CN104005115B - A kind of preparation method of ceramic alumina fiber - Google Patents

Abstract

The invention discloses a kind of preparation method of ceramic alumina fiber, the method utilization contains Al₁₃The alumina sol of micelle and Ludox are prepared spinnability precursor sol, adopt winding-up fiber-forming process to prepare gelatinous fibre, then obtain the ceramic alumina fiber of diameter 1～7 μ m through heat treatment. The sol system that the present invention adopts sol-gel process to prepare is stable, and content is controlled and impurity is few; Ceramic fibre pliability after heat treatment is good, and operability excellence, without slag ball, can be used for reinforcement, the raising strength of materials and heat resistance etc. in composite.

Description

A kind of preparation method of alumina ceramic fiber

technical field

The invention relates to the preparation of alumina ceramic fibers and belongs to the field of inorganic non-metallic materials.

Background technique

Alumina ceramic fiber belongs to inorganic crystal fiber, the main component is aluminum oxide (Al ₂ O ₃ ), and also contains a certain amount of additives, such as silicon dioxide (SiO ₂ ), iron oxide (Fe ₂ O ₃ ), etc., it It has many excellent properties, such as high strength, high temperature resistance, high melting point, strong corrosion resistance, good heat insulation performance, and small specific gravity. It can enhance the function of osteoblast bone replacement in medicine, and it is also a kind of comprehensive performance. Engineering materials have very important applications in composite materials, industry and military fields. As a thermal insulation material, Al ₂ O ₃ ceramic fiber has good thermal insulation performance, which can significantly reduce heat loss, and the maximum heat-resistant temperature can reach 1700°C. Compared with carbon fiber and metal fiber, Al ₂ O ₃ ceramic fiber has a higher thermal conductivity Low thermal expansion coefficient, good thermal shock resistance, is the first choice for high temperature insulation materials; Al ₂ O ₃ ceramic fiber is stable at high temperature, large specific surface area, can be used as a catalyst carrier.

The traditional method of preparing inorganic fibers is to heat the raw materials to make them into a molten state and spin them by melting method. However, the melting point of alumina is very high, and even if it is melted, its melt viscosity is very low, and its fibers are difficult to prepare by melting method. Therefore, people have researched and developed a variety of precursor methods to prepare Al ₂ O ₃ ceramic fibers, that is, to prepare fiber materials containing aluminum components and other organic and inorganic components through a spinning process at room temperature, and then remove them by high-temperature calcination and pyrolysis. Al ₂ O ₃ ceramic fibers can be prepared from solvents, organic substances or inorganic anions. For example, Saint-Gobain Ceramics and Plastics Co., Ltd. of the United States used a high-energy attritor to disperse α-Al ₂ O ₃ polycrystalline particles in water to prepare a slurry, then added nitric acid and aluminum sec-butoxide, and stirred vigorously at 80°C for 2 hours to obtain Sol, spinning to obtain precursor fibers, and then calcining to obtain Al ₂ O ₃ ceramic fibers (CN200480009462.4); Imperial Chemical Industries Company dissolved thiourea and polyethylene oxide in aluminum chloride solution, and then added hydration Aluminum chloride and siloxane surfactant can be used to obtain wire drawing solution, wire drawing and heat treatment to obtain Al ₂ O ₃ ceramic fiber (CN1034768A); Luoyang Xin Ju Neng High Heat Technology Co., Ltd. disperses alumina powder in water to make Suspension, then add inorganic salt solution mixed with organic acid and silica sol, finally add binder, plasticizer, dryness control agent, dispersant, stir in water bath, concentrate to form fiber colloid after reaction, after centrifugation silk, drying and heat treatment to prepare Al ₂ O ₃ polycrystalline fiber (CN103160954A); Tianjin Polytechnic University uses crystalline Al ₂ O ₃ , deionized water and aluminum powder as the main raw materials, and takes the silk forming agent as auxiliary material to obtain spinnable sol, and then Preparation of Al ₂ O ₃ ceramic fibers (CN103114352A) by fiber formation, drying and heat treatment; Uematsu et al. used viscose fiber with good hydrophilicity as the matrix fiber to impregnate the inorganic aluminum salt solution, and then obtained Al ₂ O ₃ by drying and sintering. Ceramic fibers (J.Am.Ceram.Soc.1995,78,3107); Venkatesh et al. used oxychloride inorganic salts and organic polymers as additives to prepare solutions, and then through spinning and calcination processes to obtain Al ₂ O ₃ ceramic fibers, and studied the fiber defects caused by various process factors (Mater.Lett.2002,55,189; J.Europ.Ceram.Soc.2000,20,2543). However, the above methods all use organic substances as fiber-forming additives, and the prepared Al ₂ O ₃ ceramic fibers have relatively thick diameter, poor fiber compactness, high porosity and low strength, and the fiber has high impurity content, and the component content cannot be accurately controlled.

