Composite microwave absorbing materials, their preparation methods and applications

Abstract

This invention relates to a composite absorbing material, its preparation method, and its application. The composite absorbing material comprises iron-cobalt-nickel alloy nanoparticles and an absorbing material. The absorbing material has a layered structure, in which multiple vacancies are formed between adjacent layers. The iron-cobalt-nickel alloy nanoparticles are mainly distributed in these vacancies, and the surface layer of the absorbing material is doped with nitrogen and sulfur elements. The composite absorbing material of this invention achieves tunable absorption across the entire frequency range of 20MHz to 1.5GHz through multi-loss synergy, while simultaneously reducing secondary reflections and exhibiting a high absorption rate.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic compatibility technology, and in particular to a composite absorbing material, its preparation method, and its application. Background Technology

[0002] With the rapid popularization and development of electronic devices and the high-speed development of wireless communication technologies such as 5G, a large amount of electromagnetic radiation of different frequencies is inevitably generated in the electromagnetic environment. Whether in civilian use or other critical application fields, electromagnetic radiation can cause serious electromagnetic interference between electronic components, leading to equipment malfunctions and even safety hazards such as equipment failure.

[0003] Absorbing materials are a class of functional materials that can absorb and attenuate incident electromagnetic waves, converting electromagnetic energy into heat or other forms of energy to dissipate it, or causing electromagnetic waves to disappear due to interference. However, traditional absorbing materials have the following problems: (1) They have a single loss suppression mode, resulting in poor absorption effect and difficulty in controlling the absorption frequency band, which cannot meet the absorption performance requirements under high requirements; (2) They are prone to multiple reflections. When electromagnetic waves approach the absorbing material, they cannot be directly absorbed but are reflected again, causing secondary electromagnetic wave reflection pollution and forming new sources of interference, which has divergent characteristics; (3) The electromagnetic absorption range is mostly narrow, and the absorption effect is generally limited to a certain frequency band, resulting in a single absorption frequency band. Therefore, there is an urgent need for a new type of absorbing material with multi-loss synergy, wideband tunability, and the ability to suppress secondary reflections. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite absorbing material, its preparation method, and its application to address the above problems. The composite absorbing material of the present invention achieves adjustable absorption across the entire frequency range of 20MHz to 1.5GHz through multi-loss synergy, while reducing secondary reflection and achieving a high absorption rate.

[0005] A composite microwave absorbing material includes iron-cobalt-nickel alloy nanoparticles and a microwave absorbing material. The microwave absorbing material has a layered structure, in which multiple cavities are formed between adjacent layers. The iron-cobalt-nickel alloy nanoparticles are mainly distributed in the cavities, and the surface layer of the microwave absorbing material is doped with nitrogen and sulfur elements.

[0006] In one embodiment, the absorbing material satisfies at least one of the following conditions:

[0007] (1) The substrate of the absorbing material is selected from graphite;

[0008] (2) The number of layers of the absorbing material is less than or equal to 10;

[0009] (3) The cavities in the absorbing material are elliptical in shape, with the major axis of the elliptical shape being 500nm~800nm ​​and the minor axis being 400nm~600nm;

[0010] (4) The thickness of the absorbing material is 2μm~3μnm.

[0011] In one embodiment, the iron-cobalt-nickel alloy nanoparticles satisfy at least one of the following conditions:

[0012] (1) The iron-cobalt-nickel alloy nanoparticles comprise 35wt%~45wt% Fe, 30wt%~40wt% Co, 5wt%~10wt% Ni, 5wt%~10wt% Mn and 5wt%~10wt% Al;

[0013] (2) The particle size of the iron-cobalt-nickel alloy nanoparticles is less than or equal to 150 nm.

[0014] In one embodiment, the mass ratio of the iron-cobalt-nickel alloy nanoparticles to the microwave absorbing material is 4:1 to 2:1.

[0015] In one embodiment, the total doping rate of nitrogen and sulfur elements in the surface layer of the composite absorbing material is 5% to 10%.

[0016] And / or, the mass ratio of nitrogen to sulfur is 1:1 to 2:3.

[0017] A method for preparing a composite microwave absorbing material includes the following steps:

[0018] The dispersion of the microwave absorbing substrate is mixed evenly with iron-cobalt-nickel alloy nanoparticles and dried to obtain a primary composite material.

