JP2006069805A - Method for manufacturing fine carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a long fine carbon fiber by a thermal CVD method. <P>SOLUTION: A substrate 1 having a catalyst metal layer 3 is treated by the CVD method under the stream of a gaseous starting material containing a reducing gas at a predetermined treating temperature. The mixing ratio of the reducing gas to the gaseous starting material is 0.5-1.5, and the treating temperature is 250-900°C. The gaseous starting material is a hydrocarbon gas or an alcohol gas. The reducing gas is one kind selected from H<SB>2</SB>, NH<SB>3</SB>, O<SB>2</SB>, CF<SB>4</SB>and SF<SB>6</SB>. The substrate 1 has a diffusion prevention layer 4 comprising any of nitrides, oxides or carbides, preferably silicon nitride or silicon oxide between a base body 2 and the catalyst metal layer 3. The substrate 1 is accommodated in a reaction furnace 11, and after filling the gaseous starting material containing the reducing gas and a carrier gas, only the carrier gas is filled. Thereafter, the inside of the reaction furnace is heated to the treating temperature under the gas stream comprising only the carrier gas or the carrier gas and the reducing gas, and the substrate 1 is treated by the CVD method under the gas stream comprising the gaseous starting material containing the reducing gas and the carrier gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing fine hydrocarbon fibers such as carbon nanotubes.

  A carbon nanotube is a cylindrical tube made of carbon and having a diameter on the order of nanometers. Applications of hydrogen storage materials, fuel cell catalyst carriers, field emission display (FED) emitter electrode materials, and other electronic devices are being studied. Has been.

  In order to produce the carbon nanotubes, arc discharge method, thermal chemical vapor deposition method (hereinafter, chemical vapor deposition may be abbreviated as CVD), plasma CVD method, sputtering method, laser ablation method, SiC thermal sublimation method, etc. There is. Among these methods, there is a thermal CVD method as a method for obtaining carbon nanotubes formed by being oriented perpendicularly to the substrate. The thermal CVD method is a method of manufacturing a carbon nanotube by processing a substrate having a catalytic metal layer on the surface thereof at a predetermined processing temperature in an air stream composed of a hydrocarbon gas and a carrier gas (see, for example, Patent Document 1). ).

  Patent Document 1 mentions unsaturated hydrocarbons such as acetylene, ethylene, propylene, and benzene as the hydrocarbon gas. Further, examples of the carrier gas include gases such as argon, helium, nitrogen, and hydrogen, and one or a mixture of two or more of these gases can be used. Describes only examples using argon alone. Moreover, as said process temperature, the range of 700-1000 degreeC is considered suitable.

However, in the above manufacturing method, the obtained carbon nanotubes have defects and bending caused by the defects, or cannot be grown sufficiently because carbon deposits made of amorphous carbon or the like adhere to the surroundings, and the fibers exceed 200 μm. There is an inconvenience that it is difficult to make it long.
JP 2003-277031 A JP 2002-180252 A (page 3, column 3)

  An object of the present invention is to provide a production method capable of solving such inconvenience and obtaining long fine carbon fibers by a thermal CVD method.

  In order to achieve such an object, the production method of the present invention comprises a substrate and a catalytic metal layer formed on the surface of the substrate, which are chemically treated at a predetermined processing temperature in a source gas stream containing a reducing gas. In the method for producing fine carbon fibers by treatment by vapor deposition, the mixing ratio of the reducing gas and the raw material gas (reducing gas / raw material gas) is in the range of 0.5 to 1.5, and the treatment The temperature is in the range of 250 to 900 ° C.

  In the production method of the present invention, the fine carbon fiber is oriented perpendicularly to the substrate by treating the substrate by a chemical vapor deposition (CVD) method at a predetermined treatment temperature in a source gas stream containing a reducing gas. Formed. At this time, since the source gas contains the reducing gas, defects generated in the fine carbon fibers by the reducing gas are eliminated, and the fine carbon fibers grow without bending. Further, since the reducing gas suppresses adhesion of carbon deposits such as amorphous carbon around the fine carbon fibers, the raw material gas can easily come into contact with the catalytic metal layer, and the fine carbon fibers Growth is encouraged.

  Therefore, according to the production method of the present invention, the fine carbon fibers having a long fiber length of 200 μm or more can be obtained on the substrate.

