FeSiCr magnetic powder core, preparation method thereof and current sensor

Abstract

The application relates to the technical field of magnetic powder cores, and discloses an FeSiCr magnetic powder core for a high-frequency magnetic field, a preparation method of the FeSiCr magnetic powder core and a current sensor. The preparation method of the FeSiCr magnetic powder core comprises the following steps: placing FeSiCr magnetic powder in concentrated nitric acid for passivation treatment, cleaning the FeSiCr magnetic powder in ion water for multiple times, and drying the FeSiCr magnetic powder to obtain the passivated magnetic powder; the mass of the concentrated nitric acid is 0.5% to 5% of the mass of the FeSiCr magnetic powder; placing the passivated magnetic powder in polyethylene imine for soaking, cleaning the passivated magnetic powder in deionized water to obtain the PEI-coated magnetic powder; placing the PEI-coated magnetic powder in a mixed solution of silicon resin and acetone, mixing and stirring the PEI-coated magnetic powder, water-bath heating to volatilize the acetone, crushing, sieving and pressing to obtain a green body; and placing the green body in a nitrogen atmosphere for annealing treatment to obtain the FeSiCr magnetic powder core. The prepared FeSiCr magnetic powder core can realize high resistivity, a cut-off frequency and low eddy current loss under a high-frequency magnetic field, is suitable for the performance requirements of a wide-frequency current sensor on a high-frequency magnetic core, and has the beneficial effects of simple structure and easy realization.

Description

Technical Field

[0001] This invention relates to the field of magnetic powder core technology, and in particular to a FeSiCr magnetic powder core for high-frequency magnetic fields, its preparation method, and a current sensor. Background Technology

[0002] Against the backdrop of rapid iteration in high-frequency power electronics and advanced sensor technologies, the requirements for high-frequency response and power loss of soft magnetic materials are becoming increasingly stringent. Magnetic powder core materials, represented by FeSiCr alloys, have become key fundamental materials for achieving efficient electromagnetic energy conversion and signal sensing due to their excellent electromagnetic properties (such as high saturation magnetic induction, high initial permeability, and low coercivity). However, when applications expand to the MHz band, the performance bottlenecks of these materials quickly become apparent: on the one hand, their magnetic spectrum characteristics determine that permeability decreases significantly with increasing frequency, making it difficult to maintain a stable magnetic response at high frequencies; on the other hand, the limited resistivity of the alloy itself induces strong eddy current effects at high frequencies, resulting in considerable energy loss and core temperature rise, threatening the stability and lifespan of the device. These factors collectively limit the in-depth application of traditional FeSiCr magnetic cores in broadband, high-precision current sensing scenarios.

[0003] To overcome the aforementioned bottlenecks, surface insulating coating is considered the most direct and effective material modification strategy for improving the high-frequency electromagnetic properties of materials. The optimization mechanism of this strategy is mainly reflected in two dimensions: At the magnetic level, the coating layer, acting as a non-magnetic spacer, slightly reduces the overall magnetic volume fraction of the material but introduces additional exchange decoupling between particles. This is equivalent to enhancing the effective magnetic anisotropy of the material, thereby pushing the natural resonant frequency to a higher frequency domain and allowing the permeability to remain stable over a wider frequency band. At the electrical level, the uniform and dense coating layer can construct a three-dimensional insulating network between conductive magnetic particles, greatly blocking the flow path of high-frequency eddy currents between particles, significantly increasing the resistivity of the composite, and suppressing eddy current losses at their source. The synergistic effect of these two factors effectively improves the high-frequency characteristics of the material.

[0004] Existing insulating coating technologies are mainly divided into two routes based on the different chemical properties of the materials: organic and inorganic systems. Organic coating (such as using epoxy or silicone resin) is simple to process, and the resulting film is flexible and continuous, effectively achieving particle isolation. However, its thermal stability is insufficient, making it difficult to withstand the high-temperature annealing treatment necessary to eliminate internal stress and optimize magnetic properties. Furthermore, it is prone to creep or cracking during high-pressure molding, leading to a decrease in insulation reliability. Inorganic coating (such as forming oxides, phosphates, etc.) exhibits excellent thermal stability and mechanical strength. Its insulating phase can withstand high-temperature heat treatment, thereby fully releasing molding stress, improving magnetic domain structure, and maintaining the integrity of insulation performance. However, how to construct a high-performance inorganic insulating layer with ultra-thin thickness, high density, strong adhesion, and ideal interface structure remains the core challenge of current technological breakthroughs and an important research direction for exploring the high-frequency potential of FeSiCr materials.

[0005] In summary, researching a FeSiCr magnetic powder core for high-frequency magnetic fields is of great significance. Summary of the Invention

[0006] The purpose of this invention is to propose a FeSiCr magnetic powder core for high-frequency magnetic fields, its preparation method, and a current sensor, so as to improve the problem of low cutoff frequency of existing FeSiCr magnetic powder cores under high-frequency magnetic fields.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a FeSiCr magnetic powder core, the method comprising the following steps: S100: FeSiCr magnetic powder is passivated in concentrated nitric acid, washed multiple times with deionized water, and then dried to obtain passivated magnetic powder; wherein, the mass of the concentrated nitric acid is 0.5%~5% of the mass of the FeSiCr magnetic powder; S200: The passivated magnetic powder is immersed in polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder. S300 The PEI-coated magnetic powder is placed in a mixed solution of silicone resin and acetone and stirred. The acetone is evaporated by water bath heating. The powder is then crushed, sieved, and pressed to obtain a green blank. S400 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0008] According to some embodiments of the present invention, after the passivated magnetic powder is mixed with deionized water, the pH value of the solution is not lower than 7.

