• Bulletin of the Korean Chemical Society
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• 제17권6호
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• pp.520-524
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• 1996

Solvolyses of phenyl chloroformate in water, D2O, CH3OD, 50% D2O-CH3OD, and in aqueous binary mixtures of acetone, ethanol and methanol are investigated at 25.0 ℃. Product selectivities are reported at 25 ℃ for a wide range of ethanol-water and methanol-water solvent compositions. The Grunwald-Winstein plots of first-order rate constants for phenyl chloroformate with YCl (based on 2-adamantyl chloride) show marked dispersions into three separate lines for the three aqueous mixtures with a small m value (m< 0.2) and a rate maximum for aqueous alcohol solvents. Third-order rate constants, kww, kaw, kwa and kaa were calculated from the observed kww and kaa values together with kaw and kwa calculated from the intercept and slope of the plot of 1/S vs. [alcohol]/[water]. The calculated rate constants, kcalc and mol % of ester agree satisfactorily with those of the observed rate constants, kobs and mol % of ester, supporting the stoichiometric solvation effect analysis. The kinetic solvent isotope effects determined in water and methanol are consistent with the proposed mechanism of the general base catalyzed and/or carbonyl addition for phenyl chloroformate solvolyses based on mass law and stoichiometric solvation effect studies.

• 전자공학회논문지
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• 제52권8호
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• pp.59-63
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• 2015

본 연구에서는 MONOS 플래시 메모리의 blocking oxide/trapping nitride, trapping nitride/tunneling oxide 계면 트랩을 구하기 위해 C-V 방법을 도입하였고, stoichiometric 조건을 만족하는 nitride와 silicon rich nitride를 trapping layer로 갖는 MONOS capacitor를 제작하여 각각의 interface trap 특성을 비교분석하였다. 보고에 따르면 silicon rich nitride는 stoichiometric nitride에 비해 다수의 shallow trap이 존재한다고 보고되고 있는데, 본 연구를 통해 이의 정량화가 가능함을 보였다.

• 한국세라믹학회지
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• 제39권9호
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• pp.835-839
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• 2002

Micro-Pulling Down(${\mu}$-PD)법을 이용하여 직경 1 mm, 길이 30∼35 mm의 $Er_2O_3$와 MgO가 첨가된 화학양론조성 $LiNbO_3$단결정을 성장하였다. 성장된 결정의 $Er_2O_3$와 MgO 첨가에 따른 up-conversion 특성의 변화 및 MgO 첨가량이 광손상에 미치는 영향을 관찰하기 위해 투과율을 측정하였다. 또한 $LiNbO_3$ 단결정 내의 결함유무를 광학현미경을 이용하여 관찰하였고, Electron Probe Micro Analysis(EPMA)를 이용하여 결정 내에 $Er_2O_3$와 MgO가 균일하게 분포되어있음을 확인하였다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2000년도 추계학술대회 및 발표대회 강연 및 발표논문 초록집
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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.

• 한국수소및신에너지학회논문집
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• 제15권3호
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• pp.175-186
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• 2004

In this paper, we developed the dynamic model of a fuel cell system suitable for controller design and system operation. The transient phenomena captured in the model include the flow characteristics and inertia dynamics of the compressor, the intake manifold filling dynamics, oxygen partial pressures and membrane humidity on the fuel cell voltage. In the simulations, we paid attention to the transient behavior of stack voltage and compressor pressure, stoichiometric ratio. Simulation results are presented to demonstrate the model capability. For load current following, stack voltage dynamic characteristics are plotted to understand the Electro-chemistry involved with the fuel cell system. Compressor pressure and stoichiometric ratio are strongly coupled, and independent parameters may interfere with each other, dynamic response, undershoot and overshoot.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.1017-1021
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• 1997

Solvolyses of p-methoxyphenyl chloroformate in water, D2O, CH3OD, 50% D2O-CH3OD, and in aqueous binary mixtures of acetone, ethanol and methanol are investigated at 25.0 ℃. Product selectivities are reported at 25 ℃ for a wide range of ethanol-water and methanol-water solvent compositions. The Grunwald-Winstein plots of first-order rate constants for p-methoxyphenyl chloroformate with YCl (based on 1-adamantyl chloride) show marked dispersions into three separate curves for the three aqueous mixtures with a small m value and a rate maximum for aqueous alcohol solvents. Third-order rate constants, kww, kaw, kwa and kaa were calculated from the observed kww and kaa values together with kaw and kwa calculated from the intercept and slope of the plot of 1/S vs. [alcohol]/[water]. The calculated rate constants, kcalc and mol % of ester agree satisfactorily with those of the observed rate constants, kobs and mol % of ester, supporting the stoichiometric solvation effect analysis. The kinetic solvent isotope effects determined in water and methanol are consistent with the proposed mechanism of the general base catalyzed carbonyl addition-elimination.

