A method for preparing near-stoichiometric ZrB2-doped SiC fibers

Abstract

This invention discloses a method for preparing ZrB2-doped SiC fibers with near-stoichiometric ratios. The method involves configuring a zirconium-containing multiphase ceramic precursor (PZMS) with polymethylsilane (PMS) to form a PZMS / PMS mixed precursor, which is then blended with spinning-grade polycarbosilane (PCS) to obtain a mixed precursor. This precursor is then subjected to a series of processes including melt spinning, electron beam / BCl3 crosslinking-heat treatment, high-temperature hydrogen pyrolysis, and high-temperature sintering to obtain ZrB2-doped silicon carbide fibers with a near-ideal C / Si atomic ratio, thus achieving control over the fiber composition.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide fiber technology, specifically to a method for preparing near-stoichiometric ZrB2-doped SiC fibers. Background Technology

[0002] The rapid development of modern aerospace technology is driving modern aircraft towards higher speeds and greater safety, which places higher demands on materials used in aircraft nose cones, wing leading edges, engine nozzles, and hot sections. Ultra-high temperature ceramic materials and their composites, due to their excellent properties such as high temperature resistance (>2000℃), oxidation resistance, erosion resistance, and thermal shock resistance, have become ideal candidate materials for these components.

[0003] ZrB2 ceramic, as one of the ultra-high temperature ceramic materials, not only has a high melting point (>3000℃) but also a low density (6.09 g / cm³). 3 ZirB2 ceramics possess high hardness, high modulus, high thermal conductivity, high electrical conductivity, and good chemical stability; however, their poor thermal shock resistance limits their use as key structural components. Currently, research on ZrB2 ceramics by scholars both domestically and internationally mainly focuses on ZrB2 ceramic powders, bulk materials, and ZrB2-based ceramic composites, with relatively little research on ZrB2 ceramic fibers. At present, research on zirconium-containing silicon carbide fibers and zirconium-boron-containing silicon carbide fibers in my country remains limited, with only second-generation products achieving mass production. The urgent need is to find superior methods for preparing silicon carbide fibers, improve their oxidation resistance and creep resistance under high-temperature conditions, and prepare high-performance third-generation zirconium-containing silicon carbide fibers or zirconium-boron-containing silicon carbide fibers that can be industrially produced. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing near-stoichiometric ZrB2-doped SiC fibers. The introduction of ZrB2 to dope silicon carbide fibers significantly improves their high-temperature resistance and oxidation resistance, enabling them to maintain excellent performance under extreme high-temperature and strong oxidizing environments.

[0005] To achieve the above objectives, the solution of the present invention is: A method for preparing near-stoichiometric ZrB2-doped SiC fibers includes the following steps: Step 1: Under nitrogen protection, PCS is processed using a normal pressure and high temperature method to obtain refined PCS. Step 2: Then, under nitrogen protection, zirconium-containing multiphase ceramic precursor (PZMS) and polymethylsilane (PMS) are dissolved in xylene at 80~100℃. After being stirred thoroughly, the insoluble matter is removed by filtration, and then the xylene is removed by vacuum drying to obtain refined PZMS / PMS mixed precursor. Step 3: Then, under nitrogen protection, the refined PZMS / PMS mixed precursor and refined PCS are placed in a melt spinning machine according to the ratio, heated to 240~250℃, melted and stirred evenly, and kept for 12~18 h for degassing and small molecule removal treatment. Then, the temperature is reduced to 160~170℃ and kept warm. The molten melt is spun through a spinneret and wound by a winding machine to obtain zirconium-containing polycarbosilane precursor. Step 4: Then, the zirconium-containing polycarbosilane precursor is subjected to non-melting treatment using an electron beam / BCl3 cross-linking-heat treatment method. Boron is introduced into the zirconium-containing polycarbosilane precursor. At high temperature, boron reacts with zirconium to transform into SiC-ZrB2 nano-composite ceramic fibers, thus obtaining ZrB2-doped polycarbosilane cross-linked fibers. Step 5: Then, under a hydrogen atmosphere, the ZrB2-doped polycarbosilane crosslinked wire is subjected to high-temperature pyrolysis to obtain polycarbosilane pyrolysis wire. Step 6: Finally, under argon protection, tension is applied to the polysilane pyrolysis wire, and high-temperature sintering is performed to obtain near-stoichiometric ZrB2-doped SiC fibers, wherein the ZrB2 content accounts for 1.0% of the mass of the silicon carbide fiber. wt %~5.0 wt %.

