A high thermal expansion coefficient and high entropy ceramic material and its preparation method

Abstract

This invention relates to the field of high-entropy ceramic materials technology, specifically to a high-entropy ceramic material with a high coefficient of thermal expansion and its preparation method. This invention uses nitrates of trivalent rare earth elements (La, Sm, Eu, Gd, Er, Yb, Y, Zr, Ce, Pr, Tb, etc.) as raw materials, and employs a combination of hydrothermal and sintering reaction methods to prepare high-entropy ceramic powder. The high-entropy design reduces the lattice energy, thereby increasing the coefficient of thermal expansion, and also results in lower thermal conductivity and good high-temperature phase stability.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy ceramic materials technology, specifically relating to a high-entropy ceramic material with a high coefficient of thermal expansion and its preparation method. Background Technology

[0002] Thermal barrier coatings (TBCs) are complex multilayer material systems that provide thermal insulation for critical components in advanced aerospace and gas turbines. Furthermore, TBCs protect critical components from wear, corrosion, and oxidation. The materials used typically possess the following properties: low thermal conductivity, high coefficient of thermal expansion, high melting point, resistance to sintering, and high-temperature phase stability. They also exhibit strong corrosion resistance. Among these, the coefficient of thermal expansion and thermal conductivity are the most important properties. However, the commonly used TBC material YSZ has a low coefficient of thermal expansion, resulting in a significant mismatch with the thermal expansion coefficient of the binder layer. Moreover, it undergoes a phase transition above 1200 degrees Celsius. Therefore, research into new TBC materials is necessary.

[0003] In recent years, high-entropy ceramics have accelerated the regulation of material properties through chemical bonding and band structure engineering. High-entropy ceramics are solid solutions with multiple main elements in equal or nearly equal atomic ratios, possessing advantages such as improved thermodynamic and mechanical properties. High-entropy rare-earth cerates, with their higher coefficient of thermal expansion and lower thermal conductivity than YSZ, are considered candidate materials for thermal barrier coatings in engine components. For example, the literature "(Sm 0.5 Gd 0.3 Yb 0.2 Thermal conductivity and coefficient of thermal expansion of 2Ce2O7 (Journal of Ceramics, 2017, 38(1):31-34.DOI:10.13957 / j.cnki.tcxb.2017.01.006.) was prepared using samarium oxide, gadolinium oxide, ytterbium oxide and cerium nitrate as raw materials by sol-gel method. 0.5 Gd 0.3 Yb 0.2 )2Ce2O7 ceramic material was used to improve the problem of low thermal expansion value of YSZ and large mismatch with the thermal expansion coefficient of the adhesive layer. However, the thermal expansion coefficient of this ceramic material is still low and the thermal conductivity is relatively high, which limits its application. Summary of the Invention

[0004] This invention provides a high-entropy ceramic material with a high coefficient of thermal expansion to solve the problems of low coefficient of thermal expansion, high thermal conductivity, poor thermal stability of thermal barrier coating materials, and the difficulty in synthesizing high-entropy ceramic materials and high energy consumption.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high thermal expansion coefficient high entropy ceramic material, wherein the high thermal expansion coefficient high entropy ceramic material is obtained by sintering and activation using rare earth nitrates as raw materials via a hydrothermal method, and the specific steps are as follows:

[0006] Step (1): Using pure water as a solvent, rare earth nitrates are heated and stirred in a beaker to obtain solution A. During the stirring process, ammonia water is slowly added dropwise until the pH of the reaction solution is 7, and precipitate A is obtained. The precipitate is washed with pure water several times and dried to obtain powder. The powder is dispersed in pure water to obtain suspension B.

[0007] The stirring speed is 300-400 rpm / minute; the stirring time is 0.5-1 hour; and the heating temperature is 90-100 degrees Celsius to ensure thorough mixing.

[0008] In suspension B, the mass ratio of powder to pure water is 1:5.

[0009] Step (2): Pour suspension B into a Teflon container, add potassium carbonate solution and polyvinyl alcohol solution, seal the Teflon container and place it in a stainless steel pressure vessel for hydrothermal treatment. The hydrothermal treatment is carried out in an air constant temperature oven at 225-250℃ for 48-66 hours to obtain product C.

