Preparation method of lightweight and efficient hollow multi-carbon nanotube composite wave-absorbing material
By growing carbon nanotubes in situ on the surface of MOFs derivatives and etching to form a hollow structure, the problem of lightweight and efficient electromagnetic wave absorption of microwave absorbing materials was solved, and a highly efficient electromagnetic wave absorption effect was achieved.
Patent Information
- Application Number
- CN202511677775.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2026-01-13
AI Technical Summary
Existing microwave absorbing materials suffer from problems such as impedance mismatch, poor absorption performance, uneven composition, and large mass, making it difficult to achieve lightweight and efficient absorption of electromagnetic waves.
Longer carbon nanotubes are grown in situ on the surface of MOFs derivatives, and hollow structures are formed by etching with organic acids. Combined with appropriate calcination processes, hollow multi-carbon nanotube composite materials are prepared, which enhance resistance loss and reduce filler fraction.
It achieves the effect of lightweight and efficient absorption of electromagnetic waves. By reducing the density and filling fraction of the material through impedance matching and the formation of conductive paths in the hollow multi-carbon nanotube structure, the absorption performance is improved.
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Figure CN121319871A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microwave absorbing materials technology, specifically a method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material. Background Technology
[0002] In daily life, while numerous electronic devices offer convenience, they also expose the human body to significant electromagnetic radiation, which can negatively impact health. Excessive electromagnetic waves can also interfere with the operation of precision instruments, such as aircraft navigation systems, medical diagnostic equipment, and implanted medical devices. Radar stealth technology essentially aims to prevent enemy detection radar from receiving a sufficient amount of electromagnetic waves reflected from our weapons. Electromagnetic shielding materials can be used to block electromagnetic waves from reaching the protected object through reflection, but this can cause secondary pollution. In conclusion, using reflection alone cannot fundamentally solve the social and military problems caused by electromagnetic waves. Therefore, directly absorbing all incident electromagnetic waves is a more permanent solution.
[0003] Due to problems such as impedance mismatch, poor absorption performance, uneven composition, and large mass in traditional microwave absorbing materials, metal-organic frameworks (MOFs) have begun to be used in microwave absorbing materials due to their special structural composition. The porous structure inside MOFs makes them promising microwave absorbing materials. However, their structure can be further optimized by improving the process or materials to improve their absorption performance. Since the overall structure of MOF derivatives is a chemically inert carbon skeleton, it is difficult to modify the structure again. Therefore, the improvement of the structure is mainly carried out from two aspects: precursor and calcination process. Li (LIZ, HANX, MAY, et al. MOFs-Derived Hollow Co / C Microspheres with Enhanced Microwave Absorption Performance[J]. AcsSustainableChemistry&Engineering,2018,6(7):8904-8913.) first dissolved the surfactant hexadecyltrimethylammonium bromide (CTAB) in water, and used the interaction between Co2+ and amino groups to enrich Co2+ around the CTAB vesicles. Subsequently, 2-methylimidazole was added to react with Co2+ to generate a core-shell structure with CTAB vesicles as the core and ZIFs-67 as the shell. The ZIFs-67 shell was prepared by removing CTAB using DMF via centrifugation, and then calcined to obtain a hollow carbon shell embedded with cobalt nanoparticles. This structure exhibits strong electrical loss while also being beneficial for multiple scattering and interfacial polarization. For the derivative obtained at a calcination temperature of 600℃, when the fill fraction was 30%, a 1.53 mm absorbing coating could reduce RL to -66.5 dB. Pan (PAN J, XIAW, SUNX, et al. Improvement of interfacial polarization and impedance matching for two-dimensional leaf-like bimetallic (Co,Zn) doped porous carbon nanocomposites with broadband microwave absorption [J]. Applied Surface Science, 2020, 512.) et al. prepared two-dimensional sheet-like Co / Zn bimetallic ZIFs. The calcined derivative material particles remain two-dimensional and plate-like, maintaining extremely high porosity and a large specific surface area. The derivative's main components are a carbon framework and cobalt nanoparticles, with the cobalt nanoparticles catalyzing the formation of carbon nanotubes. When the molar ratio of Co2+ to Zn2+ is 4:6, the derivative can reduce the RL to -45.2 dB and broaden the EAB to 5.7 GHz.
