Carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder and preparation method thereof

Abstract

The invention discloses a preparation method of carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder, which comprises the following specific steps: weighing ferrite synthetic components, spherical carbonyl iron powder and tetraethoxysilane according to a ratio, the ferrite synthetic components comprise 52-56 mol% of Fe2O3 and the balance of CoO, and the spherical carbonyl iron powder and the tetraethoxysilane are mixed according to a certain ratio to prepare the carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder, and the spherical carbonyl iron powder and the tetraethoxysilane are mixed according to a certain ratio to prepare the carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder. The carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder is finally obtained through the steps of ball milling, stirring, drying, primary sintering, mixing, secondary sintering and the like. The method for preparing the carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder is simple and convenient in process, safe and low in cost, and after the carbonyl iron powder, cobalt ferrite and silicon dioxide wave-absorbing powder is used for preparing wave-absorbing products, the excellent performance of broadband strong absorption is shown in the frequency band of 2-18 GHz.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing powder preparation technology, specifically relating to a carbonyl iron powder@cobalt ferrite@silicon dioxide microwave absorbing powder and its preparation method. Background Technology

[0002] Carbonyl iron powder, as a common magnetic absorbing material, possesses high permeability and saturation magnetization, exhibiting excellent absorption potential. However, its inherent drawbacks, such as high density and poor oxidation resistance, limit its application in lightweight, long-life devices. Cobalt ferrite exhibits low magnetic loss and excellent magnetic stability at high frequencies, effectively compensating for the shortcomings of carbonyl iron powder in high-frequency absorption performance. However, its permeability at high frequencies is not high, resulting in limited absorption peak when used alone. Coating the surface of carbonyl iron powder with a layer of cobalt ferrite is an effective solution that combines the advantages of both cobalt ferrite and carbonyl iron powder. Furthermore, coating the powder surface with a layer of silica further increases reflection between the internal interfaces of the powder, effectively enhancing its absorption performance.

[0003] In existing technologies, the microwave absorption performance of magnetic powders is often improved by constructing a core-shell structure on the surface of the powder. For example, Chinese patent CN 114749662A discloses a sheet-like alloy powder / manganese-zinc ferrite / silicon dioxide microwave absorbing powder and its preparation method. By sequentially coating manganese-zinc ferrite and silicon dioxide on the surface of sheet-like iron-silicon-aluminum powder, a double-layer coating structure is formed, resulting in a core / shell / shell structure sheet-like alloy powder / manganese-zinc ferrite / silicon dioxide microwave absorbing powder. This increases the multiple reflection loss of absorbed waves, improves the absorption intensity and absorption bandwidth in the low-frequency band, and enhances the microwave absorption performance of the powder. However, the high permeability and high conductivity of the sheet-like alloy will result in severe impedance mismatch and skin effect during high-frequency absorption, causing most electromagnetic waves to be reflected and difficult to be absorbed by the material. At the same time, the poor magnetic stability of manganese and zinc makes it unsuitable for high-frequency applications. Therefore, sheet-like alloy powder / manganese-zinc ferrite / silicon dioxide is only suitable for low-frequency narrow bandwidth absorption (<5GHz) in high-frequency applications. Summary of the Invention

[0004] The main technical problem addressed by this invention is to overcome the shortcomings of existing microwave absorbing materials, such as insufficient high-frequency and broadband absorption performance, poor structural stability, and complex manufacturing processes. This invention provides a method for preparing carbonyl iron powder@cobalt ferrite@silicon dioxide microwave absorbing powder. This method involves ball milling and segmented sintering processes to sequentially coat the surface of spherical carbonyl iron powder with cobalt ferrite and silicon dioxide, constructing a core-shell structure with a significant impedance gradient. This significantly enhances the material's broadband and strong absorption performance in the 2–18 GHz frequency band while improving its oxidation resistance and reducing its density.

