Preparation method of hollow microsphere silicon carbide composite wave-absorbing material

Abstract

The application relates to a preparation method of a hollow microsphere silicon carbide composite wave-absorbing material. After phenolic resin wrapped in a first composite is carbonized, a hollow structure of silicon dioxide / carbon hollow microspheres is formed, the hollow structure is beneficial to reducing impedance mismatch and improving the wave-absorbing performance of the composite wave-absorbing material, and magnetic waves are scattered and reflected in the microspheres for multiple times, thereby increasing the propagation path of electromagnetic waves. The first powder is subjected to secondary carbonization to form a hollow microsphere SiC / C / CNF composite wave-absorbing material, the first carbon layer, the second carbon layer and silicon carbide can introduce more loss mechanisms, and the energy loss modes in the wave-absorbing process are enriched. After bacterial cellulose is carbonized, a carbon nanofiber layer is formed and is distributed on the outermost layer of the hollow microsphere silicon carbide composite wave-absorbing material, the pores and fibers of the carbon nanofiber layer can effectively capture incident electromagnetic waves, the carbon nanofiber layer can increase impedance matching between the carbon nanofiber layer and air, reduce electromagnetic wave reflection, and enable more electromagnetic waves to enter the composite wave-absorbing material to be lost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and particularly relates to a preparation method of hollow microsphere silicon carbide composite wave-absorbing material. BACKGROUND

[0002] With the progress of electronic technology, more and more electronic technology products enter the life of human beings. While human beings enjoy the development of technology, they also face electromagnetic pollution brought by electronic technology products. In the traditional method, microwave absorbing materials (MAMs) are considered to be the functional materials that are better to weaken the effect of electromagnetic waves. Microwave absorbing materials can convert electromagnetic waves into joule heat through dielectric loss and magnetic loss, and interference cancellation occurs, so as to inhibit or eliminate electromagnetic radiation.

[0003] At present, microwave absorbing materials mostly have compatible magnetic and dielectric properties to achieve good impedance matching and strong electromagnetic attenuation capability. For example, microwave absorbing materials formed by Fe / C, Co / C, Ni / C, Fe / Co / C and the like, but the above materials containing magnetic metals are easy to be corroded and oxidized, and are difficult to provide long-time service in some harsh environments, such as exposure to the sun, acid rain, seawater environment.

[0004] Silicon carbide (SiC) is a kind of nanomaterial with diverse micro-morphology and rich crystal form. Due to its excellent physical, chemical, electrical and optical properties, it has become a good catalyst, semiconductor, functional ceramic and high-frequency electronic product preparation raw material. Silicon carbide also has certain acid and alkali resistance and good environmental tolerance to harsh environments. This makes silicon carbide have certain advantages in the preparation of microwave absorbing materials. However, the band gap of silicon carbide is wide, the electron transfer is slow, and the dielectric property is weak, so the prepared wave-absorbing material has poor performance. SUMMARY

[0005] The embodiment of the present application provides a preparation method of hollow microsphere silicon carbide composite wave-absorbing material, which aims to improve the problem that the dielectric property of silicon carbide as a wave-absorbing material is weak and the prepared wave-absorbing material has poor performance.

[0006] In a first aspect, the embodiments of the present application provide a preparation method of hollow microsphere silicon carbide composite wave-absorbing material, including: mixing deionized water, anhydrous ethanol and ammonia water, adding a surfactant, stirring uniformly, adding a phenolic resin and a formaldehyde solution mixture to obtain a first mixed solution. Providing a silicon source, adding the silicon source to the first mixed solution, stirring, sealing, reacting at a first preset temperature for a preset time to obtain a second mixed solution, centrifuging the second mixed solution to obtain a first compound, performing a first carbonization treatment on the first compound to obtain hollow microsphere silicon dioxide / carbon, providing purified bacterial cellulose, mixing the bacterial cellulose with the hollow microsphere silicon dioxide / carbon, freeze-drying to obtain a second compound, mixing the second compound with magnesium powder, grinding to obtain a first powder, and performing a second carbonization treatment on the first powder to obtain the hollow microsphere silicon carbide composite wave-absorbing material.

