A method for preparing high-purity niobium ingot by multi-stage refining and high-purity niobium ingot

Abstract

The application provides a method for preparing high-purity niobium ingot by using multi-stage refining and high-purity niobium ingot, and the method comprises the following steps: (1) taking aluminum particles, niobium pentoxide, a heating agent and a slagging agent as raw materials, preparing aluminum-niobium alloy ingot by using an off-furnace aluminothermic method, then performing surface treatment and crushing treatment to obtain aluminum-niobium alloy particles; (2) performing horizontal electron beam melting on the aluminum-niobium alloy particles to obtain molten niobium plates; (3) stacking a plurality of molten niobium plates, then sequentially performing vacuum diffusion welding and vacuum arc melting to obtain a primary niobium ingot; and (4) placing the primary niobium ingot in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot. The multi-stage refining process coupling system of "aluminothermic method→horizontal electron beam melting→diffusion welding→arc melting→double-gun electron beam melting" is adopted to realize the stable production of high-purity niobium with high RRR value, and effectively solves the technical problems of high energy consumption, high cost and low production efficiency existing in the traditional process.

Description

Technical Field

[0001] This invention belongs to the field of rare metal smelting and purification technology, and relates to a method for preparing high-purity niobium ingots, specifically a method for preparing high-purity niobium ingots using multi-stage refining and high-purity niobium ingots. Background Technology

[0002] Niobium is a silvery-gray, tough, and malleable refractory metal. Due to its high critical temperature (about 9.26K), high superheat critical field (about 0.2T), and good processing and forming properties, it has become a key raw material for NbTi and Nb3Sn, star materials in the field of superconductivity. It has broad application prospects in cutting-edge high-tech fields such as human nuclear magnetic resonance imaging, nuclear magnetic resonance spectrometers, magnetron-controlled Czochralski single crystal silicon, the International Thermonuclear Experimental Reactor, and accelerators.

[0003] Key indicators of niobium, such as purity and RRR (Residual Resistivity Ratio), are related to the content and types of impurity elements in niobium, directly determining its physicochemical properties. These properties, in turn, have a substantial impact on the quality and reliability of end-use applications through radiation effects. Therefore, the development of high-purity niobium with a high RRR is imperative and urgently needs to be accelerated.

[0004] At present, the preparation methods of high-purity niobium are becoming increasingly diversified.

[0005] CN 115717254A discloses a method for preparing high-purity niobium using molten salt electrolysis. The method involves first mixing niobium oxide with a carbonaceous reducing agent to form a soluble niobium carbon-based solid solution, then sintering it to form a soluble niobium carbon-based solid solution anode. This solid solution is then combined with a graphite electrode and a molten salt electrolyte to form an electrolysis system, which is then electrolyzed to obtain high-purity niobium. However, the molten salt electrolysis method for preparing high-purity niobium suffers from several drawbacks, including significant environmental pollution, high energy consumption, high equipment requirements and maintenance costs due to the corrosive nature of the molten salt electrolyte, and the potential for introducing carbon impurities through the use of a carbonaceous reducing agent, as improper impurity removal makes it difficult to obtain products with extremely high purity.

[0006] CN 104480319A discloses a method for preparing high-purity niobium by electron beam melting. This method involves controlling key indicators such as specific energy and vacuum degree during the vacuum electron beam melting process, performing 3 to 7 vacuum electron beam melting cycles on niobium strips to obtain high-purity niobium. However, the preparation of high-purity niobium by electron beam melting requires a high content of high-melting-point impurities such as tantalum and tungsten in the raw materials. If the content of these impurities in the niobium strips exceeds the standard, it is difficult to effectively remove them using this method. Furthermore, the long melting time and numerous cycles of electron beam melting result in significant loss of the niobium matrix metal, low production efficiency, and high energy consumption.

[0007] CN 117684024A discloses a method for physically purifying and preparing high-purity niobium. The method involves first subjecting niobium raw material produced by the vacuum aluminothermic process to acid washing, water washing, and drying, then welding them into electrodes for vacuum electron beam melting. Following machining, a smooth niobium ingot is obtained, and finally, high-purity niobium is obtained through degassing. However, the vacuum aluminothermic process suffers from low yield and high energy consumption. Furthermore, the subsequent processing of the niobium raw material is complex and lengthy, directly resulting in low production efficiency. Simultaneously, the machining process may introduce new impurities, and improper degassing can make it difficult to achieve the desired product purity.

[0008] In summary, developing a high-purity niobium material with a high RRR value while effectively avoiding some of the shortcomings of the aforementioned published patents has become the focus of current research in this field. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing high-purity niobium ingots using multi-stage refining, and the resulting high-purity niobium ingots. This invention uses aluminum granules, niobium pentoxide, a heating agent, and a slagging agent as raw materials, and employs a multi-stage refining process coupling system of "aluminothermic method → ​​horizontal electron beam melting → diffusion welding → electric arc melting → dual-gun electron beam melting" to achieve stable production of high-purity niobium with high residual resistivity ratio (RRR). This effectively solves the technical problems of high energy consumption, high cost, and low production efficiency inherent in traditional processes.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing high-purity niobium ingots using multi-stage refining, the method comprising the following steps:

[0012] (1) Using aluminum granules, niobium pentoxide, exothermic agent and slag-forming agent as raw materials, aluminum-niobium alloy ingots are prepared by the aluminothermic method outside the furnace, and then surface treatment and crushing treatment are carried out in sequence to obtain aluminum-niobium alloy particles.

[0013] (2) The aluminum-niobium alloy particles obtained in step (1) are placed in a horizontal electron beam melting furnace for horizontal electron beam melting to obtain a melted niobium plate;

[0014] (3) Stack several smelted niobium plates obtained in step (2), and then perform vacuum diffusion welding and vacuum arc melting in sequence to obtain primary niobium ingots;

[0015] (4) The primary niobium ingot obtained in step (3) is placed in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot.

