Preparation method of two-dimensional high-entropy ceramic matrix composite aerogel

Abstract

This invention relates to a method for preparing two-dimensional high-entropy ceramic-based composite aerogels. A polyacetylacetone metal complex is used as a ceramic precursor, and an alcohol solution is used as a solvent to prepare the precursor solution. The high-entropy ceramic-based composite hydrogel is synthesized through a hydrothermal reaction at a specific temperature, and then combined with directional freeze-drying and high-temperature annealing processes to obtain the two-dimensional high-entropy ceramic-based composite aerogel. This method uses two-dimensional sheets as the structural units of the aerogel, constructing the high-entropy ceramic-based aerogel from the bottom up through molecular-level self-assembly. This effectively solves the pulverization problem of one-dimensional fiber aerogels under pressure, broadening the application scenarios of ceramic aerogels.

Description

Technical Field

[0001] This invention relates to a method for preparing two-dimensional high-entropy ceramic-based composite aerogels, belonging to the field of aerogel technology. Background Technology

[0002] High-entropy ceramics are multi-component single-phase solid solutions composed of five or more elements in equiatomic or near-equiatomic ratios. Due to their thermodynamic high-entropy effect, structural distortion effect, kinetic lag diffusion effect, and "cocktail" effect in terms of performance, they possess many outstanding properties and have broad application prospects in thermal protection, catalysis, energy storage, thermoelectric pressing, and other fields.

[0003] Ceramic aerogels, as excellent and efficient thermal insulation materials, have been widely used in various extreme high-temperature engineering systems. However, with the continuous development of engineering technology, the requirements for aerogel materials in terms of high temperature resistance, thermal shock resistance, mechanical strength, and structural stability are increasing. High-entropy ceramics, due to their excellent thermodynamic stability and chemical homogeneity, have become a new direction for the development of ceramic aerogel materials.

[0004] Combining the design philosophy of high-entropy materials with the structural design of aerogels holds promise for further enhancing the overall performance of aerogel materials. This composite material not only maintains the excellent mechanical and thermal properties of high-entropy ceramics but also leverages the lightweight and high specific surface area of ​​aerogels, broadening its application prospects in aerospace, energy storage, and environmental protection. With further research, high-entropy ceramic aerogels are expected to play a significant role in advanced materials science.

[0005] Currently, research on high-entropy ceramic aerogels is limited. The most commonly used sol-gel method is also employed to prepare high-entropy ceramic aerogels. While this method yields ceramic aerogels with high porosity and low thermal conductivity, it does not address the issue of ceramic brittleness and lacks high compressibility and resilience under large strain. Subsequently, one-dimensional high-entropy ceramic fiber aerogels have been constructed using processes such as electrospinning, melt spinning, or solution blowing. Using one-dimensional fibers as structural units, high compressibility and resilience under large deformation have been achieved. However, fiber ceramic aerogels constructed using one-dimensional fibers as structural units exhibit low strength. Furthermore, under long-term strain service conditions, due to the continuous bending recovery of micro / nano fibers, fiber embrittlement and pulverization inevitably occur, leading to material failure. Summary of the Invention

[0006] The purpose of this invention is to disclose a method for preparing two-dimensional high-entropy ceramic-based composite aerogels. This method uses two-dimensional sheets as the structural units of the aerogel and constructs high-entropy ceramic-based aerogels from the bottom up through molecular-level self-assembly. This can effectively improve the aerogel's strength and solve problems such as structural failure caused by the embrittlement and pulverization of one-dimensional fibers, thus broadening the application scenarios of ceramic aerogels.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a two-dimensional high-entropy ceramic-based composite aerogel includes the following steps:

[0009] 1) A high-entropy ceramic precursor solution was prepared using a polyacetylacetone metal complex of five elements (Zr, Hf, Ti, Lu, and Gd) as the metal element and methanol or ethanol as the solvent. The high-entropy ceramic precursor solution was then added to a graphene aqueous solution and ultrasonically mixed to obtain a hydrothermal precursor solution. The proportion of the high-entropy ceramic precursor solution to the graphene solution was 50wt%~200wt%.

[0010] The polyacetylacetone metal complexes include polyacetylacetone titanium, polyacetylacetone zirconium, polyacetylacetone hafnium, polyacetylacetone lutetium, and polyacetylacetone gadolinium, and each polyacetylacetone metal complex in the metal element is used in equimolar amounts of the metal element.

[0011] The concentration of the high-entropy ceramic precursor solution is 200~400 mg / mL.

[0012] The concentration of the graphene aqueous solution is 2~5 mg / mL.

