A method for preparing a photo-curable rare earth doped low-oxygen silicon carbide fiber

Abstract

The application discloses a preparation method of a photocurable rare earth doped low-oxygen silicon carbide fiber, and comprises the following steps: preparing liquid sol A by taking a rare earth metal organic complex and polydimethylsilane as raw materials; obtaining a polycarbosilane precursor B containing a rare earth metal element by evaporating a solvent and high-temperature cracking reaction of the sol A; then preparing modified polycarbosilane by blending reaction of the polycarbosilane precursor B and an unsaturated organic ether; and then performing infusibilization treatment on the modified polycarbosilane by ultraviolet light irradiation under the action of a photoinitiator after melt spinning; and finally obtaining the rare earth doped low-oxygen silicon carbide fiber after high-temperature sintering treatment. f The rare earth element is introduced in the preparation of the precursor, and the rare earth element is uniformly dispersed in the silicon carbide crystal lattice, and the silicon carbide original wire is subjected to infusibilization crosslinking treatment by combining photo-curing, so that the crystal growth and electromagnetic properties of the ceramic can be better improved while the oxygen content of the silicon carbide fiber is reduced.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide fiber technology, and in particular to a method for preparing a photocurable rare earth element-doped low-oxygen silicon carbide fiber. Background Technology

[0002] Silicon carbide ceramic fiber (SiC) f Silicon carbide (SiC) is an advanced structural material primarily composed of carbon and silicon. Its superior mechanical properties and stability, such as high strength, high modulus, excellent oxidation resistance, and corrosion resistance, make it a key strategic material for ultra-high temperature structural components in high-end applications such as aerospace, aviation, military, and nuclear energy. Among the developed silicon carbide fiber preparation processes, the precursor preparation method is currently the most advanced industrial method for producing small-diameter SiC fibers. f The most commonly used and mature method involves precursor preparation, melt spinning, non-melting crosslinking treatment, and high-temperature sintering. However, in the non-melting treatment process of the precursor preparation method, if an economical air crosslinking method is used, a large amount of oxygen can easily be introduced. (SiC) f In SiCxOy, a large amount of oxygen exists in an amorphous state, which readily undergoes thermal decomposition at high temperatures, making SiC... f Performance degrades drastically at high temperatures. Improving the fiber non-melting process reduces SiC... f The oxygen content in SiC increases the efficiency of SiC production. f High-temperature performance is of great significance.

[0003] Rare earth elements are abundant and possess unique electronic structures and physicochemical properties in areas such as optics, electricity, magnetism, and thermodynamics, making them commonly used dopants in the development of various functional materials. In the preparation of SiC ceramics, rare earth oxides are often used as sintering aids, directly added to the raw materials to improve the sintering resistance and density of the ceramics. However, this physical addition makes it difficult to ensure uniform dispersion of the additives, resulting in limited modification of the electromagnetic properties of the ceramics. While chemical methods can dope rare earth elements and uniformly disperse them in the crystal lattice, current research on the preparation of rare earth-modified silicon carbide fibers using chemical doping methods is still relatively lacking. Furthermore, previous reports on the preparation of metal-doped SiC using chemical methods... f The crosslinking process is either difficult to control oxygen content or relies on equipment and instruments, so there is a need to develop simpler, cheaper and more efficient methods. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing photocurable rare-earth-doped low-oxygen silicon carbide fibers. This method involves introducing rare-earth elements into the precursor, allowing these elements to be uniformly dispersed within the silicon carbide lattice. A low-cost, high-efficiency photocuring process is then used to perform non-melting crosslinking treatment on the silicon carbide precursor fibers, thereby reducing the SiC content. fIn addition to increasing oxygen content, it can better improve the crystal growth and electromagnetic properties of ceramics.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: a method for preparing photocurable rare-earth-doped low-oxygen silicon carbide fiber, comprising the following steps:

[0006] Step 1, Preparation of rare earth-doped PCS:

[0007] Rare earth metal organic complexes and polydimethylsilane in a mass ratio of 1:30 to 200 are added to an organic solvent and mixed and reacted at 50°C for 2 to 5 hours under a protective atmosphere to obtain sol A with uniformly dispersed rare earth metal doped elements. Sol A is heated at 70 to 90°C to evaporate the organic solvent, and then subjected to a high-temperature pyrolysis and recombination reaction at 300 to 500°C under a high-purity nitrogen atmosphere to obtain polycarbosilane precursor B containing rare earth metal elements.

