Method for preparing high-purity flaky alumina based on hydrolysis method

Abstract

The invention provides a method for preparing high-purity flaky alumina based on a hydrolysis method, and belongs to the field of high-purity flaky alumina powder. The method comprises the steps that metal aluminum scraps are pretreated; the method comprises the following steps: putting metal aluminum scraps, an alkaline organic matter catalyst and a morphology control agent into water, and carrying out a hydrolysis reaction at a set temperature for a set time to obtain a reaction mixed solution; carrying out solid-liquid separation, washing and drying on the reaction mixed solution to obtain flaky aluminum hydroxide; and roasting the flaky aluminum hydroxide to remove crystal water so as to obtain high-purity flaky aluminum oxide, wherein the alkaline organic matter catalyst comprises at least one of the following components: tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; the morphology control agent comprises at least one of ammonium bifluoride and ammonium fluoride. The preparation method disclosed by the invention is simple in process flow, free of an impurity removal process, mild in reaction condition, short in reaction time and free of environmental pollution, and the product is regular in shape and high in purity.

Description

Technical Field

[0001] This application relates to the field of high-purity flake alumina powder preparation technology, and in particular to a method for preparing high-purity flake alumina based on hydrolysis. Background Technology

[0002] High-purity alumina generally refers to alumina powder with a purity greater than 99.99%. The unique physical, chemical, electrical, optical, thermal, and mechanical properties of high-purity alumina powder give it excellent characteristics such as high temperature resistance, chemical corrosion resistance, resistance to sudden temperature changes, and resistance to cracking, making it one of the cutting-edge materials of the 21st century. High-purity alumina with different purities and particle sizes exhibits vastly different physical and chemical properties, leading to diverse applications. Flake alumina (α-Al₂O₃) is a high-performance functional micropowder material that has emerged in recent years. Its scaly structure and large aspect ratio give it the dual characteristics of micron and nanomaterials, making it a promising candidate for various applications. It is widely used in polishing agents, refractory materials, high-grade ceramic coatings, fine ceramic pearlescent pigments, and cosmetic additives.

[0003] Currently, the main methods for preparing high-purity sheet-like alumina include the aluminum alkoxide hydrothermal method, the molten salt method, and the high-temperature sintering method. The aluminum alkoxide hydrothermal method has a long reaction cycle, harsh conditions, and high requirements for reaction equipment. The molten salt method has complex reaction conditions, and some molten salts are toxic, polluting the environment. The high-temperature sintering method has high energy consumption and is prone to generating secondary pollutants and product deformation. Furthermore, most conventional methods produce sheet-like alumina with low purity (<99.99%), which cannot meet the demands of high-end products. One existing technology uses hydrolysis to prepare high-purity alumina; although it can obtain high-purity products, this method cannot control the morphology of the product, making it difficult to obtain sheet-like alumina. Another technology uses aluminum isopropoxide as the main raw material and employs the aluminum alkoxide hydrothermal method to prepare high-purity sheet-like alumina. Although this technology can produce high-purity flake alumina with a grain thickness controlled to ≤1.0μm, the reaction process is relatively complicated and the reaction cycle is long. Furthermore, due to the use of raw materials with a purity of ≥99.999%, the final alumina produced has a purity of ≥99.99%, resulting in a high overall production cost and certain limitations in practical applications. Summary of the Invention

[0004] This application provides a method for preparing high-purity flake alumina based on hydrolysis, thus providing a novel approach to preparing high-purity flake alumina.

[0005] This application provides a method for preparing high-purity sheet-like alumina based on hydrolysis, the method comprising:

[0006] Pre-treat aluminum shavings;

[0007] The pretreated aluminum scraps, alkaline organic catalyst, and morphology control agent are placed in water to carry out a hydrolysis reaction at a set temperature and time to obtain a reaction mixture.

[0008] The reaction mixture was subjected to solid-liquid separation, washing, and drying to obtain flake aluminum hydroxide; and

[0009] The flake aluminum hydroxide is calcined to remove the water of crystallization, thereby obtaining high-purity flake aluminum oxide;

[0010] The alkaline organic catalyst includes at least one of the following: tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide;

[0011] The morphology control agent includes at least one of the following: ammonium bifluoride and ammonium fluoride.

