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Y2O3
Kinds of Y2O3 Selected AbstractsGrowth and characterization of Nd, Yb , yttrium oxide nanopowders obtained by sol-gel methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Rzepka Abstract Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol-gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one-phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co-doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of magneto-optical YFeO3 crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007Hui Shen Abstract The floating zone growth of magneto-optical crystal YFeO3 has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500°C. A crack- free YFeO3 single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10° deviation. The X-ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 104/cm2. A thin outer layer with Y2O3 -rich composition was found at the periphery of as-grown crystals, which was attributed to the Fe2O3 evaporation during growth. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Low-Temperature and High-Strain Rate Superplastic ZirconiaADVANCED ENGINEERING MATERIALS, Issue 3 2003Y. Sakka A superplastic ceramic with a strain rate comparable to metals based on 3% Y2O3 -doped tetragonal zirconia (3YTZ) was synthesized at relatively low temperature, based on the doping with MgO and TiO2. The desirable material properties result from both a refined preparation procedure for the zirconia, and from enhanced cation lattice diffusion due to the MgO and TiO2 doping. [source] Synthesis, Structure and Electrical Properties of Mo-doped CeO2,Materials for SOFCsFUEL CELLS, Issue 5 2009Q. Li Abstract In this paper, we report the synthesis, structure and electrical conductivity of Mo-doped compounds with a nominal chemical formula of Ce1,xMoxO2+, (x,=,0.05, 0.07, 0.1) (CMO). The formation of fluorite-like structure with a small amount of Ce8Mo12O49 impurity (JCPDS Card No. 31-0330) was confirmed using a powder X-ray diffraction (PXRD). The fluoride-type structure was retained under wet H2 and CH4 atmospheres at 700 and 800,°C, while diffraction peaks due to metal Mo were observed in dry H2 under the same condition. AC impedance measurements showed that the total conductivity increases with increasing Mo content in CMO, and among the investigated samples, Ce0.9Mo0.1O2+, exhibited the highest electrical conductivity with a value of 2.8,×,10,4 and 5.08,×,10,2 S cm,1 at 550,°C in air and wet H2, respectively. The electrical conductivity was found to be nearly the same, especially at high temperatures, in air, O2 and N2. Chemical compatibility of Ce0.9Mo0.1O2+, with 10,mol-% Y2O3 stabilised ZrO2 (YSZ) and Ce0.9Gd0.1O1.95 (CGO) oxide ion electrolytes in wet H2 was evaluated at 800,1,000,°C, using PXRD and EDX analyses. PXRD showed that CMO was found to react with YSZ electrolyte at 1,000,°C. The area specific polarisation resistance (ASPR) of Ce0.9Mo0.1O2+, on YSZ was found to be 8.58,ohm,cm2 at 800,°C in wet H2. [source] Hydrothermal Synthesis of Rare Earth (Tb, Y) Hydroxide and Oxide Nanotubes,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2003Y.-P. Fang Abstract In this paper, Tb(OH)3 and Y(OH)3 single-crystalline nanotubes with outer diameters of 30,260,nm, inner diameters of 15,120,nm, and lengths of up to several micrometers were synthesized on a large scale by hydrothermal treatment of the corresponding oxides in the presence of alkali. In addition, Tb4O7 and Y2O3 nanotubes can be obtained by calcination of Tb(OH)3 and Y(OH)3 nanotubes at 450,°C. X-ray diffraction (XRD), field-emission scanning electron microscopy, transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry, and differential scanning calorimetry (DSC) have been employed to characterize these nanotube materials. The growth mechanism of rare earth hydroxide nanotubes can be explained well by the highly anisotropic crystal structure of rare earth hydroxides. These new types of rare earth compound nanotubes with open ends have uses in a variety of promising applications such as luminescent devices, magnets, catalysts, and other functional materials. Advantages of this method for easily realizing large-scale production include that it is a simple and unique one-pot synthetic process without the need for a catalysts or template, is low cost, has high yield, and the raw materials are readily