Electromagnetic wave-absorbing agent, wave-absorbing coating and preparation method of electromagnetic wave-absorbing agent

Abstract

The invention provides an electromagnetic wave-absorbing agent, a wave-absorbing coating and a preparation method thereof, and the preparation method of the electromagnetic wave-absorbing agent comprises the following steps: fully mixing FeSiAl with Ni (NO3) 2, Fe (NO3) 2 and Zn (NO3) 2 solutions, adding ammonia water into the solutions, and adjusting the pH value of the solutions; transferring the solution into a hydrothermal reaction kettle, heating at high temperature, cooling, cleaning and drying to obtain a product; the preparation method of the wave-absorbing coating comprises the following steps: preparing a coating component A, wherein the raw material of the component A contains an electromagnetic wave-absorbing agent; and taking a proper amount of curing agent as a component B, mixing the component A and the component B, and spraying to obtain the coating. Compared with the prior art, the method for preparing the electromagnetic wave absorbing agent is simple, the cost is low, the yield is large, the requirement for synthesis equipment is low, and the obtained electromagnetic wave absorbing agent has excellent wave absorbing performance. The preparation method of the wave-absorbing coating is simple and suitable for large-scale production, and the wave-absorbing coating has good wave-absorbing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave absorbing materials, and in particular to an electromagnetic absorbing agent, a absorbing coating and a preparation method thereof. Background Art

[0002] In recent years, the rapid development of high-frequency wireless communications has brought significant convenience to daily life and scientific research. However, this has also led to a series of challenges, such as electromagnetic pollution and electromagnetic compatibility. Long-term exposure to high-density electromagnetic environments can severely impact the nervous and endocrine systems of living organisms. Furthermore, stealth technology is crucial in the military, effectively reducing the probability of military equipment being detected by enemy detection systems. This allows for unexpected attacks, breakthroughs in defenses, and reconnaissance missions during warfare, significantly enhancing operational spurts and operational safety. Consequently, electromagnetic wave absorbing materials have garnered extensive attention and research in both civilian and military fields. This has further fueled the development of electromagnetic absorbers, and in practical applications, research on absorbing materials is increasingly focused on lightweight, broadband, and high absorption capabilities.

[0003] As a typical magnetic loss material, FeSiAl alloy is feasible for large-scale application due to its relatively low price. However, its impedance mismatch results in a narrow frequency band, so composite materials can be used to effectively improve its electromagnetic parameters. Numerous studies have also shown that preparing FeSiAl into composite materials can significantly improve its microwave absorption performance. For example, Zhang et al. used chemical vapor deposition to coat a layer of carbon on the surface of FeSiAl, resulting in the sample FeSiAl@C. This composite exhibits excellent microwave absorption at low frequencies, with a 4 mm sample achieving a reflection loss of -15.68 dB at 1.25 GHz. Zhang et al. used a sol-gel method to coat a layer of MgO on the surface of FeSiAl. They found that when the MgO loading was 7.5%, the sample achieved a reflection loss of -33 dB at 13 GHz. These results demonstrate that composite materials can effectively improve the microwave absorption properties of raw materials. However, existing technologies still have many shortcomings: 1. The preparation process is complex, time-consuming, low in yield, and high in cost. 2. FeSiAl alloy, as a magnetic loss material, has a single absorption mechanism and poor performance.

[0004] CN118905215A specifically discloses an electromagnetic absorber with a flaky core-shell structure and a preparation method thereof. The electromagnetic absorber with a flaky core-shell structure comprises the following raw materials in parts by weight: a core and a shell covering the core; the core comprises a flaky soft magnetic material, and the shell is a metal oxide-carbon composite shell; the thickness of the flaky soft magnetic material is 1-1.5 μm, and the aspect ratio of the flaky soft magnetic material is 60-100; the thickness of the metal oxide-carbon composite shell is 200-300 nm, and the mass proportion of the metal oxide in the metal oxide-carbon composite shell is 30%-50%; the metal elements in the metal oxide-carbon composite shell include transition magnetic metal elements, and the transition magnetic metal includes at least one of Mn, Fe, Co, Ni, Cu, and Zn. However, the metal oxide-carbon composite shell in the electromagnetic absorber described in CN118905215A is complex to prepare. The carbon involved in the shell requires high processing temperatures (up to 700-900°C), resulting in a low surface roughness, which is not conducive to electromagnetic wave absorption. When carbon-based absorbers are used in composite absorbers, the conductive particles cause electric field losses, which are known as conductivity losses. Summary of the Invention

