• Title, Summary, Keyword: Surface charge

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Effects of Charge-discharge Rate on Morphology and Resistance of Surface Film on a Graphite Negative Electrode in an Ethylene Carbonate-based Solution (탄산 에틸렌계 용액 중에서 생성되는 흑연 음극 표면피막의 형상 및 저항에 미치는 충방전 속도의 영향)

  • Jeong, Soonki;Kim, Pogyom
    • Transactions of the Korean hydrogen and new energy society
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    • v.24 no.2
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    • pp.179-185
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    • 2013
  • The behavior of surface film formation was greatly dependent on the speed of potential cycling. In $LiClO_4$ / EC + DEC, cyclic voltammetry results showed that the peaks originated from surface film formation on graphite electrode at the high charge-discharge rate was shifted to the lower potentials as the charge-discharge rate decrease. This indicates that surface films with different morphology and thickness were formed by different charge-discharge rate. Transmission electron microscopy (TEM) results indicated that the properties such as thickness and morphology of the surface film were greatly affected by the charge-discharge rate. Electrochemical impedance spectroscopy (EIS) showed that the resistance of surface film was affected by the speed of potential cycling. In addition, the charge transfer resistance was also dependent on the charge-discharge rate indicating that the charge transfer reaction was affected by the nature of surface film. TEM and EIS results suggested that the chemical property as well as the physical property of the surface film was affected by the charge-discharge rate.

Characteristic Analysis of Electret Filters made by Electrospinning (전기방사를 통한 정전필터제조 및 특성분석)

  • Ahn, Young-Chull;Kim, Gil-Tae;Kim, Seong-Kon;Lee, Jae-Keun;Kim, Jong-Won
    • Proceedings of the SAREK Conference
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    • pp.1134-1138
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    • 2008
  • Electret filter media are used in general ventilation filters, disposable respirators, vehicle cabin filters, vacuum cleaners and room air cleaners. There are basic mechanisms of interception, inertial impaction, diffusion, gravitational settling, electrostatic attraction by which an aerosol particle can be deposited onto a fiber in a filter. The ability of fine particle removal strongly depends on the electrostatic forces between particles and polarized fibers. Thus, the stability of the fiber polarization is a major factor in the reliability of electret filters. In this study, electrical properties and filtration performance of electrospun filter media are quantitatively investigated. Electrical properties of electrospun filters have been studied on surface charge potential and surface charge density. Also the filtration performance of the electret filters are evaluated on collection efficiency. Electrospun filters show same collection efficiency with low pressure drop compare to commercialized HEPA filters. Surface charge potential and surface charge density of electrospun filters are increased with increasing applied voltage. Also collection efficiency of electrospun filters is increased with increasing surface charge potential and surface charge density.

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Equilibrium Crystal Shape of BaZrO3 and Space Charge Formation in the (011) Surface by Using Ab-Initio Thermodynamics

  • Kim, Ji-Su;Kim, Yeong-Cheol
    • Journal of the Korean Physical Society
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    • v.70 no.1
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    • pp.75-80
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    • 2017
  • We investigated the equilibrium crystal shape of $BaZrO_3$ and the space charge formation in an O-terminated (011) surface by using ab-initio thermodynamics. Twenty-two low-indexed (001), (011), and (111) surfaces were calculated to analyze their surface Gibbs-free energy under the stable condition of $BaZrO_3$. Based on the Gibbs-Wulff theorem, the equilibrium crystal shape of $BaZrO_3$ changed from cubic to decaoctahedral with decreasing Ba chemical potential. The dominant facets of $BaZrO_3$ were {001} and {011}, which were well consistent with experimental observations. The space charge formation in the (011) surface was evaluated using the space-charge model. We found that the (011) surface was even more resistive than the (001) surface.

Characterizations of Membrane for Water Treatment: Surface Charge Analysis by Electrophoresis and Acidity Measurements

  • Yongki Shim;Lee, Sangyoup;Moon, Seung-Hyeon;Jaeweon Cho
    • Korean Membrane Journal
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    • v.2 no.1
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    • pp.56-59
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    • 2000
  • The surface charge properties of a polymeric NF and a ceramic UF membranes were characterized in terms of zeta potential and acidity. Both the negative zeta potential and acidity values increased as pH increases due to ionizable acidic functional groups. Increased ionic strength reduced the acidity of the negatively-charged membrane surface as anticipated. Through these results, it can be envisioned are used to reject solutes with ionizable functional groups. Fouling of the negatively-charged membrane with natural organic matter (NOM) having a negative charge density was also investigated with respect to the surface charge. The surface charge of the NF membrane increased negatively when greater NOM adsorption onto the membrane surface occured.

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A Theoretical Study of CO Molecules on Metal Surfaces: Coverage Dependent Properties

  • Sang -H. Park;Hojing Kim
    • Bulletin of the Korean Chemical Society
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    • v.12 no.5
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    • pp.574-582
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    • 1991
  • The CO molecules adsorbed on Ni(111) surface is studied in the cluster approximation employing EH method with self-consistent charge iteration. The effect of CO coverage is simulated by allowing the variation of valence state ionization potentials of each Ni atom in model cluster according to the self-consistent charge iteration method. The CO coverage dependent C-O stretching frequency shift, adsorption site conversion, and metal work function change are attributed to the charge transfer between metal surface and adsorbate. For CO/Ni(111) system, net charge transfer from Ni surface to chemisorbed CO molecules makes surface Ni atoms be more positive with increasing coverage, and lowers Ni surface valence band. This leads to a weaker interaction between metal surface valence band and Co $2{\pi}^{\ast}$ MO, less charge transfer to a single CO molecule, and the bule shift of C-O stretching frequency. Further increase of coverage induces the conversion of 3-fold site CO to lower coordination site CO as well as the blue shift of C-O stretching frequency. This whole process is accompanied by the continuous increase of metal work function.

