Spiral multi-arm carbon nanotube as well as preparation method and application thereof

Abstract

The invention provides a spiral multi-arm carbon nanotube and a preparation method and application thereof.The preparation method comprises the steps that a ceramic plate where a catalyst is evenly dispersed is placed in a CVD chamber, then the ceramic plate is heated to the synthesis temperature in the environment that inert gas or reducing gas is introduced, after the temperature is stable, C2H2 and H2 are introduced, a reaction is conducted at the synthesis temperature, and the spiral multi-arm carbon nanotube is obtained. And after the reaction is finished, cooling the PVD chamber in an inert gas or reducing gas environment to obtain the spiral multi-arm carbon nanotube. The spiral multi-arm carbon nanotube (acidified spiral multi-arm carbon nanotube) provided by the invention has refined grains, smaller diameter, more unsaturated bonds and oxygen-containing functional groups, high internal defect degree, more appropriate dielectric property, better effective conductivity and penetration depth, higher dielectric polarization relaxation degree and higher dielectric property. And therefore, the wave-absorbing material has good electromagnetic wave attenuation capability and impedance matching characteristic, and is relatively excellent in comprehensive wave-absorbing performance.

Description

Technical Field

[0001] The invention relates to a spiral multi-arm carbon nanotube and a preparation method and application thereof, belonging to the technical field of materials, in particular to the technical field of electromagnetic wave absorption materials. Background Art

[0002] Radar detection technology, as an effective means of over-the-horizon modern warfare, is widely used to obtain battlefield information and monitor targets. The enhancement of microwave absorption capacity can greatly reduce the reflected echo signal and improve the stealth performance of weapons and equipment. Carbon nanotubes have the advantages of low density, excellent dielectric properties, high conductivity and good environmental stability. They have been widely studied in recent decades and are considered to be one of the most attractive candidates for the next generation of stealth materials. At the same time, carbon nanotubes have been shown to promote conductivity loss, Maxwell-Wagner effect and multiple scattering due to their advantages such as high electron mobility, light weight, large specific surface area and a large number of hanging sites on the surface. However, higher conductivity usually leads to stronger skin effect and shielding effect, which limits the absorption performance. Therefore, modifying carbon nanotubes to achieve high absorption performance is the main technical problem that needs to be solved at present.

[0003] Carbon nanotubes are made of single or multi-walled graphite sheets that are seamlessly rolled up. The graphite sheets are arranged in different ways in three-dimensional and two-dimensional layers, resulting in different microstructures. In three-dimensional layers, they can be divided into single-walled and multi-walled carbon nanotubes according to the number of radial layers. Figure 1 As shown, in the carbon atom SP 2 On the two-dimensional level of the hexagonal grid formed by hybridization, carbon nanotubes exist and The unit cell basis vector, the vector from A to the curling coincidence point of A' can be obtained by the unit cell basis vector Where n and m are integers, and the vector is also called the chiral vector. The curling form and physical and chemical properties of carbon nanotubes are closely related to the parameters n and m. Different carbon deposition rates at different sites will change the n and m parameters, thereby affecting the chiral vector.

[0004] Therefore, providing a new type of spiral multi-arm carbon nanotube and its preparation method and application has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a method for preparing spiral multi-arm carbon nanotubes.

[0006] Another object of the present invention is to provide a spiral multi-arm carbon nanotube, which is prepared by the above-mentioned preparation method. The spiral multi-arm carbon nanotube has low effective conductivity, high penetration depth, and obvious dielectric polarization relaxation, so that its impedance matching characteristics and electromagnetic wave attenuation performance are better, and the comprehensive wave absorption performance is better.

[0007] Another object of the present invention is to provide the application of the above-mentioned spiral multi-arm carbon nanotubes as absorbing materials or grid frames used for absorbing materials in military equipment stealth, electronic equipment anti-electromagnetic interference, medical radiation protection or aerospace.

