A two-stage method for preparing fine-grained ceramics using cold sintering-flash sintering technology

Abstract

This invention relates to a two-step method for preparing fine-grained ceramics using a cold sintering-flash calcination technique. The method includes: mixing fine-grained ceramic raw material powders into a mixed raw material and pressing it into shape; first, cold sintering to obtain a sample; and then flash calcining the sample. This method can prepare dense fine-grained ceramics at lower temperatures and in a shorter time, and it improves upon the problem of significant non-uniformity in density and grain size distribution in flash-calcined samples, providing a novel method for preparing fine-grained ceramic materials.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, and in particular relates to a two-stage method for preparing fine-grained ceramics using cold sintering-flash sintering technology. Background Technology

[0002] Fine-grained ceramics are generally considered to be bulk materials with a grain size of less than 1 μm and close-packed grains. Due to the small size effect, fine-grained ceramics possess a series of properties that differ from conventional homogeneous materials; these generally include extremely high hardness, wear resistance, corrosion resistance, thermal stability, and high-temperature mechanical properties. Therefore, they are widely used in cutting tools, aerospace and marine applications, electronic engineering, nuclear power, and other fields.

[0003] Traditional ceramic preparation methods include solid-state sintering, which suffers from drawbacks such as poor chemical composition uniformity, large grain size, low electro-optic properties, and poor repeatability of physical properties. Vacuum sintering has a narrow adjustable range of heat source characteristics, and grain proliferation can occur during sintering when using small-particle raw materials. Self-propagating combustion can synthesize some fine-grained compounds and composites in a very short time, but results show that the resulting materials have high porosity, mostly exceeding 10%, and mechanical properties cannot be guaranteed. In summary, to prepare high-performance fine-grained ceramics, new preparation technologies are needed, including new mixing, forming, and sintering techniques.

[0004] In 2010, Raj, an Indian professor at the University of Colorado, discovered that 3YSZ material could be densified within seconds at 850°C by applying an external DC electric field. Because the material rapidly shrinks and densifies in a short time, this sintering technique was named "flash sintering." Flash sintering uses simple equipment, has a low sintering temperature, a fast sintering speed, a short holding time, and requires no sintering aids, making it an excellent and innovative technique. However, due to the influence of sample temperature distribution and internal defect reactions, the density and grain size distribution of flash-sintered samples exhibit significant non-uniformity.

[0005] In 2016, Professor Randall's research team at Pennsylvania State University developed a cold sintering process (CSP) for ceramics and ceramic matrix composites; cold sintering is an ultra-low energy sintering technology.

[0006] Based on experimental research results on cold sintering and flash sintering technologies, we provide a two-step ceramic preparation method using cold sintering-flash sintering technology, offering a novel approach for the preparation of fine-grained ceramic materials. Summary of the Invention

[0007] To address the shortcomings of existing technologies, and considering that the grain growth of fine-grained ceramics is mainly affected by sintering temperature and sintering time, this invention provides a two-step method for preparing fine-grained ceramics using cold sintering-flash sintering technology. This method can prepare dense fine-grained ceramics at lower temperatures and in shorter times, and improves the problem of significant non-uniformity in density and grain size distribution of flash-sintered samples. This provides a novel method for preparing fine-grained ceramic materials.

[0008] Therefore, the present invention provides a two-step method for preparing fine-grained ceramics using cold sintering-flash sintering technology, comprising: mixing fine-grained ceramic raw material powder into a mixed raw material and pressing it into shape, first performing cold sintering to obtain a sample, and then flash sintering the sample.

[0009] In some embodiments of the present invention, the cold sintering conditions include: heating at 5-8°C / min to 180-220°C and cold sintering for 60-120 min.

[0010] According to the present invention, the cold sintering conditions include: heating to 180°C at a rate of 5°C / min and cold sintering for 60 min.

[0011] In some embodiments of the present invention, a pressure of 300-350 MPa is continuously applied during the cold sintering process.

[0012] According to the present invention, a uniaxial pressure of 300-350 MPa is continuously applied during the cold sintering process.

[0013] According to the present invention, a uniaxial pressure of, for example, 300 MPa, 310 MPa, 320 MPa, 340 MPa or 350 MPa is continuously applied during the cold sintering process.

