Device and method for preparing high-purity alumina micropowder by direct oxidation of liquid aluminum

Abstract

The application provides a device for preparing high-purity alumina micropowder by directly oxidizing liquid aluminum, comprising an aluminum melting furnace and an oxidation furnace, wherein the aluminum melting furnace is used for melting an aluminum source to obtain high-temperature liquid aluminum, and the high-temperature liquid aluminum is input into the oxidation furnace through a pipeline; a liquid aluminum feeding port and an alumina powder pneumatic output port are arranged above the oxidation furnace, the liquid aluminum feeding port is connected with the aluminum melting furnace, and an oxygen and argon mixed gas inlet is arranged below the oxidation furnace and is used for inputting mixed gas to form bubbles in the liquid aluminum, and an alumina film formed by the reaction between oxygen in the mixed gas and the liquid aluminum is around the bubbles. In the application, the oxygen in the mixed gas is reacted with the liquid aluminum in the high-temperature liquid aluminum to prepare alumina powder. The nanoscale alumina powder is obtained by breaking the bubbles, and the alumina powder is pneumatically transported out by argon. Compared with the prior art, the application has the advantages of simple process, short flow, high purity (4N-6N) of the prepared alumina micropowder, uniform nanoscale powder particle size, and high industrialized, continuous production yield.

Description

Technical Field

[0001] This invention belongs to the field of inorganic compounds and relates to an apparatus and method for preparing alumina micro powder, particularly an apparatus and method for preparing high-purity alumina micro powder by direct oxidation of liquid aluminum. Background Technology

[0002] Alumina is a white crystalline powder. High-purity alumina is typically defined as 3N (99.9% purity) or higher, including 4N (99.99% purity) and 5N (99.999% purity). High-purity alumina is characterized by good sintering performance, good dispersibility, and porosity. It also possesses excellent mechanical, thermal, and chemical properties, and is widely used in the LED industry, rare-earth tri-color phosphors, fine ceramics, sapphire crystal production, lithium-ion battery ceramic separators, integrated circuits, and catalyst supports. With the rapid development of high-tech industries such as 5G communications, rail transportation, and aerospace and military, the global annual demand for high-purity alumina is projected to grow at an average rate exceeding 20%.

[0003] Currently, the main methods for preparing high-purity alumina powder in industrial applications include aluminum choline hydrolysis, aluminum isopropoxide hydrolysis, and ammonium aluminum sulfate pyrolysis. Aluminum choline hydrolysis is the primary method for producing 4N powder (99.99% purity). However, this method requires processing aluminum into sheets or powder, easily introducing impurities, and the finished product cannot be purified, with a maximum purity of only 4N (99.99%). Aluminum isopropoxide hydrolysis involves synthesizing, purifying, hydrolyzing, and calcining aluminum and isopropanol with a catalyst to produce high-purity ultrafine alumina powder. This is currently the main method for producing 5N powder (99.999% purity). This method offers strong purity control and small particle size; however, it uses alcohol, requires high temperature and pressure, resulting in high production costs and a long process. Ammonium aluminum sulfate pyrolysis has a long production cycle, involves thermal dissolution, and the SO2 and NH3 produced during decomposition cause serious environmental pollution; therefore, this method is being gradually phased out.

[0004] The analysis of the above-mentioned prior art is as follows:

[0005] 1. The choline-aluminum hydrolysis method includes the following steps: First, high-purity aluminum blocks are cut into aluminum foil or powder with a thickness of about 0.1 mm using a cutting tool. Then, choline chloride is converted into choline using a strong anion exchange resin. Next, a certain amount of aluminum foil is added to a choline solution with a concentration of 0.1-0.2% for reaction. The hydrolysis reaction temperature should be controlled at around 80℃. During the reaction, the reaction rate is judged by the rate of hydrogen escape. When the reaction rate is very low or stops, the slurry is removed for solid-liquid separation. Simultaneously, refined aluminum is periodically added to circulate the above process. The aluminum hydroxide produced by the hydrolysis reaction is filtered, spray-dried, and calcined for phase inversion to obtain fine alumina powder. This technology does not involve a purification process. The use of cutting tools to make aluminum foil from aluminum blocks easily introduces impurities, and the highest product purity can only reach 99.99%. The choline method is currently the largest-scale 4N-grade alumina production method in China. It can only be used to produce industrial gemstones and low-end sapphire. The main drawback of this process is that it cannot be further purified; the grade of the raw material determines the grade of the produced alumina, and it is impossible to exceed the raw material level. Furthermore, during the hydrolysis process, in order to increase the reaction contact area, the aluminum material needs to be processed into sheets or powder. This process can easily introduce impurities such as Fe, Ti, Ni, and Zr. These impurities have a significant impact on the quality of sapphire.

