Preparation method of rare earth composite sintered corundum

Abstract

The application belongs to the technical field of new material preparation, and discloses a preparation method of rare earth composite sintered corundum. Industrial alumina powder is calcined, ball milled, and classified, and then mixed with alpha-Al2O3 nano seeds and rare earth oxides (lanthanum oxide, yttrium oxide, etc.) to be ground to a fine degree, and then granulated by spraying and rolled into balls to obtain green balls, which are prepared by a gradient temperature sintering process. The application effectively solves the problems of poor toughness, insufficient thermal shock resistance, high sintering temperature, and uneven distribution of rare earths leading to deformation and cracking of the existing corundum material, and obtains rare earth composite sintered corundum with high density, fine grains, high strength and toughness, excellent thermal shock resistance, and high temperature stability, which has significant technical progress and industrial application value.

Description

Technical Field

[0001] This application belongs to the field of new materials technology, specifically relating to a method for preparing rare earth composite sintered corundum. Background Technology

[0002] Sintered corundum, also known as tabular corundum, is a high-performance inorganic non-metallic material prepared from high-purity industrial alumina as the main raw material through precise batching, molding, and high-temperature rapid sintering processes. Its microstructure is characterized by well-developed α-Al₂O₃ tabular crystals, with direct bonding between the crystals forming a dense corundum framework. Benefiting from this structure, sintered corundum possesses high melting point, high hardness, good chemical stability, resistance to acid and alkali corrosion, wear resistance, and excellent creep resistance. Therefore, it is widely used in key fields such as refractory materials, machinery industry, building materials, chemicals, power, electronic ceramics, and high-temperature structural components, making it an indispensable basic material in modern high-temperature industries.

[0003] However, as the requirements for material service in high-end, high-temperature operating conditions continue to increase, sintered corundum prepared by existing technologies has gradually revealed the following shortcomings:

[0004] Firstly, its density and mechanical properties remain limited. Under traditional processes, sintered corundum typically has a high apparent porosity, making it difficult to exceed 95% density, resulting in lower flexural strength, compressive strength, and fracture toughness. Especially in environments with frequent thermal shock and rapid temperature changes, microcracks easily form within the material and propagate rapidly, leading to spalling, cracking, or even overall failure. Therefore, the toughness and thermal shock resistance of existing sintered corundum cannot fully meet the extremely high reliability requirements of applications such as aerospace, high-end metallurgy, and advanced electronic ceramics sintering.

[0005] Secondly, the preparation process presents a contradiction between high energy consumption and low performance. Currently, the sintering temperature for industrially prepared sintered corundum is typically above 1800℃, even reaching 1850–1900℃, with prolonged holding times. High-temperature, long-duration sintering not only significantly increases energy consumption and production costs but also places stringent requirements on kiln refractory materials and heating elements, resulting in high equipment maintenance costs. Attempts to save energy by lowering the sintering temperature lead to insufficient α-Al₂O₃ grain growth, weak grain boundary bonding, and the inability to eliminate residual pores, resulting in a significant decrease in material density and mechanical properties, failing to meet usage standards. This constitutes a key technical bottleneck restricting the further promotion and application of conventionally sintered corundum.

[0006] Therefore, while ensuring or even improving the mechanical properties and thermal shock resistance of materials, developing a low-energy-consumption sintered corundum and its preparation method that can meet the needs of high-end high-temperature working conditions has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] Purpose of the invention: To address the shortcomings of the prior art, this application provides a method for preparing rare earth composite sintered corundum.

[0008] The technical problems to be solved by this invention include the following aspects: First, improving the toughness and thermal shock resistance of the product, optimizing its overall performance, and enabling it to meet the needs of high-end high-temperature operating conditions. Second, reducing the sintering temperature during the preparation process, thereby reducing energy consumption. Furthermore, this invention also solves the problem of product performance consistency. When rare earth elements are added to the product, they affect the shrinkage behavior of the material, leading to deformation and cracking during sintering. Because rare earth oxides are prone to agglomeration, insufficient grinding or mixing will result in uneven distribution of rare earth elements in the corundum matrix, directly affecting the performance consistency of different parts of the product, causing over-burning in some areas and under-burning in others, thus affecting the overall quality.