[0013] 2) The precursor solution obtained in step 1) is transferred into a reaction vessel and subjected to hydrothermal reaction at 80~120℃ for 6~24h to obtain a composite hydrogel. After the reaction vessel is naturally cooled, it is taken out and dialyzed in 20~50% ethanol solution for 20~25h. After dialyzation, it is placed on a copper block and liquid nitrogen is used to make the solvent in the composite hydrogel network form ice crystals and completely solidify. Then it is taken out and placed in a freeze dryer to dry for 30~40h to obtain the composite aerogel precursor.

[0014] 3) Place the composite aerogel precursor from step 2) in an argon-protected tube furnace and heat it to 900-1100℃ at a rate of 1-5℃ / min for high-temperature annealing. Hold the temperature for 1-2 hours and cool it with the furnace to obtain the two-dimensional high-entropy ceramic-based composite aerogel.

[0015] The high-temperature annealing is specifically carried out at 1000℃, with a heating rate of 5℃ / min from RT to 600℃ and a heating rate of 2℃ / min from 600 to 1000℃.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention is the first to prepare ceramic aerogels on a two-dimensional scale, with the amount of each element in the ceramic phase being nearly equimolar and the elements being uniformly distributed.

[0018] This invention uses a polyacetylacetone metal complex as a ceramic precursor, which can be well bonded to graphene sheets through chemical bonding during the hydrothermal reaction process. After high-temperature annealing, a single-phase defect fluorite structure oxide high-entropy ceramic-based composite aerogel is obtained.

[0019] This invention enables directional structural design of two-dimensional composite aerogels, thereby improving the mechanical stability of the aerogels.

[0020] This invention does not require complex heat treatment and has a simple preparation process. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation route of the high-entropy ceramic-based composite aerogel of the present invention.

[0022] Figure 2 This is a SEM image of the high-entropy ceramic-based composite aerogel prepared in Example 1 of the present invention, parallel to the ice crystal growth direction.

[0023] Figure 3 This is a SEM image of the high-entropy ceramic-based composite aerogel prepared in Example 1 of the present invention, perpendicular to the ice crystal growth direction.

[0024] Figure 4 XRD patterns of high-entropy ceramic-based composite aerogels prepared in Examples 1-3 of this invention.

[0025] Figure 5 The mechanical property curves of the high-entropy ceramic-based composite aerogel prepared in Example 1 of this invention are shown, with the attached small figures being magnified views of local strains from 0% to 70%.

[0026] Figure 6 The mechanical property curves are for the high-entropy ceramic-based composite aerogel prepared in Comparative Example 1 of this invention. Detailed Implementation

[0027] The present invention will be further explained and described below with reference to specific embodiments.

[0028] See Figure 1 The Zr, Hf, Ti, Lu, and Gd organic precursors used in each embodiment can be synthesized according to the following steps:

[0029] (1) Hafnium oxychloride octahydrate, zirconium oxychloride octahydrate, lutetium chloride hexahydrate, and gadolinium chloride hexahydrate were dissolved in anhydrous methanol in equimolar ratio of the metal elements. After complete dissolution, acetylacetone was added and stirred for 1 hour. Then, triethylamine was added dropwise, with the molar ratio of metal element:acetylacetone:triethylamine being 1:1:3. After the addition was completed, stirring was continued for 2 hours to obtain a clear yellow solution.

[0030] (2) Pour the yellow solution obtained in step (1) into a rotary evaporator and distill it under reduced pressure at 50°C to obtain a dry powder of triethylamine hydrochloride and polyacetylacetone metal complex. Then dissolve the powder in an appropriate amount of acetone and let it stand for 48 hours.

[0031] (3) Remove the insoluble triethylamine hydrochloride in step (2) by centrifugation to obtain an acetone solution of polyacetylacetone metal complex. Pour it into a rotary evaporator flask and perform vacuum distillation until dry. The vacuum distillation temperature is 40℃ to obtain quaternary metal polyacetylacetone complex precursor powder.

[0032] (4) For the synthesis of polyacetylacetonate titanium, see Chinese patent document CN104961763A.

[0033] (5) Dissolve the polyacetylacetonate titanium and the quaternary precursor powder obtained in step (3) in methanol at the same molar ratio of metal elements to prepare a high-entropy ceramic precursor solution with a concentration of 200 mg / ml.

