• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.97-97
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• 2000

In this thesis, the metastable state diamond thin films have been deposited on Si substrates from methane-hydrogen and oxygen mixture using Microwave Plasma Enhanced Chemical Vapor deposition (MWPCVD) method. Effects of each experimental parameters of MWPCVD including methane concentrations, oxygen additions, operating pressure, deposition time, etc. on the growth rate and crystallinity were investigated. SEM, XRD, and Raman spectroscopy were employed to analyze the growth rate and morphology, crystallinity and prefered growth direction, and relative amounts of diamond and non-diamond phases respectively. As a methane concentration below 4%, the deposited films having well-defined facets could be obtained. As the methane concentration increases over 4%, the shape of films gradually changed into a amorphos form. The best crystallinity of the film at 3% in the Raman spectroscopy. Addition of oxygen to the methane-hydrogen mixture gave an improved film crystallinity at 50% oxygen concentration due to its more effectiveness in the selective removal of the non-diamond phased compared to the of H atom. on the contrary, the growth rate generally decreased by oxygen to from the more stable CO and CO2 is responsible for such an effect. Upon increasing the operating pressure and time, increased of growth rate and crystallinity were increased simultaneously.

• 한국진공학회지
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• 제12권4호
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• pp.269-274
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• 2003

The electrical, optical and structural properties of ZnNiO thin _ films deposited on Si substrates using rf-magnetron sputtering method have been investigated before and after the thermal annealing processes. The crystallinity of the ZnNiO thin film become degraded with increasing the Ni contents. This is mainly because the lattice of the thin film was expanded due to the oxygen-deficient conditions. Concerning the electrical properties of the thin film, the carrier concentration increases ($6.81\times10^{14}\textrm{cm}^{-2}$) and Hall mobility decreases (36.3 $\textrm{cm}^2$/Vㆍs) with higher doping concentration of Ni. However, the carrier concentration and Hall mobility became low ($1.10\times10^{14}\textrm{cm}^2$ and high (209.6 $\textrm{cm}^2$/Vㆍs), respectively, after the thermal annealing process at $1000 ^{\circ}C$. We also observed a strong luminescene center peaking at 546 nm in photoluminescence spectra, which was caused by a deep level center in the ZnO band gap with oxygen deficient ZnNiO structure.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.53-53
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• 2010

Car industry has required light-weight steels, but still with strong mechanical strength. To meet this requirement, a variety of researches on Fe-Al alloys have been performed. As Al is being added in a disordered manner, alloys become more ductile and show higher yield stress. At a certain concentration of Al, however, the Fe-Al alloy system falls in a second phase whose mechanical strength is worsened. To understand the microscopic role of Al, we investigate the stability and the elastic properties of various Fe-Al alloys using ab initio density functional theory. At agiven Al concentration, the equilibrium geometry is obtained among several disordered Fe-Al alloy structures by performing the geometry relaxation. The formation energies and elastic properties such as bulk moduli of the equilibrium structures are also computed as a function of Al concentration. We also investigate the effects of different elements such as Si and Mn. Fe-Si alloy systems exhibit unusual mechanical behaviors requiring further investigation to understand their physical origin. Especially, the microscopic role of Mn is investigated to find its physical origin of preventing the Fe-Al alloy system from forming an unfavorable second phase. The effect of manganese on mechanical properties of Fe-based alloys is also explored.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.271.1-271.1
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• 2013

Titania is usually used in sun-screens, tooth paste, and other daily used objects as a pigment. However, scientists have focused on titania as photocatalyst due to its excellent activities. By fabricating vanadium doped TiO2 and CuOx co-catalyzed TiO2 nano-size filter, the degradation level of the volatile organic compound (VOC) concentration was tested using 365nm UV LED as light source in a closed chamber. Main purpose for this test is to evaluate the activities of various catalysts for degrading the VOCs which are detrimental to human body and toluene and p-xylene were chosen in the VOC removal test. Target gas materials were injected into the test chamber with dry air as carrier gas which was flowed into the gas washer bottle filled with liquid form of VOC substance. When the VOC gas flows into the chamber, it is circulated by 200 mm fan in order to contact with the set-up filter on the aluminum holder. Target gas concentration in the chamber was monitored using VOC detector (miniRae3000, Raesystems) which was also placed inside the chamber. With the measured concentration, the VOC degradation efficiency and the degradation rate were evaluated and used to compare the catalytic activities.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.208-208
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• 2010

Zinc oxide (ZnO) is a functional material with interesting optical and electrical properties, a wide band gap (more than 3.3 eV), a high transmittance in the visible light region, piezoelectric properties, and a high n-type conductivity. This material has been investigated for use in many applications, such as transparent electrodes, blue light-emitting diodes, and ultra-violet detector. ZnO films grown under low oxygen pressure by thin film deposition methods show low resistivity and large free electron concentration. Therefore, reducing the background carrier concentration in ZnO films is one of the major challenges ahead of realizing high-performance ZnO-based optoelectronic devices. In this study, we deposited ZnO thin films on sapphire substrates by pulsed laser deposition (PLD) with employing an oxygen plasma source to decrease the background free-electron concentration and enhance the crystalline quality. Then, the substrate temperature was varied between 200 'C to 900 'C The vacuum chamber was initially evacuated to a pressure of $10^{-6}$ Torr, and then a pure $O_2$ gas was introduced into the chamber and the pressure during deposition was maintained at $10^{-2}$ Torr. Crystallinity and orientation of ZnO films were investigated by X-ray diffraction (XRD). The film surface was analyzed with atomic force microscope (AFM). And electrical properties were measured at room temperature by Hall measurement.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• Environmental Engineering Research
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• 제23권1호
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• pp.54-61
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• 2018

