Alumina synthetic fiber mat and air flow fusion method for preparing the same

Abstract

The application relates to the technical field of refractory materials, in particular to an alumina synthetic fiber felt and an airflow melt preparation method thereof. The airflow melt preparation method of the alumina synthetic fiber felt comprises the following steps: preparing a composite sol by using alumina powder, rare earth element powder, tetrabutyl titanate and / or tetrabutyl zirconate and nano reinforcing materials; adding an organic template agent and performing dry spinning, pre-sintering and high-temperature sintering; blowing the sintered fiber into a collector through high-speed airflow to obtain the alumina synthetic fiber felt. The rare earth element powder and the nano reinforcing materials are introduced to form a micro-nano scale reinforcing phase in the alumina synthetic fiber, which can effectively disperse stress, prevent crack propagation, improve the mechanical strength and fracture toughness of the fiber, maintain the structural integrity and performance stability of the fiber felt at high temperature, the metal oxide can enhance the hardness and wear resistance of the fiber felt, and the metal oxide also endows the fiber felt with excellent chemical stability and multiple functionalities.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refractory materials, in particular to an alumina synthetic fiber felt and a gas flow melting preparation method thereof. BACKGROUND

[0002] Alumina fiber is a high-performance ceramic material with excellent mechanical strength, high-temperature resistance, chemical stability and thermal conductivity, and has a wide range of applications in aerospace, high-temperature filters, thermal insulation materials, automotive industry and medical implants. The early melting method is mainly used for the preparation of high molecular fiber and glass fiber, and then gradually used for the preparation of fiber with lower alumina content (<70%). This method can be used for the production of continuous fibers and the preparation of short fibers. By electric heating, the inorganic oxide is melted to form a melt, and by controlling the composition and temperature of the melt, it has spinnability, and then through different fiber forming methods to form the target product. However, as the alumina content increases, the viscosity of the melt increases, which makes it difficult to control its spinnability. Therefore, the current melting method can only be used for the preparation of low-alumina-content fiber, which can only be used at a temperature lower than 1200℃, and the fiber quality is relatively low, which cannot meet the requirements of good high-temperature resistance, limiting the application range of alumina fiber.

[0003] For alumina synthetic fiber felt, the mechanical strength and toughness of traditional alumina fiber under high temperature conditions are limited, and cracks are easily expanded and broken, which cannot meet the actual application requirements. At the same time, the internal stress distribution is uneven, which is easy to form stress concentration points, thereby causing cracks and rapid expansion, resulting in material failure. In addition, high-alumina-content fiber not only needs to have higher temperature resistance, but also needs to have good mechanical strength, thermal shock resistance and chemical stability to adapt to more harsh working conditions. In order to meet the strict requirements of material performance in high-temperature environment, it is particularly urgent to develop a gas flow melting preparation method for preparing alumina synthetic fiber felt with high alumina content and excellent high-temperature resistance. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide an alumina synthetic fiber felt and a gas flow melting preparation method thereof.

[0005] The present application provides a gas flow melting preparation method for alumina synthetic fiber felt, comprising the following steps:

[0006] (1) Mixing and sol preparation: mix alumina powder and rare earth element powder, add the mixed powder into a dispersion medium, stir at room temperature for 1-2h, and then stir at 60℃ for 2-3h to obtain an aluminum sol;

[0007] adding tetrabutyl titanate and / or tetrabutyl zirconate into the anhydrous ethanol solution containing nano-reinforced materials, stirring and dissolving to form a mixed solution, slowly dropping the mixed solution into the aluminum sol to prepare a composite sol;

[0008] (2) preparing a fiber precursor: adding an organic template agent into the composite sol, fully stirring to dissolve it completely, and using dry spinning technology to form a fiber precursor from the composite sol;

[0009] (3) a heat treatment process: placing the collected fiber precursor into a muffle furnace for pre-sintering, and then transferring it to a high-temperature tube furnace for high-temperature sintering to form a sintered fiber;

[0010] (4) preparing a fiber mat by airflow melting: using an airflow melting device with a nozzle and a collector, adjusting the fiber addition amount according to the required mat density, blowing the sintered fiber into the collector by high-speed airflow, and naturally accumulating into a randomly distributed fiber network, and naturally cooling to room temperature to obtain an alumina synthetic fiber mat;

[0011] wherein, in terms of weight percentage, the alumina synthetic fiber mat is composed of: 94%-96% of alumina, 0.5%-3% of rare earth element powder, 0.1%-1% of nano-reinforced material, and 1%-4% of metal oxide, and the metal oxide is silicon dioxide and / or zirconium dioxide;

[0012] The rare earth element powder is lanthanum oxide and / or yttrium oxide, the nano-reinforced material is silicon carbide nanowire and / or boron nitride nanosheet, and tetrabutyl titanate and / or tetrabutyl zirconate are added according to the content of the metal oxide.

