Fiber surface highly-graphitized carbon coating and preparation method thereof

Abstract

The invention belongs to the field of high-temperature-resistant fiber surface coatings, and discloses a fiber surface highly-graphitized carbon coating and a preparation method thereof. The preparation method comprises the following steps: carrying out surface degumming, surface activation and catalyst-loaded soaking on fibers, and adding the catalyst-loaded fibers and an asphalt solution into a pressure kettle for reaction; taking out, putting into alcohol to clean the surface, putting into an oven to dry, and putting into a cracking furnace to graphitize. According to the obtained high-graphitization carbon coating on the fiber surface, the surface graphitization degree can reach 50% or above, and the thickness of the coating ranges from 100 nm to 800 nm. The low-temperature solvothermal method is combined with the catalyst, so that small molecules in the asphalt solution can form carbon at low temperature and high pressure, and the problem that a carbon coating is loose and not compact due to escape of a large amount of small molecules such as CO, H2 and CH4 in the high-temperature cracking process is solved.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant fiber surface coating technology, and in particular to a highly graphitized carbon coating for fiber surfaces and its preparation method. Background Technology

[0002] In fiber-reinforced ceramic matrix composite systems, especially when there are physical mismatches and chemical incompatibilities between the fibers and the matrix, it is necessary to introduce appropriate interfaces for modification and buffering. Particularly in C / SiC, C / ZrC, and C / Oxide ceramic composite systems, the significant difference in thermal expansion coefficients and atomic chemical diffusion between the fibers and the matrix easily lead to strong physical or chemical bonds between them, thus preventing sufficient improvement in the mechanical properties of the composite material. Introducing a carbon coating between the fibers and the matrix is ​​a good solution to this problem.

[0003] Currently, the main methods for preparing carbon coatings on fiber surfaces reported in the literature are chemical vapor deposition (CVD) and polycarbonate infiltration (PIP) liquid phase method. While CVD can produce relatively dense carbon coatings on fiber surfaces due to its high atomic mobility, it is highly sensitive to temperature field distribution. Furthermore, during deposition, migration is driven solely by the kinetic energy of the gaseous molecules themselves, leading to insufficient driving force for large and complex components, resulting in gradient effects between the internal and external parts of the component. On the other hand, fiber surface coatings prepared by the traditional PIP liquid phase method suffer from low atomic mobility and significant porosity and shrinkage due to the release of gaseous products during high-temperature pyrolysis. Therefore, the resulting coatings cannot be completely dense. Moreover, the PIP liquid phase method typically uses phenolic resin as a precursor, resulting in glassy carbon, rather than highly graphitized carbon with crack deflection capabilities. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above and to provide a liquid-phase preparation method for carbon coating on fiber surface with high graphitization.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: (1) After the fiber is degummed, it is surface activated by nitric acid or sulfuric acid, and then the catalyst is loaded by soaking in Ni(NO3)2 ethanol solution to obtain the fiber loaded with the catalyst. (2) After grinding the asphalt, it is added to xylene and stirred. After filtration, an asphalt solution is obtained. The fiber loaded with the catalyst is added together with the asphalt solution to a pressure-sealed container for heating and reaction. After the reaction is completed, it is ultrasonically cleaned and dried to obtain coated fiber. (3) The coated fiber is subjected to vacuum heat treatment to obtain a highly graphitized carbon coating on the fiber surface.

[0006] This invention utilizes active design to select raw materials in a directional manner and to give the carbonization process in the liquid phase method a directional driving force, thereby achieving high graphitization and high atomic migration efficiency in the preparation of carbon coatings on fiber surfaces by the liquid phase method, and finally obtaining a uniform, dense carbon coating on the fiber surface with crack deflection capability.

[0007] In the above preparation method, preferably, in step (1), the fiber includes at least one of C fiber and SiC fiber, and the surface degumming treatment includes: immersing the fiber in acetone for 12-24 hours, ultrasonically cleaning the fiber with alcohol after immersion, and then drying it in an oven at 60-80°C to obtain the fiber after surface degumming treatment.

