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Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and ...
1994-12-31
Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si, Sapphire and LaAlO{sub 3} substrates. The effect of substrate temperatures upto 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar structure with variation growth conditions. The buffer layers of YSZ and STO showed orientation. The tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa{sub 2}Cu{sub 9}O{sub 7-x} (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.
1995-04-01
Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and LaAlO3 (100) substrates. The effect of substrate temperatures up to 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa2Cu3O(7-x) (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.
2005-01-01
Composite films with compositions of 100% yttria stabilized zirconia (YSZ) and YSZ with 15, 30, 45, 62.8 (eutectic composition), 80 mol% alumina and 100% alumina films were deposited onto sapphire substrates using combustion chemical vapor deposition. Precursors of yttrium 2-ethylhexanoate, zirconium 2-ethylhexanoate and Al acetylacetonate dissolved in toluene at a total metal ion concentration of 0.002 M were used to produce films up to 1 mum thick. Flame temperatures at the substrate surfaces were 1550+-50 deg. C and deposition rates fell between of 0.76-1.7 mum/h, depending on composition. Nanohardness, determined with a Berkovich indenter, was constant at about 15 GPa for compositions less than 100% alumina. The 100% alumina films were about twice as hard as other films. The films' fracture toughness, determined with a cube ...
Study of microstructure and thermal shock behavior of two types of thermal barrier coatings
2009-01-01
Gas turbines provide one of the most severe environments challenging material systems nowadays. Only an appropriate coating system can supply protection particularly for turbine blades. This study was made by comparison of properties of two different types of thermal barrier coatings (TBCs) in order to improve the surface characteristics of high temperature components. These TBCs consisted of a duplex TBC and a five layered functionally graded TBC. In duplex TBCs, 0.35 mm thick yittria partially stabilized zirconia top coat (YSZ) was deposited by air plasma spraying and 0.15 mm thick NiCrAlY bond coat was deposited by high velocity oxyfuel spraying. 0.5 mm thick functionally graded TBC was sprayed by varying the feeding ratio of YSZ/NiCrAlY powders. Both coatings were deposited on IN 738LC...
Molybdenum disilicide composites reinforced with zirconia and silicon carbide
Compositions are disclosed consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia.
Molybdenum disilicide composites reinforced with zirconia and silicon carbide
Compositions consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia.
In vitro aging of yttria-stabilized zirconia
1989-04-01
Yttrria-stabilized zirconia was aged in distilled water, saline, and Ringer's solution for 140, 304, and 453 d. The significant decrease in strength (13% to 22%) is attributed to the phase transformation of zirconia from tetragonal to monoclinic. The effect of aging stabilized zirconia in physiological media is still unresolved.
Role of zirconia toughening in the abrasive wear of intermetallic and ceramic composites
1997-11-30
In this study, the hardness, fracture toughness, and abrasive wear behavior of three zirconia-toughened MoSi{sub 2} composites and a zirconia-toughened Al{sub 2}O{sub 3} were examined and compared with similar materials containing no zirconia second phases. Each of the composites contained 20 vol.% ZrO{sub 2}; however, the polymorph of the added zirconia particles was varied to give composites with unstabilized, partially stabilized, and fully stabilized zirconia reinforcement. It was observed that the influence of zirconia toughening on the abrasive wear behavior depended upon the nature of the toughening mechanisms activated by the zirconia addition. (orig.)
Molybdenum disilicide composites reinforced with zirconia and silicon carbide
1992-12-31
This patent pertains to compositions consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia. Fabrication, fracture toughness, and bend strength are covered.
Orthorhombic zirconia phase in ZrO{sub 2}-MgAl{sub 2}O{sub 4} composite material
1996-04-01
Zirconia is one of the major components of modern ceramic materials. Those last two decades, a very large number of studies were devoted to zirconia based ceramics. Two classes of materials can be distinguished: Zirconia Toughened Ceramics (ZTC) and zirconia based alloys in the form of Partially Stabilized Zirconia (PSZ) or Tetragonal Zirconia Polycrystals (TZP). In the field of ZTC, zirconia toughened alumina (ZTA) is certainly the most important material. Magnesium aluminum spinel (MgAl{sub 2}O{sub 4}) has similar elastic properties as alumina and therefore can as well be toughened by zirconia adding. Among very few previous papers reporting on zirconia-spinel composites, N. Claussen and col. have published results on mechanical properties of such materials. Those products could yet exhibit specific microstructural and mechanical behavior, because of the magnesium readiness to form solid solutions as well with zirconia as with alumina. Until now very few studies have been devoted to microscopic analysis of such materials. The aim of this work is to investigate by transmission electron microscopy the presence of orthorhombic zirconia grains in spinel zirconia composites.
Phase stabilization of zirconia
Stabilized zirconia containing sintered particles of alumina and zirconia in tetragonal phase is prepared by mixing alumina particles of less than 30 nanometers with zirconia particles of less than 30 nanometers in presence of a liquid to form a suspension, drying the suspension at a temperature up to about 600 deg C to remove the liquid and products thereof to form a dried suspension composed of agglomerated alumina and zirconia particles, sintering the dried suspension to fuse the particles and cooling the sintered dried suspension to an ambient temperature to produce free-standing bodies or coatings on substrates.
Phase stabilization of zirconia
1997-01-30
Stabilized zirconia containing sintered particles of alumina and zirconia in tetragonal phase is prepared by mixing alumina particles of less than 30 nanometers with zirconia particles of less than 30 nanometers in presence of a liquid to form a suspension, drying the suspension at a temperature up to about 600 deg C to remove the liquid and products thereof to form a dried suspension composed of agglomerated alumina and zirconia particles, sintering the dried suspension to fuse the particles and cooling the sintered dried suspension to an ambient temperature to produce free-standing bodies or coatings on substrates.
2010-01-01
Sulfated zirconia is an inorganic solid superacid having sulfate groups covalently bonded to its surface. In this work, sulfated zirconia is synthesized by a solvent-free method to obtain it in the nanoparticle form. This nanostructured sulfated zirconia has been evaluated in terms of (i) chemical stability to hydrolysis and to hydrogen peroxide by thermogravimetric analysis, and (ii) influences on Pt catalyst activity by cyclic voltammetry using sulfated-zirconia dispersion as a supporting electrolyte solution. The results demonstrate that our sulfated zirconia is stable almost perfectly to hydrolysis but partly decomposed by a Fenton reagent containing hydrogen peroxide and Fe^2^+. In addition, we show that oxygen reduction activity of Pt catalyst in a sulfated-zirconia dispersion is com...
Toughening of glass-ceramics by both transformable and transformed zirconia
1995-11-01
Zirconia-containing baria-silica system glass-ceramics were prepared by sintering and crystallizing cold-pressed mixtures of a barium silicate glass powder and 10 vol.% of a pre-heat-treated partially stabilized zirconia powder. At room temperature, all zirconia remained as tetragonal zirconia in glass-ceramics. Upon cooling to sub-zero temperatures tetragonal zirconia in glass-ceramics transformed to monoclinic zirconia, the amount of the transformed zirconia increasing with decreasing temperature. It was found that the room-temperature fracture toughness, K(sub IC), of glass-ceramics, evaluated by the single-edge-precracked-beam method, increased both with increasing grain size of transformable tetragonal zirconia and with increasing amount of transformed monoclinic zirconia. The former is attributed to zirconia transformation toughening, while the latter is largely due to crack deflection toughening.
Gelcast zirconia-alumina composites
1991-01-01
Near net-shaped parts of zirconia-alumina composites have been successfully formed by gelcasting, a technique which utilizes in situ polymerization of acrylamide monomers. The high solids loading required for gelcasting ({approximately}50 vol %) was obtained by controlling the pH-dependent stability of the aqueous zirconia-alumina suspensions. A strong correspondence was found among the surface charges on the particles, colloidal stability, and the maximum solids loading. 14 refs., 3 figs., 2 tabs.
Osteoblast response to zirconia-hybridized pyrophosphate-stabilized amorphous calcium phosphate
2006-03-01
Calcium phosphate bioceramics, such as hydroxyapatite, have long been used as bone substitutes because of their proven biocompatibility and bone binding properties in vivo. Recently, a zirconia-hybridized...Full Text Available
2010-01-01
Highly active and stable platinum catalysts for propane combustion were prepared by impregnating platinum on zirconia-incorporated silica by combining the high surface area of silica with the exceptional thermal stability of zirconia. The thermal stability of the platinum catalysts was examined after thermal aging at 800C for 50h. The physico-chemical states of the platinum and zirconia were investigated by using various analytical instruments, CO and H2 chemisorption, and temperature-programmed-desorption of ammonia. The platinum catalysts prepared on the zirconia-incorporated silica and treated with hydrogen peroxide showed high catalytic activity and stability in propane combustion. The high dispersion of platinum and the acid site generation achieved due to the incorporation of z...
2003-01-01
Zirconium oxide is an inert matrix candidate for the transmutation of plutonium in light water reactor (LWR). The thermal conductivity of cubic zirconia is however lower than the conductivities of UO2 and MOX. Special designs are therefore necessary to avoid high peaking temperatures close to the melting point in the zirconia pellet. Cermet would be a favorable design to improve the thermal conductivity. The suggested cermet fuel consists of fine plutonium doped stabilized zirconia particles dispersed in a metallic inert matrix. Manufacturing tests on cubic zirconia microspheres were carried out by using the internal gelation process developed at the Paul Scherrer Institute. Gelation was conducted successfully and the sintered spheres had a homogeneous single cubic structure. The lattice parameter of the cubic zirconia was estimated as a function of the Er, ...
Yttria stabilized zirconia thin films by multilayer electron-beam deposition
1986-07-01
A new method for preparing cubic stabilized zirconia thin films was studied. The method involves the electron-beam deposition of an oxide multilayer film on suitable substrates followed by aging. Yttria-zirconia multilayer films on two electrodes, molybdenum and platinum/rhodium were investigated and the cubic stabilization was determined by X-ray diffraction and dc conduction studies. Cubic yttria stabilized zirconia (YSZ) was clearly formed on the molybdenum electrode but the solid solution formed on the platinum/rhodium may be predominantly tetragonal as little or no cubic stabilization resulted. The formation of YSZ on molybdenum may be due to more favorable epitaxial growth conditions on that electrode.
2006-01-01
The aims of this work was investigated the zirconia stabilization with a mixture of resins based on silico nas promoting the Zr O 2 /Si O 2 formation. The powder was heated and characterized by TGA, DTA, FTIR, XRD and SEM/EDS. The results indicated the tetragonal and cubic phase formation stabilized at 1000 deg C/2 h. The increase of calcing temperature promoted decrease of stabilization. The amorphous silica calcined at 1000 deg C induced defects into the zirconia structure and favour the formation of more stable phases. The decrease of stabilization at high temperatures are related to growth of crystallite above of critical value. (author)
2009-01-01
Thermal barrier coating (TBCs) systems made of plasma sprayed zirconia are commonly used in gas turbine engines to lower metal components surface temperature and allow higher combustion temperature that results in higher fuel efficiency and environmentally cleaner emissions. Low thermal conductivity and long service life are the most important properties of these coatings. The objective of this work was to study the influence of a long-term heat treatment (i.e., 1200C/2000h) on different characteristics of atmospheric plasma sprayed TBCs. Two zirconia feedstock materials were evaluated, namely, yttria partially stabilized zirconia and dysprosia partially stabilized zirconia. Several spray conditions were designed and employed to achieve different coating morphologies. Microstructure ...
SIMS analysis of multi-diffusion profiles of lanthanides in stabilized zirconias
2003-01-15
To get an insight into the mechanism of cation diffusion in yttria stabilized zirconia (YSZ), the diffusion of all stable lanthanides was measured simultaneously. It was possible to identify all lanthanides with SIMS and perform depth profile analysis to get the bulk diffusion coefficients between 1270 and 1700 deg. C. From the analysis of the radius-dependency of the cation diffusion of the lanthanides, it was possible to show that the diffusion of the lanthanides is the slowest when their radius is similar to the radius of the stabilized cation (yttrium)
Two-body wear of different ceramic materials opposed to zirconia ceramic
2010-01-01
Statement of problem Little is known about the wear behavior of ceramics opposed to unveneered zirconia and whether wear varies according to microstructure, surface toughness, and flexural strength of the ceramics. Purpose The purpose of this study was to evaluate the 2-body wear resistance of 5 ceramics opposing unveneered zirconia ceramic. Material and methods Yttrium-stabilized zirconia, lithium disilicate glass ceramic, leucite-reinforced glass ceramic, fluorapatite glass ceramic, and nanofluorapatite glass ceramic specimens (n=8) were tested against standardized zirconia balls. Wear tests were performed in a dual-axis mastication simulator. Wear resistance was calculated by measuring the vertical and volumetric substance loss using a laser scanner. Specimen surfaces were evaluated at ...
1996-04-01
Single crystals of yttria-stabilized zirconia were irradiated with 400 keV Xe ion-beam at room temperature and minus 90 degrees centigrade. Defect growth was monitored in situ with Rutherford Backscattering and ion channeling techniques using a 2 MeV He ion beam.
1991-08-25
Development of oxides system ceramic has been carried forward earlier, especially partially stabilized zirconia put to practical use in broad fields owing to have high strength and brittleness, However, since more high strength and brittleness are expected according to more severe use surrounding, compositization of ceramics is going on. In this paper, it was studied on the relations between the mechanical properties and microstructure, making zirconia / alumina ceramic composites by the injection molded method. As a result, it was found that when zirconia and alumina were composited, crystal grain of alumina became fairly fine, on the other hand, zirconia was scarcely possible to fine. And then, zirconia / alumina ceramic composites showed the maximum fracture brittleness value and bending strength in about 30 volume % alumina and confirmed respectively rise about 1.5 times and about 2.5 times comparing with alumina single ceramics. 10 refs., 8 figs., 1 tab.
