A composite wave-absorbing material and its preparation method

Abstract

The present invention relates to a composite wave-absorbing material and a preparation method thereof, belonging to the technical field of microwave absorption materials. The composite wave-absorbing material described in the present invention comprises the following raw materials for preparation in parts by weight: 80-95 parts of composite magnetic powder, 0.1-1 part of conductive agent, 4-10 parts of epoxy resin, and 5-12 parts of curing agent; the composite magnetic powder comprises a magnetic powder core, a heat-resistant layer wrapping the magnetic powder core, and a hydrophobic layer wrapping the heat-resistant layer. The composite wave-absorbing material described in the present invention has good wave-absorbing performance in the frequency range of 2-18 GHz, and at the same time has good high-temperature resistance and corrosion resistance, and can meet the requirements of products for environmental adaptability and high attenuation of electromagnetic waves. The composite wave-absorbing material described in the present invention performs double-layer coating of the magnetic powder core with a heat-resistant layer and a hydrophobic layer, which can further enhance the wave-absorbing performance, corrosion resistance and high-temperature resistance of the composite wave-absorbing material.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave absorption materials, and particularly relates to a composite wave-absorbing material and a preparation method thereof. Background Art

[0002] Due to its strong attenuation characteristics of electromagnetic wave energy and the ability to be processed into special complex shapes, the loaded wave-absorbing material (microwave absorber) has a wide range of applications in microwave systems. When used as a waveguide terminal matching load element, the microwave absorber can absorb the electromagnetic wave energy from the radio frequency signal transmission channel, effectively improving the matching performance in the circuit. In addition, the loaded wave-absorbing material also plays an important role in antenna devices, precision guidance, and microwave measurement systems. Currently, the applications of the loaded wave-absorbing material mainly have the following problems: (1) The loaded wave-absorbing material absorbs electromagnetic wave energy, resulting in temperature rise, which causes the material to soften and expand, and the size mismatch, making the material's reusability poor, and ultimately leading to the deterioration of microwave performance; (2) Currently, the loaded wave-absorbing material mainly uses carbonyl iron powder as the magnetic wave-absorbing agent, and carbonyl iron powder is 100% iron element. Due to the high activity of carbonyl iron powder, during long-term use, carbonyl iron powder is prone to adsorb moisture in humid air and rust, ultimately resulting in the weakening or even disappearance of the wave-absorbing performance; (3) The particle size (D50) of the magnetic powder absorber is relatively large. When mixed with epoxy resin, it is difficult to increase the filling amount, resulting in low magnetic properties, low attenuation constant of the loaded wave-absorbing material, and ultimately poor attenuation ability of the wave-absorbing material to electromagnetic waves. Based on the above situation, there is an urgent need to study a loaded wave-absorbing material with high heat resistance, corrosion resistance, and high loss. Summary of the Invention

[0003] The purpose of the present invention is to provide a composite wave-absorbing material with high temperature resistance, corrosion resistance, and high dielectric loss and magnetic loss at the same time, by overcoming the deficiencies of the prior art.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] In the first aspect, the present invention provides a composite wave-absorbing material, which comprises the following preparation raw materials in parts by weight: 80-95 parts of composite magnetic powder, 0.1-1 part of conductive agent, 4-10 parts of epoxy resin, and 5-12 parts of curing agent;

[0006] The composite magnetic powder includes a magnetic powder core, a heat-resistant layer wrapping the magnetic powder core, and a hydrophobic layer wrapping the heat-resistant layer.

[0007] The inventors' research found that in the present invention, the magnetic powder core is double-coated with a heat-resistant layer and a hydrophobic layer in sequence. The prepared composite magnetic powder has a double coating layer of heat-resistant layer / hydrophobic layer. Compared with traditional uncoated magnetic powder and magnetic powder with only one heat-resistant layer, the composite absorbing material obtained by using the composite magnetic powder of the present invention has better corrosion resistance and high-temperature resistance, and can work in a humid and hot environment for a long time without being rusted. At the same time, the composite magnetic powder of the present invention is used in combination with a conductive agent and epoxy resin, which can make it have high dielectric loss and magnetic loss in the frequency range of 2-18 GHz, greatly improving its attenuation constant, meeting the requirements of the product for environmental adaptability and high attenuation of electromagnetic waves, and at the same time enhancing its high-temperature resistance and corrosion resistance.

