Surface-modified carbonyl iron powder, method for preparing the same, and use thereof

Abstract

The application provides a surface modified carbonyl iron powder, a preparation method and application thereof. The preparation method comprises the following steps: under alkaline conditions, an oxidizing agent is introduced into a reaction system containing a sulfate and a carbonyl iron powder to perform an oxidation reaction, so that a surface modification layer is formed on the surface of the carbonyl iron powder, the surface modification layer is alpha-M x Fe y OOH, wherein x=0-1, y=0-1, M is selected from one or more of Cu, Ni, Cr, Mo, V and Nb, and the sulfate includes FeSO4 and a sulfate of M. The alpha-M x Fe y OOH (i.e. alpha-FeOOH doped with M metal) surface modification layer effectively blocks the carbonyl iron powder from contacting with chloride ions, thereby avoiding corrosion of the carbonyl iron powder. Meanwhile, FeOOH has high magnetic loss and low electric constant, thereby expanding the broadband wave absorption effect of the carbonyl iron powder.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and more specifically, to a surface-modified carbonyl iron powder, its preparation method, and its application. Background Technology

[0002] Stealth technology has become an important aspect of modern military technology, and the research on radar-absorbing agents is a crucial link in promoting the development of radar-absorbing coatings, serving as the material basis for developing and improving the performance of radar-absorbing materials. Magnetic metal powders such as carbonyl iron, carbonyl nickel, and carbonyl cobalt, due to their simultaneous free electron absorption and magnetic loss properties, exhibit better radar absorption performance. However, they also have some drawbacks, such as poor corrosion resistance, high dielectric constant, and poor spectral characteristics. The poor corrosion resistance limits the application of carbonyl metal powders in marine environments. To improve the corrosion resistance of carbonyl metal radar-absorbing agents, inorganic or organic coating methods are often used. However, these methods are not very effective at blocking corrosion in marine environments where chloride ions are present.

[0003] Patent application No. 201711262016.X discloses a carbonyl iron powder microwave absorber and its preparation method, proposing to coat the surface of carbonyl iron powder with a resin shell to improve the dispersibility and oxidation resistance of the carbonyl iron powder. However, the use of organic surface coating in this microwave absorber causes the absorption peak to shift to higher frequencies, reducing the low-frequency absorption effect. Patent application No. 201711195023.2 discloses a modified metal powder microwave absorber and its preparation method, providing a modified metal powder microwave absorber coated with SiO2. Although SiO2 can improve the oxidation resistance of the metal powder microwave absorber, its blocking effect on chloride ions in the marine environment is limited, and long-term use in the marine environment still poses a risk of corrosion. Summary of the Invention

[0004] The main objective of this invention is to provide a surface-modified carbonyl iron powder, its preparation method, and its application, in order to solve the problem that existing microwave absorbing agents cannot simultaneously achieve both corrosion resistance and high microwave absorption performance in marine environments.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing surface-modified carbonyl iron powder is provided. The method comprises: under alkaline conditions, introducing an oxidant into a reaction system containing sulfate and carbonyl iron powder to carry out an oxidation reaction, thereby forming a surface-modified layer on the surface of the carbonyl iron powder. The surface-modified layer is α-M... x Fe y OOH, where x = 0 to 1, y = 0 to 1, M is selected from one or more of Cu, Ni, Cr, Mo, V, and Nb, and the sulfate includes sulfates of FeSO4 and M.

[0006] Furthermore, the above-mentioned alkaline conditions are conditions with a pH value of 7 to 10, preferably conditions with a pH value of 8 to 10.

[0007] Furthermore, the above oxidation reaction is carried out at 35–40°C.

[0008] Further, the above preparation method includes: step S1, mixing sulfate solution, buffer solution and carbonyl iron powder at 35-40°C to obtain carbonyl iron powder dispersion, wherein the pH value of carbonyl iron powder dispersion is 7-10, and preferably the mass concentration of carbonyl iron powder in carbonyl iron powder dispersion is 1-3.0 g / mL; step S2, introducing oxidant and NaOH solution into carbonyl iron powder dispersion to carry out oxidation reaction to obtain surface modified carbonyl iron powder, wherein the pH value of the reaction system during the oxidation reaction is 7-10, and preferably the oxidant is an oxygen-containing gas.

