A circular sheet-like alumina and its preparation method

Abstract

This application discloses a method for preparing circular sheet-like alumina, comprising the following steps: mixing an aluminum-based raw material with a composite mineralizing agent to obtain a mixture; and calcining the mixture to obtain the circular sheet-like alumina; wherein the aluminum-based raw material includes alumina hydrate and / or γ-alumina, and the composite mineralizing agent includes a first mineralizing agent and a second mineralizing agent, wherein the first mineralizing agent includes one or more of molybdenum oxide, vanadium pentoxide, and fluorides, and the second mineralizing agent includes one or more of boron oxide, boric acid, and silicon dioxide, and the mass ratio of the first mineralizing agent to the second mineralizing agent is (4~8):(10~13). This method can obtain circular sheet-like alumina with rounded boundaries and no obvious sharp edges.

Description

Technical Field

[0001] This application relates to the field of fine alumina preparation technology, and in particular to a circular sheet-like alumina and its preparation method. Background Technology

[0002] Alumina, with its excellent thermal conductivity, electrical insulation, acid resistance, high temperature resistance, high hardness, and relatively low price, is widely used as a thermally conductive filler, electrical filler, and polishing material, serving numerous high-end industries such as artificial intelligence, 5G communications, new energy, and integrated circuits. Among these, flake alumina, as a two-dimensional functional material, possesses advantages such as a smooth and flat surface, good spreadability, and significant shielding effect, playing a crucial role in pearlescent pigments, cosmetics, chemical mechanical polishing, and functional coatings.

[0003] Currently, industrially prepared sheet-like alumina is mostly hexagonal. For example, some related technologies utilize aluminum shavings and alkaline organic compounds, controlling the hydrolysis temperature and time to prepare sheet-like aluminum hydroxide, which is then calcined to obtain hexagonal sheet-like alumina. Other related technologies generate gaseous intermediate compounds that inhibit the growth of

[001] crystal planes by mixing alumina precursors, morphology modifiers, and fluxes, ultimately forming hexagonal sheet-like alumina with a large aspect ratio. However, the sharp edges of the hexagonal sheet structure lead to severe intergranular interlocking, causing a sharp increase in the viscosity of the filler system and poor flowability. In addition, the sharp edges may also cause severe wear on equipment and instruments. Therefore, the preparation of multi-morphological sheet-like alumina has become a new research hotspot. Summary of the Invention

[0004] This application provides a circular sheet-like alumina and its preparation method, which solves one of the technical problems of sharp edge structure in traditional sheet-like alumina.

[0005] A first aspect of the embodiments of this application provides a circular sheet-like alumina, wherein the projection of the sheet-like alumina onto a plane perpendicular to its thickness direction is approximately circular.

[0006] Optionally, the diameter of the circular sheet-like alumina is 3 μm to 10 μm.

[0007] Optionally, the thickness of the circular sheet-like alumina is 1 μm to 3 μm.

[0008] Optionally, the mass fraction of α-phase alumina in the lamellar alumina is greater than or equal to 96%.

[0009] A second aspect of this application provides a method for preparing the circular sheet-like alumina described in the first aspect above, comprising the following steps: mixing an aluminum-based raw material with a composite mineralizer to obtain a mixture; and calcining the mixture to obtain the sheet-like alumina; wherein the aluminum-based raw material includes alumina hydrate and / or γ-alumina, the composite mineralizer includes a first mineralizer and a second mineralizer, the first mineralizer includes one or more of molybdenum oxide, vanadium pentoxide, and fluorides, the second mineralizer includes one or more of boron oxide, boric acid, and silicon dioxide, and the mass ratio of the first mineralizer to the second mineralizer is (4~8):(10~13).

[0010] Optionally, the first mineralizing agent comprises molybdenum oxide, ammonium bifluoride, and magnesium fluoride, and the second mineralizing agent comprises boron oxide; and / or, The first mineralizing agent comprises vanadium pentoxide, ammonium fluoride, and aluminum fluoride; the second mineralizing agent comprises boric acid; and / or, The first mineralizing agent comprises molybdenum oxide, vanadium pentoxide, and aluminum fluoride; the second mineralizing agent comprises boron oxide; and / or, The first mineralizing agent comprises vanadium pentoxide, ammonium fluoride, and magnesium fluoride; the second mineralizing agent comprises boric acid; and / or, The first mineralizing agent includes molybdenum oxide, ammonium fluoride, and aluminum fluoride, and the second mineralizing agent includes boric acid and silicon dioxide.

