Broadband Absorbing Composite Material and Its Preparation Method

Abstract

The present invention discloses a broadband microwave absorbing composite material and a preparation method thereof. The preparation method includes: 1) stirring and dispersing one or both of carbon nanotubes and MXenes uniformly in an aqueous graphene oxide dispersion to obtain an absorbent slurry; 2) adding polymer microparticles of different sizes to the absorbent slurry, and then obtaining polymer microparticles coated with microwave absorbing components on the surface, namely microwave absorbing microparticles, through mechanical stirring, filtration, and vacuum drying steps; 3) according to the requirements of a multi-layer design scheme, spreading microwave absorbing microparticles with different absorbent contents and / or different sizes layer by layer from bottom to top in a hot pressing mold according to the requirements of weight and thickness; and 4) closing the mold and hot pressing to form a broadband microwave absorbing composite material. In the impedance gradient structure, the thickness of each microwave absorbing structure layer can be used to lay the absorbent microparticles according to the required thickness, which can achieve a more refined gradient of the absorbent content and better impedance gradient effect, and is beneficial to broadband impedance matching.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave absorbing materials, and in particular, to a broadband microwave absorbing composite material and a preparation method thereof. Background Art

[0002] Microwave absorbing materials are important materials that can achieve a low radar cross-section of the target object and are widely used in equipment such as military aircraft and ships. In order to achieve microwave absorbing performance with both a wide microwave absorbing bandwidth and low reflection loss, researchers usually design microwave absorbing materials into a multi-layer structure with a gradually changing impedance to expand the microwave absorbing bandwidth and reduce the reflection loss, such as multi-layer impedance-gradient microwave absorbing honeycombs, microwave absorbing foams, laminates, etc. This multi-layer design generally requires adhesives such as adhesive films to bond each layer to improve the structural strength of the microwave absorbing material. In order to improve the microwave absorbing performance, it is generally necessary to increase the number of structural layers for impedance gradient as much as possible. However, as the number of layers in the multi-layer microwave absorbing structure design increases, the risk of reducing the structural strength of the microwave absorbing material due to the use of layer-like adhesives such as adhesive films to bond each layer as a whole becomes greater and greater. In order to avoid this risk, the thickness of each layer cannot be too small, which in turn limits the number of layers in the structural design, resulting in difficulty in finely controlling the impedance gradient of the multi-layer structure and affecting the microwave absorbing performance. Therefore, the design of a multi-layer microwave absorbing structure with both microwave absorbing performance and structural strength is a major problem in the design of microwave absorbing materials. Summary of the Invention

[0003] The present invention aims to provide a broadband microwave absorbing composite material and a preparation method thereof to solve the technical problems in the prior art that the impedance gradient effect between layers cannot be finely adjusted in the design of multi-layer microwave absorbing structures and the structural strength is reduced due to the need to bond each layer with adhesives such as adhesive films between layers.

[0004] To achieve the above object, according to one aspect of the present invention, there is provided a preparation method of a broadband microwave absorbing composite material. The preparation method includes the following steps: 1) stirring and dispersing one or both of carbon nanotubes and MXenes uniformly in an aqueous graphene oxide dispersion liquid to obtain a microwave absorbing agent slurry; 2) adding polymer microparticles of different sizes to the microwave absorbing agent slurry, and then obtaining polymer microparticles coated with microwave absorbing components on the surface, namely microwave absorbing microparticles, through mechanical stirring, filtration, and vacuum drying steps; 3) spreading microwave absorbing microparticles with different microwave absorbing agent contents and / or different sizes on a hot pressing mold according to the requirements of a multi-layer design scheme; and 4) closing the hot pressing mold and obtaining a broadband microwave absorbing composite material through hot pressing forming.

[0005] Further, the multi-layer design scheme includes spreading different microwave absorbing component ratios, microwave absorbing agent coating contents, and / or microwave absorbing microparticles of different sizes layer by layer on the hot pressing mold in a spreading manner, and the thickness of each layer is between 30 μm and 5000 μm.