[0009] The core idea of ​​this invention is to incorporate rare earth oxides. Rare earth ions have a large radius, making it difficult for them to diffuse into the α-Al₂O₃ lattice. They tend to accumulate at grain boundaries, lowering the sintering temperature through grain boundary pinning and activated lattice diffusion. This allows the sintering temperature of corundum to be significantly reduced from the conventional 1800-1900℃ to 1450-1650℃, a reduction of 200-300℃. This not only saves a significant amount of energy but also reduces the requirements for sintering equipment and extends the kiln life. The main additives in this invention are lanthanum oxide and yttrium oxide. The addition of yttrium oxide can lower the sintering temperature, refine the grains, and improve toughness and thermal shock resistance. The addition of lanthanum oxide can improve high-temperature performance and chemical stability, and inhibit grain growth. The combined addition of both can achieve synergistic performance optimization: densification can be achieved at lower temperatures while obtaining excellent high-temperature mechanical properties. Cerium oxide is an auxiliary additive, which can improve thermal shock stability. The total amount of rare earth oxides added is 0.5%–2.0% of the total mass of the raw materials.

[0010] This invention also creatively introduces alumina nanocrystal seeds. During the sintering process of alumina, a transition from the transition form to the stable α-form is required, a process with a high energy barrier. Nanocrystal seeds provide more sintering active sites, accelerate material migration, reduce the sintering activation energy, and lower the sintering temperature to 1450℃ or even lower.

[0011] Nanocrystals can guide grains to form a more ideal microstructure, increasing the proportion of the α-Al₂O₃ phase and refining the grains. Furthermore, nanocrystals provide numerous nucleation sites, concentrating rare earth elements (such as yttrium oxide and lanthanum oxide) in two key regions: grain boundaries and grain surfaces. This allows rare earth elements to more easily accumulate where they can exert their effects, effectively inhibiting excessive grain growth.

[0012] The synergistic effect of using nanopowder and micropowder is far superior to using either one alone. During the mixing process, it can act as a "dispersion medium" to help rare earth elements achieve more uniform dispersion, thereby maximizing their effect of inhibiting grain growth and enhancing the material.

[0013] In addition, polyvinyl alcohol can be added as a binder to improve molding performance, depending on the specific circumstances. Ammonium citrate (0.1%–0.5%) can be added as a dispersant to promote uniform dispersion of rare earth oxides, depending on the specific circumstances.

[0014] Specifically, the method described in this invention includes the following steps:

[0015] Step 1: Calcine industrial alumina powder at 1200-1400℃ for 2-3 hours, then ball mill it. After ball milling, select alumina powder with a particle size of 1-5μm for later use.

[0016] Step 2: Weigh the alumina base material and rare earth oxides. The alumina base material includes: 92-96 parts of industrial alumina powder, 4-5 parts of the alumina powder obtained in Step 1, and 0.8-1 parts of α-Al2O3 nanocrystal seeds. The rare earth oxides are 0.5-2 parts of lanthanum oxide and 0.5-2 parts of yttrium oxide.

[0017] Mix and grind the above raw materials. After grinding, check the particle size. Stop grinding when the following conditions are met: D98≤5μm and D90≤2μm.

[0018] Step 3: Spray granulation of the slurry obtained in Step 2, rolling it into balls, controlling the diameter of the green balls to 20-25 mm and the bulk density of the green balls to 1.9-2.1 g / cm³; then dry it at 120℃ for 8-12 hours.

[0019] Step 4, high-temperature sintering is performed using a gradient temperature increase, specifically as follows:

[0020] First stage: heating rate 10-15℃ / min, heat to 600±10℃ and hold for 40-60min;

[0021] Second stage: heating rate 15-20℃ / min, heat to 1200±10℃ and hold for 20-30min;

[0022] Third stage: heating rate 10-15℃ / min, heat to 1500±10℃ and hold for 120-300min;

[0023] Step 5: Cool the furnace to room temperature, perform post-processing after cooling, and put it into storage after passing the inspection.

[0024] Specifically, in step 1, the industrial alumina is required to have a D50 of 3-8 micrometers, a specific surface area of ​​0.5-10 m² / g, an α phase content of ≥95%, and an impurity content (Na₂O) of ≤0.3%.

