A method for preparing a carbon coating on the surface of a short-cut SiC fiber

Abstract

The application discloses a preparation method of a short-cut SiC fiber surface carbon coating, and the method comprises the following steps: performing oxygen plasma modification treatment on the short-cut SiC fiber to obtain oxygen plasma modification treated SiC fiber; performing chemical metal plating on the oxygen plasma modification treated SiC fiber to obtain metal plated SiC fiber; and placing the metal plated SiC fiber in a sugar solution to perform hydrothermal reaction, so as to obtain the SiC fiber with the surface carbon coating. According to the preparation method, the SiC fiber surface is first subjected to the oxygen plasma modification treatment, so that the fiber surface is activated, and the bonding force between the carbon coating and the fiber is improved; then the fiber surface is subjected to the chemical plating, so that the carbon coating is uniformly and rapidly grown on the fiber surface; finally, in the sugar solution, the carboxymethyl cellulose sodium is added to disperse the fiber, and the catalyst is added to accelerate the growth speed of the carbon coating, so that the uniform, dense and excellent bonding performance carbon coating is finally obtained.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composite material preparation, and more specifically to a method for preparing a carbon coating on the surface of SiC fibers. Background Technology

[0002] Ceramic matrix composites reinforced with SiC fibers possess advantages such as low density, high strength, impact resistance, and resistance to high-temperature oxidation, making them highly promising for applications in aerospace, weaponry, and nuclear energy. During the preparation of fiber-reinforced ceramic matrix composites, an interface layer is often prepared on the fiber surface to adjust the bonding strength between the fiber and the matrix, creating conditions for fiber pull-out, bridging, and crack deflection. Simultaneously, the interface layer protects the fibers during composite preparation, reducing fiber damage and strength loss, thereby improving the mechanical properties of the composite material.

[0003] Currently, chemical vapor deposition (CVD) is commonly used to prepare interface layers, such as BN coatings, SiC coatings, and C coatings. However, this method suffers from drawbacks such as expensive equipment, low efficiency, high cost, and significant pollution. Taking C coating CVD as an example, the deposition temperature is generally around 1000℃, the deposition time is long, and the carbon source conversion rate is low. Furthermore, in large-scale deposition, uniformity at different locations is difficult to guarantee. In addition, CVD is generally used for depositing on fiber-woven preforms, fiber cloths, or continuous fibers. Depositing on chopped fibers easily leads to uneven deposition and fiber adhesion after deposition. Some researchers have used phenolic resin as a carbon source and employed an impregnation pyrolysis method to prepare carbon coatings on fiber surfaces. However, this coating exhibits poor adhesion to the fiber, and cracks appear with even slight increases in thickness. Zhang Xinghong et al. [CN 108532293 B] prepared carbon coatings on carbon fibers using a hydrothermal method by adjusting the pH of a sugar solution. Compared to the phenolic resin pyrolysis method, the microstructure of the carbon coating was significantly improved.

[0004] However, silicon carbide fibers are mainly composed of SiC microcrystals and SiCO amorphous phases. The physicochemical compatibility of carbon coatings with these phases is not as good as that of carbon fibers, which are mainly composed of carbon. Therefore, it is difficult to grow carbon coatings on the surface of SiC fibers. To date, there are no reports on the preparation of carbon coatings on the surface of SiC fibers by hydrothermal method. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a carbon coating on the surface of chopped SiC fibers. The method employs a hydrothermal reaction to treat the surface of the fibers, and then controls the conditions to convert sugars into C, allowing the coating to adhere well to the fibers.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses a method for preparing a carbon coating on the surface of chopped SiC fibers. The method involves subjecting chopped SiC fibers to oxygen plasma modification to obtain oxygen plasma-modified SiC fibers. Then, the oxygen plasma-modified SiC fibers are chemically plated with metal to obtain metal-plated SiC fibers. The metal-plated SiC fibers are then placed in a sugar solution for a hydrothermal reaction to obtain SiC fibers with a carbon coating on the surface. The metal is selected from at least one of Fe, Ni, and Co. The sugar solution is obtained by dissolving a sugar source, sodium carboxymethyl cellulose, and a catalyst in the solution, and then adjusting the pH to ≤7. The catalyst is selected from at least one of FeCl3, CoCl2, and NiCl2.

