Flexible wave-absorbing carbon aerogel composite material and preparation method thereof

Abstract

The invention discloses a flexible wave-absorbing carbon aerogel composite material and a preparation method thereof.According to the method, phenolic sol and graphene oxide sol are used as carbon sources, flexible pre-oxidized fiber felt is used as a reinforcement body, and in the hydrothermal reaction process, the flexible wave-absorbing carbon aerogel composite material is prepared. Phenolic sol and graphene oxide sol can wrap functional components to perform phase separation deposition along fibers of a flexible reinforcement, finally, the surfaces of the fibers of the whole reinforcement can be covered with gel particles, the functional components are uniformly distributed in a whole material framework, and by controlling the sol content and a curing process, the functional components are uniformly distributed in the whole material framework. The cured material can still have flexibility, so that the flexible wave-absorbing carbon aerogel composite material is finally obtained after pyrolysis, and the flexible wave-absorbing carbon aerogel composite material is expected to be applied to the fields of intelligent wearing, building thermal management and the like.

Description

Technical Field

[0001] The present invention relates to a flexible wave - absorbing carbon aerogel composite material and a preparation method thereof, belonging to the field of preparation of aerogel composite materials, having the property of integrated wave absorption / heat insulation, and is expected to be applied in fields such as intelligent wearables and building thermal management. Background Art

[0002] The development of radio communication technology and the popularization of corresponding electronic devices have brought great convenience to people's daily lives, but inevitably generated a large amount of electromagnetic wave pollution. Electromagnetic waves will not only interfere with precision instrument equipment, but also cause varying degrees of harm to the human nervous system, blood circulation system, reproductive system, etc. Therefore, researching and preparing high - performance wave - absorbing materials to convert harmful electromagnetic wave energy into harmless energy such as heat energy to solve electromagnetic wave pollution is a scientific research direction that has received much attention.

[0003] Developing flexible wave - absorbing materials is an important research direction. Flexible materials have good conformability and can better envelope irregular structures, avoiding more stress concentration caused by hard connections, and have broad application prospects in fields such as intelligent wearables and building thermal management. Patent application CN117247594A introduces a super - elastic and super - light regular porous composite aerogel and its preparation method and application. By subjecting a mixed dispersion of cellulose nanocrystals, MXene, and carboxylated nanotubes to directional freezing and freeze - drying, a composite aerogel with a regular porous structure is obtained, which has super - elastic mechanical properties. However, due to the presence of a large amount of natural organic substances, the stability of this aerogel is poor. Patent application CN116621151A introduces a preparation method of a three - dimensional ordered parallel - sheet - structure aerogel. A chitosan / graphene oxide precursor solution is subjected to bidirectional freezing and freeze - drying to obtain a chitosan / graphene oxide aerogel, and then petal - shaped Sn 2 S is loaded on this aerogel to obtain a three - dimensional ordered parallel - sheet - structure aerogel, which has the characteristics of low density, low filling ratio, strong absorption, and ultra - wideband absorption. However, in this aerogel, Sn 2S fails to strongly bind to the skeleton and is prone to falling off, affecting the microwave absorption performance. Cheng Yuanjing et al. used graphene oxide and graphene oxide nanoribbons as the main raw materials, and prepared aerogel materials with low density and an effective absorption bandwidth of 8.52 GHz by physical direct foaming method and high-temperature calcination. However, limited by the foaming process, the aerogel has many punched structures and a high thermal conductivity, which needs to be improved (Cheng Yuanjing, et al. Multifunctional elastic rGO hybrid aerogels for microwave absorption, infrared stealth and heat insulation[J]. Chemical Engineering Journal, 2023, 452, 139376). In the existing methods, there are the following defects:

[0004] 1. In the existing methods, the directional freezing and freeze-drying techniques are adopted, and the structural uniformity of the prepared microwave absorption materials is poor, which is not conducive to large-scale production and manufacturing.

[0005] 2. In the existing methods, ice crystals or bubbles are used for pore formation, and the pore size of the microwave absorption materials is large, which is not conducive to heat insulation.