[0008] In addition, the inventors of the present invention found that in the double coating layer of the composite magnetic powder of the present invention, the hydrophobic layer is on the outer layer of the heat-resistant layer, which can make the composite absorbing material have better high-temperature resistance and corrosion resistance. However, coating the hydrophobic layer on the inner layer of the heat-resistant layer will not only affect the high-temperature resistance and corrosion resistance of the composite absorbing material, but also reduce the dielectric loss and magnetic loss performance of the composite absorbing material, which is not conducive to the practical application of the composite absorbing material.

[0009] As a preferred embodiment of the composite absorbing material of the present invention, the magnetic powder core is at least one of rare earth cobalt-based soft magnetic material, carbonyl iron powder, ferrite magnetic powder, iron-silicon-aluminum alloy powder, and iron-silicon-chromium alloy powder.

[0010] As a preferred embodiment of the composite absorbing material of the present invention, the magnetic powder core is a rare earth cobalt-based soft magnetic material, and the D50 of the rare earth cobalt-based soft magnetic material is ≤2.5 μm.

[0011] The inventors' research found that when using the rare earth cobalt-based soft magnetic material with the specific D50 of the present invention for double coating with a heat-resistant layer and a hydrophobic layer, compared with traditional carbonyl iron powder or other magnetic powders with D50>4 μm, the particle surface of the rare earth cobalt-based soft magnetic material of the present invention has a rare earth oxide film layer with better corrosion resistance and contains a large amount of cobalt elements with better corrosion resistance, which can effectively increase the corrosion potential of the composite material and reduce the corrosion current density of the composite material. After being compounded with epoxy resin and a conductive agent, it can further enhance the corrosion resistance of the composite absorbing material. In addition, the particle size of the rare earth cobalt-based soft magnetic material of the present invention is small and nearly spherical, which can effectively improve its filling ratio, and then improve the dielectric loss and magnetic loss of the composite material, making it have higher electromagnetic wave attenuation ability.

[0012] As a preferred embodiment of the composite absorbing material of the present invention, the raw material for preparing the hydrophobic layer is a hydrophobic organic solvent.

[0013] As a preferred embodiment of the composite wave-absorbing material of the present invention, the hydrophobic organic solvent is at least one of hexamethyldisilazane, polydimethylsiloxane, and polymethylhydrosiloxane.

[0014] In a large number of comparative studies on the preparation raw materials of the hydrophobic layer, the inventors found that not all hydrophobic organic solvents can enhance the wave-absorbing performance of the composite wave-absorbing material. The dielectric constant of the hydrophobic layer prepared by using the specific hydrophobic organic solvent of the present invention is moderate, and it has good wave transmission performance. Electromagnetic waves can penetrate well without being reflected back into free space, so that most of the electromagnetic waves can enter the wave-absorbing material and be consumed. Moreover, the composite magnetic powder and epoxy resin prepared by the hydrophobic organic solvent of the present invention have better composite matching properties, are not easily expanded when heated, and can more significantly enhance the high-temperature resistance performance of the composite wave-absorbing material. In addition, compared with the traditional hydrophobic layer containing fluorine with low surface energy, the hydrophobic organic solvent of the present invention has the performance of being green and environmentally friendly, which not only solves the problems of high toxicity and environmental pollution of the traditional fluorine-containing hydrophobic layer material, but also has a lower cost.

[0015] As a preferred embodiment of the composite wave-absorbing material of the present invention, the heat-resistant layer is a silica coating layer, and the preparation raw material of the silica coating layer is a silicon source.

[0016] As a preferred embodiment of the composite wave-absorbing material of the present invention, the silicon source is at least one of tetramethyl orthosilicate, tetraethyl orthosilicate, ethyl silicate, and tetrabutyl orthosilicate.

[0017] As a preferred embodiment of the composite wave-absorbing material of the present invention, the epoxy resin is at least one of phenolic epoxy resin, alicyclic epoxy resin, glycidyl polyfunctional epoxy resin, and bisphenol S epoxy resin.

