A permanent magnet composite wave absorbing material and preparation method thereof

Abstract

The present invention relates to the field of absorbing materials, specifically to a permanent magnet composite absorbing material and a preparation method thereof. This material addresses the problem that, in the process of constructing complex microstructures in existing absorbing materials, different types of materials are difficult to evenly disperse at the contact interface. This leads to different dielectric constants after combination, resulting in poor impedance matching and difficulty in achieving multi-band tuning for electromagnetic wave absorption. The material comprises a matrix material and absorbing particles, characterized in that the absorbing particles are composed, by weight, of 40-80 parts of permanent magnet loss core micropowder, 10-30 parts of conductive loss material, and 30-50 parts of central reflective sheet material. The present invention enables close integration of different materials at the microscopic interface, resulting in a uniform and multi-scale structure. This uniform dielectric constant allows for absorption of electromagnetic waves in multiple frequency bands, resulting in enhanced absorbing capability.

Description

Technical Field

[0001] The present invention relates to the technical field of wave-absorbing materials, and in particular to a permanent magnet composite wave-absorbing material and a preparation method thereof. Background Art

[0002] Permanent magnetic absorbing material is a composite material composed of a permanent magnetic matrix and a polymer matrix. The permanent magnetic matrix in this material converts the incident electromagnetic waves through hysteresis loss, ferromagnetic resonance and eddy current effect, thereby efficiently converting and dissipating the energy of the electromagnetic waves to reduce the reflection and transmission of electromagnetic waves. In order to enhance the reflection loss and effective absorbing bandwidth of existing absorbing materials, the ordered structure of the material is mainly planned, and through hydrogen bonds and electrostatic effects, the material is prompted to spontaneously assemble into an ordered structure, thereby improving the material's absorbing efficiency.

[0003] The material with the strongest absorption ability is lanthanum-doped barium ferrite composite material. This type of material uses barium ferrite as the hard magnetic phase and has extremely high coercive force and saturation magnetization. Lanthanum replaces iron, which can significantly improve dielectric loss and impedance characteristics. However, this material still faces the problem of low impedance matching. Electromagnetic waves are easily reflected at the material interface because barium ferrite does not have too much porous structure. Therefore, related research combines graphene with other conductive materials to improve its dispersion in the matrix, such as graphene / aramid nanofiber carbonized film, to form a flexible material with a nacreous structure. There are also ferromagnetic materials that enhance the absorption of electromagnetic waves through a strong dielectric constant, eddy current loss, and natural magnetic resonance. However, all of the above materials have the problem of poor impedance matching. In addition, when faced with a multi-band electromagnetic environment, it is difficult for a single material to achieve broadband and efficient absorption. The doping between composite materials will be limited by the interface bonding and dispersion uniformity between the materials, making it difficult to achieve high absorption performance. For example, the composite between barium ferrite and graphene is difficult to form a multi-scale structure, and graphene is easy to agglomerate and difficult to be evenly distributed around the barium ferrite. Summary of the Invention

[0004] To address the problem in existing absorbing materials that, when constructing complex microstructures, different types of materials are difficult to evenly disperse at the contact interface, resulting in different dielectric constants after combination, resulting in poor impedance matching and difficulty in achieving multi-band tuning for electromagnetic wave absorption, the present invention provides a permanent magnet composite absorbing material and a preparation method thereof, the specific contents of which are as follows:

[0005] In a first aspect, the present invention provides a permanent magnet composite absorbing material, comprising a matrix material and absorbing particles, wherein the absorbing particles are composed, by weight, of 40-80 parts of permanent magnet loss core powder, 10-30 parts of conductive loss material, and 30-50 parts of central reflective sheet material;

[0006] The permanent magnet loss core powder is modified strontium ferrite, and the modified material is lanthanum nitrate or cobalt nitrate;

[0007] The conductive loss material includes a three-dimensional graphene layer material and a boron layer material;

[0008] The central reflection layer material includes Ti3CN layer material and barium titanate, and the weight ratio of the Ti3CN layer material to the barium titanate is 30-35:5-10.

[0009] This application promotes electron transmission by constructing a conductive lossy material on the surface of absorbing particles, forming a bridge grid between multiple absorbing particles, forming more conductive paths, thereby further generating more polarization centers, and forming a performance material with optimal impedance matching, allowing electromagnetic waves to better enter the gaps in the material for scattering, thereby increasing reflection loss and enhancing the material's ability to absorb electromagnetic waves. Borophene is used to improve the dispersion and dielectric connection effect of the graphene material, resulting in stronger electron scattering centers and significantly improving the absorption efficiency.

[0010] This application also uses Ti3CN sheet materials and barium titanate as reflective surfaces in impedance matching. Both have good dielectric constants, thereby making the surface reflection effect better and reducing the transmission of electromagnetic waves, so that more reflected and scattered electromagnetic waves can re-enter the material for reabsorption, thereby improving the loss effect of the absorbing particles on electromagnetic waves. Multiple losses enhance the material's ability to attenuate electromagnetic waves.

[0011] Preferably, the preparation method of the modified strontium ferrite is as follows:

[0012] Strontium nitrate, ferric nitrate and modified materials are added to 75-80 parts by weight of a citric acid aqueous solution in a weight ratio of 5-6:110-120:1, wherein the concentration of the citric acid aqueous solution is 1 mol / L, and ammonia water is added to adjust the pH value to neutral. The mixture is heated and dried to form a gel, and the gel is then sintered at 1100-1250°C for 2-6 hours to form a modified strontium ferrite powder.

