A two-dimensional or three-dimensional oxide ceramic fiber and a preparation method thereof

Abstract

The present invention relates to the technical field of ceramic fiber material preparation, in particular to a method for preparing two-dimensional or three-dimensional oxide ceramic fibers. The preparation method comprises the following steps: S1, preparation of an inorganic sol; S2, secondary acidification of the inorganic sol; S3, concentration of the inorganic sol; S4, electrospinning the spinning solution obtained in S3, and calcining and cooling the obtained oxide ceramic fibers. The present invention can obtain linear inorganic molecular chains with low branching degree and high polymerization degree by regulating the hydrolysis of the inorganic sol, ensuring the preparation of two-dimensional or three-dimensional oxide ceramic fibers by the self-template method, and realizing the continuous transformation from two-dimensional fibers to three-dimensional fibers, avoiding problems such as fiber pore defects caused by the need to add an organic polymer template and subsequent heat treatment in the existing electrospinning technology, and improving the fiber strength and adaptability to different scenarios and environments.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic fiber material preparation, and particularly to a two-dimensional or three-dimensional oxide ceramic fiber and a preparation method thereof. Background Art

[0002] Oxide ceramic fibers have excellent high-temperature resistance and have been widely used as thermal insulation materials in the thermal protection systems of advanced aircraft. However, due to the strong chemical bonds and low dislocation slip in oxides ceramics, the inherent brittleness of oxide ceramics makes them prone to fracture during bending deformation, severely limiting their service life and applications.

[0003] The preparation of nanofibers by electrospinning technology has the characteristics of high porosity, fine diameter, and easy combination with other methods. Among them, the electrospinning technology combined with the sol-gel method can prepare continuous ceramic fibers, which have the advantages of high porosity, high specific surface area, good structural stability, and good thermal stability. However, during the sol-gel formation process, the rapid hydrolysis of the ceramic precursor inorganic alcohol leads to the easy formation of a branched gel network during hydrolysis. The branched gel network has poor conductivity and low molecular weight, and cannot reach the viscosity and conductivity required for electrospinning. In addition, since the sol condensation rate after hydrolysis is too slow to obtain a linear molecular chain with a high degree of polymerization, the entanglement of molecular chains is low, and the electrospinning viscosity requirement cannot be met.

[0004] Therefore, currently, in order to meet the electrospinning preparation of oxide ceramic fibers, polymer templates (such as PVA, PVP, PEO, etc.) are often added to increase the viscosity of the inorganic sol, and then the inorganic sol is absorbed into the gel fibers, and then a high-temperature calcination process is used to remove the polymer template to obtain oxide ceramic fibers. However, after the heat treatment to remove the polymer template, a large number of pore defects will be generated on the fiber surface, causing irreversible damage to the structure of the oxide ceramic fibers. Interstitial pores are easily formed in the fibers at high temperatures, showing brittle characteristics.

[0005] In addition, traditional electrospinning usually assembles into a two-dimensional fiber membrane with anisotropic structural characteristics. Two-dimensional fiber materials have attracted much attention due to their unique structures and properties. However, due to their relatively limited planar structure and surface activity, their applications in some fields are restricted to a certain extent. Compared with two-dimensional fibers, the intertwined and interconnected structure enables three-dimensional fiber materials to have a good connectivity network and a high specific surface area, which endows them with excellent properties such as efficient absorption / insulation and selective transmission of continuous media, and plays a key role in fields such as sound absorption, heat insulation, and adsorption separation.

[0006] Therefore, regulating the transformation from two-dimensional fibers to three-dimensional fibers helps to expand the material structure, enhance functional properties, expand application fields, and enrich the structural diversity of nanomaterials. This transformation can provide a larger space and surface area, improve adsorption and catalytic performance, and enhance the mechanical strength and stability of the material, with wide applications in fields such as thermal protection, sewage treatment, biomedicine, and nanodevices.

[0007] The content in this part is only the content provided by the applicant related to the present invention, not all of which are prior arts, and some are the research findings of the applicant. Summary of the Invention

[0008] The object of the present invention is to overcome the problems in the existing polymer template addition technology, such as the generation of a large number of pore defects resulting in brittle characteristics and the application limitations of single-form ceramic fibers. A method for preparing two-dimensional or three-dimensional oxide ceramic fibers is provided. The materials prepared by this method can be used in technical fields such as thermal protection and high-temperature filtration.