[0006] 2. Aluminum alkoxide hydrolysis method

[0007] The aluminum alkoxide hydrolysis method involves synthesizing, purifying, hydrolyzing, and calcining aluminum and isopropanol with a catalyst to produce high-purity ultrafine alumina powder. Purification includes distillation and rectification; distillation yields a lower purity than rectification. The process includes the following steps: first, aluminum flakes are added to isopropanol to react and produce aluminum isopropoxide; then, aluminum isopropoxide is purified by distillation and rectification, hydrolyzed to produce hydrated cobalt oxide, and then decomposed by heating to obtain alumina. Alumina produced by this method can achieve a purity of 5N, or even 6N. Currently, high-purity alumina used in the LED sapphire crystal growth industry in Japan and the United States is mainly produced using this process. This process is relatively complex, but its main advantages are:

[0008] 1) High-purity aluminum reacts quickly with alcohols and does not need to be processed into powder or foil, thus avoiding the introduction of metal impurities during processing.

[0009] 2) The aluminum isopropoxide obtained from the reaction can be collected in gaseous form through distillation, effectively removing metallic impurities such as iron, titanium, nickel, cobalt, lead, and magnesium. The condensed high-purity aluminum isopropoxide can be further purified to remove free metallic impurities such as potassium, sodium, and zinc. This is something that other processes cannot achieve.

[0010] This method produces alumina powder with high purity and small particle size. The process offers strong control over product purity, meeting the requirements for sapphire crystal growth. However, this process requires the use of alcohol and demands high temperature and pressure, resulting in high product costs. Because of the high purity of the product produced, only sapphire crystals grown from alumina of this purity meet the requirements for LED substrates. Therefore, manufacturers worldwide producing high-quality 5N alumina have chosen the aluminum alkoxide method, and Sumitomo Chemical, the world's largest producer of 5N alumina, also uses this method.

[0011] 3. Aluminum ammonium sulfate pyrolysis method

[0012] The aluminum sulfate ammonium pyrolysis method requires first dissolving aluminum hydroxide in sulfuric acid to obtain an aluminum sulfate solution. Then, ammonium sulfate is added to the solution to react with the aluminum sulfate and produce ammonium vanadium. This ammonium vanadium is then recrystallized multiple times according to purity requirements to obtain refined ammonium vanadium. Finally, the refined ammonium vanadium is decomposed at 1250℃ to obtain alumina powder.

[0013] Although this method is relatively simple and low-cost, it has a long production cycle, suffers from thermal dissolution, and produces SO3 and NH3 that cause serious environmental pollution. Therefore, this method is being phased out.

[0014] The drawback of this method is that it is difficult to remove ions such as metallic iron, nickel, titanium, and cobalt, as well as halogen elements. The purity can only reach a maximum of 4N, which is basically the limit. In terms of purity, it has a major defect and cannot prepare large-size sapphire crystals, thus failing to meet high-end requirements.

[0015] 4. Currently, the publicly available methods for preparing high-purity nano-alumina powder using high-temperature liquid aluminum include:

[0016] Patent applications CN02114666, CN200710016471, CN201410626394, and CN201510656825 all disclose methods for obtaining aluminum hydroxide by atomizing high-temperature liquid aluminum, followed by alumina powder through processes such as filtration, drying, calcination, and pulverization. These methods are carried out in aqueous solutions or come into contact with water, making it impossible to eliminate interference from ions such as sodium, potassium, and hydroxide, resulting in uncontrollable particle size and a long process.

[0017] Patent application CN201711056607 discloses a method and special device for preparing high-purity alumina powder by high-purity aluminum atomization rapid combustion method. It uses atomized liquid aluminum droplets to react directly with oxygen to generate alumina powder. This method requires high-purity aluminum, which is costly. The particle size of the alumina powder generated after atomization cannot be controlled, and the reaction of liquid aluminum droplets is incomplete.