[0005] The purpose of the present invention is to provide an electromagnetic absorber, an absorbing coating and a preparation method thereof in order to solve the above problems. Compared with a single FeSiAl absorbing material, the electromagnetic absorber has the characteristics of high absorption intensity and wide effective absorption bandwidth at a low thickness.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The first object of the present invention is to provide an electromagnetic wave absorbing agent, wherein the structure of the electromagnetic wave absorbing agent is soft magnetic nickel zinc ferrite coated with FeSiAl; the soft magnetic nickel zinc ferrite is NiZnFeO4; and the mass ratio of FeSiAl to NiZnFeO4 in the electromagnetic wave absorbing agent is (10-30):(1-4).

[0008] Furthermore, the electromagnetic wave absorbing agent is FeSiAl@NiZnFeO4 electromagnetic wave absorbing agent.

[0009] Furthermore, when the thickness of the electromagnetic absorber is 1 to 3 mm, the absorption is -40 to -60 dB at 8 to 20 GHz, and the effective bandwidth is 2 to 5 GHz.

[0010] Furthermore, FeSiAl@NiZnFeO4 with different morphologies can be obtained by adjusting the coating amount of NiZnFeO4.

[0011] A second object of the present invention is to provide a method for preparing an electromagnetic absorbing agent, the method comprising the following steps:

[0012] Step 1: Disperse FeSiAl powder in water, add Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2, stir to dissolve, then add ammonia water, adjust the pH to 10-11, and stir to obtain solution A;

[0013] Step 2: Transfer solution A obtained in step 1 to a hydrothermal reactor for reaction. After the reaction is completed, cool the solution, centrifuge the reaction product, take the solid component, wash it, dry it, and grind it to obtain an electromagnetic absorber, wherein the electromagnetic absorber is FeSiAl@NiZnFeO4 electromagnetic absorber.

[0014] Furthermore, in step 1, the mass ratio of FeSiAl powder to Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2 is (1-3):(0.1-0.3):(0.1-0.3):(0.1-0.3).

[0015] Further preferably, in step 1, the mass ratio of FeSiAl powder to Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2 is 1:0.2:0.2:0.2.

[0016] Furthermore, in step 1, the molar concentration of the added ammonia water is 13.38 mol / L.

[0017] Furthermore, in step 1, solution A is obtained after stirring for 30 minutes.

[0018] Furthermore, in step 2, the reaction is a hydrothermal reaction, the hydrothermal reaction temperature is 150-250° C., and the reaction time is 8-10 h.

[0019] Further preferably, in step 2, the hydrothermal reaction time is 9 hours.

[0020] Furthermore, in step 2, the centrifugal separation uses a high-speed centrifuge, the rotation speed used for the centrifugal separation is 1600-2500 r / min, and the processing time is 1-2 h.

[0021] Furthermore, in step 2, the cleaning is performed three times with distilled water and anhydrous ethanol, and the drying is performed in an oven at 60°C.

[0022] The principle behind the preparation method of the electromagnetic absorber disclosed herein is to deposit soft magnetic nickel-zinc ferrite onto the surface of FeSiAl using a hydrothermal reaction method, thereby forming a FeSiAl-coated FeSiAl. The electromagnetic properties of the product can be controlled by adjusting the amount of soft magnetic nickel-zinc ferrite coating. The losses associated with ferrite in composite absorber applications primarily include hysteresis loss, resonance loss, and eddy current loss.

