A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency

Abstract

This invention is a method for preparing partially nitrided metal soft magnets with improved cutoff operating frequency. (1) Material preparation: Select iron powder with a particle size of 1-10 μm; (2) Nitriding: Place the iron powder in a tube furnace, evacuate, and introduce a mixed gas of NH3 and Ar. Heat the powder to 360-475℃ at a rate of 10℃ / min, hold for 0-6 hours, and then cool it to room temperature to obtain partially nitrided iron powder; (3) Insulation coating: Dissolve epoxy resin in acetone, add the nitrided iron powder to the solution and stir, allowing the acetone to evaporate, and the epoxy resin to precipitate and uniformly coat the surface of the iron powder to form an insulating layer, wherein the volume fraction of epoxy resin is about 5-25%; (4) Pressing: Press the powder into a magnetic ring with an inner diameter of 7 mm and an outer diameter of 13 mm under a pressure of 0.9-1.8 GPa. The nitrided iron powder prepared by this method not only maintains a high magnetic permeability, but also effectively suppresses eddy currents within the particles compared to the traditional Fe and Fe4N core-shell structures.

Description

Technical Field

[0001] This invention belongs to the field of soft magnetic material preparation technology, specifically relating to a method for preparing partially nitride metal soft magnets with improved cutoff operating frequency. Background Technology

[0002] Soft magnetic composite materials, due to their high power density and high AC permeability, are widely used in magnetic components for energy conversion, isolation, and resonance in electronic power systems. With the development of electronic technology and social informatization, the emergence of wide-bandgap semiconductors SiC and GaN has raised the cutoff frequency of power conversion electronic devices and motor controllers to GHz. Existing commercial soft magnetic composite materials, as well as amorphous nanocrystals, generally cannot match the high cutoff frequency and high power density provided by wide-bandgap semiconductors, even at MHz. Therefore, the preparation of a soft magnetic composite material with a high cutoff frequency is of great significance. Increasing the cutoff frequency of soft magnetic materials allows them to operate at higher frequencies. The cutoff frequency is when the permeability remains within 98% of the initial permeability; within this range, the operating state of the soft magnetic material is very stable. Commonly used commercial soft magnetic materials have an average particle size of approximately 50 μm. In the MHz band, eddy currents within the particles become the dominant mechanism for eddy current losses, preventing further increases in the cutoff frequency. While traditional oxide coating and insulating dielectric coating can suppress interparticle eddy current losses, they cannot effectively suppress intraparticle losses. Therefore, it is necessary to find new working methods to suppress both interparticle and intraparticle eddy currents simultaneously.

[0003] The patent application number 201610469982.8, entitled "A soft magnetic composite material and its preparation method", mentions the use of NH3 and H2 to prepare Fe and Fe4N core-shell structures. Although the shell formed by this method can suppress interparticle eddies, it cannot effectively suppress intraparticle eddies. Furthermore, the use of H2 at high temperatures during the nitriding process is very dangerous and not conducive to industrialization. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing soft magnetic materials with high cutoff frequency and high power density, which is to address the problem in the prior art that the presence of high particle eddy currents makes it difficult to increase the cutoff operating frequency of soft magnetic composite materials to the MHz or even 100MHz band.

[0005] The following technical solution is adopted to solve the technical problem of the present invention:

[0006] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0007] (1) Material preparation: Select iron powder with a particle size of 1-10μm;

[0008] (2) Nitriding: After evacuating the iron powder in a tube furnace, a mixed gas of NH3 and Ar is introduced and heated to 360-475℃ at a rate of 10℃ / min. The temperature is held for 0-6 h and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0009] (3) Insulation coating: Dissolve epoxy resin in acetone, add iron nitride powder to the solution and stir to evaporate the acetone, and the epoxy resin precipitates and uniformly coats the surface of the iron powder to form an insulating layer, wherein the volume fraction of epoxy resin is about 5-25%;

[0010] (4) Pressing: Press the magnetic ring with an inner diameter of 7 mm and an outer diameter of 13 mm under a pressure of 0.9-1.8 GPa.

[0011] In step (2), the molar ratio of NH3 and Ar in the mixed gas is 1:9-3:1.

[0012] In step (2), the vacuum level is 0.08 MPa.