[0018] The inventors' research found that not all epoxy resins can enhance the high-temperature resistance and corrosion resistance of the composite wave-absorbing material. The composite wave-absorbing material prepared by mixing the specific epoxy resin of the present invention with the double-layer coated magnetic powder can enhance the high-temperature resistance of the composite wave-absorbing material. In addition, the composite magnetic powder of the present invention has better compatibility with the specific epoxy resin, which can not only reduce the thermal expansion coefficient of the composite wave-absorbing material, but also improve the density of the composite wave-absorbing material, thereby improving its temperature resistance and corrosion resistance.

[0019] As a preferred embodiment of the composite wave-absorbing material of the present invention, the curing agent includes at least one of aromatic amines, alicyclic anhydrides, and silicone resins.

[0020] As a preferred embodiment of the composite wave-absorbing material of the present invention, the conductive agent is at least one of graphene, carbon nanotubes, ECP600JD, EC-300J, and BP-2000.

[0021] As a preferred embodiment of the composite wave-absorbing material of the present invention, the sum of the thicknesses of the heat-resistant layer and the hydrophobic layer is 30 to 60 nm.

[0022] The inventors of the present invention conducted extensive research on the amounts of the silicon source and the hydrophobic organic solvent and found that when the sum of the thicknesses of the heat-resistant layer and the hydrophobic layer of the present invention is within the above range, the wave-absorbing performance and corrosion resistance of the composite wave-absorbing material can be enhanced; while when the thickness of the double-layer coating of the composite magnetic powder is small, the corrosion resistance and wave-absorbing performance of the composite wave-absorbing material will be reduced; when the thickness of the double-layer coating of the composite magnetic powder is large, although the composite wave-absorbing material can have good corrosion resistance, its wave-absorbing performance will decline.

[0023] As a preferred embodiment of the composite wave-absorbing material of the present invention, the volume ratio of the silicon source to the hydrophobic organic solvent is silicon source:hydrophobic organic solvent = 1:(2 - 2.5).

[0024] The inventors of the present invention found in a large number of experimental studies that when the volume ratio of the silicon source to the hydrophobic organic solvent of the present invention is 1:(2 - 2.5), the heat-resistant layer and the hydrophobic layer of the composite magnetic powder can work synergistically, thereby enhancing the wave-absorbing performance, high-temperature resistance performance and corrosion resistance performance of the composite wave-absorbing material.

[0025] As a preferred embodiment of the composite wave-absorbing material of the present invention, the volume ratio of the silicon source to the hydrophobic organic solvent is silicon source:hydrophobic organic solvent = 1:2.

[0026] The inventors of the present invention found through research that when the volume ratio of the silicon source to the hydrophobic organic solvent of the present invention is 1:2, the composite wave-absorbing material has a lower coefficient of thermal expansion, better high-temperature resistance performance, and can also improve the impedance matching of the magnetic powder wave-absorbing agent, making it have better wave-absorbing performance.

[0027] As a preferred embodiment of the composite wave-absorbing material of the present invention, the preparation method of the composite magnetic powder includes the following steps:

[0028] S1. Measure anhydrous ethanol, water and ammonia water, mix them evenly, add the magnetic powder core, mix them evenly, add the silicon source, and stir to obtain a mixed material A;

[0029] S2. Drop the hydrophobic organic solvent into the mixed material A obtained in step S1, stir, and dry to obtain the composite magnetic powder.

[0030] As a preferred embodiment of the composite wave-absorbing material of the present invention, the volume ratio of the anhydrous ethanol, water and ammonia water is anhydrous ethanol:water:ammonia water = 100:25:3.

[0031] Second aspect, the present invention provides a method for preparing the above-mentioned composite wave-absorbing material, comprising the following steps:

[0032] S1. Weigh a conductive agent, a high-temperature epoxy resin, a curing agent, and composite magnetic powder, mix them evenly to obtain a mixed material B;

[0033] S2. Subject the mixed material B obtained in step S1 to vacuum degassing and molding to obtain a green body;

[0034] S3. Heat and cure the green body obtained in step S2 to obtain the composite wave-absorbing material.