[0023] A third object of the present invention is to provide an absorbing coating, wherein the raw materials of the absorbing coating include an electromagnetic absorbing agent; the raw materials of the absorbing coating also include one or more of an anti-settling agent, a dispersant, a defoaming agent, and a leveling agent; the raw materials of the absorbing coating also include a resin, a diluent, and a curing agent.

[0024] Furthermore, the mass ratio of the resin, diluent, electromagnetic absorber, anti-settling agent, dispersant, defoaming agent, leveling agent and curing agent is 100:100:550-560:0.7-1.2:0.2-0.3:0.2-0.3:0.7-1.2:10-20.

[0025] Further preferably, the mass ratio of the resin, electromagnetic absorber, diluent, anti-settling agent, dispersant, defoaming agent, leveling agent and curing agent is 63:61:350:1.6:1.6:0.7:0.7:11.

[0026] A fourth object of the present invention is to provide a method for preparing an absorbing coating, the method comprising the following steps:

[0027] Step 1: dissolving the resin in a diluent, adding one or more of an anti-settling agent, a dispersant, a defoaming agent, and a leveling agent, stirring evenly, then adding an electromagnetic absorber and dispersing evenly to obtain component A of the coating;

[0028] Step 2: Take a curing agent, called component B, add component B to component A and stir evenly to obtain a final coating. Spray the final coating onto the pretreated substrate. After the coating is dry, spray again until the target thickness is reached to obtain the absorbing coating.

[0029] Furthermore, in step 1, the diluent is butyl acetate, and the resin is hydroxypropyl resin.

[0030] Furthermore, in step 1, the anti-settling agent is selected from one or more of organic bentonite, fumed silica, modified hydrogenated castor oil, and modified polyurea N-methylpyrrolidone; the dispersant is a high molecular weight wetting and dispersing aid for solvent-based coatings; the defoamer is an organosilicon defoamer for a solvent system; and the leveling agent is an organosilicon leveling agent.

[0031] More preferably, the anti-settling agent is N-methylpyrrolidone modified polyurea.

[0032] Furthermore, in step 1, a high-speed disperser is used for dispersion, the speed of the high-speed disperser is 1600 r / min, and the dispersion time is 30 min-1 h.

[0033] Furthermore, in step 2, the curing agent is a hydroxypropyl curing agent.

[0034] Furthermore, in step 2, the spraying is performed by air spraying, the air spraying adopts a spray gun, the air pressure of the air spraying is 0.4-0.6 MPa, and the diameter of the spray gun is 1.3 mm.

[0035] Furthermore, in step 2, the substrate is a 300*300*5mm aluminum plate, and the pretreatment method is to use 80-150 mesh sandpaper to polish it in the same direction until the surface is rough, then wash it with butyl acetate three times and place it in an oven at 60°C to dry.

[0036] Furthermore, the target thickness of the coating is 1.0-1.1 mm.

[0037] The fifth object of the present invention is to provide an application of an absorbing coating, which is used for anti-interference of electronic equipment and electromagnetic protection of buildings and homes.

[0038] Compared with the prior art, the present invention has the following characteristics:

[0039] 1) Compared with a single FeSiAl absorbing material, the electromagnetic absorber prepared by the present invention uses NiZnFeO4 as a coating layer and FeSiAl as a core to form a unique core-shell structure. When electromagnetic waves are incident on the interior of the material, the absorbing material can convert most of the incident electromagnetic waves into heat energy and dissipate it into the external environment under the combined action of dielectric loss and magnetic loss. Due to the superposition of its multiple loss mechanisms, it has better reflection loss. These include resonance loss, eddy current loss, interface polarization and conductive loss. The different charges at the interface between NiZnFeO4 and FeSiAl lead to an interfacial polarization effect. In addition, the current will also propagate in FeSiAl, and during the propagation process, it will also be attenuated to varying degrees, giving it a conductive loss mechanism and high absorption intensity at low thickness. In addition, NiZnFeO4 can improve the matching impedance of FeSiAl, which can effectively increase the absorption bandwidth.

