Fluorite-pyrochlore double-phase high-entropy oxide ceramic powder and preparation method thereof

Abstract

The invention discloses fluorite-pyrochlore double-phase high-entropy oxide ceramic powder and a preparation method thereof, and relates to the technical field of high-performance ceramics. The preparation method comprises the following steps: (1) weighing ZrO2 powder, HfO2 powder, Pr6O11 powder, La2O3 powder and Sm2O3 powder with equal atomic percent, putting the ZrO2 powder, the HfO2 powder, the Pr6O11 powder, the La2O3 powder and the Sm2O3 powder into a crucible, and calcining in a muffle furnace to remove moisture and impurities; (2) carrying out ball-milling mixing on the calcined ZrO2 powder, HfO2 powder, Pr6O11 powder, La2O3 powder and Sm2O3 powder, and drying and grinding in a drying box after ball-milling to obtain high-entropy ceramic oxide precursor powder; and (3) putting the high-entropy ceramic oxide precursor powder into a muffle furnace, carrying out heat treatment in an air atmosphere, and cooling and grinding to obtain the high-entropy oxide ceramic powder with the fluorite-pyrochlore dual-phase structure. The chemical formula of the prepared double-phase high-entropy ceramic powder material is (Zr, Hf, Pr, La, Sm) O < 2-delta >, and the double-phase high-entropy ceramic powder material is of a fluorite-pyrochlore double-phase structure, and has low heat conductivity, high thermal expansion coefficient and good heat-conducting property.

Description

Technical Field

[0001] The invention relates to the technical field of high-performance ceramics, and in particular to a fluorite-pyrochlore dual-phase high-entropy oxide ceramic powder and a preparation method thereof. Background Art

[0002] High entropy ceramics, also known as high entropy compounds, are a class of solid solutions of inorganic compounds. The concept of high entropy materials is mainly derived from high entropy alloys, which aim to maximize the entropy value of the material system configuration by mixing a variety of different elements, thereby stabilizing a variety of phases and ultimately forming a solid solution that can maintain a stable single-phase structure at room temperature. Compared with traditional ceramic powders, high entropy ceramics have a more complex chemical composition and structure. They are usually composed of multiple elements that are more evenly distributed in the material and have no obvious lattice structure, but rather present a relatively disordered amorphous structure.

[0003] As a type of high entropy ceramics, high entropy oxide ceramics show great potential in applications such as radiation resistance, thermoelectricity, catalysis, coatings and energy storage. At present, fluorite and pyrochlore high entropy oxides show excellent performance in the field of coatings and have attracted widespread attention. However, materials with high hardness, low conductivity and high melting point in existing research are mostly concentrated on fluorite and pyrochlore single-phase high entropy oxides, while fluorite and pyrochlore single-phase high entropy oxides have the problem of low thermal conductivity. At present, in the latest fluorite-pyrochlore dual-phase high entropy ceramic synthesis strategy, the chemical formula prepared is A2B2O7 type, and there is no report on AO-type fluorite-pyrochlore dual-phase high entropy ceramics, which limits the diversity of high entropy fluorite-pyrochlore dual-phase ceramics and the possibility of breakthroughs in performance. Therefore, the present invention provides a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder and a preparation method thereof. Summary of the invention

[0004] The purpose of the present invention is to provide a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder and a preparation method thereof, so as to improve the thermal conductivity of the high entropy ceramic powder material.

[0005] To achieve the above object, the present invention provides a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder, the chemical formula of the dual-phase high entropy ceramic powder material is (Zr, Hf, Pr, La, Sm)O 2-δ , which is a fluorite-pyrochlore dual-phase structure, in which the molar ratio of Zr:Hf:Pr:La:Sm is 1:1:1:1:1.

[0006] The present invention also provides a method for preparing the above-mentioned fluorite-pyrochlore dual-phase high entropy oxide ceramic powder, comprising the following steps:

[0007] (1) Weigh out ZrO2, HfO2, Pr6O 11, La2O3, and Sm2O3 powders are placed in a crucible and calcined in a muffle furnace to remove moisture and impurities;

[0008] (2) The calcined ZrO2, HfO2, and Pr6O 11 , La2O3, and Sm2O3 powders are mixed by ball milling, and after the ball milling, they are placed in a drying oven for drying and grinding to obtain high entropy ceramic oxide precursor powders;

[0009] (3) placing the high entropy ceramic oxide precursor powder in a muffle furnace, performing heat treatment in an air atmosphere, and obtaining a high entropy oxide ceramic powder having a fluorite-pyrochlore dual-phase structure after cooling and grinding.

