High-frequency low-loss soft magnetic powder and preparation method thereof

Abstract

This application relates to the field of magnetic material composites, specifically to a high-frequency, low-loss soft magnetic powder and its preparation method. A method for preparing a high-frequency, low-loss soft magnetic powder includes the following steps: aluminum source preparation: urea is added to an aluminum salt solution and mixed to obtain an aluminum source solution; the aluminum salt in the aluminum salt solution includes at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; reaction coating: soft magnetic powder is added to the aluminum source solution and heated to react, obtaining coated soft magnetic powder; post-treatment: the coated soft magnetic powder is centrifuged, washed, dried, and then annealed to obtain high-frequency, low-loss soft magnetic powder. This application uses a heating reaction between aluminum salt and urea to generate boehmite nanosheets in situ on the surface of the soft magnetic powder. Annealing then eliminates internal stress, stably coating the soft magnetic powder surface with boehmite, thereby forming a large resistance between the conductive metal particles, effectively blocking the eddy current path induced by the high-frequency alternating magnetic field, thus significantly reducing eddy current loss.

Description

Technical Field

[0001] This application relates to the field of magnetic material composites, specifically to a high-frequency, low-loss soft magnetic powder and its preparation method. Background Technology

[0002] Soft magnetic composite materials (SMCs) typically possess characteristics such as high saturation magnetization, good DC superposition characteristics, and relatively high operating frequencies, making them key materials for the design and development of high-frequency, miniaturized magnetic components. The fabrication process of SMCs mainly includes steps such as surface insulation modification of metal soft magnetic powder, mixing and granulation with a binder, pressing, curing, and annealing. Specifically, forming an insulating layer on the surface of the metal soft magnetic powder through appropriate processes can effectively reduce interparticle eddy current losses in the SMC. Efficient surface insulation processes for metal soft magnetic powder are a prerequisite for improving the high-frequency performance of SMCs.

[0003] Currently, common methods for surface insulation modification of soft magnetic powders include inorganic coating and organic coating. Inorganic coating generally involves treating the soft magnetic powder with a strong oxidizing agent to form an oxide passivation film on the powder surface. Organic coating typically uses organosilicon materials, forming an organosilicon coating layer on the surface of the soft magnetic powder through a physicochemical reaction. For inorganic coating, the sheet-like soft magnetic powder is easily corroded during oxidation passivation with strong oxides, resulting in a significant decrease in magnetic permeability. For organic coating, the coating layer has poor adhesion and is prone to failure when exposed to organic solvents. Summary of the Invention

[0004] To address the technical problem of poor performance in existing soft magnetic coatings, this application provides a high-frequency, low-loss soft magnetic powder and its preparation method. This method improves the bonding force between the two by generating a boehmite coating layer in situ on the surface of the soft magnetic powder, thereby producing high-frequency, low-loss soft magnetic powder.

[0005] In a first aspect, this application provides a method for preparing high-frequency, low-loss soft magnetic powder, employing the following technical solution: A method for preparing high-frequency, low-loss soft magnetic powder includes the following steps: Aluminum source preparation: Urea is added to an aluminum salt solution and mixed to obtain an aluminum source solution; the aluminum salt in the aluminum salt solution includes at least one of aluminum sulfate, aluminum nitrate, and aluminum chloride; Reaction coating: Soft magnetic powder is added to the aluminum source solution and heated to react, thereby obtaining coated soft magnetic powder; Post-processing: The coated soft magnetic powder is centrifuged, washed, dried, and then annealed to obtain high-frequency, low-loss soft magnetic powder.

