Carbon nanotube-reinforced aluminum oxide composite fiber, and preparation method and application thereof

Abstract

The application provides a carbon nanotube reinforced alumina composite fiber and a preparation method and application thereof, wherein the preparation method comprises the following steps: adding carbon nanotubes and a polymer dispersant into an organic solvent and uniformly mixing by ultrasonic to obtain a carbon nanotube dispersion liquid; adding a spinning aid into a mixed solvent and uniformly mixing, then adding the carbon nanotube dispersion liquid and an aluminum salt solution and uniformly stirring to obtain a spinning solution; spinning the spinning solution by using a gas spraying spinning method to obtain a precursor fiber; and baking the precursor fiber and sintering the baked precursor fiber in an inert atmosphere to obtain the carbon nanotube reinforced alumina composite fiber. The composite fiber prepared by the application is in a micro-nano fiber shape, has a diameter of about 200-700 nm, and the carbon nanotubes are uniformly distributed in the fiber; and the fiber has high strength, low thermal conductivity and high conductivity, and has excellent comprehensive performance, and can meet the functional requirements of multifunctional fiber materials in the fields of aviation and spaceflight.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube-reinforced ceramic fiber composite materials, and particularly to a carbon nanotube-reinforced alumina composite fiber, its preparation method, and its application. Background Technology

[0002] Alumina possesses advantages such as high strength, high temperature resistance, wear resistance, and oxidation resistance, making it widely used in aerospace and other fields. However, spacecraft need to effectively block electromagnetic interference in outer space while withstanding complex stresses and thermal environments, thus requiring materials to possess mechanical load-bearing, thermal protection, and electromagnetic shielding functions. Since electromagnetic shielding relies on the reflection of electromagnetic waves by mobile charge carriers, or the interaction of electric dipoles, magnetic dipoles, and electromagnetic fields, and alumina itself is an insulator lacking these mechanisms, suitable reinforcing materials must be introduced to endow it with electromagnetic shielding capabilities.

[0003] Since its discovery by Iijima in 1991, carbon nanotubes have been considered an ideal candidate reinforcement for preparing multifunctional composite materials due to their advantages such as low density, excellent mechanical properties, good electrical conductivity, and thermal stability. Introducing them into an alumina matrix is ​​expected to significantly improve the mechanical, electrical, and thermal properties of the composites. Meanwhile, incorporating carbon nanotubes into ceramic matrices has proven to be an effective way to improve the oxidation resistance of carbon nanotubes while simultaneously improving the mechanical properties of the ceramic matrix.

[0004] In related technologies, carbon nanotube / alumina composite materials have been reported. For example, CN105218079B discloses a carbon nanotube / alumina bioceramic and its preparation method. However, the material prepared by this method is in bulk form and mainly focuses on improving a single property. There are no reports on the preparation of carbon nanotube / alumina composite fiber materials and the study of their multifunctionality.

[0005] Therefore, there is an urgent need to provide a carbon nanotube-reinforced alumina composite fiber, its preparation method, and its application. Summary of the Invention

[0006] This invention provides a carbon nanotube-reinforced alumina composite fiber, its preparation method, and its application. It can solve the problem that existing carbon nanotube / alumina composite materials are limited to bulk morphology and have only single functional research, which cannot simultaneously meet the needs of aerospace and other fields for multifunctional fiber materials.

[0007] In a first aspect, the present invention provides a method for preparing carbon nanotube-reinforced alumina composite fibers, the method comprising the following steps: (1) Add carbon nanotubes and polymer dispersant to an organic solvent and mix ultrasonically to obtain a carbon nanotube dispersion; (2) Add the spinning aid to the mixed solvent and mix well, then add the carbon nanotube dispersion and aluminum salt solution and stir to mix well to obtain the spinning solution; (3) The spinning solution is spun by air jet spinning to obtain precursor fibers; (4) The precursor fiber is dried and then sintered in an inert atmosphere to obtain the carbon nanotube reinforced alumina composite fiber.

