Composite electromagnetic wave-absorbing material and preparation method thereof

Abstract

The application discloses a kind of composite electromagnetic wave-absorbing materials and preparation method thereof.By coating glass, SiO2 and other materials on the outside of graphene, the coating layer has wave-transparent characteristics and can be used to adjust the impedance matching of the composite material, and can also play the role of thermal barrier layer to protect the internal graphene from being oxidized at high temperature.Specifically, a kind of composite electromagnetic wave-absorbing material with special glass / graphene coating structure is prepared by liquid sodium silicate foaming method, thereby relieving the high impedance matching characteristics of reduced graphene oxide itself and improving the electromagnetic absorption performance of the composite electromagnetic wave-absorbing material.Further, by adjusting the heat treatment temperature, the shear stress generated by thermal stress on the graphene sheet is controlled to adjust the particle size of the coating structure, and thus the adjustment of the wave-absorbing performance is realized.The preparation method of the application is simple, green and efficient, and does not have high requirements for related equipment, and a large amount of high-temperature wave-absorbing materials can be prepared in a short time.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterials, and particularly relates to a composite electromagnetic wave absorbing material and a preparation method thereof. BACKGROUND

[0002] The application of radar technology makes the modern battlefield gradually transparent, and the demand for avoiding radar detection and protecting combat units and important strategic resources promotes the gradual development of radar stealth technology. Electromagnetic stealth materials convert electromagnetic wave photon vibration energy into internal energy of the materials through the physical properties of the materials. Compared with structure optimization stealth, electromagnetic stealth materials have the advantages of portability, high efficiency, low cost, etc.

[0003] At present, the research on electromagnetic absorbing materials at home and abroad mainly includes ferrite electromagnetic absorbing materials, metal powder materials, ceramic materials and composite materials. Among them, the compounding of carbon materials and low dielectric wave-transparent ceramics is an effective way to obtain high-performance absorbing materials, and the electromagnetic wave loss modes of ceramic (glass) / carbon composite materials are electric conduction loss and dielectric loss, etc. With thermal barrier protection, the function of electromagnetic wave loss in high temperature environment can be realized.

[0004] Graphene has excellent electrical, thermal, mechanical properties and high specific surface area, and is an excellent wave absorbing material. The unique layered structure of graphene and the introduction of defects not only improve the impedance of graphene, provide vacancies for the transition of adjacent levels to the Fermi level, but also introduce fault polarization attenuation and dual polarization attenuation, which promotes the absorption of electromagnetic waves. However, when the complex permittivity is high and the complex permeability is low, the impedance fullness is obviously different from the zero reflection condition. Therefore, in order to achieve good absorption, a method for adjusting impedance matching must be designed. SUMMARY

[0005] The application aims to provide a composite electromagnetic wave absorbing material and a preparation method thereof. By coating glass, SiO2 and other materials on the outside of graphene, the coating layer not only has wave-transparent characteristics and can be used to adjust the impedance matching of the composite material, but also can play the role of a thermal barrier layer to protect the internal graphene from being oxidized at high temperatures. The application produces a composite electromagnetic wave absorbing material with a special glass / graphene coating structure by a liquid sodium silicate foaming method, thereby relieving the high impedance matching characteristics of reduced graphene oxide and improving the electromagnetic absorption performance of the composite electromagnetic wave absorbing material. The application adjusts the size of the microparticles of the coating structure by adjusting the heat treatment temperature to control the shear stress generated by thermal stress on the graphene layers, thereby realizing the adjustment of the wave absorbing performance. The preparation method of the application is simple, green and efficient, and does not have high requirements for related equipment, so that a large amount of high-temperature wave absorbing materials can be prepared in a short time.

[0006] To achieve the above object, the application provides the following technical scheme.

