Hollow hard carbon aerogel fibers and methods of making the same

Abstract

This invention discloses a hollow hard carbon aerogel fiber and its preparation method, belonging to the field of porous material preparation and electromagnetic wave absorption. The hollow hard carbon aerogel fiber and its preparation method include: mixing aramid fibers, potassium hydroxide, and dimethyl sulfoxide, and stirring thoroughly to obtain a nano-aramid fiber solution; using the nano-aramid fiber solution as the shell spinning solution and a polar solvent as the core spinning solution, obtaining hollow aramid wet gel fibers through a traction gelation process; replacing the hollow aramid wet gel fibers with an aging solution and freeze-drying to obtain hollow aramid aerogel fibers; and heat-treating the hollow aramid aerogel fibers under an inert atmosphere, followed by cooling to obtain hollow hard carbon aerogel fibers. The prepared hollow hard carbon aerogel fibers have advantages such as low density, high surface area, and high porosity.

Description

Technical Field

[0001] This invention belongs to the field of porous material preparation and electromagnetic wave absorption, specifically relating to a hollow hard carbon aerogel fiber and its preparation method. Background Technology

[0002] Lightweight, broadband, and efficient electromagnetic wave absorbing materials have broad application prospects in national defense and military stealth technology, information security risk prevention, and environmental electromagnetic pollution control. Compared with ferrite, metal, and dielectric ceramic absorbing materials, carbon-based absorbing materials have shown great potential in lightweight absorbing materials due to their low density, abundant functional groups, and tunable electrical properties. Currently, carbon-based absorbing materials, such as graphene oxide (CN112175389B), expanded graphite (CN116093631B), carbon nanotubes (CN107032325B), or polymers and biomolecular derivatives (CN115386337B), have been developed. By controlling the composition and structure at different scales, such as atomic-level defects, nano / micro-scale heterostructures, microporous structures, and macroscopic shapes, carbon-based absorbing materials can achieve specific electromagnetic responses. Although graphene aerogel has lightweight and wideband absorption characteristics, its absorption response is thick and its bulk material is fragile. When using liquid infiltration processes, it is difficult to fabricate devices with complex shapes, which to some extent limits its practical applications.

[0003] Hard carbon is an important class of carbon materials. It is non-graphitizable, has an amorphous structure, and is mainly composed of irregularly distributed crystals and defects. The discrete graphite crystals within hard carbon facilitate electron migration, and the abundant defects promote dipole relaxation. Therefore, this inherent conductivity and polarization property can effectively promote electromagnetic wave attenuation. However, polymer-derived hard carbon microwave absorbing materials synthesized based on macroscopic fabrication, microscopic assembly, and nanoscale chemical co-design have not yet been developed. Furthermore, hollow micro / nanomaterials, besides possessing low density and high specific surface area, have attracted widespread attention in the field of microwave absorbing materials due to their unique hollow structure, which enables multiple reflections and attenuation of electromagnetic waves. However, current methods for preparing these materials still suffer from drawbacks such as complex processes, high costs, and difficulty in control, limiting their widespread application in practice. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a hollow hard carbon aerogel fiber and its preparation method, thereby solving the problems in the prior art.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing hollow rigid carbon aerogel fibers includes the following steps:

[0007] Aramid fiber, potassium hydroxide, and dimethyl sulfoxide were mixed and stirred thoroughly to obtain a nano-aramid fiber solution.

[0008] Hollow aramid wet gel fibers were obtained by using a nano-aramid fiber solution as the shell spinning solution and a polar solvent as the core spinning solution through a traction gelation process.

[0009] Hollow aramid wet gel fibers are obtained by replacing them with an aging solution and freeze-drying.

[0010] Hollow aramid aerogel fibers are obtained by heat treatment under an inert atmosphere and then cooling.

[0011] Furthermore, in the nano-aramid fiber solution, the mass ratio of aramid fiber to potassium hydroxide is 1:(0.5~2).

