High-permeability corrosion-resistant absorbent and preparation method thereof

Abstract

The invention discloses a high-permeability corrosion-resistant absorbent and a preparation method thereof, and belongs to the technical field of preparation of core-shell composite particles. According to the preparation method of the high-permeability corrosion-resistant absorbent, the core-shell structure composite particles are prepared by using a stirring ball vibration-assisted sol-gel method, and the preparation method has the advantages that the process is simple and convenient, and an ultrathin, compact and complete coating layer can be coated. According to the prepared high-permeability corrosion-resistant absorbent, the coating layer has the characteristics of extremely low content of continuous compact holes and the like, so that the corrosion resistance of the absorbent is greatly improved; and the surface resistivity of the absorbent is further improved, so that the dielectric constant is reduced, and the impedance matching property and the wave-absorbing property of a corresponding wave-absorbing material are improved. The invention provides an effective method for corrosion resistance of active metal, and has a wide application prospect in the fields of radar wave absorption, electromagnetic shielding, protection and the like in a complex environment.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of core-shell composite particles, and in particular to a high magnetic permeability corrosion-resistant absorbent and a preparation method thereof. Background Art

[0002] Active particles such as metals are widely used in the biological, electrochemical, catalytic, microwave absorption and electromagnetic compatibility fields, and are in great demand in both military and civilian fields.

[0003] In the field of microwave absorbing materials, magnetic metal absorbers represented by carbonyl iron powder have become the most widely used absorbing materials due to their high saturation magnetization and magnetic permeability, but performance failure caused by metal corrosion has become a stubborn problem in its practical application. The core-shell composite particles obtained by coating the metal surface with a corrosion-resistant shell have the characteristics of both metal and shell materials, which has become the key to solving its chemical instability.

[0004] For example, the literature ( ACTA POLYMERICA SINICA. 2003, No. 5 Expect, 757-760 Page) obtained polysilazane (PSZ)-coated nano-Fe magnetic metal absorber by chemical method, and its moisture corrosion resistance was greatly improved. Journal of Inorganic Materials. 2017, 32 roll, 751-757 Page) used the atomic layer deposition method to coat a dense layer of aluminum oxide (Al2O3) on the surface of carbonyl iron powder, which greatly improved the corrosion resistance and oxidation resistance of the material. Journal of Alloys and Compounds. 2017, No. 706 Expect, 267- 273 Page) synthesized Fe / SiO2 composite particle absorber by Stöber method, and the thickness of the shell layer was about 100 nm, so that the absorber filled in the polymer matrix could maintain microwave absorption performance in NaCl solution for more than half a year. Although many methods have achieved the coating and corrosion resistance improvement of magnetic metal absorbers, especially a large number of coating technologies based on sol-gel method, which are low-cost and simple. However, there are still some problems in the existing methods for surface coating of micron-sized magnetic metal powders. First, in order to achieve excellent corrosion resistance, the coating content of shell material is relatively large (>12%), which is easy to damage the performance of active particles such as core metal; second, when the content of shell material is reduced, it is difficult to form a complete, dense and continuous coating on the surface of core particles. The existing coating methods all have detectable mesopores (tested by BET method), and their corrosion resistance needs to be further improved.

[0005] At present, there is still a lack of an absorbent with excellent environmental resistance and wave absorption performance. The above problems mainly come from the poor dispersion of particles and the presence of more self-nucleation during the coating process. The reason is that the existing coating method usually adopts stirring and dispersion by a stirring rod, the reaction liquid usually forms a laminar flow, the collision probability of the reaction hydrolysis product and the absorbent particles is low, and the solid-liquid exchange frequency is low, so that the coating reaction is dominated by the growth of surface coating crystal nuclei, which is not conducive to the densification of the coating shell; and the dispersion effect is not good, which is not conducive to the uniform coating reaction.