[0012] Optionally, the mass ratio of the alkaline organic catalyst to the water is 1:(4-40).

[0013] Optionally, the mass ratio of the aluminum shavings to the water is 1:(10-40).

[0014] Optionally, the mass ratio of the crystal morphology control agent to the aluminum metal chips is 1:(4-20).

[0015] Optionally, the set temperature is 50℃~90℃, and the set time is 1h~30h.

[0016] Optionally, the calcination temperature is 1250℃~1500℃, and the calcination holding time is 1h~2h.

[0017] Optionally, the pretreatment of the aluminum shavings includes:

[0018] The aluminum shavings are washed and dried multiple times with ultrapure water.

[0019] Optionally, the purity of the aluminum shavings is ≥99.99%, and the maximum thickness is ≤1mm.

[0020] Optionally, the drying temperature is 60℃~100℃.

[0021] Optionally, the high-purity flake alumina has a purity ≥99.999%, an α-Al2O3 content ≥99%, a grain thickness ≤0.5μm, and a radial dimension of 2μm~10μm.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] This application provides a method for preparing high-purity flake alumina based on hydrolysis. The method includes: pretreating aluminum shavings; placing the pretreated aluminum shavings, an alkaline organic catalyst, and a morphology control agent in water to perform a hydrolysis reaction at a set temperature and time to obtain a reaction mixture; performing solid-liquid separation, washing, and drying of the reaction mixture to obtain flake aluminum hydroxide; and calcining the flake aluminum hydroxide to remove water of crystallization to obtain high-purity flake alumina. The alkaline organic catalyst includes at least one of the following: tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; the morphology control agent includes at least one of the following: ammonium bifluoride and ammonium fluoride. This application uses high-purity aluminum as raw material, which undergoes a hydrolysis reaction under the action of an alkaline organic catalyst to produce high-purity aluminum hydroxide. Simultaneously, crystal morphology control agents (ammonium bifluoride and ammonium fluoride) are added during the hydrolysis process. These control agents can alter the growth mode of alumina, promote the α-phase transformation of alumina, and thus achieve control over the microstructure of alumina. Furthermore, with the increase of the amount of crystal morphology control agent added, the radial dimension of the alumina crystals gradually increases, the thickness gradually decreases, the aspect ratio of the sample increases accordingly, and the crystal morphology tends towards hexagonal. Through the control of crystal morphology using the aforementioned crystal morphology control agents, followed by calcination, high-purity flake alumina can finally be obtained. This provides a novel method for preparing high-purity flake alumina. Attached Figure Description

[0024] 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.

[0025] 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.

[0026] Figure 1 This is a schematic flowchart of a method for preparing high-purity sheet-like alumina based on hydrolysis, provided in an embodiment of this application. Detailed Implementation

[0027] 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.

[0028] The range descriptions used herein, 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 to 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 "including" and "comprise" as 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 mentioned herein, 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 through commercial purchase or prepared using existing methods.

[0029] Figure 1 This is a schematic flowchart of a method for preparing high-purity sheet-like alumina based on hydrolysis, provided in an embodiment of this application.

[0030] like Figure 1 As shown in the embodiments of this application, a method for preparing high-purity sheet-like alumina based on hydrolysis is provided, the method comprising:

[0031] S1. Pre-treat the aluminum shavings;

[0032] In some embodiments, the pretreatment of the aluminum shavings includes:

[0033] The aluminum shavings are washed and dried multiple times with ultrapure water.

[0034] The purpose of repeatedly washing the aluminum shavings with ultrapure water is to remove impurities such as dust from their surface. Failure to remove these impurities can lead to a decrease in the purity of the final product, affecting its quality.

[0035] In some embodiments, the aluminum shavings have a purity of ≥99.99% and a maximum thickness of ≤1mm.

[0036] Limiting the purity of aluminum shavings to ≥99.99% ensures high product purity from the source and reduces the introduction of impurities. Limiting the maximum thickness of the aluminum shavings to ≤1mm increases the contact area between the shavings and water and the catalyst, allowing the hydrolysis reaction to proceed more fully and rapidly. For example, the purity of the aluminum shavings can be 99.99%, 99.991%, 99.992%, 99.993%, 99.994%, 99.995%, 99.996%, 99.997%, 99.998%, 99.999%, etc.; the maximum thickness of the aluminum shavings can be 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, etc.

