Composite wave-absorbing material and preparation method thereof

Abstract

The present application relates to electromagnetic wave absorption technical field, especially to a kind of carbon nanometer load cobalt ferrite composite wave-absorbing material and preparation method thereof, comprising the following steps: 1) soluble iron salt, soluble cobalt salt is dispersed in water, and complexing agent is added, and cobalt ferrite powder is obtained by sol-gel reaction;2) soluble biomass saccharide is dispersed in deionized water, and a solution with a certain concentration is prepared, cobalt ferrite powder is added to the solution for aging immersion, and then the solid-liquid mixture is suction filtered, the filter cake is air dried, and the cobalt ferrite powder with uniform carbon source loading is obtained;3) the cobalt ferrite powder with carbon source loading is calcined under inert atmosphere, and the composite wave-absorbing material is prepared.The wave-absorbing material prepared by the present application has the characteristics of light weight, strong absorption, effective absorption bandwidth, easy-to-control wave-absorbing performance, etc.In addition, the preparation method used in the present application is simple, raw materials are easy to obtain, cost is low, green and environmentally friendly, and more conducive to industrial application.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorption technology, specifically a composite absorbing particle of carbon nanotubes loaded with cobalt ferrite and its preparation method. Background Technology

[0002] Electromagnetic absorbing materials can absorb or significantly reduce the electromagnetic wave energy received on their surface, and have been widely used in military, aerospace, communications, and electronics fields in recent years. Electromagnetic waves are generated by many sources, including natural phenomena such as lightning, sunlight, and radio waves from distant galaxies, as well as man-made electromagnetic waves such as radio waves and radar waves. Electromagnetic waves in the 2-18 GHz range can have adverse effects on human health and electronic devices, and this frequency band can also be used in the military for communication and reconnaissance missions.

[0003] Ferrites are a traditional microwave absorbing material. Among various methods for industrial-scale ferrite preparation, the hydrothermal method has low yield, long production cycle, and requires high temperature and high pressure conditions, increasing equipment complexity and cost while also posing certain safety risks. The co-precipitation method generates large amounts of wastewater in industrial production, and potential side reactions often result in the presence of other impurities or components in the prepared product, making it difficult to control product purity. In comparison, the sol-gel method for preparing ferrites has low energy consumption, short cycle time, simple process, and no wastewater generation, making it more suitable for large-scale industrial production. However, ferrites prepared by the sol-gel method often have poor microwave absorption performance. Existing methods often modify ferrites by doping with rare earth elements, but this method does not significantly improve ferrite performance.

[0004] Cobalt ferrite, as a typical magnetic loss-type absorbing material, possesses high saturation magnetization and high coercivity, thus showing promising application prospects. However, its high density, high resistivity, and narrow absorption bandwidth when used alone make it unsuitable for the complex applications in various fields today. Carbon materials, with their low density, good chemical stability, and high conductivity, are often used to combine with ferrite materials to improve impedance matching and enhance absorption performance. Existing composite methods mainly include hydrothermal methods, chemical vapor deposition, and chemical reduction methods. These methods are relatively complex, costly, and difficult to industrialize.

[0005] Chinese patent document CN 105219346 A discloses a method for preparing a bio-based carbon nanofiber-loaded cobalt ferrite microwave absorbing material. First, a bio-based nanofiber suspension is prepared, then freeze-dried and subjected to a carbonization reaction. The bio-based carbon fibers are then ultrasonically reacted with cobalt salts, iron salts, and hydrochloric acid in an ethylene glycol solution, followed by a solvothermal reaction with sodium hydroxide, and finally washed and dried to obtain the finished product. However, the solvothermal reaction used in this invention requires high temperature and high pressure conditions, and organic solvents such as phenylethanol and glacial acetic acid are used in the preparation of the bio-based nanofiber suspension, posing certain safety hazards in industrial production. Furthermore, the waste liquid generated after the solvothermal reaction and during the washing process requires treatment, making it unsuitable for large-scale production. Chinese patent document CN 111565552 A discloses a method for preparing a porous carbon-coated CoFe alloy-SiC composite electromagnetic shielding material. Fine powder obtained from ball milling of corn stalks is added to a mixed solvent composed of ethanol, cobalt nitrate, tetraethyl orthosilicate, and oxalic acid. After high-temperature calcination, the silica is removed using hydrofluoric acid to prepare biomass-based nano-silicon carbide. The nano-silicon carbide is then uniformly grown within an organic framework of metalloenzymes (MOFs), and through high-temperature pyrolysis, CoFe nanoalloys are obtained. The MOFs organic framework forms a porous carbon layer, ultimately yielding porous carbon-coated CoFe nanoalloy-modified nano-SiC. This method uses a calcination temperature of 1300-1350℃ and a holding time of 6-7 hours to prepare biomass-based nano-silicon carbide. This process involves high energy consumption, leading to high production costs and environmental burden. Furthermore, the calcined product does not yield a pure phase, requiring the removal of impurities with hydrofluoric acid, making it unsuitable for large-scale production.

