JP5288511B2 - Catalyst structure and method for producing carbon nanostructure using the same - Google Patents

Description

  The present invention relates to a catalyst structure used for efficiently generating a carbon nanostructure such as a carbon nanotube, and a method for producing a carbon nanostructure using the catalyst structure.

  Conventionally, in the production of carbon nanostructures such as carbon nanotubes, a method has been studied in which a metal capable of permeating carbon is used as a catalyst and a carbon material is grown from the catalyst.

  For example, Patent Document 1 is a method of forming carbon nanotubes on a catalyst layer containing a carburizable metal element, and includes a step of growing the carbon nanotubes upward from a protrusion provided on the catalyst layer. A method for producing carbon nanotubes has been proposed.

  Further, Patent Document 2 discloses a carbon nanostructure manufacturing method in which carbon crystals are grown by vapor phase growth from a crystal growth surface of a catalyst base material containing a catalyst material. Techniques for supplying to are disclosed.

  However, in the method of depositing the carbon material on the catalyst layer so that the carbon permeates the catalyst layer, the carbon material is more uniformly and reliably deposited on the catalyst layer, thereby improving the deposition efficiency of the carbon material. It is demanded to make it.

JP 2006-160592 A JP-A-2005-330175

  The present invention solves the above-described problems and can improve the deposition efficiency when producing a carbon nanostructure composed of carbon crystals by vapor phase growth, and carbon nanostructures using the catalyst structure An object of the present invention is to provide a method for manufacturing a structure.

  The present invention is a catalyst structure used for producing a carbon nanostructure composed of carbon crystals by vapor phase growth, wherein the first surface at least the first metal is exposed and the second surface at least the second metal is exposed. The first metal and the second metal are in contact with each other, and the first metal is made of a material mainly composed of any one selected from iron, cobalt, and nickel, and the second metal Relates to a catalyst structure made of a material containing palladium.

  In the catalyst structure of the present invention, the first metal is preferably made of a material mainly composed of iron.

  The catalyst structure of the present invention is a plate-like body having a first metal, a second metal, and a substrate, the first surface and the second surface being main surfaces, and the first metal, the second metal, The first metal is formed as a plurality of filaments, and the filaments are held by the base material at intervals so that the length direction is the thickness direction of the plate-like body. It is preferable that Moreover, it is preferable that this base material consists of silver or a silver containing alloy.

Moreover, it is preferable that the average diameter of the said filament exists in the range of 1-100 nm.

  The present invention is also a method for producing a carbon nanostructure using any of the above-described catalyst structures, wherein the first surface of the first metal is brought into contact with the first surface by bringing a carbon-containing gas into contact therewith. The present invention relates to a method for manufacturing a carbon nanostructure, which includes a step of causing carbon to penetrate into a second metal from the exposed portion through the inside of the first metal and precipitating carbon crystals from the exposed portion on the second surface of the second metal.

  In the method for producing a carbon nanostructure of the present invention, the carbon nanostructure is preferably a carbon nanotube.

  According to the present invention, by combining the first metal and the second metal whose carbon solubility limit is adjusted, the deposition efficiency when producing carbon nanostructures made of carbon crystals by vapor phase growth is improved. It is possible to provide a catalyst structure that can be produced, and a method for producing a carbon nanostructure using the catalyst structure.

It is sectional drawing shown about the example of a structure of the catalyst structure of this invention.

[Catalyst structure]
The catalyst structure of the present invention is used for producing a carbon nanostructure composed of carbon crystals by vapor phase growth, and includes a first surface where at least a first metal is exposed and a second surface where at least a second metal is exposed. The first metal and the second metal are formed in contact with each other.

