Copper-chromium-niobium powder preparation method based on FFC electrolysis process

Abstract

The invention relates to the technical field of copper-chromium-niobium powder, in particular to a copper-chromium-niobium powder preparation method based on an FFC electrolysis process, which comprises the following steps: S1, preparing a composite oxide; s2, constructing an electrolysis system; s3, melting and electrolyzing; s4, carrying out post-treatment; the method provided by the invention has the advantages of easily available raw materials, simple process steps, low equipment investment cost, short flow, environmental protection and easily controllable alloy components, and can realize batch preparation of the copper-chromium-niobium powder through large-scale production. The oxygen content of the prepared powder is lower than 0.3%, the particle size distribution is uniform, the powder can be directly used in the fields of powder metallurgy sintering, thermal spraying, laser energy deposition (DED), hot isostatic pressing and the like, a high-quality alloy raw material is provided for the high-end fields of aerospace, electronic packaging and the like, and remarkable economic and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of copper-chromium-niobium powder preparation technology, specifically to a method for preparing copper-chromium-niobium powder based on FFC electrolysis process. Background Technology

[0002] Copper-chromium-niobium alloys possess irreplaceable application value in fields such as high-temperature structural components for aerospace engines, electronic packaging materials, and heat-resistant components for the nuclear industry due to their high strength, high hardness, good high-temperature stability, and excellent electrical and thermal conductivity. The performance of copper-chromium-niobium alloys is closely related to the purity, particle size distribution, and compositional uniformity of their powder raw materials; therefore, preparing high-quality copper-chromium-niobium powder is crucial to ensuring the alloy's performance.

[0003] Currently, the main methods for preparing copper-chromium-niobium powder include mechanical alloying, vacuum arc melting-atomization, and reduction-diffusion. Mechanical alloying uses high-energy ball milling to induce plastic deformation, cold welding, and crushing of metal powder, achieving element mixing and alloying. However, this method suffers from problems such as long milling time, easy introduction of impurities, and easy powder oxidation. Furthermore, it is difficult to achieve complete alloying for high-melting-point elements like chromium and niobium. Vacuum arc melting-atomization requires first melting the metal raw material into alloy ingots, then crushing them through atomization to obtain powder. This process is complex, energy-intensive, and prone to component segregation during atomization, resulting in poor powder uniformity. Reduction-diffusion uses metal oxides as raw materials, employing reducing agents (such as aluminum and magnesium) for reduction while simultaneously utilizing element diffusion to achieve alloying. However, this method requires strict control of reduction temperature and time, and residual reducing agents can easily cause powder contamination, making subsequent impurity removal processes cumbersome.

[0004] FFC electrolysis, as a short-process, green molten salt electrochemical reduction technology, can directly prepare metals or alloys from metal oxides in one step without the need for intermediate products such as chlorides. It boasts advantages such as a short process, low pollution, and easy composition control, and has been successfully applied to the preparation of single refractory metals such as titanium, zirconium, and niobium, as well as some binary alloys. However, applying FFC electrolysis to the preparation of copper-chromium-niobium ternary alloy powders faces several technical challenges: First, the decomposition voltages of the three oxides (CuO, Cr2O3, and Nb2O5) differ significantly, easily leading to inconsistent reduction sequences under conventional electrolysis parameters, resulting in alloy composition segregation. Second, Nb2O5 is a high-melting-point oxide with a slow oxygen diffusion rate in molten salt, making complete deoxidation difficult and resulting in high oxygen content in the powder. Third, the graphite anode is prone to burn-out during electrolysis, generating carbon impurities, and the corrosion of equipment by the molten salt at high temperatures is a significant problem, affecting powder purity and production stability. Summary of the Invention

[0005] To address the above problems, this invention provides a method for preparing copper-chromium-niobium powder based on FFC electrolysis, comprising the following steps: S1. Preparation of composite oxides CuO powder, Cr2O3 powder, and Nb2O5 powder were weighed out according to a mass fraction of 20-40% Cu, 30-50% Cr, and the balance Nb. They were then ball-milled for 4-8 hours at a ball-to-material ratio of 5-10:1 and a rotation speed of 200-300 r / min. Anhydrous ethanol was added at a rate of 1-3 mL / min during the ball milling process. The mixture was then pressed, shaped, and sintered to obtain the copper-chromium-niobium composite oxide. S2, Setting up the electrolysis system The copper-chromium-niobium composite oxide was used as the cathode of the electrolytic cell, graphite as the anode, and CaCl2-NaCl mixed molten salt as the electrolyte. These components were placed sequentially in a graphite crucible, and a vacuum of 1×10⁻⁶ was applied. -2 ~5×10 -2 Argon / nitrogen gas is then introduced for protection after Pa. S3, Molten Electrolysis The temperature in the electrolytic system is raised to 700-750℃ and held for 1-1.5 hours. Then, the temperature is raised to 850-1050℃, and a DC voltage of 2.6-3.0V is applied with a current density of 80-180 mA / cm². 2 After constant voltage electrolysis for 10-16 hours, intermediate products are generated in the cathode region of the electrolytic cell, which are loose and porous metal sponges. S4, Post-processing The metal sponge was naturally cooled to 22-30℃, then ultrasonically crushed and ground to 10-100μm, washed 3-5 times with deionized water until the pH of the cleaning solution was 6.5-7.5, and finally vacuum dried to obtain the copper-chromium-niobium powder.

[0006] Furthermore, in S1, the purity of the CuO powder, Cr2O3 powder, and Nb2O5 powder is ≥99.5%, and the particle size is 50~200μm. Note: The above limitations can ensure the quality of raw materials and reduce the introduction of impurities.

[0007] Furthermore, in S1, the pressing and molding process involves holding the pressure at 20-50 MPa for 3-5 minutes. Note: The theoretical density of the green body obtained by the above pressing and molding parameters is 50~65%. The above pressing parameters can ensure the porosity and strength of the green body and facilitate oxygen ion migration.

[0008] Further, in S1, the sintering is carried out under argon / nitrogen protection, with the temperature increased to 700-900°C at a rate of 5-10°C / min, and held for 2-4 hours. Note: The above sintering method can further enhance the strength of the green body and prevent oxidation and component segregation.

