Method for preparing alpha-aluminum oxide through low-temperature induction method
By employing a low-temperature induction method, activation and pretreatment steps, combined with the removal of impurities using hydrochloric acid and carbon dioxide, and mixing with highly active nanocrystalline seeds followed by low-temperature calcination, the problem of α-alumina agglomeration was solved, improving its purity and performance, making it suitable for high-end electronic devices and advanced ceramics.
Patent Information
- Application Number
- CN202512011513.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-02-10
AI Technical Summary
The existing rotary kiln high-temperature calcination method is prone to particle agglomeration during the preparation of α-alumina, which affects its performance and purity. Moreover, the existing method is difficult to improve the purity and performance of α-alumina at the same time.
The method employs a low-temperature induction process, which includes activation treatment, pretreatment, and mixing steps. Hydrochloric acid solution is used to remove impurities from nanoparticles, carbon dioxide is used to remove sodium impurities from the alumina raw material, and highly active nanocrystal seeds are mixed with the pretreated alumina in a certain proportion and then calcined at low temperature to control the crystal structure.
Simultaneous improvement in the purity and performance of α-alumina was achieved, with product purity reaching over 99.90%, average particle size below 350nm, and specific surface area above 35m²/g, while reducing phase transition temperature and energy consumption.
Smart Images
Figure CN121494027A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of alumina preparation, and particularly relates to a method for preparing alpha-alumina by a low-temperature induction method. BACKGROUND
[0002] Alpha-alumina has excellent properties such as high hardness, high strength, wear resistance, corrosion resistance, high temperature resistance, oxidation resistance, good insulation, large surface area, small thermal expansion coefficient, good thermal shock resistance and low dielectric loss, and therefore has special uses in metallurgy, chemical industry, catalysis, flame retardation, sound insulation, insulation, electronics and fine ceramics. Alpha-alumina is generally prepared by a rotary kiln high-temperature calcination method in industry. However, the rotary kiln high-temperature calcination method requires a very high energy in the production of alumina, resulting in a high phase transition temperature of alumina in the rotary kiln high-temperature calcination process, which can even reach above 1350 DEG C. However, under the condition of a high phase transition temperature, alumina in a powder particle state is extremely easy to agglomerate, forming a series of irregular hard agglomerated structures, which are doped in alpha-alumina, and will not only affect the performance of alpha-alumina, but also make alpha-alumina lose its inherent excellent properties.
[0003] At present, in order to solve the agglomeration problem of alumina, a mineralizer is generally introduced into the rotary kiln high-temperature calcination method and the phase transition temperature is reduced, however, the purity and performance of alpha-alumina prepared by the method are poor, and it is difficult to meet the actual production and application requirements of alpha-alumina. SUMMARY
[0004] The present application provides a method for preparing alpha-alumina by a low-temperature induction method, to solve the technical problem of how to simultaneously improve the purity and performance of alpha-alumina. In a first aspect, the embodiments of the present application provide a method for preparing alpha-alumina by a low-temperature induction method, which comprises the following steps: activating alpha-alumina nanoparticles to obtain activated alpha-alumina nanoseeds; pretreating alumina raw materials by using carbon dioxide to remove sodium-containing impurities in the alumina raw materials, to obtain pretreated alumina raw materials; mixing the activated alpha-alumina nanoseeds and the pretreated alumina raw materials to obtain mixed alumina raw materials; wherein the mass m1 of the activated alpha-alumina nanoseeds and the mass m2 of the pretreated alumina raw materials satisfy: m1:m2≥1:100; calcining the mixed alumina raw materials to obtain alpha-alumina products.
[0005] Optionally, the mass m1 of the activated α-alumina nano-seeds and the mass m2 of the pretreated alumina raw material satisfy: m1:m2=(1 to 5):100.
[0006] Optionally, the particle size of the α-alumina nanoparticles is 25 nm to 35 nm.