[0008] Step 2, unsaturated ether group modification:

[0009] The polycarbosilane precursor B obtained in step one was dissolved in an anhydrous organic solvent. Under ice-water bath conditions, a certain amount of organic sulfonyl chloride was added for chlorination treatment. After stirring for 5 to 20 minutes, unsaturated organic ether and triethylamine were added, and stirring was continued for 20 to 40 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Then, excess anhydrous organic solvent was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying.

[0010] Step 3, Preparation of silicon carbide fibers:

[0011] The modified polycarbosilane obtained in step two is placed in a melt spinning apparatus and melted and degassed at 200–400°C under a high-purity nitrogen atmosphere. Then, it is spun at a speed of 50–200 m / min under a pressure of 0.2–0.6 MPa to obtain the precursor fiber. The precursor fiber is immersed in a methanol solution containing a photoinitiator, removed and dried, and then subjected to a non-melting treatment for 0.5–5 h at 100–200°C and an ultraviolet light intensity of 2–15 mW / cm² under a protective atmosphere of nitrogen, argon or a mixture thereof to obtain non-melting fiber. Subsequently, the non-melting fiber is placed in a mixture of nitrogen, nitrogen and 1% hydrogen and sintered at a high temperature of 1200–1500°C in a high-temperature furnace for 1–6 h. After the reaction is completed, rare earth-doped low-oxygen silicon carbide fiber is obtained.

[0012] Furthermore, in step one, the mass ratio of the rare earth metal organic complex to polydimethylsilane is 1:50 to 150.

[0013] Furthermore, in step one, the mass ratio of the rare earth metal organic complex to the organic solvent is 1:100 to 1000.

[0014] Furthermore, in step one, the protective atmosphere is either high-purity argon or nitrogen; the rare earth metal organic complex includes rare earth acetylacetone compounds, rare earth oxalic acid compounds, and rare earth cyclopentadienyl compounds; the organic solvent is any one of benzene, xylene, dimethyl sulfoxide, N,N-dimethylformamide, dichloromethane, n-hexane, etc.

[0015] Furthermore, the rare earth organometallic compound is a rare earth acetylacetone compound, and the metals it contains are mainly yttrium, lanthanum, praseodymium, samarium, europium, erbium, ytterbium, cerium, etc.

[0016] Furthermore, the organic solvent is either xylene or N,N-dimethylformamide.

[0017] Furthermore, in step two, the mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is 1:0.1 to 0.5, and the molar ratio of the unsaturated organic sulfonyl chloride to triethylamine is 1:1 to 5.

[0018] Furthermore, the mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is 1:0.2 to 0.4; the molar ratio of the unsaturated organic sulfonyl chloride to triethylamine is 1:2 to 3.

[0019] Furthermore, the mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is 1:0.3 to 0.4.

[0020] Furthermore, in step two, the anhydrous organic solvent includes n-hexane, n-heptane, n-octane, etc.; the organic sulfonyl chloride includes thionyl chloride, methanesulfonyl chloride, chloroform sulfonyl chloride, toluenesulfonyl chloride, etc.; and the unsaturated organic ether includes ethylene glycol vinyl ether, diethylene glycol vinyl ether, ethylene glycol monoallyl ether, 4-hydroxybutyl vinyl ether, etc.

[0021] Furthermore, in step three, the photoinitiator is dissolved in a methanol solution, and the concentration of the photoinitiator is 0.5% to 2.5%.

[0022] Furthermore, in step three, the photoinitiator is one or two of benzophenone, 1-hydroxycycloethylphenyl ketone, bibenzoyl, and benzoyl derivative I-651.

