A high magnetic permeability nanocrystalline composite transformer core material and its preparation method

Abstract

The present invention discloses a high magnetic permeability nanocrystalline composite transformer core material and a preparation method thereof. The core material comprises the following components in weight percentages: alloy powder: 70 - 82 wt%, with a particle size of 20 - 45 μm; epoxy resin matrix: 8 - 18 wt%; boron nitride nanosheet: 0.5 - 2.0 wt%, with a thickness less than 50 nm and a diameter of 0.5 - 2 μm; composite system of polytetrafluoroethylene micropowder and aluminosilicate fiber: 3 - 5 wt%, wherein the weight ratio of polytetrafluoroethylene micropowder to aluminosilicate fiber is 0.8 - 1.2:1; lithium iron phosphate nanoparticles: 2 - 5 wt%, with a particle size of 50 - 100 nm; the boron nitride nanosheets, the composite system of polytetrafluoroethylene micropowder and aluminosilicate fiber, and the lithium iron phosphate nanoparticles form a multi-scale isolation structure. A preparation method of the high magnetic permeability nanocrystalline composite transformer core material is used to prepare the above-mentioned core material. Through the synergistic effect of three components, namely boron nitride nanosheets, the composite system of polytetrafluoroethylene micropowder / aluminosilicate fiber, and lithium iron phosphate nanoparticles, the present invention realizes the unity of high magnetic permeability and low eddy current loss of the nanocrystalline composite core material at high frequencies.

Description

Technical Field

[0001] The present invention relates to the field of soft magnetic materials, and particularly to a high magnetic permeability nanocrystalline composite transformer core material and a preparation method thereof. Background Art

[0002] As a core component for energy transmission and conversion in the power system, the performance of the transformer core directly affects the efficiency, loss, and stability of the transformer. Since the early 20th century, the transformer core material has experienced a development process from silicon steel to amorphous alloy and then to nanocrystalline alloy.

[0003] Although the traditional silicon steel sheet core has a mature process, it will generate a large iron loss during high-frequency applications; although the amorphous alloy has advantages such as low coercivity and high resistivity, its saturation magnetic induction intensity is relatively low, and it is brittle and difficult to process and form. In recent years, due to its excellent soft magnetic properties, such as high saturation magnetic induction intensity, high magnetic permeability, low coercivity, and low loss, the iron-based nanocrystalline alloy has become a key direction for the preparation of transformer core materials.

[0004] However, the nanocrystalline soft magnetic material still faces the problem of excessive eddy current loss in high-frequency applications. Especially in the frequency range above 10 kHz, the eddy current loss increases with the square of the frequency, becoming the main factor restricting the material performance. This problem mainly stems from the following aspects:

[0005] In the prior art, the thickness of the nanocrystalline strip is generally 20 - 30 μm. Due to the skin effect, the current is mainly distributed on the surface of the material at high frequencies, resulting in a reduction in the effective cross-sectional area and an increase in loss;

[0006] Although the resistivity of the iron-based nanocrystalline alloy (about 100 - 120 μΩ·cm) is higher than that of pure iron (about 10 μΩ·cm), it is still insufficient in high-frequency applications and cannot effectively suppress the formation of eddy currents; the magnetic domain structure of the material is unreasonable, and the loss generated by the movement of magnetic domain walls and the rotation of magnetic domains is relatively large under high-frequency alternating magnetic fields;

[0007] The traditional nanocrystalline strip is stacked or wound into a core, and the interlayer insulation is not ideal, and there are air gaps, increasing the magnetic resistance and loss.

[0008] Currently, the common methods for reducing the high-frequency eddy current loss of nanocrystalline materials include: reducing the strip thickness, increasing the material resistivity (such as by adding elements such as Si and B), improving the heat treatment process to optimize the magnetic domain structure, and using baking insulation technology to improve the interlayer insulation. However, these methods all have their own limitations: too thin a strip will reduce the mechanical strength and filling factor; excessive addition of non-magnetic elements will reduce the saturation magnetic induction intensity; the traditional heat treatment process is difficult to precisely control the magnetic domain structure; and simply improving the interlayer insulation cannot fundamentally solve the high-frequency loss problem of the material itself.

