A method and application for preparing a composite electromagnetic wave absorbing material by high-speed shear stress

Abstract

The present invention discloses a method and application for preparing a composite electromagnetic wave absorbing material by high-speed shear stress, belonging to the technical field of functional materials. The present invention controls the granulation process by high-speed shear stress to obtain a microparticle structure with a thermal barrier protective layer composed of a composite of silicon glass and SiO2 on the outer layer and graphene on the inner layer. By controlling the heat treatment temperature, the shear stress inside the microparticles is adjusted. The method of the present invention has good repeatability, low cost, environmental friendliness, is clean and non-toxic, is easy to mass-produce, and the structure and morphology of the obtained composite electromagnetic wave absorbing material are beneficial to electromagnetic wave absorption, and it is an ideal composite electromagnetic wave absorbing material that can be practically applied.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a method and application for preparing a composite electromagnetic wave absorbing material by high-speed shear stress. Background Art

[0002] With the rapid development of information technology, especially microwave communication technology, the electromagnetic radiation pollution existing in our environment has become a problem that cannot be ignored. It not only harms human health but also interferes with the operation of electronic devices. At the same time, with the rapid development of modern electronic countermeasure technology, electromagnetic wave absorbing materials have attracted more and more extensive attention from military experts. Therefore, it is urgent to develop high-performance electromagnetic wave absorbing materials.

[0003] Currently, the electromagnetic wave absorbing materials at home and abroad mainly include several main types such as ceramic absorbing materials, carbon absorbing materials, and ferrite absorbing materials. Ferrite absorbing materials will lose their magnetism at high temperatures and thus lose their wave-absorbing performance, which greatly limits their applications. And ceramic-based absorbing materials are often heavy, which is also not conducive to their wide applications. Carbon absorbing materials (such as carbon spheres, porous carbon, carbon nanotubes, graphene, and reduced graphene oxide, etc.) have become the most widely used electromagnetic wave absorbing materials because of their advantages such as light weight, low cost, and good conductivity. However, single carbon materials still have some problems. For example, the dielectric constant of single carbon absorbing materials is often higher than that of air, with poor impedance matching, resulting in that when electromagnetic waves propagate to the material surface, they are more inclined to be reflected and difficult to enter and be absorbed, leading to poor wave-absorbing performance of single carbon absorbing materials.

[0004] Graphene materials have received extensive attention due to their unique two-dimensional structure, ultra-low density, high specific surface area, excellent environmental stability and other excellent properties. However, because the dielectric constant of graphene is higher than that of air and the impedance matching is poor, most electromagnetic waves are difficult to be absorbed when incident on the graphene surface, resulting in its poor wave-absorbing performance. Therefore, providing a new method for preparing composite electromagnetic wave absorbing materials to improve the wave-absorbing performance of graphene materials is of great significance to the field of wave-absorbing materials. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a method and application for preparing a composite electromagnetic wave absorbing material by high-speed shear stress.

[0006] To achieve the above object, the present invention provides a method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress, including the following steps:

[0007] (1) Add an aqueous sodium silicate solution to glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide, and stir and mix evenly to obtain a wet mixed solid A;

[0008] (2) Granulate the wet mixed solid A by ball milling and dry it to obtain solid powder A;

[0009] (3) Add the solid powder A and hexagonal boron nitride powder to the sodium silicate aqueous solution again to obtain wet mixed solid B;

[0010] (4) Granulate the wet mixed solid B by ball milling and dry it to obtain solid powder B;

[0011] (5) Add the solid powder B to the sodium silicate aqueous solution again to obtain wet mixed solid C;

[0012] (6) Granulate the wet mixed solid C by ball milling to form particles C with a particle size of 10 - 80 μm;

[0013] (7) Dry the particles C to obtain solid powder C;

[0014] (8) Heat-treat the solid powder C to obtain a composite electromagnetic wave absorbing material.

[0015] In the present invention, during the material mixing, the high-speed shear stress granulation process, and the heat treatment process of the reduced graphene oxide, the external glass fiber powder and hexagonal boron nitride powder form a relatively dense coating layer composed of SiO2 and sodium glass under high-speed shear stress. This coating layer has excellent wave-transmitting performance, a low dielectric constant, and after being compounded with the reduced graphene oxide, it can regulate the overall dielectric constant of the composite material within a suitable range, thereby achieving impedance matching. Therefore, this composite material structure has the potential to become an excellent electromagnetic wave absorbing material.