available. The present study has enlarged the family of nanotubes available, and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials. [source] Phase Transformation and Densification Behavior of Microwave-Sintered Si3N4,Y2O3,MgO,ZrO2 SystemINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2009Sreekumar Chockalingam A 2.45 GHz microwave-sintered Si3N4,Y2O3,MgO system containing various amounts of ZrO2 secondary additives have been studied with respect to phase transformation and densification behavior. The temperature dependent dielectric properties were measured from 25°C to 1400°C using a conventional cavity perturbation technique. Phase transformation behavior was studied using X-ray diffractometry. Microwave sintered results were compared with those of conventional sintered results. It has been found that , to , phase transformation was completed at a lower temperature in microwave-sintered samples than those of the conventionally sintered samples. Density of the microwave-sintered samples increased up to 2.5 wt% of ZrO2 addition and thereafter it showed a tendency to decrease or remain constant. The decrease in density is attributed to the pore generation caused by decomposition due to the localized over heating. [source] Influence of Wet Mechanical Mixing on Microstructure and Vickers Hardness of Nanocrystalline Ceramic,Metal CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Tatsuo Kumagai Nanocrystalline (nc) ceramic,metal composite bulk samples have been fabricated by consolidation of mixture of attrition-milled (AM) amorphous base ceramic ((ZrO2,3 mol% Y2O3),20 mol% Al2O3) and AM amorphous base metallic (Ti,48 mol% Al) powders using a pulse-current pressure sintering system. Microstructural observations revealed that the ceramic and metallic colonies appear blocky in morphology in the composite bulk samples, and both the ceramic and the metallic colonies consist of a large number of equiaxed fine grains with the sizes of 78,82 and 81,86 nm, respectively. Mechanical mixing treatments by wet ball milling in ethanol before consolidation process are effective for refinement of the ceramic and metallic colonies. In all the obtained composite bulk samples, the ceramic colonies consist of the dominant phase of tetragonal (t) ZrO2 solid solution (ss) together with the minor phases of monoclinic (m) ZrO2ss and ,-Al2O3. On the other hand, the dominant phase in the metallic colonies changes from Ti3Al (,2) to Tiss (,) with an increase in the t -ZrO2ss volume fraction by abrasion of 3 mol% yttria-stabilized tetragonal polycrystalline zirconia balls during wet mechanical mixing treatments. Such a phase transformation from ,2 to , is considered to be due to the decrease in the aluminum content in the metallic colonies by combination of aluminum with oxygen (i.e., the formation of ,-Al2O3), which is probably taken from ethanol (C2H5OH) into the powders during wet mechanical mixing treatments. The obtained nc composite bulk samples show good Vickers hardness values, which are considerably higher than those estimated from the rule of mixture. [source] Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High StrengthINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2008You Zhou Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400°C for 8 h and subsequently postsintering at 1900°C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source] Use of Enzymes for the Processing of BiomaterialsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2007Hidero Unuma Ceramic/polymer composites and hollow ceramic microspheres are receiving attention as biomaterials as a bone/tissue substitute and cancer remedy. This article describes the advantages of the use of enzymes as "controllable precipitant supplier" in the processing of such biomaterials. It has been demonstrated that hydroxyapatite (HA)/polymer composites and hollow microspheres of Y2O3, Fe3O4, and HA may be fabricated in a shorter time and using a simpler operation. [source] Yttrium oxide (Y2O3) as an inert marker in digestibility studies with dogs, blue foxes and mink fed diets containing different protein sourcesJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 9-10 2007S. G. Vhile Summary The study evaluated the use of yttrium oxide (Y2O3) as an inert marker in studies of apparent total tract digestibility in dogs, blue foxes and mink. Comparison