[0009] The method of the present invention uses the sol-gel technology, combined with secondary acidification and rotary evaporation concentration under appropriate conditions, to achieve the transformation of inorganic sol from colloidal particles to linear inorganic molecular chains with low branching degree and high polymerization degree. Then, through direct electrospinning and heat treatment, two-dimensional or three-dimensional ultra-flexible oxide ceramic fibers are obtained. This method avoids problems such as pore structure defects on the fiber surface caused by the addition of organic polymer templates and subsequent heat treatment in the prior art. The obtained single fibers are dense and defect-free, greatly improving the mechanical properties of the oxide ceramic fibers. In addition, this method is simple to operate. By regulating the concentration of hydrogen ions in the final sol through secondary acidification, the continuous transformation from two-dimensional to three-dimensional oxide ceramic fibers can be achieved. A low concentration of hydrogen ions is conducive to obtaining 2D fibers, while a high concentration of hydrogen ions can achieve 3D fibers.

[0010] The porosity of the oxide ceramic fibers obtained in the present invention is above 95%, the thermal conductivity is less than 0.028 W / m·K, the bending strain can reach 99.9% without fracture, and the three-dimensional ceramic fibers have excellent resilience performance of more than 50%. Under high-temperature heat treatment at 1200 °C, the structure does not undergo obvious damage. It can be applied to the thermal protection field to improve the upper limit of the application of oxide ceramic fibers in high-temperature environments. This continuously regulated method has the advantages of flexibility, high efficiency, and scalability.

[0011] To solve the above technical problems, the present invention provides the following technical solutions:

[0012] In the first aspect, the present invention provides a method for preparing two-dimensional or three-dimensional oxide ceramic fibers, including the following steps:

[0013] S1. Preparation of inorganic sol: Mix and stir an alcoholate, an organic solvent, water, and a first inorganic acid to obtain an inorganic sol.

[0014] S2. Secondary acidification of inorganic sol: Add a second inorganic acid to the inorganic sol obtained in S1, and then stir for 8 - 12 h to obtain a sol after secondary acidification. The molar concentration of the second inorganic acid in S2 is 0.1 - 3 mol / L; the volume ratio of the second inorganic acid added in S2 to the volume of the inorganic sol is 0.0023 - 0.18:1.

[0015] S3. Concentration of inorganic sol: Concentrate the sol after secondary acidification in S2 by rotary evaporation to obtain a rotary evaporation concentrated solution as a spinning solution.

[0016] S4. Preparation of two - dimensional or three - dimensional super - flexible oxide ceramic fibers: Electrospin the spinning solution obtained in S3 to obtain oxide ceramic fibers, and calcine the obtained oxide ceramic fibers. After cooling, a two - dimensional or three - dimensional oxide ceramic fiber membrane material is obtained.

[0017] Preferably, the second inorganic acid in S2 is added dropwise.

[0018] Preferably, the stirring temperature in S2 is room temperature.

[0019] Preferably, the volume of the second inorganic acid added in S2 is 0.1 - 3 mL.

[0020] Preferably, the volume of the second inorganic acid added in S2 is 2 - 3 mL.

[0021] Preferably, the first inorganic acid and the second inorganic acid are each independently hydrochloric acid and / or phosphoric acid. Under this preferred scheme of suitable inorganic acid types, the inorganic sol can be secondarily acidified, which is more conducive to precisely controlling the hydrogen ion concentration in the sol.

[0022] Preferably, the molar concentration of the first inorganic acid in S1 is 0.1 - 3 mol / L; in S1, the molar ratio of the alcoholate to the organic solvent, water, and the first inorganic acid is 1:(1 - 10):(2 - 10):0.01. Under this preferred scheme, the best mixing conditions for the inorganic sol can be created, which is more conducive to obtaining low - branched and high - polymerization - degree linear inorganic molecular chains through subsequent secondary acidification and rotary evaporation concentration.

[0023] Preferably, the alcoholate in S1 includes a metal alcoholate or an inorganic alcoholate.

[0024] Preferably, the organic solvent is at least one of ethanol, propanol, and acetone.

[0025] Preferably, the water is deionized water.

[0026] The metal alkoxide may be one or more of aluminum sec-butoxide, aluminum isopropoxide, tetraethyl titanate, etc., and the inorganic alkoxide may be one or more of tetraethyl orthosilicate, methyl orthosilicate, silica sol, etc.

[0027] Preferably, the conditions for rotary evaporation and concentration in S3 include: the water bath temperature is 30-60°C, the rotation speed is 40-100 rpm, and the rotary evaporation time is 2-10 min. Under these preferred rotary evaporation and concentration conditions, it can further cure the low molecular weight silicon chains, enhance their linear structure, obtain linear inorganic molecular chains with low branching degree and high polymerization degree, which is more conducive to the silica sol spinning solution to reach a viscosity and structure similar to that of the added organic polymer template, and directly perform electrospinning.

