Carbon Nanotubes and Other Carbon Materials
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Graphite exhibits a three-dimensional (3-D) stacking ordering of large graphene layers (where an individual carbon layer in the honeycomb graphite lattice is called a graphene layer) of planar hexagonal networks of carbon atoms based on sp2 bonding. In contrast, carbons consist of randomly stacked defective and relatively small graphene sheets, which are termed turbostratic carbons (T-carbons). Furthermore, carbon nanotubes are seamless cylindrical forms of such graphene layers of nanometer-size diameter, consisting of single- or concentric multilayers. The diameter of the central hollow core is basically of fullerene size (around 1 nm), and the minimum size diameter that has been observed is 0.4 nm. These carbon nanotubes are strongly related to 3-D-graphite or T-carbon when considering their large curvature. The nanotube curvature introduces some sp3 bonding into the sp2 planar bonding of the graphene sheet. Numerous unusual properties of carbon nanotubes arise from the sp2 graphene layers by imposing additional quantum confinement and topological constraints in the circumferential direction of the nanotubes. In this chapter, carbon nanotubes are first reviewed in terms of their relevance to typical carbon and graphite materials and then are connected with other fibrous forms of carbon and graphite.