Preparation method of carbon nanohorn composite wave-absorbing material with adjustable wave-absorbing frequency band

Abstract

The application discloses a preparation method of a carbon nanohorn composite wave-absorbing material with adjustable wave-absorbing frequency bands, and comprises the following steps: preparing a composite wave-absorbing material precursor by mixing a substance containing dielectric wave-absorbing material elements and graphite powder; preparing a plasma anode by pouring the composite wave-absorbing material precursor into the holes of a porous graphite rod and drying; and preparing the carbon nanohorn composite wave-absorbing material by using a pure graphite rod as a cathode and placing the prepared plasma anode into an arc furnace, vacuumizing the arc furnace, filling the arc furnace with preset gas and starting an arc, collecting the deposits on the inner wall of the reaction cavity after the reaction is completed, and performing screening treatment to obtain the carbon nanohorn composite wave-absorbing material. The carbon nanohorn composite wave-absorbing material prepared by the method has low density and excellent wave-absorbing performance without post-treatment.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding, and more specifically, relates to a method for preparing a carbon nanotube angular composite absorbing material with adjustable absorption frequency band. Background Technology

[0002] Radar absorbing materials, or simply absorbing materials, absorb and attenuate incident electromagnetic waves, converting electromagnetic energy into heat or other forms of energy, or causing the electromagnetic waves to disappear due to interference. Researchers are dedicated to developing absorbing materials with thin coatings, light weight, wide absorption bandwidth, and strong absorption performance. Carbon materials are lightweight, have tunable conductivity, high dielectric loss, excellent mechanical properties, and good corrosion resistance. However, when used alone, they suffer from narrow absorption bandwidth and weak absorption loss due to impedance mismatch and single loss mechanisms. Researchers often introduce multiple loss mechanisms by combining carbon materials with other materials to improve absorption performance. However, current research on carbon-based composite absorbing materials still faces challenges such as narrow absorption bandwidth, large coating thickness, low strength, and difficulties in engineering applications.

[0003] Single-walled carbon nanotubes, as a novel carbon nanomaterial, have the following advantages: (1) High defect content, with a large number of five-membered rings and seven-membered rings, which enhances their dielectric loss capability against electromagnetic waves; (2) Large specific surface area, with abundant pores and large internal gaps in the aggregates, which increases the number of reflections and scatterings of electromagnetic waves in the nanopores, causing electromagnetic waves to be absorbed multiple times in the pores. The increased number of reflections and scatterings indicates that more electromagnetic energy is converted into heat energy and lost; (3) Good thermal stability, with the structure only changing at temperatures as high as 1400 °C, which has a significant effect on improving the working temperature of the absorbing material; (4) High surface energy, which, after functionalization, can be grafted with a large number of functional groups on its surface, which is conducive to introducing a variety of electromagnetic loss mechanisms, making it highly promising for application in the field of electromagnetic wave absorption, and providing a new and efficient carbon nanomaterial for solving the current problems of carbon-based composite absorbing materials. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for preparing a carbon nanotube corner composite absorbing material with controllable absorption band, which can achieve controllable adjustment of absorption performance in different frequency bands, greatly broadens the absorption frequency band, and has excellent absorption performance.

[0005] This invention provides a method for preparing a carbon nanotube-shaped composite microwave absorbing material with adjustable absorption frequency bands, which may include the following steps: preparing a composite microwave absorbing material precursor: mixing a substance containing dielectric microwave absorbing material elements with graphite powder; preparing a plasma anode: pouring the composite microwave absorbing material precursor into the pores of a porous graphite rod and drying it; preparing the carbon nanotube-shaped composite microwave absorbing material: using a pure graphite rod as the cathode, and placing the prepared plasma anode in an electric arc furnace. After the electric arc furnace is evacuated, a preset gas is introduced into the electric arc furnace and the electric arc is started. After the reaction is completed, the deposits on the inner wall of the reaction chamber are collected and sieved to obtain the carbon nanotube-shaped composite microwave absorbing material.