Biodiesel production parameters and the impact analysis of the potential emissions from both soybean biodiesel and washing water stored in three different environmental conditions were investigated. The effects of the reaction temperature, methanol/oil mole ratio and catalyst concentration on biodiesel yield were considered. And the results showed optimum biodiesel yield of 99% obtained at $54^{\circ}C$, 7 methanol/oil mole ratio and 0.4 wt/wt % catalyst concentration. The potential emissions from both the biodiesel produced and washing water stored (for six weeks) in refrigerator (${\leq}10^{\circ}C$), vacuum (50 kPa) and direct exposure to atmosphere were identified and quantified. Impact analysis of the emissions involved their categorization into: terrestrial acidification, freshwater eutrophication, human toxicity, terrestrial ecotoxicity, climate change and freshwater ecotoxicity. Freshwater ecotoxicity category had the most pronounced negative impact of the potential emissions with $5.237710^{-2}kg\;1,4-DB\;eq$. emissions in Atmosphere, $4.702610^{-2}kg\;1,4-DB\;eq$. emissions in Refrigerator and $3.966110^{-2}kg\;1,4-DB\;eq$. emissions in Vacuum. Climate change had the least effect of the emissions with $6.214106^{-6}kg\;CO_2\;eq$. in Atmosphere, $3.9310^{-6}kg\;CO_2\;eq$. in Refrigerator and $1.6710^{-6}kg\;CO_2\;eq$. in Vacuum. The study showed that the order of preference of the storage environments of biodiesel is vacuum environment, refrigerated condition and exposure to atmosphere.

• Journal of the Korean Wood Science and Technology
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• 제43권6호
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• pp.792-797
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• 2015

진공가압 수지함침 처리에 의한 목재의 휨강도, 경도 및 내마모성 향상을 위하여 침엽수 3수종에 수용성 멜라민 수지를 수지농도와 처리시간별로 진공가압 처리한 후 수지함침 열압축목재(compreg)를 제조한 다음 물성을 검토하였다. 또한 같은 수종에 수용성 난연제를 도포처리하는 방법과 진공가압 후 열압처리 방법으로 제조한 다음 난연성 향상정도를 측정하였다. 수지의 농도가 높을수록 휨강도 및 브리넬 경도는 증가하였고 내마모성은 향상되었으나, 처리시간과는 일정한 경향이 없었다. 난연성은 도포시험편 보다 진공가압처리 시험편이 총 방출열량이 감소하여 진공가압처리에 의한 난연성 개선 방법이 효과가 있었다.

• 상하수도학회지
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• 제31권4호
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• pp.311-319
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• 2017

Scale formation is inevitable problem when seawater is treated by vacuum membrane distillation. The reason is the high concentration of calcium ion($Ca^{2+}$), sulfate ion(${SO_4}^{2-}$) and bicarbonate ion(${HCO_3}^-$). These ions form calcium sulfate($CaSO_4$) and calcium carbonate($CaCO_3$) on the membrane. The scale formed on membrane has to be removed, because the flux can be severely reduced and membrane wetting can be incurred. This study was carried out to investigate scale formation and effectiveness of acid cleaning in vacuum membrane distillation for SWRO brine treatment. It was found that permeate flux gradually declined until volume concentration factor(VCF) reached around 1.55 and membrane wetting started over VCF over 1.6 in the formation of precipitates containing $CaSO_4$ during VMD operation. In contrast, when calcium carbonate formed on membrane, permeate flux was gradually reduced until VCF 3.0. The precipitates containing both $CaSO_4$ and $CaCO_3$ were formed on the membrane surface and in the membrane pore.

• Membrane and Water Treatment
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• 제6권3호
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• pp.237-249
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• 2015

In this study we investigate a laboratory scale vacuum membrane distillation system to produce pure water from model oil in water emulsion. Experimental determination of liquid entry pressure (LEP) of a commercial Durapore$^{TM}$ GVPH flat sheet membrane using model emulsions in various oil concentrations has been carried out. Two different methods of liquid entry pressure determination - a frequently used, so-called static and a novel dynamic method - have been investigated. In case of static method, LEP value was found to be 2.3 bar. No significant effect of oil content on LEP was detected up to 3200 ppm. In contrast, LEP values determined with dynamic method showed strong dependence on the oil concentration of the feed and decreased from 2.0 bar to a spontaneous wetting at 0.2 bar in the range 0-250 ppm, respectively. Vacuum membrane distillation tests were also performed. The separation performance is evaluated in terms of flux behavior, total organic carbon removal and droplet size distribution of the feed and final retentate. No significant effect of oil content on the flux was found ($5.05{\pm}0.31kgm^{-2}h^{-1}$) up to 250 ppm, where a spontaneous wetting occurred. High separation performance was achieved along with the increasing oil concentration between 93.4-97.0%.