[0008] Preferably, in step (1), the carbon nanotubes are single-walled carbon nanotubes; the polymer dispersant is carbon nanotube DMF dispersant; and the organic solvent is N,N-dimethylformamide.

[0009] Preferably, the mass ratio of polymer dispersant to carbon nanotubes is (0.5~10):1.

[0010] Preferably, the mass-volume concentration of the carbon nanotube dispersion is 0.1~0.2 wt / vol.

[0011] More preferably, the ultrasonic mixing power is 500~700W and the time is 0.5~1.5h.

[0012] Preferably, in step (2), the spinning aid is polyvinyl alcohol or polyvinylpyrrolidone; the mixed solvent is obtained by compounding N,N-dimethylformamide and ethanol.

[0013] Preferably, the volume ratio of N,N-dimethylformamide to ethanol is (3~5):1.

[0014] More preferably, the amount of the mixed solvent added is 7 to 10 times the mass of the spinning aid.

[0015] Preferably, the solute in the aluminum salt solution is aluminum chloride hexahydrate or aluminum nitrate nonahydrate, and the solvent is water; the concentration of the aluminum salt solution is 37~45wt%.

[0016] Preferably, in step (2), the mass ratio of carbon nanotubes, aluminum salts and spinning aids is (0.0015~0.015):1:(0.75~1.2).

[0017] Preferably, in step (3), during the spinning process, the injection rate of the spinning solution is 2~6 mL / h, and the spinning pressure is 0.05~0.09 MPa.

[0018] Preferably, in step (4), the drying temperature is 55~65℃ and the time is 3~12h.

[0019] More preferably, in step (4), a two-stage heating process is used for sintering; wherein, in the first stage, the temperature is raised to 350~450℃ at a heating rate of 1.5~2.5℃ / min and held for 0.5~1.5h; in the second stage, the temperature is raised to 800~1600℃ at a heating rate of 3.5~4.5℃ / min and held for 1~3h.

[0020] In a second aspect, the present invention provides a carbon nanotube-reinforced alumina composite fiber, which is prepared by any of the preparation methods described in the first aspect above.

[0021] Thirdly, the present invention provides an application of carbon nanotube-reinforced alumina composite fibers in aerospace thermal protection and / or electromagnetic shielding.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects: In this invention, carbon nanotubes and a polymer dispersant are first added to an organic solvent and ultrasonically mixed to obtain a carbon nanotube dispersion. A spinning aid is then dissolved in a portion of the organic solvent to form a mixed solvent, which is then mixed thoroughly. This mixed solvent is then stirred together with the carbon nanotube dispersion and an aluminum salt solution to prepare a homogeneous spinning solution. Next, the spinning solution is spun using an air-jet spinning method to obtain precursor fibers. Finally, the precursor fibers are sintered in an inert atmosphere to obtain carbon nanotube-reinforced alumina composite fibers. These composite fibers are micro-nano-scale fibers with a diameter of approximately 200-700 nm, and the carbon nanotubes are uniformly distributed within the fibers. Furthermore, these fibers possess high strength, low thermal conductivity, and high electrical conductivity, exhibiting excellent overall performance and meeting the functional requirements of multifunctional fiber materials in aerospace and other fields. Simultaneously, this preparation method has the advantages of simple process, short preparation cycle, and low cost. 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, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an X-ray diffraction pattern of a carbon nanotube-reinforced alumina composite fiber provided in Embodiment 1 of the present invention; Figure 2 This is a high-magnification scanning electron microscope (SEM) image of a carbon nanotube-reinforced alumina composite fiber provided in Embodiment 1 of the present invention. Figure 3 This is a low-magnification scanning electron microscope (SEM) image of a carbon nanotube-reinforced alumina composite fiber provided in Embodiment 1 of the present invention. Figure 4 This is an optical micrograph of a carbon nanotube-reinforced alumina composite fiber provided in Embodiment 1 of the present invention; Figure 5 This is a scanning electron microscope image of a carbon nanotube-reinforced alumina composite fiber provided in Embodiment 2 of the present invention; Figure 6 This is a tensile stress-strain curve diagram of a carbon nanotube reinforced alumina composite fiber provided in Embodiment 1 and Comparative Example 1 of the present invention; Figure 7 This is a graph showing the electromagnetic shielding effectiveness of a carbon nanotube-reinforced alumina composite fiber as a function of frequency, provided in Embodiment 1 of the present invention; where SER represents the reflection shielding effectiveness, SEA represents the absorption shielding effectiveness, and SET represents the total shielding effectiveness. Figure 8 This is an infrared thermal imaging temperature distribution and temperature-time response curve of a carbon nanotube-reinforced alumina composite fiber provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, but 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.