[0011] Optionally, the aluminum-based raw material includes alumina hydrate and γ-alumina, wherein the mass ratio of the alumina hydrate to the γ-alumina is 3:(1~2).

[0012] Optionally, the mass ratio of the aluminum-based raw material to the composite mineralizer is (1~5):100.

[0013] Optionally, the calcination temperature is 1150 ℃~1600 ℃, the calcination time is 0.5 h~20 h, and the calcination heating rate is 5 ℃ / min~15 ℃ / min.

[0014] Compared with the prior art, the technical solution provided in this application has the following beneficial effects: The alumina in this application has a circular flake morphology, and its electron micrograph shows that its overall morphology is disk-like, without obvious sharp edges and rounded corners.

[0015] The method for preparing circular sheet-like alumina in this application uses alumina hydrate and / or γ-alumina as aluminum-based raw materials. The aluminum-based raw materials and a composite mineralizer are calcined at a specific temperature (1150 ℃~1600 ℃) to produce circular sheet-like alumina. The composite mineralizer includes a first mineralizer and a second mineralizer. The first mineralizer promotes crystal formation into sheets, and the intermediate product generated by the reaction between the first mineralizer and the aluminum-based raw materials promotes rapid crystal growth on the columnar surfaces, i.e., promotes radial crystal growth, forming a sheet-like structure. The second mineralizer forms a viscous liquid phase during calcination, which can coat the crystal surface and smooth its roundness. The first and second mineralizers work synergistically in a suitable ratio to regulate the crystal growth process of the aluminum-based raw materials during calcination, transforming the originally thermodynamically controlled crystal growth mode into a kinetically controlled crystal growth mode and regulating the crystal morphology. The growth rates in each columnar direction are similar, anisotropy is significantly reduced, and the crystal edges become rounded, ultimately forming circular sheet-like alumina with a low total interfacial energy. Furthermore, the method for preparing sheet-like alumina in this application can achieve efficient preparation of spherical sheet-like alumina with controllable particle size, narrow particle size distribution, and uniform morphology.

[0016] Furthermore, the alumina product prepared by the method for preparing circular sheet-like alumina of this application has a uniform morphology and a narrow particle size distribution, with a diameter of 3 μm to 10 μm. Even further, the mass fraction of α-phase alumina in the alumina product prepared by the method for preparing sheet-like alumina of this application can reach 96% or more.

[0017] The method for preparing circular sheet-like alumina in this application achieves particle size control and continuous, efficient preparation of sheet-like alumina. While retaining the advantages of two-dimensional sheet-like alumina materials, it solves the problems of poor fluidity and easy wear caused by sharp edges in the filler system. This is conducive to the iterative upgrading of products such as thermal conductive materials and polishing materials, and helps the development of strategic emerging industries such as semiconductors, new energy, and artificial intelligence. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and disclosure, and together with the description serve to explain the principles of this application and disclosure.

[0019] 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.

[0020] Figure 1This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 1 of this invention; Figure 2 This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 2 of the present invention; Figure 3 This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 3 of the present invention; Figure 4 This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 4 of this invention; Figure 5 This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 5 of the present invention; Figure 6 This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 6 of this invention; Figure 7 This is a scanning electron microscope image of the circular sheet-like α-alumina prepared in Example 7 of this invention; Figure 8 These are scanning electron microscope images of the sheet-like α-alumina prepared in Comparative Example 1 of this invention; Figure 9 These are scanning electron microscope images of the sheet-like α-alumina prepared in Comparative Example 2 of this invention; Figure 10 These are scanning electron microscope images of the sheet-like α-alumina prepared in Comparative Example 3 of this invention; Figure 11 This is a scanning electron microscope image of the sheet-like α-alumina prepared in Comparative Example 4 of this invention; Figure 12 This is a scanning electron microscope image of the sheet-like α-alumina prepared in Comparative Example 5 of this invention. Detailed Implementation

[0021] 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.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0023] In this application, except where expressly stated, any matters or issues not mentioned are directly applicable to those known in the art without any modification. Furthermore, any implementation described in this application can be freely combined with one or more other implementations described in this application, and the resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this application, and should not be regarded as new content not disclosed or anticipated in this application, unless those skilled in the art consider the combination to be clearly unreasonable.

