Aluminum oxide complex-phase aggregate with multilayer core-shell structure as well as preparation method and application of aluminum oxide complex-phase aggregate

Abstract

The invention discloses a multi-layer core-shell structure aluminum oxide multiphase aggregate, a preparation method and application of the multi-layer core-shell structure aluminum oxide multiphase aggregate. The aggregate comprises a porous alumina core, a spinel shell layer and an RE2O3 shell layer; wherein the spinel shell layer is formed in situ, and the RE2O3 shell layer covers the spinel shell layer in a continuous manner. The aggregate disclosed by the invention is simple in preparation process, low in high-temperature vacuum volatilization rate, excellent in thermal shock resistance and erosion resistance and suitable for being used as a lining raw material of a refractory material for high-quality steel casting and high-temperature alloy vacuum melting.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature refractory material preparation, and in particular to a multi-layer core-shell structure alumina composite aggregate, a preparation method and application thereof. Background Art

[0002] Aluminum refractories have excellent resistance to slag penetration and thermal shock, making them widely used in the melt pool area of large refining ladles, ensuring the refining and deep processing of high-quality steel. Furthermore, due to the low thermal expansion coefficient of the spinel phase, existing technologies often add spinel to the material system to improve the service performance of aluminum refractories.

[0003] In the prior art, CN116874288B discloses a method for preparing and applying plate-shaped corundum sphere refractory materials. This patent utilizes γ-Al2O3 fine powder, barium aluminate cement, rutile titanium dioxide, and graphite powder as raw materials. The raw materials are mixed, pelletized, and dried, and then sintered at room temperature to produce the plate-shaped corundum sphere refractory materials. However, this patented technology has the following drawbacks: First, it requires three rounds of pelletization, and sintering requires prolonged holding at four temperature platforms, resulting in a complex process and high cost. Second, the resulting shell structure is relatively independent of each other. In actual service, the composite powder in the intermediate transition layer will be rapidly eroded and penetrated through cracks, resulting in aggregate damage.

[0004] For example, CN116654960A discloses a method for preparing coated spherical magnesium oxide powder. This technology uses magnesium oxide as raw material, utilizes coupling agent and water-soluble surface treatment agent for modification treatment, and then prepares slurry, spray granulation, ball forming and other processes, and finally calcines to obtain spherical magnesium oxide powder. The MgO content of the magnesium oxide powder is only greater than 95%, and not only the purity of the prepared spherical magnesium oxide powder is not high, but also the preparation process is complicated. Although the spherical magnesium oxide powder prepared by this technology has good moisture resistance, the coupling agent used can introduce impurities into the raw material, affect the high temperature performance, and the preparation cost is high.

[0005] For example, the literature technology (Yin H, Liu Y, Tang Y, et al. Effect of Al2O3@CaCO3spherical particles on microstructures, phase compositions and performancesof lightweight MA spinel-corundum refractories. Ceramics International, 2021,47(22): 31548-31554.) used spinel particles, corundum powder, spinel powder and calcium carbonate powder as raw materials to prepare a lightweight spinel corundum aggregate. Although it has a low bulk density, the pores in the aggregate are large and the shell thickness cannot be controlled.

[0006] In short, the art is in urgent need of an aluminum refractory material with a simplified preparation method and excellent performance. Summary of the Invention

[0007] The present invention aims to overcome the defects of the existing technology and aims to provide an alumina refractory raw material with a simple preparation process, controllable aggregate particle size, high thermal shock resistance, ultra-low high-temperature vacuum volatility and excellent corrosion resistance. It is expected to be used in high-quality steel casting and high-temperature alloy vacuum melting processes, and solve the shortcomings of aluminum refractory materials in the existing technology.

[0008] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present application provides a multi-layer core-shell structure alumina composite aggregate, which comprises: a porous alumina core; a spinel shell layer, which is formed in situ; and a RE2O3 shell layer, which continuously covers the spinel shell layer.

[0009] Furthermore, the aggregate is spherical with a diameter of 1-5 mm, preferably 1-3 mm or 3-5 mm; and / or the diameter of the porous alumina core is 0.5-5.0 mm, preferably 0.75-2.75 mm or 2.75-4.75 mm; and / or the thickness of the spinel shell is 150~200 μm; and / or the RE2O3 is one or a mixture of more than one of yttrium oxide and lanthanum oxide, and the thickness of the RE2O3 shell is 20~30 μm.