[0035] As a preferred embodiment of the method for preparing the composite wave-absorbing material of the present invention, in step S2, the process of vacuum degassing is as follows: the revolution speed of the vacuum degassing mixer is 1200 - 1800 r / min, the stirring time is 1 - 3 min, and the vacuum degree is -92 - -98 kPa.

[0036] Using the vacuum degassing mixer of the present invention for vacuum degassing, the tank body of the vacuum degassing mixer is at 45°, and there is no need for stirring blades. Compared with the traditional vacuum stirring degassing machine, the vacuum degassing of the present invention spreads the material from the center of the tank body by the high-speed revolution and rotation of the tank body, using centrifugal force and shear force, so as to achieve the purpose of uniform stirring and bubble removal.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The composite wave-absorbing material of the present invention is compounded by adding double-coated magnetic powder, high-temperature epoxy resin, conductive agent, and curing agent, which can make it have high dielectric loss and magnetic loss and better impedance matching in the frequency range of 2 - 18 GHz, greatly improving the wave-absorbing performance; in addition, it not only enhances the corrosion resistance of the composite wave-absorbing material, but also can reduce its thermal expansion coefficient and improve the high-temperature resistance of the composite wave-absorbing material, and can meet the requirements of the product for environmental adaptability and high attenuation of electromagnetic waves;

[0039] (2) When the magnetic powder of the composite wave-absorbing material of the present invention is double-coated and the thickness of the double coating layer is controlled to be 30 - 60 nm at the same time, the wave-absorbing performance, corrosion resistance, and high-temperature resistance of the composite wave-absorbing material can be further enhanced. Description of the Drawings

[0040] Figure 1 It is a flowchart for preparing the composite wave-absorbing material of the present invention;

[0041] Figure 2 It is a transmission electron microscope morphology diagram of Y2Co8Fe9 before and after double coating in Examples 1 - 2 of the present invention;

[0042] Figure 3 It is a graph showing the relationship between the electromagnetic wave attenuation coefficient and frequency of the composite absorbing materials of Examples 1-9 and Comparative Examples 1-8 of the present invention;

[0043] Figure 4 It is a Tafel curve graph of the composite absorbing materials of Examples 1-9 and Comparative Examples 1-8 of the present invention. Detailed implementation manners

[0044] The technical solution of the present invention will be further described below in conjunction with the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention. The methods or operations used in the embodiments, unless otherwise specified, are all conventional methods or conventional operations in the art.

[0045] Example 1

[0046] An embodiment of the composite absorbing material of the present invention includes the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0047] The preparation method of the composite magnetic powder in this embodiment includes the following steps:

[0048] S1. Weigh 4000 mL of absolute ethanol, 1000 mL of water, and 120 mL of ammonia water, mix them evenly, add 486 g of Y2Co8Fe9 (with D50 ≤ 2.5 μm), stir at room temperature for 2 h, mix evenly, add 60 mL of tetraethyl orthosilicate, and stir at 40 °C for 3 h to obtain a mixed material A;

[0049] S2. Drop 120 mL of hexamethyldisilazane into the mixed material A obtained in step S1, stir at 40 °C for 5 h, and dry to obtain the composite magnetic powder.

[0050] The preparation method of the composite absorbing material in this embodiment includes the following steps:

[0051] S1. Weigh the composite magnetic powder, ECP600JD, glycidyl polyfunctional high-temperature epoxy resin, and alicyclic anhydride in proportion and add them to a beaker, stir at room temperature for 30 min to obtain a mixed material B;

[0052] S2. Put the mixed material B described in step S1 into a vacuum degassing mixer for vacuum degassing, and set the parameters: for stage A1, the revolution speed of the vacuum degassing mixer is 1200 r / min, the stirring time is 40 s, the vacuum is closed, and the stirring is on; for stage A2, the revolution speed of the vacuum degassing mixer is 1800 r / min, the stirring time is 180 s, the vacuum (vacuum degree is -95 kPa) is on, and the stirring is on; for stage A3, the revolution speed of the vacuum degassing mixer is 1300 r / min, the stirring time is 60 s, the vacuum (vacuum degree is -95 kPa) is on, and the stirring is on for vacuum degassing. Place the degassed and evenly stirred mixed material in a mold, perform molding under a pressure of 150 MPa, keep the pressure for 5 min, demold, and obtain a green body.