The sol-gel method (Sol-Gel) can overcome the shortcomings of the above-mentioned methods, and can prepare ceramic fibers with uniform microstructure and chemical composition and large aspect ratio at a relatively low temperature. The fiber has better compactness and strength. Large size and excellent flexibility, high purity of ceramic fiber, stable performance, simple preparation process, strong designability, is a method for preparing Al ₂ O ₃ ceramic fiber with good development prospects; this method mainly uses aluminum alkoxide Or inorganic salt as raw material, add organic acid catalyst, evenly dissolve in alcohol or water, undergo alcoholysis or hydrolysis and polymerization to obtain sol, concentrate the sol to a certain viscosity, spin to obtain gel fiber, and finally obtain Al ₂ O by heat treatment ₃ ceramic fibers. For example, Japan’s Sumitomo Chemical Company uses methyl aluminoxane to react with water to synthesize methyl aluminoxane polymers, then dissolves the polymers in organic solvents containing organosilicon compounds, concentrates them to obtain spinnable viscose, and dry spinning The precursor fibers were made from silk, and polycrystalline Al ₂ O ₃ ceramic fibers were obtained after calcination (J.PolymerSci.1991, 29, 495); Tan et al. used aluminum nitrate, tartaric acid and polyvinylpyrrolidone (PVP) as Raw materials, spinnable alumina sol was obtained, and Al ₂ O ₃ ceramic fibers were obtained after drying and heat treatment (Int.J.MineralsMetall.Mater.2011, 18(6), 691); Zhang et al. used polyvinyl alcohol (PVB) and hydrated aluminum nitrate as raw materials, through a similar process to obtain Al ₂ O ₃ ceramic fibers (J.Sol-GelSci.&Technol.2009,49(3),385); Chandradass et al. dissolved aluminum isopropoxide in the presence of nitric acid Heat and reflux in water, add oxalic acid and zirconium oxychloride solution after the aluminum isopropoxide is completely dissolved, evaporate and concentrate the sol to obtain a spinnable sol, and then spin, dry, and sinter to obtain Al ₂ O ₃ ceramic fibers. Effects of additives such as MgO on the structural properties of fibers (Materi.Sci.Engineer.2005,408,165; J.Europ.Ceram.Soc.2006,26,2611; J.Mater.ProcessingTechnol.2006,173,275); U.S. patents use aluminum acetate , silica sol, dimethylformamide, boric acid, etc. are used as raw materials to synthesize a precursor sol under certain conditions, extrude and spin the sol in a spinneret, and obtain Al ₂ O ₃ ceramic fibers after drying and heat treatment (USP3760049); the U.S. patent uses basic aluminum chloride, silica sol, polyvinyl alcohol, etc. as raw materials to synthesize spinning solution (USP7033537) under certain conditions, while the U.S. patent uses sodium aluminate, nitric acid, aluminum nitrate, etc. as Raw materials, the spinning solution is prepared under certain conditions, and then Al ₂ O ₃ ceramic fibers with better performance are obtained (USP4297336). In China, Shen Xiangqian and others used aluminum lactic acid nitrate as the main raw material to prepare spinnable sol through a series of processes such as mixing, rotary evaporation, and vacuum dehydration (Mining and Metallurgy Engineering 2004, 24 (5), 76). Huang Qianjun et al. used aluminum chloride, Magnesium chloride, aluminum powder, water, etc. are used as raw materials, and alumina sol is obtained through steps such as reflux and dissolution, and then an appropriate amount of polymer compound solution is added, heated and concentrated to obtain a spinnable viscous liquid (Journal of Xiamen University 2006, 45(3), 672) , while Wang Xiaorui et al. used metal aluminum and water as raw materials to make a polymerized alumina solution, and then added an appropriate amount of silica sol, polymer fiber-forming additives and organic acids to make a sol (Refractory Materials 2000, 34 (4), 203); these The sol is further processed into fibers, dried, and calcined to obtain Al ₂ O ₃ ceramic fibers. However, due to the introduction of organic polymer additives or organic groups, the fibers are prone to cause holes during heat treatment, and the fibers have poor compactness, low strength, and poor flexibility. These defects limit the use properties of the fibers.