[0037] In some embodiments, the drying temperature is 60°C to 100°C.

[0038] The drying temperature is set between 60℃ and 100℃. Drying within this temperature range ensures rapid evaporation of moisture from the aluminum shavings' surface without causing other chemical reactions or physical changes. The dried aluminum shavings avoid interference from moisture in subsequent hydrolysis reactions, ensuring the reactions proceed as expected, and also prevent the shavings from re-oxidizing due to moisture during storage. For example, the drying temperature can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 92℃, 95℃, or 100℃.

[0039] S2. The pretreated aluminum scraps, alkaline organic catalyst and morphology control agent are placed in water to carry out a hydrolysis reaction with a set temperature and a set time to obtain a reaction mixture.

[0040] In some embodiments, the alkaline organic catalyst includes at least one of the following: tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0041] The role of alkaline organic catalysts is to catalyze the hydrolysis reaction of aluminum scraps, accelerating the reaction rate. Compared to traditional alkaline reagents, these catalysts do not introduce impurity ions such as sodium and potassium, ensuring product purity. Furthermore, they remain unchanged before and after the reaction, allowing for recycling and reducing production costs.

[0042] In some embodiments, the morphology control agent includes at least one of the following: ammonium bifluoride and ammonium fluoride.

[0043] The role of morphology control agents is to regulate the microstructure of alumina. Because the different crystal faces of α-Al₂O₃ close-packed hexagonal crystals have different fluoride ion adsorption properties, the growth rates of different crystal faces in the alumina crystal are different, resulting in a plate-like microstructure.

[0044] In some embodiments, the mass ratio of the alkaline organic catalyst to the water is 1:(4-40).

[0045] Limiting the mass ratio of alkaline organic catalyst to water to 1:(4-40) ensures a suitable reaction rate, meeting production requirements and avoiding catalyst waste. If the ratio is lower than 1:40, the catalyst concentration is too low, the reaction rate is slow, and it is unsuitable for production; if the ratio is higher than 1:4, the reaction rate no longer increases, resulting in catalyst waste. For example, the mass ratio of the alkaline organic catalyst to water can be 1:4, 1:8, 1:12, 1:16, 1:20, 1:24, 1:28, 1:32, 1:36, 1:40, etc.

[0046] In some embodiments, the mass ratio of the aluminum shavings to the water is 1:(10-40).

[0047] Limiting the mass ratio of aluminum shavings to water to 1:(10-40) maintains a suitable solid content in the reaction system, facilitating reaction rate control and conserving water resources. If the ratio is lower than 1:40, insufficient water leads to a high solid content, making reaction rate control difficult; if the ratio is higher than 1:10, excessive water results in a low solid content, slowing the reaction rate and wasting water resources. For example, the mass ratio of aluminum shavings to water can be 1:10, 1:13, 1:16, 1:19, 1:22, 1:25, 1:28, 1:31, 1:34, 1:40, etc.

[0048] In some embodiments, the mass ratio of the crystal morphology control agent to the aluminum shavings is 1:(4-20).

[0049] A specific mass ratio of crystal morphology control agent to aluminum shavings of 1:(4-20) ensures the formation of regular, plate-like alumina while avoiding raw material waste. If the ratio is lower than 1:20, regularly shaped plate-like alumina cannot be obtained; if the ratio is higher than 1:4, the product retains its plate-like shape without significant variation, resulting in raw material waste. For example, the mass ratio of the crystal morphology control agent to the aluminum shavings can be 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18, 1:19, 1:20, etc.

[0050] In some embodiments, the set temperature is 50°C to 90°C, and the set time is 1 hour to 30 hours.

[0051] The hydrolysis reaction temperature is limited to 50℃–90℃ to ensure a suitable and controllable reaction rate. Below 50℃, the reaction rate slows significantly, making it unsuitable for production; above 90℃, hydrogen production is too rapid, difficult to control, and poses a risk. The hydrolysis reaction time is limited to 1h–30h to ensure complete hydrolysis and the formation of flake aluminum hydroxide. If the time is less than 1h, the reaction may be incomplete, resulting in a low product yield; if it is longer than 30h, it increases production time and cost without significantly improving the reaction efficiency. For example, the hydrolysis reaction temperature can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 88℃, 90℃, etc.; the hydrolysis reaction time can be 1h, 5h, 8h, 12h, 15h, 18h, 22h, 25h, 28h, 30h, etc.

