Aluminum-containing refractory silicon carbide fiber and method of making same
By combining a modified magnetic catalyst with an 8-hydroxyquinoline aluminum solution, low-oxygen-content aluminum-containing silicon carbide fibers were prepared, solving the problem of strength reduction of SiC fibers in high-temperature environments and realizing efficient and low-cost fiber production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FUJIAN LEADASIA NEW MATERIAL CO LTD
- Filing Date
- 2026-06-04
- Publication Date
- 2026-07-03
Smart Images
Figure CN122327418A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of ceramic matrix composite materials technology, specifically relating to an aluminum-containing high-temperature resistant silicon carbide fiber and its preparation method. Background Technology
[0002] Silicon carbide (SiC) fiber, as a core reinforcement in high-performance ceramic matrix composites (CMCs), possesses irreplaceable strategic value in extreme environments such as aerospace, energy, and defense due to its high specific strength, high specific modulus, and excellent high-temperature and chemical corrosion resistance. However, traditional SiC fibers, due to their high oxygen content, experience decomposition of the amorphous SiCxOy phase at temperatures above 1200℃, leading to rapid coarsening of β-SiC grains and the formation of microcracks, resulting in a sharp decline in fiber strength. While methods such as electron beam irradiation non-melting treatment, chemical vapor deposition non-melting treatment, and dry spinning can produce SiC ceramic fibers with low oxygen content, these methods suffer from drawbacks including high cost, low production capacity, and stringent environmental and equipment requirements, hindering industrial application. Furthermore, the high free C content and low O content in the silicon carbide fibers produced by these methods still limit their application in even higher-temperature environments.
[0003] To reduce the production cost of SiC ceramic fibers while improving their temperature resistance, doping with heterogeneous elements has become a new research direction. Introducing aluminum into SiC fibers to form a structure of β-SiC dispersed in the Si-C-Al phase can significantly improve the temperature resistance of SiC ceramic fibers. The production cost of aluminum-containing SiC ceramic fibers is mainly related to the process, including the energy consumption and efficiency of the precursor pyrolysis synthesis, melt spinning, non-melting methods, firing, and sintering processes. The precursor pyrolysis synthesis process is difficult to control precisely in terms of reaction temperature, pressure, and raw material ratios. Furthermore, organometallic compounds such as aluminum acetylacetonate are expensive, and aluminum acetylacetonate is prone to sublimation, resulting in uneven molecular weight distribution of the precursor and high oxygen content in the product. These problems easily lead to uneven diameter and surface defects in the silicon carbide fiber products, resulting in low yield. Overcoming these core problems is key to moving SiC from the laboratory to large-scale production. Summary of the Invention
[0004] To address the problems of uncontrollable precursor pyrolysis synthesis and uneven precursor polymerization in existing technologies, this invention provides an aluminum-containing high-temperature resistant silicon carbide fiber and a method for preparing the silicon carbide fiber. The technical solution is as follows: A method for preparing aluminum-containing high-temperature resistant silicon carbide fiber includes the following steps: preparing an 8-hydroxyquinoline aluminum solution, adding xylene and polycarbosilane to the 8-hydroxyquinoline aluminum solution and dissolving them completely, adding a modified magnetic catalyst, and mixing evenly to obtain a mixed solution; allowing the mixed solution to react fully in a closed environment; fixing the modified magnetic catalyst after the reaction is complete, and then removing it to obtain a reaction solution; evaporating the solvent from the reaction solution to obtain an aluminum-containing precursor; subjecting the aluminum-containing precursor to melt spinning and non-melting treatment, and then calcining at high temperature to obtain the final product; the modified magnetic catalyst has aluminum active centers coated on its surface.
[0005] Furthermore, the mass ratio of 8-hydroxyquinoline aluminum to polycarbosilane is 1:10~20; the mass ratio of the modified magnetic catalyst to 8-hydroxyquinoline aluminum is 0.1~0.5:1.
[0006] Furthermore, the complete reaction in the closed environment is carried out in a reaction vessel at 270~300℃ for 0.5~2h; in an unsealed environment, the temperature is increased to the reaction temperature at a rate of 1~3℃ / min, thereby evaporating the solvent.
[0007] Furthermore, the solvent includes one or more of xylene, benzyl alcohol, or N,N-dimethylformamide.
