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ZrO2
Terms modified by ZrO2 Selected AbstractsA TEM study on ZrO2 -rich phases in the quasibinary system ZrO2 -Zr3N4: Comparison between fast and slowly cooled samplesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005A. T. Tham Abstract A thorough comparison between the slowly and fast cooled ,,-type oxynitrides of zirconium has been carried out by means of transmission electron microscopy. This work aims at detecting and analyzing the so-called "modulated" ,, phase, which has been involved in the introduction of ordered anion vacancies through nitridation of zirconia. The gained information from the occurrence of such a modulated phase and the manner, in what it appears, do support the suggested structure model, which had been developed in early works in order to get a better understanding of the typical phase transitions in zirconium oxynitrides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Particle size of powders under hydrothermal conditionsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2003Wen-Jun Li Abstract Various non-oxide (CuI, AgI, AgCl, PbS, CuS and ZnS) and oxide (ZnO, TiO2, SnO2, CeO2 and ZrO2) powders were prepared under hydrothermal conditions to investigate the effects of temperature, pH and precursors on the particle size of powders. It was found that the particle sizes of PbS, CuS and ZnS powders were much smaller than that of CuI, AgI and AgCl powders prepared under the same conditions. The particle sizes of TiO2, SnO2, CeO2 and ZrO2 powders are much smaller than that of ZnO powders prepared under the same conditions. It is concluded that the solution conditions have a certain effect on the particle size of powders under the hydrothermal conditions. The particle size of powders increased with the rising of temperature. Additional factors affecting the particle size were uncovered through studying the nucleation mechanism. The particle size was mainly related to the Madelung constant and the electric charge number of ions. Powders with smaller particle size resulted from systems that possessed the larger Madelung constant and ionic charge number. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrochemistry of Cytochrome P450 2B6 on Electrodes Modified with Zirconium Dioxide Nanoparticles and Platin ComponentsELECTROANALYSIS, Issue 7 2008Lei Peng Abstract The direct electrochemical and electrocatalytic behavior of the immobilized cytochrome P450 2B6 (CYP2B6) on zirconium dioxide nanoparticles (ZrO2) was investigated. The film of nano-structured ZrO2 that incorporated cytochrome P450 2B6 (CYP2B6) with colloidal paltin, which was stabilized by poly-lysine (Pt-PLL), was prepared on glassy carbon electrodes. In anaerobic solutions, the immobilized CYP2B6 exhibited a reversible electron transfer between the heme electroactive center of CYP2B6 and electrodes with a formal potential of ,(0.449±0.004) V at pH,7.4. In air-saturated solutions, an increased bioelectrocatalytic reduction current could be obtained with the CYP2B6-modified electrode with the addition of anticancer drugs, such as lidocaine. This leads to the construction of disposable biosensors for drugs by utilizing the electrochemical activity and catalytic reactions of the immobilized CYP2B6. [source] Modeling of Coating Process, Phase Changes, and Damage of Plasma Sprayed Thermal Barrier Coatings on Ni-Base Superalloys,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Tilmann Beck The paper gives an overview on the modeling activities on plasma sprayed thermal barrier coating in the frame of TFB 63. In the first part, through-process modeling of the APS deposition of a ZrO2 based TBC is described. Starting from simulation of the plasma jet, heat transfer into the powder particles, particle melting, particle impact on the substrate surface, and solidification is simulated. A homogenization method is introduced to describe the mechanical properties of the resulting TBC. The second part shows simulation of interdiffusion and phase transformations of MCrAlY and intermetallic oxidation protection coatings on several cast Ni-base alloy substrates. Finally, FEM-based damage simulation of oxidation protection coatings by transversal fatigue cracks during thermomechanical fatigue loading as well as by delamination of the TBC during thermocyclic loading is discussed. [source] Preliminary study of the crack healing and strength recovery of Al2O3 -matrix compositesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2004L. JUN ABSTRACT This study focused on the crack-healing behaviour of three commercial Al2O3,ceramic-matrix