[0026] This invention provides a method for preparing carbon nanotube-reinforced alumina composite fibers, the method comprising the following steps: (1) Add carbon nanotubes and polymer dispersant to an organic solvent and mix ultrasonically to obtain a carbon nanotube dispersion; (2) Add the spinning aid to the mixed solvent and mix well, then add the carbon nanotube dispersion and aluminum salt solution and stir to mix well to obtain the spinning solution; (3) The spinning solution is spun by air jet spinning to obtain precursor fibers; (4) The precursor fiber is dried and then sintered in an inert atmosphere to obtain the carbon nanotube reinforced alumina composite fiber.

[0027] In this embodiment of the invention, carbon nanotubes and a polymer dispersant are first added to an organic solvent and ultrasonically mixed to obtain a carbon nanotube dispersion. A spinning aid is then dissolved in a portion of the organic solvent to form a mixed solvent, which is then mixed. This mixed solvent is then stirred and mixed with the carbon nanotube dispersion and an aluminum salt solution to prepare a uniform spinning solution. Next, the spinning solution is spun using an air-jet spinning method to obtain precursor fibers. Finally, the precursor fibers are sintered in an inert atmosphere to obtain carbon nanotube-reinforced alumina composite fibers. These composite fibers are micro-nano-scale fibers with a diameter of approximately 200-700 nm, and the carbon nanotubes are uniformly distributed within the fibers. Furthermore, these fibers possess high strength, low thermal conductivity, and high electrical conductivity, exhibiting excellent overall performance and meeting the functional requirements of multifunctional fiber materials in aerospace and other fields. Simultaneously, this preparation method has the advantages of simple process, short preparation cycle, and low cost.

[0028] According to some preferred embodiments, in step (1), the carbon nanotubes are single-walled carbon nanotubes; the polymer dispersant is a carbon nanotube DMF dispersant; the organic solvent is N,N-dimethylformamide; the mass ratio of the polymer dispersant to the carbon nanotubes is (0.5~10):1 (for example, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9; 1 or 10:1); the mass-volume concentration of the carbon nanotube dispersion is 0.1~0.2wt / vol% (for example, it can be 0.1wt / vol%, 0.15wt / vol% or 0.2wt / vol%); the ultrasonic mixing power is 500~700W (for example, it can be 500W, 600W or 700W), and the time is 0.5~1.5h (for example, it can be 0.5h, 1.0h or 1.5h).

[0029] In this embodiment of the invention, single-walled carbon nanotubes are preferred. During the mixing process, single-walled carbon nanotubes and a polymer dispersant are added to an organic solvent, N,N-dimethylformamide (DMF), and then ultrasonically dispersed to obtain a carbon nanotube dispersion. By reasonably controlling the mass ratio of the polymer dispersant to the carbon nanotubes, good dispersibility of the carbon nanotubes can be ensured, effectively preventing agglomeration and ensuring uniform dispersion in the solvent. If the amount of polymer dispersant is too high, the viscosity of the spinning solution will be too high, affecting spinnability and fiber structure; while if the amount is too low, its dispersing and stabilizing effect on the carbon nanotubes will be insufficient, making it difficult to inhibit agglomeration.

