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Yttria-stabilized Zirconia (yttria-stabilized + zirconia)
Selected AbstractsPreparation of a Nanoscale/SOFC-Grade Yttria-Stabilized Zirconia Material: A Quasi-Optimization of the Hydrothermal Coprecipitation ProcessINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2008Yang-Chuang Chang Yttria-stabilized zirconia (YSZ) is the key material for an electrolyte of a solid oxide fuel cell (SOFC). In order to prepare a nanoscale/SOFC-grade 8YSZ material, the hydrothermal coprecipitation process is intensively investigated for process improvement and product identification. From the characterization results of the 8YSZ product, the operation conditions were selected for process optimization. The criteria used in optimization condition determination were the reproducibility of the 8YSZ product and the particle size, the crystallinity, as well as the operation simplicity. Experimental results showed that a nanoscale/SOFC-grade 8YSZ powder was directly prepared. The quasi-optimum conditions of the process are proposed. [source] Ion-Conducting Probes for Low Temperature PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-7 2008S. A. Meiss Abstract Probes interacting with a low temperature plasma are typically built of electron conducting materials, mostly metals. We apply yttria-stabilized zirconia (YSZ) which is oxygen ion conducting at elevated temperatures and which is a typical solid electrolyte with high ionic and negligible electronic conductivity. The processes at the plasma|YSZ interface are discussed and first results of measurements with ion-conducting single- and double-probes in oxygen containing radio frequency plasmas are presented. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Continuum Mechanical Approach to Sintering of Nanocrystalline Zirconia,ADVANCED ENGINEERING MATERIALS, Issue 10 2005R. Zuo Nanocrystalline 3,mol,% yttria-stabilized zirconia was sinter-forged isothermally under varying external uniaxial stresses. The applied uniaxial stresses were relatively low, compared to the intrinsic sintering stress of the material studied. Uniaxial sintering stresses and uniaxial viscosities were experimentally determined as function of density by means of a continuum mechanical approach which involves measuring the sintering rate of a free-sintered specimen, and a specimen sintered under the application of an external uniaxial stress. The uniaxial viscosity increased strongly with density only in the final stage sintering regime. The magnitude of the uniaxial sintering stress exhibited a decrease with density. [source] Optimized La0.6Sr0.4CoO3,, Thin-Film Electrodes with Extremely Fast Oxygen-Reduction KineticsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Judith Januschewsky Abstract La0.6Sr0.4CoO3,, (LSC) thin-film electrodes are prepared on yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition at different deposition temperatures. The decrease of the film crystallinity, occurring when the deposition temperature is lowered, is accompanied by a strong increase of the electrochemical oxygen exchange rate of LSC. For more or less X-ray diffraction (XRD)-amorphous electrodes deposited between ca. 340 and 510,°C polarization resistances as low as 0.1,, cm2 can be obtained at 600,°C. Such films also exhibit the best stability of the polarization resistance while electrodes deposited at higher temperatures show a strong and fast degradation of the electrochemical kinetics (thermal deactivation). Possible reasons for this behavior and consequences with respect to the preparation of high-performance solid oxide fuel cell (SOFC) cathodes are discussed. [source] Selective control of voltage polarity in a single-chamber solid-oxide fuel cell using the same catalytic electrodes with different sizesIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 5 2008Akiyoshi Nagata Member Abstract The selective control of the voltage polarity in a single-chamber solid-oxide fuel cell (SC-SOFC) constituting the anode and cathode arranged at the same electrolyte surface of yttria-stabilized zirconia (YSZ) or samaria-doped ceria (SDC) and which can operate in a flowing mixture of hydrogen and oxygen is discussed on the basis of the dissociation and adsorption reactions due to the catalytic materials and electrode configurations. The open circuit voltage (OCV) of SC-SOFC showed the highest value when the H2:O2 ratio was around 2:1, which might be equal to the mol ratio of oxygen and hydrogen based on the reaction of water formation by the electrochemical reaction in the cell. The voltage polarity of the cell using the Pt and LSM (La0.7Sr0.3MnO3) catalysts was the same as in the conventional SOFC such that in the Pt catalysis the anode became negative whereas in the LSM catalysis the cathode was independent of the electrode configurations. In SC-SOFC using the same Pt catalyst, the larger Pt electrode functioned as the cathode desorbing the oxide ion conducting in YSZ or SDC. As a result, it was confirmed that the voltage polarity of SC-SOFC could be selectively controlled by making use of the same catalytic electrodes with different sizes, and that the I,V characteristic of the cell improved by using SDC with Pt electrodes with a surface area ratio of 2:1. