Carbon nanotube aggregates

Abstract

To provide a CNT aggregate that has high heat resistance.SOLUTION: Provided is a CNT aggregate that includes a plurality of CNT2, and contains a metallic compound 3 and an oxide 4 of the metallic compound 3, and in which the metallic compound 3 is contained in the space inside of the CNT2 or in the space surrounded by the plurality of CNT2. In this way, when a metallic compound is added to the inside of the CNT aggregate, the metallic compound is oxidized by reacting with the atmosphere or the like during or after the production process of the CNT aggregate, and an oxide is formed in the opening of the space to which the metallic compound is added, and the metallic compound is capped by the oxide. Thereby, since the metallic compound inside the CNT aggregate is blocked from the atmosphere, the separation of the metallic compound and the reaction between the metallic compound and oxygen or water in the atmosphere are suppressed, and the heat resistance of the CNT aggregate is improved.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an aggregate of carbon nanotubes (hereinafter referred to as CNTs). [Background technology]

[0002] CNT aggregates made up of multiple CNTs are expected to be used in conductive films and windings, and in recent years, there has been a demand for lower resistance due to the miniaturization of devices. For example, Non-Patent Document 1 proposes a method of lowering resistance by doping CNTs with AuCl3. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] ACS Nano, vol. 5, P. 1236, 2011 Summary of the Invention [Problem to be solved by the invention]

[0004] CNT aggregates are required to have low resistance and to be compatible with high-temperature environments such as vehicle motors. For example, even if they are placed in an atmosphere of at least 200°C or higher for 100 hours or more, they must have little change in resistance and maintain electrical resistance. However, in the method described in Non-Patent Document 1, although the effect of reducing resistance is maintained at a temperature of about 100°C, the effect of reducing resistance decreases at temperatures of 200°C or higher. This is thought to be due to the detachment of additives or deterioration due to reactions with oxygen or water in the atmosphere.

[0005] Furthermore, for n-type CNT materials for thermoelectric materials, a technology has been proposed in which alkali elements such as lithium and potassium, or a complex of potassium ions and crown ether is added to the inside of the CNT, but stability above 200°C in air has not been confirmed. Also, there are few examples of adding p-type dopants, which are relatively stable in air compared to n-type, to the inside of CNT, and similarly, there are no examples of heat resistance for more than 100 hours in air at 200°C or higher.

[0006] In view of the above, an object of the present invention is to provide a CNT aggregate having high heat resistance. [Means for solving the problem]

[0007] In order to achieve the above object, the invention described in claim 1 provides a CNT aggregate having a plurality of CNTs (2), which contains a metal compound (3) and an oxide of the metal compound (4), and the metal compound is contained in at least one of the space inside the CNT and the space surrounded by the plurality of CNTs. The metal compound is capped with an oxide, the opening of the space to which the metal compound is added is capped with an oxide, and the content of the oxide of the metal compound is higher on the opening side than on the position inside the opening.

[0008] When a metal compound is added to the inside of a CNT aggregate, the metal compound reacts with oxygen and other substances during or after the manufacturing process of the CNT aggregate, and is oxidized, forming an oxide at the opening of the space where the metal compound was added, and the metal compound is capped by this oxide. This blocks the metal compound inside the CNT aggregate from the atmosphere, suppressing the release of the metal compound and the reaction of the metal compound with oxygen and water in the atmosphere, improving the heat resistance of the CNT aggregate.

