Method for preparing alumina synthetic fiber based on electrostatic spinning

Abstract

The invention relates to the technical field of preparation of alumina fibers, in particular to a method for preparing alumina synthetic fibers based on electrostatic spinning, which comprises the following steps: adding ZIF-8 into a mixed solvent to form a metal organic framework dispersion liquid, adding aluminum sec-butoxide to form a uniform precursor solution, and performing electrostatic spinning to obtain a precursor solution; adding the yttria-stabilized zirconia dispersion liquid into the precursor solution, and finally adding polyvinylpyrrolidone to obtain a composite spinning solution; and then carrying out electrostatic spinning, heat treatment and high-temperature sintering to obtain the alumina synthetic fiber. According to the preparation method, aluminum sec-butoxide is used as a precursor, ZIF-8 is used as a structure-directing agent, ordered arrangement of aluminum oxide nanoparticles is guided through a porous structure of the material, a more compact and ordered aluminum oxide crystal structure is formed, the internal structure of the fiber is more compact, meanwhile, it is ensured that the aluminum oxide nanoparticles are evenly dispersed in the fiber, and the performance of the fiber is improved. The crystallinity and the mechanical property of the aluminum oxide synthetic fiber are improved, and the overall uniformity and consistency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of alumina fiber preparation, and in particular to a method for preparing alumina synthetic fibers based on electrostatic spinning. Background Art

[0002] Electrospinning, also known as electrospinning, utilizes an electric field to gradually stretch polymers or sols into nanometer-sized fibers. This method, capable of continuously producing nanofibers, is a simple and universal method for preparing nanofibers. Electrospun nanofibers, including electrospun ceramic fibers, exhibit exceptionally long fibers, diverse chemical compositions, uniform fiber diameters, and polycrystalline or amorphous structures. Alumina synthetic fibers are a type of high-temperature ceramic fiber that not only exhibits excellent fire resistance but also good mechanical strength and chemical stability. They are widely used in aerospace, high-temperature insulation materials, high-temperature filters, and catalyst supports.

[0003] However, in the preparation of high-temperature ceramic fibers such as alumina synthetic fibers, the existing precursor solutions have poor uniformity and stability, which will lead to inconsistent droplet size and speed during the spinning process, causing fluctuations in fiber diameter and possibly the formation of a beaded structure. Stable solution properties are the key to ensuring precise control of spinning process parameters and reducing fiber quality problems caused by solution changes; and once the spinning process is affected, the density of the internal structure of the fiber will be reduced, increasing the possibility of phase change and grain growth at high temperature, making it difficult to form a stable phase structure, thereby reducing the high-temperature stability of the alumina synthetic fiber and weakening its overall mechanical properties. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for preparing alumina synthetic fibers based on electrospinning.

[0005] A method for preparing alumina synthetic fibers based on electrospinning, comprising the following steps: (1) Preparation of composite spinning solution: Add ZIF-8 powder to a mixed solvent of ethanol and N,N-dimethylformamide, stir and disperse evenly to form a metal organic framework dispersion; Slowly add aluminum sec-butoxide to the metal organic framework dispersion and slowly stir to completely dissolve it to form a uniform precursor solution; Dispersing yttrium-stabilized zirconia powder in N,N-dimethylformamide and uniformly dispersing the powder by ultrasonic treatment to form a yttrium-stabilized zirconia dispersion; Slowly add the yttrium-stabilized zirconia dispersion to the precursor solution while maintaining continuous stirring to ensure that the two solutions are evenly mixed to form a mixed solution; Slowly adding polyvinyl pyrrolidone into the mixed solution, and continuously stirring until a stable composite spinning solution is obtained; (2) Electrospinning fibers: Use a syringe pump to eject the composite spinning solution through a nozzle to form a Taylor cone, which is then sprayed onto a receiving device to obtain a pre-spun fiber. The pre-spun fiber is placed in an oven and dried at 80°C for 3 hours. The temperature is then adjusted to 170°C and dried for another 2 hours to crosslink and solidify the pre-spun fiber. (3) Heat treatment and high-temperature sintering: The solidified as-spun fiber is placed in a high-temperature furnace and calcined at a rate of 2°C / min to 1100°C-1400°C. After cooling, it is taken out to obtain alumina synthetic fiber.

[0006] Preferably, in the composite spinning solution prepared in (1), the mass ratio of ZIF-8 powder, aluminum sec-butoxide, yttrium-stabilized zirconia powder, and polyvinyl pyrrolidone is 0.5-1:2-4:3-6:1-2.