[0009] Furthermore, the Fe in the above-mentioned carbonyl iron powder dispersion 2+ The concentration of M ions is 10–30 g / L, and the preferred concentration of M ions is 0.5–3 g / L.

[0010] Further, the buffer solution includes one or both of (Na)3PO4 and NaH2PO4. Preferably, the concentration of (Na)3PO4 in the carbonyl iron powder dispersion is 5-15 g / L, and the concentration of NaH2PO4 is 15-25 g / L. Stirring is preferably carried out during steps S1 and S2, and the stirring speed is preferably 200-700 r / min.

[0011] Further, step S2 includes: heating the oxygen-containing gas and NaOH solution to 35-40°C, and then passing the heated oxygen-containing gas and NaOH solution into a carbonyl iron powder dispersion for reaction; preferably, the concentration of the NaOH solution is 80-200 g / L, the passage rate is 20-100 L / h, the oxygen content in the oxygen-containing gas is preferably 90-99.9%, the passage rate is 20-200 mL / h, and the oxidation reaction time is preferably 10-60 min.

[0012] Furthermore, the above preparation method also includes: aging and solid-liquid separation of the product system containing surface-modified carbonyl iron powder obtained in step S2 to obtain surface-modified carbonyl iron powder, washing and drying the surface-modified carbonyl iron powder to obtain surface-modified carbonyl iron powder, preferably for an aging time of 10 to 60 minutes.

[0013] According to another aspect of the present invention, a surface-modified carbonyl iron powder is provided, which is prepared by any of the above-described preparation methods.

[0014] According to another aspect of the present invention, a chlorine-resistant microwave absorbing material is provided, comprising a matrix and a microwave absorbing agent, wherein the microwave absorbing agent is any of the above-mentioned surface-modified carbonyl iron powder, or is surface-modified carbonyl iron powder prepared by any of the above-mentioned preparation methods.

[0015] By applying the technical solution of this invention, an oxidant is introduced under alkaline conditions to cause sulfate to react on the surface of carbonyl iron powder, thereby reducing Fe... 2+ Oxidized to Fe 3+ And make M ions and Fe 3+ With OH - and O 2- This combination forms a dense, uniform α-M bond attached to the surface of carbonyl iron powder. x Fe y The OOH modified layer exhibits cation selectivity, effectively blocking contact between carbonyl iron powder and chloride ions, thus preventing corrosion of the carbonyl iron powder. Simultaneously, α-FeOOH, as an intermediate product in the oxidation of low-valence Fe to Fe₂O₃, possesses high magnetic loss and low electrical constant. Therefore, as a protective layer for carbonyl iron powder, it not only does not reduce the microwave absorption performance of the carbonyl iron powder, but also, due to the low dielectric constant of α-FeOOH, it can complement the high dielectric constant of carbonyl iron, resulting in a more balanced dielectric and magnetic permeability. This improves the dispersion characteristics of the carbonyl iron powder, giving it excellent absorption effects for both low-frequency and high-frequency electromagnetic waves, thereby expanding its broadband absorption capacity. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this invention can be combined with each other. The invention will now be described in detail with reference to the embodiments.

[0017] As described in the background section of this application, existing carbonyl iron powders with coatings cannot simultaneously achieve high microwave absorption performance and good corrosion resistance in chloride ion environments (such as marine environments). To address the above problems, this application provides a surface-modified carbonyl iron powder, its preparation method, and its applications.

[0018] In a typical embodiment of this application, a method for preparing surface-modified carbonyl iron powder is provided. The method includes: under alkaline conditions, introducing an oxidant into a reaction system containing sulfate and carbonyl iron powder to carry out an oxidation reaction, thereby forming a surface-modified layer on the surface of the carbonyl iron powder. The surface-modified layer is α-M... x Fe y OOH, where x = 0 to 1, y = 0 to 1, M is selected from one or more of Cu, Ni, Cr, Mo, V, and Nb, and the sulfate includes sulfates of FeSO4 and M.