[0006] Furthermore, the mass ratio of the dielectric absorbing material element to graphite powder can be 1:10 to 2:1. By adjusting the ratio of the dielectric absorbing material element to graphite powder, the carbon nanotube composite absorbing material can achieve high-efficiency absorption performance in different absorption frequency bands. Within the mass ratio of the dielectric absorbing material element to graphite powder of 1:10 to 2:1, the composite absorbing material can exhibit high-efficiency absorption performance in different absorption frequency bands. For example, the mass ratio can be a combination of 1:5, 1:2, 3:10, 2:5, 7:10, or higher.

[0007] Furthermore, the substance containing dielectric absorbing material elements can be one or more combinations of silicon, zinc chloride, titanium trichloride, and molybdenum pentachloride.

[0008] Furthermore, the drying temperature can be greater than 80 °C, and the drying time can be greater than 10 h; the mixing time in the process of preparing the composite absorbing material precursor is 10 min to 30 min. For example, the drying temperature can be 90 °C, the drying time can be 12 h, and the mixing time in the process of preparing the composite absorbing material precursor can be 20 min.

[0009] Furthermore, the ratio of the aperture diameter of the anode graphite rod to the diameter of the anode graphite rod can be 1:4 to 1:2. The ratio of the aperture diameter of the anode graphite rod to the diameter of the anode graphite rod can be 1:3.

[0010] Furthermore, the composite microwave absorbing material precursor can be poured into a pre-drilled graphite rod, and the mixture in the hole can be compacted with a stainless steel rod with a diameter equal to the hole diameter of the graphite rod. The compaction pressure is 0.01 MPa to 0.07 MPa.

[0011] Furthermore, the distance between the composite absorbing material precursor and the top of the hole in the radial direction perpendicular to the anode graphite rod can be 2-4 mm. Here, the composite absorbing material precursor does not completely fill the entire hole. If it were fully filled, the material in the hole would easily be blown away when the arc plasma ignites. Therefore, the hole is not fully filled, and once the arc stabilizes, the material in the hole can be completely burned. For example, the distance from the top of the hole can be 3 mm.

[0012] Furthermore, the preset gas is oxygen, carbon monoxide, carbon dioxide, or a mixture of two of these gases; the electric arc furnace is charged with the preset gas at a pressure of 0.4 bar to 1 bar, and the volume ratio of the mixed gas is 0 to 1. For example, the electric arc furnace is charged with the preset gas at a pressure of 5 bar to 0.8 bar, and the volume ratio of the mixed gas is 0.3 to 0.8.

[0013] Furthermore, the purity of the anode and cathode graphite rods is ≥99.99%. The anode and cathode are arranged in a vertical straight line, with the cathode above the anode, and the end of the cathode graphite rod closest to the anode is tapered. The diameter of the cathode and anode graphite rods is 10 mm to 60 mm, and the distance between the two electrodes is 1 to 3 mm. For example, the diameter of the cathode and anode graphite rods is 25 mm to 52 mm, and the distance between the two electrodes is 1.5 to 2.5 mm.

[0014] Furthermore, the operating current of the electric arc is 150 A to 400 A, and the arc discharge time is 1 min to 100 min. For example, the operating current of the electric arc is 200 A to 350 A, and the arc discharge time is 3 min to 80 min.

[0015] Furthermore, the sieve mesh size is 100 to 300 mesh. For example, the sieve mesh size is 200 mesh.

[0016] Specifically, a method for preparing a carbon nanotube angle composite microwave absorbing material with adjustable absorption frequency band may include the following steps: preparing a precursor for the composite microwave absorbing material: mixing a substance containing dielectric microwave absorbing material elements with graphite powder in different mass ratios, mixing for a first preset time, so that the two or more substances are mixed evenly; the first preset time is 10 min to 30 min.

[0017] Preparation of plasma anode: Pour the above-mentioned uniformly mixed material into a pre-drilled graphite rod, compact the mixed material in the hole with a stainless steel rod with a diameter equal to the hole diameter of the graphite rod, and finally place the graphite rod in a drying oven to dry for a second preset time; the drying oven can be a forced-air drying oven or a vacuum drying oven, the drying temperature can be >80 ℃, and the second preset time can be >10 h.

