• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2006.04a
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• pp.54-56
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• 2006

Single-well-gas-sparging tests were developed and evaluated for assessing the feasibility of in-situ aerobic cometabolism of trichloroethylene (TCE), using propane as a growth substrate. To evaluate transport characteristics of dissolved solutes [sulfur hexafluoride (SF6) or bromide (non-reactive tracers), propane (a growth substrate), ethylene, propylene (nontoxic surrogates to probe for CAH transformation activity), and DO], push-pull transport tests were performed. Mass balance showed about 90% of the injected bromide and about 80% of the injected SF6 were recovered, and the recoveries of other solutes were comparable with bromide and slightly higher than SF6. A series of Gas-Sparging Biostimulation tests were performed by sparging propane/oxygen/argon/SF6 gas mixtures, and temporal ground water samples were obtained from the injection well under natural gradient 'drift' conditions. The decreased time for propane depletion and the longer time to deplete SF6 as a conservative tracer indicate the progress of biostimulation. Gas-Sparging Activity tests were performed. .Propane utilization, DO consumption, and ethylene and propylene cometabolism were well demonstrated. The stimulated propane-utilizers cometabolized ethylene and propylene to produce ethylene oxide and propylene oxide, as cometabolic by-products, respectively. Gas-Sparging Acetylene Blocking tests were performed by sparging gas mixtures including acetylene to demonstrate the involvement of monooxygenase enzymes. Gas substrate degradation was essentially completely Inhibited in the presence of acetylene, and no production of the corresponding oxides was also observed. The Gas-Sparging tests supports the evidences that the successive stimulation of propane-oxidizing microorganisms, cometabolic transformation of ethylene and propylene by the enzyme responsible for methane and propane degradation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.63-63
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• 2008

Environmental monitoring sub-system has been developed using gas sensor module, Bluetooth module and PDA phone. The gas sensor module consists of $NO_2or$ CO gas sensor and signal processing chips. Gas sensor is composed of the micro-heater, sensing electrode and sensing material. Metal oxide nano-material was selectively deposited on a substrate with micro-heater and was integrated to the gas sensor module. The change in resistance of the metal oxide nano-material due to exposure of oxidizing or deoxidizing gases is utilized as the principle of this gas sensor operation mechanism. This variation detected in the gas sensor module was transferred to the PDA phone by way of Bluetooth module.

• Journal of Korean Society on Water Environment
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• v.34 no.6
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• pp.642-649
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• 2018

The effect of gas sparging on sonochemical oxidation was investigated in a 300 kHz sonoreactor under various liquid height/volume conditions ($5{\sim}30{\lambda}$, 3.4 ~ 9.0 L), determined by the wavelength of the applied frequency. The electrical input power was maintained constant for all cases . Sonochemical activity drastically decreased from $15{\lambda}$ and the liquid height of $10{\lambda}$ was suggested as the optimal height for 300 kHz without gas sparging. In our previous research, the sonochemical activity observed was five-times higher when air sparging was applied for 36 kHz. On the other hand, no enhancement was obtained at 10, 15, 25 and $30{\lambda}$ using air sparging (1, 3, and 6 L/min) for 300 kHz in this study $20{\lambda}$ and optimization of gas sparging was conducted at $20{\lambda}$ using various gases including air, Ar, $O_2$, $N_2$, and mixtures of Ar and $O_2$. It was found that gas sparging using pure Ar or pure $O_2$ resulted in lower sonochemical activity compared to that of air sparging due to the imbalance between the intensity of cavitation phenomena and the generation of oxidizing radical species. Consequently, the gas mixture of $Ar:O_2$ = 80 % : 20 % (DO saturation ${\approx}100%$) was suggested as an optimal gas sparging condition.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.6
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• pp.329-333
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• 2016

