• Title/Summary/Keyword: Gas phase reaction

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Synthesis of Nano-sized Tungsten Carbide Powders by Vapor Phase Reaction of Tungsten Ethoxide (텅스텐 에톡사이드의 기상 반응을 이용한 초미립 WC 분말의 합성)

  • 가미다;하국현;김병기
    • Journal of Powder Materials
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    • v.10 no.1
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    • pp.1-5
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    • 2003
  • Nano-sized WC powders were synthesized by vapor phase reaction using the precusor of tungsten ethoxide under helium and hydrogen atmosphere. The phases of the powder were varied with reaction Bone and gas flow rate. The powder size was about 30nm in diameter, and the tungsten carbide powder was coated by carbon layer. The synthesis of nano-sized WC powders was promoted as the hydrogen gas flow rate became higher. Inversely, tungsten oxide was formed by increasing the flow rate of helium gas. The synthesized powders were analyzed by XRD, FE-SEM, carbon analyzer etc.

The Effect of H2 Flow Rate and TMS Concentration on Synthesizing Ultrafine $\beta$-SiC Powder by Vapor Phase Reaction (기상반응에 의한 $\beta$-SiC 초미분말 합성시 수소 가스유량과 TMS 농도의 영향)

  • 유용호;어경훈;소명기
    • Journal of the Korean Ceramic Society
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    • v.36 no.8
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    • pp.853-858
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    • 1999
  • To investigate the effect of H2 flow rate and TMS[Si(CH3)4] concentration on synthesizing ultrafine ${\beta}$-SiC powder by vapor phase reaction the experiment was performed at 1100$^{\circ}C$ of the reaction temperature under the condition of 200-2000 cc/min of H2 gas flow rate and 1-10% of TMS concentration respectively. The shape of ${\beta}$-SiC particles synthesized was spherical and the size of particles decreased and the distribution of particles was more uniform with increasing H2 gas flow rate. In this case Si powders were coexisted with ${\beta}$-SiC Pure and ultrafine ${\beta}$-SiC powders without Si were obtained under the condition of above 2% of TMS concentration and below 1500 cc/min of H2 gas flow rate.

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DFT/B3LYP Study of the Substituent Effects on the Reaction Enthalpies of the Antioxidant Mechanisms of Magnolol Derivatives in the Gas-Phase and Water

  • Najafi, Meysam;Najafi, Mohammad;Najafi, Houshang
    • Bulletin of the Korean Chemical Society
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    • v.33 no.11
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    • pp.3607-3617
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    • 2012
  • In this paper, the study of various ortho- and meta-substituted Magnolol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET-PT and SPLET for substituted Magnolols have been calculated using DFT/B3LYP method in gas-phase and water. Calculated results show that electron-withdrawing substituents increase the bond dissociation enthalpy (BDE), ionization potential (IP) and oxidation/reduction enthalpy (O/RE), while electron-donating ones cause a rise in the proton dissociation enthalpy (PDE) and proton affinity (PA). In ortho- position, substituents show larger effect on reaction enthalpies than in meta-position. In comparison to gas-phase, water attenuates the substituent effect on all reaction enthalpies. In gas-phase, BDEs are lower than PAs and IPs, i.e. HAT represents the thermodynamically preferred pathway. On the other hand, SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be successfully correlated with Hammett constants (${\sigma}_m$) of the substituted Magnolols. Furthermore, calculated IP and PA values for substituted Magnolols show linear dependence on the energy of the highest occupied molecular orbital ($E_{HOMO}$).

Characterization of Synthesized WS$_2$ Solid Lubricant (합성 WS$_2$ 고체윤활제의 특성 분석)

  • 신동우;윤대현;최인혁;김인섭
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1997.10a
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    • pp.211-216
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    • 1997
  • The tungsten disulfide (WS$_2$) solid lubricant was synthesized by two different reaction processes, and the chemical and physical characteristics of synthesized WS$_2$ powder were analyzed in terms of the average particle size, morphology, crystalline phase. The solid WO$_3$ powder with the average size of 0.2 $\mu$m was reacted with CS$_2$ gas flowed with N$_2$ or 96% N$_2$ + 4% H$_2$ forming gas for 36 h and 24 h at 900$\circ$C respectively. In the case of vapour phase transport method, the 3.5 wt% iodine was added as a vapour transport reagent into the composition of tungsten and sulfur powders maintaining a constant molar ratio of W : S = 1 : 2.2. The mixture was then heat treated at 850$\circ$C for 2 weeks in vacuum The reaction product obtained showed the average size of 12 $\mu$m and the hexagonal plate shape of typical solid lubricant with 2H-WS$_2$ crystalline phase.

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Reaction of Gae-Phase Atomic Hydrogen with Chemisorbed Hydrogen Atoms on an Iron Surface

  • Kim, M. S.;Ree, J.
    • Bulletin of the Korean Chemical Society
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    • v.18 no.9
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    • pp.985-994
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    • 1997
  • The reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on Fe(110) surface is studied by use of classical trajectory procedures. Flow of energy between the reaction zone and bulk solid phase has been treated in the generalized Langevin equation approach. A London-Eyring-Polanyi-Sato energy surface is used for the reaction zone interaction. Most reactive events are found to occur in strong single-impact collisions on a subpicosecond scale via the Eley-Rideal mechanism. The extent of reaction is large and a major fraction of the available energy goes into the vibrational excitation of H2, exhibiting a vibrational population inversion. Dissipation of reaction energy to the heat bath can be adequately described using a seven-atom chain with the chain end bound to the rest of solid. The extent of reaction is not sensitive to the variation of surface temperature in the range of Ts=0-300 K in the fixed gas temperature, but it shows a minimum near 1000 K over the Tg=300-2500 K.

