Carbon fiber with continuous, homogeneous and compact ceramic coating on surface as well as preparation method and application of carbon fiber

Abstract

The invention discloses a carbon fiber with a continuous, homogeneous and compact ceramic coating on the surface and a preparation method and application of the carbon fiber, and belongs to the technical field of carbon fiber composites.The preparation method comprises the steps that a polymer precursor, a xylene solvent and a nanometer SiC-coated SiO2 core-shell structure filler are mixed to obtain dipping slurry, the dipping slurry is subjected to vacuum defoaming, and the carbon fiber with the continuous, homogeneous and compact ceramic coating on the surface is obtained; degumming a carbon fiber fabric, dipping in the dipping slurry, draining, curing, and carrying out carbonization gradient cracking to obtain the carbon fiber with a continuous, homogeneous and compact ceramic coating on the surface. The method is used for solving the technical problems that cracks or pores are easily generated on the surface interface / coating of the carbon fiber prepared by a current polymer precursor impregnation and pyrolysis method, so that the surface interface / coating is discontinuous and non-uniform.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite material technology, specifically relating to a carbon fiber with a continuous, homogeneous, and dense ceramic coating on its surface, its preparation method, and its application. Background Technology

[0002] Carbon fiber has high specific strength, excellent heat resistance and excellent creep resistance. It is often used as a reinforcement for ultra-high temperature ceramic matrix composites (UHTCMC) and is the preferred structural material for extreme service environments such as hot-end components of aero-engines and thermal protection systems of hypersonic aircraft.

[0003] The fiber-ceramic matrix interface plays a crucial role in load transfer, heterogeneous crack propagation, stress buffering, and fiber protection, and is a key factor in achieving the transition from brittle to tough in UHTCMC and in the toughening and reinforcement of the fibers. Current methods for preparing carbon fiber surface interfaces / coatings include chemical vapor deposition (CVD), sol-gel method, polymer precursor impregnation pyrolysis (PIP), and slurry coating. While CVD can produce high-quality coatings, it is costly, complex, and difficult to achieve uniform preparation on fibers with complex shapes. The sol-gel method, slurry coating, and PIP method are simple and low-cost, but PIP is more suitable for complex coatings and is widely used due to its maturity. However, the cracking and shrinkage characteristics of the resin during carbonization can easily lead to cracks or pores in the coating, causing discontinuity. Furthermore, the carbonization process can generate significant interfacial stress between the coating and the fiber, resulting in coating detachment. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a carbon fiber with a continuous, homogeneous, and dense ceramic coating on its surface, as well as its preparation method and application, in order to solve the technical problem that the carbon fiber surface interface / coating prepared by the polymer precursor impregnation pyrolysis method is prone to cracks or pores, resulting in discontinuity and non-uniformity.

[0005] This invention proposes an impregnation slurry based on a polymer precursor-nano core-shell filler system. After the slurry impregnates carbon fibers and is cured, a gradient pyrolysis process based on segmented temperature and pressure control is used to achieve gradient release of thermal stress, further suppressing the generation of pores and cracks, improving the coating density, and obtaining a uniform, continuous, and dense ceramic coating.

[0006] This invention also proposes a coating preparation method based on a polymer precursor-nanocore-shell filler system impregnation and gradient pyrolysis process, which can form a continuous, homogeneous, and dense coating on the carbon fiber surface. This method not only significantly improves the quality of coatings prepared by the PIP process, but also has good controllability and industrial application potential, providing a new solution for carbon fiber protection and composite material interface preparation.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing carbon fibers with a continuous, homogeneous, and dense ceramic coating on the surface. The method includes mixing a polymer precursor, xylene solvent, and nano-SiC@SiO2 core-shell structure filler to obtain an impregnation slurry, vacuum degassing the impregnation slurry, then placing a degummed carbon fiber fabric into the impregnation slurry for impregnation, draining and curing, and finally obtaining carbon fibers with a continuous, homogeneous, and dense ceramic coating on the surface through carbonization gradient pyrolysis.

[0008] Preferably, the nano-SiC@SiO2 core-shell structure filler is prepared by oxidizing nano-SiC particles.

[0009] Preferably, the nano-SiC particles are produced by a high-temperature air oxidation process, with process conditions including an oxidation temperature of 800-1400℃ and an oxidation time of 0.5-8h.

[0010] Preferably, the mixing process of the polymer precursor, xylene solvent and nano-SiC@SiO2 core-shell structured filler includes any one of mechanical stirring, ball milling and high-speed shear stirring.