[0006] In summary, developing a method for coating an ultra-thin, dense and complete oxide layer has important practical significance in this field, and is particularly beneficial for improving the compatibility of the material's environmental resistance and microwave absorption performance. Summary of the invention

[0007] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, a method for preparing a high magnetic permeability corrosion-resistant absorbent with a simple process and capable of coating an ultra-thin, dense and complete coating layer is provided, which adopts a stirring ball vibration-assisted sol-gel method, comprising the following steps: A reaction container with a high-density stirring ball is placed in a vibrating shaker, and a coating reaction liquid is added; the reaction container is sealed and moves along a track to provide a motion power for the high-density stirring ball and a dispersion power for the coating reaction liquid, and the solid-liquid exchange and dispersion effect are increased through the speed difference between the high-density stirring ball and the coating reaction liquid, and a coating reaction is performed to obtain a high magnetic permeability corrosion-resistant absorbent with a core-shell structure; The components of the coating reaction solution include a reaction solvent, a hydrolyzing agent, a hydrolysis source, and an absorbent to be coated; The high-density stirring ball is chemically inert during the coating reaction process, has a density 3-10 times that of the coating reaction liquid, and has a diameter of 1-10 mm; the ratio of the total mass of the high-density stirring ball to the mass of the coating reaction liquid is 1:10-3:5.

[0008] The hydrolysis method is an important method for synthesizing core-shell structured particles in this field, and usually uses a reaction solvent, a hydrolyzing agent, a hydrolysis source, and an absorbent to be coated as the reaction liquid. The hydrolysis method does not require complex equipment and harsh reaction conditions, and its reaction mechanism is relatively simple, which can reduce the occurrence of side reactions; it has many advantages such as simple equipment, mild reaction conditions, easy control of shell thickness and morphology, improved product purity, and wide applicability.

[0009] The sealed reaction container with high-density stirring balls is fixed in a constant temperature vibration shaker, and the vibration of the vibration shaker drives the high-density stirring balls to roll. The mechanical collision between the high-density stirring balls further increases the disorder inside the system, increases the collision probability between the critical crystal nuclei of the hydrolysis product and the absorbent particles in the reaction system, and increases the solid-liquid exchange frequency, so that the coating reaction is dominated by the nucleation of the surface coating, forming a high nucleation density, and obtaining a dense and uniform coating shell; in addition, it also improves the dispersibility of the particles to be coated, which is beneficial to the integrity of the particle surface coating.

[0010] The high-density stirring balls can form a significant speed difference with the coated reaction liquid at a selected density ratio, and will not cause excessive impact on the reaction container. When using high-density stirring balls of equal mass, balls with too small a diameter have limited impact kinetic energy, and the energy transmitted by vibration is dispersed, making it difficult to form a significant speed difference with the reaction liquid; balls with too large a diameter have reduced impact frequency and low particle dispersion efficiency. Therefore, its diameter also needs to be controlled within a suitable range to achieve the purpose of the present invention. Controlling the mass ratio of the high-density stirring balls and the coated reaction liquid is intended to balance the collision kinetic energy and collision frequency, and optimize particle dispersion and solid-liquid exchange frequency. When there are too few high-density stirring balls, the dispersion effect on the particles is small; when there are too many high-density stirring balls, there is not enough space between the high-density stirring balls for favorable collisions to increase the dispersion effect of the particles.

[0011] Preferably, the reaction solvent comprises a mixed solvent of water and ethanol, wherein the proportion of water is 20 vol.%-80 vol.%.

[0012] Further preferably, the high-density stirring balls include at least one of stainless steel balls, zirconium oxide balls, and aluminum oxide balls.

[0013] Depending on the type of reaction solvent, the material of the high-density stirring ball can be a stainless steel ball, a ceramic ball such as a zirconia ball, an alumina ball or other inert spheres. Such material spheres have the advantages of being easy to obtain and having good applicability in production.

[0014] Preferably, the hydrolyzing agent comprises aqueous ammonia, and the concentration of the aqueous ammonia is 25 wt.%-28 wt.%.

[0015] Preferably, the hydrolysis source includes tetraethyl orthosilicate (TEOS).

[0016] Preferably, the absorbent to be coated is a sheet-like structure with an average particle size of 3-500 μm.

[0017] Further preferably, the absorbent to be coated includes at least one of flaky carbonyl iron powder particles and flaky FeNi alloy particles.

