Carbon atoms graphite vaporization

The chains of hollow carbon may be initially chains consisting of Ni (or carbide) particles covered with graphitic carbon. The chains lying on the hot surface of the cathode are heated, and Ni atoms evaporate through defects of the outer graphitic carbon because the vapor pressure of Ni is much higher than carbon. Thus, the carbon left forms hollow graphitic layers. 

Graphite, the most important component of the lead of pencils, is a black, lustrous, electrically conducting solid that vaporizes at 1700°C. It consists of flat sheets of sp2 hybridized carbon atoms bonded covalently into hexagons like chicken wire (Fig. 5.22). There are also weak bonds between the sheets. In the commercially available forms of graphite, there are many impurity atoms trapped between the sheets these atoms weaken the already weak intersheet bonds and let... 

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. 

The first step then is to compute the energy at 0 K for the carbon atom and for the N2, 02, Br2, I2 and 1 molecules. Next the zero-point vibrational contributions are added to the molecular energies, plus the thermal corrections to convert each E(0 K) to H(T), whatever is the temperature of interest. (We will asssume it to be 298 K.) Finally the heat of vaporization of Br2 and the heats of sublimation of graphite, I2 and 1 must be included... 

Until 1985, when the fullerenes, new forms of the element carbon, were discovered, chemists knew two kinds of graphite, two kinds of diamond, and two other forms (chaoit and carbon [VI]). Fullerenes were produced by condensing vaporized carbon in an atmosphere of inert gas. C60 turns out to be very stable, but it is only one of many new clusters of carbon atoms. 

Around 1985, Kroto, Smalley, and Curl (Rice University) isolated a molecule of formula Cf,cj from the soot produced by using a laser (or an electric arc) to vaporize graphite. Molecular spectra showed that G , is unusually symmetrical It has only one type of carbon atom by 13C NMR (5143 ppm), and there are only two types of bonds (1.39 A and 1.45 A). Figure 16-16 shows the structure of C(1, which was named buckminsterfiillerene in honor of the American architect R. Buckminster Fuller, whose geodesic domes used similar five- and six-membered rings to form a curved roof. The Cg0 molecules are sometimes called buckyballs, and these types of compounds (Cgo and similar carbon clusters) are called fullerenes. 

The LJ parameters, elk and a, have been determined from the critical constants, Tc and pc, by adopting the recommendation of Nicolas et al. [11] kTJe = 1.35 andpco3/e = 0.142. However, different values for the potential depth of benzene, 22, have been determined so as to fit the vapor pressure at temperatures from 307.2 K to 553.2 K. The LJ parameters used in this work are summarized in Table 1, where the parameters for graphitic carbon atom are taken from those suggested by Steele [10]. We used the modified Lorentz -Berthelot rule for the cross parameters, that is, the arithmetic mean for o and the geometric mean for e by introducing the binary parameter ktj defined as Eq. (4). 

---