[0010] Furthermore, the bulk density of the aggregate is 3.21-3.36 g / cm 3 ; and / or, the apparent porosity of the aggregate is 10.12-11.12%.

[0011] In a second aspect, the present application also provides a method for preparing a multi-layer core-shell structured alumina composite aggregate, comprising the following steps: Step 1: Prepare Green Balls I. A first powder containing Al is used as a matrix, mixed with a binder, and then pelletized to produce Green Balls I. This step employs a pelletizing method, such as a forced mixer, to produce high-strength Green Balls I of uniform size.

[0012] Step 2: Prepare a green ball II. The green ball I is mixed with a second powder to obtain a green ball II in the form of the second powder attached to the green ball I. The second powder contains Mg and RE elements.

[0013] Step 3: Drying: Drying the green ball II; Step 4: sintering, sintering the dried green ball II to obtain a multi-layer core-shell structured alumina composite aggregate, wherein the aggregate includes an in-situ formed spinel shell layer.

[0014] Furthermore, in the above steps, the first powder is industrial alumina powder; and / or the binder is nano-aluminum hydroxide suspension; and / or the second powder is a mixed powder containing Mg(OH)2 powder and RE2O3 powder.

[0015] Furthermore, in the preparation process of green ball II, Mg(OH)2 and RE2O3 powders are first mixed by ball milling for a certain period of time to obtain a mixed powder; in the subsequent process, the mixed powder is wrapped on green ball I through a disc ball making machine to finally obtain green ball II.

[0016] Furthermore, the content of each material in the preparation method is expressed as follows in weight percentage: 53-72 parts by weight of industrial alumina powder, wherein the Al2O3 content is greater than 99.8wt%, the particle size D 0.5 <0.8μm; 15-28 parts by weight of nano-aluminum hydroxide suspension, wherein the Al(OH)3 particle size is <80nm and the concentration is 500ppm-4000ppm; 25-45 parts by weight of Mg(OH)2 powder, wherein the Mg(OH)2 content is >99.8wt% and the SiO2 content is <0.01wt%; 2-4 parts by weight of RE2O3 powder, wherein the purity of rare earth oxide is >99.9wt% and the particle size D 0.5 <5μm.

[0017] Furthermore, the preparation method of the nano-aluminum hydroxide suspension is as follows: adding the aluminum hydroxide to the pure water at a mass ratio of nano-aluminum hydroxide to pure water of 1-8:1999, and stirring until the mixture is uniformly mixed.

[0018] Furthermore, the sintering process adopts a step-by-step heat preservation method, first heating to 600-850°C and keeping it for 1-2 hours, then heating to 1480-1530°C and keeping it for 2-4 hours, and finally heating to 1700-1780°C and keeping it for 3-6 hours.

[0019] The lightweight alumina composite aggregate with a multi-layer core-shell structure prepared by the present invention has an apparent porosity of 10.12-11.12% and a bulk density of 3.21-3.36 g / cm 3 ; Under the conditions of temperature of 1700°C and pressure of 10Pa, the temperature and pressure are maintained for 1 hour, and the high-temperature vacuum volatility is 1.0~1.3%; after three repeated 1100°C-20°C water-cooling tests (that is, the aggregate is heated to 1100°C, then water-cooled to 20°C, and repeated three times), the sphere integrity percentage is 95-100%. The integrity percentage of the spheres before and after water cooling is used to characterize the thermal shock resistance of the raw material. The slag erosion depth of the sample is 100~110μm, the RE2O3 continuous shell thickness is 20~30μm, and the spinel shell continuous thickness is 150~200μm.

[0020] In a third aspect, the present application also provides an application of an aggregate, wherein the aggregate is used for steel casting or high-temperature alloy vacuum melting.

