Method for preparing low specific surface ultrafine alumina powder

Abstract

The application discloses a preparation method of low specific surface area superfine alumina powder, which comprises the following steps: acid pickling and impurity removing: industrial gamma alumina is added into an acid pickling solution, and is pressed, filtered, dried to obtain low-sodium alumina; wet grinding: the low-sodium alumina is configured into slurry, is firstly put into a stirring mill for coarse grinding treatment, and then is put into a sand mill for sand grinding treatment to obtain superfine alumina slurry; spray drying: the superfine alumina slurry is subjected to spray drying in a spray drying tower to obtain superfine alumina granulation powder; calcination and phase conversion: the superfine alumina granulation powder is put into a sagger, is transferred into a calcining furnace for calcination to obtain superfine alumina granulation calcined powder; scattering and depolymerization: the superfine alumina granulation calcined powder is subjected to airflow scattering to obtain low specific surface area superfine alumina powder. The method has low cost, simple and easy-to-control process, and the prepared superfine alumina powder has better primary crystal appearance integrity and powder dispersibility.

Description

Technical Field

[0001] This invention relates to alumina powder, and more particularly to a method for preparing low specific surface area ultrafine alumina powder. Background Technology

[0002] Low specific surface area ultrafine alumina powder is widely used in lithium battery separator coating, grinding and polishing, fine ceramics, and thermally conductive fillers due to its numerous excellent properties, including high purity, fine primary crystals, narrow distribution, good dispersibility, low oil absorption value, high strength, high hardness, and easy sintering. Currently, commercially available ultrafine alumina powder is typically obtained by wet grinding, drying, and dispersing small primary crystal calcined alumina powder. This type of ultrafine alumina powder generally suffers from high specific surface area, easy agglomeration, and low purity. To achieve small particle size, narrow distribution, and no large particles in the powder, it is necessary to completely deagglomerate the primary crystals of the small primary crystal calcined alumina through wet grinding. Although wet grinding can achieve ultrafine and narrow-distribution characteristics of alumina powder, the wet grinding process also damages the surface morphology of the original crystals, increases the interface and surface defects of the crystals, and generates a large amount of fine powder. This results in a sharp increase in the specific surface area of ​​the ultrafine alumina powder and severe agglomeration. It is difficult to achieve both ultrafineness and low specific surface area of ​​alumina powder, which increases the difficulty of downstream industry applications and may even make it unusable, greatly limiting the development of downstream fields.

[0003] There are numerous existing methods for preparing ultrafine alumina powder, mainly including aluminum alkoxide hydrolysis, ammonium aluminum carbonate pyrolysis, ammonium aluminum sulfate pyrolysis, and high-temperature calcination followed by sand milling of industrial aluminum hydroxide or industrial alumina. Among these, aluminum alkoxide hydrolysis and aluminum salt pyrolysis methods generally suffer from limitations such as high raw material prices or stringent performance requirements, cumbersome and difficult-to-control processes, unstable product performance, and environmental unfriendliness. Currently, the most widely used method is the preparation of ultrafine alumina powder by ordinary calcination, sand milling, drying, and crushing. However, the ultrafine alumina powder prepared by this method has issues such as low purity, high sodium content, uneven grain morphology and size, high specific surface area, and difficulty in dispersion, and it is impossible to achieve a balance between various properties.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing low specific surface area ultrafine alumina powder, which is low in cost, simple and easy to control in process, and produces ultrafine alumina powder with complete original crystal morphology and better powder dispersibility.

[0006] To achieve the above objectives, embodiments of the present invention provide a method for preparing low specific surface area ultrafine alumina powder, comprising the following steps: acid washing and impurity removal: adding industrial γ-alumina to an acid washing solution and filtration and drying to obtain low-sodium alumina; wet grinding: preparing the low-sodium alumina into a slurry, first placing it in a stirred mill for coarse grinding, and then placing it in a sand mill for sand grinding to obtain ultrafine alumina slurry; spray drying: spray drying the ultrafine alumina slurry in a spray drying tower to obtain ultrafine alumina granulated powder; calcination and phase inversion: placing the ultrafine alumina granulated powder into a crucible and transferring it to a calcination furnace for calcination to obtain ultrafine alumina granulated calcined powder; dispersing and deagglomeration: dispersing the ultrafine alumina granulated calcined powder with airflow to obtain low specific surface area ultrafine alumina powder.