[0013] Strontium ferrite, as a hard magnetic material, is an anisotropic magnet with a hexagonal crystal structure. It has high coercive force and stable magnetic properties.

[0014] Preferably, the method for constructing the three-dimensional graphene layer material is as follows:

[0015] The modified strontium ferrite is placed in an ethanol solution of a silane coupling agent and reacted for 6-12 hours to obtain amino strontium ferrite. The graphene oxide is prepared into an aqueous solution with a concentration of 0.3-1 mg / mL. The amino strontium ferrite and the graphene oxide aqueous solution are mixed in a mass ratio of 40-80:10-30, and ultrasonic treatment is performed for 1-2 hours to form a graphene coating liquid. After adding a reducing agent, it is filtered and the temperature is raised to 200-300°C for reaction for 6-12 hours to form a three-dimensional graphene layer material.

[0016] Preferably, the concentration of the silane coupling agent in the ethanol solution is 1-2 wt %, the reducing agent is hydrazine hydrate or hydroxylamine, and the concentration of the reducing agent is 20-60 mg / mL.

[0017] This application also provides a method for preparing the permanent magnet composite wave absorbing material, and the specific preparation steps are as follows:

[0018] S1. Modified strontium ferrite powder is aminated using a coupling agent, the aminated strontium ferrite and graphene oxide are dispersed in water, reduced, and heat-treated to obtain three-dimensional graphene strontium ferrite; boron powder is ultrasonically treated in perchloric acid, filtered and dried to obtain open-layer boron sheets, and the three-dimensional graphene strontium ferrite and open-layer boron sheets are dispersed in NMP dispersion, ultrasonically treated, and filtered to obtain a composite intercalation product;

[0019] S2. Heat-treating the composite intercalation product to obtain boron olefin bonded microparticles, placing the boron olefin bonded microparticles in a stripping solution and ultrasonically treating the microparticles to form a conductive loss layer on the surface of the modified strontium ferrite;

[0020] S3, adding the multilayer Ti3CN material and barium titanate into an aqueous solution of tetramethylammonium hydroxide and dispersing them to obtain a central reflective sheet material;

[0021] S4. Mixing the central reflector sheet material with a CTAB solution and ultrasonically treating the solution to obtain a CTAB-modified central reflector sheet material. Then, preparing the modified strontium ferrite having the conductive loss layer formed on the surface in step S2 into a dispersion, placing the CTAB-modified central reflector sheet material into the dispersion, stirring and mixing, and vacuum drying to obtain absorbing particles.

[0022] S5. Mix the absorbing particles, water, adhesive and dispersant and perform ball milling to obtain a casting slurry. Scrape the casting slurry onto the surface of the base material to form a permanent magnet composite absorbing material.

[0023] Furthermore, the specific preparation steps are as follows:

[0024] S1. Prepare modified strontium ferrite powder, use a coupling agent to aminate the modified strontium ferrite powder to obtain amino strontium ferrite, disperse the amino strontium ferrite and graphene oxide in water, reduce them, and perform heat treatment to obtain three-dimensional graphene strontium ferrite; ultrasonically treat boron powder in perchloric acid, filter and dry to obtain open-layer boron sheets, and then disperse the three-dimensional graphene strontium ferrite and the open-layer boron sheets in an NMP dispersion at a weight ratio of 30-50:10, ultrasonically treat them, and filter to obtain a composite intercalation product;

[0025] S2. Heat-treating the composite intercalation product at 400° C. for 20-60 min to obtain boron olefin bonded microparticles. The boron olefin bonded microparticles are placed in a stripping solution and ultrasonically treated to form a conductive loss layer on the surface of the modified strontium ferrite.

[0026] S3, prepare an etching solution, place the Ti3AlCN sheet material in the etching solution for reaction for 12-24 hours, centrifuge and wash, place in water for ultrasonic dispersion, filter to obtain a multilayer Ti3CN material, add the multilayer Ti3CN material and barium titanate to a 25wt% tetramethylammonium hydroxide aqueous solution and disperse for 2-5 hours to obtain a central reflection sheet material;

[0027] S4. Mixing the central reflector sheet material with a CTAB solution at a solid-liquid ratio of 3 mg:1 mL, and ultrasonically treating the mixture to obtain a CTAB-modified central reflector sheet material. Then, the modified strontium ferrite having the conductive loss layer formed on the surface in step S2 is prepared into a dispersion having a concentration of 2.0 mg / mL, and the CTAB-modified central reflector sheet material is placed in the dispersion. The mixture is stirred for 6-8 hours, and vacuum dried to obtain absorbing particles.

[0028] S5. Mix the absorbing particles, water, adhesive and dispersant and perform ball milling to obtain a casting slurry. Scrape the casting slurry onto the surface of the base material to form a permanent magnet composite absorbing material.

[0029] In the process of preparing permanent magnet composite materials, the present application uses boron powder for ultrasonic treatment in perchloric acid, which helps to destroy the interaction force between the boron powders, and its strong oxidizing property has a strong removal effect on impurities and oxide layers, increasing the quality and purity of the boron sheets. A relatively tight bond can be formed between the opened boron sheets and the modified strontium ferrite, preventing the formation of aggregates of surface-modified particles with three-dimensional graphene structures, and they will not agglomerate in subsequent heat treatment, which can effectively improve the absorption effect.