[0018] In summary, the above analysis shows that among existing industrial applications, the aluminum choline hydrolysis method requires processing aluminum into sheets or powders, which easily introduces impurities, and the finished product cannot be purified, with a maximum purity of only 4N (99.99%) and a long production process. The aluminum isopropoxide hydrolysis method offers strong purity control and small particle size, but it uses alcohol, requires high temperature and pressure, resulting in high production costs and a long process. The ammonium aluminum sulfate pyrolysis method has a long production cycle, involves thermal dissolution, and the SO3 and NH3 produced during decomposition cause serious environmental pollution. Therefore, the published methods using high-temperature liquid aluminum suffer from problems such as long processes, impurities, high costs, and incomplete reactions.

[0019] Therefore, it is necessary to develop a new technology for preparing high-purity nano-alumina powder with low cost and short process to solve the above-mentioned technical problems. Summary of the Invention

[0020] To address the aforementioned technical problems, this invention provides an apparatus and method for preparing high-purity alumina micropowder through direct oxidation of liquid aluminum, utilizing high-temperature liquid aluminum. The technical solution of this invention is as follows:

[0021] This invention provides an apparatus for the direct oxidation of liquid aluminum to prepare high-purity alumina micro powder, comprising an aluminum melting furnace and an oxidation furnace, wherein,

[0022] The aluminum melting furnace is used to melt aluminum source to obtain high-temperature liquid aluminum, and the high-temperature liquid aluminum is fed into the oxidation furnace through pipelines.

[0023] The oxidation furnace is equipped with a liquid aluminum feeding port and an alumina powder pneumatic output port at the top. The liquid aluminum feeding port is connected to the aluminizing furnace. The oxidation furnace is equipped with an oxygen-argon mixed gas inlet (hereinafter referred to as mixed gas) at the bottom, which is used to introduce mixed gas and form mixed gas bubbles in the liquid aluminum.

[0024] Preferably, a valve is provided on the connecting pipeline between the liquid aluminum feeding port and the aluminum melting furnace.

[0025] Preferably, the bottom of the oxidation furnace is provided with multiple mixed gas injection ports, which are connected to a mixed gas inlet located outside the oxidation furnace.

[0026] Preferably, the oxidation furnace is equipped with an electric stirrer, which includes a stirring rod and blades, both of which are located below the surface of the liquid aluminum.

[0027] The present invention also provides a method for directly oxidizing and preparing high-purity alumina micro powder using the aforementioned apparatus, comprising the following steps:

[0028] 1) Put the aluminum source into the aluminum melting furnace and heat it until the aluminum source is completely melted. Then open the valve to transport the high-temperature liquid aluminum into the oxidation furnace filled with mixed gas. After the liquid level in the oxidation furnace reaches the specified height, close the valve.

[0029] Preferably, the aluminum source is selected from at least one of industrial aluminum blocks, industrial aluminum powder, cleaned waste aluminum, and aluminum alloys.

[0030] Preferably, the heating temperature of the aluminum melting furnace is 850℃-1000℃.

[0031] Preferably, a certain space is left above the liquid aluminum surface in the oxidation furnace.

[0032] 2) Mixed gas is introduced into the oxidation furnace from the mixed gas inlet at the bottom of the oxidation furnace. The mixed gas enters the liquid aluminum through multiple mixed gas injection nozzles and forms mixed gas bubbles in the liquid aluminum. During the rising process of the bubbles, the oxygen in the mixed gas reacts with the liquid aluminum, and the oxygen on the outer periphery of the bubbles reacts with the liquid aluminum to form a thin film of aluminum oxide.

[0033] Preferably, the thickness of the alumina film is 0.01-0.3 μm.

[0034] Preferably, the oxygen content in the mixed gas is 10%-30%, with the remainder being nitrogen, and the purity of both oxygen and argon is not less than 99.99%, with a supply rate of 10-100 L / min.

[0035] The temperature inside the oxidation furnace is 1000-1300℃.

[0036] 3) While alumina bubble film is generated and floats to the surface in the high-temperature liquid aluminum, the electric stirrer built into the oxidation furnace rotates and the blades break the rising bubble film, generating nano-sized alumina particles that continue to float to the surface of the liquid aluminum. After the bubble film in the liquid aluminum is broken, the mixed gas wrapped in it is released, and the oxygen in it continues to react with the liquid aluminum to generate alumina bubble film and alumina powder.

[0037] Preferably, the electric stirrer rotates at a speed of 300-1000 RPM.