[0006] Further, the carbon nanotubes are carboxylated multi-walled carbon nanotubes or hydroxylated multi-walled carbon nanotubes.

[0007] Further, the carbon nanotubes have a diameter of 4 - 80 nm and a length of 0.5 - 50 μm.

[0008] Further, the polymer microparticles are microparticles selected from one or more of polystyrene, polyethylene, polypropylene, polymethyl methacrylate, polyphenylene sulfide, and polyacrylamide composite polymers.

[0009] Further, MXenes are two-dimensional transition metal carbides, nitrides, or carbonitrides, including Ti 3 C 2 Tx, Ti 2 CTx or Ti 4 C 3 Tx, where T is O, F, or OH, and the value of x is 1 - 10.

[0010] Further, the hot pressing and forming includes: after all layers are spread, hot pressing and forming are carried out at one time, the hot pressing temperature is 50 - 180 °C, the pressure is 20 - 800 MPa, and the hot pressing time is greater than 2 min.

[0011] Further, the concentration of the graphene oxide aqueous dispersion is 3 - 5 mg / ml.

[0012] Further, the mass ratio of graphene oxide to carbon nanotubes or MXenes in the absorbent slurry is 20:1 - 1:5.

[0013] According to another aspect of the present invention, a broadband absorbing composite material is provided. The broadband absorbing composite material is prepared by any of the above preparation methods.

[0014] Applying the technical solution of the present invention, in the impedance gradient structure, the thickness of each absorbing structure layer can be paved with absorbent microparticles according to the required thickness, which can achieve a more refined gradient of the absorbent content, achieve a better impedance gradient effect, and is beneficial to broadband impedance matching; since the absorbent is coated on the surface of the polymer microparticles, after forming, the absorbent can form a three-dimensional network pore structure, which is beneficial to enhancing the scattering and multiple reflection attenuation of the incident electromagnetic wave, and further enhancing the absorbing performance; in the process of the present invention, after the absorbent microparticles are spread from bottom to top and hot pressed, there is no obvious interface between layers, and the absorbent microparticles are embedded in each other's layers, without the risk of delamination, which is beneficial to maintaining the structural strength. Detailed Embodiments

[0015] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0016] In view of the problems described in the background art of the present invention, the present invention provides an integrated multi-layer broadband absorbing composite material and a preparation method thereof, aiming to solve the problems that in the design of multi-layer absorbing structures, the impedance gradient effect between layers cannot be finely adjusted, and the use of adhesives such as adhesive films between layers reduces the structural strength, so as to achieve the comprehensive performance of multi-layer impedance gradient absorbing materials with excellent absorbing performance and high structural strength, and broaden the application range of such absorbing materials.

[0017] According to a typical embodiment of the present invention, a preparation method of a broadband absorbing composite material is provided. The preparation method includes the following steps: 1) Stir and disperse one or both of carbon nanotubes and MXenes uniformly in an aqueous graphene oxide dispersion to obtain an absorber slurry; 2) Add polymer microparticles of different sizes to the absorber slurry, and then obtain polymer microparticles coated with absorber components on the surface, i.e., absorbing microparticles, through mechanical stirring, filtration, and vacuum drying steps; 3) Sprinkle absorbing microparticles with different absorber contents and / or different sizes on a hot pressing mold according to the requirements of a multi-layer design scheme; and 4) Close the hot pressing mold and obtain a broadband absorbing composite material by hot pressing.

[0018] Applying the technical solution of the present invention, in the impedance gradient structure, the thickness of each absorbing structure layer can be paved with absorber microparticles according to the required thickness, so that a more fine absorber content gradient can be achieved, a better impedance gradient effect can be obtained, which is beneficial to broadband impedance matching; since the absorber is coated on the surface of the polymer microparticles, after molding, the absorber can form a three-dimensional network pore structure, which is beneficial to enhancing the scattering and multiple reflection attenuation of incident electromagnetic waves, and further enhancing the absorbing performance; in the process of the present invention, after the absorber microparticles are spread from bottom to top and hot pressed, there is no obvious interface between layers, and the absorber microparticles are embedded in each other's layers, without the risk of delamination, which is beneficial to maintaining the structural strength.

