An airflow blowing device for SiOC precursor fibers and a method for preparing SiC nanofibers

Abstract

The present invention discloses an airflow spraying device for SiOC precursor fibers and a method for preparing SiC nanofibers. The device comprises: (1) an airflow spraying device, comprising an air inlet, an air jet, and a needle through-hole; (2) a liquid inlet device, wherein a liquid collecting tank is configured with compressed gas and an injection needle and is inserted into the airflow spraying device; and (3) a fiber collecting device based on hot airflow heating. The preparation method comprises: firstly, preparing a spinning solution with a certain viscosity, and then, by the push of compressed gas, flowing out from the needle tip, under the action of the high-speed airflow at the needle tip, the fine droplets are stretched and sprayed out as fibrous fine streams, which are sprayed into the fiber collecting device, and under the action of the upward hot airflow, the solvent evaporates, solidifies, and gathers upward to obtain polymer / SiO2 composite fibers, and then undergoes high-temperature cracking to obtain SiOC precursor fibers, and finally, undergoes in-situ growth by a high-temperature carbon thermal reduction method to obtain SiC nanofibers.

Description

Technical Field

[0001] The present invention belongs to the technical field of SiC nanofiber preparation, and in particular relates to an airflow blowing device for SiOC precursor fibers and a method for preparing SiC nanofibers. Background Art

[0002] SiC nanofibers possess excellent physical and chemical properties, including light weight, high-temperature resistance, high strength, high modulus, oxidation resistance, low thermal conductivity, and resistance to mechanical vibration. They are an important high-performance reinforcing ceramic fiber for metal- and ceramic-based composites, and have broad application prospects in industries such as machinery, metallurgy, chemicals, petroleum, ceramics, glass, and electronics. Therefore, the continuous production of large quantities of SiC nanofibers is of great significance to the application of ceramic fibers and the development of various industries.

[0003] Currently, there are many methods for preparing SiC nanofibers, including chemical vapor deposition, electrospinning, sol-gel method, precursor conversion method, etc.

[0004] Among many preparation methods, CVD is the earliest method for preparing SiC nanowires. This method involves vaporizing silicon and carbon sources at a specific pressure and temperature, and then transporting them to the substrate surface through a certain flow rate of carrier gas to form nuclei and grow SiC nanomaterials. The prepared SiC fibers have high purity, strong tensile strength and high bending strength, and have high strength and stability at high temperatures. The document "Continuous preparation of SiC nanowires by fluidized bed-chemical vapor deposition [J]. Journal of Ceramics, 2017, 38(03): 305-308" successfully prepared SiC nanofibers with a diameter of 50 to 100 nm and a length greater than 100 μm by fluidized bed chemical vapor deposition using methyltrichlorosilane as a precursor and ferrocene as a catalyst. The patent "A SiC nanowire and its preparation method and application" (patent number: CN201910903443.4) provides a method for preparing SiC nanowires by hot wire chemical vapor deposition using carbon-containing source gas and silicon-containing source gas. The precursor conversion method is also a currently used method for preparing SiC nanofibers. The patent "A Method for Preparing SiC Nanowires" (Patent No.: CN201410658149.9) uses polysiloxane as a silicon-containing polymer precursor and wood powder as a carbon source to synthesize SiC nanofibers through an in-situ reaction. In addition, the carbothermal reduction method is currently the main method for preparing SiC nanowires. The patent "A Method for Synthesizing β-SiC Nanowires" (Patent No.: CN200810150116.8) discloses a method for preparing β-SiC nanowires on the surface of bioactivated carbon sheets through a carbothermal reduction reaction at a temperature range of 1200-1400°C, using SiO generated by the high-temperature reaction of diatomaceous earth and silicon powder as a silicon source and bioactivated carbon sheets as a carbon source. The patent "A method for synthesizing β-SiC nanowires" (patent number: CN201210516420.6) uses Si powder, SiO2 powder and carbon nanotubes as raw materials, sintering them at 1200-1500°C, and then removing carbon and treating them with hydrofluoric acid to obtain β-SiC nanofibers.

