A method for preparing high-purity oxygen-free copper

Abstract

This invention discloses a method for preparing high-purity oxygen-free copper, relating to the field of metallurgical technology. The method includes multi-stage electrolytic refining, gradient-heating vacuum melting, inert gas-protected refining, electron beam melting, hydrogen plasma arc melting, directional solidification, and post-treatment steps. The multi-stage electrolytic refining utilizes a specific component electrolyte and periodically commutated current; vacuum melting is combined with bidirectional electromagnetic stirring; inert gas-protected refining is combined with a gradient reduction composite covering agent; electron beam and hydrogen plasma arc melting achieve deep purification and deoxidation; and directional solidification and two-stage annealing ensure product performance. The high-purity oxygen-free copper prepared by this invention has a conductivity of 102.3% IACS, a copper content ≥99.9999%, and an oxygen content <1.0 ppm. It exhibits high purity, low oxygen content, and excellent conductivity. The process is stable and controllable, making it suitable for high-end electronics applications.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for preparing high-purity oxygen-free copper. Background Technology

[0002] High-purity oxygen-free copper is widely used in high-end manufacturing fields such as aerospace, electronics, new energy, and nuclear industry due to its excellent electrical and thermal conductivity and good processing performance. With the rapid development of microelectronics technology, applications such as integrated circuit lead frames, high-vacuum devices, and superconducting cables have placed more stringent requirements on the purity of copper materials. Not only is an extremely low oxygen content required to prevent hydrogen embrittlement, but trace impurities must also be controlled at the ppb level to ensure the stability of the material under extreme environments.

[0003] Traditional methods for preparing high-purity oxygen-free copper mainly include vacuum melting and electrolytic refining, but these methods suffer from significant technical bottlenecks. Vacuum melting removes impurities from crude copper at high temperatures, but it is difficult to precisely control the oxygen content, resulting in an oxygen content in the finished product typically between 1-3 ppm, which cannot meet the stringent requirements of high-end electronic components. Furthermore, vacuum equipment requires significant investment, consumes a lot of energy, and has low production efficiency. Electrolytic refining effectively removes metallic impurities, but its ability to remove non-metallic impurities (such as oxygen and sulfur) is limited, and the electrolytic process introduces new impurities, making it difficult to achieve a final product purity exceeding 99.999%. In existing technologies, some processes use deoxidizers to reduce oxygen content, but residual deoxidizers can form secondary impurities, affecting the conductivity and corrosion resistance of oxygen-free copper.

[0004] For example, the invention patent document CN103540764B discloses a method for preparing high-purity oxygen-free copper material, including the following steps: (1) Select No. 1 electrolytic copper as raw material, clean and dry it, and put it into a melting crucible; (2) Before melting, draw a vacuum and continuously introduce inert gas to remove oxygen; when the vacuum degree reaches -0.1 to -0.2 MPa, heat and melt it. During the melting process, cover the surface of the copper liquid with charcoal or flake graphite and introduce inert gas for protection. At the same time, introduce inert gas into the copper liquid for further deoxidation; after No. 1 electrolytic copper melts, continue to keep it warm; (3) After the heat preservation is completed, horizontal continuous casting is performed to obtain the product. In the early stage of melting, the invention draws a high vacuum and introduces inert gas, which can remove oxygen and deoxidize to the greatest extent. During the melting process, a covering agent is used to isolate and deoxidize the product, and the inert gas is directly introduced into the copper liquid to further deoxidize it. The oxygen content of the copper material obtained by the invention can be as low as 2 ppm. However, the purity and conductivity of the product still need further improvement, making it difficult to meet the stringent requirements of high-end vacuum electronic devices.