[0008] Preferably, in step (1), the surface activation treatment includes: immersing the surface-degummed fiber in a 65% nitric acid solution or an 85% phosphoric acid solution, then sealing it and keeping it at 60-80°C for 4-8 hours, then ultrasonically cleaning it with deionized water 3-4 times, and drying it at 50-80°C to obtain the surface-activated fiber.

[0009] Preferably, in step (1), the operation of soaking the catalyst includes: immersing the surface-activated fiber in a Ni(NO3)2 ethanol solution with a concentration of 0.5~1.5mol / L at room temperature for 10~24h, and then drying it to obtain the fiber loaded with the catalyst.

[0010] Preferably, in step (2), the asphalt solution is obtained by the following method: coal tar pitch is ground and then added to xylene at a mass ratio of 1~15:85~99 and stirred for 5~10 hours. The mixture is then filtered with filter paper, leaving a transparent solution containing small molecule asphalt, which is the asphalt solution.

[0011] Preferably, in step (2), the temperature of the heating reaction is 140℃~180℃, and the holding time is 4~10h.

[0012] Preferably, in step (2), the ultrasonic cleaning involves placing the reacted material in anhydrous ethanol for ultrasonic cleaning for 1-3 minutes; the drying temperature is 40-60°C and the drying time is 5-10 hours.

[0013] Preferably, in step (3), the heat treatment regime of the vacuum heat treatment is as follows: first, the temperature is raised to 1600~2000℃ at 3~10℃ / min and held for 1~5h, and then the temperature is lowered to room temperature at 1~3℃ / min.

[0014] Preferably, depending on the mass fraction of the asphalt solution, steps (1) to (3) can be repeated more than 3 times to obtain carbon coatings on the fiber surface with different thicknesses and high uniformity, density and graphitization.

[0015] Based on a general inventive concept, the present invention also provides a highly graphitized carbon coating on the fiber surface prepared by the above method, wherein the degree of graphitization on the surface can reach more than 50%, and the coating thickness is 100nm~800nm.

[0016] Based on a general inventive concept, the present invention also provides an application of the highly graphitized carbon coating on the fiber surface prepared by the above method in the interface of ceramic matrix composite materials.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses asphalt solution as raw material for preparing carbon coating. After dissolving and filtering xylene, it selects small asphalt molecules that are easy to be highly graphitized as carbon-forming materials, which effectively solves the problem of high graphitization temperature in the traditional PIP liquid phase method for preparing carbon coating. Analogous to the carbon after high-temperature cracking of traditional phenolic resin, which is basically glassy carbon, the graphitization temperature is generally not lower than 2300℃ during the graphitization process. However, in this invention, carbon is induced by low temperature and high pressure through catalyst. The carbon structure obtained itself presents an aromatic benzene ring planar structure, which is the closest precursor to the sheet graphite structure. Therefore, typical graphitization characteristics begin to appear at 1400℃, which has a natural advantage in graphitization and can reduce the graphitization temperature to 1600~2000℃.

[0018] (2) Compared with the traditional liquid phase method for preparing carbon coatings on fiber surfaces, this invention uses a catalyst to form a gradient concentration diffusion, which enables carbon groups to migrate to the fiber surface with high efficiency and promotes carbon formation. This greatly overcomes the problem of low atomic migration rate in the original ordinary liquid phase method for preparing carbon coatings on fiber surfaces, making the fiber surface coating uniform, dense and efficient.

[0019] (3) By activating the fiber surface with nitric acid or sulfuric acid, the problem of weak bonding between the fiber and the coating during the preparation of coating by the traditional liquid phase method is overcome. This allows the fiber and the coating to have better bonding force, which is beneficial to the protection of the fiber during use and avoids the coating peeling off the fiber surface.

[0020] (4) The present invention uses a low-temperature solvothermal method combined with a catalyst to control the reaction rate of catalytic carbonization, and better homogenizes the gradient concentration diffusion. This enables small molecules in the asphalt solution to be carbonized under low temperature and high pressure, avoiding the high-temperature pyrolysis process required for traditional liquid phase carbon coating preparation. This also avoids the problem of loose and non-dense carbon coating caused by the escape of a large number of small molecules such as CO, H2, and CH4 during the high-temperature pyrolysis process. Attached Figure Description

[0021] 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.

