Composite aerogel material and preparation method and application thereof

Abstract

This invention relates to a composite aerogel material, its preparation method, and its applications. The invention selects cobalt and carbon as components of the microwave absorber, utilizing the synergistic effect between the different components to maintain a wide effective absorption bandwidth while exhibiting strong electromagnetic wave attenuation. Chitosan aerogel is prepared using directional cryogenic casting, followed by a high-temperature carbonization reaction in a tube furnace to obtain an aerogel loaded with cobalt particles. The process of this invention is simple and easy to implement; the composite aerogel microwave absorber can be prepared through directional cryogenic casting and a one-step carbonization process.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a composite aerogel material, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the rapid development of wireless communication technology and the widespread application of electronic devices, problems such as electromagnetic radiation and electrical interference have become increasingly serious, posing a significant threat to human health and precision electronic equipment. Therefore, finding solutions to electromagnetic pollution and related issues has garnered widespread attention. High-performance electromagnetic wave absorbing materials can effectively draw incident electromagnetic waves into the absorber and dissipate them as heat, thus weakening and attenuating the electromagnetic waves. This benefits human protection and the stealth capabilities of military equipment. While traditional magnetic metal absorbing materials possess high saturation magnetization and strong magnetic loss capacity, their susceptibility to oxidation and high density result in insufficient overall absorption performance, severely limiting their practical applications. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an aerogel composite material loaded with cobalt metallic particles and its preparation method, applicable to electromagnetic wave absorption. The aerogel composite material maintains a wide effective absorption bandwidth while possessing strong loss capacity. Furthermore, the preparation method of this invention is simple and easy to implement, readily adaptable for large-scale production, and shows promising prospects for industrial application.

[0005] In a first aspect, the present invention provides a method for preparing an aerogel composite material, the method comprising the following steps:

[0006] (1) Dissolve cobalt salt and chitosan in an aqueous solution, and stir with an appropriate amount of acetic acid solution to form a hydrogel precursor;

[0007] (2) The hydrogel precursor is transferred into a mold for cryogenic casting, and then dried to allow the ice crystals to sublimate, thus obtaining dry aerogel.

[0008] (3) Carbonize the dry aerogel to obtain the aerogel composite material.

[0009] Compared with existing technologies, the synthesis method of the present invention is simple and easy to implement, and the prepared aerogel composite material has a honeycomb-like pore size with cobalt metal particles loaded on the pore walls.

[0010] In a second aspect, the present invention provides an aerogel composite material prepared by the above preparation method, wherein the aerogel composite material contains C, N, O and Co elements, wherein the Co element exists in the form of an element, and the C, N and O elements are derived from the precursor chitosan.

[0011] In the aerogel composite material prepared by the present invention, firstly, the presence of the honeycomb porous structure causes multiple scattering of incident electromagnetic waves, thereby enhancing the material's loss of electromagnetic waves; secondly, metallic cobalt has high saturation magnetization and good stability, which also improves the material's magnetic loss capability; and thirdly, the porous and lightweight characteristics of the aerogel material are beneficial for broadening the application fields of the material.

[0012] A third aspect of the present invention provides a composite microwave absorbing material, the composite microwave absorbing material comprising the aforementioned aerogel composite material and an adhesive.

[0013] The above-mentioned method for preparing composite microwave absorbing materials involves mixing aerogel loaded with cobalt particles with paraffin to obtain the microwave absorbing material.

[0014] In a fourth aspect, the present invention provides an application of a composite aerogel material and / or the aforementioned composite absorbing material in the field of electromagnetic wave absorption.

[0015] The beneficial effects of this invention are as follows:

[0016] (1) In the aerogel composite material prepared by the present invention, the presence of honeycomb porous structure causes multiple scattering of incident electromagnetic waves, which enhances the material’s loss of electromagnetic waves; cobalt metal has high saturation magnetization and good stability, and at the same time improves the magnetic loss capability of the material; the porous and lightweight characteristics of aerogel material are conducive to broadening the application field of the material.