[0025] Specifically, in step 1, the α-Al2O3 nanocrystals have a diameter of 20-100 nm, a specific surface area of ​​35-100 m² / g, and an impurity content (Na2O) of ≤0.08%.

[0026] Adding lanthanum oxide can lower the sintering temperature, refine the grain size, and improve toughness and thermal shock resistance. However, if too much is added, excess La2O3 will react with Al2O3 to form lamellar lanthanum hexaaluminate (LaAl). 11 O 18 This secondary phase pins to the grain boundaries, inhibiting intergranular sintering and hindering green body shrinkage, leading to increased porosity and reduced densification. Therefore, for the purposes of this invention, the amount of lanthanum oxide added is preferably 0.5-0.7 parts.

[0027] Adding yttrium oxide can inhibit grain growth and improve high-temperature performance and chemical stability. However, excessive addition of yttrium oxide can lead to a decrease in bulk density, an increase in porosity, and a decrease in density, which in turn can reduce hardness and flexural strength. Therefore, for the purposes of this invention, the preferred amount of yttrium oxide added is 0.5-0.9 parts.

[0028] Furthermore, in step 2, the rare earth oxides consist of 0.5-2 parts lanthanum oxide, 0.5-2 parts yttrium oxide, and 0.1-0.5 parts cerium oxide. The addition of cerium oxide optimizes the microstructure, transforming the wear mechanism from grain fracture to the formation of a smooth friction layer, thus improving the material's toughness. In addition, the addition of cerium oxide can form a stronger chemical bond and mechanical interlocking structure within the material, effectively reducing porosity, enhancing interfacial adhesion, and making the coating less prone to peeling during thermal shock, thereby improving thermal shock stability.

[0029] Furthermore, the addition of hexagonal boron nitride lamellar crystals can further improve thermal shock resistance. The hexagonal boron nitride lamellar crystals described in this invention possess a layered structure, high thermal conductivity, and a low coefficient of friction, enabling the formation of weak bonding interfaces at grain boundaries. When thermal shock occurs, these weak interfaces can induce microcrack deflection and bifurcation, and absorb thermal stress energy, significantly enhancing resistance to thermal shock damage. The amount of hexagonal boron nitride lamellar crystals used is 0.5%-2.0%.

[0030] Specifically, the method described in this invention includes the following steps:

[0031] Step 1: Calcine industrial alumina powder at 1200-1400℃ for 2-3 hours, then ball mill it. After ball milling, select alumina powder with a particle size of 1-5μm for later use.

[0032] Step 2: Weigh the alumina base material, rare earth oxides, and hexagonal boron nitride plate crystals. The alumina base material includes: 92-96 parts of industrial alumina powder, 4-5 parts of the alumina powder obtained in Step 1, 0.8-1 parts of α-Al2O3 nanocrystal seeds, 0.5-2 parts of lanthanum oxide and 0.5-2 parts of yttrium oxide, and 0.5-2 parts of hexagonal boron nitride plate crystals.

[0033] Mix the above raw materials, grind them, and then test the particle size. Stop grinding when the following conditions are met: D98≤5μm and D90≤2μm.

[0034] Step 3: Spray granulation of the slurry obtained in Step 2, rolling it into balls, controlling the diameter of the green balls to 20-25 mm and the bulk density of the green balls to 1.9-2.1 g / cm³; then dry it at 120℃ for 8-12 hours.

[0035] Step 4, high-temperature sintering is performed using a gradient temperature increase, specifically as follows:

[0036] First stage: Introduce air (flow rate 2-5 L / min), heat up at a rate of 10-15℃ / min, and hold at 600±10℃ for 40-60 min;

[0037] Second stage: Evacuate to <10 Pa, then introduce argon gas (flow rate 2-5 L / min), heat up at a rate of 15-20℃ / min, heat up to 1200±10℃ and hold for 20-30 min;

[0038] The third stage involves a heating rate of 10-15℃ / min, followed by heating to 1500±10℃ and holding for 120-300 min.

[0039] Step 5: Cool the furnace to room temperature, perform post-processing after cooling, and put it into storage after passing the inspection.