[0030] It should be noted that, in the embodiments of the present invention, the carbon nanotube DMF dispersant can be purchased from the market.

[0031] According to some preferred embodiments, in step (2), the spinning aid is polyvinyl alcohol or polyvinylpyrrolidone; the mixed solvent is obtained by compounding N,N-dimethylformamide and ethanol; the volume ratio of N,N-dimethylformamide and ethanol is (3~5):1 (for example, it can be 3:1, 4:1 or 5:1), and the amount of the mixed solvent added is 7 to 10 times the mass of the spinning aid (for example, it can be 7 times, 8 times, 9 times or 10 times).

[0032] In this embodiment of the invention, when preparing the spinning solution, an appropriate amount of spinning aid is first added to the mixed solvent and stirred until homogeneous. This facilitates the formation of a spinning solution with suitable viscosity and spinnability. If the amount of spinning aid is too high, the viscosity of the spinning solution will be too high, easily clogging the needles during spinning. Conversely, if the amount is too low, the spinning solution will dry too slowly, making it difficult to solidify into filaments during collection, and may even result in droplet spraying. Furthermore, the mixed solvent is preferably a mixture of DMF and ethanol. Pure DMF systems, due to their slow evaporation rate and high viscosity, are prone to defects such as fiber adhesion, beading, and even film formation during spinning. The introduction of ethanol accelerates solvent evaporation, reduces solution viscosity and surface tension, thereby improving the uniformity and stability of filament formation and significantly enhancing the spinning process's tolerance to environmental factors such as temperature and humidity. Therefore, by combining the two, the solvent evaporation rate can be effectively controlled to match the filament formation process, ensuring more uniform and stable filament formation and significantly improving environmental adaptability (temperature and humidity, etc.).

[0033] According to some preferred embodiments, in step (2), the solute of the aluminum salt solution is aluminum chloride hexahydrate or aluminum nitrate nonahydrate, and the solvent is water; the concentration of the aluminum salt solution is 37~45wt% (for example, it can be 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt% or 45wt%).

[0034] In this embodiment of the invention, aluminum salt is added to an appropriate amount of deionized water and stirred to dissolve, thus preparing a uniform aluminum salt solution; wherein, the aluminum salt is preferably aluminum chloride hexahydrate or aluminum nitrate nonahydrate. Then, this aluminum salt solution and carbon nanotube dispersion are added together to a pre-prepared spinning aid solution, and stirred until homogeneous to directly obtain the spinning solution. This preparation process requires no additional deposition or separation steps, is simple to operate, and the components can be uniformly mixed in one step. After the resulting spinning solution is subjected to air-jet spinning treatment, a precursor fiber with uniform component distribution can be obtained.

[0035] According to some preferred embodiments, in step (2), the mass ratio of carbon nanotubes, aluminum salts and spinning aids is (0.0015~0.015):1:(0.75~1.2) (for example, it can be 0.0015:1:0.75, 0.012:1:0.75, 0.015:1:0.75, 0.01:1:0.80, 0.012:1:0.80, 0.015:1:0.80, 0.0015:1:1, 0.012:1:1, 0.015:1:1, 0.01:1:1.2, 0.012:1:1.2 or 0.015:1:1.2).

[0036] In this embodiment of the invention, by comprehensively controlling the content of carbon nanotubes, aluminum salts, and spinning auxiliaries in the spinning solution, it is not only beneficial to ensure the continuous stability of the spinning process, but also to optimize the comprehensive performance of the fiber. Among them, the amount of carbon nanotubes needs to take into account both their dispersibility in the solvent and the target content of carbon nanotubes in the fiber. Too much carbon nanotubes will easily lead to agglomeration, while too little will not have an obvious reinforcing effect on the fiber. The amount of aluminum salt not only affects the concentration of the precursor solution and the spinnability, but also determines the relative content of carbon nanotubes and matrix in the final alumina fiber. Too much aluminum salt will make the solution viscosity too high and easily clog the needle, while too little aluminum salt will result in insufficient viscosity of the spinning solution, making it difficult to form filaments continuously, and the resulting fiber strength will be low. The amount of spinning auxiliaries directly controls the spinnability of the solution. Too much aluminum salt will also cause excessive viscosity and clog the needle, while too little aluminum salt will cause the solution to dry too slowly, making it difficult to solidify into filaments during collection, and even causing the phenomenon of spraying droplets. By coordinating and optimizing the content of each component, the carbon nanotubes can be uniformly dispersed and the spinning process can be stable and smooth, thereby producing high-performance carbon nanotube-reinforced alumina composite fibers.

