Multi-stage grading precision control method for high-purity alumina powder

Abstract

This invention discloses a method for precise refinement control of high-purity alumina powder through multi-stage classification, belonging to the field of alumina classification control technology. The method includes the following steps: Step 1, raw material conveying; Step 2, constant-parameter airflow pulverization; Step 3, real-time particle size monitoring; Step 4, four-stage classification; Step 5, anti-agglomeration and loosening treatment; Step 6, verification and collection. Through multi-stage closed-loop classification and constant parameter control, the entire process of powder refinement, classification, and monitoring can be covered. This not only achieves precise control of powder particle size but also ensures batch-to-batch particle size consistency, making the powder quality more stable and providing reliable raw material support for high-purity alumina. Furthermore, through closed-loop anti-agglomeration and loosening treatment technology, the entire process control from suppressing fine powder agglomeration at the source to preventing wall adhesion during conveying is achieved, breaking through the industry bottleneck of easy powder agglomeration and improving the uniformity and purity of the powder.

Description

Technical Field

[0001] This invention relates to the field of alumina classification control technology, and more specifically, to a method for precise refinement control of multi-level classification of high-purity alumina powder. Background Technology

[0002] High-purity alumina refers to alumina powder with a purity of 99.99% or higher. It has excellent thermal stability, electrical insulation, and mechanical strength, and is a basic raw material for preparing key materials such as high-end ceramic substrates, phosphors, and sapphire. However, in actual production, the particle size distribution, particle shape, and degree of agglomeration of the powder directly affect subsequent molding, sintering, and the final performance of the product. If the particle size is uneven or the deviation is too large, it will lead to inconsistent shrinkage rate of ceramic substrates and an increase in internal defects. Therefore, multi-level classification control of the powder is necessary.

[0003] In the prior art, document CN119281493A discloses "an integrated control system for alumina grinding and grading", which includes: grinding alumina with a grinding machine, the ground alumina entering a rotatable screen through a pipeline, the rotatable screen sending photoelectric signals to a host computer, the host computer obtaining a first particle size range, the rotatable screen rotating to transport the alumina through a pipeline to a storage device, the storage device being equipped with a stirrer and a camera, the camera uploading the captured alumina image to the host computer, and the host computer obtaining a second particle size range.

[0004] The document with announcement number CN113371745A discloses "a system and method for producing high-purity alumina from fly ash resources", which includes a grinding mill, a pre-desiliconization reactor, an activation calcination reactor, an acid leaching reactor, an iron hydroxide purification reactor, a neutralization reactor, and a high-temperature calcination reactor connected in sequence along the direction of alumina extraction. The pre-desiliconization reactor is also connected to a pre-desiliconization agent dosing device, the activation calcination reactor is also connected to an activator dosing device, the acid leaching reactor is also connected to an acid leaching solution dosing device, the iron hydroxide purification reactor is also connected to an iron hydroxide purification agent dosing device, and the neutralization reactor is also connected to a neutralizer dosing device.

[0005] While existing technologies can improve particle size monitoring accuracy and achieve relatively precise classification in the alumina grinding and classification process by combining photoelectric screening and image recognition, and can also efficiently extract high-purity alumina from fly ash, remove impurities and recover by-products such as calcium silicate and silica gel through processes such as pre-desiliconization and stepwise precipitation, achieving resource utilization and near-zero emissions, existing technologies suffer from poor stability of classification parameters, insufficient particle size control precision, and lack of a closed-loop feedback adjustment mechanism, making it impossible to dynamically correct classification deviations. Furthermore, they have weak ability to inhibit powder agglomeration, limited adaptability to single classification specifications, insufficient particle size sampling and monitoring precision, and are prone to wall contamination during powder transport, making it difficult to ensure consistency between batches of high-purity alumina powder and meet the requirements for multi-level precise refinement. Summary of the Invention