[0040] Furthermore, in step 2, the rare earth oxides are 0.5-2 parts of lanthanum oxide, 0.5-2 parts of yttrium oxide, and 0.1-0.5 parts of cerium oxide.

[0041] Beneficial Effects: This invention alters the solid-state sintering mechanism of conventional sintered corundum by introducing rare earth oxides. Rare earth ions accumulate at grain boundaries, activating lattice diffusion. Simultaneously, nanocrystals provide numerous sintering active sites, enabling rapid densification of α-Al₂O₃ grains at lower temperatures. The sintering temperature is significantly reduced compared to traditional processes, resulting in substantial energy savings, lower requirements for sintering equipment, and extended kiln lifespan. Furthermore, this invention overcomes the technical challenges of rare earth oxide agglomeration and inconsistent sintering shrinkage behavior leading to product deformation and cracking.

[0042] The corundum material prepared by the method described in this invention exhibits high fracture toughness and bending strength, and demonstrates excellent mechanical stability at high temperatures. It is suitable for high-end applications such as aerospace nozzles, glass melting furnace linings, and high-temperature chemical reactors. Attached Figure Description

[0043] Figure 1 SEM image (200x magnification) of the sample material obtained in Example 1.

[0044] Figure 2 SEM image (500x magnification) of the sample material obtained in Example 1.

[0045] Figure 3 SEM image (1000x magnification) of the sample material obtained in Example 1.

[0046] Figure 4 SEM image of the comparative sample material (200x magnification)

[0047] Figure 5 SEM image of the comparative sample material (500x magnification)

[0048] Figure 6 SEM image of the comparative sample material (1000x magnification) Detailed Implementation

[0049] The technical solution of this application will be described in detail below through embodiments, but the scope of protection of this application is not limited to the embodiments described. All quantities mentioned in this invention are by weight.

[0050] Example 1

[0051] Step 1: Calcine industrial alumina powder at 1350℃ for 2 hours, then ball mill it. After ball milling, use an air classifier to select alumina powder with a particle size of 1-5μm for later use.

[0052] Step 2: Weigh 94 parts of industrial alumina powder, 5 parts of the alumina powder obtained in Step 1, 1 part of α-Al₂O₃ nanocrystals, 0.5 parts of lanthanum oxide, and 0.7 parts of yttrium oxide. Mix the above raw materials and place them in a ball mill. Use zirconia balls as the grinding medium, with a ball-to-material ratio of 3:1, and a rotation speed of 280 rpm. Premix for 30 minutes, then add an appropriate amount of deionized water and polyvinyl alcohol aqueous solution, and wet grind for 6 hours. Use a laser particle size analyzer to detect the particle size of the slurry. Stop grinding when the following conditions are met: D98 ≤ 5 μm and D90 ≤ 2 μm.

[0053] Step 3: Spray granulation is performed on the slurry obtained in Step 2 to obtain granulated powder with good flowability and a particle size of 80-200μm, with a moisture content controlled at 1%. A disc pelletizer is used with a disc inclination angle of 45-50° and a rotation speed of 25 rpm. The granulated powder is slowly added to the disc while simultaneously spraying in an appropriate amount of moisture, causing the powder to gradually roll into pellets. The green pellet diameter is controlled to 20-25mm by adjusting the feeding speed and rolling time, and the green pellet bulk density is controlled to 1.9-2.1 g / cm³. The green pellets are then placed in a forced-air drying oven and dried at 120℃ for 12 hours until the moisture content is ≤1%.

[0054] Step 4: Using a tube furnace, atmosphere box furnace, or other sintering equipment capable of performing the corresponding functions, the temperature is gradually increased, specifically as follows:

[0055] First stage: heating rate 10℃ / min, heat to 600±10℃ and hold for 60min;

[0056] Second stage: heating rate 15℃ / min, heat to 1200±10℃ and hold for 30min;

[0057] Third stage: Heating rate 10℃ / min, heat to 1500±10℃ and hold for 300min;

[0058] Step 5: Cool to room temperature with the furnace, and put into storage after passing the inspection.

[0059] The obtained SEM images of the samples are as follows Figure 1 , Figure 2 , Figure 3 As shown.

[0060] Comparative Example

[0061] The comparative example is a commercially available conventional corundum sample, and its SEM image is shown below. Figure 4 , Figure 5 , Figure 6 As shown.

