• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1063-1069
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• 2012

In present paper, we used magnesium alloy having a lower density and higher electrical conductivity for bipolar plate to reduce the weight of PEM fuel cell. The silver was coated to prevent corrosion and form passivation film on the metal surface with sputtering. In acid proof evaluation for setting optimal coating conditions, the homogeneity of coating thickness was improved by coating with the thickness of 3 ${\mu}m$ which not indicated any micro cracks and the temperature $180^{\circ}C$. The performance test and evaluation based on the clamping pressure and channel depth to determine the configuration of bipolar plate for assembling single cell was implemented. And then we assembled single cell with this bipolar plate and implemented the performance test to ensure and compare the current-voltage performance followed as several factors such as coating or non-coating, the change of clamping pressure, the change of channel depth, etc. As these results, the maximum power density of single cell with the coated bipolar plate was 192 $mW/cm^2$ and it was confirmed that the power density per unit mass was better than existing metal bipolar plate.

• Polymer(Korea)
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• v.26 no.5
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• pp.644-652
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• 2002

This study aims at developing the conductive pastes consisting of room temperature vulcanizing (RTV) silicone and metal powder as matrix and filler, respectively. Electrical and rheological properties of metal - filled polymer composites are in general strongly affected by particle shape, side and dispersion state of the filler. In highly filled systems, particles tend to form very complex agglomerated structure which is easily changed when subjected to shear deformation. And the breakdown of agglomerated particles due to shear usually leads to the change of electrical conductivity of the composite. In this study, the effect of particle size and dispersion state of filler on the electrical conductivity of the composites are investigated to offer the selection criteria of conductive filler by measuring the rheological properties of uncured composites and the electrical conductivity of the cured composites. It was found that the type of metal filler systematically affected the rheological property, the susceptibility to shear and the degree of change of electrical conductivity of the composite. The effect of shear on the properties is more conspicuous in the composites containing large particle, indicating that both rheological and electrical properties can be improved by controlling the dispersion state at a given filler content.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.225-232
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• 2011

Reactive ion etching (RIE) technique for maskless surface texturing of mc-silicon solar wafers has been applied and succeed in fabricating a grass-like black-silicon with an average reflectance of $4{\pm}1%$ in a wavelength range of 300~1,200 nm. In order to investigate the optimized texturing conditions for mass production of high quantum efficiency solar cell Surface characteristics such as the spatial distribution of average reflectance, micrscopic surface morphology and minority carrier lifetime were monitored for samples from saw-damaged $15.6{\times}15.6\;cm^2$ bare wafer to key-processed wafers as well as the mc-Si solar cells. We observed that RIE textured wafers reveal lower average reflectance along from center to edges by 1% and referred the origin to the non-uniform surface structures with a depth of 2 times deeper and half-maximum width of 3 times. Samples with anti-reflection coating after forming emitter layer also revealed longer minority carrier lifetime by 40% for the edge compared to wafer center due to size effects. As results, mc-Si solar cells with RIE-textured surface also revealed higher efficiency by 2% and better external quantum efficiency by 15% for edge positions with higher height.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.455-455
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• 2010