[0016] In this invention, the aluminothermic process described in step (1) serves as the initial step to prepare aluminum-niobium alloys with high-grade Nb, while simultaneously reducing the content of various impurity elements introduced into the raw materials; in step (2), the horizontal electron beam melting not only transforms the particles obtained after the aluminothermic process into plates (facilitating subsequent processing), but also, thanks to the deep penetration characteristics of the high-energy beam, further reduces interstitial element impurities and low-melting-point element impurities, thus initially achieving compositional homogenization; in step (3), diffusion welding eliminates defects such as micropores generated in the early melting process through interfacial atomic diffusion migration, achieving the preparation of cubic ingots without introducing any foreign matter, thus meeting the requirements of arc melting for the shape of the raw materials; in step (3), the arc melting not only helps to form a cylindrical shape to meet the requirements of the vertical feeding method of the subsequent dual-gun electron beam melting for the shape of the raw materials, but also further homogenizes the material and reduces the content of various impurity elements; in step (4), the dual-gun electron beam melting furnace utilizes the synergistic effect of the dual beams to achieve deep removal and precise control of residual trace impurities, significantly improving the purity of the niobium ingots;

[0017] The multi-stage refining process combination of "aluminothermic method → ​​horizontal electron beam melting → diffusion welding → electric arc melting → dual-gun electron beam melting" provided by this invention, through the complementary advantages and parameter matching of each stage, successfully breaks through the technical bottleneck of traditional processes in the preparation of high-purity niobium, which is difficult to achieve both high purity and high RRR value. It provides a brand-new technical path for obtaining high-purity niobium materials with high RRR value and excellent superconducting properties.

[0018] As a preferred technical solution of the present invention, the heating agent in step (1) includes potassium chlorate.

[0019] Preferably, the slag-forming agent in step (1) includes calcium oxide and calcium fluoride.

[0020] Preferably, the mass ratio of the aluminum granules, niobium pentoxide, exothermic agent, calcium oxide, and calcium fluoride is 50-51:96-98:12-14:7-9:3-5, for example, it can be 50:96:12:7:3, 50.5:97:13:8:4, 50:98:14:7:5, or 51:96:12:9:5, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the particle size of the aluminum particles is 2 to 4 mm, for example, it can be 2 mm, 2.4 mm, 2.8 mm, 3.2 mm, 3.6 mm or 4 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the purity of the aluminum particles is ≥99.99%, for example, it can be 99.99%, 99.992%, 99.994%, 99.996% or 99.998%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the particle size of the niobium pentoxide is 15-20 μm, for example, it can be 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the purity of the niobium pentoxide is ≥99.99%, for example, it can be 99.99%, 99.992%, 99.994%, 99.996% or 99.998%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the potassium chlorate has a particle size of 100-150 μm, such as 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 150 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the purity of the potassium chlorate is ≥99.5%, for example, it can be 99.5%, 99.55%, 99.6%, 99.65% or 99.7%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the particle size of the calcium oxide is 50-100 μm, for example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the purity of the calcium oxide is ≥99%, for example, it can be 99%, 99.1%, 99.2%, 99.3%, 99.4% or 99.5%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the calcium fluoride has a particle size of 100-150 μm, such as 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 150 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the purity of the calcium fluoride is ≥99.95%, such as 99.95%, 99.96%, 99.97% or 99.98%, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the designed reaction heat for preparing aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method is 670-690 kcal / kg, for example, it can be 670 kcal / kg, 675 kcal / kg, 680 kcal / kg, 685 kcal / kg or 690 kcal / kg, etc., but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0032] This invention optimizes the particle size, purity, ratio, reaction heat, and reaction equipment of raw materials during the aluminothermic process, enabling control over the niobium content in aluminum-niobium alloys. This ensures the Nb content meets the target range of 84-88 wt%. The reasons are: 1) Potassium chlorate supplements the reaction heat, ensuring that niobium pentoxide is reduced to aluminum as much as possible, increasing the niobium smelting yield to over 95%; 2) Based on high-purity raw materials and precise slag-forming design, the slag phase is efficiently separated from the aluminum-niobium alloy, reducing the content of impurities such as oxygen and nitrogen in the alloy; 3) By matching particle size and heat, the reaction rate can be controlled (avoiding excessively fast or slow reactions), ensuring a stable reaction and facilitating industrial production (e.g., large-scale preparation of blocky aluminum-niobium alloy ingots).

[0033] As a preferred technical solution of the present invention, the preparation of aluminum-niobium alloy ingots by the external aluminothermic method in step (1) includes the pretreatment, furnace lining, furnace loading and smelting processes performed sequentially.

[0034] Preferably, the pretreatment includes drying the raw materials and refractory materials.

[0035] Preferably, the refractory material includes magnesia bricks and slag, wherein the slag is aluminum-niobium slag, specifically the slag produced during the earlier preparation of aluminum-niobium alloys.

[0036] In this invention, the drying process specifically includes: placing the raw materials and refractory materials separately in a drying kiln for drying; wherein, aluminum granules need to be dried in a separate drying kiln, while other raw materials are placed in another drying kiln after being labeled separately. The reason for this is that drying the aluminum granules separately avoids premature displacement reactions with oxides within the drying kiln, preventing adverse effects on the final smelting reaction state, yield, and grade. The purpose of drying the raw materials is to remove moisture from them, reduce splashing during the smelting process, and ensure that the Nb grade in the aluminum-niobium alloy meets the target range of 84-88%. The purpose of drying the refractory materials is to improve the dryness of the furnace lining and prevent moisture in the furnace from entering the molten alloy and causing splashing.

[0037] Preferably, the drying temperature of the raw material and the refractory material is independently 110-130°C, for example, 110°C, 115°C, 120°C, 125°C or 130°C, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the drying time of the raw material is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the drying time of the refractory material is 4 to 8 hours, for example, it can be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the furnace lining process includes: sequentially laying slag and magnesia bricks in the tank, and then placing the reactor body.

[0041] Preferably, the thickness of the slag is 10-30 mm, for example, it can be 10 mm, 14 mm, 18 mm, 22 mm, 26 mm or 30 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the reaction furnace body includes a magnesium brick crucible and a steel furnace body placed outside the magnesium brick crucible, and the gap between the magnesium brick crucible and the steel furnace body is filled with slag.