[0009] Furthermore, a SiO2-B2O3-Na2CO3 gradient protective layer is coated on the surface of the graphite anode; The coating method is as follows: a. Graphite Anode Pretreatment The surface of the graphite anode was polished with 600-grit sandpaper to a roughness of Ra=3~5μm. It was then ultrasonically cleaned with anhydrous ethanol for 10~15min under ultrasonic power of 25~30W / L and ultrasonic frequency of 35~45kHz. Finally, it was vacuum dried for 30~60min under vacuum degree ≤100Pa and temperature of 80~100℃ to obtain the pretreated graphite anode. b. Preparation of SiO2-B2O3-Na2CO3 raw materials b-1. SiO2, B2O3, Na2CO3, and stabilizer are mixed in a mass ratio of 60~70:5~10:1~2:20~30, then vacuum dried at 110~120℃ for 12~24h, and ground to 100~200 mesh to obtain a mixed powder. The powder is then placed in a crucible and melted at 1400~1450℃ under argon protection for 15~20min. Finally, the melted product is cooled to room temperature and crushed to obtain -180~+300 mesh A-grade filler and -300 mesh B-grade filler. The A-grade filler and B-grade filler are mixed in a mass ratio of 6~7:3~4 to obtain the transition layer raw material. b-2. Mix SiO2, B2O3, Na2CO3 and stabilizer in a mass ratio of 30~40:15~20:3~4:20~30, and melt them for 10~15 minutes under argon protection and at a temperature of 1250~1300℃. The remaining steps are the same as b-1 to obtain the intermediate layer raw material. b-3. Mix SiO2, B2O3, Na2CO3 and stabilizer in a mass ratio of 40~50:10~15:8~12:25~35, and melt them for 15~20 minutes under argon protection and at a temperature of 1350~1400℃. The remaining steps are the same as b-1 to obtain the sealing layer raw material. c. Coating with SiO2-B2O3-Na2CO3 raw materials The transition layer material, intermediate layer material, and sealing layer material are mixed with silicone resin at a mass ratio of 3-4:1, and ethanol is added to adjust the viscosity to 800-1000 mPa·s. The tip of the graphite anode is wrapped and protected with a mask. Then, 5-8 μm transition layer material, 15-20 μm intermediate layer material, and 5-8 μm sealing layer material are sequentially coated on the surface of the graphite anode at a speed of 1000-3000 rpm. The coating time for each layer is 30-60 s. After coating, the material is dried at room temperature for 10-15 min. Finally, the coated graphite anode was pre-baked at 300~400℃ for 0.5~1h, and then heated to 800~900℃ in a vacuum environment at 5~10℃ / min, held for 1~2h, and naturally cooled to 25~30℃. The mask was then removed to obtain the SiO2-B2O3-Na2CO3 gradient protective layer. Explanation: The SiO2-B2O3-Na2CO3 coating forms a dense borosilicate glass phase at high temperatures, effectively isolating oxygen from contact with the graphite anode. The high SiO2 content in the transition layer makes its thermal expansion coefficient closer to that of the graphite anode, effectively relieving thermal stress during heating and preventing coating cracking and peeling. SiO2 undergoes a weak reaction with the graphite surface at high temperatures to form a SiC transition layer, significantly improving the bonding strength between the coating and the substrate and providing skeletal support. The high B2O3 content in the intermediate layer exhibits fluidity at 600~1100℃, which can heal microcracks in the coating, achieving self-healing. Furthermore, B2O3 has good wettability with molten salt, reducing the erosion of the coating by the molten salt. The high Na2CO3 content in the sealing layer decomposes at high temperatures to generate Na2O, forming a low-melting-point glass with SiO2 and B2O3. The protective layer further improves the density and fluidity of the coating. Na2CO3 in the coating can decompose into Na2O in the molten salt, forming a low-melting-point glass phase (melting point about 800℃) with SiO2 and B2O3, forming a dense sealing layer on the coating surface, effectively isolating oxygen. It can also react with CaCl2 in the molten salt to generate CaO, which helps stabilize the molten salt system and reduce the volatilization and decomposition of the molten salt. Furthermore, the sealing layer can significantly reduce the oxidation loss rate of the graphite anode. Carbon particles generated by the burning of the graphite anode will contaminate the molten salt and cathode products, leading to an increase in the carbon content in the copper-chromium-niobium alloy powder. The protective layer can effectively inhibit anode burning, reduce the carbon residue in the products, and significantly improve the purity of the alloy powder.

[0010] The difference in thermal expansion between the substrate and the coating can easily lead to cracks in the coating. Gradient coatings ensure a continuous distribution of the concentrations of the two phases in the coating and the substrate, eliminating interfacial stress and thus achieving the purpose of anti-oxidation and electrolyte balance. This gradient structure can effectively alleviate thermal stress and improve the coating's thermal shock resistance.

[0011] Further, in step a, a mesh groove with a depth of 1.5~2mm and a spacing of 3~5mm is machined on the surface of the pretreated graphite anode; An ethanol-water solution was prepared by mixing anhydrous ethanol and deionized water at a volume ratio of 8-9:1. Then, KH-550 was added dropwise to the ethanol-water solution at a rate of 0.5-2 mL / s under a stirring speed of 1500-2000 rpm. The amount of KH-550 added was 1-3 wt% of the ethanol-water solution. After the addition was completed, stirring was continued for 20-30 min. The solution was then allowed to stand and mature at 25-30℃ for 30-60 min to obtain a composite solution. Finally, the graphite anode with mesh grooves is immersed in the composite solution and ultrasonically treated for 10-15 minutes at an ultrasonic power of 25-30 W / L. After removal, it is dried at 80-100℃ for 20-30 minutes. Explanation: The mesh grooves provide a three-dimensional mechanical interlocking structure, enabling the coating and graphite substrate to form a mechanical interlock, which improves the bonding strength between the coating and the substrate. The surface energy of the grooves after treatment with silane coupling agent is increased, and the SiO2-B2O3-Na2CO3 slurry can penetrate into the grooves more easily, forming a continuous coating structure and reducing interface defects. The groove structure can effectively release thermal stress, and the silane coupling agent layer provides a flexible transition, which together alleviates the difference in thermal expansion coefficients between the coating and the substrate and avoids coating cracking.

[0012] Furthermore, the stabilizer is Al2O3; Note: Al2O3 has higher thermal stability and better chemical inertness, and is more compatible with the SiO2-B2O3-Na2CO3 system, which can form a denser and more stable protective layer.

[0013] The silicone resin is methylphenyl silicone resin, and the model is selected from SILIKOPHEN® P 50 / X.