[0052] S3. The reaction mixture is subjected to solid-liquid separation, washing and drying to obtain flake aluminum hydroxide;

[0053] Solid-liquid separation of the reaction mixture is used to separate the generated flake aluminum hydroxide from the liquid after the reaction, facilitating subsequent processing. Common separation methods include filtration, which leaves the solid aluminum hydroxide on filter paper while the liquid flows down through the paper; washing removes residual catalysts, morphology control agents, and other impurity ions adhering to the surface of aluminum hydroxide, further improving product purity; and drying removes adsorbed water from the surface of aluminum hydroxide, yielding pure flake aluminum hydroxide, which is then ready for subsequent calcination steps.

[0054] S4. The flake aluminum hydroxide is calcined to remove the water of crystallization, thereby obtaining high-purity flake aluminum oxide;

[0055] In some embodiments, the calcination temperature is 1250℃~1500℃, and the calcination holding time is 1h~2h.

[0056] The calcination temperature is limited to 1250℃~1500℃, and the holding time is 1h~2h. This ensures that aluminum hydroxide completely loses its water of crystallization and transforms into α-phase alumina, while avoiding excessive energy consumption. If the temperature is below 1250℃ or the time is less than 1h, the dehydration phase transformation requirements of aluminum hydroxide will not be met, and the product crystal form will not meet the standards. If the temperature is above 1500℃ or the time is longer than 2h, it will increase production energy consumption and raise costs. For example, the calcination temperature can be 1250℃, 1300℃, 1350℃, 1380℃, 1400℃, 1420℃, 1450℃, 1470℃, 1490℃, 1500℃, etc.; the calcination holding time can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 2h, etc.

[0057] In some embodiments, the high-purity flake alumina has a purity ≥99.999%, an α-Al2O3 content ≥99%, a grain thickness ≤0.5μm, and a radial dimension of 2μm to 10μm.

[0058] Therefore, this application employs a hydrolysis method to prepare high-purity flake alumina. The core process is as follows: high-purity aluminum is used as raw material, and a hydrolysis reaction occurs under the action of an alkaline organic catalyst to generate high-purity aluminum hydroxide. Simultaneously, crystal morphology control agents (ammonium bifluoride and ammonium fluoride) are added during the hydrolysis reaction. These control agents can alter the growth mode of alumina, promote the α-phase transformation of alumina, and thus achieve control over the microstructure of alumina. Specifically, as the amount of crystal morphology control agent added increases, the radial dimension of the alumina crystals gradually increases, the thickness gradually decreases, the aspect ratio of the sample increases accordingly, and the crystal morphology tends towards hexagonal. Through the control of crystal morphology using the aforementioned crystal morphology control agents, followed by calcination, high-purity flake alumina is finally obtained. This preparation process has significant advantages: the overall process is simple, requiring no additional impurity removal; the reaction conditions are mild, the reaction time is short, and the entire process is environmentally friendly. The high-purity flake alumina prepared by this method exhibits excellent properties, with a purity ≥99.999%, α-Al₂O₃ content ≥99%, and platelet-like crystals that are regular in shape, smooth in surface, well-dispersed, and free from agglomeration. The grain thickness is ≤0.5μm, and the radial dimension is 2μm~10μm. Therefore, it can be widely used in cosmetics, pearlescent pigments, high-grade coatings, and fine ceramics. For example, the purity of the high-purity flake alumina can be 99.999%, 99.9991%, 99.9992%, 99.9993%, 99.9994%, 99.9995%, 99.9996%, 99.9997%, 99.9998%, 99.9999%, etc.; and the α-Al₂O₃ content can be 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.9999%, etc. The percentages are 5%, 99.6%, 99.7%, 99.8%, 99.9%, etc.; the grain thickness can be 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.48μm, 0.5μm, etc.; the radial dimension can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 9.5μm, 10μm, etc.

[0059] This application achieves the preparation of high-purity sheet-like alumina through precise control of multiple stages, including raw material selection, reaction regulation, and process design. The specific process is as follows:

[0060] I. Source Control: Ensure high purity of raw materials and reduce the introduction of impurities.

