Method for preparing nanometer aluminum oxide based on gradient centrifugation and supercritical technology

Abstract

The invention relates to the technical field of preparation of nano aluminum oxide functional materials, in particular to a method for preparing nano aluminum oxide based on gradient centrifugation and a supercritical technology. The method comprises the following steps: carrying out dispersion treatment on a hydrophilic solvent, an aluminum oxide raw material and a dispersing agent to obtain initial slurry; under the condition of constant temperature, the initial slurry is subjected to graded grinding, and refined slurry is obtained; the graded grinding sequentially comprises first-stage grinding, second-stage grinding and third-stage grinding; carrying out gradient centrifugation on the refined slurry to obtain concentrated slurry; the gradient centrifugation sequentially comprises first-stage centrifugation, second-stage centrifugation and third-stage centrifugation; carrying out supercritical drying on the concentrated slurry by using carbon dioxide and a silane coupling agent to obtain coarse alumina powder; and drying the coarse alumina powder in vacuum to obtain the nano alumina. According to the method, through multi-unit collaborative integration of graded grinding, gradient centrifugation and supercritical drying, the production target of high-purity, narrow-particle-size-distribution and low-agglomeration-rate nanometer aluminum oxide is achieved, and the use performance of the nanometer aluminum oxide product is remarkably improved.

Description

Technical Field

[0001] This application relates to the field of nano-alumina functional material preparation technology, and in particular to a method for preparing nano-alumina based on gradient centrifugation and supercritical technology. Background Technology

[0002] Nano-alumina possesses excellent thermal stability, high hardness, good insulation, and catalytic properties, and can be widely used in high-end industries such as advanced ceramics, semiconductor polishing, lithium battery separator coatings, transparent ceramics, and thermal conductive materials. For example, high-purity nano-alumina with low agglomeration (99.99% purity and median particle size below 100nm) exhibits extremely low impurity content, high sintering activity, and fine nanoscale characteristics, showing significant application prospects in multiple high-end fields: In the new energy field, high-purity nano-alumina is a key coating material for high-performance lithium battery separators, and high-performance lithium battery separators with good performance can significantly improve battery safety and cycle life; in the semiconductor polishing field, high-purity nano-alumina, as the core grinding material for next-generation chemical mechanical polishing, can meet the extreme requirements of advanced processes for the global flatness of semiconductor wafers; in cutting-edge materials, high-purity nano-alumina is an indispensable precursor material for manufacturing transparent ceramics with high light transmittance and high hardness; in the field of thermal conductive materials, high-purity nano-alumina is a high-performance thermally conductive filler that can be widely used in thermal management interface materials for high-power electronic devices to meet the heat dissipation requirements of high-power electronic devices. However, the inherent high surface energy of nanoparticles like nano-alumina makes them highly susceptible to severe particle agglomeration, especially hard agglomeration. Hard agglomeration significantly reduces the sintering activity of high-purity nano-alumina and ultimately affects the densification and mechanical properties of products made from alumina. Therefore, hard agglomeration of nano-alumina has become a bottleneck restricting the application of high-purity nano-alumina.

[0003] To address the hard agglomeration phenomenon in nano-alumina, one can typically start from the preparation stage of nano-alumina or reprocess the prepared nano-alumina products to improve the dispersion of nano-alumina and avoid hard agglomeration. However, nano-alumina obtained through these processing methods often suffers from defects such as low purity, high agglomeration rate, or uneven particle size distribution, resulting in poor performance of the high-purity nano-alumina. Summary of the Invention

[0004] This application provides a method for preparing nano-alumina based on gradient centrifugation and supercritical technology to solve the following technical problem: how to improve the performance of high-purity nano-alumina. In a first aspect, embodiments of this application provide a method for preparing nano-alumina based on gradient centrifugation and supercritical technology, the method comprising: The hydrophilic solvent, alumina raw material, and dispersant are dispersed to obtain an initial slurry; Under constant temperature conditions, the initial slurry is subjected to graded grinding to obtain a refined slurry; wherein the graded grinding includes first-stage grinding, second-stage grinding and third-stage grinding in sequence, and the rotation speed of the first-stage grinding is less than the rotation speed of the third-stage grinding and the rotation speed of the second-stage grinding; The refined slurry is subjected to gradient centrifugation to obtain a concentrated slurry; wherein the gradient centrifugation includes first-stage centrifugation, second-stage centrifugation and third-stage centrifugation in sequence, and the speed of the first-stage centrifugation is less than the speed of the second-stage centrifugation and the speed of the third-stage centrifugation; The concentrated slurry was subjected to supercritical drying using carbon dioxide and a silane coupling agent to simultaneously complete the drying and modification, thereby obtaining crude alumina powder. The crude alumina powder was vacuum dried to obtain nano-alumina.

[0005] Optionally, the rotational speed of the first-stage grinding is 1400 r / min to 1600 r / min, and the grinding time is 30 min to 45 min; and / or The secondary grinding speed is 2400 r / min to 2600 r / min, and the secondary grinding time is 60 min to 90 min; and / or The rotation speed of the three-stage grinding is from 1800 r / min to 2200 r / min, and the grinding time is from 20 min to 30 min.

[0006] Optionally, the grinding media used in the graded grinding is grinding balls, and the particle size of the grinding balls is 0.1 mm to 0.2 mm.

[0007] Optionally, the mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy: m1:m2 = (8 to 10):1.

[0008] Optionally, the refined slurry is subjected to gradient centrifugation to obtain a concentrated slurry, including the following steps: The refined slurry was subjected to a first-stage centrifugation to obtain a first-stage precipitate and a first-stage supernatant; The primary sediment is returned as part of the initial slurry to the classifying and grinding process; The primary supernatant was subjected to secondary centrifugation to obtain a secondary precipitate; The secondary precipitate is centrifuged and washed with a washing solution to obtain a precipitate mixture; wherein the mass m3 of the washing solution and the mass m4 of the secondary precipitate satisfy the following condition: m3:m4 = (3 to 5):1; The precipitated mixture was subjected to three-stage centrifugation to obtain a concentrated slurry.

