Equal-molar-ratio seven-element high-entropy oxide and preparation process thereof

Abstract

The invention belongs to the field of synthesis of inorganic non-metallic materials, and particularly relates to an equimolar-ratio seven-element high-entropy oxide and a preparation process thereof. The preparation process comprises the following steps: putting seven oxide powder Al2O3, Y2O3, TiO2, ZrO2, NiO, CuO and CeO2 into a ball milling tank according to a molar ratio of 1: 1: 2: 2: 2: 2: 2: 2, adding absolute ethyl alcohol and zirconium oxide grinding balls, performing ball milling in a ball mill, and fully drying and sieving after ball milling to obtain mixed powder; carrying out tabletting treatment on the mixed powder to obtain a to-be-sintered green body; and putting the to-be-sintered green body into an alumina crucible, and putting the alumina crucible into a microwave oven for microwave sintering. According to the method, the equimolar-ratio seven-element high-entropy oxide (AlYTiZrNiCuCe) Ox with good solid solution is obtained, the crystallinity and element uniformity of the seven-element high-entropy oxide are improved, all the raw materials react completely, meanwhile, the process efficiency is high, and energy consumption is low.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic material synthesis, specifically relating to an equimolar ratio seven-element high-entropy oxide and its preparation process. Background Technology

[0002] High-entropy oxides, as an important branch of novel ceramic materials, possess numerous advantages such as good thermal stability, high hardness, and excellent catalytic performance, exhibiting superior performance in catalysis, energy storage, and high-temperature protection. Currently, the preparation methods for high-entropy oxides mainly rely on energy-intensive heating methods such as muffle furnaces, hot pressing sintering, and spark plasma sintering. These traditional methods primarily depend on heat conduction to achieve product preparation, typically requiring temperatures above 1600℃ and heating times of at least 1 hour. These methods still have limitations in terms of efficiency, energy consumption, and product purity, such as high energy consumption, low process efficiency, grain coarsening, and elemental segregation. Microwave sintering technology utilizes the penetrating power of microwaves to generate heat through atomic vibration and friction within a microwave field. It is highly efficient, energy-saving, and has no thermal gradient, primarily applied in binary or ternary systems. Research on pentagonal and higher-component systems is limited, and studies on equimolar heptagonal high-entropy oxides containing rare earth elements are virtually nonexistent.

[0003] Chinese invention patent application CN116789186A discloses a uniform (ZrTiCoNiNb)O high-entropy oxide powder, its preparation method, and its applications. The (ZrTiCoNiNb)O high-entropy oxide powder is prepared according to the following steps: ZrO2, TiO2, CoO, NiO, and Nb2O5 are ball-milled and mixed uniformly to obtain a raw material mixed powder; the raw material mixed powder is loaded into a crucible, a temperature field regulation mechanism is introduced, and microwave treatment is performed to obtain the (ZrTiCoNiNb)O high-entropy oxide ceramic powder material. This invention, based on the characteristics of microwave heating, introduces SiC rods into the microwave heating and insulation structure to regulate the sample temperature field, thereby obtaining a uniform and stable high-entropy oxide ceramic powder using microwave heating. The sintering process is short, rapid, environmentally friendly, and efficient, showing great application prospects. However, XRD analysis of the patent shows that the prepared powder has strong diffraction peaks of ZrO2 raw material, indicating that a large amount of ZrO2 raw material failed to react effectively through this technology, resulting in low purity of the high-entropy oxide target product.