[0014] In some embodiments of the present invention, the flash burning includes point contact flash burning, non-contact flash burning, discharge plasma flash burning, multilayer flash burning of tape casting, or graphite-assisted flash burning.

[0015] According to the present invention, the flash burning includes point contact flash burning or discharge plasma flash burning.

[0016] In some embodiments of the present invention, the conditions for point-contact flash burning include: heating to 1010-1050°C, applying a constant voltage of 280-350V to the sample, and flash burning for 30-60 seconds with a preset maximum limiting current of 0.38-0.42 A.

[0017] In some embodiments of the present invention, the conditions for the discharge plasma flash burning include: setting the peak power to 1-10 kW, the peak voltage to 10-20V, and the peak current to 100-2000A for flash burning for 10-60s.

[0018] In some embodiments of the present invention, after the cold sintering process is completed, the temperature is reduced to 60°C at a rate of 3-5°C / min, and then naturally cooled to room temperature.

[0019] In some embodiments of the present invention, the sample is cold-sintered and then naturally cooled to room temperature in the furnace, and then vacuum-dried at 55-60°C for 6-12 hours to constant weight.

[0020] In some embodiments of the present invention, the preparation method includes the following specific steps:

[0021] S1: Weigh the corresponding molar amount of fine-grained ceramic raw material powder according to the chemical formula or reaction formula of fine-grained ceramic, mix them into mixed raw materials, add ball milling beads and ball milling media, and perform wet ball milling to form raw material slurry;

[0022] S2: The raw material slurry prepared in step S1 is dried to obtain a mixed powder;

[0023] S3: Add the mixed powder prepared in step S2 to deionized water to form a mixed slurry, put the mixed slurry into a mold, and apply a pressure of 300-350 MPa at room temperature;

[0024] S4: After step S3, continue to apply a pressure of 300-350 MPa and heat to 180-220℃ at 5-8℃ / min for 60-120 min to obtain the sample; after the end, cool down to 60℃ at 3-5℃ / min and remove the sample after it has cooled to room temperature; then vacuum dry the sample at 55-60℃ for 6h-12h until constant weight.

[0025] S5: Perform point contact flash burning or discharge plasma flash burning on the sample after cold sintering in step S4.

[0026] In some embodiments of the present invention, the fine-grained ceramic raw material powder includes ceramic raw material powder capable of flash sintering.

[0027] According to the present invention, the particle size of the fine-grained ceramic raw material powder is <1μm.

[0028] In some embodiments of the present invention, wet ball milling is performed at a speed of 55-75 rpm for 24 hours in step S1.

[0029] In some embodiments of the present invention, in step S2, the raw material slurry is first stirred at a speed of 120-200 rpm and a temperature of 70-90°C for 5-10 minutes, and then the raw material slurry is placed in a vacuum oven, vacuumed to 0.04-0.06 MPa, and dried at a temperature of 55-70°C for 6-10 hours.

[0030] In some embodiments of the present invention, the particle size of the mixed powder obtained in step S2 is 40-200 nm.

[0031] In some embodiments of the present invention, the conditions for point contact flash burning in step S5 include: heating to 1010-1050°C, applying a constant voltage of 280-350V to the sample, and flash burning for 30-60s with a preset maximum limiting current of 0.38-0.42 A.

[0032] In some embodiments of the present invention, the conditions for flash burning of the discharge plasma in step S5 include: setting the peak power to 1-10 kW, the peak voltage to 10-20V, and the peak current to 100-2000A for flash burning for 10-60s.

[0033] In some embodiments of the present invention, in step S3, a corresponding mass of mixed powder is weighed according to the size of the mold and 25%-30% of deionized water by mass of the mixed powder is added and thoroughly mixed and ground to form a mixed slurry.

[0034] According to the present invention, 0.6-1.0g of mixed powder is weighed in step S3.

[0035] In some embodiments of the present invention, the mixed slurry is loaded into a dog bone mold or a cylindrical mold with a diameter of 12-14 mm.

[0036] In some embodiments of the present invention, the sample obtained in step S4 may be in the form of a dog bone, a cylinder, or a disc.

[0037] According to the present invention, when point contact flash burning is used in step S5, the sample obtained in step S4 is a dog bone-shaped sample.

[0038] According to the present invention, when the discharge plasma flash burning is used in step S5, the sample obtained in step S4 is a disc-shaped sample.

