A method for preparing zirconium in-situ doped continuous alumina ceramic fiber

Abstract

The present invention provides a method for preparing continuous alumina ceramic fibers doped with zirconium in situ. The technical solution is to adopt the method of spraying zirconium oxychloride, low-temperature aging, and freeze-drying concentration to obtain a sol-gel with excellent spinning performance. The excellent spinning performance ensures a simple drop-gel spinning process. After a high-temperature heat treatment process, continuous alumina ceramic fibers with excellent mechanical properties can be obtained. The continuous and uniform alumina ceramic fibers can be used for the preparation of high-performance ceramic fiber brushes. The present invention has the following beneficial effects: zirconium oxychloride is dissolved in an aqueous solution of polyvinyl pyrrolidone (PVP) and added to the alumina sol in the form of a spray, fully ensuring that the zirconium source is uniformly incorporated into the alumina colloid, realizing effective doping between zirconium, PVP and alumina sol, which is beneficial to maintaining the uniformity of the sol and promoting the improvement of the sol spinning performance.

Description

Technical Field

[0001] The invention relates to a method for preparing zirconium in-situ doped continuous alumina ceramic fiber, belonging to the field of ceramic fiber materials. Background Art

[0002] Alumina fiber is a high-performance inorganic fiber whose main component is alumina (Al2O3). Alumina fiber has excellent heat resistance, extremely low thermal conductivity and good chemical stability, and is widely used in industrial production, high-temperature insulation and national defense construction. However, conventional alumina fibers currently have some bottleneck problems, such as high brittleness and poor flexibility. In particular, they cannot be made into excellent continuous long fibers, which significantly restricts the use of alumina fibers in precision instruments, fine manufacturing, aerospace and other fields. However, these high-tech industries have a particularly high demand for high-performance continuous alumina ceramic fibers, and there is a serious imbalance between supply and demand. Alumina fibers are generally prepared by melt spinning, slurry spinning and sol-gel methods. Among them, the sol-gel process is easy to adjust the fiber diameter and composition, and the process conditions are simple, especially the low heat treatment temperature and low energy consumption. It has developed rapidly in recent years. However, the sol-gel method for producing alumina ceramic fibers also has key technical difficulties, namely, the spinning performance of the alumina ceramic fiber precursor gel is poor, making it difficult to obtain continuous gel filaments. In addition, the spun gel fiber filaments have obvious defects on the surface and different diameters, which seriously affect the mechanical properties of the ceramic fibers after high-temperature ceramicization. Summary of the Invention

[0003] In order to overcome the above problems, the patent of this invention proposes a method of in-situ doping with zirconium element to improve the spinning performance of alumina ceramic fiber precursor gel and realize the preparation of high-quality continuous alumina ceramic fiber.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for preparing zirconium in-situ doped continuous alumina ceramic fiber comprises the following steps:

[0006] S1, preparing alumina sol;

[0007] S2, dissolving a zirconium source in an aqueous solution of polyvinyl pyrrolidone, and adding the alumina sol in a spraying manner under reflux to obtain a zirconium-containing alumina sol;

[0008] S3, heating the zirconium-containing alumina sol to a slight boil (close to 100° C. to prevent premature loss of water), stirring and reacting at a slight boil, cooling and concentrating by vacuum distillation to obtain an alumina fiber gel;

[0009] S4, after aging the alumina fiber gel at low temperature, further removing the solvent water by freeze drying to obtain an alumina fiber precursor gel;

[0010] S5. After spinning the alumina fiber precursor gel into continuous fiber filaments, the fiber filaments are dried at a constant temperature and subjected to high-temperature heat treatment to obtain the zirconium in-situ doped continuous alumina ceramic fibers.

[0011] As a preferred embodiment, the preparation method of the alumina sol is:

[0012] Aluminum powder and aluminum salt are added to water and refluxed continuously until the aluminum powder is dissolved. After filtering out insoluble impurities, alumina sol is obtained.

[0013] As a preferred solution, the aluminum salt is selected from at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate. After the aluminum salt is dissolved in water, the total concentration does not exceed 60wt%. Excessive aluminum salt will cause the viscosity of the gel fiber to increase significantly and reduce the spinnability.

[0014] As a preferred embodiment, the reflux temperature in step S2 is 60-90° C., the concentration of the aqueous solution of polyvinyl pyrrolidone does not exceed 10 wt %, the concentration of the zirconium source does not exceed 5 wt %, and the molar ratio of aluminum to zirconium is (8-20):1. The concentrations and amounts of polyvinyl pyrrolidone and the zirconium source should not be too high to avoid unevenness in the subsequent incorporation process.

[0015] As a preferred embodiment, the zirconium source is zirconium oxychloride.

