Composite magnetic powder and wave-absorbing material thereof

Abstract

The invention relates to composite magnetic powder and a wave-absorbing material thereof. The composite magnetic powder comprises a magnetic powder inner core, a heat-resistant layer wrapping the magnetic powder inner core and a hydrophobic layer wrapping the heat-resistant layer. The composite wave-absorbing material has good wave-absorbing performance within the frequency range of 2-18 GHz, meanwhile 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 magnetic powder core is coated with the heat-resistant layer and the hydrophobic layer, so that the wave-absorbing performance, the corrosion resistance and the high-temperature resistance of the wave-absorbing material can be enhanced.

Description

Background Technology

[0001] Microwave absorbers (loaded microwave absorbers) are widely used in microwave systems due to their strong attenuation characteristics for electromagnetic wave energy and their ability to be processed into special complex shapes. When used as a waveguide terminal matching load element, microwave absorbers can absorb electromagnetic wave energy from the radio frequency signal transmission channel, effectively improving the matching performance in the circuit. In addition, loaded microwave absorbers also play an important role in antenna equipment, precision guidance and microwave measurement systems. The current application of loaded microwave absorbers mainly has the following problems: (1) Loaded microwave absorbers absorb electromagnetic wave energy, which causes the temperature to rise, resulting in softening and expansion of the material, size mismatch, poor reusability of the material, and ultimately deterioration of microwave performance; (2) Currently, loaded microwave absorbers mainly use carbonyl iron powder as a magnetic absorber. However, carbonyl iron powder is 100% iron element, and due to its high activity, it is easy to absorb moisture from the humid air and rust during long-term use, which ultimately leads to a weakening or even disappearance of the absorption performance; (3) The particle size (D) of the magnetic powder absorber 50 The relatively large loss coefficient (FCC) makes it difficult to increase the filling amount when mixed with epoxy resin, resulting in low magnetic properties and a low attenuation constant of the loaded microwave absorbing material. Ultimately, this leads to poor attenuation of electromagnetic waves by the absorbing material. Based on the above situation, there is an urgent need to study a heat-resistant, corrosion-resistant, and high-loss loaded microwave absorbing material. Summary of the Invention

[0002] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite absorbing material that is resistant to high temperature and corrosion, and has high dielectric loss and magnetic loss.

[0003] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0004] In a first aspect, the present invention provides a composite microwave absorbing material comprising the following raw materials in parts by weight: 80-95 parts of composite magnetic powder, 0.1-1 parts of conductive agent, 5-10 parts of epoxy resin, and 5-12 parts of curing agent;

[0005] The composite magnetic powder includes a magnetic powder core, a heat-resistant layer encapsulating the magnetic powder core, and a hydrophobic layer encapsulating the heat-resistant layer.

[0006] The inventors discovered that this invention employs a heat-resistant layer and a hydrophobic layer sequentially to coat the magnetic powder core in a double-layer manner. The resulting composite magnetic powder has a double-layer coating of heat-resistant and hydrophobic layers. Compared to traditional uncoated magnetic powder and magnetic powder with only one heat-resistant layer, the composite microwave absorbing material obtained using the composite magnetic powder of this invention exhibits better corrosion resistance and high-temperature resistance, and can operate for extended periods in humid and hot environments without rusting. Furthermore, the composite magnetic powder of this invention, when combined with conductive agents and epoxy resin, achieves higher dielectric and magnetic losses in the 2–18 GHz frequency range, significantly improving its attenuation constant. This meets the product's requirements for environmental adaptability and high electromagnetic wave attenuation, while also enhancing its high-temperature resistance and corrosion resistance.

[0007] Furthermore, the inventors of this invention have discovered that having the hydrophobic layer on the outer layer of the heat-resistant layer in the double-layer coating of the composite magnetic powder of this invention enables the composite absorbing material to have better high-temperature resistance and corrosion resistance. However, having the hydrophobic layer on the inner layer of the heat-resistant layer not only affects the high-temperature resistance and corrosion resistance of the composite absorbing material, but also reduces 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.

[0008] 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.

[0009] In 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, wherein the D50 of the rare earth cobalt-based soft magnetic material is ≤2.5μm.

