Continuous low temperature plasma fluidized bed coating process and system for aluminum lithium alloy powders

Abstract

The application relates to the technical field of metal powder preparation, and discloses a low-temperature plasma fluidized bed continuous coating method and system for aluminum-lithium alloy powder. Under the protection of an inert atmosphere, aluminum-lithium alloy melt is subjected to gas atomization treatment; cooling is performed through inert gas, and the temperature of the aluminum-lithium alloy powder before entering subsequent treatment is controlled to be not higher than 150 DEG C; the aluminum-lithium alloy powder is continuously conveyed to a fluidized bed reactor, and under the action of fluidizing gas, the aluminum-lithium alloy powder is in a dynamic fluidized state; the aluminum-lithium alloy powder is subjected to plasma pretreatment; a silicon-containing gas phase precursor is introduced into the fluidized bed reactor in a low-temperature interval of 80 DEG C-250 DEG C, and the low-temperature plasma activation is utilized to promote the silicon-containing gas phase precursor to chemically react at a temperature lower than a thermal decomposition threshold value, so that a dense silicon-based coating layer is uniformly deposited on the surface of the aluminum-lithium alloy powder in the fluidized state; and the aluminum-lithium alloy powder after completing the coating is cooled and collected under the protection of the inert atmosphere.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, and in particular, to a low-temperature plasma fluidized bed continuous coating method and system for aluminum-lithium alloy powder. Background Technology

[0002] Aluminum-lithium alloy powder is widely used in aerospace and high-performance chemical industries due to its low density, high specific strength, and excellent calorific value. In particular, the introduction of lithium can significantly lower the ignition temperature of the material and promote micro-explosion effects during combustion, thereby greatly improving energy release efficiency and reaction rate. However, due to the extremely high chemical reactivity and low melting and boiling points of lithium, aluminum-lithium alloy powder faces severe technical challenges in its preparation, storage, and subsequent processing. Specifically: First, lithium reacts readily with oxygen and moisture. In traditional powder preparation and subsequent transfer processes, even brief exposure can lead to severe surface oxidation, which not only alters the intended composition of the powder but also generates lithium oxide that is hygroscopic, severely affecting the powder's flowability and stability.

[0003] Secondly, existing surface coating technologies struggle to balance coating quality and component protection. To improve oxidation resistance, powder surface modification is typically required. Chemical vapor deposition (CVD) is a common method for preparing dense coatings, but it usually requires temperatures above 400°C. For aluminum-lithium alloys, this temperature range easily induces lithium volatilization and segregation, leading to uncontrolled alloy composition and ultimately degrading material properties. Although plasma-enhanced chemical vapor deposition (PECVD) can lower the deposition temperature, highly reactive aluminum-lithium alloy powders are prone to agglomeration and clumping in traditional fixed-bed or stirred-tank reactors, resulting in uneven gas-solid contact, poor coating thickness consistency, and unsuitability for continuous production.

[0004] Furthermore, existing processes generally employ a segmented operation mode involving powder preparation, temporary storage, transfer, and coating. For highly reactive materials like aluminum-lithium alloys, the transfer process of powder between different devices is difficult to completely isolate from air, easily leading to secondary oxidation and lithium loss. This discontinuous and intermittent process not only increases safety risks during production but also makes it difficult to guarantee batch stability of the final product.

[0005] In summary, existing technologies for preparing aluminum-lithium alloy powders generally suffer from problems such as significant lithium loss, poor coating uniformity, and easy oxidation. Summary of the Invention

[0006] This invention provides a low-temperature plasma fluidized bed continuous coating method and system for aluminum-lithium alloy powder. By constructing a closed inert link for the entire process of "powder making-transportation-coating-collection", the method utilizes low-temperature plasma activation to break through the thermal decomposition threshold of silicon-containing precursors, and combines the dynamic dispersion mechanism of fluidized bed to eliminate the particle agglomeration and shielding effect. This enables the in-situ construction of a submicron-level dense coating layer at temperatures below 250°C, thereby solving the technical problems in existing processes such as lithium volatilization caused by high-temperature deposition, insufficient uniformity of fixed-bed coating, and oxidation instability of powder during cross-equipment transfer.

[0007] According to one aspect of the present invention, a low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder is provided. The entire process is carried out continuously in an inert atmosphere with an oxygen content not exceeding 10 ppm. This method aims to thermodynamically suppress the surface migration and selective oxidation of lithium elements, kinetically eliminate particle agglomeration and mass transfer dead zones, and chemically enhance the bonding force between the coating layer and the substrate. This achieves a multi-dimensional synergy of minimizing lithium element loss and optimizing coating quality. The method includes the following steps: S100, under the protection of an inert atmosphere, the aluminum-lithium alloy melt is subjected to gas atomization treatment to coat the aluminum-lithium alloy powder with a plasma fluidized bed. In the early stages of alloy powder formation, lithium oxidation and volatilization are suppressed to obtain aluminum-lithium alloy powder with a clean surface and stable composition. In step S200, the aluminum-lithium alloy powder is cooled under a closed system using an inert gas, and its temperature is controlled to be no higher than 150°C before entering subsequent processing to reduce the risk of thermally induced lithium volatilization and provide thermodynamic conditions for subsequent low-temperature deposition. In step S300, the cooled aluminum-lithium alloy powder is continuously fed into a fluidized bed reactor, where it is kept in a dynamic fluidized state of continuous tumbling and dispersion under the action of fluidizing gas to eliminate particle agglomeration and obscuring. The effect ensures the uniformity of the coating process; S400, in the fluidized state, the aluminum-lithium alloy powder is subjected to plasma pretreatment to remove trace amounts of native oxide film on the surface of the aluminum-lithium alloy powder and generate active sites, which is beneficial to improve the interfacial bonding strength and deposition uniformity between the subsequent silicon-based coating layer and the aluminum-lithium alloy powder; S500, a silicon-containing gaseous precursor is introduced into the fluidized bed reactor in a low temperature range of 80℃-250℃, and the low temperature plasma activation effect is used to promote the chemical reaction of the silicon-containing gaseous precursor at a temperature below the thermal decomposition threshold, in which the aluminum-lithium alloy in the fluidized state... A dense silicon-based coating layer is uniformly deposited on the powder surface, thereby achieving high-quality coating while suppressing lithium volatilization. In S600, the coated aluminum-lithium alloy powder is cooled and collected under an inert atmosphere to prevent secondary oxidation of the silicon-based coating layer and the aluminum-lithium alloy powder body during the cooling process, ensuring coating integrity and storage stability. The entire process of inert atmosphere protection, fluidized dispersion, and low-temperature plasma activation works in conjunction with surface pretreatment to synergistically ensure the compositional stability of the aluminum-lithium alloy powder, the densification of the coating layer, and the continuity of the process at temperatures below 250°C.

[0008] Further, in step S300, the fluidizing gas is argon, nitrogen, or hydrogen, or a mixture of at least two of argon, nitrogen, or hydrogen.

[0009] Furthermore, in step S400, the plasma pretreatment time is 0.5 min to 5 min.

[0010] Furthermore, in step S400 and / or step S500, the plasma is radio frequency plasma and / or microwave plasma.

[0011] Furthermore, in step S500, the silicon-containing gaseous precursor is at least one of silane, halosilane, or organosilicon compound.

[0012] Furthermore, halosilanes include silicon tetrachloride and / or trichlorosilane.

[0013] Furthermore, in step S500, the thickness of the silicon-based coating layer is 0.05μm-2μm.

[0014] Furthermore, steps S300 to S500 are carried out continuously within the same fluidized bed reactor; and / or the operating pressure of the fluidized bed reactor is from 100 Pa to atmospheric pressure.

[0015] Furthermore, steps S200 to S600 are completed continuously in a closed conveying system, and the aluminum-lithium alloy powder does not come into contact with the outside air throughout the process.

[0016] According to another aspect of the present invention, a low-temperature plasma fluidized bed continuous coating system for aluminum-lithium alloy powder is also provided, for implementing the low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder as described above; comprising: a gas atomization powder preparation unit for preparing aluminum-lithium alloy powder; a cooling and conveying unit for cooling and continuously conveying the aluminum-lithium alloy powder; a fluidized bed plasma deposition unit for coating the aluminum-lithium alloy powder under fluidized state and plasma action; a powder collection unit for collecting the coated powder; and an atmosphere control unit for maintaining an inert atmosphere environment and controlling the oxygen content to be no higher than 10 ppm; wherein the gas atomization powder preparation unit, the cooling and conveying unit, the fluidized bed plasma deposition unit and the powder collection unit are sequentially connected and constitute a closed pipeline assembly to form a continuous inert atmosphere production link; the atmosphere control unit is connected to the continuous inert atmosphere production link.