[0019] The primary composite material is mixed with a nitrogen source and a sulfur source and heat-treated to obtain a composite microwave absorbing material.

[0020] In one embodiment, the method for preparing the microwave absorbing substrate includes: preparing graphite powder into a graphite dispersion, and obtaining the microwave absorbing substrate by gradient ultrasound and centrifugation, wherein the gradient ultrasound includes first treating at 175W~225W for 1h~2h, and then increasing to 275W~325W for 1h~2h, and the ultrasound adopts a pulse mode, and the temperature of the dispersion is ≤18℃ during the ultrasound process.

[0021] In one embodiment, the method for preparing the iron-cobalt-nickel alloy nanoparticles includes:

[0022] Metal raw materials are mixed and smelted to obtain a first product, wherein the metal raw materials include iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder, and the particle size of the metal raw materials is ≤25μm;

[0023] In a vacuum environment, the first product was thermally reduced to obtain iron-cobalt-nickel alloy nanoparticles.

[0024] In one embodiment, after removing the oxides from the surface of the primary composite material, it is heated and mixed with a nitrogen source and a sulfur source in an organic solvent at 180°C to 200°C for 4 to 6 hours. Then, it is subjected to a first heat treatment at 770°C to 820°C for 1 to 1.5 hours in a protective gas, and then cooled to 720°C to 750°C for a second heat treatment for 1 to 1.5 hours to obtain the composite microwave absorbing material.

[0025] Application of a composite absorbing material as described above in electronic devices.

[0026] The composite absorbing material of this invention achieves electromagnetic wave suppression through the synergistic effect of iron-cobalt-nickel alloy nanoparticles, the absorbing material itself, and nitrogen-sulfur co-doping on its surface. This suppresses multiple loss mechanisms, including polarization loss, conductivity loss, and magnetic loss, thus optimizing the absorption effect. It effectively absorbs and suppresses electromagnetic waves over a wide frequency range, especially achieving tunable absorption across the entire 20MHz to 1.5GHz frequency range. This allows electromagnetic waves to be essentially absorbed after passing through the composite absorbing material, thereby significantly reducing electromagnetic wave secondary propagation interference caused by secondary reflection. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a SEM image of the primary composite material obtained in Example 1 of the present invention;

[0029] Figure 2 This is a SEM image of the composite absorbing material prepared in Example 1 of the present invention;

[0030] Figure 3 This is a schematic diagram of the microwave absorption performance of the composite microwave absorbing material prepared in Example 1 of the present invention. Detailed Implementation

[0031] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. In this invention, when referring to numerical ranges, unless otherwise specified, such ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Furthermore, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0033] Through long-term experiments, the applicant discovered that although the combination of conventional magnetic materials and microwave absorbing materials can improve both conductivity and magnetic loss characteristics, it can usually only absorb electromagnetic waves in a specific frequency band, resulting in a single absorption frequency band. Furthermore, when electromagnetic waves approach the microwave absorbing material, there is still a certain problem of secondary electromagnetic wave reflection, which is not conducive to the transmission of electromagnetic wave signals.

[0034] Based on this, the present invention provides a composite microwave absorbing material, comprising iron-cobalt-nickel alloy nanoparticles and a microwave absorbing material. The microwave absorbing material has a layered structure, in which multiple cavities are formed between adjacent layers. The iron-cobalt-nickel alloy nanoparticles are mainly distributed in the cavities, and the surface layer of the microwave absorbing material is doped with nitrogen and sulfur elements.

[0035] The composite absorbing material of this invention achieves electromagnetic wave suppression through the synergistic effect of iron-cobalt-nickel alloy nanoparticles, the absorbing material itself, and nitrogen-sulfur co-doping on its surface. This suppresses multiple loss mechanisms, including polarization loss, conductivity loss, and magnetic loss, thus optimizing the absorption effect. It effectively absorbs and suppresses electromagnetic waves over a wide frequency range, especially achieving tunable absorption across the entire 20MHz to 1.5GHz frequency range. This allows electromagnetic waves to be essentially absorbed after passing through the composite absorbing material, thereby significantly reducing electromagnetic wave secondary propagation interference caused by secondary reflection.