Internal stresses and stability of the tetragonal phase in zirconia thin layers deposited by OMCVD
2008-01-01
Zirconia thin films were deposited by OMCVD (organo-metallic chemical vapour deposition) at various temperatures and oxygen partial pressures on a AISI 301 stainless steel substrate with Zr(thd)4 as precursor. The as deposited 250 nm thin zirconia films presented a structure consisting of two phases: the expected monoclinic one and also an unexpected tetragonal phase. According to the literature, the stabilization of the tetragonal phase (metastable in massive zirconia) can be related to the crystallite size and/or to the generated internal compressive stresses. To analyze the effect of internal and external stresses on the thin film behaviour, in-situ tensile experiments were performed at room temperature and at high temperature (500 deg. C). Depending on the process parameters, phase transformations and damage evolution of the films were observed. Our ...
[Hyperfine experimental investigation of zirconia ceramics]. [Annual progress report 20]
1992-09-01
This research program has encompassed a broad investigation of microscopic structure and point defect properties in insulating materials and some recent exploratory work on semiconductors. The major experimental technique is perturbed angular correlation (PAC) spectroscopy. Our research provides information about the microscopic structure, nucleation, and equilibrium of structural phases in materials under investigation. We have studied phase equilibria in monoclinic, tetragonal, and cubic zirconia in the past and have recently begun more detailed investigation of high-temperature anomalies in monoclinic zirconia and tetragonal stabilized zirconia. We also have found a number of instances where the indium PAC probe has detected subtle phase changes, small precipitate formation, and other phase behavior that are difficult to detect by conventional diffraction methods. The PAC experimental technique is described briefly in section 2, and recent research is reviewed in section 3.
Zirconia-zircon composite microfiltration membranes based on porous alumina supports
2005-01-01
Supported zirconia-zircon composite microfiltration layers produced by the dip-coating procedure are introduced for the first time. These can be produced using commercial grade monoclinic-zirconia powders having high silica content. Such membranes have the advantage of enhanced sintering due to a liquid-phase mechanism. These were prepared through dip-coating a-alumina supports with slips of zirconia powder stabilized with `aluminon' and further sintering (1050-1200degreeC). Optimum dispersant concentration and pH had been found based on sedimentation tests and UV-vis spectroscopy method. The effect of slip concentration, sintering temperature and number of coatings on the membrane characteristics has been studied. There exists a maximum sintering temperature of 1150degreeC for the creatio...
2010-01-01
This review presents a critical survey of all experimental data about the low temperature degradation of zirconia (often referred to as ''aging'') due to the tetragonal-to-monoclinic transformation, which have been collected at temperatures of interest for dental application (room temperature to about 100^oC). It is shown that the main factors affecting the aging phenomenon are (i) the stabilizer type and content, (ii) the residual stress and (iii) the grain size. It is also shown that extrapolating the low temperature degradation rate from accelerated aging tests can lead to unacceptable conclusions about the lifetime of the zirconia-based components. Finally, based on the experimental evidence, a set of engineering guidelines for the use of zirconia in restorative and prosthetic dentistr...
IMPROVED BIOCERAMIC IMPLANT COMPONENTS
2000-08-31
Objectives1. The fabrication of stabilised zirconia powered compositions fir the production of 2nd generation biomedical implants.~%~2. Evaluation of the mechanical and physical properties of the zirconia materials and their conformance with international standards.~%~3. In vivo evaluation of the materials.~%~DescriptionCeramic materials have been used successfully for medial implants for many years. In particular, alumina and zirconia are established as suitable materials for femoral heads in total hip replacements. Yttria stabilised zirconia has excellent mechanical properties in terms of strength, toughness and wear (against UHMWPE), however, there has been some concern about the long term stability of the tetragonal crystal structure under aqueous conditions.~%~The objective of the proposed work programme [continued...]
Electrophoretic deposition (EPD) was explored as an inexpensive route for fabricating the 8 mol% yttria stabilized zirconia electrolyte in solid oxide fuel cells (SOFCs). Normally, deposition of particulate ceramic powders onto a sintered porous surface yields a non uniform coating which, after sintering, results in porosity, surface roughness and cracking in the coating. To overcome this problem, the present study used a fugitive graphite interlayer between the porous air electrode supported (AES) cathode tube (doped-LaMnO{sub 3}) and the deposited zirconia film. By this approach, a fairly dense green coating ({approximately}60%) was obtained, which yielded a smooth surface and pore-free microstructure after sintering. Preliminary results on the effect of a fugitive interlayer on the unfired (green) and fired zirconia coatings are discussed.
2000-07-01
Electrophoretic deposition (EPD) was explored as an inexpensive route for fabricating the 8 mol% yttria stabilized zirconia electrolyte in solid oxide fuel cells (SOFCs). Normally, deposition of particulate ceramic powders onto a sintered porous surface yields a non uniform coating which, after sintering, results in porosity, surface roughness and cracking in the coating. To overcome this problem, the present study used a fugitive graphite interlayer between the porous air electrode supported (AES) cathode tube (doped-LaMnO{sub 3}) and the deposited zirconia film. By this approach, a fairly dense green coating ({approximately}60%) was obtained, which yielded a smooth surface and pore-free microstructure after sintering. Preliminary results on the effect of a fugitive interlayer on the unfired (green) and fired zirconia coatings are discussed.
2010-01-01
The interface between yttrium oxide partially stabilized tetragonal zirconia polycrystalline (Y-TZP) core and veneering porcelain is the site of most clinical failures. Many efforts have focused on increasing the bond strength between Y-TZP core and veneering porcelain, and such approaches include increasing the surface roughness and providing undercuts. However, each surface roughening method carries limitations. The specific aim of this study was to test the bond strengths of Y-TZP subjected to different methods (sandblasting, fine polising, and rough polising) and of veneering porcelain. Presintered zirconia blocks with rectangular parallelepiped shape were prepared, and the surfaces were roughened with different methods before sintering. Shear strength of each zirconia-veneer interface...
(Hyperfine experimental investigation of zirconia ceramics)
1992-01-01
This research program has encompassed a broad investigation of microscopic structure and point defect properties in insulating materials and some recent exploratory work on semiconductors. The major experimental technique is perturbed angular correlation (PAC) spectroscopy. Our research provides information about the microscopic structure, nucleation, and equilibrium of structural phases in materials under investigation. We have studied phase equilibria in monoclinic, tetragonal, and cubic zirconia in the past and have recently begun more detailed investigation of high-temperature anomalies in monoclinic zirconia and tetragonal stabilized zirconia. We also have found a number of instances where the indium PAC probe has detected subtle phase changes, small precipitate formation, and other phase behavior that are difficult to detect by conventional diffraction methods. The PAC experimental technique is described briefly in section 2, and recent research is reviewed in section 3.
Zirconia-based fuel cells for power generation
This paper reviews the design and operation of the high temperature solid oxide fuel cells based on yttria-stabilized zirconia electrolyte. The functional requirements of the various cell components are presented; and the materials and fabrication processes used for different cell components are described. Finally, the recent progress made toward commercialization of these cells for clean and efficient power generation is discussed.
Zirconia-based fuel cells for power generation
This paper reviews the design and operation of the high temperature solid oxide fuel cells based on yttria-stabilized zirconia electrolyte. The functional requirements of the various cell components are presented; and the materials and fabrication processes used for different cell components are described. Finally, the recent progress made toward commercialization of these cells for clean and efficient power generation is discussed.
Zirconia-based fuel cells for power generation
1992-01-01
This paper reviews the design and operation of the high temperature solid oxide fuel cells based on yttria-stabilized zirconia electrolyte. The functional requirements of the various cell components are presented; and the materials and fabrication processes used for different cell components are described. Finally, the recent progress made toward commercialization of these cells for clean and efficient power generation is discussed.
Zirconia-based fuel cells for power generation
1992-04-01
This paper reviews the design and operation of the high temperature solid oxide fuel cells based on yttria-stabilized zirconia electrolyte. The functional requirements of the various cell components are presented; and the materials and fabrication processes used for different cell components are described. Finally, the recent progress made toward commercialization of these cells for clean and efficient power generation is discussed.
Zirconia-based colors for ceramic glazes
The history of color development for use in ceramic glazes is outlined. The most significant modern development is based on zirconia and zircon. These materials have gained increasing acceptance in the industry since their introduction in the late 1950's and early 1960's, due to their superior stability during firing of the glaze.
Zirconia-based colors for ceramic glazes
1977-02-01
The history of color development for use in ceramic glazes is outlined. The most significant modern development is based on zirconia and zircon. These materials have gained increasing acceptance in the industry since their introduction in the late 1950's and early 1960's, due to their superior stability during firing of the glaze.
Single crystal growth of zirconia utilizing a skull melting technique
1979-08-01
This report reviews the problems associated with the high temperature growth of non-metallic single crystals, particularly refractory oxides. Various approaches to circumvent the problems of melt contamination and containment are discussed. The cold wall R.F. heated skull technique is discussed in detail. This technique is applied to the growth of yttria stabilized zirconia to meet specific requirements, and to establish the viability of this technique. The resulting crystals are characterized by a number of optical, chemical, and physical techniques.
Kinetic modelling of pressure filtration of ceramic powder suspensions
1995-09-01
A kinetic model developed for radial pressure filtration is described and used to study the casting behaviour of an Alumina (Al6SG) and a Zirconia (TZ3Ys) slip stabilized with Dolapix CE64. For the Zirconia slip no influence of pressure and curvature is found. The casting behaviour of the Alumina slip seems to be influenced by both the pressure and the curvature of the filtrating surface.
Kinetic modelling of pressure filtration of ceramic powder suspensions
1995-04-01
A kinetic model developed for radial pressure filtration is described and used to study the casting behaviour of an Alumina (A16SG) and a Zirconia (TZ3Ys) slip, stabilized with Dolapix CE64 polyelectrolyte. For the Zirconia slip no influence of pressure and curvature is found. The casting behaviour of the Alumina slip seems to be influenced by both the pressure and the curvature of the filtrating surface. 4 figs., 3 refs.
A series of alumina-yttria-stabilized zirconia composites containing either a high aspect ratio (5 and 30 mol%) hexagonal platelet alumina or an alumina low aspect ratio (5 and 30 mol%) spherical particulate was used to ...
Character of laser-glazed, plasma-sprayed zirconia coatings on stainless steel substrata
Partially stabilized zirconia was applied as coatings to 316L stainless steel substrata using an 80-kw arc-plasma unit. Some of these coating-substrate systems were subsequently glazed using a 10 kw CO2 ...
Electrical properties of polarized partially stabilized zirconia for biomaterials
2002-07-01
Partially stabilized zirconia (PSZ) ceramics for biomaterials were electrically polarized. The depolarization process of PSZ was investigated by thermally stabilized depolarized current (TSDC) measurement. The biocompatibility of polarized PSZ was examined using osteoblastic cell cultivation. The PSZ (containing 3 mol% Y{sub 2}O{sub 3}) pellets sintered at 1400 C for 1h were polarized at 800 C for 1h in a d.c. field of 50 Vcm{sup -1}. The proliferation of adhesive cells were accelerated on the negative charge surface and decelerated on the positive charge surface. (orig.)
Sintered electrode for solid oxide fuel cells
A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation.
Sintered electrode for solid oxide fuel cells
A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation. 4 figs.
Sintered electrode for solid oxide fuel cells
A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation.
Sintered electrode for solid oxide fuel cells
A solid oxide fuel cell fuel electrode is produced by a sintering process. An underlayer is applied to the electrolyte of a solid oxide fuel cell in the form of a slurry, which is then dried. An overlayer is applied to the underlayer and then dried. The dried underlayer and overlayer are then sintered to form a fuel electrode. Both the underlayer and the overlayer comprise a combination of electrode metal such as nickel, and stabilized zirconia such as yttria-stabilized zirconia, with the overlayer comprising a greater percentage of electrode metal. The use of more stabilized zirconia in the underlayer provides good adhesion to the electrolyte of the fuel cell, while the use of more electrode metal in the overlayer provides good electrical conductivity. The sintered fuel electrode is less expensive to produce compared with conventional electrodes made by electrochemical vapor deposition processes. The sintered electrodes exhibit favorable performance characteristics, including good porosity, adhesion, electrical conductivity and freedom from degradation.
Effect of conjoint additions of rare earth element oxides on the phase stability of zirconia
1996-08-01
The ability of the cubic phase of zirconia to accommodate in solid solution the oxides of rare earth elements with differing cationic radii has been investigated. Mixed oxide phase assemblages were prepared by hydrolyzing zirconium butoxide with solutions of rare earth element nitrates followed by drying, calcining and sintering. The resulting products were characterized by X-ray diffraction and energy dispersive spectroscopy. The cubic zirconia phase can accept into solid solution the larger, non-cubic stabilizing, rare earth element ions such as lanthanum in the presence of the cubic stabilizing oxides of yttrium and samarium. As the proportion of the larger rare earth element ions is increased the formation of pyrochlore type compounds is favored.
1997-12-31
The chemistry and microstructure of the interface between calcium doped lanthanum manganite and cubic calcia stabilized zirconia have been studied in order to investigate the chemical stability of these materials as a model system for respectively the electrode and the electrolyte in solid oxide fuel cells (SOFC). The results revealed differences in the relative amounts and the time dependence of the formation of the secondary phases (La{sub 2}Zr{sub 2}O{sub 7} and CaZrO{sub 3}), the interdiffusion between the primary phases and the lattice parameters of the different phases; especially the cubic zirconia. The most chemically stable interface was observed when the lanthanum manganite contained 30 mole% calcium on La-site. (orig.) 9 refs.
Disclosed is a cermet electrode consisting of metal particles of nickel, cobalt, iron, or alloys or mixtures thereof immobilized by zirconia stabilized in cubic form which contains discrete deposits of about 0.1 to about 5% by weight of praseodymium, dysprosium, terbium, or a mixture thereof. The solid oxide electrode can be made by covering a substrate with particles of nickel, cobalt, iron, or mixtures thereof, growing a stabilized zirconia solid oxide skeleton around the particles thereby immobilizing them, contacting the skeleton with a compound of praseodymium, dysprosium, terbium, or a mixture thereof, and heating the skeleton to a temperature of at least 500.degree. C. The electrode can also be made by preparing a slurry of nickel, cobalt, iron, or mixture and a compound of praseodymium, dysprosium, terbium, or a mixture thereof, depositing the slurry on a substrate, heating the slurry to dryness, and growing a stabilized zirconia skeleton around the metal particles.