[0017] Furthermore, it also includes independently configured fluidizing gas path, precursor gas path, and plasma working gas path; and / or the fluidized bed plasma deposition unit includes a gas distribution structure for forming a uniform fluidization state; and / or the fluidized bed plasma deposition unit includes a plasma generating device, which includes an electrode structure, configured as a ring electrode or a multi-electrode structure; and / or the fluidized bed plasma deposition unit includes a plasma generating device, which is a radio frequency plasma generating device and / or a microwave plasma generating device; and / or the cooling and transport unit adopts an inert gas circulating cooling structure.

[0018] The present invention has the following beneficial effects: 1. Continuous inert atmosphere throughout the entire process to suppress oxidation and component segregation: The oxygen content is maintained at no more than 10 ppm in an inert atmosphere throughout the entire process chain, so that gas atomization powdering, cooling, fluidized coating and collection are completed in the same closed loop, blocking the contact between aluminum-lithium alloy powder and oxygen-containing atmosphere; Since lithium has a high chemical potential and low diffusion activation energy, any trace amount of oxygen exposure will induce selective oxidation and grain boundary segregation, while the continuous closed inert environment eliminates the oxidation driving force and inhibits the surface migration of lithium, thus achieving the simultaneous maintenance of macroscopic stability of powder composition and surface chemical cleanliness.

[0019] 2. Low-temperature plasma activation reduces deposition energy barrier and suppresses lithium volatilization: By introducing low-temperature plasma in the range of 80℃–250℃, high-energy electrons and non-equilibrium excited-state particles significantly improve the reactivity of silicon-containing gaseous precursors, enabling heterogeneous nucleation and deposition at temperatures far below the thermal decomposition threshold. By replacing the traditional thermal activation path with a non-thermal plasma activation mechanism, the unavoidable thermal lithium volatilization in high-temperature chemical vapor deposition is effectively avoided, thus achieving thermodynamic compatibility between low-temperature deposition and protection of highly active alloy components.

[0020] 3. Fluidized dynamic dispersion eliminates agglomeration and shielding, and achieves uniform coating: Fluidized gas drives aluminum-lithium alloy powder to be in a state of continuous tumbling and random collision, breaking the agglomeration structure formed between particles by van der Waals forces and electrostatic forces, so that the surface of each powder is exposed to a uniform gas-phase precursor concentration field and plasma field; This dynamic mass transfer enhancement mechanism eliminates the shielding effect and diffusion dead zone that are common in fixed beds, thus ensuring the uniformity and spatial continuity of coating thickness at both geometric and mass transfer levels.

[0021] 4. Plasma pretreatment optimizes interface bonding and deposition kinetics: Plasma pretreatment is performed before formal deposition, using active particles to controllably etch and functionalize the powder surface, removing trace amounts of native oxide film and introducing dangling bonds and highly active nucleation sites; through surface energy regulation and enhanced interfacial reactivity, the chemical bonding strength between the silicon-based coating layer and the aluminum-lithium alloy substrate is significantly enhanced, reducing the risk of interfacial thermal resistance and stress concentration, and improving the mechanical stability and environmental durability of the coating layer.

[0022] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of the steps of a preferred embodiment of the low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder of the present invention; Figure 2 This is a schematic diagram of the structure of a low-temperature plasma fluidized bed continuous coating system for aluminum-lithium alloy powder according to a preferred embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a fluidized bed plasma deposition unit according to a preferred embodiment of the present invention.

[0024] Legend: 100. Gas atomization powder preparation unit; 200. Cooling and conveying unit; 300. Fluidized bed plasma deposition unit; 310. Fluidized bed reactor; 311. Gas distribution plate; 312. Fluidized powder bed; 313. Plasma reaction zone; 314. Discharge port; 320. Plasma generator; 321. Electrode structure; 330. Gas supply and control system; 331. Fluidized gas inlet; 332. Silicon precursor gas inlet; 333. Plasma working gas inlet; 334. Exhaust gas outlet; 400. Powder collection unit; 500. Atmosphere protection and exhaust system. Detailed Implementation

[0025] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0026] like Figure 1 and Figure 2As shown, the low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder in this embodiment is carried out continuously in an inert atmosphere with an oxygen content of no more than 10 ppm. This method aims to thermodynamically suppress the surface migration and selective oxidation of lithium elements, kinetically eliminate particle agglomeration and mass transfer dead zones, and chemically enhance the bonding force between the coating layer and the substrate. This achieves a multi-dimensional synergy of minimizing lithium loss and optimizing coating quality. The method includes the following steps: S100, under the protection of an inert atmosphere, the aluminum-lithium alloy melt is subjected to gas atomization treatment to form the initial layer of aluminum-lithium alloy powder. The process involves: S200, inhibiting lithium oxidation and volatilization to obtain aluminum-lithium alloy powder with a clean surface and stable composition; S200, cooling the aluminum-lithium alloy powder under a closed system using an inert gas, and controlling the temperature of the aluminum-lithium alloy powder before entering subsequent processing to not exceed 150℃, in order to reduce the risk of thermally induced lithium volatilization and provide thermodynamic conditions for subsequent low-temperature deposition; S300, continuously conveying the cooled aluminum-lithium alloy powder to a fluidized bed reactor 310, where the aluminum-lithium alloy powder is kept in a dynamic fluidized state of continuous tumbling and dispersion under the action of fluidizing gas, in order to eliminate particle agglomeration and shielding effects, ensuring... To ensure the uniformity of the coating process; S400, in the fluidized state, the aluminum-lithium alloy powder is subjected to plasma pretreatment to remove trace amounts of native oxide film on the surface of the aluminum-lithium alloy powder and generate active sites, which is beneficial to improve the interfacial bonding strength and deposition uniformity between the subsequent silicon-based coating layer and the aluminum-lithium alloy powder; S500, a silicon-containing gaseous precursor is introduced into the fluidized bed reactor 310 in a low temperature range of 80℃-250℃, and the low-temperature plasma activation effect is used to promote the chemical reaction of the silicon-containing gaseous precursor at a temperature below the thermal decomposition threshold, so that the aluminum-lithium alloy powder in the fluidized state... A dense silicon-based coating layer is uniformly deposited on the final surface, thereby achieving high-quality coating while suppressing lithium volatilization. In S600, the coated aluminum-lithium alloy powder is cooled and collected under an inert atmosphere to prevent secondary oxidation of the silicon-based coating layer and the aluminum-lithium alloy powder body during the cooling process, ensuring coating integrity and storage stability. The entire process of inert atmosphere protection, fluidized dispersion, and low-temperature plasma activation works in conjunction with surface pretreatment to synergistically ensure the compositional stability of the aluminum-lithium alloy powder, the densification of the coating layer, and the continuity of the process at temperatures below 250°C. The present invention provides a low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder. Throughout the entire process chain, an inert atmosphere with an oxygen content not exceeding 10 ppm is maintained, allowing gas atomization powder preparation, cooling, fluidized bed coating, and collection to be completed in the same closed loop, thus preventing contact between the aluminum-lithium alloy powder and the oxygen-containing atmosphere. Because lithium has a high chemical potential and low diffusion activation energy, any trace oxygen exposure will induce selective oxidation and grain boundary segregation. The continuous, sealed, inert environment, by eliminating the oxidation driving force and inhibiting lithium surface migration, achieves simultaneous maintenance of the macroscopic stability of the powder composition and the surface chemical cleanliness.By introducing low-temperature plasma within the 80℃–250℃ range, high-energy electrons and non-equilibrium excited-state particles significantly enhance the reactivity of silicon-containing gaseous precursors, enabling heterogeneous nucleation and deposition at temperatures far below the thermal decomposition threshold. By replacing the traditional thermal activation path with a non-thermal plasma activation mechanism, the unavoidable thermal lithium volatilization in high-temperature chemical vapor deposition is effectively avoided, thus achieving thermodynamic compatibility between low-temperature deposition and the protection of highly active alloy components. Fluidized gas drives the aluminum-lithium alloy powder into a state of continuous tumbling and random collisions, breaking the agglomeration structure formed between particles by van der Waals forces and electrostatic forces, ensuring that the surface of each powder particle is exposed to a uniform gaseous precursor concentration field and plasma field. This dynamic mass transfer enhancement mechanism eliminates the shielding effect and diffusion dead zone commonly found in fixed beds, thereby ensuring the uniformity and spatial continuity of the coating thickness at both geometric and mass transfer levels. Plasma pretreatment is performed before formal deposition, using active particles to controllably etch and functionalize the powder surface, removing trace amounts of native oxide film and introducing dangling bonds and highly active nucleation sites. Through surface energy modulation and enhanced interfacial reactivity, the chemical bonding strength between the silicon-based coating and the aluminum-lithium alloy substrate is significantly strengthened, reducing interfacial thermal resistance and stress concentration risks, and improving the mechanical stability and environmental durability of the coating. Inert atmosphere protection, low-temperature plasma activation, fluidized dispersion, and surface pretreatment generate synergistic effects through multidimensional coupling of thermodynamics, kinetics, and interfacial chemistry. The inert atmosphere provides a thermodynamically stable boundary, the low-temperature plasma lowers the reaction energy barrier, the fluidized state ensures mass transfer uniformity, and the surface pretreatment optimizes interfacial bonding. This synergistic effect enables the system to simultaneously minimize lithium loss, densify the coating, and achieve continuous processing at temperatures below 250°C. This invention relates to a low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder. By constructing a low-temperature plasma fluidized bed continuous coating process under a fully enclosed inert atmosphere, it thermodynamically suppresses lithium volatilization, kinetically homogenizes mass transfer, and chemically strengthens bonding forces. This achieves high-quality, high-uniformity, and high-stability coating of aluminum-lithium alloy powder under low-temperature conditions, breaking through the limitations of traditional high-temperature deposition and segmented processes. It forms a continuously operable, industrially feasible path, significantly improving the compositional stability, oxidation resistance, and long-term storage safety of aluminum-lithium alloy powder.

