Method for coating iron-based soft magnetic powder with silicon dioxide and iron-based soft magnetic powder thereof

Abstract

The application discloses a method for coating iron-based soft magnetic powder with silicon dioxide and the iron-based soft magnetic powder, and the method comprises the following steps: activating the iron-based soft magnetic powder: dispersing the iron-based soft magnetic powder obtained in step 1) in a mixed solution of anhydrous ethanol and deionized water, adding a surfactant, the surfactant being at least one of PVP, PAA, PEI and PPy, the addition amount of the surfactant being 0.6-3 wt% of the mass of the iron-based soft magnetic powder, and ultrasonic stirring for 0.5-3.5 h to obtain an activated mixed solution; coating the iron-based soft magnetic powder: adding a certain amount of a silicon source, the silicon source being at least one of TMOS, TEOS and MTEOS, and the addition amount of the silicon source being 0.5-5 wt% of the mass of the iron-based soft magnetic powder. The method can coat the iron-based soft magnetic powder with silicon dioxide, which has excellent insulation performance and excellent magnetic conductivity, and can overcome the defects that the prior art needs strict process conditions to prepare or the prepared thick coating layer affects the magnetic conductivity, and the preparation process and process conditions are simple and easy to control.

Description

Technical Field

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

[0002] Soft magnetic composite materials are an important class of functional materials, widely used in the electronics and electrical industries, such as in the manufacture of inductors, transformers, electromagnetic shields, microwave absorbers, and magnetic powder cores. Among them, metallic soft magnetic powders, especially iron-based soft magnetic powders such as iron powder and its alloy powders, have become one of the preferred raw materials for preparing high-frequency magnetic components due to their advantages such as high saturation magnetization, high permeability, and low cost. However, in high-frequency alternating magnetic fields, metallic soft magnetic powders experience a significant increase in core loss and a rapid temperature rise due to eddy current effects, severely limiting their application performance and service life under high-frequency conditions. To suppress eddy current losses, effectively insulating and coating metallic soft magnetic powder particles, such as iron-based soft magnetic powders, to isolate them from each other after subsequent pressing into magnetic powder cores is a key technical path to improve the high-frequency performance of soft magnetic composite materials.

[0003] Among numerous insulating coating materials, SiO2 (silicon dioxide) not only possesses high resistivity and high thermal stability, but it can also be coated onto the surface of magnetic powder particles using various methods. Furthermore, the thickness and microstructure of the coating layer can be adjusted by modifying the insulating coating process, making it considered an ideal coating material. However, the key to improving the performance of iron-based soft magnetic powder lies in constructing an effective silicon dioxide coating layer.

[0004] The successful implementation of this process is closely related to the inherent properties of the substrate powder, namely the coated iron-based soft magnetic powder. However, existing technologies generally use iron-based soft magnetic powders prepared by traditional processes such as water atomization, co-precipitation, or decomposition as substrate powders, which have unsatisfactory substrate conditions.

[0005] The core contradiction in existing methods for coating iron-based soft magnetic powder with silica is that, in order to obtain a complete and uniform coating effect to fully improve insulation, the iron-based soft magnetic powder coated by existing methods usually has a complete coating coverage or a relatively thick silica coating layer. However, a complete coating coverage requires extremely stringent process precision and condition control, and the steps are often very cumbersome. While a thicker silica coating layer is easier to achieve, an excessively thick non-magnetic coating layer will cause a significant decrease in the effective magnetic permeability of the magnetic powder core. Summary of the Invention

[0006] One technical problem to be solved by the present invention is to provide a method for coating iron-based soft magnetic powder with silica. This method can coat iron-based soft magnetic powder with silica and excellent insulation and magnetic properties. It can overcome the defects of the prior art, which requires strict process conditions to prepare or the excessively thick coating layer affects the magnetic permeability. Moreover, the preparation process and process conditions are simple and easy to control.

[0007] One technical solution of the present invention is to provide a method for coating iron-based soft magnetic powder with silica, comprising the following steps:

[0008] 1) Pretreatment of iron-based soft magnetic powder: Weigh a certain amount of iron-based soft magnetic powder prepared by plasma evaporation and condensation, wash it ultrasonically in a solvent, and obtain clean iron-based soft magnetic powder after sedimentation and separation.

[0009] 2) Activation of iron-based soft magnetic powder: The iron-based soft magnetic powder obtained in step 1) is dispersed in a mixture of anhydrous ethanol and deionized water, and a surfactant is added. The surfactant is at least one of PVP, PAA, PEI and PPy. The amount of surfactant added is 0.6-3 wt% of the mass of the iron-based soft magnetic powder. Stir for 0.5-3.5 h to obtain a solid-liquid mixture containing iron-based soft magnetic powder with surface activation treatment.

