Mechanism for the growth of multiwalled carbon-nanotubes from carbon black

Multiwalled carbon-nanotubes have been grown from carbon black by solid-state transformation at the anode of a modified high-temperature arc-furnace without a catalyst. A mechanism for the solid-state transformation of carbon black into nanotubes is proposed. The migration of pentagon and heptagon defects present in carbon black to regions of high tensile-stress is key to the growth mechanism. The growth process can be broken into two stages. The basic mechanism for both stages is the same; only the source of the tensile stress that drives the nanotube growth differs. In the initial stage of growth the necks between carbon-black particles are lengthened into short nanotubes by thermal forces. Electrostatic forces present in the plasma of the high-temperature arc-furnace drive the subsequent extension of the short nanotubes to multiple-micron lengths.