Preparation method of nano high-purity alumina

Abstract

The application provides a preparation method of nano high-purity alumina, and belongs to the field of alumina refining. The method comprises the following steps: adding an aluminum ammonium sulfate solution into an ammonium bicarbonate solution with a set pH value to perform a precipitation reaction, so as to obtain a high-purity aluminum ammonium carbonate precursor; mixing the high-purity aluminum ammonium carbonate precursor with an organic acid aqueous solution to obtain a mixed slurry; performing a hydrothermal reaction on the mixed slurry to obtain an intermediate; and performing calcination on the intermediate to obtain nano high-purity alumina; wherein the organic acid comprises one or more of formic acid, oxalic acid, acetic acid, citric acid, carbonic acid, malic acid, tartaric acid and adipic acid. Through the selection of raw materials, the control of reaction environment and the morphology control assisted by organic acid, the excellent performance of the high-purity nano alumina product in the aspects of purity, morphology uniformity and particle size distribution is achieved.

Description

Technical Field

[0001] This application relates to the field of alumina refining technology, and in particular to a method for preparing nano-high-purity alumina. Background Technology

[0002] Nano-high-purity alumina holds a pivotal position in contemporary materials science due to its outstanding physicochemical properties, including high melting point, high hardness, corrosion resistance, and high thermal conductivity. It has found widespread application in many key areas such as ceramic materials, electronic products, and optical devices. In the field of ceramic materials, nano-high-purity alumina significantly improves the strength, hardness, and wear resistance of ceramic products, and is widely used in the manufacture of high-performance ceramic cutting tools, ceramic bearings, and advanced ceramic matrix composites. In electronic products, its excellent insulation properties and good thermal conductivity make it an ideal choice for manufacturing electronic packaging materials, integrated circuit substrates, and heat dissipation devices. In the field of optical devices, nano-high-purity alumina can be used to prepare highly transparent optical ceramics, precision optical lenses, and optical coating materials, greatly improving the performance and quality of optical devices.

[0003] The crystal form and morphology of nano-high-purity alumina have a significant impact on its properties. Currently, some progress has been made in the research of methods to control the microstructure and crystal size of nano-high-purity alumina, but many problems have also been exposed. Some methods require grinding the high-purity alumina obtained from initial calcination, followed by a second calcination. This process route not only requires the purchase of specialized grinding equipment, increasing equipment costs, but also consumes a large amount of energy during the two calcination processes, placing extremely high demands on the high-temperature resistance and temperature control accuracy of the equipment. Furthermore, impurities are highly likely to be introduced during the grinding process, affecting the purity of the nano-high-purity alumina and making it difficult to meet the needs of high-end applications requiring extremely high purity. Other methods use organic additives such as glucose to control the morphology of alumina by adding them to the co-precipitation reaction system. However, glucose decomposes during calcination, producing a large amount of gas, which forms pores in the powder structure, severely affecting the density and mechanical properties of alumina, leading to a significant reduction in key performance indicators such as strength and toughness. Furthermore, in subsequent processing, additional washing and heat treatment steps are necessary to remove residues from glucose combustion. This not only complicates the process, extends the production cycle, and increases labor costs, but also may result in alumina powder loss during washing and heat treatment, reducing product yield. In summary, existing methods for controlling the microstructure and crystal size of high-purity nano-alumina generally suffer from stringent equipment and energy requirements, complex processes, and difficulty in guaranteeing product quality. They struggle to efficiently prepare high-purity nano-alumina products with high purity, uniform microstructure, and narrow particle size distribution. Therefore, developing a new method for preparing high-purity nano-alumina to solve these technical challenges has become a crucial issue urgently needing breakthroughs in the field of materials science. Summary of the Invention

[0004] This application provides a method for preparing high-purity nano-alumina to solve the following technical problem: how to prepare high-purity nano-alumina products with high purity, uniform microstructure, and narrow particle size distribution.

[0005] This application provides a method for preparing nano-high-purity alumina, the method comprising:

[0006] An ammonium aluminum sulfate solution was added to an ammonium bicarbonate solution with a set pH value to carry out a precipitation reaction and obtain a high-purity ammonium aluminum carbonate precursor.

[0007] The high-purity ammonium aluminum carbonate precursor was mixed with an aqueous organic acid solution to obtain a mixed slurry;

[0008] The mixture slurry is subjected to a hydrothermal reaction to obtain an intermediate;

[0009] The intermediate was calcined to obtain nano-high-purity alumina;

[0010] The organic acids include one or more of the following: formic acid, oxalic acid, acetic acid, citric acid, carbonic acid, malic acid, tartaric acid, and adipic acid.

[0011] Optionally, the set pH value is 8.5 to 9.5.

[0012] Optionally, the volume ratio of the ammonium bicarbonate solution to the ammonium aluminum sulfate solution is 1:(0.8-1.2).

