• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.1
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• pp.48-53
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• 2001

The crystal structure of ZnS fabricated by gas-liquid phase reaction was refined by the Rietveld program using X-ray diffraction data. The R-weighted pattern (R$\sub$wp/) of ZnS powder was 10.85%. The fraction of HCP phase was closely related with extra amount of H$_2$S gas. The lattice parameters and crystalline size were changed by the relative ratio of multi-phase. The luminescence property of ZnS:Cu, Al green phosphors prepared by conventional methods was good in the range of 91∼94% and 150∼190${\AA}$, respectively. According to the maximum entropy electron density(MEED) methods, any defects in (001) plane of cubic phase were not found. We suggest that both the Rietveld and maximum entropy density methods may be useful tools for studying luminescence mechanism of other phosphors materials.

• Bulletin of the Korean Chemical Society
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• v.10 no.3
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• pp.262-269
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• 1989

The gas phase thermal decomposition of 1-bromo-3-chloropropane in the presence of radical inhibitor was studied by using the conventional static system. The mechanism of unimolecular elimination channel is shown below. [...] In this scheme, the total molecular dissociation rate constant, ($k_1\;+\;k_2$), for the decomposition of $BrCH_2CH_2CH_2Cl$ was determined by pyrolyzing the $BrCH_2CH_2CH_2Cl$ in the temperature range of $380-420^{\circ}C$ and in the pressure range of 10∼100 torr. To obtain $k_3\;and\;k_4,\;and\;to\;obtain\;k_1\;and\;k_2$ independently, the thermal decompositions of allyl chloride and allyl bromide were also studied. The Arrhenius parameters for each step are as follows; $log\;A_{\infty}\;=\;14.20(sec^{-1}),\;E_a$ = 56.10(kcal/mol) for reaction path 1; $log\;A_{\infty}\;=\;12.54(sec^{-1}),\;E_a$ = 49.75(kcal/mol) for reaction path 2; $log\;A_{\infty}\;=\;13.41(sec^{-1}),\;E_a$ = 50.04(kcal/mol) for reaction path 3; $log\;A_{\infty}\;=\;12.43(sec^{-1}),\;E_a$ = 52.78(kcal/mol) for reaction path 4; Finally, the experimentally observed pressure dependence of the rate constants in each step is compared with the theoretically predicted values that are obtained by the RRKM calculations.

• Journal of Hydrogen and New Energy
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• v.19 no.5
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• pp.386-393
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• 2008

The Sulfur-iodine(SI) thermochemical cycle is one of the most promising methods for massive hydrogen production. For the purpose of continuous operation of SI cycle, phase separation characteristics into two liquid phases ($H_2SO_4$-rich phase and $HI_x$-rich phase) were directly investigated via Bunsen reaction. The experiments for Bunsen reaction were carried out in the temperature range, from 298 to 333 K, and in the $I_2/H_2O$ molar ratio of $0.109{\sim}0.297$ under a continuous flow of $SO_2$ gas. As the results, solubility of $SO_2$, decreased with increasing the temperature, had considerable influence on the global composition in the Bunsen reaction system. The amounts of impurity in each phase(HI and $I_2$ in $H_2SO_4$-rich phase and $H_2SO_4$ in $HI_x$-rich phase) were decreased with increasing $H_2SO_4$ molar ratio and temperature. To control the amounts of impurity in $HI_x$-rich phase, temperature is a factor more important than $I_2/H2_O$ molar ratio. On the other hand, the affinity between $HI_x$ and $H_2O$ was increased with increasing $I_2/H2_O$molar ratio.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.853-858
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• 2003

The reaction mechanism of the pyrolysis of sulphonyl oximes ($CH_3-C_6H_4-S(O)_2O-N=C(H)-C_6H_4Y$), in the gas phase is studied theoretically at HF/3-21G, ONIOM (B3LYP/6-31G**:HF/3-21G) and ONIOM (MP2/6- 31G**:HF/3-21G) levels. All the calculations show that the thermal decomposition of sulphonyl oximes is a concerted asynchronous process via a six-membered cyclic transition state. The activation energies (Ea) predicted by ONIOM (B3LYP/6-31G**: HF/3-21G) method are in good agreement with the experimental results for a series of tosyl arenecarboxaldoximes. Five para substituents, Y = $OCH_3$, $CH_3$, H, Cl, and $NO_2$, are employed to investigate the substituent effect on the elimination reaction. Linear Hammett correlations are obtained in all calculations in contrast to the experimental finding.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.348-353
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• 2011

By gel-casting, the silicon-polymer green bodies were prepared for silicon nitride ceramics, sintered by microwave gas phase reaction. Considering the viscosity and the idle time of slurries, we decided the operational conditions of related processes, and the optimum concentrations of raw materials powders, organic monomers, cross-linker, dispersant, initiator, and catalyst. So we could get the machinable green bodies, having about 50 MPa of bending strength without cracks by selecting drying conditions carefully.