[0036] In the laminated structure of the absorbing material, multiple holes are formed between adjacent layers. Electromagnetic waves can be absorbed by multiple reflections inside the holes. It is understood that the present invention does not restrict the distribution of holes between adjacent layers; they can be arranged in an ordered or disordered manner.

[0037] In one embodiment of the present invention, the substrate of the absorbing material is selected from graphite. Graphite has a high electron mobility. When electromagnetic waves are incident, the free electrons inside it will generate strong oscillations, converting electromagnetic energy into heat energy through conductive loss. At the same time, the large specific surface area of ​​graphite can also cause electromagnetic waves to be reflected and scattered multiple times, thereby enhancing the absorption efficiency.

[0038] In one embodiment of the present invention, the number of layers of the absorbing material is less than or equal to 10, which not only helps to improve the structural stability of the composite absorbing material, but also improves the surface doping effect.

[0039] Preferably, the substrate of the absorbing material is selected from graphite and the number of layers is less than or equal to 10. It is understood that the number of layers includes, but is not limited to, any value of 2, 4, 6, 8, or 10 layers or any range between the two.

[0040] Further preferably, the thickness of the absorbing material is 2μm~3μnm, including but not limited to any value among 2μm, 2.2μm, 2.5μm, 2.7μm, and 3μm or any range between two, which is beneficial to further improve the absorption effect and expand the absorption frequency band.

[0041] In one embodiment of the present invention, the cavities in the absorbing material are preferably elliptical, with the major axis of the elliptical shape preferably being 500nm~800nm ​​and the minor axis preferably being 400nm~600nm. This is more conducive to increasing the relative size of the cavities in the absorbing material, enabling the absorbing material to better reflect and absorb electromagnetic waves.

[0042] It is understood that the major axis of the elliptical shape includes, but is not limited to, any point value of 500nm, 600nm, 700nm, 800nm ​​or any range of values ​​between two of them, and the minor axis includes, but is not limited to, any point value of 400nm, 450nm, 500nm, 550nm, 600nm or any range of values ​​between two of them; in other embodiments, the cavities of the absorbing material may also be other shapes such as circular, conical or cylindrical, and the present invention does not limit them.

[0043] Compared to pure nickel or iron-nickel alloys, iron-cobalt-nickel alloys have better eddy current loss performance. Combining iron-cobalt-nickel alloys with graphite is beneficial for further widening the low-frequency magnetic loss band.

[0044] Preferably, the iron-cobalt-nickel alloy nanoparticles comprise 35wt%~45wt% Fe, 30wt%~40wt% Co, 5wt%~10wt% Ni, 5wt%~10wt% Mn, and 5wt%~10wt% Al. The iron-cobalt-nickel alloy with the above components, when combined with graphite, can significantly improve the charge transport efficiency of the composite microwave absorbing material and enhance its conductivity.

[0045] Preferably, the particle size of the iron-cobalt-nickel alloy nanoparticles is less than or equal to 150 nm, which is more conducive to the full embedding of the iron-cobalt-nickel alloy nanoparticles into the cavities of the absorbing material, optimizing the structure of the composite absorbing material, thereby improving the absorption performance and reducing secondary reflection interference.

[0046] In one embodiment of the present invention, the mass ratio of the iron-cobalt-nickel alloy nanoparticles to the microwave absorbing material is 4:1 to 2:1. By adjusting the mass ratio of the iron-cobalt-nickel alloy nanoparticles to the microwave absorbing material, it is beneficial to further optimize the structure of the composite microwave absorbing material, thereby improving the microwave absorption performance and reducing secondary reflection interference.

[0047] In one embodiment of the present invention, the total doping rate of nitrogen and sulfur elements in the surface layer of the composite absorbing material is 5% to 10%, including but not limited to any one of 5%, 6%, 7%, 8%, 10% or any range between the two.

[0048] In one embodiment of the present invention, the mass ratio of nitrogen to sulfur is 1:1 to 2:3, including but not limited to any one of 1:1, 4:5, 6:7, 3:4, 2:3 or any range between the two.

[0049] By adjusting the doping amounts of nitrogen and sulfur elements in the surface layer of the composite absorbing material, it is beneficial to improve the high polarization loss performance of the composite absorbing material, optimize the synergistic effect of multiple losses, thereby further improving the electromagnetic wave absorption effect and reducing secondary reflection interference.