[0009] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an external view of a CNT aggregate. [Diagram 2] FIG. 2 is a diagram showing the internal structure of a CNT aggregate. [Diagram 3] 1 is a micrograph showing the presence of molybdenum-based particles inside CNT. [Figure 4] 1 is a micrograph showing the distribution of molybdenum. [Diagram 5] 1 is a micrograph showing the distribution of chlorine. [Figure 6] 1 is a micrograph showing the distribution of oxygen. [Figure 7] This is a microscope photograph showing the presence of iron chloride inside CNT. [Figure 8] FIG. 8 is an enlarged view of the portion of FIG. 7 where iron chloride has been added. [Figure 9] 1 is a micrograph showing the distribution of carbon. [Figure 10] 1 is a micrograph showing the distribution of chlorine. [Figure 11] 1 is a micrograph showing the distribution of iron. [Figure 12] FIG. 13 is a diagram showing the detection results of oxygen. [Figure 13] FIG. 13 is a diagram showing the detection results of chlorine. [Figure 14] FIG. 1 is a graph showing the relationship between heating time and electrical resistance when molybdenum chloride is added. [Figure 15] FIG. 4 is a graph showing the relationship between heating time and the molybdenum content. [Figure 16] FIG. 13 is a graph showing the relationship between heating time and electrical resistance when iron chloride is added. [Figure 17] FIG. 13 is a diagram showing the temperature dependence of electrical resistivity in samples C-1 to C-3. [Figure 18A] FIG. 1 is a graph showing the intensity of the X-ray photoelectron spectroscopy (hereinafter referred to as XPS) spectrum versus the binding energy in the Cl2p region of sample C-3. [Figure 18B] FIG. 13 is a graph showing the intensity of the XPS spectrum versus the binding energy of the Fe2p region in sample C-3. [Figure 19] FIG. 13 is a diagram showing the results of measuring the G-band peak positions in the Raman spectra of samples C-1 to C-3. [Figure 20]FIG. 1 shows the results of thermogravimetry-differential thermal analysis (hereinafter referred to as TG-DTA) performed on Samples C-1 to C-3 and FeCl3 powder. [Figure 21] FIG. 13 is a diagram showing the internal structure of a CNT aggregate in another embodiment. [Figure 22] FIG. 13 is a diagram showing the internal structure of a CNT aggregate in another embodiment. [Figure 23] FIG. 13 is a diagram showing the internal structure of a CNT aggregate in another embodiment. [Figure 24] FIG. 13 is a diagram showing the internal structure of a CNT aggregate in another embodiment. [Diagram 25] FIG. 13 is a diagram showing the internal structure of a CNT aggregate in another embodiment. [Figure 26] FIG. 13 is a diagram showing the internal structure of a CNT aggregate in another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0012] (First embodiment) A first embodiment will be described. As shown in Fig. 1 and Fig. 2, the CNT aggregate 1 of this embodiment is formed by aggregating a plurality of CNTs 2 to form a rod-like or tape-like structure as shown in Fig. 1. Such a CNT aggregate is used, for example, in a CNT conductive film, a CNT winding for a device, a CNT winding for a motor, a CNT wire harness, etc. The length of one side of the CNT aggregate 1 is, for example, 10 µm or more. In addition, when the CNT aggregate 1 is cylindrical, the diameter of the CNT aggregate 1 is, for example, 10 µm or more. The average inner diameter of the plurality of CNTs 2 is, for example, 0.55 nm or more and 1000 nm or less.

[0013] As shown in FIG. 2, the CNT aggregate 1 contains a metal compound 3 and an oxide 4 of the metal compound 3. The metal compound 3 is for reducing the resistance of the CNT aggregate 1, and is contained in the space inside the CNT 2 and the space outside the CNT 2 surrounded by a plurality of CNTs 2 (hereinafter referred to as inter-CNT space). The metal compound 3 is composed of, for example, molybdenum chloride (MoCl5) or iron chloride (FeCl3). For simplicity, in FIG. 2, the CNT 2 is shown as a cylinder. The metal compound 3 added inside the CNT 2 is shown by a dashed line, and the metal compound 3 added outside the CNT 2 is shown by a solid line.

