Lightweight broadband wave-absorbing material, preparation method and use thereof

Abstract

The application provides a light-weight broadband wave-absorbing material and a preparation method and application thereof, and belongs to the field of wave-absorbing materials. Melamine foam (MF) is used as a matrix framework, the MF internal pore structure is constructed by carboxymethyl cellulose (CMC) impregnation, and a layered carbon foam material is prepared through carbonization. In the composite carbon foam material, the CMC sheet structure is connected with the MF framework structure with high porosity to form an interconnected layered network structure, the contact area with electromagnetic waves is increased, the electromagnetic wave loss is improved, and the high impedance matching characteristic is also possessed, so that the full-frequency effective absorption of 2-18 GHz can be realized in a wide thickness range. The composite carbon foam material has a wide application prospect in the preparation of light-weight broadband wave-absorbing materials with high impedance matching characteristics.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of wave-absorbing materials, and particularly relates to a light-weight broadband wave-absorbing material and a preparation method and use thereof. BACKGROUND

[0002] The frequent use of wireless electronic devices has led to the prevalence of electromagnetic pollution, which has now ranked the fourth after water, air and noise pollution. In order to alleviate electromagnetic pollution, researchers have been working hard to develop electromagnetic wave absorbers with broadband effective absorption. In addition, electromagnetic wave absorbing materials have important significance in radar stealth, which is related to the survivability and combat effectiveness of future weapon equipment. In order to solve the inherent defects of traditional metal wave-absorbing materials such as high density and easy corrosion, and the application in industry or harsh environment, light-weight carbon foam absorbing composite materials (such as one-dimensional nanocarbon, two-dimensional carbon nanomaterial, MOF derived materials, etc.) with light weight, corrosion resistance and ultra-wideband effective absorption potential have been reported. However, most of the reported wave-absorbing materials can only achieve broadband absorption at a limited thickness, with high absorption intensity but narrow effective absorption bandwidth, complex preparation process and high cost, and difficult mass production, inflexible application, material performance limitation, unstable finished material (dropping slag, fragile) and other problems, which greatly limit the further development of wave-absorbing materials.

[0003] Excellent impedance matching is a prerequisite for obtaining wideband absorbing materials. Similarly, excellent impedance matching is more tolerant of wideband absorbing matching thickness range. The introduction of air in high-loss absorbing materials can effectively reduce its excessively high dielectric constant. For example, researchers have constructed various customized graphene, MXene, and carbon nanofiber aerogel composites. The introduction of air in low-dielectric base materials further improves the wave-penetrating ability and provides an open channel for electromagnetic wave transmission. Such wave-absorbing structures are commonly used in stealth weapons, especially stealth aircraft, such as the lattice-like base structure represented by honeycomb, hollow glass beads, and ceramic microspheres. Therefore, researchers often choose porous base structures such as aerogels and foams. Zhang et al. reported a new type of ultra-light aerogel sphere composed of fibrous or flaky cellulose-derived nanocarbon, which can achieve an effective absorption bandwidth of 6.96 GHz at 2.92 mm (Zhang R, Wu N, Pan F, et al. Scalable manufacturing of light, multifunctional cellulose nanofiber aerogel sphere with tunable microstructure for microwave absorption [J]. Carbon, 2023, 203: 181-190.). However, the performance of the sample decreases significantly in the near thickness range, and the preparation process is relatively complex, which brings great difficulties to actual preparation and application. The reason is that the material has poor impedance matching characteristics, which can only achieve satisfactory electromagnetic wave attenuation at a specific and accurate thickness, which poses a challenge to the repeatability and stability of material preparation.

[0004] Therefore, it is of great significance to prepare new lightweight wideband absorbing materials with high impedance matching characteristics. Lightweight absorbing materials that can absorb electromagnetic waves in a wide frequency range within a tunable thickness range are of great value, which will enhance the repeatability and stability of the material's wave-absorbing performance and better serve various wave-absorbing application scenarios. SUMMARY

[0005] The purpose of the present application is to provide a lightweight wideband absorbing material and its preparation method and use.

[0006] The present application provides a composite carbon foam material, which is obtained by immersing a porous foam into a water solution of a polymer film material, drying and carbonizing the obtained material, and the concentration of the water solution of the polymer film material is 0.1-12 mg·ml -1 .