[0014] Furthermore, the preparation method of the CaCl2-NaCl mixed molten salt is as follows: 1) Raw material pretreatment CaCl2 and NaCl are vacuum dried at 62~67℃ for 4~6h, ground to 1~2mm, and then mixed at a mass ratio of CaCl2 to NaCl of 60~80:20~40 to obtain a mixed raw material. KCl is added at a mass ratio of 1~3wt% of the mixed raw material to obtain a mixed salt. 2) Melting treatment The mixed salt is heated to 250-300℃ in a graphite crucible at a rate of 3-5℃ / min and held for 10-12 hours. Then, it is heated to 850-900℃ and held for 18-24 hours to obtain molten salt. Two graphite electrodes are inserted into the molten salt as the anode and cathode, respectively. A voltage of 1.5-2.0V is applied for pre-electrolysis for 2-4 hours. After the pre-electrolysis is completed, the graphite electrodes are removed, and the mixture is naturally cooled to 22-30℃ to obtain the purified mixed molten salt for later use. Note: The CaCl2-NaCl mixed molten salt obtained by the above method can effectively lower the melting point of the molten salt, improve conductivity, and remove moisture to avoid interference. Adding KCl reduces the viscosity of the molten salt and enhances its fluidity, which is beneficial for the diffusion and migration of oxygen ions in the molten salt and accelerates the deoxidation reaction of the cathode oxide. The pre-electrolysis process can remove impurities such as moisture and metal oxides from the molten salt, improving its purity. Under a voltage of 1.5~2.0V, the metal impurity ions in the molten salt (such as Fe)... 2+ Cu2+ (etc.) will be reduced and precipitated at the cathode, while the chlorine gas generated at the anode will oxidize the organic impurities in the molten salt. The molten salt after pre-electrolysis has higher conductivity and lower impurity content, which is conducive to the stable operation of the subsequent FFC electrolysis process, and improves current efficiency and product purity. The optimized molten salt system, combined with the graphite anode protective layer, can significantly reduce the anode burn-off rate, reduce the migration of carbon impurities to the molten salt and cathode products, and improve the purity of alloy powder.

[0015] Furthermore, the ultrasonic fragmentation method is as follows: processing for 10 to 30 minutes under ultrasonic power of 500~800W and ultrasonic frequency of 20~40kHz. Note: Ultrasonic power of 500~800W can generate sufficient cavitation effect, causing the metal sponge to vibrate and impact violently in the liquid medium, effectively breaking up large particle agglomerates, while avoiding excessive power that would result in overly fine powder or localized overheating; medium-frequency ultrasound of 20~40kHz achieves the best balance between breaking efficiency and energy utilization. Too low a frequency (<20kHz) results in poor breaking effect, while too high a frequency (>40kHz) leads to rapid energy attenuation and reduced breaking efficiency.

[0016] Furthermore, in S4, the vacuum drying is carried out at a temperature of 80~120℃ and a pressure of 1×10⁻⁶. -1 ~5×10 -1 Drying treatment under Pa conditions for 6-10 hours; Note: Vacuum drying under the above conditions can prevent powder oxidation and the introduction of impurities.

[0017] Compared with existing technologies, the beneficial effects of this invention are: (1) The raw materials used in the method of the present invention are readily available, the process steps are simple, the equipment investment cost is low, the process is short, it is green and environmentally friendly, and the alloy composition is easy to control. It can realize the batch preparation of copper-chromium-niobium powder through large-scale production. The prepared powder has an oxygen content of less than 0.3% and a uniform particle size distribution. It can be directly used in powder metallurgy sintering, thermal spraying, laser energy deposition (DED), hot isostatic pressing and other fields, providing high-quality alloy raw materials for high-end fields such as aerospace and electronic packaging, with significant economic and social benefits.

[0018] (2) This invention utilizes a SiO2-B2O3-Na2CO3 gradient protective layer coated on the graphite anode surface. The high SiO2 content transition layer alleviates thermal stress during the heating process, preventing coating cracking and peeling. SiO2 reacts weakly with the graphite surface at high temperatures to form a SiC transition layer. The thermal expansion coefficient of silicon carbide is between that of graphite and the high SiO2 content transition layer, creating a gradient in thermal expansion coefficients. This effectively alleviates thermal stress and prevents the coating from cracking or peeling during heating, thereby strengthening the bonding strength and improving the coating's service life. Then, the high B2O3 content of the intermediate layer is utilized... The high Na2CO3 content in the sealing layer helps to close microcracks in the coating under high temperature conditions, achieving self-healing. Furthermore, the good wettability of B2O3 with molten salt further reduces the erosion of the coating by molten salt. Finally, the high Na2CO3 content in the sealing layer decomposes at high temperature to generate Na2O, which forms a low-melting-point glass phase with SiO2 and B2O3, further improving the density and fluidity of the coating. The transition layer provides strong adhesion, the intermediate layer provides self-healing ability, and the sealing layer provides antioxidant protection. The synergistic effect of these three layers significantly improves the service life of the graphite anode, reduces energy consumption, and improves the purity and quality of the copper-chromium-niobium alloy powder.

[0019] (3) This invention utilizes a mesh groove to process the pretreated graphite anode surface and performs surface modification treatment. The mesh groove provides a three-dimensional mechanical interlocking structure, which enables the coating to form a mechanical interlock with the graphite substrate, thereby improving the bonding strength between the coating and the substrate. The surface energy of the groove after silane coupling agent treatment is improved, and the SiO2-B2O3-Na2CO3 raw materials can more easily penetrate into the groove to form a continuous coating structure, reducing interface defects. Furthermore, the groove structure can effectively release thermal stress, and the silane coupling agent layer provides a flexible transition, which together alleviates the difference in thermal expansion coefficients between the coating and the substrate, preventing coating cracking. At the same time, adding a trace amount of KCl to the CaCl2-NaCl mixed molten salt reduces the viscosity of the molten salt and enhances its fluidity, which is conducive to the diffusion and migration of oxygen ions in the molten salt and accelerates the deoxidation reaction of the cathode oxide. The optimized molten salt system, combined with the graphite anode protective layer, can significantly reduce the anode burn-off rate, reduce the migration of carbon impurities to the molten salt and cathode products, and improve the purity of the alloy powder. Attached Figure Description

[0020] Figure 1 This is a comparison chart of the properties of copper-chromium-niobium powders obtained in Examples 1, 6-9 and Comparative Examples 4-5 of the present invention; Figure 2 This is a comparison chart of the properties of copper-chromium-niobium powders obtained in Examples 1, 14-26 and Comparative Examples 6-8 of the present invention; Figure 3 This is a comparison chart of the properties of copper-chromium-niobium powders obtained in Examples 1, 14, and 27-33 of this invention. Detailed Implementation