[0053] S3. Heat the green body described in step S2 to 85 °C for curing for 120 min, 105 °C for curing for 120 min, and 125 °C for curing for 120 min respectively, cut and polish to obtain the composite microwave absorbing material.

[0054] Example 2

[0055] An embodiment of the composite microwave absorbing material of the present invention includes the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0056] The difference between the preparation method of the composite magnetic powder in this embodiment and that in Example 1 is only that the amount of hexamethyldisilazane in step S2 is 150 mL, and the amounts and preparation methods of the other components are exactly the same. The preparation method of the composite microwave absorbing material in this embodiment is exactly the same as that in Example 1.

[0057] Example 3

[0058] An embodiment of the composite microwave absorbing material of the present invention includes the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0059] The difference between the preparation method of the composite magnetic powder in this embodiment and that in Example 1 is only that Y2Co8Fe9 (with D50 ≤ 2.5 μm) in step S1 is replaced with the same amount of carbonyl iron powder (with D50 > 4 μm), and the amounts and preparation methods of the other components are exactly the same. The preparation method of the composite microwave absorbing material in this embodiment is exactly the same as that in Example 1.

[0060] Example 4

[0061] An embodiment of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0062] The preparation method of the composite magnetic powder in this embodiment is different from that of Example 1 only in that hexamethyldisilazane in step S2 is replaced with the same amount of polydimethylsiloxane, and the amounts and preparation methods of the other components are exactly the same. The preparation method of the composite wave-absorbing material in this embodiment is exactly the same as that of Example 1.

[0063] Example 5

[0064] An embodiment of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0065] The preparation method of the composite magnetic powder in this embodiment is different from that of Example 1 only in that polydimethylsiloxane in step S2 is replaced with the same amount of methylhydrogensiloxane, and the amounts and preparation methods of the other components are exactly the same. The preparation method of the composite wave-absorbing material in this embodiment is exactly the same as that of Example 1.

[0066] Example 6

[0067] An embodiment of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of alicyclic epoxy resin, and 5.19 parts of alicyclic anhydride.

[0068] The preparation method of the composite magnetic powder in this embodiment is exactly the same as that of Example 1. The difference between the composite wave-absorbing material in this embodiment and Example 1 is only that glycidyl polyfunctional high-temperature epoxy resin in step S1 is replaced with the same amount of alicyclic epoxy resin, and the amounts and preparation methods of the other components are exactly the same.

[0069] Example 7

[0070] An embodiment of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of BP-2000, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0071] The preparation method of the composite magnetic powder in this embodiment is exactly the same as that of Example 1. The difference between the composite wave-absorbing material in this embodiment and Example 1 is only that ECP600JD in step S1 is replaced with the same amount of BP-2000, and the amounts and preparation methods of the other components are exactly the same.

[0072] Example 8

[0073] An example of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of aromatic amine.

[0074] The preparation method of the composite magnetic powder in this example is exactly the same as that in Example 1. The difference between the composite wave-absorbing material in this example and that in Example 1 is only that the alicyclic anhydride in step S1 is replaced with the same amount of aromatic amine, and the dosages of the remaining components and the preparation method are exactly the same.

[0075] Example 9

[0076] An example of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 87.85 parts of composite magnetic powder, 0.15 part of ECP600JD, 4 parts of glycidyl polyfunctional high-temperature epoxy resin, and 8 parts of alicyclic anhydride.

[0077] The preparation methods of the composite magnetic powder and the composite wave-absorbing material in this example are exactly the same as those in Example 1.

[0078] Comparative Example 1

[0079] A comparative example of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of Y2Co8Fe9, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0080] The preparation method of the wave-absorbing material in this comparative example comprises the following steps:

[0081] S1. Weigh Y2Co8Fe9 (with D50≤2.5μm), ECP600JD, glycidyl polyfunctional high-temperature epoxy resin, and alicyclic anhydride in proportion and add them to a beaker, and stir at room temperature for 30 min to obtain a mixed material A;

[0082] S2. Put the mixed material A obtained in step S1 into a vacuum stirring and defoaming machine for vacuum centrifugal defoaming, and set the parameters as follows: stage A1: 1200 r / min, time 40 s, vacuum off, stirring on; stage A2: 1800 r / min, time 180 s, vacuum (-95 kPa) on, stirring on; stage A3: 1300 r / min, time 60 s, vacuum (-95 kPa) on, stirring on, and perform vacuum high-speed centrifugal defoaming. Place the defoamed and evenly stirred mixed material in a mold, and carry out molding under a pressure of 150 MPa, with a pressure holding time of 5 min, and demold to obtain a green body;

[0083] S3. Heat the green body described in step S2 to 85°C for 120 min, 105°C for 120 min, and 125°C for 120 min respectively, then cut and polish to obtain the composite microwave absorbing material.

