High-permeability low-loss nanocrystalline magnetic powder core based on high-resistivity ultrathin insulating layer and preparation method of high-permeability low-loss nanocrystalline magnetic powder core

Abstract

The invention discloses a high-permeability and low-loss nanocrystalline magnetic powder core based on a high-resistivity ultrathin insulating layer and a preparation method thereof.According to the high-permeability and low-loss nanocrystalline magnetic powder core, the high-resistivity ultrathin molybdenum insulating layer is generated through in-situ thermal decomposition of ammonium molybdate on the surface of powder, and forming and heat treatment are combined to obtain the high-permeability and low-loss nanocrystalline magnetic powder core. The method minimizes the influence on the intrinsic characteristics of the magnetic powder core, such as magnetic conductivity and saturation magnetization intensity, is short in processing time and high in applicability, and can be widely applied to medium-high frequency electronic devices in various fields.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic powder core materials, and particularly relates to a high magnetic permeability and low loss nanocrystalline magnetic powder core based on a high resistivity ultra-thin insulating layer and a preparation method thereof. Background Art

[0002] With the emergence of third-generation semiconductors such as SiC and GaN, the development of power electronic devices with higher power density has been continuously promoted. At the same time, the demand for soft magnetic materials with excellent high-frequency properties such as high magnetic permeability (μ) and low core loss (P cv ) is also increasing continuously. Compared with traditional soft magnetic materials, magnetic powder cores have an inter-particle insulation structure with high resistivity, which can significantly reduce eddy current loss, so they have significant advantages in high-frequency applications. Compared with traditional iron, iron-silicon, ferrosilite, and iron-nickel magnetic powder cores, nanocrystalline magnetic powder cores have better high-frequency soft magnetic properties, including lower coercivity and higher resistivity, and can better meet the development trend of high-frequency, miniaturization, and high-efficiency of electronic components. However, with the increase in frequency, the eddy current loss of the magnetic powder core gradually increases. How to realize the possibility of reducing the core loss by constructing a high resistivity, well-bonded and stable insulating layer on the surface of the magnetic powder has become the focus of research.

[0003] At present, a large number of studies have been devoted to the preparation of various insulating layers. The insulating layers are mainly divided into two categories: inorganic insulating layers and organic insulating layers. Although organic insulating layers can be well combined with powders, their poor thermal stability severely limits their high-temperature annealing treatment. Inorganic materials have better resistivity and high-temperature resistance than organic materials. In recent years, most studies have focused on using inorganic insulating materials such as phosphates, SiO2, and Al2O3. The most common method is to synthesize a phosphate coating through phosphate passivation. However, this phosphate layer is prone to cracking under high pressure, while other inorganic insulating materials are prone to uneven distribution of the insulating layer and excessive dilution of the intrinsic magnetic properties of the magnetic powder core, such as saturation magnetization and magnetic permeability, during the preparation process.

[0004] As a wide-bandgap insulator, molybdenum oxide has a resistivity (ρ) as high as 186 Ω·cm and exhibits good thermal stability at high temperatures. It can construct a high-resistivity ultra-thin insulating layer on the surface of magnetic powder through the in-situ thermal decomposition of ammonium molybdate, and this insulating layer is well combined with the powder surface, continuous and stable. It can significantly reduce the core loss of the magnetic powder core while maintaining its high intrinsic magnetic properties, such as magnetic permeability and saturation magnetization. At the same time, the preparation process is simple, the reaction process is controllable, and it is suitable for industrial production.

[0005] Chinese Patent Application CN119296942A discloses a preparation process of a magnetic powder core with high magnetic permeability and low loss. The preparation process includes the following steps: synthesis of TiO2@Al2O3 nanowires; preparation of an insulating coating; powder insulation coating; and preparation of the magnetic powder core. Although this multi-step, multi-material, and multi-stage operation reduces the loss at high frequencies, the introduction of excessive non-magnetic phases results in a relatively low magnetic permeability, and the process complexity is high, making it difficult to quickly promote and apply in large-scale industrial production. Chinese Patent Application CN116417234A discloses a low-loss soft magnetic powder, its preparation method, and a soft magnetic powder core. The above preparation method includes the following steps: Step S1, pickling the metal soft magnetic powder to obtain pickled magnetic powder; Step S2, depositing a metal oxide layer or a non-metal oxide layer on the surface of the pickled magnetic powder by magnetron sputtering, and then performing vacuum heat treatment to obtain a low-loss soft magnetic powder. This patent application applies the magnetron sputtering process to the coating preparation process of soft magnetic powder, effectively improving the surface resistance of the soft magnetic powder with a relatively simple process, and preparing a low-loss soft magnetic powder that can be used at high frequencies. The soft magnetic powder core prepared therefrom also has low-loss performance at high frequencies. The magnetic powder core disclosed in this patent application can effectively suppress high-frequency eddy current loss and improve the quality factor of inductive devices. However, due to the difficulty in controlling the reaction rate, the insulating layer is prone to expand and crack, ultimately resulting in poor insulation. The literature Li, Z. et al. Ceram. Int. 48, 29705–29714 (2022) prepared a FeSiAl / MoO3 core / shell structure magnetic powder core material through a two-step heat treatment process. This method effectively suppresses the loss of the magnetic powder core material, but this method significantly reduces its magnetic permeability. When the ammonium molybdate content is 20 wt.%, the magnetic permeability is only 25.8.

