A magnetic core, its preparation method and application

Abstract

This invention relates to the field of soft magnetic materials, and more particularly to a magnetic core, its preparation method, and its applications. The invention provides a method for preparing a magnetic core, comprising the following steps: first, mixing a mixture of soluble magnesium salt and magnetic powder with ammonia water to obtain a nano-magnesium oxide precursor-coated magnetic powder; second, mixing the nano-magnesium oxide precursor-coated magnetic powder with a coupling agent solution for activation to obtain activated magnetic powder; third, mixing the activated magnetic powder with a polyamic acid solution to obtain a polyimide precursor / magnesium oxide precursor-coated magnetic powder; and fourth, subjecting the polyimide precursor / magnesium oxide precursor-coated magnetic powder to heat treatment, pressing, and sintering sequentially to obtain the magnetic core. The preparation method of this invention is low-cost, safe, reliable, and simple to operate, with good pressing and molding capabilities. The prepared magnetic core exhibits significantly improved mechanical strength, heat resistance, and resistivity, and low core loss.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic materials, and in particular to a magnetic core, its preparation method, and its application. Background Technology

[0002] Metal powder cores are key functional components for electromagnetic conversion, widely used in communications, electronics, and power industries. Under alternating magnetic fields, eddy currents are generated in the powder core, leading to heat generation and deteriorating device performance. Coating the surface of the metal powder with an insulating layer can increase the resistivity of the powder core and reduce eddy current losses. Currently, there are two main categories of coatings for the surface of powder cores: inorganic and organic materials. Inorganic materials have high resistivity and strong heat resistance, but this makes it difficult to press and form the powder core, especially large-sized cores. Organic materials have good pressing and forming capabilities, but they suffer from poor heat resistance, are prone to carbonization at high temperatures, resulting in poor insulation and high core losses. Summary of the Invention

[0003] The purpose of this invention is to provide a magnetic core, its preparation method, and its application. The magnetic core prepared by the method has good pressing and forming capabilities and low core loss.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a magnetic core, comprising the following steps:

[0006] The mixture of soluble magnesium salt and magnetic powder is first mixed with ammonia water to obtain magnetic powder coated with nano-magnesium oxide precursor.

[0007] The magnetic powder coated with the nano-magnesium oxide precursor and the coupling agent solution are mixed for the second time and activated to obtain the activated magnetic powder.

[0008] The activated magnetic powder and polyamic acid solution are mixed in a third step to obtain polyimide precursor / magnesium oxide precursor coated magnetic powder.

[0009] The magnetic powder coated with the polyimide precursor / magnesium oxide precursor is subjected to heat treatment, pressing and sintering in sequence to obtain the magnetic core.

[0010] Preferably, the mass ratio of soluble magnesium salt to magnetic powder in the mixture of soluble magnesium salt and magnetic powder is (0.5-2):(98-99.5);

[0011] The magnetic powder has a particle size of 80–400 mesh.

[0012] Preferably, the mass concentration of the ammonia water is 1-5%;

[0013] The mass ratio of the soluble magnesium salt to the volume of the ammonia in the mixture of the soluble magnesium salt and magnetic powder is (0.5-2) g : (50-1000) mL.

[0014] Preferably, the first mixture is:

[0015] Under stirring conditions, ammonia water is added dropwise to the mixture of soluble magnesium salt and magnetic powder at a dropping rate of 0.2 to 10 mL / min.

[0016] Preferably, the coupling agent solution is an acetone solution of KH560;

[0017] The concentration of the acetone solution of KH560 is 0.1–3.0 mol / L;

[0018] The mass ratio of the soluble magnesium salt in the mixture of the soluble magnesium salt and the magnetic powder to the volume ratio of the acetone solution of KH560 is (0.5-2) g : (50-100) mL.

[0019] Preferably, the mass ratio of polyamic acid in the polyamic acid solution to the magnetic powder is (0.5-2.0):100.

[0020] Preferably, the heat treatment is carried out in a protective atmosphere; the temperature of the heat treatment is 200°C, and the time is 0.5 to 2 hours.

[0021] The pressing pressure is 300-800 MPa.