[0043] Preferably, the dimensions of the magnesia brick crucible are 400–600 mm × 400–600 mm × 100–150 mm; more specifically, the length of the magnesia brick crucible is 400–600 mm, for example, 400 mm, 440 mm, 480 mm, 520 mm, 560 mm, or 600 mm, but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the width is 400–600 mm, for example, 400 mm, 440 mm, 480 mm, 520 mm, 560 mm, or 600 mm, but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the depth is 100–150 mm, for example, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, or 150 mm, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0044] In this invention, the gap between the magnesium brick crucible and the steel furnace body in the reaction furnace is filled with slag and forms a slope; after the slag filling is completed, the inside of the magnesium brick crucible needs to be cleaned.

[0045] This invention optimizes and limits the materials and volume of the reaction furnace to ensure that the heat preservation and heat dissipation during the aluminothermic reaction reach an ideal state, reducing the introduction of more impurities into the alloy liquid by traditional graphite furnace bodies and uncleaned slag, and providing a stable, safe and efficient environment for the smelting process.

[0046] Preferably, the process includes a mixing treatment before the furnace loading stage.

[0047] Preferably, the mixing process includes: mixing aluminum granules, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride according to the formula amount, and then stirring to obtain a mixed material.

[0048] Preferably, the mixing device is a V-shaped mixer with a rotation speed of 4 to 6 r / min, such as 4 r / min, 4.4 r / min, 4.8 r / min, 5.2 r / min, 5.6 r / min or 6 r / min, but not limited to the listed values; other values ​​not listed within the range are also applicable. The time is 10 to 20 min, such as 10 min, 12 min, 14 min, 16 min, 18 min or 20 min, but not limited to the listed values; other values ​​not listed within the range are also applicable.

[0049] This invention can further improve the uniformity of raw material mixing through mixing treatment, ensure sufficient and effective aluminothermic reaction, and ultimately improve the composition and microstructure uniformity of aluminum-niobium alloy ingots.

[0050] Preferably, the furnace loading process includes: placing the mixed materials into the furnace body in 2 to 4 equal portions, and compacting the materials after each loading to optimize the state of the materials in the furnace and ensure the efficiency, uniformity and safety of the subsequent aluminothermic reaction.

[0051] Preferably, the smelting process further includes a cooling treatment, the cooling treatment time being 12 to 24 hours, for example, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, etc., but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0052] It is worth noting that magnesium strips are used for ignition in the smelting process described in this invention, and after smelting, cooling treatment is required before the ingots are removed from the furnace. The amount of magnesium strip used is 20–50g, for example, 20g, 30g, 40g, or 50g, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0053] As a preferred technical solution of the present invention, the niobium content of the aluminum-niobium alloy ingot in step (1) is 84-88 wt%, for example, it can be 84 wt%, 85 wt%, 86 wt%, 87 wt% or 88 wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the particle size of the aluminum-niobium alloy particles in step (1) is 4 to 8 cm, for example, it can be 4 cm, 5 cm, 6 cm, 7 cm or 8 cm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the surface treatment in step (1) includes sandblasting and polishing performed sequentially.

[0056] Preferably, the sandblasting time is 70 to 90 minutes, for example, 70 minutes, 75 minutes, 80 minutes, 85 minutes or 90 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] In this invention, the oxide film and other impurities on the surface of aluminum-niobium alloy can be removed through surface treatment and crushing treatment, reducing the difficulty of subsequent impurity removal and preparing block materials that meet the requirements of horizontal electron beam melting furnace smelting.

[0058] As a preferred technical solution of the present invention, the vacuum degree of the horizontal electron beam melting in step (2) is 0.01 to 0.05 Pa, for example, it can be 0.01 Pa, 0.02 Pa, 0.03 Pa, 0.04 Pa or 0.05 Pa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, the power of the horizontal electron beam melting in step (2) is 300 to 500 kW, for example, it can be 300 kW, 350 kW, 400 kW, 450 kW or 500 kW, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] Preferably, the horizontal electron beam melting time in step (2) is 40 to 60 minutes, for example, it can be 40 minutes, 44 minutes, 48 ​​minutes, 52 minutes, 56 minutes or 60 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] Preferably, after the horizontal electron beam melting in step (2), a cooling process is further included. The cooling process takes 2 to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] It is worth noting that the horizontal electron beam melting furnace described in step (2) of this invention contains a cubic, recessed copper crucible with dimensions of 25-35mm × 190-210mm × 1400-1600mm; the aluminum-niobium alloy particles are placed inside the copper crucible, and no pieces are allowed to fall off the outer edge of the crucible. Melting is required once on each side during the melting process, while maintaining consistent melting parameters. This invention, through horizontal electron beam melting, can melt aluminum-niobium alloy particles into a long, narrow cubic niobium plate with flat surfaces on both sides, and can also effectively remove a significant amount of low-melting-point impurities and interstitial impurities.

[0063] As a preferred technical solution of the present invention, the number of stacked layers of the smelted niobium plate in step (3) is 5 to 8 layers, for example, it can be 5, 6, 7 or 8 layers.

[0064] Preferably, the vacuum degree of the vacuum diffusion welding in step (3) is 10. -3 ~10 -4 Pa, for example, could be 10. -3 Pa, 2×10 -4 Pa, 4×10 -4 Pa, 6×10 -4 Pa, 8×10 -4 Pa or 10 -4 Pa, etc., but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0065] Preferably, the temperature of vacuum diffusion welding in step (3) is 1500 to 1800°C, for example, it can be 1500°C, 1600°C, 1700°C or 1800°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] Preferably, the heat preservation time for vacuum diffusion welding in step (3) is 2 to 4 hours, for example, it can be 2 hours, 2.4 hours, 2.8 hours, 3.2 hours, 3.6 hours or 4 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] It is worth noting that the vacuum diffusion welding described in step (3) of this invention is carried out in a large vacuum muffle furnace, and after welding, a cuboid smelted niobium ingot with an approximately square cross-section can be obtained. This invention utilizes vacuum diffusion welding technology to weld a thinner smelted niobium plate into a thicker smelted niobium ingot, which can realize the metallurgical bonding from smelted niobium plate to smelted niobium ingot; the risk of introducing other impurities can be eliminated during the welding process, and the obtained smelted niobium ingot is more convenient for subsequent smelting and purification operations in an electric arc melting furnace.

