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Average Grain Size (average + grain_size)
Selected AbstractsPhase Morphology in Electrospun Zirconia MicrofibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Erin Davies Electrospinning of sol,gels has been used to produce zirconium-doped polymer microfibers from zirconyl chloride and poly(vinylpyrollidone) precursors. Calcination of these structures between temperatures of 370° and 930°C resulted in the formation of zirconia nanograined microfibers whose diameters ranged from 1200 to 800 nm at the higher temperatures and whose average grain size ranged from 9 to 33 nm. X-ray diffraction analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the fibers and established how this varied with calcination temperature and time. The tetragonal phase was shown to be unstable and disappeared on heating the material beyond around 750°C. The amount of zirconia yielded from the precursor material was measured and was found to be consistently greater than the theoretical yield. Average grain size within the microfibers increased with increasing calcination temperature and is effectively doubled when a 10 kPa pressure was applied. The effect of pressure also results in the creation of new crystal structures within the nanofibers and, as with traditional zirconia processing, the addition of impurity ions was found to stabilize the tetragonal phase. [source] Dielectric and magnetic properties of citrate-route-processed Li,Co spinel ferritesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007Nutan Gupta Abstract Cobalt-substituted lithium ferrites (with general composition Li0.5,x /2CoxFe2.5,x /2O4, where x = 0.0, 0.2, 0.4, 0.5 and 0.6) were prepared at lower processing temperatures (,600 °C) by the citrate route. The single-phase spinel structure was confirmed by X-ray diffraction. The average particle size of calcined powders calculated by the Scherrer formula is estimated to be 8,90 nm, whereas an average particle size of ,20 nm is observed from TEM for Co concentration x = 0.5. Average grain sizes from SEM micrographs of pellets sintered at 1000 °C (1 h) are observed to be 0.5,1 ,m, much smaller than the size reported for the standard ceramic method (2.1,6.8 ,m). The experimental density is observed to be 3.59,4.47 gm/cm3, which is greater than 85% of the densities evaluated from XRD. Compared with the standard ceramic method, lower dielectric constant (10,103) and higher dc resistivity (105,1010 , cm) is observed for Li,Co ferrites prepared by the citrate route. Improved magnetic properties, such as higher saturation magnetization (38,79 emu g,1) and Curie temperature (535 to 620 °C) are also investigated for the citrate-route-processed samples. These results demonstrate promising features of Li,Co ferrites in microwave applications. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] In-situ small-angle scattering study on the formation of a nanocrystalline soft-magnetic alloyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000D. R. Dos Santos A detailed study is presented on the nanocrystallization of the amorphous alloy Fe86Zr7Cu 1B6 (indices indicate at. %). Melt-spun ribbons were rapidly annealed by Joule heating, and the electrical resistance showed strong variations during thermal treatment. X-ray diffraction patterns indicate that these variations are related to the nucleation and growth of ,-Fe nanocrystals, and from peak profile analysis we obtained the average grain size and crystalline volume fraction for different annealing currents. The disorder-order transition was studied by in-situ small-angle X-ray scattering during conventional furnace treatments. SAXS intensity evolution for different temperatures, both below and above the crystallization temperature of the alloy, showed that a fast atomic rearrangement leads to the formation of atomic clusters before crystallization. The evolution of the size distribution function of these clusters as a function of time and temperature was obtained assuming a polydisperse system of spherical particles. [source] Effect of Applied Stress on IR transmission of Spark Plasma-Sintered AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Dibyendu Chakravarty The effect of applied stress on IR transmittance of nanocrystalline alumina prepared by spark plasma sintering was evaluated. Transparent alumina with maximum transmittance >80% was obtained over the entire mid-IR wavelength range of 3,5 ,m by applying a high stress of 275 MPa at 1150°C using specially designed high-strength compound dies. The transmittance observed was similar to previous reports at identical wavelengths, but at a lower sintering temperature. The transparent samples have an average grain size of 0.3 ,m and a hardness of 23 GPa. At lower stresses and sintering temperatures, transmittance reduced drastically due to remnant pores in the matrix as observed from the microstructural analysis. The effect of porosity was found to be critical