Disclosed is a cermet electrode consisting of metal particles of nickel, cobalt, iron, or alloys or mixtures thereof immobilized by zirconia stabilized in cubic form which contains discrete deposits of about 0.1 to about 5% by weight of praseodymium, dysprosium, terbium, or a mixture thereof. The solid oxide electrode can be made by covering a substrate with particles of nickel, cobalt, iron, or mixtures thereof, growing a stabilized zirconia solid oxide skeleton around the particles thereby immobilizing them, contacting the skeleton with a compound of praseodymium, dysprosium, terbium, or a mixture thereof, and heating the skeleton to a temperature of at least 500.degree. C. The electrode can also be made by preparing a slurry of nickel, cobalt, iron, or mixture and a compound of praseodymium, dysprosium, terbium, or a mixture thereof, depositing the slurry on a substrate, heating the slurry to dryness, and growing a stabilized zirconia skeleton around the metal particles.
A novel thin film solid oxide fuel cell for microscale energy conversion
1999-01-01
A novel approach for the fabrication and assembly of a solid oxide fuel cell system is described which enables effective scaling of the fuel delivery, manifold, and fuel cell stack components for applications in miniature and microscale energy conversion. Electrode materials for solid oxide fuel cells are developed using sputter deposition techniques. A thin film anode is formed by co-deposition of nickel and yttria-stabilized zirconia (YSZ). This approach provides a mixed conducting inter-facial layer between the nickel electrode and electrolyte layer. Similarly, a thin film cathode is formed by co-deposition of silver and yttria-stabilized zirconia. Additionally, sputter deposition of yttria-stabilized zirconia thin film electrolyte enables high quality, continuous films to be formed having thicknesses on the order of 1-2(micro)m. This will effectively lower ...
1988-06-25
Solid electrolytic fuel cells, which are high-temperature type fuel cells, chiefly employ as the solid electrolyte, stabilizing zirconia which has excellent ion conductivity, durability and economic efficiency. Solid electrolytic fuel cells can be expected to provide high generating efficiency and high-efficiency running using low-cost or plentiful fuel, and to realize avoidance of electrolyte-related problems. Among the various kinds of stabilizing zirconia, the yttria stabilizing zirconia is the most widely used, but recently, oxide ion conductors employing CeO2 as their base are drawing attention. For use as air electrodes for 1000C high-temperature operations, perovskite-type, multi-element metallic oxides containing rare earth elements in particular demonstrate excellent stability and electrical characteristics. However, attempts are also being made to use alkali earth metals and metalic transistion elements. In Japan, as a link in the chain of the Moonlight Project, thin-film fuel cells employing yttria stabilizing zirconia as the electrolyte and LaCoO3 as the air electrode were fabricated. They are now yielding favorable results in 1.2kW power generation tests. (5 figs, 1 table, 33 refs)
2008-07-15
Composites of hydroxyapatite with cubic zirconia with MgO or MgF{sub 2} were pressureless sintered at temperatures from 1000 to 1300 deg. C. The reactions and transformations of phases were monitored with X-ray diffraction. For the hydroxyapatite and zirconia composites with MgO, calcium diffused from hydroxyapatite into the zirconia, and hydroxyapatite decomposed to tri-calcium phosphate at sintering temperatures higher than 1000 deg. C. Above about 1200 deg. C, CaZrO{sub 3} was formed. Composites containing the MgF{sub 2} decomposed slower than the composites with MgO which was verified by the changes in the lattice volume of the hydroxyapatite left in the composites. Fluorine ions in MgF{sub 2} diffused into hydroxyapatite which resulted in thermal stability at high sintering temperatures. Composites with MgF{sub 2} had higher hardness than those with MgO. The lowest porosity was found in a composite initially containing 10 wt% cubic zirconia and 5 wt% MgF{sub 2}.
From rare earth doped zirconia to 1kW solid oxide fuel cell system
2006-01-01
Toho Gas R&D efforts and achievements regarding solid oxide fuel cells (SOFCs) from rare earth doped zirconia to 1kW SOFC system are described in this article. In this research, the use of Sc2O3-ZrO2 (scandia stabilized zirconia, ScSZ), which has the highest oxide ion conductivity among the zirconia systems, was investigated as an electrolyte for SOFCs. To improve the performance and mechanical reliability of SOFC cells and stacks, tetragonal phase ScSZ ceramic sheets were developed as electrolytes for SOFCs. They have flexibility, high-strength and twice the conductivity of a Y2O3-ZrO2 (Yttria stabilized zirconia, YSZ) system. Because of this electrolyte, the SOFC operating temperature was reduced to 1073K. Also, to validate the performance of this cell, the first Japanese-made 1kW SOFC s...
Yttria-stabilized zirconia supported copper oxide catalyst
1996-05-01
The authors determined the catalytic effects of copper oxide supported on YSZ in the oxidation of carbon monoxide. Oxygen vacancies in the support have been correlated with enhance catalytic activity. 81 refs., 9 figs.
Environmental Barrier Coatings Having a YSZ Top Coat
Environmental barrier coatings (EBCs) with a Si bond coat, a yttria-stabilized zirconia (YSZ) top coat, and various intermediate coats were investigated. EBCs were processed by atmospheric pressure plasma spraying. The EBC ...
Delamination-Indicating Thermal Barrier Coatings
The risk of premature failure of thermal barrier coatings (TBCs), typically composed of yttria-stabilized zirconia (YSZ), compromises the reliability of TBCs used to provide thermal protection for turbine engine ...
2010-01-01
Objectives: The metastability of the tetragonal crystal structure of yttria partial stabilized zirconia polycrystalline (Y-TZP) ceramics is a basis of concern for dental restorations. Reactions between the porcelain and the Y-TZP framework may result in a reduction of the stability of the zirconia and interface bonding caused by a transformation from tetragonal to monoclinic crystalline structure during veneering. Methods: XRD^2 micro-diffraction measurements were carried out on tapered veneered cross-sections of the interface area to generate locally resolved information of the phase content in this region. To get a high intensity X-ray beam for short measurement times a focussing polycapillary with a spot size of app. 50mm was used to evaluate the porcelain zirconia interface. Results: U...
Present status and future trends for ceramic parts and engines
1987-01-01
The author feels that there have been subtle changes in the direction of ceramic engine research in years. Before then, the emphasis was to develop countermeasures to overcome the disappointing performance of adiabatic engines which were made using partially stabilized zirconia. Current interest focuses on finding appropriate applications, namely those which make effective use of ceramic properties, and developing new materials suitable for adiabatic engines. Partially stabilized zirconia in the adiabatic diesel loses its strength around 800 degrees C. On the other hand, silicon nitride has demonstrated the ability to withstand thermal shock because of its high rupture strength. Other new materials are alumina zirconia and alumina titanium (Al2TiO3). The latter has both good thermal and rupture strength properties, making it suitable for ...
From the basis of ab initio electronic structure calculations which include the effects of thermally excited magnetic fluctuations, we predict Mn-stabilized cubic zirconia to be ferromagnetic above 500 K. We find this material, which is well known both as an imitation diamond and as a catalyst, to be half-metallic with the majority and minority spin Mn impurity states lying in zirconia's wide gap. The Mn concentration can exceed 40%. The high-T{sub C} ferromagnetism is robust to oxygen vacancy defects and to how the Mn impurities are distributed on the Zr fcc sublattice. We propose this ceramic as a promising future spintronics material.
Method of electrode fabrication for solid oxide electrochemical cells
A process for fabricating cermet electrodes for solid oxide electrochemical cells by sintering is disclosed. First, a porous metal electrode is fabricated on a solid oxide cell, such as a fuel cell by, for example, sintering, and is then infiltrated with a high volume fraction stabilized zirconia suspension. A second sintering step is used to sinter the infiltrated zirconia to a high density in order to more securely attach the electrode to the solid oxide electrolyte of the cell. High performance fuel electrodes can be obtained with this process. Further electrode performance enhancement may be achieved if stabilized zirconia doped with cerium oxide, chromium oxide, titanium oxide, and/or praseodymium oxide for electronic conduction is used. 5 figs.
Method of electrode fabrication for solid oxide electrochemical cells
A process for fabricating cermet electrodes for solid oxide electrochemical cells by sintering is disclosed. First, a porous metal electrode is fabricated on a solid oxide cell, such as a fuel cell by, for example, sintering, and is then infiltrated with a high volume fraction stabilized zirconia suspension. A second sintering step is used to sinter the infiltrated zirconia to a high density in order to more securely attach the electrode to the solid oxide electrolyte of the cell. High performance fuel electrodes can be obtained with this process. Further electrode performance enhancement may be achieved if stabilized zirconia doped with cerium oxide, chromium oxide, titanium oxide, and/or praseodymium oxide for electronic conduction is used.
1980-05-24
Stabilized zirconia ceramics appear to have considerable potential as thermal barriers or corrosion resistant coatings for application to gas turbine components. Salt corrosion tests have indicated however that under some conditions vanadium impurities in the fuel may cause accelerated failure of these coatings as a result of destabilization of the zirconia phase. The corrosion resistance, thermal stability and structure of the coatings depend to a large extent on the chemical composition of the ceramic phase. The results of a study of the behavior of plasma-sprayed Y/sub 2/O/sub 3/-Zr0/sub 2/ coatings towards combustion gases and the typical salt deposits likely to be encountered in gas turbines which burn fuels containing sodium, sulfur, lead and vanadium impurities are described.
1980-05-24
Stabilized zirconia ceramics appear to have considerable potential as thermal barriers or corrosion resistant coatings for application to gas turbine components. Salt corrosion tests have indicated however that under some conditions vanadium impurities in the fuel may cause accelerated failure of these coatings as a result of destabilization of the zirconia phase. The corrosion resistance, thermal stability and structure of the coatings depend to a large extent on the chemical composition of the ceramic phase. The results of a study of the behavior of plasma-sprayed Y/sub 2/O/sub 3/-ZrO/sub 2/ coatings towards combustion gases and the typical salt deposits likely to be encountered in gas turbines which burn fuels containing sodium, sulfur, lead and vanadium impurities are described.
2000-08-21
A grain-size-dependent reduction in the room-temperature thermal conductivity of nanocrystalline yttria-stabilized zirconia is reported for the first time. Films were grown by metal-organic chemical vapor deposition with controlled grain sizes from 10 to 100 nm. For grain sizes smaller than approximately 30 nm, a substantial reduction in thermal conductivity was observed, reaching a value of less than one-third the bulk value at the smallest grain sizes measured. The observed behavior is consistent with expectations based on an estimation of the phonon mean-free path in zirconia.(c) 2000 American Institute of Physics.
Germanium-induced stabilization of a very high-k zirconia phase in ZrO2/GeO2 gate stacks
2008-01-01
Electrical data on ZrO2/GeO2 stacks prepared by atomic oxygen beam deposition on Ge at 225 deg. C reveal a relatively weak dependence of the stack equivalent oxide thickness upon the ZrO2 thickness. This trend points to a very high zirconia dielectric permittivity (k) value which is estimated to be around 44. This is indicative of zirconia crystallization into a tetragonal phase which is also supported by x-ray diffraction data. X-ray photoelectron spectroscopy analysis is in line with the assumption that due to a finite GeO2 decomposition, Ge is incorporated into the growing ZrO2, thus, stabilizing the high-k tetragonal phase
2009-01-01
Chromate conversion coatings have been widely applied for the corrosion of different metallic substrates. However, the waste containing Cr6+ has many limitations due to the environmental consideration and health hazards. An interesting alternative seems to be the deposition on metallic surface of thin layers of yttria or zirconia or both by the sol-gel process. In this study, Ytttria and Yttria stabilized zirconia (YSZ, 8% Y2O3) thin films were used for coating commercial carbon steel substrates by sol-gel method and the dip-coating process. The evolution of organic compounds up to crystallization process as a function of heat treatments was study by FT-IR spectroscopy. The structure and morphology of the coatings were analysed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The anticorrosion performance of ...
The magnetic properties of thermally annealed Fe nanocrystals prepared through ion implantation in single crystal yttrium-stabilized zirconia (Y{sub 0.2}Zr{sub 0.8}O{sub 19}) were studied by quasistatic hysteresis loop measurements and by pulsed ferromagnetic resonance. The change of coercivity and the shape of hysteresis loops at different annealing temperature can be interpreted through the size increase of the nanocrystals. Magnetostatic coupling must be taken into account to understand the rise times of the ferromagnetic resonance, especially for the samples annealed at higher temperature.
2005-01-01
The magnetic properties of thermally annealed Fe nanocrystals prepared through ion implantation in single crystal yttrium-stabilized zirconia (Y0.2Zr0.8O19) were studied by quasistatic hysteresis loop measurements and by pulsed ferromagnetic resonance. The change of coercivity and the shape of hysteresis loops at different annealing temperature can be interpreted through the size increase of the nanocrystals. Magnetostatic coupling must be taken into account to understand the rise times of the ferromagnetic resonance, especially for the samples annealed at higher temperature
Room temperature deposition of biaxially textured yttria-stabilized zirconia (YSZ) films on amorphous glass substrates was successfully achieved by conventional pulsed-laser deposition. The influence of the surrounding gases, their pressure and the deposition time on the structure of the films was studied. A columnar growth process was revealed based on the experimental results. The grown biaxial texture appears as a kind of substrate independence, which makes it possible to fabricate in-plane aligned YSZ films on various substrates.
Reinforcement phase stability during aging of an aluminum alloy/yttria-stabilized zirconia composite
1993-11-01
In this paper the complementary issue of the sensitivity of the transformation to heat treatment is examined with a view to the optimization of the matrix microstructure of age-hardenable aluminum alloys. The authors have examined the effect of typical thermomechanical treatments upon the phase proportions of the reinforcement using 6061 aluminium alloy as a typical age-hardenable matrix. The effect of aging on the phase content of the zirconia is compared with the changes in mechanical properties of the composite on aging, as measured by Vickers Hardness. Both factors must be born in mind when formulating the optimum heat treatment for such a composite with an age-hardenable matrix.
