Preparation method of novel corrosion-resistant iron-based microwave absorbing material

Abstract

The invention relates to the field of preparation of wave-absorbing materials, in particular to a preparation method of a novel corrosion-resistant iron-based microwave wave-absorbing material. The preparation method comprises the following three steps: S1, preparation of fluorinated graphene; S2, preparation of flaky carbonyl iron powder; and S3, composite preparation. In the step S1, no acidic substance is used, but sodium cholate is added, so that the problem that fluorinated graphene is agglomerated and settled in water is effectively solved, and the stripped fluorinated graphene can be stably dispersed in an aqueous solution in a single-layer or few-layer state. According to the preparation method, hazardous chemical reagents such as acid are not introduced, and the product is high in quality, complete in structure, more environmentally friendly, safer, low in equipment requirement, few in product defect and easy to produce on a large scale. The composite wave-absorbing material prepared by the method provided by the invention still maintains relatively high magnetic conductivity at high frequency, and breaks through the snoek limit.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing material preparation, and specifically to a method for preparing a novel corrosion-resistant iron-based microwave absorbing material. Background Technology

[0002] Iron-based microwave absorbing materials are widely used in electromagnetic shielding and stealth technologies due to their high permeability and strong absorption capabilities. In existing technologies, iron-based microwave absorbing materials are often combined with graphene to improve performance; however, high-purity graphene is expensive, resulting in high material preparation costs and hindering large-scale application. Furthermore, the weak interfacial bonding between graphene and iron-based powders leads to poor coating effects and agglomeration, affecting absorption stability. Traditional iron-based materials are limited by the Snoek limit at high frequencies, resulting in decreased permeability and reduced absorption performance. The dielectric constant of composite systems is generally high, leading to poor impedance matching with air, making it difficult for electromagnetic waves to penetrate and be absorbed. In the preparation process, post-coating drying often involves oven drying, which is lengthy, inefficient, and cannot meet the demands of large-scale mass production.

[0003] Therefore, in order to solve the above problems, it is very promising to invent a preparation process for a high-performance, low-cost, mass-producible corrosion-resistant iron-based microwave absorbing material that can improve the coating effect and impedance matching, shorten the production cycle, and ultimately obtain high-performance, low-cost, mass-producible material. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a novel method for preparing corrosion-resistant iron-based microwave absorbing materials. By adding sodium cholate, this invention effectively solves the problem of fluorinated graphene agglomeration and sedimentation in water, enabling the exfoliated fluorinated graphene to be stably dispersed in aqueous solution in a single-layer or few-layer state. This preparation method avoids the introduction of acidic or other hazardous chemical reagents, produces high-quality products with intact structures, is more environmentally friendly and safer, has lower equipment requirements, fewer product defects, and is easy to scale up for production.

[0005] This invention discloses a novel method for preparing corrosion-resistant iron-based microwave absorbing materials, the method comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water and stirred evenly to obtain a dispersion. The speed and time of the shear emulsifier were set for shearing. During the shearing process, the temperature was maintained by an ice-water bath. After the shearing was completed, gradient centrifugation was performed to remove the blocky fluorinated graphene that had not settled, and the dispersion was retained. Preparation of S2 flake carbonyl iron powder: Carbonyl iron powder is placed in a ball mill, then anhydrous ethanol and zirconium oxide balls are added. The ball mill speed and time are set and ball milling is started. After the ball milling is completed, the flake carbonyl iron powder is dried to obtain it. S3 Composite Preparation: The flake carbonyl iron powder obtained in step S2 is added to distilled water and stirred for 30 min. Then, a silane coupling agent is added and stirred for another 10 min. The dispersion obtained in step S1 is then added, heated and stirred for 70 min, followed by the addition of polyvinylpyrrolidone and stirring for another 40 min. The mixed slurry is then poured into a granulator, and the inlet and outlet temperatures and rotation speed of the granulator are set for granulation to obtain the iron-based microwave absorbing material.

