Method for preparing superfine NANO spherical α-alumina

Abstract

The present application relates to the technical field of preparation of nano materials, and provides a method for preparing superfine nano spherical α-alumina. In the present application, an alumina powder raw material is evaporated in a high-temperature plasma environment, and the obtained gaseous alumina is quenched under the action of a quenching medium to obtain the superfine nano spherical α-alumina, wherein the temperature of the high-temperature plasma environment is higher than 5000 K, the cooling rate of the quenching is 500-10000 K / s, and the particle size of the superfine nano spherical α-alumina is 100 nm or less. In the present application, the alumina powder is completely evaporated in the high-temperature plasma environment, and then subjected to rapid quenching by controlling the quenching rate, and by means of the accurate regulation and control of the particle size and crystal phase of the alumina powder product, the nanoscale spherical α-alumina product is produced. The superfine nano spherical α-alumina, which has a particle size of 100 nm or less, is successfully prepared, and the obtained superfine nano spherical α-alumina has a uniform particle size and good dispersity.

Description

Method for preparing ultra-fine nanometer spherical alpha alumina

[0001] The present application claims priority to the Chinese patent application No. CN202411266069.9, filed on September 10, 2024, and entitled "Method for preparing ultra-fine nanometer spherical alpha alumina", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of nanometer material preparation, in particular to a method for preparing ultra-fine nanometer spherical alpha alumina. BACKGROUND

[0003] Nanometer corundum (alpha-Al2O3) has attracted extensive attention of researchers due to its excellent physical and chemical properties and broad application prospects. As a typical advanced inorganic non-metallic material, nanometer corundum has characteristics such as high strength, high hardness, high temperature resistance, oxidation resistance, wear resistance, good chemical stability and dielectric properties, and shows great application potential in many high-tech fields such as advanced ceramics, composite materials, functional coatings, catalyst carriers, and polishing of electronic and optical elements. However, it is still a great challenge to realize fine control synthesis of nanometer corundum particles, especially to obtain ultra-fine nanometer corundum particles with a specific surface area greater than 10 g / m 2 , and an average particle size less than 100 nm.

[0004] Currently, the synthesis technologies for ultra-fine nanometer alumina particles mainly include chemical induction high-energy ball milling method, flame spray pyrolysis method and liquid phase co-precipitation calcination method. The chemical induction high-energy ball milling method can prepare ultra-fine alpha phase alumina, but cannot obtain spherical alumina; the flame spray pyrolysis method and the liquid phase co-precipitation calcination method can prepare spherical alumina, but cannot obtain alpha phase alumina.

[0005] SUMMARY

[0006] Therefore, the purpose of the present application is to provide a method for preparing ultra-fine nanometer spherical alpha alumina. The present application successfully prepares ultra-fine nanometer spherical alpha alumina with a particle size of less than 100 nm and good dispersibility, and the process is simple.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] The present application provides a method for preparing ultra-fine nanometer spherical alpha alumina, comprising the following steps:

[0009] evaporating an alumina powder raw material in a high-temperature plasma environment, quenching gaseous alumina obtained under the action of a quenching medium to obtain the ultra-fine nanometer spherical alpha alumina;

[0010] The temperature of the high-temperature plasma environment is greater than 5000K, the cooling rate of the quenching is 500-10000K / s, and the particle size of the superfine nanometer spherical alpha alumina is less than 100nm.

[0011] Preferably, the high-temperature plasma environment is formed by exciting a thermal plasma, the thermal plasma is an arc plasma, a radio frequency plasma or a microwave plasma, the working gas of the thermal plasma is one or more of nitrogen, helium, argon, hydrogen and carbon dioxide, and the flow rate of the working gas is 0.1-800m 3 / h.

[0012] Preferably, the thermal plasma is excited by using a high-voltage direct-current power source or a high-frequency power source, and the power of the high-voltage direct-current power source or the high-frequency power source is 0.5-500kW.

[0013] Preferably, the alumina powder raw material is alpha alumina and / or gamma alumina, and the particle size of the alumina powder raw material is 0.1-50μm.

