Preparation method of densified carbon nanotube film with low infrared emissivity

Abstract

The invention discloses a densified carbon nanotube film with low infrared emissivity and a preparation method thereof, and relates to the technical field of infrared stealth materials. The method comprises the following steps: firstly carrying out heat treatment on a carbon nanotube film in an inert atmosphere, and then putting the carbon nanotube film into an acid pickling solution for treatment, and dipping the pickled carbon nanotube film in chlorosulfonic acid, and heating to volatilize the chlorosulfonic acid to obtain the densified carbon nanotube film. The infrared emissivity of the prepared carbon nanotube film can be as low as 0.25 and is only 39% of the infrared emissivity value of an initial carbon nanotube film, so that the carbon nanotube film is expected to be applied to the field of infrared stealth.

Description

Technical Field

[0001] The invention relates to the technical field of infrared stealth materials, and in particular to a method for preparing a densified carbon nanotube film with low infrared emissivity. Background Art

[0002] Infrared stealth technology is an indispensable technology in the modern military field. With the rapid development of advanced infrared detection technology, infrared stealth technology has become the focus of military attention. Under normal circumstances, since the infrared radiation intensity of an object is higher than the background, it is easy to be exposed to the infrared detector. In order to achieve infrared stealth camouflage, the infrared emissivity between the target object and the background should be close enough. However, the radiation intensity of most objects is higher than the background. Therefore, it is urgent to develop thin film materials with low infrared emissivity to meet the needs of weapons and equipment for infrared stealth performance. Carbon nanotube film has excellent environmental adaptability and is a basic material with great application potential in the military field. However, the current carbon nanotube film has the problem of high porosity and poor infrared stealth performance. Patent CN115504459A discloses a method for reducing the infrared emissivity of carbon nanotube film. They use KOH solution activation and argon atmosphere heat treatment to make the infrared emissivity of carbon nanotube film as low as 0.473 in the 3-5 μm band and as low as 0.493 in the 8-14 μm band. However, since the carbon nanotube film prepared by this method is still a porous structure, its infrared emissivity cannot be further reduced. Patent CN112299395 A discloses a method for reducing the porosity of carbon nanotube films, but does not involve changes in infrared emissivity and applications in infrared stealth. In general, due to their unique structure and physical and chemical properties, the infrared emissivity of carbon nanotubes is generally high, so there are relatively few studies on infrared stealth. Summary of the invention

[0003] In view of the shortcomings of the above background technology, the present invention provides a method for preparing a densified carbon nanotube film with low infrared emissivity. The method can significantly reduce the infrared emissivity of the densified carbon nanotube film.

[0004] The first object of the present invention is to provide a method for preparing a densified carbon nanotube film with low infrared emissivity, comprising the following steps: The carbon nanotube film is first heat-treated in an inert atmosphere and then placed in an acid-washing solution for treatment; The acid-washed carbon nanotube film is immersed in chlorosulfonic acid and heated to volatilize the chlorosulfonic acid, thereby obtaining a densified carbon nanotube film.

[0005] Preferably, the heat treatment temperature is 1050-1200° C., and the heat treatment time is 8-12 hours.

[0006] Preferably, the treatment in an acid pickling solution comprises: immersing the carbon nanotube film in an HCl solution and stirring for 12 to 24 hours; wherein the concentration of the HCl solution is 4 to 6 mol / L.

[0007] Preferably, the acid-washed carbon nanotube film is immersed in chlorosulfonic acid and heated to volatilize the chlorosulfonic acid, comprising: Chlorosulfonic acid is added dropwise to the acid-washed carbon nanotube film, treated for 1 to 2 minutes, and then heated to 145 to 155° C. to accelerate the volatilization of the chlorosulfonic acid.

[0008] Preferably, the thickness of the carbon nanotube film is 3-8 μm; and the carbon nanotubes in the carbon nanotube film are arranged in a three-dimensional network structure.

[0009] Preferably, after heating to volatilize the chlorosulfonic acid, the method further comprises: taking out the carbon nanotube film, washing it with distilled water and alcohol until it becomes neutral, and drying it in vacuum at 50-60° C. after washing.