[0006] By employing the above-mentioned technical solution, the aluminum salt is heated and hydrolyzed to make the solution acidic. At this point, the aluminum element mainly exists in the form of positively charged aluminum monomers. These positively charged aluminum monomers are electrostatically adsorbed onto the surface of the magnetic powder. The addition of urea serves as a controllable, slow-release alkali source, continuously increasing the pH of the system after decomposition. The positively charged aluminum monomers continuously dehydrate and condense on the surface of the magnetic powder, thus forming a typical boehmite nanosheet structure. Then, annealing removes the interlayer water from the boehmite nanosheet structure to eliminate the internal stress generated during the preparation process, completing the stable coating of boehmite. Boehmite is an excellent electrical insulator; it forms a huge resistance between conductive metal particles, effectively blocking the eddy current path induced by the high-frequency alternating magnetic field, thereby significantly reducing eddy current losses.

[0007] This application involves heating aluminum salts and urea to generate boehmite nanosheets in situ on the surface of soft magnetic powder. Then, annealing is used to eliminate internal stress and stably coat the surface of the soft magnetic powder with boehmite, thereby forming a huge resistance between the conductive metal particles. This effectively blocks the eddy current path induced by the high-frequency alternating magnetic field, thus significantly reducing eddy current loss.

[0008] Preferably, the molar ratio of urea to aluminum ions in the aluminum source solution is 3-5:1.

[0009] By adopting the above technical solution, when the urea content is too low, insufficient urea hydrolysis leads to OH... - Insufficient supply leads to a decrease in precipitation rate, preventing aluminum ions from being completely converted into boehmite, resulting in discontinuous boehmite coatings. When the urea content is too high, it causes an excessively high pH, ​​promoting the formation of soluble aluminates, coarsening of boehmite crystals, and a decline in coating quality. Therefore, after extensive research and experimental verification, the applicant has finally determined that the molar ratio of urea to aluminum ions in the aluminum source solution of this application should be as described above.

[0010] Preferably, in the aluminum source preparation step, urea and additives are added to the aluminum salt solution and mixed to obtain the aluminum source solution; the additives include at least one of ammonium polyacrylate and citric acid, or at least one of titanate coupling agent and transition metal salt, or KH-550; the transition metal salts include at least one of ferric nitrate and chromium nitrate.

[0011] By employing the above technical solutions, anionic ammonium polyacrylate is adsorbed onto the surface of aluminum colloidal particles, enhancing electrostatic repulsion. The polymer chains also form a steric hindrance layer, reducing the particle size of the aluminum colloidal particles and thus reducing the coating thickness deviation. Aluminum ions form a complex with citric acid, which can slowly release aluminum ions, inhibiting explosive hydrolysis, eliminating pinhole defects, and reducing coating porosity. Titanate coupling agents and KH-550 can both strengthen the interfacial bonding between boehmite and soft magnetic powder, improving the coating effect. Transition metal salts can strengthen the crystal lattice; iron nitrate doping inhibits crystal growth through lattice distortion. Chromium nitrate doping forms a solid solution, improving thermal stability.

[0012] Preferably, the additives are ammonium polyacrylate and citric acid.

[0013] By employing the above technical solution, when ammonium polyacrylate and citric acid are mixed and added, citric acid forms a complex with aluminum ions, and ammonium polyacrylate is adsorbed onto the complex, further enhancing the effects of electrostatic repulsion and steric hindrance, thereby inhibiting aggregation and promoting uniform nucleation. The carboxyl groups on citric acid bind to the hydroxyl groups on the surface of the soft magnetic powder, enhancing pre-anchoring. Ammonium polyacrylate forms hydrogen bonds with the hydroxyl groups on the boehmite surface, reducing surface energy.

[0014] Preferably, the additive is a titanate coupling agent and a transition metal salt.

[0015] By adopting the above technical solution, the titanate coupling agent is hydrolyzed into Ti-OH. The transition metal ions (iron ions or chromium ions) in the transition metal salt replace aluminum ions and enter the crystal lattice. Ti-OH condenses with it to form Ti-O-Fe or Ti-O-Cr bonds, which inhibits crystal lattice distortion and promotes interfacial chemical bridging between soft magnetic powder and boehmite coating layer, thereby improving the coating effect.

[0016] Preferably, the aluminum salt is aluminum sulfate.

