Flaky alumina and preparation method thereof

Abstract

The invention discloses flaky alumina and a preparation method thereof, the flaky alumina is in a square sheet shape and has a single crystal structure, the grain size of the flaky alumina is 300-1300 nm, and the grain thickness is less than or equal to 150 nm. The preparation method comprises the following steps: placing roasted SB powder and a quaternary ammonium base solution in a pressure container in a solid-liquid two-phase separation manner, carrying out a gas-solid reaction under certain heat treatment conditions, and drying and roasting the reacted solid powder to obtain the flaky aluminum oxide. The flaky aluminum oxide is regular in structure and flat and smooth in surface, can be used as a polishing material, a coating, a catalysis material and an adsorption material, and is simple in preparation process, easy in raw material obtaining and easy in industrial production.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material preparation, specifically relating to a sheet-like alumina with a single crystal structure and its preparation method. Background Technology

[0002] Single-crystal alumina powder is widely used as a filler, in ceramics, various glass coating materials, gemstones, and precision instrument materials due to its excellent filling properties, stability, flowability, and oil absorption value. Traditional methods for preparing plate-like single-crystal alumina mainly include hydrothermal methods, sol-gel methods, and molten salt methods.

[0003] CN201610390310.8 discloses a method for preparing plate-like single-crystal alumina. Na3FSO4 is used as a seed crystal and added to an aluminum-containing raw material along with molten salt. The mixture is calcined at 650-1000℃ and cooled. After dissolving in hot water, washing, filtering, and drying, hexagonal plate-like single-crystal alumina is obtained.

[0004] CN 201710935935.2 discloses a method for preparing single-crystal alumina ceramics. The method involves sintering alumina powder with added sintering aids using a spark plasma sintering apparatus, then spin-coating a calcium-silicon ion solution of a certain concentration onto the surface of a transparent alumina ceramic. The precursor is then removed by sintering at 800℃-1000℃ to obtain alumina single crystals. These alumina single crystals are then used as seed crystals and sintered with the alumina ceramic in a graphite abrasive mold. After polishing, the alumina single crystals are subjected to heat treatment to obtain the final alumina single crystal.

[0005] CN 202210094167.3 discloses a method for preparing spheroidal single-crystal alumina powder. Using fused alumina as raw material and alumina balls as abrasive, the fused alumina is colliding and grinding with the alumina balls under the action of compressed air to form single-crystal or polycrystalline particles. The grain boundaries of the polycrystalline particles act as defects and continue to collide and grind with the alumina balls, ultimately obtaining spheroidal single-crystal alumina powder. Summary of the Invention

[0006] This invention provides a sheet-like alumina and its preparation method. The sheet-like alumina of this invention has a single crystal structure, regular structure, and smooth surface. It can be used as a polishing material, coating, catalyst, and adsorption material. The preparation process is simple, the raw materials are readily available, and it is easy to industrialize.

[0007] The alumina of the present invention is tetragonal in shape and has a single crystal structure. The grain size of the alumina is 300-1300 nm and the grain thickness is ≤150 nm, preferably 400-1000 nm. The two pairs of included angles of the tetragonal alumina are 68°~85° and 95°~112°, respectively.

[0008] The method for preparing sheet-like alumina of the present invention includes the following steps: calcined SB powder and quaternary ammonium alkali solution are placed in a pressure-resistant container for solid-liquid phase separation and gas-solid reaction under certain heat treatment conditions. The solid powder after the reaction is dried and calcined to obtain sheet-like alumina.

[0009] In the method of this invention, the SB powder is commercially available SB powder, and the calcination conditions of the SB powder are: calcination temperature of 450-650℃ and calcination time of 2-8 hours.

[0010] In the method of the present invention, the quaternary ammonium base aqueous solution has a mass fraction of 10%-25%, and the mass ratio of the quaternary ammonium base aqueous solution to SB powder is 8:1-20:1. The quaternary ammonium base is selected from one or more of tetraethylammonium hydroxide, tetramethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0011] In the method of the present invention, anhydrous ethanol is preferably added simultaneously to the quaternary ammonium base aqueous solution, and the mass ratio of the amount of anhydrous ethanol added to the quaternary ammonium base aqueous solution is 0.1:1-0.3:1.

[0012] In the method of the present invention, the quaternary ammonium alkali solution and SB powder are placed in a reaction vessel in a liquid-solid two-phase separation state, and the vapor formed by the quaternary ammonium alkali solution in the reaction vessel at high temperature reacts with the SB powder.

[0013] In the method of the present invention, the heat treatment conditions are: temperature of 120-250℃, preferably 160-220℃, and time of 18-120 hours, preferably 24-96 hours.

[0014] In the method of the present invention, the drying conditions of the solid powder after reaction are: drying temperature of 80-120℃ and drying time of 2-12 hours; the calcination conditions are: calcination temperature of 450-650℃ and calcination time of 4-10 hours.