in developing transparency as even a marginal decrease in porosity led to substantial increase in transmittance. [source] Electrical Conductivity of Submicrometer Gadolinia-Doped Ceria Sintered at 1000°C Using Precipitation-Synthesized Nanocrystalline PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Pandurangan Muralidharan A simple synthetic strategy has been implemented to obtain low-temperature sintered fine grain size gadolinia-doped ceria, Ce0.9Gd0.1O1.95, (CGO) electrolyte pellets with a high density using weakly agglomerated particles of calcined nanopowders synthesized by a homogeneous precipitation process. The precipitants used were diethylamine (DEA process) and ammonium hydroxide in neutral precipitation (NP process). X-ray diffraction patterns revealed the single-phase crystalline CGO of a fluorite-type structure. The crystalline powder was directly synthesized from solution by the DEA process at room temperature, whereas the NP process powder was crystallized upon hydrothermal treatment at an elevated temperature. Transmission electron microscopy images showed homogeneously dispersed spherical-shaped particles of ,5 nm size for nanopowders calcined at 300°C for 4 h. A high densification range from ,96% to 99% of the theoretical was achieved for the nonconventionally low-temperature sintered pellets at 1000°C from weakly bonded particles of CGO nanopowders calcined at 300°C for 4 h without any sintering aid. The dense CGO pellets sintered at 1000°C for 4 h with an average grain size of ,150,300 nm exhibited a promising high electrical conductivity of 2.03 × 10,2 S/cm (DEA process) and 2.17 × 10,2 S/cm (NP process), measured at 650°C, and low activation energy Ea. The electrical conductivities of fine grain size low-temperature sintered CGO pellets are comparable with the literature reports of sintered pellets using sintering aids, and high-temperature sintered CGO pellets above 1300°C with a larger grain size. [source] Phase Morphology in Electrospun Zirconia MicrofibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Erin Davies Electrospinning of sol,gels has been used to produce zirconium-doped polymer microfibers from zirconyl chloride and poly(vinylpyrollidone) precursors. Calcination of these structures between temperatures of 370° and 930°C resulted in the formation of zirconia nanograined microfibers whose diameters ranged from 1200 to 800 nm at the higher temperatures and whose average grain size ranged from 9 to 33 nm. X-ray diffraction analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the fibers and established how this varied with calcination temperature and time. The tetragonal phase was shown to be unstable and disappeared on heating the material beyond around 750°C. The amount of zirconia yielded from the precursor material was measured and was found to be consistently greater than the theoretical yield. Average grain size within the microfibers increased with increasing calcination temperature and is effectively doubled when a 10 kPa pressure was applied. The effect of pressure also results in the creation of new crystal structures within the nanofibers and, as with traditional zirconia processing, the addition of impurity ions was found to stabilize the tetragonal phase. [source] Evidence for the Microwave Effect During the Annealing of Zinc OxideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007J. Binner A microwave/conventional hybrid furnace has been used to anneal virtually fully dense zinc oxide ceramics under pure conventional and a microwave/conventional hybrid heating regime with a view to obtaining evidence for the "microwave effect" during the resulting grain growth. In each case it was ensured that each sample within a series had an identical thermal history in terms of its temperature/time profile. The results showed that grain growth was enhanced during hybrid heating compared with pure conventional heating; the greatest enhancement, a factor of ,3 increase in average grain size, was observed in the range 1100°,1150°C. The grain growth exponent decreased from 3 during conventional heating to 1.4 during hybrid heating in this temperature range, suggesting an acceleration of the diffusional processes involved. Temperature gradients within the samples were found to be too small to explain the results. This suggests that clear evidence has been found to support the existence of a genuine "microwave effect." [source] Novel Fabrication Route to Al2O3,TiN Nanocomposites Via Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Lianjun Wang A novel method for the preparation of Al2O3,TiN nanocomposites was developed. A mixture of TiO2, AlN, and Ti powder was used as the starting material to synthesize the Al2O3,TiN nanocomposite under 60 MPa at 1400°C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al2O3,TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness (KIC) and bending strength (,b) of the nanostructured Al2O3,TiN composites reached 4.22±0.20 