[0010] The inventors discovered that by using the rare-earth cobalt-based soft magnetic material with a specific D50 as described in this invention for double-layer coating of a heat-resistant layer and a hydrophobic layer, compared with traditional carbonyl iron powder or other magnetic powders with D50 > 4 μm, the rare-earth cobalt-based soft magnetic material of this invention has a rare-earth oxide film layer with better corrosion resistance and contains a large amount of cobalt element with good corrosion resistance on the particle surface. This can effectively improve the corrosion potential of the composite material and reduce the corrosion current density of the composite material. After being compounded with epoxy resin and conductive agent, it can further enhance the corrosion resistance of the composite microwave absorbing material. In addition, the rare-earth cobalt-based soft magnetic material of this invention has a small particle size and is nearly spherical, which can effectively increase its filling ratio, thereby improving the dielectric loss and magnetic loss of the composite material and giving it a higher electromagnetic wave attenuation capability.

[0011] In a preferred embodiment of the composite microwave absorbing material of the present invention, the raw material for preparing the hydrophobic layer is a hydrophobic organic solvent.

[0012] In a preferred embodiment of the composite microwave absorbing material of the present invention, the hydrophobic organic solvent is at least one of hexamethyldisilazane, polydimethylsiloxane, and polymethylhydrosiloxane.

[0013] Through extensive comparative studies of raw materials used in the preparation of hydrophobic layers, the inventors discovered that not all hydrophobic organic solvents can enhance the microwave absorption performance of composite microwave absorbing materials. The hydrophobic layer prepared using the specific hydrophobic organic solvent described in this invention exhibits a moderate dielectric constant and good wave transmittance, allowing electromagnetic waves to penetrate effectively without being reflected back into free space. This ensures that the vast majority of electromagnetic waves can enter the microwave absorbing material and be consumed. Furthermore, the composite magnetic powder prepared using the hydrophobic organic solvent of this invention has better composite compatibility with epoxy resin, is less prone to expansion upon heating, and can significantly enhance the high-temperature resistance of the composite microwave absorbing material. In addition, compared to traditional hydrophobic layers containing low surface energy fluorine, the hydrophobic organic solvent of this invention is environmentally friendly, not only solving the problems of high toxicity and environmental pollution associated with traditional fluorinated hydrophobic layer materials, but also offering lower costs.

[0014] In a preferred embodiment of the composite microwave absorbing material of the present invention, the heat-resistant layer is a silicon dioxide coating layer, and the raw material for preparing the silicon dioxide coating layer is a silicon source.

[0015] In a preferred embodiment of the composite absorbing material of the present invention, the silicon source is at least one of tetramethyl orthosilicate, tetraethyl orthosilicate, ethyl silicate, and tetrabutyl orthosilicate.

[0016] In a preferred embodiment of the composite microwave absorbing material of the present invention, the epoxy resin is at least one of phenolic epoxy resin, alicyclic epoxy resin, glycidyl ether polyfunctional epoxy resin, and bisphenol S epoxy resin.

[0017] The inventors discovered that not all epoxy resins can enhance the high-temperature resistance and corrosion resistance of composite microwave absorbing materials. However, the composite microwave absorbing material prepared by mixing the specific epoxy resin described in this invention with double-layered coated magnetic powder exhibits enhanced high-temperature resistance. Furthermore, the composite magnetic powder described in this invention has better compatibility with the specific epoxy resin, which not only reduces the coefficient of thermal expansion of the composite microwave absorbing material but also increases its density, thereby improving its temperature resistance and corrosion resistance.

[0018] In a preferred embodiment of the composite microwave absorbing material of the present invention, the curing agent includes at least one of aromatic amines, alicyclic anhydrides, and organosilicon resins.

[0019] In a preferred embodiment of the composite microwave absorbing material of the present invention, the conductive agent is at least one of graphene, carbon nanotubes, ECP600JD, EC-300J, and BP-2000.

[0020] In a preferred embodiment of the composite microwave absorbing material of the present invention, the sum of the thicknesses of the heat-resistant layer and the hydrophobic layer is 30–60 nm.

[0021] The inventors of this invention conducted extensive research on the dosage of silicon source and hydrophobic organic solvent and found that when the sum of the thicknesses of the heat-resistant layer and the hydrophobic layer described in this invention is within the above-mentioned range, the microwave absorption performance and corrosion resistance of the composite microwave absorbing material can be enhanced. However, when the thickness of the double-layer coating of the composite magnetic powder is small, the corrosion resistance and microwave absorption performance of the composite microwave absorbing material are low. When the thickness of the double-layer coating of the composite magnetic powder is large, although the composite microwave absorbing material can have better corrosion resistance, it will lead to a decrease in its microwave absorption performance.

