• Transactions of the Korean hydrogen and new energy society
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• v.26 no.5
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• pp.469-476
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• 2015

The purpose of this work is to investigate main factors to design a solid-state hydrogen stroage system with magnesium hydride with 10 wt% graphite using numerical simulation tools. The heat transfer characteristic of this material was measured in order to perform the highly reliable simulation for this system. Based on the measured effective thermal conductivity, a transient heat and mass transfer simulation revealed that the total performance of hydrogen storage system is prone to depend on heat and mass transfer behaviors of hydrogen storage medium instead of its inherent kinetic rate for hydrogen adsorption. Furthermore, we demonstrate that the thermodynamic aspect between equlibrium presssure and temperature is one of key factor to design the hydrogen storage system with high performance using magnesium hydride.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1435-1440
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• 2014

The effects of the specimen size and temperature on the compressive strength of ATJ graphite were investigated. Compressive tests were conducted in accordance with ASTM C 965 at room temperature, $700^{\circ}C$ and $900^{\circ}C$. Three types of cylindrical specimen at room temperature were used in uniaxial tests, where the diameter-to - length ratios were one to two for the ASTM standard specimen, one to one for the Type I specimen, and one to 0.5 for the Type II specimen. Two kinds of cylindrical specimens, with and without antioxidant coating, were tested at elevated temperature. The Compressive strength of the expanded specimens(Type I, II) were slightly higher than that of standard specimen at room temperature. The compressive strength of a specimen with antioxidant coating increased as the temperature increased to $900^{\circ}C$. In contrast, that of the non-coated specimen decreases sharply due to the oxidation of the specimen.

• Composites Research
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• v.28 no.6
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• pp.389-394
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• 2015

The sound absorption coefficient and sound transmission loss of graphite intercalation compound (GIC) included epoxy composites were investigated. Epoxy resin was infused into the expanded GIC and the impedance tube method was employed to measure the sound absorption coefficient and sound transmission loss. Scanning electron microscopy photographs showed uniform distribution of the GIC in the epoxy matrix. The surface density of epoxy/GIC (20 wt%) composites decreased about 56% compared to that of pure epoxy. The sound absorption coefficient of composites increased about 3 times at the frequency range of 500~1000 Hz compared to the pure epoxy. The sound transmission loss of composites decreased with increasing the GIC content and it is attributed to the increase of pores in the composites.

• Composites Research
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• v.34 no.3
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• pp.148-154
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• 2021

Carbon/epoxy composite bipolar plate (BP) is a BP that is likely to replace existing graphite bipolar plate of vanadium redox flow cell (VRFB) due to its high mechanical properties and productivity. Multi-functional carbon/epoxy composite BP requires graphite coating or additional surface treatment to reduce interfacial contact resistance (ICR). However, the expanded graphite coating has the disadvantage of having low durability under VRFB operating conditions, and the surface treatments incur additional costs. In this work, an excessive resin absorption method is developed, which uniformly removes the resin rich area on the surface of the BP to expose carbon fibers by applying polyester fabric. This method not only reduces ICR by exposing carbon fibers to BP surfaces, but also forms a unique ditch pattern that can effectively hold carbon felt electrodes in place. The acidic environmental durability, mechanical properties, and gas permeability of the developed carbon/epoxy composite BP are experimentally verified.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.671-674
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• 2009

본 논문에서는 Base resin으로 열가소성 고분자인 PPS(Poly(phenylene sulfide))를 사용하였으며, 물리적 및 화학적 특성을 증대시키기 위해 주 첨가제로는 Expanded graphite와 보조 첨가제로 Glass fiber와 Carbon fiber를 사용하여 2가지의 복합 소재를 제조 하였다. 제조한 복합소재를 활용하여 최적의 사출 조건(사출 압력, 가열시간, 금형온도 등)으로 사출을 하였으며, 각각의 최종 시편을 four point probe 장치를 사용하여 전기전도도를 측정 비교 하였다.