[0010] 3) Coating of iron-based soft magnetic powder: Add a certain amount of ammonia water to the solid-liquid mixture obtained in step 2) to make the pH of the mixture 8-10, and then add a certain amount of silicon source, which is at least one of TMOS, TEOS and MTEOS. The amount of silicon source added is 0.5-5 wt% of the mass of iron-based soft magnetic powder. The mixture is then heated in a water bath at 30-50℃ and ultrasonically stirred for 2-4 hours to achieve a dense dotted coating of silicon dioxide on the surface of the iron-based soft magnetic powder.

[0011] After adopting the above steps, the method of coating iron-based soft magnetic powder with silica according to the present invention has the following advantages:

[0012] This invention uses iron-based soft magnetic powder prepared by plasma evaporation and condensation as the base powder. The iron-based soft magnetic powder has a smooth and clean surface with virtually no organic contaminants or strong chemical adsorption layers. Although it has undergone oxygenation treatment, only a very thin passivation protective layer is formed on its surface. After the pretreatment of the raw powder in step 1), its excellent surface condition provides an ideal substrate for the subsequent coating process, making it possible to construct an effective silica coating layer on the surface of the iron-based soft magnetic powder using a simple and easily controllable coating method.

[0013] The core step of this invention lies in activating the iron-based soft magnetic powder before introducing the TMOS, TEOS, or MTEOS silicon source. This activation process, also known as surface activation treatment of the iron-based soft magnetic powder, overcomes the shortcomings of existing activation techniques. Existing activation techniques involve damaging the surface of the substrate powder, such as reacting ammonia with citric acid to generate ammonium citrate, which easily accelerates metal corrosion. In contrast, the activation process of this invention does not damage the powder surface. Instead, the iron-based soft magnetic powder is placed in a solution containing the aforementioned surfactant to form a uniform molecular layer with specific charges or functional groups—the activation layer. The key function of this activation layer is that it alters the chemical microenvironment and energy distribution on the surface of the soft magnetic powder, pre-setting nucleation sites for silicon dioxide. Subsequently, TMOS, TEOS, or MTEOS are added for liquid-phase hydrolysis and condensation. In addition to the pretreatment disclosed in the prior art in step 1), an ultrasonic field is introduced into step 3) to promote liquid-phase hydrolysis, condensation, and densification coating. Because the activation layer has a selective or spatially confined effect on the adsorption of silicon source hydrolysis products, silica cannot nucleate and spread uniformly and continuously on the entire surface of the soft magnetic powder. Instead, isolated silica nanodots are preferentially formed on discrete active sites defined by the activation layer. By simply controlling the reaction conditions in steps 2) and 3), the growth rate and final size of silica nanodots can be controlled, causing them to approach each other during the growth process, ultimately forming a high-density, nanoscale and discontinuous silica nanodot lattice coating layer.

[0014] This invention addresses the inherent contradictions in existing methods for coating iron-based soft magnetic powders with silica. It overcomes the limitations of existing methods where achieving complete coating results in complex and difficult-to-control processes, while increasing coating thickness severely impairs magnetic permeability. This invention constructs a unique insulating structure: highly dispersed silica aggregates are formed on the surface of the iron-based soft magnetic powder. Although these silica aggregates are not continuous, their dense distribution results in iron-based soft magnetic powder coated with silica nanoparticles exhibiting a high-density distribution of silica nanoparticles on its surface. In application, this method provides both the insulating properties of a dense and complete coating and a high degree of retention of the original powder's magnetic properties. In other words, the silica-coated soft magnetic powder produced by this method exhibits insulating properties comparable to a complete coating layer, and its magnetic properties are superior to those of iron-based soft magnetic powder with a complete coating layer.

[0015] 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.

[0016] Further, in step 1), the solvent is anhydrous ethanol. Iron-based soft magnetic powder is added to the anhydrous ethanol at a concentration of 0.25 kg / L, followed by ultrasonic cleaning for 10-30 minutes. Using the above process parameters and steps provides an ideal substrate for subsequent coating processes, and further ensures the effective construction of a silica coating layer on the surface of the iron-based soft magnetic powder.

[0017] Furthermore, in steps 1) and 3), the ultrasound is performed using an ultrasonic disperser, with an ultrasonic frequency of 40-80 kHz and an ultrasonic power density of 0.2-0.5 W / cm². 2 By employing the specific parameters described above, the ultrasonic waves further ensured the technical effectiveness of controlling the growth rate and final size of silica nanodots, causing them to approach each other during growth, and ultimately forming a high-density, nanoscale, and discontinuous silica nanodot lattice coating layer.