[0019] The above preparation method involves introducing an oxidant under alkaline conditions to cause the sulfate to react on the surface of carbonyl iron powder, thereby converting Fe... 2+ Oxidized to Fe 3+ And make M ions and Fe 3+ With OH - and O 2- This combination forms a dense, uniform α-M bond attached to the surface of carbonyl iron powder. x Fe y The α-FeOOH modified layer exhibits cation selectivity, effectively blocking the contact between carbonyl iron powder and chloride ions, thus preventing corrosion of the carbonyl iron powder. Simultaneously, α-FeOOH, as an intermediate product in the oxidation of low-valence Fe to Fe2O3, possesses high magnetic loss and low electrical constant. Therefore, as a protective layer for carbonyl iron powder, it not only does not reduce the microwave absorption performance of the carbonyl iron powder, but also, due to the low dielectric constant of α-FeOOH, it can complement the high dielectric constant of carbonyl iron, resulting in a more balanced dielectric and magnetic permeability, thereby improving the dispersion characteristics of the carbonyl iron powder. In summary, this application, by attaching α-M... x Fe y The OOH-modified layer achieves resistance to Cl- in carbonyl iron powder. - The corrosion resistance is improved, and the broadband absorption effect of carbonyl iron powder is extended.

[0020] In one embodiment, the preferred alkaline conditions are a pH of 7-10, more preferably a pH of 8-10, and the oxidation reaction is preferably carried out at 35-40°C. When the temperature is higher than the above temperature range or the pH is lower than the above range, the surface-modified layer will be thicker, resulting in a more porous structure and less effective chloride ion blocking. When the temperature is lower than the above temperature range, the adhesion between the surface-modified layer and the carbonyl iron powder is lower, the structural stability of the formed product decreases, and the preparation time increases, leading to reduced preparation efficiency. When the pH is higher than the above value range, Fe2O3 impurities are easily formed in the surface-modified layer, reducing its purity and consequently decreasing the microwave absorption and corrosion resistance of the final product.

[0021] Those skilled in the art can use commonly used alkaline reagents to adjust the alkaline conditions of the preparation method of this application. In some embodiments of this application, buffer solution and sodium hydroxide solution are used to adjust the pH of the reaction system. The buffer solution is weakly alkaline and can better control the pH between 7 and 10. Preferably, the above preparation method includes: step S1, mixing sulfate solution, buffer solution and carbonyl iron powder at 35-40°C to obtain carbonyl iron powder dispersion, the pH of the carbonyl iron powder dispersion is 7-10, and preferably the mass concentration of carbonyl iron powder in the carbonyl iron powder dispersion is 0.1-3.0 g / mL; step S2, introducing oxidant and NaOH solution into the carbonyl iron powder dispersion to carry out an oxidation reaction to obtain surface-modified carbonyl iron powder, wherein the pH of the reaction system during the oxidation reaction is 7-10, and preferably the above oxidant is an oxygen-containing gas. Phosphate solution is used to regulate the pH of the formed carbonyl iron powder dispersion, and sodium hydroxide solution is used to control the pH of the reaction system during the reaction.

[0022] In some embodiments, Fe is preferred in the above-mentioned carbonyl iron powder dispersion. 2+ The concentration of the metal cation is 10–30 g / L, and the preferred concentration of the M ion is 0.5–3 g / L. By controlling the concentration of each metal cation within the above range, the mass ratio of metal ions in the surface-modified layer can be adjusted, thereby further improving the ion selectivity.

[0023] The buffer solution used in this application can be a commonly used weakly alkaline buffer solution in the art. To reduce costs, the buffer solution preferably includes one or more of (Na)3PO4 and NaH2PO4, and preferably the concentration of (Na)3PO4 in the carbonyl iron powder dispersion is 5-15 g / L and the concentration of NaH2PO4 is 15-25 g / L. Using (Na)3PO4 and NaH2PO4 to adjust the pH value will not introduce other impurity cations, further ensuring the purity of the surface modified layer. It is preferred to stir during the above steps S1 and S2, preferably at a stirring speed of 200-700 r / min. Stirring can make the carbonyl iron powder and the surface modified layer reaction raw materials more uniformly dispersed in the reaction system. This not only allows as much carbonyl iron powder as possible to be coated by the surface modified layer, but also further improves the structure of the surface modified layer, thereby further enhancing the corrosion resistance and microwave absorption performance of the surface modified carbonyl iron powder.