[0007] Further, the porous foam is melamine foam, cellulose-based foam, polyfurfural alcohol foam, pitch-based foam, biomass foam or polyurethane foam; the polymer film material is cellulose or its derivative, conductive polymer or gel polymer.

[0008] Further, the porous foam is melamine foam; the polymer film material is carboxymethyl cellulose.

[0009] Further, the concentration of the aqueous solution of the polymer film material is 1-5 mg·ml -1 .

[0010] Further, the time of immersion is more than 10 minutes.

[0011] Further, the time of immersion is more than 1 hour.

[0012] Further, the carbonization is carried out in an inert gas atmosphere.

[0013] Further, the temperature of carbonization is 700-900℃, and the time is 0.5-3h.

[0014] Further, the temperature of carbonization is 800℃, and the time is 1h.

[0015] Further, the thickness of the composite carbon foam material is more than 10mm.

[0016] Further, the thickness of the composite carbon foam material is more than 12mm.

[0017] The present application also provides a method for preparing the above-mentioned composite carbon foam material, which comprises the following steps:

[0018] (1) immerse the porous foam into the aqueous solution of the polymer film material, take it out and dry to obtain a precursor;

[0019] (2) carbonize the precursor to obtain the composite carbon foam material.

[0020] The present application also provides the use of the above-mentioned composite carbon foam material in the preparation of light-weight broadband wave-absorbing materials.

[0021] The application takes melamine foam (MF) as a matrix framework, constructs the internal pore structure of MF by carboxymethyl cellulose (CMC) impregnation, and prepares a carbon foam material with a layered structure through carbonization.

[0022] The application provides a simple method for manufacturing a lightweight broadband electromagnetic wave absorbing material with high impedance matching characteristics, and is suitable for industrial production.

[0023] Obviously, according to the above content of the application, according to the ordinary technical knowledge and common means in the art, other various forms of modification, replacement or change can be made without departing from the above basic technical idea of the application.

[0024] The above content of the application will be further described in detail through the specific embodiments in the form of examples. However, it should not be understood that the above subject matter of the application is limited to the following examples. Any technology achieved based on the above content of the application belongs to the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 (a) Preparation flowchart of MC and C@MC; (b) SEM images of MF, MC-1, MC-2 and MC-5 samples from left to right.

[0026] Figure 2 (a-c) SEM images of MF foam, local SEM images of MF foam before (b) and after (c) loading CMC.

[0027] Figure 3 (a-b) SEM images of MC-15 under the action of high loading CMC.

[0028] Figure 4 (a) SEM image, (b) local SEM image and (c) element mapping of C@MC-2.

[0029] Figure 5 (a-c) XPS spectra of C@MC.

[0030] Figure 6 (a) XRD spectrum and (b) Raman spectrum of C@MC.

[0031] Figure 7Electromagnetic parameters of (a) C@MC-1, (b) C@MC-2 and (c) C@MC-5.

[0032] Figure 8 Smith chart of .C@MC (sample thickness 20 mm).

[0033] Figure 9 (a) C@MC-1, (b) C@MC-2 and (c) C@MC-5 at different thicknesses R L A three-dimensional graph of values ​​versus frequencies.

[0034] Figure 10 R values ​​of C@MC-1 samples of different thicknesses L The value changes with frequency, and the thickness of the absorbing material (t) under the λ / 4 model. m ) and absorption peak frequency (f m Simulation of ) and normalized input impedance (Z in (Changes with frequency) Detailed Implementation

[0035] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0036] Melamine foam (MF) was purchased from Zhengzhou Fengtai Nanomaterials Co., Ltd., with a density of 7.5 mg / cm³. -3 .

[0037] Carboxymethyl cellulose (CMC) was purchased from Aladdin. It has a molecular weight of 90,000 and a viscosity of 50-100 MPa·s.

