Carbonyl ferromagnetic powder core for short-wave frequency band narrow-band band-pass filter and preparation method of carbonyl ferromagnetic powder core

Abstract

The invention discloses a carbonyl ferromagnetic powder core for a short-wave frequency band narrow-band band-pass filter and a preparation method of the carbonyl ferromagnetic powder core, and belongs to the technical field of magnetic materials, the carbonyl ferromagnetic powder core is prepared from the following raw materials in percentage by weight: 90-95% of carbonyl iron powder, 1-2% of tetraethoxysilane and 3-9% of phenolic resin, and an auxiliary material mainly comprises a solvent. Comprising deionized water, ethyl alcohol and ammonia water, 100g of carbonyl iron powder corresponds to 40g of deionized water, 100g of ethyl alcohol and 4ml of ammonia water, and a solvent is weighed according to the amount of the carbonyl iron powder in an equal proportion; the carbonyl ferromagnetic powder core material prepared in a hydrolysis coating mode has the advantages of high frequency and high Q, the magnetic conductivity of the carbonyl ferromagnetic powder core material is 9 (1 + / -10%), and the Q value of 10 MHz is 300-320.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and particularly to a carbonyl iron magnetic powder core for a short-wave frequency band filter and a preparation method thereof. Background Art

[0002] Carbonyl iron magnetic powder core is a soft magnetic material prepared by powder metallurgy process. Its chemical formula is Fe, and the intermediate product in its preparation process is Fe(CO)5. Its unique magnetic properties make it have unique advantages and also become an important component of soft magnetic materials. Its characteristics are high Bs, not easy to saturate when used as a DC output rectifier filter choke under large current conditions, having good constant magnetic permeability characteristics, simple manufacturing process, no need for high-temperature sintering, precise dimensions, energy-saving and labor-saving. It is widely used in various components, such as filters, short-wave heterodyne devices, power synthesis modules, etc.

[0003] A narrow-band band-pass filter is an electronic filter that allows signals within a specific frequency range to pass through while blocking other frequency signals. The magnetic powder core is used as a resonator and resonant inductor in the band-pass filter. The performance such as the self-resonant frequency, inductance value, and power capacity of the inductor is restricted by the spectral characteristics, Q value, and Bs of the magnetic powder core. Among them, too low Q value of the magnetic powder core will lead to a large frequency interval of the filter, high insertion loss, serious equipment heating, and low emission efficiency; it will also lead to low isolation, easy mutual coupling of signals, and low system transmission efficiency. In order to match the working frequency band within 10 MHz of short-wave communication, it is urgent to improve the Q value of the carbonyl iron magnetic powder core at high frequencies and reduce the loss within the 10 MHz range, so as to improve the signal transmission efficiency. It should be noted that 10 MHz is the center frequency, the bandwidth of the narrow-band filter is generally 1%, and the application frequency band is 9.95 MHz to 10.05 MHz, and the technical index focus is on 10 MHz.

[0004] In order to solve the above problems, Chinese Patent Application CN118039278A respectively realizes the high-frequency, high saturation magnetic induction intensity, and low loss of the metal magnetic powder core through inorganic coating and organic coating methods. The obtained magnetic powder core has a magnetic permeability ≥ 20, a magnetic permeability change rate ≤ 5%, and a quality factor Q ≥ 50 in the frequency range of 50 K to 100 MHz. However, the Q value of the magnetic powder core of this patent is up to 150 at the short-wave frequency band of 10 - 15 MHz, which cannot meet the requirements of low insertion loss and high isolation of the filter.

[0005] Therefore, there is an urgent need for a carbonyl iron magnetic powder core applied to a short-wave narrow-band band-pass filter in the 10 MHz range, which is required to have the characteristic of low loss (i.e., high Q value). Summary of the Invention

[0006] One of the purposes of the present invention is to provide a preparation method of a carbonyl iron magnetic powder core for a short-wave frequency band filter to solve the above problems.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a method for preparing a high-quality factor carbonyl ferromagnetic powder core for shortwave frequency band filters, the preparation raw materials including carbonyl iron powder, tetraethyl orthosilicate and phenolic resin, wherein carbonyl iron powder: 90wt%~95wt%, tetraethyl orthosilicate: 1wt%~2wt%, resin: 3wt%~9wt%, totaling 100%; also including a solvent, and the carbonyl ferromagnetic powder core is prepared by hydrolysis coating.

