• Title/Summary/Keyword: Gas phase reaction

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Gas Phase Analysis of the Diamond CVD Reaction by Hot Filament Method (열필라멘트법에 의한 다이아몬드 CVD반응의 기상 조성 분석)

  • 서문규
    • Journal of the Korean Ceramic Society
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    • v.35 no.11
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    • pp.1233-1239
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    • 1998
  • Gas phase compositions of the hot filament-assisted diamond CVD reaction were analyzed by on-line quadrupole mass analysis(QMA) technique. D2 isotope experiments showed that methance molecules were decomposed into atomic state and then recombined in to acetylene during transport the probe line. Although acetylene or ethylene was supplied instead of methane similar gas compositions were obtained when filament temperature was above 1500$^{\circ}C$ Therefore this system could be assumed near thermal equilibrium state. Filament temperature and reaction pressure variation experiments exhibited the same tendency between acetylene concentration and diamond growth rate and these results implied that acetylene molecule played the role of the reactive species in the diamond CVD reaction.

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Fabrication of Silicon Nitride Ceramics by Gel-Casting and Microwave Gas Phase Reaction Sintering(II) : Microwave Nitridation of Silicon and Microwave Sintering of Silicon Nitride (Gel-Casting 및 마이크로파 기상반응소결에 의한 질화규소 세라믹 제조에 대한 연구(II) : 마이크로파에 의한 실리콘의 질화반응 및 질화규소의 소결)

  • Bai, Kang;Woo, Sang-Kuk;Han, In-Sub;Seo, Doo-Won
    • Journal of the Korean Ceramic Society
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    • v.48 no.5
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    • pp.354-359
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    • 2011
  • Silicon nitride ceramics were prepared by microwave gas phase reaction sintering. By this method higher density specimens were obtained for short time and at low temperature, compared than ones by conventional pressureless sintering, even though sintering behaviors showed same trend, the relative density of sintered body inverse-exponentially increases with sintering temperature and/or holding time. And grain size of ${\beta}$-phase of the microwave sintered body is bigger than one of the conventional pressureless sintered one. Also they showed good bending strengths and thermal shock resistances.

Effect of pH on the Preparation of Spherical Fine Zirconia Powders Using Gas-Liquid Phase Reaction (기액반응법을 이용한 구형 지르코니아 미분체 제조시 pH의 영향)

  • 김창현;이대희;이창섭;이병교
    • Journal of the Korean Ceramic Society
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    • v.34 no.10
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    • pp.1009-1014
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    • 1997
  • Ammonia gas was blown into the solution of zirconium ion to induce precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH. The influence of pH on the phase and particle size of precipitate and calcined powders has been investigated. At pH 4.5 of zirconium solution, maximum yield of 98.7% was obtained. Above pH 4.5, there was no more increase of yield. Above pH 5.5, large aggregates consisting of primary particles were observed in precipitate and calcined powders. At pH 4.5, almost aggregate-free fine spherical zirconia powders were obtained.

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Day and Night Distribution of Gas and Particle Phases Polycyclic Aromatic Hydrocarbons (PAHs) Concentrations in the Atmosphere of Seoul (서울 대기 중 기체 및 입자상 다환방향족탄화수소 (PAHs)의 낮·밤 분포 특성)

  • Lim, Hyung Bae;Kim, Yong Pyo;Lee, Ji Yi
    • Journal of Korean Society for Atmospheric Environment
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    • v.32 no.4
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    • pp.408-421
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    • 2016
  • Day and night sampling for gas and particle phases PAHs were carried out in Seoul to characterize gas and particle phases PAHs concentrations in day and night times. There was no significant difference between day and night time for particle phase PAHs concentrations and phase distribution of PAHs, while, gas phase PAHs concentrations in daytime were about 1/2 of nighttime concentrations in both summer and winter due to photochemical reaction of gas phase PAHs during daytime. A high fraction of cancer risk for PAHs was attributed to particle phase PAHs and the excess cancer risk in winter was higher than in summer. The excess cancer risk level of total(gas+particle) PAHs in summer was partially observed when both gas and particle phase PAHs concentrations were considered as risk assessment. Based on the diagnostic ratios and factor analysis of PAHs concentrations, combustion(coal and natural gas) and vehicular emission might be the most significant contributors of PAHs and major factors for determining of PAHs concentration were different between day and night times.