[0006] In step 1, the process of the atmospheric pressure high temperature method is as follows: PCS is dissolved in xylene or toluene, and macromolecular insoluble substances are removed by filtration to obtain a PCS mixture. Then, the mixture is transferred to a three-necked flask and heated to 160°C by a salt bath. After the xylene or toluene is evaporated to dryness, the temperature is slowly raised to 240~260°C and kept at that temperature for 4~6 hours. The mixture is then cooled to room temperature to obtain purified PCS.

[0007] In step 2, the mass ratio of PZMS to PMS is 1:5 to 1:8.

[0008] In step 3, the mass ratio of refined PZMS / PMS mixed precursor to refined PCS is 1:3 to 1:8.

[0009] In step 3, the temperature of the spinneret is 160~170℃, the spinneret pressure is 0.4~0.5 MPa, and the spinneret orifice diameter is 0.3~0.4 mm.

[0010] In step 4, the electron beam / BCl3 crosslinking-heat treatment method is as follows: evacuate and replace with high-purity nitrogen three times, irradiate the zirconium-containing polycarbosilane precursor fiber with an irradiation dose of 10~12 mGy for 12 h to cause crosslinking of the fiber precursor fiber, then introduce BCl3 gas with a concentration of 3% and allow it to react for 6~12 h; subsequently, heat treat the zirconium-containing polycarbosilane precursor fiber in an inert atmosphere at 340~360℃ for 1 h to complete the annealing, so that the Si free radical deactivated fiber is completely transformed into a stable non-fusible network structure, and then cool to room temperature to obtain ZrB2-doped polycarbosilane crosslinked fiber.

[0011] In step 5, the high-temperature pyrolysis decarburization process is as follows: ZrB2-doped polycarbosilane crosslinked fibers are placed on a quartz boat and then placed inside a quartz tube. A tension of 0.45~0.5 N is applied to the polycarbosilane crosslinked fibers, a vacuum is drawn, nitrogen is replaced three times to remove air and impurities from the quartz tube, and then hydrogen is introduced at a flow rate of 4~6 L / min. The temperature is raised to 800℃ at a rate of 100~200℃ / h and held for 10 min. Then, the temperature is raised to 1250~1350℃ at a rate of 3℃ / min and held for 30~60 min to further densify the fibers. Finally, the fibers are cooled to room temperature inside the quartz tube to obtain polycarbosilane pyrolysis fibers. By changing the hydrogen concentration and sintering temperature during the fiber pyrolysis process, ceramic fibers with different carbon contents can be prepared so that the fiber composition is close to the stoichiometric ratio of silicon carbide.

[0012] In step 6, the high-temperature sintering process is as follows: vacuum is drawn and replaced three times with high-purity argon gas. The polycarbosilane pyrolysis wire is placed in a graphite sintering furnace, a tension of 0.45~0.5 N is applied, and the temperature is raised to 1700~1800℃ at a heating rate of 200~300℃ / h. The temperature is held for 10~30 min to perform sintering treatment, thereby obtaining dense near-stoichiometric SiC fibers doped with ZrB2.

[0013] The precursor conversion method for preparing SiC fibers mainly involves three key processes: (1) precursor synthesis; (2) precursor spinning and processing technology; and (3) crosslinking and firing of the precursor fibers.

