Method for preparing acid and alkali resistant broadband wave-absorbing structural body

Abstract

The invention discloses a method for preparing an acid and alkali resistant broadband wave-absorbing structural body, and relates to the technical field of electromagnetic wave absorbing materials. Synthesizing a zirconium-based metal organic framework precursor PCN-222; the preparation method comprises the following steps: pyrolyzing PCN-222 into a zirconium dioxide loaded carbon-based nanorod composite material C / ZrO2, and compounding the C / ZrO2 with polyvinylidene fluoride to obtain a composite material C / ZrO2-PVDF with different filling amounts of C / ZrO2; constructing a wave absorbing body model according to the electromagnetic parameters of C / ZrO2-PVDF, and simulating the electromagnetic performance of a wave absorbing structure body through electromagnetic simulation software; industrial preparation of the wave-absorbing structural body is carried out through mixing and hot press molding methods. The scheme provided by the invention is simple, is tolerant to acid and alkali environments, and has a wave-absorbing structural body with a wide absorption frequency band. The wave-absorbing structural body prepared by the invention can be prepared in a large area, the filler distribution is highly uniform, and the preparation process is simple and suitable for large-scale batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorbing materials, and in particular to an acid- and alkali-resistant gradient impedance multilayer wedge-shaped absorbing structure, which not only has excellent electromagnetic wave absorbing performance, but also can maintain the stability of its structure and performance in harsh acid- and alkali environments. Background Art

[0002] With the rapid development of modern electronic technology and communication technology, the application of electromagnetic waves is becoming more and more extensive, but it also brings about the problems of electromagnetic pollution and electromagnetic interference. Therefore, the research and development of electromagnetic wave absorbing materials is of great significance. Most traditional electromagnetic wave absorbing materials are based on a single absorbing mechanism, such as electrical loss, magnetic loss, etc. These materials have good absorbing effects within a specific frequency range, but often have problems such as narrow absorption bandwidth, low absorption efficiency, and poor stability. Especially in harsh environments such as acid and alkali, the performance of traditional absorbing materials will drop significantly, or even lose their absorbing ability.

[0003] Gradient impedance absorbing material is a new type of electromagnetic wave absorbing material. By changing the impedance characteristics of the material, it presents different electromagnetic parameters at different thicknesses, thereby achieving broadband and high-efficiency electromagnetic wave absorption. However, most of the existing gradient impedance absorbing materials use a single material system, which is difficult to meet the application requirements in complex environments. Especially in acid-base environments, the chemical stability of the material has become a key factor restricting its application.

[0004] Therefore, it is of great practical value and scientific research significance to develop a gradient impedance multilayer wedge-shaped absorbing structure that has excellent electromagnetic wave absorption performance and can maintain stability in acid-base environments. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention proposes an acid- and alkali-resistant gradient impedance multilayer wedge-shaped absorbing structure. The structure achieves the gradient impedance absorbing effect through the combination design of multilayer materials, and adopts acid- and alkali-resistant composite materials, so that the structure can still maintain stable performance in acid and alkaline environments.

[0006] The technical solution of the present invention is as follows:

[0007] Step 1: Synthesize zirconium-based metal organic framework PCN-222 by solvothermal method;

[0008] Step 2: Pyrolysis of the zirconium-based metal organic framework PCN-222 into zirconium dioxide-loaded carbon-based nanorod composite material C / ZrO 2 The C / ZrO 2 Composites of nanorod composites and polyvinylidene fluoride to obtain different filling amounts of C / ZrO 2Nanorod composites C / ZrO 2 -PVDF;

[0009] Step 3: Based on the above C / ZrO 2 -The electromagnetic parameters of PVDF are used to construct the absorber model, and the electromagnetic performance of the absorber structure is simulated by electromagnetic simulation software;

[0010] Simulate the electromagnetic performance of the absorbing structure through electromagnetic simulation software;

[0011] Step 4: Industrial preparation of the wave-absorbing structure by mixing and hot pressing.

[0012] Preferably, step 1 comprises: tetrakis(4-carboxyphenyl)porphyrin (H 2 -TCPP) and ZrOCl 2 8H 2 O.CF 3 COOH was placed in N,N-dimethylformamide (DMF) in proportion, heated under reflux in an oil bath, and then washed with DMF and acetone to obtain PCN-222.