[0008] The preparation method of this invention first involves oxygen plasma modification treatment of the SiC fiber surface to activate the fiber surface, increase the active sites for chemical plating, increase fiber roughness and specific surface area, improve the bonding force between the carbon coating and the fiber, and improve coating performance. Then, chemical plating is performed on the fiber surface to increase the reaction rate of the subsequent hydrothermal reaction on the fiber surface, promoting the uniform and rapid growth of the carbon coating on the fiber surface. Finally, sodium carboxymethyl cellulose is added to the sugar solution as a dispersant to make the fiber more uniformly dispersed. Then, a catalyst is used to accelerate the growth rate of the carbon coating, improve the integrity and uniformity of the carbon coating, strengthen the bonding with the fiber, and finally obtain a uniform, dense carbon coating with excellent bonding performance.

[0009] The inventors discovered that treating the surface of SiC fibers with oxygen plasma first can not only increase the active sites for electroless plating, but also enhance the bonding force between the carbon coating and the fibers through its synergy with electroless plating. In actual operation, the inventors also tried to chemically sensitize and activate the SiC fibers before electroless plating, but the final bonding performance between the carbon coating and the SiC fibers was still insufficient.

[0010] Furthermore, in this invention, sodium carboxymethyl cellulose is used as a dispersant, which not only makes the fibers more uniformly dispersed, but also serves as a carbon source. During the hydrothermal process, it is converted into a carbon coating together with the sugar source. During this process, it can further promote the uniform distribution of the carbon coating on the surface of SiC fibers, and at the same time, it is beneficial to obtain a dense carbon coating.

[0011] In a preferred embodiment, during the oxygen plasma modification, the vacuum level of the reaction chamber is controlled to be 10–100 Pa, the frequency of the oxygen plasma is 13.56 MHz, the power is 1 kW, and the processing time is 1–10 min, preferably 2–5 min, and more preferably 3 min. Controlling the plasma parameters within the above range ensures further activation of the SiC fibers while preventing a decline in the mechanical properties of the SiC fibers.

[0012] In actual operation, the fiber is placed in the reaction chamber of the oxygen plasma modification equipment, the inlet valve is closed, the reaction chamber is evacuated, oxygen is then introduced to fill the reaction chamber, and the vacuum is evacuated again. This step is repeated 2 to 5 times. Finally, the inlet valve is adjusted to stabilize the vacuum at 10 to 100 Pa, the radio frequency power supply is started to discharge, and oxygen plasma bombardment of the fiber surface begins to obtain oxygen plasma modified SiC fibers.

[0013] In a preferred embodiment, the electroless metal plating process involves adding oxygen plasma-modified SiC fibers to solution A, stirring and mixing them evenly, and then pouring solution B into solution A for electroless plating for 10–60 minutes. Solution A is obtained by dissolving at least one of ferrous sulfate, nickel sulfate, and cobalt sulfate in water. Solution B is obtained by dissolving potassium sodium tartrate, sodium citrate, and ammonium sulfate in water, and then adjusting the pH value to 12–13 with sodium hydroxide.

[0014] In a further preferred embodiment, the concentrations of ferrous sulfate, nickel sulfate, and cobalt sulfate in solution A are 10–30 g / L.

[0015] In a further preferred embodiment, the concentration of potassium sodium tartrate in solution B is 5–60 g / L, the concentration of sodium citrate is 5–30 g / L, and the concentration of ammonium sulfate is 20–60 g / L.

[0016] The inventors discovered that by chemically plating a thin layer of metal onto the fiber surface, not only can the bonding performance between the coating and the silicon carbide fiber be further improved, but also, in synergy with a catalyst, the sugar source can be decomposed and converted into a carbon coating, and the carbon coating can be evenly distributed on the surface of the SiC fiber.

[0017] In a preferred embodiment, the sugar source is selected from at least one of glucose, sucrose, maltose, and fructose, and the mass fraction of the sugar source in the sugar solution is 2-30%, preferably 10-25%. The inventors have found that controlling the concentration of the sugar source within the above range results in the most uniform carbon coating. If the amount of sugar source added is too small, the coating growth rate is too slow; if it is too large, the coating grows too quickly and is not uniform enough, and excessive carbon black will be generated in the system, reducing the coating quality.