[0006] This invention provides a method for precise control of multi-level classification of high-purity alumina powder, which can solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for precise refinement control of high-purity alumina powder through multi-stage classification, comprising: S1. Coarse α-alumina powder with a particle size of about 280.00µm is conveyed at a constant speed to the airflow pulverizing chamber through a closed channel. S2. Maintain constant pressure and carrier gas velocity in the airflow pulverizing chamber, and control the airflow collision time to complete the initial finening of powder. S3. Before the powder is classified after pulverization, a wet laser particle size analyzer is used to conduct real-time sampling and monitor the powder D50 and Span values. S4. By using a stepped speed change system combined with a closed-loop feedback mechanism, the speed of the classifying wheel and the airflow parameters are adjusted in real time to classify the powder into four grades and discharge them separately. S5. Each level of powder undergoes gas-solid separation and anti-agglomeration passivation treatment through an independent closed channel, followed by electrostatic elimination and micro-vibration loosening treatment. S6. The processed powders are stored in their respective sealed dust collection bins and output after batch verification.

[0008] Furthermore, in S1, the sealed channel is a dust-free sealed channel protected by inert gas, the conveying rate is precisely matched with the processing capacity of the airflow pulverizing chamber, and the conveying process is completely isolated from external impurities to avoid raw material contamination and moisture.

[0009] Furthermore, in S2, the constant pressure inside the airflow pulverizing chamber is 0.6±0.02MPa, the constant carrier airflow velocity is 18.5±0.3m / s, the airflow collision time is precisely controlled to 30 seconds, and the corresponding collision-speed cutting particle size Dc≈7.5µm; during the pulverization process, the chamber maintains a constant temperature of 25±1℃ and a constant humidity of ≤10%RH.

[0010] Furthermore, in S3, the sampling concentration of the wet laser particle size analyzer is controlled within the range of 10%-15% shading, and the powder D50 and Span value data are collected in real time and fed back in a closed loop.

[0011] Furthermore, in S4, the stepped speed system uses a high-precision variable frequency motor to drive the classifying wheel, and the initial speed of the classifying wheel is set to 2800±200rpm; the closed-loop feedback mechanism uses a PID algorithm to dynamically fine-tune the speed of the classifying wheel, the pressure of the crushing chamber, and the carrier gas flow rate parameters based on real-time particle size data and preset thresholds. The D50 values ​​of the four-stage powder are 0.350µm, 0.700µm, 0.950µm, and 1.350µm, respectively.

[0012] Furthermore, in S5, each level of powder corresponds to an independent sealed channel, and the gas-solid separation process is simultaneously subjected to surface passivation treatment in a high-purity inert gas atmosphere; an electrostatic elimination module and a micro-vibration loosening module are sequentially configured at the end of the channel, with a micro-vibration frequency of 5-10Hz and an amplitude of 0.5-1mm, and the entire process is maintained at 25±1℃ and humidity ≤10%RH.

[0013] Furthermore, in S6, the sealed dust collection chamber is an anti-static inert gas protection chamber. Batch verification meets the following requirements: powder D50 deviation ≤ ±0.015µm, Span fluctuation ≤ ±0.03, batch-to-batch CV value ≤ 3%, and Span value stable in the range of 1.25-1.4. After passing the verification, the powder is output for standby.

[0014] The beneficial effects of this invention's multi-stage classification and precise refinement control method for high-purity alumina powder are as follows: Through multi-stage closed-loop classification and constant parameter control, it can cover the entire process of powder refinement, classification, and monitoring. This not only achieves precise control of powder particle size but also ensures batch-to-batch particle size consistency, making the powder quality more stable and providing reliable raw material support for high-purity alumina. In addition, through closed-loop anti-agglomeration and loosening treatment technology, it achieves full-process control from suppressing fine powder agglomeration at the source to preventing wall adhesion during transportation, breaking the industry bottleneck of easy powder agglomeration and improving the uniformity and purity of the powder. At the same time, through the linkage control of parameters throughout the entire process, it improves the adaptability and subsequent processing performance of the powder, providing multiple specifications of powder for different process requirements, greatly enhancing the application adaptability and product competitiveness of high-purity alumina powder. Attached Figure Description

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and specific implementation methods.

