Graphite vaporization

Static Pressure Synthesis. Diamond can form direcdy from graphite at pressures of about 13 GPa (130 kbar) and higher at temperatures of about 3300—4300 K (7). No catalyst is needed. The transformation is carried out in a static high pressure apparatus in which the sample is heated by the discharge current from a capacitor. Diamond forms in a few milliseconds and is recovered in the form of polycrystalline lumps. From this work, and studies of graphite vaporization/melting, the triple point of diamond, graphite, and molten carbon is estimated to He at 13 GPa and 5000 K (Fig. 1)... 

The hollow interior of dodecahedrane and other organic cage compounds described in section 4.9 is much too small to envelop atoms, ions, or molecules. Tight closed-shell macromolecules have been obtained from vesicles by several research groups, by polymerization of amphiphiles possessing double or triple bonds within the membrane or at the head groups. Smaller, but well-defined, closed-shell containers have been obtained by two other methods described below, namely by directed synthesis and by formation of closed-shell all-carbon molecules in graphite vapor. 

Clustering at very high temperatures, as with high buffer gas pressures in graphite vaporization, is unfavourable to C60 formation because Cf0F itself becomes more reactive under such conditions. If the temperature decreases too rapidly, as with low... 

In 1985 Kroto and Smolly found the sharply prevailing peaks corresponding to the Ceo and C70 clusters in the mass spectra of graphite vapors. To explain the high stability of Ceo, which they called buckyball, it was assumed that it is a spherical molecule in which atoms are located in the tops of truncated icosahedra [1]. A considerable interest was piqued by buckyball (also known as fullerene) when the method of production of significant amounts of Cgo by electric arch evaporation of graphite in a helium atmosphere had been discovered [2]. 

The purification of nanotubes has been studied. It is relatively easier to purify the catalytically grown nanotubes than that from graphite vaporization. The metal catalysts and the inorganic support can be removed with HCl and HF solution. The transition metals can be dissolved in HNO3 solution. The amorphous carbon can be removed with HNO3 solution, and also by permanganate solution. Oxidation with air at mild temperatures is also effective in removing the amorphous carbon. 

Table 9.2. Formation of carbon nanotubes and fullerenes by graphite vaporization/con-densation...

---