[0008] As a preferred technical solution, the specific steps include: (1) Ingredients: weigh carbonyl iron powder, ethyl orthosilicate, phenolic resin and solvent according to the proportions, wherein the solvent includes deionized water, anhydrous ethanol and ammonia water; (2) Hydrolysis: first add anhydrous ethanol to the carbonyl iron powder weighed in step (1) and stir, then add deionized water and continue stirring, then add ammonia water and continue stirring, then add ethyl orthosilicate after stirring, continue stirring and then stop, let it stand to precipitate, pour off the supernatant, then wash the precipitate, and bake the precipitate finally obtained to obtain a powder; (3) Coating: mixing the powder obtained in step (2) with the phenolic resin weighed in step (1), stirring the mixture, and baking the mixture after stirring to obtain a powder; (4) Granulation: Grind the powder obtained in step (3) to obtain granules with a mesh size of 40-200; (5) forming, sieving the granular material obtained in step (4), adding a release agent, mixing evenly, and pressing into a solid ring-shaped green body; (6) The green body obtained in step (5) is placed in an oven for heat treatment to obtain the product.

[0009] As a further preferred technical solution, in step (2), the method for washing the precipitate is: using deionized water and anhydrous ethanol to rinse the precipitate in sequence, precipitate it, and pour off the supernatant.

[0010] As a further preferred technical solution, in step (2), the baking method is: baking in an oven at 60° C. for 4 hours.

[0011] As a further preferred technical solution, in step (3), the baking method is: baking in an oven at 60° C. for 1 hour.

[0012] As a preferred technical solution, in step (5), the release agent is selected from at least one of powder release agents such as zinc stearate and calcium stearate.

[0013] As a further preferred technical solution, in step (6), the heat treatment temperature is 140° C. and the insulation time is 2-4 hours.

[0014] The second object of the present invention is to provide a high-quality factor carbonyl iron magnetic powder core for a short-wave band filter prepared by the above method.

[0015] Compared with the prior art, for example, compared with CN118039278A: In the inorganic coating of Patent CN118039278A, only absolute ethanol is used as a solvent, while in the present application, absolute ethanol and deionized water are used as solvents, and different solvents will result in different coating effects; the order of adding tetraethyl orthosilicate and ammonia water in the inorganic coating process of Patent CN118039278A is opposite to that of the present patent, which will also affect the coating effect; the pH value needs to be tested during the inorganic coating process of this patent to determine the amount of ammonia water added; while in the present application, after a large number of experiments, it is determined that the addition amount of ammonia water in this ratio can make the hydrolysis coating more sufficient, and the pH value does not need to be tested during the inorganic coating process at a fixed ratio; after adding ammonia water in the inorganic coating of this patent, it needs to react for 3 to 6 hours, while in the present application, after adding tetraethyl orthosilicate in the last step, it only needs to be stirred and reacted for 1 hour, and the efficiency is significantly improved; the carbonyl iron magnetic powder core prepared in the present application is aimed at the specific requirements of a short-wave filter, with a magnetic permeability of 9×(1±10%), and the Q value at 10 MHz needs to meet the requirements of low insertion loss and high isolation of the filter. The Q value of this patent is up to 150 at the short-wave frequency band of 10 to 15 MHz, which cannot meet the requirements of low insertion loss and high isolation of the filter.

[0016] Compared with Patent CN118366776A, this patent uses a process of adding inorganic fillers and resin for ball milling for coating, while the present application uses a method of inorganic and organic double coating of silicon dioxide hydrolysis and adding resin. Moreover, this patent needs to carry out ball milling twice, while the present application can use a common grinding method, and the grinding method is relatively simple and convenient.

