Preparation method of iron-based soft magnetic powder with silicon dioxide coating layer

Abstract

The invention discloses a preparation method of iron-based soft magnetic powder with a silicon dioxide coating layer, which comprises ultrasonic-assisted silane hydrolysis and modification: iron-based soft magnetic powder is dispersed in a solvent, a silane coupling agent is added, the mass-volume ratio of the iron-based soft magnetic powder to the silane coupling agent is 1kg: (0.002-0.5) L, an ultrasonic field is continuously applied, mechanical stirring is carried out, and ultrasonic-assisted silane hydrolysis and modification are carried out; suspension liquid of the iron-based soft magnetic powder, the solvent, the silane coupling agent and hydrolysis products of the silane coupling agent is put into a container, a pH adjusting agent is added, the pH value is adjusted to be 8-10, an organic silicon source is added, the mixture is stirred to be uniform, the mixture is cooled to room temperature, and the iron-based soft magnetic powder is obtained. And continuously applying an ultrasonic field to the suspension in the container and mechanically stirring to finish the polycondensation reaction of silicon dioxide and form a compact coating layer on the surface of the iron-based soft magnetic powder. According to the method, the pretreatment process is simple, particle aggregation is effectively inhibited, and the coating uniformity, compactness and bonding firmness can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of magnetic functional material preparation technology, specifically a method for preparing iron-based soft magnetic powder with a silica coating. Background Technology

[0002] Iron-based soft magnetic powders, with their high saturation magnetization and low coercivity, are widely used in high-frequency inductors, electromagnetic shielding, and new energy devices. However, the inherent low resistance of the material leads to severe high-frequency eddy current losses, significantly limiting their practical applications. To overcome these shortcomings and improve the performance of iron-based soft magnetic powders, traditional processes generally include organic coating and inorganic passivation, but each has its own limitations.

[0003] While organic coatings, such as organic resin coatings, can improve insulation, they require pre-activation treatment due to poor interfacial compatibility between the powder and the organic material. Furthermore, the organic layer lacks sufficient thermal stability and is prone to decomposition and failure during the high-temperature heat treatment of the magnetic powder core. This failure has a dual negative impact: firstly, the failure of the coating layer makes it impossible to eliminate internal stress; secondly, the loss of the coating layer causes extremely high eddy current losses and significant heat generation when the magnetic powder core operates at high frequencies. This heat generation further accelerates the aging process of the coating layer. The combined effect of residual internal stress and continuously deteriorating insulation ultimately leads to an instability in the overall performance of the magnetic powder core.

[0004] While inorganic passivation, such as phosphate passivation, generates a dense coating layer through chemical reactions, it has two drawbacks: First, the thermal stability of the phosphate passivation layer itself is limited. When the temperature exceeds approximately 550°C, the passivation film may decompose, undergo crystal transformation, or lose its protective properties, becoming porous or cracked. Therefore, soft magnetic powders passivated with phosphate are not suitable for subsequent high-temperature processing. Second, the amount of phosphoric acid and the reaction time must be precisely balanced: if the phosphoric acid concentration is too low or the reaction time is insufficient, the resulting passivation layer is likely to be incomplete, too thin, or not dense enough to provide effective protection; while if the amount of phosphoric acid is too high or the reaction time is too long, the reaction will proceed excessively, not only forming a passivation layer but also consuming too much magnetic phase from the powder surface layer. For example, phosphoric acid will react with Fe on the surface of iron powder to generate FePO4 (iron phosphate), leading to a decrease in the overall magnetism of the iron powder, i.e., a significant reduction in magnetic properties.

[0005] Compared to the former two, SiO2 coating, or silica coating, is an ideal coating material due to its combination of ultra-high resistivity and excellent thermal stability, which can synergistically suppress eddy current losses and eliminate high-temperature annealing stress. However, existing silica coating technologies still have the following two shortcomings in achieving high-performance coating:

[0006] 1. The substrate powder used has inherent defects. Soft magnetic powders prepared by traditional processes such as water atomization, co-precipitation, and decomposition generally have problems such as high surface roughness, irregular morphology, and severe oxidation or contamination. These poor surface conditions not only require complex and costly surface pretreatment before coating, which may damage the inherent properties of the powder, but also restrict the uniform nucleation and growth of the silica coating layer, resulting in uneven silica coating thickness, incomplete coverage, and the presence of cracks or pores in the iron-based soft magnetic powder.

[0007] 2. Existing silica coating technologies have significant shortcomings. These include methods such as sol-gel coating for single or multiple layers, physical adsorption coating of nano-silica, and modified Stöber processes for doping soft magnetic ferrites into the silica coating layer. These existing technologies generally suffer from poor powder dispersibility, severe agglomeration, uneven thickness, localized excessive or insufficient thickness, or even incomplete coating or weak bonding, making it difficult to form a uniform, dense, and firmly bonded silica insulating layer on the surface of soft magnetic powder. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for preparing iron-based soft magnetic powder with a silica coating layer that has a simple pretreatment process, effectively inhibits particle agglomeration, and can significantly improve the coating uniformity, density and bonding strength.

[0009] The technical solution of the present invention is to provide a method for preparing iron-based soft magnetic powder with a silica coating, comprising the following steps:

[0010] 1) Ultrasonic pretreatment and dispersion: The iron-based soft magnetic powder prepared by plasma evaporation and condensation is dispersed in a solvent to form a solid-liquid mixture; ultrasonic cleaning is performed to deagglomerate and uniformly disperse the powder; after ultrasonic treatment, solid-liquid separation is performed to obtain the ultrasonically pretreated and dispersed iron-based soft magnetic powder.

