JP2018172268A - Carbon nanotube assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CNT aggregate having a low resistivity comparable to a wire rod made of copper or aluminum and excellent thermal stability. SOLUTION: This is a carbon nanotube aggregate composed of a plurality of carbon nanotubes having a layer structure of one or more layers, and any one of 2 to 6 layers occupying the total number of carbon nanotubes constituting the carbon nanotube aggregate. The ratio of the total number of each multi-walled carbon nanotube having the layer structure of is 70% or more, the carbon nanotube aggregate contains at least one additive element of boron and nitrogen, and the content ratio thereof is contained in the carbon nanotube aggregate. The carbon nanotube aggregate is characterized in that the ratio of the number of atoms to the carbon atoms is 1 to 10%, and the rate of increase in resistance after heat treatment at 150 ° C. for 1 hour is 35% or less. [Selection diagram] Fig. 1

Description

  The present invention relates to an aggregate of carbon nanotubes composed of a plurality of carbon nanotubes.

  Conventionally, as power lines and signal lines in various fields such as automobiles and industrial equipment, electric wires composed of a core wire made of one or a plurality of wires and an insulating coating covering the core wire have been used. As the material of the wire constituting the core wire, copper or a copper alloy is usually used from the viewpoint of electrical characteristics, but in recent years, aluminum or an aluminum alloy has been proposed from the viewpoint of weight reduction. For example, the specific gravity of aluminum is about 1/3 of the specific gravity of copper, and the electrical conductivity of aluminum is about 2/3 of the electrical conductivity of copper (pure aluminum is about 66% IACS when pure copper is used as the standard of 100% IACS). Yes, to allow the same current to flow through the aluminum wire as the copper wire, the cross-sectional area of the aluminum wire must be about 1.5 times the cross-sectional area of the copper wire. Even if a large aluminum wire is used, the mass of the aluminum wire is about half of the mass of the pure copper wire, so the use of the aluminum wire is advantageous from the viewpoint of weight reduction.

  Based on the above background, in recent years, higher performance and higher functionality of automobiles, industrial equipment, etc. are being promoted, and with this increase in the number of various electrical equipment, control equipment, etc. There is also a tendency for the number of wirings of electrical wiring bodies used in these devices to increase. On the other hand, in order to improve the fuel efficiency of moving bodies such as automobiles for environmental reasons, it is strongly desired to reduce the weight of wires.

  As one of the new means to achieve such further weight reduction, a new technology that uses carbon nanotubes (hereinafter sometimes abbreviated as “Carbon Nano Tube” as “CNT”) as a wire rod is proposed. Has been. CNT is a three-dimensional network structure composed of a single layer of a cylindrical body having a mesh structure of a hexagonal lattice, or a multilayer arranged substantially coaxially, and it is lightweight and has conductivity, current capacity, elasticity Because of its excellent properties such as mechanical strength, it has attracted attention as a material that can replace metals used in power lines and signal lines.

The specific gravity of CNT is about 1/5 of the specific gravity of copper (about 1/2 of aluminum), and CNT alone is theoretically higher than copper (resistivity 1.68 × 10 ⁻⁶ Ω · cm). Shows conductivity. Therefore, theoretically, if a plurality of CNTs are twisted to form a CNT aggregate, further weight reduction and high electrical conductivity can be realized. However, when a CNT aggregate in units of μm to mm is produced by twisting CNTs in nm units, there is a problem that contact resistance between the CNTs or internal defect formation is a factor and the resistance value of the entire wire increases. For this reason, it has been difficult to use CNT as a wire as it is.

  Therefore, as one of the methods for improving the conductivity of the CNT aggregate, a method has been proposed in which the CNT network structure (chirality) of the structural unit CNT is controlled and the CNT is doped.

  For example, there is a method of performing doping treatment on at least one kind of dopant on two-layer and multi-layer CNTs. In this method, when forming CNTs or after forming CNT aggregates, doping treatment is performed by sputtering, spraying, immersion, or gas phase introduction, iodine, silver, chlorine, bromine, fluorine, gold, copper, aluminum, A CNT aggregate (wire material) having a dopant containing sodium, iron, antimony, arsenic, or a combination thereof is prepared. Thereby, it is said that electrical characteristics such as high specific conductivity, low resistivity, and high conductor allowable current can be obtained (for example, Patent Document 1).

  However, when the CNT wire having the dopant as described above is subjected to heating such as heat treatment (about 200 to 100 ° C.) in its use process, the dopant physically present in the CNT network structure is There is a problem that the resistivity is remarkably increased due to separation from the network structure.

Special table 2014-517797 gazette

  An object of the present invention is to provide a CNT aggregate having a low resistivity comparable to a wire made of copper or aluminum and an excellent thermal stability.

  As a result of intensive research on CNTs to which other elements are added, the present inventors have obtained a CNT aggregate composed of a plurality of CNTs having a layer structure of one or more layers, all of which constitute the CNT aggregate. The ratio of the total number of each multi-layer CNT having a layer structure of any of 2 to 6 layers in the number of CNTs is 70% or more, and the CNT aggregate contains at least one additive element of boron and nitrogen, The content ratio is 1 to 10% in terms of the number of atoms with respect to the carbon atoms contained in the CNT aggregate, and the resistance increase rate after heat treatment at 150 ° C. for 1 hour is 35% or less. And the present invention has been completed based on this finding.

