• Title/Summary/Keyword: Graphite sheet

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Temperature dependence on the growth and structure of carbon nanotubes by thermal chemical vapor deposition (열 CVD에 의한 탄소나노튜브의 성장 및 구조의 온도 의존성)

  • Lee, Cheol-Jin;Son, Kwon-Hee;Lee, Tae-Jae;Lyu, Seung-Chul;Choi, Sung-Hun;Yoo, Jae-Eun
    • Proceedings of the KIEE Conference
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    • pp.1494-1496
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    • 2000
  • We have studied the temperature dependence on the growth and structure of carbon nanotubes using thermal chemical vapor deposition. All the carbon nanotubes have bamboo shaped multi walled structure with closed tip. The growth rate and density of carbon nanotubes increase with increasing growth temperature. The numbers of graphite sheet at the wall increase with increasing growth temperature. The crystallinity of graphite sheets become enhanced at the high growth temperature.

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Synthesis and Characterization of Phase Pure NiO Nanoparticles via the Combustion Route using Different Organic Fuels for Electrochemical Capacitor Applications

  • Srikesh, G.;Nesaraj, A. Samson
    • Journal of Electrochemical Science and Technology
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    • v.6 no.1
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    • pp.16-25
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    • 2015
  • Transition metal oxide nanocrystalline materials are playing major role in energy storage application in this scenario. Nickel oxide is one of the best antiferromagnetic materials which is used as electrodes in energy storage devices such as, fuel cells, batteries, electrochemical capacitors, etc. In this research work, nickel oxide nanoparticles were synthesized by combustion route in presence of organic fuels such as, glycine, glucose and and urea. The prepared nickel oxide nanoparticles were calcined at 600℃ for 3 h to get phase pure materials. The calcined nanoparticles were preliminarily characterized by XRD, particle size analysis, SEM and EDAX. To prepare nickel oxide electrode materials for application in supercapacitors, the calcined NiO nanoparticles were mixed with di-methyl-acetamide and few drops of nafion solution for 12 to 16 h. The above slurry was coated in the graphite sheet and dried at 50℃ for 2 to 4 h in a hot air oven to remove organic solvent. The dried sample was subjected to electrochemical studies, such as cyclic voltammetry, AC impedance analysis and chrono-coulometry studies in KOH electrolyte medium. From the above studies, it was found that nickel oxide nanoparticles prepared by combustion synthesis using glucose as a fuel exhibited resulted in low particle diameter (42.23 nm). All the nickel oxide electrodes have shown better good capacitance values suitable for electrochemical capacitor applications.

Structural and Thermal Characteristics of Graphites Treated in Acidic Solutions (산수용액에서 처리된 흑연 구조와 열적 특성)

  • Song, Seung Won;Min, Eui Hong;Lee, Dong Won;Kim, Jungsoo;Oh, Weontae
    • Korean Journal of Materials Research
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    • v.27 no.2
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    • pp.113-118
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    • 2017
  • Natural and expandable graphites were chemically treated in acidic aqueous solutions such as acetic acid or mixtures of acetic acid and nitric acid. Structures and thermal conductivities of the as-treated graphites were characterized in detail. Both graphites were significantly oxidized in the mixed acidic solution of $H_2SO_4$ and $HNO_3$, which condition was generally used for the oxidation of carbon nanotubes. This considerable oxidation of graphites caused a depression of their thermal conductivity. The structural characteristics, obtained by XRD and XPS, show that the graphites treated in the relatively weak acidic conditions (acetic acid or mixture of acetic acid and nitric acid) were quite similar to the untreated graphites. However, the thermal conductivities of both acidic-treated graphites were remarkably increased.

Postmortem analysis of a failed liquid nitrogen-cooled prepolarization coil for SQUID sensor-based ultra-low field magnetic resonance

  • Hwang, Seong-Min;Kim, Kiwoong;Yu, Kwon Kyu;Lee, Seong-Joo;Shim, Jeong Hyun
    • Progress in Superconductivity and Cryogenics
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    • v.16 no.4
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    • pp.44-48
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    • 2014
  • A liquid nitrogen-cooled prepolarization ($B_p$) coil made for ultra-low field nuclear magnetic resonance and magnetic resonance imaging (ULF-MR) designed to generate 7 mT/A was fabricated. However, with suspected internal insulation failure, the coil was investigated in order to find out the source of the failure. This paper reports detailed build of the failed $B_p$ coil and a number of analysis methods utilized to figure out the source and the mode of failure. The analysis revealed that pyrolytic graphite sheet linings put on either sides of the coil for better thermal conduction acted as an electrical bridge between inner and outer layers of the coil to short out the coil whenever a moderately high voltage was applied across the coil. A simple model circuit simulation corroborated the analysis and further revealed that the failed insulation acted effectively as a damping resistor of $R_{d,eff}=6{\Omega}$ across the coil. This damping resistance produced a 50 ms-long voltage tail after the coil current was ramped down, making the coil not suitable for use in ULF-MR, which requires complete removal of magnetic field from $B_p$ coil within milliseconds.