[0014] Preferably, the alumina powder raw material is delivered by a carrier gas, and the carrier gas is one or more of nitrogen, helium, argon, hydrogen and carbon dioxide.

[0015] Preferably, the feeding rate of the alumina powder raw material is 0-50kg / h, the flow rate of the carrier gas is 0-10m 3 / h, and neither the feeding rate of the alumina powder raw material nor the flow rate of the carrier gas is 0.

[0016] Preferably, the quenching medium is one or more of nitrogen, argon, hydrogen, helium, carbon dioxide, air, dry ice, water and ethanol.

[0017] Preferably, the flow rate of the quenching medium is 0.1-100kg / h.

[0018] Preferably, the final temperature of the quenching is 800-2000℃.

[0019] Preferably, after the quenching, the product obtained by the quenching is filtered by a filter with a water cooling device and then calcined to obtain superfine nanometer spherical alpha alumina, the calcination temperature is 400-900℃, the calcination time is 1-10h, and the temperature rising rate for rising to the calcination temperature is 10℃ / min.

[0020] The application provides a method for preparing ultrafine nanometer spherical alpha alumina, which comprises the following steps: evaporating alumina powder raw material in a high-temperature plasma environment, and quenching gaseous alumina gas obtained in a quenching medium to obtain the ultrafine nanometer spherical alpha alumina; the temperature of the high-temperature plasma environment is greater than 5000K, the cooling rate of the quenching is 500-10000K / s, and the particle size of the ultrafine nanometer spherical alpha alumina is below 100nm. The application provides a new method for preparing spherical alumina by using plasma technology, in which the alumina powder raw material is in a high-temperature plasma environment (temperature greater than 5000K), due to a huge temperature difference, the powder particles are instantaneously heated to an evaporation state (atomic state), and then rapidly quenched in a quenching section, and then rapidly condensed to form nuclei, and the particle morphology is changed to spherical morphology due to the surface tension; the application realizes accurate regulation of the particle size and crystal phase of the alumina powder product by controlling the quenching rate (the evaporation state of the alumina is rearranged to form alpha phase), due to the very fast cooling rate, the powder particles can complete the phase change process of solid-liquid-gas to gas-liquid-solid in a very short time, and the process is dispersed by the airflow, so that the nanometer alpha alumina powder with good dispersity and spherical morphology can be obtained.

[0021] The alumina powder raw material can be continuously fed into the high-temperature plasma environment for reaction, so that the high-quality spherical alpha alumina ultrafine powder can be continuously and controllably produced, while the currently used chemical induction high-energy ball milling method, flame spray pyrolysis method and liquid phase coprecipitation calcination method are intermittent methods with low product yield. The application successfully prepares the ultrafine nanometer spherical alpha alumina with a particle size below 100nm, the obtained ultrafine nanometer spherical alpha alumina has uniform particle size and good dispersity, and the plasma preparation technology has the advantages of cheap and easily available raw material, fast reaction speed, high purity of the prepared product, and easy industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the plasma device for preparing the ultrafine nanometer spherical alpha alumina in the embodiment of the application, in which, 1 is a powder raw material gas supply device, 2 is an plasma torch gas supply device, 3 is a powder feeder, 4 is a high-voltage direct-current power supply or a high-frequency power supply, 5 is a plasma torch, 6 is a circulating water cooling device, 7 is a quencher, 8 is a powder filter, 9 is a tail gas cooling tank, and 10 is a quenching medium supply device.

[0023] Figure 2 is a scanning electron microscope (SEM) image of the alpha alumina raw material used in the embodiment;

[0024] Figure 3 is an XRD crystal diffraction pattern of the gamma alumina raw material and the alpha alumina raw material used in the embodiment;

[0025] Figure 4 is an SEM image of the spherical nanometer alumina at the quenching rate in Example 1;

[0026] Figure 5 is an SEM image of the spherical nano-alumina at the quenching rate of Example 2;

[0027] Figure 6 is an SEM image of the spherical nano-alumina at the quenching rate of Example 3;

[0028] Figure 7 is an SEM image of the spherical nano-alumina at the quenching rate of Example 4;

[0029] Figure 8 is an SEM image of the spherical nano-alumina at the quenching rate of Example 5;