[0009] Therefore, it is of great significance to develop a nanocrystalline composite transformer core material that can simultaneously maintain high saturation magnetic induction intensity and high magnetic permeability while effectively reducing high-frequency eddy current loss, for improving the efficiency and performance of high-frequency transformers. Summary of the Invention

[0010] The purpose of the present invention is to provide a high-magnetic-permeability nanocrystalline composite transformer core material and its preparation method, to solve the problem of excessive eddy current loss of existing nanocrystalline materials in high-frequency applications, and to achieve the unity of high magnetic permeability and low eddy current loss.

[0011] The above technical objectives of the present invention are achieved through the following technical solutions:

[0012] A high-magnetic-permeability nanocrystalline composite transformer core material, comprising the following components in weight percentages:

[0013] Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder: 70 - 82 wt%, with a particle size of 20 - 45 μm;

[0014] Epoxy resin matrix: 8 - 18 wt%;

[0015] Hexagonal boron nitride (h-BN) nanosheets: 0.5 - 2.0 wt%, with a thickness of less than 50 nm and a diameter of 0.5 - 2 μm;

[0016] Composite system of polytetrafluoroethylene micro powder and aluminum silicate fiber: 3 - 5 wt%, where the weight ratio of polytetrafluoroethylene micro powder to aluminum silicate fiber is 0.8 - 1.2:1;

[0017] Lithium iron phosphate (LiFePO4) nanoparticles: 2 - 5 wt%, with a particle size of 50 - 100 nm.

[0018] The present invention is further provided that the epoxy resin is bisphenol A epoxy resin E51, and the epoxy resin matrix further comprises the following components:

[0019] Curing agent, which is methyltetrahydrophthalic anhydride (MTHPA), with a dosage of 3 - 5 wt% of the weight of the epoxy resin;

[0020] Accelerator, which is 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), with a dosage of 0.5 - 1.0 wt% of the weight of the epoxy resin;

[0021] Coupling agent, which is γ-glycidoxypropyltrimethoxysilane (KH560), with a dosage of 0.3 - 0.8 wt% of the total weight;

[0022] The dispersant is polyvinylpyrrolidone (PVP, K30), and the dosage is 0.2 - 0.5 wt% of the total weight.

[0023] The present invention also provides a preparation method of the above high magnetic permeability nanocrystalline composite transformer core material, including the following steps: (1) Mechanically crush and ball mill the Fe 73.5 Si 13.5 B9Cu1Nb3 alloy strip into powder with a particle size of 20 - 45 μm, and dry it in vacuum at 80°C for 4 hours; (2) Prepare a solution by mixing γ-glycidoxypropyltrimethoxysilane coupling agent and absolute ethanol in a weight ratio of 1:9, add the powder to the solution, stir at room temperature for 2 hours, and then dry it at 80°C for 6 hours; (3) Mix boron nitride nanosheets, polytetrafluoroethylene micropowder, aluminum silicate fiber, and lithium iron phosphate nanoparticles with the dispersant respectively, and ultrasonically disperse for 30 - 60 minutes to form a uniform suspension; (4) Heat the epoxy resin to 60°C, and sequentially add the suspension in step (3), and stir and mix for 30 minutes; (5) Add the surface-treated Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder, and stir and mix for 30 minutes; (6) Add the curing agent and accelerator, stir for 10 minutes, then evacuate to -0.095 MPa in a vacuum degassing box and degas for 10 minutes; (7) Pour the mixture into a mold preheated to 80°C, initially cure at 80°C for 2 hours, and post-cure at 120°C for 4 hours; (8) Place the cured composite material in a tube furnace, under nitrogen protection, heat it to 520 - 560°C at a rate of 3 - 5°C / min, hold for 0.5 - 2 hours, and then cool it to room temperature at a rate of 5°C / min.

