• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.80-86
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• 2017

In this study, nitrogen functional groups were introduced on graphite fiber (GF) to modify their electrical properties, and heating properties were investigated according to the treatment conditions. GF was prepared by a thermal solid-state reaction at $200^{\circ}C$ for 2 h. Surface properties of the nitrogen doped GF were examined by XPS, and its resistance and heating temperature were measured using a programmable electrometer and thermo-graphic camera, respectively. The XPS result showed that the nitrogen functional groups on the GF surface were increased with increasing of urea contents, and the heating property of the GF was also improved as nitrogen functional groups were introduced. The maximum heating temperature of GF treated by urea was $53.8^{\circ}C$ at 60 V, which showed 55% improved heating characteristics compared to that of non-treated GF. We ascribe this effect to introduced nitrogen functional groups on the GF surface by thermal solid-state reaction, which significantly affects the heating characteristics of GF.

• Korean Chemical Engineering Research
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• v.55 no.2
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• pp.264-269
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• 2017

To improve heating characteristics of graphite fibers, graphite fibers were copper-plated by electroless plating. The Cu-plated graphite fibers were investigated by thermos-gravimetric analysis in air to calculate quantities of copper on surface of graphite fiber according to plating time. Also, the surface temperature with applied voltage was observed by thermos-graphic camera using a strand of graphite fiber. According to the increment of plating time, the higher quantities of plated copper on graphite fiber were obtained. The electric conductivity of plated graphite fiber for 20 minutes was resulted in 1594.3 S/cm, and surface temperature of this sample showed the maximum temperature $57.2^{\circ}C$. These result could be attributed that copper having great electric conductivity are growing on graphite fiber and followed improving heating characteristics.

• Composites Research
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• v.37 no.3
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• pp.162-169
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• 2024

In this study, PAN(polyacrylonitrile)-based precursor fibers were produced through a wet-spinning process, and their morphologies and graphitization behavior were investigated in the presence of two graphitization catalysts (Ca, Ni). The graphitization catalysts were introduced into the formed pores during hot-water stretching of wet-spun PAN-based precursor fibers. The catalytic effects of graphitization catalysts were examined through crystal structure and Raman analysis. At a relatively low temperature of 1500℃, the graphitization was not significantly affected, whereas at a high temperature of 2400℃, the obtained I_D/I_G value of graphite fiber (GF-Ni100) was decreased by about twice (~0.28) compared to the untreated fibers (GF-AS~0.54). By comparing the I_D/I_G values (GF-Ca100~0.42: GF-Ni100~0.28) of Ca and Ni graphitization catalyst, it was found that the degree of graphitization of Ni graphitization catalyst showed higher influence than that of Ca graphitization catalyst. Moreover, 2D band was also observed, indicating that the graphite plane structures composed of multiple layers were developed. XRD results confirmed that the crystal inter-planar distance (d₀₀₂) of the graphite crystal was slightly decreased after the treatment with the graphitization catalyst, But, the crystal size of Ca-treated graphite fiber (GF-Ca100) was increased by up to ~5 nm.

• Polymer(Korea)
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• v.36 no.3
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• pp.321-325
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• 2012

In this work, we prepared the activated graphite nanofibers (A-GNFs) via chemical activation with KOH/GNFs ratios in a range of 0 to 5. The effect of KOH activation was studied in the surface and pore properties of the samples for electrochemical performance. The surface properties of A-GNFs were characterized by XRD and SEM measurements. The textural properties of the A-GNFs were investigated by $N_2$/77 K adsorption isotherms using Brunauer-Emmett-Teller (BET) equation. Their electrochemical behaviors were investigated by cyclic voltammetry and galvanostatic charge-discharge performance. From the results, electrochemical performances of the A-GNFs were improved with increasing the ratio of KOH reagent. It was found that specific surface area and total pore volume of the A-GNFs were increased by KOH activation.

• 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.

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.104-108
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• 2001

Naphthalene derived mesophase pitch WP) was spun into short fibers by using melt-blown technology. The pitch fibers oxidative stabilization were carried out heating rates of $2^{\circ}C/min,\;5^{\circ}C/min\;and\; 10^{\circ}/min$. The heating rate was a key factor to maximate the capacity of the Li-ion secondary battery through controlling the morphology of the graphitized fiber. The diameters of the melt-blown fibers prepared were in the range of $4{\mu}m\~16{\mu}m$ with functions of air jet speed, air temperature and the temperature of the nozzle. The graphitized fibers of $10{\mu}m$ diameters showed various morphological structure with heating rate of the stabilization. Radial, radial-random and skin-core cross-sectional structure of the fibers were observed at the respective heating rate of $2^{\circ}C/min\;5^{\circ}C/min\;and\;10^{\circ}C/min$. Most crystalline structure of graphite was obtained from the fiber stabilized at heating rate of $10^{\circ}C/min$ exhibiting the best anode performance with 400 mAh/g of capacitance and $96.8\%$ of charge/discharge efficiency.