[0037] According to some preferred embodiments, in step (3), during the spinning process, the injection rate of the spinning solution is 2~6 mL / h (for example, it can be 2 mL / h, 3 mL / h, 4 mL / h, 5 mL / h or 6 mL / h), and the spinning gas pressure is 0.05~0.09 MPa (for example, it can be 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa or 0.09 MPa).

[0038] In this embodiment of the invention, after preparing the spinning solution, the spinning solution is spun using an air-jet spinning method. During the spinning process, by further coordinating the injection rate of the spinning solution and the spinning air pressure, it is beneficial to ensure continuous and stable filament formation in the spinning process, thereby obtaining precursor fibers with uniform diameter and regular morphology.

[0039] According to some preferred embodiments, in step (4), the drying temperature is 55~65℃ (for example, it can be 55℃, 60℃ or 65℃), and the time is 3~12h (for example, it can be 3h, 5h, 8h, 10h or 12h).

[0040] According to some preferred embodiments, sintering is carried out using a two-stage heating process; wherein, in the first stage, the temperature is increased to 350-450°C (e.g., 350°C, 400°C, or 450°C) at a heating rate of 1.5-2.5°C / min (e.g., 1.5°C / min, 2.0°C / min, or 2.5°C / min), and held at that temperature for 0.5-1.5 hours (e.g., 0.5 hours, 1.0 hours, or 1.5 hours); in the second stage, the temperature is increased to 800-1600°C (e.g., 800°C, 900°C, 1000°C, 1200°C, 1500°C, 1550°C, or 1600°C) at a heating rate of 3.5-4.5°C / min (e.g., 3.5°C / min, 4.0°C / min, or 4.5°C / min), and held at that temperature for 1-3 hours (e.g., 1 hour, 2 hours, or 3 hours).

[0041] In this embodiment of the invention, the obtained precursor fibers are first transferred to a drying oven and dried at a suitable temperature. Then, under an inert atmosphere (such as nitrogen), the dried precursor fibers are sintered using a two-stage heating method. In the first stage, the temperature is increased from room temperature (25-30°C) to 350-450°C at a heating rate of 1.5-2.5°C / min and held at that temperature. In the second stage, the temperature is increased from 350-450°C to 800-1600°C at a heating rate of 3.5-4.5°C / min and held at that temperature for sintering. This promotes the alumina crystal transformation and fiber densification, while the carbon nanotubes remain stably in the inert atmosphere and exert a reinforcing effect. This two-stage heating method facilitates the acquisition of carbon nanotube-reinforced alumina composite fibers with well-preserved morphology and a dense structure. Finally, after sintering, the fibers are cooled to room temperature in the furnace.

[0042] This invention also provides a carbon nanotube-reinforced alumina composite fiber, which is prepared using any of the preparation methods described above.

[0043] The carbon nanotube-reinforced alumina composite fibers prepared by this invention are interwoven and have good continuity, possessing high strength, low thermal conductivity, and high electrical conductivity, resulting in excellent overall performance. Specifically, the electrical conductivity of these fibers can reach 2-7 S / m, with a maximum total electromagnetic shielding effectiveness exceeding 20 dB, while maintaining good low thermal conductivity and thermal insulation performance. This effectively meets the dual requirements of thermal protection and electromagnetic shielding in the aerospace field. Furthermore, the preparation method is simple, has a short cycle time, and is low in cost.