[0011] More preferably, the mixing process of the polymer precursor, xylene solvent and nano-SiC@SiO2 core-shell structure filler is ball milling.

[0012] Further preferably, the degumming process for the carbon fiber fabric includes high-temperature calcination or chemical solvent method, the impregnation process includes vacuum impregnation or pressure impregnation, the impregnation time is 0.5-4h, the draining time is 0.5h, and the curing conditions are determined by the polymer precursor used. For example, when the polymer precursor is PSZ, the curing conditions are: temperature 250-300℃, time 1-2h.

[0013] Preferably, the impregnation time is 0.5-4 hours, the draining time is 0.5 hours, and the curing time is 1-2 hours.

[0014] Preferably, the carbonization pyrolysis process employs a staged temperature and pressure controlled gradient pyrolysis process, specifically including: 1) Pre-pyrolysis stage: room temperature - 300℃, heating rate 3-5℃ / min, holding time 1-3h, vacuumed to 10 -2 Pa; 2) Main pyrolysis stage: 300℃-800℃, heating rate of 0.5-3℃ / min, holding time of 1-4h, inert atmosphere refilled to pressure of 0.8 atm; 3) High-temperature crystallization stage: 800℃-1200℃, heating rate of 0.5-3℃ / min, holding time of 1-4h, and inert atmosphere refilling to pressure of 1.5 atm; 4) Cooling annealing stage: 1200℃ to room temperature, cooling rate ≤5℃ / min, pressure release is 1.0 atm.

[0015] Preferably, the polymer precursor includes any one of polysilazane (PSZ), polycarbosilane (PCS), and polysiloxane (PSO).

[0016] Preferably, the mass fraction of the polymer precursor is 5 wt%-30 wt% relative to the total mass of the impregnation slurry; and the mass fraction of the nano-SiC@SiO2 core-shell structure filler is 10 wt%-30 wt% relative to the mass of the polymer precursor.

[0017] The present invention also provides a carbon fiber with a continuous, homogeneous, and dense ceramic coating on its surface prepared by the above preparation method. The ceramic coating on the surface of the carbon fiber comprises nano-SiC@SiO2 core-shell structure filler and ceramic generated by the pyrolysis of polymer precursor. The nano-SiC@SiO2 core-shell structure filler has a particle size of 100 nm to 500 nm. In the nano-SiC@SiO2 core-shell structure filler, the surface of the nano-SiC particles is coated with a SiO2 shell with a thickness of 5 nm to 20 nm.

[0018] This invention also provides the application of carbon fibers with the above-mentioned continuous, homogeneous, and dense ceramic coating on their surface in the field of carbon fiber reinforced ceramic matrix composites, which are the core reinforcement of high-performance ceramic matrix composites in extreme environments.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention also provides a method for preparing carbon fibers with a continuous, homogeneous, and dense ceramic coating. This method is based on a polymer precursor-nanocore-shell filler system slurry impregnation and carbonization gradient pyrolysis process, significantly improving the problems of uneven, discontinuous, and easily cracked coatings prepared by traditional polymer precursor impregnation and pyrolysis processes. In this invention, the filler in the impregnation slurry acts as a spatial volume confinement, inhibits polymer shrinkage, and reinforces the particles. The SiC core provides structural support, while the SiO2 shell has a thermal expansion coefficient closer to that of carbon fibers (carbon fiber: CTE≈-1×10⁻¹). -6 / K, SiC≈4.5×10 -6 / K, SiO2≈0.5×10 -6The coating ( / K) can serve as a stress buffer layer and also as a nucleation site for polymer pyrolysis products, thereby improving the continuity, density, and bonding ability with fibers. This method has relatively low equipment requirements, a simple process, and effectively maintains the mechanical properties of the fibers, avoiding damage to the fibers caused by high-temperature processes such as chemical vapor deposition. Vacuum degassing and drying steps directly reduce defect sources in the coating.

[0020] Furthermore, core-shell fillers can be prepared by controlling the high-temperature air oxidation process (temperature and time). This method is direct and controllable, and can produce SiO2 shells of 5nm-20nm.

[0021] Furthermore, the preferred ball milling method can ensure that the nanofillers achieve uniform dispersion at the molecular level in the polymer precursor solution, which is a prerequisite for obtaining a homogeneous coating.

[0022] Furthermore, by precisely controlling the impregnation and drying times, it is ensured that the precursor slurry can fully impregnate the carbon fiber bundles, while avoiding the introduction of internal stress due to improper curing.