[0050] It should be noted that the mass percentage of nitrogen and sulfur elements in the surface layer of the composite microwave absorbing material represents the total doping rate of nitrogen and sulfur elements in the surface layer of the composite microwave absorbing material.

[0051] This invention provides a method for preparing a composite microwave absorbing material, comprising the following steps:

[0052] The dispersion of the microwave absorbing substrate is mixed evenly with iron-cobalt-nickel alloy nanoparticles and dried to obtain a primary composite material.

[0053] The primary composite material is mixed with a nitrogen source and a sulfur source and heat-treated to obtain a composite microwave absorbing material.

[0054] By first combining the absorbing substrate with iron-cobalt-nickel alloy nanoparticles to form a special filtering structure channel, and then co-doping the surface of the composite material with nitrogen and sulfur, the composite absorbing material can meet the requirements of electrical loss and magnetic loss, and synergistically improve surface polarization loss. This gives the composite absorbing material a multi-loss mechanism of polarization loss, conductive loss and magnetic loss, thereby achieving broadband tunable absorption, reducing secondary reflection and improving absorption rate.

[0055] In one embodiment of the present invention, the preferred method for preparing the microwave absorbing substrate includes: preparing graphite powder into a graphite dispersion, obtaining the microwave absorbing substrate by gradient ultrasound and centrifugation, using specific gradient ultrasound to peel and delaminate the graphite, and combining it with a pulse mode, which is beneficial to form a certain space between adjacent layers in the graphite, and then screening out a thinner microwave absorbing substrate by centrifugation.

[0056] The gradient ultrasound process involves initial treatment at 175W~225W for 1-2 hours, followed by treatment at 275W~325W for another 1-2 hours. The ultrasound is performed in pulse mode, and the temperature of the dispersion is ≤18℃ during the process. It should be noted that pulse mode means the ultrasound waves are emitted in periodic short pulses with intermittent pauses. The duty cycle is typically 0.1%~50%, preferably 50%, with intervals of 5-10 minutes. For example, a cycle can be defined as 5 minutes of ultrasound followed by a 5-minute pause.

[0057] Preferably, the solvent for the graphite dispersion is water. Before gradient ultrasonication, the dispersion is initially carried out by magnetic stirring for 30 to 60 minutes. Centrifugation is preferably carried out in stages. The first stage of centrifugation is performed at a speed of 300 to 400 rpm for 0.5 to 1 hour to remove large unpeeled graphite particles. The second stage of centrifugation is performed at a speed of 5000 to 10000 rpm for 0.5 to 1 hour, which is more conducive to screening out thinner microwave absorbing substrates.

[0058] In one embodiment of the present invention, the solvent in the dispersion of the microwave absorbing substrate is preferably an organic solvent, including but not limited to ethanol. Preferably, adding a small amount of ionic liquid to the dispersion of the microwave absorbing substrate can reduce graphite agglomeration.

[0059] In one embodiment of the present invention, the method for preparing the iron-cobalt-nickel alloy nanoparticles includes:

[0060] Metal raw materials are mixed and smelted to obtain a first product, wherein the metal raw materials include iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder, and the particle size of the metal raw materials is ≤25μm;

[0061] In a vacuum environment, the first product was thermally reduced to obtain iron-cobalt-nickel alloy nanoparticles.

[0062] Preferably, the metal raw materials are mixed by intermittent high-energy ball milling, for example, under argon protection, ball milling at 30 rpm for 24 hours, with a 10-15 minute pause every 2 hours to cool down, and 1%-2% stearic acid added as a process control agent. The metal raw materials preferably have a purity ≥99.9%.

[0063] As a preferred method, the mixed metal raw materials are pressed into billets and then melted in an electric arc melting furnace under a vacuum argon atmosphere. Repeated melting multiple times can ensure uniform melting.

[0064] As a preferred embodiment, the thermal reduction process includes placing the first product in a copper crucible, evacuating it, and then introducing a protective gas containing hydrogen. After the first product evaporates, it reacts with hydrogen atoms to generate iron-cobalt-nickel alloy nanoparticles, which are then collected by cyclone separation.