[0013] Further, in the (1) mixing and sol preparation, after the alumina powder and the rare earth element powder are mixed, they are stirred in a high-speed stirrer at a speed of 800-1200 rpm for 20-40 min.

[0014] Further, in the (1) mixing and sol preparation, anhydrous ethanol is used as a dispersion medium, and dilute nitric acid is added to adjust the pH value to 2.5-3.5.

[0015] Further, in the (1) mixing and sol preparation, after the mixed solution is slowly dropped into the aluminum sol, it is continuously stirred and reacted at 60-80℃ for 2-6 h.

[0016] Further, in the (2) preparation of the fiber precursor, the organic template agent is polyvinyl alcohol or polyethylene glycol, and its amount is 2%-5% of the weight of the composite sol.

[0017] Further, in the (2) preparation of the fiber precursor, the dry spinning process is set with a needle inner diameter of 0.6-0.8 mm, a voltage of 12-18 kV, a fiber collection distance of 15-25 cm, and a feeding rate of 10-30 μL / min, and an aluminum foil is used as the fiber collection carrier.

[0018] Further, in the (3) heat treatment process, the pre-sintering process is performed in an air atmosphere, and the temperature is raised to 500°C at a rate of 4-6°C / min, and the temperature is maintained for 1-2 h.

[0019] Further, in the (3) heat treatment process, the high-temperature sintering is performed in a high-purity argon atmosphere in a high-temperature tube furnace, and the temperature is raised to 1300°C at a rate of 8-10°C / min, and the temperature is maintained for 2-3 h.

[0020] Further, in the (4) preparation of the fiber felt by gas flow melting, the nozzle diameter of the gas flow melting device is 0.4-0.6 mm, the gas flow velocity is set to 15-25 m / s, and the jet temperature is maintained at 1400-1600°C.

[0021] Regarding the above-mentioned part of the raw materials in the scheme:

[0022] 1. Alumina is the main component of the fiber felt, providing the basic structure and basic properties of the fiber, and has excellent mechanical strength, high-temperature resistance and chemical stability. In the high-temperature sintering process, alumina forms a stable α-Al2O3 crystal phase, which gives the fiber a very high melting point and good creep resistance, so that it can remain stable in extremely high-temperature environments.

[0023] 2. Rare earth element powder (lanthanum oxide or yttrium oxide) as a grain refiner, promotes the formation of fine grains during high-temperature sintering, prevents grain growth, helps to improve the density and uniformity of the fiber, and can improve the thermal expansion coefficient of alumina, reduce thermal stress concentration, and improve the thermal shock resistance and thermal stability of the fiber. It can also enhance the interfacial bonding force between the components inside the fiber, reduce interface defects, and improve the overall mechanical properties.

[0024] 3. Nano-enhanced materials (silicon carbide nanowires or boron nitride nanosheets) form micro-nano scale reinforcing phases inside the fiber, which can effectively disperse stress and prevent crack propagation, thereby significantly improving the fracture toughness of the fiber. By utilizing the high thermal conductivity, high strength, electrical insulation and high-temperature resistance of the material, the fiber felt is endowed with multiple functionalities. The nano-enhanced material and the matrix material form a complex three-dimensional network structure, enhancing the overall structural stability and mechanical properties of the fiber felt.

[0025] 4、Metal oxide (titanium dioxide or zirconium dioxide) can improve the hardness and wear resistance of the fiber, and improve the comprehensive performance of the fiber felt; the organic template agent (polyvinyl alcohol or polyethylene glycol) can provide temporary structural support and improve the flowability, improve the success rate and efficiency of the dry spinning and air flow melting process, and finally completely decompose at high temperature without affecting the physical and chemical properties of the fiber felt.

[0026] The application also provides the aluminum oxide synthetic fiber felt prepared by the preparation method.

