• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.4
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• pp.249-256
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• 2019

This paper presents an optimization framework of electrical impedance tomography for characterizing electrical conductivity profiles of concrete structures in two dimensions. The framework utilizes a partial-differential-equation(PDE)-constrained optimization approach that can obtain the spatial distribution of electrical conductivity using measured electrical potentials from several electrodes located on the boundary of the concrete domain. The forward problem is formulated based on a complete electrode model(CEM) for the electrical potential of a medium due to current input. The CEM consists of a Laplace equation for electrical potential and boundary conditions to represent the current inputs to the electrodes on the surface. To validate the forward solution, electrical potential calculated by the finite element method is compared with that obtained using TCAD software. The PDE-constrained optimization approach seeks the optimal values of electrical conductivity on the domain of investigation while minimizing the Lagrangian function. The Lagrangian consists of least-squares objective functional and regularization terms augmented by the weak imposition of the governing equation and boundary conditions via Lagrange multipliers. Enforcing the stationarity of the Lagrangian leads to the Karush-Kuhn-Tucker condition to obtain an optimal solution for electrical conductivity within the target medium. Numerical inversion results are reported showing the reconstruction of the electrical conductivity profile of a concrete specimen in two dimensions.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.175-176
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• 2007

Radial Basis Function Network (RBFN)을 이용하여 플라즈마 전위의 예측 모델을 개발하였다. RBFN의 예측성능은 Genetic Algorithm (GA)를 이용하여 최적화 하였다. 체계적인 모델링을 위해 통계적인 실험계획법이 적용되었으며, 실험은 반구형 유도 결합형 플라즈마 장비를 이용하여 수행이 되었다. $Cl_2$ 플라즈마에서의 데이터 측정에는 Langmuir probe가 이용되었다. 최적화된 GA-RBFN 모델을 일반 RBFN 모델과 비교하였으며, 15%정도 모델의 예측성능을 향상시켰다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.112-112
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• 2018

알루미늄 합금은 내구성과 내식성이 우수한 경량 재료이다. 그 중 Al-Mg계 5083 Al 합금은 가공성 및 용접성이 우수하여 선체 재료로 널리 이용되고 있다. 이는 선체 중량의 경량화로 인해, 연료비 절감과 빠른 선속 등 다양한 이점을 지니기 때문이다. 그러나 선박의 고속화에 따라 선체에 가해지는 유체충격이 증가하고, 압력 저하에 기인하여 캐비테이션-침식 손상이 증가할 뿐만 아니라, 염소이온이 존재하는 해수환경에서는 침식과 부식의 시너지효과로 인하여 재료의 손상이 더욱 가속화된다. 이에 대한 다양한 방지책들이 제안되고 있으나, 강한 충격압을 동반한 캐비테이션 침식-부식 복합 손상 환경에서는 다소 한계가 있다. 따라서 본 연구에서는 알루미늄 5083에 대하여 캐비테이션 환경 하에서 일정 전위를 인가하며 침식-부식 손상이 최소화 되는 전위 구간을 규명하고자 하였다. 먼저, 분극 실험을 선행하여 재료의 전기화학적 거동을 파악 한 후 적용 전위구간을 선정하여, 해당 전위를 인가한 상태에서 캐비테이션 실험을 실시하였다. 전기화학적 분극실험과 캐비테이션-전기화학 복합 실험은 $25^{\circ}C$의 해수 하에서 실시하였으며, 시험편의 노출면적은 $3.24cm^2$으로 하였다. 분극 실험은 개로전위로부터 +3 V까지 2 mV/s의 분극속도로 전위를 인가하였고, 기준전극으로 Ag/AgCl, 대극으로 백금전극을 사용하였다. 캐비테이션-전기화학 복합 실험은 정전위를 인가한 상태에서 대향형 진동법으로 진동수 20 kHz, 진폭 $30{\mu}m$ 진동을 20분간 가하였으며, 혼팁과 시험편 사이의 거리는 1 mm로 일정하게 유지하였다. 실험 후 표면 손상의 정량적 분석을 위해 인가된 전위별 전류밀도를 비교하고, 무게감소량을 측정하였으며, 손상경향 파악을 위하여 3D광학현미경과 주사전자현미경(SEM)을 통해 표면을 분석하였다.

• Journal of the Korean Chemical Society
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• v.61 no.6
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• pp.320-327
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• 2017

In a borate buffer solution, the growth kinetics and the electronic properties of passive film on cobalt were investigated, using the potentiodynamic method, chronoamperometry, and single-frequency electrochemical impedance spectroscopy. It was found out that the unstable passive film ($Co(OH)_2$) and CoO of Co formed in the low electrode potential changes to $Co_3O_4$ and CoOOH while the electrode potential increases. And the composition of the passive films was varied against the applied potential and oxidation time. The oxide film formed during the passivation process of cobalt has showed the electronic properties of p-type semiconductor, which follow from the Mott-Schottky equation.

