• Journal of the Korean institute of surface engineering
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• v.35 no.2
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• pp.113-121
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• 2002

We have investigated insulating properties of $SiO_2$ interlayer for the thin film strain gauge, which were prepared by RF magnetron sputtering method in various deposition conditions, such as Ar pressure, gas flow rates and sputtering gases. SEM, AFM and FT-IR techniques were used to analyze its structures and composition. As the Ar pressure and the flow rate increased, the insulating interlayer showed low insulating resistance due to its porous structure and defects. Oxygen deficiency in $SiO_2$ was decreased as fabricated by hydrogen reactive sputtering. We could enhance the surface mobility of sputtered adatoms by using Ar/$H_2$ sputtering gas and obtain a good surface roughness and insulating property. The optimum insulating resistance of 9.22 G$\Omega$ was obtained in Ar/30% $H_2$ mixed gas, flow rate 10sccm, and 1mTorr.

• Clean Technology
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• v.30 no.2
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• pp.71-93
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• 2024

Recently, the establishment of a hydrogen-based economy and the utilization of low-carbon energy sources, particularly for shipping and power generation, have been in high demand in order to achieve carbon neutrality by 2050. In particular, ammonia is gaining renewed attention because it is capable of serving as a key facilitator for high-efficiency green hydrogen storage and transportation and it is also capable of serving as a low-carbon energy source. Although ammonia can be synthesized through the Haber-Bosch process, the high energy consumption and carbon emissions associated with this process result in minimal carbon reduction. To address the critical drawbacks of the traditional Haber-Bosch process, various thermochemical synthesis methods have been developed recently, allowing for the synthesis of ammonia with lower carbon emissions and a higher energy efficiency. Research is also progressing in the development of high-performance catalyst materials that are capable of demonstrating sufficient ammonia synthesis performance under milder process conditions compared to conventional methods. Additionally, a variety of different processes such as chemical-looping ammonia synthesis, plasma synthesis, and mechanochemical synthesis are being applied diversely. This review aims to provide a detailed overview of the emerging ammonia synthesis technologies that have been developed to effectively store green hydrogen for future applications.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.49-52
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• 2009

The response times of monopropellant thrusters at a pulse mode were investigated experimentally as design parameters and feed pressure conditions. Five different model thrusters as injection direction/uniformity, aspect ratio of reactor, volumes of manifold and chamber were designed. As a results, two parameters, aspect ratio and manifold volume, were directly related to response characteristics. Additionally, chugging instability at reaction chamber was observed when pressure drop across the catalyst bed was increased due to high aspect ratio or when low pressure was built at reaction chamber.

• Carbon letters
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• v.13 no.4
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• pp.205-211
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• 2012

Methanol as a carbon source in chemical vapor deposition (CVD) graphene has an advantage over methane and hydrogen in that we can avoid optimizing an etching reagent condition. Since methanol itself can easily decompose into hydrocarbon and water (an etching reagent) at high temperatures [1], the pressure and the temperature of methanol are the only parameters we have to handle. In this study, synthetic conditions for highly crystalline and large area graphene have been optimized by adjusting pressure and temperature; the effect of each parameter was analyzed systematically by Raman, scanning electron microscope, transmission electron microscope, atomic force microscope, four-point-probe measurement, and UV-Vis. Defect density of graphene, represented by D/G ratio in Raman, decreased with increasing temperature and decreasing pressure; it negatively affected electrical conductivity. From our process and various analyses, methanol CVD growth for graphene has been found to be a safe, cheap, easy, and simple method to produce high quality, large area, and continuous graphene films.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.117.2-117.2
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• 2011

We probe 12CO J=2-1 and 13CO J=1-0 properties of a Virgo disk galaxy, NGC 4402 which is located near the cluster center. Our goal is to study the impact of intra cluster medium (ICM) on the molecular gas of a galaxy in the cluster environment. It has been believed that cluster galaxies are deficient in atomic hydrogen gas (HI gas) compared to their field counterparts and now there is much evidence that low density ISM can be easily removed by ram pressure caused by ICM wind. Meanwhile, no significant molecular gas deficiency of the cluster galaxy population has been found yet they show overall lower star formation rate than galaxies in the field, and it is still controversy whether dense ISM can be also stripped by the ICM wind or not. NGC 4402 with truncated HI disk($D_{HI}/D_{opt}$ ~ 0.75 and only 36%of HI gas compare to field galaxies of a similar size) and a disturbed gas morphology, appears to have strong ongoing ram pressure. Using high resolution 12 and 13CO data of NGC 4402 from a Sub Millimeter Array (SMA), we probe the molecular gas properties under strong ICM pressure. We discuss how its star formation activity and hence the global color of NGC4402 would be changed in the future.