[0017] By employing the above technical solutions, aluminum sulfate hydrolyzes slowly and uniformly upon heating. In contrast, aluminum chloride hydrolyzes too quickly, resulting in explosive nucleation and uneven grain size. Aluminum nitrate exhibits weak complexation, causing fluctuations in localized aluminum ion concentration and variations in coating thickness. A comparison of the three reveals that aluminum sulfate performs better.

[0018] Preferably, the soft magnetic powder is pretreated soft magnetic powder, and the preparation method of the pretreated soft magnetic powder includes the following steps: heating the soft magnetic powder to reduce it with hydrogen to obtain the pretreated soft magnetic powder.

[0019] By employing the above technical solution, hydrogen reduction of soft magnetic powder in advance can effectively remove the surface oxide layer, eliminate interstitial atoms in the crystal lattice, and promote grain recrystallization, thereby repairing defects. After hydrogen reduction, the active Fe atoms in the soft magnetic powder are exposed, making it easier to form Fe-O-Al bonds, eliminating interfacial stress sources, resulting in a high density of uniform nucleation sites and facilitating the formation of a continuous coating layer.

[0020] Preferably, the method for preparing the pretreated soft magnetic powder includes the following steps: heating the soft magnetic powder to undergo hydrogen reduction, and then heat-treating it in a phosphoric acid solution to obtain the pretreated soft magnetic powder.

[0021] By employing the above technical solution, a three-layer structure of FePO4-Fe2P-Fe can be formed by heat treatment with phosphoric acid solution after hydrogen reduction. The outer FePO4 layer blocks electron migration, the middle Fe2P layer buffers thermal expansion mismatch, and the Fe matrix maintains high magnetic permeability. The Fe2P nanoparticles formed by phosphoric acid treatment generate pinning forces at grain boundaries, inhibiting the growth of crystals during high-temperature sintering. The FePO4 surface contains a large number of P-OH groups, which undergo dehydration condensation with boehmite, improving the bonding quality of the coating layer.

[0022] In addition, the heat treatment of phosphoric acid solution needs to be carried out after hydrogen reduction. If it is carried out before hydrogen reduction, the phosphate will decompose and become ineffective during hydrogen reduction, and the hydrogen will reduce the phosphate ions to PH3 gas. PH3 gas will accumulate at the interface and easily cause interface delamination.

[0023] Preferably, the preparation method of the pretreated soft magnetic powder includes the following steps: acid washing the soft magnetic powder, followed by heating for hydrogen reduction to obtain the pretreated soft magnetic powder.

[0024] By employing the above technical solution, pre-treatment with acid pickling can dissolve chemically inert oxides, eliminate machining damage layers, and construct active surface microstructures. Hydrogen reduction is then used to remove impurities that acid pickling cannot reach and repair lattice defects. The combination of these two methods generates a kinetic acceleration effect, improving reduction uniformity.

[0025] Secondly, this application provides a high-frequency, low-loss soft magnetic powder, employing the following technical solution: A high-frequency, low-loss soft magnetic powder is prepared by the above-mentioned method for preparing high-frequency, low-loss soft magnetic powder.

[0026] In summary, this application has the following beneficial effects: 1. In this application, aluminum salt and urea are heated to react and generate boehmite nanosheets in situ on the surface of soft magnetic powder. Then, the internal stress is eliminated by annealing and boehmite is stably coated on the surface of soft magnetic powder. This creates a huge resistance between conductive metal particles, effectively blocking the eddy current path induced by high-frequency alternating magnetic field, thereby significantly reducing eddy current loss. 2. This application adds additives to the aluminum source solution, which helps the boehmite structure to form on the soft magnetic powder and further improves the bonding force between the two; 3. This application pre-treats the soft magnetic powder to remove oxides on the surface of the soft magnetic powder, improves the reactivity of the soft magnetic powder, and helps to form a boehmite coating layer. Detailed Implementation

[0027] The raw materials in this application include the following: Soft magnetic powder: including pure iron powder, FeSiCr powder, nanocrystalline powder, FeSiAl powder, ferrite powder, etc. This application only uses pure iron powder as an example. Ammonium polyacrylate: Commercially available product with CAS number 9003-03-6; The present application will be further described in detail below with reference to embodiments and comparative examples.

