Nanocrystalline soft magnetic powder, method for producing the same, and use thereof

Abstract

The application belongs to the technical field of soft magnetic composite materials, and particularly relates to a nanocrystalline soft magnetic powder and a preparation method and application thereof. The application creatively combines two core steps of 'nanocrystallization' and 'insulating layer construction' into one, and synchronously completes the two steps in a single-step heat treatment, which not only shortens the production cycle and reduces equipment investment, but also avoids wet chemical treatment, reduces environmental protection cost and total production cost. The insulating layer of the nanocrystalline soft magnetic alloy particles prepared by the application is generated by in-situ oxidation / nitridation of silicon elements in the alloy, and forms a firm chemical bond with the metal matrix, and there is no interface problem. The insulating layer is dense, uniform and ultrathin, and is not easy to be damaged in the subsequent pressing forming process, thereby ensuring excellent and stable insulating performance.

Description

Technical Field

[0001] This invention belongs to the field of soft magnetic composite materials technology, specifically relating to a nanocrystalline soft magnetic powder, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern electronic information technology towards higher frequencies, higher currents, and higher power densities, the integrally molded inductor, as a core magnetic component, is playing an increasingly prominent role in various high-end application scenarios. Meanwhile, nanocrystalline soft magnetic powder, with its excellent soft magnetic properties, is gradually becoming an indispensable key basic material in this field, and its market demand is showing an explosive growth trend.

[0003] However, to fully utilize the superior performance of nanocrystalline soft magnetic powder, the problem of eddy current loss between powder particles must be solved, which places extremely high demands on insulation coating technology. Currently, the mainstream insulation coating technology for nanocrystalline soft magnetic powder in the industry mainly relies on surface treatment with added materials, such as acidification treatment using inorganic or organic acids, and processes such as generating oxide coating layers using the sol-gel method.

[0004] While these traditional methods achieve interparticle insulation to some extent, their inherent defects are increasingly exposed in actual large-scale production and high-end applications, severely restricting further improvements in product performance. First, these processes are generally cumbersome and inefficient, often requiring multiple complex steps such as passivation, repeated cleaning, drying, and high-temperature curing. This not only lengthens the production cycle but also makes it difficult to meet the demands of large-scale continuous production. Second, the external insulating layer and the magnetic substrate are usually only connected by physical adsorption or weak chemical bonding, resulting in poor adhesion and questionable thermal stability of the material. This is especially true for organic insulating layers, which are prone to decomposition and failure once the ambient temperature exceeds 200°C, thus losing their insulating protective function. More importantly, this external non-magnetic insulating layer introduces a "magnetic dilution" effect into the magnetic circuit, inevitably reducing the material's saturation magnetization and effective permeability, weakening the overall performance of the device.

[0005] In addition, traditional processes also face severe challenges in terms of cost control and environmental protection. The use of large amounts of chemical reagents not only increases manufacturing costs but also generates waste liquids that are difficult to treat, which is not in line with the development concept of green manufacturing.

[0006] It is evident that existing insulation coating technology has become a bottleneck restricting the performance breakthrough of nanocrystalline soft magnetic materials. Therefore, there is an urgent need to develop a new insulation method that does not rely on external coating agents, can achieve a strong atomic-level bond between the insulation layer and the substrate, has excellent high-temperature resistance, and has a simple and efficient process. This has extremely important scientific significance and application value for promoting the technological innovation and industrial upgrading of high-end magnetic components. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing nanocrystalline soft magnetic powder. This method utilizes the silicon element in the powder itself to diffuse to the surface during high-temperature annealing and to oxidize in situ in a controllable trace oxygen atmosphere to form a dense, high-resistivity silicon-rich insulating layer, completely eliminating the need for external coating agents and achieving one-step insulation treatment.