[0004] However, in current research, since most MOF precursors are zero-dimensional particles, the derivatives obtained from carbonized MOFs are also mostly zero-dimensional particles. Furthermore, the carbonization process generates a large amount of non-conductive amorphous carbon, resulting in limited contact between conductive carbon skeletons and shorter, fewer conductive pathways in the system, leading to reduced resistive losses. To achieve high resistive losses, the filler fraction must be increased to enhance contact opportunities between carbon skeletons, but this would increase the density of the absorbing coating. Therefore, further transforming MOF derivatives into lightweight and efficient derivatives remains a significant challenge.
[0005] Based on previous work, this invention optimizes MOF derivatives in terms of both composition and structure: long carbon nanotubes are grown in situ on the surface of MOF derivatives, which enhances resistivity loss while preventing the aggregation of carbon nanotubes by the binding effect of MOFs; organic acids are used to etch MOFs into empty shell structures, and stronger organic acids can make the empty shells of MOF derivatives more porous, thus ensuring impedance matching, enhancing absorption performance, and reducing the fill fraction. Summary of the Invention
[0006] To overcome the shortcomings of the prior art, this invention provides a method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material, solving the problem of how to achieve lightweight and efficient electromagnetic wave absorption in microwave absorbing materials.
[0007] To achieve the above objectives, a method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material is designed, characterized by the following steps:
[0008] (1) Synthesis of precursors:
[0009] Dissolve 5–10 mmol of cobalt nitrate hexahydrate and 20–50 mmol of 2-methylimidazole in 40–60 ml of methanol and stir.
[0010] After both are completely dissolved, slowly pour the 2-methylimidazolium methanol solution into the metal ion methanol solution, and then continue stirring for 20 to 40 minutes.
[0011] The resulting suspension was allowed to stand for 20–30 hours to allow sufficient growth time for the precursor grains.
[0012] The purple precipitate was then washed three times with ethanol by centrifugation.
[0013] The precipitate was dried in an electric heating drying oven for 10-20 hours to obtain the precursor powder.
[0014] (2) Etching of the precursor:
[0015] Prepare 10-20 ml of gallic acid aqueous solution with a concentration of 8-10 g / L, and add the gallic acid aqueous solution dropwise to the precursor powder synthesized in step (1), and stir for 10-20 min;
[0016] The gray precipitate was then washed three times with deionized water by centrifugation, and the precipitate was dried in an electric heating drying oven for 20-30 hours.
[0017] (3) Preparation of derivative materials:
[0018] Place the precursor powder from step (2) and dicyandiamide in a mortar at a mass ratio of 1-1.5:0.5-0.8, add a small amount of ethanol, grind carefully for 10-15 minutes, and then dry.
[0019] The dried mixture was placed in a corundum crucible and calcined in a tube furnace to obtain a nanoporous carbon composite microwave absorbing material.
[0020] During the synthesis of the precursor, the centrifuge speed is 8000-10000 rpm, and the centrifugation time is 5-8 min each time; the precursor powder is a purple powder.
[0021] During the etching process of the precursor, the centrifuge speed is 8000-10000 rpm, and the centrifugation time is 10-15 min each time.
[0022] In the preparation of the derivative material, the mass ratio of the precursor powder to dicyandiamide is 1-1.2:0.5-0.8.
[0023] In the preparation of the derivative material, the calcination is carried out at a heating rate of 0.8 to 1.2 °C / min in a rare gas atmosphere to 800 to 1000 °C for 8 to 10 hours, and then naturally cooled to room temperature.
[0024] The rare gas is one or a combination of nitrogen, argon and helium.
[0025] A lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material was prepared using the method described above.
[0026] A lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material and its preparation method are applied to the efficient absorption of electromagnetic waves in social and military fields.