[0010] The second object of the present invention is to provide a densified carbon nanotube film with low infrared emissivity obtained by the above method.

[0011] The third object of the present invention is to provide a densified carbon nanotube film for use in infrared stealth.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a densified carbon nanotube film with low infrared emissivity. The present invention is based on the presence of amorphous carbon generated during preparation in the original carbon nanotube film, as well as metal catalysts and oxides thereof remaining during preparation. The amorphous carbon in the carbon nanotube film is removed by heat treatment in an inert gas environment, and the heat-treated carbon nanotube film is immersed in an HCl solution to remove the metal catalysts and oxides thereof remaining therein. Chlorosulfonic acid has high hygroscopicity and high polarity. After the carbon nanotube film is treated with chlorosulfonic acid, charge separation on a single carbon nanotube is further induced, positive charge regions and negative charge regions are generated, and the positive and negative charge sites on the tube are increased. Under the action of Coulomb charge and van der Waals force, the connection sites between the carbon nanotubes are increased, and the connection is more tightly connected, thereby achieving a densification effect. Because the connection sites between carbon nanotubes increase, the electron transmission speed in them is faster, and the conductivity is greatly improved. In the infrared band, the emissivity is proportional to the resistivity, so the infrared emissivity of the carbon nanotube film is reduced; in addition, after the densification treatment, the surface roughness of the carbon nanotube film is greatly reduced, further improving the infrared stealth performance of the carbon nanotube film. The infrared emissivity of the carbon nanotube film prepared by the present invention can be as low as 0.25, which is only 39% of the infrared emissivity value of the initial carbon nanotube film. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 SEM images of different carbon nanotube films; Figure 2 The SEM images of the initial carbon nanotube film and the densified carbon nanotube film after FIB cutting; Figure 3 AFM images of different carbon nanotube films, Ra and Rq are marked; Figure 4 Raman spectra of different carbon nanotube films; Figure 5 Comparison of G peak and D′ peak of Raman spectra of different carbon nanotube films; Figure 6 XRD spectra of different carbon nanotube films; Figure 7 is the electrical conductivity of different carbon nanotube films; Figure 8 are stress-strain curves of different carbon nanotube films; Fig. 9 is the infrared emissivity of different carbon nanotube films. DETAILED DESCRIPTION

[0014] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0015] The present invention aims to provide a method for preparing a densified carbon nanotube film, which method can significantly reduce the infrared emissivity of the densified carbon nanotube film.

[0016] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a densified carbon nanotube film with low infrared emissivity, comprising the following steps: The carbon nanotube film is first heat-treated in an inert atmosphere and then placed in an acid-washing solution for treatment; The acid-washed carbon nanotube film is immersed in chlorosulfonic acid and heated to volatilize the chlorosulfonic acid, thereby obtaining a densified carbon nanotube film.

[0017] The heat treatment temperature is 1050-1200°C, and the heat treatment time is 8-12 h.

[0018] The carbon nanotube film is placed in an acid pickling solution for treatment, including: immersing the carbon nanotube film in an HCl solution and stirring for 12 to 24 hours; wherein the concentration of the HCl solution is 4 to 6 mol / L.

[0019] The acid-washed carbon nanotube film is immersed in chlorosulfonic acid and heated to volatilize the chlorosulfonic acid, which includes: dropping chlorosulfonic acid on the acid-washed carbon nanotube film, treating for 1-2 minutes, and then heating to 145-155° C. to accelerate the volatilization of the chlorosulfonic acid therein.

[0020] The thickness of the carbon nanotube film is 3-8 μm; the carbon nanotubes in the carbon nanotube film are arranged in a three-dimensional network structure.

[0021] After heating to volatilize the chlorosulfonic acid, the method further includes: taking out the carbon nanotube film, washing it with distilled water and alcohol until it becomes neutral, and then vacuum drying it at 50-60°C after washing.

[0022] In one embodiment, a method for preparing a densified carbon nanotube film with low infrared emissivity includes the following specific steps: firstly heat-treating the carbon nanotube film in an argon atmosphere, then placing it in an HCl solution for acid treatment, and finally adding chlorosulfonic acid and heating to volatilize the chlorosulfonic acid therein to obtain a densified carbon nanotube film.