[0013] Preferably, H 2 -TCPP and ZrOCl 2 8H 2 The molar mass ratio of O is 1:(8-9), CF 3 The volume ratio of COOH to DMF solvent is 1:(20-25). After a lot of experimental adjustments, this ratio can accurately control the purity of the precursor PCN-222. The reflux temperature is 120-150°C, the reflux time is 30-60h, preferably 130°C reflux for 48h.

[0014] The open solvent thermal method uses a high temperature solvent to directly react under normal pressure conditions, which can reduce the requirements for experimental equipment and facilitate further industrial production. Compared with other technologies, this solution has high product purity, good uniformity, good dispersibility, and low production cost. In the present invention, PCN-222 with stable composition is obtained by the open solvent thermal method, which is simple to operate.

[0015] Preferably, step 2 comprises: sintering the PCN-222 precursor nanorods obtained in step 1 at 750-900° C. (preferably 800° C.) in an inert atmosphere to obtain C / ZrO 2 Nanorods, the obtained C / ZrO 2 Nanorod material and PVDF were weighed in proportion, the weighed PVDF was dissolved in DMF, and ultrasonic treatment was performed until a transparent mixed solution was obtained. 2The nanorod material is placed in the transparent mixed solution, mechanically stirred or / and ultrasonically obtained to obtain a black suspension, and then the black suspension is subjected to solvent evaporation to obtain zirconium dioxide carbon-based nanorods C / ZrO 2 Composite membrane with PVDF; C / ZrO 2 The proportion of nanorods in the composite film is 3wt% to 30wt%. After a series of ratio adjustments, this ratio of C / ZrO 2 -PVDF filling amount can take into account both high and low dielectric materials, which is beneficial to the subsequent design of absorber structure. 2 After being immersed in strong acid and strong alkali solutions for one year, its microwave absorption performance was tested.

[0016] The open solvent thermal synthesis process is simple, the precipitation separation operation is simple, the product can be collected on a large scale, and the cost is low. And through simple sintering, a carbon material with high dielectric constant is obtained, thereby optimizing impedance matching and optimizing microwave absorption performance.

[0017] Preferably, step 3 includes: combining gradient impedance with the principle of multiple scattering, performing gradient impedance by modulating multiple layers with different filling amounts to achieve broadband absorption of electromagnetic waves, designing the material into a periodic structure, and improving the absorbing strength of the absorber by the principle of multiple scattering.

[0018] According to the above C / ZrO 2 -PVDF electromagnetic parameters are used to construct the absorber structure. The absorber is composed of multiple parallel wedge-shaped structures or table-shaped structures arranged closely and periodically. Each wedge-shaped structure or table-shaped structure is composed of multiple layers of C / ZrO with different filling amounts. 2 C / ZrO nanorods 2 -PVDF membranes are stacked, and each wedge-shaped structure or terrace-shaped structure has a larger bottom area and a C / ZrO corresponding to the top of the wedge or terrace. 2 -C / ZrO in PVDF membrane 2 The filling amount of nanorods decreases in sequence; the adjacent C / ZrO 2 -PVDF membranes use a stepped structure, i.e. the upper layer of C / ZrO 2 -The area of ​​PVDF film is smaller than the next layer of C / ZrO 2 -PVDF membrane area, corresponding to the next layer of C / ZrO 2 -The periphery of the PVDF membrane is relatively close to the upper layer of C / ZrO 2 -PVDF membrane bulges around the periphery, so multi-layer C / ZrO 2 - The steps between the PVDF membranes form a wedge-shaped structure or a terrace-shaped structure, and it is further preferred that the wedge-shaped structure or the terrace-shaped structure is a quadrilateral wedge-shaped structure or a terrace-shaped structure, a pentagonal wedge-shaped structure or a terrace-shaped structure, etc., and a structure with more scattering angles is designed as much as possible;

[0019] Specific C / ZrO 2 -The number of PVDF membrane layers can be adjusted according to needs, such as 3-20 layers, etc.; each layer of C / ZrO 2 -The thickness of the PVDF film can be adjusted as needed, such as 1-5mm; the bottom area of ​​the wedge-shaped structure can be adjusted as needed, such as the bottom side length of the wedge-shaped structure is 1-20mm; the total height of the wedge-shaped structure is 10-20mm; the specific C / ZrO 2 -C / ZrO in PVDF membrane 2 Can be adjusted as needed.