[0014] After adopting the above technical solution, the method for preparing near-stoichiometric ZrB2-doped SiC fibers of the present invention has the following beneficial effects: 1. Utilizing existing equipment and optimizing raw materials: This invention can be scaled up using existing equipment without altering the original PCS production line. By optimizing the raw materials, it is compatible with existing spinning processes and is particularly suitable for large-scale production. When using polycarbosilane (PCS) as raw material, the pyrolysis products are severely carbon-rich, with a C / Si ratio typically of 1.2 to 1.4. When using polymethylsilane (PMS) as raw material, the SiC generated by pyrolysis is typically silicon-rich, with a Si / C ratio of 1.2 to 1.3. This invention uses a zirconium-containing multiphase ceramic precursor (PZMS) mixed with PMS and then combined with PCS to produce silicon carbide fibers. This reduces the excess carbon in the resulting silicon carbide fibers, enhancing their high-temperature performance, oxidation resistance, and creep resistance. The problem of excess carbon is addressed from the raw material stage. 2. Optimized crosslinking method: A two-step method of electron beam / BCl3 crosslinking and heat treatment is adopted to introduce boron atoms, which can react with the polymer molecular chains in the precursor fiber to form a crosslinked structure, thereby improving the thermal stability and mechanical strength of the precursor fiber, improving the controllability of the process and the quality of the fiber. Radiation crosslinking is a hot topic in non-oxidative crosslinking research. The electron beam / BCl3 crosslinking method can effectively reduce the oxygen content in the fiber and cleverly introduce boron. During the high-temperature treatment, boron combines with zirconium to transform into zirconium boride, thus producing SiC fibers with near stoichiometric ZrB2 doping. 3. Improve fiber yield and dual-element doping: Degassing and small molecule removal before melt spinning can effectively increase the molecular weight and crosslinking degree of the mixed precursor, thereby improving fiber yield. The introduction of ZrB2 achieves nanoscale dispersion through a two-step method (zirconium precursor + BCl3 treatment), improving antioxidant and creep resistance. The combination of electron beam crosslinking and BCl3 treatment does not affect the existing spinning process containing zirconium precursors, taking into account both fiber stability and element doping efficiency. 4. Optimized carbon and oxygen content control: After optimizing the raw materials, ceramic fibers with different carbon contents can be further prepared by changing the hydrogen concentration and sintering temperature during the fiber pyrolysis process. Once free carbon is formed in the fiber, its removal will cause pores or defects in the fiber. Therefore, this invention introduces hydrogen in the process of forming amorphous fibers to effectively reduce the carbon content in the fibers. It also optimizes the stoichiometry and is compatible with the existing polycarbosilane spinning process, making it suitable for large-scale production. 5. Pyrolysis under a hydrogen atmosphere reduces free carbon. The introduction of zirconium into silicon carbide fibers increases the decomposition temperature of the Si-OC phase, allowing the fibers to be used at higher temperatures. However, when the temperature exceeds 1600℃, zirconium-containing silicon carbide fibers still undergo amorphous phase decomposition, leading to a decrease in mechanical strength. Therefore, introducing boron into the fibers further improves their high-temperature resistance. During high-temperature processing, due to the SiC... x O yWhen the amorphous phase decomposes, the strength of Si-BCO fibers decreases significantly. However, during the subsequent high-temperature sintering process, the fibers gradually become denser and their strength increases under the sintering effect of boron. The strength of the fibers is closely related to the defects present in the fibers. However, due to the three-step decarburization control of free carbon and oxygen content in the precursor preparation, fiber crosslinking, and pyrolysis steps, the impact on the original strength and properties of the fibers during decarburization is far less than that of conventional methods (such as CN 116639983 A A high-temperature resistant near-stoichiometric continuous silicon carbide fiber and its preparation method).

[0015] 6. Significantly improves the high temperature resistance and oxidation resistance of silicon carbide fiber, with an oxidation weight gain rate lower than that of pure ZrC-SiC fiber.

[0016] Furthermore, the high-temperature sintering temperature is between 1700 and 1800℃, with the temperature controlled between 1700 and 1750℃ and ZrB2 ≤ 3%; and the temperature controlled between 1750 and 1800℃ and ZrB2 > 3%. This results in good crystallinity of silicon carbide fibers, which can maintain good fiber properties at higher temperatures. The thermal stability of the fibers can reach 1500℃, and the oxidation resistance at 1800℃ is significantly better than that of the single-phase doped system. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing ZrB2-doped SiC fibers with near-stoichiometric ratios. Detailed Implementation