[0017] (2) Compared with the prior art, the synthesis method of the present invention is simple, requiring only freeze casting and one-step high-temperature carbonization reaction to obtain the final product. Moreover, the prepared aerogel loaded with cobalt metal particles has an ordered honeycomb-like pore size, the cobalt metal particles are evenly distributed, and no other by-products are generated during the heat treatment process.

[0018] (3) The material prepared by this invention has good wave absorption effect, and therefore is expected to be widely used in the preparation of electromagnetic wave absorbing materials.

[0019] (4) A microwave absorbing material was obtained by combining aerogel loaded with cobalt particles with paraffin. The reflection loss of electromagnetic waves at high frequency (13.06 GHz) reached -62.62 dB, the matching thickness was 2.95 mm, and the effective absorption bandwidth at 3.06 mm was 8.53 GHz. The aerogel loaded with cobalt particles has excellent microwave absorption performance and therefore has wide application value. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 The image shows the XRD pattern of the aerogel loaded with cobalt particles prepared in Example 1.

[0022] Figure 2 The figure in the image is an SEM image of the final sample prepared in step (1) of Example 1.

[0023] Figure 3 The figure in the image is a TEM image of the aerogel loaded with cobalt particles obtained in Example 1.

[0024] Figure 4 Figure (a) shows the real part of the dielectric constant of the aerogel loaded with cobalt particles prepared in Example 1, Figure (b) shows the imaginary part of the dielectric constant, and Figure (c) shows the dielectric loss tangent.

[0025] Figure 5 Figure (a) shows the real part of the magnetic permeability of the aerogel loaded with cobalt particles prepared in Example 1, Figure (b) shows the imaginary part of the magnetic permeability, and Figure (c) shows the magnetic loss tangent.

[0026] Figure 6 The reflection loss diagram of the aerogel absorber loaded with cobalt particles prepared for the experimental example.

[0027] Figure 7 The image shows the SEM image of the sample prepared in Comparative Example 1.

[0028] Figure 8 The image shows the reflection loss of the sample prepared in Comparative Example 1. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] This invention provides a composite aerogel material, its preparation method, and its application.

[0031] In one embodiment of the present invention, a method for preparing a composite aerogel material includes the following steps:

[0032] (1) Dissolve cobalt salt and chitosan in an aqueous solution, and stir with an appropriate amount of acetic acid solution to form a hydrogel precursor;

[0033] (2) The hydrogel precursor is transferred into a mold for cryogenic casting, and then dried to allow the ice crystals to sublimate, thus obtaining dry aerogel.

[0034] (3) Carbonize the dry aerogel to obtain the aerogel composite material.

[0035] In some embodiments of the present invention, the cobalt salt is cobalt chloride hexahydrate or cobalt acetate.

[0036] In some embodiments of the present invention, the chitosan has a low viscosity, <200 mPa·s.

[0037] In some embodiments of the present invention, acetic acid is of analytical grade.

[0038] In some embodiments of the present invention, the addition ratio of cobalt salt, chitosan, acetic acid and deionized water is (0.1–0.5)g:(0.1–1)g:(0.1–0.5)mL:(2–30)mL; preferably (0.1–0.4)g:(0.2–0.4)g:(0.1–0.3)mL:(2–20)mL; and more preferably 0.143g:0.3g:0.2mL:10mL.

[0039] In some embodiments of the present invention, cryogenic casting is unidirectional cryogenic casting, in which a polytetrafluoroethylene mold with a metal backing is placed in liquid nitrogen and unidirectional freezing is achieved by utilizing a bottom-up temperature gradient.

[0040] In some embodiments of the present invention, the drying method is freeze-vacuum drying.

[0041] In some embodiments of the present invention, the carbonization temperature of the tube furnace is 500–900°C, the heating rate is 1–5°C / min, and the reaction time is 1–5 h; preferably, the reaction temperature is 600–800°C, the heating rate is 1.5–2.5°C / min, and the reaction time is 1.5–3.5 h; more preferably, the reaction temperature is 700°C, the heating rate is 2°C / min, and the reaction time is 2 h. During this process, the degree of graphitization of the carbonaceous material gradually increases with continuous heating, and cobalt ions are reduced to elemental Co.