[0011] 2) Ultrasonic-assisted silane hydrolysis and modification: The cleaned and dispersed iron-based soft magnetic powder obtained in step 1) is redispersed in a solvent, and a silane coupling agent is added. The mass-volume ratio of iron-based soft magnetic powder to silane coupling agent is 1 kg: (0.002~0.1) L. An ultrasonic field and mechanical stirring are then continuously applied to obtain the iron-based soft magnetic powder modified by ultrasonic assistance with silane.

[0012] 3) Ultrasonic promotion of silica polycondensation and densification coating: In the solid-liquid mixture of iron-based soft magnetic powder, solvent, silane coupling agent and its hydrolysis product obtained in step 2), a pH adjuster is added to adjust the pH value to 8-10, and an organosilicon source is added. The mass-volume ratio of iron-based soft magnetic powder to organosilicon source is 1 kg: (0.005~0.5) L. Under the condition of continuous application of ultrasonic field and mechanical stirring in a constant temperature water bath, the silica polycondensation reaction is completed and a dense coating layer is formed on the surface of iron-based soft magnetic powder.

[0013] After adopting the above steps, the preparation method of iron-based soft magnetic powder with a silica coating of the present invention has the following advantages:

[0014] This invention uses iron-based soft magnetic powder prepared by the applicant using plasma evaporation and condensation as the base powder. The iron-based soft magnetic powder, such as iron powder, iron-nickel powder, iron-cobalt powder, iron-silicon powder, iron-silicon-chromium powder, and iron-silicon-aluminum powder, has the characteristics of narrow particle size distribution, high sphericity, clean surface, and abundant active sites. It is easy to react chemically with silane coupling agents or silica precursors, and has excellent material surface chemical properties and bonding ability. It has high surface chemical activity and strong bonding ability, and its abundant active sites provide an excellent and key foundation for achieving a uniform, dense and firm silane layer and SiO2, i.e., silica insulating coating layer.

[0015] The core innovation of this invention lies in introducing an ultrasonic field into step 2) for ultrasonic-assisted silane hydrolysis and modification, and step 3) for ultrasonic-promoted silica condensation and densification coating, in addition to the ultrasonic pretreatment and dispersion methods used in existing technologies. This method overcomes the bottlenecks of existing technologies, such as damage to the substrate powder during substrate pretreatment, poor powder dispersibility of the coating powder, severe agglomeration, weak coating layer bonding, and complex processes. Utilizing the efficient dispersion and micro-mixing effects caused by the cavitation effect and acoustic flow of ultrasound, synergistic silane pre-modification promotes in-situ directional condensation of silica, eliminating heterogeneous nucleation and forming a uniform insulating layer. This invention uses the ultrasonic effect to break particle agglomeration, effectively solving the problem of particle agglomeration during the reaction process. It ensures that the silane solution can fully penetrate to the surface of each particle, achieving uniform and independent silane layer coverage, and maintaining good dispersion during subsequent condensation. This significantly improves the coating uniformity and density of iron-based soft magnetic powder with silica coating, achieving excellent uniform and dense coating effects, and well meeting the synergistic requirements of iron-based soft magnetic powder composites for high resistivity and low loss characteristics. It is particularly important to note that the ultrasonic effect depends on the specific parameter settings, and not all ultrasonic conditions can achieve the target effect of this invention: if the ultrasonic frequency or power density is too low, the cavitation effect and acoustic flow will be insufficient, failing to overcome particle agglomeration; conversely, if the ultrasonic frequency or power density is too high, although the dispersing force is enhanced, the excessively strong cavitation impact field can easily damage the silane-modified layer or silica coating layer, leading to coating layer cracking, detachment, or weak bonding. This invention, by adjusting the ultrasonic parameter range, generates cavitation bubbles and acoustic flow of moderate intensity and uniform distribution, which powerfully deagglomerates and maintains particle dispersion, promoting uniform microscale mixing, while the energy intensity is not so high as to destroy the already formed or forming coating layer structure. This allows for the controllable preparation of a uniform, dense, complete, and firmly bonded silica insulating coating layer on the surface of iron-based soft magnetic powder. The selection of this parameter range is the key to achieving excellent technical results.

[0016] Furthermore, the iron-based soft magnetic powder is any one of iron powder, iron-nickel powder, iron-cobalt powder, iron-silicon powder, iron-silicon-chromium powder, iron-silicon-aluminum powder, iron-silicon-nickel powder, iron-nickel-chromium powder, and iron-nickel-cobalt powder. Using the specific iron-based soft magnetic powders described above broadens the applicability of the process and further ensures the technical effect of providing an ideal powder substrate for subsequent coating processes.

[0017] Furthermore, in steps 1), 2), and 3), the ultrasonic field is generated by an ultrasonic field disperser, with a frequency of 20–120 kHz and a power density of 0.3–3 W / cm². 2After adopting the above specific parameters, the ultrasonic field exhibits enhanced functionality in terms of efficient dispersion and micro-mixing effects caused by ultrasonic cavitation and acoustic flow, synergistic silane pre-modification promoting in-situ directional condensation of silica, elimination of heterogeneous nucleation, and formation of a uniform insulating layer. This further ensures the maintenance of good particle dispersion and significantly improves the uniformity, density, and strong bonding of iron-based soft magnetic powder coating.

[0018] Furthermore, in step 1), the solvent is one or a mixture of two or more of anhydrous ethanol, isopropanol, and acetone, and the mass-volume ratio of iron-based soft magnetic powder to solvent is 1 kg:(1~10) L; the ultrasonic cleaning time is 30~60 min. Using the above formula and process parameters improves the ultrasonic pretreatment and dispersion effect in step 1), further ensuring the efficient dispersion effect caused by the cavitation effect and acoustic flow of ultrasound.

