High-temperature oxidation resistant high-strength carbon nanotube / silicon carbide composite film, method for preparing same, and use thereof

Abstract

The application discloses a high-temperature-oxidation-resistant high-strength carbon nanotube / silicon carbide composite film, a preparation method and application thereof. The preparation method comprises the following steps: fully contacting a carbon nanotube film with a first solution containing a water-soluble polymer containing a polar functional group, performing first impregnation and drying, fully contacting the carbon nanotube film with a second solution containing an organic silicon precursor, performing second impregnation and drying, obtaining the carbon nanotube film uniformly loaded with the organic silicon precursor, and finally performing sintering treatment to obtain the high-temperature-oxidation-resistant high-strength carbon nanotube / silicon carbide composite film. Through the synergistic effect of two-step impregnation, the compatibility of the organic silicon precursor and the carbon nanotube can be significantly improved, and the SiC uniform coating is realized. In the high-temperature pyrolysis process, the synergistic combination structure of CNT-amorphous carbon-SiC is formed, the van der Waals force between the CNTs is converted into stronger chemical / physical combination, the mechanical property of the composite film is greatly improved, and the high-temperature-oxidation-resistant property is significantly optimized.

Description

Technical Field

[0001] This invention relates to a carbon nanotube / silicon carbide composite film, and more particularly to a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, its preparation method and application, belonging to the field of materials science and technology. Background Technology

[0002] Carbon nanotubes (CNTs), as nanomaterials with ultra-high specific strength (approximately 100 GPa), high elastic modulus (approximately 1 TPa), and excellent thermal and electrical conductivity, have broad application prospects in extreme environment protection, aerospace, and electronic device packaging. However, pure CNT films have two major limitations: first, they are easily oxidized and degraded at high temperatures (>600℃), leading to the loss of mechanical properties and structural integrity; second, CNTs are only bonded by van der Waals forces, resulting in weak interlayer interactions and limited tensile and impact strength of macroscopic films, making it difficult to meet the structural stability requirements of engineering applications.

[0003] Silicon carbide (SiC) ceramics possess extremely high resistance to high-temperature oxidation (long-term stable temperature can reach above 1600℃), excellent mechanical strength (elastic modulus of about 400 GPa), and good chemical inertness, making them an ideal composite phase to compensate for the aforementioned deficiencies of silicon carbide (CNT). CNT / SiC composite materials, formed by combining CNT and SiC, can synergistically leverage the high toughness of CNT and the high-temperature resistance and oxidation resistance of SiC. They hold promise as key structural / functional materials for extreme environments, possessing irreplaceable application value in scenarios such as hot-end components of aero-engines, thermal protection coatings for spacecraft, and heat dissipation protection for high-power devices.

[0004] Therefore, developing a simple, highly controllable preparation method that can achieve uniform composite of CNTs and SiC has become a core technological requirement for promoting the engineering application of this type of composite material.

[0005] Currently, patent CN106631079A discloses a carbon nanotube silicon carbide composite material and its preparation method. Although this patent achieves the composite of CNT and SiC, it still has the following key defects, which limit the performance and application of the composite material: (1) Poor compatibility between CNT and PCS, and insufficient impregnation uniformity: The surface of pure CNT is inert and there are only weak van der Waals forces between it and PCS molecules. PCS solution is difficult to spread and adsorb evenly on the CNT surface, resulting in some CNT surfaces not being covered by PCS. After pyrolysis, SiC is unevenly dispersed in the CNT network, forming CNT-rich areas and SiC-rich areas, and it is impossible to form a continuous SiC protective shell and a cooperative force network. (2) The interlayer bonding of CNTs is weak, and the strength improvement of composite films is limited: the interlayer effect of pure CNT films depends on van der Waals forces. After direct impregnation of PCS, the SiC generated by pyrolysis mainly fills the gaps between CNTs, which fails to effectively enhance the interfacial bonding between CNTs. As a result, the tensile strength and fracture toughness of the composite film are not significantly improved (usually ≤200MPa), which makes it difficult to meet the mechanical requirements of structural materials. (3) Poor high temperature oxidation resistance: Due to uneven SiC dispersion, some CNTs are not coated by SiC. When exposed to high temperature oxidation environment, these exposed CNTs are easily oxidized and eroded, resulting in rapid decay of mechanical properties when the composite material is used for a long time above 800℃. Summary of the Invention

[0006] The main objective of this invention is to provide a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation and its preparation method, thereby overcoming the shortcomings of the prior art.