[0017] Compared with the prior art, the advantages of the present invention are as follows: (1) All raw materials of the present invention are general materials that can be purchased on the market. The silicon dioxide inorganic coating layer is prepared by a hydrolysis method. Among them, ethanol is used as a solvent and can be recycled and reused. The cost is low, the raw materials are independently controllable, the risk is low, and the hydrolysis coating method is simple and easy to operate. This coating method can effectively reduce material loss; (2) The initial magnetic permeability of the carbonyl iron magnetic powder core prepared in the present invention is: 9(1±10%), and the Q value at 10 MHz is 300 to 320; the Q value of the carbonyl iron magnetic powder core at 10 MHz is improved, and the power conversion efficiency of the material at 10 MHz is enhanced; (3) The hydrolysis coating method proposed by the present invention can also be used in the preparation of coatings for other magnetic powder cores that require high-temperature heat treatment except for carbonyl iron magnetic powder cores. The inorganic silica layer formed by hydrolysis has the characteristic of high temperature resistance and can replace the commonly used phosphating method (see Comparative Example 2) to ensure that the inorganic coating layer is not damaged at high temperatures and optimize the loss performance of the magnetic powder core. It can be applied in the preparation of iron-silicon-aluminum, iron-silicon, and iron-nickel-molybdenum magnetic powder cores. Description of the Drawings

[0018] Figure 1 It is the Q-value test curves of each embodiment and some comparative examples of the present invention. Specific Embodiments

[0019] The present invention will be further described below in conjunction with embodiments.

[0020] Embodiment 1 A method for preparing a high-quality factor carbonyl iron magnetic powder core for a short-wave frequency band filter, comprising the following steps: (1) Weigh the raw materials: carbonyl iron powder: 90 g, tetraethyl orthosilicate: 1 g; phenolic resin (Sichuan Dongcai Science & Technology Group Co., Ltd., grade: D120): 9 g; deionized water (for stirring): 36 g; absolute ethanol (for stirring): 90 g; deionized water (for cleaning): 100 g; absolute ethanol (for cleaning): 100 g; ammonia water: 3.6 g; (2) Stir the carbonyl iron powder and absolute ethanol (90 g) weighed in step (1) with an electronic stirrer. After stirring for 20 minutes, add deionized water (36 g) and continue stirring. After 10 minutes, add ammonia water and continue stirring. After stirring for 10 minutes, add tetraethyl orthosilicate and continue stirring. Stop stirring after 1 hour, let it stand for precipitation, pour off the supernatant, and wash the precipitate with deionized water (100 g) and absolute ethanol (100 g) in turn, precipitate, and pour off the supernatant. Put the finally obtained precipitate into an oven and bake at 60 °C for 4 hours to obtain a powder; (3) Coating: Stir the powder obtained in step (2) and the phenolic resin weighed in step (1) with an electronic stirrer for 30 minutes, and then put it into an oven and bake at 60 °C for 1 hour to obtain a powder material; (4) Granulation, grind the powder material obtained in step (3) and take the granular material between 40 - 200 meshes; (5) Molding, sieve the granular material obtained in step (4), add 0.2 g of zinc stearate, mix evenly, and press it into a solid ring-shaped green body; (6) Heat-treat the green body obtained in step (5) in a constant-temperature oven, the heat-treatment temperature is 140 °C, and the holding time is 2 hours; Obtain a ring-shaped magnetic powder core sample and use a Keysight 4991B precision impedance analyzer to measure the inductance (L) and the Q value at 10 MHz. The results are shown inFigure 1 ; and calculate the magnetic permeability of the magnetic powder core according to L, and the results are shown in Table 1.

[0021] Table 1 Performance test data of the sample rings prepared in Example 1 Symbol Unit or test condition Example 1 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.2 Q value Q 10MHz, 100mv 310