[0012] Furthermore, the concentration of the nano-aramid fiber solution is 5-20 mg / ml.

[0013] Furthermore, the traction gel process is as follows: a nano-aramid fiber solution and a polar solvent are injected into a coagulation bath through a coaxial needle at an injection rate of 1-20 ml / min to obtain continuous hollow aramid wet gel fibers.

[0014] Furthermore, the polar solvent is one or a mixture of several of deionized water, ethanol, and tert-butanol; the coagulation bath is one or a mixture of several of deionized water, acetic acid, and ethyl acetate.

[0015] Furthermore, the aging solution is a solution composed of tert-butanol and water in a volume ratio of 1:(3-5).

[0016] Furthermore, the inert atmosphere is nitrogen or argon.

[0017] A hollow hard carbon aerogel fiber was prepared using the method described above.

[0018] A microwave absorbing material, comprising the aforementioned hollow rigid carbon aerogel fiber.

[0019] The above-mentioned application of hollow hard carbon aerogel fiber in the preparation of microwave absorbing materials.

[0020] The beneficial effects of this invention are:

[0021] 1. The hollow hard carbon aerogel fibers prepared in this invention possess advantages such as low density, high surface area, and high porosity. These fibers exhibit multi-scale structural features, enabling effective absorption of electromagnetic waves. ① The macroscopic hollow structure improves impedance matching, promotes electromagnetic wave penetration, and facilitates multiple reflections and scattering within the hollow structure, thereby increasing electromagnetic wave attenuation. ② The unique three-dimensional network structure of the micro / nano fiber aerogel walls promotes electron transfer and improves the material's conductivity loss. ③ The abundant defects and interfaces within the ordered / disordered hybrid hard carbon structure enhance polarization loss. Therefore, the hollow hard carbon aerogel fibers achieve excellent absorption characteristics with low density, strong absorption, low thickness, and wide frequency range, making them suitable for electromagnetic wave absorption across multiple frequency bands and meeting the needs of various application scenarios.

[0022] 2. Rigid carbon aerogel fiber materials ensure effective wave absorption while reducing the overall weight of equipment, making them significant for fields such as aerospace. Rigid carbon aerogel fiber materials possess excellent thermal and chemical stability, maintaining good wave absorption performance even at high temperatures, making them suitable for applications in harsh environments. They are easy to process and integrate: Rigid carbon aerogel fibers are easily composited with other polymer matrix materials, facilitating the design and manufacture of wave-absorbing structures of various shapes and sizes to meet different structural and functional requirements. Furthermore, the preparation process is simple, the reaction conditions are mild, and continuous production is possible. In addition, rigid carbon-based aerogel fibers have broad application prospects in photothermal conversion, seawater desalination, and energy storage. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The image shows a scanning electron microscope (SEM) image of the surface of the hollow hard carbon aerogel fiber prepared in Example 1.

[0025] Figure 2 Here is a magnified scanning electron microscope image of the surface of the hollow hard carbon aerogel fiber prepared in Example 1;

[0026] Figure 3 Here is a cross-sectional scanning electron microscope image of the hollow hard carbon aerogel fiber prepared in Example 1;

[0027] Figure 4 This is a magnified scanning electron microscope image of the cross-section of the hollow hard carbon aerogel fiber prepared in Example 1;

[0028] Figure 5Transmission electron microscopy (TEM) image of the hollow hard carbon aerogel fibers prepared in Example 1;

[0029] Figure 6 High-resolution transmission electron microscopy image of the hollow hard carbon aerogel fiber prepared in Example 1;

[0030] Figure 7 Two-dimensional graph showing the microwave absorption properties of the hollow hard carbon aerogel fiber prepared in Example 1;

[0031] Figure 8 Two-dimensional graph showing the microwave absorption properties of the hollow hard carbon aerogel fiber prepared in Example 2;

[0032] Figure 9 Two-dimensional graph showing the microwave absorption properties of the hollow hard carbon aerogel fiber prepared in Example 3;

[0033] Figure 10 This is a two-dimensional diagram of the microwave absorption performance of the hollow hard carbon aerogel fiber prepared in Example 4. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The preparation process of hollow hard carbon aerogel fibers will be described below through several examples.