[0062] The corresponding detection data for Example 1 and the comparative example are as follows:

[0063] g / cm³ (MPa·m¹ / ²) (MPa) (1100℃ → water cooling, number of cycles) Comparative Example 3.3 88% 5% 3.5 80 5 destructions Example 1 3.8 96% 2% 5.2 125 >15 times without cracks

[0064] By comparing SEM images and test data, it can be seen that the product prepared by the method described in this invention has a smaller grain size and higher density compared to conventional corundum materials. Simultaneously, it improves flexural strength and thermal shock resistance.

[0065] Example 2

[0066] Example 2 is largely the same as Example 1, except that step 1 is omitted and the raw materials in step 2 are: 100 parts of industrial alumina powder, 0.5 parts of lanthanum oxide, and 0.7 parts of yttrium oxide.

[0067] Some of the sintered products developed cracks, resulting in a yield rate of less than 90%.

[0068] Example 3

[0069] Example 3 is largely the same as Example 1, except that in step 4, the heating rate is 15℃ / min, and the temperature is raised to 1500±10℃ and held for 300min.

[0070] Some of the sintered products developed cracks, resulting in a yield rate of less than 85%.

[0071] Example 4

[0072] Example 4 is largely the same as Example 1, except that in step 2, the amount of yttrium oxide used is 0.8 parts.

[0073] Example 5

[0074] Example 5 is largely the same as Example 1, except that in step 2, the amount of lanthanum oxide used is 1 part.

[0075] Example 6

[0076] Example 6 is largely the same as Example 1, except that in step 2, the rare earth oxide is 0.5 parts of lanthanum oxide.

[0077] Example 7

[0078] Example 7 is largely the same as Example 1, except that in step 2, the rare earth oxide is 0.7 parts of yttrium oxide.

[0079] Example 8

[0080] Example 8 is largely the same as Example 1, except that in step 2, the rare earth oxides are 0.5 parts lanthanum oxide, 0.7 parts yttrium oxide, and 0.3 parts cerium oxide.

[0081] The relevant test data for Examples 4-8 are shown in the table below.

[0082] MPa·m¹ / ² MPa 1000℃, MPa·m¹ / ² 1000℃, MPa 1100℃ → Water cooling, number of times Example 4 93% 4% 4.7 120 4.24 62 >15 times without cracks Example 5 92% 4% 4.8 119 4.05 60 >15 times without cracks Example 6 92% 3% 5.2 125 3.45 58 >15 times without cracks Example 7 93% 4% 4.9 119 4.74 69 >15 times without cracks Example 8 96% 2% 5.1 124 4.81 73 >20 times without cracks

[0083] Examples 4 and 5 show that excessive rare earth oxides can actually lead to a decrease in related properties. Example 8 shows that the addition of cerium oxide further improves thermal shock resistance.

[0084] Example 9

[0085] Step 1: Calcine industrial alumina powder at 1350℃ for 2 hours, then ball mill it. After ball milling, use an air classifier to select alumina powder with a particle size of 1-5μm for later use.

[0086] Step 2: Weigh 94 parts of industrial alumina powder, 5 parts of the alumina powder obtained in Step 1, 1 part of α-Al₂O₃ nanocrystals, 0.5 parts of lanthanum oxide, 0.7 parts of yttrium oxide, and 0.5 parts of hexagonal boron nitride lamellar crystals (aspect ratio > 10, coated with silicon nitride before use). Mix the above raw materials and place them in a ball mill. Use zirconia balls as the grinding medium, with a ball-to-material ratio of 3:1, and a rotation speed of 250-300 rpm. Premix for 30 minutes, then add an appropriate amount of deionized water and polyvinyl alcohol aqueous solution, and wet grind for 6 hours. Use a laser particle size analyzer to detect the particle size of the slurry. Stop grinding when the following conditions are met: D98 ≤ 5 μm and D90 ≤ 2 μm.