[0007] In one or more embodiments of the present invention, the industrial γ-alumina contains Al2O3 by mass percentage greater than or equal to 99.0% and Na2O by mass percentage less than or equal to 0.5%.

[0008] In one or more embodiments of the present invention, the pickling solution is selected from one or more of acetic acid, oxalic acid, and citric acid.

[0009] In one or more embodiments of the present invention, the coarse grinding process takes between 2 hours and 10 hours; and / or the diameter of the grinding media in the coarse grinding process is between 3.0 mm and 8.0 mm.

[0010] In one or more embodiments of the present invention, the sand milling time is between 2h and 8h; and / or, the diameter of the abrasive media in the sand milling process is between 0.2mm and 0.6mm.

[0011] In one or more embodiments of the present invention, the grinding media for the coarse grinding and sand grinding processes are selected from one or more of zirconia ceramics, alumina ceramics, and zirconium-aluminum composite ceramics.

[0012] In one or more embodiments of the present invention, the solid content of the coarsely ground alumina slurry is between 35% and 65%; and / or, the solid content of the sand-milled alumina slurry is between 20% and 45%.

[0013] In one or more embodiments of the present invention, the temperature at the inlet of the spray drying tower is between 180°C and 255°C; and / or, the rotational speed of the spray drying tower is between 8000 r / min and 18000 r / min; and / or, the temperature at the outlet of the spray drying tower is between 105°C and 135°C.

[0014] In one or more embodiments of the present invention, the calcination temperature is between 1100°C and 1400°C; and / or the calcination time is between 1 h and 10 h.

[0015] In one or more embodiments of the present invention, the device for dispersing the airflow is selected from one of an air jet mill and a steam mill; and / or, the airflow pressure for dispersing the airflow is between 0.2 MPa and 0.8 MPa.

[0016] Compared with existing technologies, the method for preparing low specific surface area ultrafine alumina powder according to embodiments of the present invention employs a series of steps: first, acid washing and impurity removal of raw materials, followed by wet grinding and drying; then, calcination and phase inversion; and finally, airflow agitation and deagglomeration. This effectively avoids the adverse effects of the traditional process of calcination followed by wet grinding and deagglomeration on the original crystal morphology, particle size, distribution, and dispersion performance of the finished ultrafine alumina powder. Furthermore, this method utilizes widely available and inexpensive raw materials, has a simple and easily controllable process, does not require any calcination aids, is environmentally friendly, facilitates large-scale industrial production, and exhibits excellent performance with a wide range of applications. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a method for preparing low specific surface area ultrafine alumina powder according to an embodiment of the present invention.

[0018] Figure 2 This is a particle size distribution diagram of ultrafine alumina powder according to Example 1 of an embodiment of the present invention;

[0019] Figure 3 This is a SEM image of ultrafine alumina powder according to Example 1 of an embodiment of the present invention;

[0020] Figure 4 This is a SEM image of ultrafine alumina powder according to Example 2 of an embodiment of the present invention;

[0021] Figure 5 This is a SEM image of ultrafine alumina powder of Example 3 according to an embodiment of the present invention;

[0022] Figure 6 This is a particle size distribution diagram of ultrafine alumina powder according to Example 4 of an embodiment of the present invention;

[0023] Figure 7 This is a SEM image of ultrafine alumina powder of Example 4 according to an embodiment of the present invention;

[0024] Figure 8 This is a particle size distribution diagram of ultrafine alumina powder according to Comparative Example 1 of an embodiment of the present invention.

[0025] Figure 9This is a SEM image of ultrafine alumina powder according to a comparative example 1 of an embodiment of the present invention.