[0084] Comparative Example 2

[0085] A comparative example of the composite microwave absorbing material of the present invention includes the following raw materials by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0086] The preparation method of the composite magnetic powder in this comparative example includes the following steps:

[0087] Weigh 4000 mL of absolute ethanol, 1000 mL of water, and 120 mL of ammonia water, mix them evenly, add 486 g of Y2Co8Fe9 (with D50 ≤ 2.5 μm), stir at room temperature for 2 h, mix evenly, drop in 120 mL of hexamethyldisilazane, stir at 40°C for 5 h, and dry to obtain the composite magnetic powder.

[0088] The preparation method of the composite microwave absorbing material in this comparative example is exactly the same as that in Example 1.

[0089] Comparative Example 3

[0090] A comparative example of the composite microwave absorbing material of the present invention includes the following raw materials by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0091] The preparation method of the composite magnetic powder in this comparative example includes the following steps:

[0092] Weigh 4000 mL of absolute ethanol, 1000 mL of water, and 120 mL of ammonia water, mix them evenly, add 486 g of Y2Co8Fe9 (with D50 ≤ 2.5 μm), stir at room temperature for 2 h, mix evenly, add 60 mL of tetraethyl orthosilicate, stir at 40°C for 3 h, and dry to obtain the composite magnetic powder.

[0093] The preparation method of the composite microwave absorbing material in this comparative example is exactly the same as that in Example 1.

[0094] Comparative Example 4

[0095] A comparative example of the composite microwave absorbing material of the present invention includes the following raw materials by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0096] The preparation method of the composite magnetic powder in this comparative example is only different from that in Example 1 in that the dosage of polydimethylsiloxane in step S2 is 180 mL, and the dosages of other components and the preparation method are exactly the same. The preparation method of the composite wave-absorbing material in this comparative example is exactly the same as that in Example 1.

[0097] Comparative Example 5

[0098] A comparative example of the composite wave-absorbing material of the present invention includes the following raw materials for preparation by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0099] The preparation method of the composite magnetic powder in this comparative example is only different from that in Example 1 in that the dosage of polydimethylsiloxane in step S2 is 100 mL, and the dosages of other components and the preparation method are exactly the same. The preparation method of the composite wave-absorbing material in this comparative example is exactly the same as that in Example 1.

[0100] Comparative Example 6

[0101] A comparative example of the composite wave-absorbing material of the present invention includes the following raw materials for preparation by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0102] The preparation method of the composite magnetic powder in this comparative example is only different from that in Example 1 in that polydimethylsiloxane in step S2 is replaced with perfluorooctyltriethoxysilane with the same dosage, and the dosages of other components and the preparation method are exactly the same. The preparation method of the composite wave-absorbing material in this comparative example is exactly the same as that in Example 1.

[0103] Comparative Example 7

[0104] A comparative example of the composite wave-absorbing material of the present invention includes the following raw materials for preparation by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of dicyandiamide, and 5.19 parts of alicyclic anhydride.

[0105] The preparation method of the composite magnetic powder in this comparative example is exactly the same as that in Example 1. The preparation method of the composite wave-absorbing material in this comparative example is only different from that in Example 1 in that glycidyl polyfunctional high-temperature epoxy resin in step S1 is replaced with dicyandiamide with the same dosage, and the dosages of other components and the preparation method are exactly the same.

