Silicon carbide-carbide multiphase micro-nano fiber as well as preparation method and ultrahigh-temperature application thereof

Abstract

The invention belongs to the technical field of ceramic fibers, and discloses a silicon carbide-carbide complex-phase micro-nano fiber as well as a preparation method and ultrahigh-temperature application thereof. The preparation method comprises the following steps: spinning polycarbosilane and a metal organic salt solution to obtain fibril, carrying out electron beam irradiation crosslinking curing in an inert atmosphere, cooling to obtain irradiation-infusible fiber, placing the irradiation-infusible fiber in the inert atmosphere, heating to 1300-1800 DEG C under the assistance of tension, and carrying out heat preservation sintering for 1-3 hours to obtain the composite material. According to the obtained silicon carbide-carbide micro-nano fiber, beta-silicon carbide is used as a matrix, and uniformly distributed carbide nanocrystals are embedded in situ among crystal grains of beta-silicon carbide nanocrystals. The silicon carbide-carbide complex phase micro-nano fiber is smooth in surface, compact in structure and good in high temperature resistance and oxidation resistance, has flexibility, ablation resistance and heat insulation performance, and can be applied to the fields of aerospace vehicle large-area heat protection materials, heat sealing materials, heat insulation materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of ceramic fiber technology, and particularly relates to a silicon carbide-carbide multiphase micro / nano fiber, its preparation method, and its ultra-high temperature application. Background Technology

[0002] Silicon carbide (SiC) microfibers and nanofibers have become key candidate materials for high-temperature thermal protection systems due to their high temperature resistance, high strength, good flexibility, and excellent infrared shielding performance. However, current technologies offer limited control over the composition of SiC microfibers and nanofibers, resulting in fibers with high impurity content and low crystallinity, making it difficult to meet high-temperature resistance requirements. For example, above 1100℃, free carbon aggregates and amorphous Si-OC phases easily form inside the fibers. When exposed to 1300℃ and above, rapid grain growth and SiO and CO degassing are induced, leading to the formation of pores and coarse SiC grains on the fiber surface, resulting in a significant decrease in mechanical properties. Therefore, the operating temperature of existing SiC microfibers in air is typically below 1300℃, and in inert atmospheres, it is generally below 1600℃, exhibiting insufficient oxidation resistance and high-temperature stability.

[0003] Highly crystalline silicon carbide micro / nanofibers, due to their intact crystal structure and few defects, can withstand temperatures up to 1600℃ in an inert atmosphere. However, above this temperature, β-SiC crystallites undergo grain boundary diffusion, leading to grain coarsening and a further decline in mechanical properties. Therefore, it is necessary to find methods to overcome this limitation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a silicon carbide-carbide multiphase micro / nano fiber with a temperature resistance of over 1600℃, its preparation method, and its ultra-high temperature application.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is to provide a method for preparing silicon carbide-carbide multiphase micro / nano fibers, comprising the following steps:

[0006] (1) Polycarbosilane, organometallic salt solution, synergistic solvent and spinning aid are mixed to obtain a spinning dispersion; The organometallic salt in the solution is tetrabutyl hafnium oxide, tetrabutyl zirconate, or tetrabutyl titanate, and the mass fraction of the organometallic salt in the solution is 60-90 wt%. The mass ratio of the polycarbosilane to the organometallic salt solution is 1:(0.05-0.5). (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is performed to obtain the fibrils; (3) The original fiber is cross-linked and cured by electron beam irradiation under an inert atmosphere, and after cooling, an irradiated non-melting fiber is obtained; the reaction process is mainly caused by the reaction of Si-H and Si-CH3 in polycarbosilane under electron beam irradiation in an inert atmosphere to generate a Si-CH2-Si bridging structure. (4) The irradiated infusible fiber is placed in an inert atmosphere and heated to 1300~1800℃ under tension assistance and sintered for 1~3 h to obtain the silicon carbide-carbide multiphase micro-nano fiber; during this stage, the irradiated infusible fiber undergoes thermal decomposition and inorganic reaction, which causes the formation of carbide and silicon carbide crystals inside the fiber.