[0030] In this application, after heat treatment, borophene will be bonded to the surface of the three-dimensional graphene, but too much borophene will also block the gaps in the graphene, making it difficult to form complex three-dimensional channels. Therefore, a stripping liquid is used to strip off the excess boron to form a more uniform single-layer borophene, thereby enhancing the electron transmission ability of the graphene surface.

[0031] The present application also forms a higher dielectric constant layer by compounding multiple layers of Ti3CN material with barium titanate. In order to better compound with modified strontium ferrite, enhance the absorption capacity of electromagnetic waves and prevent their reflection, tetramethylammonium hydroxide is used for intercalation in the process of compounding Ti3CN material with barium titanate, so that the Ti3CN material can form a corrugated structure that is more open than an accordion, so that the functional groups on the surface of the modified strontium ferrite can be more firmly connected to the surface of the Ti3CN material, and a thicker pore structure is enriched on the surface of the Ti3CN material, so that the electromagnetic waves will not directly contact the high dielectric constant layer surface, but will first pass through the complex pore structure for energy conversion and absorption, and then contact the Ti3CN material with a high dielectric constant and then reflect to form an excellent electromagnetic wave absorption effect.

[0032] Preferably, in step S1, the total solid-to-liquid ratio of the modified strontium ferrite, the open-layer boron sheet and the NMP dispersion is 90-150 mg / mL, the ultrasonic power of the ultrasonic treatment is 500 W, and the ultrasonic time is 0.5-2 h.

[0033] Preferably, the stripping liquid in step S2 is N-methylpyrrolidone or dimethyl sulfoxide, and the ultrasonic power is 200W.

[0034] Preferably, the etching solution in step S3 is a mixed solution of LiF and HCl, the solid-liquid ratio of the mixed solution is 1g:25mL, the concentration of the HCl solution is 10mol / L, and the solid-liquid ratio of the Ti3CN material to the tetramethylammonium hydroxide is 1g:10-40mL.

[0035] Preferably, the concentration of the CTAB solution in step S4 is 2.0 mg / mL.

[0036] Preferably, in step S5, the weight ratio of the wave-absorbing particles, water, adhesive and dispersant is 60-75:90-120:10:4.

[0037] The beneficial effects of the present invention are:

[0038] In the process of constructing absorbing particles, this application uses strontium ferrite as the main core of hysteresis loss and ferromagnetic resonance, which can more strongly convert incident electromagnetic waves into heat energy, thereby efficiently attenuating electromagnetic interference. The higher magnetic permeability is combined with a wider absorbing ability, thereby achieving better electromagnetic protection and increasing the effective absorption bandwidth.

[0039] This application forms a three-dimensional graphene layer on the surface of strontium ferrite as the main layer for conducting electrons, and maintains the three-dimensional structure through borophene modification, which has structural diversity and optimizes the secondary loss capacity and conductive loss capacity of strontium ferrite. Borophene with strong conductivity is used as a connecting bridge to enhance the polarization effect of the interface, promote electron transmission and conductive loss, and thus achieve a wide range of wave absorption broadband. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Graph showing experimental data of specific surface areas of the embodiments of the present invention and the comparative examples.

[0041] Figure 2 Graph showing experimental data of reflection loss values ​​for the embodiments of the present invention and the comparative example. DETAILED DESCRIPTION

[0042] The following will refer to the attached Figures 1 to 2 The embodiments of the present invention are described in detail. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0043] Preparation Example 1

[0044] Preparation of permanent magnet loss core powder and conductive loss material

[0045] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5.5:115:1:78, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and lanthanum nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1200°C for 4 hours to form a modified strontium ferrite powder.

[0046] A 1.5 wt% ethanol solution of a silane coupling agent is prepared, and the modified strontium ferrite powder is placed in the solution for reaction for 9 hours, and filtered and dried to obtain amino strontium ferrite; an aqueous solution of graphene oxide is prepared with a concentration of 0.5 mg / mL, and the amino strontium ferrite and the aqueous solution of graphene oxide are mixed, wherein the mass ratio of the amino strontium ferrite to the graphene oxide is 60:20, and ultrasonic treatment is performed for 1.5 hours to form a graphene coating solution, and a reducing agent hydrazine hydrate is added and stirred, wherein the concentration of the reducing agent in the graphene coating solution is 40 mg / mL. After the reduction is completed, the solution is filtered, and the filtrate is heated to 250° C. for reaction for 9 hours to form a three-dimensional graphene layer on the surface of the amino strontium ferrite;

[0047] An appropriate amount of boron powder was weighed and placed in 70% perchloric acid for ultrasonic treatment, and then filtered and dried to obtain an open-layer boron sheet. The open-layer boron sheet was weighed at a weight ratio of modified strontium ferrite to open-layer boron sheet of 40:10, and the open-layer boron sheet was mixed with strontium ferrite amide with a three-dimensional graphene layer formed on the surface, and then dispersed in an NMP dispersion liquid. The total solid-liquid ratio of the dispersion was 120 mg / mL. After mixing, the mixture was ultrasonically treated at an ultrasonic power of 500 W and an ultrasonic time of 1 hour, and the composite intercalation product was filtered to obtain the product.

[0048] The composite intercalation product was heat treated at 400°C for 40 minutes to obtain boron olefin bonded microparticles, which were then ultrasonically treated in a stripping solution of N-methylpyrrolidone at a power of 200W to form a conductive loss layer on the surface of the modified strontium ferrite.

