• Title/Summary/Keyword: self-propagating high-temperature synthesis(SHS)

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Computer Simulation and Verification of Adiabatic Temperature and Apparent Activity Energy of the NiO/Al Aluminothermic System

  • Song, Yuepeng;Zhu, Yanmin;Gao, Dongsheng;Guo, Jing;Kim, Hyoung Seop
    • 한국분말재료학회지
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    • 제20권5호
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    • pp.332-337
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    • 2013
  • Recently, self-propagating high-temperature synthesis (SHS), related to metallic and ceramic powder interactions, has attracted huge interest from more and more researchers, because it can provide an attractive, energy-efficient approach to the synthesis of simple and complex materials. The adiabatic temperature $T_{ad}$ and apparent activation energy analysis of different thermit systems plays an important role in thermodynamic studies on combustion synthesis. After establishing and verifying a mathematic calculation program for predicting adiabatic temperatures, based on the thermodynamic theory of combustion synthesis systems, the adiabatic temperatures of the NiO/Al aluminothermic system during self-propagating high-temperature synthesis were investigated. The effect of a diluting agent additive fraction on combustion velocity was studied. According to the simulation and experimental results, the apparent activation energy was estimated using the Arrhenius diagram of $ln(v/T_{ad}){\sim}/T_{ad}$ based on the combustion equation given by Merzhanov et al. When the temperature exceeds the boiling point of aluminum (2,790 K), the apparent activation energy of the NiO/Al aluminothermic system is $64{\pm}14$ kJ/mol. In contrast, below 2,790 K, the apparent activation energy is $189{\pm}15$ kJ/mol. The process of combustion contributed to the mass-transference of aluminum reactant of the burning compacts. The reliability of the simulation results was experimentally verified.

기계적 합금화과정에서의 in situ 열분석에 의한 Ti-25.0~37.5at%Si 분말의 합성거동 (Synthesis Behavior of Ti-25.0~37.5at%Si Powders by In situ Thermal Analysis during Mechanical Alloying)

  • 변창섭;현창용;김동관
    • 한국재료학회지
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    • 제14권5호
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    • pp.305-309
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    • 2004
  • Mechanical alloying (MA) of Ti-25.0~37.5at%Si powders was carried out in a high-energy ball mill, and in situ thermal analysis was also made during MA. In order to classify the synthesis behavior of the powders with respect to at%Si, the synthesis behavior during MA was investigated by in situ thermal analysis and X-ray diffraction (XRD). In situ thermal analysis curves and XRD patterns of Ti-25.0~26.1at%Si powders showed that there were no peaks during MA, indicating $Ti_{5}$ $Si_3$ was synthesised by a slow reaction of solid state diffusion. Those of Ti-27.1~37.5at%Si powders, however, showed that there were exothermic peaks during MA, indicating $_Ti{5}$ $Si_3$ and$ Ti_3$Si phase formation by a rapid exothermic reaction of self-propagating high-temperature synthesis (SHS). For Ti-27.1~37.5at%Si powders, the critical milling times for SHS decreased from 38.1 to 18.5 min and the temperature rise, ΔT (= peak temperature - onset temperature) increased form $19.5^{\circ}C$ to $26.7^{\circ}C$ as at%Si increased. The critical composition of Si for SHS reaction was found to be 27.1at% and the critical value of the negative heat of formation of Ti-27.1at%Si to be -1.32 kJ/g.

기계적 합금화과정에서의 in situ 열분석에 의한 Ti-50.0~66.7at%Si 분말의 합성거동 (Synthesis Behavior of Ti-50.0 ~ 66.7at%Si Powders by In situ Thermal Analysis during Mechanical Alloying)

  • 변창섭;이상호;이원희;현창용;김동관
    • 한국재료학회지
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    • 제14권5호
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    • pp.310-314
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    • 2004
  • Mechanical alloying (MA) of Ti-50.0~66.7at%Si powders was carried out in a high-energy ball mill, and in situ thermal analysis was also made during MA. In order to classify the synthesis behavior of the powders with respect to at%Si, the synthesis behavior during MA was investigated by in situ thermal analysis and X-ray diffraction (XRD). In situ thermal analysis curves and XRD patterns of Ti-50.0~59.6at%Si powders showed that there were exothermic peaks during MA, indicating TiSi, $TiS_2$, and $Ti_{5}$ $Si_4$ phase formation by a rapid exothermic reaction of self-propagating high-temperature synthesis (SHS). Those of Ti-59.8~66.7 at%Si powders, however, showed that there were no peaks during MA, indicating any Ti silicide was not synthesised until MA 240 min. For Ti-50.0~59.6at%Si powders, the critical milling times for SHS increased from 34.5 min to 89.5 min and the temperature rise, $\Delta$T (=peak temperature-onset temperature) decreased form $26.2^{\circ}C$ to $17.1^{\circ}C$ as at%Si increased. The critical composition of Si for SHS reaction was found to be 59.6at% and the critical value of the negative heat of formation of Ti-59.6at%Si to be -1.48 kJ/g.