[0021] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0022] Example 1: A method for preparing copper-chromium-niobium powder based on FFC electrolysis process, comprising the following steps: S1. Preparation of composite oxides CuO powder, Cr2O3 powder, and Nb2O5 powder were weighed according to a mass fraction of 30% Cu, 40% Cr, and the balance Nb. They were then ball-milled for 6 hours at a ball-to-powder ratio of 8:1 and a rotation speed of 250 r / min. During the ball milling process, anhydrous ethanol was added at a rate of 2 mL / min. The mixture was held at a pressure of 35 MPa for 4 minutes, and then heated to 800 °C at a rate of 8 °C / min under argon protection and held for 3 hours to obtain copper-chromium-niobium composite oxide. The purity of CuO powder, Cr2O3 powder, and Nb2O5 powder was 99.5%, and the particle size was 50~200 μm. S2, Setting up the electrolysis system A copper-chromium-niobium composite oxide was used as the cathode of the electrolytic cell, graphite as the anode, and a CaCl2-NaCl mixed molten salt as the electrolyte. These components were placed sequentially in a graphite crucible, and a vacuum of 3 × 10⁻⁶ ppm was applied. -2 Argon / nitrogen gas is then introduced for protection after Pa. The preparation method of CaCl2-NaCl mixed molten salt is as follows: 1) Raw material pretreatment CaCl2 and NaCl were vacuum dried at 65℃ for 5 hours and ground to 1~2 mm. Then, they were mixed at a mass ratio of CaCl2 to NaCl of 70:30 to obtain a mixed raw material. KCl was added at 2 wt% of the mixed raw material to obtain a mixed salt. 2) Melting treatment The mixed salt was heated to 275°C at 4°C / min in a graphite crucible and held for 12 hours. Then, it was heated to 875°C and held for 21 hours to obtain molten salt. Two graphite electrodes were inserted into the molten salt as anode and cathode, respectively. A voltage of 1.8V was applied for pre-electrolysis for 3 hours. Finally, it was naturally cooled to 26°C to obtain purified mixed molten salt for later use. S3, Molten Electrolysis The temperature in the electrolytic system was raised to 725℃ and held for 1.3 hours, then raised to 950℃, and a DC voltage of 2.8V was applied with a current density of 120mA / cm². 2 After electrolysis at constant voltage for 12 hours, an intermediate product is generated in the cathode region of the electrolytic cell, which is a loose and porous metal sponge. S4, Post-processing The metal sponge was naturally cooled to 26℃, then subjected to ultrasonic treatment at 700W power and 30kHz frequency for 20 minutes. It was then ground to 10-100μm, washed with deionized water until the cleaning solution pH reached 7.0, and finally subjected to treatment at 100℃ and 3×10⁻⁶ pressure. -1 Drying at Pa for 8 hours yielded an oxygen content of 0.22%, a particle size of 20-80 μm, and a bulk density of 3.0 g / cm³. 3 Copper-chromium-niobium powder.

[0023] Example 2: Unlike Example 1, CuO powder, Cr2O3 powder, and Nb2O5 powder were weighed out according to a mass fraction of 20% Cu, 30% Cr, and the balance Nb. The resulting copper-chromium-niobium powder had an oxygen content of 0.28%, a particle size of 30-100 μm, and a loose packing density of 2.5 g / cm³. 3 .

[0024] Example 3: Unlike Example 1, CuO powder, Cr2O3 powder, and Nb2O5 powder were weighed out according to a mass fraction of 40% Cu, 50% Cr, and the balance Nb; the resulting copper-chromium-niobium powder had an oxygen content of 0.25%, a particle size of 10~60μm, and a loose packing density of 3.5g / cm³. 3 .

[0025] Example 4: Unlike Example 1, the mixture was ball-milled for 4 hours at a ball-to-material ratio of 5:1 and a rotation speed of 200 r / min. Anhydrous ethanol was added at a rate of 1 mL / min during the ball-milling process. The mixture was held at a pressure of 20 MPa for 3 minutes. Then, under nitrogen protection, the temperature was increased to 700°C at a rate of 5°C / min and held for 2 hours to obtain copper-chromium-niobium composite oxide.

[0026] Example 5: Unlike Example 1, the mixture was ball-milled for 8 hours at a ball-to-material ratio of 10:1 and a rotation speed of 300 r / min. Anhydrous ethanol was added at a rate of 3 mL / min during the ball-milling process. The mixture was held at a pressure of 50 MPa for 5 minutes. Then, under argon protection, the temperature was increased to 900°C at a rate of 10°C / min and held for 4 hours to obtain copper-chromium-niobium composite oxide.

[0027] Example 6: Unlike Example 1, in the preparation method of CaCl2-NaCl mixed molten salt, CaCl2 and NaCl are vacuum dried at 62°C for 4 hours, ground to 1~2 mm, and then mixed at a mass ratio of CaCl2 to NaCl of 60:40 to obtain mixed raw materials. KCl is added at 1 wt% of the mixed raw materials to obtain mixed salt.

[0028] Example 7: Unlike Example 1, in the preparation method of CaCl2-NaCl mixed molten salt, CaCl2 and NaCl are vacuum dried at 67°C for 6 hours, ground to 1~2 mm, and then mixed at a mass ratio of CaCl2 to NaCl of 80:20 to obtain mixed raw materials. KCl is added at 3 wt% of the mixed raw materials to obtain mixed salt.

[0029] Example 8: Unlike Example 1, in the preparation method of CaCl2-NaCl mixed molten salt, the mixed salt is heated to 250°C at 3°C / min in a graphite crucible, held at that temperature for 10h, and then heated to 850°C and held at that temperature for 18h to obtain molten salt; two graphite electrodes are inserted into the molten salt as anode and cathode respectively, and a voltage of 1.5V is applied for pre-electrolysis for 2h to obtain purified mixed molten salt, which is finally naturally cooled to 22°C for later use.

[0030] Example 9: Unlike Example 1, in the preparation method of CaCl2-NaCl mixed molten salt, the mixed salt is heated to 300℃ at 5℃ / min in a graphite crucible, held at that temperature for 12h, and then heated to 900℃ and held at that temperature for 24h to obtain molten salt; two graphite electrodes are inserted into the molten salt as anode and cathode respectively, and a voltage of 2.0V is applied for pre-electrolysis for 4h to obtain purified mixed molten salt, which is finally naturally cooled to 30℃ for later use.

[0031] Example 10: Unlike Example 1, in S3, the temperature of the electrolytic system was raised to 700°C and held for 1 hour, then raised to 850°C, and a DC voltage of 2.6V was applied with a current density of 80mA / cm². 2 After 16 hours of constant voltage electrolysis, an intermediate product is generated in the cathode region of the electrolytic cell, which is a loose and porous metal sponge.

[0032] Example 11: Unlike Example 1, in S3, the temperature of the electrolytic system was raised to 750°C and held for 1.5 hours, then raised to 1050°C, and a DC voltage of 3.0V was applied with a current density of 180mA / cm². 2 After electrolysis at constant voltage for 10 hours, an intermediate product is generated in the cathode region of the electrolytic cell, which is a loose and porous metal sponge.

[0033] Example 12: Unlike Example 1, in S4, the metal sponge was naturally cooled to 22°C, then crushed for 10 minutes under ultrasonic power of 500W and ultrasonic frequency of 20kHz, then ground to 10~100μm, washed with deionized water until the cleaning solution pH=6.5, and finally heated at 80°C and pressure of 1×10⁻⁶. -1 Drying treatment at Pa for 6 hours.