[0026] Figure 10 This is a particle size distribution diagram of ultrafine alumina powder according to Comparative Example 2 of an embodiment of the present invention.

[0027] Figure 11 This is a SEM image of ultrafine alumina powder according to Comparative Example 2 of an embodiment of the present invention. Detailed Implementation

[0028] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0029] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0030] Ultrafine alumina powder is usually obtained by calcining hydrated alumina or industrial γ-alumina to form calcined alumina, followed by wet grinding, drying and crushing. However, the performance of ultrafine alumina powder depends on its particle size, particle size distribution, dispersibility, specific surface area and other powder indicators. These powder indicators are closely related to the original grain size of the calcined alumina raw material and the processing technology.

[0031] The finer and more uniform the original grains of calcined alumina, the smaller the particle size and narrower the distribution of the alumina powder after complete deagglomeration. The higher the sphericity and the smaller the adhesion of the original grains, the smaller the specific surface area of ​​the alumina powder after complete deagglomeration. Because the original grains of calcined alumina powder adhere less to each other, they are more easily deagglomerated into ultrafine alumina powder with the original grain size. This deagglomeration process does not easily damage the original grains, resulting in fewer new interfaces, fewer defects, and lower powder surface energy. Therefore, the obtained ultrafine alumina powder has a smaller specific surface area and is less prone to agglomeration.

[0032] like Figures 1 to 11 As shown, a method for preparing low specific surface area ultrafine alumina powder according to a preferred embodiment of the present invention includes the following steps S1-S5.

[0033] Step S1: Acid washing to remove impurities: Add industrial γ-alumina to the acid washing solution, and then filter and dry to obtain low-sodium alumina.

[0034] Specifically, in step S1, acid washing for impurity removal includes: adding industrial γ-alumina to an acid washing solution for washing, followed by pressure filtration and drying to obtain low-sodium alumina. In this step, the mass percentage of Al2O3 in the industrial γ-alumina is greater than or equal to 99.0%, and the mass percentage of Na2O is less than or equal to 0.5%. The acid washing solution is selected from one or more combinations of acetic acid, oxalic acid, and citric acid. Choosing an acid washing solution prepared with a medium-strength organic acid can remove soluble impurity ions from the industrial γ-alumina as much as possible, especially alkali metal ions such as sodium, and can also oxidize and decompose them during the subsequent calcination phase inversion process, avoiding the introduction of new impurities during the acid washing process. At the same time, acid washing for impurity removal can improve the purity of ultrafine alumina on the one hand, and avoid abnormal growth of alumina primary crystals and excessive adhesion of primary grains during calcination phase inversion process on the other hand.

[0035] Step S2: Wet grinding: Prepare low-sodium alumina into a slurry, first put it into a stirred mill for coarse grinding, and then put it into a sand mill for sand grinding to obtain ultrafine alumina slurry.

[0036] Specifically, in step S2, wet grinding includes: preparing the low-sodium alumina obtained in step S1 into an alumina slurry with a solid content between 35% and 65%, and then grinding it in a stirred mill for 2-10 hours for coarse grinding. The coarsely ground slurry is then prepared into an alumina slurry with a solid content between 20% and 45%, and then ground in a sand mill for 2-8 hours for sand milling to obtain an ultrafine alumina slurry.

[0037] The grinding media used in both coarse grinding and sand grinding are selected from one or more of zirconia ceramics, alumina ceramics, and zirconium-aluminum composite ceramics. Furthermore, the diameter of the grinding media used in coarse grinding is between 3.0 mm and 8.0 mm, while the diameter of the grinding media used in sand grinding is between 0.2 mm and 0.6 mm. The selection of grinding media diameters for coarse grinding and sand grinding improves grinding efficiency, optimizes the particle size distribution of the alumina slurry calcination precursor, and ensures that the introduction of zirconium-aluminum grinding media loss does not adversely affect the morphology and purity of the alumina primary crystals during subsequent calcination, while also meeting the requirements of downstream applications for ultrafine alumina impurities.

