Method for preparing high-purity niobium ingot through multi-stage refining and high-purity niobium ingot

Abstract

The invention provides a method for preparing a high-purity niobium ingot by utilizing multistage refining and the high-purity niobium ingot, and the method comprises the following steps: (1) taking aluminum particles, niobium pentoxide, a heat generating agent and a slag former as raw materials, preparing an aluminum-niobium alloy ingot by adopting an exothermic method outside a furnace, and then carrying out surface treatment and crushing treatment to obtain aluminum-niobium alloy particles; (2) the aluminum-niobium alloy particles are subjected to horizontal electron beam smelting, and a smelted niobium plate is obtained; (3) stacking a plurality of smelting niobium plates, and then sequentially performing vacuum diffusion welding and vacuum arc smelting to obtain a primary niobium ingot; and (4) the primary niobium ingot is placed in a double-gun electron beam smelting furnace to be smelted, and the high-purity niobium ingot is obtained. The stable production of the high-RRR value high-purity niobium is realized by adopting a multi-stage refining process coupling system of an aluminothermy method, horizontal electron beam melting, diffusion welding, electric arc melting and double-gun electron beam melting, and the technical problems of high energy consumption, high cost, low production efficiency and the like in the traditional process are effectively solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rare metal smelting and purification, and relates to a preparation method of high-purity niobium ingot, in particular to a method for preparing high-purity niobium ingot by using multi-stage refining and high-purity niobium ingot. BACKGROUND

[0002] Niobium is a silvery gray, tough, plastic refractory metal. Because it has a high critical temperature (about 9.26K), a high superheating critical field (about 0.2T), and good processing and forming properties, it has become a key raw material for superconducting star materials NbTi and Nb3Sn in the field of superconductivity, and has broad application prospects in high-tech frontier fields such as human body nuclear magnetic resonance imaging instruments, nuclear magnetic resonance spectrometers, magnetically controlled single crystal silicon, international thermonuclear experimental reactor, and accelerators.

[0003] The purity and RRR value (residual resistivity ratio) of niobium are related to the content and types of impurity elements in niobium, and directly determine the advantages and disadvantages of its physical and chemical properties. These properties will have a substantial impact on the quality reliability of the terminal application field through radiation effects. Therefore, it is imperative to develop high-purity niobium with high RRR, and it is urgent to speed up the development.

[0004] At present, the preparation methods of high-purity niobium show diversified characteristics.

[0005] CN 115717254A discloses a method for preparing high-purity niobium by molten salt electrolysis, that is, first mixing niobium oxide with a carbonaceous reducing agent to form a shape, then sintering it into a soluble anode niobium-carbon-based solid solution, subsequently forming an electrolysis system with the solid solution, a graphite electrode, and a molten salt electrolyte, and performing electrolysis to obtain high-purity niobium. However, the molten salt electrolysis method for preparing high-purity niobium has the problems of serious environmental pollution, high electrolysis energy consumption, high equipment requirements and maintenance costs due to the strong corrosiveness of the molten salt electrolyte, and the difficulty in obtaining extremely high-purity products due to the introduction of carbon impurities by using carbonaceous reducing agents and improper impurity removal.

[0006] CN 104480319A discloses a method for preparing high-purity niobium by electron beam melting, that is, by adjusting the specific electrical energy and vacuum degree and other key indicators in the vacuum electron beam melting process, the niobium strip is subjected to 3-7 times of vacuum electron beam melting to obtain high-purity niobium. However, the electron beam melting method for preparing high-purity niobium has high requirements for the content of high-melting-point impurities such as tantalum and tungsten in the raw material. If the content of these impurities in the niobium strip exceeds the standard, it is difficult to effectively remove them by this method. At the same time, the long time and multiple times of electron beam melting result in high loss of base metal niobium, low production efficiency, and high energy consumption.

[0007] CN 117684024A discloses a method for preparing high-purity niobium by physical purification, i.e., first, niobium raw material produced by vacuum aluminum thermal method is sequentially subjected to acid washing, water washing and drying treatment, then is welded into an electrode for vacuum electron beam melting, and then is mechanically processed to obtain a smooth niobium ingot, and finally is subjected to degassing treatment to obtain high-purity niobium. However, the vacuum aluminum thermal method has low production efficiency and high energy consumption, and the subsequent treatment process of the niobium raw material is complicated and long, which directly leads to low production efficiency. Meanwhile, the mechanical processing process may introduce new impurities, and the degassing treatment is difficult to control to achieve the ideal product purity.

[0008] In summary, it has become the focus of the current research in this field to develop a high-purity niobium material with a high RRR value while effectively avoiding the deficiencies in the above-mentioned published patents. SUMMARY

[0009] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for preparing high-purity niobium ingot by multi-stage refining and high-purity niobium ingot. The present application uses aluminum particles, niobium pentoxide, a heating agent, a slag forming agent, etc. as raw materials, and adopts a multi-stage refining process coupling system of "aluminum thermal method→horizontal electron beam melting→diffusion welding→arc melting→double-gun electron beam melting" to realize the stable production of high-purity niobium with a high RRR value (residual resistivity ratio), effectively solving the technical problems of high energy consumption, high cost and low production efficiency existing in the traditional process.

