A continuous method for preventing agglomeration of high-purity alumina ultrafine powder

Abstract

This invention discloses a continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder, belonging to the field of high-purity alumina powder processing. The method uses coarse α-alumina powder as raw material, which is pretreated and then pulverized in an airflow milling chamber; followed by closed-loop feedback multi-stage classification, with four levels producing powders of different particle sizes; online monitoring using a wet laser particle size analyzer to strictly control particle size indicators; subsequently, anti-agglomeration passivation is completed in a closed environment; finally, electrostatic elimination and micro-vibration loosening are performed before discharge. This invention employs a dual anti-agglomeration mechanism of constant temperature, low humidity, and closed environment + powder surface passivation modification, effectively reducing the surface activity of ultrafine powder and inhibiting adsorption and aggregation reactions between particles, thus eliminating primary agglomeration of ultrafine powder from the source; combined with end-stage electrostatic elimination and micro-vibration loosening processes, it solves the problems of secondary agglomeration and wall adhesion during powder conveying, resulting in uniformly dispersed powder particles that perfectly meet the requirements of high-precision casting molding processes.

Description

Technical Field

[0001] This invention relates to the field of high-purity alumina powder processing, and more particularly to a continuous processing method for preventing agglomeration of high-purity alumina ultrafine powder. Background Technology

[0002] The core performance indicators of high-purity alumina ceramic substrates are highly dependent on the quality of the raw material powder. Besides the strict control of powder impurity content, the particle size, particle size distribution range, and particle dispersibility are key factors determining the microstructure and overall performance of the finished ceramic product. During ceramic casting and high-temperature sintering, small-particle-size ultrafine powders can significantly increase the contact area between particles and the probability of interfacial reactions, effectively improving the fluidity, plasticity, and molding uniformity of the ceramic slurry. This promotes uniform shrinkage and densification of the green body during sintering, ultimately resulting in alumina ceramic substrates that are non-porous, highly dense, have high thermal conductivity, and high strength. Therefore, achieving precise control and uniform distribution of ultrafine alumina powder particle size is a crucial prerequisite for ensuring the quality stability of high-end alumina ceramic products.

[0003] However, two major technological bottlenecks exist in the actual production and processing, severely restricting the mass production quality of ultrafine high-purity alumina powder. First, when the alumina powder particle size is refined to below 1.0 μm, the specific surface area increases dramatically, and the surface free energy rises significantly. This leads to easy intermolecular adsorption between particles, resulting in severe soft and hard agglomeration. This directly causes a widening of the particle size distribution and a significant decrease in dispersibility, resulting in defects such as uneven thickness of the cast blank, sintering voids, and excessive grain size differences, ultimately reducing the thermal conductivity and mechanical strength of the ceramic substrate. Second, the α-phase alumina crystal structure processed by this process is dense and extremely hard, second only to diamond. Conventional mechanical pulverization and ordinary airflow pulverization processes cannot achieve precise ultrafine pulverization, leading to problems such as uncontrollable particle size, poor classification accuracy, large batch fluctuations, and low fine powder qualification rate. Therefore, the refined mass production of ultrafine powder is extremely difficult.

[0004] Existing traditional powder processing technologies mostly employ extensive crushing, fixed-parameter grading, and open-type discharge production models, lacking closed-loop precise control and professional anti-agglomeration systems. This results in numerous problems such as severe agglomeration of ultrafine powders, large particle size distribution spans, high batch-to-batch particle size deviations, poor production continuity, and insufficient product consistency. Traditional processes cannot reliably produce ultrafine, high-purity alumina powder with uniform particle size, excellent dispersibility, and consistent specifications in large batches, failing to meet the stringent requirements of high-quality, high-stability, and high-consistency raw material powders for continuous casting and large-scale sintering production of high-end electronic ceramic substrates.

[0005] Therefore, there is a need for a high-purity alumina ultrafine powder processing technology that can achieve precise grading, efficient anti-agglomeration, and stable continuous mass production, in order to solve the industry's technical challenges in ultrafine powder processing. Summary of the Invention

[0006] Purpose of the invention: This invention provides a continuous processing method for preventing agglomeration of high-purity alumina ultrafine powder, which specifically addresses a series of technical defects in existing high-purity alumina ultrafine powder processing technology, such as easy agglomeration of ultrafine particles, low particle size control accuracy, uneven particle size distribution, poor batch stability, inability to achieve large-scale continuous production, and weak adaptability of finished powder.