[0005] A method for preparing carbonyl iron powder@cobalt ferrite@silicon dioxide microwave absorbing powder includes the following steps: (1) Weighing: Weigh the ferrite synthesis component, spherical carbonyl iron powder and tetraethyl orthosilicate according to the formula, wherein the ferrite synthesis component is composed of Fe2O3 and CoO, the content of Fe2O3 is 52-56 mol%, and the remainder is CoO; (2) Ball milling: Add water accounting for 50% of the total weight of the material to the ferrite synthesis components weighed in step (1), stir to form a mixture, and ball mill in a high-speed planetary ball mill to obtain a slurry; (3) Stirring: Add the spherical carbonyl iron powder weighed in step (1) to the slurry after ball milling in step (2) and stir to form a mixture; (4) Drying: The mixed slurry obtained by stirring in step (3) is placed in a vacuum drying oven for vacuum drying; (5) First sintering: The powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder@cobalt ferrite; (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite obtained in step (5) are put into a high-speed planetary ball mill and mixed evenly. (7) Secondary sintering: The powder mixed in step (6) is placed in an atmosphere furnace for secondary sintering to obtain carbonyl iron powder@cobalt ferrite@silicon dioxide powder.

[0006] In step (1), the mass ratio of the ferrite synthesis component, spherical carbonyl iron powder and tetraethyl orthosilicate is 1.5-2.5:10:0.05-0.25.

[0007] In step (1), the D50 of the spherical carbonyl iron powder is 3-5 μm.

[0008] In step (2), the high-speed planetary ball mill has a ball milling speed of 500-600 r / min and a ball milling time of 120-150 min.

[0009] In step (4), the temperature of the vacuum drying oven is 80-120℃, the time is 300-360min, and the entire process is kept under vacuum.

[0010] In step (5), the first sintering process is as follows: under a nitrogen atmosphere, the temperature is raised from room temperature to 1200-1300℃ at a rate of 4-5℃ / min, held at a constant temperature for 3 hours, and then cooled from 1200-1300℃ to room temperature at a rate of 4-5℃ / min.

[0011] In step (6), the ball milling speed of the high-speed planetary ball mill is 300-400 r / min, and the ball milling time is 5-10 min.

[0012] In step (7), the secondary sintering process is as follows: under a nitrogen atmosphere, the temperature is raised from room temperature to 800-900℃ at a rate of 4-5℃ / min, held at a constant temperature for 2 hours, and then cooled from 800-900℃ to room temperature at a rate of 4-5℃ / min.

[0013] The technical advantages of this invention are as follows: (1) This invention uses high-energy ball milling combined with segmented sintering process to prepare core-shell structured powder. The process mainly involves physical mixing and heat treatment. It is simple and safe to operate, with few by-products. It avoids the use of high-risk chemicals and complex cleaning, filtration and liquid-phase reaction steps. It has low equipment requirements and is easy to scale up production. (2) This invention constructs a core-shell-shell composite structure by sequentially coating the surface of carbonyl iron powder with cobalt ferrite and silicon dioxide. This structure not only effectively improves the antioxidant properties of carbonyl iron powder and reduces the overall specific gravity of the powder, but also introduces multiple interfaces that cause impedance changes, increasing the interface reflection inside the powder particles, thereby significantly improving the absorption capacity of electromagnetic waves. (3) The absorbing powder prepared by the present invention can achieve strong absorption of radar waves in the 2-18GHz frequency band with low thickness, exhibiting excellent characteristics of 'thin, strong and light', which is in line with the development policy of absorbing materials. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1 (1) Weighing: Weigh 71.34g Fe2O3, 28.66g CoO, 500g 5μm spherical carbonyl iron powder, and 12g tetraethyl orthosilicate according to the formula; (2) Ball milling: The ferrite synthesis components in step (1) are transferred to a planetary ball mill and water (mass ratio 2:1) are ball milled to obtain a slurry. The ball milling process is as follows: grinding speed 600 r / min, grinding time 120 min. (3) Mixing: The slurry obtained in step (1) is mixed and stirred with the 5μm spherical carbonyl iron powder weighed in step (1) to form a mixture; (4) Drying: The mixed slurry obtained in step (3) is placed in a vacuum drying oven for drying. The drying conditions are: 100°C for 300 min, with vacuum maintained throughout. (5) First sintering: The dry powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder / cobalt ferrite powder. The sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 1250℃ for 3h, and then cooled from 1250℃ to room temperature at a rate of 5℃ / min, and then the power is turned off. (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite prepared in step (5) are put into a high-speed planetary ball mill and mixed evenly. The ball milling process is as follows: grinding speed 300r / min, grinding time 5min. (7) Secondary sintering: The powder obtained in step (6) is placed in an atmosphere furnace for sintering; carbonyl iron powder@cobalt ferrite@silicon dioxide powder is obtained; the sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 800℃ for 2h, and then cooled from 800℃ to room temperature at a rate of 5℃ / min, and then the power is turned off.