[0006] Therefore, there is an urgent need to develop a high-resistivity, thin, and dense insulating layer to optimize the magnetic properties of nanocrystalline magnetic powder cores, thereby achieving the purpose of high magnetic permeability and low loss. Summary of the Invention

[0007] Object of the Invention: The technical problem to be solved by the present invention is to provide a high-magnetic-permeability and low-loss nanocrystalline magnetic powder core based on a high-resistivity ultra-thin insulating layer and its preparation method.

[0008] Technical Solution: To solve the above technical problem, the present invention provides a preparation method of a high-magnetic-permeability and low-loss nanocrystalline magnetic powder core based on a high-resistivity ultra-thin insulating layer, including the following steps:

[0009] (1) Place the soft magnetic alloy powder in an ammonium molybdate aqueous solution, continuously perform ultrasonic oscillation and uniform stirring, and then dry the mixed solution in an oven at 80–110 °C for 1-3 hours to obtain a precursor powder with a core-shell structure;

[0010] (2) Anneal the prepared precursor powder at 400 - 430 °C for 1 - 2 h under vacuum conditions to obtain soft magnetic alloy powder with a molybdenum oxide insulating layer;

[0011] (3) Add the soft magnetic alloy powder with a molybdenum oxide insulating layer to the acetone solution of the organic resin, continuously ultrasonically oscillate and stir evenly. After the acetone completely volatilizes, obtain soft magnetic alloy powder with an inorganic - organic composite coating layer;

[0012] (4) Press and heat - treat the soft magnetic alloy powder with an inorganic - organic composite coating layer to obtain an iron - based nanocrystalline magnetic powder core.

[0013] Among them, the preparation steps of the soft magnetic alloy powder in step (1) are as follows: Weigh the raw materials according to atomic percentages, and perform induction melting under the protection of an inert gas, and air - cool to obtain a master alloy ingot; After crushing the master alloy ingot, put it into the high - frequency melting furnace of the gas atomization powder - making equipment, melt the alloy under an inert atmosphere condition. When the alloy liquid flows into the atomization chamber for atomization and dispersion, obtain alloy powder after cooling; Screen the alloy powder to obtain soft magnetic alloy powder with the target particle size.

[0014] Among them, the composition of the master alloy ingot is: (Fe a Co b Si c B d P e C f ) g Cu 0.8 Nb h , and the atomic percentages of each element satisfy: 0.6 ≤ a ≤ 0.8, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1, 0 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1, 95 ≤ g ≤ 100, 0 ≤ h ≤ 3, and a + b + c + d + e + f = 1, g + 0.8 + h = 100.

[0015] Among them, the inert gas is nitrogen or argon, the atomization pressure is 7 - 9 MPa, and the nozzle diameter is 1 - 2 mm.

[0016] Among them, the median particle size D50 of the alloy powder is 20 - 50 μm, with high sphericity, and the content of the powder with an amorphous structure in the powder is higher than 80%.

[0017] Among them, the size of the soft magnetic alloy powder with the target particle size obtained after screening is 5 - 75 μm, and it is a completely amorphous structure.

[0018] Among them, the mass percentage concentration of the ammonium molybdate aqueous solution in step (1) is 5 - 15%, the ammonium molybdate content is less than 5 wt.%, the molybdenum oxide insulating layer is discontinuous, and when the ammonium molybdate content is higher than 15 wt.%, the molybdenum oxide insulating layer is too thick and will peel off;

[0019] Among them, the organic resin described in step (3) is one or more of epoxy resin, silicone resin or epoxy-modified silicone resin, and the dosage of the organic resin is 2-3% of the mass of the powder after coating treatment.

[0020] Among them, in step (4), cold pressing is used for molding, the pressure is 1500-1800 MPa, and the pressure holding time is 30-60 s.

[0021] Among them, in step (4), the heat treatment is carried out under vacuum conditions or in an inert atmosphere, the heat treatment temperature is 480-540 °C, and the heat treatment time is 30-60 min.

