• Title/Summary/Keyword: Self-propagating reaction

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Reaction Condition Dependency of Propagating Behavior in the Polymerization Reaction by Thermal Front

  • Huh, Do-Sung;Choe, Sang-Joon;Lee, Burm-Jong
    • Bulletin of the Korean Chemical Society
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    • v.23 no.2
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    • pp.325-329
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    • 2002
  • In this study, the dependency of the behavior of propagating front on the reaction condition in frontal polymerization reaction has been studied. We have used some multifunctional acrylates as a monomer and ammonium persulfate as an initiator for the polymerization reactions. In frontal polymerization, a method of producing polymeric materials via a thermal front that propagates through the unreacted monomer/initiator solution, the behavior of self propagating front shows various dynamic patterns depending on the reaction condition. We have obtained some spin modes of propagating front in the number of 'hot spots' or 'spin heads' by changing the reaction condition. The effect of the reactor tube diameter on the mode of propagating front has also been studied by using some reactor tubes with different size of tube diameter and it has been examined in some detail by adopting an experimental method of two-tubes system.

Effect of Acid Leaching Conditions on the Properties of Cr Powder Produced by Self-propagating High-temperature Synthesis (자전연소합성법을 이용한 Cr 분말 제조시 산세조건에 따른 물성평가)

  • YongKwan Lee;YeongWoo Cho;ShinYoung Choi;SungGue Heo;Ju Won;KyoungTae Park;MiHye Lee;JaeJin Sim
    • Journal of Powder Materials
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    • v.30 no.3
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    • pp.233-241
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    • 2023
  • In this study, we evaluated the effects of acid leaching on the properties of Cr powder synthesized using self-propagating high-temperature synthesis (SHS). Cr powder was synthesized from a mixture of Cr2O3 and magnesium (Mg) powders using the SHS Process, and the byproducts after the reaction were removed using acid leaching. The properties of the recovered Cr powder were analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), particle size analysis (PSA), and oxygen content analysis. The results show that perfect selective leaching of Cr is challenging because of various factors such as incomplete reaction, reaction kinetics, the presence of impurities, and incompatibility between the acid and metal mixture. Therefore, this study provides essential information on the properties under acidic conditions during the production of high-quality Cr powder using a self-propagating high-temperature synthesis method.

Processing of NiTi Shape Memory Alloy by Self- propagating High-temperature Synthesis (자전 고온 반응 합성법을 이용한 NiTi계 형상기억 합금의 제조에 관한 연구)

  • 윤종필
    • Journal of Powder Materials
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    • v.2 no.2
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    • pp.158-164
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    • 1995
  • Synthesis of the NiTi shape memory alloy using the thermal explosion mode of the self-propagating high-temperature synthesis has been investigated. The significant fractions of intermetallics phases were found to form at the Ti/Ni powder interface during the heating to the ignition temperature and seemed to influence the relative fraction of phases in the final products. As the heating rate to the ignition temperature was increased, the combustion temperature and the fraction of NiTi in the final reaction products were increased. The synthesis reaction under 70 MPa compressive pressure yielded a reaction product with 98% theoretical density.

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Fabrication of AlN Whiskes by Self-propagating High-temperature Synthesis (자전 고온 합성법에 의한 질화 알루미늄 휘스커의 제조)

  • 이경재;장영섭;김석윤;김용석
    • Journal of the Korean Ceramic Society
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    • v.32 no.8
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    • pp.931-937
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    • 1995
  • AlN powder and whiskers were synthesized by direct nitridation of aluminum powder in pure nitrogen atmosphere. The nitridation reaction of aluminum powder was initiated by heating the sample to the ignition temperature and the reaction was finished in less than 3 minutes. AlN whisker-shaped morphology was observed predominantly when the sample was heated above 90$0^{\circ}C$.

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Synthesis Characteristics of ZnO Powder from Precursors Composed of Nitrate-Citrate Compounds (Nitrate-Citrate 혼합 전구체로부터 ZnO 입자의 합성반응 특성)

  • Yang, Si Woo;Lee, Seung Ho;Lim, Dae Ho;Yoo, Dong Jun;Kang, Yong
    • Korean Chemical Engineering Research
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    • v.54 no.3
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    • pp.299-304
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    • 2016
  • Characteristics of self-propagating reaction for the preparation of ZnO powder from precursors composed of nitrate and citrate compounds were examined. The ratio of C/N was maintained in range of 0.7~0.8 to initiate the self-propagating reaction between the reducing citrate and oxidizing nitrate groups. The samples were decomposed thermally by using TGA. The sudden decomposition occurred in the range of X > 0.5 in a very short time with a very sharp decrease of mass, indicating that the self-propagating reaction would occur. Friedman, Ozawa-Flynn-Wall and Vyazovkin methods were employed to predict the activation energy, reaction order and frequency factor of the reaction rate in the rate determining step of X < 0.5 range. The activation energy increased with increasing fractional conversion in the range of 46~130 (kJ/min). The reaction order decreased in the range of 2.9~0.9, while the frequency factor increased in the range of 85~278 ($min^{-1}$), respectively, with increasing the rate of temperature increase.