[0018] Preparation of carbon nanotube angle composite microwave absorbing material: Using a pure graphite rod as the cathode, the anode filled with the composite microwave absorbing material precursor obtained in step (2) is placed vertically opposite to the cathode. After the electric arc furnace is evacuated, the electric arc furnace is filled with a preset gas and the electric arc is started. After the reaction is completed, the deposits on the inner wall of the reaction chamber are collected and screened to obtain the carbon nanotube angle composite microwave absorbing material. By adjusting the ratio of the substance containing dielectric microwave absorbing material elements to graphite powder, the carbon nanotube angle composite microwave absorbing material can be controlled to have high-efficiency microwave absorption performance in different microwave absorption frequency bands.

[0019] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0020] (1) The present invention adopts the DC electric arc method, which is simple in equipment, low in production cost, high in production efficiency, and green and pollution-free.

[0021] (2) The present invention can realize the preparation of high-performance composite microwave absorbing materials in one step.

[0022] (3) The carbon nanotube corner composite absorbing material prepared by the present invention has low density and excellent absorbing performance without post-processing.

[0023] (4) The carbon nanotube angular composite absorbing material prepared by the present invention can achieve efficient absorption of electromagnetic waves of different frequency bands and has an extremely wide effective absorption frequency band. Attached Figure Description

[0024] Figure 1 This is a flowchart of a method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency bands, provided by the present invention.

[0025] Figure 2 The image shows a transmission electron microscope (TEM) image of the carbon nanotube corner composite absorbing material with adjustable absorption frequency band obtained in Example 1.

[0026] Figure 3 The image shows a transmission electron microscope (TEM) image of the carbon nanotube corner composite absorbing material with adjustable absorption frequency band obtained in Example 1.

[0027] Figure 4 The surface energy spectrum (Mapping) of the carbon nanotube corner composite microwave absorbing material with adjustable absorption frequency band obtained in Example 1;

[0028] Figure 5 The X-ray photoelectron diffraction (XPS) spectrum of the carbon nanotube corner composite absorbing material with adjustable absorption frequency band obtained in Example 1;

[0029] Figure 6 The electromagnetic wave reflection loss diagram of the carbon nanotube angular composite absorbing material with adjustable absorption frequency band obtained in Example 1 is shown.

[0030] Figure 7 The X-ray photoelectron diffraction (XPS) spectrum of the carbon nanotube corner composite absorbing material with adjustable absorption frequency band obtained in Example 2;

[0031] Figure 8 The electromagnetic wave reflection loss diagram of the carbon nanotube angular composite absorbing material with adjustable absorption frequency band obtained in Example 2 is shown.

[0032] Figure 9The image shows a transmission electron microscope (TEM) image of the carbon nanotube corner composite absorbing material with adjustable absorption frequency band obtained in Example 3.

[0033] Figure 10 The X-ray photoelectron diffraction (XPS) spectrum of the carbon nanotube corner composite absorbing material with adjustable absorption frequency band obtained in Example 3;

[0034] Figure 11 The electromagnetic wave reflection loss diagram is shown for the carbon nanotube angular composite absorbing material with adjustable absorption frequency band obtained in Example 3. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0036] Please see Figure 1 The present invention provides a method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band, which includes the following steps:

[0037] Preparation of composite microwave absorbing material precursor: Mixing substances containing dielectric microwave absorbing material elements with graphite powder in different mass ratios for a first preset time to ensure uniform mixing of the two or more substances.

[0038] Preparation of the plasma anode: The uniformly mixed material is poured into a pre-drilled graphite rod. A stainless steel rod with a diameter equal to the hole diameter is used to compact the mixture in the hole. Finally, the graphite rod is placed in a drying oven and dried for a second preset time.

[0039] Preparation of carbon nanotube angle composite microwave absorbing material: Using a pure graphite rod as the cathode, the anode filled with the composite microwave absorbing material precursor obtained in step (2) is placed vertically opposite to the cathode. After the electric arc furnace is evacuated, the electric arc furnace is filled with a preset gas and the electric arc is started. After the reaction is completed, the deposits on the inner wall of the reaction chamber are collected and screened to obtain the carbon nanotube angle composite microwave absorbing material. By adjusting the ratio of the substance containing dielectric microwave absorbing material elements to graphite powder, the carbon nanotube angle composite microwave absorbing material can be controlled to have high-efficiency microwave absorption performance in different microwave absorption frequency bands.

[0040] Example 1

[0041] (1) Preparation of composite microwave absorbing material precursor: Silicon powder and graphite powder are mixed at a mass ratio of 1:5 and mixed for 20 min.

