Carbon nanoshell chains (CNSCs) as a functional carbon were produced by the two-step carbonization of wood (Japanese larch) loaded with Co acetate by aqueous impregnation, similar to our earlier studies of the carbonization of Fe- and Ni-loaded woods. The wood was first carbonized at 500 °C for 2 h to form a char, and then at 900 °C for 1 h. The properties of the three CNSCs were different: The crystallinity and mesoporosity of the Co-CNSCs were about half-way between those for Fe- and Ni-CNSCs, the thermochemical stability of the Co-CNSCs was lower than for Fe- and Ni-CNSCs, and the average nanoshell diameters were 70, 55, and 110 nm for Co, Fe, and Ni, respectively. The chemical state of the three metal species present in the 500 °C-chars, was also different. The results indicated that the three Fe-group metals had their own distinctive catalysis in the carbonization of wood that usually has a high content of oxygen, although the basic mechanism of CNSCs formation was the same.
The stress graphitization behavior of isotropic pitch-based carbon fiber reinforced carbon/carbon composites heat-treated at 2000 and 2400 °C in an argon gas atmosphere was studied. The tested composites consist of needle-punched carbon fiber felt which is composed of carbon fibers with an elastic modulus of around 40 GPa roughly one order of magnitude lower than that of PAN-based carbon fibers, and a carbon matrix derived from a phenolic resin. The X-ray diffraction patterns and Raman spectra for the composite heat-treated at 2400 °C indicate that the graphitization of the matrix is significantly higher and that of carbon fiber is slightly lower than values obtained by heating the resin and fibers separately. These findings suggest that stress graphitization was observed even in a composite consisting of an isotropic pitch-based carbon fiber with a low elastic modulus.
This article describes the fundamentals of the Hall effect and magnetoresistance of graphenes in published papers including both ordinary effects and quantum effects. Because the interpretation of the papers involves various features of graphene related to the crystal structure and energy dispersion relations of carriers and carrier transport, the article is divided into two parts. Part I (presented here) describes the crystal structure and energy band, especially the Brillouin zone of a triangular lattice and the energy dispersion relations for graphenes, while Part II will be concerned with the Hall effect and magnetoresistance in ordinary and quantum effects with an emphasis on the latter.
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