[0022] Preferably, the sintering includes a first sintering, a second sintering, and a third sintering performed sequentially;

[0023] The first sintering temperature is 100–200℃, and the time is 0.5–1 hour;

[0024] The second sintering temperature is 250–400℃, and the time is 0.3–2 hours;

[0025] The third sintering temperature is 400–600℃, and the time is 0.1–0.5 h.

[0026] The present invention also provides a magnetic core prepared by the preparation method described above, comprising a magnetic powder core and nano-magnesium oxide and polyimide wrapped on the outer surface of the magnetic powder core.

[0027] The present invention also provides the application of the magnetic core described in the above technical solution in the fields of communication devices, electronic devices and power devices.

[0028] This invention provides a method for preparing a magnetic core, comprising the following steps: first, mixing a mixture of soluble magnesium salt and magnetic powder with ammonia water to obtain a magnetic powder coated with a nano-magnesium oxide precursor; second, mixing the nano-magnesium oxide precursor-coated magnetic powder with a coupling agent solution for activation to obtain activated magnetic powder; third, mixing the activated magnetic powder with a polyamic acid solution to obtain a magnetic powder coated with a polyimide precursor / magnesium oxide precursor; and fourth, subjecting the polyimide precursor / magnesium oxide precursor-coated magnetic powder to heat treatment, pressing, and sintering sequentially to obtain the magnetic core. The polyimide in the coating material prepared by the method of this invention exhibits superior adhesion, significantly improving the bonding force between metal powders, which is beneficial for the pressing and forming of the magnetic core product, resulting in high mechanical strength. Simultaneously, the nano-magnesium oxide and polyimide coating on the magnetic powder surface have good heat resistance and high resistivity, effectively reducing eddy current losses and core losses. Therefore, the preparation method of the present invention is low in cost, safe and reliable, simple to operate, has good pressing and molding ability, and the mechanical strength, heat resistance and resistivity of the prepared magnetic core are significantly improved, and the magnetic core loss is low. Detailed Implementation

[0029] This invention provides a method for preparing a magnetic core, comprising the following steps:

[0030] The mixture of soluble magnesium salt and magnetic powder is first mixed with ammonia water to obtain magnetic powder coated with nano-magnesium oxide precursor.

[0031] The magnetic powder coated with the nano-magnesium oxide precursor and the coupling agent solution are mixed for the second time and activated to obtain the activated magnetic powder.

[0032] The activated magnetic powder and polyamic acid solution are mixed in a third step to obtain polyimide precursor / magnesium oxide precursor coated magnetic powder.

[0033] The magnetic powder coated with the polyimide precursor / magnesium oxide precursor is subjected to heat treatment, pressing and sintering in sequence to obtain the magnetic core.

[0034] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0035] In this invention, a mixture of soluble magnesium salt and magnetic powder is first mixed with ammonia water to obtain magnetic powder coated with nano-magnesium oxide precursor.

[0036] The type of soluble magnesium salt described in this invention is not particularly limited; any type not familiar to those skilled in the art may be used. In a specific embodiment of this invention, the soluble magnesium salt is magnesium chloride hexahydrate.

[0037] In this invention, the mass concentration of the soluble magnesium salt in the mixture of the soluble magnesium salt and magnetic powder is preferably 1% to 3%, more preferably 1.5% to 2.5%, and most preferably 1.6%.

[0038] In this invention, the preferred mass ratio of soluble magnesium salt to magnetic powder in the mixture of soluble magnesium salt and magnetic powder is (0.5–2):(98–99.5), more preferably (0.8–1.6):(98.5–99.3), and most preferably (1.0–1.5):(99–99.2). In this invention, the preferred particle size of the magnetic powder is 80–400 mesh, more preferably 100–300 mesh, and most preferably 150–200 mesh. In this invention, the magnesium chloride is preferably calculated as magnesium chloride hexahydrate.

[0039] In this invention, the preferred method for preparing the mixture of soluble magnesium salt and magnetic powder includes: mixing the soluble magnesium salt, magnetic powder, and pure water to obtain the mixture. In this invention, the mixing is preferably performed by adding the soluble magnesium salt and magnetic powder to pure water; this invention does not impose any special limitations on the method of addition, and any method well-known to those skilled in the art can be used. In this invention, the mixing is preferably performed sequentially under mechanical stirring and ultrasonic conditions; this invention does not impose any special limitations on the rotation speed of the mechanical stirring and the frequency of the ultrasonication, and any rotation speed or frequency well-known to those skilled in the art can be used to ensure that the soluble magnesium salt and magnetic powder are sufficiently and uniformly dispersed in the water within a range of 5 to 10 minutes.

