• Journal of Electrochemical Science and Technology
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• v.14 no.2
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• pp.184-193
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• 2023

This study investigates the effects of a carbon fiber layer formed on the surface of an etched aluminum current collector on the electrochemical properties of the activated carbon electrodes for an electric double layer capacitor. A particle size analyzer, field-emission SEM, and nitrogen adsorption/desorption isotherm analyzer are employed to analyze the structure of the carbon fiber layer. The electric and electrochemical properties of the activated carbon electrodes using a carbon fiber layer are evaluated using an electrode resistance meter and a charge-discharge tester, respectively. To uniformly coat the surface with carbon fiber, we applied a planetary mill process, adjusted the particle size, and prepared the carbon paste by dispersing in a binder. Subsequently, the carbon paste was coated on the surface of the etched aluminum current collector to form the carbon under layer, after which an activated carbon slurry was coated to form the electrodes. Based on the results, the interface resistance of the EDLC cell made of the current collector with the carbon fiber layer was reduced compared to the cell using the pristine current collector. The interfacial resistance decreased from 0.0143 Ω·cm² to a maximum of 0.0077 Ω·cm². And degradation reactions of the activated carbon electrodes are suppressed in the 3.3 V floating test. We infer that it is because the improved electric network of the carbon fiber layer coated on the current collector surface enhanced the electron collection and interfacial diffusion while protecting the surface of the cathode etched aluminum; thereby suppressing the formation of Al-F compounds.

• Journal of Magnetics
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• v.3 no.2
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• pp.64-67
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• 1998

Microwave absorbing properties of ferrite-epoxy composite (absorbing layer) attached on the carbon fiber polymer composite (reflective substrate) are analyzed on the basis of wave propagation theory. A modified equation for wave-impedance-matching at the front surface of absorbing layer including the effect of electrical properties of the quasi-conducting substrate is proposed. Based on this analysis, the frequency and layer dimension that produce zero-reflection can be estimated from the intrinsic material properties of the obsorbing layer and the substrate. It is demonstrated that the microwave reflectivity of carbon fiber composite has a strong influence on the microwave absorbance of front magnetic layer.

• 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.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.149-155
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• 2005

The purpose of this study is to investigate the flexural strengthening effects of CF(Carbon Fiber) sheet for the full-scale RC beams with multi-layer CF sheets. The partial strength reduction factors of CF sheets are suggested from the full-scale RC beams tests strengthened with multi-layer CF sheets up to six layers as well as material tests. From the material tensile tests, it was observed that the average tensile strengths of CF sheets per layer are decreased as the number of CF sheets is increased. Also the steep strength reductions of CF sheets in material test results at rupture are observed compared with the structural tests results for the full-scale RC beams strengthened with multi-layer CF sheets. Finally, the partial strength reduction factors far CF sheets up to six layers are suggested considering the effects of multi-layer and unit weight of CF sheets.

• Journal of the Korean Institute of Gas
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• v.15 no.1
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• pp.35-39
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• 2011

The purpose of this paper is to analyze affecting ratios of strength safety in carbon fiber layer thickness of a composite fuel tank for FEV vehicles. To investigate affecting ratios by FEM modeling, the equivalent von Mises stress has been computed on the aluminum liner and carbon fiber layers of composite fuel tanks in hoop and helical directions respectively. According to the FEM results, the affecting ratios of an aluminum liner on the equivalent stress are 77.5% in hoop direction, 18.11% in $70^{\circ}C$ winded helical direction and 4.39% in $12^{\circ}C$ winded helical direction. These trends on the strength safety of carbon fiber layers have been shown as those of an aluminum liner even though the layer thickness ratio of $12^{\circ}C$ inclined carbon fiber is very high of 42% compared with that of hoop layer thickness. Thus, the computed results show that the strength safety of a carbon fiber fuel tank is more influenced by the winding angle rather than the fiber thickness of carbon fiber layers.

• Carbon letters
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• v.26
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• pp.102-106
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• 2018

• Carbon letters
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• v.1 no.3_4
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• pp.133-137
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• 2001

Mesoporous activated carbon fiber (ACF) was prepared from phenolic resin containing a small amount (0.1 wt %) of organic nickel complex through carbonization and steam activation. Microporous ACF as reference sample was also prepared from phenolic resin without agent. In both cases of the mesoporous ACFs and the microporous ACFs, the electric double layer capacitance of the nonaqueous electrolyte (0.5 M $TEABF_4$/PC or 1.0 M $LiClO_4$/PC) was not proportional to the BET specific surface area. This is owing to the low permeability of nonaqueous electrolyte or the low mobility of ion in narrow micropores. However, the mesoporous ACF showed higher double layer capacitance than the microporous (normal) ACF. This result suggests that the presence of many mesopores promotes the formation of effective double layer or the transfer of ion in the micropore.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.35-38
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• 2005

Carbon fiber sheets are widely used for strengthening the deteriorated RC structures. However most studies on the strengthening method of RC structures with carbon fiber sheets are concerning static problems. The purpose of this experimental study is to present the basic data on fatigue behaviors of. RC beams strengthened with carbon fiber sheets. The experimental parameters of this study are ; 1) the existence of U-shaped carbon fiber sheets at the ends for anchoring, 2) the number of carbon fiber sheet layers in strengthening the RC beams, 3) the load levels of $60\%\~90\%$ of the static bending moment strength, which is obtained form the static tests. Experimental results are estimated from the relationships of load level, displacement, number of repeated load and released energy. It is concluded that U-shaped carbon fiber sheets for end anchoring is very effective and the beams strengthened with one layer of carbon fiber sheet have longer fatigue life than that with three layers.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.224-224
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• 2012

For decades, carbon fiber has expanded their application fields from reinforced composites to energy storage and transfer technologies such as electrodes for super-capacitors and lithium ion batteries and gas diffusion layers for proton exchange membrane fuel cell. Especially in fuel cell, water repellency of gas diffusion layer has become very important property for preventing flooding which is induced by condensed water could damage the fuel cell performance. In this work, we fabricated superhydrophobic network of carbon fiber with high aspect ratio hair-like nanostructure by preferential oxygen plasma etching. Superhydrophobic carbon fiber surfaces were achieved by hydrophobic material coating with a siloxane-based hydrocarbon film, which increased the water contact angle from $147^{\circ}$ to $163^{\circ}$ and decreased the contact angle hysteresis from $71^{\circ}$ to below $5^{\circ}$, sufficient to cause droplet roll-off from the surface in millimeter scale water droplet deposition test. Also, we have explored that the condensation behavior (nucleation and growth) of water droplet on the superhydrophobic carbon fiber were significantly retarded due to the high-aspect-ratio nanostructures under super-saturated vapor conditions. It is implied that superhydrophobic carbon fiber can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell. Moreover, such nanostructuring of carbon-based materials can be extended to carbon fiber, carbon black or carbon films for applications as a cathode in lithium batteries or carbon fiber composites.

• Journal of the Korean Ceramic Society
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• v.45 no.9
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• pp.531-536
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• 2008

Reaction bonded silicon carbide (RBSC) composite for heat-exchanger was fabricated by molten Si infiltration method. For enforcing fracture toughness to reaction bonded silicon carbide composite, the surface of carbon fiber has coating layer by SiC or pyro-carbon. For SiC layer coating, CVD method was used. And for carbon layer coating, the phenol resin was used. In the case of carbon layer coating, fracture toughness and fracture strength were enhancing to 4.4 $MPa{\cdot}m^{1/2}$ and 279 MPa.