• Journal of the Korean Vacuum Society
• /
• v.14 no.2
• /
• pp.84-90
• /
• 2005

The influence of plasma parameters on the growth of $In_{0.2}Ga_{0.8}N/GaN$ heterostructures has been investigated using plasma-assisted molecular beam epitaxy. Since plasma ejects plenty of energetic particles with different energy levels and flux density at various rf power levels, plasma modulated both growth rate and optical properties significantly. For instance, surface roughness and the emission spectrum of photoluminescence were degraded at low and high rf power. According to sharp interfaces between epitaxial films and strong peaks observed from photoluminescence spectra, our experimental setup presented optimal operation range of rf powers at around 400W. The phenomena could be explained by the presence of energetic particles modulating the rate of plasma stimulated desorption and surface diffusion, and energetic particles exceeding critical value resulted in the incorporation of defects at subsurface. The optimal rf power regime increased by 100W for $In_{0.2}Ga_{0.8}N/GaN$ growth in comparison with GaN. The effects of rf power were discussed in conjunction with kinetic processes being stimulated by energetic particles.

• Applied Chemistry for Engineering
• /
• v.29 no.3
• /
• pp.318-324
• /
• 2018

In this study, PAN (polyacrylonitrile) based activated carbon fibers were prepared by water vapor activation method which is a physical activation method. Activation was performed with temperature and time as parameters. When the activation temperature reached 700, 750 and $800^{\circ}C$, the activation was carried out under the condition of a water vapor flow rate of 200 ml/min. In order to analyze the pore structure of activated carbon fibers, the specific surface area ($S_{BET}$) was measured by the adsorption/desorption isotherm of nitrogen gas and AFM analysis was performed for the surface analysis. Tensile tests were also conducted to investigate the effect of the pore structure on mechanical properties of fibers. As a result, the $S_{BET}$ of fibers after the activation showed a value of $448{\sim}902m^2/g$, the tensile strength decreased 58.16~84.92% and the tensile modulus decreased to 69.81~83.89%.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
• /
• 2004.04a
• /
• pp.186-191
• /
• 2004

Sorption kinetics of 2-chlorophenol(2-ChP), 2,4-dichlorophenol(2,4-DChP) and 2,4,5-trichlorophenol (2,4,5-TChP), onto montmorillonite modified with hexadecyltrimethyl ammonium cations(HDTMA-mont) were investigated. One-site mass transfer model(OSMTM) and two compartment first-order kinetic model(TCFOKM) were used to analyze kinetics. As expected from the number of model parameters involved, the three-parameter TCFOKM was better than the two-parameter OSMTM in describing sorption and desorption kinetics of chlorophenols in HDTMA-mont. For all chlorophenols, the results of OSMTM analysis indicate that the predominant deprotonated speciation(at pH 9.15) exhibited higher mass transfer coefficient( $k_{s}$ ) than the protonated speciation(at pH 4.85). This is because the deprotonated speciation has stronger hydrophobic interaction than protonated speciation. Most sorption completes in three hours. The fraction of the fast sorption and the first-order sorption rate constants for the fast and slow compartments in TCFOKM were determined by fitting experimental data to the TCFOKM. The results of kinetics reveal that the fraction of the fast sorption( $f_1$) and the sorption rate constants in the fast compartments( $k_1$) were in the order 2,4,5-TChP > 2,4-DChP > 2-ChP, which agrees with the magnitude of the $K_{ow}$ . The first-order sorption rate constants in the fast compartment(10$^{0.8}$ - 10$^{1.22}$ h $r^{-1}$ ) were much larger than those in the slow compartment(10$^{-1}$.74/ - 10$^{-2}$.622/ h $r^{-1}$ ).> ).).

• Journal of Soil and Groundwater Environment
• /
• v.25 no.3
• /
• pp.12-22
• /
• 2020

Managed aquifer recharge (MAR) is a promising water management strategy for securing stable water resources to overcome water shortage and water quality deterioration caused by global environmental changes. A MAR demonstration site was selected at Imgok-ri, Sangju-si, Korea, based on screening for the frequency of drought events and local water supply situations. The abundant groundwater discharging from a nearby abandoned coal mine is one of the potential recharge water sources for the MAR implementation. However, it has elevated levels of arsenic (~12 ㎍/L). In this study, the potential of the natural attenuation of arsenic by the field geological media was investigated using batch and column experiments. The adsorption and desorption parameters were obtained for two drill core samples (GM1; 21.8~22.8 m and GM2; 26.0~27.8 m depth) recovered from the potentially water-conducting fracture-zones in the injection well. The effluent arsenic concentrations were monitored during the continuous flow of the mine drainage water through the columns packed with the core samples. GM2 removed about 60% of arsenic in the influent (0.1 mg-As/L) while GM1 removed about 20%. The results suggest that natural attenuation is an acitive process occurring during the MAR operation, potentially lowering the arsenic level in the mine drainage water below the regulatory standard for drinking water. This study hence demonstrates that using the mine drainage water as the recharge water source is a viable option at the MAR demonstration site.