[0007] Preferably, in the composite spinning solution prepared in (1), the volume ratio of ethanol to N,N-dimethylformamide in the mixed solvent of ethanol and N,N-dimethylformamide is 7-8:2-3.

[0008] Preferably, in the composite spinning solution prepared in (1), 3-6 parts by mass of yttrium-stabilized zirconia powder is dispersed in 30 parts by volume of N,N-dimethylformamide.

[0009] Preferably, in the preparation of the composite spinning solution (1), polyvinyl pyrrolidone is slowly added to the mixed solution, and the continuous stirring stage includes stirring at 700 rpm for 20-30 minutes, and then adjusting the speed to 500 rpm and continuing stirring for 3-5 hours.

[0010] Preferably, in the preparation of the composite spinning solution in (1), the ultrasonic treatment time is 5-10 minutes.

[0011] Preferably, in the preparation of the composite spinning solution in (1), the stirring speed does not exceed 700 rpm.

[0012] Preferably, in the (2) electrospun fibers, the electrospinning conditions include: voltage 10-15 kV, receiving distance 10-15 cm, spinning rate 0.3-0.7 ml / h, ambient temperature 20-25° C., and humidity 30%-50%.

[0013] Preferably, the (3) heat treatment and high-temperature sintering are divided into three stages: the first stage is from room temperature to 500-550°C, and the holding time is 60 minutes; the second stage is from the first stage temperature to 1200-1300°C, and the holding time is 60 minutes; the third stage is from the second stage temperature to 1400°C, and the holding time is 90 minutes. The heating rate of the three stages is 2°C / min.

[0014] Preferably, in the (3) heat treatment and high-temperature sintering, a slow cooling method is adopted, including natural cooling or controlling the cooling rate to not exceed 2°C / min.

[0015] Specific description of some raw materials in the above scheme: 1. ZIF-8 is a metal-organic framework material composed of zinc ions (Zn²⁺) and organic ligands (such as 2-methylimidazole). It has a regular pore structure and a large specific surface area, providing abundant nucleation sites, which helps other components (such as alumina) to deposit and crystallize evenly on its surface, forming a zirconium oxide coating. The presence of ZIF-8 makes alumina and other components more evenly dispersed in the spinning solution, avoiding local aggregation, thereby improving the uniformity of the final fiber. In addition, after ZIF-8 decomposes at high temperature, it leaves nanoscale voids or defects. These structures can serve as templates for the subsequent growth of alumina crystals, promoting the formation of finer and more uniform grains, and improving the mechanical strength and thermal stability of the fiber.

[0016] 2. Aluminum sec-butoxide is an aluminum source precursor that decomposes into aluminum oxide and isopropyl alcohol at high temperatures, ensuring the content and uniform distribution of aluminum oxide in the fiber. By adjusting its dosage and decomposition conditions, the size and morphology of the aluminum oxide grains can be controlled, thereby affecting the microstructure and properties of the fiber. Aluminum oxide has a high melting point and hardness, which can improve the mechanical strength and heat resistance of the fiber.

[0017] 3. The main component of yttrium-stabilized zirconia is zirconium oxide (ZrO2), which is doped with a small amount of yttrium (Y2O3) to stabilize cubic or tetragonal zirconia. Yttrium-stabilized zirconia remains stable at high temperatures and will not undergo phase change or decomposition. It has good mechanical strength, thermal stability and thermal shock resistance.

[0018] The beneficial effects achieved by the present invention are as follows: 1. The present invention uses aluminum sec-butoxide as a precursor and ZIF-8 (metal organic framework MOFs) as a structure-directing agent to guide the orderly arrangement of alumina nanoparticles through the porous structure of the material, helping to form a denser and more ordered alumina crystal structure. The orderly arranged alumina nanoparticles make the internal structure of the fiber denser, which can improve the crystallinity and mechanical properties of the fiber. At the same time, the template effect of MOFs can ensure the uniform dispersion of alumina nanoparticles in the fiber, thereby improving the overall uniformity and consistency of the alumina synthetic fiber.

[0019] 2. The present invention introduces yttrium-stabilized zirconia to wrap alumina to form a stable phase structure at high temperature, thereby enhancing the high-temperature stability of the fiber. It can effectively inhibit phase change and grain growth at high temperature, ensure the structural integrity and stability of the fiber in a high-temperature environment, improve the durability of alumina synthetic fiber in a high-temperature environment, and extend its service life.