[0010] The mass ratio of the suspension, potassium carbonate solution, and polyvinyl alcohol solution is 2:0.5:0.5.

[0011] The potassium carbonate solution concentration is 1.5-2 wt%, and the polyvinyl alcohol solution concentration is 4-6 wt%.

[0012] Step (3): Wash the product C after the hydrothermal reaction repeatedly with pure water, centrifuge the powder D with a centrifuge, wash it with pure water several times, and put it into a vacuum drying oven to dry.

[0013] The centrifuge speed is 5000-10000 rpm, the centrifugation time is 2-10 minutes, the drying temperature is 60-80 degrees Celsius, and the drying time is 12-18 hours.

[0014] Step (4): Place the dried powder D into a muffle furnace for sintering. After sintering, cool it with the furnace to obtain a high thermal expansion coefficient and high entropy ceramic material.

[0015] The muffle furnace sintering process involves heating to 800–1200 degrees Celsius and sintering for 2–6 hours; heating from room temperature to 1000 degrees Celsius at a rate of 5 degrees Celsius per minute, and from 1000 degrees Celsius to 1200 degrees Celsius at a rate of 2 degrees Celsius per minute.

[0016] Preferably, the muffle furnace sintering process involves heating to 1100–1200 degrees Celsius and sintering for 4 hours.

[0017] The chemical formula of the high-entropy ceramic material prepared by the above method is A2B2O7, where X is the stoichiometric ratio, A is at least five rare earth elements selected from La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Y, Pr, Tb, Tm, Sc, Sr, and Lu, and the molar ratio of the elements is equal; B is at least one rare earth element selected from Ce and Zr, and the molar ratio of Ce and Zr is X:5-X, where X = 2.5 to 5.

[0018] Specifically, the chemical formula of the high-entropy ceramic material is (La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2Ce2O7、(La 1 / 5 Sm 1 / 5Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.9 Zr 0.1 )2O7、(La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.7 Zr 0.3 )2O7、(La 1 / 5 Sm 1 / 5 Eu 1 / 5Yb 1 / 5 Y 1 / 5 )2(Ce 0.5 Zr 0.5 )2O7、(La 1 / 5 Sm 1 / 5 Er 1 / 5 Yb 1 / 5 Y 1 / 5 )2Ce2O7、(La 1 / 5 Sm 1 / 5 Gd 1 / 5 Yb 1 / 5 Y 1 / 5 )2Ce2O7.

[0019] Therefore, the beneficial effects of the present invention are:

[0020] This invention uses elements such as La, Sm, Eu, Gd, Er, Yb, Y, Zr, Ce, Pr, and Tb as raw materials to prepare high-entropy ceramic materials. By utilizing high-entropy design to reduce lattice energy, the thermal expansion coefficient is increased, reducing thermal stress caused by thermal expansion mismatch and thus improving the bonding strength between the coating and the substrate. The thermal expansion coefficient of this high-entropy ceramic material is 13.00 × 10⁻⁶. -6 K -1 (1350℃).

[0021] This invention combines hydrothermal and sintering methods to prepare ceramic materials. It can fully utilize the advantages of nanocrystals prepared by hydrothermal method, while reducing the sintering temperature (below 1200℃) and sintering time (≤6 hours), avoiding the possible formation of microparticle hard agglomerates, reducing grinding and impurities, and improving the thermal expansion coefficient of the material. Attached image description:

[0022] Figure 1 SEM image (1 μm) of the high-entropy ceramic material prepared in Example 1 of this invention;

[0023] Figure 2 XRD patterns of the high-entropy ceramic materials obtained in Examples 1-4 of this invention;

[0024] Figure 3 Thermal conductivity curves of the high-entropy ceramic materials obtained in Examples 1-4 of this invention;

[0025] Figure 4 Thermal expansion coefficient curve of the high-entropy ceramic material prepared in Example 1 of this invention;

[0026] Figure 5 TG-DSC curve of the high-entropy ceramic material prepared in Example 1 of this invention.

[0027] Figure 6 XRD pattern of the high-entropy ceramic material prepared in Comparative Example 2 of this invention Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments.