[0007] Optionally, the calcination comprises a temperature rising section and a temperature holding section, the end point temperature of the temperature rising section is 1000℃ to 1200℃, and the time of the temperature holding section is 2h to 4h.
[0008] Optionally, the temperature rising rate of the temperature rising section is 3℃ / min to 5℃ / min.
[0009] Optionally, the α-alumina nanoparticles are subjected to activation treatment to obtain activated α-alumina nano-seeds, comprising the steps of: immersing the α-alumina nanoparticles in a hydrochloric acid solution to obtain a primary activation mixture; centrifuging the primary activation mixture to obtain primary activation seeds; vacuum drying the primary activation seeds to obtain activated α-alumina nano-seeds.
[0010] Optionally, the temperature of the immersion treatment is 40℃ to 60℃, and the time of the immersion treatment is 2h to 4h; and / or The temperature of the vacuum drying is ≥80℃, and the time of the vacuum drying is ≥8h.
[0011] Optionally, the alumina raw material is pretreated using carbon dioxide to remove sodium-containing impurities in the alumina raw material to obtain a pretreated alumina raw material, comprising the steps of: mixing the alumina raw material using deionized water to obtain an alumina slurry; carbonating the alumina slurry using carbon dioxide to obtain a carbonated slurry; sequentially filtering and drying the carbonated slurry to obtain a pretreated alumina raw material.
[0012] Optionally, the mass of the alumina raw material in the alumina slurry is 18% to 30% of the mass of the alumina slurry.
[0013] Optionally, the end point pH of the carbonation is 6 to 7.
[0014] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art: The method for preparing alpha-alumina by low-temperature induction method provided by the embodiment of the application sequentially completes four steps of operation of activation treatment, raw material pretreatment, mixing and calcination, and the overall process aims to reduce the phase transition temperature and inhibit agglomeration. The activation treatment step removes impurities on the surface of alpha-alumina nanoparticles and activates the alpha-alumina nanoparticles, so as to obtain activated alpha-alumina nanocrystals with high activity. The raw material pretreatment step simultaneously purifies the alumina raw material from sodium, so as to obtain high-purity pretreated alumina raw material. Subsequently, the mixing process mixes the activated alpha-alumina nanocrystals and the pretreated alumina raw material in a mass ratio of 1:100 or more, so as to ensure that the high-activity crystal seeds are uniformly dispersed in the pretreated alumina raw material. In the subsequent calcination process, the high-activity activated alpha-alumina nanocrystals can be uniformly distributed in the high-purity pretreated alumina raw material, effectively avoiding the agglomeration of alpha-alumina particles, so as to improve the dispersibility and performance of the alpha-alumina product. In addition, the high-activity activated alpha-alumina nanocrystals can also provide a large number of nucleation sites, which can induce the high-purity pretreated alumina raw material to generate alpha-phase crystals in a directional manner, reduce the generation of impurities, and improve the integrity of the crystal structure of the alpha-alumina product, thereby improving the purity of the alpha-alumina product. BRIEF DESCRIPTION OF DRAWINGS
[0015] The drawings incorporated into the specification and forming a part of the specification, show embodiments consistent with the application, and together with the specification serve to explain the principles of the application.
[0016] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative labor.
[0017] Figure 1 A process flow diagram of a method for preparing alpha-alumina by low-temperature induction method provided by the embodiment of the application; Figure 2 A detailed process flow diagram of a method for preparing alpha-alumina by low-temperature induction method provided by the embodiment of the application. DETAILED DESCRIPTION
[0018] In order to make the objects, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without any creative labor are within the scope of protection of the application.