• Journal of Korea Foundry Society
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• v.8 no.4
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• pp.422-428
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• 1988

In this study we have investigated the effects of Mm, MmH and $MmH_2$ on the matrix development in cast iron, The conclusive summary is as follows: The spheroidal graphite was observed when 0.5wt.% or more of mischmetal was added and the matrix was of ledeburite structure, but bull's eye structure was not observed. On the other hand, the bull's eye structure was observed when 0.25wt.% of MmH, or 0.25wt.% to 0.5wt.% of $MmH_2$ was added. Above limit of the additives, the matrix changed into ledeburite structure. As the hydrogen content of mischmetal compound increased from MmH, the range of additives to obtain bull's eye structure expanded. This reveals the significant effect of mischmetal hydride on matrix development in cast iron and the possibility of practical use of the additives.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.1241-1244
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• 2010

본 논문에서는 Base resin으로 열가소성 고분자인 PP(Polypropylene)를 사용하였으며, 물리적 및 화학적 특성을 증대시키기 위해 주 첨가제로는 Expanded graphite와 보조 첨가제로 Multiwall carbon nanotube를 사용하여 2가지의 복합 소재를 제조 하였다. 제조한 복합소재를 활용하여 compression molding을 하였으며, 각 함량별 시편을 four point probe 장치를 사용하여 전기전도도를 측정 비교 하였다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.05a
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• pp.207-212
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• 1999

화학반응이 일어나는 고정층 반응기의 성능을 모사하고 해석하기 위해서는 반응베드의 열 및 물질전달 특성을 정확히 아는 것이 중요하다. 본 연구에서는 화학열펌프에 사용되는 금속염-팽창흑연 다공성 반응매체의 유효열전도도와 기체투과도를 측정하였다. 유효열전도도는 전이 일차원 열류기법을 이용하여 측정하였고, 기체투과도는 Darcy's law를 이용하여 측정하였다. 팽창흑연이 함유된 반응베드의 유효열전도도와 기체투과도는 흑연을 기준으로 한 겉보기밀도에 따라 각각 14.1-36.5 W/mK, 8.0x$10^{-15}$-$10^{-12}$ $m^2$의 범위에 있었다.

• Journal of Korea Foundry Society
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• v.10 no.1
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• pp.31-42
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• 1990

The full mould casting process in one of the newly developed techniques which has many advantages. Unbonded sand mould has been prepared for the major mould and $CO^2$ gas mould has been used occasionally for comparison. Patterns were built up with expanded polystyrene and coated with three different materials. Silica, graphite and zircon were used for the coating layer. The effects on fluidity and temperature loss of molten metals were investigated. The molten metals were Al-5% Si alloy, Cu-30% Zn alloy and gray iron of approximately 4.0% of carbon equivalent. Experimental variables were runner section area, superheat, sprue height, coating materials, coating thickness and apparent density of EPS pattern. The effects of coating materials on fluidity and temperature loss of the molten metals during transient pouring are summarized as follows : As runner section area, superheat and sprue height increased, fluidity increased. Temperature loss decreased as runner section area and sprue height increased. However, reversed effects were observed in the case of superheat increment. The coating materials decreased the fluidity of each alloy in the order of silica, graphite and zircon. Zircon brought to the highest temperature loss among the coating materials used. The fluidity increased in the order gray iron, Cu-30% Zn and Al-5% Si alloy while temperature loss in the reverse order. Especially in case of reduced pressure process, the fluidity was increased apparently. Al-5% Si alloy showed the lowest temperature loss among the alloys. The increment of the apparent density of EPS pattern resulted in the fluidity decrease and temperature loss increase. The relation between fluidity and temperature loss of each alloy can be expressed by the following equation within the coating thickness limit of 0.5-1.5㎜. F^*={\frac{a}{T^*-b}}-c$ where, $F^*$ : fluidity in the Full mould, $T^*$ : temperature loss in the mould. a : parameter for full mould. b, c : constants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1361-1366
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• 2010

This research aims to develop polymer composites which can be used for PEMFC separators by injection molding process. Considering the moldability and stiffness, we used PPS(Poly(phenylene sulfide)) and PP(Polypropylene) as base resin. In order to improve electrical conductivity and physical properties, we chose glass fiber, carbon fiber, carbon black, and both expanded graphite and synthetic graphite. The 3 type composites are prepared for injection molding of PEMFC separators. and CAE(Computer Aided Engineering) analysis was conducted to optimize injection processing parameters(injection pressure, heat time, mold temperature etc.). We did successfully fabricate the separators by injection molding, and measure the electrical conductivity of the samples by using four point probe device. Conclusively, PP/SG/CB composite showed better both electrical conductivity and moldability than the others.