[0018] In a preferred embodiment, the sodium carboxymethyl cellulose has a mass fraction of 0.1% to 1% in the carbohydrate solution.

[0019] In a preferred embodiment, the mass fraction of the catalyst in the sugar solution is 0.1% to 2%. Controlling the amount of catalyst within this range results in the best uniformity of the final carbon coating. If too much catalyst is added, the hydrothermal reaction becomes too rapid, the sugar is converted into carbon too quickly, and the resulting carbon coating has poor uniformity and density.

[0020] In a preferred embodiment, the pH of the sugar solution is adjusted using at least one of acetic acid, hydrochloric acid, sulfuric acid, nitric acid, and citric acid.

[0021] In a preferred embodiment, the solid-liquid mass-volume ratio of the metal-plated SiC fiber to the sugar solution is 1g:50-200ml.

[0022] In a preferred embodiment, the hydrothermal reaction is carried out in a reactor, and the total volume of the oxygen plasma modified SiC fiber and the sugar solution accounts for 40-70% of the volume of the reactor.

[0023] In a preferred embodiment, the hydrothermal reaction temperature is 180–300°C, and the holding time is 3–10 h. In actual operation, chopped SiC fibers and a prepared sugar solution are placed in a high-pressure reactor, stirring is started, and the temperature is raised to 180–300°C, held for 3–10 h, and then cooled to room temperature to obtain chopped SiC fibers with a C coating.

[0024] In a preferred embodiment, the thickness of the carbon coating is 50 nm to 1 μm, preferably 300-900 nm.

[0025] Principles and advantages

[0026] The preparation method of this invention first involves oxygen plasma modification treatment of the SiC fiber surface to activate the fiber surface, increase the active sites for chemical plating, increase fiber roughness and specific surface area, improve the bonding force between the carbon coating and the fiber, and improve coating performance. Then, chemical plating is performed on the fiber surface to increase the reaction rate of the subsequent hydrothermal reaction on the fiber surface, promoting the uniform and rapid growth of the carbon coating on the fiber surface. Finally, sodium carboxymethyl cellulose is added to the sugar solution as a dispersant to make the fiber more uniformly dispersed. Then, a catalyst is used to accelerate the growth rate of the carbon coating, improve the integrity and uniformity of the carbon coating, strengthen the bonding with the fiber, and finally obtain a uniform, dense carbon coating with excellent bonding performance.

[0027] Compared with the prior art, the present invention has at least the following advantages:

[0028] 1. This invention uses inexpensive sugars as a carbon source and employs a low-temperature hydrothermal method to prepare a carbon coating on silicon carbide fibers, which has the advantages of low cost, high efficiency, and low pollution.

[0029] 2. The carbon coating of the present invention has a uniform and controllable thickness and is relatively dense, which can effectively improve the interfacial bonding and protect the fibers in the subsequent preparation of composite materials.

[0030] 3. The present invention uses plasma treatment, which greatly activates the fiber surface, increases fiber roughness and specific surface area, improves the bonding force between carbon coating and fiber, improves coating performance, and is conducive to further improving the performance of subsequent composite materials.

[0031] 4. The silicon carbide fiber of the present invention can use short fibers generated during the silicon carbide fiber production process as raw materials, which can enhance the effective utilization of fibers. Attached Figure Description

[0032] Figure 1 The SEM morphology of the carbon coating prepared in Example 3 of this invention.

[0033] Figure 2 SEM morphology of the carbon coating prepared in Comparative Example 1.

[0034] Figure 3 SEM morphology of the carbon coating prepared in Comparative Example 2. Detailed Implementation

[0035] To better demonstrate the objectives, technical solutions, and advantages of this invention, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0036] Example 1

[0037] S1: Place the fiber into the reaction chamber of the oxygen plasma modification equipment, close the inlet valve, evacuate the reaction chamber, then introduce oxygen to fill the reaction chamber, evacuate again, and repeat this step 2-5 times. Finally, adjust the inlet valve to stabilize the vacuum at 10-100 Pa, start the radio frequency power supply discharge, the oxygen plasma frequency is 13.56 MHz, the power is 1 kW, and begin oxygen plasma bombardment of the fiber surface for 3 minutes to further activate the fiber surface.