[0005] It is evident that developing a simple process that enables large-scale continuous production and can stably produce high-purity oxygen-free copper with high purity, low oxygen content, and excellent conductivity has become a pressing technical challenge in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-purity oxygen-free copper with high purity, low oxygen content, and excellent electrical conductivity.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing high-purity oxygen-free copper, comprising the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolytic copper is obtained by periodic commutation current electrolysis; the electrolyte used is deionized water as solvent, including the following components at the following concentrations: CuSO4 45-55 g / L, H2SO4 180-220 g / L, HCl 0.01-0.03 g / L, composite additive 0.08-0.12 g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:(0.2-0.4):2:0.1; Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace, and the melting is carried out at a vacuum degree of 5×10⁻⁶. -3 -1×10 -3 Under Pa, the temperature is increased from room temperature to 800℃ at a heating rate of 5-8℃ / min, and then increased from 800℃ to 1150-1180℃ at a heating rate of 3-5℃ / min. After the copper block is completely melted, the furnace temperature is maintained at 1150-1180℃ for 0.5-1h. During this period, the bidirectional electromagnetic stirring device is turned on, the electromagnetic stirring current is controlled at 50-80A, the stirring frequency is 20-30Hz, and the stirring method is alternating between forward rotation for 30s and reverse rotation for 30s. Step S3, Inert Gas Protected Refining: After vacuum melting and heat preservation, high-purity argon gas with a purity ≥99.999% is slowly introduced into the furnace until the furnace pressure rises to 0.10-0.12MPa. The argon gas flow rate is maintained at 15-20L / min. Then, a two-stage bottom-blowing refining process is performed. During the two-stage bottom-blowing process, a gradient reduction composite covering agent is added to the surface of the copper liquid, with a covering thickness of 150-200mm. During the refining process, the furnace temperature is maintained at 1140-1160℃. During this period, bidirectional electromagnetic stirring is continuously performed to ensure that the composite covering agent reacts fully with the copper liquid, achieving deep deoxidation and impurity removal. The current of the bidirectional electromagnetic stirring is 50-80A, and the frequency is 20-30Hz. After refining, the mixture is allowed to stand for 5-10 minutes to allow the remaining impurity particles to fully float to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The copper liquid is then cooled to room temperature with the furnace to obtain preliminary copper ingots. Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode for electron beam melting; the melting vacuum degree is better than 5×10 -5 Pa, electron beam power of 80-120kW, scanning frequency of 1000-1500Hz, melting speed of 15-25kg / h, to obtain deeply purified copper liquid; Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber, which is equipped with a non-consumable tungsten electrode. The working gas is a mixture of hydrogen and argon, wherein the hydrogen component is 30-50% and the remainder is argon. The vacuum degree of the melting chamber is maintained at 1×10⁻⁶. -3 -5×10 -4 Pa, arc current of 300-400A, arc voltage of 25-35V, molten pool temperature controlled at 1150-1180℃ to achieve deep deoxidation; smelting time controlled at 20-30min; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 150-200K / cm and the solidification pull-down speed v is 5-10mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

[0008] Preferably, the electrolysis temperature in step S1 is 55-65°C.

[0009] Preferably, the polyethylene glycol in step S1 is polyethylene glycol PEG 6000.

[0010] Preferably, the specific parameters of the periodic commutation current in step S1 are: forward current density 280-320A / m², reverse current density 30-50A / m², and commutation period of 300s forward / 10s reverse.

[0011] Preferably, the electrolyte in step S1 is purified by continuous filtration with a filtration accuracy of 0.4-0.6 μm and a circulation flow rate of 0.8-1.2 L / (min·m²) to remove solid suspended particles from the electrolyte.

[0012] Preferably, the dual-stage bottom blowing in step S3 includes a primary bottom blowing stage and a secondary bottom blowing stage. The primary bottom blowing stage has a bottom blowing tube inserted into the copper liquid to a depth of 200-250 mm, an argon flow rate of 15-20 L / min, and a bottom blowing time of 15-20 min. The secondary bottom blowing stage has a bottom blowing tube inserted to a depth of 150-200 mm, an argon flow rate of 10-15 L / min, and a bottom blowing time of 15-20 min.

[0013] Preferably, the gradient reduction composite covering agent comprises the following components in parts by weight: 94-96 parts high-purity graphite particles, 2-3 parts lamp smoke carbon black, 1-2 parts acetylene black, 0.5-1 parts calcium fluoride, and 0.1-0.3 parts nano-alumina; wherein the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

[0014] Preferably, in the hydrogen plasma arc melting process described in step S5, electromagnetic stirring technology is used, with a stirring current frequency of 10-50Hz and a magnetic field strength of 0.05-0.1T.

[0015] Preferably, during the directional solidification process described in step S6, a steady magnetic field with a magnetic induction intensity of 0.2-0.5T is applied at the front edge of the solid-liquid interface.

