel cells (SOFC) in particular are thought to be a practical, near term clean energy technology; however, current state-of-the-art wet ceramic fabrication techniques make SOFC manufacturing labour-intensive, fairly expensive and difficult to automate, and the high firing temperatures required limit the usable materials sets and increase production times. Plasma spraying (PS) is a potential next generation SOFC fabrication process that can rapidly produce fully sintered ceramic layers without the need for post deposition heat treatments; however, it is difficult to produce the thin, fully dense layers required for SOFC electrolytes using conventional plasma spray techniques, as the carrier gas based feeding configurations
typically require large feedstock powders. Suspension plasma spraying (SPS) is a
modification of conventional PS processes that uses micron or sub-micron sized feedstock
powders suspended in a carrier liquid. SPS has the potential to significantly improve coating quality and microstructural control. Thus plasma spray manufacturing methods may have the ability to both reduce cell fabrication and material costs and improve cell performance, making them an important step toward successful SOFC commercialization.
This project investigated the properties of metal supported aqueous SPS yttria stabilized
zirconia (YSZ) layers that could be used as SOFC electrolytes and developed a thorough understanding of the relationships between the base layers (substrate and cathode),
suspension and plasma spraying parameters and the resulting coating properties. Using this understanding, plasma sprayed full cells (cathode, electrolyte and anode) with optimized electrolyte microstructures with 96% density were produced and
electrochemically tested. The measured open circuit voltage values were approximately 90% of the Nernst voltages, and electrolyte area specific resistances below 0.1 Ω cm² were
obtained at 750⁰C for electrolyte thicknesses below 20 μm. Least-squares fitting was used to estimate the contributions of the YSZ bulk material, its microstructure, and the contact resistance to the measured series resistance values.
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Sønderby, Steffen. "Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-102513.
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Solid oxide fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel cell technology can gain a significant share of the electrical power market, the operation temperature needs to be reduced in order to decrease costs and improve the durability of the cells. Application of thin film electrolytes and barrier coatings is a way of achieving this goal. In this thesis, I have investigated film growth and microstructure of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) thin films deposited by physical vapor deposition. The aim is to make industrially applicable coatings suitable for application in solid oxide fuel cells (SOFCs). For this purpose, the coatings need to be thin and dense. YSZ coatings were prepared by pulsed direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) in both laboratory- and industrial-scale setups. Industrial-scale pulsed DC magnetron sputtering of YSZ showed that homogenous coating over large areas was possible. In order to increase film density of the YSZ, HiPIMS was used. By tuning deposition pressure, peak power density and substrate bias voltage it was possible to deposit noncolumnar thin films without voids and cracks as desired for SOFC applications. CGO coatings were deposited by pulsed DC magnetron sputtering with the purpose of implementing diffusion barriers to prevent reactions between Sr from the SOFC cathode and the electrolyte. A model system simulating a SOFC was prepared by depositing thin CGO and YSZ layers on cathode material. This setup allowed the study of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. The study revealed Sr to diffuse along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased. CGO thin films were implemented in metal-based SOFC and the influence of film microstructure and thickness on the electrochemical performance of the cell was studied. Cell tests showed that an area specific resistance (ASR) down to 0.27 Ωcm2 could be obtained 650 °C with sputtered CGO barrier layers in combination with a lanthanum strontium cobaltite cathode. In comparison a spin-coated CGO barrier resulted in an ASR value of 0.50 Ωcm2. This shows the high effectiveness of the sputtered barrier in obtaining state-of-the-art performance. In summary, this work provides fundamental understanding of the deposition and growth of YSZ and CGO thins films and proves the prospective of employing thin film barrier coating in order to obtain high-performing SOFCs.
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Rashkova, Boryana. "Microstructural characterization of yttria-stabilized zirconia thermal barrier coatings grown on sapphire substrates." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11293362.
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Hirahara, Ann Satoko 1972. "Fabrication of sensitive high-temperature superconducting bolometers on a yttria-stabilized zirconia membrane." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32172.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995.Vita.
Includes bibliographical references (leaves 37-38).
by Ann Satoko Hirahara.
M.S.