[0005] However, there are still some problems in the preparation of the above nanofibers. For example, the fluidized bed CVD method for preparing SiC fibers contains a lot of impurities, and the cracking of the methyltrichlorosilane precursor raw material produces corrosive hydrogen chloride gas and flammable hydrogen byproducts; the conversion method using silicon-containing precursors is cumbersome, the precursor preparation time is long, the equipment cost is high, and the production level has not yet reached industrial scale; the traditional carbon thermal reduction method uses carbon powder as a carbon source, and the product contains a lot of silicon carbide particles, low purity, difficult atmosphere control, and poor reproducibility. In response to the above problems, the applicant has improved the preparation method and proposed a method for airflow blowing molding of SiOC precursor fibers and the preparation of SiC nanofibers. Summary of the Invention

[0006] In order to solve the problems existing in the background technology, the present invention proposes an air flow blowing device for SiOC precursor fibers and a method for preparing SiC nanofibers. The invention adopts a porous spinneret, so that the spinning liquid at the needle mouth is stretched to form a Taylor cone under the action of high-speed airflow at the needle tip, and is drawn out as a fibrous fine stream, which is sprayed into a fiber collection device. Under the action of the upward hot air flow, the solvent evaporates, solidifies and gathers upward to obtain polymer / SiO2 composite fibers, and then SiOC precursor fibers are obtained by high-temperature cracking. Finally, SiC nanofibers are obtained by high-temperature carbon thermal reduction.

[0007] The technical solutions disclosed in the present invention are as follows:

[0008] 1. An airflow blowing device for SiOC precursor fibers

[0009] The airflow blowing device comprises an air injection device, a liquid inlet device, and a heating and collecting device.

[0010] The jet device includes an air compressor, a porous spinneret and an air flow pipe. The air compressor is connected to the porous spinneret through the air flow pipe I. The porous spinneret includes an upper nozzle and a lower nozzle connected to each other. The upper nozzle and the lower nozzle are respectively provided with end covers with upper and lower protrusions. The upper and lower end covers are provided with multiple evenly distributed air flow holes. The lower nozzle is provided with an air jet port connected to the air flow pipe I.

[0011] The liquid inlet device includes an injection needle, a silicone hose, a liquid collecting tank, an airflow tube II and a compressed gas cylinder. The top of the liquid collecting tank is connected to the compressed gas cylinder through the airflow tube II. The bottom of the liquid collecting tank is provided with multiple connecting holes, each of which is connected to an injection needle through a silicone hose.

[0012] The heating and collecting device includes a cylindrical pipe, an infrared heating lamp and a wire mesh cover. The cylindrical pipe is connected from top to bottom, a plurality of infrared heating lamps are evenly distributed on the inner circumference of the cylindrical pipe, and a wire mesh cover is arranged on the top.

[0013] All injection needles are respectively inserted into the air flow holes of the lower nozzle from bottom to top, and then extended from the air flow holes of the upper nozzle.

[0014] The porous spinneret is located directly below the cylindrical pipe, and a wind shield is arranged around the porous spinneret.

[0015] The diameter of the end cap of the multi-hole spinneret is 100 mm, the number of air flow holes is 10 to 40, and the hole diameter is 2 mm; the distance between the upper nozzle end cap and the lower nozzle end cap is 20 to 50 mm;

[0016] The injection needle is 160 mm long, with an outer diameter of 0.9 mm and an inner diameter of 0.6 mm; the length of the injection needle extending from the air jet is 30 to 40 mm;

[0017] The inner diameter of the connecting hole at the bottom of the liquid collecting tank is 2mm;

[0018] The cylindrical pipe has a diameter of 20 to 40 cm and a height of 50 to 70 cm.

[0019] 2. Method for preparing SiC nanofibers using the above device

[0020] The following steps are involved:

[0021] Step 1) hydrolysis of the precursor solution: polyethylene glycol (PEO), tetraethyl orthosilicate (TEOS), deionized water, and phosphoric acid are mixed in a certain proportion and stirred to fully hydrolyze the mixed solution to obtain a homogeneous precursor spinning solution with drawing properties;

[0022] Step 2) Compressed gas-assisted liquid feeding: Use a silicone hose to connect the injection needle and the liquid collection tank, fill the liquid collection tank with the precursor spinning solution prepared in step 1), open the compressed gas cylinder, and under the action of the compressed gas, the liquid in the liquid collection tank flows out from the bottom connection hole and is transported to the injection needle through the gas flow tube II;

[0023] Step 3) High-speed airflow injection: All injection needles are inserted into the spinneret, and the spinneret is connected to an air compressor. The air compressor is turned on, and a high-speed airflow is ejected from the air flow holes from bottom to top after passing through the air jet. The spinning solution flowing out of the needle tip is stretched by the high-speed airflow to form liquid filaments that are ejected upwards.