[0022] Figure 1 This is a flowchart illustrating the entire process of this invention.

[0023] Figure 2 This is a SEM image of the fiber carbon coating surface obtained by the present invention.

[0024] Figure 3 This is a SEM image of the cross-section of the fiber carbon coating obtained in this invention.

[0025] Figure 4 This is the Raman spectrum of the fiber carbon coating obtained in this invention. Detailed Implementation

[0026] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0027] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] Example 1: A method for preparing a highly graphitized carbon coating on a fiber surface according to the present invention, such as... Figure 1 As shown, the specific process steps include the following: (1) Fiber surface degumming: Carbon fiber was selected as the coating load object. The carbon fiber was soaked in acetone solution for 24 hours. After soaking, it was taken out and placed in anhydrous ethanol for ultrasonic cleaning for 3 minutes. Then it was taken out and dried at room temperature and placed in an oven at 60℃ for 5 hours to obtain degummed carbon fiber.

[0030] (2) Fiber surface activation: The degummed carbon fiber is immersed in a 65% nitric acid solution and then sealed and placed in an oven at 80°C for 4 hours. After the heat preservation is completed, the fiber is taken out and placed in deionized water for ultrasonic cleaning 3 times, each ultrasonic cleaning lasting 1 minute. Then it is taken out and placed in an oven at 60°C to dry, thus obtaining activated carbon fiber.

[0031] (3) Fiber surface catalyst loading: The activated carbon fiber was immersed in a Ni(NO3)2·5H2O ethanol solution with a concentration of 0.5mol / L for 10h at room temperature. After the immersion was completed, the fiber was taken out and dried at room temperature to obtain a fiber with Ni(NO3)2·5H2O uniformly loaded on the surface.

[0032] (4) Preparation of asphalt solution: After grinding coal tar pitch, add it to xylene and stir for 5 hours. The mass ratio of coal tar pitch to xylene is 5:95. After stirring, filter the solution with filter paper to leave a transparent solution containing small molecule pitch.

[0033] (5) Solvent thermal carbonization reaction: The fiber uniformly loaded in step (3) and the small molecule pitch transparent solution prepared in step (4) are placed together in a pressure vessel, and then the pressure vessel is moved to an oven and kept at 140°C for 8 hours. After the heat preservation is completed and the fiber is cooled, it is taken out and placed in anhydrous ethanol solution for ultrasonication for 1 minute to clean the residual Ni on the fiber surface. + After cleaning, the fibers are placed in an oven at 60°C for 5 hours to dry the surface of uneven residue on the fiber surface, thus obtaining fibers with a uniform carbon coating on the surface.

[0034] (6) Graphitization of carbon coating: The fiber coated with carbon in step (5) is placed in a pyrolysis furnace for vacuum heat treatment. The heat treatment regime is to raise the temperature to 1800℃ at 5℃ / min and then keep it at 2h. After the heat treatment is completed, the temperature is lowered at 3℃ / min. After the temperature drops to room temperature, the fiber with a high graphitization carbon coating is obtained.

[0035] A highly graphitized carbon coating on the fiber surface was prepared according to the preparation method in Example 1. The degree of graphitization on the surface can reach more than 70%, and the coating thickness is 100 nm.

[0036] Example 2: A method for preparing a highly graphitized carbon coating on a fiber surface according to the present invention, such as... Figure 1 As shown, the specific process steps include the following: (1) Fiber surface degumming: Carbon fiber was selected as the coating load. The carbon fiber was soaked in acetone solution for 24 hours. After soaking, it was taken out and placed in anhydrous ethanol for ultrasonic cleaning for 1 minute. Then it was taken out and dried at room temperature and placed in an oven at 60°C for 5 hours to obtain degummed carbon fiber.

