Flower-shaped wave-absorbing particles, wave-absorbing film, preparation method and use thereof

Abstract

The present application relates to the technical field of electromagnetic wave absorption, and particularly relates to a flower-shaped wave-absorbing particle, a preparation method of the flower-shaped wave-absorbing particle, a wave-absorbing film prepared from the flower-shaped wave-absorbing particle and an application of the wave-absorbing film. The present application takes biomass carbon source, iron salt, alkali source and surfactant as raw materials, and realizes the nanometer composite of ferrite and carbon by one-step hydrothermal method, and the ferrite and carbon are co-grown with excellent magnetic loss and excellent electric conductivity. The nanometer composite has flower-shaped micro-morphology, and the special micro-morphology further enhances the microwave loss. The ferrite / carbon wave-absorbing particle has multiple loss mechanisms such as dielectric loss, magnetic loss, internal reflection and scattering loss, thereby achieving excellent wave-absorbing performance. The preparation process is simple, the raw material cost is low, the wave-absorbing particle has good dispersibility in an organic resin solution, the sedimentation rate is small, the prepared wave-absorbing film has good wave-absorbing performance, good flexibility, is easy to be attached to a substrate, and has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorption technology, specifically a flower-shaped absorbing particle and its preparation method, as well as an absorbing film made from the flower-shaped absorbing particle and the uses of the absorbing film. Background Technology

[0002] With the high-frequency use of electronic devices, electromagnetic radiation in daily life is increasing, and its presence can significantly impact the normal operation of certain electronic devices. Furthermore, in the military field, electromagnetic interference or leakage can put equipment and personnel in extremely dangerous situations, making the development of lightweight, efficient, and broadband electromagnetic absorbing composite materials essential.

[0003] Ferrites, as a common microwave absorbing material, possess strong magnetic loss and excellent electromagnetic wave absorption performance. Compared to alloy absorbers, their density is relatively low, making them a popular choice for microwave absorbing materials. However, ferrites suffer from a single magnetic loss mechanism and have drawbacks such as narrow absorption bandwidth, high density, susceptibility to corrosion, hydrophobicity, and poor compatibility with resins. Therefore, modification of ferrites is necessary to improve their application shortcomings. Since the microwave absorption performance of ferrites mainly relies on magnetic loss, combining magnetic ferrites with carbon materials that have excellent conductivity can potentially yield microwave absorbing materials that combine electromagnetic loss and have good impedance matching. Current research on microwave absorbing materials mainly focuses on improving their absorption performance, neglecting the practical application characteristics of flower-shaped microwave absorbing particles. For example, the high cost and complex process of preparing flower-shaped microwave absorbing particles, along with their poor compatibility with resins, lead to less than ideal applications. Therefore, flower-shaped microwave absorbing particles with strong absorption performance, simple processing, low cost, and good resin compatibility have a promising industrial application prospect. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing flower-shaped microwave absorbing particles. The flower-shaped microwave absorbing particles prepared by this method have strong microwave absorption performance, good compatibility with resin, and the preparation process is simple and low in cost.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing flower-shaped microwave absorbing particles, comprising the following steps:

[0006] S11. Mix biomass carbon source, iron salt, and doped element salt in a mass ratio of 2:(2-3):(0-1), add alkali source and surfactant to it, wherein the mass ratio of alkali source to iron salt is 1.7:1, and the mass ratio of surfactant to iron salt is (1-5):1, and then add it to deionized water and stir to disperse evenly.

[0007] S12. Transfer the mixed solution to the reaction vessel and react under hydrothermal conditions at 140-220℃ for 4-24 hours. After the reaction vessel is cooled to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 40-130℃ for 6-16 hours to obtain precursor particles.

[0008] S13. The precursor particles are placed in a tube furnace and calcined at 300-600°C for 1-4 hours under an inert atmosphere of nitrogen or argon to obtain flower-shaped microwave absorbing particles.

[0009] Further improvements to the preparation method of flower-shaped absorbing particles:

[0010] Preferably, the biomass carbon source is one or a combination of two or more of fructose, xylose, glucose, and maltose.