[0016] Example 2 (1) Weighing: Weigh 73.06g Fe2O3, 26.94g CoO, 500g 5μm spherical carbonyl iron powder, and 12g tetraethyl orthosilicate according to the formula; (2) Ball milling: The ferrite synthesis components in step (1) are transferred to a planetary ball mill and water (mass ratio 2:1) are ball milled to obtain a slurry. The ball milling process is as follows: grinding speed 500 r / min, grinding time 150 min. (3) Mixing: The slurry obtained in step (1) is mixed and stirred with the 5μm spherical carbonyl iron powder weighed in step (1) to form a mixture; (4) Drying: The mixed slurry obtained in step (3) is placed in a vacuum drying oven for drying. The drying conditions are: 100°C for 300 min, with vacuum maintained throughout. (5) First sintering: The dry powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder / cobalt ferrite powder. The sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 1250℃ for 3h, and then cooled from 1250℃ to room temperature at a rate of 5℃ / min, and then the power is turned off. (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite prepared in step (5) are put into a high-speed planetary ball mill and mixed evenly. The ball milling process is as follows: grinding speed 300r / min, grinding time 5min. (7) Secondary sintering: The powder obtained in step (6) is placed in an atmosphere furnace for sintering; carbonyl iron powder@cobalt ferrite@silicon dioxide powder is obtained; the sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 800℃ for 2h, and then cooled from 800℃ to room temperature at a rate of 5℃ / min, and then the power is turned off.

[0017] Example 3 (1) Weighing: Weigh 69.78g Fe2O3, 31.22g CoO, 500g 5μm spherical carbonyl iron powder, and 12g tetraethyl orthosilicate according to the formula; (2) Ball milling: The ferrite synthesis components in step (1) are transferred to a planetary ball mill and water (mass ratio 2:1) are ball milled to obtain a slurry. The ball milling process is as follows: grinding speed 600 r / min, grinding time 120 min. (3) Mixing: The slurry obtained in step (1) is mixed and stirred with the 5μm spherical carbonyl iron powder weighed in step (1) to form a mixture; (4) Drying: The mixed slurry obtained in step (3) is placed in a vacuum drying oven for drying. The drying conditions are: 120°C for 300 min, with vacuum maintained throughout. (5) First sintering: The dry powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder / cobalt ferrite powder. The sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 4℃ / min, calcined at 1200℃ for 3h, and then cooled from 1200℃ to room temperature at a rate of 4℃ / min, and then the power is turned off. (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite prepared in step (5) are put into a high-speed planetary ball mill and mixed evenly. The ball milling process is as follows: grinding speed 300r / min, grinding time 5min. (2)(7) Secondary sintering: The powder obtained in step (6) is placed in an atmosphere furnace for sintering; carbonyl iron powder@cobalt ferrite@silicon dioxide powder is obtained; the sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 800℃ for 2h, and then cooled from 800℃ to room temperature at a rate of 5℃ / min, and then the power is turned off.