[0024] Step 4) High-temperature drying: The liquid fibers ejected from step 3 enter a cylindrical tube, where they are dried at high temperatures and move upward under the action of high-speed airflow, gathering on the wire mesh cover at the top, thereby obtaining dry polymer / SiO2 fibers.

[0025] The solvent in the liquid filament evaporates under the action of hot air flow in the cylindrical tube;

[0026] Polymer / SiO2 fiber is a composite fiber of polyethylene glycol and SiO2;

[0027] Step 5) pyrolysis: the polymer / SiO2 fiber obtained in step 4 is pyrolyzed at high temperature to obtain SiOC precursor fiber;

[0028] Step 6) Preparation of SiC Fibers by Carbothermal Reduction: The SiOC precursor fibers obtained in step 5 are placed in an atmosphere furnace, and SiC nanofibers are grown in situ in the gas phase by carbothermal reduction at high temperature.

[0029] In the step 1):

[0030] The mass ratio of polyethylene glycol, deionized water and tetraethyl orthosilicate is 1:3-10:10-15; the amount of phosphoric acid added is 1-10 drops;

[0031] Stir at room temperature for 2 to 6 hours;

[0032] The viscosity of the precursor spinning solution is in the range of 70 to 100 mPa·s.

[0033] In the step 2), the flow rate of the precursor spinning solution is controlled to be 0.5-1.5 ml / min by adjusting the size of the compressed gas flow.

[0034] In the step 3), the high-speed airflow is delivered to the spinneret at a pressure of 5 to 7 kPa, and then ejected through the air flow holes of the spinneret.

[0035] In the step 4), the temperature in the cylindrical pipe is 400-500°C.

[0036] In the step 5), the temperature of the high temperature cracking is 800-1000° C. and the time is 1-2 hours.

[0037] In step 6), the atmosphere furnace heating rate is 5° C. / min, the reaction temperature is 1400-1650° C., the pressure in the furnace is 0.02-0.04 MPa, and the reaction time is 1-5 h.

[0038] The present invention proposes to obtain SiC nanofibers by obtaining a SiOC precursor through airflow blowing and high-temperature cracking and combining it with a high-temperature carbon thermal reduction method. The porous spinneret used in the present invention can greatly increase the efficiency of fiber preparation. Combined with the high-temperature carbon thermal reduction method, it can easily achieve the preparation of a large number of SiC nanofibers, and the obtained SiC fibers have the characteristics of high modulus and high strength. The present invention adopts SiOC precursor fibers, directly introduces silicon oxygen carbon components into the system, directly performs carbon thermal reduction at high temperature, and obtains SiC nanofibers by in-situ growth in the gas phase. Compared with the preparation method of traditional ceramic fibers, the present invention has the following technical advantages:

[0039] The present invention's preparation process is relatively simple, and the multi-hole spinneret significantly increases fiber production efficiency, facilitating the production of large quantities of precursor fibers. Furthermore, the present invention employs a method that first prepares fluffy SiOC precursor fibers, followed by high-temperature carbothermal reduction to obtain SiC ceramic fibers. The fluffy SiOC precursor fibers provide ample growth space for SiC nanofibers, resulting in high production yields and low costs. The resulting SiC nanofibers possess high strength and flexibility, and have broad application prospects in composite materials, refractory materials, thermal insulation, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the airflow blowing device

[0041] Figure 2 Schematic diagram of the jet device

[0042] Figure 3 Schematic diagram of the liquid inlet device

[0043] Figure 4 Schematic diagram of the heating and collection device

[0044] Figure 5 Schematic diagram of the multi-hole spinneret used in the present invention

[0045] Figure 6 Flow chart of the preparation process of SiOC precursor and SiC nanofibers

[0046] Figure 7 Digital photo of the blown fiber

[0047] Figure 8 SEM image of SiOC precursor fiber obtained after high-temperature pyrolysis of blown fiber

[0048] Figure 9 SEM images of SiC nanofibers obtained as examples of the present invention

[0049] In the figure: air compressor 1.1, multi-hole spinneret 1.2, air flow tube I 1.3; injection needle 2.1, silicone hose 2.2, liquid collecting tank 2.3, air flow tube II 2.4, compressed gas cylinder 2.5; cylindrical pipe 3.1, infrared heating lamp 3.2, collecting wire mesh cover 3.3, and sprayed fibers 3.4. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings and examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0051] like Figures 1 to 5 As shown, the device for airflow blowing fibers used in the present invention includes the following components:

[0052] An air jet device comprising an air compressor 1.1, a multi-hole spinneret 1.2, and an air flow duct 1.3;

[0053] Liquid inlet device, including injection needle 2.1, silicone hose 2.2, liquid collecting tank 2.3, air flow tube 2.4, compressed gas cylinder 2.5;

[0054] Heating and collecting device, cylindrical pipe 3.1, infrared heating lamp 3.2, collecting wire mesh cover 3.3, and blown fiber 3.4.