[0014] The metal compound 3 is capped with an oxide 4. Specifically, as shown in FIG. 2, the openings of the CNTs 2 and the openings of the spaces between the CNTs are capped with an oxide 4. When the metal compound 3 is composed of MoCl5, the oxide 4 is a molybdenum oxide (MoO3, MoO2) or a molybdenum chloride partial oxide (MoO x Cl 5-x )

[0015] Such a CNT aggregate 1 is manufactured, for example, by the following procedure. First, a CNT film (manufactured by DexMat INC. (USA)) is placed in a vacuum and heated at 300°C to 350°C to remove moisture from the CNTs. Next, the CNT film is mixed with MoCl5 gas in an Ar atmosphere containing 1 ppm to 20 ppm O2, and then the CNT film is sealed in a container to isolate it from the atmosphere and heated at 260°C to 350°C. Then, the MoCl5 on the surface of the CNT film is removed by washing with ethanol.

[0016] In this way, MoCl5 is added as a metal compound 3 to the inside of the CNTs 2 and the spaces between the CNTs, and the openings of the CNTs 2 and the openings of the spaces between the CNTs are filled with an oxide 4, such as MoO3, MoO2, or MoO x Cl 5-xWhen the temperature during heating of the CNT film in a vacuum is set to 500°C or higher, the openings of the CNTs 2 and the openings of the spaces between the CNTs are capped with MoO3 or the like, and an oxide film (not shown) corresponding to the oxide 4 is formed on the surface of the CNT aggregate 1, and the entire CNT aggregate 1 is covered with this oxide film. This oxide film is composed of MoO3, MoO2 or MoO x Cl 5-x When FeCl3 is added as the metal compound 3, the CNT aggregate 1 can be produced by the same method.

[0017] Figures 3 to 6 are scanning transmission electron microscope photographs of the cross section of the CNT aggregate 1 produced by the above method, and show the distribution of molybdenum, oxygen, and chlorine inside the CNT aggregate 1. In Figure 3, the black circles are CNTs 2, and the other black parts are molybdenum-based particles. In Figures 4 to 6, the black parts have higher molybdenum, chlorine, and oxygen contents than the white parts.

[0018] As shown in Figures 3 to 6, molybdenum particles are contained inside CNT2 and in the spaces between CNTs. Chlorine and oxygen are distributed throughout the inside of CNT aggregate 1, but oxygen is closer to molybdenum than chlorine. This shows that the chlorine content is low at the opening of CNT2, and a cap composed mainly of molybdenum and oxygen is formed. The compound ratio in CNT aggregate 1 examined by XAFS (X-ray absorption fine structure measurement) was MoCl5:MoO3:MoO2=78.4:14.5:7.1.

[0019] 7 to 11 are scanning transmission electron microscope photographs of a CNT aggregate 1 to which FeCl3 has been added as a metal compound 3, and CNT 2 to which FeCl3 has been added is photographed from the side. FIG. 8 is an enlarged view of the portion of FIG. 7 to which FeCl3 has been added, and FIGS. 9 to 11 are diagrams showing the distribution of carbon, chlorine, and iron in the portion shown in FIG. 8, respectively. In FIGS. 8 to 11, regions R1 and R2 are the inside of the portion to which FeCl3 has been added, regions R3 and R4 are the ends of the portion to which FeCl3 has been added, and region R5 is the outside of the portion to which FeCl3 has been added.

[0020] Figure 12 shows the results of detecting oxygen from regions R1 to R5 by EELS (electron energy loss spectroscopy), and the intensity peak in the energy loss range of 500 eV to 600 eV indicates that oxygen is contained in the region. Figure 13 shows the results of detecting chlorine from regions R2 to R5 by EELS analysis, and the increase in intensity in the energy loss range of 200 eV to 210 eV indicates that chlorine is contained in the region.

[0021] From Figs. 8 to 11, it can be seen that the additive inside the CNT2 is composed of iron and chlorine. As shown in Fig. 12, oxygen was not detected in regions R1, R2, and R5, whereas oxygen peaks appeared at the dashed line parts in regions R3 and R4, and the oxygen peak in region R4 close to the opening of the CNT2 was particularly strong, indicating that a large amount of oxygen was present. Also, as shown in Fig. 13, chlorine was detected in increasing amounts in the order of regions R2 to R5. From Figs. 12 and 13, it can be seen that the additive is oxidized at the opening of the CNT2, specifically, at the end of the part inside the CNT2 where the metal compound 3 is added, and the opening of the CNT2 is capped by the oxide 4.