  FIG. 1 is a cross-sectional view showing an example of the configuration of the catalyst structure of the present invention. The catalyst structure 100 shown in FIG. 1 has a first metal 11, a second metal 12, and a base material 13, at least the first metal 11 is exposed on the first surface 1, and at least on the second surface 2. The second metal 12 is exposed. The first metal 11 and the second metal 12 are formed in contact with each other. In the catalyst structure 100 shown in FIG. 1, carbon is supplied from the first surface 1 side where the first metal 11 is exposed, and the carbon passes through the inside of the first metal 11 and the second metal 12 to the second surface 2 side. The carbon nanostructure 14 can be deposited from the exposed surface of the second metal 12 on the second surface 2 side. Hereinafter, typical embodiments of each element of the catalyst structure of the present invention will be described.

<First metal>
The first metal is made of a material mainly composed of any one selected from iron, cobalt, and nickel. The material may be an alloy. Since iron, cobalt, and nickel are all metals capable of dissolving carbon, in the catalyst structure of the present invention, the first metal made of a material mainly containing any of these is exposed at least. From one surface, carbon can penetrate into the first metal.

  In the present specification, the solid solubility limit of carbon means the minimum equilibrium concentration at which carbon precipitates when carbon is dissolved. The solid solubility limit of carbon at 1000 ° C. is about 6 atomic% for iron, about 2 atomic% for cobalt, and about 2 atomic% for nickel.

  In addition, in this specification, a main component means the component contained in the quantity exceeding 50 mass% of the whole.

  The material of the first metal is preferably one or more selected from iron, cobalt, and nickel in terms of excellent ability to permeate carbon, but as a component that does not impair the effects of the present invention. For example, palladium, platinum or the like may be contained.

  The first metal is preferably made of a material whose main component is iron because it is particularly excellent in the ability to penetrate carbon.

  The first metal may be formed of a single material, or, for example, includes a plurality of portions having different materials, such as using different materials for a portion of the exposed portion on the first surface and a portion other than the exposed portion. It may be a composite. When the composite is employed, each portion having a different material may be composed of a material mainly composed of any one selected from iron, cobalt, and nickel.

<Second metal>
The second metal is made of a material containing palladium. The material may be an alloy. By forming the second metal so as to be in contact with the first metal, the carbon taken into the first metal is likely to be precipitated as carbon crystals from the exposed surface of the second surface of the second metal.

  The second metal is particularly preferably made of a material whose main component is palladium. In this case, carbon crystals are more likely to precipitate from the exposed surface of the second surface.

  The second metal may be formed of a single material containing palladium, more preferably a single material mainly composed of palladium. For example, a portion of the exposed portion on the second surface and the exposed portion. A composite composed of a plurality of parts having different materials may be used, such as using different materials for other parts. When the composite is employed, each portion having a different material may be composed of a material containing palladium, more preferably a material mainly containing palladium.

<Base material>
As shown in FIG. 1, the catalyst structure of the present invention typically has a first metal, a second metal, and a base material, and the first surface and the second surface form a main surface. Can be made with the body. In this configuration, the base material is formed to hold the first metal and the second metal.

  The plate-like body is penetrated in the thickness direction by the first metal and the second metal, the first metal is formed as a plurality of filaments, and the filaments are mutually connected so that the length direction is the thickness direction of the plate-like body. It is preferable that the substrate is held at an interval. As a result, one end of the filament can be exposed to the first surface, the second metal can be bonded to the other end, and the second metal can be exposed granularly on the second surface. The carbon nanostructure which has can be produced | generated efficiently.

  The average diameter of the filament is preferably in the range of 1 to 100 nm. When the average diameter is 1 nm or more, a filament can be produced relatively easily. When the average diameter is 100 nm or less, carbon nanostructures having a more uniform microstructure can be efficiently generated. The average diameter of the filament is more preferably in the range of 1 to 10 nm.

  Moreover, when a some filament is mutually spaced apart and hold | maintained at a base material, this filament can be arrange | positioned at intervals of about 1-1000 nm in radial direction, for example. When the radial interval between the filaments is 1 nm or more, carbon nanostructures having a more uniform microstructure can be generated at a high density. When the filament spacing is 1000 nm or less, from the substrate surface of the carbon nanostructure filaments The vertical rising shape can be maintained particularly well. More preferably, the radial distance between the filaments is in the range of 1 to 100 nm.