[0011] Preferably, the iron salt is one of ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric sulfate.

[0012] Preferably, the alkaline source is one of urea, sodium acetate, and sodium hydroxide.

[0013] Preferably, the surfactant is one of dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG), and trisodium citrate.

[0014] Preferably, the dopant salt is one or a combination of two or more of nickel nitrate, zinc nitrate, manganese nitrate, and barium nitrate.

[0015] The second objective of this invention is to provide a flower-shaped microwave absorbing particle prepared by the above-mentioned method.

[0016] A third objective of this invention is to provide a microwave absorbing film made from the above-mentioned flower-shaped microwave absorbing particles, wherein the preparation method of the microwave absorbing film includes the following steps:

[0017] S21. Add 5-20 parts of resin and 0-15 parts of excipients to the reactor and stir thoroughly until the solid is completely dissolved and the liquid is evenly mixed to obtain a mixture.

[0018] S22. Add 1 to 20 parts of flower-shaped microwave absorbing particles to the mixture obtained in step S21 and mechanically stir to fully disperse the flower-shaped microwave absorbing particles. After confirming that the mixture is uniform and there is no agglomeration, a usable microwave absorbing coating is obtained.

[0019] S23. Pour the mixture with flower-shaped microwave absorbing particles obtained in step S22 into a mold, place it in a drying oven for drying and molding, and obtain a flexible microwave absorbing coating material.

[0020] As a further improvement to the absorbing film:

[0021] Preferably, the resin in step S21 is one of polyurethane (PU), polyvinyl alcohol (PVA), or polyacrylate; and the auxiliary material in step S22 is one of deionized water or acetone.

[0022] Preferably, the stirring speed in step S21 is 100-800 r / min and the stirring time is 20-40 min; the stirring speed in step S22 is 100-800 r / min and the stirring time is 10-60 min; and the drying temperature in step S23 is 40-100℃ and the drying time is 4-24 h.

[0023] The fourth objective of this invention is to provide an application of the above-mentioned absorbing film in the fields of electromagnetic wave shielding and absorption.

[0024] The advantages of this invention compared to the prior art are as follows:

[0025] 1) This invention provides a method for preparing flower-shaped microwave absorbing particles. By using a one-step hydrothermal method to co-grow ferrite with excellent magnetic loss and carbon material with excellent conductivity, a nanocomposite of ferrite and carbon is achieved, exhibiting a flower-shaped microstructure. This unique microstructure further enhances microwave loss. Depending on the raw materials used, the ferrite / carbon flower-shaped microwave absorbing particles are one or more of the following: iron(III) oxide / carbon, nickel-zinc ferrite / carbon, manganese-zinc ferrite / carbon, barium ferrite / carbon, etc. Iron salts and dopant salts are used as raw materials for preparing ferrites with excellent magnetic loss. The addition of biomass carbon source improves the conductivity of the particles. Alkali source and surfactant mainly promote ferrite formation and regulate the microstructure, enabling better nanocomposite formation of ferrite and carbon source. The alkaline environment provided by the alkali source facilitates the formation of ferrite particles during the hydrothermal process, and the addition of surfactant strengthens the adhesion between ferrite and carbon source, thereby achieving nanocomposite electromagnetic materials. The ferrite / carbon flower-shaped microwave absorbing particles prepared in this invention combine electromagnetic materials, effectively adjusting the impedance matching degree and internal loss mechanism of the materials. This allows electromagnetic energy to penetrate as much as possible into the material's interior and be completely consumed by the internal loss mechanism, converting electromagnetic energy into other forms of energy. The flower-shaped absorbing particles, due to their numerous intergranular gaps, effectively attenuate electromagnetic waves through reflection and scattering at the interface. This patent systematically studies the types of biomass carbon sources, surfactants, and dopant salts, controlling the microstructure of the nano-absorbing particles and increasing their absorption performance. The flower-shaped nickel-ferrite / carbon microwave absorbing particles prepared in this patent broaden the effective absorption bandwidth.