[0029] Example 1:

[0030] Step 1: Weigh six nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Eu(NO3)3·6H2O and Ce(NO3)3·6H2O, according to the rare earth element molar ratio of 1:1:1:1:1:5. Using pure water as solvent, heat and stir the rare earth nitrates in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During the stirring process, ammonia water is slowly added dropwise until the pH value of the reaction solution is 7, and precipitate A is obtained. After washing the precipitate with pure water several times, it is dried to obtain powder. Disperse it in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5.

[0031] Step 2: Pour suspension B into a Teflon container, add potassium carbonate solution and polyvinyl alcohol solution. The concentration of potassium carbonate solution is 2wt%, the concentration of polyvinyl alcohol solution is 4wt%, and the mass ratio is 2:0.5:0.5. Seal the Teflon container and place it in a stainless steel pressure vessel for hydrothermal treatment. The hydrothermal treatment is carried out in an air constant temperature oven at 250 degrees Celsius for 48 hours to obtain product C.

[0032] Step 3: Wash product C repeatedly with pure water, centrifuge to get powder D, centrifuge speed is 8000 rpm for 5 minutes, wash repeatedly with pure water, put into a vacuum drying oven to dry at 60 degrees Celsius for 12 hours.

[0033] Step 4: Place powder D into a muffle furnace for sintering at a temperature of 1100°C. The temperature is increased from room temperature to 1000°C at a rate of 5°C per minute, and from 1000°C to 1100°C at a rate of 2°C per minute. The sintering holding time is 4 hours. After sintering, the material is cooled in the furnace to obtain a high-entropy ceramic material with the chemical formula: (La... 1 / 5 Sm 1 / 5Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2Ce2O7.

[0034] The XRD diffraction pattern of the ceramic material prepared in this embodiment is as follows: Figure 2 As shown, characteristic peaks of fluorite (111), (200), (220), (311), (222), (400), (331), and (420) were detected, therefore the high-entropy ceramic material is a fluorite phase; according to the TG-DSC curve ( Figure 5 This indicates that the high-entropy ceramic material prepared in this embodiment did not undergo a phase transition at 1300℃, demonstrating its good thermal stability.

[0035] The high-entropy ceramic material prepared above was mixed with 6 wt% polyvinyl alcohol and granulated. The mass ratio of high-entropy ceramic material to polyvinyl alcohol was 2:1. The mixture was crushed, ground, and passed through an 80-mesh sieve to obtain the desired powder. 2.5 g of the powder was placed in the tableting mold of a benchtop powder press and pressed into a round sheet-like block. The pressure of the benchtop powder press was 20 MPa, and the holding time was 3 min. The ceramic block was then embedded with cerium dioxide and sintered in a muffle furnace at 1500 degrees Celsius for two hours. After furnace cooling, a test sample was obtained. The thermal conductivity of the high-entropy ceramic material prepared in this embodiment was tested using a flash laser thermal conductivity meter. The measured thermal conductivity was 1.74–0.85 W·m. –1 ·K –1 (30~1000℃), coefficient of thermal expansion is 13.29×10 -6 K-1 (1350℃).

[0036] Example 2

[0037] The difference between Example 2 and Example 1 is that step 1 is changed as follows: Seven nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Eu(NO3)3·6H2O, Ce(NO3)3·6H2O and Zr(NO3)3·5H2O, are weighed according to the rare earth element molar ratio of 1:1:1:1:1:0.5:4.5. Using pure water as solvent, the rare earth nitrates are heated and stirred in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During the stirring process, ammonia water is slowly added dropwise until the pH value of the reaction solution is 7, resulting in precipitate A. The precipitate is washed multiple times with pure water and dried to obtain powder. The powder is dispersed in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5. The rest is the same as in Example 1. The chemical formula of the obtained high thermal expansion coefficient high entropy ceramic material is: (La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.9 Zr 0.1 )2O7.

[0038] The XRD diffraction pattern of the ceramic material prepared in this embodiment is as follows: Figure 2 As shown, characteristic peaks of fluorite (111), (200), (220), (311), (222), (400), (331) and (420) were detected, therefore the high-entropy ceramic material is a fluorite phase.

[0039] The test sample prepared from the ceramic material obtained in Example 2 (same as in Example 1) was tested for thermal conductivity using a flash laser thermal conductivity meter. The measured thermal conductivity was 1.70–0.92 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 13.00×10 -6 K -1 (1350℃).