[0038] Step S3: Spray drying: The ultrafine alumina slurry is spray dried in a spray drying tower to obtain ultrafine alumina granulated powder.

[0039] Specifically, in step S3, spraying includes: placing the ultrafine alumina slurry obtained in step S2 into a spray drying tower with an inlet temperature between 180℃ and 255℃, an outlet temperature between 105℃ and 135℃, and a rotation speed between 8000 r / min and 18000 r / min for spray drying.

[0040] The selection of inlet temperature, spray drying tower speed and outlet temperature is to ensure the formation of loose and porous ultrafine alumina spherical granules during the spray drying process, while avoiding excessive moisture content in the granules and agglomeration, which helps to form loose and non-sticky granulated calcined powder during the later calcination phase inversion.

[0041] Step S4: Calcination and phase transformation: The ultrafine alumina granulated powder is placed in a sagger and transferred to a calcining furnace for calcination to obtain ultrafine alumina granulated calcined powder.

[0042] Specifically, in step S4, the calcination phase transformation includes: placing the ultrafine alumina granulated powder into a sagger and transferring it to a calcination furnace for calcination at 1100℃-1400℃ for 1-10 hours, thereby obtaining ultrafine alumina granulated calcined powder. The selection of calcination temperature and time helps the atomic structure of the ultrafine alumina granulated powder (γ-phase structure) rearrange during calcination to form α-phase alumina, improves the α-phase conversion rate, and avoids excessive crystal growth that could lead to abnormal growth of the original grains and excessive interface adhesion.

[0043] Step S5: Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by airflow to obtain ultrafine alumina powder with low specific surface area.

[0044] Specifically, in step S5, the dispersing and deagglomeration includes: dispersing the ultrafine alumina granulated calcined powder using an air jet mill or a steam mill to obtain ultrafine alumina powder with a low specific surface area. The air jet pressure for dispersing is between 0.2 MPa and 0.8 MPa. This air jet pressure range effectively disperses the original alumina powder grains that have agglomerated after calcination and phase inversion, while avoiding excessive air jet pressure that could cause grain breakage or surface defects. This effectively improves the particle size distribution of the ultrafine alumina powder and reduces its specific surface area.

[0045] This invention discloses a method for preparing low specific surface area ultrafine alumina powder. Before calcination, the powder is preferentially subjected to acid washing to remove impurities and wet grinding. By reducing the impurity content of the raw materials and ultrafine the particle size, the mass transfer process of grain growth is weakened during the phase transformation-nucleation-crystal growth process of the raw materials during calcination. This refines the original grains and reduces abnormal crystal growth caused by impurities and excessive adhesion of the original grains during the mass transfer process. As a result, the calcined alumina powder is easier to deagglomerate. At the same time, the grain morphology after dispersing and deagglomeration is more complete, with a lower specific surface area, a narrower particle size distribution, and better dispersion performance.

[0046] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0047] Example 1

[0048] Acid washing to remove impurities: Industrial γ-alumina is added to an acetic acid solution for washing, and then dried by pressure filtration to obtain low-sodium alumina.

[0049] Wet grinding: The obtained low-sodium alumina was prepared into a slurry with a solid content of 55%, and coarsely ground in a stirred mill for 6 hours, with 5mm zirconia ceramic as the grinding medium. The solid content of the slurry obtained from the coarse grinding was then adjusted to 35%, and it was transferred to a sand mill for 4 hours, with 0.3mm zirconia ceramic as the grinding medium. After sand milling, an ultrafine alumina slurry with a D50 of 0.3-0.4μm was obtained.

[0050] Spray drying: The ultrafine alumina slurry obtained in the above steps is subjected to spray drying treatment. The inlet temperature of the spray drying is 225℃, the rotation speed of the spray drying tower is 12000r / min, and the outlet temperature is 115℃, thereby obtaining ultrafine alumina granulated powder.

[0051] Calcination and phase transformation: The ultrafine alumina granulated powder obtained in the above steps is placed in a sagger and transferred to a calcining furnace for calcination at 1300℃ for 6 hours to obtain ultrafine alumina granulated calcined powder.

