Carbon Nanotube Particulates in Electron Emitters
Scientists at Carbon Nanotechnologies, Inc., Houston, Texas, U.S.A., have produced carbon nanotubes with one or more walls and outer wall diameters 0.5 to 3 nm (World Patent 2004/048,263). Using a gaseous carbon-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 carbon nanotube particulates produced were then annealed and the support material was removed. The resulting particulates (enmeshed carbon nanotubes of ropes of cross-section 10–50 nm) retained the support's approximate shape and size.
The carbon nanotubes can be activated by etching, and were blended with a matrix material of thermoplastic or thermoset polymer, metal or ceramic. The carbon nanotube particulates could be well dispersed in the polymers and had high conductivity at low loadings.
Such pastes of polymers and carbon nanotubes find use in a range of electron emission devices. For example, entangled carbon 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 carbon nanotube particulates exhibit a low ‘turn on’ emission field.
Source: Platinum Metals Review, October 2004, Volume 48, Issue 4, page 168.
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