[0027] The application has the following beneficial effects: 1. The rare earth element, metal oxide and nano reinforcing material are introduced into the aluminum oxide, so that the mechanical strength, thermal stability and oxidation resistance of the fiber felt are improved; specifically, the aluminum oxide is used as the main material, the rare earth element powder and the nano reinforcing material are introduced, the alpha-Al2O3 crystal phase is formed, and the micro-nano scale reinforcing phase is formed in the aluminum oxide synthetic fiber, so that the stress can be effectively dispersed, the crack propagation is prevented, the mechanical strength and the fracture toughness of the fiber are improved, and the structural integrity and the performance stability of the fiber felt at high temperature are maintained; at the same time, the synergistic effect of the rare earth element and the nano reinforcing material greatly improves the thermal shock resistance of the fiber felt, and the fiber felt is suitable for a working environment with frequent temperature changes; the metal oxide can enhance the hardness and wear resistance of the fiber felt, and also endows the fiber felt with excellent chemical stability and multiple functions.

[0028] 2. The aluminum oxide powder, the rare earth element powder, the tetrabutyl titanate and / or the tetrabutyl zirconate, the nano reinforcing material and the like are mixed and dispersed in anhydrous ethanol, so that the good dispersibility of the components is ensured, the uniform and stable composite sol is formed, the pH value is adjusted to promote the dissolution of the components and prevent the precipitation, the organic template agent is added into the composite sol, the temporary network structure can be formed in the melt, the appropriate viscosity range can be maintained, and the temporary structural support can be provided, so that the fiber morphology and size can be controlled.

[0029] 3. The pre-sintering and high-temperature sintering are combined, the fiber precursor is pre-sintered in an air atmosphere to remove the organic template agent and preliminarily solidify the fiber structure, and then the high-temperature sintering is performed under the protection of high-purity argon, so that the inorganic components in the fiber are subjected to solid-phase reaction to form a stable crystal structure, the mechanical strength and the high-temperature resistance of the fiber are enhanced, the integrity of the fiber structure and the performance stability are ensured, and the quality of the final product is improved.

[0030] 4、The application blows the sintered fiber into the collector by high-speed airflow, and the fiber network with random distribution is formed by natural accumulation. The high-speed airflow rapidly cools the fiber and fixes the form, avoiding the problems of crystal growth or phase change caused by slow cooling. With more and more fibers deposited, natural interweaving occurs between the fibers, forming a fiber felt with certain thickness and density. The three-dimensional porous network structure provides excellent heat insulation effect and good flexibility and compression resistance of the fiber felt. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Flow chart of the gas flow melting preparation method of the alumina synthetic fiber felt adopted in the application. DETAILED DESCRIPTION

[0032] The technical solutions of the application will be further described in detail below in combination with specific examples.

[0033] It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology realized on the basis of the above description of the application is covered within the scope of protection intended by the application. In the application, all equipment and raw materials can be purchased from the market or commonly used in the industry, and the methods in the following examples are conventional methods in the art, unless otherwise specified.

[0034] Example 1: A gas flow melting preparation method of an alumina synthetic fiber felt, as shown in the following scheme, includes the following steps: Figure 1 (1) Mixing and sol preparation: mix alumina powder and lanthanum oxide powder, stir in a high-speed stirrer at a speed of 1000 rpm for 30 min, add the mixed powder into anhydrous ethanol, and add dilute nitric acid to adjust the pH value to 3, stir at room temperature for 1.5 h, and then stir at 60℃ for 2 h to obtain an aluminum sol;

[0035] Add tetrabutyl titanate to an anhydrous ethanol solution containing silicon carbide nanowires, stir to dissolve and form a mixed solution, slowly drop the mixed solution into the aluminum sol, and continuously stir at 70℃ for 4 h to prepare a composite sol;

[0036] (2) Prepare fiber precursor: add 3% by weight of polyvinyl alcohol to the composite sol, stir thoroughly to completely dissolve, use dry spinning technology, set the needle inner diameter to 0.7 mm, the voltage to 15 kV, the fiber collection distance to 20 cm, and the feeding rate to 20 μL / min, use aluminum foil as the fiber collection carrier, and form the fiber precursor;

[0037] (3) Heat treatment process: The collected fiber precursor is placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min under air atmosphere. It is then held at this temperature for 1.5h for pre-sintering. After that, it is transferred to a high-temperature tube furnace and heated to 1300°C at a heating rate of 10°C / min under the protection of high-purity argon. It is then held at this temperature for 2.5h for high-temperature sintering to form sintered fibers.