1992-01-01
The pre-existing pore (or micro-crack) distribution in yttria-stabilized zirconia (3Y-TZP) and the fracture toughness for micro-cracking are investigated using a simple fracture statistics approach. The estimation of the pore distribution from 'modulus of rupture' data shows that only a small percentage of large pores controls the strength results and that the fracture toughness is much smaller than the normal fracture toughness measured from specimens with artificial macro-cracks. 21 refs., 1 tabs., 2 figs
2001-01-01
The powders of ZrO2 and ZrO2, containing 5 mass % Y2O3 are studied through the methods of the electronographic analysis and translucent electron microscopy. The coexistence of phases with cubic and tetragonal structures in the yttria-stabilized zirconia (YSZ) nanoparticles is determined. It is shown, that the effect on widening the heterogeneity of the yttrium concentration in the nanocrystals and the cubic phase tetragonal distortion is not determining for the YSZ powders
Fully-stabilized nanometric zirconia samples with varying degrees of porosity and grain sizes were analyzed using the coincidence Doppler broadening mode of the positron annihilation spectroscopy (PAS). A decrease in the low momentum fraction was observed and coincided with a decrease in porosity. In addition to pores, it is proposed that defects in the negatively charges grain boundary space region act as positron trapping centers; their effectiveness decreases with an increase in grain size. It is shown that PAS is sensitive to small grain size differences within the nanometric regime in these oxide materials.
2005-04-05
Fully-stabilized nanometric zirconia samples with varying degrees of porosity and grain sizes were analyzed using the coincidence Doppler broadening mode of the positron annihilation spectroscopy (PAS). A decrease in the low momentum fraction was observed and coincided with a decrease in porosity. In addition to pores, it is proposed that defects in the negatively charges grain boundary space region act as positron trapping centers; their effectiveness decreases with an increase in grain size. It is shown that PAS is sensitive to small grain size differences within the nanometric regime in these oxide materials.
Defect Interactions and Ionic Transport in Scandia Stabilized Zirconia
2009-01-01
Atomistic simulation has been used to study ionic transport in scandia-stabilized zirconia, as well as scandia and yttria-co-doped zirconia, as a function of temperature and composition. The oxygen diffusion coefficient shows a peak at a composition of 6 mole % Sc2O3. Oxygen vacancies prefer to be second nearest neighbors to yttrium ions, but have little preference between first and second neighbor positions with respect to scandium ions. The Sc-O bond length is about 2.17 compared to 2.28 for the Y-O bond. Oxygen migration between cation tetrahedra is impeded less effectively by Sc-Sc edges than by Y-Y edges. A neutral cluster of two scandium ions with an oxygen vacancy in the common first neighbor position has a binding energy of -0.56 eV. The formation of such clusters may contribute to conductivity degradation of stabilized zirconia at elevated ...
Solid solubility and diffusivity in an alumina/zirconia system
1995-10-01
Polycrystalline zirconia-coated single crystal sapphire fiber displays reconstruction of the sapphire surface in regions of contact with zirconia grains. This is a concern where ZrO{sub 2}-coated sapphire fiber is desired for reinforcement of ceramic matrices. Previous work has demonstrated pitting is partially attributed to impurity-induced transient liquid phase formation with local dissolution of alumina; however, the extent of reconstruction witnessed via microscopy suggests that other mechanisms are active. The present study has addressed the issue of solid solubility and interdiffusivity to more thoroughly understand the solid state mechanisms contributing to pitting. Single crystal sapphire and zirconia were ion implanted with zirconium and yttrium, and aluminum, respectively, and then subjected to diffusion anneals at 1,200--1,600 C to study redistribution of implanted cations. Secondary Ion Mass Spectroscopy (SIMS) was used to profile the redistribution of implanted ions for measurement of diffusion coefficients and solubility limits after heat treatments. The results will offer a significant set of data on interface stability in the alumina/zirconia system.
2009-01-01
The attachment, growth behaviour and the genetic effect of human gingival fibroblasts (HGF) cultured on titanium and different zirconia surfaces were investigated. HGF cells were cultured on (1) titanium discs with a machined surface, (2) yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP) with a smooth surface and (3) Y-TZP with 100 mum grooves. The cell proliferation activity was evaluated through a MTT assay at 24 h and 48 h, and the cell morphology was examined by SEM. The mRNA expression of integrin-beta1, type I and III collagen, laminin and fibronectin in HGF were evaluated by RT-PCR after 24 h. From the MTT assay, the mean optical density values for the titanium and grooved zirconia surfaces after 48 h of HGF adhesion were greater than the values obtained for the smooth zirconia surfaces. SEM images showed that more cells were attached to ...
2001-12-01
The purpose of this study is to clarify the performance of yttria-stabilized zirconia (YSZ) as a waste form for geological disposal of TRU-rich wastes, for example, the TRU waste arising from 4-group partitioning of HLLW (High-Level Liquid Wastes). By immobilizing the actinides in stable ceramic waste forms for a long time, imposition of the other multi-barrier materials can be reduced qualitatively and quantitatively, further, this leads to decrease a total cost of waste disposal. From property evaluations of phase stability, chemical durability, mechanical property and stability for change of waste composition by disintegration, YSZ is good enough as a host material to immobilize the TRU-rich wastes. (author)
Preparation of refractory nozzle by gelcasting of zirconia suspensions with coarse particles
2005-07-01
Zirconia suspensions with coarse particles were prepared and the rheogical behavior and sediment stability of such suspensions with different dispersants were studied. It was found that ZrO{sub 2} suspension stabilized with TAC (tri-ammonium citrate) has an obvious shear-thinning behavior and rapid settlement; In contrast, the suspension stabilized with arabic gum shows a shear-thickening behavior and hardly any settlement. Considering both fluidity and settlement stability, APA (ammonium-polyacrylate) was chosen as the dispersant to increase the solid volume fraction of ZrO{sub 2} suspension. Utilizing the above suspension, a kind of refractory nozzle for precision casting of a Cu-Cr alloy was prepared by gelcasting. Such nozzle has a very good resistance to thermal shock and flux scouring. (orig.)
Preparation of refractory nozzle by gelcasting of zirconia suspensions with coarse particles
2005-07-01
Zirconia suspensions with coarse particles were prepared and the rheogical behavior and sediment stability of such suspensions with different dispersants were studied. It was found that ZrO{sub 2} suspension stabilized with TAC (tri-ammonium citrate) has an obvious shear-thinning behavior and rapid settlement; In contrast, the suspension stabilized with arabic gum shows a shear-thickening behavior and hardly any settlement. Considering both fluidity and settlement stability, APA (ammonium-polyacrylate) was chosen as the dispersant to increase the solid volume fraction of ZrO{sub 2} suspension. Utilizing the above suspension, a kind of refractory nozzle for precision casting of a Cu-Cr alloy was prepared by gelcasting. Such nozzle has a very good resistance to thermal shock and flux scouring. (orig.)
Preparation of refractory nozzle by gelcasting of zirconia suspensions with coarse particles
2005-01-01
Zirconia suspensions with coarse particles were prepared and the rheogical behavior and sediment stability of such suspensions with different dispersants were studied. It was found that ZrO2 suspension stabilized with TAC (tri-ammonium citrate) has an obvious shear-thinning behavior and rapid settlement. In contrast, the suspension stabilized with arabic gum shows a shear-thickening behavior and hardly any settlement. Considering both fluidity and settlement stability, APA (ammonium-polyacrylate) was chosen as the dispersant to increase the solid volume fraction of ZrO2 suspension. Utilizing the above suspension, a kind of refractory nozzle for precision casting of a Cu-Cr alloy was prepared by gelcasting. Such nozzle has a very good resistance to thermal shock and flux scouring. (orig.)
Microscopic mechanism of stability in yttria-doped zirconia
The relaxed configurations of yttria-stabilized zirconia (YSZ) between 3 and 10 mol. % Y sub 2 O sub 3 were modeled within the pseudopotential technique. The vibration mode corresponding to the soft phonon in pure c-ZrO sub 2 has been calculated for each Y sub 2 O sub 3 composition. These anharmonic vibrations, associated with stabilization of YSZ, have been investigated within the self-consistent phonon approximation that makes obtainable the fine structure in spectral density. In studying the phonon dynamics, it is proposed to use the displacement probability density which can quantify very accurately the transition temperature needed to stabilize the YSZ cubic phase
Solid oxide fuel cell operable over wide temperature range
Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.
Solid oxide fuel cell operable over wide temperature range
Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.
Solid oxide fuel cell operable over wide temperature range
Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.
Interfacial material for solid oxide fuel cell
Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.
2008-07-01
We are investigating the potential use of Light Water Reactor claddings as precursor material in zirconia-based host matrices for conditioning, transmutation/burning of actinides. Two zirconium-rich alloy claddings were examined under the scope of the present studies: Zircaloy-4 and M5. Both unirradiated materials were, after complete oxidation and characterization, converted into Yttria Cubic-Stabilized-Zirconia (Y-CSZ) and pyrochlore of formula Nd{sub 2}Zr{sub 2}O{sub 7} (where Nd is used as surrogate for actinide). This paper presents the preliminary results of our investigations and the associated possible scenario for an innovative back-end fuel cycle. (authors)
2008-01-01
We are investigating the potential use of Light Water Reactor claddings as precursor material in zirconia-based host matrices for conditioning, transmutation/burning of actinides. Two zirconium-rich alloy claddings were examined under the scope of the present studies: Zircaloy-4 and M5. Both unirradiated materials were, after complete oxidation and characterization, converted into Yttria Cubic-Stabilized-Zirconia (Y-CSZ) and pyrochlore of formula Nd2Zr2O7 (where Nd is used as surrogate for actinide). This paper presents the preliminary results of our investigations and the associated possible scenario for an innovative back-end fuel cycle. (authors)
Study of the structural modifications induced by He implantation in cubic zirconia
2010-01-01
This article deals with the study of the structural modifications induced in yttria-stabilized zirconia implanted with low-energy (30keV) He ions. For this purpose, three complementary analysis techniques, namely RBS/C, XRD and TEM, were used. After implantation at 5x1016cm-2 (4at% to 1.7dpa), it is found that the disorder level is weak, and the damage likely consists in small interstitial-type defects and helium-vacancy clusters. These defects induce a tensile strain gradient in the direction normal to the implanted crystal surface. This weak damage indicates a strong mechanical resistance of the zirconia matrix against He implantation.
2010-01-01
Suspension Plasma Spray process was used for deposition of pseudo-eutectic composition of alumina-yttria-stabilized zirconia as a potential thermal barrier coating using Mettech axial III torch. Process variables including feed and plasma parameters were altered to find their effects on the formation of phases in the composite coating. The in-flight particle velocity was found to be the crucial parameter on phase formation in the resulting coatings. Low particle velocities below 650m/s result in the formation of stable phases i.e., -alumina and tetragonal zirconia. In contrast, high particle velocities more than 750m/s favor the metastable -alumina and cubic zirconia phases as dominant structures in as-deposited coatings. Accordingly, the plasma auxiliary gas and plasma power as infl...
Novel TRIP-Steel/Mg-PSZ Composite-Open Cell Foam Structures for Energy Absorption
2010-01-01
Porous materials have received extensive attention for energy absorption in the last years. In terms of this study austenitic TRIP-steel/Mg-PSZ composite-open cell foam structures are formed based on replicas using open-celled polyurethane foam as a skeleton with and without a supporting dense face (jacket) coating. Their compression strength as well as their specific energy absorption SEA has been registered as a function of the compressive strain. The zirconia addition has reinforced the composite material with the face coating up to a compressive strain of 50%. The stress-induced martensitic transformation of partially stabilized zirconia phases has been investigated as a function of the compressive strain by EBSD. The zirconia phase transformation is triggered already at low compressiv...
Fuel electrode containing pre-sintered nickel/zirconia for a solid oxide fuel cell
A fuel cell structure (2) is provided, having a pre-sintered nickel-zirconia fuel electrode (6) and an air electrode (4), with a ceramic electrolyte (5) disposed between the electrodes, where the pre-sintered fuel electrode (6) contains particles selected from the group consisting of nickel oxide, cobalt and cerium dioxide particles and mixtures thereof, and titanium dioxide particles, within a matrix of yttria-stabilized zirconia and spaced-apart filamentary nickel strings having a chain structure, and where the fuel electrode can be sintered to provide an active solid oxide fuel cell.
Fuel electrode containing pre-sintered nickel/zirconia for a solid oxide fuel cell
A fuel cell structure (2) is provided, having a pre-sintered nickel-zirconia fuel electrode (6) and an air electrode (4), with a ceramic electrolyte (5) disposed between the electrodes, where the pre-sintered fuel electrode (6) contains particles selected from the group consisting of nickel oxide, cobalt and cerium dioxide particles and mixtures thereof, and titanium dioxide particles, within a matrix of yttria-stabilized zirconia and spaced-apart filamentary nickel strings having a chain structure, and where the fuel electrode can be sintered to provide an active solid oxide fuel cell.
Fuel electrode containing pre-sintered nickel/zirconia for a solid oxide fuel cell
A fuel cell structure (2) is provided, having a pre-sintered nickel-zirconia fuel electrode (6) and an air electrode (4), with a ceramic electrolyte (5) disposed between the electrodes, where the pre-sintered fuel electrode (6) contains particles selected from the group consisting of nickel oxide, cobalt and cerium dioxide particles and mixtures thereof, and titanium dioxide particles, within a matrix of yttria-stabilized zirconia and spaced-apart filamentary nickel strings having a chain structure, and where the fuel electrode can be sintered to provide an active solid oxide fuel cell.
Fabrication and Characterization of Dual Phase Magnesia-Zirconia Ceramics Doped with Plutonia
2005-05-01
Dual phase magnesia-zirconia ceramics doped with plutonia are being studied as an inert matrix fuel (IMF) for light water reactors. The motivation of this work is to develop an IMF with a thermal conductivity superior to that of the fuels based on yttria stabilized zirconia. The concept uses the MgO phase as an efficient heat conductor to increase thermal conductivity of the composite. In this paper ceramic fabrication and characterization by scanning electron microscopy, energy and wavelength dispersive xray spectroscopy is discussed. Characterization shows that the ceramics consist of the two-phase matrix and PuO2-rich inclusions. The matrix is comprised of pure MgO phase and MgO-ZrO2-PuO2 solid solution. The PuO2-rich inclusion contained dissolved MgO and ZrO2.