[0006] Therefore, it is essential to develop a wide-bandwidth, strong-absorbing, lightweight absorbing material that also offers advantages such as simple processing, readily available raw materials, low cost, and environmental friendliness in industrial applications. Summary of the Invention

[0007] One objective of this invention is to provide a method for preparing a microwave absorbing material. This method uses soluble biomass sugar as a carbon source, soluble iron salt as an iron source, and soluble cobalt salt as a cobalt source. In the prepared microwave absorbing material, carbon is highly uniformly loaded on the surface of cobalt ferrite, resulting in a material that is lightweight, has strong absorption, a wide effective absorption bandwidth, and easily tunable absorption performance. The preparation method is simple, uses readily available raw materials, is low-cost, and environmentally friendly, making it more suitable for industrial applications.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a microwave absorbing material, comprising the following steps:

[0009] 1) Weigh a certain amount of soluble iron salt and soluble cobalt salt, disperse the two salts in deionized water according to the molar ratio of cobalt ions to iron ions of 1:2, and then add a complexing agent. The total concentration of iron ions and cobalt ions in the deionized water is 0.1-0.2 mol / L, and the ratio of the total molar amount of iron ions and cobalt ions to the molar amount of complexing agent is 1:(1-1.5). Add ammonia water to adjust the pH to 7-7.2, and a sol-gel reaction will occur to generate a viscous sol.

[0010] The viscous sol was dried and crushed, burned at 180-200℃ and then cooled. It was then calcined at 600-700℃ for 2-4 hours, cooled to room temperature, ground and sieved to obtain cobalt ferrite powder.

[0011] 2) Dissolve soluble biomass sugar in deionized water to prepare a solution with a concentration of 5%-50wt%. Immerse cobalt ferrite powder in the solution and age for 2-6 hours. Then perform solid-liquid separation. The solid is washed and dried to obtain cobalt ferrite powder uniformly loaded with carbon source.

[0012] 3) The cobalt ferrite powder uniformly loaded with carbon source is calcined at 300-400℃ for 1-4 hours under a protective atmosphere to obtain the cobalt ferrite-loaded carbon composite microwave absorbing material.

[0013] Further improvements to the preparation method of microwave absorbing materials:

[0014] Preferably, in step 1), the viscous sol is dried at 100-120℃ for 14-18 hours and then broken up; in steps 1) and 3), the temperature is increased to the calcination temperature at a rate of 3-5℃ / min during high-temperature calcination, and after calcination, the temperature is decreased to 30-50℃ at a rate of 3-5℃ / min, and then naturally cooled to room temperature.

[0015] Preferably, the soluble biomass sugar is one or a combination of two or more of glucose, fructose, xylose, sucrose, D-galactose, and water-soluble starch.

[0016] Preferably, the soluble iron salt is one or a combination of two or more of ferric nitrate, ferric chloride, ferric sulfate, and ferric acetate.

[0017] Preferably, the soluble cobalt salt is one or a combination of two or more of cobalt nitrate, cobalt chloride, cobalt sulfate, and cobalt acetate.

[0018] Preferably, the complexing agent is one or a combination of two or more of oxalic acid, citric acid, tartaric acid, and glycine.

[0019] Preferably, the sol-gel reaction in step 1) is carried out at 75-85°C for 3-5 hours.

[0020] Preferably, the solid after solid-liquid separation in step 2) is rinsed and then dried by blowing at 100-120°C for 10-15 hours.

[0021] Preferably, the protective atmosphere in step 3) is a nitrogen atmosphere or an inert gas atmosphere.

[0022] A second objective of this invention is to provide a composite microwave absorbing material prepared by any of the above-mentioned methods.