차세대 디스플레이로 널리 알려져 있는 플렉서블 디스플레이는 휴대하기 쉽고, 깨지지 않으며, 변형이 자유로워 현재 우리 사회에 크게 주목받고 있다. 플렉서블 디스플레이의 구현을 위해서는 기존의 유리 기반 디스플레이 소자 기술에 더하여 플렉서블 기판소재에 적용 가능한 투명전도막 기술의 확립이 필요하다. 디스플레이 산업에서 주로 사용되는 투명전도막은 ITO (indium tin oxide) 및 IZO (indium zinc oxide)와 같은 투명전도성 산화물 박막 (TCO, transparent conducting oxide)이다. 그런데 플라스틱 기판이 굽힘 환경에 놓이게 되면 그 위에 증착된 산화물 박막이 쉽게 파손될 수 있다. 따라서 플렉서블 디스플레이 기술에 있어서 변형에 따른 TCO 박막의 파괴 거동에 대한 연구가 필수적이다. 본 연구에서는 PET (polyethylene terephthalate) 기판 상에 증착된 IZO 박막의 반복 굽힘 시 계면구조 변화에 따른 파괴거동을 조사하였다. 플라스틱 기판의 사용을 위해서는 산소 및 수분의 투과 방지막이 필요하며 본 연구에서는 투과 방지막 (또는 보호막)으로서 $SiO_x$ 박막을 적용하였다. IZO 박막은 $In_2O_3$ - 10 wt% ZnO 타겟을 사용하여 RF magnetron sputtering법으로 $100^{\circ}C$ 미만에서 저온 증착하였다. 보호막으로 사용되는 $SiO_x$ 박막은 HMDSO (hexamethyldisiloxane)와 Ar 및 $O_2$ 혼합기체를 이용하는 PECVD 방법으로 합성하였다. 변형에 따른 TCO 박막의 파괴 거동을 조사하기 위하여 반복 굽힘 시험 (cyclic- bending test)을 실시하였다. 반복 굽힘 시험 중 실시간으로 IZO 박막의 전기저항 변화를 측정하여 박막의 파괴 거동을 모니터링 하였다. 시편 A (135 nm-thick IZO/PET), B (135 nm-thick IZO/ 90 nm-thick $SiO_x$/PET), C (135nm-thick IZO/ 300 nm-thick $SiO_x$/PET)에 대하여 곡지름 35mm, 1000회 반복 굽힘을 실시하여 변형 중의 전기저항 변화를 조사하였다. 그리고 굽힘 시험 완료 후, FE-SEM을 이용한 시편 표면형상 관찰을 통하여 균열생성 정도를 관찰하였다. 반복 굽힘 시험 결과, A 와 C 시편의 경우, 각각 반복 굽힘 20회, 550회에서 급격한 전기저항의 증가가 관찰되었다. 그러나 B 시편의 경우, 1000회 반복 굽힘 후에도 전기저항의 변화는 나타나지 않았다. 이와 같이 반복 굽힘에 의한 IZO 박막의 파괴 거동 변화는 IZO 박막과 기판의 계면구조변화에 기인한 것으로 해석된다. IZO 박막과 기판의 계면에 $SiO_x$ 층을 삽입함으로써 계면 접합강도가 향상되었을 것으로 추측된다. 따라서 변형에 대한 파괴 저항 특성이 우수한 투명전도성 산화물 박막의 형성을 위해서는 적절한 계면구조 제어를 통한 계면 접합 특성의 향상이 필요하다.

• Journal of the Korean Vacuum Society
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• v.22 no.4
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• pp.181-187
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• 2013

$Dy^{3+}$-doped $BaMoO_4$ phosphor powders were synthesized by using the solid-state reaction method and their crystalline structure, morphology and size of particles, excitation and emission properties were investigated. The structure of all the phosphor powders, irrespective of the mol ratio of $Dy^{3+}$ ions, was found to be the tetragonal system with the main diffraction peak at (112) plane. The grain particles agglomerate together to form larger clusters with increasing the mol ratio of $Dy^{3+}$ ions. The excitation spectra were composed of a broad band centered at 293 nm and weak multiline peaked in the range of 230~320 nm, which were due to the transitions of $Dy^{3+}$ ions. The emission of the phosphors peaking at 666 and 754 nm, originating from the transitions of $^4F_{9/2}{\rightarrow}^6H_{11/2}$ and $^4F_{9/2}{\rightarrow}^6H_{9/2}$ of $Dy^{3+}$ ions, was rather weak, while the intensity of blue and yellow emission peaking at 486 nm and 577 nm due to the transitions of $^4F_{9/2}{\rightarrow}^6H_{15/2}$ and $^4F_{9/2}{\rightarrow}^6H_{13/2}$ of $Dy^{3+}$ ions was significantly stronger. The experimental results suggest that the white-light emission can be realized by controlling the yellow-to-blue intensity ratio of $Dy^{3+}$ emission.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.3
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• pp.83-88
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• 2015

Coating materials used in the electron beam (EB) deposition method, which is being studied as one of the fabrication methods of thermal barrier coating, are exposed to high power electron beam at focused area during the EB deposition. Therefore the coating source for EB process is needed to form as ingot with appropriate density and microstructure to sustain their shape and stable melts status during EB deposition. In this study, we tried to find the optimum powder condition for fabrication of ingot of 8 wt% yttria stabilized zirconia which can be used for EB irradiation. It seems that the ingot, which is fabricated through bi-modal type initial powder mixture which consists of tens of micro and nano size particles, was shown better performance than the ingot which is fabricated using monolithic nanoscale powder when exposed to high power EB.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.197-202
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• 2021

