Vol.9 No.3 2017

Research paper : A super-growth method for single-walled carbon nanotube synthesis (K. Hata)−172−Synthesiology - English edition Vol.9 No.3 (2017) the mass production process. For the roles of AIST and Zeon, AIST developed methods for solving the issues, and Zeon developed ways to upscale the methods, continuous synthesis, and production technologies.The greatest black issue was “how to realize continuous synthesis.” When we succeeded in continuous synthesis and this issue became grey, Mr. Arakawa would embark on building the commercial plant. At this point, the mass production process was not established at all. I thought Mr. Arakawa was the embodiment of an excellent business manager. Unfortunately, the bankruptcy of Lehman Brothers occurred and it became extremely difcult for the company to make facility investment, and the commercial plant ceased to be.I shall explain the main elemental technologies including the development of substrate material, a coating type catalyst, large-area synthesis technology, and continuous synthesis technology. Then, I shall describe the course of the research where the elemental technologies were integrated to complete the mass production process.4.1 Elemental technologies of the mass production process4.1.1 Technological development of the substrate materialThe production process at the time when the article was published in Science used a silicon wafer as the substrate, but for mass production, it was necessary to have a substrate that was low cost as much possible, was capable of synthesizing excellent quality single-walled CNTs at high efficiency, and could be reused repeatedly. Such a substrate must show high durability at synthesis temperature of nearly 800 ºC, be highly resistant to hydrogen reduction and oxidation atmospheres due to water addition, and must not inhibit CNT synthesis. As a result of searching for a substrate that fullled such strict demands, it was found that single-walled CNTs could be synthesized at similar growth efciency and quality as silicon wafers when a Ni-Fe-Cr alloy was used as substrate material.[10] Among dozens of materials investigated, only the Ni-Fe-Cr alloy satisfied all the necessary requirements (Fig. 9). We were lucky because the Ni-Fe-Cr alloy was also excellent from the perspective of continuous production and safety. The Ni-Fe-Cr alloy is called stainless or Inconel®, and it is the most widely used economic thermal resistant metal. In fact, the material of metal mufe furnaces used at temperature of 800 ºC is usually Inconel®.There was the problem of carburization, that is, metal was carbonized and weakened when exposed to carbon at high temperature. The raw material of CNTs is hydrocarbon. Moreover, the CNTs are synthesized at high volume continuously in the synthesis furnace, and that inevitably creates a highly concentrated hydrocarbon atmosphere. The effect of carburization was extremely powerful in such synthesizing atmosphere, and for example, the metal screw that joined the metal parts of the sample holder expanded due to carburization after several hundred syntheses and destroyed the sample holder. The Ni-Fe-Cr alloy was least affected by carburization or had a high carburizing resistant property.Fig. 8 Development of mass production technologyNi-Fe-Cr 500 x 200 sizePilot plant500 x 500 metal substrate,Coated catalyst,Continuous synthesis,Metal mue,Metal showerApply iron-containingsolutionContinuous synthesis furnace, metal mue, metal showerContinuous synthesis furnace, metal mue, quartz showerLarge area synthesis furnace, showerhead, quartzVertical 4 inch,showerhead, quartzContinuous synthesis device, quartz furnace, quartz showerLow-purity nitrogen, low-purity hydrogenMetal mue,metal showerNi-Fe-Cr A4 sizeColloid ne particle spin coatingVertical small diameter, quartzLow-purity nitrogen, high-purity hydrogenHigh-purity helium, high-purity hydrogenQuartz furnace, quartz showerHigh purity nitrogen, high-purity hydrogenMetal mue furnace, quartz showerHorizontal showerhead,quartzDC sputteringNi-Fe-Cr 2 cm squareRF sputteringHorizontal small 1 inch, quartzSilicon 2 cm squareContinuous synthesisSynthesisGasSynthesis furnaceCatalystSubstrate material

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