[0008] Furthermore, the preparation of the modified magnetic catalyst includes the following steps: a. Take iron(III) oxide powder; b. Disperse ferric oxide thoroughly in a mixture of ethanol and water to obtain a dispersion; add sodium silicate to the dispersion, and then slowly add sulfuric acid dropwise while stirring, controlling the pH of the system to be weakly alkaline, and stir the reaction for 5-8 hours; separate and collect the product, wash it thoroughly and dry it to obtain the silica-coated precursor. c. Prepare a dispersion of silica-coated precursor; adjust and control the pH of the system to 3-5 using sulfuric acid; simultaneously and slowly add zirconium sulfate and sodium hydroxide solution to the system, and react for 1-2 hours; after the reaction is complete, age for 1-3 hours; separate and collect the product, wash thoroughly, and obtain the zirconium-modified precursor; d. Disperse the zirconium-modified precursor in ethanol, add aluminum isopropoxide, stir and react at room temperature for 5-8 hours, then evaporate the solvent and dry thoroughly; then calcine at 500-600 °C for 3-5 hours to obtain the modified magnetic catalyst.
[0009] Furthermore, the preparation of the iron oxide powder in step a includes the following steps: under the condition of oxygen isolation, ferric chloride and ferrous sulfate are dissolved in water to obtain an iron mixed solution; hot concentrated ammonia water is added dropwise to the iron mixed solution, the pH is adjusted to 10-11, and the reaction is stirred; after the reaction is completed, the product is separated and collected, thoroughly washed, and thoroughly dried to obtain iron oxide powder.
[0010] Furthermore, the weakly alkaline pH in step b is 8.5~10.5; the mass ratio of iron oxide to sodium silicate is 1:1~2; the slow dripping rate in step c is 0.02~0.1mL / s; the mass ratio of silica-coated precursor to zirconium sulfate is 15~25:1; the mass ratio of aluminum isopropoxide to zirconium sulfate in step d is 1.5~3:1; and the thorough drying in step d is drying at 100~120℃ for 6~12h.
[0011] Furthermore, before preparing the dispersion of the silica-coated precursor, the silica-coated precursor is first heat-treated at 200 °C for 1-3 h to complete the activation.
[0012] Furthermore, the regeneration of the modified magnetic catalyst includes the following steps: refluxing or soaking the modified magnetic catalyst with an organic solvent; drying and then calcining at 400~500℃ for 2~4 hours.
[0013] A high-temperature resistant aluminum-containing silicon carbide fiber prepared by the above method.
[0014] By adopting the above scheme, the method of the present invention has the following advantages: 1. The method of this invention can efficiently prepare precursors for aluminum-containing silicon carbide fibers with narrow distribution and low oxygen content. The aluminum-based Lewis acid active centers on the catalyst surface of this invention can selectively activate the Si-H bonds in polycarbosilanes and the aluminum source precursor, gently catalyzing the directional crosslinking of Si-O-Al bonds, avoiding random radical polymerization and excessive crosslinking side reactions. At the same time, relying on the surface confinement effect of the core-shell support, the PACS precursor chain growth is synchronous and uniform, achieving precise control of molecular weight from the reaction source. The resulting silicon carbide fiber products have strong high-temperature resistance, and the catalyst also has a long service life.
[0015] 2. Compared with conventional preparation methods that require high temperatures of 400~500℃ using aluminum acetylacetone as the aluminum source, the method of the present invention can be carried out at a lower temperature, which greatly suppresses the generation of heterochains and oxidation side reactions at high temperatures. In addition, the solid heterogeneous catalyst is easy to separate and has no homogeneous catalytic residue pollution, which can block the introduction of oxygen impurities from multiple pathways and obtain precursor products with low oxygen content.
[0016] 3. Compared with traditional non-catalytic or homogeneous catalytic systems, the PACS prepared by the method of this invention has a narrower molecular weight distribution and lower impurity content, which can significantly improve the spinnability and ceramicization properties of subsequent fibers. At the same time, the catalyst has a stable structure and can be recycled through low-temperature oxidation and carbonization, thus combining catalytic performance with the practicality of industrial applications.
[0017] 4. The catalyst of the present invention is first precisely controlled by synchronous dropwise addition of zirconium coating in an acidic water environment, then the outer aluminum component is mildly loaded by using an ethanol system in combination with aluminum isopropoxide, and finally the amorphous species are synergistically crystallized by one-step calcination. The preparation process is stable and reproducible, and does not require complex equipment or harsh conditions, making it easy to prepare in the laboratory and scale up in the industry.