[0022] In a preferred embodiment of the composite microwave 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).

[0023] The inventors of this invention discovered through extensive experimental research that when the volume ratio of the silicon source to the hydrophobic organic solvent described in this invention is 1:(2-2.5), the heat-resistant layer and the hydrophobic layer of the composite magnetic powder can synergistically enhance each other, thereby improving the microwave absorption performance, high-temperature resistance, and corrosion resistance of the composite microwave absorbing material.

[0024] In a preferred embodiment of the composite microwave 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.

[0025] The inventors of this invention have discovered that when the volume ratio of the silicon source to the hydrophobic organic solvent is 1:2, the composite microwave absorbing material has a lower coefficient of thermal expansion and better high-temperature resistance. At the same time, it can also improve the impedance matching of the magnetic powder microwave absorbing agent, thus giving it better microwave absorption performance.

[0026] As a preferred embodiment of the composite microwave absorbing material of the present invention, the method for preparing the composite magnetic powder includes the following steps:

[0027] S1. Measure anhydrous ethanol, water and ammonia, mix them evenly, add the magnetic powder core, mix evenly, add the silicon source, stir, and obtain mixture A;

[0028] S2. Add the hydrophobic organic solvent dropwise into the mixture A described in step S1, stir, and dry to obtain the composite magnetic powder.

[0029] In a preferred embodiment of the composite microwave absorbing material of the present invention, the volume ratio of anhydrous ethanol, water and ammonia is anhydrous ethanol: water: ammonia = 100:25:3.

[0030] Secondly, the present invention provides a method for preparing the above-mentioned composite microwave absorbing material, comprising the following steps:

[0031] S1. Weigh the conductive agent, high-temperature epoxy resin, curing agent and composite magnetic powder, mix them evenly to obtain mixture B;

[0032] S2. Vacuum degassing and molding of the mixture B described in step S1 are performed to obtain a green body.

[0033] S3. The blank obtained in step S2 is heated and cured to obtain the composite microwave absorbing material.

[0034] As a preferred embodiment of the preparation method of the composite microwave absorbing material of the present invention, in step S2, the vacuum degassing process is as follows: the revolution speed of the vacuum degassing stirrer is 1200-1800 r / min, the stirring time is 1-3 min, and the vacuum degree is -92--98 kPa.

[0035] Vacuum degassing is performed using the vacuum degassing mixer described in this invention. The tank of the vacuum degassing mixer is at a 45° angle and does not require stirring blades. Compared with traditional vacuum stirring degassing machines, the vacuum degassing of this invention uses the high-speed revolution and rotation of the tank to spread the material evenly from the center of the tank using centrifugal force and shear force, thereby achieving the purpose of uniform stirring and removing air bubbles.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) The composite microwave absorbing material of the present invention is made by adding double-layer coated magnetic powder, high-temperature epoxy resin, conductive agent and curing agent, which enables it to have high dielectric loss and magnetic loss and better impedance matching in the frequency range of 2 to 18 GHz, greatly improving the microwave absorbing performance; in addition, it not only enhances the corrosion resistance of the composite microwave absorbing material, but also reduces its thermal expansion coefficient and improves the high temperature resistance of the composite microwave absorbing material, which can meet the requirements of product environmental adaptability and high electromagnetic wave attenuation.

[0038] (2) When the composite absorbing material of the present invention is coated with magnetic powder in a double layer and the thickness of the double coating layer is controlled to be 30-60nm, the absorption performance, corrosion resistance and high temperature resistance of the composite absorbing material can be further enhanced. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating the preparation process of the composite microwave absorbing material described in this invention.

[0040] Figure 2 These are transmission electron microscopy (TEM) images of Y2Co8Fe9 before and after double-layer coating in Examples 1 and 2 of this invention.

[0041] Figure 3 The graphs show 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 this invention.

[0042] Figure 4 The images show the Tafel curves of the composite absorbing materials of Examples 1-9 and Comparative Examples 1-8 of this invention. Detailed Implementation

[0043] The technical solution of the present invention will be further described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the methods or operations used in the embodiments are conventional methods or operations in the art.