Contents of the invention

Aiming at the deficiencies such as poor compactness, high porosity, low strength and poor flexibility of the Al ₂ O ₃ ceramic fiber prepared in the prior art, the invention provides a preparation method of the Al ₂ O ₃ ceramic fiber.

Summary of the invention

The present invention uses alumina sol containing Al ₁₃ colloidal particles as raw material to prepare spinnable sol, only adding inorganic auxiliary agent SiO ₂ sol to the sol, without adding organic or polymer auxiliary agent, and combining the injection method to obtain Al ₂ O ₃ Ceramic fiber; its characteristic is that the alumina sol containing Al ₁₃ colloidal particles has low reactivity, and it reacts with the additive SiO ₂ at above 1300°C. SiO ₂ exists in the glass state in the fiber, making the fiber flexible. High strength, more conducive to making composite materials. Compared with aluminum silicate fiber and other Al ₂ O ₃ ceramic fibers prepared with Al ³⁺ or organic aluminum as aluminum source, it has better high temperature resistance.

Detailed description of the invention

Technical scheme of the present invention is as follows:

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

Add silica sol to alumina sol containing Al ₁₃ colloidal particles so that the mass ratio of Al ₂ O ₃ to SiO ₂ is 1: (0.25-0.67), stir and mix evenly, and then age in a water bath at 30-80°C to The viscosity is 10-160 Pa·s to obtain a precursor sol; the mass content of Al ₁₃ colloidal particles in the alumina sol is 15-50%;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.03-0.20mm, the pressure is 5-16MPa, the air temperature is 20-100°C, and the air flow rate is 5~80m/min;

(3) Gel fiber ceramicization

The gel fiber prepared in step (2) is ceramicized, and the process conditions are: heating up to 500-600°C at a speed of 0.5-5°C/min, keeping at this temperature for 0.5-2h; and then heating at a speed of 3-15°C/min Raise the temperature to 1000-1300°C, keep the temperature at this temperature for 0.5-3h, and obtain Al ₂ O ₃ ceramic fibers.

According to the present invention, preferably, the silica sol solid content described in step (1) is 15～40wt%, the mass content of Al _{13 colloid in the described alumina sol containing Al 13 colloid} is 20～48% , more preferably 30 to 40%.

According to the present invention, preferably, the water bath aging temperature in step (1) is 40-60° C., and the aging is performed until the viscosity is 50-120 Pa·s.

According to the present invention, preferably, the alumina sol containing Al ₁₃ colloidal particles described in step (1) is prepared by the following method:

Using aluminum salt solution and aluminum flakes as raw materials, the molar ratio of aluminum salt and aluminum flakes is 1: (1-5), heating and refluxing until the reaction of aluminum flakes is complete, and filtering to obtain alumina sol containing Al ₁₃ colloidal particles. Colloidal particle size ≤ 5nm. Preferably, the aluminum salt is aluminum chloride, aluminum nitrate or aluminum sulfate.

According to the present invention, preferably, the inner diameter of the spinneret hole described in step (2) is 0.08-0.15mm, the pressure is 8-12MPa; the air temperature is 40-80°C, and the air velocity is 20-60m/min.

According to the present invention, preferably, the technological condition of gel fiber ceramization in step (3) is: be heated up to 500～550 ℃ with the speed of 1～3 ℃/min, keep warm at this temperature 1～1.5h; Raise the temperature to 1000-1300°C at a rate of ~10°C/min, and keep at this temperature for 0.5-3 hours.

The viscosity described in the method step (1) of the present invention is measured at room temperature using a rotational viscometer.

The Al ₂ O ₃ ceramic fiber prepared by the method of the present invention has a fiber diameter of 1-7 μm, no slag balls, and a crystal phase of γ or δ phase Al ₂ O ₃ ; the surface of the Al ₂ O ₃ ceramic fiber is smooth, and the interior of the fiber is dense, with Very good flexibility and operability, thermal conductivity at room temperature is 0.020~0.030W/mK, excellent thermal insulation performance.