[0018] The absorbent to be coated in the present invention is made of raw materials with an average particle size of micrometers, and its microscopic morphology can be of any shape. Carbonyl iron powder particles and FeNi alloy particles with sheet structures are preferred types of absorbents because of their good wave absorbing properties.

[0019] Preferably, the content of each component, calculated as a percentage of the coating reaction solution, is as follows: absorbent to be coated <5 wt.%, hydrolysis source <2 wt.%, hydrolysis agent <2 wt.%, and the remainder is reaction solvent.

[0020] Controlling the amount of absorbent to be coated to be less than 1 / 20 (5 wt.%) of the mass of the entire coating reaction solution helps prevent excessive particles from affecting the fluidity of the reaction solution and the dispersibility of the particles. Controlling the concentration of the hydrolyzing agent to be less than 2 wt.% can avoid the defect of causing a large amount of self-nucleation of the hydrolysis source, which leads to a reduction in the efficiency of heterogeneous nucleation (coating). The concentration of the hydrolysis source in the reaction system is less than 2 wt.%, so that the concentration of the coating monomer does not form violent self-nucleation, ensuring that the heterogeneous nucleation process on the surface of the core particles proceeds at a uniform rate.

[0021] Preferably, the rotation speed of the vibrating table is 50-300 r / min.

[0022] The rotation speed of the vibration shaker is controlled within a limited range, which helps to provide sufficient kinetic energy for the high-density stirring balls in the closed reaction vessel and maintain the stability of the closed reaction vessel in the vibration shaker.

[0023] Preferably, the coating reaction temperature is 10-30°C.

[0024] The temperature of the coating reaction should be controlled within a suitable range. Too high a temperature can easily lead to the occurrence of self-nucleation, and make the nuclei of heterogeneous nucleation grow unevenly, resulting in an uneven and non-dense surface; while too low a temperature can reduce the coating efficiency. Based on the scale and conditions of production, those skilled in the art can select a suitable reaction time according to actual conditions. For example, under the same reaction conditions, the present invention can complete the coating reaction process in less than 3 hours within the above-mentioned temperature range, which is much lower than the reaction time of more than 6 hours of the traditional sol-gel method, greatly improving the production efficiency.

[0025] The present invention has the advantage of being easy to operate. For example, in actual operation, a reaction container with a high-density stirring ball can be placed in a vibrating shaker, a reaction solvent, a hydrolyzing agent, a hydrolysis source and an absorbent to be coated can be added, and the reaction parameters can be controlled by a program to react. After the coating reaction is completed, the product can be recovered and purified in a common manner in the art to obtain a core-shell structured high magnetic permeability corrosion-resistant absorbent.

[0026] In the second aspect of the present invention, a high magnetic permeability corrosion-resistant absorbent is provided, which has strong corrosion resistance, low coating content, thin coating layer, and continuous, dense and mesopore-free. The absorbent is prepared by the preparation method of the first aspect of the present invention.

[0027] Preferably, in the high magnetic permeability corrosion-resistant absorbent, the coating layer is dense and continuous, has no mesopores, has a thickness of less than 40 nm, and has no obvious reaction in a strong acid solution.

[0028] Based on the above technical solutions, the design concept and principle of the present invention are as follows: The present invention proposes an efficient reaction system with high solid-liquid exchange frequency and dispersibility. Specifically, during the entire composite core-shell particle preparation process, the reaction system is fixed in a sealable reaction container equipped with high-density stirring balls in a constant temperature vibration shaker. The stirring balls in the reaction container are driven to roll by the vibration of the vibration shaker. The mechanical collision between the stirring balls further increases the disorder inside the system, increases the collision probability between the critical crystal nuclei of the hydrolysis product and the absorbent particles in the reaction system, and improves the solid-liquid exchange frequency, so that the coating reaction is dominated by the nucleation of the surface coating, forms a high nucleation density, and obtains a dense and uniform coating shell layer; in addition, the dispersibility of the absorbent is greatly improved, and it is not easy for the particles to aggregate and not easy to form sedimentation and aggregation at the bottom, thereby forming a uniform heterogeneous nucleation process on the surface of the core particles.