[0019] Furthermore, in step 1), the mass-to-volume ratio of the iron-based soft magnetic powder to the solvent is 1 kg:(3~6) L. Using the above-mentioned optimized parameters for the mass-to-volume ratio of the iron-based soft magnetic powder to the solvent further ensures the good technical effect of ultrasonic pretreatment and dispersion in step 1).

[0020] Further, in step 2), the solvent is one or a mixture of anhydrous ethanol, isopropanol, and deionized water; the mass-volume ratio of iron-based soft magnetic powder to solvent is 1 kg:(1~10) L; the silane coupling agent is one or more of KH-550, KH-792, KH-560, and KH-570; the mechanical stirring speed is 300~800 r / min; and the reaction time is 30~90 min. Using the above formulation and process parameters improves the ultrasonic-assisted silane hydrolysis and adsorption effect in step 2), further enhancing the efficient dispersion and micro-mixing effect caused by the cavitation effect and acoustic flow of ultrasound, and synergistically promoting in-situ directional condensation polymerization of silica and eliminating heterogeneous nucleation through silane pre-modification.

[0021] Furthermore, in step 2), the mass-to-volume ratio of the iron-based soft magnetic powder to the solvent is 1 kg:(3~6) L. Using the above-mentioned optimized parameters for the mass-to-volume ratio of the iron-based soft magnetic powder to the solvent further ensures the good technical effect of the ultrasonic-assisted silane hydrolysis and modification in step 2).

[0022] Further, in step 3), the pH adjuster is one or more of ammonia, sodium hydroxide, potassium hydroxide, and organic bases; the organosilicon source is one or more of tetraethyl orthosilicate, methyl orthosilicate, and tetrapropyl orthosilicate; the temperature of the constant temperature water bath is 30~60 ℃; the mechanical stirring speed is 300~800 r / min; and the reaction time is 1~5 h. Using the above formulation and process parameters, the ultrasonic-promoted silica condensation and densification coating effect in step 3) is improved. This allows the invention to achieve the controllable construction of a continuous and dense silica coating layer on the surface of iron-based soft magnetic powder under low temperature (e.g., 30~60 ℃) and non-corrosive conditions. It further enhances the efficient dispersion and micro-mixing effect caused by the cavitation effect and acoustic flow of ultrasound, the synergistic effect of silane modification in promoting in-situ directional condensation of silica, eliminating heterogeneous nucleation, and forming a uniform insulating layer. It further ensures the technical effect of maintaining good particle dispersion and significantly improving coating uniformity and density.

[0023] Furthermore, the preparation method of the iron-based soft magnetic powder with a silica coating of the present invention further includes step 4) post-treatment: the solid-liquid mixture after the coating reaction in step 3) is allowed to settle, and then the supernatant is removed to complete the separation; the obtained powder is washed three times each with deionized water and anhydrous ethanol to remove unreacted substances, byproducts and solvents; subsequently, the washed powder is placed in a vacuum oven at 60~90 ℃ and dried for 5~8 h to finally obtain iron-based soft magnetic powder with a continuous and dense silica coating. By adopting the above steps, the good dispersion state of the iron-based soft magnetic powder particles with a silica coating of the present invention is further ensured, the uniformity and density of the silica-coated iron-based soft magnetic powder coating are significantly improved, and the technical effect of well meeting the synergistic requirements of high magnetic permeability and low loss characteristics of iron-based soft magnetic powder composite materials is achieved. Attached Figure Description

[0024] Figure 1 This is a SEM image of iron powder with a silica coating size of 1.0 μm in Example 1 of the present invention.

[0025] Figure 2 The images shown are high-magnification SEM images and EDS spectra of silicon dioxide-coated iron powder with a particle size of 1.0 μm from Example 1 of this invention.

[0026] Figure 3 In Embodiment 2 of the present invention, the ultrasonic field parameters are: frequency 20 kHz, power density 0.3 W / cm². 2 SEM image of the prepared silica-coated iron powder with a particle size of 1.0 μm.

[0027] Figure 4 In Embodiment 3 of the present invention, the ultrasonic field parameters are: frequency 60 kHz, power density 1.5 W / cm². 2SEM image of the prepared silica-coated iron powder with a particle size of 1.0 μm.

[0028] Figure 5 In Embodiment 3 of the present invention, the ultrasonic field parameters are: frequency 60 kHz, power density 1.5 W / cm². 2 TEM image of the prepared silica-coated iron powder with a particle size of 1.0 μm.

[0029] Figure 6 For Embodiment 4 of the present invention, the ultrasonic field parameters are: frequency 120 kHz, power density 3 W / cm². 2 SEM image of the prepared silica-coated iron powder with a particle size of 1.0 μm.

[0030] Figure 7 This is a SEM image of the silicon dioxide-coated iron powder with a particle size of 1.0 μm prepared in Comparative Example 3 of the present invention without the application of an ultrasonic field.

[0031] Figure 8 This is a TEM image of the silicon dioxide-coated iron powder with a particle size of 1.0 μm prepared in Comparative Example 3 of the present invention without the application of an ultrasonic field.

[0032] Figure 9 For Comparative Example 4 of this invention, the ultrasonic field parameters were: frequency 60 kHz, power density 0.2 W / cm². 2 SEM image of iron powder with a particle size of 1.0 μm coated with silica (below the scope of this invention).

[0033] Figure 10 For Comparative Example 4 of this invention, the ultrasonic field parameters were: frequency 60 kHz, power density 0.2 W / cm². 2 TEM image of silicon dioxide-coated iron powder with a particle size of 1.0 μm (below the scope of this invention).

