There are currently at least five methods for producing carbon nanotubes: (1) Chemical Vapor Deposition (CVD), (2) High Pressure Carbon Monoxide processing (HIPCO), (3) arc discharge, (4) laser ablation and (5) Plasma Enhanced Chemical Vapor Deposition (PECVD) for the surface mediated growth of vertically-aligned tubes.The first two methods are given below.
Production methods
HIPCO - (High Pressure Carbon Monoxide) processing involves rapidly mixing a gaseous catalyst precursor (such as iron carbonyl) with a flow of carbon monoxide gas in a chamber at high pressure and high temperature, when the catalyst precursor decomposes to form nanometer-sized metal particles. On the surface these tiny metal particles carbon monoxide molecules react to form carbon dioxide and carbon atoms, which bond together to form carbon nanotubes. This process selectively produces 100% single walled carbon nanotubes (SWNTs) which find wide use in electronics, biomedical applications and fuel cell electrodes.
CVD - chemical vapor deposition (CVD) processes involves mixing of a carbon containing gas with a metal-catalyst-coated substrate at a high temperature. The carbon atoms separate from the hydrocarbon gas and attach to the catalyst particles and other carbon atoms to form high-quality nanotubes. This process can be used to produce a wide variety of CNT products through modified production conditions and post-processing techniques. This process produces a mixture of nanotubes which are chemically robust and can be produced in large volumes and may contain individual and nested SWNTs.
Modification to CNT
Carbon nanotubes can be further modified in numerous ways to get desired material properties by bonding other atoms or molecules covalently to the ends or sidewalls of the nanotube or non-covalently bonded, e.g., by Van der Waals or polarization forces. Thus this doping changes its electronic properties while derivatization can make the CNTs more easily dispersed and/or soluble in liquids.