[0039] According to the present invention, before the point contact flash burning, holes are made at both ends of the dog bone-shaped sample, platinum paste is coated on the inner wall of the hole and dried, and a platinum wire is inserted into the hole coated with platinum paste and electrically connected to the electrode.

[0040] According to the present invention, the diameter of the holes at both ends of the dog bone-shaped sample is 1-1.6 mm, and the distance between the two holes is 15-20 mm.

[0041] In some embodiments of the present invention, in step S1, the mixed raw materials are loaded into a mixing bottle, and then 15%-25% of the volume of the mixing bottle is added with grinding balls; wherein the volume percentage of the grinding balls with a diameter of 2mm is 20%-30%, and the volume percentage of the grinding balls with a diameter of 5mm is 70%-80%.

[0042] According to the present invention, the grinding beads are zirconia grinding beads.

[0043] In some embodiments of the present invention, the amount of ball milling media added in step S1 is 10%-50% of the mass of the mixed raw materials.

[0044] According to the present invention, the ball milling medium is anhydrous ethanol.

[0045] According to the present invention, the fine-grained ceramic comprises (La) 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7, ZrO2, 3YSZ, 8YSZ, Gd 2-x NdxZr2O7(0.0≤x≤2.0), Gd2Zr 2-y Ce y O7 (0.0≤y≤2.0) or (La) 0.2 Nd 0.2 Y 0.2 Eu 0.2 Gd 0.2 )2Zr2O 7。

[0046] The beneficial effects of this invention are:

[0047] (1) The preparation method provided by the present invention combines cold sintering technology and flash sintering technology to prepare fine-grained ceramics. It can complete densification at a lower temperature and in a shorter time, and improves the problem of obvious non-uniformity in the density and grain size distribution of flash sintered samples, thus obtaining fine-grained ceramics with standard grain size and density.

[0048] (2) The preparation method provided by the present invention is simple, low in cost, and the whole sintering process is short, which can be carried out quickly.

[0049] (3) This invention provides a new method for the preparation of fine-grained ceramics. Attached Figure Description

[0050] Figure 1 (La) prepared in Example 1 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 XRD test results of Zr2O7 fine-grained ceramic.

[0051] Figure 2 (La) prepared in Example 1 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2Morphology and grain size diagram of Zr2O7 fine-grained ceramic at the positive extreme.

[0052] Figure 3 (La) prepared in Example 1 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Morphology and grain size diagram of the negative end of Zr2O7 fine-grained ceramic.

[0053] Figure 4 The image shows the positive end morphology and grain size of the ZrO2 fine-grained ceramic prepared in Example 2.

[0054] Figure 5 The image shows the negative end morphology and grain size of the ZrO2 fine-grained ceramic prepared in Example 2.

[0055] Figure 6 The image shows the XRD test results of the Gd2Zr2O7 fine-grained ceramic prepared in Example 3.

[0056] Figure 7 The image shows the morphology and grain size of the fine-grained Gd2Zr2O7 ceramic cathode prepared in Example 3.

[0057] Figure 8 The image shows the morphology and grain size of the fine-grained ceramic anode material of Gd2Zr2O7 prepared in Example 3.

[0058] Figure 9 (La) prepared for Comparative Example 1 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Morphology and grain size diagram of Zr2O7 fine-grained ceramic at the positive extreme.

[0059] Figure 10 (La) prepared for Comparative Example 1 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Morphology and grain size diagram of the negative end of Zr2O7 fine-grained ceramic.

[0060] Figure 11 (La) prepared for Comparative Example 2 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Morphology and grain size of Zr2O7 fine-grained ceramic.

[0061] Figure 12 (La) prepared for Comparative Example 30.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Morphology and grain size of Zr2O7 fine-grained ceramic. Detailed Implementation

[0062] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0063] This invention provides a two-step method for preparing fine-grained ceramics using cold sintering-flash sintering technology. This method can prepare dense fine-grained ceramics at lower temperatures and in a shorter time, and it improves the problem of obvious non-uniformity in density and grain size distribution of flash-sintered samples. This provides a novel method for the preparation of fine-grained ceramic materials.