[0008] The above-mentioned objective of the present invention is achieved by the following scheme: A method for preparing nanocrystalline soft magnetic powder, the method comprising the following steps: S1. The nanocrystalline powder precursor is immersed in an ethanol solution containing phosphoric acid and mixed. After filtration, washing and drying, the pretreated nanocrystalline powder precursor is obtained. S2. In a nitrogen atmosphere, heat the pretreated nanocrystalline powder precursor to 500-550°C at a heating rate of 5-15°C / min, and then hold at that temperature for 10-30 min. S3. Introduce a nitrogen-oxygen mixture containing 0.1-1 vol% oxygen and raise the temperature to 580-620°C at a rate of 1-5°C / min, then hold for 30-90 min. S4. After the heat preservation is completed, cool the furnace to 180-230°C, purge with nitrogen for 10-20 minutes, and finally cool to 5-30°C.

[0009] This invention places a pretreated nanocrystalline powder precursor in an inert atmosphere of high-purity nitrogen and heats it at a relatively rapid rate of 5-15°C / min to the nanocrystallization temperature range of 500-550°C, followed by a short holding time of 10-30 minutes. The key objectives of this stage are twofold: first, to utilize this temperature window to drive structural relaxation and atomic rearrangement in the amorphous matrix, precipitating uniformly sized and dispersed α-Fe(Si) nanocrystals, which is the structural basis for obtaining excellent soft magnetic properties; second, to prevent premature oxidation of alloying elements under the protection of the inert atmosphere. More importantly, the formation of nanocrystals is accompanied by elemental redistribution. Highly reactive silicon atoms spontaneously segregate towards the newly formed grain boundaries and the remaining amorphous phase, forming locally silicon-rich regions. This provides the initial driving force and high-concentration channels for the directional migration of silicon atoms to the particle surface, a prerequisite for achieving efficient surface enrichment.

[0010] A trace amount of oxygen (0.1%–1% by volume) is introduced into the atmosphere, and the heating rate is significantly reduced to 1–5°C / min, slowly raising the temperature from the initial plateau to the final oxidation temperature of 580–620°C. This "slow heating" provides sufficient time and a continuous energy gradient for the silicon atoms that have already begun to agglomerate, enabling them to migrate stably and continuously to the particle surface and accumulate along rapid diffusion channels such as grain boundaries, forming a high-concentration surface silicon layer. Simultaneously, the slow heating effectively suppresses abnormal growth of nanocrystals caused by drastic temperature changes, ensuring the preservation of the material's excellent soft magnetic properties.

[0011] When the temperature reaches and stabilizes at 580-620°C, the silicon atoms already enriched on the particle surface acquire extremely high diffusion kinetic energy. According to thermodynamic principles, the standard Gibbs free energy of silicon forming oxide (SiO2) is much lower than that of iron forming oxide (FeO / Fe2O3). This means that in a micro-oxygen atmosphere, silicon has an overwhelming tendency to be preferentially oxidized. Therefore, the silicon atoms on the surface will rapidly react with trace amounts of oxygen in the atmosphere, generating in situ a layer of silicon-rich oxide with SiO2 as the main chemical component (or containing Fe-Si-O amorphous phase), a dense structure, and electrical insulation. Once this layer is formed, it will continuously consume the silicon atoms diffused to the surface, forming a "pump" effect that drives the internal silicon to continuously expand outward until a dynamic equilibrium is reached. The resulting insulating layer, chemically bonded to the matrix and integrally formed, endows the magnetic powder core with excellent high-frequency, low-loss performance.

[0012] In the above preparation method, the ethanol solution containing phosphoric acid and the nanocrystalline powder precursor are mixed at a ratio of 1.5-2.5 mL: 1 g.

[0013] In the above preparation method, the concentration of the ethanol solution containing phosphoric acid is 0.5-2.0 vol.

[0014] In the above preparation method, the nanocrystalline powder precursor is silicon-containing iron-based amorphous soft magnetic alloy powder.

[0015] In the above preparation method, the median particle size of the nanocrystalline powder precursor is 10-50 μm, and the silicon content is 2-20 wt%.

