There are currently at least five methods for producing carbon nanotubes: (1) Chemical Vapor Deposition (CVD), (2) arc discharge, (3) laser ablation,
(4) HIPCO®, and (5) surface mediated growth of vertically-aligned tubes by Plasma Enhanced Chemical Vapor Deposition (PECVD). Although Unidym primarily uses HIPCO® CVD, and PECVD to synthesize commercial-quantities of CNTs, the Company controls foundational
intellectual property (IP) covering many of these methods.
More Details about production processes
- HIPCO® - (High Pressure Carbon Monoxide) processing was discovered by Dr. Smalley's team in 1998. The process 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. The catalyst precursor decomposes, and nanometer-sized metal particles form from the decomposition products.
These tiny metal particles serve as a catalyst. On the catalyst surface, 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). These carbon nanotubes can be used in electronics, biomedical applications and fuel cell electrodes.
- CVD - Unidym also employs proprietary chemical vapor deposition (CVD) processes, which involve mixing 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, i.e., some individual SWNTs, and some "nested" SWNTs. These nanotubes are chemically
robust and can be produced in large volumes.
Once carbon nanotubes have been produced, they can be further modified in numerous ways depending on the desired material properties.
Such modification may include derivatives, wherein other atoms or molecules are bonded to the nanotube. These atoms or molecules may be
covalently bonded to the ends or sidewalls of the nanotube or may be non-covalently bonded, e.g., by Van der Waals or polarization forces.
In many instances nanotube derivatives result in "doping" of a nanotube that changes its electronic properties. In addition, derivatization
can change other CNT properties that, for instance, make the CNTs more easily dispersed and/or soluble in liquids.