Carbon Nanotube Synthesis
1. “Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, high-pressure carbon monoxide (HiPco), and chemical vapor deposition (CVD). Most of these processes take place in vacuum or with process gases. CVD growth of CNTs can occur in vacuum or at atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods; advances in catalysis and continuous growth processes are making CNTs more commercially viable.” (Wikipedia. CNT Synthesis, 10/8/2012)
2. “There exist a number of methods for production of carbon nanostructures and carbon nanotubes. These may be divided in two main categories; high temperature methods and low temperature methods. Most of the high temperature methods are based on sublimation of carbon under an inert atmosphere, such as the electric arc discharge process, the laser ablation method and the solar technique. Low temperature methods are e.g. chemical vapour deposition (CVD) using the catalytic decomposition of hydrocarbons, gas phase catalytic growth from carbon monoxide, production by electrolysis, heat treatment of polymer, low temperature in situ pyrolyse or in situ catalysis. The main methods are further described below.
CVD (Chemical Vapour Deposition) is a method where carbon nanotubes are produced from gas phase by growing carbon nanotubes on a substrate by using large amounts of catalyst at a low temperature (600-1000.degree. C.). The carbon nanotubes produced contains defects, resulting in bends on the structures. Also, the catalyst is present in the resulting carbon nanotubes in various amounts, from 50% and as low as 1-10%.
Arc methods are plasma methods where a DC electric arc discharge is established between an anode and a cathode only a few millimeters apart. This creates a rather small plasma arc in the area between the electrodes. Carbon evaporated from the carbon based (e.g. graphite) anode recondenses on the cathode in the form of a deposit containing carbon nanotubes. In the original arc method published by T. W. Ebbesen, Nature 358 (1992) no externally applied magnetic field generated by permanent magnets or electromagnets was used, and no recirculation of evaporated carbon could occur. This arc method is only suited for small-scale production of carbon nanotubes in arc reactors operating at very low current and power levels--typically a few kW. Upscaling to higher power levels by increasing the arc current and/or the electrode diameter seems not feasible because the deposited carbon nanotubes will be re-evaporated from the cathode.”
[Monsen et al;, US Patent 8,277,739 (10/2/2012)]
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Roger D. Corneliussen
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Copyright 2012 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is10/2/2012.