[0016] The method of the present invention has good repeatability, low cost, environmental friendliness, is clean and non-toxic, is easy to produce on a large scale, and the structure and morphology of the synthesized composite electromagnetic wave absorbing material are beneficial to electromagnetic wave absorption, making it an ideal composite electromagnetic wave absorbing material for practical applications.

[0017] Further, the mass fraction of the sodium silicate aqueous solution added in steps (1), (3), and (5) is 6 - 8 wt% of the mixture.

[0018] Further, in step (1), the mass ratio of the glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide is 20 - 25:10 - 13:400 - 410.

[0019] Further, the mass ratio of the glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide is 2:1:40.

[0020] Further, in steps (2), (4), and (6), the ball milling granulation is carried out in a planetary ball mill. Using a planetary ball mill for high-speed shear granulation, a composite electromagnetic wave absorbing material is fabricated through a high-speed shear stress granulation process, thereby alleviating the high impedance matching characteristics of reduced graphene oxide itself and enhancing the electromagnetic absorption performance of the composite electromagnetic wave absorbing material. The outer ceramic coating also plays a role in thermal barrier protection. In the present invention, by adjusting the shear linear velocity during ball milling, the shear stress acting on the graphene sheets is controlled to adjust the microparticle size of the coating structure, and thus the adjustment of the wave absorption performance is achieved.

[0021] Further, in steps (2), (4), and (6), the shear linear velocity during ball milling is 5840 - 18840 m / s, preferably 5840 m / s, 10880 m / s, or 18840 m / s, and more preferably 18840 m / s.

[0022] Further, in steps (2), (4), and (7), the drying temperature is 400 °C.

[0023] Further, in step (8), the temperature of the heat treatment is 1000 °C, and the time of the heat treatment is 8 hours.

[0024] A composite electromagnetic wave absorbing material is prepared according to the above method.

[0025] The application of the described composite electromagnetic wave absorbing material in the field of wave absorption.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] In the present invention, through a high-speed shear stress granulation process, a microparticle structure with a thermal barrier protection layer composed of a composite of silicon glass and SiO2 on the outer layer and graphene on the inner layer is obtained. By controlling the shear linear velocity, the adjustment of the shear stress inside the microparticles is achieved, the number of graphene sheets in the coating structure microparticles is controlled, and the graphene sheets show slip, resulting in a change in the microparticle size. Thus, the high impedance matching characteristics of reduced graphene oxide itself are alleviated, the electromagnetic absorption performance is enhanced, and further the electromagnetic absorption performance of the material is adjusted.

[0028] The good wave absorption performance of the composite electromagnetic wave absorbing material of the present invention can be attributed to its special structure. The shear stress existing during the heat treatment process of the present invention causes the graphene sheets to slip, making it easier to obtain a glass / graphene coating structure with smaller microparticles. This structure enables the incident electromagnetic waves to be successfully induced into the material interior and utilizes the internal graphene layer to absorb the electromagnetic waves.

[0029] The method of the present invention has good repeatability, low cost, environmental friendliness, is clean and non-toxic, is easy to produce on a large scale, and the structure and morphology of the synthesized ceramic / graphene aerogel microwave absorption material are beneficial to electromagnetic wave absorption. It is an ideal composite electromagnetic wave absorption material for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0031] Figure 1 Scanning electron microscope (SEM) pictures of the composite electromagnetic wave absorption materials prepared in Examples 1 to 4, where (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4;

[0032] Figure 2 Schematic diagram of the microwave absorption performance of the composite electromagnetic wave absorption material prepared in Example 1 in the frequency range of 2 - 18 GHz.

[0033] Figure 3 Schematic diagram of the microwave absorption performance of the composite electromagnetic wave absorption material prepared in Example 2 in the frequency range of 2 - 18 GHz.

[0034] Figure 4 Schematic diagram of the microwave absorption performance of the composite electromagnetic wave absorption material prepared in Example 3 in the frequency range of 2 - 18 GHz.

[0035] Figure 5 Schematic diagram of the microwave absorption performance of the composite electromagnetic wave absorption material prepared in Example 4 in the frequency range of 2 - 18 GHz. DETAILED DESCRIPTION OF THE INVENTION

[0036] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0037] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0038] 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. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to those documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0039] Without departing from the scope or spirit of this invention, various modifications and variations can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0040] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0041] The reduced graphene oxide used in the following examples and comparative examples of this invention is the AP-3 type reduced graphene oxide purchased from Luobei Yunshan Carbon Industry.