[0026] 2) This invention utilizes a simple one-step hydrothermal method to prepare ferrite / carbon flower-shaped microwave absorbing particles. The carbon source used is biomass-based carbon material, which is simpler, more readily available, and less expensive than carbon materials such as graphene, carbon nanotubes, and carbon fibers. Compared to other researchers' preparation of ferrite / carbon materials, the one-step hydrothermal method reduces the process flow and simplifies experimental operation. The amorphous carbon formed by the hydrothermal reaction of biomass carbon can co-grow with ferrite particles, achieving nanoscale composite. The ferrite / carbon flower-shaped microwave absorbing particles combine high-magnetic-loss ferrite with high-dielectric-loss biomass carbon material, effectively improving the defects of ferrite such as single loss, narrow absorption bandwidth, high density, and susceptibility to corrosion. The ferrite / carbon flower-shaped microwave absorbing particles greatly enrich the absorption loss mechanism of the material, giving the composite material better impedance matching and enabling the introduction of electromagnetic waves to a greater extent for absorption loss, thus achieving superior absorption performance and a wider absorption bandwidth.

[0027] 3) The application of microwave absorbing particles is generally to mix them with resins as microwave absorbing coatings or films for engineering applications. However, most research focuses on improving the microwave absorption performance of microwave absorbing materials while neglecting the compatibility between materials and resins. As a result, although the microwave absorbing materials have good absorption performance, they are prone to sedimentation in the resin during actual applications, leading to problems such as uneven coating, easy peeling, and short service life in the final product.

[0028] The flower-shaped microwave absorbing particles prepared by this invention have good dispersibility in organic resin solutions, good compatibility with resins, and low sedimentation rate. The microwave absorbing films prepared by these particles have good microwave absorption performance, simple process flow, good flexibility, and are easy to bond with substrates, showing good application prospects.

[0029] 4) This invention further demonstrates that the ferrite / carbon particles prepared by mixing the flower-shaped microwave absorbing particles with resin underwent sedimentation experiments and produced a microwave absorbing film. This effectively illustrates that the ferrite / carbon particles prepared by this invention not only possess excellent microwave absorption performance but also exhibit good compatibility with resin, making them less prone to sedimentation in the resin. The resulting microwave absorbing film combines microwave absorption performance with flexibility. Due to the high flexibility of the microwave absorbing film, it can completely adhere to substrates of various shapes, thereby coating the substrate with a film possessing excellent microwave absorption performance to achieve microwave absorption. Furthermore, the microwave absorbing film of this invention can be customized by controlling the type and amount of particles added to obtain films with different microwave absorption properties, thus this composite material has good application prospects and practical value. Existing technologies involve adding microwave absorbing particles to carbon fiber composite materials to prepare structural-functional materials, which is fundamentally different from preparing microwave absorbing films using microwave absorbing particles in this patent. The microwave absorbing film prepared by this patent has a wider range of applications and fewer limitations, and can be applied to various matrix materials. It achieves a balance between flexibility and microwave absorption performance. Attached Figure Description

[0030] Figure 1The XRD diffraction pattern of the flower-shaped absorbing particles Fe3O4 / C prepared in Example 2.

[0031] Figure 2 The image shows a SEM image of the flower-shaped absorbing particles NiFe2O4 / C prepared in Example 5.

[0032] Figure 3 The energy spectrum of the flower-shaped absorbing particles NiFe2O4 / C prepared in Example 5 is shown.

[0033] Figure 4 The image shows the reflection loss of the flower-shaped absorbing particles Fe3O4 / C prepared in Example 2. Detailed Implementation

[0034] 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.

[0035] Example 1

[0036] Step 1: Weigh 2.66g of ferric chloride hexahydrate, 1.77g of glucose, 4.69g of urea, and 2.66g of surfactant into a beaker, add deionized water, and then stir magnetically to disperse evenly to obtain a mixed solution.

[0037] Step 2: Pour the mixed solution into a 100ml reaction vessel and heat it to 180℃ for 22h. After the reaction vessel cools to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 80℃ to obtain Fe3O4 / C nanomaterial precursor powder.

[0038] Step 3: Place the precursor powder from Step 1 into a crucible and place it in a tube furnace for calcination at 400°C under an inert atmosphere for 2 hours to obtain Fe3O4 / C nanomaterials, i.e., flower-shaped microwave absorbing particles.