[0010] To achieve the purpose of the present application, the following technical solutions are adopted:

[0011] In a first aspect, the present application provides a method for preparing high-purity niobium ingot by multi-stage refining, which comprises the following steps:

[0012] (1) Using aluminum particles, niobium pentoxide, a heating agent and a slag forming agent as raw materials, an aluminum-niobium alloy ingot is prepared by an off-furnace aluminum thermal method, and then is sequentially subjected to surface treatment and crushing treatment 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 molten niobium plate;

[0014] (3) Several molten niobium plates obtained in step (2) are stacked, and then are sequentially subjected to vacuum diffusion welding and vacuum arc melting to obtain a primary niobium ingot;

[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 the present application, the furnace outside aluminum thermal method in step (1) can prepare aluminum niobium alloy with high grade Nb as the initial link, while preliminarily reducing the content of each impurity element introduced by the raw material; in step (2), horizontal electron beam melting not only changes the particles obtained by post-processing of the aluminum thermal method into plates (convenient for subsequent processing), but also further reduces the gap element impurities and low melting point element impurities by virtue of the deep penetration characteristics of high energy beam, and preliminarily realizes the composition homogenization; in step (3), diffusion welding realizes the preparation of cubic ingots by eliminating the micro-pores and other defects generated in the previous melting without introducing any foreign matter, meeting the requirements of arc melting on the shape of the raw material; the arc melting in step (3) not only helps to form a cylinder to meet the requirements of the subsequent double-gun electron beam melting vertical feeding mode on the shape of the raw material, but also further homogenizes the material and reduces the content of each impurity element; in step (4), the double-gun electron beam melting furnace utilizes the synergistic effect of double beams to realize the deep removal and accurate control of residual trace impurities, and significantly improves the purity of niobium ingot.

[0017] The present application provides a multi-stage refining process combination of "aluminum thermal method→horizontal electron beam melting→diffusion welding→arc melting→double-gun electron beam melting", which successfully breaks through the technical bottleneck of traditional process in high-purity niobium preparation, that is, it is difficult to balance high purity and high RRR value, and provides a new technical path for obtaining high RRR value high-purity niobium material with excellent superconducting performance.

[0018] As a preferred technical solution of the present application, the heat generating 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 particles, niobium pentoxide, heat generating 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, and other values not listed in the value range are also applicable.

[0021] Preferably, the particle size of the aluminum particles is 2-4 mm, for example, it can be 2 mm, 2.4 mm, 2.8 mm, 3.2 mm, 3.6 mm or 4 mm, etc., but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0022] Preferably, the purity of the aluminum particles is ≥ 99.99%, such as can be 99.99%, 99.992%, 99.994%, 99.996%, or 99.998%, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0023] Preferably, the particle size of the niobium pentoxide is 15-20 μm, such as can be 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0024] Preferably, the purity of the niobium pentoxide is ≥ 99.99%, such as can be 99.99%, 99.992%, 99.994%, 99.996%, or 99.998%, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0025] Preferably, the particle size of the potassium chlorate is 100-150 μm, such as can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, or 150 μm, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0026] Preferably, the purity of the potassium chlorate is ≥ 99.5%, such as can be 99.5%, 99.55%, 99.6%, 99.65%, or 99.7%, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0027] Preferably, the particle size of the calcium oxide is 50-100 μm, such as can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0028] Preferably, the purity of the calcium oxide is ≥ 99%, such as can be 99%, 99.1%, 99.2%, 99.3%, 99.4%, or 99.5%, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0029] Preferably, the particle size of the calcium fluoride is 100-150 μm, such as can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, or 150 μm, etc., but is not limited to the listed values, other values not listed within the range of values are equally applicable.

[0030] Preferably, the purity of the calcium fluoride is ≥ 99.95%, for example, it can be 99.95%, 99.96%, 99.97%, or 99.98%, etc., but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0031] Preferably, the design reaction heat of the furnace outside aluminothermic process for preparing aluminum niobium alloy ingot 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, and other values not listed within the value range are also applicable.

[0032] The optimization of the particle size, purity, ratio, reaction heat, or reaction equipment of the raw materials in the furnace outside aluminothermic process can realize the regulation of the niobium content in the aluminum niobium alloy, and ensure that the Nb content in the aluminum niobium alloy meets the target of 84-88 wt%. The reasons are as follows: 1) The reaction heat is supplemented by potassium chlorate to ensure that the niobium pentoxide is reduced by aluminum as much as possible, and the smelting yield of niobium is increased to more than 95%; 2) Based on high-purity raw materials and precise slag-making design, the slag phase is efficiently separated from the aluminum niobium alloy, and the content of impurity elements such as oxygen and nitrogen in the aluminum niobium alloy is reduced; 3) The matching of particle size and heat can control the reaction rate (avoiding too fast or too slow), and ensure that the reaction proceeds smoothly, which is convenient for industrial production (such as large-scale preparation of block-shaped aluminum niobium alloy ingot).

[0033] As a preferred technical solution of the present application, the step (1) of the furnace outside aluminothermic process for preparing aluminum niobium alloy ingot comprises the following steps in sequence: pretreatment, furnace lining, furnace loading, and smelting.

[0034] Preferably, the pretreatment comprises drying treatment of the raw materials and refractory materials.

[0035] Preferably, the refractory material comprises magnesium bricks and slag, and the slag is aluminum niobium slag, specifically the slag generated in the previous preparation process of the aluminum niobium alloy.

