Carbon nanotube composite, bundled wire, method for producing carbon nanotube composite, device for producing carbon nanotube composite, and iron-based catalyst for producing carbon nanotube composite

Abstract

A carbon nanotube composite according to the present invention comprises carbon nanotubes and nanoparticles attached to the carbon nanotubes. The carbon nanotubes include metal-type carbon nanotubes and semiconductor-type carbon nanotubes, and the ratio of the number of the metal-type carbon nanotubes to the total number of the metal-type carbon nanotubes and the semiconductor-type carbon nanotubes is 39% or greater. The nanoparticles include iron.

Description

Carbon nanotube composite, wire assembly, carbon nanotube composite manufacturing method, carbon nanotube composite manufacturing apparatus, and iron-based catalyst for manufacturing carbon nanotube composite

[0001] The present disclosure relates to a carbon nanotube composite, a wire assembly, a method for producing a carbon nanotube composite, an apparatus for producing a carbon nanotube composite, and an iron-based catalyst for producing a carbon nanotube composite. This application claims priority to Japanese Patent Application No. 2024-087381, filed May 29, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] F. Yang, et al., "Chirality-specific growth of single-walled carbon nanotubes on solid alloy catalysts." Nature 510, 522-524 (2014) (Non-Patent Document 1) ７ W ６ It is disclosed that metallic carbon nanotubes having metallic properties can be obtained at a rate of 90% or more by applying a catalyst onto a substrate and heating it together with a carbon source gas in a synthesis furnace.

[0003] International Publication No. 2022 / 181692 (Patent Document 1) and Er-X. Ding, et al., "Highly conductive and transparent single-walled carbon nanotube thin films from ethanol by floating catalyst chemical vapor deposition" Nanoscale 9, 17601-17609 (2017) (Non-Patent Document 2) disclose a floating catalyst chemical vapor deposition method (FC-CVD method) as a method for obtaining single-walled carbon nanotubes with good crystallinity in high yield.

[0004] International Publication No. 2022 / 181692

[0005] F. Yang, et al., “Chirality-specific growth of single-walled carbon nanotubes on solid alloy catalysts.” Nature 510, 522-524 (2014) Er-X. Ding, et al., “Highly conductive and transparent single-walled carbon nanotube thin films from ethanol by floating Catalyst chemical vapor deposition” Nanoscale 9, 17601-17609 (2017)

[0006] A carbon nanotube composite according to the present disclosure includes carbon nanotubes and nanoparticles attached to the carbon nanotubes. The carbon nanotubes include metallic carbon nanotubes and semiconducting carbon nanotubes. The ratio of the number of the metallic carbon nanotubes to the total number of the metallic carbon nanotubes and the semiconducting carbon nanotubes is 39% or more. The nanoparticles include iron.

[0007] FIG. 1 is a transmission electron microscope image of an assembled wire including a carbon nanotube composite according to this embodiment. FIG. 2 is a graph showing an optical absorption spectrum of an assembled wire including a carbon nanotube composite. FIG. 3 is an explanatory diagram illustrating a method for determining chirality (n, m) using an electron beam diffraction image of a single carbon nanotube included in the carbon nanotube composite according to this embodiment. FIG. 4 is a flowchart illustrating a method for producing a carbon nanotube composite according to this embodiment. FIG. 5 is an explanatory diagram schematically illustrating an apparatus for producing a carbon nanotube composite according to this embodiment. FIG. 6 is a graph showing an optical absorption spectrum illustrating the ratio of ferrocenium in an iron-based catalyst for producing a carbon nanotube composite according to this embodiment.

[0008] [Problem to be Solved by the Present Disclosure] It is known that the structure of a single-walled carbon nanotube is determined by specifying its chirality. The electronic state of a single-walled carbon nanotube can be metallic (hereinafter also referred to as "metallic type") or semiconducting (hereinafter also referred to as "semiconducting type") depending on the chirality. For this reason, there is a demand for producing metallic and semiconducting single-walled carbon nanotubes depending on the application. In light of this demand, research and development is being conducted to obtain single-walled carbon nanotubes with an increased ratio (purity) of either metallic or semiconducting type by producing single-walled carbon nanotubes while controlling the chirality.

[0009] The metallic carbon nanotubes obtained by the method described in Non-Patent Document 1 are considered to be industrially ineffective due to their extremely low yield. According to Non-Patent Document 2, the proportion of metallic carbon nanotubes in carbon nanotubes obtained by conventional FC-CVD methods is said to be about 30%. Therefore, it has not yet been possible to increase the proportion of either metallic or semiconducting carbon nanotubes, particularly the proportion of metallic carbon nanotubes, and obtain single-walled carbon nanotubes with a high yield, and development of such a method is highly desired.

[0010] In view of the above circumstances, an object of the present disclosure is to provide a carbon nanotube composite having a high proportion of metal type, an assembly wire, a method for manufacturing a carbon nanotube composite, an apparatus for manufacturing a carbon nanotube composite, and an iron-based catalyst for manufacturing a carbon nanotube composite.

[0011] Effect of the Present Disclosure The present disclosure provides a carbon nanotube composite with a high proportion of metallic type, a wire assembly, a method for producing a carbon nanotube composite, an apparatus for producing a carbon nanotube composite, and an iron-based catalyst for producing a carbon nanotube composite.

[0012] [Description of Embodiments of the Present Disclosure] First, an outline of embodiments of the present disclosure will be described. The present inventors have conducted extensive research to solve the above-mentioned problems and have completed the present disclosure. The present inventors have focused on ferrocene, an iron-based catalyst precursor used in FC-CVD methods, and have conducted research and development. The present inventors have discovered that by using ferrocenium, which is an oxidized version of ferrocene, to produce single-walled carbon nanotubes by FC-CVD methods, a carbon nanotube composite with a high proportion of metallic carbon can be obtained without reducing the yield compared to conventional methods, and have arrived at the present disclosure.

[0013] Next, embodiments of the present disclosure will be described. [1] A carbon nanotube composite according to one aspect of the present disclosure includes carbon nanotubes and nanoparticles attached to the carbon nanotubes. The carbon nanotubes include metallic carbon nanotubes and semiconducting carbon nanotubes. The ratio of the number of metallic carbon nanotubes to the total number of the metallic carbon nanotubes and the semiconducting carbon nanotubes is 39% or more. The nanoparticles contain iron. A carbon nanotube composite having these characteristics has a high metallic content (purity). As a result, when the carbon nanotube composite is formed into a wire, it may be applicable as a highly conductive wire, etc.

[0014] [2] In the carbon nanotube composite according to [1], the ratio is preferably 43% or more. In this case, a carbon nanotube composite having a high ratio of metallic type can be provided.

[0015] [3] A wire assembly according to one aspect of the present disclosure preferably includes the carbon nanotube composite described in [1] or [2]. A wire assembly having such characteristics has a high ratio of metallic carbon nanotubes. Therefore, when processed into a wire, the wire assembly may be applicable as a highly conductive wire or the like.