[0018] Example 4 (1) Weighing: Weigh 69.78g Fe2O3, 31.22g CoO, 400g 5μm spherical carbonyl iron powder, and 10g tetraethyl orthosilicate according to the formula; (2) Ball milling: The ferrite synthesis components in step (1) are transferred to a planetary ball mill and water (mass ratio 2:1) are ball milled to obtain a slurry. The ball milling process is as follows: grinding speed 600 r / min, grinding time 120 min. (3) Mixing: The slurry obtained in step (1) is mixed and stirred with the 5μm spherical carbonyl iron powder weighed in step (1) to form a mixture; (4) Drying: The mixed slurry obtained in step (3) is placed in a vacuum drying oven for drying. The drying conditions are: 100°C for 300 min, with vacuum maintained throughout. (5) First sintering: The dry powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder / cobalt ferrite powder. The sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 1250℃ for 3h, and then cooled from 1250℃ to room temperature at a rate of 5℃ / min, and then the power is turned off. (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite prepared in step (5) are put into a high-speed planetary ball mill and mixed evenly. The ball milling process is as follows: grinding speed 400r / min, grinding time 10min. (7) Secondary sintering: The powder obtained in step (6) is placed in an atmosphere furnace for sintering; carbonyl iron powder@cobalt ferrite@silicon dioxide powder is obtained; the sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 800℃ for 2h, and then cooled from 800℃ to room temperature at a rate of 5℃ / min, and then the power is turned off.

[0019] Example 5 (1) Weighing: Weigh 69.78g Fe2O3, 31.22g CoO, 666.67g 5μm spherical carbonyl iron powder, and 15.34g tetraethyl orthosilicate according to the formula; (2) Ball milling: The ferrite synthesis components in step (1) are transferred to a planetary ball mill and water (mass ratio 2:1) are ball milled to obtain a slurry. The ball milling process is as follows: grinding speed 600 r / min, grinding time 120 min. (3) Mixing: The slurry obtained in step (1) is mixed and stirred with the 5μm spherical carbonyl iron powder weighed in step (1) to form a mixture; (4) Drying: The mixed slurry obtained in step (3) is placed in a vacuum drying oven for drying. The drying conditions are: 100°C for 300 min, with vacuum maintained throughout. (5) First sintering: The dry powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder / cobalt ferrite powder. The sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 1250℃ for 3h, and then cooled from 1250℃ to room temperature at a rate of 5℃ / min, and then the power is turned off. (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite prepared in step (5) are put into a high-speed planetary ball mill and mixed evenly. The ball milling process is as follows: grinding speed 300r / min, grinding time 5min. (7) Secondary sintering: The powder obtained in step (6) is placed in an atmosphere furnace for sintering; carbonyl iron powder@cobalt ferrite@silicon dioxide powder is obtained; the sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 900℃ for 2h, and then cooled from 900℃ to room temperature at a rate of 5℃ / min, and then the power is turned off.

[0020] Example 6 (1) Weighing: Weigh 69.78g Fe2O3, 31.22g CoO, 500g 5μm spherical carbonyl iron powder, and 2.5g tetraethyl orthosilicate according to the formula; (2) The remaining steps are the same as in Example 1.

[0021] Example 7 (1) Weighing: Weigh 69.78g Fe2O3, 31.22g CoO, 500g 5μm spherical carbonyl iron powder, and 12.5g tetraethyl orthosilicate according to the formula; (2) The remaining steps are the same as in Example 1.

[0022] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that 5μm spherical carbonyl iron powder is not added, and tetraethyl orthosilicate is 2g. Other steps and dosages are the same as in Example 1.

[0023] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that tetraethyl orthosilicate is not added, and steps (6) and (7) are not included.

[0024] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that tetraethyl orthosilicate, 5μm spherical carbonyl iron powder are not added, and steps (3), (6), and (7) are not included.