[0034] Figure 11 This is a SEM image of the silicon dioxide-coated iron-nickel powder with a particle size of 1.0 μm in Example 5 of the present invention.

[0035] Figure 12 This is a SEM image of the silicon dioxide-coated iron-nickel powder with a particle size of 600 nm in Example 6 of the present invention.

[0036] Figure 13 This is a SEM image of the silicon dioxide-coated iron-nickel powder with a particle size of 300 nm in Example 7 of the present invention.

[0037] Figure 14 This is a SEM image of silicon dioxide-coated iron-cobalt powder from Example 8 of the present invention. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and comparative examples. It should be noted that these descriptions of specific embodiments are intended to aid in understanding the present invention but do not constitute a limitation thereof. Furthermore, the technical features involved in the various specific embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Iron-based soft magnetic powder can also be called iron-based soft magnetic powder. The iron-based soft magnetic powder described in this invention includes not only the iron powder, iron-nickel powder, and iron-cobalt powder mentioned in the following examples, but also common soft magnetic powder materials with iron as the main component, found in fields such as iron-silicon powder, iron-silicon-chromium powder, iron-silicon-aluminum powder, iron-silicon-nickel powder, iron-nickel-chromium powder, iron-nickel-cobalt powder, and iron-nickel-molybdenum powder. SiO2 is silicon dioxide. TEOS is tetraethyl orthosilicate. TMOS is methyl orthosilicate. TPOS is tetrapropyl orthosilicate. Silane coupling agent KH-550 is γ-aminopropyltriethoxysilane. Silane coupling agent KH-792 is N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane or a diamino silane coupling agent. Silane coupling agent KH-560 is γ-glycidoxypropyltrimethoxysilane. Silane coupling agent KH570 is γ-(methacryloyloxy)propyltrimethoxysilane.

[0040] Example 1

[0041] 1) Ultrasonic pretreatment and dispersion: 100 kg of iron powder with a particle size of 1.0 μm prepared by our plasma evaporation and condensation method was dispersed in 400 L of anhydrous ethanol and placed in an ultrasonic disperser under an ultrasonic field. The mass-volume ratio of iron powder to solvent was 1 kg: 4 L, the frequency of the ultrasonic field was 40 kHz, and the power density was 1.2 W / cm³. 2 The mixture was processed for 30 minutes; after ultrasonication, solid-liquid separation was performed to obtain cleaned and dispersed iron powder.

[0042] 2) Ultrasonic-assisted silane hydrolysis and modification: The iron powder obtained in step 1) was redispersed in a mixed solvent of 340 L anhydrous ethanol and 60 L deionized water, with a mass-to-volume ratio of iron powder to solvent of 1 kg: 4 L; 1.2 L of silane coupling agent KH-550 was added, with a mass-to-volume ratio of iron powder to KH-550 of 1 kg: 0.012 L; then, continuous ultrasonic field and mechanical stirring were performed, with an ultrasonic field frequency of 40 kHz and a power density of 1.2 W / cm³. 2 The mechanical stirring speed was 400 r / min, and the reaction was carried out for 60 min under these conditions to obtain a solid-liquid mixture after ultrasonic-assisted silane modification.

[0043] 3) Ultrasonic promotion of silica polycondensation and densification coating: In the solid-liquid mixture of iron powder, solvent, silane coupling agent and its hydrolysis product obtained in step (2), 30 L of ammonia water was added to adjust the pH value to 8, and then 2 L of methyl orthosilicate was added. The mass-volume ratio of iron powder to methyl orthosilicate was 1 kg: 0.02 L. In a constant temperature water bath at 50 ℃, an ultrasonic field and mechanical stirring were continuously applied to the suspension in the container. The ultrasonic field frequency was 40 kHz and the power density was 1.2 W / cm³. 2 The mechanical stirring speed was 400 r / min, and the reaction was carried out for 2 h under these conditions to complete the condensation reaction of silica and form a dense coating layer on the surface of iron powder.

[0044] 4) Post-processing: The solid-liquid mixture after the reaction in step 3) was settled and the supernatant was removed; the obtained iron powder was washed three times each with deionized water and anhydrous ethanol, and then placed in a vacuum oven at 80 ℃ for 6 h to finally obtain iron powder with a continuous and dense silica coating.

[0045] Comparative Example 1: Phosphated Coated Iron Powder

[0046] 1) Ultrasonic pretreatment and dispersion: 100g of iron powder with a particle size of 1.0 μm prepared by our plasma evaporation and condensation method was dispersed in 400 mL of anhydrous ethanol solvent. The mass-volume ratio of iron powder to solvent was 1 g: 4 mL. The mixture was placed in an ultrasonic disperser and an ultrasonic field was applied. The ultrasonic field frequency was 40 kHz and the power density was 1.2 W / cm³. 2 The mixture was processed for 30 minutes; after ultrasonication, solid-liquid separation was performed to obtain cleaned and dispersed iron powder.

[0047] 2) Phosphating coating of iron powder: The iron powder obtained in step 1) is placed in a beaker and redispersed in 70 mL of anhydrous ethanol solvent. The mass-volume ratio of iron powder to anhydrous ethanol solvent is 1 g: 0.7 mL. 3 mL of phosphoric acid is added. The beaker is placed in a constant temperature water bath at 70℃ and mechanical stirring is continuously applied at a speed of 400 r / min. The stirring reaction time is about 40 min until the solvent is evaporated.

[0048] 3) Post-processing: Place the sample obtained in step 2) in a vacuum oven at 80 ℃ for 6 h to dry it and obtain iron powder with a phosphated insulating coating.