[0024] The present invention is further configured such that the purity of the nitrogen gas for heat treatment in step (8) is greater than 99.9%, and the oxygen content is lower than 10 ppm to prevent the iron-based nanocrystalline particles from oxidizing at high temperatures.

[0025] The present invention is further configured such that the heat treatment temperature in step (8) is 540°C and the holding time is 1 hour.

[0026] The present invention is further configured such that the heating rate in step (8) is 4°C / min.

[0027] In summary, the present invention has the following beneficial effects:

[0028] In the prior art, the addition of non-magnetic components will dilute the volume fraction of the magnetic material, and theoretically reduce the saturation magnetic induction intensity and magnetic permeability of the composite material; the addition of conductive polymers or semiconductor materials will increase the conductivity of the material, and theoretically increase the eddy current loss. However, the combination in the present invention produces an effect contrary to the prior art, specifically as follows:

[0029] h-BN nanosheets: Non-magnetic materials generally reduce the saturation magnetic induction intensity and magnetic permeability of composite materials. However, their two-dimensional sheet-like structure shows a preferred orientation arrangement in the epoxy matrix, forming an ordered microstructure. This not only cuts off the eddy current path but also improves the magnetic domain structure through a stress release mechanism, thereby increasing the effective magnetic permeability of the material. The high thermal conductivity property of h-BN also accelerates heat dissipation and reduces the magnetic property degradation caused by temperature rise.

[0030] PTFE / aluminum silicate fiber composite system: Generally reduces the magnetic filling rate, but the formed micro-air gap network structure actually optimizes the magnetic flux path, reduces stray magnetic flux and eddy current loss. This air gap network also provides a stress buffer zone, alleviates the interface detachment problem caused by thermal expansion mismatch, and improves the mechanical stability and service life of the material.

[0031] LiFePO4 nanoparticles: As an ionic conductor, it has poor electronic conductivity itself and generally reduces the overall performance of the material. However, in the present invention, the phosphide / oxide composite interface layer formed by the interfacial reaction between its structure and iron-based nanocrystals effectively regulates the magnetic domain wall motion energy through magnetic ion substitution and electron transition mechanisms, significantly reduces the hysteresis loss at high frequencies, and improves the temperature stability of the material at the same time.

[0032] Moreover, there is a synergistic enhancement effect among the three components, which is as follows:

[0033] Interfacial synergistic effect: A small amount of oxygen released by LiFePO4 during heat treatment combines with B atoms at the edges of h-BN to form B-O bonds, enhancing the bonding force between h-BN and the matrix; meanwhile, the presence of h-BN promotes a more uniform interfacial reaction between LiFePO4 and iron-based nanocrystals.

[0034] Magnetic domain structure optimization synergy: h-BN nanosheets affect the magnetic domain arrangement through stress regulation; the PTFE / aluminum silicate fiber network regulates the magnetic domain size through micro-air gaps; the LiFePO4 interface layer affects the magnetic domain wall energy through magnetic ion exchange. The combined action of the three forms an optimized magnetic domain structure, minimizing the magnetic domain wall motion loss of the material under high-frequency alternating magnetic fields.

[0035] Resistivity gradient distribution synergy: The three materials form a resistivity gradient distribution from the core of nanocrystalline particles to the matrix in the composite system. Its gradient structure can more effectively suppress the formation of eddy currents than a uniform high-resistance structure while maintaining good magnetic properties.

[0036] In summary, through the synergistic effect of three components, namely boron nitride nanosheets, PTFE micro-powder / aluminum silicate fiber composite system, and lithium iron phosphate nanoparticles, the present invention realizes the unity of high magnetic permeability and low eddy current loss of nanocrystalline composite core materials at high frequencies, which is as follows:

[0037] (1) The multi-scale spatial confinement effect and conductive path regulation are realized: The three components form a nano-micro-macro multi-scale structure control system in the material. Boron nitride nanosheets are arranged perpendicular to the magnetic flux direction in a two-dimensional sheet structure; the combination of polytetrafluoroethylene micropowder and aluminum silicate fiber forms a micron-scale three-dimensional network; lithium iron phosphate nanoparticles are mainly distributed on the surface of iron-based nanocrystalline particles. This hierarchical isolation structure effectively cuts off the long-range conductive path in the material, making the resistivity of the composite material reach 800 - 1200 μΩ·cm.

