Vacuum passivation treatment device and method for low-oxygen niobium powder

Abstract

The invention relates to the technical field of metal material processing, in particular to a vacuum passivation treatment device and method for low-oxygen niobium powder, and aims to solve the problems that the oxygen control precision of an existing low-oxygen niobium powder passivation process is low, the oxygen content increase rate exceeds the standard due to the fact that the protective layer binding force is weak, and matching devices are insufficient in synergism. The method comprises the following steps: pre-filling low-oxygen niobium powder in an inert atmosphere, carrying out high-vacuum heating to T1 (150-250 DEG C), degassing and activating, introducing metal organic compound vapor to form an alloy transition layer, carrying out pulse oxygen introduction-rapid vacuumizing to realize dynamic micro-oxidation circulation, heating to T2 (300-450 DEG C), and alternately introducing nitriding / carbonizing / silicifying gas to form a nano laminated layer, and cooling and discharging under a protective atmosphere (optional fluorine-containing gas surface modification). The surface of the prepared niobium powder is of an alloy transition layer-initial oxide layer-nanometer lamination composite structure, and the oxygen content increase range is smaller than 200 ppm after the niobium powder is exposed for 120 hours in the environment with the temperature being 40 DEG C and the relative humidity being 75%. The matching device comprises a vacuum reaction chamber, a branch gas source subsystem (inertia / oxygen / nitridation, metal organic and carbonization / silicification), a gas alternating control module and a central control system, can automatically and synergistically complete the whole process, overcomes the defects in the prior art, and is suitable for industrial production.

Description

Technical Field

[0001] This application relates to the field of metal material processing technology, and in particular to a vacuum passivation treatment apparatus and method for low-oxygen niobium powder. Background Technology

[0002] Low-oxygen niobium powder is in high demand in the high-end equipment manufacturing field due to its excellent low-temperature superconductivity, high-temperature strength, and chemical stability. However, the high atomic activity on the surface of niobium powder makes it prone to reacting with oxygen in the air, leading to an increase in oxygen content and compromising its low-oxygen properties and performance. Therefore, passivation treatment is necessary to form a protective layer on its surface. Existing low-oxygen niobium powder passivation methods have significant limitations: traditional passivation often uses static oxygen oxidation or a single coating (such as a nitriding layer or a carbide layer). Static oxygen oxidation makes it difficult to precisely control the oxygen concentration, easily resulting in local oxygen content exceeding the standard, causing the loss of the low-oxygen advantage of niobium powder. The single coating has weak adhesion to the niobium powder matrix and is prone to detachment during storage (e.g., at 40°C and 75% relative humidity), failing to provide long-term oxygen barrier. As a result, the oxygen content of niobium powder often increases by more than 200 ppm after 120 hours of exposure, seriously affecting its application in high-end fields such as superconducting materials and high-precision electronic components. Furthermore, existing devices lack the ability to precisely coordinate multi-step gas switching and temperature control, making it difficult to achieve stable industrial production.

[0003] To address the problems mentioned above, a vacuum passivation device and method for low-oxygen niobium powder have been invented. Summary of the Invention

[0004] To address the shortcomings of existing low-oxygen niobium powder passivation methods, which struggle to simultaneously achieve precise control over oxidation levels and ensure a robust surface protective layer, leading to excessive oxygen content increases during niobium powder storage and impaired subsequent application performance, as well as insufficient automation and coordination of supporting equipment, this invention aims to provide a vacuum passivation method for low-oxygen niobium powder. This method utilizes a multi-step collaborative process to form a firmly bonded and structurally controllable protective system on the niobium powder surface, effectively inhibiting oxidation. Simultaneously, it provides a vacuum passivation device adapted to this method, achieving automation and stability in the processing. Ultimately, this method yields low-oxygen niobium powder that still meets requirements for oxygen content increases after storage under specific humid and hot conditions, ensuring its application value in high-end fields.

[0005] This application provides a vacuum passivation treatment method for low-oxygen niobium powder, which adopts the following technical solution: including the following steps: S1. Pretreatment and loading: Low-oxygen niobium powder is loaded into the passivation reactor under an inert atmosphere; S2. Primary deep degassing and activation: The reactor is evacuated to a high vacuum and heated to the first temperature T1 for degassing and activation; S3. Interface pre-alloying: Metal-organic compound vapor is introduced into the reactor to form an alloy transition layer on the surface of niobium powder, and then the residual gas is removed; S4. Dynamic micro-oxidation cycle treatment: Maintain temperature T1, pulse oxygen is introduced into the reactor and then quickly vacuumed. This operation is repeated multiple times. S5. Nanolayer reinforcement treatment: Adjust the reactor temperature to the second temperature T2, and introduce at least two different reaction gases in an alternating cycle to form a nanolayer reinforcement structure by alternating deposition on the surface of niobium powder. S6. Cooling and Discharge: After processing, cool and remove the passivated niobium powder under a protective atmosphere.