[0023] After adopting the above scheme, the gain effect of the present invention is as follows:

[0024] This invention involves blending rare earth metal-organic complexes with polydimethylsilane to form a liquid sol A. Sol A undergoes solvent evaporation and a high-temperature reaction to yield a rare earth-doped polycarbosilane precursor B. Because the rare earth elements are uniformly dispersed in the sol, uniform doping of rare earth elements within the silicon carbide lattice can be achieved. Therefore, the doping content of rare earth elements can be adjusted by controlling the amount of rare earth metal-organic complexes used. Chemical doping of rare earth elements can hinder the migration of reactive ions and reduce the crystal migration rate, thereby regulating the growth of the silicon carbide lattice. Simultaneously, the rare earth dopant exists in oxide form at high temperatures, acting as a sintering aid to enable SiC sintering at lower temperatures, thus improving the SiC... f Sintering densifies SiC, enhancing its high-temperature stability; the unique electronic properties of rare earth elements can also alter SiC. f The dielectric properties of the fiber are SiC. f This provides possibilities for electromagnetic applications, expanding the application scope of SiC. f Scope of application.

[0025] This invention utilizes ultraviolet light irradiation for non-melting treatment. The equipment is simple and, compared to existing technologies, does not require expensive specialized equipment. The equipment is simple, easy to operate and control, and suitable for industrial production. It can effectively reduce costs and avoid increasing oxygen content, thus producing high-performance rare-earth modified silicon carbide fibers. Detailed Implementation

[0026] The present invention will be described in detail below with reference to specific embodiments.

[0027] This invention provides a method for preparing photocurable rare-earth-doped low-oxygen silicon carbide fibers, comprising the following steps:

[0028] Step 1, Preparation of rare earth-doped PCS:

[0029] Under the protection of high-purity argon or nitrogen, rare earth metal organic complexes and polydimethylsilane are added to an organic solvent at a mass ratio of 1:30-200, and the mixture is reacted at 50°C for 2-5 hours to obtain a sol A with uniformly dispersed rare earth metal doped elements. The mass ratio of the rare earth metal organic complex to the solvent is 1:100-1000. The rare earth metal organic complex includes rare earth acetylacetone compounds, rare earth oxalic acid compounds, and rare earth cyclopentadienyl compounds; in this embodiment, a rare earth acetylacetone compound is preferred. The metals contained are mainly yttrium, lanthanum, praseodymium, samarium, europium, erbium, ytterbium, cerium, etc. The organic solvent is benzene, xylene, dimethyl sulfoxide, N,N-dimethylformamide, dichloromethane, n-hexane, etc.; in this embodiment, xylene or N,N-dimethylformamide is preferred as the solvent. In this embodiment, the mass ratio of the rare earth metal organic complex to polydimethylsilane is preferably 1:50-150.

[0030] Sol A containing rare earth metal elements is heated at 70-90°C to evaporate the solvent. In this embodiment, the preferred heating temperature is 80°C. Subsequently, a high-temperature pyrolysis and recombination reaction is carried out at 300-500°C under a high-purity nitrogen atmosphere to obtain polycarbosilane precursor B containing rare earth metal elements.

[0031] Step 2, unsaturated ether group modification:

[0032] The rare earth metal-containing polycarbosilane precursor B obtained in step one was dissolved in an anhydrous organic solvent. Under ice-water bath conditions, a certain amount of organic sulfonyl chloride was added for chlorination. After stirring for 5–20 minutes, unsaturated organic ether and triethylamine were added, and stirring continued for 20–40 minutes. After the reaction was complete, ammonium salts and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Excess solvent was removed by vacuum distillation, and finally, the modified polycarbosilane was obtained by vacuum drying. (For parts not described in this step, existing methods can be followed; see Ceramics for synthesis reference.) International, 2020, 46, 28300-28307; Patent Publication No.: CN110204730A); wherein, the organic sulfonyl chloride includes thionyl chloride, methanesulfonyl chloride, chloroform sulfonyl chloride, toluenesulfonyl chloride, etc., and the mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is 1:0.1-0.5; the unsaturated organic ether includes ethylene glycol vinyl ether, diethylene glycol vinyl ether, ethylene glycol monoallyl ether, 4-hydroxybutyl vinyl ether, etc., and the polycarbosilane precursor B... The mass ratio of the unsaturated organic ether to the anhydrous organic solvent is 1:0.2-0.5; the anhydrous organic solvent includes n-hexane, n-heptane, n-octane, etc.; the molar ratio of the unsaturated organic sulfonyl chloride to triethylamine is 1:1-5; in this embodiment, the mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is preferably 1:0.2-0.4; in this embodiment, the mass ratio of the polycarbosilane precursor B to the unsaturated organic ether is preferably 1:0.3-0.4; in this embodiment, the molar ratio of the unsaturated organic sulfonyl chloride to triethylamine is preferably 1:2-3.