[0034] Example 1

[0035] A 50 wt% high-entropy ceramic precursor solution was added to a 3 mg / ml graphene aqueous solution. The mixture was ultrasonically dispersed for 20 min to ensure homogeneity, then shaken to remove air bubbles. The mixture was placed in a polytetrafluoroethylene-lined reactor and subjected to a hydrothermal reaction at 120 °C for 6 h in a forced-air drying oven. After complete cooling of the reactor, GO-PHEC was obtained. 0.5 Composite hydrogels were then formed; subsequently, the hydrogels were dialyzed in 20% ethanol solution for 24 h. After dialyzation, the hydrogels were placed on a copper block and liquid nitrogen was used to cause the solvent in the hydrogel network to form ice crystals and completely solidify. The gels were then removed and freeze-dried for 40 h to obtain GO-PHEC. 0.5 Composite aerogel precursor.

[0036] Aerogel structures constructed through directional freezing, such as Figure 2 , Figure 3 As shown. Figure 2 The image is a SEM image parallel to the ice crystal growth direction, in which the high-entropy ceramic-based composite sheets are arranged in an orderly manner along the ice crystal growth direction. Figure 3 The image is a SEM image perpendicular to the ice crystal growth direction, showing that the high-entropy ceramic-based composite sheets are randomly arranged in this direction, consistent with the design.

[0037] The composite aerogel precursor was placed in an argon-protected tube furnace and annealed at 1000 °C. The heat treatment process involved a heating rate of 5 °C / min from RT to 600 °C and a heating rate of 2 °C / min from 600 to 1000 °C. After furnace cooling, the precursor was removed to obtain the two-dimensional high-entropy ceramic matrix (GO-HEC). 0.5 Composite aerogel.

[0038] Example 2

[0039] A 100 wt% high-entropy ceramic precursor solution was added to a 3 mg / ml graphene aqueous solution and ultrasonically dispersed for 20 min to ensure homogeneity. The mixture was then shaken to remove air bubbles and placed in a polytetrafluoroethylene-lined reactor. A hydrothermal reaction was carried out at 120 °C for 6 h in a forced-air drying oven. After complete cooling of the reactor, the GO-PHEC1 composite hydrogel was obtained. The hydrogel was then dialyzed in a 20% ethanol solution for 24 h. After dialyzing, the hydrogel was placed on a copper block and liquid nitrogen was used to freeze the solvent in the hydrogel network into ice crystals until complete solidification. The solidified hydrogel was then placed in a freeze dryer for 40 h to obtain the GO-PHEC1 composite aerogel precursor.

[0040] The composite aerogel precursor was placed in an argon-protected tube furnace and annealed at 1000 °C. The heat treatment process involved a heating rate of 5 °C / min from RT to 600 °C and a heating rate of 2 °C / min from 600 °C to 1000 °C. After removal, the two-dimensional GO-HEC1 composite aerogel was obtained.

[0041] Example 3

[0042] A high-entropy ceramic precursor solution was added to a 3 mg / ml graphene aqueous solution at a ratio of 150 wt%. The mixture was ultrasonically dispersed for 20 min to ensure homogeneity, then shaken to remove air bubbles. The mixture was placed in a polytetrafluoroethylene-lined reactor and subjected to a hydrothermal reaction at 120 °C for 6 h in a forced-air drying oven. After the reactor had completely cooled, GO-PHEC was obtained. 1.5 Composite hydrogels were then formed; subsequently, the hydrogels were dialyzed in 20% ethanol solution for 24 h. After dialyzation, the hydrogels were placed on a copper block and liquid nitrogen was used to cause the solvent in the hydrogel network to form ice crystals and completely solidify. The gels were then removed and freeze-dried for 40 h to obtain GO-PHEC. 1.5 Composite aerogel precursor.

[0043] The composite aerogel precursor was placed in an argon-protected tube furnace and annealed at 1000 °C. The heat treatment process involved a heating rate of 5 °C / min from RT to 600 °C and a heating rate of 2 °C / min from 600 to 1000 °C. After removal, the two-dimensional GO-HEC was obtained. 1.5 Composite aerogel.

[0044] Example 4

[0045] A high-entropy ceramic precursor solution was added to a 3 mg / ml graphene aqueous solution at a ratio of 200 wt%. The mixture was ultrasonically dispersed for 20 min to ensure homogeneity, then shaken to remove air bubbles. The mixture was then placed in a polytetrafluoroethylene-lined reactor and subjected to a hydrothermal reaction at 120°C for 6 h in a forced-air drying oven. After the reactor had completely cooled, GO-PHEC was obtained. 2.0 Composite hydrogels were then formed; subsequently, the hydrogels were dialyzed in 20% ethanol solution for 24 h. After dialyzation, the hydrogels were placed on a copper block and liquid nitrogen was used to cause the solvent in the hydrogel network to form ice crystals and completely solidify. The gels were then removed and freeze-dried for 40 h to obtain GO-PHEC. 2.0 Composite aerogel precursor.

