Aluminum powder processing technology with high-precision control of oxygen content

Abstract

The application discloses an aluminum powder processing technology with high-precision oxygen content control, which comprises a heating and holding unit, a nitrogen atomization unit, an atomized droplet condensation unit, an aluminum powder particle grading unit and a nitrogen filtering unit, nitrogen gas purified by the nitrogen filtering unit is sent to a gas balance unit, acetone is added into the gas balance unit through an acetone conveying unit, then the oxygen content of the nitrogen gas in the gas balance unit is adjusted to 0.6% to 1.5%, finally, 60% to 70% of the total amount of the nitrogen gas in the gas balance unit is returned to the nitrogen atomization unit for recycling, 20% to 30% of the total amount of the nitrogen gas is compressed by a compressor, heated by a heating furnace and then returned to the nitrogen atomization unit for recycling, and 10% to 20% of the total amount of the nitrogen gas is returned to the aluminum powder particle grading unit for recycling. The aluminum powder prepared by the application has controllable oxygen content, small fluctuation range of the oxygen content, good fluidity, high tap density and high sphericity.

Description

Technical Field

[0001] This invention belongs to the technical field of aluminum paste production process for solar cells, specifically relating to an aluminum powder processing technology that can control oxygen content with high precision. Background Technology

[0002] Back-point contact crystalline silicon solar cells, also known as localized aluminum back field or back passivation, or LBSF or PERC (passivation emitter rear contact) cells, are a type of high-efficiency cell easily industrialized. Compared to conventional cells, this type of cell has a passivation film deposited on the back. The passivation film is perforated or grooved using methods such as lasers, and aluminum paste is printed onto the passivation film. The back electric field is led out through point or line contacts. This cell structure maintains the back field effect while reducing the contact area between the back metal and the semiconductor, significantly reducing the recombination rate at the interface, thus enabling the cell to achieve a high conversion efficiency. Currently, the photoelectric conversion efficiency of this type of monocrystalline cell can reach 22.8% in mass production. PERC crystalline silicon cell aluminum paste is a functional paste formed by uniformly mixing and dispersing aluminum powder, inorganic binder, organic carrier, and a small amount of additives. It is applied to the back of the crystalline silicon solar cell to form a back field, which then conducts the current to the back electrode. Aluminum powder is a key raw material in the production of PERC crystalline silicon cell aluminum paste. The technical indicators of the aluminum powder, such as its flowability and tap density, as well as the control of its oxygen content, are crucial to the product quality of the aluminum paste. In existing technologies, aluminum powder production typically employs atomization. The atomization process mainly includes heating and holding, nitrogen atomization, atomized droplet condensation, aluminum powder particle classification, and nitrogen filtration and recycling. However, the aluminum powder produced in this process suffers from the following problems: First, to reduce and eliminate the aluminum powder's binding ability, a certain amount of water is introduced into the atomization system during the nitrogen atomization process. The water's oxidizing power causes the aluminum powder surface to form an oxide or hydroxide layer, thereby removing the active aluminum and significantly reducing its surface activity, thus eliminating its binding and adsorption capabilities. However, aluminum powder produced using water for surface oxidation exhibits a rough, uneven surface with poor sphericity, and its flowability and tap density are also unsatisfactory. In subsequent use, the unstable oxides generated during hydroxide dehydration can lead to scum and black spots on the aluminum powder. Secondly, in addition to controlling the flowability and tap density of the aluminum powder, PERC crystalline silicon battery aluminum paste also requires control of its oxygen content. The oxygen content of the aluminum powder is closely related to the oxygen content in the nitrogen gas operating medium within the atomization system; the higher the oxygen content in the nitrogen gas, the higher the oxygen content of the product. PERC crystalline silicon battery aluminum paste requires an oxygen content not exceeding 2.6 wt%, thus requiring the oxygen content of the nitrogen atomization production system to not exceed 3.5 wt%. Due to the irrationality of existing production processes, it is difficult to stably control the oxygen content of the atomization system below 3.5 wt% during atomization, resulting in large fluctuations in the oxygen content of the produced aluminum powder and an inability to achieve precise control of the aluminum powder's oxygen content. Therefore, it is objectively necessary to develop an advanced aluminum powder processing technology that can improve the production quality of aluminum powder and precisely control the fluctuation range of its oxygen content. Summary of the Invention

[0003] In order to solve the technical problems existing in the background art, the purpose of this invention is to provide an advanced aluminum powder processing technology that can improve the production quality of aluminum powder and accurately control the fluctuation range of oxygen content in aluminum powder.

[0004] This invention discloses an aluminum powder processing technology with high-precision oxygen content control, comprising a heating and insulation unit, a nitrogen atomization unit, an atomized droplet condensation unit, an aluminum powder particle classification unit, and a nitrogen filtration unit. Nitrogen purified by the nitrogen filtration unit is sent to a gas balance unit. Simultaneously, acetone is added to the gas balance unit via an acetone delivery unit. The nitrogen-oxygen content (volume percentage) entering the gas balance unit is then adjusted to 0.6%–1.5%. When the nitrogen-oxygen content in the gas balance unit falls below 0.6%, air needs to be added to the gas balance unit to raise the nitrogen-oxygen content to 0.6%–1.5%. If the nitrogen-oxygen content in the balancing unit is higher than 1.5%, high-purity nitrogen needs to be added to the gas balancing unit. The purity of the high-purity nitrogen is 99.5%, which reduces the nitrogen-oxygen content in the gas balancing unit to 0.6%–1.5%. Finally, 60%–70% of the total nitrogen in the gas balancing unit is returned to the nitrogen atomization unit for recycling. 20%–30% of the total nitrogen in the gas balancing unit is compressed by a compressor to 7.0 MPa–8.5 MPa and then sent to a heating furnace to be heated to 500℃–520℃ before being returned to the nitrogen atomization unit for recycling. 10%–20% of the total nitrogen in the gas balancing unit is returned to the aluminum powder particle classification unit for recycling.