[0061] (1) Select high-purity aluminum scraps: limit the purity of metal aluminum scraps to ≥99.99% (e.g., 99.99% to 99.999%), reduce the introduction of impurities (e.g., other metal ions, non-metallic impurities) from the source, and lay the foundation for the high purity (≥99.999%) of the final product.

[0062] (2) Pretreatment to remove surface impurities: Aluminum chips are washed with ultrapure water multiple times to thoroughly remove dust and other impurities attached to the surface; then dried at 60℃~100℃ to avoid moisture residue interfering with subsequent reactions and further ensure the cleanliness of raw materials.

[0063] (3) Control the morphology of aluminum chips: limit the maximum thickness of aluminum chips to ≤1mm (e.g., 0.1mm~1mm) to increase their contact area with the reaction system, ensure a more complete hydrolysis reaction, and reduce the purity drop caused by unreacted raw material residue.

[0064] II. Reaction Regulation: Directed Generation of High-Purity Flake Aluminum Hydroxide

[0065] (1) Use of impurity-free catalysts: Alkaline organic catalysts such as tetraethylammonium hydroxide and tetramethylammonium hydroxide are used to replace traditional inorganic bases such as sodium hydroxide and potassium hydroxide. These catalysts do not introduce metal impurity ions such as sodium and potassium, and their properties are stable before and after the reaction, allowing for recycling and avoiding impurity contamination.

[0066] (2) Precisely control the reaction ratio: The mass ratio of catalyst to water is limited to 1:(4~40) to ensure appropriate catalytic efficiency, avoid incomplete reaction due to low concentration, and prevent excessive waste; the mass ratio of aluminum scrap to water is 1:(10~40) to maintain appropriate solid content, ensure controllable reaction rate, and reduce impurity generation caused by uneven local reaction; the hydrolysis temperature is controlled at 50℃~90℃ and the time is 1h~30h to ensure sufficient reaction while avoiding safety risks and side reactions caused by excessive hydrogen production at high temperature.

[0067] (3) Directional control of morphology: Ammonium bifluoride or ammonium fluoride is added as a morphology control agent. The fluoride ions released by the agent selectively adsorb onto different crystal planes of α-Al2O3, resulting in different growth rates of each crystal plane—increased radial size and decreased thickness, ultimately forming a lamellar morphology. By controlling the mass ratio of the agent to aluminum chips to 1:(4~20), a regular lamellar structure (radial 2μm~10μm, thickness ≤0.5μm) is ensured, and excessive waste is avoided.

[0068] III. Post-processing purification: further improving purity and crystal form transformation

[0069] (1) Solid-liquid separation and washing: After the hydrolysis reaction, solid-liquid separation is achieved by filtration, and then the surface of aluminum hydroxide is washed to remove soluble impurities such as residual catalysts and morphology control agents. After drying, high-purity flake aluminum hydroxide is obtained.

[0070] (2) Calcination to achieve crystal transformation and dehydration: Calcination is carried out at 1250℃~1500℃ for 1h~2h to completely remove the water of crystallization from aluminum hydroxide and transform it into a stable α-Al2O3 phase (content ≥99%). No new impurities are introduced during this process, and the high temperature further removes any possible residual trace organic matter, finally obtaining high-purity flake aluminum oxide with a purity ≥99.999%.

[0071] In summary, the embodiments of this application control the entire process of "high-purity raw material pretreatment → impurity-free catalytic hydrolysis → directional morphology regulation → purification and crystal transformation" to reduce impurities at the source, avoid pollution during the reaction, and enhance purification through post-treatment. The final result is high-purity flake alumina with a purity ≥99.999%, α-Al2O3 content ≥99%, and regular morphology (flaky, radial diameter 2μm~10μm, thickness ≤0.5μm). Moreover, the entire process does not require additional impurity removal steps, making it highly efficient and environmentally friendly.

[0072] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0073] Example 1

[0074] This embodiment provides a method for preparing high-purity sheet-like alumina based on hydrolysis, the method including the following steps:

[0075] S11. Metal aluminum shavings with a purity of 99.99% and a maximum thickness of ≤1mm are washed three times with ultrapure water and then dried in a forced-air drying oven at 80℃ for later use.

