Double-layer oxide insulation coated amorphous magnetic powder core and preparation method thereof

Abstract

The invention discloses a double-layer oxide insulation coated amorphous magnetic powder core and a preparation method thereof, and the preparation method comprises the following steps: (1) adding amorphous magnetic powder into an acidic potassium permanganate aqueous solution, stirring, filtering after reaction, cleaning, and drying to obtain single-layer coated passivated magnetic powder B; (2) adding the magnetic powder B into a tetraethoxysilane-ethanol solution, stirring for hydrolysis reaction under an alkaline condition, and then cleaning and drying to obtain double-layer oxide coated magnetic powder C; (3) adding the magnetic powder C into a resin acetone solution, stirring until acetone is completely volatilized, carrying out vacuum drying, and passing through a sieve of-40 to + 120 meshes to obtain magnetic powder D; and (4) pressing and annealing to obtain the double-layer oxide insulation coated amorphous magnetic powder core. According to the method, the coating method that acidic potassium permanganate in-situ passivation is combined with SiO2 is adopted, the electromagnetic performance of the magnetic powder core is improved, and the magnetic powder core has the high-voltage breakdown resistance characteristic and the high-temperature stability.

Description

Technical Field

[0001] The present invention relates to the technical field of amorphous soft magnetic powder cores, and specifically, to a double-layer oxide insulated coated amorphous powder core and a method for preparing the same. Background Art

[0002] A powder core is a metal matrix composite material prepared by using soft magnetic powder as a raw material, compounding it with an insulating medium, and adopting a powder metallurgy process. It is commonly used to make components such as inductors, filters, and chokes, and is widely applied in fields such as communication, computers, power electronics, and national defense. With the rapid development of the electronics industry, the operating frequency of powder cores has gradually developed from kHz to MHz. However, under high-frequency conditions, the eddy current effect is significantly enhanced, resulting in large eddy current losses, thus limiting the application of powder cores. To solve this problem, using amorphous magnetic powder with high resistivity as the powder core material has become an ideal choice for reducing high-frequency losses.

[0003] Currently, phosphating, as a common surface treatment method, is widely used in the inorganic insulation coating of powder cores. However, since amorphous soft magnetic powder does not have the grain boundary structure and crystal defects of traditional alloys, it has strong corrosion resistance, making it difficult to form a continuous and dense phosphating insulation layer on its surface, thus greatly limiting the development and application of amorphous powder cores. To solve the above problems, the Chinese invention patent with the publication number CN118430959A discloses an insulated coated powder core and a method for preparing the same. This method passivates amorphous magnetic powder multiple times with phosphoric acid aqueous solutions with a low to high concentration gradient, slows down the nucleation rate of the phosphating layer, and improves the uniformity of the phosphating coating layer. The Chinese invention patent with the publication number CN115475935A discloses a method for preparing an iron-based soft magnetic composite powder and the iron-based soft magnetic composite powder. This method first generates a phosphate layer on the powder surface with a phosphoric acid solution, and then continues to treat it with a mixed solution of potassium permanganate and phosphoric acid to obtain an insulating protective layer with a gradient distribution of phosphate and oxide. However, the disadvantage of the phosphoric acid insulation layer is its poor thermal stability. Usually, partial powdering occurs after 200 °C, and as the temperature further increases, the phosphating layer will gradually be damaged.