[0021] Due to the adoption of the above technical solution, the present invention has the following positive effects compared with the prior art: First, the aggregate prepared by the present invention achieves significant lightweighting while also improving thermal shock resistance. Research has shown that strictly controlling the temperature between 600°C and 850°C during the initial sintering phase allows aluminum hydroxide to decompose in situ and generate pores. Furthermore, the "salt mother phase" structure left behind by the aluminum hydroxide raw material ensures that intracrystalline pores are not completely eliminated during the medium-temperature sintering process (i.e., the 600-850°C range), thereby forming a porous alumina core structure, effectively reducing the bulk density of the alumina refractory aggregate and achieving lightweighting. Furthermore, these intracrystalline pore structures ensure the thermal shock resistance of the alumina refractory aggregate and effectively disperse stress.

[0022] Secondly, the aggregate prepared by this invention significantly improves its service performance. Research has shown that when the second-stage sintering temperature is strictly controlled within the range of 1480°C to 1530°C and maintained for 2-4 hours, the Mg(OH)2 attached to the outer layer decomposes into light-burned MgO. Furthermore, MgO and Al2O3 (produced during the sintering process) form a dense and uniform spinel layer in situ at high temperatures. Because the mass transfer rate of MgO is greater than that of Al2O3 during the in-situ spinel formation chemical reaction, MgO migrates toward the core and eventually reacts with Al2O3 to form a spinel layer. RE2O3 remains on the outer surface of the sphere, forming a continuous RE2O3 shell that covers the spinel shell, resulting in a continuous and dense RE2O3 shell structure. The result is a porous alumina core + a continuous and dense spinel shell + a continuous and dense RE2O3 shell (P-alumina@D-spinel@RE2O3 core-shell structure). The inventors have found that, on the one hand, RE2O3 as a sintering agent reduces the sintering temperature in the final stage and shortens the holding time, which plays a role in reducing energy consumption and increasing the density of the material; on the other hand, due to the MgO-RE2O3 (such as Y2O 3、 The insolubility of the RE2O3 binary structure at high temperatures allows the formation of a continuous, dense rare earth oxide shell. Furthermore, RE2O3 itself, as a rare earth oxide, effectively resists slag erosion. The in-situ formation of the spinel layer and dense RE2O3 shell not only ensures aggregate strength, but also reduces intracrystalline volatility under high-temperature vacuum conditions and minimizes slag erosion and penetration distance. This significantly improves the serviceability of the aggregate. Furthermore, the thickness of the spinel and RE2O3 shells can be controlled by adjusting the ratio of the raw materials added.

[0023] Third, the aggregate preparation method of this application has been significantly simplified, significantly improving efficiency. Through research, the inventors of this application have proposed a "one-step, two-ball, three-temperature" preparation method, which significantly optimizes the process compared to the prior art. The "two-ball" method refers to the process of obtaining a three-layer structure (P alumina @ D spinel @ RE2O3 core-shell) through only two ball-forming steps, eliminating at least one ball-forming step compared to the prior art (e.g., the prior art CN116874288B). The "one-step" method refers to the green balls II being placed in a kiln (furnace) and sintered once to obtain the finished product. The "three-temperature" method refers to the inventors' improved sintering process, which requires only three heating and holding stages to complete the entire sintering process, significantly shortening the process flow compared to the prior art. Of course, those skilled in the art will appreciate that the "one-step, two-ball, three-temperature" method is a feasible solution for sintering the aggregate described herein. If other performance or structural requirements arise, those skilled in the art are encouraged to appropriately adjust the ball-forming, kiln-feeding, and temperature settings based on this method. Thus, the preparation method of this application can significantly reduce energy consumption and improve aggregate preparation efficiency.

[0024] Therefore, the present invention has the characteristics of simple process and controllable aggregate particle size. The prepared lightweight alumina composite aggregate with a multi-layer core-shell structure has a low high-temperature vacuum volatility rate, excellent thermal shock resistance and excellent hydration resistance, and is suitable for the vacuum melting process of high-temperature alloys or the vacuum secondary refining process of clean steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the microstructure of the multi-layer core-shell structure lightweight alumina composite aggregate in Example 1.

[0026] Figure 2 This is the microstructure of the multi-layer core-shell structure lightweight alumina composite aggregate in Example 4.