[0018] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0019] Example 1 A method for preparing near-stoichiometric ZrB2-doped SiC fibers, such as... Figure 1 As shown, it includes the following steps: Step 1: Under nitrogen protection, dissolve 600g of PCS in 1200mL of xylene, filter to remove large insoluble molecules, and obtain a PCS mixture. Then transfer it to a three-necked flask and heat it to 160℃ through a salt bath. After the xylene evaporates to dryness, slowly raise the temperature to 240℃ and keep it at that temperature for 4 hours. Cool it to room temperature to obtain purified PCS. Step 2: Then, under nitrogen protection, 12.5g of zirconium-containing multiphase ceramic precursor (PZMS, containing 6...) was used... wt Using % Zr and 62.5g of polymethylsilane (PMS) as raw materials, it was dissolved in 200 mL of xylene at 80℃. After being stirred thoroughly, the insoluble matter was removed by filtration, and then the xylene was removed by vacuum drying at 120℃ to obtain a refined PZMS / PMS mixed precursor. Step 3: Then, under nitrogen protection, 60 g of refined PZMS / PMS mixed precursor and 450 g of refined PCS are placed in a melt spinning machine according to the ratio, heated to 240℃, melted and stirred evenly, and kept for 12 h for degassing and small molecule removal treatment. Then, the temperature is reduced to 170℃ and kept at that temperature. The molten melt is spun through a spinneret and wound by a winding machine to obtain zirconium-containing polycarbosilane precursor. The temperature of the spinneret is 170℃ (consistent with the temperature of the melt), the spinning pressure is 0.4 MPa, and the spinneret orifice diameter is 0.3 mm. Step 4: Then, vacuum the filaments and replace them with high-purity nitrogen three times. Irradiate the zirconium-containing polycarbosilane precursor fibers with an irradiation dose of 10 mGy for 12 h to crosslink the fiber precursor fibers. Then, introduce 3% BCl3 gas and allow it to react for 6 h. Subsequently, heat-treat the zirconium-containing polycarbosilane precursor fibers at 340℃ in an inert atmosphere for 1 h to complete the annealing process, so that the Si free radical deactivated fibers are completely transformed into a stable non-fusible network structure. Then, cool to room temperature to obtain ZrB2-doped polycarbosilane crosslinked fibers. Step 5: Then, place the ZrB2-doped polycarbosilane crosslinked fiber on a quartz boat and place it inside a quartz tube. Apply a tension of 0.45 N to the polycarbosilane crosslinked fiber, evacuate the vacuum, replace the nitrogen gas three times to remove air and impurities from the quartz tube, then introduce hydrogen gas at a flow rate of 5 L / min, raise the temperature to 800℃ at a rate of 150℃ / h, hold for 10 min, then raise the temperature to 1250℃ at a rate of 3℃ / min, hold for 50 min to further densify the fiber, and then cool to room temperature inside the quartz tube to obtain polycarbosilane pyrolysis fiber; Step 6: Finally, evacuate the vacuum and replace it with high-purity argon three times. Place the polycarbosilane pyrolysis wire in a graphite sintering furnace, apply a tension of 0.45 N, raise the temperature to 1700℃ at a heating rate of 200℃ / h, hold for 15 min, and perform sintering treatment to obtain dense near-stoichiometric SiC fibers doped with ZrB2.