[0065] In one embodiment of the present invention, before the primary composite material is dried, the mixing system of the dispersion of the microwave absorbing substrate and the iron-cobalt-nickel alloy nanoparticles is adjusted to an acidic environment, which is beneficial to remove oxides from the surface of the primary composite material.

[0066] In one embodiment of the present invention, after removing the oxides on the surface of the primary composite material, it is heated and mixed with a nitrogen source and a sulfur source in an organic solvent at 180°C to 200°C for 4 to 6 hours. Then, it is subjected to a first heat treatment at 770°C to 820°C for 1 to 1.5 hours in a protective gas, and then cooled to 720°C to 750°C for a second heat treatment for 1 to 1.5 hours to obtain the composite microwave absorbing material.

[0067] Preferably, the nitrogen source is ammonia water and the sulfur source is sodium sulfide.

[0068] The present invention also provides an application of the composite absorbing material described above in electronic devices.

[0069] Applying the composite absorbing material provided by this invention to electronic devices enhances their reliability and security, and allows for flexible adjustment of the absorption frequency band in different application scenarios. It is understood that the composite absorbing material can be used to fabricate absorbing devices in electronic devices, and this invention does not limit the specific structure of such devices.

[0070] The composite microwave absorbing material, its preparation method, and its application will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0071] Example 1

[0072] Add 1g of graphite powder to 50mL of aqueous solution and stir magnetically for 30min for initial dispersion. Then, sonicate at 200W for 1h, then increase to 300W for 1h, with a pulse mode of 50% duty cycle. The temperature of the dispersion during sonication should be ≤18℃. Centrifuge the dispersion at 400rpm / h for 30min to remove large unpeeled graphite particles, then centrifuge at 8000rpm / h for 30min to obtain the precipitate as the microwave absorbing substrate. Redisperse the microwave absorbing substrate in ethanol for later use, and add a small amount of ionic liquid to reduce agglomeration.

[0073] Metal powders of Fe, Co, Ni, Mn, and Al with a purity ≥99.9% were mixed in a mass ratio of 6:5:1:1:1 and placed in a high-energy ball mill jar (ball-to-powder ratio 5:1). Under argon protection, the mixture was ball-milled at 300 rpm for 24 hours, with a 15-minute pause every 2 hours to cool it down. 1% stearic acid was added as a process control agent. The ball-milled powder was pressed into a compact and melted in an electric arc melting furnace under a vacuum argon atmosphere at a current of 500 A. The melting was repeated 5 times to ensure uniformity, ultimately yielding a precipitate. The precipitate was placed in a copper crucible and evacuated to a vacuum of 2 × 10⁻⁶. - After passing through ³Pa, a mixture of hydrogen and argon gas is introduced. After the precipitate evaporates, it reacts with hydrogen atoms to generate iron-cobalt-nickel alloy nanoparticles, which are then collected by cyclone separation.

[0074] A dispersion containing 100g of microwave absorbing substrate was mixed with 300g of iron-cobalt-nickel alloy nanoparticles to embed the nanoparticles into the microwave absorbing substrate. Hydrochloric acid was then added to create an acidic environment to remove surface oxides. After drying, a primary composite material was obtained. Its SEM image is shown below. Figure 1 As shown.

[0075] 300g of the primary composite material, 10g of ammonia, and 10g of sodium sulfide were dissolved in an ethanol solution and heated at 180℃ for 6 hours. Then, the mixture was treated in argon atmosphere at 800℃ for 1 hour, followed by further treatment at 750℃ for 1 hour to obtain the composite microwave absorbing material. Its SEM image is shown below. Figure 2 As shown.

[0076] Example 2

[0077] Add 1g of graphite powder to 50mL of aqueous solution and stir magnetically for 30min for initial dispersion. Then, sonicate at 175W for 1h, then increase to 275W for 1h, with a pulse mode of 50% duty cycle. The temperature of the dispersion during sonication should be ≤18℃. Centrifuge the dispersion at 400rpm / h for 30min to remove large unpeeled graphite particles, then centrifuge at 8000rpm / h for 30min to obtain the precipitate as the microwave absorbing substrate. Redisperse the microwave absorbing substrate in ethanol for later use, and add a small amount of ionic liquid to reduce agglomeration.