[0022] The content of the present invention includes the high magnetic permeability and low loss nanocrystalline magnetic powder core prepared by the described preparation method.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0024] (1) The present invention uses ammonium molybdate thermal decomposition to in-situ generate a continuous and defect-free ultra-thin molybdenum oxide insulating layer with high resistivity on the powder surface, effectively achieving the insulation coating effect. The insulating layer prepared by this method has high resistivity, thin thickness and good thermal stability.

[0025] (2) After pressing and annealing, the magnetic powder core prepared by this process has the performance advantages of good frequency stability and high matching degree of magnetic permeability and loss at high frequencies, that is, it can maintain high magnetic permeability and high saturation magnetization intensity on the basis of reducing loss, meeting the technical requirements of miniaturization and high frequency.

[0026] (3) At the same time, the present invention uses the gas atomization method to prepare iron-based amorphous soft magnetic alloy powder, and the obtained powder has a higher sphericity and a more uniform particle distribution, which is beneficial to subsequent pressing and in-situ coating.

[0027] (4) The preparation process of the present invention is simple, with low cost, mature process and suitable for large-scale production. Description of the drawings

[0028] Figure 1 It is a scanning electron microscope image of the amorphous powder prepared in Example 1;

[0029] Figure 2 It is a particle size distribution diagram of the sieved amorphous powder prepared in Example 1;

[0030] Figure 3 It is a DSC curve diagram of the amorphous powder prepared in Example 1;

[0031] Figure 4 It is a scanning electron microscope image of the alloy powder before and after molybdenum oxide coating in Example 1;

[0032] Figure 5 The hysteresis loop curve of the nanocrystalline magnetic powder core prepared in Example 1;

[0033] Figure 6 The curve of the loss of the nanocrystalline magnetic powder core prepared in Example 1 varying with frequency;

[0034] Figure 7 The curve of the magnetic permeability of the nanocrystalline magnetic powder core prepared in Example 1 varying with frequency;

[0035] Figure 8 The curve of the DC bias characteristic of the nanocrystalline magnetic powder core prepared in Example 1. Specific implementation mode

[0036] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with the drawings and specific embodiments.

[0037] Example 1

[0038] Based on the iron-based nanocrystalline alloy (Fe 0.72 Co 0.04 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 A preparation method for preparing an iron-based nanocrystalline magnetic powder core, comprising the following steps:

[0039] (1) Weigh the iron, cobalt, boron, silicon, copper, niobium and iron-carbon master alloy (with a carbon mass percentage of 5%) and iron-phosphorus master alloy (with a phosphorus mass percentage of 26.4%) with a purity greater than 99 wt.% purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd. according to the atomic percentage, and carry out induction melting under the protection of a high-purity argon atmosphere. The melting temperature is 1250 °C to 1350 °C, and the melting furnace time is 15 minutes to obtain a (Fe 0.72 Co 0.04 P 0.05 C 0.0 2B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 master alloy ingot;

[0040] (2) Use the gas atomization method to make powder, and use (Fe 0.72 Co 0.04 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7Cu 0.8 Nb 1.5 The master alloy ingot is inductively melted into a qualified alloy liquid under an argon protection atmosphere. The alloy liquid flows out from the bottom leak hole of the melting quartz tube and meets a high-speed and high-pressure argon gas flow with a pressure of 8 Mpa through a nozzle with a diameter of 1.2 mm and is atomized into fine droplets. The atomized droplets are quickly solidified into soft magnetic alloy powder in a closed atomization cylinder.

[0041] (3) Screen the soft magnetic alloy powder with a 400-mesh sieve to obtain powder with the target particle size;

[0042] (4) Powder surface modification treatment: Add 0.5 g of ammonium molybdate to 9.5 g of deionized water to prepare an ammonium molybdate aqueous solution with a concentration of 5 wt.% as the precursor. Place 5 g of the soft magnetic alloy powder after the screening treatment in step (3) into the precursor solution, continuously perform ultrasonic oscillation and uniform stirring, and then dry the mixed solution in an oven at 110 °C for 2 hours to obtain a precursor powder with a core-shell structure;

[0043] (5) Anneal the precursor powder with the core-shell structure at 400 °C for 1 h under vacuum conditions to obtain soft magnetic alloy powder coated with a molybdenum oxide insulating layer;

[0044] (6) Add 2 g of the soft magnetic alloy powder with a molybdenum oxide insulating layer to an acetone (AR, Sinopharm Chemical Reagent Co., Ltd.) solution of epoxy resin (W-6C, Macklin). The mass ratio of epoxy resin to acetone is 1:5, and the mass of epoxy resin is 2% of the mass of the powder. Continuously stir for 20 min under ultrasonic vibration. After the acetone completely volatilizes, place the powder in an oven and dry it at 100 °C for 30 min to obtain powder coated with a composite of epoxy resin and molybdenum oxide;

[0045] (7) Cold press the powder coated with a composite of epoxy resin and molybdenum oxide, and at the same time select zinc stearate accounting for 0.5% of the powder mass as a lubricant for demolding; The cold pressing conditions are as follows: After putting the powder into the mold, apply force at a rate of 1000 N / s, and keep the pressure at 1800 MPa for 60 s through a hydraulic press to prepare a ring-shaped magnetic powder core material;

[0046] (8) Vacuum anneal the formed magnetic powder core material at 510 °C and keep it warm for 30 min to obtain a nanocrystalline magnetic powder core.

