Method for producing silicon carbide ceramic fibers combining sol-gel and dry spinning

Abstract

The application discloses a method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning. The method comprises the following steps: 1) after preparing a second silicon-based sol, a spinning aid is added to prepare a spinnable silicon-based sol; 2) the spinnable silicon-based sol is prepared into fiber filaments by using a dry spinning process; 3) the fiber filaments are cracked into silicon-carbon-oxygen fibers; and 4) the silicon-carbon-oxygen fibers are sintered into silicon carbide ceramic fibers. The method is different from a mainstream polycarbosilane precursor method for preparing silicon carbide ceramic fibers, does not need a non-melting treatment process, has the advantages of adjustable composition, low raw material cost and simple process and the like, and has important significance for low-cost preparation of silicon carbide ceramic fibers.

Description

Technical Field

[0001] This invention relates to the field of dry spinning technology, and more particularly to a method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning. Background Technology

[0002] Silicon carbide fiber, as a new type of ceramic fiber, has a series of excellent properties such as high temperature resistance, oxidation resistance, high tensile strength, good creep resistance and good compatibility with ceramic matrix. It has broad application prospects in high-tech fields such as aerospace, weaponry, shipbuilding and nuclear industry.

[0003] The main methods for preparing silicon carbide fibers include: chemical vapor deposition (CVD), ultrafine powder sintering, activated carbon fiber conversion, precursor conversion, and sol-gel methods. CVD produces high-purity silicon carbide ceramic fibers, but the coarse fiber diameter makes weaving impossible and hinders large-scale production. Ultrafine powder sintering can produce high-purity α-SiC fibers, but structural defects occur during the decomposition and removal of organic polymers, severely affecting their mechanical properties and hindering industrial applications. Activated carbon fiber conversion produces silicon carbide ceramic fibers with low raw material costs, but the fibers still contain micropores, making them prone to cracking and severely impacting their mechanical properties. Precursor conversion, through processes such as polycarbosilane synthesis, melt spinning, non-melting treatment, and pyrolysis sintering, produces silicon carbide ceramic fibers with good performance and high purity, but the reaction cycle is long, the process is complex, and the cost is high.

[0004] The principle of the sol-gel method is to use inorganic salts or metal alkoxides as raw materials, dissolve the precursors in a solvent to form a homogeneous solution, achieving near-molecular-level mixing. The precursors undergo hydrolysis and alcoholysis reactions in the solvent, while simultaneously undergoing condensation polymerization to obtain linear particles with nanoscale dimensions, forming a sol. When the sol reaches a certain viscosity (in the range of 1–1000 Pa·s), it is spun into gel fibers at room temperature, dried, and sintered to obtain ceramic fibers.

[0005] Currently, the production of silicon carbide ceramic fibers still suffers from drawbacks such as low production efficiency, high cost, and complex preparation. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning.

[0007] The technical solution adopted in this invention is as follows:

[0008] (I) A method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning

[0009] The method specifically includes the following steps:

[0010] 1) After preparing the second silica-based sol, a spinning aid is added to prepare a spinnable silica-based sol;

[0011] The second silicon-based sol is prepared using deionized water, tetraethyl orthosilicate, sintering aid, supplementary carbon source, supplementary silicon source, and silicon carbide nanoparticle suspension as the main raw materials.

[0012] Step 1) specifically comprises, by mass parts:

[0013] 1.1) Add 10 to 30 parts of tetraethyl orthosilicate as a silicon source to 15 to 30 parts of deionized water, then add 1 to 5 parts of sintering aid and stir to obtain the first silicon-based sol.

[0014] In step 1.1), the sintering aid is aluminum nitrate nonahydrate particles.

[0015] 1.2) Add supplementary carbon source, supplementary silicon source, and 5-20 parts of silicon carbide nanoparticle suspension to the first silicon-based sol, and stir to obtain the second silicon-based sol; wherein the mass fraction of silicon carbide nanoparticles in the silicon carbide nanoparticle suspension is 2-10%, and the particle size is 200-500 nm.

[0016] In step 1.2), by mass parts, for every 5 to 20 parts of silicon carbide nanoparticle suspension: the carbon source is one or more of the following: 2 to 10 parts of sucrose, 2 to 10 parts of glucose, 2 to 15 parts of polyacrylonitrile, 5 to 20 parts of phenolic resin and 2 to 10 parts of carbon powder suspension; the silicon source is 5 to 15 parts of methyltrimethoxysilane and / or 2 to 10 parts of silicon powder suspension.