Synthesis of Z-type hexaferrite Ba₃Co₂Fe₂₄O₄₁ (Ba₃Z) and Ba_1.5La_1.5Co₂Fe₂₄O₄₁ (Ba_1.5La_1.5Z) powders were tried using molten salt synthesis after primary calcination. Ba₃Z calcined at 1000℃ was formed with both M-type and Y-type hexaferrite, and then Z-type was obtained when sintered with molten salt at 1150℃ and 1200℃. In the case of Ba_1.5La_1.5Z calcined at 1000℃, however, M-type hexaferrite, CoFe₂O₄ (Spinel phase), and LaFeO₃ were synthesized. As a result, Z-type hexaferrite was not synthesized after sintering with molten salt. In addition, the aspect ratio of the particles decreased as the sintering temperature increased with molten salt synthesis. To obtain a single-phase Ba_1.5La_1.5Z with a high aspect ratio, it is expected the raw materials have to calcine below the temperature of a spinel phase formation before sintering with molten salt.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.253-259
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• 2021

Plastic wastes generated from household waste are separated by mixed discharge with foreign substances, and recycling is relatively low. In this study, the effect of the ratio and content of mixed plastic waste coarse aggregate(MPWCA)s and mixed plastic waste fine aggregate(MPWFA)s filled with blast furnace slag fine powder on the slump and compressive strength of concrete was evaluated experimentally. The MPWCAs were found to have a similar fineness modulus, but have a single particle size distribution with a smaller particle size compared to coarse aggregates. However, the MPWFAs were found to have a single particle size distribution with a larger fineness modulus and particle size compared to fine aggregates. Meanwhile, the effect of improving the density and filling pores by the blast furnace slag fine power was found to be greater in the MPWFA compared to the MPWCA. As the amount of the mixed plastic waste aggregate(MPWA)s increased, the slump and compressive strength of concrete decreased. In particular, the lower the slump and compressive strength of concrete was found to decrease the greater the amount of MPWFA than MPWCA when the amount of MPWA was the same. This is because of the entrapped air and voids formed under the angular- and ROD-shaped aggregates among the MPWFAs. On the other hand, the addition of the admixture and the increase in the unit amount of cement were found to be effective in improving the compressive strength of the concrete with MPWAs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.732-740
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• 2019

Evaporative humidification using a humidifying element is widely used for humidification of a building or a data center. The performance of a humidifying element is commonly expressed as humidification efficiency, which is used independent of air temperature, humidity and water temperature. In this study, a series of tests were conducted at two air conditions (data center and commercial building) using two different humidifying elements (cellulose/PET and Glasdek) changing the frontal air velocity and water temperature. Results showed that the measured humidification efficiency was dependent on the air condition and water temperature. In fact, even dehumidification occurred at the inlet of the humidifying element at the air condition of commercial building. The reason was due to the inlet water temperature, which was lower than the dew point air temperature. As the difference between the inlet water and the dew point air temperature increased, the humidification efficiency decreased. This suggest that proper thermal model should account for the inlet region, where the amount of moisture transfer may be different from the other part of the humidification element. A simple analysis on the thermal performance of the cellulose/PET humidification element showed that the Sherwood number was adequately predicted, whereas the friction factor was ovepredicted, probably due to the simplification of the channel geometry and the neglection of the water film on the element surface.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.80-85
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• 2019

Vanadium dioxide is a well-known metal-insulator phase transition material. Lots of researches of vanadium redox flow batteries have been researched as large scale energy storage system. In this study, vanadium oxide($VO_x$) thin films were applied to cathode for lithium ion battery. The $VO_x$ thin films were deposited on Si substrate($SiO_2$ layer of 300 nm thickness was formed on Si wafer via thermal oxidation process), quartz substrate by RF magnetron sputter system for 60 minutes at $500^{\circ}C$ with different RF powers. The surface morphology of as-deposited $VO_x$ thin films was characterized by field-emission scanning electron microscopy. The crystallographic property was confirmed by Raman spectroscopy. The optical properties were characterized by UV-visible spectrophotometer. The coin cell lithium-ion battery of CR2032 was fabricated with cathode material of $VO_x$ thin films on Cu foil. Electrochemical property of the coin cell was investigated by electrochemical analyzer. As the results, as increased of RF power, grain size of as-deposited $VO_x$ thin films was increased. As-deposited thin films exhibit $VO_2$ phase with RF power of 200 W above. The transmittance of as-deposited $VO_x$ films exhibits different values for different crystalline phase. The cyclic performance of $VO_x$ films exhibits higher values for large surface area and mixed crystalline phase.