A Study on Heat Dissipation Characteristics of PMMA Composite Films with Phase Change Material (상변화물질을 이용한 PMMA 복합필름의 방열 성능 향상에 관한 연구)

  • Kwon, Junhyuk;Yoon, Bumyong;Cho, Seung-hyun;Lee, Stephanie K.;Kim, Hyung-ick;Kim, Donghyun;Park, Kyungui;Suhr, Jonghwan
    • Composites Research
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    • v.30 no.5
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    • pp.288-296
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    • 2017
  • The focus of this study is to experimentally investigate the heat dissipation characteristics of poly (methyl methacrylate) (PMMA) composite films with phase change materials (PCM) to resolve heat build-up problems encountered in various electronic devices. In this study, two different types of phase change materials were used to fabricate the composite films by compression molding method and PCM paste sealing method then compared. It was observed in this study that the heat dissipation capability of PCM/PMMA composite films was remarkably enhanced by applying graphite sheet or graphene film into the composite due to their high thermal conductivity. These PCM/ PMMA composite films were attached on the hot spot inside smart phone and tested its surface temperature change according to time. The heat dissipation capability of PCM/PMMA composite film incorporated smart phone was increased 154% and hybrid PCM/PMMA composite film incorporated smart phone was increased 286% over the reference, respectively.

A Study on the Electrochemical Properties of Porous Carbon Electrode according to the Organic Solvent Contents (유기용매의 함량비에 따른 다공성 탄소전극의 전기화학적 특성 연구)

  • Lim, Jung-Ae;Choi, Jae-Hwan
    • Applied Chemistry for Engineering
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    • v.19 no.2
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    • pp.185-190
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    • 2008
  • In order to increase the surface area of electrodes for electrosorption, porous carbon electrodes were fabricated by a wet phase inversion method. A carbon slurry consisting of a mixture of activated carbon powder (ACP), polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP) as a solvent was cast directly on a graphite sheet. The cast film was then immersed in pure water for phase inversion. The physical and electrochemical properties of the electrodes were investigated using scanning electron microscopy (SEM), porosimetry, and cyclic voltammetry. The SEM images verified that the pores of various sizes were formed uniformly on the electrode surface. The average pore sizes determined for the electrodes fabricated with various NMP contents ranged from 64.2 to 82.4 nm and the size increased as the NMP content increased. All of the voltammograms showed a typical behavior of charging and discharging characteristic at the electric double layer. The electrical capacitance ranged from 3.88 to $5.87F/cm^2$ depending on the NMP contents, and the electrical capacitance increased as the solvent content decreased. The experimental results showed that the solvent content is an important variable controlling pore size and ultimately the capacitance of the electrode.

Properties of Nanocomposites Based on Polymer Blend Containing PVDF, Carbon Fiber and Carbon Nanotube (PVDF를 포함한 고분자 블렌드와 탄소섬유/탄소나노튜브를 이용한 복합재료의 특성)

  • Kim, Jeong Ho;Son, Kwonsang;Lee, Minho
    • Applied Chemistry for Engineering
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    • v.25 no.1
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    • pp.14-19
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    • 2014
  • Nanocomposites based on poly(methyl methacrylate) (PMMA)/poly(vinylidene fluoride) (PVDF) and poly(ethylene terephthalate) (PET)/(PVDF) blended with carbon fibers (CF) and carbon nanotube (CNT) were prepared by melt mixing in the twin screw extruder. Morphologies of the PMMA/PVDF/CF/CNT and PET/PVDF/CF/CNT nanocomposites were investigated using SEM. The aggregation of CNT was observed in PMMA/PVDF/CF/CNT nanocomposites while the good dispersion of CNT was shown in PET/PVDF/CF/CNT nanocomposites. In SEM image of PET/PVDF/CF/CNT nanocomposite, the CNT were mainly located at the PET domain of phase-separated PET/PVDF blend due to the ${\pi}-{\pi}$ interaction between the phenyl ring of PET and graphite sheet of the CNT's surface. In addition, a fairly good compatibility between PET/PVDF matrix and CF was shown in the SEM image. In the case of PET/PVDF nanocomposites blended with the co-addition of CF and CNT, the volume electrical resistivity decreased while no change was observed in PMMA/PVDF/CF/CNT composites. The degree of CNT dispersion in morphology results was consistent with the electrical conductivity results. From the DSC results, the crystallization temperature (Tc) of PET/PVDF/CF/CNT nanocomposites increased due to the co-addition of CF and CNTs acting as a nucleating agent. Flexural modulus of PET/PVDF/CF/CNT were sharply enhanced due to increasing the interaction between PET and CF.

Fabrication and Characterization of Porous Carbon Electrode for Electrosorption (전기흡착용 다공성 탄소전극의 제조 및 특성 분석)

  • Park, Nam-Soo;Choi, Jae-Hwan
    • Journal of Korean Society of Environmental Engineers
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    • v.30 no.4
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    • pp.409-414
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    • 2008
  • Porous carbon electrode for electrosorption was prepared by a wet phase inversion method. Carbon slurry that was a mixture of activated carbon powder(ACP) and PVdF solution was cast directly upon a graphite sheet by means of a casting knife. Porous carbon electrodes were fabricated by immersing the cast film in pure water as a non solvent. Physical and electrochemical properties of carbon electrodes prepared with various ACP contents(50.0, 75.0, 83.3, 87.5, 90.0 wt %). From the SEM images we can verify that the electrode was porous. The average pore sizes determined for the electrodes fabricated with various ACP contents ranged from 72.7 to 86.4 nm and the size decreased as the ACP content increased. The electrochemical properties were characterized by cyclic voltammetry(CV) method. All of the voltammograms showed typical behavior of an electric double layer charging/discharging on the carbon surface. The capacitance increased with the ACP content and the values ranged from 2.18 F/cm$^2$ for 50 wt% ACP to 4.77 F/cm$^2$ for 90 wt% ACP.