Method for preparing spherical aluminum tantalum alloy powder based on segmented voltage molten salt electrolysis

Abstract

The invention provides a method for preparing spherical aluminum tantalum alloy powder based on segmented voltage molten salt electrolysis. The method comprises the following steps: mixing Ta2O5 powder with a pore-forming agent and a conductive agent, pressing into a sheet, sintering at high temperature to prepare a Ta2O5 cathode sheet, carrying out segmented electrolysis in cryolite-based molten salt by taking graphite as an anode, and carrying out electrolysis at low voltage in the first stage, so that Ta2O5 is subjected to solid-state electrodeoxidation to be converted into tantalum particles; and then, the voltage is increased, aluminum ions in the molten salt are electrically deposited on the surfaces of the tantalum particles to form metal aluminum, aluminum-tantalum alloying reaction is induced, and the alloy product spontaneously forms spherical particles through the reaction heat release effect. The spherical aluminum tantalum alloy powder has the advantages of being short in technological process and low in cost, and the spherical aluminum tantalum alloy powder is uniform in particle size, high in sphericity degree, good in fluidity and suitable for the technical fields of laser beam / electron beam 3D printing, cladding forming, injection forming, thermal spraying and the like.

Description

[0001] The present invention belongs to the field of aluminum-based high-temperature alloy preparation, and specifically relates to a method for preparing spherical aluminum-tantalum alloy by adopting a molten salt electrolysis method. Background Art

[0002] Additive manufacturing, as a next-generation manufacturing technology, is a key path forward for the transformation and upgrading of the global manufacturing industry. Aluminum-tantalum alloys, due to their combination of high strength, high-temperature resistance, and corrosion resistance, have garnered extensive attention and research in the additive manufacturing field in recent years. The "National New Materials Industry Development Plan" and the "Guiding Catalogue of Key Products and Services in Strategic Emerging Industries" list aluminum and tantalum alloys for additive manufacturing as key development areas.

[0003] As the raw material for additive manufacturing, parameters such as the sphericity and particle size uniformity of aluminum-tantalum alloy powder are crucial and directly affect the quality, precision and mechanical properties of the final product. At present, the industry generally adopts high-temperature melting of aluminum and tantalum alloy raw materials to form alloy liquid, and then produces spherical aluminum alloy powder through post-processing processes such as atomization. In the prior art, the patent with publication number CN106216703A reports a method for preparing spherical aluminum alloy powder for 3D printing. The aluminum alloy is heated in a melting chamber to form an alloy liquid flow, and a Laval annular gap tightly coupled nozzle is used to atomize the alloy liquid flow, so that the metal liquid flow forms spherical aluminum alloy powder under the impact of high-speed gas. However, due to the huge difference in physical properties between metallic tantalum and aluminum, especially the melting point of tantalum (2996°C) is much higher than the boiling point of aluminum (2327°C), the alloy melting temperature is high, and the smelting process inevitably produces evaporation loss of aluminum components, making it difficult to accurately control the composition of the alloy powder; at the same time, the metal atomization process is complex, the equipment investment is large, and the production cost is high, resulting in the high price of spherical aluminum-tantalum alloy powder, which seriously restricts its large-scale application in the field of additive manufacturing.

[0004] We previously developed a method for preparing spherical aluminum-tantalum alloy powder using segmented voltage molten salt electrolysis. Tantalum oxide powder is pressed into tantalum oxide sheets as the cathode. Electrolysis is then performed in an electrolyte molten salt containing aluminum ions (such as cryolite). This deoxidizes the tantalum oxide to produce metallic tantalum particles. Simultaneously, aluminum ions are electrodeposited at the cathode to form metallic aluminum, inducing an in-situ aluminum-tantalum alloying reaction to produce aluminum-tantalum alloy powder. However, this process suffers from two key bottlenecks: 1) poor cathode conductivity: tantalum oxide has low conductivity and electron transport is difficult at the cathode, resulting in slow electrodeoxidation kinetics and low current efficiency; 2) compositional segregation of the alloy product: Single-step constant voltage electrolysis tends to induce preferential aluminum deposition in the conductive areas of the cathode, leading to localized aluminum enrichment and resulting in product compositional segregation.