[0018] Furthermore, in steps 1), 2), and 3), the mechanical stirring speed is 300-700 r / min. Using these specific parameters further ensures the technical effect of controlling the growth rate and final size of silica nanodots, causing them to approach each other during growth, and ultimately forming a high-density, nanoscale, and discontinuous silica nanodot lattice coating layer.

[0019] Furthermore, the method for coating iron-based soft magnetic powder with silica further includes step 4) post-processing: the product after coating in step 3) is separated into solid and liquid phases, and the resulting powder is washed three times each with deionized water and anhydrous ethanol; subsequently, the washed powder is dried in a vacuum oven at 60-90 ℃ for 5-8 hours to obtain iron-based soft magnetic powder with a silica coating layer. By using the above process parameters and steps, the technical effect of the silica-coated soft magnetic powder being equivalent to that of a fully coated layer in terms of insulation performance and superior to that of iron-based soft magnetic powder with a fully coated layer is further ensured.

[0020] Another technical problem to be solved by the present invention is to provide a silica-coated iron-based soft magnetic powder that has both dense and complete insulating properties when applied, and retains the magnetic properties of the original powder to a high extent.

[0021] Another technical solution of the present invention is to provide a silicon dioxide-coated iron-based soft magnetic powder prepared by the above-described method, wherein the silicon dioxide is attached to the surface of the iron-based soft magnetic powder in a discontinuous, high-density distributed dot-like form.

[0022] With the above structure, the silica-coated iron-based soft magnetic powder of the present invention has the following advantages: The silica-coated iron-based soft magnetic powder of the present invention possesses a special insulating structure, namely, highly dispersed silica aggregates are formed on the surface of the iron-based soft magnetic powder. Although these silica aggregates are not continuously coated, their dense distribution gives the silica-coated iron-based soft magnetic powder of the present invention a high-density distribution of silica nanoparticles on its surface. In application, it possesses both the insulating properties of a dense and complete coating and retains the magnetic properties of the original powder to a high degree. That is, the silica-coated soft magnetic powder exhibits insulating properties comparable to a complete coating layer, and its magnetic properties are superior to those of iron-based soft magnetic powder with a complete coating layer.

[0023] Furthermore, when the particle size of the silica-coated iron-based soft magnetic powder is greater than 800 nm, the surface of the silica-coated iron-based soft magnetic powder is a discontinuous, dot-like silica coating layer; when the particle size of the silica-coated iron-based soft magnetic powder is less than 300 nm, the surface of the silica-coated iron-based soft magnetic powder is a continuous silica coating layer. The reason for this unique coating state is that when the iron-based soft magnetic powder has a larger particle size (greater than 800 nm), silica nanodots can be formed using the techniques described above; while when the iron-based soft magnetic powder has a smaller particle size (less than 300 nm), due to the high surface energy effect of the small-diameter nanoparticles, surfactants and silica are more easily adsorbed or grown on the powder surface, forming a dense coating layer. The silica-coated iron-based soft magnetic powder obtained by this invention, through the coating layer characteristics that continuously vary within a certain particle size range, compared with the products obtained by conventional silica coating methods, retains a higher degree of magnetic properties of the base iron-based soft magnetic powder, which is significantly better than similar coated powders, while also exhibiting insulation properties comparable to a complete coating layer, making it more suitable for applications in related fields. Attached Figure Description

[0024] Figure 1 This is a transmission electron microscope (TEM) image of Embodiment 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope (SEM) image of Embodiment 1 of the present invention.

[0026] Figure 3 This is a scanning electron microscope image of the iron-based soft magnetic powder prepared by the plasma evaporation and condensation method of the present invention.

[0027] Figure 4 This is a scanning electron microscope image of Embodiment 5 of the present invention.

[0028] Figure 5 This is a transmission electron microscope image of Embodiment 6 of the present invention.

[0029] Figure 6This is a scanning electron microscope image of Embodiment 7 of the present invention.

[0030] Figure 7 This is a scanning electron microscope image of Comparative Example 1 of the present invention.

[0031] Figure 8 This is a scanning electron microscope image of Comparative Example 2 of the present invention.

[0032] Figure 9 This is a scanning electron microscope image of Comparative Example 3 of the present invention.

[0033] Figure 10 This is a scanning electron microscope image of Comparative Example 4 of the present invention. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the description of these specific embodiments is for the purpose of aiding understanding the present invention, but does 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.

[0035] Iron-based soft magnetic powder can also be called iron-based soft magnetic powder or raw 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. PVP is polyvinylpyrrolidone. PAA is polyacrylic acid. PEI is polyethyleneimine. PPy is conductive polypyrrole. TMOS is methyl orthosilicate. TEOS is tetraethyl orthosilicate. MTEOS is methyltriethoxysilane. APTES is silane coupling agent. KH-550 is γ-aminopropyltriethoxysilane. Ultrasound is also called ultrasonic field or ultrasonic wave field.