[0038] (4) Preparation of fiber felt by airflow melting: An airflow melting device with a nozzle diameter of 0.5 mm was used, the airflow velocity was set to 20 m / s, and the spraying temperature was maintained at 1500℃. Based on the felt density of 20 g / m³, 3 Adjust the amount of fiber added, and blow the sintered fibers into a collector through a high-speed airflow. The fibers will naturally accumulate into a randomly distributed fiber network and be naturally cooled to room temperature to obtain alumina synthetic fiber felt.

[0039] The composition of alumina synthetic fiber felt by weight percentage is: 96% alumina, 1% lanthanum oxide, 0.5% silicon carbide nanowires, and 2.5% titanium dioxide.

[0040] Example 2: A method for preparing alumina synthetic fiber felt by airflow melting, as follows: Figure 1 As shown, the following steps are included: (1) Mixing and sol preparation: Alumina powder and yttrium oxide powder are mixed and stirred at 1000 rpm for 30 min in a high-speed stirrer. The mixed powder is added to anhydrous ethanol and dilute nitric acid is added to adjust the pH value to 3. The mixture is stirred at room temperature for 1.5 h and then stirred at 60°C for 2.5 h to obtain aluminum sol.

[0041] Tetrabutyl zirconate was added to an anhydrous ethanol solution containing boron nitride nanosheets and stirred to dissolve to form a mixed solution. The mixed solution was then slowly added dropwise to aluminum sol and stirred continuously at 70°C for 5 hours to obtain a composite sol.

[0042] (2) Preparation of fiber precursor: Add 4% by weight of polyethylene glycol to the composite sol, stir thoroughly to dissolve completely, use dry spinning technology, set the needle inner diameter to 0.7 mm, voltage to 15 kV, take-up distance to 20 cm, feed rate to 20 μL / min, and use aluminum foil as take-up carrier to form fiber precursor;

[0043] (3) Heat treatment process: The collected fiber precursor is placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min under air atmosphere. It is then held at this temperature for 1.5h for pre-sintering. After that, it is transferred to a high-temperature tube furnace and heated to 1300°C at a heating rate of 10°C / min under the protection of high-purity argon. It is then held at this temperature for 2.5h for high-temperature sintering to form sintered fibers.

[0044] (4) Airflow melt preparation of fiber felt: use airflow melt device with nozzle diameter of 0.5 mm, airflow speed is set to 20 m / s, jet temperature is maintained at 1500℃, according to the density of the felt 20g / m 3 Adjust the fiber addition amount, blow the sintered fiber into the collector by high-speed airflow, and naturally accumulate into a random fiber network, naturally cool to room temperature, to obtain an alumina synthetic fiber felt.

[0045] The composition of the alumina synthetic fiber felt is: alumina 95%, yttrium oxide 2%, boron nitride nanosheet 0.8%, and zirconium dioxide 2.2% by weight percentage.

[0046] Example 3: An airflow melt preparation method of an alumina synthetic fiber felt, as shown in Figure 1 (1) Mixing and sol preparation: mix alumina powder, lanthanum oxide powder and yttrium oxide powder, stir in a high-speed stirrer at a speed of 1000 rpm for 30 min, add the mixed powder into anhydrous ethanol, and add dilute nitric acid to adjust the pH value to 3, stir at room temperature for 1.5 h, then stir at 60℃ for 2.5 h to obtain an aluminum sol;

[0047] Add tetrabutyl titanate and tetrabutyl zirconate to the anhydrous ethanol solution containing silicon carbide nanowires and boron nitride nanosheets, stir to dissolve to form a mixed solution, slowly drop the mixed solution into the aluminum sol, and continuously stir at 80℃ for 6 h to prepare a composite sol;

[0048] (2) Preparation of fiber precursor: add 5% polyvinyl alcohol by weight to the composite sol, stir thoroughly to dissolve completely, use dry spinning technology, set the needle inner diameter to 0.7 mm, the voltage to 15 kV, the fiber collection distance to 20 cm, and the feeding rate to 20 μL / min, use aluminum foil as the fiber collection carrier to form the fiber precursor;

[0049] (3) Heat treatment process: place the collected fiber precursor in a muffle furnace, heat to 500℃ at a rate of 5℃ / min in air atmosphere, and pre-sinter for 1.5 h, then transfer to a high-temperature tube furnace, heat to 1300℃ at a rate of 10℃ / min under high-purity argon protection, and high-temperature sinter for 2.5 h to form sintered fibers;

[0050] (4) Airflow melt preparation of fiber felt: use airflow melt device with nozzle diameter of 0.5 mm, airflow speed is set to 20 m / s, jet temperature is maintained at 1500℃, according to the density of the felt 20g / m 3 Adjust the fiber addition amount, blow the sintered fiber into the collector by high-speed airflow, and naturally accumulate into a random fiber network, naturally cool to room temperature, to obtain an alumina synthetic fiber felt.