[0007] The preparation method of this invention involves introducing ultra-high temperature ceramic nanocrystals (such as ZrC, TiC, HfC, etc.) into silicon carbide micro / nanofibers. These nanocrystals possess extremely high melting points (e.g., ZrC melting point 3540℃, TiC melting point 3140℃, HfC melting point 3928℃) and thermal stability, enabling them to maintain structural stability at high temperatures. Introducing them into SiC micro / nanofibers effectively inhibits grain growth and structural degradation at high temperatures, while simultaneously enhancing antioxidant properties through the formation of a dense oxide film, thereby significantly improving the high-temperature stability of the fibers.

[0008] This invention overcomes the problems of high oxygen content and oxide doping in micro / nano fibers caused by air pre-oxidation in existing technologies. It controls low oxygen content through curing and sintering processes under an inert atmosphere, and regulates the content of the carbide second phase by adjusting the mass ratio of polycarbosilane and organometallic salt solutions, thereby achieving finer microstructure control. Combined with electron beam irradiation and tension-assisted in-situ ultra-high temperature transformation, highly crystalline multiphase micro / nano fibers are obtained. The introduction of the carbide second phase significantly improves the high-temperature stability of the fibers, achieving a temperature resistance of up to 2100℃, solving the technical problem that fibers prepared by existing technologies cannot withstand ultra-high temperatures above 1700℃.

[0009] In the above preparation method, preferably, the solvent of the organometallic salt solution is n-butanol; the co-solvent is at least one of xylene, acetone, N,N-dimethylformamide and chloroform; the spinning aid is at least one of polyvinylpyrrolidone, polyvinyl alcohol and polystyrene; and the mass ratio of polycarbosilane, organometallic salt solution, co-solvent and spinning aid is 1:(0.05~0.5):(0.5~3):(0.05~0.2).

[0010] Preferably, in step (1), the mixing method is water bath stirring or ultrasonic mixing. The water bath stirring speed is 400~1000 r / min and the duration is 2~8 h, and the ultrasonic mixing duration is 2~5 h. This stirring method can form a more stable dispersion.

[0011] Preferably, in step (2), the conditions for electrospinning are: voltage of 10~25 kV, take-up distance of 10~25 cm, and feed rate of 0.8~2 mL / h.

[0012] Preferably, in step (3), the electron beam irradiation dose is 10~20 MGy, the electron beam irradiation time is 1~5 h, and non-melting irradiated fibers are obtained after cooling.

[0013] Preferably, in steps (3) and (4), the inert atmosphere is argon or nitrogen.

[0014] Preferably, in step (4), the value of the tension is 0.1~10 N.

[0015] Based on a general inventive concept, the present invention also provides a silicon carbide-carbide multiphase micro / nanofiber prepared by the aforementioned preparation method. The silicon carbide-carbide multiphase micro / nanofiber uses β-silicon carbide nanocrystals as a matrix, with uniformly distributed carbide nanocrystals in situ embedded between the grains of the β-silicon carbide nanocrystals. The carbide nanocrystals are hafnium carbide nanocrystals, zirconium carbide nanocrystals, or titanium carbide nanocrystals. The average grain size of the nanocrystals contained in the silicon carbide-carbide multiphase micro / nanofiber is 5–25 nm. The diameter of the silicon carbide-carbide multiphase micro / nanofiber is 0.5–5.0 μm. The silicon carbide-carbide multiphase micro / nanofiber does not contain an oxide phase.

[0016] Preferably, the silicon carbide-carbide multiphase micro / nanofibers described above contain only silicon carbide and zirconium carbide biphases.

