• Membrane Journal
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• v.26 no.2
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• pp.159-165
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• 2016

Polyimide hollow fiber membrane modules were prepared in order to investigate the process of multi stage gas separation. The modules performance was carried out using 50/50 of $N_2/SF_6$ mixed gas. The membrane modules has been tested for measuring gas flow rate and concentration under various stage cut at 0.5 MPa. The membrane modules showed a high recovery ratio at the same stage cut as $N_2/SF_6$ selectivity increased. Two stage process was fulfilled for improving $SF_6$ recovery ratio and $SF_6$ concentration. Eventually, two stage process showed higher performance of $SF_6$ recovery ratio and concentration ($SF_6$ recovery ratio = 95%, $SF_6$ conc. = 98%).

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.68-72
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• 2009

This study investigated dry etching of acrylic in capacitively coupled $SF_6$, $SF_6/O_2$ and $SF_6/CH_4$ plasma under a low vacuum pressure. The process pressure was 100 mTorr and the total gas flow rate was fixed at 10 sccm. The process variables were the RIE chuck power and the plasma gas composition. The RIE chuck power varied in the range of $25{\sim}150\;W$. $SF_6/O_2$ plasma produced higher etch rates of acrylic than pure $SF_6$ and $O_2$ at a fixed total flow rate. 5 sccm $SF_6$/5 sccm $O_2$ provided $0.11{\mu}m$/min and $1.16{\mu}m$/min at 25W and 150W RIE of chuck power, respectively. The results were nearly 2.9 times higher compared to those at pure $SF_6$ plasma etching. Additionally, mixed plasma of $SF_6/CH_4$ reduced the etch rate of acrylic. 5 sccm $SF_6$/5 sccm $CH_4$ plasma resulted in $0.02{\mu}m$/min and $0.07{\mu}m$/min at 25W and 150W RIE of chuck power. The etch selectivity of acrylic to photoresist was higher in $SF_6/O_2$ plasma than in pure $SF_6$ or $SF_6/CH_4$ plasma. The maximum RMS roughness (7.6 nm) of an etched acrylic surface was found to be 50% $O_2$ in $SF_6/O_2$ plasma. Besides the process regime, the RMS roughness of acrylic was approximately $3{\sim}4\;nm$ at different percentages of $O_2$ with a chuck power of 100W RIE in $SF_6/O_2$ plasma etching.

• KEPCO Journal on Electric Power and Energy
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• v.8 no.2
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• pp.111-118
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• 2022

SF₆ is used as an insulating gas because of its excellent electrical insulation properties, non-toxicity, and non-inflammability. On the other hand, the global warming potential of SF₆ is 23,900 times higher than that of CO₂. The Korea electric power cooperation (KEPCO) is responsible for 80% of the domestic SF₆ usage, and approximately 6,000 tons are currently charged in electrical and power facilities. KEPCO will gradually replace the insulating gas with SF₆-free gas from 2023. SF₆ decomposition facilities are required because more than 60 tons of SF₆ will need to be disposed of annually from existing equipment. This study developed a novel decomposition and pollution control system that can process 60 tons of SF₆ per year. This facility can decompose more than 97.7% of SF₆, with the emissions of hazardous and toxic materials below the legal limit.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.96-99
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• 2003

In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in $SF_6$ and $SF_6$-Ar mixtures have described. The transport coefficients for electrons in (0.1[%])$SF_6$-Ar, (0.5[%])$SF_6$-Ar, (1.0[%])$SF_6$-Ar, (3.0[%])$SF_6$-Ar and (5.0[%])$SF_6$-Ar mixtures were measured by time-of-flight method, and the electron energy distribution function and the parameters of the velocity and the diffusion were determined by the variation of the collision cross-sections with energy.

• 전기의세계
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• v.28 no.4
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• pp.39-46
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• 1979

The effective ionization coefficient in $SF_{6}$/$N_{2}$ mixtures was attempted to derive from the pure gases. Measurements of static breakdown voltage were made under the uniform field at pressures up to 4 bar in order to compare with the results obtained from this assumption. The relative performance of $SF_{6}$/$N_{2}$ mixtures to pure $SF_{6}$ was also investigated. The effect of surface roughness on discharge thresholds in $SF_{6}$/$N_{2}$ mixtures was calculated employing the simplified model and mesurements of breakdown voltages for a gap with an artificial protrustion were also made. The experimental results show that the effective ionization coefficient in gas mixtures can not be reliably estimated from the values measured for the pure gases. Therefore, basic parameters for $SF_{6}$/$N_{2}$ mixtures must be measured by investigation of the mixtures themselves. The relative performance of mixtures to pure $SF_{6}$ could be considered with the values of pR.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2202-2204
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• 2005

