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문장혁(J.-H. Moon),김윤제(Youn J. Kim),한전건(J.-G. Han) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The characteristics plasma flow of an atmospheric plasma torch used for thermal plasma processing is studied. In<br/> general, it is produced by the arc-gas interactions between a cathode tip and an anode nozzle. The performance of nontransferred<br/> plasma torch is significantly dependent on jet flow characteristics out of the nozzle. In this work, the<br/> distribution of gas flow that goes out to the atmosphere through a plenum chamber and nozzle is analyzed to evaluate<br/> the performance of atmospheric plasma torch. Numerical analysis is carried out with various angles of an inlet flow<br/> which can create different swirl flow fields. Moreover, the size of plasma plume is experimentally depicted.
제일원리 계산법을 이용한 비정질 실리콘 내에서의 리튬 이온 확산 예측
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
We have studied the lithium absorption in crystalline silicon with the strain effects on unit cell using density functional theory calculation. We have concluded that the dependences of the lithium diffusion were on the local volume and environmental. In the various strained cells, the effect of the lattice deformation about migration barriers for the motion of the lithium atom has been fit on the linear regression equation based on the volume of silicon surrounding lithium impurity and the migration distance of lithium atom. This result has applied to the calculation of diffusion coefficient in amorphous silicon which was generated by annealing from crystalline structure at 3000K. The migration barriers and attempt frequency, by Arrhenius formula, of lithium in the amorphous silicon structures has been determined by local environment using the linear regression equation. Then, the statistical method, kinetic Monte Carlo method, has been demonstrated for the diffusion coefficient of lithium. Finally, we have parameterized in terms of the amorphous effects into Arrhenius diffusion formula. This study have supported that the diffusion of lithium in amorphous silicon is faster than that in crystalline silicon.
제일원리 계산법을 이용한 리튬 이차 전지의 음극 물질의 비교 및 예측
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
An investigation of Li-M (M:Si, Ge, Sn) alloys using ab initio calculation is presented. Ab initio calculation methods performed for total energy calculations, structural optimizations, electric and mechanical properties with Li-Sn, Li-Ge, Li-Si. To achieve anode materials design, specific characteristics, such as large volume change and elastic softening, are compared in Group 14 chemistry.
제일원리 계산법을 이용한 실리콘 음극 소재의 그래핀 코팅 효과 분석
문장혁(Janghyuk Moon),조경재(Kyeongjae Cho),조맹효(Maenghyo Cho) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Computational study on the effect of graphene coating to Si anode material is performed by using density functional theory calculations. We construct the atomic model to examine interactions between amorphous silicon and graphene during lithiation. The lithiation of Si anode increases the mechanical contact force between outer graphene layer and amorphous silicon and the shear resistance is also increased. To explain the interaction between graphene and silicon we examine the charge distribution of silicon and graphene considering lithiation insertion. The number of density, electro field distribution and electric potential are also calculated. Charge-non polar interaction between Li-ion and graphene increase the contact energy between graphene-silicon. To calculate the contact force, we simplified interaction atomic force model. In this theoretical study, potential improvement of cyclability and improved mechanical properties of graphene coating for Si anode have been investigated.