[0064] Example 1

[0065] This embodiment provides a two-step method for preparing fine-grained ceramics using cold sintering-flash sintering technology, including the following specific steps:

[0066] S1: According to the reaction formula 1 / 5La₂O₃ + 1 / 5Nd₂O₃ + 1 / 5Sm₂O₃ + 1 / 5Eu₂O₃ + 1 / 5Gd₂O₃ + 2ZrO₂ → (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Weigh out 0.01 mol of each of La2O3 (99.99%, 50nm), Nd2O3 (99.5%, <200nm), Sm2O3 (99.5%, 40nm), Eu2O3 (99.99%, <200nm), and Gd2O3 (99.8%, <100nm), and weigh out 0.1 mol of ZrO2 (99.99%, <100nm). Mix them together to form a mixed raw material and put it into a mixing bottle. Add 20% of the volume of the mixing bottle with zirconia grinding beads, including 80 grinding beads with a diameter of 2mm and 20 grinding beads with a diameter of 5mm. Add anhydrous ethanol at 30% of the mass of the mixed raw material and seal the mixing bottle. Place the mixing bottle on the roller of a ball mill and wet ball mill at 60 rpm for 24 hours to form a raw material slurry.

[0067] S2: Pour the raw material slurry prepared in step S1 into a beaker, add a magnetic stir bar, and stir magnetically for 5 minutes at 200 rpm and 90°C in a fume hood. After the slurry is basically dry, place the beaker in a vacuum oven, cover the opening of the beaker with aluminum foil to prevent slurry from splashing, make even holes on the aluminum foil cover, evacuate to 0.04 MPa, and dry at 55°C for 6 hours to obtain a mixed powder with a particle size of 40-200 nm.

[0068] S3: Weigh 0.8g of the mixed powder prepared in step S2 into an agate mortar, add 30% of the mass percentage of the mixed powder of deionized water and mix and grind thoroughly to form a mixed slurry. Put the mixed slurry into a dog bone mold, sieve it, and apply a uniaxial pressure of 350MPa at room temperature.

[0069] S4: After step S3, a uniaxial pressure of 350 MPa is continuously applied, and the heating mantle is heated to 180℃ at 5℃ / min and cold sintered for 60 min to obtain a dog bone-shaped sample. After the process, the temperature is reduced to 60℃ at 5℃ / min. After the sample has cooled to room temperature naturally, it is demolded and removed. The sample is then vacuum dried at 60℃ for 6 hours. The gauge length of the dried dog bone sample is 26.80 mm × 2.94 mm × 1.80 mm.

[0070] S5: The dog bone-shaped sample obtained in step S4 is perforated at both ends, with a diameter of 1.5 ± 0.1 mm and a distance of approximately 19 mm between the two perforations. Platinum paste is coated onto the inner walls of the perforations and dried. After drying, the sample is placed in a flash-firing muffle furnace. A platinum wire is inserted into the platinum-coated perforation and electrically connected to the electrode. A constant voltage of 300 V is applied to the dog bone sample, with a maximum current limit of 0.4 A. The sample is then heated to 1050 °C. After flash-firing, the power supply changes from a constant voltage state to a constant current state. Once the current reaches the preset maximum current limit of 0.4 A, the sample is flash-firing for 30 seconds before power is cut off to obtain (La). 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7 fine-grained ceramic.

[0071] The (La) prepared in this embodiment 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7 fine-grained ceramics were tested by XRD as follows Figure 1 As shown, the results indicate that (La) was completely synthesized. 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2The high-entropy phase of 2Zr2O7; partial samples from both ends of the positive and negative electrodes in the middle section of the dog bone sample were taken and their relative density was determined by the Archimedes method, and the average grain size was measured by electron microscopy. Figure 2 As shown, the relative density of the dog bone sample at the positive end was 97.6%, and the average grain size was 0.96 ± 0.34 µm; Figure 3 As shown, the relative density of the negative electrode of the dog bone sample is 95.4%, and the average grain size is 0.78±0.31 µm, both of which meet the standard for fine-grained ceramics; and the positive and negative electrodes of the dog bone sample are dense and uniform.

[0072] Example 2

[0073] This embodiment provides a two-step method for preparing fine-grained ceramics using cold sintering-flash sintering technology, including the following specific steps:

[0074] S1: Weigh 0.2 mol of ZrO2 (99.99%, <100 nm) and put it into a mixing bottle. Then add 20% of the volume of the mixing bottle with zirconia grinding beads, including 70 grinding beads with a diameter of 2 mm and 15 grinding beads with a diameter of 5 mm. Add anhydrous ethanol at 30% of the raw material mass and seal the mixing bottle. Place the mixing bottle on the roller of the grinding mill and perform wet ball milling at 60 rpm for 24 hours to form a raw material slurry.