[0005] Furthermore, the gas balance unit includes a gas balance tank and an inlet pipe and an outlet pipe installed on the gas balance tank. The inlet pipe is connected to a nitrogen filtration unit. Nitrogen and acetone purified by the nitrogen filtration unit both enter the gas balance tank through the inlet pipe. The gas balance tank is equipped with a gas oxygen content detector, a high-purity nitrogen inlet pipe, and an air inlet pipe. The air inlet pipe is used to replenish air, and the high-purity nitrogen inlet pipe is used to replenish high-purity nitrogen. A first solenoid valve is installed on the high-purity nitrogen inlet pipe, and a second solenoid valve is installed on the air inlet pipe. The outlet pipe has three outlets. The first outlet sends 60% to 70% of the total nitrogen through a first circulation pipe to the nitrogen atomization unit. The second outlet sends 20% to 30% of the total nitrogen through a second circulation pipe to the compressor. The third outlet sends 10% to 20% of the total nitrogen through a third circulation pipe to the aluminum powder particle classification unit.

[0006] Furthermore, the gas balance tank is equipped with a dew point detector. The acetone delivery unit includes a steam generator and an acetone feed port and a nitrogen inlet pipe installed on the steam generator. Acetone is added to the steam generator through the acetone feed port, and nitrogen is added to the steam generator through the nitrogen inlet pipe. Acetone vapor is formed under the action of the added nitrogen. The purity of the added nitrogen is 99.5%. The formed acetone vapor enters the gas balance tank through the acetone feed pipe. A third solenoid valve is installed on the acetone feed pipe. The dew point value of the acetone vapor needs to be controlled between -15℃ and -30℃.

[0007] Furthermore, the temperature of the heating and insulation unit needs to be controlled between 800℃ and 850℃.

[0008] Furthermore, the atomization temperature of the nitrogen atomization aluminum liquid unit is 420℃~480℃, and the nitrogen pressure is 4.5MPa~8.5MPa.

[0009] Furthermore, the pressure of 60% to 70% of the total nitrogen in the gas balance unit returning to the nitrogen atomization unit needs to be adjusted to a slightly positive pressure state, which is 2000 Pa to 6000 Pa.

[0010] Furthermore, the aluminum powder particle classification unit includes a centrifugal classifier, a cyclone classifier, and a double cyclone classifier connected in series. The lower part of the centrifugal classifier, the cyclone classifier, and the double cyclone classifier are all equipped with aluminum powder receiving hoppers. 10% to 20% of the total nitrogen in the gas balance unit is returned to the centrifugal classifier.

[0011] Furthermore, the nitrogen filtration unit includes a bag filter and a receiving tank located at the bottom of the bag filter. The nitrogen discharged from the bag filter enters the gas balance unit. The bag filter is equipped with a back-flushing device, which uses high-purity nitrogen as the back-flushing gas source.

[0012] Compared with existing nitrogen atomization technology, the advantages of this invention are: Firstly, this invention uses acetone instead of water as a surface passivating agent in the atomization production of molten aluminum. This not only achieves the same passivation effect as water on the aluminum powder surface, but also effectively improves the product quality and performance of the aluminum powder. Firstly, acetone has extremely high volatility, making it easy to enter the nitrogen atomization unit for the atomization reaction. Secondly, acetone has excellent adhesion to the aluminum powder surface, completely and thoroughly coating the surface of the aluminum powder particles, creating a thin acetone film. Compared to the problems of protrusions, depressions, and sharp corners caused by the oxidation reaction of water passivation, acetone-aluminum... The powder tends to be spherical, with a smoother surface and easier flow. Thirdly, due to the lubricating effect of acetone, the droplets are more likely to shrink into spherical shapes during atomization, resulting in better sphericity of the atomized aluminum powder. Smaller powder balls can more easily enter the gaps between larger powder balls, filling the gaps in a stepwise manner and greatly reducing the porosity inside the aluminum powder product. This results in aluminum powder with higher tap density. Fourthly, in subsequent applications of aluminum powder, whether in aquatic or organic environments, acetone will not adversely affect the performance of the aluminum powder, and the subsequent adaptability of the aluminum powder is relatively stable. Secondly, during the nitrogen circulation process, this invention can adjust the oxygen content of the circulating nitrogen entering the nitrogen atomization aluminum liquid unit by supplementing air or high-purity nitrogen, depending on whether the oxygen content of the nitrogen is too low or too high. This adjustment method is advanced and reasonable, and can quickly and efficiently control the oxygen content of the nitrogen atomization aluminum liquid unit precisely within the range of 0.6% to 1.5%, thereby achieving precise control of the fluctuation range of the oxygen content in aluminum powder. This invention can ensure that the fluctuation range of the oxygen content in aluminum powder does not exceed 0.01 wt%. In summary, the technology of this device is advanced. The aluminum powder produced by this invention not only has the advantages of good fluidity, high tap density, and high sphericity, but also has controllable oxygen content. The production quality and product performance of the aluminum powder are excellent, which can generate good economic benefits and is easy to promote and use. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the process of the present invention; In the diagram: 1-Heating and heat preservation unit, 2-Nitrogen atomization unit, 3-Atomized droplet condensation unit, 4-Aluminum powder particle classification unit, 5-Nitrogen filtration unit, 6-Gas balance unit, 61-Gas balance tank, 62-Inlet pipe, 63-Outlet pipe, 64-Gas oxygen content detector, 65-High-purity nitrogen inlet pipe, 66-Air inlet pipe, 67-First solenoid valve, 68-Second solenoid valve, 69-First circulation pipe, 610-Second circulation pipe, 611-Third circulation pipe, 612-Dew point detector, 7-Acetone delivery unit, 71-Steam generator, 72-Acetone feed port, 73-Nitrogen replenishment pipe, 74-Acetone feed pipe, 75-Third solenoid valve, 8-Compressor, 9-Heating furnace. Implementation

[0014] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention are within the protection scope of the present invention. Example 1