[0023] Among them, the thickness of the carbon nanotube film is 3~8 μm, and the carbon nanotubes in the carbon nanotube film are arranged in a three-dimensional network structure.

[0024] The heat treatment was carried out in an argon atmosphere at a temperature of 1100 °C, a heat treatment time of 10 h, and a heating rate of 5 °C / min.

[0025] The carbon nanotube film is placed in an HCl solution for acid treatment, specifically, the carbon nanotube film is immersed in an HCl solution with a concentration of 5 mol / L and stirred for 24 h.

[0026] Chlorosulfonic acid is added dropwise and heated to volatilize the chlorosulfonic acid therein. Specifically, chlorosulfonic acid is added dropwise on the carbon nanotube film, treated for 1 minute, and then heated to 150° C. to accelerate the volatilization of the chlorosulfonic acid therein.

[0027] The second aspect of the present invention provides a densified carbon nanotube film with low infrared emissivity obtained by the above method.

[0028] A third aspect of the present invention provides an application of a densified carbon nanotube film in infrared stealth.

[0029] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0030] Example 1 A method for removing impurities from a carbon nanotube film comprises the following steps: A carbon nanotube film with a size of 10 mm×10 mm was placed in a tubular furnace and heated to 1100°C in an inert atmosphere at a heating rate of 5°C / min. The temperature was kept for 10 h and then cooled to room temperature to obtain a CNT-1 film.

[0031] Example 2 A method for removing impurities from a carbon nanotube film comprises the following steps: (1) A carbon nanotube film with a size of 10 mm × 10 mm was placed in a tube furnace and heated to 1100 °C in an inert atmosphere at a heating rate of 5 °C / min for 10 h, followed by cooling to room temperature; (2) The carbon nanotube film cooled to room temperature was immersed in a 5 mol / L HCl solution and stirred at room temperature for 24 h; (3) The immersed carbon nanotube film was washed with deionized water several times until it became neutral, and then dried at 50-60 °C for 24 h to obtain a CNT-2 film.

[0032] Example 3 A method for preparing a densified carbon nanotube film with low infrared emissivity comprises the following steps: (1) A carbon nanotube film with a size of 10 mm × 10 mm was placed in a tube furnace and heated to 1100 °C in an inert atmosphere at a heating rate of 5 °C / min for 10 h, followed by cooling to room temperature; (2) The carbon nanotube film cooled to room temperature is immersed in a 5 mol / L HCl solution, stirred at room temperature for 24 h, and the immersed carbon nanotube film is washed several times with deionized water until it is neutral, and then dried at 50-60 °C for 24 h; (3) Finally, chlorosulfonic acid was added to the dried carbon nanotube film. After treatment for 1 min, the film was heated to 150 °C to accelerate the volatilization of chlorosulfonic acid. The treatment lasted for about 45 min. The film was washed with deionized water several times until neutral. The film was then dried at 50-60 °C for 24 h to obtain a DCNT film.

[0033] The carbon nanotube films prepared in Examples 1 to 3 and the initial carbon nanotube films were characterized in terms of microstructure and performance: Figure 1 shows the SEM images of the initial carbon nanotube film and the carbon nanotube films prepared in Examples 1 to 3. Figure 1 (a) is the SEM image of the initial carbon nanotube film (P-CNT film); (b) is the SEM image of the carbon nanotube film after heat treatment (CNT-1 film); (c) is the SEM image of the carbon nanotube film after acid treatment (CNT-2 film); (d) is the SEM image of the densified carbon nanotube film (DCNT film). The magnification is 50,000. It can be seen that the original carbon nanotube film contains granular impurities, and due to the weak connection between the tubes, the tube bundle structure is loose, forming a large number of voids and cracks. This structural defect not only affects the efficiency of stress transfer between tubes, but also increases the contact resistance, thereby adversely affecting the overall performance of carbon nanotubes. When the carbon nanotubes are heat treated at 1100 ° C in an argon environment, most of the amorphous carbon is removed, and the structure of the carbon nanotubes becomes purer, which not only restores its sp 2 The hybridized graphite structure is also an effective means to improve the performance of carbon nanotubes. In contrast, the microstructure of the carbon nanotube film washed with hydrochloric acid does not seem to have changed significantly. This is because most of the metal catalysts are wrapped inside the carbon nanotubes, and only a small amount of catalyst exists between the tubes. The hydrochloric acid treatment mainly removes the metal catalysts in the gaps between the tubes, while the catalysts wrapped inside are not removed because they are protected by the carbon layer, so the microstructure does not change much. However, when the carbon nanotube film is treated with chlorosulfonic acid (CSA), its structure becomes significantly tighter. In this densified carbon film, the carbon nanotubes are stacked tightly together, and the gaps between the tubes are significantly reduced, showing a tightly interwoven structural feature.