[0075] S2: Pour the raw material slurry prepared in step S1 into a beaker, add a magnetic stir bar, and stir magnetically for 5 minutes at 200 rpm and 90°C in a fume hood. After the slurry is basically dry, put the beaker into a vacuum oven, cover the opening of the beaker with aluminum foil to prevent the slurry from splashing, make even holes on the aluminum foil cover, evacuate to 0.04 MPa, and dry at 55°C for 6 hours to obtain powder with a particle size of 40-200 nm.

[0076] S3: Weigh 0.8g of the powder prepared in step S2 into an agate mortar, add 30% of the mass percentage of deionized water to the mixed powder and mix and grind thoroughly to form a mixed slurry. Put the mixed slurry into a dog bone mold, sieve it, and apply a uniaxial pressure of 350MPa at room temperature.

[0077] S4: After step S3, a uniaxial pressure of 350 MPa is continuously applied, and the heating mantle is heated to 180℃ at 5℃ / min and cold sintered for 60 min to obtain a dog bone-shaped sample. After the process, the temperature is reduced to 60℃ at 5℃ / min. After the sample has cooled to room temperature naturally, it is demolded and removed. The sample is then vacuum dried at 60℃ for 6 hours. The gauge length of the dried dog bone sample is 26.80 mm × 2.94 mm × 1.80 mm.

[0078] S5: Make holes at both ends of the dog bone-shaped sample obtained in step S4. The hole diameter is 1.5±0.1mm and the distance between the two holes is about 19mm. Coat the inner wall of the hole with platinum paste and dry it. After drying, put it into a special muffle furnace for flash firing. Insert the platinum wire into the hole coated with platinum paste and connect it to the electrode. Apply a constant voltage of 300 V to the dog bone-shaped sample and limit the current to 0.4 A. Then heat it to 1010℃. After flash firing occurs, the power supply changes from constant voltage to constant current. After the current reaches the preset maximum limit current of 0.4 A, keep the sample flash firing for 30s before power is cut off to obtain ZrO2 fine-grained ceramic.

[0079] Samples from both ends of the positive and negative electrodes of the ZrO2 fine-grained ceramic dog bone sample prepared in this embodiment were taken and their relative density was determined by the Archimedes method, and their average grain size was measured by electron microscopy. Figure 4 As shown, the relative density of the dog bone sample at the positive end was 98.3%, and the average grain size was 0.78 ± 0.42 µm; Figure 5 As shown, the relative density of the negative electrode of the dog bone sample is 96.3%, and the average grain size is 0.74±0.36 µm, both of which meet the standard for fine-grained ceramics; and the positive and negative electrodes of the dog bone sample are dense and uniform.

[0080] Example 3

[0081] This embodiment provides a two-step method for preparing fine-grained ceramics using cold sintering-flash sintering technology, including the following specific steps:

[0082] S1: Weigh out 0.05 mol of Gd2O3 (99.8%, <100nm) and 0.1 mol of ZrO2 (99.99%, <100nm) according to the reaction formula Gd2O3 + 2ZrO2 → Gd2Zr2O7, mix them into a mixed raw material and put it into a mixing bottle. Then add 20% of the volume of the mixing bottle with zirconia grinding beads, including 80 grinding beads with a diameter of 2mm and 20 grinding beads with a diameter of 5mm. Add anhydrous ethanol at 30% of the mass of the mixed raw material and seal the mixing bottle. Place the mixing bottle on the roller of the grinding mill and wet ball mill at 60 rpm for 24 hours to form a raw material slurry.

[0083] S2: Pour the raw material slurry prepared in step S1 into a beaker, add a magnetic stir bar, and stir magnetically for 5 minutes at 200 rpm and 90°C in a fume hood. After the slurry is basically dry, put the beaker into a vacuum oven, cover the opening of the beaker with aluminum foil to prevent the slurry from splashing, make even holes on the aluminum foil cover, evacuate to 0.04 MPa, and dry at 55°C for 6 hours to obtain a mixed powder with a particle size of less than 100 nm.