That is, the gist configuration of the present invention is as follows.
[1] A carbon nanotube aggregate composed of a plurality of carbon nanotubes having a layer structure of one or more layers,
The ratio of the total number of each multi-walled carbon nanotube having a layer structure of 2 to 6 layers, accounting for 70% or more of the total number of carbon nanotubes constituting the carbon nanotube aggregate,
The carbon nanotube aggregate includes at least one additive element of boron and nitrogen, and the content ratio thereof is 1 to 10% in terms of the number of atoms with respect to the carbon atoms contained in the carbon nanotube aggregate,
An aggregate of carbon nanotubes, wherein the rate of increase in resistance after heat treatment at 150 ° C. for 1 hour is 35% or less.
[2] A carbon nanotube aggregate composed of a plurality of carbon nanotubes having a layer structure of one or more layers,
The ratio of the total number of each multi-walled carbon nanotube having a layer structure of 2 to 6 layers, accounting for 70% or more of the total number of carbon nanotubes constituting the carbon nanotube aggregate,
The carbon nanotube aggregate includes at least one additive element of boron and nitrogen, and the content ratio thereof is 1 to 10% in terms of the number of atoms with respect to the carbon atoms contained in the carbon nanotube aggregate,
The aggregate of carbon nanotubes, wherein at least a part of the additive element is covalently bonded to a carbon atom constituting the carbon nanotube.
[3] The above-mentioned [1], wherein the ratio of the total number of each multi-walled carbon nanotube having a layer structure of any of 2 to 6 layers in the total number of carbon nanotubes constituting the aggregate of carbon nanotubes is 90% or more. Alternatively, the carbon nanotube aggregate according to [2].
[4] From the above [1] to [3], the ratio of the total number of multi-walled carbon nanotubes having a two-layer structure or a three-layer structure to the total number of carbon nanotubes constituting the carbon nanotube aggregate is 70% or more. ] The carbon nanotube aggregate according to any one of the above.
[5] The ratio according to [4], wherein the ratio of the total number of each multi-walled carbon nanotube having a two-layer structure or a three-layer structure to the total number of carbon nanotubes constituting the carbon nanotube aggregate is 90% or more. Carbon nanotube aggregate.
[6] Any one of the above [1] to [5], wherein at least a part of the additive element exists between layers of the multilayer carbon nanotube layer structure and is covalently bonded to the carbon atom. An aggregate of carbon nanotubes described in 1.
[7] The carbon nanotube according to [6], wherein an average interatomic distance between the additive elements present between layers of the layer structure, measured along the longitudinal direction of the multilayer carbon nanotube, is 50 to 500 nm. Aggregation.

  According to the present invention, the thermal stability is remarkably improved as compared with the conventional CNT aggregate, and the resistivity equivalent to that of copper or aluminum can be realized, and the electrical characteristics and thermal stability can be improved. It is possible to provide a significantly improved CNT aggregate.

FIG. 1 is a diagram schematically showing a configuration of a CNT aggregate according to an embodiment of the present invention. (A) and (b) are a perspective view of the aggregate and an electron microscope image, and (c) and (d) ) Is an enlarged view of a bundle of CNTs and an electron microscope image thereof, and (e) and (f) are perspective views of the CNTs constituting the bundle of CNTs and an electron microscope image thereof. FIG. 2 is an X-ray absorption spectrum of the CNT aggregate according to the embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of the CNT of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Fig.1 (a)-(f) is a figure which shows schematically the structure of the CNT aggregate | assembly which concerns on embodiment of this invention. Note that the CNT aggregate in FIG. 1 shows an example, and the shape, dimensions, and the like of each component according to the present invention are not limited to those in FIG.

  As shown in FIGS. 1A and 1B, the CNT aggregate 1 according to this embodiment is composed of a plurality of CNT bundles 11, 11,... Having a layer structure of one or more layers. These bundles of CNTs are twisted together. The outer diameter of the CNT aggregate 1 is preferably 0.01 to 1 mm.

  As shown in the enlarged views of FIGS. 1C and 1D, the bundle 11 of CNTs is a bundle of a plurality of CNTs 11a, 11a,. The direction is almost aligned.

  The CNTs 11a constituting the CNT bundle 11 are cylindrical bodies having a single-layer structure or a multi-layer structure, and are called SWNT (single-walled nanotube) and MWNT (multi-walled nanotube), respectively. In FIGS. 1 (c) to (f), only a multi-layer CNT having a two-layer structure is shown for convenience, but actually, a single-wall CNT having a one-layer structure or each layer structure having three or more layers is used. Multilayer CNTs may be present. In addition, in this specification, when it is simply described as “CNT”, it is a case where a single-layer structure CNT and a CNT having a multilayer structure of two or more layers are not distinguished, and when it is described as “multilayer CNT” This is a case where it is limited to CNTs having a multilayer structure of two or more layers.

  The CNT 11a is a three-dimensional network structure in which two cylindrical bodies T1 and T2 having a hexagonal lattice network structure are arranged substantially coaxially, and is called DWNT (Double-walled nanotube). The hexagonal lattice, which is a structural unit, is a six-membered ring in which a carbon atom is arranged at the apex, and these are continuously bonded adjacent to another six-membered ring.