[0008] In order to achieve the above objectives, on the one hand, the present invention provides a method for preparing a spiral multi-arm carbon nanotube, wherein the preparation method comprises:

[0009] First, a ceramic plate with a uniformly dispersed catalyst is placed in a CVD chamber, and then heated to a synthesis temperature in an environment of inert gas or reducing gas. After the temperature stabilizes, C2H2 and H2 are introduced and reacted at the synthesis temperature. After the reaction is completed, the PVD chamber is cooled in an inert gas or reducing gas environment to obtain the spiral multi-arm carbon nanotubes.

[0010] As a specific embodiment of the above preparation method of the present invention, the preparation method further comprises:

[0011] Mixing concentrated nitric acid and concentrated sulfuric acid to obtain a mixed acid;

[0012] The spiral multi-arm carbon nanotubes are added to the mixed acid and subjected to acidification treatment under stirring. After the acidification treatment, the product is filtered, washed and dried in sequence to obtain acidified spiral multi-arm carbon nanotubes.

[0013] As a specific embodiment of the preparation method described above in the present invention, the inert gas includes nitrogen, helium, argon or neon, and the reducing gas includes hydrogen.

[0014] As a specific embodiment of the preparation method described above of the present invention, the reaction temperature is 600-1000° C. and the reaction time is 60-90 min.

[0015] As a specific embodiment of the preparation method described above in the present invention, the flow rates of C2H2 and H2 are 4-6 mL / min and 8-12 mL / min respectively.

[0016] As a specific embodiment of the preparation method described above in the present invention, the catalyst is a mixture of PCl3 and Ni, and the mass ratio of the two is 1:2-1:1.

[0017] As a specific embodiment of the above preparation method of the present invention, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:4-1:2.

[0018] As a specific embodiment of the above preparation method of the present invention, the temperature of the acidification treatment is 60-80°C and the time is 2-5h.

[0019] In the present invention, under the action of unsaturated bond attack, catalytic effect and other factors, the carbon nanotube changes from a single carbon six ring to a carbon five ring and a carbon seven ring. The formation of the carbon five ring makes the carbon nanotube bend inward; the carbon seven ring makes the carbon nanotube bend outward, and a carbon five-seven ring produces a turning structure, thereby forming a periodic spiral structure. As a chiral material, the spiral carbon nanotube shows excellent frequency adaptability and electromagnetic adjustability, and can achieve broadband radar absorption. Acid treatment is an important step in the modification and purification of carbon nanotubes. By introducing new functional groups on the surface of CNTs through acidification, it can continue to be grafted or surface modified with other reagents, thereby improving the dispersibility and solubility of CNTs.

[0020] On the other hand, the present invention further provides a spiral multi-arm carbon nanotube, wherein the spiral multi-arm carbon nanotube is prepared by the above-mentioned method for preparing the spiral multi-arm carbon nanotube.

[0021] As a specific embodiment of the above-mentioned spiral multi-arm carbon nanotube of the present invention, the spiral multi-arm carbon nanotube is an acidified spiral multi-arm carbon nanotube.

[0022] As a specific embodiment of the spiral multi-arm carbon nanotubes described above in the present invention, the spiral multi-arm carbon nanotubes have abundant unsaturated bonds and oxygen-containing functional groups, a diameter of 50-100nm, a relatively short tube length of only 2-5μm, and are curled and arranged in a regular and tight manner with a very short pitch of 50-100nm, presenting a symmetrical growth pattern.

[0023] On the other hand, the present invention also provides the use of the above-mentioned spiral multi-arm carbon nanotubes as absorbing materials or grid frames used for absorbing materials in military equipment stealth, electronic equipment anti-electromagnetic interference, medical radiation protection or aerospace.

[0024] The spiral multi-arm carbon nanotubes (acidified spiral multi-arm carbon nanotubes) provided by the present invention have refined grains, small diameters, more unsaturated bonds and oxygen-containing functional groups, high internal defectivity, more suitable dielectric properties, better effective conductivity and penetration depth, higher degree of dielectric polarization relaxation, and thus good electromagnetic wave attenuation capability and impedance matching characteristics, and better comprehensive wave absorbing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 Schematic diagram of the chiral parameters of carbon nanotubes.

[0027] Figure 2 1 is the XRD pattern of HCNT, AHCNT, CNT and ACNT in Test Example 1. From top to bottom in the XRD pattern, they are CNT, ACNT, HCNT and AHCNT respectively.