[0020] Preferably, step 4 comprises: according to the structural design of step 3, by mixing the absorbent zirconium dioxide carbon-based nanorods C / ZrO 2 Combined with the polymer matrix PVDF, a uniformly distributed absorbing film is generated. The absorbing film is placed in a mold for hot pressing to obtain a uniform periodic structure. Through the combination of composite and other schemes, an acid- and alkali-resistant broadband absorbing structure is obtained.

[0021] Compared with the prior art, the materials and methods of the present invention have the following advantages:

[0022] (1) The method of the present invention adopts an open solvent method to synthesize PCN-222, and obtains uniformly dispersed microrods, which can be precipitated, separated and washed, and the operation is simple. Figure 1 .

[0023] (2) The composite absorbing material of the present invention is prepared by pyrolysis of an organic metal framework template, wherein zirconium dioxide is uniformly fixed on a one-dimensional carbon nanorod, C / ZrO 2 The material has excellent acid and alkali resistance. After being immersed in strong acid and alkali solutions for one year, it still has relatively excellent wave absorption performance, which solves the problem that metal is easy to oxidize and deteriorate and affects the wave absorption performance of the material. Figure 2 , 4 .

[0024] (3) The present invention uses gradient impedance and multiple scattering effects to solve the problem of narrow absorption frequency band and achieve the ideal result of broadband absorption of electromagnetic waves. Compared with the wave absorption effect, it not only greatly improves the wave absorption amount of the material, but also effectively improves the absorption intensity. Figure 6 .

[0025] (4) The present invention can also adjust the structural parameters as needed to adjust the wave absorbing performance.

[0026] Compared with the authorized patent, the process is simple, with high acid and alkali tolerance, stable absorbing performance, highly uniform filler distribution, small filler dosage, and excellent absorbing performance. The process is suitable for large-scale mass production, and overcomes the problems widely existing in the existing absorber technology, such as harsh synthesis conditions, easy oxidation and deterioration of metals, deterioration of absorbing performance after long-term use, and narrow absorption frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 Scanning electron microscopy of a randomly selected area of ​​the sample prepared in step 1, the sample particle size length is 1 μm, and there is no uneven distribution area.

[0029] Figure 2 This is an electron microscope comparison of the sample prepared in step 2 after being immersed in strong acid and strong alkali for 365 days.

[0030] Figure 3 Schematic diagram of the reflection loss performance of the sample prepared in step 2 at different filling rates.

[0031] Figure 4 C / ZrO of the sample prepared in step 2 after being immersed in strong acid and strong base for 365 days 2 Comparison of reflection loss when the filling rate is 10wt%.

[0032] Figure 5 This is a schematic diagram of the structure of the absorber with a multi-layer gradient impedance wedge structure according to the present invention.

[0033] Figure 6 This is a performance diagram of the reflection loss results of the multi-layer gradient impedance wedge structure absorber described in the present invention.

[0034] Figure 7 Schematic diagram of the electric field distribution of the multi-layer gradient impedance wedge structure absorber of the present invention.

[0035] Figure 8 Schematic diagram of loss distribution of the multi-layer gradient impedance wedge structure absorber of the present invention.

[0036] Table 1 is a periodic unit model parameter table of the multi-layer gradient impedance wedge structure absorber of the present invention (from top to bottom according to the model). DETAILED DESCRIPTION

[0037] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0038] Example 1

[0039] Step 1: Solvothermal synthesis of zirconium-based metal-organic frameworks

[0040] Add 2-4 g of H 2 -TCPP and 9g ZrOCl 2 8H 2 O was placed in a flask containing 750 ml of DMF, stirred evenly, and then 30-37 ml of CF 3 COOH, and stirred for another hour. Heat in an oil bath at 130°C for 48 hours. After the reactor cooled to room temperature, the precipitate was separated by centrifugation, then washed with DMF for the third time and acetone twice, and finally dried in vacuum at 60°C.