[0023] Furthermore, by controlling the temperature and pressure in stages to achieve the gradient release of thermal stress, the generation of pores and cracks is further suppressed, and the coating density is improved: in the main pyrolysis stage, the microcracks generated by the violent escape of volatiles are suppressed by regulating the gas pressure; in the high-temperature crystallization stage, the growth of grain boundary pores is suppressed by regulating the high pressure, thereby improving the coating density.

[0024] Furthermore, polysilazane, polycarbosilane, and polysiloxane, upon pyrolysis, primarily generate SiCN, SiC, and SiOC ceramics, respectively. These ceramic phases exhibit good chemical compatibility with carbon fibers and possess excellent high-temperature stability and oxidation resistance, providing a reliable matrix performance guarantee for the coating.

[0025] Furthermore, flexible control over composition and structure is possible. The number of impregnation cycles and the concentration of polymer precursors in the slurry can be adjusted to regulate the shell thickness, and the size (100–500 nm) and distribution density of the core-shell filler can be controlled to optimize the coating's mechanical / thermal properties. Specifically, the filler particle size should not be too large (>500 nm), as large particles exhibit a significant difference in shrinkage rate compared to the matrix during pyrolysis, easily forming stress concentration points and leading to microcracks in the coating. Additionally, the small contact area between large particles and the carbon fiber surface increases the risk of coating delamination. Conversely, the filler particle size should not be too small (<100 nm), as small-diameter fillers have high surface energy and are prone to forming clusters in the coating, disrupting structural continuity.

[0026] This invention also provides a carbon fiber with a continuous, homogeneous, and dense ceramic coating on its surface, prepared by the above-described method. The polymer precursor pyrolysis ceramic serves as the continuous matrix of the coating, ensuring both the continuity of the coating and the integrity of the matrix, while the nanofiller reinforces and densifies the matrix. The combination of these two elements results in a more continuous, uniform ceramic coating that is less prone to cracking or porosity. The particle size (100-500 nm) ensures good dispersibility of the filler, allowing it to be uniformly distributed within the polymer precursor matrix and avoiding stress concentration points caused by agglomeration. Simultaneously, the nanoscale effect also contributes to better toughening. The SiO2 shell thickness (5-20 nm) balances the self-healing capability with its impact on the SiC core properties. Too thin a shell results in insufficient healing material, while too thick a shell may affect the overall reinforcing effect of the filler.

[0027] This invention also provides the application of the aforementioned carbon fibers in the field of carbon fiber reinforced ceramic matrix composites. A continuous, homogeneous, dense interfacial coating with good fiber bonding can effectively transfer loads from the matrix to the high-strength carbon fibers and improve the toughness of the composite material. Simultaneously, the excellent coating can better protect the carbon fibers from high-temperature oxidation corrosion, thereby broadening the application prospects of the composite material in extreme environments such as aerospace and new energy. Attached Figure Description

[0028] Figure 1 The images shown are scanning electron microscope (SEM) images and EDS spot scan data of carbon fiber with a continuous, homogeneous, and dense uniform coating prepared in Example 1 of the present invention; wherein, Figure a is a 200x SEM image; Figure b is a 5000x magnified image of the area marked in Figure a; Figures c and d are the EDS spot scan results of the area marked in Figure b; Figure 2 This is a scanning electron microscope image of carbon fiber with a uniform coating prepared in Example 2 of the present invention; Figure 3 A scanning electron microscope image of carbon fiber with a uniform coating prepared in Example 3 of the present invention; Figure 4 This is a scanning electron microscope image of carbon fiber obtained in Comparative Example 1 of the present invention; Figure 5 This is a scanning electron microscope image of carbon fiber obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0030] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0031] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0032] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0033] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0036] Example 1 This embodiment provides a method for preparing carbon fibers with a continuous, homogeneous, and dense ceramic coating on the surface, including the following steps: S1: A certain amount of SiC particles with a particle size of 200nm are oxidized in a box furnace to obtain SiC@SiO2 core-shell structured filler; the oxidation process temperature is 1200℃ and the oxidation time is 2h. S2: Using 90% xylene as solvent and 10% polysilazane (PSZ) as solute, 20% SiC@SiO2 core-shell structure filler (compared to the polymer precursor) is added to prepare a slurry. After mixing, the slurry is ball-milled to obtain a uniformly dispersed impregnation slurry. The slurry is then defoamed under vacuum. The ball milling speed is 300 rpm, the ball milling time is 2 hours, and the ball milling material (milling jar and grinding balls) is zirconium oxide. S3: The carbon fiber fabric is degummed using a high-temperature calcination method. After degumming, it is placed in a slurry for vacuum impregnation, then removed, drained, and cured in an oven. The high-temperature calcination temperature is 800℃, the time is 2 hours, and the heating rate is 3-5℃ / min. The vacuum impregnation time is 0.5 hours, the draining time is 0.5 hours, and the curing temperature is 250℃ for 2 hours. S4: The cured carbon fiber fabric is placed in a high-temperature pyrolysis furnace for carbonization and pyrolysis. The carbonization and pyrolysis process adopts a staged temperature and pressure controlled gradient pyrolysis process. 1. Pre-pyrolysis stage. Temperature range: room temperature - 300℃, heating rate: 5℃ / min, holding time: 2h, vacuum level: 10℃. - 2 Pa; 2. Main pyrolysis stage. 300℃-800℃, heating rate 1℃ / min, holding time 2h, inert atmosphere refilled to pressure 0.8 atm; 3. High-temperature crystallization stage. 800℃-1200℃, heating rate 3℃ / min, holding time 2h, inert atmosphere refilled to pressure 1.5 atm; 4. Cooling and annealing stage. 1200℃ to room temperature, cooling rate 3℃ / min, pressure release 1.0 atm.