[0013] Optionally, the molar concentration of the ammonium bicarbonate solution is 1.8 mol / L to 2.2 mol / L, and the molar concentration of the ammonium aluminum sulfate solution is 0.09 mol / L to 0.22 mol / L.

[0014] Optionally, the precipitation reaction temperature is 60℃~80℃, and the precipitation reaction time is 3h~5h.

[0015] Optionally, the molar concentration of the organic acid aqueous solution is 0.2 mol / L to 0.6 mol / L.

[0016] Optionally, the solid-liquid ratio of the mixed slurry is 1:(5-10).

[0017] Optionally, the temperature of the hydrothermal reaction is 100℃~140℃, and the time of the hydrothermal reaction is 6h~8h.

[0018] Optionally, the calcination temperature is 1230℃~1270℃, and the calcination holding time is 3h~6h.

[0019] Optionally, the nano-high-purity alumina meets the following properties: purity ≥ 99.99%, particle size D50 of 200nm~400nm.

[0020] The technical solutions provided in this application have the following advantages compared with the prior art:

[0021] This application provides a method for preparing nano-high-purity alumina. The method includes: adding an aluminum ammonium sulfate solution to an ammonium bicarbonate solution with a set pH value to carry out a precipitation reaction to obtain a high-purity aluminum ammonium carbonate precursor; mixing the high-purity aluminum ammonium carbonate precursor with an aqueous organic acid solution to obtain a mixed slurry; subjecting the mixed slurry to a hydrothermal reaction to obtain an intermediate; and calcining the intermediate to obtain nano-high-purity alumina. The organic acid includes one or more of formic acid, oxalic acid, acetic acid, citric acid, carbonic acid, malic acid, tartaric acid, and adipic acid. This application achieves excellent performance in terms of purity, morphological uniformity, and particle size distribution of the high-purity nano-alumina product through the synergistic effects of raw material selection, reaction environment control, and organic acid-assisted morphology regulation.

[0022] Using ammonium bicarbonate and ammonium aluminum sulfate as raw materials, the two react to generate ammonium aluminum carbonate precursor, avoiding the introduction of complex impurities; the organic acids (formic acid, oxalic acid, etc.) used in the hydrothermal stage can be decomposed into volatile substances (such as CO2, H2O) in the subsequent roasting process, leaving no solid residue and reducing the introduction of impurities; through the continuous process of precipitation-hydrothermal-roasting, pollution caused by additional processing in intermediate steps is avoided, ultimately ensuring the high purity of the product.

[0023] Meanwhile, during the precipitation reaction stage, an aluminum ammonium sulfate solution is added to the ammonium bicarbonate solution with a set pH value to create a stable reaction environment and promote the uniform nucleation and growth of the aluminum ammonium carbonate precursor. In the hydrothermal reaction, organic acids modify the particle surface through coordination with aluminum ions, guiding the directional development of particles. At the same time, the high temperature and high pressure environment promotes the homogenization of particle morphology. The calcination process realizes the transformation of the intermediate into alumina, maintains the consistency of morphology, and finally obtains a uniform microstructure.

[0024] Furthermore, in the precipitation reaction, the reaction environment of the raw material solution is controlled to enable the precursor particles to grow synchronously, laying the foundation for a narrow particle size distribution. In the hydrothermal reaction, organic acids can inhibit excessive particle aggregation and abnormal growth, while the uniform dispersion of the mixed slurry provides consistent growth conditions for the particles. The calcination stage achieves stable transformation of the crystals, avoids large fluctuations in particle size, and ultimately obtains a product with a narrow particle size distribution range. Attached Figure Description

[0025] 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.

[0026] 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.

[0027] Figure 1 A schematic flowchart illustrating a method for preparing nano-high-purity alumina provided in this application embodiment;

[0028] Figure 2 The particle size distribution diagram of nano-high-purity alumina provided in Example 1 of this application;

[0029] Figure 3 This is a particle size distribution diagram of nano-high-purity alumina provided in Example 2 of this application;

[0030] Figure 4 This is a particle size distribution diagram of nano-high-purity alumina provided in Example 3 of this application;

[0031] Figure 5 The particle size distribution diagram of nano-high-purity alumina provided in Comparative Example 1 of this application;

[0032] Figure 6 The particle size distribution diagram of nano-high-purity alumina provided in Comparative Example 2 of this application;

[0033] Figure 7 The particle size distribution diagram of nano-high-purity alumina provided in Comparative Example 3 of this application. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] Figure 1 This is a schematic flowchart illustrating a method for preparing nano-high-purity alumina, as provided in an embodiment of this application.

[0037] like Figure 1 As shown in the embodiments of this application, a method for preparing nano-high-purity alumina is provided, the method comprising:

[0038] S1. Add ammonium aluminum sulfate solution to ammonium bicarbonate solution with a set pH value to carry out precipitation reaction and obtain high-purity ammonium aluminum carbonate precursor.

