• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.705-708
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• 2014

We demonstrate the blue InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) with an embedded air-gap photonic crystal (PC) which was fabricated by the lateral epitaxial overgrowth of GaN layer on the tungsten (W) nano-masks. The periodic air-gap PC was formed by the chemical reaction of hydrogen with GaN on the W nano-mask. The optical output power of LEDs with an air-gap PC was increased by 26% compared to LEDs without an air-gap PC. The enhanced optical output power was attributed to the improvement in internal quantum efficiency and light extraction efficiency by the air-gap PC embedded in GaN layer.

• YAKHAK HOEJI
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• v.26 no.1
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• pp.25-27
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• 1982

We had reported that s-triazine can readily be converted into the corresponding 5-substituted pyrimide. In order to develop new synthetic method of 5-fluorouracil, we tried to replace eliminating fragment, 1, 3-dimethylurea, by fluoroacetamide, which was expected to undergo nucleophilic attack by proton extraction of both .alpha.-hydrogen and aminohydrogen by lithium diisopropylamide (LDA). We found that 5-fluorouracil could be transformed from s-triazine under strong base condition like LDA as well as other 5-substituted pyrimidines.

• Journal of Soil and Groundwater Environment
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• v.10 no.2
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• pp.35-43
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• 2005

Bioslurping combines the three remedial approaches of bioventing, vacuum-enhanced free-product recovery, and soil vapor extraction. Bioslurping is less effective in tight (low-permeability) soils. The greatest limitation to air permeability is excessive soil moisture. Optimum soil moisture is very soil-specific. Too much moisture can reduce air permeability of the soil and decrease its oxygen transfer capability. Too little moisture will inhibit microbial activity. So Modified Fenton reaction as chemical treatment which can overcome the weakness of Bioslurping was experimented for simultaneous treatment. Although the diesel removal efficiency of SVE process increased in proportion to applied vacuum pressure, SVE process was difficulty to remediation quickly semi- or non-volatile compounds absorbed soil strongly. And SVE process had variation of efficiency with distance from the extraction well and depth a air flow form of hemisphere centering around the well. Below 0.1 % hydrogen peroxide shows the potential of using hydrogen peroxide as oxygen source but the co-oxidation of chemical and biological treatment was impossible because of the low efficiency of Modified Fenton reaction at 0.1 % (wt) hydrogen peroxide. NTA was more efficiency than EDTA as chelating agent and diesel removal efficiency of Modified Fenton reaction increased in proportion to hydrogen peroxide concentration. Hexadecane as typical aliphatic compound was removed less than Toluene as aromatic compound because of its structural stability in Modified Fenton reaction. What minimum 10% hydrogen peroxide concentration has good remediation efficiency of diesel contaminated groundwater may show the potential use of Modified Fenton reaction after bioslurping treatment.

• Journal of Soil and Groundwater Environment
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• v.20 no.6
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• pp.111-116
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• 2015

The soil sample obtained from shooting area contaminated with Pb, Cu, and Zn was investigated to determine the chemical forms of heavy metals with Tessier’s sequential extraction method, which is constituted of five fractions such as ‘exchangeable’, ‘bound to carbonate’, ‘bound to oxide’, ‘bound to organic matter’, and residual fractions. The amount of organic matter was measured by loss on ignition (LOI) and then the results of ‘bound to organic matter’ and LOI were compared. The sequential extraction results show that 4.7%-45% of Pb, 6.2%-25.9% of Cu and 3.9%-15.3% of Zn belong to the ‘bound to organic matter’ fraction, but LOI result shows that only 1.0%-2.8% of organic matter exists in the soil sample. In heavy medium separation tests, because Pb and Cu extracted in ‘bound to organic matter’ and residual fractions were removed, the heavy metals in the fractions would exist as heavier forms. These results suggest that the part of heavy metal extracted in ‘bound to organic matter’ fraction would result from the oxidation of metallic forms by hydrogen peroxide and nitric acid used in the fraction, and, consequently, that the ‘bound to organic matter’ fraction should be investigated in detail to determine the removal method and treatment capacity when the Tessier’s sequential extraction method is used to examine heavy metal contaminants resulted from elemental metal like bullets.

• Elastomers and Composites
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• v.34 no.4
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• pp.350-359
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• 1999

Conversion and oil-yield of a used automotive tire sample in supercritical decomposition and extraction for three solvents such as water, 28% ammoina solution and ammonia, were compared. Supercritical extraction with ammonia gave the highest conversion and oil-yield at the same temperature and pressure. In this paper, supercritical ammonia was used as major solvent and tetralin acting as hydrogen-donor, was used as cosolvent. As the amount of tetralin increased, oil-yield was Increased. When a tire sample was extracted by supercritical ammonia, oil-yield was 48.8% at $280^{\circ}C$, 22.3MPa. But when the weight ratio of tetralin to tire sample (weight of tetralin/weight of tire sample) was 5, oil-yield was 61.2% at $280^{\circ}C$ and 22.3 MPa. These phenomena indicate that as radicals produced in supercritical decomposition become stable, the polymerization and the second decomposition of products may be inhibited. Supercritical extraction of a tire sample swollen by tetralin gave high oil-yield although the amount of tetralin was a little.