[0087] Step 3: Spray granulation of the slurry obtained in Step 2 to obtain granulated powder with good flowability and a particle size of 80-200μm, with a moisture content controlled at 1%. A disc pelletizer is used, with a disc inclination angle of 45-50° and a rotation speed of 25 rpm. The granulated powder is slowly added to the disc while simultaneously spraying in an appropriate amount of moisture, causing the powder to gradually roll into pellets. The green pellet diameter is controlled to 20-25mm by adjusting the feeding speed and rolling time, and the green pellet bulk density is controlled to 1.9-2.1 g / cm³. The green pellets are placed in a forced-air drying oven and dried at 120℃ for 12 hours until the moisture content is ≤1%.

[0088] Step 4, using a tube furnace with gradient heating, specifically:

[0089] First stage: Introduce air (flow rate 2-5 L / min), heat up at a rate of 10℃ / min, heat to 600±10℃ and hold for 40-60 min;

[0090] Second stage: Evacuate to <10 Pa, then introduce argon gas (flow rate 2-5 L / min), heat up at a rate of 15℃ / min, heat up to 1200±10℃ and hold for 20-30 min;

[0091] The third stage involves a heating rate of 10℃ / min, heating to 1450–1600℃ and holding for 120–300 min.

[0092] Step 5: Cool to room temperature with the furnace, and put into storage after passing the inspection.

[0093] Example 10

[0094] Example 10 is largely the same as Example 9, except that 0.3 parts of cerium oxide are added.

[0095] Example 11

[0096] Example 11 is largely the same as Example 1, except that 0.3% ammonium citrate is added to the raw materials as a dispersant.

[0097] Example 12

[0098] Example 12 is largely the same as Example 9, except that 0.3% ammonium citrate is added to the raw materials as a dispersant.

[0099] Example 13

[0100] Example 13 is largely the same as Example 9, except that after sintering, it is rapidly cooled to below 1200°C at a rate of ≥50°C / min, and then allowed to cool naturally.

[0101] MPa·m¹ / ² MPa 1000℃, MPa·m¹ / ² 1000℃, MPa 1100℃ → Water cooling, number of times Example 9 96% 2% 5.2 125 5.02 89 >25 times without cracks Example 10 96% 2% 5.2 125 5.12 91 >25 times without cracks Example 11 96% 2% 5.0 121 4.51 68 >15 times without cracks Example 12 96% 2% 5.1 122 4.75 75 >25 times without cracks Example 13 96% 2% 5.3 125 5.03 89 >25 times without cracks

[0102] As can be seen from Examples 11 and 12, the effect of adding a dispersant is negligible for this invention; therefore, no additional dispersant is needed. Example 13 shows a slight improvement in fracture toughness, mainly because rapid cooling can form fine amorphous or metastable phases of the rare earth phase, or even a continuous thin film along grain boundaries, which is beneficial for load transfer and crack deflection, thereby improving fracture toughness.

[0103] The above description is merely a preferred embodiment of this application and is not intended to limit this application.

Claims

1. A method for preparing rare earth composite sintered corundum, characterized in that, Includes the following steps: Step 1: Calcine the industrial alumina powder at 1200-1400℃ for 2-3 hours, and then ball mill it. After ball milling, select alumina powder with a particle size of 1-5μm for later use. Step 2: Weigh the alumina base material and rare earth oxides. The alumina base material includes: 92-96 parts of industrial alumina powder, 4-5 parts of the alumina powder obtained in Step 1, and 0.8-1 parts of α-Al2O3 nanocrystals. The rare earth oxides are 0.5-2 parts of lanthanum oxide and 0.5-2 parts of yttrium oxide. Mix and grind the above raw materials. After grinding, check the particle size until the following conditions are met and stop grinding: D98≤5μm and D90≤2μm. Step 3: Spray granulation of the slurry obtained in Step 2, rolling it into balls, controlling the diameter of the green balls to 20-25 mm and the bulk density of the green balls to 1.9-2.1 g / cm³; then dry it at 120℃ for 8-12 hours; Step 4, high-temperature sintering is performed using a gradient temperature increase, specifically as follows: First stage: heating rate 10-15℃ / min, heat to 600±10℃ and hold for 40-60min; Second stage: heating rate 15-20℃ / min, heat to 1200±10℃ and hold for 20-30min; Third stage: heating rate 10-15℃ / min, heat to 1450–1600℃ and hold for 120–300min; Step 5: Cool the furnace to room temperature, perform post-processing after cooling, and put it into storage after passing the inspection.