[0049] Preparation Example 2

[0050] Preparation of permanent magnet loss core powder and conductive loss material

[0051] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5:110:1:75, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and cobalt nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1100°C for 2 hours to form a modified strontium ferrite powder.

[0052] A 1 wt% silane coupling agent ethanol solution is prepared, and the modified strontium ferrite powder is placed in the solution for reaction for 6 hours, and filtered and dried to obtain amino strontium ferrite; an aqueous solution of graphene oxide is prepared with a concentration of 0.3 mg / mL, and the amino strontium ferrite and the aqueous solution of graphene oxide are mixed, wherein the mass ratio of the amino strontium ferrite to the graphene oxide is 40:10, and ultrasonic treatment is performed for 1 hour to form a graphene coating solution, and a reducing agent hydroxylamine is added and stirred, wherein the concentration of the reducing agent in the graphene coating solution is 20 mg / mL. After the reduction is completed, the solution is filtered, and the filtrate is heated to 200° C. and reacted for 6 hours to form a three-dimensional graphene layer on the surface of the amino strontium ferrite;

[0053] An appropriate amount of boron powder was weighed and placed in 70% perchloric acid for ultrasonic treatment, and then filtered and dried to obtain an open-layer boron sheet. The open-layer boron sheet was weighed at a weight ratio of modified strontium ferrite to open-layer boron sheet of 30:10, and the open-layer boron sheet was mixed with strontium ferrite amide with a three-dimensional graphene layer formed on the surface, and then dispersed in an NMP dispersion liquid. The total solid-liquid ratio of the dispersion was 90 mg / mL. After mixing, the mixture was ultrasonically treated at an ultrasonic power of 500 W and an ultrasonic time of 0.5 h. The composite intercalation product was filtered to obtain the product.

[0054] The composite intercalation product was heat treated at 400°C for 20 minutes to obtain boron olefin bonded microparticles, which were then ultrasonically treated in a stripping solution of dimethyl sulfoxide at a power of 200W to form a conductive loss layer on the surface of the modified strontium ferrite.

[0055] Preparation Example 3

[0056] Preparation of permanent magnet loss core powder and conductive loss material

[0057] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5:110:1:80, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and lanthanum nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1250°C for 6 hours to form a modified strontium ferrite powder.

[0058] A 2 wt % ethanol solution of a silane coupling agent is prepared, and the modified strontium ferrite powder is placed in the solution for reaction for 12 hours, and filtered and dried to obtain amino strontium ferrite; an aqueous solution of graphene oxide is prepared at a concentration of 1 mg / mL, and the amino strontium ferrite and the aqueous solution of graphene oxide are mixed, wherein the mass ratio of the amino strontium ferrite to the graphene oxide is 80:30, and ultrasonic treatment is performed for 2 hours to form a graphene coating solution, and a reducing agent, hydrazine hydrate, is added and stirred, wherein the concentration of the reducing agent in the graphene coating solution is 60 mg / mL. After the reduction is completed, the solution is filtered, and the filtrate is heated to 300° C. and reacted for 12 hours to form a three-dimensional graphene layer on the surface of the amino strontium ferrite;

[0059] An appropriate amount of boron powder was weighed and placed in 70% perchloric acid for ultrasonic treatment, and then filtered and dried to obtain an open-layer boron sheet. The open-layer boron sheet was weighed at a weight ratio of modified strontium ferrite to open-layer boron sheet of 50:10, and the open-layer boron sheet was mixed with strontium ferrite amide with a three-dimensional graphene layer formed on the surface, and then dispersed in an NMP dispersion liquid with a total solid-liquid ratio of 150 mg / mL. After mixing, the mixture was ultrasonically treated at an ultrasonic power of 500 W and an ultrasonic time of 2 h, and the composite intercalation product was filtered to obtain the product.

[0060] The composite intercalation product was heat treated at 400°C for 60 minutes to obtain boron olefin bonded microparticles, which were then ultrasonically treated in a stripping solution of N-methylpyrrolidone at a power of 200W to form a conductive loss layer on the surface of the modified strontium ferrite.

[0061] Preparation Example 4 - Unconstructed three-dimensional graphene layer material

[0062] Preparation of permanent magnet loss core powder and conductive loss material

[0063] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5.5:115:1:78, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and lanthanum nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1200°C for 4 hours to form a modified strontium ferrite powder.

[0064] A 1.5 wt% ethanol solution of a silane coupling agent was prepared, and the modified strontium ferrite powder was placed in the solution for reaction for 9 hours, and filtered and dried to obtain strontium ferrite amide; an appropriate amount of boron powder was weighed and placed in 70% perchloric acid for ultrasonic treatment, and filtered and dried to obtain an open-layer boron sheet; an open-layer boron sheet was weighed at a weight ratio of strontium ferrite amide to open-layer boron sheet of 40:10, and the open-layer boron sheet and strontium ferrite amide were mixed and dispersed in an NMP dispersion solution with a total solid-liquid ratio of 100 mg / mL. After mixing, the mixture was ultrasonically treated at an ultrasonic power of 500 W and an ultrasonic time of 1 hour, and the composite intercalation product was filtered to obtain a composite intercalation product;

[0065] The composite intercalation product was heat treated at 400°C for 40 minutes to obtain boron olefin bonded microparticles, which were then ultrasonically treated in a stripping solution of N-methylpyrrolidone at a power of 200W to form a conductive loss layer on the surface of the modified strontium ferrite.