[0044] Example 1

[0045] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0046] The method for preparing the composite magnetic powder described in this embodiment includes the following steps:

[0047] S1. Weigh 4000mL of anhydrous ethanol, 1000mL of water and 120mL of ammonia, mix them evenly, add 486g of Y2Co8Fe9 (with D50≤2.5μm), stir at room temperature for 2h, mix evenly, add 60mL of tetraethyl orthosilicate, stir at 40℃ for 3h to obtain mixture A.

[0048] S2. Add 120 mL of hexamethyldisilazane to the mixture A described in step S1, stir at 40°C for 5 h, and dry to obtain composite magnetic powder.

[0049] The preparation method of the composite absorbing material described in this embodiment includes the following steps:

[0050] S1. Weigh the composite magnetic powder, ECP600JD, glycidyl type multifunctional high-temperature epoxy resin and alicyclic anhydride according to the proportion and add them to a beaker. Stir at room temperature for 30 minutes to obtain mixture B.

[0051] S2. Place the mixture B described in step S1 into a vacuum degassing mixer for vacuum degassing, and set the parameters as follows: A1 stage, the revolution speed of the vacuum degassing mixer is 1200 r / min, the stirring time is 40 s, the vacuum is turned off, and the stirring is turned on; A2 stage, 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 turned on, and the stirring is turned on; A3 stage, 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 turned on, and the stirring is turned on. Perform vacuum degassing, place the degassed and uniformly stirred mixture into a mold, and mold it under a pressure of 150 MPa for 5 min. Demold to obtain the green body.

[0052] S3. The blanks described in step S2 are heated to 85°C for 120 min, 105°C for 120 min, and 125°C for 120 min respectively, then cut and polished to obtain the composite microwave absorbing material.

[0053] Example 2

[0054] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0055] The preparation method of the composite magnetic powder in this embodiment differs from that in Example 1 only in that the amount of hexamethyldisilazane used in step S2 is 150 mL; the amounts of the remaining components and the preparation method 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.

[0056] Example 3

[0057] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0058] The preparation method of the composite magnetic powder described in this embodiment differs from that in Example 1 only in that Y2Co8Fe9 (with D50≤2.5μm) in step S1 is replaced with the same amount of carbonyl iron powder (with D50>4μm). The amounts of other components and the preparation method are exactly the same. The preparation method of the composite microwave absorbing material described in this embodiment is exactly the same as that in Example 1.

[0059] Example 4

[0060] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0061] The preparation method of the composite magnetic powder described in this embodiment differs from that in Example 1 only in that hexamethyldisilazane in step S2 is replaced with the same amount of polydimethylsiloxane; the amounts of other components and the preparation method are exactly the same. The preparation method of the composite microwave absorbing material described in this embodiment is exactly the same as that in Example 1.

[0062] Example 5

[0063] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0064] The preparation method of the composite magnetic powder described in this embodiment differs from that in Example 1 only in that polydimethylsiloxane in step S2 is replaced with the same amount of methylhydrosiloxane; the amounts of other components and the preparation method are exactly the same. The preparation method of the composite microwave absorbing material described in this embodiment is exactly the same as that in Example 1.

[0065] Example 6

[0066] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of alicyclic epoxy resin, and 5.19 parts of alicyclic anhydride.

[0067] The preparation method of the composite magnetic powder described in this embodiment is exactly the same as that in Example 1. The only difference between the composite microwave absorbing material described in this embodiment and that in Example 1 is that the glycidyl type multifunctional high-temperature epoxy resin in step S1 is replaced with the same amount of alicyclic epoxy resin; the amounts of the remaining components and the preparation method are exactly the same.

[0068] Example 7

[0069] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of BP-2000, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0070] The preparation method of the composite magnetic powder described in this embodiment is exactly the same as that in Example 1. The only difference between the composite microwave absorbing material described in this embodiment and that in Example 1 is that ECP600JD in step S1 is replaced with the same amount of BP-2000; the amounts of other components and the preparation method are exactly the same.

[0071] Example 8

[0072] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of aromatic amine.

