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 in which a metallic compound 3 is added to the inside or outside of CNT2, and the surface is covered with an oxide film 4 composed of an oxide of the metallic compound 3. According to this, since the metallic compound 3 is blocked from the atmosphere by the oxide film 4 covering the surface of the CNT aggregate, the separation of the metallic compound 3 and the reaction between the metallic compound 3 and oxygen or water in the atmosphere are suppressed, and the heat resistance of the CNT aggregate is improved.SELECTED DRAWING: Figure 3

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 low resistance due to the miniaturization of devices. 3 A method for reducing the resistance by doping has been proposed. [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 for 100 hours or more, there must be little change in resistance and electrical resistance must be maintained. 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 reaction 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), in which a metal compound (3) is added to at least one of the interior and exterior of the CNTs, and the surface is covered with an oxide film (4) composed of an oxide of the metal compound.

[0008] According to this, the metal compounds are isolated from the atmosphere by the oxide film that covers the surface of the CNT aggregate, suppressing the detachment of the metal compounds and their reactions with oxygen and water in the atmosphere, thereby 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] FIG. 1 is a cross-sectional view of a CNT aggregate. [Figure 4] 1 is a micrograph showing the molybdenum content. [Diagram 5] 1 is a micrograph showing the oxygen content. [Figure 6] 1 is a micrograph showing the chlorine content. [Figure 7] FIG. 13 is a diagram showing the relationship between heating time and electrical resistance. [Figure 8] FIG. 13 is a diagram showing the temperature dependence of electrical resistivity in samples C-1 to C-3. [Figure 9A] 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 9B] 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 10] 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 11] 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. 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 Figs. 1 and 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 CNT conductive films, CNT windings for devices, CNT windings for motors, CNT wire harnesses, etc. The length of one side of the CNT aggregate 1 is, for example, 10 µm or more. Furthermore, when the CNT aggregate 1 is cylindrical, the diameter of the CNT aggregate 1 is, for example, 10 µm or more. Furthermore, the density of the CNT aggregate 1 is, for example, 0.8 g / cm 3The 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, in a CNT aggregate 1, a metal compound 3 such as a metal chloride is added to the inside and outside of a CNT 2 in order to reduce resistance. Here, molybdenum chloride (MoCl 5 2, the CNT 2 is shown as a cylinder for simplicity. 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] As shown in Fig. 3, the surface of the CNT aggregate 1 is covered with an oxide film 4 made of an oxide of a metal compound 3. The oxide film 4 is intended to isolate the metal compound 3 from the atmosphere and to suppress the release of the metal compound 3 and the reaction of the metal compound 3 with oxygen or water in the atmosphere. 5 When molybdenum oxide (MoO 3 , MoO 2 ) or 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 to 500°C or higher to remove moisture from the CNTs 2. Next, O 2 The CNT film and MoCl were 5 After mixing the gases, the CNT film is sealed in a container to isolate it from the atmosphere and heated at 260°C to 350°C. Then, the MoCl on the CNT film surface is removed by washing with ethanol. 5 Remove.

[0016] In this way, MoCl was added as the metal compound 3 to the inside or outside of the CNT2. 5 is added, and the surface becomes MoO 2In this manufacturing method, the surface of the CNT aggregate 1 is covered with the oxide film 4, and the opening of the CNT 2 is filled with the oxide of the metal compound 3, such as MoO 2 etc. are capped.

[0017] 4 to 6 are scanning electron microscope photographs of the cross section of the CNT aggregate 1 produced by the above method, and show the molybdenum, oxygen, and chlorine contents inside and on the surface of the CNT aggregate 1. In Figs. 4 to 6, the white parts have higher molybdenum, oxygen, and chlorine contents than the black parts. As shown in Figs. 4 to 6, the surface of the CNT aggregate 1 has higher molybdenum and oxygen contents and lower chlorine contents compared to the inside of the CNT aggregate 1. This shows that an oxide film 4 composed mainly of molybdenum and oxygen is formed on the surface of the CNT aggregate 1.

[0018] FIG. 7 is a diagram showing the results of investigating the heat resistance of the CNT aggregate 1 produced by the above method. The horizontal axis of the graph in FIG. 7 is the heating time when a heating test was performed at 230°C in the atmosphere, and the vertical axis is the electrical resistivity measured by the four-terminal measurement method at room temperature after the CNT aggregate was removed from the heating device. In FIG. 7, the open circles indicate the electrical resistivity of the CNT aggregate 1 having a molybdenum oxide film thicker than 1 nm and thinner than 10 nm formed on its surface, and the open squares indicate the electrical resistivity of the CNT aggregate 1 having a molybdenum oxide film with a thickness of 10 nm formed on its surface. In FIG. 7, the open triangles indicate the electrical resistivity of a CNT aggregate without an oxide film formed on its surface, and this CNT aggregate contained AuCl 3 is added.