[0007] In some embodiments, the providing of the purified bacterial cellulose includes: soaking the bacterial cellulose in an alkali solution with a concentration of 0.2 mol / L to 0.5 mol / L, and water-bathing at a temperature of 60°C to 100°C for 2h to 4h, and then washing the bacterial cellulose soaked in the alkali solution to neutral with deionized water to obtain the purified bacterial cellulose.

[0008] In some embodiments, the adding of the silicon source to the first mixed solution, stirring, sealing, and reacting at a first preset temperature for a preset time to obtain a second mixed solution, and centrifuging the second mixed solution to obtain a first compound includes: adding the silicon source to the first mixed solution, stirring, sealing, and reacting at a temperature of 80°C to 120°C for 20h to 30h to obtain the second mixed solution. Cooling the second mixed solution to a temperature of 20°C to 25°C, centrifuging the cooled second mixed solution to obtain a precipitate, washing the precipitate with anhydrous ethanol and deionized water for 3 to 5 times, and placing the washed precipitate in a drying box at a temperature of 50°C to 80°C for drying for 10h to 15h to obtain the first compound.

[0009] In some embodiments, the first carbonization treatment on the first compound includes: placing the first compound in a tube furnace in an inert gas environment at a temperature of 600°C to 1000°C for carbonization for 2h to 3h, and the tube furnace has a temperature rising speed of 5°C / min to 15°C / min.

[0010] In some embodiments, the second carbonization treatment on the first powder includes: placing the first powder in a tube furnace in an inert gas environment at a temperature of 600°C to 1000°C for carbonization for 2h to 3h, and the tube furnace has a temperature rising speed of 5°C / min to 15°C / min.

[0011] In some embodiments, the silicon source includes at least one of tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane, ethyltriethoxysilane.

[0012] In some embodiments, the surfactant includes at least one of cetyltrimethylammonium chloride, cetyltrimethylammonium bromide, dodecyltrimethylammonium chloride.

[0013] In some embodiments, the mass ratio of the second composite to the magnesium powder is (6:1) to (10:1).

[0014] In some embodiments, the phenolic resin is added in an amount of 12 g / L to 18 g / L. The silicon source is added in an amount of 80 ml / L to 100 ml / L.

[0015] In some embodiments, the inert gas includes nitrogen and / or argon.

[0016] Compared with the related art, the embodiments of the present application provide a preparation method of a hollow microsphere silicon carbide composite wave-absorbing material. After the phenolic resin wrapped inside the first composite is carbonized, the phenolic resin is dehydrated and decomposed to form a hollow structure of the silica / carbon hollow microsphere, which is beneficial to reducing impedance mismatch and improving the wave-absorbing performance of the composite wave-absorbing material, so that the electromagnetic wave is scattered and reflected multiple times inside the microsphere, increasing the propagation path and absorption opportunity of the electromagnetic wave. The first powder is subjected to secondary carbonization to form a hollow microsphere SiC / C / CNF composite wave-absorbing material. The first carbon layer, the second carbon layer, and the silicon carbide can introduce more loss mechanisms, such as conductive loss and polarization loss, enriching the energy loss mode in the wave-absorbing process and improving the wave-absorbing performance. The carbon nanofiber layer formed after the bacterial cellulose is carbonized is distributed on the outermost layer of the hollow microsphere silicon carbide composite wave-absorbing material. The pores and fibers of the carbon nanofiber layer can effectively capture the incident electromagnetic wave, increasing the initial contact and interaction opportunity of the electromagnetic wave with the hollow microsphere SiC / C / CNF composite wave-absorbing material. The carbon nanofiber layer can increase the impedance matching between the air and the hollow microsphere SiC / C / CNF composite wave-absorbing material, reduce the reflection of the electromagnetic wave, and enable more electromagnetic waves to enter the inside of the composite wave-absorbing material for loss. Moreover, the incident electromagnetic wave will be scattered multiple times in the carbon nanofiber layer, prolonging the propagation path of the electromagnetic wave in the composite wave-absorbing material and increasing the probability of electromagnetic wave absorption. The carbon nanofiber also has good electrical conductivity, which can enhance the electrical loss of the surface of the composite wave-absorbing material, convert electromagnetic wave energy into heat, enable more electromagnetic waves to be absorbed, and improve the wave-absorbing performance of the composite wave-absorbing material. BRIEF DESCRIPTION OF DRAWINGS

[0017] One or more embodiments are illustrated by way of example in the figures that are not intended to be limiting of the present embodiments. Like numbers refer to like elements throughout. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the present embodiments.

