Soft magnetic composite material and preparation method thereof
By coating soft magnetic powder with nickel-zinc ferrite, a Ni-Zn ferrite layer with high resistivity and magnetic properties is generated, which solves the problem of reduced magnetic permeability and saturation magnetization in the existing technology, achieves low loss and DC bias resistance at high frequencies, and simplifies the process flow.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-04-07
AI Technical Summary
The insulating coating material of existing soft magnetic powder cores is a non-magnetic material, which leads to a decrease in magnetic permeability and saturation magnetization. Moreover, the existing coating process is complex and costly, making it difficult to maintain low loss and DC bias resistance at high frequencies.
A Ni-Zn ferrite insulating layer is generated by co-precipitation reaction of nickel-zinc ferrite precursor and soft magnetic powder. The layer is then formed by high-temperature heat treatment to form a coating layer with high resistivity and magnetic properties, simplifying the annealing process and avoiding the glue removal step.
A balance between high resistivity and high permeability is achieved, which improves the high-frequency performance and DC bias resistance of soft magnetic composite materials, simplifies the preparation process, and reduces costs.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of soft magnetic materials technology, and in particular to a soft magnetic composite material and its preparation method. Background Technology
[0002] To meet the stringent requirements of high frequency, high efficiency, and small size for power electronics in 5G communications, new energy vehicles, and artificial intelligence, metal powder cores, as a key branch of soft magnetic materials, are undergoing continuous technological innovation. Magnetic powder cores achieve comprehensive optimization of their macroscopic magnetic properties by constructing a distributed air gap structure through precise insulating coating on the surface of magnetic metal micropowder. This unique structure allows them to simultaneously achieve high saturation magnetization to handle high power and effectively suppress eddy currents through the insulating layer, maintaining low core losses even at higher operating frequencies. More importantly, the insulating coating and dispersed air gaps together endow the magnetic powder core with excellent DC bias resistance, ensuring stable permeability and preventing saturation of inductors under high current operation. Therefore, continuously optimizing insulating layer materials and coating processes to further reduce high-frequency losses while improving permeability has become the core path for the development of metal powder core technology, targeting more advanced future applications.
[0003] Insulating coating materials for soft magnetic powders can be divided into three main categories: inorganic coating, organic coating, and inorganic-organic composite coating. Organic coating typically refers to the use of organic insulating materials such as silicone resin, epoxy resin, and polyimide to insulate metal magnetic powder. These organic materials not only have extremely high resistivity but also good adhesion properties. They can improve the insulation properties of the metal magnetic powder core while also greatly improving its formability. Inorganic coating typically refers to forming an inorganic insulating layer with extremely high resistivity on the surface of metal magnetic powder through physical mixing, acid corrosion, and in-situ growth. For example, silicon dioxide and alumina are physically mixed with metal magnetic powder and adhered to the surface through electrostatic adsorption; weak acids such as phosphoric acid and oxalic acid are used to corrode the surface of the metal magnetic powder to form inorganic salts; and titanium dioxide and silicon dioxide are produced in-situ on the surface of the metal magnetic powder through hydrolysis reactions of titanate esters and tetraethyl orthosilicate.