[0006] 3. In the existing methods, the binding between the functional components and the skeleton is weak, and it is easy to fall off and affect the performance. Summary of the Invention

[0007] In order to improve the above flexible microwave absorption materials and preparation methods, the present invention provides a flexible microwave absorption carbon aerogel composite material and its preparation method. Through hydrothermal reaction, functional particles are introduced into the aerogel skeleton during the sol-gel process, and then pyrolytic carbonization is carried out to realize the preparation of the flexible microwave absorption carbon aerogel composite material, making up for the defects of large holes and uneven structure in the existing methods, and is expected to be applied in the fields of intelligent wear, building thermal management, etc.

[0008] To achieve the above object, the specific technical solution of the present invention is a preparation method of a flexible microwave absorption carbon aerogel composite material, including the following steps:

[0009] (1) Mix the phenolic sol and graphene oxide sol evenly, and add functional components to obtain a precursor solution;

[0010] (2) Vacuum impregnate the fiber felt with the precursor solution in (1), place it in a closed container, and then carry out curing. After cooling, a wet gel is obtained;

[0011] (3) Dry the wet gel in (2) to obtain an organic precursor of the carbon aerogel composite material;

[0012] (4) Pyrolyze the organic precursor of the carbon aerogel composite material in an inert atmosphere to obtain a flexible microwave-absorbing carbon aerogel composite material.

[0013] In the above technical solution, to improve the microwave absorption ability of the carbon aerogel composite material, a functional component or its precursor is added in step (1).

[0014] Further, the fiber felt is a pre-oxidized fiber felt, and the density range of the pre-oxidized fiber felt is 15 mg / cm 3 ~200 mg / cm 3 .

[0015] Further, the fiber diameter range of the pre-oxidized fiber felt is 0.5 μm to 20 μm.

[0016] Further, the functional component is one or more of iron oxide, barium titanate, silicon nitride, silicon carbide or their precursors.

[0017] Further, the phenolic sol is one or more of sol systems such as formaldehyde / phenol sol, formaldehyde / resorcinol sol, furfural / resorcinol sol, etc.

[0018] Further, the temperature range of the high-temperature pyrolysis of the organic precursor of the carbon aerogel composite material is 600 °C to 1200 °C.

[0019] Further, the heating rate range of the high-temperature pyrolysis of the organic precursor of the carbon aerogel composite material is 0.1 °C / min to 10 °C / min.

[0020] Further, the particle size range of the functional component particles is 10 nm to 500 nm.

[0021] The present invention also provides a flexible microwave-absorbing carbon aerogel composite material prepared by the above method.

[0022] The principle of the present invention is: during the hydrothermal reaction sol-gel process, the functional precursor will react to form a functional component. At the same time, the phenolic sol and the graphene oxide sol will entrap the functional component and perform phase separation deposition along the fibers of the flexible reinforcement. Eventually, the fiber surfaces of the entire reinforcement will be covered by gel particles, and the functional components will be evenly distributed in the entire material skeleton. By controlling the sol content and the curing process, it can be ensured that the cured material still has flexibility, and thus a flexible microwave-absorbing carbon aerogel composite material is finally obtained after pyrolysis.

[0023] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0024] 1. The present invention does not involve freeze-drying and can manufacture large-sized flexible microwave-absorbing carbon aerogel composite materials.

[0025] 2. The present invention creates pores by means of hydrothermal sol-gel, which can reduce the pore size of the microwave absorbing material and improve the heat insulation effect.

