A method for preparing high-entropy ceramic based on flashover variable current and high-entropy ceramic

Abstract

This invention discloses a method for preparing high-entropy ceramics based on flash current switching and the high-entropy ceramics themselves. The method includes the following steps: 1. According to the chemical formula (Bi... 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 1) Take Bi₂O₃, BaCO₃, Na₂CO₃, SrCO₃, CaCO₃ and TiO₂ powders, mix them by wet ball milling, and dry them to obtain mixture A; 2) Place mixture A in a crucible, place the crucible in a muffle furnace for pre-calcination, and then wet ball mill, dry and sieve the pre-calcined powder to obtain (Bi 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 3. TiO3 powder; 4. Bi 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 4. TiO3 powder is placed in a mold and pressed to form a high-entropy ceramic green body; 5. The high-entropy ceramic green body is placed in a tube furnace and heated from room temperature to 650℃ at a heating rate of 10℃ / min. Then, a voltage of 150V / cm and a current density of 20~40mA / mm are applied to both ends of the ceramic green body. 2 An electric field is applied, and flash burning continues for 60 seconds after the flash burning phenomenon begins, resulting in a high-entropy ceramic with high energy storage density.

Description

Technical Field

[0001] This invention belongs to the field of lead-free ceramic materials technology, specifically a method for preparing high-entropy ceramics based on flash current and the high-entropy ceramics themselves. Background Technology

[0002] High-entropy oxides are a class of solid solution materials composed of five or more elements in a homogeneous manner. To date, a variety of single-phase multi-component compounds with different structures have been successfully synthesized, including rock salt, fluorite, perovskite, and spinel structures. These compounds have excellent mechanical, thermal, catalytic, and energy storage properties. However, the traditional synthesis of high-entropy oxides relies on the use of heating furnaces, which require long-term heating, high-temperature storage, and cooling. Excessive heating time leads to excessive growth of ceramic grains, which destroys the structural and functional properties of the densified ceramic, including hardness, strength, and energy storage capacity.

[0003] To reduce sintering temperature and time, various sintering technologies have been developed. For example, Luo et al. used spark plasma sintering to prepare (Y) at a pressure of 40 MPa. 0.2 Gd 0.2 Er 0.2 Yb 0.2 Lu 0.2 Although the sintering time of 2Zr2O7 ceramics was shortened to 5 minutes, the sintering temperature was still as high as 1600 ℃, which did not fully meet the energy-saving requirements. Wu et al. prepared (La) ceramics by sintering at a low temperature of 400-800 ℃ for 10 min using an ultra-high pressure sintering method (10 GPa). 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Eu 0.2 2Zr2O7 ceramics, however, are difficult to apply to ceramic products with complex geometries due to their high pressure requirements, expensive and specialized equipment. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing high-entropy ceramics based on flash current conversion and the high-entropy ceramics themselves, which involves short preparation time, low temperature, and high energy density.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for preparing high-entropy ceramics based on flash current switching includes the following steps:

[0007] Step 1, according to the chemical formula (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2Ca 0.2 TiO3 is obtained by taking Bi2O3, BaCO3, Na2CO3, SrCO3, CaCO3 and TiO2 powders, mixing them by wet ball milling, and then drying them to obtain mixture A;

[0008] Step 2: Place mixture A in a crucible, place the crucible in a muffle furnace for pre-calcination, and then sequentially wet-mill, dry, and sieve the pre-calcined powder to obtain (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 )TiO3 powder;

[0009] Step 3, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 powder is placed into a mold, and a preliminary blank is pressed out by mechanical force. Then, it is solidified by static pressing to obtain (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green body, with holes drilled at both ends of the ceramic green body;

[0010] Step 4, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green bodies were placed in a tube furnace and heated from room temperature to 650°C at a heating rate of 10°C / min. Then, a voltage of 150V / cm and a current density of 20~40mA / mm were applied to both ends of the ceramic green body. 2 An electric field was applied, and flash burning continued for 60 seconds after the flash burning phenomenon began. The power was then cut off, and the furnace was cooled to room temperature to obtain high-entropy ceramic (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3.

[0011] Furthermore, the wet ball milling in steps 1 and 2 is performed using wet planetary ball milling, and the mass ratio of material:ball:alcohol is 1:1.2:1.5.

[0012] Furthermore, in step 2, the pre-firing involves heating from room temperature to 870~910℃ at a heating rate of 5℃ / min for 5 hours.

[0013] Furthermore, the sieving in step 2 is through a 120-mesh sieve.

[0014] Furthermore, in step 3, the cold isostatic pressing involves placing the blank into a cold isostatic press and holding it under a pressure of 200 MPa for 3 minutes.

[0015] Furthermore, in step 4, an electric field is applied to both ends of the ceramic green body using a 1500W DC power supply.

