• Journal of Korean Society on Water Environment
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• v.28 no.3
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• pp.401-408
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• 2012

High-voltage dielectric discharges are an emerging technique in environmental pollutant degradation, which that are characterized by the production of hydroxyl radicals as the primary degradation species. The initiation and propagation of the electrical discharges depends on several physical, chemical, and electrical parameters such as 1st and 2nd voltage of power, gas supply, conductivity and pH. These parameters also influence the physical and chemical characteristics of the discharges, including the production of reactive species such as OH, $H_2O_2$ and $O_3$. The experimental results showed that the optimum 1st voltage and air flow rate for RNO (N-Dimethyl-4-nitrosoaniline, indicator of the generation of OH radical) degradation were 160 V (2nd voltage of is 15 kV) and 4 L/min, respectively. As the increased of the 2nd voltage (4 kV to 15 kV), RNO degradation, $H_2O_2$ and $O_3$ generation were increased. The conductivity of the solution was not influencing the RNO degradation and $H_2O_2$ and $O_3$ generation. The effects pH was not high on RNO degradation. However, the lower pH and the conductivity, the higher $H_2O_2$ and $O_3$ generation were observed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1646-1649
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• 2012

The $O_2$ annealing technique has considerably suppressed the leakage current of GaN power devices, but this forms NiO at Ni-based Schottky contact with increasing on-resistance. The purpose of the present study was to fabricate 1.5 kV GaN Schottky barrier diodes by improving $O_2$-annealing process and GaN buffer. The proposed $O_2$ annealing performed after alloying ohmic contacts in order to avoid NiO construction. The ohmic contact resistance ($R_C$) was degraded from 0.43 to $3.42{\Omega}-mm$ after $O_2$ annealing at $800^{\circ}C$. We can decrease RC by lowering temperature of $O_2$ annealing. The isolation resistance of test structure which indicated the surface and buffer leakage current was significantly increased from $2.43{\times}10^7$ to $1.32{\times}10^{13}{\Omega}$ due to $O_2$ annealing. The improvement of isolation resistance can be caused by formation of group-III oxides on the surface. The leakage current of GaN Schottky barrier diode was also suppressed from $2.38{\times}10^{-5}$ to $1.68{\times}10^{-7}$ A/mm at -100 V by $O_2$ annealing. The GaN Schottky barrier diodes achieved the high breakdown voltage of 700, 1400, and 1530 V at the anode-cathode distance of 5, 10, and $20{\mu}m$, respectively. The optimized $O_2$ annealing and $4{\mu}m$-thick C-doped GaN buffer obtained the high breakdown voltage at short drift length. The proposed $O_2$ annealing is suitable for next-generation GaN power switches due to the simple process and the low the leakage current.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.582-587
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• 2006

Decomposition behavior of $ferro-Si_3N_4$was investigated with varying temperature and holding time in mud components for high temperature refractory applications. Porosities gradually increased with increasing temperature and holding time due to the carbothermal reduction of $Si_3N_4\;and\;SiO_2$. Silicon monoxide (SiO) as a intermediate resulted from evaporation of $Si_3N_4\;and\;SiO_2$ reacted with C sources to generate needle-like ${\beta}-SiC$ and Fe in $Si_3N_4$ acted as a catalyst in order to enhance growth of SiC grain with the preferred orientation. SiC generation yield increased with increasing holding time, all of the $Si_3N_4\;and\;SiO_2$ affected on SiC formation up to 2h. However, SiC generation was only dependent on residual $SiO_2$ over 2h, because the carbothermal reduction reaction of $Si_3N_4$ was no longer possible at that time.