[0084] S3: Weigh 2g of the mixed powder prepared in step S2 into an agate mortar, add 30% of the mass percentage of the mixed powder of deionized water and mix and grind thoroughly to form a mixed slurry. Put the mixed slurry into a cylindrical mold, sieve it and apply a uniaxial pressure of 350MPa at room temperature.

[0085] S4: After step S3, a uniaxial pressure of 350 MPa is continuously applied, and the heating mantle is heated to 180℃ at 5℃ / min and cold sintered for 60 min to obtain a disc-shaped sample. After the process, the temperature is reduced to 60℃ at 5℃ / min. After the sample cools naturally to room temperature, it is demolded and removed. The sample is then vacuum dried at 60℃ for 6 hours. The gauge length of the dried disc sample is 12.10 mm in diameter and 1.96 mm in thickness.

[0086] S5: Wrap the circular sample obtained in step S4 with a 0.5 mm thick graphite felt, then press it between two 30 mm diameter graphite punches for discharge plasma flash calcination; apply a constant uniaxial pressure of 20 MPa, set the peak power to 4 kW, peak voltage to 10 V, and peak current to 600 A. After discharge, the power drops rapidly, and the current is manually reduced to maintain the current for 2-5 s. After flash calcination for 30 s, fine-grained Gd2Zr2O7 ceramic is obtained.

[0087] The fine-grained Gd₂Zr₂O₇ ceramic prepared in this embodiment was tested by XRD as follows: Figure 6 As shown, the results indicate that Gd₂Zr₂O₇ was completely synthesized. Samples from both sides of the positive and negative electrodes of the circular wafer were taken and their relative density was determined using the Archimedes method, and the average grain size was measured using electron microscopy. Figure 7 As shown, the relative density of the positive electrode surface of the disc-shaped sample is 98.2%, and the average grain size is 0.46 ± 0.26 µm; Figure 8 As shown, the relative density of the negative electrode surface of the disc-shaped sample is 96.4%, and the average grain size is 0.43±0.16 µm, both of which meet the standard for fine-grained ceramics; and the positive and negative electrodes of the disc-shaped sample are dense and uniform.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing ceramics by cold pressing followed by flash sintering, including the following specific steps:

[0090] S1: Weigh out 0.01 mol of La2O3 (99.99%, 50nm), Nd2O3 (99.5%, <200nm), Sm2O3 (99.5%, 40nm), Eu2O3 (99.99%, <200nm), and Gd2O3 (99.8%, <100nm), and weigh out 0.1 mol of ZrO2 (99.99%, <100nm). Mix them together to form a mixed raw material and put it into a mixing bottle. Add 20% of the volume of the mixing bottle with zirconia grinding beads, including 80 grinding beads with a diameter of 2mm and 20 grinding beads with a diameter of 5mm. Add anhydrous ethanol at 30% of the mass of the mixed raw material and seal the mixing bottle. Place the mixing bottle on the roller of a ball mill and wet ball mill at 60 rpm for 24 hours to form a raw material slurry.

[0091] S2: Pour the raw material slurry prepared in step S1 into a beaker, add a magnetic stir bar, and stir magnetically for 5 minutes at 200 rpm and 90°C in a fume hood. After the slurry is basically dry, place the beaker in a vacuum oven, cover the opening of the beaker with aluminum foil to prevent slurry from splashing, make even holes on the aluminum foil cover, and dry at 0.04 MPa and 55°C for 6 hours to obtain a mixed powder with a particle size of 40-200 nm.

[0092] S3: Weigh 0.8g of the mixed powder prepared in step S2, sieve it, and put it into a dog bone mold. Apply a uniaxial pressure of 350MPa at room temperature, hold the pressure for 2 minutes, and then demold the sample. The gauge length of the dog bone sample is 26.80 mm × 2.94 mm × 1.80 mm.

[0093] S4: The dog bone-shaped sample obtained in step S3 is perforated at both ends, with a diameter of 1.5 ± 0.1 mm and a distance of approximately 19 mm between the two perforations. Platinum paste is coated onto the inner walls of the perforations and dried. After drying, the sample is placed in a flash-firing muffle furnace. A platinum wire is inserted into the platinum-coated perforation and electrically connected to the electrode. A constant voltage of 300 V is applied to the dog bone-shaped sample, with a maximum current limit of 0.4 A. The sample is then heated to 1050 °C. After flash-firing, the power supply changes from a constant voltage state to a constant current state. Once the current reaches the preset maximum current limit of 0.4 A, the sample is flash-firing for 30 seconds before power is cut off to obtain (La). 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7 fine-grained ceramic.

