共查询到20条相似文献,搜索用时 0 毫秒
1.
Y. L. Song S. C. Tsai C. Y. Chen T. K. Tseng C. S. Tsai J. W. Chen Y. D. Yao 《Journal of the American Ceramic Society》2004,87(10):1864-1871
This paper presents new findings on ultrasonic spray pyrolysis of zirconium hydroxyl acetate precursor drops whose sizes were precisely measured using laser light diffraction technique. Precursor concentration plays a predominant role in determination of product particle size. At 0.01 wt% precursor concentration, conventional spray pyrolysis at 750°C using precursor drops 5–8 μm in diameter, generated by an ultrasonic nebulizer at 2.66 MHz, yielded uniform spherical yttria-stabilized zirconia (YSZ) particles 73 nm in diameter measured by scanning electron microscopy. The YSZ particle diameters were much smaller than those predicted by the one-particle-per-drop mechanism. Under similar reaction conditions, the high-throughput ultrasound-modulated two-fluid (UMTF) spray pyrolysis of larger precursor drops (28-μm peak diameter) also yielded spherical dense particles; they were significantly smaller in size than those produced by the low-throughput conventional ultrasonic spray pyrolysis of smaller drops (6.8-μm peak diameter). 相似文献
2.
Hydrolysis-assisted spray pyrolysis (HASP) using dimethyl oxalate as hydrolyte was found to be applicable to precipitation of solid, spherical BaTiO3 powder with uniform composition when the stock solution concentration was high (>1.0 M ). Solid, dense powder with uniform composition was successfully obtained because barium titanium oxalate was prepared from partial hydrolysis of dimethyl oxalate and coprecipitation of oxalate with barium and titanium during the hydrolysis–precipitation process, and then the oxalate particles became seeds in the following process. The sintered sample from the as-prepared BaTiO3 powder led to a higher dielectric constant and lower loss. 相似文献
3.
Bertrand Dubois Daniel Ruffier Philippe Odier 《Journal of the American Ceramic Society》1989,72(4):713-715
Fine yttria-stabilized zirconia powders were prepared by the spray pyrolysis of aqueous solutions of ZrOCl2 ·8H2 O and Y(NO3 )3 ·5H2 O (3 mol%). An appropriate thermal treatment resulted in slightly porous spherical particles with a narrow size distribution. The sintering ability of these powders was evaluated. 相似文献
4.
Morphological Control of Zirconia Nanoparticles through Combustion Aerosol Synthesis 总被引:1,自引:0,他引:1
Ceramic oxide nanoparticles produced by flame-based processes are typically agglomerated, which can limit their use in some applications. In this paper, a novel combustion synthesis method that utilizes the spraying of combustible droplets into a premixed flame to produce nanoscale crystalline particles of agglomerated and unagglomerated morphologies is described. Although the same flame-based experimental setup is used in both cases, variation in peak flame temperatures results in a corresponding variation between fractallike agglomerates and single isolated spherical particles. TEM/ED analysis shows that both classes of particles are the tetragonal crystal phase of zirconia. In the case of the unagglomerated spherical particles, results indicate that each precursor solution droplet, which acts as the feed, produces multiple spherical ceramic nanoparticles with a number mean diameter of 90 nm. The use of an inertial impaction stage in the precursor feed line to eliminate large feed droplets leads to a decrease in the number mean diameter to 60 nm, suggesting that crystalline spherical nanoparticles can be produced in a continuous flame-based process through control of the feed droplet size. 相似文献
5.
Ljiljana S. erovi Slobodan K. Milonji Ljilana V. Zivkovi Dragan P. Uskokovi 《Journal of the American Ceramic Society》1996,79(8):2215-2217
Fine agglomerate-free spherical β-SiC powder was synthesized from a dispersion of colloidal silica, saccharose, and boric acid, by means of an ultrasonic spray pyrolysis method. Droplets of 2.2 μm were formed with an aerosol generator, operated at 2.5 MHz, and carried into a reaction furnace at 900°C with argon. Spherical X-ray amorphous gel particles of 1.1 μm were obtained. β-SiC particles with a mean diameter of 0.79 μm and spherical shape resulted when the SiC gel precursor particles were heated at 1500°C in argon. 相似文献
6.