was made with total faecal collection, and use of chromic oxide (Cr2O3) as marker respectively. Four experimental diets were added 0.1 g/kg yttrium oxide and 10 g/kg chromic oxide and fed to four animals of each species. Faecal recovery of yttrium oxide was 94.4% (SEM ± 1.0), and of chromic oxide 105.8% (SEM ± 1.5). The digestibilities of dry matter, crude protein, crude fat, starch and total carbohydrates obtained by total collection and yttrium oxide as marker showed close similarity, and in most cases not significant differences, independent of species and diets. In dogs, overall digestibilities of main nutrients with chromic oxide as marker were not significantly different from overall means obtained with yttrium oxide (p > 0.05). Overall digestibility of dry matter, crude protein and total carbohydrates in blue foxes and mink was significantly higher with chromic oxide than with yttrium oxide (p < 0.05). In dogs and blue foxes, digestibilities of individual amino acids determined by use of yttrium oxide were not different from values obtained using total collection of faeces, both within diets and for overall mean (p > 0.05). Overall amino acid digestibilities in dogs determined with chromic oxide as marker were similar to corresponding figures for yttrium oxide, whereas use of chromic oxide resulted in significantly higher digestibilites for a number of amino acids compared with yttrium oxide in foxes and mink (p < 0.05). The digestibilities of most main nutrients and amino acids revealed no interaction between diet and method (p > 0.05). The study showed that yttrium oxide can be used in low concentration in the feed, and allows high accuracy of analyses and thereby precise digestibility determination. It is concluded that yttrium oxide is an alternative inert marker to chromic oxide in the studied species. [source] A comparative study of single-line and Rietveld strain,size evaluation procedures using MgO ceramicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2002Suminar Pratapa Strain,size evaluations from diffraction line broadening for MgO ceramic materials have been compared using single-line integral-breadth and Rietveld procedures with the Voigt function. Diffraction data were measured by Bragg,Brentano X-ray diffractometry (XRD), without incident beam monochromatization, and neutron diffractometry (ND) to encompass near-surface and bulk effects, respectively. The specimens consisted of sets of MgO ceramics and MgO,Y2O3 ceramic composites sintered over a range of temperatures. An MgO ceramic sintered at 1723,K for 2,h exhibited slightly less XRD broadening than the standard LaB6 NIST 660 SRM, and was therefore selected to make instrument profile corrections for both XRD and ND data. It was found for both data types that: (a) sintering initially relieves residual strain present in the MgO powder used to sinter the ceramics and also promotes grain growth; (b) residual strain of the MgO ceramic minimizes as the sintering temperature increases, and then increases with further rise in the sintering temperature, presumably as a result of intragranular interactions associated with grain growth; and (c) introduction of the second phase (Y2O3) increases strain and inhibits crystal growth. The single-line and Rietveld methods gave similar strain values from both the XRD and ND data within the limits of experimental error, but there were substantial differences between the single-line and Rietveld size estimates determined with the XRD and ND data. [source] UV Raman spectroscopic study on the phase transformation of ZrO2, Y2O3,ZrO2 and SO42,/ZrO2JOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2002Can Li The phase evolution of zirconia (ZrO2), sulfated zirconia (SO42,/ZrO2) and yttrium oxide incorporated zirconia (Y2O3,ZrO2) from the tetrahedral phase to the monoclinic phase was studied using UV Raman spectroscopy, visible Raman spectroscopy and x-ray diffraction (XRD). It is clearly observed that there are discrepancies between the results from the UV Raman spectra, visible Raman spectra and XRD patterns. The phase change from tetragonal to monoclinic is always earlier or at lower calcination temperatures as observed by UV Raman spectroscopy than by visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD supply the information mainly from the bulk. The inconsistency in the results from the three