[0040] In this invention, the mass concentration of the ammonia water is preferably 1-5%, more preferably 2-4%, and most preferably 2.5-3.5%.

[0041] In this invention, the mass ratio of magnesium chloride to the volume of ammonia in the mixture of magnesium chloride and magnetic powder is preferably (0.5-2) g: (50-1000) mL, more preferably (0.8-1.6) g: (80-300) mL, and most preferably (1.0-1.3) g: (100-200) mL.

[0042] In this invention, the first mixing is preferably carried out by adding ammonia water dropwise to the mixture of magnesium chloride and magnetic powder at a dropping rate of 0.2 to 10 mL / min under stirring conditions. In this invention, the stirring speed is preferably 50 to 100 rpm, more preferably 60 to 80 rpm; the dropping rate is preferably 0.2 to 10 mL / min, more preferably 2 to 8 mL / min, and most preferably 3 to 5 mL / min.

[0043] After the first mixing is completed, the present invention preferably includes sequential stirring and filtration; the stirring speed is preferably 50-100 rpm, more preferably 60-80 rpm; the time is preferably 1 hour. The present invention does not impose any special limitations on the filtration process, and any process well known to those skilled in the art can be used.

[0044] After obtaining the magnetic powder coated with the nano-magnesium oxide precursor, the present invention mixes the magnetic powder coated with the nano-magnesium oxide precursor with a coupling agent solution for a second time and activates it to obtain the activated magnetic powder.

[0045] In this invention, the coupling agent solution is preferably an acetone solution of KH560; the concentration of the acetone solution of KH560 is preferably 0.1-3.0 mol / L, more preferably 0.5-2.5 mol / L, and most preferably 1.0-2.0 mol / L; the mass ratio of magnesium chloride in the mixture of magnesium chloride and magnetic powder to the volume ratio of the acetone solution of KH560 is preferably (0.5-2) g:(50-100) mL, more preferably (0.8-1.6) g:(60-90) mL, and most preferably (1.0-1.3) g:(70-80) mL.

[0046] In this invention, the second mixing is preferably achieved by adding the nano-magnesium oxide precursor coated magnetic powder to the coupling agent solution.

[0047] The present invention does not impose any special limitations on the conditions for the second mixing; conditions well known to those skilled in the art can be used to ensure uniform dispersion of the two materials.

[0048] In this invention, the activation is preferably carried out under stirring conditions; the stirring method is preferably mechanical stirring; the stirring time is preferably 30 minutes; this invention does not impose any special limitation on the stirring rate, and a rate well known to those skilled in the art can be used.

[0049] In this invention, the purpose of the activation is to promote the coating of the polyimide precursor onto the surface of the magnetic powder.

[0050] After activation, the present invention preferably includes sequential cleaning and filtration; the cleaning agent used is preferably ethanol; the present invention does not have any special limitations on the filtration, and any process known to those skilled in the art can be used.

[0051] After obtaining the activated magnetic powder, the present invention mixes the activated magnetic powder with a polyamic acid (PAA) solution to obtain polyimide precursor / magnesium oxide precursor coated magnetic powder.

[0052] In this invention, the concentration of polyamic acid in the polyamic acid solution is preferably 0.1–0.5 g / mL, more preferably 0.6–1.0 g / mL, and most preferably 1.0–2.0 g / mL. In this invention, the solvent for the polyamic acid solution is preferably dimethylacetamide.

[0053] In this invention, the preferred method for preparing the polyamic acid solution includes mixing polyamic acid and dimethylacetamide to obtain the polyamic acid solution. In this invention, the mixing is preferably carried out under stirring conditions. This invention does not impose any special limitations on the stirring conditions; conditions well-known to those skilled in the art can be used, as long as a uniformly dispersed polyamic acid solution is obtained.

[0054] In this invention, the mass ratio of polyamic acid in the polyamic acid solution to the total mass of the soluble magnesium salt and magnetic powder is preferably (0.5-2.0):100, more preferably (0.8-1.6):100, and most preferably (1.0-1.3):100.