[0006] Preferably, in step S1, the mass ratio of the fluorinated graphite to sodium cholate is 1:(0.1~0.5).

[0007] Preferably, in step S1, the mass ratio of the fluorinated graphite to distilled water is 1:100.

[0008] Preferably, in step S1, the rotation speed of the shear emulsifier is 8000 rpm and the time is 10 min.

[0009] Preferably, in step S1, the rotor diameter used in the shear emulsifier is 27.6 mm.

[0010] Preferably, in step S1, the temperature of the ice-water bath is 5°C.

[0011] Preferably, in step S1, the first centrifugation speed of the gradient centrifugation is 2000 rpm, the second centrifugation speed is 8000 rpm, and the centrifugation time for both stages is 20 min.

[0012] Preferably, in step S2, the mass ratio of carbonyl iron powder to zirconium oxide balls is 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol is 1:1.5.

[0013] Preferably, in step S3, the mass ratio of the flake carbonyl iron powder to the silane coupling agent is 1:(3~7); the mass ratio of the flake carbonyl iron powder to the dispersion is 1:0.6; and the mass ratio of the flake carbonyl iron powder to polyvinylpyrrolidone is 1:(20~30).

[0014] Preferably, in step S3, the inlet temperature of the granulator is 230°C, the outlet temperature is 140°C, and the rotation speed is set to 10,000 rpm; the granulator is a centrifugal spray granulator.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a novel method for preparing corrosion-resistant iron-based microwave absorbing materials, which has the following characteristics: (1) In the preparation of fluorinated graphene, a large number of new surfaces are generated during the shearing process of fluorinated graphene being exfoliated into fluorinated graphene sheets. These new surfaces have high surface energy and have a strong tendency to attract each other through van der Waals forces, recombine or aggregate into large particles, and then settle. To avoid this phenomenon, the amphiphilic molecule sodium cholate is added in this process. Its molecular structure is hydrophilic at one end (hydroxyl and carboxyl groups) and hydrophobic at the other end (steroidal ring structure). During the shearing process, sodium cholate is physically adsorbed onto the surface of fluorinated graphene. Utilizing its amphiphilicity, it provides a dual stabilizing mechanism of electrostatic repulsion and steric hindrance, ensuring that the exfoliated fluorinated graphene can be stably dispersed in the aqueous solution in a monolayer or few-layer state, rather than re-aggregating and settling.

[0016] (2) This method of preparing fluorinated graphene is simple, does not introduce acidic or other hazardous chemical reagents, produces high-quality products with complete structures, is more environmentally friendly and safe, has low equipment requirements, produces fewer product defects, and is easy to scale up.

[0017] (3) The composite absorbing material prepared by the method provided by the present invention still maintains high permeability at high frequencies, breaking through the snoek limit. Attached Figure Description

[0018] Figure 1 Transmission electron microscopy image of iron-based microwave absorbing material Detailed Implementation The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0019] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0020] Example 1: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.3 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0021] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0022] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:5. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:20. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0023] Example 2: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.1 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0024] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0025] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:3. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:22. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0026] Example 3: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.2 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0027] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0028] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:4. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:25. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0029] Example 4: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.4 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0030] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0031] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:6. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:27. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0032] Example 5: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.5 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0033] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0034] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:7. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:30. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0035] Example 6: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene was dissolved in distilled water and stirred until a uniform dispersion was obtained. Then, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0036] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0037] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:5. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:20. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0038] Example 7: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.3 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 minutes for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, centrifugation was performed at a speed of 2000 rpm for 20 minutes. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0039] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0040] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 was added to distilled water and stirred for 30 min. Then, a silane coupling agent was added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:5. Stirring was continued for 10 min. Then, the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:20. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0041] Example 8: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.3 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0042] Preparation of S2 composite: Carbonyl iron powder was added to distilled water and stirred for 30 min, then silane coupling agent was added. The mass ratio of flake carbonyl iron powder to silane coupling agent was 1:5. Stirring was continued for 10 min, then the dispersion obtained in step S1 was added, and the mixture was heated and stirred for 70 min. Polyvinylpyrrolidone was then added and stirred for 40 min. The mass ratio of flake carbonyl iron powder to dispersion was 1:0.6, and the mass ratio of flake carbonyl iron powder to polyvinylpyrrolidone was 1:20. The mixed slurry was then poured into a centrifugal spray granulator. The inlet temperature of the granulator was set to 230℃, the outlet temperature to 140℃, and the rotation speed to 10000 rpm for centrifugal spray drying to obtain iron-based microwave absorbing material.