[0005] To overcome the shortcomings of the existing technology, the present invention provides a method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis, and proposes an innovative solution: by introducing a conductive enhancement phase into the cathode to construct a three-dimensional electron transport network, and adopting a staged constant voltage electrolysis strategy to control the reaction sequence, the decoupling of oxide deoxidation and alloying reaction and process optimization are achieved. Specifically, a conductive phase is added during the cathode preparation stage to form a permeable conductive network in the matrix, which improves the cathode conductivity, significantly accelerates electron transport, and provides electric deoxidation current efficiency; voltage is controlled in steps during the electrolysis stage: in the first stage (2.0-3.0V), tantalum oxide electric deoxidation reaction (Ta2O5+10e - →2Ta+5O 2 -), when the current reaches the platform current (marking the completion of deoxidation), the second stage begins, and the voltage is raised to 3.0~4.0V (higher than the critical potential of aluminum deposition). At this time, the aluminum ions in the molten salt are directionally deposited on the surface of the new tantalum particles (Al 3 ++3e - →Al(l)), triggering uniform in-situ alloying. This design completely eliminates non-selective aluminum deposition in undeoxidized areas, eliminating compositional deviations. Simultaneously, the exothermic heat of the alloying reaction promotes melting and spheroidization of the product particles, significantly improving the uniformity of the product composition and shape. The resulting powder meets the stringent compositional accuracy and fluidity requirements of laser / electron beam 3D printing, providing a low-cost, short-process core material solution for the additive manufacturing of high-performance aluminum-tantalum alloys. Summary of the Invention

[0006] The present invention provides a method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis, which is characterized by comprising the following steps:

[0007] 1. A method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis, characterized by comprising the following steps:

[0008] S1: Ta2O5 powder and a pore-forming agent are mixed uniformly in a mass ratio of 1:0.5-1, and a dextrin binder equivalent to 5%-10% of the total mass of the two powders and a conductive agent of 1%-5% are added. After mixing uniformly, the green body is molded into a green body; after the green body is fully dried, it is heated to 300-600°C and kept at this temperature for 1-3 hours to decompose the pore-forming agent, and then the temperature is further raised to 900-1200°C and heated for 1-10 hours, and the green body is sintered to obtain a Ta2O5 sintered body as an electrolytic cathode material;

[0009] S2: The Ta2O5 sheet connected to the wire is used as the cathode and the graphite electrode is used as the anode. Under the protection of argon atmosphere, it is immersed in cryolite-based molten salt for electrolysis at an electrolysis temperature of 800-1010°C and an electrolysis voltage of 2.5-5.0V. After the electrolysis is completed, the cathode is removed from the molten salt and cooled to room temperature.

[0010] S3: The cooled cathode product is crushed and ground into powder, heated and washed in a cleaning solution, filtered, and the filter cake is rinsed with water. Finally, it is dried in an oven to obtain spherical aluminum-tantalum alloy powder.

[0011] 2. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, wherein the pore-forming agent is one or more of ammonium bicarbonate, ammonium chloride, sodium bicarbonate, PMMA powder, or PS microspheres; and the conductive agent is one or more of metal tantalum powder, graphite powder, or carbon fiber.

[0012] 3. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, characterized in that the pressure of the molding is 1 to 15 MPa.

[0013] 4. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1 is characterized in that the main components of the cryolite-based molten salt are 20% to 50% Na3AlF6, 0% to 40% K3AlF6, and 10% to 30% AlF3, and 0% to 10% LiF and 1% to 6% Al2O3 are added as additives.