[0038] Example 1: Method for preparing composite carbon foam materials

[0039] A schematic diagram of the process for preparing composite carbon foam materials is shown below. Figure 1 As shown in a. The specific steps are as follows:

[0040] Melamine foam was cut into uniform small pieces and cleaned in an ultrasonic cleaner with anhydrous ethanol and deionized water for several minutes. After cleaning, it was dried. The dried melamine foam was then immersed in carboxymethyl cellulose aqueous solutions of different concentrations shown in Table 1. After immersion for 1 hour, it was removed and dried in an oven at 60°C for 12 hours to obtain uniformly carboxymethyl cellulose-impregnated melamine foam precursors MC, which were named MC-1, MC-2, and MC-5 according to the concentration of the carboxymethyl cellulose aqueous solution used.

[0041] MC-1, MC-2, MC-5 were carbonized in a tube furnace at a heating rate of 10 ℃min-1to 800 ℃, and then kept at 800 ℃ for 1 h under the continuous flow of high-purity argon to obtain the composite carbon foam material C@MC, which was named as C@MC-1, C@MC-2, C@MC-5 according to the concentration of the adopted aqueous solution of carboxymethyl cellulose.

[0042] Table 1 Concentration of aqueous solution of carboxymethyl cellulose used in preparing samples and physical properties of the obtained samples

[0043]

[0044]

[0045] Comparative Example 1, method for preparing a comparative composite carbon foam material

[0046] Referring to the method of Example 1, the only difference is that the concentration of the aqueous solution of carboxymethyl cellulose used is replaced by 15 mg·ml-1. -1 A melamine foam precursor MC-15 uniformly impregnated with carboxymethyl cellulose is prepared. Then, carbonization is carried out according to the method of Example 1 to obtain a comparative composite carbon foam material, which is named as C@MC-15.

[0047] The beneficial effects of the present application are demonstrated by the following experimental examples.

[0048] Experimental Example 1 Microscopic morphology and structure characterization

[0049] 1. Experimental method

[0050] The microscopic structure of the samples was studied using a scanning electron microscope (SEM, Nova Nano 450, USA). The X-ray diffraction (XRD) pattern of the samples was tested with an X-ray diffractometer (DY-1291, Philips, Netherlands) with Cu Kα line. The Raman spectrum data of the samples were tested on a laser Raman spectrometer (Renishaw in Via, UK). The X-ray photoelectron spectroscopy (XPS) data of the samples were tested by an X-ray photoelectron spectrometer (ESCALAB 250Xi, Thermo, USA).

[0051] 2. Experimental results

[0052] Figure 2 The internal structure of MF before and after the formation of the layered structure is shown. The foam density after the MF skeleton film formation can be adjusted by loading different concentrations of CMC aqueous solution (Table 1). The scanning electron microscope (SEM) images Figure 1 b) show the correlation between the increase in density and the number of closed films in the porous skeleton. From Figure 3It can be seen that the excessive CMC loading in MC-15 leads to further increase of sample density and deformation of the overall size and shape of the skeleton Figure 3 , which is attributed to the maximum internal stress during in-situ film formation. In addition to deformation, the increase of CMC loading in the structure leads to the formation of a closed shell covering the entire MF skeleton, as shown in Figure 3 , which is not an ideal structure for electromagnetic wave absorption. At the same time, the increased specific surface area and local aggregation structure of the material provide conditions for improving the transmission and attenuation of electromagnetic waves. After carbonization, the layered network structure of C@MC-2 becomes compact Figure 4 due to the large elimination of oxygen and nitrogen-containing functional groups. However, the overall structure of the skeleton is not destroyed, and the layered structure is effectively retained, which indicates that the composite foam has good thermal stability and can provide an excellent conduction loss network to attenuate electromagnetic waves.

[0053] X-ray photoelectron spectroscopy (XPS) shows that the C@MC sample contains C, N and O elements Figure 5 , which is consistent with the corresponding energy dispersive spectroscopy (EDS) spectrum of the SEM image Figure 4 . The XRD pattern Figure 6 a) shows that the MF exhibits a typical amorphous dispersion peak, which gradually decreases with the increase of the concentration of CMC aqueous solution. The sample after carbonization shows a weak diffraction peak at 26°, corresponding to the (002) plane of graphite, indicating that C@MC has a graphite crystallite structure, but the crystallinity and order are poor. In the Raman spectrum Figure 6 b), the intensity ratio (I D / I G ) of the D band and the G band of C@MC-1, C@MC-2 and C@MC-5 is 1.09, 1.08 and 1.06, respectively, indicating a low degree of graphitization and weak electrical conductivity of the material.