[0043] Example 9: A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, comprising the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water at a mass ratio of 1:0.3 and a mass ratio of fluorinated graphene to distilled water of 1:100. After stirring until a uniform dispersion was obtained, a shear emulsifier with a rotor diameter of 27.6 mm was set at a speed of 8000 rpm for 10 min for shearing. During the shearing process, an ice-water bath was used to maintain the temperature at 5℃. After shearing, gradient centrifugation was performed. The first centrifugation speed was 2000 rpm, and the second centrifugation speed was 8000 rpm, with a centrifugation time of 20 min for both stages. After centrifugation, the unsettled blocky fluorinated graphene was removed, and the dispersion was retained.

[0044] Preparation of S2 flake-shaped carbonyl iron powder: Carbonyl iron powder was placed in a ball mill, then anhydrous ethanol and zirconia balls with a diameter of 6 mm were added. The mass ratio of carbonyl iron powder to zirconia balls was 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol was 1:1.5. The ball mill speed was set to 600 rpm and the time was set to 16 hours before ball milling began. After ball milling was completed, the powder was placed in a forced-air drying oven at 60℃ and dried for 4 hours to obtain flake-shaped carbonyl iron powder.

[0045] Preparation of S3 composite: The flake carbonyl iron powder obtained in step S2 is added to distilled water and stirred for 30 min. Then, a silane coupling agent is added, with a mass ratio of flake carbonyl iron powder to silane coupling agent of 1:5. Stirring is continued for 10 min. Then, the dispersion prepared in step S1 is added and heated and stirred for 70 min, with a mass ratio of flake carbonyl iron powder to dispersion of 1:0.6. The mixed slurry is then poured into a centrifugal spray granulator. The inlet temperature of the granulator is set to 230℃, the outlet temperature to 140℃, and the rotation speed is set to 10000 rpm for centrifugal spray drying to obtain the iron-based microwave absorbing material.

[0046] Example 10: A method for preparing a corrosion-resistant composite microwave absorbing material, characterized in that: (1) Graphene modification: Weigh out graphene powder and disperse it in pure water. Disperse it ultrasonically for 2 hours to obtain a graphene dispersion. Add the dispersion to a hydrothermal reactor lined with polytetrafluoroethylene, add hydrofluoric acid (mass concentration of hydrofluoric acid is 20%), tighten the hydrothermal reactor to seal it, place it in an oven and keep it at 240℃ for 10 hours. After the reaction is completed, cool it naturally and filter it. Wash the filter cake with pure water 5 times until its pH value reaches neutral.

[0047] (2) Preparation of flake carbonyl iron powder: Weigh carbonyl iron powder and put it into a planetary ball mill. Add anhydrous ethanol as a process control agent and add zirconia balls with a diameter of 6 mm as grinding balls (i.e., the ball-to-material ratio is 100:1). After ball milling at 800 rpm for 24 hours, take out the iron powder, put it into a forced-air drying oven and dry it at 60℃ for 2 hours to obtain flake carbonyl iron powder with a diameter-to-thickness ratio of about 10:1.