Ignition of a Vertically Positioned Fuel Plate by Thermal Radiation (열복사에 의한 수직연료면의 점화현상 해석)

  • 한조영;백승욱
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2353-2364
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    • 1995
  • The ignition phenomena of a solid fuel plate of polymethyl-methacrylate(PMMA), which is vertically positioned and exposed to a thermal radiation source, is numerically studied here. A two-dimensional transient model includes such various aspects as thermal decomposition of PMMA, gas phase radiation absorption, gas phase chemical reaction and air entrainment by natural convection. Whereas the previous studies considers the problem approximately in a one-dimensional form by neglecting the natural convection, the present model takes account of the two-dimensional effect of radiation and air entrainment. The inert heating of the solid fuel is also taken into consideration. Radiative heat transfer is incorporated by th Discrete Ordinates Method(DOM) with the absorption coefficient evaluated using gas species concentration. The thermal history of the solid fuel plate shows a good agreement compared with experimental results. Despite of induced natural convective flow that induces heat loss from the fuel surface, the locally absorbed radiant energy, which is converted to the internal energy, is found to play an important role in the onset of gas phase ignition. The ignition is considered to occur when the rate of variation of gas phase reaction rate reaches its maximum value. Once the ignition takes place, the flame propagates downward.

Prediction of Thermal Expansion Coefficients using the Second Phase Fraction and Void of Al-AlN Composites Manufactured by Gas Reaction Method (가스반응법으로 제작된 Al-ALN 복합재의 제 2상 분율과 기공에 따른 열팽창계수 예측)

  • Yoon, Juil
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.18 no.4
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    • pp.41-47
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    • 2019
  • The advent of highly integrated, high-power electronics requires low a coefficient of thermal expansion performance to prevent delamination between the heat dissipation material and substrate. This paper reports a preliminary study on the manufacturing technology of gas reaction control composite material, focusing on the prediction of the thermal expansion coefficients of Al-AlN composite materials. We obtained numerical equivalent property values by using finite element analysis and compared the values with theoretical formulas. Al-AlN should become the optimal composite material when the proportion of the reinforcing phase is approximately 0.45.

Metal-Organic Vapor Phase Epitaxy IV. MOVPE and ALE Reaction Mechanisms (MOVPE 단결정층 성장법 IV. MOVPE 및 ALE 반응경로)

  • 정원국
    • Journal of the Korean institute of surface engineering
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    • v.24 no.1
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    • pp.1-17
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    • 1991
  • Understanding of the detailed reaction mechanisms during MOVPE and ALE is essential to further improve the properties of the grown crystals and the controllability of the growth parameters. The unified models for the detailed reaction paths are not available at this stage. The study, however, has been advanced to the extent that consensus on some of the reaction paths can be drawn from the scattered data. Metalakyls such as TMGa and TMIn seem to nearly fully decompose in the gas phase through homogeneous reaction at the typical MOVPE growth temperature. Hydrides such as AsH3 and PH3, on the contrary. seem to decompose heterogeneously onthe substrate surfaces as well as homogeneously in the gas phase. However, at lower temperatures, where ALE crystals are typically grown, the growth process is strongly dependent on the surface reactions. It seems that steric hindrance effects which the radicals reaching the substrate exhibit on the surface the growth rate a function of the metalalkyle supply durations. In addition, dydrogens released from hydrides seem to play an essential role in removing carbons leberated from the metalalkyls. High growth temperatures also seem to be effective in desorbing carbons from surface. The understanding of the reaction mechanisms was possible though diverse appraaches utilizing many ex-situ and in-situ diagnostic techniques and genuine experimental designs. It is the purpose of this paper to review and discuss many of these efforts and to draw some possible conclusions from them.