[0015] The sheet-like alumina of the present invention can be widely used in the fields of adsorption, catalysis, and refractory materials.

[0016] Compared with existing technologies, the single-crystal tetragonal plate-shaped alumina prepared by the method of the present invention has a regular structure and smooth surface, the preparation process is simple, the raw materials are readily available, and it is easy to industrialize. Attached Figure Description

[0017] Figure 1 The image shows a low-magnification scanning electron microscope (SEM) image of the material prepared in Example 1.

[0018] Figure 2 This is a high-magnification scanning electron microscope (SEM) image of the material prepared in Example 1.

[0019] Figure 3 Transmission electron microscope (TEM) image of the material prepared in Example 1.

[0020] Figure 4 The TEM single-crystal diffraction spectrum of the material prepared in Example 1.

[0021] Figure 5 The image shows a scanning electron microscope (SEM) image of the material prepared in Comparative Example 1.

[0022] Figure 6 The image shows the TEM polycrystalline diffraction pattern of the material prepared in Comparative Example 1.

[0023] Figure 7 The image shows a scanning electron microscope (SEM) image of the material prepared in Comparative Example 2. Figure 8 This is a scanning electron microscope (SEM) image of the alumina prepared in Comparative Example 3. Figure 9 This is a scanning electron microscope (SEM) image of the alumina prepared in Comparative Example 4. Detailed Implementation

[0024] The technical solution and effects of the present invention will be further illustrated below with reference to the embodiments, but the invention is not limited to the following embodiments. The characterization and measurement methods for alumina involved in the present invention are as follows: the morphology, thickness, and size of alumina crystals are characterized by scanning electron microscopy; the diffraction patterns of alumina crystals are characterized by transmission electron microscopy. Example 1

[0025] SB powder produced by Sasol GmbH (Germany) was calcined at 550°C for 4 hours. 67g of a 20% tetraethylammonium hydroxide solution and 15g of anhydrous ethanol were weighed to form a mixed solution. This solution, along with 5g of the calcined SB powder, were placed separately in a reaction vessel, isolated from each other by a small polytetrafluoroethylene (PTFE) beaker. The ethanol solution of the tetraethylammonium hydroxide was on the outside of the beaker, while the SB powder was inside. The reaction was carried out at 200°C for 48 hours. After cooling, the solid powder was dried at 100°C for 6 hours and then calcined at 550°C for 6 hours. The resulting alumina was a single-crystal tetragonal lamellar structure with a grain size of 300-1300 nm and a thickness ≤150 nm. Example 2

[0026] SB powder was calcined at 450℃ for 6 hours. 55g of a 23% tetraethylammonium hydroxide solution and 11g of anhydrous ethanol were weighed to form a mixed solution. This solution was then placed separately from 5g of the calcined SB powder in a reaction vessel, separated by a small polytetrafluoroethylene (PTFE) beaker. The ethanol solution of the tetraethylammonium hydroxide was on the outside of the beaker, while the SB powder was inside. The reaction was carried out at 180℃ for 72 hours. After cooling, the solid powder was dried at 110℃ for 8 hours and then calcined at 600℃ for 4 hours. The resulting alumina had a single-crystal structure with a grain size of 630-730 nm and a thickness of 70-90 nm. Example 3

[0027] SB powder was calcined at 500℃ for 5.5 hours. 74g of 17% tetraethylammonium hydroxide and 7.4g of anhydrous ethanol were weighed to form a mixed solution. This solution was then placed separately from 5g of the calcined SB powder in a reaction vessel, separated by a small polytetrafluoroethylene (PTFE) beaker. The ethanol solution of the tetraethylammonium hydroxide was on the outside of the beaker, while the SB powder was inside. The reaction was carried out at 160℃ for 94 hours. After cooling, the solid powder was dried at 90℃ for 7 hours and then calcined at 500℃ for 8 hours. The resulting alumina had a monocrystalline structure with a grain size of 510-800 nm and a thickness of 70-90 nm. Example 4

[0028] Samples were prepared according to the same material ratio as in Example 1, except that ethanol was replaced with an equal amount of water. The resulting alumina had a single-crystal flake structure, with a grain size of 280-650 nm and a thickness of 60-78 nm for the single-crystal tetragonal flake alumina. Compared to the addition of ethanol, the size of the flake alumina obtained from the gas-solid reaction was reduced.

[0029] Comparative Example 1 The sample was prepared according to the material ratio of Example 1, except that SB powder was immersed in an ethanol-water solution of tetraethylammonium hydroxide in the reaction vessel, and the two underwent a liquid-solid hydrothermal reaction. The resulting alumina grains were large-sized, non-single-crystal, petal-shaped crystals without sharp edges. The resulting scanning electron microscope image is shown below. Figure 5 The transmission electron microscopy diffraction pattern is shown in the figure. Figure 6 .