[0106] Comparative Example 8

[0107] A comparative example of the composite wave-absorbing material of the present invention comprises the following raw materials for preparation in parts by weight: 90 parts of composite magnetic powder, 0.37 part of ECP600JD, 4.44 parts of glycidyl polyfunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0108] The preparation method of the composite magnetic powder in this comparative example comprises the following steps:

[0109] S1. Weigh 4000 mL of absolute ethanol, 1000 mL of water, and 120 mL of ammonia water, mix them evenly, add 486 g of Y2Co8Fe9 (with D50 ≤ 2.5 μm), stir at room temperature for 2 h, mix evenly, drop in 120 mL of hexamethyldisilazane, and stir at 40 °C for 5 h to obtain a mixed material A;

[0110] S2. Add 60 mL of tetraethyl orthosilicate to the mixed material A obtained in step S1, stir at 40 °C for 3 h, and dry to obtain the composite magnetic powder.

[0111] The preparation method of the composite wave-absorbing material in this comparative example is exactly the same as that in Example 1.

[0112] Effect Example 1

[0113] Figure 1 is the preparation flow chart of the composite wave-absorbing material of the present invention. Figure 2 are the transmission electron microscope morphology diagrams of Y2Co8Fe9 in the composite wave-absorbing materials of Examples 1-2 of the present invention before and after coating. Among them, (a) is the transmission electron microscope morphology diagram of Y2Co8Fe9 before coating, (b) is the transmission electron microscope morphology diagram of Y2Co8Fe9 in the composite wave-absorbing material of Example 1 after coating, the sum of the thicknesses of its heat-resistant layer and hydrophobic layer is 30 nm, and (c) is the transmission electron microscope morphology diagram of Y2Co8Fe9 in the composite wave-absorbing material of Example 2 after double-layer coating, the sum of the thicknesses of its heat-resistant layer and hydrophobic layer is 60 nm. It can be seen that Figure 2 the more the amount of hydrophobic organic solvent used for coating the magnetic powder, the thicker the thickness of its double-layer coating.

[0114] Effect Example 2

[0115] To verify the wave-absorbing performance of the composite wave-absorbing material of the present invention, the composite wave-absorbing materials of Examples 1-9 and Comparative Examples 1-8 of the present invention were subjected to electromagnetic tests, and the corresponding electromagnetic wave attenuation coefficients were calculated. The test method is as follows: Take a coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm inside the composite wave-absorbing material, use a vector network analyzer, and test its magnetoelectric parameters (complex permittivity and complex permeability) at 2-18 GHz through the coaxial method. The test results are as Figure 3 shown.

[0116] Figure 3It is a graph showing the relationship between the electromagnetic wave attenuation coefficient and frequency of the composite absorbing materials of Examples 1-9 and Comparative Examples 1-8 of the present invention.

[0117] It can be seen from Figure 3 that the composite absorbing materials of Examples 1-9 have relatively high electromagnetic wave attenuation coefficients at 2-18 GHz, and from high to low, they are: Example 1 > Example 2 > Example 9 > Example 4 > Example 5 > Example 6 > Example 7 > Example 8 > Example 3. Among them, the composite absorbing material of Example 1 has the highest electromagnetic wave attenuation coefficient at 2-18 GHz, and as the frequency increases, the electromagnetic wave attenuation coefficient of the composite absorbing material of Example 1 can be as high as 1400 m -1 Above, it has a relatively high attenuation ability for electromagnetic waves; while the electromagnetic wave attenuation coefficients of the composite absorbing materials of Comparative Examples 1-8 at 2-18 GHz are all less than 800 m -1 , indicating that their attenuation ability for electromagnetic waves is poor and it is not conducive to the practical application of the composite absorbing materials.

[0118] Effect Example 3

[0119] In order to further verify the corrosion resistance of the composite absorbing materials of the present invention, the composite absorbing materials of Examples 1-9 and Comparative Examples 1-8 of the present invention were subjected to electrochemical corrosion Tafel curve tests. The test method was as follows: Using a Chenhua 760E electrochemical workstation, the three-electrode method was adopted, with a saturated calomel electrode as the reference electrode, a platinum electrode as the counter electrode, and a 1×1 cm 2 composite material as the working electrode, and its Tafel curve in a 3.5 wt% NaCl solution was tested. The test results are as Figure 4 shown.