[0055] In this invention, the third mixing is preferably carried out under stirring conditions, and the stirring method is preferably mechanical stirring. The mechanical stirring time is preferably 0.5 to 1 hour, more preferably 0.6 to 0.8 hours. This invention does not impose any special limitation on the rotation speed of the mechanical stirring; any rotation speed well known to those skilled in the art can be used to ensure a uniformly dispersed mixture within the above-mentioned time range.

[0056] After the third mixing is completed, the present invention preferably includes drying, wherein the drying temperature is preferably 60–200°C, more preferably 80–160°C, and most preferably 100–130°C; and the drying time is preferably 2 hours. In the present invention, the purpose of the drying is to remove organic solvents.

[0057] After obtaining the polyimide precursor / magnesium oxide precursor coated magnetic powder, the present invention sequentially heat-treats, presses and sinters the polyimide precursor / magnesium oxide precursor coated magnetic powder to obtain the magnetic core.

[0058] In this invention, the heat treatment is preferably carried out in a protective atmosphere, preferably a nitrogen atmosphere; the temperature of the heat treatment is preferably 200°C, the time is preferably 0.5 to 2 hours, more preferably 0.8 to 1.6 hours, and most preferably 1.0 to 1.3 hours.

[0059] In this invention, the heat treatment causes the polyimide acid to undergo a dehydration reaction and amidation to generate polyimide.

[0060] In this invention, the pressing pressure is preferably 300-800 MPa, more preferably 400-700 MPa, and most preferably 500-600 MPa; the pressing time is preferably 6-10 s, more preferably 3-6 s, and most preferably 1-3 s.

[0061] In this invention, the sintering preferably includes a first sintering, a second sintering, and a third sintering performed sequentially; the temperature of the first sintering is preferably 100–200°C, more preferably 120–180°C, and most preferably 130–160°C; the time is preferably 0.5–1 h, more preferably 0.6–0.9 h, and most preferably 0.7–0.8 h; the temperature of the second sintering is preferably 250–400°C, more preferably 280–360°C, and most preferably 300–320°C; the time is preferably 0.3–2 h, more preferably 0.5–1.6 h, and most preferably 0.8–1.3 h; the temperature of the third sintering is preferably 400–600°C, more preferably 450–550°C, and most preferably 480–520°C; the time is preferably 0.1–0.5 h, more preferably 0.2–0.4 h, and most preferably 0.3 h. In this invention, the sintering atmosphere is preferably an inert gas; the inert gas is preferably argon.

[0062] In this invention, the sintering process generates a nano-magnesium oxide / polyimide insulating coating material on the surface of the magnetic powder, while simultaneously increasing the resistivity between the metal magnetic powders, reducing the eddy current loss of the magnetic core, and obtaining a magnetic core product with excellent magnetic properties.

[0063] The present invention also provides a magnetic core prepared by the preparation method described above, comprising a magnetic powder core and nano-magnesium oxide and polyimide wrapped on the outer surface of the magnetic powder core.

[0064] This invention also provides applications of the magnetic core described in the above-described technical solutions in the fields of communication devices, electronic devices, and power devices. This invention does not impose any special limitations on the methods used in these applications; methods well-known to those skilled in the art can be employed.

[0065] The magnetic core, its preparation method, and its application provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0066] Example 1

[0067] According to the mass ratio of 0.5:99.5, 5g of magnesium chloride hexahydrate and 995g of magnetic powder with a particle size of 150 mesh were added to 500mL of pure water, and mechanical stirring and ultrasonic dispersion were carried out for 5min in sequence to obtain a mixture of magnesium chloride and magnetic powder.

[0068] Under mechanical stirring at 80 rpm, 100 mL of ammonia solution with a mass concentration of 1% was added dropwise to the mixture of magnesium chloride and magnetic powder at a dropping rate of 0.5 mL / min. After stirring for 1 hour, the mixture was filtered to obtain magnetic powder coated with nano-magnesium oxide precursor.

[0069] The magnetic powder coated with the nano-magnesium oxide precursor was added to 50 mL of acetone solution with a concentration of 0.5 mol / mL KH560. After activation treatment for 30 min under mechanical stirring, it was washed with ethanol and filtered to obtain the activated magnetic powder.