MPa·m1/2 and 746±28 MPa, respectively. [source] Fractographic Montage for a Si3N4,SiC NanocompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Monika Ka, iarová A silicon nitride,silicon carbide nanocomposite has been prepared by an in situ method that utilizes C+SiO2 carbo-thermal reduction during the sintering process. The materials consist of a silicon nitride matrix, with an average grain size of 140 nm, and inter- and intragranular SiC particles with sizes of approximately 250 and 45 nm, respectively. The four-point bending strength and its distribution were investigated. The fracture origins were identified and characterized using fractographic methods, and a fractographic montage of the Weibull plot and fracture origins was constructed. The fracture origins were subsurface and volume located processing defects with sizes from 5 to 460 ,m, mainly in the form of clusters of pores, together with clusters of large SiC grains. [source] Anomalous Dynamical Charge Change Behavior of Nanocrystalline 3C-SiC upon CompressionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004Haozhe Liu Using diamond anvil cell (DAC) technique, in situ high-pressure Raman scattering and energy-dispersive X-ray diffraction (EDXRD) experiments were used at room temperature to study 3C-SiC with an average grain size of 30 nm. In contrast to its bulk counterpart, a decrease of the Born's transverse effective charge of these nanocrystals was observed with increasing pressure from measurements of the longitudinal and transverse optical phonon modes (longitudinal optical,transverse optical) splitting. This is therefore indicative of a diminishing ionicity of nanocrystalline 3C-SiC on compression. [source] Microstructural Evolution of Calcium-Doped ,-AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Arzu Altay Effect of different calcium doping levels on the microstructure of high-purity ,-alumina was studied as a function of sintering time and temperature using scanning electron microscopy (SEM). Microstructural evolution was related to hypothetical calcium excess at the grain boundaries (,Ca) that was calculated assuming zero solubility of calcium in bulk ,-alumina. Under all sintering conditions, grains were uniform in size and equiaxed for low calcium concentrations (<3 Ca atoms/nm2). The grain morphology became elongated when the calcium concentration at the grain boundaries reached calcium excess of ,Ca= 3,3.5 Ca atoms/nm2 in all samples. The average grain sizes of undoped samples were ,10% larger than the average grain sizes of low-calcium-doped samples. This decrease is believed to be due to solute drag effect of segregated Ca impurities on the grain boundary mobility. For the samples that were sintered at 1500° and 1600°C, slablike abnormally grown grains appeared for critical calcium excess concentrations of ,Ca= 4.5,8 Ca atoms/nm2. With abnormally grown grains a dramatic increase in average grain size was observed. However, when the calcium concentration was increased further, above certain calcium excess concentration depending on sintering temperature, a significant decrease in grain size was observed. In contrast to samples sintered at 1500° and 1600°C, when the samples sintered at 1400°C, although the hypothetical calcium coverage exceeded ,Ca= 11 Ca atoms/nm2, only few grains grew abnormally without significantly affecting the average grain size. Observations clearly indicated that calcium impurities caused elongated (slablike) grain morphology when their excess concentrations reached a critical level at the grain boundaries. [source] Revisit to the Origin of Grain Growth Anomaly in Yttria-Doped Barium TitanateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Jung-Kun Lee In this study, the effect of atmosphere during calcining and sintering of Y2O3 -doped BaTiO3 was investigated to reveal the origin of the anomaly of grain growth and conductivity as a function of Y2O3 content. Samples with various atmospheric histories were prepared. Microstructural and electrical variations were observed using SEM, dielectric (,r vs T) and thermopower measuring techniques, and impedance spectroscopy. An abrupt decrease in grain growth and a transition from semiconducting to insulating behavior were observed when the Y2O3 concentration exceeded 0.3 mol% and the samples were heat-treated in an O2 atmosphere. In contrast, the samples treated under N2+ 5% H2 atmosphere revealed neither grain growth anomaly nor conductivity anomaly even though the Y2O3 concentration was much greater than 3 mol%. The undoped BaTiO3 samples also demonstrated increased average grain size with increased oxygen partial pressure. Therefore, it was suggested that the grain growth anomaly did not result from the formation of cation vacancies V,Ba or V,,Ti. To investigate the origin of the grain growth anomaly, the Curie temperature, concentration of free electrons, and impedance spectra were measured. The grain growth anomaly and conductivity anomaly