[0040] 2) The electromagnetic absorber prepared by the present invention can obtain FeSiAl@NiZnFeO4 with different morphologies by adjusting the coating amount of NiZnFeO4. The surface roughness of FeSiAl@NiZnFeO4 is controlled by controlling the amount of NiZnFeO4 particles attached to the FeSiAl surface. Increasing the surface roughness is beneficial to the absorption of electromagnetic waves. On the one hand, it can increase the number of scattering points. As the surface roughness increases, more tiny bumps and scattering points will form on the surface of the material. The scattering points can more effectively scatter and attenuate the incident electromagnetic waves, thereby improving the material's absorption performance. On the other hand, it can improve the impedance matching effect, allowing electromagnetic waves to more effectively enter the material and be absorbed.

[0041] 3) In the present invention, the FeSiAl@NiZnFeO4 electromagnetic absorber used to prepare the absorbing coating is prepared by a liquid phase method. The absorbing coating is then prepared by mixing the electromagnetic absorber with other raw materials and then forming a coating by air spraying. This method for preparing the absorbing coating is simple and low-cost, with a reaction temperature below 300°C. It does not require complex synthesis equipment and can be mass-produced to produce the excellent FeSiAl@NiZnFeO4 electromagnetic absorber (with an absorption of -40 to -60 dB at 8 to 20 GHz and an effective bandwidth of 2 to 5 GHz at a thickness of 1 to 3 mm). BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the X-ray diffraction pattern of FeSiAl@NiZnFeO4-1 prepared in Example 1 of the present invention;

[0043] Figure 2 This is a SEM photo of FeSiAl@NiZnFeO4-1 prepared in Example 1 of the present invention;

[0044] Figure 3 This is a SEM photo of FeSiAl@NiZnFeO4-2 prepared in Example 2 of the present invention;

[0045] Figure 4 This is a SEM photo of FeSiAl@NiZnFeO4-3 prepared in Example 3 of the present invention;

[0046] Figure 5 This is the reflection loss spectrum of FeSiAl@NiZnFeO4-1 prepared in Example 1 of the present invention;

[0047] Figure 6 This is the reflection loss spectrum of FeSiAl@NiZnFeO4-2 prepared in Example 2 of the present invention;

[0048] Figure 7 This is the reflection loss spectrum of FeSiAl@NiZnFeO4-3 prepared in Example 3 of the present invention;

[0049] Figure 8 This is a photo of the FeSiAl@NiZnFeO4 absorbing coating prepared in Example 4 of the present invention.

[0050] Figure 9 This is a graph showing the test results of the FeSiAl@NiZnFeO4 absorbing coating prepared in Example 4 using the arch method. DETAILED DESCRIPTION

[0051] The present invention is described in detail below with reference to specific embodiments, but is by no means intended to limit the present invention. Any features, such as preparation methods, materials, structures, or composition ratios, that are not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0052] The present invention discloses an electromagnetic absorber comprising soft magnetic nickel-zinc ferrite coated with FeSiAl, and a method for preparing the electromagnetic absorber and its absorbing coating. The method comprises the following steps: 1) thoroughly mixing FeSiAl with a solution of Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2 in a certain proportion, adding NH3·H2O solution to the solution, and adjusting the pH of the solution to 10-11. 2) transferring the solution to a hydrothermal reactor and heating it at high temperature for 9 hours. After the reactor cools to room temperature, the reaction product is removed, cleaned, and dried to obtain the product. The method for preparing the absorbing coating comprises the following steps: 1) preparing component A of the coating. A certain amount of diluent is added to an appropriate amount of resin and stirred until the resin is completely dissolved. An appropriate amount of additive is added to a beaker, stirred evenly, and then a certain amount of FeSiAl / NiZnFeO4 composite magnetic absorber is added. The mixture is evenly dispersed using a high-speed disperser to obtain component A of the coating. 2) mixing components A and B and spraying. Take an appropriate amount of curing agent, called component B, add component B to component A and stir evenly to prepare the final coating. Use air spray to spray the above coating onto the pretreated substrate. After the coating is surface dry, spray again until the target thickness is reached.