[0027] Figure 3 This is a macroscopic photograph of the multi-layer core-shell structure lightweight alumina composite aggregate in Example 6. DETAILED DESCRIPTION

[0028] In order to further understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments, which does not limit the scope of protection of the present invention.

[0029] Example 1: This embodiment provides a method for preparing a multi-layer core-shell structure lightweight alumina composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 53 parts by weight of industrial alumina powder are added with 28 parts by weight of a nano-aluminum hydroxide suspension as a binder, wherein the concentration of the nano-aluminum hydroxide suspension is 3000 ppm; and a high-strength green ball I is prepared by a forced mixer ball-forming method. The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the nano-aluminum hydroxide to pure water at a mass ratio of 6:1999, and stirring and mixing the mixture evenly.

[0030] Step 2: Add 45 parts by weight of Mg(OH)2 powder and 2 parts by weight of Y2O3 powder to a ball mill and mill for 1 hour to obtain a uniformly mixed second powder; add the green ball I prepared in step 1 and the second powder to a disc ball making machine so that the second powder adheres to the green ball I, thereby producing green ball II; Step 3, drying the green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 600°C and keep it for 2 hours, then heat it to 1500°C and keep it for 3 hours, and finally heat it to 1700°C and keep it for 6 hours. Cool it naturally in the furnace to obtain a lightweight alumina composite aggregate with a multi-layer core-shell structure.

[0031] After testing, the thickness of the Y2O3 continuous shell of the aggregate in this embodiment is 20 μm, and the thickness of the spinel shell is 150 μm.

[0032] Example 2: This embodiment provides another method for preparing a multi-layer core-shell structure lightweight alumina composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 72 parts by weight of industrial alumina powder are added with 15 parts by weight of a nano-aluminum hydroxide suspension as a binder, wherein the concentration of the nano-aluminum hydroxide suspension is 500 ppm; and a high-strength green ball I is prepared by a forced mixer ball-forming method. The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the nano-aluminum hydroxide to pure water at a mass ratio of 1:1999, and stirring and mixing the mixture evenly.

[0033] Step 2: Add 25 parts by weight of Mg(OH)2 powder and 3 parts by weight of La2O3 powder to a ball mill and mill for 2 hours to obtain a uniformly mixed second powder; add the green ball I prepared in step 1 and the second powder to a disc ball making machine so that the second powder adheres to the green ball I, thereby obtaining green ball II; Step 3: drying the prepared green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 850°C and keep it for 1 hour, then heat it to 1480°C and keep it for 4 hours, and finally heat it to 1780°C and keep it for 3 hours. Cool it naturally in the furnace to obtain a lightweight alumina composite aggregate with a multi-layer core-shell structure.

[0034] After testing, the thickness of the La2O3 continuous shell of the aggregate in this embodiment is 25 μm, and the thickness of the spinel shell is 170 μm.

[0035] Example 3: This embodiment provides another method for preparing a multi-layer core-shell structure lightweight alumina composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 67 parts by weight of industrial alumina powder are added with 24 parts by weight of a nano-aluminum hydroxide suspension as a binder, wherein the concentration of the nano-aluminum hydroxide suspension is 1000 ppm; and a high-strength green ball I is prepared by a forced mixer ball-forming method. The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the nano-aluminum hydroxide to pure water at a mass ratio of 2:1999, and stirring and mixing the mixture evenly.

[0036] Step 2: Add 30 parts by weight of Mg(OH)2 powder and 3 parts by weight of RE2O3 powder (1.5 parts by weight of La2O3 + 1.5 parts by weight of Y2O3) to a ball mill and mill for 2 hours to obtain a uniformly mixed second powder; add the green ball I prepared in step 1 and the second powder to a disc ball making machine so that the second powder adheres to the green ball I, thereby producing green ball II; Step 3: drying the prepared green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 700°C and keep it for 1.5 hours, then heat it to 1530°C and keep it for 2 hours, and finally heat it to 1750°C and keep it for 4 hours. Cool it naturally in the furnace to obtain a lightweight alumina composite aggregate with a multi-layer core-shell structure.

[0037] According to the test, the thickness of the RE2O3 continuous shell of the aggregate in this embodiment is 26 μm, and the thickness of the spinel shell is 180 μm.

