Vol.9 No.3 2017

Research paper : A super-growth method for single-walled carbon nanotube synthesis (K. Hata)−170−Synthesiology - English edition Vol.9 No.3 (2017) In my research policy, the nal research topic was “to develop mass production technology by the super-growth method and to make available single-walled CNTs as industrial material.” Assuming a synthesis furnace of a length of 20 m and a width of 1 m to continuously manufacture single-walled CNTs by the super-growth method, the production volume was calculated at 10 tons per year. Ten tons is not that high in industrial level, but at the time, the production volume of single-walled CNTs in the world was estimated to be 6 tons.[9] If there was one super-growth synthesis furnace, it would be possible to manufacture more single-walled CNTs than the rest of the world. I thought this would be a breakthrough in terms of production volume and price.If the super-growth method had 1,000 times the growth efficiency of the conventional method, the sales cost of single-walled CNTs that was several tens of thousands of yen per gram would become 1/1,000, or the sale price would be several tens of thousands of yen per kilogram. This would enable the use of single-walled CNTs as industrial material. I was certain that this would generate major innovation. This was the research topic that fullled my research policy.3 Objective of the research3.1 Development of mass production technology for single-walled CNTs3.1.1 Industrial mass production method and technical conceptHow do we realize industrial mass production based on the super-growth method?When the article was published in Science, the sample size was about 1 cm square, the catalyst was formed by an expensive sputtering method, the substrate was a silicon wafer, and the synthesis was done one batch at a time. Industrial mass production was far away in the distance.However, the super-growth method had several important characteristics in realizing the industrial mass production process, and we did not mention any of them in the Science paper. First, the super-growth method had the world’s best synthesis yield of single-walled CNTs per volume and time of a reaction furnace. This meant that if we achieved mass production, we would be superior in terms of productivity and cost against other competing methods. Second, since super-growth involved adding water to the synthesis atmosphere of regular CNTs, we believed the process was scalable. Third, the super-growth method is a reaction process under atmospheric pressure without using vacuum, plasma, or high pressure. Due to these characteristics, we could construct an open system synthesis furnace. This was a great advantage in continuous synthesis. Finally, the optimal growth temperature of the super-growth method was 800 ºC. This indicated that a metal synthesis furnace could be used instead of quartz or ceramic. From these characteristics, we imagined a manufacturing process for continuous synthesis of single-walled CNTs using a large metal synthesis furnace in an open system.Figure 6 shows the process that we conceived as the mass production process of the super-growth method for single-walled CNTs at low cost while maximizing these characteristics. This was a process in which a metal lm is used as substrate material, a catalyst is coated onto the lm, continuous synthesis is done on a belt conveyor, and the substrate material can be reused.What I nd interesting is that the lab-scale synthesis process shown in the top part of Fig. 6 and the industrial mass production process shown in the bottom part of Fig. 6 are both super-growth methods, but the elemental technologies are totally different. The top is an academic process while the bottom is an industrial process. I think this figure clearly points out the large difference between academia and industry, and the difficulty of transferring technology developed in the academia to industry.The manufacturing process where single-walled CNTs are continuously synthesized on flat substrate material was research that no one had ever attempted in the history of mankind, and it was necessary to conduct enormous amount of technological development. We expected it would kick off innovative effects, and we could build a network of intellectual properties that prevented entry of third parties. The innovative effect was the cost reduction to 1/1000 of the conventional method. However, there were many technologies that had to be developed and we could not fail in any area. If we failed in developing just one elemental technology, mass production would not be possible even if we achieved everything else. Therefore, it was obvious that this technological development would be extremely high risk and high return. Also, we could not utilize the existing manufacturing facilities for commercial production. Large facility investment was necessary for product realization. Carbon nanotubesReuse substrateContinuous synthesisChemical catalystMetal lmIndustrial mass productionCarbon nanotubesSynthesis one substrate at a timeVacuum vapor deposition catalystSilicon substrateSynthesis in laboratoryCoatingFig. 6 Lab-scale vs. mass production process

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