[0016] [4] A method for producing a carbon nanotube composite according to one embodiment of the present disclosure includes the steps of: preparing a liquid carbon source, ferrocene, a sulfur-containing auxiliary catalyst, and an oxidant; mixing the liquid carbon source, ferrocene, the sulfur-containing auxiliary catalyst, and the oxidant and maintaining the mixture at room temperature for 60 minutes or more to obtain a mixed raw material containing ferrocenium formed by oxidizing the ferrocene; and charging the mixed raw material into a reactor and heating the mixed raw material to 1000°C or higher to cause a reaction, thereby obtaining a carbon nanotube composite. By using this method for producing a carbon nanotube composite, a carbon nanotube composite with a high proportion of metallic carbon can be obtained in good yield.

[0017] [5] In the method for producing a carbon nanotube composite according to [4], it is preferable that a gaseous carbon source is further introduced into the reactor in the step of obtaining the carbon nanotube composite. In this case, a carbon nanotube composite having a high proportion of metallic carbon may be obtained in a higher yield.

[0018] [6] In the method for producing a carbon nanotube composite according to [4] or [5], the oxidizing agent is preferably at least one selected from the group consisting of metal nitrates, metal chlorides, peroxides, and oxoacids. In this case, a carbon nanotube composite having a high proportion of metal type may be obtained in higher yield.

[0019] [7] In the method for producing a carbon nanotube composite according to any one of [4] to [6], the liquid carbon source preferably contains at least one carbon compound selected from the group consisting of alcohols, ketones, and aromatic hydrocarbons, and the carbon compound preferably has 10 or less carbon atoms. In the method for producing a carbon nanotube composite, the sulfur-containing co-catalyst preferably is at least one selected from the group consisting of thiophene, carbon disulfide, octasulfur, and ethylene sulfide. In this case, a carbon nanotube composite with a high proportion of metallic carbon may be obtained in higher yield.

[0020] [8] A carbon nanotube composite manufacturing apparatus according to one embodiment of the present disclosure includes a reactor including a reaction tube and a heating device for heating the reaction tube from the outside, an inlet pipe for supplying a mixed raw material into the reaction tube, and a preparation unit for preparing the mixed raw material to be supplied to the inlet pipe. The mixed raw material includes a liquid carbon source, ferrocenium, a sulfur-containing auxiliary catalyst, and an oxidizer. The carbon nanotube composite manufacturing apparatus having such characteristics allows for the efficient production of carbon nanotube composites with a high metallic ratio.

[0021] [9] In the carbon nanotube composite manufacturing apparatus according to [8], it is preferable that the inlet pipe further supplies a gaseous carbon source into the reaction tube. In this case, a carbon nanotube composite having a high proportion of metallic carbon may be obtained in a higher yield.

[0022]

[10] In the carbon nanotube composite production apparatus according to [8] or [9], the oxidizing agent is preferably at least one selected from the group consisting of metal nitrates, metal chlorides, peroxides, and oxoacids. In this case, a carbon nanotube composite having a high proportion of metal type may be obtained in higher yield.

[0023]

[11] In the carbon nanotube composite production apparatus according to any one of [8] to

[10] , the liquid carbon source preferably contains at least one carbon compound selected from the group consisting of alcohols, ketones, and aromatic hydrocarbons, and the carbon compound preferably has 10 or less carbon atoms. In the carbon nanotube composite production apparatus, the sulfur-containing co-catalyst preferably is at least one selected from the group consisting of thiophene, carbon disulfide, octasulfur, and ethylene sulfide. In this case, a carbon nanotube composite with a high proportion of metallic carbon may be obtained in higher yield.

[0024]

[12] An iron-based catalyst for producing a carbon nanotube composite according to one embodiment of the present disclosure includes ferrocenium. The iron-based catalyst for producing a carbon nanotube composite has at least one absorption peak in a light absorption spectrum obtained by ultraviolet-visible-infrared spectroscopy in a wavelength range of 600 nm to 650 nm, and is used for producing a carbon nanotube composite. The iron-based catalyst for producing a carbon nanotube composite having such characteristics allows carbon nanotube composites with a high proportion of metallic carbon nanotubes to be obtained in good yield.

[0025] [Details of the embodiment of the present disclosure] One embodiment according to the present disclosure (hereinafter also referred to as "the present embodiment") will be described in further detail below, but the present disclosure is not limited thereto. The following description may be made with reference to the drawings, and the same or corresponding elements in the present specification and drawings will be designated by the same reference numerals, and the same description will not be repeated. The drawings are shown with the scale adjusted appropriately to facilitate understanding of each component, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

[0026] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and only a unit is specified for B, the units of A and B are the same. Furthermore, when a compound or the like is expressed in a chemical formula in this specification, if the atomic ratio is not particularly limited, the chemical formula is intended to include any known atomic ratio and is not necessarily limited to only those within a stoichiometric range.

[0027] As used herein, "carbon nanotubes" refers to single-walled carbon nanotubes unless otherwise specified. As used herein, "carbon nanotube composite" refers to a composite containing, in addition to a plurality of carbon nanotubes, a catalyst used in the production of the carbon nanotubes or decomposition products of the catalyst (for example, iron, copper, sulfur, etc., as described below). As used herein, "wire assembly" refers to an assembly (composition) formed by assembling a plurality of the carbon nanotube composites.

[0028] [Carbon nanotube composite] The carbon nanotube composite according to this embodiment includes carbon nanotubes and nanoparticles attached to the carbon nanotubes. The carbon nanotubes include metallic carbon nanotubes and semiconducting carbon nanotubes. The ratio of the number of metallic carbon nanotubes to the total number of the metallic carbon nanotubes and the semiconducting carbon nanotubes is 39% or more. The nanoparticles contain iron. A carbon nanotube composite having these characteristics has a higher ratio (purity) of metallic carbon nanotubes than conventional ones. As a result, when the carbon nanotube composite is made into a wire, it may be suitable for use as a highly conductive wire, etc.

[0029] <Carbon Nanotubes> The carbon nanotube composite contains carbon nanotubes as described above. In this specification, "carbon nanotubes" refers to single-walled carbon nanotubes unless otherwise specified as described above. The term "single-walled carbon nanotubes" may also include cup-stacked carbon nanotubes, which have a structure in which graphene is stacked in the shape of a paper cup with an open bottom.

[0030] Fig. 1 is a transmission electron microscope image of an assembled wire including a carbon nanotube composite according to this embodiment. As shown in Fig. 1, an assembled wire 100 is formed from a plurality of carbon nanotube composites. The carbon nanotube composite includes carbon nanotubes 101 and nanoparticles 102 attached to the carbon nanotubes 101. Details of the assembled wire 100 will be described later.

[0031] The shape of the carbon nanotube is not particularly limited, and may be either closed or open at the end. A cone made of graphene may be formed at one or both ends of the carbon nanotube.

[0032] The length of the carbon nanotubes is not particularly limited and may be appropriately selected depending on the application. The length of the carbon nanotubes may be, for example, 10 μm or more and 600 mm or less, or 100 μm or more and 600 mm or less. The length of the carbon nanotubes is measured using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

[0033] The diameter of the carbon nanotubes is not particularly limited and may be appropriately selected depending on the application. The diameter of the carbon nanotubes may be, for example, 0.6 nm or more, 0.7 nm or more, or 0.8 nm or more. The diameter of the carbon nanotubes may be 10 nm or less, or 5 nm or less. The diameter of the carbon nanotubes is preferably 3 nm or less, and more preferably 2.5 nm or less.

