• 한국재료학회지
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• 제19권1호
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• pp.13-17
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• 2009

A semi-empirical method to estimate the surface tension of molten alloys at different oxygen partial pressures is suggested in this study. The surface tension of molten Ag-Sn and Ag-Cu alloys were calculated using the Butler equation with the surface tension value of pure substance at a given oxygen partial pressure. The oxygen partial pressure ranges were $2.86{\times}10^{-12}$－$1.24{\times}10^{-9}$ Pa for the Ag-Sn system and $2.27{\times}10^{-11}$－$5.68{\times}10^{-4}$ Pa for the Ag-Cu system. In this calculation, the interactions of the adsorbed oxygen with other metallic constituents were ignored. The calculated results of the Ag-Sn alloys were in reasonable accordance with the experimental data within a difference of 8%. For the Ag-Cu alloy system at a higher oxygen partial pressure, the surface tension initially decreased but showed a minimum at $X_{Ag}$ = 0.05 to increase as the silver content increased. This behavior appears to be related to the oxygen adsorption and the corresponding surface segregation of the constituent with a lower surface tension. Nevertheless, the calculated results of the Ag-Cu alloys with the present model were in good agreement with the experimental data within a difference of 10%.

• Bulletin of the Korean Chemical Society
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• 제9권1호
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• pp.32-36
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• 1988

The isotherms of oxygen chemisorption on polycrystaline nickel surface are obtained at various temperatures between 298K and 523K from intensity measurernent of O 1s xps peaks, and the activation energy of the chemisorption is estimated as a function of the coverage. The activation energy extrapolated to zero coverage is found to be -5.9 kJ/mol. The negative activation energy can be taken as a strong implication of the propriety of a currently accepted chemisorption model, in which molecularly adsorbed precursor state is assumed to exist. The residence time of this precursor state is estimated by assuming a molecularly physisorbed state for the precursor state and assuming a pairwise interaction energy of Lennard-Jones 12-6 potential between an admolecule and each substrate nickel atom. The sticking coefficients are also calculated from the isotherms. The calculated results agree well with those obtained by others with different methods.

• Coupled systems mechanics
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• 제3권4호
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• pp.329-344
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• 2014

In this work, quantum molecular dynamics simulations (QMD) are preformed to study the hydrogen molecules in three types of carbon nanostructures, $C_{60}$ fullerene, (5,5) and (9,0) carbon nanotubes and graphene layers. Interactions between hydrogen and the nanostructures is of importance to understand hydrogen storage for the development of hydrogen economy. The QMD method overcomes the difficulties with empirical interatomic potentials to model the interaction among hydrogen and carbon atoms in the confined geometry. In QMD, the interatomic forces are calculated by solving the Schrodinger's equation with the density functional theory (DFT) formulation, and the positions of the atomic nucleus are calculated with the Newton's second law in accordance with the Born-Oppenheimer approximation. It is found that the number of hydrogen atoms that is less than 58 can be stored in the $C_{60}$ fullerene. With larger carbon fullerenes, more hydrogen may be stored. For hydrogen molecules passing though the fullerene, a particular orientation is required to obtain least energy barrier. For carbon nanotubes and graphene, adsorption may adhere hydrogen atoms to carbon atoms. In addition, hydrogen molecules can also be stored inside the nanotubes or between the adjacent layers in graphite, multi-layer graphene.

• 한국환경과학회지
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• 제27권11호
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• pp.975-982
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• 2018

In this study, zeolite (Z-C1) was synthesized using a fusion/hydrothermal method from coal fly ash. The morphological structures of Z-C1 were confirmed to be highly crystalline with a cubic crystal structure. Exchange capacities of $Ca^{2+}$ and $Mg^{2+}$ ions in a single and a mixed solution reached equilibrium within 120 min. The exchange kinetics of these ions were well predicted by the pseudo-second-order rate equation. The exchange isotherms of the $Ca^{2+}$ and $Mg^{2+}$ ions matched the Langmuir isotherm better than the Freundlich isotherm. The maximum cation exchange capacities ($q_m$) obtained by the Langmuir isotherm model were 2.11 mmol/g (84.52 mg/L) and 1.13 mmol/g (27.39 mg/L) for the $Ca^{2+}$ and $Mg^{2+}$ ions, respectively.