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Characteristic Analysis of Electret Filters made by Electrospinning (전기방사를 통해 제조된 정전기 보유 필터의 표면전위 및 대전량에 따른 성능특성 분석)

  • Kim, Gil-Tae;Ahn, Young-Chull;Lee, Jae-Keun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.12
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    • pp.820-824
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    • 2008
  • Electret filter media are used in general ventilation filters, disposable respirators, vehicle cabin filters, vacuum cleaners and room air cleaners. There are basic mechanisms of interception, inertial impaction, diffusion, gravitational settling, electrostatic attraction by which an aerosol particle can be deposited onto a fiber in a filter. The ability of fine particle removal strongly depends on the electrostatic forces between particles and polarized fibers. Thus, the stability of the fiber polarization is a major factor in the reliability of electret filters. In this study, the electret filter is made by electrospinning process using Polystyrene which is dissolved by 5 : 5 of Tetrahydrofuran (THF) and Dimethylformamide (DMF). Also the electrical properties and the filtration performances of electrospun filter media are Quantitatively investigated. Electrical properties of electrospun filters have been studied on surface charge potential and surface charge density. Also the filtration performance of the electret filters are evaluated on collection efficiency. The surface charge potential and the surface charge density of electrospun PS filters are increased with increasing applied voltage and saturated at 30 kV of applied voltage. Also collection efficiency of electro spun filters is increased with increasing surface charge potential and surface charge density. But the surface charge potential is decreased by natural decay and it causes deterioration of particle collection efficiency.

Synthesis of Polystyrene Nanoparticles with Monodisperse Size Distribution and Positive Surface Charge Using Metal Stearates

  • Kim, Mi-Sun;Kim, Seok-Ki;Lee, Jun-Young;Cho, Seung-Hyun;Lee, Ki-Hoon;Kim, Jun-Kyung;Lee, Sang-Soo
    • Macromolecular Research
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    • v.16 no.2
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    • pp.178-181
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    • 2008
  • Polystyrene (PS) nanospheres with a monodisperse size distribution, positive surface charge and high molecular weight were successfully synthesized using various types of metal stearates in an aqueous NaOH medium. The diameter of the PS nanospheres was controlled from 80 to 450 nm by changing the type of metal stearate. It was also found that controlling the NaOH concentration in solution was important for producing monodisperse PS nanoparticles. The nanospheres prepared with zinc stearate possessed a positive surface charge of 60 to 80 mV, confirming that PS particles were functionalized with metal stearates. It is believed that the metal stearates provide PS particles with not only colloidal stability but also a positive surface charge.

Electrohydrodynamic Analysis of Dielectric Guide Flow Due to Surface Charge Density Effects in Breakdown Region

  • Lee, Ho-Young;Kang, In Man;Lee, Se-Hee
    • Journal of Electrical Engineering and Technology
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    • v.10 no.2
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    • pp.647-652
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    • 2015
  • A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

Analysis of 3-Dimensional Electric Fields with Surface Charge Method (표면전하법을 이용한 일반 3차원 전계해석)

  • 박종근;김광수
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.34 no.9
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    • pp.341-348
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    • 1985
  • This paper deals with a surface charge simulation method of calculating three-dimensional electric fields and capacitance. The principle is to divide the electrode surface into rectangular or triangular elements of which charge density is the linear function of the electrode coordinate and to formulate a linear equation for the coefficients of charge density function and to determine those coefficients by boundary conditions. It has been shown that the method can give satisfactory results for thin rectangular plates where the other methods is difficult to be applied.

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Effects of Soil Organic Matter on Surface Charge Characteristics of Paddy and Upland Soils (논과 밭 토양의 표면전하 특성에 미치는 토양 유기물 영향)

  • Lim, Sook-Il;Lee, Moon-Yong;Hyun, Seung-Hun;Lee, Sang-Eun;Jeong, Chang-Yoon;Kim, Jeong-Gyu
    • Korean Journal of Soil Science and Fertilizer
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    • v.31 no.4
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    • pp.414-419
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    • 1998
  • The contribution of soil organic matter on the soil surface charge characteristic of paddy and upland soils weathered from granite or limestone was evaluated. The surface charge characteristics of the soils with and without soil organic matter by pre-treatment with hydrogen peroxide was determined at pH 3.5~9.0 range using the ion adsorption method. Regardless of soil organic matter removal, the soil surface negative charge increased linearly by the increase of pH with high statistical significance at all kinds of soils. Here, the differential increasement of soil surface negative charge by pH inclease, dCEC/dpH, was proposed as the parameter of pH dependency of the soil surface charge. The dCEC/dpH of soils with organic matter was in the range of 0.91~4.59, while it was dramatically decreased to the range 0.16~1.91 by the removal of organic matter. The soil surface charge derived from soil organic matter ranged from 15% to 82% to the total amount of surface charge. The magnitude of surface charge carried by 1% of soil organic matter showed considerable differences between soils from 0.22 to $5.03cmol^+\;kg^{-1}$. The effect of soil organic matte on the dCEC/dpH was higher in paddy soils with high oxalic acid extractable Fe than upland soils.

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