• Proceedings of the Korean Fiber Society Conference
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• 1998.10a
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• pp.505-507
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• 1998

Li이온 전지는 높은 작동전압(3.03V), 높은 에너지밀도 등의 특성 때문에 최근 급격히 발달하는 휴대용 전자기기에 크게 이용되고 있다 흑연은 리튬이온(직경 0.61$\AA$)의 삽입에 따라 층간거리(이론값 3.354$\AA$)가 3.7$\AA$까지 증가하기 때문에 반복되는 충방전에 따라 전지의 형태안정성에 관한 문제가 발생하게된다. 한편 흑연의 선단면에서 전해액과 반응하여 충방전 효율이 감소되는 원인이 된다. (중략)

• Composites Research
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• v.19 no.2
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• pp.7-12
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• 2006

Graphite particle/carbon fiber hybrid conductive polymer composites were fabricated by the compression molding technique. Graphite particles were mixed with an epoxy resin to impart the electrical conductivity in the composite materials. In this study, graphite reinforced conductive polymer composites with high filler loadings were manufactured to accomplish high electrical conductivity above 100S/cm. Graphite particles were the main filler to increase the electrical conductivity of composites by direct contact between graphite particles. While high filler loadings are needed to attain good electrical conductivity, the composites becomes brittle. So carbon fiber was added to compensate weakened mechanical property. With increasing the carbon fiber loading ratio, the electrical conductivity gradually decreased because non-conducting regions were generated in the carbon fiber cluster among carbon fibers, while the flexural strength increased. In the case of carbon fiber 20wt.% of the total system, the electrical conductivity decreased 27%, whereas the flexural strength increased 12%.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.227-227
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• 2003

흑연(graphite), 석탄(coal), 숯(char), soot(검댕이) 등의 탄소로 이루어진 재료들은 비정질부터 완전한 흑연결정까지 다양한 구조를 나타낸다. 이러한 탄소재료의 구조의 출발물질 뿐 아니라 열처리에 따라 강한 영향을 받는다 이러한 구조는 여러 구조인자에 의해 특성화되는데, 구조인자로는 층간거리 d, 결정립 크기 Lc 그리고 결정립 직경 La이다. 이런 구조 인자의 지식은 흑연화, 탄소화, 가스화 등과 같은 다양한 공정을 이해하는데 매우 중요하다. 많은 연구자들은 XRD, Raman 분광, 고분해능 TEM 등과 같은 여러 기술을 통하여 이러한 구조인자에 대한 해석을 시도하였다. 그 중 XRD는 정량적 분석에 있어서 가장 많이 이용되는 기술이다. XRD 회절피크의 위치로부터 층간거리 d를 구할 수 있으며, 결정립 크기 Lc 및 결정립 직경 La는 피크의 line 퍼짐(반가폭)으로 직접 구할 수 있다. 한편 섬유상 흡착제로 이용되는 등방성 탄소섬유는 이산화탄소 또는 수증기에 의해 쉽게 활성화되어 최고 약 2,500 $m^2$/g의 고 비 표면적을 얻을 수 있다. 이렇게 활성화 후 고 비표면적을 나타내는 이유는 좁은 분포를 나타내는 미세기공의 기공구조 때문에 발생하는 것으로 알려져 있다.

• Analytical Science and Technology
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• v.6 no.5
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• pp.479-487
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• 1993

Potassium-Graphite Fiber Intercalation Compounds(K-GFIC) have been prepared from well oriented pitch-based Graphite fiber by the transformed two-bulbs method with variation of reaction temperatures of graphite($T_g$ : $450^{\circ}C$, $400^{\circ}C$, $350^{\circ}C$, $300^{\circ}C$, $250^{\circ}C$). The stage transition process of K-GFICs was studied by X-ray diffraction methods, and we have observed peaks with d-values of (001) diffraction of $5.40{\AA}$ and $8.78({\pm}0.01){\AA}$, which are charecteristic for the stage 1 and stage 2, respectively. The stage stability and energy states of K-GFICs were studied by UV/VIS spectrophotometer. As a results, We found that the minimum values of reflactance of K-GFICs with pure stage was moved to higher energy pristine Graphite fiber's. But because of mixtured stage, we could not observe minimum reflectance in the visible region at high reaction temperatures($400^{\circ}C$, $450^{\circ}C$). From X-ray diffraction and UV/VIS sepctrophotometry data, we can suggest that K-GFICs with lower stage has many charge carriers existed between C atoms of graphite Layers. And then, these results also provides information on the electrical and other physical properties of K-GFICs.