[0009] Optionally, the speed of the first-stage centrifugation is 800 r / min to 1200 r / min, and the time of the first-stage centrifugation is 10 min to 15 min; and / or The secondary centrifugation speed is 4800 r / min to 5200 r / min, and the secondary centrifugation time is 20 min to 30 min; and / or The speed of the three-stage centrifugation is 8000 r / min to 12000 r / min, and the time of the three-stage centrifugation is 15 min to 20 min.

[0010] Optionally, the temperature of the supercritical drying is 31°C to 35°C, the pressure of the supercritical drying is 7.5 MPa to 8.5 MPa, and the time of the supercritical drying is 1 h to 2 h.

[0011] Optionally, the temperature of the graded grinding is 25°C to 40°C; and / or The vacuum drying temperature is 100℃ to 120℃, the vacuum degree is 0.08MPa to 0.10MPa, and the vacuum drying time is 1h to 2h.

[0012] Optionally, the mass m5 of the silane coupling agent and the mass m6 of the concentrated slurry satisfy: m5:m6 = (95 to 105):1; and / or The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following: m7:m8:m9 = (600 to 1000):100:(0.3 to 0.8).

[0013] Optionally, the dispersion treatment speed is 280 r / min to 320 r / min, and the dispersion treatment time is 40 min to 60 min.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing nano-alumina based on gradient centrifugation and supercritical technology. The method first disperses the hydrophilic solvent, alumina raw material, and dispersant. This reduces the agglomeration of the alumina raw material, preventing alumina particle clumping during the initial stage of graded grinding, thus obtaining a uniformly dispersed initial slurry. Furthermore, graded grinding is carried out under constant temperature conditions, with the first-stage grinding speed lower than the third-stage grinding speed, and the third-stage grinding speed lower than the second-stage grinding speed. This balances the refining efficiency and particle integrity of the graded grinding, preventing excessive grinding from increasing the particle size distribution of the nano-alumina, resulting in a refined slurry with a uniform particle size distribution. Next, the refined slurry is subjected to gradient centrifugation, with the first-stage centrifugation speed lower than the second-stage centrifugation speed, and the second-stage centrifugation speed lower than the third-stage centrifugation speed. This gradient centrifugation refines the morphology of the nano-alumina, reducing the proportion of ultrafine nano-alumina particles, ultimately obtaining a concentrated slurry with a concentrated particle size distribution. Furthermore, supercritical drying of the concentrated slurry using carbon dioxide and a silane coupling agent not only preserves the nanoscale dispersion of alumina particles but also ensures that the silane coupling agent is uniformly coated on the particle surface of the concentrated slurry. This simultaneously completes the drying and surface modification of the concentrated slurry, completely resolving the traditional contradiction between drying agglomeration and subsequent modification. Finally, vacuum drying removes moisture and dispersant from the coarse alumina powder, achieving the production target of high-purity, narrow-size distribution, and low agglomeration rate of nano-alumina, significantly improving the performance of the nano-alumina product. Attached Figure Description The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This application provides a schematic flowchart of a method for preparing nano-alumina based on gradient centrifugation and supercritical technology in an embodiment of the present application. Figure 2 This is a detailed flowchart illustrating a method for preparing nano-alumina based on gradient centrifugation and supercritical technology, provided in an embodiment of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] The range descriptions used in this application, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "comprising" and others used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships involved in this document, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained by purchasing from the market or by existing methods.

[0019] It should be noted that in order to solve the hard agglomeration phenomenon of nano alumina, it is generally possible to start from the preparation stage of nano alumina, or to reprocess the prepared nano alumina products. Specifically: (1) Reprocessing: Grind the prepared nano alumina. Traditional grinding is mostly done by grinding alumina particles with a grinding medium at a fixed speed to form nano alumina products. This process is prone to problems such as over-grinding or insufficient refinement of alumina. Moreover, the grinding method is generally carried out under normal temperature conditions. The grinding medium will generate a lot of heat by friction when grinding alumina particles. The accumulation of this heat may lead to increased wear of the grinding medium, resulting in the nano alumina being mixed with some grinding medium, which affects the purity of the nano alumina. Although purification processes can be introduced after grinding to improve the purity of nano-alumina, most purification processes are carried out in steps of centrifugation and multiple water washing. This not only makes it difficult to accurately classify the particle size of nano-alumina, but also easily leads to uneven dispersion of nano-alumina particles during water washing, resulting in impurities remaining in nano-alumina. In addition, after water washing, a drying process (such as vacuum drying or spray drying) is required to remove the washing liquid. However, during the drying process, there will be surface tension at the solid-liquid interface between nano-alumina and the washing liquid, which can easily lead to severe agglomeration of nanoparticles, further affecting the performance of nano-alumina. Therefore, after the drying process, a modifier can be introduced to modify nano-alumina to prevent agglomeration. However, the process of anti-agglomeration modification is relatively complicated, and the modifier is unevenly distributed, which affects the particle size distribution of nano-alumina. (2) Improvement of the preparation stage of nano-alumina: Improve the preparation process of nano-alumina to a direct synthesis method, such as vapor deposition and sol-gel method. While vapor deposition (CVD) can produce low-agglomeration, high-purity nano-alumina, it requires expensive production equipment and generates extremely high energy consumption during the process. Furthermore, CVD has low raw material utilization, resulting in high prices for the final low-agglomeration, high-purity nano-alumina, hindering its widespread application in fields other than semiconductor polishing. The sol-gel method, while not requiring expensive equipment, faces a trade-off between purity and cost: The sol-gel method typically involves converting a precursor into aluminum hydroxide gel, followed by drying and crystal transformation processes to form nano-alumina. However, the aluminum hydroxide gel undergoes severe agglomeration during the drying stage due to capillary forces, affecting the performance of the nano-alumina.

[0020] Therefore, current treatment methods for the hard agglomeration of high-purity nano-alumina are insufficient to balance the purity, agglomeration rate, and particle size distribution of nano-alumina, resulting in poor performance of nano-alumina.