[0039] The optimal reflection loss value of the Fe3O4 / C nanomaterial in this embodiment was tested to be -45.03dB, and the effective absorption bandwidth was 3.06GHz.

[0040] Example 2

[0041] Step 1: Weigh 2.66g of ferric chloride hexahydrate, 1.77g of fructose, 4.69g of urea, and 4.69g of DTAB into a beaker, add deionized water, and then stir magnetically to disperse evenly to obtain a mixed solution.

[0042] Step 2: Pour the mixed solution into a 100ml reaction vessel and heat it to 180℃ for 22h. After the reaction vessel cools to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 80℃ to obtain Fe3O4 / C nanomaterial precursor powder.

[0043] Step 3: Place the precursor powder from Step 1 into a crucible and place it in a tube furnace for calcination at 400°C under an inert atmosphere for 2 hours to obtain Fe3O4 / C nanomaterials, i.e., flower-shaped microwave absorbing particles.

[0044] Tests showed that the optimal reflection loss value of the Fe3O4 / C nanomaterial in this embodiment is -62.65dB, and the effective absorption bandwidth is 1.95GHz.

[0045] Example 3

[0046] Step 1: Weigh 2.66g of ferric chloride hexahydrate, 1.77g of xylose, 4.69g of urea, and 4.69g of PEG into a beaker, add deionized water, and then stir magnetically to disperse evenly to obtain a mixed solution.

[0047] Step 2: Pour the mixed solution into a 100ml reaction vessel and heat it to 180℃ for 24 hours. After the reaction vessel cools to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 80℃ to obtain Fe3O4 / C nanomaterial precursor powder.

[0048] Step 3: Place the precursor powder from Step 1 into a crucible and place it in a tube furnace for calcination at 400°C under an inert atmosphere for 2 hours to obtain Fe3O4 / C nanomaterials, i.e., flower-shaped microwave absorbing particles.

[0049] Tests showed that the optimal reflection loss value of the Fe3O4 / C nanomaterial in this embodiment was -47.53dB, and the effective absorption bandwidth was 2.29GHz.

[0050] Example 4

[0051] Step 1: Weigh 1.77g of ferric chloride hexahydrate, 0.95g of nickel nitrate, 1.77g of fructose, 4.69g of urea, and 4.69g of PEG into a beaker, add deionized water, and then stir magnetically to disperse evenly to obtain a mixed solution.

[0052] Step 2: Pour the mixed solution into a 100ml reaction vessel and heat it to 180℃ for 22h. After the reaction vessel cools to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 80℃ to obtain NiFe2O4 / C nanomaterial precursor powder.

[0053] Step 3: Place the precursor powder from Step 1 into a crucible and place it in a tube furnace for calcination at 400°C under an inert atmosphere for 2 hours to obtain NiFe2O4 / C nanomaterials, i.e., flower-shaped microwave absorbing particles.

[0054] Tests showed that the optimal reflection loss value of the NiFe2O4 / C nanomaterial in this embodiment reached -50.99dB, and the effective absorption bandwidth was 3.64GHz.

[0055] Example 5

[0056] Step 1: Weigh 1.77g of ferric chloride hexahydrate, 0.95g of nickel nitrate, 1.77g of glucose, 4.69g of urea, and 4.69g of DTAB into a beaker, add deionized water, and then stir magnetically to disperse evenly to obtain a mixed solution.

[0057] Step 2: Pour the mixed solution into a 100ml reaction vessel and heat it to 180℃ for 22h. After the reaction vessel cools to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 80℃ to obtain NiFe2O4 / C nanomaterial precursor powder.

[0058] Step 3: Place the precursor powder from Step 1 into a crucible and place it in a tube furnace for calcination at 400°C under an inert atmosphere for 2 hours to obtain NiFe2O4 / C nanomaterials, i.e., flower-shaped microwave absorbing particles.

[0059] Tests showed that the optimal reflection loss value of the NiFe2O4 / C nanomaterial in this embodiment reached -61.22dB, and the effective absorption bandwidth was 2.64GHz.