[0068] As a preferred technical solution of the present invention, the current of vacuum arc melting in step (3) is 9 to 10 kA, for example, it can be 9 kA, 9.2 kA, 9.4 kA, 9.6 kA, 9.8 kA or 10 kA, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] Preferably, the voltage of the vacuum arc melting in step (3) is 40 to 45V, for example, it can be 40V, 41V, 42V, 43V, 44V or 45V, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] Preferably, the vacuum degree of the vacuum arc melting in step (3) is 0.01 to 0.03 Pa, for example, it can be 0.01 Pa, 0.015 Pa, 0.02 Pa, 0.025 Pa or 0.03 Pa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] It is worth noting that the present invention can further reduce the content of impurity elements in cuboid niobium ingots by vacuum arc melting, and obtain cylindrical primary niobium ingots.

[0072] As a preferred technical solution of the present invention, the feeding method of the primary niobium ingot in the smelting process in step (4) is vertical feeding.

[0073] Preferably, the smelting process in step (4) includes a first smelting, a second smelting, and a third smelting performed sequentially.

[0074] Preferably, the power of the first melting is 530 to 630 kW, for example, it can be 530 kW, 550 kW, 570 kW, 590 kW, 610 kW or 630 kW, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0075] Preferably, the melting speed of the first melting is 3 to 5 mm / min, for example, it can be 3 mm / min, 3.4 mm / min, 3.8 mm / min, 4.2 mm / min, 4.6 mm / min or 5 mm / min, but is not limited to the listed values. Other values ​​within the range that are not listed are also applicable.

[0076] Preferably, the cooling time for the first melting is 13 to 15 hours, for example, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0077] Preferably, the power of the second melting is 550 to 610 kW, for example, 550 kW, 570 kW, 590 kW or 610 kW, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0078] Preferably, the melting speed of the second melting is 2 to 4 mm / min, for example, it can be 2 mm / min, 2.5 mm / min, 3 mm / min, 3.5 mm / min or 4 mm / min, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0079] Preferably, the cooling time for the second melting is 13 to 15 hours, for example, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] Preferably, the power of the third melting is 600 to 640 kW, for example, it can be 600 kW, 610 kW, 620 kW, 630 kW or 640 kW, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] Preferably, the melting speed of the third melting is 1 to 3 mm / min, for example, it can be 1 mm / min, 1.5 mm / min, 2 mm / min, 2.5 mm / min or 3 mm / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] Preferably, the cooling time for the third melting is 13 to 15 hours, for example, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0083] As a preferred embodiment of the present invention, the first aspect of the present invention provides a method for preparing high-purity niobium ingots using multi-stage refining, the method comprising the following steps:

[0084] (1) Using aluminum granules, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, aluminum-niobium alloy ingots with a niobium content of 84-88 wt% were prepared by the aluminothermic method outside the furnace. Then, surface treatment and crushing treatment were carried out in sequence to obtain aluminum-niobium alloy particles with a particle size of 4-8 cm.

[0085] The mass ratio of aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide, and calcium fluoride is 50–51:96–98:12–14:7–9:3–5; the aluminum particles have a particle size of 2–4 mm and a purity ≥99.99%; the niobium pentoxide has a particle size of 15–20 μm and a purity ≥99.99%; the potassium chlorate has a particle size of 100–150 μm and a purity ≥99.5%; the calcium oxide has a particle size of 50–100 μm and a purity ≥99%; and the calcium fluoride has a particle size of 100–150 μm and a purity ≥99.95%.

[0086] The designed reaction heat for preparing aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method is 670-690 kcal / kg;

[0087] The aluminum-niobium alloy ingot preparation method using the out-of-furnace aluminothermic process includes the following steps in sequence: pretreatment, furnace lining, material mixing, furnace loading, smelting, and cooling.

[0088] The pretreatment includes drying the raw materials and refractory materials; the drying temperature of the raw materials and refractory materials is independently 110-130℃; the drying time of the raw materials is 6-10 hours; and the drying time of the refractory materials is 4-8 hours.

[0089] The furnace construction process includes: laying slag and magnesia bricks with a thickness of 10-30 mm in sequence in the tank, and then placing the reactor body; the reactor body includes a magnesia brick crucible with dimensions of 400-600 mm × 400-600 mm × 100-150 mm and a steel furnace body placed outside the magnesia brick crucible, and the gap between the magnesia brick crucible and the steel furnace body is filled with slag;

[0090] The mixing process includes: mixing aluminum granules, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride according to the formula, and then stirring the mixture for 10 to 20 minutes using a V-shaped mixer at a speed of 4 to 6 r / min to obtain the mixed material;

[0091] The furnace loading process includes: placing the mixed materials into the reactor body in 2 to 4 equal portions, and compacting the materials after each loading;

[0092] The cooling process takes 12 to 24 hours.

[0093] The surface treatment includes sandblasting and polishing processes performed sequentially, with the sandblasting process taking 70 to 90 minutes.

[0094] (2) The aluminum-niobium alloy particles obtained in step (1) are placed in a horizontal electron beam melting furnace for horizontal electron beam melting and cooling treatment to obtain a melted niobium plate;

[0095] The horizontal electron beam melting process involves a vacuum degree of 0.01–0.05 Pa, a power of 300–500 kW, and a time of 40–60 min; the cooling process takes 2–4 h.

[0096] (3) Stack 5 to 8 layers of smelted niobium plates obtained in step (2), and then perform vacuum diffusion welding and vacuum arc melting in sequence to obtain primary niobium ingots;

[0097] The vacuum degree of the vacuum diffusion welding is 10. -3 ~10 -4 Pa, temperature 1500~1800℃, time 2~4h;

[0098] The vacuum arc melting process uses a current of 9–10 kA, a voltage of 40–45 V, and a vacuum level of 0.01–0.03 Pa.

[0099] (4) The primary niobium ingot obtained in step (3) is placed in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot;

[0100] The smelting process includes a first smelting, a second smelting, and a third smelting performed sequentially; the power of the first smelting is 530-630kW, the smelting speed is 3-5mm / min, and the cooling time is 13-15h; the power of the second smelting is 550-610kW, the smelting speed is 2-4mm / min, and the cooling time is 13-15h; the power of the third smelting is 600-640kW, the smelting speed is 1-3mm / min, and the cooling time is 13-15h.

