JP2005047763A - Carbon nano- and micro-meter structures and method for manufacturing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To separately manufacture carbon nano-substances, each having a uniform shape/structure and size, in a high yield with high productivity; and to provide the carbon nano-substances having new structures. <P>SOLUTION: Nano- and micro-meter carbon structures, each having a fiber-like shape or a tubular shape can be formed by using, as templates, porous materials such as an anodically oxidized film or an electrolytically etched film of aluminum, having nano- or micro-meter level pores, then infiltrating/filling an organic polymer compound such as polyvinylchloride, which is liquefied in a process of carbonization by thermal decomposition, into template pores of a nano- or micro-meter level in the liquefying stage, and carbonizing. A high productivity can be obtained by mixing each porous material in a flaky or crushed state with the organic polymer compound powder, and reacting the resulting mixture. In each formed carbon structure, a graphene sheet is orientated in the direction nearly perpendicular to the major axis direction of the structure and forms a laminate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to nanometer and micrometer level fiber-like and tube-like carbon structures, so-called carbon nano, microstructures, and methods for producing the same.

In recent years, elucidation of the fine structure and physical properties of nano-level carbon structures such as carbon nanotubes and carbon nanofibers has been promoted, and various attempts have been made to apply the physical properties together with the nano-sized structure.
For example, FED electrodes using the field emission effect due to their conductivity and nano-level structure, application to probe electrodes, etc., or applications from hollow structures as foreign material inclusion materials, capacitors that have a large surface area Although there is no time for enumeration, etc., all these applications of nanocarbon materials are related to the structure and physical properties, and different structures have different physical properties. It is necessary to obtain a nanostructure with a high yield.

For this reason, a laser ablation method and a CVD (chemical vapor deposition) method have been developed as a method for producing carbon nanomaterials and a method for producing a larger amount of carbon nanomaterials.
However, the carbon nanomaterials formed by these methods have various sizes and shapes, so that they can be separated from the accompanying amorphous carbon and fibrillated entangled carbon nanomaterials. Therefore, it is difficult to obtain a carbon nanomaterial having a substantially sufficient yield and a target structure.
The creation of carbon nanomaterials with the desired structure and the improvement in yield were fundamental issues in the application of these carbon nanomaterials.

As an improvement measure, a method of growing carbon nanomaterials using a porous material having nano-level fine pores as a template has been proposed.
T.A. Kyotani, L .; Tsai, and A.A. Tomita, Chem. Mater. , 7 (1995) 1427-8 T.A. Kyotani, L .; Tsai, and A.A. Tomita, Chem. Mater. , 8 (1996) 2109-2113 Non-Patent Documents 1 and 2 impregnate a mixture of furfuryl alcohol and oxalic acid on an alumina membrane filter having a pore size of several hundreds of nanometers and a thickness of about 60 μm. A carbon nanotube of the same size as the above pore diameter was created using this porous material as a template by heat treatment at 3 ° C. for 3 hours, and an oxide film having a small pore diameter of 3 nm and a thickness of 75 μm was added to 2.5% propylene. -It has been reported that carbon nanotubes having the same diameter as the template were produced by heating at 800 ° C in a nitrogen mixed gas. The obtained carbon nanotubes had a structure in which the carbon hexagonal network surface was along the tube major axis direction.

Japanese Patent Laid-Open No. 2003-146632 In addition, in Patent Document 3, a polymer film in which a fine hole having a diameter of several tens to several hundreds of nanometers and a depth of 1 to several tens of μm is formed by etching after ion irradiation and ion irradiation is also used. The shape of the template is obtained by applying a monomer such as acrylonitrile or a derivative thereof, filling the fine holes, polymerizing and carbonizing or graphitizing at 800 to 3000 ° C. It has been disclosed to obtain carbon nanotubes that retain the same. These carbon nanotubes were multi-walled carbon nanotubes in which a graphene sheet was rounded into a cylindrical shape. According to these methods, carbon nanotubes having a linear diameter and a uniform structure are formed. These carbon nanotube production methods can create nanomaterials with uniform shapes, structures, and sizes, but each of the resulting nanomaterials has a typical carbon hexagonal network along the long axis of the nanotube. Although the carbon nanotubes are high and the yield is improved, the productivity cannot always be improved due to the structure of the template.

  The present invention provides a template that is easy to make and has good productivity as a manufacturing method for separately creating nanomaterials with uniform shapes, structures, and sizes, and a new manufacturing method with high productivity and yield using the template, and a novel method thereby Carbon nanomaterials with a unique structure are provided.

The present invention uses a porous material having a pore size of nanometer and micrometer level as a template,
Fiber or tube-shaped, characterized in that an organic polymer compound liquefied in the process of carbonization by pyrolysis is permeated and filled in the template nano- and micrometer-level template pores in the liquefaction stage and then carbonized. In which the porous material template is in the form of flakes or strips, and the organic polymer compound is mixed with the organic polymer compound in the above-described process in the above process. As well as
As the porous material, an aluminum anodic oxide film and an aluminum etching film are adopted,
The organic polymer compound is PVC (polyvinyl chloride), PVA (polyvinyl alcohol), or PAA (polyacrylamide),
The nano and micrometer carbon structures formed by the above method are formed by laminating carbon hexagonal network surfaces (graphene sheets) oriented substantially perpendicular to the major axis direction of the structure.