[0027] In this embodiment, in step S300, the fluidizing gas is argon, nitrogen, or hydrogen, or a mixture of at least two of argon, nitrogen, or hydrogen. Choosing argon or nitrogen as the fluidizing medium firstly maintains a chemically inert environment within the system. The aluminum-lithium alloy powder has extremely high surface free energy, and in the fluidized state, it continuously exposes fresh surfaces due to violent collisions, making it highly reactive with active gases. Argon, as a monatomic inert gas, has extremely high ionization energy and chemical stability, providing stable fluidization motive force without participating in any chemical reaction, and also acting as a diluent to adjust the partial pressure of the precursor. Although nitrogen is a diatomic molecule, its kinetic rate for nitriding with the aluminum-lithium alloy is extremely low within the low-temperature range not exceeding 250 degrees Celsius, primarily playing a role in inert physical isolation. By occupying the free volume within the reactor, argon or nitrogen effectively blocks contact between residual oxygen and the surface of the aluminum-lithium alloy powder, synergistically maintaining an inert atmosphere with an oxygen content not exceeding 10 ppm, thus inhibiting the oxidation and volatilization of lithium. When hydrogen is selected as the fluidizing gas or its mixture, its role transcends that of a simple fluidizing carrier, transforming into an in-situ reducing agent. Hydrogen atoms possess extremely strong diffusion capabilities and reduction potentials. In a low-temperature plasma environment, hydrogen molecules are dissociated into active hydrogen atoms, which can preferentially undergo reduction reactions with trace amounts of native oxide films (such as lithium oxide and aluminum oxide) on the surface of aluminum-lithium alloy powder, generating water molecules that are carried out of the system by the gas flow. This process not only further purifies the surface but also provides truly clean active nucleation sites for subsequent silicon-based coating, significantly enhancing the interface activation effect of plasma pretreatment in step S400, thereby improving the bonding strength between the coating layer and the substrate. Using a mixture of argon, nitrogen, and hydrogen allows for the controllable adjustment of physicochemical properties. For example, the low molecular weight of hydrogen can increase the plasma breakdown voltage and electron density, enhancing the overall plasma activity. The high heat capacity and thermal conductivity of argon can precisely control the microscopic temperature field distribution within the fluidized bed, preventing lithium volatilization caused by local hot spots. Nitrogen maintains the overall chemical inertness, reducing costs. This multi-component synergistic mechanism ensures that the gas-solid contact efficiency, heat transfer rate, and reactant concentration gradient within the fluidized bed are all optimal, guaranteeing the uniform growth of the silicon-based coating in the fluidized state. The specific gas selection directly affects the discharge characteristics and reaction pathway of the plasma. Argon, as a buffer gas, can stabilize the plasma sheath and protect the highly active aluminum-lithium alloy powder from lattice damage caused by direct bombardment by high-energy ions. Meanwhile, active free radicals of hydrogen or nitrogen in the plasma (such as H and N) can participate in surface reactions, regulate the decomposition pathway of silicon-based precursors, promote the formation of a dense coating structure without hydrogen impurities, and avoid material performance degradation caused by the introduction of gaseous impurities.

[0028] In this embodiment, the plasma pretreatment time in step S400 is 0.5 min to 5 min. During the atomization and cooling process, an extremely thin primary passivation film, mainly composed of aluminum oxide and lithium oxide, inevitably forms on the surface of the aluminum-lithium alloy powder. The plasma pretreatment utilizes high-energy ion bombardment and active free radical chemical reaction to controllably etch this passivation layer. The lower limit of 0.5 minutes is set to ensure sufficient energy dose to penetrate and remove this physical barrier. If the time is too short, the etching will be insufficient, and the residual oxides will become nucleation obstacles for the subsequent silicon-based coating layer, resulting in decreased adhesion or discontinuous coating. Within the range of 0.5 to 5 minutes, the plasma can systematically remove surface contaminants and induce abundant dangling bonds, vacancies, and high-energy steps on the powder surface, thereby establishing a high-density chemisorption site, providing thermodynamic driving force for heterogeneous nucleation in step S500. Although the overall process temperature is controlled below 250℃, the bombardment of high-energy particles within the plasma sheath can cause localized instantaneous temperature rises. If the pretreatment time exceeds the upper limit of 5 minutes, continuous ion bombardment will lead to two negative effects: lithium elements will preferentially sputter due to their low binding energy in the alloy, resulting in an aluminum-rich and lithium-poor surface layer, disrupting the compositional uniformity of the alloy design; and lithium elements may diffuse and segregate at grain boundaries, forming a new subsurface oxide layer. Therefore, the 5-minute upper limit is a necessary constraint on the physical effects of plasma, ensuring that the bulk stoichiometry of the aluminum-lithium alloy powder is not compromised while using plasma for surface modification. In the fluidized bed reactor 310, the particles are in a high-frequency tumbling state; the treatment time of 0.5 to 5 minutes matches the average residence time of the particles in the reactor. This time window is sufficient to ensure that each powder particle receives a uniform and sufficient plasma irradiation dose during multiple cycles and mixing, thereby achieving surface uniformity under batch processing; too short a time will lead to uneven processing, while too long a time will lead to localized overheating and agglomeration, disrupting the stability of the fluidized state. The setting of this time parameter also reflects the synergy with subsequent deposition steps; after 0.5 to 5 minutes of activation, the powder surface is in a metastable state with high surface energy; at this time, the introduction of silicon-containing gaseous precursors can maximize the use of the high surface activity, promote the adsorption and decomposition of precursor molecules, thereby achieving a seamless connection from physical activation to chemical deposition and reducing the activity decay caused by surface relaxation.