[0022] 14 and 15 are diagrams showing the results of investigating the heat resistance of the CNT aggregate 1 produced by the above method. The horizontal axis of the graphs in FIG. 14 and FIG. 15 is the heating time when a heating test was performed at 230°C in the atmosphere. The vertical axis of the graph in FIG. 14 is the electrical resistivity measured by a four-terminal measurement method at room temperature after removing the CNT aggregate 1 from the heating device. The vertical axis of the graph in FIG. 15 is the molybdenum content ratio. In FIG. 14, the white circles indicate the electrical resistivity of the CNT aggregate 1 in which molybdenum chloride is added to the inside of the CNT2 and the space between the CNTs, and the white triangles indicate the electrical resistivity of the CNT aggregate in which AuCl3 is added to the surface. In FIG. 15, the molybdenum content is measured by irradiating the CNT aggregate 1 and the SiO2 substrate with X-rays while the CNT aggregate 1 is placed on the SiO2 substrate, and the molybdenum content ratio is the amount of molybdenum detected when the amount of Si detected is set to 1. The molybdenum content was measured using EDX-7000 (Shimadzu Corporation).

[0023] As shown in Figure 14, when the CNT aggregate with AuCl3 added to the surface is heated at 230°C, the electrical resistance increases in a short time and returns to the electrical resistance before addition. In contrast, the electrical resistance of CNT aggregate 1, in which molybdenum chloride is added inside CNT2 and in the spaces between CNTs, remains low even after long-term heating.

[0024] Fig. 16 is a graph of the electrical resistivity of the CNT aggregate 1 to which iron chloride has been added. In Fig. 16, the open circles indicate the electrical resistivity of the CNT aggregate 1 to which iron chloride has been added inside the CNT2 and in the spaces between the CNTs, and the open triangles indicate the electrical resistivity of the CNT aggregate to which AuCl3 has been added to the surface. As shown in Fig. 16, the CNT aggregate 1 to which iron chloride has been added inside the CNT2 and in the spaces between the CNTs maintains a low electrical resistance even after long-term heating.

[0025] In addition, in an experiment conducted by the present inventors, when MoCl5 powder was heated to 230°C in the air, it disappeared in about 3 hours. This is thought to be because MoCl5 changed to MoCl4, which has a high sublimability, as shown in the following chemical formula. From this, it can be said that MoCl5 is unstable at 230°C in the air.

[0026] (chemical 1) MoCl5+H2O → MoCl4+HCl+O2 15, the amount of molybdenum contained in the CNT aggregate 1 hardly changes even when heated at 230° C. In this way, it is found that the molybdenum chloride added to the CNT aggregate 1 is retained without being dispersed, and the molybdenum chloride in the CNT aggregate 1 is stable at 230° C.

[0027] As described above, in this embodiment, the resistance of the CNT aggregate 1 is reduced by adding the metal compound 3 to the inside of the CNTs 2 and the spaces between the CNTs. Then, by capping the openings of the CNTs 2 and the spaces between the CNTs with the oxide 4 of this metal compound 3, the metal compound 3 inside the CNTs 2 and in the spaces between the CNTs is shielded from the atmosphere, so that heat resistance is improved compared to the conventional art, and heat resistance of 200° C. or more is obtained.

[0028] The above characteristics can also be confirmed in a test in which the CNT film was doped with FeCl3. Here, Galvorn CNT Tape manufactured by DexMat INC. (USA) was used as the CNT film. The initial resistance of the CNT film was 33.8 ± 6.9 μΩcm. When this CNT film was heat-treated in air at 350°C for 1 hour, the initial resistance after heat treatment was 61.2 ± 8.4 μΩcm. In addition, three types of samples, C-1 to C-3, were prepared by using the CNT film after heat treatment and the CNT film after heat treatment that was further doped. C-1 is a CNT film that was only heat-treated, C-2 is a CNT film doped with IBr after heat treatment, and C-3 is a CNT film doped with FeCl3 after heat treatment. For C-2, anhydrous FeCl3 with a purity of 99.9% manufactured by Sigma Aldrich was used without purification and added as a dopant. For C-3, 98% pure IBr manufactured by Sigma Aldrich was used without purification and added as a dopant. In the doping process, the CNT film and the dopant were placed together in a sealed container filled with inert gas and treated at 270°C for 24 hours. After the doping process, the CNT film was washed several times with ethanol to remove excess dopant adsorbed on its surface.

