A borate rare earth-based high-entropy ceramic nanofiber and its preparation method

Abstract

This invention discloses a borate rare earth-based high-entropy ceramic nanofiber and its preparation method, relating to the field of high-entropy ceramic technology, and includes the following steps: adding a spinning aid, rare earth salt, and boric acid sequentially to a solvent and stirring until homogeneous to obtain a spinning solution; electrospinning the spinning solution and pre-oxidizing it to obtain a pre-oxidized precursor fiber; placing the pre-oxidized precursor fiber in an inert gas, calcining it at high temperature, and cooling it to obtain the borate rare earth-based high-entropy ceramic nanofiber.

Description

Technical Field

[0001] This invention relates to the field of high-entropy ceramics technology, specifically to a borate rare-earth-based high-entropy ceramic nanofiber and its preparation method. Background Technology

[0002] Ceramic nanofibers are lightweight materials with high aspect ratios and circular or elliptical cross-sections. Due to their advantages such as low density, low thermal conductivity, high toughness, and high temperature resistance, they are widely used in aerospace, petrochemical, and metallurgical fields. Currently, methods for preparing ceramic nanofibers include stretching, phase separation, self-assembly, template spinning, and electrospinning. Among these, electrospinning has become a commonly used method due to its advantages of low cost, controllable process, and the ability to spin a wide variety of materials. However, with increasingly higher requirements for material diversity and functionality, preparing a single ceramic component using only electrospinning technology is insufficient to meet the demands of extreme environments. High-entropy materials, with their thermodynamic high-entropy effect, kinetic hysteresis diffusion effect, "cocktail effect" in performance, and lattice distortion effect, can optimize the mechanical, electrical, and thermal properties of ceramic materials. Therefore, a multi-component high-entropy design strategy is introduced into the preparation of ceramic nanofibers to improve the overall performance of the material.

[0003] Existing technologies contain a considerable amount of research on high-entropy ceramic nanofibers. Patent CN114751737A describes a method for obtaining high-entropy zirconate-based ceramic nanofibers with a single fluorite crystal phase and uniform elemental distribution by combining a spinning aid with a rare-earth zirconate-based material, followed by electrospinning and high-temperature calcination. These nanofibers exhibit a thermal conductivity as low as 0.23 W·m. -1 ·K -1 ， It can be widely used in fields such as thermal insulation and ceramic toughening. Patent CN115467048A discloses a ceramic fiber structure of Re3TaO7, ReTaO4, or ReTa3O9 with stoichiometric ratio, synthesized by electrospinning and high-temperature calcination using rare earth niobates or tantalates as precursors, with a thermal conductivity as low as 0.1 W·m. -1 ·K -1 This material can be widely used in thermal insulation. Patent CN113135755A uses five or more rare earth salts containing cerium to prepare a spinning solution, which is then electrospun and calcined at high temperature to produce a high-entropy ceric acid rare earth nanofiber ceramic membrane. This membrane exhibits good flexibility and structural uniformity, and has broad application prospects in thermal insulation, radiation protection, and other fields. It is evident that current patents on high-entropy ceramic fibers mainly focus on research into mechanical properties and thermal stability, but suffer from insufficient material chemical diversity and limited functional application areas.

[0004] Therefore, developing a novel rare-earth borate-based high-entropy ceramic nanofiber is expected to break through the limitations of existing material systems and achieve breakthroughs in its application in functional fields such as electromagnetic wave absorption. Summary of the Invention

[0005] The purpose of this invention is to provide a borate rare earth-based high-entropy ceramic nanofiber and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing borate rare earth-based high-entropy ceramic nanofibers includes the following steps: S1: Add the spinning aid, rare earth salt and boric acid to the solvent in sequence, stir evenly to obtain the spinning solution; S2: Electrospinning the spinning solution and pre-oxidizing it to obtain pre-oxidized precursor fibers; S3: The pre-oxidized precursor fibers were placed in an inert gas, calcined at high temperature, and cooled to obtain borate rare earth-based high-entropy ceramic nanofibers.

