A method and system for the continuous preparation of high-purity aluminum nitride powder using a fluidized bed method.

Abstract

This invention relates to a continuous, fluidized bed preparation method for high-purity aluminum nitride powder, comprising: mixing alumina powder and conductive carbon black, adding a dispersant, and then grinding, granulating, and pre-fluidized dispersing to obtain a fluidized homogeneous mixture; the material is in a suspended fluidized state and is subsequently dried and impurity removed to obtain a pretreated material; using nitrogen as the fluidizing medium and nitriding reaction gas, the material is kept in a stable suspended fluidized state and a carbothermic reduction nitriding reaction is completed under preset conditions to obtain coarse aluminum nitride powder; using a mixture of nitrogen and inert gas as the fluidizing medium, the material is kept in a suspended fluidized state and residual carbon is removed from the powder in an oxygen-free environment to obtain decarburized aluminum nitride powder; and particle size classification, cooling, and automated packaging are performed under a nitrogen-sealed fluidized bed atmosphere to obtain high-purity aluminum nitride powder. This invention achieves continuous, fluidized bed preparation of aluminum nitride powder, resulting in a significant improvement in product quality.

Description

Technical Field

[0001] This invention belongs to the field of advanced electronic ceramic material preparation technology, specifically relating to a method and system for the continuous preparation of high-purity aluminum nitride powder using a full-process fluidized bed. Background Technology

[0002] Aluminum nitride powder is the core material for preparing high thermal conductivity aluminum nitride ceramic substrates and tacks. It is widely used in high-end fields such as semiconductor packaging, high-power electronic devices, aerospace, and defense. Its preparation process is mainly based on carbothermal reduction, which has the advantages of wide availability of raw materials and easy scalability.

[0003] However, existing carbothermal reduction methods for preparing aluminum nitride powder all employ static / batch processes, which present several technical bottlenecks: 1. Traditional processes are segmented operations, requiring manual or mechanical handling of materials to different reactor bodies. During this process, materials are easily exposed to air, leading to increased oxygen content in the powder and affecting the product's thermal properties; 2. During the reaction, the material is in a static, stacked state, resulting in insufficient contact with the reaction gases and heat medium, low mass and heat transfer efficiency, and problems such as uneven reaction and low nitride conversion rate. Furthermore, the powder has high impurity content and poor batch-to-batch consistency, making it difficult to obtain high-quality powder; 3. Static processes require repeated heating and cooling, resulting in high heat loss, high energy consumption, and low production efficiency, failing to meet the large-scale, high-quality demands of high-end aluminum nitride powder applications; 4. In recent years, there have been some attempts at fluidization technology, but these have only been applied to a single stage of aluminum nitride preparation, failing to achieve continuous fluidized operation throughout the entire process. Moreover, current single-stage fluidization technologies are prone to powder agglomeration, deposition, and bridging, leading to fluidization failure.

[0004] Therefore, how to achieve continuous fluidized operation throughout the entire process, accurately control product quality, and significantly reduce energy consumption in the preparation of aluminum nitride powder has become an urgent technical problem to be solved. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a method and system for the continuous, fluidized bed preparation of high-purity aluminum nitride powder. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a method for the continuous preparation of high-purity aluminum nitride powder using a fluidized bed process, comprising the following steps: S1. After mixing alumina powder and conductive carbon black, a dispersant is added and the mixture is ground. The ground material is granulated and the particle size is controlled to a preset size. Then, nitrogen is introduced into the granulated material in a fluidized bed homogenizer for pre-fluidized dispersion to obtain a fluidized bed homogenizer. S2. The fluidized homogenized material is conveyed to a continuous fluidized pretreatment device through a nitrogen pneumatic conveying system. Under the nitrogen fluidized atmosphere, the material is made to be in a suspended fluidized state and is dried and removed in sequence to obtain the pretreated material. S3. The pretreated material is continuously conveyed to a high-temperature rotary fluidization reactor through a nitrogen pneumatic conveying system. Nitrogen is used as the fluidization medium and nitriding reaction gas to make the material in a stable suspended fluidized state and complete the carbothermic reduction nitriding reaction under preset conditions to obtain aluminum nitride coarse powder. S4. The aluminum nitride coarse powder is conveyed to a high-temperature decarburization furnace through a nitrogen pneumatic conveying system. A mixture of nitrogen and inert gas is used as the fluidization medium to make the material in a suspended fluidized state and remove residual carbon from the powder in an oxygen-free environment to obtain decarburized aluminum nitride powder. S5. The decarburized aluminum nitride powder is transported to the post-processing and finished product packaging section through a nitrogen pneumatic conveying system. Under the nitrogen-sealed fluidized atmosphere, it is subjected to particle size classification, cooling and automated packaging to obtain high-purity aluminum nitride powder.

[0006] In one embodiment of the present invention, step S1 includes: After wet mixing of alumina powder and conductive carbon black at a molar ratio of (3.0-4.0):1, octylphenol polyoxyethylene ether dispersant at a mass ratio of 3-5% is added. The mixture is then ball-milled to uniformly coat the alumina surface with carbon black, forming a composite precursor. The precursor phase composite material is granulated to control the particle size D50 to be 0.5-1.2 μm, forming a fluidizable precursor phase composite material; Nitrogen gas is introduced into the composite precursor in a fluidized homogenizing apparatus for pre-fluidized dispersion to obtain the fluidized homogenized material.

