• Journal of Korean Society of Water and Wastewater
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• v.33 no.3
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• pp.205-213
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• 2019

Batch adsorption tests were performed to evaluate the applicability of adsorption kinetic model by using hydrogel chitosan bead crosslinked with glutaraldehyde (HCB-G) for Cu(II) as cation and/or phosphate as anion. Pseudo first and second order model were applied to determine the sorption kinetic property and intraparticle and Boyd equation were used to predict the diffusion of Cu(II) and phosphate at pore and boundary-layer, respectively. According to the value of theoretical and experimental uptake of Cu(II) and phosphate, pseudo second order is more suitable. On comparison with the value of adsorption rate constant (k), phosphate kinetic was 2-4 times faster than that of Cu(II) at any experimental condition indicating the electrostatic interaction between ${NH_3}^+$ and phosphate is dominated at the presence of single component. However, when Cu(II) and phosphate simultaneously exist, the value of k for phosphate was sharply decreased and then the difference was not significant. Both diffusion models confirmed that the sorption rate was controlled by film mass transfer at the beginning time (t < 3 hr) and pore diffusion at next time section (t > 6 hr).

• International Journal of Precision Engineering and Manufacturing-Green Technology
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• v.5 no.5
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• pp.613-621
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• 2018

The electrically assisted brazing of a ferritic stainless steel with nickel-based filler metal is experimentally investigated. During electrically assisted brazing of a lap joint, the temperature of the joint is first rapidly increased to a brazing temperature and held nearly constant for a specific period using a pulsed electric current. Microstructural analysis results strongly suggest that the electric current during electrically assisted brazing enhances diffusion between the filler metal and the ferritic stainless steel, thus inducing significantly thicker diffusion zones compared with induction brazing. The mechanical test results show that the strength of the electrically assisted brazing joint is comparable to or even superior to those of the joint fabricated by induction brazing, while the process time of the electrically assisted brazing is significantly shorter than that of induction brazing.

• Bulletin of the Korean Chemical Society
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• v.4 no.5
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• pp.223-227
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• 1983

A molecular dynamic computer experiment was performed on a system of 108 particles composed of a single polymer chain and solvent molecules. The state considered was in the immediate neighborhood of the triple point of the system. The polymer itself is an analog of a freely jointed chain. The Lennard-Jones potential was used to represent the interactions between all particles except for that between the chain elements forming a bond in the polymer chain, for which the interaction was expressed by a harmonic potential. The self-diffusion coefficient and velocity autocorrelation function (VACF) of a polymer were calculated at various chain lengths $N_p$, and various interaction strengths between solvent molecules and a polymer chain element. For self-diffusion coefficients D, the Einstein relation holds good; as chain length $N_p$ increases the D value decreases, and D also decreases as ${\varepsilon}_{cs}$ (the interaction parameter between the chain element and solvent molecules) increases. The relaxation time of velocity autocorrelation decreases as ${\varepsilon}_{cs}$ increases, and it is constant for various chain lengths. The diffusion coefficients in various conditions reveal that our systems are in a free draining limit as is well known from the behavior of low molecular weight polymers, this also agrees with the Kirkwood-Riesman theory.

• Journal of the Korean institute of surface engineering
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• v.34 no.5
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• pp.475-480
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• 2001

Diffusion of Cu into the low-k para-xylene based plasma polymer (pXPP) thin films deposited by plasma-enhanced chemical vapor deposition using the para-xylene precursor was comparatively measured using various methods. Cu layer was deposited on the surfaces of pXPPs treated by $N_2$ plasma generated in a magnetically enhanced inductively coupled plasma reactor. Diffusion characteristics of Cu into pXPPs were measured using Rutherford backscattering spectroscopy (RBS), secondary ion mass spectroscopy (SIMS), cross-sectional transmission electron microscopy (XTEM), and current-voltage (I-V) measurements for the vacuum-annealed Cu/pXPPs for 1 hour at $450^{\circ}C$ and were compared. The results showed a correlation between the I-V measurement and SIMS data are correlated and have a sensitivity enough to evaluate the dielectric properties but the RBS or XTEM measurements are not sufficient to conclude the electrical properties of low-k dielectrics with Cu in the film bulk. The additional results indicate that the pXPP layers are quite resistant to Cu diffusion at the annealing temperature of $450^{\circ}C$ compared to the other previously reported organic low-k materials.

• Journal of Electrochemical Science and Technology
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• v.4 no.2
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• pp.71-80
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• 2013

The study of methyl viologen ($MV^{2+}$) mediated oxygen reduction in electrolytic ethanol media possesses potential application in the electrochemical synthesis of hydrogen peroxide mainly due to the advantages of the much increased solubility of molecular oxygen ($O_2$) and high degree of reversibility of $MV^{2+/{\bullet}+}$ redox couple. The diffusion coefficients of both $MV^{2+}$ and $O_2$ were investigated via electrochemical techniques. For the first time, $MV^{2+}$ mediated $O_2$ reduction in electrolytic ethanol solution has been proved to be feasible on both boron-doped diamond and micro-carbon disc electrodes. The electrocatalytic response is demonstrated to be due to the radical cation, $MV^{{\bullet}+}$. The homogeneous electron transfer step is suggested to be the rate determining step with a rate constant of $(1{\pm}0.1){\times}10^5M^{-1}s^{-1}$. With the aid of a simulation program describing the EC' mechanism, by increasing the concentration ratio of $MV^{2+}$ to $O_2$ electrochemical catalysis can be switched from a partial to a 'total catalysis' regime.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.191-195
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• 2007