[0042] The glass instruments and equipment used are all common instruments and equipment in this field.

[0043] Example 1

[0044] (1) Add an aqueous sodium silicate solution (with a mass fraction of 8 wt% of the mixture) to glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide with a mass ratio of 2:1:40, and stir and mix evenly to obtain a moist mixed solid A;

[0045] (2) Shear granulate the mixed solid A using a planetary ball mill at a linear velocity of 18840 m / s, and place it in an oven at 400 °C for drying to obtain a solid powder A;

[0046] (3) Add the aqueous sodium silicate solution (with a mass fraction of 8 wt% of the mixture) again to the solid powder A and hexagonal boron nitride powder to obtain a mixed solid B;

[0047] (4) Shear granulate the mixed solid B using a planetary ball mill at a linear velocity of 18840 m / s, and place it in an oven at 400 °C for drying to obtain a solid powder B;

[0048] (5) Add the aqueous sodium silicate solution (with a mass fraction of 8 wt% of the mixture) again to the solid powder B to obtain a mixed solid C;

[0049] (6) Shear granulate the mixed solid C using a planetary ball mill at a linear velocity of 18840 m / s to form particles C with a particle size of 10 - 80 μm;

[0050] (7) Place the particles C in an oven at 400 °C for drying to obtain the composite electromagnetic wave absorbing material.

[0051] Example 2

[0052] (1) Add an aqueous sodium silicate solution (with a mass fraction of 7 wt% of the mixture) to glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide with a mass ratio of 2:1:40, and stir and mix evenly to obtain a moist mixed solid A;

[0053] (2) Shear granulate the mixed solid A using a planetary ball mill at a linear velocity of 5840 m / s, and place it in an oven at 400 °C for drying to obtain solid powder A;

[0054] (3) Add an aqueous sodium silicate solution (with a mass fraction of 7 wt% of the mixture) again to solid powder A and hexagonal boron nitride powder to obtain a mixed solid B;

[0055] (4) Shear granulate the mixed solid B using a planetary ball mill at a linear velocity of 5840 m / s, and place it in an oven at 400 °C for drying to obtain solid powder B;

[0056] (5) Add an aqueous sodium silicate solution (with a mass fraction of 6 wt% of the mixture) again to solid powder B to obtain a mixed solid C;

[0057] (6) Shear granulate the mixed solid C using a planetary ball mill at a linear velocity of 5840 m / s to form particles C with a particle size of 600 - 900 μm;

[0058] (7) Place the particles C in an oven at 400 °C for drying to obtain solid powder C;

[0059] (8) Place solid powder C in a high-temperature air furnace for heat treatment at 1000 °C for 8 hours to obtain the composite electromagnetic wave absorbing material.

[0060] Example 3

[0061] (1) Add an aqueous sodium silicate solution (with a mass fraction of 6 wt% of the mixture) to glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide with a mass ratio of 2:1:40, and stir and mix evenly to obtain a moist mixed solid A;

[0062] (2) Shear granulate the mixed solid A using a planetary ball mill at a linear velocity of 10880 m / s, and place it in an oven at 400 °C for drying to obtain solid powder A;

[0063] (3) Add an aqueous sodium silicate solution (both with a mass fraction of 6 wt% of the mixture) to solid powder A and hexagonal boron nitride powder to obtain mixed solid B;

[0064] (4) Use a planetary ball mill to shear granulate the mixed solid B at a linear velocity of 10880 m / s, and place it in an oven at 400 °C to dry to obtain solid powder B;

[0065] (5) Add an aqueous sodium silicate solution (both with a mass fraction of 6 wt% of the mixture) to solid powder B to obtain mixed solid C;

[0066] (6) Use a planetary ball mill to shear granulate the mixed solid C at a linear velocity of 10880 m / s to form particles C with a particle size of 200 - 400 μm;

[0067] (7) Place the particles C in an oven at 400 °C to dry to obtain solid powder C;

[0068] (8) Place the solid powder C in a high-temperature air furnace for heat treatment at 1000 °C for 8 hours to obtain a composite electromagnetic wave absorption material.

