• Title, Summary, Keyword: diffuse layer model

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A new method to predict swelling pressure of compacted bentonites based on diffuse double layer theory

  • Sun, Haiquan
    • Geomechanics and Engineering
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    • v.16 no.1
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    • pp.71-83
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    • 2018
  • Compacted bentonites were chosen as the backfill material and buffer in high level nuclear waste disposal due to its high swelling pressure, high ion adsorption capacity and low permeability. It is essential to estimate the swelling pressure in design and considering the safety of the nuclear repositories. The swelling pressure model of expansive clay colloids was developed based on Gouy-Chapman diffuse double layer theory. However, the diffuse double layer model is effective in predicting low compaction dry density (low swelling pressure) for certain bentonites, and invalidation in simulating high compaction dry density (high swelling pressure). In this paper, the new relationship between nondimensional midplane potential function, u, and nondimensional distance function, Kd, were established based on the Gouy-Chapman theory by considering the variation of void ratio. The new developed model was constructed based on the published literature data of compacted Na-bentonite (MX80) and Ca-bentonite (FoCa) for sodium and calcium bentonite respectively. The proposed models were applied to re-compute swelling pressure of other compacted Na-bentonites (Kunigel-V1, Voclay, Neokunibond and GMZ) and Ca-bentonites (FEBEX, Bavaria bentonite, Bentonite S-2, Montigel bentonite) based on the reported experimental data. Results show that the predicted swelling pressure has a good agreement with the experimental swelling pressure in all cases.

Modeling of Acid/Base Buffer Capacity of soils (토양의 산/염기 완충능의 모델링)

  • 김건하
    • Journal of Korea Soil Environment Society
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    • v.3 no.3
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    • pp.3-10
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    • 1998
  • Acid/Base buffer capacity of soil is very important in prediction of contaminant transport for its direct impact on pH change of the system composed of soil-contaminant-water, In this research, diffuse double layer theory as well as two layer electrostatic adsorption model are applied to develop a theoretical model of buffer capacity of soil. Model application procedures are presented as well. Buffer capacity of Georgia kaolinite and Milwhite kaolinite was measured by acid-base titration. Model prediction and experimental results are compared.

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On the Chemical Evolution of Collapsing Starless Cores

  • Seo, Young-Min;Lee, Jeong-Eun;Kim, Jong-Soo;Hong, Seung-Soo
    • The Bulletin of The Korean Astronomical Society
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    • v.35 no.2
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    • pp.73.2-73.2
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    • 2010
  • In order to understand internal dynamics of starless cores, molecular line emissions are usually observed. From profiles of the molecular lines, internal motions of starless cores have been deduced using a simple radiative transfer model such as the two-layer model (Myers et al.1996). This brings complexities arising from the chemical evolution. The motivation of this study is to follow the chemical evolution of a starless core that goes through gravitational contraction. For this purpose, we have performed hydrodynamical simulations with a marginally unstable Bonnor-Ebert sphere as an initial condition. We follow the chemical evolution of this core with changing conditions such as the chemical reaction rate at the dust surface and the strength of radiation field that penetrate into the core. At the core center, the molecules suffer from a higher degree of molecular depletion on the dust covered by ice rather than on the bare silicate dust. The stronger radiation field dissociates more molecules at the core envelope. From analysis on the line profile using the two-layer model, we found that the speed of inward motion deduced from the HCN F = 2-1 line adequately traces the true infall speed, when the dust is covered by ice and the core is exposed to the diffuse interstellar radiation field. Under different conditions, the two-layer model significantly underestimate the infall speed.

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CFD Analysis on a Flow Channel of a Bipolar Plate with Varying Cross-sectional Area in a PEM Fuel Cell (PEM 연료전지용 Bipolar Plate의 변화단면 유로에 대한 CFD 해석)

  • Yang, Dong-Jin;Park, Woon-Jean
    • New & Renewable Energy
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    • v.3 no.3
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    • pp.14-19
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    • 2007
  • A flow channel model of a bipolar plate with varying cross-sectional area was newly designed for improving performance and efficiency of a PEM fuel cell stack. As a result, the varying cross-sectional area model showed poor uniformity in velocity distribution, however, maximum velocity in the flow path is about 30% faster than that of the uniform cross-sectional area model. The proposed varying cross-sectional area model is expected to diffuse operating fluids more easily into diffusion layer because it has relatively higher values in pressure distribution compared with other flow channel models. It is expected that the implementation of the varying cross-sectional area model can reduce not only the mass transport loss but also the activation loss in a PEM fuel cell, and open circuit voltage of a fuel cell can thus be increased slightly.

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Surface characteristics of TiO$_2$ in the Alcohol-Water Cosolvent System

  • Yoon, Sun-Hee;Shin, Yong-Il;Park, Sang-Won
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • pp.112-115
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    • 2000
  • Surface complex models(SCMs)은 최근 흡착모델링에 대한 관심사가 부각되면서 수질(표면수, 지하수)오염에 대한 영향을 예측하고 흡착결과를 파악하는데 많은 주목을 받고 있다. SCMs의 흡착모델의 하나인 diffuse double layer model(DDLM)은 특정조건에서 Gouy-Chapman 이론을 바탕으로 설명하고 있지만, 실제와는 상당한 차이를 보인다. 따라서 본 논문은 기존의 자료를 바탕으로 TiO$_2$/용매(수용액/ 물-에탄올(1:1))간의 거리를 추정해 감에 따라, 각 실험적 변수에 따른 electrical double layer(EDL)의 흡착형태의 변화를 알아보았다. 또한, cosolvent가 존재할때, 흡착모델 형태의 변화와 흡착결과에 대한 영향에 대해 알아보았다.

