• Carbon letters
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• v.3 no.4
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• pp.205-209
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• 2002

In the reaction of gas-solid phases, the microwave energy plays a role as a catalyst, because it causes friction between adjacent molecules and enables an unique characteristics of interior heating of the materials. When the dipole gases are adsorbed inside of the pore of carbon materials, the gases are decomposed by the microwave energy and reacted with the carbon atoms. Using this principle, we could make the activated carbon from coconut shell within 20 minute, and this residence time for activation is about 1/16 of rotary kiln. The BET surface area of activated carbon made by microwave is about $1,100m^2/g$ similar to conventional method of rotary kiln. In this study, the power of microwave generator was 400~1000W, and the gas for activation was steam mainly.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.258-263
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• 1999

In this study, the numerical and experimental investigations were conducted to understand ultrasonic wave propagation and to evaluate the degree of fiber waviness in thick composites nondestructively. The path, energy and traveling time of insonified wave were predicted by adopting the ray and plane wave theories. In the analysis, the composites were assumed to have continuous fiber with sinusoidal waviness in a matrix and were modeled as stacks of infinitesimally short length off-axis elements with varying fiber orientation along the length direction. From the experiments on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness, the energy distributions of received wave were obtain for the various positions of transmitter. It was observed that the energy of wave was converged to the adjacent peaks of fiber waviness. The location where maximum energy of wave was detected from the experiments showed good agreement with the location obtained from theoretical predictions. Finally, the test procedure was Proposed to evaluate fiber waviness in thick composites by considering the energy of wave and relative distance between transmitter and receiver.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.168-171
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• 1999

For the axial crushing tests of various shape of tubes, it was reported that composite tubes need trigger mechanism to avoid brittle failure. In this study, static axial crush tests were performed with the new aluminum/GFRP hybrid tubes. Glass/Epoxy prepregs were wrapped around aluminum tube and co-cured. The failure of hybrid tube was stable and progressive without trigger mechanism, and specific energy absorption was increased to maximum 34% in comparison with aluminum tube. Effective energy absorption is possible for inner aluminum tube because wrapped composite tube constrain the deflection of aluminum tube and reduce the folding length. The failure of hybrid composite tube was stable without trigger mechanism because inner aluminum tube could play the role of crack initiator and controller. Aluminum/Glass-Epoxy hybrid tube is suitable for the vehicle front structure due to effective energy absorption capability, easy production, and simple application for RTM process.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.84-87
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• 2000

Square tubes used for vehicle structure components have an important role on keeping its stiffness and preserving occupant safety in vehicle collision and rollover in which it experience axial collapse, bending collapse or both. Bending collapse, which absorbs kinetic energy of the impact and retains a survival space for the occupant, is a dominant failure mode in oblique collision and rollover. Thus, in this paper, the bending collapse characteristics such as the maximum bending moment and energy absorption capacity of the square tube replaced by light-weight material were evaluated and presented. The bending test of cantilever tubes which were fabricated with aluminum, GFRP and aluminum/ GFRP hybrid by co-curing process was performed. Then the maximum bending moment and the energy absorption capacity from the moment-angle curve were evaluated. Based on the test results, it was found that aluminum/ GFRP hybrid tube can show better specific energy absorption capacity compared to the pure aluminum or GFRP tube and can convert unstable collapse mode which may occur in pure GFRP tube to stable collapse mode like a aluminum tube in which plastic hinge is developed.

• Interaction and multiscale mechanics
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• v.1 no.3
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• pp.317-328
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• 2008

When carbon-filled rubber specimens are subjected to cyclic loading, they do not return to their initial state after loading and subsequent unloading, but exhibit a residual strain or permanent deformation. We propose a specific form of the pseudo-elastic energy function to represent cyclic loading for incompressible, isotropic materials with stress softening and residual strain. The essence of the pseudo-elasticity theory is that material behaviour in the primary loading path is described by a common elastic strain energy function, and in unloading, reloading or secondary unloading paths by a different strain energy function. The switch between strain energy functions is controlled by the incorporation of a damage variable into the strain energy function. An extra term is added to describe the permanent deformation. The finite element implementation of the proposed model is presented in this paper. All parameters in the proposed model and elastic law can be easily estimated based on experimental data. The numerical analyses show that the results are in good agreement with experimental data.