[0029] In this embodiment, in steps S400 and / or S500, the plasma is radio frequency plasma and / or microwave plasma. Both radio frequency and microwave plasmas are non-equilibrium plasmas, with electron temperatures reaching several electron volts (tens of thousands of Kelvin), while the temperature of heavy particles (neutral gas molecules, ions, powder particles) can still be maintained in the range of near room temperature to 250°C. Electrons and metastable particles provide sufficient energy to cause bond breaking, excitation, and dissociation in the silicon-containing gaseous precursor (e.g., ...). , The plasma power is used to initiate heterogeneous nucleation reactions. The temperature of the gas phase and the particle body is always controlled within the range of 80℃-250℃, and the overall system temperature does not rise due to plasma power. This achieves the separation of electron activation energy supply and system thermodynamic temperature, avoiding the high temperature of more than 400℃ required by traditional thermal CVD, and suppressing thermally induced volatilization / thermally induced volatilization and grain boundary segregation of lithium in aluminum-lithium alloy. Radio frequency plasma (RF plasma) is used for powder surface pretreatment. The discharge zone is isolated from the reaction chamber or without inserted metal electrodes to avoid contamination, making it suitable for high-purity aluminum-lithium alloy systems. It can form a spatially uniform active particle field (O, H, Ar metastable states, and ultraviolet photons) on the fluidized bed cross-section, uniformly etching and reducing powders in a continuously tumbling state. Suitable for short pretreatment times of 0.5-5 minutes, it can effectively remove trace amounts of native Al2O3 / Li2O oxide films and introduce dangling bonds and hydrogen / silicon-containing active functional groups onto the surface. This treatment method, synergistic with fluidized bed treatment, ensures that all circulating particles receive approximately equal doses of active particle irradiation, avoiding localized inactivation caused by shielding in a fixed bed, and providing a uniform high-energy surface for subsequent deposition. Microwave plasma, compared to RF discharge, can generate a higher concentration of active free radicals (SiH). X The use of microwave plasma (H, etc.) significantly accelerates the decomposition rate of silicon-containing precursors under low partial pressure and low temperature conditions; strong dissociation but low heavy particle heating is conducive to the formation of silicon-based diamond-like structures or microcrystalline / nanocrystalline silicon films, rather than loose polymer-like deposition, promoting the formation of dense, low-defect coating layers; it can be used in conjunction with the gas distribution plate 311 of the fluidized bed to establish a more uniform active species concentration field in the particle-dense region, improving the macroscopic uniformity of the deposition reaction; the application of microwave plasma in S500 compensates for insufficient thermal activation at low temperatures by increasing the concentration of active intermediates in the gas phase precursor reaction order, so that the deposition reaction still has a considerable rate and film quality at ≤250℃. The plasma is a combination of radio frequency plasma and microwave plasma. For small-to-medium throughput laboratory systems, radio frequency plasma can be used to reduce equipment complexity; for industrial scale-up continuous fluidized beds, microwave plasma can be used to obtain a larger volume and higher activity discharge zone. It can also be used in series or in combination (RF start-up, MW main deposition) to balance arc initiation stability and deposition rate. Regardless of whether the plasma is radio frequency plasma or microwave plasma, it can be superimposed on the upper or side of the fluidized bed without disrupting the fluidized gas-solid dynamics. By tuning the power and gas composition, it forms a spatiotemporally uniform activation-deposition coupling field with the tumbling of fluidized particles. This eliminates the adverse factors caused by hot filaments (contamination, high temperature) and DC arc light (local overheating, easy to cause lithium volatilization), which is completely consistent with the core concept of "low temperature, inertness, and continuity" of this invention.

[0030] In this embodiment, in step S500, the silicon-containing gas-phase precursor is at least one of silane, halosilane, or organosilicon compound. Silane, halosilane, and organosilicon compounds all have relatively low bond dissociation energies (such as Si-H bonds and Si-Cl bonds), which are highly compatible with the energy levels of non-equilibrium active particles (high-energy electrons, metastable atoms) generated by radio frequency or microwave plasma. In the low-temperature range of 80℃-250℃, it is difficult to open these chemical bonds by thermal energy alone, while low-temperature plasma can provide directional activation energy, prompting the precursor to undergo homogeneous pyrolysis or heterogeneous surface reaction. Compared with siloxane compounds that require extremely high pyrolysis temperatures, the precursor selected in this invention can be rapidly converted into silicon active species under the low-temperature conditions defined in this invention, thereby ensuring the deposition rate and density of the silicon-based coating layer without increasing the substrate temperature. Silanes (such as silane and disilane), which do not contain halogens or carbon, primarily decompose into silane groups under plasma conditions. Their deposition products are typically high-purity silicon or hydrogenated amorphous silicon with extremely low impurity content, forming a dense physical barrier that effectively blocks oxygen diffusion into the aluminum-lithium alloy matrix without introducing corrosive byproducts. Halogenated silanes (such as trichlorosilane and silicon tetrachloride), containing chlorine atoms, can undergo a displacement reaction with trace amounts of residual oxygen on the aluminum-lithium alloy surface in a plasma environment, further aiding in surface cleaning and promoting the directional alignment of silicon atoms. These precursors help form a highly crystalline silicon-based coating layer, improving the coating's mechanical strength and wear resistance. Organosilicon compounds (such as hexamethyldisiloxane and tetramethylsilane), containing organic ligands, can undergo polymerization reactions under low-temperature plasma conditions to form ceramic precursor layers containing Si-C and Si-O bonds. These coating layers typically exhibit good toughness and coating integrity, buffering volume changes in the aluminum-lithium alloy powder during subsequent processing or applications. If an oxygen-containing precursor (such as tetraethyl orthosilicate, TEOS) is used, carbon dioxide or water will be released at high temperatures, which will directly lead to the oxidation of highly active lithium. However, silanes, halosilanes, and organosilicon compounds mainly undergo reducing or inert deposition reactions under the synergistic effect of an inert atmosphere and low-temperature plasma, avoiding the generation of oxygen-containing byproducts. This choice cuts off the chemical path of lithium oxidation or hydrolysis at high temperatures from the gas source end, forming a double guarantee with the inert atmosphere protection throughout the process, ensuring that lithium exists stably in the alloy powder in a metallic state, rather than being lost in the form of oxides. The aforementioned precursors are mostly gaseous or have high vapor pressure at room temperature, making them easy to uniformly disperse in the fluidized bed reactor 310 via a carrier gas (fluidizing gas). In the fluidized state, the high concentration of precursor molecules can penetrate deep into the microscopic gaps of the powder agglomerates with the airflow, achieving permeation coating in conjunction with the tumbling of the particles. The high reactivity of the precursors ensures that even in a fluidized bed with a short gas-solid contact time, chemical adsorption and nucleation can be rapidly completed on the particle surface, thereby obtaining a uniform coating effect.

[0031] In this embodiment, the halosilane includes silicon tetrachloride and / or trichlorosilane. The Si–Cl bond energies in silicon tetrachloride and trichlorosilane molecules are significantly lower than those in the Si–O bonds, and they are easily dissociated by high-energy electron collisions in radio frequency or microwave low-temperature plasma fields to form SiCl. X Silicon tetrachloride and trichlorosilane are active intermediates. Compared to oxysilane precursors that require higher pyrolysis temperatures, silicon tetrachloride and trichlorosilane undergo almost no significant thermal decomposition at a bulk temperature of 80℃–250℃, but can be selectively excited and dissociated under non-equilibrium low-temperature plasma electron energy distribution. This characteristic allows the silicon-containing precursor to undergo chemical reactions only in the plasma activation region, while the overall system remains at a low temperature, ensuring: feasibility of low-temperature deposition (replacing the >400℃ required for high-temperature thermal CVD); and suppression of thermally induced lithium volatilization (the substrate temperature does not rise to the range where lithium evaporates significantly). Chlorine radicals have strong oxyphilicity and strong hydrogen abstraction capabilities in the plasma environment, and can react simultaneously with deposition: reacting with trace residual oxide films (Al2O3, Li2O) on the surface of aluminum-lithium alloy powder to generate volatile chlorine oxides (such as AlCl3(g), LiCl(g) or easily desorbable complexes), thereby assisting in the removal of passivation layers that were not completely removed by plasma pretreatment; and reacting with surface-adsorbed water molecules or hydroxyl groups to generate HCl, which is carried out of the system by the carrier gas, reducing the adverse effect of the surface hydroxyl layer on the compactness of the coating layer. This "deposition-in-situ surface cleaning" mechanism, in synergy with the plasma pretreatment in step S400, further enhances the actual contact area and interfacial bonding energy between the silicon-based coating layer and the aluminum-lithium alloy substrate. Silicon tetrachloride and trichlorosilane exhibit different but complementary behaviors in plasma-assisted deposition. Silicon tetrachloride, with its symmetrical molecular structure and lack of Si–H bonds, produces plasma decomposition products primarily of Si atoms and Cl radicals, resulting in high-purity, dense amorphous or microcrystalline silicon layers. Its hydrogen-free nature reduces the sensitivity to atmospheric hydrolysis caused by the introduction of Si–H bonds in the coating layer. Trichlorosilane, containing Si–H bonds, retains some hydrogen in the plasma, which helps regulate the stress of the deposited layer and slightly increases the deposition rate. Its lower boiling point and higher vapor pressure facilitate stable and uniform gas phase distribution in a fluidized bed.