techniques suggests that the phase transformation of zirconia starts from its surface region and then gradually develops into its bulk. For SO42,/ZrO2 and Y2O3,ZrO2, the transformation from the tetragonal to the monoclinic phase is significantly retarded owing to the presence of the sulfated groups and the yttrium oxide. Particularly, the tetragonal phase of Y2O3,ZrO2 can be maintained up to 800 °C although its phase at the surface region changed into monoclinic at 500 °C. Copyright © 2002 John Wiley & Sons, Ltd. [source] Boson Peak, Elastic Properties, and Rigidification Induced by the Substitution of Nitrogen for Oxygen in Oxynitride GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Nicolas F. Richet The effects of the substitution of nitrogen for oxygen on the heat capacity and vibrational entropy of three yttrium aluminosilicate glasses with 0, 3.4, and 7.4 mol% Si3N4 have been investigated from 10 to 300 K. The partial molar heat capacity and entropy of Si3N4 calculated from these and previous measurements indicate stronger average bonding than for SiO2 units, whereas the values derived for Y2O3 are consistent with the dual network modifying and Al3+ charge-compensating role of yttrium. The low-frequency part of the vibrational densities of states g(,) and the boson peaks g(,)/,2 derived from the inversion of the heat capacities indicate that nitrogen rigidifies the TO4 (T=Si, Al) tetrahedral network and that yttrium hampers the librational motion of the AlO4 tetrahedra, which contribute to the excitations associated with the boson peak. Along with data reported previously for borate and silicate glasses, these results for oxynitrides show a general monotonically increasing relation between transverse acoustic velocities and the temperature of the calorimetric boson peak. Illustrating the universal phenomenology of the boson peak, all these data collapse on the same master curve when plotted in a reduced form. [source] Design, Preparation, and Characterization of Graded YSZ/La2Zr2O7 Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Hongfei Chen Large-area spallation and crack formation during service are big problems of plasma-sprayed thermal barrier coatings (TBCs), owing to their weak bond strengths and high residual stresses. Functional gradient TBCs with a gradual compositional variation along the thickness direction are proposed to mitigate these problems. In this paper, a six-layer structured TBC composed of Y2O3 partially stabilized ZrO2 (YSZ) and La2Zr2O7 (LZ), was prepared by plasma spraying with dual powder feeding ports. This coating had a gradient composition and function. Thermal conductivity of the coating was comparable with that of a single LZ coating while the coefficient of thermal expansion was nearly equal to that of YSZ single coating. The experiment was conducted to compare the thermal shock resistance of a graded coating with a conventional YSZ/LZ double-layer system. Changes in weight and morphology of specimens before and after thermal shock tests were analyzed. Results demonstrated that the thermal shock resistance of the graded coating was superior to the double-layer coating. Typically, a barely visible pimple-like spallation was present on the surface of the graded coating after 21 cycles. On the other hand, obvious delamination was observed for a double-layer coating after six to seven cycles. Special focus was also placed on a comparative investigation of stresses that are closely related to spallation via the use of numerical simulation. [source] Spark Plasma Sintering of an Infrared-Transparent Y2O3,MgO NanocompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010DongTao Jiang A novel optically transparent ceramic nanocomposite Y2O3,MgO was produced using spark plasma sintering technique. Sintering parameters was optimized to obtain fully dense material while maintaining nanoscale grain size. The sintered nanocomposite has an excellent infrared transmission as a result of small grain size and homogeneous microstructure. Postsinter annealing can significantly improve the transmission. Overly larger grain size severely degrades the transmittance. [source] Sintering Behavior and Conductivity Study of Yttrium-Doped BaCeO3,BaZrO3 Solid Solutions Using ZnO AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009He Wang The effect of ZnO on the crystal structure, sintering