[0038] 4) After the bubbles rise to the surface of the liquid aluminum, they burst and the alumina film breaks into nano-sized powder, which, together with the nano-sized alumina particles generated in the liquid aluminum, is dispersed by the airflow in the space above the liquid aluminum surface.

[0039] Preferably, the average particle size of the nanoscale powder is 0.05-0.5 μm.

[0040] 5) A positive pressure is maintained above the liquid aluminum surface in the oxidation furnace. The scattered alumina powder is pneumatically transported into the radiator by argon gas in the mixed gas through the alumina powder pneumatic output port at the top for cooling.

[0041] Preferably, the temperature of the radiator area does not exceed 260°C.

[0042] 6) The cooled alumina powder and argon enter the gas-powder separation device to separate the alumina powder for collection, and the argon enters the mixed gas supply device for recycling.

[0043] The alumina powder has a particle size of 0.05-0.5 μm and an alumina purity of 99.99% (4N) or higher.

[0044] The present invention has the following beneficial effects:

[0045] This invention utilizes an oxygen-argon mixture introduced into high-temperature liquid aluminum to form bubbles. The oxygen in the bubbles reacts with the liquid aluminum to prepare alumina powder. The bubbles are then broken up to obtain nano-sized alumina powder. Compared with existing technologies, this invention features a simpler process, shorter flow, and produces alumina micro-powder with high purity (4N-6N). The nano-sized powder has uniform particle size and can be industrialized for continuous production with high output. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a structural diagram of the apparatus for preparing high-purity alumina micro powder by direct oxidation of liquid aluminum according to the present invention.

[0048] Among them, 1-alumina melting furnace; 2-high temperature liquid aluminum; 3-valve; 4-oxidation furnace; 5-oxygen-argon mixed gas inlet; 6-oxygen-argon mixed gas injection port; 7-electric stirrer; 8-alumina powder pneumatic output port; 9-stirring rod and blades; 10-liquid aluminum feeding port. Detailed Implementation

[0049] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0050] This invention provides an apparatus for the direct oxidation of liquid aluminum to prepare high-purity alumina micro powder, such as... Figure 1 As shown, it includes an aluminum melting furnace 1 and an oxidation furnace 4, wherein,

[0051] The aluminum melting furnace 1 is used to melt the aluminum source to obtain high-temperature liquid aluminum 2, and the high-temperature liquid aluminum 2 is fed into the oxidation furnace 4 through a pipeline.

[0052] The oxidation furnace 4 is equipped with a liquid aluminum feeding port 10 and an alumina powder pneumatic output port 8 above it. The liquid aluminum feeding port 10 is connected to the aluminum melting furnace 1. The oxidation furnace 4 is equipped with an oxygen-argon mixed gas inlet 5 below it, which is used to introduce mixed gas and form mixed gas bubbles in the liquid aluminum. The oxygen in the mixed gas around the bubbles reacts with the liquid aluminum to form an alumina film. When the bubbles rise to the surface of the liquid aluminum, the bubbles burst, and the alumina film breaks into nanoparticles, which enter the space above the liquid aluminum and are collected through the alumina powder pneumatic output port 8.

[0053] In one embodiment of the present invention, a valve 3 is provided on the connecting pipeline between the liquid aluminum feeding port 10 and the aluminum melting furnace 1, for inputting liquid aluminum into the oxidation furnace 4 in stages.

[0054] In one embodiment of the present invention, the bottom of the oxidation furnace 4 is provided with a plurality of oxygen-argon mixed gas injection ports 6, which are connected to a mixed gas inlet 5 located outside the oxidation furnace 4, for forming fine mixed gas bubbles in the liquid aluminum and increasing the contact area between the bubbles and the liquid aluminum.

[0055] In one embodiment of the present invention, the oxidation furnace 4 is provided with an electric stirrer 7, which includes a stirring rod and blades 9. The stirring rod and blades 9 are both located below the liquid aluminum surface and are used to break up the rising mixed gas bubble film to increase the number of gas-liquid reactions.

[0056] The present invention also provides a method for directly oxidizing and preparing high-purity alumina micro powder using the aforementioned apparatus, comprising the following steps:

[0057] 1) Put the aluminum source into the aluminum melting furnace 1 and heat it until the aluminum source is completely melted. Then open the valve 3 to transport the high-temperature liquid aluminum 2 into the oxidation furnace 4 filled with mixed gas. After the liquid level in the oxidation furnace 4 reaches the specified height, close the valve 3.

