![]() ![]() The induction thermal plasma method can produce up to 2 grams of nanotube material per minute, which is higher than the arc discharge or the laser ablation methods. Different single-wall carbon nanotube diameter distributions can be synthesized. Typically, a feedstock of carbon black and metal catalyst particles is fed into the plasma, and then cooled down to form single-walled carbon nanotubes. The thermal plasma is induced by high-frequency oscillating currents in a coil, and is maintained in flowing inert gas. The method is similar to arc discharge in that both use ionized gas to reach the high temperature necessary to vaporize carbon-containing substances and the metal catalysts necessary for the ensuing nanotube growth. Īnother way to produce single-walled carbon nanotubes with a plasma torch is to use the induction thermal plasma method, implemented in 2005 by groups from the University of Sherbrooke and the National Research Council of Canada. The fumes created by the flame contain SWNT, metallic and carbon nanoparticles and amorphous carbon. A gaseous mixture of argon, ethylene and ferrocene is introduced into a microwave plasma torch, where it is atomized by the atmospheric pressure plasma, which has the form of an intense 'flame'. The process is also continuous and low cost. Doing so, the growth of SWNT is more efficient (decomposing the gas can be 10 times less energy-consuming than graphite vaporization). In this method, the aim is to reproduce the conditions prevailing in the arc discharge and laser ablation approaches, but a carbon-containing gas is used instead of graphite vapors to supply the necessary carbon. Single-walled carbon nanotubes can also be synthesized by a thermal plasma method, first invented in 2000 at INRS ( Institut national de la recherche scientifique) in Varennes, Canada, by Olivier Smiljanic. However, it is more expensive than either arc discharge or chemical vapor deposition. ![]() The laser ablation method yields around 70% and produces primarily single-walled carbon nanotubes with a controllable diameter determined by the reaction temperature. ![]() Later that year the team used a composite of graphite and metal catalyst particles (the best yield was from a cobalt and nickel mixture) to synthesize single-walled carbon nanotubes. When they heard of the existence of nanotubes they replaced the metals with graphite to create multi-walled carbon nanotubes. This process was developed by Richard Smalley and co-workers at Rice University, who at the time of the discovery of carbon nanotubes, were blasting metals with a laser to produce various metal molecules. A water-cooled surface may be included in the system to collect the nanotubes. Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses. In laser ablation, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is led into the chamber. Īrc-discharge technique uses higher temperatures (above 1,700 ☌) for CNT synthesis which typically causes the expansion of CNTs with fewer structural defects in comparison with other methods. The yield for this method is up to 30% by weight and it produces both single- and multi-walled nanotubes with lengths of up to 50 micrometers with few structural defects. During this process, the carbon contained in the negative electrode sublimates because of the high-discharge temperatures. ![]() However the first macroscopic production of carbon nanotubes was made in 1992 by two researchers at NEC's Fundamental Research Laboratory. Nanotubes were observed in 1991 in the carbon soot of graphite electrodes during an arc discharge, by using a current of 100 amps, that was intended to produce fullerenes. Large quantities of nanotubes can be synthesized by these methods advances in catalysis and continuous growth are making CNTs more commercially viable. CVD growth of CNTs can occur in vacuum or at atmospheric pressure. Most of these processes take place in a vacuum or with process gases. Techniques have been developed to produce carbon nanotubes in sizable quantities, including arc discharge, laser ablation, high-pressure carbon monoxide disproportionation, and chemical vapor deposition (CVD). ![]()
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