[0029] The preparation method of the present invention is simple and efficient, and can cover the dispersibility of particles in the reaction system. The surface shell layer of the prepared core-shell composite particles has the characteristics of ultra-low content, completeness, continuity and density, and can greatly improve the corrosion resistance of the particles while retaining the functionality of the core particles to the greatest extent. This technology provides an effective method for the corrosion resistance of active metals. The corrosion-resistant magnetic core-shell absorber particles obtained by this method have broad application prospects in the fields of radar absorption, electromagnetic shielding and protection in complex environments.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects: The invention provides a method for preparing a high magnetic permeability corrosion-resistant absorbent, and proposes a stirring ball vibration-assisted sol-gel method for preparing core-shell structure composite particles, which has the advantages of simple process and can be coated with an ultra-thin, dense and complete coating layer.

[0031] The present invention provides a high magnetic permeability corrosion-resistant absorber, the coating layer of which has the characteristics of extremely low continuous dense pore content, which greatly improves the corrosion resistance of the absorber; and has the advantages of low coating content and ultra-thinness, which further improves the surface resistivity of the absorber, thereby reducing the dielectric constant, improving the impedance matching and absorbing performance of the corresponding absorbing material, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The scanning electron microscope (SEM) images and transmission electron microscope (TEM) images of Examples 1-4; Figure 2 The N2 adsorption and desorption experiment and pore size distribution diagram of Example 3; Figure 3 It is the N2 adsorption and desorption experiment and pore size distribution diagram of Comparative Example 1; Figure 4 It is a comparison chart of acid etching pH of Examples 1-4 and Comparative Example 1; Figure 5 The saturation magnetization intensity comparison diagram of Examples 1-4 and Comparative Example 1 is shown in FIG. Figure 6 This is a comparison diagram of electromagnetic parameters of Examples 1-4 and Comparative Example 1 when the filling fraction in paraffin is 25 vol.%; Figure 7 This is a comparison chart of reflection loss performance of Examples 1-4 and Comparative Example 1 when the filling fraction in paraffin is 25 vol.% and the thickness is 1 mm. DETAILED DESCRIPTION

[0033] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0034] Example 1 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: 20 zirconia balls with a diameter of 10 mm were placed in a 200 mL polyethylene (PE) bottle, 54 mL deionized water and 108 mL anhydrous ethanol were added, and the reaction container was fixed in a constant temperature shaking table, the temperature was set to 20°C, and the speed was set to 150 r / min; after the system was stable, 1 mL NH3·H2O and 0.3 mL TEOS were added in sequence, and 2 g of flaky carbonyl iron powder was added after pre-hydrolysis for 10 min. The reaction time was set to 3 h, and the reaction container should be sealed except when adding chemicals; after the coating reaction was completed, the product was taken out for washing and placed in a 60°C oven for drying for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0035] 0.05 g of high magnetic permeability corrosion-resistant absorbent was placed in 20 mL of hydrochloric acid solution (pH=1.08), and the pH change was tested and recorded every 5 minutes. The pH did not change significantly within 40 minutes. In contrast, the uncoated carbonyl iron powder absorbent caused a dramatic change in pH value from the moment it was added to the hydrochloric acid solution.

[0036] The high permeability corrosion-resistant absorbent and paraffin were mixed evenly at a volume fraction of 25 vol.% for electromagnetic parameter testing. The electromagnetic parameters of the material were tested using the coaxial method according to the steps specified in SJ 20512-1995 "Test Methods for Complex Permittivity and Complex Permeability of Microwave High Loss Solid Materials", the same below. It was measured that when the thickness was 1 mm, the absorption bandwidth with reflection loss <-10 dB in 2-18 GHz was 4 GHz (11-15 GHz).