[0047] The thickness of the molybdenum oxide insulating layer of the nanocrystalline magnetic powder core material prepared in this example is only 7 nm. The saturation magnetization intensity of the magnetic powder core material is 145 emu / g, and the loss at 0.05 T and 1 MHz is 2131 mW / cm 3 , and the magnetic permeability remains at 60 at a frequency of 20 MHz. Under an external magnetic field of 100 Oe, the magnetic permeability remains at 60% of that without a magnetic field.

[0048] The soft magnetic powder prepared in Example 1 was observed using a scanning electron microscope (SEM), and the results are as Figure 1 shown. It can be Figure 1 seen that the prepared powder has a high sphericity, a smooth surface, and no obvious defects. Compared with flaky powder, spherical powder is more conducive to uniformly coating an insulating layer on the powder subsequently, and the generated insulating layer is not easily broken during the subsequent cold pressing process, so it can more effectively suppress eddy current loss at high frequencies.

[0049] The soft magnetic powder prepared in Example 1 was observed using a laser particle size analyzer, and the results are as Figure 2 shown. The average particle size of the powder after screening in Example 1 is 24 μm.

[0050] The thermal performance parameters of the soft magnetic powder prepared in Example 1 were detected using a differential scanning calorimeter (DSC), as Figure 3 shown. The initial crystallization temperature of the powder was measured to be T x1 at 520 °C and the secondary crystallization temperature T x2 at 578 °C under the condition of a heating rate of 40 °C / min.

[0051] The powder morphology before and after molybdenum oxide coating in Example 1 was observed using a scanning electron microscope, and the results are as Figure 4 shown. The surface of the untreated powder is smooth. After molybdenum oxide coating, the surface roughness of the powder increases, indicating that a continuous and uniform molybdenum oxide insulating layer is formed on the powder surface.

[0052] The saturation magnetization intensity (M s ) of the nanocrystalline magnetic powder core in Example 1 was measured using a vibrating sample magnetometer (VSM) (the maximum external magnetic field is 800 kA / m), and the hysteresis loop is as Figure 5 shown. The magnetic powder core after coating treatment still maintains a high saturation magnetization intensity of 145 emu / g.

[0053] The loss of the nanocrystalline magnetic powder core was measured using a B-H analyzer in cooperation with a power amplifier under the condition of an external magnetic field of 0.05 T, as Figure 6 shown. The loss of the nanocrystalline magnetic powder core in Example 1 increases with the increase of frequency under the condition of 0.05 T, and the loss is only 2131 mW / cm 3 at 0.05 T and 1 MHz.

[0054] The magnetic permeability of the sample was measured using an impedance analyzer under the condition of 1 A / m, as Figure 7 shown. The magnetic permeability of the nanocrystalline magnetic powder core in Example 1 can remain at 60 at a frequency of 20 MHz, and its high-frequency performance is excellent.

[0055] The DC bias performance of the nanocrystalline magnetic powder core was tested using a broadband LCR tester with a DC current source under the conditions of 0.5 V and 100 kHz. As Figure 8 shown, under an external magnetic field of 100 Oe, the magnetic permeability of the nanocrystalline magnetic powder core prepared in Example 1 can still be maintained at 60% of that without a magnetic field, showing excellent DC bias resistance, and the material can work at a larger current.

[0056] Example 2

[0057] A preparation method of an iron-based nanocrystalline magnetic powder core based on an iron-based nanocrystalline alloy (Fe 0.76 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb1 includes the following steps:

[0058] (1) The raw material iron, cobalt, boron, silicon, copper, niobium and iron-carbon master alloy (mass percentage of carbon is 5%) and iron-phosphorus master alloy (mass percentage of phosphorus is 26.4%) purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd. were proportioned by atomic percentage and subjected to induction melting under the protection of a high-purity argon atmosphere. The melting temperature was 1250 °C to 1350 °C, and the melting time in the furnace was 15 minutes to obtain a (Fe 0.76 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb1 master alloy ingot with uniform composition;