[0020] 3. The present invention combines electrospinning, segmented temperature rise sintering, etc. to improve the quality consistency and reliability of the fiber, and adopts a gradual temperature rise method for high-temperature sintering to promote the complete crystallization and densification of alumina, reduce stress concentration and structural defects, and help improve the thermal stability of alumina synthetic fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic flow chart of the method for preparing alumina synthetic fibers based on electrospinning adopted in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to specific embodiments.

[0023] Example 1: A method for preparing alumina synthetic fibers based on electrospinning, such as Figure 1 As shown, the following steps are included: (1) Preparation of composite spinning solution: 0.75 g ZIF-8 powder was added to a mixed solvent of 75 ml ethanol and 25 ml N,N-dimethylformamide, and stirred to disperse uniformly to form a metal organic framework dispersion; Slowly add 3 g of aluminum sec-butoxide to the metal organic framework dispersion and stir slowly at 300 rpm to completely dissolve it to form a uniform precursor solution; 4.5 g of yttrium-stabilized zirconia powder was dispersed in 30 ml of N,N-dimethylformamide and ultrasonicated for 7 minutes to form a yttrium-stabilized zirconia dispersion; Slowly add the yttrium-stabilized zirconia dispersion to the precursor solution while continuously stirring at 500 rpm to form a mixed solution; 1.5 g of polyvinyl pyrrolidone was slowly added to the mixed solution, and the mixture was stirred at 700 rpm for 25 minutes, and then the speed was adjusted to 500 rpm and stirred for 4 hours to obtain a stable composite spinning solution; (2) Electrospinning fibers: A syringe pump is used to eject the composite spinning solution through a nozzle to form a Taylor cone, which is then sprayed onto a receiving device to obtain a pre-spun fiber. The conditions include a voltage of 12 kV, a receiving distance of 12 cm, a spinning rate of 0.5 ml / h, an ambient temperature of 22 °C, and a humidity of 40%. The pre-spun fiber is placed in an oven and dried at 80 °C for 3 hours. The temperature is then adjusted to 170 °C and dried for another 2 hours to crosslink and solidify the pre-spun fiber. (3) Heat treatment and high-temperature sintering: The solidified as-spun fiber is placed in a high-temperature furnace, and the temperature is raised from room temperature to 525°C, kept warm for 60 minutes, then raised from 525°C to 1250°C, kept warm for 60 minutes; finally, raised from 1250°C to 1400°C, kept warm for 90 minutes; the heating rate is 2°C / min, and the cooling rate is controlled not to exceed 2°C / min. After cooling, the fiber is taken out to obtain alumina synthetic fiber.

[0024] Example 2: A method for preparing alumina synthetic fibers based on electrospinning, such as Figure 1 As shown, the following steps are included: (1) Preparation of composite spinning solution: 1 g ZIF-8 powder was added to a mixed solvent of 80 ml ethanol and 20 ml N,N-dimethylformamide, and stirred to disperse uniformly to form a metal organic framework dispersion; Slowly add 4 g of aluminum sec-butoxide to the metal organic framework dispersion and stir slowly at 300 rpm to completely dissolve it to form a uniform precursor solution; 6 g of yttrium-stabilized zirconia powder was dispersed in 30 ml of N,N-dimethylformamide and ultrasonicated for 10 minutes to form a yttrium-stabilized zirconia dispersion; Slowly add the yttrium-stabilized zirconia dispersion to the precursor solution while continuously stirring at 500 rpm to form a mixed solution; 2 g of polyvinyl pyrrolidone was slowly added to the mixed solution, and the mixture was stirred at 700 rpm for 30 minutes, and then the speed was adjusted to 500 rpm and stirred for 5 hours to obtain a stable composite spinning solution; (2) Electrospinning fibers: A syringe pump is used to eject the composite spinning solution through a nozzle to form a Taylor cone, which is then sprayed onto a receiving device to obtain a pre-spun fiber. The conditions include a voltage of 15 kV, a receiving distance of 15 cm, a spinning rate of 0.7 ml / h, an ambient temperature of 25 °C, and a humidity of 50%. The pre-spun fiber is placed in an oven and dried at 80 °C for 3 hours. The temperature is then adjusted to 170 °C and dried for another 2 hours to crosslink and solidify the pre-spun fiber. (3) Heat treatment and high-temperature sintering: The solidified as-spun fiber is placed in a high-temperature furnace, and the temperature is raised from room temperature to 550°C, kept warm for 60 minutes, then raised from 550°C to 1300°C, kept warm for 60 minutes; finally, raised from 1300°C to 1400°C, kept warm for 90 minutes; the heating rate is 2°C / min, and the cooling rate is controlled not to exceed 2°C / min. After cooling, the fiber is taken out to obtain alumina synthetic fiber.