[0013] In step (2), the flow rate of the mixed gas of NH3 and Ar introduced is 30-60 Sccm.

[0014] The preparation method of this invention employs a nitriding process, selecting carbonyl iron powder of 1-10 μm size that is easy to mass-produce and has low eddy current loss, and using the nitriding process to obtain partially nitrided magnetic powder. During the nitriding process, the partially nitrided iron powder is generated by controlling the nitriding temperature, the ratio of NH3 and Ar gases, and the nitriding time. By precisely controlling the NH3 and Ar ratio, the nitriding process proceeds slowly, uniformly, and with a gradient. The resulting spherical iron nitrided powder exhibits a gradual decrease in Fe phase concentration and an increase in Fe4N phase concentration from the inside out. Because the Fe and Fe4N phases are distributed throughout the spherical particles, our partially nitrided iron powder not only maintains high magnetic permeability but also effectively suppresses intraparticle eddy currents compared to traditional Fe / Fe4N core-shell structures.

[0015] The preparation method of this invention employs a nitriding process, selecting 1-10 μm carbonyl iron powder that is easy to mass-produce and has low eddy current loss, and using the nitriding process to obtain partially nitrided magnetic powder. By varying the holding time, the Fe4N phase content can be controlled, ultimately increasing the cutoff operating frequency of the soft magnetic composite material from 8.23 ​​MHz to 154.88 MHz. Utilizing the advantages of Fe4N's high saturation magnetization and resistivity, the obtained partially nitrided magnetic powder achieves a saturation magnetization of 180-200 emu / g and a magnetic ring cutoff operating frequency of 100 MHz. This invention uses NH3 and Ar gases to nitrid Fe powder, which is safer than traditional NH3 and H2. H2 is colorless and odorless, and at high temperatures, leaks are difficult to detect and can easily explode. Therefore, our exploration of using NH3 and Ar to nitrid Fe powder has greater industrialization potential. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation process of the present invention;

[0017] Figure 2 The temperature and NH3 and Ar gas ratio ranges corresponding to the embodiments with better nitriding effect in this invention are shown. Under the condition of maintaining nitriding for two hours, the temperature range and NH3 and Ar ratio within the shaded area in the figure can obtain partially nitrided iron powder with excellent performance.

[0018] Figure 3 The left image shows the X-ray diffraction patterns of Examples 1, 2, 3, 4, 5, and 6, indicating the formation of partially nitrided iron powder. The right image shows the X-ray diffraction patterns of Samples 7, 8, and 9 prepared by nitriding at 425°C for 0 / 1 / 2 hours, indicating the formation of partially nitrided iron powder with excellent performance. The X-ray diffraction patterns of other examples are similar to these.

[0019] Figure 4 The hysteresis loop diagrams of the vibrating samples of Examples 7 / 8 / 9 of the present invention, prepared by nitriding at 425℃ for 0 / 1 / 2 hours, were measured by a magnetometer.

[0020] Figure 5 The magnetic permeability spectra of samples 7 / 8 / 9 prepared by nitriding at 425℃ for 0 / 1 / 2 hours according to the present invention;

[0021] Figure 6 The images show the morphology of the iron powder used in this invention before and after nitriding. The left image shows the morphology of the iron powder before nitriding, and the right image shows the morphology of the iron powder after nitriding.

[0022] Figure 7The images show the morphology and EDS elemental analysis of the nitrided particles after the nitridation process of this invention. The left image is a cross-sectional morphology of the particles, and the right image is an elemental distribution diagram of the cross-section. In the right image, the small white dots represent nitrogen (N) elements, which gradually increase from the inside to the outside of the particle cross-section, indicating that the metal has undergone uniform and gradient partial nitriding. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0026] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0027] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. Then, a mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 3:1. The temperature is raised to 360℃ at a rate of 10℃ / min, held for 2 h, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0028] (3) Pressing: 0.8 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0029] Example 2

[0030] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0031] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0032] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 3:1. The temperature is raised to 420℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0033] (3) Pressing: 0.8 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0034] Example 3

[0035] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0036] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0037] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 60 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 1:1. The temperature is raised to 375℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0038] (3) Pressing: 0.8 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0039] Example 4

[0040] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0041] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0042] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 60 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 1:1. The temperature is raised to 400℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0043] (3) Pressing: 0.8 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0044] Example 5

[0045] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0046] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0047] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 60 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 1:1. The temperature is raised to 425℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0048] (3) Pressing: 1.6 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 1.8 GPa.

