In United States Patent 7625545, JFE Engineering Corporation (Tokyo, JP) inventors Yasuhiko Nishi, Hirotaka Mukai, Daisuke Ozamoto reveal a process for producing a tape-like material uniformly containing highly pure single-walled or multi-walled carbon nanotubes by a high-performance field emission electrode. The carbon nanotubes are synthesized by arc discharge, wherein an inert gas or inert gas-containing mixed gas is jetted onto a cathode with a carbon material from the inside of a hollow electrode used as an anode, and simultaneously an arc is generated to form a path of arc discharge along a stream of the gas. At the same time, by relative movement of the electrodes, the cathode spot of the arc is rotated on the cathode, and the synthesized carbon nanotubes are formed into a tape. Last year, the JFE Group introduced the first automotive steel incorporating carbon nanotubes for higher strength and lower weight.
FIG. 13 is a schematic illustration showing JFE's arc discharge between carbon material electrodes, including the anodes, performed in processes for producing a tape-like material containing carbon nanotubes and for producing the carbon nanotube.
FIG. 13 shows a process for producing highly pure CNT tapes 31A and 31B in two lines. Hollow carbon electrodes 11A and 11B with an outer diameter of 10 mm and an inner diameter of 4 mm were used as anodes, and a single cylindrical carbon electrode 2A with a diameter of 35 mm was used as the cathode. The cathode spots were moved in spirals with the same pitch on the cathode by linearly moving the hollow carbon electrodes 11A and 11B in a direction of the axis of the cathode while rotating the cathode. The arc discharge was performed at a current of 100 A and a voltage of 20 V (arc length: about 1 mm) in an open space (in a normal atmosphere under atmospheric pressure), using pure argon gas as the gas supplied through the hollow electrodes. Each flow rate of the gas was set at 1 L/min.
FIG. 12 shows scanning electron micrographs (SEM photographs) of a carbon nanotube tape.
After the arc discharge, highly pure CNT is synthesized in a tape form having a width of about 2 to 3 mm and a thickness of about 100 micron in the spiral region on the cathode where the cathode spot had been moved. The width and the thickness of the CNT tape can be varied depending on the form and size of the electrodes and synthesis conditions. FIG. 12 shows SEM photographs (a) and (b) of the resulting highly pure CNT tape. Although spherical pieces of amorphous carbon of about 1 micron are attached on the surface of the tape, the inside of the tape is constituted of aggregate of highly pure carbon nanotubes. Such an amount of amorphous carbon can be easily removed by heat treatment in an oxidizing atmosphere.
FIG. 8 (the table) is a representation of the results of carbon nanotube synthesis with different carbon materials, illustrating the rotating arc process for producing carbon nanotubes.
FIG. 10 is representation of the mechanism of carbon nanotube tape production. This tape-like material was observed with a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and it was thus found that the material was constituted of an aggregate of highly pure carbon nanotubes. It is believed that the production mechanism of the tape-like material, that is, a highly pure carbon nanotube tape or highly pure CNT.
Carbon nanotubes are the subject of a new report by iRAP, Inc that will be published soon. The report examines the activities of more than 160 companies involved in producing carbon nanomaterials and more than 400 companies incorporating those nanotubes into new products. The report thoroughly examines the current state of the carbon nanotube market as well as new manufacturing techniques.
