Section IV
Synthesis of Macroscopic Quantities of C


  1. The Apparatus

    While the truncated icosahedron structure was compelling and appealing, it could not be confirmed until macroscopic quantities of C were obtained. The breakthrough came in 1990 when Wolfgang Krätschmer (Max Planck Institute, Heidelberg, Germany) and Donald Huffman (University of Arizona, Tucson, AZ) discovered C in graphitic carbon "soot", produced by evaporating graphite electrodes via resistive heating in an atmosphere of ~ 100 torr helium (1 atm = 760 torr) (Krätschmer & Lamb, 1990).

    Although the soot contained only a few percent by weight of C, it could be conveniently extracted using benzene as solvent. The red-brown benzene solution could be decanted from the black insoluble soot and then dried using gentle heat, leaving a residue of dark brown to black crystalline material. Mass spectral analysis of this material showed peaks at 720 (C) and 840 (C) in an approximate ratio of 10:1.

    Shortly after the Krätschmer synthesis was reported, Smalley's group at Rice published a modified design for the " C generator" (Haufler, 1990). In the Smalley apparatus (Figure IV.A), an electric arc is maintained between two nearly contacting graphite electrodes. Hence, most of the power is dissipated in the arc and not in resistive heating of the rod. The entire electrode assembly is enclosed in a reaction kettle that is filled with ~ 100 torr pressure of helium. Black soot, like that observed by Krätschmer, is produced, and extraction with organic solvents yields fullerenes.

    Figure IV.A:
    Schematic diagram of the contact-arc apparatus used to generate macroscopic quantities of C.


  2. The Experimental Results

    Note: Background material on ultraviolet and infrared spectroscopy should be presented in this section.

    Interestingly, the original goal of the Krätschmer/Huffman study was not to generate C. Rather, it was to generate graphite "soot" in the lab and compare the spectral properties of this material with those of interstellar carbon dust. They initially detected the presence of C in their soot samples by observing three broad features in the ultraviolet spectrum. In addition, they saw four sharp infrared bands superimposed on a rather large continuum background absorption from the graphitic carbon which comprised >95% of the sample (Krätschmer & Fostiroupoulos, 1990). Theorists had previously shown that C, because of its unusually high symmetry, would have only four infrared-active vibrational modes, and the positions of the peaks observed by Krätschmer et al. closely matched the calculated line positions.


  3. Separation of C and C

    Note: Background material on chromatography should be presented in this section.

    Kroto's group at Sussex was the first to show that the mixture of C and C, obtained using the Krätschmer synthetic technique, could be cleanly separated by column chromatography (Taylor, 1990). The Kroto chromatographic separation (alumina, hexane) produced pure C as a mustard-colored solid that appeared brown or black with increasing film thickness. It gave beautiful magenta solutions. C was a reddish-brown solid and thicker films were grayish-black. Its solutions were orange or amber.


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