[0010] Preferably, in step (1), the calcination temperature in the muffle furnace is 900° C. and the calcination time is 2 h.

[0011] Preferably, in step (2), the powder is placed in a planetary ball mill for ball milling, the ball milling medium is ethanol, the ball milling speed is 280-330 r / min, the ball milling time is 10 h, and the ball-to-material ratio is 1:10.

[0012] Preferably, in step (2), the drying temperature is 60 to 120° C. and the drying time is 12 to 20 hours.

[0013] Preferably, in step (3), the heat treatment method is staged calcination, first heating to 1200°C at 5°C / min, then heating to 1500°C at 2°C / min, then heating to 1600°C at 1°C / min, and then calcining at 1600°C for 5h.

[0014] Preferably, in step (3), the cooling method is staged cooling. After the calcination is completed, the temperature is first lowered to 1500°C at a rate of 1°C / min, then lowered to 1200°C at a rate of 2°C / min, and then lowered to 500°C at a rate of 5°C / min to cool with the furnace.

[0015] Therefore, the present invention provides a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder and a preparation method thereof, and the specific beneficial effects are as follows:

[0016] 1. The high entropy ceramic powder prepared by the present invention has two crystal structures, fluorite phase and pyrochlore phase. The fluorite phase is the Fm-3m space group, and its specific composition is often manifested as interlaced twins, in which anions are arranged in the most densely packed manner, and cations occupy the regular tetrahedral voids; the pyrochlore phase belongs to the Oh7-Fd-3m isometric crystal system, and there are usually two cations inside it that achieve overall valence electron balance, in which the cations with larger ionic radius and the oxygen ions form oxygen octahedral vertex arrangement to form a crystal skeleton structure, and the cations with smaller ionic radius are located in the gaps of the oxygen octahedral crystal skeleton. The two phases coexist in the high entropy lattice, and have the characteristics of high purity, stable phase structure and uniform element distribution;

[0017] 2. The high entropy ceramic powder prepared by the present invention uses the cubic rare earth multivalent element Pr as the matrix to control the formation of two phases. As a solid solution substrate, it is easier to grow fluorite and pyrochlore phases with the same cubic structure. At the same time, due to the coexistence of multiple valence states, the disordered electrons in the high entropy system can reach a balanced state, thereby making the structure more stable. 4+ As the matrix of fluorite phase formation, Hf 4+ The ionic radius is similar to that of La, making it easier to integrate into the system and maintain stability. 3+ and Sm 3+ As large-radius ions, they increase the radius difference inside the system, increase the degree of lattice distortion, and thus increase the defect density to achieve the effect of reducing thermal conductivity and enhancing hardness.

[0018] 3. After long-term calcination, the high-entropy ceramic powder prepared by the present invention does not undergo any phase decomposition reaction, has an extremely low thermal conductivity (0.827 W / m·℃) at 100℃, and a thermal conductivity of 1.40 W / m·℃ at 1100℃. The thermal expansion coefficient at 1100℃ reaches 11.60×10 -6 ℃ -1 Compared with single-phase fluorite and single-phase pyrochlore high entropy oxides, dual-phase high entropy ceramic materials have lower thermal conductivity and higher thermal expansion coefficient;

[0019] 4. The present invention adopts mechanical wet grinding and solid phase reaction preparation, which can ensure sufficient and uniform mixing of elements, and has the advantages of simple operation, short production cycle and industrialization.

[0020] Among them, the reasons why the above-mentioned dual-phase high entropy oxide ceramic powder prepared by the present invention has lower thermal conductivity and higher thermal expansion coefficient are mainly as follows:

[0021] (1) The differences in radius and mass of various elements cause an increase in internal disorder and a corresponding increase in lattice distortion, which leads to an increase in oxygen vacancy concentration, enhances phonon scattering, and thus reduces thermal conductivity;

[0022] (2) The two-phase structure is at the critical point between disorder and order, and the lattice distortion and relaxation are more obvious, resulting in a reduction in the phonon free path. Specifically, the emergence of the two-phase structure leads to more severe scattering of the phonons in the heat conduction process at the interface between different phases, thus causing a decrease in thermal conductivity.