[0025] Example 3: A method for preparing alumina synthetic fibers based on electrospinning, such as Figure 1 As shown, the following steps are included: (1) Preparation of composite spinning solution: 0.5 g ZIF-8 powder was added to a mixed solvent of 70 ml ethanol and 30 ml N,N-dimethylformamide, and stirred to disperse uniformly to form a metal organic framework dispersion; Slowly add 2 g of aluminum sec-butoxide to the metal organic framework dispersion and stir slowly at 300 rpm to completely dissolve it to form a uniform precursor solution; 3 g of yttrium-stabilized zirconia powder was dispersed in 30 ml of N,N-dimethylformamide and ultrasonicated for 5 minutes to form a yttrium-stabilized zirconia dispersion; Slowly add the yttrium-stabilized zirconia dispersion to the precursor solution while continuously stirring at 500 rpm to form a mixed solution; 1 g of polyvinyl pyrrolidone was slowly added to the mixed solution, and the mixture was stirred at 700 rpm for 20 minutes, and then the speed was adjusted to 500 rpm and stirred for 3 hours to obtain a stable composite spinning solution; (2) Electrospinning fibers: A syringe pump is used to eject the composite spinning solution through a nozzle to form a Taylor cone, which is then sprayed onto a receiving device to obtain a pre-spun fiber. The conditions include a voltage of 10 kV, a receiving distance of 10 cm, a spinning rate of 0.3 ml / h, an ambient temperature of 20 °C, and a humidity of 30%. The pre-spun fiber is placed in an oven and dried at 80 °C for 3 hours. The temperature is then adjusted to 170 °C and dried for another 2 hours to crosslink and solidify the pre-spun fiber. (3) Heat treatment and high-temperature sintering: The solidified as-spun fiber is placed in a high-temperature furnace, and the temperature is raised from room temperature to 500°C, kept warm for 60 minutes, then raised from 500°C to 1200°C, kept warm for 60 minutes; finally, raised from 1200°C to 1400°C, kept warm for 90 minutes; the heating rate is 2°C / min, and the cooling rate is controlled not to exceed 2°C / min. After cooling, the fiber is taken out to obtain alumina synthetic fiber.

[0026] Comparative Example 1: Compared with Example 1, in this comparative example, ZIF-8 powder is not used in (1) preparing the composite spinning solution. Specifically, (1) preparing the composite spinning solution: adding aluminum sec-butoxide to a mixed solvent of ethanol and N,N-dimethylformamide, stirring to completely dissolve it, and forming a uniform precursor solution; Slowly add the yttrium-stabilized zirconia dispersion to the precursor solution while maintaining continuous stirring to ensure that the two solutions are evenly mixed to form a mixed solution; slowly add polyvinyl pyrrolidone to the mixed solution while maintaining stage stirring until a stable composite spinning solution is obtained; The other steps and process parameters are consistent with those in Example 1 to obtain alumina synthetic fibers.

[0027] Comparative Example 2: Compared with Example 1, in this comparative example, ZIF-8 powder and yttrium-stabilized zirconia powder are not used in (1) preparing the composite spinning solution. Specifically, (1) preparing the composite spinning solution: adding aluminum sec-butoxide to a mixed solvent of ethanol and N,N-dimethylformamide, stirring to completely dissolve it, and forming a uniform precursor solution; slowly adding polyvinyl pyrrolidone to the precursor solution, and continuously stirring until a stable composite spinning solution is obtained; The other steps and process parameters are consistent with those in Example 1 to obtain alumina synthetic fibers.

[0028] Performance testing: The alumina synthetic fibers obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to relevant performance tests, including thermal stability, mechanical properties, and electrical properties tests; 1. Thermal stability: Place the fiber sample in a high-temperature furnace, gradually increase the temperature from room temperature to 1600°C at a heating rate of 5°C / min, keep warm for 2 hours, and observe the appearance of the alumina synthetic fiber after natural cooling.

[0029] 2. Mechanical properties: Fix the fiber sample on the tensile fixture of the universal testing machine, set the tensile rate to 5 mm / min, the test environment to room temperature and humidity to 40%, start the universal testing machine, record the force-displacement data during the stretching process until the fiber breaks, record the maximum tensile force and elongation at break, and calculate the tensile strength and elastic modulus of the fiber based on the tensile stress-strain curve.