  At this time, if the mixing ratio of the reducing gas and the raw material gas is less than 0.5 or exceeds 1.5, the fiber length of the fine carbon fiber cannot be made 700 μm or more. Further, if the processing temperature of the CVD method is less than 250 ° C., the raw material gas cannot be decomposed, and the production of the fine carbon fibers becomes difficult. If the processing temperature exceeds 900 ° C., the fiber length of the fine carbon fibers is increased. It cannot be 700 μm or more.

In the production method of the present invention, hydrocarbon gas or alcohol gas can be used as the raw material gas. Examples of the reducing gas include one compound selected from the group consisting of H ₂ , NH ₃ , O ₂ , CF ₄ , and SF ₆ .

In the thermal CVD method, the production of carbon nanotubes using a hydrocarbon gas containing H ₂ is described in the literature (see Patent Document 2). In the thermal CVD method described in the above document, a Si substrate with a catalytic metal layer made of Ni on the surface is inserted into an electric furnace and heated to 1200 ° C., methane gas is 30 cc / min, hydrogen gas is 70 cc / min, and argon Gas is circulated at a rate of 400 cc / min for 5 minutes. However, according to the study by the present inventors, at such a high temperature, the fiber length of the fine carbon fiber cannot be made 700 μm or more as described above.

  By the way, since the treatment by the CVD method is carried out at a high temperature within the above range, there is a concern that the catalyst metal layer and the substrate diffuse to each other with time and the catalyst metal is deactivated. Therefore, in the production method of the present invention, it is preferable that the substrate is provided with a diffusion preventing layer for preventing mutual diffusion between the substrate and the catalyst metal layer between the substrate and the catalyst metal layer.

  According to the diffusion preventing layer, mutual diffusion between the catalytic metal layer and the substrate is prevented, so that the catalytic metal layer can maintain catalytic activity and promote the growth of the fine carbon fibers. it can. Examples of the diffusion preventing layer include those made of any of nitride, oxide, and carbide, and more specifically, those made of silicon nitride or silicon oxide.

  Specifically, the manufacturing method of the present invention includes a step of housing the substrate in a reaction furnace, a step of filling the reaction furnace with the source gas containing the reducing gas and a carrier gas, and the reducing gas. A step of filling the reaction furnace with only the carrier gas after filling the raw material gas containing the carrier gas and the carrier gas; and after filling only the carrier gas, under an air flow comprising only the carrier gas or the carrier gas And heating the interior of the reactor to a treatment temperature within the above range under an air stream comprising the reducing gas, and after the heating, the substrate is separated from the source gas containing the reducing gas and the carrier gas. And a step of treating by chemical vapor deposition at the treatment temperature.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 1 is an explanatory sectional view of a substrate used in the manufacturing method of the present embodiment, FIG. 2 is a system configuration diagram showing an example of a CVD apparatus used in the manufacturing method of the present embodiment, and FIG. 3 is a CVD of the manufacturing method of the present embodiment. It is a graph which shows an example of the heat history in a method.

  The method for producing fine carbon fibers according to the present embodiment produces long carbon nanotubes oriented in the direction perpendicular to the surface of the substrate 1 shown in FIG. The substrate 1 may be a substrate in which a catalytic metal layer 3 is directly formed on the surface of a substrate 2 as shown in FIG. 1 (a), and the substrate 2 and the catalytic metal as shown in FIG. 1 (b). A diffusion preventing layer 4 may be provided between the layer 3 and the layer 3.

  For the substrate 2, a conventionally known material such as Si or glass can be used. The metal forming the catalyst metal layer 3 may be a simple substance of Fe, Co, Ni, or an alloy thereof. Also, it may be an alloy of a simple substance or alloy of Fe, Co, Ni and a metal such as W, Mo, Ta, Pt, Cr. The catalytic metal layer 3 can be formed by sputtering, vapor deposition, spin coating or the like, and preferably has a thickness of 100 nm or less.

  In order to prevent mutual diffusion between the substrate 2 and the catalytic metal layer 3, the diffusion prevention layer 4 can be made of any one of nitride, oxide or carbide, and more specifically, silicon nitride, oxide. The thing which consists of silicon etc. can be mentioned. Moreover, the board | substrate 1 may be equipped with the conductor layer etc. under the catalyst metal layer 3 according to a use.

  In the present embodiment, next, the substrate 1 is accommodated in the tubular furnace 11 shown in FIG. 2, and processed by the CVD method at a processing temperature in the range of 250 to 900 ° C. in a hydrocarbon gas stream containing a reducing gas. Do. The tubular furnace 11 is a reaction furnace for processing by the CVD method. As shown in FIG. 2, a gas supply conduit 13 is provided with a heater 12 on the outer periphery and supplies a predetermined gas to the tubular furnace 11 at one end. A gas discharge conduit 14 for discharging gas from the tubular furnace 11 is connected to the other end.