Huarui Xu Lian Gao Hongchen Gu Jingkun Guo Dongsheng Yan 《Journal of the American Ceramic Society》2002,85(1):139-144
To avoid the formation of hollow particles during spray pyrolysis, a spray hydrolysis reaction method (SHRM) was studied. Unlike the conventional spray pyrolysis that uses metal salt as a precursor and dry air as a carrier gas, the SHRM introduces a mixture of metal salt and dimethyl oxalate (DMO) as precursors and a gas mixture of water vapor and air as the carrier gas. Spherical, solid CeO2 particles characterized by SEM, BET, and density analysis were produced by the SHRM using Ce(NO3 )3 and DMO as the precursors. DMO, as an internal precipitant, hydrolyzed and produced oxalic acid, which precipitated with cerium ions to form volume precipitation in the whole droplet at enough temperature and relative humidity. The volume precipitation induced by the in situ formation of oxalic acid in the whole droplet prevented Ce(NO3 )3 nucleation at the droplet surfaces, thus avoiding the formation of hollow particles which usually occur in the conventional spray pyrolysis process. XRD and IR analysis showed that cerium oxalate was an intermediate product in the SHRM process. 相似文献
7.
Elliott B. Slamovich Frederick F. Lange 《Journal of the American Ceramic Society》1990,73(11):3368-3375
Micrometer size polydispersed spheres of zirconia were produced via electrostatic atomization and pyrolysis of aqueous zirconium acetate-yttrium acetate precursors. Varying the precursor composition in the ZrO2 -rich region of the ZrO2 -Y2 O3 binary system resulted in the production of either single-crystal (0 and 10 mol% Y2 O3 O or dense polycrystalline (3 mol% Y2 O3 ) zirconia spheres of similar size distribution for densification studies. Powders of either the singlecrystal or the polycrystalline particles exhibited contrasting densification behavior; viz., powder compacts composed of polycrystalline particles obtained significantly higher endpoint densities than their single-crystal counterparts. Microstructural observations showed that while necks between single-crystal particles reached a stable size, necks between polycrystalline particles continued to grow. 相似文献
8.
Yingkai Liu Chenglin Zheng Wengzhong Wang Yiongjie Zhan Guang Hou Wang 《Journal of the American Ceramic Society》2002,85(12):3120-3122
ZrO2 nanorods are prepared by annealing precursor powders produced in the novel inverse microemulsion system. The length and diameter of ZrO2 nanorods are a few micrometers and 40–100 nm, respectively. The microstructure of the resultant nanorods are studied by XRD, TEM, selected area electron diffraction, and Raman spectroscopy. The ZrO2 nanorods are single crystalline and have monoclinic structure. The formation of ZrO2 nanorods is discussed. 相似文献
9.
Synthesis and Colloidal Processing of Zirconia Nanopowder 总被引:6,自引:0,他引:6
Nanosized tetragonal 3 mol% Y2 O3 -doped ZrO2 powder was produced by hydrothermal precipitation from metal chlorides and urea sol followed by a washing–drying treatment and calcination. The effects on powder properties of powder washing by water and ethanol with subsequent centrifuging, with possible deagglomeration using microtip ultrasonication, were experimentally shown. Ultrasonic irradiation induced pressure waves, which generated cavities that could violently collapse, producing intense stress. This induced stress was effective in minimizing secondary particle size, deagglomerating the powder, redispersing the ZrO2 after all the washing–centrifuging cycles, and minimizing mean aggregate size after final calcination. A uniformly aggregated tetragonal ZrO2 nanopowder with a mean secondary particle size of ∼45 nm and without hard agglomerates was prepared. The properties of the nanopowders produced by colloidal processing and CIP were studied. Determination of the best suspension parameters allowed for low-temperature sinterability, which resulted in a nanograined ∼95 nm ceramic. 相似文献
10.