[0021] To address the aforementioned shortcomings, this application provides a method for preparing nano-alumina based on gradient centrifugation and supercritical technology. The specific technical solution is as follows: Figure 1 An exemplary schematic diagram of a method for preparing nano-alumina based on gradient centrifugation and supercritical technology provided in this application embodiment is shown; like Figure 1 As shown in the embodiments of this application, a method for preparing nano-alumina based on gradient centrifugation and supercritical technology is provided, the method comprising: S1. The hydrophilic solvent, alumina raw material and dispersant are dispersed to obtain an initial slurry; S2. Under constant temperature conditions, the initial slurry is subjected to graded grinding to obtain a refined slurry; wherein the graded grinding includes primary grinding, secondary grinding and tertiary grinding in sequence, and the rotation speed of the primary grinding is less than the rotation speed of the tertiary grinding and the rotation speed of the secondary grinding. S3. The refined slurry is subjected to gradient centrifugation to obtain a concentrated slurry; wherein the gradient centrifugation includes first-stage centrifugation, second-stage centrifugation and third-stage centrifugation in sequence, and the rotation speed of the first-stage centrifugation is less than the rotation speed of the second-stage centrifugation and the rotation speed of the third-stage centrifugation; S4. The concentrated slurry is subjected to supercritical drying using carbon dioxide and silane coupling agent to simultaneously complete the drying and modification, thereby obtaining crude alumina powder; S5. The crude alumina powder is vacuum dried to obtain nano-alumina.

[0022] It should be noted that the alumina raw material can have a purity of ≥99.99% and a median particle size of 200nm to 500nm.

[0023] It should be noted that the dispersant can be polyethylene glycol 4000; the hydrophilic solvent can be deionized water.

[0024] It should be noted that this graded grinding can be carried out in a horizontal turbine nano-sand mill, and the constant temperature state of this graded grinding can be achieved by a jacketed temperature control system, with a temperature fluctuation of ±1℃.

[0025] It should be noted that the type of silane coupling agent can be KH-560 silane coupling agent; the supercritical drying process is divided into a pressurization reaction stage and a depressurization stage. In the pressurization reaction stage, the supercritical carbon dioxide will dissolve the water and dispersant in the concentrated slurry. In the depressurization stage, the pressure can be slowly released at a depressurization rate of 0.5 MPa / h, so that the supercritical carbon dioxide is converted into gas and escapes. At the same time, in the depressurization stage, the silane coupling agent can be uniformly coated on the particle surface of the concentrated slurry to simultaneously achieve the drying and anti-agglomeration modification of the concentrated slurry.

[0026] It should be noted that the method for preparing nano-alumina based on gradient centrifugation and supercritical technology provided in this application embodiment overcomes the defects of low purity, high agglomeration rate, and uneven particle size distribution in traditional processes through multi-unit synergistic innovation of the entire process of graded sand milling + gradient centrifugation + supercritical drying, thereby improving the performance of high-purity nano-alumina. The specific mechanism is as follows: I. Solution strategy for uneven particle size distribution: dual-stage control of graded grinding + gradient centrifugation.

[0027] Traditional sand milling processes often result in a wide particle size distribution of alumina particles (large particles are not refined, and small particles are excessively broken) due to uneven grinding intensity. The method provided in this application achieves precise control of the nano-alumina particle size through the synergy of temperature control, stepped rotation speed graded sand milling, and gradient centrifugation. 1. Staged grinding process: A stepped speed design is adopted, consisting of primary grinding (low speed) → secondary grinding (highest speed) → tertiary grinding (medium speed) (primary grinding < tertiary grinding < secondary grinding). Combined with temperature control of staged grinding (to avoid particle agglomeration or phase change caused by thermal effects), the primary grinding at low speed first removes large-diameter coarse slag from the initial slurry and initially dissociates particle agglomerates in the initial slurry. Then, the secondary grinding at high speed can refine the medium-sized nano-alumina particles in the initial slurry. Finally, the tertiary grinding at medium speed is used to adjust the particle size distribution of nano-alumina, balancing the refining efficiency and particle integrity of staged grinding, and preventing the increase in the particle size dispersion of nano-alumina caused by over-grinding.

[0028] 2. Centrifugation process: A gradient centrifugation design is adopted, consisting of primary centrifugation (low speed) → secondary centrifugation (medium speed) → tertiary centrifugation (high speed). The refined slurry is graded and separated according to particle size: the primary centrifugation at low speed removes large particles that are not refined in the refined slurry (for recycling), while the secondary centrifugation at medium speed separates the target nano-alumina particles with medium particle size from the refined slurry and refines some large particles. The tertiary centrifugation at high speed removes excessively small broken particles from the refined slurry (to avoid an excessively wide particle size distribution) and at the same time modifies the morphology of nano-alumina, reducing the proportion of ultrafine nano-alumina particles, and finally obtaining a concentrated slurry with a concentrated particle size distribution.

[0029] II. Solution for low purity: Simultaneous removal of impurities through graded grinding with temperature control, gradient centrifugation, and centrifugal washing.

[0030] In traditional grinding processes, phase transition impurities (such as the transformation of γ-Al₂O₃ to α-Al₂O₃) caused by grinding media wear, dispersant residue, or thermal effects are the main reasons for the low purity of nano-alumina. The method provided in this application achieves full-process control of impurities in nano-alumina through an integrated design of graded grinding temperature control and gradient centrifugation + centrifugal washing. 1. Graded grinding temperature control: By regulating the temperature, phase change of the initial slurry (such as the generation of impurity phases) caused by high temperature during graded grinding is avoided, and the wear of grinding media (such as zirconia beads) is reduced (the hardness of grinding media is more stable under constant temperature conditions), thereby reducing the introduction of impurities into nano alumina from the source.

[0031] 2. Gradient centrifugation + centrifugal washing: During gradient centrifugation, washing liquid is simultaneously introduced to remove soluble impurities such as dispersant residue and grinding debris online. For example, while removing large particles in the first stage of centrifugation, the washing liquid can rinse away the dispersant on the surface of the nano-alumina particles in the slurry; while separating the target nano-alumina particles, the second stage of centrifugation can further wash away fine impurities between the nano-alumina particles, achieving simultaneous particle size classification and impurity removal, and significantly improving the purity of the concentrated slurry.