[0007] One of the technical solutions of the present application: a preparation method of a composite electromagnetic wave absorbing material, comprising the following steps:

[0008] (1) dispersing SiO2 aerogel powder, glass fiber powder and reduced graphene oxide into a sodium silicate solution, uniformly mixing to obtain a mixed solution A;

[0009] (2) drying and crushing the mixed solution A to obtain a composite material powder A;

[0010] (3) dispersing the composite material powder A and SiO2 aerogel powder into a sodium silicate solution to obtain a mixed solution B;

[0011] (4) drying and crushing the mixed solution B to obtain a composite material powder B;

[0012] (5) dispersing the composite material powder B and SiO2 aerogel powder into a sodium silicate solution to obtain a mixed solution C;

[0013] (6) drying and crushing the mixed solution C to obtain a composite material powder C;

[0014] (7) high-temperature treatment of the composite material powder C to obtain the composite high-temperature electromagnetic wave absorbing material.

[0015] Preferably, the solvent of the sodium silicate solution in steps (1), (3) and (5) is water.

[0016] Preferably, in step (1), the mass ratio of SiO2 aerogel powder, glass fiber powder, sodium silicate in the sodium silicate solution and reduced graphene oxide is 0.95-1.05:3.70-4.08:1.54-1.71:7.39-8.17.

[0017] Preferably, in step (3), the mass ratio of SiO2 aerogel powder and sodium silicate in the sodium silicate solution is 0.95-1.05:29.46-31.75.

[0018] Preferably, in step (5), the mass ratio of SiO2 aerogel powder and sodium silicate in the sodium silicate solution is 0.95-1.05:21.58-23.26.

[0019] Preferably, the concentration of the sodium silicate solution in steps (1) and (3) is 73.3wt.%; the concentration of the sodium silicate solution in step (5) is 53.7wt.%.

[0020] Preferably, the drying temperature in steps (2), (4) and (6) is 110-130℃.

[0021] Preferably, the high temperature treatment temperature in step (7) is 400-1350 DEG C, and the time is 1h.

[0022] The graphene of the present application forms a relatively dense coating layer composed of a glass phase outside during the mixing of materials and the heat treatment process. The coating layer has excellent wave transmission performance, a low dielectric constant, and can regulate the overall dielectric constant of the composite material in a suitable range after being combined with graphene, thereby realizing impedance matching. At the same time, the coating layer is mainly composed of high-temperature-resistant components such as SiO2 and sodium glass, and can realize the oxidation protection of graphene at high temperatures during the graphene coating process. Therefore, the composite material structure has the potential to become an excellent high-temperature electromagnetic absorbing material.

[0023] The second technical scheme of the present application provides a composite electromagnetic wave absorbing material prepared according to the preparation method of the composite electromagnetic wave absorbing material.

[0024] The third technical scheme of the present application provides an application of the composite electromagnetic wave absorbing material in shielding electromagnetic radiation.

[0025] The beneficial technical effects of the present application are as follows:

[0026] The present application prepares a high-temperature composite electromagnetic wave absorbing material with a special glass / graphene coating structure through a mixing / heat treatment method, thereby relieving the high impedance matching characteristics of reduced graphene oxide itself, improving the electromagnetic absorbing performance, and the outer glass phase simultaneously plays a role of thermal barrier protection. The present application controls the number of graphene sheet layers in the coating structure microparticles by adjusting the heat treatment temperature. The preparation method of the present application is simple, green and efficient, and does not have high requirements for related equipment, and can realize the mass production of wave absorbing materials in a short time.

[0027] After the material mixing, the graphene and the liquid sodium silicate preliminarily form a coating structure, and after repeated crushing and mixing, the components gradually form a glass-coated microparticle structure. Under the action of high-temperature stress, the graphene sheet layer slips, the size of the microparticles changes, and the electromagnetic absorbing performance of the material is adjusted.