[0019] The range descriptions, such as numerical range, ratio range, etc. described in the present application include all possible sub-ranges and single values within the range, for example, the range description of "1 to 6" or "1~6" covers all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single values (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "comprise", etc. used herein mean "including but not limited to"; the relationship terms "first", "second", etc. are only used to distinguish different entities or operations, and do not imply actual sequence or relationship; "and / or" means that multiple cases can exist independently or simultaneously; "at least one", "multiple", "at least one", etc. refer to any combination of the corresponding objects, including single or multiple combinations of objects. The proportional relationship involved herein, such as mass ratio, molar ratio, etc. should be understood as the corresponding relationship between the front and the back in the proportional form according to the description order. The raw materials, reagents, instruments and equipment used herein can be purchased or prepared by existing methods.
[0020] Figure 1 An exemplary flowchart of a method for preparing alpha-alumina by low-temperature induction method is shown; As Figure 1 shown, the method for preparing alpha-alumina by low-temperature induction method provided by the embodiments of the present application comprises: S1. Activating alpha-alumina nanoparticles to obtain activated alpha-alumina nanoseeds; S2. Using carbon dioxide to pretreat alumina raw material to remove sodium-containing impurities in the alumina raw material, to obtain pretreated alumina raw material; S3. Mixing the activated alpha-alumina nanoseeds and the pretreated alumina raw material to obtain mixed alumina raw material; wherein the mass m1 of the activated alpha-alumina nanoseeds and the mass m2 of the pretreated alumina raw material satisfy: m1:m2≥1:100; S4. Calcining the mixed alumina raw material to obtain alpha-alumina product.
[0021] It should be noted that the alumina raw material can be an industrial alumina raw material. The industrial alumina raw material generally contains sodium-containing impurities. The mass content of the sodium-containing impurities can be 0.3%.
[0022] It should be noted that the activation of alpha-alumina nanoparticles is generally to soak the alpha-alumina nanoparticles in an acidic solution (such as hydrochloric acid or nitric acid, etc.) to optimize the morphology of the alpha-alumina nanoparticles, and at the same time remove the oxide impurities wrapped on the surface of the alpha-alumina nanoparticles, to realize the synchronous improvement of the activity and dispersibility of the alpha-alumina nanoseeds.
[0023] It should be noted that the pretreatment of alumina raw materials generally involves using carbon dioxide to convert sodium impurities in the alumina raw materials into soluble sodium salts. These sodium salts are then further processed... It should be noted that the method for preparing α-alumina via low-temperature induction provided in this application embodiment first eliminates the interference of impurities on performance through two core operations: directional impurity removal and seed crystal induction. Then, by controlling the crystal structure through seed crystals, the purity and performance of α-alumina are simultaneously improved. The specific mechanism is as follows: 1. Improve purity: Targeted removal of sodium-containing impurities Pre-treating alumina raw materials with carbon dioxide improves the purity of subsequent α-alumina production. The specific effects are as follows: (1) Targeted impurity removal: Sodium impurities (such as Na2O) in alumina raw materials will react with carbon dioxide to generate sodium salts (such as Na2CO3). These sodium salts can be removed by subsequent processes (such as washing and filtration), directly reducing the sodium content in the pretreated alumina raw materials.
[0024] (2) Avoid the influence of residual impurities: If sodium impurities in alumina raw materials are not removed, these sodium impurities will form low-melting-point phases during calcination. These low-melting-point phases will not only reduce the purity of α-alumina products, but also destroy the integrity of α-alumina crystals. Therefore, pretreatment of alumina raw materials can solve the purity problem of α-alumina products from the source.
[0025] 2. Performance Enhancement: Seed Induction and Low-Temperature Control The performance improvement of α-alumina depends on the combination of activated α-alumina nanocrystals and low-temperature calcination, and is mainly achieved through the optimized crystal structure of α-alumina: (1) Seed-induced regular growth: The activated α-alumina nanocrystals serve as growth templates, which can guide the pretreated alumina raw materials to grow α-phase crystals in a directional manner, reduce the generation of amorphous or other impurity phases (such as γ-alumina), and improve the integrity of the crystal structure of α-alumina products.