[0028] Example 1

[0029] A method for preparing high-frequency, low-loss soft magnetic powder, characterized by comprising the following steps: Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution; Reaction coating: 25g of soft magnetic powder was added to the aluminum source solution and heated at 150℃ for 10h to obtain coated soft magnetic powder; Post-processing: The coated soft magnetic powder was centrifuged, washed, and dried, and then annealed in nitrogen at 350°C for 1 hour to obtain high-frequency, low-loss soft magnetic powder.

[0030] Example 2-3

[0031] Examples 2-3 are based on the preparation method of Example 1, but the concentration of urea is adjusted as shown in Table 1.

[0032] Comparative Example 1 Comparative Example 1 is soft magnetic powder that has not undergone any treatment.

[0033] Performance testing The high-frequency, low-loss soft magnetic powders of Examples 1-3 and Comparative Example 1 were subjected to the following performance tests, and the test results are shown in Table 1.

[0034] 1. Service life The total loss of high-frequency, low-loss soft magnetic powder was determined according to IEC 60404-6.

[0035] 2. Creep resistance The permeability A of the high-frequency low-loss soft magnetic powder at 1 kHz is determined according to ASTM A342, and the permeability B of the high-frequency low-loss soft magnetic powder at 10 MHz is determined according to IEC 62333-3. Then the permeability retention rate at 10 MHz is (B / A)*100%.

[0036] Table 1. Urea concentration and performance test results for Examples 1-3 and Comparative Example 1

[0037] Referring to Table 1, comparing Examples 1-3 and Comparative Example 1, it can be seen that coating the surface of soft magnetic powder with boehmite can effectively improve the performance of the soft magnetic powder. The reason is that boehmite can be generated in situ on the surface of the soft magnetic powder using aluminum sulfate and urea, thus forming a boehmite coating layer. Since boehmite is an excellent electrical insulator, it creates a huge resistance between conductive metal particles, effectively blocking the eddy current path induced by the high-frequency alternating magnetic field, thereby significantly reducing eddy current losses.

[0038] As the concentration of urea increases, the performance of the high-frequency, low-loss soft magnetic powder initially rises and then falls. This is because, with increasing urea concentration, the OH groups produced by urea hydrolysis... - As the pH increases, aluminum ions gradually transform into boehmite, forming a continuous coating layer, thereby improving the performance of the high-frequency, low-loss soft magnetic powder. However, if the pH exceeds a certain range, it leads to excessively high pH, ​​promoting the formation of soluble aluminates, coarsening of the boehmite crystals, and a decrease in coating quality, thus reducing the performance of the high-frequency, low-loss soft magnetic powder.

[0039] Comparing Examples 1-3, Example 1 showed the best performance; therefore, Example 1 is preferred.

[0040] Examples 4-6

[0041] Example 4 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea and 3 g of ammonium polyacrylate to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0042] Example 5 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea and 0.05 mol of citric acid to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0043] Example 6 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol urea, 3 g ammonium polyacrylate and 0.05 mol citric acid to 1 L aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0044] The high-frequency, low-loss soft magnetic powders from Examples 4-6 were subjected to the performance tests described above, and the test results are shown in Table 2.

[0045] Table 2. Types of adjuvants and performance test results for Examples 1 and 4-6.

[0046] Referring to Table 2, a comparison of Examples 1 and 4-6 shows that adding ammonium polyacrylate or citric acid alone, or a mixture of ammonium polyacrylate and citric acid, further improves the performance of the high-frequency, low-loss soft magnetic powder when preparing the aluminum source solution. This is because anionic ammonium polyacrylate adsorbs onto the surface of the aluminum colloidal particles, enhancing electrostatic repulsion. The polymer chains also form a steric hindrance layer, reducing the particle size of the aluminum colloidal particles and thus reducing the coating thickness deviation. Aluminum ions form a complex with citric acid, which slowly releases aluminum ions, inhibiting explosive hydrolysis, eliminating pinhole defects, and reducing coating porosity.

