JP2003137522A - Production method for carbon nanotube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a carbon nanotube uniform in shape and dimension, and also having high purity without needing a complicated refining process. SOLUTION: This method comprises irradiating the ion beam of a catalyst material to the gas of a carbon compound being a raw material of carbon nanotube in a reaction vessel, and generating the carbon nanotube by using an ion in the ion beam as a nucleus.

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 carbon nanotubes having improved shape / dimension uniformity.

[0002]

2. Description of the Related Art Carbon nanotubes (CNTs) are cylindrical substances obtained by rolling a single layer (graphene sheet) of graphite in which carbon 6-membered rings are continuous, and have a diameter of about 1 nm to several tens of nm and a length of about 1 nm. It is about 1 μm. Carbon nanotubes include single-walled carbon nanotubes (SWCNTs) consisting of only one layer and multi-walled CNTs (MWCNT) in which many layers are concentric. Carbon nanotubes may also be referred to as carbon nanofibers.

So far, the characteristics of carbon nanotubes include: (1) shape characteristics (small tip diameter and large aspect ratio), (2) electronic properties (behavior as semiconductor or metal depending on winding and diameter of graphene sheet, etc.), Excellent properties such as (3) high adsorption performance and (4) excellent mechanical properties have been found.

Utilizing these characteristics, for example, a probe of a scanning probe microscope (SPM), an emitter for field emission display (FED), a hydrogen storage material, a negative electrode of a lithium secondary battery, a field effect transistor, a composite material, etc. A wide variety of applications are expected.

Various methods have been proposed so far for producing carbon nanotubes, but as a method particularly suitable for industrial mass production, chemical vapor deposition (CVD) is used.
Law) is drawing attention. In the manufacturing method by the CVD method, a carbon compound gas as a raw material is brought into contact with catalyst particles at 800 to 1200 ° C. to generate carbon nanotubes on the catalyst particles. As the raw material _{gas, CH 4, CO, H 2} /
In addition to CO mixed gas (H ₂ : CO = 1: 3) and the like, acetylene, ethylene, benzene and the like are used, and as the catalyst particles, Fe ₂ O ₃ / Al ₂ O ₃ mixed powder, Fe ₂ O ₃ / SiO ₂ are used. ₂
Mixed powder, Fe (CO) ₅ , Fe, Co, Ni, Co-
Ni or the like is used.

The general manufacturing procedure is as follows: (1) place catalyst powder in a baking dish in a reaction vessel (quartz glass tube, etc.), (2) decompress the vessel with a vacuum pump, and (3) heat to 200 ° C. Volatilizes and removes unnecessary components in the system, (4) 800 to 1 while flowing the source gas
The temperature is raised to 200 ° C. and kept for a predetermined time to produce carbon nanotubes, and (5) after cooling to room temperature, the carbon nanotubes (soot-like products) are taken out.

However, in the conventional method by the above-mentioned CVD method, the obtained carbon nanotubes contain, as impurities, a large amount of carbon such as amorphous carbon and graphite, which has not grown in the tube, in addition to the catalyst substance. Therefore, a purification step for removing these impurities was required as a post-treatment.

As a typical example of this purification step, a product containing carbon nanotubes and impurities is immersed in a 60% nitric acid solution and boiled at 100 to 120 ° C. for about 4 hours, and then the washed recovered product is in the air. Bake at 580-650 ° C. The purity of the carbon nanotubes thus obtained was about 60 to 90%.

As described above, the CVD method is suitable for industrial mass production, but there is a problem that high-purity carbon nanotubes cannot be obtained even if a complicated purification step is performed as a post-treatment. .

On the other hand, as a method other than the CVD method, in the method disclosed in Japanese Patent Laid-Open No. 11-106208, the carbonaceous solid surface is irradiated with an ion beam under high vacuum to generate carbon nanotubes in the irradiated portion. Let This method has the advantage that carbon nanotubes of high purity can be obtained because impurities are not mixed in because the carbon nanotubes are grown from the W-based solid under high vacuum.

However, since the growth is carried out from a solid surface having low reactivity, carbon nanotubes cannot be produced or the size / shape (aspect ratio) of the produced carbon nanotubes becomes non-uniform depending on the irradiation method. There was a problem that things were unavoidable.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing carbon nanotubes of high purity and of uniform size and shape (aspect ratio) without the need for complicated purification steps.

[0013]

In order to achieve the above-mentioned object, the method for producing carbon nanotubes of the present invention is such that an ion beam of a catalytic substance is applied to a gas of a carbon compound as a raw material of carbon nanotubes in a reaction vessel. The irradiation is characterized in that carbon nanotubes are generated by using the ions in the ion beam as nuclei.