[0030] Figure 9 is an XRD image of the spherical nano-alumina at different quenching rates of Examples 1-5, wherein A-E correspond to Examples 1-5, respectively;

[0031] Figure 10 is an XRD image of the spherical nano-alumina obtained after plasma treatment of raw materials of Examples 6 and 7;

[0032] Figure 11 is an XRD image of the spherical nano-alumina obtained after treatment of the quenching medium of Examples 7-10. DETAILED DESCRIPTION

[0033] The present application provides a method for preparing ultra-fine nano-spherical α-alumina, comprising the following steps:

[0034] evaporating the alumina powder raw material in a high-temperature plasma environment, and quenching the obtained gaseous alumina gas under the action of a quenching medium to obtain the ultra-fine nano-spherical α-alumina;

[0035] The temperature of the high-temperature plasma environment is greater than 5000K, the cooling rate of the quenching is 500-10000K / s, and the particle size of the ultra-fine nano-spherical α-alumina is less than 100nm.

[0036] In the present application, all the raw materials / components are commercially available products well known to those skilled in the art, unless otherwise specified.

[0037] In the present application, the temperature of the high-temperature plasma environment is greater than 5000K; the high-temperature plasma environment is preferably formed by exciting a thermal plasma, which is preferably an arc plasma, a radio frequency plasma or a microwave plasma. The present application preferably uses a high-voltage direct current power source or a high-frequency power source to excite the thermal plasma, when the thermal plasma is an arc plasma, the excitation power source is a high-voltage direct current power source, and when the thermal plasma is a radio frequency plasma or a microwave plasma, the excitation power source is a high-frequency power source. The present application obtains an arc plasma, a radio frequency plasma or a microwave plasma by changing the type of power source. In the present application, the power of the high-voltage direct current power source or the high-frequency power source is preferably 0.5-500kW, more preferably 15-30kW. In the present application, the working gas (i.e. the gas for generating plasma) of the thermal plasma is preferably one or more of nitrogen, helium, argon, hydrogen and carbon dioxide gas, and the flow rate of the working gas is preferably 0.1-800m 3 / h, further preferably 0.5-500m 3 / h, more preferably 3-100m 3 / h.

[0038] In the present application, the alumina powder raw material is preferably α-alumina and / or γ-alumina, and the particle size of the alumina powder raw material is preferably 0.1-50μm, i.e. the present application uses micron or nanometer α-alumina and / or γ-alumina as the raw material. In the present application, the purity of the alumina powder raw material is preferably 4N grade.

[0039] In the present application, the alumina powder raw material is preferably delivered by a carrier gas, which is preferably one or more of nitrogen, helium, argon, hydrogen and carbon dioxide gas. In the present application, the feeding rate of the alumina powder raw material is preferably 0-50kg / h, and is not 0, and in the embodiments of the present application, the feeding rate of the alumina powder raw material is 1-20g / min, which can be specifically 1, 5, 10, 15 or 20g / min. In the present application, the flow rate of the carrier gas is preferably 0-10m 3 / h, preferably 0.1-5m 3 / h, more preferably 0.4-2.5m 3 / h.

[0040] The present application controls the feeding amount and residence time of the alumina powder raw material (controls the flow rate of the carrier gas) and the operating power of the plasma power source, thereby controlling the speed of the raw material passing through the high-temperature plasma environment (plasma high-temperature zone), so that the alumina raw material is completely evaporated in the thermal plasma atmosphere of the high-temperature plasma environment.

[0041] In the present application, the quenching medium is preferably one or more of nitrogen, argon, hydrogen, helium, carbon dioxide, air, dry ice, water and ethanol, and the temperature of the quenching medium is room temperature. In the embodiments of the present application, the quenching medium is preferably a mixed medium of nitrogen, supersaturated water vapor and nitrogen, or a mixed medium of supersaturated ethanol vapor and nitrogen. In the present application, the flow rate of the quenching medium is preferably 0.1-100 kg / h, and is not 0, more preferably 0.5-50 kg / h, and further preferably 3-30 kg / h. In the present application, the cooling rate of the quenching is preferably 500-10000 K / s, and can be specifically 500 K / s, 1000 K / s, 3000 K / s, 6000 K / s, 9000 K / s; and the final temperature of the quenching is preferably 800-2000℃.