[0007] Technical Solution: To solve the above-mentioned technical problems, according to one aspect of the present invention, more specifically, a continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder, through a synergistic process design of constant-condition pulverization, closed-loop dynamic classification, online real-time monitoring, closed anti-agglomeration treatment, and anti-static loose discharge, the method achieves precise and controllable particle size control, no agglomeration, high consistency, and continuous mass production of ultrafine powder while ensuring powder purity and processing efficiency. Specifically, it includes the following steps: S1, Raw material pretreatment High-purity, industrial-grade α-alumina coarse powder with uniform initial particle size was selected as the base raw material, with the initial particle size stably controlled at approximately 280.00 μm. To avoid impurities and large particle agglomerates affecting the subsequent grinding and classification accuracy, the coarse powder was first pretreated. This involved sieving to remove impurities, dust purification, and agglomeration, eliminating oversized particles, impurities, and agglomerates to ensure the powder was loose, clean, and uniform in size. After pretreatment, the raw material was uniformly, steadily, and at a constant speed fed into the airflow grinding chamber via a closed, quantitative feeding mechanism. This eliminated instability in the grinding process caused by feeding fluctuations, laying the foundation for precise grinding and classification.

[0008] S2, Constant Pressure and Constant Speed ​​Airflow Pulverization To address the issues of uneven grinding and uncontrolled particle size distribution caused by the high hardness of α-alumina, this invention employs a constant-pressure, constant-velocity airflow collision grinding mode to create a stable, uniform, and controllable grinding environment. During the grinding process, the internal conditions of the grinding chamber are controlled in a closed-loop manner throughout, strictly maintaining a constant working pressure of 0.6±0.02MPa and a stable carrier gas flow rate of 18.5±0.3m / s, ensuring a uniform and stable airflow field within the chamber, free from turbulence, negative pressure, and velocity fluctuations. The pre-treated coarse powder raw material rapidly enters the grinding chamber under the traction of a high-speed carrier gas flow. High-speed collisions, shearing, and friction occur between particles, coupled with uniform stirring within the chamber, resulting in continuous grinding for 30 seconds. This achieves thorough and uniform grinding of the coarse powder. Under these conditions, the corresponding particle size distribution (Dc≈7.5μm) achieved by the collision speed is equivalent to a cutting diameter of approximately 7.5μm. This efficiently breaks large coarse powder particles into ultrafine powder intermediates that meet grading requirements, while avoiding over-grinding and under-grinding, ensuring uniform particle size distribution and stable quality after grinding.

[0009] S3, Closed-loop feedback hierarchical control The mixed powder, after being pulverized by airflow, enters a high-precision classification system. This invention employs an intelligent stepped variable speed classification control system, the core of which is to achieve the sieving and separation of powders of different particle sizes by precisely controlling the rotation speed of the classifying wheel. The reference rotation speed of the classifying wheel is set at 2800±200 rpm, and it is equipped with a closed-loop feedback intelligent control mechanism. The system can collect real-time data on operating conditions such as pulverizing airflow pressure, carrier airflow velocity, powder feed concentration, and discharge particle size, and dynamically correct the rotation speed of the classifying wheel and airflow operating parameters in real time to offset process deviations caused by equipment operation and environmental fluctuations. This invention specifically sets four precise classification levels (1, 2, 3, and 4), each corresponding to a fixed target median particle size, namely D50=0.350μm, D50=0.700μm, D50=0.950μm, and D50=1.350μm, respectively. The classification mode can be freely switched according to different product production needs to achieve precise, directional, and efficient classification of multi-specification ultrafine high-purity alumina powder.

[0010] S4, Online Particle Size Real-Time Monitoring To ensure the consistency and stability of powder particle size during mass production, this invention employs a wet laser particle size analyzer for online real-time sampling and monitoring throughout the entire process, dynamically controlling powder particle size quality. During testing, the powder sampling concentration is strictly controlled, maintaining the detection opacity consistently within the 10%-15% range to avoid detection errors caused by excessively high or low concentrations, ensuring accurate and reliable test data. The system monitors core powder particle size indicators in real time, strictly controlling: powder D50 deviation ≤ ±0.015μm, Span value (particle size distribution span) stably controlled within the 1.25-1.4 range, and Span fluctuation ≤ ±0.03. Simultaneously, through data benchmarking and calibration, the coefficient of variation (CV) of powder performance between production batches is strictly guaranteed to be ≤3%, comprehensively controlling powder particle size accuracy and batch stability from a testing perspective, eliminating batch quality differences.