  Further, the present invention provides a fiber or tube-like nano, micrometer, characterized in that the carbon hexagonal mesh surface (graphene sheet) is oriented and laminated in a direction substantially perpendicular to the long axis direction of the fiber or tube. It is a carbon structure.

The carbon nanostructure material manufacturing method of the present invention uses a porous material such as an anodic oxide film that can be easily obtained by a known method as a template, and is mixed with a carbon raw material in the form of flakes or strips as a liquid phase reaction process. As it progresses, high production efficiency and yield can be expected compared to those by vapor phase methods such as CVD.
The porous material used as these templates is formed into a film on the substrate, but when used as a template, it is cut and crushed to a size suitable for the reaction process, for example, in mm units or less. By using thin pieces and thin pieces of the size, it can be handled as a mixed phase mixed with the raw material polymer powder, and it is possible to adopt a process with high productivity and suitable for mass production.
This process does not require metal catalysts such as CVD, and can only obtain carbon nanostructured materials with high purity in size and shape, or depending on the manufacturing conditions, carbon at the fiber, tube, nano, or micrometer level Nanostructured materials can be created separately.
In addition, the present invention is a novel process using a liquid phase of a liquefied polymer, and the formed carbon nanostructure material is a laminate of carbon hexagonal network graphene structures perpendicular to the long axis of the tube or fiber. Thus, the graphene sheet lamination surface, which is a so-called cross section of these graphites, forms the surface of the fiber or tube.
These surfaces are physicochemically active, and new applications of their physical properties are expected.

The present invention utilizes the property that certain organic polymer compounds such as PVC, PVA, and PAA are liquefied in the process of thermal decomposition, and the aluminum porous anodic oxide film having a pore size of nanometer level or micrometer level. Using a porous material such as an aluminum electrolytic etching foil with a pore size as a template, these micro-sized pores are infiltrated and filled with a raw material in the liquefaction stage to carbonize them, and nano and micro using these pores as templates. It forms a carbon structure at the meter level.
Organic polymer materials that are liquefied in the process of carbonization by such thermal decomposition or exhibit fluidity in the form of pitch are not limited to the examples given in this specification, but liquefaction of these organic polymer compounds. Many combinations are possible based on the fluidity and wettability of the template material, the size of the target carbon structure, the aspect ratio, etc., so these conditions are set according to the target carbon nanostructure material. It can be selected as appropriate.

The nano- and micro-carbon structures formed by this process have a structure in which hexagonal net-like graphene sheets are laminated in a direction substantially perpendicular to the major axis of fibers, tubes, and the like.
Such a structure is different from a structure in which graphene sheets are rounded in a cylindrical shape or aligned along the long axis direction like nanofibers formed by the same method as nanotubes and carbon fibers by CVD method, etc. The so-called cross section of the sheet is arranged along the side surfaces of these nano- and micro-structures to form the outer surface thereof.
Although the details of the physical properties of these surfaces have not yet been elucidated, their structures are expected to have high chemical and physical activity, and future applications are expected.

Aluminum anodic oxide films and aluminum etching foils are suitable as templates having nano- and micrometer-level pore diameters, respectively, but the sizes such as the pore diameter and aspect ratio can be changed and selected depending on the production conditions.
Also, the template material can be used as long as it is a porous material having pores of the same size as those of the aluminum oxide film and satisfies predetermined conditions such as withstanding the formation conditions of the precursor.

Also, as described later, when PVC and PVA are used as the carbon nanocarbon structure raw material, the structure formed is different, and when PVC is used, nanofibers are formed, but when PVA is used as the raw material, It becomes a nanotube. This is considered to be due to the viscosity at the time of liquefaction derived from both raw materials, but by utilizing such a difference in properties, it is possible to make different nanostructures to be generated according to these raw materials. .
As described above, although there is a difference in the nanostructure formed by the raw material, in principle, any organic polymer polymer that can be liquefied in the thermal decomposition process as the raw material can be adopted.

Formation of carbon nanostructure An aluminum foil having a purity of 99.99% was electropolished and anodized in a 0.3 mol dm ^-3 oxalic acid solution to form a porous film.
The electric field conditions were bath temperature: 0 ° C., current density: 5 mAcm ⁻² , 3 h, bath temperature: 17 ° C., constant voltage: 40 V, 10 h.
After the porous film is formed, the metal film is dissolved in a bromine-methanol solution to take out the oxide film, which is immersed in a 5 mass% phosphoric acid solution for 2 hours to dissolve the hole bottom called a barrier layer to form a tunnel-like hole. .
This was washed and dried to obtain a template composed of a flaky film having tunnel-like holes having a hole diameter of 60 to 90 nm and a depth of several to 10 μm.