[0017] Specifically, in the toner suspension, the mass fraction of toner is 2-10%; in the silicon powder suspension, the mass fraction of silicon powder is 2-10%.

[0018] 1.3) Add 0.5 to 5.5 parts of spinning aid to the second silica-based sol obtained in step 1.2), stir, and obtain a spinnable silica-based sol. The viscosity of the spinnable silica-based sol is 100 to 200 Pa·s.

[0019] In step 1.3), the spinning aid is polyethylene oxide.

[0020] 2) The spinnable silica-based sol is made into fiber filaments using a dry spinning process.

[0021] 3) The fiber filaments are broken down into silicon-carbon-oxygen fibers at high temperature;

[0022] In step 3), the high-temperature pyrolysis specifically involves heating to 600℃ to 1200℃ at a heating rate of 2 to 5℃ / min under a protective gas, holding at that temperature for 1 to 2 hours, and then cooling down.

[0023] 4) Sinter silicon-carbon-oxygen fibers at high temperature into silicon carbide ceramic fibers;

[0024] In step 4), the high-temperature sintering specifically involves heating to 1300-1900°C at a heating rate of 2-5°C / min under a protective gas, holding at that temperature for 1-2 hours, and then cooling down.

[0025] Specifically, the diameter of the silicon carbide ceramic fiber is approximately 10–50 μm.

[0026] In the method of this invention, the composition of the spinnable silica-based sol is highly designable and easily controlled, and the performance of silicon carbide ceramic fibers can be effectively improved by controlling the composition. Specifically, the ease of composition control means that, given that each component can dissolve or be incorporated into the final product, different raw materials can be selected and their addition amounts can be changed to achieve a better spinning sol effect.

[0027] The performance of silicon carbide ceramic fibers prepared by the method of this invention depends on multiple factors, but the preparation of a sol with good spinnability is a key factor affecting its performance. These key factors include the uniformity of the sol system, the continuity of the fibers, the density of the prepared fiber surface, and the presence of pores within the fibers. The spinning sols obtained by the method of this invention are all experimentally verified to have good spinnability, thus demonstrating feasibility. Based on the spinning sols with good spinning performance obtained by the method of this invention, silicon carbide ceramic fibers with good morphology and uniform diameter can be obtained through dry spinning.

[0028] (II) A dry spinning apparatus suitable for the method of the present invention

[0029] In step 2), a dry spinning device is used to produce fiber filaments from spinnable silica-based sol.

[0030] The dry spinning device includes a raw filament extrusion module, an infrared drying lamp, an infrared heating box, and a take-up spool. The raw filament extrusion module is connected to an external gas compressor. The raw filament extrusion module uses the gas compressor to extrude spinnable silica-based sol into fiber filaments. An infrared heating box is arranged downstream of the raw filament extrusion module. The infrared heating box has openings at both ends and infrared drying lamps are arranged inside. A take-up spool for winding the fiber filaments is arranged downstream of the infrared heating box.

[0031] The raw filament extrusion module includes a supply tube support, an airflow conduit, a supply tube adapter, a spinning supply tube, and a metal micro-syringe needle. The supply tube support is placed on an operating table, and the spinning supply tube is supported above the supply tube support. The cavity of the spinning supply tube is filled with spinnable silica-based sol. One end of the spinning supply tube is sealed and connected to the supply tube adapter. An airflow conduit passes through the supply tube adapter and extends into the spinning supply tube. The other end of the airflow conduit is connected to the outlet of the gas compressor. The other end of the spinning supply tube is sealed and connected to a metal micro-syringe needle as the filament outlet. The metal micro-syringe needle is connected to the cavity of the spinning supply tube.

[0032] In step 2), the process of using the dry spinning device to produce spinnable silica-based sol into fiber filaments is as follows: After pouring the spinnable silica-based sol into the spinning supply tube, the spinning supply tube is sealed. Compressed air is introduced into the spinning supply tube by a gas compressor. The gas pressure of the compressed air introduced by the gas compressor is used to squeeze the spinnable silica-based sol out from the needle of the metal micro-syringe to obtain fiber filaments. Then, the fiber filaments are threaded into an infrared heating box and dried by an infrared lamp in the infrared heating box. After the ends of the fiber filaments pass out of the infrared heating box, they are wound onto a take-up spool. The above process is repeated until all the spinnable silica-based sol in the spinning supply tube is squeezed out and all the fiber filaments are wound onto the take-up spool.

