Wave-absorbing agent, preparation method thereof and wave-absorbing material

Abstract

The application discloses a wave-absorbing agent, a preparation method thereof and a wave-absorbing material. The wave-absorbing agent comprises carbon fibers and sheet-shaped zinc oxide, and the sheet-shaped zinc oxide is arranged on the surface of the carbon fibers. The wave-absorbing agent solves the problem that the high conductivity of the carbon fibers and the low impedance matching result in the incident electromagnetic waves being easily reflected and not easily entering the inside of the wave-absorbing material.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, and particularly relates to a microwave absorbing agent, its preparation method, and microwave absorbing materials. Background Technology

[0002] Carbon-based materials are widely used in the field of microwave absorbing materials due to their light weight, high electrical conductivity, high thermal conductivity, and corrosion resistance. Among them, carbon fiber and its composites, with their high strength, high modulus, and electrical conductivity, are considered promising new microwave absorbing materials. However, due to the poor impedance matching characteristics of carbon fiber, incident electromagnetic waves are easily reflected and do not easily penetrate the interior of the microwave absorbing material. Therefore, studying the microwave absorption mechanism of carbon fiber and performing secondary processing on carbon fiber to improve its microwave absorption performance has become a current research hotspot. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a microwave absorbing agent, its preparation method, and a microwave absorbing material, which solves the problem that incident electromagnetic waves are easily reflected and do not easily enter the interior of the microwave absorbing material due to the high conductivity and low impedance matching of carbon fibers.

[0004] The first aspect of the present invention provides a microwave absorbing agent comprising carbon fibers and sheet-like zinc oxide, wherein the sheet-like zinc oxide is disposed on the surface of the carbon fibers.

[0005] Furthermore, the mass ratio of the carbon fiber to the sheet-like zinc oxide is 1:(0.8-3).

[0006] Furthermore, the length of the sheet-like zinc oxide is 3μm-9μm.

[0007] The second aspect of the present invention provides a method for preparing the above-mentioned microwave absorbing agent, the method comprising: (1) mixing a soluble zinc salt, an alkaline solution and a solvent to obtain a mixed solution, and then rapidly cooling it to obtain a solution containing seed crystals; (2) immersing carbon fibers in the solution containing seed crystals, and then drying and dehydrating them to obtain carbon fibers with seed crystals on their surface; (3) immersing the carbon fibers with seed crystals on their surface in a mixed solution comprising hexamethylenetetramine, a zinc source and oxalic acid, and drying them to obtain the microwave absorbing agent.

[0008] Further, in step (1), the concentration of the soluble zinc salt in the mixture is 0.2-0.4 mmol / L, and the concentration of the alkaline solution is 0.4-0.8 mmol / L.

[0009] Furthermore, in step (2), the drying and dehydration temperature is not lower than 125°C.

[0010] Furthermore, in step (2), the carbon fiber is pre-anodized before being immersed in the solution containing the seed crystal.

[0011] Further, in step (3), the mass ratio of hexamethylenetetramine, zinc source and oxalic acid in the mixture comprising hexamethylenetetramine, zinc source and oxalic acid is 1:(1-3):(0.1-0.3).

[0012] Furthermore, in step (3), the immersion of the carbon fiber with seed crystals on the surface into a mixture of hexamethylenetetramine, zinc source and oxalic acid is carried out in a sealed hydrothermal environment, and the hydrothermal environment temperature is 95℃-125℃, and the immersion time is 6-24h.

[0013] A third aspect of the present invention provides a microwave absorbing material, the microwave absorbing material comprising the microwave absorbing agent described in the first aspect of the present invention or the microwave absorbing agent obtained by the method described in the second aspect of the present invention.

[0014] Compared with existing technologies: The microwave absorbing agent of this invention comprises carbon fibers and sheet-like zinc oxide, wherein the sheet-like zinc oxide is disposed on the surface of the carbon fibers. The ZnO crystals possess a dipole moment along the polar direction. The induced dipole polarization of the ZnO nanocrystals is beneficial for microwave absorption. Disposing of ZnO nanocrystals on the carbon fiber surface can improve the impedance matching performance of the composite material, resulting in a green and efficient microwave absorbing material. Furthermore, the large specific surface area of ​​the sheet-like zinc oxide also promotes multiple reflection loss of electromagnetic waves. Compared to using one-dimensional nanowires attached to the carbon fiber surface, although this can improve the microwave absorption performance of the material to some extent, the antenna effect and dielectric resonance caused by the large aspect ratio of the one-dimensional nanowires lead to a decrease in reflection loss at high frequencies. In contrast, this invention uses sheet-like zinc oxide, which increases the proportion of the polar plane, effectively retains a large specific surface area and a large number of gaps that allow for multiple reflection absorption of electromagnetic waves, while eliminating the antenna effect generated by the sharp points. This allows for an impedance matching close to 1 across a wider wavelength range, resulting in a larger absorption bandwidth. Therefore, the microwave absorbing agent composed in this invention solves the problem that incident electromagnetic waves are easily reflected and do not easily enter the interior of the microwave absorbing material due to the high conductivity and low impedance matching of carbon fibers. Attached Figure Description