[0016] Prior to heat treatment, this invention employs a crucial surface activation pretreatment step on the nanocrystalline powder precursor to remove obstacles for efficient silicon diffusion and in-situ film formation. Specifically, the silicon-iron-based amorphous alloy nanocrystalline powder precursor prepared by rapid quenching inevitably reacts with oxygen and moisture in the air during storage and transportation, forming a complex and loosely structured natural oxide layer, primarily composed of hydrated iron oxide (Fe2O3·xH2O). This physically attached and uneven oxide layer not only lacks excellent insulation properties but, more importantly, acts as a barrier, significantly hindering the diffusion channels of silicon atoms from the alloy interior to the particle surface during subsequent heat treatment, resulting in a discontinuous and non-dense in-situ insulating layer. This invention utilizes a mild yet efficient acid washing process: immersing the powder precursor in a 0.5-2.0% (v / v) dilute phosphoric acid ethanol solution and stirring at room temperature for 5-10 minutes. Phosphoric acid can effectively dissolve and remove the iron oxide layer on the surface, while using ethanol as a solvent can reduce the activity of the acid, avoid excessive corrosion of the alloy substrate, and facilitate subsequent rapid drying. After washing and vacuum drying, the resulting amorphous alloy particles are clean and atomically fresh. This creates ideal initial interface conditions for the smooth diffusion and uniform film formation of silicon atoms during subsequent heat treatment, which is a necessary prerequisite for ensuring the final high-quality insulating layer.

[0017] In the above preparation method, the nanocrystalline powder precursor is composed of a Fe-Si-BM system, wherein M includes at least one of Nb and Cu.

[0018] The present invention also provides a nanocrystalline soft magnetic powder, which is prepared by the above-described preparation method.

[0019] In the aforementioned nanocrystalline soft magnetic powder, the surface of the nanocrystalline soft magnetic alloy particles is coated with an insulating layer; wherein the insulating layer is a silicon-rich insulating layer, and the insulating layer is bonded to the surface of the nanocrystalline soft magnetic alloy particles by chemical bonds, and is generated by the in-situ reaction of silicon elements contained in the nanocrystalline soft magnetic alloy particles themselves.

[0020] In the aforementioned nanocrystalline soft magnetic powder, the main components of the silicon-rich insulating layer include at least one of silicon oxide, silicon nitride, and silicon oxynitride, with a thickness of 5-50 nm.

[0021] The present invention also provides an application of the above-mentioned nanocrystalline soft magnetic powder in electronic components, wherein the electronic components include one of high-frequency switching power supplies, inverters, filters, inductors and mutual inductors.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention creatively combines the two core steps of "nano-crystallization" and "insulating layer construction" into one, and completes them simultaneously in a single-step heat treatment. This not only shortens the production cycle and reduces equipment investment, but also avoids wet chemical treatment, thereby reducing environmental protection costs and total production costs.

[0023] 2. The insulating layer of the nanocrystalline soft magnetic alloy particles prepared by this invention is generated by in-situ oxidation / nitridation of silicon elements inside the alloy, forming a strong chemical bond with the metal matrix, eliminating interface problems. This insulating layer is dense, uniform, and ultra-thin, and is not easily damaged during subsequent pressing and molding processes, ensuring excellent and stable insulation performance.

[0024] 3. The nanocrystalline soft magnetic alloy particles prepared by this invention form a high-quality insulating layer, which effectively suppresses eddy current losses at high frequencies, so that the prepared magnetic powder cores still maintain extremely low core losses and stable permeability at high frequencies of hundreds of kHz or even MHz.

[0025] 4. The nanocrystalline soft magnetic alloy particles prepared by this invention have a very small "dilution effect" on the overall magnetism of the powder because the insulating layer is a thin layer generated in situ rather than a large amount of externally added non-magnetic material. This allows the magnetic powder core to maintain a high saturation magnetic induction intensity and effective magnetic permeability.

[0026] 5. By precisely controlling parameters such as atmosphere composition (e.g., oxygen partial pressure), temperature, and time during the heat treatment process, this invention can synergistically control the thickness, composition, and density of the insulating layer, as well as the grain size of the nanocrystals, providing the possibility for customized development of magnetic powder core materials to meet different application requirements. Detailed Implementation

[0027] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0028] The nanocrystalline powder precursor was prepared by the following method: S1, according to Fe 82.8 Si 8.8 B 1.5 Nb 5.7 Cu 1.2 The high-purity raw materials were weighed according to the (wt%) composition ratio, placed in a vacuum induction melting furnace, evacuated and filled with high-purity argon gas, and melted at 1500℃ to obtain a uniform alloy liquid. After casting and cooling, the alloy ingot was obtained.