[0038] (2) The multi-field coupling mechanism of magneto-electric-thermal is established: The three components form a complementary and synergistic effect in the multi-field coupling of electromagnetic heat. Boron nitride nanosheets have high thermal conductivity and can effectively conduct heat while blocking current; the micro-air gap network formed by the polytetrafluoroethylene / aluminum silicate fiber composite system increases both resistance and provides thermal stress buffering; lithium iron phosphate nanoparticles increase electron scattering through the interface layer. This multi-field coupling mechanism enables the material to maintain stable magnetic properties during high-frequency operation and significantly reduces the material temperature rise.

[0039] (3) The interfacial chemical interaction and mutual catalysis are realized: The three components undergo interfacial chemical interactions during high-temperature heat treatment. Partial interfacial reactions occur between lithium iron phosphate and the surface of iron-based nanocrystalline particles, forming (Fe,Li)3(PO4)2 and Fe2P phases, which increase the interfacial resistivity; boron nitride nanosheets form B-O-C bonds with the epoxy matrix, enhancing the bonding force with the matrix; a hydrogen bond network is formed between lithium iron phosphate and boron nitride, strengthening the overall structure.

[0040] (4) The disorder-order structure transformation is realized: The three components induce the disorder-order structure transformation of iron-based nanocrystals during heat treatment, promoting the ordered arrangement of Si atoms in the α-Fe(Si) phase. This atomic-scale ordered structure affects the magnetocrystalline anisotropy and magnetic permeability of the material, increasing the initial magnetic permeability of the material. Specific implementation mode

[0041] A high magnetic permeability nanocrystalline composite transformer core material, and its component ratio is:

[0042] Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder (particle size: 25 - 35 μm): 70 - 82 wt%;

[0043] Epoxy resin (bisphenol A epoxy resin E51): 8 - 18 wt%;

[0044] Curing agent (methyltetrahydrophthalic anhydride MTHPA): 3 - 5 wt% of the weight of the epoxy resin;

[0045] Accelerator (2,4,6-tris(dimethylaminomethyl)phenol (DMP-30): 0.5 - 1.0 wt% of the weight of the epoxy resin;

[0046] Coupling agent (γ-glycidyletheroxypropyltrimethoxysilane (KH560): 0.3 - 0.8 wt% of the weight of the epoxy resin;

[0047] Dispersant (polyvinylpyrrolidone PVP, K30): 0.2 - 0.5 wt% of the weight of the epoxy resin;

[0048] Hexagonal boron nitride nanosheets (h-BN, thickness 30 nm, diameter 1 μm): 0.5 - 2.0 wt%;

[0049] Composite system of polytetrafluoroethylene micropowder and aluminosilicate fiber: 3 - 5 wt%, where the weight ratio of polytetrafluoroethylene micropowder to aluminosilicate fiber is 0.8 - 1.2:1.

[0050] Lithium iron phosphate (LiFePO4) nanoparticles (particle size 80 nm): 2 - 5 wt%.