[0016] Figure 1 This is a schematic diagram of the process flow for a multi-stage classification and precise refinement control method for high-purity alumina powder according to the present invention. Detailed Implementation

[0017] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] Example like Figure 1 As shown, a technical solution is provided: a method for precise control of multi-stage classification of high-purity alumina powder, comprising: Step 1: Raw material conveying Coarse α-alumina powder with a particle size of about 280.00µm is conveyed at a constant speed to the airflow pulverizing chamber through a closed channel. Specifically, the sealed channel is a dust-free sealed channel protected by inert gas. The conveying rate is precisely matched with the processing capacity of the airflow pulverizing chamber. The entire conveying process is isolated from external impurities, avoiding contamination and moisture of the raw materials.

[0019] First, the sealed channel is fully sealed. The channel body is formed by seamless welding process, and high temperature resistant sealing rings are installed at the interface. At the same time, high purity inert gas is continuously introduced from the feed end of the channel to form a stable positive pressure environment inside the channel. The positive pressure prevents external air, dust particles and water vapor from seeping in. The feed inlet is equipped with a sealing gate. After the raw material is introduced, the gate closes automatically to block the contact path between the raw material and external impurities. Finally, adjust the operating frequency and feeding speed of the sealed conveying mechanism to precisely match the rated processing capacity of the airflow pulverizer. Maintain a low-speed and stable feeding state during the conveying process to avoid the raw material being conveyed too fast, causing accumulation and blockage at the hopper opening, or conveying too slowly, causing material interruption and idling. Ensure that coarse powder enters the airflow pulverizer continuously, stably, and without impurities.

[0020] Step 2, Constant Parameter Airflow Pulverization Maintaining constant pressure and carrier gas velocity within the airflow pulverizing chamber and controlling the airflow collision time completes the initial finening of powder. Specifically, the constant pressure inside the airflow pulverizing chamber is 0.6±0.02MPa, the constant carrier airflow velocity is 18.5±0.3m / s, the airflow collision time is precisely controlled at 30 seconds, and the corresponding collision-speed cutting particle size Dc≈7.5µm; during the pulverization process, the chamber maintains a constant temperature of 25±1℃ and a constant humidity of ≤10%RH.

[0021] First, the high-precision pressure sensor and pneumatic flow control valve of the airflow pulverizing chamber are activated to collect the pressure and carrier gas velocity data in the chamber in real time. The valve opening is dynamically calibrated through a closed-loop control circuit to keep the pressure in the chamber stable at 0.6±0.02MPa and the carrier gas velocity precisely locked at 18.5±0.3m / s, thus establishing a uniform and stable high-pressure and high-speed airflow field, providing a constant and reliable power basis for powder collision and refinement. Then, after the airflow field parameters stabilize and meet the standards, the feed valve of the crushing chamber is opened, so that the α-alumina coarse powder is evenly dispersed into the chamber. The high-speed carrier gas carries the coarse powder and moves at high speed along the special guide channel in the chamber. High-frequency, high-speed rigid collisions occur between particles and between particles and the wear-resistant lining of the chamber wall. The high-precision electronic timing module is started simultaneously, and the timing starts from the time when the powder completely enters the airflow field, and the total time of airflow collision is precisely controlled to be 30 seconds. Next, during the entire powder collision refining process, the integrated constant temperature and humidity unit inside the chamber is turned on. Through the built-in multi-point temperature and humidity sensors, the environmental parameters inside the chamber are captured in real time, and the heating / cooling components and dehumidification unit are dynamically adjusted in conjunction to maintain a constant temperature environment of 25±1℃ and a relative humidity of ≤10%RH throughout the process. This reduces the surface energy of the refined powder from an environmental perspective and inhibits the occurrence of primary agglomeration. After the final 30-second collision cycle, the main airflow injection intensity is gradually reduced. At this point, the powder has undergone sufficient high-speed collision and has completed the initial particle size reduction, accurately forming a collision-cut particle size of approximately 7.5µm. The refined powder is uniformly suspended in the airflow inside the chamber, with a uniform particle size base and no obvious agglomerates, providing qualified powder material for subsequent real-time particle size monitoring and multi-stage classification.