[0059] (2) The gas atomization method was used to make powder. The (Fe 0.76 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb1 master alloy ingot was inductively melted into a qualified alloy liquid under an argon protection atmosphere. The alloy liquid flowed out from the bottom leak hole of the melting quartz tube and met a high-speed and high-pressure argon gas flow with a pressure of 8 Mpa through a nozzle with a diameter of 1.2 mm and was atomized into fine droplets. The atomized droplets quickly solidified into soft magnetic alloy powder in a closed atomization cylinder;

[0060] (3) The soft magnetic alloy powder was screened with a 400-mesh sieve to obtain powder with a target particle size;

[0061] (4) Powder surface modification treatment: 0.7 g of ammonium molybdate was added to 9.3 g of deionized water to prepare an ammonium molybdate aqueous solution with a concentration of 7 wt.% as a precursor. 5 g of soft magnetic alloy powder after sieving in step (3) was placed in the precursor solution, and ultrasonic oscillation was continuously carried out and stirred uniformly. Then the mixed solution was dried in an oven at 110 °C for 2 hours to obtain a precursor powder with a core-shell structure;

[0062] (5) The precursor powder was annealed at 400 °C for 1 h under vacuum conditions to obtain a powder coated with a molybdenum oxide insulating layer;

[0063] (6) 2 g of soft magnetic alloy powder with a molybdenum oxide insulating layer was added to an acetone (AR, Sinopharm Chemical Reagent Co., Ltd.) solution of epoxy resin (W-6C, Macklin). The mass ratio of epoxy resin to acetone was 1:5, and the mass of epoxy resin was 2% of the mass of the powder. Stirring was continuously carried out under ultrasonic vibration for 20 min. After the acetone completely volatilized, the powder was placed in an oven and dried at 100 °C for 30 min to obtain a powder coated with a composite of epoxy resin and molybdenum oxide;

[0064] (7) Cold pressing and forming were carried out on the above composite-coated powder, and zinc stearate accounting for 0.5% of the powder mass was selected as a lubricant for demolding; the cold pressing conditions were as follows: after the powder was put into the mold, force was applied at a rate of 1000 N / s, and a ring-shaped magnetic powder core material was prepared by holding pressure at 1800 MPa for 60 s through a hydraulic press;

[0065] (8) The formed magnetic powder core material was vacuum annealed at 510 °C and held for 30 min to obtain a nanocrystalline magnetic powder core.

[0066] The thickness of the molybdenum oxide insulating layer prepared in this example was only 8 nm, the saturation magnetization intensity of the magnetic powder core material was 143 emu / g, and the loss at 0.05 T and 1 MHz was 2245 mW / cm 3 , and the magnetic permeability remained at 58 at a frequency of 20 MHz. Under an external magnetic field of 100 Oe, the magnetic permeability remained at 64% of that without a magnetic field.

[0067] Example 3

[0068] Based on an iron-based nanocrystalline alloy (Fe 0.68 Co 0.08 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 A preparation method for an iron-based nanocrystalline magnetic powder core, comprising the following steps:

[0069] (1) The raw material iron, cobalt, boron, silicon, copper, niobium and iron-carbon master alloy (mass percentage of carbon is 5%) and iron-phosphorus master alloy (mass percentage of phosphorus is 26.4%) purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd. are proportioned by atomic percentage, and are melted by induction melting under the protection of high-purity argon atmosphere. The melting temperature is 1250 °C to 1350 °C, and the melting furnace time is 15 minutes to obtain a master alloy ingot with uniform composition (Fe 0.68 Co 0.08 P 0.05 C 0.0 2B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 master alloy ingot;

[0070] (2) The powder is prepared by gas atomization method. The (Fe 0.68 Co 0.08 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 master alloy ingot is melted by induction into a qualified alloy liquid under the protection of argon atmosphere. The alloy liquid flows out from the bottom orifice of the melting quartz tube, meets with a high-speed and high-pressure argon gas flow with a pressure of 8 Mpa through a nozzle with a diameter of 1.2 mm and is atomized into fine droplets. The atomized droplets are quickly solidified into soft magnetic alloy powder in a closed atomization cylinder;

[0071] (3) The soft magnetic alloy powder is screened with a 400-mesh sieve to obtain powder with the target particle size;

[0072] (4) Powder surface modification treatment: 0.5 g of ammonium molybdate is added to 9.5 g of deionized water to prepare an ammonium molybdate aqueous solution with a concentration of 5 wt.% as a precursor. 5 g of the soft magnetic alloy powder after the screening treatment in step (3) is placed in the precursor solution, continuously ultrasonically oscillated and evenly stirred, and then the mixed solution is dried in an oven at 110 °C for 2 hours to obtain a precursor powder with a core-shell structure;

[0073] (5) The precursor powder is annealed at 400 °C for 1 h under vacuum conditions to obtain a powder coated with an insulating molybdenum oxide layer;

[0074] (6) Add 2 g of soft magnetic alloy powder with a molybdenum oxide insulating layer to an acetone (AR, Sinopharm Chemical Reagent Co., Ltd.) solution of epoxy resin (W-6C, Macklin). The mass ratio of epoxy resin to acetone is 1:5, and the mass of epoxy resin is 2% of the mass of the powder. Continuously stir for 20 min under ultrasonic vibration. After the acetone has completely evaporated, place the powder in an oven and dry it at 100 °C for 30 min to obtain powder coated with a composite of epoxy resin and molybdenum oxide.