• Journal of the Korean Chemical Society
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• v.24 no.4
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• pp.295-301
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• 1980

The electrical conductivity of solid electrolyte $RbAg_4I_5$ single crystal was studied at various temperatures. The four-probe method was used in measuring the conductance with an ac signal imposed on the specimen. The ionic conductivity was $0.284 ohm^{-1} cm^{-1}\;at\;25^{\circ}C$, and the activation energy for $Ag^+$ ion migration was calulated to be 1.70 kcal/mole. These values agree well with those reported for polycrystalline samples. Reactions at $Ag/RbAg_4I_5$ interface were studied by cyclic voltammetry with a silver reference electrode. It was found that silver ion is reversibly reduced at silver surfaces below zero volt, and iodide was oxidized above +0.67 volt.The anodic current arising from the oxidation of the electrode was small in magnitude initially over a wide range of potential, but, after silver was cathodically deposited on the electrode, reversing the potential sweep to the anodic direction resulted in a sharp peak of anodic current.

• 전기의세계
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• v.44 no.4
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• pp.14-21
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• 1995

전해질(지중, 수중 혹은 해수중) 내부에 있는 금속구조물의 부식을 방지하는 가장 효과적인 방법인 전기방식법에는 양극방식법(anodic protection method)과 음극방식법(cathodic protection method)이 있다. 양극방식법은 피방식구조물을 자연전위 보다 높게 유지함으로써 구조물의 표면에 저항이 높은 피막을 형성시켜 부식을 방지하는 방법으로서, 금속의 재질에 따라 적용이 불가능한 경우가 많으며, 또, 가능하다 할지라도 유지 및 보수에 상당한 주의가 요구되므로 잘 쓰이지 않고 있는 반면에, 음극방식법은 거의 모든 재질에 적용 가능할 뿐만 아니라 유지 및 보수가 쉬우므로 현장에서 가장 널리 쓰이고 있음에 따라 전기방식법 하면 대부분 음극방식법을 지칭하는 것으로 이해되고 있다. 본고에서는 전기방식법을 이해하는데 도움이 되는 부식 메카니즘, 음극방식법의 원리, 음극방식법의 종류 및 설계법 등에 관하여 간략히 기술하고자 한다.

• Membrane Journal
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• v.13 no.1
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• pp.37-46
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• 2003

The electrokinetic effect can be found in cases of the fluid flowing across the charged membrane micropores. The externally applied body force originated from the electrostatic interaction between the nonlinear Poisson-Boltzmann field and the flow-induced electrical field is taken into the equation of motion. The electrostatic potential profile is computed a priori by applying the finite difference scheme, and an analytical solution to the Navier-Stokes equation of motion for slit-like pore is obtained via the Green's function. An explicit analytical expression for the flow-induced streaming potential is derived as functions of relevant physicochemical parameters. The influences of the electric double layer, the surface potential of the wall, and the charge condition of the pore wall upon the velocity profile as well as the streaming potential are examined. With increasing of either the electric double layer thickness or the surface potential, the average fluid velocity is entirely reduced, while the streaming potential increases.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.2
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• pp.49-54
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• 2005

Measuring ground resistance is a typical way of performance evaluation of a grounding electrode. Among various ground resistance measurement methods, FOP (Fall-Of-Potential) method has been widely used, especially in case of a relatively large grounding electrode such as a substation grounding mesh grid Since FOP measurement line has to be increased as the size of grounding electrode increases, however, it is often that securing long enough FOP-line is practically impossible. In this paper, a sophisticated interpretation method of FOP measurement ma which is applicable to large grounding electrode networks, is presented.

• Geophysics and Geophysical Exploration
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• v.19 no.1
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• pp.45-50
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• 2016

Generally, a point source has been routinely used in the electrical resistivity measurements because of easy installation. If steel-cased wells are used as long electrodes, we can expect the better depth of investigation. However, the resistivity data with long electrodes can not be processed with a conventional inversion algorithm because a long electrode produces the different primary potential distribution compared with the point source. In this study, we proposed a new technique to process the electrical resistivity data with long electrodes by replacing the long electrode with a sequence of point electrodes. Comparing the potentials obtained from the technique with the analytic/numerical solution, we ensure that the proposed technique can be used for the numerical resistivity modeling based on the finite difference or finite element method.

• Resources Recycling
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• v.8 no.3
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• pp.18-25
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• 1999

The study on the electrosorption of cobalt ions onto a porous activated carbon fiber (ACF) was performed to treat radioactive liquid wastes resulting from chemical or electrochemical decontamination and to regenerate the spent carbon electrode, Cyclic voltammetry was investigated on a rotating-disk electrode (RDE) to determine the region of potentials within which only double-layer charging should occur. The application of an electric potential increased the sorption of the cobalt ions. The adsorbed cobalt Ions could be released into the solution by reversing the appling potential, showing the reversibility of the process.