[0042] In the present application, the completely evaporated alumina raw material is rapidly quenched to form stable nanoscale spherical α-alumina product by condensation crystallization. By selecting and controlling the cooling medium, including the flow rate of the gaseous quenching medium (such as argon, nitrogen, etc.) and / or the entrainment of the liquid quenching medium, the present application regulates the quenching rate to achieve rapid and accurate regulation of the particle size and crystal phase of the alumina powder product. Due to the very fast cooling rate, the particles can complete the phase change process from solid-liquid-gas to gas-liquid-solid in a very short time, and the process is dispersed by the gas flow, so that the alumina product does not agglomerate, and the particles have high dispersibility, and therefore the nanoscale α-alumina powder with uniform particle size, good dispersibility and spherical morphology can be obtained.

[0043] In the embodiments of the present application, the plasma device shown in FIG. 1 is preferably used to prepare ultrafine nanoscale spherical α-alumina. In the present application, the plasma device comprises:

[0044] a powder raw material gas supply device 1 for providing a carrier gas for conveying the powder raw material;

[0045] a powder feeder 3 in communication with the outlet of the powder raw material gas supply device 1;

[0046] a plasma torch 5 (i.e. a plasma generator) in communication with the outlet of the powder feeder 3, the plasma torch 5 is connected with a high-voltage direct-current power supply or a high-frequency power supply 4, and is in communication with a plasma torch gas supply device 2 for providing working gas for the plasma; a cold water jacket is provided on the inner wall of the plasma torch 5, and the circulating water of a circulating water cooling device 6 enters the cold water jacket to ensure that the device will not be burned out;

[0047] a quencher 7 in communication with the lower part of the reaction cavity of the plasma torch 5, the quencher 7 is in communication with a quenching medium supply device 10;

[0048] A powder filter 8 with a water cooling device, which is connected to the outlet of the quenching device 7;

[0049] and a tail gas cooling tank 9, which is connected to the tail gas outlet of the powder filter 8, and the tail gas outlet of the tail gas cooling tank 9 is connected to the quenching medium inlet of the quenching device 7.

[0050] The process for preparing ultra-fine nanometer spherical alpha alumina by using the plasma device in the embodiment of the application is as follows (taking plasma as arc plasma, plasma working gas as argon, and quenching medium as gas medium as examples):

[0051] First, the circulating water cooling device 6 is started, argon is filled into the plasma generator of the plasma device, after all the gas is replaced by argon, high-voltage power is provided by a high-voltage direct current power supply or a high-frequency power supply, then the arc is pulled out by short-circuiting the anode and cathode of the arc cylinder, and the excitation coil is started to constrain the arc position to the lower part of the cathode tip, thereby forming a uniform and stable plasma high-temperature area. This large-area plasma area is called "diffused or dispersed 'arc plasma' " due to its relatively uniform and low-density state, and the average temperature is more than 5000K;

[0052] After the arc of the device is stabilized, the flow rates of the corresponding working gas, carrier gas and quenching gas are adjusted, the device power reaches the set value, the powder feeder is started, and the alumina powder raw material is pushed out of the hopper and then carried into the plasma high-temperature area by the carrier gas. Due to the huge temperature difference, the particles are instantaneously heated to the evaporation state;

[0053] Then the evaporation-state material enters the quenching device at the lower part of the plasma reaction chamber, the quenching medium is supplied by the quenching medium supply device at a certain flow rate, the powder vapor is instantaneously and uniformly quenched by the high-speed quenching medium, the particles rapidly nucleate and condense, and the particle morphology becomes spherical morphology with good dispersibility due to the surface tension;

[0054] After that, the prepared ultra-fine nanometer spherical alpha alumina is collected in the filter and further cooled, and the generated tail gas is cooled in the tail gas cooling tank and can be recycled to the quenching section as quenching medium.

[0055] In the embodiment of the application, the plasma device is used, the carrier gas continuously sends the alumina powder raw material into the plasma torch for reaction, so that high-quality spherical ultra-fine nanometer alpha alumina powder can be continuously and controllably produced. Moreover, the process is simple, easy to operate, low in production cost, high in production efficiency, and suitable for industrial production.