[0075] (7) Cold press the powder coated with a composite of epoxy resin and molybdenum oxide. At the same time, select zinc stearate accounting for 0.5% of the powder mass as a lubricant for demolding. The conditions for cold pressing are as follows: After putting the powder into the mold, apply force at a rate of 1000 N / s, and use a hydraulic press to hold the pressure at 1800 MPa for 60 s to prepare a ring-shaped magnetic powder core material.

[0076] (8) Vacuum anneal the formed magnetic powder core material at 510 °C and hold for 30 min to obtain a nanocrystalline magnetic powder core.

[0077] The thickness of the molybdenum oxide insulating layer prepared in this example is only 7.3 nm. The saturation magnetization intensity of the magnetic powder core material is 146 emu / g, and the loss at 0.05 T and 1 MHz is 2466 mW / cm 3 , and the magnetic permeability remains at 65 at a frequency of 20 MHz. Under an external magnetic field of 100 Oe, the magnetic permeability remains at 61% of that without a magnetic field.

[0078] Example 4

[0079] Based on an iron-based nanocrystalline alloy (Fe 0.72 Co 0.04 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 A preparation method for an iron-based nanocrystalline magnetic powder core, comprising the following steps:

[0080] (1) Weigh raw material iron, cobalt, boron, silicon, copper, niobium, and iron-carbon master alloy (mass percentage of carbon is 5%) and iron-phosphorus master alloy (mass percentage of phosphorus is 26.4%) with a purity greater than 99 wt.% purchased from Zhongnuoxin Cai (Beijing) Technology Co., Ltd. according to atomic percentages. Under the protection of a high-purity argon atmosphere, conduct induction melting at a melting temperature of 1250 °C to 1350 °C for 15 minutes to obtain a compositionally uniform (Fe 0.72 Co 0.04 P 0.05 C 0.0 2B 0.08Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 Master alloy ingot;

[0081] (2) Use gas atomization to make powder. Melt the (Fe 0.72 Co 0.04 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 Master alloy ingot is inductively melted into alloy liquid with qualified composition under the protection of argon atmosphere. The alloy liquid flows out from the leakage hole at the bottom of the melting quartz tube, meets with a high-speed and high-pressure argon gas flow with a pressure of 8 Mpa through a nozzle with a diameter of 1.2 mm and is atomized into fine droplets. The atomized droplets are quickly solidified into soft magnetic alloy powder in a closed atomization cylinder;

[0082] (3) Screen the soft magnetic alloy powder with a 400-mesh sieve to obtain powder with the target particle size;

[0083] (4) Powder surface modification treatment: Add 0.5 g of ammonium molybdate to 9.5 g of deionized water to prepare an ammonium molybdate aqueous solution with a concentration of 5 wt.% as the precursor. Place 5 g of the soft magnetic alloy powder after screening in step (3) into the precursor solution, continuously ultrasonically vibrate and stir evenly, and then dry the mixed solution in an oven at 110 °C for 2 hours to obtain precursor powder with a core-shell structure;

[0084] (5) Anneal the precursor powder at 420 °C for 1 h under vacuum conditions to obtain powder coated with an insulating molybdenum oxide layer;

[0085] (6) Add 2 g of the soft magnetic alloy powder with an insulating molybdenum oxide layer to the acetone (AR, Sinopharm Chemical Reagent Co., Ltd.) solution of epoxy resin (W-6C, Macklin). The mass ratio of epoxy resin to acetone is 1:5, and the mass of epoxy resin is 2% of the mass of the powder. Continuously stir under ultrasonic vibration for 20 min. After the acetone completely evaporates, place the powder in an oven and dry it at 100 °C for 30 min to obtain powder coated with a composite of epoxy resin and molybdenum oxide;

[0086] (7) Cold press the powder coated with a composite of epoxy resin and molybdenum oxide, and at the same time select zinc stearate accounting for 0.5% of the powder mass as a lubricant for demolding; The cold pressing conditions are: After putting the powder into the mold, apply force at a rate of 1000 N / s, and keep the pressure at 1800 MPa for 60 s through a hydraulic press to prepare a ring-shaped magnetic powder core material;

[0087] (8) The formed magnetic powder core material is vacuum annealed at 510 °C and held for 60 min to obtain the nanocrystalline magnetic powder core.