[0073] The preparation method of the composite magnetic powder described in this embodiment is exactly the same as that in Example 1. The only difference between the composite microwave absorbing material described in this embodiment and that in Example 1 is that the alicyclic anhydride in step S1 is replaced with the same amount of aromatic amine; the amounts of the remaining components and the preparation method are exactly the same.

[0074] Example 9

[0075] An embodiment of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 87.85 parts of composite magnetic powder, 0.15 parts of ECP600JD, 4 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 8 parts of cycloaliphatic anhydride.

[0076] The preparation methods of the composite magnetic powder and composite microwave absorbing material described in this embodiment are exactly the same as those in Embodiment 1.

[0077] Comparative Example 1

[0078] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of Y2Co8Fe9, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0079] The preparation method of the microwave absorbing material described in this comparative example includes the following steps:

[0080] S1. Weigh Y2Co8Fe9 (with D50≤2.5μm), ECP600JD, glycidyl type multifunctional high-temperature epoxy resin and alicyclic anhydride according to the proportion and add them to a beaker. Stir at room temperature for 30 minutes to obtain mixture A.

[0081] S2. Place the mixture A described in step S1 into a vacuum centrifuge for vacuum centrifugation and degassing. Set the parameters as follows: A1 stage: 1200 r / min, time 40 s, vacuum off, stirring on; A2 stage: 1800 r / min, time 180 s, vacuum (-95 kPa) on, stirring on; A3 stage: 1300 r / min, time 60 s, vacuum (-95 kPa) on, stirring on. Perform high-speed vacuum centrifugation and degassing. Place the degassed and uniformly stirred mixture into a mold and press it under a pressure of 150 MPa for 5 min. Demold to obtain the green body.

[0082] S3. The blanks described in step S2 are heated to 85°C for 120 min, 105°C for 120 min, and 125°C for 120 min respectively, then cut and polished to obtain the composite microwave absorbing material.

[0083] Comparative Example 2

[0084] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0085] The method for preparing the composite magnetic powder described in this comparative example includes the following steps:

[0086] Weigh 4000 mL of anhydrous ethanol, 1000 mL of water and 120 mL of ammonia, mix them evenly, add 486 g of Y2Co8Fe9 (with D50≤2.5 μm), stir at room temperature for 2 h, mix evenly, add 120 mL of hexamethyldisilazane dropwise, stir at 40 °C for 5 h, dry to obtain composite magnetic powder.

[0087] The preparation method of the composite absorbing material described in this comparative example is exactly the same as that in Example 1.

[0088] Comparative Example 3

[0089] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0090] The method for preparing the composite magnetic powder described in this comparative example includes the following steps:

[0091] Weigh 4000 mL of anhydrous ethanol, 1000 mL of water and 120 mL of ammonia, 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, dry, and obtain composite magnetic powder.

[0092] The preparation method of the composite absorbing material described in this comparative example is exactly the same as that in Example 1.

[0093] Comparative Example 4

[0094] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0095] The preparation method of the composite magnetic powder described in this comparative example differs from that of Example 1 only in that the amount of polydimethylsiloxane used in step S2 is 180 mL, while the amounts of other components and the preparation method are exactly the same. The preparation method of the composite microwave absorbing material described in this comparative example is exactly the same as that of Example 1.

[0096] Comparative Example 5

[0097] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0098] The preparation method of the composite magnetic powder described in this comparative example differs from that of Example 1 only in that the amount of polydimethylsiloxane used in step S2 is 100 mL, while the amounts of other components and the preparation method are exactly the same. The preparation method of the composite microwave absorbing material described in this comparative example is exactly the same as that of Example 1.

[0099] Comparative Example 6

[0100] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0101] The preparation method of the composite magnetic powder described in this comparative example differs from that of Example 1 only in that polydimethylsiloxane in step S2 is replaced with the same amount of perfluorooctyltriethoxysilane; the amounts of other components and the preparation method are exactly the same. The preparation method of the composite microwave absorbing material described in this comparative example is exactly the same as that of Example 1.

[0102] Comparative Example 7

[0103] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of dicyandiamide, and 5.19 parts of alicyclic anhydride.

[0104] The preparation method of the composite magnetic powder described in this comparative example is exactly the same as that in Example 1. The only difference between the preparation method of the composite microwave absorbing material described in this comparative example and that in Example 1 is that the glycidyl-type multifunctional high-temperature epoxy resin in step S1 is replaced with the same amount of dicyandiamide; the amounts of the remaining components and the preparation method are exactly the same.