[0022] Step 3: Real-time particle size monitoring Before the powder is classified after pulverization, a wet laser particle size analyzer is used to conduct real-time sampling and monitor the powder's D50 and Span values. Specifically, the wet laser particle size analyzer samples at a concentration controlled within the shading range of 10%-15%, and collects powder D50 and Span values ​​in real time with closed-loop feedback.

[0023] A small amount of representative sample is extracted from the fine powder suspended in the pulverizing chamber through a negative pressure closed sampling pipeline and sent directly into the wet dispersion chamber of the particle size analyzer. Deionized water is pre-filled in the chamber as a dispersion medium. A low-frequency and mild ultrasonic device is activated simultaneously to fully disperse the powder in the liquid phase and deagglomerate fine agglomerates, preventing the agglomerates from overlapping and causing the test data to be distorted. The shading degree is strictly limited to the range of 10%-15% by relying on the photoelectric concentration sensor built into the particle size analyzer to detect the light transmittance in real time. This is linked to the sample pump to dynamically fine-tune the feed amount of powder sample and the replenishment amount of dispersion. When the shading degree is too low, powder is automatically added; when it is too high, the dispersion is automatically diluted. The entire process is a closed-loop calibration to accurately lock the detection concentration range. In addition, the raw data of powder D50 and Span values ​​collected by the wet laser particle size analyzer are transmitted to the closed-loop feedback control unit in real time and without delay through a dedicated communication bus. The transmission process adopts a data verification protocol to avoid data loss or distortion caused by signal interference, and to ensure the timeliness of feedback adjustment. Finally, the closed-loop feedback control unit performs real-time filtering on the received granular data, eliminating abnormal data caused by instantaneous sampling fluctuations and instrument environmental interference, and using only stable and effective D50 and Span values ​​as the core basis for adjusting the grading parameters to ensure accurate and reliable subsequent grading control.

[0024] Step 4, Four-level classification By using a stepped speed control system combined with a closed-loop feedback mechanism, the speed of the classifying wheel and the airflow parameters are adjusted in real time to classify the powder into four grades and discharge them separately. Specifically, the stepped speed control system uses a high-precision variable frequency motor to drive the classifying wheel, with the initial speed of the classifying wheel set at 2800±200rpm. The closed-loop feedback mechanism uses a PID algorithm to dynamically fine-tune the speed of the classifying wheel, the pressure of the crushing chamber, and the carrier gas flow rate parameters based on real-time particle size data and preset thresholds. The D50 values ​​of the four-stage powders are 0.350µm, 0.700µm, 0.950µm, and 1.350µm, respectively.

[0025] First, the classifying wheel is precisely driven by the servo control system. After the machine is turned on, a certain period of time (e.g., 5-10 minutes) of no-load dynamic balance calibration is performed to avoid speed fluctuations caused by mechanical assembly errors, so that the classifying wheel is stably maintained in the initial speed range of 2800±200rpm, providing basic power conditions for powder classification. The PID control module of the closed-loop feedback mechanism receives the powder D50 and Span value data transmitted in step 3 in real time, compares the measured data with the preset D50 standard threshold of the four-level powder frame by frame, and automatically outputs an adjustment signal to slightly increase the speed of the classifying wheel and finely adjust and reduce the pressure of the grinding chamber and the carrier air flow rate when the measured particle size is too large. When the measured particle size is too small, the parameters are finely adjusted in the opposite direction. The centrifugal force and air flow drag are dynamically balanced throughout the process to accurately match the classification particle size requirements. In addition, the classifier wheel is equipped with four independent flow guide chambers. The chambers are precisely matched with the movement trajectory of the powder. Based on the principle that the centrifugal force increases with the increase of the particle size, the powders of different sizes are separated at the force field equilibrium position. The small-sized powder enters the first-level channel with the central airflow, while the large-sized powder is thrown to the periphery and enters the second to fourth-level channels in sequence. The entire process is completed under the protection of inert gas, avoiding cross-mixing of powders and the ingress of external impurities. Finally, during the classification process, the linkage between the classification wheel speed, airflow parameters and powder particle size is continuously monitored to form a real-time closed-loop adjustment circuit. This ensures that the D50 of each powder is strictly locked at the preset value, with the deviation controlled within ±0.015µm. The four grades of powder are then introduced into corresponding independent closed channels to provide uniform, unmixed qualified powder materials for subsequent anti-agglomeration passivation and loosening treatment.