• Clean Technology
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• v.18 no.4
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• pp.419-425
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• 2012

This work explored the characteristics and the photocatalytic activities of S element-doped $TiO_2$ (S-$TiO_2$) and N element-doped $TiO_2$ (N-$TiO_2$) for the decomposition of gas-phase isopropyl alcohol (IPA) at sub-ppm concentrations, using a plug-flow reactor irradiated by 8-W daylight lamp or visible light-emitting-diodes (LEDs). In addition, the generation yield of acetone during photocatalytic processes for IPA at sub-ppm levels was examined. The surface characteristics of prepared S- and N-$TiO_2$ photocatalysts were analyzed to indicate that they could be effectively activated by visible-light irradiation. Regarding both types of photocatalysts, the cleaning efficiency of IPA increased as the air flow rate (AFR) was decreased. The average cleaning efficiency determined via the S-$TiO_2$ system for the AFR of 2.0 L $min^{-1}$ was 39%, whereas it was close to 100% for the AFR of 0.1 L $min^{-1}$. Regarding the N-$TiO_2$ system, the average cleaning efficiency for the AFR of 2.0 L $min^{-1}$ was above 90%, whereas it was still close to 100% for the AFR of 0.1 L $min^{-1}$. In contrast to the cleaning efficiencies of IPA, both types of photocatalysts revealed a decreasing trend in the generation yields of acetone with decreasing the AFR. Consequently, the N-$TiO_2$ system was preferred for cleaning of sub-ppm IPA to S-$TiO_2$ system and should be operated under low AFR conditions to minimize the acetone generation. In addition, 8-W daylight lamp exhibited higher cleaning efficiency of IPA than for visible LEDs.

• Journal of Power System Engineering
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• v.18 no.6
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• pp.106-112
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• 2014

The diesel engine, which has high compression ratio than other heat engines, has been using as the main power source of marine transport. Especially, since marine diesel engines offer better specific fuel consumption (SFC), it is environment-friendly compared to those used in other industries. However, attentio should be focused on emissions such as nitrous oxide ($N_2O$) which is generated from combustion of low-grade fuels. Because $N_2O$ in the atmosphere is very stable, the global warming potential (GWP) of $N_2O$ is 310 times as large as that of $CO_2$, and it becomes a source of secondary contamination after photo-degradation in the stratosphere. It has been hitherto noted on the $N_2O$ exhaust characteristics from stationary power plants and land transportations, but reports on $N_2O$ emission from the marine diesel engine are very limited. In this experimental study, a author investigated $N_2O$ emission characteristics by using changed diesel fuel components of nitrogen and sulfur concentration, assessed on the factors which affect $N_2O$ generation in combustion. The experimental results showed that $N_2O$ emission exhibited increasement with increasing of sulfur concentration in fuel. However, all kinds of nitrogen component additives used in experiment could not change $N_2O$ emission.

• Journal of Environmental Science International
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• v.18 no.11
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• pp.1215-1224
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• 2009

This study evaluated the applicability of visible-light-driven N- and S-doped titanium dioxide($TiO_2$) for the control of low-level dimethyl sulfide(DMS) and dimethyl disulfide(DMDS). In addition, a photocatalytic unit(PU)-adsorption hybrid was evaluated in order to examine the removal of DMS and DMDS which exited the PU and a gaseous photocatalytic byproduct($SO_2$) which was generated during the photocatalytic processes. Fourier-Tranform-Infrared(FTIR) spectrum exhibited different surface characteristics among the three-types of catalysts. For the N- and S-doped $TiO_2$ powders, a shift of the absorbance spectrum towards the visible-light region was observed. The absorption edge for both the N- and S-doped $TiO_2$ was shifted to $\lambda$ 720 nm. The N-doped $TiO_2$ was superior to the S-doped $TiO_2$ in regards to DMS degradation. Under low input concentration(IC) conditions(0.039 and 0.027 ppm for DMS and DMDS, respectively), the N-doped $TiO_2$ revealed a high DMS removal efficiency(above 95%), but a gradual decreasing removal efficiency under high IC conditions(7.8 and 5.4 ppm for DMS and DMDS, respectively). Although the hybrid system exhibited a superior characteristic to PU alone regarding the removal efficiencies of both DMS and DMDS, this capability decreased during the course of a photocatalytic process under the high IC conditions. The present study identified the generation of sulfate ion on the catalyst surface and sulfur dioxide(maximum concentrations of 0.0019 and 0.0074 ppm for the photocatalytic processes of DMS and DMDS, respectively) in effluent gas of PU. However, this generation of $TiO_2$ would be an insignificant addition to indoor air quality levels.