Disinfection by electrolysis would be useful for small wastewater treatment plant, combined sewer overflow, ballast water, swimming pool, and fish farming, where the transport, storage, and the use of chlorine gas is limited. This study investigated the feasibility of the electrolysis of dilute hydrochloric acid (HCl) for disinfection. The effects of HCl concentration, voltage and reaction time on the generation of oxidizing agents, HOCl, $O_3$, and $H_2O_2$, were examined in a series of batch test. The highest current efficiency was 99.3% which was found at 2.2%, 3 V, and 5 min of HCl concentration, voltage, and reaction time, respectively. Continuous electrolysis at 2.2% HCl, 3 V, and 5 min of the hydraulic retention time showed 97.4% of the current efficiency. Addition of sodium chloride up to 20 g/L linearly increased the oxidizing agents production. 92.2% of total coliforms were removed by the contact with the electrolyzed water.

• Journal of the Korean Society of Combustion
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• v.4 no.1
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• pp.27-38
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• 1999

We constructed a wire-cylinder type pulsed corona discharge system for $NO_x$ removal, which was operated in room temperature. A emission spectrometer was built with a boxcar averager and monochrometer equipped with photo-multiplier tube detector. The sensitivity of the emission spectrometer was greatly improved by synchronizing the emission spectrometer with pulsed corona discharge system using a triggered spark-gap switch. $N_2$ spectrum($c^3{\Pi}_u{\rightarrow}X^1{\Sigma}_g{^+}$) was measured in the range of 300 - 450 nm and oxidizing OH radical emission($A^2{\Sigma}^+{\rightarrow}X^2{\Pi}$) was measured in case $N_2$ was supplied with water bubbling. As wet gas composition of inlet $N_2$ supplied in the discharge system increased, the intensity of OH emission was increased and saturated at wet gas composition 50%. We also investigated additive effect of $C_2H_4,\;H_2O,\;H_2O_2$ on the intensity of OR emission and $NO/NO_2/NO_x$ reduction and analysed the related reaction mechanism in corona discharge process. $H_2O_2$ additive increased the intensity of OH emission and $NO/NO_x$ reduction.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.2
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• pp.321-324
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• 2020

In this work, we developed a selective etching process for GaN that is a key process in p-GaN/AlGaN/GaN enhancement-mode (E-mode) power switching field-effect transistor (FET) fabrication. In order to achieve a high current density of p-GaN/AlGaN/GaN E-mode FET, the p-GaN layer beside the gate region must be selectively etched whereas the underneath AlGaN layer should be maintained. A selective etching process was implemented by oxidizing the surface of the AlGaN layer and the GaN layer by adding O2 gas to Cl2/N2 gas which is generally used for GaN etching. A selective etching process was optimized using Cl2/N2/O2 gas mixture and a high selectivity of 53:1 (= GaN/AlGaN) was achieved.

• Journal of the Korean Ceramic Society
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• v.23 no.5
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• pp.1-8
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• 1986

This paper is concerned with a gas sensor composed of semi-conducting ${\gamma}$-$Fe_2O_3$ ceramics made by oxidizing $Fe_2O_3$ sintered body. Acicular $\alpha$-FeOOH powder prepared by precipitation of $FeSO_4$.$7H_2O$ solution was transformed to $FeSO_4$ sintered at 700$^{\circ}$-850$^{\circ}$C for 1 hr. and then oxidized to ${\gamma}$-$Fe_2O_3$ The gas sensitive properties of ${\gamma}$-$Fe_2O_3$ ceramic bodies based on the lectrical resistance change was measured in 0.5-2 vol% $H_2$ and $C_2$ $H_2$ gas at 35$0^{\circ}C$ The specific surface area of sintered specimen largely dependent on the sintering temperature and grain shape directly affected the gas sensitive pro-perties of ${\gamma}$-$Fe_2O_3$gas sensor. Specimens having larger specific surface area showed better sensitivity which means the electrical resistance change due to oxidation and reduction process occurs on ly at the surface of grains microscopically in the ${\gamma}$-$Fe_2O_3$ceramics. Micropores made in $Fe_2O_3$ powder during dehydration of $\alpha$-FeOOH can not prompt the gas sensitive properties of sintered ${\gamma}$-$Fe_2O_3$ because they are sintered or closed in the grains during sintering process and dose not affect the specific surface area of sintered body.

• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1180-1186
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• 2001

W $O_3$-Sn $O_2$thin film sensors with approximately 1${\mu}{\textrm}{m}$ in thickness were fabricated by using a high-vacuum resistance-heating evaporator, were annealed at 50$0^{\circ}C$ for 4 hours in air, and then their crystallinities and surface microstructures were analyzed. As results of gas-sensing characteristics to oxidizing gas, N $O_2$, and reducing gas, CO, of 100 ppm, the highest gas sensitivities (S= $R_{gas}$/ $R_{air}$) were the W $O_3$thin-film sensor measured at 25$0^{\circ}C$ for N $O_2$(S≒1000) and the Sn $O_2$thin-film sensor measured at 15$0^{\circ}C$ to 25$0^{\circ}C$ range for CO (S≒0.25), respectively.ely.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.87-93
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• 2004

Nitrocarburizing was carried out with various $CH_4$ gas composition with 4 torr gas pressure at $570^{\circ}C$ for 3 hours and post oxidation was carried out with 100% $O_2$ gas atmosphere with 4 torr at different temperatures for various time. In the case of plasma nitrocarburizing, It is that the ratio of ${\varepsilon}-Fe_{2-3}$(N, C) and ${\gamma}^{\prime}-Fe_4$(C, N), which comprise the compound layer phase, depend on concentrations of $N_2$ gas and $CH_4$ such that when the concentration of $N_2$ and $CH_4$ increased, the ratio of ${\gamma}^{\prime}-Fe_4$(C, N) decreased, but the ratio of ${\varepsilon}-Fe_{2-3}$(N, C) increased. The thickness of compound layer consistently increased as gas concentration increased regardless of $N_2$ and $CH_4$ expect when the concentration of $CH_4$ was 3.5 volume%, it decreased insignificantly. When oxidizing for 15min in the temperature range of $460{\sim}570{^\circ}C$, the study found small amount of $Fe_3O_4$ at the temperature of $460{^\circ}C$ and also found that amounts of $Fe_2O_3$. and $Fe_3O_4$ on the surface and amount of ${\gamma}^{\prime}-Fe_4$(C, N) in the compound layer increased as the increased over $460^{\circ}C$, but the thickness of the compound layer decreased. Corrosion resistance was influenced by oxidation times and temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.271-274
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• 2000

Gas sensor materials capable of detecting hydrogen gases (H$_2$) or nitrogen oxides (NO$\_$x/, primarily NO and NO$_2$) with high sensitivity have attracted much interest in conjunction with the growing concern to the protection of global environments. Beside conventional sensor materials, such as semiconductors., conducting polymers and solid electrolytes, the potential of sensor materials with a new method for detecting hydrogen gases or nitrogen oxides gas has also been tested. The breakdown voltage of porous varistors shifted to a low electric field upon exposure to H$_2$ gas, whereas it shifted to a reverse direction in an atmosphere containing oxidizing gases such as O$_3$ and NO$_2$ in the temperature range of 300 to 600$^{\circ}C$. Furthermore, it was found that the magnitude of the breakdown voltage shift, i. e. the magnitude of sensitivity, was well correlated with gas concentration, and that the H$_2$ sensitivity was improved by controlling the composition of the Bi$_2$O$_3$ rich grain boundary phase. However, NO$\_$x/ sensing properties of porous varistors have not been studies in detail. The objective of the present study is to investigate the effect of the composition of the Bi$_2$O$_3$ rich grain boundary phase and other additive such as A1$_2$O$_3$ on the hydrogen gases (H$_2$) sensing properties of porous ZnO based varistors.