[0032] In this embodiment, in step S500, the thickness of the silicon-based coating layer is 0.05μm-2μm. The lower limit ≥0.05μm ensures the formation of a continuous and dense shielding layer, achieving anti-oxidation and lithium diffusion inhibition functions; the upper limit ≤2μm avoids coating layer peeling due to internal stress mismatch, thermal mismatch, or brittle cracking, and prevents excessive consumption of precursor gas and deposition time. The thickness range of 0.05μm-2μm matches the low-temperature plasma fluidized bed deposition kinetics, ensuring batch uniformity. With a coating layer thickness between 0.05μm and 2μm, it is not necessary to increase the substrate temperature or significantly increase the plasma power to improve the deposition rate (avoiding local hot spots); low-temperature, short-time deposition can achieve the target thickness, further shortening the cumulative residence time of highly active powder in the reaction zone and reducing the probability of lithium diffusing along grain boundaries to the surface and being volatilized; the continuous, dense, but not excessively thick coating layer maintains its integrity during subsequent cooling and collection, preventing the appearance of re-oxidation windows. The coating thickness is between 0.05μm and 2μm, which can slightly improve the flowability of ultrafine aluminum-lithium alloy powder (reduce van der Waals adsorption between particles); it does not affect the rapid film breaking behavior in subsequent pressing, sintering or combustion processes (too thick may become a heat insulation or contamination medium); it keeps the overall particle size distribution of the powder basically unchanged, avoiding significant changes in packing density or stacking behavior.

[0033] In this embodiment, steps S300 to S500 are performed continuously within the same fluidized bed reactor 310; and / or the operating pressure of the fluidized bed reactor 310 is from 100 Pa to atmospheric pressure. The fluidized bed reactor 310 simultaneously serves as a receiving container for cooled powder, a reaction chamber for plasma pretreatment, and a coating site for low-temperature deposition, constructing a continuous process link from start to finish. In traditional segmented processes, when powder is transferred from the cooling unit to the coating unit, even in a glove box, it is difficult to avoid micro-leakage or residual oxygen adsorption during valve switching. This invention, through process reuse within a single reactor, completely eliminates the high-risk window period for transfer between equipment, ensuring that the aluminum-lithium alloy powder remains under the same inert gas field protection from below 150°C until coating is completed, thus eliminating the oxidation path of lithium elements from a spatial structure perspective; the continuous fluidization process avoids temperature fluctuations caused by frequent start-stop cycles of powder feeding and discharging, preventing lithium segregation induced by thermal cycling. Limiting the operating pressure to a wide range from 100 Pa to atmospheric pressure is to synergistically adapt to the ignition mechanism of low-temperature plasma and the gas-solid dynamics of fluidized beds. In the low-pressure region (100 Pa-10 kPa), the mean free path of gas molecules increases, electrons accelerate a longer distance in the electric field, and acquire higher energy, making it easier to induce ionization and dissociation of silicon-containing precursors. This allows for the maintenance of a stable plasma sheath at lower power, reducing thermal radiation to the powder bulk and further enhancing the core advantages of low-temperature deposition. At low pressure, the gas density decreases, and the gas-phase diffusion coefficient of precursor molecules to the particle surface increases, which helps to achieve deeper penetration in the complex particle packing structure of the fluidized bed and improves coating uniformity. At atmospheric pressure (approximately 101.325 kPa) increases gas density, providing greater drag at the same apparent gas velocity. This facilitates stable fluidization of fine aluminum-lithium alloy powder, reduces channeling and throttling phenomena, and ensures particles are in an ideal dynamic dispersion state. Atmospheric pressure operation eliminates the need for complex vacuum maintenance systems, significantly reducing equipment complexity and operating costs for continuous production, and facilitating industrial scale-up. Continuous pretreatment and deposition within the same reactor result in a high spatial overlap between the plasma physical field, the fluidizing gas dynamic field, and the chemical reaction field. The powder surface after S400 plasma pretreatment is in a highly active metastable state (rich in dangling bonds), immediately followed by the S500 deposition stage. This avoids surface activity decay due to relaxation or adsorbed impurities, significantly improving the interfacial bonding energy of the silicon-based coating. In a single reactor, the fluidizing gas serves as the fluidization medium, the plasma working gas, and the carrier gas for the precursor. This three-in-one gas flow channel design ensures that the contact probability between active particles and particle surfaces remains highly consistent in both space and time, solving the edge effect or bottom deposition problems commonly found in fixed beds.

[0034] In this embodiment, steps S200 to S600 are completed continuously in a closed conveying system, and the aluminum-lithium alloy powder does not come into contact with the outside air throughout the process. Lithium in the aluminum-lithium alloy has extremely high electrochemical activity, with a standard electrode potential much lower than that of aluminum. In powder form, the extremely high specific surface area makes lithium atoms readily react with trace amounts of oxygen and water vapor in the environment. This invention, through a closed conveying system, strictly controls the oxygen partial pressure to below 10 ppm, ensuring that the Gibbs free energy on the surface of the aluminum-lithium alloy powder cannot support the spontaneous oxidation reaction, thus blocking lithium oxidation. Even at room temperature, water vapor can undergo a violent exothermic reaction with lithium; the closed system cuts off the water vapor source, eliminating localized micro-corrosion and lithium hydroxide formation caused by surface-adsorbed water, thereby ensuring the chemical purity of the powder surface. In traditional processes, powder is inevitably exposed to the workshop atmosphere during cooling, sieving, transfer, and loading. Even if the exposure time is only a few seconds, the highly active aluminum-lithium alloy surface will quickly adsorb a layer of oxygen atoms, which will diffuse into the matrix during subsequent heating or fluidization, forming a dense lithium oxide / alumina mixed layer. This invention eliminates the exposure risk of all intermediate steps through a single-line closed loop of "preparation-cooling-fluidization-coating-collection", ensuring that the powder has only an extremely thin native oxide film on its surface before entering the S400 plasma pretreatment step. This significantly reduces the energy consumption of subsequent plasma cleaning and improves the interfacial bonding strength between the coating layer and the matrix. Lithium is not only chemically reactive but also has a high saturated vapor pressure. In segmented processes, the powder undergoes multiple thermal cycles of "cooling-exposure-reheating," each heating inducing preferential volatilization of lithium. The closed continuous system of this invention ensures that the powder undergoes only one controlled low-temperature heat treatment (≤250℃) in step S500, with no temperature oscillations throughout. This single, stable thermal history effectively suppresses the diffusion and volatilization of lithium along grain boundaries, ensuring the consistency of the final product's chemical composition with the design values. The closed conveying system and the fluidized bed reactor 310 constitute a complete, fully enclosed inert gas path. The fluidizing gas, carrier gas, and system purge gas all come from the same high-purity gas source, forming a unidirectional positive or slightly negative pressure flow, preventing external contaminant gases from backflowing through equipment gaps. This system-level inert environment design, combined with the low-temperature deposition (≤250℃) in step S500, makes low temperature and oxygen-free a complementary double insurance. Low temperature reduces reactivity, and oxygen-free eliminates the reaction medium, jointly minimizing lithium loss. Aluminum-lithium alloy powder poses a risk of spontaneous combustion in air. The closed continuous system completely encloses the highly active powder in pipes and containers, eliminating the safety hazards caused by dust leakage and the interference of human operation differences and environmental humidity fluctuations on the process. This ensures that the surface condition, oxygen content and coating quality of each batch of products remain highly consistent, meeting the stringent reproducibility requirements of industrial production.