[0024] Any method steps, processes, and operations described in this application should not be construed as necessarily requiring them to be performed in a particular order as discussed or shown, unless explicitly specified. It should also be understood that additional or alternative steps may be used unless otherwise stated.

[0025] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0026] Any specific numerical values ​​disclosed herein (including the endpoints of numerical ranges) are not limited to their exact values, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Furthermore, with respect to the disclosed numerical ranges, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values ​​of the range, the endpoint values ​​with specific point values ​​within the range, and the specific point values ​​themselves; these new numerical ranges should also be considered as specifically disclosed herein.

[0027] Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art, and if a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.

[0028] First aspect Some embodiments of this application provide a circular sheet-like alumina. This alumina has a circular sheet-like morphology, resembling a disc, with no obvious sharp edges and rounded corners.

[0029] The sheet-like alumina has rounded edges, and its projection onto a plane perpendicular to its thickness direction is approximately circular. In some embodiments, the circularity of this projection is ≥0.85, and optionally, the circularity of this projection is ≥0.9.

[0030] Circularity, as understood in the art, is used to quantitatively describe how closely a particle's projected outline approximates an ideal circle; it is also known as shape factor or roundness. Circularity = 4πA / P², where A is the area of ​​a single particle's projection, and P is its projected perimeter. This value is calculated using image analysis software (e.g., ImageJ) after acquiring particle images through scanning electron microscopy (SEM). At least 10 fields of view are randomly photographed, with at least 10 complete particles selected from each field, for a total of ≥100 particles. The roundness value of each particle's projection is calculated, and the arithmetic mean is taken as the final roundness. The closer the roundness is to 1, the closer the particle shape is to an ideal circle, and the smoother the edges without sharp corners. Conversely, particles with rough edges or sharp corners have a significantly increased perimeter, resulting in a roundness value much less than 1.

[0031] In some implementations, the aspect ratio of the projection is (1~1.2):1. The aspect ratio of the projection has a meaning known in the art, referring to the ratio of the longest diameter (Feret diameter, i.e., the maximum Feret diameter) to the shortest diameter (minimum Feret diameter) of the particle's projected profile. This value can also be obtained by acquiring particle images using a scanning electron microscope (SEM) and then calculating it using image analysis software (e.g., ImageJ). At least 10 fields of view are randomly photographed, with at least 10 complete particles selected from each field of view, for a total number of particles ≥100. The aspect ratio of the projection for each particle is calculated, and the arithmetic mean is taken as the final aspect ratio. The aspect ratio of the projection measures the elongation of the projected alumina particles; for needle-like or rod-shaped particles, the aspect ratio is much greater than 1.

[0032] In some embodiments, the aspect ratio of the circular sheet-like alumina prepared in this application is 1.3 to 9.

[0033] The alumina products prepared by the method of this application exhibit uniform morphology and narrow particle size distribution. In some embodiments, the diameter of the plate-like alumina is between 3 μm and 10 μm. The diameter of the plate-like alumina can also be obtained by acquiring particle images using a scanning electron microscope (SEM) and then calculating them using image analysis software (e.g., ImageJ). At least 10 fields of view are randomly photographed, with at least 10 intact particles selected from each field of view, for a total number of particles ≥100. The diameter of each particle is calculated, and the arithmetic mean is taken as the final diameter.

[0034] In some embodiments, the thickness of the lamellar alumina is 1 μm to 3 μm. The thickness of the lamellar alumina can also be obtained by acquiring particle images using a scanning electron microscope (SEM) and then calculating it using image analysis software (such as ImageJ). At least 10 fields of view are randomly photographed, with at least 10 intact particles selected in each field of view, for a total of ≥100 particles. The thickness of each particle is calculated, and the arithmetic mean is taken as the final thickness.

[0035] In some embodiments, the mass fraction of α-phase alumina in the lamellar alumina is greater than or equal to 96%.