[0034] Example 13: Unlike Example 1, in S4, the metal sponge was naturally cooled to 30°C, then subjected to ultrasonic treatment at 800W power and 40kHz frequency for 30 minutes, followed by grinding to 10~100μm, washing with deionized water until the cleaning solution pH=7.5, and finally subjected to treatment at 120°C and 5×10⁻⁶ pressure. -1 Drying treatment at Pa for 10 hours.

[0035] Example 14: Unlike Example 1, a SiO2-B2O3-Na2CO3 gradient protective layer is coated on the surface of the graphite anode; The coating method is as follows: a. Graphite Anode Pretreatment The surface of the graphite anode was polished with 600-grit sandpaper to a roughness of Ra=4μm. It was then ultrasonically cleaned with anhydrous ethanol for 13 min at an ultrasonic power of 28W / L and an ultrasonic frequency of 40kHz. Finally, it was vacuum dried for 45 min at a vacuum degree of 100Pa and a temperature of 90℃ to obtain the pretreated graphite anode. b. Preparation of SiO2-B2O3-Na2CO3 raw materials b-1. SiO2, B2O3, Na2CO3, and Al2O3 are mixed in a mass ratio of 65:8:1:25, then vacuum dried at 115℃ for 18 hours, and ground to 100~200 mesh to obtain a mixed powder. The powder is then placed in a crucible and melted at 1425℃ under argon protection for 18 minutes. Finally, the molten product is cooled to room temperature and crushed to obtain A-grade filler of -180~+300 mesh and B-grade filler of -300 mesh. The A-grade filler and B-grade filler are mixed in a mass ratio of 6:4 to obtain the transition layer raw material. b-2. Mix SiO2, B2O3, Na2CO3 and Al2O3 in a mass ratio of 35:18:3:25 and melt them for 13 minutes under argon protection and at a temperature of 1275℃. The remaining steps are the same as in b-1 to obtain the intermediate layer raw material. b-3. Mix SiO2, B2O3, Na2CO3 and Al2O3 in a mass ratio of 45:13:10:30 and melt them for 18 minutes under argon protection and at a temperature of 1375℃. The remaining steps are the same as b-1 to obtain the sealing layer raw material. c. Coating with SiO2-B2O3-Na2CO3 raw materials The transition layer material, intermediate layer material, and sealing layer material were mixed with silicone resin at a mass ratio of 3.5:1, and ethanol was added to adjust the viscosity to 900 mPa·s. The graphite anode tip was wrapped and protected with a mask. Then, 7 μm of transition layer material, 17 μm of intermediate layer material, and 7 μm of sealing layer material were sequentially coated on the graphite anode surface at a speed of 2000 rpm. The coating time for each layer was 45 s. After coating, the material was dried at room temperature for 13 min. Finally, the coated graphite anode was pre-baked at 350℃ for 0.8h, and then heated to 850℃ at 8℃ / min in a vacuum environment, held for 1.5h, and naturally cooled to 28℃. The mask was then removed to obtain the SiO2-B2O3-Na2CO3 gradient protective layer.

[0036] Example 15: Unlike Example 14, the graphite anode was ultrasonically cleaned for 10 min with anhydrous ethanol at an ultrasonic power of 25 W / L and an ultrasonic frequency of 35 kHz, and then vacuum dried for 30 min at a vacuum degree of 100 Pa and a temperature of 80 °C to obtain the pretreated graphite anode.

[0037] Example 16: Unlike Example 14, the graphite anode was ultrasonically cleaned for 15 min with anhydrous ethanol at an ultrasonic power of 30 W / L and an ultrasonic frequency of 45 kHz, and then vacuum dried for 60 min at a vacuum degree of 100 Pa and a temperature of 100 °C to obtain the pretreated graphite anode.

[0038] Example 17: Unlike Example 14, in b-1, SiO2, B2O3, Na2CO3, and Al2O3 were mixed in a mass ratio of 60:5:1:20, then vacuum dried at 11°C for 12 hours, and ground to 100-200 mesh to obtain a mixed powder. The powder was then placed in a crucible and melted for 15 minutes under argon protection at 1400°C. Finally, the molten product was cooled to room temperature and crushed to obtain -180~+300 mesh A-grade filler and -300 mesh B-grade filler. The A-grade filler and B-grade filler were mixed in a mass ratio of 6:4 to obtain the transition layer raw material.

[0039] Example 18: Unlike Example 14, in b-1, SiO2, B2O3, Na2CO3, and Al2O3 were mixed in a mass ratio of 70:10:2:30, then vacuum dried at 120°C for 24 hours, and ground to 100~200 mesh to obtain a mixed powder. The powder was then placed in a crucible and melted for 20 minutes under argon protection at a temperature of 1450°C. Finally, the molten product was cooled to room temperature and crushed to obtain A-grade filler of -180~+300 mesh and B-grade filler of -300 mesh. The A-grade filler and B-grade filler were mixed in a mass ratio of 7:3 to obtain the transition layer raw material.

[0040] Example 19: Unlike Example 14, in b-2, SiO2, B2O3, Na2CO3, and Al2O3 were mixed in a mass ratio of 30:15:3:20, then vacuum dried at 110°C for 12 hours, and ground to 100-200 mesh to obtain a mixed powder. The powder was then placed in a crucible and melted for 10 minutes under argon protection at 1250°C. Finally, the molten product was cooled to room temperature and crushed to obtain -180~+300 mesh A-grade filler and -300 mesh B-grade filler. The A-grade filler and B-grade filler were mixed in a mass ratio of 6:4 to obtain the intermediate layer raw material.

[0041] Example 20: Unlike Example 14, in b-2, SiO2, B2O3, Na2CO3, and Al2O3 were mixed in a mass ratio of 40:20:4:30, then vacuum dried at 120°C for 24 hours, and ground to 100~200 mesh to obtain a mixed powder. The powder was then placed in a crucible and melted for 15 minutes under argon protection at a temperature of 1300°C. Finally, the molten product was cooled to room temperature and crushed to obtain A-grade filler of -180~+300 mesh and B-grade filler of -300 mesh. The A-grade filler and B-grade filler were mixed in a mass ratio of 7:3 to obtain the intermediate layer raw material.

[0042] Example 21: Unlike Example 14, in b-3, SiO2, B2O3, Na2CO3, and Al2O3 were mixed in a mass ratio of 40:10:8:25, then vacuum dried at 110°C for 12 hours, and ground to 100~200 mesh to obtain a mixed powder. The powder was then placed in a crucible and melted for 15 minutes under argon protection at a temperature of 1350°C. Finally, the molten product was cooled to room temperature and crushed to obtain A-grade filler of -180~+300 mesh and B-grade filler of -300 mesh. The A-grade filler and B-grade filler were mixed in a mass ratio of 6:4 to obtain the sealing layer raw material.