[0009] According to some embodiments of the present invention, the particle size of the FeSiCr magnetic powder is 5~40μm.

[0010] According to some embodiments of the present invention, the mass of the concentrated nitric acid is 1.0% to 5% of the mass of the FeSiCr magnetic powder.

[0011] According to some embodiments of the present invention, the mass of the polyethyleneimine is 1.8 to 2.0% of the mass of the FeSiCr magnetic powder.

[0012] According to some embodiments of the present invention, the mass of the silicone resin is 1.8 to 2.0% of the mass of the FeSiCr magnetic powder.

[0013] According to some embodiments of the present invention, the annealing process includes: (1) Increase the temperature to 180℃ at a rate of 2℃ / min and keep it at 180℃ for 1 hour; (2) Increase the temperature to 500℃ at a rate of 1.5℃ / min and keep it at 500℃ for 1 hour; (3) Cool down to 50℃ at 2℃ / min.

[0014] According to some embodiments of the present invention, the immersion time of the passivated magnetic powder and the polyethyleneimine is 30-40 minutes.

[0015] According to some embodiments of the present invention, the water bath heating temperature is 50 degrees Celsius.

[0016] According to some embodiments of the present invention, the pressing pressure is 1500~2000MPa.

[0017] According to some embodiments of the present invention, prior to the passivation treatment, the process further includes: ultrasonically cleaning the FeSiCr magnetic powder in acetone and drying it.

[0018] To achieve the above objectives, a second aspect of the present invention provides a FeSiCr magnetic powder core, wherein the FeSiCr magnetic powder core is prepared by the above-described preparation method; the FeSiCr magnetic powder used to prepare the FeSiCr magnetic powder core contains 85% to 93% Fe by mass, 3.0% to 7.0% Si by mass, and 4.0% to 8.0% Cr by mass.

[0019] According to some embodiments of the present invention, the molar ratio of Fe, Si and Cr in the FeSiCr magnetic powder is (88.4~88.9):(5.6~5.9):(5.4~6).

[0020] To achieve the above objectives, a third aspect of the present invention provides a current sensor comprising a FeSiCr magnetic powder core; The FeSiCr magnetic powder core is the FeSiCr magnetic powder core described above, or the FeSiCr magnetic powder core prepared by the above preparation method.

[0021] Therefore, compared with the prior art, the present invention has the following beneficial effects: The method for preparing FeSiCr magnetic powder cores provided by this invention includes the following steps: FeSiCr magnetic powder is passivated in concentrated nitric acid, washed multiple times with deionized water, and then dried to obtain passivated magnetic powder; wherein the mass of concentrated nitric acid is 0.5%~5% of the mass of FeSiCr magnetic powder; the passivated magnetic powder is immersed in polyethyleneimine (PEI), washed with deionized water, to obtain PEI-coated magnetic powder; the PEI-coated magnetic powder is mixed and stirred in a mixed solution of silicone resin and acetone, heated in a water bath to evaporate the acetone, and then crushed, sieved, and pressed to obtain a green blank; the green blank is annealed in a nitrogen atmosphere to obtain the FeSiCr magnetic powder core. This invention, by adjusting the preparation process of the FeSiCr magnetic powder core, enables the FeSiCr magnetic powder core to achieve higher resistivity, cutoff frequency, and lower eddy current loss under high-frequency magnetic fields, making it suitable for the performance requirements of high-frequency magnetic cores in broadband current sensors, and also possessing the advantages of simple structure and ease of implementation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of a method for preparing FeSiCr magnetic powder core according to an embodiment of the present invention; Figure 2 The images show the SEM microstructure of the FeSiCr magnetic powder cores in Examples 1-5 and Comparative Example 1 of this invention. Figure 3 The diagram shows a comparison of the hysteresis loops of the FeSiCr magnetic powder cores in Examples 1-5 and Comparative Example 1 of this invention.

[0024] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0027] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0028] Against the backdrop of rapid iteration in high-frequency power electronics and advanced sensor technologies, the requirements for high-frequency response and power loss of soft magnetic materials are becoming increasingly stringent. Magnetic powder core materials, represented by FeSiCr alloys, have become key fundamental materials for achieving efficient electromagnetic energy conversion and signal sensing due to their excellent electromagnetic properties (such as high saturation magnetic induction, high initial permeability, and low coercivity). However, when applications expand to the MHz band, the performance bottlenecks of these materials quickly become apparent: on the one hand, their magnetic spectrum characteristics determine that permeability decreases significantly with increasing frequency, making it difficult to maintain a stable magnetic response at high frequencies; on the other hand, the limited resistivity of the alloy itself induces strong eddy current effects at high frequencies, resulting in considerable energy loss and core temperature rise, threatening the stability and lifespan of the device. These factors collectively limit the in-depth application of traditional FeSiCr magnetic cores in broadband, high-precision current sensor scenarios.

