• Journal of the Korean Ceramic Society
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• v.44 no.5 s.300
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• pp.155-159
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• 2007

Blue light-emitting phosphors having the excitation spectrum range of the medium-long ultraviolet ($280nm{\sim}400nm$) have been prepared by solid state reaction method. As a starting material the natural alkaline feldspar powder produced from the domestic mine field in Buyeo, Chungnam-do. The photoluminescence characteristics and crystal structures have been analyzed for the phosphor samples. The powder mixture of the natural alkaline feldspar and the rare-earth oxide was calcined at $800{\sim}1000^{\circ}C\;for\;3{\sim}4h$ in air. The calcined samples we fully ground at room temperature and then heat-treated in the mild reducing gas atmosphere of $5%H_2-95%N_2$ mixture at $1100{\sim}1150^{\circ}C\;for\;3{\sim}4h$. The natural alkaline feldspar material consists of the monoclinic orthoclase ($KAlSi_3O_8$) and the triclinic albite ($NaAlSi_3O_8$) phases. At the $0.5wt%Eu_2O_3$ addition the PL spectrum showed the maximum intensity and with further increase of $Eu_2O_3$ the PL intensity decreased. The albite phase disappeared in the $Eu_2O_3$ doped phosphors. The effect of the co-doped activator on the PL characteristics have been also discussed.

• Fire Science and Engineering
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• v.23 no.4
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• pp.120-129
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• 2009

Identification of the exact cause of a building fire is generally difficult, because the source and initially ignited objects are often severely damaged or even lost during the early stages of the fire. We made an experimental attempt to reasonably estimate the burning during the very early stages of a fire, and identify its source and causes. The case we studied was an apartment fire, which occurred in Tokyo, in July 2002. The fire was extinguished just after flashover, and the on-site investigations suggested the fire started from the TV and TV stand, which had been damaged so severely that it was difficult to conclude that the TV was the ultimate cause of the fire, simply from the on-site investigation. We conducted a series of burn tests using a TV and other products identical to those actually used in the apartment. Tests were set-up and procedures were carefully studied to recreate the conditions of the articles that remained, and of the room itself. The tests demonstrated that the conditions in the apartment could be recreated only when the fire started inside the TV and came into close contact with dresser.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.286-287
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• 2006

Barium titanate ($BaTiO_3$) glycolate particles were synthesized at temperature as low as $100^{\circ}C$ through glycothermal reaction by using $Ba(OH)_2{\cdot}8H_2O$ and amorphous titanium hydrous gel as precursors and ethylene glycol as solvent. The particle size and morphology of $BaTiO_3$ glycolate powders can be controlled by varying the reaction conditions such as the reaction temperature and Ba:Ti molar ratio of starting precursors. After glycothermal treatment at $220^{\circ}C$ for 24 h in 1.25:1(Ba:Ti), the average particle size of the $BaTiO_3$ glycolate powder was about 200-400 nm and low agglomeration. $BaTiO_3$ powders were formed by heat-treating the glycolate powder in air at $500-1000^{\circ}C$. As a result, the size of $BaTiO_3$ crystallites changed from around 50-300 nm. It is also demonstrated that the size and shape of $BaTiO_3$ particles investigated as a function of calcination temperature. The $BaTiO_3$ particles obtained from optimum synthesis condition were pressed, sintered and measured for the dielectric property. The $BaTiO_3$ ceramics sintered at $1250^{\circ}C$ for 2 h had 98 % of theoretical density. The ceramics have an average grain size of about $1\;{\mu}m$ and displays the high dielectric constant (~3100) and low dielectric loss (<0.1) at room temperature.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.206-211
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• 2012

Graphene has recently received high attention as a promising material for various applications, and many related studies have been undertaken to reveal its basic mechanical properties. However, the tribological properties of graphene film fabricated by the chemical vapor deposition (CVD) method are barely known. In this study, the contact angle and frictional wear characteristics of graphene coated copper film were investigated under room temperature, normal air pressure, and no lubrication condition. The contact angle was measured by sessile drop method and the wear test was carried out under normal loads of 660 mN and 2940 mN, respectively. The tribological behaviors of a graphene coating layer were also examined. Compared to heat treated bare copper foil, the graphene coated one shows a higher contact angle and lower friction coefficient.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.4
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• pp.15-23
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• 2002

In most cryogenic liquid rocket engines, liquid oxygen manifold and injector are not thermally insulated from room temperature environment fur reducing system complexity and the weight. This feature of cryogenic liquid rocket engine results in the situation that cryogenic liquid oxygen flow is easy to be vaporized especially in the vicinity of the manifold and the injector wall. The research in this paper is focused on two-phase flow phenomena of liquid oxygen in rocket engine. Vapor fraction was estimated by comparing the measured two-phase flow pressure drop in engine manifold and the injector with ideal single phase pressure drop. Heat flux into cryogenic flow is estimated by measuring the wall temperature on the engine manifold to examine boiling characteristics. Suitable correlations for cryogenic two-phase flow were also reviewed to see their applicability. In addition, the effect of vapor generation in liquid rocket engine manifold and injector on engine performance and stability was considered.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.4
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• pp.222-228
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• 2009