[0026] (2) Controlling the particle dispersibility of α-alumina: The mass ratio of activated α-alumina nanocrystals to pretreated alumina raw materials is ≥1:100, which can ensure that the activated α-alumina nanocrystals are evenly distributed in the pretreated alumina raw materials and avoid particle agglomeration of α-alumina during calcination. At the same time, low-temperature calcination (compared to the traditional high-temperature calcination method of rotary kiln) can further reduce the degree of particle sintering and expansion of α-alumina products, ensuring that α-alumina products have good dispersibility. The improvement of the dispersibility of α-alumina products is directly related to the mechanical, optical and other properties of α-alumina products.
[0027] 3. Synchronization Mechanism: Coordinated Optimization of Purity and Performance Increased purity provides the foundation for performance optimization of α-alumina products, creating a positive cycle: (1) The removal of sodium impurities eliminates the interference of sodium impurities on the induced growth of activated α-alumina nanocrystals, allowing α-phase crystals to form more regularly, thereby indirectly improving the performance of α-alumina products.
[0028] (2) The seed crystals induce the formation of a regular α-alumina crystal structure. The regular α-alumina crystal structure itself reduces the space for impurities to be wrapped or adsorbed, further consolidating the purity advantage of α-alumina products, and ultimately achieving the simultaneous improvement of the performance and purity of α-alumina products.
[0029] In some optional embodiments, the mass m1 of the activated α-alumina nanocrystals and the mass m2 of the pretreated alumina raw material satisfy the following: m1:m2 = (1 to 5):100.
[0030] In these embodiments, activated α-alumina nanocrystals with a mass ratio of (1 to 5):100 to the pretreated alumina raw material can be uniformly distributed in the pretreated alumina raw material, avoiding particle agglomeration of α-alumina during calcination and optimizing the performance of the α-alumina product; in addition, during calcination, these activated α-alumina nanocrystals can induce the pretreated alumina raw material to form α-phase crystals in a directional manner, reducing the generation of impurity phases and improving the purity of the α-alumina product.
[0031] The mass m1 of the activated α-alumina nanocrystal seed can be 1, 2, 3, 4 or 5.
[0032] In some alternative embodiments, the α-alumina nanoparticles have a particle size of 25 nm to 35 nm.
[0033] In these embodiments, α-alumina nanoparticles with a particle size of 25 nm to 35 nm have a large specific surface area. After activation, they can form uniformly dispersed activated α-alumina nanocrystals with a small particle size. These activated α-alumina nanocrystals can not only avoid agglomeration during calcination and optimize the performance of α-alumina products, but also induce the pretreated alumina raw materials to form α-phase crystals in a directional manner, reduce the generation of impurity phases, and improve the purity of α-alumina products.
[0034] The particle size of the α-alumina nanoparticles can be 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 31nm, 32nm, 33nm, 34nm or 35nm.
[0035] In some optional embodiments, the calcination includes a heating section and a holding section, wherein the final temperature of the heating section is 1000°C to 1200°C and the holding period is 2 hours to 4 hours.
[0036] In these embodiments, compared to the traditional rotary kiln high-temperature calcination method, the heating section with an end temperature of 1000°C to 1200°C allows the holding section to be carried out at a lower temperature, which can reduce the phase transformation temperature during the calcination process, decrease the degree of sintering and growth of α-alumina product particles, ensure good dispersibility of α-alumina product, and optimize the performance of α-alumina product. In addition, the holding section with a duration of 2h to 4h can promote a full reaction between activated α-alumina nanocrystals and pretreated alumina raw materials. By activating α-alumina nanocrystals, the pretreated alumina raw materials are oriented to form α-phase crystals, reducing the formation of impurity phases and improving the purity of α-alumina product.
[0037] In some alternative embodiments, the heating rate of the heating section is 3°C / min to 5°C / min.
[0038] In these embodiments, a heating rate of 3°C / min to 5°C / min can achieve uniform heating, prevent the agglomeration of activated α-alumina nanocrystals, ensure good dispersibility of the α-alumina product, and optimize the performance of the α-alumina product.