[0041] Step 2: Pyrolysis of precursor to prepare electromagnetic absorber

[0042] The PCN-222 nanorods obtained in step 1 are sintered at high temperature in an inert atmosphere to obtain C / ZrO 2 Nanorods, and select C / ZrO 2 Nanorod material and PVDF were weighed in proportion, the weighed PVDF was dissolved in DMF, and ultrasonic treatment was performed until a transparent mixed solution was obtained. 2 The nanorod material is placed in the transparent mixed solution and mechanically stirred to obtain a black suspension; the black suspension is subjected to solvent evaporation to obtain zirconium dioxide carbon-based nanorods C / ZrO with different filling amounts. 2 Composite membrane with PVDF, in which zirconium dioxide carbon-based nanorods C / ZrO 2 The total proportion is from 3wt% to 30wt%.

[0043] Step 3: Build the absorber model and perform electromagnetic simulation

[0044] According to the impedance matching principle, the electromagnetic wave is incident on the top layer, which is C / ZrO with low electromagnetic parameters. 2 -PVDF composite materials, to achieve the purpose of electromagnetic waves entering the absorbing structure; through the principle of gradient impedance, the electromagnetic parameters are increased layer by layer, electromagnetic waves of different frequency bands are absorbed in turn, and the effective absorption bandwidth of the material is broadened; according to the principle of multiple scattering, the absorber structure is periodically designed, and the absorption intensity of the absorber is improved by using a structure with more scattering angles. The parameters of the absorbing structure with the best performance are optimized through electromagnetic simulation software.

[0045] Table 1 Periodic unit model parameter table of multilayer gradient impedance wedge structure (quadrilateral) absorber (including tolerance)

[0046]

[0047] Figure 3 Single-layer C / ZrO with different filling amounts and thicknesses (1, 2, 3, 4, 5 mm) 2 The wave absorption performance of PVDF membrane;

[0048] Figure 4 Single-layer C / ZrO with a filling content of 10% and different thicknesses (1, 2, 3, 4, 5 mm) 2 Compared with the original PVDF membrane, the absorption performance after immersion in acidic and alkaline conditions for 365 days; it can be seen from the figure that the C / ZrO 2 It has good acid and alkali resistance compared to PVDF membrane.

[0049] Step 4: Industrial preparation of the wave-absorbing structure by mixing and hot pressing.

[0050] According to the structural design parameters of step 3, the absorbent zirconium dioxide carbon-based nanorods C / ZrO 2 Combined with the polymer matrix PVDF, a uniformly distributed absorbing film is generated. The absorbing film is placed in a mold for hot pressing (temperature 200-230°C) to obtain a uniform periodic structure. Through combination with composite and other schemes, an acid- and alkali-resistant broadband absorbing structure is obtained.

[0051] Figure 6 This is a performance diagram of the reflection loss results of the multi-layer gradient impedance wedge structure absorber. It can be seen that the multi-layer gradient impedance wedge structure absorber has a relatively ideal absorbing performance in the S-Ku band. When the thickness is 14.5 mm, the effective absorption bandwidth is as high as 14.16 GHz (basically from 3.84 GHz to 18 GHz), and it effectively absorbs 88.5% of the incident electromagnetic wave energy above the frequency range.

[0052] The electric field distribution diagram of the multi-layer gradient impedance wedge structure absorber is shown in Figure 7 .

[0053] Schematic diagram of loss distribution of the multi-layer gradient impedance wedge structure absorber Figure 8 .

[0054] The above only describes some of the best embodiments of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. All changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing an acid-base resistant broadband absorbing structure, characterized in that: The following steps are involved: Step 1: Synthesize zirconium-based metal organic framework PCN-222 by solvothermal method; Step 2: Pyrolyze the zirconium-based metal organic framework PCN-222 into a zirconium dioxide-loaded carbon-based nanorod composite material C / ZrO2, and use an ultrasonic method to compound the C / ZrO2 nanorod composite material with polyvinylidene fluoride to obtain a composite material C / ZrO2-PVDF with different filling amounts of C / ZrO2 nanorods; Step 3: construct an absorber model based on the electromagnetic parameters of the C / ZrO2-PVDF, and simulate the electromagnetic performance of the absorber structure through electromagnetic simulation software; Step 4: Industrial preparation of the wave-absorbing structure by mixing and hot pressing.