[0066] Preparation Example 5: Borophene layer not constructed on the surface of three-dimensional graphene layer

[0067] Preparation of permanent magnet loss core powder and conductive loss material

[0068] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5.5:115:1:78, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and lanthanum nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1200°C for 4 hours to form a modified strontium ferrite powder.

[0069] A 1.5 wt% ethanol solution of a silane coupling agent is prepared, and the modified strontium ferrite powder is placed in the solution for reaction for 9 hours, and filtered and dried to obtain amino strontium ferrite; an aqueous solution of graphene oxide is prepared with a concentration of 0.5 mg / mL, and the amino strontium ferrite and the aqueous solution of graphene oxide are mixed, wherein the mass ratio of the amino strontium ferrite to the graphene oxide is 60:20, and ultrasonic treatment is performed for 1.5 hours to form a graphene coating solution, and a reducing agent hydrazine hydrate is added and stirred, wherein the concentration of the reducing agent in the graphene coating solution is 40 mg / mL. After the reduction is completed, the solution is filtered, and the filtrate is heated to 250° C. for reaction for 9 hours to form a three-dimensional graphene layer on the surface of the amino strontium ferrite;

[0070] Preparation Example 6 - Boron powder is not dispersed using perchloric acid

[0071] Preparation of permanent magnet loss core powder and conductive loss material

[0072] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5.5:115:1:78, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and lanthanum nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1200°C for 4 hours to form a modified strontium ferrite powder.

[0073] A 1.5 wt% ethanol solution of a silane coupling agent is prepared, and the modified strontium ferrite powder is placed in the solution for reaction for 9 hours, and filtered and dried to obtain amino strontium ferrite; an aqueous solution of graphene oxide is prepared with a concentration of 0.5 mg / mL, and the amino strontium ferrite and the aqueous solution of graphene oxide are mixed, wherein the mass ratio of the amino strontium ferrite to the graphene oxide is 60:20, and ultrasonic treatment is performed for 1.5 hours to form a graphene coating solution, and a reducing agent hydrazine hydrate is added and stirred, wherein the concentration of the reducing agent in the graphene coating solution is 40 mg / mL. After the reduction is completed, the solution is filtered, and the filtrate is heated to 250° C. for reaction for 9 hours to form a three-dimensional graphene layer on the surface of the amino strontium ferrite;

[0074] An appropriate amount of boron powder was weighed and placed in water for ultrasonic treatment, filtered and dried to obtain dispersed boron powder, dispersed boron powder was weighed with a weight ratio of modified strontium ferrite to dispersed boron powder of 40:10, and the dispersed boron powder was mixed with strontium amine ferrite with a three-dimensional graphene layer formed on the surface, and then dispersed in NMP dispersion liquid, with a total solid-liquid ratio of 120 mg / mL. After mixing, ultrasonic treatment was performed at an ultrasonic power of 500 W and an ultrasonic time of 1 hour, and the composite intercalation product was obtained by filtration;

[0075] The composite intercalation product was heat treated at 400°C for 40 minutes to obtain boron olefin bonded microparticles, which were then ultrasonically treated in a stripping solution of N-methylpyrrolidone at a power of 200W to form a conductive loss layer on the surface of the modified strontium ferrite.

[0076] Preparation Example 7 - Boron-Olene-Bound Microparticles Not Placed in Stripping Solution for Ultrasonic Treatment

[0077] Preparation of permanent magnet loss core powder and conductive loss material

[0078] Strontium nitrate, ferric nitrate, lanthanum nitrate, and citric acid are weighed in a weight ratio of 5.5:115:1:78, and a citric acid aqueous solution having a concentration of 1 mol / L is prepared. The strontium nitrate, ferric nitrate, and lanthanum nitrate are added to the citric acid solution and mixed evenly. Ammonia water is then added to adjust the pH value to neutral (pH=7, ±0.1). Water is removed by heating to form a gel-like substance. The gel is then sintered at 1200°C for 4 hours to form a modified strontium ferrite powder.

[0079] A 1.5 wt% ethanol solution of a silane coupling agent is prepared, and the modified strontium ferrite powder is placed in the solution for reaction for 9 hours, and filtered and dried to obtain amino strontium ferrite; an aqueous solution of graphene oxide is prepared with a concentration of 0.5 mg / mL, and the amino strontium ferrite and the aqueous solution of graphene oxide are mixed, wherein the mass ratio of the amino strontium ferrite to the graphene oxide is 60:20, and ultrasonic treatment is performed for 1.5 hours to form a graphene coating solution, and a reducing agent hydrazine hydrate is added and stirred, wherein the concentration of the reducing agent in the graphene coating solution is 40 mg / mL. After the reduction is completed, the solution is filtered, and the filtrate is heated to 250° C. for reaction for 9 hours to form a three-dimensional graphene layer on the surface of the amino strontium ferrite;

[0080] An appropriate amount of boron powder was weighed and placed in 70% perchloric acid for ultrasonic treatment, and then filtered and dried to obtain an open-layer boron sheet. The open-layer boron sheet was weighed at a weight ratio of modified strontium ferrite to open-layer boron sheet of 40:10, and the open-layer boron sheet was mixed with strontium ferrite amide with a three-dimensional graphene layer formed on the surface, and then dispersed in an NMP dispersion liquid. The total solid-liquid ratio of the dispersion was 120 mg / mL. After mixing, the mixture was ultrasonically treated at an ultrasonic power of 500 W and an ultrasonic time of 1 hour, and the composite intercalation product was filtered to obtain the product.