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Microstructure Control of Sintered Porous Yttria-Stabilized Zirconia as a Durable Thermal Shielding MaterialINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2009Kazuya Sasaki The microstructure of a thermal shielding material affects its thermal conductivity and mechanical property. In this study, the effects of the sintering temperature and the polymethyl methacrylate powder as a pore-former on the microstructure of a sintered porous yttria-stabilized zirconia (YSZ), which is used as a durable thermal shielding material, were investigated. It became clear that the microstructure of the sintered YSZ could be controlled by the particle size and the amount of the pore-former and the sintering temperature. The effect of the yttria amount in the YSZ on the microstructure was also clarified. [source] Thermal Conductivity of the Rare-Earth Strontium AluminatesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2010Chunlei Wan The thermal conductivity of a series of complex aluminates, RE2SrAl2O7, with different rare-earth (RE) ions, has been measured up to 1000°C. There is a strong dependence on the atomic number of the RE ion, ranging from an approximately 1/T dependence for the lanthanum strontium aluminate to an almost temperature-independent behavior of the dysprosium strontium aluminate. The latter conductivity is comparable with that of yttria-stabilized zirconia, the current material of choice for thermal barrier coatings. The temperature dependence of the thermal conductivities of all the aluminates studied can be fit to a standard phonon,phonon scattering model, modified to account for a minimum phonon mean free path, in which the difference in behavior is attributed to increased phonon,phonon scattering with the atomic mass of the RE ion. Although a satisfactory parametric fit is obtained, the model does not take into account either the detailed layer structure of the aluminates, consisting of alternating rock-salt and perovskite layers in a natural superlattice structure, or the site preferences of the RE ion. This suggests that further model development is warranted. [source] Effect of the Starting Microstructure on the Thermal Properties of As-Sprayed and Thermally Exposed Plasma-Sprayed YSZ CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009Yang Tan Thermal barrier coatings (TBCs) experience thermal gradients, excessive temperature, and high heat flux from hot gases in turbines during service. These extended thermal effects induce sintering and significant microstructure changes, which alter the resulting thermal conductivity of the TBCs. To study the effects of different starting microstructures on the sintering behavior, plasma-sprayed yttria-stabilized zirconia (YSZ) TBCs produced from different starting powders and process parameters were subjected to thermal aging at several temperatures and time intervals, after which their thermal conductivity was measured at room temperature. The thermal conductivity results were analyzed by introducing the Larson,Miller parameter, that describes the creep-like behavior of thermal conductivity increase with annealing temperature and time. One set of coatings was also annealed under the same conditions and the thermal conductivities were measured at elevated temperatures. The temperature-dependent thermal conductivity data were analyzed and used to predict the long-term thermal property behavior for a general YSZ coating design. [source] Pressureless Sintering of 3Y-TZP/Stainless-Steel Composite LayersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Mahdi Dourandish A pressureless sintering method was utilized to fabricate metal/ceramic joints out of yttria-stabilized zirconia (3Y-TZP) and stainless steels (SS). Ultrafine (150 nm) and nanoscale (75 nm) 3Y-TZP particles and micrometric 17-4PH, 316L, and 420 SS (<31 ,m) powders were tested. Isothermal and nonisothermal sintering behaviors of the powders and composite layers in hydrogen, argon, and vacuum atmospheres were examined. It was found that the mismatch strain between the zirconia ceramic and SS during cosintering is significant, which leads to bond cracking and joint failure. Nevertheless, interlayer diffusion of Zr, Fe, and Cr and the formation of a reaction zone, particularly during vacuum sintering, enables an accommodation of the residual stresses caused by the mismatch shrinkage upon cooling. The formation of a porous region close to the metal layer was observed. Sinter joining of zirconia to 420 SS is more successful compared with austenitic steel because of a lower difference in the coefficient of thermal expansion. [source] Dense Alumina,Zirconia Coatings Using the Solution Precursor Plasma Spray ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Dianying Chen For the first time, dense coatings have been made by the