[0032] III. Solutions for high agglomeration rates: A non-agglomeration process involving supercritical drying and simultaneous modification.

[0033] In traditional processes, surface tension during drying (e.g., capillary forces generated by moisture evaporation during oven drying) leads to severe agglomeration of nano-alumina particles. Subsequent modification (e.g., silane coupling agent treatment) is insufficient to completely disperse these agglomerates, resulting in poor dispersibility of the nano-alumina product. The method provided in this application overcomes this limitation through supercritical drying combined with simultaneous modification. 1. Supercritical drying: Supercritical carbon dioxide fluid (without surface tension) is used to dry the concentrated slurry, avoiding the "hard agglomeration" (irreversible chemical bonding between particles) caused by surface tension in traditional drying, and preserving the nanoscale dispersion state of alumina particles.

[0034] 2. Simultaneous Modification: During the supercritical drying process, a silane coupling agent is added. Utilizing the high diffusivity of supercritical fluids, the silane coupling agent can uniformly coat the particle surface of the concentrated slurry, simultaneously completing the drying and surface modification of the concentrated slurry. A hydrophobic layer forms on the surface of the modified alumina particles, reducing soft agglomeration (van der Waals forces between nano-alumina particles) during subsequent vacuum drying or storage, thus completely resolving the traditional contradiction between drying agglomeration and subsequent modification.

[0035] IV. Improvement of the performance of high-purity nano-alumina.

[0036] By optimizing the entire process of graded sand milling + gradient centrifugation + supercritical drying, the nano-alumina product exhibits high purity, narrow particle size distribution, and low agglomeration rate, directly improving its performance in high-end applications. 1. Catalyst support: Narrow particle size distribution ensures uniform distribution of active sites in nano-alumina. High-purity nano-alumina can avoid the inhibition of catalytic reaction by impurities and improve catalytic efficiency. 2. Electronic ceramics: The low agglomeration rate results in uniform dispersion of nano-alumina particles. The ceramics formed after sintering of nano-alumina have high density and stable dielectric properties. 2. Coatings or inks: High-purity nano-alumina can avoid coating defects caused by impurities. The narrow particle size distribution of nano-alumina can make the coating more uniform and improve the wear resistance and corrosion resistance of the coating.

[0037] In summary, the present application provides a method for preparing nano-alumina based on gradient centrifugation and supercritical technology. This method integrates multiple units of graded grinding, gradient centrifugation, and supercritical drying into a highly efficient process chain, which completely solves the core defects in the traditional preparation of nano-alumina. It achieves the production goal of high-purity, narrow-size distribution, and low-agglomeration rate nano-alumina, and significantly improves the performance of nano-alumina products.

[0038] In some optional embodiments, the primary grinding speed is 1400 r / min to 1600 r / min, and the primary grinding time is 30 min to 45 min; and / or The secondary grinding speed is 2400 r / min to 2600 r / min, and the secondary grinding time is 60 min to 90 min; and / or The rotation speed of the three-stage grinding is from 1800 r / min to 2200 r / min, and the grinding time is from 20 min to 30 min.

[0039] In these embodiments, primary grinding at a speed of 1400 r / min to 1600 r / min and a time of 30 min to 45 min can remove large-sized coarse slag from the initial slurry and initially dissociate particle agglomerates in the initial slurry, which is beneficial for subsequent secondary grinding. In addition, secondary grinding at a speed of 2400 r / min to 2600 r / min and a time of 60 min to 90 min can refine medium-sized nano-alumina particles in the initial slurry, which is beneficial for obtaining nano-alumina of the target particle size. Furthermore, tertiary grinding at a speed of 1800 r / min to 2200 r / min and a time of 20 min to 30 min can adjust the particle size distribution of nano-alumina, balance the refining efficiency and particle integrity of the primary grinding, and prevent excessive grinding from increasing the particle size dispersion of nano-alumina.

[0040] The rotational speed of the first-stage grinding can be 1400 r / min, 1410 r / min, 1420 r / min, 1430 r / min, 1440 r / min, 1450 r / min, 1500 r / min, 1550 r / min or 1600 r / min.

[0041] The time for the first-stage grinding can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 40 min, or 45 min.

[0042] The rotational speed of the secondary grinding can be 2400 r / min, 2420 r / min, 2440 r / min, 2460 r / min, 2480 r / min, 2500 r / min, 2550 r / min or 2600 r / min.

[0043] The time for the secondary grinding can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, or 90 min.

[0044] The rotational speed of the three-stage grinding can be 1800 r / min, 1850 r / min, 1900 r / min, 1950 r / min, 2000 r / min, 2050 r / min, 2100 r / min, 2150 r / min or 2200 r / min.

[0045] The time for the three-stage grinding can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, or 30 min.

[0046] In some alternative embodiments, the grinding media used in the graded grinding is grinding balls with a particle size of 0.1 mm to 0.2 mm.

[0047] In these embodiments, grinding balls with a particle size of 0.1 mm to 0.2 mm can effectively promote primary, secondary, and tertiary grinding, prevent excessive graded grinding from increasing the particle size dispersion of nano-alumina, and improve the purity of nano-alumina.

[0048] The particle size of the grinding ball can be 0.1mm, 0.12mm, 0.14mm, 0.16mm, 0.18mm or 0.20mm.

[0049] It should be noted that the grinding ball can be made of zirconium oxide.

[0050] In some alternative embodiments, the mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy: m1:m2 = (8 to 10):1.

[0051] In these embodiments, grinding balls with a mass-to-initial slurry mass ratio of (8 to 10):1 can effectively promote primary, secondary, and tertiary grinding, prevent excessive grading and grinding that could lead to increased particle size dispersion of nano-alumina, and improve the purity of nano-alumina.

[0052] The mass m1 of the grinding ball can be 8.0, 8.5, 9.0, 9.5 or 10.0.