• Journal of the Korean Society of Tobacco Science
• /
• v.30 no.2
• /
• pp.117-124
• /
• 2008

A solid phase microextraction (SPME) method in combination with gas chromatography/mass spectrometric techniques was used for the extraction and quantification of 12 selected agrochemical residues in tobacco. The parameters such as the type of SPME fiber, adsorption/desorption time and the extraction temperature affecting the precision and accuracy of the SPME method were investigated and optimized. Among three types of fibers investigated, polyacrylate (PA), polydimethylsiloxane (PDMS) and polydimethylsiloxane-divinylbenzene (PDMS-DVB), PDMS fiber was selected for the extractions of the agrochemicals. The SPME device was automated and on-line coupled to a gas chromatograph with a mass spectrometer. Mass spectrometry (MS) was used and two different instruments, a quadrupole MS and triple quadrupole MS-MS mode, were compared. The performances of the two GC-MS instruments were comparable in terms of linearity (in the range of 0.01$\sim$0.5 $\mu$g/mL) and sensitivity (limits of detection were in the low ng/mL range). The triple quadrupole MS-MS instrument gave better precision than that of quadrupole MS system, but generally the relative standard deviations for replicates were acceptable for both instruments (< 15%). The LODs was fully satisfied the requirements of the CORESTA GRL. Recoveries of 12 selected agrochemicals in tobacco yielded more than 80% and reproducibility was found to be better than 10% RSD so that SPME procedure could be applied to the quantitative analysis of agrochemical residues in tobacco.

• Membrane and Water Treatment
• /
• v.11 no.2
• /
• pp.97-109
• /
• 2020

Membrane fouling is the main drawback of membrane technology. Frequent membrane cleaning and membrane replacement are, therefore, required to reduce membrane fouling that causes permeate flux reduction, lower rejection, or higher operating pressure. Studies have proved that the alteration of membrane properties is the key controlling factor in lessening membrane fouling. Among stimuli-responsive membranes, thermo-responsive membrane is the most popular, with a drastic phase transition and swelling-shrinking behavior caused by the temperature change. In this study, the thermo-responsive ability of two commercial membranes, PolyCera® Titan membrane and PolyCera® Hydro membrane, at different temperatures was studied on the antifouling function of the membrane in palm oil mill effluent (POME) treatment. The evaluation of the membrane's thermo-responsive ability was done through three cycles of adsorption (fouling) and desorption (defouling) processes in a membrane filtration process. The experimental result depicted that PolyCera® Hydro membrane had a higher membrane permeability of 67.869 L/㎡.h.bar than PolyCera® Titan membrane at 46.011 L/㎡.h.bar. However, the high membrane permeability of PolyCera® Hydro membrane was compensated with low removal efficiency. PolyCera® Titan membrane with a smaller mean pore size had better rejection performance than PolyCera® Hydro membrane for all tested parameters. On the other hand, PolyCera® Titan membrane had a better hydrodynamic cleaning efficiency than PolyCera® Hydro membrane regardless of the hydrodynamic cleaning temperature. The best hydrodynamic cleaning performed by PolyCera® Titan membrane was at 35℃ with the flux recovery ratio (FRR) of 99.17 ± 1.43%. The excellent thermo-responsive properties of the PolyCera® Titan membrane could eventually reduce the frequency of membrane replacement and lessen the use of chemicals for membrane cleaning. This outstanding exploration helps to provide a solution to the chemical industry and membrane technology bottleneck, which is the membrane fouling, thus reducing the operating cost incurred by the membrane fouling.