[0078] Metal powders of Fe, Co, Ni, Mn, and Al with a purity ≥99.9% were mixed in a mass ratio of 7:6:1:1:1 and placed in a high-energy ball mill jar (ball-to-powder ratio 5:1). Under argon protection, the mixture was ball-milled at 300 rpm for 24 hours, with a 15-minute pause every 2 hours to cool it down. 1% stearic acid was added as a process control agent. The ball-milled powder was pressed into a compact and melted in an electric arc melting furnace under a vacuum argon atmosphere at a current of 500 A. The melting was repeated 5 times to ensure uniformity, ultimately yielding a precipitate. The precipitate was placed in a copper crucible and evacuated to a vacuum of 2 × 10⁻⁶. - After passing through ³Pa, a mixture of hydrogen and argon gas is introduced. After the precipitate evaporates, it reacts with hydrogen atoms to generate iron-cobalt-nickel alloy nanoparticles, which are then collected by cyclone separation.

[0079] A dispersion containing 100g of microwave absorbing substrate was mixed and stirred with 200g of iron-cobalt-nickel alloy nanoparticles to embed the iron-cobalt-nickel alloy nanoparticles into the microwave absorbing substrate. Then, hydrochloric acid was added to form an acidic environment to remove the oxides on the surface. After drying, a primary composite material was obtained.

[0080] 400g of primary composite material, 10g of ammonia water, and 10g of sodium sulfide were dissolved in an ethanol solution and heated at 180℃ for 4 hours. Then, the mixture was treated in argon gas at 770℃ for 1 hour and then further treated at 720℃ for 1 hour to obtain the composite microwave absorbing material.

[0081] Example 3

[0082] Add 1g of graphite powder to 50mL of aqueous solution and stir magnetically for 30min for initial dispersion. Then, sonicate at 200W for 1.5h, then increase to 300W for 1.5h, with a pulse mode of 50% duty cycle. The temperature of the dispersion during sonication should be ≤18℃. Centrifuge the dispersion at 400rpm / h for 30min to remove large unpeeled graphite particles, then centrifuge at 8000rpm / h for 30min to obtain the precipitate as the microwave absorbing substrate. Redisperse the microwave absorbing substrate in ethanol for later use, and add a small amount of ionic liquid to reduce agglomeration.

[0083] Metal powders of Fe, Co, Ni, Mn, and Al with a purity ≥99.9% were mixed in a mass ratio of 16:14:3:3:3 and placed in a high-energy ball mill jar (ball-to-powder ratio 5:1). Under argon protection, the mixture was ball-milled at 300 rpm for 24 hours, with a 15-minute pause every 2 hours to cool it down. 1% stearic acid was added as a process control agent. The ball-milled powder was pressed into a compact and melted in an electric arc melting furnace under a vacuum argon atmosphere at a current of 500 A. The melting was repeated 5 times to ensure uniformity, ultimately yielding a precipitate. The precipitate was placed in a copper crucible and evacuated to a vacuum of 2 × 10⁻⁶. -After passing through ³Pa, a mixture of hydrogen and argon gas is introduced. After the precipitate evaporates, it reacts with hydrogen atoms to generate iron-cobalt-nickel alloy nanoparticles, which are then collected by cyclone separation.

[0084] A dispersion containing 100g of microwave absorbing substrate was mixed and stirred with 300g of iron-cobalt-nickel alloy nanoparticles to embed the iron-cobalt-nickel alloy nanoparticles into the microwave absorbing substrate. Then, hydrochloric acid was added to form an acidic environment to remove the oxides on the surface. After drying, a primary composite material was obtained.

[0085] 300g of primary composite material, 10g of ammonia water, and 10g of sodium sulfide were dissolved in an ethanol solution and heated at 190℃ for 1.25h. Then, the mixture was treated in argon gas at 800℃ for 1.25h and then further treated at 730℃ for 1.25h to obtain the composite microwave absorbing material.