[0020] Example 2 A method for preparing near-stoichiometric ZrB2-doped SiC fibers includes the following steps: Step 1: Under nitrogen protection, dissolve 300g of PCS in 900mL of toluene, filter to remove large insoluble molecules, and obtain a PCS mixture. Then transfer it to a three-necked flask and heat it to 160℃ through a salt bath. After the toluene evaporates, slowly raise the temperature to 260℃ and keep it at that temperature for 6 hours. Cool it to room temperature to obtain purified PCS. Step 2: Then, under nitrogen protection, 12.5g of zirconium-containing multiphase ceramic precursor (PZMS, containing 6...) was used... wtUsing % Zr and 68.75g of polymethylsilane (PMS) as raw materials, it was dissolved in 200mL of xylene at 90℃. After being stirred thoroughly, the insoluble matter was removed by filtration, and then the xylene was removed by vacuum drying at 120℃ to obtain a refined PZMS / PMS mixed precursor. Step 3: Then, under nitrogen protection, 70 g of refined PZMS / PMS mixed precursor and 210 g of refined PCS are placed in a melt spinning machine according to the ratio, heated to 250℃, melted and stirred evenly, and kept for 15 h for degassing and small molecule removal treatment. Then, the temperature is reduced to 170℃ and kept at that temperature. The molten melt is spun through a spinneret and wound by a winding machine to produce zirconium-containing polycarbosilane precursor. The temperature of the spinneret is 170℃ (consistent with the temperature of the melt), the spinning pressure is 0.5 MPa, and the spinneret orifice diameter is 0.3 mm. Step 4: Then, vacuum the filaments and replace them with high-purity nitrogen three times. Irradiate the zirconium-containing polycarbosilane precursor fibers with an irradiation dose of 11 mGy for 12 h to crosslink the fiber precursor fibers. Then, introduce 3% BCl3 gas and allow it to react for 6 h. Subsequently, heat-treat the zirconium-containing polycarbosilane precursor fibers at 350℃ in an inert atmosphere for 1 h to complete the annealing process, so that the Si free radical deactivated fibers are completely transformed into a stable non-fusible network structure. Then, cool to room temperature to obtain ZrB2-doped polycarbosilane crosslinked fibers. Step 5: Then, place the ZrB2-doped polycarbosilane crosslinked fiber on a quartz boat and place it inside a quartz tube. Apply a tension of 0.48 N to the polycarbosilane crosslinked fiber, evacuate the vacuum, replace the nitrogen gas three times to remove air and impurities from the quartz tube, then introduce hydrogen gas at a flow rate of 6 L / min, raise the temperature to 800℃ at a rate of 180℃ / h, hold for 10 min, then raise the temperature to 1280℃ at a rate of 3℃ / min, hold for 40 min to further densify the fiber, and then cool to room temperature inside the quartz tube to obtain polycarbosilane pyrolysis fiber; Step 6: Finally, evacuate the vacuum and replace it with high-purity argon three times. Place the polycarbosilane pyrolysis wire in a graphite sintering furnace, apply a tension of 0.48 N, raise the temperature to 1750℃ at a heating rate of 300℃ / h, hold for 15 min, and perform sintering treatment to obtain dense near-stoichiometric SiC fibers doped with ZrB2.

[0021] Example 3 A method for preparing near-stoichiometric ZrB2-doped SiC fibers includes the following steps: Step 1: Under nitrogen protection, dissolve 500g of PCS in 1000mL of xylene, filter to remove large insoluble molecules, and obtain a PCS mixture. Then transfer the mixture to a three-necked flask and heat it to 160℃ in a salt bath. After the xylene evaporates to dryness, slowly raise the temperature to 240℃ and keep it at that temperature for 4 hours. Cool it to room temperature to obtain purified PCS. Step 2: Then, under nitrogen protection, 12.5g of zirconium-containing multiphase ceramic precursor (PZMS, containing 6...) was used... wt Using Zr and 100g of polymethylsilane (PMS) as raw materials, the mixture was dissolved in 300mL of xylene at 100℃. After thorough stirring, the insoluble matter was removed by filtration, and the xylene was removed by vacuum drying at 120℃ to obtain a refined PZMS / PMS mixed precursor. Step 3: Then, under nitrogen protection, 80 g of refined PZMS / PMS mixed precursor and 300 g of refined PCS are placed in a melt spinning machine according to the ratio, heated to 240℃, melted and stirred evenly, and kept for 18 h for degassing and small molecule removal treatment. Then, the temperature is reduced to 160℃ and kept at that temperature. The molten melt is spun through a spinneret and wound through a winding machine to produce zirconium-containing polycarbosilane precursor. The temperature of the spinneret is 160℃ (consistent with the temperature of the melt), the spinning pressure is 0.4 MPa, and the spinneret orifice diameter is 0.4 mm. Step 4: Then, vacuum the filaments and replace them with high-purity nitrogen three times. Irradiate the zirconium-containing polycarbosilane precursor fibers with an irradiation dose of 12 mGy for 12 h to crosslink the fiber precursor fibers. Then, introduce 3% BCl3 gas and allow it to react for 8 h. Subsequently, heat-treat the zirconium-containing polycarbosilane precursor fibers at 340℃ in an inert atmosphere for 1 h to complete the annealing process, so that the Si free radical deactivated fibers are completely transformed into a stable non-fusible network structure. Then, cool to room temperature to obtain ZrB2-doped polycarbosilane crosslinked fibers. Step 5: Then, place the ZrB2-doped polycarbosilane crosslinked fiber on a quartz boat and place it inside a quartz tube. Apply a tension of 0.5 N to the polycarbosilane crosslinked fiber, evacuate the vacuum, replace the nitrogen gas three times to remove air and impurities from the quartz tube, then introduce hydrogen gas at a flow rate of 5 L / min, raise the temperature to 800℃ at a rate of 180℃ / h, hold for 10 min, then raise the temperature to 1300℃ at a rate of 3℃ / min, hold for 30 min to further densify the fiber, and then cool to room temperature inside the quartz tube to obtain polycarbosilane pyrolysis fiber; Step 6: Finally, evacuate the vacuum and replace it with high-purity argon three times. Place the polycarbosilane pyrolysis wire in a graphite sintering furnace, apply a tension of 0.5 N, raise the temperature to 1780℃ at a heating rate of 300℃ / h, hold for 12 min, and perform sintering treatment to obtain dense near-stoichiometric SiC fibers doped with ZrB2.