[0081] The composite intercalation product is heat-treated at 400° C. for 40 minutes to obtain boron-olefin-bonded particles, which modify the surface of the strontium ferrite to form a conductive loss layer. Example 1

[0082] LiF and 10 mol / L HCl were mixed at a solid-liquid ratio of 1 g: 25 mL to form an etching solution, and then a Ti3AlCN sheet material was placed in the etching solution to react for 18 hours. After centrifugal cleaning, it was ultrasonically dispersed in water and filtered to obtain a multilayer Ti3CN material. 33 parts of the multilayer Ti3CN material and 8 parts of barium titanate were weighed and added to a 25 wt% aqueous solution of tetramethylammonium hydroxide and dispersed for 3 hours. The solid-liquid ratio of the Ti3CN material to the tetramethylammonium hydroxide was 1 g: 25 mL to obtain a central reflection sheet material.

[0083] The central reflection sheet material was mixed with a CTAB solution having a concentration of 2.0 mg / mL at a solid-liquid ratio of 3 mg:1 mL, and ultrasonically treated to obtain a CTAB-modified central reflection sheet material. 80 parts of the modified strontium ferrite having a conductive loss layer formed on the surface obtained in Preparation Example 1 were prepared into a dispersion having a concentration of 2.0 mg / mL, and the CTAB-modified central reflection sheet material was placed in the dispersion, stirred and mixed for 7 hours, and vacuum dried to obtain absorbing particles.

[0084] The absorbing particles, water, polyester adhesive TPU and dispersant ammonium polyacrylate are mixed in a weight ratio of 70:105:10:4 and ball-milled to obtain a casting slurry, which is then scraped onto the surface of a base material to form a permanent magnet composite absorbing material. Example 2

[0085] LiF and 10 mol / L HCl were mixed at a solid-liquid ratio of 1 g: 25 mL to form an etching solution, and then a Ti3AlCN sheet material was placed in the etching solution to react for 12 hours. After centrifugal cleaning, it was ultrasonically dispersed in water and filtered to obtain a multilayer Ti3CN material. 30 parts of the multilayer Ti3CN material and 5 parts of barium titanate were weighed and added to a 25 wt% aqueous solution of tetramethylammonium hydroxide and dispersed for 2 hours. The solid-liquid ratio of the Ti3CN material to the tetramethylammonium hydroxide was 1 g: 10 mL to obtain a central reflection sheet material.

[0086] The central reflection sheet material was mixed with a CTAB solution having a concentration of 2.0 mg / mL at a solid-liquid ratio of 3 mg:1 mL, and ultrasonically treated to obtain a CTAB-modified central reflection sheet material. 50 parts of the modified strontium ferrite having a conductive loss layer formed on the surface obtained in Preparation Example 2 was prepared into a dispersion having a concentration of 2.0 mg / mL, and the CTAB-modified central reflection sheet material was placed in the dispersion, stirred and mixed for 6 hours, and vacuum dried to obtain absorbing particles.

[0087] The absorbing particles, water, polyester adhesive TPU and dispersant ammonium polyacrylate are mixed in a weight ratio of 60:90:10:4 and ball-milled to obtain a casting slurry, which is then scraped onto the surface of a base material to form a permanent magnet composite absorbing material. Example 3

[0088] LiF and 10 mol / L HCl were mixed at a solid-liquid ratio of 1 g: 25 mL to form an etching solution, and then a Ti3AlCN sheet material was placed in the etching solution to react for 24 hours. After centrifugal cleaning, it was ultrasonically dispersed in water and filtered to obtain a multilayer Ti3CN material. 35 parts of the multilayer Ti3CN material and 10 parts of barium titanate were weighed and added to a 25 wt% aqueous solution of tetramethylammonium hydroxide and dispersed for 5 hours. The solid-liquid ratio of the Ti3CN material to the tetramethylammonium hydroxide was 1 g: 40 mL to obtain a central reflection sheet material.

[0089] The central reflection sheet material was mixed with a CTAB solution having a concentration of 2.0 mg / mL at a solid-liquid ratio of 3 mg:1 mL, and ultrasonically treated to obtain a CTAB-modified central reflection sheet material. 110 parts of the modified strontium ferrite having a conductive loss layer formed on the surface obtained in Preparation Example 3 was prepared into a dispersion having a concentration of 2.0 mg / mL, and the CTAB-modified central reflection sheet material was placed in the dispersion, stirred and mixed for 8 hours, and vacuum dried to obtain absorbing particles.

[0090] The absorbing particles, water, polyester adhesive TPU and dispersant ammonium polyacrylate are mixed in a weight ratio of 75:120:10:4 and ball-milled to obtain a casting slurry, which is then scraped onto the surface of a base material to form a permanent magnet composite absorbing material.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that the permanent magnetic loss core powder and the conductive loss material used are those prepared in Preparation Example 4.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that the permanent magnetic loss core powder and the conductive loss material used are those prepared in Preparation Example 5.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that the permanent magnetic loss core powder and the conductive loss material used are those prepared in Preparation Example 6.

[0097] Comparative Example 4

[0098] The difference between this comparative example and Example 1 is that the permanent magnetic loss core powder and the conductive loss material used are those prepared in Preparation Example 7.