[0042] (2) Preparation of plasma anode: Pour the composite absorbing material precursor from step (1) into a graphite rod with a 4 mm aperture, and compact it with a rod with a diameter equal to the aperture. The pressure is 0.03 MPa. Then place it in a vacuum drying oven, set the temperature to 80 ℃, and dry for 12 h.

[0043] (3) Preparation of composite absorbing material: The anode material from step (2) was placed in a plasma furnace as the anode, and a graphite rod with one end sharpened was used as the cathode. Plasma treatment was performed under a carbon dioxide atmosphere of 0.5 bar. The working current was 350 A. Finally, the mixture was allowed to stand for 1 h, and the product was collected to obtain the carbon nanotube angle composite absorbing material.

[0044] The transmission electron microscope (TEM) image of the carbon nanotube corner composite absorbing material in this embodiment is as follows: Figure 2 and 3 As shown, the surface energy spectrum (Mapping) is as follows: Figure 4 As shown; X-ray photoelectron diffraction (XPS) pattern as follows Figure 5 As shown in the figure, the electromagnetic wave reflection loss diagram is as follows: Figure 6 As shown. By Figure 2 It can be seen that the nano-corner structure is intact, and the surface is encapsulated by particulate matter. From Figure 3 This allows for the further determination that the particles coating the surface of the nano-angles are amorphous. Surface energy spectrum of the carbon nano-angle composite microwave absorbing material (…). Figure 4 The results showed that the particles were composed of Si and O, therefore the particles coated on the nano-corner surface were ultimately determined to be amorphous silicon oxide. Amorphous silicon oxide can effectively improve the impedance matching capability of the absorbing material. Figure 5 The data shows that the silicon content of the carbon nanotube corner composite absorbing material in this embodiment is 5.17%, which reflects the level of amorphous silicon oxide loading. Figure 6 The electromagnetic wave reflection loss diagram of the carbon nanotube angle composite absorbing material shows that the carbon nanotube angle composite absorbing material prepared in this embodiment has excellent absorption capability in the Ku band, with an effective absorption bandwidth of 5 GHz and a maximum reflection loss of 46.98 dB.

[0045] Example 2

[0046] (1) Preparation of composite microwave absorbing material precursor: Silicon powder and graphite powder are mixed at a mass ratio of 1:4 for 20 min.

[0047] (2) Preparation of plasma anode: Pour the composite absorbing material precursor from step (1) into a graphite rod with a 4 mm aperture, and compact it with a rod with a diameter equal to the aperture. The pressure is 0.04 MPa. Then place it in a vacuum drying oven, set the temperature to 80 ℃, and dry for 12 h.

[0048] (3) Preparation of composite absorbing material: The anode material from step (2) was placed in a plasma furnace as the anode, and a graphite rod with one end sharpened was used as the cathode. Plasma treatment was performed under a carbon dioxide atmosphere of 0.6 bar. The working current was 400 A. Finally, the mixture was allowed to stand for 1 h, and the product was collected to obtain the carbon nanotube angle composite absorbing material.

[0049] The X-ray photoelectron diffraction (XPS) pattern of the carbon nanotube composite absorbing material in this embodiment is as follows: Figure 7 As shown in the figure, the electromagnetic wave reflection loss diagram is as follows: Figure 8 As shown. Figure 7 The data shows that the silicon content of the carbon nanotube corner composite microwave absorbing material in this embodiment is 9.796%, indicating that the amount of amorphous silicon oxide loaded on the carbon nanotube corners has increased. Figure 8 The electromagnetic wave reflection loss diagram of the carbon nanotube angle composite absorbing material shows that the carbon nanotube angle composite absorbing material prepared in this embodiment has excellent absorption capability in the X-band, with an effective absorption bandwidth of 3.2 GHz and a maximum reflection loss of 49.7 dB.

[0050] Example 3

[0051] (1) Preparation of composite microwave absorbing material precursor: Silicon and graphite powder are mixed at a mass ratio of 3:10 for 20 min.

[0052] (2) Preparation of plasma anode: Pour the composite absorbing material precursor from step (1) into a graphite rod with a 4 mm hole, and compact it with a rod with a diameter equal to the hole diameter at a pressure of 0.02 MPa. Then place it in a vacuum drying oven, set the temperature to 80 °C, and dry for 12 h.