[0037] Example 2 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: 20 zirconia balls with a diameter of 10 mm were placed in a 200 mL PE bottle, 54 mL deionized water and 108 mL anhydrous ethanol were added, and the reaction container was fixed in a constant temperature shaking table, the temperature was set to 20 ℃, and the speed was set to 150 r / min; after the system was stable, 1 mL NH3·H2O and 0.3 mL TEOS were added in sequence, and 1 g of flaky carbonyl iron powder was added after pre-hydrolysis for 10 min. The reaction time was set to 3 h. Except when adding chemicals, the reaction container should be sealed; after the coating reaction was completed, the product was taken out for washing and placed in a 60 ℃ oven for drying for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0038] 0.05 g of high magnetic permeability corrosion-resistant absorbent was placed in 20 mL of hydrochloric acid solution (pH=1.08). The pH change was tested and recorded every 5 minutes. The results showed that the pH did not change significantly within 40 minutes.

[0039] The high magnetic permeability corrosion-resistant absorbent and paraffin were mixed evenly at a volume fraction of 25 vol.%, and the electromagnetic parameter test was carried out. It was measured that when the thickness was 1 mm, the absorption bandwidth with reflection loss <-10 dB in the range of 2-18 GHz was 5.2 GHz (11.1-16.3 GHz).

[0040] Example 3 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: Place 20 zirconia balls with a diameter of 10 mm in a 200 mL PE bottle, add 54 mL deionized water and 108 mL anhydrous ethanol, fix the reaction container in a constant temperature shaking table, set the temperature to 20 ℃, and set the speed to 150 r / min; after the system is stable, add 1 mL NH3·H2O and 0.3 mL TEOS in sequence, and add 0.75 g flaky carbonyl iron powder after pre-hydrolysis for 10 min. Set the reaction time to 3 h. Except when adding chemicals, the reaction container should be sealed; after the coating reaction is completed, take out the product for washing, and place it in a 60 ℃ oven for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0041] The specific surface area and pore size of the high magnetic permeability corrosion-resistant absorbent particles were tested by N2 adsorption and desorption test. The pore distribution results showed that there were no pores on the surface, and the specific surface area test result was 1.23 m 2 / g.

[0042] 0.05 g of high magnetic permeability corrosion-resistant absorbent was placed in 20 mL of hydrochloric acid solution (pH=1.08). The pH change was tested and recorded every 5 minutes. The results showed that the pH did not change significantly within 40 minutes.

[0043] The high magnetic permeability corrosion-resistant absorber was mixed with paraffin at a volume fraction of 25 vol.% and the electromagnetic parameters were tested. When the thickness was 1 mm, the absorption bandwidth with reflection loss <-10 dB in the range of 2-18 GHz was 6.5 GHz (11.5-18 GHz).

[0044] Example 4 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: 20 zirconia balls with a diameter of 10 mm were placed in a 200 mL PE bottle, 54 mL deionized water and 108 mL anhydrous ethanol were added, and the reaction container was fixed in a constant temperature shaking table, the temperature was set to 20 ℃, and the speed was set to 150 r / min; after the system was stable, 1 mL NH3·H2O and 0.3 mL TEOS were added in sequence, and 0.5 g flaky carbonyl iron powder was added after pre-hydrolysis for 10 min. The reaction time was set to 3 h. Except when adding chemicals, the reaction container should be sealed; after the coating reaction was completed, the product was taken out for washing and placed in a 60 ℃ oven for drying for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0045] 0.05 g of high magnetic permeability corrosion-resistant absorbent was placed in 20 mL of hydrochloric acid solution (pH=1.08). The pH change was tested and recorded every 5 minutes. The results showed that the pH did not change significantly within 40 minutes.

[0046] The high permeability corrosion-resistant absorber was mixed with paraffin at a volume fraction of 25 vol.% and the electromagnetic parameters were tested. When the thickness was 1 mm, the absorption bandwidth with reflection loss <-10 dB in the range of 2-18 GHz was 4.4 GHz (13.6–18 GHz).