[0018] Figure 1 is a flow chart of a preparation method of some hollow microsphere silicon carbide composite wave-absorbing materials provided by the embodiments of the present application.

[0019] Figure 2 is a structural schematic diagram of some hollow microsphere silicon carbide composite wave-absorbing materials provided by the embodiments of the present application. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0021] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "several" and "a plurality of" is two or more, unless otherwise explicitly specified.

[0022] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.

[0023] In this paper, the reference to "embodiments" means that the specific features, structures or characteristics described in conjunction with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it independent or alternative to other embodiments. In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0024] In a first aspect, the embodiments of the present application provide a preparation method of a hollow microsphere silicon carbide composite wave-absorbing material, please refer to Figure 1 , Figure 1 is a flow chart of a preparation method of some hollow microsphere silicon carbide composite wave-absorbing materials provided by the embodiments of the present application. The preparation method comprises the following steps:

[0025] Step S1: mixing deionized water, anhydrous ethanol and ammonia water, then adding a surfactant and stirring uniformly, and then adding a phenolic resin and a formaldehyde solution to obtain a first mixed solution.

[0026] The surfactant is a substance capable of significantly reducing the surface tension of a liquid, capable of promoting the dispersion of the phenolic resin in the system, and forming a stable emulsion or reducing the agglomeration and precipitation of the phenolic resin in the system. For example, the surfactant includes at least one of cetyltrimethylammonium chloride, cetyltrimethylammonium bromide, and dodecyltrimethylammonium chloride.

[0027] The phenolic resin is a synthetic resin, which is obtained by condensation polymerization of a phenolic compound and an aldehyde compound under the action of a catalyst. Generally, the carbon content in the phenolic resin is usually about 70% to 80%, and because the carbon content in the phenolic resin is high, during the carbonization process, as the temperature rises, the phenolic resin gradually loses the adsorbed water and some small molecular substances, and the resin begins to decompose. As the temperature continues to rise, the macromolecular chains of the resin are broken and decomposed to produce some gas products such as carbon monoxide, carbon dioxide, methane, etc., and the final calcination product is mainly carbonaceous material.

[0028] In some embodiments, the amount of the phenolic resin added is 12 g / L to 18 g / L.

[0029] Step S2: providing a silicon source, adding the silicon source into the first mixed solution, stirring, sealing, and reacting at a first preset temperature for a preset time to obtain a second mixed solution, centrifuging the second mixed solution to obtain a first composite, and performing a first carbonization treatment on the first composite to obtain the hollow silica / carbon microspheres.

[0030] The silicon source is mixed with the first mixed solution, and the silicon source can react with the phenolic resin in the first mixed solution to obtain a brown first composite. The first composite is wrapped with the phenolic resin inside, and part of the phenolic resin is attached to the outer surface of the first composite. The first composite is carbonized at a high temperature to obtain the hollow silica / carbon microspheres. Please refer to Figure 2 The phenolic resin wrapped inside the first composite is carbonized to form a hollow structure 131 of the hollow silica / carbon microsphere 13, and the phenolic resin is carbonized to form a first carbon layer 11 on the inner wall of the hollow silica / carbon microsphere 13. Part of the phenolic resin attached to the outer surface of the first composite forms a second carbon layer 12 on the outer wall of the hollow silica / carbon microsphere 13.

[0031] The first carbon layer 11 and the second carbon layer 12 have a special microstructure, such as a porous, nanoscale structure, etc. The scattering and reflection of electromagnetic waves can be enhanced, the propagation path of electromagnetic waves in the composite wave-absorbing material is prolonged, and the absorption probability of electromagnetic waves is improved. Moreover, the first carbon layer 11 and the second carbon layer 12 are composed of carbon materials, which have excellent dielectric properties and can effectively interact with electromagnetic waves, converting electromagnetic wave energy into heat or other forms of energy through dielectric loss, thereby reducing electromagnetic radiation of electromagnetic waves. The density of the first carbon layer 11 and the second carbon layer 12 is relatively low, and the first carbon layer 11 and the second carbon layer 12 have good chemical stability, which is convenient for use in some application scenarios with strict weight restrictions, such as aerospace, transportation, etc.