composites: TiCP/Al2O3, ZrO2/Al2O3 and SiCW/Al2O3. Vickers indentation was used to introduce surface flaws with different loads of 49, 98 and 196 N. Then the cracked specimens were annealed in air for 1 h at 1000, 1200 and 1400 °C. The annealing treatment was also conducted at 1200 °C in vacuum for 1 h. Results showed that the annealing treatments increased the indentation strength, but the extent of the increase was different. When annealed in air, the main crack-healing mechanism of TiCP/Al2O3 and SiCW/Al2O3 composites was chemical reaction. When annealed in vacuum, stress relaxation caused much less strength recovery. The main crack-healing mechanism of ZrO2/Al2O3 was the existence of low melting eutectic and the rearrangement of grains caused by ZrO2(m), ZrO2(t) transformation in the crack-opening process zone. The effects of annealing temperature, atmosphere and indentation load on the degree of strength recovery were all related to the crack-healing mechanisms. [source] Hollow Mesoporous Zirconia Nanocapsules for Drug DeliveryADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Shaoheng Tang Abstract Hollow mesoporous zirconia nanocapsules (hm -ZrO2) with a hollow core/porous shell structure are demonstrated as effective vehicles for anti-cancer drug delivery. While the highly porous feature of the shell allows the drug, doxorubicin(DOX), to easily pass through between the inner void space and surrounding environment of the particles, the void space in the core endows the nanocapsules with high drug loading capacity. The larger the inner hollow diameter, the higher their DOX loading capacity. A loading of 102% related to the weight of hm -ZrO2 is achieved by the nanocapsules with an inner diameter of 385,nm. Due to their pH-dependent charge nature, hm -ZrO2 loaded DOX exhibit pH-dependent drug releasing kinetics. A lower pH offers a faster DOX release rate from hm -ZrO2. Such a property makes the loaded DOX easily release from the nanocapsules when up-taken by living cells. Although the flow cytometry reveals more uptake of hm -ZrO2 particles by normal cells, hm -ZrO2 loaded DOX release more drugs in cancer cells than in normal cells, leading to more cytotoxicity toward tumor cells and less cytotoxicity to healthy cells than free DOX. [source] Synthesis, Structure and Electrical Properties of Mo-doped CeO2,Materials for SOFCsFUEL CELLS, Issue 5 2009Q. Li Abstract In this paper, we report the synthesis, structure and electrical conductivity of Mo-doped compounds with a nominal chemical formula of Ce1,xMoxO2+, (x,=,0.05, 0.07, 0.1) (CMO). The formation of fluorite-like structure with a small amount of Ce8Mo12O49 impurity (JCPDS Card No. 31-0330) was confirmed using a powder X-ray diffraction (PXRD). The fluoride-type structure was retained under wet H2 and CH4 atmospheres at 700 and 800,°C, while diffraction peaks due to metal Mo were observed in dry H2 under the same condition. AC impedance measurements showed that the total conductivity increases with increasing Mo content in CMO, and among the investigated samples, Ce0.9Mo0.1O2+, exhibited the highest electrical conductivity with a value of 2.8,×,10,4 and 5.08,×,10,2 S cm,1 at 550,°C in air and wet H2, respectively. The electrical conductivity was found to be nearly the same, especially at high temperatures, in air, O2 and N2. Chemical compatibility of Ce0.9Mo0.1O2+, with 10,mol-% Y2O3 stabilised ZrO2 (YSZ) and Ce0.9Gd0.1O1.95 (CGO) oxide ion electrolytes in wet H2 was evaluated at 800,1,000,°C, using PXRD and EDX analyses. PXRD showed that CMO was found to react with YSZ electrolyte at 1,000,°C. The area specific polarisation resistance (ASPR) of Ce0.9Mo0.1O2+, on YSZ was found to be 8.58,ohm,cm2 at 800,°C in wet H2. [source] Synthesis of Luminescent ZrO2:Eu3+ Nanoparticles and Their Holographic Sub-Micrometer Patterning in Polymer CompositesADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Tsedev Ninjbadgar Abstract Here, the facile synthesis of fluorescent ZrO2:Eu3+ nanoparticles with luminescence quantum yield of up to 8.7% that can be easily dispersed in organic solvents and utilized for the preparation of organic/inorganic volume holographic gratings is presented. The nanoparticles are prepared through a one-step solvothermal process resulting in spherical particles with a mean size of 4,nm that were highly crystalline directly after the synthesis, without any need for calcination treatment. Detailed luminescence studies of the nanoparticles as a function of Eu3+ content demonstrate that the dopant concentration and its site symmetry play an important role in the emissive properties and lifetime