[0037] (2) Fiber surface activation: The degummed carbon fiber is immersed in a 65% nitric acid solution and then sealed and placed in an oven at 80°C for 6 hours. After the heat preservation is completed, the fiber is taken out and placed in deionized water for ultrasonic cleaning 3 times, each ultrasonic cleaning lasting 2 minutes. Then it is taken out and placed in an oven at 60°C to dry, thus obtaining activated carbon fiber.

[0038] (3) Fiber surface catalyst loading: The activated carbon fiber was immersed in a Ni(NO3)2·5H2O ethanol solution with a concentration of 1.5mol / L for 10h at room temperature. After the immersion was completed, the fiber was taken out and dried at room temperature to obtain a fiber with Ni(NO3)2·5H2O uniformly loaded on the surface.

[0039] (4) Preparation of asphalt solution: After grinding coal tar pitch, add it to xylene and stir for 6 hours. The mass ratio of coal tar pitch to xylene is 10:90. After stirring, filter the solution with filter paper to leave a transparent solution containing small molecule pitch.

[0040] (5) Solvent thermal carbonization reaction: The fiber uniformly loaded in step (3) and the small molecule pitch transparent solution prepared in step (4) are placed together in a pressure vessel, and then the pressure vessel is moved to an oven and kept at 160°C for 4 hours. After the heat preservation is completed and the fiber is cooled, it is taken out and placed in anhydrous ethanol solution for ultrasonication for 1 minute to clean the residual Ni on the fiber surface. + After cleaning, the fibers are placed in an oven at 60°C for 5 hours to dry the surface of uneven residue on the fiber surface, thus obtaining fibers with a uniform carbon coating on the surface.

[0041] (6) Graphitization of carbon coating: The fiber coated with carbon in step (5) is placed in a pyrolysis furnace for vacuum heat treatment. The heat treatment regime is to heat up to 2000℃ at 2℃ / min and then hold for 2 hours. After the holding is completed, the fiber is cooled down at 1℃ / min. After it is cooled to room temperature, the fiber with a high graphitized carbon coating is obtained.

[0042] A highly graphitized carbon coating on the fiber surface was prepared according to the preparation method in Example 2. The degree of graphitization on the surface can reach more than 90%, and the coating thickness is 0.5 μm.

[0043] Example 3: A method for preparing a highly graphitized carbon coating on a fiber surface according to the present invention, such as... Figure 1 As shown, the specific process steps include the following: (1) Fiber surface degumming: Silicon carbide fiber was selected as the coating load. The carbon fiber was soaked in acetone solution for 24 hours. After soaking, it was taken out and placed in anhydrous ethanol for ultrasonic cleaning for 2 minutes. Then it was taken out and dried at room temperature and placed in an oven at 60°C for 5 hours to obtain degummed silicon carbide fiber.

[0044] (2) Fiber surface activation: The degummed carbon fiber is immersed in a phosphoric acid solution with a mass fraction of 85%, and then sealed and placed in an oven at 80°C for 4 hours. After the heat preservation is completed, the fiber is taken out and placed in deionized water for ultrasonic cleaning 4 times, each ultrasonic cleaning time is 1 minute. Then it is taken out and placed in an oven at 60°C to dry, and the activated carbon fiber is obtained.

[0045] (3) Fiber surface catalyst loading: The activated silicon carbide fiber was immersed in a Ni(NO3)2·5H2O ethanol solution with a concentration of 0.8mol / L for 12h at room temperature. After the immersion was completed, the fiber was taken out and dried at room temperature, thereby obtaining a fiber with Ni(NO3)2·5H2O uniformly loaded on the surface.

[0046] (4) Preparation of asphalt solution: After grinding coal tar pitch, add it to xylene and stir for 5 hours. The mass ratio of coal tar pitch to xylene is 15:85. After stirring, filter the solution with filter paper to leave a transparent solution containing small molecule pitch.