[0047] Example 5 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: 20 zirconia balls with a diameter of 10 mm were placed in a 200 mL PE bottle, 54 mL deionized water and 108 mL anhydrous ethanol were added, and the reaction container was fixed in a constant temperature shaking table, the temperature was set to 20 °C, and the speed was set to 150 r / min; after the system was stable, 3 mL NH3·H2O and 3 mL TEOS were added in sequence, and after pre-hydrolysis for 10 min, 1 g of flaky FeNi alloy particles with a particle size distribution of 10-500 μm were added, and the reaction time was set to 3 h. Except when adding chemicals, the reaction container should be sealed; after the coating reaction was completed, the product was taken out for washing and placed in a 60 °C oven for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0048] The high magnetic permeability corrosion-resistant absorber was mixed with paraffin at a volume fraction of 15 vol.% and then the electromagnetic parameters were tested. When the thickness was 1 mm, the microwave absorption performance of RL < 6 dB in the range of 0.55-2.2 GHz could be achieved.

[0049] Example 6 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: Five zirconia balls (~15 g) with a diameter of 10 mm were placed in a 200 mL PE bottle, and 54 mL deionized water and 108 mL anhydrous ethanol were added. The reaction vessel was fixed in a constant temperature shaking table, the temperature was set to 20 ℃, and the speed was set to 150 r / min. After the system was stable, 1 mL NH3·H2O and 0.3 mL TEOS were added in sequence. After pre-hydrolysis for 10 min, 0.75 g flaky carbonyl iron powder was added. The reaction time was set to 3 h. Except when adding chemicals, the reaction vessel should be sealed. After the coating reaction was completed, the product was taken out for washing and placed in a 60 ℃ oven for drying for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0050] Example 7 The preparation method of the high magnetic permeability corrosion-resistant absorbent comprises the following steps: 30 zirconia balls (~90 g) with a diameter of 10 mm were placed in a 200 mL PE bottle, 54 mL deionized water and 108 mL anhydrous ethanol were added, and the reaction container was fixed in a constant temperature shaking table, the temperature was set to 20 ℃, and the speed was set to 150 r / min; after the system was stable, 1 mL NH3·H2O and 0.3 mL TEOS were added in sequence, and 0.75 g flaky carbonyl iron powder was added after pre-hydrolysis for 10 min. The reaction time was set to 3 h. Except when adding chemicals, the reaction container should be sealed; after the coating reaction was completed, the product was taken out for washing and placed in a 60 ℃ oven for drying for 6 h to obtain a high magnetic permeability corrosion-resistant absorbent.

[0051] Comparative Example 1 In this comparative example, 54 mL of deionized water and 108 mL of anhydrous ethanol were added to a three-necked flask reaction vessel, and fixed in a water bath, the temperature was set to 20 °C, and the stirring rod was set to a speed of 150 r / min. The reaction system is exactly the same as that in Example 3, that is, after the system is stable, 1 mL of NH3·H2O and 0.3 mL of TEOS are added in sequence, and 0.75 g of flaky carbonyl iron powder is added after pre-hydrolysis for 10 min. In order to complete the reaction, the reaction time is extended to 12 h. Except when adding drugs, the reaction vessel should be sealed. After the reaction is completed, the product is taken out for washing, and placed in a 60 °C oven for 6 h to obtain a carbonyl iron powder composite absorbent.

[0052] The specific surface area and pore size of carbonyl iron powder composite absorbent particles were tested by N2 adsorption and desorption test. The pore distribution results showed that there were a large number of pores on the surface with a pore size of 4-5 nm. The specific surface area test result was 1.85 m 2 / g.

[0053] 0.05 g of carbonyl iron powder composite absorbent was placed in 20 mL of hydrochloric acid solution (pH=1.08). The pH change was tested and recorded every 5 minutes. The results showed that the pH changed significantly within 40 minutes, and the pH increased from 1.08 to 1.4.

[0054] The carbonyl iron powder composite absorber and paraffin were mixed evenly at a volume fraction of 25 vol.% for electromagnetic parameter testing. When the thickness was 1 mm, the absorption bandwidth with reflection loss <-10 dB in the range of 2-18 GHz was 0 GHz.

[0055] The microscopic morphology of the high magnetic permeability corrosion resistant absorbent of Examples 1-4 was observed by SEM and TEM. The SEM images of Examples 1-4 show that the carbonyl iron powder@SiO2 core-shell particles (i.e., high magnetic permeability corrosion resistant absorbent) obtained by the stirring ball vibration assisted sol-gel method have excellent dispersibility and uniformity; the TEM image shows that the thickness of the SiO2 shell layer is very uniform, controllable and dense.