[0056] The application also preferably calcines the ultra-fine nanometer spherical alpha alumina collected in the filter. In the application, the temperature of the calcination is preferably 400-900°C, more preferably 500-700°C, the time is preferably 1-10h, more preferably 2-6h, and the temperature rising rate to the temperature of the calcination is preferably 10°C / min. In the application, the calcination is preferably carried out in a tube furnace or a muffle furnace, and both the furnace tube and the crucible are made of corundum. The application removes impurities by the calcination, such as removing carbon evaporated and adhered to the powder at high temperature from the electrode of the thermal plasma excitation power source (mainly graphite electrode). After the calcination, the product is slowly cooled to room temperature.

[0057] In the application, the particle size of the ultra-fine nanometer spherical alpha alumina is 100nm or less, the specific surface area is 10-100g / m 2 , and the purity after the calcination is 4N grade.

[0058] In order to further illustrate the application, the method for preparing ultra-fine nanometer spherical alpha alumina provided by the application is described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the application.

[0059] The alumina raw material (Al2O3) used in the following examples is a flaky micron (1-5μm) γ or α phase raw material. Fig. 2 is a scanning electron microscope image of the α alumina raw material used in the examples, and Fig. 3 is an XRD crystal diffraction pattern of the γ alumina raw material (Raw γ-Al2O3) and the α alumina raw material (Raw α-Al2O3) used in the examples.

[0060] Example 1

[0061] Preparation of ultra-fine nanometer spherical alpha alumina:

[0062] A magnetic rotating arc plasma torch (the operating power of the plasma arc is 15kW) is used to generate a thermal plasma, wherein the thermal plasma is generated by nitrogen gas with a flow rate of 0.6m 3 / h, and the temperature of the high temperature zone of the generated thermal plasma is greater than 5000K; a carrier gas (nitrogen gas with a flow rate of 0.5Nm 3 / h) is used to transport the α phase alumina raw material (the feeding amount is 1g / min), and the alumina raw material is completely evaporated under the action of the thermal plasma; the completely evaporated alumina particles are condensed under the condition of nitrogen gas as a quenching medium and a quenching rate of 500K / s, and then collected, the final quenching temperature is less than 1000°C, and the product is collected in a filter with a water cooling device, and then calcined at 700°C for 2h and cooled to room temperature to obtain the ultra-fine nanometer spherical alpha alumina.

[0063] Example 2

[0064] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 1, with the difference from Example 1 being that the quenching rate was 1000 K / s.

[0065] Example 3

[0066] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 1, with the difference from Example 1 being that the quenching rate was 3000 K / s.

[0067] Example 4

[0068] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 1, with the difference from Example 1 being that the quenching rate was 6000 K / s.

[0069] Example 5

[0070] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 1, with the difference from Example 1 being that the quenching rate was 9000 K / s.

[0071] Example 6

[0072] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 5, with the difference from Example 5 being that the quenching medium was a mixed medium of supersaturated ethanol vapor and nitrogen.

[0073] Example 7

[0074] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 6, with the difference from Example 6 being that the raw material was γ-phase alumina.

[0075] Example 8

[0076] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 7, with the difference from Example 7 being that the quenching medium was a mixed medium of supersaturated water vapor and nitrogen.

[0077] Example 9

[0078] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 7, with the difference from Example 7 being that the quenching medium was dry ice (powder).

[0079] Example 10

[0080] The ultrafine nanometer spherical α-alumina was prepared according to the method of Example 7, with the difference from Example 7 being that the quenching medium was nitrogen.

[0081] Figures 4 to 8 are SEM images of the spherical nanometer alumina at different quenching rates according to Examples 1 to 5, respectively. As shown in Figures 4 to 8, the particle size distribution is below 100 nm, and the particle size decreases with the increase of the quenching rate, so that the average particle size can be controlled.