[0036] Example 1

[0037] A method for preparing hollow rigid carbon aerogel fibers includes the following steps:

[0038] S1, Preparation of hollow aramid aerogel fibers:

[0039] 1g of para-aramid fiber, 1g of potassium hydroxide, and 100ml of dimethyl sulfoxide were mixed and magnetically stirred for 5 days in the dark to obtain a 10mg / ml nano-aramid fiber solution. The nano-aramid fiber solution and a polar solvent were injected into a coagulation bath through a coaxial needle at an injection rate of 10ml / min to obtain continuous hollow aramid wet gel fibers (wherein, the polar solvent was deionized water, the coagulation bath was deionized water, the inner channel diameter of the coaxial needle was 0.8mm, and the outer channel diameter was 1.5mm). The prepared hollow aramid wet gel fibers were aged in a water / tert-butanol solution with a volume ratio of 1:3, with replacement every 6 hours for 3 times. Then, the fibers were frozen in a -20℃ freezer for 24 hours and freeze-dried for 12 hours to obtain hollow aramid aerogel fibers.

[0040] S2, Preparation of hollow hard carbon aerogel fibers:

[0041] The hollow aramid aerogel fibers prepared in S1 were placed in a tube furnace and heated to 1200℃ at a heating rate of 5℃ / min under nitrogen atmosphere protection and held for 2 hours. Then, the temperature was naturally lowered to obtain hollow hard carbon aerogel fibers.

[0042] The structure and properties of the hollow hard carbon aerogel fibers prepared in this embodiment are tested below:

[0043] Figure 1 The surface morphology of hollow rigid carbon aerogel fibers was revealed, showing a uniform and regular fiber with a dense, wrinkled surface. Figure 2 ). Figure 3 The cross-sectional morphology of hollow rigid carbon aerogel fibers is characterized by annular, closed rigid carbon fiber aerogel walls and cavities penetrating the fiber axis, with an internal three-dimensional network structure of interconnected fibers. Figure 4 and Figure 5 ). Figure 6 High-resolution transmission electron microscopy (HRTEM) images of hard carbon fibers show that the hard carbon structure possesses the characteristics of discrete graphite microcrystals and defects. The aerogel fibers have an outer diameter of 0.8 mm, an inner diameter of 0.5 mm, and a wall thickness of 150 μm; the specific surface area is 320 m² / m³. 2 / g, porosity 90wt%.

[0044] Using the hollow carbon aerogel fibers obtained in Example 1 as the absorbent, the carbon aerogel fibers were uniformly mixed with paraffin wax to prepare an annular sample with an outer diameter of 7.0 mm and an inner diameter of 3.0 mm for microwave absorption performance testing. Figure 7 As shown, when the filler content is 2wt% and the thickness is 2.55mm, the minimum reflection loss reaches -61.47dB, and when the thickness is 2.35mm, the maximum absorption bandwidth is 6.68GHz.

[0045] Example 2

[0046] A method for preparing hollow rigid carbon aerogel fibers includes the following steps:

[0047] S1, Preparation of hollow aramid aerogel fibers:

[0048] 0.5 g of para-aramid fiber, 1 g of potassium hydroxide, and 100 ml of dimethyl sulfoxide were mixed and magnetically stirred for 7 days in the dark to obtain a 5 mg / ml nano-aramid fiber solution. The nano-aramid fiber solution and a polar solvent were injected into a coagulation bath through a coaxial needle at an injection rate of 10 ml / min to obtain continuous hollow aramid wet gel fibers (wherein, the polar solvent was a mixture of deionized water and ethanol, the coagulation bath was a mixture of deionized water and acetic acid, and the inner channel diameter of the coaxial needle was 0.2 mm and the outer channel diameter was 0.4 mm). The prepared hollow aramid wet gel fibers were aged in a water / tert-butanol solution with a volume ratio of 1:4, with replacement every 12 hours for 2 times. Then, the fibers were frozen in a -40°C freezer for 24 hours and freeze-dried for 24 hours to obtain hollow aramid aerogel fibers.