In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in $SF_6$ and $SF_6-Ar$ mixtures have described. The transport coefficients for electrons in (0.1[%]) $SF_6-Ar$, (0.5[%])$SF_6-Ar$,(1.0[%])$SF_6-Ar$,(3.0[%])$SF_6-Ar$ and(5.0[%]) $SF_6-Ar$ mixtures were measured by time-of- flight method, and the electron energy distribution function and the parameters of the velocity and the diffusion were determined by the variation of the collision cross-sections with energy.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1494-1495
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• 2007

In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in $SF_6$ and $SF_6$-Ar mixtures have described. The transport coefficients for electrons in (0.1[%])$SF_6$-Ar, (0.5[%])$SF_6$-Ar, (1.0[%])$SF_6$-Ar, (3.0[%])$SF_6$-Ar and (5.0[%])$SF_6$-Ar mixtures were measured by time-of-flight method, and the electron energy distribution function and the parameters of the velocity and the diffusion were determined by the variation of the collision cross-sections with energy.

• Membrane Journal
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• v.22 no.3
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• pp.201-207
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• 2012

In this study, we investigated permeation of single gas ($N_2$, $O_2$, $CF_4$, and $SF_6$) through flat sheet membrane composed of PDMS (poly-dimethylsiloxane) and PEBAX (polyether block amides). Gas permeation experiment was performed with various feed pressure. Permeability was estimated using permeation flux measured by continuous-flow technique. The permeability of gases except $SF_6$ in PDMS were decreased with the upstream pressure increased. $SF_6$ is much more permeable than $CF_4$, which is due to higher critical temperature of $SF_6$. The permeability decreased in the following order: $O_2$ > $N_2$ > $SF_6$ > $CF_4$. On the other hand, the permeability of gases in PEBAX followed the order: $O_2$ > $N_2$ > $CF_4$ > $SF_6$ which are opposite of the order of kinematic diameter (${\AA}$)($SF_6$ > $CF_4$ > $N_2$ > $O_2$). The $SF_6/CF_4$ pure gas selectivity in PDMS was 2.1 at 0.7 MPa.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.8
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• pp.142-149
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• 2010

This paper describes dielectric characteristics of $SF_6$ and dry-air gases under lightning impulse voltages in a quasi-uniform electric field. In order to simulate to a quasi-uniform electric field, electric field utilization factor of the used sphere-plane electrode is 71[%]. The gas pressure of $SF_6$ ranges from 0.1 to 0.2[MPa] and that of dry-air ranges from 0.2 to 0.6[MPa]. Electrical breakdown voltages of $SF_6$ and dry-air gases are measured and analyzed as functions of the polarity of lightning impulse voltage and gas pressure. As a result, the electrical breakdown voltage of both gases under the positive lightning impulse voltage is higher than that under the negative one. The electrical breakdown voltage in $SF_6$ is almost higher than 2.67 times compared to dry-air. The results presented in this paper can be used as a useful information to evaluate the capability of alternative insulation gases for $SF_6$ in power distribution equipment with prominent ability against lightning surge.

• Korean Chemical Engineering Research
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• v.48 no.5
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• pp.660-667
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• 2010

In this research polyimide, Matrimid 5218, hollow fiber membrane was used to recover sulfur hexafluoride($SF_6$) which is one of the six greenhouse gases from $N_2/SF_6$ mixture gas. Fibers were spun from using dry-wet phase inversion method. The module was manufactured by fabricating fibers after surface coating with silicone elastomer. The scanning electron microscopy(SEM) studies showed that the produced fibers typically had an asymmetric structure; a dense top layer supported by a sponge-like substructure. The developed module had a permeance of 0.78-1.36 GPU for $N_2$ with $N_2/SF_6$ selectivity of 2.44-5.08 at various pressure and temperature. For recovery of $SF_6$, a membrane module and 10 vol.% $SF_6$ from $N_2/SF_6$ mixture gas was used. The effects of various operating condition such as pressure, temperature, and retentate side flow rate were tested. When pressure and temperature were increased and retentate flow rate was decreased, the $SF_6$ purity in recovered gas was increased up to 37.5 vol.% with decreasing recovery ratio. When retentate flow rate was increased pressure and temperature was decreased, the $SF_6$ recovery ratio in retentate side was increased up to 89% with decreasing the $SF_6$ purity in retentate side.