solution precursor plasma spray (SPPS) process. The conditions are described for the deposition of dense Al2O3,40 wt% 7YSZ (yttria-stabilized zirconia) coatings; the coatings are characterized and their thermal stability is evaluated. X-ray diffraction analysis shows that the as-sprayed coating is composed of ,-Al2O3 and tetragonal ZrO2 phases with grain sizes of 72 and 56 nm, respectively. The as-sprayed coating has a 95.6% density and consists of ultrafine splats (1,5 ,m) and unmelted spherical particles (<0.5 ,m). The lamellar structure, typical of conventional plasma-sprayed coatings, is absent at the same scale in the SPPS coating. The formation of a dense Al2O3,40 wt% 7YSZ coating is favored by the lower melting point of the eutectic composition, and resultant superheating of the molten particles. Phase and microstructural thermal stabilities were investigated by heat treatment of the as-sprayed coating at temperatures of 1000°,1500°C. No phase transformation occurs, and the grain size is still in the nanometer range after the 1500°C exposure for 2 h. The coating hardness increases from 11.8 GPa in the as-coated condition to 15.8 GPa following 1500°C exposure due to a decrease in coating porosity. [source] Ni,YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical CharacterizationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Trine Klemensø Nickel (Ni),yttria-stabilized zirconia (YSZ) cermets are a prevalent material used for solid oxide fuel cells. The cermet degrades upon redox cycling. The degradation is related to microstructural changes, but knowledge of the mechanisms has been limited. Direct current conductivity measurements were performed on cermets and cermets where the Ni component was removed. Measurements were carried out before, during, and after redox cycling the cermet. The cermet conductivity degraded over time due to sintering of the nickel phase. Following oxidizing events, the conductivity of the cermets improved, whereas the conductivity of the YSZ phase decreased. An improved model of the redox degradation mechanism was established based on the measurements. [source] YSZ-Induced Crystallographic Reorientation of Ni Particles in Ni,YSZ CermetsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Miguel A. Laguna-Bercero Metal,ceramic interfaces in Ni,YSZ (YSZ, yttria-stabilized zirconia)-textured porous cermets prepared by reduction of NiO,YSZ directionally solidified eutectics have been studied by transmission electron microscopy and X-ray pole figure experiments. Before reduction of NiO, the interfacial plane isbut after reduction, the Ni phase does not maintain the same crystallographic orientation as the NiO parent phase. Ni undergoes an interface-induced crystallographic reorientation to form the lower energy (002)Ni,(002)YSZ interface. This process has been studied as a function of the reduction temperature, and it seems to be more effective at ,800°C. Metal,ceramic low-energy interfaces prevent Ni particle coarsening and impart long-term stability to the cermet. [source] Electrophoretic Deposition of YSZ Particles on Non-Conducting Porous NiO,YSZ Substrates for Solid Oxide Fuel Cell ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Laxmidhar Besra This paper reports a method of performing electrophoretic deposition (EPD) on non-conducting substrates overcoming the requirement of a conducting substrate through the use of porous substrates. The conductivity of the substrate is therefore no longer a limiting factor in the application of EPD. This method is applicable to the fabrication of thick or thin layers of ceramic or metal for various applications. As an example, thin and dense yttria-stabilized zirconia (YSZ) layers have been deposited on a non-conducting NiO,YSZ substrate by EPD from a non-aqueous suspension. A solid oxide fuel cell constructed on these sintered bilayers exhibited power densities of 384 and 611 mW/cm2 at 750° and 850°C, respectively. [source] Low-Temperature Fabrication of Oxide Composites for Solid-Oxide Fuel CellsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004Hongpeng He Composites of yttria-stabilized zirconia (YSZ) with Sr-doped LaCrO3 (LSC) and Sr-doped LaMnO3 (LSM) were prepared by impregnation of a porous YSZ matrix with aqueous solutions of the appropriate metal salts, followed by sintering to various temperatures. XRD measurements showed that perovskite phases formed after sintering at 1073 K, a temperature well below that at which solid-state reactions with YSZ occur. The conductivities of the LSC,YSZ and LSM,YSZ composites prepared in this way were maximized at a sintering temperature of 1373 K for LSC,YSZ and 1523 K for LSM,YSZ, although reasonable conductivities were achieved at much lower temperatures. The conductivities of the two composites increased much more rapidly with the content of the conductive oxide than has been found with conventional composites formed by mixing and sintering the oxide powders. The implications for using this approach to develop novel electrodes for SOFC applications are discussed. [source] Optimization