[0060] Example 6

[0061] Add 5 parts of polyvinyl alcohol resin and 15 parts of deionized water to the reactor and stir thoroughly until the solid is completely dissolved and the liquid is evenly mixed to obtain a mixture.

[0062] Two portions of the Fe3O4 / C flower-shaped microwave absorbing particles prepared in Example 2 were added to the above mixture. The addition ratio of Fe3O4 / C flower-shaped microwave absorbing particles in the microwave absorbing film was 10% (mass percentage). The mixture was ultrasonically dispersed and mechanically stirred. The mixture was then poured into a mold and placed in a vacuum drying oven at 80°C for 8 hours to obtain the microwave absorbing film.

[0063] According to the test, the optimal reflection loss value of the absorbing film in this embodiment is -45.83dB, and the effective absorption bandwidth is 1.1GHz.

[0064] Example 7

[0065] Take 17 parts of polyurethane resin and add 3 parts of Fe3O4 / C flower-shaped microwave absorbing particles from Example 2 to mix. The addition ratio of Fe3O4 / C flower-shaped microwave absorbing particles in the microwave absorbing film is 15% (mass percentage). The mixture is ultrasonically dispersed and mechanically stirred. Then, the mixture is poured into a mold and placed in a vacuum drying oven at 80°C for 8 hours to obtain the microwave absorbing film.

[0066] According to the test, the optimal reflection loss value of the absorbing film in this embodiment is -40.5dB, and the effective absorption bandwidth is 2.4GHz.

[0067] Example 8

[0068] Take 17 parts of polyurethane resin and mix it with 3 parts of NiFe2O4 / C flower-shaped microwave absorbing particles from Example 5. The addition ratio of NiFe2O4 / C flower-shaped microwave absorbing particles in the microwave absorbing film is 15% (mass percentage). The mixture is ultrasonically dispersed and mechanically stirred. Then, the mixture is poured into a mold and placed in a vacuum drying oven at 80°C for 8 hours to obtain the microwave absorbing film.

[0069] According to the test, the optimal reflection loss value of the absorbing film in this embodiment is -60.43dB, and the effective absorption bandwidth is 1.76GHz.

[0070] The optimal reflection loss value and effective absorption bandwidth of the flower-shaped absorbing particles tested in Examples 1-5 show that the absorption performance of the particles prepared by this invention can reach above -45dB, exhibiting excellent electromagnetic wave absorption performance. By controlling the carbon source, surfactant, and dopant elements, the performance of the resulting absorbing particles varies. Furthermore, the optimal reflection loss value and effective absorption bandwidth of the absorbing films tested in Examples 6-8 show that when the absorbing films prepared by combining the absorbing particles with resin are applied, the film absorption performance can reach above -40dB. This indicates that the films prepared by this invention can absorb more than 99.99% of electromagnetic waves, possessing excellent absorption performance, and the film performance can be selected and controlled according to the amount and type of absorbing particles added.

[0071] The XRD diffraction patterns, SEM images, and RL patterns of the ferrite / carbon nanocomposites, i.e., the flower-shaped microwave absorbing particles, prepared in Examples 1-5 are shown below. Figure 1-4 As shown, where Figure 1 The XRD diffraction pattern of the flower-shaped absorbing particles Fe3O4 / C prepared in Example 2; Figure 2 SEM image of the flower-shaped microwave absorbing particles NiFe2O4 / C prepared in Example 5; Figure 3 The energy spectrum of the flower-shaped absorbing particles NiFe2O4 / C prepared in Example 5; Figure 4 The image shows the reflection loss of the flower-shaped absorbing particles Fe3O4 / C prepared in Example 2. Figure 1-4It can be seen that ferrite / carbon nanocomposite materials were successfully prepared. Figure 1 Ferrite and carbon (C) nanoscale composites Figures 2-3 Fe3O4 / C nanocomposites exhibit excellent properties. Figure 4 ).