[0036] In the present application, the drying treatment specifically comprises: placing the raw materials and refractory materials in drying kilns respectively for drying treatment; wherein the aluminum particles are placed in a drying kiln for drying alone, and the other raw materials are placed in another drying kiln for drying after being labeled respectively. The reason is that the drying of aluminum particles alone can avoid the displacement reaction with oxides in the drying kiln, preventing adverse effects on the final smelting reaction state, yield, and grade. The purpose of drying treatment of the raw materials is to remove the moisture in the raw materials, reduce the splashing phenomenon in the smelting process, and ensure that the Nb grade in the aluminum niobium alloy meets the target of 84-88. The purpose of drying treatment of the refractory materials is to improve the drying degree of the lining in the reaction furnace, and avoid the water in the furnace from entering the alloy liquid in the smelting reaction to cause splashing.

[0037] Preferably, the drying temperature of the raw material and the refractory material is independently 110-130℃, for example, it can be 110℃, 115℃, 120℃, 125℃ or 130℃, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0038] Preferably, the drying time of the raw material is 6-10h, for example, it can be 6h, 7h, 8h, 9h or 10h, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0039] Preferably, the drying time of the refractory material is 4-8h, for example, it can be 4h, 5h, 6h, 7h or 8h, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0040] Preferably, the furnace building process comprises: laying the slag and the magnesia brick in the groove in turn, and then placing the reaction furnace body.

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

[0042] Preferably, the reaction furnace body comprises a magnesia brick crucible and a steel furnace body outside the periphery of the magnesia brick crucible, and the gap between the magnesia brick crucible and the steel furnace body is filled with slag.

[0043] Preferably, the size of the magnesia brick crucible is 400-600mm x 400-600mm x 100-150mm; more specifically, the length of the magnesia brick crucible is 400-600mm, for example, it can be 400mm, 440mm, 480mm, 520mm, 560mm or 600mm, etc., but not limited to the listed values, other values not listed in the value range are also applicable; the width is 400-600mm, for example, it can be 400mm, 440mm, 480mm, 520mm, 560mm or 600mm, etc., but not limited to the listed values, other values not listed in the value range are also applicable; the depth is 100-150mm, for example, it can be 100mm, 110mm, 120mm, 130mm, 140mm or 150mm, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

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

[0045] The application can further ensure the heat preservation and heat dissipation of the aluminum thermal reaction to reach an ideal state by optimizing the material and volume of the reaction furnace body, and reduce the introduction of more impurities into the alloy liquid by the traditional graphite furnace body and the furnace slag which is not cleaned, thereby providing a stable, safe and efficient environment for the smelting process.

[0046] Preferably, the furnace loading step further comprises a mixing treatment.

[0047] Preferably, the mixing treatment comprises: mixing aluminum particles, niobium pentoxide, a heating agent, calcium oxide and calcium fluoride according to the formula amount, and then performing stirring treatment to obtain a mixture.

[0048] Preferably, the stirring treatment device is a V-shaped mixer, and the rotation speed is 4-6 r / min, for example, which can be 4 r / min, 4.4 r / min, 4.8 r / min, 5.2 r / min, 5.6 r / min or 6 r / min, but is not limited to the listed values, and other values not listed in the value range are also applicable; the time is 10-20 min, for example, which can be 10 min, 12 min, 14 min, 16 min, 18 min or 20 min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0049] The application can further improve the uniformity of the raw material mixing through the mixing treatment, ensure the full and effective aluminum thermal reaction, and finally improve the composition and uniformity of the aluminum-niobium alloy ingot.

[0050] Preferably, the furnace loading step comprises: placing the mixture in the reaction furnace body in 2-4 equal parts, and tamping the material after each placement to optimize the state of the material in the furnace and ensure the efficiency, uniformity and safety of the subsequent aluminum thermal reaction.

[0051] Preferably, the smelting step further comprises a cooling treatment, and the cooling treatment time is 12-24 h, for example, which can be 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0052] It is worth noting that a magnesium strip is used for ignition in the smelting step of the application, and after smelting, cooling treatment is required before the furnace is discharged to take the ingot. The amount of the magnesium strip used is 20-50 g, for example, which can be 20 g, 30 g, 40 g or 50 g, but is not limited to the listed values, and other values not listed in the value range are also applicable.

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

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

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

[0056] Preferably, the sandblasting time is 70-90min, for example, it can be 70min, 75min, 80min, 85min or 90min, etc., but not limited to the listed values, other values not listed within the value range are also applicable.

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

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

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

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

[0061] Preferably, the horizontal electron beam melting in step (2) further includes a cooling treatment, and the cooling treatment time is 2-4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, etc., but not limited to the listed values, other values not listed within the value range are also applicable.

[0062] It is worth mentioning that the horizontal electron beam smelting furnace in step (2) of the present application is internally provided with a cuboid, grooved copper crucible with a size of 25-35mmx190-210mmx1400-1600mm; the aluminum-niobium alloy particles are internally provided in the copper crucible, and no bulk is allowed to drop outside the crucible edge. During the smelting process, the front and back surfaces need to be smelted once respectively, and the smelting parameters remain consistent. The present application can not only smelt the aluminum-niobium alloy particles into narrow and long cuboid, smooth front and back surface smelted niobium plates, but also effectively realize the substantial removal of low melting point impurity elements and interstitial impurity elements.