[0101] It is worth noting that the cooling methods mentioned in this invention are all furnace-in-flight cooling.

[0102] Secondly, the present invention provides a high-purity niobium ingot, which is prepared by the method provided in the first aspect.

[0103] Preferably, the purity of the high-purity niobium ingot is ≥99.99%, for example, it can be 99.99%, 99.991%, 99.992%, 99.993%, 99.994% or 99.995%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0104] Preferably, the content of other impurities in the high-purity niobium ingot meets the following indicators:

[0105] O≤5ppm, N≤5ppm, C≤5ppm, H≤1ppm, Zr≤10ppm, Si≤10ppm, Mo≤10ppm, Ta≤30ppm, W≤10ppm, Cr≤10ppm, Ni≤10ppm, Fe≤10ppm, Ti≤10ppm, Cu≤10ppm, Al≤10ppm.

[0106] Preferably, the residual resistivity ratio (RRR) of the high-purity niobium ingot is ≥360, for example, it can be 360, 362, 364, 366, 368, 370 or 378, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0107] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0108] Compared with the prior art, the present invention has the following beneficial effects:

[0109] (1) This invention uses the out-of-furnace aluminothermic reduction method. By optimizing the types and ratios of raw materials, the heat of reaction, the shape and size of the crucible, etc., a high-purity aluminum-niobium alloy with a Nb content of 84-88 wt% was successfully prepared. Furthermore, through the subsequent smelting process, the aluminum-niobium alloy was successfully verified in the field of high-purity metals.

[0110] (2) This invention utilizes vacuum diffusion welding technology to achieve solid-state connection of smelted niobium plates. Under the premise of vacuum environment and no other foreign matter is introduced, it effectively isolates the intrusion of gaseous impurities such as oxygen and nitrogen in the air, welding wire / flux used in traditional fusion welding, explosives used in explosive welding, etc. While preparing the raw material shape that meets the requirements of the electric arc melting furnace, it also ensures the purity of the smelted niobium plate.

[0111] (3) This invention utilizes the coupling of a multi-stage refining process of “aluminothermic method → ​​horizontal electron beam melting → diffusion welding → electric arc melting → dual-gun electron beam melting”. By complementing the advantages and matching the parameters in each process, it successfully breaks through the technical bottleneck of traditional processes in preparing high-purity niobium, which is difficult to achieve both high purity and high RRR value. This provides a new technical path for obtaining high-purity niobium materials with high RRR value and excellent superconducting properties.

[0112] (4) Compared with the vacuum aluminothermic method, the furnace aluminothermic reduction method used in this invention to prepare high Nb content aluminum-niobium alloy has the advantages of low energy consumption, low cost and high production efficiency. In addition, the vacuum diffusion welding does not require expensive equipment and welding wire and involves almost no operation, further reducing production costs. Thus, it effectively solves the technical problems of high energy consumption, high cost and low production efficiency of traditional processes. Attached Figure Description

[0113] Figure 1 This is a process flow diagram of the method for preparing high-purity niobium ingots using multi-stage refining provided in Embodiment 1 of the present invention;

[0114] Figure 2 This is a microstructure diagram of the high-purity niobium ingot provided in Example 1 of the present invention. Detailed Implementation

[0115] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0116] Example 1

[0117] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining, such as... Figure 1 As shown, the method includes the following steps:

[0118] (1) Using aluminum granules, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, aluminum niobium alloy ingots with a niobium content of 86wt% were prepared by the out-of-furnace aluminothermic method. Then, surface treatment and crushing treatment were carried out in sequence to obtain aluminum niobium alloy particles with a particle size of 4-8cm.

[0119] The mass ratio of aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide, and calcium fluoride is 50:97:13:8:4; the aluminum particles have a particle size of 3 mm and a purity of 99.99%; the niobium pentoxide has a particle size of 20 μm and a purity of 99.99%; the potassium chlorate has a particle size of 100 μm and a purity of 99.5%; the calcium oxide has a particle size of 50 μm and a purity of 99%; and the calcium fluoride has a particle size of 100 μm and a purity of 99.95%.

[0120] The designed reaction heat for the preparation of aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method is 680 kcal / kg;

[0121] The aluminum-niobium alloy ingot preparation method using the out-of-furnace aluminothermic process includes the following steps in sequence: pretreatment, furnace lining, material mixing, furnace loading, smelting, and cooling.

[0122] The pretreatment includes drying the raw materials and refractory materials; the drying temperature of the raw materials and refractory materials is 120°C independently; the drying time of the raw materials is 8 hours; and the drying time of the refractory materials is 6 hours.

[0123] The furnace construction process includes: laying slag and magnesia bricks with a thickness of 20mm in sequence in the tank, and then placing the reaction furnace body; the reaction furnace body includes a magnesia brick crucible with dimensions of 500mm×500mm×120mm and a steel furnace body placed outside the magnesia brick crucible, and the gap between the magnesia brick crucible and the steel furnace body is filled with slag.

[0124] The mixing process includes: mixing aluminum granules, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride according to the formula, and then stirring the mixture for 15 minutes at a speed of 5 r / min using a V-shaped mixer to obtain the mixed material;

[0125] The furnace loading process includes: placing the mixed materials into the reactor body in three equal portions, and compacting the materials after each loading.

[0126] The cooling process takes 18 hours.

[0127] The surface treatment includes sandblasting and polishing performed sequentially, with the sandblasting process taking 80 minutes.

[0128] (2) The aluminum-niobium alloy particles obtained in step (1) are placed in a horizontal electron beam melting furnace for horizontal electron beam melting and cooling treatment to obtain a melted niobium plate;

[0129] The horizontal electron beam melting process involves a vacuum of 0.05 Pa, a power of 380 kW, and a melting time of 50 min; the cooling process takes 3 h.

[0130] (3) Stack 6 layers of smelted niobium plates obtained in step (2), and then perform vacuum diffusion welding and vacuum arc melting in sequence to obtain primary niobium ingots;

[0131] The vacuum degree of the vacuum diffusion welding is 10. -3 Pa, temperature 1600℃, time 3h;

[0132] The vacuum arc melting process uses a current of 10kA, a voltage of 42V, and a vacuum level of 0.01Pa.