[0053] The method for preparing the electromagnetic wave absorbing agent of the present invention is simple, low-cost, high-yield, and requires few synthesis equipment, and the obtained electromagnetic absorber has excellent wave absorbing performance. The preparation method of the wave absorbing coating is simple and suitable for large-scale production and has good wave absorbing performance.

[0054] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0055] In the following examples, FeSiAl was purchased from Red Star Amorphous Materials Co., Ltd., model 1K101; the resin was ST1660 hydroxy acrylic resin, produced by Shanghai Huayi Fine Chemical Co., Ltd., with a hydroxyl value between 2.7% and 4.8% and a solid content between 56% and 69%; the anti-settling agent was purchased from BYK Additives (Shanghai) Co., Ltd., model BYK-410; the dispersant was purchased from BYK Additives (Shanghai) Co., Ltd., model BYK-161; the defoamer was purchased from BYK Additives (Shanghai) Co., Ltd., model BYK-077; the leveling agent was purchased from BYK Additives (Shanghai) Co., Ltd., model BYK-306; and the curing agent was a hydroxypropyl curing agent, purchased from Shanghai Huayi Fine Chemical Co., Ltd., model N3300.

[0056] Example 1

[0057] The present invention provides a method for preparing an electromagnetic wave absorbing agent (FeSiAl@NiZnFeO4 electromagnetic wave absorbing agent), comprising the following steps:

[0058] Step 1: Add 1g of FeSiAl powder to 15mL of distilled water and disperse evenly. Then, add 0.1g of Ni(NO3)2, 0.1g of Fe(NO3)2, and 0.1g of Zn(NO3)2. Continue stirring until the solids dissolve. While stirring, add a certain amount of ammonia (NH3·H2O solution) (13.38mol / L). The pH of the solution is controlled at 10.5 to obtain Solution A.

[0059] Step 2: Transfer Solution A obtained in Step 1 to a hydrothermal reactor, which was then transferred to an oven preheated to 200°C for 9 hours. After the reaction was complete, the reactor was removed and cooled to room temperature to obtain a reaction product. The solids were separated by centrifugation at 2000 rpm for 1 hour. The solids were then washed three times with distilled water and then with anhydrous ethanol, then dried in a 60°C oven for 3 hours. The dried product was ground in a mortar until no visible particles remained, yielding the FeSiAl@NiZnFeO4-1 electromagnetic absorber.

[0060] Example 2

[0061] The present invention provides a method for preparing an electromagnetic wave absorbing agent (FeSiAl@NiZnFeO4 electromagnetic wave absorbing agent), comprising the following steps:

[0062] Step 1: Add 1g of FeSiAl powder to 15mL of distilled water and disperse evenly. Then, add 0.2g of Ni(NO3)2, 0.2g of Fe(NO3)2, and 0.2g of Zn(NO3)2. Continue stirring until the solids dissolve. Then, add a certain amount of ammonia (NH3·H2O solution) (13.38mol / L) while stirring. The pH of the solution is controlled at 11 to obtain Solution A.

[0063] Step 2: Transfer Solution A obtained in Step 1 to a hydrothermal reactor, which was then transferred to an oven preheated to 250°C for 9 hours. After the reaction was complete, the reactor was removed and cooled to room temperature to obtain a reaction product. The product was centrifuged at 2200 rpm for 1.5 hours to separate the solids. The solids were then washed three times with distilled water and then three times with anhydrous ethanol, then dried in a 60°C oven for 4 hours. The dried product was ground in a mortar until no visible particles remained, yielding the FeSiAl@NiZnFeO4-2 electromagnetic absorber.