[0032] The hollow structure 131 of the silica / carbon hollow microsphere 13 is beneficial to reduce impedance mismatch and improve the wave-absorbing performance of the composite wave-absorbing material. The hollow structure 131 can also reduce the density of the composite wave-absorbing material, thereby reducing the weight of the composite wave-absorbing material and making the composite wave-absorbing material lightweight. The hollow structure 131 can also cause multiple scattering and reflection of electromagnetic waves inside the microsphere, increasing the propagation path and absorption opportunity of electromagnetic waves.

[0033] In some embodiments, the method for preparing the first composite by adding a silicon source into the first mixed solution, stirring, sealing, and reacting at a first preset temperature for a preset time period to obtain a second mixed solution, and centrifuging the second mixed solution includes: adding the silicon source into the first mixed solution, stirring, sealing, and reacting at a temperature of 80-120°C for 20-30h to obtain the second mixed solution. The second mixed solution is cooled to 20-25°C, and the cooled second mixed solution is centrifuged to obtain a precipitate. The precipitate is washed with anhydrous ethanol and deionized water for 3-5 times, and the washed precipitate is placed in a drying box at a temperature of 50-80°C for drying for 10-15h to obtain the first composite.

[0034] In some embodiments, the silicon source includes at least one of tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane, and ethyltriethoxysilane. The silicon source is added in an amount of 80-100ml / L.

[0035] In some embodiments, the one-time carbonization treatment of the first composite includes: placing the first composite in a tubular furnace at a temperature of 600-1000°C in an inert gas environment for carbonization for 2-3h, and the tubular furnace has a temperature rising speed of 5-15°C / min. The inert gas includes nitrogen and / or argon.

[0036] Step S3: providing the purified bacterial cellulose, mixing the bacterial cellulose with the silica / carbon hollow microsphere, and freeze-drying to obtain a second composite.

[0037] Bacterial cellulose is a natural polymer material synthesized by microorganisms. It is produced by certain bacterial strains, such as Acetobacter xylinum, under specific culture conditions. Bacterial cellulose has a fine three-dimensional network structure, and the fiber diameter is usually at the nanometer level. Bacterial cellulose has high crystallinity and excellent mechanical properties. The main component of bacterial cellulose is cellulose, which has a high carbon content and oxygen content. After carbonization, the obtained carbon nanofiber has higher mechanical strength and higher chemical stability. Moreover, the source of bacterial cellulose is extensive, and its production is not limited by season and geographical environment, and it is environmentally friendly.

[0038] After mixing bacterial cellulose with silica / carbon hollow microspheres and freeze-drying, freeze-drying helps to promote the attachment of bacterial cellulose on the surface of silica / carbon hollow microspheres, forming a more compact and stable second composite.

[0039] In some embodiments, the purified bacterial cellulose includes soaking the bacterial cellulose in an alkali solution with a concentration of 0.2 mol / L to 0.5 mol / L, and water-bathing at a temperature of 60°C to 100°C for 2h to 4h. Then, the bacterial cellulose soaked in the alkali solution is washed with deionized water until it is neutral, obtaining the purified bacterial cellulose. The alkali solution can be a strong sodium hydroxide solution, a potassium hydroxide solution, etc. The alkali solution can remove impurities such as proteins and pectin in the bacterial cellulose, so as to purify the bacterial cellulose.

[0040] In some embodiments, the purification of bacterial cellulose also includes acid treatment, enzyme treatment, ultrasonic treatment, etc.

[0041] Step S4: mixing the second composite with magnesium powder and grinding to obtain a first powder. The first powder is subjected to secondary carbonization treatment to obtain a hollow microspherical silicon carbide composite wave-absorbing material.

[0042] The secondary carbonization treatment can carbonize the silica into silicon carbide, and the magnesium powder is used to provide a large amount of heat for the carbonization of the second composite, promoting the progress of the carbonization. Please refer to Figure 2 Under the action of carbonization, the bacterial cellulose forms a carbon nanofiber (CNF) network structure distributed in the outermost layer of the hollow microspherical silicon carbide composite wave-absorbing material 10, i.e. the carbon nanofiber layer 14. Among them, the hollow microspherical silicon carbide composite wave-absorbing material 10 is a hollow microspherical SiC / C / CNF composite wave-absorbing material.