• Journal of the Korean Chemical Society
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• v.65 no.2
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• pp.145-150
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• 2021

The present study describes a hands-on experiment to help students understand the concept of phase change or phase transition and its application in a phase change material (PCM). PCMs are substances that have the capability of storing and releasing large amounts of thermal energy. They act as energy storage materials that provide an effective way to save energy by reducing the electricity required for heating and cooling. Lauric acid (LA) was selected as an example of the PCM. Students investigated the temperature change of LA and the temperature (of air) inside the test tube. The differences in the temperatures of the systems helped students understand how PCMs work. A one-group pretest and posttest design was implemented with 34 grade-11 students in science and mathematics. Students' understanding was assessed using a multiple-choice test and a questionnaire. The findings revealed that the designed activity helped students understand the concept of phase change and its application to materials for thermal energy storage.

• Journal of the Semiconductor & Display Technology
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• v.17 no.4
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• pp.16-20
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• 2018

Graphene is attracting attention due to its outstanding properties as line material for next-generation semiconductor. Graphene pattern technology is essential to apply graphene line. Selective graphene oxide reduction as one of graphene pattern method does not require a substrate thereby a high flexibility device can be applied. Particularly, the method using photon energy has advantages of short process time and environment friendly. In this review, we introduce the photocatalytic method and the photo-thermal energy conversion method using photon energy in the selective reduction process of graphene oxides.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1787-1793
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• 2018

The power conversion efficiency of perovskite solar cells has reached 23.3%. Although significant developments have been made through intensive studies, the stability issue is still challenging. Passivation of perovskite solar cells with a transparent polymer provides better stability; however, there are a few disadvantages of organic polymer such as low thermal stability, weak adhesion and the lack of water retention ability. In this work, we prepared a dual Parylene-F/C layer with 3-methacryloxypropyltrimethoxysilane, A-174, to combine the advantages of organic and inorganic materials. As a result, A-174 treated dual Parylene-F/C layer demonstrated improved passivation effects compared to a single Parylene layer due to the strong binding of Parylene and the water retention ability by $SiO_2$ formed from A-174. This synergetic effects can be expanded to the combination of other organic materials and organosilane compounds.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.3
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• pp.250-256
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• 2004

Magnesium and its alloys have the high potential as hydrogen storage materials because of their highest hydrogen storage capacity, low density and abundant resources. But poor kinetic properties of hydriding and dehydriding and high working temperature have limited their practical applications. In this study, the Mg-Ni binary alloys with different amount of Ni were produced by gravity casting and characterized in order to investigate the relationship between the microstructures and hydriding properties. The maximum hydrogen absorption capacity decreased, but the absorption kinetics increased with Ni content. The difference in the absorption kinetics was resulted from the differences in the sort and shape of primary solid phases and eutectic microstructure.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.3
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• pp.190-196
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• 2002

Ni/MH 박막전지의 전극으로 사용될 수 $Mg_{2}Ni$박막을 스퍼터링방법으로 제조하였다. $Mg_{2}Ni$합금박막은 Mg, Ni타?을 이용하여 동시에 스퍼터링함으로서 제조하였다. KOH 액체전해질 및 $Ni(OH)_2$전극을 이용하여 전기화학실험을 하였다. $Mg_2Ni$ 박막의 초기 싸이클 특성에 미치는 열처리 효과를 조사하기 위하여, $200-550^{\circ}C$로 변화시키면서 진공중에서 열처리를 하였다. 열처리온도가 $300^{\circ}C$ 이하에서는 초기방전용량이 증가하였으며, $400^{\circ}C$ 열처리시에는 활성화시의 방전용량이 약 160mAh/g으로 가장 크게 나타났다.