[0064] Example 3

[0065] The present invention provides a method for preparing an electromagnetic wave absorbing agent (FeSiAl@NiZnFeO4 electromagnetic wave absorbing agent), comprising the following steps:

[0066] Step 1: Add 1g of FeSiAl powder to 15mL of distilled water and disperse evenly. Then, add 0.3g of Ni(NO3)2, 0.3g of Fe(NO3)2, and 0.3g of Zn(NO3)2. Continue stirring until the solids dissolve. Then, add a certain amount of ammonia (NH3·H2O solution) (13.38mol / L) while stirring. The pH of the solution is controlled at 10.2 to obtain Solution A.

[0067] Step 2: Transfer Solution A obtained in Step 1 to a hydrothermal reactor, which was then transferred to an oven preheated to 250°C for 9 hours. After the reaction was complete, the reactor was removed and cooled to room temperature to obtain a reaction product. The product was centrifuged at 1800 rpm for 2 hours to separate the solids. The solids were then washed three times with distilled water and then with anhydrous ethanol, then dried in a 60°C oven for 3 hours. The dried product was ground in a mortar until no visible particles remained, yielding the FeSiAl@NiZnFeO4-3 electromagnetic absorber.

[0068] Example 4

[0069] The present invention provides a method for preparing a microwave absorbing coating (FeSiAl@NiZnFeO4 microwave absorbing coating), comprising the following steps:

[0070] Step 1: 63g of ST1660 hydroxypropylene resin was placed in a 250mL beaker, 61g of butyl acetate was added thereto and stirred thoroughly with a glass rod until the ST1660 hydroxypropylene resin was completely dissolved and the solution was clear. 1.6g of anti-settling agent and 1.6g of defoaming agent, 0.7g of leveling agent and 0.7g of dispersant were weighed respectively and added to the beaker and stirred evenly. Then, 350g of FeSiAl@NiZnFeO4 electromagnetic absorber (electromagnetic absorber prepared by the preparation method of Example 1) was added while stirring. After all the addition was completed, the mixture was transferred to a high-speed disperser and dispersed at 1600r / min for 45min to obtain component A.

[0071] Step 2: Take 11g of hydroxypropyl curing agent, called component B of the coating, add it to component A obtained in step 1 and stir evenly to obtain the coating. Take a 300*300*5mm aluminum plate, use 100-grit sandpaper to grind it in the same direction until the surface is rough, and use butyl acetate to wash away the aluminum chips on the surface. Then transfer the aluminum plate to a 60℃ oven for drying. Transfer the prepared coating to the hopper of a spray gun connected to a 0.5MPa air compressor with a spray gun diameter of 1.3mm. Use air spraying to spray the coating onto the aluminum plate cooled to room temperature. After the coating is dry, spray it again. After 9 sprayings, the coating thickness reaches 1mm, which is the prepared electromagnetic wave absorbing coating.

[0072] Figure 1 This is the X-ray diffraction pattern of FeSiAl@NiZnFeO4 obtained in Example 1 of the present invention. It can be seen that Example 1 retains the characteristic peaks of FeSiAl while adding characteristic peaks of NiZnFeO4 at 30°, 35°, and 62.5°, indicating that NiZnFeO4 has been successfully composited on FeSiAl.

[0073] Figure 2 This is a SEM image of FeSiAl@NiZnFeO4 prepared in Example 1 of the present invention. It can be seen that NiZnFeO4 has been successfully coated on FeSiAl. Unlike the smooth surface of FeSiAl, the surface of the composite FSA is relatively rough.

[0074] Figure 3 This is an SEM image of FeSiAl@NiZnFeO4 prepared in Example 2 of the present invention. It can be seen that the surface roughness increases after coating. Comparing Examples 1 and 2, it is demonstrated that the addition amounts of Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2 affect the micromorphology of FeSiAl@NiZnFeO.