[0053] Figure 2 An exemplary schematic diagram illustrates a detailed process flow diagram of a method for preparing nano-alumina based on gradient centrifugation and supercritical technology provided in an embodiment of this application; In some alternative implementations, such as Figure 2 As shown, the refined slurry is subjected to gradient centrifugation to obtain a concentrated slurry, including the following steps: S301. The refined slurry is subjected to primary centrifugation to obtain primary precipitate and primary supernatant; S302. The primary precipitate is returned to the graded grinding process as part of the initial slurry. S303. The primary supernatant is subjected to secondary centrifugation to obtain a secondary precipitate; S304. The secondary precipitate is centrifuged and washed with a washing solution to obtain a precipitate mixture; wherein the mass m3 of the washing solution and the mass m4 of the secondary precipitate satisfy: m3:m4 = (3 to 5):1; S305. The precipitated mixture is subjected to three-stage centrifugation to obtain a concentrated slurry.

[0054] In these embodiments, the refined slurry is centrifuged in one stage to obtain a primary supernatant, and then the primary supernatant is centrifuged in two stages to obtain a secondary precipitate. The secondary precipitate is then washed by centrifugation with a washing liquid to obtain a precipitate mixture. Finally, the precipitate mixture is centrifuged in three stages. By using a gradient centrifugation method and separating the refined slurry according to particle size, a concentrated slurry with a concentrated particle size distribution can be obtained.

[0055] The mass m3 of the washing liquid can be 3.0, 3.5, 4.0, 4.5 or 5.0.

[0056] In some optional embodiments, the rotation speed of the first-stage centrifugation is 800 r / min to 1200 r / min, and the first-stage centrifugation time is 10 min to 15 min; and / or The secondary centrifugation speed is 4800 r / min to 5200 r / min, and the secondary centrifugation time is 20 min to 30 min; and / or The speed of the three-stage centrifugation is 8000 r / min to 12000 r / min, and the time of the three-stage centrifugation is 15 min to 20 min.

[0057] In these embodiments, primary centrifugation at a speed of 800 to 1200 rpm for 10 to 15 minutes removes large, unrefined particles from the slurry, forming primary sediment. This primary sediment can be returned to the classifying and grinding process, achieving efficient utilization of the raw materials and improving the efficiency of alumina raw material utilization. Secondly, secondary centrifugation at a speed of 4800 to 5200 rpm for 20 to 30 minutes separates the target nano-alumina of medium particle size from the slurry and refines some large particles, facilitating tertiary centrifugation. Furthermore, tertiary centrifugation at a speed of 8000 to 12000 rpm for 15 to 20 minutes removes excessively small, broken particles from the slurry, preventing an overly wide particle size distribution. Simultaneously, tertiary centrifugation can refine the morphology of the nano-alumina, reducing the proportion of ultrafine nano-alumina particles, ultimately obtaining a concentrated slurry with a concentrated particle size distribution.

[0058] The rotational speed of this primary centrifuge can be 800 r / min, 850 r / min, 900 r / min, 950 r / min, 1000 r / min, 1050 r / min, 1100 r / min, 1150 r / min or 1200 r / min.

[0059] The time for the first-stage centrifugation can be 10 min, 11 min, 12 min, 13 min, 14 min, or 15 min.

[0060] The rotational speed of the secondary centrifuge can be 4800 r / min, 4850 r / min, 4900 r / min, 4950 r / min, 5000 r / min, 5050 r / min, 5150 r / min or 5200 r / min.

[0061] The time for the secondary centrifugation can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, or 30 min.

[0062] The rotational speed of this three-stage centrifuge can be 8000 r / min, 8500 r / min, 9000 r / min, 9500 r / min, 10000 r / min, 10500 r / min, 11500 r / min or 12000 r / min.

[0063] The time for the three-stage centrifugation can be 15 min, 16 min, 17 min, 18 min, 19 min, or 20 min.

[0064] In some alternative embodiments, the supercritical drying temperature is 31°C to 35°C, the supercritical drying pressure is 7.5 MPa to 8.5 MPa, and the supercritical drying time is 1 h to 2 h.

[0065] In these embodiments, supercritical drying at a temperature of 31°C to 35°C, a pressure of 7.5 MPa to 8.5 MPa, and a time of 1 h to 2 h can keep the carbon dioxide in a supercritical state, avoiding hard agglomeration caused by surface tension in traditional drying and preserving the nanoscale dispersion of alumina particles. At the same time, this supercritical drying allows water and dispersant in the concentrated slurry to diffuse into the supercritical carbon dioxide, achieving drying of the concentrated slurry and partial removal of impurities.

[0066] The temperature for supercritical drying can be 31℃, 32℃, 33℃, 34℃ or 35℃.

[0067] The pressure for supercritical drying can be 7.5 MPa, 7.6 MPa, 7.7 MPa, 7.8 MPa, 7.9 MPa, 8.0 MPa, or 8.5 MPa.

[0068] The supercritical drying time can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h or 2.0h.

[0069] In some alternative embodiments, the temperature of the graded grinding is 25°C to 40°C; and / or The vacuum drying temperature is 100℃ to 120℃, the vacuum degree is 0.08MPa to 0.10MPa, and the vacuum drying time is 1h to 2h.

[0070] In these embodiments, graded grinding at a temperature of 25°C to 40°C avoids the heat generated by friction between the grinding balls and the alumina in the initial slurry, improves the stability of graded grinding, prevents over-gradation which would lead to increased particle size dispersion of the nano-alumina, and improves the purity of the nano-alumina. Furthermore, vacuum drying at a temperature of 100°C to 120°C, a vacuum degree of 0.08 MPa to 0.10 MPa, and a time of 1 to 2 hours effectively removes residual moisture or dispersants from the coarse alumina powder, resulting in high-purity nano-alumina.

[0071] The temperature for this graded grinding can be 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, 35℃ or 40℃.

[0072] The vacuum drying temperature can be 100℃, 105℃, 110℃, 115℃ or 120℃.

[0073] The vacuum degree of this vacuum drying can be 0.080MPa, 0.085MPa, 0.090MPa, 0.095MPa or 0.10MPa.

[0074] The vacuum drying time can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, or 2 hours.

[0075] In some optional embodiments, the mass m5 of the silane coupling agent and the mass m6 of the concentrated slurry satisfy: m5:m6 = (95 to 105):1; and / or The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following: m7:m8:m9 = (6 to 10):100:(0.3 to 0.8).