[0026] 3. The present invention introduces functional components in the sol-gel stage, which can ensure their uniform distribution into the aerogel framework structure and are not easily detached. Description of the Drawings

[0027] Figure 1 It is a flowchart of the preparation method of the flexible microwave absorbing carbon aerogel composite material of the present invention. Detailed Embodiments

[0028] The present invention will be further described below in conjunction with the drawings and embodiments:

[0029] Example 1:

[0030] A flexible microwave absorbing carbon aerogel composite material and its preparation method include the following steps:

[0031] (1) Add 1.6 g of ferric chloride (as a functional precursor) to 200 g of pure water, stir and dissolve it. Subsequently, add 40 g of formaldehyde solution (formalin) and 23 g of phenol to this solution, and stir and dissolve to obtain a phenolic sol. Add 4 g of ascorbic acid to a solution with a graphene oxide concentration of 10 mg / mL in 200 mL, and stir and dissolve to obtain a graphene oxide sol. Add the phenolic sol to the graphene oxide sol, and stir evenly to obtain a reaction precursor solution. Among them, ascorbic acid is a reducing agent, which is used to reduce graphene oxide to graphene during the curing process in step (2).

[0032] (2) Cut a pre-oxidized fiber felt with a size of 100 mm × 100 mm × 3 mm and a density of 60 mg / cm 3 and place it in a corresponding mold. Pour the precursor solution in (1) into the mold and evacuate the air bubbles under vacuum. Subsequently, close the mold and place it in an oven, cure at 70 °C for 4 h, 90 °C for 4 h, and 120 °C for 4 h. After the mold cools down, demold to obtain a wet gel.

[0033] (3) Place the wet gel in (2) in an oven for drying, dry at 50 °C for 12 h, 70 °C for 12 h, and 90 °C until the weight no longer changes, to obtain an organic precursor of the carbon aerogel composite material.

[0034] (4) Under a nitrogen atmosphere, heat the carbon aerogel composite material precursor in (3) to 700 °C at a rate of 2 °C / min and hold for 2 h for pyrolysis to obtain an iron oxide-doped flexible microwave absorbing carbon aerogel composite material. Ferric chloride will first turn into iron hydroxide during the curing process in step (2), and then dehydrate and turn into iron oxide during the pyrolysis process in step (4), serving as a functional component.

[0035] The density of the finally prepared flexible microwave-absorbing carbon aerogel composite is 0.07 g / cm 3 , it can be folded at 90° without damage. In the frequency range of 2 - 18 GHz, the minimum reflection loss is -40.25 dB, the effective absorption bandwidth is 8.45 GHz, and the thermal conductivity at room temperature is 0.0351 W / (m·K).

[0036] Example 2:

[0037] A flexible microwave-absorbing carbon aerogel composite and its preparation method, including the following steps:

[0038] (1) Add 40 g of formaldehyde solution (formalin), 23 g of phenol, and 0.1 g of oxalic acid to 200 g of pure water, stir and dissolve. Then add 3 g of silicon carbide ceramic particles and 0.3 g of polyethyleneimine to this solution, stir and disperse evenly to obtain a phenolic sol. Add 4 g of ascorbic acid to 200 mL of a solution with a graphene oxide concentration of 10 mg / mL, stir and dissolve to obtain a graphene oxide sol. Add the phenolic sol to the graphene oxide sol, stir evenly to obtain a reaction precursor solution.

[0039] (2) Cut a pre-oxidized fiber felt with a size of 100 mm × 100 mm × 3 mm and a density of 60 mg / cm 3 and place it in a corresponding mold. Pour the precursor solution in (1) into the mold and evacuate the air bubbles under vacuum. Then seal the mold and place it in an oven, cure at 70 °C for 4 h, 90 °C for 4 h, and 120 °C for 4 h. After the mold cools down, demold to obtain a wet gel.

[0040] (3) Place the wet gel in (2) in an oven for drying, dry at 50 °C for 12 h, 70 °C for 12 h, and 90 °C until the weight no longer changes to obtain an organic precursor of the carbon aerogel composite.

[0041] (4) Pyrolyze the carbon aerogel composite precursor in (3) in a nitrogen atmosphere at a heating rate of 2 °C / min to 700 °C and hold for 2 h to obtain a silicon carbide-doped flexible microwave-absorbing carbon aerogel composite.

[0042] The density of the finally prepared flexible microwave-absorbing carbon aerogel composite is 0.09 g / cm 3 , it can be folded at 90° without damage. In the frequency range of 2 - 18 GHz, the minimum reflection loss is -36.42 dB, the effective absorption bandwidth is 8.76 GHz, and the thermal conductivity at room temperature is 0.0362 W / (m·K).