[0004] Currently, the primary concern in coating processes is the magnetic dilution effect. Both inorganic and organic coatings use non-magnetic materials for the insulating layer, and the introduction of these non-magnetic materials leads to a decrease in magnetic permeability and saturation magnetization. Furthermore, annealing is an essential step in the fabrication of metal magnetic powder cores, typically at temperatures above 400℃. Therefore, the currently mainstream organic coating process requires a debinding step during annealing, significantly increasing the number of steps and costs. As for inorganic coatings, physical mixing methods are simple and efficient, but it's difficult to guarantee the integrity and density of the coating. Acid corrosion requires consideration of complex issues such as acid corrosion rate, reaction layer thickness, and waste liquid treatment. In-situ coating offers better density and integrity, but also suffers from low reaction efficiency, difficulty in controlling coating layer thickness, and cumbersome reaction steps. Summary of the Invention
[0005] To address the problem that the insulating coating of existing soft magnetic powder cores affects their magnetic properties, this invention provides a soft magnetic composite material with high resistance and high permeability, and a method for preparing the same.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: First, the present invention provides a method for preparing a soft magnetic composite material, which includes the following steps: S1. A mixed metal salt solution containing nickel, zinc and iron salts is mixed with a precipitant to carry out a co-precipitation reaction, and the precipitate is obtained, which is the Ni-Zn ferrite precursor. S2. Mix the Ni-Zn ferrite precursor obtained in step S1 with the soft magnetic powder to obtain a mixed powder; S3. The mixed powder obtained in step S2 is heat-treated at a temperature of 600℃-900℃ to obtain the soft magnetic composite material.
[0007] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, the metal salt in the mixed metal salt solution also includes cobalt salt.
[0008] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, the anion in the mixed metal salt solution is Cl. - and / or NO3 - ; And / or, the precipitant is a soluble hydroxide or ammonia.
[0009] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, the molar ratio of the total metal cations in the mixed metal salt solution to the precipitant is 2:(5.57 ~ 6.28).
[0010] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, step S1 further includes the following steps after the coprecipitation reaction: aging and filtering the reaction system sequentially to obtain the precipitate.
[0011] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, in step S2, the weight of the Ni-Zn ferrite precursor accounts for 3 to 5% of the weight of the soft magnetic powder.
[0012] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, in step S2, the soft magnetic powder is at least one of Fe-Si powder, Fe-Si-Al powder, Fe-Si-Cr powder, Fe-Ni powder, and ferrite powder.
[0013] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, step S3 is as follows: the mixed powder obtained in step S2 is mixed with the binder and then granulated; the granulated powder is pressed into a ring and then heat-treated at a temperature of 600℃-900℃ to obtain the soft magnetic composite material.
[0014] In a preferred embodiment of the preparation method of the soft magnetic composite material of the present invention, the adhesive is polyvinyl alcohol.
[0015] In addition, the present invention also provides a soft magnetic composite material, which is prepared by the above method.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a solid-state reaction to generate Ni-Zn ferrite on the surface of soft magnetic powder, thereby forming a layer of Ni-Zn ferrite. Ni-Zn ferrite possesses high resistivity and subferromagnetism, thus the insulating material coating the soft magnetic powder exhibits both high resistance and magnetic properties, solving the current problem of balancing insulating coating and magnetic properties in soft magnetic powder.
[0017] In addition, the reaction temperature for the formation of Ni-Zn ferrite is higher than the annealing temperature of soft magnetic powder, and Ni-Zn ferrite itself also has ceramic properties and a certain degree of high temperature resistance, so that the debinding process does not need to be considered during the annealing process. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0019] In existing technologies, when insulating soft magnetic powders, whether inorganic or organic coatings are used, the insulating coating layer is always a non-magnetic material. This leads to a decrease in the magnetic permeability and saturation magnetization of the soft magnetic powder. To address the problems of existing technologies, this invention first provides a method for preparing a soft magnetic composite material, which includes the following steps: S1. A mixed metal salt solution containing nickel, zinc and iron salts is mixed with a precipitant to carry out a co-precipitation reaction, and the precipitate is obtained, which is the Ni-Zn ferrite precursor. S2. Mix the Ni-Zn ferrite precursor obtained in step S1 with the soft magnetic powder to obtain a mixed powder; S3. The mixed powder obtained in step S2 is heat-treated at a temperature of 600℃-900℃ to obtain the soft magnetic composite material.