In this study, we estimated the performance of PEMFC's unit cell as changing operating temperature in different inlet humidity condition at cathode side but anode dry, and tried to match experimental results with 1-dimensional simulation. We used $Nafion^{\circledR}112$ membrane and a self-manufactured PEMFC with active area of $25cm^{2}$ was used in this study. The range of operating temperature was $40{\sim}70^{\circ}C$ and oxygen through bubbled humidity chamber was supplied $0{\sim}80$% humidity condition as changing water temperature in humidity chamber. For figuring out governing equations, represent water contents in electrolyte membrane, the linear forward difference method was applied about time progress and quadratic central difference method was used about space progress. It was assumed that pressure terms were linearly changed due to thin electrolyte membrane. In low operating temperature condition, $40{\sim}60^{\circ}C$, increasing temperature rarely effected cell performance but we can see performance drop at $70^{\circ}C$. By modifying Henrry's constant and/or diffusion coefficient, the modified one-dimensional model was accomplished for calculation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.1
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• pp.1-18
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• 2020

Molten salt solutions consisting of eutectic LiCl-KCl and concentrations of samarium chloride (0.5 to 3.0 wt%) at 500℃ were analyzed using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV technique gave the average diffusion coefficient for Sm³⁺ over the concentration range. Equipped with Sm³⁺ diffusion coefficient, the Randles-Sevcik equation predicted Sm³⁺ concentration values that agree with the given experimental values. From CV measurements; the anodic, cathodic, and half-peak potentials were identified and subsequently used as a parameter to acquire EIS spectra. A six-element Voigt model was used to model the EIS data in terms of resistance-time constant pairs. The lowest resistances were observed at the half-peak potential with the associated resistance-time constant pairs characterizing the reversible reaction between Sm³⁺ and Sm²⁺. By extrapolation, the Voigt model estimated the polarization resistance and established a polarization resistance-concentration relationship.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.1
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• pp.24-29
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• 2002

In this paper, the microstructure and the dielectric properties of Sr$\_$1-x/CaxTiO$_3$(0$\leq$x$\leq$0.2)-based grain boundary layer ceramics were investigated. The sintering temperature and time were 1420∼152 0$\^{C}$ and 4 hours in N$_2$ gas, respectively. The average grain size and the lattice constant were decreased with increasing content of Ca, but the average grain size was increased with increase of sintering temperature. The second phase foamed by the thermal diffusion of CuO from the surface leads to verb high apparent dielectric constant, $\xi$$\_$r/>50000 and low dielectric loss, tan$\delta$<0.05. X-ray diffraction patterns of Sr$\_$1-x/CaxTiO$_3$ exhibited cubic structure, and the peaks shifted upward and the peak intensity were decreased with x. This is due to the lattice contraction as Sr is replaced by Ca with a smaller ionic radius. The specimens treated thermal diffusion for 2hrs in 1150$\^{C}$ exhibited nonlinear current-voltage characteristic, and its nonlinear coefficient(a) was overt 7.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.879-884
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• 2001

In this paper, the structural and dielectric properties of (Sr$_{l-x}$Ca$_{x}$)TiO$_3$ (0$\leq$x$\leq$0.2) -based grain boundary layer ceramics were investigated by XRD, SEM and HP4194A. The ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were 1420~152$0^{\circ}C$ and 4 hours, respectively. The average grain size and the lattice constant were decreased with increasing content of Ca. The average grain size was increased with increase of sintering temperature. The relative density of all specimens was 96~98%. The 2nd Phase formed by the thermal diffusion of CuO from the surface leads to very excellent dielectric properties, that is, $\varepsilon$$_{r}$>50000, tan $\delta$<0.05, $\Delta$C<$\pm$10%. The appropriate Ca content was under 15 ㏖%.s under 15 ㏖%.%.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.3
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• pp.115-124
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• 1997

We measured the variance of eddy diffusion and associated ‘diffusion coefficients’ in coastal regions of Korea by observing the separation distances among multiple drifters deployed simultaneously at the same initial position. The variance of eddy diffusion was found to be proportional to $t^m$, where t is the time and m is a non-integer scaling exponent between 1.5 and 3.5. The observed scaling exponent of eddy diffusion cannot be reproduced by diffusion models employing constant eddy diffusivity. In this study, we applied fractal theory in simulating exponential increase of variance of eddy diffusion. We employed the fGn(fractional Gaussian noise) as a ‘modified’ random walks corresponding to the oceanic eddy diffusion. The variance of eddy diffusion, which corresponds to the fBm(fractional Brown motion) of our diffusion model, is proportional to $t^{2H}$, where H is Hurst scaling exponent. The temporal increase of the variance. with scaling exponent between 1 and 2, was successfully reproduced by our fractal diffusion model. However, our model cannot reproduce scaling exponent greater than 2. The scaling exponents greater than 2 are associated with the velocity shear of the mean flow.