[0006] Optionally, in step S3, the organometallic compound is selected from trimethylaluminum, tetraethylsilane, or tert-butylzirconia; the treatment pressure is 0.1-2 Pa, and the treatment time is 2-15 minutes.

[0007] Optionally, in step S5, the alternating cycle includes: sequentially introducing a first reaction gas G1 while maintaining the first condition, drawing a vacuum, introducing a second reaction gas G2 while maintaining the second condition, and drawing a vacuum again, thus forming a complete cycle; wherein the pressure in the first condition and the second condition are each independently 30-100 Pa, and the processing time is each independently 1-5 minutes; the cycle is repeated 5-30 times.

[0008] Optionally, the first reactive gas G1 is nitrogen or ammonia.

[0009] Optionally, the second reaction gas G2 is a carbon-containing gas source or a silicon-containing gas source; the carbon-containing gas source is a mixture of methane, acetylene, or ethylene with an inert gas; the silicon-containing gas source is a mixture of silane and an inert gas.

[0010] Optionally, after step S5, step S5.1 final surface modification is also included: fluorine-containing gas is introduced into the reactor at 100-200°C for surface treatment.

[0011] Optionally, the first temperature T1 is 150-250℃, and the second temperature T2 is 300-450℃.

[0012] Optionally, the niobium powder has an alloy transition layer, an initial oxide layer, and a nano-stacked reinforcement layer distributed sequentially from the substrate outwards; and after the niobium powder is exposed to an environment of 40°C and 75% relative humidity for 120 hours, its oxygen content increases by less than 200 ppm.

[0013] A vacuum passivation treatment apparatus for low-oxygen niobium powder, comprising: The vacuum reaction chamber contains a material tray for holding niobium powder and a heating device. A vacuum system, connected to the vacuum reaction chamber, is used to establish and maintain the required vacuum environment; A gas supply system is connected to the vacuum reaction chamber; And the central control system; The gas supply system includes at least: The first gas source subsystem is used to provide inert gas, oxygen, and nitriding reaction gas; The second gas source subsystem is used to provide organometallic compound vapors; The third gas source subsystem is used to provide carbonization or siliconization reaction gases; The central control system is configured to automatically control the vacuum system, heating device, and each gas source subsystem according to a preset program, and perform the following operations in sequence: evacuate the chamber to a high vacuum and perform heating and degassing; introduce metal-organic compound vapor from the second gas source subsystem for interface pre-alloying treatment; pulsely introduce oxygen from the first gas source subsystem and rapidly evacuate it for dynamic micro-oxidation cycle treatment; alternately introduce reactive gases from the first gas source subsystem and the third gas source subsystem for nano-layering strengthening treatment.

[0014] Optionally, the gas supply system further includes a gas alternation control module, which is connected to the first gas source subsystem and the third gas source subsystem; The gas alternation control module includes a high-speed switching valve group and a timing controller. The timing controller is configured to: control the high-speed switching valve group to periodically and alternately introduce the nitriding reaction gas from the first gas source subsystem and the carbide or siliconization reaction gas from the third gas source subsystem into the vacuum reaction chamber, and trigger the vacuum system to briefly pump out gas between each gas introduction cycle to remove residual gas.

[0015] In summary, this application includes the following beneficial technical effects: 1. The interface pre-alloying step forms an alloy transition layer through metal-organic compound vapor, which greatly improves the bonding force between the subsequent protective layer and the niobium powder matrix; the dynamic micro-oxidation cycle uses pulse oxygenation + rapid vacuuming to precisely control the thickness of the initial oxide layer and avoid local over-oxidation; the nano-layer strengthening treatment further enhances the surface anti-oxidation barrier performance by alternately depositing different material layers, and the multi-step synergy ensures the comprehensiveness and stability of the passivation effect. 2. The low-oxygen niobium powder prepared by this method forms a composite protective structure on its surface consisting of an alloy transition layer, an initial oxide layer, and a nano-layered reinforcing layer. After exposure to an environment of 40°C and 75% relative humidity for 120 hours, the oxygen content increase is less than 200 ppm, demonstrating its ability to maintain low-oxygen properties over a long period. This meets the stringent requirements for raw material purity in high-end niobium-based materials. 3. The device achieves precise supply of different types of gas through the gas source subsystem (first, second, and third gas sources). Combined with the gas alternation control module (high-speed switching valve group + timing controller), it can realize the periodic alternation of gas introduction and residual gas removal in the nano-stacking stage. The central control system coordinates with the vacuum system and heating device according to the preset program to realize the full-process automated control, ensuring the repeatability and industrial adaptability of the processing process and reducing human operation errors.

[0016] Instruction manual illustrations Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a flowchart of step S1 in this invention; Figure 3 This is a flowchart of step S2 in this invention; Figure 4 This is a flowchart of step S3 in this invention; Figure 5 This is a flowchart of step S4 in this invention.