[0014] 5. According to claim 1, a method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis is characterized in that: the electrolysis process adopts a staged constant voltage control method, the electrolysis voltage in the first stage is 2.0~3.0V, and Ta2O5 electro-deoxidation to form Ta particles occurs; the electrolysis power supply in the second stage is 3.0~4.0V, and metallic aluminum electrodeposition reaction and in-situ aluminum-tantalum alloying reaction occur.

[0015] 6. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1 is characterized in that the product cleaning liquid is one or a mixture of HCl, H2SO4, HNO3, and AlCl3 solutions.

[0016] Beneficial effects of the present invention:

[0017] 1) The present invention breaks through the core bottleneck while retaining the advantages of the one-step short process through the coordinated design of the conductive enhancement phase and the staged constant voltage electrolysis. First, a three-dimensional conductive network is constructed in the tantalum oxide cathode to greatly improve the cathode conductivity, so that the electric deoxidation current efficiency is significantly improved; secondly, a time-decoupled staged voltage control is adopted: the first stage (2.0~3.0V) focuses on the solid-state electric deoxidation of tantalum oxide to generate metallic tantalum particles, and the second stage (3.0~4.0V) accurately induces the in-situ uniform electrodeposition of aluminum ions on the surface of the tantalum particles, completely eliminating the risk of preferential deposition of aluminum in the undeoxidized area in the one-step method. This design not only maintains the simplicity of the process flow, but also significantly improves the alloying efficiency and composition uniformity through precise time and space control of the reaction path.

[0018] 2) Low-temperature, high-efficiency alloying and zero aluminum loss characteristics are further enhanced. In a molten salt medium at 800-1010°C, staged electrolysis ensures that aluminum is deposited only on the surface of completely deoxidized tantalum particles. This in-situ alloying directly produces an aluminum alloy with a precise stoichiometric ratio. This completely avoids the compositional loss problem caused by the lower boiling point of aluminum than that of tantalum in traditional smelting processes, thereby improving aluminum utilization.

[0019] 3) Self-heating spheroidization effect and improved product performance. Staged voltage control concentrates the alloying reaction on the tantalum particle surface, releasing more concentrated interfacial reaction heat and promoting micro-region melting. Simultaneously, the cathode conductive network enhances the cathode's overall thermal conductivity, allowing the molten alloy particles to efficiently spheroidize under surface tension and accelerate solidification to form an ultrafine, monodisperse powder. The resulting powder has the fluidity and bulk density required for high-precision additive manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0021] Figure 1 SEM image of Ta2O5 cathode

[0022] Figure 2 SEM image of tantalum nanoparticles

[0023] Figure 3 XRD pattern of Al3Ta product

[0024] Figure 4 Differential Scanning Calorimetry (DSC) Curves of Aluminum-Tantalum Alloying Process

[0025] Figure 5 SEM image and EDS elemental analysis results of spherical Al3Ta products

[0026] Figure 6 TEM image and EDS element distribution results of spherical Al3Ta products DETAILED DESCRIPTION

[0027] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention.

[0028] Example 1:

[0029] S1. Ta2O5 and NH4HCO3 were mixed in a mass ratio of 1:1, 7% dextrin solution (mass concentration of 10%) was added as a binder, and 5% tantalum powder was added as a conductive agent. After thorough mixing, the mixture was pressed into a circular sheet with a diameter of 20 mm using a mold at a pressing pressure of 7 MPa. The obtained sheet was thoroughly dried and then calcined in a muffle furnace at 300°C for 1 hour to allow NH4HCO3 to thermally decompose into gas and escape, leaving pores in the Ta2O5 sheet. The temperature was then raised to 1200°C and sintered for 2 hours to obtain a Ta2O5 sintered sheet. A nickel-chromium wire was used as a conductor to assemble the Ta2O5 cathode ( Figure 1 );