The alumina sol containing Al ₁₃ colloidal particles synthesized by the sol method in the present invention is homogeneous and transparent, stable in properties, the particle size of the colloidal particles is less than 5nm, the components can be adjusted within a certain range, and there is no need to add polymer additives. Silkiness: The Al ₂ O ₃ ceramic fiber prepared by the blowing method has a diameter of 1-7 μm and no slag balls. At the same time, the diameter of the ceramic fiber is small and uniform, with good flexibility, high strength and good usability.

Technical characteristics of the present invention and good effect are as follows:

1. The present invention uses a sol-gel method to prepare Al ₂ O ₃ ceramic fibers, and the process temperature is low, which can effectively save energy. The components of the raw materials are mixed in the solution at the molecular level, the microstructure of the fiber is easy to control, the mass fraction of Al ₂ O ₃ and SiO ₂ can be precisely controlled, and the impurity content is low.

2. The alumina sol used in the present invention is a sol containing Al ₁₃ colloidal particles, and the particle size of the colloidal particles is less than 5nm, with stable properties.

3. The precursor sol prepared by the present invention is uniform and transparent, has stable properties and can be stored for a long time, and has good fiber-forming properties without adding polymer additives.

4. The invention adopts the blowing method to form fibers, and the prepared ceramic fibers have a diameter of 1-7 μm and no slag balls.

Description of drawings

Figure 1 is the XRD spectrum of the Al ₂ O ₃ ceramic fiber obtained in Example 1 of the present invention.

Fig. 2 is the XRD spectrum of the Al ₂ O ₃ ceramic fiber obtained in Example 2 of the present invention.

Fig. 3 is a SEM photo of Al ₂ O ₃ ceramic fibers obtained in Example 2 of the present invention.

Fig. 4 is a high-magnification SEM photo of Al ₂ O ₃ ceramic fibers obtained in Example 2 of the present invention.

Fig. 5 is a high-magnification SEM photo of the cross section of the Al ₂ O ₃ ceramic fiber obtained in Example 2 of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but is not limited thereto.

The alumina sol containing Al ₁₃ micelle described in the embodiment is prepared as follows:

Use aluminum chloride solution and aluminum flakes as raw materials, the molar ratio of aluminum chloride and aluminum flakes is 1: (1-5), heat and reflux until the reaction of aluminum flakes is complete, and filter to obtain alumina containing Al ₁₃ colloidal particles Sol, colloidal particle diameter ≤ 5nm, colloidal particle diameter less than 5nm.

Example 1

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

80g of SiO sol with a solid content of 29.5wt% was added to _472g of alumina sol containing Al ₁₃ colloidal particles (the mass fraction of Al ₁₃ colloidal particles in the Al ₂ O ₃ sol was 31.4%, and the mass fraction of Al ₂ O ₃ was 20.0 %), stirred and mixed evenly, and then aged in a 60°C water bath to a viscosity of 30Pa·s to obtain a precursor sol;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.10mm, the pressure is 8MPa, the air temperature is 60°C, and the air flow rate is 40m/min;

(3) Gel fiber ceramicization

The gel fiber prepared in step (2) is ceramicized, and the process conditions are: heating up to 500°C at a rate of 2°C/min, and keeping at this temperature for 2 hours; then raising the temperature to 1100°C at a rate of 5°C/min, at Keep it warm for 2 hours to obtain Al ₂ O ₃ ceramic fibers.

The Al ₂ O ₃ ceramic fiber obtained in this example is γ-Al ₂ O ₃ ceramic fiber, the fiber diameter is _3-7 μm, the content of Al ₂ O ₃ is 80.0 wt%, and the content of SiO ₂ is 20.0 wt % _; The surface of the fiber is smooth and the inside of the fiber is dense.

Example 2

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

70g of _SiO2 sol with a solid content of 29.5wt% was added to 260g of alumina sol containing _Al13 colloidal particles ₍ the mass fraction of _Al13 colloidal particles in the _Al2O3 sol was 37.3%, and the mass fraction of _Al2O3 was 23.8 _% %), stirred and mixed evenly, and then aged in a 50°C water bath to a viscosity of 50Pa·s to obtain a precursor sol;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.08mm, the pressure is 12MPa, the air temperature is 50°C, and the air flow rate is 60m/min;

(3) Gel fiber ceramicization

The gel fiber prepared in step (2) is ceramicized. The process conditions are as follows: heat up to 600°C at a rate of 1°C/min, and keep at this temperature for 1 hour; then heat up to 1200°C at a rate of 10°C/min. Keep it warm for 1.5h to obtain Al ₂ O ₃ ceramic fibers.