[0024] As mentioned above, the reaction temperature of this application affects the morphology of the final product. To reduce temperature fluctuations and make the surface modified layer more uniform and dense, step S2 preferably includes: heating the oxygen-containing gas and NaOH solution to 35-40°C, and then passing the heated oxygen-containing gas and NaOH solution into the carbonyl iron powder dispersion for reaction, to obtain the carbonyl iron powder dispersion after reaction. Preferably, the concentration of NaOH solution is 80-200 g / L, the input rate is 20-100 mL / h, the oxygen content in the oxygen-containing gas is 90%-99.9%, and the input rate is 20-200 mL / h. By controlling the concentration and input rate of NaOH and oxygen-containing gas within the above-mentioned ranges, the formation rate of ferric iron can be effectively controlled, avoiding the formation of ferric hydroxide precipitate in an alkaline environment due to excessively rapid formation of ferric iron, thereby ensuring the uniform formation of α-M on the surface of carbonyl iron powder. x Fe y OOH modified layer. Preferably, the oxidant is added as an oxygen-containing gas, allowing oxygen to be introduced into the reaction system in the form of dispersed small bubbles. This improves dispersion within the reaction system, further achieving the effect of uniform reaction and enhancing the density and uniformity of the surface modified layer. The preferred oxidation reaction time is 10–60 min. Oxidation reaction times shorter than this range may result in incomplete coating of the carbonyl iron powder surface, while oxidation reaction times longer than this range may cause over-coating, leading to a decrease in microwave absorption performance.

[0025] In one embodiment, the preferred preparation method further includes: sequentially aging and solid-liquid separation of the product system containing surface-modified carbonyl iron powder obtained in step S2 to obtain surface-modified carbonyl iron powder; washing and drying the surface-modified carbonyl iron powder to obtain surface-modified carbonyl iron powder; preferably, the aging treatment time is 10 min to 60 min. The aging treatment can further grow the crystals in the surface-modified layer, reduce lattice defects, and thus improve its mechanical properties; finally, solid-liquid separation, washing, and drying are performed to obtain the target product.

[0026] In another typical embodiment of this application, a surface-modified carbonyl iron powder is provided, which is prepared by any of the above-described preparation methods. This application achieves this by coating the surface of the carbonyl iron powder with α-M... x Fe yAn OOH (i.e., α-FeOOH doped with M metal) surface modification layer effectively blocks the contact between carbonyl iron powder and chloride ions by utilizing the cation selectivity of this surface modification layer, thereby preventing the carbonyl iron powder from being corroded. Simultaneously, α-FeOOH itself has high magnetic loss and low electrical constant. Therefore, as a surface modification layer for carbonyl iron powder, it not only does not reduce the microwave absorption performance of carbonyl iron powder, but also, due to the low dielectric constant of α-FeOOH, it can combine with the high dielectric constant of carbonyl iron, resulting in a more balanced dielectric and magnetic permeability. This improves the dispersion characteristics of carbonyl iron powder, giving it excellent absorption effects for both low-frequency and high-frequency electromagnetic waves, thus expanding the broadband microwave absorption effect of carbonyl iron powder.

[0027] In another typical embodiment of this application, a chlorine-resistant microwave absorbing material is provided, comprising a matrix and a microwave absorbing agent, wherein the microwave absorbing agent is any of the above-mentioned surface-modified carbonyl iron powder, or is surface-modified carbonyl iron powder prepared by any of the above-mentioned preparation methods.

[0028] The microwave absorbing material using the surface-modified carbonyl iron powder of this application not only has stronger corrosion resistance, but also improves the dispersion characteristics of carbonyl iron, so that the microwave absorbing material has a good absorption effect on both low-frequency and high-frequency electromagnetic waves, thereby expanding the broadband absorption effect of the microwave absorbing material.

[0029] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0030] Example 1

[0031] Step (1)

[0032] 0.5 g of sodium phosphate, 1 g of sodium dihydrogen phosphate, and 30 mL of deionized water were added to a 100 mL reactor, and the temperature was raised to 38 °C. Subsequently, 10 mL of FeSO4 (0.2 g / mL) and 2.5 mL of Cr2(SO4)3 (0.1 g / mL) solution were continuously added. After the solution was mixed and stirred evenly, carbonyl iron powder was added. After adding 56 g of carbonyl iron powder, the reactor was kept under stirring (stirring speed of 500 r / min) to obtain a carbonyl iron powder dispersion with a pH of 8–8.5.