[0020] In the above preparation method, nickel salt, zinc salt, and iron salt are all soluble salts of their respective metals, which are mixed with a precipitant to generate Ni-Zn ferrite precursors. During heat treatment, the Ni-Zn ferrite precursors decompose and undergo a solid-state reaction on the surface of the soft magnetic powder to generate Ni-Zn ferrite with a spinel phase. Ni-Zn ferrite has high resistivity and ferrimagnetism. Therefore, the insulating material coating the soft magnetic powder of this invention has both high resistivity and magnetic properties, solving the current problem of balancing insulating coating and magnetic properties of soft magnetic powder.
[0021] In addition, the reaction temperature for the formation of Ni-Zn ferrite is higher than the annealing temperature of soft magnetic powder, and Ni-Zn ferrite itself also has ceramic properties, so it has a certain high temperature resistance, which means that the debinding process does not need to be considered during the annealing process.
[0022] Preferably, the metal salt in the mixed metal salt solution also includes a cobalt salt. The introduction of the cobalt salt allows cobalt to form Ni-Zn-Co ferrite as a dopant element, and the introduction of cobalt can improve the cutoff frequency and Curie temperature.
[0023] Those skilled in the art can select which soluble metal salt to use as the preparation raw material according to actual needs. For example, nitrates or chlorides with good solubility can be preferred. When nitrates are used as the preparation raw material, the anion in the mixed metal salt solution is NO3. - When chloride is used as a raw material, the anion in the mixed metal salt solution is Cl. - .
[0024] Furthermore, the proportions of various metal salts in the mixed metal salt solution can be determined according to the designed stoichiometric ratio. For example, nickel salt, zinc salt, iron salt, and cobalt salt can be dissolved in deionized water according to their stoichiometric ratios to prepare a mixed salt solution. Preferably, the molar ratio of metal cations in the mixed metal salt solution is Ni.2+ Zn 2+ Fe 3+ =1:1:2-1:1.5:2.
[0025] Preferably, the metal salt in the mixed metal salt solution is composed of nickel chloride, zinc chloride, cobalt chloride, and ferric chloride.
[0026] Preferably, the precipitant is a soluble hydroxide or ammonia. When a soluble hydroxide or ammonia is used as the precipitant, the mixed metal salt solution undergoes a co-precipitation reaction with the precipitant to generate a Ni-Zn ferrite precursor containing an amorphous hydroxide precipitate. Preferably, the soluble hydroxide is sodium hydroxide and / or potassium hydroxide. The precipitant solution can be prepared by dissolving the precipitant in deionized water.
[0027] Preferably, the molar ratio of the total metal cations in the mixed metal salt solution to the precipitant is 2:(5.57 ~ 6.28).
[0028] Preferably, in step S1, the coprecipitation reaction is carried out under conditions where the pH value is 10-11.
[0029] Preferably, in step S1, the coprecipitation reaction is carried out under stirring conditions. The stirring speed can be selected according to actual needs, for example, a stirring speed of 1200 rpm.
[0030] Preferably, in step S1, after the coprecipitation reaction, the following steps are further included: aging and filtering the reaction system sequentially to obtain the precipitate. More preferably, the aging method is as follows: after the coprecipitation reaction is completed, the resulting suspension is kept at a constant temperature for several hours. Aging allows the newly formed precipitate to undergo sufficient crystallization and phase transformation, converting the unstable primary precipitate into more stable hydroxide or basic salt crystals, and dissolving and redepositing fine particles onto larger particles, thus optimizing the particle size distribution. Furthermore, filtration can separate the precipitate from the mother liquor; for example, vacuum filtration can be used to separate the precipitate from the mother liquor.
[0031] Preferably, step S1 further includes the following steps after filtration: washing and / or drying the precipitate. For example, after vacuum filtration, the filter cake can be repeatedly washed with hot deionized water to thoroughly remove impurities entrained in the precipitate until the washed liquid is neutral. Drying can remove physically adsorbed water from the precipitate, yielding a dry, loose Ni-Zn ferrite precursor powder. Drying can be performed using conventional methods of the prior art, such as drying in a drying oven.
[0032] Preferably, in step S2, the weight of the Ni-Zn ferrite precursor accounts for 3-5% of the weight of the soft magnetic powder.