[0033] Step 3, Preparation of silicon carbide fibers:

[0034] The modified polycarbosilane obtained in step two is placed in a melt spinning apparatus and melted and degassed at 200–400°C under high-purity nitrogen protection. Then, it is spun at 50–200 m / min under a pressure of 0.2–0.6 MPa to obtain precursor fibers. The precursor fibers are then immersed in a methanol solution containing a photoinitiator at a concentration of 0.5–2.5%. After drying, the fibers are subjected to a non-melting treatment at 100–200°C under ultraviolet light irradiation at an intensity of 2–15 mW / cm² for 0.5–5 hours to obtain non-melting fibers. Subsequently, the non-melting fibers are placed in a protective atmosphere of nitrogen, nitrogen, and a mixture of nitrogen and 1% hydrogen and sintered at 1200–1500°C in a high-temperature furnace for 1–6 hours. Once the reaction is complete, rare-earth-doped low-oxygen silicon carbide fibers are obtained.

[0035] The photoinitiator is one or two of benzophenone, 1-hydroxycycloethylphenyl ketone, bibenzoyl, and benzoyl derivative I-651.

[0036] The method for preparing rare-earth-doped low-oxygen silicon carbide fibers provided by this invention involves blending rare-earth metal organic complexes with polydimethylsilane to form a liquid sol A. Sol A undergoes solvent evaporation and high-temperature reaction to obtain a rare-earth-doped polycarbosilane precursor B. Precursor B is then chlorinated with an unsaturated organic ether to introduce crosslinkable unsaturated ether groups into the precursor's branches. After melt spinning, the precursor undergoes non-melting treatment under ultraviolet irradiation with a photoinitiator. Compared to existing technologies that involve blending polycarbosilane and unsaturated silazane to introduce vinyl groups, followed by two-step curing processes including photoinitiator spraying, ultraviolet pre-curing, and heat treatment, this invention offers a shorter photocuring time, simpler equipment, and easier operation and control. The resulting high-performance rare-earth-modified silicon carbide fibers have rare-earth metals uniformly doped in the crystal lattice and low oxygen content, effectively controlling the crystal growth of silicon carbide fibers and improving their photoelectric and mechanical properties.

[0037] Example 1

[0038] 40g of yttrium acetylacetonate and 4kg of polydimethylsilane were dissolved in 25L of N,N-dimethylformamide solution and heated at 50°C for 3h under a nitrogen atmosphere to obtain a sol with uniformly dispersed rare earth metal doped elements. The sol was then heated at 80°C to evaporate the solvent, dried, and placed in a reactor for high-temperature pyrolysis and recombination at 350°C under a high-purity nitrogen atmosphere to obtain a yttrium-doped polycarbosilane precursor.

[0039] 2 kg of yttrium-doped polycarbosilane was dissolved in 15 L of n-hexane solution. Under ice-water bath conditions, 400 g of thionyl chloride was added for chlorination. After stirring for 10 minutes, 600 g of ethylene glycol ether and 800 g of triethylamine were added and stirred for 30 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Excess n-hexane was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying.

[0040] 1 kg of modified polycarbosilane was placed in a melt spinning apparatus under high-purity nitrogen protection. After melting and degassing at 350°C, the precursor fiber was spun at 100 m / min under a pressure of 0.5 MPa. The precursor fiber was then immersed in a methanol solution containing 1% benzophenone and benzoyl derivative I-651. After drying, it was spun under a nitrogen atmosphere at 10 mW / cm². 2 Infusible fibers were obtained by infusing at 200℃ for 2 hours under ultraviolet light irradiation. These fibers were then subjected to a pyrolysis reaction in a furnace at 1300℃ for 3 hours in a mixture of nitrogen and 1% hydrogen. The resulting yttrium-doped low-oxygen silicon carbide fiber had a doping content of 1% yttrium, an oxygen content of 1.5%, a strength of 2.8 GPa at room temperature, an elastic modulus of 260 GPa, and a volume resistivity of approximately 3.6 KΩ / cm.