[0004] At the same time, the amorphous magnetic powder can also be insulated and coated by physical methods to form an insulating layer on its surface. For example, the Chinese invention patent with the publication number CN115064331A discloses a powder core and a method for preparing the same. This method coats a SiO 2 insulating layer on the surface of amorphous magnetic powder, and the thickness of the insulating layer is 20 - 250 nm. Increasing the heat treatment temperature of the powder core can effectively release the internal stress during the pressing process, thereby reducing the hysteresis loss. However, since the SiO 2 particles do not chemically bond with the surface of the amorphous magnetic powder, but combine with the magnetic powder through intermolecular forces, the SiO2 The insulating layer is not tightly combined with the magnetic powder. In order to enable SiO 2 particles to better combine with the amorphous magnetic powder substrate, the Chinese invention patent with the publication number CN115424854A provides a magnetic powder core and a preparation method thereof. This method first generates a phosphoric acid layer on the surface of the amorphous magnetic powder using phosphoric acid, and then generates a SiO 2 insulating layer outside the phosphated layer by hydrolysis of sodium silicate, finally forming a phosphate / SiO 2 double-layer coating structure. However, as mentioned above, the phosphoric acid layer will gradually decompose above 200 °C; at the same time, due to the weak dipole interaction between phosphate ions and SiO 2 molecules, the combination of SiO 2 with the amorphous magnetic powder is still not tight enough.

[0005] Therefore, how to improve the insulation coating effect of amorphous magnetic powder, prepare a high-performance insulation coating layer, and thus improve the magnetic properties of the amorphous magnetic powder core has become a key problem to be solved urgently at present. Summary of the Invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a double-layer oxide insulation-coated amorphous magnetic powder core and a preparation method thereof.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A preparation method of a double-layer oxide insulation-coated amorphous magnetic powder core includes the following steps:

[0009] (1) Passivation of amorphous magnetic powder: Add amorphous magnetic powder to an acidic potassium permanganate aqueous solution and stir. After the reaction ends, filter, wash, and dry to obtain passivated magnetic powder B with a single-layer coating;

[0010] (2) SiO 2 coating: Add magnetic powder B to a tetraethyl orthosilicate-ethanol solution, and under alkaline conditions, stir for hydrolysis reaction. After that, wash and dry to obtain magnetic powder C with a double-layer oxide coating;

[0011] (3) Organic coating and granulation: Add magnetic powder C to a resin acetone solution, stir until the acetone completely volatilizes, dry under vacuum, and pass through a -40 to +120 mesh sieve to obtain magnetic powder D;

[0012] (4) Pressing and annealing: Press magnetic powder D into a shape, and then perform annealing treatment to obtain a double-layer oxide insulation-coated amorphous magnetic powder core.

[0013] Preferably, in step (1), the amorphous magnetic powder is one or both of FeSiBCr and FeSiB amorphous magnetic powders with a particle size in the range of 3 μm - 30 μm.

[0014] Preferably, in step (1), the amorphous magnetic powder is subjected to particle size ratio, and the mass ratio of the magnetic powder with large particle size to the magnetic powder with small particle size is 1:10 to 10:1.

[0015] Preferably, based on the mass of the amorphous magnetic powder in step (1), the mass proportion of potassium permanganate is 0.5 wt.% to 5 wt.%, the mass proportion of water is 10 wt.% to 60 wt.%, and dilute sulfuric acid is used to adjust the pH of the solution to 0.5 to 5.

[0016] Preferably, the reaction temperature in step (1) is 45 to 80 °C, and the reaction time is 10 to 120 min.

[0017] Preferably, based on the mass of magnetic powder B in step (2), the mass proportion of tetraethyl orthosilicate is 1 wt.% to 8 wt.%, the mass proportion of absolute ethanol is 10 wt.% to 60 wt.%, and ammonia water is used to adjust the pH of the solution to 9 to 12.

[0018] Preferably, the reaction temperature in step (2) is 30 to 70 °C, and the reaction time is 30 to 180 min.

[0019] Preferably, the drying temperature after cleaning in steps (1) and (2) is 70 to 150 °C, and the drying time is 30 to 90 min.

[0020] Preferably, the resin used in step (3) is at least one of epoxy resin and silicone resin. Based on the mass of magnetic powder C, the overall mass proportion of the resin is 1 wt.% to 5 wt.%, and the mass proportion of acetone used is 10 wt.% to 40 wt.%.

[0021] Preferably, a curing agent is further added to the resin acetone solution in step (3), and the mass ratio of the curing agent to magnetic powder C is 0.5 wt.% to 5 wt.%.