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The vacancy diffusion and the formation of dislocation in graphene : Tight-binding molecular dynamics simulation

  • Lee, Gun-Do;Yoon, Eui-Joon;Hwang, Nong-Moon
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.54-55
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    • 2010
  • Vacancy defects in graphene can be created by electron or ion irradiation and those induce ripples which can change the electronic properties of graphene. Recently, the formation of defect structures such as vacancy defects and non-hexagonal rings has been reported in the high resolution transmission electron microscope (HR-TEM) of reduced graphene oxide [1]. In those HR-TEM images, it is noticed that the dislocations with pentagon-heptagon (5-7) pairs are formed and diffuses. Interestingly, it is also observed that two 5-7 pairs are separated and diffuse far away from each other. The separation of 5-7 pairs has been known to be due to their self-diffusion. However, from our tight-binding molecular dynamics simulation, it is found that the separation of 5-7 pairs is due to the diffusion of single vacancy defects and coalescence with 5-7 pairs. The diffusion and coalescence of single vacancy defects is too fast to be observed even in HR-TEM. We also implemented Van der Waals interaction in our tight-binding carbon model to describe correctly bi-layer and multi-layer graphene. The compressibility of graphite along c-axis in our tight-binding calculation is found to be in excellent agreement with experiment. We also discuss the difference between single layer and bi-layer graphene about vacancy diffusion and reconstruction.

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Moisture Induced Hump Characteristics of Shallow Trench-Isolated nMOSFET (Shallow Trench Isolation 공정에서 수분에 의한 nMOSFET의 Hump 특성)

  • Lee, Young-Chul
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.10 no.12
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    • pp.2258-2263
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    • 2006
  • In this parer, hump characteristics of short-channel nMOSFETs induced by moistures of the ILD(inter-layer dielectric) layer in the shallow trench isolation (STI) process are investigated and the method for hump suppression is proposed Using nMOSFETs with various types of the gate and a measurement of TDS-APIMS (Thermal Desorption System-Atmospheric Pressure ionization Mass Spectrometry), hump characteristics were systematically analyzed and the systemic analysis based hump model was presented; the ILD layer over poly-Si gate of nMOSFET generates moistures, but they can't diffuse out of the SiN layer due to the upper SiN layer. Consequently, they diffuses into the edge between the gate and STI and induces short-channel hump. In order to eliminate moisture in the ILD layer by out-gassing method, the annealing process prior to the deposition of the SiN layer was carried out. As the result, short-channel humps of the nMOSFETs were successfully suppressed.

Electrical Properties of Tungsten Oxide Interfacial Layer for Silicon Solar Cells

  • Oh, Gyujin;Kim, Eun Kyu
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.196.2-196.2
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    • 2015
  • There are various issues fabricating the successful and efficient solar cell structures. One of the most important issues is band alignment technique. The solar cells make the carrier in their active region over the p-n junction. Then, electrons and holes diffuse by minority carrier diffusion length. After they reach the edge of solar cells, there exist large energy barrier unless the good electrode are chosen. Many various conductor with different work functions can be selected to solve this energy barrier problem to efficiently extract carriers. Tungsten oxide has large band gap known as approximately 3.4 eV, and usually this material shows n-type property with reported work function of 6.65 eV. They are extremely high work function and trap level by oxygen vacancy cause them to become the hole extraction layer for optical devices like solar cells. In this study, we deposited tungsten oxide thin films by sputtering technique with various sputtering conditions. Their electrical contact properties were characterized with transmission line model pattern. The structure of tungsten oxide thin films were measured by x-ray diffraction. With x-ray photoelectron spectroscopy, the content of oxygen was investigated, and their defect states were examined by spectroscopic ellipsometry, UV-Vis spectrophotometer, and photoluminescence measurements.

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The Change in Geotechnical Properties of Clay Liner and the Contamination Behavior of Groundwater Due to Contaminant (오염물질에 의한 점토 차수재의 역학적 특성변화 및 지하수 오염거동)

  • Ha, Kwang-Hyun;Lee, Sang-Eun;Chung, Sung-Rae;Chun, Byung-Sik
    • Journal of Soil and Groundwater Environment
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    • v.13 no.1
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    • pp.13-23
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    • 2008
  • The triaxial compression tests and consolidation tests using NaCl solution and leachates as substitute pore (or saturated) water in samples were carried out to find out the behavior characteristics of strength, deformation and permeability coefficient of contaminated clay. Also, the chemical property analysis on the clay samples using scanning electron microscope and energy dispersive x-ray spectrometer were involved. The magnitudes of composition ratio were shown in the order of O, C, Si, Al, and Fe as a result of chemical composition analysis for clay samples. Besides, as the results of triaxial compression tests and consolidation tests, the shear strength, compression and permeability properties were increased with increasing in the concentration of contaminant (NaCl). It may be considered that these circumstances be caused by the changes of soil structure to flocculent structure due to the decrease in the thickness of diffuse double layer with increasing in the concentration of electrolyte. MT3D model was also using to grasp the procedures that the groundwater may be contaminated by the leachates permeated through the clay liner. The results of contaminant transport analysis showed a tendency that the predicted concentration of groundwater was higher with increasing in the initial concentration of $Cl^-$ ion and increased as a nonlinear curves with time. The transportation distance calculated by the use of regression equation between the distance from contaminant source and the concentration of $Cl^-$ ion was increased with increasing the initial concentration.