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

[0064] Preferably, the vacuum degree of the vacuum diffusion welding in step (3) is 10 -3 ~10 -4 Pa, for example, it can be 10 -3 Pa, 2x10 -4 Pa, 4x10 -4 Pa, 6x10 -4 Pa, 8x10 -4 Pa or 10 -4 Pa, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0065] Preferably, the temperature of the vacuum diffusion welding in step (3) is 1500-1800℃, for example, it can be 1500℃, 1600℃, 1700℃ or 1800℃, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0066] Preferably, the holding time of the vacuum diffusion welding in step (3) is 2-4h, for example, it can be 2h, 2.4h, 2.8h, 3.2h, 3.6h or 4h, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0067] It is worth mentioning that the vacuum diffusion welding in step (3) of the present application is carried out in a large vacuum muffle furnace, and after the welding is completed, a long rectangular cuboid smelted niobium ingot with a square cross section can be obtained. The present application uses vacuum diffusion welding technology to weld relatively thin smelted niobium plates into relatively thick smelted niobium ingots, which can realize the metallurgical bonding from smelted niobium plate to smelted niobium ingot; during the welding process, the risk of introducing other impurities can be eliminated, and the obtained smelted niobium ingot is more convenient for subsequent smelting and purification operations in an electric arc smelting furnace.

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

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

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

[0071] It is worth noting that the present application can further reduce the content of impurity elements in the cuboid niobium ingot by vacuum arc melting to obtain a cylindrical primary niobium ingot.

[0072] As a preferred technical solution of the present application, the feeding mode of the primary niobium ingot in the melting treatment in step (4) is vertical feeding.

[0073] Preferably, the melting treatment in step (4) includes a first melting, a second melting and a third melting performed in sequence.

[0074] Preferably, the power of the first melting is 530-630 kW, for example, it can be 530 kW, 550 kW, 570 kW, 590 kW, 610 kW or 630 kW, etc., but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0075] Preferably, the melting speed of the first melting is 3-5 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, etc., but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0076] Preferably, the cooling time of the first melting is 13-15 h, for example, it can be 13 h, 13.5 h, 14 h, 14.5 h or 15 h, etc., but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0077] Preferably, the power of the second melting is 550-610 kW, for example, it can be 550 kW, 570 kW, 590 kW or 610 kW, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0078] Preferably, the melting speed of the second melting is 2-4 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, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0079] Preferably, the cooling time of the second melting is 13-15 h, for example, it can be 13 h, 13.5 h, 14 h, 14.5 h or 15 h, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0080] Preferably, the power of the third melting is 600-640 kW, for example, it can be 600 kW, 610 kW, 620 kW, 630 kW or 640 kW, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0081] Preferably, the melting speed of the third melting is 1-3 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, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0082] Preferably, the cooling time of the third melting is 13-15 h, for example, it can be 13 h, 13.5 h, 14 h, 14.5 h or 15 h, etc., but not limited to the listed values, other values not listed in the value range are also applicable.

[0083] As a preferred technical solution of the present application, the first aspect of the present application provides a method for preparing high-purity niobium ingot by multi-stage refining, which comprises the following steps:

[0084] (1) Taking aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, an aluminum-niobium alloy ingot with a niobium content of 84-88 wt% is prepared by an off-furnace aluminothermic method, and then surface treatment and crushing treatment are sequentially performed to obtain aluminum-niobium alloy particles with a particle size of 4-8 cm;

[0085] The mass ratio of the aluminum particle, the di-niobium pentoxide, the potassium chlorate, the calcium oxide and the calcium fluoride is 50-51:96-98:12-14:7-9:3-5; the particle size of the aluminum particle is 2-4mm, and the purity is greater than or equal to 99.99%; the particle size of the di-niobium pentoxide is 15-20μm, and the purity is greater than or equal to 99.99%; the particle size of the potassium chlorate is 100-150μm, and the purity is greater than or equal to 99.5%; the particle size of the calcium oxide is 50-100μm, and the purity is greater than or equal to 99%; and the particle size of the calcium fluoride is 100-150μm, and the purity is greater than or equal to 99.95%;

[0086] The design reaction heat of the aluminum-niobium alloy ingot prepared by the ex-thermal aluminum method is 670-690Kcal / kg;

[0087] The aluminum-niobium alloy ingot prepared by the ex-thermal aluminum method comprises the pretreatment, the furnace building segment, the mixing treatment, the furnace loading segment, the smelting segment and the cooling treatment which are sequentially performed;

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

[0089] The furnace building segment comprises: laying the slag and the magnesite brick with the thickness of 10-30mm in the groove body in sequence, and then placing the reaction furnace body; the reaction furnace body comprises the magnesite crucible with the size of 400-600mm*400-600mm*100-150mm and the steel furnace body which is externally arranged at the periphery of the magnesite crucible, and the gap between the magnesite crucible and the steel furnace body is filled with the slag;

[0090] The mixing treatment comprises: mixing the aluminum particle, the di-niobium pentoxide, the heat generating agent, the calcium oxide and the calcium fluoride according to the formula amount, and then stirring the mixture by using the V-shaped mixer at the rotating speed of 4-6r / min for 10-20min to obtain the mixed material;

[0091] The furnace loading segment comprises: placing the mixed material into the reaction furnace body in 2-4 times, and tamping the material after each time of placing the material is completed;

[0092] The cooling time is 12-24h;

[0093] The surface treatment comprises the sand blasting treatment and the polishing treatment which are sequentially performed, and the sand blasting time is 70-90min;

[0094] (2) placing the aluminum-niobium alloy particles obtained in step (1) into a horizontal electron beam melting furnace to perform horizontal electron beam melting and cooling treatment, thereby obtaining a molten niobium plate;

[0095] The vacuum degree of the horizontal electron beam melting is 0.01-0.05 Pa, the power is 300-500 kW, and the time is 40-60 min; the cooling treatment time is 2-4 h.