Estimation of oxygen ionic conductivity in nickel-zirconia composite by oxygen permeation method
2010-01-01
The oxygen transport in the nickel-zirconia composite was investigated using the oxygen permeation method. A disk-shaped sample made of nickel (40vol%) and yttria-stabilized zirconia (YSZ) was used to construct a permeation cell. By exposing one side of the sample to a CO2 gas stream and the other side to a CO stream at elevated temperatures, oxide ions were extracted from CO2 and transported to the other side to oxidize CO. The oxygen permeation flux through the composite was determined by analyzing the effluent from the permeation cell, and the oxygen ionic conductivity of the composite was derived from the permeation data and the oxygen partial pressures. It was shown that the oxygen ionic conductivity of the composite YSZ fraction was about one third of that for the single-phase zirc...
Dynamic behavior of zirconia ceramics in uniaxial compression
1991-01-01
A novel Split Hopkinson Pressure Bar (SHPB) method called the stress reversal Hopkinson technique developed at UCSD, is successfully used to subject ceramic samples to predetermined compressive-stress pulses. Transformation plasticity in magnesia-partially stabilized zirconia (Mg-PSZ) and yttria-tetragonal zirconia polycrystal (Y-TZP) is investigated. The samples tested in SHPB show a trilinear stress-strain behavior. The longitudinal and transverse strains are measured by strain gages mounted on the samples. The lateral surfaces of Mg-PSZ samples show extensive surface rumpling and microcracking parallel to the loading axis after the test. Reloading of these samples to higher stress levels did not reveal additional inelasticity. Cuboid samples loaded initially to attain transformation saturation, are then reloaded in a direction perpendicular to the ...
2010-01-01
Porous bilayer films of yttria-doped zirconia and strontia-doped lanthanum manganite are deposited by using electron beam evaporation. For practical use in solid oxide fuel cells, fully-stabilized zirconia is a candidate for the solid electrolyte due to its high oxygen diffusion rate. Longer triple phase boundary, which consists of catalyst, reacting gas and solid electrolyte in the cathode, is helpful for the exchange of oxygen gas and ions. By glancing angle deposition, higher density of triple phase boundary is achieved in the form of catalyst and electrolyte bilayer structure. This kind of triple phase boundary can be estimated from SEM images and it is rather easier than from conventional composite cathode which can only be analyzed with assistance of mathematic simulation. The resist...
Zirconia-pillared tetrasilicic fluoromica
1993-01-01
Zirconia-pillared tetrasilicic fluoromicas are prepared from sodium tetrasilicic mica, Na-[Mg[sub 2.5]Si[sub 4]O[sub 10]F[sub 2, using a commercial zirconyl acetate solution as the source of the zirconium polyoxocation pillars. Reproducible results are conveniently obtained without any preliminary heating of the pillaring solution, and the pillaring reaction is performed at ambient temperature. The resulting zirconia-pillared mica has a consistently higher crystallinity and layer spacing than pillared clays prepared from zirconyl chloride solutions adn shows significantly higher thermal stability, an important factor in potential catalytic applications. Zirconia-pillared tetrasilicic fluoromica is a microporous material containing two-dimensional galleries with a height of 11 [angstrom]. The surface area is high, about 300 m[sup 2]/g. After treatment in steam at 760[degrees]C for 17 h, the surface area is reduced only to [approximately]200 m[sup 2]/g. Thus, very small particles of ZrO[sub 2] dispersed between 10-[angstrom]-thick mica layers have been stabilized. 39 refs., 7 figs., 3 tabs.]]
2010-01-01
In this research, Yttria Stabilized Zirconia (3YTZP) - carbon nanotube (CNT) composites are fabricated by direct in-situ growth of CNTs on the Zirconia particles, followed by densification via the Spark Plasma Sintering (SPS) technique. Scanning electron microscopy analysis of the 3YTZP-CNT powders shows uniform distribution of CNTs without the formation of agglomerates frequently seen with the traditional ex-situ mixing of CNTs in ceramic compositions. The samples were sintered to nearly 100% theoretical density and with a finer grain size microstructure. High Resolution Transmission Electron Microscopy (HRTEM) and Raman Spectroscopy confirm CNT retention in the sintered nanocomposites up to 1600degreeC. The flexural strength increases from 260MPa for samples without CNTs sintered at 1600...
1993-09-10
The following experiment has been performed on coating a partially stabilized zirconia substrate with [beta]-tricalcium phosphate ([beta]-TCP), and surfaces of the experimental test pieces were analyzed using X-ray diffraction and SEM observation. The experiment consisted of the following processes: Calcium metaphosphate (CP) was applied on surface of zirconia sinters with partially stabilized yttria solution and heated to 1000[degree]C to bond CP with the sinters; further, slurries made by mixing CP[center dot]calcium pyrophosphate (C2P) and tetracalcium phosphate (C4P) at different ratios were applied thereon; and then heated to temperatures from 1000[degree]C to 1300[degree]C. This paper describes the following experimental results: The [beta]-TCP can be best coated when the sinters using CP-C4P mixed slurry are heated to 1200[degree]C; and the reaction to generate [beta]-TCP from CP and C4P occurs via C2P. 13 refs., 5 figs., 2 tabs.
Properties of zirconia-based fuels for plutonium utilization in reactors
1999-07-01
A zirconia-based inert matrix fuel is studied for economical plutonium incineration in light water reactors. The proposed fuel materials are composed of zirconium oxide (matrix), yttrium oxide (stabilizer), erbium oxide (burnable poison), and plutonium oxide and form a single-phase solid solution. Three important properties of these materials were investigated: the thermal conductivity, the safety-relevant retention of fission products, and the leaching behavior in pure water and in simulated pore waters (bentonite near field).
Multi-step damage accumulation in irradiated crystals
2009-01-01
This article presents a model of damage accumulation in irradiated crystals. This model is based on the assumption that the damage accumulation occurs through a series of structural transformations triggered by the destabilization of the current structure of crystals. Formal equations describing the damage accumulation build-up and experimental assessment of the model are presented and discussed in the framework of the actual knowledge of radiation effects in oxide crystals (yttria-stabilized zirconia (YSZ) and magnesium-aluminate spinel (MAS)), silicon carbide crystals and zirconia implanted nickel crystals. (orig.)
Microwave sintering of continuous zirconia ceramic fibers
1994-04-01
Continuous yttria-stabilized zirconia ceramic fibers approximately 10-15 {mu}m in diameter have been rapidly sintered by pulling them through a tuned, 2.45 GHz single-mode TE{sub 103} microwave cavity in ambient air. The resulting fibers were analyzed by X-ray diffraction, scanning electron microscopy, and single-filament tensile tests. They were found to be unsplit, to have a submicron grain structure and a tetragonal crystal structure, and to exhibit considerable strength and flexibility.
Experimental measurements on the effect of insulated pistons on engine performance and heat transfer
1996-09-01
Data have been gathered to compare the performance of steel crown pistons coated with yttria stabilized zirconia or mullite to an uncoated piston. The effect of coated pistons on in-cylinder heat transfer was determined from curves of ISFC versus centroid of heat release. Error analysis of the measurements showed uncertainty of {+-} 3% in ISFC and {+-} 2 crank angle degrees in the centroid of heat release could be expected for the data. Particulate emissions increased at advanced injection timings with the mullite coated piston while the zirconia coated piston showed an increase in particulate and NO{sub x} at advanced timings.
2010-01-01
For the first time, the effect of microscale shear stress induced by both mechanical compression and ball-milling on the phase stability of nanocrystalline tetragonal zirconia (t-ZrO2) powders was studied in water free, inert atmosphere. It was found that nanocrystalline t-ZrO2 powders are extremely sensitive to both macroscopic uniaxial compressive strain and ball-milling induced shear stress and easily transform martensitically into the monoclinic phase. A linear relationship between applied compressive stress and the degree of tetragonal to monoclinic (t-
Radiation stability of ceramics: Test cases of zirconia and spinel
2007-01-01
The study of the effects of radiation in ceramics of potential use in electronic, space and nuclear industries appears to be a major challenge in the next decades. The collect and analysis of data dealing with the production and recovery of radiation damage in this type of materials are thus tasks of prime interest. In this article, we present a review of the main structural and chemical modifications observed in test case ceramics (yttria-stabilized zirconia and magnesium-aluminate spinel) submitted to ion bombardment and thermal treatments. We show that the stability under irradiation depends on the intrinsic properties of the materials and on irradiation parameters such as the ion energy, fluence and temperature. We also demonstrate that the recovery of damage upon annealing at elevated temperatures induces drastic physico-chemical modifications of the matrix. ...
2010-01-01
Suspension plasma spraying (SPS) allows processing a stabilized suspension of nanometer-sized feedstock particles to form thick (from 20 to 100mm, average values) deposits. The void content and porous network of such deposits are difficult to quantify (in terms of void and size distributions, anisotropy, etc.) using conventional techniques due to their low resolution. The combination of ultra-small-angle X-ray scattering (USAXS) and helium pycnometry permits to address some of the characteristics of this void network. Deposits of yttria-partially stabilized zirconia (YSZ) were manufactured by plasma spraying a suspension made of solid sub-micrometer-sized particles (50 and 400nm) with several sets of spray operating parameters. Results indicate that the average void size exhibits the same ...
Experimental study of the thermal conductivity of metal oxides co-doped yttria stabilized zirconia
2008-01-01
Doping of yttria stabilized zirconia (YSZ) with metal oxides has been reported to have the potential of increasing the thermal insulation capability and phase stability of YSZ at higher application temperatures. In order to select the dopant oxides, it is important to understand the effects of the dopants, in terms of the ionic radius, mass, and valence, on various thermal and mechanical properties of the doped YSZ. In this study, a series of metal oxides, tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), scandium oxide (Sc2O3), ytterbium oxide (Yb2O3) and cerium oxide (CeO2) were incorporated to 7YSZ (7wt% yttria) by mechanical alloying and sintering; the thermal conductivity changes of the doped 7YSZ were investigated. The oxide dopants that exist as defect clusters within the zirco...
Dynamical stabilization by phonon-phonon interaction exemplified in cubic zirconia
2008-01-01
Cubic zirconia exhibits a soft phonon mode (X{sup -}{sub 2}), which becomes dynamically unstable at low temperatures. Previous ab initio invest.igations into the temperature-induced stabilization of the soft mode treated it as an independent anharmonic oscillator. Calculations presented here, using the self consistent ab initio lattice dynamical (SCAILD) method to evaluate the phonons at 2570 K, show that the soft mode should not be treated independently of other phonon modes. Phonon-phonon interactions stabilize the X{sup -}{sub 2} mode. Furthermore, the effective potential experienced by the mode takes on a quadratic form.
Determination of the cerium oxidation state in cerium vanadate
1995-01-01
Use of low-quality fuels in gas turbines can lead to vanadium hot corrosion of stabilized-zirconia turbine blade coatings. The stabilizing oxide reacts with V2O5 in the melt, forming a vanadate, thus removing the stabilizer from the zirconia. To better understand the vanadation reaction of one such oxide, CeO2, the authors have employed X-ray absorption spectroscopy to determine the oxidation state of the resulting vanadate, CeVO4. A comparison of the cerium vanadate X-ray absorption spectra with Ce4+ and Ce3+ standards has established that the cerium valence in this compound is 3+. This result indicates that cerium is reduced during CeVO4 formation and suggests that the vanadium reactant remains in the 5+ oxidation state
Synthesis and Stability of a Nanoparticle-Infiltrated Solid OxideFuel Cell Electrode
Nanoparticulate catalysts infiltrated into SOFC (Solid OxideFUel Cell) electrodes can significantly enhance the cell performance, butthe stability of these electrodes has been an open issue. An infiltrationprocedure is reported that leads to a stable scandia-stablized zirconia(SSZ) cathode electrode performance.
Synthesis and Stability of a Nanoparticle-Infiltrated Solid OxideFuel Cell Electrode
2006-11-20
Nanoparticulate catalysts infiltrated into SOFC (Solid OxideFUel Cell) electrodes can significantly enhance the cell performance, butthe stability of these electrodes has been an open issue. An infiltrationprocedure is reported that leads to a stable scandia-stablized zirconia(SSZ) cathode electrode performance.
2001-01-01
Investigates the influence of annealing temperature on the atomic structure of yttria-stabilized zirconia (YSZ). Deposition of YSZ on nickel superalloy substrates by plasma spraying; Observation of neutron powder diffraction patterns on barrier coatings; Application of Rietveld refinement technique Other identifier: Journal of the American Ceramic Society 84 (3), pp. 678-680, 2001 Language: en_US
Catalytic converter for next generation turbine engines
2004-01-01
EB-PVD thermal barrier coatings (TBCs) are used on advanced turbine blades to increase the engine efficiency and improve the blade performance. partially yttria stabilized zirconia (PYSZ) is the standard material for current TBC applications. Lower thermal stability of the PYSZ-based TBCs, however, seriously affects the performance at demanding service temperatures. For the new generation turbines where higher operating gas temperatures (
2006-01-01
The ceramic-materials, especially grain refining 3mol%-yttria-stabilized tetragonal zirconia polycrystals, 3Y-TZP, has investigated for the deformation mechanism and mechanical properties of super plastically deformed in high temperature. There are many reports of the thermal properties concerning zirconia-based family materials as thermal barrier coating (TBC) and also as inert matrix fuel (IMF) although few reports belong with the super plastically materials which is expected to apply the nuclear energy field. This paper describes the outline of the neutron irradiation test on the thermal properties of 3Y-TZP. The measured data of thermal diffusivity for the 3Y-TZP and the outlines of the thermal properties for zirconia-based materials applied to the TBC/IMF are also described in this report. The thermal diffusivity is measured by the laser flash method. (L/F ...