[0015] Figure 1 This is a SEM image of the microwave absorber from Example 1. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0017] The first aspect of the present invention provides a microwave absorbing agent comprising carbon fibers and sheet-like zinc oxide, wherein the sheet-like zinc oxide is disposed on the surface of the carbon fibers.

[0018] In the microwave absorbing agent of this invention, the plate-like zinc oxide is disposed on the surface of the carbon fiber. The ZnO crystals possess a dipole moment along the polar direction. The induced dipole polarization of the ZnO nanocrystals is beneficial for microwave absorption. By placing ZnO nanocrystals on the carbon fiber surface, the impedance matching performance of the composite material can be improved, resulting in a green and efficient microwave absorbing material. Furthermore, the large specific surface area of ​​the plate-like zinc oxide also promotes multiple reflection loss of electromagnetic waves. Compared to one-dimensional nanowires attached to the carbon fiber surface, although they can improve the microwave absorption performance to some extent, the antenna effect and dielectric resonance caused by the large aspect ratio of the one-dimensional nanowires lead to a decrease in reflection loss at high frequencies. In contrast, this invention uses plate-like zinc oxide, which increases the proportion of the polar plane, effectively retains a large specific surface area and a large number of gaps that allow for multiple reflection and absorption of electromagnetic waves, while eliminating the antenna effect generated by the sharp points. This allows for an impedance matching close to 1 across a wider wavelength range, resulting in a larger absorption bandwidth. Therefore, the microwave absorbing agent of this invention solves the problem that the high conductivity and low impedance matching of carbon fibers cause incident electromagnetic waves to be easily reflected and difficult to penetrate the interior of the microwave absorbing material.

[0019] According to an embodiment of the present invention, the mass ratio of the carbon fiber to the lamellar zinc oxide in the above-mentioned absorbing agent is 1:(0.8-3). The inventors have discovered that if the content of lamellar zinc oxide is too high, a large dielectric loss cannot be achieved, thus preventing the incident electromagnetic waves from being consumed by the absorbing agent. If the content of lamellar zinc oxide is too low, the impedance matching of the absorbing agent is too small, preventing electromagnetic waves from entering the interior of the absorbing body, thus failing to achieve a good absorption effect. Therefore, by using the carbon fiber and lamellar zinc oxide composition of this application, a large amount of electromagnetic waves can enter the absorbing body while being attenuated within it, achieving an effective absorption effect.

[0020] According to embodiments of the present invention, the length of the sheet-like zinc oxide in the above-mentioned microwave absorbing agent is 3μm-9μm. The inventors discovered that if the length of the sheet-like zinc oxide is too short, most of the carbon fiber matrix is ​​directly exposed on the outer surface and in contact with the incident electromagnetic wave, causing the electromagnetic wave to be directly reflected by the material and unable to penetrate the microwave absorbing agent; if the length of the sheet-like zinc oxide is too long, due to the rigidity of the zinc oxide crystal, large sheets are prone to detachment, leading to separation of the zinc oxide and the carbon fiber. Therefore, by controlling the length of the sheet-like zinc oxide on the carbon fiber surface within the above-mentioned range in the microwave absorbing agent of this application, it is possible to maintain the sheet-like zinc oxide firmly covering the carbon fiber surface while obtaining an impedance matching closer to 1 and excellent microwave absorption capability.

[0021] Specifically, the length of the sheet zinc oxide can be understood as the distance between the end of the sheet zinc oxide furthest from the carbon fiber surface and the end closest to the carbon fiber surface.