[0096] (3) stacking 5-8 layers of the melted niobium plate obtained in step (2), and then sequentially performing vacuum diffusion welding and vacuum arc melting to obtain a primary niobium ingot;

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

[0098] The current of the vacuum arc melting is 9-10 kA, the voltage is 40-45 V, and the vacuum degree is 0.01-0.03 Pa;

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

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

[0101] It is worth mentioning that the cooling mentioned in the method is all furnace cooling.

[0102] In the second aspect, the application provides a high-purity niobium ingot prepared by the method provided in the first aspect.

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

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

[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 high-purity niobium ingot has a residual resistivity ratio (RRR) ≥ 360, for example, it can be 360, 362, 364, 366, 368, 370 or 378, etc., but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0107] The numerical range of the present application not only includes the above-mentioned point values, but also includes any point values between the above-mentioned numerical ranges that are not listed, and due to the limited space and for the sake of simplicity, the present application does not exhaustively list the specific point values included in the range.

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

[0109] (1) The present application adopts an out-of-furnace aluminothermic reduction method, and through the synergistic control of the types and ratios of raw materials, reaction heat, crucible shape and size, etc., successfully prepares high-purity aluminum niobium alloy with a Nb content of 84-88wt%; and through subsequent smelting links, the aluminum niobium alloy is successfully verified in the field of high-purity metals;

[0110] (2) The present application uses vacuum diffusion welding technology to realize the solid-state connection of smelting niobium plates, effectively isolates the intrusion of gas impurities such as oxygen and nitrogen in the air, welding wire / welding flux used in traditional fusion welding, explosives used in explosive welding, etc. under the premise of vacuum environment and without introducing other foreign matters, and also ensures the purity of the smelting niobium plates on the premise of preparing raw materials in the shape required by the arc smelting furnace;

[0111] (3) The present application uses the coupling of the multi-stage refining process of "aluminothermic method→horizontal electron beam smelting→diffusion welding→arc smelting→double-gun electron beam smelting", and through the complementary advantages and parameter matching in each process, successfully breaks through the technical bottleneck that the traditional process is difficult to balance high purity and high RRR value in the preparation of high-purity niobium, and provides a new technical path for obtaining high-purity niobium material with excellent superconducting performance and high RRR value;

[0112] (4) Compared with the vacuum aluminothermic method, the out-of-furnace aluminothermic reduction method used in the present application for preparing 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 need to use expensive equipment and welding wire, and almost does not involve too many operations, further reducing the production cost; thereby effectively solving the technical problems of high energy consumption, high cost and low production efficiency existing in the traditional process. 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 in any way.

[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 building step comprises: laying the slag and the magnesia brick with a thickness of 20 mm in the groove body in turn, and then placing the reaction furnace body; the reaction furnace body comprises a magnesia brick crucible with a size of 500 mm*500 mm*120 mm and a steel furnace body arranged outside the periphery of the magnesia brick crucible, and the gap between the magnesia brick crucible and the steel furnace body is filled with the slag;

[0124] The mixing treatment comprises: mixing the aluminum particles, the niobium pentoxide, the heat generating agent, the calcium oxide and the calcium fluoride according to the formula amount, and then stirring and treating the mixture by using a V-shaped mixer at a rotating speed of 5 r / min for 15 min to obtain the mixed material;

[0125] The furnace loading step comprises: placing the mixed material into the reaction furnace body in three equal times, and tamping the material after each time of loading is completed;

[0126] The cooling treatment is performed for 18 h;

[0127] The surface treatment comprises the sand blasting treatment and the polishing treatment which are performed in turn, and the sand blasting treatment is performed for 80 min;

[0128] (2) placing the aluminum-niobium alloy particles obtained in step (1) into a horizontal electron beam melting furnace to perform horizontal electron beam melting and cooling treatment, thereby obtaining a molten niobium plate;

[0129] The vacuum degree of the horizontal electron beam melting is 0.05 Pa, the power is 380 kW, and the time is 50 min; and the cooling treatment is performed for 3 h;

[0130] (3) stacking 6 layers of the molten niobium plate obtained in step (2), and then performing vacuum diffusion welding and vacuum arc melting in turn, thereby obtaining a primary niobium ingot;

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

[0132] The current of the vacuum arc melting is 10 kA, the voltage is 42 V, and the vacuum degree is 0.01 Pa;

[0133] (4) placing the primary niobium ingot obtained in step (3) into a double-gun electron beam melting furnace to perform melting treatment, thereby obtaining the high-purity niobium ingot;

[0134] The melting treatment comprises the first melting, the second melting and the third melting which are performed in turn; the power of the first melting is 580 kW, the melting speed is 4 mm / min, and the cooling time is 14 h; the power of the second melting is 610 kW, the melting speed is 3 mm / min, and the cooling time is 13 h; and the power of the third melting is 640 kW, the melting speed is 1 mm / min, and the cooling time is 15 h.

