• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.2
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• pp.45-50
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• 2008

Molecular flows inside a guide block in the OLED(organic luminescent emitting device) deposition process have been simulated using DSMC(direct simulation Monte Carlo) method. Because the organic materials are evaporated under vacuum, molecules flow at a high Knudsen number of the free molecular regime, where the continuum mechanics is not valid. A guide block is designed as a part of the linear cell source to transport the evaporated materials to a deposition chamber, When solving the flows, the inlet boundary condition is proved to affect significantly the whole flow pattern. Thus, it is proposed that the pressure should be specified at the inlet. From the analysis of the density distributions at the nozzle exit of the guide block, it is shown that the longer nozzle can emit molecules more straightly. Finally, a nondimensionalized mass flow profile is obtained by numerical experiments, where various nozzle widths and inlet pressures are tested.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.753-762
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• 2004

Conceptual studies of a combined-cycle engine have been conducted. Herein, the results are presented. The engine is composed of ejector-jet, ramjet, scramjet and rocket modes, and will be mounted on the Single-Stage-to-Orbit aerospace plane. Propellants are hydrogen and oxygen. Calculated engine thrust performances and cooling requirement of the engine are presented. Pitching moment of the plane with the engine will be balanced even in the vacuum condition. The experimental results of the inlet and the ejector-jet, ramjet and scramjet modes are presented. The effect of the airframe configuration on the engine performance and the thermal environment in the in-side of the plane are also presented. Through the investigations, possibilities of the combined-cycle engine and the aerospace plane are being made clear now.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.409-414
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• 2009

Since cryogens are stored at very low temperatures, the cryogenic storage systems are quite sensitive to heat leaks. Even though the vessel operated under sealed condition with vacuum insulation and reflective coatings are used, the heat leakage into the vessel is still unavoidable. Therefore, this paper concerns with numerical study of self-pressurization used to analysis the optimum design with the variation volume fraction, effect of heat flux and storage pressure of liquid nitrogen. The result shows that as the volume fraction increases, the pressure rise reduces and the relatively at atmosphere pressure is better than the higher one. In addition, higher heat flux leads the pressure rise increases faster than low one. The additional of heat pipe system to reduce the pressure rise rate also has been done. By this comparison, the optimum design for storage umbilical cord blood can be selected.

• Applied Science and Convergence Technology
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• v.23 no.1
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• pp.44-47
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• 2014

In this study, we investigated the basic properties of N-doped ethylcyclohexene plasma polymer thin films that deposited by radio frequency (13.56 MHz) plasma-enhanced chemical vapor deposition (PECVD) method with controlled ammonia flow rate. Ethylcyclohexene was used as organic precursor with hydrogen gas as the precursor bubbler gas. Additionally, ammonia ($NH_3$) gas was used as nitrogen dopant. The as-grown polymerized thin films were analyzed using ellipsometry, Fourier-transform infrared [FT-IR] spectroscopy, UV-Visible spectroscopy, and water contact angle measurement. We found that with increasing plasma power, film thickness is gradually increased while optical transmittance is drastically decreased. However, under the same plasma condition, water contact angle is decreased with increasing $NH_3$ flow rate. The FT-IR spectra showed that the N-doped ethylcyclohexene plasma polymer films were completely fragmented and polymerized from ethylcyclohexane.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.2
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• pp.96-101
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• 1988

This work is concerned with the fabrication process and photo-response characteristics of Cd S/(p) Si solar cells. In order to fabricate the cell. low grade Si wafer has been used as an absorber and Cd S which works as a window material has been prepared by vacuum evaporation. Cd S thin film, as evaporated, is polycristal and resistance is very high but these properties are improved by annealing. The properties of the fabricated cells are found to depend largely on the transmittance of Cd S. The effects of Cd S thickness and annealing condition on the fill factor and efficiency of the cell are investigated quantitatively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.117-120
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• 1999

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made of Matsuoka's composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. The Gas of sintering process was oxygen, nitrogen, argon, air respectively. The microstructure of ZnO varistors be made use of SEM equipment. The condition of DC degradation tests were conducted at $115\pm2^{\circ}C$ for periods up to 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Resistance-frequency and capacitance-frequency analysis are accomplished to the understanding of electrical properties as DC degradation test. From above analysis, it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test.

• Journal of the Korean Ceramic Society
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• v.24 no.1
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• pp.41-46
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• 1987

When barium titanate was synthesized in soild-solid reaction the abnormal expansion occurred from 900$^{\circ}C$ to 1100$^{\circ}C$. The equi-molecular mixture of BaCO3 and TiO2 was sintered from 800$^{\circ}C$ to 1300$^{\circ}C$ on the condition of air, vacuum and CO2 atmosphere. After that the specimens were tested closely with XRD, Dilatometer, SEM and EDS. The result indicated that; 1. The crystal phase which was concerned with expansion of BaTiO3 was Ba2TiO4 as the intermediate crystal phase. 2. The formation of Ba2TiO4 was affected by the firing atmosphere. 3. The expansion occurred when BaTiO3 changed to Ba2TiO4 and pore also expanded by the expansion of BaTiO3 body just as the model of expansion.

• Proceedings of the KAIS Fall Conference
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• 2001.05a
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• pp.91-94
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• 2001

Powder Metallurgy method have been used to fabricate TiC base composite with ferrous binder. TiC base composite has versatile hardness and is usable as sintered, or after heat treatment as required by the given applications. Smooth, round TiC grains impart high wear resistance and lubricity as well known characteristics of this composite. Annealed composite can be formed by conventional machining and be hardened up to 70 H$\_$R/C in vacuum. The optimizing fabrication process enables this composite to improve mechanical properties in heat, wear and corrosion environments. This study has examine the relationship between fabrication condition and mechanical property in TiC-Cr-Mo-Fe Composite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.579-582
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• 2000

This paper described on the fabrication of SOI(Si-on-insulator) structures with buried cavities by SDB technology and eletrochemical etch-stop. The cavity was fabricated the upper handling wafer by Si anisotropic etch technique. SDB process was performed to seal the fabricated cavity under vacuum condition at -760mmHg. In the SDB process, captured air and moisture inside of the cavities were removed by making channels towards outside. After annaling(100$0^{\circ}C$, 60 min.), the SDB SOI structure was thinned by electrochemical etch-stop. Finally, it was fabricated the SDB SOI structure with buried cavities as well as an accurate control and a good flatness.

• Journal of Surface Science and Engineering
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• v.50 no.6
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• pp.504-509
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• 2017

In order to improve corrosion resistance for cast stainless steel in seawater, the characteristics of corrosion resistance after plasma ion nitriding was investigated. Plasma ion nitriding process was conducted in a mixture of nitrogen of 25% and hydrogen of 75% at substrate temperature ranging from 350 to $500^{\circ}C$ for 10 hours using pulsed-DC glow discharge plasma with working pressure of 250 Pa in vacuum condition. Corrosion tests were carried out for as-received and plasma ion nitrided specimens. The corrosion characteristics were investigated by measurement of weight loss and observation of surface morphology. In anodic polarization experiment, relatively less damage depth and weight loss were presented at a nitrided temperature of $400^{\circ}C$, attributing to the formation of S-phase.