[0047] When ammonium polyacrylate and citric acid are added together, citric acid forms a complex with aluminum ions, and ammonium polyacrylate adsorbs onto the complex, further enhancing the effects of electrostatic repulsion and steric hindrance, thereby inhibiting aggregation and promoting uniform nucleation. The carboxyl groups on citric acid bind to the hydroxyl groups on the surface of the soft magnetic powder, enhancing pre-anchoring. Ammonium polyacrylate forms hydrogen bonds with the hydroxyl groups on the boehmite surface, reducing the surface energy.

[0048] Examples 7-12

[0049] Example 7 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea and 10 g of titanate coupling agent to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0050] Example 8 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea and 10 g of KH-550 to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0051] Example 9 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea and 0.4 g of ferric nitrate to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0052] Example 10 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea and 0.4 g of chromium nitrate to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0053] Example 11 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol urea, 10 g titanate coupling agent and 0.4 g ferric nitrate to 1 L aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0054] Example 12 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol urea, 10 g KH-550 and 0.4 g ferric nitrate to 1 L aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution.

[0055] The high-frequency, low-loss soft magnetic powders from Examples 7-12 were subjected to the performance tests described above, and the test results are shown in Table 3.

[0056] Table 3. Types of adjuvants and performance test results for Examples 1 and 7-12.

[0057] Referring to Table 3, a comparison of Examples 1 and 7-12 shows that when preparing the aluminum source solution, adding titanate coupling agent, KH-550, ferric nitrate, chromium nitrate alone, or a mixture of titanate coupling agent and ferric nitrate, can further improve the effect of the high-frequency, low-loss soft magnetic powder. However, adding a mixture of KH-550 and ferric nitrate tends to cause mutual interference, which in turn affects the effect of the high-frequency, low-loss soft magnetic powder.

[0058] The reason is that both titanate coupling agents and KH-550 can strengthen the interfacial bonding between boehmite and soft magnetic powder, improving the coating effect. Transition metal salts can strengthen the crystal lattice; iron nitrate doping, in particular, inhibits crystal growth through lattice distortion. Chromium nitrate doping forms a solid solution, improving thermal stability.

[0059] The titanate coupling agent hydrolyzes into Ti-OH, and the iron ions in ferric nitrate replace aluminum ions in the crystal lattice. Ti-OH condenses with it to form Ti-O-Fe bonds, which inhibits lattice distortion and promotes interfacial chemical bridging between soft magnetic powder and boehmite coating layer, thereby improving the coating effect.

[0060] KH-550 hydrolyzes into Si-OH and -NH2. Ferric nitrate combines with -NH2 to form a complex precipitate, which blocks the surface of the soft magnetic powder, reduces the nucleation sites of boehmite, and leads to uneven coating.

[0061] Examples 13-14

[0062] Example 13 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum nitrate solution (aluminum nitrate concentration 0.2 mol / L) and mix to obtain aluminum source solution.

[0063] Example 14 is based on the preparation method of Example 1, but the steps for preparing the aluminum source are adjusted as follows: Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum chloride solution (aluminum chloride concentration 0.2 mol / L) and mix to obtain aluminum source solution.

[0064] The high-frequency, low-loss soft magnetic powders from Examples 13-14 were subjected to the performance tests described above, and the test results are shown in Table 4.

[0065] Table 4. Types of aluminum salts and performance test results for Examples 1 and 13-14.