[0030] S2. Weigh 500 g of a mixed salt of Na3AlF6:K3AlF6:AlF3 in a mass ratio of 35%, 35%, and 30%, and add 3% LiF and 5% Al2O3 as additives. Place it in a graphite crucible and heat it to 850°C in an argon atmosphere at a heating rate of 10°C / min to melt it. Use the Ta2O5 sheet prepared in step S1 as the cathode and the graphite crucible as the anode, apply a constant voltage of 2.5 V, and during the electrolysis process, the Ta2O5 cathode first undergoes a solid-state electrodeoxidation reaction to generate Ta particles ( Figure 2 ), after the current reaches the platform current, the voltage is increased to 3.5V, so that the aluminum ions in the molten salt precipitate liquid aluminum on the surface of the tantalum particles through electrodeposition reaction, thereby inducing an in-situ alloying reaction between aluminum and tantalum to generate Al3Ta products ( Figure 3 ), due to the exothermic reaction of the alloy ( Figure 4 , the shaded part is the exothermic peak), which promotes the spontaneous formation of spherical morphology of Al3Ta particles; after 2 hours of electrolysis, the power is turned off, the cathode is taken out of the molten salt, and cooled to room temperature;

[0031] S3. The product after electrolysis in step S2 was ground into powder, and then stirred in a saturated AlCl3 solution at 80°C for 3h to clean the molten salt and impurities on the surface to obtain spherical Al3Ta particle products ( Figure 5-6 ).

[0032] Example 2:

[0033] S1. Ta2O5 and NH4Cl were mixed in a mass ratio of 1:0.5, and 10% polyvinyl alcohol solution (5% by mass concentration) was added as a binder and 5% graphite powder as a conductive agent. After thorough mixing, the mixture was pressed into a circular sheet with a diameter of 20 mm using a mold at a pressing pressure of 10 MPa. The resulting sheet was thoroughly dried and then calcined in a muffle furnace at 600°C for 1 hour to allow the NH4Cl to thermally decompose into gas and escape, leaving pores in the Ta2O5 sheet. The temperature was then raised to 900°C and sintered for 10 hours to obtain a Ta2O5 sintered sheet, which was then assembled into a Ta2O5 cathode using nickel-chromium wire as a conductor.

[0034] S2. Weigh 500g of mixed salt according to the mass ratio of Na3AlF6:K3AlF6:AlF3 in 30%, 40% and 30%, and add 10% LiF and 6% Al2O3 as additives, put it into a graphite crucible, and melt it at a heating rate of 10°C / min in an argon atmosphere to 850°C. Use the Ta2O5 sheet prepared in step S1 as the cathode and the graphite crucible as the anode, apply 2.0V constant voltage electrolysis, during the electrolysis process, the Ta2O5 cathode first undergoes a solid-state electrodeoxidation reaction to generate Ta particles, and after the current reaches the platform current, increase the voltage to 4.0V, so that the aluminum ions in the molten salt precipitate liquid aluminum on the surface of the tantalum particles through the electrodeposition reaction, thereby inducing an in-situ alloying reaction between aluminum and tantalum to generate Al3Ta products. Due to the heat release of the alloying reaction, the Al3Ta particles spontaneously form a spherical morphology; after 10h of electrolysis, turn off the power, remove the cathode sheet from the molten salt, and cool it to room temperature;

[0035] S3. The product after electrolysis in step S2 is ground into powder, and then stirred in a dilute HCl solution at 80°C for 3 hours to wash off the molten salt and impurities on the surface to obtain spherical Al3Ta particle products.

[0036] Example 3:

[0037] S1. Ta2O5 and NaHCO3 were mixed in a mass ratio of 1:1, 7% dextrin solution (mass concentration of 10%) was added as a binder, and 5% carbon fiber was added as a conductive agent. After thorough mixing, the mixture was pressed into a circular sheet with a diameter of 20 mm using a mold at a pressing pressure of 10 MPa. The resulting sheet was fully dried and then calcined in a muffle furnace at 600°C for 1 hour to allow the NaHCO3 to thermally decompose into gas and escape, leaving pores in the Ta2O5 sheet. The temperature was then raised to 1000°C and sintered for 2 hours to obtain a Ta2O5 sintered sheet, which was then assembled into a Ta2O5 cathode using nickel-chromium wire as a conductor.