[0040] Example 3

[0041] The difference between Example 3 and Example 1 is that step 1 is changed as follows: Seven nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Eu(NO3)3·6H2O, Ce(NO3)3·6H2O and Zr(NO3)3·5H2O, are weighed according to the rare earth element molar ratio of 1:1:1:1:1:1.5:3.5. Using pure water as solvent, the rare earth nitrates are heated and stirred in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During the stirring process, ammonia water is slowly added dropwise until the pH value of the reaction solution is 7, resulting in precipitate A. The precipitate is washed multiple times with pure water and dried to obtain powder. The powder is dispersed in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5. The rest is the same as in Example 1. The chemical formula of the obtained high thermal expansion coefficient high entropy ceramic material is: (La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.7 Zr 0.3 )2O7.

[0042] The XRD diffraction pattern of the ceramic material prepared in this embodiment is as follows: Figure 2 As shown, characteristic peaks of fluorite (111), (200), (220), (311), (222), (400), (331) and (420) were detected, therefore the high-entropy ceramic material is a fluorite phase.

[0043] The test sample prepared from the ceramic material obtained in Example 3 (same as in Example 1) was tested for thermal conductivity using a flash laser thermal conductivity meter. The measured thermal conductivity was 1.67–1.01 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 12.60×10 -6 K -1 (1350℃).

[0044] Example 4

[0045] Example 4 differs from Example 1 in that step 1 is changed as follows: Seven nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Eu(NO3)3·6H2O, Ce(NO3)3·6H2O, and Zr(NO3)3·5H2O, are weighed according to a rare earth element molar ratio of 1:1:1:1:1:2.5:2.5. Using pure water as a solvent, the rare earth nitrates are heated and stirred in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During the stirring process, ammonia water is slowly added dropwise until the pH of the reaction solution is 7, resulting in precipitate A. The precipitate is washed multiple times with pure water, dried, and then dispersed in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5. The rest is the same as in Example 1. The chemical formula of the obtained high thermal expansion coefficient high entropy ceramic material is: (La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.5 Zr 0.5 )2O7.

[0046] The XRD diffraction pattern of the ceramic material prepared in this embodiment is as follows: Figure 2 As shown, characteristic peaks of fluorite (111), (200), (220), (311), (222), (400), (331) and (420) were detected, therefore the high-entropy ceramic material is a fluorite phase.

[0047] The test sample prepared from the ceramic material obtained in Example 4 (same as in Example 1) was tested for thermal conductivity using a flash laser thermal conductivity meter. The measured thermal conductivity was 1.46–0.99 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 12.02×10 -6 K -1 (1350℃).

[0048] Example 5:

[0049] Example 5 differs from Example 1 in that step 1 is modified as follows: Six nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Er(NO3)3·6H2O, and Ce(NO3)3·6H2O, are weighed according to a rare earth element molar ratio of 1:1:1:1:1:5. Using pure water as the solvent, the rare earth nitrates are heated and stirred in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During stirring, ammonia water is slowly added dropwise until the pH of the reaction solution reaches 7, resulting in precipitate A. The precipitate is washed multiple times with pure water, dried, and then dispersed in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5. The rest is the same as in Example 1. The chemical formula of the obtained high thermal expansion coefficient high-entropy ceramic material is: (La... 1 / 5 Sm 1 / 5 Er 1 / 5 Yb 1 / 5 Y 1 / 5 )2Ce2O7.

[0050] The test sample prepared from the ceramic material obtained in Example 5 (same as in Example 1) was tested using a flash laser thermal conductivity meter. The thermal conductivity of the high-entropy ceramic material prepared in this example was measured to be 1.77–1.04 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 12.89×10 -6 K -1 (1350℃).

[0051] Example 6:

[0052] Example 6 differs from Example 1 in that step 1 is modified as follows: Six nitrates—La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Gd(NO3)3·6H2O, and Ce(NO3)3·6H2O—are weighed according to a rare earth element molar ratio of 1:1:1:1:1:5. Using pure water as the solvent, the rare earth nitrates are heated and stirred in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During stirring, ammonia water is slowly added dropwise until the pH of the reaction solution reaches 7, resulting in precipitate A. The precipitate is washed multiple times with pure water, dried, and then dispersed in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5. The rest is the same as in Example 1. The chemical formula of the obtained high thermal expansion coefficient high-entropy ceramic material is: (La... 1 / 5 Sm 1 / 5 Gd 1 / 5 Yb1 / 5 Y 1 / 5 )2Ce2O7.

