JP2541434B2 - Carbon nano tube manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a large amount of carbon nanotubes having a narrow aspect ratio and a narrow diameter distribution range in order to realize application to the industrial field, particularly to the electronics industry.

[0002]

2. Description of the Related Art A nanotube is a substance in which a plurality of cylinders, each having a few atomic layers in thickness and rounded atomic planes of graphite-like carbon, are nested, and which is an extremely minute substance having an outer diameter of nm order. The nanotube was discovered in 1991 (Nature 354, 56-58, 199).
1) It is attracting worldwide attention as a material that is expected to have various applications such as one-dimensional wires and catalysts.

Recently, we have discovered a method for the mass synthesis of nanotubes. Generally, in the arc discharge of carbon used for producing nanotubes, plasma is generated in a reaction vessel filled with an inert gas while containing carbon molecular species such as C, C2, and C3. These small carbon species then solidify into larger structures such as soot, fullerenes, nanotubes, or dense solids in the next step. According to the study by the present inventors, it was confirmed that the yield of nanotubes greatly depends on the gas partial pressure in the chamber in which it is formed.
It was found to be optimized between 00 and 2500 torr.
However, since the temperature of the reaction chamber was not controlled, the reaction temperature in the system fluctuated greatly and there was a large temperature gradient.

[0004]

According to the above method, although the yield of nanotubes is high, the size distribution of the product is quite wide and it is difficult to control it. The aspect ratio (length / diameter ratio) distribution was also very wide, 20-1000. When applied to one-dimensional wires, catalysts, etc., narrowing the distribution of the aspect ratio and the distribution of length and diameter are important issues.

The present invention controls the diameter and length of the nanotubes by maintaining the temperature of the plasma, that is, the temperature of the reaction system for producing the nanotubes at a constant temperature, by precisely controlling the temperature of the reaction chamber, The purpose is to narrow the distribution of length and diameter.

[0006]

It is hypothesized that the size of the produced nanotubes depends on the cooling efficiency of the plasma and the chemical reaction rate of carbon condensation. This can be understood from the fact that the nanotubes grow in a vapor phase growth mode, and in this growth mode, temperature control is very important for obtaining a defect-free good quality crystal. The cooling rate of the plasma obviously depends on the temperature of the reaction chamber.
It was found that generating a carbon plasma in a temperature controlled oven significantly improved the quality of the nanotube sample. The synthesizer is shown in FIG. This apparatus comprises a circuit composed of a movable positive electrode 5 and a negative electrode 3 for generating arc discharge plasma 2, a power supply device 10 for these circuits, an oven 1 equipped with a heating / cooling device for covering the electrode portion, and heating of the oven 1. A temperature control device 9 for controlling the cooling device, a chamber 8 for covering the entire oven, an exhaust device 11 for exhausting the inside of the chamber, and a gas introduction device (including a pressure gauge) 12 for sending a rare gas to the chamber. The feature of this apparatus is that it is equipped with an oven 1 capable of heating and cooling a plasma portion and a temperature control device 9 for the oven 1. Using this oven 1,
By controlling the temperature of the plasma portion generated by the nanotubes, it is possible to reduce the size distribution of the nanotubes and dramatically improve the spectrum ratio.

Further, it was found that the nanotubes grow more uniformly when the temperature of the reaction system is kept constant. When the temperature of the reaction system fluctuates, defects such as 5-membered ring and 7-membered ring are formed in the network of the 6-membered ring of the nanotube, and as a result, the ends may be closed or bent (Nature (356, 776-). 77
8, 1992). Preventing this is a factor for obtaining a high-quality carbon nanotube longer than before.

By changing the experimental conditions and performing trials,
It has been found that the plasma temperature varies between 2500 ° C and 4000 ° C. This is the temperature calculated by assuming black-body radiation. The oven temperature can be set to form a constant temperature gradient in the reaction vessel, which can control the cooling rate of the plasma. Therefore, the temperature of the plasma is determined. That is, the growth rate of nanotubes can be controlled under the optimum conditions.

[0009]

EXAMPLE The gas pressure in the reaction vessel was kept constant at 500 Torr of He gas, and a DC voltage of 18 V was applied between two carbon rods 3.5 facing each other in the reaction vessel. The resulting current is approximately 100 A and the solids 4 containing the nanotubes are deposited on the cathode carbon rod. The deposit was then crushed and sonicated in ethanol. Sample size is TEM and SEM
Was evaluated.

Under the following conditions, the temperature condition is 500 ° C. to 40 ° C.
Experiments were carried out by changing the temperature between 00 ° C. (the limit temperature for the device performance), and the results shown in Table 1 were obtained. Table 1 which does not control the temperature of the oven (No oven in the table) is also shown as a comparative example.
It was shown to. The average aspect ratio was better for the samples obtained in the temperature controlled reaction vessel. Reaction system temperature
Although the formation of nanotubes was observed even at 500 ° C,
Yield is always poor and no improvement in aspect ratio
It was Is found in the average length of the nanotubes is high temperature of the reaction system
It became clear that as the temperature increased, the distribution of length and diameter also became narrower as the temperature of the reaction system increased.
Therefore, it has been found that the production of nanotubes under these conditions clearly improves the quality of the sample.

Regarding the gas pressure in the reaction vessel,
Similar results were obtained at 500-2500 Torr.

[0012]

[Table 1]

[0013]

Industrial Applicability According to the production method of the present invention, nanotubes can be produced in high yield and in a large amount in a large amount, and the industrial utility is extremely high in the production of a new material using nanotubes.

[Brief description of drawings]

FIG. 1 is a schematic view of a mass production apparatus for nanotubes.

[Explanation of symbols]

 1 Oven 2 Arc Plasma 3 Negative Electrode 4 Nanotubes 5 Positive Electrode 6 Electron 7 Carbon Molecular Species 8 Reaction Chamber 9 Temperature Control Device 10 DC Power Supply 11 Pump 12 Noble Gas Cylinder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References NATURE, 354-7! (1991) P. 56-58 NATURE, 358-16! (1992) PP. 220-222

Claims (2)

(57) [Claims] 1. When a carbon nanotube is formed by arc discharge in a rare gas to evaporate and then condense carbon to form carbon nanotubes, the temperature range of the reaction system filled with the rare gas is set to 10 degrees.
It is controlled to be constant within the range of 00 ℃ to 4000 ℃.
The temperature of the plasma is reduced by arc discharge while
Normalized and contains carbon nanotubes on the cathode carbon rod
A method for producing a carbon nanotube, which comprises depositing a solid . 2. The temperature range of the reaction system is 2000 ° C. to 400 ° C.
The arc discharge is performed at 0 ° C, and the arc discharge is performed.
A method for producing a carbon nanotube as described.