[0017] Based on a general inventive concept, the present invention also provides an application of the silicon carbide-carbide multiphase micro / nanofiber in the ultra-high temperature field, using the silicon carbide-carbide multiphase micro / nanofiber to prepare materials resistant to ultra-high temperatures of 1700℃~2100℃.

[0018] In the above applications, preferably, the material is a thermal protection material, thermal sealing material, or thermal insulation material for aerospace vehicles.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The method for preparing silicon carbide-carbide micro / nano fibers provided by this invention utilizes a synergistic solvent that exhibits good compatibility with polycarbosilane and various organometallic salt small molecules, resulting in a more stable spinning dispersion with better spinnability. The irradiated fibers, after cross-linking and curing by electron beam irradiation, have a lower oxygen content, reducing the presence of unfavorable interfacial amorphous phases. Simultaneously, this facilitates the formation of strong interfacial bonds between the carbide nanocrystals formed in situ through carbothermal reduction reaction during high-temperature heat treatment and silicon carbide. By inhibiting interfacial atomic diffusion, it hinders grain boundary migration of silicon carbide grains at high temperatures, thereby improving structural stability. Furthermore, the preparation method provided by this invention has a simple process, the multiphase fiber structure is easy to control, and it is convenient for large-scale production.

[0020] 2. The carbides introduced in this invention are all ultra-high temperature carbides (such as ZrC, TiC, HfC, etc.), whose melting points (>3000℃) are much higher than those of silicon carbide (~2700℃ decomposition and sublimation). They can still maintain solid state and structural integrity in ultra-high temperature environments (such as >1800℃) close to or exceeding the decomposition temperature of silicon carbide. Although silicon carbide itself has good oxidation resistance, in extreme high temperature (>1500℃) and oxygen-rich environments, the silica protective layer formed on its surface will become unstable (active oxidation or volatilization). However, the ultra-high temperature carbides introduced in this invention will generate high-melting-point, more stable oxides in oxidizing environments. These oxides can form a more effective diffusion barrier, slow down the diffusion rate of oxygen into the material, thereby providing better protection in high-temperature and oxygen-rich environments and synergistically improving the overall oxidation resistance limit of the fiber.

[0021] 3. The silicon carbide-carbide micro / nanofiber provided by this invention uses β-silicon carbide as the matrix, and contains zirconium carbide, hafnium carbide, or titanium carbide nanocrystals that are in situ embedded between β-silicon carbide grains and uniformly distributed. The silicon carbide-carbide multiphase micro / nanofiber has a smooth surface and a dense structure. The uniformly dispersed ultra-high temperature carbide nanocrystals inside the fiber greatly improve the high temperature resistance and oxidation resistance of the silicon carbide micro / nanofiber. The silicon carbide-carbide micro / nanofiber also has flexibility, ablation resistance, and thermal insulation properties, and can be applied to large-area thermal protection materials, thermal sealing materials, and thermal insulation materials for aerospace vehicles. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 SEM image of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1; Figure 2 The image shows the XRD pattern of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1. Figure 3 SEM image of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1 after treatment with argon atmosphere at 2100℃ for 30 min. Figure 4 An optical photograph of the compression and rebound of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1 after being treated with argon atmosphere at 2100℃ for 30 min. Figure 5 The compressive stress-strain curve of the silicon carbide-carbide multiphase micro / nanofiber prepared in Example 1 after being treated with argon atmosphere at 2100℃ for 30 min. Figure 6 An optical photograph of the surface of the fiber mat made of silicon carbide-carbide multiphase micro / nanofiber prepared in Example 1 after ablation with an oxyacetylene flame at 1850°C for 30 min. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0026] Unless otherwise specified, all medicines / reagents used are commercially available.