Roger Mueller Rainer Jossen Sotiris E. Pratsinis Mark Watson M. Kamal Akhtar 《Journal of the American Ceramic Society》2004,87(2):197-202
Synthesis of zirconia nanoparticles by flame spray pyrolysis (FSP) at high production rates is investigated. Product powder is collected continuously in a baghouse filter unit that is cleaned periodically by air-pressure shocks. Nitrogen adsorption (BET), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) are used to characterize the product powder. The effect of powder production rate (up to 600 g/h), dispersion gas flow rate, and precursor concentration on product particle size, crystallinity, morphology, and purity is investigated. The primary particle size of zirconia is controlled from 6 to 35 nm, while the crystal structure consists of mostly tetragonal phase (80–95 wt%), with the balance monoclinic phase at all process conditions. The tetragonal crystal size is close to the primary particle size, which indicates weak agglomeration of single crystals. 相似文献
11.
Noboru Tohge Masahiro Tatsumisago Tsutomu Minami Motoaki Adachi Yasuo Kousaka Kikuo Okuyama 《Journal of the American Ceramic Society》1991,74(9):2117-2122
The morphology and crystalline phases of superconducting fine particles with a composition of Bi2 Ca1 Sr2 Cu2 Ox were studied in terms of preparation conditions, using an aerosol flow reactor with varying temperature profiles: constant, increasing, and humped temperature distributions. The temperature profile in the reactor was found to affect greatly the morphology of the superconducting particles produced. The humped distribution with maximum temperatures over 900°C provided solid particles consisting mainly of the 80 K phase, when other preparation conditions were optimized. This finding indicates the possibility of controlling the morphology, as well as the crystalline phases, of superconducting particles by spray pyrolysis. 相似文献
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14.
Bismuth Oxide Nanoparticles by Flame Spray Pyrolysis 总被引:6,自引:0,他引:6
Bismuth oxide nanostructured particles were made via the flame spray pyrolysis (FSP) of bismuth nitrate that had been dissolved in a solution of ethanol/nitric acid or in acetic acid. These self-sustaining spray flames produced tetragonal β-Bi2 O3 . The use of ethanol/nitric acid solutions resulted in a mixture of hollow, shell-like, and solid nanograined particles. The particle homogeneity was improved as the content of acetic acid in the precursor solution increased. Solid bismuth oxide nanoparticles were prepared consistent with percolation theory, accounting for the specific volume of the product and the precursor. Using pure acetic acid as the solvent, the effect of FSP variables on spray flame and product powder characteristics was investigated. The specific surface area of the Bi2 O3 particles could be controlled over a range of 20–80 m2 /g by the liquid feed and oxygen gas flow rates for powder production rates of 6–46 g/h. 相似文献
15.
A polymeric precursor spin-coating technique is illustrated in which yttrium-stabilized zirconia (YSZ) thin films are produced on Si, Al2 O3 , and NaCl at temperatures less than 350°C. High-resolution transmission electron microscopy (HRTEM) examinations show that the YSZ films are nanocrystalline (grain size of less than 5 nm), fully dense, and have a stabilized cubic fluorite structure. Using the polymeric precursor spin coating method, unsupported nanocrystalline thin films of YSZ with thicknesses ranging from 30 to 1000 nm are prepared by transferring the films from a host substrate to metallic TEM grids with unsupported areas exceeding 1 mm2 . 相似文献
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17.
Preparation of Strontium Ferrite Particles by Spray Pyrolysis 总被引:4,自引:0,他引:4
Yoshihide Senzaki† James Caruso† Mark J. Hampden-Smith† Toivo T. Kodas‡ Lu-Min Wang§ 《Journal of the American Ceramic Society》1995,78(11):2973-2976
Crystalline, submicrometer strontium ferrite powders, including SrFeO2.97 , SrFe2 O4 , Sr2 FeO4 , Sr3 Fe2 O6.16 , and SrFe12 O19 , were prepared by spray pyrolysis of an aqueous solution of mixed metal nitrates. The Sr:Fe mole ratio in the precursor solution was retained in the final products. Phase-pure materials were typically obtained only at the highest temperatures investigated (>1100°C) and powders prepared at lower temperatures frequently contained crystalline Fe2 O3 . The as-prepared particles were unagglomerated, polycrystalline, and hollow at lower temperatures, but densified in the gas phase at higher temperatures to give solid particles. The strontium ferrite (SrFe12 O19 ) system was studied in detail as a representative example of the Sr-Fe-O system. At temperatures of 1200°C, dense, phase-pure magnetoplumbite-structure material, SrFe12 O19 , was obtained, while at lower temperatures, small amounts of Fe2 O3 were observed. The particles prepared at 800° and 1100°C were 0.1-1.0 μm in diameter, and consisted of crystallites <100 nm, and were nearly solid. The difficulty in forming phase-pure SrFe12 O19 was the different thermal decomposition temperatures of Sr(NO3 )2 (725°C) and Fe(NO3 )3 9H2 O (125°C) as demonstrated by thermogravimetric analysis in the SrFe12 O19 system. 相似文献
18.