[0048] (3) Preparation of composite microwave absorbing material: using a stirrer at 500 rpm, flake carbonyl iron powder is dispersed in anhydrous ethanol and stirred for 30 min to obtain CIP dispersion; silane coupling agent KH550 and distilled water are added dropwise to CIP dispersion and stirred continuously at 800 rpm for 1 h; then modified graphene dispersion (prepared by dispersing the modified graphene in anhydrous ethanol in step 1, with a solid content of 5%) is added and stirred for 4 h in an oil bath at 60 ℃; the mixed dispersion is filtered and the composite is placed in a vacuum drying oven and vacuum dried at 60 ℃ for 4 h; the composite material is passed through a 50-mesh sieve and then vacuum sealed for storage.

[0049] The performance of the iron-based microwave absorbing materials prepared in Examples 1-10 was tested (dispersion was measured using a laser particle size analyzer; coating rate was observed and statistically analyzed using a scanning electron microscope (SEM); reflection loss (RL) and effective absorption bandwidth (EAB, RL≤-10dB) were tested in the 8-18GHz frequency band using a vector network analyzer; corrosion rate was tested using a neutral salt spray test (5% NaCl solution, 35℃, 72h); dielectric constant (ε') was tested in the 10GHz frequency band using the resonant cavity method). The test data are shown in the table below:

[0050] The test data in the table above shows that Example 6, without the addition of sodium cholate, had a dispersion of only 65% ​​and a coating rate of 70%, which were lower than those of Examples 1-5 with the addition of sodium cholate. In Example 1, the performance was optimal when the mass ratio of fluorinated graphene to sodium cholate was 1:0.3. Excessive sodium cholate would lead to enhanced intermolecular interactions, thus slightly reducing the dispersion effect. The low dispersion meant that the fluorinated graphene could not uniformly coat the iron powder surface, making it difficult for electromagnetic waves to be fully absorbed. Therefore, the minimum RL value was only -16.8dB and the EAB was only 2.5GHz; the dielectric constant ε' reached 14.5, resulting in poor impedance matching. Sodium cholate, as an amphiphilic molecule, provides a dual stabilizing effect of electrostatic repulsion and steric hindrance by physically adsorbing onto the surface of fluorinated graphene, preventing the fluorinated graphene sheets from re-aggregating and assisting in the exfoliation process. In Example 7, the dispersion of the fluorinated graphene decreased from 95% to 80%, and the coating rate decreased from 96% to 85%. Residual agglomerated fluorinated graphene leads to uneven internal structure of the composite material, increasing electromagnetic wave reflection loss. The minimum RL value changes from -32.5dB to -23.7dB, and the EAB shrinks from 6.2GHz to 3.8GHz. This is because gradient centrifugation can remove unpeeled blocky fluorinated graphene and agglomerated fluorinated graphene particles stepwise, retaining only a single layer of dispersed fluorinated graphene. Single centrifugation cannot completely separate fine agglomerates. Example 8 has a minimum RL value of -20.3dB, an EAB of 3.1GHz, and a corrosion rate of 0.058mm / year, which is worse than Example 1. This is because the sheet-like carbonyl iron powder prepared by ball milling has a specific aspect ratio, which can break through the Snoek limit at high frequencies and maintain high permeability; while Example 8 directly uses the original carbonyl iron powder, which is granular, and the high-frequency permeability decays significantly. At the same time, the sheet-like structure can increase the contact area with fluorinated graphene, improve the coating density, and enhance corrosion resistance. In Example 9, without the addition of polyvinylpyrrolidone, the dielectric constant ε' increased from 10.2 to 15.8, resulting in a deterioration in impedance matching. This led to a decrease in the minimum RL value from -32.5 dB to -25.4 dB, and a reduction in EAB from 6.2 GHz to 4.3 GHz. However, corrosion resistance was less affected because the coating rate still reached 90%. This is because polyvinylpyrrolidone, as a dispersant and dielectric modifier, can reduce the dielectric constant of the composite material, making ε' closer to the air impedance and improving the efficiency of electromagnetic waves entering the material. In Example 10, the fluorinated graphene had a dispersion of 78% and a coating rate of 82%. The minimum RL value was -19.5 dB, and the EAB was 3.3 GHz, both lower than in Example 1. The corrosion rate was 0.042 mm / year, due to surface defects caused by residual hydrofluoric acid, resulting in decreased corrosion resistance. The ε' value was 17.6, indicating poor impedance matching. Example 10 uses hydrofluoric acid to modify graphene. Hydrofluoric acid is a highly corrosive reagent that can easily lead to material defects. Graphene is also expensive and has poor dispersibility. The fluorinated graphene prepared in this invention does not require strong acid, has a mild process, produces a complete product structure, and has stronger interfacial bonding with iron powder.