[0069] Example 4

[0070] (1) Add an aqueous sodium silicate solution (both with a mass fraction of 6 wt% of the mixture) to glass fiber powder, hexagonal boron nitride powder, and reduced graphene oxide with a mass ratio of 2:1:40, and stir and mix evenly to obtain a wet mixed solid A;

[0071] (2) Use a planetary ball mill to shear granulate the mixed solid A at a linear velocity of 18840 m / s, and place it in an oven at 400 °C to dry to obtain solid powder A;

[0072] (3) Add an aqueous sodium silicate solution (both with a mass fraction of 6 wt% of the mixture) to solid powder A and hexagonal boron nitride powder again to obtain mixed solid B;

[0073] (4) Use a planetary ball mill to shear granulate the mixed solid B at a linear velocity of 18840 m / s, and place it in an oven at 400 °C to dry to obtain solid powder B;

[0074] (5) Add an aqueous sodium silicate solution (with a mass fraction of 6 wt% in both cases) to solid powder B again to obtain mixed solid C;

[0075] (6) Use a planetary ball mill to shear granulate the mixed solid C at a linear velocity of 18840 m / s to form particles C with a particle size of 10 - 80 μm;

[0076] (7) Place the particles C in an oven at 400 °C to dry to obtain solid powder C;

[0077] (8) The solid powder C is placed in a high-temperature air furnace and heat-treated at 1000° C. for 8 hours to obtain a composite electromagnetic wave absorbing material.

[0078] Figure 1 These are scanning electron microscope (SEM) images of the composite electromagnetic wave absorbing materials prepared in Examples 1 to 4, where (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4.

[0079] Figures 2 to 5 The following are schematic diagrams of the wave absorbing performance of the composite electromagnetic wave absorbing materials prepared in Examples 1 to 4 in the frequency range of 2 to 18 GHz. Figures 2 to 5 It can be seen that the composite material prepared in Example 1 has a reflection loss value of -9.03 dB at 8.48 GHz, corresponding to a thickness of 5.5 mm; the composite electromagnetic wave absorbing material prepared in Example 2 has a reflection loss value of -11.44 dB at 8.16 GHz, corresponding to a thickness of 5.5 mm, and the composite electromagnetic wave absorbing material prepared in Example 3 has significantly better absorbing performance than Example 2, especially the composite electromagnetic wave absorbing material prepared in Example 4 has a reflection loss value of -24.33 dB, corresponding to a thickness of 5.5 mm. The present invention uses a high-speed shear stress granulation process to gradually form a microparticle structure of glass-coated graphene from each component. By controlling the shear linear velocity during ball milling, the number of graphene sheets in the microparticles of the coated structure is controlled. The stress is released by heat treatment, thereby causing the graphene sheets to slip and the size of the microparticles to change, thereby alleviating the high impedance matching characteristics of the reduced graphene oxide itself, improving the electromagnetic absorption performance, and thus adjusting the electromagnetic absorption performance of the material. The shear stress present during the ball milling shearing process of the present invention causes the graphene sheets to slip, making it easier to obtain a glass / graphene-coated structure with smaller particles. This structure allows incident electromagnetic waves to be successfully channeled into the material's interior, where they are absorbed by the internal graphene layers. The composite electromagnetic wave absorbing material exhibits optimal absorption performance, particularly when the planetary ball mill is operated at a linear speed of 18,840 m / s and heat-treated at 1,000°C for 8 hours (Example 4).

[0080] Comparative Example 1

[0081] Same as Example 4, except that the heat treatment temperature in step (8) is 600°C.

[0082] Comparative Example 2

[0083] Same as Example 4, except that the heat treatment temperature in step (8) is 800°C.

[0084] Comparative Example 3

[0085] Same as Example 4, except that the heat treatment temperature in step (8) is 1200°C.

[0086] Comparative Example 4

[0087] Same as Example 4, except that the heat treatment temperature in step (8) is 1400 °C.

[0088] Comparative Example 5

[0089] Same as Example 4, except that the linear velocity during shear granulation in steps (2), (4), and (6) is 3500 m / s.

[0090] Comparative Example 6

[0091] Same as Example 4, except that the linear velocity during shear granulation in steps (2), (4), and (6) is 2000 m / s.

[0092] Comparative Example 7

[0093] Same as Example 4, except that the linear velocity during shear granulation in steps (2), (4), and (6) is 1000 m / s.

