• 한국재료학회지
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• 제9권4호
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• pp.341-344
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• 1999

We reported compositional separation(CS) into Co-enriched and Cri-enriched components inside the grains of Co-Cr based thin films prepared by rf sputtering. CS strongly depends on the sputtering conditions of substrate temperature and target composition. Tuning the microstructure of the Co-Cr films is important in order to employ the CS for high-density magnetic recording. We investigated the origin of CS from thermodynamic viewpoint. We employ a spinodal decomposition-like model to describe the origin of the CS in Co-Cr films. We consider the total free energy of the Co-Cr films as the sum of several free energies of; 1) thermodynamic mixing entropy of a binary solid solution, 2) magnetic ordering interaction(MOI) energy below the Curie temperature, and 3) excess interaction energy(XS) caused by the sputtering process as a function of temperature and composition. Those energies distorted the total free energy like the spinodal decomposition and caused the compositionally separated fine microstructure inside the grains. If the second derivative of the total free energy with respect to Cr composition becomes negative at a given substrate temperature, we may observe a metastable compositional separation inside the Co-Cr alloy films. We expect to exploit the microstructure of CS for ultra-high density magnetic recording.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.223-226
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• 2005

For $CO_2-free$ hydrogen production and better utilization of the produced carbon, catalytic decomposition of methane over rubber-grade carbon blacks manufactured from coal tar was carried out. The catalytic activities of several domestic carbon blacks were compared. A pelletized carbon black exhibited considerably lower activity and activation energy than the fluffy( loose) carbon black of the same grade. This difference is considered due to the binder that was added during pelletization. For pelletized carbon blacks, a tendency was observed that the activity per unit mass of catalyst increased with the specific surface area of the carbon black. Another tendency was also observed that the activation energy increased with the primary particle size or decrease of the specific surface area.

• 대한수학회보
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• 제56권1호
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• pp.265-276
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• 2019

For a simple implementation, a linear convex splitting scheme was coupled with the Fourier spectral method for the Cahn-Hilliard equation with a logarithmic free energy. However, an inappropriate value of the splitting parameter of the linear scheme may lead to incorrect morphologies in the phase separation process. In order to overcome this problem, we present a nonlinear convex splitting Fourier spectral scheme for the Cahn-Hilliard equation with a logarithmic free energy, which is an appropriate extension of Eyre's idea of convex-concave decomposition of the energy functional. Using the nonlinear scheme, we derive a useful formula for the relation between the gradient energy coefficient and the thickness of the interfacial layer. And we present numerical simulations showing the different evolution of the solution using the linear and nonlinear schemes. The numerical results demonstrate that the nonlinear scheme is more accurate than the linear one.

• Smart Structures and Systems
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• 제30권3호
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• pp.221-237
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• 2022

This paper is concerned with nonlinear modeling and efficient numerical simulation of electrostrictive materials and structures. Two types of such materials are considered: relaxor ferroelectric ceramics and electrostrictive polymers. For ceramics, a geometrically linear formulation is developed, whereas polymers are studied in a geometrically nonlinear regime. In the paper, we focus on constitutive modeling first. For the reversible constitutive response under consideration, we introduce the augmented Helmholtz free energy, which is composed of a purely elastic part, a dielectric part and an augmentation term. For the elastic part, we involve an additive decomposition of the strain tensor into an elastic strain and an electrostrictive eigenstrain, which depends on the polarization of the material. In the geometrically nonlinear case, a corresponding multiplicative decomposition of the deformation gradient tensor replaces the additive strain decomposition used in the geometrically linear formulation. For the dielectric part, we first introduce the internal energy, to which a Legendre transformation is applied to compute the free energy. The augmentation term accounts for the contribution from vacuum to the energy. In our formulation, the augmented free energy depends not only on the strain and the electric field, but also on the polarization and an internal polarization; the latter two are internal variables. With the constitutive framework established, a Finite Element implementation is briefly discussed. We use high-order elements for the discretization of the independent variables, which include also the internal variables and, in case the material is assumed incompressible, the hydrostatic pressure, which is introduced as a Lagrange multiplier. The elements are implemented in the open source code Netgen/NGSolve. Finally, example problems are solved for both, relaxor ferroelectric ceramics and electrostrictive polymers. We focus on thin plate-type structures to show the efficiency of the numerical scheme and its applicability to thin electrostrictive structures.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.911-916
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• 2012

Ion selectivity in a simple cyclic peptide nanotube, composed of four cyclo[-(D-Ala-Glu-D-Ala-Gln)$_2-$] units, is investigated by calculating the PMF profiles of $Na^+$, $K^+$, and $Cl^-$ ions permeating through the peptide nanotube in water. The final PMF profiles of the ions obtained from the umbrella sampling (US) method show an excellent agreement with those from the thermodynamic integration (TI) method. The PMF profiles of $Na^+$ and $K^+$ display free energy wells while the PMF curve of $Cl^-$ features free energy barriers, indicating the selectivity of the cyclic peptide nanotube to cations. Decomposition of the total mean force into the contribution from each component in the system is also accomplished by using the TI method. The mean force decomposition profiles of $Na^+$ and $K^+$ demonstrate that the dehydration free energy barriers by water molecules near the channel entrance and inside the channel are completely compensated for by attractive electrostatic interactions between the cations and carbonyl oxygens in the nanotube. In the case of $Cl^-$, the dehydration free energy barriers are not eliminated by an interaction between the anion and the peptide nanotube, leading to the high free energy barriers in the PMF profile. Calculations of the coordination numbers of the ions with oxygen atoms pertaining to either water molecules or carbonyl groups in the peptide nanotube reveal that the stabilization of the cations in the midplane regions of the nanotube arises from the favorable interaction of the cations with the negatively charged carbonyl oxygens.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.791-793
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• 2009

