A method for preparing a high-purity alumina sol

Abstract

The application belongs to the technical field of inorganic material preparation, and discloses a method for preparing high-purity alumina sol. The method comprises the following steps: taking raw aluminum or refined high-purity aluminum as raw material, reacting with alcohol to generate aluminum alcoholate, mixing with water after purification and refining, fully hydrolyzing, and separating the generated alcohol. Deionized water is added to the crude pseudo-boehmite, and the mixture is stirred at 120 DEG C to 250 DEG C, dried, and calcined at 500 DEG C to 1100 DEG C to obtain alumina of different crystal forms. The alumina is mixed with a dispersing agent and deionized water, and is ground and refined for 1 to 12 hours to obtain uniformly dispersed alumina sol. The obtained alumina sol is translucent, can produce obvious Tyndall effect, has a D50 particle size of less than 100 nm, a ZETA potential of less than -30 mV, and no obvious precipitation within half a year of standing. The application has simple operation, low pollution, and can be used in the fields of battery material modification and precision polishing.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation technology and relates to a method for preparing high-purity alumina sol. Background Technology

[0002] Alumina ( Alumina is an important inorganic non-metallic material with various crystalline structures. Each crystalline form is widely used in different fields due to its unique crystal structure and physicochemical properties. Currently discovered alumina crystalline forms include... etc., among which It is the most thermodynamically stable phase, while the others are transition phases. Among them, boehmite (… During the calcination process, the following can be obtained: Alumina, with its isocrystalline phase, possesses high specific surface area, strong adsorption capacity, good catalytic activity, and thermal stability, making it suitable for applications such as catalyst supports, adsorbents, chip polishing materials, and battery materials. With technological advancements, the purity requirements for alumina are becoming increasingly stringent.

[0003] Commonly used alumina sol (also known as aluminum sol) is a colloid of hydrated alumina and an important precursor to activated alumina. It is mainly prepared by dissolving metallic aluminum or boehmite using acids (hydrochloric acid, nitric acid, etc.). It appears as a transparent or translucent liquid with a strongly acidic pH (2-4). The colloidal particle size is between 1-100 nm. It is mainly used in petrochemical catalysts, refractory materials and ceramics industries, coatings and surface treatments, precision casting and electronic materials, and lithium battery material modification. It often requires calcination or high-temperature treatment before use, and its application still has some limitations.

[0004] The product obtained after calcination Crystalline alumina is insoluble in water and easily agglomerates when improperly dispersed. This is due to the high surface energy of alumina powder and the interaction forces such as van der Waals forces and electrostatic attraction between particles. This agglomeration phenomenon is even more severe when the alumina particle size is reduced to the nanometer scale. In use, improperly dispersed alumina particles have uneven size distribution, poor suspension and stability, and fail to achieve the expected performance. Taking the lithium battery field as an example, when using poorly dispersed alumina slurry to coat the cathode material, the agglomerated alumina cannot form a uniform and complete coating layer on the surface of the cathode material, causing some active materials to be directly exposed to the electrolyte, which cannot effectively inhibit the corrosion of the cathode material by the electrolyte. Furthermore, the interfacial bonding force between the agglomerated alumina coating and the cathode material is weak, and it is easy to fall off during charge-discharge cycles, failing to form a stable protective layer and effectively inhibiting the dissolution of transition metal elements and the destruction of the material structure. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a method for preparing high-purity boehmite through alkoxide hydrolysis. Different crystalline forms of alumina are obtained through hydrothermal treatment and calcination. A stable and uniform alumina sol is then obtained by mechanical grinding and dispersing with a suitable dispersant. The prepared alumina sol exhibits a significant Tyndall effect, small particle size (<100nm), and high stability. Compared to traditional alumina sols, it causes less environmental pollution and eliminates the need for calcination, offering significant advantages in application. Through long-term practical experience, the inventors have discovered that high-temperature hydrothermal treatment is crucial; the alumina sol obtained from boehmite that has not undergone high-temperature hydrothermal treatment suffers from poor stability and cannot be stored for long periods.