[0011] S5, Sealed anti-agglomeration passivation treatment Addressing the core challenges of high surface energy and easy agglomeration in ultrafine powders below 1μm, this invention abandons the traditional open production model and adopts a fully enclosed powder conveying and processing channel, achieving powder processing without any external exposure. After classification, the ultrafine powder enters an independent enclosed processing channel. The system precisely controls the environmental conditions throughout the process, maintaining a constant temperature and humidity environment with low humidity. Specifically, the temperature is controlled at 25±1℃ and the humidity ≤10%RH. This low-temperature, low-humidity enclosed environment significantly reduces the surface activity of the ultrafine powder, weakening the molecular adsorption forces between particles. Simultaneously, a dedicated anti-agglomeration passivation treatment process within the channel modifies and optimizes the surface of the ultrafine powder, effectively inhibiting the spontaneous aggregation and adhesion of nanoscale ultrafine particles. From both the production environment and process dimensions, this invention eliminates the problem of primary powder agglomeration at the source, significantly improving powder dispersibility. At the same time, the enclosed channel isolates external dust, moisture, and impurities, ensuring the high purity of the powder.

[0012] S6. Static electricity elimination and micro-vibration loosening discharge During high-speed conveying in a closed channel, ultrafine powders are highly susceptible to electrostatic adsorption due to particle friction and airflow scouring, leading to problems such as fine powder adhering to the wall, secondary particle agglomeration, and powder accumulation and clumping, affecting the quality of the output and the continuity of production. To address this, this invention integrates a dedicated electrostatic elimination module and a micro-vibration loosening discharge module at the end of the closed channel. The electrostatic elimination module neutralizes the electrostatic charge generated during powder conveying in real time, completely eliminating the electrostatic adsorption effect; the accompanying micro-vibration mechanism continuously vibrates at low frequency, promptly shaking off fine powder adhering to the inner wall of the channel, preventing fine powder from adhering to the wall and accumulating, while simultaneously loosening and dispersing the discharged powder, effectively preventing secondary agglomeration and clumping. The qualified powder after this dual anti-agglomeration and loosening treatment can achieve continuous, uniform, and stable discharge, ultimately yielding high-purity alumina ultrafine powder with excellent dispersibility, uniform particle size, no agglomeration, and no impurities.

[0013] Beneficial effects: (1) The present invention adopts a dual anti-agglomeration mechanism of constant temperature and low humidity closed environment + powder surface passivation modification, which effectively reduces the surface activity of ultrafine powder, inhibits the adsorption and aggregation reaction between particles, and eliminates the phenomenon of primary agglomeration of ultrafine powder from the source; combined with the end electrostatic elimination and micro-vibration loosening process, it completely solves the problem of secondary agglomeration and wall adhesion during the powder conveying process, and the final powder particles are evenly dispersed without obvious agglomerates, which perfectly meets the requirements of high-precision casting molding process.

[0014] (2) This invention relies on a triple precision control system of constant working condition crushing, closed-loop feedback dynamic classification, and online laser particle size real-time monitoring, which can realize fine control of powder particle size and stably achieve high precision indicators of D50 deviation ≤ ±0.015μm and Span fluctuation ≤ ±0.03. At the same time, it strictly controls the batch-to-batch CV value ≤3%, which completely solves the problems of large particle size fluctuation, wide distribution and obvious batch differences in traditional processes, and greatly improves the stability of powder quality.