[0039] This application describes the preparation of an aluminum ammonium carbonate precursor (NH4)Al(OH)2CO3 with a concentrated particle size distribution and uniform crystal size via a precipitation reaction.

[0040] In some implementations, the set pH value is 8.5 to 9.5.

[0041] Limiting the pH of ammonium bicarbonate solution to 8.5–9.5 can maintain a weakly alkaline environment, promoting the formation of Al in ammonium aluminum sulfate. 3+ With HCO3 in ammonium bicarbonate - / CO3 2- A directional reaction occurs, forming a stable ammonium aluminum carbonate precipitate. When the pH is below 8.5, the hydrogen ion concentration is too high, and bicarbonate ions easily decompose into carbon dioxide, leading to incomplete precipitation. When the pH is above 9.5, excess hydroxide ions can cause aluminum ions to form aluminum hydroxide as a by-precipitate, reducing the purity of the precursor. For example, the set pH value can be 8.5, 8.7, 8.9, 9.0, 9.2, 9.3, 9.4, 9.5, etc.

[0042] In some embodiments, the volume ratio of the ammonium bicarbonate solution to the ammonium aluminum sulfate solution is 1:(0.8 to 1.2).

[0043] The volume ratio of ammonium bicarbonate solution to ammonium aluminum sulfate solution is limited to 1:(0.8-1.2) to ensure thorough mixing of the two solutions and uniform contact between aluminum ions, bicarbonate ions, and carbonate ions, avoiding excessively high local concentrations that could lead to particle agglomeration or uneven composition. A volume ratio less than 1:0.8 (excess ammonium aluminum sulfate solution): excessively high local aluminum ion concentrations can easily generate irregularly shaped, agglomerated particles or produce aluminum hydroxide impurities. A volume ratio greater than 1:1.2 (excess ammonium bicarbonate solution): increased unreacted ammonium bicarbonate and ammonia residues increase the burden on subsequent washing steps, requiring more steps to remove ammonium salt impurities. For example, the volume ratio of the ammonium bicarbonate solution to the ammonium aluminum sulfate solution can be 1:0.8, 1:0.9, 1:1.0, 1:1.05, 1:1.1, 1:1.15, 1:1.18, 1:1.2, etc.

[0044] In some embodiments, the molar concentration of the ammonium bicarbonate solution is 1.8 mol / L to 2.2 mol / L, and the molar concentration of the ammonium aluminum sulfate solution is 0.09 mol / L to 0.22 mol / L.

[0045] The concentration of ammonium bicarbonate is limited to 1.8–2.2 mol / L, and the concentration of ammonium aluminum sulfate is limited to 0.09–0.22 mol / L. The high concentration of ammonium bicarbonate provides sufficient bicarbonate and carbonate ions and maintains an alkaline environment (ammonium bicarbonate hydrolyzes to produce hydroxide ions), ensuring complete conversion of aluminum ions to ammonium aluminum carbonate while suppressing the occurrence of aluminum hydroxide side reactions. For example, the molar concentration of the ammonium bicarbonate solution can be 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.05 mol / L, 2.1 mol / L, 2.12 mol / L, 2.15 mol / L, 2.2 mol / L, etc.; and the molar concentration of the ammonium aluminum sulfate solution can be 0.09 mol / L, 0.11 mol / L, 0.13 mol / L, 0.15 mol / L, 0.17 mol / L, 0.19 mol / L, 0.21 mol / L, 0.22 mol / L, etc.

[0046] In some embodiments, the precipitation reaction is carried out at a temperature of 60°C to 80°C and for a reaction time of 3 to 5 hours.

[0047] The precipitation reaction temperature is limited to 60–80℃, and the reaction time is 3–5 hours. 60–80℃ increases the diffusion rate of aluminum ions, bicarbonate ions, and carbonate ions, promoting uniform nucleation and growth of ammonium aluminum carbonate precipitate. Too low a temperature leads to a slow reaction and may be incomplete; too high a temperature (above 80℃) accelerates the decomposition of ammonium bicarbonate (generating ammonia, carbon dioxide, and water), causing localized fluctuations in pH and ion concentration, thus disrupting the uniformity of the precipitation. 3–5 hours ensures complete precipitation of aluminum ions into ammonium aluminum carbonate. Too short a time (less than 3 hours) results in incomplete reaction; too long a time (more than 5 hours) increases the probability of Brownian collisions in the already formed particles, making them prone to aggregation (early Ostwald ripening stage), thus disrupting particle size uniformity. For example, the reaction temperature of the precipitation reaction can be 60℃, 63℃, 65℃, 68℃, 70℃, 73℃, 76℃, 80℃, etc.; the reaction time of the precipitation reaction can be 3h, 3.5h, 4h, 4.2h, 4.5h, 4.7h, 5h, 5h, etc.