[0029] To overcome the aforementioned bottlenecks, surface insulating coating is considered the most direct and effective material modification strategy for improving the high-frequency electromagnetic properties of materials. The optimization mechanism of this strategy is mainly reflected in two dimensions: At the magnetic level, the coating layer, acting as a non-magnetic spacer, slightly reduces the overall magnetic volume fraction of the material but introduces additional exchange decoupling between particles. This is equivalent to enhancing the effective magnetic anisotropy of the material, thereby pushing the natural resonant frequency to a higher frequency domain and allowing the permeability to remain stable over a wider frequency band. At the electrical level, the uniform and dense coating layer can construct a three-dimensional insulating network between conductive magnetic particles, greatly blocking the flow path of high-frequency eddy currents between particles, significantly increasing the resistivity of the composite, and suppressing eddy current losses at their source. The synergistic effect of these two factors effectively improves the high-frequency characteristics of the material.

[0030] Existing insulating coating technologies are mainly divided into two routes based on the different chemical properties of the materials: organic and inorganic systems. Organic coating (such as using epoxy or silicone resin) is simple to process, and the resulting film is flexible and continuous, effectively achieving particle isolation. However, its thermal stability is insufficient, making it difficult to withstand the high-temperature annealing treatment necessary to eliminate internal stress and optimize magnetic properties. Furthermore, it is prone to creep or cracking during high-pressure molding, leading to a decrease in insulation reliability. Inorganic coating (such as forming oxides, phosphates, etc.) exhibits excellent thermal stability and mechanical strength. Its insulating phase can withstand high-temperature heat treatment, thereby fully releasing molding stress, improving magnetic domain structure, and maintaining the integrity of insulation performance. However, how to construct a high-performance inorganic insulating layer with ultra-thin thickness, high density, strong adhesion, and ideal interface structure remains the core challenge of current technological breakthroughs and an important research direction for exploring the high-frequency potential of FeSiCr materials.

[0031] In summary, researching a FeSiCr magnetic powder core for high-frequency magnetic fields is of great significance.

[0032] This invention discloses a FeSiCr magnetic powder core for high-frequency magnetic fields, in order to improve the problem that the cutoff frequency of existing FeSiCr magnetic powder cores is not high under high-frequency magnetic fields.

[0033] Example 1

[0034] This invention discloses a FeSiCr magnetic powder core, the preparation method of which includes the following steps:

[0035] S100: 50g of FeSiCr magnetic powder was placed in 0.25g of concentrated nitric acid for passivation treatment, washed multiple times with deionized water and dried to obtain the passivated magnetic powder.

[0036] Specifically, including: S110: Immerse 50g of FeSiCr magnetic powder in 100ml of acetone and ultrasonically clean for 15min; after cleaning, place it in a fume hood and let it stand and dry for 24h to obtain pretreated FeSiCr magnetic powder.

[0037] The molar ratio of Fe, Si, and Cr in FeSiCr magnetic powder is 88.6:5.8:5.6, which means that the mass percentages of Fe, Si, and Cr are 91.59%, 3.02%, and 5.39%, respectively.

[0038] FeSiCr magnetic powder can be completely immersed in acetone. After cleaning, transfer the FeSiCr magnetic powder to a fume hood and allow it to dry.

[0039] It should be noted that the purpose of this static drying is to completely evaporate the acetone in the magnetic powder, and the static drying time is not limited to 24 hours.

[0040] S120: Place the pretreated FeSiCr magnetic powder in 0.25g of nitric acid solution and stir for 10min under constant temperature water bath at 50℃; after stirring, place the reaction product in an oven and dry at 120℃ for 1h.

[0041] The purpose of this step is to form a passivation layer on the outside of the FeSiCr particles.

[0042] S130: Wash the dried product with deionized water.

[0043] The purpose of this step is to dissolve the hydrogen ions in the reaction product in deionized water so as to avoid the presence of hydrogen ions affecting subsequent steps.

[0044] S140: Measure the pH value of the solution after cleaning.

[0045] The purpose of this step is to verify the degree of hydrogen ion removal in step S130.

[0046] This step involves measuring the pH value of the solution using pH test paper.

[0047] S150: If the pH value is less than 7, repeat S130~S140; if the pH value is not less than 7, continue to the next step.

[0048] The purpose of this step is to determine whether you need to clean it again.

[0049] S200: The passivated magnetic powder is immersed in 1g of polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder.

[0050] Specifically, including: S210 places the passivated magnetic powder in 1g of polyethyleneimine and soaks it for 30min.

[0051] S220 uses deionized water to wash the soaked product twice.

[0052] S230 places the cleaned product in an oven and dries it at 80°C for 1 hour.

[0053] S300 involves mixing and stirring PEI-coated magnetic powder in a mixed solution of silicone resin and acetone, then heating it in a water bath to evaporate the acetone. The resulting green body is then crushed, sieved, and pressed.

[0054] Specifically, including: S310: Mix 1g of silicone resin with acetone until the silicone resin is completely dissolved in the acetone.

[0055] S320: Mix the PEI-coated magnetic powder in the S310 mixture solution and stir continuously in a 50°C constant temperature water bath until the acetone is completely evaporated.

[0056] S330: The product of S320 after stirring is crushed and sieved through a 200-mesh sieve.

[0057] S340: The sieved product is pressed into a ring-shaped green body under a pressure of 1800MPa.

[0058] S400 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0059] Specifically, including: S410 places the green billet in a tube furnace and introduces a nitrogen atmosphere into the furnace.

[0060] The S420 is heated to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour.

[0061] The S430 is heated to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour.