  The property of the CNT 11a depends on the chirality of the cylindrical body as described above. Chirality is broadly divided into armchair type, zigzag type, and other chiral types. Armchair type is metallic, chiral type is semiconducting, and zigzag type shows intermediate behavior. Therefore, the conductivity of CNTs varies greatly depending on which chirality is present, and in order to improve the conductivity of CNT aggregates, it has been important to increase the proportion of armchair CNTs that exhibit metallic behavior. It was. On the other hand, it has been found that doping a chiral CNT having semiconducting properties with a substance (heterogeneous element) having an electron donating property or an electron accepting property exhibits a metallic behavior. In addition, in general metals, doping of different elements causes scattering of conduction electrons inside the metal, resulting in a decrease in conductivity. Similarly, when metallic CNTs are doped with different elements. , Causing a decrease in conductivity.

  Thus, since the doping effect on metallic CNT and semiconducting CNT can be said to have a trade-off relationship from the viewpoint of conductivity, theoretically, metallic CNT and semiconducting CNT are produced separately. In addition, it is desirable to combine these after performing doping treatment only on the semiconducting CNTs. However, it is difficult to selectively produce metallic CNT and semiconducting CNT selectively with the current manufacturing technique, and the metallic CNT and semiconducting CNT are produced in a mixed state. For this reason, in order to improve the conductivity of the CNT aggregate composed of a mixture of metallic CNTs and semiconducting CNTs, it is indispensable to select a CNT structure in which doping treatment with different elements / molecules is effective.

  Therefore, in this embodiment, in order to obtain a CNT aggregate having a low resistivity, the CNTs having a number of layers that can maximize the effect of the doping treatment are configured to have a predetermined ratio, and the CNT aggregate An appropriate amount of a predetermined additive element is contained in the element, and at least a part of the additive element is covalently bonded to the carbon atoms constituting the CNT.

In the present embodiment, in the CNT aggregate 11 composed of an aggregate of a plurality of CNTs 11a, 11a,..., Any one of 2 to 6 layers in the total number of CNTs 11a, 11a,. The ratio of the total number of each multi-walled CNT having 70 is 70% or more, preferably 90% or more. That is, the total number of all CNTs constituting one CNT aggregate is N _TOTAL , and the sum of the numbers of multilayer CNTs having any one of 2-6 layers among all the CNTs is defined as N _{CNT (2)} , N _{CNT (3)} , N _{CNT (4)} , N _{CNT (5)} and N _{CNT (6)} can be expressed by the following formula (1).
(N _{CNT (2)} + N _{CNT (3)} + N _{CNT (4)} + N _{CNT (5)} + N _{CNT (6)} ) / N _TOTAL × 100 (%) ≥ 70 (%) (1)

In addition, a multi-walled CNT having a small number of layers such as a two-layer structure or a three-layer structure has a relatively higher conductivity than a multi-walled CNT having a larger number of layers. Therefore, in this embodiment, in the CNT aggregate 11 composed of an aggregate of a plurality of CNTs 11a, 11a,..., A two-layer structure or a three-layer structure occupying the total number of CNTs 11a, 11a,. The ratio of the total number of the multi-walled CNTs is preferably 70% or more, and more preferably 90% or more. In this case, the ratio can be expressed by the following formula (2).
(N _{CNT (2)} + N _{CNT (3)} ) / N _TOTAL × 100 (%) ≧ 70 (%) (2)

  Conventionally used dopants such as iodine are usually introduced into the innermost layer of the multi-walled CNTs or into the gaps between the CNTs formed by a plurality of CNTs. The interlayer distance of the multilayer CNT is equivalent to 0.335 nm, which is the interlayer distance of graphite, and it is difficult in terms of size for the dopant to enter the interlayer of the multilayer CNT. Therefore, in the CNT using the conventional dopant, the doping effect is manifested by introducing the dopant into and outside the CNT, but particularly in the case of the multi-layer CNT, it is located inside the outermost layer and the innermost layer. In the tube, the dope effect is hardly exhibited.

  In contrast, nitrogen and boron, which are additive elements in the present invention, are completely different from the conventional dopant. In other words, the conventional dopant exhibits a doping effect by physically interposing or adhering inside and outside of the CNT, but nitrogen and boron used in the present invention are part of the carbon atoms constituting the CNT. By substituting and accompanied by chemical bonds (covalent bonds) with surrounding carbon atoms, it is considered that the doping effect is more stably exhibited. Furthermore, since nitrogen and carbon have a smaller atomic size than conventional dopants such as iodine, they may be able to intervene between the layers of multi-walled CNTs. Expression is expected.

  In particular, in the present invention, nitrogen or boron is bridged by a covalent bond between carbon and carbon constituting each layer between the layers of the multilayer CNT having any one of 2 to 6 layers. It is considered that a conductive path can be formed. Furthermore, in the case of multilayer CNT having a two-layer structure or a three-layer structure, it is considered that the CNTs contribute to the formation of a bundle having a hexagonal close-packed structure. Such a structure is considered to further improve the conductivity, and it is presumed that the doping effect in the multilayer CNT having the two-layer structure or the three-layer structure is the highest. Therefore, in the present invention, attention is focused on the total number of multilayer CNTs having any one of 2 to 6 layers included in the CNT aggregate, and further on the total number of multilayer CNTs having a two-layer structure or a three-layer structure.