[0039] The heating rate of this heating section can be 3℃ / min, 3.5℃ / min, 4.0℃ / min, 4.5℃ / min or 5.0℃ / min.
[0040] Figure 2 An exemplary schematic diagram illustrates a detailed process flow diagram of a method for preparing α-alumina by low-temperature induction according to an embodiment of this application. In some alternative implementations, such as Figure 2 As shown, α-alumina nanoparticles are activated to obtain activated α-alumina nanocrystals, including the following steps: S101. Immerse α-alumina nanoparticles in hydrochloric acid solution to obtain a primary activated mixture; S102. Centrifuge the primary activation mixture to obtain primary activation seed crystals; S103. The primary activated seed crystals are vacuum dried to obtain activated α-alumina nanocrystals.
[0041] In these embodiments, hydrochloric acid solution is first used to remove surface impurities and oxides from α-alumina nanoparticles, which can optimize the morphology of α-alumina nanoparticles. Then, centrifugation can separate the primary activated seed crystals and hydrochloric acid solution. Finally, vacuum drying can separate the liquid phase attached to the surface of the primary activated seed crystals, resulting in pure and uniformly dispersed activated α-alumina nanoparticles.
[0042] It should be noted that the mass fraction of this hydrochloric acid solution can be 15%.
[0043] It should be noted that the primary activated seed crystals obtained after centrifugation can be repeatedly rinsed with deionized water until the pH value of the rinsing solution reaches 7, thereby obtaining pure primary activated seed crystals.
[0044] In some optional embodiments, the soaking treatment is performed at a temperature of 40°C to 60°C for a duration of 2 hours to 4 hours; and / or The vacuum drying temperature is ≥80℃, and the vacuum drying time is ≥8h.
[0045] In these embodiments, immersion treatment at a temperature of 40°C to 60°C for 2 to 4 hours allows the α-alumina nanoparticles to react fully with the hydrochloric acid solution, promoting the formation of soluble salts from impurities and oxides on the surface of the α-alumina nanoparticles. These soluble salts can enter the liquid phase, purifying the α-alumina nanoparticles and obtaining a primary activated mixture. Furthermore, vacuum drying at a temperature ≥80°C for ≥8 hours separates the residual liquid phase from the primary activated seed crystals, yielding pure and uniformly dispersed activated α-alumina nanoparticles.
[0046] The soaking temperature can be 40℃, 45℃, 50℃, 55℃ or 60℃.
[0047] The soaking time can be 2.0h, 2.5h, 3.0h, 3.5h or 4.0h.
[0048] In some optional embodiments, the alumina raw material is pretreated with carbon dioxide to remove sodium-containing impurities, resulting in pretreated alumina raw material, including the following steps: S201. Alumina raw materials are mixed with deionized water to obtain alumina slurry; S202. Carbonate the alumina slurry using carbon dioxide to obtain a carbonated slurry; S203. The carbonated slurry is filtered and dried sequentially to obtain pretreated alumina raw material.
[0049] In these embodiments, deionized water is first used to form an alumina slurry from the alumina raw material. This facilitates the mixing of carbon dioxide and the alumina slurry during the subsequent carbonation process. Through carbonation, sodium-containing impurities in the alumina slurry are oxidized to form soluble sodium salts, thus separating sodium oxide from the alumina raw material. Subsequently, through filtration and drying, a pretreated alumina raw material with low sodium content can be obtained, which helps to reduce the impurity content in the α-alumina product and improve the purity of the α-alumina product.
[0050] In some alternative embodiments, the mass of the alumina raw material in the alumina slurry is 18% to 30% of the mass of the alumina slurry.
[0051] In these embodiments, the alumina raw material being 18% to 30% of the mass of the alumina slurry is beneficial for the subsequent carbonation process, in order to remove most of the sodium-containing oxide impurities from the alumina raw material.