[0028] The good electromagnetic absorbing performance of the glass / graphene high-temperature wave absorbing composite material of the present application can be attributed to its special structure. The shear stress existing in the high-temperature treatment process of the present application makes the graphene sheet layer slip, and the glass / graphene coating structure with smaller microparticles is more easily obtained. This structure can successfully induce electromagnetic waves into the material interior when electromagnetic waves are incident, and absorb the electromagnetic waves by using the internal graphene layer. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1TEM images of the glass / graphene high-temperature wave-absorbing composite materials prepared in Examples 1-4. Among them, (a) is the TEM image of Example 1, (b) is the TEM image of Example 2, (c) is the TEM image of Example 3, and (d) is the TEM image of Example 4.

[0030] Figure 2 Wave-absorbing performance schematic diagram of the glass / graphene high-temperature wave-absorbing composite materials prepared in Examples 1-4.

[0031] Among them, (a) is the wave-absorbing performance schematic diagram of Example 1, (b) is the wave-absorbing performance schematic diagram of Example 2, (c) is the wave-absorbing performance schematic diagram of Example 3, and (d) is the wave-absorbing performance schematic diagram of Example 4. DETAILED DESCRIPTION

[0032] The detailed description set forth below of various example implementations of the application describes and discloses only the particular aspects of the application and is not intended to limit the application as a whole in any way. The application can be implemented in the absence of any element or elements not specifically disclosed.

[0033] Further, for numerical ranges that are expressly recited herein, it is specifically intended that each and every intermediate value and sub-range within the recited ranges be "incorporated" into the range. It is specifically intended that the endpoints of the ranges are included in the ranges themselves. It is also specifically intended that the individual values included in the ranges are included in the ranges themselves.

[0034] Unless defined otherwise, all technical and scientific terms and any acronyms used herein have the same meanings as commonly understood by one of ordinary skill in the art in the field of the application. Although any methods and materials similar or equivalent to those described herein can be used in the practice of the present application, the preferred methods and materials are described herein.

[0035] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0036] The reduced graphene oxide used in the following examples and comparative examples of the present application is AP-3 type reduced graphene oxide purchased from Luobei Yunshan Carbon Industry.

[0037] Each raw material used in the following examples and comparative examples of the present application is a commercially available product.

[0038] Example 1

[0039] Preparation of the glass / graphene high-temperature wave-absorbing composite material:

[0040] (1) Under the electromagnetic stirring of an electromagnetic stirrer, 0.1 g of SiO2 aerogel powder and 3.89 g of glass fiber powder were dispersed into 2.22 g of an aqueous sodium silicate solution (concentration of 73.3 wt.%), 7.78 g of reduced graphene oxide was added, and the mixture was uniformly mixed to obtain a mixed solution A;

[0041] (2) The mixed solution A was dried in an oven at 120°C, and then broken to obtain composite material powder A with a particle size of not more than 40 μm;

[0042] (3) The composite material powder A and 0.1 g of SiO2 aerogel powder were again dispersed into 3.5 g of an aqueous sodium silicate solution (concentration of 73.3 wt.%) to obtain a mixed solution B;

[0043] (4) The mixed solution B was dried in an oven at 120°C, and then broken to obtain composite material powder B with a particle size of not more than 40 μm;

[0044] (5) The composite material powder B and 0.1 g of SiO2 aerogel powder were again dispersed into 4.6 g of an aqueous sodium silicate solution (concentration of 53.7 wt.%) to obtain a mixed solution C;

[0045] (6) The mixed solution C was dried in an oven at 120°C, and then broken to obtain composite material powder C with a particle size of not more than 40 μm;

[0046] (7) The composite material powder C was placed in a high-temperature air furnace for high-temperature treatment at 400°C for 1 h to obtain the composite high-temperature electromagnetic wave absorbing material.