[0042] In one embodiment of the present invention, an aerogel composite material is obtained by the above preparation method. The aerogel contains C, N, O and Co elements, wherein the Co element exists in the form of elemental form, and the C, N and O elements are derived from the precursor chitosan.

[0043] The aerogel loaded with cobalt particles forms a honeycomb-like pore structure through directional cryogenic casting. Then, in a tube furnace under a nitrogen atmosphere, cobalt ions are reduced to metallic cobalt by the matrix carbon to form the final composite material.

[0044] In one embodiment of the present invention, a composite microwave absorbing material is provided, the composite microwave absorbing material comprising the aforementioned aerogel composite material and an adhesive; further, the mass ratio of the aerogel composite material and the adhesive is 0.5-2:8-9.5, more preferably 1:9.

[0045] Furthermore, the adhesive is paraffin wax.

[0046] The paraffin is solid paraffin. The solid paraffin and the aerogel loaded with cobalt particles are mixed by stirring or other means, and the paraffin is not on the surface of the aerogel loaded with cobalt particles.

[0047] In one embodiment of the present invention, the method for preparing a composite microwave absorbing material involves mixing an aerogel loaded with cobalt particles and a binder to obtain the composite microwave absorbing material.

[0048] Furthermore, the temperature at which the aerogel and binder loaded with cobalt particles are mixed is 40–60°C.

[0049] After uniform mixing of cobalt-loaded aerogel and paraffin, the cobalt-loaded aerogel and paraffin form a basically uniform distribution in the cobalt-loaded aerogel composite microwave absorbing material. Mixing at a certain high temperature enhances the fluidity of the paraffin, facilitating uniform mixing between the paraffin and the cobalt-loaded aerogel.

[0050] In one embodiment of the present invention, the application of the aerogel loaded with cobalt metal particles and / or the composite absorbing material in the field of electromagnetic wave absorption is described.

[0051] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0052] Example 1

[0053] (1) Dissolve 0.143g cobalt chloride hexahydrate, 0.3g chitosan and 0.2mL acetic acid in 10mL deionized water. After mechanical stirring, a transparent hydrogel precursor is formed. Then, the hydrogel is transferred to a mold and cryogenically cast to form chitosan aerogel.

[0054] (2) Transfer the above aerogel to a tube furnace, heat it to 700°C at a heating rate of 2°C / min and hold it for 2 hours, then let it cool naturally to room temperature.

[0055] Figure 1 The image shows the XRD pattern of the aerogel loaded with cobalt particles prepared in Example 1, confirming that it was prepared from cobalt and carbon.

[0056] Figure 2The image shown is an SEM image of the sample obtained in Example 1, which shows that the pore size of the aerogel is 10 μm.

[0057] Figure 3 The figure in the image is a TEM image of the aerogel loaded with cobalt metal particles obtained in Example 1.

[0058] Example 2

[0059] (1) Dissolve 0.286g cobalt chloride hexahydrate, 0.3g chitosan and 0.2mL acetic acid in 10mL deionized water. After mechanical stirring, a transparent hydrogel precursor is formed. Then the hydrogel is transferred to a mold and cryogenically cast to form chitosan aerogel.

[0060] (2) Transfer the above aerogel to a tube furnace, heat it to 700°C at a heating rate of 2°C / min and hold it for 2 hours, then let it cool naturally to room temperature.

[0061] Experimental Example

[0062] The aerogel containing cobalt particles from Example 1 and paraffin were mixed (mass ratio 1:9) to obtain a composite microwave absorbing material. Electromagnetic parameters were tested using an Agilent Technologies E8363A electromagnetic vector network analyzer, and the microwave absorption performance of the material was calculated based on these parameters. Figure 4 The results are shown in –6.

[0063] from Figure 4 As can be seen, the aerogel composite microwave absorbing material loaded with cobalt particles has a strong dielectric loss.

[0064] from Figure 5 As can be seen, the aerogel composite microwave absorbing material loaded with cobalt particles has strong magnetic loss.