Hydrogen has been recognized of the energy source for the future, in terms of the most environmentally acceptable energy source. A pressurized fluidized bed reactor made of carbon steel with 0.076 m I.D. and 1.0 m in height was employed for the thermocatalytic decomposition of methane to produce amount of $CO_2$ - free hydrogen with validity from a commercial point of view. The fluidized bed was proposed for withdrawing of product carbons from the reactor continuously. The methane decomposition rate with the carbon black N330 catalyst was rapidly reached a quasi-steady state and remained for several hour. The methane thermocatalytic decomposition reaction was carried out at the temperature range of 850 - 950 $^{\circ}C$, methane gas velocity of 2.0 $U_{mf}$ and the operating pressure of 1.0 -3.0 bar. Effect of operating parameters such as reaction temperature, pressure on the reaction rates was investigated and predicted the effect of a change in conditions on a chemical equilibrium thermodynamically, according to Le Chatelier's principle.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.93-96
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• 2007

Catalytic activities of color and conductive carbon blacks in ethane decomposition for $CO_2-free$ hydrogen production were investigated. The ethane decomposition was carried out in a conventional fixed bed reactor under atmospheric pressure at 973-1173 K for 2 hours. When the decomposition in the presence of carbon black was compared with the non-catalytic thermal decomposition, the former exhibited significantly higher ethane conversion, higher C(s) selectivity and lower ethylene selectivity with small increase of the methane selectivity, which resulted in higher hydrogen yield. This indicates that carbon black is catalytically effective for dehydrogenation of ethane as well as subsequent decomposition of ethylene. All the carbon blacks exhibited stable catalytic activity with time. In durability tests, fluffy N-330 and BP2000 maintained their activities for 36 hours.

• Korean Chemical Engineering Research
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• 제43권3호
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• pp.352-359
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• 2005

본 논문에서는 암모니아의 전해 분해를 위한 분리막 반응기의 음극방 및 양극방에서 물의 전해에 따른 암모니아 용액의 pH 변화가 고찰되었으며, 단위 전해 셀이 적층된 다단 전해 반응기에서의 암모니아의 연속식 분해 특성이 평가되었다. 분리막을 가지는 반응기에서 암모니아 용액의 전해 반응 시, 양극에서는 pH가 8 이하에서부터 수소 이온이 생성되는 물 분해 반응이 일어나며, 음극에서는 pH가 11 이상에서부터 수산기 이온이 생성되는 물 분해 반응이 일어나 암모니아 용액의 pH를 변화시켜 암모니아 전해 분해에 영향을 크게 미쳤으며, 음이온 교환막을 사용하는 경우가 양이온 교환막을 사용하는 경우보다 양극방에서 암모니아 분해에 유리한 알카리 분위기를 보다 효과적으로 유지할 수 있었다. 분리막 전해 반응기의 특성을 이용하여 자체 pH 조정 기능을 가지는 연속식 암모니아 전해 반응기가 새롭게 고안하였고, 여기서는 pH-조정조 탱크 용액을 두고 이의 용액 일부를 음극방으로 순환시킴으로써, 양극방으로 주입되는 pH-조정조의 용액의 pH를 높여 암모니아 분해율을 높일 수 있었다. 또한, 그러한 반응기를 이용한 salt-free 연속식 암모니아 전해 분해 공정이 제시되었으며, 이러한 공정에서는 염소 이온을 가지는 암모니아 용액의 80％까지 연속적으로 암모니아를 환경에 무해한 질소로 분해 시킬 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2385-2391
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• 2018

This paper is devoted to detecting decomposition characteristics of Iodotrifluoromethane ($CF_3I$) under alternating current (AC) discharges or load current interruptions. The decomposition products are measured utilizing chromatography-mass spectroscopy. It is found that less than 1% $CF_3I$ gas decomposed after several interruptions at load current of 200 A or hundred times of AC discharges. However, under interruptions at a current of 400 A, more than 95% $CF_3I$ gas decomposed into carbon tetrafluoride ($CF_4$) and hexafluoroethane ($C_2F_6$). The equilibrium compositions based on Gibbs free energy minimization of $CF_3I$ was calculated to explain the decomposition mechanism.

• Korean Chemical Engineering Research
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• 제61권4호
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• pp.487-495
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• 2023

암모니아는 인류의 식량문제를 해결할 수 있는 비료 생산의 주요 원료임과 동시에 무탄소 연료이면서 친환경적인 수소 운반자로서 중요한 에너지원으로 알려져 있다. 그래서 지금까지도 암모니아를 합성하거나 분해하는 기술들이 각광을 받고 있다. 암모니아 합성 및 분해 반응을 촉진시키기 위해서는 반드시 촉매 재료가 필요하다. 고성능 및 값싼 암모니아 합성 및 분해용 신촉매를 설계하기 위해서는 무수히 많은 합성 가능한 촉매 후보군들을 다루어야만 하는데 전통적인 접근법만으로 탐색 및 분석을 하기엔 시간적, 경제적인 비용이 많이 들 수밖에 없다. 최근에 4차 산업혁명의 핵심기술에 속하는 머신러닝을 이용하여 이용하여 고성능 촉매를 빠르고 정확하게 찾을 수 있는 탐색 모델이 개발되어 왔다. 본 연구에서는 암모니아 합성 및 분해용 반응 메커니즘에 대해서 알아보고, 고성능 및 경제적인 암모니아 합성 및 분해 촉매를 효율적으로 탐색할 수 있는 머신러닝 기반 방법에 대한 최신 연구 및 전망을 기술하였다.