[0007] In one embodiment of the present invention, step S2 includes: The fluidized homogenized material is conveyed to a continuous pretreatment unit via a nitrogen pneumatic conveying system, and nitrogen gas with a flow rate of 3-4 m / s is introduced to dry the material in a suspended fluidized state at a drying temperature of 120-200℃. After cooling, HCl gas with a flow rate of 3-4 m / s is introduced to remove impurities from the dried material to obtain the pretreated material.

[0008] In one embodiment of the present invention, in step S3, The furnace body of the high-temperature rotary fluidized bed reactor is made of SiN and AlN ceramic composite furnace tubes, and the rotation speed is 2-15 r / min; The reaction conditions for the carbothermic reduction nitridation reaction include: nitrogen flow rate of 0.8-2.0 m / s, furnace temperature of 1700-1800℃, system pressure of 0.10-0.15 MPa, material residence time of 2.5-4.0 h, and the material in a stable suspended fluidized state in the furnace.

[0009] In one embodiment of the present invention, in step S4, The compound gas comprises a mixture of nitrogen, argon, and carbon dioxide, with a volume ratio of nitrogen, argon, and carbon dioxide of (5:3:2) to (7:2:1); the flow rate of the compound gas is 0.5-1.5 m / s; the temperature inside the high-temperature decarbonization furnace is 850-950℃; and the material residence time is 1.5-3.0 h.

[0010] In one embodiment of the present invention, in step S5, The high-purity aluminum nitride powder has a particle size D50 ≤ 1.07 μm, oxygen content ≤ 0.60%, nitrogen content 33.2~34.2%, carbon content ≤ 320 ppm, and specific surface area 3.27~3.47 m². 2 / g.

[0011] Another embodiment of the present invention provides a system for the continuous, fluidized bed preparation of high-purity aluminum nitride powder, used to implement the method described in the above embodiments, comprising: the system being a fully enclosed continuous structure with internal pressure greater than external atmospheric pressure; the system including multiple fluidization units, an intelligent control unit, and a nitrogen protection unit, wherein, The multiple fluidization units include, in sequence, a fluidization homogenizing device, a continuous fluidization pretreatment device, a high-temperature rotary fluidization reactor, a high-temperature decarbonization furnace, a fluidization grading device, a fluidization post-treatment device, and an automated sealed packaging device. A buffer chamber is provided between two adjacent fluidization units. The buffer chamber and the fluidization unit are connected by a nitrogen pneumatic conveying system for material transport. The discharge rate of the previous section is equal to the feed rate of the next section. Each fluidization unit is equipped with a pressure regulating valve, a gas inlet, and a tail gas recovery port.

[0012] In one embodiment of the present invention, the nitrogen pneumatic conveying system is a dense phase pneumatic conveying system; The nitrogen pneumatic conveying system is equipped with fluidization nozzles at each port connecting to the previous fluidization unit, and the airflow direction of the fluidization nozzles is towards the inlet of the next fluidization unit.

[0013] In one embodiment of the present invention, the pressure within the system is 0.10–0.15 MPa; A dual dynamic sealing structure, consisting of an airlock valve and a nitrogen curtain, is adopted at the inlet of the fluidized bed homogenizing device, the grading port of the fluidized bed grading device, and the outlet of the automated sealed packaging device.

[0014] In one embodiment of the present invention, the system further includes: an intelligent control unit and a nitrogen protection unit; The intelligent control unit includes multiple sensors connected to a PLC controller. These multiple sensors include a powder flow rate sensor, a suspension monitoring sensor, a temperature and pressure sensor, and an atmosphere concentration sensor. The powder flow rate sensor is installed at the inlet and outlet of the buffer chamber. The suspension monitoring sensor and the temperature and pressure sensor are installed inside each fluidization unit. The atmosphere concentration sensor includes an oxygen sensor and a gas composition sensor installed inside each fluidization unit and at the target point. The nitrogen protection unit includes a nitrogen generator, a nitrogen storage tank, a compound gas mixing tank, and nitrogen inlets and exhaust gas recovery ports located in each core fluidization unit. The nitrogen generator is connected to the nitrogen storage tank, which is connected to each gas inlet via a pipeline. The inlet of the compound gas mixing tank is connected to the nitrogen storage tank and an inert gas source, and the outlet is connected to the inlet of the high-temperature decarbonization unit.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is based on the carbothermal reduction method and uses nitrogen as the core fluidizing medium. By placing the entire process of granulation material dispersion, pretreatment, carbothermal reduction nitridation reaction, decarburization, post-treatment, and packaging in a fluidized environment, and using a nitrogen pneumatic conveying system to achieve continuous, closed-loop transport between processes, the entire process is protected by closed nitrogen, achieving continuous fluidized operation from raw materials to finished products. Compared to existing static / intermittent processes, this avoids material contact with air during transport, significantly reducing the oxygen content of the powder. Simultaneously, the fluidized state allows for full contact between the material and the reactant gas, significantly improving mass and heat transfer efficiency and solving the problems of uneven reaction and low nitridation conversion rate. Continuous production eliminates heat loss from repeated heating and cooling, significantly reducing energy consumption and improving production efficiency. Therefore, this method solves the technical bottlenecks in existing aluminum nitride powder preparation, such as insufficient reaction, difficulty in controlling oxygen impurities, poor batch stability, and low production efficiency. It not only achieves continuous fluidized preparation of aluminum nitride powder but also significantly improves product quality and optimizes production efficiency and energy consumption. Attached Figure Description