[0035] like Figure 2 and Figure 3As shown, the low-temperature plasma fluidized bed continuous coating system for aluminum-lithium alloy powder in this embodiment is used to implement the low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder as described above; it includes: a gas atomization powder preparation unit 100 for preparing aluminum-lithium alloy powder; a cooling and conveying unit 200 for cooling and continuously conveying the aluminum-lithium alloy powder; a fluidized bed plasma deposition unit 300 for coating the aluminum-lithium alloy powder under fluidized state and plasma action; a powder collection unit 400 for collecting the coated powder; and an atmosphere control unit for maintaining an inert atmosphere environment and controlling the oxygen content to be no higher than 10 ppm; wherein, the gas atomization powder preparation unit 100, the cooling and conveying unit 200, the fluidized bed plasma deposition unit 300, and the powder collection unit 400 are sequentially connected and form a closed pipeline assembly to form a continuous inert atmosphere production link; the atmosphere control unit is connected to the continuous inert atmosphere production link. This invention relates to a low-temperature plasma fluidized bed continuous coating system for aluminum-lithium alloy powder. This system comprises a sealed pipeline assembly consisting of a gas atomization powder preparation unit 100, a cooling and conveying unit 200, a fluidized bed plasma deposition unit 300, and a powder collection unit 400, forming a leak-free, continuous inert atmosphere production chain. Unlike traditional segmented operations involving powder preparation, storage, transfer, and coating, this system integrates powder forming, cooling, surface modification, and collection into a single sealed pipeline. The aluminum-lithium alloy powder remains completely isolated from the external atmosphere, eliminating the risk of oxygen and moisture intrusion due to process changes, valve switching, or manual operation. The atmosphere control unit is directly connected to the sealed pipeline, enabling real-time monitoring and dynamic adjustment of the oxygen content within the system, ensuring it remains stably below 10 ppm. This provides absolute thermodynamic protection for the aluminum-lithium alloy powder and inhibits the oxidation kinetics of lithium. The system's structural design allows the powder to directly enter the cooling and coating process after preparation, eliminating the need for the traditional thermal cycle of "cooling – room temperature storage – reheating." Lithium in aluminum-lithium alloys is prone to grain boundary segregation and surface enrichment during repeated heating and cooling. Through continuous flow operation, the powder undergoes only one controlled low-temperature heat treatment process (≤250℃ in the fluidized bed), significantly reducing the preferential volatilization and diffusion loss of lithium. The continuous pipeline design eliminates auxiliary time such as loading, unloading, and vacuuming in intermittent production, enabling high-throughput production and avoiding surface state fluctuations caused by differences in exposure time between different batches of powder, ensuring high product quality uniformity.The fluidized bed plasma deposition unit 300, as the core reaction hub of the system, has a structural design that perfectly matches the process requirements of the aforementioned method. The sealed pipeline assembly provides a stable gas-tight environment for the fluidized bed, ensuring that the fluidizing gas can serve as a carrier gas to maintain an inert atmosphere, as a power source to drive powder tumbling, and as a plasma working medium. This multifunctional gas channel design ensures that each powder particle can uniformly receive plasma surface activation and coating deposition in the fluidized state. Due to the overall sealed and well-insulated nature of the system, combined with the precise temperature control of the cooling and conveying unit 200, the low-temperature reaction field of 80℃–250℃ in the fluidized bed can be stably maintained, avoiding temperature fluctuations caused by heat dissipation or external interference, thereby ensuring the uniform growth of the silicon-based coating layer. In response to the flammable and explosive nature of aluminum-lithium alloy powder, a closed-loop pipeline assembly, in conjunction with an atmosphere control unit, constitutes an intrinsically safe design. The fully enclosed system confines the flammable metal powder within the pipeline, isolating it from oxidizers (oxygen) and ignition sources (static electricity or friction in the air), significantly reducing the risk of dust explosions. The system not only protects the powder from environmental pollution but also prevents highly reactive powder or trace byproducts generated during its processing from leaking into the external environment, meeting the requirements of green manufacturing and safe production standards. The low-temperature plasma fluidized bed continuous coating system for aluminum-lithium alloy powder of this invention, through a fully enclosed continuous pipeline architecture consisting of a gas atomization powder preparation unit 100, a cooling and conveying unit 200, a fluidized bed plasma deposition unit 300, and a powder collection unit 400, works in conjunction with an atmosphere control unit to successfully construct an inert material flow field with controlled oxygen content, a single thermal history, and a stable reaction environment. This not only completely solves the problems of oxidation and lithium loss in the processing of high-activity aluminum-lithium alloy powder from a physical structure perspective, but also perfectly adapts to the requirements of low-temperature plasma fluidized bed technology for airtightness, temperature control accuracy, and gas-solid flow state. It achieves seamless connection and continuous operation from powder preparation to surface modification. This system integration solution breaks through the technical bottleneck of existing equipment in processing high-activity metal powders.

[0036] In this embodiment, it also includes independently configured fluidizing gas path, precursor gas path, and plasma working gas path; and / or the fluidized bed plasma deposition unit 300 includes a gas distribution structure for forming a uniform fluidization state; and / or the fluidized bed plasma deposition unit 300 includes a plasma generating device 320, which includes an electrode structure 321, which is configured as a ring electrode or a multi-electrode structure; and / or the fluidized bed plasma deposition unit 300 includes a plasma generating device 320, which is a radio frequency plasma generating device and / or a microwave plasma generating device; and / or the cooling and transport unit 200 adopts an inert gas circulating cooling structure. Independently configured fluidizing gas, precursor gas, and plasma working gas paths enable precise diversion, independent control, and mutual interference suppression of multi-component gases. Through these independent paths, each fluidizing gas, precursor carrier gas, and plasma working gas can be configured with a mass flow controller, allowing for independent and precise adjustment of their respective flow rates, partial pressures, and pulse timing, avoiding component crosstalk and flow coupling caused by shared gas paths. The plasma working gas (e.g., Ar, H2) and fluidizing gas can be independently optimized; the plasma working gas focuses on maintaining stable electron density and breakdown field strength, while the fluidizing gas focuses on particle drag and fluidization quality. Independent gas paths prevent the precursor from entering the discharge region and affecting impedance matching, thus preventing arc instability or discharge extinction. The precursor gas path can be separately equipped with preheating and mixing sections to ensure a uniform concentration field before entering the fluidized bed. Independent control also enables pulsed or gradient feeding, suppressing homogeneous nucleation in the gas phase, increasing the proportion of heterogeneous deposition on the surface, and reducing dust and wall deposition. The fluidized bed plasma deposition unit 300 includes a gas distribution structure to form a uniform fluidized state and construct a spatially uniform fluidized field and gas-solid interface. The gas distribution structure (such as a porous plate, sintered metal, or nozzle array) optimizes the porosity and pore size distribution, allowing the gas to enter the bed with a uniform pressure drop and velocity profile, eliminating local high-speed channels (channeling) and large bubbles (nodding), and ensuring that all aluminum-lithium alloy powders participate in the fluidization process. Uniform fluidization makes the particles present an ideal fully mixed state in the bed, shortening the residence time distribution of particles in the reactor and improving the batch uniformity of the coating thickness. The uniformly distributed airflow is conducive to heat dissipation and prevents lithium volatilization caused by local hot spots. Uniform fluidization ensures that the particles are uniformly distributed in the plasma interaction zone, avoiding the shielding effect caused by excessively high local particle density or the energy waste caused by excessively low local density, and realizing the spatial synergy of "fluidized state-plasma field".The plasma generator 320 includes an electrode structure 321, which is configured as a ring electrode or a multi-electrode structure to expand the plasma interaction volume, improve spatial uniformity and system stability. The ring electrode forms a closed discharge loop in the radial direction, generating an axisymmetric plasma sheath, making the concentration of active particles in the center of the fluidized bed and the near-wall region more uniform, overcoming the non-uniformity of "strong near electrode and weak far electrode" in the single electrode structure. The multi-electrode structure can realize the spatial distribution and phase control of power, forming a composite plasma field with multiple overlapping discharge zones, further expanding the effective activation volume and adapting to the needs of high-throughput continuous production. The ring or multi-electrode structure usually adopts an external or water-cooled design to reduce direct contact with highly active powders, reduce the metal impurity doping of electrode materials (such as tungsten and molybdenum) into the coating layer, and improve product purity. The plasma generator 320 is a radio frequency plasma generator and / or a microwave plasma generator, matching the requirements of low-temperature deposition and achieving synergy between high-energy electrons and low thermal load. Radio frequency plasma (RF), at a frequency of 13.56MHz, has a moderate collision frequency between electrons and neutral gas, forming a large-area, uniform, and stable non-equilibrium plasma, which is suitable for gentle and uniform pretreatment and deposition of powder, avoiding local overheating. Microwave plasma (MW), at a frequency of 2.45GHz, has a significantly higher electron density than radio frequency discharge, generating a high density of active free radicals, which can achieve efficient decomposition of precursors at lower gas phase temperatures, and is particularly suitable for rapid deposition at low temperatures (≤250℃). The combined synergistic effect of radio frequency and microwave can achieve dual-peak regulation of electron energy distribution: radio frequency maintains discharge stability, microwave enhances reactivity, and the synergy of the two further reduces the deposition temperature and improves the density of the coating layer. The cooling and conveying unit 200 adopts an inert gas circulating cooling structure to achieve low-temperature closed-loop cooling, component protection, and energy recovery. The inert gas (such as high-purity argon or nitrogen) circulating cooling is carried out in a closed pipeline, so the powder does not come into contact with air. The cooling medium itself is part of the inert protective gas, doubly blocking the oxidation and volatilization paths. The circulating cooling structure can be equipped with a heat exchanger to remove the sensible heat of the powder from the system for preheating the feed or recovering energy, thereby improving the system's energy efficiency. By adjusting the circulating gas flow rate and temperature, the cooling rate can be controlled and adjusted to avoid thermal stress cracks inside the powder caused by rapid cooling. The closed loop avoids the condensation and adsorption of ambient moisture in the cooling section, ensuring that the powder surface entering the fluidized bed is dry and clean, providing an ideal substrate for subsequent plasma pretreatment and deposition.