[0023] (3) The heat transfer coefficients between different phases are different, which will also increase the resistance to heat transfer. At the same time, the appearance of the second phase increases the density of defects inside the lattice, resulting in a decrease in thermal conductivity.

[0024] (4) The lattice parameter of the pyrochlore phase in the dual-phase ceramic is relatively large. Generally speaking, materials with larger lattice parameters will also cause larger dimensional changes during the heating process, resulting in an increase in the thermal expansion coefficient.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Example 1 (Zr, Hf, Pr, La, Sm)O of the present invention 2-δ XRD pattern of

[0027] Figure 2 Example 2 (Zr, Hf, Pr, La, Sm)O 2-δ XRD pattern of

[0028] Figure 3 Example 1 (Zr, Hf, Pr, La, Sm)O of the present invention 2-δ SEM-EDS images of

[0029] Figure 4 Example 1 (Zr, Hf, Pr, La, Sm)O of the present invention 2-δ Thermal conductivity versus temperature graph;

[0030] Figure 5 Example 1 (Zr, Hf, Pr, La, Sm)O of the present invention 2-δ The thermal expansion coefficient varies with temperature;

[0031] Figure 6 Example 1 (Zr, Hf, Pr, La, Sm)O of the present invention 2-δ XRD pattern after annealing at 1600℃ for 30h. DETAILED DESCRIPTION

[0032] The present invention provides a fluorite-pyrochlore dual-phase high entropy ceramic powder, the chemical formula of the dual-phase high entropy ceramic powder material is (Zr, Hf, Pr, La, Sm)O 2-δ, which is a fluorite-pyrochlore two-phase structure, in which each element exists in an equimolar ratio, and δ depends on the concentration of oxygen vacancies in the structure.

[0033] The thermal conductivity of the high entropy dual-phase ceramic powder material is 0.827W / m·℃~1.40W / m·℃ in the temperature range of 100~1100℃, and the thermal expansion coefficient reaches 11.60×10 -6 ℃ -1 , and also has good high temperature phase stability (1600℃).

[0034] The present invention also provides a method for preparing the above-mentioned fluorite-pyrochlore dual-phase high entropy ceramic powder material, comprising the following steps:

[0035] (1) Select ZrO2, HfO2, Pr6O with equal atomic percentages 11 , La2O3, and Sm2O3 powders are used as raw materials, and each rare earth and metal element is introduced in an equal molar ratio. After weighing, the powder mixture is placed in a crucible and calcined at 900°C in a muffle furnace for 2 hours to remove moisture and impurities.

[0036] (2) A planetary ball mill is used for ball milling, the ball milling medium is ethanol, the ball milling speed is 280-330 r / min, the ball milling time is 10 h, and the ball-to-material ratio is 1:10. The product is then placed in a drying oven and dried at 60-120° C. for 12-20 h and then ground to obtain a high entropy ceramic oxide precursor powder.

[0037] (3) The high entropy ceramic oxide precursor powder was placed in a muffle furnace and calcined in an air atmosphere. The temperature was first increased to 1200°C at 5°C / min, then increased to 1500°C at 2°C / min, and then increased to 1600°C at 1°C / min. The powder was then calcined at 1600°C for 5 h. After calcination, the temperature was decreased to 1500°C at a rate of 1°C / min, then decreased to 1200°C at a rate of 2°C / min, and then decreased to 500°C at a rate of 5°C / min. The powder was cooled in the furnace and ground to obtain a sintered dual-phase (Zr, Hf, Pr, La, Sm)O 2-δ High entropy ceramic powder materials.

[0038] The present invention is further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, simplifications made without violating the spirit and principle of the present invention should all be equivalent replacement methods and are included in the protection scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application, and all belong to the scope of protection of the present invention.

[0039] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0040] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0041] Unless otherwise specified in the present invention, the reagents, instruments, and equipment used are those commonly used by technicians in this field.

[0042] Example 1

[0043] This embodiment provides a method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder, comprising the following steps:

[0044] (1) ZrO2 (1.2322 g), HfO2 (2.105 g), Pr6O 11 (1.7024 g), La2O3 (1.629 g), and Sm2O3 (1.7436 g) powders were placed in a crucible and calcined at 900°C in a muffle furnace for 2 h to remove moisture and impurities.

