• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1276-1282
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• 1995

• Korean Journal of Metals and Materials
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• v.49 no.6
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• pp.425-439
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• 2011

A review of the development history of interatomic potential models for ionic materials was carried out paying attention to the way of future development of an interatomic potential model that can cover ionic, covalent and metallic bonding materials simultaneously. Earlier pair potential models based on fixed point charges with and without considering the electronic polarization effect were found to satisfactorily describe the fundamental physical properties of crystalline oxides (Ti oxides, $SiO_2$, for example) and their polymorphs, However, pair potential models are limited in dealing with pure elements such as Ti or Si. Another limitation of the fixed point charge model is that it cannot describe the charge variation on individual atoms depending on the local atomic environment. Those limitations lead to the development of many-body potential models(EAM or Tersoff), a charge equilibration (Qeq) model, and a combination of a many-body potential model and the Qeq model. EAM+Qeq can be applied to metal oxides, while Tersoff+Qeq can be applied to Si oxides. As a means to describe reactions between Si oxides and metallic elements, the combination of 2NN MEAM that can describe both covalent and metallic elements and the Qeq model is proposed.

• Proceedings of the KIEE Conference
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• 2000.07e
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• pp.108-112
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• 2000

The electric charge generated by flowing insulation liquid can create hazardous spark in transfer line and receiving tank etc. These electrification has generally been measured by current measurement with a ammeter connected to the receiving tank. This paper reports on the experimental result obtained by this method. As a experimental results: The injected charge value for unit volume increased in the following condition, the edge of the needle electrode was sharp, the number of needle electrode was fewer, the edge of the needle electrode was located close to the inside wall. When the charge density in the charge reducer is constant, electrode current and electrode potential by the charge injection from outside increase with increasing of oil velocity and streaming current. The electrode potential in charge reducer is made maximum value at edge point of reducer inside and minimum value at center line of charge reducer.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.183-188
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• 2011

In this article, the effect of the crystal structural environment of $Pr^{3+}$ ions on the photoluminescence (PL) characteristics of double tungstates, such as $A(M_{1-X}Pr_X)W_2O_8$ (A=Li, Cs, M = In, Y, Sc, La; $0.007{\leq}x{\leq}0.1$) and $La_{1.96}Pr_{0.04}W_3O_{12}$ are characterized. By varying the ion radius in A and M sites, the structural environment of $Pr^{3+}$ ions were modified. The structural criteria, that is, the point charge electrostatic potentials V around the $Pr^{3+}$ activator, were calculated using the crystal structural parameters. The point charge potential V can be a valid criterion for $^3P_o$ quenching in various double tungstates. When the calculated V values are large (> 6.0), the luminescence from the $^3P_0$ level becomes dominant. When the calculated V values are about 3.8, the $^1D_2$ line appears weakly but $^3P_0$-level luminescence is absent. When the calculated V values are small (< 2.0), the luminescence from the $^1D_2$ level becomes dominant and $^3P_0$-level luminescence is absent. At 2.0$^3P_o$ quenching to $^1D_2$ level occurs substantially in accordance with the structural criterion of the point charge potential model.

• Journal of Electrochemical Science and Technology
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• v.8 no.3
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• pp.244-249
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• 2017

This paper presents the results of an investigation into the isoamperic point of cyclic voltammograms, which is defined as the singular point where the voltammograms of various scan rates converge. The origin of the unique point is first considered from a theoretical perspective by formulating the voltammetric curves as a system of linear equations, the solution of which indicates that a trivial solution is only available at the potential at which the net current is zero during the reverse potential scan. In addition, by way of a mathematical formulation, it was also shown that the isoamperic point is dependent on the switching potential of the potential scanning. To validate these findings, theoretical and practical cyclic voltammmograms were studied using finite-element based digital simulations and 3-electrode cell experiments. The new understanding of the nature of the isoamperic point provides an opportunity to measure the charge transfer effects without the influence of the mass transfer effects when determining the thermodynamic and kinetic characteristics of a faradaic system.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.6
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• pp.619-625
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• 1991

Phenomena of streaming electrification of insulting oil(T.O) is studied where the oil is contacted with solid insulating materials when it is pumped through a circulating system in a large power transformer. The leakage current, the electrical potential at the neutral terminal point of the transformer and the surface electrical potential of the oil are investigated. And the leakage current from the neutral terminal point is measured as a function of a bias polarity applied to a transformer case to investigate the polarty of ion which is absorbed in the case at the interface between the case and oil. As a result, it is found that insulating materials, and it is suggested that the leakage current is the sum of the relaxation current by positive charge from insulating oil to the neutral terminal point and by electrification current from negative charge electrified by the contact with solid insulating materials.

• Environmental Engineering Research
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• v.8 no.4
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• pp.222-227
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• 2003

• Bulletin of the Korean Chemical Society
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• v.26 no.7
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• pp.1083-1089
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• 2005

Most experimental studies available in the literature on filtration are based on observed average zeta potential of particles (usually 10 measurements). However, analyses of data using the average zeta potential alone can lead to misleading and erroneous conclusions about the attachment behavior because of the variation of particle zeta potentials and the heterogeneous distribution of the collector surface charge. To study characteristics of zeta potential, zeta potential distributions (ZPDs) of silica particles under 9 different chemical conditions were investigated. Contrary to many researchers’ assumptions, most of the ZPDs of silica particles were broad. The solids concentration removal was better near the isoelectric point (IEP) as many researchers have noticed, thus proper destabilization of particles is very important to achieve better particle removal in particle separation processes. While, the mean zeta potential of silica particles at a given coagulant dose was a function of particle concentration; the amount of needed coagulant for particle destabilization was proportional to the total surface charge area of particles in the suspension.

• Corrosion Science and Technology
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• v.12 no.1
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• pp.40-49
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• 2013

Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio- dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH, while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM), surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by pH. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH 8.4, 0.2M citrate solution but was increased by magnesium at the solution of pH 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute, decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface. It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral pH solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [$Cl^-$] around 0.025 M of [$Cl^-$] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly basic solutions.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.115.1-115.1
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• 2014

Atom-thick 2-dimensional materials such as graphene, h-BN and MoS2 hold substantial potential for applications in future molecular-scale integrated electronics, transparent conducting membranes, nanocomposites, etc. From a fundamental point of view, 2-dim crystal-solid substrates can also serve as a unique system to study various physicochemical phenomena occurring at low dimensions or interfaces. In this talk, I will present our recent Raman spectroscopy studies on the surface science problems of graphene: interfacial charge transfer, molecular diffusion in confined space and structural deformation.