[0030] 3. Electrical properties: Fix the fiber sample on a four-probe test platform, set the current range to 1mA, the test environment to room temperature and humidity to 40%, start the four-probe tester, record the voltage drop and current values, and calculate the resistivity based on the measured voltage drop and current values.

[0031] The test results are shown in the following table.

[0032] Table 1 Test results of various properties of alumina synthetic fiber

[0033] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing alumina synthetic fibers based on electrospinning, characterized in that: The following steps are involved: (1) Preparation of composite spinning solution: Add ZIF-8 powder to a mixed solvent of ethanol and N,N-dimethylformamide, stir and disperse evenly to form a metal organic framework dispersion; Slowly add aluminum sec-butoxide to the metal organic framework dispersion and slowly stir to completely dissolve it to form a uniform precursor solution; Dispersing yttrium-stabilized zirconia powder in N,N-dimethylformamide and uniformly dispersing the powder by ultrasonic treatment to form a yttrium-stabilized zirconia dispersion; Slowly add the yttrium-stabilized zirconia dispersion to the precursor solution while maintaining continuous stirring to ensure that the two solutions are evenly mixed to form a mixed solution; Slowly adding polyvinyl pyrrolidone into the mixed solution, and continuously stirring until a stable composite spinning solution is obtained; (2) Electrospinning fibers: Use a syringe pump to eject the composite spinning solution through a nozzle to form a Taylor cone, which is then sprayed onto a receiving device to obtain a pre-spun fiber. The pre-spun fiber is placed in an oven and dried at 80°C for 3 hours. The temperature is then adjusted to 170°C and dried for another 2 hours to crosslink and solidify the pre-spun fiber. (3) Heat treatment and high-temperature sintering: The solidified as-spun fiber is placed in a high-temperature furnace and calcined at a rate of 2°C / min to 1100°C-1400°C. After cooling, it is taken out to obtain alumina synthetic fiber.

2. The method for preparing alumina synthetic fiber based on electrospinning according to claim 1, characterized in that: In the composite spinning solution prepared in (1), the mass ratio of ZIF-8 powder, aluminum sec-butoxide, yttrium-stabilized zirconia powder, and polyvinyl pyrrolidone is 0.5-1:2-4:3-6:1-2.

3. The method for preparing alumina synthetic fiber based on electrospinning according to claim 1, characterized in that: In the composite spinning solution prepared in (1), the volume ratio of ethanol to N,N-dimethylformamide in the mixed solvent of ethanol and N,N-dimethylformamide is 7-8:2-3.

4. The method for preparing alumina synthetic fibers based on electrospinning according to claim 1, characterized in that: In the preparation of the composite spinning solution (1), 3-6 parts by mass of yttrium-stabilized zirconia powder are dispersed in 30 parts by volume of N,N-dimethylformamide.

5. The method for preparing alumina synthetic fiber based on electrospinning according to claim 1, characterized in that: In the (1) preparation of the composite spinning solution, polyvinyl pyrrolidone is slowly added to the mixed solution, and the stirring is continued for 20-30 minutes at 700 rpm, and then the speed is adjusted to 500 rpm and the stirring is continued for 3-5 hours.

6. The method for preparing alumina synthetic fibers based on electrospinning according to claim 1, characterized in that: In the preparation of the composite spinning solution in (1), the ultrasonic treatment time is 5-10 minutes.

7. The method for preparing alumina synthetic fibers based on electrospinning according to claim 1, characterized in that: In the preparation of the composite spinning solution described in (1), the stirring speed does not exceed 700 rpm.

8. The method for preparing alumina synthetic fibers based on electrospinning according to claim 1, characterized in that: In the (2) electrospinning fibers, the electrospinning conditions include: voltage of 10-15 kV, receiving distance of 10-15 cm, spinning rate of 0.3-0.7 ml / h, ambient temperature of 20-25° C., and humidity of 30%-50%.

9. The method for preparing alumina synthetic fibers based on electrospinning according to claim 1, characterized in that: The (3) heat treatment and high-temperature sintering are divided into three stages. The first stage is from room temperature to 500-550°C, and the holding time is 60 minutes; the second stage is from the first stage temperature to 1200-1300°C, and the holding time is 60 minutes; the third stage is from the second stage temperature to 1400°C, and the holding time is 90 minutes. The heating rate of the three stages is 2°C / min.

10. The method for preparing alumina synthetic fibers based on electrospinning according to claim 1, characterized in that: During the (3) heat treatment and high-temperature sintering, a slow cooling method is adopted, including natural cooling or controlling the cooling rate to not exceed 2°C / min.

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