[0028] Figure 3 This is the laser Raman spectrum of HCNT, AHCNT, CNT and ACNT in Test Example 2. From top to bottom in the laser Raman spectrum are AHCNT, HCNT, ACNT and CNT respectively.

[0029] Figure 4a-4d IR spectra of CNT, ACNT, HCNT and AHCNT in Test Example 3.

[0030] Figure 5a-Figure 5b This is the SEM image of CNT in Test Example 4.

[0031] Figure 5c-5d This is the SEM image of ACNT in Test Example 4.

[0032] Figure 5e-5f This is the SEM image of HCNT in Test Example 4.

[0033] Figure 5g-Figure 5h This is the SEM image of AHCNT in Test Example 4.

[0034] Figure 5i-5j This is the TEM image of AHCNT in Test Example 4.

[0035] Figure 6a-6c The complex dielectric constants and electrical loss factors of CNT, ACNT, HCNT and AHCNT in Test Example 5 are shown respectively.

[0036] Figure 6d-Figure 6e The total effective conductivity and penetration depth of CNT, ACNT, HCNT and AHCNT in Test Example 5 are respectively.

[0037] Figure 6f The Cole-Cole curves of CNT, ACNT, HCNT and AHCNT in Test Example 5 are shown in FIG.

[0038] Figure 7a Graph showing the relationship between the attenuation coefficients of CNT, ACNT, HCNT and AHCNT and the frequency in Test Example 6.

[0039] Figure 7b-7c They are respectively the three-dimensional model diagram and the two-dimensional plane diagram / two-dimensional contour diagram of the reflection loss of CNT in Test Example 6.

[0040] Figure 7d-7e They are respectively the three-dimensional model diagram and the two-dimensional plane diagram / two-dimensional contour diagram of the reflection loss of ACNT in Test Example 6.

[0041] Figure 7f-7g They are respectively the three-dimensional model diagram and the two-dimensional plane diagram / two-dimensional contour diagram of the reflection loss of HCNT in Test Example 6.

[0042] Figure 7h-Figure 7i They are respectively the three-dimensional model diagram and the two-dimensional plane diagram / two-dimensional contour diagram of the reflection loss of AHCNT in Test Example 6. DETAILED DESCRIPTION

[0043] It should be noted that the term "comprises" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] "Scope" disclosed in the present invention is given in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, for a specific parameter, a range of 60-120 and 80-110 is listed, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4 and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0045] In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in the present invention, and "0-5" is just an abbreviation of these numerical combinations.

[0046] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0047] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0048] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0049] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to the normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0050] Example 1

[0051] This embodiment provides an acidified helical multi-arm carbon nanotube, which is prepared by a method comprising the following specific steps:

[0052] A mixed gas of acetylene (C2H2) and hydrogen (H2) is used as a raw material, and a magnetron sputtering method (PVD) is used to prepare spiral multi-arm carbon nanotubes, specifically comprising: firstly, a ceramic plate with a uniformly dispersed catalyst (a combined catalyst of PCl3 and Ni, the mass ratio of the two is 1:2, that is, the present embodiment adopts the synergistic catalysis of PCl3 and Ni to achieve) is placed in a PVD chamber, and then heated to a synthesis temperature (800°C) at a speed of 5°C / min in an environment where N2 is introduced;

[0053] After the temperature stabilized, C2H2 and H2 were introduced to react at the synthesis temperature for 60 min, and the gas flow rates of C2H2 and H2 were fixed at 5 mL / min and 10 mL / min, respectively. After the reaction was completed, the PVD chamber was cooled to room temperature in a H2 environment to obtain spiral multi-arm carbon nanotubes.

[0054] The method comprises the following steps: mixing concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3 in a beaker to obtain a mixed acid; taking 5 g of the prepared spiral multi-arm carbon nanotubes and adding them to 200 mL of the mixed acid, stirring them ultrasonically for 3 hours, and maintaining the reaction temperature at 60° C. for acidification; separating the reactants by filtration with a vacuum pump after the acidification, and repeatedly washing with deionized water until the pH value of the solution after washing is neutral; and finally placing the product after the reaction in a drying oven for drying to obtain acidified spiral multi-arm carbon nanotubes, which are recorded as AHCNTs.