[0048] S2. The high-purity aluminum ammonium carbonate precursor is mixed with an organic acid aqueous solution to obtain a mixed slurry;

[0049] In some embodiments, the organic acid includes one or more of formic acid, oxalic acid, acetic acid, citric acid, carbonic acid, malic acid, tartaric acid, and adipic acid.

[0050] In some embodiments, the molar concentration of the organic acid aqueous solution is 0.2 mol / L to 0.6 mol / L.

[0051] The concentration of the organic acid is limited to 0.2–0.6 mol / L. The organic acid coordinates with aluminum ions (or aluminum ions released from the dissolution of ammonium aluminum carbonate) through its carboxyl groups, modifying the particle surface, inhibiting excessive grain growth, and guiding the directional development of particles (e.g., plate-like, spherical, etc.) through selective adsorption on different crystal planes. Concentrations below 0.2 mol / L result in insufficient coordination, failing to effectively inhibit grain growth and agglomeration, and poor morphology control. Concentrations above 0.6 mol / L may cause excessive organic acid to form stable and difficult-to-decompose organoaluminum salt complexes with aluminum ions, which are difficult to completely remove during subsequent calcination (requiring higher temperatures or longer times, easily leading to sintering), increasing the impurity content of the product. For example, the molar concentration of the organic acid aqueous solution can be 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.55 mol / L, 0.6 mol / L, etc.

[0052] In some embodiments, the solid-liquid ratio of the mixture is 1:(5-10).

[0053] Limiting the solid-liquid ratio of the mixed slurry to 1:(5-10) (g / mL) ensures sufficient dispersion of precursor particles in the organic acid solution, provides ample reaction space, promotes uniform hydrothermal reaction, and prevents particle agglomeration caused by excessively high local concentrations. A solid-liquid ratio less than 1:10 (too much liquid) dilutes the organic acid concentration, weakening its surface modification and morphology control effects on particles. A solid-liquid ratio greater than 1:5 (too much solid) results in an overly viscous slurry, reducing heat transfer (affecting temperature uniformity) and mass transfer (impeded diffusion of organic acid and aluminum ions), leading to uneven reaction, wider particle size distribution of intermediates, and inconsistent morphology. For example, the solid-liquid ratio of the mixed slurry can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc.

[0054] S3. The mixture slurry is subjected to a hydrothermal reaction to obtain an intermediate;

[0055] In the hydrothermal reaction stage, this application utilizes organic acids to regulate the morphology of precursor particles, inhibit aggregation, and optimize crystallinity.

[0056] In some embodiments, the temperature of the hydrothermal reaction is 100°C to 140°C, and the time of the hydrothermal reaction is 6 hours to 8 hours.

[0057] The hydrothermal process is limited to a temperature of 100–140℃ and a duration of 6–8 hours. The high-pressure hydrothermal environment of 100–140℃ provides energy to promote the decomposition of the precursor ammonium aluminum carbonate (usually producing boehmite, i.e., aluminum hydroxide or aluminum hydroxide) and its interfacial reaction with organic acids. High temperature accelerates the dissolution-recrystallization process, reconstructing the particle surface and optimizing crystal integrity (e.g., recrystallizing amorphous or poorly crystallized regions). Temperatures above 140℃ result in excessively rapid reaction, rapid particle growth, and easy agglomeration. Temperatures below 100℃ result in insufficient driving force, slow or absent dissolution-recrystallization, and failure of morphology control. 6–8 hours ensures the complete completion of the dissolution-recrystallization process, yielding a well-formed, well-crystallized intermediate (usually aluminum hydroxide). Less than 6 hours results in incomplete crystal development and unsatisfactory morphology. More than 8 hours can lead to abnormal particle growth due to the Ostwald ripening effect (small particles dissolving and depositing onto larger particles), disrupting particle size uniformity. For example, the temperature of the hydrothermal reaction can be 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 135℃, 140℃, etc.; the time of the hydrothermal reaction can be 6h, 6.5h, 7h, 7.2h, 7.5h, 7.7h, 8h, 8h, etc.

[0058] S4. The intermediate is calcined to obtain nano-high-purity alumina;

[0059] In the calcination stage, this application completely and controllably transforms the intermediate obtained by hydrothermal treatment (aluminum hydroxide or aluminum hydroxide) into a thermodynamically stable nano-α-alumina crystal phase, while inhibiting particle sintering and excessive growth.

[0060] In some embodiments, the calcination temperature is 1230℃~1270℃, and the calcination holding time is 3h~6h.