were associated with abrupt changes in all the measurements. These abrupt changes could be explained by the partial incorporation of donor dopants. Consequently, the origin of the anomaly in the microstructure and electrical properties are discussed in terms of grain-boundary segregation of the donor dopant. [source] Preparation of Hydroxyapatite Lathlike Particles Using High-Speed Dispersing EquipmentJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2001George C. Koumoulidis Hydroxyapatite lathlike monocrystalline particles were prepared using high-energy dispersing equipment in combination with a pH shock-wave method. The Ca/P atomic ratios were very close to theoretical, and the acidic group content was very small. The particles were nonporous, with anisotropic crystal growth and average grain size ,140,1300 nm in length, ,20,100 nm in width, and ,10,40 nm in thickness. The high-speed dispersing equipment created the proper hydrodynamic conditions for lathlike particle growth in the [001] direction. The hydroxyapatite particles formed aggregates of 1,5 ,m average diameter. [source] Sintering of Partially Stabilized Zirconia by Microwave Heating Using ZnO,MnO2,Al2O3 Plates in a Domestic Microwave OvenJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Satoru Fujitsu Partially stabilized zirconia (PSZ) powders were fully densified by microwave heating using a domestic microwave oven. Pressed powder compacts of PSZ were sandwiched between two ZnO,MnO2,Al2O3 ceramic plates and put into the microwave oven. In the first step, PSZ green pellets were heated by self-heating of ZnO,MnO2,Al2O3 ceramics (1000°C). In the second step, the heated PSZ pellets absorbed microwave energy and self-heated up to a higher temperature (1250°C), leading to densification. The density of PSZ obtained by heating in the microwave oven for 16 min was 5.7 g/cm3, which was approximately equal to the density of bodies sintered at 1300°C for 4 h or 1400°C for 16 min by the conventional method. The average grain size of the sample obtained by this method was larger than the average grain size of samples sintered by the conventional method with a similar heating process. [source] Thermoelectric properties of rapid hot pressed polycrystalline Ag1,xPb18SbTe20 synthesized from doping PbTe nanocrystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Xingliang Xin Abstract Polycrystalline thermoelectric (TE) materials of n-type and with compositions of Ag1,xPb18SbTe20 (x,=,0, 0.1, 0.2) were prepared by rapid hot pressing from alloy powders, which were obtained by ball milling crystalline ingots. The ingots were synthesized from PbTe nanoparticles, made by solvothermal reactions, and Ag, Sb and Te powders via vacuum-sealed melting in quartz ampoules. Through rapid hot pressing at 748,K for 15,min under 80,MPa, the polycrystalline samples possessed 95% relative densities with the average grain size of 5,µm. The electrical resistivity, Seebeck coefficient and thermal conductivity of the Ag1,xPb18SbTe20 (x,=,0, 0.1, 0.2) samples were measured in the range from room temperature (RT) to 673,K. The thermal conductivity was dramatically decreased, caused by scattering of phonons from grain boundaries and interfaces. By optimizing the values of carrier concentration and carrier transference, the Ag1,xPb18SbTe20 (x,=,0.2) sample achieved a maximum ZT value of 1.019 at 673,K. [source] Investigation of ZnTe thin films grown by Pulsed Laser Deposition methodPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007B. Kotlyarchuk Abstract This paper is devoted to optimization of the Pulsed Laser Deposition (PLD) growth condition of ZnTe films on various substrates and subsequent investigation of relevant parameters of growth process, structural, optical and electrical properties of grown films. Studies of the effect of growth parameters on the structural quality and properties of grown films were carried out. X-ray diffraction measurements showed that the ZnTe films, which have been deposited at optimal substrate temperatures, were characterized by a (111) preferred orientation with large average grain size. The optical transmission and reflectance in the energy range 1.5,5.5 eV for films grown at various substrate temperatures were measured. We calculated the variation in the absorption coefficient with the photon energy from the transmittance spectrum for samples grown at various substrate temperatures. Obtained data were analyzed and the value of the absorption coefficient, for allowed direct transitions, has been determined as a function of photon energy. We found that the undoped ZnTe films, which were grown by the PLD method, are typically p-type and possess resistivity in the range of 103 , cm at room temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of grain size on reactive diffusion between titanium and aluminiumPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2010Piotr Wiecinski Abstract The aim of this paper was to examine the effect of titanium substrate structure refinement (to the nanometric scale) on the chemical and phase composition of Ti-Al intermetallic layers. The material examined in the study was commercially available pure titanium with average grain size of 65 ,m and 60 nm. The aluminium layer with thickness of 5 ,m were obtained on both substrates using magnetron sputtering technique. After annealing more phase from Ti , Al system on nano-crystalline titanium were observed compared to micro-crystalline one. The obtained intermetallic layer was thicker and more homogeneous on nano-crystalline substrate. The grain size of the substrate was effected on the topography, thickness and microstructure of the diffusive Ti-Al layers. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A convenient synthesis of nanocrystalline chalcopyrite, CuFeS2 using single-source precursorsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 12 2009Sujit D. Disale Abstract Nanocrystalline chalcopyrite (CuFeS2) have been synthesized using single-source precursors, CuL2 and Cu(LH)2Cl2 (where LH = monoacetylferrocene thiosemicarbazone) by pyrolysis and solvothermal decomposition methods. The nanocrystals were characterized by UV,visible spectroscopy, X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray analysis. The magnetic character was determined by the hysteresis loop. CuFeS2 nanocrystallites prepared by the pyrolysis of CuL2 and Cu(LH)2Cl2 have a cubic phase and rod-like morphology with diameters of about 18 and 15 nm, respectively, and lengths of about 195,390 and 100,145 nm, respectively. However, CuFeS2 nanoparticles obtained by solvothermal route from CuL2 and Cu(LH)2Cl2, which are capped with ethylene glycol, possess a nearly spherical shape with an average grain size of 16 and 11 nm, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Composite Platinum/Silicon Dioxide Films Deposited using CVDCHEMICAL VAPOR DEPOSITION, Issue 3 2005P. Martin Abstract We report the low temperature deposition of platinum/silicon dioxide composite films from tetraethylorthosilicate (TEOS) and platinum acetylacetonate (Pt(acac)2). The simultaneous CVD of TEOS and Pt(acac)2, in the presence of oxygen, has been shown to reduce the decomposition temperature of TEOS to as low as 320,°C (from 600,°C without Pt(acac)2). Composite films were grown at temperatures ranging from 300,°C to 440,°C, using an estimated 5:1 flow rate of TEOS to Pt(acac)2 and in 0,70% oxygen atmosphere. The overall growth rate was maximized at 400,°C and the overall activation energy of the thin film formation was ,80 kJ mol,1. The SiO2 phase was amorphous and the platinum phase crystalline with an average grain size of 9 nm as determined by X-ray diffraction (XRD). An in-situ Fourier-transform infrared (FTIR) spectroscopy study of the gas phase was undertaken to provide confirmation of the low temperature decomposition of TEOS promoted by Pt(acac)2. Despite the high Si/Pt ratio in the feed, the maximum observed Si/Pt ratio in the film was 1:1, suggesting a cooperative TEOS-Pt(acac)2 decomposition mechanism. [source] Microstructural Evolution of Calcium-Doped ,-AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Arzu Altay Effect of different calcium doping levels on the microstructure of high-purity ,-alumina was studied as a function of sintering time and temperature using scanning electron microscopy (SEM). Microstructural evolution was related to hypothetical calcium excess at the grain boundaries (,Ca) that was calculated assuming zero solubility of calcium in bulk ,-alumina. Under all sintering conditions, grains were uniform in size and equiaxed for low calcium concentrations (<3 Ca atoms/nm2). The grain morphology became elongated when the calcium concentration at the grain boundaries reached calcium excess of ,Ca= 3,3.5 Ca atoms/nm2 in all samples. The average grain sizes of undoped samples were ,10% larger than the average grain sizes of low-calcium-doped samples. This decrease is believed to be due to solute drag effect of segregated Ca impurities on the grain boundary mobility. For the samples that were sintered at 1500° and 1600°C, slablike abnormally grown grains appeared for critical calcium excess concentrations of ,Ca= 4.5,8 Ca atoms/nm2. With abnormally grown grains a dramatic increase in average grain size was observed. However, when the calcium concentration was increased further, above certain calcium excess concentration depending on sintering temperature, a significant decrease in grain size was observed. In contrast to samples sintered at 1500° and 1600°C, when the samples sintered at 1400°C, although the hypothetical calcium coverage exceeded ,Ca= 11 Ca atoms/nm2, only few grains grew abnormally without significantly affecting the average grain size. Observations clearly indicated that calcium impurities caused elongated (slablike) grain morphology when their excess concentrations reached a critical level at the grain boundaries. [source] | ||||||||||||||||