Single-Walled Tubes and Encapsulation of Nanocrystals into Carbon Clusters

Single-walled carbon nanotubes can be prepared in an arc discharge between graphite electrodes of which the anode contains transition metals and their mixtures. Gram-quantities of single-walled tubes (SWT) can be obtained when a mixture of Fe/Ni, Fe/Co, or Ni/Co is used in the anode. Diameters of the SWT produced from Ni or Fe fall in the range of 0.70 to 1.00 nm compared to 0.85 to 1.30 nm of those produced with mixed Fe/Ni or Ni/Co. The SWT are a few microns long and capped at both ends. They do not associate directly to the metal particles. In contract, YC₂ filled anode produced short SWT radiating from the YC₂ particles. For B, Mg, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, and Ta, crystals of the carbides are encapsulated into the growing carbon nanoclusters. For Si, Cr, Zn, Pd, Ag, W, and Pt the nanotubes are formed but no encapsulation is observed. The presence of Ti, however, inhibits the formation of the carbon cages. The thermodynamics of the formation of the carbides is considered to set criteria and predict the encapsulation into the nanotubes. The growth of the strings of beads is discussed in conjunction with existing growth models.