[0043] Example 22: Unlike Example 14, in b-3, SiO2, B2O3, Na2CO3, and Al2O3 were mixed in a mass ratio of 50:15:12:35, then vacuum dried at 120°C for 24 hours, and ground to 100~200 mesh to obtain a mixed powder. The powder was then placed in a crucible and melted for 20 minutes under argon protection at a temperature of 1400°C. Finally, the molten product was cooled to room temperature and crushed to obtain -180~+300 mesh Grade A filler and -300 mesh Grade B filler. The Grade A filler and Grade B filler were mixed in a mass ratio of 7:3 to obtain the sealing layer raw material.

[0044] Example 23: Unlike Example 14, in c, the transition layer material, intermediate layer material, and sealing layer material are mixed with silicone resin at a mass ratio of 3:1, and ethanol is added to adjust the viscosity to 800 mPa·s. The graphite anode tip is wrapped and protected using a mask. Then, 5 μm of transition layer material, 15 μm of intermediate layer material, and 5 μm of sealing layer material are sequentially coated on the graphite anode surface at a speed of 1000 rpm. Each coating time is 30 s. After coating, the material is dried at room temperature for 10 min.

[0045] Example 24: Unlike Example 14, in c, the transition layer material, intermediate layer material, and sealing layer material were mixed with silicone resin at a mass ratio of 4:1, and ethanol was added to adjust the viscosity to 1000 mPa·s. The graphite anode tip was protected by a mask, and then 8 μm of transition layer material, 20 μm of intermediate layer material, and 8 μm of sealing layer material were sequentially coated on the graphite anode surface at a speed of 3000 rpm. Each coating time was 60 s, and the coating was dried at room temperature for 15 min after coating.

[0046] Example 25: Unlike Example 14, in c, the coated graphite anode was pre-baked at 300°C for 0.5h, and then heated to 800°C at 5°C / min in a vacuum environment, held for 1h, and naturally cooled to 25°C. The mask was then removed to obtain a SiO2-B2O3-Na2CO3 gradient protective layer.

[0047] Example 26: Unlike Example 14, in c, the coated graphite anode was pre-baked at 400°C for 1 hour, and then heated to 900°C at 10°C / min in a vacuum environment, held for 2 hours, and naturally cooled to 30°C. The mask was then removed to obtain a SiO2-B2O3-Na2CO3 gradient protective layer.

[0048] Example 27: Unlike Example 14, in step a, a mesh groove with a depth of 1.8 mm and a spacing of 4 mm is machined on the surface of the pretreated graphite anode; An ethanol-water solution was prepared by mixing anhydrous ethanol and deionized water at a volume ratio of 8.5:1. Then, KH-550 was added dropwise to the ethanol-water solution at a rate of 1.2 mL / s while stirring at 1700 rpm. The amount of KH-550 added was 2 wt% of the ethanol-water solution. After the addition was completed, stirring was continued for 25 min. The solution was then allowed to stand and mature at 28 °C for 45 min to obtain a composite solution. Finally, the graphite anode with mesh grooves was immersed in the composite solution and ultrasonically treated for 13 minutes at an ultrasonic power of 28 W / L. After removal, it was dried at 90℃ for 25 minutes.

[0049] Example 28: Unlike Example 27, a mesh groove with a depth of 1.5 mm and a spacing of 3 mm is machined on the surface of the pretreated graphite anode.

[0050] Example 29: Unlike Example 27, a mesh groove with a depth of 2 mm and a spacing of 5 mm is machined on the surface of the pretreated graphite anode.

[0051] Example 30: Unlike Example 27, an ethanol-water solution was prepared by mixing anhydrous ethanol and deionized water at a volume ratio of 8:1. Then, KH-550 was added dropwise to the ethanol-water solution at a rate of 0.5 mL / s under a stirring speed of 1500 rpm. The amount of KH-550 added was 1 wt% of the ethanol-water solution. After the addition was completed, stirring was continued for 20 min, and the solution was allowed to stand and mature at 25°C for 30 min to obtain a composite solution.

[0052] Example 31: Unlike Example 27, an ethanol-water solution was prepared by mixing anhydrous ethanol and deionized water at a volume ratio of 9:1. Then, KH-550 was added dropwise to the ethanol-water solution at a rate of 2 mL / s under a stirring speed of 2000 rpm. The amount of KH-550 added was 3 wt% of the ethanol-water solution. After the addition was completed, stirring was continued for 30 min, and the solution was allowed to stand and mature at 30°C for 60 min to obtain a composite solution.

[0053] Example 32: Unlike Example 27, the graphite anode with mesh grooves was finally immersed in the composite solution and ultrasonically treated for 10 minutes at an ultrasonic power of 25 W / L. After being taken out, it was dried at 80°C for 20 minutes.

[0054] Example 33: Unlike Example 27, the graphite anode with mesh grooves was finally immersed in the composite solution and ultrasonically treated for 10 minutes at an ultrasonic power of 30 W / L. After being taken out, it was dried at 100°C for 30 minutes.

[0055] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and aims to illustrate the practical application effect of the present invention.

[0056] 1. Investigate the effects of electrolysis voltage, molten salt composition, and preparation method on the properties of copper-chromium-niobium powder. Comparative Example 1: Unlike Example 1, in S3, a DC voltage of 2.4V is applied.

[0057] Conclusion: In Comparative Example 1, a DC voltage of 2.4V resulted in an oxygen content of 1.2% and a Nb content of only 25.3% in the copper-chromium-niobium powder, indicating severe segregation. It can be concluded that an electrolysis voltage of ≥2.6V is required to ensure the reduction of Nb₂O₅.

[0058] Comparative Example 2: Unlike Example 1, the molten salt was pure CaCl2 molten salt.

[0059] Conclusion: The molten salt in Comparative Example 2, which is pure CaCl2 molten salt, has the following defects: poor fluidity of molten salt, cathode breakage, and oxygen content of 0.5%. This indicates that mixed molten salt can effectively improve the conductivity and stability of the cathode. Comparative Example 3: Unlike Example 1, copper-chromium-niobium powder was prepared using a mechanical alloying method.

[0060] Conclusion: The preparation of copper-chromium-niobium powder by mechanical alloying in Comparative Example 3 resulted in the following defects: oxygen content of 0.8%, carbon content of 0.3%, and deviation of ±2.8%. This indicates that the copper-chromium-niobium powder prepared by the method of the present invention has better purity and uniformity.

[0061] This invention features an environmentally friendly process: one-step reduction with zero chlorine emissions, a process reduction of 60%+, and energy consumption 30-40% lower than the vacuum arc method; uniform composition: composition deviation ≤ ±1.5%, superior to mechanical alloying (±3-5%); excellent purity: oxygen content ≤0.3%, carbon content ≤0.1%, purity ≥99.5%; and strong stability: cathode breakage rate <5%, solving pollution and corrosion problems and making it suitable for industrial applications.