[0041] Example 2

[0042] 60g of yttrium acetylacetone and 4.8kg of polydimethylsilane were dissolved in 30L of xylene solution and heated at 50°C for 3 hours under a nitrogen atmosphere to obtain a sol with uniformly dispersed rare earth metal doping elements. The sol was then heated at 80°C to evaporate the solvent, dried, and placed in a reactor for high-temperature pyrolysis and recombination at 450°C under a high-purity nitrogen atmosphere to obtain a yttrium-doped polycarbosilane precursor.

[0043] 2 kg of yttrium-doped polycarbosilane was dissolved in 20 L of n-hexane solution. Under ice-water bath conditions, 800 g of toluenesulfonyl chloride was added for chlorination. After stirring for 10 minutes, 600 g of ethylene glycol ether and 800 g of triethylamine were added and stirred for 30 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Excess n-hexane was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying.

[0044] 1 kg of modified polycarbosilane was placed in a melt spinning apparatus under high-purity nitrogen protection. After melting and degassing at 350°C, the precursor fiber was spun at 100 m / min under a pressure of 0.5 MPa. The precursor fiber was then immersed in a methanol solution containing 2% 1-hydroxycycloethylphenyl ketone, dried, and then spun under a nitrogen atmosphere at 10 mW / cm². 2Infusible fibers were obtained by infusing at 200℃ for 2 hours under ultraviolet light irradiation. These fibers were then subjected to a pyrolysis reaction in a furnace at 1300℃ for 3 hours in a mixture of nitrogen and 1% hydrogen. The resulting yttrium-doped low-oxygen silicon carbide fiber had a doping content of 1.4% yttrium, an oxygen content of 1.8%, a strength of 2.5 GPa at room temperature, an elastic modulus of 245 GPa, and a volume resistivity of approximately 2.9 KΩ / cm.

[0045] Example 3

[0046] 60g of cerium acetylacetone and 6kg of polydimethylsilane were dissolved in 30L of xylene solution and heated at 50°C for 3 hours under a nitrogen atmosphere to obtain a sol with uniformly dispersed rare earth metal doped elements. The sol was then heated at 80°C to evaporate the solvent, dried, and placed in a reactor for high-temperature pyrolysis and recombination at 450°C under a high-purity nitrogen atmosphere to obtain a cerium-doped polycarbosilane precursor.

[0047] 2 kg of cerium-doped polycarbosilane was dissolved in 20 L of n-octane solution. Under ice-water bath conditions, 400 g of thionyl chloride was added for chlorination. After stirring for 10 minutes, 700 g of 4-hydroxybutylvinyl ether and 1.4 kg of triethylamine were added and stirred for 30 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Excess n-hexane was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying.

[0048] 1 kg of modified polycarbosilane was placed in a melt spinning apparatus under high-purity nitrogen protection. After melting and degassing at 350°C, the precursor fiber was spun at 150 m / min under a pressure of 0.5 MPa. The precursor fiber was then immersed in a methanol solution containing 2% 1-hydroxycycloethylphenyl ketone, dried, and then spun under a nitrogen atmosphere at 15 mW / cm². 2 Infusible fibers were obtained by infusing at 200℃ for 1 hour under ultraviolet light irradiation. These fibers were then subjected to a pyrolysis reaction in a nitrogen and 1% hydrogen mixture in a furnace at 1350℃ for 5 hours. The resulting cerium-doped low-oxygen silicon carbide fiber exhibited a yttrium content of 1.42%, an oxygen content of 1.3%, a strength of 2.6 GPa at room temperature, an elastic modulus of 270 GPa, and a volume resistivity of approximately 3.3 KΩ / cm.

[0049] Example 4

[0050] 45g of cerium acetylacetone and 6kg of polydimethylsilane were dissolved in 30L of xylene solution and heated at 50°C for 3 hours under a nitrogen atmosphere to obtain a sol with uniformly dispersed rare earth metal doping elements. The sol was then heated at 80°C to evaporate the solvent, dried, and placed in a reactor for high-temperature pyrolysis and recombination at 450°C under a high-purity nitrogen atmosphere to obtain a cerium-doped polycarbosilane precursor.