  The gas supply conduit 13 branches to the branch pipes 15a, 15b and 15c on the upstream side, the branch pipe 15a to the carrier gas source 16, the branch pipe 15b to the hydrocarbon gas source 17, and the branch pipe 15c to the reducing gas source 18. Each is connected. Further, the branch pipes 15a, 15b, and 15c are respectively provided with mass flows 19a, 19b, and 19c that circulate gas supplied from the gas sources 16, 17, and 18 to the tubular furnace 11 in a predetermined amount. On the other hand, the gas discharge conduit 14 includes an on-off valve 20.

  As the carrier gas supplied from the carrier gas source 16, an inert gas such as helium, argon or nitrogen can be used. Examples of the hydrocarbon gas supplied from the hydrocarbon gas source 17 include hydrocarbons such as acetylene, methane, ethylene, and benzene, but alcohol may be used in place of the hydrocarbon.

Further, as the reducing gas supplied from the reducing gas source 18, a gas that is thermally decomposed at the treatment temperature within the above range and has an effect of cutting the C—C bond can be used, for example, H ₂ , One compound selected from the group consisting of NH ₃ , O ₂ , CF ₄ , and SF ₆ can be given.

  In the present embodiment, after the substrate 1 is accommodated in the tubular furnace 11, the on-off valve 20 of the gas discharge conduit 14 is closed, and the carrier gas, the hydrocarbon gas, the reducing property are supplied from the gas sources 16, 17, 18. A gas is supplied, and the inside of the tubular furnace 11 is completely replaced with the carrier gas, the hydrocarbon gas, and the reducing gas, so that the carrier gas, the hydrocarbon gas, and the reducing gas are contained in the tubular furnace 11. Fill. Each gas has the same composition as that used when forming the carbon nanotubes described later.

  Next, after opening the on-off valve 20 and exhausting each gas, the on-off valve 20 is closed again. Then, only the carrier gas is supplied from the carrier gas source 16, and the tubular furnace 11 is completely replaced with the carrier gas, whereby the tubular furnace 11 is filled with the carrier gas.

  Next, after opening the on-off valve 20 and discharging the carrier gas, only the carrier gas is supplied again from the carrier gas source 16, and the inside of the tubular furnace 11 is heated to the processing temperature under the flow of the carrier gas. As shown in FIG. 3, for example, the heating is performed by raising the temperature to a treatment temperature or higher in 30 minutes, and then maintaining the treatment temperature by maintaining it in the carrier gas stream for, for example, 20 minutes. The treatment temperature needs to be a temperature at which the hydrocarbon gas is thermally decomposed, and is appropriately selected within a range of 250 to 900 ° C. according to the hydrocarbon gas (750 ° C. in the example of FIG. 3). The heating is performed by supplying the reducing gas from the reducing gas source 18 together with the carrier gas, and completely replacing the inside of the tubular furnace 11 with the carrier gas and the reducing gas. You may carry out in the airflow of mixed gas with this reducing gas.

  Next, when the temperature in the tubular furnace 11 is stabilized at the processing temperature, a mixed gas of the carrier gas, the hydrocarbon gas, and the reducing gas is supplied from each gas source 16, 17, 18 to a predetermined gas. After supplying the composition and completely replacing the inside of the tubular furnace 11 with the mixed gas, the carbon nanotubes are formed on the substrate 1 by holding at the processing temperature for 20 minutes under the mixed gas stream. In the mixed gas, the mixing ratio A (reducing gas / hydrocarbon gas) of the reducing gas and the hydrocarbon gas needs to be in the range of 0.5 to 1.5. In the mixed gas, the mixing ratio B (reducing gas / carrier gas) between the hydrocarbon gas and the carrier gas is, for example, in the range of 0.04 to 0.08. In order to obtain the composition, for example, when the total flow rate is 230 sccm (standard cc per minute), the carrier gas has a flow rate of 200 to 210 sccm, the hydrocarbon gas has a flow rate of 10 to 20 sccm, The flow rate of the reducing gas is 10 to 15 sccm.

  And after the said time passage, it cools as shown in FIG. As a result, it is possible to obtain a long carbon nanotube with few defects and bends and a fiber length of 700 μm or more on the substrate 1. Next, examples of the present invention and comparative examples will be described.