[0051] The preparation method is as follows: (1) The Fe 73.5 Si 13.5 B9Cu1Nb3 alloy strip is mechanically crushed and ball-milled to prepare a powder with a particle size of 20 - 45 μm, and dried in vacuum at 80 °C for 4 hours; (2) A solution is prepared by mixing γ-glycidyletheroxypropyltrimethoxysilane coupling agent and absolute ethanol at a weight ratio of 1:9, the powder is added to the solution, stirred at room temperature for 2 hours, and then dried at 80 °C for 6 hours; (3) The hexagonal boron nitride nanosheets, polytetrafluoroethylene micropowder, aluminosilicate fiber, and lithium iron phosphate nanoparticles are respectively mixed with the dispersant, and ultrasonically dispersed for 30 - 60 minutes to form a uniform suspension; (4) The epoxy resin is heated to 60 °C, and the suspension in step (3) is added in sequence, and stirred and mixed for 30 minutes; (5) The surface-treated Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder is added, and stirred and mixed for 30 minutes; (6) The curing agent and accelerator are added, stirred for 10 minutes, and then evacuated to -0.095 MPa in a vacuum degassing box for 10 minutes; (7) The mixture is poured into a mold preheated to 80 °C, preliminarily cured at 80 °C for 2 hours, and post-cured at 120 °C for 4 hours; (8) The cured composite material is placed in a tube furnace, heated from room temperature to 520 - 560 °C at a rate of 3 - 5 °C / min under 99.9% nitrogen protection, held for 0.5 - 2 hours, and then cooled to room temperature at a rate of 5 °C / min.

[0052] For the above iron core material and its preparation method, the present invention designs the following experiments to verify the above technical effects:

[0053] A total of 7 groups of formulations were designed for the experiment, including 5 experimental groups and 2 control groups. The formulation design is shown in Table 1 below:

[0054] Table 1: Design Table of Experimental Groups and Control Groups

[0055]

[0056] Note: The addition amounts of the curing agent and the accelerator are percentages relative to the weight of the epoxy resin.

[0057] Among them, Control Group 1: Basic formulation, only containing iron-based nanocrystalline powder and epoxy resin system.

[0058] Control Group 2: Commercial Fe 73.5 Si 13.5 B9Cu1Nb3 nanocrystalline ribbon, after standard heat treatment (550 °C, 1 hour).

[0059] Experimental Groups 1 - 3: Add single components respectively to evaluate the independent effects of each single component.

[0060] Experimental Group 4: Add two components of h-BN and PTFE / aluminum silicate fiber, but without LiFePO4, to verify the synergistic effect between the two-dimensional barrier layer and the three-dimensional network structure.

[0061] Experimental Group 5: Complete formulation, containing three components, to verify the complete multi-scale synergistic mechanism.

[0062] (1) DC Magnetic Property Test

[0063] Test method: Vibrating Sample Magnetometer (VSM) Equipment: LakeShore 8600 VSM system Test conditions: Room temperature, maximum external magnetic field strength ±20 kOe. The test results are shown in Table 2:

[0064] Table 2: Magnetic Property Test Table

[0065]

[0066] (2) AC Magnetic Loss Test

[0067] Test method: AC magnetic loss test system Equipment: IWATSUSY-8232B-H analyzer Test conditions: Toroidal sample, 100 turns of primary coil, 50 turns of secondary coil, temperature 25 °C. The test results are shown in Table 3 below,

[0068] Table 3: Magnetic Loss Test Table

[0069]

[0070] (3) Frequency Characteristic Test

[0071] Test method: Impedance analyzer Equipment: Agilent E4991A impedance analyzer Test conditions: Frequency range 1 kHz - 1 MHz, excitation voltage 0.5 V, temperature 25 °C. The test results are shown in Table 4 as follows:

[0072] Table 4: Frequency characteristic test table

[0073]

[0074] (4) Resistivity and skin depth test

[0075] Test method: Four-probe method and impedance analysis method Equipment: RTS-9 room temperature four-probe tester, Agilent E4991A impedance analyzer Test conditions: Room temperature, four-probe spacing 1 mm, test current 10 mA. The test results are shown in Table 5 as follows:

[0076] Table 5: Spot rough filtration and skin depth test table

[0077]

[0078] (5) Synergistic effect verification

[0079] ① Thermal behavior analysis

[0080] Test method: Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) Equipment: NETZSCH STA449F3 Jupiter thermal analyzer Test conditions: Temperature range 25 - 600 °C, heating rate 10 °C / min, N2 atmosphere. The test results are shown in Table 6 as follows:

[0081] Table 6: Thermal analysis result test table

[0082]