[0094] Take the samples prepared by this comparative example (La) 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2The relative density and average grain size of a portion of the positive and negative electrodes in the middle section of a Zr2O7 fine-grained ceramic dog bone sample were determined using the Archimedes method. Figure 9 As shown, the relative density of the dog bone sample at the positive end was 96.2%, and the average grain size was 1.05 ± 0.46 µm; Figure 10 As shown, the relative density of the negative electrode of the dog bone sample is 90.3%, and the average grain size is 0.68±0.26 µm. The density and grain size of the positive and negative electrodes of the dog bone sample are quite different.

[0095] Comparative Example 2

[0096] This comparative example provides a method for preparing fine-grained ceramics by cold pressing followed by pressureless sintering, including the following specific steps:

[0097] S1: Weigh out 0.01 mol of La2O3 (99.99%, 50nm), Nd2O3 (99.5%, <200nm), Sm2O3 (99.5%, 40nm), Eu2O3 (99.99%, <200nm), and Gd2O3 (99.8%, <100nm), and weigh out 0.1 mol of ZrO2 (99.99%, <100nm). Mix them together to form a mixed raw material and put it into a mixing bottle. Add 20% of the volume of the mixing bottle with zirconia grinding beads, including 80 grinding beads with a diameter of 2mm and 20 grinding beads with a diameter of 5mm. Add anhydrous ethanol at 30% of the mass of the mixed raw material and seal the mixing bottle. Place the mixing bottle on the roller of a ball mill and wet ball mill at 60 rpm for 24 hours to form a raw material slurry.

[0098] S2: Pour the raw material slurry prepared in step S1 into a beaker, add a magnetic stir bar, and stir magnetically for 5 minutes at 200 rpm and 90°C in a fume hood. After the slurry is basically dry, place the beaker in a vacuum oven, cover the opening of the beaker with aluminum foil to prevent slurry from splashing, make even holes on the aluminum foil cover, and dry at 0.04 MPa and 55°C for 6 hours to obtain a mixed powder with a particle size of 40-200 nm.

[0099] S3: Weigh 0.8g of the mixed powder prepared in step S2 and grind it in an agate mortar. After sieving, put it into a dog bone mold and apply a uniaxial pressure of 350MPa at room temperature. Hold the pressure for 2 minutes and then demold the sample. The gauge length of the dog bone sample is 26.80 mm × 2.94 mm × 1.80 mm.

[0100] S4: The dog bone-shaped sample obtained in step S3 is placed in a muffle furnace for pressureless sintering. It is heated to 800℃ at 10℃ / min, then to 1500℃ at 5℃ / min for 3 hours. Subsequently, it is cooled to 1200℃ at 3℃ / min, then to 800℃ at 5℃ / min, and then allowed to cool naturally in the furnace to obtain (La). 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7 fine-grained ceramic.

[0101] The (La) prepared in this comparative example 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 The morphology and grain size of fine-grained Zr2O7 ceramics are as follows: Figure 11 As shown, the relative density measured by the Archimedes method was 80.3%, and the average grain size was 1.55±0.49µm, which did not meet the standard for fine-grained ceramics.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing fine-grained ceramics combining cold sintering and pressureless sintering, including the following specific steps:

[0104] S1: Weigh out 0.01 mol of La2O3 (99.99%, 50 nm), Nd2O3 (99.5%, <200 nm), Sm2O3 (99.5%, 40 nm), Eu2O3 (99.99%, <200 nm), and Gd2O3 (99.8%, <100 nm), and weigh out 0.1 mol of ZrO2 (99.99%, <100 nm). Mix them together to form a mixed raw material and put it into a mixing bottle. Add 20% of the volume of the mixing bottle with zirconia grinding beads, including 80 grinding beads with a diameter of 2 mm and 20 grinding beads with a diameter of 5 mm. Add anhydrous ethanol at 30% of the mass of the mixed raw material and seal the mixing bottle. Place the mixing bottle on the roller of a ball mill and wet ball mill at 60 rpm for 24 hours to form a raw material slurry.

