• Bulletin of the Korean Chemical Society
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• 제26권11호
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• pp.1783-1789
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• 2005

Modeling of a steam generator crevice in a nuclear power system needs to take into account both thermalhydraulic and chemical phenomena. As a first step towards developing a reliable model, a chemical equilibrium model was developed to predict chemical speciation in a magnetite-packed crevice by adopting the “tableau” method. The model was benchmarked with the available experimental data and the maximum deviation did not exceed two orders of magnitude. The developed model was applied to predict the chemical speciation in a magnetite-packed crevice. It was predicted that caustic environment was developed by the concentration of NaOH and the dissolution of magnetite. The model indicated that the dominant aqueous species of iron in the caustic crevice was $FeO_2\;^-$. The increase of electrochemical corrosion potential observed in the experiment was rationalized by the decrease of dissolved hydrogen concentration due to a boiling process. It was predicted that under the deaerated condition magnetite was oxidized to hematite.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1009-1014
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• 2012

The influence of magnetic fields on chemical processes has long been the subject of interest to researchers. For this time numerous investigations show that commonly the effect of a magnetic field on chemical reactions is insignificant with impact less than 10 percent. However, there are some papers that point to the observation of external magnetic field effect on chemical and biochemical systems actually having a significant impact on the reactions. Thus, of great interest is an active search for rather simple but realistic models, that are based on physically explicit assumptions and able to account for a strong effect of low magnetic fields. The present work theoretically deals with two models explaining how an applied weak magnetic field might influence the steady state of a non-equilibrium chemical system. It is assumed that external magnetic field can have effect on the rates of radical reactions occurring in a system. This, in turn, leads to bifurcation of the nonequilibrium stationary state and, thus, to a drastic change in the properties of chemical systems (temperature and reagent concentration).

• Korea-Australia Rheology Journal
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• 제14권2호
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• pp.63-70
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• 2002

Chemical mechanical planarization (CMP) is the polishing process enabled by both chemical and mechanical actions. CMP is used in the fabrication process of the integrated circuits to achieve adequate planarity necessary for stringent photolithography depth of focus requirements. And recently copper is preferred in the metallization process because of its low resistivity. We have studied the effects of chemical reaction on the polishing rate and surface planarity in copper CMP by means of numerical simulation solving Navier-Stokes equation and copper diffusion equation. We have performed pore-scale simulation and integrated the results over all the pores underneath the wafer surface to calculate the macroscopic material removal rate. The mechanical abrasion effect was not included in our study and we concentrated our focus on the transport phenomena occurring in a single pore. We have observed the effects of several parameters such as concentration of chemical additives, relative velocity of the wafer, slurry film thickness or ash)tract ratio of the pore on the copper removal rate and the surface planarity. We observed that when the chemical reaction was rate-limiting step, the results of simulation matched well with the experimental data.

• 대한화학회지
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• 제52권1호
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• pp.84-95
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• 2008

이 연구에서는 대기 중에서 물이 증발하는 현상을 상평형 그림으로 설명하는 중등학교 화학전공 교 사들의 선개념을 알아보았다. 이 연구에서 개발한 설문을 실시하기 위하여 25명의 화학전공 과학 교사들을 선 정하였으며, 그 중에서 6명에게 설문지의 응답에 대한 생각을 면담으로 알아보았다. 연구 대상자 중 10명의 교 사를 선정하여, 이 연구에서 개발한 수업에 의해 선개념이 변화하는지 알아보았다. 연구 결과, 많은 교사들이 물의 증발 현상을 상평형 그림으로 설명할 수 없다고 생각하는 것으로 밝혀졌다. 또한 그들은 증기 압력과 상 평형 그림의 세로축과도 관련이 없다고 생각하였다. 그러나 그들은 수업을 통해 지구과학에서 다루는 포화 수 증기량 곡선을 적용함으로써 상평형 그림의 증기 압력 곡선을 설명할 수 있다는 점을 깨달았다. 그들은 이미 포화 수증기량 곡선에서 물질의 포화 상태와 불포화 상태, 평형 이동 과정 등에 대한 개념을 적용하는 과정을 알고 있었기 때문이다. 지구과학과 화학을 통합한 과학 수업을 통한 개념 변화에 의해 교사들은 증발과 같은 자연 현상을 상평형 그림으로 이해할 수 있게 되었다.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1305-1311
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• 2014

