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Volume 2012 (2012)
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Volume 2012, Issue 255
Displaying 1-11 of 11 articles from this issue
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Research Papers
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Yutaka Kaburagi, Miu Ohoyama, Yuhki Yamaguchi, Emi Shindou, Akira Yosh ...Article type: Research Papers
2012 Volume 2012 Issue 255 Pages 225-230
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL FREE ACCESSBacteria cellulose prepared from nata de coco which is composed of pure cellulose nanofibers. The nanofibers were dispersed in ethanol or distilled water and were stirred and then filtered to obtain paper-like sheets. The diameters of the nanofibers were in the range of 30 to 60 nm. The sheets were carbonized and then heat-treated at temperatures between 2400 and 3200 °C in a high purity Ar flow under atmospheric pressure, and the texture and structure of the heat-treated sheets were investigated. Cellulose-based carbon materials are known to be one of nongraphitizing carbons. However, graphitization of the carbon sheets was observed as a result of the heat treatments, and was especially apparent for those from the nanofibers dispersed in ethanol. The development of a graphite structure in the carbon nanofibers of the sheets seems to be attributed to graphitization on the surface of nongraphitizing carbon, and the surface graphitization seems to extend to the insides of the carbon nanofibers with very thin diameters of 30-60 nm. The graphitization degree of the 3200 °C-treated sheet derived from the nanofibers dispersed in ethanol was nearly comparable to that for a commercial graphite nanofiber powder VGCF®. However, the improvement in structural perfection with heat treatment for the carbon sheets was less remarkable in comparison with that for typical graphitizing carbons. The limited graphitization behavior of the heat-treated sheets may be attributed to their heterogeneous structure.View full abstractDownload PDF (2622K) -
Tomohiro Tojo, Teruyuki Tokutake, Keita Komiyama, Yoong Ahm Kim, Takuy ...Article type: Research Papers
2012 Volume 2012 Issue 255 Pages 231-236
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL FREE ACCESSWe performed high temperature heat-treatment to remove metallic impurities from carbon nanoscrolls and evaluated their structures. It was found from elemental analysis that samples heat-treated above 1500 °C have been effectively purified, and became free of metallic species. In addition, the amount of oxygen was reduced to about 2 at.%. Further analysis revealed that interlayer distance became 0.336 nm which is comparable to that of ideal graphite (0.335 nm), at a relatively low temperature such as 1200 °C. It was experimentally and theoretically shown that open-edges started to bond with each other above 2000 °C and mainly transformed into a larger diameter cylindrical structure. Moreover, it was found that the Raman D′ band associated with open-edges disappeared above 2000 °C. On the other hand, the D′ band was still apparent in samples heat-treated below 1800 °C. The study suggests that metal-free carbon nanoscrolls with active edges can be effectively obtained by heat-treating the pristine sample at 1500-1800 °C.View full abstractDownload PDF (3149K) -
Yasuhiro Ouchi, Asami Takenaka, Taro Kinumoto, Tomoki Tsumura, Masahir ...Article type: Research Papers
2012 Volume 2012 Issue 255 Pages 237-244
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL FREE ACCESSThe intercalation mechanism for carbon fibers was discussed. Li-intercalation compounds of pitch-based carbon fibers (Li-ICCFs) were synthesized through electrical contact between lithium metal and carbon fibers in an electrolytic cell. Li-ICCFs containing both high- and low-stages were synthesized with all the carbon fibers used. It was also shown that high- and low-stage structures of Li-ICCFs coexisted during the intercalation process. The intercalation behavior of carbon fibers was discussed from the aspect of the crystallite size of the carbon fibers and the de-intercalation behavior of the Li-ICCFs obtained. It was found that the de-intercalation behavior of the carbon fiber differed from that of graphite such as graphitized sheets. It was shown that different crystallinity in the internal texture of the carbon fiber is related to the intercalation behavior, making it different from graphite.View full abstractDownload PDF (2783K) -
Hiroyku Hara, Taro Kinumoto, Tomoki Tsumura, Masahiro ToyodaArticle type: Research Papers