[0026] Step 5: Anti-agglomeration and loosening treatment Each grade of powder undergoes gas-solid separation and anti-agglomeration passivation treatment through an independent closed channel, followed by electrostatic elimination and micro-vibration loosening treatment; Specifically, each powder level corresponds to an independent sealed channel, and the gas-solid separation process is carried out simultaneously with surface passivation treatment in a high-purity inert gas atmosphere; at the end of the channel, an electrostatic elimination module and a micro-vibration loosening module are configured in sequence, with a micro-vibration frequency of 5-10Hz and an amplitude of 0.5-1mm, and the entire process is maintained at 25±1℃ and humidity ≤10%RH.

[0027] First, the four-stage powders enter separate, isolated, and unconnected sealed channels. High-purity inert gas is continuously introduced into the channels to maintain a slightly positive pressure environment. The powder and carrier gas are efficiently separated by a multi-stage cyclone separation structure. During the separation process, a small amount of special passivating agent is sprayed in atomized form to form an ultra-thin passivation film on the surface of the powder particles, which precisely reduces the surface activity of the particles, inhibits the aggregation of fine powder, and avoids the formation of agglomerates. Then, the separated and passivated powder flow passes vertically through the electrostatic elimination module. The module has a built-in high-pressure ion air bar. The ion air evenly covers the cross section through which the powder flows, accurately neutralizing the static charge generated by friction during the conveying process, eliminating the powder agglomeration caused by electrostatic adsorption, and preventing the powder from adsorbing on the inner wall of the channel and forming wall-mounted accumulation. It also includes the fixed installation of an electromagnetic micro-vibration loosening module downstream of the static elimination module. The module is rigidly connected to the inner wall of the channel and outputs low-frequency micro-vibration force at a preset frequency of 5-10Hz and amplitude of 0.5-1mm. This force continuously acts on the inner wall of the channel, shaking off the trace amounts of powder adhering to the inner wall and breaking up the light and soft agglomerates formed during the powder conveying process. The vibration intensity is controllable and will not damage the original particle shape and particle size distribution of the powder. Finally, the entire independent sealed channel is equipped with multiple temperature and humidity sensors that are linked in real time with the constant temperature and humidity unit to dynamically adjust the environmental parameters inside the channel, stably maintaining a constant temperature of 25±1℃ and a low humidity environment of ≤10%RH. This completely isolates the intrusion of external air, water vapor and impurities, ensuring that the powder does not agglomerate or become contaminated by impurities during the entire process of preventing agglomeration and loosening, and is transported to the corresponding sealed dust collection bin in a uniform, loose and stable state.

[0028] Step 6: Verification and Collection The processed powders are stored in their respective sealed dust collection bins and output after batch verification is completed. Specifically, the sealed dust collection chamber is an anti-static inert gas protection chamber. Batch calibration meets the following requirements: powder D50 deviation ≤ ±0.015µm, Span fluctuation ≤ ±0.03, batch-to-batch CV value ≤ 3%, and Span value stable in the range of 1.25-1.4. After passing the calibration, the powder is output for standby.

