Preparation method and application of C / Al2MgO4 composite microwave absorbing material

Abstract

This invention relates to the field of microwave absorbing materials technology, and particularly to a method for preparing and applying a C / Al2MgO4 composite microwave absorbing material. The preparation method includes: (1) pre-drying papermaking sludge, ball milling, and sieving to obtain sludge powder; (2) adding an acidifying solution to activate the sludge powder, followed by drying; (3) calcining the dried product obtained in step (2) at a constant temperature under an inert atmosphere to obtain a pyrolysis product; (4) preparing a modifier-potassium hydroxide aqueous solution; (5) immersing the pyrolysis product in the modifier solution for 4-6 hours and drying; (6) calcining the material obtained in step (5) at a constant temperature of 600-900ºC under an inert atmosphere to obtain a modified product; (7) dispersing the modified product in an excess acid solution, stirring, and then drying for 12-24 hours to obtain the final product. This invention utilizes papermaking sludge in a resource-efficient manner, is simple to prepare, has low cost, and produces a C / Al2MgO4 composite microwave absorbing material with a unique structure and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a method for preparing and applying a C / Al2MgO4 composite microwave absorbing material. Background Technology

[0002] With the rapid development of modern electronic information technology, more and more electronic devices have become indispensable tools in our lives and work. They are widely used in military (radar) and civilian (computers, navigation, communication, electrical equipment) fields, making significant contributions to social progress and development. At the same time, people are also facing increasingly serious problems of interference and radiation from electronic devices. Silent, odorless, and colorless electromagnetic waves exist in human living spaces, not only interfering with communications but also seriously endangering human health, making it the fourth largest form of pollution after water pollution, air pollution, and noise pollution. Therefore, electromagnetic pollution has become one of the focal points of concern in human society. To eliminate the harm of electromagnetic pollution, protection is necessary. However, we have noticed that while protection is being implemented, the reflected electromagnetic waves will again generate radiation and interference. This necessitates finding a wave-absorbing material that can absorb and attenuate electromagnetic wave radiation.

[0003] Paper mill sludge, a solid waste generated during the pulping and papermaking process, poses a serious threat to the ecological environment if not properly treated due to the pollutants in its concentrate and papermaking wastewater. In recent years, with the booming development of the paper industry, the production of paper mill sludge has increased significantly, making its treatment and disposal difficult and costly, thus becoming a bottleneck for the industry's development. Currently, my country's treatment of paper mill sludge mainly focuses on sanitary landfill, incineration, agricultural use, and as a filler material. However, excessive landfilling occupies a large amount of land and causes soil pollution. Furthermore, while incinerating paper mill sludge recovers some heat energy, heavy metals in the sludge pollute the air with the spread of smoke and dust, and the combustion of large quantities of paper mill sludge emits significant amounts of CO2 greenhouse gases. Therefore, it is necessary to reduce the proportion of sludge landfill and incineration, and further increase the proportion of sludge treated and disposed of in agriculture, building materials, and other high-value resource utilization applications.

[0004] Considering the compositional characteristics of papermaking sludge, which contains a large amount of lignin, cellulose, and a small amount of inorganic minerals, the carbon skeleton structure formed after heat treatment has a large specific surface area, making it a highly promising adsorbent material. In recent years, there have been reports on the development and utilization of papermaking sludge to prepare adsorbent materials, but many problems remain, such as low utilization rate, immature processes, and limited product variety. While the carbon skeleton structure formed after heat treatment of papermaking sludge possesses characteristics such as large specific surface area, porous structure, certain conductivity, and low cost, its direct application in the preparation of microwave absorbing materials still suffers from low absorption capacity.