[0038] S2. Weigh 500g of mixed salt according to the mass ratio of Na3AlF6:K3AlF6:AlF3 in 50%, 30% and 20%, and add 3% LiF and 5% Al2O3 as additives, put it into a graphite crucible, and heat it to 1000℃ in an argon atmosphere at a heating rate of 10℃ / min to melt it. Use the Ta2O5 sheet prepared in step S1 as the cathode and the graphite crucible as the anode, apply 2.5V constant voltage electrolysis, during the electrolysis process, the Ta2O5 cathode first undergoes solid-state electrodeoxidation reaction to generate Ta particles, and after the current reaches the platform current, increase the voltage to 3.1V, so that the aluminum ions in the molten salt precipitate liquid aluminum on the surface of the tantalum particles through electrodeposition reaction, thereby inducing an in-situ alloying reaction between aluminum and tantalum to generate Al3Ta products. Due to the heat release of the alloy reaction, the Al3Ta particles spontaneously form a spherical morphology; after 5h of electrolysis, turn off the power, remove the cathode sheet from the molten salt, and cool it to room temperature;

[0039] S3. The product after electrolysis in step S2 was ground into powder, and then stirred in a saturated AlCl3 solution at 80°C for 3h to wash off the molten salt and impurities on the surface to obtain spherical Al3Ta particle products.

Claims

1. A method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis, characterized in that: The following steps are involved: S1: Ta2O5 powder and a pore-forming agent are mixed uniformly in a mass ratio of 1:0.5-1, and a dextrin binder equivalent to 5%-10% of the total mass of the two powders and a conductive agent of 1%-5% are added. After mixing uniformly, the green body is molded into a green body; after the green body is fully dried, it is heated to 300-600°C and kept at this temperature for 1-3 hours to decompose the pore-forming agent, and then the temperature is further raised to 900-1200°C and heated for 1-10 hours, and the green body is sintered to obtain a Ta2O5 sintered body as an electrolytic cathode material; S2: The Ta2O5 sheet connected to the wire is used as the cathode and the graphite electrode is used as the anode. Under the protection of argon atmosphere, it is immersed in cryolite-based molten salt for electrolysis at an electrolysis temperature of 800-1010°C and an electrolysis voltage of 2.5-5.0V. After the electrolysis is completed, the cathode is removed from the molten salt and cooled to room temperature. S3: The cooled cathode product is crushed and ground into powder, heated and washed in a cleaning solution, filtered, and the filter cake is rinsed with water. Finally, it is dried in an oven to obtain spherical aluminum-tantalum alloy powder.

2. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, characterized in that: The pore-forming agent is one or more of ammonium bicarbonate, ammonium chloride, sodium bicarbonate, PMMA powder or PS microspheres; the conductive agent is one or more of metal tantalum powder, graphite powder or carbon fiber.

3. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, characterized in that: The pressure of the compression molding is 1-15 MPa.

4. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, characterized in that: The main components of the cryolite-based molten salt are 20% to 50% of Na3AlF6, 0% to 40% of K3AlF6, and 10% to 30% of AlF3, while 0% to 10% of LiF and 1% to 6% of Al2O3 are added as additives.

5. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, characterized in that: The electrolysis process adopts a staged constant voltage control method. The electrolysis voltage in the first stage is 2.0-3.0V, during which Ta2O5 is electro-deoxidized to generate Ta particles. The electrolysis power supply in the second stage is 3.0-4.0V, during which metallic aluminum is electro-deposited and an in-situ aluminum-tantalum alloying reaction occurs.

6. The method for preparing spherical aluminum-tantalum alloy powder based on segmented voltage molten salt electrolysis according to claim 1, characterized in that: The product cleaning liquid is one or a mixture of HCl, H2SO4, HNO3, and AlCl3 solutions.

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