[0055] Example 2

[0056] This embodiment provides a spiral multi-arm carbon nanotube, which is prepared by a method comprising the following specific steps:

[0057] A mixed gas of acetylene (C2H2) and hydrogen (H2) is used as a raw material, and a magnetron sputtering method (PVD) is used to prepare spiral multi-arm carbon nanotubes, specifically comprising: firstly, a ceramic plate with a uniformly dispersed catalyst (a combined catalyst of PCl3 and Ni, the mass ratio of the two is 1:2, that is, the present embodiment adopts the synergistic catalysis of PCl3 and Ni to achieve) is placed in a PVD chamber, and then heated to a synthesis temperature (800°C) at a speed of 5°C / min in an environment where N2 is introduced;

[0058] After the temperature stabilized, C2H2 and H2 were introduced to react at the synthesis temperature for 60 min. The gas flow rates of C2H2 and H2 were fixed at 5 mL / min and 10 mL / min, respectively. After the reaction, the PVD chamber was cooled to room temperature in a H2 environment to obtain spiral multi-arm carbon nanotubes, which were recorded as HCNTs.

[0059] Comparative Example 1

[0060] This comparative example provides a straight carbon nanotube, which is prepared by a method comprising the following specific steps:

[0061] A mixed gas of acetylene (C2H2) and hydrogen (H2) is used as a raw material, and a magnetron sputtering method (PVD) is used to prepare spiral multi-arm carbon nanotubes, specifically comprising: placing a ceramic plate with a uniformly dispersed catalyst (Ni catalyst, that is, the comparative example uses Ni catalyst alone for catalysis) in a PVD chamber, and then heating it to a synthesis temperature (800°C) at a speed of 5°C / min in an environment where N2 is introduced;

[0062] After the temperature stabilized, C2H2 and H2 were introduced to react at the synthesis temperature for 60 min, where the gas flow rates of C2H2 and H2 were fixed at 5 mL / min and 10 mL / min, respectively. After the reaction, the PVD chamber was cooled to room temperature in a H2 environment to obtain straight carbon nanotubes, which were recorded as CNTs.

[0063] Comparative Example 2

[0064] This comparative example provides an acidified straight carbon nanotube, which is prepared by a preparation method comprising the following specific steps:

[0065] The acidification of the straight carbon nanotubes is also achieved using concentrated nitric acid and concentrated sulfuric acid, specifically including: first, concentrated nitric acid and concentrated sulfuric acid are put into a beaker in a volume ratio of 1:3 and mixed to obtain a mixed acid; then, 5 g of the straight carbon nanotubes prepared in Comparative Example 1 are taken and added to 200 mL of the mixed acid, ultrasonically stirred for 3 hours, and the reaction temperature is maintained at 60°C for acidification treatment; after the acidification treatment, the reactants are separated by filtration using a vacuum pump, and repeatedly washed with deionized water until the pH value of the solution after rinsing is neutral; the product after the reaction is placed in a drying oven for drying to obtain acidified straight carbon nanotubes, recorded as ACNT.

[0066] Test Example 1

[0067] In this test example, XRD analysis was performed on HCNT, AHCNT, CNT and ACNT respectively. The obtained XRD patterns are shown in the figure below. Figure 2 As shown, Figure 2 From top to bottom, they are CNT, ACNT, HCNT, and AHCNT. Figure 2 It can be seen that each group of samples has an obvious characteristic peak at 2θ=25.5°, corresponding to the (002) crystal plane of carbon nanotubes, which shows that the above preparation and treatment technology routes can achieve good carbon nanotube generation. HCNT, AHCNT, CNT and ACNT all have obvious impurity peaks at 2θ=37.3°, 43.2°, 50.1°, etc., which shows that both acidification and spiralization treatment introduce a small amount of impurities into the material system. For the two groups of carbon nanotubes after acidification, namely AHCNT and ACNT, the half-peak width of the characteristic peak at 2θ=25.5° is significantly increased, which shows that acidification has the effect of refining the grains.