[0047] (5) Solvent thermal carbonization reaction: The fiber uniformly loaded in step (3) and the small molecule pitch transparent solution prepared in step (4) are placed together in a pressure vessel, and then the pressure vessel is moved to an oven and kept at 180°C for 8 hours. After the heat preservation is completed and cooled, the fiber is taken out and placed in anhydrous ethanol solution for ultrasonication for 1 minute to clean the residual Ni on the fiber surface. + After cleaning, the fibers are placed in an oven at 60°C for 5 hours to dry the surface of uneven residue on the fiber surface, thus obtaining fibers with a uniform carbon coating on the surface.

[0048] (6) Graphitization of carbon coating: The fiber coated with silicon carbide in step (5) is placed in a pyrolysis furnace for vacuum heat treatment. The heat treatment regime is to heat up to 1600℃ at 3℃ / min and then hold for 5h. After the holding is completed, the fiber is cooled down at 1℃ / min. After it is cooled to room temperature, the fiber with a high graphitization carbon coating is obtained.

[0049] A highly graphitized carbon coating on the fiber surface was prepared according to the preparation method in Example 3. The degree of graphitization on the surface can reach more than 50%, and the coating thickness is 0.8 μm.

[0050] Example 4: A method for preparing a highly graphitized carbon coating on a fiber surface according to the present invention, such as... Figure 1 As shown, the specific process steps include the following: (1) Fiber surface degumming: Silicon carbide fiber was selected as the coating load. The carbon fiber was soaked in acetone solution for 24 hours. After soaking, it was taken out and placed in anhydrous ethanol for ultrasonic cleaning for 1 minute. Then it was taken out and dried at room temperature and placed in an oven at 60°C for 5 hours to obtain degummed silicon carbide fiber.

[0051] (2) Fiber surface activation: The degummed carbon fiber is immersed in a phosphoric acid solution with a mass fraction of 85%, and then sealed and placed in an oven at 80°C for 10 hours. After the heat preservation is completed, the fiber is taken out and placed in deionized water for ultrasonic cleaning 3 times, each ultrasonic cleaning time is 1 minute. Then it is taken out and placed in an oven at 60°C to dry, and the activated carbon fiber is obtained.

[0052] (3) Fiber immersion with catalyst: The activated silicon carbide fiber was immersed in a Ni(NO3)2·5H2O ethanol solution with a concentration of 1.2 mol / L for 12 h at room temperature. After immersion, the fiber was removed and dried at room temperature to obtain a fiber with Ni(NO3)2·5H2O uniformly loaded on its surface.

[0053] (4) Preparation of asphalt solution: After grinding coal tar pitch, add it to xylene and stir for 5 minutes. The mass ratio of coal tar pitch to xylene is 8:92. After stirring, filter the solution with filter paper to leave a transparent solution containing small molecule pitch.

[0054] (5) Solvent thermal carbonization reaction: The fiber uniformly loaded in step (3) and the small molecule pitch transparent solution prepared in step (4) are placed together in a pressure vessel, and then the pressure vessel is moved to an oven and kept at 150°C for 6 hours. After the heat preservation is completed and cooled, the fiber is taken out and placed in anhydrous ethanol solution for ultrasonication for 1 minute to clean the residual Ni on the fiber surface. + After cleaning, the fibers are placed in an oven at 60°C for 8 hours to dry the surface, thus obtaining fibers with a uniform carbon coating on the surface.

[0055] (6) Graphitization of carbon coating: The fiber coated with silicon carbide in step (5) is placed in a pyrolysis furnace for vacuum heat treatment. The heat treatment regime is to heat up to 1800℃ at 3℃ / min and then keep it at 4h. After the heat treatment is completed, the fiber is cooled down at 1℃ / min. After it is cooled down to room temperature, the fiber with a high graphitization carbon coating is obtained.

[0056] A highly graphitized carbon coating on the fiber surface was prepared according to the preparation method in Example 4. The degree of graphitization on the surface can reach more than 70%, and the coating thickness is 0.6 μm.