[0049] Comparative Example 2: Iron powder coated with silicone resin

[0050] 1) Ultrasonic pretreatment and dispersion: 100 g of iron powder with a particle size of 1.0 μm prepared by our company's plasma evaporation and condensation method was dispersed in 400 mL of anhydrous ethanol. The mass-volume ratio of iron powder to anhydrous ethanol solvent was 1 g: 4 mL. The mixture was placed in an ultrasonic cleaner and an ultrasonic field was applied. The ultrasonic field frequency was 40 kHz and the power density was 1.2 W / cm². 2 The mixture was processed for 30 minutes; after ultrasonication, solid-liquid separation was performed to obtain cleaned and dispersed iron powder.

[0051] 2) Silane hydrolysis and modification: The iron powder obtained in step 1) was redispersed in a mixed solvent of 340 mL anhydrous ethanol and 60 mL deionized water, and 1.2 mL of silane coupling agent KH-550 was added. The mixture was mechanically stirred at a speed of 400 r / min and reacted for 60 min under these conditions to obtain a pretreated solid-liquid mixture.

[0052] 3) Dissolving the silicone resin: Dissolve 2 mL of silicone resin completely in 20 mL of acetone solution.

[0053] 4) Coating with silicone resin: Mix the silicone resin acetone solution obtained after dissolving in step 3) with the silane-modified iron powder obtained in step 2), and react for 60 min under mechanical stirring at 400 r / min until the acetone is basically evaporated to obtain iron powder coated with silicone resin.

[0054] 5) Post-processing: Place the sample obtained in step 4) in a vacuum oven at 80 ℃ for 6 h to dry it and obtain iron powder with an organosilicon resin insulating coating.

[0055] In Example 1, 20 g of each of the coated iron powder samples obtained from Comparative Example 1 and Comparative Example 2 were added to 1.8 g of epoxy resin powder and 5 mL of acetone, respectively. After thorough mixing, each sample was dried in a vacuum oven at 80 °C. After drying, each sample was pressed into a magnetic ring with an outer diameter of 8 mm, an inner diameter of 5 mm, and a height of 2 ± 0.02 mm. After heat treatment, the electromagnetic properties were tested. The results are shown in the table below.

[0056] Table 1 Electromagnetic performance data of Example 1, Comparative Examples 1 and 2

[0057]

[0058] [a] Relative permeability loss rate = [(μ i -μ e ) / μ i ]х100%. μ i : Permeability of the original powder-pressed magnetic core (uncoated), μ eEffective magnetic permeability of a silicon dioxide-coated powder-pressed magnetic core.

[0059] like Figure 1 and Figure 2 As shown, the iron powder prepared by the ultrasonic-assisted silane modification process forms a complete and dense silica coating layer on its surface; the EDS elemental distribution spectrum further confirms that the Si element, i.e., the Si element, exhibits a continuous and uniform distribution on the powder surface, indicating that the SiO2 coating layer has completely covered the substrate. As shown in Table 1, under the same insulation coating process and magnetic ring forming test conditions, the magnetic properties and insulation resistance of the magnetic ring prepared in Example 1 are significantly better than those of Comparative Example 1 and Comparative Example 2.

[0060] Examples 2-4

[0061] 1) Ultrasonic pretreatment and dispersion: 100 kg of iron powder with a particle size of 1.0 μm prepared by our company's plasma evaporation and condensation method was dispersed in 100 L of acetone. The mass-to-volume ratio of iron powder to acetone solvent was 1 kg:1 L. The mixture was placed in an ultrasonic disperser and an ultrasonic field was applied. The ultrasonic field frequency was 40 kHz and the power density was 1.2 W / cm³. 2 The process was carried out for 60 minutes; after the ultrasonic treatment, solid-liquid separation was performed to obtain cleaned and dispersed iron powder.

[0062] 2) Ultrasonic-assisted silane hydrolysis and modification: The iron powder obtained in step 1) was redispersed in a mixed solvent of 50 L isopropanol and 50 L deionized water, with a mass-to-volume ratio of 1 kg to 1 L for iron powder to mixed solvent. 0.2 L of silane coupling agent KH-560 was added, with a mass-to-volume ratio of 1 kg to 0.002 L for iron powder to KH-560. The reaction was carried out under continuous ultrasonic field and mechanical stirring for 30 min. The specific parameters of the ultrasonic field are shown in Table 2. The mechanical stirring speed was 300 r / min, resulting in a solid-liquid mixture modified by ultrasonic assistance.

[0063] 3) Ultrasonic promotion of silica polycondensation and densification coating: In the solid-liquid mixture of iron powder, solvent, silane coupling agent and its hydrolysis product obtained in step (2), 10 L of ammonia water was added to adjust the pH value to 9, and then 0.5 L of tetraethyl orthosilicate was added. The mass-volume ratio of iron powder to tetraethyl orthosilicate was 1 kg: 0.005 L. In a constant temperature water bath at 30 ℃, an ultrasonic field and mechanical stirring were continuously applied. The specific parameters of the ultrasonic field are shown in Table 2. The mechanical stirring speed was 300 r / min. Under these conditions, the reaction was carried out for 5 hours to complete the silica polycondensation reaction and form a dense coating layer on the surface of the iron powder.

[0064] 4) Post-processing: The solid-liquid mixture after the reaction in step 3) was settled and the supernatant was removed; the obtained iron powder was washed three times each with deionized water and anhydrous ethanol, and then placed in a vacuum oven at 60 ℃ for 8 h to finally obtain iron powder with a continuous and dense silica coating.