[0027] Example 1 This embodiment provides a silicon carbide-carbide composite micro / nanofiber, using β-silicon carbide as the matrix and containing zirconium carbide nanocrystals uniformly distributed and in situ embedded within the β-silicon carbide matrix; the preparation method of the silicon carbide-carbide composite micro / nanofiber includes the following steps: (1) Polycarbosilane, tetrabutyl zirconate solution (mass fraction of 80 wt%, solvent is n-butanol), xylene, acetone and polyvinylpyrrolidone are mixed in a mass ratio of 1:0.5:0.3:0.2:0.05 and ultrasonically mixed for 4 h to obtain a uniform and transparent spinning dispersion. (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is carried out under the conditions of 15 kV voltage, 15 cm take-up distance and 2 mL / h feed rate to obtain the original fiber. (3) The original fiber is cross-linked and cured by electron beam irradiation. The electron beam irradiation dose is 15 MGy, the atmosphere is nitrogen, the irradiation time is 2 h, and after cooling, irradiation non-melting fiber is obtained. (4) Under an inert atmosphere, the irradiated non-melting fiber is placed in a graphite furnace, heated to 1800°C under the condition of tension provided by the compression of a 1N graphite frame, and sintered at 1800°C for 1 h. After cooling, silicon carbide-carbide multiphase micro-nano fibers are obtained.

[0028] The silicon carbide-carbide composite micro-nano fibers prepared in this embodiment have very good flexibility and high temperature resistance. The silicon carbide-carbide composite micro-nano fibers prepared in step (4) are uniformly laid to form a fiber felt with a thickness of about 10 mm. The fiber felt is subjected to ultra-high temperature (2100℃) test to evaluate its application performance as a heat protection material.

[0029] Figure 1 This is a scanning electron microscope (SEM) image of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1. Figure 1 As shown, the fiber obtained in this embodiment has a smooth surface, a dense structure, and an average diameter of 2.58 ± 0.83 μm.

[0030] Figure 2 The image shows the XRD pattern of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1. Figure 2 It can be seen that the fiber prepared in this embodiment has high crystallinity, is composed of silicon carbide phase and zirconium carbide phase, and does not contain oxide phase. The average grain size of silicon carbide is 11.01 nm and the average grain size of zirconium carbide is 10.32 nm.

[0031] Figure 3 The image shows a SEM image of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1 after treatment with argon atmosphere at 2100℃ for 30 min. Figure 3 It can be seen that the fiber surface remains smooth, with no obvious large particles attached.

[0032] Figure 4 An optical photograph of the silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1, after being treated with argon atmosphere at 2100℃ for 30 min, cooled, and then stacked layer by layer into a fiber sponge, followed by compression and rebound. Figure 4 It can be seen that the fiber sponge can fully rebound after compression, proving its structural stability at ultra-high temperatures.

[0033] Figure 5The stress-strain curves of the silicon carbide-carbide multiphase micro / nano fiber felt prepared in Example 1 were obtained after being treated with argon atmosphere at 2100℃ for 30 min, cooled, and then stacked layer by layer to form a fiber sponge, followed by compression testing. Figure 5 It can be seen that the fiber sponge treated at 2100℃ can reach a strength of 97.76 kPa after being compressed to 80%, showing good compressive strength and resilience, proving its application potential at ultra-high temperatures.

[0034] Example 2 This embodiment provides a silicon carbide-carbide composite micro / nanofiber, using β-silicon carbide as the matrix, with hafnium carbide nanocrystals in situ embedded in the β-silicon carbide matrix and uniformly distributed inside; the preparation method of the silicon carbide-carbide composite micro / nanofiber includes the following steps: (1) Polycarbosilane, tetrabutyl hafnium oxide solution (mass fraction of 80 wt%, solvent is n-butanol), xylene, acetone and polyvinylpyrrolidone are mixed in a mass ratio of 1:0.5:0.3:0.2:0.05 and ultrasonically mixed for 4 h to obtain a uniform and transparent spinning dispersion; (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is carried out under the conditions of 15 kV voltage, 15 cm take-up distance and 2 mL / h feed rate to obtain the original fiber. (3) The original fiber is cross-linked and cured by electron beam irradiation. The electron beam irradiation dose is 15 MGy, the atmosphere is nitrogen, the irradiation time is 2 h, and after cooling, irradiation non-melting fiber is obtained. (4) Under an inert atmosphere, the irradiated non-melting fiber is placed in a graphite furnace, heated to 1800°C under the condition of tension provided by the compression of a 1N graphite frame, and sintered at 1800°C for 2 h. After cooling, silicon carbide-carbide multiphase micro-nano fibers are obtained.