[0015] (3) This invention adopts an integrated closed production line design for crushing, grading, anti-agglomeration treatment, and loose discharge. The entire process is free of powder exposure and external contamination, enabling continuous and stable production 24 hours a day. It eliminates the drawbacks of traditional intermittent production, excessive manual intervention, and large fluctuations in operating conditions, significantly improving production efficiency and ensuring stable product qualification rates. It is perfectly suited to the industrial and large-scale mass production needs of high-end alumina ceramic powder. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method of 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] Reference Figure 1 A continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder, characterized by comprising the following steps: S1. Raw material pretreatment: α-alumina coarse powder with an initial particle size of 280.00μm is selected as raw material. After screening to remove impurities, loosening agglomerates, and dust purification pretreatment, it is uniformly conveyed to the airflow pulverizing chamber through a closed quantitative feeding mechanism. S2. Constant pressure and constant speed airflow pulverization: The constant working conditions are maintained in the airflow pulverization chamber, and the pressure in the chamber is controlled at 0.6±0.02MPa and the carrier airflow velocity is 18.5±0.3m / s. The raw material is pulverized by high-speed airflow collision, shearing and stirring for 30s. The corresponding collision speed cutting particle size Dc≈7.5μm is obtained to obtain a mixed ultrafine powder intermediate. S3. Closed-loop feedback multi-stage classification control: When mixed powder enters the classification system, the classification wheel speed is controlled at 2800±200rpm. The classification wheel speed and airflow parameters are dynamically corrected in real time through a closed-loop feedback mechanism. Four classification levels are set: 1, 2, 3, and 4, which correspond to the production of target powders with D50=0.350μm, D50=0.700μm, D50=0.950μm, and D50=1.350μm, respectively. S4. Real-time online particle size monitoring: Powder samples are inspected in real time using a wet laser particle size analyzer, with the sampling opacity controlled at 10%-15%. Powder parameters are strictly controlled: D50 deviation ≤ ±0.015μm, Span value 1.25-1.4, Span fluctuation ≤ ±0.03, and batch-to-batch CV value ≤ 3%. S5. Sealed constant temperature and low humidity anti-agglomeration passivation treatment: The graded powder enters an independent sealed channel, and the ambient temperature is controlled at 25±1℃ and the humidity is ≤10%RH throughout the process. Gas-solid separation and anti-agglomeration passivation modification treatment of powder are completed in a sealed environment. S6. Static electricity elimination and micro-vibration loosening continuous discharge: At the end of the closed channel, the static electricity of the powder is neutralized by the static electricity elimination module, and the micro-vibration loosening module is used to prevent fine powder from sticking to the wall and secondary agglomeration, so as to realize the continuous and stable discharge of high-purity alumina ultrafine powder.

[0019] Example 1

[0020] This embodiment describes a preferred process for the production of conventional high thermal conductivity alumina ceramic substrates. The specific processing steps are as follows: α-alumina coarse powder with a particle size of 280.00 μm was selected, and after impurity removal, it was sent into the airflow pulverizing chamber; The pressure inside the crushing chamber is controlled at 0.6 MPa and the carrier air velocity is 18.5 m / s. High-speed airflow collision crushing lasts for 30 seconds. The grading wheel speed is set to 2800 rpm, the 2nd grading gear is selected, and the target D50 = 0.700 μm; Online monitoring with a wet laser particle size analyzer was conducted, with a sampling shading level of 12%, and control measures including Span=1.3, D50 deviation ±0.01μm, and batch CV=2.5%. The temperature is maintained at 25℃ and the humidity at 8%RH throughout the process, and the powder completes gas-solid separation and anti-agglomeration passivation in a closed channel. Static electricity is eliminated at the end of the channel, and micro-vibration loosens the material, allowing for continuous discharge.

[0021] After processing in this embodiment, the resulting high-purity alumina ultrafine powder is loose in appearance, free of lumps and agglomerates. The median particle size (D50) is stably controlled at around 0.700 μm, the particle size distribution span value is 1.3, the particle size deviation is extremely small, and the batch variation coefficient is only 2.5%. The powder exhibits excellent overall uniformity and dispersibility. This powder specification is suitable for mainstream continuous casting molding processes for alumina ceramic substrates. After sintering, the substrate has high density, uniform thermal conductivity, and stable mechanical properties, without defects such as voids or warping, resulting in a significant improvement in product yield.

[0022] Example 2

[0023] The process flow in this embodiment is basically the same as that in Embodiment 1, using the same raw material pretreatment, constant pressure and constant speed crushing, closed anti-agglomeration, and electrostatic loose discharge processes. The core difference lies in adapting the classification parameters to the production requirements of medium-sized powders: adjusting the classification wheel speed to 2600 rpm, selecting a 3-level classification setting, and setting the powder target D50 = 0.950 μm; precisely controlling the process parameters during the online detection stage to control the powder D50 deviation ≤ ±0.012 μm, the particle size distribution Span value to be stable at 1.35, and the CV value of the entire batch of powder to be controlled at 2.8%; maintaining an ambient temperature of 24℃ and an ambient humidity of 9%RH throughout the process to ensure anti-agglomeration effect and operational stability.