[0016] Figure 1 A schematic flow diagram of a method for the continuous preparation of high-purity aluminum nitride powder using a fluidized bed method, provided in an embodiment of the present invention; Figure 2 The image shows the XRD pattern of the aluminum nitride sample prepared in this invention. Figure 3 SEM image of the aluminum nitride sample prepared in this invention; Figure 4This is a particle size distribution diagram of the aluminum nitride sample prepared in this invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0018] Example 1 This invention provides a continuous fluidized bed method for preparing high-purity aluminum nitride powder. This method integrates fluidization technology into the entire process of aluminum nitride preparation by carbothermal reduction, using nitrogen as the core fluidization medium to simultaneously achieve material suspension fluidization reaction, continuous pneumatic conveying, and oxygen-free closed protection, thus balancing high product quality and large-scale production.

[0019] Please see Figure 1 , Figure 1 This is a schematic flow diagram of a continuous fluidized bed method for preparing high-purity aluminum nitride powder, provided as an embodiment of the present invention. This method integrates fluidization technology into the entire process of aluminum nitride preparation via carbothermal reduction, using nitrogen as the core fluidization medium to simultaneously achieve material suspension fluidization reaction, continuous pneumatic conveying, and oxygen-free enclosed protection. Specifically, it includes the following steps: S1. After mixing alumina powder and conductive carbon black, a dispersant is added and the mixture is ground. The ground material is granulated and the particle size is controlled to a preset size. Then, nitrogen is introduced into the granulated material in a fluidized bed homogenizer for pre-fluidized dispersion to obtain a fluidized bed homogenizer. S2. The fluidized homogenized material is conveyed to the continuous fluidized pretreatment unit through a nitrogen pneumatic conveying system. Under the nitrogen fluidized atmosphere, the material is made to be in a suspended fluidized state and is dried and removed in sequence to obtain the pretreated material. S3. The pretreated material is continuously fed into a high-temperature rotary fluidized bed reactor. Nitrogen is used as the fluidizing medium and nitriding reaction gas to make the material in a stable suspended fluidized state and complete the carbothermic reduction nitriding reaction under preset conditions to obtain aluminum nitride coarse powder. S4. The coarse aluminum nitride powder is conveyed to the high-temperature decarburization furnace through a nitrogen pneumatic conveying system. The mixed gas of nitrogen and inert gas is used as the fluidization medium to make the material in a suspended fluidized state and remove residual carbon in the powder in an oxygen-free environment to obtain decarburized aluminum nitride powder. S5. The decarburized aluminum nitride powder is transported to the post-processing and finished product packaging section through a nitrogen pneumatic conveying system. Under the nitrogen-sealed fluidized atmosphere, it is subjected to particle size classification, cooling and automated packaging to obtain high-purity aluminum nitride powder.

[0020] The entire process of steps S1-S5 above adopts a closed nitrogen protection system, and the material is always in a fluidized environment of nitrogen or compound gas, with no contact with air.

[0021] This embodiment of the method is based on carbothermal reduction and uses nitrogen as the core fluidizing medium. By placing the entire process of granulation material dispersion, pretreatment, carbothermal reduction nitridation reaction, decarburization, post-treatment, and packaging in a fluidized environment, and using a nitrogen pneumatic conveying system to achieve continuous, closed-loop transport between processes, the entire process employs closed-loop nitrogen protection, eliminating material contact with air and achieving continuous fluidized operation from raw materials to finished products. Compared to existing static / intermittent processes, this avoids material contact with air during transport, significantly reducing the oxygen content of the powder. Simultaneously, the fluidized state allows for full contact between the material and the reactant gases, significantly improving mass and heat transfer efficiency and solving problems such as uneven reaction and low nitridation conversion rate. Continuous production eliminates heat loss from repeated heating and cooling, significantly reducing energy consumption and improving production efficiency. Therefore, this method solves the technical bottlenecks in existing aluminum nitride powder preparation, such as insufficient reaction, difficulty in controlling oxygen impurities, poor batch stability, and low production efficiency. It not only achieves continuous fluidized preparation of aluminum nitride powder but also significantly improves product quality and optimizes production efficiency and energy consumption.

[0022] In one specific embodiment, step S1 employs interface-coordinated dispersion and homogenization technology for automated batching and fluidized bed mixing, specifically including: Industrial-grade high-purity alumina powder with a purity ≥ 99.99% is wet-mixed with conductive carbon black at a mass ratio of 3.0-4.0:1 in an aqueous phase. Then, a dispersant is added to the aqueous phase system for wet mixing. Octylphenol polyoxyethylene ether OP-10 can be used as the dispersant, and the mass of the dispersant is 3-5% of the total mass of alumina powder and conductive carbon black.