[0058] In one embodiment of the present invention, the aluminum source is selected from at least one of industrial aluminum blocks, industrial aluminum powder, cleaned waste aluminum, and aluminum alloys.

[0059] In one embodiment of the present invention, the heating temperature of the aluminum melting furnace 1 is 850℃-1000℃, at which high-temperature liquid aluminum 2 is obtained in the aluminum melting furnace 1, and the temperature of the high-temperature liquid aluminum 2 is the same as the heating temperature of the aluminum melting furnace 1. The heating method of the aluminum melting furnace 1 is not limited to electric furnace heating, electric arc heating, or silicon molybdenum rod heating, etc.

[0060] In one embodiment of the present invention, a certain space is left above the liquid aluminum surface in the oxidation furnace 4 to allow alumina powder to escape after the alumina bubbles burst. Preferably, this space occupies 1 / 4 of the volume of the oxidation furnace 4.

[0061] 2) The mixed gas is introduced into the oxidation furnace 4 from the oxygen-argon mixed gas inlet 5 at the bottom of the oxidation furnace 4. The mixed gas enters the liquid aluminum through multiple oxygen-argon mixed gas injection nozzles 6, forming mixed gas bubbles in the liquid aluminum. During the rising process of the bubbles, the oxygen in the mixed gas reacts with the liquid aluminum, and the oxygen on the outer periphery of the bubbles reacts with the liquid aluminum to form a thin film of aluminum oxide.

[0062] In one embodiment of the present invention, the thickness of the alumina film is 0.01-0.3 μm.

[0063] In one embodiment of the present invention, the oxygen content in the mixed gas is 10%-30% (by volume), with the remainder being argon. The purity of both oxygen and argon is not less than 99.99%, and the supply rate is 10-100 L / min. The applicant's research has found that if pure oxygen is introduced or the oxygen content in the mixed gas is too high, there will be safety hazards. Maintaining the oxygen content in the mixed gas within this range allows for sufficient oxygen reaction and ensures that the gas released after bubble bursting is primarily argon, preventing excessive oxygen pressure within the oxidation furnace 4.

[0064] In one embodiment of the present invention, the temperature inside the oxidation furnace 4 is 1000-1300℃. If the temperature inside the oxidation furnace 4 is too low, the reaction rate is slow and the efficiency of alumina production is low; if the temperature is too high, the reaction is difficult to control and the molten aluminum is prone to volatilization.

[0065] The reaction equation for this step is: 4Al + 3O2 = 2Al2O3. The amount of liquid aluminum added to the oxidation furnace 4 is much greater than the amount of oxygen introduced into the mixed gas, which ensures that the liquid aluminum is in excess and the reaction continues.

[0066] 3) As alumina bubble film is generated and rises in the high-temperature liquid aluminum, the electric stirrer 7 built into the oxidation furnace 4 rotates, and the stirring rod and blades 9 break up the rising bubble film, generating nano-sized alumina particles that continue to float to the surface of the liquid aluminum. After the bubble film in the liquid aluminum breaks, the mixed gas trapped inside is released, and the oxygen in the mixed gas continues to react with the liquid aluminum to generate alumina bubble film and alumina powder.

[0067] In one embodiment of the present invention, the electric stirrer 7 operates at a speed of 300-1000 RPM. The stirring rod and blades of the electric stirrer can be made of high-temperature resistant materials such as graphite and corundum.

[0068] 4) After the bubbles rise to the surface of the liquid aluminum, they burst and the alumina film breaks into nano-sized powder, which, together with the nano-sized alumina particles generated in the liquid aluminum, is dispersed by the airflow in the space above the liquid aluminum surface.

[0069] In one embodiment of the present invention, the average particle size of the nanoscale powder is 0.05-0.5 μm.

[0070] 5) A positive pressure is maintained above the liquid aluminum surface inside the oxidation furnace 4. The scattered alumina powder is pneumatically transported into the radiator (not shown in the figure) by argon gas in the mixed gas through the alumina powder pneumatic output port 8 at the top for cooling.

[0071] In one embodiment of the present invention, considering that the temperature resistance of the bag filter dust collector used subsequently is typically 150-260℃, the temperature of the heat sink area does not exceed 260℃. The cooling method of the heat sink is not limited to air cooling, liquid cooling, etc.

[0072] 6) The cooled alumina powder and argon enter the gas-powder separation device to separate the alumina powder for collection, and the argon enters the mixed gas supply device for recycling.