[0016] As a preferred solution, in step S4, the aging temperature is 4-8°C and the aging time is not less than 30 days. Too short an aging time cannot ensure sufficient cross-linking reaction between the components in the gel at low temperature.

[0017] As a preferred solution, in step S4, the vacuum degree of the freeze drying is lower than 100 Pa and the time does not exceed 48 hours. A long freeze drying process under high vacuum degree will lead to excessive dehydration of the gel, affecting the subsequent spinning performance.

[0018] As a preferred solution, the constant temperature drying temperature is 40-60°C.

[0019] As a preferred solution, in step S5, the temperature of the high temperature heat treatment is 800-1200°C.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. Dissolve zirconium oxychloride in an aqueous solution of polyvinyl pyrrolidone (PVP) and add it to the alumina sol in the form of a spray to fully ensure that the zirconium source is evenly incorporated into the alumina colloid, thereby achieving effective doping between zirconium, PVP and alumina sol, which is beneficial to maintaining the uniformity of the sol and promoting the improvement of the sol spinning performance.

[0022] 2. The long-term low-temperature aging process fully ensures the slow and effective combination of the polycondensate chains of zirconium and alumina sol, ultimately enhancing the mechanical strength of the obtained ceramic fiber.

[0023] 3. The freeze-drying concentration method helps to remove water molecules inside the gel, accelerate and deepen the gel aging process, and the dehydration method under freeze-drying is mild and will not cause gel solidification caused by excessive concentration, which can ensure good spinning performance of the sol.

[0024] 4. The good spinnability of the gel creates a simple glue spinning process. Without external force, the gel can be evenly drawn for more than 1m by its own gravity. The diameter of the fiber obtained by glue spinning is small and uniform, which helps to simplify the air-drying process (no more than 0.5h), can ensure the quality of the finished product, and has high mechanical tensile strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0026] Figure 1 This is a scanning electron microscope image of zirconium-doped continuous alumina ceramic fiber.

[0027] Figure 2 This is a high-resolution scanning electron microscope image of zirconium-doped continuous alumina ceramic fibers. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0029] Example 1

[0030] Weigh 20g of aluminum powder and dissolve it in 100ml of water. Disperse it under continuous stirring for more than 4 hours. Add 35g of aluminum nitrate to the dispersion and disperse it under continuous stirring for more than 2 hours. Then continue to reflux until the aluminum powder dissolves. After filtering out insoluble impurities, obtain alumina sol. Stir the alumina sol under continuous stirring at 60°C. Add a zirconium oxychloride PVP aqueous solution (aluminum-zirconium molar ratio 15:1) to the above sol in the form of a spray. The aqueous solution contains 10% PVP was added by spraying for about 30 minutes to ensure the uniformity of the sol; the reaction was continued under slight boiling reflux stirring for more than 12 hours, and after cooling, it was concentrated by reduced pressure distillation to 20% of the original mass to obtain a zirconium-doped alumina fiber gel; the above-mentioned alumina fiber gel was placed in a refrigerator for refrigeration and sealed and aged for 30 days at a low temperature (6°C) for a long time; the gel after low-temperature aging was placed in a freeze dryer to continue to remove part of the solvent water (vacuum degree less than 100 Pa), and freeze-dried for 48 hours to obtain an alumina fiber precursor gel with excellent spinning performance; after the alumina fiber precursor gel returned to room temperature (30°C), it was placed in a syringe without a needle and gradually dripped into fiber filaments under gravity at room temperature; the filaments formed by dripping were about 1.2m long, and after drying in a constant temperature box (45°C) for 30 minutes, they were collected by a roller; a high-temperature heat treatment at 1000°C for 36 hours was performed to obtain alumina continuous ceramic fibers with uniform diameter (about 20μm), see Figure 1 The obtained fibers are small, uniform, continuous and without obvious breaks as shown in the scanning electron microscope images. Figure 2 The high-resolution scanning electron microscope image also shows that the ceramic fiber filaments are dense, the surface is smooth, and there are no obvious defects. Its tensile strength can reach 250Mpa.

[0031] Example 2

[0032] Weigh 20g of aluminum powder and dissolve it in 100ml of water. Stir continuously for more than 4 hours. Add 40g of aluminum chloride to the dispersion and stir continuously for more than 2 hours. Then continue to reflux until the aluminum powder dissolves. Filter insoluble impurities to obtain alumina sol. Stir continuously the alumina sol at 90°C and add a zirconium oxychloride PVP aqueous solution (aluminum-zirconium molar ratio 12:1) to the above sol in the form of a spray. The aqueous solution contains 10% PVP is sprayed and added for about 60 minutes to ensure the uniformity of the sol; the reaction is continued with slight boiling reflux stirring for more than 12 hours, and after cooling, it is concentrated by reduced pressure distillation to 20% of the original mass to obtain a zirconium-doped alumina fiber gel; the above-mentioned alumina fiber gel is placed in a refrigerator for refrigeration and sealed and aged for 40 days at a long-term low temperature (6°C); the gel after low-temperature aging is placed in a freeze dryer to continue to remove part of the solvent water (vacuum degree is less than 100Pa), and freeze-dried for 36 hours to obtain an alumina precursor fiber gel with excellent spinning performance; after the alumina fiber precursor gel returns to room temperature (30°C), it is placed in a syringe without a needle and gradually dripped into fiber filaments under gravity at room temperature; the filaments formed by dripping are about 1 meter long, and after drying in a constant temperature box (45°C) for 30 minutes, they are collected with a roller; high-temperature heat treatment at 900°C for 36 hours obtains alumina continuous ceramic fibers with uniform diameter (about 15μm) and a tensile strength of up to 200Mpa.