[0029] The four-stage powder is precisely introduced into the corresponding dedicated antistatic inert gas protection chamber through independent closed conveying pipelines. The inner wall of the dust collection chamber is treated with an antistatic coating. High-purity inert gas is continuously introduced into the chamber to form a stable positive pressure protection layer. The bottom is equipped with a porous and breathable filter plate to prevent powder leakage and ensure smooth airflow. The chamber opening is equipped with a quick-sealing gate valve that closes and locks immediately after the powder is introduced, completely isolating the external air, dust, water vapor and static interference, and avoiding powder agglomeration or impurity contamination during the collection stage. The batch verification process involves allowing the powder to stand in the silo for a period of time (e.g., 10-15 minutes) to eliminate local density differences. Then, using a sterile, sealed sampler, equal amounts of powder are extracted from three different heights (top, middle, and bottom) in the silo and mixed to form a representative sample. The sample is then subjected to comprehensive and precise testing using a wet laser particle size analyzer. The four core indicators—D50 deviation, Span fluctuation, batch-to-batch CV value, and Span range—are checked one by one. The test data is uploaded to the quality control system in real time and generates an unalterable batch quality report, effectively avoiding subjective errors from manual testing. Finally, after verifying that all four core indicators meet the preset standards, the sealed unloading mechanism at the bottom of the silo is activated. The powder is output at a constant speed under continuous protection of inert gas and directly enters the aseptic sealing packaging process. There are no open exposure links throughout the process. If the test indicators fail to meet the standards, the powder is sent back to the fourth-level grading process for re-grading through a dedicated sealed return pipeline. At the same time, the system records abnormal parameters and triggers early warning prompts, forming a closed-loop quality control throughout the entire process to ensure that every batch of powder output meets the stringent quality requirements of high-purity alumina powder.

[0030] Comparative Example 1 Referring to prior art document CN119281493A in the background section, the details are as follows: Grinding and conveying: The alumina raw material is fed into the grinding mill to complete the grinding process. The ground alumina powder is then conveyed to the rotatable screen through a special pipeline.

[0031] Initial sieving and diameter measurement: The rotatable screen has multiple layers of screens with progressively decreasing apertures, and each screen is equipped with an infrared circuit. After the powder enters the screen, it is sieved. The infrared circuit sends a detection signal to the host computer in real time, and the host computer determines the first particle size range of the powder based on this signal.

[0032] Temporary storage and retesting: After screening, the rotatable screener rotates, and the powder falls into the storage container under the action of gravity; the stirrer in the storage container continuously stirs the powder, and the camera simultaneously captures dynamic images of the powder and uploads them to the host computer. The host computer obtains the second particle size range of the powder through image contour extraction and analysis.

[0033] Grinding determination: The host computer integrates the first and second particle size ranges to determine the final particle size range of the powder; if the particle size exceeds the preset standard, the storage device will return the powder to the grinder for re-grinding; if it meets the standard, the powder will be directly conveyed to the cyclone classifier.

[0034] Graded discharge: The powder enters the multi-stage cyclone classifier, where it is precisely graded according to the particle size difference by the cooperation of the turbine fan and the cyclone separation mechanism at each stage, and finally outputs graded alumina powder.

[0035] Comparative Example 2 Referring to prior art document CN113371745A in the background section, the details are as follows: Fly ash pretreatment: The fly ash to be treated is fed into a grinder for grinding. After grinding, the powder is sieved through a screen. Qualified fine powder is discharged into the pre-desiliconization reactor, while unqualified coarse powder is returned to the grinder for grinding again.

[0036] Pre-desiliconization reaction: Add sodium hydroxide, calcium hydroxide and other pre-desiliconization agents to the pre-desiliconization reactor, and control the reaction time to 30-1000 min; after the reaction, the mud-water mixture is separated into solid and liquid in the first sedimentation tank, the precipitate is sent to the activation and calcination reactor, and the supernatant is discharged into the calcium silicate purification reactor.

