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Feb 24th, 2012
 
Development of large-scale synthesis process and dispersion technique for extra-fine and long carbon nanotubes
 
Hitachi Chemical Co., Ltd. (Head Office: Tokyo; President and CEO: Kazuyuki Tanaka; Capital: 15.5 billion yen; hereinafter referred to as "Hitachi Chemical") has recently developed a new large-scale synthesis process for carbon nanotubes (hereinafter referred to as “CNTs”).
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Extra-fine And Long CNT Growing on the Heat-resistant Beads
Extra-fine And Long CNT Growing on the Heat-resistant Beads

This process is based on a technique to synthesize continuously large-scale, extra-fine, and long CNTs 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.


 
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