[0073] The alumina powder has a particle size of 0.05-0.5 μm and an alumina purity of 99.99% (4N) or higher.

[0074] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. An apparatus for preparing high-purity alumina micro powder by direct oxidation of liquid aluminum, characterized in that, Including aluminum melting furnaces and oxidation furnaces, among which, The aluminum melting furnace is used to melt aluminum source to obtain high-temperature liquid aluminum, and the high-temperature liquid aluminum is fed into the oxidation furnace through pipelines. The oxidation furnace is equipped with a liquid aluminum feeding port and an alumina powder pneumatic output port above it. The liquid aluminum feeding port is connected to the aluminizing furnace. The oxidation furnace is equipped with an oxygen-argon mixed gas inlet below it, which is used to introduce the mixed gas and form bubbles in the liquid aluminum. The oxidation furnace is equipped with an electric stirrer, which includes a stirring rod and blades, both of which are located below the surface of the liquid aluminum.

2. The apparatus for preparing high-purity alumina micro powder by direct oxidation of liquid aluminum according to claim 1, characterized in that, A valve is installed on the connecting pipe between the liquid aluminum feeding port and the aluminum melting furnace.

3. The apparatus for preparing high-purity alumina micro powder by direct oxidation of liquid aluminum according to claim 2, characterized in that, The bottom of the oxidation furnace is provided with multiple mixed gas injection ports, which are connected to a mixed gas inlet located outside the oxidation furnace.

4. A method for directly oxidizing and preparing high-purity alumina micro powder using the apparatus according to any one of claims 1 to 3, characterized in that, Includes the following steps: 1) Put the aluminum source into the aluminum melting furnace and heat it until the aluminum source is completely melted. Then open the valve to transport the high-temperature liquid aluminum into the oxidation furnace filled with mixed gas. After the liquid level in the oxidation furnace reaches the specified height, close the valve. 2) Mixed gas is introduced into the oxidation furnace from the mixed gas inlet at the bottom of the oxidation furnace. The mixed gas enters the liquid aluminum through multiple mixed gas injection nozzles and forms mixed gas bubbles in the liquid aluminum. During the rising process of the bubbles, the oxygen in the mixed gas reacts with the liquid aluminum, and the oxygen on the outer periphery of the bubbles reacts with the liquid aluminum to form a thin film of aluminum oxide. 3) While alumina bubble film is generated and floats to the surface in the high-temperature liquid aluminum, the electric stirrer built into the oxidation furnace rotates and the blades break the rising bubble film, generating nano-sized alumina particles that continue to float to the surface of the liquid aluminum. After the bubble film in the liquid aluminum is broken, the mixed gas wrapped in it is released, and the oxygen in it continues to react with the liquid aluminum to generate alumina bubble film and alumina powder. 4) After the bubbles rise to the surface of the liquid aluminum, they burst and the alumina film breaks into nano-sized powder, which, together with the nano-sized alumina particles generated in the liquid aluminum, is dispersed by the airflow in the space above the liquid aluminum surface. 5) A positive pressure is maintained above the liquid aluminum surface in the oxidation furnace. The scattered alumina powder is pneumatically transported into the radiator by argon in the mixed gas through the alumina powder pneumatic output port at the top for cooling. 6) The cooled alumina powder and argon enter the gas-powder separation device to separate the alumina powder for collection, and the argon enters the mixed gas supply device for recycling.

5. The method according to claim 4, characterized in that, In step 1), the heating temperature of the aluminum melting furnace is 850℃-1000℃; and / or A certain space is left above the liquid aluminum in the oxidation furnace, and the space occupies 1 / 4 of the volume of the oxidation furnace.

6. The method according to claim 4, characterized in that, In step 2), the thickness of the alumina film is 0.01-0.3 μm; and / or The mixed gas contains 10%-30% oxygen and the remainder is argon, with both oxygen and argon having a purity of not less than 99.99%, and a supply rate of 10-100 L / min; and / or The temperature inside the oxidation furnace is 1000-1300℃.

7. The method according to claim 4, characterized in that, In step 3), the electric stirrer rotates at a speed of 300-1000 RPM.

8. The method according to claim 4, characterized in that, In step 5), the temperature of the radiator area does not exceed 260°C.

9. The method according to claim 4, characterized in that, In step 6), the alumina powder has a particle size of 0.05-0.5 μm and an alumina purity of 99.99% or higher.

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