2. The method for preparing rare earth composite sintered corundum according to claim 1, characterized in that, Specifically, in step 1, the industrial alumina is required to have a D50 of 3-8 micrometers, a specific surface area of ​​0.5-10 m² / g, an α phase content of ≥95%, and an impurity content of ≤0.3%.

3. The preparation method of rare earth composite sintered corundum according to claim 1, characterized in that, In step 2, the α-Al2O3 nanocrystal seeds have a particle size of 20-100 nm, a specific surface area of ​​35-100 m² / g, and an impurity content of ≤0.08%.

4. The method for preparing rare earth composite sintered corundum according to claim 1, characterized in that, Step 1: Calcine the industrial alumina powder at 1200-1400℃ for 2-3 hours, and then ball mill it. After ball milling, select alumina powder with a particle size of 1-5μm for later use. Step 2: Weigh the alumina base material, rare earth oxides, and hexagonal boron nitride plate-like crystals. The alumina base material includes: 92-96 parts of industrial alumina powder, 4-5 parts of the alumina powder obtained in Step 1, and 0.8-1 parts of α-Al2O3 nanocrystal seeds. The rare earth oxides are 0.5-2 parts of lanthanum oxide and 0.5-2 parts of yttrium oxide. The hexagonal boron nitride plate-like crystals are 0.5-2 parts. Mix the above raw materials, grind them, and then test the particle size until the following conditions are met: D98≤5μm and D90≤2μm. Step 3: Spray granulation of the slurry obtained in Step 2, rolling it into balls, controlling the diameter of the green balls to 20-25 mm and the bulk density of the green balls to 1.9-2.1 g / cm³; then dry it at 120℃ for 8-12 hours; Step 4, high-temperature sintering is performed using a gradient temperature increase, specifically as follows: First stage: Introduce air at a flow rate of 2-5 L / min, with a heating rate of 10-15℃ / min, and hold at 600±10℃ for 40-60 min. Second stage: Evacuate to <10 Pa, then introduce argon gas at a flow rate of 2-5 L / min, heating rate of 15-20℃ / min, and heat to 1200±10℃ and hold for 20-30 min. The third stage involves a heating rate of 10-15℃ / min, followed by heating to 1450–1600℃ and holding for 120–300 min. Step 5: Cool the furnace to room temperature, perform post-processing after cooling, and put it into storage after passing the inspection.

5. The method for preparing rare earth composite sintered corundum according to claims 1-4, characterized in that, In step 2, the rare earth oxides are 0.5-0.9 parts of lanthanum oxide and 0.5-0.7 parts of yttrium oxide.

6. The method for preparing rare earth composite sintered corundum according to claims 1-4, characterized in that, In step 2, the rare earth oxides are 0.5-0.9 parts of lanthanum oxide, 0.5-0.7 parts of yttrium oxide, and 0.3-0.5 parts of cerium oxide.

7. The method for preparing rare earth composite sintered corundum according to claims 1-4, characterized in that, In step 2, the rare earth oxides are 0.5 parts lanthanum oxide, 0.7 parts yttrium oxide, and 0.3 parts cerium oxide.

8. The method for preparing rare earth composite sintered corundum according to claims 1-4, characterized in that, In step 2, the grinding is carried out in a ball mill with zirconia balls as the grinding medium, a ball-to-material ratio of 3:1, a rotation speed of 250-300 rpm, and premixed for 30 minutes. Then, an appropriate amount of deionized water and polyvinyl alcohol aqueous solution are added, and wet grinding is carried out for 4-8 hours.

9. The method for preparing rare earth composite sintered corundum according to claims 1-4, characterized in that, In step 2, the polyvinyl alcohol aqueous solution has a concentration of 2-5% and is used in an amount of 3-5% of the total mass of the powder.

10. The method for preparing rare earth composite sintered corundum according to claims 1-4, characterized in that, The aforementioned rolling spherical formation process involves first obtaining granulated powder, then using a disc rolling spherical forming machine with a disc inclination angle of 45-50° and a rotation speed of 20-30 rpm. The granulated powder is slowly added to the disc, while an appropriate amount of water is sprayed in at the same time, causing the powder to gradually roll into sphericals.

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