[0120] It can be seen from Figure 4 that the corrosion potentials of the composite absorbing materials of Examples 1-9 of the present invention are all within the range of -0.4 to 0 V. Among them, the corrosion potential of the composite absorbing material of Example 1 is the closest to 0. And by fitting the Tafel curves of Examples 1-9, it can be seen that the composite absorbing material of Example 1 has a lower corrosion current, indicating that the composite absorbing material of Example 1 has the best corrosion resistance. Compared with Examples 1-9, the corrosion potentials of the composite absorbing materials of Comparative Examples 1-8 are more deviated from 0, and by fitting the Tafel curves of Comparative Examples 1-8, it can be seen that the composite absorbing materials of Comparative Examples 1-8 have higher corrosion currents, indicating that their corrosion resistance is poor.

[0121] Effect Example 4

[0122] In order to further verify the high-temperature resistance performance and corrosion resistance performance of the composite wave-absorbing material of the present invention, the thermal expansion coefficient and Hast test of the composite wave-absorbing materials of Examples 1-9 and Comparative Examples 1-8 of the present invention were tested. The test methods are as follows, and the test results are shown in Table 1 below.

[0123] (1) Thermal expansion coefficient test: A cylinder with a bottom diameter of 0.6 cm and a length of 2.5 cm was cut from the composite wave-absorbing material, and its thermal expansion coefficient from room temperature to 300 °C was tested using a thermal dilatometer.

[0124] (2) Hast test: The composite wave-absorbing material was placed in a high-temperature, high-pressure and high-humidity accelerated aging test chamber for testing. The test conditions were: 120 °C, 2.0×10 5 Pa, 100% relative humidity.

[0125] Table 1

[0126]

[0127]

[0128] As can be seen from Table 1, compared with the composite wave-absorbing materials of Comparative Examples 1-8, the composite wave-absorbing materials of Examples 1-9 have a lower thermal expansion coefficient, indicating better high-temperature resistance performance. At the same time, from the Hast test results, it can be seen that the composite wave-absorbing materials of Examples 1-9 have better corrosion resistance in a humid and hot environment, which is beneficial to the practical application of the composite wave-absorbing material, and the corrosion resistance of Example 1 is the best.

[0129] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite wave-absorbing material, characterized in that, The preparation raw materials include the following parts by weight: 80-95 parts of composite magnetic powder, 0.1-1 part of conductive agent, 4-10 parts of epoxy resin, and 5-12 parts of curing agent; The composite magnetic powder includes a magnetic powder core, a heat-resistant layer wrapping the magnetic powder core, and a hydrophobic layer wrapping the heat-resistant layer; The preparation raw material of the hydrophobic layer is a hydrophobic organic solvent; The heat-resistant layer is a silica coating layer, and the preparation raw material of the silica coating layer is a silicon source; The sum of the thicknesses of the heat-resistant layer and the hydrophobic layer is 30-60 nm; The volume ratio of the silicon source to the hydrophobic organic solvent is silicon source: hydrophobic organic solvent = 1: (2-2.5).

2. The composite wave-absorbing material according to claim 1, wherein, The magnetic powder core is at least one of rare earth cobalt-based soft magnetic materials, carbonyl iron powder, ferrite magnetic powder, iron-silicon-aluminum alloy powder, and iron-silicon-chromium alloy powder.

3. The composite wave-absorbing material according to claim 2, wherein The magnetic powder core is a rare earth cobalt-based soft magnetic material, and the D50 of the rare earth cobalt-based soft magnetic material is ≤ 2.5 μm.

4. The composite wave-absorbing material according to claim 1, wherein, The hydrophobic organic solvent is at least one of hexamethyldisilazane, polydimethylsiloxane, and polymethylhydrosiloxane.

5. The composite wave-absorbing material according to claim 1, characterized in that, The volume ratio of the silicon source to the hydrophobic organic solvent is silicon source: hydrophobic organic solvent = 1:

2.

6. The preparation method of the composite wave-absorbing material according to any one of claims 1 to 5, characterized in that, It includes the following steps: S1. Weigh the conductive agent, epoxy resin, curing agent, and composite magnetic powder, mix them evenly to obtain a mixed material B; S2. Perform vacuum degassing and molding on the mixed material B in step S1 to obtain a green body; S3. Heat and cure the green body in step S2 to obtain the composite microwave absorbing material.

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