[0037] The prepared carbon fibers with uniform coating and the EDS spot scan results of the fiber surface are as follows: Figure 1 As shown: Figure 1 The image shows the morphology of the carbon fiber surface coating prepared according to Example 1. For example... Figure 1 (a) and Figure 1 As shown in (b), a continuous, homogeneous and complete ceramic coating was successfully formed on the carbon fiber surface, in which uniformly distributed nanoparticles are clearly visible. Figure 1 Figures (c) and (d) show EDS spot scan analysis results confirming that the characteristic regions on the coating surface are mainly composed of Si and C elements, indicating that the chemical composition of the coating is silicon carbide (SiC).

[0038] Example 2 This invention provides a method for preparing a continuous, homogeneous, and dense ceramic coating on the surface of carbon fibers. The steps are basically the same as in Example 1, except that the mass fraction of PSZ in the impregnation slurry is 15%, and the mass fraction of xylene is 85%. The prepared carbon fibers with a uniform coating are as follows: Figure 2 As shown, the coating also exhibits excellent continuity and homogeneity.

[0039] Example 3 This invention provides a method for preparing a continuous, homogeneous, and dense ceramic coating on the surface of carbon fibers. The steps are basically the same as in Example 1, except that the mass fraction of PSZ in the impregnation slurry is 20%, and the mass fraction of xylene is 80%. The prepared carbon fibers with a uniform coating are as follows: Figure 3 As shown, it can be observed that the coating still maintains a high degree of continuity and homogeneity, and its thickness is slightly increased compared to Examples 1 and 2.

[0040] Example 4 The implementation steps of this embodiment are basically the same as those of Embodiment 1, except that the SiC powder used has a particle size of 50 nm, and the morphology of the obtained fiber surface coating is as follows. Figure 5 As shown (using 50nm SiC micropowder as filler), due to the small particle size and high specific surface energy of the filler, it underwent severe spontaneous agglomeration in the slurry and on the fiber surface, forming a large number of irregular clusters. This uncontrollable agglomeration behavior directly resulted in a highly heterogeneous final coating that could not achieve continuous coverage. This result indicates that the particle size and structural design of the filler are crucial.

[0041] Comparative Example 1 This comparative example uses the traditional PIP process to prepare a ceramic coating on the fiber surface as a comparison. The preparation method includes the following steps: S1: Prepare a slurry using xylene (85% by mass) as solvent and polysilazane (PSZ) (15% by mass) as solute. After homogenization, impregnate the slurry and then defoam the slurry under vacuum. S2: The carbon fiber fabric is degummed using a high-temperature calcination method. After degumming, it is placed in a slurry for vacuum impregnation, then removed, drained, and cured in an oven. The high-temperature calcination temperature is 800℃, the time is 2 hours, and the heating rate is 3-5℃ / min. The vacuum impregnation time is 0.5 hours, the draining time is 0.5 hours, and the curing temperature is 250℃ for 2 hours. S3: The cured carbon fiber fabric is placed in a high-temperature pyrolysis furnace for carbonization and pyrolysis. The carbonization and pyrolysis process adopts a staged temperature and pressure controlled gradient pyrolysis process. 1. Pre-pyrolysis stage. Temperature range: room temperature - 300℃, heating rate: 5℃ / min, holding time: 2h, vacuum level: 10℃. - 2Pa; 2. Main pyrolysis stage. 300℃-800℃, heating rate 1℃ / min, holding time 2h, inert atmosphere refilled to pressure 0.8 atm; 3. High-temperature crystallization stage. 800℃-1200℃, heating rate 3℃ / min, holding time 2h, inert atmosphere refilled to pressure 1.5 atm; 4. Cooling and annealing stage. 1200℃ to room temperature, cooling rate 3℃ / min, pressure release 1.0 atm.