[0022] Preferably, the drying temperature of the magnetic powder in step (3) is 50 to 80 °C, and the drying time is 60 to 180 min.

[0023] Preferably, the pressure for pressing and forming in step (4) is 600 to 1800 MPa, the pressure holding time is 5 to 60 s, the annealing temperature is 400 to 550 °C, and the annealing holding time is 1 h to 5 h.

[0024] The present invention sequentially performs particle size ratio, in-situ passivation, SiO 2 coating, organic coating, pressing and forming, and heat treatment on the amorphous magnetic powder. Among them, the in-situ passivation uses an acidic potassium permanganate aqueous solution, and SiO 2Coating is carried out by hydrolyzing tetraethyl orthosilicate, and for organic coating, one or more of silicone resin and epoxy resin can be used. During the preparation of magnetic powder, first, the surface of the amorphous magnetic powder is in-situ passivated with a strongly oxidizing acidic potassium permanganate solution, and a Fe / Mn composite oxide insulating layer can be formed on the surface of the highly corrosion-resistant amorphous magnetic powder, providing nucleation sites for subsequent physical coating and effectively enhancing the binding strength between SiO 2 and the amorphous magnetic powder. Then, through the hydrolysis reaction of tetraethyl orthosilicate, an additional SiO 2 insulating layer is formed on the surface of the magnetic powder, ultimately forming a double-layer coating structure composed of a Fe / Mn composite oxide insulating layer and a SiO 2 insulating layer. This method makes full use of the strong oxidizing property of the acidic potassium permanganate solution to form a dense in-situ passivated oxide insulating layer on the surface of the highly corrosion-resistant amorphous magnetic powder. Based on the excellent properties of the oxide insulating layer in suppressing eddy current loss, electrical breakdown resistance, and high-temperature resistance, the present invention adopts an in-situ passivation method with acidic potassium permanganate combined with SiO 2 coating method. The prepared iron-based amorphous magnetic powder core has the characteristics of high-frequency low loss, high-voltage breakdown resistance, and high-temperature stability, can significantly improve the conversion efficiency of high-frequency switching power supplies, meet the strict working environment requirements of high frequency, high voltage, and high temperature in new energy vehicle electric drive systems, etc., and has important application value in the field of power electronics.

[0025] Compared with phosphides, metal oxides have a higher decomposition temperature, so they can be processed at a higher annealing temperature, effectively eliminating the internal stress generated during the pressing process, thereby improving the effective magnetic permeability of the amorphous magnetic powder core and reducing the hysteresis loss. In addition, metal oxides have similar chemical properties to SiO2. Under alkaline conditions, Fe 2 O 3 undergoes a hydrolysis reaction to form Fe-OH groups, and at the same time, tetraethyl orthosilicate hydrolyzes to generate Si-OH under alkaline conditions. The two groups form Fe-O-Si bonds through hydrolysis condensation reactions, and heat treatment accelerates this reaction. This combination enables SiO2 to bind more firmly to the amorphous magnetic powder substrate, thus solving the problems of poor binding between the SiO2 insulating layer and the amorphous magnetic powder, and being prone to peeling and breaking during the pressing process. In addition, the high resistivity, high breakdown voltage resistance, and excellent temperature resistance of Fe 2 O 3 and oxides such as SiO 2 effectively improve the electromagnetic performance and service performance of the amorphous magnetic powder core.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Improve magnetic permeability and reduce hysteresis loss. By forming a double-layer coating structure of Fe / Mn composite oxide insulating layer and SiO2 insulating layer on the surface of amorphous magnetic powder, the magnetic powder can be processed at a higher annealing temperature, effectively eliminating the internal stress generated during the pressing process, thereby improving the effective magnetic permeability of the amorphous magnetic powder core, reducing the hysteresis loss, and enhancing the overall performance of the magnetic powder core.