[0037] Calcium silicate purification: Calcium oxide, calcium chloride and other desiliconizing agents are added to the calcium silicate purification reactor. After the reaction, the mixture is separated by precipitation in the second precipitation tank. The supernatant is recycled to the pre-desiliconization reactor. The precipitate is high-purity calcium silicate.

[0038] Activation and calcination: Add activators such as sodium carbonate and sodium bicarbonate to the activation and calcination reactor, and calcine at 100-1500℃ for 10-500 minutes to convert the stable crystalline substances in fly ash into active components. The calcination product is discharged into the acid leaching reactor.

[0039] Acid leaching of aluminum: Add hydrochloric acid, sulfuric acid and other acid leaching solutions to the acid leaching reactor and carry out the acid leaching reaction at 25-100℃ for 30-600 min; the reaction product settles in the third sedimentation tank, and the supernatant (containing aluminum ions) is discharged into the ferric hydroxide purification reactor, and the precipitate is silica gel.

[0040] Iron removal and purification: Sodium hydroxide, sodium carbonate and other purifying agents are added to the ferric hydroxide purification reactor. After the reaction, the mixture is separated in the fourth precipitation tank. The supernatant (containing aluminate) is discharged into the neutralization reactor, and the precipitate is ferric hydroxide.

[0041] Neutralization and aluminum precipitation: Hydrochloric acid, nitric acid and other neutralizing agents are added to the neutralization reactor to adjust the pH of the system. After sedimentation, the system is separated in the fifth sedimentation tank. The aluminum hydroxide precipitate is sent to the high-temperature calcination reactor, and the supernatant is recycled to the ferric hydroxide purification reactor.

[0042] High-temperature aluminum production: Aluminum hydroxide precipitate is calcined at 400-1500℃ for 10-300 minutes, and after dehydration and decomposition, high-purity alumina powder is finally obtained.

[0043] To illustrate the difference between the high-purity alumina powder prepared using this control method and the comparative powder, we conducted the following experiment: Experimental objective: By comparing the high-purity alumina powder prepared by the multi-level classification and precise refinement control method of this invention with that prepared by comparative document CN119281493A (Comparative Example 1) and comparative document CN113371745A (Comparative Example 2), the advanced nature and practicality of the technical solution of this invention are verified from four core indicators: particle size accuracy, particle size distribution uniformity, batch stability, and powder agglomeration degree.

[0044] Experimental preparation: Experimental materials: All three experiments used the same batch of coarse α-alumina powder with a particle size of about 280.00µm. The purity of the raw materials was 99.99%, eliminating interference from differences in raw materials.

[0045] Experimental environment: The ambient temperature was uniformly controlled at 25±1℃ and the relative humidity was ≤10%RH to avoid the influence of temperature and humidity fluctuations on the powder state.

[0046] Testing equipment: The same calibrated wet laser particle size analyzer is used, and the sampling shading is strictly controlled at 10%-15% to ensure consistent testing accuracy.

[0047] Experimental batches: Five parallel batches of powder were prepared consecutively for each of the three experimental groups to ensure experimental repeatability.

[0048] Experimental Groups: Example group: Powder was prepared using the multi-level classification and precise refinement control method for high-purity alumina powder of the present invention.

[0049] Comparative Example 1: Powder was prepared using the integrated control system for alumina grinding and classification disclosed in prior art document CN119281493A.

[0050] Comparative Example 2: Powder was prepared using the method for producing high-purity alumina from fly ash disclosed in comparative document CN113371745A.

[0051] Experimental results: Experimental conclusion: Particle size accuracy: The D50 deviation of the example group was strictly controlled within ±0.015µm, which is far better than that of comparative examples 1 and 2, achieving precise and controllable particle size.

[0052] Uniformity of distribution: The Span value of the example group was stable in the range of 1.25-1.4, with a concentrated particle size distribution. The comparative example group had a wide distribution and an imbalance between the proportion of fine powder and coarse powder.

[0053] Batch stability: The batch CV value of the example group is ≤3%, and the batch consistency is excellent. The batch of the comparative example group fluctuates greatly and cannot meet the stability requirements of mass production.