[0034] The "diameter" of the carbon nanotube refers to the outer diameter of a carbon nanotube (hereinafter also referred to as "one carbon nanotube") randomly selected from the plurality of carbon nanotubes 101 constituting the wire assembly 100 that appears in the microscope image shown in FIG. 1 . The method for measuring the outer diameter of one carbon nanotube is as follows. That is, a cross section of one carbon nanotube at a randomly selected location is observed using a TEM or SEM. Furthermore, the distance between the two most distant points on the circumference of the one carbon nanotube in the cross section is determined as the diameter of the carbon nanotube. It is clear from the microscope image shown in FIG. 1 that determining the diameter of a carbon nanotube from a cross section at a randomly selected location on one carbon nanotube makes it extremely unlikely that the diameter will be an abnormal value. When the carbon nanotube includes the cone portion at one or both ends, the outer diameter is measured at a location excluding the cone portion.

[0035] Of the carbon nanotubes constituting the carbon nanotube composite, it is preferable that 85% of the carbon nanotubes, by number, have a "diameter" of 2.5 nm or less. Furthermore, it is preferable that 100% of the carbon nanotubes constituting the carbon nanotube composite have a "diameter" of 3 nm or less. These characteristics are confirmed by randomly selecting 100 carbon nanotubes from a carbon nanotube assembly wire and applying the above-described diameter measurement method to each of the carbon nanotubes.

[0036] (Metallic Carbon Nanotubes and Semiconducting Carbon Nanotubes) As described above, the carbon nanotubes include metallic carbon nanotubes and semiconducting carbon nanotubes. In this specification, "metallic carbon nanotubes" and "semiconducting carbon nanotubes" respectively mean carbon nanotubes having a metallic electronic state and carbon nanotubes having a semiconducting electronic state, and are defined as follows. That is, a "metallic carbon nanotube" refers to a carbon nanotube that exhibits an absorption peak in the energy range of 1.3 eV to 1.8 eV in a graph showing the optical absorption spectrum of the carbon nanotube composite measured using an ultraviolet-visible-near-infrared spectrophotometer. In particular, when a carbon nanotube is represented by a chiral vector (C) expressed by the following formula (1), a carbon nanotube in which "n-m" is a multiple of 3 is defined as a metallic carbon nanotube.

[0037] On the other hand, "semiconducting carbon nanotubes" refer to carbon nanotubes that exhibit absorption peaks in the energy ranges of 0.4 eV to 0.7 eV and 0.7 eV to 1.2 eV in the graph above. When carbon nanotubes are expressed by a chiral vector (C) expressed by the following formula (1), carbon nanotubes in which "n-m" is not a multiple of 3 are defined as semiconducting carbon nanotubes. Chiral vector (C) = na １ +ma ２ (1)

[0038] Here, the "chiral vector (C)" refers to a vector expressed by connecting the following two points. That is, a carbon nanotube has a cylindrical structure in which graphene, which is made up of carbon atoms arranged in a hexagonal plane, is rolled up. In order to seamlessly form a cylindrical carbon nanotube from this planar graphene, it is necessary to overlap one hexagon with another hexagon on the graphene. In this case, the vector connecting the center points of the one hexagon and the other hexagon to be overlapped is called the chiral vector (C). The chiral vector (C) is a vector that is expressed by the basis vector a of the lattice that constitutes the graphene. １ and a ２ and m can be expressed as in the above formula (1). Furthermore, in the above formula (1), the combination of integers (n, m), which are elements constituting the chiral vector (C), is called the chirality (or "chiral index"). By specifying the chirality, the structure of the carbon nanotube is uniquely determined.

[0039] FIG. 2 is a graph showing the optical absorption spectrum of an assembly line including a carbon nanotube composite. In the coordinate system of FIG. 2, the X axis (horizontal axis) represents energy (eV), and the Y axis (vertical axis) represents absorbance. In FIG. 2, assembly line 1 (spectrum represented by a dashed line) and assembly line 2 (spectrum represented by a solid line) have a first absorption peak (hereinafter referred to as "S") in the energy range of 0.4 eV to 0.7 eV. １１ peak) and a second absorption peak in the energy range of 0.7 eV to 1.2 eV (hereinafter referred to as “S ２２ It has a peak. １１ The peak is the S of the semiconducting carbon nanotube. １１ This is an absorption peak due to the band gap. ２２ The peak is the S of the semiconducting carbon nanotube. ２２ This is an absorption peak due to the band gap. Therefore, it is understood that the assembly wire 1 and the assembly wire 2 each contain semiconducting carbon nanotubes.

[0040] Furthermore, in FIG. 2, the assembled wires 1 and 2 have a third absorption peak (hereinafter referred to as “M １１ In particular, M １１ The absorption peaks appear in the energy range of 1.4 to 1.5 eV and in the energy range of 1.5 to 1.8 eV. １１ The peak is the M １１ The absorption peak is due to the band gap. Therefore, it is understood that the assembly wire 1 and the assembly wire 2 each contain metallic carbon nanotubes.

[0041] (Ratio of the number of metallic carbon nanotubes) In the carbon nanotube composite, the ratio of the number of metallic carbon nanotubes to the total number of metallic carbon nanotubes and semiconducting carbon nanotubes is 39% or more. This ratio is preferably 43% or more. This ratio is more preferably 45% or more, and even more preferably 50% or more. Theoretically, the upper limit of the ratio of the number of metallic carbon nanotubes to the total number of metallic carbon nanotubes and semiconducting carbon nanotubes is 100%. However, this ratio may be 99% or less, 95% or less, 90% or less, 80% or less, 70% or less, or 60% or less, respectively.

[0042] In the carbon nanotube composite, the ratio of the number of metallic carbon nanotubes to the total number of metallic carbon nanotubes and semiconducting carbon nanotubes can be determined by the following method, for example, with reference to Figure 3. Figure 3 is an explanatory diagram illustrating a method for determining the chirality (n, m) using an electron diffraction image of a single carbon nanotube contained in the carbon nanotube composite according to this embodiment.

[0043] First, the carbon nanotube composite is manufactured according to a method for manufacturing a carbon nanotube composite, as described below, to obtain the wire assembly. The wire assembly is observed using a TEM (product name (product number): "2200FS" manufactured by JEOL Ltd.), resulting in an electron diffraction image of the individual carbon nanotubes contained in the carbon nanotube composite, as shown in FIG. 3 . Next, the distance δ between the spots of the center line appearing in the electron diffraction image and the distances (d1, d2, d3, etc.) from the center line to the lines other than the center line appearing in the electron diffraction image are measured. Next, the distances (e.g., d2 and d3 in FIG. 3 ) from the center line to two lines (hereinafter also referred to as "measured lines") with the greatest spot intensity are selected. Furthermore, the distance δ between the spots of the center line and the distances d2 and d3 from the center line to the measured lines are substituted into the following formula to determine the chirality (n, m) of the carbon nanotubes appearing in the electron diffraction image. The following formula for calculating the chirality (n, m) varies depending on the distances (d1, d2, d3, etc.) from the selected center line to the lines other than the center line (H. Jiang, et al., Carbon 45, 662 (2007)).