• Bulletin of the Korean Chemical Society
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• 제13권3호
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• pp.230-235
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• 1992

The conformational analysis has been done for catecholamines (dopamine, norepinephrine, and epinephrine) in the cationic and di-anionic states. The species responsible for adsorption on silver metal surface is anionic deprotonated at hydroxyl groups of catechol moiety, i.e., di-anionic states of catecholamines. This was deduced from Fourier-transform Raman spectra of sodium salts of catecholamines. High resolution proton NMR (400 MHz) spectra of catecholamines in basic and neutral $D_2O$ solution show that the conformations of norepinephrine and epinephrine in the di-anionic states are preferred in gauche, but not for dopamine in the di-anionic state. However the energy difference between trans and gauche of catecholamines in the protonated cationic states is small enough to rotate freely through C-C bond in ethylamine moiety. The conformational calculations using an empirical potential function and the hydration shell model (a program CONBIO) show consistent with above experimental results. The calculations suggest that the species of catecholamines adsorbed on silver metal surface would be in favor of the gauche conformations.

• Journal of Electrochemical Science and Technology
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• 제12권1호
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• pp.92-100
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• 2021

In this study, the use of waste food grade aluminium foil and mild steel as a sacrificial electrode in an electrocoagulation system was developed to remove reactive red 111 from wastewater. The effect of different parameters like pH, current density, electrode material, and different electrode configurations was investigated. Optimum operating conditions for maximum COD removal were determined as, 6 mA/㎠ current density and 30 min at 5 pH for aluminium foil and 7 pH for mild steel. Maximum COD reduction obtained at optimum conditions using monopolar 4 electrodes, monopolar 2 electrodes and bipolar electrode configuration were 96.5%, 89.3%, and 90.2% for Mild steel as a sacrificial electrode and 92.1%, 84.2%, and 88.6% for aluminium foil as a sacrificial electrode. The consumption of electrode and energy for both the electrodes of different configurations were calculated and compared. Using batch experimental data, a continuous-flow reactor was developed. Sludge analysis using Fourier Transform Infra-Red Spectroscopy (FTIR) analysis was done. Different adsorption kinetic models and isotherms were developed and it was found that pseudo second-order model and Langmuir isotherm fit best with the experimental data obtained.

• 방사성폐기물학회지
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• 제21권4호
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• pp.427-438
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• 2023

Thermodynamic sorption modeling can enhance confidence in assessing and demonstrating the radionuclide sorption phenomena onto various mineral adsorbents. In this work, Ca-montmorillonite was successfully purified from Bentonil-WRK bentonite by performing the sequential physical and chemical treatments, and its geochemical properties were characterized using X-ray diffraction, Brunauer-Emmett-Teller analysis, cesium-saturation method, and controlled continuous acid-base titration. Further, batch experiments were conducted to evaluate the adsorption properties of Cs(I) and Sr(II) onto the homoionic Ca-montmorillonite under ambient conditions, and the diffuse double layer model-based inverse analysis of sorption data was performed to establish the relevant surface reaction models and obtain corresponding thermodynamic constants. Two types of surface reactions were identified as responsible for the sorption of Cs(I) and Sr(II) onto Ca-montmorillonite: cation exchange at interlayer site and complexation with edge silanol functionality. The thermodynamic sorption modeling provides acceptable representations of the experimental data, and the species distributions calculated using the resulting reaction constants accounts for the predominance of cation exchange mechanism of Cs(I) and Sr(II) under the ambient aqueous conditions. The surface complexation of cationic fission products with silanol group slightly facilitates their sorption at pH > 8.