[0054] The above experimental results show that the present application immerses the melamine foam into the carboxymethyl cellulose aqueous solution, takes it out and dries and carbonizes it, and by controlling the concentration of the carboxymethyl cellulose aqueous solution, a composite carbon foam with a semi-closed skeleton structure is obtained, which provides conditions for improving the transmission and attenuation of electromagnetic waves.

[0055] Experimental Example 2: Electromagnetic wave absorption performance characterization

[0056] 1. Experimental method

[0057] The sample was tested for electromagnetic parameters in the frequency range of 2-18 GHz using an N5230 type vector network analyzer produced by Agilent Company, USA. The sample was prepared as a concentric ring for testing, and the inner diameter of the concentric ring was 3.04 mm and the outer diameter was 7 mm.

[0058] 2. Experimental Results

[0059] The electromagnetic parameters of the C@MC samples were measured using a vector network analyzer, and the corresponding electromagnetic wave absorption characteristics were analyzed. Due to the low conductivity of amorphous carbon, the real part ε′ of the complex dielectric constant of C@MC-1, C@MC-2, and C@MC-5 is 1.2–1.9, while the imaginary part ε″ is only 0.3–1.9. Figure 7 ).

[0060] Further evaluation of the impedance matching characteristics of C@MC is presented in the Smith circle, showing the normalized real and imaginary parts of the input impedance for C@MC-1, C@MC-2, and C@MC-5 in the 2-18 GHz frequency range. Figure 8 (Thickness is 20mm). The absolute value of the reflection coefficient (Γ) is less than one-third (in the cyan dashed line area), indicating a reflection loss (R). L The impedance is below -10dB. It can be seen that the Γ values ​​of C@MC-1, C@MC-2, and C@MC-5 all fall completely within the cyan dashed line area, thanks to their excellent impedance matching characteristics. With a thickness greater than 10mm, the effective absorption bandwidth of C@MC almost covers the entire test frequency band (2-18GHz). Figure 9 ).

[0061] like Figure 10 The five-pointed star represents the material thickness t in the experimental test. m (represented as t) m exp). All t m The exp values ​​all lie well on the λ / 4 curve, indicating that the λ / 4 rule governs t. m and absorption peak frequency f m The relationship between these factors, and the destructive interference effect, contributes to the attenuation of electromagnetic waves. Furthermore, the minimum reflection loss peak value is related to Z... in The optimal impedance matching of 1 is consistent. As the thickness increases, destructive interference can also occur at larger wavelengths, manifested as the absorption peak shifting to lower frequencies.

[0062] The above experimental results demonstrate that the composite carbon foam material of this invention not only improves electromagnetic wave loss but also possesses high impedance matching characteristics. With a thickness greater than 10 mm, the material can achieve effective absorption across the entire frequency range of 2-18 GHz. This composite carbon foam material shows broad application prospects in the preparation of lightweight, broadband electromagnetic wave absorbing materials with high impedance matching characteristics.

Claims

1. Use of a composite carbon foam material in the preparation of a lightweight broadband wave-absorbing material, characterized in that, The composite carbon foam material is obtained by immersing a porous foam into an aqueous solution of a polymeric film material having a concentration of 0.1 to 12 mg ml -1 ; drying and carbonizing the porous foam; wherein the porous foam is melamine foam and the polymeric film material is carboxymethyl cellulose.

2. Use according to claim 1, characterized in that, The concentration of the aqueous solution of the polymer film material is 1-5 mg-ml -1 .

3. Use according to any one of claims 1-2, characterized in that, The time of the immersion is more than 10 minutes.

4. Use according to any one of claims 1 to 2, characterized in that, The carbonization is carried out in an inert gas atmosphere.

5. Use according to any one of claims 1-2, characterized in that, The temperature of the carbonization is 700-900℃, and the time is 0.5-3h.

6. Use according to any one of claims 1 to 2, characterized in that, The thickness is more than 10mm.

7. Use according to any one of claims 1 to 2, characterized in that, The preparation method of the composite carbon foam material comprises the following steps: (1) immersing the porous foam into an aqueous solution of a polymer film material, taking it out and drying to obtain a precursor; (2) carbonizing the precursor to obtain a composite carbon foam material.

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