[0033] Preferably, in step S2, the soft magnetic powder is at least one of Fe-Si powder, Fe-Si-Al powder, Fe-Si-Cr powder, Fe-Ni powder, and ferrite powder, for example, FeSi... 6.5 As a soft magnetic powder.
[0034] Preferably, step S3 is as follows: the mixed powder obtained in step S2 is mixed with the binder and then granulated; the granulated powder is pressed into a ring and then heat-treated at a temperature of 600℃-900℃ to obtain the soft magnetic composite material.
[0035] Preferably, the adhesive is polyvinyl alcohol.
[0036] Preferably, the metal salt in the mixed metal salt solution is composed of nickel chloride, zinc chloride, cobalt chloride, and ferric chloride; the precipitant is NaOH solution; and the soft magnetic powder is FeSi. 6.5 The adhesive is polyvinyl alcohol. More preferably, the metal salt in the mixed metal salt solution is composed of nickel chloride, zinc chloride, cobalt chloride, and ferric chloride; the total concentration of metal cations in the mixed metal salt solution is 2.0 mol / L; the precipitant is NaOH solution with a NaOH concentration of 6 mol / L; the volume ratio of the mixed metal salt solution to the NaOH solution is 1:1; the soft magnetic powder is FeSi. 6.5 In step S2, the weight of the Ni-Zn ferrite precursor accounts for 4% of the weight of the soft magnetic powder; the binder is polyvinyl alcohol.
[0037] In addition, the present invention also provides a soft magnetic composite material prepared by the above method. The soft magnetic composite material of the present invention has high electrical resistance and high magnetic permeability.
[0038] The present invention will be further described below through specific embodiments.
[0039] In the following examples, metal chlorides were used as metal salt raw materials, and the purity of each raw material was as follows: Nickel chloride hexahydrate 98.0% zinc chloride 98.0% , cobalt chloride hexahydrate 99.0% ferric chloride hexahydrate 99.0% and NaOH 96.0%.
[0040] Example 1 An embodiment of the soft magnetic composite material and its preparation method of the present invention is as follows: 1. Preparation of a mixed metal salt solution: Dissolve nickel chloride hexahydrate, zinc chloride, and ferric chloride hexahydrate in 175 mL of deionized water. The total concentration of metal cations in the mixed metal salt solution is 2.0 mol / L; the molar ratio of metal cations in the mixed metal salt solution is Ni 2+ Zn 2+ Fe 3+ =1:1:2; 2. Dissolve sodium hydroxide in 175 mL of deionized water to obtain a NaOH solution, and then heat it in a water bath; the concentration of NaOH in the NaOH solution is 6 mol / L. 3. Quickly pour the prepared mixed metal salt solution into the NaOH solution at 90 ℃, control the pH value to 10, and stir continuously with a stirrer at a speed of 1200 rpm. The reaction process lasts for about 35 minutes (during the reaction, cover the reaction vessel with a plastic lid to avoid evaporation of the solution). 4. After the reaction is complete, let it stand for aging. After aging, filter the cake repeatedly with deionized water and anhydrous ethanol until the pH of the washing liquid is 7. 5. After washing the filter cake, place it in a 60 ℃ oven and dry for 24 h to obtain dry and loose Ni-Zn ferrite precursor powder; 6. Mix the Ni-Zn ferrite precursor powder obtained in step 5 with FeSi 6.5 The soft magnetic powder is thoroughly mixed, and the weight of the Ni-Zn ferrite precursor accounts for a certain percentage of the FeSi content. 6.5 4% by weight of soft magnetic powder is used to obtain a mixed powder; 7. Mix the powder obtained in step 6 with 15 wt% polyvinyl alcohol binder and granulate it. Press the granulated powder into a ring with an inner diameter of 3.04 mm, an outer diameter of 7.5 mm, and a thickness of 2.0~3.0 mm under an axial pressure of 1270.0 MPa. 8. Place the pressed ring sample in a muffle furnace and raise the temperature to 800~900 ℃ in air atmosphere at a heating rate of 1.5 ℃ / min. Then hold the temperature and sinter for 9 h to obtain a soft magnetic composite material.