[0017] Figure 6 This is a flowchart of step S5 in this invention; Figure 7 This is a flowchart of step S6 in this invention.

[0018] Figure 8 This is a flowchart of step S5.1 in this invention. Detailed Implementation

[0019] The present application will be further described in detail below with reference to the accompanying drawings. In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0020] A vacuum passivation treatment method for low-oxygen niobium powder includes the following steps: S1. Pretreatment and Loading: This step is the basic preparation for passivation treatment. The core objective is to prevent the low-oxygen niobium powder from being pre-oxidized by contact with air during the loading stage, and to lay the foundation for subsequent uniform treatment. The surface atoms of low-oxygen niobium powder are highly active. When exposed to air at room temperature, it easily reacts rapidly with oxygen and water vapor, leading to an increase in the initial oxygen content and destroying the low-oxygen characteristics of the raw material. Therefore, the entire process must be carried out under the protection of an inert atmosphere (such as argon, nitrogen, etc.): First, inert gas is introduced into the passivation reactor to replace the air in the chamber until the oxygen content in the chamber drops below 10 ppm, ensuring that there are no residual oxidizing gases. Then, the low-oxygen niobium powder, which has been vacuum dried (to remove surface adsorbed water vapor), is evenly spread on the material tray in the reactor. The thickness of the spread is controlled at 2-5 cm (preferably 3 cm). If it is too thin, it will reduce the efficiency of a single treatment. If it is too thick, it will easily lead to uneven gas contact and temperature conduction between the inside and the surface of the niobium powder, affecting the consistency of subsequent processing steps. After loading, the inert atmosphere is maintained until the reactor is sealed to prevent the niobium powder from contacting air. S2. Primary Deep Degassing and Activation: This step aims to remove impurities adsorbed on the surface and shallow layers of niobium powder and activate the surface atoms of niobium powder to create favorable conditions for subsequent interfacial reactions. If impurities (mainly water vapor, oil, and a small amount of air components) remain, they will hinder the bonding of the subsequent alloy transition layer, oxide layer, and niobium powder matrix. After surface atom activation, its reactivity with organometallic compounds, oxygen, and other reactants can be significantly enhanced. During operation, the reactor is first evacuated to a high vacuum state (vacuum degree ≤1×10⁻²Pa, preferably 5×10⁻³Pa) using a vacuum system to remove residual gas from the chamber. Then, the heating device is started to raise the reactor temperature to the first temperature T1 (150-250℃, preferably 200℃), with the heating rate controlled at 3-8℃ / min to avoid sudden temperature rise that could cause niobium powder agglomeration. After reaching T1, the temperature is maintained for 1-3 hours (preferably 2 hours). During this period, the chamber pressure is monitored in real time using a vacuum gauge to ensure that the pressure remains stable within the high vacuum range. Too low a temperature (<150℃) will prevent the complete removal of stubborn impurities such as chemically adsorbed water, while too high a temperature (>250℃) may cause slight self-oxidation of the niobium powder, both of which will affect the subsequent treatment effect. S3. Interface Pre-alloying: This step forms an alloy transition layer on the surface of niobium powder, solving the problem of weak bonding between the niobium powder matrix and subsequent protective layers (oxide layer, nano-stacks) due to large differences in crystal structure, thus providing a "transition bridge" for the subsequent protective structure. During operation, the reactor temperature T1 and high vacuum are maintained. Organometallic compound vapor (trimethylaluminum, tetraethylsilane, or tert-butylzirconia, preferably trimethylaluminum) is introduced into the chamber through a dedicated gas source subsystem. Simultaneously, the valve is adjusted to control the chamber processing pressure at 0.1-2 Pa (preferably 0.8 Pa)—too low pressure will result in insufficient vapor concentration, leading to voids in the alloy layer; too high pressure will result in an excessively thick alloy layer, affecting the adhesion of the subsequent protective layer. Maintain this state for 2-15 minutes (preferably 8 minutes) to allow the metal atoms (such as Al, Si, Zr) in the organometallic compound to fully react with the activated atoms on the niobium powder surface, forming a uniform alloy transition layer with a thickness of 30-80 nm (preferably 50-60 nm). After the reaction is completed, restart the vacuum system to remove the residual organometallic compound vapor and reaction byproducts from the chamber to ensure that there are no impurities interfering with subsequent steps. S4. Dynamic Micro-Oxidation Cyclic Treatment: The core of this step is to precisely control the thickness and uniformity of the initial oxide layer on the niobium powder surface, avoiding "over-oxidation" (excessive oxide layer leading to embrittlement) or "under-oxidation" (incomplete oxide layer), thus providing a stable substrate for subsequent nano-layering. The initial oxide layer (mainly composed of Nb2O5) needs to be thin and continuous, so as to both tightly bond with the alloy