[0135] The microstructure of the high-purity niobium ingot provided by the embodiment is shown in FIG. 1, wherein (a) is a scanning electron microscope image, (b) and (c) are transmission electron microscope images. Figure 2 It can be seen from FIG. 1 that the microstructure of the high-purity niobium ingot provided by the embodiment is pure and free of microscopic inclusions. Figure 2

[0136] Embodiment 2

[0137] The embodiment provides a method for preparing a high-purity niobium ingot by using multi-stage refining, and the method comprises the following steps:

[0138] (1) taking aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, an aluminum-niobium alloy ingot with a niobium content of 84wt% is prepared by using an off-furnace aluminothermic method, and then surface treatment and crushing treatment are sequentially performed to obtain aluminum-niobium alloy particles with a particle size of 5-7 cm;

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

[0140] The design reaction heat of the off-furnace aluminothermic method for preparing the aluminum-niobium alloy ingot is 670 Kcal / kg;

[0141] The off-furnace aluminothermic method for preparing the aluminum-niobium alloy ingot comprises sequentially performed pretreatment, furnace lining, mixing treatment, furnace loading, smelting and cooling treatment;

[0142] The pretreatment comprises drying treatment of the raw materials and refractory materials; the drying temperatures of the raw materials and the refractory materials are independently 110 °C; the drying time of the raw materials is 10 h; and the drying time of the refractory materials is 8 h;

[0143] The furnace lining comprises sequentially laying, in a tank body, a slag with a thickness of 10 mm and a magnesia brick, and then placing a reaction furnace body; the reaction furnace body comprises a magnesia brick crucible with a size of 400 mm×400 mm×150 mm and a steel furnace body externally arranged at the periphery of the magnesia brick crucible, and a gap between the magnesia brick crucible and the steel furnace body is filled with a slag;

[0144] The mixing treatment comprises mixing the aluminum particles, the niobium pentoxide, a heat generating agent, the calcium oxide and the calcium fluoride according to the formula amount, and then stirring the mixture by using a V-shaped mixer at a rotating speed of 4 r / min for 20 min to obtain a mixed material;​

[0145] The furnace charging step comprises: placing the mixture into the reaction furnace body in two equal times, and tamping the material after each time of placing is completed;

[0146] The cooling treatment time is 20h;

[0147] The surface treatment comprises sand blasting and polishing in sequence, and the sand blasting time is 70min;

[0148] (2) placing the aluminum-niobium alloy particles obtained in step (1) into a horizontal electron beam melting furnace to perform horizontal electron beam melting and cooling treatment, thereby obtaining a melted niobium plate;

[0149] The vacuum degree of the horizontal electron beam melting is 0.02Pa, the power is 450kW, and the time is 60min; the cooling treatment time is 2.5h;

[0150] (3) stacking 5 layers of the melted niobium plate obtained in step (2), and then performing vacuum diffusion welding and vacuum arc melting in sequence, thereby obtaining a primary niobium ingot;

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

[0152] The current of the vacuum arc melting is 9kA, the voltage is 45V, and the vacuum degree is 0.03Pa;

[0153] (4) placing the primary niobium ingot obtained in step (3) into a double-gun electron beam melting furnace to perform melting treatment, thereby obtaining the high-purity niobium ingot;

[0154] The melting treatment comprises first melting, second melting and third melting in sequence; the power of the first melting is 530kW, the melting speed is 3mm / min, and the cooling time is 13h; the power of the second melting is 550kW, the melting speed is 2mm / min, and the cooling time is 13h; the power of the third melting is 600kW, the melting speed is 1mm / min, and the cooling time is 13h.

[0155] Example 3

[0156] The embodiment provides a method for preparing a high-purity niobium ingot by using multi-stage refining, and the method comprises the following steps:

[0157] (1) taking aluminum particles, niobium pentoxide, potassium chlorate, calcium oxide and calcium fluoride as raw materials, and preparing an aluminum-niobium alloy ingot with a niobium content of 88wt% by using an off-furnace aluminothermic method, and then performing surface treatment and crushing treatment in sequence, thereby obtaining aluminum-niobium alloy particles with a particle size of 5-8cm;

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

[0159] The design reaction heat of the aluminum-niobium alloy ingot prepared by the ex-thermal aluminum method is 690Kcal / kg;

[0160] The aluminum-niobium alloy ingot prepared by the ex-thermal aluminum method comprises the pretreatment, the furnace building segment, the mixing treatment, the furnace loading segment, the smelting segment and the cooling treatment which are sequentially performed;

[0161] The pretreatment comprises the drying treatment of the raw materials and the refractory materials; the drying temperature of the raw materials and the refractory materials is independently 130℃; the drying time of the raw materials is 6h; the drying time of the refractory materials is 4h;

[0162] The furnace building segment comprises: laying the slag and the magnesite brick with the thickness of 30mm in the groove body in sequence, and then placing the reaction furnace body; the reaction furnace body comprises the magnesite brick crucible with the size of 600mm×600mm×100mm and the steel furnace body which is externally arranged at the periphery of the magnesite brick crucible, and the gap between the magnesite brick crucible and the steel furnace body is filled with the slag;

[0163] The mixing treatment comprises: mixing the aluminum particles, the di-niobium pentoxide, the heat generating agent, the calcium oxide and the calcium fluoride according to the formula amount, and then stirring the mixture by using the V-shaped mixer at the rotating speed of 6r / min for 10min to obtain the mixed material;

[0164] The furnace loading segment comprises: placing the mixed material into the reaction furnace body for 4 times on average, and tamping the material after each time of placing the material is completed;

[0165] The cooling time of the cooling treatment is 24h;

[0166] The surface treatment comprises the sand blasting treatment and the polishing treatment which are sequentially performed; the sand blasting time is 90min;

[0167] (2) placing the aluminum-niobium alloy particles obtained in step (1) into a horizontal electron beam melting furnace to perform horizontal electron beam melting and cooling treatment, thereby obtaining a molten niobium plate;

[0168] The vacuum degree of the horizontal electron beam melting is 0.05Pa, the power is 300kW, and the time is 40min; the cooling time of the cooling treatment is 4h;