[0105] Comparative Example 8

[0106] A comparative example of the composite microwave absorbing material of the present invention comprises the following raw materials in parts by weight: 90 parts of composite magnetic powder, 0.37 parts of ECP600JD, 4.44 parts of glycidyl-type multifunctional high-temperature epoxy resin, and 5.19 parts of alicyclic anhydride.

[0107] The method for preparing the composite magnetic powder described in this comparative example includes the following steps:

[0108] S1. Weigh 4000mL of anhydrous ethanol, 1000mL of water and 120mL of ammonia, mix them evenly, add 486g of Y2Co8Fe9 (with D50≤2.5μm), stir at room temperature for 2h, mix evenly, add 120mL of hexamethyldisilazane dropwise, stir at 40℃ for 5h to obtain mixture A;

[0109] S2. Add 60 mL of tetraethyl orthosilicate to the mixture A described in step S1, stir at 40 °C for 3 h, and dry to obtain composite magnetic powder.

[0110] The preparation method of the composite absorbing material described in this comparative example is exactly the same as that in Example 1.

[0111] Example of effect 1

[0112] Figure 1 This is a flowchart illustrating the preparation process of the composite absorbing material described in this invention. Figure 2 The images show the transmission electron microscope (TEM) morphology of Y2Co8Fe9 in the composite absorbing materials of Examples 1 and 2 of this invention before and after coating. (a) is the TEM morphology of Y2Co8Fe9 before coating; (b) is the TEM morphology of Y2Co8Fe9 in the composite absorbing material of Example 1 after coating, where the sum of the thicknesses of the heat-resistant layer and the hydrophobic layer is 30 nm; and (c) is the TEM morphology of Y2Co8Fe9 in the composite absorbing material of Example 2 after double-layer coating, where the sum of the thicknesses of the heat-resistant layer and the hydrophobic layer is 60 nm. Figure 2 It can be seen that the more hydrophobic organic solvent is used when coating magnetic powder, the thicker the double coating layer becomes.

[0113] Example 2

[0114] To verify the microwave absorption performance of the composite absorbing material described in this invention, electromagnetic tests were conducted on the composite absorbing materials of Examples 1-9 and Comparative Examples 1-8, and the corresponding electromagnetic wave attenuation coefficients were calculated. The test method was as follows: a coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm was placed inside the composite absorbing material. Using a vector network analyzer, its magnetoelectric parameters (complex permittivity and complex permeability) at 2-18 GHz were tested using the coaxial method. The test results are as follows. Figure 3 As shown.

[0115] Figure 3The graph shows 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 this invention.

[0116] from Figure 3 It can be seen that the composite absorbing materials of Examples 1 to 9 have high electromagnetic wave attenuation coefficients in the range of 2 to 18 GHz, in descending order: 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 in the range of 2 to 18 GHz, and as the frequency increases, the electromagnetic wave attenuation coefficient of the composite absorbing material of Example 1 can reach as high as 1400 m. -1 The above-mentioned materials exhibit high attenuation capabilities for electromagnetic waves; while the composite absorbing materials in Comparative Examples 1–8 all have electromagnetic wave attenuation coefficients of less than 800 mΩ at 2–18 GHz. -1 This indicates that its ability to attenuate electromagnetic waves is poor, which is not conducive to the practical application of composite absorbing materials.

[0117] Example 3

[0118] To further verify the corrosion resistance of the composite microwave absorbing material described in this invention, the composite microwave absorbing materials of Examples 1-9 and Comparative Examples 1-8 of this invention were subjected to electrochemical corrosion Tafel curve tests. The test method was as follows: using a Chenhua 760E electrochemical workstation, a three-electrode method was adopted, with a saturated calomel electrode as the reference electrode and a platinum electrode as the counter electrode, at a depth of 1×1 cm. 2 The composite material was used as the working electrode, and its Tafel curve in 3.5 wt% NaCl solution was tested. The test results are as follows: Figure 4 As shown.