[0029] Then, to investigate the temperature dependency of electrical resistivity in C-1 to C-3, electrical resistivity was measured in an inert gas atmosphere. The electrical resistivity was measured at a temperature increase rate of 25°C per minute. Figure 17 shows the measurement results. As shown in this figure, the electrical resistivity increased in all three types of samples when heated from room temperature. Among them, C-3 had a lower rate of increase in resistance with increasing temperature than C-2, and the change was also small.

[0030] In addition, as described above, by covering the surface of the CNT aggregate 1 with an oxide film of the metal compound 3, the metal compound 3 is isolated from the atmosphere, and thus the heat resistance is further improved. This was confirmed by analyzing the properties of the doped CNT film. The analysis included Raman spectroscopy (hereinafter referred to as Raman), XPS, and TG-DTA. For Raman, an excitation wavelength of 532 nm was used, and a confocal Raman microscope, InVia Qontor (UK) manufactured by Renishaw was used. For XPS, a PHI 5000 VersaProveII manufactured by ULVAC-PHI, inc. (JAPAN), was used to focus X-rays to a spot size of 200 μm in diameter on the sample, and the X-rays were performed under 50 W. The X-ray source used was Al-Kα radiation, hν=1486.6 eV. For TG-DTA, which was performed to evaluate the thermal stability of each sample, a TG-DTA 6300 manufactured by Hitachi High-Tech Corporation (JAPAN) was used. The TG-DTA measurement temperature range was set to 40°C to 1000°C, and the scanning rate was set to a temperature increase of +10.0°C per minute. An alumina pan was used, and air was introduced at a rate of 100 mL per minute.

[0031] In the XPS measurements, in order to detect Fe and Cl inside the FeCl3-doped CNTs, we focused on the peaks in the Fe2p region around 712 eV and the Cl2p region around 198 eV. Figures 18A and 18B show the relationship between the XSP spectrum intensity (au) and the binding energy (eV) in the Cl2p region around 198 eV and the Fe2p region around 712 eV in C-3, respectively. Each figure shows, from top to bottom, before heating, after heating for 50 hours, and after heating for 120 hours.

[0032] 18A and 18B, in the XPS spectrum of C-3, no disappearance of the peak or change in the peak shape was observed in the region of interest before and after heating. Therefore, it can be said that FeCl3 is held in the CNT even at a high temperature of about 220°C, which is assumed when the CNT aggregate 1 is applied to a motor or the like.

[0033] In addition, the shift of the G-band peak position in the Raman spectrum reflects the state of p-type doping of the CNT. FIG. 19 shows the results of measuring the G-band peak position of the Raman spectrum for C-1 to C-3 using excitation light with an excitation wavelength of 532 nm. A high-temperature storage test was performed for each sample, and the G-band peak position was measured before and after heat treatment in the high-temperature storage test. However, for C-1, since it is an undoped sample and is considered not to change before and after heat treatment, only the measurement result before heat treatment is shown.

[0034] The G band peak positions of C-2 and C-3 before heat treatment in the high-temperature storage test are 1601 cm -1 and 1609 cm -1 and the peak position of C-1 is 1593 cm -1 In comparison, the peak shift was larger in proportion to the change in electrical resistivity. In contrast, after heat treatment in the high-temperature storage test, the peak shift was 1596 m for C-3. -1 On the other hand, the value did not change in C-3, suggesting that the p-type doping state was maintained in C-3 before and after the heat treatment.