[0028] (2) Reduce eddy current loss. By constructing a double-layer oxide coating structure with high resistivity on the surface of amorphous magnetic powder, the insulation ability between magnetic powders is further improved, and eddy currents are restricted inside the amorphous magnetic powder, thereby reducing the eddy current loss of the magnetic powder core.

[0029] (3) Enhance the bonding force of the insulating layer. Utilizing the chemical property similarity of Fe 2 O 3 and SiO2, Fe-O-Si bonds are formed through hydrolysis and condensation reactions under alkaline conditions, enabling the SiO2 insulating layer to bind more firmly to the amorphous magnetic powder substrate, solving the problem of easy shedding and fragmentation of the SiO2 insulating layer during the pressing process.

[0030] (4) Improve electromagnetic performance and service performance. Fe 2 O 3 and oxides such as SiO2 have high resistivity, high breakdown voltage resistance, and excellent temperature resistance characteristics, which effectively improve the electromagnetic performance and service performance of the amorphous magnetic powder core.

[0031] (5) Improve corrosion resistance and temperature resistance. The strong oxidizing property of acidic potassium permanganate solution forms a dense in-situ passivation oxide layer on the surface of amorphous magnetic powder, improving the corrosion resistance and temperature resistance of the magnetic powder. Description of the Drawings

[0032] Figure 1 Relationship between magnetic properties and frequency of FeSiBCr amorphous magnetic powder core after different insulation coating treatments (a) Magnetic permeability, (b) Magnetic loss.

[0033] Figure 2 Relationship between magnetic properties and frequency of FeSiB amorphous magnetic powder core after different insulation coating treatments (a) Magnetic permeability, (b) Magnetic loss.

[0034] Figure 3 Microscopic morphology of the surface of FeSiBCr amorphous magnetic powder after in-situ passivation with acidic potassium permanganate in Comparative Example 1 of the present invention.

[0035] Figure 4 Microscopic morphology of the surface of FeSiBCr amorphous magnetic powder after being coated with SiO 2 in Comparative Example 2 of the present invention.

[0036] Figure 5For the FeSiBCr amorphous magnetic powder in Example 1 of the present invention, in-situ passivation with acidic potassium permanganate + SiO 2 The microscopic morphology of the surface after double-layer coating.

[0037] Figure 6 is a metal oxide / SiO 2 Schematic diagram of the double-layer insulating layer structure. Detailed implementation manners

[0038] The present invention will be further described in detail with reference to specific embodiments below. However, the implementation manners of the present invention are not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0039] The epoxy resin used in the embodiment is Tian Tai TT310 para-aminophenol trifunctional epoxy resin, the silicone resin is Shin-Etsu KR5235 polyester-modified silicone resin, and the curing agent is 4,4′-diaminodiphenyl sulfone.

[0040] Example 1

[0041] In this embodiment, a preparation method of an insulated coated magnetic powder core is provided. The magnetic powder used is FeSiBCr amorphous magnetic powder, and the preparation method includes the following steps.

[0042] Magnetic powder particle size ratio: FeSiBCr amorphous magnetic powders with median particle sizes of 10 μm and 3 μm are proportioned by weight at 7:3 to obtain a mixed magnetic powder A.

[0043] Passivation of amorphous magnetic powder: 5 g of potassium permanganate is dissolved in 30 g of deionized water, and the pH of the solution is adjusted to 1 with dilute sulfuric acid. Then 100 g of magnetic powder A is added to the prepared potassium permanganate passivation solution, and it is sufficiently stirred for 20 min under the condition of a 75°C water bath. After washing, it is dried at 120°C for 30 min to obtain passivated magnetic powder B.

[0044] SiO 2 Coating: 3 g of tetraethyl orthosilicate is dissolved in 30 g of absolute ethanol, and the pH of the solution is adjusted to 10 with ammonia water. Then 100 g of magnetic powder B is added to the prepared tetraethyl orthosilicate-ethanol solution, and it is stirred at 50°C for 60 min. After washing, it is dried at 120°C for 30 min to obtain an amorphous magnetic powder C coated with a double-layer oxide.