[0057] Example 5: A method for preparing a highly graphitized carbon coating on a fiber surface according to the present invention, such as... Figure 1 As shown, the specific process steps include the following: (1) Fiber surface degumming: Carbon fiber was selected as the coating load. The carbon fiber was soaked in acetone solution for 24 hours. After soaking, it was taken out and placed in anhydrous ethanol for ultrasonic cleaning for 1 minute. Then it was taken out and dried at room temperature and placed in an oven at 60°C for 5 hours to obtain degummed carbon fiber.

[0058] (2) Fiber surface activation: The degummed carbon fiber is immersed in a 65% nitric acid solution and then sealed and placed in an oven at 80°C for 6 hours. After the heat preservation is completed, the fiber is taken out and placed in deionized water for ultrasonic cleaning 3 times, each ultrasonic cleaning lasting 2 minutes. Then it is taken out and placed in an oven at 60°C to dry, thus obtaining activated carbon fiber.

[0059] (3) Fiber surface catalyst loading: The activated carbon fiber was immersed in a Ni(NO3)2·5H2O ethanol solution with a concentration of 0.5mol / L for 10h at room temperature. After the immersion was completed, the fiber was taken out and dried at room temperature to obtain a fiber with Ni(NO3)2·5H2O uniformly loaded on the surface.

[0060] (4) Preparation of asphalt solution: After grinding coal tar pitch, add it to xylene and stir for 6 hours. The mass ratio of coal tar pitch to xylene is 1:99. After stirring, filter the solution with filter paper to leave a transparent solution containing small molecule pitch.

[0061] (5) Solvent thermal carbonization reaction: The fiber uniformly loaded in step (3) and the small molecule pitch transparent solution prepared in step (4) are placed together in a pressure vessel, and then the pressure vessel is moved to an oven and kept at 160°C for 4 hours. After the heat preservation is completed and the fiber is cooled, it is taken out and placed in anhydrous ethanol solution for ultrasonication for 1 minute to clean the residual Ni on the fiber surface. +After cleaning, the fibers are placed in an oven at 60°C for 5 hours to dry the surface of uneven residue on the fiber surface, thus obtaining fibers with a uniform carbon coating on the surface.

[0062] (6) Graphitization of carbon coating: The fiber coated with carbon in step (5) is placed in a pyrolysis furnace for vacuum heat treatment. The heat treatment regime is to heat up to 2000℃ at 2℃ / min and then hold for 2 hours. After the holding is completed, the fiber is cooled down at 1℃ / min. After it is cooled to room temperature, the fiber with a high graphitized carbon coating is obtained.

[0063] (7) Repeat steps (1) to (6) above 4 times, wherein the vacuum heat treatment temperature in step (6) is set to 1000℃ in the first and third times, and the vacuum heat treatment temperature in step (6) is set to 2000℃ in the second and fourth times.

[0064] A highly graphitized carbon coating on the fiber surface was prepared according to the preparation method in Example 5. The degree of graphitization on the surface can reach more than 90%, and the coating thickness is 0.2 μm.

[0065] Example 6: A method for preparing a highly graphitized carbon coating on a fiber surface according to the present invention, such as... Figure 1 As shown, the specific process steps include the following: (1) Fiber surface degumming: Silicon carbide fiber was selected as the coating load. The carbon fiber was soaked in acetone solution for 24 hours. After soaking, it was taken out and placed in anhydrous ethanol for ultrasonic cleaning for 1 minute. Then it was taken out and dried at room temperature and placed in an oven at 60°C for 5 hours to obtain degummed silicon carbide fiber.

[0066] (2) Fiber surface activation: The degummed carbon fiber is immersed in a phosphoric acid solution with a mass fraction of 85%, and then sealed and placed in an oven at 80°C for 10 hours. After the heat preservation is completed, the fiber is taken out and placed in deionized water for ultrasonic cleaning 3 times, each ultrasonic cleaning time is 1 minute. Then it is taken out and placed in an oven at 60°C to dry, and the activated carbon fiber is obtained.

[0067] (3) Fiber surface catalyst loading: The activated silicon carbide fiber was immersed in a Ni(NO3)2·5H2O ethanol solution with a concentration of 0.6mol / L for 12h at room temperature. After the immersion was completed, the fiber was taken out and dried at room temperature to obtain a fiber with Ni(NO3)2·5H2O uniformly loaded on the surface.