of the luminescent centers. It is shown that the luminescence quantum yield of the colloidal ZrO2:Eu3+ nanoparticles increases with dopant concentration up to a critical concentration of 11 mol% while the luminescence lifetime is shortened from 1.8 to 1.4 ms. Holographic photopolymerization of suitable monomer mixtures containing the luminescent nanoparticles demonstrated the ability to inscribe volume Bragg gratings (refractive index contrast n1 up to 0.011) with light-emissive properties, evidencing the high suitability of this approach for the fabrication of tailored nanomaterials for elaborate and demanding applications. [source] Martensitic Phase Transformation of Isolated HfO2, ZrO2, and HfxZr1,,,xO2 (0,<,x,<,1) Nanocrystals,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2005J. Tang Abstract We previously reported that, during the reactions to make nanocrystals of HfO2 and Hf-rich HfxZr1,,,xO2, a tetragonal-to-monoclinic phase transformation occurs that is accompanied by a shape change of the particles (faceted spherical to nanorods) when the temperature at which the reaction is conducted is changed from 340,to 400,°C. We now conclude that this concomitant phase and shape change is a result of the martensitic transformation of isolated nanocrystals in a hot liquid, where twinning plays a crucial role in accommodating the shape-change-induced strain. That such change was not observed during the reactions forming ZrO2 and Zr-rich HfxZr1,,,xO2 nanocrystals is attributed to the higher driving force needed in those instances compared to that needed for producing HfO2 and Hf-rich HfxZr1,,,xO2 nanocrystals. We also report here the post-synthesis, heat-induced phase transformation of HfxZr1,,,xO2 (0,<,x,<,1) nanocrystals. As temperature increases, all the tetragonal nanocrystals transform to the monoclinic phase accompanied by an increase in particle size (as evidenced by X-ray diffraction and transmission electron microscopy), which confirms that there is a critical size for the phase transformation to occur. When the monoclinic nanorods are heated above a certain temperature the grains grow considerably; under certain conditions a small amount of tetragonal phase appears. [source] A Hybrid Inorganic,Organic Semiconductor Light-Emitting Diode Using ZrO2 as an Electron-Injection LayerADVANCED MATERIALS, Issue 34 2009Nurlan Tokmoldin A hybrid inorganic,polymer light-emitting diode that uses ZrO2 and MoO3 charge-injection layers exhibits enhanced electron injection and allows the use of a variety of red-, green-, and blue-light-emitting polymers. [source] Influence of Wet Mechanical Mixing on Microstructure and Vickers Hardness of Nanocrystalline Ceramic,Metal CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Tatsuo Kumagai Nanocrystalline (nc) ceramic,metal composite bulk samples have been fabricated by consolidation of mixture of attrition-milled (AM) amorphous base ceramic ((ZrO2,3 mol% Y2O3),20 mol% Al2O3) and AM amorphous base metallic (Ti,48 mol% Al) powders using a pulse-current pressure sintering system. Microstructural observations revealed that the ceramic and metallic colonies appear blocky in morphology in the composite bulk samples, and both the ceramic and the metallic colonies consist of a large number of equiaxed fine grains with the sizes of 78,82 and 81,86 nm, respectively. Mechanical mixing treatments by wet ball milling in ethanol before consolidation process are effective for refinement of the ceramic and metallic colonies. In all the obtained composite bulk samples, the ceramic colonies consist of the dominant phase of tetragonal (t) ZrO2 solid solution (ss) together with the minor phases of monoclinic (m) ZrO2ss and ,-Al2O3. On the other hand, the dominant phase in the metallic colonies changes from Ti3Al (,2) to Tiss (,) with an increase in the t -ZrO2ss volume fraction by abrasion of 3 mol% yttria-stabilized tetragonal polycrystalline zirconia balls during wet mechanical mixing treatments. Such a phase transformation from ,2 to , is considered to be due to the decrease in the aluminum content in the metallic colonies by combination of aluminum with oxygen (i.e., the formation of ,-Al2O3), which is probably taken from ethanol (C2H5OH) into the powders during wet mechanical mixing treatments. The obtained nc composite bulk samples show good Vickers hardness values, which are considerably higher than those estimated from the rule of mixture. [source] Fabrication and Application of an Oxide Thermoelectric SystemINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2007Ryoji Funahashi A plate-shaped thermoelectric module was prepared using 