[0033] Example 3

[0034] Weigh 15g of aluminum powder and dissolve it in 100ml of water. Disperse it under continuous stirring for more than 4 hours. Add 40g of aluminum chloride to the dispersion and disperse it under continuous stirring for more than 3 hours. Then continue to reflux until the aluminum powder dissolves. After filtering out insoluble impurities, obtain alumina sol. Stir the alumina sol under 60℃ and add a zirconium oxychloride PVP aqueous solution (aluminum zirconium molar ratio 18:1) to the above sol in the form of a spray. The aqueous solution contains 10% PVP is sprayed and added for about 45 minutes to ensure the uniformity of the sol; the reaction is continued with slight boiling reflux stirring for more than 12 hours, and after cooling, it is concentrated by reduced pressure distillation to 20% of the original mass to obtain a zirconium-doped alumina fiber gel; the above-mentioned alumina fiber gel is placed in a refrigerator for refrigeration and sealed and aged for a long time at low temperature (4°C) for 60 days; the gel after low-temperature aging is placed in a freeze dryer to continue to remove part of the solvent water (vacuum degree less than 100Pa), and freeze-dried for 24 hours to obtain an alumina precursor fiber gel with excellent spinning performance; after the alumina fiber precursor gel returns to room temperature (35°C), it is placed in a syringe without a needle and gradually dripped into fiber filaments under gravity at room temperature; the filaments formed by dripping are as long as 1.5m, and after drying in a constant temperature box (45°C) for 30 minutes, they are collected with a roller; high-temperature heat treatment at 1100°C for 36 hours obtains alumina continuous ceramic fibers with uniform diameter (about 25μm) and a tensile strength of up to 220Mpa.

[0035] Example 4

[0036] Weigh 20g of aluminum powder and dissolve it in 100ml of water. Stir continuously for more than 4 hours. Add 30g of aluminum nitrate to the dispersion and stir continuously for more than 5 hours. Then continue to reflux until the aluminum powder dissolves. Filter insoluble impurities to obtain alumina sol. Stir continuously the alumina sol at 80℃ and add a zirconium oxychloride PVP aqueous solution (aluminum zirconium molar ratio 10:1) to the above sol in the form of a spray. The aqueous solution contains 10% PVP is sprayed and added for about 35 minutes to ensure the uniformity of the sol; the reaction is continued with slight boiling reflux stirring for more than 12 hours, and after cooling, it is concentrated by reduced pressure distillation to 12% of the original mass to obtain a zirconium-doped alumina fiber gel; the above-mentioned alumina fiber gel is placed in a refrigerator for refrigeration and sealed and aged at a low temperature (5°C) for a long time for 35 days; the gel after low-temperature aging is placed in a freeze dryer to continue to remove part of the solvent water (vacuum degree less than 100Pa), and freeze-dried for 30 hours to obtain an alumina precursor fiber gel with excellent spinning performance; after the alumina fiber precursor gel returns to room temperature (28°C), it is placed in a syringe without a needle and gradually dripped into fiber filaments under gravity at room temperature; the filaments formed by dripping are up to 1.0m long, and after drying in a constant temperature box (40°C) for 10 minutes, they are collected with a roller; high-temperature heat treatment at 1200°C for 36 hours obtains alumina continuous ceramic fibers with uniform diameter (about 20μm) and a tensile strength of up to 230Mpa.

[0037] Comparative Example 1

[0038] This comparative example differs from Example 1 in that zirconium oxychloride powder was added directly, rather than sprayed. The resulting filaments were too short to be collected using a roller. They were heat-treated at 1000°C for 36 hours, but mechanical properties could not be tested due to their short length.

[0039] Comparative Example 2

[0040] This comparative example differs from Example 2 in that it does not employ a low-temperature sealing aging method, but rather directly ages the gel at room temperature. Due to the prolonged aging of the gel at room temperature, it partially hardens, resulting in poor fiber formation by dripping. The resulting fibers are also too short to be collected using a roller. Despite a high-temperature heat treatment at 900°C for 36 hours, the fibers are too short to be tested for mechanical properties.