[0005] To improve the microwave absorption performance of materials, physical or chemical modification methods are generally used to regulate the material structure. For example, modifiers such as KOH and ZnCl2 are used to create pores, thereby enhancing the performance of the absorbing material. However, since silicon in papermaking sludge is mostly present in the amorphous form of SiO2, its content is usually limited and cannot completely form ceramic phases such as SiC. Furthermore, there will be excess SiO2. To prepare C / Si composite absorbing materials, additional silicon or carbon sources must be added, undoubtedly increasing the complexity and cost of the process. In addition, KOH reacts violently with carbon materials, easily leading to excessive micropore development. When using carbon framework materials from different sources, the amount of such modifiers used will vary significantly and the preparation process must be strictly controlled, because excessively developed micropores will affect the multiple scattering of electromagnetic waves, interfering with the microwave absorption performance of the product. Furthermore, there are currently no reports on the technology of using papermaking sludge as raw material to modify microwave absorbing materials with KOH through pore-forming. Based on the role of pore-forming agents in existing technologies, it is speculated that applying them to papermaking sludge raw materials to prepare microwave absorbing materials may still result in the preparation of C / Si composite microwave absorbing materials, but it is difficult to directly obtain ceramic phase composite materials. This is because ceramic phase composite materials require a ceramicization sintering temperature of over 1500℃, which will interfere with the pore-forming structure obtained by the pore-forming agent in the early stage, and easily lead to the collapse of the microporous structure. Therefore, it is difficult to balance the technical conflicts in preparing ceramic phase microwave absorbing materials.

[0006] Based on this, developing a novel microwave absorbing material that efficiently and rationally utilizes papermaking sludge can not only effectively alleviate various ecological and environmental pressures caused by the large-scale discharge and accumulation of papermaking sludge, but also reduce the production cost of microwave absorbing materials, turning waste into treasure and taking into account environmental, economic and social benefits. Summary of the Invention

[0007] This invention provides a method for preparing C / Al2MgO4 composite microwave absorbing material and its application. While making resource-efficient use of papermaking sludge, the preparation is simple and low-cost, and a ceramic phase composite microwave absorbing material is obtained. Its unique structure and excellent performance provide potential for the development and application of high-temperature resistant and oxidation-resistant composite microwave absorbing materials, and solve the problems existing in the prior art.

[0008] One of the technical solutions adopted in this invention is:

[0009] A method for preparing a C / Al2MgO4 composite microwave absorbing material is provided, comprising the following steps:

[0010] (1) After pre-drying the papermaking sludge, ball mill it and sieve it through a 100-200 mesh screen to obtain sludge powder;

[0011] (2) Take the sludge powder from step (1), add acidification solution and soak for 4-6 hours, wash with deionized water and anhydrous ethanol multiple times until neutral, dry at 100±10℃ for 12-24 hours to obtain the dried product for later use.

[0012] (3) The dried product of the acid-washed sludge obtained in step (2) is calcined at 500℃ for 1-3 hours under an inert atmosphere to obtain the pyrolysis product for later use.

[0013] (4) Prepare a modified potassium hydroxide aqueous solution;

[0014] (5) The pyrolysis product obtained in step (3) is immersed in the potassium hydroxide aqueous solution in step (4) and stirred continuously for 4-6 hours, and dried at 70-90℃ for 12-24 hours to obtain a dried mixture;

[0015] (6) The dried mixture obtained in step (5) is calcined at 600-900℃ for 3-5 hours under an inert atmosphere and then cooled to room temperature to obtain the modified product.

[0016] (7) Disperse the modified product obtained in step (6) in an excess of acid solution, stir continuously for 2-6 hours, wash repeatedly with deionized water and anhydrous ethanol until neutral, and dry at 90-100℃ for 12-24 hours to obtain a porous ceramic composite microwave absorbing material.

[0017] Furthermore, the pre-drying temperature in step (1) is 100-110℃.

[0018] Further, in step (2), the mass-to-volume ratio of sludge powder to acidification liquid is 1:10; the acidification liquid is 10-30wt% HCl.

[0019] Furthermore, the pyrolysis product of step (3) is a mixture including carbon and ash. The chemical composition of the ash is shown in Table 1 below.

[0020] Furthermore, in step (4), the concentration of the potassium hydroxide aqueous solution is 0.5-1.5 mol / L.

[0021] Furthermore, in step (5), the mass ratio of the potassium hydroxide aqueous solution to the pyrolysis product after acidification in step (3) is 1-2.5:1.

[0022] Furthermore, in steps (3) and (6), the inert atmosphere is Ar, and the calcination is carried out in a tubular furnace; the specific surface area of ​​the resulting porous ceramic composite microwave absorbing material reaches 182-325 m². 2 / g.