[0007] Another object of the present invention is to provide the application of the high-strength carbon nanotube / silicon carbide composite film that is resistant to high-temperature oxidation.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: The first aspect of this invention provides a method for preparing a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, comprising: The carbon nanotube film is brought into full contact with a first solution containing a water-soluble polymer with polar functional groups for a first impregnation, followed by a first drying, so that the water-soluble polymer is adsorbed onto the surface of the carbon nanotube film to form a polar transition layer. A carbon nanotube film with a polar transition layer is brought into full contact with a second solution containing an organosilicon precursor for a second impregnation, followed by a second drying, to obtain a carbon nanotube film uniformly loaded with an organosilicon precursor, wherein the organosilicon precursor can be pyrolyzed to generate silicon carbide. The carbon nanotube film with uniformly loaded organosilicon precursor is sintered in a protective atmosphere, so that the generated silicon carbide is uniformly coated on the surface of the carbon nanotube film through amorphous carbon to form a silicon carbide layer. At the same time, silicon carbide and amorphous carbon are uniformly dispersed and filled in the gaps contained in the carbon nanotube film, thus obtaining a high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation.

[0009] A second aspect of the present invention provides a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation prepared by the preparation method, comprising a carbon nanotube film and a silicon carbide layer coated on the surface of the carbon nanotube film, wherein silicon carbide and amorphous carbon are uniformly dispersed and filled in the gaps contained in the carbon nanotube film.

[0010] A third aspect of the present invention provides the application of the high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation in the fields of aerospace, high-temperature protection and industrial or advanced energy devices.

[0011] The preparation method of this invention, through a two-step impregnation process, fundamentally solves the core defects of the prior art and has the following significant advantages compared with the prior art: 1) This invention uses a water-soluble polymer containing polar functional groups that is both hydrophilic and oleophilic. After impregnation, it can be firmly adsorbed onto the surface of the carbon nanotube film through hydrogen bonding, forming a polar transition layer on its surface. This polar transition layer can significantly improve the inertness of the carbon nanotube surface, thereby reducing the wetting angle between the subsequent organosilicon precursor solution and the carbon nanotube surface. The organosilicon precursor molecules can interact with the water-soluble polymer molecular chains through van der Waals forces, spreading evenly and penetrating into every corner of the carbon nanotube network. This ensures that after pyrolysis, silicon carbide uniformly coats the carbon nanotubes and fills the gaps, avoiding local enrichment and significantly improving the compatibility between the organosilicon precursor and the carbon nanotubes, thus achieving uniform silicon carbide coating. 2) Water-soluble polymers are not only compatibility modifiers but also bonding bridges between carbon nanotubes. After drying, the molecular chains of water-soluble polymers form physical cross-links between carbon nanotubes, initially enhancing the interlayer bonding force of carbon nanotubes. During subsequent high-temperature pyrolysis, the water-soluble polymers undergo a carbonization reaction to generate amorphous carbon, which forms a synergistic bonding structure of "CNT-amorphous carbon-SiC" with SiC and carbon nanotubes. This transforms the van der Waals forces between carbon nanotubes into stronger chemical / physical bonds, increasing the tensile strength of the composite film to over 200 MPa, strengthening the interfacial bonding between CNTs, and significantly improving mechanical properties. 3) The high-temperature oxidation resistance of the composite film of the present invention is significantly optimized. The uniformly coated silicon carbide layer forms a continuous anti-oxidation barrier, completely isolating the carbon nanotubes from oxygen. At the same time, the amorphous carbon generated by the carbonization of the water-soluble polymer can fill the tiny pores of the silicon carbide layer, further improving the anti-oxidation protection system. After the composite film is ablated in an air atmosphere at 1000°C for 60 seconds, the mass loss rate is ≤5%. 4) The preparation method of the present invention can improve the conversion rate and process economy of organosilicon precursors: the adsorption and fixation of organosilicon precursors by water-soluble polymer molecular chains can effectively reduce the volatilization loss of organosilicon precursors during pyrolysis, thereby increasing the SiC conversion rate from 60-70% in the prior art to more than 85% and reducing raw material loss; at the same time, the two-step impregnation process does not require the addition of expensive coupling agents or modifiers, the process steps are simple, and it is easy to scale up production. Attached Figure Description