behavior, and electrical conductivity of yttrium-doped BaCeO3,BaZrO3 was investigated by unfixing or fixing the yttrium content noted as BaCe0.5Zr0.3Y0.2,xZnxO2.9,0.5x and BaCe0.5Zr0.3Y0.2O2.9+yZnO, respectively. Studies on the two series revealed that BaO·ZnO eutectic, rather than ZnO, was responsible for the sintering densification. For BaCe0.5Zr0.3Y0.2,xZnxO2.9,0.5x, the evaporation of ZnO·BaO eutectic was observed after sintering at 1300°C for 10 h, and few impurities were detected by XRD with x<0.20. For BaCe0.5Zr0.3Y0.2O2.9+yZnO, the concomitant loss of BaO with ZnO caused A-site deficiency and led to impurities of Y2O3 for y=0.08 and 0.14, and Y2BaZnO5 for y=0.20 during the sintering. For both series, ZnO enhanced the relative density, which was above 97% with x or y varying from 0.02 to 0.08. Energy-dispersive X-ray spectroscopy analysis revealed that ZnO hardly entered the perovskite phase. The conductivity study also suggested that ZnO did not serve as a dopant and that yttrium content was essential for sustaining a high ionic conduction. Excessive ZnO was especially detrimental to the grain boundary conduction and thus lowered the total electrical conduction. The optimized composition of BaCe0.5Zr0.3Y0.2O2.9+0.04ZnO has been obtained, with both a high relative density (,98.5%) and a high electrical conductivity (1.35 × 10,2 S/cm at 600°C). [source] The Structure of Yttrialite and Its Identification Using Laboratory and Synchrotron-Based Powder X-Ray DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009William J. Heward A highly crystalline sample of the impurity stabilized phase y -Y2Si2O7, generally known as yttrialite, has been formed from the melt of a glass with a nominal composition of 62(SiO2),10(Al2O3),28(Y2O3) mol%. Powder X-ray diffraction patterns were collected using in-house instrumentation and the 11-BM diffractometer at the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. Rietveld refinements were carried out on the patterns using two structural models. On patterns collected using in-house instrumentation the correct structure assignment was difficult to determine; however, the extremely high-quality data afforded by the 11-BM instrument showed conclusively that the sample was found to crystallize in the monoclinic system (SG=P21/m) with lattice parameters a=5.03032(6), b=8.06892(6), c=7.33620(6) Å, and ,=108.673(1). Furthermore, simulations have shown that it is likely that this structure model can be used to describe natural yttrialite or yttrialite that is formed at low temperatures, though the possibility that such materials are paracrystalline is also discussed. [source] Microstructure of Nanocrystalline Yttria-Doped Zirconia Thin Films Obtained by Sol,Gel ProcessingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Benjamin Butz Nano- and microcrystalline yttria-stabilized zirconia (YSZ) thin films with a dopant concentration of 8.3±0.3 mol% Y2O3 were prepared with a variation in grain size by two orders of magnitude. A sol,gel-based method with consecutive rapid thermal annealing was applied to fabricate YSZ films, resulting in about 400 nm YSZ on sapphire substrates. The average grain sizes were varied between 5 nm and 0.5 ,m by heat treatment in the temperature range of 650°,1350°C for 24 h. High-resolution (HRTEM) and conventional transmission electron microscopy analyses confirmed specimens,irrespective of the thermal treatment,consisting of cubic (c -)ZrO2 grains with nanoscaled tetragonal precipitates coherently embedded in the cubic matrix. Energy-dispersive X-ray spectroscopy and HRTEM on a large number of specimens yielded a homogeneous yttria concentration within the grains and at the grain boundaries with the absence of impurities, i.e. silica at the grain boundaries. [source] Biomorphic Silicon Nitride Ceramics with Fibrous Morphology Prepared by Sol Infiltration and Reduction,NitridationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Min Luo Biomorphic silicon nitride (Si3N4) ceramics with fibrous morphology were fabricated by combining sol,gel infiltration with carbothermal reduction nitridation from wood precursor. Y2O3 -incorporated silica sol was used as the infiltrated solution to promote the formation of fibrous Si3N4 grain at 1600°C under high nitrogen pressure (0.6 MPa). The influence of sintering conditions (additive and temperature) on the phase composition and microstructure of sintering bodies was analyzed, and the reaction mechanism is discussed. [source] Formation of High-Quality, Epitaxial La2Zr2O7 Layers on Biaxially Textured Substrates by Slot-Die Coating of Chemical Solution PrecursorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Sung-Hun Wee Crystallization studies were performed of epitaxial La2Zr2O7 (LZO) films on biaxially textured Ni,3at.