[0070] Dissolve 5g of polyamic acid (0.5% of the total mass of magnesium chloride hexahydrate and magnetic powder) in 50mL of dimethylacetamide and stir until evenly dispersed to obtain a PAA solution.

[0071] The activated magnetic powder was added to the PAA solution and mechanically stirred for 0.5 h. Then it was dried at 80 °C for 2 h to remove the organic solvent, thus obtaining polyimide precursor / magnesium oxide precursor coated magnetic powder.

[0072] The polyimide precursor / magnesium oxide precursor coated magnetic powder was heat-treated at 200°C for 0.5 h under a nitrogen atmosphere to obtain polyimide precursor / magnesium oxide coated magnetic powder.

[0073] The polyimide precursor / magnesium oxide coated magnetic powder is pressed at a pressure of 350 MPa for 3 seconds to obtain a magnetic core.

[0074] The magnetic core was subjected to a first sintering (100℃, 0.5h), a second sintering (300℃, 0.3h), and a third sintering (500℃, 0.2h) in sequence to obtain the magnetic core;

[0075] The magnetic core was tested at 50 mT and 100 kHz, and the loss of the magnetic core was 195 mW / cm. 3 With a permeability of 43, the magnetic core exhibits excellent magnetic properties and low magnetic loss.

[0076] Example 2

[0077] At a mass ratio of 0.8:99.2, 8g of magnesium chloride hexahydrate and 992g of magnetic powder with a particle size of 150 mesh were added to 500mL of pure water, and mechanical stirring and ultrasonic dispersion were carried out for 5min in sequence to obtain a mixture of magnesium chloride and magnetic powder.

[0078] Under mechanical stirring at 80 rpm, 100 mL of ammonia solution with a mass concentration of 1% was added dropwise to the mixture of magnesium chloride and magnetic powder at a dropping rate of 0.5 mL / min. After stirring for 1 hour, the mixture was filtered to obtain magnetic powder coated with nano-magnesium oxide precursor.

[0079] The magnetic powder coated with the nano-magnesium oxide precursor was added to 50 mL of acetone solution with a concentration of 0.8 mol / mL KH560. After activation treatment for 30 min under mechanical stirring, it was washed with ethanol and filtered to obtain the activated magnetic powder.

[0080] Dissolve 8g of polyamic acid (0.8% of the total mass of magnesium chloride hexahydrate and magnetic powder) in 80mL of dimethylacetamide and stir until evenly dispersed to obtain a PAA solution.

[0081] The activated magnetic powder was added to the PAA solution and mechanically stirred for 0.5 h. Then it was dried at 80 °C for 2 h to remove the organic solvent, thus obtaining polyimide precursor / magnesium oxide precursor coated magnetic powder.

[0082] The polyimide precursor / magnesium oxide precursor coated magnetic powder was heat-treated at 200°C for 0.5 h under a nitrogen atmosphere to obtain polyimide precursor / magnesium oxide coated magnetic powder.

[0083] The polyimide precursor / magnesium oxide coated magnetic powder is pressed at a pressure of 350 MPa for 3 seconds to obtain a magnetic core.

[0084] The magnetic core was subjected to a first sintering (100℃, 0.5h), a second sintering (300℃, 0.3h), and a third sintering (500℃, 0.2h) in sequence to obtain the magnetic core;

[0085] The magnetic core was tested at 50 mT and 100 kHz, and the loss of the magnetic core was 185 mW / cm. 3 With a permeability of 44, the magnetic core exhibits excellent magnetic properties and low magnetic loss.

[0086] Example 3

[0087] According to the mass ratio of 1.5:98.5, 15g of magnesium chloride hexahydrate and 985g of magnetic powder with a particle size of 150 mesh were added to 500mL of pure water, and mechanical stirring and ultrasonic dispersion were carried out for 5min in sequence to obtain a mixture of magnesium chloride and magnetic powder.

[0088] Under mechanical stirring at 80 rpm, 100 mL of ammonia solution with a mass concentration of 1% was added dropwise to the mixture of magnesium chloride and magnetic powder at a dropping rate of 0.5 mL / min. After stirring for 1 hour, the mixture was filtered to obtain magnetic powder coated with nano-magnesium oxide precursor.