[0038] Example 4: This embodiment provides another method for preparing a multi-layer core-shell structure lightweight alumina composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 60 parts by weight of industrial alumina powder are added with 20 parts by weight of a nano-aluminum hydroxide suspension as a binder, wherein the concentration of the nano-aluminum hydroxide suspension is 4000 ppm; and a high-strength green ball I is prepared by a forced mixer ball-forming method. The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the nano-aluminum hydroxide to pure water at a mass ratio of 8:1999, and stirring and mixing the mixture evenly.

[0039] Step 2: Add 36 parts by weight of Mg(OH)2 powder and 4 parts by weight of RE2O3 powder (2 parts by weight of La2O3 + 2 parts by weight of Y2O3) to a ball mill and mill for 3 hours to obtain a uniformly mixed second powder; add the green ball I prepared in step 1 and the second powder to a disc ball making machine so that the second powder adheres to the green ball I, thereby producing green ball II; Step 3: drying the prepared green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 750°C and keep it for 1.5 hours, then heat it to 1510°C and keep it for 2 hours, and finally heat it to 1750°C and keep it for 5 hours. Cool it naturally in the furnace to obtain a lightweight alumina composite aggregate with a multi-layer core-shell structure.

[0040] According to the test, the thickness of the RE2O3 continuous shell of the aggregate in this embodiment is 30 μm, and the thickness of the spinel shell is 150 μm.

[0041] Example 5: This embodiment provides another method for preparing a multi-layer core-shell structure lightweight alumina composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 53 parts by weight of industrial alumina powder are added with 15 parts by weight of a nano-aluminum hydroxide suspension as a binder, wherein the concentration of the nano-aluminum hydroxide suspension is 500 ppm; and high-strength green balls I are prepared by a forced mixer ball-forming method. The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the nano-aluminum hydroxide to pure water at a mass ratio of 1:1999, and stirring and mixing the mixture evenly.

[0042] Step 2: Add 25 parts by weight of Mg(OH)2 powder and 2 parts by weight of Y2O3 powder to a ball mill and mill for 1 hour to obtain a uniformly mixed second powder; add the green ball I prepared in step 1 and the second powder to a disc ball making machine so that the second powder adheres to the green ball I, thereby obtaining green ball II; Step 3: drying the prepared green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 600°C and keep it for 1 hour, then heat it to 1480°C and keep it for 2 hours, and finally heat it to 1700°C and keep it for 3 hours. Cool it naturally in the furnace to obtain a lightweight alumina composite aggregate with a multi-layer core-shell structure.

[0043] According to the test, the thickness of the RE2O3 continuous shell of the aggregate in this embodiment is 24 μm, and the thickness of the spinel shell is 165 μm.

[0044] Example 6: This embodiment provides another method for preparing a multi-layer core-shell structure lightweight alumina composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 72 parts by weight of industrial alumina powder are added to 28 parts by weight of a nano-aluminum hydroxide suspension as a binder, wherein the concentration of the nano-aluminum hydroxide suspension is 4000 ppm; and a high-strength green ball I is prepared by a forced mixer ball-forming method. The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the nano-aluminum hydroxide to pure water at a mass ratio of 8:1999, and stirring and mixing the mixture evenly.

[0045] Step 2: Add 45 parts by weight of Mg(OH)2 powder and 4 parts by weight of La2O3 powder to a ball mill and mill for 3 hours to obtain a uniformly mixed second powder; add the green ball I prepared in step 1 and the second powder to a disc ball making machine so that the second powder adheres to the green ball I, thereby obtaining green ball II; Step 3: drying the prepared green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 850°C and keep it for 2 hours, then heat it to 1530°C and keep it for 4 hours, and finally heat it to 1780°C and keep it for 6 hours. Cool it naturally in the furnace to obtain a lightweight alumina composite aggregate with a multi-layer core-shell structure.

[0046] According to the test, the thickness of the RE2O3 continuous shell of the aggregate in this embodiment is 30 μm, and the thickness of the spinel shell is 200 μm.