140 pairs of p -type Ca3Co4O9 (Co-349) and n -type LaNiO3 (Ni-113) bulks. The hot-pressed thermoelectric oxide bulks were connected with an Ag paste, incorporating oxide powder, and Ag sheets. The module's open-circuit voltage increases with increasing hot-side temperature (TH) and reaches 4.5 V at a TH of 1072 K in air. No deterioration in output power was seen when power generation was carried out 10 times at a TH of 723 K with intermediate cooling to room temperature. The module was successfully used to charge a lithium-ion battery in a mobile phone. Thermoelectric modules composed of p -type Co-349 and n -type CaMnO3 (Mn-113) bulks, which have a pipe shape, were constructed using Ag electrodes and stainless-steel tubes. The devices were connected with the stainless-steel tube coated with ZrO2 by thermal spray using a dielectric paste composed of silica glass and iron oxide. Power generation was carried out in flame by combustion of natural gas. Water flowed inside the stainless-steel tube for cooling. One module consisting of 54 pairs of legs can generate 1.5 V, 0.28 W, and steam simultaneously by installing in an instantaneous water heater. Power generation was carried out four times with intermediate cooling. Deterioration in the open-circuit voltage of the module was not observed after the fourth combustion. [source] Structure of nanoporous zirconia-based powders synthesized by different gel-combustion routesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Jorge R. Casanova Zirconia-based ceramics that retain their metastable tetragonal phase at room temperature are widely studied due to their excellent mechanical and electrical properties. When these materials are prepared from precursor nanopowders with high specific surface areas, this phase is retained in dense ceramic bodies. In this work, we present a morphological study of nanocrystalline ZrO2,2.8 mol% Y2O3 powders synthesized by the gel-combustion method, using different organic fuels , alanine, glycine, lysine and citric acid , and calcined at temperatures ranging from 873 to 1173,K. The nanopore structures were investigated by small-angle X-ray scattering. The experimental results indicate that nanopores in samples prepared with alanine, glycine and lysine have an essentially single-mode volume distribution for calcination temperatures up to 1073,K, while those calcined at 1173,K exhibit a more complex and wider volume distribution. The volume-weighted average of the nanopore radii monotonically increases with increasing calcination temperature. The samples prepared with citric acid exhibit a size distribution much wider than the others. The Brunauer,Emmett,Teller technique was used to determine specific surface area and X-ray diffraction, environmental scanning electron microscopy and transmission electron microscopy were also employed for a complete characterization of the samples. [source] Preparation and microstructure characterization of ball-milled ZrO2 powder by the Rietveld method: monoclinic to cubic phase transformation without any additiveJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2002S. Bid The phase transformation kinetics of high-energy ball-milled monoclinic ZrO2 have been studied in detail by Rietveld powder structure refinement analysis. In the present study, no stabilizing compound was required to obtain the cubic phase. The fine-grain powder was milled in a planetary ball mill for up to several hours at different BPMRs (ball to powder mass ratios): 10:1, 20:1, 35:1 and 40:1. During the process of ball milling, the monoclinic phase is gradually transformed to the cubic phase. The relative phase abundances of the respective phases, the particle sizes, the r.m.s. strains, the lattice parameter changes, etc., have been estimated from Rietveld analysis of X-ray powder diffraction data. It has been found that a higher BPMR exerts more influence on rapid phase transformation. In the m - to c -ZrO2 phase transformation, no formation of an intermediate tetragonal ZrO2 phase has been found. The small change in the lattice volume of m -ZrO2, which is very close to the lattice volume of c -ZrO2, caused by ball milling may be attributed to this phase change. The formation of the c phase is noticed, in general, after just 1,h of ball milling, and the particle size of the m phase is reduced to a large extent at the first stage of milling and remains almost unchanged with increasing milling time. However, the particle size of the c phase increases with increasing milling time for the samples milled with higher BPMRs (35:1 and 40:1), suggesting that quenching caused by a high impact