[0023] The mixture was then ball-milled in a horizontal ball mill. Through the mechanical force of the ball mill, carbon black was uniformly coated on the surface of the alumina particles, forming a composite precursor with excellent flowability. After ball milling, the material was granulated in a spray granulation drying tower, controlling the particle size D50 to be 0.5-1.2 μm, thereby obtaining a fluidizable precursor phase composite material.

[0024] Then, nitrogen gas is introduced into the composite precursor in a fluidized bed homogenizing device for pre-fluidization and dispersion, further breaking up agglomerates to obtain a stable and fluidizable fluidized bed homogenate. For example, the fluidized bed homogenizing device can be a raw material storage tank.

[0025] This step, through the synergistic effect of dispersants, ball milling mechanical force, and granulation, solves the technical challenge of fluidizing alumina and carbon black, achieving a transformation from "non-fluidizable" to "stable fluidization." It effectively optimizes powder flowability, improves powder flowability from the source, eliminates primary agglomeration, and avoids fluidization failure caused by powder agglomeration and bridging during subsequent fluidization processes, laying the foundation for stable operation throughout the entire process. By precisely controlling the particle size D50 (0.5-1.2 μm) and matching the air velocity with the particle size in subsequent stages (low air velocity for fine powder to prevent entrainment, and high air velocity for coarse powder to ensure suspension), it achieves "no entrainment, no deposition."

[0026] In one specific embodiment, step S2, which involves continuous fluidization preprocessing, specifically includes: The fluidized homogenized material is conveyed to the continuous pretreatment unit via a nitrogen dense-phase pneumatic conveying system. The conveying pipeline of the nitrogen dense-phase pneumatic conveying system is equipped with fluidization nozzles, with the airflow direction directed towards the inlet of the next fluidization unit. Nitrogen is injected in real-time during the conveying process to break up any bridging or deposition of powder within the pipeline, preventing blockages. The continuous pretreatment unit can be a raw material storage tank. This storage tank can be the same device as the fluidized homogenization unit or a different device. If it is the same device, the nitrogen dense-phase pneumatic conveying system is not required.

[0027] In a continuous fluidized bed pretreatment unit, nitrogen gas is introduced at a flow rate of 3-4 m / s to dry the material in a suspended fluidized state at a drying temperature of 120-200℃ to remove adsorbed water from the material. After drying, the material is cooled down, and then HCl gas at a flow rate of 3-4 m / s is introduced to fluidize and remove impurities such as volatile substances, iron, and calcium, resulting in pretreated material.

[0028] This step controls the gas flow rate to keep the material in a suspended fluidized state, preventing powder agglomeration and sedimentation, and effectively removing moisture and impurities in the suspended fluidized state, thus avoiding the introduction of impurities in subsequent reactions.

[0029] In one specific embodiment, step S3, which involves a high-temperature fluidized bed nitriding reaction, specifically includes: The pretreated material is continuously conveyed to a high-temperature rotary fluidized bed reactor via a nitrogen pneumatic conveying system. The reactor is a horizontal reactor with a SiN / AlN ceramic composite furnace tube. It has a material conveying mechanism that can rotate around an axis, allowing the material to pass sequentially from the front buffer zone through the heating section, the holding section, and the cooling section to the rear end. Gas inlets and outlets are provided at the buffer zone and the rear end, respectively, to form an axial airflow. Furthermore, the furnace rotation speed is 2-15 r / min, nitrogen is used as the fluidizing medium and nitriding reaction gas, the nitrogen flow rate is controlled at 0.8-2.0 m / s, the furnace temperature is 1700-1800℃, the system pressure is 0.10-0.15 MPa, and the material residence time in the furnace is 2.5-4.0 h. By adjusting the nitrogen flow rate and the furnace rotation speed, the material is kept in a stable suspended fluidized state in the furnace to complete the carbothermic reduction nitriding reaction. The reaction equation is Al2O3+3C+N2=2AlN+3CO, and coarse aluminum nitride powder is obtained.

[0030] This step, through the synergistic effect of the rotation of the furnace body and the axial airflow, enables the material to be in a stable suspended fluidized state inside the furnace. This not only effectively prevents high-temperature wall adhesion and material deviation, but also ensures that the material is in full contact with nitrogen, greatly improving the nitriding conversion rate and ensuring product consistency.

[0031] In one specific embodiment, step S4 employs a controlled atmosphere compounding oxygen-free decarburization technology for fluidized bed oxygen-free decarburization, specifically including: Aluminum nitride coarse powder is conveyed to a high-temperature decarburization furnace via a nitrogen pneumatic conveying system. A mixed gas of nitrogen and inert gas is used as the fluidizing medium. Specifically, the mixed gas is a mixture of nitrogen, argon, and carbon dioxide in a volume ratio of (5:3:2) to (7:2:1). The mixed gas is supplied on demand after being proportioned online by a mixed gas mixing tank. The flow rate of the mixed gas is controlled at 0.5-1.5 m / s to maintain the material in a fluidized state. The furnace temperature is 850-950℃, and the material residence time is 1.5-3.0 h. Residual carbon in the powder is removed under an oxygen-free environment to obtain decarburized aluminum nitride powder.