[0016] Preferably, the annealing process in step S7 is a two-stage annealing process. The annealing temperature of the first stage is 300-350℃ and the holding time is 1.5-2h. The annealing temperature of the second stage is 450-500℃ and the holding time is 2-3h.

[0017] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The method for preparing high-purity oxygen-free copper disclosed in this invention uses a gelatin-thiazolidin-2-thione-PEG-hydroxypropanesulfonic acid pyridine salt composite additive system in the electrolysis stage. Thiazolidine-2-thione preferentially adsorbs on the high index crystal plane of the cathode surface, inhibits dendrite growth and promotes the co-deposition and removal of impurities with large hydrogen overpotentials such as As and Sb. PEG reduces the entrainment of organic matter in the electrolyte through steric hindrance effect. Hydroxypropanesulfonic acid pyridine salt can work synergistically with other components. Its sulfonic acid anion and pyridine ring functional group can flocculate the fine suspended anode mud generated during electrolysis, reduce the entry of impurities into the cathode copper by mechanical adhesion, and inhibit the oxidation reaction on the cathode copper surface, thereby reducing the oxygen content of electrolytic copper.

[0018] (2) The method for preparing high-purity oxygen-free copper disclosed in this invention, compared with the uniform heating mode of traditional vacuum melting, effectively avoids microcracks caused by thermal stress inside the copper block by gradient heating, and reduces secondary inclusions of impurities; the combination of dual-stage bottom blowing and gradient reduction composite covering agent not only achieves deep removal of dissolved oxygen in copper liquid, significantly reducing oxygen content, but also removes trace amounts of harmful impurities such as sulfur and phosphorus that are difficult to remove in traditional processes, greatly improving the mechanical and electrical properties of copper materials, and solving the technical pain points of incomplete impurity removal and easy oxidation of copper liquid in existing refining processes.

[0019] (3) The method for preparing high-purity oxygen-free copper disclosed in this invention combines electron beam melting and hydrogen plasma arc melting for secondary deep purification, breaking through the purification limit of a single melting process. Electron beam melting achieves efficient removal of macroscopic impurities, while hydrogen plasma arc melting utilizes the reducing properties of hydrogen and the high-temperature characteristics of plasma to not only further remove residual trace oxygen but also decompose residual trace intermetallic compounds in the copper liquid, making the copper purity reach 6N grade or higher, far exceeding the 5N grade purity that can be achieved by existing single melting processes; at the same time, the combination of electromagnetic stirring during hydrogen plasma arc melting effectively avoids component segregation in the copper liquid, significantly improving the uniformity of copper composition and solving the problem of uneven composition and large performance fluctuations in the preparation of high-purity copper.

[0020] (4) The method for preparing high-purity oxygen-free copper disclosed in this invention, with its optimized design of directional solidification and two-stage annealing, not only improves the crystal quality of copper but also enhances its processing performance and dimensional stability. The precise control of the solid-liquid interface temperature gradient and the application of a stable magnetic field during directional solidification enable the copper ingot to form a uniform columnar crystal structure, reducing grain boundary defects. The two-stage annealing effectively eliminates residual stress inside the copper ingot, avoiding deformation and cracking problems in subsequent processing. At the same time, it further improves the conductivity of the copper material, exceeding the expected conductivity of high-purity copper under existing processes, and meeting the stringent requirements of high-end electronics, aerospace and other fields for ultra-high-purity oxygen-free copper.

[0021] (5) The method for preparing high-purity oxygen-free copper disclosed in this invention is composed of high-purity graphite particles, lamp smoke black, acetylene black, calcium fluoride and nano alumina in a specific weight ratio. The components work synergistically and complement each other. The gradient reduction system achieves deep deoxidation of the copper liquid surface and interior. The specific adsorption effect of calcium fluoride is used to remove trace impurities. At the same time, the nano alumina is used to regulate the grain growth in advance, realizing the integration of deoxidation, impurity removal, anti-oxidation and grain refinement. Moreover, the components have high purity and suitable particle size, and will not introduce new impurities. It can effectively ensure the purity of copper liquid and the stability of subsequent copper material performance, and solve the technical pain points of existing single covering agents with single function, incomplete deoxidation and impurity removal, and easy to affect the purity of copper materials. Detailed Implementation