[0133] (4) The primary niobium ingot obtained in step (3) is placed in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot;

[0134] The smelting process includes a first smelting, a second smelting, and a third smelting performed sequentially; the first smelting has a power of 580kW, a smelting speed of 4mm / min, and a cooling time of 14h; the second smelting has a power of 610kW, a smelting speed of 3mm / min, and a cooling time of 13h; and the third smelting has a power of 640kW, a smelting speed of 1mm / min, and a cooling time of 15h.

[0135] The microstructure of the high-purity niobium ingot provided in this embodiment is as follows: Figure 2 As shown, (a) is a scanning electron microscope (SEM) image, and (b) and (c) are transmission electron microscope (TEM) images. According to... Figure 2 It can be seen that the high-purity niobium ingot provided in this embodiment has a pure microstructure and is free of microscopic inclusions.

[0136] Example 2

[0137] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining, the method comprising the following steps:

[0138] (1) Using aluminum granules, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, aluminum niobium alloy ingots with a niobium content of 84wt% were prepared by the out-of-furnace aluminothermic method. Then, surface treatment and crushing treatment were carried out in sequence to obtain aluminum niobium alloy particles with a particle size of 5-7cm.

[0139] The mass ratio of aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide, and calcium fluoride is 51:96:12:7:5; the aluminum particles have a particle size of 2 mm and a purity of 99.99%; the niobium pentoxide has a particle size of 15 μm and a purity of 99.99%; the potassium chlorate has a particle size of 120 μm and a purity of 99.55%; the calcium oxide has a particle size of 80 μm and a purity of 99.2%; and the calcium fluoride has a particle size of 130 μm and a purity of 99.96%.

[0140] The designed reaction heat for the preparation of aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method is 670 kcal / kg;

[0141] The aluminum-niobium alloy ingot preparation method using the out-of-furnace aluminothermic process includes the following steps in sequence: pretreatment, furnace lining, material mixing, furnace loading, smelting, and cooling.

[0142] The pretreatment includes drying the raw materials and refractory materials; the drying temperature of the raw materials and refractory materials is 110°C independently; the drying time of the raw materials is 10 hours; and the drying time of the refractory materials is 8 hours.

[0143] The furnace construction process includes: laying slag and magnesia bricks with a thickness of 10mm in sequence in the tank, and then placing the reaction furnace body; the reaction furnace body includes a magnesia brick crucible with dimensions of 400mm×400mm×150mm and a steel furnace body placed outside the magnesia brick crucible, and the gap between the magnesia brick crucible and the steel furnace body is filled with slag.

[0144] The mixing process includes: mixing aluminum granules, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride according to the formula, and then stirring the mixture for 20 minutes at a speed of 4 r / min using a V-shaped mixer to obtain the mixed material;

[0145] The loading process includes: placing the mixed materials into the reactor body in two equal portions, and compacting the materials after each loading.

[0146] The cooling process takes 20 hours.

[0147] The surface treatment includes sandblasting and polishing performed sequentially, with the sandblasting process taking 70 minutes.

[0148] (2) The aluminum-niobium alloy particles obtained in step (1) are placed in a horizontal electron beam melting furnace for horizontal electron beam melting and cooling treatment to obtain a melted niobium plate;

[0149] The horizontal electron beam melting process involves a vacuum of 0.02 Pa, a power of 450 kW, and a melting time of 60 min; the cooling process takes 2.5 h.

[0150] (3) Stack 5 layers of smelted niobium plates obtained in step (2), and then perform vacuum diffusion welding and vacuum arc melting in sequence to obtain primary niobium ingots;

[0151] The vacuum degree of the vacuum diffusion welding is 5×10⁻⁶. -4 Pa, temperature 1700℃, time 2h;

[0152] The vacuum arc melting process uses a current of 9kA, a voltage of 45V, and a vacuum level of 0.03Pa.

[0153] (4) The primary niobium ingot obtained in step (3) is placed in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot;

[0154] The smelting process includes a first smelting, a second smelting, and a third smelting performed sequentially; the first smelting has a power of 530kW, a smelting speed of 3mm / min, and a cooling time of 13h; the second smelting has a power of 550kW, a smelting speed of 2mm / min, and a cooling time of 13h; the third smelting has a power of 600kW, a smelting speed of 1mm / min, and a cooling time of 13h.

[0155] Example 3

[0156] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining, the method comprising the following steps:

[0157] (1) Using aluminum granules, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, aluminum niobium alloy ingots with a niobium content of 88wt% were prepared by the out-of-furnace aluminothermic method. Then, surface treatment and crushing treatment were carried out in sequence to obtain aluminum niobium alloy particles with a particle size of 5-8cm.

[0158] The mass ratio of aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide, and calcium fluoride is 50.5:98:14:9:3; the aluminum particles have a particle size of 4 mm and a purity of 99.99%; the niobium pentoxide has a particle size of 20 μm and a purity of 99.99%; the potassium chlorate has a particle size of 150 μm and a purity of 99.5%; the calcium oxide has a particle size of 100 μm and a purity of 99%; and the calcium fluoride has a particle size of 150 μm and a purity of 99.95%.

[0159] The designed reaction heat for the preparation of aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method is 690 kcal / kg;

[0160] The aluminum-niobium alloy ingot preparation method using the out-of-furnace aluminothermic process includes the following steps in sequence: pretreatment, furnace lining, material mixing, furnace loading, smelting, and cooling.

[0161] The pretreatment includes drying the raw materials and refractory materials; the drying temperature of the raw materials and refractory materials is 130°C independently; the drying time of the raw materials is 6 hours; and the drying time of the refractory materials is 4 hours.

[0162] The furnace construction process includes: laying slag and magnesia bricks with a thickness of 30mm in sequence in the tank, and then placing the reaction furnace body; the reaction furnace body includes a magnesia brick crucible with dimensions of 600mm×600mm×100mm and a steel furnace body placed outside the magnesia brick crucible, and the gap between the magnesia brick crucible and the steel furnace body is filled with slag.