[0033] Specifically, in step 2), the gas pressure is 0.005 to 0.1 MPa, and the winding speed on the take-up drum is 25 to 200 r / min.

[0034] The method of the present invention can control the diameter of silicon carbide ceramic fibers. Specifically, the diameter of silicon carbide ceramic fibers can be controlled by adjusting parameters in the dry spinning process, such as the diameter of the spinning needle, the strength of the gas pressure provided by the gas compressor, and the rotation speed of the take-up drum.

[0035] The beneficial effects of this invention are as follows:

[0036] (1) This invention differs from the mainstream polycarbosilane precursor method for preparing silicon carbide ceramic fibers. It does not use polycarbosilane as a raw material, which greatly reduces the cost of raw materials. The method of this invention does not require a non-melting process, which shortens the preparation cycle and makes the process simpler. It is of great significance for the preparation of low-cost silicon carbide ceramic fibers.

[0037] (2) The present invention uses the sol-gel method to prepare a spinnable silica-based sol with excellent spinning performance. The composition of the spinnable silica-based sol is highly designable, the composition of the spinnable silica-based sol is easy to control, and the process is simple.

[0038] (3) The present invention combines the sol-gel method and dry spinning process to prepare silicon carbide ceramic fibers. The method of the present invention does not require non-melting treatment, and the diameter of silicon carbide ceramic fibers can be effectively controlled by improving the dry spinning process, forming silicon carbide ceramic fibers with good continuity and uniform diameter, which makes it easy to realize the large-scale preparation of silicon carbide ceramic fibers. Attached Figure Description

[0039] Figure 1 The dry spinning apparatus of the present invention;

[0040] Figure 2 The preparation process of the method of the present invention;

[0041] Figure 3 The image shows the actual silicon carbide ceramic fibers prepared in Example 1.

[0042] Figure 4 The image shows a scanning electron microscope (SEM) image of the silicon carbide ceramic fibers prepared in Example 1.

[0043] Figure 5 The image shows the X-ray diffraction (XRD) pattern of the silicon carbide ceramic fibers prepared in Example 1.

[0044] Among them, 1. supply tube support, 2. airflow duct, 3. supply tube adapter, 4. spinning supply tube, 5. spinning needle, 6. infrared drying lamp, 7. infrared heating box, 8. fiber filament, and 9. take-up drum. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0046] The process of the method of the present invention is as follows Figure 2 As shown, the specific steps include:

[0047] 1) Design a silica-based sol component with excellent spinning performance, and prepare a spinnable silica-based sol by using a spinning aid-assisted sol-gel method: After preparing the second silica-based sol, add a spinning aid to prepare a spinnable silica-based sol;

[0048] The second silica-based sol is prepared using deionized water, tetraethyl orthosilicate, sintering aid, supplementary carbon source, supplementary silicon source, and silicon carbide nanoparticle suspension as raw materials.

[0049] By mass fraction, the specific preparation process of the spinnable silica-based sol in this step is as follows:

[0050] 1.1) Add 10-30 parts of tetraethyl orthosilicate (TEOS) as a silicon source and 1-5 parts of sintering aid to 15-30 parts of deionized water, and stir until a clear and transparent first silicon-based sol is obtained.

[0051] The stirring time is 30 to 120 minutes.

[0052] The sintering aid is aluminum nitrate nonahydrate (Al(NO3)3·9H2O) particles.

[0053] 1.2) Add supplementary carbon source, supplementary silicon source, and 5-20 parts of silicon carbide (SiC) nanoparticle suspension to the first silicon-based sol, and stir to obtain the second silicon-based sol;

[0054] The stirring time is 20 to 60 minutes.

[0055] In the silicon carbide nanoparticle suspension, the mass fraction of silicon carbide nanoparticles is 2-10%, and the particle size is 200-500 nm.

[0056] Of which, by mass parts:

[0057] In step 1.2) above, for every 5-20 parts of silicon carbide nanoparticle suspension, by mass fraction: the supplementary carbon source is one or more of the following: 2-10 parts of sucrose, 2-10 parts of glucose, 2-15 parts of polyacrylonitrile, 5-20 parts of phenolic resin, and 2-10 parts of carbon (C) powder suspension, with the carbon powder having a mass fraction of 2-10% in the carbon powder suspension; the supplementary silicon source is 5-15 parts of methyltrimethoxysilane and / or 2-10 parts of silicon (Si) powder suspension with a mass fraction of 2-10%, with the silicon powder having a mass fraction of 2-10% in the silicon powder suspension.