[0028] The rotary evaporation can start vacuum concentration on a rotary evaporator, and the volume of the concentrated sol obtained is 10-30 mL.

[0029] Furthermore, different concentration conditions result in concentrated sols with different viscosities and spinning efficiencies.

[0030] Preferably, the conditions for electrospinning in S4 include: the voltage is 15-25 kV, the feeding speed is 0.1-2 mL / h, the receiving distance is 10-25 cm, the temperature is 15-30°C, and the humidity is 10%-70%; under these preferred electrospinning conditions, it can achieve the best spinning efficiency and is more conducive to collecting two-dimensional or three-dimensional oxide ceramic fibers.

[0031] Furthermore, the obtained spinning solution is transferred to a syringe and then electrospun.

[0032] Preferably, the conditions for calcination in S4 include: the heating rate is 1-10°C / min, the holding temperature is 700-800°C, and the time is 0.5-2 h. Under these preferred calcination conditions, it can remove the residual organic substances in the oxide ceramic fibers and is more conducive to obtaining a complete and dense fiber structure.

[0033] Furthermore, the calcination can be carried out in a muffle furnace.

[0034] Preferably, when the target product is two-dimensional oxide ceramic fibers, the molar concentration and volume dosage of the second inorganic acid in S2 are adjusted so that the concentration of hydrogen ions in the sol after secondary acidification obtained in S2 is 0.02-0.1 mol / L. Under these preferred hydrogen ion concentration conditions, it can accurately control the pH of the sol and then adjust the enrichment degree of more positive charges on the surface of the sol colloid, which is more conducive to realizing the preparation of two-dimensional oxide ceramic fibers.

[0035] Preferably, when the target product is three-dimensional oxide ceramic fibers, the molar concentration and volume dosage of the second inorganic acid S2 are adjusted so that the concentration of hydrogen ions in the sol after secondary acidification obtained from S2 is 0.1 - 0.3 mol / L. Under this preferred hydrogen ion concentration condition, it can accurately control the pH of the sol and further adjust the enrichment degree of more negative charges on the surface of the sol colloid, which is more conducive to the preparation of three-dimensional oxide ceramic fibers.

[0036] The present invention also provides a two-dimensional oxide ceramic fiber, which is prepared by the method for preparing two-dimensional or three-dimensional oxide ceramic fibers based on the self-template method described above.

[0037] Preferably, the porosity of the two-dimensional oxide ceramic fiber of the present invention is above 95%, the thermal conductivity is less than 0.028 W / m·K, the bending strain reaches 99.9% without fracture, and the structure is not significantly damaged under high-temperature heat treatment at 1200°C.

[0038] The present invention also provides a three-dimensional oxide ceramic fiber, which is prepared by the method for preparing two-dimensional or three-dimensional oxide ceramic fibers based on the self-template method described above.

[0039] Preferably, the porosity of the three-dimensional oxide ceramic fiber of the present invention is above 99%, the thermal conductivity is less than 0.028 W / m·K, the bending strain reaches 99.9% without fracture, it has excellent resilience performance of more than 50%, and the structure is not damaged under high-temperature heat treatment at 1200°C.

[0040] The technical principle of the present invention is as follows:

[0041] Secondary acidification can promote the conversion of the original colloid particles into low-polymerization-degree linear inorganic molecular chains. After rotary evaporation and concentration, the linear inorganic molecular chains can be cured to further enhance their linear structure, obtaining low-branching-degree and high-polymerization-degree linear inorganic molecular chains, achieving a viscosity and structure similar to those of adding an organic polymer template, and directly performing electrospinning. It solves the problem of fiber defects caused by the organic polymer template, and the obtained single fiber is dense and defect-free, greatly improving the mechanical properties of the oxide ceramic fiber.

[0042] Meanwhile, the concentration of the sol acid is regulated by secondary acidification to further adjust the enrichment degree of positive and negative charges on the surface of the silica colloid. When the acid concentration in the final solution is low, during the fiber formation process, under the electrostatic induction and polarization of the electrostatic field force, the fiber carries a positive charge. The positively charged nozzle tip will repel the fiber, and the negatively charged collector will attract the fiber. Therefore, the fiber will be more likely to accumulate and form a two-dimensional structure. On the contrary, when the acid concentration in the final solution is high, during the fiber formation process, under the electrostatic induction and polarization of the electrostatic field force, the fiber carries a negative charge. The positively charged nozzle tip will attract the fiber, and the negatively charged collector will repel the fiber. At the same time, the fibers themselves will also repel each other due to electrostatic repulsion. The interaction of these forces results in the easier formation of a three-dimensional structure with large pores and loose packing between fibers. The present invention can greatly meet the usage requirements of different oxide ceramic fiber forms in different scenarios by regulating the continuous transformation from two-dimensional to three-dimensional oxide ceramic fibers.