[0045] Prepare an organic resin solution (adhesive): 0.6 g of epoxy resin, 3 g of silicone resin, and 1 g of curing agent are dissolved in 20 g of acetone, and after ultrasonic treatment for 20 min at room temperature, an organic resin solution is obtained.

[0046] Organic coating granulation: Add 100g of magnetic powder C to the above organic resin solution, stir at a uniform speed until the acetone is completely volatilized, dry at 70°C for 60min, and pass through a -40 to +120 mesh sieve to obtain magnetic powder D.

[0047] Pressing annealing: The magnetic powder D is pressed into a magnetic powder core with an outer diameter of 20 mm, an inner diameter of 16 mm, and a height of 5.5 mm. The pressing pressure is 1200 MPa. After holding the pressure for 10 seconds, the formed magnetic powder core is annealed and kept warm for 60 minutes at 500°C in an argon atmosphere. After chamfering, the surface of the magnetic powder core is sprayed with insulation treatment.

[0048] Comparative Example 1

[0049] This comparative example 1 provides a method for preparing an insulating coated magnetic powder core. The difference between this comparative example and Example 1 is that only the FeSiBCr amorphous magnetic powder is subjected to in-situ passivation coating with acidic potassium permanganate, and the rest of the preparation methods and parameters are the same as those in Example 1.

[0050] Comparative Example 2

[0051] This comparative example provides a method for preparing an insulating coated magnetic powder core. The difference between this comparative example and Example 1 is that only the FeSiBCr amorphous magnetic powder is subjected to SiO 2 The remaining preparation methods and parameters are the same as those in Example 1.

[0052] Comparative Example 3

[0053] In this comparative example, a method for preparing a magnetic powder core is adopted. The magnetic powder used is FeSiBCr amorphous magnetic powder. The preparation method includes the following steps.

[0054] Magnetic powder particle size ratio: FeSiBCr amorphous magnetic powders with median particle sizes of 10 μm and 3 μm were mixed in a weight ratio of 7:3 to obtain mixed magnetic powder A.

[0055] Phosphating of amorphous magnetic powder: dissolve 0.5 g of phosphoric acid in 30 g of acetone, then add 100 g of magnetic powder A into the prepared phosphoric acid-acetone solution, stir thoroughly in a 45°C water bath until the acetone is completely volatilized, and dry at 120°C for 30 min to obtain phosphated magnetic powder E.

[0056] Prepare an organic resin solution: dissolve 0.6 g of epoxy resin, 3 g of silicone resin and 1 g of curing agent in 20 g of acetone, and ultrasonicate at room temperature for 20 min to obtain an organic resin solution.

[0057] Organic coating granulation: Add magnetic powder E to the prepared organic resin solution, stir at a uniform speed until the acetone is completely volatilized, dry at 70°C for 60 minutes, and pass through a -40 to +120 mesh sieve to obtain magnetic powder F.

[0058] Pressing and annealing: Press the magnetic powder F into a magnetic powder core with an outer diameter of 20 mm, an inner diameter of 16 mm, and a height of 5.5 mm. The pressing pressure is 1200 MPa. After holding the pressure for 10 s, anneal the formed magnetic powder core in an argon atmosphere at 500 °C for 60 min. After chamfering, spray an insulating treatment on the surface of the magnetic powder core.

[0059] Wind the magnetic powder cores obtained in Example 1 and Comparative Examples 1-3 above with a 0.25 mm * 2 copper wire for 20 turns, and then measure the magnetic permeability of the magnetic powder cores and the losses at 50 mT, 100 kHz, 200 kHz, and 300 kHz respectively. The test results are recorded in Table 1.