  In addition, when the ratio of the total number of each multi-layer CNT having a layer structure of any of 2 to 6 layers in the total number of CNTs constituting the CNT aggregate is less than 70%, a single-layer structure or 7 layers or more The ratio of CNTs having a multilayer structure is increased, the doping effect is reduced as a whole of the CNT aggregate, and the resistivity tends to increase.

  In the present embodiment, the CNT aggregate includes at least one additive element of boron and nitrogen. Moreover, the content ratio of such an additional element is an atomic ratio with respect to the carbon atoms contained in the CNT aggregate, and is 1 to 10%. As a result, N-type or P-type CNTs are obtained and the conductivity is increased.

  The content ratio of the additive element can be evaluated by semi-quantitative analysis by X-ray photoelectron spectroscopy (X-ray Photoelectron Spectroscopy). Specific measurement conditions will be described on the example page.

  In particular, the CNT aggregate of the present embodiment is characterized in that at least a part of the additive element is covalently bonded to the carbon atoms constituting each CNT 11a. That is, at least a part of the additive element replaces a part of the carbon constituting the six-membered ring, which is a structural unit of CNT, or a defective part.

  In a CNT aggregate having a conventional dopant, the dopant is only physically held or attached inside or outside (surface) of the network structure, which is a structural unit of CNT, and is not covalently bonded. Such a chemically strong bond was not involved. Therefore, when the CNT aggregate having such a conventional dopant is subjected to a heat treatment of about 200 to 100 ° C., for example, the dopant is detached from the inside or outside of the CNT network structure, and the resistivity is abrupt. Invited to rise.

  In contrast, the CNT aggregate of the present embodiment is different from the conventional CNT aggregate having a dopant, and at least a part of the additive element is a part of carbon constituting a six-membered ring that is a structural unit of CNT, Alternatively, it is covalently bonded to an adjacent carbon atom so as to replace the defect portion, and is incorporated in the CNT molecular chain as an element constituting the CNT network structure. Therefore, even after the heat treatment as described above, the additive elements are not easily detached from the CNT network structure, and excellent electrical conductivity can be maintained well, compared with the conventional CNT aggregate. Stability can be greatly improved.

  Note that the fact that at least a part of the additive element is covalently bonded to the carbon atom constituting the CNT network structure includes, for example, a nitrogen-carbon covalent bond from the absorption energy position of the X-ray absorption energy of the nitrogen element. Can be confirmed.

Specifically, CNTs are placed under a high vacuum of 10 ⁻⁹ Pa, and the sample is irradiated with X-ray energy: 385 to 430 eV. The intensity of the incident X-ray is I0, the current value flowing through the sample is I1, and the ratio of I1 / I0 is taken. When the horizontal axis is X-ray energy and the vertical axis is I1 / I0, an X-ray absorption spectrum as shown in FIG. 2 is obtained.

  In FIG. 2, a plurality of absorption peaks with numbers 0 to 4 can be confirmed. Among these absorption peaks, 0 to 1 show close values compared to the absorption spectrum of nitrogen observed in a sample in which silicon carbide (SiC) is doped with nitrogen (N). Here, silicon carbide is a compound in which carbon and silicon form a diamond structure through a covalent bond, and it is assumed that nitrogen doped in silicon carbide also takes four-coordinates in silicon carbide. Therefore, the absorption spectrum of nitrogen of 0 to 1 includes that the CNT includes a structure having a four-coordinate structure such as a diamond structure of silicon carbide, that is, a part of nitrogen in the CNT has a multi-layer structure. It can be judged that this indicates that a three-dimensional covalent bond is formed with the carbon atoms constituting the CNT network structure between the CNT layers. Such a three-dimensional bond is considered to play a role of connecting the inner layer and the outer layer of the multilayer CNT. Such a three-dimensional bond is, for example, a nitrogen-carbon covalent bond as shown in FIG. Here, FIG. 3 is an enlarged view of the II cross section of the CNT of FIG.

  2 to 4 are similar to the absorption spectrum of nitrogen of pyridine. This means that the CNT contains a secondary planar structure such as a pyridine molecule, that is, a part of the nitrogen in the CNT replaces a part of the carbon constituting the network structure of the CNT, and the surroundings. It can be judged that it has a two-dimensional covalent bond with the carbon atom.

  Moreover, in the CNT aggregate of the present embodiment, it is preferable that at least a part of the additive element exists between layers of the multilayer CNT layer structure. In the case of multi-walled CNTs, by increasing the conductivity between the layers, the number of CNT layers that can be used as a conductive path can be increased. That is, the presence of the additive element particularly between the layers of the multi-walled CNTs can increase the conductivity between the layers, and as a result, the CNT aggregate can exhibit particularly excellent conductivity. Furthermore, it is more preferable that at least a part of the additive elements present between the layers of the multi-walled CNT are covalently bonded to the carbon atoms constituting the multi-walled CNT. Thereby, the electroconductivity between the layers of multilayer CNT can further be improved.