[0032] This step effectively removes residual carbon without introducing oxygen impurities, avoiding an increase in the oxygen content of the powder and obtaining low-oxygen, low-carbon aluminum nitride powder, thus solving the problem that traditional decarburization processes easily lead to secondary oxidation of the powder.

[0033] In one specific embodiment, step S5 involves post-processing and finished product packaging, specifically including: The decarburized aluminum nitride powder is conveyed to a fluidized bed classifier via a nitrogen pneumatic conveying system. The fluidized bed classifier can be a closed vibrating screen.

[0034] The fluidized bed classifier was evacuated and purged with nitrogen. Particle size classification was performed under a nitrogen-sealed fluidized bed atmosphere, and powders with a particle size D50 ≤ 1.07 μm were screened out. The classified powders were then cooled under a nitrogen-sealed fluidized bed atmosphere. Finally, they were packaged in an automated, sealed packaging unit, with the packaging process also protected by nitrogen, to obtain high-purity aluminum nitride powder.

[0035] The high-purity aluminum nitride powder prepared by the above steps has a purity ≥99.95%, oxygen content ≤0.60%, nitrogen content 33.2-34.2%, carbon content ≤320ppm, specific surface area 3.27-3.47m² / g, and particle size distribution D50=0.8-1.2μm.

[0036] Example 2 Based on Example 1, this example provides a system for the continuous preparation of high-purity aluminum nitride powder using a fully fluidized bed method, which is used to implement the method of Example 1.

[0037] The system is a fully enclosed continuous architecture, with the internal pressure maintained at 0.10-0.15 MPa, always higher than the external atmospheric pressure, forming a stable slightly positive pressure environment. The system includes a core fluidization unit, an intelligent control unit, and a nitrogen protection unit.

[0038] The core fluidization unit comprises a fully enclosed and interconnected fluidized bed mixing device, a continuous fluidized bed pretreatment device, a high-temperature rotary fluidized bed reactor, a high-temperature decarbonization furnace, a fluidized bed classifier, a fluidized bed post-treatment device, and an automated sealed packaging device, arranged sequentially. Buffer chambers are located between adjacent fluidization units. Material transport between the buffer chambers and fluidization units is achieved via a nitrogen pneumatic conveying system. This system uses negative pressure to transport material from the buffer chambers to the next stage, ensuring that the discharge rate of the previous stage is equal to the feed rate of the next stage. Each fluidization unit is equipped with a pressure regulating valve, a gas inlet, and a tail gas recovery port. The gas inlet and tail gas recovery port facilitate gas introduction and tail gas recovery within the fluidization unit. The pressure regulating valve adjusts the internal gas pressure of the fluidization unit and connects to a PLC controller to achieve independent pressure control, ensuring a smooth pressure gradient throughout the entire line.

[0039] This embodiment controls the buffer hopper to ensure that the discharge rate of the previous section is equal to the feed rate of the next section, achieving continuous feeding, stable discharge, and smooth flow transition, thus preventing system shutdown caused by material shortage or stagnation.

[0040] This embodiment creates a stable micro-positive pressure environment by controlling the system pressure at 0.10-0.15 MPa, ensuring that the system pressure is always higher than the external atmospheric pressure. This fundamentally eliminates the risk of moisture and oxygen absorption under negative pressure, ensuring the reliable maintenance of the entire process under oxygen-free conditions, and providing the necessary conditions for preparing high-purity aluminum nitride powder with low oxygen content.

[0041] Furthermore, the nitrogen pneumatic conveying system adopts a dense-phase pneumatic conveying system. Dense-phase constant-flow conveying ensures that the material is uniformly dispersed and suspended within the pipeline, without sudden changes in speed. The nitrogen pneumatic conveying system is equipped with fluidizing nozzles at each port connecting to the preceding fluidization unit. The airflow direction of these nozzles is directed towards the inlet of the following fluidization unit, used to break up bridging or deposition of powder within the pipeline in real time, ensuring smooth dense-phase pneumatic conveying and eliminating the risk of pipe blockage.

[0042] Furthermore, a dual dynamic sealing structure combining an airlock valve and a nitrogen curtain is adopted at the inlet of the fluidized bed homogenizing device, the grading port of the fluidized bed grading device, and the outlet of the automated sealed packaging device. The airlock valve is used to maintain a seal while allowing materials to pass through continuously, and the nitrogen curtain forms a high-speed nitrogen flow barrier at the opening to prevent outside air from entering. A slight positive pressure is maintained inside the sealed cavity to form a nitrogen barrier.

[0043] In one specific embodiment, the system further includes an intelligent control unit and a nitrogen protection unit.

[0044] The intelligent control unit includes multiple sensors connected to a PLC controller. These sensors include a powder flow rate sensor, a suspension monitoring sensor, a temperature and pressure sensor, and an atmosphere concentration sensor. The powder flow rate sensor is installed at the inlet and outlet of the buffer silo. The suspension monitoring sensor and the temperature and pressure sensor are installed inside each fluidization unit. The atmosphere concentration sensors include oxygen sensors and gas composition sensors installed inside each fluidization unit and at key points (such as material inlets, grading ports, and packaging ports). All sensors are connected to the PLC controller, which receives real-time data from the sensors and performs coordinated control of the wind speed, pressure, furnace rotation speed, and gas flow rate in each section, achieving fully automated operation.