[0043] Example 3:

[0044] A flexible wave-absorbing carbon aerogel composite material and a preparation method thereof, comprising the following steps:

[0045] (1) Add 1.6 g of ferric chloride to 200 g of pure water, stir and dissolve it. Subsequently, add 20 g of furfural and 23 g of resorcinol to this solution, and stir and dissolve to obtain a phenolic aldehyde sol. Add 4 g of ascorbic acid to a solution with a graphene oxide concentration of 10 mg / mL in 200 mL, stir and dissolve to obtain a graphene oxide sol. Add the phenolic aldehyde sol to the graphene oxide sol, and stir evenly to obtain a reaction precursor solution.

[0046] (2) Cut a pre-oxidized fiber felt with a size of 100 mm × 100 mm × 3 mm and a density of 40 mg / cm 3 and place it in a corresponding mold. Pour the precursor solution in (1) into the mold and exhaust the air bubbles under vacuum. Subsequently, close the mold and place it in an oven, cure at 90 °C for 4 h, cure at 120 °C for 4 h, and cure at 140 °C for 4 h. After the mold cools down, demold to obtain a wet gel.

[0047] (3) Place the wet gel in (2) in an oven for drying, dry at 50 °C for 12 h, dry at 70 °C for 12 h, and dry at 90 °C until the weight no longer changes to obtain an organic precursor of the carbon aerogel composite material.

[0048] (4) Pyrolyze the carbon aerogel composite material precursor in (3) in a nitrogen atmosphere at a heating rate of 2 °C / min to 800 °C and hold for 2 h to obtain an iron oxide-doped flexible wave-absorbing carbon aerogel composite material.

[0049] The density of the finally prepared flexible wave-absorbing carbon aerogel composite material is 0.08 g / cm 3 , it can be folded at 90° without damage. In the frequency range of 2 - 18 GHz, the minimum reflection loss is -55.48 dB, the effective absorption bandwidth is 7.45 GHz, and the room temperature thermal conductivity is 0.0358 W / (m·K).

[0050] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. Those of ordinary skill in the art can understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification, and the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for preparing a flexible microwave-absorbing carbon aerogel composite material, characterized in that: The following steps are involved: The phenolic sol and the graphene oxide sol are uniformly mixed, and functional components are added to obtain a precursor solution; The fiber felt is vacuum impregnated with a precursor solution and placed in a sealed container, then cured and cooled to obtain a wet gel; Drying the wet gel to obtain an organic precursor of a carbon aerogel composite material; The organic precursor of the carbon aerogel composite material is pyrolyzed at high temperature in an inert atmosphere to obtain a flexible microwave-absorbing carbon aerogel composite material.

2. The preparation method according to claim 1, characterized in that: The fiber felt is a pre-oxidized silk fiber felt, and the density range of the pre-oxidized silk fiber felt is 15 mg / cm 3 ~200mg / cm 3 .

3. The preparation method according to claim 1, characterized in that: The fiber diameter of the pre-oxidized silk fiber felt ranges from 0.5 μm to 20 μm.

4. The preparation method according to claim 1, characterized in that: The functional component is one or more of iron oxide, barium titanate, silicon nitride, silicon carbide or their precursors.

5. The preparation method according to claim 1, characterized in that: The phenolic sol is one or more of formaldehyde / phenol sol, formaldehyde / resorcinol sol, furfural / resorcinol sol.

6. The preparation method according to claim 1, characterized in that: The temperature range of high temperature pyrolysis of the organic precursor of the carbon aerogel composite material is 600°C to 1200°C.

7. The preparation method according to claim 1, characterized in that: The heating rate range of the high temperature pyrolysis of the organic precursor of the carbon aerogel composite material is 0.1° C. / min to 10° C. / min.

8. The preparation method according to claim 1, characterized in that: The particle size of the functional component particles ranges from 10 nm to 500 nm.

9. A flexible wave-absorbing carbon aerogel composite material prepared according to the method of any one of claims 1 to 8.

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