[0056] The N2 adsorption and desorption experiment and pore size distribution diagram of Example 3 are shown in FIG. Figure 2 As shown; the N2 adsorption and desorption experiment and pore size distribution diagram of Comparative Example 1 are shown Figure 3 The specific surface area test results of Example 3 and Comparative Example 1 show that the carbonyl iron powder@SiO2 core-shell particles obtained by the stirring ball vibration assisted sol-gel method have no pores on the surface, and the specific surface area test result is 1.23 m 2 / g. The carbonyl iron powder@SiO2 core-shell particles (i.e., carbonyl iron powder composite absorbent) obtained by traditional methods have a large number of pores on their surface, with a pore size of 4-5 nm and a specific surface area test result of 1.85 m 2 This comparison result shows that the core-shell particles obtained by the stirring ball vibration-assisted sol-gel method have a smaller specific surface area and a denser and non-porous shell.

[0057] The comparison of acid etching pH between Examples 1-4 and Comparative Example 1 is shown in the figure below: Figure 4 As shown. The results of the acid etching pH comparison diagram of Examples 1-4 and Comparative Example 1 show that the carbonyl iron powder @ SiO2 core-shell particles obtained by the stirring ball vibration assisted sol-gel method still have very good stability in a strong acid environment with a pH of about 1, while the carbonyl iron powder @ SiO2 core-shell particles obtained by the traditional method are severely corroded. The shell layer obtained by the stirring ball vibration assisted sol-gel method has an efficient protective effect on the active metal core and can greatly improve its corrosion resistance.

[0058] The saturation magnetization intensity comparison diagram of Examples 1-4 and Comparative Example 1 is as follows: Figure 5 As shown. The comparison of the saturation magnetization intensity of Examples 1-4 and the comparative example shows that the saturation magnetization intensity of the carbonyl iron powder @ SiO2 core-shell particles obtained by the stirring ball vibration-assisted sol-gel method is significantly higher than that of the carbonyl iron powder @ SiO2 core-shell particles obtained by the traditional method. It can be seen that the stirring ball vibration-assisted sol-gel method can use less non-magnetic material to achieve complete, uniform and dense coating of the core particles, while greatly retaining the saturation magnetization intensity of the core particles and giving them excellent corrosion resistance.

[0059] The electromagnetic parameters of Examples 1-4 and Comparative Example 1 when the filling fraction in paraffin is 25 vol.% are compared as shown in the figure below: Figure 6As shown; the reflection loss performance comparison diagram of Examples 1-4 and Comparative Example 1 in paraffin with a filling fraction of 25 vol.% and a thickness of 1 mm is shown as follows Figure 7 shown. Figure 6 , Figure 7 It shows that compared with the carbonyl iron powder @ SiO2 core-shell particles obtained by the traditional method, the carbonyl iron powder @ SiO2 core-shell particles obtained by the stirring ball vibration assisted sol-gel method have lower dielectric constant and higher magnetic permeability, thus showing better impedance matching and stronger loss capacity, and finally can achieve broadband microwave absorption at a composite material thickness of 1 mm. This is mainly due to the uniform shell thickness obtained by the stirring ball vibration assisted sol-gel method, which reduces the interface polarization compared to the non-uniform shell and further reduces the dielectric constant; the ultra-thin shell thickness and efficient reaction reduce the introduction of impurities and maximize the retention of magnetic permeability.

[0060] The above embodiment uses carbonyl iron powder @ SiO2 core-shell particles as an example to illustrate the method for preparing ultra-thin, complete and densely coated absorbers by a stirring ball vibration-assisted sol-gel method, but is not limited to carbonyl iron powder and magnetic metal absorbers. The method of the present invention can also be applied to the preparation of ultra-low content complete coating shell layers on the surfaces of other active particles.