[0012] 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 only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a macroscopic morphology diagram of the high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation prepared in Example 1 of the present invention. Figure 2 This is a surface SEM image of a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation prepared with a PCS solution containing 10 wt% PCS in Example 1 of this invention. Figure 3 This is an XPS image of a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation prepared with a PCS solution containing 10 wt% PCS in Example 1 of this invention. Figure 4 This is a TG data graph of a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation prepared with a PCS solution containing 10 wt% PCS in Example 1 of the present invention. Figure 5 This is a quasi-static stress-strain curve of carbon nanotube / silicon carbide composite films prepared by the present invention using PCS solutions with different PCS contents. Figure 6 This is a macroscopic morphology image of the high-strength carbon nanotube / silicon carbide composite film with high temperature oxidation resistance prepared by PCS solution with PCS content of 10wt% in Example 1 of the present invention before ablation. Figure 7 This is a macroscopic morphology image of the high-strength carbon nanotube / silicon carbide composite film with high temperature oxidation resistance prepared by PCS solution with PCS content of 10wt% in Example 1 of the present invention after ablation. Figure 8 This is a surface SEM image of the high-strength carbon nanotube / silicon carbide composite film with high temperature oxidation resistance prepared by a PCS solution with a PCS content of 10wt% in Example 1 of the present invention after ablation. Figure 9 This is an EDS element distribution diagram at the crack after ablation of a high-strength carbon nanotube / silicon carbide composite film prepared with a PCS solution containing 10 wt% PCS in Example 1 of this invention. Figure 10 This is a statistical chart showing the mass loss rate of high-strength carbon nanotube / silicon carbide composite films resistant to high-temperature oxidation prepared by PCS solutions with different PCS contents according to the present invention after ablation. Figure 11This is a macroscopic morphology diagram of the composite film prepared in Comparative Example 1. Detailed Implementation

[0014] To address the aforementioned deficiencies in the existing technology, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The main feature is the use of a two-step impregnation synergistic process design to provide a simple and highly controllable method for preparing high-strength carbon nanotube / silicon carbide composite films, achieving the following technical effects: (1) Improve the compatibility between organosilicon precursors and carbon nanotubes to achieve uniform dispersion and complete coating of SiC in carbon nanotube networks; (2) Enhance the interfacial bonding force between carbon nanotubes and significantly improve the tensile strength, fracture toughness and other mechanical properties of the composite film; (3) Improve the high temperature oxidation resistance of composite materials to ensure that their structure and performance remain stable when used in an oxidizing environment above 1000℃ for a long time.

[0015] The following will further explain the technical solution, its implementation process, and its principles. However, it should be understood that within the scope of this invention, the above-mentioned technical features of this invention and the technical features specifically described below (in embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here.

[0016] As one aspect of the technical solution of this invention, the method for preparing a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation includes: The carbon nanotube (CNT) film is brought into full contact with a first solution containing a water-soluble polymer with polar functional groups for a first impregnation, followed by a first drying, so that the water-soluble polymer is adsorbed onto the surface of the carbon nanotube film to form a polar transition layer. A carbon nanotube film with a polar transition layer is brought into full contact with a second solution containing an organosilicon precursor for a second impregnation, followed by a second drying, to obtain a carbon nanotube film uniformly loaded with an organosilicon precursor, wherein the organosilicon precursor can be pyrolyzed to generate silicon carbide. The carbon nanotube film uniformly loaded with the organosilicon precursor is sintered in a protective atmosphere, causing the organosilicon precursor to pyrolyze into silicon carbide. The water-soluble polymer is carbonized to generate amorphous carbon. The silicon carbide is uniformly coated on the surface of the carbon nanotube film through the amorphous carbon to form a silicon carbide layer. At the same time, silicon carbide and amorphous carbon are uniformly dispersed and filled in the gaps contained in the carbon nanotube film, thus obtaining a high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation.

[0017] In some embodiments, the preparation method specifically includes: acidifying the original carbon nanotube film to remove impurities and amorphous carbon, followed by a first impregnation.