[0030] Comparative Example 2 SB powder was calcined at 550℃ for 4 hours. 67g of 20% tetraethylammonium hydroxide and 15g of anhydrous ethanol were weighed to form a mixed solution. This solution, along with 5g of the calcined SB powder, was placed separately in a reaction vessel. The two solutions were isolated within the vessel using a small polytetrafluoroethylene (PTFE) beaker, with the ethanol-water solution of tetraethylammonium hydroxide on the outside of the beaker and the SB powder inside. The mixture was subjected to a gas-solid reaction at 180℃ for 6 hours. After cooling, the solid powder was dried at 100℃ for 6 hours and then calcined at 550℃ for 6 hours. Figure 7 The image shown is a scanning electron microscope image of the alumina prepared in this comparative example. It does not form a regular morphology sample and cannot produce tetragonal plate-shaped alumina.

[0031] Comparative Example 3 SB powder was calcined at 500℃ for 6 hours. 30g of 8% tetraethylammonium hydroxide and 15g of anhydrous ethanol were weighed to form a mixed solution. This solution, along with 5g of the calcined SB powder, was placed separately in a reaction vessel. The two solutions were isolated within the vessel using a small polytetrafluoroethylene (PTFE) beaker, with the ethanol-water solution of tetraethylammonium hydroxide on the outside of the beaker and the SB powder inside. The mixture was subjected to a gas-solid reaction at 200℃ for 24 hours. After cooling, the solid powder was dried at 110℃ for 6 hours and then calcined at 550℃ for 4 hours. Figure 8 The image shown is a scanning electron microscope image of the alumina prepared in this comparative example. It does not form a regular morphology sample and cannot produce tetragonal plate-shaped alumina.

[0032] Comparative Example 4 Commercially available boehmite was calcined at 550°C for 4 hours. 67g of a 20% tetraethylammonium hydroxide solution and 15g of anhydrous ethanol were weighed to form a mixed solution. This solution, along with 5g of calcined boehmite powder, was placed separately in a reaction vessel. The two solutions were isolated within the vessel using a small polytetrafluoroethylene (PTFE) beaker, with the ethanol-water solution of tetraethylammonium hydroxide on the outside of the beaker and the commercially available boehmite inside. The reaction was carried out at 200°C for 48 hours. After cooling, the solid powder was dried at 100°C for 6 hours and then calcined at 550°C for 6 hours. Figure 9 The scanning electron microscope images of the alumina prepared for this comparative example show two morphological samples: hexagonal lamellar alumina and tetragonal lamellar alumina.

Claims

1. A tabular alumina characterized by: The shape is a square sheet, has a single crystal structure, the grain size of the sheet-shaped alumina is 300-1300 nm, and the grain thickness is ≤150 nm, preferably 400-1000 nm.

2. The platelet-like alumina of claim 1, wherein: The two pairs of included angles of the square sheet-shaped alumina range from 68° to 85° and 95° to 112°, respectively.

3. A process for the production of the flaky alumina according to claim 1 or 2, characterized in that The method comprises the following steps: placing the calcined SB powder and a quaternary ammonium base solution in a pressure-resistant container for solid-liquid two-phase separation, carrying out a gas-solid reaction under certain heat treatment conditions, drying and calcining the solid powder after the reaction to obtain sheet-shaped alumina.

4. The method of claim 3, wherein: The calcination conditions of the SB powder are as follows: the calcination temperature is 450-650 ℃, and the calcination time is 2-8 hours.

5. The method of claim 3, wherein: The mass fraction of the quaternary ammonium base aqueous solution is 10%-25%, and the mass ratio of the quaternary ammonium base aqueous solution to the SB powder is 8:1-20:

1.

6. The method of claim 3, wherein: The quaternary ammonium base is selected from one or more of tetraethylammonium hydroxide, tetramethylammonium hydroxide and tetrapropylammonium hydroxide.

7. The method of claim 3, wherein: Anhydrous ethanol is added to the quaternary ammonium base aqueous solution, and the mass ratio of the anhydrous ethanol to the quaternary ammonium base aqueous solution is 0.1:1-0.3:

1.

8. The method of claim 3, wherein: The heat treatment conditions are as follows: the temperature is 120-250 ℃, preferably 160-220 ℃, and the time is 18-120 hours, preferably 24-96 hours.

9. The method of claim 3, wherein: The drying conditions of the solid powder after the reaction are as follows: the drying temperature is 80-120 ℃, and the drying time is 2-12 hours; and the calcination conditions are as follows: the calcination temperature is 450-650 ℃, and the calcination time is 4-10 hours.

10. The sheet-shaped alumina according to claim 1 or 2 can be applied in the fields of adsorption, catalysis and refractory materials.

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