[0051] The composition of the aluminum oxide synthetic fiber felt is, by weight percentage: aluminum oxide 94%, lanthanum oxide 0.75%, yttrium oxide 0.75%, silicon carbide nanowire 0.3%, boron nitride nanosheet 0.3%, titanium dioxide 1.5%, and zirconium dioxide 2.4%.

[0052] Comparative Example 1: No rare earth element powder (lanthanum oxide powder of Example 1) is used, specifically:

[0053] (1) Mixing and sol preparation: aluminum oxide powder is added to anhydrous ethanol, and dilute nitric acid is added to adjust the pH value to 3, stirred at room temperature for 1.5 h, and then stirred at 60°C for 2 h to obtain an aluminum sol;

[0054] (1) The remaining steps of mixing and sol preparation, (2) preparation of fiber precursor, (3) heat treatment process, (4) preparation of fiber felt by gas flow melting, and the composition of the aluminum oxide synthetic fiber felt are consistent with Example 1.

[0055] Comparative Example 2: No titanium tetrabutoxide and silicon carbide nanowire is used, specifically:

[0056] (1) Mixing and sol preparation: aluminum oxide powder and lanthanum oxide powder are mixed, stirred in a high-speed stirrer at a speed of 1000 rpm for 30 min, the mixed powder is added to anhydrous ethanol, and dilute nitric acid is added to adjust the pH value to 3, stirred at room temperature for 1.5 h, and then stirred at 60°C for 2 h to obtain an aluminum sol, which is a composite sol;

[0057] The remaining steps (2) preparation of fiber precursor, (3) heat treatment process, (4) preparation of fiber felt by gas flow melting, and the composition of the aluminum oxide synthetic fiber felt are consistent with Example 1.

[0058] Performance test: the aluminum oxide synthetic fiber felt of Examples 1-3 and Comparative Examples 1-2 is tested for related performance;

[0059] 1. High temperature resistance: according to ASTM C1114-15 (Test Method for Dimensional Changes of Ceramic Materials Under Thermal Exposures), a sample with a size of 25mm x 25mm x 100mm is prepared, a vernier caliper with a precision of ±0.01mm is used to measure the length of the sample, the sample is placed in a high temperature furnace, and the temperature is raised to 1600°C at a rate of 10°C / min, and kept for 1 hour, then naturally cooled to room temperature, the length of the sample is measured again using the vernier caliper, and the shrinkage rate is calculated.

[0060] 2. Mechanical properties: according to ASTM C1275-18 (Tensile Strength of Ceramic Fibers and Fiber Felt), prepare samples with a width of 25 mm and a length of 150 mm, fix the samples on the grips of a universal testing machine, ensuring firm and uniform clamping, apply a tensile force at a rate of 1 mm / min until the sample breaks, record the maximum load and displacement at break, and calculate the tensile strength.

[0061] The same as the tensile strength test, apply small amplitude cyclic loading on the universal testing machine at a loading speed of 0.1 mm / min for 5 cycles, record the stress-strain curve, and calculate the elastic modulus.

[0062] 3. Thermal shock resistance: according to ASTM C773-19 (Determination of Thermal Shock Resistance of Ceramic Materials), prepare samples with dimensions of 50 mm x 50 mm x 10 mm, pre-sinter in air at 1000°C for 1 hour, quickly heat the samples to 1000°C and maintain for 1 minute, immediately remove the samples and immerse them in room temperature water for 1 minute, repeat the heating-cooling cycle 10 times, check the surface cracks and peeling of the samples, and record the damage degree.

[0063] 4. Thermal conductivity: according to ASTM E1461-13 (Determination of Thermal Diffusivity of Solid Materials by the Laser Flash Method), prepare circular or square thin sheet samples with a thickness of 1-2 mm, place the samples on the sample stage of the laser flash instrument, ensuring good contact, use a short pulse laser to irradiate the back of the sample, causing the sample to instantaneously heat up, measure the temperature change on the front of the sample with an infrared detector, calculate the thermal diffusivity based on the measured temperature response curve, and calculate the thermal conductivity in combination with the density and specific heat capacity.

[0064] The results of the performance tests are shown in Table 1.