[0052] The mass of the alumina raw material in the alumina slurry can be 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 times the mass of the alumina slurry.
[0053] In some alternative embodiments, the endpoint pH of the carbonation is 6 to 7.
[0054] In these embodiments, carbonation with an endpoint pH of 6 to 7 can fully remove sodium-containing oxidized impurities from the alumina slurry, thereby obtaining pretreated alumina raw materials with low sodium content, which is beneficial for reducing the impurity content in α-alumina products and improving the purity of α-alumina products.
[0055] The final pH of the carbonation can be 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7.0.
[0056] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.
[0057] Example 1 like Figure 2 As shown, a method for preparing α-alumina by low-temperature induction includes: S101. Immerse 50g of α-alumina nanoparticles in a 15% hydrochloric acid solution to obtain a primary activated mixture; S102. Centrifuge the primary activation mixture at 4000 r / min for 10 min to obtain primary activation seed crystals; then wash the primary activation seed crystals 5 times with deionized water to obtain purified primary activation seed crystals; S103. The purified primary activated seed crystals are vacuum dried to obtain activated α-alumina nanocrystals; S201. Mix 200g of alumina raw material with 800g of deionized water to obtain alumina slurry; S202. Carbonate the alumina slurry to pH 7 using carbon dioxide to obtain a carbonated slurry; S203. The carbonated slurry is filtered and dried sequentially to obtain pretreated alumina raw material; S3. Mix 4g of activated α-alumina nanocrystals and 200g of pretreated alumina raw material to obtain mixed alumina raw material; wherein the mass m1 of the activated α-alumina nanocrystals and the mass m2 of the pretreated alumina raw material satisfy: m1:m2≥1:100; S4. Calcine the mixed alumina raw materials to obtain α-alumina product.
[0058] The mass m1 of the activated α-alumina nanocrystal seeds and the mass m2 of the pretreated alumina raw material satisfy the following condition: m1:m2=4g:200g.
[0059] The particle size of the α-alumina nanoparticles is 30 nm.
[0060] The calcination process includes a heating section and a holding section. The final temperature of the heating section is 1100℃, and the holding time is 3 hours.
[0061] The heating rate in the heating section is 4℃ / min.
[0062] The soaking temperature was 50℃, and the soaking time was 3 hours. The vacuum drying temperature is 80℃, and the vacuum drying time is 8 hours.
[0063] The mass of alumina raw material in the alumina slurry is 20% of the mass of the alumina slurry.
[0064] The final pH of carbonation is 7.
[0065] Example 2 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The primary activated seed crystals were rinsed 6 times with deionized water to obtain purified primary activated seed crystals.
[0066] S201. Mix 250g of alumina raw material with 750g of deionized water to obtain alumina slurry.
[0067] The mass m1 of the activated α-alumina nanocrystals and the mass m2 of the pretreated alumina raw material satisfy the following condition: m1:m2=6g:250g.
[0068] The final temperature of the heating stage is 1050℃, and the holding time is 3.5h.
[0069] The heating rate in the heating section is 3.5℃ / min.
[0070] The soaking temperature was 45℃, and the soaking time was 3.5 hours. The vacuum drying temperature is 80℃, and the vacuum drying time is 9 hours.
[0071] The mass of alumina raw material in the alumina slurry is 25% of the mass of the alumina slurry.
[0072] The final pH of carbonation is 6.
[0073] Example 3 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The primary activated seed crystals were rinsed 6 times with deionized water to obtain purified primary activated seed crystals.
[0074] S201. Mix 180g of alumina raw material with 820g of deionized water to obtain alumina slurry.
[0075] The mass m1 of the activated α-alumina nanocrystal seeds and the mass m2 of the pretreated alumina raw material satisfy the following condition: m1:m2=8g:182g.
[0076] The final temperature of the heating stage is 1200℃, and the holding time is 2.5h.
[0077] The heating rate in the heating section is 4.5℃ / min.