[0055] like Figure 6 As shown, the embodiments of the present invention are as follows:

[0056] Example 1

[0057] a. 1 g of polyethylene glycol (PEO) was dissolved in 10 g of deionized water, and then 10 g of tetraethyl orthosilicate (TEOS, 99%) and 1 drop of phosphoric acid were added to the PEO solution. The mixed solution was magnetically stirred at room temperature for 4 h to obtain a homogeneous precursor spinning solution.

[0058] b. Aspirate the precursor spinning solution into the injection needle tube, connect the injection needle with a silicone hose, and insert the needle into the spinneret. The needle model is 20G, and the syringe injection speed is set to 0.5ml / min.

[0059] c. Turn on the infrared heating lamp in the collecting device to maintain the temperature in the collecting device at about 500°C, and set up a wire mesh cover on the top of the collecting device for collecting fibers.

[0060] d. Connect the spinneret to the air compressor, turn on the air compressor switch and the airflow switch, maintain the gas pressure at 5kPa, and allow the high-speed airflow to draw the liquid at the needle mouth upward to form liquid filaments, and obtain dry polymer / SiO2 composite fibers at the top of the collection device.

[0061] e. The polymer / SiO2 composite fiber was placed in a muffle furnace and pyrolyzed at 700°C for 2 h at a heating rate of 5°C / min to obtain SiOC precursor fiber.

[0062] f. The SiOC precursor fiber was placed in an atmosphere furnace and subjected to a carbothermal reduction reaction at 1450°C for 5 h at a heating rate of 5°C / min to obtain SiC nanofibers.

[0063] The digital photo of the polymer / SiO2 fiber obtained by blowing in this embodiment is as follows Figure 7 As shown by Figure 7 From a and b in this embodiment, it can be seen that the fibers obtained by blowing are fluffy, large in quantity and volume. Figure 7 From the figures c and d, we can see that the precursor fibers obtained by spraying are about 0.8dm 3 It weighs only 4.00g in a small volume, and its fluffy volume provides sufficient growth space for the growth of SiC nanowires in the subsequent carbothermal reduction reaction.

[0064] Example 2

[0065] a. 1.5 g of polyethylene glycol (PEO) was dissolved in 15 g of deionized water, and then 15 g of tetraethyl orthosilicate (TEOS, 99%) and 2 drops of phosphoric acid were added to the PEO solution. The mixed solution was magnetically stirred at room temperature for 6 h to obtain a homogeneous precursor spinning solution.

[0066] b. Aspirate the precursor spinning solution into the injection needle tube, connect the injection needle with a silicone hose, and insert the needle into the spinneret. The needle model is 20G, and the syringe injection speed is set to 0.7ml / min.

[0067] c. Turn on the infrared heating lamp in the collecting device to maintain the temperature in the collecting device at about 500°C, and set up a wire mesh cover on the top of the collecting device for collecting fibers.

[0068] d. Connect the spinneret to the air compressor, turn on the air compressor switch and the airflow switch, maintain the gas pressure at 6kPa, and allow the high-speed airflow to draw the liquid at the needle mouth upward to form liquid filaments, and obtain dry polymer / SiO2 composite fibers at the top of the collection device.

[0069] e. The polymer / SiO2 composite fiber was placed in a muffle furnace and pyrolyzed at 600°C for 2h at a heating rate of 5°C / min to obtain SiOC precursor fiber.

[0070] f. The SiOC precursor fiber was placed in an atmosphere furnace and subjected to carbothermal reduction reaction at 1500°C for 4h at a heating rate of 5°C / min to obtain SiC nanofibers.

[0071] Example 3

[0072] a. 2 g of polyethylene glycol (PEO) was dissolved in 30 g of deionized water, and then 30 g of tetraethyl orthosilicate (TEOS, 99%) and 5 drops of phosphoric acid were added to the PEO solution. The mixed solution was magnetically stirred at room temperature for 6 h to obtain a homogeneous precursor spinning solution.

[0073] b. Aspirate the precursor spinning solution into the injection needle tube, connect the injection needle with a silicone hose, and insert the needle into the spinneret. The needle model is 20G, and the syringe injection speed is set to 1ml / min.

