• 전기화학회지
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• 제12권1호
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• pp.1-10
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• 2009

This article reviewed transport behaviours of electroactive species in ionic compounds, focusing on chemical diffusion of Li through the transition metal oxide in a current flowing condition. For this purpose, a distinction has been first briefly made between migration and diffusion with respect to current, driving force and charge of electroactive species considered. Then, the equations for chemical diffusion are derived theoretically in open-circuit and current flowing conditions. Finally, the experimental methods such as ac impedance spectroscopy and current (potential) transient techniques are described in details for characterising chemical diffusion. In addition, the role of the thermodynamic enhancement factor in chemical diffusion is discussed.

• Journal of Radiation Protection and Research
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• 제16권2호
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• pp.27-39
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• 1991

압축된 국산벤토나이트에서 Sr-85, Cs-237, Co-60 및 Am-241의 확산연구를 수행하였다. 본 실험에서는 원통형으로 압축된 벤토나이트 시료의 중앙부에서 축 방향으로 방사성핵종의 확산이동이 이루어지도록 하여 각 방사성핵종의 확산계수를 측정하였다 그리고 벤토나이트의 열처리 온도와 압축밀도가 확산에 미치는 영향 등을 분석하였다. Sr-85, Cs-137, Co-60 및 Am-241의 겉보기 확산계수는 각각 $1.07{\times}10^{-11},\;6.705{\times}10^{-13},\;1.226{\times}10^{-13},\;1.310{\times}10^{-14},\;m^2/sec$로 측정되었다. 그리고 시료의 압축 밀도를 $1.8g/cm^2$에서 $2.0g/cm^2$으로 증가시켰을 때, Cs-137의 확산계수는 약 1/4로 감소되어 나타났다. 반면, 열처리된 벤토나이트의 경우에는 확산계수가 크게 변하지 많았는데, 이는 $150^{\circ}C$ 이하의 온도에서는 국산 벤토나이트가 방사성핵종의 이동을 지연시킬 수 있는 화학적 방벽으로서 사용할 수 있다는 가능성을 보여준 것이라 생각된다. 그리고 음이온 Cl-36의 화산계수를 이용하여 도출한 각 방사성핵종의 공극확산계수와 표면확산계수를 측정한 겉보기확산계수와 비교해 볼 때, 전체 방사성 핵종의 확산이동에 있어서 표면확산이동이 지배적인 것으로 나타났다.

• 공업화학
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• 제30권4호
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• pp.445-452
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• 2019

Shear thickening is an intriguing phenomenon in the fields of chemical engineering and rheology because it originates from complex situations with experimental and numerical measurements. This paper presents results from the numerical modeling of the particle-fluid dynamics of a two-dimensional mixture of colloidal particles immersed in a fluid. Our results reveal the characteristic particle behavior with an application of a shear force to the upper part of the fluid domain. By combining the lattice Boltzmann and discrete element methods with the calculation of the lubrication forces when particles approach or recede from each other, this study aims to reveal the behavior of the suspension, specifically shear thickening. The results show that the calculated suspension viscosity is in good agreement with the experimental results. Results describing the particle deviation, diffusivity, concentration, and contact numbers are also demonstrated.

• 청정기술
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• 제7권3호
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• pp.187-194
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• 2001

석탄가스화 복합발전(IGCC)의 탈황공정에 사용되는 비아연계 탈황제 중 경제성이 우수한 천연망간광석을 이용하여 황화수소 제거반응에 대한 특성을 연구하였다. $H_2S$와 천연망간광석 탈황제 사이의 반응에 대한 초기 반응 속도를 $400{\sim}800^{\circ}C$의 온도범위에서 열중량 분석기로 실험하였다. 그 결과로 황화수소 제거반응 시 초기 반응은 1차 반응이었고, 반응속도상수는 Arrhenius 식에 잘 적용할 수 있었다. 또한 황화반응이 확산에 의해 제어되는 조건에서 농도 구배가 선형을 나타내었으며, 이를 통하여 유효 확산 계수를 온도에 따른 Arrhenius식으로 나타내었다. 이 결과를 통하여 황화 반응 시 확산에 대한 활성화 에너지와 반응 빈도 인자를 구하였다.

• Macromolecular Research
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• 제11권3호
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• pp.157-162
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• 2003

6FDA-based polyimides were prepared from the thermal imidization reaction of 6FDA with diamines of BAPAF, DAP, and DABA having a polar group of hydroxyL or carboxyl. Properties of the dense polyimide membranes were characterized and their gas permeation properties for H$_2$, $CO_2$, $O_2$, $N_2$, and CH$_4$ were investigated. Permeabilities, diffusion coefficients and diffusivity selectivities of polar group-containing polyimide membranes including 6FDA-BAPAF, 6FDA-DAP, and 6FDA-DABA polymer for the gases did not change largely. The separation properties of 6FDA-TrMPD polyimide membrane used as a reference polymer were compared with those of the polyimide membranes mentioned above. It was found that the polyimides of 6FDA-BAPAF, 6FDA-DAP, and 6FDA-DABA, which were soluble in alcohol or/and 2-methoxyethanol, could be applicable to the preparation of a dense composite membrane by dip-coating method.

