• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.1028-1034
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• 1999

Poly(lactic acid) is expected to be one of the most promising biodegradable polymers. However, the high molecular weight polymer could be obtained by ring-opening polymerization process conventionally, which raises the production cost and decreases the final yield. In this study, linear and star-shaped poly(L-lactic acid)s were prepared by direct solution polycondensation method and their physical and thermal properties were examined. Tin compounds were found to be effective catalyst for the preparation of high molecular weight polymers. When 0.2g (0.5 wt % of monomer) of $SnCl_2$ and 100 mL of p-xylene were used, the polymer yield and molecular weight were relatively high. As a means to obtain higher molecular weight polymer easily in the direct polycondensation system, dipentaerythritol(dipet) or pentaerythritol(pet) was introduced as a multifunctional branching monomer to provide a star-shaped poly(lactic acid). Moderately high molecular weight polymers with the inherent viscosity values up to 1.14 dL/g(weight-average molecular weight of about 140000 by GPC) were obtained and could be cast strong and transparent films.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.1
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• pp.9-13
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• 2002

Recently, Organic electroluminescent devices (OELDs) have been demonstrated the medium sized full color display with effective multi-layer thin films. In this study, the multi-layer OELDs were prepared on the patterened ITO (indium tin oxide)/glass substrates by the vacuum thermal evaporation method. The low molecule compounds such as $Alq_3$(trim-(8-hydroxyquinoline)aluminum) and CTM (carrier transfer material) as the electron transport and injection layers as well as TPD (triphenyl-diamine) and CuPc (copper phthalocyanine) as the hole transport and injection layers were used. The luminance was rapidly increased above the threshold voltage of 10 V. The luminance and emission spectrum for the OELDs samples with $A1/CTM/Alq_3$/TPD/1TO structures were found to be 430 cd/$m^2$and 512 nm at 17 V showing green color emission. In contrast, the samples with $Li-A1/Alq_3$/TPD/CuPC/1TO multi-structures showed 508 nm in emission spectrum and 650 cd/$m^2$at 17 V in the luminance. The increment of luminance may be ascribed to the improved efficiency of recombination in the region of the emission layers by the deposition of CuPc as hole injection layer and the low work function of the Li-Al electrode compared to the Al electrode.

• Applied Biological Chemistry
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• v.39 no.4
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• pp.320-326
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• 1996

Seven antioxidative flavonoids were isolated from Jindalrae flowers (Rhododendron mnonulatum Turcz.), an edible plant in Korea. These compounds were identified as afzelin, ampelopsin, catechin, myricetin, myricitrin, quercetin and quercitrin on the basis of IR, UV, FAB-MS, $^1H\;NMR,\;and\;^{13}C\;NMR$ data. These compounds were consisted of two flavonols, three flavonol glycosides, a flavane, and a dihydroflavonol. The flavonol glycosides (14.4 g) present in th ethyl ether and ethyl acetate fractions comprised up to 82% of their total flavonoid amount (17.6 g) finally recovered by means of polyamide C-200 column chromatography, preparative TLC, recrystallization, and Sephadex LH-20 column chromatography. The antioxidant activities were measured in an ethanol solution of linoleic acid in the presence of ferric thiocyanate. The antioxidant efficiency increased in the order of afzrlin<$\alpha-tocopherol$

• Journal of Environmental Policy
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• v.6 no.3
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• pp.33-56
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• 2007