[0022] A second aspect of the present invention provides a method for preparing the above-mentioned microwave absorbing agent. According to an embodiment of the present invention, the method includes:

[0023] S1: Preparation of a solution containing seed crystals

[0024] According to an embodiment of the present invention, a soluble zinc salt, an alkaline solution, and a solvent are mixed to obtain a mixture, which is then rapidly cooled to obtain a solution containing seed crystals. Specifically, the soluble zinc salt and the alkaline solution are dissolved separately in a solvent heated to 55°C-65°C, and then the two solutions are mixed and subjected to an agitated water bath (temperature 55-65°C, water bath time 25-35 min). The soluble zinc salt and the alkaline solution react to generate Zn(OH)2. The mixture is then removed and immediately placed in a prepared ice-water mixture for rapid cooling to prevent the seed crystals from growing too quickly.

[0025] Furthermore, the concentration of the soluble zinc salt in the mixture is 0.2-0.4 mmol / L, and the concentration of the alkaline solution is 0.4-0.8 mmol / L.

[0026] It should be noted that those skilled in the art can select the soluble zinc salt, alkaline solution, and solvent according to actual needs. For example, the soluble zinc salt includes at least one of zinc acetate dihydrate, zinc chloride, and zinc nitrate; the alkaline solution includes sodium hydroxide, sodium hydroxide, ammonium salt, etc.; and the solvent is ethanol.

[0027] S2: Preparation of carbon fibers with surface-coated seed crystals

[0028] In this step, carbon fibers are immersed in the solution containing seed crystals, and then dried and dehydrated to obtain carbon fibers with seed crystals on the surface. Specifically, the carbon fibers are immersed in the solution containing seed crystals obtained above, stirred at room temperature, and dried in an oven to dehydrate the Zn(OH)2 attached to the carbon fibers to obtain ZnO nanoparticles. Then, the carbon fibers are cooled at room temperature, and the above process is repeated to ensure that the ZnO nanoparticles on the surface of the carbon fibers are fully attached, thereby obtaining carbon fibers with seed crystals on the surface.

[0029] According to an embodiment of the present invention, the drying temperature in the oven is not lower than 125°C, which allows Zn(OH)2 to be dehydrated to obtain ZnO nanoparticles, thereby forming zinc oxide seed crystals that are firmly attached to the surface of carbon fibers.

[0030] According to an embodiment of the present invention, before immersing the carbon fiber in the solution containing the seed crystal, the carbon fiber is pre-anodized. This etches the surface of the carbon fiber, increasing its surface roughness and improving the bonding strength between zinc oxide and the carbon fiber. Furthermore, oxidizing the active carbon atoms on the carbon fiber surface increases the number and types of oxygen-containing functional groups (hydroxyl, carbonyl, and carboxylic acid groups), thereby increasing the interfacial interaction between the sheet-like zinc oxide and the carbon fiber and promoting the adhesion strength between the zinc oxide seed layer and the carbon fiber. Simultaneously, the oxygen-containing functional groups can promote dipole polarization, generating polarization relaxation that consumes some electromagnetic waves. For example, using continuous carbon fiber as the anode and a graphite plate as the cathode, an electric field is applied to electrolytically oxidize the carbon fiber in an ammonium bicarbonate electrolyte aqueous solution for 60-150 s at a current density of 0.5-3 A / m. 2 .

[0031] S3: Plate-like zinc oxide growth

[0032] According to an embodiment of the present invention, the carbon fibers with seed crystals coated on the surface obtained above are immersed in a mixture comprising hexamethylenetetramine (HMTA), a zinc source, and oxalic acid. Hexamethylenetetramine and the zinc salt respectively provide hydroxide ions (OH-). - ) and zinc ions (Zn 2+ HMTA also acts as a buffer, slowing down the reaction of OH groups. - This ensures the release rate and maintains the continuous growth of ZnO. 2+ and C2O4 2- OH - A chemical reaction occurs, precipitating ZnC₂O₄·Zn(OH)₂. Because Zn… 2+ It belongs to metal ions with strong polarization ability, and under hydrothermal conditions, it reacts with O. 2- The attraction is stronger, therefore the generated ZnC2O4·Zn(OH)2 readily decomposes to produce ZnO. After drying, the microwave absorber is obtained. The specific process is shown in the following equation.