[0052] Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by air jet mill with an air pressure of 0.6 MPa to obtain ultrafine alumina powder.

[0053] Test data for the finished ultrafine alumina powder: Al2O3 content 99.93%, Na2O content 312ppm, particle size D10: 0.276μm, D50: 0.443μm, D90: 0.736μm, D99: 1.16μm, specific surface area 6.0428m². 2 / g.

[0054] The particle size distribution of the ultrafine alumina powder obtained in Example 1 is shown in the figure below. Figure 2 As shown. Figure 3 This is a SEM image of ultrafine alumina powder. From... Figure 2 and Figure 3 It can be seen that the obtained ultrafine alumina powder particles are spherical, narrowly distributed, without large particles, have good dispersibility and no agglomeration, and have a low specific surface area.

[0055] Example 2

[0056] Acid washing to remove impurities: Industrial γ-alumina is added to oxalic acid solution for washing, and then dried by pressure filtration to obtain low-sodium alumina.

[0057] Wet grinding: The obtained low-sodium alumina was prepared into a slurry with a solid content of 50%, and coarsely ground in a stirred mill for 8 hours, with 5mm zirconia ceramic as the grinding medium. The solid content of the slurry obtained from the coarse grinding was then adjusted to 30%, and transferred to a sand mill for 5 hours, with 0.3mm zirconia ceramic as the grinding medium. After sand milling, an ultrafine alumina slurry with a D50 of 0.2-0.3μm was obtained.

[0058] Spray drying: The ultrafine alumina slurry obtained in the above steps is subjected to spray drying treatment. The inlet temperature of the spray drying is 210℃, the rotation speed of the spray drying tower is 10000r / min, and the outlet temperature is 115℃, thereby obtaining ultrafine alumina granulated powder.

[0059] Calcination and phase inversion: The ultrafine alumina granulated powder obtained in the above steps is placed in a sagger and transferred to a calcining furnace for calcination at 1250℃ for 4 hours to obtain ultrafine alumina granulated calcined powder.

[0060] Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by air jet mill with an air pressure of 0.7 MPa to obtain ultrafine alumina powder.

[0061] Test data for the finished ultrafine alumina powder: Al2O3 content 99.93%, Na2O content 327ppm, particle size D10: 0.217μm, D50: 0.345μm, D90: 0.524μm, D99: 0.768μm, specific surface area 7.2302m². 2 / g.

[0062] Figure 4 This is a SEM image of the ultrafine alumina powder from Example 2. (From...) Figure 4 It can be seen that the obtained ultrafine alumina powder particles are spherical, with fine grains, no large particles, good dispersibility and no agglomeration, and low specific surface area.

[0063] Example 3

[0064] Acid washing to remove impurities: Industrial γ-alumina is washed in a mixed solution of acetic acid and oxalic acid, and then dried by pressure filtration to obtain low-sodium alumina.

[0065] Wet grinding: The obtained low-sodium alumina was prepared into a slurry with a solid content of 40%, and coarsely ground in a stirred mill for 8 hours, with 5mm zirconia ceramic as the grinding medium. The solid content of the slurry obtained from the coarse grinding was then adjusted to 25%, and transferred to a sand mill for 5 hours, with 0.3mm zirconia ceramic as the grinding medium. After sand milling, an ultrafine alumina slurry with a D50 of 0.3-0.4μm was obtained.

[0066] Spray drying: The ultrafine alumina slurry obtained in the above steps is subjected to spray drying treatment. The inlet temperature of the spray drying is 215℃, the rotation speed of the spray drying tower is 8500r / min, and the outlet temperature is 120℃, thereby obtaining ultrafine alumina granulated powder.

[0067] Calcination and phase transformation: The ultrafine alumina granulated powder obtained in the above steps is placed in a sagger and transferred to a calcining furnace for calcination at 1250℃ for 2 hours to obtain ultrafine alumina granulated calcined powder.