[0027] Compared with the prior art, this invention provides a method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material. This material has a hollow multi-nanotube structure, which is beneficial for impedance matching. On the other hand, it means that only a small amount of hollow multi-carbon nanotube composite microwave absorbing material needs to be added to achieve similar resistance loss, effectively reducing the filling fraction and density of the microwave absorbing filler, and effectively solving the problem of how to achieve lightweight and efficient electromagnetic wave absorption in microwave absorbing materials. Attached Figure Description
[0028] Figure 1 This is a morphology diagram of the hollow multi-carbon nanotube composite microwave absorbing material of the present invention.
[0029] Figure 2 TEM image of hollow carbon nanotubes prepared by calcination.
[0030] Figure 3 The two curves represent the loss constants of multi-carbon nanotube composite absorbing materials and hollow multi-carbon nanotube composite absorbing materials when filled with 20% and 7% respectively.
[0031] Figure 4 The diagram shows the microwave absorption capability of hollow multi-nanotubes filled with 7%. Detailed Implementation
[0032] The present invention will now be further described with reference to the accompanying drawings.
[0033] A method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material includes the following steps: (1) Synthesis of the precursor:
[0034] Dissolve 5–10 mmol of cobalt nitrate hexahydrate and 20–50 mmol of 2-methylimidazole in 40–60 ml of methanol and stir.
[0035] After both are completely dissolved, slowly pour the 2-methylimidazolium methanol solution into the metal ion methanol solution, and then continue stirring for 20 to 40 minutes.
[0036] The resulting suspension was allowed to stand for 20–30 hours to allow sufficient growth time for the precursor grains.
[0037] The purple precipitate was then washed three times with ethanol by centrifugation.
[0038] The precipitate was dried in an electric heating drying oven for 10-20 hours to obtain the precursor powder.
[0039] (2) Etching of the precursor:
[0040] Prepare 10-20 ml of gallic acid aqueous solution with a concentration of 8-10 g / L, and add the gallic acid aqueous solution dropwise to the precursor powder synthesized in step (1), and stir for 10-20 min;
[0041] The gray precipitate was then washed three times with deionized water by centrifugation, and the precipitate was dried in an electric heating drying oven for 20-30 hours.
[0042] (3) Preparation of derivative materials:
[0043] Place the precursor powder from step (2) and dicyandiamide in a mortar at a mass ratio of 1-1.5:0.5-0.8, add a small amount of ethanol, grind carefully for 10-15 minutes, and then dry.
[0044] The dried mixture was placed in a corundum crucible and calcined in a tube furnace to obtain a nanoporous carbon composite microwave absorbing material.
[0045] During the synthesis of the precursor, the centrifuge speed is 8000-10000 rpm, and the centrifugation time is 5-8 min each time; the precursor powder is a purple powder.
[0046] During the etching process of the precursor, the centrifuge speed is 8000-10000 rpm, and the centrifugation time is 10-15 min each time.
[0047] In the preparation of the derivative material, the mass ratio of the precursor powder to dicyandiamide is 1-1.2:0.5-0.8.
[0048] In the preparation of the derivative material, the calcination is carried out at a heating rate of 0.8 to 1.2 °C / min in a rare gas atmosphere to 800 to 1000 °C for 8 to 10 hours, and then naturally cooled to room temperature.
[0049] Rare gases are one or a combination of nitrogen, argon and helium.
[0050] A lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material was prepared using the method described above.
[0051] A lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material and its preparation method are applied to the efficient absorption of electromagnetic waves in social and military fields.
[0052] The material of this invention has a hollow multi-nanotube structure, which is beneficial for impedance matching. On the other hand, it means that only a small amount of hollow multi-carbon nanotube composite absorbing material needs to be added to achieve similar resistance loss, effectively reducing the filling fraction and density of the absorbing filler.