The melting point of the base material is preferably higher than the generation temperature of the carbon nanostructure. In this case, deformation of the catalyst structure during carbon crystal growth hardly occurs, and a uniform-shaped carbon nanostructure can be generated more reliably.

  As the material of the base material, carbon is not substantially dissolved in the carbon in that carbon nanostructures having a more uniform shape can be efficiently generated by controlling the permeation direction of the carbon crystal. A material that does not react with the first metal and does not form a compound or alloy with the first metal is preferable. Typically, silver and silver-containing alloys are preferred because they are inexpensive, easy to process, and chemically stable. As the silver-containing alloy, an Ag—Pd alloy, an Ag—Pt alloy, an Ag—Au alloy, or the like can be preferably used.

[Production of catalyst structure]
The catalyst structure having a shape as shown in FIG. 1 can be formed by, for example, the following method. A solid or hollow thin wire or rod-shaped first metal material is filled into a pipe-shaped base material. By drawing this through a drawing die and plastically deforming it, the diameter is reduced by wire drawing, and the pipe-shaped base material is further filled to reduce the diameter. By repeating the above operation, a filament having a diameter of nanometer level is produced.

  The first metal is formed by cutting both ends of the filament so that the obtained filament has a desired length. The length of the filament can be, for example, about 1 to 1000 μm. When the length of the filament is 1 μm or more, it is easy to produce the catalyst structure, and when it is 1000 μm or less, carbon can be efficiently supplied to the second metal.

  The cut surface is preferably polished by, for example, ion milling or laser beam processing. Thereafter, one of the cut surfaces is covered with a second metal material. In this way, a catalyst structure can be formed.

  As the wire drawing method, a method capable of plastically deforming the first metal material or the composite material of the first metal material and the base material to reduce the diameter can be employed. Is preferably at least one selected from drawing, extrusion, roll, and forging. When two or more of these processes are performed in combination, for example, a material formed into a bar shape or the like is thinned to a certain degree by roll processing, and then further reduced in diameter by drawing or extrusion, or bar-shaped by forging. A method of reducing the diameter by drawing or extruding after embossing the material so as to apply stress in the radial direction of the material and thinning the wire to a certain degree can be employed. When performing diameter reduction processing, it is preferable to appropriately select processing conditions that do not cause rapid plastic deformation in order to prevent deterioration of physical properties of the material.

  Hereinafter, a more specific procedure for producing the catalyst structure will be described. First, in order to form the first metal, a filament is produced by drawing iron. For example, an ultra-high purity iron (purity 99.998% by mass) wire having a diameter of 1 mm is inserted into a pure silver (purity 99.99% by mass) pipe, and the diameter is reduced by wire drawing 1 to iron (Fe) and silver (Ag). To obtain a composite wire. Next, the composite wire is cut into a length of about 50 cm, and 61 bundles are bundled and fitted, inserted into a silver pipe having an outer diameter of 20 mm and an inner diameter of 16 mm, and reduced in diameter by the wire drawing process 2. Thereafter, a softening process is performed by an annealing process (for example, 700 ° C. × 1 hour in a hydrogen / argon mixed gas stream). The fitting, the wire drawing process 2 and the annealing process are repeated until the diameter of the iron (Fe) filament becomes, for example, 10 nm.

The composite wire having an iron (Fe) filament diameter of 10 nm obtained above is cut into a circular shape and polished until the height of the cylinder reaches 50 μm. Further, silver (Ag) is etched using a mixed aqueous solution of hydrogen peroxide and ammonia to expose the iron (Fe) filaments on the two bottom surfaces of the cylinder. By the above operation, a cylindrical composite in which a plurality of iron (Fe) filaments are held on a silver (Ag) base material with an interval of 30 nm can be obtained.