[0022] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. Example 1

[0023] A method for preparing high-purity oxygen-free copper includes the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolysis is performed using periodic commutation current to obtain electrolytic copper; the electrolyte used is deionized water as the solvent, and includes the following components at the following concentrations: CuSO4 45g / L, H2SO4 180g / L, HCl 0.01g / L, and composite additive 0.08g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:0.2:2:0.1. Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace, and the melting is carried out at a vacuum degree of 5×10⁻⁶. -3 At Pa, the temperature was increased from room temperature to 800℃ at a heating rate of 5℃ / min, and then increased from 800℃ to 1150℃ at a heating rate of 3℃ / min. After the copper block was completely melted, the furnace temperature was maintained at 1150℃ for 0.5h. During this period, the bidirectional electromagnetic stirring device was turned on, the electromagnetic stirring current was controlled at 50A, the stirring frequency was 20Hz, and the stirring method was adopted by alternating forward rotation for 30s and reverse rotation for 30s. Step S3, Inert Gas Protected Refining: After vacuum melting and heat preservation, high-purity argon gas with a purity ≥99.999% is slowly introduced into the furnace until the furnace pressure rises to 0.10MPa. The argon gas flow rate is maintained at 15L / min. Then, a two-stage bottom-blowing refining process is performed. During the two-stage bottom-blowing process, a gradient reduction composite covering agent is added to the surface of the copper liquid, with a covering thickness of 150mm. During the refining process, the furnace temperature is maintained at 1140℃. During this period, bidirectional electromagnetic stirring is continuously performed to ensure that the composite covering agent reacts fully with the copper liquid, achieving deep deoxidation and impurity removal. The current of the bidirectional electromagnetic stirring is 50A, and the frequency is 20Hz. After refining, the mixture is allowed to stand for 5 minutes to allow the remaining impurity particles to fully float to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The copper liquid is cooled to room temperature with the furnace to obtain preliminary copper ingots. Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode for electron beam melting; the melting vacuum degree is better than 5×10 -5 Pa, electron beam power of 80kW, scanning frequency of 1000Hz, melting speed of 15kg / h, to obtain deeply purified copper liquid; Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber, which is equipped with a non-consumable tungsten electrode. The working gas is a mixture of hydrogen and argon, with hydrogen comprising 30% and argon as the remainder. The vacuum degree of the melting chamber is maintained at 1×10⁻⁶. -3 Pa, arc current of 300A, arc voltage of 25V, molten pool temperature controlled at 1150℃ to achieve deep deoxidation; smelting time controlled at 20min; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 150K / cm and the solidification pull-down speed v is 5mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

[0024] The electrolysis temperature in step S1 is 55℃; the polyethylene glycol in step S1 is polyethylene glycol PEG 6000; the specific parameters of the periodic commutation current in step S1 are: forward current density 280A / m², reverse current density 30A / m², and commutation period of 300s forward / 10s reverse; the electrolyte in step S1 is purified by continuous filtration with a filtration accuracy of 0.4μm and a circulation flow rate of 0.8L / (min·m²) to remove solid suspended particles in the electrolyte.

[0025] The dual-stage bottom blowing in step S3 includes a primary bottom blowing and a secondary bottom blowing. The primary bottom blowing tube is inserted into the copper liquid to a depth of 200 mm, the argon flow rate is 15 L / min, and the bottom blowing time is 15 min. The secondary bottom blowing tube is inserted to a depth of 150 mm, the argon flow rate is 10 L / min, and the bottom blowing time is 15 min.

[0026] The gradient reduction composite covering agent comprises the following components in parts by weight: 94 parts high-purity graphite particles, 2 parts lamp smoke carbon black, 1 part acetylene black, 0.5 parts calcium fluoride, and 0.1 parts nano-alumina; the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

[0027] In the hydrogen plasma arc melting process described in step S5, electromagnetic stirring technology is used, with a stirring current frequency of 10Hz and a magnetic field strength of 0.05T. In the directional solidification process described in step S6, a steady magnetic field is applied at the front of the solid-liquid interface, with a magnetic induction intensity of 0.2T. In the annealing treatment described in step S7, a two-stage annealing treatment is performed. The annealing temperature of the first stage is 300℃, and the holding time is 1.5h. The annealing temperature of the second stage is 450℃, and the holding time is 2h. Example 2