[0023] Furthermore, the roasting temperature in step (6) is preferably 700-900℃.

[0024] Further, in step (7), the acid solution is an HCl solution. The amount of HCl solution used is ≥150mL.

[0025] Furthermore, the industrial analysis and ash chemical composition and corresponding weight percentage of the acidified papermaking sludge are shown in Table 1.

[0026]

[0027] The second technical solution adopted in this invention is:

[0028] The C / Al2MgO4 composite microwave absorbing material prepared by the above method is provided as a high-temperature and radiation-resistant microwave absorbing material for applications in national defense and military radar, high-temperature electromagnetic shielding equipment, aerospace and other fields.

[0029] The beneficial effects of this invention are:

[0030] 1. The main raw material used in this invention is papermaking sludge solid waste. By effectively recycling and pretreating it and using it to prepare microwave absorbing material powder, not only is waste turned into treasure, but the preparation of microwave absorbing material is also made cheaper. The papermaking sludge used in this invention contains 15.21 wt% biochar. During the calcination process under an inert atmosphere, a porous C / Al2MgO4 composite material is formed, which enhances the microwave absorption performance of the composite material.

[0031] 2. In the preparation method of this invention, the KOH modifier undergoes a strong chemical reaction with the carbon in the raw material at a high temperature of 700-900℃, creating a large number of pores and forming a porous structure by "corroding" and "etching" the carbon skeleton. By reasonably controlling the amount of KOH modifier, the collapse of pores on the carbon skeleton is avoided, ensuring the performance of the microwave absorbing material. While achieving the above-mentioned pore-forming effect, the remaining KOH at the high temperature of 700-900℃ reacts with SiO2 in the pyrolysis product ash to generate K2SiO3, which can be removed by acid washing (reacting with HCl to generate KCl and silicic acid). Therefore, after the SiO2 in the ash is consumed, the high temperature of 700-900℃ further promotes the reaction between MgO and Al2O3 in the ash to generate the Al2MgO4 ceramic phase. This invention presents a novel method for preparing Al2MgO4 ceramic phase materials, overcoming the current challenge of conflicting pore-forming and ceramic sintering temperatures in carbon materials. This method allows for the production of ceramic phase microwave absorbing materials at KOH activation temperatures (700-900℃). Compared to existing technologies where SiC ceramic phase formation requires temperatures above 1500℃ and Al2MgO4 ceramic phase sintering requires 1200℃, this invention, prepared at 700-900℃, not only avoids the potential damage to the microporous structure caused by high-temperature treatments above 1000℃ but also shortens the preparation cycle. The resulting Al2MgO4 ceramic phase microwave absorbing material, due to its excellent high-temperature resistance and oxidation resistance, further expands its application potential. The formation of the magnesium-aluminum spinel phase is presumably due to the KOH and SiO2 reaction promoting the reaction between MgO and Al2O3. While ZnCl2, also used as a pore-forming agent, may have the potential to form pores and serve as a ceramic raw material, its preparation process is more complex. Furthermore, experiments have shown that the microwave absorbing material obtained from it is still SiC, and it completely lacks the ability to generate the aforementioned Al2MgO4 ceramic phase microwave absorbing material.

[0032] 3. The present invention adopts the process steps of "acid washing activation + pore-forming modification + controlled pyrolysis", which does not require a ceramic sintering temperature of more than 1000℃ to construct the unique structure of mesoporous carbon / Al2MgO4. Attached Figure Description

[0033] Figure 1 The XRD pattern of the composite microwave absorbing material in Example 1 of this invention is shown.

[0034] Figure 2 This is a scanning electron microscope (SEM) image of the composite microwave absorbing material of the present invention;

[0035] Figure 3 The N2 adsorption-desorption curve and pore size distribution diagram of the composite microwave absorbing material of the present invention are shown below.

[0036] Figure 4 These are the test results of the microwave absorption performance of the composite microwave absorbing material of this invention. Detailed Implementation

[0037] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0039] The following embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions should first refer to the guidelines given in this application, or may be performed according to experimental manuals or conventional conditions in the art, or by referring to experimental methods known in the art. Unless otherwise specified, all methods are conventional methods in the art.