[0037] This invention provides a low-temperature plasma fluidized bed continuous coating method and system for aluminum-lithium alloy powder, belonging to the field of metal powder surface modification technology. Addressing the problems of lithium volatilization, poor uniformity of fixed-bed coating, and easy oxidation during powder transfer caused by high-temperature vapor deposition in existing technologies, this invention continuously couples powder preparation, online cooling and conveying, and fluidized bed plasma-enhanced chemical vapor deposition under a constant inert atmosphere. At a temperature not exceeding 250°C, plasma activation promotes the low-temperature decomposition of silicon-containing precursors, and combined with the continuous tumbling and dispersion of particles in a fluidized state, uniform and dense coating of the aluminum-lithium alloy powder is achieved. Simultaneously, the continuous sealed inert environment effectively avoids powder oxidation and lithium loss during processing. The key to this invention lies in the synergistic effect between low-temperature plasma activation, fluidized bed dynamic contact, and inert atmosphere protection, enabling the deposition process to achieve a high-quality coating while significantly reducing the temperature. Experimental results show that compared to high-temperature chemical vapor deposition methods, the lithium loss rate is reduced from approximately 18% to below 2%, the coating uniformity is significantly improved, and the powder's oxidation resistance is significantly enhanced. This invention enables continuous preparation and low-temperature, high-quality coating of aluminum-lithium alloy powder, and has promising prospects for industrial application.

[0038] The beneficial effects of the low-temperature plasma fluidized bed continuous coating method and system for aluminum-lithium alloy powder of the present invention are as follows: The key to this invention lies not in any single technical means, but in the synergistic effect formed between low-temperature plasma activation, fluidized bed particle dynamic dispersion, and a continuously sealed inert atmosphere. Plasma significantly reduces the energy required for precursor decomposition, enabling the deposition reaction to proceed below 250°C; the fluidized bed structure keeps particles in a high-frequency tumbling and dispersed state, eliminating the agglomeration and shielding effects commonly found in fixed beds; and the continuous inert atmosphere prevents oxidation of the powder and loss of lithium during preparation and transfer. The coupling of these three elements makes high-quality coating possible under low-temperature conditions.

[0039] Experimental results demonstrate that this synergistic system produces significant effects. Under conventional chemical vapor deposition conditions of approximately 450°C, the lithium loss rate in aluminum-lithium alloy powder can reach about 18%, while under the low-temperature conditions of this invention, the lithium loss rate can be reduced to below 2%, a reduction of over 80%. This result significantly exceeds the range that can be explained by simply lowering the temperature, demonstrating the significant effect of the coupling effect of plasma activation and fluidized dynamic deposition on suppressing lithium volatilization.

[0040] Meanwhile, compared with fixed-bed plasma deposition methods, this invention achieves uniform deposition of the coating layer in a fluidized state, avoiding problems such as localized uncoated areas or uneven thickness caused by particle accumulation. Test results show that the obtained silicon-based coating layer has a uniform thickness distribution, a dense structure, significantly reduced oxygen content on the powder surface, and significantly improved oxidation resistance in an air environment.

[0041] Further comparisons show that without any of the aforementioned key factors, it is difficult to achieve the same technical effect. Under plasma-free conditions, the deposition temperature needs to be significantly increased to achieve precursor decomposition, leading to increased lithium volatilization; in a non-fluidized state, the powder is prone to agglomeration, resulting in a significant decrease in coating uniformity; in a discontinuous inert environment, the powder rapidly oxidizes during transfer, accompanied by lithium loss. This indicates that the technical effect of this invention stems from the synergy of multiple factors, rather than a simple superposition of a single technical means.

[0042] Therefore, this invention is not a conventional combination of existing gas atomization powder production technology and fluidized bed PECVD technology. Instead, through the synergistic design of process conditions and structure, it achieves high-quality coating of highly active aluminum-lithium alloy powder under low-temperature conditions, and significantly improves the material's compositional stability and environmental adaptability. This technical solution has good feasibility and industrial application prospects.

[0043] like Figure 1 As shown, the continuous integrated system of the present invention includes a gas atomization powder making unit 100, an online powder cooling and conveying unit 200, a fluidized bed plasma deposition unit 300 (fluidized bed plasma enhanced chemical vapor deposition unit) and a powder collection unit 400. Each unit is connected by a closed pipeline and is in a uniform inert atmosphere protection environment, thereby forming a continuous production system from alloy melt to coated powder.

[0044] The gas atomization powder-making unit 100 is used to atomize aluminum-lithium alloy melt into spherical powder under inert gas protection. Argon or nitrogen is used as the atomizing gas during the atomization process to ensure that the powder does not undergo oxidation during generation. The generated high-temperature powder then directly enters the powder online cooling and conveying unit 200, where it is rapidly cooled by methods such as gas cooling, cyclone separation, or pneumatic conveying. During this process, the circulating inert gas can quickly remove heat from the powder, reducing the powder temperature to below 150°C in a short time, thereby reducing lithium volatilization and preventing powder sintering or agglomeration. The cooled powder is continuously conveyed to the fluidized bed plasma deposition unit 300 in a closed conveying channel.

[0045] like Figure 3 As shown, the fluidized bed plasma deposition unit 300 includes a fluidized bed reactor 310.

[0046] The fluidized bed reactor 310 is equipped with a gas distribution plate 311, above which a fluidized powder bed 312 is formed to support the aluminum-lithium alloy powder. The gas distribution plate 311 enables the fluidizing gas to be evenly distributed at the bottom of the reactor, thereby ensuring that the powder bed forms a stable fluidized state.

[0047] The central region of the fluidized bed reactor 310 is the plasma reaction zone 313, which is the functional area during the reaction process. The region is not a solid structural component. The fluidized bed reactor 310 is connected to the plasma generator 320, which applies electromagnetic energy to the plasma reaction zone 313 through the electrode structure 321 to excite low-temperature plasma within the reaction zone. The plasma can be generated by an radio frequency power supply or a microwave power supply, thereby producing a large number of highly reactive ions, electrons, and free radicals under relatively low temperature conditions.

[0048] The fluidized bed reactor 310 has separate and independent gas inlets, including a fluidizing gas inlet 331 at the bottom of the reactor, a silicon precursor gas inlet 332 on the side wall of the reactor, and a plasma working gas inlet 333 for supplying gas to the plasma reaction zone 313. The fluidizing gas, plasma working gas, and silicon precursor gas are functionally independent and can be the same or different types of gas. Each gas is introduced into the reactor under the control of the gas supply and control system 330 and precisely regulated by a mass flow controller.

[0049] During operation, the aluminum-lithium alloy powder is fluidized under the action of fluidizing gas and is uniformly distributed in the fluidized powder bed 312. The fluidization state causes the powder particles to continuously tumble and mix, thereby enabling them to fully contact the gaseous reactants during the reaction.

[0050] Silicon precursor gas is activated by plasma to generate highly reactive silicon-based free radicals. These active free radicals can be deposited on the powder surface at relatively low temperatures to form a silicon-based coating layer.

[0051] The waste gas generated during the reaction is discharged through the waste gas outlet 334 located at the top of the reactor and treated by the atmosphere protection and exhaust system 500 to maintain a stable inert atmosphere environment inside the system. A powder discharge port 314 is provided on the lower side wall of the fluidized bed reactor 310. The discharge port 314 can be connected to the downstream unit via a star feeder, rotary valve, or closed valve. After coating, the powder is conveyed through the discharge port 314 to the powder collection unit 400, where it is collected and stored after being cooled to room temperature under closed conditions.

[0052] In the method of this invention, a significant synergistic effect is formed between low-temperature plasma activation, fluidized bed particle dynamic mixing, and continuous inert atmosphere protection. Plasma can promote the decomposition of silicon precursors at lower temperatures, enabling the deposition reaction to proceed at temperatures below 250°C; the fluidized bed structure keeps powder particles in a continuously tumbling and dispersed state, ensuring that each particle can uniformly contact the active reactants; and the continuous inert atmosphere system prevents the powder from coming into contact with air during preparation and coating, thereby significantly reducing the risk of oxidation.

[0053] The method of the present invention will be described below through specific embodiments.

[0054] Example 1: In a pure argon atmosphere with an oxygen content of less than 5 ppm, the Al-5Li (mass fraction) alloy melt was heated to approximately 780°C and subjected to gas atomization treatment at an atomization pressure of 1.0 MPa, thereby obtaining spherical powder with an average particle size of approximately 45 μm. The generated powder was rapidly cooled by circulating cooling argon gas and then transported to fluidized bed reactor 310 through a closed conveying pipeline.

[0055] The reactor temperature was controlled at 120℃. Argon gas was first introduced to excite radio frequency plasma, and the fluidized powder underwent a 2-minute plasma pretreatment to remove impurities adsorbed on the powder surface and activate it. Subsequently, a silane-containing reactive gas was introduced into the reactor, and the plasma discharge state was maintained for deposition for 15 minutes. The final product was an aluminum-lithium alloy powder with a silicon-based coating approximately 150 nm thick.