[0035] The silicon carbide-carbide composite micro / nano fibers prepared in this embodiment have excellent flexibility and high temperature resistance. The fiber diameter is 2~5.0 μm. The obtained fibers are composed of four elements: Si, Hf, O and C. Hafnium carbide nanocrystals are uniformly embedded in the silicon carbide matrix and can still maintain flexibility after treatment at 2100℃.

[0036] The fiber prepared in this embodiment has high crystallinity, is composed of silicon carbide phase and hafnium carbide phase, and does not contain oxide phase. The average grain size of silicon carbide is 21 nm and the average grain size of hafnium carbide is 25 nm.

[0037] Example 3 This embodiment provides a silicon carbide-carbide composite micro / nanofiber, using β-silicon carbide as the matrix and containing uniformly distributed titanium carbide nanocrystals embedded in the β-silicon carbide matrix. The preparation method of the silicon carbide-carbide composite micro / nanofiber includes the following steps: (1) Polycarbosilane, tetrabutyl titanate solution (mass fraction of 80 wt%, solvent is n-butanol), xylene, DMF and polyvinylpyrrolidone are mixed in a mass ratio of 1:0.5:0.3:0.2:0.05 and ultrasonically mixed for 4 h to obtain a uniform and transparent spinning dispersion. (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is carried out under the conditions of 15 kV voltage, 15 cm take-up distance and 2 mL / h feed rate to obtain the original fiber. (3) The original fiber is cross-linked and cured by electron beam irradiation. The electron beam irradiation dose is 15 MGy, the atmosphere is nitrogen, the irradiation time is 2 h, and after cooling, irradiation non-melting fiber is obtained. (4) Under an inert atmosphere, the irradiated non-melting fiber is placed in a graphite furnace and heated to 1800°C. Under the condition of tension provided by a 1N graphite frame compression, it is sintered at 1800°C for 2 h. After cooling, silicon carbide-carbide multiphase micro-nano fibers are obtained.

[0038] The silicon carbide-carbide composite micro / nano fibers prepared in this embodiment have excellent flexibility and high temperature resistance. The fiber diameter is 2~5.0 μm. The obtained fibers are composed of four elements: Si, Ti, O and C. Titanium carbide nanocrystals are uniformly embedded in the silicon carbide matrix and can still maintain flexibility after treatment at 2100℃.

[0039] The fiber prepared in this embodiment has high crystallinity and is composed of silicon carbide phase and titanium carbide phase, without oxide phase. The average grain size of silicon carbide is 23 nm and the average grain size of titanium carbide is 25 nm.

[0040] Example 4 This embodiment provides a silicon carbide-carbide composite micro / nanofiber, using β-silicon carbide as the matrix, with hafnium carbide nanocrystals in situ embedded in the β-silicon carbide matrix and uniformly distributed inside; the preparation method of the silicon carbide-carbide composite micro / nanofiber includes the following steps: (1) Polycarbosilane, tetrabutyl hafnium oxide solution (mass fraction of 85 wt%, solvent is n-butanol), xylene, acetone and polyvinylpyrrolidone are mixed in a mass ratio of 1:0.5:0.3:0.2:0.05 and ultrasonically mixed for 4 h to obtain a uniform and transparent spinning dispersion; (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is carried out under the conditions of 15 kV voltage, 15 cm take-up distance and 2 mL / h feed rate to obtain the original fiber. (3) The original fiber is cross-linked and cured by electron beam irradiation. The electron beam irradiation dose is 20 MGy, the atmosphere is nitrogen, the irradiation time is 2 h, and after cooling, irradiation non-melting fiber is obtained. (4) Under an inert atmosphere, the irradiated non-melting fiber is placed in a graphite furnace and heated to 1800°C. Under the condition of tension provided by a 5N graphite frame compression, it is sintered at 1800°C for 2 h. After cooling, silicon carbide-carbide multiphase micro-nano fibers are obtained.