2012 Volume 2012 Issue 255 Pages 245-253
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL FREE ACCESSExfoliated carbon fibers (ExCFs) of PAN- and pitch-based carbon fibers prepared by electrochemical processing followed by a rapid heat treatment have a large amount of edges which are seldom observed in carbon nanotubes because they have gone through the formation of graphite oxide and fragmentation. This was clarified by the analysis of thermal programmed desorption and temperature programmed oxidation of the ExCFs. Carboxyl groups were generated at the edges by electrochemical processing. Subsequently the number of carboxyl groups decreased as a result of the rapid heat treatment, while the number of oxygen functional groups derived from CO increased. The differences in morphology of ExCFs prepared from PAN- and pitch-based carbon fibers seem to reflect the texture of the initial carbon fibers.View full abstractDownload PDF (2996K)
Account
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Eiichi Yasuda, Takashi Akatsu, Yasuhiro Tanabe, Kazumasa Nakamura, Yas ...Article type: Account
2012 Volume 2012 Issue 255 Pages 254-265
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSNano-sized carbon fibers (∼500 nmϕ) have received great attention not only for scientific research but also for energy and/or electrical device applications etc. Carbon nanofibers (CNFs) have been developed and different morphologies have been obtained. The morphology of the CNF depends on the raw material and the production process. In this paper we investigate the ways to produce CNFs and have classified them into five classes. 1: CVD process, 2: Template carbonization process, 3: Electro-spinning process, 4: Polymer blend process and 5: Wet spinning process. The differences in the morphology of the CNFs produced with different processes come from the different raw materials and the different mechanism of the fiber formation, such as deposition, drying speed (agglomeration speed)，spinning speed (molecular orientation) and so on. We summarized the fundamentals of morphology formation as fiber diameter, surface configuration and continuity with different processes investigated in the latest reports.View full abstractDownload PDF (4366K)
Review Paper
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Shin MukaiArticle type: Review Papers
2012 Volume 2012 Issue 255 Pages 266-273
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSCarbon gels are unique porous carbons, which are typically obtained through the carbonization of resorcinol–formaldehyde gels. They are practically an aggregate of nanometer-sized carbon particles. Nanopores, mostly in the size range of mesopores, exist between the particles. Smaller pores, micropores being the majority, also exist within the particles. Therefore, this material has a hierarchical pore system in which short micropores are directly connected to mesopores. This pore system can be tuned quite precisely, by simply adjusting the synthesis conditions, such as the amount of catalyst used for synthesis, and the drying conditions of the precursor RF gel. As the precursor RF gel is synthesized through a sol–gel transition, there is a high possibility that its morphology can be easily controlled. We have actually examined the possibility of controlling of the morphology of carbon gels, and have succeeded in obtaining them in the form of disks, microspheres and microhoneycombs. Details of such carbon gels are reported.View full abstractDownload PDF (5335K) -
Tomokazu Fukutsuka, Shohei Maruyama, Kohei Miyazaki, Takeshi AbeArticle type: Review Papers
2012 Volume 2012 Issue 255 Pages 274-279
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSCarbonaceous materials have been widely investigated as negative electrode materials of lithium-ion batteries (LIBs). In this review, the properties of nano-carbon materials for use as negative electrodes are summarized from the viewpoint of their morphology. As nano-carbon materials, carbon nanospheres (zero dimension), carbon nanotubes (one dimension), carbon nanofibers (one dimension), graphene (two dimension), and so on were covered. The advantages and disadvantages of nano-carbon materials as the negative electrode in LIBs are discussed.View full abstractDownload PDF (5095K) -
Masaru Tachibana, Shigeki YamadaArticle type: Review Papers
2012 Volume 2012 Issue 255 Pages 280-291