The nickel oxide, the most widely used cathode material for the molten carbonate fuel cell (MCFC), has several disadvantages including NiO dissolution, poor mechanical strength, and corrosion phenomena during MCFC operation. The surface modification of NiO with lanthanum maintains the advantages, such as performance and stability, and suppresses the disadvantages of NiO cathode because the modification results in the formation of $LaNiO_3$ phase which has high conductivity, stability, and catalytic activity. As a result, La-modified NiO cathode shows low NiO dissolution, high degree of lithiation, and mechanical strength, and high cell performance and catalytic activity in comparison with the pristine NiO. These enhanced physico-chemical and electrochemical properties and the durability in marine environment allow MCFC to marine application as a auxiliary propulsion system.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.118-120
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• 2003

The behavior of viscous fingerings caused by an external force is investigated by using a two­phase lattice Boltzmann method. The effects of the modified capillary number, the viscosity contrast, and the modified Darcy-Rayleigh number on the instability of interfaces are found. The calculated wave numbers are in good agreement with the theoretical ones in the range of wave numbers smaller than 10, but the calculated ones tend to become smaller than the theoretical ones in higher wave numbers.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1767-1772
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• 2008

A microcantilever is a well-known MEMS structure for sensing bio-chemical molecules. When bio-chemical molecules are adsorbed on the microcantilever's surface, resonance frequency shift is generated. There are two issues in this phenomena. The first one is which one between mass change and surface stress change effects is more dominant on the resonance frequency shift. The second one is what will be the performance change when the boundary condition is changed from cantilevers to double clamped beams. We have studied the effect of surface stress change and compared it with that of mass change by using FEM analysis. Furthermore, for microstructures having different boundary conditions, we have studied Q-factor, which determines the detection limit of micro/nano mechanical sensors.

• Korea-Australia Rheology Journal
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• 제20권3호
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• pp.143-152
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• 2008

Simulations of solutions of flexible polymer molecules during flow in simple or complex confined geometries are performed. Concentrations from ultradilute up to near the overlap concentration are considered. As concentration increases, the hydrodynamic migration effects observed in dilute solution unidirectional flows (Couette flow, Poiseuille flow) become less prominent, virtually vanishing as the overlap concentration is approached. In a grooved channel geometry, the groove is almost completely depleted of polymer chains at high Weissenberg number in the dilute limit, but at finite concentration this depletion effect is dramatically reduced. Only upon inclusion of hydrodynamic interactions can these phenomena be properly captured.

• Korea-Australia Rheology Journal
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• 제20권3호
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• pp.153-164
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• 2008

Modeling and experiments of three electrospinning systems have been presented and they are i) axisymmetric instabilities in electrospinning of various polymeric solutions, ii) non-isothermal modeling of polymer melt electrospinning, and iii) control of nanoparticle distribution and location via confined self-assembly of block copolymers during electrospinning. It has been demonstrated that predicted simulations are in good agreement with corresponding electro spinning experiments, and theoretical analysis provides fundamental understanding of phenomena that take place during electrospinning of various polymeric liquids.

• Bulletin of the Korean Chemical Society
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• 제24권10호
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• pp.1449-1454
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• 2003

A new equation has been derived on the basis of ${\delta}G^o$ = -RT lnK, linear behavior of the enthalpy of micellization with temperature, and the Gibbs-Helmholtz relation. It describes correctly the dependence of critical micelle concentration $(X_{CMC})$ on temperature and has yielded excellent fitting results for various surfactant systems. The new equation results in the linear behavior of the entropy of micellization with temperature and accounts for the compensation phenomena observed for the micellization in aqueous solutions, along with the linear dependence of the enthalpy of micellization on temperature. These results imply that the new equation of $X_{CMC}(T)$ accounts for the temperature dependence of CMC correctly.