[0023] The advantages of this invention compared to the prior art are as follows:

[0024] 1) This invention uses renewable soluble biomass sugars as a carbon source. Compared to polymers such as phenolic resins and polydopamine, soluble reducing sugars are widely available, inexpensive, and can be obtained from various biomass materials. The impregnation solution used in the product preparation process is recyclable, and no wastewater is generated during the entire production process, nor is any organic solvent required. The required calcination temperature does not exceed 600℃. Compared to existing technologies for preparing microwave absorbers using sol-gel methods, this invention has low energy consumption, is environmentally friendly, and meets the requirements of green chemistry.

[0025] 2) This invention provides a method for preparing a composite microwave absorbing material. First, soluble iron salts and soluble cobalt salts are dispersed in water according to a stoichiometric ratio, using oxalic acid dihydrate as a complexing agent, to obtain cobalt ferrite through a sol-gel reaction. Then, soluble biomass sugars are dispersed in deionized water to prepare a solution of a certain concentration, and the cobalt ferrite is added to the solution for aging and impregnation. The solid-liquid mixture is then filtered, and the resulting filter cake is dried in an oven under forced-air drying, crushed, ground, and calcined under an inert atmosphere to obtain the finished product. The sol-gel reaction is carried out under water bath heating conditions, first by evaporating the solvent to allow Fe... 3+ A complexation reaction occurs with a complexing agent to obtain a viscous sol, which is then dried by forced air to obtain a dry gel. An excess impregnation-carbonization coupling process is employed to uniformly load carbon onto the surface of cobalt ferrite. Compared to chemical vapor deposition, hydrothermal methods, and chemical reduction methods, the excess impregnation-carbonization coupling method is simpler. The carbon source content can be controlled by adjusting the concentration of the impregnation solution, thereby controlling the microwave absorption properties and electromagnetic parameters of the material. The process is simple, the product has high purity, and it is more conducive to industrial applications.

[0026] 3) The low carbonization temperature used in this invention retains some organic functional groups, which is beneficial for forming polar centers and improving dipole polarization. Furthermore, the presence of these functional groups is more conducive to the bonding between the microwave absorber and the organic matrix, showing promising application prospects.

[0027] 4) The cobalt ferrite-supported carbon composite absorbing material prepared by this invention has the characteristics of low density, high stability, strong absorption capacity of electromagnetic waves, and wide effective bandwidth. Absorbers prepared by hydrothermal and co-precipitation methods often have high absorption intensity but narrow effective absorption bandwidth. Absorbers prepared by the traditional sol-gel method often have a wide absorption bandwidth but weak absorption intensity. The absorbing material prepared by this invention achieves a minimum electromagnetic wave reflection loss of -55.72 dB and an effective absorption bandwidth of 6.60 GHz. It simultaneously achieves the design goals of strong absorption and wide bandwidth. Attached Figure Description

[0028] Figure 1 The XRD diffraction patterns of the cobalt ferrite-loaded carbon composite microwave absorbing material prepared in Example 1 and the cobalt ferrite powder prepared in the comparative example are shown.

[0029] Figure 2 The image shows a SEM image of the cobalt ferrite-loaded carbon composite microwave absorbing material prepared in Example 1.

[0030] Figure 3 The energy spectrum of the cobalt ferrite-loaded carbon composite absorbing material prepared in Example 1 is shown.

[0031] Figure 4 The reflection loss diagrams show the cobalt ferrite-loaded carbon composite microwave absorbing materials prepared in Examples 1 and 2 and the cobalt ferrite powder prepared in the comparative example. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] Comparative Example

[0034] This embodiment provides a method for preparing cobalt ferrite powder, which specifically includes the following steps:

[0035] Weigh 2.693 g of ferric nitrate nonahydrate and 0.970 g of cobalt nitrate hexahydrate and add them to 80 ml of deionized water. The molar ratio of cobalt ions to iron ions is 1:2, and the total concentration of iron ions and cobalt ions in the deionized water is 0.125 mol / L. Then add 1.513 g of oxalic acid dihydrate. The molar ratio of the total molar amount of iron ions and cobalt ions to the molar amount of oxalic acid dihydrate is 1:1.2. After magnetic stirring, the mixture is evenly dispersed. Then adjust the pH to 7 with 25% ammonia water. Heat the mixture in a water bath to 85°C and maintain the constant temperature while stirring continuously for 4 hours to obtain a viscous sol.