[0054] Agglomeration inhibition effect: The agglomeration rate of the example group was ≤1.2%, which effectively solved the problem of fine powder agglomeration. The comparative example lacked a full-process anti-agglomeration design, and the agglomeration problem was prominent.

[0055] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for precise control of multi-stage classification of high-purity alumina powder, characterized in that: S1. Coarse α-alumina powder with a particle size of about 280.00µm is conveyed at a constant speed to the airflow pulverizing chamber through a closed channel. S2. Maintain constant pressure and carrier gas velocity in the airflow pulverizing chamber, and control the airflow collision time to complete the initial finening of powder. S3. Before the powder is classified after pulverization, a wet laser particle size analyzer is used to conduct real-time sampling and monitor the powder D50 and Span values. S4. By using a stepped speed change system combined with a closed-loop feedback mechanism, the speed of the classifying wheel and the airflow parameters are adjusted in real time to classify the powder into four grades and discharge them separately. S5. Each level of powder undergoes gas-solid separation and anti-agglomeration passivation treatment through an independent closed channel, followed by electrostatic elimination and micro-vibration loosening treatment. S6. The processed powders are stored in their respective sealed dust collection bins and output after batch verification.

2. The method for precise refinement control of high-purity alumina powder through multi-stage classification according to claim 1, characterized in that: In S1, the sealed channel is a dust-free sealed channel protected by inert gas. The conveying rate is precisely matched with the processing capacity of the airflow pulverizing chamber. The entire conveying process is isolated from external impurities, avoiding contamination and moisture of the raw materials.

3. The method for precise refinement control of high-purity alumina powder through multi-stage classification according to claim 1, characterized in that: In S2, the constant pressure inside the airflow pulverizing chamber is 0.6±0.02MPa, the constant carrier airflow velocity is 18.5±0.3m / s, the airflow collision time is precisely controlled to 30 seconds, and the corresponding collision-speed cutting particle size Dc≈7.5µm; during the pulverization process, the chamber maintains a constant temperature of 25±1℃ and a constant humidity of ≤10%RH.

4. The method for precise refinement control of high-purity alumina powder through multi-stage classification according to claim 1, characterized in that: In step S3, the sampling concentration of the wet laser particle size analyzer is controlled within the range of 10%-15% shading, and the powder D50 and Span values ​​are collected in real time and fed back in a closed loop.

5. The method for precise refinement control of high-purity alumina powder through multi-stage classification according to claim 1, characterized in that: In S4, the stepped speed control system uses a high-precision variable frequency motor to drive the classifying wheel, and the initial speed of the classifying wheel is set to 2800±200rpm. The closed-loop feedback mechanism uses a PID algorithm to dynamically fine-tune the speed of the classifying wheel, the pressure of the crushing chamber, and the carrier gas flow rate parameters based on real-time particle size data and preset thresholds. The D50 values ​​of the four-stage powders are 0.350µm, 0.700µm, 0.950µm, and 1.350µm, respectively.

6. The method for precise refinement control of high-purity alumina powder through multi-stage classification according to claim 1, characterized in that: In S5, each powder level corresponds to an independent sealed channel, and the gas-solid separation process is simultaneously subjected to surface passivation treatment in a high-purity inert gas atmosphere; at the end of the channel, an electrostatic elimination module and a micro-vibration loosening module are sequentially configured, with a micro-vibration frequency of 5-10Hz and an amplitude of 0.5-1mm, and the entire process is maintained at 25±1℃ and humidity ≤10%RH.

7. The method for precise refinement control of high-purity alumina powder through multi-stage classification according to claim 1, characterized in that: In S6, the sealed dust collection chamber is an anti-static inert gas protection chamber. Batch verification meets the following requirements: powder D50 deviation ≤ ±0.015µm, Span fluctuation ≤ ±0.03, batch-to-batch CV value ≤ 3%, and Span value stable in the range of 1.25-1.

4. After passing the verification, the powder is output for standby.

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