[0022] Example 4 A method for preparing near-stoichiometric ZrB2-doped SiC fibers includes the following steps: Step 1: Under nitrogen protection, dissolve 400g of PCS in 800mL of toluene, filter to remove large insoluble molecules, and obtain a PCS mixture. Then transfer it to a three-necked flask and heat it to 160℃ through a salt bath. After the toluene evaporates, slowly raise the temperature to 260℃ and keep it at that temperature for 6 hours. Cool it to room temperature to obtain purified PCS. Step 2: Then, under nitrogen protection, 12.5g of zirconium-containing multiphase ceramic precursor (PZMS, containing 6...) was used... wt Using % Zr and 87.5 g of polymethylsilane (PMS) as raw materials, it was dissolved in 200 mL of xylene at 80 °C. After being stirred thoroughly, the insoluble matter was removed by filtration, and then the xylene was removed by vacuum drying at 120 °C to obtain a refined PZMS / PMS mixed precursor. Step 3: Then, under nitrogen protection, 90 g of refined PZMS / PMS mixed precursor and 270 g of refined PCS are placed in a melt spinning machine according to the ratio, heated to 240℃, melted and stirred evenly, and kept for 18 h for degassing and small molecule removal treatment. Then, the temperature is reduced to 160℃ and kept at that temperature. The molten melt is spun through a spinneret and wound by a winding machine to obtain zirconium-containing polycarbosilane precursor. The temperature of the spinneret is 160℃ (consistent with the temperature of the melt), the spinning pressure is 0.4 MPa, and the spinneret orifice diameter is 0.3 mm. Step 4: Then, vacuum the filaments and replace them with high-purity nitrogen three times. Irradiate the zirconium-containing polycarbosilane precursor fibers with an irradiation dose of 12 mGy for 12 h to crosslink the fiber precursor fibers. Then, introduce 3% BCl3 gas to allow the reaction to proceed for 10 h. Subsequently, heat-treat the zirconium-containing polycarbosilane precursor fibers at 360℃ in an inert atmosphere for 1 h to complete the annealing process. This allows the Si free radical deactivated fibers to be completely transformed into a stable non-fusible network structure. Finally, cool the fibers to room temperature to obtain ZrB2-doped polycarbosilane crosslinked fibers. Step 5: Then, place the ZrB2-doped polycarbosilane crosslinked fiber on a quartz boat and place it inside a quartz tube. Apply a tension of 0.5 N to the polycarbosilane crosslinked fiber, evacuate the vacuum, replace the nitrogen gas three times to remove air and impurities from the quartz tube, then introduce hydrogen gas at a flow rate of 6 L / min, raise the temperature to 800℃ at a rate of 200℃ / h, hold for 10 min, then raise the temperature to 1320℃ at a rate of 3℃ / min, hold for 30 min to further densify the fiber, and then cool to room temperature inside the quartz tube to obtain polycarbosilane pyrolysis fiber; Step 6: Finally, evacuate the vacuum and replace it with high-purity argon three times. Place the polycarbosilane pyrolysis fiber in a graphite sintering furnace, apply a tension of 0.5 N, raise the temperature to 1800℃ at a heating rate of 300℃ / h, hold for 12 min, and perform sintering treatment to obtain dense near-stoichiometric SiC fibers doped with ZrB2.