[0038] S2: Prepare solution A: ferrous sulfate solution with a concentration of 15 g / L, and add the oxygen plasma-treated SiC fibers to it and stir evenly; then prepare solution B: potassium sodium tartrate with a concentration of 10 g / L, sodium citrate with a concentration of 5 g / L, and ammonium sulfate with a concentration of 20 g / L, and adjust the pH of the solution to 12 with sodium hydroxide; finally, pour solution B into solution A, perform chemical plating for 20 min, and obtain chemically plated modified fibers after washing and filtering.

[0039] S3: Dissolve sucrose and sodium carboxymethyl cellulose in deionized water, wherein the mass fraction of sucrose is 10%, the mass fraction of sodium carboxymethyl cellulose is 0.5%, the mass fraction of FeCl3 added is 0.2%, and titrate with hydrochloric acid to adjust the pH of the solution to 3.

[0040] S4: Place the oxygen plasma-treated chopped SiC fibers and the prepared sugar solution into a high-pressure reactor. The ratio of chopped SiC fibers to sugar solution is 1g:50ml, and the total volume of the fibers and sugar solution accounts for 50% of the reactor volume. Start stirring and heat to 200℃, hold for 5 hours, and then cool to room temperature to obtain chopped SiC fibers with a C coating thickness of about 150nm.

[0041] Example 2

[0042] S1: Place the fiber into the reaction chamber of the oxygen plasma modification equipment, close the inlet valve, evacuate the reaction chamber, then introduce oxygen to fill the reaction chamber, evacuate again, and repeat this step 2-5 times. Finally, adjust the inlet valve to stabilize the vacuum at 10-100 Pa, start the radio frequency power supply discharge, and begin oxygen plasma bombardment of the fiber surface for 3 minutes to further activate the fiber surface.

[0043] S2: Prepare solution A: a nickel sulfate solution with a concentration of 20 g / L, and add the oxygen plasma-treated SiC fibers to it and stir evenly; then prepare solution B: potassium sodium tartrate with a concentration of 15 g / L, sodium citrate with a concentration of 10 g / L, and ammonium sulfate with a concentration of 25 g / L, and adjust the pH of the solution to 12 with sodium hydroxide; finally, pour solution B into solution A, perform chemical plating for 30 minutes, and obtain chemically plated modified fibers after washing and filtering.

[0044] S3: Dissolve sucrose and sodium carboxymethyl cellulose in deionized water, wherein the mass fraction of sucrose is 15%, the mass fraction of sodium carboxymethyl cellulose is 0.6%, the mass fraction of CoCl2 added is 0.5%, and titrate with hydrochloric acid to adjust the pH of the solution to 2.

[0045] S4: The oxygen plasma-treated chopped SiC fibers and the prepared sugar solution were placed in a high-pressure reactor. The ratio of chopped SiC fibers to sugar solution was 1g:80ml, and the total volume of the fibers and sugar solution accounted for 60% of the reactor volume. Stirring was started, and the temperature was raised to 210℃ and held for 6 hours. Then, it was cooled to room temperature to obtain chopped SiC fibers with a C coating thickness of about 300nm.

[0046] Example 3

[0047] S1: Place the fiber into the reaction chamber of the oxygen plasma modification equipment, close the inlet valve, evacuate the reaction chamber, then introduce oxygen to fill the reaction chamber, evacuate again, and repeat this step 2-5 times. Finally, adjust the inlet valve to stabilize the vacuum at 10-100 Pa, start the radio frequency power supply discharge, and begin oxygen plasma bombardment of the fiber surface for 3 minutes to further activate the fiber surface.

[0048] S2: Prepare solution A: a cobalt sulfate solution with a concentration of 25 g / L, and add the SiC fibers treated with oxygen plasma to it and stir evenly; then prepare solution B: potassium sodium tartrate with a concentration of 30 g / L, sodium citrate with a concentration of 30 g / L, and ammonium sulfate with a concentration of 25 g / L, and adjust the pH of the solution to 12 with sodium hydroxide; finally, pour solution B into solution A, perform chemical plating for 30 min, and obtain chemically plated modified fibers after washing and filtering.