[0018] 5. The catalyst of the present invention avoids phase separation and particle agglomeration caused by co-precipitation of zirconium and aluminum components through stepwise coating, so that the aluminum-based active sites on the surface are highly uniformly dispersed; the preparation and simultaneous crystallization of ZrO2 and Al2O3 on the support not only ensures the stability of the structure, but also solves the problem of active component sintering and support structure collapse at high temperature by strengthening the bonding effect of the core-shell interface, so that the catalyst has excellent structural stability and regeneration performance. Attached Figure Description
[0019] Figure 1 This is a comparison diagram of the initial tensile strength of silicon carbide fibers in each embodiment and the comparative example; Figure 2 This is a comparison chart of the tensile strength of silicon carbide fibers obtained after the 10th cycle of the catalysts used in each embodiment and comparative example. Detailed Implementation
[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Catalyst Example 1: (1) Nano-iron oxide was fully dispersed in a mixture of ethanol and water to obtain a dispersion. Sodium silicate with a mass of 1.5 times that of nano-iron oxide was added to the dispersion. Sulfuric acid was slowly added dropwise while stirring, and the pH of the system was controlled to be 9.5. The reaction was stirred for 6 hours. The product was separated and collected by magnetic separation, washed thoroughly and dried to obtain a silica-coated precursor. (2) Take 20g of silica-coated precursor and heat-treat it at 200℃ for 2h, then prepare a dispersion; use sulfuric acid to adjust and control the pH of the system to 4; take 1g of zirconium sulfate to prepare an aqueous solution, and add it to the system dropwise at a rate of 0.05mL / s with sodium hydroxide solution, and react for 1h; after the reaction is completed, age for 2h; separate and collect the product, wash it thoroughly, and obtain the zirconium-modified precursor; (3) Disperse the zirconium-modified precursor in ethanol, add 2.5 g of aluminum isopropoxide, stir the reaction at room temperature for 6 h, remove the solvent by evaporation, dry at 110 °C for 8 h, and then calcine at 550 °C for 4 h to obtain the modified magnetic catalyst.
[0022] Catalyst Example 2: The difference between this example and Catalyst Example 1 is as follows: (1) Nano-iron oxide was fully dispersed in a mixture of ethanol and water to obtain a dispersion. Sodium silicate was added to the dispersion, and sulfuric acid was slowly added dropwise while stirring. The pH of the system was controlled to be 8.5. The reaction was stirred for 6 hours. The product was separated and collected by magnetic separation, washed thoroughly and dried to obtain a silica-coated precursor.
[0023] Catalyst Example 3: The difference between this example and Catalyst Example 1 is as follows: (2) Take 20g of silica-coated precursor to prepare a dispersion; use sulfuric acid to adjust and control the pH of the system to 4; take 1g of zirconium sulfate to prepare an aqueous solution, and add it to the system simultaneously with sodium hydroxide solution at a rate of 0.05mL / s, and react for 1h; after the reaction is completed, age for 2h; separate and collect the product, wash thoroughly, and obtain zirconium-modified precursor.
[0024] Catalyst Example 4: The difference between this example and Catalyst Example 1 is as follows: (2) Take 20g of silica-coated precursor and heat-treat it at 200℃ for 2h, then prepare a dispersion; use sulfuric acid to adjust and control the pH of the system to 4; take 1g of zirconium sulfate to prepare an aqueous solution, and add it to the system simultaneously with sodium hydroxide solution at a rate of 0.05mL / s, and react for 1h; after the reaction is completed, age for 2h; separate and collect the product, wash it thoroughly, and calcine it at 550℃ for 3~5h to obtain zirconium-modified precursor.
[0025] Catalyst Example 5: The difference between this example and Catalyst Example 1 is as follows: (2) Take 20g of silica-coated precursor and heat-treat it at 200℃ for 2h, then prepare a dispersion; use sulfuric acid to adjust and control the pH of the system to 4; take 1g of zirconium sulfate to prepare an aqueous solution, and add it to the system simultaneously with sodium hydroxide solution at a rate of 0.1mL / s, and react for 1h; after the reaction is completed, age for 2h; separate and collect the product, wash it thoroughly, and obtain the zirconium-modified precursor.
[0026] Catalyst Comparative Example 1: The difference between this and Catalyst Example 1 is that: Instead of coating the iron oxide with silicon dioxide in step (1), the zirconium modification in step (2) is carried out directly.
[0027] Catalyst Comparative Example 2: The difference between this and Catalyst Example 1 is: Instead of performing zirconium modification in step (2), proceed directly to step (3).