[0007] Further, in step S1, the spinning aid is one or more of polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol, or polyethylene oxide.

[0008] Further, in step S1, the rare earth elements in the rare earth salt are five or more of the rare earth metal yttrium and lanthanide rare earth metals; the rare earth salt is one or more of rare earth chloride salt, rare earth nitrate salt, rare earth acetate salt, rare earth iodide salt, and rare earth bromide salt.

[0009] Further, in step S1, the solvent is one or more of deionized water, anhydrous ethanol, dimethylformamide, isopropanol, and n-propanol.

[0010] Further, in step S1, the mass ratio of spinning aid, solvent, and rare earth salt is (3-25):100:(30-100); the molar ratio of boric acid to rare earth salt is (1.5-7.5):1; the stirring water bath temperature is 30-80℃, and the stirring water bath time is 0.5-10h.

[0011] Furthermore, in step S2, during the electrospinning process, the spinning voltage is 15-23kV, the injection speed is 7-25μl / min, the receiving distance is 10-25cm, the spinning humidity is 25-50%, and the spinning temperature is 20-40℃.

[0012] Further, in step S2, the pre-oxidation specifically includes: pre-oxidation at 80-120℃ for 4-8 hours, pre-oxidation at 120-180℃ for 12-24 hours, and pre-oxidation at 220-260℃ for 4-8 hours.

[0013] Furthermore, in step S3, the inert gas is one or more of argon, nitrogen, and hydrogen.

[0014] Further, in step S3, the high-temperature calcination specifically involves: first heating to 400-600℃ at a heating rate of 1-5℃ / min, and then heating to 800-1300℃ at a heating rate of 1-4℃ / min, with a holding time of 1-4h.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses rare earth salts and boric acid as precursors. On one hand, the thermal decomposition of boric acid introduces boron, which fills the interstitial spaces of the crystal lattice and combines with rare earth metal elements to form a stable rare earth borate crystal structure, thereby stabilizing the distorted crystal lattice caused by rare earth elements. On the other hand, the introduction of boron can refine rare earth grains, reduce the number of grain boundaries, suppress rare earth element segregation, and ensure its uniform distribution in the crystal lattice. Simultaneously, the introduction of boron after the pyrolysis of boric acid can reduce the high dielectric constant caused by rare earth metals, preventing electromagnetic waves from being unable to penetrate the ceramic material and achieving a good impedance matching effect. Furthermore, during the low-temperature pre-oxidation stage, boric acid forms glassy boron oxide, promoting the bonding of rare earth salts with the carbon skeleton after the decomposition of the spinning aid, preventing fiber breakage and collapse, thus contributing to the formation of a continuous ribbon network structure and improving the electromagnetic wave absorption performance of the ceramic material.

[0016] 2. This invention employs electrospinning technology to prepare high-entropy ceramic fibers, effectively suppressing the agglomeration of ceramic particles, promoting the formation of a single, stable solid solution phase, and improving the structural stability of ceramic materials. The ceramic fibers formed using this method possess a unique three-dimensional porous structure with a ribbon-like network, which facilitates multiple reflections and scattering during electromagnetic wave absorption, enhancing the loss mechanism.

[0017] 3. This invention effectively prevents the cracking and porosity of ceramic fibers caused by incomplete decomposition of the spinning aid by controlling the stepwise pre-oxidation removal, thus maintaining the continuity of the ceramic fibers. Simultaneously, gradient temperature control regulates crystallization formation, promoting uniform nucleation and slow growth of borate rare-earth-based grains, maintaining good crystallinity of the ceramic fibers, thereby obtaining high-quality ceramic fibers. Furthermore, this invention features a simple process, enabling mass production. The prepared borate rare-earth-based high-entropy ceramic nanofibers have a unique structure and outstanding microwave absorption properties, showing broad application prospects in the fields of functional ceramics and electromagnetic protection materials. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 1 of this invention. Figure 2This is a scanning electron microscope image of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 1 of the present invention. Figure 3 This is a reflection loss diagram of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 1 of the present invention. Figure 4 The reflection loss diagram of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 2 of this invention; Figure 5 Reflection loss diagram of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 3 of this invention; Figure 6 The reflection loss diagram of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 4 of this invention; Figure 7 Reflection loss diagram of the borate rare earth-based high-entropy ceramic nanofibers prepared in Example 5 of this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the following examples, the rare earth salts and solvents are all of chemical purity or higher.