[0053] Example 1
[0054] (1) Synthesis of the precursor: 6.87 mmol of cobalt nitrate hexahydrate and 24.36 mmol of 2-methylimidazole were dissolved in 50 ml of methanol and stirred until completely dissolved. The 2-methylimidazole methanol solution was then slowly poured into the metal ion methanol solution. Stirring continued for 20 min. The resulting suspension was allowed to stand for 24 h to allow sufficient growth time for the precursor crystals. The purple precipitate was then washed three times with ethanol by centrifugation (10,000 rpm, 5 min each time). The precipitate was dried in an electric heating oven for 12 h to obtain a purple powder, which was the precursor.
[0055] (2) Etching of the precursor: Prepare 10 ml of 10 g / L gallic acid aqueous solution and add it dropwise to the precursor powder synthesized in the previous step, and stir for 10 min. Then wash the gray precipitate three times with deionized water by centrifugation (10000 rpm, 10 min each time), and place the precipitate in an electric heating drying oven to dry for 24 h.
[0056] (3) Preparation of the derivative material: The dried precursor and dicyandiamide were placed in a mortar at a mass ratio of 1:0.5, a small amount of ethanol was added, and the mixture was carefully ground for 10 min, followed by drying. The dried mixture was placed in a corundum crucible and calcined in a tube furnace at a heating rate of 1 °C / min in a N2 atmosphere to 800 °C for 8 h, and then naturally cooled to room temperature to obtain a hollow multi-carbon nanotube composite microwave absorbing material.
[0057] Example 2
[0058] (1) Synthesis of the precursor: 6.87 mmol of cobalt nitrate hexahydrate and 24.36 mmol of 2-methylimidazole were dissolved in 50 ml of methanol and stirred until completely dissolved. The 2-methylimidazole methanol solution was then slowly poured into the metal ion methanol solution. Stirring continued for 20 min. The resulting suspension was allowed to stand for 24 h to allow sufficient growth time for the precursor crystals. The purple precipitate was then washed three times with ethanol by centrifugation (10,000 rpm, 5 min each time). The precipitate was dried in an electric heating oven for 12 h to obtain a purple powder, which was the precursor.
[0059] (2) Etching of the precursor: Prepare 10 ml of 10 g / L gallic acid aqueous solution and add it dropwise to the precursor powder synthesized in the previous step, and stir for 10 min. Then wash the gray precipitate three times with deionized water by centrifugation (10000 rpm, 10 min each time), and place the precipitate in an electric heating drying oven to dry for 24 h.
[0060] (3) Preparation of the derivative material: The dried precursor and dicyandiamide were placed in a mortar at a mass ratio of 1:0.5, a small amount of ethanol was added, and the mixture was carefully ground for 10 min, followed by drying. The dried mixture was placed in a corundum crucible and calcined in a tube furnace at a heating rate of 1 °C / min in a N2 atmosphere to 900 °C for 8 h, and then naturally cooled to room temperature to obtain a hollow multi-carbon nanotube composite microwave absorbing material.
[0061] Example 3
[0062] (1) Synthesis of the precursor: 6.87 mmol of cobalt nitrate hexahydrate and 24.36 mmol of 2-methylimidazole were dissolved in 50 ml of methanol and stirred until completely dissolved. The 2-methylimidazole methanol solution was then slowly poured into the metal ion methanol solution. Stirring continued for 20 min. The resulting suspension was allowed to stand for 24 h to allow sufficient growth time for the precursor crystals. The purple precipitate was then washed three times with ethanol by centrifugation (10,000 rpm, 5 min each time). The precipitate was dried in an electric heating oven for 12 h to obtain a purple powder, which was the precursor.
[0063] (2) Etching of the precursor: Prepare 10 ml of 10 g / L gallic acid aqueous solution and add it dropwise to the precursor powder synthesized in the previous step, and stir for 10 min. Then wash the gray precipitate three times with deionized water by centrifugation (10000 rpm, 10 min each time), and place the precipitate in an electric heating drying oven to dry for 24 h.