[0006] The technical solution of the present invention:

[0007] A method for preparing high-purity alumina sol, comprising the following steps:

[0008] Step 1: Mix aluminum metal, alcohol and catalyst and reflux for 2-24 hours to obtain crude aluminum alkoxide. After purification, crude aluminum alkoxide is used to obtain liquid aluminum alkoxide.

[0009] Step 2: The liquid aluminum alkoxide obtained in Step 1 is mixed with water and hydrolyzed. Then, the alcohol produced by hydrolysis is separated and recovered, and pseudoboehmite or pseudoboehmite wet material is obtained.

[0010] Step 3: Prepare a boehmite slurry by mixing the boehmite or wet boehmite obtained in Step 2 with deionized water, and then perform hydrothermal stirring at 120-250℃ for 2-24 hours to obtain the boehmite slurry.

[0011] Step 4: Dry the pseudo-boehmite slurry obtained in Step 3, and calcine the resulting powder at a high temperature of 500~1100℃ to obtain alumina powder; the obtained alumina powder has an Al2O3 content higher than 99.99wt.%, Na2O content lower than 0.002wt.%, Fe2O3 content lower than 0.003wt.%, and SiO2 content lower than 0.003wt.%.

[0012] Step 5: Mix the alumina powder obtained in Step 4 with the dispersant and deionized water, and grind for 1-12 hours. The resulting product is high-purity alumina sol. The obtained high-purity alumina sol has a particle size (D50) of less than 100 nm, a Zeta potential of less than -30 mV, and exhibits a significant Tyndall effect. It can be stably stored for more than 6 months.

[0013] In step 1, the alcohol is one of isopropanol, sec-butanol, and isooctanol;

[0014] In step 1, the catalyst is one of anhydrous aluminum trichloride, aluminum isopropoxide, and aluminum isooctoxide.

[0015] In step 1, the molar ratio of metallic aluminum to alcohol is 1:1 to 1:4;

[0016] In step 1, the molar ratio of metallic aluminum to catalyst is 1000:1 to 10:1;

[0017] In step 2, the molar ratio of the aluminum alkoxide to water is 1:3 to 1:100;

[0018] In step 5, the dispersant consists of component A and component B. Component A is one or a mixture of two or more of the following: citric acid, malic acid, tartaric acid, fumaric acid, ammonium citrate, ammonium malate, ammonium tartrate, and ammonium fumarate. Component B is one or a mixture of two or more of the following: polyacrylic acid, benzenesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, ammonium polyacrylate, ammonium benzenesulfonate, p-toluenesulfonate, ammonium dodecylbenzenesulfonate, and ammonium laurylate.

[0019] In step 5, the mass ratio of dispersant component A to component B is 5:1 to 1:5;

[0020] In step 5, the mass ratio of alumina powder to dispersant is 1000:1 to 5:1;

[0021] In step 5, the mass ratio of the alumina powder to deionized water is 1:20 to 1:3;

[0022] In step 5, the grinding method is high-energy ball milling, horizontal sand milling, or vertical sand milling.

[0023] The beneficial effects of this invention are as follows: The hydrothermal process of this invention transforms poorly crystallized boehmite into boehmite with higher crystallinity and regular morphology, which can reduce agglomeration behavior. Furthermore, the calcined particles are regular in shape and less prone to entanglement, resulting in good slurry suspension and reduced sedimentation. It also makes the hydroxyl groups on the surface of alumina particles more uniform, improving wettability and dispersibility in water and reducing agglomeration. Simultaneously, the use of a composite dispersant improves the dispersibility of alumina. Therefore, the alumina powder dispersion sol prepared by this invention can be stored stably for a long time. Compared with traditional alumina sol (also known as alumina sol) dispersed in boehmite, it has more uniform particles, better suspension, and a wider range of applications. Attached Figure Description

[0024] Figure 1 The image shows a comparison of XRD patterns before and after ball milling for the product in Specific Example 1.