Oxidation of Ethanol in the Gas Phase with Alcohol Oxidase and Alcohol Dehydrogenase (Alcohol Oxidase와 Alcohol Dehydrogenase를 이용한 기상에서의 Ethanol의 산화반응)

  • 박현규;장호남김동옥
    • KSBB Journal
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    • v.9 no.3
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    • pp.239-245
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    • 1994
  • The effects of reaction temperature and the level of hydration(water activity) were studied for gas phase reactions of alcohol oxidase and alcohol dehydrogenase immobilized on DEAE-cellulose and controlled pore glass(CPG). Optimum reaction temperature zone of gas phase reaction was similar to that of aqueous phase reaction. The activity of alcohol oxidase increased dramatically and the stability decreased when the water activity was increased from 0.3 to 0.8. The apparent activation energies of the gas phase reaction decreased approaching the values obtained in the aqueous phase reaction as the water activity increased. In the both cases of alcohol oxidase and alcohol dehydrogenase, the rate constants of the gas phase reaction were lower than those of aqueous phase reaction by two orders of magnitude and these results could be correlated to the vapor-liquid equilibrium data of the substrate, ethanol.

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Synthesis and Shape Control of Calcium Carbonate Fine Powders by Liquid-Gas Reaction Method (액상-기상 반응법에 의한 탄산칼슘 미분말의 합성과 형상제어)

  • 민경소;최상흘
    • Journal of the Korean Ceramic Society
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    • v.28 no.3
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    • pp.205-214
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    • 1991
  • Calcium carbonate fine powders were synthesized by blowing CO2 gas in CaO or Ca(OH)2 suspension, and the shapes of powders obtained were examined for each synthetic condition. When water was used as a solvent, ultrafine calcite powders with the average size of∼0.03$\mu\textrm{m}$ were obtained. When synthesized using methanol as a solvent, amorphous phase and spherical vaterite phase were obtained by suction filtering and non-filtering, respectively. Reaction did not occured in ethanol medium, but spherical vaterite phase was obtained by adding ethylene glycol in ethanol.

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Interaction of Gas-phase Atomic Hydrogen with Chemisorbed Oxygen Atoms on a Silicon Surface

  • Lee, Sang-Kwon;Ree, Jong-Baik;Kim, Yoo-Hang;Shin, Hyung-Kyu
    • Bulletin of the Korean Chemical Society
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    • v.32 no.5
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    • pp.1527-1533
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    • 2011
  • The reaction of gas-phase atomic hydrogen with oxygen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. We have calculated the probability of the OH formation and energy deposit of the reaction exothermicity in the newly formed OH in the gas-surface reaction H(g) + O(ad)/Si${\rightarrow}$ OH(g) + Si. All reactive events occur in a single impact collision on a subpicosecond scale, following the Eley-Rideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability is dependent upon the gas temperature and shows the maximum near 1000 K, but it is essentially independent of the surface temperature. The reaction probability is also independent upon the initial excitation of the O-Si vibration. The reaction energy available for the product state is carried away by the desorbing OH in its translational and vibrational motions. When the initial excitation of the O-Si vibration increases, translational and vibrational energies of OH rise accordingly, while the energy shared by rotational motion varies only slightly. Flow of energy between the reaction zone and the solid has been incorporated in trajectory calculations, but the amount of energy propagated into the solid is only a few percent of the available energy released in the OH formation.

Density Functional Theory Study of Competitive Reaction Pathways of Ti+ with Fluorinated Acetone in the Gas Phase

  • Hong, Ki-Ryong;Kim, Tae-Kyu
    • Journal of the Korean Chemical Society
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    • v.56 no.1
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    • pp.14-19
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    • 2012
  • We investigate the doublet and quartet potential energy surfaces associated with the gas-phase reaction between $Ti^+$ and $CF_3COCH_3$ for two plausible reaction pathways, $TiF_2^+$ and $TiO^+$ formation pathways by using the density functional theory (DFT) method. The molecular structures of intermediates and transition states involved in these reaction pathways are optimized at the DFT level by using the PBE0 functional. All transition states are identified by using the intrinsic reaction coordinate (IRC) method, and the resulting reaction coordinates describe how $Ti^+$ activates $CF_3COCH_3$ and produces $TiF_2^+$ and $TiO^+$ as products. On the basis of presented results, we propose the most favorable reaction pathway in the reaction between $Ti^+$ and $CF_3COCH_3$.

Synthesis and Characterization of Ultrafine $\beta$-SiC Powder by Vapor Phase Reaction (기상합성법에 의한 $\beta$-SiC 초미분말 합성 및 특성)

  • 어경훈;이승호;유용호;소명기
    • Journal of the Korean Ceramic Society
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    • v.35 no.11
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    • pp.1190-1196
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    • 1998
  • Ultrafine ${\beta}$-SiC powders were synthesized by the vapor phase reaction of TMS[Si(CH3)4] in hydrogen The reaction temperature and TMS concentration were varied from 1000 to 1400$^{\circ}C$ and from 1 to 10% respectively. The average particle size and phase of the powders were analyzed by TEM and XRD. Ultrafine ${\beta}$-SiC powders were synthesized above 1000$^{\circ}C$ and the crystallinity of the powders increased with increasing reaction temperature. Shape of the particles were spherical and had average size of about 20 nm which showed no difference as the reaction temperature and TMS concentration increased. From the FT-IR analysis the absorption bands of Si-C of the powders shifted to higher wavenumber as the reaction temperature increased,. Under the condition of total gas flow above 1500cc/min ${\beta}$-SiC and poly-Si powders were obtained simultaneously. The Si-O bond intensity was increased under the condition of total gas flow rate above 1000cc/min which might be due to oxidation formed on poly-Si.

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