[0036] Example 1

[0037] 1) Take 1 kg of iron powder with an average particle size of 1.0 μm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 4 L of anhydrous ethanol. The ultrasonic frequency is 40 kHz and the ultrasonic power density is 0.2 W / cm³. 2 The mechanical stirring speed was 300 r / min, and the stirring was carried out for 30 min. After sedimentation and separation, clean iron powder was obtained.

[0038] 2) Add 0.5L of deionized water, 3L of anhydrous ethanol and 30g of polyvinylpyrrolidone to the iron powder washed in step 1), stir at room temperature for 1 hour, and mechanically stir at 300r / min.

[0039] 3) Transfer the activated mixture from step 2) to a 40°C water bath, add 0.45L of ammonia water while ultrasonically stirring, adjust the pH to 9, then add 5g of tetraethyl orthosilicate, and continue ultrasonically stirring in a 40°C water bath for 3 hours. The ultrasonic frequency is 40kHz and the ultrasonic power density is 0.2W / cm³. 2 The mechanical stirring speed is 300 r / min.

[0040] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 90°C and dried for 6 hours to obtain iron powder with a silica coating.

[0041] Example 2

[0042] 1) Take 1 kg of iron powder with an average particle size of 1.0 μm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 4 L of anhydrous ethanol. The ultrasonic frequency is 50 kHz and the ultrasonic power density is 0.3 W / cm³. 2 The mechanical stirring speed was 500 r / min, and the stirring was carried out for 15 minutes. After sedimentation and separation, clean iron powder was obtained.

[0043] 2) Add 0.6L of deionized water, 3L of anhydrous ethanol and 6g of polyacrylic acid to the iron powder washed in step 1), stir at room temperature for 0.5h, and the mechanical stirring speed is 500r / min.

[0044] 3) Transfer the activated mixture from step 2) to a 30°C water bath, add 0.3L of ammonia water while ultrasonically stirring, adjust the pH to 8, then add 10g of tetraethyl orthosilicate, and continue ultrasonic stirring in a 30°C water bath for 2 hours. The ultrasonic frequency is 50kHz and the ultrasonic power density is 0.3W / cm³. 2 The mechanical stirring speed is 500 r / min.

[0045] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 80°C and dried for 8 hours to obtain iron powder with a silica coating layer.

[0046] Example 3

[0047] 1) Take 1 kg of iron powder with an average particle size of 1.0 μm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 4 L of anhydrous ethanol. The ultrasonic frequency is 60 kHz and the ultrasonic power density is 0.4 W / cm³. 2The mechanical stirring speed was 600 r / min, and the stirring was carried out for 10 min. After sedimentation and separation, clean iron powder was obtained.

[0048] 2) Add 0.3L of deionized water, 1.75L of anhydrous ethanol and 12g of cetyltrimethylammonium bromide to the iron powder washed in step 1), stir at room temperature for 1 hour, and mechanically stir at 600r / min.

[0049] 3) Transfer the activated mixture from step 2) to a 45°C water bath, add 0.4L of ammonia water while ultrasonically stirring, adjust the pH to 9, then add 20g of methyl orthosilicate, and continue ultrasonic stirring in a 45°C water bath for 3 hours. The ultrasonic frequency is 60kHz and the ultrasonic power density is 0.4W / cm³. 2 The mechanical stirring speed is 600 r / min.

[0050] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 60°C and dried for 9 hours to obtain iron powder with a silica coating layer.

[0051] Example 4

[0052] 1) Take 2 kg of iron powder with an average particle size of 1.0 μm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 8 L of anhydrous ethanol. The ultrasonic frequency is 70 kHz and the ultrasonic power density is 0.5 W / cm³. 2 The mechanical stirring speed was 700 r / min, and the stirring was carried out for 10 minutes. After sedimentation and separation, clean iron powder was obtained.

[0053] 2) Add 1.2L of deionized water, 6.8L of anhydrous ethanol and 40g of oleic acid to the iron powder washed in step 1), stir at room temperature for 2 hours, and mechanically stir at 700r / min.

[0054] 3) Transfer the activated mixture from step 2) to a 45°C water bath, add 1.5L of ammonia water under ultrasonic stirring, adjust the pH to 10, then add 60g of methyltriethoxysilane, and continue ultrasonic stirring in a 45°C water bath for 3 hours. The ultrasonic frequency is 70kHz and the ultrasonic power density is 0.5W / cm³. 2 The mechanical stirring speed is 700 r / min.

[0055] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 70°C and dried for 7 hours to obtain iron powder with a silica coating layer.