[0016] Furthermore, the current density in step 4 is 30 mA / mm². 2 .

[0017] A high-entropy ceramic with a grain size of 0.59~1.06 μm.

[0018] Furthermore, under a breakdown electric field of 320 kV / cm, the energy storage density is 5.8 J / cm². 3 .

[0019] Compared with the prior art, the present invention has the following technical effects:

[0020] This invention, by controlling the current density during flash firing, makes the applied electric field during flash firing more conducive to promoting material diffusion and densification, significantly reducing the sintering temperature and shortening the sintering time. The flash firing time is controlled to 60s, and the flash firing temperature is controlled to 891~906℃. At the same time, it effectively inhibits excessive grain growth, controlling the ceramic grain size to 0.59~1.06 μm, thus obtaining a high-entropy ceramic with excellent energy storage performance.

[0021] At a voltage of 150V / cm and a current density of 30mA / mm 2 Under these conditions, the grain size of high-entropy ceramics prepared by 60s rapid flash calcination is significantly smaller than that of (Bi) ceramics prepared by traditional solid-state methods. 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 The grain size of TiO3 high-entropy ceramics is reduced by nearly half, and the increased grain boundary density with high resistivity is conducive to increasing the breakdown electric field, enabling high-entropy ceramics to achieve an energy storage density of up to 5.8 J / cm² under a breakdown electric field of 320 kV / cm. 3 . Attached Figure Description

[0022] Figure 1 The curves showing the change of furnace temperature with current density during the preparation of high-entropy ceramics in Examples 1 to 3 of this invention;

[0023] Figure 2 The voltage variation curves with furnace temperature during the preparation of high-entropy ceramics in Examples 1-3 of this invention;

[0024] Figures 3(a) to 3(c): SEM images of the high-entropy ceramics prepared in Examples 1 to 3 of the present invention;

[0025] Figure 4 Elemental distribution diagram of the high-entropy ceramic prepared in Example 2 of this invention;

[0026] Figure 5 XRD pattern of the high-entropy ceramic prepared in Example 2 of this invention;

[0027] Figure 6 The unipolar PE curve of the high-entropy ceramic prepared in Example 2 of this invention under the critical electric field and 10 Hz. Detailed Implementation

[0028] The specific content of the present invention will be further explained in detail below with reference to the embodiments.

[0029] The wet ball milling in Examples 1 to 3 all adopted wet planetary ball milling, and the mass ratio of material:ball:alcohol was 1:1.2:1.5.

[0030] Example 1

[0031] Step 1, according to the chemical formula (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 is obtained by taking Bi2O3, BaCO3, Na2CO3, SrCO3, CaCO3 and TiO2 powders, mixing them by wet ball milling, and then drying them to obtain mixture A;

[0032] Step 2: Place mixture A in a crucible, place the crucible in a muffle furnace, and heat it from room temperature to 870°C at a heating rate of 5°C / min for 5 hours. Then, wet-mill the pre-calcined powder, dry it, and pass it through a 120-mesh sieve to obtain (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 )TiO3 powder;

[0033] Step 3, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 powder was placed into a dog bone-shaped mold and pressed into a blank by mechanical force. The blank was then placed in a cold isostatic press and held at 200 MPa for 3 minutes to obtain a (Bi) blank with a cross-sectional dimension of 20 mm × 3 mm. 0.2 Ba0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green body, with holes drilled at both ends of the ceramic green body;

[0034] Step 4: Tie the two platinum wires from the tube furnace into the holes at both ends of the ceramic green body, so that (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green bodies are suspended in a tube furnace. Platinum wires are connected to a 1500W DC power supply via clamps. The temperature is increased from room temperature to 650℃ at a heating rate of 10℃ / min. Then, a voltage of 150V / cm and a current density of 20mA / mm are applied to both ends of the ceramic green body. 2 An electric field was applied, and flash burning continued for 60 seconds after the flash burning phenomenon began. The power was then cut off, and the furnace was cooled to room temperature to obtain high-entropy ceramic (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3.

[0035] Example 2

[0036] Step 1, according to the chemical formula (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 is obtained by taking Bi2O3, BaCO3, Na2CO3, SrCO3, CaCO3 and TiO2 powders, mixing them by wet ball milling, and then drying them to obtain mixture A;

[0037] Step 2: Place mixture A in a crucible, place the crucible in a muffle furnace, and heat it from room temperature to 890°C at a heating rate of 5°C / min for 5 hours. Then, wet-mill the pre-calcined powder, dry it, and pass it through a 120-mesh sieve to obtain (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 )TiO3 powder;

[0038] Step 3, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2TiO3 powder was placed into a dog bone-shaped mold and pressed into a blank by mechanical force. The blank was then placed in a cold isostatic press and held at 200 MPa for 3 minutes to obtain a (Bi) blank with a cross-sectional dimension of 20 mm × 3 mm. 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green body, with holes drilled at both ends of the ceramic green body;

[0039] Step 4: Tie the two platinum wires from the tube furnace into the holes at both ends of the ceramic green body, so that (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic greens are suspended in a tube furnace. Platinum wires are connected to a 1500W DC power supply via clamps, and the temperature is increased from room temperature to 650℃ at a heating rate of 10℃ / min. Then, a voltage of 150V / cm and a current density of 30mA / mm are applied to both ends of the ceramic green. 2 An electric field was applied, and flash burning continued for 60 seconds after the flash burning phenomenon began. The power was then cut off, and the furnace was cooled to room temperature to obtain high-entropy ceramic (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3.