transition layer and provide a good adhesion surface for nano-layering. During operation, the reactor temperature T1 is kept constant, and a "pulse-type oxygenation-rapid vacuuming" cycle mode is adopted: each time, a small amount of oxygen (flow rate 0.3-0.8 L / min) is introduced into the chamber through the gas source subsystem, and the oxygenation time is controlled at 5-15 seconds (preferably 10 seconds) so that the oxygen only reacts with the alloy layer on the surface of the niobium powder; after the oxygenation is completed, the vacuum system is immediately started to rapidly pump air for 30-60 seconds (preferably 30 seconds) to restore the chamber pressure to a high vacuum state, remove unreacted residual oxygen, and avoid accumulation leading to over-oxygenation; this "oxygenation-vacuuming" operation is cycled 15-25 times (preferably 20 times) to ensure that a complete initial oxide layer with a thickness of 10-30 nm (preferably 20-25 nm) is formed on the surface of all niobium powder particles, without local oxygen-deficient areas. S5. Nanolayer Reinforcement Treatment: This step constructs an alternating nanolayer structure to form a "multi-layer barrier," significantly improving the antioxidant properties and structural stability of niobium powder. Single-material protective layers are prone to grain boundary defects, allowing oxygen to permeate. Alternating nanolayers (such as NbN / NbC, NbN / NbSi2) utilize grain boundary dislocations of different materials to block the permeation path. Furthermore, the layered structure exhibits superior toughness compared to a single coating, reducing the risk of cracking during storage. During operation, the reactor temperature is first raised to a second temperature T2 (300-450℃, preferably 380℃) using a heating device and held for 20-40 minutes (preferably 30 minutes) to ensure a uniform and stable chamber temperature. Then, the process is cyclical: "Introduce the first reaction gas → Hold for reaction → Vacuum → Introduce the second reaction gas → Hold for reaction → Vacuum." The first reaction gas G1 is a nitriding reaction gas (nitrogen or ammonia, preferably ammonia). After introduction, the chamber pressure is controlled at 30-100 Pa (preferably 60 Pa), and the reaction is held for 1-5 minutes. For 3 minutes (preferably 3 minutes), a nitrided layer (such as NbN) is formed on the surface of the initial oxide layer. After vacuuming to remove residual G1, a second reaction gas G2 (a carbonization gas source or a silicon-containing gas source, preferably a mixture of methane and inert gas) is introduced. The pressure is controlled at 30-100 Pa and the temperature is maintained for 1-5 minutes to form a carbonized layer (such as NbC) or a silicided layer (such as NbSi2). The above cycle is repeated 5-30 times (preferably 20 times) to finally form a uniform nanolayer with a total thickness of 300-800 nm (preferably around 600 nm) on the surface of the niobium powder. S6. Cooling and Discharging: This step aims to prevent secondary oxidation or stress cracking of niobium powder and protective structure at high temperatures during cooling, ensuring stable passivation. The niobium powder protective layer (especially the nanolayered structure) is not fully stable at high temperatures. Direct contact with air can easily lead to an increase in oxygen content. Simultaneously, rapid cooling can cause thermal stress between the niobium powder matrix and the protective layer due to the difference in thermal expansion coefficients, potentially causing cracking of the protective layer. During operation, first turn off the heating device and continue to circulate an inert protective gas (such as argon, flow rate 2-5 L / min, preferably 3 L / min) into the reactor, allowing the chamber to cool naturally at a rate of 5-10°C / min (avoiding forced cooling that could cause excessive stress). Once the chamber temperature has dropped to room temperature (approximately 25°C), stop the inert gas flow, slowly open the reactor door, remove the passivated low-oxygen niobium powder, and immediately seal it for storage to prevent contact with air during subsequent storage. S5.1 Final Surface Modification: This step is an optional optimization process. Its core purpose is to further improve the corrosion resistance and hydrophobicity of the nanolayer surface, expanding the application scenarios of niobium powder in humid and corrosive environments. Although nanolayers (such as NbN / NbC) have excellent antioxidant properties, they are prone to electrochemical corrosion in environments containing corrosive ions such as Cl⁻. Fluoride-modified layers (such as NbF5) have good hydrophobicity and corrosion resistance, forming a "secondary protection" on the surface of the nanolayer. During operation, after the S5 nanolayer strengthening treatment is completed, maintain the reactor temperature T2 (or reduce it to 100-200℃, depending on the actual process, preferably 380℃), introduce fluorine-containing gas (such as a mixture of sulfur hexafluoride and inert gas) into the chamber, control the chamber pressure to 30-50Pa (preferably 40Pa), and keep it at this temperature for 8-15 minutes (preferably 10 minutes) to allow the fluorine-containing gas to react with the surface of the nanolayer, forming a uniform fluoride modification layer with a thickness of 3-10nm (preferably 5nm); after the treatment is completed, start the vacuum system to remove the residual fluorine-containing gas, and then proceed with cooling and discharge according to the S6 process.