Neutron Diffraction Study of Powders Prepared by Self-propagating High Temperature Synthesis

  • Park, Yong;Kim, Y S.;Y. D. Hahn;S. H. Shim;Lee, J. S.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2000.11a
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    • pp.11-12
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    • 2000
  • Non-stoichiometric ceramics of $Ni_{x}ZnO_{1-x}Fe_{2}O_{4}$ were prepared by self-propagating high temperature synthesis reaction with various processing conditions and their stoichometric numbers were determined by neutron diffraction. The neutron diffraction patterns were measured at room temperature using monochromatic neutrons with a wave length of 0.18339 nm from a Ge(331) mocochromator at a 90 degree take off angle. The Rietveld refinement of each pattern converged to good agreement (x2=1.88-2.24). The neutron diffraction analysis revealed the final stoichiometries of the ferrites were $Ni_{0.38}Zn_{0.62}Fe_{2}O_{4}$ and $Ni_{0.33}Zn_{0.67}Fe_{2}O_{4]$, respectively. This supports that final stoichiometric number of the self-propagating high temperature synthesis product can be controlled by the processing parameters during the combustion reaction.

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Fabrication Process of Laminated Composites by Self-propagating High-temperature Synthesis Reaction (자전고온반응에 의한 적층복합재료의 제조공정)

  • 김희연;정동석;홍순형
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.05a
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    • pp.155-158
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    • 2002
  • Fabrication process of metal/intermetallic laminated composites by using self-propagating high temperature synthesis(SHS) reactions between Ni and Al elemental metal foils have been investigated. Al foils were sandwiched between Ni foils and heated in a vacuum hot press to the melting point of aluminium. SHS reaction kinetics was thermodynamically analyzed through the final volume fraction of the unreacted Al related with the initial thickness ratio of Ni:Al and diffusion bonding stage before SHS reaction. Thermal aging of laminated composites resulted in the formation of functionally gradient series of intermetallic phases. Microstructure showed that the main phases of intermetallics were NiAl and $Ni_3Al$ having higher strength at room and high temperatures. The volume fractions of intermetallic phases were measured as 82.4, 58.6, 38.4% in 1:1, 2:1, 4:1 initial thickness ratio of Ni:Al.

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Forming Mechanism of TiC Hollow Fibers during Self-Propagating High Temperature Synthesis (자전연소합성 반응중 속빈 TiC 섬유의 형성 기구)

  • 윤존도;방환철
    • Journal of the Korean Ceramic Society
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    • v.37 no.4
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    • pp.332-337
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    • 2000
  • Forming mechanism of fibrous TiC during self-propagating high temperature synthetic reaction was analyzed and suggested. It was revealed that critical temperature for the stable fiber formation was not the melting point of TiC, but the eutectic reaction temperature of TiC and C. Minimum amount of TiC diluent addition required to form fibers was calculated to be 25.6%, which was consistent with the experimental result. Synthesized fibers were found hollow tube-like. The morphology was explained by the diffusion rates of C and Ti in TiC, and by the molar volume chnage of C during the reaction. Expanding shell model was suggested for the hollow fiber formation mechanism.

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Finite Element Analysis of the Self-propagating High-temperature Synthesis Of $MoSi_2$ ($MoSi_2$ 자전 고온 반응 합성의 유한 요소 해석)

  • 채수원;손창현;김용석
    • Journal of the Korean Society for Precision Engineering
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    • v.15 no.12
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    • pp.120-127
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    • 1998
  • The finite element method has been used to model and analyze the heat transfer phenomena during manufacturing process of $MoSi_2$ by SHS(Self-propagating High-temperature Synthesis). For this purpose nonlinear transient heat transfer analyses by using ANSYS have been performed to estimate the temperature distributions and the peak temperature in the test specimen. The effects of manufacturing process parameters such as pre-heating temperatures, the velocity of reaction zone have been investigated. The results of the analysis have been compared with the experimental results.

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A Study on Self-Propagating High-Temperature Synthesis of TiC-Ni-Mo Based Cermet (SHS공정에 의한 TiC-Ni-Mo 분말 합성 및 소결체 제조)

  • 송인혁;전재호;한유동
    • Journal of the Korean Ceramic Society
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    • v.35 no.7
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    • pp.749-756
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    • 1998
  • TiC-Ni and TiC-Ni-Mo cermet powders were produced by Self-propagating High temperature Synthesis (SHS) process. The cooling rate of synthesized powders were controlled by using the V-shaped copper jig and the carbide size decreased with increasing the cooling rate I. e decreasing the width of copper jig Round shape carbide particles were produced after SHS reaction in TiC-Ni as well as TiC-Ni-Mo powders. Local segregation of Mo rich phases was observed in SHS powder of TiC-Ni-Mo and the uneven dis-triobution of Mo promoted the faster growth rate of carbide particles during sintering compared to the same composition specimen with commercial TiC powder. Howogeneous microstructure of TiC-Ni-Mo cermet was obtained when the elemental Mo powder was mixed with the SHS powder of TiC-Ni.

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