[0045] (2) A planetary ball mill was used for ball milling, the ball milling medium was ethanol, the ball-to-material ratio was 1:10, and the ball milling was first performed for half an hour in a clockwise direction at a speed of 280 r / min, followed by a 10-minute pause, and then a half-hour counterclockwise ball milling was performed at a speed of 280 r / min, followed by a 10-minute pause, which was a cycle, with a total effective ball milling time of 10 hours. Then, the product was dried at 100° C. for 14 hours and then fully ground to obtain a high-entropy ceramic oxide precursor powder.

[0046] (3) The high entropy ceramic oxide precursor powder was placed in a muffle furnace and calcined in an air atmosphere. The temperature was first increased to 1200°C at 5°C / min, then increased to 1500°C at 2°C / min, and then increased to 1600°C at 1°C / min. The powder was then calcined at 1600°C for 5 h. After calcination, the temperature was decreased to 1500°C at a rate of 1°C / min, then decreased to 1200°C at a rate of 2°C / min, and then decreased to 500°C at a rate of 5°C / min. The powder was cooled in the furnace and ground to obtain a sintered dual-phase (Zr, Hf, Pr, La, Sm)O 2-δ High entropy ceramic powder materials.

[0047] The (Zr, Hf, Pr, La, Sm)O prepared in this example 2-δ High entropy ceramic powder material was tested by X-ray diffraction, and the results showed Figure 1 As shown. Figure 1 It can be seen that the diffraction peaks correspond to fluorite and pyrochlore dual phases, indicating that fluorite-pyrochlore dual phase structure high entropy ceramics are obtained.

[0048] The (Zr, Hf, Pr, La, Sm)O prepared in this example 2-δ SEM-EDS images of high entropy ceramic powder materials are shown below: Figure 3 As shown. Figure 3 It can be seen that (Zr, Hf, Pr, La, Sm)O 2-δ The high-entropy ceramic powder material has successfully achieved high-density sintering, and there are no obvious pores on the surface. No obvious segregation or aggregation of other elements was observed, indicating that the five elements were successfully dissolved in the high-entropy lattice.

[0049] (Zr,Hf,Pr,La,Sm)O 2-δ The thermal conductivity of the high entropy ceramic powder material is calculated based on the thermal diffusion coefficient measured by the laser method; the thermal expansion coefficient is measured using a high-temperature dilatometer produced by Netzsch DIL402SE of Germany. The test range of thermal conductivity and thermal expansion coefficient is 25-1100℃; the dual-phase high entropy ceramic powder material is placed in a high-temperature box furnace for 30h high-temperature thermal stability test.

[0050] Take 0.5 g of (Zr, Hf, Pr, La, Sm)O prepared in this example 2-δ High entropy ceramic powder material, thermal conductivity changes with temperature as Figure 4 As shown. Figure 4 It can be seen that its thermal conductivity is 0.827W / m·℃~1.40W / m·℃ in the temperature range of 100~1100℃. The thermal expansion coefficient changes with temperature as shown in Figure 5 As shown by Figure 5 It can be seen that its thermal expansion coefficient reaches 11.60×10 at a temperature of 1100°C. -6℃ -1 .

[0051] The (Zr, Hf, Pr, La, Sm)O prepared in this example 2-δ The high entropy dual-phase ceramic powder material was annealed at 1600℃ for 30h and then subjected to X-ray diffraction testing. The results are as follows: Figure 6 As shown. Figure 6 It can be seen that the powder material still maintains the fluorite-pyrochlore dual-phase structure, indicating that the high-entropy dual-phase ceramic powder material has excellent high-temperature phase stability.

[0052] Example 2

[0053] This embodiment provides a method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder, comprising the following steps:

[0054] (1) Weigh ZrO2 (2.4644 g), HfO2 (4.21 g), Pr6O 11 (3.4048 g), La2O3 (3.258 g), and Sm2O3 (3.4872 g) powders were placed in a crucible and calcined at 900°C in a muffle furnace for 2 h to remove moisture and impurities.

[0055] (2) A planetary ball mill was used for ball milling, the ball milling medium was ethanol, the ball-to-material ratio was 1:10, and the ball milling was first performed for half an hour in a clockwise direction at a speed of 330 r / min, followed by a pause of 10 minutes, and then the counterclockwise ball milling was performed for half an hour at a speed of 330 r / min, followed by a pause of 10 minutes, which was a cycle, and the total effective ball milling time was 10 hours. Then, the powder was dried at 120° C. for 12 hours and then fully ground to obtain a high entropy ceramic oxide precursor powder.