[0042] The prepared fiber surface coating, such as Figure 4 As shown, the fiber surface coating is cracked and discontinuous, which contrasts sharply with embodiments 1-3 of this invention. The coating is uneven, discontinuous, and exhibits significant cracking and loss of structural integrity. This result directly confirms the inherent shrinkage cracking problem of the traditional PIP process.

[0043] comprehensive Figures 1 to 3 The results demonstrate that the core advantage of this invention lies in the fact that the introduced nano-core-shell filler effectively acts as a nucleation site during the polymer precursor pyrolysis process, and significantly inhibits the shrinkage of pyrolysis products through its volume confinement effect, thereby obtaining a dense coating structure in a wide range of slurry concentrations.

[0044] Example 5 This invention provides a method for preparing a continuous, homogeneous, and dense ceramic coating on the surface of carbon fibers. The steps are basically the same as in Example 1, except that: 1) In S1, the SiC particles used have a particle size of 500 nm, the oxidation process temperature is 1400℃, and the oxidation time is 8h, so as to obtain a filler with a SiO2 shell thickness of about 20 nm.

[0045] 2) In S2, the impregnation slurry uses 70% xylene as solvent, 30% polysilazane (PSZ) as solute, and 30% SiC@SiO2 core-shell structure filler (compared to the polymer precursor) is added. The mixing process adopts high-speed shear stirring method.

[0046] 3) In S3, the vacuum impregnation time is 4 hours.

[0047] 4) The carbonization pyrolysis process parameters of S4 are adjusted as follows: heating rate of 3℃ / min and holding time of 1h in the pre-pyrolysis stage; heating rate of 0.5℃ / min and holding time of 1h in the main pyrolysis stage; heating rate of 0.5℃ / min and holding time of 1h in the high-temperature crystallization stage.

[0048] The carbon fiber surface coating prepared in this embodiment is continuous, dense, and has a uniform thickness.

[0049] Example 6 This invention provides a method for preparing a continuous, homogeneous, and dense ceramic coating on the surface of carbon fibers. The steps are basically the same as in Example 1, except that: 1) In S1, by controlling the oxidation process (temperature 1000℃, time 4h), SiC@SiO2 core-shell structure filler with a SiO2 shell thickness of about 15 nm was obtained.

[0050] 2) In S2, the impregnation slurry uses xylene with a mass fraction of 92.5% as solvent, polycarbosilane (PCS) with a mass fraction of 7.5% as solute, and adds 25% SiC@SiO2 core-shell structure filler (compared to polymer precursor).

[0051] 3) The carbonization pyrolysis process parameters of S4 are adjusted as follows: heating rate of 4℃ / min and holding time of 2.5h in the pre-pyrolysis stage; heating rate of 2℃ / min and holding time of 2.5h in the main pyrolysis stage; heating rate of 2℃ / min and holding time of 2.5h in the high-temperature crystallization stage.

[0052] The carbon fiber surface coating prepared in this embodiment has good homogeneity and density, verifying the effectiveness of the key intermediate parameters.

[0053] Example 7 This invention provides a method for preparing a continuous, homogeneous, and dense ceramic coating on the surface of carbon fibers. The steps are basically the same as in Example 1, except that: 1) In S2, the impregnation slurry uses 95% xylene as solvent, 5% polysiloxane as solute, and 10% SiC@SiO2 core-shell structure filler (compared to the polymer precursor). The mixing process uses mechanical stirring.

[0054] 2) The carbonization pyrolysis process parameters of S4 are adjusted as follows: the holding time for the main pyrolysis stage is 4 hours; the holding time for the high-temperature crystallization stage is 4 hours.

[0055] The successful formation of a complete coating on the carbon fiber surface prepared in this embodiment demonstrates the effectiveness of the ratio of low-content polymer precursor to filler and the endpoint values ​​of process parameters.