[0075] Figure 4 This is an SEM image of FeSiAl@NiZnFeO4 prepared in Example 3. As the amount of Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2 added increases, the surface roughness increases further, and blocky and strip-shaped NiZnFeO4 can be clearly observed.

[0076] Figure 5 This is the reflection loss spectrum of FeSiAl@NiZnFeO4 prepared in Example 1. It can be seen that when the thickness is 1.5 mm, the absorption reaches -45.7 dB at 14.23 GHz, and the effective bandwidth reaches 3.3 GHz.

[0077] Figure 6This is the reflection loss spectrum of FeSiAl@NiZnFeO4 prepared in Example 2. It can be seen that at a thickness of 1.2 mm, an absorption of -51.49 dB can be achieved within 15.36 GHz, and the effective bandwidth is 4.11 GHz.

[0078] Figure 7 This is the reflection loss spectrum of FeSiAl@NiZnFeO4 prepared in Example 3. It can be seen that the reflection loss value of Example 3 with a thickness of 2.15 mm reaches -50 dB at 10 GHz, which also shows excellent ability to absorb electromagnetic waves.

[0079] Figure 8 This is a photo of the FeSiAl@NiZnFeO4 absorbing coating prepared in Example 4.

[0080] Figure 9 The results of the arch method test on the FeSiAl@NiZnFeO4 absorbing coating prepared in Example 4 show that its reflection loss is less than -10 dB in the 6.3-11.1 GHz range, indicating that it can absorb 90% of electromagnetic waves. The absorption bandwidth is 4.8 GHz, and the maximum absorption peak occurs at 8.5 GHz, with a maximum reflection loss of -13.3 dB.

[0081] Untreated sheet FSA (FeSiAl) has poor electromagnetic compatibility, resulting in a small reflection loss value in the range of 0.1-18 GHz. The reflection loss value of 1 mm FSA at 18 GHz is -20.37 dB, and the effective bandwidth is only 1.51 GHz.

[0082] When the coverage of NiZnFeO4 is low (Example 1), the reflection loss and effective absorption bandwidth are improved compared to the untreated sheet FSA. When the thickness is 1.5 mm, the absorption reaches -45.7 dB at 14.23 GHz. The effective bandwidth is also improved, which can effectively cover the frequency band of 12.3-15.6 GHz and reaches 3.3 GHz. This shows that compounding is an effective way to improve impedance matching.

[0083] When the coverage of NiZnFeO4 reaches the preferred level (Example 2), the sample can achieve an absorption of -51.49 dB within 15.36 GHz, with an effective bandwidth of 4.11 GHz and a coverable frequency band of 13.92-18 GHz.

[0084] However, as the loading amount is further increased (Example 3), the absorption performance may decrease. The 2.15 mm sample has a reflection loss value of -50 dB at 10 GHz, and still has excellent ability to absorb electromagnetic waves, but the bandwidth is only 2.73 GHz at this time, which is lower than that of the preferred sample. It is speculated that this may be because excessive NiZnFeO4 coverage causes impedance matching to be misaligned, resulting in performance degradation.

[0085] In the present invention, the reaction temperature is 150-250°C, and an excellent performance FeSiAl@NiZnFeO4 electromagnetic absorber can be prepared. When the thickness of the prepared FeSiAl@NiZnFeO4 electromagnetic absorber is 1-3 mm, the absorption is -40-60 dB at 8-20 GHz, and the effective bandwidth is 2-5 GHz.

[0086] The FeSiAl@NiZnFeO4 electromagnetic absorber of the present invention is prepared using a liquid-phase process. FeSiAl alloy is coated with NiZnFeO4. By adjusting the coating amount of NiZnFeO4, FeSiAl@NiZnFeO4 with different morphologies can be obtained. The resulting coated structure effectively controls the electromagnetic parameters, resulting in reduced reflection loss and increased effective absorption bandwidth. This method offers advantages such as simplicity, low cost, high yield, and minimal synthesis equipment requirements, making it suitable for large-scale industrial production.