[0018] Furthermore, the acidification treatment is carried out using concentrated nitric acid and ultrasonic treatment at room temperature for 20-40 minutes.

[0019] In some embodiments, the original carbon nanotube film used in this invention has a thickness between 5 and 15 µm, and the carbon nanotubes contained are multi-walled carbon nanotubes with a number of 10 to 18 multi-walled cells and a diameter of 18 ± 0.28 μm.

[0020] In some embodiments, the water-soluble polymer may contain polar functional groups such as hydroxyl, carboxyl, or amino groups. The water-soluble polymer can act as a surface modifier and binder, improving the compatibility of carbon nanotubes with the organosilicon precursor and strengthening the bonding between carbon nanotubes.

[0021] In some preferred embodiments, the water-soluble polymer may include, but is not limited to, one or more combinations of polyvinyl alcohol (PVA), polyethylene glycol (PEG, number average molecular weight of 2000-6000), sodium carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), etc., and is more preferably polyvinyl alcohol and polyethylene glycol, which have fewer residual impurities after carbonization.

[0022] Taking PVA (polyvinyl alcohol) as an example, its molecular chain contains a large number of hydroxyl groups (-OH), exhibiting both hydrophilic and lipophilic properties. After impregnation, it can be firmly adsorbed onto the CNT surface through hydrogen bonding, forming a polar transition layer on the CNT surface. This polar transition layer can significantly improve the inertness of the CNT surface, reducing the wetting angle between the subsequent organosilicon precursor solution and the CNT surface. The organosilicon precursor can interact with the PVA molecular chain through van der Waals forces, spreading evenly and penetrating into every corner of the CNT network. This ensures that SiC uniformly coats the CNTs and fills the gaps after pyrolysis, avoiding localized enrichment. PVA is not only a compatibility modifier but also a bonding bridge between CNTs. After drying, the PVA molecular chains form physical cross-links between CNTs, initially enhancing the interlayer bonding force of CNTs. During the subsequent high-temperature pyrolysis process, PVA undergoes a carbonization reaction to generate amorphous carbon, which forms a synergistic bonding structure of "CNT-amorphous carbon-SiC" with SiC and CNTs. This transforms the van der Waals forces between CNTs into stronger chemical / physical bonds, increasing the tensile strength of the composite film to over 200 MPa and significantly improving its mechanical properties.

[0023] In some embodiments, the first solution comprises a water-soluble polymer containing polar functional groups and a first solvent.

[0024] The first solvent may be one or a combination of water, formic acid, dimethyl sulfoxide, etc., but is not limited to these.

[0025] In some preferred embodiments, the content (mass concentration) of the water-soluble polymer containing polar functional groups in the first solution is 1~5 wt%. If the concentration is below 1 wt%, the solution may not be able to adhere to the sample surface, and if the concentration is above 5 wt%, the coating thickness formed on the sample surface may be too thick, affecting the interfacial bonding.

[0026] In some embodiments, the first impregnation temperature is room temperature, and the time is 0.5 to 2 hours. The dual mechanism of this first impregnation is: firstly, through the interaction between hydroxyl groups and the CNT surface, it improves the surface polarity of CNTs, thereby enhancing the wetting and adsorption effect of subsequent organosilicon precursors; secondly, it acts as a temporary binder with subsequent carbonization precursors, strengthening the bonding between CNTs and filling SiC pores. After the first impregnation, the pore structure and surface energy of the CNT film are optimally matched with the permeation characteristics of the organosilicon precursor solution, ensuring uniform loading of the organosilicon precursor.

[0027] In some implementations, the first drying can be drying at a temperature of 60-100°C for 1-3 hours.

[0028] In some implementations, the thickness of the polar transition layer is 0.5 to 1 μm.

[0029] In some embodiments, the organosilicon precursor is a pyrolytic precursor that can generate silicon carbide (SiC), such as one or more combinations of polycarbosilane (PCS), polysilane, polysiloxane, polycarbosilane-polysiloxane copolymer, etc., but not limited thereto. These precursors have pyrolysis temperatures of approximately 1000-1200°C and can all generate SiC.

[0030] In some embodiments, the preparation method specifically includes: mixing the organosilicon precursor with a second solvent to obtain a second solution; the second solvent is an organic solvent that can dissolve the organosilicon precursor and does not react with the water-soluble polymer.