[0163] The mixing process includes: mixing aluminum granules, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride according to the formula, and then stirring the mixture for 10 minutes at a speed of 6 r / min using a V-shaped mixer to obtain the mixed material;

[0164] The furnace loading process includes: placing the mixed materials into the reactor body in four equal portions, and compacting the materials after each loading.

[0165] The cooling process takes 24 hours.

[0166] The surface treatment includes sandblasting and polishing processes performed sequentially, with the sandblasting process taking 90 minutes.

[0167] (2) The aluminum-niobium alloy particles obtained in step (1) are placed in a horizontal electron beam melting furnace for horizontal electron beam melting and cooling treatment to obtain a melted niobium plate;

[0168] The horizontal electron beam melting process involves a vacuum of 0.05 Pa, a power of 300 kW, and a melting time of 40 min; the cooling process takes 4 h.

[0169] (3) Stack 8 layers of smelted niobium plates obtained in step (2), and then perform vacuum diffusion welding and vacuum arc melting in sequence to obtain primary niobium ingots;

[0170] The vacuum degree of the vacuum diffusion welding is 10. -4 Pa, temperature 1800℃, time 4h;

[0171] The vacuum arc melting process uses a current of 9.5 kA, a voltage of 40 V, and a vacuum level of 0.02 Pa.

[0172] (4) The primary niobium ingot obtained in step (3) is placed in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot;

[0173] The smelting process includes a first smelting, a second smelting, and a third smelting performed sequentially; the first smelting has a power of 630kW, a smelting speed of 5mm / min, and a cooling time of 15h; the second smelting has a power of 610kW, a smelting speed of 4mm / min, and a cooling time of 15h; the third smelting has a power of 640kW, a smelting speed of 3mm / min, and a cooling time of 15h.

[0174] Example 4

[0175] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0176] In this embodiment, the mass ratio of aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride in step (1) is adjusted to 40:100:15:10:6, and the designed reaction heat is 700 kcal / kg.

[0177] Example 5

[0178] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0179] In this embodiment, the size of the magnesium brick crucible described in step (1) is adjusted to 350mm×400mm×80mm.

[0180] The niobium content in the aluminum-niobium alloy ingot provided in this embodiment is 78 wt%.

[0181] Example 6

[0182] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0183] In this embodiment, the vacuum degree of the horizontal electron beam melting in step (2) is adjusted to 0.08 Pa and the power is adjusted to 290 kW.

[0184] Example 7

[0185] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0186] In this embodiment, the vacuum degree of the horizontal electron beam melting in step (2) is adjusted to 0.03 Pa and the power is adjusted to 600 kW.

[0187] Example 8

[0188] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0189] In this embodiment, the vacuum degree of the vacuum diffusion welding in step (3) is 10. -2 Pa, temperature 1400℃, time 5h.

[0190] Example 9

[0191] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0192] In this embodiment, the vacuum degree of the vacuum diffusion welding in step (3) is 10. -3 Pa, temperature 2000℃, time 1h.

[0193] Example 10

[0194] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0195] In this embodiment, the vacuum arc melting in step (3) uses a current of 12kA, a voltage of 50V, and a vacuum degree of 0.05Pa.

[0196] Example 11

[0197] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0198] In this embodiment, the vacuum arc melting current in step (3) is 8kA, the voltage is 50V, and the vacuum degree is 0.03Pa.

[0199] Example 12

[0200] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0201] In this embodiment, the melting process in the dual-gun electron beam melting furnace described in step (4) is adjusted to: a single melting is carried out under the conditions of 600kW power and 2mm / min speed.

[0202] Example 13

[0203] This embodiment provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Embodiment 1 is that:

[0204] In this embodiment, the melting process in the dual-gun electron beam melting furnace described in step (4) is adjusted as follows: the first melting power is 500kW and the melting speed is 6mm / min; the second melting power is 520kW and the melting speed is 5mm / min; the third melting power is 650kW and the melting speed is 4mm / min.

[0205] Comparative Example 1

[0206] This comparative example provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Example 1 is that:

[0207] This comparative example modifies the preparation of aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method in step (1) to the preparation of aluminum-niobium alloy ingots in a vacuum reactor; wherein, the vacuum degree during the preparation process is 0.05 Pa.

[0208] Comparative Example 2

[0209] This comparative example provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Example 1 is that:

[0210] This comparative example modifies the vacuum diffusion welding described in step (3) to electron beam welding.

[0211] Comparative Example 3

[0212] This comparative example provides a method for preparing high-purity niobium ingots using multi-stage refining. The only difference between this method and Example 1 is that:

[0213] This comparative example omits the smelting process described in step (4).

[0214] The high-purity niobium ingots provided in the above embodiments and comparative examples were subjected to compositional analysis and RRR measurement, and the results are shown in Table 1.

[0215] Table 1

[0216]

[0217]

[0218] According to Table 1, the following points can be observed:

[0219] (1) Comprehensive analysis of Examples 1-3 shows that the present invention prepares niobium ingots with both high purity and high RRR value by coupling multi-stage refining processes and complementing each refining process with complementary advantages and parameter matching.

[0220] (2) Comprehensive analysis of Examples 1, 4-5 and Comparative Example 1 shows that the furnace-outside aluminothermic method provided by the present invention is one of the decisive factors in the preparation of high-grade aluminum-niobium alloy ingots. Compared with the furnace-outside aluminothermic method, when the vacuum aluminothermic method provided by Comparative Example 1 is used, the product obtained after the aluminothermic reaction is not separated into slag and gold, and aluminum-niobium alloy blocks cannot be obtained.

[0221] In addition, factors such as the raw material ratio and the size of the magnesium brick crucible during the aluminothermic process can affect the niobium content in the resulting aluminum-niobium alloy, thereby affecting the purity and RRR value of the niobium ingot. More specifically, using the raw material ratio and designed reaction heat provided in Example 4 will lead to severe aluminothermic reaction splashing, causing the alloy liquid and slag to mix, making it difficult to separate the slag from the metal and thus failing to obtain the aluminum-niobium alloy ingot.

[0222] (3) Comprehensive analysis of Examples 6-13 shows that the parameters of each step in the niobium ingot preparation process will affect the grade of the obtained niobium ingot, thus proving the necessity of limiting the process parameters in each step of the preparation process.