[0087] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An electromagnetic wave absorbing agent, characterized in that: The structure of the electromagnetic wave absorbing agent is soft magnetic nickel-zinc ferrite coated with FeSiAl; The soft magnetic nickel-zinc ferrite is NiZnFeO4; The mass ratio of FeSiAl to NiZnFeO4 in the electromagnetic absorber is (10-30):(1-4).

2. The electromagnetic absorbing agent according to claim 1, characterized in that When the thickness of the electromagnetic absorber is 1 to 3 mm, the absorption is -40 to -60 dB at 8 to 20 GHz, and the effective bandwidth is 2 to 5 GHz.

3. A method for preparing the electromagnetic absorbing agent according to any one of claims 1 to 2, characterized in that: The preparation method comprises the following steps: Step 1: Disperse FeSiAl powder in water, add Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2, stir to dissolve, then add ammonia water, adjust the pH to 10-11, and stir to obtain solution A; Step 2: Transfer solution A obtained in step 1 to a hydrothermal reactor for reaction. After the reaction is completed, cool the solution, centrifuge the reaction product, take the solid component, wash it, dry it, and grind it to obtain an electromagnetic absorber, wherein the electromagnetic absorber is FeSiAl@NiZnFeO4 electromagnetic absorber.

4. The method for preparing the electromagnetic absorbing agent according to claim 3, wherein: In step 1, the mass ratio of FeSiAl powder to Ni(NO3)2, Fe(NO3)2, and Zn(NO3)2 is (1-3):(0.1-0.3):(0.1-0.3):(0.1-0.3); In step 1, the molar concentration of the added ammonia water is 13.38 mol / L; In step 1, solution A was obtained after stirring for 30 minutes.

5. The method for preparing the electromagnetic absorbing agent according to claim 3, characterized in that: In step 2, the reaction is a hydrothermal reaction, the hydrothermal reaction temperature is 150-250° C., and the reaction time is 8-10 h; The centrifugal separation in step 2 is performed at a speed of 1600-2500 r / min and for a time of 1-2 h.

6. A radar absorbing coating, characterized in that: The raw material of the absorbing coating comprises the electromagnetic absorbing agent according to any one of claims 1 to 2; The raw materials of the absorbing coating further include one or more of an anti-settling agent, a dispersant, a defoaming agent, and a leveling agent; The raw materials of the absorbing coating also include resin, diluent and curing agent.

7. The radar absorbing coating according to claim 6, characterized in that: The mass ratio of the resin, diluent, electromagnetic absorber, anti-settling agent, dispersant, defoamer, leveling agent and curing agent is 100:100:550-560:0.7-1.2:0.2-0.3:0.2-0.3:0.7-1.2:10-20.

8. A method for preparing an absorbing coating according to any one of claims 6 to 7, characterized in that: The preparation method comprises the following steps: Step 1: dissolving the resin in a diluent, adding one or more of an anti-settling agent, a dispersant, a defoaming agent, and a leveling agent, stirring evenly, then adding an electromagnetic absorber and dispersing evenly to obtain component A of the coating; Step 2: Take a curing agent, called component B, add component B to component A and stir evenly to obtain a final coating. Spray the final coating onto the pretreated substrate. After the coating is dry, spray again until the target thickness is reached to obtain the absorbing coating.

9. The method for preparing the radar absorbing coating according to claim 8, wherein: In step 1, the diluent is butyl acetate and the resin is hydroxypropyl resin; In step 1, the anti-settling agent is selected from one or more of organic bentonite, fumed silica, modified hydrogenated castor oil, and modified polyurea N-methylpyrrolidone; the dispersant is a high molecular weight wetting and dispersing aid for solvent-based coatings; the defoamer is an organosilicon defoamer for a solvent system; and the leveling agent is an organosilicon leveling agent.

10. The method for preparing the radar absorbing coating according to claim 8, wherein: In step 2, the curing agent is a hydroxypropyl curing agent.

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