• Korean Chemical Engineering Research
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• 제57권6호
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• pp.861-867
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• 2019

차세대 리튬이차전지용 음극활물질로 각광을 받고있는 $Li_4Ti_5O_{12}$는 높은 수명특성, 낮은 비가역용량 그리고 충방전시 부피팽창이 거의 없는 물질이다. 하지만 낮은 전기전도도로 인하여 높은 전류밀도에서는 용량특성이 현저하게 낮아지는 단점을 가지고 있다. 이 문제점을 해결하기 위해 P123을 첨가한 졸-겔법으로 기공구조의 $Li_4Ti_5O_{12}$를 합성하였다. 제조된 샘플들의 물리적 특성을 분석하기 위해 XRD, SEM, BET를 사용하였고, 전기화학적 특성은 사이클테스트, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)로 분석을 하였다. P123/Ti = 0.01mol의 비율로 만들어진 $Li_4Ti_5O_{12}$에서 가장 균일한 입자사이즈, 높은 비표면적, 그리고 상대적으로 높은 기공의 분포를 보였다. EIS분석 결과 기공구조의 $Li_4Ti_5O_{12}$의 경우 저항을 나타내는 반원의 크기가 현저하게 감소하였으며, 전극 내 저항값이 줄어들었음을 알 수 있었다. 율속 테스트결과 0.2C에서 178 mAh/g, 0.5C에서 170 mAh/g, 5C에서 110 mAh/g 그리고 10C에서 90 mAh/g의 용량을 유지하였고 용량회복율 또한 99%로 매우 우수하였다.

• Food Science and Biotechnology
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• 제16권5호
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• pp.771-777
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• 2007

Sliced and whole root of rehmannia were dehydrated in a laboratory dryer at 40, 60, 80, and $100^{\circ}C$ to evaluate the kinetic parameters for dehydration of rehmannia. The drying curves of both samples were characterized by a falling-rate drying period only. Sliced rehmannia dried 1.1 to 3.1 times faster than whole root of rehmannia depending on drying temperature. Equilibrium moisture content (EMC) of rehmannia samples at the drying temperature tested were 0.069-0.078 g water/g dry solid, which was coincided with the monolayer moisture content (0.06 and 0.07 g water/g dry solid) evaluated from desorption isotherms using GAB (Guggenheim-Anderson-de Boer) model. A logarithmic model for thin layer drying was applied to evaluate the drying time to reach EMC ($t_{EMC}$) and drying constant (k). The effect of temperature on $1/t_{EMC}$ and k was described by the Arrhenius model with activation energy values of 32.56 and 47.14 kJ/mol determined using the former parameter, and 34.27 and 38.26 kJ/mol determined using the latter parameter for sliced and whole root of rehmannia, respectively.

• 한국전기전자재료학회논문지
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• 제24권4호
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• pp.285-289
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• 2011

In this study, lead-free $(K_{0.5}Na_{0.5+X})(Nb_{0.96}Sb_{0.04})O_3+0.2mol%La_2O_3+1.2mol%$ $K_4CuNb_8O_{23}$ (X= 0~0.025) ceramics were fabricated by normal sintering method at $1060^{\circ}C$ for 5 h. Microstructures, piezoelectric and dielectric properties of specimens were investigated with special emphasis in the influence of Na excess addition. The grain size of specimen was slightly decreased with increasing Na content. In the 2 [mol%] Na excess addition of NKNS ceramics, density, electromechanical coupling factor, piezoelectric constant and electromechancal quality factor of specimen were found to reach the optimum values of 4.25 [$g/cm^3$], 0.4357, 154.43 [pC/N] and 580, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.66-67
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• 2005

In this study, in order to develop multilayer piezoelectric actuator, PMN-PNN-PZT ceramics were fabricated using $Li_2CO_3-Na_2CO_3$ as sintering aids and their piezoelectric and dielectric characteristics were investigated with the function of PNN substitution. With increasing PNN substitution, dielectric constant(${\varepsilon}r$), electromechanical coupling factor(kp), and piezoelectric d constant($d_{33}$) were increased at 10~12[mol%] PNN substitution and then decreased at all sintering temperature. With increasing PNN substitution, phase changed from tetragonal to rhombohedral at [10~12mol%] PNN substitution. At the 12[mol%] PNN substituted PMN-PZT composition ceramic sintered at 950[$^{\circ}C$], density, ${\varepsilon}r$, kp, $d_{33}$ and Qm showed the optimum value of 7.79[$g/cm^3$], 1160, 0.599, 419[pC/N) and 894, respectively for multilayer piezoelectric actuator application.

• Bulletin of the Korean Chemical Society
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• 제34권10호
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• pp.3022-3026
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• 2013

The adsorption of carbon dioxide on graphene sheets was theoretically investigated using density functional theory (DFT) and MP2 calculations. Geometric parameters and adsorption energies were computed at various levels of theory. The $CO_2$ chemisorption energies on graphene-$C_{40}$ assuming high pressure are predicted to be 71.2-72.1 kcal/mol for the lactone systems depending on various C-O orientations at the UCAM-B3LYP level of theory. Physisorption energies of $CO_2$ on graphene were predicted to be 2.1 and 3.3 kcal/mol, respectively, at the single-point $UMP2/6-31G^{**}$ level of theory for perpendicular and parallel orientations.