[0047] Example 2

[0048] Preparation of a glass / graphene high-temperature wave-absorbing composite material:

[0049] (1) Under the electromagnetic stirring of an electromagnetic stirrer, 0.1 g of SiO2 aerogel powder was dispersed into 2.22 g of an aqueous sodium silicate solution (concentration of 73.3 wt.%), 7.78 g of reduced graphene oxide was added, and the mixture was uniformly mixed to obtain a mixed solution A;

[0050] (2) The mixed solution A was dried in an oven at 120°C, and then broken to obtain composite material powder A with a particle size of not more than 40 μm;

[0051] (3) The composite material powder A and 0.1 g of SiO2 aerogel powder were again dispersed into 3.5 g of an aqueous sodium silicate solution (concentration of 73.3 wt.%) to obtain a mixed solution B;

[0052] (4) The mixed solution B was dried in an oven at 120°C, and then broken to obtain composite material powder B with a particle size of not more than 40 μm;

[0053] (5) the composite material powder B and 0.1 g of SiO2 aerogel powder are dispersed again into 4.6 g of sodium silicate aqueous solution (concentration of 53.7 wt.%) to obtain a mixed solution C;

[0054] (6) the mixed solution C is placed in an oven at 120°C to dry and then crushed again to obtain a composite material powder C with a particle size of not more than 40 μm;

[0055] (7) the composite material powder C is placed in a high-temperature air furnace at 400°C for high-temperature treatment for 1 h to obtain the composite high-temperature electromagnetic wave absorbing material.

[0056] Example 3

[0057] Preparation of glass / graphene high-temperature wave-absorbing composite material:

[0058] (1) under electromagnetic stirring of an electromagnetic stirrer, 3.89 g of glass fiber powder is dispersed into 2.22 g of sodium silicate aqueous solution (concentration of 73.3 wt.%), 7.78 g of reduced graphene oxide is added, and mixed uniformly to obtain a mixed solution A;

[0059] (2) the mixed solution A is dried in an oven at 120°C and then crushed to obtain a composite material powder A with a particle size of not more than 40 μm;

[0060] (3) the composite material powder A and 0.1 g of SiO2 aerogel powder are dispersed again into 3.5 g of sodium silicate aqueous solution (concentration of 73.3 wt.%) to obtain a mixed solution B;

[0061] (4) the mixed solution B is placed in an oven at 120°C to dry and then crushed again to obtain a composite material powder B with a particle size of not more than 40 μm;

[0062] (5) the composite material powder B and 0.1 g of SiO2 aerogel powder are dispersed again into 4.6 g of sodium silicate aqueous solution (concentration of 53.7 wt.%) to obtain a mixed solution C;

[0063] (6) the mixed solution C is placed in an oven at 120°C to dry and then crushed again to obtain a composite material powder C with a particle size of not more than 40 μm;

[0064] (7) the composite material powder C is placed in a high-temperature air furnace at 600°C for high-temperature treatment for 1 h to obtain the composite high-temperature electromagnetic wave absorbing material.

[0065] Example 4

[0066] Preparation of glass / graphene high-temperature wave-absorbing composite material:

[0067] (1) Under the electromagnetic stirring of an electromagnetic stirrer, 0.1 g of SiO2 aerogel powder and 3.89 g of glass fiber powder were dispersed into 2.22 g of an aqueous sodium silicate solution (concentration of 73.3 wt.%), 7.78 g of reduced graphene oxide was added, and the mixture was uniformly mixed to obtain a mixed solution A;

[0068] (2) After the mixed solution A was dried in an oven at 120°C, the composite material powder A with a particle size of not more than 40 μm was obtained by crushing;

[0069] (3) The composite material powder A and 0.1 g of SiO2 aerogel powder were again dispersed into 3.5 g of an aqueous sodium silicate solution (concentration of 73.3 wt.%) to obtain a mixed solution B;

[0070] (4) After the mixed solution B was dried in an oven at 120°C, the composite material powder B with a particle size of not more than 40 μm was obtained by crushing again;

[0071] (5) The composite material powder B and 0.1 g of SiO2 aerogel powder were again dispersed into 4.6 g of an aqueous sodium silicate solution (concentration of 53.7 wt.%) to obtain a mixed solution C;

[0072] (6) After the mixed solution C was dried in an oven at 120°C, the composite material powder C with a particle size of not more than 40 μm was obtained by crushing again;

[0073] (7) The composite material powder C was placed in a high-temperature air furnace for high-temperature treatment at 1350°C for 1 h to obtain the composite high-temperature electromagnetic wave absorbing material.