[0033] Step (2)

[0034] Continuous stirring (stirring speed 500 r / min) was performed, and the NaOH and O2 input devices on both sides of the reactor were simultaneously turned on. A constant temperature bath was set between the input devices and the reactor, with the temperature of the constant temperature bath being 38℃. The materials input into the reactor were preheated to the reaction temperature in the constant temperature bath for 3 minutes before being introduced into the reactor. The concentration of NaOH was 120 g / L, and the input rate was 60 mL / h. The input rate of O2 was 100 mL / h. NaOH and O2 were continuously input for 10 minutes, with O2 being blown into the reactor in the form of highly dispersed very small bubbles. Throughout the process, the pH value of the reaction system was controlled at 8.4.

[0035] Step (3)

[0036] After the reaction was complete, the mixture was aged for 10 minutes, filtered, washed, and spray-dried to obtain a product with α-Cr coating. 0.2 Fe 0.8 OOH carbonyl iron powder.

[0037] Example 2

[0038] Step (1)

[0039] 0.5 g of sodium phosphate, 1 g of sodium dihydrogen phosphate, and 30 mL of deionized water were added to a 100 mL reactor, and the temperature was raised to 40 °C. Subsequently, 9 mL of FeSO4 (0.2 g / mL) and 2 mL of CuSO4 (0.1 g / mL) solution were continuously added. After the solution was mixed and stirred evenly, carbonyl iron powder was added. After adding 106 g of carbonyl iron powder, the reactor was kept under stirring (stirring speed of 500 r / min) to obtain a carbonyl iron powder dispersion with a pH of 8–8.5.

[0040] Step (2)

[0041] Continuous stirring (stirring speed 500 r / min) was performed, and the NaOH and O2 input devices on both sides of the reactor were simultaneously turned on. A constant temperature bath was set between the input devices and the reactor, with the temperature of the constant temperature bath being 40℃. The materials input into the reactor were preheated to the reaction temperature in the constant temperature bath for 3 minutes before being introduced into the reactor. The concentration of NaOH was 120 g / L, the input rate was 58 mL / h, and the input rate of O2 was 98 mL / h. NaOH and O2 were continuously input for 10 minutes, with O2 being blown into the reactor in the form of highly dispersed very small bubbles.

[0042] Step (3)

[0043] After the reaction was complete, the mixture was aged for 10 minutes, filtered, washed, and spray-dried to obtain a product coated with α-Cu. 0.1 Fe 0.9 OOH carbonyl iron powder.

[0044] Example 3

[0045] Step (1)

[0046] 0.5 g of sodium phosphate, 1 g of sodium dihydrogen phosphate, and 30 mL of deionized water were added to a 100 mL reactor, and the temperature was raised to 40 °C. Subsequently, 9 mL of FeSO4 (0.2 g / mL) and 2.5 mL of NiSO4 (0.1 g / mL) solution were continuously added. After the solution was mixed and stirred evenly, carbonyl iron powder was added. After adding 56 g of carbonyl iron powder, the reactor was kept under stirring (stirring speed of 500 r / min) to obtain a carbonyl iron powder dispersion with a pH of 8–8.5.

[0047] Step (2)

[0048] Continuous stirring (stirring speed 500 r / min) was performed, and the NaOH and O2 input devices on both sides of the reactor were simultaneously turned on. A constant temperature bath was installed between the input devices and the reactor, with the temperature of the constant temperature bath set at 40℃. The materials input into the reactor were preheated to the reaction temperature in the constant temperature bath for 3 minutes before being introduced into the reactor. The concentration of NaOH was 120 g / L, and the input rate was 60 mL / h. The input rate of O2 was 100 mL / h. NaOH and O2 were continuously input for 12 minutes, with O2 being blown into the reactor in the form of highly dispersed very small bubbles.

[0049] Step (3)

[0050] After the reaction was complete, the mixture was aged for 10 minutes, filtered, washed, and spray-dried to obtain a-Ni coated with α-Ni. 0.2 Fe 0.8 OOH carbonyl iron powder.

[0051] Example 4

[0052] The difference from Example 1 is that the temperature of the constant temperature bath in step (2) is 40°C.

[0053] Example 5

[0054] The difference from Example 1 is that the temperature of the constant temperature bath in step (2) is 35°C.

