• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.213-214
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• 2023

The burden of housing heating costs has increased as energy prices such as global oil prices (28.1%), LNG (38%) and minerals (100%) have soared due to the Ukraine crisis. Accordingly, an electrically conductive cement composites had developed using waste carbon materials such as waste cathode materials, waste CNTs, and waste carbon fibers, and the heat generation performance was evaluated.

• Carbon letters
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• v.11 no.4
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• pp.304-310
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• 2010

To manufacture a carbon/carbon composite the coal tar pitch was used as the matrix precursor and the PAN (polyacrylonitrile)-based carbon fiber was used as the reinforcing material to weave 3-directional preform. For pressure carbonization HIP equipment was used to produce a maximum temperature of $1000^{\circ}C$ and a maximum pressure of 100 MPa. The carbonization was induced by altering the dwell temperature between $250^{\circ}C$ and $420^{\circ}C$, which is an ideal temperature for the moderate growth of the mesophase nucleus that forms within the molten pitch during the pressure carbonization process. The application of high pressure during the carbonization process inhibits the mesophase growth and leads to the formation of spherical carbon particles that are approximately 30 nm in size. Most particles were spherical, but some particles were irregularly shaped. The spread of the carbon particles was larger on the surface of the carbon fiber than in the interior of the matrix pocket.

• Korean Journal of Materials Research
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• v.30 no.10
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• pp.522-532
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• 2020

Conductive polymer composites with high electrical and mechanical properties are in demand for bipolar plates of phosphoric acid fuel cells (PAFC). In this study, composites based on natural graphite/fluorinated ethylene propylene (FEP) and different ratios of carbon black are mixed and hot formed into bars. The overall content of natural graphite is replaced by carbon black (0.2 wt% to 3.0 wt%). It is found that the addition of carbon black reduces electrical resistivity and density. The density of composite materials added with carbon black 3.0 wt% is 2.168 g/㎤, which is 0.017 g/㎤ less than that of non-additive composites. In-plane electrical resistivity is 7.68 μΩm and through-plane electrical resistivity is 27.66 μΩm. Compared with non-additive composites, in-plane electrical resistivity decreases by 95.7 % and through-plane decreases by 95.9 %. Also, the bending strength is about 30 % improved when carbon black is added at 2.0 wt% compared to non-additive cases. The decrease of electrical resistivity of composites is estimated to stem from the carbon black, which is a conductive material located between melted FEP and acts a path for electrons; the increasing mechanical properties are estimated to result from carbon black filling up pores in the composites.

• Composites Research
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• v.20 no.6
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• pp.1-7
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• 2007

Expanded graphite/carbon fiber hybrid conductive polymer composites were fabricated by the preform molding technique. The conductive fillers were mechanically mixed with a phenol resin to provide an electrical property to composites. The conductive filler loading was fixed at 60wt.% to accomplish a high electrical conductivity. Expanded graphites were excellent in forming a conductive networking by direct contacts between them while it was hard to get the high flexural strength over 40MPa with using only expanded graphite and phenol resin. In this study, carbon fibers were added in composites to compensate the weakened flexural strength. The effect of carbon fibers on the mechanical and electrical properties was examined according to the weight ratio of carbon fiber. As the carbon fiber ratio increased, the flexural strength increased until the carbon fiber ratio of 24wt.%, and then decreased afterward. The electrical conductivity gradually decreased as the increase of the carbon fiber ratio. This was attributed to the non-conducting regions generated among the carbon fibers and the reduction of the direct contact areas between expanded graphites.