[0076] S21. Add 200mL of ultrapure water, 5g of pretreated aluminum shavings, 32mL of tetramethylammonium hydroxide solution (25wt.% aqueous solution) and 0.25g of ammonium fluoride to a 500mL conical flask. Place the flask in a constant temperature water bath at 90℃ and stir the mixture at a constant speed for 1.5h. When no gas is released from the reaction flask and all the aluminum shavings in the flask are converted into white powder, the reaction is complete and a reaction mixture is obtained.

[0077] S31. Filter the reaction mixture. The filtrate is the catalyst solution, which can be recycled. The filter cake is flake aluminum hydroxide. Wash it multiple times with ultrapure water, and then place it in a vacuum drying oven at 90°C for 24 hours to remove adsorbed water.

[0078] S41. The dried flake aluminum hydroxide is placed in a muffle furnace and calcined at 1250℃ for 2 hours to obtain high-purity flake aluminum oxide powder with an aluminum oxide purity of 99.9992%, an α-Al2O3 content of 99.4%, a grain thickness of ≤0.5μm, a radial dimension of 2μm~4μm, a smooth surface, and a flake shape.

[0079] Example 2

[0080] This embodiment provides a method for preparing high-purity sheet-like alumina based on hydrolysis, the method including the following steps:

[0081] S12. Metal aluminum shavings with a purity of 99.99% and a maximum thickness of ≤1mm are washed three times with ultrapure water and then dried in a forced-air drying oven at 80℃ for later use.

[0082] S22. Add 200mL of ultrapure water, 10g of pretreated aluminum shavings, 48mL of tetraethylammonium hydroxide solution (25wt.% aqueous solution) and 0.50g of ammonium bifluoride to a 500mL conical flask. Place the flask in a constant temperature water bath at 80℃ and stir the mixture at a constant speed for 2.5h. When no gas is released from the reaction flask and all the aluminum shavings in the flask are converted into white powder, the reaction is complete and a reaction mixture is obtained.

[0083] S32. Filter the reaction mixture. The filtrate is the catalyst solution, which can be recycled. The filter cake is flake aluminum hydroxide. Wash it multiple times with ultrapure water, and then place it in a vacuum drying oven at 90°C for 24 hours to remove adsorbed water.

[0084] S42. The dried flake aluminum hydroxide is placed in a muffle furnace and calcined at 1300℃ for 1 hour to obtain high-purity flake aluminum oxide powder with an aluminum oxide purity of 99.9993%, an α-Al2O3 content of 99.1%, a grain thickness of ≤0.5μm, a radial dimension of 2μm~4μm, a smooth surface, and a flake shape.

[0085] Example 3

[0086] This embodiment provides a method for preparing high-purity sheet-like alumina based on hydrolysis, the method including the following steps:

[0087] S13. Metal aluminum shavings with a purity of 99.99% and a maximum thickness of ≤1mm are washed three times with ultrapure water and then dried in a forced-air drying oven at 80℃ for later use.

[0088] S23. Add 200mL of ultrapure water, 10g of pretreated aluminum shavings, 48mL of tetrapropylammonium hydroxide solution (25wt.% aqueous solution) and 0.75g of ammonium fluoride to a 500mL conical flask. Place the flask in a constant temperature water bath at 70℃ and stir the mixture at a constant speed for 6 hours. When no gas is released from the flask and all the aluminum shavings in the flask are converted into white powder, the reaction is complete and a reaction mixture is obtained.

[0089] S33. Filter the reaction mixture. The filtrate is the catalyst solution, which can be recycled. The filter cake is flake aluminum hydroxide. Wash it multiple times with ultrapure water, and then place it in a vacuum drying oven at 90°C for 24 hours to remove adsorbed water.

[0090] S43. The dried flake aluminum hydroxide is placed in a muffle furnace and calcined at 1400℃ for 1 hour to obtain high-purity flake aluminum oxide powder with an aluminum oxide purity of 99.9992%, an α-Al2O3 content of 99.3%, a grain thickness of ≤0.5μm, a radial dimension of 4μm~6μm, a smooth surface, and a flake-like, regular shape.

[0091] Example 4

[0092] This embodiment provides a method for preparing high-purity sheet-like alumina based on hydrolysis, the method including the following steps:

[0093] S14. Metal aluminum shavings with a purity of 99.99% and a maximum thickness of ≤1mm are washed three times with ultrapure water and then dried in a forced-air drying oven at 80℃ for later use.