[0065] Table 1. Performance test results of aluminum oxide synthetic fiber felt

[0066]

[0067] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the present application shall be covered by the claims of the present application.

Claims

1. An air-laid process for the production of an alumina synthetic fiber mat, characterized in that, The method comprises the following steps: (1) mixing and sol preparation: mixing alumina powder and rare earth element powder, adding the mixed powder into a dispersion medium, stirring at room temperature for 1-2 h, and stirring at 60 DEG C for 2-3 h to obtain an aluminum sol; adding tetrabutyl titanate and / or tetrabutyl zirconate into anhydrous ethanol solution containing nano-enhanced materials, stirring and dissolving to form a mixed solution, slowly dropping the mixed solution into the aluminum sol to prepare a composite sol; (2) preparing a fiber precursor: adding an organic template agent into the composite sol, fully stirring to completely dissolve the organic template agent, and using a dry spinning technology to form a fiber precursor from the composite sol; (3) heat treatment process: placing the collected fiber precursor into a muffle furnace for pre-sintering, and then transferring to a high-temperature tube furnace for high-temperature sintering to form a sintered fiber; (4) preparing a fiber felt by airflow melting: using an airflow melting device with a nozzle and a collector, adjusting the fiber addition amount according to the required felt density, blowing the sintered fiber into the collector by high-speed airflow, naturally accumulating into a random fiber network, and naturally cooling to room temperature to obtain an alumina synthetic fiber felt; wherein, the alumina synthetic fiber felt comprises, by weight percentage: 94%-96% of alumina, 0.5%-3% of rare earth element powder, 0.1%-1% of nano-enhanced material, and 1%-4% of metal oxide, the metal oxide being titanium dioxide and / or zirconium dioxide; the rare earth element powder is lanthanum oxide and / or yttrium oxide, the nano-enhanced material is silicon carbide nanowire and / or boron nitride nanosheet, and the tetrabutyl titanate and / or tetrabutyl zirconate is added according to the content of the metal oxide; in the (4) preparing a fiber felt by airflow melting, the nozzle diameter of the airflow melting device is 0.4-0.6 mm, the airflow speed is set to 15-25 m / s, and the spraying temperature is maintained at 1400-1600 DEG C.

2. An air-laid process for the production of an alumina synthetic fiber mat according to claim 1, characterized in that, in the (1) mixing and sol preparation, after the alumina powder and the rare earth element powder are mixed, the mixed powder is stirred in a high-speed stirrer at a speed of 800-1200 rpm for 20-40 min.

3. The method of claim 1, wherein the aluminum oxide synthetic fiber mat is produced by air-laying. in the (1) mixing and sol preparation, anhydrous ethanol is used as the dispersion medium, and dilute nitric acid is added to adjust the pH value to 2.5-3.

5. ​ 4. The method of claim 1, wherein the aluminum oxide synthetic fiber mat is produced by air-laying. 5 in the (1) mixing and sol preparation, after the mixed solution is slowly dropped into the aluminum sol, the stirring reaction is continuously performed at 60-80 DEG C for 2-6 h.

5. The method of claim 1, wherein the aluminum oxide synthetic fiber mat is produced by air-laying. 5 in the (2) preparing a fiber precursor, the organic template agent is polyvinyl alcohol or polyethylene glycol, and the amount of the organic template agent is 2%-5% of the weight of the composite sol.

6. The method of claim 1, wherein the aluminum oxide synthetic fiber mat is produced by air-laying. in the (2) preparing a fiber precursor, the needle inner diameter is set to 0.6-0.8 mm, the voltage is set to 12-18 kV, the fiber collection distance is set to 15-25 cm, the feeding rate is set to 10-30 μL / min, and aluminum foil is used as the fiber collection carrier during the dry spinning process.

7. The method of claim 1, wherein the aluminum oxide synthetic fiber mat is produced by air-laying. 5 in the (3) heat treatment process, the pre-sintering process is performed in an air atmosphere, the temperature is raised to 500 DEG C at a temperature raising rate of 4-6 DEG C / min, and the temperature is maintained for 1-2 h.

8. The method of claim 1, wherein the aluminum oxide synthetic fiber mat is produced by air-laying. 5 In the (3) heat treatment process, high-temperature sintering is carried out in a high-purity argon protection high-temperature tube furnace, and the temperature is raised to 1300℃ at a rate of 8-10℃ / min, and the temperature is kept for 2-3h.

9. An alumina synthetic fiber felt prepared by the production process according to any one of claims 1 to 8.

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