[0086] Example 4

[0087] Add 1g of graphite powder to 50mL of aqueous solution and stir magnetically for 30min for initial dispersion. Then, sonicate at 225W for 2h, then increase to 325W for 2h, with a pulse mode of 50% duty cycle. The temperature of the dispersion during sonication should be ≤18℃. Centrifuge the dispersion at 400rpm / h for 30min to remove large unpeeled graphite particles, then centrifuge at 8000rpm / h for 30min to obtain the precipitate as the microwave absorbing substrate. Redisperse the microwave absorbing substrate in ethanol for later use, and add a small amount of ionic liquid to reduce agglomeration.

[0088] Metal powders of Fe, Co, Ni, Mn, and Al with a purity ≥99.9% were mixed in a mass ratio of 9:8:2:2:2 and placed in a high-energy ball mill jar (ball-to-powder ratio 5:1). Under argon protection, the mixture was ball-milled at 300 rpm for 24 hours, with a 15-minute pause every 2 hours to cool it down. 1% stearic acid was added as a process control agent. The ball-milled powder was pressed into a compact and melted in an electric arc melting furnace under a vacuum argon atmosphere at a current of 500 A. The melting was repeated 5 times to ensure uniformity, ultimately yielding a precipitate. The precipitate was placed in a copper crucible and evacuated to a vacuum of 2 × 10⁻⁶. - After passing through ³Pa, a mixture of hydrogen and argon gas is introduced. After the precipitate evaporates, it reacts with hydrogen atoms to generate iron-cobalt-nickel alloy nanoparticles, which are then collected by cyclone separation.

[0089] A dispersion containing 100g of microwave absorbing substrate was mixed and stirred with 400g of iron-cobalt-nickel alloy nanoparticles to embed the iron-cobalt-nickel alloy nanoparticles into the microwave absorbing substrate. Then, hydrochloric acid was added to form an acidic environment to remove the oxides on the surface. After drying, a primary composite material was obtained.

[0090] 250g of primary composite material, 10g of ammonia water, and 10g of sodium sulfide were dissolved in an ethanol solution and heated at 200℃ for 6 hours. Then, the mixture was treated in argon gas at 820℃ for 1.5 hours and then further treated at 750℃ for 1.5 hours to obtain the composite microwave absorbing material.

[0091] Example 5

[0092] The difference between Example 5 and Example 1 is that gradient ultrasound was not used when preparing the microwave absorbing substrate. After initial dispersion, it was directly centrifuged after ultrasonic treatment at 250W for 2 hours.

[0093] Comparative Example 1

[0094] The difference between Comparative Example 1 and Example 1 is that an equal amount of iron-chromium-cobalt alloy nanoparticles were used instead of iron-cobalt-nickel alloy nanoparticles, and the composite material was prepared by mixing it with the dispersion of the microwave absorbing substrate.

[0095] Comparative Example 2

[0096] The difference between Comparative Example 2 and Example 1 is that an equal amount of silver nanoparticles were used instead of iron-cobalt-nickel alloy nanoparticles, and the composite material was prepared by mixing it with the dispersion of the microwave absorbing substrate.

[0097] Comparative Example 3

[0098] The difference between Comparative Example 3 and Example 1 is that no sulfur source was used; only a nitrogen source was used to dope and prepare the composite microwave absorbing material.

[0099] Comparative Example 4

[0100] The difference between Comparative Example 4 and Example 1 is that no nitrogen source was used; only a sulfur source was used to dope and prepare the composite microwave absorbing material.

[0101] Comparative Example 5

[0102] The difference between Comparative Example 5 and Example 1 is that no doping was performed, and the primary composite material was directly used as the composite microwave absorbing material.

[0103] The microwave absorbing substrates, iron-cobalt-nickel alloy nanoparticles, and composite microwave absorbing materials prepared in all embodiments were characterized (characterization methods included SEM), and the results are as follows: Figure 1 , Figure 2 And as shown in Tables 1 to 3.

[0104] Table 1

[0105]

[0106] Table 2

[0107]

[0108] Table 3

[0109]

[0110] The composite absorbing materials prepared in all embodiments and comparative examples were subjected to performance tests (referencing GB / T32596 for testing absorption bandwidth and absorption loss), and the results are as follows. Figure 3 As shown in Table 4.