[0051] 2 kg of cerium-doped polycarbosilane was dissolved in 20 L of n-octane solution. Under ice-water bath conditions, 400 g of thionyl chloride was added for chlorination. After stirring for 10 minutes, 700 g of 4-hydroxybutylvinyl ether and 1.4 kg of triethylamine were added and stirred for 30 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Excess n-hexane was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying.

[0052] 1 kg of modified polycarbosilane was placed in a melt spinning apparatus under high-purity nitrogen protection. After melting and degassing at 350°C, the precursor fiber was spun at 150 m / min under a pressure of 0.5 MPa. The precursor fiber was then immersed in a methanol solution containing 2% 1-hydroxycycloethylphenyl ketone, dried, and then spun under a nitrogen atmosphere at 15 mW / cm². 2 Infusible fibers were obtained by infusing at 200℃ for 1 hour under ultraviolet light irradiation. These fibers were then subjected to a pyrolysis reaction in a furnace at 1350℃ for 5 hours in a mixture of nitrogen and 1% hydrogen. The resulting cerium-doped low-oxygen silicon carbide fiber had a yttrium content of 1.0%, an oxygen content of 1.1%, a strength of 2.7 GPa at room temperature, an elastic modulus of 280 GPa, and a volume resistivity of approximately 3.2 KΩ / cm.

[0053] Comparative Example 1

[0054] 27g of titanium acetylacetone and 6kg of polydimethylsilane were dissolved in 30L of xylene solution and heated and mixed at 50°C for 3h under a nitrogen atmosphere to obtain a sol with uniform dispersion of titanium doping elements. The solution sol was then heated at 80°C to evaporate the solvent, dried, and placed in a reactor for high-temperature pyrolysis and recombination reaction at 450°C under a high-purity nitrogen atmosphere to obtain a titanium-doped polycarbosilane precursor.

[0055] 2 kg of the prepared titanium-doped polycarbosilane was dissolved in 20 L of n-octane solution. Under ice-water bath conditions, 400 g of thionyl chloride was added for chlorination treatment. After stirring for 10 minutes, 700 g of 4-hydroxybutylvinyl ether and 1.4 kg of triethylamine were added and stirred for 30 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Excess n-octane was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying.

[0056] 1 kg of modified polycarbosilane was placed in a melt spinning apparatus under high-purity nitrogen protection. After melting and degassing at 350°C, the precursor fiber was spun at 150 m / min under a pressure of 0.5 MPa. The precursor fiber was then immersed in a methanol solution containing 2% 1-hydroxycycloethylphenyl ketone, dried, and then spun under a nitrogen atmosphere at 15 mW / cm². 2 Infusible fibers were obtained by infusing at 200℃ for 1 hour under ultraviolet light irradiation. These fibers were then subjected to a pyrolysis reaction in a furnace at 1350℃ for 5 hours in a mixture of nitrogen and 1% hydrogen. The resulting titanium-doped silicon carbide fiber contained 1.1% titanium and 2.1% oxygen. It exhibited a strength of 2.3 GPa at room temperature, an elastic modulus of 250 GPa, and a volume resistivity of approximately 3.8 KΩ / cm.

[0057] The performance of the doped silicon carbide fibers prepared in Examples 1-4 and Comparative Example 1 of this invention was tested, and the test results are shown in Table 1.

[0058] Table 1 shows the performance parameters of the doped silicon carbide fibers in Examples 1-4 and Comparative Example 1.

[0059]

[0060] As shown in the table above, this invention achieves the molecular-level introduction of rare earth metals into polycarbosilane through the sol-gel formation of rare earth complexes and polydimethylsilane. This results in a uniform distribution and controllable content of rare earth elements in silicon carbide fibers. Furthermore, the introduction of highly active unsaturated ether groups capable of crosslinking into the rare earth-containing polycarbosilane branches enables low-temperature photocuring of silicon carbide precursor fibers. This keeps the oxygen content in the fibers below 2%, and the abundant rare earth doping elements effectively regulate the crystal growth of silicon carbide fibers, improving their photoelectric and mechanical properties. This photocuring crosslinking treatment avoids the problems of increased oxygen content and high costs caused by high-energy electron or radiation radiation during the air heat treatment curing process of traditional metal-doped precursor fibers.