[0036] Second aspect This application provides a method for preparing sheet-like alumina according to any embodiment of the first aspect described above, comprising the following steps: An aluminum-based raw material is mixed with a composite mineralizer to obtain a mixture; and The mixture was calcined to obtain flake-shaped alumina.

[0037] Aluminum-based raw materials include alumina hydrate and / or γ-alumina.

[0038] The composite mineralizer includes a first mineralizer and a second mineralizer. The first mineralizer includes one or more of molybdenum oxide, vanadium pentoxide, and fluorides. The second mineralizer includes one or more of boron oxide, boric acid, and silicon dioxide.

[0039] The mass ratio of the first mineralizer to the second mineralizer is (4~8):(10~13). Understandably, the mass ratio of the first mineralizer to the second mineralizer can be 4:10, 4:11, 4:13, 5:10, 5:11, 5:12, 5:13, 8:10, 8:11, 8:13, and any ratio between them or any range between any two ratios.

[0040] The method for preparing circular sheet-like alumina disclosed in this application uses alumina hydrate and / or γ-alumina as the aluminum-based raw material. The aluminum-based raw material and a composite mineralizer are calcined together to produce circular sheet-like alumina. The composite mineralizer includes a first mineralizer and a second mineralizer. The first mineralizer promotes crystal formation into sheets. The intermediate product generated by the reaction between the first mineralizer and the aluminum-based raw material promotes rapid crystal growth on the columnar surfaces, i.e., promotes radial growth of alumina crystals to form a sheet-like structure. The second mineralizer forms a viscous liquid phase during calcination, which can coat the crystal surface and smooth the crystal surface. The first and second mineralizers work synergistically in an appropriate ratio to regulate the crystal growth process of the aluminum-based raw material during calcination, transforming the originally thermodynamically controlled crystal growth mode into a kinetically controlled crystal growth mode and regulating the crystal morphology process. The growth rates in each columnar direction are similar, anisotropy is significantly reduced, and the crystal edges become rounded, ultimately forming sheet-like alumina with a low total interfacial energy.

[0041] Molybdenum ions in molybdenum oxide can enter the crystal lattice of alumina, inducing rapid crystal growth on the cylindrical surface and promoting crystal sheet formation.

[0042] Vanadium ions in vanadium pentoxide can also enter the alumina lattice, inducing rapid crystal growth on the cylindrical surface and promoting crystal sheet formation.

[0043] The fluorine element in fluorides can react with alumina to form a gaseous intermediate, aluminum fluoride. The adsorption energy and growth rate of this intermediate differ on different crystal planes, primarily promoting rapid crystal growth on the cylindrical plane and facilitating crystal formation. In some embodiments, the fluoride includes one or more of ammonium fluoride, ammonium hydrogen fluoride, magnesium fluoride, and aluminum fluoride.

[0044] Boron oxide, boric acid, and silicon dioxide form a viscous liquid phase during calcination, which coats the crystal surface and helps to smooth the crystal surface.

[0045] In some embodiments, the first mineralizing agent comprises a fluoride and molybdenum oxide. In other embodiments, the first mineralizing agent comprises a fluoride and vanadium pentoxide. In still other embodiments, the first mineralizing agent comprises a fluoride, molybdenum oxide, and vanadium pentoxide.

[0046] For example, the first mineralizing agent includes molybdenum oxide, ammonium bifluoride, and magnesium fluoride, and the second mineralizing agent includes boron oxide.

[0047] For example, the first mineralizing agent includes vanadium pentoxide, ammonium fluoride and aluminum fluoride, and the second mineralizing agent includes boric acid.

[0048] For example, the first mineralizing agent includes molybdenum oxide, vanadium pentoxide, and aluminum fluoride, and the second mineralizing agent includes boron oxide.

[0049] For example, the first mineralizing agent includes vanadium pentoxide, ammonium fluoride and magnesium fluoride, and the second mineralizing agent includes boric acid.

[0050] For example, the first mineralizing agent includes molybdenum oxide, ammonium fluoride and aluminum fluoride, and the second mineralizing agent includes boric acid and silicon dioxide.