[0111] Table 4

[0112]

[0113] As shown in Tables 1-4, the composite absorbing material provided by this invention achieves tunable absorption across the entire frequency range of 20MHz to 1.5GHz, while reducing secondary reflections and exhibiting a high absorption rate. Comparative Examples 1 and 2, using iron-chromium-cobalt alloy and nano-silver particles respectively to suppress electromagnetic waves in terms of magnetic loss, suffer from a single permeability frequency response, resulting in poor absorption at high frequencies. Comparative Examples 3 and 4, using nitrogen doping and sulfur doping respectively, optimize dielectric loss, but lack magnetic loss components and exhibit uneven doping, leading to decreased high-frequency absorption and significant fluctuations in the absorption frequency band. Comparative Example 5 shows decreased high-frequency absorption and significant fluctuations in the absorption frequency band.

[0114] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0115] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A composite microwave absorbing material, characterized in that, The material includes iron-cobalt-nickel alloy nanoparticles and a microwave absorbing material. The microwave absorbing material has a layered structure, in which multiple cavities are formed between adjacent layers. The iron-cobalt-nickel alloy nanoparticles are mainly distributed in the cavities, and the surface of the microwave absorbing material is doped with nitrogen and sulfur elements.

2. The composite absorbing material according to claim 1, characterized in that, The absorbing material satisfies at least one of the following conditions: (1) The substrate of the absorbing material is selected from graphite; (2) The number of layers of the absorbing material is less than or equal to 10; (3) The cavities in the absorbing material are elliptical in shape, with the major axis of the elliptical shape being 500nm~800nm ​​and the minor axis being 400nm~600nm; (4) The thickness of the absorbing material is 2μm~3μnm.

3. The composite absorbing material according to claim 1, characterized in that, The iron-cobalt-nickel alloy nanoparticles satisfy at least one of the following conditions: (1) The iron-cobalt-nickel alloy nanoparticles comprise 35wt%~45wt% Fe, 30wt%~40wt% Co, 5wt%~10wt% Ni, 5wt%~10wt% Mn and 5wt%~10wt% Al; (2) The particle size of the iron-cobalt-nickel alloy nanoparticles is less than or equal to 150 nm.

4. The composite absorbing material according to claim 1, characterized in that, The mass ratio of the iron-cobalt-nickel alloy nanoparticles to the microwave absorbing material is 4:1 to 2:

1.

5. The composite absorbing material according to claim 1, characterized in that, The total doping rate of nitrogen and sulfur elements in the surface layer of the composite microwave absorbing material is 5%~10%; And / or, the mass ratio of nitrogen to sulfur is 1:1 to 2:

3.

6. A method for preparing a composite microwave absorbing material, characterized in that, Includes the following steps: The dispersion of the microwave absorbing substrate was mixed evenly with iron-cobalt-nickel alloy nanoparticles and dried to obtain a primary composite material. The primary composite material is mixed with a nitrogen source and a sulfur source and heat-treated to obtain a composite microwave absorbing material.

7. The method for preparing the composite absorbing material according to claim 6, characterized in that, The method for preparing the microwave absorbing substrate includes: preparing graphite powder into a graphite dispersion, and obtaining the microwave absorbing substrate by gradient ultrasound and centrifugation. The gradient ultrasound includes first treating at 175W~225W for 1h~2h, and then increasing to 275W~325W for 1h~2h. The ultrasound adopts a pulse mode, and the temperature of the dispersion is ≤18℃ during the ultrasound process.

8. The method for preparing the composite absorbing material according to claim 6, characterized in that, The preparation method of the iron-cobalt-nickel alloy nanoparticles includes: Metal raw materials are mixed and smelted to obtain a first product, wherein the metal raw materials include iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder, and the particle size of the metal raw materials is ≤25μm; The first product was thermally reduced in a vacuum environment to obtain iron-cobalt-nickel alloy nanoparticles.

9. The method for preparing the composite absorbing material according to claim 6, characterized in that, After removing the surface oxides of the primary composite material, it is heated and mixed with nitrogen and sulfur sources in an organic solvent at 180°C to 200°C for 4 to 6 hours. Then, it is subjected to a first heat treatment at 770°C to 820°C for 1 to 1.5 hours in a protective gas environment, followed by a second heat treatment at 720°C to 750°C for 1 to 1.5 hours to obtain the composite microwave absorbing material.

10. The application of a composite absorbing material as described in any one of claims 1 to 5 in electronic devices.

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