[0083] ② High-temperature long-term performance stability test

[0084] Test method: High-temperature magnetic property retention rate test Equipment: Customized high-temperature magnetic property test system Test conditions: 100 kHz, 0.05 T, temperature 150 °C, duration 24 hours. The test results are shown in Table 7 as follows:

[0085] Table 7: High-temperature long-term performance stability test table

[0086]

[0087] ③ Influence of heat treatment temperature change on the synergistic effect

[0088] Test method: Compare the performance of the samples of experimental group 5 under different heat treatment temperatures. Parameter changes: Heat treatment at 520 °C, 540 °C and 560 °C for 1 hour. The test results are shown in Table 8:

[0089] Table 8: Performance test table under different heat treatment temperatures

[0090]

[0091] ④ Influence of heat treatment time change on the synergistic effect

[0092] Test method: Compare the performance of the samples of experimental group 5 under different heat treatment times. Parameter changes: Insulation at 540 °C for 0.5 hour, 1 hour and 2 hours. The test results are shown in Table 9:

[0093] Table 9: Performance test table under different heat treatment times

[0094]

[0095] ⑤ Influence of heating rate change on the synergistic effect

[0096] Test method: Compare the performance of the samples of experimental group 5 under different heating rates. Parameter changes: Heat up to 540 °C at 2 °C / min, 4 °C / min and 6 °C / min, and keep warm for 1 hour. The test results are shown in Table 10:

[0097] Table 10: Performance test table under different heating rates

[0098]

[0099] Based on the above experimental data, the following conclusions can be drawn:

[0100] 1. Multi-scale spatial confinement effect:

[0101] From the resistivity data, the resistivity of experimental group 5 (three-component complete formula) reaches 950 μΩ·cm, which is much higher than that of the single-component experimental group (380 - 450 μΩ·cm) and the two-component experimental group 4 (680 μΩ·cm), indicating that the three components form an efficient multi-scale isolation structure.

[0102] The skin depth test results show that the skin depth of experimental group 5 (255 μm) is more than 2.5 times that of control group 1 (100 μm), proving that the multi-scale spatial confinement effect effectively improves the high-frequency electromagnetic performance.

[0103] Thermal behavior analysis shows that the thermal conductivity of experimental group 5 (3.5 W / m·K) is significantly higher than that of the basic formulation (0.8 W / m·K), and far exceeds that of the single-component formulation (1.0 - 2.3 W / m·K), verifying the synergistic enhancement of multiple components in heat conduction.

[0104] The high-temperature long-term performance stability test shows that the iron loss increase rate of experimental group 5 is only 7.0%, while that of control group 1 is as high as 28.9%, proving that the synergistic effect of multiple components significantly improves the thermal stability of the material.

[0105] The temperature rise test results show that the temperature rise of experimental group 5 after working at 100 kHz for 8 hours is only 35℃, much lower than that of control group 1 (85℃) and the single-component group (62 - 70℃), confirming the effectiveness of the multi-field coupling mechanism.

[0106] 2. Influence of process parameters on the synergistic effect

[0107] The results of the process parameter comparison experiment show that:

[0108] The heat treatment temperature has a significant influence on the synergistic effect. 540℃ is the optimal heat treatment temperature. At this temperature, the interface layer thickness is moderate (15 nm), and the h-BN orientation degree is the highest (85%), showing the best comprehensive performance.

[0109] The performance is the best when the heat treatment time is 1 hour. If the time is too short (0.5 hour), the interface reaction is insufficient. If the time is too long (2 hours), the interface layer becomes too thick, affecting the magnetic properties.

[0110] A heating rate of 4℃ / min is most conducive to forming a complete PTFE / fiber network structure while ensuring that the nanocrystal particle size is small and uniform.

[0111] This experimental design system verifies the synergistic effect of three components: h-BN nanosheets, PTFE / aluminum silicate fiber composite system, and LiFePO4 nanoparticles in the nanocrystalline composite transformer core material. The experimental results show that the synergy of these three substances realizes the unity of high magnetic permeability and low eddy current loss of the nanocrystalline composite material in high-frequency applications.