[0051] In some embodiments, the aluminum-based raw material includes alumina hydrate and γ-alumina, with a mass ratio of alumina hydrate to γ-alumina of 3:(1-2). Exemplarily, the mass ratio of alumina hydrate to γ-alumina is 3:1, 3:1.5, or 3:2. In some embodiments, the alumina hydrate is alumina trihydrate.

[0052] It should be noted that γ-alumina has a well-known meaning in the art, referring to γ-phase aluminum oxide.

[0053] In some embodiments, γ-alumina may be industrial alumina, which refers to raw material used in electrolytic aluminum plants after being calcined at a temperature below 1000°C.

[0054] In some embodiments, the mass ratio of aluminum-based raw material to composite mineralizer is (1-5):100. Exemplarily, the mass ratio of aluminum-based raw material to composite mineralizer is 1:100, 2:100, 2.1:100, 2.6:100, 2.9:100, 3:100, 3.6:100, 4:100, or 5:100. In some optional embodiments, the mass ratio of aluminum-based raw material to composite mineralizer is (2-4):100, more specifically (2.1-3.6):100.

[0055] In some embodiments, the calcination temperature is 1150 °C to 1600 °C, the calcination time is 0.5 h to 20 h, and the calcination heating rate is 5 °C / min to 15 °C / min. Understandably, the calcination temperature is independently selected from 1150 °C, 1200 °C, 1300 °C, 1400 °C, 1500 °C, 1600 °C, and any value or range between these values. Optionally, the calcination temperature is 1400 °C to 1500 °C. The calcination time is independently selected from 0.5 h, 1 h, 2 h, 2.5 h, 5 h, 7.5 h, 10 h, 12.5 h, 15 h, 17.5 h, 20 h, and any value or range between these values. The heating rate of calcination is independently selected from 5 ℃ / min, 8 ℃ / min, 10 ℃ / min, 12 ℃ / min, 15 ℃ / min and any value between them or any range between any two values.

[0056] The above mixing methods include, but are not limited to, mechanical mixing and wet mixing.

[0057] The above-mentioned calcination methods include, but are not limited to, tunnel kiln calcination, shuttle kiln calcination, rotary kiln calcination, etc.

[0058] In some embodiments, the above preparation method further includes dispersing the obtained sheet-like alumina. Dispersion methods include, but are not limited to, airflow dispersion and mechanical dispersion.

[0059] Example To better understand this application, the following description, in conjunction with embodiments, further illustrates this application. However, the scope of protection claimed in this application is not limited to the scope of the embodiments.

[0060] In the following examples, unless otherwise specified, all experimental instruments, raw materials, and quantities involved are commercially available products or can be prepared by known methods. Experimental methods not specifying particular conditions in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0061] Unless otherwise specified, the specific parameters used in each step of the material preparation process in each embodiment and comparative example are the same.

[0062] Example 1 Alumina trihydrate with a particle size D50 of 10 μm was used as the aluminum-based raw material, and boron oxide, molybdenum oxide, ammonium bifluoride, and magnesium fluoride were used as composite mineralizing agents. The mass ratio of boron oxide, molybdenum oxide, ammonium bifluoride, and magnesium fluoride in the composite mineralizing agent was 5:1:2:8. The mass ratio of the composite mineralizing agent to the aluminum-based raw material was 13:500. The aluminum-based raw material and the composite mineralizing agent were mixed in a mixer at a rate of 300 r / min for 30 min. The mixture was then placed in a crucible and fed into a muffle furnace, where it was calcined at 1450 °C for 120 min at a heating rate of 5 °C / min. After dispersing the calcined product, spherical flake-shaped alumina was obtained.

[0063] The morphology of the sheet-like alumina was characterized, such as... Figure 1 As shown, Figure 1 The image shows a scanning electron microscope (SEM) image of the sheet-like alumina powder obtained in Example 1. The powder exhibits a circular, sheet-like morphology with rounded edges and no obvious sharp corners. The sheet-like alumina single crystal has a diameter of approximately 8 μm and a thickness of approximately 1 μm, with an α-phase alumina mass fraction greater than 96%.