[0049] Example 6

[0050] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0051] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0052] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 60 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 1:1. The temperature is raised to 450℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0053] (3) Pressing: 1.6 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 1.8 GPa.

[0054] Example 7

[0055] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0056] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0057] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 3:7. The temperature is raised to 425℃ at a rate of 10℃ / min, held for 0h, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0058] (3) Pressing: 1.6 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0059] Example 8

[0060] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0061] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0062] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 3:7. The temperature is raised to 425℃ at a rate of 10℃ / min, held for 1h, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0063] (3) Pressing: 1.6 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0064] Example 9

[0065] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0066] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0067] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 3:7. The temperature is raised to 425℃ at a rate of 10℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0068] (3) Pressing: The nitrided iron powder is added to 1.6 wt.% epoxy resin binder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0069] Example 10

[0070] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0071] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0072] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 3:7. The temperature is raised to 425℃ at a rate of 10℃ / min, held for 6h, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0073] (3) Pressing: 0.8 wt.% of epoxy resin binder is added to the nitrided iron powder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0074] Example 11

[0075] A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, comprising the following specific steps:

[0076] (1) Material preparation: Select iron powder with a particle size of 1-10 μm;

[0077] (2) Nitriding: Iron powder is placed in a tube furnace, and a vacuum is drawn to a vacuum degree of 0.08 MPa. A mixed gas of NH3 and Ar with a flow rate of 30 Sccm is introduced, wherein the molar ratio of NH3 and Ar is 1:9. The temperature is raised to 475℃ at a rate of 10℃ / min, held for 6h, and then cooled to room temperature with the furnace to obtain nitrided iron powder.

[0078] (3) Pressing: The nitrided iron powder is added to 1.6 wt.% epoxy resin binder and the magnetic ring is formed under a pressure of 0.9 GPa.

[0079] X-ray diffraction patterns of samples prepared by nitriding at 425℃ for 0 / 1 / 2 hours show the formation of the Fe4N phase, and the Fe4N content continuously increases with increasing holding time, completing partial nitriding of Fe. Hysteresis loop diagrams obtained by a vibrating sample magnetometer of the samples prepared by nitriding at 425℃ for 0 / 1 / 2 hours show a slight decrease in saturation magnetization with increasing Fe4N content, remaining generally stable, indicating that nitriding has little effect on saturation magnetization. Impedance analysis of the permeability spectra of the samples prepared by nitriding at 425℃ for 0 / 1 / 2 hours shows that the cutoff frequency increases from 8.23 ​​MHz to 154.88 MHz with increasing Fe4N content, demonstrating a significant increase in the material's cutoff frequency.

Claims

1. A method for preparing partially nitride metal soft magnets with improved cutoff operating frequency, characterized in that... The specific steps are as follows: (1) Material preparation: Select iron powder with a particle size of 1-10μm; (2) Nitriding: After evacuating the iron powder in a tube furnace, a mixture of NH3 and Ar is introduced. The molar ratio of NH3 to Ar is 1:9-3:

1. The temperature is raised to 360-475℃ at a rate of 10℃ / min and held for 0-6 h. The iron powder is then cooled to room temperature with the furnace to obtain partially nitrided iron powder. (3) Insulation coating: Dissolve epoxy resin in acetone, add iron nitride powder to the solution and stir, so that the acetone evaporates, epoxy resin precipitates and uniformly coats the surface of iron powder to form an insulating layer, wherein the volume fraction of epoxy resin is 5-25%; (4) Pressing: Press the magnetic ring into an inner diameter of 7 mm and an outer diameter of 13 mm under a pressure of 0.9-1.8 GPa.

2. The method for preparing partially nitride metal soft magnets with improved cutoff operating frequency according to claim 1, characterized in that: In step (2), the vacuum is drawn to make the initial vacuum level 0.08 MPa.

3. The method for preparing partially nitride metal soft magnets with improved cutoff operating frequency according to claim 2, characterized in that: In step (2), the flow rate of the mixed gas of NH3 and Ar introduced is 30-60 Sccm.

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