[0025] Figure 2 The image shown is a TEM image of the product in Specific Embodiment 1.

[0026] Figure 3 The image shows the Tyndall effect of the product in Specific Implementation Example 1.

[0027] Figure 4 The TEM image is for the specific comparative example 1 product.

[0028] Figure 5 The TEM image shows the product in Comparative Example 2. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings and technical solutions.

[0030] Example 1

[0031] Take 60 g of aluminum granules (processed from industrial aluminum ingots, purity 99.7%), rinse with ethanol, and then dry in an 80℃ forced-air drying oven for 4 h. Place the dried aluminum granules into a 1 L three-necked flask, and add 400 g of isopropanol and 10 g of aluminum isopropoxide to the flask. Heat and reflux the material in the three-necked flask for 4 h; then perform vacuum distillation, controlling the system pressure to below 0.005 MPa and the liquid temperature to 180–200℃. Collect the distillate, which is aluminum isopropoxide. 408 g of freshly prepared aluminum isopropoxide by vacuum distillation was added to a 1 L three-necked flask. Under mechanical stirring (200 r / min) in an 80 °C water bath, 125 g of deionized water was added to the flask containing the aluminum isopropoxide using a peristaltic pump at a rate of 4 mL / min. After the water addition was complete, stirring was continued for 4 h, and the product was then transferred to a vacuum drying oven and dried under vacuum at 60 °C for 6 h. 120 g of the dried sample (pseudoboehmite) was placed in a 1 L hydrothermal reactor, and 500 g of deionized water was added and thoroughly mixed. The mixture was then hydrothermally stirred at 160 °C for 6 h at a stirring rate of 200 r / min. The slurry obtained after hydrothermal treatment was dried in an 80℃ forced-air drying oven for 12 h. After drying, it was pulverized, and the resulting powder was calcined in a muffle furnace at 800℃ for 4 h. Alumina balls (0.5 mm in diameter) and 60 g of calcined alumina powder were placed in the grinding jar of a vertical sand mill, along with 340 g of deionized water, 1 g of ammonium citrate, and 1 g of ammonium polyacrylate. The mixture was then ball-milled at high speed for 2 h to obtain alumina sol. The average particle size of the obtained alumina colloid was 57 nm, and the Zeta potential was -40 mV. This product remained stable for more than 6 months without precipitation. After acid dissolution, the calcined alumina powder was tested for impurities using ICP. The results showed that the Na₂O content was 0.0008%, the Fe₂O₃ content was 0.0015%, and the SiO₂ content was 0.0018%. Figure 1 The XRD comparison images of the obtained products before and after ball milling show that the crystal phase of alumina after ball milling is the same as that before ball milling, and no crystal phase change has occurred; at the same time, the XRD diffraction peaks of the product after ball milling are weaker, indicating that the particle size is smaller after ball milling. Figure 2The image shows a TEM image of the product, indicating that a regular two-dimensional sheet-like structure was formed after ball milling. Figure 3 This is an optical image of the Tyndall effect produced by the obtained product, and the optical path can be clearly seen.

[0032] Comparative Example 1

[0033] Other conditions and parameters were the same as in Example 1, but the boehmite was not subjected to hydrothermal treatment; instead, it was directly calcined after vacuum drying. The resulting colloidal particles had an average particle size of 53 nm (particle micromorphology as shown in the attached figure). Figure 4 As shown in the figure, the Zeta potential is -37mV. After standing for 1 month, precipitation occurs, indicating that the alumina sol obtained without hydrothermal treatment of the boehmite precursor has poor stability.

[0034] Comparative Example 2

[0035] Other conditions and parameters were the same as in Example 1, but when only a single dispersant (1g, 2g ammonium polyacrylate or 1g, 2g ammonium citrate) was used, the final product was a white slurry, which did not exhibit the Tyndall effect. This indicates that the target product cannot be obtained using a single dispersant. A single dispersant can only exert one of the steric hindrance or electrostatic repulsion stabilizing effects, resulting in the dispersant not being able to completely coat the alumina surface or the system having insufficient stability, thus failing to form a synergistic effect.