[0223] (4) Comprehensive analysis of Example 1 and Comparative Example 2 shows that compared with vacuum diffusion welding, electron beam welding requires a specific electron beam furnace, which has extremely high production costs. It is suitable for butt welding of plates. Moreover, the high-energy beam of electron beam welding will generate local high temperature, which may lead to large thermal stress and deformation. It is not only difficult to ensure the requirements of arc melting on the shape of raw materials, but also easy to introduce high melting point impurity elements and interstitial impurity elements into the area around the weld.

[0224] (5) Comprehensive analysis of Example 1 and Comparative Example 3 shows that the dual-gun electron beam melting process is mainly used to deeply remove impurity elements in niobium ingots. If the melting process in the dual-gun electron beam melting furnace is omitted, the impurity content in the obtained niobium ingot will be too high and it will be difficult to achieve the RRR of more than 360.

[0225] Omitting any refining process will reduce the purity of niobium ingots, further demonstrating the synergistic effect of the multi-stage refining process of "horizontal electron beam melting → diffusion welding → electric arc melting → dual-gun electron beam melting", providing a new technical path for obtaining high-purity niobium materials with high RRR values ​​and excellent superconducting properties.

[0226] In summary, this invention uses aluminum granules, niobium pentoxide, exothermic agents, slag-forming agents, etc. as raw materials, and adopts a multi-stage refining process coupling system of "aluminothermic method → ​​horizontal electron beam melting → diffusion welding → electric arc melting → dual-gun electron beam melting" to achieve stable production of high-purity niobium with high RRR (residual resistivity ratio). This effectively solves the technical problems of high energy consumption, high cost, and low production efficiency in traditional processes.

[0227] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing a high purity niobium ingot using multi-stage refining, characterized by, The method includes the following steps: (1) Using aluminum granules, niobium pentoxide, exothermic agent and slag-forming agent as raw materials, aluminum-niobium alloy ingots with niobium content of 84~88wt% are prepared by the aluminothermic method outside the furnace. Then, surface treatment and crushing treatment are carried out in sequence to obtain aluminum-niobium alloy particles with a particle size of 4~8cm. The exothermic agent includes potassium chlorate; the slag-forming agent includes calcium oxide and calcium fluoride; the mass ratio of aluminum particles, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride is 50~51:96~98:12~14:7~9:3~5; the designed reaction heat of the aluminothermic process for preparing aluminum-niobium alloy ingots is 670~690 kcal / kg; The aluminothermic process for preparing aluminum-niobium alloy ingots includes a pretreatment, furnace lining, furnace loading, and smelting process performed sequentially. The pretreatment includes drying the raw materials and refractory materials. The furnace lining process includes laying slag and magnesia bricks sequentially in a tank, and then placing the reaction furnace body. The reaction furnace body includes a magnesia brick crucible and a steel furnace body placed around the magnesia brick crucible, with slag filling the gap between the magnesia brick crucible and the steel furnace body. The smelting process also includes a cooling process, which lasts for 12-24 hours. (2) The aluminum-niobium alloy particles obtained in step (1) are placed in a horizontal electron beam melting furnace for horizontal electron beam melting to obtain a melted niobium plate; (3) Stack the smelted niobium plates obtained from several steps (2), and then perform vacuum diffusion welding and vacuum arc melting in sequence to obtain primary niobium ingots; (4) The primary niobium ingot obtained in step (3) is placed in a double-gun electron beam melting furnace for melting treatment to obtain the high-purity niobium ingot.

2. The method for producing a high-purity niobium ingot using multi-stage refining according to claim 1, characterized by, The process prior to the furnace loading stage also includes material mixing; The mixing process includes: mixing aluminum granules, niobium pentoxide, exothermic agent, calcium oxide and calcium fluoride according to the formula, and then stirring to obtain a mixed material.

3. The method for producing a high purity niobium ingot using multi-stage refining according to claim 1, characterized by, The vacuum degree of the horizontal electron beam melting in step (2) is 0.01~0.05 Pa; The power of the horizontal electron beam melting in step (2) is 300~500kW; The horizontal electron beam melting time in step (2) is 40~60 min.

4. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 1, characterized in that, The number of stacked layers of the smelted niobium plates in step (3) is 5 to 8.

5. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 1, characterized in that, The vacuum degree of the vacuum diffusion welding in step (3) is 10. -3 ~10 -4 Pa; The temperature for vacuum diffusion welding in step (3) is 1500~1800℃; The heat preservation time for vacuum diffusion welding in step (3) is 2~4h.

6. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 1, characterized in that, The current for vacuum arc melting in step (3) is 9~10kA; The voltage for vacuum arc melting in step (3) is 40~45V; The vacuum degree of the vacuum arc melting in step (3) is 0.01~0.03 Pa.

7. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 1, characterized in that, In step (4), the primary niobium ingot is fed vertically during the smelting process.

8. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 1, characterized in that, The smelting process in step (4) includes a first smelting, a second smelting, and a third smelting performed sequentially.

9. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 8, characterized in that, The power of the first smelting is 530~630kW; The melting speed of the first melting is 3~5 mm / min; The cooling time for the first melting is 13-15 hours.

10. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 8, characterized in that, The power of the second melting process is 550~610kW; The melting speed for the second melting process is 2-4 mm / min; The cooling time for the second melting is 13-15 hours.

11. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 8, characterized in that, The power of the third smelting is 600~640kW; The melting speed for the third melting process is 1~3 mm / min; The cooling time for the third melting process is 13-15 hours.

12. A high-purity niobium ingot, characterized in that, The high-purity niobium ingot is prepared by the method according to any one of claims 1-11; The purity of the high-purity niobium ingot is ≥99.99%, and the content of other impurities meets the following indicators: O≤5ppm, N≤5ppm, C≤5ppm, H≤1ppm, Zr≤10ppm, Si≤10ppm, Mo≤10ppm, Ta≤30ppm, W≤10ppm, Cr≤10ppm, Ni≤10ppm, Fe≤10ppm, Ti≤10ppm, Cu≤10ppm, Al≤10ppm.

13. The high-purity niobium ingot according to claim 12, characterized in that, The residual resistivity ratio of the high-purity niobium ingot is ≥360.

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