Extra-fine and long carbon nanotubes growing on heat-resistant beads. Image: Hitachi Chemical |
Hitachi
Chemical has recently developed a new large-scale synthesis process for
carbon nanotubes (hereinafter referred to as “CNTs”). This process is
based on a technique to synthesize continuously large-scale, extra-fine,
and long CNTs (CNTs whose diameter is 10 nm or smaller and length is
several hundred micrometers) of high purity with three walls on an
average, and is expected to enhance the speed for practical use of CNTs
in all fields. In addition, based on the dispersion technique that is
indispensable for realizing CNT characteristics, Hitachi Chemical has
developed a dispersion liquid, which decreases damage on CNTs and has
high stability. Hitachi Chemical will start providing samples of the
extra-fine and long CNT, the dispersion liquid, and the related
materials synthesized by this process.
CNTs
have excellent properties such as high flexibility, high electrical
conductivity, high heat conductivity, high strength, and so on thanks to
its peculiar structure and is expected to be applied to various fields
including environment & energy, and electronics. The technique to
synthesize on a large scale and with high purity the extra-fine and long
CNTs among various kinds of CNTs, however, has not been established and
the quantity obtained through the process was very small. In addition,
the process required purification processes using chemicals such as
strong acid and was difficult to put to practical use.
Then,
Hitachi Chemical has established the process to synthesize the
extra-fine and long CNTs continuously by improving the fluidized-bed
synthesis, which is the existing industrial process, in collaboration
with Dr. Suguru Noda, Ph.D, Associate Professor, the University of
Tokyo. This is a process that grows CNTs on heat-resistant beads on
whose surface the metal catalyst is supported before separating and
collecting easily the CNTs from the beads, and produces CNTs
continuously by repeating this process, growth, separation, and
collection. This process has enabled us to control the average diameter
of the CNTs to 10 nm or smaller with the use of a smaller catalyst on
the beads. This process also enables us to make the CNT length long to
several hundred micrometers or longer because it enables us to control
the reaction time at any length of time. In addition, this process, as
excellent features, has high CNT production efficiency per reaction
volume that results in the prospect of lower cost and requires no
purification processes because the CNTs obtained through this process
include little catalyst residues and amorphous carbon, and have high
purity.
On
the other hand, regarding the dispersion technique that is
indispensable for realizing the characteristics of CNTs, Hitachi
Chemical has developed a new dispersion liquid that decreases damage to
CNTs and has high stability by improving the dispersion agent and the
method through implementation of a joint research with Dr. Bunshi
Hugetsu, Ph.D, Professor, Hokkaido University. By utilizing this
dispersion liquid, Hitachi Chemical is going to make a transparent
conductive film and respond to customization to meet the applications in
the future.
It
is expected that the extra-fine and long CNT obtained from this process
can add such functions as high electrical conductivity, high heat
conductivity, and high strength to the products with a little addition
in comparison to the conventional multi-walled CNTs.