[0099] Comparative Example 5 - The central reflective sheet material was not intercalated with tetramethylammonium hydroxide

[0100] LiF and 10 mol / L HCl were mixed at a solid-liquid ratio of 1 g:25 mL to form an etching solution, and then Ti3AlCN sheet material was placed in the etching solution to react for 18 hours. After centrifugal cleaning, it was ultrasonically dispersed in water and filtered to obtain a multilayer Ti3CN material. 33 parts of the multilayer Ti3CN material and 8 parts of barium titanate were added to deionized water for dispersion and mixing, and then filtered and dried to obtain a central reflection sheet material.

[0101] The central reflection sheet material was mixed with a CTAB solution having a concentration of 2.0 mg / mL at a solid-liquid ratio of 3 mg:1 mL, and ultrasonically treated to obtain a CTAB-modified central reflection sheet material. 80 parts of the modified strontium ferrite having a conductive loss layer formed on the surface obtained in Preparation Example 1 were prepared into a dispersion having a concentration of 2.0 mg / mL, and the CTAB-modified central reflection sheet material was placed in the dispersion, stirred and mixed for 7 hours, and vacuum dried to obtain absorbing particles.

[0102] The absorbing particles, water, polyester adhesive TPU and dispersant ammonium polyacrylate are mixed in a weight ratio of 70:105:10:4 and ball-milled to obtain a casting slurry, which is then scraped onto the surface of a base material to form a permanent magnet composite absorbing material.

[0103] Experiments and data

[0104] The specific surface area and electromagnetic wave absorption performance of the permanent magnet composite absorbing materials prepared in the above embodiments and comparative examples were tested. The specific testing methods are as follows:

[0105] Specific surface area test: The specific surface area of ​​the sample was determined by the nitrogen adsorption-desorption isotherm method. Specifically, nitrogen adsorption and desorption were carried out at -196°C, and then calculated using the BET model.

[0106] Electromagnetic wave absorption performance test: The complex dielectric constant and complex magnetic permeability of the sample were measured using a vector network analyzer (VNA). The sample was mixed with paraffin and pressed into shape. The electromagnetic parameters of the sample within the frequency range were measured using the coaxial line method to obtain the reflection loss and absorption bandwidth.

[0107] Specific surface area: m 2 / g

[0108] Reflection loss value RL: unit dB, matching thickness is 2.4mm

[0109] Effective absorption bandwidth EAB: unit GHz

[0110] The specific data are shown in Table 1 below:

[0111]

[0112] Draw a line graph of the specific surface area and reflection loss values ​​in Table 1, as shown in Figure 1 and Figure 2 shown.

[0113] analyze

[0114] It can be seen from the data in Table 1 that the permanent magnet composite absorbing materials prepared in Example 1, Example 2 and Example 3 have excellent specific surface area, reflection loss value and effective absorption bandwidth. Not only are the reflection loss values ​​excellent, but they can also have excellent absorption effects on electromagnetic waves of different frequencies.

[0115] From the data in Table 1, it can be seen that the specific surface area of ​​Comparative Example 1 is extremely low, its reflection loss value is reduced to a certain extent, and the range of the effective absorption bandwidth is also relatively low. The difference between Comparative Example 1 and the embodiment is that the three-dimensional graphene layer material is not constructed. Therefore, it can be shown that the presence of the three-dimensional graphene layer material can greatly increase the specific surface area of ​​the absorbing material, thereby forming a more complex reflection and absorption structure, thereby increasing the absorption performance of electromagnetic waves.

[0116] Through Table 1 and Figure 1 、 Figure 2 It can be seen from the data that the specific surface area of ​​Comparative Example 2 has decreased to a certain extent, and the reflection loss value has also decreased to a certain extent, and its effective absorption bandwidth has decreased significantly. The difference between Comparative Example 2 and Example 1 is that the borophene layer is not constructed on the surface of the three-dimensional graphene layer. It can be proved that the presence of borophene can increase the specific surface area and reflection loss value of the absorbing material to a certain extent, and can significantly improve the effective absorption bandwidth.

[0117] It can be seen from the experimental data in Table 1 that the specific surface area, reflection loss value, and effective absorption bandwidth of Comparative Example 3 all decreased to a certain extent, but the decrease was not large. The difference between Comparative Example 3 and Example 1 is that the boron powder was not dispersed using perchloric acid, which proves that the pretreatment operation of the boron powder can improve the quality of boron forming borophene on the three-dimensional graphene surface to a certain extent, thereby forming a continuous borophene layer, playing a corresponding electron-conducting role, and thus improving the absorbing performance of the absorbing material.

[0118] The experimental data in Table 1 show that the specific surface area of ​​Comparative Example 4 decreases to a certain extent, but the reflection loss value and the effective absorption bandwidth do not decrease much. The difference between Comparative Example 4 and Example 1 is that the boron olefin-bonded particles are not ultrasonically treated in a stripping solution. Therefore, it can be proved that stripping off excess boron powder can effectively reduce pore blockage, thereby improving the absorption performance.

[0119] The experimental data of Comparative Example 5 in Table 1 show that Comparative Example 5 has a better specific surface area, and the reflection loss value and the effective absorption bandwidth have decreased to a certain extent. Compared with Example 1, the central reflection layer material of Comparative Example 5 was not intercalated with tetramethylammonium hydroxide, resulting in insufficient expansion and failure to form a composite with a sufficient amount of permanent magnetic loss core powder. Therefore, it can be proved that subjecting the central reflection layer to more intercalation treatment can effectively increase the contact probability between the layer material and the permanent magnetic loss core powder, thereby forming a thicker particle aggregate, thereby increasing the absorption performance of electromagnetic waves.