[0034] Figure 2 The FIB-SEM images of the initial carbon nanotube film and the carbon nanotube film prepared in Example 3 are shown. Figure 2 (a) is the SEM image of the cross section of the P-CNT film after FIB cutting, with a magnification of 5000; (b) is the SEM image of the cross section of the P-CNT film after FIB cutting, with a magnification of 15000; (c) is the SEM image of the cross section of the DCNT film after FIB cutting, with a magnification of 5000; (d) is the SEM image of the cross section of the DCNT film after FIB cutting, with a magnification of 25000; It can be seen from the figure that after being treated with chlorosulfonic acid (CSA), the densification effect of the carbon nanotube film is significant, and its thickness is reduced from the original 6.3 microns to 2.3 microns. In addition, the proportion of holes and gaps on the cross section has also been significantly reduced, and at the same time, the delamination phenomenon of the film has been effectively alleviated. The treated carbon nanotube film shows a more compact and dense structural feature.

[0035] Figure 3The FIB-SEM images of the initial carbon nanotube film and the carbon nanotube films prepared in Examples 1 to 3 are shown. Figure 3 (a) is the AFM image of the P-CNT film; (b) is the AFM image of the CNT-1 film; (c) is the AFM image of the CNT-2 film; (d) is the AFM image of the DCNT film. It can be seen from the figure that the roughness parameters Rq (root mean square roughness) and Ra (arithmetic mean roughness) of the CNT film decreased from 70.3 nm and 55.4 nm to 21.5 nm and 13.7 nm, respectively.

[0036] Figure 4 The Raman spectra of the initial carbon nanotube film and the carbon nanotube film prepared in Examples 1 to 3 are shown. It can be observed that the intensity ratio of the D band to the G band (I D / I G ) showed a slight decrease. This phenomenon can be attributed to the fact that the heat treatment and hydrochloric acid treatment effectively removed the amorphous carbon and metal catalyst in the film, while reducing the sp 3 The number of hybridized carbon atoms and structural kinks. Further chlorosulfonic acid treatment leads to I D / I G The increase in the ratio may be due to the fact that chlorosulfonic acid, as a strong oxidant, oxidized the carbon nanotubes and introduced new functional groups and defects.

[0037] Figure 5 The comparison of the G peak and D' peak in the Raman spectra of the initial carbon nanotube film and the carbon nanotube film prepared in Examples 1 to 3 is shown. The characteristics of the G band and the D' band in the Raman spectrum of the initial carbon nanotube film are obvious. During the purification process, the vibration signal of the D' band related to the E2g mode gradually weakened, and after the chlorosulfonic acid (CAS) treatment, the characteristics of the D' band can hardly be observed. This change may be closely related to the densification process of the carbon nanotube film. In this process, the strong mutual attraction between individual carbon nanotubes may reduce the intensity of the unbonded vibration.

[0038] FIG6 shows the XRD spectra of the initial carbon nanotube film and the carbon nanotube films prepared in Examples 1 to 3. At an angle of 26.5° (interplanar spacing of 0.334 nm), all samples show a similar characteristic peak corresponding to the diffraction of the (111) plane of CNT. It is noteworthy that the diffraction peak width of the densified CNT film after treatment with chlorosulfonic acid (CSA) is significantly wider than that of other samples. This increase in peak width is likely due to the aggregation of CNTs.

[0039] Depend on Figures 1 to 6It can be concluded that the carbon nanotubes in the carbon nanotube film prepared in Example 3 change from being loosely stacked and filling the gaps to being tightly stacked and entangled with each other, the contact sites increase dramatically, and the transmission resistance of electrons therein is significantly reduced.