[0094] S24. Add 200mL of ultrapure water, 10g of pretreated aluminum shavings, 48mL of tetrabutylammonium hydroxide solution (25wt.% aqueous solution) and 1.0g of ammonium bifluoride to a 500mL conical flask. Place the flask in a constant temperature water bath at 60℃ and stir the mixture at a constant speed for 13h. When no gas is released from the flask and all the aluminum shavings in the flask are converted into white powder, the reaction is complete and a reaction mixture is obtained.

[0095] S34. Filter the reaction mixture. The filtrate is the catalyst solution, which can be recycled. The filter cake is flake aluminum hydroxide. Wash it multiple times with ultrapure water, and then place it in a vacuum drying oven at 90°C for 24 hours to remove adsorbed water.

[0096] S44. The dried flake aluminum hydroxide is placed in a muffle furnace and calcined at 1400℃ for 1 hour to obtain high-purity flake aluminum oxide powder with an aluminum oxide purity of 99.9991%, an α-Al2O3 content of 99.2%, a grain thickness of ≤0.25μm, a radial dimension of 6μm~8μm, a smooth surface, a flake shape, a regular shape, and good dispersibility.

[0097] Example 5

[0098] This embodiment provides a method for preparing high-purity sheet-like alumina based on hydrolysis, the method including the following steps:

[0099] S15. Metal aluminum shavings with a purity of 99.99% and a maximum thickness of ≤1mm are washed three times with ultrapure water and then dried in a forced-air drying oven at 80℃ for later use.

[0100] S25. Add 200mL of ultrapure water, 10g of pretreated aluminum shavings, 48mL of tetraethylammonium hydroxide solution (25wt.% aqueous solution) and 1.25g of ammonium fluoride to a 500mL conical flask. Place the flask in a constant temperature water bath at 50℃ and stir at a uniform speed for 30h. When no gas is released from the reaction flask and all the aluminum shavings in the flask are converted into white powder, the reaction is complete and a reaction mixture is obtained.

[0101] S35. Filter the reaction mixture. The filtrate is the catalyst solution, which can be recycled. The filter cake is flake aluminum hydroxide. Wash it multiple times with ultrapure water, and then place it in a vacuum drying oven at 90°C for 24 hours to remove adsorbed water.

[0102] S45. The dried flake aluminum hydroxide is placed in a muffle furnace and calcined at 1500℃ for 1 hour to obtain high-purity flake aluminum oxide powder with an aluminum oxide purity of 99.9992%, an α-Al2O3 content of 99.3%, a grain thickness of ≤0.25μm, a radial dimension of 8μm~10μm, a smooth surface, a hexagonal flake shape, a regular shape, no agglomeration or twinning, and good dispersibility.

[0103] Comparative Example 1

[0104] This comparative example is based on Example 1, with the following specific adjustments:

[0105] Ammonium fluoride is not added in the hydrolysis reaction of S21.

[0106] Comparative Example 2

[0107] This comparative example is based on Example 1, with the following specific adjustments:

[0108] In the hydrolysis reaction of S21, the tetramethylammonium hydroxide solution was adjusted to a sodium hydroxide solution with a concentration of 50 mg / L.

[0109] Comparative Example 3

[0110] This comparative example is based on Example 1, with the following specific adjustments:

[0111] The aluminum shavings in S11 are adjusted to a purity of 99.9%.

[0112] The properties of the alumina powders obtained in Examples 1-5 and Comparative Examples 1-3, including their shape, alumina purity, α-Al2O3 content, grain thickness, and radial size, are summarized in Table 1.

[0113] Table 1. Performance of alumina powders in Examples 1-5 and Comparative Examples 1-3

[0114]

[0115]

[0116] As shown in Table 1, Examples 1 to 5 all yielded high-purity flake-shaped alumina powder with an alumina purity ≥99.999% and an α-Al₂O₃ content ≥99%. Comparative experiments were conducted based on Example 1. In Comparative Example 1, the addition of ammonium fluoride as a crystal morphology control agent during the hydrolysis reaction resulted in an alumina product with an irregular block shape rather than flakes. In Comparative Example 2, the tetramethylammonium hydroxide solution was replaced with a sodium hydroxide solution during the hydrolysis reaction, introducing sodium ions and resulting in an alumina product with a purity <99.999%. In Comparative Example 3, the raw material was adjusted to 99.9% pure aluminum shavings, resulting in an alumina product with a purity <99.999%.