• Applied Chemistry for Engineering
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• v.19 no.6
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• pp.624-628
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• 2008

Nitrous oxide ($N_2O$), known as one of the major greenhouse gases, is an important component of the earth's atmosphere, and gives rise to precursor of acid rain and photochemical smog. For the removal of $N_2O$ and other nitrogen oxides, the SCR reaction system with various reductants is widely used. This study is based on the results of experimental and theoretical examinations on the catalytic decomposition of sole nitrous oxide ($N_2O$) and selective catalytic reduction of $N_2O$ with $CH_4$ in the presence of oxygen using mixed metal oxide catalysts obtained from hydrolatcite-type precursors. When $CH_4$ is fed together with a reductant, it affects positively on the $N_2O$ decomposition activity. At an optimum ratio of $CH_4$ to $O_2$ mole ratio, the $N_2O$ conversion activity is enhanced on the SCR reaction with partial oxidation of methane.

• Journal of Korean Society on Water Environment
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• v.27 no.2
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• pp.194-199
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• 2011

This study has been carried out to evaluate the performance of $PbO_2$ electrode for the purpose of degradation of N,N-Dimethyl-4-nitrosoaniline (RNO, indicator of OH radical), generation of ozone and decolorization of Rhodamine B (RhB) in water. The effect of the applied current (0.2~1.2 A), electrolyte type (NaCl, KCl and $Na_2SO_4$), electrolyte concentration (0.0~2.5 g/L) and solution pH (3~11) were evaluated. Experimental results showed that RhB and RNO removal were increased with the increase of current, NaCl dosage and decrease of pH. Ozone generation tendencies appeared with the almost similar to the RhB and RNO degradation, except of solution pH (Ozone generation was increased with increase of pH). Optimum current for RhB degradation and consumption of electric power was 1.0 A. The RhB degradation with Cl type electrolyte were higher than that with the sulfate type. Optimum NaCl dosage for RhB degradation was 1.0 g/L.

• Journal of Animal Environmental Science
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• v.13 no.1
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• pp.1-12
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• 2007

Stored animal manure is considered as a significant agricultural source of methane $(CH_4)$ and nitrous oxide $(N_2O)$ which have 23 and 297 times higher global warming effect when compared to carbon dioxide $(CO_2)$. Uncertainties caused by lack of understanding physical and biochemical environment in stored animal manure and by errors of emission measurement methods, even though many researches measuring $CH_4\;and\;N_2O$ emissions from stored manure have been conducted for a few decades. In this paper, general information of $CH_4\;and\;N_2O$ generation and emissions from stored animal manure and the measurement methods for quantifying $CH_4\;and\;N_2O$ emissions are discussed.

• Journal of Environmental Science International
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• v.22 no.12
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• pp.1561-1569
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• 2013

This study carried out a laboratory scale plasma reactor about the characteristics of chemically oxidative species (${\cdot}OH$, $H_2O_2$ and $O_3$) produced in dielectric barrier discharge plasma. It was studied the influence of various parameters such as gas type, $1^{st}$ voltage, oxygen flow rate, electric conductivity and pH of solution for the generation of the oxidant. $H_2O_2$ and $O_3$.) $H_2O_2$ and $O_3$ was measured by direct assay using absorption spectrophotometry. OH radical was measured indirectly by measuring the degradation of the RNO (N-Dimethyl-4-nitrosoaniline, indicator of the generation of OH radical). The experimental results showed that the effect of influent gases on RNO degradation was ranked in the following order: oxygen > air >> argon. The optimum $1^{st}$ voltage for RNO degradation were 90 V. As the increased of $1^{st}$ voltage, generated $H_2O_2$ and $O_3$ concentration were increased. The intensity of the UV light emitted from oxygen-plasma discharge was lower than that of the sun light. The generated hydrogen peroxide concentration and ozone concentration was not high. Therefore it is suggested that the main mechanism of oxidation of the oxygen-plasma process is OH radical. The conductivity of the solution did not affected the generation of oxidative species. The higher pH, the lower $H_2O_2$ and $O_3$ generation were observed. However, RNO degradation was not varied with the change of the solution pH.