[0064] Example 2 Alumina trihydrate with a particle size D50 of 3 μm was used as the aluminum-based raw material, and boric acid, vanadium pentoxide, ammonium fluoride, and aluminum fluoride were used as a composite mineralizing agent. The mass ratio of boric acid, vanadium pentoxide, ammonium fluoride, and aluminum fluoride in the composite mineralizing agent was 5:1:3:8, and the mass ratio of the composite mineralizing agent to the aluminum-based raw material was 18:625. The aluminum-based raw material and the composite mineralizing agent were mixed in a mixer for 30 min. Then, the mixture was calcined in a muffle furnace at 1300℃ for 150 min, with a heating rate of 5℃ / min. After dispersing the calcined product, spherical flake-shaped alumina was obtained.

[0065] The morphology of the sheet-like alumina was characterized, such as... Figure 2 As shown, Figure 2 The image shown is a scanning electron microscope image of the sheet-like alumina powder obtained in Example 2. Its morphology also exhibits a circular sheet-like shape without obvious edges. The sheet-like alumina single crystal has a diameter of approximately 6 μm and a thickness of approximately 1 μm, with an α-phase alumina mass fraction greater than 96%.

[0066] Example 3 Alumina trihydrate with a particle size D50 of 3 μm was used as the aluminum-based raw material, and boron oxide, molybdenum oxide, vanadium pentoxide, and aluminum fluoride were used as composite mineralizing agents. The mass ratio of boron oxide, molybdenum oxide, ammonium bifluoride, and magnesium fluoride in the composite mineralizing agent was 5:1:1:8. The mass ratio of the composite mineralizing agent to the aluminum-based raw material was 21:1000. The aluminum-based raw material and the composite mineralizing agent were mixed in a mixer for 30 min. The mixture was then placed in a crucible and fed into a muffle furnace, where it was calcined at 1400℃ for 150 min at a heating rate of 5℃ / min. After dispersing the calcined product, spherical flake-shaped alumina was obtained.

[0067] The morphology of the sheet-like alumina was characterized, such as... Figure 3 As shown, Figure 3 The image shows a scanning electron microscope image of the lamellar alumina powder obtained in Example 3. Its morphology also exhibits a rounded, flat shape with smooth edges and no obvious corners. The diameter of this lamellar alumina single crystal is approximately 5 μm, but its thickness is greater than that of the lamellar alumina in Example 2, approximately 2 μm, with an α-phase alumina mass fraction greater than 96%.

[0068] Example 4 Alumina trihydrate with a particle size D50 of 1 μm was used as the aluminum-based raw material, and boric acid, vanadium pentoxide, ammonium fluoride, and magnesium fluoride were used as a composite mineralizing agent. The mass ratio of boric acid, vanadium pentoxide, ammonium fluoride, and magnesium fluoride in the composite mineralizing agent was 4:1:2:8. The mass ratio of the composite mineralizing agent to the aluminum-based raw material was 29:1000. The aluminum-based raw material and the composite mineralizing agent were mixed in a mixer for 30 min. The mixture was then placed in a crucible and fed into a muffle furnace, where it was calcined at 1350 °C for 120 min at a heating rate of 10 °C / min. After dispersing the calcined product, spherical flake-shaped alumina was obtained.

[0069] Figure 4 The image shows a scanning electron microscope image of the alumina powder obtained in Example 4. Its morphology is also circular and plate-like, with rounded edges and no obvious sharp corners. The diameter of the alumina single crystal is about 4 μm and the thickness is about 3 μm. The mass fraction of α phase alumina is greater than 96%.

[0070] Example 5 A mixture of γ-phase alumina with a particle size D50 of 8 μm and alumina trihydrate with a particle size D50 of 10 μm was used as the aluminum-based raw material, with a mass ratio of γ-phase alumina to alumina trihydrate of 2:3. Boric acid, silica, molybdenum oxide, ammonium fluoride, and aluminum fluoride were used as a composite mineralizer. The mass ratio of boric acid, silica, molybdenum oxide, ammonium fluoride, and aluminum fluoride in the composite mineralizer was 5:3:1:4:8. The mass ratio of the composite mineralizer to the aluminum-based raw material was 9:250. The aluminum-based raw material and the composite mineralizer were mixed by placing them in a mixer and mixing for 30 min. The mixture was then placed in a crucible and fed into a muffle furnace, where it was calcined at 1350 °C for 150 min at a heating rate of 10 °C / min. After dispersing the calcined product, spherical flake-shaped alumina was obtained.