[0031] In some preferred embodiments, the second solvent may be toluene, but may also be replaced with other organic solvents capable of dissolving the organosilicon precursor and not reacting with the water-soluble polymer, such as one or more combinations of xylene, cyclohexane, and n-heptane, but not limited thereto. These solvents have solubility properties comparable to toluene, ensuring sufficient dissolution of the organosilicon precursor without damaging the water-soluble polymer already adsorbed on the surface of the carbon nanotubes. Only the drying temperature needs to be adjusted according to the solvent boiling point (e.g., the drying temperature for xylene needs to be increased to 80-100°C).

[0032] In some preferred embodiments, the content (mass concentration) of the organosilicon precursor in the second solution is 2 to 10 wt%. If the content is less than 2 wt%, the silicon carbide layer formed on the surface of the carbon nanotubes may not be dense, and if the content is greater than 10 wt%, thermal mismatch between the silicon carbide and the carbon nanotube film may occur, making the sample brittle and causing wrinkles to form on the surface.

[0033] In some embodiments, the second impregnation is carried out at room temperature for 1 to 3 hours.

[0034] In some embodiments, the second drying can be baking at a temperature of 150~200°C for 1~2 hours, while simultaneously performing a pre-curing treatment to allow the organosilicon precursor to undergo initial cross-linking.

[0035] In some embodiments, the preparation method specifically includes: placing the pre-cured carbon nanotube film in a tube furnace, introducing a protective gas, first heating to 800-900°C, holding at that temperature for 1-3 hours, and then further heating to 1000-1200°C for sintering for 1-3 hours. This sintering temperature ensures complete conversion of the organosilicon precursor to SiC (e.g., the critical temperature for PCS pyrolysis conversion is ≥1000°C), while also preventing structural damage or oxidation of CNTs at excessively high temperatures. This sintering process requires a stepped heating and holding temperature to ensure the release of thermal stress between the generated silicon carbide and carbon nanotubes; otherwise, surface silicon carbide cracking may occur.

[0036] In some preferred embodiments, the protective gas includes an inert gas, such as argon, which can also be replaced by other inert gases such as nitrogen and helium. These gases can isolate oxygen at high temperatures, preventing the oxidation of carbon nanotubes and water-soluble polymer carbonization products. Nitrogen is less expensive and more suitable for industrial production.

[0037] Furthermore, the flow rate of the protective gas is 50~100 ml / min.

[0038] Furthermore, the heating rate is 5~10℃ / min, and the holding time is 1~3h.

[0039] In some more specific embodiments, a method for preparing a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation includes the following steps: ① Take a carbon nanotube film, immerse it in a water-soluble polymer aqueous solution for the first impregnation, and dry it after impregnation; ② Prepare an organosilicon precursor solution using toluene or other organic solvents, immerse the dried product obtained in step ① into the organosilicon precursor solution for a second impregnation, and dry it after impregnation. ③ Place the dried product obtained in step ② into a tube furnace, introduce an inert gas as a protective atmosphere, first heat to 800~900℃, hold for 1~3 hours, continue heating to 1000~1200℃ and hold for 1~3 hours, so that the organosilicon precursor is pyrolyzed into SiC, and after cooling, a high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation is obtained.

[0040] In summary, the preparation method of the present invention can improve the conversion rate and process economy of organosilicon precursors. The adsorption and fixation effect of water-soluble polymer molecular chains on organosilicon precursors can effectively reduce the volatilization loss of organosilicon precursors during pyrolysis, thereby increasing the SiC conversion rate from 60-70% in the prior art to over 85% and reducing raw material loss. At the same time, the two-step impregnation process does not require the addition of expensive coupling agents or modifiers, the process steps are simple, and it is easy to scale up production.

[0041] As another aspect of the technical solution of the present invention, it also relates to a high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation prepared by the above preparation method.

[0042] In some embodiments, the high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation comprises a carbon nanotube film and a silicon carbide (SiC) layer coated on the surface of the carbon nanotube film. Simultaneously, silicon carbide and amorphous carbon are uniformly dispersed and filled within the gaps in the carbon nanotube film. This silicon carbide layer significantly optimizes the high-temperature oxidation resistance, and the uniformly coated SiC layer forms a continuous antioxidant barrier, completely isolating CNTs from oxygen. Furthermore, the amorphous carbon generated by the carbonization of water-soluble polymers fills the micropores of the SiC layer, further improving the antioxidant protection system.