[0060] Table 1: Magnetic properties of FeSiBCr amorphous magnetic powder cores with different insulation coating treatments

[0061]

[0062] Test the voltage breakdown resistance performance of the magnetic powder cores obtained in Example 1 and Comparative Examples 1-3 above, and measure the leakage current I of the magnetic powder cores at 100 V voltage l and the breakdown voltage V at 1 mA current b . The test results are recorded in Table 2.

[0063] Table 2: Voltage resistance performance of FeSiBCr amorphous magnetic powder cores with different insulation coating treatments

[0064]

[0065] Example 2

[0066] In this example, a preparation method of an insulated coated magnetic powder core is provided. The magnetic powder used is FeSiB amorphous magnetic powder, and the preparation method includes the following steps.

[0067] Magnetic powder selection: Select FeSiB amorphous magnetic powder with a median particle size of 15 μm as magnetic powder A, and the mass of magnetic powder A is 100 g.

[0068] Passivation of amorphous magnetic powder: Dissolve 3 g of potassium permanganate in 20 g of deionized water, adjust the pH of the solution to 2 with dilute sulfuric acid, then add 100 g of magnetic powder A to the prepared potassium permanganate solution, stir well at 60 °C in a water bath for 30 min, wash, and dry at 100 °C for 60 min to obtain passivated magnetic powder B.

[0069] SiO 2Coating: Dissolve 5 g of tetraethyl orthosilicate in 30 g of absolute ethanol, adjust the pH of the solution to 9 with ammonia water, then add 100 g of magnetic powder B to the prepared tetraethyl orthosilicate-ethanol solution, stir at 45 °C for 60 min, wash, and dry at 100 °C for 60 min to obtain amorphous magnetic powder C coated with a double-layer oxide.

[0070] Prepare an organic resin solution (adhesive): Dissolve 0.3 g of epoxy resin, 1.5 g of silicone resin, and 1 g of curing agent in 20 g of acetone, and ultrasonically treat for 20 min at room temperature to obtain an organic resin solution.

[0071] Organic coating granulation: Add passivated magnetic powder C to the organic resin solution, stir evenly until the acetone completely evaporates, dry at 80 °C for 60 min, and pass through a -40 to +120 mesh sieve to obtain magnetic powder D.

[0072] Pressing and annealing: Press magnetic powder C into a magnetic powder core with an outer diameter of 20 mm, an inner diameter of 16 mm, and a height of 5.5 mm. The pressing pressure is 1000 MPa. After holding the pressure for 15 s, anneal the formed magnetic powder core in a nitrogen atmosphere at 400 °C for 120 min. After chamfering, perform spray insulation treatment on the surface of the magnetic powder core.

[0073] Comparative Example 4

[0074] In this Comparative Example 4, a preparation method of an insulated coated magnetic powder core is provided. The difference between this comparative example and Example 1 is that only in-situ passivation coating is performed on the FeSiB amorphous magnetic powder, and the remaining preparation methods and parameters are the same as those in Example 1.

[0075] Comparative Example 5

[0076] In this Comparative Example 5, a preparation method of an insulated coated magnetic powder core is provided. The difference between this comparative example and Example 1 is that only SiO 2 coating is performed on the FeSiB amorphous magnetic powder, and the remaining preparation methods and parameters are the same as those in Example 1.

[0077] Comparative Example 6

[0078] In this Comparative Example 6, a preparation method of a magnetic powder core is adopted. The magnetic powder used is FeSiB amorphous magnetic powder, and the preparation method includes the following steps.

[0079] Magnetic powder selection: Select FeSiB amorphous magnetic powder with a median particle size of 15 μm as magnetic powder A; the mass of magnetic powder A is 100 g.

[0080] Amorphous magnetic powder phosphating: Dissolve 1.0 g of phosphoric acid in 40 g of acetone, then add 100 g of magnetic powder A to the prepared phosphoric acid-acetone solution, and stir well at 45 °C in a water bath until the acetone completely evaporates. Dry at 100 °C for 60 min to obtain phosphated magnetic powder H.