[0025] Comparative Example 4 (1) Weighing: Weigh 71.34g Fe2O3, 28.66g CoO, 500g 5μm spherical carbonyl iron powder, and 12g tetraethyl orthosilicate according to the formula; (2) Ball milling: The ferrite synthesis components in step (1) are transferred to a planetary ball mill and water (mass ratio 2:1) are ball milled to obtain a slurry. The ball milling process is as follows: grinding speed 600 r / min, grinding time 120 min. (3) Drying: The mixed slurry obtained in step (2) is placed in a vacuum drying oven for drying. The drying conditions are: 100°C for 300 min, with vacuum maintained throughout. (4) Sintering: The second dried powder obtained in step (3) is placed in an atmosphere furnace for sintering to obtain cobalt ferrite powder. The sintering conditions are set as follows: under nitrogen atmosphere, the heating rate is 5℃ / min, calcined at 1250℃ for 3h, and then cooled from 1250℃ to room temperature at a rate of 5℃ / min, and then the power is turned off. (5) Mixing: The tetraethyl orthosilicate, 5μm spherical carbonyl iron powder and the cobalt ferrite prepared in step (4) are weighed in step (1) and mixed evenly in a high-speed planetary ball mill. The ball milling process is a grinding speed of 300r / min and a grinding time of 5min.

[0026] Comparative Example 5 Comparative Example 5 replaces the ferrite components in Example 1 with Fe2O3, MnCO3, and ZnO. The difference lies in step (1), while the other steps and amounts are the same as in Example 1. Step (1) specifically involves weighing: 63.33g of ferrite synthesis components, 32.67g of MnCO3, 4g of ZnO; 500g of 5μm spherical carbonyl iron powder; and 12g of tetraethyl orthosilicate.

[0027] Performance testing and testing methods Preparation of microwave absorbing product sample: 32g of powder and 8g of paraffin were placed in a beaker, initially dispersed, and then placed in an oven at 80℃. After keeping it warm for 30 minutes, the mixture was stirred evenly with a glass rod and then placed in a mold to make a sample with an inner diameter of 3.04mm, an outer diameter of 7.00mm, and a thickness of 3mm. Microwave absorption performance testing: The microwave absorption performance of the microwave absorbing product sample was tested using the coaxial method of a vector network analyzer. The equipment used was model N5222B. Its dielectric constant and permeability were measured to calculate its reflection loss (RL). The formula is as follows: z in =z c tanλ(γd)

[0028] The microwave absorbing powders obtained in the examples and comparative examples were used to prepare microwave absorbing product samples according to the above method, and the microwave absorption performance was tested. The data when the matching thickness was 1.5 mm are shown in Table 1:

[0029] As shown in Table 1, when the simulated absorbing coating thickness is 1.5 mm, the carbonyl iron powder@cobalt ferrite@silica core-shell structure absorbing powders prepared in the specific embodiments 1-7 of the present invention all exhibit better absorbing performance than the comparative examples. In the 10-16 GHz frequency band, Examples 1-7 all show strong absorption peaks (>32 dB), and their effective absorption bandwidth (absorption bandwidth less than -10 dB) can reach about 6 GHz. (1) The comparative examples 1 and 3 with cobalt ferrite@silica single-layer coating have smaller reflectivity peaks of about -16 to -19 dB and narrower bandwidth of only about 2 GHz. The single cobalt ferrite magnetic component on the surface cannot achieve broadband strong absorption. (2) Comparative Example 2, which is carbonyl iron powder@cobalt ferrite monolayer coating, has a bandwidth of about 5.5 GHz, but the peak reflectivity is relatively small, about -20 dB. The introduction of the surface silica layer is crucial for further improving the absorption intensity and optimizing impedance matching. (3) Although the peak reflectance and bandwidth of the mechanically mixed powder in Comparative Example 4 are better than those in Comparative Examples 1-3, the overall performance is still not as good as that of the present invention. The simple physical mixing on the surface cannot form an effective core-shell interface. (4) The overall absorption performance of the carbonyl iron powder@manganese zinc ferrite@silica double-layer coating of Comparative Example 5 is poor (lower peak reflectivity, narrow bandwidth, only about 3GHz), and its absorption performance is generally biased towards low frequency. The absorption performance of the present invention is concentrated above 10GHz, which shows the magnetic stability advantage of cobalt ferrite at high frequency. This reflects the correctness of the material system selection of the present invention, and it is not a simple choice to replace manganese zinc ferrite with cobalt ferrite.

