A manufacturing technology for carbon nanotubes (CNTs) capable of mass-producing aligned CNTs at lower cost has been developed by National Institute of Advanced Industrial Science and Technology (AIST), Nanotube Research Center (Ibaraki, JP) Super Growth CNT Team Leader Kenji Hata with researchers Satoshi Yasuda and Motoo Yumura.
An apparatus (CVD apparatus (1)) having a reaction chamber (3) for accommodating a substrate (2) formed with a metal catalyst film and means (gas supply pipes (5, 6)) for supplying a feedstock gas (9) and a catalyst activating material (10) into the reaction chamber (3) for manufacturing CNTs aligned in a direction perpendicular to the catalyst film surface (2a) of the substrate (2), wherein the means for supplying the feedstock gas (9) and the catalyst activating material (10) have a plurality of ejection holes placed at positions facing the catalyst film surface (2a) of the substrate (2), and the ejecting direction of the ejection holes is adjusted to the direction of alignment of CNTs grown from the metal catalyst film. The apparatus is detailed in U.S. Patent Application 20100062157.
Figure Apparatus for CNT Growth
Well-known thin metal films used so far for the synthesis of the CNT include iron chloride thin film, iron thin film, iron-molybdenum thin film, alumina-iron thin film, alumina-cobalt thin film, and alumina-iron-molybdenum thin film.
In the CNTs obtained by the manufacturing method of the invention, when manufactured as single-walled CNTs, the specific surface area is extremely large which is from 600 to 1300 m2/g for unopened products. The specific surface area of the unopened products can be increased by applying an opening treatment.
As the opening treatment, a dry process using oxygen, carbon dioxide or water vapor, or a reflux treatment with hydrogen peroxide, and a wet process using a cutting treatment with high temperature hydrochloric acid, etc. have been known. In a case of applying the opening treatment, the specific surface area can be from 1300 to 2500 m2/g.
The value for the specific surface area was determined by measuring a liquid nitrogen adsorption/desorption isotherm at 77K using BELSORP-MINI manufactured by Bell Japan Inc. and measuring the specific surface area based on the adsorption/desorption isotherm.
The CNT aggregate obtained by the manufacturing method of the invention can provide high alignment and provide anisotropy for electric properties (for example, electric conductivity), optical properties (for example, transmittance), and mechanical properties (for example, Young's modulus) between the direction of alignment and the direction perpendicular thereto. The degree of the anisotropy is 1:3 or more and the upper limit value thereof is about 1:100.
From the foregoings, when compared with the conventional method of supplying the feedstock gas and the catalyst activating material from one end wall of the reaction chamber 3 only by way of a single nozzle (opening of the other gas supply pipe 6), it has been found that according to the method of the invention of supplying at least the feedstock gas and the catalyst activating material from the shower head 14, the life time of the catalyst is extended to continue the growth of CNTs for a long time and the consumption amount of the feedstock gas and the catalyst activating material is decreased and, as a result, CNTs can be manufactured in a remarkably great amount, at a reduced cost and stability. Further, it has been found that the obtained CNT aggregate is excellent in the purity, the specific surface area, and the alignment.
The CNTs obtained by the manufacturing apparatus and the manufacturing method of the invention can provide single-walled carbon nanotubes selectively but it is also possible to selectively manufacture double-walled carbon nanotubes or multi-walled carbon nanotubes respectively by controlling the thickness of the catalyst film.
As the opening treatment, a dry process using oxygen, carbon dioxide or water vapor, or a reflux treatment with hydrogen peroxide, and a wet process using a cutting treatment with high temperature hydrochloric acid, etc. have been known. In a case of applying the opening treatment, the specific surface area can be from 1300 to 2500 m2/g.
The value for the specific surface area was determined by measuring a liquid nitrogen adsorption/desorption isotherm at 77K using BELSORP-MINI manufactured by Bell Japan Inc. and measuring the specific surface area based on the adsorption/desorption isotherm.