[0022] Example 2 A preparation method of a high-quality factor carbonyl iron magnetic powder core for a short-wave frequency band filter, comprising the following steps: (1) Weigh the raw materials: 92 g of carbonyl iron powder, 1.5 g of tetraethyl orthosilicate, 6.5 g of phenolic resin, 36.8 g of deionized water (for stirring), 92 g of absolute ethanol (for stirring), 100 g of deionized water (for cleaning), 100 g of absolute ethanol (for cleaning), and 4 ml of ammonia water; (2) Stir the carbonyl iron powder and absolute ethanol (92 g) weighed in step (1) with an electronic stirrer. After stirring for 20 minutes, add deionized water (36.8 g) and continue stirring. After 10 minutes, add ammonia water and continue stirring. After stirring for 10 minutes, add tetraethyl orthosilicate and continue stirring. Stop stirring after 1 hour, let it stand for precipitation, pour off the supernatant, and wash the precipitate with deionized water (100 g) and absolute ethanol (100 g) in turn, precipitate, and pour off the supernatant. Put the finally obtained precipitate into an oven and bake at 60 °C for 4 hours to obtain powder; (3) Coating: Stir the powder obtained in step (2) and the phenolic resin weighed in step (1) with an electronic stirrer for 30 minutes, and then put it into an oven and bake at 60 °C for 1 hour to obtain powder material; (4) Granulation, grind the powder material obtained in step (3) and take the granular material between 40 - 200 meshes; (5) Molding, sieve the granular material obtained in step (4), add 0.2 g of zinc stearate, mix evenly, and press it into a solid ring-shaped green body; (6) Heat-treat the green body in step (5) in a constant-temperature oven, the heat-treatment temperature is 140 °C, and the holding time is 3 hours; The obtained ring-shaped magnetic powder core sample is used to test the inductance (L) and the 10 MHz Q value with a Keysight 4991B precision impedance analyzer, and the results are shown in Figure 1 ; and calculate the magnetic permeability of the magnetic powder core according to L, and the results are shown in Table 2.

[0023] Table 2 Test data of the sample rings prepared in Example 2 Symbol Unit or test condition Example 2 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.0 Q value Q 10MHz, 100mv 312

[0024] Example 3 A preparation method of a high-quality factor carbonyl iron magnetic powder core for a short-wave frequency band filter, comprising the following steps: (1) Weigh the raw materials: 95 g of carbonyl iron powder, 2 g of tetraethyl orthosilicate, 3 g of phenolic resin, 38 g of deionized water (for stirring), 95 g of absolute ethanol (for stirring), 100 g of deionized water (for cleaning), 100 g of absolute ethanol (for cleaning), and 4 ml of ammonia water; (2) Stir the carbonyl iron powder and absolute ethanol (95 g) weighed in step (1) with an electronic stirrer. After stirring for 20 minutes, add 38 g of deionized water and continue stirring. After 10 minutes, add ammonia water and continue stirring. After stirring for 10 minutes, add tetraethyl orthosilicate and continue stirring. Stop stirring after 1 hour, let it stand for precipitation, pour off the supernatant, wash the precipitate with 100 g of deionized water and 100 g of absolute ethanol in sequence, precipitate, and pour off the supernatant. Put the finally obtained precipitate into an oven and bake at 60 °C for 4 hours to obtain powder; (3) Coating: Stir the powder obtained in step (2) and the phenolic resin weighed in step (1) with an electronic stirrer for 30 minutes. After stirring is completed, put it into an oven and bake at 60 °C for 1 hour to obtain powder material; (4) Granulation: Grind the powder material obtained in step (3) and take the granular material between 40 - 200 mesh; (5) Molding: Screen the granular material obtained in step (4), add 0.2 g of zinc stearate, mix evenly, and press it into a solid ring-shaped green compact; (6) Heat-treat the green compact in step (5) in a constant-temperature oven. The heat-treatment temperature is 140 °C and the holding time is 4 hours; Obtain the ring-shaped magnetic powder core sample and test the inductance (L) and 10 MHz Q value using a Keysight 4991B precision impedance analyzer. The results are shown in Figure 1 ; and calculate the magnetic permeability of the magnetic powder core according to L. The results are shown in Table 3.

[0025] Table 3 Test data of the sample ring prepared in Example 3 Symbol Unit or test condition Example 3 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.0 Q value Q 10MHz, 100mv 316

[0026] Comparative Example 1 A preparation method of carbonyl iron magnetic powder core, the specific steps are as follows: Weigh 100 g of carbonyl iron powder, 3 g of phenolic resin (Sichuan Dongcai Science & Technology Group Co., Ltd., grade: D120), 40 g of absolute ethanol, and 5 g of phosphoric acid. Mix absolute ethanol and phosphoric acid, stir with an electronic stirrer for 10 minutes, then add carbonyl iron powder and phenolic resin and stir for 30 minutes; then through drying, grinding and screening, take the granular material between 40 mesh and 100 mesh, add 0.2 g of zinc stearate, mix evenly, press it into a solid ring-shaped green compact, and heat-treat it at 140 °C in a constant-temperature oven for 4 h.

