Scientists at Carbon Nanotechnologies, Inc., Houston, Texas, U.S.A., have produced carbon (C) nanotubes with one or more walls and outer wall diameters 0.5 to 3 nm (World Patent 2004/048,263). Using a gaseous C-containing feedstock, preferably, methane, but other hydrocarbons, alcohols and/or CO are permitted, they contacted a catalyst of Fe, Mo, Ru, Rh, Pd, Os, Ir or Pt, on a particulate support (magnesia of cross-section < 1000 µm) at 500–1500°C. The C nanotube particulates produced were then annealed and the support material was removed. The resulting particulates (enmeshed C nanotubes of ropes of cross-section 10–50 nm) retained the support's approximate shape and size.

The C nanotubes can be activated by etching, and were blended with a matrix material of thermoplastic or thermoset polymer, metal or ceramic. The C nanotube particulates could be well dispersed in the polymers and had high conductivity at low loadings.

Such pastes of polymers and C nanotubes find use in a range of electron emission devices. For example, entangled C nanotubes with one or more walls can be used to produce cathode components in field emission devices, such as electron discharge tubes, amplifiers, and oscillators. As electrical emitters, the C nanotube particulates exhibit a low ‘turn on’ emission field.