[0055] Example 6

[0056] The difference from Example 1 is that the temperature of the constant temperature bath in step (2) is 45°C.

[0057] Example 7

[0058] The difference from Example 1 is that the temperature of the constant temperature bath in step (2) is 30°C.

[0059] Example 8

[0060] The difference from Example 1 is that in step (1), 0.5g sodium phosphate, 2.2g sodium dihydrogen phosphate and 30mL deionized water are added to a 100mL reactor, the temperature is raised to 38℃, and the pH value of the carbonyl iron powder dispersion is controlled at 7 to 7.5.

[0061] Example 9

[0062] The difference from Example 1 is that in step (1), 0.82g of sodium phosphate, 1.3g of sodium dihydrogen phosphate and 30mL of deionized water are added to a 100mL reactor, the temperature is raised to 38℃, and the pH value of the carbonyl iron powder dispersion is controlled between 9.5 and 10.

[0063] Example 10

[0064] The difference from Example 1 is that in step (1), 1.8g of sodium phosphate, 0.6g of sodium dihydrogen phosphate and 30mL of deionized water are added to a 100mL reactor, the temperature is raised to 38℃, and the pH value of the carbonyl iron powder dispersion is controlled at 6 to 6.5.

[0065] Example 11

[0066] The difference from Example 1 is that the concentration of NaOH solution in step (2) is 80 g / L.

[0067] Example 12

[0068] The difference from Example 1 is that the concentration of the NaOH solution in step (2) is 200 g / L.

[0069] Example 13

[0070] The difference from Example 1 is that the concentration of NaOH solution in step (2) is 50 g / L.

[0071] Example 14

[0072] The difference from Example 1 is that the concentration of NaOH solution in step (2) is 230 g / L.

[0073] Example 15

[0074] The difference from Example 1 is that the rate at which the NaOH solution is introduced in step (2) is 20 L / h.

[0075] Example 16

[0076] The difference from Example 1 is that the rate at which the NaOH solution is introduced in step (2) is 100 L / h.

[0077] Example 17

[0078] The difference from Example 1 is that the rate at which the NaOH solution is introduced in step (2) is 10 L / h.

[0079] Example 18

[0080] The difference from Example 1 is that the rate at which the NaOH solution is introduced in step (2) is 120 L / h.

[0081] Example 19

[0082] The difference from Example 1 is that the O2 input rate in step (2) is 20 mL / h.

[0083] Example 20

[0084] The difference from Example 1 is that the O2 input rate in step (2) is 10 mL / h.

[0085] Example 21

[0086] The difference from Example 1 is that the O2 input rate in step (2) is 120 mL / h.

[0087] Example 22

[0088] The difference from Example 1 is that NaOH and O2 are continuously input for 60 minutes in step (2).

[0089] Example 23

[0090] The difference from Example 1 is that NaOH and O2 are continuously input for 5 minutes in step (2).

[0091] Example 24

[0092] The difference from Example 1 is that NaOH and O2 are continuously input for 80 minutes in step (2).

[0093] Comparative Example 1

[0094] Shaanxi Xinghua TP carbonyl iron powder (particle size 3-5μm).