[0027] That is, compared with Example 1, in this comparative example, phosphoric acid is used for surface treatment of carbonyl iron powder, and silica coating is not adopted.

[0028] The obtained toroidal magnetic powder core samples are used to test the inductance (L) and 10 MHz Q value by using a Keysight 4991B precision impedance analyzer. The results are shown in Figure 1 ; and the magnetic permeability of the magnetic powder core is calculated according to L. The results are shown in Table 4.

[0029] Table 4 Test data of the sample rings prepared in Comparative Example 1 Symbol Unit or test condition Comparative Example 1 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.1 Q value Q 10MHz, 100mv 250

[0030] Comparative Example 2 A method for preparing a high-quality factor carbonyl iron magnetic powder core, the specific steps are as follows: Weigh 95 g of carbonyl iron powder, 3 g of phenolic resin (Sichuan Dongcai Science & Technology Group Co., Ltd., grade: D120), 95 g of absolute ethanol (for stirring), 100 g of deionized water (for cleaning), 100 g of absolute ethanol (for cleaning). Mix the absolute ethanol and carbonyl iron powder, and stir with an electronic stirrer for 10 minutes, then add ammonia water and stir for 10 minutes, and then add tetraethyl orthosilicate and stir for 1 hour. After stirring, let it stand for precipitation and pour off the supernatant. Use deionized water (100 g) and absolute ethanol (100 g) to wash, precipitate, and pour off the supernatant of the precipitate in turn. Put the finally obtained precipitate into an oven and bake at 60 °C for 4 hours to obtain a powder; stir the dried powder and phenolic resin with an electronic stirrer for 30 minutes, put it into an oven and bake at 60 °C for 1 hour after stirring, grind and sieve, take the granular material between 40 mesh and 100 mesh, add 0.2 g of zinc stearate, mix evenly, press it into a solid toroidal green body, and heat-treat it at 140 °C in a constant-temperature oven for 4 h.

[0031] That is, compared with Example 3, in this comparative example, a hydrolysis process without adding deionized water is used for silica inorganic coating of carbonyl iron powder.

[0032] The obtained toroidal magnetic powder core samples are used to test the inductance (L) and 10 MHz Q value by using a Keysight 4991B precision impedance analyzer. The results are shown in Figure 1 ; and the magnetic permeability of the magnetic powder core is calculated according to L. The results are shown in Table 5.

[0033] Table 5 Test data of the sample rings prepared in Comparative Example 2 Symbol Unit or test condition Example 1 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.0 Q value Q 10MHz, 100mv 260

[0034] Comparative Example 3 A method for preparing a high-quality factor carbonyl iron magnetic powder core, the specific steps are as follows: Weigh 95 g of carbonyl iron powder, 3 g of phenolic resin (Sichuan Dongcai Science & Technology Group Co., Ltd., grade: D120), 95 g of absolute ethanol (for stirring), 100 g of deionized water (for cleaning), and 100 g of absolute ethanol (for cleaning). Mix the absolute ethanol and carbonyl iron powder, and stir with an electronic stirrer for 10 minutes. Then add tetraethyl orthosilicate and stir for 1 hour. Subsequently, add ammonia water and stir for 10 minutes. After stirring, let it stand for precipitation and pour off the supernatant. Use deionized water (100 g) and absolute ethanol (100 g) to wash the precipitate in turn, followed by precipitation and pouring off the supernatant. Put the finally obtained precipitate into an oven and bake at 60 °C for 4 hours to obtain powder. Stir the dried powder and phenolic resin with an electronic stirrer for 30 minutes. After stirring, put it into an oven and bake at 60 °C for 1 hour. Grind and sieve, take the granular material between 40 mesh and 100 mesh, add 0.2 g of zinc stearate, mix evenly, press it into a solid ring-shaped green body, and heat-treat it at 140 °C in a constant-temperature oven for 4 hours with a holding time of 4 h.

[0035] That is, compared with Example 3, in this comparative example, the addition order of ammonia water and tetraethyl orthosilicate was swapped.

[0036] The obtained toroidal magnetic powder core sample was used to test the inductance (L) and 10 MHz Q value with a Keysight 4991B precision impedance analyzer. The results are shown in Figure 1 ; and calculate the magnetic permeability of the magnetic powder core according to L. The results are shown in Table 5.