of a Composite Working Electrode for a New Family of Electrochemical Cell for NO DecompositionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2003Kazuyuki Matsuda The electrochemical properties of a composite (NiO)x,(yttria-stabilized zirconia (YSZ))1,x working electrode for a new type of electrochemical cell for NO decomposition in the presence of excess oxygen are investigated. It is shown that the dependence of the NO conversion on the value of the current passed through the electrochemical cell with a nanoporous (NiO)x,(YSZ)1,x working electrode is linear and that the value of current efficiency depends on the NO and O2 gas concentrations only (,= [NO] /([NO] + 2[O2]). The optimum NiO addition (35% by volume) to the YSZ resulted in a decrease of the cell operating voltage and, as a result, in a decrease in the electrical power required for NO decomposition. The observed high performance of the composite working electrode at this composition is consistent with the effective medium percolation theory, which predicts the ambipolar transport behavior of the composite mixed ionic,electronic (YSZ,NiO) conductors as a function of the volume fraction of each of the randomly distributed constituent phases. [source] Effect of Slurry Rheological Properties on the Coating of Ceramic Honeycombs with Yttria-Stabilized-Zirconia WashcoatsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2000Christos Agrafiotis Recently, a novel automotive catalyst design, based on the use of palladium supported on yttria-stabilized zirconia (YSZ), was proposed. In the present work, the coating of cordierite honeycomb samples with YSZ slurries for the preparation of such washcoats was investigated. The loading percentage, homogeneity, and reproducibility were found to depend strongly on the slurry viscosity. Parameters such as the slurry-solids content, pH, type of powder used, and use and quantity of the dispersants were optimized for the preparation of stable, low-viscosity YSZ slurries, adjustments that could lead to an efficient coating process for honeycomb structures. [source] Steam reforming of propane in a zirconia membrane reactor with a Rh-supported Ce0.15Zr0.85O2 catalystASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009K. Kusakabe Abstract The steam reforming (SR) of propane for hydrogen production at 400,600 °C in a porous yttria-stabilized zirconia (YSZ) membrane reactor was investigated. The YSZ membrane was used as a hydrogen selective membrane. A Rh-supported Ce0.15Zr0.85O2 catalyst was packed in the membrane reactor because the catalyst was found to be the most suitable catalyst for the low-temperature SR of propane on the basis of the results obtained using a packed bed reactor. The conversion of propane in the membrane reactor was higher than that in a packed bed reactor due to the shift of equilibrium toward the hydrogen-producing side. In spite of relatively low permeation selectivity (ideal H2/CO selectivity = 9 at 100 °C), hydrogen permeation through the membrane caused an increase in the CO2 fraction and a decrease in the CO fraction in reformed gas. This indicates that the water-gas shift reaction was an important contributor in the product distribution in the membrane reactor. Meanwhile, the methane fraction remained largely unchanged, regardless of selective hydrogen permeation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Direct utilization of ethanol on ceria-based anodes for solid oxide fuel cellsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Massimiliano Cimenti Abstract The direct utilization of ethanol was investigated in CuCeO2, CuZr0.35Ce0.65O2 (ZDC) and Cu/RuZr0.35Ce0.65O2 anodes for solid oxide fuel cells (SOFC). The anodes were prepared by impregnation with nitrate precursors on a porous layer of yttria-stabilized zirconia (YSZ) obtained by tape casting, while (La0.8Sr0.2MnO3,,) LSM cathodes were screen-printed. The cells were tested in both hydrogen and ethanol. The outlet gas composition was monitored with a gas chromatograph, which showed that almost all the ethanol was decomposed, mainly to H2, CH4, CO, H2O and C2H4. The maximum power outputs obtained in ethanol were 0.075 and 0.400 W/cm2 on CuCeO2|YSZ|LSM and CuZDC|YSZ|LSM, respectively. All cells were more active in alcohol than in hydrogen with the peak performance occurring after approximately 4 h. That is, the power density initially increased, peaked and then decreased. This behavior was likely a consequence of carbon deposition that initially results in an improvement of the electronic conductivity in the anode but later results in the blocking of the active sites. Zirconia doping (in the ZDC anodes) resulted in better stability and, in addition, the initial activity of the ZDC anodes could be recovered after approximately 1 h of exposure to humidified hydrogen, whereas the initial activity of the ceria anodes could not be recovered. The addition of ruthenium (<0.5 wt%) further improved the stability by delaying the onset of carbon formation. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||