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Title: A study of tungsten nanopowder formation by self-propagating high-temperature synthesis

Abstract

Molten salt-assisted self-propagating high-temperature synthesis of nanocrystalline W powder was studied experimentally. The technique involves the reduction of WO{sub 3} in the presence of sodium chloride using three different reducing agents: magnesium (Mg), sodium azide (NaN{sub 3}), and sodium borohydride (NaBH{sub 4}). The effects of the mole fraction of sodium chloride on temperature distributions, combustion parameters, phase compositions, and morphology of the final products were determined. The sodium chloride-assisted method reported here has been found to be effective for lowering combustion temperature and producing uniform and spherical W nanopowders of average particle size around 20-200, 100-200, and 20-50 nm. The effect of combustion temperature on tungsten particle size is discussed, and a sketch describing the chemistry of combustion is proposed.

Authors:
;  [1];  [2]
  1. Rapidly Solidified Materials Research Center, Chungnam National University, 220 Gung-Dong, Yuseong, Daejeon 305-764 (Korea, Republic of)
  2. Korea Atomic Energy Research Institute (KAERI), 150 Duckjin-Dong, Yuseong, Daejeon 305-353 (Korea, Republic of)
Publication Date:
OSTI Identifier:
20677688
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 142; Journal Issue: 3; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; TUNGSTEN; POWDERS; NANOSTRUCTURES; SYNTHESIS; REDUCTION; TUNGSTEN OXIDES; TEMPERATURE DISTRIBUTION; PHASE DIAGRAMS; TEMPERATURE DEPENDENCE; MORPHOLOGY; SODIUM CHLORIDES

Citation Formats

Nersisyan, H.H., Won, C.W., and Lee, J.H.. A study of tungsten nanopowder formation by self-propagating high-temperature synthesis. United States: N. p., 2005. Web. doi:10.1016/j.combustflame.2005.03.012.
Nersisyan, H.H., Won, C.W., & Lee, J.H.. A study of tungsten nanopowder formation by self-propagating high-temperature synthesis. United States. doi:10.1016/j.combustflame.2005.03.012.
Nersisyan, H.H., Won, C.W., and Lee, J.H.. 2005. "A study of tungsten nanopowder formation by self-propagating high-temperature synthesis". United States. doi:10.1016/j.combustflame.2005.03.012.
@article{osti_20677688,
title = {A study of tungsten nanopowder formation by self-propagating high-temperature synthesis},
author = {Nersisyan, H.H. and Won, C.W. and Lee, J.H.},
abstractNote = {Molten salt-assisted self-propagating high-temperature synthesis of nanocrystalline W powder was studied experimentally. The technique involves the reduction of WO{sub 3} in the presence of sodium chloride using three different reducing agents: magnesium (Mg), sodium azide (NaN{sub 3}), and sodium borohydride (NaBH{sub 4}). The effects of the mole fraction of sodium chloride on temperature distributions, combustion parameters, phase compositions, and morphology of the final products were determined. The sodium chloride-assisted method reported here has been found to be effective for lowering combustion temperature and producing uniform and spherical W nanopowders of average particle size around 20-200, 100-200, and 20-50 nm. The effect of combustion temperature on tungsten particle size is discussed, and a sketch describing the chemistry of combustion is proposed.},
doi = {10.1016/j.combustflame.2005.03.012},
journal = {Combustion and Flame},
number = 3,
volume = 142,
place = {United States},
year = 2005,
month = 8
}
  • The formation mechanism of MoSi{sub 2} by self-propagating high-temperature synthesis (SHS) was studied by quenching the reaction front into liquid nitrogen or in a copper block. The microstructural analysis of the front indicated that the formation of MoSi{sub 2} occurs via dissolution of Mo into Si melt followed by MoSi{sub 2} precipitation. The effects of processing variables including Mo particle size, preheating temperature, and diluent content on the MoSi{sub 2} particle size were discussed, based on the mechanism proposed in this study.
  • In self-propagating high-temperature synthesis (SHS), the exothermic heats of reaction usually involving solid reactants are sufficient for the process to sustain itself once the reactant mixture is ignited. Much research has been done on the application of SHS for the synthesis of many high-temperature materials. Advantages of SHS include the simplicity of apparatus as well as the absence of the need for external heating other than the small amount of heat for ignition. furthermore, due to the fact that the SHS process typically takes place above 2,000 C, many of the impurities volatilize, often yielding a product containing less impuritiesmore » than in the reactant mixture. Among the numerous materials synthesized by SHS, TiC has attracted much attention because of its superior high-temperature resistance and strength, hardness, and wear resistance. Conventional TiC production methods such as the carbothermic reduction of titanium dioxide, the titanium hydride process, and chemical vapor deposition suffer from the shortcomings of high oxygen or hydrogen content and low purity, which adversely affect the mechanical properties of the product. The main objectives of this work were to study the effect of SHS on lowering the impurity content of the product and to examine the effect of the reactant mixing ratio on the product microstructure.« less
  • Silicon nitride has played a prominent role among the structural ceramics, and it is one of the few ceramic materials currently used in structural applications such as cutting tools, turbochargers for car engines, and various components for gas turbines. These developments have been possible due to its oxidation resistance, high strength and low thermal expansion coefficient, which in combination with its moderately high thermal conductivity affords an excellent behavior under thermal shock. For further applications of this material in structural components, however, two main limitations, fracture resistance and cost, must be overcome. In the present work the authors present amore » new route to obtain high toughness silicon nitride with a bimodal microstructure using silicon nitride powder obtained by self-propagating high-temperature synthesis (SHS). The cost of this powder is between one fourth to one fifth that of the standard silicon nitride powder used, and in addition, the powder contains the seeding {beta}-Si{sub 3}N{sub 4} single crystal particles which lead to the development of a bimodal microstructure during sintering.« less
  • Graphical abstract: Nano-sized amorphous boron powders were synthesized by active dilution self-propagating high-temperature synthesis (SHS) method. The effects of endothermic reaction rate, the possible chemical reaction mechanism and active dilution model for synthesis of the product were also discussed. Highlights: ► Nano-sized amorphous boron powders were synthesized by active dilution self-propagating high-temperature synthesis method. ► The morphology, particle size and purity of the samples could be effectively controlled via changing the endothermic rate. ► The diluter KBH{sub 4} played an important role in active dilution synthesis of amorphous nano-sized boron powders. ► The active dilution method could be further popularizedmore » and become a common approach to prepare various inorganic materials. - Abstract: Nano-sized amorphous boron powders were synthesized by active dilution self-propagating high-temperature synthesis (SHS) method at temperatures ranging from 700 °C to 850 °C in a SHS furnace using Mg, B{sub 2}O{sub 3} and KBH{sub 4} as raw materials. Samples were characterized by X-ray powder diffraction (XRD), Laser particle size analyzer, Fourier transform infrared spectra (FTIR), X-ray energy dispersive spectroscopy (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission TEM (HRTEM). The boron powders demonstrated an average particle size of 50 nm with a purity of 95.64 wt.%. The diluter KBH{sub 4} played an important role in the active dilution synthesis of amorphous nano-sized boron powders. The effects of endothermic reaction rate, the possible chemical reaction mechanism and active dilution model for synthesis of the product were also discussed.« less
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