[0035] TG-DTA was performed on C-1 to C-3 and FeCl3 powder. As a result, as shown in Figure 20, FeCl3 showed different thermal stability depending on whether it was doped or not. That is, in the thermogravimetry (TG) of only FeCl3 powder, a weight loss was confirmed from around 200°C, while in C-3, a rapid weight loss was confirmed from around 500°C and 700°C. The latter is a weight loss of CNT itself, since the slope is almost the same as the rapid weight loss in C-1 at temperatures near 500°C and 700°C, while the former is a weight loss of FeCl3. From this, it is considered that FeCl3 and CNT encapsulated in CNT became thermally stable compared to when they were alone. This phenomenon was also confirmed in C-2, which supports the result that thermal stability is improved by encapsulating other substances.

[0036] In addition, since the metal compound 3 in the space between the CNTs is protected by the oxide 4 and the CNTs 2, the higher the density of the CNTs 2, the higher the heat resistance. Specifically, the density of the CNTs 2 is 0.1 g / cm 3 It is desirable that the content is 0.6 g / cm or more. 3 More preferably, it is 0.8 g / cm or more. 3 More preferably, the above is true.

[0037] (Other embodiments) The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the claims.

[0038] For example, in the above embodiment, the case where MoCl5 and FeCl3 are added to the CNT aggregate 1 as the metal compound 3 has been described, but other metal chlorides may be added, or metal compounds other than metal chlorides may be added.

[0039] In the above embodiment, the metal compound 3 is added to the space inside the CNTs 2 and the space between the CNTs, but as shown in Figures 21 and 22, the metal compound 3 may be added only to the space inside the CNTs 2. In this case, as in the first embodiment, the openings of the CNTs 2 are capped with the oxide 4 of the metal compound 3, and the metal compound 3 inside the CNT aggregate is shielded from the atmosphere, so that the heat resistance is improved compared to the conventional case, and a heat resistance of 200°C or more can be obtained.

[0040] 23 to 25, the metal compound 3 may be added only to the spaces between the CNTs. In this case, as in the first embodiment, the openings of the spaces between the CNTs are capped with the oxide 4 of the metal compound 3, and the metal compound 3 inside the CNT aggregate is shielded from the atmosphere, improving heat resistance compared to the conventional art and achieving heat resistance of 200° C. or more. As shown in FIG. 26, the metal compound 3 may be added to the space surrounded by a bundle of multiple CNTs 2. [Explanation of symbols]

[0041] 2. CNTs 3 Metal compounds 4. Oxides

Claims

1. A carbon nanotube aggregate comprising a plurality of carbon nanotubes (2), A metal compound (3), The oxide of the metal compound (4), the metal compound is contained in at least one of an internal space of the carbon nanotube and a space surrounded by a plurality of the carbon nanotubes; the metal compound is capped with the oxide; A carbon nanotube aggregate in which the opening of the space to which the metal compound is added is capped with the oxide, and the opening side has a higher content of the oxide of the metal compound than a position inside the opening.

2. 2. The carbon nanotube aggregate according to claim 1, wherein the metal compound is composed of a metal chloride.

3. the metal chloride is molybdenum chloride; 3. The carbon nanotube aggregate according to claim 2, wherein the oxide is an oxide or a partial oxide of molybdenum chloride.

4. the metal chloride is iron chloride; The carbon nanotube aggregate according to claim 2 , wherein the oxide is an oxide or a partial oxide of iron chloride.

5. A carbon nanotube aggregate comprising a plurality of carbon nanotubes (2), A metal compound (3), The oxide of the metal compound (4), the metal compound is contained in at least one of an internal space of the carbon nanotube and a space surrounded by a plurality of the carbon nanotubes; the metal compound is a metal chloride, ferric chloride; The carbon nanotube aggregate, wherein the oxide is an oxide or partial oxide of iron chloride.

6. 6. The aggregate of carbon nanotubes according to claim 1, wherein the length of one side or the diameter is 10 μm or more.

7. Density is 0.8 g / cm ３ The aggregate of carbon nanotubes according to any one of claims 1 to 6.

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