[0021] A vacuum passivation treatment device for low-oxygen niobium powder, the device having a vertical structure (occupying an area of ​​1.2m × 0.8m and a height of 2.5m), and the structure of each core component is as follows: Vacuum reaction chamber: Material: The main body of the chamber is made of 316L stainless steel (12mm thick), and the inner wall is electrolytically polished (roughness Ra≤0.2μm) to prevent impurities from adsorbing; a quartz observation window (15cm in diameter and 10mm thick) is provided at the top for easy observation of the internal condition of the chamber; a detachable drain valve (stainless steel) is provided at the bottom for periodic cleaning of residual powder. Material tray: 3 layers of porous quartz trays (each layer is 30cm in diameter and 5cm in height, with Φ2mm through holes and 5mm hole spacing), fixed in the middle of the chamber by a quartz bracket, which can achieve uniform heating of niobium powder and full contact with gas; an infrared temperature probe (measurement range 0-600℃, accuracy ±1℃) is installed below the material tray to provide real-time feedback of the temperature inside the chamber. Heating device: Six sets of infrared heating tubes (500W power per tube, wavelength 2-5μm) are arranged around the inner wall of the chamber. They are controlled by a PID temperature control module with a temperature range of 50-500℃ and a temperature control accuracy of ±2℃. The heating tubes are covered with quartz protective sleeves to prevent powder from directly contacting the heating elements. Vacuum system: Components: Mechanical pump (model 2XZ-4, pumping speed 4L / s, ultimate vacuum 2Pa) and molecular pump (model F-100 / 160, pumping speed 100L / s, ultimate vacuum 5×10⁻). 4 The pumps are connected in series, with the mechanical pump serving as the backing pump and the molecular pump as the high vacuum pump; an electromagnetic vent valve (DN15) and a vacuum check valve (DN20) are installed between them to prevent gas backflow. Vacuum testing: A vacuum gauge assembly (including a resistance vacuum gauge, measuring range 10) is installed between the chamber and the vacuum system. 5 -10⁻¹Pa; Ionization vacuum gauge, measuring range 10⁻¹-10⁻ 5 The system monitors the vacuum level inside the cavity in real time (Pa) and transmits the data to the central control system. Gas supply system: Gas source storage: Each gas source subsystem is equipped with a 40L high-pressure steel cylinder (material 37Mn, working pressure 15MPa). The cylinder outlet is equipped with a pressure regulator (accuracy ±0.01MPa), a pressure gauge (range 0-25MPa), and a safety valve (starting pressure 18MPa). Gas piping: All piping is made of Φ6mm stainless steel (wall thickness 1.5mm). The piping is equipped with a gas filter (filtration accuracy 0.1μm, material PTFE), a mass flow controller (MFC, measurement range 0-10L / min, accuracy ±1%FS) and a solenoid valve (response time ≤0.1s, voltage 24VDC); the second gas source subsystem piping is wrapped with a heating tape (heating temperature 50-80℃) to prevent the condensation of metal-organic compound vapors. Gas alternation control module: High-speed switching valve assembly: contains 4 two-position three-way solenoid valves, which are respectively connected to the first gas source subsystem (ammonia), the third gas source subsystem (methane mixture), the chamber inlet and the vacuum system inlet. Timing controller: It adopts a PLC controller, which can preset the cycle period (adjustable from 1 to 100 seconds), gas introduction time (adjustable from 0.5 to 10 minutes) and vacuuming time (adjustable from 0.5 to 5 minutes), and realize parameter setting and status display through touch screen (7-inch, resolution 800×480). Central control system: It adopts an industrial computer (CPU i5-10400, memory 8GB, hard disk 1TB) to connect components such as vacuum gauge group, temperature probe, MFC, solenoid valve, heating module, etc., and realizes data interaction through RS485 communication protocol. Example 1: Basic Vacuum Passivation Treatment S1. Pretreatment and loading: Open the argon valve of the first gas source subsystem and introduce argon gas at a flow rate of 5L / min into the vacuum reaction chamber until the oxygen content in the chamber drops below 10ppm; then, evenly spread 10kg of low-oxygen niobium powder (initial oxygen content 350ppm, particle size 5-10μm, purity 99.95%) that has been vacuum dried at 100℃ for 2h on the loading tray (ply thickness 3cm), close the chamber door, and maintain the argon atmosphere until the loading process is completed. S2. Primary deep degassing and activation: The central control system triggers the vacuum system, first starting the mechanical pump to evacuate to 1 Pa, and then starting the molecular pump to evacuate to a high vacuum state of 5×10⁻³ Pa; at the same time, the infrared heating tube is controlled to heat up to the first temperature T1=200℃ at a rate of 5℃ / min and hold for 2 hours; during the process, the chamber pressure is monitored in real time by the vacuum gauge group to ensure that the pressure during the degassing process is stable at ≤1×10⁻² Pa, so as to fully remove the residual water vapor and oil on the surface of niobium powder and activate the surface atoms of niobium powder. S3. Interface pre-alloying: Maintain chamber temperature at 200℃ and vacuum at 5×10⁻³Pa. Switch the central control system to the second gas source subsystem, open the trimethylaluminum vapor valve (using argon gas at a flow rate of 1L / min as the carrier gas, with a trimethylaluminum vapor concentration of 5vol%), adjust the valve opening to stabilize the chamber pressure at 0.8Pa, and hold for 8 minutes. After the reaction is complete, close the second gas source subsystem, start the vacuum system to evacuate for 15 minutes, restore the chamber pressure to 5×10⁻³Pa, and remove residual trimethylaluminum vapor and reaction byproducts. XRD analysis shows that an Al-Nb alloy transition layer of approximately 50nm thick has formed on the surface of the niobium powder at this point. S4. Dynamic Micro-oxidation Cycle Treatment: Maintain the chamber temperature at 200℃. The central control system switches to the oxygen valve of the first gas source subsystem, adopting a "pulse oxygen supply - rapid vacuuming" mode: each oxygen supply lasts 10 seconds (oxygen flow rate 0.5L / min), and immediately after oxygen supply, the vacuum system is activated for 30 seconds to restore the chamber pressure to 5×10⁻³Pa. This operation is repeated 20 times. During the process, the oxygen content in the chamber is monitored in real time by an oxygen concentration sensor to ensure that the residual oxygen is ≤1×10⁻³Pa after each cycle. 