[0021] Example 1: A method for preparing borate rare earth-based high-entropy ceramic nanofibers: S1: Dissolve 7g of polyvinylpyrrolidone in a mixed solvent of 50mL anhydrous ethanol and 50mL deionized water, and stir in a water bath at 50℃ for 2h to obtain dispersion A; S2: Add 10g of yttrium chloride hexahydrate, 10g of samarium chloride hexahydrate, 10g of europium chloride hexahydrate, 10g of erbium chloride hexahydrate, and 10g of ytterbium chloride hexahydrate to 100mL of dispersion A, and stir in a water bath at 50℃ for 2h to obtain dispersion B; S3: Add 0.9 mol of boric acid to 100 mL of dispersion B, stir in a water bath at 50 °C for 8 h to obtain spinning solution; S4: Electrospinning the spinning solution. The spinning process is characterized by a spinning voltage of 20kV, a feeding speed of 20μl / min, a receiving distance of 20cm, a spinning humidity of 40%, and a spinning temperature of 35℃ to obtain precursor fibers. S5: The precursor fibers were pre-oxidized sequentially at 100℃ for 6 hours, at 150℃ for 24 hours, and at 240℃ for 6 hours to obtain pre-oxidized precursor fibers. S6: The pre-oxidized precursor fiber was placed in an argon / hydrogen mixed atmosphere, first heated to 500℃ at a heating rate of 5℃ / min, then heated to 800℃ at a heating rate of 2℃ / min, held at this temperature for 4 hours, and then cooled to obtain (Y). 0.2 Sm 0.2 Eu 0.2 Er 0.2 Yb 0.2 BO3 high-entropy ceramic nanofibers.

[0022] Example 2: A method for preparing borate rare earth-based high-entropy ceramic nanofibers: S1: Dissolve 7g of polyvinylpyrrolidone in a mixed solvent of 50mL anhydrous ethanol and 50mL deionized water, and stir in a water bath at 50℃ for 2h to obtain dispersion A; S2: Add 10g of yttrium chloride hexahydrate, 10g of samarium chloride hexahydrate, 10g of europium chloride hexahydrate, 10g of erbium chloride hexahydrate, and 10g of ytterbium chloride hexahydrate to 100mL of dispersion A, and stir in a water bath at 50℃ for 2h to obtain dispersion B; S3: Add 0.9 mol of boric acid to 100 mL of dispersion B, stir in a water bath at 50 °C for 8 h to obtain spinning solution; S4: Electrospinning the spinning solution. The spinning process is characterized by a spinning voltage of 20kV, a feeding speed of 20μl / min, a receiving distance of 20cm, a spinning humidity of 40%, and a spinning temperature of 35℃ to obtain precursor fibers. S5: The precursor fibers were pre-oxidized sequentially at 120℃ for 6 hours, at 180℃ for 12 hours, and at 250℃ for 8 hours to obtain pre-oxidized precursor fibers. S6: The pre-oxidized precursor fiber was placed in an argon / hydrogen mixed atmosphere, first heated to 500℃ at a heating rate of 4℃ / min, then heated to 800℃ at a heating rate of 2℃ / min, held at this temperature for 3 hours, and then cooled to obtain (Y). 0.2 Sm 0.2 Eu 0.2 Er 0.2 Yb 0.2 BO3 high-entropy ceramic nanofibers.