[0040] In the following specific embodiments, unless otherwise specified, slight deviations may exist within the weighing accuracy range for the measurement parameters of the raw material components. For temperature and time parameters, acceptable deviations due to instrument testing accuracy or operational precision are permissible. The equipment and raw materials used are commercially available or commonly used in the art.

[0041] The papermaking sludge used in the following specific examples originated from papermaking sludge from a paper mill in Taiyuan, Shanxi Province. The industrial analysis and ash chemical composition of the acidified papermaking sludge used in the examples are shown in Table 2 below.

[0042]

[0043] Example 1

[0044] A method for preparing a C / Al2MgO4 composite microwave absorbing material includes the following steps:

[0045] (1) The papermaking sludge was pre-dried at 100°C and then ball-milled and sieved through a 100-mesh sieve to obtain sludge powder;

[0046] (2) Weigh 10g of sludge powder prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (20wt% HCl) to the conical flask and treat for 4h. Then wash it repeatedly with deionized water and anhydrous ethanol until neutral. Dry it at 100℃ for 24h for later use.

[0047] (3) The sludge after acid washing obtained in step (2) is heated to 500°C at 5°C / min under argon flow and kept at the temperature for 2 hours for controlled pyrolysis to obtain pyrolysis products for later use.

[0048] (4) Prepare a 0.5 mol / L potassium hydroxide aqueous solution as a modifier;

[0049] (5) Weigh 1.4g of the pyrolysis product and immerse it in 50mL of 0.5mol / L potassium hydroxide aqueous solution and stir continuously for 6h. Then dry it at 90℃ for 12h to obtain a dry mixture.

[0050] (6) The mixture obtained in step (5) is heated to 700°C at 5°C / min under an argon flow and kept at the temperature for 3 hours for controlled pyrolysis to obtain the modified product for later use;

[0051] (7) Disperse the modified product obtained in step (6) in an excess (150 ml) of hydrochloric acid solution, stir continuously for 2 h, wash repeatedly with deionized water and anhydrous ethanol until neutral, and dry at 100 °C for 12 h to obtain C / Al2MgO4 composite microwave absorbing material.

[0052] Example 2

[0053] A method for preparing a C / Al2MgO4 composite microwave absorbing material includes the following steps:

[0054] (1) The papermaking sludge was pre-dried at 110°C and then ball-milled and sieved through a 150-mesh sieve to obtain sludge powder;

[0055] (2) Weigh 10g of sludge powder prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (30wt% HCl) to the conical flask and treat for 4h. Then wash it several times with deionized water and anhydrous ethanol until neutral. Dry it at 100℃ for 20h and set aside.

[0056] (3) The sludge after acid washing obtained in step (2) is heated to 500°C at 5°C / min under argon flow and kept at the temperature for 3h for controlled pyrolysis to obtain pyrolysis products for later use.

[0057] (4) Prepare a 1.0 mol / L potassium hydroxide aqueous solution as a modifier;

[0058] (5) Weigh 1.4g of the pyrolysis product and immerse it in 50mL of 1.0mol / L potassium hydroxide aqueous solution and stir continuously for 4h. Dry it at 80℃ for 12h to obtain a dry mixture;

[0059] (6) The mixture obtained in step (5) is heated to 700°C at 5°C / min under an argon flow and kept at the temperature for 4 hours for controlled pyrolysis to obtain the modified product for later use;

[0060] (7) Disperse the modified product obtained in step (6) in an excess (200 ml) of hydrochloric acid solution, stir continuously for 4 h, wash repeatedly with deionized water and anhydrous ethanol until neutral, and dry at 90 °C for 16 h to obtain C / Al2MgO4 composite microwave absorbing material.

[0061] Example 3

[0062] A method for preparing a C / Al2MgO4 composite microwave absorbing material includes the following steps:

[0063] (1) The papermaking sludge was pre-dried at 100°C and then ball-milled and sieved through a 200-mesh sieve to obtain sludge powder;

[0064] (2) First, weigh 10g of sludge powder prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (30wt%HCl) to the conical flask and treat for 4h. Then wash it repeatedly with deionized water and anhydrous ethanol until neutral. Dry it at 100℃ for 24h for later use.