[0053] (3) Preparation of composite absorbing material: The anode material from step (2) was placed in a plasma furnace as the anode, and a graphite rod with one end sharpened was used as the cathode. Plasma treatment was performed under a carbon dioxide atmosphere of 0.7 bar. The working current was 330 A. Finally, the mixture was allowed to stand for 1 h, and the product was collected to obtain the carbon nanotube angle composite absorbing material.

[0054] The transmission electron microscope (TEM) image of the carbon nanotube corner composite absorbing material in this embodiment is as follows: Figure 9 As shown, the X-ray photoelectron diffraction (XPS) pattern is as follows: Figure 10 As shown in the figure, the electromagnetic wave reflection loss diagram is as follows: Figure 11 As shown. Figure 9 This indicates that as the proportion of silicon powder increases, the structure of carbon nano-angles in the product does not change significantly, suggesting that increasing the silicon content does not affect the structure of the carbon nano-angle composite microwave absorbing material. Figure 10The data shows that the silicon content of the carbon nanotube corner composite microwave absorbing material in this embodiment is 10.46%, indicating that the amount of amorphous silicon oxide loaded on the carbon nanotube corner is further increased. Figure 11 The reflection loss diagram of the carbon nano-angle composite absorbing material shows that the carbon nano-angle composite absorbing material prepared in this embodiment has excellent absorption capability in the C-band, with an effective absorption bandwidth of 2.3 GHz and a maximum reflection loss of 40.03 dB. As the content of amorphous silica on the nano-angle surface increases, the absorption peak of the nano-angle composite absorbing material shifts to lower frequencies. The absorption frequency band of the carbon nano-angle composite absorbing material can be controlled by adjusting the content of amorphous silica.

Claims

1. A method for preparing a carbon nanotube angular composite microwave absorbing material with tunable absorption frequency band, characterized in that, Includes the following steps: Preparation of precursors for composite microwave absorbing materials: Mixing a substance containing dielectric microwave absorbing material elements with graphite powder; Preparation of plasma anode: The composite absorbing material precursor is poured into the pores of a porous graphite rod and dried; Preparation of carbon nanotube angle composite microwave absorbing material: A pure graphite rod was used as the cathode, and the prepared plasma anode was placed in an electric arc furnace. After the electric arc furnace was evacuated, a preset gas was introduced into the furnace and the electric arc was started. After the reaction was completed, the deposits on the inner wall of the reaction chamber were collected and sieved to obtain the carbon nanotube angle composite microwave absorbing material. The substances containing dielectric absorbing material elements are one or more combinations of silicon, zinc chloride, titanium trichloride and molybdenum pentachloride; The preset gas is oxygen, carbon monoxide, carbon dioxide, or a mixture of two of them; The mass ratio of the substance containing dielectric absorbing material elements to graphite powder is 1:10 to 2:

1.

2. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1, characterized in that: The drying temperature is greater than 80℃ and the drying time is greater than 10h; the mixing time in the process of preparing the composite microwave absorbing material precursor is 10min~30min.

3. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1 or 2, characterized in that: The ratio of the aperture of the anode graphite rod to the diameter of the anode graphite rod is 1:4 to 1:

2.

4. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1 or 2, characterized in that: The composite absorbing material precursor is located 2-4 mm from the top of the hole in the radially perpendicular direction of the anode graphite rod.

5. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1, characterized in that: The electric arc furnace is charged with a preset gas of 0.4 bar to 1 bar, and the volume ratio of the mixed gas is 0 to 1.

6. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1 or 2, characterized in that: The graphite rod has a purity of ≥99.99%, and the cathode graphite rod is tapered at the end near the anode. The diameters of the cathode and anode graphite rods are 10mm to 60mm, and the distance between the two electrodes is 1 to 3mm.

7. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1 or 2, characterized in that: The working current of the electric arc is 150A to 400A, and the arc discharge time is 1min to 100min.

8. The method for preparing a carbon nanotube angular composite microwave absorbing material with adjustable absorption frequency band according to claim 1 or 2, characterized in that: The sieve mesh size is 100 to 300 mesh.

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