[0058] Furthermore, supplementary carbon source, supplementary silicon source, and silicon carbide suspension are all necessary components. During the preparation process, without the addition of supplementary carbon source, supplementary silicon source, and silicon carbide suspension, silicon carbide fibers cannot be formed; instead, silicon oxide fibers or silicon carbide with low content and uncharacterizable composition will result.

[0059] 1.3) Add 0.5 to 5.5 parts of spinning aid to the second silica-based sol, stir, and prepare a spinnable silica-based sol;

[0060] The stirring time is 1 to 6 hours.

[0061] The viscosity of the spinnable silica-based sol is 100–200 Pa·s.

[0062] The spinning aid is polyethylene oxide (PEO).

[0063] Specifically, the viscosity of the spinnable silica sol is related to the amount of spinning aid added: the more spinning aid added, the higher the viscosity of the spinnable silica sol and the better the fiber continuity. In practice, the content of the spinning aid polyethylene oxide (PEO) should not be too high or too low, and the mass fraction of the spinning aid in the spinnable silica sol should be controlled between 5% and 12%. Otherwise, the spinnable silica sol will be too viscous to flow smoothly from the spinning needle, or too sparse to spin continuously.

[0064] 2) The spinnable silica-based sol is used to produce fiber filaments using a dry spinning process;

[0065] The specific process for preparing the fiber precursor is as follows: a spinnable silica-based sol is filled into the spinning supply tube 4, and the fiber precursor is obtained by extrusion, drying, and winding.

[0066] During the extrusion process, the gas pressure introduced into the spinning supply tube 4 must be continuously and stably controlled at 0.005 to 0.1 MPa, and the winding speed must be 25 to 200 r / min.

[0067] 3) The fiber filaments 8 collected on the take-up spool 9 are pyrolyzed at high temperature to remove the organic components in the fiber and transform it into inorganic ceramic fiber to obtain silicon carbon oxygen fiber.

[0068] The high-temperature pyrolysis process specifically involves placing the fiber filaments into a tube furnace for pyrolysis, heating them to 600℃~1200℃ at a heating rate of 2~5℃ / min under a protective gas, holding them at that temperature for 1~2 hours, and then cooling them down with the furnace.

[0069] Furthermore, after the fiber precursor is placed into the tube furnace, a vacuum pump is first used to perform vacuum treatment to prevent air from entering the furnace during the reaction and causing oxidation of the fiber; during the high-temperature pyrolysis process, the flow rate of the protective gas is 0–0.3 m / s. 3 / min.

[0070] 4) Silicon carbon oxygen fibers are sintered at high temperature to obtain silicon carbide ceramic fibers;

[0071] The high-temperature sintering process specifically involves placing silicon-carbon-oxygen fibers into a high-temperature sintering furnace for sintering. Under a protective gas, the temperature is increased to 1300–1900°C at a rate of 2–5°C / min, held at that temperature for 1–2 hours, and then cooled down with the furnace.

[0072] Furthermore, the preferred option is to raise the temperature to 1300–1800°C.

[0073] The gas pressure inside the high-temperature sintering furnace is 10. -3 ~10 -2 Pa is used to densify the fibers, forming a stable silicon carbide structure, thus preparing dense and uniform silicon carbide ceramic fibers.

[0074] The protective gases used in the above processes are argon or nitrogen.

[0075] In practice, the above-mentioned stirring process can all be carried out on a magnetic stirrer.

[0076] Furthermore, in step 2) above, the following method is used: Figure 1 The dry spinning apparatus shown produces fiber filaments from spinnable silica-based sol.

[0077] The dry spinning device includes a raw filament extrusion module, an infrared drying lamp 6, an infrared heating box 7, and a take-up spool 9. The raw filament extrusion module is connected to an external gas compressor. The raw filament extrusion module uses the gas pressure provided by the gas compressor to extrude the spinnable silica-based sol into fiber filaments 8. The infrared heating box 7 is arranged downstream of the raw filament extrusion module. The infrared heating box 7 has openings at both ends and infrared drying lamps 6 are arranged inside. The fiber filaments 8 pass through the infrared heating box 7 through the openings at both ends of the box. The take-up spool 9 for winding the fiber filaments 8 is arranged downstream of the infrared heating box 7.