[0112] Especially under the high-frequency condition of 100 kHz, the iron loss of experimental group 5 is only 185 W / kg, which is more than 60% lower than that of the control group, and at the same time maintains a high initial magnetic permeability of 10500, about 1.4 times that of control group 1. The synergistic effect of the three components proves the core technical solution of the present invention.

[0113] In addition, the process parameter experiment shows that by optimizing the heat treatment temperature, time, and heating rate, the synergistic effect of the components can be further strengthened, providing corresponding references for subsequent industrialization.

[0114] This specific embodiment is only an interpretation of the present invention and does not limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

Claims

1. A high magnetic permeability nanocrystalline composite transformer core material, characterized in that: The composition includes the following weight percentages: Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder: 70-82wt%, particle size 20-45μm; Epoxy resin matrix: 8-18wt%; Boron nitride nanosheets: 0.5-2.0wt%, thickness less than 50nm, diameter 0.5-2μm; Composite system of polytetrafluoroethylene powder and aluminum silicate fiber: 3-5wt%, wherein the weight ratio of polytetrafluoroethylene powder to aluminum silicate fiber is 0.8-1.2:1; Lithium iron phosphate nanoparticles: 2-5wt%, particle size 50-100nm; The composite system of boron nitride nanosheets, polytetrafluoroethylene micropowder and aluminum silicate fiber and lithium iron phosphate nanoparticles together form a multi-scale isolation structure.

2. The high magnetic permeability nanocrystalline composite transformer core material according to claim 1, characterized in that: The epoxy resin matrix also includes the following components: Curing agent, methyltetrahydrophthalic anhydride, used in an amount of 3-5wt% of the weight of the epoxy resin; The accelerator is 2,4,6-tris(dimethylaminomethyl)phenol, and the amount used is 0.5-1.0wt% of the weight of the epoxy resin; The coupling agent is γ-glycidyloxypropyltrimethoxysilane, and the amount used is 0.3-0.8wt% of the total weight; The dispersant is polyvinyl pyrrolidone, and the amount used is 0.2-0.5wt% of the total weight.

3. A method for preparing a high magnetic permeability nanocrystalline composite transformer core material as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Fe 73.5 Si 13.5 The B9Cu1Nb3 alloy strip was prepared into 20-45 μm powder by mechanical crushing and ball milling, and vacuum dried at 80 °C for 4 hours; (2) preparing a solution of γ-glycidyloxypropyltrimethoxysilane coupling agent and anhydrous ethanol in a weight ratio of 1:9, adding the powder to the solution, stirring at room temperature for 2 hours, and drying at 80° C. for 6 hours; (3) mixing boron nitride nanosheets, polytetrafluoroethylene powder, aluminum silicate fibers and lithium iron phosphate nanoparticles with a dispersant respectively, and performing ultrasonic dispersion for 30-60 minutes to form a uniform suspension; (4) Heat the epoxy resin to 60° C., add the suspension in step (3) in sequence, and stir and mix for 30 minutes; (5) Adding surface treated Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder, stirred and mixed for 30 minutes; (6) Add curing agent and accelerator, stir for 10 minutes, evacuate to -0.095 MPa in a vacuum degassing box, and degas for 10 minutes; (7) pouring the mixture into a mold preheated to 80°C, preliminarily curing at 80°C for 2 hours, and post-curing at 120°C for 4 hours; (8) The cured composite material is placed in a tubular furnace, and under nitrogen protection, the temperature is raised to 520-560°C at a rate of 3-5°C / min, and after being kept at this temperature for 0.5-2 hours, the composite material is cooled to room temperature at a rate of 5°C / min.

4. The preparation method according to claim 3, characterized in that: The nitrogen purity in step (8) is greater than 99.9%, and the oxygen content is less than 10 ppm.

5. The preparation method according to claim 3, characterized in that: The heat treatment temperature in step (8) is 540°C and the holding time is 1 hour.

6. The preparation method according to claim 3, characterized in that: The heating rate in step (8) is 4°C / min.

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