[0065] from Figure 6 As can be seen, the aerogel absorbing material loaded with cobalt particles exhibits excellent electromagnetic wave absorption performance. The absorption effect is best at a thickness of 2.95 mm, achieving a reduction of -62.62 dB; at 3.06 mm, the effective absorption bandwidth is 8.53 GHz.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that in step (1), the mass of cobalt chloride hexahydrate is increased to 0.286 g, while the rest remains unchanged. Electromagnetic parameters were tested using an Agilent Technologies E8363A electromagnetic vector network analyzer, and the absorption performance of the material was calculated based on the electromagnetic parameters, showing poor absorption effect.

[0068] Figure 7 The SEM image of the material prepared in Comparative Example 1 shows that due to the high content of cobalt salt, agglomeration of metallic cobalt particles occurred on the pore walls of the aerogel. Figure 8 The performance diagram of the sample prepared for Comparative Example 1 shows that the reflection loss is not as good as that of Example 1 in the 2–18 GHz range, and the absorption performance is poor.

[0069] 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 an aerogel composite material, characterized in that, Includes the following steps: (1) Cobalt salt and chitosan are dissolved in an aqueous solution, and a hydrogel precursor is formed by adding an appropriate amount of acetic acid solution and stirring. The addition ratio of cobalt salt, chitosan, acetic acid and deionized water is (0.1–0.143) g: (0.1–1) g: (0.1–0.5) mL: (2–30) mL. The cobalt salt is cobalt chloride hexahydrate. (2) The hydrogel precursor is transferred into the mold for cryogenic casting, and then dried to sublimate the ice crystals to obtain dry aerogel; the polytetrafluoroethylene mold with a metal backing is placed in liquid nitrogen to achieve unidirectional cryogenic casting. (3) Carbonize the dry aerogel to obtain the aerogel composite material; In the aerogel composite material, the presence of a honeycomb porous structure causes multiple scattering of incident electromagnetic waves, thereby enhancing the material's ability to absorb electromagnetic waves.

2. The preparation method according to claim 1, characterized in that, The chitosan has a low viscosity, with a viscosity of <200 mPa·s; the acetic acid is of analytical grade.

3. The preparation method according to claim 1, characterized in that, The ratio of cobalt salt, chitosan, acetic acid and deionized water is: (0.1–0.143) g : (0.2–0.4) g : (0.1–0.3) mL : (2–20) mL.

4. The preparation method according to claim 3, characterized in that, The ratio of cobalt salt, chitosan, acetic acid, and deionized water is 0.143 g: 0.3 g: 0.2 mL: 10 mL.

5. The preparation method according to claim 1, characterized in that, The dry aerogel was placed in a tube furnace for primary carbonization; the carbonization temperature of the tube furnace was 500–900℃, the heating rate was 1–5℃ / min, and the reaction time was 1–5h.

6. The preparation method according to claim 5, characterized in that, The carbonization temperature is 600–800 ℃, the heating rate is 1.5–2.5 ℃ / min, and the reaction time is 1.5–3.5 h.

7. The preparation method according to claim 6, characterized in that, The carbonization temperature is 700 °C, the heating rate is 2 °C / min, and the reaction time is 2 h.

8. The aerogel composite material prepared by the preparation method according to any one of claims 1-7, characterized in that, The aerogel composite material contains C, N, O and Co elements, wherein Co exists in elemental form, and C, N and O elements are derived from the precursor chitosan.

9. A composite microwave absorbing material, characterized in that, The composite absorbing material includes the aerogel composite material and adhesive as described in claim 8.

10. The composite absorbing material according to claim 9, characterized in that, The mass ratio of the aerogel composite material to the adhesive is (0.5-2):(8-9.5).

11. The composite absorbing material according to claim 10, characterized in that, The mass ratio of the aerogel composite material to the adhesive is 1:

9.

12. The composite absorbing material according to claim 10, characterized in that, The adhesive is paraffin wax.

13. The composite absorbing material according to claim 9, characterized in that, A composite microwave absorbing material is obtained by mixing aerogel composite materials and adhesives.

14. The composite absorbing material according to claim 13, characterized in that, The aerogel composite material and the adhesive are mixed at a temperature of 40–60 °C.

15. The application of the aerogel composite material of claim 8 and / or the composite absorbing material of any one of claims 9-14 in the field of electromagnetic wave absorption.

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