• The Korean Journal of Ceramics
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• 제2권1호
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• pp.19-24
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• 1996

The phase distribution and interface chemistry by the solid-state reaction between SiC and nickel were studied at temperatures between $550 \;and\; 1250^{\circ}C$ for 0.5-100 h. The reaction with the formation of silicides and carbon was first observed above $650^{\circ}C$. At $750^{\circ}C$, as the reaction proceeded, the initially, formed $Ni_3Si_2$ layer was converted to $Ni_2$Si. The thin nickel film reacted completely with SiC after annealing at $950^{\circ}C$ for 2 h. The thermodynamically stable $Ni_2$Si is the only obsrved silicide in the reaction zone up to $1050^{\circ}C$. The formation of $Ni_2$Si layers with carbon precipitates alternated periodically with the carbon free layers. At temperatures between $950^{\circ}C$ and $1050^{\circ}C$, the typical layer sequences in the reaction zone is determined by quantitative microanalysis to be $SiC/Ni_2$$Si+C/Ni_2$$Si/Ni_2$$Si+C/…Ni_2$Si/Ni(Si)/Ni. The mechanism of the periodic band structure formation with the carbon precipitation behaviour was discussed in terms of reaction kinetics and thermodynamic considerations. The reaction kinetics is proposed to estimate the effective reaction constant from the parabolic growth of the reaction zone.

• 마이크로전자및패키징학회지
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• 제10권3호
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• pp.37-42
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• 2003

전자 패키징에 사용되는 솔더합금에 납을 함유됨으로써 인하여 야기되는 환경적 문제와 인체 유해성 때문에 Pb-Sn 합금계를 대체할 수 있는 새로운 무연 솔더 재료의 필요성이 대두되고 있다. 새로운 솔더합금의 개발에 있어서 솔더 조인트의 신뢰성이 가장 중요한 문제라고 할 수 있는데, 솔더 조인트의 신뢰성은 솔더와 기판 사이의 계면 반응 형태와 그 정도에 의해서 크게 영향을 받기 때문에 솔더와 기판 사이의 계면 현상에 관한 더 깊은 이해가 필요하게 된다 솔더링 동안 기판/솔더 계면에서 가장 먼저 생성되는 금속간 화합물의 상을 예측하기 위한 열역학적인 방법이 제안되었다. 계면 에너지와 석출 구동력의 함수로 표현되는 각각의 금속간 화합물에 대한 핵생성 활성화 에너지를 비교함으로써 활성화 에너지가 가장 낮은 금속간 화합물이 가장 먼저 생성된다고 예측하였다. 거기에 더해 에너지를 기반으로 한 계산을 통하여 솔더 조인트에서 금속간 화합물의 입자 형상을 설명하였다. 울퉁불퉁한 계면을 가진 금속간 화합물의 Jackson의 parameter 값은 2보다 작은 반면 평평한 입자의 경우 2보다 크게 된다.

• 콘크리트학회논문집
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• 제17권5호
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• pp.857-868
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• 2005

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

• 한국진공학회지
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• 제8권4B호
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• pp.514-518
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• 1999

Gold (Au) is not supposed to react with sapphire(single crystalline ) under thermodynamic equillibrium, therefore, a strong adhesion between these two dissimilar materials is not expected. However, pull test showed that the gold film sputter-deposited onto annealed and pre-sputtered sapphire exhibited very strong adhesion even without post-deposition annealing. Strongly and weakly adhered samples as a result of the pull testing were selected to investigate the adhesion mechanisms with Auger electron spectroscopy. The Au/ interfaces were analyzed using a new technique that probes the interface on the film using Auger electron escape depth. It revealed that one or two monolayers of Au-Al-O compound formed at the Au/Sapphire interface when AES in the UHV chamber. It showed that metallic aluminum was detected on the surface of sapphire substrates after irradiating for 3 min. with 7keV Ar+ -ions. These results agree with TRIM calculations that yield preferential ion-beam etching. It is concluded that the formation of Au-Al-O compound, which is responsible for the strong metal-ceramic bonding, is due to ion-induced cleaning and reduction of the sapphire surface, and the kinetic energy of depositing gold atoms, molecules, and micro-particles as a driving force for the inter-facial reaction.