[0015] The aluminum powder processing technology described in Example 1, which allows for high-precision control of oxygen content, includes a heating and heat preservation unit 1, a nitrogen atomization unit 2, an atomized droplet condensation unit 3, an aluminum powder particle classification unit 4, and a nitrogen filtration unit 5. Heating and heat preservation unit 1: The heating and heat preservation unit is transported from the aluminum plant and first added to the transfer furnace. After being heated by natural gas to reach the required temperature of 750°C, it is then injected into the heat preservation furnace through the flow channel and the temperature is controlled at 800°C in the heat preservation furnace. Nitrogen atomization unit 2: Through the nozzle inside the atomizer, under the conditions of atomization temperature of 420℃ and nitrogen pressure of 4.5MPa, the nitrogen is sprayed into the atomization chamber in a mist form. Under the action of return air nitrogen and cooling water in the jacket outside the atomizer, the nitrogen shrinks into a ball and the surface cools and solidifies. Before atomization, the prepared nitrogen needs to be filled into the atomizer that has been evacuated beforehand, so that the nitrogen pressure in the system is slightly higher than the external atmospheric pressure. Atomized droplet condensation unit 3: The fine droplets solidified on the surface flow with nitrogen to the atomized droplet condensation unit 3 for further cooling until completely solidified. The atomized droplet condensation unit 3 adopts a series-connected shell-and-tube heat exchanger and a tube-and-shell heat exchanger used in the prior art. Aluminum Powder Particle Classification Unit 4: After fully solidified fine aluminum powder particles enter the aluminum powder particle classification unit 4 and undergo multi-stage separation, aluminum powder particles with different particle sizes can be obtained. The aluminum powder particle classification unit 4 includes a centrifugal classifier, a cyclone classifier, and a double cyclone classifier connected in series. The lower part of the centrifugal classifier, cyclone classifier, and double cyclone classifier is equipped with an aluminum powder receiving hopper. The aluminum powder particle size obtained by the centrifugal classifier is between 25 and 33 μm, and the aluminum powder particle size obtained by the cyclone classifier is between 7.5 and 8.5 μm. The cyclone classifier is equipped with a bypass pipe. The coarser powder is thrown to the side and enters the bypass pipe under the action of centrifugal force. The aluminum powder particle size obtained by the bypass pipe is between 12 and 15 μm, and the aluminum powder particle size obtained by the double cyclone classifier is between 3 and 4 μm. Nitrogen filtration unit 5: Nitrogen filtration unit 5 includes a bag filter and a receiving tank located at the bottom of the bag filter. The nitrogen discharged from the bag filter enters the gas balance unit. The bag filter is equipped with a back-blowing device, which uses high-purity nitrogen as the back-blowing gas source. The nitrogen discharged from the double cyclone classifier of the aluminum powder particle classification unit 4 enters the bag filter. After dust removal by the bag filter, the obtained aluminum powder particle size is between 1 and 2 μm. The back-blowing device blows supersonic nitrogen into the bag filter in the opposite direction to make the aluminum powder detach from the outer wall of the bag and settle into the lower receiving tank. This part of the nitrogen enters the system and also participates in the system circulation. The nitrogen purified by nitrogen filtration unit 5 is then sent to gas balance unit 6. Simultaneously, acetone is added to gas balance unit 6 via acetone delivery unit 7. The added acetone mixes with the nitrogen in gas balance unit 6 and then enters nitrogen atomization unit 2 for atomization. Acetone has extremely high volatility, making it easy to enter nitrogen atomization unit 2 after mixing with nitrogen. Furthermore, due to its excellent adhesion to aluminum powder surfaces, acetone can completely and thoroughly coat the aluminum powder particles, resulting in more spherical aluminum powder with a smoother surface, better flowability, and higher tap density. In subsequent applications, whether in aquatic or organic environments, acetone will not adversely affect the performance of the aluminum powder. Finally, the oxygen content of the nitrogen entering gas balance unit 6 is adjusted... When the nitrogen-oxygen content in gas balance unit 6 is below 0.6%, air needs to be added to gas balance unit 6 to increase the nitrogen-oxygen content to 0.6-1.5%. When the nitrogen-oxygen content in gas balance unit 6 is above 1.5%, high-purity nitrogen (99.5% purity) needs to be added to gas balance unit 6 to reduce the nitrogen-oxygen content to 0.6-1.5%. Finally, 60% of the total nitrogen in gas balance unit 6 is returned to nitrogen atomization unit 2 for recycling, and 30% of the total nitrogen in gas balance unit 6 is compressed by compressor 8 at 8.0 MPa and then sent to heating furnace 9 to be heated to 500°C before being returned to nitrogen atomization unit 2 for recycling. 10% of the total nitrogen in gas balance unit 6 is returned to aluminum powder particle classification unit 4 for recycling, thus forming a nitrogen recycling system. By adjusting the oxygen content of the nitrogen entering gas balance unit 6, precise control of the oxygen content in the produced aluminum powder can be achieved. Furthermore, the three-way nitrogen circulation design effectively improves nitrogen utilization and ensures efficient operation of the aluminum powder production process. In this invention, the oxygen content in nitrogen is expressed as a volume percentage, the oxygen content in aluminum powder is expressed as a mass percentage, and the nitrogen purity is expressed as a volume percentage.