[0117] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0118] (1) In the embodiments of this application, not only are aluminum scraps with a purity of ≥99.99% used to prepare flake alumina with a purity of ≥99.99%, but the reaction process is simple, there is no impurity removal process, the reaction conditions are mild, the reaction time is short, and there is no environmental pollution. At the same time, the flake alumina obtained has a regular morphology and a grain thickness of ≤0.5μm.

[0119] (2) In the embodiments of this application, the prepared high-purity flake alumina has a purity of ≥99.999%, an α-Al2O3 content of ≥99%, and regular flake-shaped crystals with smooth surfaces, good dispersibility, no agglomeration, a crystal thickness of ≤0.5μm, and a radial size controlled between 2μm and 10μm. This precisely matches the stringent requirements for material purity and microstructure in high-end fields such as cosmetics, pearlescent pigments, high-grade coatings, and fine ceramics. Furthermore, by controlling the crystal morphology, the radial size of the alumina crystals can be increased, the thickness reduced, the aspect ratio improved, and the morphology can approach a hexagonal shape, further optimizing product performance.

[0120] (3) In this embodiment, the overall process only includes four core steps: pretreatment, hydrolysis reaction, solid-liquid separation and drying, and calcination. No additional impurity removal process is required, which greatly simplifies the operation process and reduces the complexity of production. The reaction conditions are mild (hydrolysis temperature 50℃~90℃), the reaction time is short (1h~30h), and the parameters of each step (such as calcination temperature 1250℃~1500℃, holding time 1h~2h) are precisely optimized, which can ensure that the reaction is fully carried out and avoid energy waste, which is conducive to improving production efficiency and is suitable for large-scale industrial production.

[0121] (4) In the embodiments of this application, alkaline organic catalysts such as tetraethylammonium hydroxide are used, which do not introduce impurity ions such as sodium and potassium, and can be recycled, thereby reducing costs while ensuring product purity.

[0122] (5) In the embodiments of this application, the entire preparation process is washed with ultrapure water, with no harmful chemical emissions, and the catalyst can be recycled, reducing waste generation, meeting the requirements of green production, and being environmentally friendly.

[0123] 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 herein.

Claims

1. A method for preparing high-purity flake alumina based on hydrolysis, the method comprising: Pre-treat aluminum shavings; The pretreated aluminum scraps, alkaline organic catalyst, and morphology control agent are placed in water to carry out a hydrolysis reaction at a set temperature and time to obtain a reaction mixture. The reaction mixture was subjected to solid-liquid separation, washing, and drying to obtain flake aluminum hydroxide; and The flake aluminum hydroxide is calcined to remove the water of crystallization, thereby obtaining high-purity flake aluminum oxide; The alkaline organic catalyst includes at least one of the following: tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide; The morphology control agent includes at least one of the following: ammonium bifluoride and ammonium fluoride.

2. The method according to claim 1, characterized in that, The mass ratio of the alkaline organic catalyst to the water is 1:(4-40).

3. The method according to claim 1, characterized in that, The mass ratio of the aluminum shavings to the water is 1:(10-40).

4. The method according to claim 1, characterized in that, The mass ratio of the crystal morphology control agent to the aluminum metal chips is 1:(4-20).

5. The method according to claim 1, characterized in that, The set temperature is 50℃~90℃, and the set time is 1h~30h.

6. The method according to claim 1, characterized in that, The roasting temperature is 1250℃~1500℃, and the roasting holding time is 1h~2h.

7. The method according to claim 1, characterized in that, The pretreatment of aluminum shavings includes: The aluminum shavings are washed and dried multiple times with ultrapure water.

8. The method according to claim 7, characterized in that, The purity of the aluminum shavings is ≥99.99%, and the maximum thickness is ≤1mm.

9. The method according to claim 7, characterized in that, The drying temperature is 60℃~100℃.

10. The method according to claim 1, characterized in that, The high-purity flake alumina has a purity ≥99.999%, an α-Al2O3 content ≥99%, a grain thickness ≤0.5μm, and a radial dimension of 2μm~10μm.

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