  Furthermore, palladium (Pd) is formed with a thickness of, for example, 10 nm on only one of the bottom surfaces of the composite obtained above by a vapor deposition method such as sputtering. With the above method, the catalyst structure of the present invention can be produced.

  In the present invention, the shape of the exposed portion on the first surface of the first metal can be arbitrarily set. For example, if a tape-like material is used as the ultra-high purity iron wire drawn by the above method, the first metal having a rectangular exposed surface can be formed. In addition, the shape of the first metal can be appropriately designed according to the shape of the target carbon nanostructure.

[Method for producing carbon nanostructure]
The present invention also provides a method for producing a carbon nanostructure using the catalyst structure as described above. In the method for producing a carbon nanostructure of the present invention, by bringing a carbon-containing gas into contact with the first surface, carbon is introduced into the second metal from the exposed portion of the first surface of the first metal through the inside of the first metal. The present invention relates to a method for producing a carbon nanostructure, which includes a step of permeating and precipitating a carbon crystal from an exposed portion on a second surface of a second metal.

  According to the present invention, the shape of the second metal in the catalyst structure can be freely designed, and according to the method for producing a carbon nanostructure of the present invention, various carbon nanostructures can be produced. Specifically, a carbon nanotube, a carbon nanofiber, a carbon nanotape, a carbon nanohorn, etc. can be illustrated preferably, and a carbon nanotube can be illustrated more typically.

  For example, a typical method for producing a carbon nanostructure will be described with reference to an example in which the catalyst structure 100 shown in FIG. 1 is used.

  Examples of the carbon-containing gas to be brought into contact with the first surface for vapor growth of the carbon nanostructure include hydrocarbon gases such as methane gas, propane gas, ethylene gas, and acetylene gas, and alcohols such as methyl alcohol gas and ethyl alcohol gas. Gases generally used for the production of carbon nanostructures such as system gases and carbon monoxide can be used. When the catalyst structure is made of a material having a relatively low deformation temperature, an alcohol-based gas capable of generating a carbon nanostructure at a lower temperature is preferably used. The carbon-containing gas may be used alone or in combination of two or more.

  In the present invention, only the carburizing carbon-containing gas may be brought into contact with the first surface, or a mixed gas of carburizing carbon-containing gas and non-carburizing gas may be brought into contact with the first surface. . Examples of the non-carburizing gas include argon, nitrogen, hydrogen, carbon dioxide, water, and the like.

  Since the generated carbon nanostructure may be decomposed by a carburizing gas or its decomposition gas, a gas that does not substantially alter the generated carbon crystal is formed on the second surface side of the catalyst structure as a carrier gas. It is preferable to supply as. Preferable carrier gases include inert gases such as argon and nitrogen. When the carrier gas as described above is used, the generation of impurities can be suppressed and a carbon nanostructure having a higher purity can be generated. In this case, the carbon-containing gas is not supplied to the vicinity of the second surface of the catalyst structure, and pressure due to the intrusion of carbon from the second surface toward the inside of the catalyst structure is not applied, so that the carbon is supersaturated in the vicinity of the second surface. Thus, the carbon crystal is precipitated efficiently.

In addition, by spraying a combination of a carburizing carbon-containing gas and a non-carburizing gas on the first surface, or by performing a treatment for removing attached carbon by ions such as plasma,
It is preferable to prevent carbon from adhering to the first surface.

  In the present invention, it is preferable to bring a reducing gas into contact with the second surface before or when carbon crystals are precipitated. The second surface of the catalyst structure may be oxidized through the catalyst structure manufacturing process, the surface processing process for the second surface, and the like. By bringing the reducing gas into contact with the second surface, it is possible to remove the metal oxide layer on the surface of the second metal, and to generate the carbon nanostructure in a more uniform shape. Examples of the method of bringing the reducing gas into contact include a method of bringing an atmospheric gas containing hydrogen gas or the like into contact with the second surface.