[0089] The magnetic powder coated with the nano-magnesium oxide precursor was added to 50 mL of acetone solution with a concentration of 1.0 mol / mL KH560. After activation treatment for 30 min under mechanical stirring, it was washed with ethanol and filtered to obtain the activated magnetic powder.

[0090] Dissolve 15g of polyamic acid (1.5% of the total mass of magnesium chloride hexahydrate and magnetic powder) in 75mL of dimethylacetamide and stir until evenly dispersed to obtain a PAA solution.

[0091] The activated magnetic powder was added to the PAA solution and mechanically stirred for 1.0 h. Then it was dried at 80 °C for 2 h to remove the organic solvent, thus obtaining polyimide precursor / magnesium oxide precursor coated magnetic powder.

[0092] The polyimide precursor / magnesium oxide precursor coated magnetic powder was heat-treated at 200°C for 0.5 h under a nitrogen atmosphere to obtain polyimide precursor / magnesium oxide coated magnetic powder.

[0093] The polyimide precursor / magnesium oxide coated magnetic powder is pressed at a pressure of 300 MPa for 3 seconds to obtain a magnetic core.

[0094] The magnetic core was subjected to a first sintering (100℃, 0.5h), a second sintering (300℃, 0.3h), and a third sintering (500℃, 0.3h) in sequence to obtain the magnetic core;

[0095] The magnetic core was tested at 50 mT and 100 kHz, and the loss of the magnetic core was 210 mW / cm. 3 With a permeability of 41, the magnetic core exhibits excellent magnetic properties and low magnetic loss.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic core, characterized in that, Includes the following steps: The mixture of soluble magnesium salt and magnetic powder is first mixed with ammonia water to obtain magnetic powder coated with nano-magnesium oxide precursor. The magnetic powder coated with the nano-magnesium oxide precursor and the coupling agent solution are mixed for the second time and activated to obtain the activated magnetic powder. The activated magnetic powder and polyamic acid solution are mixed in a third step to obtain polyimide precursor / magnesium oxide precursor coated magnetic powder. The magnetic powder coated with the polyimide precursor / magnesium oxide precursor was subjected to heat treatment, pressing and sintering in sequence to obtain the magnetic core. The sintering includes a first sintering, a second sintering and a third sintering performed sequentially; The first sintering temperature is 100–200℃, and the time is 0.5–1 hour; The second sintering temperature is 250–400℃, and the time is 0.3–2 hours; The third sintering temperature is 400–600℃, and the time is 0.1–0.5 h.

2. The preparation method according to claim 1, characterized in that, The mass ratio of soluble magnesium salt to magnetic powder in the mixture of soluble magnesium salt and magnetic powder is (0.5-2):(98-99.5); The magnetic powder has a particle size of 80–400 mesh.

3. The preparation method according to claim 1, characterized in that, The mass concentration of the ammonia solution is 1-5%; The mass ratio of the soluble magnesium salt to the volume of the ammonia in the mixture of the soluble magnesium salt and magnetic powder is (0.5-2) g : (50-1000) mL.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The first mixture is: Under stirring conditions, ammonia water is added dropwise to the mixture of soluble magnesium salt and magnetic powder at a dropping rate of 0.2 to 10 mL / min.

5. The preparation method according to claim 1, characterized in that, The coupling agent solution is an acetone solution of KH560; The concentration of the acetone solution of KH560 is 0.1–3.0 mol / L; The mass ratio of the soluble magnesium salt in the mixture of the soluble magnesium salt and the magnetic powder to the volume ratio of the acetone solution of KH560 is (0.5-2) g : (50-100) mL.

6. The preparation method according to claim 1, characterized in that, The mass ratio of polyamic acid in the polyamic acid solution to the magnetic powder is (0.5-2.0):

100.

7. The preparation method according to claim 1, characterized in that, The heat treatment is carried out in a protective atmosphere; the temperature of the heat treatment is 200°C, and the time is 0.5 to 2 hours. The pressing pressure is 300-800 MPa.

8. The magnetic core prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It includes a magnetic powder core and nano-magnesium oxide and polyimide wrapped around the outer surface of the magnetic powder core.

9. The application of the magnetic core according to claim 8 in the fields of communication devices, electronic devices and power devices.