[0064] (3) Preparation of the derivative material: The dried precursor and dicyandiamide were placed in a mortar at a mass ratio of 1:0.5, a small amount of ethanol was added, and the mixture was carefully ground for 10 min, followed by drying. The dried mixture was placed in a corundum crucible and calcined in a tube furnace at a heating rate of 1 °C / min in a N2 atmosphere to 1000 °C for 8 h, and then naturally cooled to room temperature to obtain a hollow multi-carbon nanotube composite microwave absorbing material.
[0065] Example 4
[0066] (1) Synthesis of the precursor: 6.87 mmol of cobalt nitrate hexahydrate and 24.36 mmol of 2-methylimidazole were dissolved in 50 ml of methanol and stirred until completely dissolved. The 2-methylimidazole methanol solution was then slowly poured into the metal ion methanol solution. Stirring continued for 20 min. The resulting suspension was allowed to stand for 24 h to allow sufficient growth time for the precursor crystals. The purple precipitate was then washed three times with ethanol by centrifugation (10,000 rpm, 5 min each time). The precipitate was dried in an electric heating oven for 12 h to obtain a purple powder, which was the precursor.
[0067] (2) Etching of the precursor: Prepare 10 ml of 10 g / L gallic acid aqueous solution and add it dropwise to the precursor powder synthesized in the previous step, and stir for 10 min. Then wash the gray precipitate three times with deionized water by centrifugation (10000 rpm, 10 min each time), and place the precipitate in an electric heating drying oven to dry for 24 h.
[0068] (3) Preparation of the derivative material: The dried precursor and dicyandiamide were placed in a mortar at a mass ratio of 1.2:0.5, a small amount of ethanol was added, and the mixture was carefully ground for 10 min, and then dried. The dried mixture was placed in a corundum crucible and calcined in a tube furnace at a heating rate of 1 °C / min in a N2 atmosphere to 800 °C for 8 h, and then naturally cooled to room temperature to obtain a hollow multi-carbon nanotube composite microwave absorbing material.
[0069] Example 5
[0070] (1) Synthesis of the precursor: 6.87 mmol of cobalt nitrate hexahydrate and 24.36 mmol of 2-methylimidazole were dissolved in 50 ml of methanol and stirred until completely dissolved. The 2-methylimidazole methanol solution was then slowly poured into the metal ion methanol solution. Stirring continued for 20 min. The resulting suspension was allowed to stand for 24 h to allow sufficient growth time for the precursor crystals. The purple precipitate was then washed three times with ethanol by centrifugation (10,000 rpm, 5 min each time). The precipitate was dried in an electric heating oven for 12 h to obtain a purple powder, which was the precursor.
[0071] (2) Etching of the precursor: Prepare 10 ml of 10 g / L gallic acid aqueous solution and add it dropwise to the precursor powder synthesized in the previous step, and stir for 10 min. Then wash the gray precipitate three times with deionized water by centrifugation (10000 rpm, 10 min each time), and place the precipitate in an electric heating drying oven to dry for 24 h.
[0072] (3) Preparation of the derivative material: The dried precursor and dicyandiamide were placed in a mortar at a mass ratio of 1.4:0.5, a small amount of ethanol was added, and the mixture was carefully ground for 10 min, followed by drying. The dried mixture was placed in a corundum crucible and calcined in a tube furnace at a heating rate of 1 °C / min in a N2 atmosphere to 800 °C for 8 h, and then naturally cooled to room temperature to obtain a hollow multi-carbon nanotube composite microwave absorbing material.
[0073] Comparative Example
[0074] (1) Synthesis of the precursor: 6.87 mmol of cobalt nitrate hexahydrate and 24.36 mmol of 2-methylimidazole were dissolved in 50 ml of methanol and stirred until completely dissolved. The 2-methylimidazole methanol solution was then slowly poured into the metal ion methanol solution. The stirring was continued for 20 min. The resulting suspension was allowed to stand for 24 h to allow sufficient time for the precursor crystals to grow. The purple precipitate was then washed three times with ethanol by centrifugation (10,000 rpm, 5 min each time). The precipitate was dried in an electric heating oven for 12 h to obtain the precursor.