[0094] Effect Verification

[0095] In order to verify the wave absorption performance of the products obtained by the present invention, the products in Examples 1-4 and Comparative Examples 1-7 were subjected to microwave absorption tests. The test method is as follows: The electromagnetic wave absorption performance test mainly measures the complex permittivity and complex permeability of the material and through the following formula:

[0096]

[0097]

[0098] The quality of the wave absorption performance can be intuitively represented by the Reflection Loss (RL) value, which can be expressed by the following formula according to the transmission line theory:

[0099]

[0100]

[0101] Where f, d, and c are the frequency, absorber thickness, and the speed of light in free space respectively; Z0 - characteristic impedance of the space; Z in - input impedance. A reflection loss RL value < -10 dB represents 90.00% effective absorption, a reflection loss RL value < -20 dB represents 99.00% effective absorption, and a reflection loss RL value < -30 dB represents 99.90% effective absorption. The attenuation of electromagnetic waves in the material can be expressed by the following formula:

[0102]

[0103] Calculations are carried out to obtain the reflection loss value of the material. The electromagnetic wave absorption performance of the sample is studied using an Agilent VNA, model N5245A network vector analyzer. The sample powder and paraffin are uniformly mixed in a molten state of paraffin at a ratio of 20 wt.% of the sample mass to the total mass, and then pressed into a mold with an inner diameter of 3.04 mm and an outer diameter of 7 mm to obtain the required hollow coaxial cylinder. In the frequency range of 2 - 18 GHz, the number of sampling points is 201, and the real and imaginary parts of the complex permittivity and complex permeability of the sample are retained. The tangent of the dielectric loss angle and the tangent of the magnetic loss angle are equal to the ratio of the real part to the imaginary part. The test results are shown in Table 1.

[0104] Table 1 Microwave Absorption Test

[0105]

[0106] As can be seen from Table 1, the products of Examples 1 - 4 all have the best microwave absorption in the C - band or X - band. From the comparison between Example 4 and Examples 2 - 3 and Comparative Examples 5 - 7, it can also be seen that the linear velocity during shear granulation has an impact on the wave - absorbing performance. Only when the linear shear velocity is at a relatively high rotational speed, a large shear stress can accumulate between the graphene sheets, which is beneficial to granulation and sheet dispersion, and improves the wave - absorbing performance of the material. From the comparison between Example 4 and Comparative Examples 1 - 3, it can also be seen that heat treatment at high temperature, as well as the type and proportion of raw materials, are also important for the wave - absorbing performance. This is because graphene has been mostly wrapped by components such as sodium silicate during the granulation process. Only at a relatively high temperature can the shear stress accumulated during the shear granulation process be fully released, and the surface can be fully oxidized, thereby adjusting the impedance matching to improve the wave - absorbing performance.

[0107] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress, characterized in that, It includes the following steps: (1) Add an aqueous sodium silicate solution to glass fiber powder, hexagonal boron nitride powder and reduced graphene oxide, and stir and mix evenly to obtain a wet mixed solid A; (2) Ball-mill and granulate the wet mixed solid A, and dry it to obtain a solid powder A; (3) Add the solid powder A and hexagonal boron nitride powder to an aqueous sodium silicate solution again to obtain a wet mixed solid B; (4) Ball-mill and granulate the wet mixed solid B, and dry it to obtain a solid powder B; (5) Add the solid powder B to an aqueous sodium silicate solution again to obtain a wet mixed solid C; (6) Ball-mill and granulate the wet mixed solid C to form particles C with a particle size of 10-80 μm; (7) Dry the particles C to obtain a solid powder C; (8) Heat-treat the solid powder C to obtain a composite electromagnetic wave absorbing material; In steps (2), (4) and (6), the shear linear velocity during ball-milling is 5840-18840 m / s; In step (8), the heat-treatment temperature is 1000 °C and the heat-treatment time is 8 hours.

2. The method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress according to claim 1, characterized in that, In steps (1), (3) and (5), the mass fraction of the added aqueous sodium silicate solution is 6-8 wt% of the mixture.

3. The method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress according to claim 1, characterized in that, In step (1), the mass ratio of glass fiber powder, hexagonal boron nitride powder and reduced graphene oxide is 20-25:10-13:400-410.

4. The method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress according to claim 3, characterized in that, The mass ratio of glass fiber powder, hexagonal boron nitride powder and reduced graphene oxide is 2:1:

40.

5. The method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress according to claim 1, characterized in that, In steps (2), (4) and (6), the ball-milling and granulation are all carried out in a planetary ball mill.

6. The method for preparing a composite electromagnetic wave absorbing material by high-speed shear stress according to claim 1, characterized in that, In steps (2), (4) and (7), the drying temperature is 400 °C.

7. A composite electromagnetic wave absorbing material, characterized in that, Prepared according to any one of claims 1-6.

8. Application of the composite electromagnetic wave absorbing material according to claim 7 in the field of wave absorption.

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