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Lai, Tzi-Huei. "Computational studies of defect distribution and diffusion near interfaces in Yttria-stabilized Zirconia." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607803.
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Milshtein, Jarrod D. "Yttria-stabilized zirconia membrane stability in fluoride melts for the magnesium SOM process." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12163.
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Thesis (M.S.)--Boston UniversityOne proposed industry method for the direct electrolysis of magnesium oxide for magnesium production is the Solid Oxide Membrane (SOM) process. The SOM process offers an energy efficient, low-cost magnesium production alternative with much lower environmental impact compared to other methods of primary magnesium production. During the SOM process, MgO is dissolved in a molten CaF2-MgF2 flux. A yttria-stabilized zirconia (YSZ) membrane is submerged in the flux, and this membrane acts as an oxygen anion conducting SOM tube. The YSZ membrane separates the cathode and flux from the anode. When an electric potential is applied across the electrolysis cell, magnesium cations travel through the flux and are reduced at a stainless steel cathode. Oxygen anions simultaneously move through the YSZ membrane to a liquid silver anode, where the anions are oxidized. The SOM process has been demonstrated successfully on the laboratory scale, but in order for the SOM process to be commercially viable, electrolysis cells must operate for thousands of hours. The stability of the YSZ membrane limits the operating life of the SOM electrolysis cell. This thesis determines YSZ membrane stability in oxyfluoride fluxes for the SOM process so that membrane degradation can be better understood and controlled. One primary degradation pathway of YSZ in the SOM process has been determined to be yttria depletion out of the YSZ membrane. Yttria concentration profiles in YSZ membranes were determined using x-ray spectroscopy, and the concentration profiles were used to analyzed the depletion process. The yttria depletion mechanism was determined to be chemical diffusion, and the diffusion process was modeled. A method of controlling the yttria depletion process by adding small concentrations of YF3 to the flux is described, modeled, and experimentally proven. An optimal range of YF3 concentrations to add to the flux is determined for increasing YSZ membrane stability. This study investigated the role of flux impurities on YSZ membrane stability. The effect of impurities on YSZ membrane stability had not been studied or described before this work. Impurities tested are common to magnesium ores: calcia, silica, sodium oxide, and sodium peroxide. Any degradation effects due to these impurities were analyzed, and methods to remove the negative effects of impurities were described when possible.
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Mahade, Satyapal. "Functional Performance of Gadolinium Zirconate/Yttria Stabilized Zirconia Multi-Layered Thermal Barrier Coatings." Licentiate thesis, Högskolan Väst, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-9854.
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Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing the turbine inlet temperature has pushed YSZ toits upper limit. Above 1200°C, issues such as poor phase stability, high sinteringrates, and susceptibility to CMAS (calcium magnesium alumino silicates) degradation have been reported for YSZ based TBCs. Among the new materials,gadolinium zirconate (GZ) is an interesting alternative since it has shown attractive properties including resistance to CMAS attack. However, GZ has a poor thermo-chemical compatibility with the thermally grown oxide leading to poor thermal cyclic performance of GZ TBCs and that is why a multi-layered coating design seems feasible.This work presents a new approach of depositing GZ/YSZ multi-layered TBCs by the suspension plasma spray (SPS) process. Single layer YSZ TBCs were also deposited by SPS and used as a reference.The primary aim of the work was to compare the thermal conductivity and thermal cyclic life of the two coating designs. Thermal diffusivity of the YSZ single layer and GZ based multi-layered TBCs was measured using laser flash analysis (LFA). Thermal cyclic life of as sprayed coatings was evaluated at 1100°C, 1200°C and 1300°C respectively. It was shown that GZ based multi-layered TBCs had a lower thermal conductivity and higher thermal cyclic life compared to the single layer YSZ at all test temperatures. The second aim was to investigate the isothermal oxidation behaviour and erosion resistance of the two coating designs. The as sprayed TBCs were subjected toisothermal oxidation test at 1150°C. The GZ based multi-layered TBCs showed a lower weight gain than the single layer YSZ TBC. However, in the erosion test,the GZ based TBCs showed lower erosion resistance compared to the YSZ singlelayer TBC. In this work, it was shown that SPS is a promising production technique and that GZ is a promising material for TBCs.