[0041] Example 2 An embodiment of the soft magnetic composite material and its preparation method of the present invention is as follows: 1. Preparation of a mixed metal salt solution: Dissolve nickel chloride hexahydrate, zinc chloride, and ferric chloride hexahydrate in 175 mL of deionized water. The total concentration of metal cations in the mixed metal salt solution is 2.0 mol / L; the molar ratio of metal cations in the mixed metal salt solution is Ni 2+ Zn2+ Fe 3+ =1:1.5:2; 2. Dissolve potassium hydroxide in 175 mL of deionized water to obtain a KOH solution, and then heat it in a water bath; the concentration of KOH in the KOH solution is 5.57 mol / L. 3. Quickly pour the prepared mixed metal salt solution into a KOH solution at 90 ℃, control the pH value to 11, and stir continuously with a stirrer at a speed of 1200 rpm. The reaction process lasts for about 35 minutes (during the reaction, cover the reaction vessel with a plastic lid to avoid evaporation of the solution). 4. After the reaction is complete, let it stand for aging. After aging, filter the cake repeatedly with deionized water and anhydrous ethanol until the pH of the washing liquid is 7. 5. After washing the filter cake, place it in a 60 ℃ oven and dry for 24 h to obtain dry and loose Ni-Zn ferrite precursor powder; 6. Thoroughly mix the Ni-Zn ferrite precursor powder obtained in step 5 with the Fe-Si-Al soft magnetic powder. The weight of the Ni-Zn ferrite precursor accounts for 3% of the weight of the Fe-Si-Al soft magnetic powder to obtain a mixed powder. 7. Mix the powder obtained in step 6 with 15 wt% polyvinyl alcohol binder and granulate it. Press the granulated powder into a ring with an inner diameter of 3.04 mm, an outer diameter of 7.5 mm, and a thickness of 2.0~3.0 mm under an axial pressure of 1270.0 MPa. 8. Place the pressed ring sample in a muffle furnace and sinter at 600 °C for 9 h in an air atmosphere to obtain a soft magnetic composite material.
[0042] Example 3 An embodiment of the soft magnetic composite material and its preparation method of the present invention differs from that of Embodiment 1 only in that: In step 2 of this embodiment, the concentration of NaOH in the NaOH solution is 6.28 mol / L; in step 6, the weight percentage of the Ni-Zn ferrite precursor in FeSi... 6.5 5% of the weight of the soft magnetic powder; in step 9, the sintering temperature is 750℃.
[0043] Comparative Example 1 The only difference between the preparation method of this comparative example of soft magnetic composite material and Example 1 is that the metal salt in the mixed metal salt solution in this comparative example consists of nickel chloride hexahydrate and zinc chloride. Specifically, step 1 of this comparative example is as follows: nickel chloride hexahydrate and zinc chloride are dissolved in 175 mL of deionized water, and the concentrations of nickel chloride hexahydrate and zinc chloride in the mixed metal salt solution are the same as in Example 1.
[0044] Comparative Example 2 The only difference between the preparation method of this comparative example of soft magnetic composite material and Example 1 is that the metal salt in the mixed metal salt solution in this comparative example consists of nickel chloride hexahydrate and ferric chloride hexahydrate. Specifically, step 1 of this comparative example is as follows: nickel chloride hexahydrate and ferric chloride hexahydrate are dissolved in 175 mL of deionized water, and the concentrations of nickel chloride hexahydrate and ferric chloride hexahydrate in the mixed metal salt solution are the same as in Example 1.