[0016] Furthermore, the gas balance unit 6 includes a gas balance tank 61 and an inlet pipe 62 and an outlet pipe 63 installed on the gas balance tank 61. The inlet pipe 62 is connected to the nitrogen filter unit 5. The nitrogen and acetone purified by the nitrogen filter unit 5 both enter the gas balance tank 61 through the inlet pipe 62. The gas balance tank 61 is equipped with a gas oxygen content detector 64, a high-purity nitrogen inlet pipe 65, and an air inlet pipe 66. The air inlet pipe 66 is used to replenish air, and the high-purity nitrogen inlet pipe 65 replenishes high-purity nitrogen. A first solenoid valve 67 is installed on the high-purity nitrogen inlet pipe 65, and a second solenoid valve 68 is installed on the air inlet pipe 66. The outlet pipe 63 has three outlets. The first outlet is... The first circulation pipe 69 sends 60-70% of the total nitrogen to the nitrogen atomization unit 2. The oxygen content of the aluminum powder is closely related to the oxygen content in the nitrogen operating medium within the nitrogen atomization unit 2. The higher the oxygen content in the nitrogen, the higher the oxygen content of the product. Higher oxygen content also means poorer inhibition of the aluminum powder's activity by nitrogen. This process uses an interlocking control system for the gas oxygen content detector 64, the first solenoid valve 67, and the second solenoid valve 68. The gas oxygen content detector 64 can utilize the structure used in existing technologies, enabling precise control of the nitrogen oxygen content. The pressure at which 60% of the total nitrogen in the gas balance unit 7 returns to the nitrogen atomization unit 2 needs to be adjusted to a slightly positive pressure state. The slightly positive pressure is 2000 Pa. The entire aluminum powder production system needs to maintain a slightly positive pressure state to prevent external air from entering the system. Inevitably, there will be instances of excessive pressure. To maintain stable system pressure, a micro-pressure venting device is installed on the gas balance tank. If the pressure becomes too high, a portion of nitrogen will be released to stabilize the pressure. The second outlet sends 30% of the total nitrogen to the compressor via the second circulation pipe 610, and the third outlet sends 10% of the total nitrogen to the aluminum powder particle classification unit via the third circulation pipe 611. This 10% of the total nitrogen enters the vortex structure at the bottom of the centrifugal classifier, forming a cyclone. This cyclone lifts the aluminum powder falling from the centrifugal classifier and separates the finer aluminum powder that is adhered to the coarse aluminum powder, causing it to rise and enter the cyclone. A classifier participates in the cyclone classification process, and the nitrogen entering here is also mixed with the system nitrogen, forming a cycle. Preferably, a dew point detector 612 is installed on the gas balance tank 61. The dew point detector 612 is used to detect the dew point value of acetone vapor in the gas balance tank. The dew point detector 612 can adopt the structure used in the prior art. The acetone delivery unit 7 includes a steam generator 71 and an acetone feed port 72 and a nitrogen inlet pipe 73 installed on the steam generator 71. Acetone is added to the steam generator 71 through the acetone feed port 72, and nitrogen is added to the steam generator 71 through the nitrogen inlet pipe 73. Acetone forms acetone vapor under the action of the added nitrogen. The purity of the added nitrogen is 99%.5% of the acetone vapor is generated and enters the gas balance tank 71 through the acetone feed pipe 74. The acetone feed pipe 74 is equipped with a third solenoid valve 75. The dew point of the acetone vapor needs to be controlled at -15℃. Aluminum powder coated with acetone can significantly reduce the adhesion and adsorption force on the surface, and can also protect the aluminum powder, isolate the aluminum powder from direct contact with air, and make the oxygen content of the aluminum powder relatively stable for a certain period of time. However, the more acetone is coated on the surface of the aluminum powder, the lower the probability of oxidation. But too much acetone will make the surface of the aluminum powder basically unoxidized or form oxide film holes. During storage or use, such aluminum powder will have re-adsorption, agglomeration, or safety problems due to high temperature or water contact caused by the volatilization of acetone. Therefore, controlling the amount of acetone used is an important matter in atomization production. The dew point of the acetone vapor is controlled at -15℃. Then, according to the dew point display value exceeding the dew point range, the valve opening of the third solenoid valve 75 on the acetone feed pipe is adjusted to keep the dew point within the set range. .

[0017] In the aluminum powder production process of this embodiment 1, firstly, acetone is used instead of water as a surface passivating agent in the aluminum liquid atomization process. This not only performs the same passivation function as water but also effectively improves the product quality and performance. Secondly, a gas balance unit is used to adjust the oxygen content of nitrogen, thereby achieving precise control of the oxygen content of the aluminum powder. The oxygen content of the aluminum powder can be precisely controlled within the required range. The advanced process technology employed in this invention results in aluminum powder with controllable oxygen content and minimal fluctuation. The oxygen content of the obtained aluminum powder is controlled between 0.12 and 0.22 wt%, with a fluctuation range not exceeding 0.01%. Furthermore, the aluminum powder exhibits good fluidity, high tap density, and high sphericity. The obtained aluminum powder has significant advantages in transportation, storage, slurry preparation, and the production of finished silicon wafers. 1. Acetone passivation of the aluminum powder surface prevents oxidation by air, ensuring that the aluminum powder product does not show significant changes in oxygen content over a considerable period of time; 2. Good fluidity prevents the aluminum powder from sticking or clumping due to compression during storage and transportation; it is easy to disperse evenly when mixed with glass powder before making slurry, preventing local accumulation; 3. Good sphericity ensures the aluminum powder is free of protrusions, depressions, and sharp corners, preventing localized melting due to the fragility of irregular structure joints during sintering, thus avoiding uneven temperature and silicon wafer warping; 4. High tap density and uniform distribution ensure the adhesion and tensile strength of the silicon wafer, preventing surface powdering, beading, blistering, etc. Example 2