[0019] In a typical embodiment of the present invention, the multi-layer design scheme includes spreading different absorber component ratios, absorber coating contents, and / or absorber microparticles of different sizes layer by layer on a hot pressing mold in a spreading manner, and the thickness of each layer is between 30 μm and 5000 μm. Among them, the carbon nanotubes are carboxylated multi-walled carbon nanotubes or hydroxylated multi-walled carbon nanotubes, and these two kinds of carbon nanotubes have better dispersibility in water, which is more conducive to forming a uniform distribution in the final material system. Preferably, the carbon nanotubes have a tube diameter of 4-80 nm and a length of 0.5-50 μm, and within this range, the carbon nanotubes have better absorbing effects and are more easily dispersed uniformly in the medium.

[0020] According to a typical embodiment of the present invention, the polymer microparticles are microparticles formed by selecting one or more of polystyrene, polyethylene, polypropylene, polymethyl methacrylate, polyphenylene sulfide, and polyacrylamide composite polymers, and these types of polymers can all be formed by hot pressing. MXenes are two-dimensional transition metal carbides, nitrides, or carbonitrides, including Ti 3 C 2 Tx, Ti 2 CTx or Ti 4 C 3 Tx, where T is O, F, or OH, and the value of x ranges from 1 to 10.

[0021] Preferably, the hot pressing molding includes: after all layers are spread, hot pressing is performed at one time, the hot pressing temperature is 50 to 180 °C, the pressure is 20 to 800 MPa, and the hot pressing time is greater than 2 min. Under these process conditions, the effect of impedance gradient can be achieved by one-time hot pressing, avoiding the realization of impedance gradient through complex bonding between different impedance gradient layers; the impedance gradient achieved in this way is more continuous; and the overall mechanical properties of the formed material are better. Preferably, the concentration of the graphene oxide aqueous dispersion is 3 to 5 mg / ml.

[0022] According to a typical embodiment of the present invention, the mass ratio of graphene oxide to carbon nanotubes or MXenes in the absorbent slurry is 20:1 to 1:5. Controlling the mass ratio of graphene oxide to carbon nanotubes or MXenes in the absorbent slurry within this range can obtain a better absorption effect.

[0023] According to a typical embodiment of the present invention, a broadband absorbing composite material is provided. The broadband absorbing composite material is prepared by the above preparation method.

[0024] The beneficial effects of the present invention will be further described below in conjunction with the embodiments.

[0025] Example 1

[0026] 1) Prepare the absorbent slurry: Add carboxylated multi-walled carbon nanotubes with different parts and diameters of 8 - 15 nm and lengths of 3 - 5 μm to the graphene oxide dispersion of 5 mg / ml, and mechanically stir and disperse for 30 minutes to obtain the absorbent slurry. The ratio of graphene oxide to carbon nanotubes in the absorbent slurry is 1:0.2, 1:0.5, 1:0.7, 1:1, 1:1.5, 1:2, 1:3 respectively;

[0027] 2) Add polystyrene microspheres with a size of 30 μm to the seven ratios of absorbent slurry obtained in step 1), and mechanically stir and disperse at high speed for 120 minutes to coat the absorbent on the surface of the polystyrene microspheres.

[0028] 3) Filter out the polystyrene microspheres coated in step 2), and vacuum dry them in a vacuum drying oven at 90 °C for 12 hours to obtain polystyrene microspheres with an absorbing component coated on the surface, i.e., absorbing particles (denoted as: R102, R105, R107, R110, R115, R120, R130);

[0029] 4) According to the multi-layer design scheme optimized by simulation, lay the R130, R120, R115, R110, R107, R105, and R102 type absorbing particles layer by layer from bottom to top in a hot pressing mold, and ensure that each layer is evenly laid.

[0030] 5) Hot press at 100 °C for 20 minutes under a pressure of 300 MPa to obtain a multi-layer broadband absorbing composite material.