[0078] The soaking temperature was 55℃, and the soaking time was 2.5 hours. The vacuum drying temperature is 80℃, and the vacuum drying time is 10 hours.
[0079] The mass of alumina raw materials in alumina slurry is 18% to 30% of the mass of alumina slurry.
[0080] The final pH of carbonation is 6.5.
[0081] Comparative Example 1 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: α-alumina nanoparticles are added directly without any activation treatment.
[0082] Comparative Example 2 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: The mass m1 of the activated α-alumina nanocrystal seeds and the mass m2 of the pretreated alumina raw material satisfy the following: m1:m2=8:100.
[0083] Comparative Example 3 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: The final temperature of the heating phase is 900℃.
[0084] Comparative Example 4 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: The final temperature of the heating phase is 1400℃.
[0085] Relevant experimental and effect data: The α-alumina products of each embodiment and comparative example were collected, and the purity, sodium oxide content, α-phase conversion rate, average particle size and specific surface area of the α-alumina products were statistically analyzed. The results are shown in Table 1.
[0086] Table 1. Performance parameters of α-alumina products for each embodiment and comparative example.
[0087] As shown in Table 1, the method for preparing α-alumina using a low-temperature induction method provided in this application involves two core operations: directional impurity removal and seed crystal induction. First, it eliminates the interference of impurities on performance. Then, it controls the crystal structure through seed crystals, achieving a simultaneous improvement in the purity and performance of α-alumina. Ultimately, it yields α-alumina with a purity of over 99.90%, an average particle size below 350 nm, and a specific surface area of over 35 m². 2 α-alumina products with a yield of / g or more.
[0088] Compared to Example 1, Comparative Example 1 did not perform activation treatment on the α-alumina nanoparticles. This resulted in insufficient surface nucleation sites for the α-alumina nanoparticles, hindering the α-phase transformation of the pretreated alumina raw material. Consequently, the α-alumina product particles agglomerated, leading to an increase in average particle size and a decrease in specific surface area. Furthermore, it introduced impurities into the α-alumina product, affecting its purity. In contrast, Comparative Example 2 used excessive activated α-alumina nanocrystals. While this could promote the α-phase transformation rate of the pretreated alumina raw material, excessive activated α-alumina nanocrystals were prone to over-agglomeration. The agglomerated activated α-alumina nanocrystals contained small amounts of impurities, affecting the purity of the α-alumina product.
[0089] Compared to Example 1, Comparative Example 3 used a lower final temperature in the heating stage, which resulted in insufficient driving force for the α-phase transformation of the pretreated alumina raw material during the calcination stage. This led to an increase in impurities in the α-alumina product, affecting its purity. Furthermore, the lower heating stage resulted in insufficient induction of the activated α-alumina nanocrystals, causing incomplete growth and easy agglomeration of the α-alumina particles, leading to a slight increase in the specific surface area of the α-alumina product. Comparative Example 4 used a higher final temperature in the heating stage, which resulted in severe sintering of the α-alumina particles, significantly increasing the average particle size and reducing the specific surface area of the α-alumina product. Additionally, the higher final temperature in the heating stage promoted sufficient α-phase transformation of the pretreated alumina raw material, and high-temperature sintering reduced the residue of impurities; however, the overall energy consumption was higher.
[0090] In summary, the method for preparing α-alumina via a low-temperature induction method provided in this application first eliminates the interference of impurities on performance, and then controls the crystal structure through seed crystals, achieving a simultaneous improvement in the purity and performance of α-alumina. Ultimately, it yields a purity of over 99.90%, an average particle size below 350 nm, and a specific surface area of over 35 m². 2 α-alumina products with a yield of / g or more.