Various types of refrigerators become popular in the market such as a common refrigerator, kimchi refrigerator and wine cellar. It is required to develop a multi type refrigerator combining these refrigerators to save space and energy consumption. In this study, the performance of a multi type refrigerator, which consists of one machine room and three evaporators, was measured in a bench type multi refrigerator. The multi type refrigerator was tested by varying the number of refrigerator cabinet, refrigerant charge, and temperature conditions. In addition, the multi type refrigerator with a suction line heat exchanger(SLHX) was tested to improve system performance. Based on the experimental data, the multi type refrigerator showed better performance than the conventional refrigerator(single type system). Besides, the COP of the single system increased from 1.0 to 1.37, and those of the dual and triple system increased from 1.29 to 1.39, and 1.22 to 1.51, respectively, by applying the SLHX.

• Journal of Sericultural and Entomological Science
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• v.53 no.2
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• pp.101-109
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• 2015

To extend shelf life of mulberry fruits, usually expensive freeze drying of freezing process is required. In this study an economic to multipurpose agricultural products dryers with mulberry dryer and technique was developed to reduce postharvest processing cost. Fuel and electricity consumption for drying were lowest when drying temperature was $60^{\circ}C$. And various drying conditions (fuel 3 hrs, heat 1 hr, room temperature air velocity 51 hrs) of the developed dryer were analyzed to improve drying performance. Dried mulberry fruits had dark brown color and marketable high quality explain the semi-dried characteristics.

• Transactions of Materials Processing
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• v.30 no.6
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• pp.306-310
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• 2021

In this study, IF steel, which has a body-centered cubic (BCC) crystal structure, was fabricated as a 25 mm-long cube, and then processed for one cycle without intermediate heat treatment by applying MADF Ver.1 and Ver.2 processes. MADF processing was performed with graphite lubrication for each pass at room temperature. The development of the microstructure and texture was analyzed and compared by the location of the specimen using EBSD measurements of the IF steel. Vickers hardness test and miniature tensile test were also performed to analyze the mechanical properties. The coarse grain size of 742.6 ㎛ of the as-received IF steel was refined to a grain size of 53.0 ㎛ after one cycle of MADF Ver.1 processing and 27.0 ㎛ after MADF Ver.2 processing. Vicker's hardness of the as-received IF steel at 94 Hv was increased to 185.6 Hv and 191.2 Hv after one cycle of MADF Ver.1 and Ver.2 processing, respectively.

• Journal of the Korea Institute of Building Construction
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• v.18 no.6
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• pp.569-576
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• 2018

In modern society, a huge number of the buildings have been constructed with RC structure. RC structures have many structural instabilities due to earthquake, typhoon, construction fault, design phase errors. Therefore, many reinforcement methods are being implemented to solve this problem. In the reinforcement method, the organic epoxy adhesive used in the FRP reinforcing method is abruptly damaged when exposed to high temperature, which is directly connected to the fall of the reinforcing material. Therefore, the present study was conducted to develop inorganic refractory mortar with a certain level of adhesion ability to reduce the heat transferred to FRP reinforcement when exposed to high temperatures. As a result of the test, it showed high adhesion strength at room temperature condition with the inclusion of EVA resin, and showed no performance deterioration up to about $300^{\circ}C$ even under heating conditions. Also, it was confirmed that the backside temperature was lower as the thickness increased, and converged to a constant temperature of about $780^{\circ}C$ after 2 hours of heating.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.11-15
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• 2018

Torque tubes in High Temperature Superconducting (HTS) motor transfer torque from superconducting field winding rotor to the room temperature shaft. It should have minimum heat conduction property for minimizing the load on cryo-refrigerator. Generally, these torque tubes are made with stainless steel material because of high strength, very low outgassing and low thermal contraction properties at cryogenic temperatures and vacuum conditions. With recent developments in composite materials, these torque tubes could be made of composites such as Kevlar and S-Glass, which have the required properties like high strength and low thermal conductivity at cryogenic temperatures, but with a reduced weight. Development and testing of torque tubes made of these composites for HTS motor are taken up at Bharat Heavy Electricals Limited (BHEL), Hyderabad in collaboration with Central Institute of Plastics and Engineering Technology (CIPET), Chennai and Indian Institute of Technology (IIT), Kharagpur. As these materials are subjected to vacuum, it is important to measure their outgassing rates under vacuum conditions before manufacturing prototype torque tubes. The present study focusses on the outgassing characteristics of Kevlar and S-Glass, using an Outgassing Measurement System (OMS), developed at IIT Kharagpur. The OMS facility works under vacuum environment, in which the test samples are exposed to vacuum conditions over a sufficient period of time. The outgassing measurements for the composite samples were obtained using pressure-rise technique. These studies are useful to quantify the outgassing rate of composite materials under vacuum conditions and to suggest them for manufacturing composite torque tubes used in HTS motors.