[0043] The beneficial effects of the above technical solutions of the present invention are as follows:

[0044] (1) In the present invention, the inorganic sol has a linear inorganic molecular chain with a low degree of branching and a high degree of polymerization similar to that of organic polymers. It is possible to use the inorganic sol molecular chain as a template and combine the secondary acidification and rotary evaporation concentration under suitable conditions to ripen its linear inorganic molecular chain, further enhancing the linear structure to achieve the viscosity and conductivity for electrospinning. It breaks through the limitation that electrospinning to prepare oxide ceramic fibers requires an organic polymer template, avoids problems such as pore defects caused by adding an organic polymer template after heat treatment to the fiber structure. The obtained single fiber is dense and defect-free, greatly improving the mechanical properties of the oxide ceramic fibers.

[0045] (2) Secondary acidification can accurately regulate the pH of the sol and thus adjust the enrichment degree of positive and negative charges on the surface of the sol colloid, realizing the precise regulation and continuous transformation of oxide ceramic fibers from two-dimensional to three-dimensional. This continuous regulation method has the advantages of high flexibility, high efficiency, and wide expandability, etc., can meet the requirements of different fields and applications, and improves the production efficiency and functional diversity of fiber materials.

[0046] (3) The porosity of the oxide ceramic fiber membrane material obtained by the present invention is greater than 95%, the thermal conductivity is less than 0.028 W / m·K, the bending strain can reach 99.9% without fracture, the temperature resistance is greater than 1200 °C, and the three-dimensional ceramic fiber has an excellent resilience performance of more than 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a process flow chart of a method for preparing two-dimensional or three-dimensional oxide ceramic fibers of the present invention;

[0048] Figure 2This is a physical picture of the two-dimensional silica ceramic fiber membrane prepared in Example 1 of the present invention;

[0049] Figure 3 This is an SEM image of the silica ceramic fiber membrane prepared in Example 1 of the present invention;

[0050] Figure 4 This is a physical picture of the silica ceramic fiber sponge prepared in Example 2 of the present invention;

[0051] Figure 5 This is an SEM image of the silica ceramic fiber sponge prepared in Example 2 of the present invention. Detailed implementation manners

[0052] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0053] The present invention provides a method for preparing two-dimensional or three-dimensional oxide ceramic fibers.

[0054] As Figure 1 shown, the method includes the following steps:

[0055] (1) Preparation of inorganic sol: Mix metal alkoxide / inorganic alkoxide, organic solvent, deionized water, and inorganic acid in a beaker according to a certain molar ratio, and stir evenly at room temperature in a magnetic stirrer with a rotation speed of 400 - 700 rpm for 8 - 12 h to obtain inorganic sol;

[0056] (2) Secondary acidification of inorganic sol: Drop inorganic acid into the sol obtained in step (1), and then continue to stir evenly at room temperature in a magnetic stirrer with a rotation speed of 400 - 700 rpm for 8 - 12 h to obtain the sol after secondary acidification;

[0057] (3) Concentration of inorganic sol: Transfer the sol after secondary acidification in step (2) to a round-bottom flask, fix it on a rotary evaporator, with a rotary evaporation temperature of 30 - 60 °C, a rotation speed of 40 - 100 rpm, a rotary evaporation time of 2 - 10 min, and the concentrated sol volume is 10 - 30 mL. The concentrated sol is used as the spinning solution;

[0058] (4) Preparation of two-dimensional / three-dimensional super-flexible oxide ceramic fibers: Transfer the spinning solution obtained in step (3) to a syringe, adjust the electrospinning voltage, propulsion speed, receiving distance, temperature, and humidity, perform electrospinning, obtain oxide ceramic fibers through electrospinning technology, transfer the obtained ceramic fibers to a muffle furnace, heat them up to 700 - 800 °C at a heating rate of 1 - 10 °C / min and hold for 0.5 - 2 h, and then naturally cool to obtain two-dimensional / three-dimensional super-flexible oxide ceramic fibers.