1989-03-01
Seven commercially available yttria-tetragonal zirconia polycrystal (Y-TZP) materials were evaluated. Room temperature properties were measured before and after heat treatments at 1000C. Microstructure and phase stability were also examined. In all but one case, the Y-TZPs showed very little change in room temperature properties after long times at this temperature. Results show that pressure-assisted processing greatly improves the strength by reducing porosity and keeping the grain size extremely fine, but this reduces the toughness because finer grains are more difficult to transform. In addition, a small amount of cubic zirconia appears to enhance the toughness of fine-grained Y-TZP while maintaining good strength. During processing, a small amount of cubic zirconia is formed and allowed to grow. This creates regions poor in yttria which can transform spontaneously in the presence of a crack-tip stress field.
Development and testing of multi-phase glazes for adhesive bonding to zirconia substrates
2010-01-01
Objectives: The aims of the study were to develop and test multi-phase glaze coatings for zirconia restorations, so that the surface could be etched and adhesively bonded. Methods: Zirconia disc specimens (n=125, 16mmx1mm) were cut from cylinders of Y-TZP (yttria-stabilized tetragonal zirconia polycrystals) ZS-Blanks (Kavo, Everest) and sintered overnight. Specimens were subjected to the recommended firing cycles, and next sandblasted. The specimens were divided into 5 groups of 25, with Group 1 as the sandblasted control. Groups 2-5 were coated with overglaze materials (P25 and IPS e.max Ceram glazes) containing secondary phases. Group 2 was (wt%): 10% hydroxyapatite (HA)/P25 glaze, Group 3: 20% IPS Empress 2 glass-ceramic/glaze, Group 4: 20% IPS Empress 2 glass/glaze and Group 5: 30% IPS...
1997-05-01
Polished and thin sections from used graphite-bonded CaO-stabilized zirconia submerged entry nozzles were observed under the optical microscopes and by means of the electron optics. A new mechanism for the excessive slagline attack is advanced as follows: Once graphite dissolves in the metal, the slag comes in contact with zirconia particles embedded in the graphite bond which have been receded in contour. The graphite bond reduces SiO{sub 2}, Na{sub 2}O, MgO and probably B{sub 2}O{sub 3} in the mold flux to SiO, Na, Mg and B. The gaseous products diffuse into ZrO{sub 2} particles through their pores and oxidize to form low-melting compounds with the CaO, thus destabilizing the zirconia. In addition, the compounds etch grain boundaries, resulting in loose particles with well-defined roundness. Fresh slag penetrates the weakened particles and breaks them down into pieces, which are, in turn, dispersed into the slag. When the slag reaches the graphite-rich region, the metal replaces the slag. The process then repeats itself. (author).
2000-07-01
The use of Yttria concentrates has been proposed to substitute the high purity Yttria in the zirconia stabilization. The elements terbium, dysprosium, holmium, erbium and ytterbium, classified as heavy rare earths, are the main impurities in these concentrates, due to their presence in yttrium ores. Besides that, the chemical similarities of these elements need the utilization of complex purification techniques. Considering the importance of the employed dopant on zirconia crystallization, this work shows the quantitative phases analysis of powders and ceramics of stabilized zirconia doped with 3 and 9 mol % of high purity Yttria and with a 85 wt % Yttria concentrate. This determination was performed using the Rietveld refinement of the X-ray diffraction data. The powders were synthesized by the hydroxides coprecipitation route, which includes treatments with ethanol and butanol, drying, calcination at 800 deg C for 1 hour and milling in a ball mill and in an attrition mill. The ceramics pellets were pressed uniaxially and sintered at 1550 deg C for 1 hour. The powders and sintered pellets were also characterized by X-ray fluorescence analysis, laser diffraction, gas adsorption (B.E.T.), scanning electron microscopy and determination of apparent density by the Archimedes method. The results showed the same stabilization behavior when it was employed high purity Yttria and a concentrate of this oxide. It was also observed the predominating formation of tetragonal and cubic phases when the dopant concentration is 3 and 9 mol %, respectively. (author)
2008-01-31
Type 316L stainless steel (SS) is one of the candidate materials proposed for application in pyrochemical reprocessing plants. In the present work, yttria-stabilized zirconia coatings of 300 {mu}m were applied over type 316L SS with a metallic bond coating of 50 {mu}m by an optimized plasma spray process, and were assessed for the corrosion behaviour in molten LiCl-KCl medium at 873 K for periods of 5 h, 100 h, 250 h and 500 h. The as-coated and tested samples were examined by optical microscopy and SEM for homogeneity, penetration of molten salt through coating and corrosion of type 316L SS substrate. The results indicated that the yttria-stabilized zirconia coatings performed well without significant degradation and corrosion attack. Laser melting of the coated samples using CO{sub 2} laser was attempted to consolidate the coatings. The development of large grains with segmented cracks was noticed after laser melting, though the coating defects have been eliminated.
Yttria-stabilized zirconia-based composites with adaptive thermal conductivity
2010-01-01
Thermal conductivity trends in a "chameleon coating" thin film were characterized with a time-domain thermoreflectance (TDTR) technique. A yttria-stabilized zirconia (YSZ)-based nanocomposite material containing 21vol.% silver (Ag) was employed for this study. The thermal conductivity (k) of the as-deposited composite film was measured with TDTR and found to have a value of 7.4+-1.4Wm-1K-1. The film was then annealed at 500degreeC for 1h to stimulate Ag flow from within the composite to the surface via diffusion. The Ag that coalesced on the surface during annealing was removed to expose the underlying porous YSZ matrix, and the sample was reexamined with the TDTR technique. The thermal conductivity of the porous nanocomposite YSZ material was then measured to be 1.6+-0.2Wm-1K-1, which is ...
2010-01-01
Thin film (40-600nm) yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC) were deposited on NiO-YSZ anodes and fused silica substrates by RF sputtering, using low applied power without the use of post deposition annealing heat treatment. YSZ film showed a nanocrystalline structure and consisted of the Zr.85Y.15O1.93 (fcc) phase. The film was dense and the YSZ/anode interface was continuous and crack free. According to preliminary in-plane conductivity measurements (temperature range 550-750^oC) on the YSZ film, the activation energy for ionic conduction was found to be 1.18+/-0.01eV.
2008-01-01
A low pressure plasma process has been developed which enables deposition of oxide layers from micro droplets introduced into a reactor. With this process, up to 50m thick porous yttria-stabilized zirconia (YSZ) coatings have been deposited. Zirconyl and yttrium nitrates (ZrO(NO3)2 and Y(NO3)3) dissolved in water were used as precursors. These precursors are introduced as micrometric droplets into a plasma discharge. After interacting with the plasma, the droplets are deposited onto the substrate to form the YSZ coating. The velocity and diameter of the solution droplets injected into the reactor were studied with an on-line Particle Dynamics Analyser to propose a mechanism for the formation of the coating. The structure and composition of the coatings have been characterized by Scanni...
Thin film synthesis of novel electrode materials for solid-oxide fuel cells
1997-12-01
Electrode materials for solid-oxide fuel cells are developed using sputter deposition. A thin film anode is formed by co-deposition of nickel and yttria-stabilized zirconia. This approach is suitable for composition grading and the provision of a mixed-conducting interracial layer to the electrolyte layer. Similarly, synthesis of a thin film cathode proceeds by co-deposition of silver and yttria- stabilized zirconia. The sputter deposition of a thin film solid- oxide fuel cell is next demonstrated. The thin film fuel cell microstructure is examined using scanning electron microscopy whereas the cell performance is characterized through current-voltage measurement and corresponding impedance spectroscopy.
This disclosure addresses the issue of providing a metallic-ceramic overlay coating that potentially serves as an interface or bond coat layer to provide enhanced oxidation resistance to the underlying superalloy substrate via the formation of a diffusion barrier regime within the supporting base material. Furthermore, the metallic-ceramic coating is expected to limit the growth of a continuous thermally grown oxide (TGO) layer that has been primarily considered to be the principal cause for failure of existing TBC systems. Compositional compatibility of the metallic-ceramic with traditional yttria-stabilized zirconia (YSZ) top coats is provided to further limit debond or spallation of the coating during operational use. A metallic-ceramic architecture is disclosed wherein enhanced oxidation resistance is imparted to the surface of nickel-based superalloy or single crystal metal substrate, with simultaneous integration of the yttria stabilized zirconia (YSZ) within the metallic-ceramic overlayer.
This disclosure addresses the issue of providing a metallic-ceramic overlay coating that potentially serves as an interface or bond coat layer to provide enhanced oxidation resistance to the underlying superalloy substrate via the formation of a diffusion barrier regime within the supporting base material. Furthermore, the metallic-ceramic coating is expected to limit the growth of a continuous thermally grown oxide (TGO) layer that has been primarily considered to be the principal cause for failure of existing TBC systems. Compositional compatibility of the metallic-ceramic with traditional yttria-stabilized zirconia (YSZ) top coats is provided to further limit debond or spallation of the coating during operational use. A metallic-ceramic architecture is disclosed wherein enhanced oxidation resistance is imparted to the surface of nickel-based superalloy or single crystal metal substrate, with simultaneous integration of the yttria stabilized zirconia (YSZ) within the metallic-ceramic overlayer.
This disclosure addresses the issue of providing a metallic-ceramic overlay coating that potentially serves as an interface or bond coat layer to provide enhanced oxidation resistance to the underlying superalloy substrate via the formation of a diffusion barrier regime within the supporting base material. Furthermore, the metallic-ceramic coating is expected to limit the growth of a continuous thermally grown oxide (TGO) layer that has been primarily considered to be the principal cause for failure of existing TBC systems. Compositional compatibility of the metallic-ceramic with traditional yttria-stabilized zirconia (YSZ) top coats is provided to further limit debond or spallation of the coating during operational use. A metallic-ceramic architecture is disclosed wherein enhanced oxidation resistance is imparted to the surface of nickel-based superalloy or single crystal metal substrate, with simultaneous integration of the yttria stabilized zirconia (YSZ) within the metallic-ceramic overlayer.
2010-01-01
We report on the interface characteristics of yttria-stabilized zirconia films grown on silicon substrates. From x-ray reflectivity analysis we found that the film thickness and interface roughness decreased as the growth temperature increased, indicating that the growth mechanism varies and the chemical reaction is limited to the interface as the growth condition varies. Furthermore, the packing density of the film increased as the growth temperature increased and the film thickness decreased. X-ray photoelectron spectroscopy analysis of very thin films revealed that the amount of chemical shift increased as the growth temperature increased. Intriguingly, the direction of the chemical shift of Zr was opposite to that of Si due to the second nearest neighbor interaction
Synthesis and characterization of bulk and coatings of hydroxyapatite using methanol precursor
Hydroxyapatite, an important bioceramic was synthesized in the bulk form and developed as a coating by a sol-gel route using alcoholic precursor. The bioactive coating was developed on bio-inert {alpha}-alumina and yttria stabilized zirconia substrates. The apatite phase began to form after the heat treatment of the precursor at 500 deg. C for 10 min. The complete crystallization of the apatite was obtained at 800 deg. C heat treatment for 10 min. The phase composition of the bulk and the coatings was identified by FT-IR spectroscopic and powder X-ray diffraction (XRD) techniques. Surface morphology was determined by scanning electron microscopy. The study indicates different surface textures for the powder and for the coatings on {alpha}-alumina and yttria stabilized zirconia substrates.
Synthesis and characterization of bulk and coatings of hydroxyapatite using methanol precursor
2008-01-01
Hydroxyapatite, an important bioceramic was synthesized in the bulk form and developed as a coating by a sol-gel route using alcoholic precursor. The bioactive coating was developed on bio-inert alpha-alumina and yttria stabilized zirconia substrates. The apatite phase began to form after the heat treatment of the precursor at 500 deg. C for 10 min. The complete crystallization of the apatite was obtained at 800 deg. C heat treatment for 10 min. The phase composition of the bulk and the coatings was identified by FT-IR spectroscopic and powder X-ray diffraction (XRD) techniques. Surface morphology was determined by scanning electron microscopy. The study indicates different surface textures for the powder and for the coatings on alpha-alumina and yttria stabilized zirconia substrates
Structural stability and optical properties of nanocrystalline zirconia
2010-01-01
Nanoparticles of the cubic phase of zirconia (ZrO2) of size range 4.5-8.7 nm have been synthesized by alkaline hydrolysis of a zirconium salt followed by solvothermal reaction. Subsequently, the room-temperature stability of cubic ZrO2 nanoparticles has been explored with the goal of understanding how crystal structure tends to transform into a structure of higher symmetry with decreasing crystallite size. The room-temperature-stable cubic phase in nanosized ZrO2 has been observed to transform into the monoclinic phase at 873 K. The crystalline phases of ZrO2 nanocrystals have been determined quantitatively by Rietveld refinement. Lattice constant and internal strain increase with decreasing particle size. Growth kinetics studies have established that cubic nanocrystals are more stable at smaller crystallite ...
Structural stability and optical properties of nanocrystalline zirconia
2010-01-01
Nanoparticles of the cubic phase of zirconia (ZrO2) of size range 4.5-8.7 nm have been synthesized by alkaline hydrolysis of a zirconium salt followed by solvothermal reaction. Subsequently, the room-temperature stability of cubic ZrO2 nanoparticles has been explored with the goal of understanding how crystal structure tends to transform into a structure of higher symmetry with decreasing crystallite size. The room-temperature-stable cubic phase in nanosized ZrO2 has been observed to transform into the monoclinic phase at 873 K. The crystalline phases of ZrO2 nanocrystals have been determined quantitatively by Rietveld refinement. Lattice constant and internal strain increase with decreasing particle size. Growth kinetics studies have established that cubic nanocrystals are more stable at ...