energy followed by an annealing effect may play a vital role, which is further manifested in the agglomeration of small particles. [source] Support-dependent activity of noble metal substituted oxide catalysts for the water gas shift reactionAICHE JOURNAL, Issue 10 2010Parag A. Deshpande Abstract The water gas shift reaction was carried out over noble metal ion substituted nanocrystalline oxide catalysts with different supports. Spectroscopic studies of the catalysts before and after the reaction showed different surface phenomena occurring over the catalysts. Reaction mechanisms were proposed based upon the surface processes and intermediates formed. The dual site mechanism utilizing the oxide ion vacancies for water dissociation and metal ions for CO adsorption was proposed to describe the kinetics of the reaction over the reducible oxides like CeO2. A mechanism based on the interaction of adsorbed CO and the hydroxyl group was proposed for the reaction over ZrO2. A hybrid mechanism based on oxide ion vacancies and surface hydroxyl groups was proposed for the reaction over TiO2. The deactivation of the catalysts was also found to be support dependent. Kinetic models for both activation and deactivation were proposed. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Fe2O3 on Ce-, Ca-, or Mg-stabilized ZrO2 as oxygen carrier for chemical-looping combustion using NiO as additiveAICHE JOURNAL, Issue 8 2010Magnus Rydén Abstract Oxygen-carrier particles for chemical-looping combustion have been manufactured by freeze granulation. The particles consisted of 60 wt % Fe2O3 as active phase and 40 wt % stabilized ZrO2 as support material. Ce, Ca, or Mg was used to stabilize the ZrO2. The hardness and porosity of the particles were altered by varying the sintering temperature. The oxygen carriers were examined by redox experiments in a batch fluidized-bed reactor at 800,950°C, using CH4 as fuel. The experiments showed good reactivity between the particles and CH4. NiO was used as an additive and was found to reduce the fraction of unconverted CH4 with up to 80%. The combustion efficiency was 95.9% at best and was achieved using 57 kg oxygen carrier per MW fuel. Most produced oxygen carriers appear to have been decently stable, but using Ca as stabilizer resulting in uneven results. Further, particles sintered at high temperatures had a tendency to defluidize. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Micro-Raman study of Zr-substituted Bi4Ti3O12 ceramicsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2007S. R. Das Abstract We have studied the lattice vibrational modes of Zr-substituted Bi4Ti3O12 ceramics using micro-Raman spectroscopy. Replacement of Zr at the Ti site in the perovskite block is found from the increase in the lattice parameters as a function of Zr contents. Combined X-ray diffraction patterns and Raman analysis suggested less than 40 mole% Zr solubility in Bi4Ti3O12. At 40 mole% of Zr substitution or above, the unreacted monoclinic-phase ZrO2 is observed in the X-ray diffraction patterns and the Raman spectra. The incorporation of Zr in Bi4Ti3O12 reduces the soft mode wavenumber and the transition temperature. Moreover, temperature dependent studies confirmed the ferroelectric to paraelectric transition in Bi4Ti3O12 at about 675 °C. On increasing the Zr content up to 40% on the Ti sites of Bi4Ti3O12, a systematic decrease in the phase transition temperature from 675 to 630 °C was observed. Copyright © 2007 John Wiley & Sons, Ltd. [source] UV Raman spectroscopic study on the phase transformation of ZrO2, Y2O3,ZrO2 and SO42,/ZrO2JOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2002Can Li The phase evolution of zirconia (ZrO2), sulfated zirconia (SO42,/ZrO2) and yttrium oxide incorporated zirconia (Y2O3,ZrO2) from the tetrahedral phase to the monoclinic phase was studied using UV Raman spectroscopy, visible Raman spectroscopy and x-ray diffraction (XRD). It is clearly observed that there are discrepancies between the results from the UV Raman spectra, visible Raman spectra and XRD patterns. The phase change from tetragonal to monoclinic is always earlier or at lower calcination temperatures as observed by UV Raman spectroscopy than by visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD supply the information mainly from the bulk. The inconsistency in the results from the three techniques suggests that the phase transformation of zirconia starts from its surface region and then gradually develops into its bulk. For SO42,/ZrO2 and Y2O3,ZrO2, the transformation from the tetragonal to the monoclinic phase is significantly retarded owing