[0049] S3: Dissolve sucrose and sodium carboxymethyl cellulose in deionized water, wherein the mass fraction of sucrose is 20%, the mass fraction of sodium carboxymethyl cellulose is 0.4%, the mass fraction of FeCl3 added is 0.8%, and titrate with hydrochloric acid to adjust the pH of the solution to 1.

[0050] S4: Place the oxygen plasma-treated chopped SiC fibers and the prepared sugar solution into a high-pressure reactor. The ratio of chopped SiC fibers to sugar solution is 1g:120ml, and the total volume of the fibers and sugar solution accounts for 65% of the reactor volume. Start stirring and heat to 220℃, hold for 6 hours, and then cool to room temperature to obtain chopped SiC fibers with a C coating.

[0051] The morphology of the prepared coating is as follows Figure 1 As shown, the coating thickness is about 500 nm and it is well bonded to the fiber. As can be seen from the figure, the carbon coating is uniformly distributed on the surface of the chopped SiC fiber.

[0052] Example 4

[0053] S1: Place the fiber into the reaction chamber of the oxygen plasma modification equipment, close the inlet valve, evacuate the reaction chamber, then introduce oxygen to fill the reaction chamber, evacuate again, and repeat this step 2-5 times. Finally, adjust the inlet valve to stabilize the vacuum at 10-100 Pa, start the radio frequency power supply discharge, and begin oxygen plasma bombardment of the fiber surface for 3 minutes to further activate the fiber surface.

[0054] S2: Prepare solution A: a 15 g / L solution of ferrous sulfate and nickel sulfate, and add the oxygen plasma-treated SiC fibers to it and stir evenly; then prepare solution B: a 30 g / L solution of potassium sodium tartrate, a 30 g / L solution of sodium citrate, and a 30 g / L solution of ammonium sulfate, and adjust the pH of the solution to 12 with sodium hydroxide; finally, pour solution B into solution A, perform chemical plating for 50 minutes, and after cleaning and filtration, obtain the chemically plated modified fibers.

[0055] S3: Dissolve sucrose and sodium carboxymethyl cellulose in deionized water, wherein the mass fraction of sucrose is 20%, the mass fraction of sodium carboxymethyl cellulose is 0.4%, the mass fraction of NiCl2 added is 1.2%, and titrate with hydrochloric acid to adjust the pH of the solution to 1.

[0056] S4: The oxygen plasma-treated chopped SiC fibers and the prepared sugar solution were placed in a high-pressure reactor. The ratio of chopped SiC fibers to sugar solution was 1g:120ml, and the total volume of the fibers and sugar solution accounted for 65% of the reactor volume. Stirring was started, and the temperature was raised to 220℃ and held for 6 hours. Then, it was cooled to room temperature to obtain chopped SiC fibers with a C coating thickness of about 700nm.

[0057] Example 5

[0058] S1: Place the fiber into the reaction chamber of the oxygen plasma modification equipment, close the inlet valve, evacuate the reaction chamber, then introduce oxygen to fill the reaction chamber, evacuate again, and repeat this step 2-5 times. Finally, adjust the inlet valve to stabilize the vacuum at 10-100 Pa, start the radio frequency power supply discharge, and begin oxygen plasma bombardment of the fiber surface for 3 minutes to further activate the fiber surface.

[0059] S2: Prepare solution A: 15 g / L ferrous sulfate and 15 g / L cobalt sulfate solution, and add the oxygen plasma-treated SiC fibers to it and stir evenly; then prepare solution B: 35 g / L potassium sodium tartrate, 35 g / L sodium citrate, and 35 g / L ammonium sulfate, and adjust the pH of the solution to 12 with sodium hydroxide; finally, pour solution B into solution A, perform chemical plating for 60 minutes, and obtain chemically plated modified fibers after washing and filtration.

[0060] S3: Dissolve sucrose and sodium carboxymethyl cellulose in deionized water, wherein the mass fraction of sucrose is 25%, the mass fraction of sodium carboxymethyl cellulose is 0.7%, the mass fraction of FeCl3 added is 2.2%, and titrate with hydrochloric acid to adjust the pH of the solution to 0.