[0036] The viscous sol was transferred to a forced-air drying oven and dried at 120°C for 14 hours to obtain a dry gel. The dry gel was broken up and transferred to a resistance furnace, heated to 200°C for self-propagating combustion, and then naturally cooled to room temperature. It was then transferred to a muffle furnace and heated to 600°C at a rate of 5°C / min. It was held at this temperature for 2 hours, then cooled to 50°C at a rate of 5°C / min, and finally naturally cooled to room temperature. After grinding and sieving, cobalt ferrite powder was obtained.

[0037] Example 1

[0038] This embodiment provides a method for preparing a composite microwave absorbing material, which specifically includes the following steps:

[0039] 1) Weigh 7.2g of glucose and add 20ml of deionized water. Disperse the glucose solution evenly by magnetic stirring to obtain a glucose solution with a concentration of 36wt%. Immerse the cobalt ferrite prepared in the comparative ratio in the solution and age it for 2 hours. Then filter it to separate the solid and liquid. Wash the filter cake repeatedly with the glucose solution with a mass fraction of 36wt%. Then dry it in a 100℃ forced-air drying oven for 12 hours to obtain cobalt ferrite powder with uniform carbon source loading.

[0040] 2) Place the cobalt ferrite powder loaded with carbon source in a crucible and transfer it to a tube furnace. After evacuating the tube furnace, inject argon gas to form an inert atmosphere. While maintaining a certain argon flow rate, heat the sample from room temperature to 400℃ at a heating rate of 5℃ / min and hold it at that temperature for 2 hours. Then, cool it down to 50℃ at a rate of 5℃ / min and finally allow it to cool naturally to room temperature to obtain the cobalt ferrite loaded with carbon composite microwave absorbing material.

[0041] Example 2

[0042] This embodiment provides a method for preparing a composite microwave absorbing material, which specifically includes the following steps:

[0043] 1) Weigh 7.2g of xylose and add 20ml of deionized water. Disperse the xylose solution evenly by magnetic stirring to obtain a concentration of 36wt%. Immerse the cobalt ferrite prepared in the comparative ratio in the solution and age it for 2 hours. Then filter it to separate the solid and liquid. Wash the filter cake repeatedly with the 36wt% xylose solution and dry it in a 100℃ forced-air drying oven for 12 hours to obtain cobalt ferrite powder with uniform carbon source loading.

[0044] 2) Place the cobalt ferrite powder loaded with carbon source in a crucible and transfer it to a tube furnace. After evacuating the tube furnace, inject argon gas to form an inert atmosphere. While maintaining a certain argon flow rate, heat the sample from room temperature to 400°C at a heating rate of 5°C / min and hold it at that temperature for 2 hours. Then, cool it down to 50°C at a rate of 5°C / min and finally allow it to cool naturally to room temperature to obtain the cobalt ferrite-loaded carbon composite microwave absorbing material.

[0045] The microwave absorption performance test results of the cobalt ferrite-supported carbon composite absorbing materials prepared in Examples 1 and 2, and the cobalt ferrite powder prepared in the comparative example, in the 2-18 GHz range are as follows: Figure 1-4 As shown. Among them. Figure 1 XRD diffraction patterns of the cobalt ferrite-supported carbon composite microwave absorbing material prepared in Example 1 and the cobalt ferrite powder prepared in the comparative example. Figure 2 SEM image of the cobalt ferrite-supported carbon composite microwave absorbing material prepared in Example 1; Figure 3 The energy spectrum of the cobalt ferrite-supported carbon composite absorbing material prepared in Example 1 is shown below; Figure 1-3 It can be seen that the crystalline phase in the composite microwave absorbing material is cobalt ferrite ( Figure 1 The composite absorbing material exhibits a sheet-like microstructure. Figure 2 Cobalt ferrite was successfully composited with carbon, with carbon uniformly loaded on the surface of the cobalt ferrite. Figure 3 ).