[0065] (3) The sludge after acid washing obtained in step (2) is heated to 500°C at 5°C / min under argon flow and kept at the temperature for 3h for controlled pyrolysis to obtain pyrolysis products for later use.

[0066] (4) Prepare a 1.0 mol / L potassium hydroxide aqueous solution as a modifier;

[0067] (5) Weigh 1.4g of the pyrolysis product and immerse it in 50mL of 1.0mol / L potassium hydroxide aqueous solution and stir continuously for 6h. Dry it at 80℃ for 12h to obtain a dry mixture;

[0068] (6) The mixture obtained in step (5) is heated to 800°C at 5°C / min under an argon flow and kept at that temperature for 3 hours to obtain the modified product for later use;

[0069] (7) Disperse the modified product obtained in step (6) in an excess (160 ml) of hydrochloric acid solution, stir continuously for 4 h, wash repeatedly with deionized water and anhydrous ethanol until neutral, and dry at 90 °C for 24 h to obtain C / Al2MgO4 composite microwave absorbing material.

[0070] Example 4

[0071] A method for preparing a C / Al2MgO4 composite microwave absorbing material includes the following steps:

[0072] (1) The papermaking sludge was pre-dried at 100°C and then ball-milled and sieved through a 200-mesh sieve to obtain sludge powder;

[0073] (2) Weigh 10g of sludge powder prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (10wt% HCl) to the conical flask and treat for 4h. Then wash it repeatedly with deionized water and anhydrous ethanol until neutral. Dry it at 110℃ for 24h for later use.

[0074] (3) The sludge after acid washing obtained in step (2) is heated to 500°C at 5°C / min under argon flow and kept at the temperature for 2 hours for controlled pyrolysis to obtain pyrolysis products for later use.

[0075] (4) Prepare a 1.5 mol / L potassium hydroxide aqueous solution as a modifier;

[0076] (5) Weigh 1.4g of the pyrolysis product and immerse it in 50mL of 1.5mol / L potassium hydroxide aqueous solution and stir continuously for 6h. Then dry it at 80℃ for 12h to obtain a dry mixture.

[0077] (6) The mixture obtained in step (5) is heated to 700°C at 5°C / min under an argon flow and kept at the temperature for 4 hours for controlled pyrolysis to obtain the modified product for later use;

[0078] (7) Disperse the modified product obtained in step (6) in an excess (200 ml) hydrochloric acid solution, stir continuously for 6 h, wash repeatedly with deionized water and anhydrous ethanol until neutral, and dry at 100 °C for 12 h to obtain C / Al2MgO4 composite microwave absorbing material.

[0079] Performance testing:

[0080] I. XRD pattern

[0081] The composite microwave absorbing materials prepared in the embodiments of the present invention were subjected to XRD pattern analysis. The main phase composition of the C / Al₂MgO₄ composite microwave absorbing materials prepared in each embodiment was carbon and Al₂MgO₄ phases. Taking Example 1 as an example, its XRD pattern is as follows: Figure 1 As shown.

[0082] II. Scanning Electron Microscopy (SEM)

[0083] The scanning electron microscope (SEM) in the above embodiments is as follows: Figure 2 As shown, in Examples 1-3, activation with an appropriate amount of KOH ultimately formed a porous C / Al2MgO4 composite microwave absorbing material. In contrast, in Example 4, the carbon pore structure collapsed and the porous structure was destroyed. The N2 adsorption-desorption curves and pore size distribution diagrams of each example are shown below. Figure 3 The obtained BET specific surface areas were 182.1, 312.5, 325.8 and 145.2 m², respectively. 2 / g.

[0084] III. Absorption Performance Test

[0085] The porous composite microwave absorbing materials prepared in Examples 1-4 were tested for minimum reflection loss versus frequency. The results are shown below. Figure 4As shown in the figure, the composite microwave absorbing material prepared in Example 1, with a coating thickness of 2.0 mm, has a minimum reflection loss of -25.5 dB and an effective bandwidth of 5.0 GHz; the composite microwave absorbing material prepared in Example 2, with a coating thickness of 2.0 mm, has a minimum reflection loss of -54.4 dB and an effective bandwidth of 5.2 GHz; the composite microwave absorbing material prepared in Example 3, with a coating thickness of 2.0 mm, has a minimum reflection loss of -46.9 dB and an effective bandwidth of 5.2 GHz; in contrast, the composite microwave absorbing material prepared in Example 4 exhibits poor microwave absorption performance and cannot meet the requirements of practical use.