[0023] The spinning-grade polycarbosilane (PCS) used was produced by Fujian Liya New Materials Co., Ltd., with a molecular weight of 1100-1300 and a softening point of 200-215℃. The polymethylsilane (PMS) and zirconium-containing multiphase ceramic precursor (PZMS) used were produced by Hunan Bowang Carbon Ceramics Co., Ltd., with PMS having a molecular weight of approximately 1500, a melting point of 30℃, and a density of 0.95 g / cm³. 3 The ceramic yield is >65%, the chemical properties are stable, and it can be stored and used at room temperature; PZMS is a solid or viscous liquid at room temperature, the ceramic yield is 88%, and the ZrC content is adjustable from 10% to 70%.

[0024] The properties of the near-stoichiometric ZrB2-doped silicon carbide fibers prepared in each embodiment and the undoped silicon carbide fiber (Liya third-generation silicon carbide fiber) prepared in Comparative Example 1 were tested according to the national standard GB / T43760-2024 for silicon carbide fibers. The ZrB2 content was analyzed and converted according to the known elemental analysis method (ICP-OES). The results are shown in Table 1.

[0025] Table 1 Performance data of silicon carbide fiber

[0026] Note: The strength retention rate was obtained by testing the silicon carbide fiber after heat treatment at 1500℃ in an argon atmosphere for 1 h.

[0027] As shown in Table 1, by introducing ZrB2 to dope silicon carbide fibers, the resulting near-stoichiometric silicon carbide fibers have a C / Si ratio close to 1, while the silicon carbide fibers of Comparative Example 1 (undoped) have a C / Si ratio of 1.05, indicating a higher carbon content. The ZrB2 content in the silicon carbide fibers prepared in Examples 1-4 is approximately 1%. wt %~5 wt The oxygen content of the fiber was controlled within a certain range, and the overall oxygen content of the fiber was kept at a low level (all <1%). wt (%), doping with ZrB2 did not significantly impair the chemical purity of the fiber.

[0028] The silicon carbide fiber in Comparative Example 1 exhibited the highest tensile strength (3.6 GPa), significantly higher than the silicon carbide fiber in the Examples (2.2~2.7 GPa). This may be due to the introduction of ZrB2 particles (or the second phase) creating stress concentration points or increasing the modulus within the fiber, thus leading to a decrease in strength. However, ZrB2 doping significantly improved the fiber's strength retention rate in argon at 1500°C (80.1%~88.6% vs 62.3%). This is closely related to the high-temperature stability of ZrB2: ZrB2 has a high melting point of 3245°C and can suppress SiC grain coarsening at high temperatures, delaying structural degradation by pinning grain boundaries. Furthermore, at high temperatures, ZrB2 can oxidize to form ZrO2 and B2O3 glass phases, filling surface defects and hindering oxygen diffusion. In Example 4, the silicon carbide fiber (ZrB2 content reached 4.1%)... wt The percentage may be due to excessive doping, which may cause a decrease in both strength and retention rate, indicating that there may be a threshold for doping.

[0029] In summary, ZrB2 doping expands the application range of silicon carbide fibers by improving high-temperature stability and enhancing rigidity. It can maintain excellent performance in extreme high-temperature and strong oxidizing environments, and can better meet the needs of high-temperature structural components in harsh environments such as aerospace and nuclear energy.