Note that the presence of the additive element between the multilayer CNT layers and the bonding state thereof can be confirmed, for example, by the following method.
First, a transmission electron microscope is used for observation of multilayer CNT. Furthermore, nitrogen or boron present inside the CNT can be confirmed by electron energy loss spectroscopy (Electron Energy Loss Spectroscopy, EELS). EELS is a technique for analyzing the elemental composition and chemical bonding state of a sample by analyzing the inelastically scattered electrons by causing the incident electrons to lose energy due to interaction with the sample substance. By combining with a scanning transmission electron microscope (STEM) installed in the above-mentioned electron microscope, a minute region can be measured with high spatial resolution. By these methods, it is possible to perform mapping of nitrogen atoms or boron atoms existing in the structure of CNT.

  Moreover, it is preferable that the average nearest interatomic distance of the additive element which exists between the layers of the layer structure of multilayer CNT is 50-500 nm, More preferably, it is 50-250 nm. The measurement can be performed using a transmission electron microscope. In this measurement, since a wider range of mapping is required than in the case of the analysis of the composition and bonding state described above, energy dispersive X-ray spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy) is used in addition to STEM. Mapping.

  Note that the mapping analysis includes information not only on the surface but also in the depth direction. Therefore, in the present invention, for example, in the case of measurement of X-ray fluorescence of nitrogen, element mapping is performed from a plane parallel to the longitudinal direction of CNT, and a portion where X-ray intensity derived from nitrogen is clearly stronger than the background is arbitrarily selected. When the point O is observed as a point A along the longitudinal direction of the CNT along which the same strength as the point O can be confirmed, the distance between the point O and the point A is the nearest interatomic distance. Define. In addition, by performing EELS analysis, it is possible to distinguish an additive element existing between layers of the multilayer CNT layer structure and an additive element constituting the CNT layer.

In the present embodiment, it is preferable that the G / D ratio, which is the ratio between the G band of the Raman spectrum and the D band derived from crystallinity, is controlled within a predetermined range. Here, the D band appears in the vicinity of a Raman shift of 1350 cm ⁻¹ and can be said to be a peak of a spectrum derived from a defect. The ratio of the D band to the G band (G / D ratio) is used as an index of the amount of defects in the CNT, and it is determined that the larger the G / D ratio, the fewer the defects in the CNT.

  In the CNT aggregate 11 of the present embodiment, the G / D ratio, which is the ratio of the G band of the Raman spectrum to the D band derived from crystallinity, is preferably 50 or more.

<Method for producing carbon nanotube aggregate>
The CNT aggregate of this embodiment is manufactured by the following method.

(1) Synthesis of CNT CNT can be produced using, for example, a floating catalyst vapor deposition (CCVD) method. Specifically, the starting material is supplied from the upper part of the reaction furnace, and the CNT generated from the lower part of the reaction path is recovered.

  As a starting material, it is preferable to use a mixed solution containing at least a carbon source, a nitrogen or boron source, a catalyst, and a CNT growth promoter.

Here, as the carbon source, for example, decalin, benzene, hexane, toluene or the like can be used.
As the nitrogen source, for example, pyridine, benzylamine and the like can be used.
As the boron source, for example, decaborane, triisopropylpyrate boronate, or the like can be used.
As the catalyst, for example, a metal catalyst made from an organic metal complex such as ferrocene, cobaltocene, or nickelocene can be used.
As the CNT growth promoter, for example, thiophene can be used.

  The mixed solution is preferably stirred in an ultrasonic cleaner that is kept at 50 to 80 degrees before being supplied to the reaction path.

  Further, the inside of the reaction furnace is preferably heated to 1200 to 1500 degrees. Moreover, it is preferable to use hydrogen gas as a carrier gas for supplying the starting material into the reaction furnace. For example, the reaction furnace is installed in a vertical type, and a starting material is supplied from the upper part of the furnace, and CNTs generated from the lower part of the furnace are discharged and collected.

(2) Production of CNT aggregate A CNT aggregate is produced from the collected powdery CNTs. The form of the CNT aggregate is not limited. For example, the produced CNTs may be collected into a sheet to form a CNT aggregate, and further bundled to form a CNT wire. Moreover, it is preferable that the obtained CNT wire is highly purified by heating at 300-700 degreeC, for example in air | atmosphere, and also giving an acid treatment. Then, the CNT wire obtained in this way may be twisted and twisted in the longitudinal direction to form a twisted wire.

<Electrical properties of aggregate of carbon nanotubes>
The CNT aggregate of this embodiment preferably has a resistivity of 7.5 × 10 ⁻⁵ Ω · cm or less when the CNT aggregate is manufactured. In addition, although such a CNT aggregate has a slightly higher resistivity than the resistivity of copper 1.68 × 10 ⁻⁶ Ω · cm and the resistivity of aluminum 2.65 × 10 ⁻⁶ Ω · cm, it is good Resistivity of 10 ⁻⁵ order or less is achieved. Therefore, if the CNT aggregate of the present embodiment is used as a wire substitute for copper or aluminum wire, weight reduction can be realized while maintaining the same resistivity as copper or aluminum.