[0045] In this embodiment, oxygen sensors are installed at key points such as the feeding port, grading port, and packaging port. When the oxygen content exceeds the standard, automatic gas replenishment interlock is performed to ensure that the oxygen content is controlled throughout the process.

[0046] The nitrogen protection unit includes a nitrogen generator, a nitrogen storage tank, a mixed gas mixing tank, and nitrogen inlets and exhaust gas recovery ports located in each core fluidization unit. The nitrogen generator is connected to the nitrogen storage tank, which is connected to each inlet via pipelines. Each exhaust gas recovery port is connected to an exhaust gas purification system via pipelines. The purification system includes a dust collector, a filter, and a dehumidifier. The purified gas is then compressed and returned to the nitrogen storage tank, forming a closed-loop cycle with a nitrogen recovery rate ≥90%. The inlet of the mixed gas mixing tank is connected to the nitrogen storage tank and an inert gas source (such as argon or carbon dioxide cylinders), and its outlet is connected to the inlet of the high-temperature decarbonization unit, used to supply precisely proportioned nitrogen, argon, and carbon dioxide mixtures as needed.

[0047] Furthermore, the nitrogen circulation and recovery system features real-time gas replenishment and exhaust regulation functions. A pressure sensor monitors the pressure throughout the system and automatically adjusts the opening of the gas replenishment and exhaust valves to maintain a constant system pressure. All flanges, valves, and rotating parts utilize high-temperature resistant, oxygen-free seals to ensure stable maintenance of a slightly positive pressure during long-term operation.

[0048] The full-process fluidized continuous preparation system provided by this invention constructs a complete, positive-pressure closed fluidized production system by adopting multiple fluidized units and connecting each unit through a nitrogen pneumatic conveying system. This system provides reliable structural support for realizing full-process oxygen-free continuous production and effectively solves the problems of sealing, conveying and pressure matching when multiple devices are connected in series.

[0049] Example 3 Based on Examples 1 and 2, this example further illustrates the method and effects of the full-process fluidized continuous preparation of high-purity aluminum nitride powder according to the present invention through the following experiments.

[0050] A method for the continuous preparation of high-purity aluminum nitride powder using a fluidized bed process includes the following steps: S1. Automated Batching and Fluidized Homogenization: High-purity alumina powder (99.95%) and conductive carbon black are wet-mixed at a molar ratio of 1:3.5. Then, 4% (by mass) of OP-10 (based on the total mass of alumina powder and conductive carbon black) is added. The mixture is then ball-milled in a horizontal ball mill to ensure that the carbon black uniformly coats the surface of the alumina particles, forming a composite precursor with excellent flowability. After ball milling, the material is granulated in a spray granulation drying tower, controlling the particle size D50 to 0.8 μm, thereby obtaining a fluidizable precursor phase composite material. Finally, nitrogen is introduced into the raw material storage tank for pre-fluidized dispersion to obtain a fluidized homogenized mixture. S2. Continuous fluidized bed pretreatment: Nitrogen gas with a flow rate of 3.5 m / s is continuously introduced into the raw material storage tank to dry the material in a suspended fluidized bed state. The drying temperature is 180℃. After cooling, HCl gas with a flow rate of 3.5 m / s is introduced to remove impurities from the dried material to obtain pretreated material. S3. High-temperature fluidized bed nitriding reaction: The pretreated material is transported to a high-temperature rotary fluidized bed reactor with a furnace speed of 10 r / min, a nitrogen flow rate of 1.5 m / s, a furnace temperature of 1750℃, a system pressure of 0.12 MPa, and a material residence time of 3.0 h to complete the nitriding reaction and obtain coarse aluminum nitride powder. S4. Oxygen-free decarburization: Aluminum nitride coarse powder is conveyed to a high-temperature decarburization furnace. A compound gas with a nitrogen to argon volume ratio of 8:2 is used as the fluidizing medium, with a flow rate of 1.0 m / s. The furnace temperature is controlled at 900℃ and the material residence time is 2.0 h to complete oxygen-free decarburization. S5. Fluidized bed post-processing and finished product packaging: The decarburized powder is pneumatically conveyed to the classifier through nitrogen flow fluidization, and powder with D50=0.95μm is screened out. The powder is cooled to room temperature in a nitrogen-sealed fluidized bed atmosphere and then automatically sealed and packaged to obtain high-purity aluminum nitride powder.

[0051] Testing revealed that the prepared high-purity aluminum nitride powder had a purity of 99.97%, an oxygen content of 0.58%, a carbon content of 280 ppm, a particle size distribution D50 of 1.006 μm, and a batch stability coefficient of variation of 1.7%, meeting the requirements for semiconductor packaging applications.