• 한국수소및신에너지학회논문집
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• 제7권1호
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• pp.11-18
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• 1996

The Laves phase alloy hydrides have some promising properties as electrode materials in reversible metal hydride batteries. In this work, the hydrogen storage performance, crystallographic parameters, surface morphology, surface area and electrochemical characteristics of the non-stoichiometric $ZrMn_{0.3}V_{0.7}Ni_{1.4+{\alpha}}$, $ZrMn_{0.5}V_{0.5}Ni_{1.4+{\alpha}}$($\alpha$ =0.0, 0.2, 0.4, 0.6) alloys were examined. These as-cast alloys were found to have mainly a cubic C15-type Laves phase structure by X -ray diffraction analysis. The equilibrium pressure of the alloy were increased as $\alpha$ increased in both two types alloy. In case of $ZrMn_{0.5}V_{0.5}Ni_{1.4+{\alpha}}$ alloys, discharge efficiency and the rate capability of the alloy were decreased as $\alpha$ increased but, these values were increased in case of $ZrMn_{0.3}V_{0.7}Ni_{1.4+{\alpha}}$ alloys. The differences of these electrode properties observed were dependent on the reaction surface area and the catalytic activity of unit area of the each electrode.

• Journal of Electrochemical Science and Technology
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• 제2권2호
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• pp.97-102
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• 2011

Different amounts of excess lithium in the range of x = 0~0.3 were added to $Li_{1+x}[Mn_{0.720}Ni_{0.175}Co_{0.105}]O_2$ cathode materials synthesized using the co-precipitation method to investigate its microstructure and electrochemical properties. Pure layered structure without impurities was confirmed in the XRD pattern analysis and increasing peak intensity of $Li_2MnO_3$ was observed along with the addition of over 0.2 mol Li. The initial discharge capacity of the stoichiometric composition was determined to be 246 mAh/g, while the discharge capacity of the addition of 0.1 mol Li was obtained to be 241 mAh/g, which was not significantly different from that of the stoichiometric composition. However, the discharge capacities decreased dramatically after the addition of 0.2 and 0.3 mol Li to 162 mAh/g and 146 mAh/g, respectively. In the rate capability test, the active $Li_{1+x}[Mn_{0.720}Ni_{0.175}Co_{0.105}]O_2$ cathode material of the stoichiometric composition showed a dramatic decrease in its discharge capacity with increasing C-rate, as evidenced by the result that the discharge capacity at 5C was 13% compared with 0.1C. On the other hand, the discharge capacity of compositions containing excess lithium was improved at higher current rates. The cycling test showed that the composition containing an excess of 0.1 mol Li had the most outstanding capacity retention.

• 한국세라믹학회지
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• 제41권1호
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• pp.92-95
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• 2004

Micro-Pulling Down (${\mu}$-PD) 법을 이용하여 $MnO_2$와 $Tb_4O_7$를 첨가하여 crack. 열 strain 등의 결함이 없는 화학양론조성의 $LiNbO_3$ 단결정을 c-축으로 직경 1.0mm, 길이 25-30mm의 크기로 성장시켰다. Electron Probe Micro Analysis (EPMA)를 이용하여 결정 내에 $MnO_2$와 $Tb_4O_7$이 균일하게 분포되어 있음을 확인하였다. 또한 Fourier Transform-Infrared Spectrophotometer (FT-IR)을 사용하여 OH 흡수밴드를 관찰하였고, 성장된 결정의 $MnO_2$와 $Tb_4O_7$ 첨가에 따른 형광특성의 변화를 측정하였다.

• 대한환경공학회지
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• 제32권8호
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• pp.747-753
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• 2010

본 연구는 바이오필터의 기질분해특성을 파악하기 위하여 휘발성유기화합물을 대상으로 임계부하량과 기질특성의 상관관계를 분석하였고, 탄소물질수지를 이용한 생물반응의 양론적 해석을 수행하였다. 반응기에 공급된 기질은 단일물질이며, toluene, styrene, MEK, MIBK를 선정하였다. 바이오필터의 기질임계부하량은 toluene은 $46.9\;g/m^3{\cdot}hr$, styrene은 $25.8\;g/m^3{\cdot}hr$, MEK는 $96.3\;g/m^3{\cdot}hr$, MIBK는 $66.5\;g/m^3{\cdot}hr$이었으며, 임계부하량은 옥탄올-물 분배계수(KOW)와 높은 상관관계를 보였다. 또한 기질부하량이 증가할수록 물질수지 중 $CO_2$에 의한 탄소회수율은 낮아졌고, 바이오매스에 의한 탄소회수율은 높아지는 경향을 보였다. 생물양론적 해석을 통하여 추정된 biomass yield (g biomass/g substrate)는 기질부하량이 증가할수록 커졌으며, toluene은 0.31~0.57, styrene은 0.29~0.57, MEK는 0.08~0.56, MIBK는 0.14~0.53의 변화폭을 보였다.