ABSTRACT This work is a review of the experimental results from the literature for single-component metal and simple metal-oxide particles. Criteria for correlating particle morphology, i.e., whether the particles are solid or hollow, with process parameters and material properties during spray pyrolysis are presented and compared with the data available in the literature. The materials were classified into two categories for which the precursor: (1) melts and (2) does not melt before chemical reaction takes place, and separate criteria were used for each category based on the work of Jayanthi et al. (1993) J. Aerosol Sci. 19:478. In systems where the precursor melts before chemical reaction occurs, e.g., decomposition of nitrates of Mg, Al, Fe, Zn, Pb, Ni, Co, Pd, Mn, Cu, Sr, and Ag, the particle morphology is determined primarily by the densities and formula weights of the reactant and product compounds unless high temperature densification or puffing up of the particles due to gases evolved during the chemical reaction alter the morphology. In systems where the precursor undergoes nucleation to form a solid crust which does not melt before chemical reaction takes place, e.g., Ba(C2H3O2)2, Al2(SO4)3, Zr(C2H3O2)2, and Zn(C2H3O2)2, solubility and density of the precursor as well as the operating temperature are the main factors that affect the product particle morphology. Overall, particle morphologies predicted by the criteria were in agreement with experimental observations reported in the literature. 相似文献
19.
Nonisothermal Synthesis of Yttria-Stabilized Zirconia Nanopowder through Oxalate Processing: II, Morphology Manipulation 总被引:3,自引:1,他引:2
Oleg Vasylkiv Yoshio Sakka Hanna Borodians'ka 《Journal of the American Ceramic Society》2001,84(11):2484-2488
A novel, nontraditional route for controlling the morphology of yttria-stabilized zirconia nanopowders is explained. For understanding the real nature of yttrium zirconium oxalate nonisothermal decomposition and for the development of nanosize 3 mol% Y2 O3 ·97mol% ZrO2 , mass spectrometry, X-ray, and TEM investigation were used. Characteristics of zirconia crystallization under nonisothermal heating conditions were studied. Morphology evolution during Y-Zr oxalate nonisothermal decomposition was investigated to optimize the heating schedule of calcination. The nonlinear heating regime has been used to produce nanosized Y2 O3 -stabilized tetragonal ZrO2 powder with the finest primary crystallites and narrowest secondary aggregate size distribution. 相似文献
20.
Bingwen Yan Clayton V. McNeff Peter W. Carr Alon V. McCormick 《Journal of the American Ceramic Society》2005,88(3):707-713
Monodisperse, spherical, and nonporous zirconia particles ranging from submicrons to microns for use as supports for capillary electrophoresis and chromatography were synthesized by the controlled hydrolysis of zirconium tetra-alkoxides in alcohol solutions in the presence of long-chain organic acids. Particle characteristics varied as a function of water concentration, the chain length of the organic acid, aging time, temperature, and extent of stirring. Changing these experimental parameters affected particle size, particle size distribution, and the degree of particle aggregation. Submicron particles were made by increasing the water concentration and decreasing aging time. Particle size increases as temperature during the aging period increases. Most importantly, large monodisperse particles (4 μm) could be made by extended stirring. In general, we found that particle size increases as the chain length of the organic acid increases. We also found that gentle rotation during the aging period prevented both particle settling and secondary nucleation. This allowed the production of large particles. BET nitrogen adsorption uptake measurements demonstrate that the particles could be sintered, without aggregating them, to remove virtually all internal porosity. 相似文献