[0018] The aluminum powder processing technology described in Example 2, which allows for high-precision control of oxygen content, includes a heating and heat preservation unit 1, a nitrogen atomization unit 2, an atomized droplet condensation unit 3, an aluminum powder particle classification unit 4, and a nitrogen filtration unit 5. Heating and heat preservation unit 1: The heating and heat preservation unit is transported from the aluminum plant and first added to the transfer furnace. After being heated by natural gas to the required temperature of 800℃, it is then injected into the heat preservation furnace through the flow channel and the temperature is controlled at 825℃ in the heat preservation furnace. Nitrogen atomization unit 2: Through the nozzle inside the atomizer, under the conditions of atomization temperature of 450℃ and nitrogen pressure of 6.5MPa, the nitrogen is sprayed into the atomization chamber in a mist form. Under the action of return air nitrogen and cooling water in the jacket outside the atomizer, the nitrogen shrinks into a ball and the surface cools and solidifies. Before atomization, the prepared nitrogen needs to be filled into the atomizer that has been evacuated beforehand, so that the nitrogen pressure in the system is slightly higher than the external atmospheric pressure. Atomized droplet condensation unit 3: The fine droplets solidified on the surface flow with nitrogen to the atomized droplet condensation unit 3 for further cooling until completely solidified. The atomized droplet condensation unit 3 adopts a series-connected shell-and-tube heat exchanger and a tube-and-shell heat exchanger used in the prior art. Aluminum Powder Particle Classification Unit 4: After fully solidified fine aluminum powder particles enter the aluminum powder particle classification unit 4 and undergo multi-stage separation, aluminum powder particles with different particle sizes can be obtained. The aluminum powder particle classification unit 4 includes a centrifugal classifier, a cyclone classifier, and a double cyclone classifier connected in series. The lower part of the centrifugal classifier, cyclone classifier, and double cyclone classifier is equipped with an aluminum powder receiving hopper. The aluminum powder particle size obtained by the centrifugal classifier is between 25 and 33 μm, and the aluminum powder particle size obtained by the cyclone classifier is between 7.5 and 8.5 μm. The cyclone classifier is equipped with a bypass pipe. The coarser powder is thrown to the side and enters the bypass pipe under the action of centrifugal force. The aluminum powder particle size obtained by the bypass pipe is between 12 and 15 μm, and the aluminum powder particle size obtained by the double cyclone classifier is between 3 and 4 μm. Nitrogen filtration unit 5: Nitrogen filtration unit 5 includes a bag filter and a receiving tank located at the bottom of the bag filter. The nitrogen discharged from the bag filter enters the gas balance unit. The bag filter is equipped with a back-blowing device, which uses high-purity nitrogen as the back-blowing gas source. The nitrogen discharged from the double cyclone classifier of the aluminum powder particle classification unit 4 enters the bag filter. After dust removal by the bag filter, the obtained aluminum powder particle size is between 1 and 2 μm. The back-blowing device blows supersonic nitrogen into the bag filter in the opposite direction to make the aluminum powder detach from the outer wall of the bag and settle into the lower receiving tank. This part of the nitrogen enters the system and also participates in the system circulation. The nitrogen purified by nitrogen filtration unit 5 is then sent to gas balance unit 6. Simultaneously, acetone is added to gas balance unit 6 via acetone delivery unit 7. The added acetone mixes with the nitrogen in gas balance unit 6 and then enters nitrogen atomization unit 2 for atomization. Acetone has extremely high volatility, making it easy to enter nitrogen atomization unit 2 after mixing with nitrogen. Furthermore, due to its excellent adhesion to aluminum powder surfaces, acetone can completely and thoroughly coat the aluminum powder particles, resulting in more spherical aluminum powder with a smoother surface, better flowability, and higher tap density. In subsequent applications, whether in aquatic or organic environments, acetone will not adversely affect the performance of the aluminum powder. Finally, the oxygen content of the nitrogen entering gas balance unit 6 is adjusted... When the nitrogen-oxygen content in gas balance unit 6 is below 0.6%, air needs to be added to gas balance unit 6 to increase the nitrogen-oxygen content to 0.6-1.5%. When the nitrogen-oxygen content in gas balance unit 6 is above 1.5%, high-purity nitrogen (99.5% purity) needs to be added to gas balance unit 6 to reduce the nitrogen-oxygen content to 0.6-1.5%. Finally, 65% of the total nitrogen in gas balance unit 6 is returned to nitrogen atomization unit 2 for recycling, and 25% of the total nitrogen in gas balance unit 6 is compressed by compressor 8 at 8.2 MPa and then sent to heating furnace 9 to be heated to 510°C before being returned to nitrogen atomization unit 2 for recycling. 15% of the total nitrogen in the gas balance unit 6 is returned to the aluminum powder particle classification unit 4 for recycling, thus forming a nitrogen recycling system. By adjusting the oxygen content of the nitrogen entering the gas balance unit 6, precise control of the oxygen content of the produced aluminum powder can be achieved. On the other hand, by designing a three-way nitrogen circulation, the efficient operation of the aluminum powder production process can be effectively guaranteed while effectively improving nitrogen utilization.

[0019] Furthermore, the gas balance unit 6 includes a gas balance tank 61 and an inlet pipe 62 and an outlet pipe 63 installed on the gas balance tank 61. The inlet pipe 62 is connected to the nitrogen filter unit 5. The nitrogen and acetone purified by the nitrogen filter unit 5 both enter the gas balance tank 61 through the inlet pipe 62. The gas balance tank 61 is equipped with a gas oxygen content detector 64, a high-purity nitrogen inlet pipe 65, and an air inlet pipe 66. The air inlet pipe 66 is used to replenish air, and the high-purity nitrogen inlet pipe 65 replenishes high-purity nitrogen. A first solenoid valve 67 is installed on the high-purity nitrogen inlet pipe 65, and a second solenoid valve 68 is installed on the air inlet pipe 66. The outlet pipe 63 has three outlets, with the first outlet connected to... 65% of the total nitrogen gas is sent to nitrogen atomization unit 2 via the first circulation pipe 69. The oxygen content of the aluminum powder is closely related to the oxygen content in the nitrogen gas operating medium within nitrogen atomization unit 2. The higher the oxygen content in the nitrogen gas, the higher the oxygen content of the product. Higher oxygen content also means poorer inhibition of the aluminum powder's activity by nitrogen. This process uses an interlocking control system for the gas oxygen content detector 64, the first solenoid valve 67, and the second solenoid valve 68. The gas oxygen content detector 64 can utilize the structure used in existing technologies, enabling precise control of the nitrogen oxygen content. The pressure at which 65% of the total nitrogen gas in the gas balance unit 7 returns to nitrogen atomization unit 2 needs to be adjusted to a slightly positive pressure state. The slightly positive pressure is 4000 Pa. The entire aluminum powder production system needs to maintain a slightly positive pressure state to prevent external air from entering the system. Inevitably, there will be instances of excessive pressure. To maintain stable system pressure, a micro-pressure venting device is installed on the gas balance tank. If the pressure becomes too high, a portion of nitrogen will be released to stabilize the pressure. The second outlet sends 25% of the total nitrogen to the compressor via the second circulation pipe 610, and the third outlet sends 15% of the total nitrogen to the aluminum powder particle classification unit via the third circulation pipe 611. The remaining 15% of the total nitrogen enters the vortex structure at the bottom of the centrifugal classifier, forming a cyclone. This cyclone lifts the aluminum powder falling from the centrifugal classifier and separates the finer aluminum powder that is adhered to the coarse aluminum powder, causing it to rise and enter the cyclone. A classifier participates in the cyclone classification process, and the nitrogen entering here is also mixed with the system nitrogen, forming a cycle. Preferably, a dew point detector 612 is installed on the gas balance tank 61. The dew point detector 612 is used to detect the dew point value of acetone vapor in the gas balance tank. The dew point detector 612 can adopt the structure used in the prior art. The acetone delivery unit 7 includes a steam generator 71 and an acetone feed port 72 and a nitrogen inlet pipe 73 installed on the steam generator 71. Acetone is added to the steam generator 71 through the acetone feed port 72, and nitrogen is added to the steam generator 71 through the nitrogen inlet pipe 73. Acetone forms acetone vapor under the action of the added nitrogen. The purity of the added nitrogen is 99%.5% of the acetone vapor is generated and enters the gas balance tank 71 through the acetone feed pipe 74. The acetone feed pipe 74 is equipped with a third solenoid valve 75. The dew point of the acetone vapor needs to be controlled at -22℃. Aluminum powder coated with acetone can significantly reduce surface adhesion and adsorption, and also protect the aluminum powder, preventing direct contact between the aluminum powder and air, thus stabilizing the oxygen content of the aluminum powder for a certain period of time. However, the more acetone coating the aluminum powder surface, the lower the probability of oxidation, but excessive coating can lead to oxidation. Acetone can prevent aluminum powder from oxidizing or forming oxide film defects. However, during storage or use, the volatilization of acetone can cause re-adsorption, agglomeration, or safety issues due to high temperatures or contact with water. Therefore, controlling the amount of acetone used is crucial in atomization production. The dew point of acetone vapor needs to be controlled at -22℃. If the dew point reading exceeds this range, the opening of the third solenoid valve 75 on the acetone feed pipe should be adjusted to keep the dew point within the set range.