A ratio of 0.1 to 0.2 g of powder of polyvinyl chloride (PVC: Sekisui Chemical TS-1000R) or polyvinyl alcohol (PVA: Unitika UP-180) per 1 cm ^{2 of} flaky template The mixture was put in an alumina boat, heated to 300 ° C. at a heating rate of 400 Kh ⁻¹ in an argon atmosphere, held for 30 min, further heated to 600 ° C. and held for 1 h.
After cooling, the product was immersed in a 10 mass% sodium hydroxide solution to dissolve the template to obtain a precursor of a carbon nanostructure.
The SEM image of the precursor by the obtained PVA is shown in FIG. 1 (scale is 1 μm). The diameter was almost the same as that of the above template regardless of the raw material, and the length was slightly shorter at 3 to 5 μm for PVC and 3 μm for PVA.
These precursors were further heated to 1500 ° C. at a heating rate of 300 Kh ⁻¹ in an argon atmosphere, held for 1 h, and heat-treated to obtain carbon nanostructures.

The structure of these precursors is amorphous carbon according to X-ray diffraction. However, when it is further heat treated at 1500 ° C. for 1 h in an argon atmosphere, it has a layered structure carbon similar to graphite having a layer spacing of 0.345 nm on the carbon 002 plane. (Referred to as “turbulent structure carbon”).
The SEM images of the carbon nanostructures by PVC and PCA are shown in FIGS. 2 (A) and 2 (B), respectively.
The yield was about 5% in the case of PVC and PVA, but a yield of about 20% was achieved when polyacrylamide (PAA) was used.

  FIGS. 3A and 3B show TEM images and HRTEM lattice images of carbon nanostructures using PVC as a raw material. These structures are in the form of dense fibers or filaments. In FIG. 3B, the vertical direction is the major axis direction of the nanostructures. From the lattice image, the nanofibers made from PVC are carbon hexagonal networks. It can be seen that the surface is a platelet type with the surface almost perpendicular to the major axis direction.

  4A and 4B are TEM images and HRTEM lattice images of carbon nanostructures using PVA as a raw material, respectively, and have a hollow tube shape as shown in the TEM image of FIG. In addition, as shown in FIG. 4B, the carbon hexagonal network surface is slightly inclined but has a large angle in the major axis direction.

Formation of Carbon Microstructure An aluminum electrolytic etching foil industrially produced for electrolytic capacitors was used as a template. Although it is a so-called aluminum etch foil, it has a porous structure with innumerable tunnel-like pores of μm size and can be easily obtained.
The organic polymer compound serving as the carbon source and the production conditions are the same as in the case of Example 1, but a microstructure having a diameter of 1 μm or less and a length of several tens of μm is obtained in accordance with the template form. It was.
The structure was almost the same as that of the above-mentioned PVC except for the size, and was a structure in which carbon hexagonal networks were laminated in a direction perpendicular to the long axis direction of the fiber.

  The nano- and micro-carbon structures of the present invention still have many aspects that have to wait for the elucidation of their physical properties. However, due to their expected chemical and physical activity and fine structure, the lithium-ion battery negative electrode material, A wide range of applications such as multilayer capacitors or storage materials such as hydrogen and methane are expected.

SEM image of the precursor made from PVA. (A): SEM image of carbon nanostructure carbonized at 1500 ° C. after treatment at 600 ° C. using PVC as a raw material, (B): Carbon nanostructure carbonized at 1500 ° C. after treatment at 600 ° C. using PVA as a raw material SEM image of the body. TEM image (A) and HRTEM lattice image (B) of carbon nanostructures made from PVC. TEM images (A) and HRTEM lattice images (B) of carbon nanostructures made from PVA.

Claims (7)

A porous material with a pore size of nanometer and micrometer level is used as a template.
Fiber or tube-shaped, characterized in that an organic polymer compound liquefied in the process of carbonization by pyrolysis is permeated and filled in the template nano- and micrometer-level template pores in the liquefaction stage and then carbonized. Method of forming nano, micrometer carbon structures. The porous material template is in the form of flakes or strips, and the organic polymer compound is mixed with this in the above process as a powder,
A method of forming a fiber or tube-like nano, micrometer carbon structure according to claim 1. The porous material is an aluminum anodic oxide film,
A method of forming a fiber or tube-like nano, micrometer carbon structure according to claim 1 or 2. The porous material is an aluminum etching film,
A method of forming a fiber or tube-like nano, micrometer carbon structure according to claim 1 or 2.   5. The method for forming a fiber or tube-like nano / micrometer carbon structure according to claim 1, wherein the organic polymer compound is PVC, PVA, or PAA. The nano, micrometer carbon structure is characterized in that a carbon hexagonal network surface (graphene sheet) is oriented and oriented substantially perpendicular to the major axis direction of the structure,
A method of forming a fiber or tube-like nano, micrometer carbon structure according to claims 1-5.   A fiber or tube-like nano / micrometer carbon structure characterized in that a carbon hexagonal mesh surface (graphene sheet) is oriented and laminated in a direction substantially perpendicular to the long axis direction of the fiber or tube.

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