[0059] The present invention provides a method for preparing two-dimensional or three-dimensional oxide ceramic fibers, belonging to the technical field of ceramic fiber material preparation. In this method, metal alkoxides / inorganic alkoxides are first hydrolyzed in an acidic environment to obtain colloidal particles. Secondary acidification is carried out to adjust the enrichment degree of positive and negative charges on the surface of silica colloids and promote the condensation of colloidal particles, resulting in linear inorganic molecular chains with low polymerization degrees. Then, rotary evaporation concentration is used to further ripen the molecular chains and enhance their linear structures, obtaining linear inorganic molecular chains with low branching degrees and high polymerization degrees. Finally, two-dimensional / three-dimensional ultra-flexible oxide ceramic fiber membrane materials are obtained through electrospinning and heat treatment technologies. This method avoids problems such as pore defects in the fiber structure caused by adding organic polymer templates after heat treatment. The obtained single fibers are dense and defect-free, greatly improving the mechanical properties of single oxide ceramic fibers. In addition, in this method, the continuous transformation from two-dimensional to three-dimensional oxide ceramic fibers can be achieved only by secondary acidification to regulate the hydrogen ion concentration in the final sol. A low hydrogen ion concentration can obtain 2D fibers, while a high hydrogen ion concentration can obtain 3D fibers. The porosity of the obtained oxide ceramic fibers is above 95%, the thermal conductivity is less than 0.028 W / m·K, the bending strain can reach 99.9% without fracture, and the three-dimensional ceramic fibers have excellent resilience properties of more than 50%. The structure does not undergo obvious damage under high-temperature heat treatment at 1200 °C, and it can be applied to the thermal protection field to improve the upper limit of the application of oxide ceramic fibers in high-temperature environments. This continuous regulation method has the advantages of flexibility, high precision, high efficiency, and scalability. This method can meet the needs of different fields and applications, improve the production efficiency and functional diversity of fiber materials, and promote the development and application of new functional fiber materials.

[0060] The following is illustrated with specific examples. The testing methods for each performance parameter in the following examples and comparative examples are as follows: The porosity is obtained by the pressure pump method, the thermal conductivity is obtained by Hot Disk TPS2500S with reference to the international standard ISO22007-2, and the bending strain is obtained by an electronic universal testing machine Instron5969.

[0061] Example 1

[0062] A method for preparing a super-flexible two-dimensional silica ceramic fiber membrane without an organic polymer template, comprising the following steps:

[0063] (1) Mix tetraethyl orthosilicate, isopropanol, deionized water, and oxalic acid (molar concentration of 1 mol / L) in a beaker according to a molar ratio of 1:10:5:0.01, and stir evenly at room temperature for 12 h to obtain a silica sol;

[0064] (2) Add 0.1 mL of oxalic acid with a molar concentration of 1 mol / L dropwise to the silica sol obtained in step (1), and then continue to stir evenly at room temperature for 12 h at a stirring rate of 400 rpm to obtain the silica sol after secondary acidification. The molar concentration of hydrogen ions in the silica sol after secondary acidification is 0.02 mol / L;

[0065] (3) Transfer 50 mL of the silica sol after secondary acidification in step (2) to a round-bottom flask, fix it on a rotary evaporator, set the temperature of the water bath to 60 °C, and rotate at 85 rpm. Then start vacuum concentration and timekeeping. Stop rotary evaporation when the rotary evaporation time is 7 min, remove the round-bottom flask to obtain the spinning solution after rotary evaporation and concentration;

[0066] (4) Transfer the spinning solution obtained in step (3) to a syringe for electrospinning. Set the voltage to 18 kV, the feeding speed to 1 mL / h, the receiving distance to 15 cm, the temperature to 25 °C, and the humidity to 45 ± 5%. Transfer the obtained ceramic fibers to a muffle furnace, heat them up to 800 °C at a heating rate of 5 °C / min and hold for 0.5 h, and then cool naturally to obtain a silica ceramic fiber membrane without an organic polymer template;

[0067] (5) The obtained super-flexible two-dimensional silica ceramic fiber membrane has a porosity of 90%, a thermal conductivity of 0.0285 W / m·K, a bending strain of up to 99.5% without fracture, and at the same time has an excellent resilience performance of 50%. The structure does not undergo obvious damage under high-temperature heat treatment at 1250 °C, and the macroscopic and microscopic morphologies are as Figure 2 and Figure 3 shown.