[0061] Combined with the test results, the oxide coating layer of the high magnetic permeability corrosion-resistant absorber has the characteristics of low content and ultra-thinness, and its coating content can be controlled below 3.6 wt.%, which can effectively retain the functional characteristics of the core particles without being affected. Compared with the existing fully coated materials, the coating layer of the present invention has the characteristics of extremely low content of continuous dense pores, which can greatly improve the corrosion resistance of the absorber, and it can stably exist in harsh environments such as pH=1 solution. The ultra-thin, dense and complete coating layer of the high magnetic permeability corrosion-resistant absorber can further increase the surface resistivity of the absorber, thereby reducing the dielectric constant and improving the impedance matching and absorbing performance of the corresponding absorbing material.

[0062] The key to the present invention is to obtain high solid-liquid exchange frequency and particle dispersion effects through high-density stirring ball vibration, and to obtain a suitable coating monomer concentration by controlling the concentration and temperature of the hydrolysis source. This technology can achieve complete and dense coating of the particle surface when the coating content is less than 3.6 wt.%. Taking the coated carbonyl iron powder as an example, the coated core-shell composite particles can stably exist in a strong acid solution with a pH of 1, and the 1 mm thick absorbing material with it as the absorbent can achieve strong absorption of less than -10 dB at 11.5-18 GHz.

[0063] In summary, the present invention provides an effective method for the corrosion resistance of active metals, and the prepared high magnetic permeability corrosion-resistant absorber has broad application prospects in the fields of radar absorption, electromagnetic shielding and protection in complex environments.

[0064] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a high magnetic permeability corrosion-resistant absorbent, characterized in that: The steps include: A reaction container with a high-density stirring ball is placed in a vibrating shaker, and a coating reaction liquid is added; the reaction container is sealed and moves along a track to provide movement power for the high-density stirring ball and dispersion power for the coating reaction liquid, and the solid-liquid exchange and dispersion effect are increased by the speed difference between the high-density stirring ball and the coating reaction liquid, and a coating reaction is performed to obtain a high magnetic permeability corrosion-resistant absorbent with a core-shell structure; wherein the components of the coating reaction liquid include a reaction solvent, a hydrolyzing agent, a hydrolysis source, and an absorbent to be coated; the high-density stirring ball is chemically inert during the coating reaction, and its density is 3-10 times the density of the coating reaction liquid, and its diameter is 1-10 mm; the ratio of the total mass of the high-density stirring ball to the mass of the coating reaction liquid is 1:10-3:

5.

2. The method for preparing the high magnetic permeability corrosion-resistant absorbent according to claim 1, characterized in that: The reaction solvent includes a mixed solvent of water and ethanol, wherein the proportion of water is 20 vol.%-80 vol.%.

3. The method for preparing the high magnetic permeability corrosion-resistant absorbent according to claim 1, characterized in that: The hydrolyzing agent includes aqueous ammonia, and the concentration of the aqueous ammonia is 25 wt.%-28 wt.%.

4. The method for preparing the high magnetic permeability corrosion-resistant absorbent according to claim 1, characterized in that: The hydrolysis source includes tetraethoxysilane.

5. The method for preparing the high magnetic permeability corrosion-resistant absorbent according to claim 1, characterized in that: The absorbent to be coated is in a sheet-like structure with an average particle size of 3-500 μm.

6. The method for preparing the high magnetic permeability corrosion resistant absorbent according to claim 1, characterized in that: Calculated by the percentage of the components in the coating reaction solution, the content of each component is as follows: absorbent to be coated <5 wt.%, hydrolysis source <2 wt.%, hydrolysis agent <2 wt.%, and the remainder is reaction solvent.

7. The method for preparing the high magnetic permeability corrosion-resistant absorbent according to claim 1, characterized in that: The rotating speed of the vibration shaker is 50-300 r / min.

8. The method for preparing the high magnetic permeability corrosion resistant absorbent according to claim 1, characterized in that: The coating reaction temperature is 10-30°C.

9. A high magnetic permeability corrosion resistant absorbent, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. The high magnetic permeability corrosion-resistant absorbent according to claim 9, characterized in that: In the high magnetic permeability corrosion-resistant absorbent, the coating layer is dense and continuous, has no mesopores, has a thickness of less than 40 nm, and has no obvious reaction in a strong acid solution.

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