[0076] In these embodiments, a silane coupling agent with a mass ratio of (95 to 105):1 to the concentrated slurry can uniformly coat the surface of alumina particles. During supercritical drying, the silane coupling agent uniformly coated on the surface of alumina particles can form a hydrophobic layer, which can prevent agglomeration between nano-alumina particles in the subsequent vacuum drying stage. In addition, a hydrophilic solvent, alumina raw material, and dispersant with a mass ratio of (6 to 10):100:(0.3 to 0.8) can uniformly disperse the alumina raw material in the liquid phase, reduce the degree of agglomeration of the alumina raw material, and avoid the phenomenon of alumina particle clumping in the initial stage of graded grinding.

[0077] The mass m5 of the silane coupling agent can be 95, 96, 97, 98, 99, 100, 101, 102, 103, 104 or 105.

[0078] In some alternative embodiments, the dispersion treatment speed is 280 r / min to 320 r / min, and the dispersion treatment time is 40 min to 60 min.

[0079] In these embodiments, the dispersion treatment with a rotation speed of 280 r / min to 320 r / min and a time of 40 min to 60 min can make the alumina raw material uniformly dispersed in the liquid phase of the hydrophilic solvent and the dispersant. The dispersion effect of the dispersant can reduce the agglomeration degree of the alumina raw material and avoid the phenomenon of alumina particles clumping in the initial stage of graded grinding.

[0080] The rotational speed of the dispersion treatment can be 280 r / min, 285 r / min, 290 r / min, 295 r / min, 300 r / min, 305 r / min, 315 r / min or 320 r / min.

[0081] The dispersion processing time can be 40 min, 45 min, 50 min, 55 min, or 60 min.

[0082] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0083] Example 1 Using 99.99% purity, median particle size D 50 It is a high-purity alumina raw material with a wavelength of 300nm.

[0084] like Figure 1 As shown, a method for preparing nano-alumina based on gradient centrifugation and supercritical technology includes: S1. Disperse 700g of hydrophilic solvent, 100g of alumina raw material and 0.5g of dispersant to obtain an initial slurry; S2. Under constant temperature conditions, the initial slurry is subjected to graded grinding to obtain a refined slurry; wherein, the graded grinding includes first-stage grinding, second-stage grinding and third-stage grinding in sequence, and the rotation speed of first-stage grinding is < rotation speed of third-stage grinding < rotation speed of second-stage grinding; S301. The refined slurry is centrifuged in one stage to obtain a primary precipitate and a primary supernatant; S302. The primary sedimentation is used as part of the initial slurry and returned to the classifying and grinding process; S303. Centrifuge the primary supernatant a second time to obtain a secondary precipitate; S304. The secondary precipitate is centrifuged and washed with washing solution to obtain a precipitate mixture; wherein the mass m3 of washing solution and the mass m4 of secondary precipitate satisfy: m3:m4=3:1; the volume ratio of washing solution to deionized water and ethanol is 3:1; repeat the centrifugation and washing step twice; S305. The precipitated mixture is subjected to three-stage centrifugation to obtain a concentrated slurry; S4. The concentrated slurry is subjected to supercritical drying using carbon dioxide and silane coupling agent at a speed of 150 r / min to simultaneously complete the drying and modification, thereby obtaining crude alumina powder. S5. Vacuum dry the coarse alumina powder to obtain nano alumina.

[0085] The primary grinding speed is 1500 r / min, and the primary grinding time is 40 min; The rotation speed for the secondary grinding was 2500 r / min, and the grinding time was 80 min. The three-stage grinding speed is 2000 r / min, and the three-stage grinding time is 25 min.

[0086] The grinding media used in graded grinding are grinding balls with a particle size of 0.1 mm to 0.2 mm.

[0087] The mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy the following ratio: m1:m2=9:1.

[0088] The centrifuge speed for the first stage was 1000 r / min, and the centrifugation time was 12 min. The secondary centrifuge speed was 5000 r / min, and the secondary centrifuge time was 25 min; The centrifuge speed for the three stages was 10,000 r / min, and the centrifugation time was 18 min.

[0089] The supercritical drying temperature was 33℃, the supercritical drying pressure was 8.0MPa, and the supercritical drying time was 1.5h.

[0090] The temperature for graded grinding is 30℃; The vacuum drying temperature was 110℃, the vacuum degree was 0.09MPa, and the vacuum drying time was 1.5h.

[0091] The mass m5 of the silane coupling agent and the mass m6 of the concentrated slurry satisfy the following ratio: m5:m6=100:1; The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following formula: m7:m8:m9 = 700:100:0.5.

[0092] The dispersion speed was 300 r / min, and the dispersion time was 50 min.

[0093] Example 2 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The first-stage grinding time is 45 minutes; The secondary grinding time is 90 minutes; The time for the third-stage grinding is 20 minutes.

[0094] The mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy the following ratio: m1:m2=8:1.

[0095] The first stage of centrifugation takes 15 minutes; The secondary centrifugation time is 30 minutes; The three-stage centrifugation time is 15 minutes.

[0096] The temperature for supercritical drying was 31℃, the pressure for supercritical drying was 7.5MPa, and the time for supercritical drying was 1h.

[0097] The temperature for graded grinding is 25℃; The vacuum drying temperature is 100℃, the vacuum degree is 0.08MPa, and the vacuum drying time is 1h.

[0098] The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following formula: m7:m8:m9 = 1000g:100g:0.3g.

[0099] The dispersion rotation speed was 300 r / min, and the dispersion time was 40 min.

[0100] Example 3 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The first-stage grinding time is 30 minutes; The secondary grinding time is 60 minutes; The third-stage grinding time is 30 minutes.

[0101] The mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy the following ratio: m1:m2=10:1.

[0102] The first stage of centrifugation takes 10 minutes; The secondary centrifugation time is 20 minutes; The three-stage centrifugation time is 20 minutes.

[0103] The supercritical drying temperature was 35℃, the supercritical drying pressure was 8.5MPa, and the supercritical drying time was 1h.