[0081] Prepare organic binder: Dissolve 0.3 g of epoxy resin, 1.5 g of silicone resin and 1 g of curing agent in 20 g of acetone, and ultrasonically treat for 20 min at room temperature to obtain an organic resin solution.

[0082] Organic coating and granulation: Add magnetic powder H to the above organic resin solution, stir evenly until the acetone completely evaporates, then dry at 80 °C for 60 min, and pass through a -40 to +120 mesh sieve to obtain magnetic powder I.

[0083] Pressing and annealing: Press magnetic powder I into a magnetic powder core with an outer diameter of 20 mm, an inner diameter of 16 mm, and a height of 5.5 mm. The pressing pressure is 1000 MPa. After holding the pressure for 15 s, anneal the formed magnetic powder core in a nitrogen atmosphere at 400 °C for 120 min. After chamfering, spray an insulating treatment on the surface of the magnetic powder core.

[0084] Wind the magnetic powder cores obtained in Example 2 and Comparative Examples 4-6 above with a 0.25 mm * 2 copper wire for 20 turns, and then respectively test the magnetic permeability of the magnetic powder cores and the loss conditions at 50 mT, 100 kHz, 200 kHz and 300 kHz. The test results are recorded in Table 3.

[0085] Table 3: Magnetic properties of FeSiB amorphous magnetic powder cores with different insulation coating treatments

[0086]

[0087] Test the voltage breakdown resistance performance of the magnetic powder cores obtained in Example 2 and Comparative Examples 4-6 above, and respectively test the leakage current I of the magnetic powder cores at 100 V voltage l and the breakdown voltage V at 1 mA current b . The test results are recorded in Table 4.

[0088] Table 4: Voltage resistance performance of FeSiB amorphous magnetic powder cores with different insulation coating treatments

[0089]

[0090] From the test results of the above examples and comparative examples, the following conclusions can be drawn:

[0091] For the amorphous magnetic powder core with double-layer oxide coating, the effective magnetic permeability at 1 MHz is compared with that of the in-situ passivated amorphous magnetic powder core and the SiO 2The magnetic permeability of the coated amorphous magnetic powder core is not significantly reduced compared to that without coating, and is improved compared to the amorphous magnetic powder core treated with phosphating.

[0092] The amorphous magnetic powder core of Example 1 has the lowest magnetic loss at 100 kHz, 200 kHz, and 300 kHz. Compared with the single coating layers of Comparative Example 1 and Comparative Example 2, the magnetic loss at 50 mT and 300 kHz is decreased by 14.40% and 12.22% respectively. Compared with the phosphated amorphous magnetic powder core of Comparative Example 3, the magnetic loss at 50 mT and 300 kHz is decreased by 26.06%.

[0093] The amorphous magnetic powder core of Example 2 has the lowest magnetic loss at 100 kHz, 200 kHz, and 300 kHz. Compared with the single coating layers of Comparative Example 4 and Comparative Example 5, the magnetic loss at 50 mT and 300 kHz is decreased by 12.72% and 18.13% respectively. Compared with the phosphated amorphous magnetic powder core of Comparative Example 6, the magnetic loss at 50 mT and 300 kHz is decreased by 28.87%.

[0094] The leakage current I of the amorphous magnetic powder core coated with a double-layer oxide is less than 0.01 mA at 100 V voltage, far lower than the leakage current in the comparative examples. Under the condition of a leakage current of 1 mA, the breakdown voltage V l is greater than 720 V, and even greater than 840 V. Compared with the single coating layer in the comparative examples, the voltage withstand performance is significantly improved. b When analyzed in combination with the attached drawings, there is an obvious passivation layer on the surface of the FeSiBCr amorphous magnetic powder prepared by in-situ passivation. The obvious insulating layer shedding is observed on the surface of the FeSiBCr amorphous magnetic powder coated with SiO