[0065] Comparative Example 3

[0066] 1) Ultrasonic pretreatment and dispersion: 100 kg of iron powder with a particle size of 1.0 μm prepared by our plasma evaporation and condensation method was dispersed in 100 L of acetone. The mass-to-volume ratio of iron powder to anhydrous ethanol solvent was 1 kg: 1 L. The mixture was placed in an ultrasonic cleaner and an ultrasonic field was applied. The ultrasonic field frequency was 40 kHz and the power density was 1.2 W / cm³. 2 The mixture was processed for 60 minutes; after ultrasonication, solid-liquid separation was performed to obtain cleaned and dispersed iron powder.

[0067] 2) Silane hydrolysis and modification (without ultrasound): The iron powder obtained in step 1) is redispersed in a mixed solvent of 50 L isopropanol and 50 L deionized water, with a mass-to-volume ratio of 1 kg to 1 L for iron powder to mixed solvent. 0.2 L of silane coupling agent KH-560 is added, with a mass-to-volume ratio of 1 kg to 0.002 L for iron powder to KH-560. The reaction is carried out for 30 min under mechanical stirring at only 300 r / min to obtain a suspension after silane hydrolysis and modification.

[0068] 3) Silica polycondensation and coating (without ultrasound): 10 L of ammonia water was added to the solid-liquid mixture of iron powder, solvent, silane coupling agent and its hydrolysis product obtained in step (2), the pH value was adjusted to 9, and then 0.5 L of tetraethyl orthosilicate was added. The mass-volume ratio of iron powder to tetraethyl orthosilicate was 1 kg: 0.005 L. The mixture was placed in a constant temperature water bath at 30 ℃ with mechanical stirring at 300 r / min. The reaction was carried out for 5 h under these conditions to complete the polycondensation reaction of silica and form a dense coating layer on the surface of iron powder.

[0069] 4) Post-processing: The supernatant of the solid-liquid mixture after the reaction in step 3) was removed by sedimentation; the obtained iron powder was washed three times each with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 60 °C for 8 h to finally obtain iron powder with a continuous and dense silica coating.

[0070] Comparative Example 4

[0071] 1) Ultrasonic pretreatment and dispersion: 100 kg of iron powder with a particle size of 1.0 μm, prepared by our company's plasma evaporation and condensation method, was dispersed in 100 L of acetone. The mass-to-volume ratio of iron powder to acetone solvent was 1 kg: 1 L. The mixture was placed in an ultrasonic cleaner and an ultrasonic field was applied. The ultrasonic field frequency was 40 kHz and the power density was 1.2 W / cm². 2 Process for 60 minutes; after ultrasonication, solid-liquid separation is completed, and cleaned and dispersed iron powder is obtained.

[0072] 2) Ultrasonic-assisted silane hydrolysis and modification (ultrasonic parameters are below the scope of this invention): The iron powder obtained in step 1) is redispersed in a mixed solvent of 50 L isopropanol and 50 L deionized water, with a mass-to-volume ratio of 1 kg to 1 L for iron powder to mixed solvent. 0.2 L of silane coupling agent KH-560 is added, with a mass-to-volume ratio of 1 kg to 0.002 L for iron powder to KH-560. The reaction is carried out under continuous ultrasonic field and mechanical stirring for 30 min. The specific parameters of the ultrasonic field are shown in Table 2. The mechanical stirring speed is 300 r / min, resulting in a solid-liquid mixture modified by ultrasonic assistance.

[0073] 3) Ultrasonic promotion of silica polycondensation and densification coating (ultrasonic parameters are lower than the scope of this invention): 10 L of ammonia water was added to the solid-liquid mixture of iron powder, solvent, silane coupling agent and its hydrolysis product obtained in step (2), the pH value was adjusted to 9, and then 0.5 L of tetraethyl orthosilicate was added. The mass-volume ratio of iron powder to tetraethyl orthosilicate was 1 kg: 0.005 L. The mixture was continuously subjected to an ultrasonic field and mechanical stirring in a constant temperature water bath at 30 ℃. The specific parameters of the ultrasonic field are shown in Table 2. The mechanical stirring speed was 300 r / min. The reaction was carried out for 5 h under these conditions to complete the silica polycondensation reaction and form a dense coating layer on the surface of the iron powder.

[0074] 4) Post-processing: The supernatant of the solid-liquid mixture after the reaction in step 3) was removed by sedimentation; the obtained iron powder was washed three times each with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 60 °C for 8 h to finally obtain iron powder with a continuous and dense silica coating.

[0075] Table 2. Effect of ultrasonic power on particle size distribution (PSD) in steps 2) and 3).

[0076]

[0077] As shown in Table 2, the ultrasonic field parameters applied in steps 2) and 3) have a significant impact on the particle size distribution (PSD) of the silica-coated iron powder product. Data from Examples 2-4 in Table 2 show that with increasing ultrasonic frequency and power density, the particle size of the silica-coated composite powder significantly decreases, with the particle size D50 decreasing from 4.0 μm to 1.4 μm, and the proportion of large particles (D90) decreasing simultaneously. This demonstrates that applying appropriate ultrasonic treatment during the silane modification and SiO2 coating polycondensation steps can effectively suppress the agglomeration of powder particles during the coating process. The D50 of the sample obtained in Comparative Example 3 (without ultrasonic treatment) is as high as 8.2 μm, an increase of 193% compared to Example 3. This difference reveals the agglomeration effect caused by the rapid reaction of SiO2 under conditions of ultrasonic field absence. The data from Comparative Example 4 further corroborates the importance of ultrasound parameters. While its D50 (5.2 μm) is better than Comparative Example 3 without ultrasound, it is still significantly higher than Example 3 using the same frequency but with suitable parameters. This indicates that when the ultrasound power density is too low, its effect on inhibiting aggregation is limited and cannot achieve the dispersion effect expected by this invention. Combined with... Figure 3-10 Microscopic morphology analysis further corroborates this: the samples of Comparative Example 3 (without ultrasonic treatment) and Comparative Example 4 (ultrasonic parameters below the scope of this invention) showed obvious particle aggregation and local detachment and obvious unevenness of the silica coating layer. However, the appropriate ultrasonic parameters (Example 3) can achieve uniform dispersion of D50 = 2.8 μm and ensure the integrity of the coating layer structure, highlighting the dual necessity of the synergistic effect of ultrasound in "inhibiting aggregation" and "promoting dense coating".

