A high-entropy polyacetylacetone compound precursor and a high-entropy ceramic nanofiber aerogel preparation method

Abstract

The application belongs to the field of advanced ceramic materials, and relates to a high-entropy polyacetylacetone compound precursor and a preparation method of high-entropy ceramic nanofiber aerogel, which solves the problems of easy grain growth and crystallization pulverization of traditional ceramic aerogel at high temperature. The preparation steps are as follows: synthesizing high-entropy polyacetylacetone compound precursor powder, preparing a spinning solution and adding a phase stabilizer and a polymer spinning aid, obtaining precursor fibers through far-field electrospinning, and obtaining high-entropy ceramic nanofiber aerogel with a fiber diameter of 200-2000 nm through gradient high-temperature annealing treatment. The material has good flexibility and thermal stability, and is suitable for efficient heat insulation scenes in extreme environments such as aerospace thermal protection.

Description

Technical Field

[0001] This invention belongs to the field of advanced ceramic materials, specifically relating to a method for preparing a high-entropy polyacetylacetone precursor and a high-entropy ceramic nanofiber aerogel. This material is suitable for high-efficiency thermal insulation in extreme environments such as aerospace thermal protection systems, nuclear reactor thermal insulation components, and ultra-high temperature industrial equipment. Background Technology

[0002] The development of aerospace, nuclear energy equipment, and high-temperature industrial equipment has created an urgent need for ultra-lightweight thermal insulation materials that can withstand extreme environments (>1300 °C). Traditional ceramic materials are prone to phase transformation and abnormal grain growth under high-temperature conditions, which directly leads to a significant decrease in their mechanical strength, making them unable to meet the requirements of extreme service environments. Therefore, the development of new high-temperature resistant thermal insulation ceramic materials has become an important research direction in this field.

[0003] "High entropy" is an emerging material design concept. Professor Ye Junwei first proposed the concept of high-entropy alloys in 2004, and in the same year, Cantor et al. from Oxford University also proposed the concept of multi-principal element alloys. In 2015, Rost et al. from North Carolina State University first reported entropy-stable oxide ceramics with rock-salt structures, i.e., high-entropy ceramics. Since then, high-entropy ceramics have become a research hotspot in the field of inorganic non-metallic materials. High entropy is generally defined as a multi-principal element alloy composed of five or more principal elements in equiatomic or near-equiatomic ratios. It exhibits thermodynamic high-entropy effects, structural lattice distortion effects, kinetic slow diffusion effects, and a "cocktail" effect in terms of performance.

[0004] In the prior art, Chinese patent CN118005398A proposed a method of doping with rare earth elements, which can effectively reduce the thermal conductivity of materials and increase their coefficient of thermal expansion. However, existing ceramic aerogels are still prone to grain growth and crystallization under drastic temperature gradient changes or long-term high-temperature exposure, causing problems such as decreased strength and structural collapse, making it difficult to meet the requirements of extreme service environments such as new aircraft. Summary of the Invention

[0005] (a) Technical problems to be solved The present invention aims to solve the technical problem that traditional ceramic aerogels are prone to grain growth and crystallization in high-temperature environments, which leads to a decrease in strength and structural collapse.

[0006] (II) Technical Solution To address the aforementioned problems, this invention proposes a method that synthesizes a high-entropy polyacetylacetone precursor and utilizes its polymer properties to increase the degree of polymerization of the precursor, thereby inhibiting the growth of fiber grains during the ceramization stage and ultimately obtaining a high-entropy ceramic nanofiber aerogel with good flexibility and strength. The core idea of ​​this invention lies in combining multiple metal sources in polymer form and using electrospinning and high-temperature treatment processes to regulate the elemental composition and micro / nano structures such as crystal lattice boundaries, inhibiting grain growth and improving thermal stability and mechanical flexibility.

[0007] The preparation method of this invention includes four steps: preparation of a high-entropy polyacetylacetone precursor, preparation of a high-entropy polyacetylacetone precursor sol-spinning solution, preparation of precursor nanofibers by far-field electrospinning, and preparation of high-entropy ceramic nanofiber aerogels by gradient high-temperature annealing. Figure 1 As shown, the details are as follows: Preparation of S1 high-entropy polyacetylacetone precursor An equal amount of metal source is dissolved in a solvent. Ligands are added at a metal source:ligand molar ratio of 1:0.5-2 and stirred for 50-200 min. Triethylamine is added dropwise at a metal source:triethylamine molar ratio of 1:1-6 and stirring is continued. The product is dried under reduced pressure at 25-50 °C. The product is soaked in an extractant, centrifuged at 50 rpm to 5000 rpm, and the supernatant is collected. The solid powder is obtained by rotary evaporation at 20-60 °C to obtain the precursor.