[0068] Test Example 2

[0069] In this test example, laser Raman spectroscopy was performed on HCNT, AHCNT, CNT and ACNT respectively. The obtained laser Raman spectra are shown in the figure below. Figure 3 As shown, Figure 3 From top to bottom they are AHCNT, HCNT, ACNT and CNT. Figure 3 It can be seen that in 100-300cm -1 The micro-peak at corresponds to the radial breathing mode (RBM), which belongs to the single-phonon first-order Raman diffraction process and is related to the radial correlation vibration of C atoms, which is an important basis for carbon nanotubes. The diameter of carbon nanotubes dt can be calculated. Through calculation, the diameter of AHCNT and HCNT is about 50nm, and the diameter of spiral carbon nanotubes, i.e. AHCNT and HCNT, is larger than that of straight carbon nanotubes, i.e. ACNT and CNT; and the RBM peak ratio of CNT is the most obvious, which may be related to its most complete diameter structure.

[0070] At frequency shift 1500-1600cm -1 The nearby Lorentz peak corresponds to the G mode of carbon nanotubes, which originates from the E 2g The G mode is the tangential vibration mode of carbon atoms along the surface of the carbon tube, which belongs to the first-order single-phonon Raman diffraction process. For SCNTs, i.e. single-walled carbon nanotubes, the G mode will also produce a weak peak at a low frequency shift, forming a double-peak structure. For MCNTs, i.e. multi-walled carbon nanotubes, this feature is relatively weak. The D peak of carbon nanotubes appears at a frequency shift of 1250-1450cm -1 Nearby, it originates from the lattice defects in the system, belongs to the second-order single-phonon Raman diffraction process, and is the Brillouin zone boundary mode. Its intensity I D and G peak intensity I G It is often used to characterize the defect density in the structure. Parameter I of each group of samples, namely AHCNT, HCNT, ACNT and CNT D / I G The values ​​are 0.86, 0.70, 0.67, and 0.61, respectively, indicating that acidification and helicalization will further increase the defect degree of carbon nanotubes. -1 ), which is related to the K point at the boundary of the Brillouin zone and belongs to the second-order two-phonon Raman diffraction process.

[0071] Test Example 3

[0072] In this test example, infrared spectroscopy analysis was performed on HCNT, AHCNT, CNT and ACNT to analyze the effects of acidification and helicalization on the bonding and functional groups of carbon nanotubes. The obtained infrared spectra are shown in the figure below. Figure 4a-4d As shown. Figure 4a-4d It can be seen that the samples have a high concentration of ions at 3500, 3020, 1720, 1500 and 1100 cm -1There are multiple groups of obvious absorption peaks near the wave number, and the corresponding functional groups are -OH, -CH3, C=O, C=C and CO. After comparison, it can be found that the number of unsaturated bonds and oxygen-containing functional groups in the acidified carbon nanotubes increases, and the number of unsaturated bonds in the spiralized carbon nanotubes increases. The reason is that during the acidification process, the free oxygen of nitric acid and sulfuric acid will break the carbon-carbon single bond to form CO2, thereby destroying and thinning the carbon nanotubes. At the fracture, carbon atoms will combine with oxygen atoms to form C=O and CO, or these two combinations will be carried out at the same time to form -COOH. In the spiralization process, the carbon 6 ring will be broken to produce carbon 5 ring and carbon 7 ring. Unsaturated bonds are easily generated in this process.

[0073] Test Example 4

[0074] In this test example, SEM analysis was performed on HCNT, AHCNT, CNT and ACNT to examine their microscopic morphology. The obtained SEM images are as follows: Figure 5a-5h As shown. Figure 5a-5h It can be seen that after acidification, both straight carbon nanotubes and spiral multi-arm carbon nanotubes have shortened their tube lengths (the length of acidified spiral multi-arm carbon nanotubes is about 2-5μm) and become entangled with each other. According to research reports by Green, Tang and others, strong acids can chemically cut carbon nanotubes to obtain open carbon nanotubes with end groups such as carboxyl and hydroxyl groups. Therefore, the diameter of straight carbon nanotubes / spiral multi-arm carbon nanotubes after acidification is shortened, forming many chemically active points, which in turn produce entanglement. Due to the formation of carbon five rings and carbon seven rings in carbon nanotubes and the spiral stacking effect, the diameter of the spiralized carbon nanotubes changes.