[0004] Rare earth ions (such as Y) in a seven-element system 3 ⁺ / Ce 4(⁺) Large differences in radius and mismatched diffusion rates at high temperatures lead to compositional segregation, making it difficult to achieve effective solid solution of elements. The study "Ultra-dense dislocations stabilized in highentropy oxide ceramics" (Nature Communications, 2022, 13:2871) shows that high-entropy oxides synthesized by traditional methods have ultra-dense dislocation structures, but the elemental distribution is not uniform enough. Chinese invention patent application CN118290129A discloses a high-entropy oxide ceramic and its preparation method. The method involves ball milling Al₂O₃ powder, ZrO₂ powder, NiO powder, TiO₂ powder, CuO powder, Y₂O₃ powder, and CeO₂ powder in a molar ratio of 0.4:0.1:0.1:0.1:0.1:0.1:0.1–0.4 to obtain a mixed powder. The mixed powder is then dried, ground, sieved, and molded at 30–70 MPa to obtain a preform. The preform is then microwave-sintered at 1150–1350 °C to obtain the high-entropy oxide ceramic. The high-entropy oxide ceramic prepared by this invention exhibits high hardness and density, as well as good fracture toughness. However, XRD analysis of the samples prepared by this invention showed that the seven metal atoms were not dissolved in the same sublattice position. The samples prepared by this technique did not contain the phase composition of a seven-membered high-entropy oxide and were not classified as such. Instead, they consisted of Y3Al2(AlO4)3, (Y,Ce)(Nb,Ti)2O6, and Al4Ni. 15 The mixture consists of three compounds; in addition, the technology requires that the molar content of Al2O3, which has no microwave absorption capability, must be 36% or more, while the molar content of NiO and TiO2, which have microwave absorption capability, is only about 9%. This greatly weakens the microwave absorption capability of the mixed raw materials, reduces the thermal conductivity effect of the microwave absorbing material components on the entire mixed raw materials, significantly increases the microwave input power, and thus increases energy consumption. Summary of the Invention

[0005] To address the shortcomings of existing methods, this invention provides an equimolar ratio heptagonal high-entropy oxide and its preparation process, obtaining a well-solidified equimolar ratio heptagonal high-entropy oxide (AlYTiZrNiCuCe)Ox, filling the research gap of equimolar ratio heptagonal high-entropy oxides, improving the crystallinity and elemental uniformity of heptagonal high-entropy oxides, ensuring complete reaction of various raw materials, and overcoming the problems of low process efficiency and high energy consumption in existing preparation methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing an equimolar ratio seven-membered high-entropy oxide includes the following steps: S1. Seven oxide powders, Al2O3, Y2O3, TiO2, ZrO2, NiO, CuO, and CeO2, are placed in a ball mill jar in a molar ratio of 1:1:2:2:2:2:2. Anhydrous ethanol and zirconium oxide grinding balls are added, and the mixture is ball-milled in a ball mill. After ball milling, the mixture is thoroughly dried and sieved to obtain a mixed powder. S2. The mixed powder described in step S1 is compressed into tablets to obtain a blank to be fired. S3. Place the blank to be fired described in step S2 into an alumina crucible and put it into a microwave oven for microwave sintering.

[0007] Preferably, the particle size of Al2O3 is 0.5-10 μm, the particle size of Y2O3 is 3-10 μm, the particle size of TiO2 is 1-10 μm, the particle size of ZrO2 is 1-10 μm, the particle size of NiO is 1-10 μm, the particle size of CuO is 3-10 μm, and the particle size of CeO2 is 1-10 μm.

[0008] Preferably, the total weight ratio of the anhydrous ethanol to the seven oxide powders is 2-10:1.

[0009] Preferably, the ball-to-material ratio in the ball mill jar is 2-10:1.

[0010] Preferably, the ball mill rotates at a speed of 300-500 r / min and the ball milling time is 6-12 h.

[0011] Preferably, the tableting pressure is 10-20 MPa and the holding time is 0.5-5 min.

[0012] Preferably, the microwave sintering is performed by heating to 1200-1350°C at a heating rate of 3-7°C / min and holding at that temperature for 45-75 minutes.

[0013] Preferably, the alumina crucible is dried before use, and an alumina pad is placed at the bottom of the alumina crucible beforehand.

[0014] An equimolar ratio heptagonal high-entropy oxide prepared by the above-described preparation process, wherein the equimolar ratio heptagonal high-entropy oxide is (AlYTiZrNiCuCe)Ox, and the value of x ranges from 1.8 to 2.2.