  Moreover, the CNT aggregate of this embodiment is excellent in thermal stability. For example, even when the heat treatment is performed at 150 ° C. or more for 1 hour or more in the atmosphere, the resistivity does not significantly increase before and after the heat treatment. That is, the CNT aggregate of this embodiment has an increase rate of resistivity after heat treatment at 150 ° C. for 1 hour [(resistivity after heat treatment−resistivity before heat treatment) × 100 / resistivity before heat treatment] Preferably it is 35% or less, More preferably, it is 25% or less.

  The CNT aggregate according to the embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and includes all aspects included in the concept of the present invention and the claims. Various modifications can be made within the range described above.

  For example, you may comprise a CNT covering electric wire provided with the CNT aggregate | assembly of the said embodiment, and the coating layer which coat | covers the outer periphery of this CNT aggregate.

  Moreover, you may comprise the wire harness which has at least one said CNT covering electric wire.

  Next, in order to further clarify the effects of the present invention, examples and comparative examples will be described, but the present invention is not limited to these examples.

Example 1
The synthesis of the CNT aggregate was performed using a floating catalyst vapor deposition (CCVD) method.
First, decahydronaphthalene as a carbon source (manufactured by Sigma Aldrich Japan LLC), pyridine as a nitrogen source (manufactured by Wako Pure Chemical Industries, Ltd.), ferrocene as a catalyst (manufactured by Sigma Aldrich Japan LLC), and reaction accelerator The thiophenes (manufactured by Sigma-Aldrich Japan LLC) were mixed at a molar ratio of 100: 1.0: 3.0: 3.0, respectively, to prepare raw material solutions.
Next, the above raw material solution that has been ultrasonically applied in a water bath at 50 ° C. immediately before is supplied by spraying into an alumina tube having an inner diameter of 60 mm and a length of 1600 mm heated to 1200 ° C. by an electric furnace. At this time, hydrogen was supplied at 9.5 L / min as a carrier gas.

  The obtained CNTs were collected in a sheet form by a collecting machine, and these were collected to produce a CNT aggregate, and further the CNT aggregate was bundled to produce a CNT wire. The obtained CNT wire was heated to 400 to 650 ° C. in the atmosphere and further subjected to acid treatment a plurality of times to achieve high purity. The obtained CNT was twisted and formed into a wire while being pulled in the longitudinal direction.

(Examples 2 to 4)
In Examples 2 to 4, except that the compounding ratio of pyridine in the raw material solution used in CCVD was changed so that the additive element in the obtained CNT aggregate had an atomic ratio with respect to the carbon atoms shown in Table 1. In the same manner as in Example 1, CNT synthesis to wire production was performed. For example, in Example 2, the blending ratio (mol ratio) of pyridine was changed so that pyridine was 5.0 with respect to decahydronaphthalene 100.

(Examples 5 and 6)
In Examples 5 and 6, in the obtained CNT aggregate, the ratio of the total number of each multilayer CNT having a two-layer structure or a three-layer structure to the total number of CNTs constituting the CNT aggregate is shown in Table 1. In the same manner as in Example 1, except that the blending ratio of ferrocene and thiophene in the raw material solution used in CCVD was changed so that the number of acid treatment steps and treatment time after synthesis were reduced. From synthesis to wire preparation.

(Examples 7 and 8)
In Examples 7 and 8, the raw material solution used in CCVD was changed to CNT, which is a nitrogen source, and triisopyrrolyl borate (manufactured by Merck) was used as a boron source. From synthesis to wire preparation.

(Examples 9 and 10)
In Examples 9 and 10, the CNT synthesis was performed in the same manner as in Example 1 except that the raw material solution used in CCVD was replaced with decaborane as a boron source (manufactured by Sigma Aldrich) instead of pyridine as a nitrogen source. To wire rod.

(Comparative Example 1)
In Comparative Example 1, the raw material solution used in CCVD was changed so that decahydronaphthalene, ferrocene, and thiophene were in a molar ratio of 100: 1.0: 0.01, respectively, and the acid treatment after synthesis was performed. In addition to reducing the number of steps and processing time, and further placing the acid-treated CNT wire together with solid iodine in a quartz tube, sealing and heating at a temperature of 100 to 300 ° C. for 1 to 10 hours, In the same manner as in Example 1, CNT synthesis to wire production was performed.

(Comparative Example 2)
In Comparative Example 2, CNT synthesis was performed to wire preparation in the same manner as in Comparative Example 1, except that the CNT wire after acid treatment was immersed in nitric acid.

(Comparative Example 3)
In Comparative Example 3, the mixing ratio (mol ratio) of pyridine in the raw material solution used in CCVD was changed in the same manner as in Example 1 except that pyridine was 0.2 with respect to decahydronaphthalene 100. The process from synthesis of CNT to wire production was performed.

(Comparative Example 4)
In Comparative Example 4, the mixing ratio (mol ratio) of pyridine in the raw material solution used in CCVD was changed so that pyridine was 5.0 with respect to decahydronaphthalene 100, and in the obtained CNT aggregate, Ferrocene and thiophene in the raw material solution used in CCVD so that the ratio of the total number of each multi-walled CNT having a two-layer structure or three-layer structure to the total number of CNTs constituting the body is the ratio shown in Table 1 CNT synthesis was performed to wire preparation in the same manner as in Example 1 except that the blending ratio was changed and the number of acid treatment steps after synthesis and the treatment time were reduced.