Resistance of thermal barrier ceramic coatings to hot salt corrosion
1980-01-01
Stabilized zirconia ceramics appear to have considerable potential as thermal barriers or corrosion-resistant coatings for application to gas turbine components. Salt corrosion tests have indicated however that under some conditions vanadium impurities in the fuel may cause accelerated failure of these coatings as a result of destabilization of the zirconia phase. The corrosion resistance, thermal stability and structure of the coatings depend to a large extent on the chemical composition of the ceramic phase. The results of a study of the behavior of plasma-sprayed Y/sub 2/O/sub 3/-ZrO/sub 2/ coatings towards combustion gases and the typical salt deposits likely to be encountered in gas turbines which burn fuels containing sodium, sulfur, lead, and vanadium impurities are described.
2010-01-01
Abstract: Thermal barrier coatings (TBCs) are widely adopted to protect mechanical components in gas turbine engines operating at high temperature. Basically, the surface temperature of these components must be low enough to retain material properties within acceptable bounds and to extend component life. From this standpoint, air plasma-sprayed (APS) ceria and yttria co-stabilized zirconia (CYSZ) is particularly promising because it provides enhanced thermal insulation capabilities and resistance to hot corrosion. However, essential mechanical properties, such as hardness and Young's modulus, have been less thoroughly investigated. Knowledge of Young's modulus is of concern because it has a significant effect on strain tolerance and stress level and, hence, on durability. The focus of the...
Preparation of yttria-stabilized zirconia-ceria kernels as fuel precursors using internal gelation
2008-01-01
Ceria-doped yttria-stabilized zirconia kernels were prepared by internal gelation and the effect that the concentration of HMTA and urea used in the initial broth had on the structure and properties of the gel was studied. Most combinations of urea and HMTA were found to provide gels with a smooth surface, which were assumed to be dense. However, a high quantity of urea and a low quantity of HMTA generated a gel with a rough surface, which was assumed to be porous and limited the formation of cracks during the thermal treatment of kernels. These kernels were then compacted using a repressing method whereby pellets with a sintered density up to 86% TD were formed. It was also found that the presence of urea is necessary to obtain good mechanical properties. (orig.)
Performance of an anode-supported SOFC with anode functional layers
2008-01-01
Before fabrication of dense yttria-stabilized zirconia films, several thin anode functional layers (AFL) were fabricated onto porous NiO/yttria-stabilized zirconia anode substrates using slurry spin coating. The effect of AFL thickness on gas impermeability and performance of a cell was investigated by studying the effect of AFL thickness on the open-circuit voltage, ohmic resistance, I-V characteristics and electrode overpotential of cells. The results of investigation indicated that as the AFL thickness increased, the gas impermeability of cells was generally improved and the ohmic resistance of cells was increased. The cell with a 5-mum-thick AFL exhibited an excellent cell performance, for example, a single cell with this AFL exhibited an output power of 2.63 W cm-2 at 800 deg. C when hydrogen was used as fuel and an oxygen was used as ...
Microscopic observation of laser glazed yttria-stabilized zirconia coatings
2010-01-01
Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a th...
MOCVD of yttria stabilized zirconia on Co-Cr
1995-08-01
Thin films of yttria stabilized zirconia (YSZ) were deposited by metal organic chemical vapor deposition (MOCVD) on cobalt-chromium (Co-Cr) alloys used for orthopedic implants. TMHD derivatives were preferred for the metalorganic sources over the less expensive fluorinated beta-diketonates as the latter left up to 1% fluorine in the film, as determined by Auger spectroscopy. Crystalline cubic structure of these YSZ films was verified by X-ray diffraction. Columnar grain growth gave a rough surface on thicker YSZ films, which increased wear of the mating polyethylene component during simulation tests. YSZ films under one micron thick were mirror smooth and reduced wear of the polymer component by 70% compared to uncoated Co-Cr. Film adhesion was excellent.
Low-Temperature Superionic Conductivity in Strained Yttria-Stabilized Zirconia
2010-01-01
Very high lateral ionic conductivities in epitaxial cubic yttria-stabilized zirconia (YSZ) synthesized on single-crystal SrTiO3 and MgO substrates by reactive direct current magnetron sputtering are reported. Superionic conductivities (i.e., ionic conductivities of the order 1 -1cm-1) are observed at 500 degreeC for 58-nm-thick films on MgO. The results indicate a superposition of two parallel contributions - one due to bulk conductivity and one attributable to conduction along the film-substrate interface. Interfacial effects dominate the conductivity at low temperatures (
Interfacial thermal resistance in nanocrystalline yttria-stabilized zirconia
2002-01-01
The grain-size dependent thermal conductivity of nanocrystalline yttria-stabilized zirconia from 6-480K is reported. The thermal conductivity for a grain size of 10 nm is reduced to approximately half that of coarse-grained or single-crystal material at all measured temperatures. A method for determining the interfacial resistance to thermal transport in polycrystalline materials from measurements of grain-size-dependent thermal conductivity is described and applied. The results suggest a new strategy for identifying improved thermal barrier materials by choosing materials with large interfacial thermal resistance and reduced dimensionality or grain size, rather than by focusing on minimization of bulk thermal conductivity alone
Inert matrix fuel behaviour in test irradiations
2006-01-01
Among others, three large irradiation tests on inert matrix fuels have been performed during the last five years: the two irradiation tests IFA-651 and IFA-652 in the OECD Halden Material Test Reactor and the OTTO irradiation in the High Flux Reactor in Petten. While the OTTO irradiation is already completed, the other two irradiations are still ongoing. The objectives of the experiments differ: for OTTO, the focus was on the comparison of different concepts of IMF, i.e. homogeneous fuel versus different types of heterogeneous fuel. In IFA-651, single phase yttria stabilized zirconia (YSZ) doped with Pu is compared with MOX. In IFA-652, the potential of calcia stabilized zirconia (CSZ) as a matrix with and without thoria is evaluated. The design of the three experiments is explained and th...
Improved surface proton conduction of yttrium-stabilized zirconia via acidic modifications
2008-01-01
This work studied the acidic surface modifications on the conduction properties of yttrium-stabilized zirconia (YSZ) nanocrystals using sulfuric and phosphoric acid protonation techniques with an aim to discover suitable additives of the proton-conducting membranes for intermediate temperature operation. All YSZ nanostructures were hydrothermally prepared and the sample surfaces were modified with sulfate or phosphate groups by subsequently immersing the as-prepared samples into sulfuric or phosphoric acid. The obtained samples were characterized by X-ray diffraction, high-resolution transmission electron microscope, element analysis, infrared spectra, N2 adsorption/desorption, and impedance spectroscopy. It was found that the samples exhibited a cubic fluorite structure with a grain size ...
Glass-Phase Movement in Yttria-Stabilized Zirconia/Alumina Composites
2010-01-01
The mechanism for siliceous liquid-phase movement during sintering and thermal etching is investigated using single crystal alumina rods in a yttria-stabilized zirconia (YSZ) matrix. Bulk glass-phase extraction and intergranular movement during sintering is attributed to a chemically driven force; however, glass-phase expulsion is predominately due to thermal expansion differences in the glass phase, alumina fiber, and YSZ matrix. An increased understanding of the glass-phase mechanism will facilitate the reduction of the resistive grain-boundary phase, which consequently will decrease the operating temperature of high-temperature solid oxide fuel cells. In this paper, we demonstrated that scavengers such as alumina in combination with a suitable thermal treatment can be used to purify the...
2008-01-01
Mechanical properties and slow crack growth (SCG) behavior of a 10Ce-TZP/Al2O3 nanocomposite currently developed as a biomaterial are considered. Fracture toughness is determined for sharp, long (double torsion) and short (indentation) cracks and a good agreement is found between the two types of cracks. The main toughening mechanism in the nanocomposite is the tetragonal to monoclinic phase transformation of the ceria-stabilized zirconia (Ce-TZP) phase. Transformation at the surface of ground specimens leads to surface compressive induced stresses and an increase in strength. Crack velocity curves (V-KI curves) are obtained under static and cyclic fatigue using the double torsion method. The static V-KI curve in air reveals the three stages characteristic of stress corrosion with a thresh...
Fabrication of Yttria stabilized zirconia thin films on poroussubstrates for fuel cell applications
A process for the deposition of yttria stabilized zirconia (YSZ) films, on porous substrates, has been developed. These films have possible applications as electrolyte membranes in fuel cells. The films were deposited from colloidal suspensions through the vacuum infiltration technique. Films were deposited on both fully sintered and partially sintered substrates. A critical cracking thickness for the films was identified and strategies are presented to overcome this barrier. Green film density was also examined, and a method for improving green density by changing suspension pH and surfactant was developed. A dependence of film density on film thickness was observed, and materials interactions are suggested as a possible cause. Non-shorted YSZ films were obtained on co-fired substrates, and a cathode supported solid oxide fuel cell was constructed and characterized.
Fabrication of Yttria stabilized zirconia thin films on poroussubstrates for fuel cell applications
2003-06-16
A process for the deposition of yttria stabilized zirconia (YSZ) films, on porous substrates, has been developed. These films have possible applications as electrolyte membranes in fuel cells. The films were deposited from colloidal suspensions through the vacuum infiltration technique. Films were deposited on both fully sintered and partially sintered substrates. A critical cracking thickness for the films was identified and strategies are presented to overcome this barrier. Green film density was also examined, and a method for improving green density by changing suspension pH and surfactant was developed. A dependence of film density on film thickness was observed, and materials interactions are suggested as a possible cause. Non-shorted YSZ films were obtained on co-fired substrates, and a cathode supported solid oxide fuel cell was constructed and characterized.
Experiments and modeling of rapid solidification of plasma-sprayed yttria-stabilized zirconia
2009-01-01
Thermal barrier coatings (TBCs) are widely used to increase the working temperature and improve the high-temperature corrosion resistance of base materials. Thermal spraying methods such as air plasma spraying (APS) are convenient techniques to deposit TBCs. This work examines the rapid solidification of APS-deposited yttria-stabilized zirconia (YSZ), by modeling the non-equilibrium solidification of a single molten particle. The model solves the so-called hyperbolic equations for heat and mass transfer to predict interface undercooling and velocity as a function of time, and also predicts the morphology of the solidification front (and thus the microstructural characteristics of rapidly solidified YSZ) as a function of interface velocity. Results are presented of a single particle solidif...
Enhanced ionic transport in fine-grained scandia-stabilized zirconia ceramics
2010-06-01
In this work, the transport properties of fine-grained scandia-stabilized zirconia ceramics with low Si content have been investigated. These materials were prepared from ZrO{sub 2}-6 mol% Sc{sub 2}O{sub 3} nanopowders synthesized by a nitrate-lysine gel-combustion route. High relative densities and excellent electrical properties were obtained, even for sintering temperatures as low as 1350 C. Our electrochemical impedance spectroscopy study showed that both the volume fraction of grain boundaries and the specific grain-boundary conductivity are significantly enhanced with decreasing grain size, resulting in a higher total ionic conductivity. (author)
Electrical and dielectric behaviors of Ti3SiC2/Yttria-stabilized zirconia composites
Ti3SiC2/3Y-TZP (3 mol % Yttria-stabilized zirconia) composites were prepared by spark plasma sintering. The effective dc conductivities of the composites have been measured and the percolation threshold was determined. The dielectric behavior of the composites was studied in the frequency range 102-4107 Hz. The results show that the dielectric constant increased remarkably with the Ti3SiC2 concentration, when the Ti3SiC2 concentration was close to percolation threshold. This may be attributed to the critical behavior of the dielectric constant near the percolation threshold as well as to the polarization effects between the clusters inside the composites.
1992-01-01
The simultaneous reaction of zirconium oxychloride and yttrium chloride with a mixture of sodium and potassium nitrates (M.P. 225 deg c) at 450 deg C leads either to tetragonal or to cubic stabilized zirconia according to the proportion of yttrium. Chemically homogeneous powders are obtained; they consist in micronic agglomerates the size of which depends on the extraction conditions. Each agglomerate is formed by the gathering of spherical crystallites with diameter below 10 nm. The large specific surface area of powders and their ability for sintering allow to consider applications in the ceramic field and for heterogeneous catalysis.
Effect of yttria-stabilized zirconia sintering temperature on mixed potential sensor performance
2010-01-01
In this article, the influence of yttria-stabilized zirconia (YSZ) sintering temperature on a Pt/YSZ/La0.8Sr0.2CrO3 mixed potential sensor performance is reported. The sintering temperature of YSZ was varied from 1000 to 1200^oC. Mercury porosity measurements were performed to estimate the porosity and tortuosity of the YSZ sample as a function of sintering temperature. Further, the surface area of YSZ was computed by the BET method. After YSZ characterization, the unbiased and biased sensor response was recorded. The 1000^oC sintered YSZ sample was taken as the reference for comparison purposes. Experimental results indicated a 30% reduction in porosity for the 1200^oC sintered YSZ sample, resulting in a 14-fold increase in the sensor response rise time. In addition, for the same sample, ...
2010-01-01
Strontium substituted lanthanum manganite and yttria stabilized zirconia solid oxide fuel cell composite electrodes were impregnated with nano-particles of strontium substituted lanthanum manganite or alumina. A clear positive effect was observed on low performing electrodes and on good performing electrodes if the temperature was kept low after the impregnation with strontium substituted lanthanum manganite. On good performing electrodes the effect disappeared on heating. Alumina nano-particles had a detrimental effect on the activity of the strontium substituted lanthanum manganite based electrodes
EMBEDDED OPTICAL SENSORS FOR THERMAL BARRIER COATINGS
In this first year of the program we have focused on the selection of rare-earth dopants for luminescent sensing in thermal barrier coating materials, the effect of dopant concentration on several of the luminescence characteristics and initial fabrication of one type of embedded sensor, the ''red-line'' sensor. We have initially focused on erbium as the lanthanide dopant for luminescence doping of yttria-stabilized zirconia and europium as the lanthanide for luminescence doping of gadolinium zirconate. The latter exhibits a temperature-dependent luminescence lifetime up to at least 1100 C. A buried layer, ''red-line'' sensor in an electron-beam deposited yttria-stabilized zirconia coating with erbium has been demonstrated and exhibits a temperature-dependent luminescence lifetime up to at least 400 C.
