Graphitization structure

The properties of mesophase pitch-based carbon fibers can vary significantly with fiber texture. Inspection of the cross-section of a circular mesophase fiber usually shows that the graphitic structure converges toward the center of the fiber. This radial texture develops when flow is fully developed during extrusion through the spinnerette. Endo [48] has shown that this texture of mesophase pitch-based carbon fibers is a direct reflection of their underlying molecular structure. 

Since PAN-based carbon fibers tend to be fibrillar in texture, they are unable to develop any extended graphitic structure. Hence, the modulus of a PAN-based fiber is considerably less than the theoretical value (a limit which is nearly achieved by mesophase fibers), as shown in Fig. 9. On the other hand, most commercial PAN-based fibers exhibit higher tensile strengths than mesophase-based fibers. This can be attributed to the fact that the tensile strength of a brittle material is eontrolled by struetural flaws [58]. Their extended graphitic structure makes mesophase fibers more prone to this type of flaw. The impure nature of the pitch preciusor also contributes to their lower strengths. 

Key Words—Carbon nanotubes, vapor-grown carbon fibers, high-resolution transmission electron microscope, graphite structure, nanotube growth mechanism, toroidal network. 

As it can be observed from the high resolution images of tubules (Fig. 9(a)) their graphitic structure is generally defective. The defects can be of different... 

There are now clear experimental indications that nanotubes are not perfect in the sense defined in the introduction[12,13,19,20]. The first full paper dedicated to this issue was by Zhou et o/.[19], where both pressure and intercalation experiments indicated that the particles in the sample (including nanotubes) could not be perfectly closed graphitic structures. It was pro-... 

It is known that the electrical properties of CNTs insulator, semiconductor or metal, are caused by the structure in graphitic sheet [2,3]. It is difficult to observe the individual graphitic structure in a sheet of CNT by TEM, because... 

SWCNTs exhibit exceptional properties which are directly related to their defect-free graphitic structure. The current list of possible applications includes ... 

The formation of fullerenes and CNTs has also been affected by their environmental atmosphere [22] and, in particular, a hydrogen atmosphere plays an important role in forming graphitic structures of multi-walled CNTs (MWCNTs) in the form of buckybundles [24]. Intercalation into MWCNTs has been difficult or impossible, because there is no space for intercalants to enter into a Russian-doll-type structure of the nanotubes. However, the buckybundles formed in the hydrogen arc discharge were found to be successfully intercalated with potassium and ferric chloride (FeCl3) without breaking the... 

In the last decade two-dimensional (2D) layers at surfaces have become an interesting field of research [13-27]. Many experimental studies of molecular adsorption have been done on metals [28-40], graphite [41-46], and other substrates [47-58]. The adsorbate particles experience intermolecular forces as well as forces due to the surface. The structure of the adsorbate is determined by the interplay of these forces as well as by the coverage (density of the adsorbate) and the temperature and pressure of the system. In consequence a variety of superstructures on the surfaces have been found experimentally [47-58], a typical example being the a/3 x a/3- structure of adsorbates on a graphite structure (see Fig. 1). 

The actual structure of practical carbonaceous materials deviates more or less from the ideal graphite structure. Even number of structural defects. Moreover,... 

NOTE Do not confuse graphitization with graphitic corrosion, which is different. Graphitic corrosion causes the iron in cast iron to selectively leach out, leaving behind a porous graphite structure. 

Explain why the size of the silicon atom does not permit a silicon analog of the graphite structure. 

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