[0061] The calcination temperature is limited to 1230–1270℃, and the holding time is 3–6 hours. 1230–1270℃ is the typical temperature range for the stable formation of α-alumina (the α phase is the thermodynamically stable phase of alumina). This temperature ensures that the intermediate (alumina hydroxide transforming into alumina and water, or aluminum hydroxide transforming into alumina and water) undergoes a series of dehydration and phase transformations (e.g., γ-alumina → θ-alumina → α-alumina) to completely transform into α-alumina. Temperatures above 1270℃: the atomic diffusion rate on the particle surface increases sharply, leading to severe sintering and agglomeration, and a significant increase in particle size; temperatures below 1230℃ (especially below 1200℃): the phase transformation may be incomplete, leaving residual metastable alumina phases such as γ and θ. The time factor: a holding time of 3–6 hours ensures complete crystal transformation (especially from the θ phase to the α phase). Less than 3 hours: Phase transformation may be incomplete, leaving residual γ or θ phase alumina; More than 6 hours: Even at temperatures of 1230-1270℃, grains will continue to grow slowly through solid-state diffusion (Ostwald ripening), resulting in the final α-alumina particle size (D50) exceeding the nanoscale target range (greater than 400nm), and a decrease in specific surface area. For example, the calcination temperature can be 1230℃, 1235℃, 1240℃, 1245℃, 1250℃, 1255℃, 1265℃, 1270℃, etc.; the calcination holding time can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6 hours, etc.

[0062] In some embodiments, the nano-high-purity alumina meets the following properties: purity ≥ 99.99%, and particle size D50 of 200 nm to 400 nm.

[0063] This application provides a method for controlling the crystal morphology and particle size distribution of nano-alumina. The specific process is as follows: First, high-purity ammonium aluminum carbonate precursor is prepared by the ammonium salt method. During this process, the microstructure of the precursor is initially controlled by adjusting parameters such as reaction temperature and raw material concentration. Next, high-purity ammonium aluminum carbonate is mixed with organic acids (including formic acid, oxalic acid, acetic acid, citric acid, carbonic acid, malic acid, tartaric acid, adipic acid, etc.) to prepare a slurry. Then, the mixed slurry is subjected to a hydrothermal reaction. By adjusting conditions such as organic acid concentration, hydrothermal time, and hydrothermal temperature, the morphology and grain size of ammonium aluminum carbonate are further controlled, while reducing grain activity to prevent abnormal grain growth in subsequent processes. Finally, the product obtained from the hydrothermal reaction is calcined in a high-temperature furnace to obtain a high-purity nano-alumina product with uniform microstructure and narrow particle size distribution. The high-purity nano-alumina prepared by this invention has the characteristics of purity of over 99.99%, controllable crystal morphology, and narrow particle size distribution (D50 = 200-400 nm). For example, the purity of the nano-high-purity alumina can be 99.99%, 99.991%, 99.993%, 99.995%, 99.996%, 99.997%, 99.998%, 99.999%, etc.; and the particle size D50 can be 200nm, 230nm, 270nm, 300nm, 330nm, 360nm, 390nm, 400nm, etc.

[0064] This application achieves precise control throughout the entire process, from raw material reaction and morphology optimization to crystal transformation, by step-by-step regulating key process parameters. This results in the final preparation of high-purity nano-alumina products with uniform microstructure and narrow particle size distribution. The specific mechanism is as follows:

[0065] (1) High Purity Guarantee Mechanism: In terms of raw material selection, high-purity ammonium aluminum sulfate (self-produced, purity controllable) and ammonium bicarbonate are used to reduce the introduction of impurities; the ammonium bicarbonate solution is filtered to remove impurities before precipitation reaction, further reducing the impurity content. At the same time, during the precipitation stage, the pH value (weakly alkaline environment) and raw material concentration ratio are controlled to promote the directional reaction of aluminum ions and bicarbonate ions to generate ammonium aluminum carbonate, inhibiting the generation of by-products such as aluminum hydroxide and avoiding impurity residues. In addition, easily decomposable organic acids (such as formic acid, oxalic acid, etc.) are selected in the hydrothermal stage, which can be completely decomposed into gases (such as CO2, H2O) during the subsequent roasting process, leaving no solid residues and avoiding the introduction of new impurities; at the same time, the concentration of organic acids is controlled to prevent the excessive generation of difficult-to-remove organoaluminum salt impurities. Furthermore, the roasting stage is carried out at high temperature in an air atmosphere, which can completely remove crystal water, residual organic matter, etc. in the intermediate, and finally obtain a product with a purity ≥99.99%.