[0043] In some preferred embodiments, the high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation contains 2-15 wt% silicon carbide (SiC) and 5-10 wt% amorphous carbon.

[0044] In some preferred embodiments, the thickness of the silicon carbide layer is 1 to 3 µm.

[0045] Furthermore, the high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation has a tensile strength of 200 MPa or higher, preferably 300 MPa or higher.

[0046] Furthermore, the high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation can withstand aerobic ablation at temperatures above 1000°C. Preferably, the mass loss rate after ablation in an air atmosphere at 1000°C for 60 seconds is ≤5%.

[0047] As another aspect of the technical solution of the present invention, it also relates to the application of the high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation in the fields of aerospace, high temperature protection and industrial applications, and advanced energy devices.

[0048] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. It should be noted that the following embodiments are intended to facilitate understanding of this invention and are not intended to limit it in any way. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the manufacturer.

[0049] Example 1 The carbon nanotube film was immersed in concentrated nitric acid (70%) and sonicated at room temperature for 30 minutes to remove impurities and amorphous carbon. It was then repeatedly rinsed with deionized water until neutral (pH approximately 7), followed by washing three times with anhydrous ethanol. It was then vacuum dried at 80°C for 4 hours until constant weight. After removal, it was placed in an oven and dried at 80°C for 2 hours. Next, the acidified carbon nanotube film was immersed in a 1.5 wt% PVA aqueous solution for 1 hour, and then dried in an oven at 50°C for 1 hour. A 10 wt% PCS toluene solution was prepared and mixed thoroughly using magnetic stirring. The carbon nanotube film, which had been immersed in the PVA solution, was further immersed in the PCS solution for 2 hours. The film was then slowly lifted with tweezers, excess solution was drained, and it was hung vertically in a fume hood. The carbon nanotube film was then placed in an oven and treated at 150–200°C for 1–2 hours to allow for initial cross-linking of the PCS. The pre-cured sample was placed in a tube furnace and high-purity nitrogen gas (flow rate of 100 ml / min) was introduced. The temperature was increased to 800°C at a rate of 5°C / min and held for 1 hour to form amorphous SiC. The temperature was then increased to 1200°C and held for 2 hours. An inert atmosphere was maintained throughout the process to prevent oxidation. The sample was then allowed to cool naturally to room temperature to obtain a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation.

[0050] Figure 1 This is a macroscopic morphology image of the high-strength carbon nanotube / silicon carbide composite film that is resistant to high-temperature oxidation. It can be seen that the film is intact, can be bent at will, and has good processability.

[0051] Figure 2This is a surface SEM image of the high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation prepared with a PCS solution containing 10wt% PCS in this embodiment. It can be seen that a dense silicon carbide ceramic layer is formed on the surface of the carbon nanotube film, with a complete structure and no obvious defects.

[0052] Figure 3 This is an XPS image of a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, prepared in this embodiment using a PCS solution with a PCS content of 10wt%. It shows obvious Si-C bonds, indicating that silicon carbide was generated at 1200℃.

[0053] Figure 4 This embodiment describes a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, prepared using a PCS solution with a PCS content of 10 wt%. Figure 4 The TG data of "CNT / SiC-10" in the image is compared with that of the original carbon nanotube film. Figure 4 The addition of a silicon carbide protective layer ("Raw CNT") can effectively increase the high-temperature stability of carbon-based thin films.

[0054] Figure 5 These are quasi-static stress-strain curves of carbon nanotube / silicon carbide composite films prepared with PCS solutions of different PCS contents in some embodiments of the present invention. The composite films prepared with PCS contents of 2wt%, 6wt%, and 10wt% are labeled as "CNT / SiC-2", "CNT / SiC-6", and "CNT / SiC-10", respectively. It can be seen that compared with the original carbon nanotube (CNT) film, the ultimate tensile strength of the composite film is enhanced with the increase of PCS content. When the PCS content is 10wt%, the ultimate tensile strength of the composite film reaches 248MPa, which is 155.7% higher than that of the original CNT film of 97MPa.