[0036] Comparative Example 3

[0037] 100 g of commercially available high-purity boehmite (also known as diaspore, with a purity of 99.99% or higher) was placed in a muffle furnace and calcined at 800°C for 4 hours. The calcined product was then removed and ground using a vertical sand mill under the same conditions as in Example 1. The final product was a white slurry that did not exhibit the Tyndall effect and had a particle size of approximately 70 nm (particle microstructure as shown in Figure 1). Figure 5 As shown in the figure, the Zeta potential was -23 mV, and the slurry solidified after one week. This boehmite was produced by high-temperature hydrothermal treatment of aluminum hydroxide. Compared with the boehmite produced by hydrothermal treatment of pseudoboehmite used in Example 1, the alumina grains obtained by calcination were larger, the dispersant was not easily completely coated, and the crystallinity was higher, the surface inertness was stronger, and the adsorption of the dispersant was weaker, resulting in a larger particle size and poorer suspension of the prepared slurry. This indicates that high crystallinity of the precursor is not a necessary condition for obtaining translucent alumina colloid, because commercially available boehmite is fully crystallized boehmite, while the precursor in Example 1 is incompletely crystallized boehmite (pseudoboehmite); transmission electron microscopy analysis showed that the microscopic lamellar structure is the key to obtaining translucent alumina sol.

[0038] Comparative Example 4

[0039] Commercially available high-purity aluminum hydroxide (analytical grade), 120 g, was placed in a muffle furnace and calcined at 800℃ for 4 h. The calcined aluminum hydroxide was then removed and ground using a vertical sand mill under the same grinding conditions as in Example 1. Due to the large size and overly complete crystallization of aluminum hydroxide crystals, severe dehydration occurred during calcination, forming dense, hard agglomerates that were difficult to disperse completely during ball milling. Furthermore, the aluminum hydroxide surface had few and unevenly distributed hydroxyl groups, resulting in poor adsorption of the dispersant and poor dispersion uniformity and suspension stability of the slurry. The final product was a white slurry, lacking the Tyndall effect, with an average particle size of 90 nm and a Zeta potential of -20 mV. The slurry solidified after standing for one week. This indicates that when the precursor of the alumina powder is gibbsite, a translucent sol cannot be obtained, for the same reason as in Comparative Example 3. A layered microstructure is key to obtaining a translucent alumina sol.

[0040] Comparative Example 5

[0041] Other conditions and parameters were the same as in Example 1, but the calcination temperature was 1200℃ (the product was α-phase alumina). The final product did not have the Tyndall effect, was easy to settle, had a particle size of more than 200 nm, and a Zeta potential of less than -10 mV, which indicates that α-phase alumina is not suitable.

[0042] Comparative Example 6

[0043] Other conditions and parameters were the same as in Example 1, but the hydrothermal temperature was 100°C, the average particle size of the resulting colloid was 55 nm, and the Zeta potential was -39 mV. However, precipitation occurred after standing for 2 months, indicating that the hydrothermal treatment temperature of the boehmite precursor was not suitable, and the resulting alumina sol could not be stable for a long time.

[0044] Example 2

[0045] The conditions and parameters were the same as in Example 1, but the calcination temperature was 1100°C. The resulting product was a semi-transparent sol with the Tyndall effect, an average particle size of 63 nm, and a Zeta potential of -42 mV.