• 설비공학논문집
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• 제9권1호
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• pp.33-42
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• 1997

The reciprocating compressors are widely used in industrial fields for its simplicity in principle and high efficiency. But the design of it requires rigorous experiments due to its high dependence on many design parameters. In this work, a mathematical model is developed so that we can analyze the gas-solid interaction during the whole working processes of a reciprocating compressor. The governing equations, which represent the fluid-solid interaction, was derived from the unsteady Bernoulli's equation with the assumption of quasi-steady working process. The valve itself was assumed to be a one degree of freedom spring-mass-damper system. A simple thermodynamic relation, the ideal gas state equation, was used to give it an external force term assuming that the refrigerant behaves like an ideal gas. It was suggested to use a motor of higher driving frequency to enhance the performance of the reciprocating compressor without causing a faster failure of the valve.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.154-155
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• 2006

This study investigated a mechanism for controlling the shape of Cu nanocrystals fabricated using the polyol process, which considers the thermodynamic transition from a facetted surface to a rough surface and the growth mechanisms of nanocrystals with facetted or rough surfaces. The facetted surfaces were stable at relatively low temperatures due to the low entropy of perfectly facetted surfaces. Nanocrystals fabricated using a coordinative surfactant stabilized the facetted surface at a higher temperature than those fabricated using a non-coordinative surfactant. The growth rate of the surface under a given driving force was dependent on the surface structure, i.e., facetted or rough, and the growth of a facetted surface was a thermally activated process. Surface twins decreased the activation energy for growth of the facetted surface and resulted in rod- or wire-shaped nanocrystals

• 대한화학회지
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• 제37권1호
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• pp.105-111
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• 1993

수용액내에서 란탄족 금속(III)이온과 광학 활성을 지닌 L-proline간의 안정도 상수(1:1)값들을 pH 적정 방법을 사용하여 이온강도 0.1M $NaClO_4$, 25$^{\circ}C$ 조건에서 구하였다. 안정도 상수값은 경란탄족과 중란탄족 금속 사이에 "gadolinium break" 현상을 나타내었으며, 리간드 산도와 안정도 상수값의 관계로 부터 L-proline이 두자리 리간드로 작용함을 알 수 있었다. 열역학적 함수값(${\Delta}H$, ${\Delta}S$)들을 같은 조건에서 엔탈피 적정 방법으로 구하였다. lanthanide(III)-L-proline 착물 형성은 흡열 반응 및 큰 엔트로피 변화량(${\Delta}S$)을 나타내었으며 엔트로피 변화량은 L-proline 고리의 견고성으로 인해 과량의 탈수 효과에 의한 것으로 판단되었다. lanthanide(III)-anthranilate 착물 형성의 열역학적 함수값과 비교하여 본 결과, L-proline의 헤테로 고리 질소 원자와 카르복실기가 결합에 참여하여 킬레이트를 형성하였으며, anthranilate와 L-proline착물의 엔탈피 변화량(${\Delta}H$) 차이는 두 리간드 내에 존재하는 질소 원자의 염기도 차이에 의한 것으로 판단되었다.

• 한국안전학회지
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• 제11권4호
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• pp.143-150
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• 1996