• 센서학회지
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• 제4권2호
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• pp.51-57
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• 1995

Indium Tin Oxide (ITO) 박막을 $In_{2}O_{3}$(90mol%) : $SnO_{2}$(10mo1%)의 조성비를 가지는 타겟을 사하여 rf 마그네트론 스퍼터링 법으로 제작하였다. 기판온도 100, 200, 300, 400, $500^{\circ}C$ 와 열처리 온도 300, 400, $500^{\circ}C$로 변화시켜 주면서 제작하였으며 X-ray 회절 패턴, 전기적 특성, 투과도, SEM 사진 등으로 분석하였다. 그 결과 기판온도를 증가시킬수록 결정성, 전기 전도도와 투과도가 향상되었다. 그러나 공기 중에서 열처리 온도를 증가함에 따라 도리어 전도도는 감소하였다. 기판온도 $300^{\circ}C$ 이상에서 $3000\;{\AA}$ 두께를 가지고 성장된 ITO 박막은 약 $2{\times}10^{-4}{\Omega}cm$의 저항률과 85% 이상의 가시광 투과율을 가졌다.

• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.2973-2978
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• 2009

The decomposition reaction mechanism of $CH_3CF_2O$ radical formed from hydroflurocarbon, $CH_3CHF_2$ (HFC-152a) in the atmosphere has been investigated using ab-initio quantum mechanical methods. The geometries of the reactant, products and transition states involved in the decomposition pathways have been optimized and characterized at DFT-B3LYP and MP2 levels of theories using 6-311++G(d,p) basis set. Calculations have been carried out to observe the effect of basis sets on the optimized geometries of species involved. Single point energy calculations have been performed at QCISD(T) and CCSD(T) level of theories. Out of the two prominent decomposition channels considered viz., C-C bond scission and F-elimination, C-C bond scission is found to be the dominant path involving a barrier height of 12.3 kcal/mol whereas the F-elimination path involves that of a 28.0 kcal/mol. Using transition-state theory, rate constant for the most dominant decomposition pathway viz., C-C bond scission is calculated at 298 K and found to be 1.3 ${\times}$ 10$^4s{-1}$. Transition states are searched on the potential energy surfaces involving both decomposition channels and each of the transition states are characterized. The existence of transition states on the corresponding potential energy surface are ascertained by performing Intrinsic Reaction Coordinate (IRC) calculation.

• 한국세라믹학회지
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• 제27권7호
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• pp.943-951
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• 1990

Steady-state sublimation vapour pressures of anhydrous bismuth triiodide have been measured by the continuous gravimetric Kundsen-effusion method from 430.0 to 558.9 K and equilibrium sublimation pressures were obtained from the steady-state data. Condensation coefficients and their temperature dependence have been derived from the effusiion measurement. Condensation coefficients ranged from 0.159 to 0.048(475 to 500K), the activation enthalpy and entropy for condensation have been obtained as -93.38kTmol-1 and -212.70JK-1mol-1. The standard sublimation enthalpy changes derived by both second(modified sigma function) and third(average enthalpy method) law methods were 138.261$\pm$0.023, 138.74$\pm$0.002kJmol-1 respectively. The standard sublimation entropy change derived by modified sigma function was 191.98$\pm$0.047 JK-1mol-1. The reliable standard sublimation enthalpy change based on a correlation of ΔgcrHom(298.15K) and ΔgcrSom(298.15K), a recommended p(T) equation has been obtained for BiI3(cr) ; 1g(p/Pa)=-C/(T/K)＋5.0711g(T/K)-2.838$\times$10-3(T/K)-7.758$\times$103(K/T)2＋1.4519 where p is in Pa, T in Kelvin, ΔgcrHom(298.15K) in kJmol-1 and C=(ΔgcrHom(298.15K)-8.7358)/1.9146$\times$10-2.

• 한국식품영양학회지
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• 제10권3호
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• pp.370-374
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• 1997

시판 식혜에 Saccharomyces cerevisiae를 가해 29$^{\circ}C$에서 10일간 발효시켜서 식혜주를 제조하였다. TLC 및 HPLC 분석 결과 발효에 따라 수크로오스는 2일째부터 글루코오스와 프룩토오스로 가수분해되어 발효되었다. 수크로오스는 6일째에 완전히 없어지고, 8일째에는 글루코오스, 프룩토오스 모두 없어졌다. 에탄올은 6.6%를 나타냈다. 시판 식혜주의 아미노산 함량은 0.32$\mu$mol/ml, 단백질 함량은 226$\mu\textrm{g}$/ml을 나타냈다. pH는 3.21, 산도는 2.5ml를 나타냈다. 한계덱스트린은 1H-NMR로 분석 결과 시판 식혜와 구조상 차이가 없었다. $\alpha$-1,4- 결합에 대한 $\alpha$-1,6- 결합의 비율은 25:1을 나타냈다. 관능검사 결과, 맛은 와인과 비슷하였다.

• 한국식품영양학회지
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• 제10권3호
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• pp.360-364
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• 1997

멥쌀식혜에 Saccharomyces cerevisae를 가해 28$^{\circ}C$에서 10일간 발효시켜서 식혜주를 제조하였다. TLC 및 HPLC 분석 결과 발효에 따라 글루코오스는 하루, 말토오스는 4일, 말토트리오스는 6일까지만 존재하였다. 그러나, 분자량이 큰 말토올리고당과 한계덱스트린은 발효되지 않았다. 에탄올은 6.5%를 나타냈다. 식혜주의 아미노산 함량은 2.9$\mu$mol/ml, 단백질 함량은 457$\mu\textrm{g}$/ml를 나타냈다. pH는 3.67, 산도는 3.1ml를 나타냈다. 한계덱스트린은 1H-NMR로 분석 결과 식혜에 존재하는 것과 구조상 변화가 없었다. $\alpha$-1,4-결합에 대한 $\alpha$-1,6-결합의 비율도 5.6:1을 나타냈다. 관능검사 결과, 맛은 와인과 비슷하였다.