Use of chemicals has greatly increased along with development of human civilization. Concerns about potential effects of chemicals on human health and environment have also grown accordingly. Due to the enormous number of chemicals being used, however, it is neither practical nor feasible to regulate all the chemicals. Therefore, it is necessary to identify chemicals that deserve more immediate attention, based on the effects on receptors to be protected. This study was initiated by the need for developing management policies for Shihwa-Banwol Techno Valley and its vicinities of korea, where complaints and concerns on environmental contamination have been raised for long time. This study to identifies major chemicals that deserve most immediate attention in environmental health management in this area. For this purpose, the study employed CHEMS-1(Chemical Hazard Evaluation for Management Strategies), and used chemical data from Toxics Release Inventory(TRI) and environmental contamination data from the environmental pollution monitoring network. Top priority pollutants identified in Shihwa-Banwol Techno Valley area were metals and volatile organic compounds, such as dichloromethane, trichloroethylene, diazinon, tetrachloroethylene, chromium compounds, tin compounds, chloroacetic acid, ethyl acetate, and zinc compounds, in an order of decreasing importance. An evaluation of physicochemical properties of the priority chemicals and the environmental pollution monitoring network database in Shihwa-Banwol Techno Valley suggested that the media that are of potential concern would be the atmosphere and aquatic environment.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.67-74
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• 2010

Chromate conversion coating is a coating technique used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, tin, and their alloys to slow corrosion. The process uses various toxic chromium compounds, which may include hexavalent chromium. The industry is developing less toxic alternatives in order to comply with substance restriction legislation, such as RoHS. One alternative is to develop a Cr-free coating solution. In this study, eco-friendly, Cr-free solutions (urethane solution S-700, organic/inorganic solution with Si LRO-317) were used. Test specimens were dried in a drying oven at $190^{\circ}C$ for 3, 5, 7, and 9 minutes. Corrosion resistance was evaluated using a salt spray test for 72 hours. The results show that the optimum corrosion resistance was achieved at $190^{\circ}C$ for five minutes for EGI and three or five minutes for HDGI, respectively. The adhesive properties of the two types of coating solutions were superior regardless of drying time.

• Journal of the Korean Applied Science and Technology
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• v.29 no.2
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• pp.311-316
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• 2012

We are investigated to an electrochemical characteristic for Langmuir-Blodgett (LB) films by cyclic voltammetry method. The phospholipid compound was deposited by using the LB method on the Indium tin oxide(ITO) glass. We tried to measure the electrochemical by using cyclic voltammetry with three-electrode system(an Ag/AgCl reference electrode, a platinum wire counter electrode and LB film-coated ITO working electrode) in 0.5, 1.0, 1.5 and 2.0 N $NaClO_4$ solution. A measuring range was reduced from initial potential -1350 mV, continuously oxidized to 1650 mV. As a result, LB films of the phospholipid compounds are appeared irreversible process caused by only the oxidation current from the cyclic voltammogram. The diffusivity(D) effect of LB films decreased with increasing of phospholipid compound amount.

• Journal of information and communication convergence engineering
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• v.7 no.1
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• pp.72-77
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• 2009

Three different procedures for adding Pd compounds to $SnO_2$ particles have been investigated. These processes are: (1) coprecipitation; (2) dried powder impregnation; and (3) calcined powder impregnation. The microstructures of $SnO_2$ particles have been analyzed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). In the coprecipitaion method, the process does not restrain the growth of $SnO_2$ particles and it forms huge agglomerates. In the dried powder impregnation method, the process restrains the growth of $SnO_2$ particles and the surfaces of the agglomerates have many minute pores. In the calcined powder impregnation method, the process restrains the growth of $SnO_2$ particles further and the agglomerates have a lot more minute pores. The sensitivity ($S=R_{air}/R_{gas}$) of the $SnO_2$ gas sensor made by the calcined powder impregnation process shows the highest value (S = 21.5 at 5350 ppm of $C_3H_8$) and the sensor also indicates the lowest operating temperature of around $410^{\circ}C$. It is believed that the best result is caused by the plenty of minute pores at the surface of the microstructure and by the catalyst Pd that is dispersed at the surface rather than the inside of the agglomerate. Schematic models of Pd distribution in and on the three different $SnO_2$ particles are presented.