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSCarbon nanowalls (CNWs) are vertically oriented two-dimensional carbon sheets on substrates, which are typically fabricated by plasma-enhanced chemical vapor deposition. Each CNW originates from the stacking of several graphene sheets. A more detailed examination of the structure shows a domain structure that consists of nanographite domains, several tens of nanometers in size. Such a unique morphology and the structure of CNWs have attracted much attention for fundamental studies and various applications such as electronic and energy devices. In this review, we consider the structural characterization of CNWs by Raman spectroscopy and transmission electron microscopy. Furthermore, we examine one of unique transport properties of CNWs, Anderson weak localization. We also show the possibility of using CNWs for a catalytic support in fuel cells as a potential application.View full abstractDownload PDF (4783K) -
Kyoichi Oshida, Kenji Takeuchi, Takuya Hayashi, Morinobu EndoArticle type: Review Papers
2012 Volume 2012 Issue 255 Pages 292-304
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSTechniques for the structural and morphological characterization of carbon materials using microscopy and image processing are reviewed. These techniques are high resolution transmission electron microscopy (HRTEM), three dimensional transmission electron microscopy (3D-TEM) and two dimensional fast Fourier transform (2D-FFT). They are applied to the structural analysis of carbon nanotubes loaded with metal particles, activated carbon, and thin graphite. A HRTEM with Cs corrector can achieve a high resolution of less than 0.1 nm even if the acceleration voltage is 80 kV. The more precise three dimensional structure of the carbon nanotubes and activated carbon can be revealed by using 3D-TEM combined with HRTEM. The 2D-FFT of lattice images of HRTEM can analyze the structure of nano structured carbons, like selected area electron diffraction (SAED) which is difficult to apply to the microscopic area. 2D-FFT can be an alternative technique to SAED for nano-size analysis. HRTEM, 3D-TEM, and image processing thus can provide a powerful tool for the analysis of the structure and morphology of nanostructured carbons.View full abstractDownload PDF (14863K)
Recent Doctoral Thesis
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Ken-ichi SakaiArticle type: Recent Doctoral Thesis
2012 Volume 2012 Issue 255 Pages 305-307
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSThe present thesis focused on the local electronic structure of graphene edges, which is characterized by two distinct edge geometry (zigzag and armchair edges), investigated by scanning tunneling microscopy (STM) at low temperature and ultra high vacuum condition. In Part 1, fabrication of graphene edges and their thermal stability are discussed. Graphene edges formed by oxidation reaction on graphite substrate tended align parallel to armchair direction. It is figured out that the armchair edge is thermally favorable than zigzag edge due to the energy gain coming from the delocalization of π-electrons. In Part 2, STM study about electron wave interference in the vicinity of armchair edges is described. In this study three-symmetric fine structure was discovered on individual bright site in honeycomb superlattice. Through the theoretical calculation it was revealed that the K–K′ intervalley scattering specific to a presence of an armchair edge is responsible for the generation of honeycomb superlattice. Furthermore, STM simulation result was in excellent agreement with the fine structure experimentally observed. Fine structure was appeared due to the antiphase coupling of wave function between nearest neighbor bright sites mediated by STM tip. In Part 3, direct observation of graphene edges in presence and absence of magnetic fields was summarized. Short zigzag edges embedded in armchair edge contributed to the enhancement of electron density distribution, as the generation of edge states. STM observation under applied magnetic field indicated that the strong electron density near both zigzag and armchair edges could be ascribed to Landau levels on the Fermi energy. In summary, the present thesis clarified the correlation between local geometric structure and electronic structure at the graphene edges by means of STM.View full abstractDownload PDF (741K)
TANSO salon
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Hidekazu TouharaArticle type: TANSO Salon
2012 Volume 2012 Issue 255 Pages 309-311
Published: November 15, 2012
Released on J-STAGE: December 17, 2012
JOURNAL RESTRICTED ACCESSDownload PDF (916K)
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