[0033] C6H 12 N₄ + 6H₂O → 6HCHO + 4NH₃

[0034] NH3 + H2O → NH4 + +OH -

[0035] 2Zn 2+ +2OH - +C2O4 2- →ZnC2O4·Zn(OH)2

[0036] 2ZnC2O4·Zn(OH)2+O2→4ZnO+4CO2+2H2O

[0037] Specifically, an aqueous solution containing hexamethylenetetramine, zinc source, and oxalic acid is used as the growth solution. Carbon fibers with ZnO nanocrystals attached are immersed in the growth solution. The beaker containing the carbon fibers is sealed and placed in an oven to complete the self-assembly process of the nanosheets. After removal, the nanosheets are ultrasonically treated for 5-20 minutes and dried to obtain a microwave absorbing agent with sheet-like zinc oxide attached to the surface.

[0038] According to an embodiment of the present invention, the mass ratio of hexamethylenetetramine, zinc source, and oxalic acid in the mixture comprising hexamethylenetetramine, zinc source, and oxalic acid is 1:(1-3):(0.1-0.3). The inventors have found that if the amount of hexamethylenetetramine added is too small, zinc oxide cannot be directly generated into zinc oxide nanosheets on the carbon fiber surface; if the amount of hexamethylenetetramine added is too large, the pH of the solution becomes too high, causing a large amount of zinc to exist in the solution in ionic form, or even preventing the formation of zinc oxide. Simultaneously, if the amount of oxalic acid added is too small, coarse rod-like structures will form, connecting to form a thick layer of zinc oxide attached to the carbon fiber, failing to provide an electromagnetic wave reflection path; while if the concentration of oxalic acid is too high, the nanosheets will grow too quickly and too large, failing to connect to the carbon fiber. Therefore, this application uses a growth solution with the above-described composition, which can grow sheet-like zinc oxide on the carbon fiber surface, thereby improving the microwave absorption performance of the microwave absorber.

[0039] According to an embodiment of the present invention, the carbon fibers with seed crystals on their surface are immersed in a mixture comprising hexamethylenetetramine, a zinc source, and oxalic acid in a sealed hydrothermal environment at a temperature of 95°C-125°C for 6-24 hours. This allows for control of the growth rate of zinc oxide nanosheets, resulting in an aspect ratio that effectively increases microwave absorption performance, leading to effective dielectric loss and impedance matching, and ultimately, an absorbing agent with excellent microwave absorption properties.

[0040] The conductive network composed of carbon fibers in the absorbing agent of this invention provides a large amount of conductive loss, while the large specific surface area of ​​the lamellar zinc oxide provides multiple reflection paths, impedance matching, and various polarization relaxation mechanisms, greatly improving the absorption performance of the absorbing agent, thereby achieving excellent reflection loss and a large effective absorption bandwidth. Specifically, the reflection loss of the absorbing agent of this invention can reach -10 to -57.2 dB, and the maximum absorption bandwidth can reach 6.1 GHz, exhibiting excellent electromagnetic wave dissipation capability and absorption performance.

[0041] It should be noted that the features and advantages described above for the absorbing agent also apply to the method for preparing the absorbing agent, and will not be repeated here.

[0042] A third aspect of this invention provides a microwave absorbing material, which includes the microwave absorbing agent described in the first aspect of this invention or the microwave absorbing agent obtained by the method described in the second aspect of this invention. It should be noted that the features and advantages described above for the microwave absorbing agent and its preparation method also apply to this microwave absorbing material, and will not be repeated here.

[0043] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0044] Example 1

[0045] (1) Dissolve 0.25 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 60 °C for 30 minutes. Then place the reaction solution into a prepared ice-water mixture to obtain a solution containing seed crystals.

[0046] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the carbon fiber in the solution containing seed crystals obtained in step (1) for 50 minutes, remove the carbon fiber and transfer it into an empty beaker, put it in an oven at 150°C and heat it for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0047] (3) Weigh 2.5 mmol of zinc chloride and add it to 100 ml of deionized water. After stirring and dissolving, add 5 mmol of hexamethylenetetramine and 0.25 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing the carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0048] Example 2

[0049] (1) Dissolve 0.2 mmol of zinc acetate dihydrate and 0.4 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 65 °C for 25 minutes. Then place the reaction solution into a prepared ice-water mixture to obtain a solution containing seed crystals.

[0050] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 40 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 130°C and heat it for 15 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 4 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0051] (3) Weigh 2.5 mmol of zinc chloride and add it to 100 ml of deionized water. After stirring and dissolving, add 5 mmol of hexamethylenetetramine and 0.5 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 6 hours. After taking it out, sonicate it for 10 minutes and dry it to obtain the microwave absorbing agent.

