Characterization of fullerene soots and carbon arc electrode deposits

The main product of the evaporation of graphite rods in an electric arc under inert gas atmosphere is fullerene soot, a material that has been shown to exhibit properties quite different from those of conventional soots or carbon blacks (H. Werner et al., Chem. Phys. Lett., 194 (1992) 62). Except for conditions optimized for fullerene production, slag-like electrode deposits are formed in this process in quantities at least comparable to the yield in soluble fullerenes. These deposits have been shown to contain considerable amounts of graphitic nanotubes only if they are prepared under certain well-defined conditions (S. Iijima, Nature, 354 (1991) 56) where fullerene yield is poor. We have examined fullerene soots and electrode deposits prepared under a variety of conditions by transmission electron microscopy, powder X-ray diffraction and oxidation experiments monitored by thermogravimetry. Fullerene soots were collected from various spots in the evaporation chamber located at different distances from the arc plasma in order to detect effects of post-formational annealing. A fresh cathode deposit is compared with a cathode deposit that had been exposed to the arc plasma as the anode after deposition. Our results show that the occurrence of ordered graphitic structures in fullerene soot depends on inert gas pressure as well as on the influence of heat and radiation on soot deposited in the vicinity of the arc plasma. In thermal gravimetric experiments increasing amounts of graphitic structures are shown to lead to marked differences in combustion profiles. The combustion temperature of cathode deposit is found to increase further after partial anodic evaporation of the sample.