[0066] Referring to Table 4, a comparison of Examples 1 and 13-14 shows that aluminum sulfate is the most effective of the three aluminum salts. This is because aluminum sulfate hydrolyzes slowly and uniformly upon heating. In contrast, aluminum chloride hydrolyzes too quickly, resulting in explosive nucleation and uneven grain size. Aluminum nitrate exhibits weak complexation, leading to fluctuations in local aluminum ion concentration and variations in coating thickness. A comparison of the three reveals that aluminum sulfate is the most effective.

[0067] Examples 15-19

[0068] Example 15 is based on the preparation method of Example 1, but the preparation method of high-frequency low-loss soft magnetic powder is adjusted as follows: Pretreatment: The soft magnetic powder was heated to undergo hydrogen reduction (450℃, 3h) to obtain pretreated soft magnetic powder; Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution; Reaction coating: 25g of pretreated soft magnetic powder was added to the aluminum source solution and heated at 150℃ for 10h to obtain coated soft magnetic powder.

[0069] Example 16 is based on the preparation method of Example 1, but the preparation method of high-frequency low-loss soft magnetic powder is adjusted as follows: Pretreatment: The soft magnetic powder was heated to undergo hydrogen reduction (450℃, 3h), and then impregnated in 0.5mol / L phosphoric acid solution at 60℃ for 10min to obtain pretreated soft magnetic powder; Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution; Reaction coating: 25g of pretreated soft magnetic powder was added to the aluminum source solution and heated at 150℃ for 10h to obtain coated soft magnetic powder.

[0070] Example 17 is based on the preparation method of Example 1, but the preparation method of high-frequency low-loss soft magnetic powder is adjusted as follows: Pretreatment: The soft magnetic powder was immersed in 0.5 mol / L phosphoric acid solution at 60℃ for 10 min, and then heated for hydrogen reduction (450℃, 3 h) to obtain pretreated soft magnetic powder; Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution; Reaction coating: 25g of pretreated soft magnetic powder was added to the aluminum source solution and heated at 150℃ for 10h to obtain coated soft magnetic powder.

[0071] Example 18 is based on the preparation method of Example 1, but the preparation method of high-frequency low-loss soft magnetic powder is adjusted as follows: Pretreatment: The soft magnetic powder was acid-washed in 10% hydrochloric acid solution for 20 min, and then heated for hydrogen reduction (450℃, 3 h) to obtain pretreated soft magnetic powder; Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution; Reaction coating: 25g of pretreated soft magnetic powder was added to the aluminum source solution and heated at 150℃ for 10h to obtain coated soft magnetic powder.

[0072] Example 19 is based on the preparation method of Example 1, but the preparation method of high-frequency low-loss soft magnetic powder is adjusted as follows: Pretreatment: The soft magnetic powder was acid-washed in 10% hydrochloric acid solution for 20 min, then heated for hydrogen reduction (450℃, 3 h), and then immersed in 0.5 mol / L phosphoric acid solution at 60℃ for 10 min to obtain pretreated soft magnetic powder; Aluminum source preparation: Add 0.8 mol of urea to 1 L of aluminum sulfate solution (aluminum sulfate concentration 0.1 mol / L) and mix to obtain aluminum source solution; Reaction coating: 25g of pretreated soft magnetic powder was added to the aluminum source solution and heated at 150℃ for 10h to obtain coated soft magnetic powder.

[0073] The high-frequency, low-loss soft magnetic powders of Examples 15-19 were subjected to the above performance tests, and the test results are shown in Table 5.

[0074] Table 5 Performance test results for Examples 1 and 15-19

[0075] Referring to Table 5, a comparison of Examples 1 and 15-19 shows that pre-reduction of the soft magnetic powder with hydrogen can effectively improve the performance of the high-frequency, low-loss soft magnetic powder. This is because pre-reduction with hydrogen effectively removes the surface oxide layer, eliminates interstitial atoms in the lattice, and allows for grain recrystallization, thereby repairing defects. After hydrogen reduction, the active Fe atoms in the soft magnetic powder are exposed, making it easier to form Fe-O-Al bonds, eliminating interfacial stress sources, resulting in a high density of uniform nucleation sites and facilitating the formation of a continuous coating layer.