%W substrates having thin Y2O3 (10 nm) seed layers. LZO films were deposited under controlled humid atmosphere using reel-to-reel slot-die coating of chemical solution precursors. Controlled crystallization under various processing conditions has revealed a broad phase space for obtaining high-quality, epitaxial LZO films without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c -axis aligned LZO films with no random orientation were obtained even at relatively low annealing temperatures of 850°,950°C in flowing one atmosphere gas mixtures of Ar,4% H2 with an effective oxygen partial pressure of P(O2),10,22 atm. Texture and reflection high-energy electron diffraction analyses reveal that low-temperature-annealed samples have strong cube-on-cube epitaxy and high surface crystallinity, comparable to those of LZO film annealed at high temperature of 1100°C. In addition, these samples have a smoother surface morphology than films annealed at higher temperatures. Ni diffusion rate into the LZO buffer film is also expected to be significantly reduced at the lower annealing temperatures. [source] Contact Damage of Silicon Carbide/Boron Nitride NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2007Takafumi Kusunose To investigate the deformation mechanism of silicon carbide (SiC)/boron nitride (BN) nanocomposites, Hertzian contact tests were performed on monolithic SiC, and nanocomposite and microcomposite SiC/BN. Monolithic SiC had the typical microstructure of hot-pressed SiC with Y2O3 and Al2O3 additives, composed of slightly large grains in small matrix grains. The microcomposite comprised large BN grains dispersed along the grain boundaries of elongated SiC grains, while the nanocomposite showed a finer microstructure with fine BN particles and small matrix grains. These microstructural differences led to differences in the mechanism of contact damage. The damage of the monolithic SiC and the SiC/BN microcomposite exhibited classical Hertzian cone fracture and many large cracks, whereas the damage observed in the nanocomposites appeared to be quasi-plastic deformation. [source] Crystallographic Orientation of Y2Ba4CuMOx (M=Nb, Zr, Ag) Nanoparticles Embedded in Bulk, Melt-Textured YBCO Studied by EBSDJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007A. Koblischka-Veneva Crystallographic orientations of Y,Ba,Cu,O (YBCO) and embedded Y2Ba4CuMOx (M=Nb, Zr, Ag) nanoparticles in bulk, melt-textured YBCO samples are studied by electron backscatter diffraction. Y2BaCuO5 particles exhibit no preferred orientation but have a strong negative influence on the matrix orientation. In contrast, the nanoparticles do not disturb the texture of the YBCO matrix. Depending on the preparation route, a different particle orientation with respect to the matrix is obtained. Untextured nanoparticles are formed by solid-state reaction during the melt process by adding oxides (Nb2O5 or Y2O3) to the precursor powder. Preformed Y2Ba4CuMOx particles added to the precursor in the form of prereacted nanopowder exhibit a dominant single orientation related to the surrounding YBCO matrix. [source] Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride: (II) Effects of Magnesium Compound and Yttria AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007Xinwen Zhu The effects of the magnesium compound and yttria additives on the processing, microstructure, and thermal conductivity of sintered reaction-bonded silicon (Si) nitride (SRBSN) were investigated using two additive compositions of Y2O3,MgO and Y2O3,MgSiN2, and a high-purity coarse Si powder as the starting powder. The replacement of MgO by MgSiN2 leads to the different characteristics in RBSN after complete nitridation at 1400°C for 8 h, such as a higher ,-Si3N4 content but finer ,-Si3N4 grains with a rod-like shape, different crystalline secondary phases, lower nitrided density, and coarser porous structure. The densification, ,,, phase transformation, crystalline