• Journal of the Korean Chemical Society
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• v.18 no.2
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• pp.126-131
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• 1974

Trioctylamine-and tricaprylylmethylammonium chloride-tungstate salts have been prepared by solvent extraction from the sodium tungstate solution of various acidities(pH = 2, 4, 6). The molecular weights of the amine-tungstate salts thus obtained could be cryoscopically measured in benzene by means of a home-built Wheatstone bridge utilizing thermistor with sensitivity of 1/$4000^{\circ}C$. The cryoscopic data along with the results of chemical analysis and infrared spectra of the salts indicate that the amine-tungstates prepared at pH = 2 and 4 are all metatungstate whereas the salt obtained at pH = 6 is an unknown form quite different from the expected paratungstate.R = 0.14. By hydrogen bonding a guanidyl nitrogen of a sulfaguanidine molecule is linked to the sulfonyl oxygens of the other molecules indirectly through two different water molecules. The role of water molecule is both a .
nor and an acceptor in hydrogen-bonding formation and these hydrogen bonds are tetrahedrally o？ented. The hydrogen-bonding networks form infinite molecular layers parallel to (001) plane.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.241.1-241.1
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• 2014

The large-area high-power radio-frequency (RF) driven ion sources based on the negative hydrogen (deuterium) ion beam extraction are the major components of neutral beam injection (NBI) systems in future large-scale fusion devices such as an ITER and DEMO. Positive hydrogen (deuterium) RF ion sources were the major components of the second NBI system on ASDEX-U tokamak. A test large-area high-power RF ion source (LAHP-RaFIS) has been developed for steady-state operation at the Korea Atomic Energy Research Institute (KAERI) to extract the positive ions, which can be used for the NBI heating and current drive systems in the present fusion devices, and to extract the negative ions for negative ion-based plasma heating and for future fusion devices such as a Fusion Neutron Source and Korea-DEMO. The test RF ion source consists of a driver region, including a helical antenna and a discharge chamber, and an expansion region. RF power can be transferred at up to 10 kW with a fixed frequency of 2 MHz through an optimized RF matching system. An actively water-cooled Faraday shield is located inside the driver region of the ion source for the stable and steady-state operations of RF discharge. The characteristics and uniformities of the plasma parameter in the RF ion source were measured at the lowest area of the expansion bucket using two RF-compensated electrostatic probes along the direction of the short- and long-dimensions of the expansion region. The plasma parameters in the expansion region were characterized by the variation of loaded RF power (voltage) and filling gas pressure.

• Journal of Korean Society on Water Environment
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• v.36 no.1
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• pp.48-54
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• 2020

This paper presents a screening protocol for the selection of solvents available for the solvent extraction desalination process. The desalination solvents hypothetically and theoretically require the capability of (1) Forming hydrogen bonds with water, (2) Absorbing some water molecules into its non-polar solvent layer, (3) Changing solubility for water-solvent separation, and (4) Rejecting salt ions during absorption. Similar to carboxylic acids, amine solvents are solvent chemicals applicable for desalination. The key parameter for selecting the potential solvent was the octanol-water partitioning coefficient (Kow) of which preferable value for desalination was in the range of 1-3. Six of the 30 amine solvents can absorb water and have a variable, i.e., temperature swing solubility with water molecule for water-solvent separation. Also, the hydrogen bonding interaction between solvent and water must be stronger than the ion-dipole interaction between water and salt, which means that the salt ions must be broken from the water and only water molecules absorbed for the desalination. In the final step, three solvents were selected as desalination solvents to remove salt ions and recover water. The water recovery of these three solvents were 15.4 %, 2.8 %, 10.5 %, and salt rejection were 76 %, 98 %, 95 %, respectively. This study suggests a new screening protocol comprising the theoretical and experimental approaches for the selection of solvents for the desalination method which is a new and challenges the desalination process in the future.

• Journal of the Korean Chemical Society
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• v.22 no.5
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• pp.320-325
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• 1978

In order to elucidate the mechanism associated with the solvent extraction of uranium(VI) using DEPA and DPPA as extractant the uranium(VI) complexes formed during the solvent extraction were isolated and characterized by means of IR, NMR, chemical analysis and molecular weight determination. It has been found that uranium(VI) replaces the acidic hydrogen ions of the extractants DEPA and DPPA to form chelated polynuclear complexes, the molecular weight of U(VI)-DEPA complex being $2.1{\times}10^4$. The isolated U(VI)-DEPA complex has been found to be the same chemical species as is formed during the solvent extraction process. In case of DEPA the distribution coefficient of uranium is the largest of the pure aqueous uranium solution and is increasing for the acidic solutions in the order of $H_3PO_4.

• Journal of Environmental Science International
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• v.19 no.3
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• pp.379-387
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• 2010

Sediments of Little Scioto (LS) River in Ohio was contaminated by poor disposal of creosote from Baker Wood Creosoting Facility. Among the primary compounds of creosote, Polycyclic Aromatic Hydrocarbons (PAHs) are the most common ingredient PAHs are known for toxic, carcinogenic and mutagenic compounds. There are many difficulties to remove the PAHs in nature environment because their characteristics are having a less water-solubility, volatile and low mobility properties as increasing the molecular weight. The generation of hydroxyl radicals (${\cdot}OH$) and hydrogen peroxide ($H_2O_2$) forms as well as high temperature (5000 K) and pressure (1000 atm) by a physico-chemical effects of ultrasound during a cavitation collapse can promote the degradation and desorption of PAHs in sediment And it can also produces shock wave and microjets which are able to change the size and surface of particle in solid-liquid system as one of physical effects. Therefore, we explored to understand the role of particle size, the effect of elimination for PAHs concentration by ultrasound and optimize the conditions for ultrasonic treatment. The condition of various size of particles (> $150{\mu}m$, < $150{\mu}m$) and solid-liquid ratio (12.5g/L, 25g/L) for the treatment was considered and ultrasonic power (430 W/L) with liquid - hexane extraction and microwave extraction method were applied after ultrasound treatment.