[0078] The raw fiber extrusion module includes a supply tube support 1, an airflow conduit 2, a supply tube adapter 3, a spinning supply tube 4, and a metal micro-injector needle 5. The supply tube support 1 is placed on the operating table, and the spinning supply tube 4 is supported on top of the supply tube support 1. The cavity of the spinning supply tube 4 is filled with spinnable silica-based sol. One end of the spinning supply tube 4 is sealed and connected to the supply tube adapter 3. The airflow conduit 2 passes through the supply tube adapter 3 and extends into the cavity of the spinning supply tube 4. The other end of the airflow conduit 2 is connected to the outlet of the gas compressor. The other end of the spinning supply tube 4 is sealed and connected to the metal micro-injector needle 5 as the outlet of the fiber raw fiber 8. The metal micro-injector needle 5 is connected to the cavity of the spinning supply tube 4.

[0079] Specifically, the gas compressor introduces compressed air into the spinning supply tube 4. By controlling the gas pressure of the compressed air, the expulsion speed of the metal micro-syringe needle 5 can be controlled.

[0080] In step 2) above, the process of using a dry spinning device to produce fiber precursor 8 from spinnable silica sol is specifically as follows:

[0081] After the spinnable silica-based sol is poured into the spinning supply tube 4, the spinning supply tube 4 is sealed. Compressed air is introduced into the spinning supply tube 4 by a gas compressor. The gas pressure provided by the gas compressor forces the spinnable silica-based sol to be extruded from the needle 5 of a metal micro-syringe, obtaining fiber filaments 8. The fiber filaments 8 are then threaded into an infrared heating chamber 7 and dried in the infrared heating chamber 7 by an infrared drying lamp 6 to remove the solvent and solidify the fibers. After solidification and drying, the ends of the fiber filaments 8 are threaded out of the infrared heating chamber 7 and continuously wound onto a take-up spool 9. The above process is repeated until all the spinnable silica-based sol inside the spinning supply tube 4 is extruded and all the fiber filaments 8 are wound onto the take-up spool 9. Finally, the fiber filaments in a fixed shape are collected on the take-up spool 9.

[0082] This device utilizes the gas pressure provided by the gas compressor and the stretching effect of the take-up drum 9 to perform dry spinning of spinnable silica-based sol. Under the action of the infrared drying lamp 6 inside the infrared heating box 7, the solvent evaporates and the fiber solidifies. Finally, the fixed-shape fiber filaments 8 are collected on the take-up drum.

[0083] Specifically, the gas pressure applied by the gas compressor to the spinning supply pipe 4 needs to be continuous and stable, with a gas pressure of 0.005 to 0.1 MPa, which is conducive to forming fibers with uniform diameter and good continuity.

[0084] Specifically, the temperature in the infrared heating box 7 is 400-600℃, the length of the infrared heating box 7 (the length between the two ends of the opening) is preferably 60-100cm, and the winding speed of the take-up drum 9 is preferably 25-200r / min. This is conducive to the full evaporation of solvent in the fiber and avoids the phenomenon of yarn tangling at the take-up drum 9.

[0085] The silicon carbide ceramic fibers prepared by the method of the present invention are mainly composed of silicon carbide, and their diameter is 10-50 μm.

[0086] The embodiments of the present invention are as follows:

[0087] Example 1

[0088] 1) First, prepare the sol using the sol-gel method: Add 15g of deionized water and then 15g of tetraethyl orthosilicate (TEOS). After stirring evenly, add 1.5g of Al(NO3)3·9H2O and continue stirring. Then add 5g of sucrose and 10g of methyltrimethoxysilane. After stirring evenly, add 5g of silicon carbide (SiC) nanoparticle suspension with a mass fraction of 3% and a particle size of 200-500nm and 3g of polyacrylonitrile particles. Finally, add 2g of polyethylene oxide (PEO) particles to prepare a spinnable sol.

[0089] 2) Pour the spinnable sol into the spinning supply tube for dry spinning.

[0090] 3) Then, the fiber filaments collected on the take-up spool are placed in a tube furnace and heated at a heating rate of 2℃ / min, and kept at 1000℃ for 1 hour.

[0091] 4) Take out the pyrolyzed fibers and put them into a high-temperature sintering furnace for sintering. Increase the temperature to 1800℃ at a heating rate of 3℃ / min and hold for 2 hours. Then cool down with the furnace to obtain silicon carbide ceramic fibers.