• 한국토양비료학회지
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• 제25권3호
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• pp.220-230
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• 1992

우리나라에서 토양(土壤) 온도(溫度)를 정규적으로 관측(觀測)하고 있는 기상청(氣象廳) 산하(傘下) 기상대(氣象臺) 및 관측소(觀測所) 관측(觀測) 노장(露長)의 토양시료(土壤試料)를 채취(採取)하여 토양(土壤)의 열전도(熱傳度) 특성(特性)과 관련이 깊은 토양(土壤)의 용적밀도(容積密度), 토성(土性), 유기물(有機物) 함량(含量) 등 물리적(物理的) 특질(特質)을 분석(分析)하였으며, 토양(土壤)의 열확산(熱擴散) 계수(係數)를 산출(算出)하였다. 기상청(氣象廳) 산하(傘下) 기상대(氣象臺) 및 관측소(觀測所) 토양(土壤)의 물리적(物理的) 특성(特性)을 조사한 결과(結果) 0-10cm의 표토(表土)는 52%가 사양토(砂壤土)였으며, 양토(壤土)와 미사질양토(微砂質壤土)가 38%, 그리고 식양토(埴壤土) 및 미사질식토(微砂質埴土)가 10%이었다. 이들 토양(土壤)의 열특성(熱特性)과 관계가 깊은 용적밀도(容積密度)는 사토(砂土)가 $1.41g/cm^3$, 양토(壤土)와 미사질양토(微砂質壤土)가 $1.33g/cm^3$, 그리고 식양토9埴壤土) 및 미사질식토(微砂質埴土)가 $1.21g/cm^3$로 토성(土性)이 미세할수록 낮은 값을 보였다. 열확산(熱擴散) 계수(係數)는 평균(平均) $3.53{\times}10^{-3}cm^3/sec$이었으며, $1.159-8.401{\times}10^{-3}cm^3/sec$의 범위에 있었다. 특히 유기물(有機物) 함량(含量)이 높고 용적밀도(容積密度)가 낮은 제주도(濟州道) 토양(土壤)의 열확산(熱擴散) 계수(係數)는 표토(表土)에서 $2{\times}10^{-3}cm^3/sec$으로 다른 지역의 토양(土壤)보다 현저히 낮았다. 토심(土深) 30cm 이하(以下) 토양(土壤)의 열확산(熱擴散) 계수(係數)는 평균(平均) $6.81{\times}10^{-3}cm^3/sec$로 $1.54-16.12{\times}10^{-3}cm^3/sec$의 범위를 보여 표토(表土)보다 높았다. 열확산(熱擴散) 계수(係數)로부터 계산(計算)된 표토(表土)의 일주간(日週期) 불역심(不易深)(damping depth)은 5.92-13.65cm였으며, 깊이 30cm이하의 연주기(年週期) 불역심(不易深)은 124-342cm이었다. 한편, 실험실내(實驗室內)에서 열선막대법에 의하여 측정(測定)된 열확산9熱擴散) 계수(係數)와 용적밀도(容積密度) 및 토양수분함량(土壤水分含量)과의 관계로부터 열확산(熱擴散) 계수(係數)를 추정(推定)할 수 있는 중회귀(重回歸) 모델을 이용하면 토양온도(土壤溫度)가 부족한 지점(地點)의 열확산(熱擴散) 계수(係數)를 추정(推定)할 수 있게 되었다.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 Proceedings of the second conference of aseanian membrane society
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• pp.140-143
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• 2004

Compatibility of polymeric materials governs their suitability for nearly all potential applications. An aspect of compatibility that is frequently important for fluoropolymers is their ability to isolate fluids by serving as a barrier to mass transport. This property is commonly expressed as permeability. In ideal cases, both solubility and diffusivity are constant at any given temperature and so the permeability is also a constant.(omitted)

• Korean Membrane Journal
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• 제3권1호
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• pp.51-58
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• 2001

The surface of Poly(ether imide) (PEI) membranes has been sulfonated using CIS03H. The resulting membranes were characterized through the analysis of ESCA and contact angle measurements The sulfonated PEI membranes were exposed to gases of $O_2$, $N_2$, and $CO_2$ to measure the permeation rates and ideal separation factors. In addition, the diffusivities and solubilities of individual gases were measured. The diffusivity effect is more dominant than the solubility one on gas transports.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 Proceedings of the second conference of aseanian membrane society
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• pp.33-38
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• 2004

Molecular modeling of gas permeation through zeolite membranes with/without intercrystalline region was carried out. Molecular dynamics (MD) and Monte Carlo (MC) simulations were performed to estimate the diffusion coefficient and adsorption parameters respectively, and our proposed combined method of molecular simulation techniques with a permeation theory (CMP) was used to estimate gas permeability. The calculated permeability of gases (Ar, He, Ne, $N_2$, $0_2$, $CH_4$) at 301 K for the single crystal membrane model was about one order of magnitude larger than the experiential values, although the dependence on the molecular weight of the permeating species agreed with experiments. On the other hand, the estimated permeability using the diffusivity and adsorption parameters of the intercrystalline region model was in good agreement with the experiments. The consistency between experiments and the estimated values means the importance of considering the intercrystalline region and the validity of CMP method to predict the performance of zeolite membranes.

• 대한기계학회논문집B
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• 제31권12호
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• pp.1009-1016
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• 2007

Numerical study on preferential diffusion effects in flame structure in $CH_4-H_2$ diffusion flames is conducted with detailed chemistry. Comparison of flame structures with mixture-averaged species diffusion and suppression of the diffusivities of $H_2$ and H was made. Discernible differences in flame structures are displayed with three species diffusion models. The behaviors of maximum flame temperatures with those species diffusion models are not explained by scalar dissipation rate but by the nature of chemical kinetics. It is seen that the modifcation of flame structure is mainly due to the preferential diffusion of H2 and thereby the nature of chemical kinetics. It is also found that the behaviors of major species with the three species diffusion models are addressed to the nature of chemical kinetics, and this is evident by examining importantly contributing reaction steps to the production and destruction of those chemical species.