[0062] 2. Investigate the effect of the preparation method of CaCl2-NaCl mixed molten salt on the properties of copper-chromium-niobium powder. Comparative Example 4: Unlike Example 1, KCl was not added to the mixed salt.

[0063] Comparative Example 5: Unlike Example 1, graphite electrodes were not used to purify the mixed molten salt.

[0064] Conclusion: Based on the comparison of Examples 1, 6-7 and Comparative Example 4, it can be concluded that the lack of KCl in the mixed salt has an adverse effect on the performance of copper-chromium-niobium. This is because the addition of KCl can form a eutectic system with a lower melting point, making the molten salt more fluid and having higher ion conduction efficiency at the electrolysis temperature (950℃). The better ion conduction helps to stabilize the electrolysis process, promotes more complete reduction of cathode oxides, and may reduce side reactions. As a result, the purity of copper-chromium-niobium powder decreases and the cathode breakage rate increases during the FFC electrolysis reaction. A comparison of Examples 1, 8-9, and Comparative Example 5 shows that not using graphite electrodes to purify the mixed molten salt has an adverse effect on the performance of copper-chromium-niobium. This is because in Examples 1 and 8-9, inserting graphite electrodes into the molten salt for purification can remove trace amounts of moisture and oxygen-containing impurities that may remain in CaCl2 and NaCl during drying and melting. However, in Comparative Example 5, the unpurified molten salt causes water molecules to be reduced to H2 at the cathode and oxidized to O2 at the anode during electrolysis. These side reactions consume electrical energy, reduce current efficiency, generate metal hydrides or oxides at the cathode, contaminating the product, and generate oxygen at the anode, corroding the graphite electrode. Consequently, the purity of the copper-chromium-niobium powder decreases, and the cathode breakage rate increases during the FFC electrolysis process.

[0065] 2. Investigate the effect of coating the graphite anode surface with a SiO2-B2O3-Na2CO3 gradient protective layer on the properties of copper-chromium-niobium powder. Comparative Example 6: Unlike Example 14, SiO2, B2O3, Na2CO3 and Al2O3 were directly mixed in a mass ratio of 65:8:1:25 to obtain SiO2-B2O3-Na2CO3 raw material without gradient classification.

[0066] Comparative Example 7: Unlike Example 14, the packing material was not crushed into Grade A and Grade B packing materials respectively.

[0067] Comparative Example 8: Unlike Example 14, the thicknesses of the transition layer material, intermediate layer material, and sealing layer material are uniform.

[0068] Conclusion: A comparison of Examples 1 and 14-26 shows that coating the graphite anode surface with a SiO2-B2O3-Na2CO3 gradient protective layer further enhances the performance of copper-chromium-niobium powder. This is because the SiO2-B2O3-Na2CO3 coating forms a dense physical barrier at high temperatures, effectively isolating oxygen from contacting the graphite anode, thus significantly slowing down the carbon corrosion rate. Slowing down anode corrosion means a significant reduction in carbon impurities introduced by the anode. Simultaneously, a high-quality protective layer also reduces the activity of other oxygen-containing impurities in the molten salt, making the reduction reaction at the cathode more thorough. These two aspects work together to achieve higher purity copper-chromium-niobium powder. Furthermore, a stable anode and a clean electrolytic environment result in a more uniform current distribution and smaller fluctuations during electrolysis, reducing cathode structural damage (such as thermal stress cracking or impurity erosion) caused by excessively high local current density or impurity interference, thereby lowering the cathode breakage rate. Therefore, Example 14 was selected as the further optimization scheme.

[0069] Comparing Examples 14, 17-22, and Comparative Examples 6 and 7, it can be seen that Comparative Example 6 directly mixes all raw materials, resulting in a coating with uniform composition, unlike the gradient structure of Example 14. This leads to cracking problems: the thermal expansion coefficients of different components differ. During the heating and cooling cycles of the electrolysis process, the uniformly composed coating generates enormous thermal stress, making it prone to cracking or peeling off from the graphite substrate. When cracks appear in the coating, molten salt rapidly erodes the internal graphite anode along the cracks, rendering its protective effect ineffective, and even causing the detached fragments to become new sources of contamination. Therefore, its performance parameters will be significantly worse than those of Example 14, and may even be worse than Example 1 without a protective layer. Comparative Example 7, by not classifying and compounding the fillers and using spherical particles of a single particle size, leaves more voids during stacking, making the coating relatively loose, with a lower packing density and weakened impermeability. It cannot effectively prevent the molten salt electrolyte from penetrating and eroding into the coating, thereby reducing the coating's service life and protective effect.

[0070] As can be seen from the comparison of Examples 14, 23-24 and Comparative Example 8, setting the three coatings with different functions (transition layer, intermediate layer and sealing layer) to a uniform thickness has an adverse effect on the performance of copper-chromium-niobium powder. This is because uniform thickness may not be able to achieve the optimal function of each layer, resulting in insufficient stress buffering or poor blocking effect, which reduces the stability of the coating under long-term high-temperature service and slightly weakens the performance parameters.

[0071] 3. Investigate the effect of pretreatment of graphite anode surface processing on the properties of copper-chromium-niobium powder. Conclusion: A comparison of Examples 1, 14, and 27-33 shows that processing the pretreated graphite anode surface with mesh grooves and immersing it in a composite solution can further enhance the performance of copper-chromium-niobium powder. This is because the present invention, by processing mesh grooves on the pretreated graphite anode surface and performing surface modification treatment, utilizes the mesh grooves to provide a three-dimensional mechanical interlocking structure, enabling the coating and graphite substrate to form a mechanical interlock, thereby improving the bonding strength between the coating and the substrate. The surface energy of the grooves after silane coupling agent treatment is improved, and the SiO2-B2O3-Na2CO3 raw materials can more easily penetrate into the grooves to form a continuous coating structure, reducing interface defects. Furthermore, the groove structure can effectively release thermal stress, and the silane coupling agent layer provides a flexible transition, jointly alleviating the difference in thermal expansion coefficients between the coating and the substrate, preventing coating cracking, and thus improving the performance of copper-chromium-niobium powder.