[0061] In addition, the high-temperature pyrolysis process of the precursor fiber uses 1% hydrogen to promote the reduction and decomposition of introduced organic components, further controlling the carbon and oxygen content in the product. This method is simple to operate, requires minimal equipment, and is suitable for the industrial continuous production of low-oxygen-content, high-performance continuous silicon carbide fibers.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design features of this case shall fall within the protection scope of this case.

Claims

1. A method for preparing photocurable rare-earth-doped low-oxygen silicon carbide fiber, characterized in that: Includes the following steps: Step 1, Preparation of rare earth-doped PCS: Rare earth metal organic complexes and polydimethylsilane in a mass ratio of 1:30 to 200 are added to an organic solvent and mixed and reacted at 50°C for 2 to 5 hours under a protective atmosphere to obtain a sol A with uniformly dispersed rare earth metal doped elements. The sol A is heated at 70 to 90°C to evaporate the organic solvent, and then subjected to a high-temperature pyrolysis and recombination reaction at 300 to 500°C under a high-purity nitrogen atmosphere to obtain a polycarbosilane precursor B containing rare earth metal elements. The rare earth metal organic complex is a rare earth acetylacetone compound containing metals such as yttrium, lanthanum, praseodymium, samarium, europium, erbium, ytterbium, and cerium. Step 2, unsaturated ether group modification: The polycarbosilane precursor B obtained in step one was dissolved in an anhydrous organic solvent. Under ice-water bath conditions, a certain amount of organic sulfonyl chloride was added for chlorination treatment. After stirring for 5 to 20 minutes, unsaturated organic ether and triethylamine were added, and stirring was continued for 20 to 40 minutes. After the reaction was completed, ammonium salt and excess raw materials were removed by high-speed centrifugation and acetonitrile extraction. Then, excess anhydrous organic solvent was removed by vacuum distillation. Finally, the modified polycarbosilane was obtained by vacuum drying. Step 3, Preparation of silicon carbide fibers: The modified polycarbosilane obtained in step two is placed in a melt spinning apparatus and melted and degassed at 200–400°C under a high-purity nitrogen atmosphere. Then, it is spun into precursor fibers at a pressure of 0.2–0.6 MPa and a speed of 50–200 m / min. The precursor fibers are then immersed in a methanol solution containing a photoinitiator, dried, and then irradiated at 100–200°C under a protective atmosphere of nitrogen, argon, or a mixture thereof, with an ultraviolet light intensity of 2–15 mW / cm². 2 The fibers are subjected to non-melting treatment under irradiation for 0.5–5 hours to obtain non-melting fibers. Then, the non-melting fibers are placed in a mixture of nitrogen, nitrogen and 1% hydrogen and sintered at high temperature in a furnace at 1200–1500℃ for 1–6 hours. After the reaction is completed, rare earth doped low oxygen silicon carbide fibers can be obtained.

2. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: In step one, the mass ratio of the rare earth metal organic complex to polydimethylsilane is 1:50 to 150.

3. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: In step one, the mass ratio of the rare earth metal organic complex to the organic solvent is 1:100 to 1000.

4. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: In step one, the protective atmosphere is either high-purity argon or nitrogen; the organic solvent is any one of benzene, xylene, dimethyl sulfoxide, N,N-dimethylformamide, dichloromethane, or n-hexane.

5. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: The organic solvent is either xylene or N,N-dimethylformamide.

6. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: In step two, the mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is 1:0.1 to 0.

5.

7. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: The mass ratio of the polycarbosilane precursor B to the organic sulfonyl chloride is 1:0.2 to 0.

4.

8. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: In step two, the anhydrous organic solvent includes n-hexane, n-heptane, and n-octane; the organic sulfonyl chloride includes sulfoxide, methanesulfonyl chloride, chloroform sulfonyl chloride, and toluenesulfonyl chloride; and the unsaturated organic ether includes ethylene glycol vinyl ether, diethylene glycol vinyl ether, ethylene glycol monoallyl ether, and 4-hydroxybutyl vinyl ether.

9. The method for preparing a photocurable rare-earth-doped low-oxygen silicon carbide fiber as described in claim 1, characterized in that: In step three, a photoinitiator with a concentration of 0.5% to 2.5% is dissolved in a methanol solution.

Images