[0031] Example 2

[0032] 1) Prepare an absorbent slurry: Add carboxylated multi-walled carbon nanotubes with a diameter of 8 - 15 nm and a length of 0.5 - 2 μm to a 5 mg / ml graphene oxide dispersion liquid, and mechanically stir and disperse for 30 minutes to obtain an absorbent slurry. The ratio of graphene oxide to carbon nanotubes in the dispersion liquid is 1:1.5;

[0033] 2) Respectively mix seven portions of the absorbent slurry obtained in step 1) with polystyrene microspheres of sizes 113 μm, 87 μm, 65 μm, 46 μm, 25 μm, 17 μm, and 8 μm, and mechanically stir and disperse at high speed for 120 minutes to coat the absorbent on the surface of the polystyrene microspheres.

[0034] 3) Filter out the polystyrene microspheres coated in step 2), and vacuum dry them in a vacuum drying oven at 90 °C for 12 hours to obtain polystyrene microspheres with an absorbing component coated on the surface, i.e., absorbing particles (denoted as: D113, D087, D065, D046, D025, D017, D008);

[0035] 4) According to the multi-layer design scheme optimized by simulation, lay the D008, D017, D025, D046, D065, D087, and D113 type absorbing particles layer by layer from bottom to top in a hot pressing mold, and ensure that each layer is evenly laid.

[0036] 5) Hot press at 100 °C for 40 minutes under a pressure of 300 MPa to obtain a multi-layer broadband absorbing composite material.

[0037] Example 3

[0038] 1) Preparation of microwave absorbing agent slurry: Different amounts of MXenes were added to the graphene oxide dispersion with a concentration of 3 mg / ml, and mechanically stirred for 30 minutes to obtain the microwave absorbing agent slurry. The mass ratios of graphene oxide to MXenes in the microwave absorbing agent slurry were 1:0.1, 1:0.3, 1:0.5, 1:0.7, 1:0.9, 1:1.0, 1:1.1, and 1:1.2, respectively;

[0039] 2) Polyethylene microspheres with a size of 30 μm were added to the eight slurries of microwave absorbing agents obtained in step 1), and mechanically stirred at high speed for 60 minutes to coat the microwave absorbing agents on the surface of the polystyrene microspheres.

[0040] 3) The coated polyethylene microspheres were filtered out and vacuum-dried in a vacuum drying oven at 90 °C for 12 hours to obtain polyethylene microspheres with microwave absorbing components coated on the surface, namely microwave absorbing particles (denoted as: M101, M103, M105, M107, M109, M110, M111, M112);

[0041] 4) According to the multi-layer design scheme optimized by simulation, microwave absorbing particles of types M112, M111, M110, M109, M107, M105, M103, and M101 were spread layer by layer from bottom to top in a hot pressing mold, and the spreading of each layer was required to be uniform.

[0042] 5) Under a pressure of 10 MPa, hot pressing was carried out at 180 °C for 40 minutes to obtain a multi-layer broadband microwave absorbing composite material.

[0043] Example 4

[0044] 1) Preparation of microwave absorbing agent slurry: Carboxylated multi-walled carbon nanotubes with a diameter of 8 - 15 nm and a length of 5 - 10 μm were added to the graphene oxide dispersion with a concentration of 5 mg / ml, and mechanically stirred for 30 minutes to obtain the microwave absorbing agent slurry. The mass ratios of graphene oxide to carbon nanotubes in the microwave absorbing agent slurry were 1:0.1, 1:0.3, 1:0.6, 1:1, 1:1.4, and 1:1.6, respectively;

[0045] 2) Polyethylene microspheres with a size of 50 μm were added to the six slurries of microwave absorbing agents obtained in step 1), and mechanically stirred at high speed for 120 minutes to coat the microwave absorbing agents on the surface of the polyethylene microspheres.