[0015] The positive and beneficial effects of this invention are: Equimolar ratios of seven-membered high-entropy oxides have not been prepared in existing technologies. Chinese invention patent application CN118290129A discloses a high-entropy oxide ceramic and its preparation method; however, the high-entropy oxide described is not a seven-membered high-entropy oxide. This is because the XRD analysis results disclosed in this invention show that the prepared sample does not contain any seven-membered high-entropy oxide phases, but rather consists of Y3Al2(AlO4)3, (Y,Ce)(Nb,Ti)2O6, and Al4Ni. 15 The mixture of the three compounds indicates that this patented technology cannot meet the requirements for preparing seven-element high-entropy oxides. Furthermore, this technology requires a non-absorbing Al2O3 molar content of 36% or higher, reducing the proportion of absorbing NiO and TiO2, significantly weakening the absorption capacity of the mixed raw materials. This undoubtedly reduces the thermal conductivity of the absorbing material components to the entire mixed raw material, significantly increasing microwave input power and thus energy consumption. In addition, Chinese invention patent application CN116789186A discloses a uniform (ZrTiCoNiNb)O high-entropy oxide powder, its preparation method, and its application. This technology presents a five-element high-entropy oxide, and the XRD pattern disclosed in this patent shows strong diffraction peaks of ZrO2 raw material in the prepared powder, indicating that a large amount of ZrO2 raw material failed to react effectively through this technology. The high-entropy oxide target product has low purity, indicating that this patented technology still has significant shortcomings in the preparation of high-entropy oxides. This invention is the first to prepare equimolar ratio seven-member high-entropy oxide (AlYTiZrNiCuCe)Ox powder, filling the research gap in equimolar ratio seven-member high-entropy oxides, and achieving the following positive and beneficial effects: 1. Compared to traditional preparation methods, such as muffle furnace sintering and hot pressing sintering, which require synthesizing high-entropy oxide ceramics at temperatures of 1600℃ or even higher and heating times typically not less than 1 hour, the microwave heating technology of this invention utilizes atomic vibration and frictional heat generation in a microwave field. This significantly reduces the sintering temperature and shortens the sintering time, featuring rapid heating and uniform heat field distribution. It greatly saves time and energy, achieving low carbon emissions. The preparation of heptagonal high-entropy oxides can be achieved by pressureless sintering at 1200-1350℃ for 45-75 minutes. The heptagonal high-entropy oxide prepared by this invention… The oxide-based cubic crystal form, belonging to space group 225 Fm-3m, exhibits lower anisotropy in Young's modulus, shear modulus, and hardness, effectively improving the material's hardness and wear resistance. Furthermore, the lower sintering temperature facilitates grain refinement, avoiding grain coarsening caused by high temperatures. Compared to traditional preparations at 1600℃, the seven-element high-entropy oxide powder of this invention exhibits a more uniform particle size distribution, with a particle size of approximately 10 μm, and no obvious particle sintering. The prepared powder shows uniform elemental distribution without significant segregation, resulting in higher phase purity. Additionally, this invention uses only approximately 8% Al2O3 powder, while the molar content of NiO and TiO2, which enhance microwave absorption capabilities, is approximately 17%. This significantly increases the microwave-absorbing material's ability to convert microwave energy into heat, thereby improving the heating rate and thermal conductivity, ultimately reducing microwave input power, resulting in high process efficiency and low energy consumption.

[0016] 2. In traditional heating, small-sized ions tend to diffuse preferentially, leading to localized component segregation. This invention innovatively utilizes the unique heating effect of microwave fields. Under the action of microwave fields, a highly active environment is formed inside the material. This efficient energy transfer method injects strong momentum into the solid solution process of large-sized cerium plasma, significantly reducing the energy barrier for the diffusion and migration of large-sized ions such as cerium ions. It greatly activates the synchronous migration and synergistic diffusion of ions of different sizes such as cerium in the material, effectively driving large-sized cerium ions to overcome spatial resistance, greatly improving the uniformity and efficiency of solid solution, suppressing the formation of impurity phases, and solving the problem of difficult solid solution of rare earth elements.

[0017] The rapid overall heating characteristics of microwaves can greatly shorten the residence time of materials in the high-temperature region and significantly suppress the formation and growth of thermodynamically metastable impurity phases (such as cerium-rich second phases). This fundamentally solves the common problem of impurity phase interference in rare earth doped materials, and provides a powerful means for the efficient and uniform solid solution of large-size rare earth ions in functional materials (such as solid electrolytes, phosphors, and catalytic materials). It has important industrial value for improving the electrochemical performance, optical performance and stability of materials, and opens up new avenues for the development of rare earth functional materials.