  The generation temperature of the carbon nanostructure in the present invention is not particularly limited, and may be appropriately selected depending on the properties of the catalyst structure used, the type of the carbon-containing gas, and the like, and is set to about 500 to 960 ° C., for example. be able to. However, depending on the manufacturing conditions, the catalyst structure may be deformed, and impurities may adhere to the first metal or the second metal, resulting in alloying or compounding of the first metal or the second metal, resulting in catalytic activity. There may be a change in quality. In particular, when the exposed portion of the second metal exposed to the second surface is deformed or altered, it is difficult to reliably grow a carbon nanostructure having a desired shape. It is preferable to set the temperature so that the first metal and the second metal are not deformed or altered as much as possible. For example, when the first metal is composed mainly of iron, the generation temperature of the carbon nanostructure is set to not less than the A1 transformation temperature of iron (for example, 723 ° C. which is the A1 transformation temperature of pure iron), particularly not less than 850 ° C. be able to.

  A more typical aspect of the method for producing a carbon nanostructure will be described below. The catalyst structure is inserted into a heat-resistant pressure-resistant heat treatment furnace tube equipped with an electric furnace, a gas introduction / exhaust system, a growth temperature control system, a vacuum control system, a gas flow meter, and the like, which are heating devices. The heat and pressure resistant heat treatment furnace tube is preferably separated into a gas supply side space and a deposition side space by the catalyst structure. In the space on the gas supply side, for example, a partition wall or the like is appropriately provided to adjust the gas flow path to supply the carbon-containing gas. A carrier gas is supplied to the space on the deposition side.

  First, a carrier gas such as argon gas is supplied into the heat and pressure resistant heat treatment furnace tube, and the temperature is set to about 850 ° C., for example. After that, for example, methane gas is allowed to flow as a carbon-containing gas on the gas supply side, for example, for 1 hour, the temperature is gradually lowered to, for example, 500 ° C., the supply of methane gas is stopped, and then the temperature is cooled to room temperature. By the above method, the carbon nanostructure can be generated from the deposition side.

  In the present invention, for the purpose of generating the carbon nanostructure more efficiently, it is preferable to contact the first metal in the ionized state of carbon obtained by decomposition of the carbon-containing gas. Specifically, ionized carbon can be accelerated by an electric field and collide with the first metal. By supplying carbon in an ionized state, the solubility of carbon in the first metal can be improved, and a higher concentration of carbon can be supplied to the second metal, so that the production efficiency of the carbon nanostructure can be improved. .

  As a method of supplying ionized carbon to the first metal, for example, plasma carburizing treatment or the like can be employed. In plasma carburization, ionized carbon is supplied by generating a plasma of carbon-containing gas by applying a voltage between the furnace tube supplied with the carbon-containing gas and the catalyst structure to cause glow discharge. The method of doing etc. can be adopted.

  The carbon nanostructure produced by the production method using the catalyst structure of the present invention has a uniform shape and high purity. For example, it can be used in various applications such as electronic circuits, high-strength composite materials, electric wire materials, and cushion materials. It can be suitably applied.

[Experimental example]
Hereinafter, although an example of an experiment is given and the present invention is explained in detail, the present invention is not limited to these.

A circular iron foil having a thickness of 50 μm and a diameter of 10 mm was prepared. A surface of the iron foil was used as a gas supply surface and a deposition surface, respectively, and a palladium film having a thickness of 100 nm was formed on a part of each surface by a sputtering method to produce an evaluation iron foil. By the above method, the following four fan-shaped regions having the same area were formed on the evaluation iron foil.
Region A Gas supply surface: With palladium film, Precipitation surface: With palladium film Region B Gas supply surface: With palladium film, Precipitation surface: Without palladium film Region C Gas supply surface: Without palladium film, Deposition surface: Region with palladium film D Gas supply surface: no palladium film, deposition surface: no palladium film The iron foil for evaluation described above is set in a heat treatment apparatus capable of supplying gas independently to the gas supply surface and the deposition surface, and carbon is provided on the gas supply surface side. Carbon monoxide (CO) gas as the containing gas and argon gas as the carrier gas were supplied to the deposition surface side, respectively, and held at 850 ° C. for 60 minutes. The deposits were deposited on the gas supply surface and the deposition surface of the evaluation iron foil. Generated.