[0052] XRD patterns were used to analyze the phase structure of the samples, particle size distribution maps showed the characteristics of the powder size, and SEM images were used to observe the microstructure and particle state of the materials, as shown below. Figure 2 , Figure 3 , Figure 4 As shown in the figure, the diffraction peak positions and intensities in the XRD pattern correspond perfectly to the standard aluminum nitride phase card, with no impurity phase diffraction peaks appearing, indicating high sample phase purity and excellent crystallinity. Particle size analysis results show that the sample has D50 = 1.006 μm, D10 = 0.647 μm, and D90 = 3.113 μm, exhibiting a narrow overall particle size distribution range and uniform particle size. SEM images visually demonstrate the regular particle morphology, with no obvious adhesion or agglomeration between particles, a smooth surface, and a dense microstructure. The particle size data and microstructure observations corroborate each other.

[0053] This invention applies fluidization technology to the entire process of aluminum nitride powder preparation, combining it with carbothermal reduction and several core supporting technologies. Compared with existing static / batch processes, it has the following significant advantages: 1. Significantly Improved Product Quality: The entire process is protected by nitrogen gas, eliminating any contact between materials and air. The resulting aluminum nitride powder has an oxygen content ≤0.6%, a carbon content ≤320ppm, a nitrogen content of 33.2~34.2%, a particle size D50 ≤1.07μm, and a specific surface area of ​​3.27~3.47m² / g. Compared to aluminum nitride powder prepared by existing processes (oxygen content ≤1%, carbon content ≤400ppm, nitrogen content 32.5~34.2%, particle size D50 ≤1.54μm, specific surface area ≥2.0m² / g), the product of this invention exhibits superior performance. Furthermore, fluidization ensures uniform material reaction, resulting in a batch stability coefficient of variation ≤1.8%. 2. Production efficiency and energy consumption optimization: The entire process is continuous and uninterrupted, which greatly shortens the production cycle and improves production efficiency by more than 80% compared with the traditional static process; the fluidized mass and heat transfer efficiency is high and there is no heat loss from repeated heating and cooling, which reduces energy consumption by more than 30%, while nitrogen recycling further reduces operating costs. 3. Precise and controllable fluidization state: Through intelligent feedback and regulation from multiple sensors, parameters such as gas flow rate are dynamically adjusted to ensure that the material always maintains a stable suspended fluidization state, solving the problems of powder agglomeration, deposition, and bridging, and realizing the stable application of fluidization technology in the entire process of aluminum nitride preparation; 4. High degree of automation and scalability: The system operates automatically throughout the entire process, and is controlled in real time by a PLC controller with almost no human intervention. Moreover, the core fluidized furnace can be scaled up to meet the large-volume demand for aluminum nitride powder in high-end fields. 5. Significant and scalable technological barriers: This invention is the first to realize the continuous fluidized bed preparation of aluminum nitride powder, integrating multiple core technologies such as interface synergistic dispersion, oxygen-free decarburization, and intelligent control, forming significant technological barriers; at the same time, this fluidized bed preparation system can be extended to the preparation of other high-end ceramic powders such as silicon nitride, silicon carbide, and aluminum oxynitride, and can be widely used in high-end fields such as semiconductor packaging, power devices, and aerospace.

[0054] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for the continuous preparation of high-purity aluminum nitride powder using a full-process fluidized bed reactor, characterized in that, Including the following steps: S1. After mixing alumina powder and conductive carbon black, a dispersant is added and the mixture is ground. The ground material is granulated and the particle size is controlled to a preset size. Then, nitrogen is introduced into the granulated material in a fluidized bed homogenizer for pre-fluidized dispersion to obtain a fluidized bed homogenizer. S2. The fluidized homogenized material is conveyed to a continuous fluidized pretreatment device through a nitrogen pneumatic conveying system. Under the nitrogen fluidized atmosphere, the material is made to be in a suspended fluidized state and is dried and removed in sequence to obtain the pretreated material. S3. The pretreated material is continuously conveyed to a high-temperature rotary fluidization reactor through a nitrogen pneumatic conveying system. Nitrogen is used as the fluidization medium and nitriding reaction gas to make the material in a stable suspended fluidized state and complete the carbothermic reduction nitriding reaction under preset conditions to obtain aluminum nitride coarse powder. S4. The aluminum nitride coarse powder is conveyed to a high-temperature decarburization furnace through a nitrogen pneumatic conveying system. A mixture of nitrogen and inert gas is used as the fluidization medium to make the material in a suspended fluidized state and remove residual carbon from the powder in an oxygen-free environment to obtain decarburized aluminum nitride powder. S5. The decarburized aluminum nitride powder is transported to the post-processing and finished product packaging section through a nitrogen pneumatic conveying system. Under the nitrogen-sealed fluidized atmosphere, it is subjected to particle size classification, cooling and automated packaging to obtain high-purity aluminum nitride powder.

2. The method for preparing high-purity aluminum nitride powder using a full-process fluidized bed method according to claim 1, characterized in that, Step S1 includes: After wet mixing of alumina powder and conductive carbon black at a molar ratio of (3.0-4.0):1, octylphenol polyoxyethylene ether dispersant at a mass ratio of 3-5% is added. The mixture is then ball-milled to uniformly coat the alumina surface with carbon black, forming a composite precursor. The precursor phase composite material is granulated to control the particle size D50 to be 0.5-1.2 μm, forming a fluidizable precursor phase composite material; Nitrogen gas is introduced into the composite precursor in a fluidized homogenizing apparatus for pre-fluidized dispersion to obtain the fluidized homogenized material.