[0008] The metal source is any four or more of the following: nitrates, chlorides, acetates, bromides, and iodides of alkaline earth metals, transition metals, and lanthanide rare earth elements; the solvent used to prepare the precursor is any one or a mixture of anhydrous methanol, anhydrous ethanol, n-propanol, isopropanol, and N,N-dimethylformamide; the ligand is acetylacetone; and the extractant is one or a mixture of acetone and tetrahydrofuran.

[0009] Preparation of S2 high-entropy polyacetylacetone precursor sol spinning solution The precursor powder obtained from S1 is added to the solvent at a molar ratio of 1:1 to 10, and yttrium acetate or yttrium nitrate is added at a molar ratio of 1:0.1 to 10. After thorough stirring, a polymeric spinning aid is added and stirred again to obtain a spinning solution with a viscosity of 1 to 100 mPa·s at 20 to 30 °C. The mass ratio of polymeric spinning aid to organic solvent is 5 to 40:1000.

[0010] The solvent used to prepare the spinning solution is one or more of methanol, ethanol, and acetic acid in any proportion; the polymeric spinning aid is one or more of polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyhydroxyacetic acid, polylactic acid, polyvinylpyrrolidone, polyurethane, and polyacrylamide in any proportion.

[0011] S3 Far-field electrospinning for the preparation of precursor nanofibers Nanofibers were produced by far-field electrospinning using the spinning solution obtained from S2. The process parameters for far-field electrospinning were as follows: the distance between the spinning needle and the collecting device was 0.5–1.0 m, the spinning solution propulsion speed was 0.5–3.0 ml / h, the spinning voltage was 15–40 kV, the spinning ambient temperature was 20–40 °C, and the humidity was 30–60%.

[0012] S4 gradient high-temperature annealing for the preparation of high-entropy ceramic nanofiber aerogels The precursor nanofibers prepared by S3 were subjected to gradient high-temperature annealing to obtain high-entropy ceramic nanofiber aerogels with fiber diameters of 200–2000 nm. The process parameters for gradient high-temperature annealing were as follows: heating from room temperature to 400–600 °C at a rate of 0.1–5 °C / min and holding for 1–24 h; then heating to 600–1300 °C at a rate of 1–10 °C / min and holding for 1–5 h; cooling to 400–800 °C at a rate of 2–5 °C / min and holding for 1–4 h; and finally cooling naturally to room temperature.

[0013] The present invention also protects the high-entropy ceramic nanofiber aerogel prepared by the above preparation method. The material is composed of high-entropy oxide ceramics, has a fluffy three-dimensional structure, uniform fiber diameter that is adjustable in the range of 200 to 2000 nm, no defects such as pores or cracks inside the material, and can maintain structural stability under extreme high temperature environments.

[0014] (III) Beneficial Effects Compared with the prior art, the present invention has the following beneficial effects: 1. This invention synthesizes a high-entropy polyacetylacetone precursor and increases its degree of polymerization. Combined with electrospinning and gradient high-temperature annealing processes, it effectively controls the elemental composition and micro / nano structure of the material's lattice and grain boundaries, significantly inhibiting the growth of fiber grains during the ceramization stage and solving the technical problem of abnormal grain growth in traditional ceramic materials at high temperatures.

[0015] 2. The high-entropy ceramic nanofiber aerogel prepared by this invention has excellent thermal stability. Under drastic temperature gradient changes or long-term high-temperature exposure, it does not exhibit significant grain growth or crystallization, thus avoiding material strength reduction and structural collapse. It is suitable for extreme high-temperature insulation scenarios with temperatures >1300 °C.

[0016] 3. The high-entropy ceramic nanofiber aerogel prepared by this invention has excellent flexibility and mechanical strength, and the fiber diameter is uniform and adjustable in the range of 200-2000 nm. The material is free of defects such as pores and cracks and has excellent structural density.