[0052] Example 3

[0053] (1) Dissolve 0.3 mmol of zinc acetate dihydrate and 0.6 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 55 °C for 35 minutes. Then place the reaction solution in a prepared ice-water mixture to obtain a solution containing seed crystals.

[0054] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 30 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 140°C and heat it for 10 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 5 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0055] (3) Weigh 2.5 mmol of zinc chloride and add it to 100 ml of deionized water. After stirring and dissolving, add 2.5 mmol of hexamethylenetetramine and 0.35 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0056] Example 4

[0057] (1) Dissolve 0.5 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 60 °C for 30 minutes. Then place the reaction solution in the prepared ice-water mixture to obtain a solution containing seed crystals.

[0058] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 60 minutes, remove the fiber and transfer it into an empty beaker, put it in an oven at 160°C and heat it for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0059] (3) Weigh 2.5 mmol of zinc chloride and add it to 100 ml of deionized water. After stirring and dissolving, add 2.5 mmol of hexamethylenetetramine and 0.6 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 24 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0060] Example 5

[0061] (1) Dissolve 0.25 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 65 °C for 25 minutes. Then place the reaction solution into a prepared ice-water mixture to obtain a solution containing seed crystals.

[0062] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 50 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 125°C and heat it for 15 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0063] (3) Weigh 2.5 mmol of zinc acetate and add it to 100 ml of deionized water. After stirring and dissolving, add 5 mmol of hexamethylenetetramine and 0.25 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing the carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0064] Example 6

[0065] (1) Dissolve 0.3 mmol of zinc acetate dihydrate and 0.6 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 55 °C for 35 minutes. Then place the reaction solution in a prepared ice-water mixture to obtain a solution containing seed crystals.

[0066] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 50 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 125°C and heat it for 15 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0067] (3) Weigh 2.5 mmol of zinc acetate and add it to 100 ml of deionized water. After stirring and dissolving, add 7.5 mmol of hexamethylenetetramine and 0.45 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing the carbon fiber and heat it in an oven at 90°C for 6 hours. After taking it out, sonicate it for 10 minutes and dry it to obtain the microwave absorbing agent.

[0068] Example 7

[0069] (1) Dissolve 0.5 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 55 °C for 35 minutes. Then place the reaction solution in the prepared ice-water mixture to obtain a solution containing seed crystals.

[0070] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2Immerse the fiber in the solution containing seed crystals obtained in step (1) for 35 minutes, remove the fiber and transfer it into an empty beaker, put it in an oven at 150°C and heat it for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 5 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0071] (3) Weigh 2.5 mmol of zinc acetate and add it to 100 ml of deionized water. After stirring and dissolving, add 2.5 mmol of hexamethylenetetramine and 0.6 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0072] Example 8

[0073] (1) Dissolve 0.2 mmol of zinc acetate dihydrate and 0.4 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 60 °C for 30 minutes. Then place the reaction solution in the prepared ice-water mixture to obtain a solution containing seed crystals.

[0074] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 50 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 125°C and heat it for 15 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0075] (3) Weigh 2.5 mmol of zinc acetate and add it to 100 ml of deionized water. After stirring and dissolving, add 2.5 mmol of hexamethylenetetramine and 0.75 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 24 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0076] Example 9

[0077] (1) Dissolve 0.25 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 60 °C for 30 minutes. Then place the reaction solution into a prepared ice-water mixture to obtain a solution containing seed crystals.

[0078] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 50 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 150°C and heat it for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0079] (3) Weigh 2.5 mmol of zinc nitrate and add it to 100 ml of deionized water. After stirring and dissolving, add 5 mmol of hexamethylenetetramine and 0.25 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing the carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0080] Example 10

[0081] (1) Dissolve 0.2 mmol of zinc acetate dihydrate and 0.4 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 65 °C for 25 minutes. Then place the reaction solution into a prepared ice-water mixture to obtain a solution containing seed crystals.

[0082] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 40 minutes, remove the fiber and transfer it to an empty beaker, put it in an oven at 130°C and heat it for 15 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 4 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0083] (3) Weigh 2.5 mmol of zinc nitrate and add it to 100 ml of deionized water. After stirring and dissolving, add 3.75 mmol of hexamethylenetetramine and 0.5 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 6 hours. After taking it out, sonicate it for 10 minutes and dry it to obtain the microwave absorbing agent.