[0023] Example 3: A method for preparing borate rare earth-based high-entropy ceramic nanofibers: S1: Dissolve 8g of polyvinylpyrrolidone in a mixed solvent of 50mL anhydrous ethanol and 50mL deionized water, and stir in a water bath at 60℃ for 2h to obtain dispersion A; S2: Add 16g of yttrium nitrate hexahydrate, 16g of samarium nitrate hexahydrate, 16g of europium nitrate hexahydrate, 16g of erbium nitrate hexahydrate, and 16g of ytterbium nitrate hexahydrate to 100mL of dispersion A, and stir in a water bath at 60℃ for 4h to obtain dispersion B; S3: Add 1.35 mol of boric acid to 100 mL of dispersion B, stir in a water bath at 50 °C for 8 h to obtain spinning solution; S4: Electrospinning the spinning solution. The spinning process is characterized by a spinning voltage of 80kV, a feeding speed of 20μl / min, a receiving distance of 20cm, a spinning humidity of 40%, and a spinning temperature of 35℃ to obtain precursor fibers. S5: The precursor fibers were pre-oxidized sequentially at 100℃ for 6 hours, at 150℃ for 24 hours, and at 240℃ for 6 hours to obtain pre-oxidized precursor fibers. S6: The pre-oxidized precursor fiber was placed in an argon / hydrogen mixed atmosphere, first heated to 500℃ at a heating rate of 5℃ / min, then heated to 1000℃ at a heating rate of 2℃ / min, held at this temperature for 4 hours, and then cooled to obtain (Y). 0.2 Sm 0.2 Eu 0.2 Er 0.2 Yb 0.2 BO3 high-entropy ceramic nanofibers.

[0024] Example 4: A method for preparing borate rare earth-based high-entropy ceramic nanofibers: S1: Dissolve 7g of polyacrylonitrile in 100mL of dimethylformamide and stir in a water bath at 50℃ for 2h to obtain dispersion A; S2: Add 10g of yttrium chloride hexahydrate, 10g of samarium chloride hexahydrate, 10g of europium chloride hexahydrate, 10g of erbium chloride hexahydrate, and 10g of ytterbium chloride hexahydrate to 100mL of dispersion A, and stir in a water bath at 60℃ for 2h to obtain dispersion B; S3: Add 0.9 mol of boric acid to 100 mL of dispersion B, stir in a water bath at 50 °C for 8 h to obtain spinning solution; S4: Electrospinning the spinning solution. The spinning process is carried out with a spinning voltage of 22kV, a feeding speed of 15μl / min, a receiving distance of 18cm, a spinning humidity of 40%, and a spinning temperature of 40℃ to obtain precursor fibers. S5: The precursor fibers were pre-oxidized sequentially at 120℃ for 6 hours, at 180℃ for 24 hours, and at 240℃ for 6 hours to obtain pre-oxidized precursor fibers. S6: The pre-oxidized precursor fiber was placed in an argon / hydrogen mixed atmosphere, first heated to 500℃ at a heating rate of 4℃ / min, then heated to 800℃ at a heating rate of 3℃ / min, held at this temperature for 4 hours, and then cooled to obtain (Y).0.2 Sm 0.2 Eu 0.2 Er 0.2 Yb 0.2 BO3 high-entropy ceramic nanofibers.

[0025] Example 5: A method for preparing borate rare earth-based high-entropy ceramic nanofibers: S1: Dissolve 10g of polyacrylonitrile in 100mL of dimethylformamide and stir in a water bath at 30℃ for 2h to obtain dispersion A; S2: Add 14g of yttrium chloride hexahydrate, 14g of samarium chloride hexahydrate, 14g of europium chloride hexahydrate, 14g of erbium chloride hexahydrate, and 14g of ytterbium chloride hexahydrate to 100mL of dispersion A, and stir in a water bath at 50℃ for 2h to obtain dispersion B; S3: Add 1.25 mol of boric acid to dispersion B and stir in a water bath at 50°C for 8 hours to obtain spinning solution; S4: Electrospinning the spinning solution. The spinning process is carried out with a spinning voltage of 20kV, a feeding speed of 15μl / min, a receiving distance of 20cm, a spinning humidity of 40%, and a spinning temperature of 35℃ to obtain precursor fibers. S5: The precursor fibers were pre-oxidized sequentially at 100℃ for 6 hours, at 150℃ for 24 hours, and at 240℃ for 6 hours to obtain pre-oxidized precursor fibers. S6: The pre-oxidized precursor fiber was placed in an argon / hydrogen mixed atmosphere, first heated to 500℃ at a heating rate of 5℃ / min, then heated to 800℃ at a heating rate of 2℃ / min, held at this temperature for 4 hours, and then cooled to obtain (Y). 0.2 Sm 0.2 Eu 0.2 Er 0.2 Yb 0.2 BO3 high-entropy ceramic nanofibers.