[0055] Figure 6 This is a macroscopic morphology image of a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, prepared with a PCS solution containing 10wt% PCS, before ablation. The surface is smooth and flat. Figure 7 This is a macroscopic morphology image of the high-strength carbon nanotube / silicon carbide composite film after ablation, which is resistant to high-temperature oxidation. The overall surface structure is intact and there is no obvious damage.

[0056] Figure 8 This is a surface SEM image of a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, prepared with a PCS solution containing 10 wt% PCS. The surface silicon carbide forms a smooth glassy SiO2 in a high-temperature oxygen environment, but cracks appear in the oxide layer due to thermal stress. Figure 9This is an EDS elemental distribution diagram of the crack at the ablation site of the high-strength carbon nanotube / silicon carbide composite film that is resistant to high-temperature oxidation. It can be seen that the surface is enriched with Si and O.

[0057] Figure 10 This is a statistical chart showing the mass loss rate of high-strength carbon nanotube / silicon carbide composite films with high temperature oxidation resistance prepared by PCS solutions with different PCS contents in some embodiments of the present invention after ablation. As the PCS content increases, it plays a positive role in protecting the carbon nanotubes in the composite film from oxidation during the ablation process at 1000℃, and the mass loss rate is only in the range of 2.6% to 4.8%.

[0058] Example 2 The difference between this embodiment and Example 1 is that the PCS content in the PCS solution is 2 wt%, and the second impregnation time is 3 hours. Everything else is the same as in Example 1, and the quasi-static stress-strain curve is as follows. Figure 5 As shown, the quality loss rate data is as follows: Figure 10 As shown.

[0059] Example 3 The difference between this embodiment and Example 1 is that the PCS content in the PCS solution is 6 wt%, and the second impregnation time is 1 hour. Everything else is the same as in Example 1, and the quasi-static stress-strain curve is as follows: Figure 5 As shown, the quality loss rate data is as follows: Figure 10 As shown.

[0060] Example 4 The difference between this embodiment and Embodiment 1 is that the temperature was increased to 800°C at a rate of 5°C / min, held for 1 hour to form amorphous SiC, and then further increased to a sintering temperature of 1000°C. Everything else was the same as in Embodiment 1. The tensile strength test result was 219 MPa, and the mass loss rate after ablation was 3.4%.

[0061] Example 5 The difference between this embodiment and Embodiment 1 is that the temperature was increased to 900°C at a rate of 10°C / min, held for 1 hour to form amorphous SiC, and then further increased to a sintering temperature of 1100°C. Everything else was the same as in Embodiment 1. The tensile strength test result was 228 MPa, and the mass loss rate after ablation was 2.9%.

[0062] Example 6 The difference between this embodiment and Example 1 is that the solvent in the PCS solution is xylene. Everything else is the same as in Example 1. The tensile strength test result was 239 MPa, and the mass loss rate after ablation was 2.7%.

[0063] Example 7 The difference between this embodiment and Embodiment 1 is that PVA solute is replaced with PEJ. Everything else is the same as in Embodiment 1. The tensile strength test result was 241 MPa, and the mass loss rate after ablation was 2.8%.

[0064] Example 8 The difference between this embodiment and Example 1 is that the PVA content in the PVA solution is 1 wt%, and the first immersion time is 2 hours. Everything else is the same as in Example 1. The tensile strength test result is 221 MPa, and the mass loss rate after ablation is 3.0%.

[0065] Example 9 The difference between this embodiment and Example 1 is that the PVA content in the PVA solution is 5 wt%, and the first immersion time is 0.5 h. Everything else is the same as in Example 1. The tensile strength test result is 239 MPa, and the mass loss rate after ablation is 3.5%.

[0066] Comparative Example 1 The difference between this comparative example and Example 1 is that it was not soaked in an aqueous solution containing 1.5 wt% PVA. The resulting composite film had poorer formation, and its macroscopic morphology was as follows. Figure 11 As shown, due to thermal mismatch, wrinkles appeared on the surface of the film. In addition, the sample was too brittle to meet the test requirements, so the tensile strength could not be tested. The mass loss rate after ablation was 3.8%.