[0075] In this test example, AHCNT was also subjected to TEM analysis, and the obtained TEM image is shown in the following figure. Figure 5i and Figure 5j As shown, Figure 5j In the figure, the lower right parts A and B correspond to the crystalline part and the amorphous part respectively. Figure 5i and Figure 5j It can be seen that the acidified helical multi-arm carbon nanotubes are all curled and arranged in a regular and tight manner with a very short pitch, showing a symmetrical growth pattern.

[0076] Test Example 5

[0077] This test case examines the electrical properties of HCNT, AHCNT, CNT and ACNT. Figure 6a-6cThey are the complex dielectric constant and electric loss angle of carbon nanotubes with different treatment methods (the mass ratio with paraffin is 6:4). It can be seen from the figure that with the increase of frequency, the real part of the dielectric constant of each group of carbon nanotubes continues to decrease. This is a dispersion phenomenon caused by the polarization hysteresis of the medium. In addition, the spiral carbon nanotubes have more stable dispersion characteristics, and the frequency sensitivity of the dielectric performance is less than that of the straight carbon nanotubes, which is conducive to the realization of wide-band electromagnetic wave absorption. With the increase of frequency, the imaginary part of the dielectric constant of the above carbon nanotube materials tends to decrease, indicating that the resistance loss plays an important role in the electric loss. Therefore, the total effective conductivity and penetration depth of carbon nanotubes with different treatment methods are further characterized and calculated. The calculation results are shown in Figure 6d and Figure 6e As shown in the figure, it can be seen that the effective conductivity of each group of samples increases with the increase of frequency, while the penetration depth decreases accordingly. After acid treatment, the effective conductivity of straight carbon nanotubes and spiral carbon nanotubes decreases, and the penetration depth increases. It can be seen that electromagnetic waves can pass through acidified carbon nanotubes more easily, but are strongly attenuated in non-acidified samples. Figure 6c It can be seen that the maximum electrical loss angle of straight carbon nanotubes and spiral multi-arm carbon nanotubes is 0.65, indicating that they have good electrical loss performance. After acid treatment, the electrical loss angles of both types of materials have decreased. This may be caused by nitric acid and sulfuric acid cutting carbon nanotubes and attaching a large number of oxygen-containing functional groups on their surfaces, destroying the conjugated π bonds between carbon and carbon, thereby weakening the conductivity of the material.

[0078] As the frequency decreases, the imaginary part of the dielectric constant and the electrical loss angle of each group of carbon nanotubes also fluctuate in many places, indicating that they have multiple dielectric loss mechanisms. Therefore, the Cole-Cole curve is used to analyze its polarization relaxation characteristics. Figure 6f The three-dimensional Cole-Cole curves of carbon nanotubes treated in different ways. Each group of samples spirals up as the frequency increases. Multiple Debye semicircles appear in each group of carbon nanotubes, indicating that each group of samples has multiple forms of dielectric polarization relaxation. And in each group of samples, the spiral radius of the acid-treated spiral carbon nanotube curve is larger, indicating that it has a larger Debye radius and a higher degree of dielectric polarization relaxation. The multi-arm carbon nanotubes after acid-treated spiralization have more defects such as carbon-carbon double bonds and abundant epoxy functional groups, and their polarization relaxation ability is stronger.

[0079] Test Example 6

[0080] This test example examines the electromagnetic attenuation performance and electromagnetic wave absorption performance of HCNT, AHCNT, CNT and ACNT respectively. Figure 7a The attenuation coefficient of CNT, ACNT, HCNT and AHCNT varies with frequency. Figure 7aIt can be seen that the attenuation coefficient of each group of carbon nanotubes increases with the increase of frequency, and the attenuation coefficients of the unacidified group of two types of carbon nanotubes are greater than those of the acidified group, and the maximum values ​​are both over 300.

[0081] Figure 7b-Figure 7i The three-dimensional model diagram and two-dimensional plane diagram / two-dimensional contour diagram of reflection loss of CNT, ACNT, HCNT and AHCNT are shown in Table 1. The minimum reflection loss and the widest effective absorption frequency band of each group of samples are shown in Table 1.