[0056] Example 8 This invention provides a method for preparing a continuous, homogeneous, and dense ceramic coating on the surface of carbon fibers. The steps are basically the same as in Example 1, except that: 1) In S1, the SiC particles used have a particle size of 50 nm (far smaller than the lower limit of 100 nm in claim 3).

[0057] 2) In S2, 40% of the small particle size filler is added (which exceeds the upper limit of claim 1 compared to the polymer precursor).

[0058] The carbon fiber surface coating prepared in this embodiment exhibits obvious agglomeration and discontinuity. The above description is merely illustrative of the technical concept of this invention and should not be construed as limiting the scope of protection of this invention. Any modifications made to the technical solution based on the technical concept proposed in this invention fall within the scope of protection of the claims of this invention.

Claims

1. A method of making carbon fibers having a continuous, homogeneous, dense ceramic coating on the surface, characterized in that, The carbon fiber with continuous, homogeneous and dense ceramic coating on the surface is prepared by mixing a polymer precursor, a xylene solvent and a nano SiC@SiO2 core-shell structure filler to obtain an impregnation slurry, vacuum defoaming the impregnation slurry, impregnating a carbon fiber fabric in the impregnation slurry after removing glue from the carbon fiber fabric, draining and solidifying, and gradient pyrolysis after carbonization.

2. A method of making a carbon fiber having a continuous, homogeneous, dense ceramic coating on the surface according to claim 1, characterized in that, The nano SiC@SiO2 core-shell structure filler is prepared by oxidizing nano SiC particles.

3. A method of making a carbon fiber having a continuous, homogeneous, dense ceramic coating on the surface of the carbon fiber according to claim 1, characterized in that, The high-temperature air oxidation process has process conditions including an oxidation temperature of 800-1400℃ and an oxidation time of 0.5-8h.

4. A method of making a carbon fiber having a continuous, homogeneous, dense ceramic coating on the surface according to claim 3, characterized in that, The mixing process of the polymer precursor, the xylene solvent and the nano SiC@SiO2 core-shell structure filler includes any one of mechanical stirring, ball milling and high-speed shearing stirring.

5. The method for preparing carbon fibers with a continuous, homogeneous, and dense ceramic coating on the surface according to claim 1, characterized in that, The impregnation time is 0.5-4h, and the draining time is 0.5h.

6. The method of making a carbon fiber having a continuous, homogeneous, dense ceramic coating on the surface of the carbon fiber according to claim 1, wherein, The gradient pyrolysis process adopts a segmented temperature and pressure control gradient pyrolysis process, specifically including: 1) Pre-cracking stage: room temperature - 300 °C, heating rate 3-5 °C / min, holding time 1-3 h, vacuum extraction to 10 -2 Pa; 2) main pyrolysis stage: 300℃-800℃, heating rate 0.5-3℃ / min, holding time 1-4h, inert atmosphere backfill to pressure 0.8 atm; 3) high-temperature crystallization stage: 800℃-1200℃, heating rate 0.5-3℃ / min, holding time 1-4h, inert atmosphere backfill to pressure 1.5 atm; 4) cooling and annealing stage: 1200℃-room temperature, cooling rate ≤5℃ / min, pressure release 1.0 atm.

7. The method of making a carbon fiber having a continuous, homogeneous, dense ceramic coating on the surface of the carbon fiber according to claim 1, wherein, The polymer precursor includes any one of polysilazane, polycarbosilane and polysiloxane.

8. The method of making a carbon fiber having a continuous, homogeneous, dense ceramic coating on the surface of the carbon fiber according to claim 1, wherein, The mass fraction of the polymer precursor relative to the total mass of the impregnation slurry is 5 wt%-30 wt%, and the mass fraction of the nano SiC@SiO2 core-shell structure filler relative to the mass of the polymer precursor is 10 wt%-30 wt%.

9. Carbon fibers having a continuous, homogeneous, dense ceramic coating prepared by the process of any of claims 1-6, characterized in that, The ceramic coating composition on the surface of the carbon fiber includes nano SiC@SiO2 core-shell structure filler and ceramic produced by pyrolysis of the polymer precursor, the particle size of the nano SiC@SiO2 core-shell structure filler is 100 nm-500 nm, and in the nano SiC@SiO2 core-shell structure filler, the nano SiC particles are coated with a SiO2 shell with a thickness of 5 nm-20 nm.

10. The use of the carbon fiber with continuous, homogeneous and dense ceramic coating on the surface in claim 9 in the field of carbon fiber reinforced ceramic matrix composites.

Images