[0066] (2) Microscopic morphology uniformity control mechanism: During the precipitation reaction stage, by controlling the reaction temperature (60-80℃) and time (3-5h), the uniform nucleation and growth of the aluminum ammonium carbonate precursor is ensured, initially forming particles with a concentrated particle size distribution; the optimization of the solution volume ratio (1:(0.8-1.2)) avoids morphological abnormalities caused by excessively high local concentrations. At the same time, during the hydrothermal reaction stage, organic acids coordinate with aluminum ions through carboxyl groups, modifying the surface of the precursor particles, forming steric hindrance to inhibit agglomeration, and guiding the directional development of particles (such as regular morphologies such as plate-like and spherical shapes) through selective adsorption; the regulation of hydrothermal temperature (100-140℃) and time (6-8h) promotes the dissolution-recrystallization of the particle surface, further optimizing the crystal integrity and making the intermediate morphology more uniform. In addition, during the calcination stage, the precise control of temperature (1230-1270℃) and holding time (3-6h) ensures that the intermediate is uniformly converted into α-alumina, avoiding morphological damage caused by local overheating.

[0067] (3) Mechanism for achieving narrow particle size distribution: During the precipitation stage, by controlling the raw material concentration ratio (ammonium bicarbonate to ammonium aluminum sulfate concentration ratio of 10-20) and reaction conditions, the precursor particles are nucleated synchronously and grow uniformly, resulting in a concentrated initial particle size distribution. Simultaneously, during the hydrothermal stage, a solid-liquid ratio (1:(5-10)) ensures sufficient particle dispersion, and combined with the inhibitory effect of organic acids, prevents particle collision and agglomeration. Precise control of hydrothermal time avoids abnormal particle growth caused by Ostwald ripening, ensuring a narrow particle size distribution in the intermediate. Furthermore, during the calcination stage, reasonable temperature and time settings suppress excessive grain growth and sintering, ultimately stabilizing the product particle size D50 at 200-400 nm, resulting in a narrow distribution range.

[0068] In summary, this application demonstrates several significant advantages in the preparation of nano-high-purity alumina, as detailed below:

[0069] (1) Excellent and controllable product quality: The prepared nano-high-purity alumina has a purity of over 99.99%, with a particle size D50 stable in the range of 200-400 nm and a narrow particle size distribution, which can meet the stringent requirements of high-end fields for ultra-high purity and uniform particle size. At the same time, by adjusting the process parameters at each stage, the crystal form (stable α phase) and micromorphology (such as plate-like, spherical, etc.) of the product can be precisely controlled to adapt to the application needs of different scenarios.

[0070] (2) The process design is scientific and rigorous, with strong controllability: A step-by-step control strategy is adopted, and the parameters at each stage are set reasonably. In the precipitation stage, the precise control of pH (8.5-9.5), solution volume ratio (1:(0.8-1.2)), concentration, and reaction conditions ensures that the precursor ammonium aluminum carbonate has concentrated particle size and uniform crystal size. In the hydrothermal stage, the morphology and crystal size of the intermediate are further controlled by optimizing the type of organic acid (0.2-0.6 mol / L), solid-liquid ratio (1:(5-10)), and hydrothermal parameters. In the calcination stage, the strict limitation of temperature (1230-1270℃) and holding time (3-6h) ensures complete crystal transformation and stable particle size. The parameters of the entire process are clear, easy to operate, and highly repeatable, which is conducive to industrial replication.

[0071] (3) Targeted solutions to key pain points in the industry: The process design directly addresses common problems in the preparation of nano alumina, avoiding precursor agglomeration and impurity (such as aluminum hydroxide) generation by controlling precipitation conditions; using organic acid coordination to modify the particle surface, reducing grain activity and effectively preventing abnormal grain growth during subsequent calcination; and precisely controlling calcination parameters to avoid metastable phase (γ, θ phase) residue and prevent excessive sintering of particles, ensuring stable and controllable product quality.

[0072] (4) The process is simple, efficient, and widely applicable: The overall process only includes three core steps: precipitation reaction, hydrothermal reaction, and calcination. It is easy to operate, requires no complex equipment, has relatively low energy consumption, and has the potential for large-scale production. At the same time, the range of organic acids that can be selected is wide (covering 8 types including formic acid and oxalic acid). The products can be customized by adjusting the types of organic acids and process parameters to meet the diverse needs of different application scenarios.

[0073] 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.

[0074] Example 1

[0075] This embodiment provides a method for preparing nano-high-purity alumina, including the following steps:

[0076] S11. Preparation of high-purity aluminum ammonium carbonate precursor: Purchased ammonium bicarbonate was dissolved in high-purity water, filtered, and a purified ammonium bicarbonate solution (concentration 2 mol / L) was obtained. The pH of the solution was adjusted to 9 using ammonia. High-purity aluminum ammonium sulfate produced by Chalco Shandong Co., Ltd. was dissolved in an equal volume of high-purity water to obtain an aluminum ammonium sulfate solution (concentration 0.2 mol / L). An equal volume of the aluminum ammonium sulfate solution was added to the above ammonium bicarbonate solution, and a precipitation reaction was carried out at a reaction temperature of 60℃ for 5 hours to obtain the high-purity aluminum ammonium carbonate precursor.