[0053] The test sample prepared from the ceramic material obtained in Example 6 (same as in Example 1) was tested for thermal conductivity using a flash laser thermal conductivity meter. The measured thermal conductivity of the high-entropy ceramic material prepared in this example was 1.80–0.96 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 12.54×10 -6 K -1 (1350℃).

[0054] Example 7

[0055] The difference between Example 7 and Example 1 is that step 4 is modified as follows: powder D is placed in a muffle furnace for sintering at a temperature of 800 degrees Celsius, a heating rate of 5 degrees Celsius per minute, a holding time of 4 hours, and then cooled with the furnace after sintering; the rest is the same as in Example 1.

[0056] The test sample prepared from the ceramic material obtained in Example 7 (same as in Example 1) was tested for thermal conductivity using a flash laser thermal conductivity meter. The measured thermal conductivity was 1.95–0.99 m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 12.69×10 -6 K -1 (1350℃).

[0057] Example 8

[0058] The difference between Example 8 and Example 1 is that step 4 is modified as follows: powder D is placed in a muffle furnace for sintering at a temperature of 1200 degrees Celsius. The heating rate is 5 degrees Celsius per minute from room temperature to 1000 degrees Celsius, and 2 degrees Celsius per minute from 1000 degrees Celsius to 1200 degrees Celsius. The sintering holding time is 4 hours, and the furnace is cooled after sintering. The rest is the same as in Example 1.

[0059] The test sample prepared from the ceramic material obtained in Example 8 (same as in Example 1) was tested using a flash laser thermal conductivity meter. The thermal conductivity of the high-entropy ceramic material prepared in this example was measured to be 1.76–0.89 m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 13.01×10 -6 K -1 (1350℃).

[0060] Comparative Example 1

[0061] The difference between Comparative Example 1 and Example 1 is that step 1 is changed as follows: La(NO3)3·6H2O, Ce(NO3)3·6H2O, and Zr(NO3)3·5H2O are weighed according to a rare earth element molar ratio of 1:1:5. Using pure water as the solvent, the rare earth nitrates are heated and stirred in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During stirring, ammonia water is slowly added dropwise until the pH of the reaction solution reaches 7, resulting in precipitate A. The precipitate is washed multiple times with pure water, dried, and then dispersed in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5. The rest is the same as in Example 1. The chemical formula of the obtained ceramic material is: La2(Ce2)3·6H2O ... 0.5 Zr 0.5 )2O7.

[0062] The test sample prepared from the ceramic material obtained in Comparative Example 1 (same as in Example 1) was tested for thermal conductivity using a flash laser thermal conductivity meter. The measured thermal conductivity was 2.16–1.65 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 11.58×10 -6 K -1 (1000℃).

[0063] Comparative Example 2

[0064] Step A: Preparation of high-entropy ceramic powder:

[0065] Step (A-1): Weigh seven oxides, La2O3, Sm2O3, Eu2O3, Yb2O3, Y2O3, ZrO2, and CeO2, in a molar ratio of 1:1:1:1:1:2.5:2.5. Use pure water as a solvent and ball mill them together. The mass ratio of pure water, powder, and grinding beads is 2:1:1.5. The ratio of large, medium, and small grinding beads is 2:2:1. The diameters of the grinding beads are 10 mm, 7 mm, and 5 mm. The rotation speed is 400 rpm, and the ball milling time is 12 hours to obtain slurry A.

[0066] Step (A-2): Pass slurry A through a 200-mesh sieve. The sieve aperture size of a 200-mesh standard sieve is 0.075mm. Place it in an oven to dry at a temperature of 100℃ for 12 hours. After drying, pass the powder through a 200-mesh sieve again to obtain powder B.