[0017] 4. This invention uses far-field electrospinning technology to prepare precursor fibers, combined with gradient high-temperature annealing process, so that the elements of high-entropy ceramics are evenly distributed on the fiber body, realizing uniform doping of elements, giving full play to the "cocktail" effect of high-entropy materials, and further improving the comprehensive performance of materials. Attached Figure Description

[0018] Figure 1 Flowchart for the preparation of high-entropy polyacetylacetone precursor; Figure 2 This is a photograph of the high-entropy polyacetylacetone precursor powder obtained in Example 1 of the present invention. Figure 3 These are SEM and EDS images of the high-entropy polyacetylacetone precursor obtained in Example 1 of this invention. Figure 4 Here is a SEM image of the high-entropy ceramic nanofibers obtained in Example 1 of this invention; Figure 5 EDS image of high-entropy ceramic nanofibers obtained in Example 1 of this invention; Figure 6 This is a physical image of the high-entropy ceramic nanofibers obtained in Example 2 of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. In the following embodiments, unless otherwise specified, the raw materials or processing techniques are all conventional commercially available raw materials or conventional processing techniques within the field.

[0020] Example 1 Preparation of S1 high-entropy polyacetylacetone precursor powder Equal amounts of five metal sources—LaCl3·7H2O, CeCl3·7H2O, YCl3·6H2O, YbCl3·6H2O, and ZrOCl2·8H2O—were dissolved in methanol and stirred at room temperature for 2 hours to obtain a transparent solution. 30 g of triethylamine and 20 g of acetylacetone were dissolved in methanol, and this solution was then added to the aforementioned metal source / methanol mixture. The mixture was stirred at room temperature for another 5 hours. The resulting solution was then subjected to vacuum drying at 40 °C. The product after vacuum drying was thoroughly soaked in tetrahydrofuran. The soaked solution was then poured into centrifuge tubes and centrifuged at 3000 rpm. The supernatant was collected, and the filter residue was removed. The supernatant was then rotary evaporated at 50 °C using a rotary evaporator, with n-hexane added during the evaporation process. The resulting solid powder was collected, yielding the high-entropy polyacetylacetone precursor powder. A photograph of this powder is shown below. Figure 2As shown, SEM and EDS photos are as follows: Figure 3 As shown.

[0021] Preparation of S2 spinning solution The precursor powder obtained from S1 and yttrium acetate were added to methanol at a molar ratio of 1:0.1 and stirred at room temperature until completely dissolved. Polyethylene oxide (PEO) was dissolved in methanol at a mass ratio of 2:0.03 (methanol:PEO) and stirred at 70 °C for 24 h until completely dissolved and clear, which was used as a spinning aid. 2 g of the dissolved spinning aid was added to 5 g of the above mixture of precursor and yttrium acetate and stirred at room temperature for 24 h to obtain a uniform and transparent high-entropy polyacetylacetone precursor sol spinning solution. The viscosity of the spinning solution at 25 °C was 50 mPa·s.

[0022] S3 Far-field electrospinning for the preparation of precursor nanofibers The spinning solution obtained in S2 was drawn into a 10 mL medical syringe, which was then connected to the electrospinning device. The spinning solution was pushed into the spinning needle in the electrospinning box at a rate of 3.0 mL / h. The electrospinning voltage was stabilized at 25 kV by a high-voltage power supply, and the distance between the spinning needle and the collecting device was maintained at 0.7 m. The temperature inside the electrospinning box was maintained at 25 °C, and the humidity was maintained at 50%. The precursor nanofibers obtained by spinning were collected using the collecting device.

[0023] S4 gradient high-temperature annealing for the preparation of high-entropy ceramic nanofiber aerogels The precursor nanofibers collected in S3 were subjected to high-temperature annealing in a box furnace. A gradient heating program was set, heating from room temperature to 500 °C at a heating rate of 5 °C / min and holding for 2 h; then heating to 1200 °C at a heating rate of 5 °C / min and holding for 3 h; then cooling to 600 °C at a cooling rate of 3 °C / min and holding for 2 h; finally, natural cooling to room temperature was performed to complete the ceramization transformation, yielding a high-entropy ceramic nanofiber aerogel. SEM images of the aerogel are shown below. Figure 4 As shown, the EDS image is as follows Figure 5 As shown in the EDS image, five rare earth ions (La, Ce, Y, Yb) and zirconium (Zr) ions are uniformly distributed on the ceramic fiber, achieving uniform element doping. The fiber diameter is about 800 nm.

[0024] Example 2 Following the same procedure as in Example 1, replacing the elements with ZrOCl2·8H2O, LaCl3·7H2O, CeCl3·7H2O, SmCl3·6H2O, HfOCl2·8H2O, HoCl3·6H2O, and ErCl3·6H2O, high-entropy oxide ceramic nanofibers were obtained. The physical material is shown below. Figure 6 As shown.