[0056] Example 5

[0057] 1) Take 2 kg of iron-nickel powder with an average particle size of 800 nm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 8 L of anhydrous ethanol. The ultrasonic frequency is 80 kHz and the ultrasonic power density is 0.5 W / cm³. 2 The mechanical stirring speed was 550 r / min, and the stirring was carried out for 30 min. After sedimentation and separation, clean iron-nickel powder was obtained.

[0058] 2) Add 1.2L of deionized water, 6.7L of anhydrous ethanol and 50g of polyvinylpyrrolidone to the iron powder washed in step 1), and stir at room temperature for 3.5h with a mechanical stirring speed of 550r / min.

[0059] 3) Transfer the activated mixture from step 2) to a 40°C water bath, add 1.2L of ammonia water under ultrasonic stirring, adjust the pH to 10, then add 80g of tetraethyl orthosilicate, and continue ultrasonic stirring in a 40°C water bath for 3.5h. The ultrasonic frequency is 80kHz and the ultrasonic power density is 0.5W / cm³. 2 The mechanical stirring speed is 550 r / min.

[0060] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 80°C and dried for 7 hours to obtain iron-nickel powder with a silica coating.

[0061] Example 6

[0062] 1) Take 2 kg of iron-nickel powder with an average particle size of 300 nm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 8 L of anhydrous ethanol. The ultrasonic frequency is 80 kHz and the ultrasonic power density is 0.5 W / cm³. 2 The mechanical stirring speed was 550 r / min, and the stirring was carried out for 30 min. After sedimentation and separation, clean iron-nickel powder was obtained.

[0063] 2) Add 1.2L of deionized water, 6.7L of anhydrous ethanol and 50g of polyvinylpyrrolidone to the iron powder washed in step 1), and stir at room temperature for 3.5h with a mechanical stirring speed of 550r / min.

[0064] 3) Transfer the activated mixture from step 2) to a 40°C water bath, add 1.2L of ammonia water under ultrasonic stirring, adjust the pH to 10, then add 80g of tetraethyl orthosilicate, and continue ultrasonic stirring in a 40°C water bath for 3.5h. The ultrasonic frequency is 80kHz and the ultrasonic power density is 0.5W / cm³. 2 The mechanical stirring speed is 550 r / min.

[0065] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 80°C and dried for 7 hours to obtain iron-nickel powder with a silica coating.

[0066] Example 7

[0067] 1) Take 1 kg of iron-cobalt powder with an average particle size of 800 nm prepared by plasma evaporation and condensation method, and ultrasonically wash it in 4 L of anhydrous ethanol. The ultrasonic frequency is 60 kHz and the ultrasonic power density is 0.4 W / cm³. 2 The mechanical stirring speed was 450 r / min, and the stirring was carried out for 20 min. After sedimentation and separation, clean iron-cobalt powder was obtained.

[0068] 2) Add 0.5L of deionized water, 1.5L of anhydrous ethanol and 20g of polyvinylpyrrolidone to the iron powder washed in step 1), stir at room temperature for 2 hours, and mechanically stir at 450r / min.

[0069] 3) Transfer the activated mixture from step 2) to a 50°C water bath, add 0.5L of ammonia water while ultrasonically stirring, adjust the pH to 10, then add 50g of tetraethyl orthosilicate, and continue ultrasonic stirring in a 50°C water bath for 2 hours. The ultrasonic frequency is 60kHz and the ultrasonic power density is 0.4W / cm³. 2 The mechanical stirring speed is 450 r / min.

[0070] 4) After the product of the mixture after coating in step 3) settles, place it on a strong magnet to make the powder aggregate and settle. Then remove the supernatant to complete the separation. The obtained powder is washed three times with deionized water and anhydrous ethanol respectively. Then the washed powder is placed in a vacuum oven at 90°C and dried for 6 hours to obtain iron-cobalt powder with silica coating.

[0071] Comparative Example 1

[0072] 1 kg of iron-nickel powder prepared by plasma evaporation and condensation was ultrasonically washed in anhydrous ethanol, and after sedimentation separation, clean iron-nickel powder was obtained. 0.5 L of deionized water, 30 L of anhydrous ethanol, and 30 g of polyvinylpyrrolidone were added to the pretreated iron-nickel powder, and the mixture was stirred at room temperature for 1 h. The mixture was then transferred to a 40 °C water bath, and mechanical stirring at 450 r / min and a frequency of 60 kHz with a power density of 0.4 W / cm² were applied simultaneously. 2 Under ultrasonic stirring, 0.45 L of ammonia was added to adjust the pH of the system to 9. Then, 0.4 kg of tetraethyl orthosilicate was added, and ultrasonic stirring was continued in a 45°C water bath for 3 h. After the product settled, it was washed three times with deionized water and anhydrous ethanol, respectively, and then dried in a vacuum oven at 70°C for 7 h to obtain silica-coated iron-nickel powder.