[0051] In summary, the addition of sodium cholate improves the dispersion and coating efficiency of fluorinated graphene, and its electrostatic repulsion and steric hindrance properties affect its microwave absorption performance. Gradient centrifugation improves the purity of fluorinated graphene, flake iron powder breaks the Snoek limit, and polyvinylpyrrolidone improves impedance matching. The iron-based microwave absorbing material prepared by the method provided in this invention has a minimum RL value of 32.5 dB, an EAB of 6.2 GHz, a corrosion rate of 0.015 mm / year, and an ε' of 10.2, all of which are superior to those of traditional graphene.

[0052] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a novel corrosion-resistant iron-based microwave absorbing material, characterized in that, Includes the following steps: Preparation of S1 fluorinated graphene: Fluorinated graphene and sodium cholate were dissolved in distilled water and stirred evenly to obtain a dispersion. The speed and time of the shear emulsifier were set for shearing. During the shearing process, the temperature was maintained by an ice-water bath. After the shearing was completed, gradient centrifugation was performed to remove the blocky fluorinated graphene that had not settled, and the dispersion was retained. Preparation of S2 flake carbonyl iron powder: Carbonyl iron powder is placed in a ball mill, then anhydrous ethanol and zirconium oxide balls are added. The ball mill speed and time are set and ball milling is started. After the ball milling is completed, the flake carbonyl iron powder is dried to obtain it. S3 Composite Preparation: The flake carbonyl iron powder obtained in step S2 is added to distilled water and stirred for 30 min. Then, a silane coupling agent is added and stirred for another 10 min. Then, the dispersion obtained in step S1 is added, heated and stirred for 70 min, followed by the addition of polyvinylpyrrolidone and stirring for another 40 min. The mixed slurry is then poured into a granulator, and the inlet and outlet temperatures and rotation speed of the granulator are set for granulation to obtain the iron-based microwave absorbing material.

2. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S1, the mass ratio of the fluorinated graphite to sodium cholate is 1:(0.1~0.5).

3. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S1, the mass ratio of the fluorinated graphite to distilled water is 1:

100.

4. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S1, the rotation speed of the shear emulsifier is 8000 rpm and the time is 10 min.

5. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S1, the rotor diameter used in the shear emulsifier is 27.6 mm.

6. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S1, the temperature of the ice-water bath is 5°C.

7. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S1, the first centrifugation speed of the gradient centrifugation is 2000 rpm, the second centrifugation speed is 8000 rpm, and the centrifugation time for both stages is 20 min.

8. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S2, the mass ratio of carbonyl iron powder to zirconium oxide balls is 1:10; the mass ratio of carbonyl iron powder to anhydrous ethanol is 1:1.

5.

9. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S3, the mass ratio of the flake carbonyl iron powder to the silane coupling agent is 1:(3~7); the mass ratio of the flake carbonyl iron powder to the dispersion is 1:0.6; and the mass ratio of the flake carbonyl iron powder to polyvinylpyrrolidone is 1:(20~30).

10. The method for preparing a novel corrosion-resistant iron-based microwave absorbing material according to claim 1, characterized in that, In step S3, the inlet temperature of the granulator is 230°C, the outlet temperature is 140°C, and the rotation speed is set to 10,000 rpm; the granulator is a centrifugal spray granulator.

Images