• Journal of the Korean Society for Heat Treatment
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• v.33 no.1
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• pp.20-24
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• 2020

Single crystal diamonds are in great demand in such fields as mechanical, electronic applications and optoelectronics. Large area single crystal diamonds are attracting attention in future industries for mass production and low cost. In this study, hot filament CVD (HFCVD) is used to grow large area single crystal diamond. However, the growth rate of large area single crystal diamond using HFCVD is known to be very low. The goal of this study is to use single crystal diamond substrates in HFCVD with methane-hydrogen gas mixtures to increase the growth rate of single crystal diamond and to optimize the conditions by analysing the effects of deposition conditions for high quality crystallinity. The deposition pressure, the ratio of CH₄/H₂ gas, the substrate temperature and the distance between the filament and the substrate were optimized. The sample used a 4×4 (mm²) size single crystal diamond substrate (100), the CH₄/H₂ gas ratio was fixed at 5%, the substrate temperature was synthesized to about 1000℃. At this time, the deposition pressure was changed to three types of 50, 75, 85 Torr and deposited. Finally, optimization was investigated under pressure conditions to analyse the growth rate and quality of single crystal diamond.

• Journal of the Korean Institute of Gas
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• v.9 no.3 s.28
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• pp.9-14
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• 2005

To estimate the explosion characteristics of converted gas, the study was examined into effects of altering oxygen concentration and adding hydrogen. From the result of the experiment, as the concentration of converted gas and hydrogen were increased at $21\%$ oxygen concentration, the lower explosion limit was low. Minimum explosion oxygen concentration was $6\%$. Maximum explosion pressure of converted gas was $4.61 kg_f/cm^2$, now Maximum explosion pressure rising velocity was $130.75 kg_f/cm^2/s$ at converted gas concentration $40\%$. Also, minimum ignition energy was 0.13 mJ at converted gas concentration $50\%$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.250.2-250.2
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• 2014

Currently, teeth whitening method which is applicable to dental surgery is that physician expertises give medical treatment to teeth directly dealed with a high concentration of hydrogen peroxide and carbamide peroxide. If hydrogen peroxide concentration is too high for treatment of maximized teeth whitening effect [1], it is harmful to the human body [2]. To the maximum effective and no harmful teeth whitening effect in a short period of time at home, we have observed the whitening effect using carbamide peroxide (15%) and a low-temperature atmospheric pressure plasma jet which is regulated by the Food and Drug Administration. The gas supplied conditions of the non-thermal atmospheric pressure plasma jet was with the humidified (0.6%) gas in nitrogen or air at gas flow rate of 1000 sccm. Also, the measurement of chemical species from the jet was carried out using the optical emission spectroscopy (OES), the evidence of increased reactive oxygen species compared to non-humidified plasma jet. We have found that the whitening effect of the plasma is very excellent through this experiment, when bovine teeth are treated in carbamide peroxide (15%) and water vapor (0.2 to 1%). The brightness of whitening teeth was increased up to 2 times longer in the CIE chromaticity coordinates. The colorimetric spectrometer (CM-3500d) can measure color degree of whitening effect.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.6
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• pp.905-912
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• 2011

In this study, the novel concept catalytic reactor was designed for water-gas shift reaction (WGS) under high pressure. The novel concept catalytic reactor was composed of an autoclave, the catalyst, and liquid water. Cu-ZnO/$Al_2O_3$ as the low temperature shift catalyst was used for WGS reaction. WGS in the novel concept catalytic reactor was carried out at the ranges of 150~$250^{\circ}C$ and 30~50 atm. The liquid water was filled at the bottom of the autoclave catalytic reactor and the catalyst of pellet type was located at the gas-liquid water interface. It was concluded that WGS reaction occurred over the surface of catalysts partially wetted with liquid water. The conversion of CO for WGS was also controlled with changing content of Cu and ZnO used as the catalytic active components. Meanwhile, the catalyst of honey comb type coated with Cu-ZnO/$Al_2O_3$ was used in order to increase the contact area between wet-surface of catalyst and the reactants of gas phase. It was confirmed from these experiments that $H_2$/CO ratio of the simulated coal gas increased from 0.5 to 0.8 by WGS at gas-liquid water interface over the wet surface of honey comb type catalyst at $250^{\circ}C$ and 50 atm.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.4
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• pp.413-418
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• 2022

This paper presents two-phase condensation heat transfer and pressure drop characteristics of R32 and R454B as an alternative refrigerant to R410A in a 9.52 mm OD microfin tube. The test facility has a straight, horizontal test section with an active length of 2.0 m and is cooled by cold water circulated in a surrounding annular space. The heat transfer coefficients of the annular space were obtained using the modified Wilson plot method. Average condensation heat transfer coefficient and pressure drop data are presented at the condensation temperature of 35℃ for the range of mass flux 100-400 kg/m²s. The average condensation heat transfer coefficients of R32 refrigerant are 35-47% higher than R410A at the mass flux considered in the study, while R454B data are similar to R410A. The average pressure drop of R32 and R454B are much higher than R410A and they are 134-224% and 151-215% of R410A, respectively. R32 and R454B have relatively low GWP and high heat transfer characteristics, so they are suitable as alternatives for R410A.