[0120] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A permanent magnet composite absorbing material, comprising a matrix material and absorbing particles, characterized in that: The wave-absorbing particles are composed of 40-80 parts by weight of permanent magnetic loss core powder, 10-30 parts of conductive loss material and 30-50 parts of central reflective sheet material; The permanent magnet loss core powder is modified strontium ferrite, and the modified material is lanthanum nitrate or cobalt nitrate; The conductive loss material includes a three-dimensional graphene layer material and a boron layer material; The central reflection layer material includes Ti3CN layer material and barium titanate, and the weight ratio of the Ti3CN layer material to the barium titanate is 30-35:5-10.

2. The permanent magnet composite absorbing material according to claim 1, characterized in that: The preparation method of the modified strontium ferrite is as follows: Strontium nitrate, ferric nitrate and modified materials are added to 75-80 parts by weight of an aqueous solution of citric acid in a weight ratio of 5-6:110-120:1, where the concentration of the aqueous solution of citric acid is 1 mol / L. Ammonia water is added to adjust the pH value to neutral, and the solution is heated and dried to form a gel. The gel is then sintered at 1100-1250°C for 2-6 hours to form a modified strontium ferrite powder.

3. The permanent magnet composite absorbing material according to claim 1, characterized in that: The method for constructing the three-dimensional graphene layer material is as follows: The modified strontium ferrite is placed in an ethanol solution of a silane coupling agent and reacted for 6-12 hours to obtain amino strontium ferrite. The graphene oxide is prepared into an aqueous solution with a concentration of 0.3-1 mg / mL. The amino strontium ferrite and the graphene oxide aqueous solution are mixed in a mass ratio of 40-80:10-30, and ultrasonic treatment is performed for 1-2 hours to form a graphene coating liquid. After adding a reducing agent, it is filtered and the temperature is raised to 200-300°C for reaction for 6-12 hours to form a three-dimensional graphene layer material.

4. The permanent magnet composite absorbing material according to claim 3, characterized in that: The concentration of the silane coupling agent in the ethanol solution is 1-2 wt %, the reducing agent is hydrazine hydrate or hydroxylamine, and the concentration of the reducing agent is 20-60 mg / mL.

5. The method for preparing a permanent magnet composite absorbing material according to any one of claims 1 to 4, characterized in that: The specific preparation steps are as follows: S1. Modified strontium ferrite powder is aminated using a coupling agent, the aminated strontium ferrite and graphene oxide are dispersed in water, reduced, and heat-treated to obtain three-dimensional graphene strontium ferrite; boron powder is ultrasonically treated in perchloric acid, filtered and dried to obtain open-layer boron sheets, and the three-dimensional graphene strontium ferrite and open-layer boron sheets are dispersed in NMP dispersion, ultrasonically treated, and filtered to obtain a composite intercalation product; S2. Heat-treating the composite intercalation product to obtain boron olefin bonded microparticles, placing the boron olefin bonded microparticles in a stripping solution and ultrasonically treating the microparticles to form a conductive loss layer on the surface of the modified strontium ferrite; S3, adding the multilayer Ti3CN material and barium titanate into an aqueous solution of tetramethylammonium hydroxide and dispersing them to obtain a central reflective sheet material; S4. Mixing the central reflector sheet material with a CTAB solution and ultrasonically treating the solution to obtain a CTAB-modified central reflector sheet material. Then, preparing the modified strontium ferrite having the conductive loss layer formed on the surface in step S2 into a dispersion, placing the CTAB-modified central reflector sheet material into the dispersion, stirring and mixing, and vacuum drying to obtain absorbing particles. S5. Mix the absorbing particles, water, adhesive and dispersant and perform ball milling to obtain a casting slurry. Scrape the casting slurry onto the surface of the base material to form a permanent magnet composite absorbing material.

6. The method for preparing a permanent magnet composite absorbing material according to claim 5, characterized in that: In the step S1, the total solid-to-liquid ratio of the modified strontium ferrite, the open-layer boron sheet and the NMP dispersion is 90-150 mg / mL, the ultrasonic power of the ultrasonic treatment is 500 W, and the ultrasonic time is 0.5-2 h.

7. The method for preparing a permanent magnet composite absorbing material according to claim 5, characterized in that: In step S2, the stripping solution is N-methylpyrrolidone or dimethyl sulfoxide, and the ultrasonic power is 200W.

8. The method for preparing a permanent magnet composite absorbing material according to claim 5, characterized in that: In step S3, the etching solution is a mixed solution of LiF and HCl, the solid-liquid ratio of the mixed solution is 1g:25mL, the concentration of the HCl solution is 10mol / L, and the solid-liquid ratio of the Ti3CN material to the tetramethylammonium hydroxide is 1g:10-40mL.

9. The method for preparing a permanent magnet composite absorbing material according to claim 5, characterized in that: The concentration of the CTAB solution in step S4 is 2.0 mg / mL.

10. The method for preparing a permanent magnet composite absorbing material according to claim 5, characterized in that: In step S5, the weight ratio of the absorbing particles, water, adhesive and dispersant is 60-75:90-120:10:4.

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