[0028] Example 1: (1) 5g of 8-hydroxyquinoline aluminum was added to 300mL of DMF solution, heated and stirred to dissolve, and then 300mL of xylene was slowly added to the solution to obtain an aluminum source solution; 75g of PCS was added to 150mL of xylene and stirred to dissolve to obtain a PCS solution; the aluminum source solution and PCS solution were slowly mixed, and 1.5g of the modified magnetic catalyst prepared in Example 1 was added to obtain a mixed solution; the obtained mixed solution was transferred to a reaction vessel, heated to 280℃ at a heating rate of 5℃ / min, and kept at that temperature for 1h; (2) After the reaction is complete, the catalyst is fixed to the top of the reactor by magnetic attraction and naturally cooled to obtain a mixed solution containing aluminum precursor; under an argon atmosphere, the mixed solution is heated to 280°C at a rate of 2°C / min, the solvent is evaporated and condensed for recovery, and then the system is naturally cooled to room temperature to obtain PACS; (3) Set the spinning temperature to 335℃, the spinning pressure to 0.8MPa, and the winding speed to 205m / min. Spin the obtained PACS. Heat the obtained raw filament to 200℃ at a rate of 3℃ / min and keep it at that temperature for 10h. Then cool it naturally to room temperature. Then heat it to 1100℃ at a rate of 5℃ / min and keep it at that temperature for 30min to obtain aluminum-containing silicon carbide fiber.
[0029] Following the method of Example 1, experiments were conducted on the remaining examples and comparative examples according to the correspondence in Table 1.
[0030] Table 1: Catalyst Selection and Corresponding Catalysts
[0031] Example Sample Testing: The tensile strength σ (GPa) of the aluminum-containing silicon carbide fibers prepared in each embodiment and comparative example was tested using a tensile test method under uniaxial tensile load at room temperature and atmospheric conditions. The tensile strength was calculated using the formula σ (GPa) = 12.732f / d. 2 The calculations were performed, where the fiber breaking force was f (cN) and the diameter was d (μm). The tensile strength results for each sample are as follows: Figure 1 As shown, with Figure 1 The average tensile strength was calculated from the data, and the mechanical properties of the samples were evaluated using the average tensile strength. The aluminum-containing silicon carbide fibers prepared in each example and comparative example were placed in a rapid heating air atmosphere heat treatment furnace and held at 900°C for 1 hour. Their tensile strength was tested and compared with the initial average tensile strength to calculate the high-temperature strength retention rate.
[0032] The catalysts recovered in each embodiment were recycled and reused 10 times. After each use, the catalysts were thoroughly washed with an organic solvent. The average tensile strength of the aluminum-containing silicon carbide fibers obtained in the 10th cycle was calculated, and the results are as follows: Figure 2 As shown, with Figure 2 The mean values of the data were calculated and compared with the initial tensile strength to calculate the cyclic strength retention rate, thereby evaluating the catalyst's lifespan. The results are shown in Table 2.
[0033] Table 2: Mechanical properties of aluminum-containing silicon carbide fibers
[0034] Depend on Figure 1 It can be seen that the tensile strength distribution of the aluminum-containing silicon carbide fibers prepared by the method of the present invention is relatively uniform, indicating that the method of the present invention can better control product quality and achieve a high product yield.
[0035] As shown in Table 2, the performance of Comparative Example 3, which did not use a catalyst, was significantly worse than all the examples and other comparative examples, indicating that the method of the present invention can significantly improve the strength and high-temperature resistance of aluminum-containing silicon carbide fibers. Comparative Example 1 used a catalyst without silica coating, resulting in silicon carbide fibers with extremely poor strength and much shorter lengths during spinning compared to other examples. Furthermore, after the first cycle, only half of the catalyst was recovered, indicating that the catalyst structure collapsed at this point, with much catalyst remaining in the product and most of its catalytic activity lost. This demonstrates that silica coating is crucial for the complete separation and recovery of the catalyst and is a prerequisite for the successful implementation of the preparation method of the present invention. Comparative Example 2 used a catalyst without zirconium modification. After 10 cycles, the product's cycle strength retention rate was only 39.7%, indicating a significant decrease in the catalyst's catalytic life. This demonstrates that the zirconium modification step in the method of the present invention can improve the structural stability of the catalyst and extend its service life.