[0043] Silicon carbide (SiC) is an inorganic non-metallic material composed of silicon and carbon. It has excellent chemical, physical, electrical and optical properties. Silicon carbide has high hardness and chemical stability, and has good environmental tolerance to acids, bases and salts. It has great development prospects in the field of microwave absorbing materials.

[0044] The dielectric constant of silicon carbide is relatively high, which can cause poor impedance matching with free space, so that more electromagnetic waves are reflected on the surface of the material. The dielectric constant of carbon material is relatively easy to adjust, and the first carbon layer 11 and the second carbon layer 12 can optimize the overall impedance matching, reduce reflection, and enhance the entry and absorption of electromagnetic waves. The loss mechanism of silicon carbide itself is relatively single, and the combination of the first carbon layer 11 and the second carbon layer 12 with silicon carbide can introduce more loss mechanisms, such as conductive loss and polarization loss, enrich the energy loss mode in the wave absorption process, and improve the wave absorption performance.

[0045] The pores and fibers of the carbon nanofiber layer 14 can effectively capture the incident electromagnetic waves, increasing the initial contact and interaction opportunities of electromagnetic waves with the hollow microsphere SiC / C / CNF composite wave-absorbing material. The carbon nanofiber layer 14 can increase the impedance matching between the air, reduce the reflection of electromagnetic waves, and enable more electromagnetic waves to enter the inside of the composite wave-absorbing material for loss. Moreover, the incident electromagnetic waves will undergo multiple scattering in the carbon nanofiber layer 14, prolonging the propagation path of the electromagnetic waves in the composite wave-absorbing material and increasing the probability of electromagnetic wave absorption. The carbon nanofiber also has good electrical conductivity, which can enhance the electrical loss of the surface of the composite wave-absorbing material, convert electromagnetic wave energy into heat, and enable more electromagnetic waves to be absorbed.

[0046] In some embodiments, the secondary carbonization treatment of the first powder includes placing the first powder in a tubular furnace in an inert gas environment at a temperature of 600-1000°C for 2-3h, and the heating rate of the tubular furnace is 5-15°C / min. The inert gas includes nitrogen and / or argon.

[0047] It should be noted that the above-mentioned first carbonization refers to the first carbonization treatment, and the second carbonization refers to the second carbonization treatment. The above-mentioned first and second refer to operation steps, not operation times.

[0048] In some embodiments, the mass ratio of the second composite to magnesium powder is (6:1)-(10:1).

[0049] The embodiment of the present application provides a preparation method of hollow microsphere silicon carbide composite wave-absorbing material 10. After the phenolic resin wrapped in the first composite is carbonized, the phenolic resin is dehydrated and decomposed to form a hollow structure 131 of the silicon dioxide / carbon hollow microsphere 13, the hollow structure 131 is beneficial to reduce impedance mismatch and improve the wave-absorbing performance of the composite wave-absorbing material, and can also make electromagnetic waves multiple scattering and reflection in the microsphere, increase the propagation path and absorption opportunity of electromagnetic waves. The first powder is carbonized twice to form the hollow microsphere SiC / C / CNF composite wave-absorbing material, the first carbon layer 11 and the second carbon layer 12 in combination with silicon carbide can introduce more loss mechanisms, such as conductive loss and polarization loss, enrich the energy loss mode in the wave-absorbing process, and improve the wave-absorbing performance. The carbon nanofiber layer 14 formed under the action of carbonization is distributed in the outermost layer of the hollow microsphere silicon carbide composite wave-absorbing material 10, the pores and fibers of the carbon nanofiber layer 14 can effectively capture the incident electromagnetic waves, increase the initial contact and interaction opportunity of electromagnetic waves with the hollow microsphere SiC / C / CNF composite wave-absorbing material. The carbon nanofiber layer 14 can increase the impedance matching between the air and the hollow microsphere SiC / C / CNF composite wave-absorbing material, reduce the reflection of electromagnetic waves, and enable more electromagnetic waves to enter the inside of the composite wave-absorbing material for loss. And the incident electromagnetic waves will multiple scattering in the carbon nanofiber layer 14, prolong the propagation path of electromagnetic waves in the composite wave-absorbing material, and increase the probability of electromagnetic wave absorption. The carbon nanofiber also has good electrical conductivity, which can enhance the electrical loss of the surface of the composite wave-absorbing material, convert electromagnetic wave energy into heat, and enable more electromagnetic waves to be absorbed.