이규화몰리브덴 고온발열체의 고온산화거동 (High-Temperature Oxidation of MoSi2 Heating Elements)

  • 서창열;장대가;심건주;조덕호;김원백
    • 한국재료학회지
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    • 제6권1호
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    • pp.57-66
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    • 1996
  • MoSi2 heating elements were fabricated by sintering of MoSi2 powders which were synthesized through SHS(Self-propagating high-temperature synthesis). Their high-temperature oxidation behavior in air through SHS(Self-propagating high-temperature synthesis). Their high-temperature oxidation behavior on air at 1000-1600$^{\circ}C$ was investigated through a high-temperature X-ray diffractomer and isothermal heating in a muffle furnace. The thermal expansion of MoSi2 and SiO2 was studied by measuring their lattice parameters on heating. The linear expansion coeffcient of MoSi2 along c-axis was about 1.5 times larger than that along a-axis showing a strong thermal anisotropy. Few $\mu\textrm{m}$-thick Mo5Si3 layer was found beneath SiO2 layer suggesting that The major reaction products would be SiO2 and Mo5Si3. The Si-rich bentonite resulted in the faster growth of MoSi2 grains probably by enhancing the mass transport when they are melted during high-temperature oxidation.

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고온 자전 연소합성법과 기계적 미분에 의한 준나노 크기의 Ba-Zn Ferrite 분말의 제조 (Preparation of Quasi-nano-sized of Ba-Zn Ferrites Powders by Self-Propagating High Temperature Synthesis and Mechanical Milling)

  • 최경숙;이종재;김혁돈;최용;이상헌
    • 전기학회논문지
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    • 제57권4호
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    • pp.625-628
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    • 2008
  • Ba-Zn ferrite powders for electromagnetic insulator were synthesized by self-propagating high-temperature synthesis(SHS) with a reaction of $xBaO_2+(1-x)ZnO+0.5Fe_2O_3+Fe{\rightarrow}Ba_xZn_{1-x}Fe_2O_4$. In this study, phase indentification of SHS products was carried out by using x-ray diffractometry and quasi-nano sized Ba-Zn powders were prepared by a pulverizing process. SHS mechanism was studied by thermodynamical analysis about oxidation reaction among $BaO_2,\;ZnO,\;Fe_2O_3$, and Fe. As oxygen pressure increases from 0.25 MPa to 1.0 MPa, the SHS reactions occur well and make clearly the SHS products. X-ray analysis shows that final SHS products formed with the ratio of $BaO_2/ZnO$ of 0.25, 1.0 and 4.0, are mainly $Ba_xZn_{1-x}Fe_2O_4$. Based on thermodynamical evaluation, the heat of formation increases in the order of $ZnFe_2O_4,\;BaFe_2O_4$, and $Ba_xZn_{1-x}Fe_2O_4$. This supports that $Ba_xZn_{1-x}Fe_2O_4$ phase is predominately formed during SHS reaction. The SHS reactions to form $Ba_xZn_{1-x}Fe_2O_4$ depends on oxygen partial pressure, and the heat of formation during the SHS reaction. The SHS reactions tends to occur well with increasing the oxygen partial pressure and BaO2/ZnO ratio in the reactants This means that the SHS reaction for the formation of Ba-Zn ferrite includes the reduction of BaO2/ZnO and the oxidation of Fe. $Ba_xZn_{1-x}Fe_2O_4$ powders after pulverizing is agglomeratedwith a size of about $50{\mu}m$, in which quasi-nano sized particles with about 300nm are present.

SHS법에 의한 $Ti_xZr_{1-x}C$ 고용체의 합성 및 특성 연구 (A Study on Synthesis and Characterization of $Ti_xZr_{1-x}C$ Solid-Solution by Self-propagation High Temperature Synthesis Method)

  • 이형복;오유근;이성민
    • 한국세라믹학회지
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    • 제34권7호
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    • pp.731-737
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    • 1997
  • TixZr1-xC(0$0^{\circ}C$, 5.1 mm/sec respectively. The relative density, three point flexural strength, and the hardness of composites, which was sintered at 190$0^{\circ}C$ for 60 min by using hot-pressing under a pressure of 30 MPa, were 99%, 525 MPa and 24 GPa respectively.

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