[0169] (3) stacking 8 layers of the smelted niobium plate obtained in step (2), and then sequentially performing vacuum diffusion welding and vacuum arc melting to obtain a primary niobium ingot;

[0170] The vacuum diffusion welding has a vacuum degree of 10 -4 Pa, a temperature of 1800℃, and a time of 4h;

[0171] The vacuum arc melting has a current of 9.5kA, a voltage of 40V, and a vacuum degree of 0.02Pa;

[0172] (4) placing the primary niobium ingot obtained in step (3) into a double-gun electron beam melting furnace to perform a melting treatment, to obtain the high-purity niobium ingot;

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

[0174] Example 4

[0175] The embodiment provides a method for preparing a high-purity niobium ingot by using multi-stage refining, and the method is only different from the method in the embodiment 1 in that:

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

[0177] Example 5

[0178] The embodiment provides a method for preparing a high-purity niobium ingot by using multi-stage refining, and the method is only different from the method in the embodiment 1 in that:

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

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

[0181] Example 6

[0182] The embodiment provides a method for preparing a high-purity niobium ingot by using multi-stage refining, and the method is only different from the method in the embodiment 1 in that:

[0183] 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] The present example provides a method for preparing high-purity niobium ingot by multi-stage refining, which is only different from example 1 in that:

[0186] 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] The present example provides a method for preparing high-purity niobium ingot by multi-stage refining, which is only different from example 1 in that:

[0189] The vacuum degree of the vacuum diffusion welding in step (3) is adjusted to 10 -2 Pa, the temperature is 1400℃, and the time is 5h.

[0190] Example 9

[0191] The present example provides a method for preparing high-purity niobium ingot by multi-stage refining, which is only different from example 1 in that:

[0192] The vacuum degree of the vacuum diffusion welding in step (3) is adjusted to 10 -3 Pa, the temperature is 2000℃, and the time is 1h.

[0193] Example 10

[0194] The present example provides a method for preparing high-purity niobium ingot by multi-stage refining, which is only different from example 1 in that:

[0195] The current of the vacuum arc melting in step (3) is adjusted to 12kA, the voltage is adjusted to 50V, and the vacuum degree is adjusted to 0.05 Pa.

[0196] Example 11

[0197] The present example provides a method for preparing high-purity niobium ingot by multi-stage refining, which is only different from example 1 in that:

[0198] The current of the vacuum arc melting in step (3) is adjusted to 8kA, the voltage is adjusted to 50V, and the vacuum degree is adjusted to 0.03 Pa.

[0199] Example 12

[0200] The embodiment provides a method for preparing high-purity niobium ingot by multi-stage refining, and the method is only different from the embodiment 1 in that:

[0201] The embodiment adjusts the melting treatment in the double-gun electron beam melting furnace in the step (4) to be performed under the conditions of 600 kW power and 2 mm / min speed.

[0202] Embodiment 13

[0203] The embodiment provides a method for preparing high-purity niobium ingot by multi-stage refining, and the method is only different from the embodiment 1 in that:

[0204] The embodiment adjusts the melting treatment in the double-gun electron beam melting furnace in the step (4) to be performed under the conditions of 500 kW power and 6 mm / min speed in the first melting, 520 kW power and 5 mm / min speed in the second melting, and 650 kW power and 4 mm / min speed in the third melting.

[0205] Comparative example 1

[0206] The comparative example provides a method for preparing high-purity niobium ingot by multi-stage refining, and the method is only different from the embodiment 1 in that:

[0207] The comparative example adjusts the preparation of the aluminum niobium alloy ingot in the furnace-outside aluminum thermal method in the step (1) to be prepared in a vacuum reaction furnace, and the vacuum degree in the preparation process is 0.05 Pa.

[0208] Comparative example 2

[0209] The comparative example provides a method for preparing high-purity niobium ingot by multi-stage refining, and the method is only different from the embodiment 1 in that:

[0210] The comparative example adjusts the vacuum diffusion welding in the step (3) to be electron beam welding.

[0211] Comparative example 3

[0212] The comparative example provides a method for preparing high-purity niobium ingot by multi-stage refining, and the method is only different from the embodiment 1 in that:

[0213] The comparative example omits the melting treatment in the step (4).

[0214] The high-purity niobium ingots provided by the above embodiment and comparative example are subjected to component detection and RRR measurement, and the results are shown in Table 1.

[0215] Table 1

[0216]

[0217]

[0218] The following points can be known according to Table 1:

[0219] (1) It can be known from the comprehensive analysis of Examples 1-3 that the niobium ingot with high purity and high RRR value is prepared by coupling multi-stage refining processes and matching parameters in each refining process;

[0220] (2) It can be known from the comprehensive analysis of Examples 1, 4-5 and Comparative Example 1 that the ex-thermal aluminum process provided by the present application is one of the decisive factors for preparing high-grade aluminum-niobium alloy ingot. Compared with the ex-thermal aluminum process, when the vacuum aluminum process provided by Comparative Example 1 is used, the slag and metal obtained after the aluminum thermal reaction cannot be separated, and the aluminum-niobium alloy block cannot be obtained;

[0221] In addition, factors such as raw material ratio and size of magnesium brick crucible in the ex-thermal aluminum process preparation process will affect the content of metallic niobium in the aluminum-niobium alloy, and further affect the purity and RRR value of the niobium ingot; more specifically, using the raw material ratio and design reaction heat provided by Example 4 will cause serious spattering during the aluminum thermal reaction, resulting in mixing of alloy liquid and slag, making it difficult to separate slag and metal, and making it impossible to obtain an aluminum-niobium alloy ingot;