[0046] Example 3

[0047] Take 60 g of high-purity aluminum block (purity 99.996%), rinse with ethanol, and then dry in an oven at 80℃ for 4 h; put the dried aluminum block into a 2 L three-necked flask, and add 1500 g of isooctyl alcohol and 1 g of anhydrous aluminum trichloride to the three-necked flask. The material in the three-necked flask was heated and refluxed for 12 h; then the resulting product (crude aluminum isooctanol) was poured from the three-necked flask through a 100-mesh stainless steel sieve into a 5 L three-necked flask, and the aluminum isooctanol was continuously stirred at 300 r / min in a 95°C water bath, while 1500 g of deionized water was introduced using a peristaltic pump at a rate of 50 mL / min; after the water was added, stirring was continued for 4 h, and the resulting mixture was centrifuged at 8000 r / min to remove the supernatant. The solid wet material was dispersed with 500 mL of deionized water, and the slurry was placed in a 2 L high-pressure hydrothermal reactor, stirred at 200 r / min, and kept at 140°C for 8 h; the remaining steps and parameters were the same as in Example 1. The obtained alumina colloid had an average particle size of 57 nm and a Zeta potential of -39 mV. This product could be stably stored for more than 6 months without precipitation. After acid dissolution, the calcined alumina powder was tested for impurity content using ICP. The results showed that the Na2O content was 0.0005%, the Fe2O3 content was 0.0005%, and the SiO2 content was 0.001%.

[0048] Example 4

[0049] Other conditions and parameters are the same as in Example 1, but a high-energy ball mill is used for grinding. The grinding jar and grinding balls are made of corundum. The ball mill speed is 1500 r / min and the grinding time is 4 h. The average particle size of the resulting alumina colloid is 68 nm and the Zeta potential is -37 mV. The product can be stored stably for more than 6 months without precipitation.

Claims

1. A method for preparing high-purity alumina sol, characterized in that, The steps are as follows: Step 1: Mix aluminum metal, alcohol and catalyst and reflux for 2-24 hours to obtain crude aluminum alkoxide. After purification, crude aluminum alkoxide is used to obtain liquid aluminum alkoxide. Step 2: The liquid aluminum alkoxide obtained in Step 1 is mixed with water and hydrolyzed. Then, the alcohol produced by hydrolysis is separated and recovered, and pseudoboehmite or pseudoboehmite wet material is obtained. Step 3: Prepare a boehmite slurry by mixing the boehmite or wet boehmite obtained in Step 2 with deionized water, and then perform hydrothermal stirring at 120-250℃ for 2-24 hours to obtain the boehmite slurry. Step 4: Dry the pseudo-boehmite slurry obtained in Step 3, and calcine the resulting powder at a high temperature of 500~1100℃ to obtain alumina powder. Step 5: Mix the alumina powder obtained in step 4 with the dispersant and deionized water, and grind for 1-12 hours. The resulting product is high-purity alumina sol.

2. The preparation method according to claim 1, characterized in that, In step 1, The alcohol mentioned is one of isopropanol, sec-butanol, and isooctanol; The catalyst is one of anhydrous aluminum trichloride, aluminum isopropoxide, and aluminum isooctoxide. The molar ratio of the metallic aluminum to the alcohol is 1:1 to 1:4; The molar ratio of aluminum to catalyst is 1000:1 to 10:

1.

3. The preparation method according to claim 1, characterized in that, In step 2, the molar ratio of the aluminum alkoxide to water is 1:3 to 1:

100.

4. The preparation method according to claim 1, characterized in that, In step 5, The dispersant comprises component A and component B. Component A is one or a mixture of two or more of the following: citric acid, malic acid, tartaric acid, fumaric acid, ammonium citrate, ammonium malate, ammonium tartrate, and ammonium fumarate. Component B is one or a mixture of two or more of the following: polyacrylic acid, benzenesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, ammonium polyacrylate, ammonium benzenesulfonate, p-toluenesulfonate, ammonium dodecylbenzenesulfonate, and ammonium laurylate. The mass ratio of dispersant component A to component B is 5:1 to 1:5; The mass ratio of alumina powder to dispersant is 1000:1 to 5:1; The mass ratio of the alumina powder to deionized water is 1:20 to 1:

3. The grinding method is high-energy ball milling, horizontal sand milling, or vertical sand milling.

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