[0067] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation, characterized in that, include: The carbon nanotube film is brought into full contact with a first solution containing a water-soluble polymer with polar functional groups for a first impregnation, followed by a first drying, so that the water-soluble polymer is adsorbed onto the surface of the carbon nanotube film to form a polar transition layer. A carbon nanotube film with a polar transition layer is brought into full contact with a second solution containing an organosilicon precursor for a second impregnation, followed by a second drying, to obtain a carbon nanotube film uniformly loaded with an organosilicon precursor, wherein the organosilicon precursor can be pyrolyzed to generate silicon carbide. The carbon nanotube film with uniformly loaded organosilicon precursor is sintered in a protective atmosphere, so that the generated silicon carbide is uniformly coated on the surface of the carbon nanotube film through amorphous carbon to form a silicon carbide layer. At the same time, silicon carbide and amorphous carbon are uniformly dispersed and filled in the gaps contained in the carbon nanotube film, thus obtaining a high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation.

2. The preparation method according to claim 1, characterized in that, include: The original carbon nanotube film is acidified and then impregnated for the first time; preferably, the acidification is carried out with concentrated nitric acid and ultrasonic treatment at room temperature for 20-40 min. Preferably, the original carbon nanotube film has a thickness of 5~15 µm, contains multi-walled carbon nanotubes with 10~18 multi-walled cells and a diameter of 18±0.28 µm.

3. The preparation method according to claim 1, characterized in that: The water-soluble polymer contains polar functional groups including hydroxyl, carboxyl, or amino groups; Preferably, the water-soluble polymer includes one or more combinations of polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, and polyvinylpyrrolidone.

4. The preparation method according to claim 1, characterized in that: The first solution comprises a water-soluble polymer containing polar functional groups and a first solvent; Preferably, the first solvent includes one or more of water, formic acid, and dimethyl sulfoxide; And / or, the content of the water-soluble polymer containing polar functional groups in the first solution is 1~5 wt%; And / or, the temperature of the first impregnation is room temperature, and the time is 0.5~2h; And / or, the temperature of the first drying is 60~100℃, and the time is 1~3h; And / or, the thickness of the polar transition layer is 0.5~1 μm.

5. The preparation method according to claim 1, characterized in that: The organosilicon precursor includes one or more combinations of polycarbosilane, polysilane, polysiloxane, and polycarbosilane-polysiloxane copolymer; And / or, the preparation method includes: mixing an organosilicon precursor with a second solvent to obtain a second solution; The organic solvent is an organic solvent that can dissolve organosilicon precursors and does not react with water-soluble polymers.

6. The preparation method according to claim 5, characterized in that: The second solvent includes one or more combinations of toluene, xylene, cyclohexane, and n-heptane; And / or, the content of the organosilicon precursor in the second solution is 2~10 wt%; And / or, the second impregnation temperature is room temperature, and the time is 1~3 hours; And / or, the second drying temperature is 150~200℃, the time is 1~2h, and a pre-curing treatment is carried out at the same time to allow the organosilicon precursor to initially cross-link.

7. The preparation method according to claim 6, characterized in that, include: The pre-cured carbon nanotube film is placed in a tube furnace, a protective gas is introduced, the temperature is first raised to 800~900℃, held for 1~3 hours, and then the temperature is raised to 1000~1200℃ for sintering for 1~3 hours. Preferably, the protective gas includes an inert gas, and more preferably includes one or a combination of nitrogen, argon, and helium; Preferably, the flow rate of the protective gas is 50~100 ml / min; Preferably, the heating rate is 5~10℃ / min.

8. A high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation, prepared by any one of claims 1 to 7, comprising a carbon nanotube film and a silicon carbide layer coated on the surface of the carbon nanotube film, wherein silicon carbide and amorphous carbon are uniformly dispersed and filled in the gaps contained in the carbon nanotube film.

9. The high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation according to claim 8, characterized in that: The high-strength carbon nanotube / silicon carbide composite film resistant to high-temperature oxidation contains 2-15 wt% silicon carbide and 5-10 wt% amorphous carbon. And / or, the thickness of the silicon carbide layer is 1~3 µm; And / or, the tensile strength of the high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation is above 200 MPa, preferably above 300 MPa; And / or, the high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation can withstand aerobic ablation at temperatures above 1000°C, and preferably, the mass loss rate after 60 seconds of ablation is less than 5%.

10. The application of the high-strength carbon nanotube / silicon carbide composite film resistant to high temperature oxidation as described in claim 8 or 9 in the fields of aerospace, high temperature protection and industrial or advanced energy devices.

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