3. The method for preparing high-purity aluminum nitride powder using a full-process fluidized bed method according to claim 1, characterized in that, Step S2 includes: The fluidized homogenized material is conveyed to a continuous pretreatment unit via a nitrogen pneumatic conveying system, and nitrogen gas with a flow rate of 3-4 m / s is introduced to dry the material in a suspended fluidized state at a drying temperature of 120-200℃. After cooling, HCl gas with a flow rate of 3-4 m / s is introduced to remove impurities from the dried material to obtain the pretreated material.

4. The method for preparing high-purity aluminum nitride powder using a full-process fluidized bed continuous process according to claim 1, characterized in that, In step S3, The furnace body of the high-temperature rotary fluidized bed reactor is made of SiN and AlN ceramic composite furnace tubes, and the rotation speed is 2-15 r / min; The reaction conditions for the carbothermic reduction nitridation reaction include: nitrogen flow rate of 0.8-2.0 m / s, furnace temperature of 1700-1800℃, system pressure of 0.10-0.15 MPa, material residence time of 2.5-4.0 h, and the material in a stable suspended fluidized state in the furnace.

5. The method for preparing high-purity aluminum nitride powder using a full-process fluidized bed method according to claim 1, characterized in that, In step S4, The compound gas comprises a mixture of nitrogen, argon, and carbon dioxide, with a volume ratio of nitrogen, argon, and carbon dioxide of (5:3:2) to (7:2:1); the flow rate of the compound gas is 0.5-1.5 m / s; the temperature inside the high-temperature decarbonization furnace is 850-950℃; and the material residence time is 1.5-3.0 h.

6. The method for preparing high-purity aluminum nitride powder using a full-process fluidized bed method according to claim 1, characterized in that, In step S5, The high-purity aluminum nitride powder has a particle size D50 ≤ 1.07 μm, oxygen content ≤ 0.60%, nitrogen content 33.2~34.2%, carbon content ≤ 320 ppm, and specific surface area 3.27~3.47 m². 2 / g.

7. A system for the continuous, fluidized bed preparation of high-purity aluminum nitride powder, characterized in that, A system for implementing the method as described in any one of claims 1-6, comprising: the system being a fully enclosed continuous architecture with internal pressure greater than external atmospheric pressure; the system comprising multiple fluidization units, an intelligent control unit, and a nitrogen protection unit, wherein, The multiple fluidization units include, in sequence, a fluidization homogenizing device, a continuous fluidization pretreatment device, a high-temperature rotary fluidization reactor, a high-temperature decarbonization furnace, a fluidization grading device, a fluidization post-treatment device, and an automated sealed packaging device. A buffer chamber is provided between two adjacent fluidization units. The buffer chamber and the fluidization unit are connected by a nitrogen pneumatic conveying system for material transport. The discharge rate of the previous section is equal to the feed rate of the next section. Each fluidization unit is equipped with a pressure regulating valve, a gas inlet, and a tail gas recovery port.

8. The system for the continuous, fluidized bed preparation of high-purity aluminum nitride powder according to claim 7, characterized in that, The nitrogen pneumatic conveying system adopts a dense phase pneumatic conveying system. The nitrogen pneumatic conveying system is equipped with fluidization nozzles at each port connecting to the previous fluidization unit, and the airflow direction of the fluidization nozzles is towards the inlet of the next fluidization unit.

9. The system for the continuous, fluidized bed preparation of high-purity aluminum nitride powder according to claim 7, characterized in that, The system pressure is 0.10–0.15 MPa; A dual dynamic sealing structure, consisting of an airlock valve and a nitrogen curtain, is adopted at the inlet of the fluidized bed homogenizing device, the grading port of the fluidized bed grading device, and the outlet of the automated sealed packaging device.

10. The system for the continuous, fluidized bed preparation of high-purity aluminum nitride powder according to claim 7, characterized in that, The system also includes: an intelligent control unit and a nitrogen protection unit; The intelligent control unit includes multiple sensors connected to a PLC controller. These multiple sensors include a powder flow rate sensor, a suspension monitoring sensor, a temperature and pressure sensor, and an atmosphere concentration sensor. The powder flow rate sensor is installed at the inlet and outlet of the buffer chamber. The suspension monitoring sensor and the temperature and pressure sensor are installed inside each fluidization unit. The atmosphere concentration sensor includes an oxygen sensor and a gas composition sensor installed inside each fluidization unit and at the target point. The nitrogen protection unit includes a nitrogen generator, a nitrogen storage tank, a compound gas mixing tank, and nitrogen inlets and exhaust gas recovery ports located in each core fluidization unit. The nitrogen generator is connected to the nitrogen storage tank, which is connected to each gas inlet via a pipeline. The inlet of the compound gas mixing tank is connected to the nitrogen storage tank and an inert gas source, and the outlet is connected to the inlet of the high-temperature decarbonization unit.

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