[0029] S2. The above alloy ingot is reheated to 1500°C in an atomizing furnace and atomized with high-pressure argon gas at 4MPa. The powder is collected and obtained as a nanocrystalline powder precursor spherical powder with a median particle size (D50) of 20μm through airflow classification.

[0030] Example 1

[0031] S1. Prepare an ethanol solution containing 1.0% phosphoric acid (85wt% phosphoric acid raw material). Weigh 100g of the nanocrystalline powder precursor powder and add it to 200mL of the above solution. Stir at room temperature for 5 minutes, then filter and rinse three times with 100mL of anhydrous ethanol. Spread the powder in a stainless steel tray and dry it in an 80°C vacuum drying oven for 2 hours. S2. The dried nanocrystalline soft magnetic powder precursor is loaded into a quartz tube, the tube opening is covered with a glass sieve, leaving a gas flow gap, and placed in a tube atmosphere furnace. The furnace door is closed, and a vacuum is drawn to -0.1 MPa using a mechanical pump. Then, high-purity N2 is backfilled to atmospheric pressure. This process is repeated 3 times to replace the air, and then annealing is performed. S3. Under a nitrogen atmosphere, heat to 550°C at 10°C / min and hold for 15 min. Then, introduce a mixture of N2 and 0.5 vol% O2 at a total flow rate of 1 L / min, heat to 600°C at 2°C / min and hold for 60 min, maintaining the furnace pressure at +100 Pa. After holding, keep the atmosphere constant and cool the furnace to 200°C. Then switch to pure N2 (1 L / min) and continue cooling to room temperature.

[0032] Example 2

[0033] S1. Prepare an ethanol solution containing 1.0% phosphoric acid (85wt% phosphoric acid raw material). Weigh 100g of the nanocrystalline powder precursor powder and add it to 200mL of the above solution. Stir at room temperature for 5 minutes, then filter and rinse three times with 100mL of anhydrous ethanol. Spread the powder in a stainless steel tray and dry it in an 80°C vacuum drying oven for 2 hours. S2. The dried nanocrystalline soft magnetic powder precursor is loaded into a quartz tube, the tube opening is covered with a glass sieve, leaving a gas flow gap, and placed in a tube atmosphere furnace. The furnace door is closed, and a vacuum is drawn to -0.1 MPa using a mechanical pump. Then, high-purity N2 is backfilled to atmospheric pressure. This process is repeated 3 times to replace the air, and then annealing is performed. S3. Under a nitrogen atmosphere, heat to 550°C at 10°C / min and hold for 15 min. Then, introduce a mixture of N2 and 0.1 vol% O2 at a total flow rate of 1 L / min, heat to 600°C at 2°C / min and hold for 60 min, maintaining the furnace pressure at +100 Pa. After holding, keep the atmosphere constant and cool the furnace to 200°C. Then switch to pure N2 (1 L / min) and continue cooling to room temperature.

[0034] Example 3

[0035] S1. Prepare an ethanol solution containing 1.0% phosphoric acid (85wt% phosphoric acid raw material). Weigh 100g of the nanocrystalline powder precursor powder and add it to 200mL of the above solution. Stir at room temperature for 5 minutes, then filter and rinse three times with 100mL of anhydrous ethanol. Spread the powder in a stainless steel tray and dry it in an 80°C vacuum drying oven for 2 hours. S2. The dried nanocrystalline soft magnetic powder precursor is loaded into a quartz tube, the tube opening is covered with a glass sieve, leaving a gas flow gap, and placed in a tube atmosphere furnace. The furnace door is closed, and a vacuum is drawn to -0.1 MPa using a mechanical pump. Then, high-purity N2 is backfilled to atmospheric pressure. This process is repeated 3 times to replace the air, and then annealing is performed. S3. Under a nitrogen atmosphere, heat to 550°C at 10°C / min and hold for 15 min. Then, introduce a mixture of N2 and 1.0 vol% O2 at a total flow rate of 1 L / min, heat to 600°C at 2°C / min and hold for 60 min, maintaining the furnace pressure at +100 Pa. After holding, keep the atmosphere constant and cool the furnace to 200°C. Then switch to pure N2 (1 L / min) and continue cooling to room temperature.