to the presence of the sulfated groups and the yttrium oxide. Particularly, the tetragonal phase of Y2O3,ZrO2 can be maintained up to 800 °C although its phase at the surface region changed into monoclinic at 500 °C. Copyright © 2002 John Wiley & Sons, Ltd. [source] EXAFS study of the Fex/ZrO2 composite nanomaterials obtained by sol,gel synthesisJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Vladimir Kriventsov The local Zr and Fe arrangements in the nanocomposite system Fex/ZrO2 (x=0-0.2) obtained by sol-gel method were studied by EXAFS. The phase composition was found to vary significantly on iron loading. For the samples calcined at 500 or 600°C, at x,0.01, the formed ZrO2 is a mixture of monoclinic and tetragonal structures. Only tetragonal structure is revealed at x,0.05 with the exception of Fe0.2/ZrO2, calcined at 500°C, where new non-typically short Zr-Zr distances (3.29, 3.43Å) were observed. At low iron loading (less than one monolayer) Fe3+ ions were found to localize within the pre-surface layers of ZrO2 nanoparticles showing property of isolated ions. For greater Fe loading, iron exhibits either two-dimensional layer structure or two-phase system. [source] Multi-component fitting XAFS analysis of molybdate species during catalyst preparation by the molten salt methodJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Nobuyuki Matsubayashi The goal of the present study was to elucidate the formation mechanisms of highly dispersed catalysts by the molten salt method. For this purpose, multi-component fitting Mo K-edge EXAFS analysis was applied to the structure of molybdate catalysts prepared in KNO3 and NaNO3. The analysis revealed that MoO3 dissolved in molten salts was at first transformed into polymolybdate anions and finally into MoO42- anions. The transformation into MoO42- anions took place at a lower temperature when NaNO3 was used as molten salt than KNO3. In contrast, polymolybdate anions were stable even at higher temperature when ZrO2 was added as a support of molybdate. [source] Design, Preparation, and Characterization of Graded YSZ/La2Zr2O7 Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Hongfei Chen Large-area spallation and crack formation during service are big problems of plasma-sprayed thermal barrier coatings (TBCs), owing to their weak bond strengths and high residual stresses. Functional gradient TBCs with a gradual compositional variation along the thickness direction are proposed to mitigate these problems. In this paper, a six-layer structured TBC composed of Y2O3 partially stabilized ZrO2 (YSZ) and La2Zr2O7 (LZ), was prepared by plasma spraying with dual powder feeding ports. This coating had a gradient composition and function. Thermal conductivity of the coating was comparable with that of a single LZ coating while the coefficient of thermal expansion was nearly equal to that of YSZ single coating. The experiment was conducted to compare the thermal shock resistance of a graded coating with a conventional YSZ/LZ double-layer system. Changes in weight and morphology of specimens before and after thermal shock tests were analyzed. Results demonstrated that the thermal shock resistance of the graded coating was superior to the double-layer coating. Typically, a barely visible pimple-like spallation was present on the surface of the graded coating after 21 cycles. On the other hand, obvious delamination was observed for a double-layer coating after six to seven cycles. Special focus was also placed on a comparative investigation of stresses that are closely related to spallation via the use of numerical simulation. [source] ZrW2O8,ZrO2 Continuous Functionally Graded Materials Fabricated by In Situ Reaction of ZrO2 and WO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Li Sun ZrO2 powder and ZrO2+WO3 powder mixture were stacked, cocompacted, and cosintered in a cylindrical die, the processing steps commonly used to fabricate multilayer materials. The soak duration and the mass ratio among layers in the processing have been varied to yield a wide range of final sintered samples. At appropriate soak durations, the sintered samples resulted in continuous functionally graded materials (FGMs) made of ZrW2O8 and ZrO2. In other words, instead of the expected discrete, multiple-layered materials, the resulting samples are characterized by the axially, continuously varying physical properties. The continuous FGM structure is formed by several mechanisms: the balance between the reaction of ZrO2 and WO3 and the decomposition of ZrW2O8, as well as the sublimation and diffusion of WO3. The continuous FGMs can be utilized to