[0088] The thickness of the molybdenum oxide insulating layer prepared in this example is only 5.8 nm, the saturation magnetization of the magnetic powder core material is 145 emu / g, the loss is 2031 mW / cm3 at 0.05 T and 1 MHz, the magnetic permeability remains at 61 at a frequency of 20 MHz, and the magnetic permeability remains at 60% of that without an external magnetic field under an external magnetic field of 100 Oe.

[0089] Example 5

[0090] Based on the iron-based nanocrystalline alloy (Fe 0.72 Co 0.04 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 A preparation method for an iron-based nanocrystalline magnetic powder core, comprising the following steps:

[0091] (1) The raw material iron, cobalt, boron, silicon, copper, niobium and iron-carbon master alloy (mass percentage of carbon is 5%) and iron-phosphorus master alloy (mass percentage of phosphorus is 26.4%) purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd. are proportioned by atomic percentage, and are induction melted under the protection of a high-purity argon atmosphere. The melting temperature is 1250 °C to 1350 °C, and the melting furnace time is 15 minutes to obtain a compositionally uniform (Fe 0.72 Co 0.04 P 0.05 C 0.0 2B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5 master alloy ingot;

[0092] (2) Use the gas atomization method to make powder, and use (Fe 0.72 Co 0.04 P 0.05 C 0.02 B 0.08 Si 0.09 ) 97.7 Cu 0.8 Nb 1.5The master alloy ingot is inductively melted into a qualified alloy liquid under an argon protection atmosphere. The alloy liquid flows out from the bottom leak hole of the melting quartz tube and meets a high-speed and high-pressure argon gas flow with a pressure of 8 Mpa through a nozzle with a diameter of 1.2 mm and is atomized into fine droplets. The atomized droplets are rapidly solidified into soft magnetic alloy powder in a closed atomization cylinder;

[0093] (3) Sieving the soft magnetic alloy powder with a 400-mesh sieve to obtain powder with a target particle size;

[0094] (4) Powder surface modification treatment: Add 0.9 g of ammonium molybdate to 9.1 g of deionized water to prepare an ammonium molybdate aqueous solution with a concentration of 9 wt.% as a precursor. Place 5 g of the soft magnetic alloy powder after sieving in step (3) into the precursor solution, continuously ultrasonically oscillate and stir evenly, and then dry the mixed solution in an oven at 110 °C for 2 hours to obtain a precursor powder with a core-shell structure;

[0095] (5) Anneal the precursor powder at 400 °C for 1 h under vacuum conditions to obtain powder coated with an insulating molybdenum oxide layer;

[0096] (6) Add 2 g of the soft magnetic alloy powder with an insulating molybdenum oxide layer to an acetone (AR, Sinopharm Chemical Reagent Co., Ltd.) solution of epoxy resin (W-6C, Macklin). The mass ratio of epoxy resin to acetone is 1:5, and the mass of epoxy resin is 2% of the mass of the powder. Continuously stir under ultrasonic vibration for 20 min. After the acetone has completely evaporated, place the powder in an oven and dry it at 100 °C for 30 min to obtain powder coated with a composite of epoxy resin and molybdenum oxide;

[0097] (7) Cold press the powder coated with a composite of epoxy resin and molybdenum oxide, and at the same time select zinc stearate accounting for 0.5% of the powder mass as a lubricant for demolding; the cold pressing conditions are as follows: After putting the powder into the mold, apply force at a rate of 1000 N / s, and keep the pressure at 1800 MPa for 60 s through a hydraulic press to prepare a ring-shaped magnetic powder core material;

[0098] (8) Vacuum anneal the formed magnetic powder core material at 510 °C and keep it warm for 30 min to obtain a nanocrystalline magnetic powder core.

[0099] The thickness of the insulating molybdenum oxide layer prepared in this example is only 12 nm. The saturation magnetization intensity of the magnetic powder core material is 139 emu / g, and the loss at 0.05 T and 1 MHz is 2407 mW / cm 3 , and the magnetic permeability remains at 55 at a frequency of 20 MHz. Under an external magnetic field of 100 Oe, the magnetic permeability remains at 66% of that without a magnetic field.

[0100] Comparative Example 1

[0101] The preparation process of Comparative Example 1 refers to Example 1, with the difference that ammonium molybdate treatment is not carried out (i.e., steps 4 and 5 are omitted), and the rest is the same as in Example 1. Due to the lack of high-resistivity oxides to reduce the contact resistance between particles, the eddy current loss of the magnetic powder core material increases, and the performance deteriorates. The magnetic powder core material has a loss as high as 2770 mW / cm at 0.05 T and 1 MHz. 3 .