[0026] Testing: The high-entropy ceramic nanomaterials prepared in the above examples were uniformly mixed with paraffin at a mass ratio of 4:6 and pressed into coaxial ring samples with an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 2.5-3.5 mm. The electromagnetic parameters of the samples were tested using a vector network analyzer (VNA, Keysight E5071c, Malaysia) at 2.0-18.0 GHz via the coaxial air line method.

[0027] Test conclusion: This invention uses electrospinning technology to precisely control the crystallinity, crystal phase composition and microstructure of ceramic nanofibers by adjusting the heat treatment temperature and the composition ratio of borate, giving them a unique ribbon network structure and exhibiting excellent electromagnetic wave absorption performance.

[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing borate rare-earth-based high-entropy ceramic nanofibers, characterized by: Includes the following steps: S1: Add the spinning aid, rare earth salt and boric acid to the solvent in sequence, stir evenly to obtain the spinning solution; S2: Electrospinning the spinning solution and pre-oxidizing it to obtain pre-oxidized precursor fibers; S3: The pre-oxidized precursor fiber was placed in an inert gas, calcined at high temperature, and cooled to obtain borate rare earth-based high-entropy ceramic nanofibers. In step S1, the rare earth elements in the rare earth salt are five or more of the rare earth metal yttrium and lanthanide rare earth metals; the rare earth salt is one or more of rare earth chloride salt, rare earth nitrate salt, rare earth acetate salt, rare earth iodide salt, and rare earth bromide salt. In step S1, the mass ratio of spinning aid, solvent, and rare earth salt is (3-25):100:(30-100); the molar ratio of boric acid to rare earth salt is (1.5-7.5):1; the stirring water bath temperature is 30-80℃, and the stirring water bath time is 0.5-10h. In step S2, the pre-oxidation specifically includes: pre-oxidation at 80-120℃ for 4-8 hours, pre-oxidation at 120-180℃ for 12-24 hours, and pre-oxidation at 220-260℃ for 4-8 hours.

2. The method of claim 1, wherein the borate-based rare earth high-entropy ceramic nanofiber is prepared by the method comprising: preparing a precursor solution by dissolving a rare earth element and a borate in a solvent; and performing electrospinning on the precursor solution to prepare the borate-based rare earth high-entropy ceramic nanofiber. In step S1, the spinning aid is one or more of polyvinylpyrrolidone, polyacrylonitrile, polyvinyl alcohol, or polyethylene oxide.

3. The method for preparing borate rare earth-based high-entropy ceramic nanofibers according to claim 1, characterized in that: In step S1, the solvent is one or more of deionized water, anhydrous ethanol, dimethylformamide, isopropanol, and n-propanol.

4. The method for preparing borate rare earth-based high-entropy ceramic nanofibers according to claim 1, characterized in that: In step S2, during the electrospinning process, the spinning voltage is 15-23kV, the injection speed is 7-25μl / min, the receiving distance is 10-25cm, the spinning humidity is 25-50%, and the spinning temperature is 20-40℃.

5. The method for preparing borate rare earth-based high-entropy ceramic nanofibers according to claim 1, characterized in that: In step S3, the inert gas is one or more of argon, nitrogen, and hydrogen.

6. The method for preparing borate rare earth-based high-entropy ceramic nanofibers according to claim 1, characterized in that: In step S3, the high-temperature calcination specifically involves: first heating to 400-600℃ at a heating rate of 1-5℃ / min, and then heating to 800-1300℃ at a heating rate of 1-4℃ / min, with a holding time of 1-4h.

7. The borate rare earth-based high entropy ceramic nanofibers prepared by the method according to any one of claims 1-6.

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