[0041] The silicon carbide-carbide composite micro / nano fibers prepared in this embodiment have excellent flexibility and high temperature resistance. The fiber diameter is 1~3 μm. The obtained fibers are composed of four elements: Si, Hf, O and C. Hafnium carbide nanocrystals are uniformly embedded in the silicon carbide matrix and can still maintain flexibility after treatment at 2100℃.

[0042] The fiber prepared in this embodiment has high crystallinity, is composed of silicon carbide phase and hafnium carbide phase, and does not contain oxide phase. The average grain size of silicon carbide is 21 nm and the average grain size of hafnium carbide is 23 nm.

[0043] Example 5 This embodiment provides a silicon carbide-carbide composite micro / nanofiber, using β-silicon carbide as the matrix, with hafnium carbide nanocrystals in situ embedded in the β-silicon carbide matrix and uniformly distributed inside; the preparation method of the silicon carbide-carbide composite micro / nanofiber includes the following steps: (1) Polycarbosilane, tetrabutyl hafnium oxide solution (mass fraction of 85 wt%, solvent is n-butanol), xylene, acetone and polyvinylpyrrolidone are mixed in a mass ratio of 1:0.2:0.3:0.2:0.05 and ultrasonically mixed for 4 h to obtain a uniform and transparent spinning dispersion; (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is carried out under the conditions of 20 kV voltage, 15 cm take-up distance and 2 mL / h feed rate to obtain the original fiber. (3) The original fiber is cross-linked and cured by electron beam irradiation. The electron beam irradiation dose is 15 MGy, the atmosphere is nitrogen, the irradiation time is 2 h, and after cooling, irradiation non-melting fiber is obtained. (4) Under an inert atmosphere, the irradiated non-melting fiber is placed in a graphite furnace and heated to 1700°C. Under the condition of tension provided by a 5N graphite frame compression, it is sintered at 1700°C for 2 h. After cooling, silicon carbide-carbide multiphase micro-nano fibers are obtained.

[0044] The silicon carbide-carbide composite micro / nano fibers prepared in this embodiment have excellent flexibility and high temperature resistance. The fiber diameter is 1~3μm. The obtained fibers are composed of four elements: Si, Hf, O and C. Hafnium carbide nanocrystals are uniformly embedded in the silicon carbide matrix and can still maintain flexibility after treatment at 2100℃.

[0045] The fiber prepared in this embodiment has high crystallinity, is composed of silicon carbide phase and hafnium carbide phase, and does not contain oxide phase. The average grain size of silicon carbide is 17 nm and the average grain size of hafnium carbide is 18 nm.

[0046] Example 6 This embodiment provides an application of silicon carbide-carbide multiphase micro / nanofibers in the ultra-high temperature field, used to prepare thermal protection materials, thermal sealing materials, or thermal insulation materials for aerospace vehicles that can withstand ultra-high temperatures of 1700℃~2100℃. To verify its ultra-high temperature performance, fiber mats made from silicon carbide-carbide multiphase micro / nanofibers prepared in Example 1 were subjected to thermal protection performance tests at high temperatures.

[0047] The silicon carbide-carbide multiphase micro / nanofibers prepared by the method in Example 1 were uniformly laid up to a density of 50 mg / cm³. 3 A 3 mm thick fiber felt was used. One surface of the fiber felt was ablated using an oxyacetylene flame, causing the hot surface temperature to rapidly reach and stabilize at 1850°C for 30 minutes.

