Arc Discharge Method: The arc discharge method is the primary method for producing carbon nanotubes. The specific process involves placing graphite electrodes in a reaction vessel filled with helium or argon gas, generating an electric arc between the electrodes at temperatures reaching approximately 4000 degrees Celsius. Under these conditions, the graphite evaporates, producing fullerenes (C60), amorphous carbon, and single-walled or multi-walled carbon nanotubes. The relative yields of these products can be adjusted by controlling the catalyst and the hydrogen content in the vessel.
Chemical Vapor Deposition (CVD): The chemical vapor deposition method introduces hydrocarbons or carbon-containing oxides into a high-temperature tubular furnace containing a catalyst, where they undergo catalytic decomposition to form carbon nanotubes. CVD overcomes some of the limitations of the arc discharge method.
Laser Evaporation Method: The specific process of laser evaporation is as follows: A graphite target consisting of a metal catalyst/graphite mixture is placed in the middle of a long quartz tube, which is then placed inside a heating furnace. When the furnace temperature reaches a certain level, inert gas is introduced into the tube, and a laser beam is focused onto the graphite target. Under laser irradiation, gaseous carbon is generated. As this gaseous carbon and catalyst particles are carried by the gas flow from the high-temperature zone to the low-temperature zone, they grow into CNTs under the action of the catalyst.
Low-Temperature Solid-Phase Pyrolysis Method: The solid-phase pyrolysis method produces carbon nanotubes by preparing intermediates. First, metastable nanoscale silicon-carbon nitride (Si-C-N) ceramic intermediates are prepared. Then, these nano-ceramic intermediates are placed in a boron nitride cauldron and heated in a graphite resistance furnace for decomposition. Nitrogen gas is simultaneously introduced as a protective gas. After approximately 1 hour of heating, the nano-intermediate powder begins to pyrolyze, and carbon atoms migrate to the surface.
Ion bombardment method: In a vacuum furnace, carbon is evaporated by ion or electron discharge, and the precipitate containing carbon nanotubes and other structures is collected on a condenser.
Polymerization Synthesis Method
In the preparation of CNT carbon nanotubes, the polymerization synthesis method generally refers to the method of replication and amplification using a template. The general preparation process of CNT carbon nanotubes is similar to that of organic synthesis reactions, and its side reactions are complex and diverse, making it difficult to guarantee that all carbon nanotubes in the same batch are armchair-shaped or serrated nanotubes.