[0119] from Figure 4 It can be seen that the corrosion potentials of the composite absorbing materials in Examples 1-9 of this invention are all within the range of -0.4 to 0V. Among them, the corrosion potential of the composite absorbing material in Example 1 is closest to 0. Fitting the Tafel curves of Examples 1-9 shows that the composite absorbing material in Example 1 has a lower corrosion current, indicating that the composite absorbing material in Example 1 has the best corrosion resistance. Compared with Examples 1-9, the corrosion potentials of the composite absorbing materials in Comparative Examples 1-8 are further away from 0. Fitting the Tafel curves of Comparative Examples 1-8 shows that the corrosion currents of the composite absorbing materials in Comparative Examples 1-8 are higher, indicating that their corrosion resistance is poor.

[0120] Example of effect 4

[0121] To further verify the high-temperature resistance and corrosion resistance of the composite microwave absorbing material described in this invention, the thermal expansion coefficient and Hast test of the composite microwave absorbing materials of Examples 1-9 and Comparative Examples 1-8 were tested. The test methods are shown below, and the test results are shown in Table 1 below.

[0122] (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 microwave absorbing material, and its thermal expansion coefficient from room temperature to 300℃ was tested using a thermal expansion meter.

[0123] (2) Hast test: The composite microwave absorbing material was placed in a high-temperature, high-pressure, and high-humidity accelerated aging test chamber for testing. The test conditions were: 120℃, 2.0×10 5 Pa, 100% relative humidity.

[0124] Table 1

[0125]

[0126]

[0127] As shown in Table 1, compared with the composite absorbing materials of Comparative Examples 1-8, the composite absorbing materials of Examples 1-9 have a lower coefficient of thermal expansion, indicating better high-temperature resistance. Meanwhile, the Hast test results show that the composite absorbing materials of Examples 1-9 have better corrosion resistance in humid and hot environments, which is beneficial for the practical application of composite absorbing materials, with Example 1 exhibiting the best corrosion resistance.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite magnetic powder comprising a magnetic powder core, a heat-resistant layer wrapping the magnetic powder core, and a hydrophobic layer wrapping the heat-resistant layer, wherein the hydrophobic layer is prepared from a hydrophobic organic solvent, the heat-resistant layer is a silica coating layer, the silica coating layer is prepared from a silicon source, and 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 magnetic powder of claim 1 wherein the magnetic powder is a magnetic powder of a ferrite. The magnetic material of the magnetic powder core is one or more of rare earth cobalt-based soft magnetic material, carbonyl iron, ferrite, iron-silicon-aluminum alloy, or iron-silicon-chromium alloy.

3. The composite magnetic powder of claim 2 wherein the binder is a thermosetting resin. The magnetic powder core is a rare earth cobalt-based soft magnetic material, the D 50 ≤2.5 μm.

4. The composite magnetic powder of claim 1 wherein the magnetic powder is a ferrite powder. The hydrophobic organic solvent is one or more of hexamethyldisilazane, polydimethylsiloxane, or polymethylhydrosiloxane.

5. The composite magnetic powder of claim 1 wherein the magnetic powder is a ferrite powder. The silicon source is selected from tetramethyl orthosilicate, tetraethyl orthosilicate, ethyl orthosilicate, and tetrabutyl orthosilicate.

6. The composite magnetic powder according to any one of claims 1 to 5, wherein the binder resin is a resin having a glass transition temperature of 50°C or higher. The sum of the thicknesses of the heat-resistant layer and the hydrophobic layer is 30-60 nm.

7. The composite magnetic powder as claimed in any of the prior claims, characterized in that, The preparation thereof comprises the following steps: A. adding the magnetic powder core to a mixture of ethanol, water, and ammonia, mixing uniformly, adding a silicon source, and stirring to obtain a mixture A; B. adding (dropping) the hydrophobic organic solvent to the mixture A, stirring, and drying to obtain the composite magnetic powder.

8. The composite magnetic powder according to the preceding claim, characterized in that The volume ratio of the ethanol, water, and ammonia is 100:25:

3.

9. A wave-absorbing material based on the composite magnetic powder of any preceding claim, which is prepared from the following raw materials in parts by weight: composite magnetic powder 80-95 parts, conductive agent 0.1-1 part, epoxy resin 4-10 parts, and curing agent 5-12 parts.

10. The wave-absorbing material according to the preceding claim, characterized in that The epoxy resin is a high-temperature epoxy resin, which can be selected from phenolic epoxy resin, alicyclic epoxy resin, glycidyl-type multifunctional epoxy resin, and bisphenol S-type epoxy resin.

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