2. The method according to claim 1, characterized in that Step 1 comprises: placing tetrakis(4-carboxyphenyl)porphyrin (H2-TCPP), ZrOCl2·8H2O and CF3COOH in N,N-dimethylformamide (DMF) in proportion, heating under reflux in an oil bath, and washing with DMF and acetone to obtain PCN-222.

3. The method according to claim 2, characterized in that The molar mass ratio of H2-TCPP to ZrOCl2·8H2O is 1:(8-9), and the volume ratio of CF3COOH to DMF solvent is 1:(20-25); the reflux temperature is 120-150°C, and the reflux time is 30-60h, preferably 130°C for 48h.

4. The method according to claim 1, characterized in that Step 2 comprises: sintering the PCN-222 precursor nanorods obtained in step 1 at 750-900° C. (preferably 800° C.) in an inert atmosphere to obtain C / ZrO2 nanorods, weighing the obtained C / ZrO2 nanorod material and PVDF in proportion, dissolving the weighed PVDF in DMF, ultrasonically treating until a transparent mixed solution is obtained, placing the weighed C / ZrO2 nanorod material in the transparent mixed solution, mechanically stirring or / and ultrasonically treating to obtain a black suspension, and then subjecting the black suspension to solvent evaporation, thereby obtaining a composite film of zirconium dioxide carbon-based nanorods C / ZrO2 and PVDF; the proportion of C / ZrO2 nanorods in the composite film is 3wt% to 30wt%.

5. The method according to claim 1, characterized in that Step 3 includes: combining gradient impedance with the principle of multiple scattering, performing gradient impedance modulation by multiple layers of different filling amounts to achieve broadband absorption of electromagnetic waves, designing the material into a periodic structure, and improving the absorption strength of the absorber through the principle of multiple scattering.

6. The method according to claim 5, characterized in that The absorber structure is constructed according to the electromagnetic parameters of C / ZrO2-PVDF. The absorber is composed of a plurality of parallel wedge-shaped structures or terrace-shaped structures arranged closely and periodically. Each wedge-shaped structure or terrace-shaped structure is composed of a plurality of C / ZrO2-PVDF films with different filling amounts of C / ZrO2 nanorods stacked on top of each wedge-shaped structure or terrace-shaped structure. The filling amount of C / ZrO2 nanorods in the C / ZrO2-PVDF film corresponding to the wedge-shaped top or terrace-shaped top decreases in sequence. The gap between adjacent C / ZrO2-PVDF films is A stepped structure is adopted, that is, the area of ​​the upper C / ZrO2-PVDF membrane layer is smaller than the area of ​​the lower C / ZrO2-PVDF membrane layer, and the corresponding periphery of the lower C / ZrO2-PVDF membrane layer protrudes relative to the periphery of the upper C / ZrO2-PVDF membrane layer, so that the steps between the multiple layers of C / ZrO2-PVDF membranes form a wedge-shaped structure or a terrace-shaped structure. It is further preferred that the wedge-shaped structure or terrace-shaped structure is a quadrilateral wedge-shaped structure or terrace-shaped structure, a pentagonal wedge-shaped structure or terrace-shaped structure, etc., and a structure with more scattering angles is designed as much as possible.

7. The method according to claim 6, characterized in that The specific number of layers of C / ZrO2-PVDF membrane can be adjusted as needed, such as 3-20 layers, etc.; the thickness of each layer of C / ZrO2-PVDF membrane can be adjusted as needed, such as 1-5mm, etc.; the bottom area of ​​the wedge-shaped structure can be adjusted as needed, such as the bottom side length of the wedge-shaped structure is 1-20mm; the total height of the wedge-shaped structure is 10-20mm; the C / ZrO2 in each layer of C / ZrO2-PVDF membrane can be adjusted as needed.

8. The method according to claim 1, characterized in that Step 4 includes: according to the structural design of step 3, the absorbent zirconium dioxide carbon-based nanorods C / ZrO2 are combined with the polymer matrix PVDF by a mixing method to generate a uniformly distributed absorbing film, the absorbing film is placed in a mold for hot pressing to obtain a uniform periodic structure, and an acid-base resistant broadband absorbing structure is obtained by combining with composite and other schemes.

9. A broadband wave absorbing structure prepared by the method according to any one of claims 1 to 8.

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