[0102] Comparative Example 2

[0103] The preparation process of Comparative Example 2 refers to Example 1, with the difference that the formed magnetic powder core material is vacuum annealed at 550 °C and held for 30 min to obtain a nanocrystalline magnetic powder core. Due to the too high heat treatment temperature, after XRD detection, it is found that in addition to a single α-Fe, there is also an Fe-B phase, which deteriorates the soft magnetic properties of the material. After measurement, the magnetic permeability of this magnetic powder core material is only 23 at a frequency of 1 MHz; the loss is as high as 5234 mW / cm at 0.05 T and 1 MHz. 3 .

[0104] Comparative Example 3

[0105] The preparation process of Comparative Example 3 refers to Example 1, with the difference that the concentration of ammonium molybdate is 20 wt.%, and the rest is the same as in Example 1. Due to the too high concentration of ammonium molybdate, the insulating layer is too thick and exfoliates, the contact resistance increases, resulting in an increase in the core loss, and too much non-magnetic phase is introduced, greatly reducing the magnetic permeability of the magnetic powder core. The magnetic powder core material has a loss as high as 2870 mW / cm at 0.05 T and 1 MHz. 3 , and the magnetic permeability is only 45 at a frequency of 1 MHz.

Claims

1. A preparation method of a high magnetic permeability and low loss nanocrystalline magnetic powder core based on a high resistivity ultra-thin insulating layer, characterized in that, It includes the following steps: (1) Place the soft magnetic alloy powder in an aqueous solution of ammonium molybdate, continuously ultrasonically oscillate and stir evenly, and then dry the mixed solution in an oven at 80 - 110 °C for 1 - 3 hours to obtain a precursor powder with a core - shell structure; (2) Anneal the prepared precursor powder at 400 - 430 °C for 1 - 2 h under vacuum conditions to obtain soft magnetic alloy powder with a molybdenum oxide insulating layer; (3) Add the soft magnetic alloy powder with a molybdenum oxide insulating layer to an acetone solution of an organic resin, continuously ultrasonically oscillate and stir evenly, and after the acetone completely volatilizes, obtain soft magnetic alloy powder with an inorganic - organic composite coating layer; (4) Press and shape the soft magnetic alloy powder with an inorganic - organic composite coating layer and perform heat treatment to obtain an iron - based nanocrystalline magnetic powder core.

2. The preparation method according to claim 1, wherein The preparation steps of the soft magnetic alloy powder in step (1) are as follows: Weigh the raw materials according to atomic percentages and perform induction melting under the protection of an inert gas, and air - cool to obtain a master alloy ingot; After crushing the master alloy ingot, put it into the high - frequency melting furnace of an air - atomization powder - making device, melt the alloy under an inert atmosphere condition, and when the alloy liquid flows into the atomization chamber for atomization and dispersion, obtain alloy powder after cooling; Screen the alloy powder to obtain soft magnetic alloy powder with a target particle size.

3. The preparation method according to claim 2, wherein The master alloy ingot has the following composition: (Fe a Co b Si c B d P e C f ) g Cu 0.8 Nb h , and the atomic percentages of each element satisfy: 0.6 ≤ a ≤ 0.8, 0 ≤ b ≤ 1, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1, 0 ≤ e ≤ 0.1, 0 ≤ f ≤ 0.1, 95 ≤ g ≤ 100, 0 ≤ h ≤ 3, and a + b + c + d + e + f = 1, g + 0.8 + h = 100.

4. The preparation method according to claim 2, wherein, The inert gas is nitrogen or argon, the atomization pressure is 7 - 9 MPa, and the nozzle diameter is 1 - 2 mm.

5. The preparation method according to claim 2, wherein The median particle size D50 of the alloy powder is 20 - 50 μm, and the size of the soft magnetic alloy powder with a target particle size obtained after screening is 5 - 75 μm, and it is a completely amorphous structure.

6. The preparation method according to claim 1, characterized in that, The mass percentage concentration of the ammonium molybdate aqueous solution in step (1) is 5 - 15%.

7. The preparation method according to claim 1, characterized in that, The organic resin in step (3) is one or several of epoxy resin, silicone resin, or epoxy - modified silicone resin, and the dosage of the organic resin is 2 - 3% of the mass of the powder after coating treatment.

8. The preparation method according to claim 1, characterized in that, In step (4), cold pressing is used for pressing and shaping, the pressure is 1500 - 1800 MPa, and the pressure - holding time is 30 - 60 s.

9. The preparation method according to claim 1, wherein In step (4), the heat treatment is carried out under vacuum conditions or in an inert atmosphere, the heat treatment temperature is 480 - 540 °C, and the heat treatment time is 30 - 60 min.

10. A high - magnetic - permeability and low - loss nanocrystalline magnetic powder core prepared by the preparation method according to any one of claims 1 - 9.

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