According to the present invention, the diameter of the carbon nanotube can be controlled by the ionic mass (ie, the ionic radius), and the length of the carbon nanotube can be controlled by the ion beam accelerating voltage, so that the carbon having a desired size and shape (aspect ratio) can be controlled. Since only carbon nanotubes can be generated, and the generated carbon nanotubes are heavier than the buoyancy received from the atmosphere consisting of the raw material gas and the ions, only the carbon nanotubes freely fall to the bottom of the reaction vessel, which is, so to speak, "gravity sorting." Can be easily separated from the impurities and highly purified.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an apparatus for carrying out the method for producing carbon nanotubes of the present invention. Carbon nanotube manufacturing apparatus 1 according to the present invention
Is a reaction vessel 1 for carrying out a reaction for producing carbon nanotubes.
0, a carbon nanotube recovery chamber 12 provided under the reaction vessel 10, an ionization chamber 14 for ionizing a catalyst substance,
Ions generated in the ionization chamber 14 and the reaction container 10
It is basically composed of a mass separation type ion gun 16 for irradiating inside.

Carbon nanotubes are manufactured by the following procedure using the apparatus shown in FIG.

First, after exhausting the inside of the reaction vessel 10, a gas of a carbon compound as a raw material of carbon nanotubes is introduced into the reaction vessel 10. Reaction vessel 10 after introduction of raw material gas
The internal gas pressure may be about normal pressure (1 atm). As the source gas, CH ₄ , CO, H ₂ / CO mixed gas (H ₂ : CO =
1: 3), acetylene, ethylene, benzene and the like can be used. In general, the raw material gas used for producing carbon nanotubes by the conventional CVD method can be used for the method of the present invention.

The raw material gas in the reaction vessel 10 is heated to and held at the reaction temperature. The reaction temperature is generally 800 to 1200 ° C.
It is a degree.

On the other hand, a catalyst substance is loaded into the ionization chamber 14 and ionized. Catalytic materials are generally particulate (powder)
To prepare. As the catalyst powder, Fe ₂ O ₃ / Al ₂ O ₃ mixed powder, Fe ₂ O ₃ / SiO ₂ mixed powder, Fe (CO) ₅ ,
Fe, Co, Ni, Co-Ni or the like is used. Generally, the catalytic material used in the conventional production of carbon nanotubes by the CVD method can be used in the method of the present invention.

Ions 20 of the catalytic substance generated in the ionization chamber 14 are supplied to the electron gun 16, accelerated in the electron gun 16, and introduced into the reaction container 10 as an ion beam 22. The ion gun 16 is a mass separation type, and by applying an AC voltage to the quadrupole on the same principle as the mass spectrometer,
Ions 22 are formed by selectively accelerating only ions of a predetermined mass number.

When the source gas 24 held at the above reaction temperature is irradiated with the ion beam 22 in the reaction vessel 10, the ion particles 26 (atom-shaped or cluster-shaped) of the catalytic substance forming the ion beam 22 are formed. ) As a nucleus, the carbon nanotube 28 grows. Ion beam 22
Is composed of only the ions 26 having a predetermined ionic mass, that is, an ionic radius as described above, and therefore, the uniformity of the diameter of the carbon nanotubes 28 formed by using the nuclei is extremely high. At the same time, the length of the carbon nanotubes produced can be controlled by controlling the ion beam accelerating voltage, so the uniformity of the shape (aspect ratio) is extremely high.

Further, since it is produced in the reaction system consisting only of the raw material gas and the catalyst ions, no other impurities are mixed. Moreover, since the ionic particles having a predetermined radius are surely generated as nuclei, carbon components other than carbon nanotubes are not generated. Therefore, the purity of the produced carbon nanotube is extremely high.

The generated carbon nanotubes 28 have a weight larger than the buoyancy received from the atmosphere composed of the raw material gas 24 and the ions 26, so that the carbon nanotubes 28 naturally fall and fall.
Deposit in the lower recovery chamber 12. Due to this "gravitational sorting" effect, the recovered carbon nanotubes are further enhanced in purity and uniformity of shape and size.

[0024]

According to the present invention, there is provided a method for producing carbon nanotubes of high purity and having a uniform size and shape (aspect ratio) without the need for complicated purification steps.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an apparatus for carrying out the carbon nanotube manufacturing method of the present invention.

[Explanation of symbols]

1 ... Carbon nanotube production apparatus of the present invention 10 ... Reaction vessel 12 ... Collection room 14 ... Ionization room 16 ... Ion gun 20 ... Catalytic substance ions 22 ... Ion beam 24 ... Raw material gas for carbon nanotubes 26 ... Ion particles irradiated on the source gas 24 28 ... Generated carbon nanotube

Claims (2)

[Claims] 1. A carbon nanotube is produced by irradiating a gas of a carbon compound, which is a raw material for carbon nanotubes, with an ion beam of a catalytic substance in a reaction vessel, with the ions in the ion beam as nuclei. Method for producing carbon nanotubes. 2. The method according to claim 1, wherein the ion beam is formed by accelerating the ions of the catalyst substance by a mass separation type ion gun.