[0062] S440 cools down to 50°C at a rate of 2°C / min.

[0063] Example 2

[0064] This invention discloses a FeSiCr magnetic powder core, the preparation method of which includes the following steps: S100: 50g of FeSiCr magnetic powder was placed in 0.5g of concentrated nitric acid for passivation treatment, washed multiple times with deionized water and dried to obtain passivated magnetic powder.

[0065] Specifically, including: S110: Immerse 50g of FeSiCr magnetic powder in 100ml of acetone and ultrasonically clean for 15min; after cleaning, place it in a fume hood and let it stand and dry for 24h to obtain pretreated FeSiCr magnetic powder.

[0066] In this step, the molar ratio of Fe, Si, and Cr in the FeSiCr magnetic powder is 88.6:5.8:5.6, and the mass percentages of Fe, Si, and Cr are 91.59%, 3.02%, and 5.39%, respectively.

[0067] S120: Place the pretreated FeSiCr magnetic powder in 0.5g of nitric acid solution and stir for 10min under constant temperature water bath at 50℃; after stirring, place the reaction product in an oven and dry at 120℃ for 1h.

[0068] S130: Wash the dried product with deionized water.

[0069] S140: Measure the pH value of the solution after cleaning.

[0070] S150: If the pH value is less than 7, repeat S130~S140; if the pH value is not less than 7, continue to the next step.

[0071] S200: The passivated magnetic powder is immersed in 1g of polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder.

[0072] Specifically, including: S210 places the passivated magnetic powder in 1g of polyethyleneimine and soaks it for 30min.

[0073] S220 uses deionized water to wash the soaked product twice.

[0074] S230 places the cleaned product in an oven and dries it at 80°C for 1 hour.

[0075] S300 involves mixing and stirring PEI-coated magnetic powder in a mixed solution of silicone resin and acetone, then heating it in a water bath to evaporate the acetone. The resulting green body is then crushed, sieved, and pressed.

[0076] Specifically, including: S310: Mix 1g of silicone resin with acetone until the silicone resin is completely dissolved in the acetone.

[0077] S320: Mix the PEI-coated magnetic powder in the S310 mixture solution and stir continuously in a 50°C constant temperature water bath until the acetone is completely evaporated.

[0078] S330: The product of S320 after stirring is crushed and sieved through a 200-mesh sieve.

[0079] S340: The sieved product is pressed into a ring-shaped green body under a pressure of 1800MPa.

[0080] S400 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0081] Specifically, including: S410 places the green billet in a tube furnace and introduces a nitrogen atmosphere into the furnace.

[0082] The S420 is heated to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour.

[0083] The S430 is heated to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour.

[0084] S440 cools down to 50°C at a rate of 2°C / min.

[0085] Example 3

[0086] This invention discloses a FeSiCr magnetic powder core, the preparation method of which includes the following steps: S100: 50g of FeSiCr magnetic powder was placed in 0.75g of concentrated nitric acid for passivation treatment, washed multiple times with deionized water and dried to obtain passivated magnetic powder.

[0087] Specifically, including: S110: Immerse 50g of FeSiCr magnetic powder in 100ml of acetone and ultrasonically clean for 15min; after cleaning, place it in a fume hood and let it stand and dry for 24h to obtain pretreated FeSiCr magnetic powder.

[0088] In this step, the molar ratio of Fe, Si, and Cr in the FeSiCr magnetic powder is 88.6:5.8:5.6, and the mass percentages of Fe, Si, and Cr are 91.59%, 3.02%, and 5.39%, respectively.

[0089] S120: Place the pretreated FeSiCr magnetic powder in 0.75g of nitric acid solution and stir for 10min under constant temperature water bath at 50℃; after stirring, place the reaction product in an oven and dry at 120℃ for 1h.

[0090] S130: Wash the dried product with deionized water.

[0091] S140: Measure the pH value of the solution after cleaning.

[0092] S150: If the pH value is less than 7, repeat S130~S140; if the pH value is not less than 7, continue to the next step.

[0093] S200: The passivated magnetic powder is immersed in 1g of polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder.

[0094] Specifically, including: S210 places the passivated magnetic powder in 1g of polyethyleneimine and soaks it for 30min.

[0095] S220 uses deionized water to wash the soaked product twice.

[0096] S230 places the cleaned product in an oven and dries it at 80°C for 1 hour.

[0097] S300 involves mixing and stirring PEI-coated magnetic powder in a mixed solution of silicone resin and acetone, then heating it in a water bath to evaporate the acetone. The resulting green body is then crushed, sieved, and pressed.

[0098] Specifically, including: S310: Mix 1g of silicone resin with acetone until the silicone resin is completely dissolved in the acetone.

[0099] S320: Mix the PEI-coated magnetic powder in the S310 mixture solution and stir continuously in a 50°C constant temperature water bath until the acetone is completely evaporated.

[0100] S330: The product of S320 after stirring is crushed and sieved through a 200-mesh sieve.

[0101] S340: The sieved product is pressed into a ring-shaped green body under a pressure of 1800MPa.

[0102] S400 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0103] Specifically, including: S410 places the green billet in a tube furnace and introduces a nitrogen atmosphere into the furnace.

[0104] The S420 is heated to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour.

[0105] The S430 is heated to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour.

[0106] S440 cools down to 50°C at a rate of 2°C / min.