[0067] Step (A-3): Powder B is placed in a muffle furnace for sintering at a temperature of 1200 degrees Celsius. The temperature is increased from room temperature to 1000 degrees Celsius at a rate of 5 degrees Celsius per minute, and then increased from 1000 degrees Celsius to 1200 degrees Celsius at a rate of 2 degrees Celsius per minute. The sintering time is 6 hours. After sintering, the powder is cooled in the furnace to obtain the ceramic material. The chemical formula of the obtained ceramic material is: (La...) 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.5 Zr 0.5 )2O7.

[0068] The XRD pattern of the ceramic material prepared in this embodiment showed impurity peaks. Figure 6 High-entropy ceramic powder was not fully synthesized.

[0069] Comparative Example 3:

[0070] Step A: Preparation of high-entropy ceramic powder:

[0071] Step (A-1): Weigh six nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Yb(NO3)3·5H2O, Y(NO3)3·6H2O, Eu(NO3)3·6H2O, and Ce(NO3)3·6H2O, according to the rare earth element molar ratio of 1:1:1:1:1:5. Using pure water as a solvent, heat and stir the rare earth nitrates in a beaker to obtain solution A. The stirring speed is 300 rpm / min, the stirring time is 0.5 hours, and the heating temperature is 95 degrees Celsius. During the stirring process, ammonia water is slowly added dropwise until the pH of the reaction solution is 7, resulting in precipitate A. After washing the precipitate with pure water several times, dry it to obtain powder. Disperse the powder in pure water to obtain suspension B. The mass ratio of powder to pure water in suspension B is 1:5.

[0072] Step (A-2): Pour suspension B into a Teflon container, add potassium carbonate solution and polyvinyl alcohol solution. The concentration of potassium carbonate solution is 2wt% and the concentration of polyvinyl alcohol solution is 4wt%. Seal the Teflon container and place it in a stainless steel pressure vessel for hydrothermal treatment. The hydrothermal treatment is carried out in an air constant temperature oven at 250°C for 48 hours.

[0073] Step (A-3): Wash the product C from the hydrothermal reaction repeatedly with pure water, centrifuge to obtain powder D at 8000 rpm for 5 minutes, wash repeatedly with pure water, and dry in a vacuum drying oven at 60 degrees Celsius for 12 hours to obtain the ceramic material with the chemical formula: (La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5Y 1 / 5 )2Ce2O7.

[0074] High-entropy ceramic powder was not fully synthesized using only the hydrothermal method.

[0075] Comparative Example 4

[0076] Step A: Preparation of high-entropy ceramic powder:

[0077] Step (A-1): Weigh seven oxides, La2O3, Sm2O3, Eu2O3, Yb2O3, Y2O3, ZrO2, and CeO2, in a molar ratio of 1:1:1:1:1:2.5:2.5. Use pure water as a solvent and ball mill the mixture. The mass ratio of pure water to powder is 2:1. The ball milling speed is 400 rpm and the ball milling time is 12 hours to obtain slurry A.

[0078] Step (A-2): Pass slurry A through a 200-mesh sieve. The sieve aperture size of a 200-mesh standard sieve is 0.075mm. Place it in an oven to dry at a temperature of 80℃ for 12 hours. Pass the dried powder through a 200-mesh sieve again to obtain powder B.

[0079] Step (A-3): Powder B is placed in a muffle furnace for sintering at a temperature of 1500 degrees Celsius, a heating rate of 5 degrees Celsius per minute, and a sintering time of 8 hours. After sintering, it is cooled in the furnace to obtain the ceramic material, whose chemical formula is (La). 1 / 5Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.5 Zr 0.5 )2O7.

[0080] The thermal conductivity of the high-entropy ceramic material prepared in this embodiment was measured using a flare laser thermal conductivity meter, and the thermal conductivity ranged from 1.46 to 1.05 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 11.82×10 -6 K -1 (1350℃).