[0036] Compared to Example 1, the catalyst used in Example 2 had a pH of 8.5 during the preparation of the silica coating, resulting in a significant decrease in the tensile strength of the silicon carbide fibers. The amount of catalyst recovered during the preparation process was also reduced. This may be because the lower pH value makes the coating more prone to defects, exposing the internal iron(III) oxide layer, and the increased catalyst residue affects fiber strength. The catalyst used in Example 3 was not heat-activated before zirconium modification, resulting in fewer alumina active centers grafted onto the catalyst, decreased catalytic performance, and consequently, reduced product strength and high-temperature resistance. The catalyst used in Example 4 underwent high-temperature calcination during zirconium modification, leading to a decrease in the strength and high-temperature resistance of the resulting silicon carbide fibers. This is likely due to the reduced catalytic performance of the catalyst prepared by this method. Furthermore, the cycle performance of the sample in Example 4 also decreased significantly, indicating that the simultaneous crystallization method of this invention can improve the structural strength of the catalyst and extend its service life. The reduced cycle life of the catalyst in Example 5 indicates that during zirconium modification, a rapid dropwise addition rate of zirconium raw materials and alkali is detrimental to uniform zirconium coating and affects the structural strength of the catalyst.
[0037] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.
Claims
1. A method for preparing aluminum-containing high-temperature resistant silicon carbide fiber, characterized in that, Includes the following steps: An 8-hydroxyquinoline aluminum solution was prepared, and xylene and polycarbosilane were added to the solution and dissolved completely. A modified magnetic catalyst was then added and mixed thoroughly to obtain a mixture. The mixture was then allowed to react completely in a closed environment. After the reaction was complete, the modified magnetic catalyst was fixed and removed to obtain a reaction solution. The solvent in the reaction solution was evaporated to obtain an aluminum-containing precursor. The aluminum-containing precursor was then subjected to melt spinning and non-melting treatment, followed by high-temperature calcination to obtain the final product. The modified magnetic catalyst has aluminum active centers coated on its surface. The preparation of the modified magnetic catalyst includes the following steps: a. Take iron(III) oxide powder; b. Disperse ferric oxide thoroughly in a mixture of ethanol and water to obtain a dispersion; add sodium silicate to the dispersion, and then slowly add sulfuric acid dropwise while stirring, controlling the pH of the system to be weakly alkaline, and stir the reaction for 5-8 hours; separate and collect the product, wash it thoroughly and dry it to obtain the silica-coated precursor. c. Prepare a dispersion of silica-coated precursor; adjust and control the pH of the system to 3-5 using sulfuric acid; simultaneously and slowly add zirconium sulfate and sodium hydroxide solution to the system, and react for 1-2 hours; after the reaction is complete, age for 1-3 hours; separate and collect the product, wash thoroughly, and obtain the zirconium-modified precursor; d. Disperse the zirconium-modified precursor in ethanol, add aluminum isopropoxide, stir and react at room temperature for 5-8 hours, then evaporate the solvent and dry thoroughly; then calcine at 500-600℃ for 3-5 hours to obtain the modified magnetic catalyst.
2. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, The mass ratio of 8-hydroxyquinoline aluminum to polycarbosilane is 1:10~20; the mass ratio of the modified magnetic catalyst to 8-hydroxyquinoline aluminum is 0.1~0.5:
1.
3. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, The complete reaction in the closed environment is carried out in a reaction vessel at 270~300℃ for 0.5~2h; in an unsealed environment, the temperature is increased to the reaction temperature at a rate of 1~3℃ / min to remove the solvent.
4. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, The solvent includes one or more of xylene, benzyl alcohol, or N,N-dimethylformamide.
5. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, The preparation of the iron oxide powder in step a includes the following steps: In the absence of oxygen, ferric chloride and ferrous sulfate are dissolved in water to obtain a mixed iron solution; hot concentrated ammonia is added dropwise to the mixed iron solution to adjust the pH to 10-11, and the reaction is stirred; after the reaction is completed, the product is separated and collected, washed thoroughly, and dried thoroughly to obtain iron(III) oxide powder.
6. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, The weakly alkaline pH in step b is 8.5~10.5; the mass ratio of iron oxide to sodium silicate is 1:1~2; the slow dripping rate in step c is 0.02~0.1 mL / s; the mass ratio of silica-coated precursor to zirconium sulfate is 15~25:1; the mass ratio of aluminum isopropoxide to zirconium sulfate in step d is 1.5~3:1; the thorough drying in step d is drying at 100~120℃ for 6~12 hours.
7. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, Before preparing the dispersion of the silica-coated precursor, the silica-coated precursor is first heat-treated at 200℃ for 1~3h to complete the activation.
8. The method for preparing aluminum-containing high-temperature resistant silicon carbide fiber according to claim 1, characterized in that, The regeneration of the modified magnetic catalyst includes the following steps: refluxing or soaking the modified magnetic catalyst with an organic solvent; drying and then calcining at 400-500℃ for 2-4 hours.
9. An aluminum-containing high-temperature resistant silicon carbide fiber prepared by the method of claim 1.