[0050] In a second aspect, the embodiment of the present application also provides an electronic device including the hollow microsphere silicon carbide composite wave-absorbing material prepared by the preparation method of the first aspect. The hollow microsphere silicon carbide composite wave-absorbing material can be used for the shell of the electronic device or the specific surface of the electronic device, to effectively block the interference of external electromagnetic waves, prevent the electromagnetic waves generated in the device from radiating outward, ensure the normal operation of the device, and reduce electromagnetic pollution.

[0051] The preparation method of the hollow microsphere silicon carbide composite wave-absorbing material will be described below in combination with specific embodiments.

[0052] Embodiment 1

[0053] (1) 50 ml of deionized water, 20 ml of anhydrous ethanol and 0.3 ml of mixed hexadecyl trimethyl ammonium bromide were added to 1 g of phenolic resin, stirred at room temperature for 10 min, and then 0.8 ml of formaldehyde was added and stirred to obtain a first mixed solution.

[0054] (2) 10 ml tetraethyl orthosilicate was added to the first mixture and stirred for 1 h, then placed in a 100 ml polytetrafluoroethylene liner, and reacted at a temperature of 100°C for 24 h to obtain a second mixture. The second mixture was cooled to 25°C, and the cooled second mixture was centrifuged to obtain a first composite. The first composite was placed in a nitrogen environment, carbonized in a tube furnace at a temperature of 800°C at a temperature rise rate of 10°C / min for 2 h to obtain silica / carbon hollow microspheres.

[0055] (3) 1 g of the silica / carbon hollow microspheres were mixed with the purified bacterial cellulose, and then placed in a freeze dryer at a temperature of -40°C for 48 h to obtain a second composite.

[0056] (4) 5 g of the second composite were mixed with 0.5 g of magnesium powder to obtain a first powder, which was placed in a magnetic boat and carbonized in a tube furnace at a temperature of 800°C at a temperature rise rate of 10°C / min for 2 h in a nitrogen environment to obtain a hollow microspherical carbonized silicon composite wave-absorbing material.

[0057] Example 2

[0058] (1) 50 ml of deionized water, 20 ml of anhydrous ethanol, and 0.3 ml of a mixture were added to 1 g of cetyltrimethylammonium bromide, stirred at room temperature for 10 min, and then 1.6 g of phenol formaldehyde resin and 0.4 ml of formaldehyde were added and stirred to obtain a first mixture.

[0059] (2) 8 ml of tetraethyl orthosilicate was added to the first mixture and stirred for 1 h, then placed in a 100 ml polytetrafluoroethylene liner, and reacted at a temperature of 100°C for 24 h to obtain a second mixture. The second mixture was cooled to 25°C, and the cooled second mixture was centrifuged to obtain a precipitate, which was washed with anhydrous ethanol and deionized water three times, and the washed precipitate was placed in a drying oven at a temperature of 60°C for 12 h to obtain a first composite. The first composite was placed in a nitrogen environment, carbonized in a tube furnace at a temperature of 900°C at a temperature rise rate of 10°C / min for 2 h to obtain silica / carbon hollow microspheres.

[0060] (3) 10 g of bacterial cellulose was placed in 50 ml of a 0.5 mol / L sodium hydroxide solution and water-bathed at 80°C for 3 h, and then soaked in deionized water until neutral to obtain purified bacterial cellulose. 2 g of the silica / carbon hollow microspheres were mixed with the purified bacterial cellulose, and then placed in a freeze dryer at a temperature of -40°C for 48 h to obtain a second composite.

[0061] (4) 5 g of the second composite is mixed with 0.5 g of magnesium powder to obtain a first powder, the first powder is placed in a magnetic boat and placed in a nitrogen environment, carbonized in a tube furnace at a temperature of 900 ℃ and a temperature rising speed of 10 ℃ / min for 2 h to obtain hollow microspherical silicon carbide composite wave-absorbing material.

