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Room: Salon 6
Location: Clarion Plaza Hotel
Session Chairs: John Moore, Dept. of Met and Matls, Colorado School of Mines, Golden, CO 80401-1887; Iver Anderson, Ames Laboratory, Iowa State University, 122 Metals Development Bldg, Ames, IA 50011-3020
CHEMICAL SYNTHESIS AND PROCESSING OF NANOSTRUCTURED ALUMINUM NITRIDE POWDERS: G.M. Chow, L.K. Kurihara, R. Rayne, L.S. Choi, P.E. Schoen, Naval Research Laboratory, Washington, DC 20375; M.I. Baraton, Laboratory for Ceramics and Surface Treatment, University of Limoges, France; Laboratory for Moelcular Interfacial Interactions, Code 6930/Center for Bio/Molecular Science and Engineering, also at Department of Biochemistry, Georgetown University, Washington, DC; Materials Science Division; Chemistry Division
Nanostructured ceramic AlN materials are fabricated using chemical routes. The precursor powders of aluminum hydroxide are synthesized by hydrolysis of aluminum tri sec butoxide. These precursor powders are calcined and subsequently transformed to nanoscale AlN powders by nitriding in an ammonia environment furnace at temperatures to 1100°C. The AlN powders are consolidated to green bodies by cold isostatic pressing. The green bodies are sintered in a nitrogen furnace for densification. Characterization techniques include XRD, TEM, HRTEM, DSC, and surface FTIR. The effects of solvent, pH on the control of particle size, particle size distribution and agglomeration are addressed.
FREEZE DRYING SYNTHESIS OF OXIDE POWDERS: A STEP TO POWDER ENGINEERING: O.A. Shlyakhtin, V.V. Ischenko, O.A. Brylev, N.N. Oleinikov, Department of Chemistry, Moscow State University, 119899 Moscow, Russia
Spray freezing of multicomponent aqueous solutions followed by freeze drying leads to formation of homogeneous salt powders with stable and extensive porous structure. The influence of specific microstructure on the properties of fine powders obtained by thermal decomposition of these precursors remains underestimated. Indeed the decomposition of the native freeze dried salt precursor resulted in the formation of single phase LiCoO2 at T=300°C while breaking the aggregates before decomposition led to multiphase product. In the other case carefully controlled influence on the microstructure of the intermediates allowed us to accelerate 3-5 times the rate of grain growth during annealing of Fe2O3 and BaZrO3 fine powders.
FRONTIERS IN PREPARATION OF Si3N4 POWDER BY RFPCVD: Rioyu Hong, Guoliang Zheng, Hongzhong Li, and Jianmin Ding, Inst. of Chem. Metallurgy, Chinese Academy of Sciences, Beijing 100080, China; Energy Research Corp., Great Pasture Road, Danbury, CT 06813
Radio frequency plasma chemical vapor deposition (RFPCVD) method is used to prepare ultrafine Si3N4 powder on a large scale. The characteristics of the RFPCVD method are given. It is pointed out that there are three kinds of mathematical models for the RF plasma generator and RFPCVD reactor: thermodynamic, hydrodynamic, and aerosol dynamic models with respective features. Research work on theoretical and technical studies for the preparation of ultrafine Si3N4 powder are given in detail. At last, the existing problems of the RFPCVD technology are given: (1) The thermodynamic, hydrodynamic and technical studies should be combined together. (2) Hydrodynamic modeling should be made for the RF plasma generator and CVD reactor simultaneously. (3) The improvements for preparing the Si3N4 powder should be combined with the aftertreatment of the product and also should be related to its sintered properties. (4) The improvements of the Si3N4 ceramic should be combined with the preparation of composite ceramics or surface modification of Si3N4 particles.
9:45 am BREAK
PREPARATION OF COMPOSITE PARTICLES BY RAW MATERIAL SOLUTION INJECTION: Hiroyuki Nakamura*, Yun-Fa Chen+, Kunio Kimura*, Hiroshi Tateyama*, Hideharu Hirosue*, Kyushu National Industrial Institute Japan , +Institute of Chemical Metallurgy, China
Composite particles, which are expected as raw materials for composite, are often prepared by alkoxide method or homogeneous precipitation method. However, using these methods, it seems to be rather difficult to control structure of the coating layer (ex. multi-layered, homogeneously mixed, graduated layered). From this point of view, the presenters tried to prepare composite particles by injecting raw material solution into a dispersion of core particles (diameter: micro meter order). The presenters believe that this method will make it easier to control the structure of coating layer. In this presentation, preparation of alumina-hydrate coated SiC whiskers is investigated. We used SiC whiskers as core particles and aluminum salt (nitrate, chloride, sulfate) solution as raw material solution, relationships between preparation conditions (injection speed, concentration of core particles etc.) and morphology of coated particles were explored. Moreover, application of this method for preparation of double-layer coated particles will be presented.
REACTIVE SYNTHESIS OF CERAMIC POWDERS: John J. Moore, Dennis W. Readey, Dept. of Met. and Matls Engr., Colorado School of Mines, Golden, CO 80401-1887
Reactive synthesis has been used to synthesize a number of different ceramic powders, such as TiB2, SiC, Si3N4. This paper will discuss the effect of reaction parameters, e.g., type of synthesis reaction, exothermicity of reaction, reactant particle size, reaction temperature and time, on the control of the size of the product powder, product yield, chemistry and purity.
SYNTHESIS OF ALUMINUM NITRIDE POWDERS USING DC-PLASMA PROCESSING: Paul Prichard, Matthew Besser, Daniel Sordelet, Iver Anderson, Ames Laboratory (USDOE), Iowa State University, Ames, IA 50011-3020
Experiments were performed to synthesize AlN powders by reacting Al with N using a conventional dc-plasma as a heat source. Attempts to form AlN powders by feeding Al powder into a nitrogen-rich plasma open to the atmosphere produced mainly aluminum oxide. Subsequent experiments were run inside a chamber which was backfilled with nitrogen. The nitrogen environment suppressed the formation of aluminum oxide, but little AlN was formed by using Al powder as the feedstock material. A furnace and crucible assembly was designed to feed molten Al directly into a convergent nozzle positioned directly at the face of the dc-plasma gun. Powders formed using this arrangement show a significant increase in the level of AlN formation. The presence of AlN was verified by chemical analysis and X-ray diffraction. Results were dependent upon chamber pressure, plasma velocity and molten liquid feed rate. The experimental parameters, equipment design and results will be reported in detail, and a suggested reaction mechanism will be discussed.
MECHANOCHEMICAL SYNTHESIS OF ULTRAFINE CERAMIC POWDERS: J. Ding, T. Tsuzuki, P.G. McCormick, Research Centre for Advanced Mineral and Materials Processing, The University of Western Australia, Nedlands, Perth, WA 6907, Australia
The synthesis of ultrafine alumina and zirconia powders by mechanochemical reaction has been investigated using x-ray diffraction, TEM and DSC measurements. Mechanical milling of AlCl3 or ZrCl4 with CaO resulted in nanoscale mixtures of the starting phases, with no evidence of the occurrence of any reaction during milling. The formation of separated 10-20 nm particles of g-Al2O3 within a CaCl2 matrix occurred after heat treating the as-milled AlCl3/CaO mixture above 350°C. Cubic ZrO2, particles 5-10 nm in diameter, were formed after heat treatment above 300°C. With both reactions, removal of the CaCl2 by-product phase was carried out using an appropriate solvent. Measurements of the effect of heat treatment temperature on crystal structure and particle size will be reported.
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