[0018] In addition, no raw material phase was detected in the high-entropy ceramic phase described in this invention, which indicates that all raw materials in this invention participated in the reaction and the reaction was complete, resulting in a seven-element solid solution in which seven elements randomly occupy the same sublattice position, i.e., a seven-element high-entropy oxide ceramic. The prepared seven-element high-entropy oxide ceramic has higher purity.

[0019] 3. Larger raw material particle sizes result in lower specific surface energy, making atomic diffusion and solid solution more difficult, and also lower raw material prices. This invention uses micron-sized raw materials, reducing raw material costs, solving the problem of difficult atomic diffusion and solid solution between coarse-sized raw materials, lowering the difficulty of preparing high-entropy oxide ceramics, and strongly promoting their market application. Attached Figure Description

[0020] Figure 1 The XRD diffraction patterns of the seven-membered high-entropy oxides with equal molar ratios in Examples 1-3 of this invention are shown below. Figure 2 These are SEM microstructure images of the equimolar ratio seven-element high-entropy oxides in Examples 1 and 3 of this invention. Figure 3 This is a SEM elemental distribution diagram of the equimolar ratio seven-element high-entropy oxide of Example 1 of the present invention; Figure 4 This is a SEM elemental distribution diagram of the equimolar ratio seven-element high-entropy oxide of Example 3 of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to some specific embodiments.

[0022] Example 1 A process for preparing an equimolar ratio seven-member high-entropy oxide (AlYTiZrNiCuCe)O2 includes the following steps: S1. Seven oxide powders (Al2O3, Y2O3, TiO2, ZrO2, NiO, CuO, and CeO2) with a purity of not less than 99.9% are placed in a ball mill jar in a molar ratio of 1:1:2:2:2:2:2. The particle sizes are as follows: Al2O3 0.5-10 μm, Y2O3 3-10 μm, TiO2 1-10 μm, ZrO2 1-10 μm, and NiO 1-10 μm. The powder consisted of 3-10 μm CuO particles and 1-10 μm CeO2 particles, with anhydrous ethanol and zirconium oxide grinding balls added. The total weight ratio of anhydrous ethanol to the seven oxide powders was 2:1, and the ball-to-powder ratio in the ball mill was 2:1. The mixture was ball-milled in a planetary ball mill at a speed of 300 r / min for 12 h. After ball milling, the mixture was thoroughly dried at 60 °C and passed through a 200-mesh sieve to obtain a uniformly mixed powder. S2. The mixed powder described in step S1 is compressed into tablets at a pressure of 20 MPa and a holding time of 1 min. The diameter of the pressed blank is 30 mm and the thickness is 4 mm. S3. Before use, the alumina crucible is dried in a drying oven at 80℃ for 2 hours. A pre-pressed alumina pad (approximately 50 MPa or higher) is placed at the bottom of the crucible. The blank to be sintered, obtained in step S2, is placed on top of the alumina pad inside the crucible. The crucible is then placed in a microwave oven for microwave sintering. The temperature is increased to 1300℃ at a rate of 5℃ / min and held for 45 minutes. After holding, the crucible is allowed to cool naturally. The product is then tested, and the test results are shown below. Figure 1-3 .

[0023] from Figure 1 As shown in the XRD pattern of Sample 1, the prepared sample is mainly a high-entropy oxide phase, yielding a seven-element solid solution with seven elements randomly occupying the same sublattice positions. Only a weak diffraction peak of the AlCe intermetallic compound is observed, but its intensity is extremely low, indicating its very low content. This demonstrates complete and good solid solution for each atom, and the prepared product is an equimolar seven-element high-entropy oxide. Furthermore, the XRD pattern shows that the seven-element high-entropy oxide obtained in this invention inherits the crystal structure of ZrO2, is cubic, and belongs to space group 225 Fm-3m.

[0024] The sample prepared in Example 1 was analyzed by SEM, such as... Figure 2 a and its enlarged illustration Figure 2 As shown in c, there are no obvious traces of a second phase, the particle surface is relatively smooth, the powder particle size is relatively uniform, the powder particle diameter is about 10μm, and there is no obvious particle sintering phenomenon.