[0075] (2) Improved preparation of derivative materials: The dried precursor and a certain mass of dicyandiamide were placed in a mortar at a mass ratio of 1:2. A small amount of ethanol was added, and the mixture was carefully ground for 10 min, followed by drying. The dried mixture was placed in a corundum crucible and calcined in a tube furnace at a heating rate of 1 °C / min in a N2 atmosphere to 800 °C for 8 h, followed by natural cooling to room temperature.
[0076] Electromagnetic parameter measurement method: The calcined derivative and a determined mass fraction of paraffin wax were weighed and mixed, then placed in a 75℃ oven to melt the paraffin wax. The derivative powder and paraffin wax were carefully ground to ensure thorough mixing until the paraffin wax cooled. Samples with an outer diameter of 7 mm and an inner diameter of 3.04 mm were then pressed using a mold. Testing was performed using a vector network analyzer manufactured by the company, with a test frequency range of 2–18 GHz.
[0077] Figure 1 The image shows the morphology of a hollow carbon nanotube composite microwave absorbing material, exhibiting a dodecahedral hollow shell structure with a central pore diameter of approximately 500 nm. Both the outer and inner surfaces of the shell show the formation of carbon nanotubes approximately 500 nm in length and the distribution of Co nanoparticles. Some Co particles are even located at the tips of the carbon nanotubes, demonstrating that during calcination, the hollow shell undergoes further pyrolysis of dicyandiamide, breaking of coordination bonds, formation of elemental Co, and catalytic generation of carbon nanotubes. These carbon nanotubes, combined with the hollow shell structure, easily form complex conductive pathways, facilitating conductivity loss.
[0078] Figure 2 TEM images of the hollow carbon nanotubes prepared by calcination clearly show that the calcined derivative inherits the dodecahedral hollow shell structure of the precursor. The diameter of the central pore is approximately 300 nm, which is smaller than the diameter measured by SEM. Numerous carbon nanotubes (indicated by orange arrows) are clearly observed to form on the outer surface of the derivative, with lengths of approximately 300–500 nm. Combined with the SEM results, this demonstrates that the carbon-containing small molecules generated from dicyandiamide pyrolysis can still be catalyzed by Co nanoparticles on the hollow shell to grow carbon nanotubes.
[0079] Figure 3The two curves represent the loss constants of the multi-carbon nanotube composite absorbing material and the hollow multi-carbon nanotube composite absorbing material when filled with 20% and 7% of the carbon nanotubes, respectively. It is clear that at most frequencies, the loss constant of the latter is only slightly weaker than that of the former. This is because the precursor of the latter has been etched into a hollow shell structure, and the calcined derivative inherits this hollow shell structure. Thus, with similar carbon skeleton volumes in both derivatives, the hollow shell structure has a smaller mass, resulting in a smaller mass fraction of the derivative.
[0080] Figure 4 The absorption capability of hollow multi-nanotubes with a 7% filling content is shown. As the coating thickness increases, the peak reflection loss gradually shifts to the right, consistent with the quarter-wavelength destructive theory. At a coating thickness of 2.31 mm, the lowest reflection loss reaches -58.88 dB, with an EAB of 5.5 GHz (10.2–15.7 GHz), and a specific reflection loss absolute value of 364 dB / mm. The hollow shell structure formed after etching is not destroyed during carbonization; the carbon nanotubes growing from the inner and outer surfaces of the shell still form a conductive network with the entire carbon framework. Simultaneously, the doping of nitrogen and oxygen atoms generated by pyrolysis provides strong dipole polarization, and the abundant pores and loose structure on the shell wall enhance interfacial polarization. Co nanoparticles also contribute magnetic loss, demonstrating that the hollow multi-nanotube composite absorbing material is an excellent lightweight absorbing filler.
[0081] The beneficial effects of this invention are as follows:
[0082] (1) In this invention, gallic acid, which is a strong acid among organic acids, is used to etch the precursor powder to obtain hollow precursor powder. Then, it is mixed with dicyandiamide in a certain proportion and calcined to prepare hollow multi-carbon nanotube composite microwave absorbing material.