[0104] The temperature for graded grinding is 40℃; The vacuum drying temperature is 120℃, the vacuum degree is 0.10MPa, and the vacuum drying time is 1h.

[0105] The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following formula: m7:m8:m9 = 600g:100g:0.8g.

[0106] The dispersion speed was 300 r / min, and the dispersion time was 60 min.

[0107] Comparative Example 1 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: Supercritical drying is not used; conventional drying is employed directly. Furthermore, the temperature during the classification and grinding process is not controlled; the temperature fluctuates between 35℃ and 50℃. The conventional drying process is as follows: The concentrated slurry was spread evenly on an enamel tray using a scraper, and then placed in a forced-air drying oven and dried at 80°C for 6 hours to obtain a hard, crusty dry block. The dry block was then initially crushed using a mortar and pestle to obtain crushed powder. The crushed powder and silane coupling agent were then mixed in a high-speed mixer in a dry mixing manner for 10 minutes to achieve surface modification of the alumina powder and obtain coarse alumina powder.

[0108] The first-stage grinding time is 40 minutes; The secondary grinding time is 75 minutes; The time for the third-stage grinding is 25 minutes.

[0109] The mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy the following ratio: m1:m2=9:1.

[0110] The first stage of centrifugation takes 12 minutes; The secondary centrifugation time is 25 minutes; The three-stage centrifugation time is 18 minutes.

[0111] The mass m5 of the silane coupling agent and the mass m6 of the concentrated slurry satisfy the following ratio: m5:m6=100:1; The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following formula: m7:m8:m9 = 800:100:0.5.

[0112] The dispersion speed was 300 r / min, and the dispersion time was 50 min.

[0113] Comparative Example 2 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: Supercritical drying is not used; freeze drying is employed directly. Simultaneously, the temperature during the classification and grinding process is not controlled; the temperature fluctuates between 35℃ and 50℃. The freeze-drying process is as follows: The concentrated slurry was redispersed in deionized water to form a diluted slurry. The diluted slurry was quickly poured into a freeze-drying tray and rapidly frozen into a solid at an ultra-low temperature (-60℃) to obtain a frozen sample. The frozen sample was placed in a vacuum freeze dryer and sublimated for 24 hours under conditions of cold trap temperature < -50℃ and vacuum degree < 10Pa. After drying, a loose white flocculent powder was obtained, which is the freeze-dried nano alumina powder. The dried nano alumina powder and silane coupling agent were then mixed in a high-speed mixer by dry mixing for 10 minutes to achieve surface modification of the alumina powder and obtain coarse alumina powder.

[0114] The first-stage grinding time is 40 minutes; The secondary grinding time is 75 minutes; The time for the third-stage grinding is 25 minutes.

[0115] The mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy the following ratio: m1:m2=9:1.

[0116] The first stage of centrifugation takes 12 minutes; The secondary centrifugation time is 25 minutes; The three-stage centrifugation time is 18 minutes.

[0117] The mass m5 of the silane coupling agent and the mass m6 of the concentrated slurry satisfy the following ratio: m5:m6=100:1; The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following formula: m7:m8:m9 = 800:100:0.5.

[0118] The dispersion speed was 300 r / min, and the dispersion time was 50 min.

[0119] Comparative Example 3 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: In the grading and grinding stage, the grinding is carried out directly in a three-stage grinding manner, that is, the grading and grinding speed is 2000 r / min and the grading and grinding time is 25 min.

[0120] Comparative Example 4 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: During the gradient centrifugation stage, the centrifugation was carried out directly in a three-stage manner, that is, the gradient centrifugation speed was 10000 r / min and the gradient centrifugation time was 18 min.

[0121] Relevant experimental and effect data: Nano-alumina was obtained from each of the embodiments and comparative examples, and the surface characteristics and performance parameters of these nano-alumina were statistically analyzed. The results are shown in Table 1.

[0122] Table 1. Surface characteristics and performance parameters of nano-alumina in each embodiment and comparative example.

[0123] As shown in Table 1, the method for preparing nano-alumina based on gradient centrifugation and supercritical technology provided in this application integrates multiple units of graded grinding, gradient centrifugation and supercritical drying into a highly efficient process chain, which completely solves the core defects in the traditional preparation of nano-alumina and achieves the production goal of high-purity, narrow particle size distribution and low agglomeration rate of nano-alumina, significantly improving the performance of nano-alumina products.

[0124] Compared to Example 1, Comparative Example 1 did not use supercritical drying but directly used ordinary drying, which led to the agglomeration of nano-alumina particles, affecting the purity, average median particle size, specific surface area, and agglomeration rate of nano-alumina. Comparative Example 2 did not use supercritical drying and replaced it with freeze-drying. Although freeze-drying effectively removed impurities from the concentrated slurry, it could not achieve the surface modification of nano-alumina particles in the concentrated slurry by the silane coupling agent. This resulted in a larger average median particle size (D50) of the nano-alumina and increased agglomeration among the particles.

[0125] Compared to Example 1, Comparative Example 3 did not use graded grinding but directly used the parameters of three-stage grinding, lacking the fine treatment of first-stage and second-stage grinding. This resulted in uneven graded grinding, with the median particle size of the nano-alumina particles being larger and wider in distribution, and a smaller specific surface area. Comparative Example 4, on the other hand, directly used three-stage centrifugation, without first-stage and second-stage centrifugation. This failed to effectively remove large alumina particles and impurities from the refined slurry, leading to reduced purity of the nano-alumina and a larger median particle size, smaller specific surface area, and higher agglomeration rate.

[0126] In summary, the embodiments of this application provide a method for preparing nano-alumina based on gradient centrifugation and supercritical technology. This method overcomes the defects of low purity, high agglomeration rate and uneven particle size distribution in traditional processes through multi-unit synergistic innovation of the whole process of graded sand milling + gradient centrifugation + supercritical drying, thereby improving the performance of high-purity nano-alumina.