[0092] The actual image of the obtained silicon carbide ceramic fiber is shown below. Figure 3 As shown. By Figure 3 It can be seen that the silicon carbide ceramic fibers obtained by using this invention have good continuity and are tightly wound. Its microstructure is as follows: Figure 4 As shown. By Figure 4 It can be seen that the silicon carbide ceramic fiber has a smooth surface with no obvious defects, making it an excellent silicon carbide ceramic fiber material. The XRD pattern of the obtained silicon carbide ceramic fiber is shown below. Figure 5 As shown. By Figure 5 It can be seen that the prepared silicon carbide ceramic fibers contain a 3C-SiC structure, which proves that the obtained fibers are silicon carbide ceramic fibers.

[0093] Example 2

[0094] 1) First, prepare the sol using the sol-gel method: Add 15g of deionized water, then add 15g of tetraethyl orthosilicate (TEOS) and stir until homogeneous. Add 1.5g of Al(NO3)3·9H2O and continue stirring. Then add 5g of glucose and 10g of methyltrimethoxysilane and stir until homogeneous. Add 3g of silicon carbide (SiC) nanoparticle suspension with a mass fraction of 3% and a particle size of 200-500nm, 6g of carbon (C) powder suspension with a mass fraction of 3%, 4g of silicon (Si) powder suspension with a mass fraction of 3%, and 5g of phenolic resin particles. Finally, add 2g of polyethylene oxide (PEO) particles to prepare a spinnable sol.

[0095] 2) Pour the spinnable sol into the spinning supply tube for dry spinning.

[0096] 3) Then, the fiber filaments collected on the take-up spool are placed in a tube furnace and heated at a heating rate of 2℃ / min, and kept at 1000℃ for 1 hour.

[0097] 4) Take out the pyrolyzed fibers and put them into a high-temperature sintering furnace for sintering. Increase the temperature to 1800℃ at a heating rate of 2℃ / min and hold for 2 hours. Then cool down with the furnace to obtain silicon carbide ceramic fibers.

[0098] Example 3

[0099] 1) First, prepare the sol using the sol-gel method: Add 15g of deionized water and then 15g of tetraethyl orthosilicate (TEOS). After stirring evenly, add 1.5g of Al(NO3)3·9H2O and continue stirring. Then add 10g of methyltrimethoxysilane and stir evenly. Add 7g of silicon carbide (SiC) nanoparticle suspension with a mass fraction of 3% and a particle size of 200-500nm and 10g of C powder suspension with a mass fraction of 3%. Finally, add 2g of polyethylene oxide (PEO) particles to prepare the spinnable sol.

[0100] 2) Pour the spinnable sol into the spinning supply tube for dry spinning.

[0101] 3) Then, the fiber filaments collected on the take-up spool are placed in a tube furnace and heated at a heating rate of 2℃ / min, and kept at 800℃ for 1 hour.

[0102] 4) Take out the pyrolyzed fibers and put them into a high-temperature sintering furnace for sintering. Increase the temperature to 1800℃ at a heating rate of 2℃ / min and hold for 2 hours. Then cool down with the furnace to obtain silicon carbide ceramic fibers.

[0103] All embodiments of the present invention employ the following methods: Figure 1 The dry spinning apparatus shown produces fiber precursors from spinnable silica-based sol. In various embodiments of the present invention, the resulting silicon carbide ceramic fibers exhibit no uneven thickness on the same fiber and can be continuously spun for 3-5 hours without fiber breakage, demonstrating good continuity and uniform diameter. In specific implementations, the fiber diameter is controlled by adjusting parameters in the dry spinning process, such as the diameter of the spinning needle, the strength of the gas pressure provided by the gas compressor, and the rotation speed of the take-up drum.