[0048] The results show that the fiber mat made of silicon carbide-carbide multiphase micro / nano fibers obtained in Example 1 can resist the oxyacetylene ablation environment at 1850℃, and the fiber mat still has excellent flexibility after ablation. Figure 6 This confirms its high-temperature ablation resistance.

[0049] Figure 6 The image shows the surface optical photograph of the fiber mat made of silicon carbide-carbide multiphase micro-nano fibers prepared in Example 1 after being ablated by an oxyacetylene flame at 1850°C for 30 minutes. The fiber membrane can still bend and recover after ablation, which proves its potential for thermal protection applications at ultra-high temperatures. It can be further used to prepare thermal protection materials, thermal sealing materials or thermal insulation materials for aerospace vehicles.

[0050] Comparative Example 1 This comparative example provides a method for preparing silicon carbide micro / nano fibers. The only difference from Example 1 is that tetrabutyl zirconate solution is not added to the spinning dispersion obtained in step (1).

[0051] The silicon carbide micro / nanofibers obtained in this comparative example are composed of three elements: Si, O, and C. After being heat-treated at 1700℃ for 30 minutes, they exhibited bending and pulverization. The comparative experiment shows that the carbide nanocrystals in the micro / nanofibers prepared by the method provided in this invention play a key role in improving the temperature resistance of the fibers.

[0052] Comparative Example 2 This comparative example provides a method for preparing silicon carbide-zirconium carbide micro / nano fibers. Compared with Example 1, the only difference is that in step (3), electron beam irradiation crosslinking and curing are not used, but air non-melting crosslinking is used. The temperature is 210°C and the crosslinking time is 2 h. After cooling, air non-melting fibers are obtained.

[0053] The silicon carbide-zirconium carbide micro / nanofibers obtained in this comparative example are composed of four elements: Si, O, C, and Zr. The fibers contain multiple phases of silicon carbide, zirconium oxide, zirconium carbide, and silicon oxide, rather than just a two-phase system of silicon carbide and zirconium carbide. The fibers exhibit pulverization after being heat-treated at 1400℃ for 30 min. The comparative experiment demonstrates that electron beam irradiation crosslinking in the micro / nanofibers prepared by the method provided in this invention plays a key role in improving the temperature resistance of the fibers.

[0054] Comparative Example 3 This comparative example provides a method for preparing silicon carbide-zirconium carbide micro / nano fibers. The only difference from Example 1 is that the electron beam irradiation dose used for cross-linking and curing in step (3) is 5 MGy.

[0055] The silicon carbide-zirconium carbide micro / nano fibers obtained in this comparative example are composed of four elements: Si, O, C, and Zr. After irradiation with 5 MGy, the fibers underwent a certain degree of cross-linking, but the degree of cross-linking was insufficient. After treatment, the fibers partially fused together, losing their original fiber morphology and flexibility.

[0056] Comparative Example 4 This comparative example provides a method for preparing silicon carbide-zirconium carbide micro / nano fibers. The only difference from Example 1 is that step (4) does not use graphite frame compression to provide tension.

[0057] The silicon carbide-zirconium carbide micro / nanofibers obtained in this comparative example are composed of four elements: Si, O, C, and Zr. However, during the high-temperature crystallization / densification process, the fibers cannot be effectively oriented axially and random shrinkage cannot be suppressed, which exacerbates the structural inhomogeneity and looseness. This significantly reduces their in-plane tensile strength, which is detrimental to their ultra-high temperature applications. Tested using a universal testing machine, their tensile strength is only 0.3 MPa, while the fiber membrane prepared under the same conditions in Example 1 has a tensile strength of 2.0 MPa.