[0049] S2, Preparation of hollow hard carbon aerogel fibers:

[0050] The hollow aramid aerogel fibers prepared in S1 were placed in a tube furnace and heated to 800℃ at a heating rate of 5℃ / min under argon atmosphere protection and held for 5h. Then, the temperature was naturally cooled to obtain hollow hard carbon aerogel fibers.

[0051] The properties of the hollow hard carbon aerogel fibers prepared in this embodiment are tested below:

[0052] The aerogel fiber has an outer diameter of 0.5 mm, an inner diameter of 0.2 mm, and a wall thickness of 150 μm; the specific surface area of ​​the aerogel fiber is 100 m². 2 / g, porosity 80wt%. For example... Figure 8 As shown, when the filler content is 2wt%, the minimum reflection loss reaches -16.34dB at a thickness of 4.9mm, and the maximum absorption bandwidth is 5.32GHz at a thickness of 2.8mm.

[0053] Example 3

[0054] A method for preparing hollow rigid carbon aerogel fibers includes the following steps:

[0055] S1, Preparation of hollow aramid aerogel fibers:

[0056] 1 g of para-aramid fiber, 0.5 g of potassium hydroxide, and 50 ml of dimethyl sulfoxide were mixed and magnetically stirred for 7 days in the dark to obtain a nano-aramid fiber solution with a concentration of 20 mg / ml. The nano-aramid fiber solution and a polar solvent were injected into a coagulation bath through a coaxial needle at an injection rate of 20 ml / min to obtain continuous hollow aramid wet gel fibers (wherein, the polar solvent was a mixture of deionized water and ethanol, the coagulation bath was a mixture of deionized water and ethyl acetate, and the inner channel diameter of the coaxial needle was 2.3 mm and the outer channel diameter was 2.8 mm). The prepared hollow aramid wet gel fibers were aged in a water / tert-butanol solution with a volume ratio of 1:4, with replacement every 8 hours for 3 times. Then, the fibers were frozen in a -60°C freezer for 24 hours and freeze-dried for 48 hours to obtain hollow aramid aerogel fibers.

[0057] S2, Preparation of hollow hard carbon aerogel fibers:

[0058] The hollow aramid aerogel fibers prepared in S1 were placed in a tube furnace and heated to 1600℃ at a heating rate of 10℃ / min under argon atmosphere protection and held for 1h. Then, the temperature was naturally cooled to obtain hollow hard carbon aerogel fibers.

[0059] The performance of the hollow hard carbon aerogel fiber prepared in this embodiment is tested below:

[0060] The aerogel fiber has an outer diameter of 1.4 mm, an inner diameter of 1 mm, and a wall thickness of 200 μm; its specific surface area is 500 m². 2 / g, with a porosity of 95wt%.

[0061] Using the hollow carbon aerogel fibers obtained in this embodiment as the absorbent, the carbon aerogel fibers were uniformly mixed with paraffin wax to prepare a ring-shaped sample with an outer diameter of 7.0 mm and an inner diameter of 3.0 mm for microwave absorption performance testing. Figure 9 As shown, the minimum reflection loss reaches -53.4dB when the thickness is 1.6mm, and the maximum absorption bandwidth is 5.52GHz when the thickness is 1.9mm, achieving a relatively ideal wave absorption effect with low thickness.