[0077] S21. Preparation of mixed slurry: The high-purity aluminum ammonium carbonate precursor obtained in step S11 is mixed with an aqueous solution of organic acid (concentration of 0.2 mol / L, organic acid is formic acid) to obtain a uniformly dispersed mixed slurry (solid-liquid ratio of 1:5).

[0078] S31. Preparation of intermediate by hydrothermal reaction: The mixed slurry obtained in step S21 is subjected to hydrothermal reaction, with the hydrothermal temperature set at 100℃ and the hydrothermal time set at 8h; after the reaction is completed, the intermediate is obtained by filtration, washing and drying.

[0079] S41. Calcination to obtain nano-high-purity alumina: The intermediate obtained in step S31 is placed in a high-alumina crucible and calcined in air at a temperature of 1250℃ for 3 hours to obtain nano-high-purity alumina. This product has a regular morphology, controllable particle size, a D50 of 211 nm, and a purity ≥99.99%.

[0080] Example 2

[0081] This embodiment provides a method for preparing nano-high-purity alumina, including the following steps:

[0082] S11. Preparation of high-purity aluminum ammonium carbonate precursor: Purchased ammonium bicarbonate was dissolved in high-purity water, filtered, and a purified ammonium bicarbonate solution (concentration 2 mol / L) was obtained. The pH of the solution was adjusted to 9 using ammonia. High-purity aluminum ammonium sulfate produced by Chalco Shandong Co., Ltd. was dissolved in an equal volume of high-purity water to obtain an aluminum ammonium sulfate solution (concentration 0.15 mol / L). An equal volume of the aluminum ammonium sulfate solution was added to the above ammonium bicarbonate solution, and a precipitation reaction was carried out at a reaction temperature of 70℃ for 4 hours to obtain the high-purity aluminum ammonium carbonate precursor.

[0083] S21. Preparation of mixed slurry: The high-purity aluminum ammonium carbonate precursor obtained in step S11 is mixed with an aqueous solution of organic acid (concentration of 0.4 mol / L, organic acid is oxalic acid) to obtain a uniformly dispersed mixed slurry (solid-liquid ratio of 1:8).

[0084] S31. Preparation of intermediate by hydrothermal reaction: The mixed slurry obtained in step S21 is subjected to hydrothermal reaction, with the hydrothermal temperature set at 120℃ and the hydrothermal time set at 7h; after the reaction is completed, the intermediate is obtained by filtration, washing and drying.

[0085] S41. Calcination to obtain nano-high-purity alumina: The intermediate obtained in step S31 is placed in a high-alumina crucible and calcined in air at a temperature of 1250℃ for 3 hours to obtain nano-high-purity alumina. This product has a regular morphology, controllable particle size, a D50 of 304nm, and a purity ≥99.99%.

[0086] Example 3

[0087] This embodiment provides a method for preparing nano-high-purity alumina, including the following steps:

[0088] S11. Preparation of high-purity aluminum ammonium carbonate precursor: Purchased ammonium bicarbonate was dissolved in high-purity water, filtered, and a purified ammonium bicarbonate solution (concentration 2 mol / L) was obtained. The pH of the solution was adjusted to 9 using ammonia. High-purity aluminum ammonium sulfate produced by Chalco Shandong Co., Ltd. was dissolved in an equal volume of high-purity water to obtain an aluminum ammonium sulfate solution (concentration 0.2 mol / L). An equal volume of the aluminum ammonium sulfate solution was added to the above ammonium bicarbonate solution, and a precipitation reaction was carried out at a reaction temperature of 80℃ for 3 hours to obtain the high-purity aluminum ammonium carbonate precursor.

[0089] S21. Preparation of mixed slurry: The high-purity aluminum ammonium carbonate precursor obtained in step S11 is mixed with an aqueous solution of organic acid (concentration of 0.6 mol / L, organic acid is acetic acid) to obtain a uniformly dispersed mixed slurry (solid-liquid ratio of 1:10).

[0090] S31. Preparation of intermediate by hydrothermal reaction: The mixed slurry obtained in step S21 is subjected to hydrothermal reaction, with the hydrothermal temperature set at 140℃ and the hydrothermal time at 6h; after the reaction is completed, the intermediate is obtained by filtration, washing and drying.

[0091] S41. Calcination to obtain nano-high-purity alumina: The intermediate obtained in step S43 is placed in a high-alumina crucible and calcined in air at a temperature of 1250℃ for 3 hours to obtain nano-high-purity alumina. This product has a regular morphology, controllable particle size, a D50 of 395nm, and a purity ≥99.99%.

[0092] Comparative Example 1

[0093] Comparative Example 1 is based on Example 1, but differs from Example 1 in that:

[0094] In step S11, the precipitation reaction temperature is 100°C, and all other conditions are the same as in Example 1.