The CNT aggregate obtained by the manufacturing method of the invention can provide high alignment and provide anisotropy for electric properties (for example, electric conductivity), optical properties (for example, transmittance), and mechanical properties (for example, Young's modulus) between the direction of alignment and the direction perpendicular thereto. The degree of the anisotropy is 1:3 or more and the upper limit value thereof is about 1:100.
From the foregoings, when compared with the conventional method of supplying the feedstock gas and the catalyst activating material from one end wall of the reaction chamber 3 only by way of a single nozzle (opening of the other gas supply pipe 6), it has been found that according to the method of the invention of supplying at least the feedstock gas and the catalyst activating material from the shower head 14, the life time of the catalyst is extended to continue the growth of CNTs for a long time and the consumption amount of the feedstock gas and the catalyst activating material is decreased and, as a result, CNTs can be manufactured in a remarkably great amount, at a reduced cost and stability. Further, it has been found that the obtained CNT aggregate is excellent in the purity, the specific surface area, and the alignment.
The CNTs obtained by the manufacturing apparatus and the manufacturing method of the invention can provide single-walled carbon nanotubes selectively but it is also possible to selectively manufacture double-walled carbon nanotubes or multi-walled carbon nanotubes respectively by controlling the thickness of the catalyst film.
The CNT Forest synthesized by the Super Growth method consists of SWCNTs (99.5%) and the SWCNTs are aligned in a single direction. The SWCNTs in CNT Forest have larger diameters and are of higher purity than other SWCNTs. Focusing on these characteristics, we examined opening process by oxidation, through which the tips and walls of SWCNTs were holed to increase their specific surface areas. The CNT Forest was heated to temperatures of 350 to 600 °C at a rate of 1 °C/min in dry air and oxidized by oxygen in air in order to hole the structure.
Kenji Hata (Leader), Super Growth CNT Team, the Nanotube Research Center (Director: Sumio Iijima), Hiroaki Hatori (Senior Research Scientist), Energy Storage Materials Group, the Energy Technology Research Institute (Director: Hiroo Hasegawa), and others of the National Institute of Advanced Industrial Science and Technology (AIST) (President: Tamotsu Nomakuchi) have developed a fibrous material with a specific surface area of 2240 m2/g by using single-walled carbon nanotubes (SWCNTs).
Materials with large specific surface areas are used for energy storage as electricity storage devices including capacitors. They are also used for storage, purification and separation of substances. Many existing materials are brittle and it was difficult to make them into easy-to-handle solids while maintaining their specific surface areas.
In this study, the tips and walls of the aligned SWCNTs synthesized using “Super Growth method” were holed by oxidation. A fibrous material with a specific surface area of 2240 m2/g was produced by this opening process. The specific surface area of the new material is larger than that of porous silica and activated carbon which are exiting materials with high specific surface areas. A prototype capacitor that was fabricated by using this material as its electrodes was found to have a high energy density of 24.7 Wh/kg and a high power density of 98.9 kW/kg.
The performance of the prototype was better than that of conventional capacitors. Furthermore, substances that are included in the SWCNTs can be selected by adjusting the hole diameter, which is controlled by varying the temperature in the opening process. It is expected that this novel electrode material will help realize a compact, light, high-performance capacitor. Further, the material is expected to have a wide variety of applications, ranging from energy storage to substance storage.
AIST is collaborating with Zeon Corporation to develop a technique for the industrial mass production of CNT Forest, which is used to obtain a material with a high specific surface area, and a high-performance capacitor will be developed in collaboration with Nippon Chemi-Con Corporation; these will be carried out under the "Nanotechnology Program: Carbon Nanotube Capacitor Development Program," commissioned by NEDO.
Zeon Corporation is a Japan-based manufacturer that operates in three business segments. The Elastomer segment mainly manufactures and sells synthetic rubber, synthetic latex and chemical compounds. The High-function Materials segment mainly manufactures and sells synthetic perfumes, organic synthetic chemicals, electronic materials, toner-related products and high-function resins. The Others segment offers reaction injection molding (RIM) equipment, medical equipment, vinyl compound, packaging materials and housing materials. Zeon has 48 subsidiaries and eight associated companies.
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