[0073] Comparative Example 2

[0074] One kg of iron-cobalt powder prepared by plasma evaporation-condensation was ultrasonically washed in anhydrous ethanol, and after sedimentation separation, clean iron powder was obtained. 0.5 L of deionized water, 3 L of anhydrous ethanol, and 30 g of polyvinylpyrrolidone were added to the pretreated iron-cobalt powder, and the mixture was stirred at room temperature for 1 h. The mixture was then transferred to a 40 °C water bath, and mechanical stirring at 450 r / min and a frequency of 60 kHz with a power density of 0.4 W / cm² were applied simultaneously. 2 4.5 L of ammonia was added under ultrasonic stirring to adjust the pH of the system to 9. Then 10 g of tetraethyl orthosilicate was added, and ultrasonic stirring was continued in a 45 ℃ water bath for 1 h. After the product settled, it was washed three times with deionized water and anhydrous ethanol, respectively, and then dried in a vacuum oven at 80 ℃ for 8 h. The product was then collected.

[0075] Comparative Example 3

[0076] 100 g of iron powder prepared by plasma evaporation and condensation was ultrasonically washed in anhydrous ethanol, and after sedimentation, clean iron powder was obtained. 250 mL of anhydrous ethanol and 30 mL of ammonia were added to the pretreated iron powder, and the mixture was stirred at room temperature for 30 min to form mixture A. 10 g of tetraethyl orthosilicate was weighed and added to 100 mL of anhydrous ethanol, and stirred at room temperature for 30 min to form mixture B. Mixture B was slowly added dropwise to mixture A, and the mixture was stirred at room temperature for 1 h. After sedimentation, the product was washed three times each with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 70 ℃ for 7 h to obtain silica-coated iron powder.

[0077] Comparative Example 4

[0078] 100 g of iron powder prepared by plasma evaporation and condensation was ultrasonically washed in anhydrous ethanol, and after sedimentation separation, clean iron powder was obtained. 500 mL of anhydrous ethanol was added to the pretreated iron powder, and the mixture was stirred at room temperature for 10 min to ensure thorough dispersion. Then, 10 mL of deionized water was added to the mixture, and 3 g of silane coupling agent KH-550 was added dropwise. The mixture was then transferred to a 50 °C water bath and stirred for 1 h. Subsequently, 2 mL of ammonia water was added, and 10 g of tetraethyl orthosilicate was slowly added dropwise. The reaction temperature was increased to 60 °C and stirred for 23 h. After the reaction, the coated powder was washed three times with anhydrous ethanol and dried in a vacuum oven at 60 °C for 24 h to obtain silica-coated iron powder.

[0079] Table 1 shows the effective magnetic permeability and powder resistance of the iron-based soft magnetic powders prepared by plasma evaporation-condensation method, the magnetic powder cores prepared in the examples and comparative examples:

[0080]

[0081] Permeability is a magnetic parameter describing the ease with which magnetic powder cores can be magnetized. It is one of the important performance parameters of the soft magnetic properties of magnetic powder cores and has a significant impact on their performance in engineering applications. 100 kHz and 1 MHz are the frequencies of the alternating magnetic field used to test permeability. Testing permeability at low frequencies (100 kHz) and high frequencies (1 MHz) respectively, if the coated powder still exhibits permeability comparable to that at low frequencies at high frequencies, it proves that the material is suitable for high-frequency operation.

[0082] Powder resistance refers to the resistance of the coated powder. Iron-based soft magnetic powders inherently have low resistance. By coating their surface with an insulating layer, such as the silica coating layer in this invention, the powder's resistance can be effectively increased. The thicker the insulating layer, the higher the powder resistance and the better the insulation performance. Higher powder resistance makes the material more suitable for high-frequency operation. However, excessively thick coatings can lead to lower permeability and poorer magnetic properties. The embodiments of this invention, however, significantly increase resistivity while maintaining high permeability, thus obtaining an optimal material.

[0083] Figure 1 This is a TEM image of the silicon dioxide dot-coated iron-based soft magnetic composite powder prepared in Example 1 of this invention. Figure 1 As shown, it can be clearly observed that nano-sized, amorphous dot-like silica coatings are densely attached to the surface of the powder particles. Moreover, within the same field of view, smaller powder particles (<300nm) exhibit a complete and continuous silica coating. Together, they constitute the unique coating state of the silica-coated iron-based soft magnetic powder obtained in this invention under different particle size distributions.