[0062] Comparative Example 1

[0063] (1) 50 ml of deionized water, 20 ml of anhydrous ethanol and 0.3 ml of hexadecyl trimethyl ammonium bromide are mixed and added to 1 g of formaldehyde, stirred at room temperature for 10 min, and then 0.8 ml of formaldehyde is added and stirred to obtain a first mixed solution.

[0064] (2) 10 ml of tetraethyl orthosilicate is added to the first mixed solution and stirred for 1 h, then placed in a 100 ml polytetrafluoroethylene liner, and reacted at a temperature of 100 ℃ for 24 h to obtain a second mixed solution. The second mixture is cooled to 25 ℃, and the cooled second mixture is centrifuged to obtain a first composite. The first composite is placed in a nitrogen environment, carbonized in a tube furnace at a temperature of 800 ℃ and a temperature rising speed of 10 ℃ / min for 2 h to obtain silica microspheres.

[0065] (3) 1 g of the silica microspheres is mixed with purified bacterial cellulose, and then placed at a temperature of -40 ℃ and freeze-dried for 48 h to obtain a second composite.

[0066] (4) 5 g of the second composite is mixed with 0.5 g of magnesium powder to obtain a first powder, the first powder is placed in a magnetic boat and placed in a nitrogen environment, carbonized in a tube furnace at a temperature of 800 ℃ and a temperature rising speed of 10 ℃ / min for 2 h to obtain hollow microspherical silicon carbide composite wave-absorbing material.

[0067] Comparative Example 2

[0068] (1) 50 ml of deionized water, 20 ml of anhydrous ethanol and 0.3 ml of hexadecyl trimethyl ammonium bromide are mixed and added to 1 g of formaldehyde, stirred at room temperature for 10 min, and then 1.2 g of phenolic resin and 0.8 ml of formaldehyde are added and stirred to obtain a first mixed solution.

[0069] (2) 10 ml of tetraethyl orthosilicate is added to the first mixed solution and stirred for 1 h, then placed in a 100 ml polytetrafluoroethylene liner, and reacted at a temperature of 100 ℃ for 24 h to obtain a second mixed solution. The second mixture is cooled to 25 ℃, and the cooled second mixture is centrifuged to obtain a first composite. The first composite is placed in a nitrogen environment, carbonized in a tube furnace at a temperature of 800 ℃ and a temperature rising speed of 10 ℃ / min for 2 h to obtain silica / carbon hollow microspheres.

[0070] (3) The silica / carbon hollow microspheres are mixed and ground with 0.5 g of magnesium powder to obtain a first powder. The first powder is placed in a magnetic boat and placed in a nitrogen environment in a tube furnace with a temperature of 800℃ and a temperature rising speed of 10℃ / min for carbonization for 2h to obtain a hollow microspherical silicon carbide composite wave-absorbing material.

[0071] The wave-absorbing performance of the composite wave-absorbing materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 is tested respectively.

[0072] The thickness of the composite wave-absorbing material in Example 1 is 2.1mm, and the minimum reflection loss value RL min at 11.56GHz is -48.6dB, and the effective absorption frequency band is 4.50GHz.

[0073] The thickness of the composite wave-absorbing material in Example 2 is 1.8mm, and the minimum reflection loss value RL min at 10.6GHz is -60.8dB, and the effective absorption frequency band is 5.10GHz.

[0074] The thickness of the composite wave-absorbing material in Comparative Example 1 is 2.3mm, and the minimum reflection loss value RL min at 8.9GHz is -35.6dB, and the effective absorption frequency band is 3.2GHz.

[0075] The thickness of the composite wave-absorbing material in Comparative Example 2 is 2.5mm, and the minimum reflection loss value RL min at 9.6GHz is -32.5dB, and the effective absorption frequency band is 2.8GHz.