[0105] S2: Pour the raw material slurry prepared in step S1 into a beaker, add a magnetic stir bar, and stir magnetically for 5 minutes at 200 rpm and 90°C in a fume hood. After the slurry is basically dry, place the beaker in a vacuum oven, cover the opening of the beaker with aluminum foil to prevent slurry from splashing, make even holes on the aluminum foil cover, and dry at 0.04 MPa and 55°C for 6 hours to obtain a mixed powder with a particle size of 40-200 nm.

[0106] S3: Weigh 0.8g of the mixed powder prepared in step S2 into an agate mortar, add 30% of the mass percentage of the mixed powder of deionized water and mix and grind thoroughly to form a mixed slurry. Put the mixed slurry into a dog bone mold, sieve it, and apply a uniaxial pressure of 350MPa at room temperature.

[0107] S4: After step S3, a uniaxial pressure of 350 MPa is continuously applied, and the heating mantle is heated to 180℃ at 5℃ / min and cold sintered for 60 min to obtain a dog bone-shaped sample. After the process, the temperature is reduced to 60℃ at 5℃ / min. After the sample has cooled to room temperature naturally, it is demolded and removed. The sample is then vacuum dried at 60℃ for 6 hours. The gauge length of the dried dog bone sample is 26.80 mm × 2.94 mm × 1.80 mm.

[0108] S5: The dog bone-shaped sample obtained in step S4 is placed in a muffle furnace for pressureless sintering. It is heated to 800℃ at 10℃ / min, then to 1500℃ at 5℃ / min for 3 hours. Subsequently, it is cooled to 1200℃ at 3℃ / min, then to 800℃ at 5℃ / min, and then allowed to cool naturally in the furnace to obtain (La). 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7 fine-grained ceramic.

[0109] The (La) prepared in this comparative example 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 The morphology and grain size of fine-grained Zr2O7 ceramics are as follows: Figure 12 As shown, the relative density measured by the Archimedes method was 94.4%, and the average grain size was 1.61±0.49µm, which did not meet the standard for fine-grained ceramics.

[0110] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing fine-grained ceramics using a two-stage cold sintering-flash sintering technique, characterized in that, The specific steps include the following: S1: Weigh out the corresponding molar amount of fine-grained ceramic raw material powder according to the chemical formula of fine-grained ceramic, mix them into mixed raw materials, add ball milling beads and ball milling media, and perform wet ball milling to form raw material slurry; The fine-grained ceramic includes (La) 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 )2Zr2O7、Gd 2-x NdxZr2O7, Gd2Zr 2-y Ce y O7 or (La 0.2 Nd 0.2 Y 0.2 Eu 0.2 Gd 0.2 )2Zr2O7; Gd 2-x In NdxZr2O7, 0.0 ≤ x ≤ 2.0; in Gd2Zr... 2-y Ce y In O7, 0.0 ≤ y ≤ 2.0; S2: The raw material slurry prepared in step S1 is dried to obtain a mixed powder; S3: Add the mixed powder prepared in step S2 to deionized water to form a mixed slurry, put the mixed slurry into a mold, and apply a pressure of 300-350 MPa at room temperature; S4: After step S3, continue to apply a pressure of 300-350 MPa and sinter the sample at 180-220℃ for 60-120 min while raising the temperature at 5-8℃ / min. After the sintering is completed, lower the temperature to 60℃ at 3-5℃ / min and remove the sample after it has cooled to room temperature. Then, vacuum dry the sample at 55-60℃ for 6-12 h until it reaches constant weight. S5: Perform point-contact flash firing on the sample after cold sintering in step S4; The conditions for point-contact flash burning include: heating to 1010-1050℃, applying a constant voltage of 280-350V to the sample, and flash burning for 30-60s with a preset maximum current limit of 0.38-0.42 A.

2. The preparation method according to claim 1, characterized in that, In step S1, wet ball milling is performed at a speed of 55-75 rpm for 24 hours; in step S2, the raw material slurry is first stirred at a speed of 120-200 rpm and a temperature of 70-90℃ for 5-10 minutes, and then the raw material slurry is placed in a vacuum oven, vacuumed to 0.04-0.06 MPa, and dried at a temperature of 55-70℃ for 6-10 hours.

3. The preparation method according to claim 1, characterized in that, The particle size of the mixed powder obtained in step S2 is 40-200 nm.

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