[0047] Example 7: In order to test the performance of the aggregates prepared in Examples 1-6 above and the aggregates prepared by the prior art (it should be noted that in order to make the results comparable, the testing of various performance indicators adopts unified conditions, for example, the high-temperature vacuum volatility is measured at a temperature of 1700°C and a pressure of 10Pa, and the heat and pressure are maintained for 1 hour; the sphere integrity percentage is measured after three times of water cooling at 1100-20°C, and the sphere integrity percentage before and after water cooling is used to characterize the thermal shock resistance of the raw material), the results are shown in the following table:

[0048] It can be seen from the above table that the key performance of the aggregate designed in this application is better than that of the existing technology when used in high temperature environment.

[0049] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A multi-layer core-shell structure alumina composite aggregate, characterized in that: The aggregate includes: porous alumina core; a spinel shell layer, the spinel shell layer being formed in situ; and, A RE2O3 shell layer covers the spinel shell layer in a continuous manner.

2. The multi-layer core-shell structure lightweight alumina composite aggregate according to claim 1, characterized in that: The aggregate is spherical and has a diameter of 1-5 mm; and / or, The diameter of the porous alumina core is 0.5-5 mm; and / or, The thickness of the spinel shell is 150-200 μm; and / or, The RE2O3 is one of yttrium oxide and lanthanum oxide or a mixture of more than one thereof, and the thickness of the RE2O3 shell is 20-30 μm.

3. A multi-layer core-shell structure lightweight alumina composite aggregate according to claim 1 or 2, characterized in that: The bulk density of the aggregate is 3.21-3.36 g / cm 3 and / or, The apparent porosity of the aggregate is 10.12-11.12%.

4. A method for preparing a multi-layer core-shell structured alumina composite aggregate, characterized in that: The method comprises the following steps: Step 1: preparing green ball I, using a first powder containing Al as a matrix, mixing with a binder, and then forming a ball to obtain green ball I; Step 2: preparing a green ball II, mixing the green ball I with a second powder, and attaching the second powder to the green ball I to obtain a green ball II, wherein the second powder contains Mg and RE elements; Step 3: Drying: Drying the green ball II; Step 4: sintering, sintering the dried green ball II to obtain a multi-layer core-shell structured alumina composite aggregate, wherein the aggregate includes an in-situ formed spinel shell layer.

5. The preparation method according to claim 4, characterized in that The first powder is industrial alumina powder; and / or, The binder is a nano-aluminum hydroxide suspension; and / or, The second powder is a mixed powder containing Mg(OH)2 powder and RE2O3 powder.

6. The preparation method according to claim 5, characterized in that The content of each material in the preparation method is expressed as follows in weight percentage: 53-72 parts by weight of industrial alumina powder, wherein the Al2O3 content is greater than 99.8wt% and the particle size is D 0.5 <0.8μm; 15-28 parts by weight of nano-aluminum hydroxide suspension, wherein the Al(OH)3 particle size is less than 80 nm and the concentration is 500 ppm-4000 ppm; 25-45 parts by weight of Mg(OH)2 powder, wherein the Mg(OH)2 content is greater than 99.8wt% and the SiO2 content is less than 0.01wt%; 2-4 parts by weight of RE2O3 powder, wherein the purity of rare earth oxide is greater than 99.9wt% and the particle size is D 0.5 <5μm.

7. The preparation method according to claim 5 or 6, characterized in that: The preparation method of the nano-aluminum hydroxide suspension is as follows: adding the aluminum hydroxide to the pure water according to the mass ratio of the nano-aluminum hydroxide to the pure water of 1-8:1999, and stirring until the mixture is uniform.

8. The preparation method according to any one of claims 4 to 6, characterized in that The sintering process adopts a step-by-step heat preservation method, first heating to 600-850°C and keeping it for 1-2 hours, then heating to 1480-1530°C and keeping it for 2-4 hours, and finally heating to 1700-1780°C and keeping it for 3-6 hours.

9. Use of the aggregate according to claims 1-3 or the aggregate prepared by the method according to claims 4-8, characterized in that: The aggregate is used for preparing castables and bricks.

10. Use of the aggregate according to claims 1-3 or the aggregate prepared by the method according to claims 4-8, characterized in that: The aggregate is used for steel casting or high-temperature alloy vacuum melting.

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