[0046] The composite aerogel precursor was placed in an argon-protected tube furnace and annealed at 1000 °C. The heat treatment process involved a heating rate of 5 °C / min from RT to 600 °C and a heating rate of 2 °C / min from 600 to 1000 °C. After removal, the two-dimensional GO-HEC was obtained. 2.0 Composite aerogel.

[0047] The product structure characterization and performance evaluation are as follows:

[0048] The XRD patterns of the composite aerogels prepared in Examples 1-3 above are as follows: Figure 4 As shown. By Figure 4 It is known that high-entropy ceramic-based aerogels have been successfully synthesized.

[0049] Subsequently, the GO-HEC prepared in Example 2 was taken. 0.5 The mechanical properties of the composite aerogel were evaluated. Based on the aerogel's dimensional data, the gauge length was determined, and compression tests were conducted. Compression curves were obtained under loading speeds of 5 mm / min and strains of 30%, 60%, and 90%. (Specific details are as follows...) Figure 5 As shown. By Figure 5 It can be seen that high-entropy ceramic-based composite aerogels still have excellent compression resilience under a large strain of 90%.

[0050] Comparative Example 1

[0051] Using the same high-entropy ceramic precursor solution, except that the hydrothermal solution is only an aqueous graphene solution, and other steps are the same as in Example 2, a graphene hydrogel is obtained. A vacuum impregnation process is used to combine the high-entropy ceramic precursor with the graphene hydrogel, while the heat treatment process remains unchanged. The mechanical properties of the resulting GO-HEC composite aerogel are as follows: Figure 6 As shown, under the same strain, the mechanical properties of the high-entropy ceramic-based composite aerogel obtained by in-situ hydrothermal modification are far superior to those of the high-entropy ceramic-based aerogel obtained by impregnation process.

Claims

1. A method for preparing a two-dimensional high-entropy ceramic-based composite aerogel, characterized in that, Includes the following steps: 1) A high-entropy ceramic precursor solution was prepared using a polyacetylacetone metal complex of five elements (Zr, Hf, Ti, Lu, and Gd) as the metal element and methanol or ethanol as the solvent. The high-entropy ceramic precursor solution was then added to a graphene aqueous solution and ultrasonically mixed to obtain a hydrothermally soluble precursor solution. The proportion of the high-entropy ceramic precursor solution to the graphene solution was 50 wt%–200 wt%. 2) The precursor solution obtained in step 1) is transferred into a reaction vessel and subjected to hydrothermal reaction at 80~120℃ for 6~24h to obtain a composite hydrogel. After the reaction vessel is naturally cooled, it is taken out and dialyzed in 20~50% ethanol solution for 20~25h. After dialyz, it is placed on a copper block and liquid nitrogen is used to make the solvent in the composite hydrogel network form ice crystals and completely solidify. Then it is removed and placed in a freeze dryer to dry for 30~40h to obtain the composite aerogel precursor. 3) Place the composite aerogel precursor from step 2) in an argon-protected tube furnace and heat it to 900-1100℃ at a rate of 1-5℃ / min for high-temperature annealing. Hold the temperature for 1-2 hours and cool it with the furnace to obtain the two-dimensional high-entropy ceramic-based composite aerogel.

2. The method for preparing a two-dimensional high-entropy ceramic-based composite aerogel as described in claim 1, characterized in that, In step 1), the polyacetylacetone metal complex includes polyacetylacetone titanium, polyacetylacetone zirconium, polyacetylacetone hafnium, polyacetylacetone lutetium, and polyacetylacetone gadolinium, and each polyacetylacetone metal complex in the metal element is used in equimolar amounts of the metal element.

3. The method for preparing a two-dimensional high-entropy ceramic-based composite aerogel as described in claim 1, characterized in that, In step 1), the concentration of the high-entropy ceramic precursor solution is 200~400 mg / mL.

4. The method for preparing a two-dimensional high-entropy ceramic-based composite aerogel as described in claim 1, characterized in that, In step 1), the concentration of the graphene aqueous solution is 2~5 mg / mL.

5. The method for preparing a two-dimensional high-entropy ceramic-based composite aerogel as described in claim 1, characterized in that, In step 3), the high-temperature annealing is carried out at 1000℃. The heating process is as follows: the heating rate is 5℃ / min from RT to 600℃, the heating rate is 2℃ / min from 600 to 1000℃, and the temperature is held at 1000℃ for 2 hours.

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