[0068] Example 2

[0069] A preparation method of a super-flexible three-dimensional intertwined and curled structure silica ceramic fiber sponge without an organic polymer template, comprising the following steps:

[0070] (1) Mix tetraethyl orthosilicate, acetone, deionized water, and phosphoric acid (molar concentration of 1 mol / L) in a beaker according to a molar ratio of 1:8:10:0.01, and stir evenly at room temperature for 12 h to obtain a silica sol;

[0071] (2) Add 3 mL of phosphoric acid with a molar concentration of 1 mol / L dropwise to the silica sol obtained in step (1), and then continue to stir evenly at room temperature for 12 h at a stirring rate of 500 rpm to obtain the silica sol after secondary acidification. The molar concentration of hydrogen ions in the silica sol after secondary acidification is 0.3 mol / L;

[0072] (3) Transfer 50 mL of the silica sol after secondary acidification in step (2) to a round-bottom flask, fix it on a rotary evaporator, set the temperature of the water bath to 60 °C, and rotate at 85 rpm. Then start vacuum concentration and timekeeping. Stop rotary evaporation when the rotary evaporation time is 8 min, remove the round-bottom flask, and obtain the spinning solution after rotary evaporation and concentration;

[0073] (4) Transfer the spinning solution obtained in step (3) to a syringe for electrospinning. Set the voltage to 20 kV, the pushing speed to 1.5 mL / h, the receiving distance to 15 cm, the temperature to 25 °C, and the humidity to 50%. Transfer the obtained ceramic fibers to a muffle furnace, heat them to 800 °C at a heating rate of 5 °C / min and hold for 0.5 h, and then naturally cool to obtain a silica ceramic fiber sponge with a super-flexible three-dimensional intertwined and curled structure without an organic polymer template.

[0074] (5) The porosity of the obtained silica ceramic fiber sponge with a super-flexible three-dimensional intertwined and curled structure is 99%, the thermal conductivity is 0.0283 W / m·K, the bending strain can reach 99.9% without fracture, and at the same time it has excellent resilience performance of more than 50%. The structure does not undergo obvious damage under high-temperature heat treatment at 1250 °C, and the macroscopic and microscopic morphologies are as Figure 4 and Figure 5 shown.

[0075] Example 3

[0076] A preparation method of an alumina ceramic fiber sponge with a super-flexible three-dimensional intertwined and curled structure without an organic polymer template, comprising the following steps:

[0077] (1) Mix aluminum isopropoxide, absolute ethanol, deionized water, and nitric acid (molar concentration of 1 mol / L) in a beaker according to a molar ratio of 1:5:10:0.01, and stir evenly at room temperature for 12 h to obtain an aluminum sol;

[0078] (2) Add 2 mL of nitric acid with a molar concentration of 1 mol / L dropwise to the aluminum sol obtained in step (1). The volume ratio of the added second inorganic acid to the volume of the inorganic sol is...:1. Then continue to stir evenly at room temperature for 12 h, and the stirring rate is 450 rpm to obtain the aluminum sol after secondary acidification. The hydrogen ion molar concentration in the aluminum sol after secondary acidification is 0.28 mol / L;

[0079] (3) Transfer 40 mL of the aluminum sol after secondary acidification in step (2) to a round-bottom flask, fix it on a rotary evaporator, set the temperature of the water bath to 50 °C, and rotate at 85 rpm. Then start vacuum concentration and timekeeping. Stop rotary evaporation when the rotary evaporation time is 6 min, remove the round-bottom flask, and obtain the spinning solution after rotary evaporation and concentration;

[0080] (4) Transfer the spinning solution obtained in step (3) to a syringe for electrospinning. Set the voltage at 18 kV, the feeding rate at 0.5 mL / h, the receiving distance at 15 cm, the temperature at 25 °C, and the humidity at 28%. Transfer the obtained ceramic fibers to a muffle furnace, heat them up to 800 °C at a heating rate of 5 °C / min and hold for 1 h, and then naturally cool to obtain a super-flexible three-dimensional intertwined and coiled structure alumina ceramic fiber sponge without an organic polymer template.

[0081] (5) The porosity of the obtained super-flexible three-dimensional intertwined and coiled structure alumina ceramic fiber sponge is 98%, the thermal conductivity is 0.027 W / m·K, the bending strain can reach 99% without fracture, and it also has an excellent resilience performance of 50%. The structure does not break under high-temperature heat treatment at 1400 °C.

[0082] Example 4

[0083] Referring to Example 3, the difference is that the stirring rate in step (2) is different, specifically 480 rpm. The molar concentration of hydrogen ions in the aluminum sol after secondary acidification is 0.027 mol / L.

[0084] The porosity of the obtained three-dimensional intertwined and coiled structure alumina ceramic fiber sponge is above 98%, the thermal conductivity is 0.0275 W / m·K, the bending strain reaches 99.5% without fracture, and it also has an excellent resilience performance of 60%. The structure does not undergo obvious damage under high-temperature heat treatment at 1450 °C.

[0085] Compared with Example 3, the heat insulation performance of this example is poorer.