[0086] Analysis suggests that in Examples 1-3, the microwave absorbing material possesses a certain degree of porosity, achieving a good pore-forming effect. This not only endows the material with excellent dielectric properties but also enhances its electromagnetic loss capability through the porous structure. In contrast, in Example 4, the pore structure collapses. Although it exhibits strong electromagnetic loss capability, the strong dielectric loss capability leads to impedance mismatch, preventing electromagnetic waves from penetrating the material's interior and resulting in reflection and thus weaker microwave absorption capability.

[0087] The above microwave absorption performance test process is as follows: First, the sample is uniformly mixed with 70% paraffin by mass. Then, the mixture is pressed into a cylindrical block with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. Finally, the relative complex permittivity of the sample is measured in the frequency range of 2-18 GHz using a vector network analyzer (VNA, Agilent N5230). ) and permeability ( The reflection loss (RL) value of the material is simulated and calculated based on transmission line theory.

[0088] The preparation method and application of the C / Al2MgO4 composite microwave absorbing material provided by this invention have been described in detail above. The specific embodiments described above should not be construed as limiting the scope of protection of this invention. Any substitutions, improvements, or modifications made to the embodiments of this invention by those skilled in the art will fall within the scope of protection of this invention.

[0089] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing a C / Al2MgO4 composite microwave absorbing material, characterized in that, Includes the following steps: (1) After pre-drying the papermaking sludge, ball mill it and sieve it through a 100-200 mesh screen to obtain sludge powder; (2) Take the sludge powder from step (1), add acidification solution and soak for 4-6 hours, then wash repeatedly until neutral, and dry at 100±10℃ for 12-24 hours to obtain the dried product for later use. (3) The dried product obtained in step (2) is calcined at 500℃ for 1-3 hours under an inert atmosphere to obtain a pyrolysis product for later use; the pyrolysis product is a mixture including carbon and ash, wherein the chemical composition of the ash includes: SiO2: 30%-60%, Al2O3: 10%-20%, MgO: 3%-6%, CaO: 2%-4%, TiO2: 2%-5%, K2O: 1%-4%, P2O5: 0.5%-3%; (4) Prepare a modified potassium hydroxide aqueous solution; the concentration of the potassium hydroxide aqueous solution is 0.5-1.5 mol / L; (5) Immerse the pyrolysis product obtained in step (3) in the potassium hydroxide aqueous solution in step (4) at a mass ratio of 1-2.5:1, stir for 4-6 hours, and dry at 70-90℃ for 12-24 hours to obtain a dry mixture. (6) The dried mixture from step (5) is calcined at 600-900℃ for 3-5 hours under an inert atmosphere and then cooled to room temperature to obtain the modified product. (7) Disperse the modified product from step (6) in an excess acid solution, stir continuously for 2-6 hours, wash repeatedly until neutral, and dry at 90-100℃ for 12-24 hours to obtain a porous ceramic composite microwave absorbing material.

2. The preparation method according to claim 1, characterized in that, Step (2) The mass-to-volume ratio of sludge powder to acidification liquid is 1:10; the acidification liquid is 10-30wt% HCl.

3. The preparation method according to claim 1, characterized in that, In steps (3) and (6), the inert atmosphere is Ar, and the calcination is carried out in a tubular furnace; the specific surface area of ​​the resulting porous ceramic composite microwave absorbing material reaches 182-325 m². 2 / g.

4. The preparation method according to claim 1, characterized in that, Step (7) The acid solution is hydrochloric acid solution.

5. The C / Al2MgO4 composite microwave absorbing material prepared by the preparation method according to any one of claims 1-4 is used as a high-temperature resistant microwave absorbing material in military, high-temperature electromagnetic shielding equipment, and aerospace fields.

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