본 연구는 선형, 비선형 hygrothermal 응력 문제를 위한 explicit-Implicit 유한요소 해석 모델 개발에 관한 것이다. 부가적으로 moilsture 확산 방정식, J-적분 평가를 위한 균열 요소 및 가상 균열 진전법이 도입된다. 시간 변화에 따른 균열 추진력을 계산하기 위하여 선형 탄성 파괴 역학(LEFM)이론이 고려되며 재료의 기공은 실온에서 액체 상태의 습기로 포화되어 있으며 온도가 상승함에 따라 증기화된다는 가정하에서 균열 추진력과 증기 효과의 관계가 연구된다. 이상 기체방정식은 각 시간 단계에서 증기에 의한 열역학적 압력을 계산하기 위하여 이용된다. 다공질 재료의 시간 종속 응답을 지배하는 방정식들은 혼합이론에 기초하며 다공질 재료의 유체 흐름을 위한 Darcy의 법칙과 Von-Mises 항복 기준을 포함하고 있는 Perzyna의 점소성 모델이 첨가된다. 또한 Green-Naghdi 응력률이 중첩된 강체 운동하에서 응력 텐서 invariant로 사용되며, 모델링을 위하여 사각요소가 이용되고 비선형 지배 방정식을 풀기 위하여 full Newton-Raphson법에 의한 반복법이 사용된다. 본 연구를 통하여 얻은 결과는 다음과 같다. 1) 본 유한요소 프로그램은 복합재의 hygrothermal 파괴 해석에 매우 유용하게 적용될 수 있다. 2) 습기의 온도에 의한 영향을 가지는 재료의 J-적분을 정확히 예측하기 위하여는 증기 효과를 고려하여야 한다. 왜냐하면 초기단계에 균열 전파력이 가속되기 때문이다. 3) 본 해석을 위해 Uncoupled scheme에 의한 결과도 Coupled scheme에 결과에 비해 아주 타당하므로 CPU 측면에서 매우 경제적인 Uncoupled scheme이 추천된다.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2523-2528
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• 2014

In the present study, at first, azo Schiff base ligand of (N,N'-bis(5-phenylazosalicylaldehyde)-ethylenediamine) ($H_2L$) has been synthesized by condensation reaction of 5-phenylazosalicylaldehyde and ethylenediamine in 2:1 molar ratio, respectively. Then, its cobalt complex (CoL) was synthesized by reaction of $Co(OAc)_2{\cdot}4H_2O$ with ligand ($H_2L$) in 1:1 molar ratio in ethanol solvent. This ligand and its cobalt complex containing azo functional groups were characterized using elemental analysis, $^1H$-NMR, UV-vis and IR spectroscopies. Subsequently, the interaction between native calf thymus deoxyribonucleic acid (ct-DNA) and CoL complex was investigated in 10 mM Tris/HCl buffer solution, pH = 7 using UV-vis absorption, thermal denaturation technique and viscosity measurements. From spectrophotometric titration experiments, the binding constant of CoL complex with ct-DNA was found to be $(2.4{\pm}0.2){\times}10^4M^{-1}$. The thermodynamic parameters were calculated by van't Hoff equation.The enthalpy and entropy changes were $5753.94{\pm}172.66kcal/mol$ and $43.93{\pm}1.18cal/mol{\cdot}K$ at $25^{\circ}C$, respectively. Thermal denaturation experiments represent the increasing of melting temperature of ct-DNA (about $0.93^{\circ}C$) due to binding of CoL complex. The results indicate that the process is entropy-driven and suggest that hydrophobic interactions are the main driving force for the complex formation.

• 한국물환경학회지
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• 제30권5호
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• pp.491-502
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• 2014

As meteorology is the driving force for lake thermodynamics and mixing processes, the effects of climate change on the physical limnology and associated ecosystem are emerging issues. The potential impacts of climate change on the physical features of a reservoir include the heat budget and thermodynamic balance across the air-water interface, formation and stability of the thermal stratification, and the timing of turn over. In addition, the changed physical processes may result in alteration of materials and energy flow because the biogeochemical processes of a stratified waterbody is strongly associated with the thermal stability. In this study, a novel modeling framework that consists of an artificial neural network (ANN), a watershed model (SWAT), a reservoir operation model(HEC-ResSim) and a hydrodynamic and water quality model (CE-QUAL-W2) is developed for projecting the effects of climate change on the reservoir water temperature and thermal stability. The results showed that increasing air temperature will cause higher epilimnion temperatures, earlier and more persistent thermal stratification, and increased thermal stability in the future. The Schmidt stability index used to evaluate the stratification strength showed tendency to increase, implying that the climate change may have considerable impacts on the water quality and ecosystem through changing the vertical mixing characteristics of the reservoir.