[0044]

[0045] From the chirality (n, m), it is possible to evaluate whether the carbon nanotubes appearing in the electron beam diffraction image are metallic carbon nanotubes or semiconducting carbon nanotubes. Finally, the above-described method is applied to the electron beam diffraction images of the individual carbon nanotubes contained in the carbon nanotube composite that constitutes the assembled wire. From the above, the ratio of the number of metallic carbon nanotubes to the total number of metallic carbon nanotubes and semiconducting carbon nanotubes in the carbon nanotube composite can be determined.

[0046] <Nanoparticles> The carbon nanotube composite contains nanoparticles attached to the carbon nanotubes as described above. The nanoparticles may be the catalyst used to produce the carbon nanotubes or decomposition products of the catalyst (e.g., iron, copper, sulfur, etc., as described below), and have a nano-sized particle size. In the carbon nanotube composite, the nanoparticles contain iron. The nanoparticles may contain sulfur.

[0047] As described below, the catalyst, sulfur-containing auxiliary catalyst, etc. used to produce the carbon nanotubes decompose at the temperature (1000°C or higher) at which the carbon nanotube composite is produced in the reactor. Therefore, decomposition products of the catalyst, sulfur-containing auxiliary catalyst, etc. may exist as nanoparticles attached to the carbon nanotubes when the carbon nanotubes are recovered from the reactor. The shape, size, and diameter of the nanoparticles can be determined by observing them together with the carbon nanotubes using the TEM or SEM described above.

[0048] [Wire Assembly] The wire assembly according to this embodiment includes the carbon nanotube composite. Specifically, as described above, the wire assembly is an assembly formed by assembling a plurality of the carbon nanotube composites. Because the wire assembly has a high proportion of metallic carbon nanotubes, when it is made into a wire, it may be applicable as a highly conductive wire or the like.

[0049] <Shape, Length, and Diameter of Assembly Wire> The shape of the assembly wire is not particularly limited and may be changed appropriately depending on the application. For example, the assembly wire may have a thread-like shape in which a plurality of carbon nanotube composites are assembled and aligned in the longitudinal direction (see FIG. 1 ).

[0050] The length of the wire assembly is not particularly limited and may be changed as appropriate depending on the application. The length of the wire assembly may be, for example, 100 μm or more, 1000 μm or more, or 10 mm or more. There is no particular upper limit to the length of the wire assembly. From a manufacturing standpoint, the length of the wire assembly may be 100 m or less. The length of the wire assembly is measured by observation with a scanning electron microscope, an optical microscope, or visual observation.

[0051] The diameter of the wire assembly is not particularly limited and may be changed as appropriate depending on the application. The diameter of the wire assembly may be, for example, 0.1 μm or more, or 1 μm or more. There is no particular upper limit to the diameter of the wire assembly. From a manufacturing standpoint, the wire assembly may be 100 μm or less. For example, when the diameter of the wire assembly is smaller than the length of the wire assembly, the length direction of the carbon nanotube wire assembly corresponds to the longitudinal direction.

[0052] In this specification, the "diameter" of the wire assembly refers to the average outer diameter of one of the multiple wire assembly (hereinafter also referred to as "one carbon nanotube wire assembly") that appears under a microscope. The average outer diameter of one carbon nanotube wire assembly is measured as follows: A cross section of one carbon nanotube wire assembly at two randomly selected locations is observed with a transmission electron microscope or a scanning electron microscope. Furthermore, the distance between the two most distant points on the circumference of one carbon nanotube wire assembly on the cross section is measured as the outer diameter. Finally, the average value of the outer diameters at the two locations is calculated. This average value corresponds to the diameter of the wire assembly.

[0053] [Method for Manufacturing Carbon Nanotube Composite] The carbon nanotube composite can be manufactured by any suitable manufacturing method. From the viewpoint of yield and the like, the carbon nanotube composite is preferably obtained by the following manufacturing method. That is, the method for manufacturing a carbon nanotube composite according to this embodiment includes the steps of: preparing a liquid carbon source, ferrocene, a sulfur-containing auxiliary catalyst, and an oxidant; mixing the liquid carbon source, ferrocene, the sulfur-containing auxiliary catalyst, and the oxidant and maintaining this mixed state at room temperature for 60 minutes or more to obtain a mixed raw material containing ferrocenium formed by oxidizing the ferrocene; and charging the mixed raw material into a reactor and heating the mixed raw material to 1000°C or higher to cause a reaction, thereby obtaining a carbon nanotube composite. By using this method for manufacturing a carbon nanotube composite, a carbon nanotube composite with a high proportion of metallic carbon nanotubes can be obtained with high yield.

[0054] The present inventors have focused on producing single-walled carbon nanotubes using ferrocenium, which is obtained by oxidizing ferrocene, an iron-based catalyst precursor used in FC-CVD. It has been discovered that in this case, single-walled carbon nanotubes can be obtained with an increased proportion of metallic nanotubes without reducing the yield compared to conventional methods. Hereinafter, each step included in the method for producing a carbon nanotube composite according to this embodiment will be described with reference to FIG. 4. FIG. 4 is a flowchart illustrating the method for producing a carbon nanotube composite according to this embodiment.

[0055] 4, the method for producing a carbon nanotube composite according to this embodiment includes a step S10 of preparing a liquid carbon source, ferrocene, a sulfur-containing auxiliary catalyst, and an oxidizing agent (hereinafter also referred to as a "step S10 of preparing raw materials"). The purpose of the step S10 of preparing raw materials is to prepare various raw materials necessary for obtaining single-walled carbon nanotubes with a higher proportion of metallic nanotubes without reducing the yield compared to conventional methods. In the step S10 of preparing raw materials, a liquid carbon source, ferrocene, a sulfur-containing auxiliary catalyst, and an oxidizing agent are prepared as described above.

[0056] (Liquid Carbon Source) The liquid carbon source can be used in the present production method without any particular limitation, as long as it is a liquid carbon source conventionally used for the purpose of obtaining carbon nanotubes by the FC-CVD method. In particular, the liquid carbon source preferably contains at least one carbon compound selected from the group consisting of alcohols, ketones, and aromatic hydrocarbons. Furthermore, from the viewpoint of improving yield, the carbon compound preferably has 10 or fewer carbon atoms. The alcohol is preferably at least one selected from the group consisting of ethanol, methanol, propanol, and butanol. The ketone is preferably at least one selected from the group consisting of acetone, methyl ethyl ketone, and methyl isobutyl ketone. The aromatic hydrocarbon is preferably at least one selected from the group consisting of toluene, xylene, and benzene. The liquid carbon source is more preferably at least one selected from the group consisting of methanol, ethanol, acetone, toluene, xylene, and 2-propanol. Furthermore, the carbon compound preferably has 7 or fewer carbon atoms. The liquid carbon source may be prepared using a known production method or may be obtained commercially.

[0057] (Ferrocene) When carbon nanotubes are obtained by the FC-CVD method, ferrocene serves as a catalyst precursor. Specifically, ferrocene is oxidized by the oxidizing agent in the next step (step of obtaining a mixed raw material), and a part or all of it is converted to ferrocenium. When carbon nanotubes are obtained, the ferrocenium and a sulfur-containing auxiliary catalyst described below react in a reactor or the like to form a catalyst body, and the catalyst body contributes to the reaction of the liquid carbon source, thereby producing carbon nanotubes. Ferrocene may be prepared using a known production reaction, or may be obtained from the market.