[0020] In the aluminum powder production process of this embodiment 2, firstly, acetone is used as a surface passivating agent to replace water in the aluminum liquid atomization production. This not only performs the same passivation function as water but also effectively improves the product quality and performance. Secondly, a gas balance unit is used to adjust the oxygen content of nitrogen, thereby achieving precise control of the oxygen content of the aluminum powder. The oxygen content of the aluminum powder can be precisely controlled within the required range. The advanced process technology employed in this invention results in aluminum powder with controllable oxygen content and minimal fluctuation. The oxygen content of the obtained aluminum powder is controlled between 0.23 and 0.35 wt%, with a fluctuation range not exceeding 0.01%. Furthermore, the aluminum powder exhibits good fluidity, high tap density, and high sphericity. The obtained aluminum powder has significant advantages in transportation, storage, slurry preparation, and finished silicon wafer production. 1. Acetone passivation of the aluminum powder surface prevents oxidation by air, ensuring that the aluminum powder product does not show significant changes in oxygen content over a considerable period of time; 2. Good fluidity prevents the aluminum powder from sticking or clumping due to compression during storage and transportation; it is easy to disperse evenly when mixed with glass powder before making slurry, preventing local accumulation; 3. Good sphericity ensures the aluminum powder is free of protrusions, depressions, and sharp corners, preventing localized melting due to the fragility of irregular structure joints during sintering, thus avoiding uneven temperature and silicon wafer warping; 4. High tap density and uniform distribution ensure the adhesion and tensile strength of the silicon wafer, preventing surface powdering, beading, blistering, etc. Example 3

[0021] The aluminum powder processing technology described in Example 3, which allows for high-precision control of oxygen content, includes a heating and heat preservation unit 1, a nitrogen atomization unit 2, an atomized droplet condensation unit 3, an aluminum powder particle classification unit 4, and a nitrogen filtration unit 5. Heating and heat preservation unit 1: The aluminum plant supplies the unit. It is first added to the converter and heated by natural gas to reach the required temperature of 880°C. Then, it is injected into the heat preservation furnace through the flow channel and the temperature is controlled at 850°C in the heat preservation furnace. Nitrogen atomization unit 2: Through the nozzle inside the atomizer, under the conditions of atomization temperature of 480℃ and nitrogen pressure of 8.5MPa, the nitrogen is sprayed into the atomization chamber in a mist form. Under the action of return air nitrogen and cooling water in the jacket outside the atomizer, the nitrogen shrinks into a ball and the surface cools and solidifies. Before atomization, the prepared nitrogen needs to be filled into the atomizer that has been evacuated beforehand so that the nitrogen pressure in the system is slightly higher than the external atmospheric pressure. Atomized droplet condensation unit 3: The fine droplets solidified on the surface flow with nitrogen to the atomized droplet condensation unit 3 for further cooling until completely solidified. The atomized droplet condensation unit 3 adopts a series-connected shell-and-tube heat exchanger and a tube-and-shell heat exchanger used in the prior art. Aluminum Powder Particle Classification Unit 4: After fully solidified fine aluminum powder particles enter the aluminum powder particle classification unit 4 and undergo multi-stage separation, aluminum powder particles with different particle sizes can be obtained. The aluminum powder particle classification unit 4 includes a centrifugal classifier, a cyclone classifier, and a double cyclone classifier connected in series. The lower part of the centrifugal classifier, cyclone classifier, and double cyclone classifier is equipped with an aluminum powder receiving hopper. The aluminum powder particle size obtained by the centrifugal classifier is between 25 and 33 μm, and the aluminum powder particle size obtained by the cyclone classifier is between 7.5 and 8.5 μm. The cyclone classifier is equipped with a bypass pipe. The coarser powder is thrown to the side and enters the bypass pipe under the action of centrifugal force. The aluminum powder particle size obtained by the bypass pipe is between 12 and 15 μm, and the aluminum powder particle size obtained by the double cyclone classifier is between 3 and 4 μm. Nitrogen filtration unit 5: Nitrogen filtration unit 5 includes a bag filter and a receiving tank located at the bottom of the bag filter. The nitrogen discharged from the bag filter enters the gas balance unit. The bag filter is equipped with a back-blowing device, which uses high-purity nitrogen as the back-blowing gas source. The nitrogen discharged from the double cyclone classifier of the aluminum powder particle classification unit 4 enters the bag filter. After dust removal by the bag filter, the obtained aluminum powder particle size is between 1 and 2 μm. The back-blowing device blows supersonic nitrogen into the bag filter in the opposite direction to make the aluminum powder detach from the outer wall of the bag and settle into the lower receiving tank. This part of the nitrogen enters the system and also participates in the system circulation. The nitrogen purified by nitrogen filtration unit 5 is then sent to gas balance unit 6. Simultaneously, acetone is added to gas balance unit 6 via acetone delivery unit 7. The added acetone mixes with the nitrogen in gas balance unit 6 and then enters nitrogen atomization unit 2 for atomization. Acetone has extremely high volatility, making it easy to enter nitrogen atomization unit 2 after mixing with nitrogen. Furthermore, due to its excellent adhesion to aluminum powder surfaces, acetone can completely and thoroughly coat the aluminum powder particles, resulting in more spherical aluminum powder with a smoother surface, better flowability, and higher tap density. In subsequent applications, whether in aquatic or organic environments, acetone will not adversely affect the performance of the aluminum powder. Finally, the oxygen content of the nitrogen entering gas balance unit 6 is adjusted... When the nitrogen-oxygen content in gas balance unit 6 is below 0.6%, air needs to be added to gas balance unit 6 to increase the nitrogen-oxygen content to 0.6-1.5%. When the nitrogen-oxygen content in gas balance unit 6 is above 1.5%, high-purity nitrogen (99.5% purity) needs to be added to gas balance unit 6 to reduce the nitrogen-oxygen content to 0.6-1.5%. Finally, 70% of the total nitrogen in gas balance unit 6 is returned to nitrogen atomization unit 2 for recycling, and 20% of the total nitrogen in gas balance unit 6 is compressed by compressor 8 at 8.5 MPa and then sent to heating furnace 9 to be heated to 520°C before being returned to nitrogen atomization unit 2 for recycling. 20% of the total nitrogen in the gas balance unit 6 is returned to the aluminum powder particle classification unit 4 for recycling, thus forming a nitrogen recycling system. By adjusting the oxygen content of the nitrogen entering the gas balance unit 6, precise control of the oxygen content of the produced aluminum powder can be achieved. On the other hand, by designing a three-way nitrogen circulation, the efficient operation of the aluminum powder production process can be effectively guaranteed while effectively improving the nitrogen utilization rate.