[0030] The above embodiments and figures are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A method for preparing near-stoichiometric ZrB2-doped SiC fibers, characterized in that: Includes the following steps: Step 1: Under nitrogen protection, PCS is processed using a normal pressure and high temperature method to obtain refined PCS. Step 2: Then, under nitrogen protection, PZMS and PMS are dissolved in xylene at 80~100℃. After thorough stirring, the insoluble matter is removed by filtration, and then the xylene is removed by vacuum drying to obtain a refined PZMS / PMS mixed precursor. Step 3: Then, under nitrogen protection, the refined PZMS / PMS mixed precursor and refined PCS are placed in a melt spinning machine according to the ratio, heated to 240~250℃, melted and stirred evenly, and kept for 12~18 h for degassing and small molecule removal treatment. Then, the temperature is reduced to 160~170℃ and kept warm. The molten melt is spun through a spinneret and wound by a winding machine to obtain zirconium-containing polycarbosilane precursor. Step 4: Then, the zirconium-containing polycarbosilane precursor is subjected to non-melting treatment using an electron beam / BCl3 cross-linking-heat treatment method. Boron is introduced into the zirconium-containing polycarbosilane precursor. At high temperature, boron reacts with zirconium to transform into SiC-ZrB2 nano-composite ceramic fibers, thus obtaining ZrB2-doped polycarbosilane cross-linked fibers. Step 5: Then, under a hydrogen atmosphere, the ZrB2-doped polycarbosilane crosslinked wire is subjected to high-temperature pyrolysis to obtain polycarbosilane pyrolysis wire. Step 6: Finally, under argon protection, tension is applied to the polysilane pyrolysis wire, and high-temperature sintering is performed to obtain near-stoichiometric ZrB2-doped SiC fibers, wherein the ZrB2 content accounts for 1.0% of the mass of the silicon carbide fiber. wt %~5.0 wt % In step 1, the process of the atmospheric pressure high temperature method is as follows: PCS is dissolved in xylene or toluene, and the macromolecular insoluble matter is removed by filtration to obtain a PCS mixture. Then, the mixture is transferred to a three-necked flask and heated to 160°C by a salt bath. After the xylene or toluene is evaporated to dryness, the temperature is slowly raised to 240~260°C and kept at that temperature for 4~6 hours. The mixture is then cooled to room temperature to obtain purified PCS. In step 2, the mass ratio of PZMS to PMS is 1:5 to 1:8; in step 3, the mass ratio of refined PZMS / PMS mixed precursor to refined PCS is 1:3 to 1:

8. In step 4, the electron beam / BCl3 crosslinking-heat treatment method is as follows: evacuate and replace with high-purity nitrogen three times, irradiate the zirconium-containing polycarbosilane precursor fiber with an irradiation dose of 10~12 mGy for 12 h to cause crosslinking of the fiber precursor fiber, then introduce 3% BCl3 gas to allow the reaction to proceed for 6~12 h; subsequently, heat treat the zirconium-containing polycarbosilane precursor fiber in an inert atmosphere at 340~360℃ for 1 h to complete the annealing, so that the Si free radical deactivated fiber is completely transformed into a stable non-fusible network structure, and then cool to room temperature to obtain ZrB2-doped polycarbosilane crosslinked fiber; In step 5, the high-temperature pyrolysis decarbonization process is as follows: ZrB2-doped polycarbosilane crosslinked fibers are placed on a quartz boat and then placed inside a quartz tube. A tension of 0.45~0.5 N is applied to the polycarbosilane crosslinked fibers. A vacuum is drawn, and nitrogen is replaced three times to remove air and impurities from the quartz tube. Then, hydrogen is introduced at a flow rate of 4~6 L / min, and the temperature is raised to 800℃ at a rate of 100~200℃ / h and held for 10 min. Then, the temperature is raised to 1250~1350℃ at a rate of 3℃ / min and held for 30~60 min to further densify the fibers. Finally, the fibers are cooled to room temperature inside the quartz tube to obtain polycarbosilane pyrolysis fibers.

2. The method for preparing near-stoichiometric ZrB2-doped SiC fibers according to claim 1, characterized in that: In step 3, the temperature of the spinneret is 160~170℃, the spinneret pressure is 0.4~0.5 MPa, and the spinneret orifice diameter is 0.3~0.4 mm.

3. The method for preparing near-stoichiometric ZrB2-doped SiC fibers according to claim 1, characterized in that: In step 6, the high-temperature sintering process is as follows: vacuum is drawn and replaced three times with high-purity argon gas. The polycarbosilane pyrolysis wire is placed in a graphite sintering furnace, a tension of 0.45~0.5 N is applied, and the temperature is raised to 1700~1800℃ at a heating rate of 200~300℃ / h. The temperature is held for 10~30 min to perform sintering treatment, thereby obtaining dense near-stoichiometric SiC fibers doped with ZrB2.

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