[0095] Performance testing

[0096] The surface-modified carbonyl iron powder obtained in the examples was mixed with paraffin (mass ratio 85:15) to fabricate coaxial rings (outer diameter 7 mm, inner diameter 3 mm). The electromagnetic parameters (real part e', imaginary part e”, real part u', and imaginary part u” of the dielectric constant, were tested before and after immersion in 5% NaCl brine. The same tests were performed on Comparative Example 1 to obtain the corresponding electromagnetic parameters. Furthermore, the colors of the coaxial rings before and after brine immersion were compared. The results are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0101] The preparation method of this application involves introducing an oxidant under alkaline conditions to cause the sulfate to react on the surface of carbonyl iron powder, thereby converting Fe... 2+ Oxidized to Fe 3+ And make M ions and Fe 3+ With OH - and O 2- This combination forms a dense, uniform α-M bond attached to the surface of carbonyl iron powder. x Fe y The OOH modified layer exhibits cation selectivity, effectively blocking contact between carbonyl iron powder and chloride ions, thus preventing corrosion of the carbonyl iron powder. Simultaneously, α-FeOOH, as an intermediate product in the oxidation of low-valence Fe to Fe₂O₃, possesses high magnetic loss and low electrical constant. Therefore, as a protective layer for carbonyl iron powder, it not only does not reduce the microwave absorption performance of the carbonyl iron powder, but also, due to the low dielectric constant of α-FeOOH, it can complement the high dielectric constant of carbonyl iron, resulting in a more balanced dielectric and magnetic permeability. This improves the dispersion characteristics of the carbonyl iron powder, giving it excellent absorption effects for both low-frequency and high-frequency electromagnetic waves, thereby expanding its broadband absorption capacity.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing surface-modified carbonyl iron powder, characterized in that, The preparation method includes: Under alkaline conditions, an oxidant is introduced into a reaction system containing sulfate and carbonyl iron powder to carry out an oxidation reaction, thereby forming a surface-modified layer on the surface of the carbonyl iron powder. The surface-modified layer is α-M. x Fe y OOH, where x = 0~1, y = 0~1, and x is not equal to 0, y is not equal to 0; M is selected from one or more of Cu, Ni, Cr, Mo, V, and Nb. The sulfates include sulfates of FeSO4 and M; Step S1: At 35~40℃, sulfate solution, buffer solution and carbonyl iron powder are mixed to obtain carbonyl iron powder dispersion. The pH value of the carbonyl iron powder dispersion is 7~10, and the mass concentration of carbonyl iron powder in the carbonyl iron powder dispersion is 1~3.0 g / mL. The buffer solution includes (Na)3PO4 and NaH2PO4. Step S2: An oxidant and NaOH solution are introduced into the carbonyl iron powder dispersion to carry out an oxidation reaction, thereby obtaining surface-modified carbonyl iron powder. The pH value of the reaction system during the oxidation reaction is 7-10, and the oxidant is an oxygen-containing gas.

2. The preparation method according to claim 1, characterized in that, The alkaline conditions are those with a pH value of 7 to 10.

3. The preparation method according to claim 2, characterized in that, The alkaline conditions are those with a pH value of 8 to 10.

4. The preparation method according to claim 1, characterized in that, The oxidation reaction is carried out at 35~40℃.

5. The preparation method according to claim 1, characterized in that, Fe in carbonyl iron powder dispersion 2+ The concentration of M ions is 10~30 g / L, and the concentration of M ions is 0.5~3 g / L.

6. The preparation method according to claim 1, characterized in that, The concentration of (Na)3PO4 in the carbonyl iron powder dispersion is 5~15 g / L, and the concentration of NaH2PO4 is 15~25 g / L.

7. The preparation method according to claim 1, characterized in that, Stirring is performed during steps S1 and S2 at a speed of 200-700 r / min.

8. The preparation method according to claim 1, characterized in that, Step S2 includes: After heating the oxygen-containing gas and the NaOH solution to 35-40°C, the heated oxygen-containing gas and the NaOH solution are then passed into the carbonyl iron powder dispersion to carry out the reaction.

9. The preparation method according to claim 1, characterized in that, The concentration of the NaOH solution is 80~200g / L, and the influent rate is 20~100L / h.

10. The preparation method according to claim 1, characterized in that, The oxygen-containing gas has an oxygen content of 90-99.9% and an injection rate of 20-200 mL / h.

11. The preparation method according to claim 1, characterized in that, The oxidation reaction takes 10 to 60 minutes.

12. The preparation method according to claim 1, characterized in that, The preparation method further includes: The product system containing surface-modified carbonyl iron powder obtained in step S2 is subjected to aging and solid-liquid separation to obtain the surface-modified carbonyl iron powder. The surface-modified carbonyl iron powder is then washed and dried to obtain the surface-modified carbonyl iron powder.

13. The preparation method according to claim 12, characterized in that, The aging process takes 10 to 60 minutes.

14. A surface-modified carbonyl iron powder, characterized in that, The surface-modified carbonyl iron powder is prepared by the preparation method according to any one of claims 1 to 13.

15. A chlorine-resistant microwave absorbing material, comprising a matrix and a microwave absorbing agent, characterized in that, The microwave absorber is the surface-modified carbonyl iron powder as described in claim 14, or the surface-modified carbonyl iron powder prepared by any one of claims 1 to 13.

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