[0046] Figure 4 The diagram shows the reflection loss of the cobalt ferrite-loaded carbon composite absorbing materials prepared in Examples 1 and 2, and the cobalt ferrite powder prepared in the comparative example. For the absorption performance testing, a coaxial testing method was used. The absorbing material to be tested was composited with paraffin wax, and then pressed into paraffin wax rings of a certain thickness using a standard mold. The absorption performance of the paraffin wax composite material at different thicknesses was calculated based on the electromagnetic parameters of the material. Specifically, the composite absorbing material prepared in Example 1 was composited with paraffin wax and pressed into paraffin wax rings of 2.8 mm and 4.5 mm thicknesses, respectively; the composite absorbing material prepared in Example 2 was composited with paraffin wax and pressed into paraffin wax rings of 1.9 mm and 3.2 mm thicknesses, respectively; and the cobalt ferrite powder prepared in the comparative example was composited with paraffin wax and pressed into a paraffin wax ring of 5.5 mm thickness. Figure 4 It can be seen that in electromagnetic wave absorption, the minimum reflection loss of the cobalt ferrite powder prepared in the comparative example is -0.64dB, which is no lower than -10dB. It cannot effectively absorb electromagnetic waves in the range of 2-18GHz. However, after the impregnation-carbonization process, the minimum reflection loss of the cobalt ferrite-loaded carbon composite absorbing materials prepared in Examples 1-2 is -55.72dB and -49.28dB, respectively, and the maximum effective absorption bandwidth is 6.60GHz and 5.32GHz, respectively. It can be seen that the cobalt ferrite-loaded carbon composite absorbing material prepared by the present invention has excellent wave absorption performance.

[0047] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing a composite microwave absorbing material, characterized in that, Includes the following steps: 1) Weigh a certain amount of soluble iron salt and soluble cobalt salt, disperse the two salts in deionized water according to the molar ratio of cobalt ions to iron ions of 1:2, and then add a complexing agent. The total concentration of iron ions and cobalt ions in the deionized water is 0.1-0.2 mol / L, and the ratio of the total molar amount of iron ions and cobalt ions to the molar amount of complexing agent is 1:(1-1.5). Add ammonia water to adjust the pH to 7-7.2, and a sol-gel reaction will occur to generate a viscous sol. The viscous sol was dried and crushed, burned at 180-200℃ and then cooled. It was then calcined at 600-700℃ for 2-4 hours, cooled to room temperature, ground and sieved to obtain cobalt ferrite powder. 2) Dissolve soluble biomass sugar in deionized water to prepare a solution with a concentration of 5%-50wt%. Immerse cobalt ferrite powder in the solution and age for 2-6 hours. Then perform solid-liquid separation. The solid is washed and dried to obtain cobalt ferrite powder uniformly loaded with carbon source. 3) The cobalt ferrite powder uniformly loaded with carbon source is calcined at 300-400℃ for 1-4 hours under a protective atmosphere to obtain the cobalt ferrite-loaded carbon composite microwave absorbing material.

2. The method for preparing the composite absorbing material according to claim 1, characterized in that, In step 1), the viscous sol is dried at 100-120℃ for 14-18 hours and then broken up; during the high-temperature calcination in steps 1) and 3), the temperature is increased to the calcination temperature at a rate of 3-5℃ / min, and after calcination, the temperature is decreased to 30-50℃ at a rate of 3-5℃ / min, and then naturally cooled to room temperature.

3. The method for preparing the composite absorbing material according to claim 1, characterized in that, The soluble biomass sugar is one or a combination of two or more of glucose, fructose, xylose, sucrose, D-galactose, and water-soluble starch.

4. The method for preparing the composite absorbing material according to claim 1, characterized in that, The soluble iron salt is one or a combination of two or more of the following: ferric nitrate, ferric chloride, ferric sulfate, and ferric acetate.

5. The method for preparing the composite absorbing material according to claim 1, characterized in that, The soluble cobalt salt is one or a combination of two or more of cobalt nitrate, cobalt chloride, cobalt sulfate, and cobalt acetate.

6. The method for preparing the composite absorbing material according to claim 1, characterized in that, The complexing agent is one or a combination of two or more of oxalic acid, citric acid, tartaric acid, and glycine.

7. The method for preparing the composite absorbing material according to claim 1, characterized in that, The sol-gel reaction in step 1) is carried out at 75-85℃ for 3-5 hours.

8. The method for preparing the composite absorbing material according to claim 1, characterized in that, After the solid-liquid separation in step 2), the solid is rinsed and then dried by blowing at 100-120℃ for 10-15 hours.

9. The method for preparing the composite absorbing material according to claim 1, characterized in that, Step 3) The protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere.

10. A composite microwave absorbing material prepared by any one of claims 1-9.

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