• 농약과학회지
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• 제18권4호
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• pp.236-246
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• 2014

농약은 작물을 보호하기 위하여 사용되지만 환경을 오염시키는 원인이 되기도 한다. 그러므로 농약의 물리화학적 특성, 독성 자료 및 환경행적 자료를 통해 위해성 평가를 수행하여 안전하게 관리가 가능하다면 등록이 결정된다. 환경중 행적을 예측하기 위해 우리나라의 기상자료, 작물 재배력 및 토양통을 이용하여 butachlor, iprobenfos, carbofuran, tebuconazole을 대상으로 수계 중 잔류농도를 추정하였다. 예측모형으로 과수용 농약은 PA5를, 벼재배용 농약은 RICEWQ와 SCI-GROW를 이용하였다. 수계모니터링에서 butachlor와 iprobenfos의 최대값은 예측모형의 peak 농도보다 낮았고 최소값은 예측모형의 연평균농도보다 낮아 RICEWQ를 벼 재배환경 중 잔류농약의 농도 추정에 이용할 수 있음을 확인하였다. 토양흡착계수가 낮은 carbofuran은 RICEWQ와 SCI-GROW에 적용시 지표수계보다 지하수로의 이동량이 훨씬 많은 것으로 산출되어 RICEWQ는 지하수로의 수계노출농도를 예측하기에는 적절하지 못하였다. 수계 모니터링에서 과수용 농약인 tebuconazole이 검출되지 않아 예측모형으로 산출한 값과 비교하기 어려웠으나 수계를 통한 잔류농약의 추정에 이용할 수 있을 것으로 사료된다.

• 대한토목학회논문집
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• 제39권6호
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• pp.751-758
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• 2019

본 연구는 오염부지의 위해성 평가를 위해 수치모의 기반 오염물질의 노출이동경로 평가에 활용가능한 개념모델을 제시하였다. 이를 위하여 1차원으로 유한차분 기법을 적용하여 지하수 내 오염물질 이송확산을 모의하였다. 불포화대 경로에서의 수리지질학적 및 오염물질 매개변수가 가질 수 있는 범위를 설정하여 범용 시나리오 및 오염물질별 시나리오를 구성하여 모의에 적용하였다. 모델에서는 흡착 및 생분해를 갖는 유한차분 1 차원 이송확산이 고려되었고, 또한 초기 농도가 시간이 지남에 따라 고갈되는 것을 가정하였다. 일반 시나리오의 결과는 지하수 침투율이 감소함에 따라, 오염원에서 지하수면까지의 경로가 길어질수록 지하수면으로 유입되는 지점의 농도 범위는 낮아졌다. 특히, 높은 생분해 속도와 오염원의 빠른 고갈의 경우, 범용 시나리오가 좁은 범위의 지하수 유입농도 예측치를 보여주었다.

• 대한지하수환경학회지
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• 제2권1호
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• pp.22-29
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• 1995

유동 세균 입자는 지체계수를 감소시키므로써 지하수에서 소수성 오염물의 이동을 촉진시킨다. 그 크기와 표면의 적당한 물리화학적 조건으로 인하여 세균은 효율적인 오염물의 운반자가 될 수 있다. 이러한 운반자가 있을 때, 그 계는 액상, 입상, 그리고 고상의 3 상으로 해석되어야한다. 오염물은 각 상에 모두, 혹은 그 중의 일부에 존재할 수 도 있다. 본 연구에서는 세균이 있는 경우, 생화학적으로 분해 가능한 유기성 오염물의 다공매질에서의 거동을 물질수지에 기초하여 수학적 모델로 묘사한다. 세균의 액상과 고상사이의 물질 전이 및 오염물의 액상과 입상사이의 물질 전이는 동역학적 관계식으로 나타냈다. 모델 결과를 일반화하기 위하여 무차원화를 수행했고, 그 해를 구하여 세균에 의한 오염물의 가속이송 효과를 알 수 있었다. 모델 결과는 문헌상의 실험결과와 비교되었다. 모델 결과로부터 오염물은 그 계의 Damkohler I 수가 10 이상일 경우 국지 평형 가정을 할 수 있었으며, 세균의 성장율과 주입 농도 등이 오염물의 청소에 아주 중요한 요소임을 알 수 있었다.