[0074] The TEM images of the glass / graphene high-temperature wave-absorbing composite materials prepared in Examples 1-4 are shown in Figure 1 . Among them, (a) is the TEM image of Example 1, (b) is the TEM image of Example 2, (c) is the TEM image of Example 3, and (d) is the TEM image of Example 4.

[0075] Comparative Example 1

[0076] The difference compared with Example 4 is only that high-temperature treatment is not performed.

[0077] Comparative Example 2

[0078] The difference compared with Example 4 is only that glass fibers are not added.

[0079] Comparative Example 3

[0080] The difference compared with Example 4 is only that SiO2 aerogel powder is not added.

[0081] Effect verification

[0082] (1) In order to verify the wave-absorbing performance of the product obtained in the application, the products in Examples 1-4 and Comparative Examples 1-3 were subjected to microwave absorption tests. The test method is as follows: the electromagnetic wave absorption performance test is mainly to determine the complex permittivity and complex permeability of the material and to pass through the following formula:

[0083]

[0084]

[0085] The pros and cons of the wave-absorbing 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:

[0086]

[0087]

[0088] Wherein f, d, c are frequency, thickness of the absorber and speed of light in free space respectively; Z0 is space impedance; Z in is input impedance. The reflection loss RL value <-10 dB represents 90.00% effective absorption, the reflection loss RL value <-20 dB represents 99.00% effective absorption, and the reflection loss RL value <-30 dB represents 99.90% effective absorption. The electromagnetic wave attenuation in the material can be expressed by the following formula:

[0089]

[0090] The reflection loss value of the material was calculated. The electromagnetic wave absorption performance of the sample was studied by using the network vector analyzer VNA, N5245A type of Agilent Company, USA. The sample powder was uniformly mixed with paraffin in a proportion of 40 wt.% of the total mass of the sample in the molten state of paraffin, and was pressed into a hollow coaxial cylinder with an inner diameter of 3.04 mm and an outer diameter of 7 mm. In the frequency range of 2-18 GHz, the number of sampling points was 201, and the real and imaginary parts of the complex permittivity and complex permeability of the sample, the dielectric loss tangent and the magnetic loss tangent were equal to the ratio of the real part to the imaginary part. The test results are shown in Table 1.

[0091] Table 1 Microwave absorption test

[0092]

[0093] As can be seen from the table, the products of Examples 1-4 all have the best microwave absorption in the Ku band; it can also be seen from the comparison of Example 4 and Comparative Examples 1-3 that high-temperature treatment and the type and proportion of raw materials are very important for the wave-absorbing performance.

[0094] And the product of example 4 is also tested for wave absorption performance with various materials. Among them, the device filling amount refers to the ratio of the composite material to the mass of the paraffin ring required for testing; the thickness refers to the thickness of the composite material forming the device. The test results are shown in Table 2.

[0095] Table 2 Wave absorption performance of other materials

[0096]

[0097] The preparation of other materials in Table 2 is as follows:

[0098] FENG JT, HOU YH, WANG YC, et al. Synthesis of Hierarchical ZnFe2O4@SiO2@RGO Core-Shell Microspheres for Enhanced Electromagnetic Wave Absorption[J]. Acs Applied Materials & Interfaces, 2017, 9(16): 14103-11.

[0099] LI X, ZHOU QH, HUANG YY, et al. Nanoindentation and abrasion in Fe3O4 / rGO reinforced epoxy electromagnetic protective coatings[J]. Journal of Alloys and Compounds, 2021, 887.