[0084] Figure 2 These are SEM images of the same sample. Figure 2 As shown, due to the extremely dense and thin distribution of the nano-sized dot-like silica coating layer, the powder particles maintain a smooth spherical shape on a macroscopic scale, exhibiting a morphology similar to a continuous coating layer. This observation demonstrates that the dot-like coating layer formed in this invention possesses high coverage density and extremely thin characteristics, achieving a macroscopic effect of near-continuous coating on a macroscopic scale. Figure 1 TEM images have confirmed that its smooth macroscopic surface is composed of a dense and uniform nano-dot coating layer. Achieving the above results requires not only effective chemical activation of the powder surface through surfactants but also a high degree of dependence on the inherent physical properties of the substrate powder. The iron-based soft magnetic powder prepared by the plasma evaporation-condensation method used in this invention exhibits a smooth surface and good dispersibility as shown in SEM images. Figure 3 This provides a crucial prerequisite for subsequent uniform activation and successful coating.

[0085] As can be seen from the data in Table 1, the powder resistivity of Example 1 is significantly improved compared to the original powder, while the effective permeability of its magnetic powder core is only slightly lower than that of the corresponding magnetic powder core of the original iron powder. The effective permeability of the magnetic powder cores corresponding to Examples 1-4 is lower than that of the corresponding magnetic powder core of the original iron powder, and the decrease increases with the increase of silicon source addition, but all examples achieve a significant improvement in powder resistivity.

[0086] Figure 4 and 6 The SEM images for Examples 5 and 7 show that the dot-coated iron-nickel and iron-cobalt powders still exhibit regular spherical shapes, proving that this method can still achieve a silica dot-coated layer with high coverage density and extremely thin properties on the original iron-nickel and iron-cobalt powders. Comparing Example 5 with the original iron-nickel powder and Example 7 with the original iron-cobalt powder, both examples demonstrate that while achieving a significant increase in powder resistivity, the magnetic properties of the corresponding magnetic powder core are maintained. Figure 5 The TEM image of Example 6 clearly shows a continuous and uniform silica coating on the surface of powder particles with a particle size of less than 300 nm. This result is due to the extremely high surface energy of the nano-effect powder particles when the substrate powder has a particle size of less than 300 nm, making it easy for surfactants and subsequent silica to coat the powder surface, resulting in a continuous silica coating layer. Table 1 shows that Example 6 significantly improves insulation performance while maintaining its magnetic properties. Examples 1-7 highlight that, under the process conditions provided by this invention, when the substrate powder particle size is greater than 800 nm, the silica coating layer exhibits a discontinuous, dotted distribution; when the substrate powder particle size is less than 300 nm, the silica coating layer exhibits a continuous distribution.

[0087] The coating substrate powder described in this invention is not limited to the pure iron powder, iron-nickel powder, and iron-cobalt powder listed in the examples. It also includes other common iron-based soft magnetic powders, such as iron-silicon powder, iron-silicon-aluminum powder, iron-silicon-chromium powder, and iron-silicon-nickel powder.

[0088] Comparative Example 1 is an example described in the background art: In order to obtain a complete and uniform coating effect to fully improve insulation, in the example of a thicker silica coating layer, the amount of silicon source such as tetraethyl orthosilicate added is 0.4 kg, reaching 40 wt%, which is far greater than the amount of silicon source added in this invention, which is 0.5-5 wt%. Figure 7 The SEM image for Comparative Example 1 shows that, due to the excessively thick coating, although complete coating of the powder was achieved, severe agglomeration occurred, resulting in irregular powder shapes. Table 1 shows that while the excessively thick coating significantly improved the insulation performance of Comparative Example 1, it also led to a substantial decrease in the effective permeability of its magnetic powder core, thus deteriorating its soft magnetic properties.

[0089] Comparative Example 2 exceeds the process conditions of this invention. For example, after adding a silicon source such as tetraethyl orthosilicate, the ultrasonic stirring time in Comparative Example 2 is 1 hour, while the ultrasonic stirring time in this invention is 2-4 hours. The ultrasonic stirring time is too short to achieve effective coating of the powder. Figure 8 The SEM image for Comparative Example 2 shows that no SiO2 coating layer can be observed on the outer layer of the powder. This is because the hydrolysis time of the silicon source, such as TEOS, is too short to achieve coating of the powder. Therefore, the data in Table 1 show that the effective permeability of the magnetic powder core and the powder resistance of the powder in Comparative Example 2 are not much different from those of the original powder. That is, although the permeability meets the requirements, the insulation performance is far different.