[0040] FIG7 shows the conductivity of the initial carbon nanotube film and the carbon nanotube films prepared in Examples 1 to 3. The conductivity of the carbon nanotube films prepared in Examples 1 and 2 only slightly increased due to the lack of effective contact points. Remarkably, the conductivity of the carbon nanotube film prepared in Example 3 increased rapidly to 223086.28 S / m, which is more than one order of magnitude higher than the original CNT film. As theoretically analyzed, the contact sites between carbon nanotubes increased dramatically, the electron transport resistance decreased, and the conductivity increased significantly.

[0041] Figure 8 shows the mechanical properties of the initial carbon nanotube film and the carbon nanotube films prepared in Examples 1 to 3. It can be seen that the carbon nanotube film prepared in Example 3 has a tensile strength of 314.32 MPa, which has extremely high mechanical strength.

[0042] FIG9 shows the infrared emissivity test results of the initial carbon nanotube film and the carbon nanotube films prepared in Examples 1 to 3. The results show that the far-infrared emissivity of the initial carbon nanotube film is 0.64. The far-infrared emissivity of the carbon nanotube films prepared in Examples 1 and 2 is slightly reduced to 0.57. It is noteworthy that the far-infrared emissivity of the CNT film prepared in Example 3 is greatly reduced to 0.25.

[0043] In summary, the present invention provides a method for preparing a densified carbon nanotube film with low infrared emissivity, specifically: first heat-treating the carbon nanotube film in an inert atmosphere to remove impurities on the surface of the carbon nanotubes, then using an acid solution to remove the catalyst nanoparticles introduced when preparing the carbon nanotubes, and finally immersing it in chlorosulfonic acid and heating it to volatilize the chlorosulfonic acid therein to obtain a densified carbon nanotube film. The infrared emissivity of the carbon nanotube film prepared by the present invention can be as low as 0.25, which greatly reduces the infrared emissivity of the carbon nanotube film, making it expected to be used in the field of infrared stealth.

[0044] The present invention describes preferred embodiments and their effects. However, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a densified carbon nanotube film with low infrared emissivity, characterized in that: The following steps are involved: The carbon nanotube film is first heat-treated in an inert atmosphere and then placed in an acid-washing solution for treatment; The acid-washed carbon nanotube film is immersed in chlorosulfonic acid and heated to volatilize the chlorosulfonic acid, thereby obtaining a densified carbon nanotube film.

2. The method for preparing a densified carbon nanotube film with low infrared emissivity according to claim 1, characterized in that: The heat treatment temperature is 1050-1200°C, and the heat treatment time is 8-12 h.

3. The method for preparing a densified carbon nanotube film with low infrared emissivity according to claim 1, characterized in that: The carbon nanotube film is placed in an acid pickling solution for treatment, including: immersing the carbon nanotube film in an HCl solution and stirring for 12 to 24 hours; wherein the concentration of the HCl solution is 4 to 6 mol / L.

4. The method for preparing a densified carbon nanotube film with low infrared emissivity according to claim 1, characterized in that: The acid-washed carbon nanotube film is immersed in chlorosulfonic acid and heated to volatilize the chlorosulfonic acid, including: Chlorosulfonic acid is added dropwise to the acid-washed carbon nanotube film, treated for 1 to 2 minutes, and then heated to 145 to 155 °C to accelerate the volatilization of chlorosulfonic acid.

5. The method for preparing a densified carbon nanotube film with low infrared emissivity according to claim 1, characterized in that: The thickness of the carbon nanotube film is 3-80 μm; the carbon nanotubes in the carbon nanotube film are arranged in a three-dimensional network structure.

6. The method for preparing a densified carbon nanotube film with low infrared emissivity according to claim 1, characterized in that: After heating to volatilize the chlorosulfonic acid, the method further includes: taking out the carbon nanotube film, washing it with distilled water and alcohol until it becomes neutral, and then vacuum drying it at 50-60°C after washing.

7. A densified carbon nanotube film with low infrared emissivity obtained by the method according to any one of claims 1 to 6.

8. Use of the densified carbon nanotube film according to claim 7 in the field of infrared stealth.

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