[0068] Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by air jet mill with an air pressure of 0.75 MPa to obtain ultrafine alumina powder.

[0069] Test data for the finished ultrafine alumina powder: Al2O3 content 99.92%, Na2O content 289ppm, particle size D10: 0.137μm, D50: 0.255μm, D90: 0.486μm, D99: 0.654μm, specific surface area 8.1217m². 2 / g.

[0070] Figure 5 This is a SEM image of the ultrafine alumina powder from Example 3. Figure 5 It can be seen that the obtained ultrafine alumina powder particles are finer, have better sphericity, no abnormal large-particle growth, and have a low specific surface area.

[0071] Example 4

[0072] Acid washing to remove impurities: Industrial γ-alumina is added to citric acid solution for washing, and then dried by pressure filtration to obtain low-sodium alumina.

[0073] Wet grinding: The obtained low-sodium alumina was prepared into a slurry with a solid content of 60%, and coarsely ground in a stirred mill for 6 hours, using 5mm zirconia ceramic as the grinding medium. The solid content of the slurry obtained from the coarse grinding was then adjusted to 40%, and transferred to a sand mill for 2 hours, using 0.3mm zirconia ceramic as the grinding medium. After sand milling, an ultrafine alumina slurry with a D50 of 0.6-0.7μm was obtained.

[0074] Spray drying: The ultrafine alumina slurry obtained in the above steps is subjected to spray drying treatment. The inlet temperature of the spray drying is 245℃, the rotation speed of the spray drying tower is 8500r / min, and the outlet temperature is 110℃, thereby obtaining ultrafine alumina granulated powder.

[0075] Calcination and phase transformation: The ultrafine alumina granulated powder obtained in the above steps is placed in a sagger and transferred to a calcining furnace for calcination at 1350℃ for 9 hours to obtain ultrafine alumina granulated calcined powder.

[0076] Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by air jet mill with an air jet pressure of 0.35 MPa to obtain ultrafine alumina powder.

[0077] Test data for the finished ultrafine alumina powder: Al2O3 content 99.94%, Na2O content 341ppm, particle size D10: 0.448μm, D50: 0.752μm, D90: 1.54μm, D99: 1.887μm, specific surface area 3.5314m². 2 / g.

[0078] The particle size distribution of the ultrafine alumina powder obtained in Example 4 is shown in the figure below. Figure 6 As shown. Figure 7 This is a SEM image of ultrafine alumina powder. From... Figure 6 and Figure 7 It can be seen that the particle size of the obtained ultrafine alumina powder can be controlled according to the changes in conditions. The sphericity of the obtained ultrafine alumina powder is still high, the grain surface is smooth, the dispersion is good and there is no obvious agglomeration, and the specific surface area is low and controllable.

[0079] Comparative Example 1

[0080] Acid washing to remove impurities: Industrial γ-alumina is added to an acetic acid solution for washing, and then dried by pressure filtration to obtain low-sodium alumina.

[0081] Calcination and phase inversion: The low-sodium alumina obtained in the above steps is placed in a sagger and transferred to a calcining furnace for calcination at 1350℃ for 9 hours to obtain large-particle-size calcined alumina powder.

[0082] Wet grinding: The obtained large-particle-size calcined alumina powder was prepared into a slurry with a solid content of 60%, and coarsely ground in a stirred mill for 6 hours, with 5mm zirconia ceramic as the grinding medium. The solid content of the slurry obtained from the coarse grinding was then adjusted to 40%, and transferred to a sand mill for 4 hours, with 0.3mm zirconia ceramic as the grinding medium. After sand milling, an ultrafine alumina slurry with a D50 of 0.9–1.0 μm was obtained.

[0083] Spray drying: The ultrafine alumina slurry obtained in the above steps is subjected to spray drying treatment. The inlet temperature of the spray drying is 245℃, the rotation speed of the spray drying tower is 8500r / min, and the outlet temperature is 110℃, thereby obtaining ultrafine alumina granulated powder.