[0095] Comparative Example 2:

[0096] Comparative Example 2 is based on Example 2, but differs from Example 2 in that:

[0097] In step S31, the hydrothermal reaction temperature is 80°C, and all other conditions are the same as in Example 2.

[0098] Comparative Example 3:

[0099] Comparative Example 3 is based on Example 3, but differs from Example 3 in that:

[0100] In step S21, the concentration of the organic acid is 0.05 mol / L, and all other conditions are the same as in Example 3.

[0101] The particle size of the high-purity nano-alumina obtained in Examples 1-3 and Comparative Examples 1-3 was measured, as shown in Table 1. The particle size distribution is shown in the figure below. Figures 2-7 As shown in Table 2, the impurity content of the high-purity nano-alumina obtained in Examples 1-3 and Comparative Examples 1-3 is also shown in Table 2.

[0102] Table 1. Particle size of high-purity nano-alumina in Examples 1-3 and Comparative Examples 1-3

[0103] Example 1 161 211 460 Example 2 167 304 625 Example 3 270 395 739 Comparative Example 1 215 749 2942 Comparative Example 2 178 641 1901 Comparative Example 3 330 1109 9827

[0104] Table 2. Impurity content of high-purity nano-alumina in Examples 1-3 and Comparative Examples 1-3

[0105]

[0106] pass Figures 2-7 As shown in Table 1, the nano-high-purity alumina prepared in Examples 1-3 has a concentrated particle size distribution, and the particle size D50 is controlled within the range of 200-400 nm. Table 2 shows that the purity of the nano-high-purity alumina in Examples 1-3 is greater than 99.99%.

[0107] In Comparative Example 1, the reaction temperature was above 100℃, and the reaction process between ammonium bicarbonate and ammonium aluminum sulfate was too rapid, causing particle agglomeration, with large-sized alumina particles being the majority. Figure 5 As shown in Comparative Example 1.

[0108] In Comparative Example 2, the hydrothermal temperature was 80℃. The organic acid had little effect on regulating the crystal form and morphology of ammonium aluminum carbonate, resulting in a dispersed particle distribution and failing to achieve the desired narrow particle size distribution. Figure 6 As shown in Comparative Example 2.

[0109] In Comparative Example 3, the organic acid concentration was 0.05 mol / L. This low concentration was insufficient to inhibit grain growth, resulting in larger alumina powder particles. Figure 7 As shown in Comparative Example 3.

[0110] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0111] (1) In the embodiments of this application, the process flow is simple and the equipment and energy consumption requirements are low. The method of controlling the crystal form and morphology of high-purity nano alumina in this application only includes three steps: precursor preparation, intermediate control and calcination. The overall process flow is short, the operation steps are few, the operation difficulty is low, and the overall energy consumption is relatively low.

[0112] (2) In the embodiments of this application, the crystal form and morphology are controllable and the particle size distribution range is narrow. This application controls the crystal form, morphology and particle size distribution range of ammonium aluminum carbonate by controlling the reaction temperature and reaction time in the reaction process of the precursor and intermediate step by step, and then calcining to obtain high-purity nano-alumina with uniform size and regular morphology.

[0113] 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 nano-high-purity alumina, the method comprising: An ammonium aluminum sulfate solution was added to an ammonium bicarbonate solution with a set pH value to carry out a precipitation reaction and obtain a high-purity ammonium aluminum carbonate precursor. The high-purity ammonium aluminum carbonate precursor was mixed with an aqueous organic acid solution to obtain a mixed slurry; The mixture slurry is subjected to a hydrothermal reaction to obtain an intermediate; The intermediate was calcined to obtain nano-high-purity alumina; The organic acids include one or more of the following: formic acid, oxalic acid, acetic acid, citric acid, malic acid, tartaric acid, and adipic acid; The set pH value is 8.5–9.5; The volume ratio of the ammonium bicarbonate solution to the ammonium aluminum sulfate solution is 1:(0.8-1.2); The molar concentration of the ammonium bicarbonate solution is 1.8 mol / L to 2.2 mol / L, and the molar concentration of the ammonium aluminum sulfate solution is 0.09 mol / L to 0.22 mol / L. The precipitation reaction temperature is 60℃~80℃, and the precipitation reaction time is 3h~5h; The molar concentration of the organic acid aqueous solution is 0.2 mol / L to 0.6 mol / L; The solid-liquid ratio of the mixed slurry is 1:(5-10), and the unit is g / mL; The hydrothermal reaction temperature is 100℃~140℃, and the hydrothermal reaction time is 6h~8h; The roasting temperature is 1230℃~1270℃, and the roasting holding time is 3h~6h; The nano-high-purity alumina meets the following properties: purity ≥ 99.99%, particle size D50 is 200nm~400nm.

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