[0078] The powder samples obtained from Examples 2, 3, 4 and Comparative Example 3 were mixed with epoxy resin under the same conditions, pressed into rings, annealed, and their electromagnetic properties were tested, as shown in the table below.

[0079] Table 3 Electromagnetic performance data of the examples and comparative examples

[0080]

[0081] [a] Relative permeability loss rate = [(μ i -μ e ) / μ i ]х100%. μ i : Permeability of the original powder-pressed magnetic core (uncoated), μ e Effective magnetic permeability of a silicon dioxide-coated powder-pressed magnetic core.

[0082] The relative loss rate of magnetic permeability in Comparative Example 4 is as high as 38%, and the insulation resistance is only 128 MΩ, which is far lower than the levels of Examples 2, 3, and 4 of this invention. This indicates that although an ultrasonic field was also applied in steps 2) and 3) of Comparative Example 4, the power density (0.2 W / cm²) was significantly lower.2 The ultrasonic energy is below the lower limit required by this invention. The ultrasonic energy is insufficient to effectively overcome particle agglomeration and ensure uniform mixing of reactants and uniform adsorption and growth of silane / silica on the particle surface, resulting in a significant decrease in coating quality and performance deterioration.

[0083] Examples 5-7

[0084] 1) Ultrasonic pretreatment and dispersion: Take 100 kg of iron-nickel powder prepared by our company's plasma evaporation and condensation method (specific particle size parameters are shown in Table 4), disperse it in 1000 L of anhydrous ethanol, with a mass-to-volume ratio of iron-nickel powder to solvent of 1 kg: 10 L, and place it in an ultrasonic cleaner to apply an ultrasonic field. The ultrasonic field frequency is 50 kHz, and the power density is 0.8 W / cm³. 2 Process for 30 minutes; after ultrasonication, complete solid-liquid separation to obtain cleaned and dispersed iron-nickel powder.

[0085] 2) Ultrasonic-assisted silane hydrolysis and modification: The iron-nickel powder obtained in step 1) was redispersed in 1000 L of anhydrous ethanol, with a mass-to-volume ratio of iron-nickel powder to solvent of 1 kg: 10 L; the amount of silane coupling agent KH-570 shown in Table 4 was added; the mass-to-volume ratio of iron-nickel powder to KH-570 is shown in Table 4; then, continuous ultrasonic field and mechanical stirring were performed, with an ultrasonic field frequency of 50 kHz and a power density of 0.8 W / cm³. 2 The mechanical stirring speed was 800 r / min, and the reaction was carried out for 90 min under these conditions to obtain a solid-liquid mixture after ultrasonic-assisted silane modification.

[0086] 3) Ultrasonic-promoted silica polycondensation and densification coating: In the solid-liquid mixture of iron-nickel powder, solvent, silane coupling agent, and its hydrolysis products obtained in step 2), 25 kg of potassium hydroxide was added to adjust the pH to 10. Then, tetrapropyl orthosilicate (TPOS) was added in the amounts shown in Table 4. The mass-volume ratio of iron-nickel powder to tetrapropyl orthosilicate is shown in Table 4. An ultrasonic field and mechanical stirring were continuously applied in a 40 ℃ constant temperature water bath. The ultrasonic field frequency was 50 kHz, and the power density was 0.8 W / cm³. 2 The mechanical stirring speed was 800 r / min, and the reaction was carried out for 3 h under these conditions to complete the condensation reaction of silica and form a dense coating layer on the surface of the iron-nickel powder.

[0087] 4) Post-processing: The solid-liquid mixture after the reaction in step 3) was settled and the supernatant was removed; the obtained iron-nickel powder was washed three times each with deionized water and anhydrous ethanol, and then placed in a vacuum oven at 80 °C for 8 h to finally obtain iron-nickel powder with a continuous and dense silica coating.

[0088] Table 4 Parameter data for Examples 5-7

[0089]

[0090] Example 8

[0091] 1) Ultrasonic pretreatment and dispersion: 100 kg of iron-cobalt powder with a particle size of 1.0 μm, prepared by our plasma evaporation and condensation method, was dispersed in 600 L of anhydrous ethanol and placed in an ultrasonic cleaner under an ultrasonic field. The mass-volume ratio of iron-cobalt powder to solvent was 1 kg: 6 L, the ultrasonic field frequency was 80 kHz, and the power density was 2 W / cm³. 2 After ultrasonication, solid-liquid separation is performed to obtain cleaned and dispersed iron-cobalt powder.

[0092] 2) Ultrasonic-assisted silane hydrolysis and modification: The iron-cobalt powder obtained in step 1) was redispersed in a mixed solvent of 300 L anhydrous ethanol and 300 L deionized water, with a mass-to-volume ratio of 1 kg: 6 L for iron-cobalt powder to solvent; 2.4 L of silane coupling agent KH-792 was added, with a mass-to-volume ratio of 1 kg: 0.024 L for iron-cobalt powder to KH-792; then, continuous ultrasonic field and mechanical stirring were performed, with an ultrasonic field frequency of 80 kHz and a power density of 2 W / cm³. 2 The mechanical stirring speed was 800 r / min, and the reaction was carried out for 90 min under these conditions to obtain a solid-liquid mixture after ultrasonic-assisted silane modification.