[0025] This specific embodiment is only used to illustrate the present invention and is not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-entropy polyacetylacetone precursor sol-spinning solution and a high-entropy ceramic nanofiber aerogel, comprising the following four steps: Preparation of S1 high-entropy polyacetylacetone precursor: An equimolar amount of metal source was dissolved in sufficient solvent. The ligand and triethylamine were dissolved in equal amounts of methanol or ethanol according to the metal source:ligand molar ratio of 1:0.5-2 and the metal source:triethylamine molar ratio of 1:1-6. The ligand and triethylamine solution was then atomized and added to the metal source solution. The mixture was dried under reduced pressure at 25-50 °C. The product was soaked in an extractant, centrifuged at 50 rpm to 5000 rpm, and the supernatant was collected. The supernatant was then rotary evaporated at 20-60 °C to obtain a solid powder, which is the precursor. Preparation of S2 high-entropy polyacetylacetone precursor sol-spinning solution: The precursor powder obtained from S1 was added to a solvent at a molar ratio of 1:1 to 10, and yttrium acetate or yttrium nitrate was added at a molar ratio of 1:0.1 to 10. After thorough stirring, a polymeric spinning aid was added and stirred again to obtain a solution with a viscosity of 0.1 to 100 Pa at 20 to 30 °C. The spinning solution of s has a mass ratio of polymeric spinning aid to organic solvent of 5-40:1000. S3 Far-field electrospinning preparation of precursor nanofibers: Nanofibers were prepared by far-field electrospinning using the spinning solution obtained in S2. The process parameters for far-field electrospinning were as follows: the distance between the spinning needle and the collecting device was 0.5–1.0 m, the spinning solution propulsion speed was 0.5–3.0 ml / h, the spinning voltage was 15–40 kV, the spinning environment temperature was 20–40 °C, and the humidity was 30–60%. Preparation of high-entropy ceramic nanofiber aerogels by gradient high-temperature annealing (S4): The precursor nanofibers obtained by S3 were subjected to gradient high-temperature annealing to obtain high-entropy ceramic nanofiber aerogels with fiber diameters of 200–2000 nm. The process parameters for gradient high-temperature annealing were as follows: heating from room temperature to 400–600 °C at a rate of 0.1–5 °C / min and holding for 1–24 h; then heating to 600–1300 °C at a rate of 1–10 °C / min and holding for 1–5 h; cooling to 400–800 °C at a rate of 2–5 °C / min and holding for 1–4 h; and finally cooling naturally to room temperature.

2. The preparation method according to claim 1, characterized in that, The metal source is any four or more of the following: nitrates, chlorides, acetates, bromides, and iodides of alkaline earth metals, transition metals, and lanthanide rare earth elements.

3. The preparation method according to claim 1, characterized in that, The ligand is acetylacetone.

4. The preparation method according to claim 1, characterized in that, The solvent used to prepare the precursor is any one or a mixture of anhydrous methanol, anhydrous ethanol, n-propanol, isopropanol, and N,N-dimethylformamide.

5. The preparation method according to claim 1, characterized in that, The extractant is one or a mixture of acetone and tetrahydrofuran.

6. The preparation method according to claim 1, characterized in that, The solvent used to prepare the spinning solution is one or more of methanol, ethanol, and acetic acid in any proportion.

7. The preparation method according to claim 1, characterized in that, The polymeric spinning aid is one or more of polyethylene glycol, polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyhydroxyacetic acid, polylactic acid, polyvinylpyrrolidone, polyurethane, and polyacrylamide in any proportion.

8. The preparation method according to claim 1, characterized in that, The high-entropy ceramic nanofiber aerogel is composed of high-entropy oxide ceramics, has a fluffy three-dimensional structure, uniform fiber diameter that is adjustable in the range of 200 to 2000 nm, no defects such as pores or cracks inside the material, and can maintain structural stability under extreme high temperature environments.

9. The preparation method according to claim 1, characterized in that, The distance between the spinning needle and the collecting device in the far-field electrospinning is 0.5 to 1.0 m, the spinning voltage is 15 to 40 kV, the spinning ambient temperature is 20 to 40 °C, and the humidity is 30 to 60%.

10. The preparation method according to claim 1, characterized in that, The gradient high-temperature annealing has a heating rate of 0.1–10 °C / min, a cooling rate of 2–5 °C / min, and a maximum annealing temperature of 600–1300 °C.

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