[0107] Example 4

[0108] This invention discloses a FeSiCr magnetic powder core, the preparation method of which includes the following steps: S100: 50g of FeSiCr magnetic powder is placed in 1g of concentrated nitric acid for passivation treatment, washed multiple times with deionized water and dried to obtain passivated magnetic powder.

[0109] Specifically, including: S110: Immerse 50g of FeSiCr magnetic powder in 100ml of acetone and ultrasonically clean for 15min; after cleaning, place it in a fume hood and let it stand and dry for 24h to obtain pretreated FeSiCr magnetic powder.

[0110] In this step, the molar ratio of Fe, Si, and Cr in the FeSiCr magnetic powder is 88.6:5.8:5.6, and the mass percentages of Fe, Si, and Cr are 91.59%, 3.02%, and 5.39%, respectively.

[0111] S120: Place the pretreated FeSiCr magnetic powder in 1g of nitric acid solution and stir for 10min under constant temperature water bath at 50℃; after stirring, place the reaction product in an oven and dry at 120℃ for 1h.

[0112] S130: Wash the dried product with deionized water.

[0113] S140: Measure the pH value of the solution after cleaning.

[0114] S150: If the pH value is less than 7, repeat S130~S140; if the pH value is not less than 7, continue to the next step.

[0115] S200: The passivated magnetic powder is immersed in 1g of polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder.

[0116] Specifically, including: S210 places the passivated magnetic powder in 1g of polyethyleneimine and soaks it for 30min.

[0117] S220 uses deionized water to wash the soaked product twice.

[0118] S230 places the cleaned product in an oven and dries it at 80°C for 1 hour.

[0119] S300 involves mixing and stirring PEI-coated magnetic powder in a mixed solution of silicone resin and acetone, then heating it in a water bath to evaporate the acetone. The resulting green body is then crushed, sieved, and pressed.

[0120] Specifically, including: S310: Mix 1g of silicone resin with acetone until the silicone resin is completely dissolved in the acetone.

[0121] S320: Mix the PEI-coated magnetic powder in the S310 mixture solution and stir continuously in a 50°C constant temperature water bath until the acetone is completely evaporated.

[0122] S330: The product of S320 after stirring is crushed and sieved through a 200-mesh sieve.

[0123] S340: The sieved product is pressed into a ring-shaped green body under a pressure of 1800MPa.

[0124] S400 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0125] Specifically, including: S410 places the green billet in a tube furnace and introduces a nitrogen atmosphere into the furnace.

[0126] The S420 is heated to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour.

[0127] The S430 is heated to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour.

[0128] S440 cools down to 50°C at a rate of 2°C / min.

[0129] Example 5

[0130] This invention discloses a FeSiCr magnetic powder core, the preparation method of which includes the following steps: S100: 50g of FeSiCr magnetic powder was placed in 1.25g of concentrated nitric acid for passivation treatment, washed multiple times with deionized water and dried to obtain the passivated magnetic powder.

[0131] Specifically, including: S110: Immerse 50g of FeSiCr magnetic powder in 100ml of acetone and ultrasonically clean for 15min; after cleaning, place it in a fume hood and let it stand and dry for 24h to obtain pretreated FeSiCr magnetic powder.

[0132] In this step, the molar ratio of Fe, Si, and Cr in the FeSiCr magnetic powder is 88.6:5.8:5.6, and the mass percentages of Fe, Si, and Cr are 91.59%, 3.02%, and 5.39%, respectively.

[0133] S120: Place the pretreated FeSiCr magnetic powder in 1.25g of nitric acid solution and stir for 10min under constant temperature water bath at 50℃; after stirring, place the reaction product in an oven and dry at 120℃ for 1h.

[0134] S130: Wash the dried product with deionized water.

[0135] S140: Measure the pH value of the solution after cleaning.

[0136] S150: If the pH value is less than 7, repeat S130~S140; if the pH value is not less than 7, continue to the next step.

[0137] S200: The passivated magnetic powder is immersed in 1g of polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder.

[0138] Specifically, including: S210 places the passivated magnetic powder in 1g of polyethyleneimine and soaks it for 30min.

[0139] S220 uses deionized water to wash the soaked product twice.

[0140] S230 places the cleaned product in an oven and dries it at 80°C for 1 hour.

[0141] S300 involves mixing and stirring PEI-coated magnetic powder in a mixed solution of silicone resin and acetone, then heating it in a water bath to evaporate the acetone. The resulting green body is then crushed, sieved, and pressed.

[0142] Specifically, including: S310: Mix 1g of silicone resin with acetone until the silicone resin is completely dissolved in the acetone.

[0143] S320: Mix the PEI-coated magnetic powder in the S310 mixture solution and stir continuously in a 50°C constant temperature water bath until the acetone is completely evaporated.

[0144] S330: The product of S320 after stirring is crushed and sieved through a 200-mesh sieve.

[0145] S340: The sieved product is pressed into a ring-shaped green body under a pressure of 1800MPa.

[0146] S400 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0147] Specifically, including: S410 places the green billet in a tube furnace and introduces a nitrogen atmosphere into the furnace.

[0148] The S420 is heated to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour.

[0149] The S430 is heated to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour.

[0150] S440 cools down to 50°C at a rate of 2°C / min.

[0151] Comparative Example 1

[0152] This invention discloses a FeSiCr magnetic powder core as a comparative example. The preparation method of the FeSiCr magnetic powder core includes the following steps: S100: Soak 50g of FeSiCr magnetic powder in 100ml of acetone and ultrasonically clean for 15min; after cleaning, place it in a fume hood and let it stand and dry for 24h to obtain pretreated FeSiCr magnetic powder.