[0222] (3) It can be known from the comprehensive analysis of Examples 6-13 that the parameters of each link in the preparation process of the niobium ingot will affect the grade of the obtained niobium ingot, thereby proving the necessity of limiting the process parameters in each link of the preparation process;

[0223] (4) It can be known from the comprehensive analysis of Example 1 and Comparative Example 2 that compared with vacuum diffusion welding, electron beam welding requires a specific electron beam furnace, the production cost is extremely high, and it is suitable for butt welding of plates, and the high-energy beam of electron beam welding will produce local high temperature, which may cause large thermal stress and deformation, not only it is difficult to guarantee the shape requirement of the raw material for arc melting, but also high melting point impurity elements and interstitial impurity elements are easily introduced in the surrounding area of the weld;

[0224] (5) It can be known from the comprehensive analysis of Example 1 and Comparative Example 3 that the double-gun electron beam melting process is mainly used for deep removal of impurity elements in the niobium ingot. If the melting treatment in the double-gun electron beam melting furnace is omitted, the impurity content in the obtained niobium ingot will be high, and it is difficult to achieve the index of RRR exceeding 360;

[0225] Omitting any one of the refining processes will reduce the purity of the niobium ingot, further proving the synergistic effect of the multi-stage refining process of “horizontal electron beam melting → diffusion welding → arc melting → double-gun electron beam melting”, and providing a new technical path for obtaining high-RRR high-purity niobium material with excellent superconducting performance.

[0226] In summary, the application uses aluminum particles, niobium pentoxide, a heat generating agent, a slag forming agent and the like as raw materials, and adopts a multi-stage refining process coupling system of "aluminum thermal method→horizontal electron beam melting→diffusion welding→arc melting→double gun electron beam melting" to realize stable production of high RRR value (residual resistivity ratio) high purity niobium, and effectively solves the technical problems of high energy consumption, high cost and low production efficiency existing in the traditional process.

[0227] The applicant declares that the above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the application, which can be easily thought of by any person skilled in the art, falls within the protection scope and disclosure scope of the application.

Claims

1. A method for preparing high-purity niobium ingots using multi-stage refining, characterized in that, 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 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. (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 preparing high-purity niobium ingots using multi-stage refining according to claim 1, characterized in that, The heating agent in step (1) includes potassium chlorate; Preferably, the slag-forming agent in step (1) includes calcium oxide and calcium fluoride; 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; Preferably, the designed reaction heat for preparing aluminum-niobium alloy ingots by the out-of-furnace aluminothermic method is 670–690 kcal / kg.

3. The method for preparing high-purity niobium ingots using multi-stage refining according to claim 1 or 2, characterized in that, The preparation of aluminum-niobium alloy ingots by the external aluminothermic method in step (1) includes the following steps in sequence: pretreatment, furnace lining, furnace loading, and smelting. Preferably, the pretreatment includes drying the raw materials and refractory materials; Preferably, the furnace lining process includes: sequentially laying slag and magnesia bricks in the tank, and then placing the reactor body; 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. Preferably, the size of the magnesium brick crucible is 400-600mm × 400-600mm × 100-150mm; Preferably, the process before the furnace loading stage also includes a mixing treatment; 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; Preferably, the smelting process further includes a cooling treatment, the cooling treatment lasting 12 to 24 hours.

4. The method for preparing high-purity niobium ingots using multi-stage refining according to any one of claims 1-3, characterized in that, The niobium content of the aluminum-niobium alloy ingot in step (1) is 84-88 wt%. Preferably, the particle size of the aluminum-niobium alloy particles in step (1) is 4-8 cm.

5. The method for preparing high-purity niobium ingots using multi-stage refining according to any one of claims 1-4, characterized in that, The vacuum degree of the horizontal electron beam melting in step (2) is 0.01 to 0.05 Pa; Preferably, the power of the horizontal electron beam melting in step (2) is 300-500kW; Preferably, the horizontal electron beam melting time in step (2) is 40 to 60 minutes.

6. The method for preparing high-purity niobium ingots using multi-stage refining according to any one of claims 1-5, characterized in that, The number of stacked layers of the smelted niobium plates in step (3) is 5 to 8; Preferably, the vacuum degree of the vacuum diffusion welding in step (3) is 10. -3 ~10 -4 Pa; Preferably, the temperature of the vacuum diffusion welding in step (3) is 1500–1800°C; Preferably, the heat preservation time for vacuum diffusion welding in step (3) is 2 to 4 hours.

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

8. The method for preparing high-purity niobium ingots using multi-stage refining according to any one of claims 1-7, characterized in that, In step (4), the primary niobium ingots are fed vertically during the smelting process. Preferably, 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; Preferably, the melting speed of the first melting is 3-5 mm / min; Preferably, the cooling time for the first melting is 13-15 hours; Preferably, the power of the second melting process is 550-610 kW; Preferably, the melting speed of the second melting is 2-4 mm / min; Preferably, the cooling time for the second melting is 13-15 hours; Preferably, the power of the third melting process is 600-640 kW; Preferably, the melting speed of the third melting is 1-3 mm / min; Preferably, the cooling time for the third melting is 13 to 15 hours.

10. A high-purity niobium ingot, characterized in that, The high-purity niobium ingot is prepared by the method according to any one of claims 1-9; Preferably, 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; Preferably, the residual resistivity ratio of the high-purity niobium ingot is ≥360.

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