[0084] Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by air jet mill with an air jet pressure of 0.35 MPa to obtain ultrafine alumina powder.

[0085] Test data for the finished ultrafine alumina powder: Al2O3 content 99.93%, Na2O content 367ppm, particle size D10: 0.299μm, D50: 0.985μm, D90: 2.63μm, D99: 5.69μm, specific surface area 8.5691m². 2 / g.

[0086] The particle size distribution of the ultrafine alumina powder obtained in Comparative Example 1 is shown in the figure below. Figure 8 As shown. Figure 9 This is a SEM image of ultrafine alumina powder. From... Figure 8 and Figure 9It can be seen that the obtained ultrafine alumina powder particles have irregular angular morphology and the overall grain size is relatively large. The sand milling process damages the original grains to a certain extent, producing fine powder, increasing the defects on the surface of the original grains, causing an abnormal increase in specific surface area, aggravated agglomeration, and difficulty in dispersion, while reducing grinding efficiency. In the end, the grain morphology, specific surface area, and particle size distribution of the final product are all poor.

[0087] Comparative Example 2

[0088] Acid washing to remove impurities: Industrial γ-alumina is added to an acetic acid solution for washing, and then dried by pressure filtration to obtain low-sodium alumina.

[0089] Calcination phase transformation: The low-sodium alumina obtained in the above steps is placed in a sagger and transferred to a calcining furnace for calcination at 1250℃ for 2 hours to obtain large-particle-size calcined alumina powder.

[0090] Wet grinding: The obtained large-particle-size calcined alumina powder was prepared into a slurry with a solid content of 40%, and coarsely ground in a stirred mill for 8 hours, with 5mm zirconia ceramic as the grinding medium. The solid content of the slurry obtained from the coarse grinding was then adjusted to 25%, and transferred to a sand mill for 5 hours, with 0.3mm zirconia ceramic as the grinding medium. After sand milling, an ultrafine alumina slurry with a D50 of 0.4-0.6μm was obtained.

[0091] Spray drying: The ultrafine alumina slurry obtained in the above steps is subjected to spray drying treatment. The inlet temperature of the spray drying is 215℃, the rotation speed of the spray drying tower is 8500r / min, and the outlet temperature is 120℃, thereby obtaining ultrafine alumina granulated powder.

[0092] Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by air jet mill with an air pressure of 0.75 MPa to obtain ultrafine alumina powder.

[0093] Test data for the finished ultrafine alumina powder: Al2O3 content 99.92%, Na2O content 305ppm, particle size D10: 0.158μm, D50: 0.502μm, D90: 1.91μm, D99: 5.05μm, specific surface area 12.9358m². 2 / g.

[0094] The particle size distribution of the ultrafine alumina powder obtained in Comparative Example 2 is shown in the figure below. Figure 10 As shown. Figure 11 This is a SEM image of ultrafine alumina powder. From... Figure 10 and Figure 11It can be seen that the obtained ultrafine alumina powder particles have irregular angular morphology and the overall grain size is relatively large. The sand milling process damages the original grains to a certain extent, producing fine powder, increasing the defects on the surface of the original grains, causing an abnormal increase in specific surface area, aggravated agglomeration, and difficulty in dispersion, while reducing grinding efficiency. In the end, the grain morphology, specific surface area, and particle size distribution of the final product are all poor.

[0095] The performance comparison of Examples 1-4 and Comparative Examples 1-2 is shown in Table 1 below.

[0096] Table 1 Performance comparison of Examples 1-4 and Comparative Examples 1-2

[0097] Example 1 99.93 0.276 0.443 0.736 1.16 6.0428 Example 2 99.93 0.217 0.345 0.524 0.786 7.2302 Example 3 99.92 0.137 0.255 0.486 0.654 8.1217 Example 4 99.94 0.448 0.752 1.54 1.887 3.5314 Comparative Example 1 99.93 0.299 0.985 2.63 5.69 8.5691 Comparative Example 2 99.92 0.158 0.502 1.91 5.05 12.8358

[0098] As shown in the table above, the method for preparing low specific surface area ultrafine alumina powder of the present invention can produce ultrafine alumina powder with a median diameter between 0.2-0.8 μm and controllable particle size. Furthermore, by placing the wet grinding step beforehand, this method solves the problem that conventional calcined alumina post-processing methods, which use airflow to disperse and deagglomerate the original crystals, cannot achieve submicron level particle size and must employ wet grinding. This improves the integrity of the original crystal morphology and the dispersibility of the ultrafine alumina powder, and also makes the post-processing steps more energy-efficient and effective.