• Korean Journal of Soil Science and Fertilizer
• /
• v.44 no.1
• /
• pp.15-21
• /
• 2011

Transport of heavy metals such as Cd is affected by several rate-limiting processes including adsorption and desorption by exchange reactions in soils. In this study, column transport and batch kinetic experiments were performed to assess Cd mobility in a double-layered soil with a reclaimed saline and sodic soil (SSS) as top soil and macroporous granule (MPG) as a bottom layer. For individual soil layer having different physical and chemical properties, Cd was considered to be nonlinear reactivity with the soil matrix in layered soils. The dispersive equation for reactive solutes was solved with three types of boundary conditions for the interface between soil layers. The adsorption of Cd with respect to the saline-sodic sandy loam and the MPG indicated that the nature of the sites or the mechanisms involved in the sorption process of Cd was different and the amounts of Cd for both of samples increases with increasing amounts of equilibrium concentration whereas the amount of Cd adsorbed in saline-sodic sandy loam soil was higher than that in MPG. The results of breakthrough curve indicating relative Cd retardation accompanied by layer material and sequence during leaching showed that the number of pore volumes to reach the maximum relative concentration of 1 increased in the order of MPG, SSS, and double layer of SSS-MPG. Breakthrough curves (BTCs) from column experiments were well predicted with our double-layered model where independently derived solute physical and retention parameters were implemented.

• Carbon letters
• /
• v.28
• /
• pp.87-95
• /
• 2018

This study examined the influence of operating parameters on the electrosorptive recovery system of lithium ions from aqueous solutions using a spinel-type lithium manganese oxide adsorbent electrode and investigated the electrosorption kinetics and isotherms. The results revealed that the electrosorption data of lithium ions from the lithium containing aqueous solution were well-fitted to the Langmuir isotherm at electrical potentials lower than -0.4 V and to the Freundlich isotherm at electrical potentials higher than -0.4 V. This result may due to the formation of a thicker electrical double layer on the surface of the electrode at higher electrical potentials. The results showed that the electrosorption reached equilibrium within 200 min under an electrical potential of -1.0 V, and the pseudo-second-order kinetic model was correlated with the experimental data. Moreover, the adsorption of lithium ions was dependent on pH and temperature, and the results indicate that higher pH values and lower temperatures are more suitable for the electrosorptive adsorption of lithium ions from aqueous solutions. Thermodynamic results showed that the calculated activation energy of $22.61kJ\;mol^{-1}$ during the electrosorption of lithium ions onto the adsorbent electrode was primarily controlled by a physical adsorption process. The recovery of adsorbed lithium ions from the adsorbent electrode reached the desorption equilibrium within 200 min under reverse electrical potential of 3.5 V.

• Applied Chemistry for Engineering
• /
• v.19 no.6
• /
• pp.680-684
• /
• 2008

The formation of methane hydrate ($CH_4$ hydrate) in silica sand and decomposition experiments were performed at $7.0^{\circ}C$ using a newly designed reactor. Temperature profile within silica sand bed was measured by thermocouples installed at different height of reactor. Both temperature and pressure are the main parameters for the formation (measured by adsorption experiment) and decomposition (measured by desorption experiment) of methane hydrate. Experiment of methane hydrate formation at 8 MPa and $7.0^{\circ}C$ showed that 70% of methane was converted to hydrate and the recovery of methane by the decomposition of methane hydrate was 82%.

• Transactions of the Korean hydrogen and new energy society
• /
• v.24 no.2
• /
• pp.128-135
• /
• 2013

The nuclear fuel cycle plant is composed of various subsystems such as a fuel storage and delivery system (SDS), a tokamak exhaust processing system, a hydrogen isotope separation system, and a tritium plant analytical system. Korea is sharing in the construction of the International Thermonuclear Experimental Reactor (ITER) fuel cycle plant with the EU, Japan, and the US, and is responsible for the development and supply of the SDS. Hydrogen isotopes are the main fuel for nuclear fusion reactors. Metal hydrides offer a safe and convenient method for hydrogen isotope storage. The storage of hydrogen isotopes is carried out by absorption and desorption in a metal hydride bed. These reactions require heat removal and supply respectively. Accordingly, the rapid storage and delivery of hydrogen isotopes are enabled by a rapid cooling and heating of the metal hydride bed. In this study, we designed and manufactured a vertical-type hydrogen isotope storage bed, which is used to enhance the cooling performance. We present the experimental details of the cooling performances of the bed using various cooling parameters. We also present the modeling results to estimate the heat transport phenomena. We compared the cooling performance of the bed by testing different cooling modes, such as an isolation mode, a natural convection mode, and an outer jacket helium circulation mode. We found that helium circulation mode is the most effective which was confirmed in our model calculations. Thus we can expect a more efficient bed design by employing a forced helium circulation method for new beds.