[0082] Figure 9 is an XRD pattern of the spherical nano-alumina prepared in Examples 1-5 at different quenching rates. In Figure 9, A is Example 1, B is Example 2, C is Example 3, D is Example 4, and E is Example 5. As shown in Figure 9, the content of the alpha phase of the product increases with the increase of the quenching rate, and pure alpha phase nano-spherical alumina can be finally produced.

[0083] The spherical nano-alumina prepared in Examples 6-10 has a particle size of less than 100 nm.

[0084] Figure 10 is an XRD pattern of the spherical nano-alumina prepared in Examples 6 and 7 after plasma treatment of the raw material. In Figure 10, Raw alpha / ethanol represents Example 6, and Raw gamma / ethanol represents Example 7. As shown in Figure 10, when the crystal phase of the alumina raw material is gamma phase, the method of the present application can rearrange the crystal phase of the product to form alpha phase alumina.

[0085] Figure 11 is an XRD pattern of the spherical nano-alumina prepared in Examples 7-10 after treatment with different quenching media. In Figure 11, ethanol represents Example 7, H2O represents Example 8, dry ice represents Example 9, and N2 represents Example 10. As shown in Figure 11, when the quenching medium is entrained, the latent heat of the medium can be used to increase the cooling rate, and finally pure alpha phase nano-alumina product is obtained.

[0086] The above description is only the preferred embodiments of the present application, and does not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing ultrafine nanospherical α-alumina, characterized by, The method comprises the following steps: The alumina powder raw material is evaporated in a high-temperature plasma environment, and the gaseous alumina obtained is quenched by a quenching medium to obtain the superfine nanometer spherical alpha alumina. The temperature of the high-temperature plasma environment is greater than 5000K, the cooling rate of the quenching is 500-10000K / s, and the particle size of the superfine nanometer spherical alpha alumina is less than 100nm.

2. The method of claim 1, wherein, The high-temperature plasma environment is formed by exciting a thermal plasma, the thermal plasma is an arc plasma, a radio frequency plasma or a microwave plasma, the working gas of the thermal plasma is one or several of nitrogen, helium, argon, hydrogen and carbon dioxide, and the flow rate of the working gas is 0.1-800 m 3 / h.

3. The method of claim 2, wherein, The working gas flow rate is 0.5-500 m 3 / h.

4. The method of claim 2, wherein, The high-temperature plasma is excited by a high-voltage direct-current power supply or a high-frequency power supply, and the power of the high-voltage direct-current power supply or the high-frequency power supply is 0.5-500kW.

5. The method of claim 4, wherein, The power of the high-voltage direct-current power supply or the high-frequency power supply is 15-30kW.

6. The method of claim 1, wherein, The alumina powder raw material is alpha alumina and / or gamma alumina, and the particle size of the alumina powder raw material is 0.1-50μm.

7. The method according to claim 1 or 6, characterized in that, The alumina powder raw material is transported by a carrier gas, and the carrier gas is one or more of nitrogen, helium, argon, hydrogen and carbon dioxide.

8. The method of claim 7, wherein, The feed rate of the alumina powder raw material is 0-50 kg / h, the flow rate of the carrier gas is 0-10 m 3 / h, and neither the feed rate of the alumina powder raw material nor the flow rate of the carrier gas is 0.

9. The method of claim 8, wherein, The feed rate of the alumina powder feedstock is 1 to 20 g / min, and the flow rate of the carrier gas is 0.1 to 5 m 3 / h.

10. The method of claim 1, wherein, The quenching medium is one or more of nitrogen, argon, hydrogen, helium, carbon dioxide, air, dry ice, water and ethanol.

11. The method of claim 10, wherein, The flow rate of the quenching medium is 0.1-100kg / h.

12. The method of claim 1, 10 or 11, wherein, The cooling rate of the quenching is 1000-9000K / s.

13. The method of claim 1, 10 or 11, wherein, The final temperature of the quenching is 800-2000℃.

14. The method of claim 1, wherein, After the quenching, the product obtained by the quenching is filtered by a filter with a water cooling device, calcined to obtain the superfine nanometer spherical alpha alumina, the calcination temperature is 400-900℃, the calcination time is 1-10h, the temperature rising rate to the calcination temperature is 10℃ / min.

15. The method of claim 14, wherein, The calcination temperature is 500-700℃.

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