[0036] Example 4

[0037] S1. Prepare an ethanol solution containing 1.0% phosphoric acid (85wt% phosphoric acid raw material). Weigh 100g of the nanocrystalline powder precursor powder and add it to 200mL of the above solution. Stir at room temperature for 5 minutes, then filter and rinse three times with 100mL of anhydrous ethanol. Spread the powder in a stainless steel tray and dry it in an 80°C vacuum drying oven for 2 hours. S2. The dried nanocrystalline soft magnetic powder precursor is loaded into a quartz tube, the tube opening is covered with a glass sieve, leaving a gas flow gap, and placed in a tube atmosphere furnace. The furnace door is closed, and a vacuum is drawn to -0.1 MPa using a mechanical pump. Then, high-purity N2 is backfilled to atmospheric pressure. This process is repeated 3 times to replace the air, and then annealing is performed. S3. Under a nitrogen atmosphere, heat to 550°C at 10°C / min and hold for 15 min. Then, introduce a mixture of N2 and 0.5 vol% O2 at a total flow rate of 1 L / min, heat to 580°C at 2°C / min and hold for 60 min, maintaining the furnace pressure at +100 Pa. After holding, keep the atmosphere constant and cool the furnace to 200°C. Then switch to pure N2 (1 L / min) and continue cooling to room temperature.

[0038] Comparative Example 1: The only difference from Example 1 is that the annealing atmosphere in step S3 is high-purity N2 throughout the process.

[0039] Comparative Example 2: The only difference from Example 1 is that the annealing atmosphere in step S3 is air throughout.

[0040] Comparative Example 3: The only difference from Example 1 is that the nanocrystalline powder precursor powder was not treated with phosphate ethanol solution.

[0041] Comparative Example 4: The only difference from Example 1 is that in step S3, the mixed gas is N2 + 0.05% O2.

[0042] Comparative Example 5: The only difference from Example 1 is that in step S3, the mixed gas is N2 + 2.0% O2.

[0043] Comparative Example 6: The only difference from Example 1 is that the annealing was performed by heating to 550°C at a rate of 10°C / min under a nitrogen atmosphere and holding for 15 min.

[0044] Comparative Example 7: The only difference from Example 1 is that the annealing process involves introducing a mixture of N2 and 0.5% O2 at a total flow rate of 1 L / min, raising the temperature to 600°C at a rate of 2°C / min, and holding it at that temperature for 60 minutes.

[0045] Comparative Example 8: S1. Prepare a 1.0% (v / v) phosphoric acid ethanol solution. Weigh 100 g of nanocrystalline powder precursor powder (Fe-Si-B-Nb powder, D50=20 μm), add it to 200 mL of the above solution, stir at room temperature for 5 minutes, filter, and wash three times with 100 mL of anhydrous ethanol. Spread the powder in a stainless steel tray and dry it in an 80°C vacuum drying oven for 2 hours. S2. The dried nanocrystalline soft magnetic powder precursor is bonded and mixed with 0.2% (mass fraction, the same below) of epoxy resin to obtain a mixture. The mixture is pressed into a magnetic ring with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm under a pressure of 3 GPa. S3. Load the ring-shaped soft magnetic composite material into a quartz tube, cover the tube opening with a glass sieve, leaving a gap for gas flow, and place it in a tube atmosphere furnace. Close the furnace door, use a mechanical pump to evacuate to -0.1 MPa, then backfill with high-purity N2 to atmospheric pressure, repeat 3 times to replace the air, and then perform annealing; S4. Under a nitrogen atmosphere, heat to 550°C at 10°C / min and hold for 15 min. Then, introduce a mixture of N2 and 0.5% O2 at a total flow rate of 1 L / min, heat to 600°C at 2°C / min and hold for 60 min, maintaining the furnace pressure at +100 Pa. After holding, keep the atmosphere constant and cool the furnace to 200°C. Then switch to pure N2 (1 L / min) and continue cooling to room temperature.