4 Pa; FE-SEM observation showed that a uniform initial oxide layer (Nb2O5) of about 20 nm thick was formed on the surface of the alloy transition layer, with no local over-oxidation phenomenon. S5. Nanolayer Strengthening Treatment: The central control system controls the heating tube to raise the chamber temperature to the second temperature T2=380℃ at a rate of 8℃ / min, and holds it at this temperature for 30 minutes; then, the gas alternation control module is triggered to execute the "nitriding-vacuuming-carbonization-vacuuming" cycle: First, the ammonia valve of the first gas source subsystem is opened, and ammonia gas at a flow rate of 2L / min is introduced, the chamber pressure is adjusted to 60Pa, and the temperature is held for 3 minutes to form a nitriding layer (NbN) with a thickness of about 15nm on the surface of the initial oxide layer; Second, the ammonia valve is closed, and the vacuum system is started to evacuate for 1 minute. The process involves several steps: First, reducing the chamber pressure to 5 × 10⁻³ Pa to remove residual ammonia. Second, opening the methane-argon mixed gas valve of the third gas source subsystem (methane concentration 10 vol%, flow rate 3 L / min) to adjust the chamber pressure to 60 Pa and holding it at that temperature for 3 minutes to form a carbide layer (NbC) approximately 15 nm thick on the nitrided layer surface. Third, closing the mixed gas valve and evacuating the vacuum system for 1 minute to restore high vacuum. This cycle is repeated 20 times, ultimately forming an "Al-Nb alloy layer - Nb₂O₅ oxide layer - (NbN / NbC)" on the niobium powder surface. 20 The composite structure is "stacked", with a total protective layer thickness of approximately 620 nm. S6. Cooling and Discharge: Turn off the heating tube and keep the argon gas from the first gas source subsystem flowing in (flow rate 3L / min) to allow the chamber to cool naturally to room temperature (about 25°C); open the chamber door, take out the passivated low-oxygen niobium powder, seal it and store it for testing. Performance test results: To highlight the advantages of the method of this invention, two comparative examples were set up simultaneously for comparative testing. Comparative example 1 adopted the traditional static oxygen passivation process, and comparative example 2 adopted the traditional single nitride coating passivation process. All three used the same batch of low-oxygen niobium powder (initial oxygen content 350ppm). The specific test results are as follows: Oxygen content stability: After being exposed to a constant temperature and humidity chamber at 40°C and 75% relative humidity for 120 hours, the oxygen content of the low-oxygen niobium powder in Example 1 was 495 ppm, with an increase of only 145 ppm. The oxygen content of Comparative Example 1 (static oxygenation process: vacuum furnace evacuated to 1×10⁻² Pa, then statically oxygenated to 5 Pa and held at 200°C for 1 hour) reached 680 ppm after exposure, with an increase of 330 ppm. The oxygen content of Comparative Example 2 (single nitriding process: vacuum furnace evacuated to 5×10⁻³ Pa, then heated to 380°C and held at 60 Pa for 60 minutes) reached 610 ppm after exposure, with an increase of 260 ppm. Surface protective layer status: FE-SEM observation showed that the composite protective layer of Example 1 was continuous without cracks and had a uniform thickness (approximately 620 nm); the surface oxide layer of Comparative Example 1 was locally cracked and had an uneven thickness (150-300 nm), without a complete protective layer structure; although the single nitride coating of Comparative Example 2 had a thickness of 300 nm, there was obvious peeling at the edge area, and it could not form continuous protection. Coating adhesion: The coating adhesion was tested using the cross-cut test. The composite protective layer of Example 1 achieved an adhesion level of 0 (no peeling). Comparative Example 1 did not form an effective adhesion due to the lack of a complete coating. The single nitrided coating of Comparative Example 2 had an adhesion level of only 3, with large-area peeling at the edge. Physical properties: The loose packing density of niobium powder in Example 1 was 2.15 g / cm³, and the flowability was 32 s / 50 g; in Comparative Example 1, due to the cracking of the oxide layer, the niobium powder agglomerated, and the loose packing density dropped to 1.92 g / cm³, and the flowability deteriorated to 45 s / 50 g; the loose packing density of niobium powder in Comparative Example 2 was 2.01 g / cm³, and the flowability was 38 s / 50 g, which was better than Comparative Example 1, but still not as good as Example 1. Results Analysis: Comparative Example 1, lacking pre-alloying and nano-layering steps, could not accurately control the oxidation level during static oxygenation, leading to cracking of the protective layer and excessive increase in oxygen content. Although Comparative Example 2 formed a thicker nitrided coating, the lack of an interface alloy transition layer resulted in poor adhesion between the coating and the substrate, causing it to detach during storage and failing to meet the low oxygen requirements. In contrast, Example 1, through a synergistic design of "alloy transition layer enhancing adhesion - dynamic micro-oxidation for precise oxygen control - nano-layering for enhanced barrier," ensured the integrity of the protective layer, achieved precise oxygen content control, and maintained the good physical properties of niobium powder, fully demonstrating the advanced nature of the method of this invention.