  In Example 1, the substrate 1 having the configuration shown in FIG. 1A is accommodated in the tubular furnace 11 shown in FIG. 2, and the carrier gas, the hydrocarbon gas, and the like from each gas source 16, 17, 18, A CVD process was performed by supplying a mixed gas with the reducing gas.

  In the substrate 1, a catalytic metal layer 3 made of Fe and having a thickness of 50 angstroms is directly formed on a base 2 made of Si. In the mixed gas, helium is used as the carrier gas, acetylene is used as the hydrocarbon gas, and hydrogen is used as the reducing gas.

  In the CVD process, after the substrate 1 is accommodated in the tubular furnace 11, the on-off valve 20 of the gas discharge conduit 14 is closed, and helium, acetylene, and hydrogen are supplied from the gas sources 16, 17, 18 to form carbon nanotubes described later. The tube furnace 11 was filled with helium, acetylene, and hydrogen by completely replacing the inside of the tube furnace 11 with helium, acetylene, and hydrogen.

  Next, after opening the on-off valve 20 and discharging each gas, the on-off valve 20 is closed again, only helium is supplied from the carrier gas source 16, and the inside of the tubular furnace 11 is completely replaced with helium. The furnace 11 was filled with helium. Next, after opening the on-off valve 20 and discharging helium, only helium is supplied again from the carrier gas source 16, and the inside of the tubular furnace 11 is heated to a processing temperature of 750 ° C. for 30 minutes under a helium stream, The mixture was held at a helium stream for 20 minutes to stabilize the treatment temperature.

Next, when the temperature in the tubular furnace 11 is stabilized at the processing temperature, a mixed gas of helium, acetylene, and hydrogen is supplied from each gas source 16, 17, 18 to the reducing gas (hydrogen). The mixing ratio A (H ₂ / C ₂ H ₂ ) with the hydrocarbon gas (acetylene) is 1, and the mixing ratio B (H ₂ / He) between the reducing gas and the carrier gas (helium) is 0. 0.048 was supplied and the inside of the tubular furnace 11 was completely replaced with the mixed gas, and then the processing temperature was maintained for 20 minutes under the mixed gas stream to form carbon nanotubes on the substrate 1. Then, it was allowed to cool.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 1]
In Comparative Example 1, after the temperature in the tubular furnace 11 was stabilized at the processing temperature, a mixed gas of helium, acetylene, and hydrogen was supplied from each gas source 16, 17, 18 to the mixing ratio A (H ₂ / C ₂ H ₂ ) was 0.3, and the composition was supplied in such a manner that the mixing ratio B (H ₂ / He) of the reducing gas to the carrier gas (helium) was 0.053. The carbon nanotubes were formed on the substrate 1 in exactly the same manner as in FIG.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 2]
In Comparative Example 2, after the temperature in the tubular furnace 11 is stabilized at the processing temperature, a mixed gas of helium, acetylene, and hydrogen is supplied from each gas source 16, 17, 18 to the mixing ratio A (H ₂ / C ₂ H ₂ ) is 3, and the composition ratio of the reducing gas and the carrier gas (helium) B (H ₂ / He) is 0.158, and the composition is supplied as in Example 1. Carbon nanotubes were formed on the substrate 1 in exactly the same manner.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 3]
In Comparative Example 3, after the temperature in the tubular furnace 11 was stabilized at the processing temperature, helium and acetylene were supplied from the gas sources 16 and 17 in the composition shown in Table 1, and a mixed gas containing no hydrogen was used. Except for the above, carbon nanotubes were formed on the substrate 1 in exactly the same manner as in Example 1.

  Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.

  In Examples 2 to 4, carbon nanotubes were formed on the substrate 1 in the same manner as in Example 1 except that the substrate 1 having the configuration shown in FIG. In the substrate 1, a catalytic metal layer 3 made of Fe and having a thickness of 50 Å is formed on a base 2 made of Si via a diffusion prevention layer 4 made of silicon nitride (SiN) and having a thickness of 3000 Å.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 4]
In Comparative Example 4, carbon nanotubes were formed on the substrate 1 in exactly the same manner as in Comparative Example 1, except that the substrate 1 having the configuration shown in FIG.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 5]
In Comparative Example 5, carbon nanotubes were formed on the substrate 1 in exactly the same manner as in Comparative Example 2, except that the substrate 1 having the configuration shown in FIG.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 6]
In Comparative Example 6, after the temperature in the tubular furnace 11 was stabilized at the processing temperature, helium and acetylene were supplied from the gas sources 16 and 17 in the composition shown in Table 1, and a mixed gas containing no hydrogen was obtained. Except for the use, carbon nanotubes were formed on the substrate 1 in exactly the same manner as in Comparative Example 4.

Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.
[Comparative Example 7]
In Comparative Example 7, carbon nanotubes were formed on the substrate 1 in exactly the same manner as in Example 2 except that the treatment temperature was 1000 ° C.

  Table 1 shows the treatment conditions and the fiber length of the obtained carbon nanotubes.

表１から、処理温度７５０℃で、前記混合ガスにおいて前記還元性ガス（水素）と前記炭化水素ガス（アセチレン）との混合比Ａ（Ｈ_２／Ｃ_２Ｈ_２）が０．５〜１．５の範囲にあり、前記還元性ガスと前記キャリヤガス（ヘリウム）との混合比Ｂ（Ｈ_２／Ｈｅ）が０．０４〜０．０８の範囲にある場合（実施例１〜４）には繊維長が７００〜１０００μｍとなり、長尺のカーボンナノチューブが得られることが明らかである。

From Table 1, at a treatment temperature of 750 ° C., the mixing ratio A (H ₂ / C ₂ H ₂ ) of the reducing gas (hydrogen) and the hydrocarbon gas (acetylene) in the mixed gas is 0.5 to 1. When the mixing ratio B (H ₂ / He) of the reducing gas and the carrier gas (helium) is in the range of 0.04 to 0.08 (Examples 1 to 4). It is clear that the fiber length is 700 to 1000 μm, and long carbon nanotubes can be obtained.

  On the other hand, when the mixing ratio A is less than 0.5 (Comparative Examples 1 and 4) or when the mixing ratio A exceeds 1.5 (Comparative Examples 2 and 5), the fiber length is 700 μm. It is clear that long carbon nanotubes cannot be obtained.

  Further, when the reducing gas is not included at all (Comparative Examples 3 and 6), and even when the reducing gas is included and the treatment temperature exceeds 900 ° C. (Comparative Example 7), the fiber length is all. It is clear that it is less than 700 μm, and long carbon nanotubes cannot be obtained.

Explanatory sectional drawing of the board | substrate used for the manufacturing method of this invention. The system block diagram which shows an example of the CVD apparatus used for the manufacturing method of this invention. The graph which shows an example of the thermal history in CVD method of the manufacturing method of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Base | substrate, 3 ... Catalyst metal layer, 4 ... Diffusion prevention layer, 11 ... Reactor, 17 ... Hydrocarbon gas source, 18 ... Reducing gas source.

Claims (7)

In a method for producing a fine carbon fiber by treating a substrate comprising a substrate and a catalytic metal layer formed on the surface of the substrate by a chemical vapor deposition method at a predetermined treatment temperature under a source gas stream containing a reducing gas,
The mixing ratio of the reducing gas and the source gas (reducing gas / source gas) is in the range of 0.5 to 1.5, and the treatment temperature is in the range of 250 to 900 ° C. A method for producing fine carbon fibers.   2. The method for producing fine carbon fibers according to claim 1, wherein the source gas is a hydrocarbon gas or an alcohol gas. _3. The fine carbon fiber according to claim 1, wherein the reducing gas is one compound selected from the group consisting of H ₂ , NH ₃ , O ₂ , CF ₄ , and SF ₆ . Production method.   The said board | substrate is equipped with the diffusion prevention layer which prevents the mutual diffusion of this base | substrate and this catalyst metal layer between the said base | substrate and the said catalyst metal layer. The manufacturing method of the fine carbon fiber of Claim 1.   5. The method for producing fine carbon fibers according to claim 4, wherein the diffusion preventing layer is made of any one of nitride, oxide or carbide.   6. The method for producing fine carbon fibers according to claim 5, wherein the diffusion preventing layer is made of silicon nitride or silicon oxide. Accommodating the substrate in a reactor;
Filling the reaction furnace with the source gas containing the reducing gas and a carrier gas;
Filling the reaction furnace with only the carrier gas after filling the source gas containing the reducing gas and the carrier gas;
After filling only the carrier gas, heating the inside of the reactor to a treatment temperature in the above range under an air stream consisting only of the carrier gas or an air stream consisting of the carrier gas and the reducing gas;
2. The method according to claim 1, further comprising a step of treating the substrate by chemical vapor deposition at the treatment temperature in an air stream comprising the source gas containing the reducing gas and the carrier gas after the heating. The manufacturing method of the fine carbon fiber of any one of Claim 6.

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