Claims

1. A method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning, characterized in that: The method specifically includes the following steps: 1) After preparing the second silica-based sol, a spinning aid is added to prepare a spinnable silica-based sol; The second silicon-based sol is prepared using deionized water, tetraethyl orthosilicate, sintering aid, supplementary carbon source, supplementary silicon source, and silicon carbide nanoparticle suspension as the main raw materials. Step 1) specifically comprises, by mass parts: 1.1) Add 10 to 30 parts of tetraethyl orthosilicate as a silicon source to 15 to 30 parts of deionized water, then add 1 to 5 parts of sintering aid and stir to obtain the first silicon-based sol. 1.2) Add supplementary carbon source, supplementary silicon source, and 5-20 parts of silicon carbide nanoparticle suspension to the first silicon-based sol, and stir to obtain the second silicon-based sol; In the silicon carbide nanoparticle suspension, the mass fraction of silicon carbide nanoparticles is 2-10%, and the particle size is 200-500 nm. 1.3) Add 0.5 to 5.5 parts of spinning aid to the second silica-based sol, stir, and obtain a spinnable silica-based sol. The viscosity of the spinnable silica-based sol is 100 to 200 Pa·S. 2) The spinnable silica-based sol is used to produce fiber filaments using a dry spinning process; 3) The fiber filaments are broken down into silicon-carbon-oxygen fibers; 4) Sinter silicon carbon oxygen fibers into silicon carbide ceramic fibers.

2. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 1, characterized in that: In step 1.1), the sintering aid is aluminum nitrate nonahydrate particles.

3. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 1, characterized in that: In step 1.2), by mass parts: The supplementary carbon source is one or more of the following: 2-10 parts sucrose, 2-10 parts glucose, 2-15 parts polyacrylonitrile, 5-20 parts phenolic resin, and 2-10 parts toner suspension, wherein the mass fraction of toner in the toner suspension is 2-10%. The supplementary silicon source is 5-15 parts of methyltrimethoxysilane and / or 2-10 parts of silicon powder suspension, wherein the mass fraction of silicon powder in the silicon powder suspension is 2-10%.

4. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 1, characterized in that: In step 1.3), the spinning aid is polyethylene oxide.

5. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 1, characterized in that: In step 3), the pyrolysis specifically involves heating to 600℃~1200℃ at a heating rate of 2~5℃ / min under a protective gas, holding at that temperature for 1~2 h, and then cooling down.

6. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 1, characterized in that: In step 4), sintering specifically involves heating to 1300-1900℃ at a heating rate of 2-5℃ / min under a protective gas, holding at that temperature for 1-2 hours, and then cooling down.

7. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 1, characterized in that: In step 2), a dry spinning device is used to produce fiber filaments from spinnable silica-based sol. The dry spinning device includes a raw filament extrusion module, an infrared drying lamp (6), an infrared heating box (7), and a take-up spool (9). The raw filament extrusion module is connected to an external gas compressor. The raw filament extrusion module uses the gas compressor to extrude spinnable silica-based sol into fiber raw filaments (8). An infrared heating box (7) is arranged downstream of the raw filament extrusion module. The infrared heating box (7) has openings at both ends and an infrared drying lamp (6) is arranged inside. A take-up spool (9) for winding the fiber raw filaments (8) is arranged downstream of the infrared heating box (7). The raw filament extrusion module includes a supply tube support (1), an airflow conduit (2), a supply tube adapter (3), a spinning supply tube (4), and a metal micro-injector needle (5). The supply tube support (1) is placed on the operating table, and the spinning supply tube (4) is supported above the supply tube support (1). The cavity of the spinning supply tube (4) is filled with spinnable silica-based sol. One end of the spinning supply tube (4) is sealed and connected to the supply tube adapter (3). The airflow conduit (2) is inserted through the supply tube adapter (3). One end of the airflow conduit (2) extends into the spinning supply tube (4), and the other end of the airflow conduit (2) is connected to the outlet of the gas compressor. The other end of the spinning supply tube (4) is sealed and connected to the metal micro-injector needle (5) as the outlet of the fiber raw filament (8).

8. The method for preparing silicon carbide ceramic fibers by combining sol-gel and dry spinning according to claim 7, characterized in that: In step 2), the process of using the dry spinning device to produce fiber precursors from spinnable silica sol (8) is specifically as follows: After the spinnable silica-based sol is poured into the spinning supply tube (4), the spinning supply tube (4) is sealed. The gas compressor introduces compressed air into the spinning supply tube (4). The gas pressure provided by the gas compressor is used to squeeze the spinnable silica-based sol out from the needle (5) of the metal micro-syringe to obtain the fiber filament (8). Then the fiber filament (8) is inserted into the infrared heating box (7) and dried in the infrared heating box (7) by the infrared drying lamp (6). The end of the fiber filament (8) is wound on the take-up drum (9) after it passes out of the infrared heating box (7). The gas pressure is 0.005~0.1MPa and the winding speed on the take-up drum (9) is 25~200 r / min.

Images