[0074] c. Turn on the infrared heating lamp in the collecting device to maintain the temperature in the collecting device at about 500°C, and set up a wire mesh cover on the top of the collecting device for collecting fibers.

[0075] d. Connect the spinneret to the air compressor, turn on the air compressor switch and the airflow switch, maintain the gas pressure at 7kPa, and allow the high-speed airflow to draw the liquid at the needle mouth upward to form liquid filaments, and obtain dry polymer / SiO2 composite fibers at the top of the collection device.

[0076] e. The polymer / SiO2 composite fiber was placed in a muffle furnace and pyrolyzed at 800°C for 1.5h at a heating rate of 5°C / min to obtain SiOC precursor fiber.

[0077] f. The SiOC precursor fiber was placed in an atmosphere furnace and subjected to a carbothermal reduction reaction at 1550°C for 6 h at a heating rate of 5°C / min to obtain SiC nanofibers.

[0078] The SEM image of the SiOC precursor fiber obtained after high-temperature pyrolysis of the blown fiber in this embodiment is shown in FIG. Figure 8 As shown by Figure 8 It can be seen that the original structure of the blown fiber is not destroyed after the cracking, and it still remains in a fibrous shape.

[0079] Example 4

[0080] a. 1 g of polyethylene glycol (PEO) was dissolved in 15 g of deionized water, and then 3 g of tetraethylorthosilicate (TEOS, 99%) and 1 drop of phosphoric acid were added to the PEO solution. The mixed solution was magnetically stirred at room temperature for 3 h to obtain a homogeneous precursor spinning solution.

[0081] b. Aspirate the precursor spinning solution into the injection needle tube, connect the injection needle with a silicone hose, and insert the needle into the spinneret. The needle model is 20G, and the syringe injection speed is set to 0.6ml / min.

[0082] c. Turn on the infrared heating lamp in the collecting device to maintain the temperature in the collecting device at about 500°C, and set up a wire mesh cover on the top of the collecting device for collecting fibers.

[0083] d. Connect the spinneret to the air compressor, turn on the air compressor switch and the airflow switch, maintain the gas pressure at 5kPa, and allow the high-speed airflow to draw the liquid at the needle mouth upward to form liquid filaments, and obtain dry polymer / SiO2 composite fibers at the top of the collection device.

[0084] e. The polymer / SiO2 composite fiber was placed in a muffle furnace and pyrolyzed at 500°C for 1.5h at a heating rate of 5°C / min to obtain SiOC precursor fiber.

[0085] f. The SiOC precursor fiber was placed in an atmosphere furnace and subjected to carbothermal reduction reaction at 1600°C for 4 h at a heating rate of 5°C / min to obtain SiC nanofibers.

[0086] The SEM images of the SiC nanowires prepared in this example are shown in FIG. Figure 9 As shown by Figure 9 It can be seen that the diameter of the prepared SiC fiber is at the nanometer level, the fiber is slender, and has a high aspect ratio.