[0040] Example 3

[0041] Step 1, according to the chemical formula (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 is obtained by taking Bi2O3, BaCO3, Na2CO3, SrCO3, CaCO3 and TiO2 powders, mixing them by wet ball milling, and then drying them to obtain mixture A;

[0042] Step 2: Place mixture A in a crucible, place the crucible in a muffle furnace, and heat it from room temperature to 910°C at a heating rate of 5°C / min for 5 hours. Then, wet-mill the pre-calcined powder, dry it, and pass it through a 120-mesh sieve to obtain (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 )TiO3 powder;

[0043] Step 3, (Bi) 0.2 Ba 0.2Na 0.2 Sr 0.2 Ca 0.2 TiO3 powder was placed into a dog bone-shaped mold and pressed into a blank by mechanical force. The blank was then placed in a cold isostatic press and held at 200 MPa for 3 minutes to obtain a (Bi) blank with a cross-sectional dimension of 20 mm × 3 mm. 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green body, with holes drilled at both ends of the ceramic green body;

[0044] Step 4: Tie the two platinum wires from the tube furnace into the holes at both ends of the ceramic green body, so that (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic greens are suspended in a tube furnace. Platinum wires are connected to a 1500W DC power supply via clamps. The temperature is increased from room temperature to 650℃ at a heating rate of 10℃ / min. Then, a voltage of 150V / cm and a current density of 40mA / mm are applied to both ends of the ceramic green. 2 An electric field was applied, and flash burning continued for 60 seconds after the flash burning phenomenon began. The power was then cut off, and the furnace was cooled to room temperature to obtain high-entropy ceramic (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3.

[0045] The high-entropy ceramics prepared in Examples 1 to 3 were polished, ground, and cleaned in sequence to obtain samples with a thickness of 0.1 to 0.15 mm. Gold electrodes with a diameter of 1.5 mm were sprayed onto both sides of the samples using a magnetron sputtering instrument to obtain samples for testing ferroelectric properties.

[0046] from Figure 1 It can be seen that under different current densities, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramics all exhibited flash burning characteristics. It is obvious that the onset temperature of flash burning is very close under different current densities, indicating that the current density has a negligible effect on the onset temperature of flash burning.

[0047] from Figure 2It can be seen that the voltage change with temperature during the flash burning process includes three stages: the incubation period, the flash burning period, and the steady state period. During the incubation period, the electric field strength is the same as the constant voltage output at the beginning. After the flash burning phenomenon occurs, the voltage gradually decreases with the increase of temperature to the steady state period, fluctuating within a small range.

[0048] As can be seen from Figures 3(a) to 3(b), the high-entropy ceramic samples prepared in Examples 1 to 3 all exhibit a dense morphology and low porosity, indicating that flash calcination in a very short time can achieve ceramic densification. Nano Measurer software was used to calculate 20–40 mA / mm². 2 The average grain sizes of the ceramics at the specified current densities are shown in Table 1, which are 0.59 μm, 0.68 μm, and 1.06 μm, respectively. Clearly, the grain size gradually increases with increasing current density, suggesting that the grain growth and densification processes in the flash-fired samples are mainly controlled by current density. Higher current densities lead to higher steady-state power dissipation, resulting in higher sample temperatures through Joule heating, providing sufficient driving force for grain growth and densification, ultimately leading to their realization. Similarly, the shrinkage rates of the high-entropy ceramic samples before and after flash-fire were calculated, as shown in Table 1. Notably, the shrinkage rate did not increase with increasing grain size, even at 20 mA / mm². 2 At a current density of 40 mA / mm², the grain size is the smallest, but the low current density leads to uneven grain growth, with some grains accumulating together and accompanied by a small number of pores. 2 At this point, the grain size increases significantly, the sample exhibits bending, and the shrinkage rate decreases, reaching the current density threshold. This is especially true at 30 mA / mm². 2 At the current density, the grain size of the high-entropy ceramic prepared is similar to that of (Bi) ceramics previously prepared by the inventors' team using a solid-state method. 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 Compared to TiO3, the grain size has been reduced by nearly half, achieving the goal of controlling the ceramic grain size through flash firing, thereby improving energy storage performance.