[0082] Table 1 Reflection loss and effective absorption frequency band of each group of carbon nanotubes

[0083]

[0084] By the above Figure 7b-Figure 7i As shown in Table 1, although the acid treatment will reduce the conductive loss of the material, it introduces defects and oxidized groups into the material, which can not only improve the impedance matching characteristics of the material, but also promote polarization relaxation. Helical carbon nanotubes have a unique microstructure and stable frequency adaptability, and their overall absorption performance is better. By comparison, the sample with better overall absorption performance is the AHCNT group. When the matching thickness is 1.79mm, the maximum reflection loss at 12.60GHz can reach -32.14dB, and when the matching thickness is 1.53mm, it has the maximum effective absorption bandwidth, which can reach 5.60GHz.

[0085] From the above experimental results, we can see that AHCNT, i.e., acidified helical multi-arm carbon nanotubes, has refined carbon nanotube grains, more unsaturated bonds and oxygen-containing functional groups, improved defectivity, more suitable dielectric properties, better effective conductivity and penetration depth, and a higher degree of dielectric polarization relaxation, and thus has good electromagnetic attenuation ability and impedance matching characteristics, and the overall absorbing performance is the best: when the matching thickness is 1.79mm, its maximum reflection loss can reach -32.14dB at 12.60GHz, and when the matching thickness is 1.53mm, it has a maximum effective absorbing bandwidth of 5.60GHz.

[0086] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

Claims

1. A method for preparing a spiral multi-arm carbon nanotube, characterized in that: The preparation method comprises: First, a ceramic plate with a uniformly dispersed catalyst is placed in a CVD chamber, and then heated to a synthesis temperature in an environment of inert gas or reducing gas. After the temperature stabilizes, C2H2 and H2 are introduced and reacted at the synthesis temperature. After the reaction is completed, the PVD chamber is cooled in an inert gas or reducing gas environment to obtain the spiral multi-arm carbon nanotubes.

2. The preparation method according to claim 1, characterized in that: The preparation method further comprises: Mixing concentrated nitric acid and concentrated sulfuric acid to obtain a mixed acid; The spiral multi-arm carbon nanotubes are added to the mixed acid and subjected to acidification treatment under stirring. After the acidification treatment, the product is filtered, washed and dried in sequence to obtain acidified spiral multi-arm carbon nanotubes.

3. The preparation method according to claim 1 or 2, characterized in that: The reaction temperature is 600-1000°C and the reaction time is 60-90min; Preferably, the inert gas includes nitrogen, helium, argon or neon, and the reducing gas includes hydrogen.

4. The preparation method according to claim 1 or 2, characterized in that: The flow rates of C2H2 and H2 were 4-6 mL / min and 8-12 mL / min, respectively.

5. The preparation method according to claim 1 or 2, characterized in that: The catalyst is a mixture of PCl3 and Ni, and the mass ratio of the two is 1:2-1:

1.

6. The preparation method according to claim 2, characterized in that: The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:4-1:

2.

7. The preparation method according to claim 2, characterized in that: The temperature of the acidification treatment is 60-80°C and the time is 2-5h.

8. A spiral multi-arm carbon nanotube, characterized in that: The spiral multi-arm carbon nanotube is prepared by the method for preparing the spiral multi-arm carbon nanotube according to any one of claims 1 to 7.

9. The spiral multi-arm carbon nanotube according to claim 8, characterized in that: The spiral multi-arm carbon nanotube is an acidified spiral multi-arm carbon nanotube; Preferably, the spiral multi-arm carbon nanotubes have abundant unsaturated bonds and oxygen-containing functional groups, a diameter of 50-100 nm, a tube length of 2-5 μm, and are curled and arranged in a regular and tight manner with a pitch of 50-100 nm, presenting a symmetrical growth pattern.

10. Application of the spiral multi-arm carbon nanotubes as claimed in claim 8 or 9 as absorbing materials or grid frames used for absorbing materials in military equipment stealth, electronic equipment anti-electromagnetic interference, medical radiation protection or aerospace.

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