[0090] Comparative Example 3 shows the conventional Stöber method for coating soft magnetic metal powder with silica. Comparative Example 3 yielded a complete coating layer, as shown in the SEM image below. Figure 9 The results show that a complete silica coating layer was formed on the surface of the powder in Comparative Example 3, but the thickness was uneven, resulting in an ellipsoidal shape and multiple protrusions on the surface. In particular, the effective magnetic permeability was significantly lower than that of the examples, and the powder resistance was also not ideal (Table 1).

[0091] Comparative Example 4 is a complete encapsulation, through Figure 10It can be clearly observed that a relatively uniform and continuous silica coating layer was formed on the surface of the powder in Comparative Example 4, and the powder still exhibited a relatively regular spherical shape. However, Comparative Example 4 only achieved complete coating of the iron-based soft magnetic powder by adding a silane coupling agent, slowly adding TEOS, and significantly extending the hydrolysis and condensation time of TEOS. The process was complex, difficult to operate, and time-consuming. Table 1 shows that Comparative Example 4 improved the insulation performance of the original iron powder, but the improvement effect was not significantly different from that of the examples. Furthermore, the effective permeability of the magnetic powder core corresponding to Comparative Example 4 was lower than that of the magnetic powder core corresponding to the examples. That is, the examples not only have comparable insulation performance to Comparative Example 4, but also exhibit better magnetic properties.

[0092] Examples 1-7 above illustrate that the coated powder provided by the present invention has a regular morphology, good dispersibility, excellent insulation properties, and its corresponding magnetic powder core can maintain good magnetic properties. Moreover, the coating method is simple and easy to control, and it has the technical effects described in the invention. Compared with comparative examples 1-4, i.e., the prior art, it has outstanding substantive features and significant progress.

[0093] 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, or improvements 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 coating iron-based soft magnetic powder with silica, characterized in that, Includes the following steps: 1) Pretreatment of iron-based soft magnetic powder: Weigh a certain amount of iron-based soft magnetic powder prepared by plasma evaporation and condensation, wash it ultrasonically in a solvent, and obtain clean iron-based soft magnetic powder after sedimentation and separation. 2) Activation of iron-based soft magnetic powder: The iron-based soft magnetic powder obtained in step 1) is dispersed in a mixture of anhydrous ethanol and deionized water, and a surfactant is added. The surfactant is at least one of PVP, PAA, PEI and PPy. The amount of surfactant added is 0.6-3 wt% of the mass of the iron-based soft magnetic powder. Stir for 0.5-3.5 h to obtain a solid-liquid mixture containing iron-based soft magnetic powder with surface activation treatment. 3) Coating of iron-based soft magnetic powder: Add a certain amount of ammonia water to the solid-liquid mixture obtained in step 2) to make the pH of the mixture 8-10, and then add a certain amount of silicon source, which is at least one of TMOS, TEOS and MTEOS. The amount of silicon source added is 0.5-5 wt% of the mass of iron-based soft magnetic powder. The mixture is then heated in a water bath at 30-50℃ and ultrasonically stirred for 2-4 hours to achieve a dense dotted coating of silicon dioxide on the surface of the 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 coating iron-based soft magnetic powder with silica according to claim 1, characterized in that: In step 1), the solvent is anhydrous ethanol. Iron-based soft magnetic powder is added to the anhydrous ethanol at a concentration of 0.25 kg / L, and ultrasonic cleaning is performed for 10-30 minutes.

4. The method for coating iron-based soft magnetic powder with silica according to claim 1, characterized in that: In steps 1) and 3), the ultrasound was performed using an ultrasonic disperser, with an ultrasonic frequency of 40-80 kHz and an ultrasonic power density of 0.2-0.5 W / cm². 2 .

5. The method for coating iron-based soft magnetic powder with silica according to claim 3, characterized in that: In steps 1), 2), and 3), the mechanical stirring speed is 300-700 r / min.

6. The method for coating iron-based soft magnetic powder with silica according to claim 1, characterized in that: It also includes step 4) post-processing: after the product is coated in step 3), the solid and liquid are 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 ℃ and dried for 5-8 hours to obtain iron-based soft magnetic powder with a silica coating.

7. A silica-coated iron-based soft magnetic powder prepared by the method according to any one of claims 1 to 6, characterized in that, Silica adheres to the surface of iron-based soft magnetic powder in a discontinuous, high-density dotted form.

8. The silica-coated iron-based soft magnetic powder according to claim 7, characterized in that, When the particle size of the silicon dioxide-coated iron-based soft magnetic powder is greater than 800 nm, the surface of the silicon dioxide-coated iron-based soft magnetic powder is a discontinuous dotted silicon dioxide coating layer; when the particle size of the silicon dioxide-coated iron-based soft magnetic powder is less than 300 nm, the surface of the silicon dioxide-coated iron-based soft magnetic powder is a continuous silicon dioxide coating layer.

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