The Al ₂ O ₃ ceramic fiber obtained in this example is δ-Al ₂ O ₃ ceramic fiber, the fiber diameter is 4-7 μm, the content of Al ₂ O ₃ is 75.0 wt%, and the content of SiO ₂ is 25.0 wt _{% ;} The surface of the fiber is smooth and the inside of the fiber is dense.

Example 3

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

The 80g solid content is _29.5wt % SiO sol joins in the alumina sol containing 220g Al ₁₃ micelle (the Al ₁₃ micelle mass fraction is 39.3% in the sol, Al ₂ O ₃ mass fraction is 25.0%), stir Mix evenly, then age in a 70°C water bath to a viscosity of 100Pa·s to obtain a precursor sol;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.15mm, the pressure is 10MPa, the air temperature is 50°C, and the air flow rate is 80m/min;

(3) Gel fiber ceramicization

The gel fiber prepared in step (2) is ceramicized. The process conditions are as follows: heat up to 550°C at a rate of 2°C/min and keep at this temperature for 1 hour; then heat up to 1200°C at a rate of 8°C/min. Keep it warm for 2 hours to obtain Al ₂ O ₃ ceramic fibers.

The Al ₂ O ₃ ceramic fiber obtained in this example is δ-Al ₂ O ₃ ceramic fiber, the fiber diameter is _3-6 μm, the content of Al ₂ O ₃ is 70.0wt%, and the content of SiO ₂ is 30.0wt% _; The surface of the fiber is smooth and the inside of the fiber is dense.

Example 4

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

With embodiment 2;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.10mm, the pressure is 15MPa, the air temperature is 60°C, and the air flow rate is 100m/min;

(3) Gel fiber ceramicization

The gel fiber prepared in step (2) is ceramicized. The process conditions are as follows: heat up to 500°C at a rate of 5°C/min, and keep at this temperature for 2 hours; then heat up to 1000°C at a rate of 8°C/min. Keep it warm for 1 hour to obtain Al ₂ O ₃ ceramic fibers.

The Al ₂ O ₃ ceramic fiber obtained in this example is γ--Al ₂ O ₃ ceramic fiber, the fiber diameter is 4-6 μm, the content of Al ₂ O ₃ is 80.0wt%, and the content of SiO ₂ is 20.0wt%; Al ₂ O ₃ The surface of the ceramic fiber is smooth, and the inside of the fiber is dense.

Example 5

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

80g solid content is _29.5wt % SiO sol joins in 472g the alumina sol that contains Al ₁₃ micelle (in sol, Al ₁₃ micelle mass fraction is 31.8%, Al ₂ O ₃ mass fraction is 20.0%), stir Mix evenly, then age in a 50°C water bath to a viscosity of 60Pa·s to obtain a precursor sol;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.15mm, the pressure is 10MPa, the air temperature is 60°C, and the air flow rate is 80m/min;

(3) Gel fiber ceramicization

With embodiment 2.

The Al ₂ O ₃ ceramic fiber obtained in this example is δ-Al ₂ O ₃ ceramic fiber, the fiber diameter is 2-6 μm, the content of Al ₂ O ₃ is 80.0 wt%, and the content of SiO ₂ is 20.0 wt _{% ;} The surface of the fiber is smooth and the inside of the fiber is dense.

Example 6

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

With embodiment 2;

(2) Preparation of gel fibers by blowing into fibers

With embodiment 2;

(3) Gel fiber ceramicization

The gel fiber prepared in step (2) is ceramicized. The process conditions are as follows: heat up to 500°C at a rate of 5°C/min, and keep at this temperature for 2 hours; then heat up to 1000°C at a rate of 8°C/min. Keep it warm for 2 hours to obtain Al ₂ O ₃ ceramic fibers.

The Al ₂ O ₃ ceramic fiber obtained in this example is γ-Al ₂ O ₃ ceramic fiber, the fiber diameter is _3-7 μm, the content of Al ₂ O ₃ is 75.0 wt%, and the content of SiO ₂ is 25.0 wt % _; The surface of the fiber is smooth and the inside of the fiber is dense.