[0019] As shown in Figure 7, when a CNT aggregate without an oxide film formed on its surface was heated at 230 °C, the electrical resistance increased in a short time and the AuCl 3 In contrast, in the CNT aggregate 1 on whose surface the oxide film 4 is formed, the electrical resistance does not increase significantly even after heating for a long period of time, but remains small.

[0020] As described above, in this embodiment, the resistance of the CNT aggregate 1 is reduced by adding the metal compound 3 to the inside and outside of the CNT 2. Then, by covering the surface of the CNT aggregate 1 with the oxide film 4 composed of an oxide of this metal compound 3, the metal compound 3 is shielded from the atmosphere, and thus the heat resistance is improved compared to the conventional art, and heat resistance of 200°C or more is obtained.

[0021] Moreover, as described above, by capping the openings of the CNTs 2 with an oxide of the metal compound 3, the metal compound 3 inside the CNTs 2 is isolated from the atmosphere, thereby further improving the heat resistance.

[0022] This indicates that the FeCl 3 This can also be confirmed in the doping test. 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 CNT films after heat treatment and CNT films after heat treatment that were further doped. C-1 is a CNT film that was only heat-treated, C-2 is a CNT film that was doped with IBr after heat treatment, and C-3 is a CNT film that was doped with FeCl after heat treatment. 3 C-2 is a CNT film doped with 99.9% pure anhydrous FeCl manufactured by Sigma Aldrich. 3 was used as a dopant without purification. For C-3, 98% pure IBr manufactured by Sigma Aldrich was used as a dopant without purification. In the doping process, the CNT film and the dopant were allowed to coexist in a sealed container filled with an inert gas, and the process was carried out 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.

[0023] Then, to investigate the temperature dependency of the electrical resistivity of C-1 to C-3, the 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 8 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.

[0024] The thermal stability was also 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.

[0025] In the XPS measurements, FeCl 3 To detect Fe and Cl inside the CNT doped with Fe, we focused on the peaks in the Fe2p region around 712 eV and the Cl2p region around 198 eV. Figures 9A and 9B show the relationship between the intensity (au) of the XSP spectrum 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.

[0026] As can be seen from Fig. 9A and Fig. 9B, in the XPS spectrum of C-3, disappearance of the peak or change in the peak shape in the region of interest was not observed before and after heating. Therefore, 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, FeCl 3 It can be said that the above is maintained.

[0027] In addition, the shift of the G-band peak position in the Raman spectrum reflects the state of p-type doping of the CNT. Figure 10 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.

[0028] 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.

[0029] In TG-DTA, C-1 to C-3 and FeCl 3 The powder was analyzed. As a result, as shown in Figure 11, FeCl 3 The thermal stability of FeCl2 was different depending on whether it was doped or not. 3Thermogravimetry (TG) of the powder alone confirmed a weight loss from around 200°C, while C-3 confirmed a rapid weight loss from around 500°C and 700°C. The latter was due to the weight loss of the CNTs themselves, as the slope was almost the same as the rapid weight loss in C-1 at temperatures around 500°C and 700°C, while the former was due to FeCl 3 This suggests that the weight loss is due to FeCl encapsulated in the CNTs. 3 It is believed that the CNTs became more thermally stable than when they were alone. This phenomenon was also confirmed in C-2, which supports the result that the thermal stability is improved by encapsulating other substances.

[0030] (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.

[0031] For example, in the above embodiment, the metal compound 3 is MoCl 5 is added to the CNT aggregate 1, other metal chlorides may be added, or metal compounds other than metal chlorides may be added. Also, the metal compound 3 may be added only to the inside of the CNTs 2, or only to the outside of the CNTs 2. [Explanation of symbols]

[0032] 2. CNTs 3 Metal compounds 4. Oxide film

Claims

1. A carbon nanotube aggregate comprising a plurality of carbon nanotubes (2), A metal compound (3) is added to at least one of the inside and the outside of the carbon nanotube, An aggregate of carbon nanotubes, the surface of which is covered with an oxide film (4) composed of an oxide of the metal compound.

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

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

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

5. Density is 0.8 g / cm ３ 5. The aggregate of carbon nanotubes according to claim 1, wherein the carbon nanotube aggregate is a carbon nanotube aggregate having a diameter of 100 nm or more.

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