[0072] The sedimentation performance of Fe3O4 nanoparticles and the Fe3O4 / C nanofloral absorbing particles prepared in Example 2 were tested in resin. Observations of sedimentation before sedimentation, after 4 hours of sedimentation, and after 16 hours of sedimentation revealed that Fe3O4 nanoparticles settle very easily in the resin, exhibiting poor dispersion and integration with the resin matrix. This could lead to problems such as easy detachment of the absorbing coating and short service life if combined with resin to form a composite material. However, this invention combines Fe3O4 with carbon (C) at the nanoscale, modifying the ferrite surface and reducing its density, thus enabling better integration with the resin matrix and significantly reducing the sedimentation rate. The Fe3O4 / C nanoparticles prepared in this invention have good compatibility with the resin matrix, and the resulting absorbing composite material exhibits excellent absorbing performance and is not prone to detachment, showing promising prospects for industrial applications.

[0073] The flexibility of the microwave absorbing film materials in Examples 6-8 of this invention was measured according to GB / T1731, and the flexibility was ≤1mm, indicating excellent flexibility. The microwave absorbing film is thin and extremely flexible, can be folded at will, and has a smooth surface with good fusion between the particles and resin, making it difficult to detach.

[0074] 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 microwave absorbing film made of flower-shaped absorbing particles, characterized in that, The method for preparing the microwave absorbing film includes the following steps: S21. Add 5-20 parts of resin and 0-15 parts of excipients to the reactor and stir thoroughly until the solid is completely dissolved and the liquid is uniformly mixed to obtain a mixture; the resin is one of polyurethane resin (PU), polyvinyl alcohol resin (PVA), and polyacrylate resin; the excipient is one of deionized water and acetone. S22. Add 1 to 20 parts of flower-shaped microwave absorbing particles to the mixture obtained in step S21 and mechanically stir to fully disperse the flower-shaped microwave absorbing particles. After confirming that the mixture is uniform and there is no agglomeration, a usable microwave absorbing coating is obtained. S23. Pour the mixture with flower-shaped microwave absorbing particles obtained in step S22 into a mold, place it in a drying oven for drying and molding, and obtain a flexible microwave absorbing coating material. The method for preparing the flower-shaped microwave absorbing particles includes the following steps: S11. A mixture of biomass carbon source, iron salt, and dopant element salt in a mass ratio of 2:(2-3):(0-1) is prepared. An alkali source and a surfactant are added to the mixture. The mass ratio of the alkali source to the iron salt is 1.7:1, and the mass ratio of the surfactant to the iron salt is (1-5):

1. The mixture is then added to deionized water and stirred until evenly dispersed. The surfactant is one of dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (CTAB), or polyethylene glycol (PEG). Alternatively, the dopant element salt is one or a combination of two or more of nickel nitrate, zinc nitrate, manganese nitrate, and barium nitrate. S12. Transfer the mixed solution to the reaction vessel and react at 140~220℃ for 4~24h under hydrothermal conditions. After the reaction vessel is cooled to room temperature, centrifuge the obtained product and wash it alternately with deionized water and ethanol until neutral. Dry it at 40~130℃ for 6~16h to obtain precursor particles. S13. The precursor particles are placed in a tube furnace and calcined at 300-600℃ for 1-4 hours under an inert atmosphere of nitrogen or argon to obtain flower-shaped microwave absorbing particles.

2. The microwave absorbing film according to claim 1, characterized in that, The biomass carbon source is one or a combination of two or more of fructose, xylose, glucose, and maltose.

3. The microwave absorbing film according to claim 1, characterized in that, The iron salt is one of ferric chloride hexahydrate, ferric nitrate nonahydrate, or ferric sulfate.

4. The microwave absorbing film according to claim 1, characterized in that, The alkaline source is one of urea, sodium acetate, or sodium hydroxide.

5. The microwave absorbing film according to claim 1, characterized in that, The stirring speed in step S21 is 100-800 r / min, and the stirring time is 20-40 min; the stirring speed in step S22 is 100-800 r / min, and the stirring time is 10-60 min; the drying temperature in step S23 is 40-100℃, and the drying time is 4-24 h.

6. The application of the absorbing film according to any one of claims 1-5 in the field of electromagnetic wave shielding or absorption.

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