(Comparative Example 5)
In Comparative Example 5, in a CNT aggregate obtained by using pyrazine (made by Wako Pure Chemical Industries, Ltd.) in the raw material solution used in CCVD as a blending ratio (mol ratio) of 120 relative to decahydronaphthalene 100, CNT assembly Ferrocene and thiophene in the raw material solution used in CCVD so that the ratio of the total number of each multi-walled CNT having a two-layer structure or three-layer structure to the total number of CNTs constituting the body is the ratio shown in Table 1 CNT synthesis was performed to wire preparation in the same manner as in Example 1 except that the blending ratio was changed and the number of acid treatment steps after synthesis and the treatment time were reduced.

(Comparative Example 6 or 8)
In Comparative Example 6 or 8, the raw material solution used in CCVD was replaced with decaborane (Sigma Aldrich) as a boron source instead of pyridine as a nitrogen source, and decaborane was changed to 4 or 15 with respect to decahydronaphthalene 100. Except for the above, the same procedure as in Example 1 was followed from the synthesis of CNT to the formation of a wire.

(Comparative Example 7)
In Comparative Example 7, as a raw material used in CCVD, the carbon source was methanol (manufactured by Wako Pure Chemical Industries, Ltd.), the boron source was decaborane, and the blending ratio was 0.5 with respect to methanol 100. In the same manner as in Example 1, the synthesis from CNT to wire was performed.

[Evaluation]
Measurements and evaluations shown below were performed using the carbon nanotube aggregates according to the above Examples and Comparative Examples. Conditions for each measurement and evaluation are as follows. The results are shown in Table 1.

(A) Measurement of atomic ratio of additive element to carbon atom The content ratio of nitrogen or boron in the CNT aggregate was evaluated by semi-quantitative analysis by X-ray photoelectron spectroscopy (X-ray Photoelectron Spectroscopy). This will be described in detail below.
First, CNT recovered immediately after synthesis (before twisting) is exposed to acetone, placed on medicine-wrapping paper, flattened with a glass slide, and dried. The dried CNT sample is about 1 × 1 cm and becomes a CNT aggregate having a thickness of about 2 mm.
The aggregate is acid-treated to remove impurities and then subjected to XPS analysis. In XPS analysis, X-rays are incident on a sample and photoelectrons emitted from the surface are detected. The measurement is performed using a multifunctional scanning X-ray photoelectron spectrometer (PHI5000 Versaprobe, ULVAC-PHI Co., Ltd.) with the incident X-ray source being monochromatic Al-Kα ray and an escape angle of 90 °. It was. Furthermore, in order to perform semi-quantification, Wide-scan was performed about the binding energy of 1350-0eV. For each sample, measurement was performed by selecting five arbitrary locations (N = 5), and the average value was defined as the atomic ratio of nitrogen or boron to carbon atoms.
The iodine content in the CNT aggregate was also evaluated by semi-quantitative analysis using XPS analysis. The measurement conditions and analysis method for XPS analysis were the same as those for nitrogen or boron.

(B) Confirmation of covalent bond between additive element and carbon atom After confirming the structure between CNT layers with a transmission electron microscope (TEM), it was confirmed by EELS spectrum mapping that the structure was nitrogen, boron or iodine. . Furthermore, the covalent bond was judged from the spectrum energy of the obtained EELS spectrum. Observation by TEM was performed using an atomic resolution analytical electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.). Furthermore, the scanning transmission electron microscope (STEM) installed in said electron microscope was used for EELS spectrum mapping.
The observation sample was a dispersion liquid in which synthesized CNTs were dispersed in ethanol with ultrasonic waves. This dispersion was dropped on a TEM observation mesh and observed.

(C) Measurement of the distance between the nearest atoms of the additive element The distance between the nearest atoms of the additive element was determined by EELS spectrum mapping using a scanning transmission electron microscope (STEM, the same as above) and energy dispersive X using the STEM. It was confirmed by performing a line spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy) analysis. The observation sample was a dispersion liquid in which synthesized CNTs were dispersed in ethanol with ultrasonic waves. This dispersion was dropped on a TEM observation mesh and observed.

(D) Observation of CNT layer structure The CNT layer structure was confirmed by a transmission electron microscope (TEM). For TEM observation, an atomic resolution analytical electron microscope (same as above) was used. The observation sample was a dispersion liquid in which synthesized CNTs were dispersed in ethanol with ultrasonic waves. This dispersion was dropped on a TEM observation mesh and observed.

(E) Resistivity A CNT aggregate was connected to a resistance measuring machine (manufactured by Keithley, device name “DMM2000”), and resistance measurement was performed by a four-terminal method. Resistivity is r = RA / L (R :: resistance, A: CNT
The resistivity was calculated based on the calculation formula of the cross-sectional area of the aggregate, L: measurement length). The test piece was 40 mm in length. In addition, the said test was performed about 3 each CNT aggregates before and after 150 degreeC 1 hour heat processing (N = 3), the average value was calculated | required, and the resistivity before and behind each CNT aggregate heating (Ω · cm). The resistivity is preferably as small as possible. In this example, before the heating, 7.5 × 10 ⁻⁵ Ω · cm or less is regarded as an acceptable level, and the increase rate of the resistivity after the heat treatment (%) [(after the heat treatment )-(Resistivity before heat treatment) × 100 / Resistivity before heat treatment] was 35% or less as an acceptable level.