[0100] ZHUT, CHANGSC, SONGYF, et al. PVP-encapsulated CoFe2O4 / rGO composites with controllable electromagnetic wave absorption performance[J]. Chemical Engineering Journal, 2019, 373:755-66.

[0101] (2) In order to verify the wave-absorbing performance of the product obtained in the application at different frequencies, the glass / graphene prepared in Examples 1-4 was subjected to a return loss test in the frequency range of 2-18 GHz, and the test method was as follows: a vector network analyzer coaxial ring method test. The return loss test is mainly to determine the complex permittivity and complex permeability of the material and to calculate the reflection loss value of the material through the above-mentioned formula (1-5). The electromagnetic wave absorption performance of the sample was studied by using a VNA, N5245A type network vector analyzer of Agilent Company of the United States; 20wt.% of the sample powder was added to the paraffin in a molten state and uniformly mixed, and was 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 was 201, and the real and imaginary parts of the complex permittivity and complex permeability of the sample, the dielectric loss tangent and the magnetic loss tangent were equal to the ratio of the real part to the imaginary part. The test results are shown in Figure 2

[0102] Figure 2 The wave-absorbing performance of the glass / graphene high-temperature wave-absorbing composite material prepared in Examples 1-4 is shown in the figure.

[0103] Among them, (a) is the wave-absorbing performance schematic diagram of Example 1, (b) is the wave-absorbing performance schematic diagram of Example 2, (c) is the wave-absorbing performance schematic diagram of Example 3, and (d) is the wave-absorbing performance schematic diagram of Example 4. As can be seen from the figure, when the temperature is 1350℃, the composite material has the smallest reflection loss value and the largest absorption bandwidth, that is, Example 4 has better electromagnetic wave absorption performance than other examples.

[0104] The above-described examples only describe the preferred modes of the application and do not limit the scope of the application. Without departing from the design spirit of the application, various modifications and improvements to the technical solutions of the application made by those skilled in the art shall fall within the protection scope determined by the claims of the application.​

Claims

1. A preparation method of a composite electromagnetic wave absorbing material, characterized in that, The method comprises the following steps: (1) dispersing SiO2 aerogel powder, glass fiber powder and reduced graphene oxide into a sodium silicate solution, mixing uniformly to obtain a mixed solution A; (2) drying the mixed solution A and crushing to obtain a composite material powder A; (3) dispersing the composite material powder A and SiO2 aerogel powder into a sodium silicate solution to obtain a mixed solution B; (4) drying the mixed solution B and crushing to obtain a composite material powder B; (5) dispersing the composite material powder B and SiO2 aerogel powder into a sodium silicate solution to obtain a mixed solution C; (6) drying the mixed solution C and crushing to obtain a composite material powder C; (7) performing high-temperature treatment on the composite material powder C to obtain the composite electromagnetic wave absorbing material; The temperature of the high-temperature treatment is 1350℃, and the time is 1h.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of the SiO2 aerogel powder, the glass fiber powder, the sodium silicate in the sodium silicate solution and the reduced graphene oxide is 0.95-1.05:3.70-4.08:1.54-1.71:7.39-8.

17.

3. The method of claim 1, wherein, In step (3), the mass ratio of the SiO2 aerogel powder and the sodium silicate in the sodium silicate solution is 0.95-1.05:29.46-31.

75.

4. The method of claim 1, wherein, In step (5), the mass ratio of the SiO2 aerogel powder and the sodium silicate in the sodium silicate solution is 0.95-1.05:21.58-23.

26.

5. The preparation method according to claim 1, characterized in that, In steps (1) and (3), the concentration of the sodium silicate solution is 73.3wt.%; in step (5), the concentration of the sodium silicate solution is 53.7wt.%.

6. The method of claim 1, wherein, In steps (2), (4) and (6), the drying temperature is 110℃-130℃.

7. A composite electromagnetic wave absorbing material prepared by the method according to any one of claims 1-6.

Images