EMBEDDED OPTICAL SENSORS FOR THERMAL BARRIER COATINGS
2004-12-16
In this first year of the program we have focused on the selection of rare-earth dopants for luminescent sensing in thermal barrier coating materials, the effect of dopant concentration on several of the luminescence characteristics and initial fabrication of one type of embedded sensor, the ''red-line'' sensor. We have initially focused on erbium as the lanthanide dopant for luminescence doping of yttria-stabilized zirconia and europium as the lanthanide for luminescence doping of gadolinium zirconate. The latter exhibits a temperature-dependent luminescence lifetime up to at least 1100 C. A buried layer, ''red-line'' sensor in an electron-beam deposited yttria-stabilized zirconia coating with erbium has been demonstrated and exhibits a temperature-dependent luminescence lifetime up to at least 400 C.
Development of a plasma coating system for induction melting zirconium in a graphite crucible
1993-05-26
A plasma coating system has been developed for induction melting zirconium at 1900 C using a graphite crucible. This laminated coating system consists of plasma spraying the following materials onto the graphite: (1) molybdenum or tungsten, (2) a 50% blend by weight of the metal powder and calcia-stabilized zirconium oxide, and (3) calcia-stabilized zirconia followed by painting a final coating of nonstabilized zirconia on top of the plasma-sprayed coating system. Zirconium was melted in argon using both laminating systems without any degradation of the graphite crucible and with only a minimal amount of carbon absorption. This novel approach that is being proposed as an alternative method of melting zirconium alloys offers substantial cost savings over the standard practice of electric arc melting using a consumable electrode.
Crystal Structures of Zirconia from First Principles and Self-Consistent Tight Binding
1998-12-01
The origin of the relative stability of the cubic, tetragonal, and monoclinic phases of zirconia (ZrO{sub 2} ) is investigated. To obtain accurate energies we adopt a new all-electron bandstructure approach within the local density approximation, based on muffin tin orbitals. We also develop a self-consistent tight-binding model with which to study the energies for different structures. The tight-binding model enables us to analyze {ital ab initio} and experimental phase stabilities in terms of ionic versus covalent effects, including polarization of the anions, and promises to be useful for rapid simulation of more complex systems. {copyright} {ital 1998} {ital The American Physical Society}
Composite cathodes of 50/50 vol percent LSM-YSZ (La1-xSrxMnO3-yttria stabilized zirconia) were deposited onto dense YSZ electrolytes by a colloidal deposition technique. The cathode characteristics were then examined by scanning electron microscopy (SEM) and studied by an impedance spectroscopy (IS). Conditioning effects of the LSM-YSZ cathodes were seen, and remedies for these effects were proposed for improving the performance of a solid oxide fuel cell (SOFC). LSM surface contamination and modification, cathode bonding to the YSZ electrolyte, changing Pt electrode and bonding paste, and curvature of sintered YSZ electrolytes led to some changes in microstructure and variability in cell performances.
2002-12-06
Composite cathodes of 50/50 vol percent LSM-YSZ (La1-xSrxMnO3-yttria stabilized zirconia) were deposited onto dense YSZ electrolytes by a colloidal deposition technique. The cathode characteristics were then examined by scanning electron microscopy (SEM) and studied by an impedance spectroscopy (IS). Conditioning effects of the LSM-YSZ cathodes were seen, and remedies for these effects were proposed for improving the performance of a solid oxide fuel cell (SOFC). LSM surface contamination and modification, cathode bonding to the YSZ electrolyte, changing Pt electrode and bonding paste, and curvature of sintered YSZ electrolytes led to some changes in microstructure and variability in cell performances.
2007-02-15
An 8 mol% yttria-stabilized zirconia (8YSZ) films are electrophoretically deposited on the La{sub 0.8}Sr{sub 0.2}MnO{sub 3} substrate using 8YSZ nanocrystallites prepared by a sol-gel process. Effects of liquid suspension on the particle zeta potential and degree of agglomeration at different pH values are investigated. When the pH value deviates from the point of zero charge (PZC), the adsorption of protons on particle surfaces cause higher zeta potential and well-dispersed suspension. The optimal values of the iodine concentration, applied voltage and deposition time for the electrophoretic deposition of 8YSZ films are also found.
Cermet sphere-pac concept for inert matrix fuel
2003-01-01
In the inert matrix fuel concept, plutonium reprocessed from spent fuel is burned in an inert matrix, e.g. yttria-stabilized zirconia. Coming from wet reprocessing, the internal gelation can perform an easy micro-spheres production. Utilization of these particles in a sphere-pac realizes a direct fuel production. Besides being economical, this direct usage offers an almost dustless fabrication. One disadvantage of yttria-stabilized zirconia as matrix is its low thermal conductivity. A further reduction by the macroscopic structure of a sphere bed seems unacceptable. This can be eluded by the insertion of a highly conducting phase. Similar to the cermet concept with the embedment of ceramic fuel into metal, the infiltration of a fine metal fraction into a coarse ceramic fuel fraction is studied here. The initial thermal conductivity shows much higher calculated values ...
Band structure of TiO sub 2 -doped yttria-stabilized zirconia probed by soft-x-ray spectroscopy
The electronic structure of TiO sub 2 -doped yttria-stabilized zirconia (YSZ) has been studied by soft-X-ray emission spectroscopy (SXES) and X-ray absorption spectroscopy (XAS). The valence band is mainly composed of the O 2p state. The O 1s XAS spectrum exhibits the existence of the Ti 3d unoccupied state under the Zr 4d conduction band. The intensity of the Ti 3d unoccupied state increases with increasing TiO sub 2 concentration. The energy separation between the top of the valence band and the bottom of the Ti 3d unoccupied state is in accord with the energy gap, as expected from dc-polarization and total conductivity measurements. (author)
Thermodynamic stability of oxygen point defects in cubic Zirconia
2010-09-29
Zirconia (ZrO2) is an important material with technological applications which are affected by point defect physics. Ab-initio calculations are performed to understand the structural and electronic properties of oxygen vacancies and interstitials in different charge states in cubic zirconia. We find oxygen interstitials in cubic ZrO2 can have five different configurations - dumbbell, dumbbell, crowd-ion, octahedral, and distorted dumbbell. For a neutral and singly charged oxygen interstitial, the lowest energy configuration is the dumbbell, while for a doubly charged oxygen interstitial the octahedral site is energetically the most favorable. Both the oxygen interstitial and the oxygen vacancy are negative-U, so that the singly charged defects are unstable at any Fermi level. The thermodynamic stability of these defects are studied in terms of Fermi level, oxygen partial pressure and temperature. A method to determine the chemical potential of the system as a function of temperature and pressure is proposed.
2008-01-01
The hydrogen economy has been risen as new option for supply the growing global demand for energy. A fuel cell is an electrochemical device able to use hydrogen as a energy source. Carbon dioxide (CO2) emission is very low so it is ecologically friendly, once energy is produced by a reaction of hydrogen and oxygen. The production of energy from hydrogen fuelled devices can be done even in small unities and in a distributed way. It can bring energy for isolated communities, where traditional energy distribution systems can not be reached. A fuel cell is composed essentially of 3 components: anode, cathode and the electrolyte. In present days, there are many materials proposed for use as electrolyte in fuel cells. Among then, Yttria stabilized zirconia (YSZ) is the most studied and effectively used in solid oxide fuel cell. Tape casting technology is a cheap, simple and ...
Study of factors influencing the microstructure and phase content of ultrafine Y-TZP
2003-05-25
2{approx}3.5 mol%Y{sub 2}O{sub 3} stabilized zirconia powders were prepared by mixing pure zirconia and Y(NO{sub 3}){sub 3} solution. The sintering ability of these powders was investigated. The results show that with the increasing amount of yttria, the grain size decreases while the density and the (t+c)-ZrO{sub 2} phase fraction increase. It is not sufficient in stabilizing all the zirconia when the doped yttria is less than 2.5 mol%. Several experimental rules about the microstructure and phase content developing with sintering temperature and soaking time are presented. The critical grain size for the retention of high-temperature tetragonal phase in 3Y-TZP is about 0.5 {mu}m. A 3Y-TZP sample with grain size about 0.3 {mu}m, relative density higher than 99%, (t+c)-ZrO{sub 2} phase fraction more than 90%, was obtained when it was sintered at 1450 deg. C for 2 h in air.
Study of factors influencing the microstructure and phase content of ultrafine Y-TZP
2003-01-01
2approx3.5 mol%Y2O3 stabilized zirconia powders were prepared by mixing pure zirconia and Y(NO3)3 solution. The sintering ability of these powders was investigated. The results show that with the increasing amount of yttria, the grain size decreases while the density and the (t+c)-ZrO2 phase fraction increase. It is not sufficient in stabilizing all the zirconia when the doped yttria is less than 2.5 mol%. Several experimental rules about the microstructure and phase content developing with sintering temperature and soaking time are presented. The critical grain size for the retention of high-temperature tetragonal phase in 3Y-TZP is about 0.5 mum. A 3Y-TZP sample with grain size about 0.3 mum, relative density higher than 99%, (t+c)-ZrO2 phase fraction ...
2010-01-01
Thick plasma sprayed thermal barrier coatings are suitable for thermal and hot corrosion protection of metal components in land-based turbine and diesel engines. In this work, ceria-yttria co-stabilized zirconia coatings were deposited by atmospheric plasma spraying in a mixture of non-transformable tetragonal t' and cubic c zirconia phases. Free-standing coatings were isothermally annealed at 1315^oC for different times and their crystal structure was studied by XRD. No phase decomposition occurred. Columnar grains grew in the molten splats with increasing annealing time according to a preferential direction and, after 50h of heat treatment, they were partially replaced by equiaxed grains. Both in-plane and out-of-plane thermal expansion coefficients (CTEs) were measured from coating expa...
Recent progress in zirconia-based fuel cells for power generation
High temperature solid oxide fuel cells based upon yttria-stabilized zirconia electrolyte offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. This paper reviews the designs, materials and fabrication processes used for such fuel cells. Most progress to date has been achieved with tubular geometry cells. A large number of tubular cells have been electrically tested, some to times up to 30,000 hours; these cells have shown excellent performance and performance stability. In addition, successively larger size electric generators utilizing these cells have been designed, built and operated since 1984. Two 25 kW power generation field test units have recently been fabricated; these units represent a major milestone in the commercialization of zirconia-based fuel cells for power generation.
Recent progress in zirconia-based fuel cells for power generation
High temperature solid oxide fuel cells based upon yttria-stabilized zirconia electrolyte offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. This paper reviews the designs, materials and fabrication processes used for such fuel cells. Most progress to date has been achieved with tubular geometry cells. A large number of tubular cells have been electrically tested, some to times up to 30,000 hours; these cells have shown excellent performance and performance stability. In addition, successively larger size electric generators utilizing these cells have been designed, built and operated since 1984. Two 25 kW power generation field test units have recently been fabricated; these units represent a major milestone in the commercialization of zirconia-based fuel cells for power generation.
Recent progress in zirconia-based fuel cells for power generation
1992-01-01
High temperature solid oxide fuel cells based upon yttria-stabilized zirconia electrolyte offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. This paper reviews the designs, materials and fabrication processes used for such fuel cells. Most progress to date has been achieved with tubular geometry cells. A large number of tubular cells have been electrically tested, some to times up to 30,000 hours; these cells have shown excellent performance and performance stability. In addition, successively larger size electric generators utilizing these cells have been designed, built and operated since 1984. Two 25 kW power generation field test units have recently been fabricated; these units represent a major milestone in the commercialization of zirconia-based fuel cells for power generation.
Recent progress in zirconia-based fuel cells for power generation
1992-12-01
High temperature solid oxide fuel cells based upon yttria-stabilized zirconia electrolyte offer a clean, pollution-free technology to electrochemically generate electricity at high efficiencies. This paper reviews the designs, materials and fabrication processes used for such fuel cells. Most progress to date has been achieved with tubular geometry cells. A large number of tubular cells have been electrically tested, some to times up to 30,000 hours; these cells have shown excellent performance and performance stability. In addition, successively larger size electric generators utilizing these cells have been designed, built and operated since 1984. Two 25 kW power generation field test units have recently been fabricated; these units represent a major milestone in the commercialization of zirconia-based fuel cells for power generation.
Neutron scattering characterization of pure and rare-earth modified zirconia catalysis.
The combined application of neutron powder diffraction, small angle neutron scattering and neutron inelastic scattering has led to improved understanding of the crystal phases, defect structure, microstructure and hydroxyl/water dynamics in pure and lanthanide-modified zirconia catalysts. Powder diffraction experiments quantified the degree of stabilization and provided evidence for static, oxygen vacancy-induced atomic displacements in stabilized zirconia. Quantitative assessment of Bragg peak breadths led to measurements of ''grain size'', representing coherency length of long-range ordered atomic arrangements (crystals). Small angle neutron scattering provided a separate measurement of ''grain size'', representing the average size of the primary particles in the aggregates, and the evolution of porosity (micro- versus meso-) and surface roughness caused by RE modification and heat treatment. Finally, the dynamics of hydrogen atoms associated with surface hydroxyls and adsorbed water was investigated by neutron-inelastic scattering, revealing changes in frequency and band breadth of O-H stretch, H-O-H bend, and librational motion of water molecules.
Neutron scattering characterization of pure and rare-earth modified zirconia catalysis.
1997-11-18
The combined application of neutron powder diffraction, small angle neutron scattering and neutron inelastic scattering has led to improved understanding of the crystal phases, defect structure, microstructure and hydroxyl/water dynamics in pure and lanthanide-modified zirconia catalysts. Powder diffraction experiments quantified the degree of stabilization and provided evidence for static, oxygen vacancy-induced atomic displacements in stabilized zirconia. Quantitative assessment of Bragg peak breadths led to measurements of ''grain size'', representing coherency length of long-range ordered atomic arrangements (crystals). Small angle neutron scattering provided a separate measurement of ''grain size'', representing the average size of the primary particles in the aggregates, and the evolution of porosity (micro- versus meso-) and surface roughness caused by RE modification and heat treatment. Finally, the dynamics of hydrogen atoms associated with surface hydroxyls and adsorbed water was investigated by neutron-inelastic scattering, revealing changes in frequency and band breadth of O-H stretch, H-O-H bend, and librational motion of water molecules.
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