[0046] 3) The coated polyethylene microspheres were filtered out and vacuum-dried in a vacuum drying oven at 90 °C for 12 hours to obtain polyethylene microspheres with microwave absorbing components coated on the surface, namely microwave absorbing particles (denoted as: E101, E103, E106, E110, E114, E116);

[0047] 4) According to the multi-layer design scheme optimized by simulation, absorbent particles of types E116, E114, E110, E106, E103, and E101 are spread layer by layer from bottom to top in the hot pressing mold, and the spreading of each layer needs to be ensured to be uniform.

[0048] 5) Under a pressure of 300 MPa, hot press at 180 °C for 60 minutes to obtain a multi-layer structure broadband absorbing composite material.

[0049] The relevant technical parameters of the above embodiments are shown in Table 1.

[0050] Table 1

[0051]

[0052] From the above description, it can be seen that the method for preparing a broadband absorbing composite material provided by the above embodiments of the present invention achieves the following technical effects:

[0053] 1) In the impedance gradient structure, the thickness of each absorbing structure layer can be used for laying absorbent particles according to the required thickness, which can achieve a more refined gradient of absorbent content, achieve a better impedance gradient effect, and is beneficial to broadband impedance matching;

[0054] 2) Since the absorbent is coated on the surface of polymer particles, after molding, the absorbent can form a three-dimensional network pore structure, which is beneficial to enhancing the scattering and multiple reflection attenuation of incident electromagnetic waves, and further enhancing the absorbing performance;

[0055] 3) In this process, after the absorbent particles are spread layer by layer from bottom to top and hot pressed, there is no obvious interface between layers, and the absorbent particles are embedded in each other's layers, without the risk of delamination, which is beneficial to maintaining the structural strength.

[0056] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of broadband absorbing composite material, characterized in that, it comprises the following steps: 1) Stir and disperse one or both of carbon nanotubes and MXenes in an aqueous graphene oxide dispersion to obtain an absorbent slurry; 2) Add polymer microparticles of different sizes to the absorbent slurry, and then obtain polymer microparticles coated with absorbent components on the surface, namely absorbent microparticles, through mechanical stirring, filtration, and vacuum drying steps; 3) According to the requirements of the multi-layer design scheme, spread the absorbent microparticles with different absorbent coating contents and different sizes in a hot pressing mold; and 4) Close the hot pressing mold and obtain the broadband absorbing composite material by hot pressing; The multi-layer design scheme includes spreading the absorbent microparticles with different absorbent component ratios, different absorbent coating contents, and different sizes layer by layer in the hot pressing mold in a spreading manner, and the thickness of each layer is between 30 μm and 5000 μm.

2. The preparation method according to claim 1, characterized in that, the carbon nanotubes are carboxylated multi-walled carbon nanotubes or hydroxylated multi-walled carbon nanotubes.

3. The preparation method according to claim 2, characterized in that, the carbon nanotubes have a tube diameter of 4 - 80 nm and a length of 0.5 - 50 μm.

4. The preparation method according to claim 1, characterized in that, the polymer microparticles are microparticles formed by one or more selected from polystyrene, polyethylene, polypropylene, polymethyl methacrylate, polyphenylene sulfide, and polyacrylamide composite polymers.

5. The preparation method according to claim 1, characterized in that, The MXenes are two-dimensional transition metal carbides, nitrides or carbonitrides, including Ti 3 C 2 Tx, Ti 2 CTx or Ti 4 C 3 Tx, where T is O, F or OH, and the value of x ranges from 1 to 10.

6. The preparation method according to claim 1, characterized in that, the hot pressing includes: after all layers are spread, hot pressing is carried out at one time, the hot pressing temperature is 50 - 180 °C, the pressure is 20 - 800 MPa, and the hot pressing time is greater than 2 min.

7. The preparation method according to claim 1, characterized in that, the concentration of graphene oxide in the aqueous graphene oxide dispersion is 3 - 5 mg / ml.

8. The preparation method according to claim 1, characterized in that, the mass ratio of graphene oxide to the carbon nanotubes or MXenes in the absorbent slurry is 20:1 - 1:

5.

9. A broadband absorbing composite material, characterized in that, it is prepared by the preparation method according to any one of claims 1 to 8.

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