[0095] However, the coating layer on the surface of the FeSiBCr amorphous magnetic powder coated with a double-layer oxide is evenly distributed, indicating that the oxide layer after passivation with acidic potassium permanganate can make the SiO 2 particles better adhere to the surface of the amorphous magnetic powder. 2 By comparing the magnetic properties of the amorphous magnetic powder cores obtained from the comparative examples and the examples, it can be concluded that the double-layer oxide-coated amorphous magnetic powder prepared by in-situ passivation with acidic potassium permanganate and SiO

[0096] coating can obtain amorphous magnetic powder with high magnetic permeability, low loss, and high voltage breakdown resistance. 2 ​

Claims

1. A method for preparing a double-layer oxide insulation-coated amorphous magnetic powder core, characterized in that: The following steps are involved: (1) Passivation of amorphous magnetic powder: Add amorphous magnetic powder into an acidic potassium permanganate aqueous solution and stir. After the reaction is completed, filter, wash and dry to obtain a single-layer coated passivated magnetic powder B; (2) SiO2 coating: Magnetic powder B is added to a tetraethyl orthosilicate-ethanol solution and stirred under alkaline conditions for hydrolysis reaction, followed by washing and drying to obtain a double-layer oxide-coated magnetic powder C; (3) Organic coating granulation: Add magnetic powder C to the resin acetone solution, stir until the acetone is completely volatilized, vacuum dry, and pass through a -40 to +120 mesh sieve to obtain magnetic powder D; (4) Pressing and annealing: The magnetic powder D is pressed into shape and then annealed to obtain a double-layer oxide insulation-coated amorphous magnetic powder core.

2. The preparation method according to claim 1, characterized in that: The amorphous magnetic powder in step (1) is one or both of FeSiBCr and FeSiB amorphous magnetic powders with a particle size in the range of 3 μm-30 μm; the amorphous magnetic powder is proportioned by particle size, and the mass ratio of the large particle size magnetic powder to the small particle size magnetic powder is 1:10 to 10:

1.

3. The preparation method according to claim 1, characterized in that: In step (1), the mass of the amorphous magnetic powder is used as the calculation basis, the mass proportion of potassium permanganate is 0.5wt.% to 5wt.%, the mass proportion of water is 10wt.% to 60wt.%, and the pH of the solution is adjusted to 0.5 to 5 using dilute sulfuric acid.

4. The preparation method according to claim 1, 2 or 3, characterized in that: The reaction temperature in step (1) is 45-80° C., and the reaction time is 10-120 min; the reaction temperature in step (2) is 30-70° C., and the reaction time is 30-180 min.

5. The preparation method according to claim 4, characterized in that: In step (2), the mass of magnetic powder B is used as the calculation basis, the mass proportion of tetraethyl orthosilicate is 1wt.% to 8wt.%, the mass proportion of anhydrous ethanol is 10wt.% to 60wt.%, and ammonia water is used to adjust the solution pH to 9 to 12.

6. The preparation method according to claim 5, characterized in that: The resin used in step (3) is at least one of epoxy resin and silicone resin. Based on the mass of magnetic powder C, the overall mass of the resin accounts for 1wt.% to 5wt.%, and the mass of acetone used accounts for 10wt.% to 40wt.%.

7. The preparation method according to claim 6, characterized in that: In step (3), a curing agent is also added to the resin acetone solution, and the mass ratio of the curing agent to the magnetic powder C is 0.5% to 5%.

8. The preparation method according to claim 1, 2 or 3, characterized in that: In step (4), the pressure of the pressing molding is 600-1800 MPa, the holding time is 5-60 s, the annealing temperature is 400-550° C., and the annealing holding time is 1 h to 5 h.

9. The preparation method according to claim 1, 2 or 3, characterized in that: The drying temperature after cleaning in steps (1) and (2) is 70-150° C., and the drying time is 30-90 min. The drying temperature of the magnetic powder in step (3) is 50-80° C., and the drying time is 60-180 min.

10. A double-layer oxide insulation-coated amorphous magnetic powder core prepared by the method according to any one of claims 1 to 9.

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