[0058] (Sulfur-containing co-catalyst) When carbon nanotubes are obtained by the FC-CVD method, the sulfur-containing co-catalyst serves as a co-catalyst that supports the catalytic function of the above-mentioned ferrocenium in the reactor. The sulfur-containing co-catalyst can be used in the present production method without any particular limitation, as long as it is a sulfur source used for the purpose of obtaining carbon nanotubes. In particular, the sulfur-containing co-catalyst is preferably a catalyst that can be used to produce thiophene (C ４ H ４ S), carbon disulfide (CS) ２ ), eight sulfur (S ８ ) and ethylene sulfide.

[0059] (Oxidizing Agent) The oxidizing agent serves to oxidize the ferrocene in the next step (the step of obtaining the mixed raw material) to convert it into ferrocenium. This allows single-walled carbon nanotubes to be obtained in this production method without decreasing the yield and with a higher proportion of metallic nanotubes compared to conventional methods. The oxidizing agent is preferably at least one selected from the group consisting of metal nitrates, metal chlorides, peroxides, and oxoacids. Examples of metal nitrates include copper(II) nitrate trihydrate, copper(II) nitrate anhydrous, silver nitrate, and iron(II) nitrate. Examples of metal chlorides include copper(I) chloride, copper(II) chloride, silver(I) chloride, and iron(III) chloride. Other peroxides, such as hydrogen peroxide and sodium peroxide, and oxoacids such as sulfuric acid, nitric acid, and phosphoric acid, can be suitably used as oxidizing agents to oxidize the ferrocene to convert it into ferrocenium.

[0060] <Step of Obtaining Mixed Raw Material> The method for producing a carbon nanotube composite according to this embodiment includes a step S20 of mixing the liquid carbon source, the ferrocene, the sulfur-containing auxiliary catalyst, and the oxidizing agent, and maintaining this mixed state at room temperature for 60 minutes or more to obtain a mixed raw material containing ferrocenium formed by oxidizing the ferrocene (hereinafter also referred to as the "step S20 of obtaining mixed raw material"). The purpose of the step S20 of obtaining mixed raw material is to obtain a mixed raw material containing ferrocenium formed by oxidizing the ferrocene by reacting the oxidizing agent and ferrocene, among the raw materials described above, under predetermined conditions.

[0061] (Mixed Raw Material Containing Ferrocenium) As an example of step S20 for obtaining a mixed raw material, a process for obtaining a mixed raw material containing ferrocenium from ethanol as a liquid carbon source, ferrocene, and a metal nitrate (copper (II) nitrate trihydrate) as an oxidizing agent will be described below. First, a ferrocene-ethanol solution is prepared by adding ferrocene to ethanol. This ferrocene-ethanol solution may contain the sulfur-containing auxiliary catalyst (e.g., thiophene). Next, the metal nitrate (copper (II) nitrate trihydrate) is mixed with the ferrocene-ethanol solution, and this mixed state is allowed to stand (maintain) at room temperature for 60 minutes or more. As a result, the ferrocene in the ferrocene-ethanol solution is oxidized by the metal nitrate (copper (II) nitrate trihydrate) to form ferrocenium. In this oxidation reaction, the ratio of iron (Fe) atoms in ferrocene to copper (Cu) atoms in the metal nitrate (copper (II) nitrate trihydrate) is preferably 0.01 to 1 in terms of Cu / Fe ratio. The Cu / Fe ratio is more preferably 0.1 to 0.5, and may be 0.3. In this manner, a mixed raw material containing ferrocenium is obtained.

[0062] In step S20 of obtaining the mixed raw material, the mixed state of the raw materials described above may be maintained at room temperature for one day or more, two days or more, or four days or more. This increases the degree of oxidation of ferrocene, i.e., the ratio of ferrocenium in the mixed raw material. There is no particular upper limit to the period for which the mixed state of the raw materials is maintained, but considering production efficiency, it may be within seven days at room temperature.

[0063] The presence of ferrocenium in the mixed raw material can be confirmed by the appearance of at least one absorption peak in the wavelength range of 600 nm to 650 nm in the optical absorption spectrum obtained by ultraviolet-visible-infrared spectroscopic analysis. For example, the presence of ferrocenium in the mixed raw material can be confirmed by the appearance of an absorption peak in the wavelength range of 400 to 800 nm in the optical absorption spectrum measured using an ultraviolet-visible-near-infrared spectrophotometer (product name (model number): "Cary5000" manufactured by Agilent).

[0064] <Step of Obtaining Carbon Nanotube Composite> The method for producing a carbon nanotube composite according to this embodiment includes step S30 of obtaining a carbon nanotube composite by charging the mixed raw materials into a reactor and heating the mixed raw materials to 1000° C. or higher to cause a reaction (hereinafter also referred to as "step S30 of obtaining a carbon nanotube composite"). The purpose of step S30 of obtaining a carbon nanotube composite is to obtain a carbon nanotube composite by heating the mixed raw materials described above under appropriate conditions.

[0065] Specifically, in step S30 of obtaining the carbon nanotube composite, the mixed raw material is supplied to a reactor at 1000°C or higher, preferably 1000 to 1500°C, for example, 1040°C, and heated in situ to produce carbon nanotubes. Additionally, in the reactor, the ferrocenium and sulfur-containing auxiliary catalyst are either left intact or decomposed, and some or all of them adhere to the carbon nanotubes, thereby obtaining the carbon nanotube composite. In this reaction, the ratio of iron (Fe) atoms in the ferrocenium and ferrocene to sulfur (S) atoms in the sulfur-containing auxiliary catalyst is preferably 0.1 to 2 in terms of S / Fe ratio. The S / Fe ratio may be 0.3. As a result, the carbon nanotube composite is obtained in good yield.

[0066] In step S30 of obtaining the carbon nanotube composite, a gaseous carbon source may be further introduced into the reactor in order to improve the yield. In this embodiment, the gaseous carbon source and the mixed raw material are supplied in a mixed state to the reactor. That is, the gaseous carbon source and the mixed raw material are supplied in a mixed state to a reactor at a temperature of 1000°C or higher, preferably 1000 to 1500°C, for example, 1040°C, and heated in situ to produce carbon nanotubes. The gaseous carbon source is preferably at least one carbon compound selected from the group consisting of methane, ethane, propane, butane, pentane, hexane, acetylene, and carbon monoxide. In order to improve the yield, the carbon compound preferably has 10 or less carbon atoms.

[0067] The carbon nanotube composite obtained in step S30 of obtaining a carbon nanotube composite has a higher proportion of metallic carbon nanotubes than conventional carbon nanotube composites produced by the FC-CVD method, as explained in the section [Carbon Nanotube Composite] above. Various characteristics of the carbon nanotube composite are as explained in the section [Carbon Nanotube Composite] above, so redundant explanations will not be repeated.