[0046] After mixing and granulating 30 g of the nanocrystalline soft magnetic powder prepared in Examples 1-4 and Comparative Examples 1-8 with 2.0 wt% epoxy resin, 4 g of the granulated powder was pressed into a magnetic ring with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm under a pressure of 600 MPa, and the ring was cured at 200°C for 1 hour before performance testing.

[0047] Table 1: Performance test results of nanocrystalline soft magnetic powders prepared in Examples 1-4 and Comparative Examples 1-8

[0048] As shown in Table 1, compared with Comparative Examples 1-8, Examples 1-4, by adopting a combination process of phosphating pretreatment and step-by-step controlled atmosphere annealing, have better magnetic permeability and insulation resistance than Comparative Examples 1-8. Therefore, the optimal combination is to first perform phosphating pretreatment, then introduce a mixture of N2 + 0.5% vol O2 in the multi-stage annealing stage, and hold at 600°C for 60 minutes.

[0049] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0050] Although the present invention has been described in detail and specific embodiments have been cited, it will be apparent to those skilled in the art that various changes or modifications can be made without departing from the spirit and scope of the invention.

Claims

1. A method for preparing nanocrystalline soft magnetic powder, characterized in that, The method includes the following steps: S1. The nanocrystalline powder precursor is immersed in an ethanol solution containing phosphoric acid and stirred. After filtration, washing and drying, the pretreated nanocrystalline powder precursor is obtained. S2. In a nitrogen atmosphere, heat the pretreated nanocrystalline powder precursor to 500-550°C at a heating rate of 5-15°C / min, and then hold at that temperature for 10-30 min. S3. Introduce a nitrogen-oxygen mixture containing 0.1-1 vol% oxygen and raise the temperature to 580-620°C at a rate of 1-5°C / min, then hold for 30-90 min. S4. After the heat preservation is completed, cool the furnace to 180-230°C, purge with nitrogen for 10-20 minutes, and finally cool to 5-30°C.

2. The preparation method according to claim 1, characterized in that, The phosphoric acid-containing ethanol solution and the nanocrystalline powder precursor were mixed at a ratio of 1.5-2.5 mL: 1 g.

3. The preparation method according to claim 1, characterized in that, The concentration of the ethanol solution containing phosphoric acid is 0.5-2.0 vol.

4. The preparation method according to claim 1, characterized in that, The precursor for the nanocrystalline powder is a silicon-containing iron-based amorphous soft magnetic alloy powder.

5. The preparation method according to claim 1, characterized in that, The median particle size of the nanocrystalline powder precursor is 10-50 μm, and the silicon content is 2-20 wt%.

6. The preparation method according to claim 1, characterized in that, The nanocrystalline powder precursor is composed of an Fe-Si-BM system, wherein M includes at least one of Nb and Cu.

7. A nanocrystalline soft magnetic powder, characterized in that, The nanocrystalline soft magnetic powder is prepared by the preparation method described in claim 1.

8. The nanocrystalline soft magnetic powder according to claim 7, characterized in that, The surface of the nanocrystalline soft magnetic alloy particles is coated with an insulating layer; wherein the insulating layer is a silicon-rich insulating layer, and the insulating layer is bonded to the surface of the nanocrystalline soft magnetic alloy particles by chemical bonds, and is generated by the in-situ reaction of silicon elements contained in the nanocrystalline soft magnetic alloy particles themselves.

9. The nanocrystalline soft magnetic powder according to claim 8, characterized in that, The main components of the silicon-rich insulating layer include at least one of silicon oxide, silicon nitride, and silicon oxynitride, and the thickness is 5-50 nm.

10. The application of the nanocrystalline soft magnetic powder as described in claim 7 in electronic components, characterized in that, The electronic components include one of the following: high-frequency switching power supply, inverter, filter, inductor, and current transformer.

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