[0068] (4) Preparation of asphalt solution: After grinding coal tar pitch, add it to xylene and stir for 5 hours. The mass ratio of coal tar pitch to xylene is 3:97. After stirring, filter the solution with filter paper to leave a transparent solution containing small molecule pitch.

[0069] (5) Solvent thermal carbonization reaction: The fiber uniformly loaded in step (3) and the small molecule pitch transparent solution prepared in step (4) are placed together in a pressure vessel, and then the pressure vessel is moved to an oven and kept at 150°C for 6 hours. After the heat preservation is completed and cooled, the fiber is taken out and placed in anhydrous ethanol solution for ultrasonication for 1 minute to clean the residual Ni on the fiber surface. + After cleaning, the fibers are placed in an oven at 60°C for 8 hours to dry the surface, thus obtaining fibers with a uniform carbon coating on the surface.

[0070] (6) Graphitization of carbon coating: The fiber coated with silicon carbide in step (5) is placed in a pyrolysis furnace for vacuum heat treatment. The heat treatment regime is to heat up to 1800℃ at 3℃ / min and then keep it at 4h. After the heat treatment is completed, the fiber is cooled down at 1℃ / min. After it is cooled down to room temperature, the fiber with a high graphitization carbon coating is obtained.

[0071] (7) Repeat steps (1) to (6) above 4 times, wherein the vacuum heat treatment temperature in step (6) is set to 900°C in the first and third times, and the vacuum heat treatment temperature in step (6) is set to 1800°C in the second and fourth times.

[0072] A highly graphitized carbon coating on the fiber surface was prepared according to the preparation method in Example 6. The degree of graphitization on the surface can reach more than 70%, and the coating thickness is 0.3 μm.

[0073] The highly graphitized carbon coating on the fiber surface prepared by the preparation methods of Examples 1 to 6 has significant advantages such as uniformity, density and good fiber bonding strength. At the same time, due to the high degree of graphitization, it also has a significant crack deflection effect when applied to the interface of ceramic matrix composites, which can greatly reduce stress concentration at the interface of ceramic matrix composites and prevent cracks from penetrating the fibers, thus providing better toughness and impact resistance for ceramic matrix composites.

[0074] In summary, this invention is based on the characteristics, research status and existing problems of the liquid phase method for preparing fiber coatings. Combining the advantage that small molecules of pitch are easy to graphitize, it provides a method for preparing carbon coatings on fiber surfaces by using catalysts and solvothermal to promote low-temperature carbonization and the gradient concentration diffusion mechanism of fiber surface in step (5), and completes the graphitization of carbon coatings at a relatively low temperature.

[0075] In terms of preparation method, coal tar pitch, which is easily graphitized, is first selected as the raw material. Then, through dissolution and filtration, smaller molecule pitch that is more easily graphitized is selected as the carbon source. Using catalysts and solvothermal methods, carbon is formed on the fiber surface under low temperature and high pressure. Gradient concentration diffusion promotes the continuous migration of small pitch molecules from the far end of the fiber surface to the fiber surface, thereby increasing the thickness of the surface carbon coating. The carbon formation principle of this method is significantly different from the traditional liquid-phase PIP method for preparing carbon coatings on fiber surfaces. The traditional liquid-phase PIP method requires high-temperature pyrolysis to obtain a carbon coating and suffers from problems such as low surface atomic mobility, uneven thickness, poor bonding strength, loose porosity, and numerous cracks during the preparation process. However, this low-temperature carbon formation method not only overcomes the above-mentioned defects of the traditional liquid-phase PIP method, but also, through the directional selection of the carbon source, can generate carbon with a planar structure similar to aromatic benzene rings on the fiber surface in advance, thus significantly reducing the graphitization temperature.

[0076] The highly graphitized carbon coating on the fiber surface obtained in Example 5, through... Figure 2 SEM images of the fiber side show a uniform and dense carbon coating covering the fiber surface, with virtually no cracks or defects; from Figure 3 SEM images of the fiber cross-section show that the coating is uniformly surrounding the outside of the fiber, forming a concentric cylinder with a thickness of approximately 2 μm.

