• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.486-487
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• 2007

$Bi_2Sr_2Ca_{n-1}Cu_nO_x$(n=0, 1, 2) thin films have been fabricated by co-deposition at an ultra-low growth rate using ion beam sputtering(IBS) method. The growth rates of the films was set in the region from 0.17 to 0.27 nm/min. MgO(100) was used as a substrate. In order to appreciate stable existing region of Bi 2212 phase with temperature and ozone pressure, the substrate temperature was between 655 and $820^{\circ}C$ and the highly condensed ozone gas pressure in vacuum chamber was varied between $2{\times}10^{-6}{\sim}4{\times}10^{-5}$ Torr. Bi 2212 phase appeared in the temperature range of 750 and $795^{\circ}C$ and single phase of Bi 2201 existed in the lower region than $785^{\circ}C$. Whereas, $PO_3$ dependance on structural formation was scarcely observed regardless of the pressure variation.

• Journal of Ocean Engineering and Technology
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• v.30 no.5
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• pp.356-360
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• 2016

Recently, the lifetime extension of nuclear power plants has been considered. Thus, it is necessary to consider facility safety management and economic management. However, when the bolts in nuclear power plants are replaced and the turbines of nuclear power plant are disassembled, numerous problems are found in relation to stuck bolts in clamping parts. In order to solve these problems, a hybrid vacuum chamber was first designed and manufactured. It can perform arc ion plating and sputtering, which were used to deposit Ti/TiN on an A913 B7 bolt. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted to determine the composition and characteristics of the bolt, and tests were conducted to determine how long the bolt could endure under various conditions in a nuclear power plant. The SEM and XRD results clearly showed a continual and even coating layer. When this TiN-coated bolt is used in a nuclear power plant, the lifetime can be extended compared to a conventional bolt, but it is necessary to determine what additional properties are required.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.299-304
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• 2008

Starting characteristics of the axi-symmetric second throat exhaust diffuser (STED) with zero-secondary flows are numerically investigated. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with enhanced wall treatment are solved to simulate the diffusing evolutions of the nozzle plume. Minimum (optimum) starting pressure difference of 20$\sim$25% between 1-D theory and the measured data validated from previous results[5] is also applied to predict the range of an effective diffuser expansion ratio (Ad/At) in this system.

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.46-51
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• 1990

Laser plasma was generated by a 1GW iodine photodissociation laser ($\lambda$=1.315$\mu\textrm{m}$, E=12.7J) whose output beam was focused on a molybdenum target surface. The experiment was conducted in a vacuum chamber under 1D-sTorr and several tens of laser shooting were necessary for sufficient exposure for the PBS resist of 111m thickness. Aluminium was coated on the top of the resist by 0.1$\mu\textrm{m}$ thickness which acts as an X-ray filter to cut off the visible and the ultraviolet lights. A bio-specimen was put directly on the aluminium coated resist and located at a distance of 3 cm from the X-ray source. The replicas of a steel mesh, spider's web. and a red blood cell were obtained by this technique and were observed by Nomarski microscope and SEM. The limitation of its resolution is determined by the X-ray source size and Fresnel diffraction effect, and its theoretical prediction is well matched with the experimental results. In this experiment, a resolution better than 0.1$\mu\textrm{m}$ could be obtained. ained.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.66-72
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• 2018

A numerical study was conducted to investigate the performance characteristics of a STED with various pressure ratios (PRs) and cone shapes. Due to momentum loss, the pressure in vacuum chamber increased with cone angle for a PR of 75. Also, the STED is started between PRs of 36 and 37 in the case of a cone angle of $15^{\circ}$ and a blockage ratio (BR) of 15%. The results for various PRs and cone shapes are presented, and the optimal cone shape is found to have a cone angle of between $5{\sim}20^{\circ}$ and a BR of between 15~40%.

• Korean Journal of Metals and Materials
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• v.47 no.12
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• pp.828-833
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• 2009

As a fundamental study in the development of a distillation process for ferromanganese alloy melts, the evaporation behavior of an electrolytic manganese melt under reduced pressure was investigated. The melt temperature, vacuum degree, surface area of the melt, and reaction time were considered as experimental variables. The amount of vaporized manganese increases linearly as the reaction time increases, and the evaporation of manganese was promoted by increasing the temperature and surface area of the melt. In the pressure range below the equilibrium vapor pressure of manganese, the amount of vaporized manganese per unit surface area of the melt increased sharply with a decrease of the pressure in the reaction chamber. An empirical equation for the evaporation rate of manganese was derived by regression analysis. The evaporation coefficient of manganese was determined to be approximately $3.84{\times}10^{-3}(g{\cdot}K^{1/2})/(Pa{\cdot}cm^2{\cdot}min)$ under the investigated conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.5
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• pp.65-72
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• 2021

700 W class laboratory model Hall thruster, which can be used for the orbit control or station keeping of small satellites, was developed. The size of the discharge channel was determined using a scaling law, and the magnetic field was designed to be symmetric with respect to the midline of the discharge channel and to be maximized outside the discharge channel. Base pressure of a vacuum chamber was maintained below 2.0×10^-5 Torr during experiments, and the thrust was measured by a thrust stand. The anode flow rate and coil current were varied with the fixed anode voltage at 300 V. Under the operation condition at 2.36 mg/s anode flow rate and 2.4 A coil current, performance was optimized as 38 mN thrust, 1,540 s total specific impulse, and 50 % anode efficiency at 620 W anode power.