[0045] Comparative Example 3 The only difference between the preparation method of this comparative example of soft magnetic composite material and Example 1 is that the metal salt in the mixed metal salt solution in this comparative example consists of zinc chloride and ferric chloride hexahydrate. Specifically, step 1 of this comparative example is as follows: zinc chloride and ferric chloride hexahydrate are dissolved in 175 mL of deionized water, and the concentrations of zinc chloride and ferric chloride hexahydrate in the mixed metal salt solution are the same as in Example 1.
[0046] Comparative Example 4 The only difference between the preparation method of this comparative example of soft magnetic composite material and Example 1 is that the metal salt in the mixed metal salt solution in this comparative example is composed of copper chloride and barium chloride. Specifically, step 1 of this comparative example is as follows: copper chloride and barium chloride are dissolved in 175 mL of deionized water, and the total concentration of metal cations in the mixed metal salt solution is 2.0 mol / L.
[0047] Comparative Example 5 The only difference between the preparation method of this comparative soft magnetic composite material and that of Example 1 is that the preparation method of this comparative soft magnetic composite material is as follows: FeSiAl powder is placed in an air atmosphere and annealed at 600-700℃ for 30-90 min.
[0048] Example of effect This example tested the electrical resistance and magnetic properties of the soft magnetic composite materials prepared in Examples 1-2 and Comparative Example 5. The test results are shown in Table 1 below. The testing equipment and parameters are as follows: 1. Resistance: Measured using a Chroma withstand voltage tester (model 19073) at 25 ℃ and 50 V.
[0049] 2. Permeability and cutoff frequency: Measured using a Keysight precision impedance analyzer under test conditions of 25°C.
[0050] Table 1
[0051] As can be seen from Table 1, the soft magnetic composite material prepared by the method of the present invention has high electrical resistance and high magnetic permeability.
[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing a soft magnetic composite material, characterized in that, Includes the following steps: S1. A mixed metal salt solution containing nickel, zinc and iron salts is mixed with a precipitant to carry out a co-precipitation reaction, and the precipitate is obtained, which is the Ni-Zn ferrite precursor. S2. Mix the Ni-Zn ferrite precursor obtained in step S1 with the soft magnetic powder to obtain a mixed powder; S3. The mixed powder obtained in step S2 is heat-treated at a temperature of 600℃-900℃ to obtain the soft magnetic composite material.
2. The method for preparing the soft magnetic composite material according to claim 1, characterized in that, The metal salts in the mixed metal salt solution also include cobalt salts.
3. The method for preparing the soft magnetic composite material according to claim 1 or 2, characterized in that, The anion in the mixed metal salt solution is Cl. - and / or NO3 - ; And / or, the precipitant is a soluble hydroxide or ammonia.
4. The method for preparing the soft magnetic composite material according to any one of claims 1-3, characterized in that, The molar ratio of the total metal cations in the mixed metal salt solution to the precipitant is 2:(5.57 ~ 6.28).
5. The method for preparing the soft magnetic composite material according to any one of claims 1-4, characterized in that, In step S1, after the coprecipitation reaction, the following steps are also included: aging and filtering the reaction system sequentially to obtain the precipitate.
6. The method for preparing the soft magnetic composite material according to claim 1, characterized in that, In step S2, the weight of the Ni-Zn ferrite precursor accounts for 3-5% of the weight of the soft magnetic powder.
7. The method for preparing the soft magnetic composite material according to claim 1, characterized in that, In step S2, the soft magnetic powder is at least one of Fe-Si powder, Fe-Si-Al powder, Fe-Si-Cr powder, Fe-Ni powder, and ferrite powder.
8. The method for preparing the soft magnetic composite material according to claim 1, characterized in that, Step S3 is as follows: the mixed powder obtained in step S2 is mixed with the binder and then granulated. The granulated powder is pressed into a ring and then heat-treated at a temperature of 600℃-900℃ to obtain the soft magnetic composite material.
9. The method for preparing the soft magnetic composite material according to claim 8, characterized in that, The adhesive is polyvinyl alcohol.
10. A soft magnetic composite material, characterized in that, It is prepared by the method described in any one of claims 1-9.