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Metal-Organic Vapor Phase Epitaxy IV. MOVPE and ALE Reaction Mechanisms (MOVPE 단결정층 성장법 IV. MOVPE 및 ALE 반응경로)

  • 정원국
    • Journal of the Korean institute of surface engineering
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    • v.24 no.1
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    • pp.1.1-1.1
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    • 1991
  • Understanding of the detailed reaction mechanisms during MOVPE and ALE is essential to further improve the properties of the grown crystals and the controllability of the growth parameters. The unified models for the detailed reaction paths are not available at this stage. The study, however, has been advanced to the extent that consensus on some of the reaction paths can be drawn from the scattered data. Metalakyls such as TMGa and TMIn seem to nearly fully decompose in the gas phase through homogeneous reaction at the typical MOVPE growth temperature. Hydrides such as AsH3 and PH3, on the contrary. seem to decompose heterogeneously onthe substrate surfaces as well as homogeneously in the gas phase. However, at lower temperatures, where ALE crystals are typically grown, the growth process is strongly dependent on the surface reactions. It seems that steric hindrance effects which the radicals reaching the substrate exhibit on the surface the growth rate a function of the metalalkyle supply durations. In addition, dydrogens released from hydrides seem to play an essential role in removing carbons leberated from the metalalkyls. High growth temperatures also seem to be effective in desorbing carbons from surface. The understanding of the reaction mechanisms was possible though diverse appraaches utilizing many ex-situ and in-situ diagnostic techniques and genuine experimental designs. It is the purpose of this paper to review and discuss many of these efforts and to draw some possible conclusions from them.

Theoretical Studies on the Addition Reactions of Ketene with NH3 in the Gas Phase and in Non-Aqueous Solutions

  • Kim, Chang-Kon;Lee, Kyung A;Chen, Junxian;Lee, Hai-Whang;Lee, Bon-Su;Kim, Chan-Kyung
    • Bulletin of the Korean Chemical Society
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    • v.29 no.7
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    • pp.1335-1343
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    • 2008
  • Theoretical studies on the un-catalyzed and catalyzed aminations of ketene with $NH_3$ and $(NH_3)_2$, respectively, were studied using MP2 and hybrid density functional theory of B3LYP at the 6-31+G(d,p) and 6- 311+G(3df,2p) basis sets in the gas phase and in benzene and acetonitrile solvents. In the gas phase reaction, the un-catalyzed mechanism was the same as those previously reported by others. The catalyzed mechanism, however, was more complicated than expected requiring three transition states for the complete description of the C=O addition pathways. In the un-catalyzed amination, rate determining step was the breakdown of enol amide but in the catalyzed reaction, it was changed to the formation of enol amide, which was contradictory to the previous findings. Starting from the gas-phase structures, all structures were re-optimized using the CPCM method in solvent medium. In a high dielectric medium, acetonitrile, a zwitterions formed from the reaction of $CH_2$=C=O with $(NH_3)_2$, I(d), exists as a genuine minimum but other zwitterions, I(m) in acetonitrile and I(d) in benzene become unstable when ZPE corrected energies are used. Structural and energetic changes induced by solvation were considered in detail. Lowering of the activation energy by introducing additional $NH_3$ molecule amounted to ca. −20 $\sim$ −25 kcal/mol, which made catalyzed reaction more facile than un-catalyzed one.

HBr Formation from the Reaction between Gas-phase Bromine Atom and Vibrationally Excited Chemisorbed Hydrogen Atoms on a Si(001)-(2 X1) Surface

  • Ree, J.;Yoon, S.H.;Park, K.G.;Kim, Y.H.
    • Bulletin of the Korean Chemical Society
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    • v.25 no.8
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    • pp.1217-1224
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    • 2004
  • We have calculated the probability of HBr formation and energy disposal of the reaction exothermicity in HBr produced from the reaction of gas-phase bromine with highly covered chemisorbed hydrogen atoms on a Si (001)-(2 ${\times}$1) surface. The reaction probability is about 0.20 at gas temperature 1500 K and surface temperature 300 K. Raising the initial vibrational state of the adsorbate(H)-surface(Si) bond from the ground to v = 1, 2 and 3 states causes the vibrational, translational and rotational energies of the product HBr to increase equally. However, the vibrational and translational motions of product HBr share most of the reaction energy. Vibrational population of the HBr molecules produced from the ground state adsorbate-surface bond ($v_{HSi}$ =0) follows the Boltzmann distribution, but it deviates seriously from the Boltzmann distribution when the initial vibrational energy of the adsorbate-surface bond increases. When the vibration of the adsorbate-surface bond is in the ground state, the amount of energy dissipated into the surface is negative, while it becomes positive as vHSi increases. The energy distributions among the various modes weakly depends on surface temperature in the range of 0-600 K, regardless of the initial vibrational state of H(ad)-Si(s) bond.