• Food Science and Preservation
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• v.16 no.2
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• pp.166-171
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• 2009

The effects of vacuum precooling(VP) on the shelf-life of polyethylene film(PE) packaged King oyster mushrooms(Pleurotus eryngii) during storage at $-1^{\circ}C$ were investigated. VP was conducted below $0^{\circ}C$ in a $-1^{\circ}C$ cold chamber of 40 minutes, and mushrooms were stored for 30 days in batches of 1kg. The weight loss of the VP-treated mushroom was slightly lower than that of control. The $O_2$ concentrations of VP-treated mushroos, within 4 days of storage, were 2.44-14.50 %/kg-package/hr, thus higher than control values(2.01-8.19%/kg-package/hr). $CO_2$ generation of VP-treated mushrooms, again within 4 days of storage, was 0.47%/kg-package/hr, thus lower than that of controls(0.58%/kg-package/hr). The $CO_2/O_2$ ratio peaked on day 4 of storage in the control group, tbut no such peak was observed in VP-treated mushrooms. In the VP-treated fungi, lightness was higher, and redness and yellowness lower, than in controls, at all storage times.. In VP-treated mushrooms, strength, hardness and chewiness were significantly higher than in controls, but there were no significant differemces in springiness or cohesiveness. Softening and breakdown of under-cap wrinkles were observed in control mushrooms stored for 30 days, but occurred to a lesser extent in VP-treated fungi. Stipe reticulum tissue vessels in the 30 day-stored VP-treated mushrooms were relatively well-defined and clear, but were softer and diffuse in the control fungi. The results thus confirmed that VP after harvest enhanced mushroom shelf-life and PE packaging prolonged storage time. The data will have industrial applications.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.16-22
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• 2008

We studied plasma etching of polycarbonate in $O_2/SF_6$, $O_2/N_2$ and $O_2/CH_4$. A capacitively coupled plasma system was employed for the research. For patterning, we used a photolithography method with UV exposure after coating a photoresist on the polycarbonate. Main variables in the experiment were the mixing ratio of $O_2$ and other gases, and RF chuck power. Especially, we used only a mechanical pump for in order to operate the system. The chamber pressure was fixed at 100 mTorr. All of surface profilometry, atomic force microscopy and scanning electron microscopy were used for characterization of the etched polycarbonate samples. According to the results, $O_2/SF_6$ plasmas gave the higher etch rate of the polycarbonate than pure $O_2$ and $SF_6$ plasmas. For example, with maintaining 100W RF chuck power and 100 mTorr chamber pressure, 20 sccm $O_2$ plasma provided about $0.4{\mu}m$/min of polycarbonate etch rate and 20 sccm $SF_6$ produced only $0.2{\mu}m$/min. However, the mixed plasma of 60 % $O_2$ and 40 % $SF_6$ gas flow rate generated about $0.56{\mu}m$ with even low -DC bias induced compared to that of $O_2$. More addition of $SF_6$ to the mixture reduced etch of polycarbonate. The surface roughness of etched polycarbonate was roughed about 3 times worse measured by atomic force microscopy. However examination with scanning electron microscopy indicated that the surface was comparable to that of photoresist. Increase of RF chuck power raised -DC bias on the chuck and etch rate of polycarbonate almost linearly. The etch selectivity of polycarbonate to photoresist was about 1:1. The meaning of these results was that the simple capacitively coupled plasma system can be used to make a microstructure on polymer with $O_2/SF_6$ plasmas. This result can be applied to plasma processing of other polymers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.213-218
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• 2010

A cooling system utilizing liquid helium to chill the cryopanel (800 mm $\times$ 700 mm dimensions) down to 4.2 K was designed, implemented, and tested to verify the role of the cryopanel as a heat sink for the payload of a spacecraft inside the large thermal vacuum chamber (effective dimensions : 8 m ($\Phi$) $\times$ 10 m (L)) of KARI (Korea Aerospace Research Institute). Two LHe (Liquid Helium) Dewars, one for the main supply and the other for refilling, were used to supply liquid helium or cold helium gas into this cryopanel, and flow control for the target temperature of the cryopanel within requirements was done through fine adjustment of the pressure inside the LHe Dewars. The return helium gas from the cryopanel was reused as a thermal barrier to minimize the heat influx on the core liquid helium supply pipe. The test verified a cooling time of around three hours from the ambient temperature to 40 K (combined standard uncertainty of 194 mK), the capacity for maintaining the cryopanel at intermediate temperatures, and a 1 K uniformity over the entire cryopanel surface at around 40 K with 20 W cooling power.