[0091] In addition, this application provides a method for preparing α-alumina by low-temperature induction. This method first activates α-alumina nanoparticles with a specific particle size range to obtain activated α-alumina nanocrystals. These activated α-alumina nanocrystals can provide a large number of nucleation sites for the formation of α-alumina products. These nucleation sites can reduce the phase transformation temperature of α-alumina. Compared with the traditional rotary kiln high-temperature calcination method, the phase transformation temperature of the pretreated alumina raw material is reduced by 200°C to 400°C, which effectively reduces the energy consumption and equipment burden of the calcination process.
[0092] In addition, this application provides a method for preparing α-alumina by low-temperature induction. This method removes impurities and oxides from the surface of α-alumina nanoparticles using hydrochloric acid solution, and removes sodium-containing impurities from the alumina raw material by carbonation of carbon dioxide. The entire method does not introduce other impurities that may affect the purity of the α-alumina product, and finally obtains an α-alumina product with a purity of over 99.90%, which can meet the high purity requirements of the high-end electronic equipment field for α-alumina products.
[0093] Furthermore, this application provides a method for preparing α-alumina via a low-temperature induction method. The α-alumina product obtained by this method has a uniform and fine average particle size distribution, good dispersibility, and significantly reduces agglomeration. Additionally, the average particle size of the α-alumina product can be between 200 nm and 400 nm, resulting in a specific surface area of up to 30 m². 2 / g to 52m 2 It has a high specific surface area between / g and . In addition, this α-alumina product has high sintering activity, which makes it more suitable for applications in high-end refractories, advanced ceramics, electronic materials and other fields.
[0094] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.
Claims
1. A method for preparing α-alumina by low-temperature induction, characterized in that, The method includes: α-alumina nanoparticles were activated to obtain activated α-alumina nanocrystals; The alumina raw material is pretreated with carbon dioxide to remove sodium impurities, resulting in pretreated alumina raw material. The activated α-alumina nanocrystals and the pretreated alumina raw material are mixed to obtain a mixed alumina raw material; wherein, the mass m1 of the activated α-alumina nanocrystals and the mass m2 of the pretreated alumina raw material satisfy: m1:m2≥1:100; The mixed alumina raw materials are calcined to obtain α-alumina products.
2. The method according to claim 1, characterized in that, The mass m1 of the activated α-alumina nanocrystals and the mass m2 of the pretreated alumina raw material satisfy the following: m1:m2 = (1 to 5):
100.
3. The method according to claim 1, characterized in that, The α-alumina nanoparticles have a particle size of 25 nm to 35 nm.
4. The method according to claim 1, characterized in that, The calcination includes a heating section and a holding section. The final temperature of the heating section is 1000℃ to 1200℃, and the holding time is 2h to 4h.
5. The method according to claim 4, characterized in that, The heating rate of the heating section is 3℃ / min to 5℃ / min.
6. The method according to claim 1, characterized in that, Activation treatment of α-alumina nanoparticles to obtain activated α-alumina nanocrystals includes the following steps: The α-alumina nanoparticles were soaked in hydrochloric acid solution to obtain a primary activated mixture; The primary activation mixture was centrifuged to obtain primary activation seed crystals; The primary activated seed crystals were vacuum dried to obtain activated α-alumina nanocrystals.
7. The method according to claim 5, characterized in that, The soaking temperature is 40°C to 60°C, and the soaking time is 2 hours to 4 hours; and / or The vacuum drying temperature is ≥80℃, and the vacuum drying time is ≥8h.
8. The method according to claim 1, characterized in that, Pretreatment of alumina raw materials with carbon dioxide to remove sodium impurities and obtain pretreated alumina raw materials includes the following steps: Alumina raw materials are mixed with deionized water to obtain alumina slurry; Carbonic acidification of the alumina slurry is performed using carbon dioxide to obtain a carbonated slurry; The carbonated slurry is filtered and dried sequentially to obtain pretreated alumina raw material.
9. The method according to claim 8, characterized in that, The mass of alumina raw material in the alumina slurry is 18% to 30% of the mass of the alumina slurry.
10. The method according to claim 8, characterized in that, The final pH of the carbonation is 6 to 7.