Claims

1. A method for preparing SiC nanofibers, wherein the method uses an airflow blowing device for SiOC precursor fibers, including an air injection device, a liquid inlet device, and a heating and collecting device; The jet device comprises an air compressor (1.1), a porous spinneret (1.2) and an airflow pipe I (1.3); the air compressor (1.1) is connected to the porous spinneret (1.2) via the airflow pipe I (1.3); the porous spinneret (1.2) comprises an upper nozzle (1.21) and a lower nozzle (1.22) connected to each other; the upper nozzle (1.21) and the lower nozzle (1.22) are respectively provided with an upper convex end cap and a lower convex end cap; the upper and lower end caps are provided with a plurality of evenly distributed airflow holes (1.23); the lower nozzle (1.22) is provided with an air jet port connected to the airflow pipe I (1.3); The liquid inlet device comprises an injection needle (2.1), a silicone hose (2.2), a liquid collecting tank (2.3), an airflow tube II (2.4), and a compressed gas cylinder (2.5); the top of the liquid collecting tank (2.3) is connected to the compressed gas cylinder (2.5) via the airflow tube II (2.4); a plurality of connecting holes are provided at the bottom of the liquid collecting tank (2.3), and each connecting hole is connected to the injection needle (2.1) via the silicone hose (2.2); The heating and collecting device comprises a cylindrical pipe (3.1), an infrared heating lamp (3.2) and a wire mesh cover (3.3); the cylindrical pipe (3.1) is connected to each other from top to bottom; a plurality of infrared heating lamps (3.2) are evenly distributed on the inner circumference of the cylindrical pipe (3.1); and a wire mesh cover (3.3) is provided on the top; All injection needles (2.1) are inserted from bottom to top into the respective air flow holes (1.23) of the lower nozzle (1.22) of the porous spinneret (1.2), and then extend from the air flow holes (1.23) of the upper nozzle (1.21); the porous spinneret (1.2) is located directly below the cylindrical pipe (3.1); It is characterized by: The following steps are involved: Step 1) Hydrolysis of the precursor solution: polyethylene glycol, tetraethyl orthosilicate, deionized water, and phosphoric acid are mixed in a certain proportion and stirred to fully hydrolyze the mixed solution to obtain a homogeneous precursor spinning solution with drawing properties; Step 2) Compressed gas-assisted liquid feeding: Use a silicone hose to connect the injection needle (2.1) and the liquid collecting tank (2.3), and pour the precursor spinning solution prepared in step 1) into the liquid collecting tank (2.3). Open the compressed gas cylinder. Under the action of the compressed gas, the liquid in the liquid collecting tank (2.3) flows out from the bottom connection hole and is then transported to the injection needle (2.1) through the gas flow tube II. Step 3) High-speed airflow injection: All injection needles (2.1) are inserted into the spinneret, and the spinneret is connected to an air compressor. The air compressor is turned on, and a high-speed airflow is ejected from the air flow hole (1.23) from bottom to top after passing through the air jet. The spinning liquid flowing out of the needle tip of the injection needle (2.1) is stretched by the high-speed airflow to form liquid filaments that are ejected upwards; Step 4) High-temperature drying: The liquid fibers ejected in step 3 enter the cylindrical pipe (3.1), are dried at high temperature in the cylindrical pipe (3.1), and move upward under the action of high-speed airflow, and gather upward on the wire mesh cover (3.3) at the top, thereby obtaining dry polymer / SiO2 fibers; Step 5) Pyrolysis: The polymer / SiO2 fiber obtained in step 4 is pyrolyzed at high temperature to obtain SiOC precursor fiber; Step 6) Preparation of SiC Fibers by Carbothermal Reduction: The SiOC precursor fibers obtained in step 5 are placed in an atmosphere furnace and grown in situ in the gas phase by carbothermal reduction at high temperature to obtain SiC nanofibers.

2. The method for preparing SiC nanofibers according to claim 1, wherein The diameter of the end cap of the porous spinneret (1.2) is 100 mm, the number of the airflow holes (1.23) is 10 to 40, and the hole diameter is 2 mm; the distance between the end cap of the upper nozzle (1.21) and the end cap of the lower nozzle (1.22) is 20 to 50 mm; The injection needle (2.1) is 160 mm long, with an outer diameter of 0.9 mm and an inner diameter of 0.6 mm; the length of the injection needle (2.1) extending from the air jet outlet is 30 to 40 mm; The inner diameter of the connecting hole at the bottom of the liquid collecting tank (2.3) is 2 mm; The cylindrical pipe (3.1) has a diameter of 20-40 cm and a height of 50-70 cm.

3. The method for preparing SiC nanofibers according to claim 1, wherein In the step 1): The mass ratio of polyethylene glycol, deionized water and ethyl orthosilicate is 1:3~10:10~15; the amount of phosphoric acid added is 1~10 drops; Stir at room temperature for 2 to 6 h; The viscosity of the precursor spinning solution is in the range of 70~100 mPa·s.

4. The method for preparing SiC nanofibers according to claim 1, wherein In the step 2), the flow rate of the precursor spinning solution is controlled to be 0.5-1.5 ml / min by adjusting the size of the compressed gas flow.

5. The method for preparing SiC nanofibers according to claim 1, wherein In the step 3), the high-speed airflow is delivered to the spinneret at a pressure of 5-7 kPa, and then ejected through the air flow holes of the spinneret.

6. The method for preparing SiC nanofibers according to claim 1, wherein In the step 4), the temperature inside the cylindrical pipe (3.1) is 400-500°C.

7. The method for preparing SiC nanofibers according to claim 1, wherein In step 5), the high temperature cracking temperature is 800-1000° C. and the time is 1-2 hours.

8. The method for preparing SiC nanofibers according to claim 1, wherein In step 6), the atmosphere furnace heating rate is 5°C / min, the reaction temperature is 1400-1650°C, the pressure in the furnace is 0.02-0.04 MPa, and the reaction time is 1-5 hours.

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