[0099] In summary, the method for preparing low specific surface area ultrafine alumina powder of the present invention employs a series of steps: acid washing and impurity removal of raw materials, wet grinding and drying, calcination and phase inversion, followed by airflow dispersing and deagglomeration. This effectively avoids the adverse effects of the traditional process of calcination followed by wet grinding and deagglomeration on the original crystal morphology, particle size, distribution, and dispersion performance of the finished ultrafine alumina powder. Furthermore, this method utilizes widely available and inexpensive raw materials, has a simple and easily controllable process, does not require any calcination aids, is environmentally friendly, facilitates large-scale industrial production, and exhibits excellent performance with a wide range of applications.

[0100] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing low specific surface area ultrafine alumina powder, characterized in that, Includes the following steps: Pickling to remove impurities: Industrial γ-alumina is added to the pickling solution and then filtered and dried to obtain low-sodium alumina; Wet grinding: The low-sodium alumina is prepared into a slurry, first put into a stirred mill for coarse grinding, and then put into a sand mill for sand grinding to obtain an ultrafine alumina slurry; Spray drying: The ultrafine alumina slurry is spray dried in a spray drying tower to obtain ultrafine alumina granulated powder; Calcination phase transformation: The ultrafine alumina granulated powder is placed in a sagger and transferred to a calcining furnace for calcination to obtain ultrafine alumina granulated calcined powder; Dispersion and deagglomeration: The ultrafine alumina granulated calcined powder is dispersed by airflow to obtain ultrafine alumina powder with low specific surface area; In the aforementioned industrial γ-alumina, the mass percentage of Al2O3 is greater than or equal to 99.0%, and the mass percentage of Na2O is less than or equal to 0.5%. The temperature at the inlet of the spray drying tower is between 180℃ and 255℃; the rotation speed of the spray drying tower is between 8000 r / min and 18000 r / min; the temperature at the outlet of the spray drying tower is between 105℃ and 135℃; the calcination temperature is between 1100℃ and 1400℃; the calcination time is between 1 h and 10 h; and the air pressure for air dispersion is between 0.2 MPa and 0.8 MPa.

2. The method for preparing low specific surface area ultrafine alumina powder as described in claim 1, characterized in that, The pickling solution is selected from one or more of acetic acid, oxalic acid, and citric acid.

3. The method for preparing low specific surface area ultrafine alumina powder as described in claim 1, characterized in that, The coarse grinding process takes between 2 hours and 10 hours; and / or the diameter of the grinding media used in the coarse grinding process is between 3.0 mm and 8.0 mm.

4. The method for preparing low specific surface area ultrafine alumina powder as described in claim 1, characterized in that, The sand milling process takes between 2 hours and 8 hours; and / or the diameter of the grinding media used in the sand milling process is between 0.2 mm and 0.6 mm.

5. The method for preparing low specific surface area ultrafine alumina powder as described in claim 1, characterized in that, The grinding media used in the coarse grinding and sand grinding processes are selected from one or more of zirconia ceramics, alumina ceramics, and zirconium-aluminum composite ceramics.

6. The method for preparing low specific surface area ultrafine alumina powder as described in claim 1, characterized in that, The solid content of the coarsely ground alumina slurry is between 35% and 65%; and / or, the solid content of the sand-milled alumina slurry is between 20% and 45%.

7. The method for preparing low specific surface area ultrafine alumina powder as described in claim 1, characterized in that, The device for dispersing the airflow is selected from either an air jet mill or a steam mill.

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