• Polymer(Korea)
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• v.25 no.3
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• pp.367-374
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• 2001

The electromagnetic interference (EMI) shielding effectiveness (SE) of poly(vinylidene fluoride) (PVDF) composites was investigated using carbon nanofiber fillers prepared by catalytic chemical vapor deposition of various carbon-containing gases over Ni and Ni-Cu catalysts. The electrical conductivity of carbon nanofiber which was regarded as the key property of filler for the application of EMI shielding ranged from 4.2 to 22.4 S/cm at a pressure of 10000 psi. The electrical conductivity of carbon nanofiber/PVDF composites ranged from 0.22 to 2.46 S/cm and the EMI SE of those was in the range of 2∼13 dB. The electrical conductivity of carbon nanofibers increased with the increase in heat treatment temperature and time, while the electrical conductivity of the composites increased rapidly at the initial heat treatment and then approached a certain value with the further increase of heat treatment. The SE of the composites showed a maximum at the medium heat treatment and was proportional to the electrical conductivity of the composites. It was concluded that the specific surface area of carbon nanofibers decreased with the continual heat treatment and the specific surface area of filler was an important factor for the SE of the composites.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1523-1526
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• 2012

In this work, we prepared activated multi-walled carbon nanotubes/polyacrylonitrile (A-MWCNTs/C) composites by film casting and activation method. Electrochemical properties of the composites were investigated in terms of serving as MWCNTs-based electrode materials for electric double layer capacitors (EDLCs). As a result, the A-MWCNTs/C composites had much higher BET specific surface area, and pore volume, and lower volume ratio of micropores than those of pristine MWCNTs/PAN ones. Furthermore, some functional groups were added on the surface of the A-MWCNTs/C composites. The specific capacitance of the A-MWCNTs/C composites was more than 4.5 times that of the pristine ones at 0.1 V discharging voltage owing to the changes of the structure and surface characteristics of the MWCNTs by activation process.

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.442-446
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• 2002

Design of microwave absorbers using high frequency properties of fiber reinforced composites are investigated. Two kinds of composite materials (glass and carbon) are used and their complex permittivity and permeability are measured by transmission/reflection technique using network analyzer. Low dielectric constant and nearly zero dielectric loss are determined in glass fiber composite. However, carbon fiber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.697-700
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• 2002

Porous anodic aluminum oxide(AAO) templates prepared by anodizing method were used for growing multiwalled carbon nanotubes(CNTs). AAO templates with the homogeneous pore diameter and length were obtained by two step anodizing technique. Using AAO templates, vertically well-ordered two-dimensional carbon nanotube arrays were fabricated. We investigated the field emission property of CNTs grown using different catalyst metals in vacuum chamber (<$10^{-7}$ Torr) on AAO Template. To explain the different emission property, the surface reaction between catalysts and alumina pores which inserted carbon species of $C_2H_2$ using High resolution transmission electron microscopy (HRTEM) was studied.

• Carbon letters
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• v.17 no.1
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• pp.33-38
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• 2016

In the present study, exfoliated graphite nanoplatelets (xGnP) with different particle sizes were coated onto polyacrylonitrile-based carbon fibers by a direct coating method. The flexural properties, interlaminar shear strength, and the morphology of the xGnP-coated carbon fiber/phenolic matrix composites were investigated in terms of their longitudinal flexural strength and modulus, interlaminar shear strength, and by optical and scanning electron microscopic observations. The results were compared with a phenolic matrix composite counterpart prepared without xGnP. The flexural properties and interlaminar shear strength of the xGnP-coated carbon fiber/phenolic matrix composites were found to be higher than those of the uncoated composite. The flexural and interlaminar shear strengths were affected by the particle size of the xGnP, while the particle size had no significant effect on the flexural modulus. It seems that the interfacial contacts between the xGnP-coated carbon fibers and the phenolic matrix play a role in enhancing the flexural strength as well as the interlaminar shear strength of the composites.

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.458-463
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• 2002

Carbon nanotubes were synthesized at various conditions using Ni-catalytic thermal chemical vapor deposition method and their characteristic properties were investigated by SEM, TEM and Raman spectroscopy. Carbon nanotubes were formed on very fine Ni-catalytic particles. The carbon nanotubes synthesized by thermal decomposition of acetylene at $700^{\circ}C$ had a coiled shape, while those synthesized at $850^{\circ}C$ showed a curved and Y-shape having a bamboo-like morphology. It was found that the carbon nanotube was also made on the fine Ni-catalytic particles formed on the surface of 100~400nm sized large ones after pretreatment with $NH_3$.ber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.