Example 7

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

With embodiment 1;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.08mm, the pressure is 12MPa, the air temperature is 50°C, and the air flow rate is 50m/min;

(3) Gel fiber ceramicization

With embodiment 1.

The Al ₂ O ₃ ceramic fiber obtained in this example is γ _- Al ₂ O ₃ ceramic fiber, the fiber diameter is 1-4 μm, the content of Al ₂ O ₃ is _80.0wt %, and the content of SiO ₂ is 20.0wt%. The surface of the fiber is smooth and the inside of the fiber is dense.

Example 8

A kind of preparation method _{of Al2O3ceramic} fiber, comprises steps as follows:

(1) Preparation of spinnable precursor sol

With embodiment 2;

(2) Preparation of gel fibers by blowing into fibers

The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.06mm, the pressure is 16MPa, the air temperature is 70°C, and the air flow rate is 80m/min;

(3) Gel fiber ceramicization

With embodiment 2.

The Al ₂ O ₃ ceramic fiber obtained in this example is γ-Al ₂ O ₃ ceramic fiber, the fiber diameter is 1-5 μm, the content of Al ₂ O ₃ is _75.0wt %, and the content of SiO ₂ is 25.0wt% _; The surface of the fiber is smooth and the inside of the fiber is dense.

Claims (8)

1. a kind of Al ₂ O _The preparation method of ceramic fiber, comprises steps as follows: (1) Preparation of spinnable precursor sol Add silica sol to alumina sol containing Al ₁₃ colloidal particles so that the mass ratio of Al ₂ O ₃ to SiO ₂ is 1: (0.25-0.67), stir and mix evenly, and then age in a water bath at 30-80°C to The viscosity is 10-160 Pa·s to obtain a precursor sol; the mass content of Al ₁₃ colloidal particles in the alumina sol is 15-50%; (2) Preparation of gel fibers by blowing into fibers The precursor sol prepared in step (1) is blown into fibers to obtain gel fibers; process conditions: the inner diameter of the spinneret hole is 0.03-0.20mm, the pressure is 5-16MPa, the air temperature is 20-100°C, and the air flow rate is 5~80m/min; (3) Gel fiber ceramicization The gel fiber prepared in step (2) is ceramicized, and the process conditions are: heating up to 500-600°C at a speed of 0.5-5°C/min, keeping at this temperature for 0.5-2h; and then heating at a speed of 3-15°C/min Raise the temperature to 1000-1300°C, keep the temperature at this temperature for 0.5-3h, and obtain Al ₂ O ₃ ceramic fibers. 2. The method for preparing Al ₂ O ₃ ceramic fibers according to claim 1, characterized in that the solid content of the silica sol in step (1) is 15-40%. 3. The method for preparing Al ₂ O ₃ ceramic fibers according to claim 1, characterized in that the mass content of Al ₁₃ colloidal particles in the alumina sol described in step (1) is 20-48%. 4 . The method for preparing Al ₂ O ₃ ceramic fibers according to claim 1 , characterized in that, in step (1), the water bath aging temperature is 40-60° C., and the aging is performed until the viscosity is 50-120 Pa·s. 5. Al according to claim ₁ O _The preparation method of ceramic fiber is characterized in that the alumina sol containing Al colloidal particles described in step ( ₁ ) is prepared by the following method: Using aluminum salt solution and aluminum flakes as raw materials, the molar ratio of aluminum salt and aluminum flakes is 1: (1-5), heating and refluxing until the reaction of aluminum flakes is complete, and filtering to obtain alumina sol containing Al ₁₃ colloidal particles. 6 . The method for preparing Al ₂ O ₃ ceramic fibers according to claim 1 , characterized in that the inner diameter of the spinneret hole in step (2) is 0.08-0.15 mm, and the pressure is 8-12 MPa. 7 . The method for preparing Al ₂ O ₃ ceramic fibers according to claim 1 , characterized in that the air temperature in step (2) is 40-80° C., and the air velocity is 20-60 m/min. 8. The preparation method of Al ₂ O ₃ ceramic fibers according to claim 1, characterized in that the process conditions for ceramicizing gel fibers in step (3) are: heating up to 500 °C at a rate of 1-3°C/min ~550°C, keep at this temperature for 1~1.5h; then raise the temperature to 1000~1300°C at a speed of 5~10°C/min, and keep at this temperature for 0.5~3h.