[0086] Example 5

[0087] Referring to Example 3, the difference is that the addition amount of nitric acid in step (2) is different, specifically 2 mL. The molar concentration of hydrogen ions in the aluminum sol after secondary acidification is 0.025 mol / L.

[0088] The porosity of the obtained three-dimensional intertwined and coiled structure alumina ceramic fiber sponge is 97%, the thermal conductivity is 0.026 W / m·K, the bending strain reaches 98% without fracture, and it also has an excellent resilience performance of 40%. The structure does not break under high-temperature heat treatment at 1400 °C.

[0089] Compared with Example 3, the compression and resilience performance of this example is poorer.

[0090] Example 6

[0091] Referring to Example 3, the difference is that the conditions for rotary evaporation and concentration in step (3) are different, and the temperature is 60 °C.

[0092] The obtained three-dimensional interwoven and crimped structure alumina ceramic fiber sponge has a porosity of 99%, a thermal conductivity of 0.0275 W / m·K, a flexural strain of up to 98% without fracture, and at the same time has an excellent resilience performance of 60%, and the structure does not break under high-temperature heat treatment at 1500 °C.

[0093] Compared with Example 3, the bending performance of this example is poor.

[0094] Example 7

[0095] Referring to Example 3, the difference is that in step (1), the material ratio is different, and the amount of absolute ethanol is adjusted so that the molar ratio of aluminum isopropoxide, absolute ethanol, deionized water, and nitric acid is 1:9:2:0.1, and the molar concentration of hydrogen ions in the silica sol after secondary acidification is 0.25.

[0096] The obtained three-dimensional interwoven and crimped structure alumina ceramic fiber sponge has a porosity of 98%, a thermal conductivity of 0.025 W / m·K, a flexural strain of up to 98% without fracture, and at the same time has an excellent resilience performance of 40%, and the structure does not break under high-temperature heat treatment at 1500 °C.

[0097] Compared with Example 3, the compression and resilience performance of this example is poor.

[0098] Example 8

[0099] Referring to Example 3, the difference is that in step (4), the calcination temperature is different, specifically 750 °C.

[0100] The obtained three-dimensional interwoven and crimped structure alumina ceramic fiber sponge has a porosity of 97%, a thermal conductivity of 0.029 W / m·K, a flexural strain of up to 98% without fracture, and at the same time has an excellent resilience performance of 60%, and the structure does not break under high-temperature heat treatment at 1450 °C.

[0101] Compared with Example 3, the heat insulation performance of this example is poor.

[0102] Comparative Example 1

[0103] Referring to Example 3, the difference is that step (2) is not carried out, but subsequent steps such as step (3) are directly carried out.

[0104] The obtained three-dimensional interwoven and crimped structure alumina ceramic fiber sponge has a porosity of more than 80%, a thermal conductivity of 0.05 W / m·K, a flexural strain of up to 50% without fracture, and at the same time has an excellent resilience performance of 10%, and the structure does not undergo obvious damage under high-temperature heat treatment at 1050 °C.

[0105] Comparative Example 2

[0106] Referring to Example 3, the difference is that the volume ratio of nitric acid to inorganic sol in step (2) is different. Nitric acid is adjusted so that the volume ratio of nitric acid to inorganic sol is 0.18:1, and the hydrogen ion molar concentration in the silica sol after secondary acidification is 0.29 mol / L.

[0107] The obtained three-dimensional intertwined and curled structure alumina ceramic fiber sponge has a porosity of 70%, a thermal conductivity of 0.06 W / m·K, a bending strain of up to 60% without fracture, and at the same time has an excellent resilience performance of 20%. The structure is not significantly damaged under high-temperature heat treatment at 950 °C.

[0108] Comparative Example 3

[0109] Referring to Example 3, the difference is that the stirring time in step (2) is different, specifically 4 h.

[0110] The obtained three-dimensional intertwined and curled structure alumina ceramic fiber sponge has a porosity of 60%, a thermal conductivity of 0.07 W / m·K, a bending strain of up to 60% without fracture, and at the same time has an excellent resilience performance of 20%. The structure is not significantly damaged under high-temperature heat treatment at 900 °C.

[0111] Comparative Example 4

[0112] Referring to Example 3, the difference is that the molar concentration of inorganic acid in step (2) is different, specifically 5 mol / L, and the hydrogen ion molar concentration in the silica sol after secondary acidification is 0.5 mol / L.

[0113] The obtained three-dimensional intertwined and curled structure alumina ceramic fiber sponge has a porosity of 60%, a thermal conductivity of 0.04 W / m·K, a bending strain of up to 60% without fracture, and at the same time has an excellent resilience performance of 20%. The structure is not damaged under high-temperature heat treatment at 1000 °C.