[0061] S4: The oxygen plasma-treated chopped SiC fibers and the prepared sugar solution were placed in a high-pressure reactor. The ratio of chopped SiC fibers to sugar solution was 1g:150ml, and the total volume of the fibers and sugar solution accounted for 65% of the reactor volume. Stirring was started, and the temperature was raised to 250℃ and held for 8 hours. Then, it was cooled to room temperature to obtain chopped SiC fibers with a C coating thickness of about 900nm.

[0062] Comparative Example 1

[0063] Except for the absence of the FeCl3 catalyst, the other conditions were the same as in Example 3. The resulting carbon coating was significantly thinner, and the efficiency of carbon coating preparation was lower. The coating condition is as follows: Figure 2 As shown.

[0064] Comparative Example 2

[0065] Except for the absence of plasma treatment, the other conditions were the same as in Example 3. The prepared carbon coating had poor adhesion to the fiber and exhibited peeling. The condition of the coating is as follows: Figure 3 As shown.

[0066] Comparative Example 3

[0067] Except for replacing oxygen plasma treatment with nitric acid activation treatment, the other conditions were the same as in Example 3. The prepared carbon coating was as well bonded as in Comparative Example 2, but the coating still showed some peeling.

[0068] Comparative Example 4

[0069] Except for the absence of chemical plating, the conditions were the same as in Example 3. The prepared coating was uneven and thinner than in Example 3, with an average thickness of about 350 nm.

Claims

1. A method for preparing a carbon coating on the surface of chopped SiC fibers, characterized in that: Short-cut SiC fibers are modified by oxygen plasma to obtain oxygen plasma-modified SiC fibers. Then, the oxygen plasma-modified SiC fibers are chemically plated with metal to obtain metal-plated SiC fibers. The metal-plated SiC fibers are placed in a sugar solution for hydrothermal reaction to obtain SiC fibers with a carbon-coated surface. The metal is selected from at least one of Fe, Ni, and Co. The sugar solution is obtained by dissolving a sugar source, sodium carboxymethyl cellulose, and a catalyst in water and then adjusting the pH to ≤7. The catalyst is selected from at least one of FeCl3, CoCl2, and NiCl2.

2. The method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1, characterized in that: During the oxygen plasma modification, the vacuum degree of the reaction chamber is controlled at 10-100 Pa, the frequency of the oxygen plasma is 13.56 MHz, the power is 1 kW, and the processing time is 1-10 min.

3. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The electroless metal plating process is as follows: oxygen plasma modified SiC fibers are added to solution A and stirred until uniform. Then, solution B is poured into solution A and electroless plating is performed for 10-60 minutes. Solution A is obtained by dissolving at least one of ferrous sulfate, nickel sulfate, and cobalt sulfate in water. Solution B is obtained by dissolving potassium sodium tartrate, sodium citrate, and ammonium sulfate in water and then adjusting the pH value to 12-13 with sodium hydroxide.

4. The method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 3, characterized in that: In solution A, the concentrations of ferrous sulfate, nickel sulfate, and cobalt sulfate are 10–30 g / L. In solution B, the concentration of potassium sodium tartrate is 5–60 g / L, the concentration of sodium citrate is 5–30 g / L, and the concentration of ammonium sulfate is 20–60 g / L.

5. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The sugar source is selected from at least one of glucose, sucrose, maltose, and fructose, and the mass fraction of the sugar source in the sugar solution is 2-30%.

6. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The sodium carboxymethyl cellulose has a mass fraction of 0.1% to 1% in the carbohydrate solution.

7. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The catalyst has a mass fraction of 0.1% to 2% in the carbohydrate solution.

8. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The pH of the sugar solution is adjusted using at least one of acetic acid, hydrochloric acid, sulfuric acid, nitric acid, and citric acid. The solid-liquid mass-volume ratio of the metal-plated SiC fiber to the sugar solution is 1g:50-200ml.

9. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The hydrothermal reaction is carried out in a reactor, and the total volume of the metallized SiC fibers and the sugar solution accounts for 40-70% of the reactor volume. The hydrothermal reaction temperature is 180–300℃, and the holding time is 3–10 hours.

10. A method for preparing a carbon coating on the surface of chopped SiC fibers according to claim 1 or 2, characterized in that: The thickness of the carbon coating is between 50 nm and 1 μm.

Images