Claims

1. A method for preparing copper-chromium-niobium powder based on FFC electrolysis process, characterized in that, Includes the following steps: S1. Preparation of composite oxides CuO powder, Cr2O3 powder, and Nb2O5 powder were weighed out according to a mass fraction of 20-40% Cu, 30-50% Cr, and the balance Nb. They were then ball-milled for 4-8 hours at a ball-to-material ratio of 5-10:1 and a rotation speed of 200-300 r / min. Anhydrous ethanol was added at a rate of 1-3 mL / min during the ball milling process. The mixture was then pressed, shaped, and sintered to obtain the copper-chromium-niobium composite oxide. S2, Setting up the electrolysis system The copper-chromium-niobium composite oxide was used as the cathode of the electrolytic cell, graphite as the anode, and CaCl2-NaCl mixed molten salt as the electrolyte. These components were placed sequentially in a graphite crucible, and a vacuum of 1×10⁻⁶ was applied. -2 ~5×10 -2 Argon / nitrogen gas is then introduced for protection after Pa. S3, Molten Electrolysis The temperature in the electrolytic system is raised to 700-750℃ and held for 1-1.5 hours. Then, the temperature is raised to 850-1050℃, and a DC voltage of 2.6-3.0V is applied with a current density of 80-180 mA / cm². 2 After constant voltage electrolysis for 10-16 hours, intermediate products are generated in the cathode region of the electrolytic cell, which are loose and porous metal sponges. S4, Post-processing The metal sponge was naturally cooled to 22-30℃, then ultrasonically crushed and ground to 10-100μm, washed 3-5 times with deionized water until the pH of the cleaning solution was 6.5-7.5, and finally vacuum dried to obtain the copper-chromium-niobium powder.

2. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 1, characterized in that, In S1, the purity of CuO powder, Cr2O3 powder, and Nb2O5 powder is ≥99.5%, and the particle size is 50~200μm.

3. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 1, characterized in that, In S1, the pressing and molding process involves holding the pressure at 20-50 MPa for 3-5 minutes.

4. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 1, characterized in that, In S1, the sintering is carried out under argon / nitrogen protection, with the temperature increased to 700-900°C at a rate of 5-10°C / min, and held for 2-4 hours.

5. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 1, characterized in that, A SiO2-B2O3-Na2CO3 gradient protective layer is coated on the surface of the graphite anode; The coating method is as follows: a. Graphite Anode Pretreatment The surface of the graphite anode was polished with 600-grit sandpaper to a roughness of Ra=3~5μm. It was then ultrasonically cleaned with anhydrous ethanol for 10~15min under ultrasonic power of 25~30W / L and ultrasonic frequency of 35~45kHz. Finally, it was vacuum dried for 30~60min under vacuum degree ≤100Pa and temperature of 80~100℃ to obtain the pretreated graphite anode. b. Preparation of SiO2-B2O3-Na2CO3 raw materials b-1. SiO2, B2O3, Na2CO3, and stabilizer are mixed in a mass ratio of 60~70:5~10:1~2:20~30, then vacuum dried at 110~120℃ for 12~24h, and ground to 100~200 mesh to obtain a mixed powder. The powder is then placed in a crucible and melted at 1400~1450℃ under argon protection for 15~20min. Finally, the melted product is cooled to room temperature and crushed to obtain -180~+300 mesh A-grade filler and -300 mesh B-grade filler. The A-grade filler and B-grade filler are mixed in a mass ratio of 6~7:3~4 to obtain the transition layer raw material. b-2. Mix SiO2, B2O3, Na2CO3 and stabilizer in a mass ratio of 30~40:15~20:3~4:20~30, and melt them for 10~15 minutes under argon protection and at a temperature of 1250~1300℃. The remaining steps are the same as b-1 to obtain the intermediate layer raw material. b-3. Mix SiO2, B2O3, Na2CO3 and stabilizer in a mass ratio of 40~50:10~15:8~12:25~35, and melt them for 15~20 minutes under argon protection and at a temperature of 1350~1400℃. The remaining steps are the same as b-1 to obtain the sealing layer raw material. c. Coating with SiO2-B2O3-Na2CO3 raw materials The transition layer material, intermediate layer material, and sealing layer material are mixed with silicone resin at a mass ratio of 3-4:1, and ethanol is added to adjust the viscosity to 800-1000 mPa·s. The tip of the graphite anode is wrapped and protected with a mask. Then, 5-8 μm transition layer material, 15-20 μm intermediate layer material, and 5-8 μm sealing layer material are sequentially coated on the surface of the graphite anode at a speed of 1000-3000 rpm. The coating time for each layer is 30-60 s. After coating, the material is dried at room temperature for 10-15 min. Finally, the coated graphite anode is pre-baked at 300~400℃ for 0.5~1h, and then heated to 800~900℃ in a vacuum environment at 5~10℃ / min, held for 1~2h, and naturally cooled to 25~30℃. The mask is then removed to obtain the SiO2-B2O3-Na2CO3 gradient protective layer.

6. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 5, characterized in that, In step a, a mesh groove with a depth of 1.5~2mm and a spacing of 3~5mm is machined on the surface of the pretreated graphite anode; Next, an ethanol-water solution was prepared by mixing anhydrous ethanol and deionized water at a volume ratio of 8-9:

1. Then, KH-550 was added dropwise to the ethanol-water solution at a rate of 0.5-2 mL / s under a stirring speed of 1500-2000 rpm. The amount of KH-550 added was 1-3 wt% of the ethanol-water solution. After the addition was completed, stirring was continued for 20-30 min. The solution was then allowed to stand and mature at 25-30℃ for 30-60 min to obtain a composite solution. Finally, the graphite anode with mesh grooves is immersed in the composite solution and ultrasonically treated for 10-15 minutes at an ultrasonic power of 25-30 W / L. After removal, it is dried at 80-100℃ for 20-30 minutes.

7. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 5, characterized in that, The stabilizer is Al2O3.

8. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 5, characterized in that, The method for preparing the CaCl2-NaCl mixed molten salt is as follows: 1) Raw material pretreatment CaCl2 and NaCl were vacuum dried at 62-67℃ for 4-6 hours, ground to 1-2 mm, and then mixed at a mass ratio of CaCl2 to NaCl of 60-80:20-40 to obtain a mixed raw material. KCl was added at a mass ratio of 1-3 wt% of the mixed raw material to obtain a mixed salt. 2) Melting treatment The mixed salt is heated to 250-300℃ in a graphite crucible at a rate of 3-5℃ / min and held for 10-12 hours. Then, it is heated to 850-900℃ and held for 18-24 hours to obtain molten salt. Two graphite electrodes are inserted into the molten salt as the anode and cathode, respectively. A voltage of 1.5-2.0V is applied for pre-electrolysis for 2-4 hours. After the pre-electrolysis is completed, the graphite electrodes are removed and the mixture is naturally cooled to 22-30℃ to obtain the purified mixed molten salt for later use.

9. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 1, characterized in that, The ultrasonic fragmentation method is as follows: processing for 10 to 30 minutes under ultrasonic power of 500~800W and ultrasonic frequency of 20~40kHz.

10. The method for preparing copper-chromium-niobium powder based on FFC electrolysis process as described in claim 1, characterized in that, In S4, the vacuum drying is carried out at a temperature of 80~120℃ and a pressure of 1×10⁻⁶. -1 ~5×10 -1 Drying treatment at Pa for 6-10 hours.

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