• Bulletin of the Korean Chemical Society
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• v.21 no.8
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• pp.823-827
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• 2000

Gas-Phase reactions of methyl and ethyl nitrites with anionic nucleophiles of SH-, F- and OH- are investigated theoretically at the MP2/6-311+G* level. The SN2 processes are all highly exothermic and proceed with a typ-icaI double-weIl reaction coordinate profile. The elimination reactions of methyl nitrite with SH- and F- are double-well energy surface processes,with stabilizedproduct complexes of NO-...H2S and NO-...HF, pro-ceeding by an E1 cb-like E2 mechanism. The $\beta-elimination$ of ethyl nitrite is an E2 type process. The $\alpha-elimi-nation$ reactions of methyl and ethyl nitrites with OH- have triple-well energy profiles of Elcb pathway with an $\alpha-carbanion$ intermediate which is stabilized bythe vicinal $nc\alpha-{\sigma}*o-N$ charge transfer interactions. CompIex-ation ofmethyl carbanion with HF seems to provide a stable intermediate within a triple-well energy profile of El cb channel in the reaction of F- with methyl nitrite.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.137-142
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• 2018

With the development of the electronic-materials industry, multi-functional metal-composite materials with high thermal conductivity and low thermal expansion must be developed for high reliability and high life expectancy. This paper is a preliminary study on the manufacturing technology of gas reaction control composite material, focusing on the prediction of the equivalent thermal properties of Al-AlN composite materials. Numerical equivalent property values are obtained by using finite element analysis and compared with theoretical formulas. Al-AlN composite materials should become the optimal composite material when the proportion of the reinforcing phase is less than 0.5.

• Bulletin of the Korean Chemical Society
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• v.7 no.3
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• pp.231-235
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• 1986

MNDO and ab initio calculations for gas phase reactions of alkoxide-exchange at silicon and carbon centers have been performed. Results show that MNDO values of ${\Delta}$E's of these reactions closely parallel those of the STO-3G method. The alkoxide-exchange at silicon is shown to be facile due to the formation of stable five-coordinate intermediate while the reaction at carbon is predicted to proceed with high barrier; the difference in this substitution behavior between carbon and silicon is shown to be due to an easy valence shell expansion of silicon in accommodating an extra bond in the formation of stable five-coordinate intermediates.

• Bulletin of the Korean Chemical Society
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• v.7 no.4
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• pp.279-282
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• 1986

The MNDO calculations were performed in order to investigate the gas-phase reaction mechanism of 2-propene-1-al oxide, as a model compound of dypnone oxide(1,3-diphenyl-2-butene-1-one oxide) with the chloride ion. Optimized geometries and heats of formation for two probable concerted pathways, CHO and H migration, were determined and their activation energies were obtained. MO results show that although the formyl migration is thermodynamically more favorable than the hydride migration, the latter kinetically predominates over the formyl migration, which is contrary to the established migrating preferences. It is concluded that the hydride migratory propensity is catalyzed by the chloride ion by reducing the capability of the carbonyl ${\pi}$ bond to participate in the migration.

• Journal of Hydrogen and New Energy
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• v.8 no.1
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• pp.31-41
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• 1997

In order to investigate the mechanism of electrochemical hydrogenation reaction on Zr-based Laves phase hydrogen storage alloy electrodes, electrochemical charge/discharge characteristics, potentiostatic/dynamic polarizations and electrocehmical impedance spectroscopy(EIS) of Zr-Ti-Mn-Ni and Zr-Ti-Mn-Ni-M(M=Fe, Co, Al) alloys were examined. Electrochemical discharge capacities of the alloys were quite different with gas charge capacities. Therefore, it was considered that discharge capacities of the alloys depend on electrochemical kinetic factors rather then thermodynamic ones. Discharge efficiencies were increased linearly with exchange current densities. The results of potentiostatic/dynamic polarization measurements showed that electrochemical charge and discharge reaction of Zr-based Laves phase hydrogen storage alloys is controlled by charge transfer process at the electrode surface. The EIS measurements also confirmed this result.