  From the results shown in Table 1, each of the CNT aggregates according to Examples 1 to 8 of the present invention has each layer structure of any one of 2 to 6 layers that occupies the total number of CNTs constituting each CNT aggregate. The ratio of the total number is 70% or more, includes at least one additive element of boron and nitrogen, and the content ratio is 1 to 10% in terms of the number of atoms with respect to the carbon atoms contained in the CNT aggregate, It was confirmed that at least a part of the additive element is covalently bonded to the carbon constituting the CNT, and exhibits low resistivity and excellent thermal stability.

  In contrast, the CNT aggregate according to Comparative Example 1 contains iodine as an additive element, and since iodine is not covalently bonded to carbon, the resistivity after heating is significantly increased. Compared with the CNT aggregates of Examples 1 to 8, the thermal stability is remarkably inferior. Further, in the CNT aggregate according to Comparative Example 2, since the nitrogen as the additive element is not covalently bonded to the carbon constituting the CNT, the resistivity after heating is greatly increased, and Example 1 of the present invention Compared with CNT aggregates of -10, the thermal stability is significantly inferior.

  Moreover, since the CNT aggregate according to Comparative Examples 3 and 6 has an additive element content ratio of less than 1% in terms of the number of atoms with respect to the carbon atoms contained in the CNT aggregate, the CNT aggregates of Examples 1 to 10 of the present invention Compared to the aggregate, the resistivity is high and the thermal stability is also inferior. In the CNT aggregates according to Comparative Examples 4 and 7, the ratio of the total number of multi-layer CNTs having any one of 2 to 6 layers in the total number of CNTs constituting each CNT aggregate is 70%. Therefore, the thermal stability is inferior to the CNT aggregates of Examples 1 to 10 of the present invention. In addition, the CNT aggregates according to Comparative Examples 5 and 8 have an additive element content rate of more than 10% in terms of the number of atoms with respect to the carbon atoms contained in the CNT aggregate. Compared to the aggregate, the resistivity is high and the thermal stability is also inferior. This is presumably because the boron and nitrogen-containing carbides attached to the CNT surface without being covalently bonded are heated, thereby reducing the crystallinity of the CNT and increasing the resistance.

DESCRIPTION OF SYMBOLS 1 Carbon nanotube aggregate 11 Bundle of carbon nanotubes 11a Carbon nanotube T1 Tubular body T2 Tubular body

Claims (7)

An aggregate of carbon nanotubes composed of a plurality of carbon nanotubes having a layer structure of one or more layers,
The ratio of the total number of each multi-walled carbon nanotube having a layer structure of 2 to 6 layers, accounting for 70% or more of the total number of carbon nanotubes constituting the carbon nanotube aggregate,
The carbon nanotube aggregate includes at least one additive element of boron and nitrogen, and the content ratio thereof is 1 to 10% in terms of the number of atoms with respect to the carbon atoms contained in the carbon nanotube aggregate,
An aggregate of carbon nanotubes, wherein the rate of increase in resistance after heat treatment at 150 ° C. for 1 hour is 35% or less. An aggregate of carbon nanotubes composed of a plurality of carbon nanotubes having a layer structure of one or more layers,
The ratio of the total number of each multi-walled carbon nanotube having a layer structure of 2 to 6 layers, accounting for 70% or more of the total number of carbon nanotubes constituting the carbon nanotube aggregate,
The carbon nanotube aggregate includes at least one additive element of boron and nitrogen, and the content ratio thereof is 1 to 10% in terms of the number of atoms with respect to the carbon atoms contained in the carbon nanotube aggregate,
The aggregate of carbon nanotubes, wherein at least a part of the additive element is covalently bonded to a carbon atom constituting the carbon nanotube.   The ratio of the total number of multi-walled carbon nanotubes having any one of 2 to 6 layers in the total number of carbon nanotubes constituting the aggregate of carbon nanotubes is 90% or more. An aggregate of carbon nanotubes described in 1.   4. The ratio of the total number of multi-walled carbon nanotubes each having a two-layer structure or a three-layer structure to the total number of carbon nanotubes constituting the carbon nanotube aggregate is 70% or more. 5. 2. The aggregate of carbon nanotubes according to item 1.   5. The carbon nanotube aggregate according to claim 4, wherein a ratio of a total number of each multi-walled carbon nanotube having a two-layer structure or a three-layer structure to a total number of carbon nanotubes constituting the carbon nanotube aggregate is 90% or more. .   6. The carbon according to claim 1, wherein at least a part of the additive element exists between layers of the multilayer carbon nanotube layer structure and is covalently bonded to the carbon atom. Nanotube aggregate.   The aggregate of carbon nanotubes according to claim 6, wherein an average interatomic distance between the additional elements existing between layers of the layer structure, measured along the longitudinal direction of the multi-walled carbon nanotube, is 50 to 500 nm.