[0025] from Figure 3 It can be seen that the sample contains all elements, and each element is evenly distributed at the micrometer scale, indicating that each element is well dissolved in solid solution, which shows the successful preparation of the equimolar ratio seven-member high-entropy oxide phase.

[0026] Example 2 A process for preparing an equimolar ratio seven-member high-entropy oxide (AlYTiZrNiCuCe)O2 includes the following steps: S1. Seven oxide powders (Al2O3, Y2O3, TiO2, ZrO2, NiO, CuO, and CeO2) with a purity of not less than 99.9% are placed in a ball mill jar in a molar ratio of 1:1:2:2:2:2:2. The particle sizes are as follows: Al2O3 0.5-10 μm, Y2O3 3-10 μm, TiO2 1-10 μm, ZrO2 1-10 μm, and NiO 1-10 μm. The powder consisted of 3-10 μm CuO particles and 1-10 μm CeO2 particles, with anhydrous ethanol and zirconium oxide grinding balls added. The total weight ratio of anhydrous ethanol to the seven oxide powders was 2:1, and the ball-to-powder ratio in the ball mill was 2:1. The mixture was ball-milled in a planetary ball mill at a speed of 300 r / min for 12 h. After ball milling, the mixture was thoroughly dried at 60 °C and passed through a 200-mesh sieve to obtain a uniformly mixed powder. S2. The mixed powder described in step S1 is compressed into tablets at a pressure of 20 MPa and a holding time of 1 min. The diameter of the pressed blank is 30 mm and the thickness is 4 mm. S3. Before use, the alumina crucible is dried in a drying oven at 80℃ for 2 hours. Alumina pads, pre-pressed to a pressure of 50MPa or higher, are placed at the bottom of the crucible. The blank to be sintered, obtained in step S2, is placed on top of the alumina pads inside the crucible. The crucible is then placed in a microwave oven for microwave sintering. The temperature is increased to 1300℃ at a rate of 5℃ / min and held for 75 minutes. After holding, the crucible is allowed to cool naturally. The product is then tested, and the test results are shown below. Figure 1 .

[0027] from Figure 1 The XRD pattern of Sample 2 shows that the prepared sample is mainly a high-entropy oxide phase, obtaining a seven-element solid solution with seven elements randomly occupying the same sublattice positions. Compared with Sample 1, the type of the second phase has changed; the AlCe compound has disappeared, and only a weak diffraction peak of the Ni-Al-O compound is present. However, the intensity of the Ni-Al-O compound diffraction peak is extremely low, indicating that its content is extremely low. This shows that each atom is completely and well dissolved, and the prepared product is an equimolar seven-element high-entropy oxide. In addition, XRD diffraction pattern analysis shows that the obtained seven-element high-entropy oxide inherits the crystal structure of ZrO2, is cubic, and belongs to space group 225 Fm-3m.

[0028] Example 3 A process for preparing an equimolar ratio seven-member high-entropy oxide (AlYTiZrNiCuCe)O2 includes the following steps: S1. Seven oxide powders (Al2O3, Y2O3, TiO2, ZrO2, NiO, CuO, and CeO2) with a purity of not less than 99.9% are placed in a ball mill jar in a molar ratio of 1:1:2:2:2:2:2. The particle sizes are as follows: Al2O3 0.5-10 μm, Y2O3 3-10 μm, TiO2 1-10 μm, ZrO2 1-10 μm, and NiO 1-10 μm. The powder consisted of 3-10 μm CuO particles and 1-10 μm CeO2 particles, with anhydrous ethanol and zirconium oxide grinding balls added. The total weight ratio of anhydrous ethanol to the seven oxide powders was 2:1, and the ball-to-powder ratio in the ball mill was 2:1. The mixture was ball-milled in a planetary ball mill at a speed of 300 r / min for 12 h. After ball milling, the mixture was thoroughly dried at 60 °C and passed through a 200-mesh sieve to obtain a uniformly mixed powder. S2. The mixed powder described in step S1 is compressed into tablets at a pressure of 20 MPa and a holding time of 1 min. The diameter of the pressed blank is 30 mm and the thickness is 4 mm. S3. Before use, the alumina crucible is dried in a drying oven at 80℃ for 2 hours. An alumina pad, pre-pressed to a pressure of 50MPa or higher, is placed at the bottom of the crucible. The blank to be sintered, obtained in step S2, is placed on top of the alumina pad inside the crucible and then placed in a microwave oven for microwave sintering. The temperature is increased to 1350℃ at a rate of 5℃ / min and held for 45 minutes. After holding, the crucible is allowed to cool naturally. The product is then tested, and the test results are shown below. Figure 1 , Figure 2 and Figure 4 .