[0093] 3) Ultrasonic promotion of silica polycondensation and densification coating: In the solid-liquid mixture of iron-cobalt powder, solvent, silane coupling agent and its hydrolysis product obtained in step (2), 10 kg of sodium hydroxide was added as a pH adjuster to adjust the pH to 10. Then, a mixture of 5 L of tetraethyl orthosilicate and 5 L of methyl orthosilicate was added as a silicon source. The mass-volume ratio of iron-cobalt powder to silicon source was 1 kg: 0.1 L. An ultrasonic field and mechanical stirring were continuously applied in a 60 ℃ constant temperature water bath. The ultrasonic field frequency was 80 kHz and the power density was 2 W / cm³. 2 The mechanical stirring speed was 400 r / min, and the reaction was carried out for 1 h under these conditions to complete the condensation reaction of silica and form a dense coating layer on the surface of iron-cobalt powder.

[0094] 4) Post-processing: The solid-liquid mixture after the reaction in step 3) was settled and the supernatant was removed; the obtained iron-cobalt powder was washed three times each with deionized water and anhydrous ethanol, and then placed in a vacuum oven at 80 °C for 6 h to finally obtain iron-cobalt powder with a continuous and dense silica coating.

[0095] As shown in Examples 5-8, the preparation method of iron-based soft magnetic powder with a silica coating provided by the present invention has significant universality and controllability. This method has been successfully applied to different types of iron-based soft magnetic powders and FeNi (iron-nickel powder) and iron-cobalt powder with different particle sizes. Furthermore, Examples 5-7, by adjusting the amounts of silane coupling agent and silicon source (as shown in Table 4), can all effectively prepare soft magnetic composite powders with a continuous and dense SiO2 insulating coating.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing iron-based soft magnetic powder with a silica coating, characterized in that: Includes the following steps: 1) Ultrasonic pretreatment and dispersion: The iron-based soft magnetic powder prepared by plasma evaporation and condensation is dispersed in a solvent to form a solid-liquid mixture; ultrasonic cleaning is performed to deagglomerate and uniformly disperse the powder; after ultrasonic treatment, solid-liquid separation is performed to obtain the ultrasonically pretreated and dispersed iron-based soft magnetic powder. 2) Ultrasonic-assisted silane hydrolysis and modification: The cleaned and dispersed iron-based soft magnetic powder obtained in step 1) is redispersed in a solvent, and a silane coupling agent is added. The mass-volume ratio of iron-based soft magnetic powder to silane coupling agent is 1 kg: (0.002~0.1) L. An ultrasonic field and mechanical stirring are then continuously applied to obtain the iron-based soft magnetic powder modified by ultrasonic assistance with silane. 3) Ultrasonic promotion of silica polycondensation and densification coating: Add a pH adjuster to the solid-liquid mixture of iron-based soft magnetic powder, solvent, silane coupling agent and its hydrolysis product obtained in step 2) to adjust the pH value to 8-10, add an organosilicon source, and the mass-volume ratio of iron-based soft magnetic powder to organosilicon source is 1 kg: (0.005~0.5) L. Under the conditions of constant temperature water bath, continuous application of ultrasonic field and mechanical stirring, the silica polycondensation reaction is completed and a dense coating layer is formed on the surface of iron-based soft magnetic powder.

2. The method for coating iron-based soft magnetic powder with silica according to claim 1, characterized in that: The iron-based soft magnetic powder is any one of iron powder, iron-nickel powder, iron-cobalt powder, iron-silicon powder, iron-silicon-chromium powder, iron-silicon-aluminum powder, iron-silicon-nickel powder, iron-nickel-chromium powder, and iron-nickel-cobalt powder.

3. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 1, characterized in that: In steps 1), 2), and 3), the ultrasonic field is generated using an ultrasonic disperser, with a frequency of 20–120 kHz and a power density of 0.3–3 W / cm². 2 .

4. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 1, characterized in that: The solvent in step 1) is one or a mixture of two or more of anhydrous ethanol, isopropanol and acetone, and the mass-volume ratio of iron-based soft magnetic powder to solvent is 1 kg: (1~10) L; the ultrasonic cleaning time is 30~60 min.

5. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 1, characterized in that: In step 1), the mass-volume ratio of iron-based soft magnetic powder to solvent is 1 kg: (3~6) L.

6. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 1, characterized in that: The solvent in step 2) is one or a mixture of anhydrous ethanol, isopropanol, and deionized water; the mass-volume ratio of iron-based soft magnetic powder to solvent is 1 kg: (1~10) L; the silane coupling agent is one or more of KH-550, KH-792, KH-560, and KH-570; the mechanical stirring speed is 300~800 r / min; and the reaction time is 30~90 min.

7. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 6, characterized in that: In step 2), the mass-volume ratio of iron-based soft magnetic powder to solvent is 1 kg:(3~6) L.

8. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 1, characterized in that: In step 3), the pH adjuster is one or more of ammonia, sodium hydroxide, potassium hydroxide, and organic base; the organosilicon source is one or more of tetraethyl orthosilicate, methyl orthosilicate, and tetrapropyl orthosilicate; the temperature of the constant temperature water bath is 30~60 ℃; the speed of the mechanical stirrer is 300~800 r / min; and the reaction time is 1~5 h.

9. The method for preparing iron-based soft magnetic powder with a silica coating according to claim 1, characterized in that: It also includes step 4) post-processing: the solid-liquid mixture after the coating reaction in step 3) is separated, and the obtained powder is washed three times each with deionized water and anhydrous ethanol; then, the washed powder is placed in a vacuum oven at 60~90°C and dried for 5~8 hours to finally obtain iron-based soft magnetic powder with a continuous dense silica coating layer.

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