[0049] Table 1. Preparation of high-entropy ceramics (Bi) at different current densities 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 The flash sintering initiation temperature, average grain size, and shrinkage rate of TiO3 ceramics.

[0050]

[0051] from Figure 4 It can be seen that the elements are evenly distributed in the high-entropy ceramic prepared in Example 2, indicating that the solid solution reaction was completed within a dozen seconds of flash calcination, forming a single-phase structure. This proves that flash calcination can accelerate the mass transfer rate, realize the rapid synthesis of high-entropy oxides, and after rapid solid solution, the metal elements are very evenly distributed in the crystal.

[0052] from Figure 5 It can be seen that the flash calcination method can prepare single-phase high-entropy ceramics with dense and uniform microstructure in just 60 s, proving that the electric field promotes the single-phase formation rate and overcomes the hindrance effect of the sluggish diffusion effect of high-entropy ceramics on the diffusion of matter.

[0053] from Figure 6 It can be seen that, under a breakdown electric field of 320 kV / cm, the high-entropy ceramic prepared in Example 2 exhibits the optimal energy storage density of 5.8 J / cm. 3 Bi 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 The energy storage density of TiO3 high-entropy ceramics is only [missing information]. W rec ≈2.2 J / cm 3 As can be seen, the high-entropy ceramic prepared in Example 2 has a significantly improved energy storage density compared to the high-entropy ceramic prepared by the traditional sintering method. The increase in energy storage density relies on the combined effect of polarization difference and breakdown electric field. On the one hand, the external electric field of flash sintering promotes the diffusion and densification process of the material, significantly reduces the sintering temperature and shortens the sintering time, effectively inhibits excessive grain growth, and the increased grain boundary density with high resistivity is conducive to the increase of breakdown electric field. On the other hand, under the action of the external electric field, a large number of defects are introduced into the flash sintering sample. During the movement of internal charges in the ceramic under the action of the electric field, these defects are captured, causing local accumulation of charges and uneven charge distribution, thereby increasing polarization.

Claims

1. A method for preparing high-entropy ceramics based on flash current, characterized in that, Includes the following steps: Step 1, according to the chemical formula (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 is obtained by taking Bi2O3, BaCO3, Na2CO3, SrCO3, CaCO3 and TiO2 powders, mixing them by wet ball milling, and then drying them to obtain mixture A; Step 2: Place mixture A in a crucible, place the crucible in a muffle furnace for pre-calcination, and then sequentially wet-mill, dry, and sieve the pre-calcined powder to obtain (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 )TiO3 powder; Step 3, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 powder is placed into a mold, and a preliminary blank is pressed out by mechanical force. Then, it is solidified by static pressing to obtain (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green body, with holes drilled at both ends of the ceramic green body; Step 4, (Bi) 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3 high-entropy ceramic green bodies were placed in a tube furnace and heated from room temperature to 650°C at a heating rate of 10°C / min. Then, a voltage of 150V / cm and a current density of 20~40mA / mm were applied to both ends of the ceramic green body. 2 An electric field was applied, and flash burning continued for 60 seconds after the flash burning phenomenon began. The power was then cut off, and the furnace was cooled to room temperature to obtain high-entropy ceramic (Bi). 0.2 Ba 0.2 Na 0.2 Sr 0.2 Ca 0.2 TiO3.

2. The method for preparing high-entropy ceramics based on flash current according to claim 1, characterized in that, Both steps 1 and 2 involve wet planetary ball milling, with a material-to-ball-to-alcohol mass ratio of 1:1.2:1.

5.

3. The method for preparing high-entropy ceramics based on flash current according to claim 1, characterized in that, The pre-firing in step 2 involves heating from room temperature to 870~910℃ at a rate of 5℃ / min for 5 hours.

4. The method for preparing high-entropy ceramics based on flash current according to claim 1, characterized in that, The sieving in step 2 is through a 120-mesh sieve.

5. The method for preparing high-entropy ceramics based on flash current according to claim 1, characterized in that, The cold isostatic pressing in step 3 involves placing the blank into a cold isostatic press and holding it under a pressure of 200 MPa for 3 minutes.

6. The method for preparing high-entropy ceramics based on flash current according to claim 1, characterized in that, Step 4 uses a 1500W DC power supply to apply an electric field to both ends of the ceramic green body.

7. The method for preparing high-entropy ceramics based on flash current according to claim 1, characterized in that, The current density in step 4 is 30 mA / mm. 2 .

8. A high-entropy ceramic prepared by the method for preparing high-entropy ceramics based on flash current as described in any one of claims 1 to 7, characterized in that, The size of the ceramic grains is 0.59~1.06 μm.

9. The high-entropy ceramic according to claim 8, characterized in that, At a breakdown electric field of 320 kV / cm, the energy storage density is 5.8 J / cm². 3 .

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