[0044] This invention also provides an application of carbon nanotube-reinforced alumina composite fibers in aerospace thermal protection and / or electromagnetic shielding.

[0045] To more clearly illustrate the technical solution and advantages of the present invention, the following detailed description of a carbon nanotube-reinforced alumina composite fiber, its preparation method, and its application is provided through several embodiments; wherein, the polymer dispersant is carbon nanotube DMF dispersant purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0046] Example 1: (1) Add 0.1g of carbon nanotubes (single-walled carbon nanotubes) and 0.5g of polymer dispersant (carbon nanotube DMF dispersant) to 100mL of organic solvent (N,N-dimethylformamide) and sonicate at 600W for 1h to obtain carbon nanotube dispersion; (2) Add 8g of aluminum salt (aluminum chloride hexahydrate) to 10mL of deionized water and stir magnetically for 2h to obtain a transparent aluminum salt solution; Add 6g of spinning aid (polyvinyl alcohol) to 60mL of mixed solvent (N,N-dimethylformamide and ethanol in a volume ratio of 4:1) and stir until well mixed. Then add the above carbon nanotube dispersion and aluminum salt solution and stir magnetically for 12h to obtain the spinning solution. (3) The spinning solution is spun by air jet spinning, and the fibers are collected by a collection device to obtain precursor fibers; wherein the injection rate of the spinning solution is 4 mL / h and the spinning air pressure is 0.07 MPa. (4) The precursor fiber was transferred to a drying oven and dried at 60°C for 5 hours. Then, under an inert atmosphere (nitrogen), the temperature was first increased from room temperature (25°C) to 400°C at a heating rate of 2°C / min and held for 1 hour. After that, the temperature was increased from 400°C to 1000°C at a heating rate of 4°C / min and held for 3 hours for sintering. After sintering, the temperature was lowered to room temperature with the furnace to obtain carbon nanotube reinforced alumina composite fiber.

[0047] Example 2 Example 2 is basically the same as Example 1, except that in step (4), the precursor fiber is transferred to a drying oven and dried at 60°C for 5 hours. Then, under an inert atmosphere (nitrogen), the temperature is increased from room temperature (25°C) to 1000°C at a heating rate of 3°C / min and held for 5 hours for sintering. After sintering, the temperature is reduced to room temperature with the furnace to obtain carbon nanotube reinforced alumina composite fiber.

[0048] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that step (1) is removed, and in step (2), 8g of aluminum salt (aluminum chloride hexahydrate) is added to 10mL of deionized water and magnetically stirred for 2h to obtain a transparent aluminum salt solution; 6g of spinning aid (polyvinyl alcohol) is added to 60mL of mixed solvent (N,N-dimethylformamide and ethanol in a volume ratio of 4:1) and stirred until well mixed, and then the aluminum salt solution is added and magnetically stirred for 12h to obtain a spinning solution.

[0049] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that in step (4), the precursor fiber is transferred to a drying oven and dried at 60°C for 5 hours. Then, in an air atmosphere, the temperature is first raised from room temperature (25°C) to 400°C at a heating rate of 2°C / min and held for 3 hours for sintering. After sintering, the temperature is lowered to room temperature with the furnace to obtain carbon nanotube reinforced alumina composite fiber.

[0050] The carbon nanotube-reinforced alumina composite fibers obtained in the examples and comparative examples were subjected to performance tests, and the test results are as follows: Figures 1 to 8 As shown in Table 1; the resistance was tested with a multimeter and the conductivity of the fiber material was calculated; the electromagnetic shielding effectiveness was measured by a vector network analyzer using the waveguide method; the tensile strength test was performed using the paper template method.

