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    Section IV
    Synthesis of Macroscopic Quantities of C

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* Index *

    * The Apparatus <#SApparatus>
    * The Experimental Results <#SEResults>
    * Separation of C and C <#SSeparation>
    * Activity IV (optional) <#Activity4>

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   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
      Kr�tschmer (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) (Kr�tschmer & 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 Kr�tschmer 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 Kr�tschmer,
      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.

      Index <#index>

   2. The Experimental Results

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

      Interestingly, the original goal of the Kr�tschmer/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 (Kr�tschmer & 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 Kr�tschmer et al.
      closely matched the calculated line positions.

      Index <#index>

   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 Kr�tschmer 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.

      <full_act4.html>

      Index <#index>

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