[0058] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing silicon carbide-carbide multiphase micro / nano fibers, characterized in that, Includes the following steps: (1) Polycarbosilane, organometallic salt solution, synergistic solvent and spinning aid are mixed to obtain a spinning dispersion; The organometallic salt in the solution is tetrabutyl hafnium oxide, tetrabutyl zirconate, or tetrabutyl titanate, and the mass fraction of the organometallic salt in the solution is 60-90 wt%. The mass ratio of the polycarbosilane to the organometallic salt solution is 1:(0.05-0.5). (2) Using the spinning dispersion as the spinning solution and a flat plate as the receiver, electrospinning is performed to obtain the fibrils; (3) The original fiber is cross-linked and cured by electron beam irradiation under an inert atmosphere, and then cooled to obtain irradiated non-melting fiber; (4) The irradiated non-melting fiber is placed in an inert atmosphere, heated to 1300~1800℃ under tension assistance and sintered for 1~3 h to obtain the silicon carbide-carbide multiphase micro-nano fiber.

2. The method for preparing silicon carbide-carbide multiphase micro / nano fibers according to claim 1, characterized in that, In step (1), the solvent of the organometallic salt solution is n-butanol; the co-solvent is at least one of xylene, acetone, N,N-dimethylformamide and chloroform; the spinning aid is at least one of polyvinylpyrrolidone, polyvinyl alcohol and polystyrene; the mass ratio of polycarbosilane, organometallic salt solution, co-solvent and spinning aid is 1:(0.05~0.5):(0.5~3):(0.05~0.2).

3. The method for preparing silicon carbide-carbide multiphase micro / nanofibers according to claim 1, characterized in that, In step (1), the mixing method is water bath stirring or ultrasonic mixing. The water bath stirring speed is 400~1000 r / min and the duration is 2~8 h. The ultrasonic mixing duration is 2~5 h.

4. The method for preparing silicon carbide-carbide multiphase micro / nanofibers according to claim 1, characterized in that, In step (2), the conditions for electrospinning are: voltage of 10~25 kV, take-up distance of 10~25 cm, and feed rate of 0.8~2 mL / h.

5. The method for preparing silicon carbide-carbide multiphase micro / nanofibers according to claim 1, characterized in that, In step (3), the electron beam irradiation dose is 10~20 MGy, the electron beam irradiation time is 1~5 h, and after cooling, non-melting irradiated fibers are obtained.

6. The method for preparing silicon carbide-carbide multiphase micro / nano fibers according to claim 1, characterized in that, In steps (3) and (4), the inert atmosphere is argon or nitrogen.

7. The method for preparing silicon carbide-carbide multiphase micro / nanofibers according to claim 1, characterized in that, In step (4), the tension value is 0.1~10 N.

8. A silicon carbide-carbide multiphase micro / nanofiber prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The silicon carbide-carbide multiphase micro / nanofiber uses β-silicon carbide nanocrystals as a matrix, with uniformly distributed carbide nanocrystals embedded in situ between the grains of the β-silicon carbide nanocrystals. The carbide nanocrystals are hafnium carbide nanocrystals, zirconium carbide nanocrystals, or titanium carbide nanocrystals. The average grain size of the nanocrystals contained in the silicon carbide-carbide multiphase micro / nanofiber is 5~25 nm. The diameter of the silicon carbide-carbide multiphase micro / nanofiber is 0.5~5.0 μm. The silicon carbide-carbide multiphase micro / nanofiber does not contain an oxide phase.

9. An application of silicon carbide-carbide multiphase micro / nanofibers prepared by the preparation method according to any one of claims 1 to 7 in the ultra-high temperature field, characterized in that, Materials resistant to ultra-high temperatures of 1700℃~2100℃ were prepared using the silicon carbide-carbide multiphase micro-nano fibers.

10. The application of silicon carbide-carbide multiphase micro / nanofibers according to claim 9 in the ultra-high temperature field, characterized in that, The material is a thermal protection material, thermal sealing material, or thermal insulation material for aerospace vehicles.

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