[0114] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing two-dimensional or three-dimensional oxide ceramic fibers, characterized in that, It includes the following steps: S1. Preparation of inorganic sol: Mix and stir an alcoholate, an organic solvent, water, and a first inorganic acid to obtain an inorganic sol; The molar concentration of the first inorganic acid in S1 is 0.1 - 3 mol / L; the molar ratio of the alcoholate to the organic solvent, water, and the first inorganic acid is 1:(1 - 10):(2 - 10):0.01 - 0.05; The alcoholate in S1 includes a metal alcoholate or an inorganic alcoholate, the organic solvent is at least one of ethanol, propanol, and acetone, and the water is deionized water; the conditions for mixing and stirring include: the stirring speed is 400 - 700 rpm, and the time is 8 - 12 h; S2. Secondary acidification of the inorganic sol: Add a second inorganic acid to the inorganic sol obtained in S1, and then stir for 8 - 12 h to obtain a sol after secondary acidification; the molar concentration of the second inorganic acid in S2 is 0.1 - 3 mol / L; the volume ratio of the second inorganic acid added in S2 to the volume of the inorganic sol is 0.0023 - 0.18:1; S3. Concentration of the inorganic sol: Rotavapor-concentrate the sol after secondary acidification in S2, and the obtained rotavapor-concentrated solution is used as a spinning solution; The conditions for rotavapor concentration in S3 include: the water bath temperature is 30 - 60 °C, the rotation speed is 40 - 100 rpm, and the rotavapor time is 2 - 10 min; S4. Preparation of two-dimensional or three-dimensional ultra-flexible oxide ceramic fibers: Electrospinning the spinning solution obtained in S3 to obtain oxide ceramic fibers, and calcining the obtained oxide ceramic fibers. After cooling, a two-dimensional or three-dimensional oxide ceramic fiber membrane material is obtained.

2. The preparation method of a two-dimensional or three-dimensional oxide ceramic fiber according to claim 1, characterized in that: The second inorganic acid in S2 is added dropwise, and the stirring rate is controlled at 300 - 600 rpm, and the stirring temperature is room temperature; the volume of the second inorganic acid added in S2 is 0.1 - 3 mL.

3. The preparation method of a two-dimensional or three-dimensional oxide ceramic fiber according to claim 1, characterized in that: The first inorganic acid and the second inorganic acid are each independently hydrochloric acid and / or phosphoric acid.

4. The preparation method of a two-dimensional or three-dimensional oxide ceramic fiber according to claim 1, characterized in that: The conditions for the electrospinning in S4 include: the voltage is 15 - 25 kV, the feeding speed is 0.1 - 2 mL / h, the receiving distance is 10 - 25 cm, the temperature is 15 - 30 °C, and the humidity is 10% - 70%; The conditions for the calcining in S4 include: the heating rate is 1 - 10 °C / min, the holding temperature is 700 - 800 °C, and the time is 0.5 - 2 h.

5. The preparation method of a two-dimensional or three-dimensional oxide ceramic fiber according to claim 1, characterized in that: When the target product is two-dimensional oxide ceramic fibers, adjust the molar concentration and volume dosage of the second inorganic acid in S2 so that the concentration of hydrogen ions in the sol after secondary acidification obtained in S2 is 0.02 - 0.1 mol / L; When the target product is three-dimensional oxide ceramic fibers, adjust the molar concentration and volume dosage of the second inorganic acid in S2 so that the concentration of hydrogen ions in the sol after secondary acidification obtained in S2 is 0.1 - 0.3 mol / L.

6. A two-dimensional oxide ceramic fiber, characterized in that, It is a method for preparing a two-dimensional or three-dimensional oxide ceramic fiber as described in any one of claims 1 - 5. The porosity of the two-dimensional oxide ceramic fiber is above 95%, the thermal conductivity is less than 0.028 W / m·K, the bending strain reaches 99.9% without fracture, and the structure is not damaged under high-temperature heat treatment at 1200 °C.

7. A three-dimensional oxide ceramic fiber, characterized in that, It is prepared by the method for preparing a two-dimensional or three-dimensional oxide ceramic fiber according to any one of claims 1 to 5. The porosity of the three-dimensional oxide ceramic fiber is more than 99%, the thermal conductivity is less than 0.028 W / m·K, the bending strain reaches 99.9% without fracture, it has excellent resilience performance of more than 50%, and the structure is not damaged under high-temperature heat treatment at 1200 °C.

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