secondary phase, and microstructure during the post-sintering were investigated in detail. For both cases, the similar microstructure observed suggests that the ,-Si3N4 nuclei in RBSN may play a dominant role in the microstructural evolution of SRBSN rather than the intergranular glassy chemistry during post-sintering. It is found that the SRBSN materials exhibit an increase in the thermal conductivity from ,110 to ,133 (Wm·K),1 for both cases with the increased time from 6 to 24 h at 1900°C, but there is almost no difference in the thermal conductivity between them, which can be explained by the similar microstructure. The present investigation reveals that as second additives, the MgO is as effective as the MgSiN2 for enhancing the thermal conductivity of SRBSN. [source] Synthesis, Physical, and Mechanical Properties of Bulk Zr3Al3C5 CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007Lingfeng He An in situ reactive hot-pressing process using zirconium (zirconium hydride), aluminum, and graphite as staring materials and Si and Y2O3 as additives was used to synthesize bulk Zr3Al3C5 ceramics. This method demonstrates the advantages of easy synthesis, lower sintering temperature, high purity and density, and improved mechanical properties of synthesized Zr3Al3C5. Its electrical and thermal properties were measured. Compared with ZrC, Zr3Al3C5 has a relatively low hardness (Vickers hardness of 12.5 GPa), comparable stiffness (Young's modulus of 374 GPa), but superior strength (flexural strength of 488 GPa) and toughness (fracture toughness of 4.68 MPa·m1/2). In addition, the stiffness decreases slowly with increasing temperature and at 1600°C remains 78% of that at ambient temperature, indicating that Zr3Al3C5 is a potential high-temperature structural ceramic. [source] Correlation Between Microstructure and Creep Behavior in Liquid-Phase-Sintered ,-Silicon CarbideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006M. Castillo-Rodríguez The influence of increasing the sintering time from 1 to 7 h on the microstructure evolution and the mechanical properties at high temperature was studied in ,-silicon carbide (,-SiC) sintered in argon atmosphere with Y2O3,Al2O3 (10% weight) as liquid phase (LPS-,-SiC). The density decreased from 98.8% to 94.9% of the theoretical value, the grain size increased from 0.64 to 1.61 ,m, and some of the grains became elongated. The compression tests were performed in argon atmosphere, between 1450°C and 1625°C and stresses between 25 and 450 MPa, with the strain rate being between 4.2 × 10,8 and 1.5 × 10,6 s,1. The stress exponent n and the activation energy Q were determined, finding values of n between 2.4±0.1 and 4.5±0.2 and Q=680±35 kJ/mol for samples sintered for 1 h, and n between 1.2±0.1 and 2.4±0.1 and Q=710±90 kJ/mol for samples sintered for 7 h. The correlation between these results and the microstructure indicates that grain-boundary sliding and the glide and climb of dislocations, both accommodated by bulk diffusion, may be two independent deformation mechanisms operating. At the temperatures of the tests, the existence of solid-state reactions between SiC and the sintering additives is responsible of the microstructural changes observed. These effects are not a consequence of the process of deformation, but rather they are because of the thermal treatment of the material during the creep. [source] Electronic Structure and Bonding of All Crystalline Phases in the Silica,Yttria,Silicon Nitride Phase Equilibrium DiagramJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004Wai-Yim Ching This paper reviews the structures and properties of 10 binary, ternary, and quaternary crystals within the equilibrium phase diagram of the SiO2,Y2O3,Si3N4 system. They are binary compounds SiO2, Y2O3, Si3N4; ternary compounds Si2N2O, Y2Si2O7, and YSi2O5; and quaternary crystals Y2Si3N4O3 (M-melilite), Y4Si2O7N2, (N-YAM), YSiO2N (wallastonite), and Y10(SiO4)6N2 (N-apatite, N-APT). Although the binary compounds are well-known and extensively studied, the ternary and the quaternary crystals are not. Most of the ternary and the quaternary crystals simply have been referenced as secondary phases in the processing of nitrogen ceramics. Their crystal structures are complex and not precisely determined. In the quaternary crystals, there exists O/N disorder in that the exact atomic positions of