[0068] [Carbon nanotube composite manufacturing apparatus] The carbon nanotube composite can be manufactured using an appropriate manufacturing apparatus. From the viewpoint of yield and the like, the carbon nanotube composite is preferably obtained using the following manufacturing apparatus. That is, the carbon nanotube composite manufacturing apparatus according to this embodiment comprises a reactor including a reaction tube and a heating device that heats the reaction tube from the outside, an inlet pipe that supplies a mixed raw material into the reaction tube, and a preparation unit that prepares the mixed raw material to be supplied to the inlet pipe. The mixed raw material contains a liquid carbon source, ferrocenium, a sulfur-containing auxiliary catalyst, and an oxidizer. A carbon nanotube composite with a high proportion of metallic carbon can be obtained with high yield using a carbon nanotube composite manufacturing apparatus having these characteristics.

[0069] The present inventors have focused on producing single-walled carbon nanotubes using ferrocenium, which is obtained by oxidizing ferrocene, an iron-based catalyst precursor used in FC-CVD, as described above. In this case, the present inventors newly installed a preparation section for preparing a mixed raw material containing ferrocenium in a carbon nanotube composite production apparatus. As a result, they discovered that by supplying the mixed raw material from the preparation section to a reactor through the inlet tube and producing a carbon nanotube composite, single-walled carbon nanotubes with a high proportion of metallic nanotubes can be obtained without reducing the yield compared to conventional methods. Hereinafter, the carbon nanotube composite production apparatus according to this embodiment will be described with reference to FIG. 5. FIG. 5 is an explanatory diagram schematically illustrating the carbon nanotube composite production apparatus according to this embodiment.

[0070] The carbon nanotube composite manufacturing apparatus 10 according to this embodiment includes a reactor including a reaction tube 12 and a heating device 11 that heats the reaction tube 12 from the outside. The manufacturing apparatus 10 further includes an inlet pipe 13 that supplies the mixed raw material into the reaction tube 12, and a preparation unit 14 that prepares the mixed raw material to be supplied to the inlet pipe 13. The inlet pipe 13 is disposed on one side of a first end 12c of the reaction tube 12. In order to supply the mixed raw material to the inlet pipe 13, the preparation unit 14 is also preferably disposed on one side of the first end 12c of the reaction tube 12, similar to the inlet pipe 13. Each component of the manufacturing apparatus 10 will be described below.

[0071] <Reaction Furnace> As described above, the manufacturing apparatus 10 includes a reaction furnace including the reaction tube 12 and the heating device 11 that heats the reaction tube 12 from the outside. In the manufacturing apparatus 10 shown in Fig. 5, the reaction furnace is a horizontal furnace, but this is merely an example. This embodiment also includes an embodiment in which the reaction furnace is a vertical furnace.

[0072] (Reaction Tube) The reaction tube 12 is a cylindrical body where the above-described mixed raw material and carrier gas are introduced to produce a carbon nanotube composite. Because the reaction tube 12 is a cylindrical body, it has a first end 12c, which is one end, and a second end 12d, which is the other end. The introduction tube 13 and the preparation unit 14 are disposed on the first end 12c side of the reaction tube 12. When the FC-CVD method is applied to the production apparatus 10, the above-described mixed raw material is introduced into the interior of the reaction tube 12 from the first end 12c side through the introduction tube 13 together with the carrier gas, and then passes through the interior toward the second end 12d side without stagnation. During this time, a carbon nanotube composite is produced from the mixed raw material. Examples of the carrier gas include hydrogen, nitrogen, argon, and helium.

[0073] Any known material for producing carbon nanotube composites can be used for the reaction tube 12, as long as it has heat resistance and the like sufficient to withstand temperatures up to approximately 1500°C. For example, the reaction tube 12 may be made of at least one material selected from the group consisting of quartz, alumina, mullite, and kanthal. When heated in the reaction tube 12, the components contained in the mixed raw material supplied to the reaction tube 12, such as the liquid carbon source, ferrocenium, and sulfur-containing auxiliary catalyst, are partially or completely thermally decomposed. The thermal decomposition temperature of ferrocenium is approximately 400 to 500°C, the thermal decomposition temperature of a sulfur-containing auxiliary catalyst such as thiophene is approximately 750 to 850°C, and the thermal decomposition temperature of a liquid carbon source such as ethanol is approximately 650 to 750°C.

[0074] (Heating Device) The heating device 11 heats the reaction tube 12 from the outside thereof and includes a heating element that heats the inside of the reaction tube 12 up to a maximum of about 1500° C. An example of the heating device 11 is an electric furnace equipped with a heater as a heating element, but is not limited thereto as long as it includes a heating element that can heat the inside of the reaction tube 12 up to about 1500° C.

[0075] <Inlet Pipe> The production apparatus 10 includes an inlet pipe 13 that supplies the mixed raw material into the reaction tube 12. The inlet pipe 13 is disposed on the first end 12c side of the reaction tube 12. The inlet pipe 13 may be any known metal pipe or the like that can introduce the mixed raw material and carrier gas into the first end 12c of the reaction tube 12 at an appropriate amount and speed, without any particular limitation. The material of the housing that constitutes the inlet pipe 13 is preferably unreactive with the liquid carbon source, ferrocenium, sulfur-containing auxiliary catalyst, oxidant, and ferrocene contained in the mixed raw material.

[0076] It is preferable that the inlet pipe 13 further supplies a gaseous carbon source into the reaction tube 12. In this case, the yield of the carbon nanotube composite may be improved. In this embodiment, the gaseous carbon source and the mixed raw material may be supplied in a mixed state into the reaction furnace. The gaseous carbon source is the same as the gaseous carbon source described in the above section [Method for producing a carbon nanotube composite], so redundant description will not be repeated.

[0077] Furthermore, the gaseous carbon source and the mixed raw material are preferably heated in the inlet pipe 13 to be partially or completely vaporized. In this embodiment, the gaseous carbon source and the mixed raw material can be supplied to the reactor in a mixed state in which they are partially or completely vaporized. In this embodiment, the inside of the inlet pipe 13 is preferably heated to about 120 to 300°C.

[0078] <Preparation Unit> The production apparatus 10 further includes a preparation unit 14 that prepares the mixed raw material to be supplied to the inlet pipe 13. The preparation unit 14 is preferably disposed on the first end 12c side of the reaction tube 12, similar to the inlet pipe 13, in order to supply the mixed raw material to the inlet pipe 13. The shape and size of the preparation unit 14 are not particularly limited as long as it has a space in which the mixed raw material can be prepared. Similar to the inlet pipe 13, the material of the housing that forms the preparation unit 14 is preferably unreactive with the liquid carbon source, ferrocenium, sulfur-containing auxiliary catalyst, oxidant, and ferrocene contained in the mixed raw material.

[0079] The mixed raw material prepared in the preparation unit 14 contains a liquid carbon source, ferrocenium, a sulfur-containing auxiliary catalyst, and an oxidizer. The mixed raw material is the same as the mixed raw material described in the above section [Method for producing a carbon nanotube composite], so a duplicated description will not be repeated. The liquid carbon source, ferrocenium, sulfur-containing auxiliary catalyst, and oxidizer contained in the mixed raw material are also the same as the respective raw materials described in the above section [Method for producing a carbon nanotube composite], so a duplicated description will not be repeated.

[0080] In the case where the above-described method for producing a carbon nanotube composite is applied, the preparation unit 14 is a place where the liquid carbon source, the ferrocene, the sulfur-containing auxiliary catalyst, and the oxidant are mixed and the mixed state is maintained at room temperature for 60 minutes or more, whereby a mixed raw material containing ferrocenium formed by oxidizing the ferrocene can be prepared in the preparation unit 14.