Claims

1. A method for preparing carbonyl iron powder@cobalt ferrite@silicon dioxide microwave absorbing powder, characterized in that, Includes the following steps: (1) Weighing: Weigh the ferrite synthesis component, spherical carbonyl iron powder and tetraethyl orthosilicate according to the formula, wherein the ferrite synthesis component is composed of Fe2O3 and CoO, the content of Fe2O3 is 52-56 mol%, and the remainder is CoO; (2) Ball milling: Add water accounting for 50% of the total weight of the material to the ferrite synthesis components weighed in step (1), stir to form a mixture, and ball mill in a high-speed planetary ball mill to obtain a slurry; (3) Stirring: Add the spherical carbonyl iron powder weighed in step (1) to the slurry after ball milling in step (2) and stir to form a mixture; (4) Drying: The mixed slurry obtained in step (3) is placed in a vacuum drying oven for vacuum drying; (5) First sintering: The powder obtained in step (4) is placed in an atmosphere furnace for sintering to obtain carbonyl iron powder@cobalt ferrite; (6) Mixing: The tetraethyl orthosilicate weighed in step (1) and the carbonyl iron powder@cobalt ferrite obtained in step (5) are put into a high-speed planetary ball mill and mixed evenly. (7) Secondary sintering: The powder mixed in step (6) is placed in an atmosphere furnace for secondary sintering to obtain carbonyl iron powder@cobalt ferrite@silicon dioxide powder.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the ferrite synthesis component, spherical carbonyl iron powder and tetraethyl orthosilicate is 1.5-2.5:10:0.05-0.

25.

3. The preparation method according to claim 1, characterized in that, In step (1), the D50 particle size of the spherical carbonyl iron powder is 3-5 μm.

4. The preparation method according to claim 1, characterized in that, In step (2), the ball milling speed is 500-600 r / min and the ball milling time is 120-150 min.

5. The preparation method according to claim 1, characterized in that, In step (4), the vacuum drying temperature is 80-120℃ and the time is 300-360min.

6. The preparation method according to claim 1, characterized in that, In step (5), the process of the first sintering is as follows: under a nitrogen atmosphere, the temperature is raised from room temperature to 1200-1300℃ at a heating rate of 4-5℃ / min, held at a constant temperature for 3 hours, and then cooled to room temperature at a rate of 4-5℃ / min.

7. The preparation method according to claim 1, characterized in that, In step (6), the high-speed planetary ball mill used for mixing has a ball milling speed of 300-400 r / min and a ball milling time of 5-10 min.

8. The preparation method according to claim 1, characterized in that, In step (7), the secondary sintering process is as follows: under a nitrogen atmosphere, the temperature is raised from room temperature to 800-900℃ at a heating rate of 4-5℃ / min, held at a constant temperature for 2 hours, and then cooled to room temperature at a rate of 4-5℃ / min.

9. A carbonyl iron powder@cobalt ferrite@silicon dioxide microwave absorbing powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The microwave absorbing powder is a composite powder with a core-shell structure, the core being spherical carbonyl iron powder, the middle layer being cobalt ferrite, and the outer shell being silicon dioxide.

10. The carbonyl iron powder@cobalt ferrite@silicon dioxide microwave absorbing powder according to claim 9, characterized in that, It has strong absorption performance for radar waves in the 2-18GHz frequency band.

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