the anions cannot be uniquely determined. It is envisioned that a variety of cation,anion bonding configurations exist in these complex crystals. The electronic structure and bonding in these crystals are, therefore, of great interest and are indispensable for a fundamental understanding of structural ceramics. We have used ab initio methods to study the structure and bonding properties of these 10 crystals. For crystals with unknown or incomplete structural information, we use an accurate total energy relaxation scheme to obtain the most likely atomic positions. Based on the theoretically modeled structures, the electronic structure and bonding in these crystals are investigated and related to various local cation,anion bonding configurations. These results are presented in the form of atom-resolved partial density of states, Mulliken effective charges, and bond order values. It is shown that Y,O and Y,N bonding are not negligible and should be a part of the discussion of the overall bonding schemes in these crystals. Spectroscopic properties in the form of complex, frequency-dependent dielectric functions, X-ray absorption near-edge structure (XANES), and the electron energy-loss near-edge structure (ELNES) spectra in these crystals also are calculated and compared. These results are discussed in the context of specific bonding configurations between cations (silicon and yttrium) and anions (oxygen and nitrogen) and their implications on intergranular thin films in polycrystalline Si3N4 containing rare-earth elements. [source] Photoluminescence of Cerium-Doped ,-SiAlON MaterialsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Rong-Jun Xie Cerium-doped ,-SiAlON (MxSi12,(m+n)Alm+nOnN16,n) materials have been prepared by gas-pressure sintering and post-hot-isostatic-press (HIP) annealing, using four powder mixtures of ,-Si3N4, AlN, and either (i) CeO2, (ii) CeO2+ Y-,-SiAlON seed, (iii) CeO2+ Y2O3, or (iv) CeO2+ CaO. Cerium-containing CeAl(Si6,zAlz)(N10,zOz) (JEM) phase, rather than Ce-,-SiAlON phase, forms in the sample with only CeO2, whereas a single-phase ,-SiAlON generates in samples with dual doping (CeO2+ Y2O3 and CeO2+ CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; ,-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and ,-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5d band, because the coordination of Ce3+ in JEM and ,-SiAlON is nitrogen enriched. [source] Thermochemistry of Glasses in the Y2O3 -Al2O3 -SiO2 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Yahong Zhang Enthalpies of drop solution in molten 2PbO-B2O3 at 1078 K were measured for glasses along the 2YAlO3 -3SiO2 and return ½Y3Al5O12 -3SiO2 joins. The onset glass transition temperature increases slightly with increasing silica content and Y/Al. Enthalpies of mixing were calculated on the basis of amorphous end members. Strongly negative heats of mixing support the absence of miscibility gaps except possibly for very high silica content, consistent with experimental phase analyses, which indicate much narrower miscibility gaps compared with the phase diagrams calculated on the basis of previous data and the CALPHAD formalism. [source] Cubic-Formation and Grain-Growth Mechanisms in Tetragonal Zirconia PolycrystalJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003Koji Matsui The microstructure in Y2O3 -stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°,1500°C was examined to clarify the role of Y3+ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y2O3 concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grain-boundary faces in Y-TZP and Y3+ ions segregated at their grain boundaries over a width of ,10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y3+ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y3+ ions segregating along the grain boundary, respectively. [source] Properties of Nitrogen-Containing Yttria,Alumina,Silica Melts and GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Noritaka Saito The viscosity and solubility of nitrogen in Y2O3,Al2O3,SiO2 melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y2O3,Al2O3,SiO2 melts was decreased, the solubility of nitrogen into the melts was increased with increased Y2O3 content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y2O3 content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network. [source] | |||||||||||||||||||||||||||||||