[0081] [Iron-Based Catalyst for Producing Carbon Nanotube Composites] The iron-based catalyst for producing carbon nanotube composites according to this embodiment contains ferrocenium. The iron-based catalyst for producing carbon nanotube composites has at least one peak in its optical absorption spectrum obtained by ultraviolet-visible-infrared spectroscopy that appears in a wavelength range of 600 nm to 650 nm, and is used for producing carbon nanotube composites. By using an iron-based catalyst for producing carbon nanotube composites having such characteristics, carbon nanotube composites with a high proportion of metallic carbon nanotubes can be obtained in good yield.

[0082] (Ferrocenium) The iron-based catalyst for producing a carbon nanotube composite contains ferrocenium. As described above, ferrocenium is produced by oxidizing ferrocene with an oxidizing agent. Specifically, the ferrocenium is produced by oxidizing the divalent iron in ferrocene to trivalent iron. The ferrocenium may be produced by oxidizing ferrocene with the oxidizing agent described above, particularly at least one selected from the group consisting of metal nitrates, metal chlorides, peroxides, and oxoacids, or may be produced in the step of obtaining the raw material mixture described above.

[0083] (Optical Absorption Spectrum) The iron-based catalyst for producing a carbon nanotube composite has at least one absorption peak in the optical absorption spectrum obtained by ultraviolet-visible-infrared spectroscopic analysis, which appears in the wavelength range of 600 nm to 650 nm, and therefore it is understood that the iron-based catalyst for producing a carbon nanotube composite contains ferrocenium produced by oxidation of divalent iron in ferrocene to trivalent iron.

[0084] The higher the ratio of ferrocenium in the iron-based catalyst for producing a carbon nanotube composite, i.e., the higher the ratio of ferrocene oxidized to ferrocenium (oxidation degree), the sharper the absorption peak appears in the optical absorption spectrum. Therefore, it is estimated that when using the iron-based catalyst for producing a carbon nanotube composite, which has an optical absorption spectrum with a sharp absorption peak in the wavelength range of 600 nm to 650 nm, a carbon nanotube composite can be obtained in good yield and with a high ratio of metallic carbon nanotubes.

[0085] Fig. 6 is a graph showing an optical absorption spectrum illustrating the ratio of ferrocenium in the iron-based catalyst for producing a carbon nanotube composite according to this embodiment. Specifically, the graph in Fig. 6 shows an optical absorption spectrum in the wavelength range of 400 to 800 nm measured using an ultraviolet-visible-near-infrared spectrophotometer (product name (model number): "Cary5000", manufactured by Agilent). Hereinafter, the magnitude of the ratio of ferrocenium (the ratio of ferrocene oxidized to ferrocenium (oxidation degree)) in the iron-based catalyst for producing a carbon nanotube composite will be explained with reference to Fig. 6.

[0086] The optical absorption spectrum shown by the dashed line in Fig. 6 is the spectrum of a control solution 61, which was measured using a solution immediately after metal nitrate (copper (II) nitrate trihydrate) was mixed with the ferrocene-ethanol solution. The optical absorption spectrum shown by the dashed line in Fig. 6 is the spectrum of a ferrocenium-containing solution 62, which was measured using a mixed solution prepared by mixing metal nitrate (copper (II) nitrate trihydrate) with the ferrocene-ethanol solution and leaving (maintaining) this mixed state at room temperature for 60 minutes. The optical absorption spectrum shown by the solid line in Fig. 6 is the spectrum of a ferrocenium-containing solution 63, which was measured using a mixed solution prepared by mixing metal nitrate (copper (II) nitrate trihydrate) with the ferrocene-ethanol solution and leaving (maintaining) this mixed state at room temperature for 96 hours (4 days). 6, the iron-based catalyst for producing a carbon nanotube composite corresponding to the mixed solution (ferrocenium-containing solution 63) exhibiting the optical absorption spectrum shown by the solid line has a sharp absorption peak in the wavelength range of 600 nm to 650 nm, indicating a high proportion of ferrocenium. Therefore, it is presumed that the iron-based catalyst for producing a carbon nanotube composite corresponding to ferrocenium-containing solution 63 can produce a carbon nanotube composite with a high yield and a high proportion of metallic carbon nanotubes.

[0087] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited thereto. In these examples, the inventors produced a carbon nanotube composite according to the flowchart of the production method illustrated in FIG. 4, thereby obtaining an assembled wire containing the carbon nanotube composite. The production method was carried out using a production apparatus having a vertical reactor. The inner diameter of the internal space of the reaction tube of the production apparatus used in these examples was 22 mm, and the length was 1000 mm. The length of the heating device 11 (electric furnace) was 900 mm. In the following description, Samples 1 and 2 are examples, and Sample 101 is a comparative example.

[0088] [Manufacturing a wire assembly including multiple carbon nanotube composites] <Sample 1> (Step S10 of preparing raw materials) First, ethanol as a liquid carbon source, ferrocene, thiophene as a sulfur-containing co-catalyst, and metal nitrate (copper (II) nitrate trihydrate) as an oxidant were prepared by purchasing them from the market. These raw materials were then fed into a preparation section 14 provided in the manufacturing apparatus 10.

[0089] (Step S20 of Obtaining a Mixed Raw Material) In the preparation unit 14, ferrocene and thiophene were dissolved in ethanol to prepare a ferrocene-ethanol solution. The ferrocene content in the ferrocene-ethanol solution was set to 0.5% by mass. Furthermore, by adjusting the thiophene content in the ferrocene-ethanol solution, the number of iron atoms N in the ferrocene-ethanol solution was adjusted. Ｆｅ and the number of sulfur atoms, N Ｓ Ratio to N Ｓ / N Ｆｅ was set to 0.3.

[0090] Next, in the preparation section 14, metal nitrate (copper (II) nitrate trihydrate) was mixed with the ferrocene-ethanol solution, and this mixed state was left (maintained) at room temperature for 60 minutes. The amount of metal nitrate (copper (II) nitrate trihydrate) mixed per 100 parts by mass of the ferrocene-ethanol solution was 0.19 parts by mass. As a result, the ferrocene in the ferrocene-ethanol solution was oxidized, and part of the ferrocene was converted to ferrocenium. From the above, a mixed raw material was obtained. The mixed raw material was supplied to an inlet tube 13 for the purpose of being supplied from the preparation section 14 to a reactor (reaction tube 12).

[0091] (Step S30 of Obtaining Carbon Nanotube Composite) The mixed raw material was heated by being introduced from the inlet pipe 13 into a reactor (reaction tube 12) heated to 1040°C. As a result, a carbon nanotube composite was produced from the mixed raw material. Specifically, the mixed raw material and a carrier gas were mixed from the inlet pipe 13 so that the concentration of hydrogen gas as the carrier gas was 28.5% by volume, and then supplied to the reactor (reaction tube 12) at a flow rate of 1400 sccm (approximately 1.4 L / m). At this time, the reaction tube 12 was heated by the heating device 11 (electric furnace) so that the inside thereof reached 1040°C. The temperature from the first end 12c to the second end 12d of the reaction tube 12 was uniformly 1040°C.