[0076] According to the wave-absorbing performance test results, by comparing the above examples and comparative examples, it can be seen that the composite wave-absorbing materials in Example 1 and Example 2 have strong absorption ability for electromagnetic waves, and the composite wave-absorbing materials in Example 1 and Example 2 can absorb a wider range of electromagnetic frequencies, effectively reducing the radiation effect of electromagnetic waves. By comparing Example 1 and Comparative Example 1, the composite wave-absorbing material in Comparative Example 1 has a non-hollow structure of silicon carbide microspheres, and the first carbon layer inside the silicon carbide microspheres and the second carbon layer on the outer surface are not present. The loss mechanism of silicon carbide itself is relatively single, the band gap is relatively wide, the dielectric performance is relatively weak, and the absorption ability for electromagnetic waves is relatively weak. By comparing Example 1 and Comparative Example 2, no bacterial cellulose is added in Comparative Example 2, so that the outermost layer of the composite wave-absorbing material in Comparative Example 2 does not contain a carbon nanofiber layer. Compared with the composite material in Example 1, the composite wave-absorbing material in Comparative Example 1 has fewer absorption paths for electromagnetic waves, and electromagnetic waves are not easy to scatter, so that electromagnetic waves cannot be fully absorbed and lost. Compared with Example 1, the wave-absorbing performance of the composite wave-absorbing material prepared in Comparative Example 2 is poor.

[0077] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; under the idea of the present application, the technical features in the above examples or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for simplicity; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a hollow microsphere silicon carbide composite wave-absorbing material, characterized in that, include: After mixing deionized water, anhydrous ethanol and ammonia, a surfactant is added and stirred until homogeneous. Then, phenolic resin and formaldehyde solution are added and mixed to obtain the first mixture. A silicon source is provided, and the silicon source is added to the first mixture, stirred, sealed, and reacted at a first preset temperature for a preset time to obtain a second mixture. The second mixture is centrifuged to obtain a first composite. The first composite is subjected to a carbonization treatment to obtain silicon dioxide / carbon hollow microspheres. Purified bacterial cellulose is provided, and the bacterial cellulose is mixed with the silica / carbon hollow microspheres and then freeze-dried to obtain a second complex. The second composite is mixed with magnesium powder and then ground to obtain a first powder. The first powder is then subjected to a secondary carbonization treatment to obtain a hollow microsphere silicon carbide composite microwave absorbing material.

2. The production method according to claim 1, characterized by, The purified bacterial cellulose provided includes: Bacterial cellulose was soaked in an alkaline solution with a concentration of 0.2 mol / L to 0.5 mol / L and then bathed in a water bath at a temperature of 60°C to 100°C for 2 to 4 hours. The bacterial cellulose soaked in the alkaline solution was then washed with deionized water until neutral to obtain purified bacterial cellulose.

3. The preparation method according to claim 1, characterized in that, The process involves adding the silicon source to the first mixture, stirring, sealing, and reacting at a first preset temperature for a preset time to obtain a second mixture. Centrifuging the second mixture yields a first composite, comprising: The silicon source is added to the first mixture, stirred, sealed, and reacted at a temperature of 80°C to 120°C for 20 to 30 hours to obtain the second mixture; The second mixture is cooled to 20°C to 25°C, and the cooled second mixture is centrifuged to obtain a precipitate. The precipitate is washed 3 to 5 times with anhydrous ethanol and deionized water. The washed precipitate is placed in a drying oven at 50°C to 80°C and dried for 10 to 15 hours to obtain the first complex.

4. The method of claim 1, wherein, The step of performing a carbonization treatment on the first composite includes: The first composite was placed in an inert gas environment and carbonized in a tube furnace at a temperature of 600°C to 1000°C for 2 to 3 hours, with the heating rate of the tube furnace being 5°C / min to 15°C / min.

5. The preparation method according to claim 1, characterized in that, The second carbonization treatment of the first powder includes: The first powder is placed in an inert gas environment and carbonized in a tube furnace at a temperature of 600°C to 1000°C for 2 to 3 hours, wherein the heating rate of the tube furnace is 5°C / min to 15°C / min.

6. The production method according to any one of claims 1 to 5, characterized by, The silicon source includes at least one of tetraethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, and ethyltriethoxysilane.

7. The production method according to any one of claims 1 to 5, characterized by, The surfactant includes at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride.

8. The method of claim 1, wherein, The mass ratio of the second composite to the magnesium powder is (6:1) to (10:1).

9. The method of claim 1, wherein, The amount of phenolic resin added is 12 g / L to 18 g / L; The amount of silicon source added is 80 ml / L to 100 ml / L.

10. The method of claim 4, wherein, The inert gas includes nitrogen and / or argon.

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