[0077] Raman spectroscopy was performed on carbon coatings after heat treatment at different temperatures. The carbon coatings on the fiber surface after heat treatment at different temperatures were detected using a Horiba Scientific LabRAMHR Evolution Raman spectrometer (Japan). The test conditions were: excitation wavelength 514 nm, test range 100–1800 cm⁻¹. -1 .

[0078] See the test results of carbon coatings after heat treatment at different temperatures. Figure 4 As shown in the figure, typical graphitization characteristics begin to appear at 1400℃. As the temperature increases to above 1600℃, the G peak shifts to a higher vibrational frequency, and the full width at half maximum (FWHM) of the G band decreases significantly. I D / I G The strength increased significantly, indicating that the degree of graphitization of the carbon coating increased substantially.

Claims

1. A method for preparing a highly graphitized carbon coating on a fiber surface, characterized in that, Includes the following steps: (1) After the fiber is degummed, it is surface activated by nitric acid or sulfuric acid, and then the catalyst is loaded by soaking in Ni(NO3)2 ethanol solution to obtain the fiber loaded with the catalyst. (2) After grinding the asphalt, it is added to xylene and stirred. After filtration, an asphalt solution is obtained. The fiber loaded with the catalyst is added together with the asphalt solution to a pressure-sealed container for heating and reaction. After the reaction is completed, it is ultrasonically cleaned and dried to obtain coated fiber. (3) The coated fiber is subjected to vacuum heat treatment to obtain a highly graphitized carbon coating on the fiber surface.

2. The preparation method according to claim 1, characterized in that, In step (1), the fiber includes at least one of C fiber and SiC fiber. The surface degumming process includes: immersing the fiber in acetone for 12-24 hours, ultrasonically cleaning the fiber with alcohol after immersion, and then drying it in an oven at 60-80°C to obtain the surface degummed fiber.

3. The preparation method according to claim 1, characterized in that, In step (1), the surface activation treatment includes: immersing the surface-degummed fiber in a 65% nitric acid solution or an 85% phosphoric acid solution, then sealing it and keeping it at 60-80°C for 4-8 hours, then ultrasonically cleaning it with deionized water 3-4 times, and drying it at 50-80°C to obtain the surface-activated fiber.

4. The preparation method according to claim 1, characterized in that, In step (1), the operation of soaking the catalyst includes: immersing the surface-activated fiber in a Ni(NO3)2 ethanol solution with a concentration of 0.5~1.5mol / L at room temperature for 10~24h, and then drying it to obtain the fiber loaded with the catalyst.

5. The preparation method according to claim 1, characterized in that, In step (2), the asphalt solution is obtained by the following method: coal tar pitch is ground and then added to xylene at a mass ratio of 1~15:85~99 and stirred for 5~10 hours. The mixture is then filtered with filter paper, leaving a transparent solution containing small molecule asphalt, which is the asphalt solution.

6. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the heating reaction is 140℃~180℃, and the holding time is 4~10h.

7. The preparation method according to claim 1, characterized in that, In step (2), the ultrasonic cleaning involves placing the reacted material in anhydrous ethanol and ultrasonicating it for 1 to 3 minutes; the drying temperature is 40 to 60°C and the drying time is 5 to 10 hours.

8. The preparation method according to claim 1, characterized in that, In step (3), the heat treatment regime of the vacuum heat treatment is as follows: first, the temperature is raised to 1600~2000℃ at 3~10℃ / min and held for 1~5h, and then the temperature is lowered to room temperature at 1~3℃ / min.

9. A highly graphitized carbon coating on the fiber surface obtained by the preparation method according to any one of claims 1-8, characterized in that, Its surface graphitization degree can reach more than 50%, and its coating thickness is 100nm~800nm.

10. The application of a highly graphitized carbon coating on a fiber surface obtained by any one of claims 1-8 in the interface of a ceramic matrix composite material.

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