[0024] The medium-particle-size high-purity alumina ultrafine powder prepared in this embodiment meets all the industry's high-end production standards. The powder particles are uniformly dispersed, free of agglomeration and impurities, with a narrow particle size distribution range and high batch stability. It is perfectly suited for the preparation processes of alumina structural ceramics, heat dissipation substrates, and precision ceramic components requiring medium particle size. The product exhibits excellent forming effect and sintering performance, and possesses extremely high industrial application value. 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 continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder, characterized in that, Includes the following steps: S1. Raw material pretreatment: α-alumina coarse powder with an initial particle size of 280.00μm is selected as raw material. After screening to remove impurities, loosening agglomerates, and dust purification pretreatment, it is uniformly conveyed to the airflow pulverizing chamber through a closed quantitative feeding mechanism. S2. Constant pressure and constant speed airflow pulverization: The constant working conditions are maintained in the airflow pulverization chamber, and the pressure in the chamber is controlled at 0.6±0.02MPa and the carrier airflow velocity is 18.5±0.3m / s. The raw material is pulverized by high-speed airflow collision, shearing and stirring for 30s. The corresponding collision speed cutting particle size Dc≈7.5μm is obtained to obtain a mixed ultrafine powder intermediate. S3. Closed-loop feedback multi-stage classification control: When mixed powder enters the classification system, the classification wheel speed is controlled at 2800±200rpm. The classification wheel speed and airflow parameters are dynamically corrected in real time through a closed-loop feedback mechanism. Four classification levels are set: 1, 2, 3, and 4, which correspond to the production of target powders with D50=0.350μm, D50=0.700μm, D50=0.950μm, and D50=1.350μm, respectively. S4. Real-time online particle size monitoring: Powder samples are inspected in real time using a wet laser particle size analyzer, with the sampling opacity controlled at 10%-15%. Powder parameters are strictly controlled: D50 deviation ≤ ±0.015μm, Span value 1.25-1.4, Span fluctuation ≤ ±0.03, and batch-to-batch CV value ≤ 3%. S5. Sealed constant temperature and low humidity anti-agglomeration passivation treatment: The graded powder enters an independent sealed channel, and the ambient temperature is controlled at 25±1℃ and the humidity is ≤10%RH throughout the process. Gas-solid separation and anti-agglomeration passivation modification treatment of powder are completed in a sealed environment. S6. Static electricity elimination and micro-vibration loosening continuous discharge: At the end of the closed channel, the static electricity of the powder is neutralized by the static electricity elimination module, and the micro-vibration loosening module is used to prevent fine powder from sticking to the wall and secondary agglomeration, so as to realize the continuous and stable discharge of high-purity alumina ultrafine powder.

2. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: In step S1, the raw material pretreatment needs to remove oversized particles, impurities, and agglomerates to ensure that the feed powder is loose, clean, and uniform in size. The feeding process is also closed to prevent deviations in the crushing conditions caused by feeding fluctuations.

3. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: In step S2, the airflow field inside the airflow pulverizing chamber is uniform and stable, with no turbulence, negative pressure, or flow velocity fluctuations. Through high-speed particle collisions, frictional shearing, and combined with the stirring effect inside the chamber, the coarse powder is fully and uniformly pulverized, avoiding the problems of over-pulverization and insufficient pulverization.

4. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: In step S3, the closed-loop feedback mechanism collects real-time data on the crushing air pressure, carrier air velocity, powder feed concentration, and discharge particle size, dynamically offsetting process deviations caused by equipment operation and environmental fluctuations, and achieving precise directional grading of multi-specification powders.

5. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: In step S4, detection errors are avoided by controlling the shading degree in a fixed range, and calibration is performed based on real-time data to comprehensively ensure the accuracy of powder particle size and the consistency of batch production.

6. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: In step S5, a fully enclosed, non-exposed processing mode is adopted. The surface activity of the ultrafine powder is reduced by the constant temperature and low humidity environment, which weakens the adsorption force of the particle molecules. Combined with surface passivation modification, the agglomeration of ultrafine powder is inhibited from the source. At the same time, external impurities and water vapor pollution are isolated to ensure the high purity quality of the powder.

7. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: In step S6, the electrostatic elimination module completely neutralizes the electrostatic charge generated by powder conveying friction and airflow scouring. The micro-vibration mechanism operates continuously at low frequency, shaking off the fine powder adhering to the inner wall of the channel and loosening the discharged powder, thus completely eliminating the phenomenon of secondary agglomeration and clumping of powder.

8. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: The overall process adopts an integrated closed production line for crushing, grading, anti-agglomeration passivation, and electrostatic loosening discharge, which can achieve 24-hour uninterrupted continuous mass production and is suitable for the industrial-scale production of high-end alumina ceramic powder.

9. The continuous anti-agglomeration treatment method for high-purity alumina ultrafine powder according to claim 1, characterized in that: The four types of ultrafine powders prepared are suitable for the differentiated production needs of ultrathin casting, thick film sintering, high-strength ceramics, and high thermal conductivity substrates. The powders have excellent dispersibility and uniform particle size distribution, which can effectively improve the sintering density, thermal conductivity and mechanical properties of alumina ceramics.

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