[0022] Example 2: Vacuum passivation treatment including final surface modification: Processing steps: In Example 2, based on Example 1, a final surface modification step S5.1 is added after the S5 nanolayer strengthening treatment. The remaining operating parameters are completely consistent with those in Example 1. The specific steps of S5.1 are as follows: maintain the chamber temperature at 380°C, switch the central control system to a fluorine-containing gas source (a mixture of sulfur hexafluoride SF6 and argon, with an SF6 concentration of 2 vol%), introduce the mixed gas at a flow rate of 1.5 L / min, adjust the chamber pressure to 40 Pa, and maintain the temperature for 10 minutes. During the process, SF6 reacts with NbN / NbC on the surface of the nanolayer to form a fluoride modification layer (NbF5) with a thickness of about 5 nm. After the treatment, close the fluorine-containing gas valve, start the vacuum system to evacuate for 20 minutes, restore the chamber pressure to 5 × 10⁻³ Pa, and then execute the S6 cooling and unloading steps. Performance test results: After being exposed to an environment of 40°C and 75% relative humidity for 120 hours, the oxygen content of the low-oxygen niobium powder in Example 2 was 480 ppm, an increase of only 130 ppm, which is further reduced compared to Example 1; In the corrosion resistance test, after being immersed in a 5 wt% NaCl solution for 24 hours, there were no rust marks on the surface after removal, and the weight loss rate was <0.01%, which is better than Example 1 (weight loss rate 0.03%), proving that the fluoride modification layer can further improve the surface density and corrosion resistance. Example Description In the above embodiments, the organometallic compound selected is trimethylaluminum, the reaction gas G1 is ammonia, and the reaction gas G2 is a mixture of methane. All of these are within the scope of "trimethylaluminum / tetraethylsilane / tert-butylzirconia", "nitrogen / ammonia", and "carbon-containing gas source / silicon-containing gas source" as defined in the claims. Those skilled in the art can replace them with other qualified raw materials to achieve similar protective effects. The parameters such as temperature (T1=200℃, T2=380℃), pressure (interface pre-alloying 0.8Pa, nano-stacking 60Pa), time (interface pre-alloying 8 minutes, single gas reaction 3 minutes), and number of cycles (dynamic micro-oxidation 20 times, nano-stacking 20 times) are all taken within the range defined in the claims. In practical applications, they can be adjusted according to the niobium powder particle size (e.g., 1-5μm, 10-20μm) and the processing batch (e.g., 5kg, 20kg). As long as the core requirements of "strong bonding of alloy transition layer, controllable oxide layer thickness, and uniform and continuous nano-stacking" are met, they all fall within the protection scope of this invention. The various components of the device (such as the vacuum system, gas alternation control module, and central control system) achieve precise coordination through a preset program, which can stably reproduce the method of the present invention. This solves the problems of "untimely gas switching, uneven temperature control, and low degree of automation" in existing devices, and provides reliable equipment support for industrial production.