[0056] (3) The high entropy ceramic oxide precursor powder was placed in a muffle furnace and calcined in an air atmosphere. The temperature was first increased to 1200°C at 5°C / min, then increased to 1500°C at 2°C / min, and then increased to 1600°C at 1°C / min. The powder was then calcined at 1600°C for 5 h. After calcination, the temperature was decreased to 1500°C at a rate of 1°C / min, then decreased to 1200°C at a rate of 2°C / min, and then decreased to 500°C at a rate of 5°C / min. The powder was cooled in the furnace and ground to obtain a sintered dual-phase (Zr, Hf, Pr, La, Sm)O 2-δ High entropy ceramic powder materials.

[0057] The (Zr, Hf, Pr, La, Sm)O prepared in this example 2-δ High entropy ceramic powder material was tested by X-ray diffraction, and the results showed Figure 2 As shown. Figure 2It can be seen that the diffraction peaks correspond to fluorite and pyrochlore dual phases, indicating that fluorite-pyrochlore dual phase structure high entropy ceramics are obtained.

[0058] The (Zr, Hf, Pr, La, Sm)O prepared in this example 2-δ The thermal conductivity, thermal expansion coefficient and thermal stability test of high entropy ceramic powder material are the same as those in Example 1. Take 0.5g (Zr, Hf, Pr, La, Sm) O 2-δ High entropy ceramic powder material, the thermal conductivity of the material is measured to be 0.825W / m·℃~1.39W / m·℃ in the temperature range of 100~1100℃, and the thermal expansion coefficient reaches 11.70×10-6·℃ at a temperature of 1100℃ -1 The high entropy ceramic powder material still maintains a fluorite-pyrochlore dual-phase structure after annealing at 1600°C for 30 hours, and has excellent high-temperature phase stability.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A fluorite-pyrochlore dual-phase high entropy oxide ceramic powder, It is characterized in that The chemical formula of the dual-phase high entropy ceramic powder material is (Zr, Hf, Pr, La, Sm)O 2-δ , which is a fluorite-pyrochlore dual-phase structure, in which the molar ratio of Zr:Hf:Pr:La:Sm is 1:1:1:1:

1.

2. A method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder as claimed in claim 1, It is characterized in that The following steps are involved: (1) Weigh out ZrO with equal atomic percentage 2 , HfO 2 , Pr 6 O 11 ,La 2 O 3 、Sm 2 O 3 The powder is placed in a crucible and calcined in a muffle furnace to remove moisture and impurities; (2) After calcination, ZrO 2 , HfO 2 , Pr 6 O 11 ,La 2 O 3 、Sm 2 O 3 The powders are mixed by ball milling, and after the ball milling, they are placed in a drying oven for drying and grinding to obtain high entropy ceramic oxide precursor powders; (3) placing the high entropy ceramic oxide precursor powder in a muffle furnace, performing heat treatment in an air atmosphere, and obtaining a high entropy oxide ceramic powder having a fluorite-pyrochlore dual-phase structure after cooling and grinding.

3. The method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder according to claim 2, Features: In the step (1), the calcination temperature in the muffle furnace is 900° C. and the calcination time is 2 hours.

4. The method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder according to claim 2, Features: In the step (2), the powder is placed in a planetary ball mill for ball milling, the ball milling medium is ethanol, the ball milling speed is 280-330 r / min, the ball milling time is 10 h, and the ball-to-material ratio is 1:

10.

5. The method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder according to claim 2, Features: In the step (2), the drying temperature is 60 to 120° C. and the drying time is 12 to 20 hours.

6. The method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder according to claim 2, Features: In the step (3), the heat treatment method is staged calcination, firstly heating to 1200°C at 5°C / min, then heating to 1500°C at 2°C / min, then heating to 1600°C at 1°C / min, and then calcining at 1600°C for 5h.

7. The method for preparing a fluorite-pyrochlore dual-phase high entropy oxide ceramic powder according to claim 2, Features: In the step (3), the cooling method is staged cooling. After the calcination is completed, the temperature is first lowered to 1500°C at a rate of 1°C / min, then lowered to 1200°C at a rate of 2°C / min, and then lowered to 500°C at a rate of 5°C / min to cool along with the furnace.

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