[0076] Heat treatment with phosphoric acid solution after hydrogen reduction can further improve the performance of high-frequency, low-loss soft magnetic powder. This is because heat treatment with phosphoric acid solution after hydrogen reduction forms a FePO4-Fe2P-Fe three-layer structure. The outer FePO4 layer blocks electron migration, the middle Fe2P layer buffers thermal expansion mismatch, and the Fe matrix maintains high magnetic permeability. The Fe2P nanoparticles formed by phosphoric acid treatment generate pinning forces at grain boundaries, inhibiting grain growth during high-temperature sintering. The abundant P-OH groups on the FePO4 surface undergo dehydration condensation with boehmite, improving the bonding quality of the coating layer.

[0077] The heat treatment of phosphoric acid solution needs to be carried out after hydrogen reduction. If it is carried out before hydrogen reduction, the phosphate will decompose and become ineffective during hydrogen reduction, and the hydrogen will reduce the phosphate ions to PH3 gas. The PH3 gas will accumulate at the interface and easily cause interface delamination.

[0078] Acid washing before hydrogen reduction can also improve the performance of high-frequency, low-loss soft magnetic powder. This is because pre-acid washing dissolves chemically inert oxides, eliminates machining damage layers, and builds active surface microstructures. Then, hydrogen reduction removes impurities that acid washing cannot reach and repairs lattice defects. The combination of these two processes generates a kinetic acceleration effect, improving reduction uniformity.

[0079] Therefore, acid washing before hydrogen reduction and heat treatment with phosphoric acid solution after hydrogen reduction yield better results.

[0080] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing high-frequency, low-loss soft magnetic powder, characterized in that, Includes the following steps: Aluminum source preparation: Add urea to the aluminum salt solution and mix to obtain the aluminum source solution; The aluminum salt in the aluminum salt solution includes at least one of aluminum sulfate, aluminum nitrate and aluminum chloride; Reaction coating: Soft magnetic powder is added to the aluminum source solution and heated to react, thereby obtaining coated soft magnetic powder; Post-processing: The coated soft magnetic powder is centrifuged, washed, dried, and then annealed to obtain high-frequency, low-loss soft magnetic powder.

2. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 1, characterized in that: The molar ratio of urea to aluminum ions in the aluminum source solution is 3-5:

1.

3. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 1, characterized in that: In the aluminum source preparation step, urea and additives are added to the aluminum salt solution and mixed to obtain the aluminum source solution; the additives include at least one of ammonium polyacrylate and citric acid, or at least one of titanate coupling agent and transition metal salt, or KH-550; the transition metal salts include at least one of ferric nitrate and chromium nitrate.

4. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 3, characterized in that: The additives are ammonium polyacrylate and citric acid.

5. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 3, characterized in that: The additives are titanate coupling agents and transition metal salts.

6. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 1, characterized in that: The aluminum salt is aluminum sulfate.

7. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 1, characterized in that: The soft magnetic powder is a pretreated soft magnetic powder, and the preparation method of the pretreated soft magnetic powder includes the following steps: heating the soft magnetic powder to reduce it with hydrogen to obtain the pretreated soft magnetic powder.

8. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 7, characterized in that: The preparation method of the pretreated soft magnetic powder includes the following steps: heating the soft magnetic powder to reduce it with hydrogen, and then heat-treating it in a phosphoric acid solution to obtain the pretreated soft magnetic powder.

9. The method for preparing high-frequency, low-loss soft magnetic powder according to claim 7, characterized in that: The preparation method of the pretreated soft magnetic powder includes the following steps: acid washing the soft magnetic powder, followed by heating for hydrogen reduction to obtain the pretreated soft magnetic powder.

10. A high-frequency, low-loss soft magnetic powder, characterized in that: It is prepared by the method of any one of claims 1-9 for preparing high-frequency low-loss soft magnetic powder.

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