[0022] Furthermore, the gas balance unit 6 includes a gas balance tank 61 and an inlet pipe 62 and an outlet pipe 63 installed on the gas balance tank 61. The inlet pipe 62 is connected to the nitrogen filtration unit 5. The nitrogen and acetone purified by the nitrogen filtration unit 5 both enter the gas balance tank 61 through the inlet pipe 62. The gas balance tank 61 is equipped with a gas oxygen content detector 64, a high-purity nitrogen inlet pipe 65, and an air inlet pipe 66. The air inlet pipe 66 is used to replenish air, and the high-purity nitrogen inlet pipe 65 replenishes high-purity nitrogen. A first solenoid valve 67 is installed on the high-purity nitrogen inlet pipe 65, and a second solenoid valve 68 is installed on the air inlet pipe 66. The outlet of the outlet pipe 63 is... There are three outlets. The first outlet sends 60-70% of the total nitrogen gas to the nitrogen atomization unit 2 through the first circulation pipe 69. The oxygen content of the aluminum powder is closely related to the oxygen content in the nitrogen gas, the medium running in the nitrogen atomization unit 2. The higher the oxygen content in the nitrogen gas, the higher the oxygen content of the product. The higher the oxygen content, the worse the inhibition of the activity of the aluminum powder by the nitrogen gas. This process uses the gas oxygen content detector 6464, the first solenoid valve 67, and the second solenoid valve 68 for interlocking control. The gas oxygen content detector 64 can adopt the structure used in the existing technology, which can achieve precise control of the nitrogen oxygen content. The pressure required for 70% of the total nitrogen gas in the gas balance unit 7 to return to the nitrogen atomization unit 2 needs to be... To maintain a slightly positive pressure state (6000 Pa), the entire aluminum powder production system needs to be kept under this pressure to prevent external air from entering. However, occasional pressure spikes are unavoidable. To ensure system pressure stability, a slight pressure venting device is installed on the gas balance tank. If the pressure becomes too high, some nitrogen will be released to stabilize the pressure. The second outlet sends 20% of the total nitrogen to the compressor via the second circulation pipe 610, and the third outlet sends 10% of the total nitrogen to the aluminum powder particle classification unit via the third circulation pipe 611. This 10% of the total nitrogen enters the vortex structure at the bottom of the centrifugal classifier, forming a cyclone that can disperse the nitrogen from the centrifugal classifier. The aluminum powder falling from the classifier is lifted up, and the finer aluminum powder that is stuck to the coarse aluminum powder is separated. It rises and enters the cyclone classifier to participate in the cyclone classification process. The nitrogen entering here also mixes with the nitrogen in the system, forming a cycle. Preferably, the gas balance tank 61 is equipped with a dew point detector 612. The acetone delivery unit 7 includes a steam generator 71 and an acetone feed port 72 and a nitrogen inlet pipe 73 on the steam generator 71. Acetone is added to the steam generator 71 through the acetone feed port 72, and nitrogen is added to the steam generator 71 through the nitrogen inlet pipe 73. Acetone forms acetone vapor under the action of the added nitrogen. The purity of the added nitrogen is 99%.5% of the acetone vapor is generated and enters the gas balance tank 71 through the acetone feed pipe 74. A third solenoid valve 75 is installed on the acetone feed pipe 74. The dew point value of the acetone vapor needs to be controlled at -30℃. A dew point detector 612 is used to detect the dew point value of the acetone vapor in the gas balance tank. The dew point detector 612 can adopt the structure used in existing technology. Acetone-coated aluminum powder can significantly reduce surface adhesion and adsorption, and also protect the aluminum powder, isolating it from direct contact with air, thus making the oxygen content of the aluminum powder relatively stable for a certain period of time. The more acetone coating an aluminum powder surface, the lower its chance of oxidation. However, excessive acetone can prevent oxidation or create oxide film defects. Such aluminum powder, during storage or use, may experience re-adsorption, agglomeration, or safety issues due to acetone volatilization, high temperatures, or contact with water. Therefore, controlling the amount of acetone used is crucial in atomization production. The dew point of acetone vapor needs to be controlled at -30℃. If the dew point reading exceeds this range, adjust the opening of the third solenoid valve 75 on the acetone feed pipe to keep the dew point within the set range.