reduce the thermal stress induced from a thermal gradient loading within a material system. This study shows that the processing steps typically used for multilayer FGMs can also be used to create continuous FGMs for some special material combinations. [source] Pressureless Sintering t -zirconia@,-Al2O3 (54 mol%) Core,Shell Nanopowders at 1120°C Provides Dense t -Zirconia-Toughened ,-Al2O3 NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Min Kim Zirconia-toughened alumina (ZTA) is of growing importance in a wide variety of fields exemplified by ZTA prosthetic implants. Unfortunately, ZTA composites are generally difficult to process because of the need to preserve the tetragonal zirconia phase in the final dense ceramic, coincident with the need to fully densify the ,-Al2O3 component. We report here that liquid-feed flame spray pyrolysis of mixtures of metalloorganic precursors of alumina and zirconia at varying compositional ratios provide access in one step to core,shell nanoparticles, wherein the shell is ,-Al2O3 and the core is a perfect single crystal of tetragonal (t -) zirconia. Pressureless sintering studies provided parameters whereby these nanopowder compacts could be sintered to full density (>99%) at temperatures just above 1100°C converting the shell component to ,-Al2O3 but preserving the t -ZrO2 without the need for any dopants. The final average grain sizes of these sintered compacts are ,200 nm. The resulting materials exhibit the expected response to mechanical deformation with the subsequent production of monoclinic ZrO2. These materials appear to offer a low-temperature, low-cost route to fine-grained ZTA with varied Al2O3:t -ZrO2 compositions. [source] Thermodynamic Reassessment of ZrO2,CaO SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009Kun Wang In this work, several thermodynamic assessments adopted widely for ZrO2,CaO system are reviewed and examined, the existing discrepancies are summarized, and a new assessment is carried out based on the formation enthalpy of two compounds (CaZr4O9 and Ca6Zr19O44) and experimental activity data concerning cubic solid solution. The thermodynamic parameters of all phases have been optimized by the least squares minimization procedure, a self consistent set of the optimized Gibbs energy parameters has been derived, which can be safely used to extrapolate into the multicomponent system. Compared with experimental data and the results in this work as well as the results reported previously, it is demonstrated that the present thermodynamic assessment is in better agreement with most of the experiments. [source] Fabrication and Characterization of Anode-Supported Tubular Solid-Oxide Fuel Cells by Slip Casting and Dip Coating TechniquesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Lan Zhang High-performance anode-supported tubular solid-oxide fuel cells (SOFCs) have been successfully developed and fabricated using slip casting, dip coating, and impregnation techniques. The effect of a dispersant and solid loading on the viscosity of the NiO/Y2O3,ZrO2 (NiO/YSZ) slurry is investigated in detail. The viscosity of the slurry was found to be minimum when the dispersant content was 0.6 wt% of NiO/YSZ. The effect of sintering temperature on the shrinkage and porosity of the anode tubes, densification of the electrolyte, and performance of the cell at different solid loadings is also investigated. A Ni/YSZ anode-supported tubular cell fabricated from the NiO/YSZ slurry with 65 wt% solid loading and sintered at 1380°C produced a peak power output of ,491 and ,376 mW/cm2 at 800°C in wet H2 and CH4, respectively. With the impregnation of Ce0.8Gd0.2O2 (GDC) nanoparticles, the peak power density increased to ,1104 and ,770 mW/cm2 at 800°C in wet H2 and CH4, respectively. GDC impregnation considerably enhances the electrochemical performance of the cell and significantly reduces the ohmic and polarization resistances of thin solid electrolyte cells. [source] Aqueous Colloidal Processing of ZTA CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009Susana M. Olhero Two different zirconia-alumina composites, ZTA-30 (70 wt% Al2O3+30 wt% ZrO2) and ZTA-60 (40 wt% Al2O3+60 wt% ZrO2), with potential for orthopedic applications, were processed in aqueous media and consolidated by slip casting (SC), hydrolysis-assisted solidification (HAS), and gelcasting (GC) from suspensions containing 50 vol% solids loading. For comparison purposes, the same ceramic compositions were also consolidated by die pressing of freeze-dried granules (FG). In the HAS process, 5 wt% of Al2O3 in the precursor mixture was replaced by