[0153] S200: The pretreated FeSiCr magnetic powder is placed in a mixed solution of silicone resin and acetone and stirred. The acetone is evaporated by water bath heating. After crushing, sieving and pressing, a green blank is obtained.

[0154] Specifically, including: S210: Mix 1g of silicone resin with acetone until the silicone resin is completely dissolved in the acetone.

[0155] S220: The pretreated FeSiCr magnetic powder is placed in the mixed solution of S210 and mixed, and stirred continuously in a constant temperature water bath at 50℃ until the acetone is completely evaporated.

[0156] S230: The product of S320 after stirring is crushed and sieved through a 200-mesh sieve.

[0157] S240: The sieved product is pressed into a ring-shaped green body under a pressure of 1800MPa.

[0158] S300 annealed the green blank in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

[0159] Specifically, including: S310 places the green billet in a tube furnace and introduces a nitrogen atmosphere into the furnace.

[0160] The S320 is heated to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour.

[0161] The S330 is heated to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour.

[0162] S340 cools down to 50℃ at a rate of 2℃ / min.

[0163] The properties of the FeSiCr magnetic powder cores prepared in Comparative Example 1 and Examples 1-5 are characterized below.

[0164] The microstructure of the FeSiCr magnetic powder cores of Examples 1-5 and the FeSiCr magnetic powder core of Comparative Example 1 was characterized by scanning electron microscopy.

[0165] Figure 2 The images show the SEM microstructure of the FeSiCr magnetic powder cores from Examples 1-5 and Comparative Example 1. Figure 2 Each FeSiCr magnetic powder core contains FeSiCr particles of different sizes. The FeSiCr magnetic powder cores in the embodiments of the present invention have better compactness and structural integrity.

[0166] The magnetic field performance of the FeSiCr magnetic powder cores of Examples 1-5 and the FeSiCr magnetic powder core of Comparative Example 1 was tested using a vibrating sample magnetometer (VSM-300).

[0167] Figure 3 The diagram shows a comparison of the hysteresis loops of the FeSiCr magnetic powder cores in Examples 1-5 and the FeSiCr magnetic powder core in Comparative Example 1. Figure 3 As shown, the hysteresis loops of each FeSiCr magnetic powder core have the same coercive field, different remanence, and different magnetic saturation intensities. The magnetic powder cores in Examples 2-4 have smaller remanence and magnetic saturation intensities. The remanence and magnetic saturation intensities of the FeSiCr magnetic powder cores are also related to the amount of concentrated nitric acid added in the preparation method; the greater the amount of concentrated nitric acid added, the smaller the remanence of the FeSiCr magnetic powder core. When the amount of concentrated nitric acid added is 1% to 2.5% of the total amount of FeSiCr magnetic powder cores, the magnetic saturation intensities of the FeSiCr magnetic powder cores do not differ significantly.

[0168] The density of the FeSiCr magnetic powder cores of Examples 1-5 and the FeSiCr magnetic powder core of Comparative Example 1 was measured using the Archimedes displacement method.

[0169] The densities of the FeSiCr magnetic powder cores in Comparative Example 1 and Examples 1-5 were 6.27 g / cm³. 3 6.19 g / cm 3 6.16 g / cm 3 6.15 g / cm 3 6.12 g / cm 3 6.01 g / cm 3 The densities of the FeSiCr magnetic powder cores in the embodiments of the present invention are all lower than those of the FeSiCr magnetic powder cores in Comparative Example 1, and the density of the FeSiCr magnetic powder cores is related to the amount of concentrated nitric acid added in the preparation method of the embodiments of the present invention; the greater the amount of concentrated nitric acid added, the lower the density of the FeSiCr magnetic powder cores. This indicates that the addition of concentrated nitric acid is beneficial to the coating of FeSiCr particles by polyethyleneimine and silicone resin, and the amount of concentrated nitric acid added can regulate the passivation reaction process of FeSiCr magnetic powder with concentrated nitric acid.

[0170] The effective permeability of the FeSiCr magnetic powder cores of Examples 1-5 and Comparative Example 1 was measured using an LCR meter (Tonghui, TH2826A). The effective permeability of the FeSiCr magnetic powder cores of Comparative Example 1 and Examples 1-5 were 53, 42, 36, 33, 30, and 28, respectively.

[0171] The effective magnetic permeability of the FeSiCr magnetic powder cores in the embodiments of the present invention is greater than that of the FeSiCr magnetic powder core in Comparative Example 1. Furthermore, the effective magnetic permeability of the FeSiCr magnetic powder core is related to the amount of concentrated nitric acid added in the preparation method of the embodiments of the present invention; the greater the amount of concentrated nitric acid added, the lower the effective magnetic permeability of the FeSiCr magnetic powder core. This indicates that the addition of concentrated nitric acid reduces the effective magnetic permeability of the FeSiCr magnetic powder core.

[0172] The cutoff frequencies of the FeSiCr magnetic powder cores in Examples 1-5 and Comparative Example 1 were measured using an impedance analyzer (Keysight, E4991B). The cutoff frequencies of the FeSiCr magnetic powder cores in Comparative Example 1 and Examples 1-5 were 114 MHz, 139 MHz, 161 MHz, 176 MHz, 192 MHz, and 202 MHz, respectively.