Observe the generation state of deposits on the gas supply surface and the precipitation surface in the regions A to D with an electron microscope, and separate the area where carbon generation is recognized and the area where carbon generation is not recognized into a black and white pattern. Thus, image analysis was performed by a method for obtaining the ratio of the area in which carbon formation was recognized in the visual field. As a result, the state of deposit formation was as follows.
Region A: The area where carbon formation was observed on the precipitation surface was about 50% of the observation field. Region B: The area where carbon formation was observed on the precipitation surface was about 15% of the observation field. Region C: The area where carbon formation was observed on the precipitation surface was about 80% of the observation field. Region D: The area where carbon formation was observed on the precipitation surface was about 20% of the observation field.

  As a result of Raman spectroscopic analysis of the deposit, the deposit on the gas supply surface was graphite with many defects or amorphous carbon, and the deposit on the precipitation surface was graphite with few defects.

  In the above results for the regions A to D, it is preferable that the generation of deposits on the gas supply surface is less in terms of improving the deposition efficiency of carbon crystals, and the generation of deposits on the precipitation surface is more. preferable. From the comparison between the region A and the region B and the comparison between the region C and the region D, it can be seen that formation of a deposit on the precipitation surface is promoted by forming a palladium film on the precipitation surface. Further, from the comparison between the region A and the region C, when forming a palladium film on the deposition surface, it is better not to use the palladium film on the gas supply surface, which is better in promoting the formation of deposits on the deposition surface. I understand.

  That is, the deposition efficiency of carbon crystals can be improved by forming a palladium film corresponding to the second metal of the present invention on at least the precipitation surface side of the iron foil corresponding to the first metal of the present invention. It can be seen that the effect of improving the precipitation efficiency of the carbon crystal can be obtained particularly well when is formed only on the precipitation surface side.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The carbon nanostructure produced by the production method using the catalyst structure of the present invention can be suitably applied to various applications such as electronic circuits, high-strength composite materials, electric wire materials, and cushion materials.

  100 catalyst structure, 1st surface, 2nd surface, 11 1st metal, 12 2nd metal, 13 base material, 14 carbon nanostructure.

Claims (5)

A catalyst structure used for producing a carbon nanostructure composed of carbon crystals by vapor phase growth,
A plate-shaped body having a first metal, a second metal, and a base material, wherein the first surface where the first metal is exposed at least and the second surface where the second metal is exposed are the main surfaces;
The plate-like body is penetrated in the thickness direction by the first metal and the second metal,
The first metal is formed as a plurality of filaments;
The filaments are held by the base material at intervals so that the length direction is the thickness direction of the plate-like body,
One end of the filament is exposed on the first surface, the second metal is bonded to the other end, and the second metal is exposed on the second surface,
The first metal is made of a material mainly composed of cobalt or nickel,
The second metal is a catalyst structure made of a material containing palladium.   The catalyst structure according to claim 1, wherein the substrate is made of silver or a silver-containing alloy.   The catalyst structure according to claim 1, wherein an average diameter of the filament is in a range of 1 to 100 nm. A method for producing a carbon nanostructure using the catalyst structure according to any one of claims 1 to 3,
By bringing a carbon-containing gas into contact with the first surface, carbon penetrates into the second metal from the exposed portion of the first metal through the inside of the first metal, and the second metal The manufacturing method of a carbon nanostructure including the process of depositing a carbon crystal from the exposed part in the said 2nd surface.   The method for producing a carbon nanostructure according to claim 4, wherein the carbon nanostructure is a carbon nanotube.

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