[0092] Thereafter, the wire assembly of Sample 1 containing the carbon nanotube composites formed in the reaction tube 12 was collected. TEM observation confirmed that the wire assembly of Sample 1 was composed of a plurality of carbon nanotube composites. The carbon nanotube composites contained carbon nanotubes, iron nanoparticles attached to the carbon nanotubes, sulfur nanoparticles, and copper nanoparticles.

[0093] <Sample 2> Sample 2, an assembled wire containing a plurality of carbon nanotube composites, was obtained in the same manner as Sample 1, except that in step S20 of obtaining the mixed raw material, the mixture obtained by mixing the raw materials was maintained in that mixed state at room temperature for 4 days (96 hours). TEM observation confirmed that the assembled wire of Sample 2 was also formed from a plurality of carbon nanotube composites. The carbon nanotube composite contained carbon nanotubes, iron nanoparticles attached to the carbon nanotubes, sulfur nanoparticles, and copper nanoparticles.

[0094] <Sample 101> Ethanol, ferrocene, and thiophene were prepared as raw materials in the raw material preparation step S10. In other words, no oxidizing agent was prepared. Furthermore, the raw materials were supplied to the inlet tube 13 without going through the mixed raw material preparation step S20, and then supplied from the inlet tube 13 to the reaction tube 12. Except for these changes, an assembled wire containing a plurality of carbon nanotube composites of Sample 101 was obtained in the same manner as Sample 1. TEM observation confirmed that the assembled wire of Sample 101 was also formed from a plurality of carbon nanotube composites. The carbon nanotube composite contained carbon nanotubes, iron nanoparticles attached to the carbon nanotubes, and sulfur nanoparticles.

[0095] [Evaluation] <Diameter of Carbon Nanotube Composites> For Sample 1, Sample 2, and Sample 101, the diameters of the carbon nanotube composites were calculated using the method described above, and the ratio of those with a diameter of 3 nm or less and the ratio of those with a diameter of 2.5 nm or less were determined based on the number of nanotubes. The results are shown in Table 1. In Table 1, the ratios are each expressed as a percentage (%) based on the number of nanotubes.

[0096] <Ratio of metallic carbon nanotubes in carbon nanotube composites> For Sample 1, Sample 2, and Sample 101, the ratio of the number of metallic carbon nanotubes to the total number of metallic carbon nanotubes and semiconducting carbon nanotubes in the carbon nanotube composites (hereinafter also simply referred to as "ratio of metallic carbon nanotubes") was determined by the method described above. The results are shown in Table 1. In Table 1, the ratios are each expressed as a percentage (%) based on the number of nanotubes.

[0097]

[0098] [Discussion] The wire assembly containing multiple carbon nanotube composites of Samples 1 and 2 had a ratio of metallic carbon nanotubes exceeding 39%. On the other hand, the wire assembly containing multiple carbon nanotube composites of Sample 101 had a ratio of metallic carbon nanotubes less than 39%. Therefore, the wire assembly containing multiple carbon nanotube composites of Samples 1 and 2 has a high ratio of metallic carbon nanotubes, and when made into wire, it is expected to be suitable as a highly conductive wire, etc.

[0099] Although the embodiments and examples of the present disclosure have been described above, it is also intended from the beginning that the configurations of the above-described embodiments and examples can be combined as appropriate.

[0100] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0101] 1, 2, 100 Wire assembly, 101 Carbon nanotube, 102 Nanoparticle, 10 Manufacturing apparatus, 11 Heating device, 12 Reaction tube, 12c First end, 12d Second end, 13 Inlet tube, 14 Preparation section, 20, 21, 22 Iron-based catalyst for producing carbon nanotube composite, 61 Control solution not containing ferrocenium, 62, 63 Solutions containing ferrocenium, S10 Step of preparing raw materials, S20 Step of obtaining mixed raw materials, S30 Step of obtaining a carbon nanotube composite.

Claims

1. A carbon nanotube composite comprising: carbon nanotubes and nanoparticles attached to the carbon nanotubes; the carbon nanotubes include metallic carbon nanotubes and semiconducting carbon nanotubes; the ratio of the number of the metallic carbon nanotubes to the total number of the metallic carbon nanotubes and the semiconducting carbon nanotubes is 39% or more; and the nanoparticles contain iron.

2. The carbon nanotube composite according to claim 1, wherein the ratio is 43% or more.

3. An assembly wire comprising the carbon nanotube composite according to claim 1 or 2.

4. A method for producing a carbon nanotube composite, comprising: a step of preparing a liquid carbon source, ferrocene, a sulfur-containing auxiliary catalyst, and an oxidizing agent; a step of mixing the liquid carbon source, the ferrocene, the sulfur-containing auxiliary catalyst, and the oxidizing agent, and maintaining this mixed state at room temperature for 60 minutes or more to obtain a mixed raw material containing ferrocenium formed by the oxidation of the ferrocene; and a step of charging the mixed raw material into a reactor, heating the mixed raw material to 1000°C or higher to cause a reaction, thereby obtaining a carbon nanotube composite.

5. The method for producing a carbon nanotube composite according to claim 4, wherein a gaseous carbon source is further introduced into the reactor in the step of obtaining the carbon nanotube composite.

6. The method for producing a carbon nanotube composite according to claim 4 or 5, wherein the oxidizing agent is at least one selected from the group consisting of metal nitrates, metal chlorides, peroxides and oxoacids.

7. A method for producing a carbon nanotube composite according to any one of claims 4 to 6, wherein the liquid carbon source contains at least one carbon compound selected from the group consisting of alcohols, ketones, and aromatic hydrocarbons, and the carbon compound has 10 or less carbon atoms, and the sulfur-containing co-catalyst is at least one selected from the group consisting of thiophene, carbon disulfide, octasulfur, and ethylene sulfide.

8. An apparatus for producing a carbon nanotube composite, comprising: a reactor including a reaction tube and a heating device for heating the reaction tube from the outside; an inlet pipe for supplying a mixed raw material into the reaction tube; and a preparation section for preparing the mixed raw material to be supplied to the inlet pipe, wherein the mixed raw material contains a liquid carbon source, ferrocenium, a sulfur-containing auxiliary catalyst, and an oxidant.

9. The carbon nanotube composite manufacturing apparatus according to claim 8, wherein the inlet pipe further supplies a gaseous carbon source into the reaction tube.

10. The carbon nanotube composite manufacturing apparatus according to claim 8 or 9, wherein the oxidizing agent is at least one selected from the group consisting of metal nitrates, metal chlorides, peroxides and oxoacids.

11. A carbon nanotube composite manufacturing apparatus according to any one of claims 8 to 10, wherein the liquid carbon source contains at least one carbon compound selected from the group consisting of alcohols, ketones, and aromatic hydrocarbons, and the carbon compound has 10 or less carbon atoms, and the sulfur-containing auxiliary catalyst is at least one selected from the group consisting of thiophene, carbon disulfide, octasulfur, and ethylene sulfide.

12. An iron-based catalyst for producing carbon nanotube composites, which contains ferrocenium, and in which at least one absorption peak in the optical absorption spectrum obtained by ultraviolet-visible-infrared spectroscopic analysis appears in the wavelength range of 600 nm to 650 nm, and which is used in the production of carbon nanotube composites.

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