[0056] Scanning electron microscopy revealed a continuous and uniform coating layer structure on the powder surface. X-ray photoelectron spectroscopy analysis showed that the coating layer was mainly composed of Si and SiOx, forming a good interfacial bond with the base metal. The results indicated that the obtained powder exhibited a low lithium loss rate and significantly improved oxidation stability in air.

[0057] Example 2: Under powdering conditions similar to those in Example 1, the cooled powder was fed into a microwave plasma fluidized bed reactor 310. A deposition reaction was carried out at 150°C with a reaction gas containing silicon tetrachloride for 20 minutes, thereby obtaining an aluminum-lithium alloy powder with a silicon-based composite coating on its surface. This powder exhibited good coating adhesion and environmental stability.

[0058] To verify the technical effectiveness of the method of this invention, comparative experiments were conducted on powders obtained under different process conditions. First, uncoated aluminum-lithium alloy powder was prepared as a comparative sample. After being placed in air for 24 hours, XPS testing revealed a significant increase in the oxygen content on the powder surface, while the lithium content on the surface significantly decreased.

[0059] In addition, the traditional high-temperature chemical vapor deposition method was used to perform silicon coating treatment on aluminum-lithium alloy powder at 450°C.

[0060] Experimental results show that lithium volatilizes significantly during high-temperature deposition, and ICP analysis shows that the lithium content decreases by about 18%, and some powder surfaces show coating cracking.

[0061] In another comparative experiment, silicon deposition of powder was performed using a fixed-bed PECVD apparatus at 150°C. Although a silicon layer was formed, the coating thickness was uneven due to powder agglomeration during the reaction, and uncoated particles remained in some local areas.

[0062] Elemental analysis was performed on the powders obtained from different processes, and the results are shown in Table 1.

[0063] The experimental data show that the method of the present invention can effectively suppress lithium volatilization while significantly reducing the deposition temperature, and can obtain a more uniform coating layer.

[0064] To further evaluate the antioxidant properties of the powder, different powder samples were placed in air and kept at 150°C for 4 hours, and the oxidation weight gain was measured. The experimental results showed that the oxidation weight gain of the uncoated powder was approximately 6.8%, while the oxidation weight gain of the coated powder prepared using the method of this invention was only 2.1%. This result indicates that the silicon-based coating can significantly improve the antioxidant stability of aluminum-lithium alloy powder.

[0065] As can be seen from the above embodiments, the method of the present invention can achieve continuous preparation and surface coating of aluminum-lithium alloy powder under low-temperature conditions. The synergistic effect of low-temperature plasma-enhanced deposition, fluidized bed dynamic mixing, and inert atmosphere protection throughout the process allows the silicon-based coating layer to be uniformly deposited on the powder surface at temperatures not exceeding 250°C, while significantly reducing lithium volatilization loss and improving the environmental stability of the powder. Therefore, the present invention has good feasibility and industrial application prospects.

[0066] Matters not covered in this invention are common knowledge.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely examples 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 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.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for continuous low-temperature plasma fluidized bed coating of aluminum-lithium alloy powder, characterized in that, The entire process is carried out continuously in an inert atmosphere with an oxygen content not exceeding 10 ppm. A low-temperature plasma fluidized bed continuous coating system for aluminum-lithium alloy powder is used. The system includes: a gas atomization powder preparation unit (100) for preparing aluminum-lithium alloy powder; a cooling and conveying unit (200) for cooling and continuously conveying the aluminum-lithium alloy powder; a fluidized bed plasma deposition unit (300) for coating the aluminum-lithium alloy powder under fluidized state and plasma action; the fluidized bed plasma deposition unit (300) includes a fluidized bed reactor (310); a powder collection unit (400) for collecting the coated powder; and an atmosphere control unit for maintaining an inert atmosphere environment and controlling the oxygen content not exceeding 10 ppm. The gas atomization powder preparation unit (100), cooling and conveying unit (200), fluidized bed plasma deposition unit (300), and powder collection unit (400) are sequentially connected to form a closed pipeline assembly to form a continuous inert atmosphere production chain. The atmosphere control unit is connected to the continuous inert atmosphere production chain and includes the following steps: S100. Under the protection of an inert atmosphere, the aluminum-lithium alloy melt is subjected to gas atomization treatment to inhibit the oxidation and volatilization of lithium elements in the early stage of aluminum-lithium alloy powder formation, thereby preparing aluminum-lithium alloy powder with a clean surface and stable composition. S200: The aluminum-lithium alloy powder is cooled by inert gas under closed conditions, and the temperature of the aluminum-lithium alloy powder before entering the subsequent processing is controlled to be no higher than 150°C, so as to reduce the risk of thermal lithium volatilization and provide thermodynamic conditions for subsequent low-temperature deposition. S300: The cooled aluminum-lithium alloy powder is continuously fed into the fluidized bed reactor (310). Under the action of fluidizing gas, the aluminum-lithium alloy powder is in a dynamic fluidized state of continuous tumbling and dispersion to eliminate particle agglomeration and shielding effect, and ensure the uniformity of the coating process. In step S300, the fluidizing gas is hydrogen, or a mixture of argon and hydrogen, or a mixture of nitrogen and hydrogen, or a mixture of argon, nitrogen and hydrogen. S400. Under fluidized conditions, aluminum-lithium alloy powder is subjected to plasma pretreatment to remove trace amounts of native oxide film on the surface of aluminum-lithium alloy powder and generate active sites, which is beneficial to improve the interfacial bonding strength and deposition uniformity between the subsequent silicon-based coating layer and aluminum-lithium alloy powder. In step S400, the plasma pretreatment time is 0.5 min to 5 min; S500, introduces silicon-containing gaseous precursor into fluidized bed reactor (310) in the low temperature range of 80℃-250℃, and uses low temperature plasma activation to promote the silicon-containing gaseous precursor to undergo chemical reaction at a temperature below the thermal decomposition threshold, uniformly depositing a dense silicon-based coating layer on the surface of fluidized aluminum-lithium alloy powder, thereby achieving high-quality coating while suppressing lithium volatilization. In step S500, the silicon-containing gaseous precursor is at least one of silane or halosilane; In step S500, the thickness of the silicon-based coating layer is 0.05 μm-2 μm; S600: The coated aluminum-lithium alloy powder is cooled and collected under an inert atmosphere to prevent secondary oxidation of the silicon-based coating layer and the aluminum-lithium alloy powder body during the cooling process, thus ensuring the integrity of the coating and storage stability. The entire process of inert atmosphere protection, fluidized dispersion, and low-temperature plasma activation works in conjunction with surface pretreatment to synergistically ensure the compositional stability, coating densification, and process continuity of aluminum-lithium alloy powder at temperatures below 250°C. Steps S200 to S600 are completed continuously in a closed conveying system, and the aluminum-lithium alloy powder does not come into contact with the outside air throughout the process.

2. The low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder according to claim 1, characterized in that, In step S400 and / or step S500, the plasma is radio frequency plasma and / or microwave plasma.

3. The method for continuous low-temperature plasma fluidized bed coating of aluminum-lithium alloy powder according to claim 1, characterized in that, Steps S300 to S500 are carried out continuously within the same fluidized bed reactor (310); and / or the working pressure of the fluidized bed reactor (310) is from 100 Pa to atmospheric pressure.

4. The low-temperature plasma fluidized bed continuous coating method for aluminum-lithium alloy powder according to claim 1, characterized in that, It also includes independently configured fluidizing gas path, precursor gas path and plasma working gas path.

5. The method for continuous low-temperature plasma fluidized bed coating of aluminum-lithium alloy powder according to claim 1, characterized in that, The fluidized bed plasma deposition unit (300) includes a gas distribution structure for forming a uniform fluidized state.

6. The method for continuous low-temperature plasma fluidized bed coating of aluminum-lithium alloy powder according to claim 1, characterized in that, The fluidized bed plasma deposition unit (300) includes a plasma generating device (320), which includes an electrode structure (321) configured as a ring electrode or a multi-electrode structure.

7. The method for continuous low-temperature plasma fluidized bed coating of aluminum-lithium alloy powder according to claim 1, characterized in that, The fluidized bed plasma deposition unit (300) includes a plasma generator (320), which is a radio frequency plasma generator or a microwave plasma generator.

8. The method for continuous low-temperature plasma fluidized bed coating of aluminum-lithium alloy powder according to claim 1, characterized in that, The cooling and conveying unit (200) adopts an inert gas circulation cooling structure.

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