[0023] In the aluminum powder production process of this embodiment 3, firstly, acetone is used instead of water as a surface passivating agent in the aluminum liquid atomization process. This not only performs the same passivation function as water but also effectively improves the product quality and performance. Secondly, a gas balance unit is used to adjust the oxygen content of nitrogen, thereby achieving precise control of the oxygen content of the aluminum powder. The oxygen content of the aluminum powder can be precisely controlled within the required range. The advanced process technology employed in this invention results in aluminum powder with controllable oxygen content and a small fluctuation range. The oxygen content of the produced aluminum powder is controlled between 0.36 and 0.6 wt%, with a fluctuation range not exceeding 0.01%. Furthermore, the aluminum powder exhibits good fluidity, high tap density, and high sphericity. The obtained aluminum powder has significant advantages in transportation, storage, slurry preparation, and finished silicon wafers: 1. Acetone passivation of the aluminum powder surface prevents oxidation by air, ensuring that the aluminum powder product does not show significant changes in oxygen content over a considerable period of time; 2. Good fluidity prevents the aluminum powder from sticking or clumping due to compression during storage and transportation; it is easy to disperse evenly when mixed with glass powder before slurry preparation, preventing localized accumulation; 3. Good sphericity, with no protrusions, depressions, or sharp corners in the obtained aluminum powder. During sintering, the fragility of the irregular structure joints prevents localized melting, resulting in uneven temperature and warping of the silicon wafer; 4. High tap density and uniform distribution ensure the adhesion and tensile strength of the silicon wafer, preventing surface powdering, beading, blistering, etc.

Claims

1. An aluminum powder processing technology with high-precision control over oxygen content, characterized in that: The system includes a heating and insulation unit (1), a nitrogen atomization unit (2), an atomized droplet condensation unit (3), an aluminum powder particle classification unit (4), and a nitrogen filtration unit (5). Nitrogen purified by the nitrogen filtration unit (5) is sent to a gas balance unit (6), while acetone is added to the gas balance unit (6) via an acetone delivery unit (7). The oxygen content of the nitrogen entering the gas balance unit (6) is then adjusted to 0.6%–1.5%. Finally, 60% of the total nitrogen in the gas balance unit (6) is... 70% to 80% of the nitrogen is returned to the nitrogen atomization unit (2) for recycling. 20% to 30% of the total nitrogen in the gas balance unit (6) is compressed to 7.0 MPa to 8.5 MPa by the compressor (8) and then sent to the heating furnace (9) to be heated to 500℃ to 520℃ before being returned to the nitrogen atomization unit (2) for recycling. 10% to 20% of the total nitrogen in the gas balance unit (6) is returned to the aluminum powder particle classification unit (4) for recycling. The gas balance unit (6) includes a gas balance tank (61). The gas balance tank (61) is equipped with an inlet pipe (62) and an outlet pipe (63). The inlet pipe (62) is connected to the nitrogen filtration unit (5). The nitrogen and acetone purified by the nitrogen filtration unit (5) enter the gas balance tank (61) through the inlet pipe (62). The gas balance tank (61) is equipped with a dew point detector (612). The acetone delivery unit (7) includes a steam generator (71) and an acetone feed port (72) and a nitrogen inlet pipe (63) on the steam generator (71). 73), acetone is added to the steam generator (71) through the acetone feed port (72), and nitrogen is added to the steam generator (71) through the nitrogen inlet pipe (73). Acetone forms acetone vapor under the action of the added nitrogen. The purity of the added nitrogen is 99.5%. The formed acetone vapor enters the gas balance tank (61) through the acetone feed pipe (74). The acetone feed pipe (74) is equipped with a third solenoid valve (75). The dew point value of acetone vapor needs to be controlled between -15℃ and -30℃.

2. The aluminum powder processing technology with high-precision oxygen content control according to claim 1, characterized in that: The method for adjusting the nitrogen and oxygen content in the gas balance unit (6) is as follows: when the nitrogen and oxygen content in the gas balance unit (6) is lower than 0.6%, air is added to the gas balance unit (6) to increase the nitrogen and oxygen content in the gas balance unit (6) to 0.6% to 1.5%. When the nitrogen and oxygen content in the gas balance unit (6) is higher than 1.5%, high-purity nitrogen is added to the gas balance unit (6) with a purity of 99.5% to reduce the nitrogen and oxygen content in the gas balance unit (6) to 0.6% to 1.5%.

3. The aluminum powder processing technology with high-precision oxygen content control according to claim 1, characterized in that: The gas balance tank (61) is equipped with a gas oxygen content detector (64), a high-purity nitrogen inlet pipe (65), and an air inlet pipe (66). The air inlet pipe (66) is used to replenish air, and the high-purity nitrogen inlet pipe (65) is used to replenish high-purity nitrogen. The high-purity nitrogen inlet pipe (65) is equipped with a first solenoid valve (67), and the air inlet pipe (66) is equipped with a second solenoid valve (68). The outlet pipe (63) has three outlets. The first outlet sends 60% to 70% of the total nitrogen to the nitrogen atomization unit (2) through the first circulation pipe (69). The second outlet sends 20% to 30% of the total nitrogen to the compressor through the second circulation pipe (610). The third outlet sends 10% to 20% of the total nitrogen to the aluminum powder particle classification unit through the third circulation pipe (611).

4. The aluminum powder processing technology with high-precision control of oxygen content according to claim 1, characterized in that: The temperature of the heating and insulation unit (1) needs to be controlled between 800℃ and 850℃.

5. The aluminum powder processing technology with high-precision control of oxygen content according to claim 1, characterized in that: The atomization temperature of the nitrogen atomization aluminum liquid unit (2) is 420℃~480℃, and the nitrogen pressure is 4.5MPa~8.5MPa.

6. The aluminum powder processing technology with high-precision control of oxygen content according to claim 1, characterized in that: The pressure of 60% to 70% of the total nitrogen in the gas balance unit (6) returning to the nitrogen atomization unit (2) needs to be adjusted to a slightly positive pressure state, which is 2000 Pa to 6000 Pa.

7. The aluminum powder processing technology with high-precision oxygen content control according to claim 1, characterized in that: The aluminum powder particle classification unit (4) includes a centrifugal classifier, a cyclone classifier and a double cyclone classifier connected in series. The lower part of the centrifugal classifier, the cyclone classifier and the double cyclone classifier are all equipped with aluminum powder receiving hoppers. 10% to 20% of the total nitrogen in the gas balance unit (6) is returned to the centrifugal classifier.

8. The aluminum powder processing technology with high-precision oxygen content control according to claim 1, characterized in that: The nitrogen filtration unit (5) includes a bag filter and a receiving tank at the bottom of the bag filter. The nitrogen discharged from the bag filter enters the gas balance unit. The bag filter is equipped with a back-flushing device, which uses high-purity nitrogen as the back-flushing gas source.

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