[0083] (2) Gallic acid etches the precursor into an empty shell structure, and due to its strong acidity, the hydrolyzed H + It also has a certain etching effect on the hollow shell walls. This introduces larger voids and multilayered structures into the hollow shell walls, leading to a loosening of the shell walls. The carbon skeleton in the final calcined derivative also appears loose, with obvious stratification. This greatly increases the contact area of the carbon skeleton, making it easier for it to contact other conductive components, reducing the barrier to free electron movement, and improving resistance loss.
[0084] (3) The addition of dicyandiamide helps carbon nanotubes grow in situ on the inner and outer surfaces of the hollow shell wall of the derivative. The conductive pathway formed by carbon nanotubes and hollow loose carbon skeleton, the dipole polarization brought by heteroatoms, the magnetic loss of Co nanoparticles, multiple scattering, rich porosity and multilayer structure enhance the interface polarization and impedance matching, ensuring the excellent microwave absorption performance of hollow multi-carbon nanotube composite microwave absorbing material. The hollow structure is beneficial to impedance matching on the one hand, and on the other hand, it means that only a small amount of hollow multi-carbon nanotube composite microwave absorbing material needs to be added to achieve similar resistance loss, effectively reducing the filling fraction and density of microwave absorbing filler.
Claims
1. A method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material, characterized in that, Includes the following steps: (1) Synthesis of precursors: Dissolve 5–10 mmol of cobalt nitrate hexahydrate and 20–50 mmol of 2-methylimidazole in 40–60 ml of methanol and stir. After both are completely dissolved, slowly pour the 2-methylimidazolium methanol solution into the metal ion methanol solution, and then continue stirring for 20 to 40 minutes. The resulting suspension was allowed to stand for 20–30 hours to allow sufficient growth time for the precursor grains. The purple precipitate was then washed three times with ethanol by centrifugation. The precipitate was dried in an electric heating drying oven for 10-20 hours to obtain the precursor powder. (2) Etching of the precursor: Prepare 10-20 ml of gallic acid aqueous solution with a concentration of 8-10 g / L, and add the gallic acid aqueous solution dropwise to the precursor powder synthesized in step (1), and stir for 10-20 min; The gray precipitate was then washed three times with deionized water by centrifugation, and the precipitate was dried in an electric heating drying oven for 20-30 hours. (3) Preparation of derivative materials: Place the precursor powder from step (2) and dicyandiamide in a mortar at a mass ratio of 1-1.5:0.5-0.8, add a small amount of ethanol, grind carefully for 10-15 minutes, and then dry. The dried mixture was placed in a corundum crucible and calcined in a tube furnace to obtain a nanoporous carbon composite microwave absorbing material.
2. The method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material according to claim 1, characterized in that: During the synthesis of the precursor, the centrifuge speed is 8000-10000 rpm, and the centrifugation time is 5-8 min each time; the precursor powder is a purple powder.
3. The method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material according to claim 1, characterized in that: During the etching process of the precursor, the centrifuge speed is 8000-10000 rpm, and the centrifugation time is 10-15 min each time.
4. The method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material according to claim 1, characterized in that: In the preparation of the derivative material, the mass ratio of the precursor powder to dicyandiamide is 1-1.2:0.5-0.
8.
5. The method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material according to claim 1, characterized in that: In the preparation of the derivative material, the calcination is carried out at a heating rate of 0.8 to 1.2 °C / min in a rare gas atmosphere to 800 to 1000 °C for 8 to 10 hours, and then naturally cooled to room temperature.
6. The method for preparing a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material according to claim 5, characterized in that: The rare gas is one or a combination of nitrogen, argon and helium.
7. A lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material is prepared by the method described in any one of claims 1-6.
8. The application of a lightweight and efficient hollow multi-carbon nanotube composite microwave absorbing material and its preparation method in the social and military fields for efficient absorption of electromagnetic waves.