equivalent amounts of AlN to promote the consolidation of the suspensions. Ceramics consolidated via GC exhibited higher green (three-point bend) strengths (,17 MPa) than those consolidated by other techniques. Further, these ceramics also exhibited superior fracture toughness and flexural strength properties after sintering for 1 h at 1600°C in comparison with those consolidated by other techniques, including conventional die pressing (FG). [source] Mechanochemical Activation-Assisted Low-Temperature Synthesis of CaZrO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007Guotian Ye Calcium zirconate (CaZrO3, CZ) was prepared using a solid-state reaction with mechanochemical activation through vibro-milling, aiming at completing the reaction CaO+ZrO2=CaZrO3 at relatively low calcination temperatures. Changes in the crystallite size and homogeneity of the mixed components CaO and ZrO2 in the starting mixtures were observed with different milling times. The influence of milling on the incipient temperature of CZ formation and completion of CZ formation was investigated. It is concluded that milling of the reactants for 20 h lowered the incipient temperature of CZ formation from 800° to 600°C, and the temperature of complete CZ formation from above 1100° to 800°C. [source] Structural and Dielectric Characterization of Nanocrystalline (Ba, Pb)ZrO3 Developed by Reverse Micellar SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Tokeer Ahmad Nanocrystalline zirconates of barium and lead have been synthesized using a modified reverse micellar route (avoiding alkoxides). The entire solid solution of Ba1,xPbxZrO3 (0,x,1) has been synthesized for the first time. Powder X-ray diffraction studies show the monophasic nature of the powders after heating at 800°C except minor impurities of ZrO2 (2%,3%) at a higher lead content (x=0.50 and 0.75). The oxides crystallize in the cubic structure till x=0.25; for higher values, they crystallize in the orthorhombic structure. The particle size obtained from X-ray line-broadening studies and transmission electron microscopic studies is found to be in the range of 20,60 nm for all the oxides obtained after heating at 800oC. The grain size of the solid solution of Ba1,xPbxZrO3 (0,x,1) was found to increase with the lead content. The dielectric constant of the solids corresponding to Ba1,xPbxZrO3 (0,x,1) was found to be a maximum at x=0.50. Note that the cubic to orthorhombic transition is also observed between x=0.25 and 0.5. Dielectric properties with respect to variation in frequency and temperature are reported for these nanocrystalline oxides for the first time. [source] Pressureless Densification of Zirconium Diboride with Boron Carbide AdditionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006S. C. Zhang Zirconium diboride (ZrB2) was densified (>98% relative density) at temperatures as low as 1850°C by pressureless sintering. Sintering was activated by removing oxide impurities (B2O3 and ZrO2) from particle surfaces. Boron oxide had a high vapor pressure and was removed during heating under a mild vacuum (,150 mTorr). Zirconia was more persistent and had to be removed by chemical reaction. Both WC and B4C were evaluated as additives to facilitate the removal of ZrO2. Reactions were proposed based on thermodynamic analysis and then confirmed by X-ray diffraction analysis of reacted powder mixtures. After the preliminary powder studies, densification was studied using either as-received ZrB2 (surface area ,1 m2/g) or attrition-milled ZrB2 (surface area ,7.5 m2/g) with WC and/or B4C as a sintering aid. ZrB2 containing only WC could be sintered to ,95% relative density in 4 h at 2050°C under vacuum. In contrast, the addition of B4C allowed for sintering to >98% relative density in 1 h at 1850°C under vacuum. [source] Preparation of Whisker ,-Spodumene Glass,CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006Hu Anmin ,-spodumene glass,ceramics with a whisker-like microstructure were prepared from the following materials (in wt%): 64.5 SiO2, 18.0 Al2O3, 4.2 Li2O, 4 ZrO2, and 8 MgF2. Scanning electron microscope (SEM) analysis showed that phase separation in the base glass leads to the formation of a primary crystal phase of MgF2 that promotes the formation of spherical ,-spodumene. Whisker spodumene crystals surrounded by spherical crystals are observed at 720°C after 1 h, and the whisker crystals grow at the cost of spherical crystals with increasing temperature and time. The flexural strengths of the glass,ceramics reach a maximum of 228 MPa after heat treatment at 850°C for 1 h. [source] | ||||||||||||||||||||||||||||||||||