[0081] Comparative Example 5:

[0082] The difference between Comparative Example 5 and Example 1 is that step 1 is changed to: weighing seven nitrates, La(NO3)3·6H2O, Sm(NO3)3·6H2O, Nd(NO3)3·6H2O, Dy(NO3)3·6H2O, Er(NO3)3·6H2O, Ce(NO3)3·6H2O, and Zr(NO3)3·5H2O, according to the rare earth element molar ratio of 1:1:1:1:1:2.5:2.5. Using pure water as a solvent, rare earth nitrates were heated and stirred in a beaker to obtain solution A. The stirring speed was 300 rpm / min, the stirring time was 0.5 hours, and the heating temperature was 95 degrees Celsius. During the stirring process, ammonia water was slowly added dropwise until the pH of the reaction solution reached 7, resulting in precipitate A. The precipitate was washed several times with pure water and dried to obtain powder. This powder was dispersed in pure water to obtain suspension B, with a powder-to-pure water mass ratio of 1:5. The rest was the same as in Example 1. The chemical formula of the obtained ceramic material is: (La 1 / 5 Sm 1 / 5 Nd 1 / 5 Dy 1 / 5 Er 1 / 5 )2(Ce 0.5 Zr 0.5 )2O7.

[0083] The test sample prepared from the ceramic material obtained in Comparative Example 5 (same as in Example 1) was used to test the thermal conductivity of the ceramic material prepared in this example using a flash laser thermal conductivity meter. The measured thermal conductivity was 1.54-1.10 W·m. –1 ·K –1 (30~1000℃); coefficient of thermal expansion is 11.97×10 -6 K -1 (1350℃).

[0084] Table 1 Comparison of thermal conductivity and coefficient of thermal expansion of ceramic materials prepared in the examples and comparative examples.

[0085]

[0086] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A high thermal expansion coefficient, high entropy ceramic material, characterized in that, The chemical formula of the high-entropy ceramic material is: (La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2Ce2O7、(La 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Y 1 / 5 )2(Ce 0.9 Zr 0.1 )2O7.

2. A method for preparing a high thermal expansion coefficient, high entropy ceramic material according to claim 1, characterized in that, Includes the following steps: Step (1): After mixing rare earth nitrate and pure water evenly, heat and stir. During the stirring process, slowly add ammonia water until the pH of the reaction solution is 7 to obtain precipitate A. Wash the precipitate with pure water several times, dry it, and obtain powder. Disperse it in pure water to obtain suspension B. Step (2): Pour suspension B into a Teflon container, add potassium carbonate solution and polyvinyl alcohol solution, seal the Teflon container and place it in a stainless steel pressure vessel for hydrothermal treatment to obtain product C; Step (3): Wash the product C after the hydrothermal reaction repeatedly with pure water, centrifuge the powder D with a centrifuge, wash it with pure water several times, and put it into a vacuum drying oven to dry. Step (4): Place the dried powder D into a muffle furnace for sintering. After sintering, cool the powder with the furnace to obtain high-entropy ceramic powder.

3. The method for preparing high thermal expansion coefficient high entropy ceramic material according to claim 2, characterized in that, The heating and stirring time in step (1) is 0.5-1 hour, and the temperature is 90-100 degrees Celsius.

4. The method for preparing high thermal expansion coefficient high entropy ceramic material according to claim 2, characterized in that, In step (1), the mass ratio of powder to pure water in suspension B is 1:

5.

5. The method for preparing high thermal expansion coefficient high entropy ceramic material according to claim 2, characterized in that, The potassium carbonate concentration in step (2) is 1.5-2 wt%, and the polyvinyl alcohol concentration is 4-6 wt%. The mass ratio of the suspension B, potassium carbonate solution, and polyvinyl alcohol solution is 2:0.5:0.

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6. The method for preparing high thermal expansion coefficient high entropy ceramic material according to claim 2, characterized in that, The hydrothermal treatment temperature in step (2) is 225-250 degrees Celsius, and the treatment time is 48-66 hours.

7. The method for preparing high thermal expansion coefficient high entropy ceramic material according to claim 2, characterized in that, The centrifugation rate in step (3) is 5000-10000 rpm per minute, and the centrifugation time is 2-10 minutes; The vacuum drying temperature is 60-80 degrees Celsius, and the drying time is 12-18 hours.

8. The method for preparing high thermal expansion coefficient high entropy ceramic material according to claim 2, characterized in that, The sintering described in step (4) is as follows: heating to 800~1200 degrees Celsius and sintering for 2~6 hours; heating from room temperature to 1000 degrees Celsius at a rate of 5 degrees Celsius per minute, and heating from 1000 degrees Celsius to 1200 degrees Celsius at a rate of 2 degrees Celsius per minute.

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