[0127] In addition, this application provides a method for preparing nano-alumina based on gradient centrifugation and supercritical technology. This method can balance the refinement efficiency and purity of nano-alumina in the initial slurry through temperature control and gradient speed graded sand milling. At the same time, through the integrated centrifugation design of gradient centrifugation and centrifugal washing, the recovery of coarse nano-alumina particles, particle size classification and impurity removal can be carried out simultaneously. In addition, by taking advantage of the synergistic effect of carbon dioxide and silane coupling agent in supercritical drying, the traditional limitations of post-drying agglomeration and subsequent modification can be overcome, and a complete and efficient nano-alumina preparation process chain can be formed.

[0128] Furthermore, this application provides a method for preparing nano-alumina based on gradient centrifugation and supercritical technology, which has the following characteristics: 1. Excellent product performance: The average median particle size (D50) of the prepared nano-alumina is 30 nm to 80 nm, the purity of the nano-alumina is ≥99.99%, the agglomeration rate of the nano-alumina is <5%, and the specific surface area is 150 m². 2 / g to 250m 2 / g, this nano-alumina can meet the stringent requirements of high-end fields such as semiconductors and optics for the particle size, purity and dispersibility of nano-alumina; 2. High raw material and energy utilization: Gradient centrifugation can achieve a coarse particle recovery rate of >90%, reducing the waste of nano-alumina raw materials; temperature-controlled staged grinding can avoid ineffective energy consumption. At the same time, the fineness efficiency of staged grinding can be improved by more than 30% compared with traditional grinding, and the unit energy consumption is reduced by 20% to 25%. 3. High degree of process integration and stability: The integration of multiple steps such as "gradual grinding + gradient centrifugation + centrifugal washing + supercritical drying + modification" can significantly shorten the production cycle time by more than 40%; in addition, the parameters of each step are highly adjustable, and the performance deviation of different batches of nano alumina can be controlled to <3%, which meets the industrial continuous production requirements of nano alumina. 4. Significant economic benefits: It adopts mature industrial-grade equipment, eliminating the need for additional high-end synthesis equipment; and the grinding beads used in the graded grinding and the dispersants used in the dispersion treatment can be recycled. The total production cost per unit weight of nano alumina is 40% to 50% lower than that of the direct synthesis method, combining both technical and economic advantages.

[0129] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing nano-alumina based on gradient centrifugation and supercritical technology, characterized in that, The method includes: The hydrophilic solvent, alumina raw material, and dispersant are dispersed to obtain an initial slurry; Under constant temperature conditions, the initial slurry is subjected to graded grinding to obtain a refined slurry; wherein the graded grinding includes primary grinding, secondary grinding and tertiary grinding in sequence, and the rotation speed of the primary grinding is less than the rotation speed of the tertiary grinding and the rotation speed of the secondary grinding. The refined slurry is subjected to gradient centrifugation to obtain a concentrated slurry; wherein the gradient centrifugation includes first-stage centrifugation, second-stage centrifugation and third-stage centrifugation in sequence, and the speed of the first-stage centrifugation is less than the speed of the second-stage centrifugation and the speed of the third-stage centrifugation; The concentrated slurry was subjected to supercritical drying using carbon dioxide and a silane coupling agent to simultaneously complete the drying and modification, thereby obtaining crude alumina powder. The crude alumina powder was vacuum dried to obtain nano-alumina.

2. The method according to claim 1, characterized in that, The primary grinding speed is 1400 r / min to 1600 r / min, and the primary grinding time is 30 min to 45 min; and / or The secondary grinding speed is 2400 r / min to 2600 r / min, and the secondary grinding time is 60 min to 90 min; and / or The rotation speed of the three-stage grinding is from 1800 r / min to 2200 r / min, and the grinding time is from 20 min to 30 min.

3. The method according to claim 1, characterized in that, The grinding media used in the graded grinding is grinding balls, and the particle size of the grinding balls is 0.1 mm to 0.2 mm.

4. The method according to claim 3, characterized in that, The mass m1 of the grinding ball and the mass m2 of the initial slurry satisfy the following condition: m1:m2 = (8 to 10):

1.

5. The method according to claim 1, characterized in that, The refined slurry is subjected to gradient centrifugation to obtain a concentrated slurry, including the following steps: The refined slurry was subjected to a first-stage centrifugation to obtain a first-stage precipitate and a first-stage supernatant; The primary sediment is returned as part of the initial slurry to the classifying and grinding process; The primary supernatant was subjected to secondary centrifugation to obtain a secondary precipitate; The secondary precipitate is centrifuged and washed with a washing solution to obtain a precipitate mixture; wherein the mass m3 of the washing solution and the mass m4 of the secondary precipitate satisfy the following condition: m3:m4 = (3 to 5):1; The precipitated mixture was subjected to three-stage centrifugation to obtain a concentrated slurry.

6. The method according to claim 1 or 5, characterized in that, The first-stage centrifugation speed is 800 r / min to 1200 r / min, and the first-stage centrifugation time is 10 min to 15 min; and / or The secondary centrifugation speed is 4800 r / min to 5200 r / min, and the secondary centrifugation time is 20 min to 30 min; and / or The speed of the three-stage centrifugation is 8000 r / min to 12000 r / min, and the time of the three-stage centrifugation is 15 min to 20 min.

7. The method according to claim 1, characterized in that, The supercritical drying temperature is 31°C to 35°C, the supercritical drying pressure is 7.5 MPa to 8.5 MPa, and the supercritical drying time is 1 h to 2 h.

8. The method according to claim 1, characterized in that, The temperature of the graded grinding is 25°C to 40°C; and / or The vacuum drying temperature is 100℃ to 120℃, the vacuum degree is 0.08MPa to 0.10MPa, and the vacuum drying time is 1h to 2h.

9. The method according to claim 1, characterized in that, The mass m5 of the silane coupling agent and the mass m6 of the concentrated slurry satisfy: m5:m6 = (95 to 105):1; and / or The mass m7 of the hydrophilic solvent, the mass m8 of the alumina raw material, and the mass m9 of the dispersant satisfy the following: m7:m8:m9 = (600 to 1000):100:(0.3 to 0.8).

10. The method according to claim 1, characterized in that, The dispersion process is carried out at a rotation speed of 280 r / min to 320 r / min, and the dispersion process takes 40 min to 60 min.

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