[0071] The morphology of the sheet-like alumina was characterized, such as... Figure 5 As shown, Figure 5 The image shows a scanning electron microscope image of the sheet-like alumina powder obtained in Example 5. The morphology of the sheet-like alumina single crystal is circular sheet-like structure. The diameter of the sheet-like alumina single crystal is 9 μm and the thickness is about 1 μm. The mass fraction of α phase alumina is greater than 96%.

[0072] Example 6 It is basically the same as Example 1, except that the calcination temperature is 1150℃ and the calcination time is 150 min at 1150℃.

[0073] The morphology of the sheet-like alumina was characterized, such as... Figure 6 As shown, Figure 6The image shows a scanning electron microscope image of the sheet-like alumina powder obtained in Example 6. Some of the particles have begun to show sharp edges. The diameter of the sheet-like alumina single crystal is about 8 μm, and the mass fraction of α-phase alumina is greater than 96%.

[0074] Example 7 It is basically the same as Example 1, except that the calcination temperature is 1600℃ and calcination is carried out at 1600℃ for 120 minutes.

[0075] The morphology of the sheet-like alumina was characterized, such as... Figure 7 As shown, Figure 7 The image shows a scanning electron microscope (SEM) image of the lamellar alumina powder obtained in Example 7. Although it exhibits a circular lamellar structure, the particle size distribution begins to widen. After calcination, the product begins to agglomerate, making it difficult to break and disperse. The diameter of the lamellar alumina single crystal is approximately 9 μm, with an α-phase alumina mass fraction greater than 96%.

[0076] Comparative Example 1 It is basically the same as Example 1, except that the calcination temperature is 1100℃ and calcination is carried out at 1100℃ for 150 minutes.

[0077] The morphology of the sheet-like alumina prepared in this embodiment was characterized, such as... Figure 8 As shown, Figure 8 The image shown is a scanning electron microscope image of the flaky alumina powder obtained in Comparative Example 1, which shows a significant increase in the boundaries and angles of its morphology.

[0078] Comparative Example 2 It is basically the same as Example 1, except that the calcination temperature is 1650℃ and the calcination time is 120 min at 1650℃.

[0079] The morphology of the sheet-like alumina prepared in this embodiment was characterized, such as... Figure 9 As shown, Figure 9 The image shows a scanning electron microscope image of the flaky alumina powder obtained in Comparative Example 2. The boundaries and angles of the morphology are greatly increased, and there is a tendency for the particles to form porcelain after calcination. The powder agglomerates severely, making it extremely difficult to break and disperse.

[0080] Comparing Comparative Examples 1 and 2 with Example 1, it is shown that calcination temperature has a certain influence on the morphology of flake alumina, and better morphology can be obtained when the calcination temperature is within the range of 1150 ℃ to 1600 ℃.

[0081] Comparative Example 3 It is basically the same as Example 1, except that the mass ratio of the composite mineralizer to the aluminum-based raw material is 6:100.

[0082] The morphology of the sheet-like alumina prepared in this embodiment was characterized, such as... Figure 10 As shown, Figure 10 The image shown is a scanning electron microscope image of the flaky alumina powder obtained in Comparative Example 3. The boundaries and angles of its morphology have increased to a certain extent, and the particle size distribution has become much wider, indicating that the appropriate proportion of composite mineralizer is crucial for the preparation of spherical flaky alumina.

[0083] Comparative Example 4 It is basically the same as Example 1, except that the composite mineralizer is molybdenum oxide, ammonium bifluoride and magnesium fluoride.

[0084] The morphology of the sheet-like alumina prepared in Comparative Example 4 was characterized, such as... Figure 11 As shown, Figure 11 The image shown is a scanning electron microscope image of the alumina powder obtained in Comparative Example 4. The boundaries and edges of its morphology are very obvious, and the projection shows a hexagonal feature, which is significantly different from the results of Example 1.

[0085] Comparing Comparative Example 4 and Example 1, the composite mineralizer in Example 1 contains both a first mineralizer and a second mineralizer, whereas Comparative Example 4 uses a single type of composite mineralizer (i.e., only the first mineralizer). The results demonstrate that the synergistic effect of the first and second mineralizers is required to obtain spherical, plate-like alumina with rounded particle boundaries and no obvious sharp edges.