[0037] Table 6 Test data of the sample ring prepared in Comparative Example 3 Symbol Unit or test condition Example 1 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.2 Q value Q 10MHz, 100mv 248

[0038] Comparative Example 4 A method for preparing a high-quality factor carbonyl iron magnetic powder core, the specific steps are as follows: Weigh 95 g of carbonyl iron powder, 3 g of phenolic resin (Sichuan Dongcai Science & Technology Group Co., Ltd., grade: D120), 45 g of absolute ethanol, and nano-silica powder (Shanghai Macklin Reagent). Add the carbonyl iron powder, nano-silica powder, absolute ethanol, and phenolic resin into a ball mill tank together, set the rotation speed to 50 rpm, and the coating time to 1 h. After stirring, put it into an oven and bake at 60 °C for 1 hour. Grind and sieve, take the granular material between 40 mesh and 100 mesh, add 0.2 g of zinc stearate, mix evenly, press it into a solid ring-shaped green body, and heat-treat it at 140 °C in a constant-temperature oven for 4 hours with a holding time of 4 h.

[0039] That is, compared with Example 3, in this comparative example, a process of adding inorganic fillers and resin for ball milling was used for coating.

[0040] The toroidal magnetic powder core samples were used to measure the inductance (L) and the Q value at 10 MHz with a Keysight 4991B Precision Impedance Analyzer. The results are shown in Figure 1 ; and the magnetic permeability of the magnetic powder core was calculated based on L. The results are shown in Table 5.

[0041] Table 7 Test data of the sample ring prepared in Comparative Example 4 Symbol Unit or test condition Example 1 Initial permeability <![CDATA[μ i > 10kHz, 100mv 9.1 Q value Q 10MHz, 100mv 226

[0042] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbonyl ferromagnetic powder core for a short-wave frequency band narrow-band bandpass filter, characterized in that: The preparation raw materials include carbonyl iron powder, tetraethyl orthosilicate and phenolic resin, wherein the carbonyl iron powder: 90wt%~95wt%, tetraethyl orthosilicate: 1wt%~2wt%, resin: 3wt%~9wt%, totaling 100%; and also include solvent, and the carbonyl ferromagnetic powder core is prepared by hydrolysis coating.

2. The method according to claim 1, characterized in that: The specific steps include: (1) Ingredients: weigh carbonyl iron powder, ethyl orthosilicate, phenolic resin and solvent according to the proportions, wherein the solvent includes deionized water, anhydrous ethanol and ammonia water; (2) Hydrolysis: first add anhydrous ethanol to the carbonyl iron powder weighed in step (1) and stir, then add deionized water and continue stirring, then add ammonia water and continue stirring, then add ethyl orthosilicate after stirring, continue stirring and then stop, let it stand to precipitate, pour off the supernatant, then wash the precipitate, and bake the precipitate finally obtained to obtain a powder; (3) Coating: mixing the powder obtained in step (2) with the phenolic resin weighed in step (1), stirring the mixture, and baking the mixture after stirring to obtain a powder; (4) Granulation: Grind the powder obtained in step (3) to obtain granules with a mesh size of 40-200; (5) forming, sieving the granular material obtained in step (4), adding a release agent, mixing evenly, and pressing into a solid ring-shaped green body; (6) The green body obtained in step (5) is placed in an oven for heat treatment to obtain the product.

3. The method according to claim 2, characterized in that In step (2), the method for washing the precipitate is: using deionized water and anhydrous ethanol to rinse the precipitate in sequence, precipitate it, and pour off the supernatant.

4. The method according to claim 3, characterized in that In step (2), the baking method is: baking in an oven at 60° C. for 4 hours.

5. The method according to claim 2, characterized in that: In step (3), the baking method is: baking in an oven at 60° C. for 1 hour.

6. The method according to claim 2, characterized in that In step (5), the release agent is selected from at least one of zinc stearate and calcium stearate.

7. The method according to claim 2, characterized in that In step (6), the heat treatment temperature is 140° C. and the insulation time is 2-4 hours.

8. Carbonyl ferromagnetic powder core for shortwave frequency band filter prepared by the method of any one of claims 1 to 7.

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