[0051] Table 1 Depend on Figure 1 The X-ray diffraction pattern shows that when the fiber prepared in Example 1 is calcined at below 1000°C under an inert atmosphere, its phase is γ-phase alumina. Figure 2 The high-magnification microstructure shows that the fiber has a solid structure with carbon nanotubes distributed within it. Figure 3 The low-magnification microstructure indicates that the obtained fibers are interwoven and have good continuity, and Figure 4 Light microscopy confirmed that although carbon nanotubes exhibited localized accumulation, they were uniformly distributed across the fibers overall. (Comparison...) Figure 6 It can be observed that, compared to the pure alumina fiber in Comparative Example 1, the mechanical properties of the material with added carbon nanotubes are significantly enhanced. (Data from Table 1 and...) Figure 7 Furthermore, it can be seen that the electrical conductivity and electromagnetic shielding performance of the fiber in Example 1 are significantly improved, with a conductivity of 2~7 S / m and a maximum total shielding effectiveness exceeding 20 dB. Figure 8 It can be seen that the thermal conductivity of materials with added carbon nanotubes is similar to that without (0.03~0.04 W / (m·K) at room temperature), maintaining excellent thermal insulation performance. Furthermore, Figure 5The fiber morphology obtained by directly heating to 1000℃ for sintering in Example 2 is poor; Comparative Example 2 shows that carbon nanotubes will oxidize when calcined at high temperature in air atmosphere, causing the material to lose its conductivity and electromagnetic shielding effect.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon nanotube-reinforced alumina composite fibers, characterized in that, The preparation method includes the following steps: (1) Add carbon nanotubes and polymer dispersant to an organic solvent and mix ultrasonically to obtain a carbon nanotube dispersion; (2) Add the spinning aid to the mixed solvent and mix well, then add the carbon nanotube dispersion and aluminum salt solution and stir to mix well to obtain the spinning solution; (3) The spinning solution is spun by air jet spinning to obtain precursor fibers; (4) The precursor fiber is dried and then sintered in an inert atmosphere to obtain the carbon nanotube reinforced alumina composite fiber.

2. The preparation method according to claim 1, characterized in that, In step (1), the carbon nanotubes are single-walled carbon nanotubes; the polymer dispersant is carbon nanotube DMF dispersant; and the organic solvent is N,N-dimethylformamide. Preferably, the mass ratio of polymer dispersant to carbon nanotubes is (0.5~10):1; More preferably, the mass-volume concentration of the carbon nanotube dispersion is 0.1~0.2 wt / vol%; and / or The ultrasonic mixing power is 500~700W, and the time is 0.5~1.5h.

3. The preparation method according to claim 1, characterized in that, In step (2), the spinning aid is polyvinyl alcohol or polyvinylpyrrolidone; The mixed solvent is obtained by compounding N,N-dimethylformamide and ethanol; preferably, the volume ratio of N,N-dimethylformamide and ethanol is (3~5):1; More preferably, the amount of the mixed solvent added is 7 to 10 times the mass of the spinning aid.

4. The preparation method according to claim 1, characterized in that, In step (2), the solute of the aluminum salt solution is aluminum chloride hexahydrate or aluminum nitrate nonahydrate, and the solvent is water; preferably, the concentration of the aluminum salt solution is 37~45wt%.

5. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of carbon nanotubes, aluminum salts and spinning aids is (0.0015~0.015):1:(0.75~1.2).

6. The preparation method according to claim 1, characterized in that, In step (3), during the spinning process, the injection rate of the spinning solution is 2~6 mL / h, and the spinning pressure is 0.05~0.09 MPa.

7. The preparation method according to claim 1, characterized in that, In step (4), the drying temperature is 55~65℃ and the time is 3~12h.

8. The preparation method according to claim 1, characterized in that, In step (4), sintering is carried out by two-stage heating; in the first stage, the temperature is raised to 350-450℃ at a heating rate of 1.5-2.5℃ / min and held for 0.5-1.5h; in the second stage, the temperature is raised to 800-1600℃ at a heating rate of 3.5-4.5℃ / min and held for 1-3h.

9. A carbon nanotube-reinforced alumina composite fiber, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 8.

10. The application of the carbon nanotube-reinforced alumina composite fiber according to claim 9 in aerospace thermal protection and / or electromagnetic shielding.

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