[0086] Comparative Example 5 It is basically the same as Example 1, except that the mass ratio of boron oxide, molybdenum oxide, ammonium bifluoride and magnesium fluoride in the composite mineralizer is 3:1:2:8.

[0087] The morphology of the sheet-like alumina prepared in Comparative Example 5 was characterized, such as... Figure 12 As shown, Figure 12 The image shown is a scanning electron microscope image of the alumina powder obtained in Comparative Example 5. The boundaries and sharp angles of its morphology are still distinct, and the edges are not rounded, showing a significant difference from the results of Example 1. This indicates that a mass ratio of the first mineralizer to the second mineralizer in the composite mineralizer within the range of (4~8):(10~13) can yield alumina with a circular, plate-like morphology, with rounded boundaries and no obvious sharp angles. When the content of the composite mineralizer is too low, the boundaries and sharp angles of the resulting plate-like alumina morphology are very distinct.

[0088] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

[0089] Although preferred embodiments have been described in this specification, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this specification.

[0090] Obviously, those skilled in the art can make various modifications and variations to this specification without departing from its spirit and scope. Therefore, if such modifications and variations fall within the scope of the claims and their equivalents, this specification is also intended to include such modifications and variations.

Claims

1. A circular sheet-like alumina, characterized in that, The projection of the sheet-like alumina onto a plane perpendicular to its thickness direction is approximately circular.

2. The circular sheet-like alumina according to claim 1, characterized in that, The diameter of the sheet-like alumina is 3 μm to 10 μm.

3. The sheet-like alumina according to claim 1, characterized in that, The thickness of the circular sheet-like alumina is 1 μm to 3 μm.

4. The circular sheet-like alumina according to claim 1, characterized in that, The mass fraction of α-phase alumina in the lamellar alumina is greater than or equal to 96%.

5. A method for preparing circular sheet-like alumina as described in any one of claims 1 to 4, characterized in that, Includes the following steps: An aluminum-based raw material is mixed with a composite mineralizer to obtain a mixture; and The mixture was calcined to obtain the sheet-like alumina; The aluminum-based raw material includes alumina hydrate and / or γ-alumina, and the composite mineralizer includes a first mineralizer and a second mineralizer. The first mineralizer includes one or more of molybdenum oxide, vanadium pentoxide, and fluoride, and the second mineralizer includes one or more of boron oxide, boric acid, and silicon dioxide. The mass ratio of the first mineralizer to the second mineralizer is (4~8):(10~13).

6. The preparation method according to claim 5, characterized in that, The fluoride includes one or more of ammonium fluoride, ammonium hydrogen fluoride, magnesium fluoride, and aluminum fluoride.

7. The preparation method according to claim 6, characterized in that, The first mineralizing agent comprises molybdenum oxide, ammonium bifluoride, and magnesium fluoride; the second mineralizing agent comprises boron oxide; and / or, The first mineralizing agent comprises vanadium pentoxide, ammonium fluoride, and aluminum fluoride; the second mineralizing agent comprises boric acid; and / or, The first mineralizing agent comprises molybdenum oxide, vanadium pentoxide, and aluminum fluoride; the second mineralizing agent comprises boron oxide; and / or, The first mineralizing agent comprises vanadium pentoxide, ammonium fluoride, and magnesium fluoride; the second mineralizing agent comprises boric acid; and / or, The first mineralizing agent includes molybdenum oxide, ammonium fluoride, and aluminum fluoride, and the second mineralizing agent includes boric acid and silicon dioxide.

8. The preparation method according to claim 5, characterized in that, The aluminum-based raw material includes alumina hydrate and γ-alumina, and the mass ratio of the alumina hydrate to the γ-alumina is 3:(1~2).

9. The preparation method according to any one of claims 5 to 8, characterized in that, The mass ratio of the composite mineralizer to the aluminum-based raw material is (1~5):

100.

10. The preparation method according to any one of claims 5 to 8, characterized in that, The calcination temperature is 1150 ℃~1600 ℃, the calcination time is 0.5 h~20 h, and the calcination heating rate is 5 ℃ / min~15 ℃ / min.

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