[0084] Example 11

[0085] (1) Dissolve 0.3 mmol of zinc acetate dihydrate and 0.6 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 55 °C for 35 minutes. Then place the reaction solution in a prepared ice-water mixture to obtain a solution containing seed crystals.

[0086] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 60 minutes, remove the fiber and transfer it into an empty beaker, put it in an oven at 160°C and heat it for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 3 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0087] (3) Weigh 2.5 mmol of zinc nitrate and add it to 100 ml of deionized water. After stirring and dissolving, add 2.5 mmol of hexamethylenetetramine and 0.6 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0088] Example 12

[0089] (1) Dissolve 0.5 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 60 °C for 30 minutes. Then place the reaction solution in the prepared ice-water mixture to obtain a solution containing seed crystals.

[0090] (2) The anodized T300 carbon fiber was subjected to electrolytic oxidation treatment in an ammonium bicarbonate electrolyte aqueous solution (using T300 carbon fiber as the anode and a graphite plate as the cathode, an electric field was applied to the carbon fiber for 100s, and the current density was 1.5A / m). 2 Immerse the fiber in the solution containing seed crystals obtained in step (1) for 30 minutes, remove the fiber and transfer it into an empty beaker, put it in an oven at 140°C, heat it for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 5 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0091] (3) Weigh 2.5 mmol of zinc nitrate and add it to 100 ml of deionized water. After stirring and dissolving, add 2.5 mmol of hexamethylenetetramine and 0.25 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing carbon fiber and heat it in an oven at 90°C for 24 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0092] Example 13

[0093] (1) Dissolve 0.5 mmol of zinc acetate dihydrate and 0.5 mmol of sodium hydroxide in 80 ml of ethanol solution respectively, stir until dissolved, mix the two solutions, add ethanol to 200 ml, and shake in a water bath at 60 °C for 30 minutes. Then place the reaction solution in the prepared ice-water mixture to obtain a solution containing seed crystals.

[0094] (2) Immerse T300 carbon fiber in the solution containing seed crystals obtained in step (1) for 30 minutes, remove the fiber and transfer it into an empty beaker, put it into an oven at 140°C, heat for 5 minutes, then remove it and cool it at room temperature for 5 minutes. Repeat the above steps 5 times to obtain carbon fiber with zinc oxide seed crystals on the surface.

[0095] (3) Weigh 2.5 mmol of zinc nitrate and add it to 100 ml of deionized water. After stirring and dissolving, add 5 mmol of hexamethylenetetramine and 0.25 mmol of oxalic acid. Add carbon fiber with seed crystals on the surface. Seal the beaker containing the carbon fiber and heat it in an oven at 90°C for 12 h. After taking it out, sonicate it for 10 min and dry it to obtain the microwave absorbing agent.

[0096] The microwave absorbers obtained in Examples 1-13 were subjected to SEM testing. Figure 1 SEM images of the microwave absorbing agent obtained in Example 1 are shown. Sheet-like carbon fibers are grown on the surface of carbon fibers, and the length of the sheet-like zinc oxide on the surface of carbon fibers is shown in Table 1. The mass ratio of zinc oxide to carbon fibers in the microwave absorbing agent and the results of characterizing the microwave absorption performance and electromagnetic wave dissipation performance of the obtained microwave absorbing agent are also shown in Table 1.

[0097] Characterization methods for the reflection loss and maximum absorption bandwidth of the absorbing agent: Measurements were performed in the range of 2.0–18.0 GHz using a vector network analyzer (VNA, Agilent E5071C), employing the coaxial method. The test sample was prepared by uniformly mixing the absorber at 10 wt% in a paraffin matrix and compacting it into a coaxial ring with an outer diameter of 7.00 mm, an inner diameter of 3.04 mm, and a thickness of 2 mm.

[0098] Table 1

[0099]

[0100]

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wave-absorbing agent, characterized by comprising: The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

2. A method of preparing the wave-absorbing agent of claim 1, characterized by, The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns. The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns. The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns. The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

3. The method of claim 2, wherein, The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

4. The method of claim 2, wherein, The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

5. The method of claim 2, wherein, The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

6. The method of claim 2, wherein, The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

7. The method of claim 2, wherein, The wave-absorbing material comprises carbon fibers and flaky zinc oxide, the flaky zinc oxide is arranged on the surface of the carbon fibers, the mass ratio of the carbon fibers to the flaky zinc oxide is 1:(0.8-3), and the length of the flaky zinc oxide is 3-9 microns.

8. A wave-absorbing material, characterized by, ​

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