[0173] The cutoff frequencies of the FeSiCr magnetic powder cores in the embodiments of the present invention are all greater than those of the FeSiCr magnetic powder cores in Comparative Example 1, and the cutoff frequency of the FeSiCr magnetic powder cores is related to the amount of concentrated nitric acid added in the preparation method of the embodiments of the present invention; the greater the amount of concentrated nitric acid added, the greater the cutoff frequency of the FeSiCr magnetic powder cores. This indicates that the addition of concentrated nitric acid can increase the cutoff frequency of the FeSiCr magnetic powder cores.

[0174] It should be understood that the cutoff frequency of a magnetic powder core is the lower limit of its effective operating frequency for a specific application. Above this frequency, due to factors such as significantly increased core losses, decreased permeability, or skin effect, the magnetic powder core is no longer suitable for efficient operation.

[0175] The resistivity of the FeSiCr magnetic powder cores from Examples 1-5 and Comparative Example 1 was measured using an impedance analyzer (Tonghui TH2829A). The resistivity of the FeSiCr magnetic powder cores from Comparative Example 1 and Examples 1-5 were 0.37 Ω•cm, 0.55 Ω•cm, 0.68 Ω•cm, 0.77 Ω•cm, 0.86 Ω•cm, and 0.98 Ω•cm, respectively.

[0176] The resistivity of the FeSiCr magnetic powder cores in the embodiments of the present invention is greater than that of the FeSiCr magnetic powder core in Comparative Example 1, and the resistivity of the FeSiCr magnetic powder core is related to the amount of concentrated nitric acid added in the preparation method of the embodiments of the present invention; the greater the amount of concentrated nitric acid added, the greater the resistivity of the FeSiCr magnetic powder core. This indicates that the addition of concentrated nitric acid can increase the resistivity of the FeSiCr magnetic powder core.

[0177] Under the conditions of 100kHz frequency and 50mT magnetic field, the power loss, hysteresis loss and eddy current loss of the FeSiCr magnetic powder cores of Examples 1-5 and Comparative Example 1 were measured by BH analyzer (SY-8218).

[0178] It should be understood that power loss is the undesirable energy dissipation in electrical, electronic, or magnetic systems due to various physical mechanisms, typically released as heat. Power loss directly affects system efficiency, temperature rise, reliability, and lifespan. Power loss in magnetic materials mainly includes hysteresis loss caused by domain flipping to overcome internal friction, eddy current loss caused by induced eddy current heating, and residual / abnormal loss caused by dynamic jumping of domain walls.

[0179] It should be understood that eddy current loss is the energy loss of a magnetic material caused by induced eddy currents in an alternating magnetic field. At high frequencies, the skin effect causes the magnetic field to concentrate only on the surface, resulting in uneven distribution of eddy currents inside, which can easily lead to abnormal eddy current loss.

[0180] The power loss of the FeSiCr magnetic powder cores in Comparative Example 1 and Examples 1-5 was 156 mW / cm². 3 152mW / cm 3 151mW / cm 3 158 mW / cm 3 168 mW / cm 3 174mW / cm 3 The power loss of the FeSiCr magnetic powder cores in Examples 3-5 of this invention is greater than that of the FeSiCr magnetic powder core in Comparative Example 1. The power loss of the FeSiCr magnetic powder core in Example 2 of this invention is less than that of the FeSiCr magnetic powder core in Example 1. The power loss of the FeSiCr magnetic powder core in Example 1 of this invention is less than that of the FeSiCr magnetic powder core in Comparative Example 1. The power loss of the FeSiCr magnetic powder core is related to the amount of concentrated nitric acid added in the preparation method of this invention. After the concentration of concentrated nitric acid is greater than 1% of the mass of FeSiCr magnetic powder, the greater the amount of concentrated nitric acid added, the greater the power loss of the FeSiCr magnetic powder core.

[0181] The hysteresis losses of the FeSiCr magnetic powder cores in Comparative Example 1 and Examples 1-5 were 82 mW / cm.3 99mW / cm 3 111mW / cm 3 122mW / cm 3 135 mW / cm 3 142mW / cm 3 The eddy current losses of the FeSiCr magnetic powder cores in Comparative Example 1 and Examples 1-5 were 72 mW / cm². 3 51mW / cm 3 39mW / cm 3 34mW / cm 3 31mW / cm 3 29mW / cm 3 .

[0182] The hysteresis losses of the FeSiCr magnetic powder cores in Examples 1-5 of this invention are all greater than those of the FeSiCr magnetic powder core in Comparative Example 1, and the greater the amount of concentrated nitric acid added, the greater the hysteresis loss. The eddy current losses of the FeSiCr magnetic powder cores in Examples 1-5 of this invention are all less than those of the FeSiCr magnetic powder core in Comparative Example 1, and the greater the amount of concentrated nitric acid added, the smaller the eddy current loss. This indicates that the addition of concentrated nitric acid, while increasing the hysteresis loss of the FeSiCr magnetic powder core, also helps to reduce the eddy current loss.