[0023] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. 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 all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A vacuum passivation treatment method for low-oxygen niobium powder, characterized in that, Includes the following steps: S1. Pretreatment and loading: Low-oxygen niobium powder is loaded into the passivation reactor under an inert atmosphere; S2. Primary deep degassing and activation: The reactor is evacuated to a high vacuum and heated to the first temperature T1 for degassing and activation; S3. Interface pre-alloying: Metal-organic compound vapor is introduced into the reactor to form an alloy transition layer on the surface of niobium powder, and then the residual gas is removed; S4. Dynamic micro-oxidation cycle treatment: Maintain temperature T1, pulse oxygen is introduced into the reactor and then quickly vacuumed. This operation is repeated multiple times. S5. Nanolayer reinforcement treatment: Adjust the reactor temperature to the second temperature T2, and introduce at least two different reaction gases in an alternating cycle to form a nanolayer reinforcement structure by alternating deposition on the surface of niobium powder. S6. Cooling and Discharge: After processing, cool and remove the passivated niobium powder under a protective atmosphere.

2. The vacuum passivation treatment method for low-oxygen niobium powder according to claim 1, characterized in that, In step S3, the organometallic compound is selected from trimethylaluminum, tetraethylsilane, or tert-butylzirconia; the treatment pressure is 0.1-2 Pa, and the treatment time is 2-15 minutes.

3. The vacuum passivation treatment method for low-oxygen niobium powder according to claim 1, characterized in that, In step S5, the alternating cycle includes: sequentially introducing the first reaction gas G1 while maintaining the first condition, drawing a vacuum, introducing the second reaction gas G2 while maintaining the second condition, and drawing a vacuum again, thus forming a complete cycle; wherein the pressure in the first condition and the second condition are each independently 30-100 Pa, and the processing time is each independently 1-5 minutes; the cycle is repeated 5-30 times.

4. The vacuum passivation treatment method for low-oxygen niobium powder according to claim 3, characterized in that, The first reactive gas G1 is nitrogen or ammonia.

5. The vacuum passivation treatment method for low-oxygen niobium powder according to claim 3, characterized in that, The second type of reactant gas G2 is a carbon-containing gas source or a silicon-containing gas source; the carbon-containing gas source is a mixture of methane, acetylene, or ethylene with an inert gas; the silicon-containing gas source is a mixture of silane and an inert gas.

6. A vacuum passivation treatment method for low-oxygen niobium powder according to any one of claims 1-5, characterized in that, After step S5, the process also includes step S5.1 final surface modification: at 100-200°C, a fluorine-containing gas is introduced into the reactor for surface treatment.

7. A vacuum passivation treatment method for low-oxygen niobium powder according to any one of claims 1-5, characterized in that, The first temperature T1 is 150-250℃, and the second temperature T2 is 300-450℃.

8. A low-oxygen niobium powder prepared by the method according to any one of claims 1-7, characterized in that, The niobium powder has an alloy transition layer, an initial oxide layer, and a nano-layered reinforcement layer distributed sequentially from the substrate outwards; and after being exposed to an environment of 40°C and 75% relative humidity for 120 hours, the oxygen content of the niobium powder increases by less than 200 ppm.

9. A vacuum passivation treatment apparatus for producing low-oxygen niobium powder according to any one of claims 1-7, characterized in that, include: The vacuum reaction chamber contains a material tray for holding niobium powder and a heating device. A vacuum system, connected to the vacuum reaction chamber, is used to establish and maintain the required vacuum environment; A gas supply system is connected to the vacuum reaction chamber; And the central control system; The gas supply system includes at least: The first gas source subsystem is used to provide inert gas, oxygen, and nitriding reaction gas; The second gas source subsystem is used to provide organometallic compound vapors; The third gas source subsystem is used to provide carbonization or siliconization reaction gases; The central control system is configured to automatically control the vacuum system, heating device, and each gas source subsystem according to a preset program, and perform the following operations in sequence: evacuate the chamber to a high vacuum and perform heating and degassing; introduce metal-organic compound vapor from the second gas source subsystem for interface pre-alloying treatment; pulsely introduce oxygen from the first gas source subsystem and rapidly evacuate it for dynamic micro-oxidation cycle treatment; alternately introduce reactive gases from the first gas source subsystem and the third gas source subsystem for nano-layering strengthening treatment.

10. A vacuum passivation treatment apparatus for low-oxygen niobium powder according to claim 9, characterized in that, The gas supply system also includes a gas alternation control module, which is connected to the first gas source subsystem and the third gas source subsystem. The gas alternation control module includes a high-speed switching valve group and a timing controller. The timing controller is configured to: control the high-speed switching valve group to periodically and alternately introduce the nitriding reaction gas from the first gas source subsystem and the carbide or siliconization reaction gas from the third gas source subsystem into the vacuum reaction chamber, and trigger the vacuum system to briefly pump out gas between each gas introduction cycle to remove residual gas.

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