[0062] Example 4

[0063] A method for preparing hollow rigid carbon aerogel fibers includes the following steps:

[0064] S1, Preparation of hollow aramid aerogel fibers:

[0065] 1g of para-aramid fiber, 2g of potassium hydroxide, and 100ml of dimethyl sulfoxide were mixed and magnetically stirred for 7 days in the dark to obtain a 10mg / ml nano-aramid fiber solution. The nano-aramid fiber solution and a polar solvent were injected into a coagulation bath through a coaxial needle at an injection rate of 1ml / min to obtain continuous hollow aramid wet gel fibers (where the polar solvent was a mixture of deionized water and tert-butanol, the coagulation bath was a mixture of deionized water and ethyl acetate, and the inner channel diameter of the coaxial needle was 1.2mm and the outer channel diameter was 2mm). The prepared hollow aramid wet gel fibers were aged in a water / tert-butanol solution with a volume ratio of 1:5, with replacement every 4 hours for 4 times. Then, the fibers were frozen in a -80℃ freezer for 24 hours and freeze-dried for 72 hours to obtain hollow aramid aerogel fibers.

[0066] S2, Preparation of hollow hard carbon aerogel fibers:

[0067] The hollow aramid aerogel fibers prepared in S1 were placed in a tube furnace and heated to 1400℃ at a heating rate of 10℃ / min under nitrogen atmosphere protection and held for 2 hours. Then, the temperature was naturally lowered to obtain hollow hard carbon aerogel fibers.

[0068] The performance of the hollow hard carbon aerogel fiber prepared in this embodiment is tested below:

[0069] The aerogel fiber has an outer diameter of 1.5 mm, an inner diameter of 0.9 mm, and a wall thickness of 300 μm; its specific surface area is 435 m². 2 / g, with a porosity of 92wt%.

[0070] The hollow carbon aerogel fibers obtained in this embodiment were used as absorbents. The carbon aerogel fibers were uniformly mixed with paraffin wax to prepare an annular sample with an outer diameter of 7.0 mm and an inner diameter of 3.0 mm for microwave absorption performance testing. (See attached image) Figure 10 As shown, the lowest reflection loss reaches -41.61dB when the thickness is 4.95mm, and the maximum absorption bandwidth is 5.28GHz when the thickness is 2.4mm.

[0071] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a hollow hard carbon aerogel fiber, characterized by, Includes the following steps: Aramid fiber, potassium hydroxide, and dimethyl sulfoxide were mixed and stirred thoroughly to obtain a nano-aramid fiber solution. Hollow aramid wet gel fibers were obtained by using a nano-aramid fiber solution as the shell spinning solution and a polar solvent as the core spinning solution through a traction gelation process. Hollow aramid wet gel fibers are obtained by replacing them with an aging solution and freeze-drying. Hollow aramid aerogel fibers are obtained by heat treatment under an inert atmosphere and then cooling. The traction gel process is as follows: a nano-aramid fiber solution and a polar solvent are injected into a coagulation bath through a coaxial needle at an injection rate of 1-20 ml / min to obtain continuous hollow aramid wet gel fibers. The polar solvent is one or a mixture of several of deionized water, ethanol, and tert-butanol; the coagulation bath is one or a mixture of several of deionized water, acetic acid, and ethyl acetate. The aging solution is a solution composed of tert-butanol and water in a volume ratio of 1:(3~5).

2. The method for preparing hollow hard carbon aerogel fibers according to claim 1, characterized in that, In the nano-aramid fiber solution, the mass ratio of aramid fiber to potassium hydroxide is 1:(0.5~2).

3. The method for preparing hollow hard carbon aerogel fibers according to claim 1, characterized in that, The concentration of the nano-aramid fiber solution is 5-20 mg / ml.

4. The method for preparing hollow hard carbon aerogel fiber according to claim 1, characterized in that, The inert atmosphere is nitrogen or argon.

5. A hollow hard carbon aerogel fiber, characterized by, It is prepared by the method described in any one of claims 1-4.

6. A wave-absorbing material, characterized by, Includes the hollow rigid carbon aerogel fiber as described in claim 5.

7. The application of the hollow hard carbon aerogel fiber as described in claim 5 in the preparation of microwave absorbing materials.

Images