During the synthesis of fullerenes via arc evaporation (in an inert atmosphere
of argon and helium) it was discovered that the cathodic deposit contained
a variety of closed graphidic (ie graphite-like) structures - among these
Shortly afterwards in the same lab as Sumio Iijima first discovered and
identified these nanoparticles as nanotubes two scientists called Thomas
Ebbeson and Pulickel Ajayan showed that nanotubes could be produced in
bulk through the same method by simply varying the conditions
However, this only gave multi-walled nanotubes (MWNTs)
It was later discovered that to make single-walled nanotubes (SWNT's) you
simply had to add a metal such as cobalt into the reaction mixture.
An alternative method of preparing SWNTs is via the original method of
fullerene synthesis - laser evaporation of graphite (ie shining a laser
onto a graphite block and displacing a couple of layers of weakly bonded
hexagonal carbon and it reacting to form SWNTs)
However these bundled together to form so-called nanotube ropes:
A Picture of an oven used in the laser evaporation of graphite can be found
Since these methods were developed substantial progress has been
made (particularly in Japan where they have always been at the forefront
of nanotechnology) on improving the production techniques for carbon nanotubes,
including increased production efficiency, higher purity and the development
of new techniques.
Other techniques were developed, including fusion salt electrolytic, thermal
decomposition, high temperature furnace laser abrasion and irradiation
with argon ions.
Initially, nanotubes could only be produced in very small quantities, with
yields of less than one percent of the weight of electrode consumption.
But in 1992 NEC was able to boost the yield to 30 percent of the weight
of the electrode consumption by raising the pressure of the inert gas atmosphere
by ten times to about one atmosphere and simultaneously reducing the plasma
temperature. Also important was increasing the diameters of the electrodes.
In 1997 Researchers at Meijo University (in Nagoya) developed a process
for producing carbon nanotubes which features both high speed of tube formation
and increased purity of the tubes. The researchers discovered that the
nano particles could easily be removed from the mixture of tubes and particles
by heating the surface of the negative electrode accumulation in air to
several hundred degrees centigrade for 30 minutes. This separation occurs
because of the big difference in the heat oxidizing speed of the tubes
and particles. In the initial experiments, 6mm diameter carbon rods were
used in a hydrogen atmosphere, and a current of 50A DC was applied for
Also in 1997, the National Institute of Materials and Chemical Research
developed a process for producing carbon nanotubes by irradiating amorphous
carbon (soot) with argon gas ions. In this process, a 10mm diameter amorphous
carbon substrate is irradiated by a 5mm diameter argon ion beam perpendicular
to it for about one hour. The nanotubes are formed surrounding the area
exposed to the beam and are oriented in a radial pattern.
In 1998 Osaka Gas Company Ltd and the Kansai New Technology Laboratory
jointly developed a process for producing carbon nanotubes which results
in a batch purity of about 50 percent. Until then, purity levels had generally
been only been about two or three percent because of contamination by soot
and other by-products. This was attained through the electrodecomposition
of a fluorocarbon compound to remove the fluorine atoms and produce an
intermediate form of carbon. This intermediate carbon is then irradiated
with an electron beam to produce the carbon nanotubes.
This process is said to be well suited for large-scale production. In contrast,
the conventional carbon electrode arc discharge process only permitted
production of several grams per day. Osaka Gas is Japan's second largest
supplier of household gas. In mid-1999 the National Institute of Materials
and Chemical Research and Showa Denko K.K. announced that they were constructing
a pilot plant that would produce carbon nanotubes at a rate of several
hundred kilograms daily. This plant will use a catalytic gas phase reaction
of a hydrocarbon raw material at a temperature in excess of 1000 degrees(C).
This will be the largest scale of production of carbon nanotubes to date.
The project is being supported by the Ministry of International Trade and
Industry (MITI) as part of its "Frontier Carbon Technology" project.
Page, Introduction, The
Basics of Nanotubes, From Buckyballs
to Nanotubes, Synthesis of Nanotubes,
and Future Uses for Nanotubes,