• Journal of Life Science
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• v.8 no.5
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• pp.473-478
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• 1998

The radical scavenging activity of the methanol extracts was in the order of doenjang〉 meju〉 soybean. The metha-nol extracts were further fractionated with dichloromethane, ethyl acetate, butanol and water in sequence. Among the solvent fractions of the methanol extracts, the ethyl acetate fraction demonstrated high levels of radical scave-nging activity. On the other hands, the nitrite scavenging activity of the methanol extrats was in the order of doen-jang〉soybean〉meju. All fractions from doenjang were exhibited the strong nitrite scavenging effect. Especially, $H_2O$, EtOAc and BuOH fractions with 6gmg/10$m\ell$ concentration exhibited much stronger nitrite scavenging effect than that of L-ascorbic acid. The ethyl acetate fraction showed remarkable antioxidant and nitrite scavenging effects compared with the other fractions obtained from soybean, meju and doenjang. The ethyl acetate fraction of doenjang was fur-ther purified by repeated chromoatograpic methods and isolated three compounds. There are identified as genistin, dai-dzein and genistein on the basis of spectral data.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.69-69
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• 2017

For several decades, industrial processes consume a huge amount of raw water for various objects that consequently results in the generation of large amounts of wastewater. There effluents are mainly treated by conventional technologies such are aerobic, anaerobic treatment and chemical coagulation. But, there processes are not suitable for eliminating all hazardous chemical compounds form wastewater and generate a large amount of toxic sludge. Therefore, other processes have been studied and applied together with these techniques to enhance purification results. These techniques include photocatalysis, absorption, advanced oxidation processes, and ozonation, but also have their own drawbacks. In recent years, electrochemical techniques have received attention as wastewater treatment process that show higher purification results and low toxic sludge. There are many kinds of electrode materials for electrochemical process, among them, boron doped diamond (BDD) attracts attention due to good chemical and electrochemical stability, long lifetime and wide potential window that necessary properties for anode electrode. So, there are many researches about high quality BDD, among them, researches are focused BDD on Si substrate. But, Si substrate is hard to apply electrode application due to the brittleness and low life time. And other substrates are also not suitable for wastewater treatment electrode due to high cost. To solve these problems, Ti has been candidate as substrate in consideration of cost and properties. But there are critical issues about adhesion that must be overcome to apply Ti as substrate. In this study, to overcome this problem, TiN interlayer is introduced between BDD and Ti substrate. TiN has higher electrical and thermal conductivity, melting point, and similar crystalline structure with diamond. The TiN interlayer was deposited by reactive DC magnetron sputtering (DCMS) with thickness of 50 nm, $1{\mu}m$. The microstructure of BDD films with TiN interlayer were estimated by FE-SEM and XRD. There are no significant differences in surface grain size despite of various interlayer. In wastewater treatment results, the BDD electrode with TiN (50nm) showed the highest electrolysis speed at livestock wastewater treatment experiments. It is thought to be that TiN with thickness of 50 nm successfully suppressed formation of TiC that harmful to adhesion. And TiN with thickness of $1{\mu}m$ cannot suppress TiC formation.

• Journal of the Korean Chemical Society
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• v.7 no.3
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• pp.216-224
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• 1963

Reaction of organic chlorine containing ester, alcohol, and acids with metallic tin and zinc in dimethyl formamide solvent gave a good yield of organo metallic complex. The same reaction under a mixed U.V. irradiation could not give an appreciable yield of the complex except in the case of an elevated reaction temperature. The solvation effect of dimethyl formamide of the metallic complex formation was markedetly increased as compared to the reaction in toluene and cyclohexane. In case of chlorine containing carboxylic acid, the formation of organo chloro zinc complex of the salt was observed. The reaction of organo zinc complex with a carbonyl precursor gave the addition product together with a dimerized product. Especially the aldehyde species enhanced the formation of zinc complex. The addition reaction was simple and convenient, but the yield was not high.(30-40% for the acid, 73% for the ester, 14.6% for alcohol). The result was discussed on basis of solvent effect and the procedures were described.