[0041] Comparative Example 3

[0042] This comparative example differs from Example 3 in that, rather than freeze-drying for further dehydration, the precursor gel was aged and then returned to room temperature for direct spin-drying. The precursor gel had a high water content, resulting in intermittent fibers, some approximately 0.5 μm long. After drying in a thermostat (45°C) for 30 minutes, the fibers were collected using a roller. Heat treatment at 1100°C for 36 hours yielded alumina ceramic fibers with a diameter of approximately 60 μm and a tensile strength of approximately 90 MPa.

[0043] Comparative Example 4

[0044] This comparative example differs from Example 4 in that a centrifugal spinning process is employed instead of a gel-drip spinning process. The precursor gel, at room temperature, gradually forms fiber filaments under the action of centrifugal force. These filaments are relatively short, with the longest being approximately 0.3 m. After drying in a constant temperature oven (40°C) for 10 minutes, they are directly heat-treated at 1200°C for 36 hours, yielding alumina ceramic fibers with a diameter of approximately 50 μm and a tensile strength of approximately 60 MPa.

[0045] Comparison of Example 1 with Comparative Example 1 shows that the process of spraying zirconium oxychloride into the PVP aqueous solution is irreplaceable. This solution can ensure uniform doping of the zirconium source and the gel, while also ensuring good spinning performance of the gel.

[0046] Comparison of Example 2 with Comparative Example 2 shows that the low-temperature sealing and aging solution is irreplaceable. This process fully ensures the slow and effective combination of the polycondensate chains of zirconium and alumina sol, while avoiding excessive dehydration and maintaining good spinning performance of the precursor gel.

[0047] Comparison of Example 3 with Comparative Example 3 demonstrates that freeze-drying followed by dehydration is irreplaceable. This technique facilitates the continued removal of water molecules from the gel, accelerating and deepening the gel aging process. This is crucial for the smooth progress of the subsequent drip spinning process and is also a crucial condition for obtaining fine, high-strength, continuous fibers.

[0048] Comparison of Example 4 with Comparative Example 4 shows that the gel spinning process is irreplaceable. This process is not only simple, but also, with the excellent spinning performance of the gel, can ensure the production of continuous long fibers with small and uniform diameters and excellent mechanical tensile properties.

[0049] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing zirconium in-situ doped continuous alumina ceramic fiber, characterized in that: The steps include: S1, preparing alumina sol; S2, dissolving a zirconium source in an aqueous solution of polyvinyl pyrrolidone, and adding the alumina sol in a spraying manner under reflux to obtain a zirconium-containing alumina sol; S3, heating the zirconium-containing alumina sol to a slight boil, stirring and reacting at a slight boil, cooling and concentrating by vacuum distillation to obtain an alumina fiber gel; S4, sealing and aging the alumina fiber gel at low temperature, and then removing the solvent water by freeze drying to obtain an alumina fiber precursor gel; S5, spinning the alumina fiber precursor gel into fiber filaments by using a drop-coating method, drying the fiber filaments at a constant temperature, and performing a high-temperature heat treatment to obtain the zirconium in-situ doped continuous alumina ceramic fiber; In step S4, the aging temperature is 4-8°C and the aging time is not less than 30 days; In step S4, the vacuum degree of the freeze-drying is lower than 100 Pa and the time does not exceed 48 hours.

2. The method for preparing zirconium in-situ doped continuous alumina ceramic fiber according to claim 1, characterized in that: The preparation method of the alumina sol is: Aluminum powder and aluminum salt are added to water and refluxed continuously until the aluminum powder is dissolved. After filtering out insoluble impurities, alumina sol is obtained.

3. The method for preparing zirconium in-situ doped continuous alumina ceramic fiber according to claim 2, characterized in that: The aluminum salt is selected from at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate. After the aluminum salt is dissolved in water, the total concentration does not exceed 60 wt%.

4. The method for preparing zirconium in-situ doped continuous alumina ceramic fiber according to claim 1, wherein: The reflux temperature in step S2 is 60-90° C., the concentration of the aqueous solution of polyvinyl pyrrolidone does not exceed 10 wt %, the concentration of the zirconium source does not exceed 5 wt %, and the molar ratio of aluminum to zirconium is (8-20):

1.

5. The method for preparing zirconium in-situ doped continuous alumina ceramic fiber according to claim 4, characterized in that: The zirconium source is zirconium oxychloride.

6. The method for preparing zirconium in-situ doped continuous alumina ceramic fiber according to claim 1, characterized in that: The constant temperature drying temperature is 40-60°C.

7. The method for preparing zirconium in-situ doped continuous alumina ceramic fiber according to claim 1, characterized in that: In step S5, the temperature of the high temperature heat treatment is 800-1200°C.

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