[0183] In summary, the FeSiCr magnetic powder core of this invention is prepared by the following steps: (1) FeSiCr magnetic powder is passivated in concentrated nitric acid, washed multiple times with deionized water, and dried to obtain passivated magnetic powder; (2) The passivated magnetic powder is soaked in polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder; (3) The PEI-coated magnetic powder is mixed and stirred in a mixed solution of silicone resin and acetone, heated in a water bath to evaporate the acetone, crushed, sieved, and pressed to obtain a green blank; (4) The green blank is annealed in a nitrogen atmosphere to obtain the FeSiCr magnetic powder core. The magnetic powder core prepared by this invention, through the synergistic effect of FeSiCr magnetic powder, concentrated nitric acid, polyethyleneimine, and silicone resin, can achieve high resistivity, cutoff frequency, and low eddy current loss under high-frequency magnetic field, which is suitable for the performance requirements of high-frequency magnetic cores in broadband current sensors, and has the beneficial effects of simple structure and easy implementation.

[0184] The present invention also discloses a FeSiCr magnetic powder core, which is a FeSiCr magnetic powder core prepared by the above-described preparation method.

[0185] Specifically, the FeSiCr magnetic powder core has a composite coating structure of matrix / inorganic insulating layer / interface coupling layer / organic insulating layer, with FeSiCr magnetic powder as the matrix, SiO2 formed by nitric acid oxidation as the inorganic insulating layer, polyethyleneimine as the interface coupling layer, and silicone resin as the organic insulating layer.

[0186] The FeSiCr magnetic powder used in the preparation has a mass percentage of 85%~93% Fe, 3.0%~7.0% Si, and 4.0%~8.0% Cr. The preferred molar ratio of Fe, Si, and Cr in the FeSiCr magnetic powder is (88.4~88.9):(5.6~5.9):(5.4~6).

[0187] The concentrated nitric acid used in the preparation is 0.5% to 5% of the mass of the FeSiCr magnetic powder. Preferably, the mass of the concentrated nitric acid is 1% to 5%.

[0188] The mass of polyethyleneimine used in the preparation is 1.8% to 2% of the mass of FeSiCr magnetic powder.

[0189] The mass of the silicone resin used in the preparation is 1.8% to 2% of the mass of the FeSiCr magnetic powder.

[0190] The present invention also discloses a current sensor, which includes the FeSiCr magnetic powder core described above or the FeSiCr magnetic powder core prepared by the above preparation method.

[0191] This current sensor can measure magnetic fields under wide-band or high-frequency magnetic fields using FeSiCr magnetic powder cores.

[0192] The above are merely exemplary embodiments of the present invention and do not limit the scope of the patent of the present invention. All equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a FeSiCr magnetic powder core, characterized in that, Includes the following steps: FeSiCr magnetic powder was passivated by placing it in concentrated nitric acid, washing it several times with deionized water, and then drying it to obtain passivated magnetic powder; wherein the mass of the concentrated nitric acid was 0.5% to 5% of the mass of the FeSiCr magnetic powder. The passivated magnetic powder was immersed in polyethyleneimine and washed with deionized water to obtain PEI-coated magnetic powder. The PEI-coated magnetic powder is placed in a mixed solution of silicone resin and acetone and stirred. The acetone is evaporated by heating in a water bath. The powder is then crushed, sieved, and pressed to obtain a green body. The green blank was annealed in a nitrogen atmosphere to obtain FeSiCr magnetic powder core.

2. The preparation method according to claim 1, characterized in that, When the passivated magnetic powder is mixed with deionized water, the pH value of the solution is not lower than 7.

3. The preparation method according to claim 1, characterized in that, The particle size of the FeSiCr magnetic powder is 5~40μm; The mass of the concentrated nitric acid is 1.0% to 5% of the mass of the FeSiCr magnetic powder.

4. The preparation method according to claim 1, characterized in that, The mass of the polyethyleneimine is 1.8~2.0% of the mass of the FeSiCr magnetic powder; The mass of the silicone resin is 1.8 to 2.0% of the mass of the FeSiCr magnetic powder.

5. The preparation method according to claim 1, The annealing process includes: The temperature was increased to 180℃ at a rate of 2℃ / min and held at 180℃ for 1 hour. The temperature was increased to 500℃ at a rate of 1.5℃ / min and held at 500℃ for 1 hour. Cool down to 50℃ at a rate of 2℃ / min.

6. The preparation method according to claim 1, characterized in that, The passivated magnetic powder is immersed in the polyethyleneimine for 30-40 minutes. The water bath heating temperature is 50 degrees Celsius; The pressing pressure is 1500~2000MPa.

7. The preparation method according to claim 1, characterized in that, Prior to the passivation process, the following is also included: The FeSiCr magnetic powder was ultrasonically cleaned in acetone and then dried.

8. A FeSiCr magnetic powder core, characterized in that, The FeSiCr magnetic powder core is prepared by the preparation method according to any one of claims 1-7; the FeSiCr magnetic powder used to prepare the FeSiCr magnetic powder core has a mass percentage of 85%~93%, a mass percentage of 3.0%~7.0%, and a mass percentage of 4.0%~8.0% for Fe, Si, and Cr.

9. The FeSiCr magnetic powder core according to claim 8, characterized in that, The molar ratio of Fe, Si, and Cr in the FeSiCr magnetic powder is (88.4~88.9):(5.6~5.9):(5.4~6).

10. A current sensor, characterized in that... Including FeSiCr magnetic powder cores; The FeSiCr magnetic powder core is the FeSiCr magnetic powder core as described in claim 8 or 9, or the FeSiCr magnetic powder core prepared by the preparation method described in any one of claims 1-7.

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