[0029] from Figure 1 As shown in the diffraction pattern of Sample 3, the prepared sample mainly consists of a high-entropy oxide phase. A seven-element solid solution was obtained, with seven elements randomly occupying the same sublattice positions. Only weak diffraction peaks of the Ni-Al-O compound were observed, but the relative intensity of the Ni-Al-O diffraction peaks was further reduced compared to Sample 2, indicating that Ni-Al-O was further dissolved and its content was further reduced. This demonstrates that each atom is completely and well dissolved, and the prepared product is an equimolar seven-element high-entropy oxide. Furthermore, XRD diffraction pattern analysis revealed that the obtained seven-element high-entropy oxide inherits the crystal structure of ZrO2, is cubic, and belongs to space group 225 (Fm-3m).

[0030] The sample prepared in Example 3 was analyzed by SEM, such as... Figure 2 b and its enlarged illustration Figure 2 As shown in d, there are no obvious traces of a second phase, the particle surface is relatively smooth, the powder particle size is relatively uniform, the powder particle size is about 10μm, and there is no obvious particle sintering phenomenon.

[0031] from Figure 4 It can be seen that the sample contains all elements and the elements are evenly distributed, indicating the successful preparation of the equimolar ratio of the seven-member high-entropy oxide phase.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A preparation process for an equimolar ratio of seven-membered high-entropy oxides, characterized in that, Includes the following steps: S1. Seven oxide powders, Al2O3, Y2O3, TiO2, ZrO2, NiO, CuO, and CeO2, are placed in a ball mill jar in a molar ratio of 1:1:2:2:2:2:

2. Anhydrous ethanol and zirconium oxide grinding balls are added, and the mixture is ball-milled in a ball mill. After ball milling, the mixture is thoroughly dried and sieved to obtain a mixed powder. S2. The mixed powder described in step S1 is compressed into tablets to obtain a blank to be fired. S3. Place the blank to be fired described in step S2 into an alumina crucible and put it into a microwave oven for microwave sintering.

2. The preparation process of the equimolar ratio seven-member high-entropy oxide according to claim 1, characterized in that, The particle sizes of Al2O3 are 0.5-10 μm, Y2O3 are 3-10 μm, TiO2 are 1-10 μm, ZrO2 are 1-10 μm, NiO are 1-10 μm, CuO are 3-10 μm, and CeO2 are 1-10 μm.

3. The preparation process of the equimolar ratio seven-member high-entropy oxide according to claim 1, characterized in that, The total weight ratio of anhydrous ethanol to the seven oxide powders is 2-10:

1.

4. The preparation process of the equimolar ratio seven-member high-entropy oxide according to claim 1, characterized in that, The ball-to-material ratio in the ball mill jar is 2-10:

1.

5. The preparation process of the equimolar ratio seven-member high-entropy oxide according to claim 1, characterized in that, The ball mill rotates at a speed of 300-500 r / min and the milling time is 6-12 h.

6. The preparation process of the equimolar ratio seven-member high-entropy oxide according to claim 1, characterized in that, The tablet compression pressure is 10-20 MPa, and the holding time is 0.5-5 min.

7. The preparation process of the equimolar ratio seven-member high-entropy oxide according to claim 1, characterized in that, The microwave sintering process involves heating the temperature to 1200-1350℃ at a rate of 3-7℃ / min and holding it at that temperature for 45-75min.

8. The preparation process of the equimolar ratio seven-member high-entropy oxide according to any one of claims 1-7, characterized in that, The alumina crucible is dried before use, and an alumina pad is placed at the bottom of the alumina crucible beforehand.

9. An equimolar ratio heptagonal high-entropy oxide prepared by the preparation process described in any one of claims 1-8.

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