[0028] A method for preparing high-purity oxygen-free copper includes the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolysis is performed using periodic commutation current to obtain electrolytic copper; the electrolyte used is deionized water as the solvent, and includes the following components at the following concentrations: CuSO4 47g / L, H2SO4 190g / L, HCl 0.015g / L, and composite additive 0.09g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:0.25:2:0.1. Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace, and the melting is carried out under a vacuum of 4×10⁻⁶. -3 At Pa, the temperature was increased from room temperature to 800℃ at a heating rate of 6℃ / min, and then increased from 800℃ to 1160℃ at a heating rate of 3.5℃ / min. After the copper block was completely melted, the furnace temperature was maintained at 1160℃ for 0.6h. During this period, the bidirectional electromagnetic stirring device was turned on, the electromagnetic stirring current was controlled at 60A, the stirring frequency was 23Hz, and the stirring method of alternating forward rotation for 30s and reverse rotation for 30s was adopted. Step S3, Inert Gas Protected Refining: After vacuum melting and heat preservation, high-purity argon gas with a purity ≥99.999% is slowly introduced into the furnace until the furnace pressure rises to 0.11MPa. The argon gas flow rate is maintained at 16L / min. Then, a two-stage bottom-blowing refining process is performed. During the two-stage bottom-blowing process, a gradient reduction composite covering agent is added to the surface of the copper liquid, with a covering thickness of 160mm. During the refining process, the furnace temperature is maintained at 1145℃. During this period, bidirectional electromagnetic stirring is continuously performed to ensure that the composite covering agent reacts fully with the copper liquid, achieving deep deoxidation and impurity removal. The current of the bidirectional electromagnetic stirring is 60A, and the frequency is 23Hz. After refining, the mixture is allowed to stand for 6 minutes to allow the remaining impurity particles to fully float to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The copper liquid is cooled to room temperature with the furnace to obtain preliminary copper ingots. Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode for electron beam melting; the melting vacuum degree is better than 5×10 -5Pa, electron beam power of 90kW, scanning frequency of 1200Hz, melting speed of 17kg / h, to obtain deeply purified copper liquid; Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber, which is equipped with a non-consumable tungsten electrode. The working gas is a mixture of hydrogen and argon, with hydrogen comprising 35% and argon as the remainder. The vacuum degree of the melting chamber is maintained at 9 × 10⁻⁶. -4 Pa, arc current of 330A, arc voltage of 28V, molten pool temperature controlled at 1160℃ to achieve deep deoxidation; smelting time controlled at 23min; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 160K / cm and the solidification pull-down speed v is 6mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

[0029] The electrolysis temperature in step S1 is 57℃; the polyethylene glycol in step S1 is polyethylene glycol PEG 6000; the specific parameters of the periodic commutation current in step S1 are: forward current density 290A / m², reverse current density 35A / m², and commutation period of 300s forward / 10s reverse; the electrolyte in step S1 is continuously filtered and purified with a filtration accuracy of 0.5μm and a circulation flow rate of 0.9L / (min·m²) to remove solid suspended particles in the electrolyte; the dual-stage bottom blowing in step S3 includes primary bottom blowing and secondary bottom blowing, wherein the primary bottom blowing tube is inserted into the copper liquid to a depth of 220mm, the argon flow rate is 17L / min, and the bottom blowing time is 16min; the secondary bottom blowing tube is inserted to a depth of 170mm, the argon flow rate is 12L / min, and the bottom blowing time is 17min.

[0030] The gradient reduction composite covering agent comprises the following components in parts by weight: 94.5 parts high-purity graphite particles, 2.3 parts lamp smoke carbon black, 1.2 parts acetylene black, 0.6 parts calcium fluoride, and 0.15 parts nano-alumina; the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

[0031] In the hydrogen plasma arc melting process described in step S5, electromagnetic stirring technology is used, with a stirring current frequency of 20Hz and a magnetic field strength of 0.06T. In the directional solidification process described in step S6, a steady magnetic field is applied at the front edge of the solid-liquid interface, with a magnetic induction intensity of 0.3T. In the annealing treatment described in step S7, a two-stage annealing treatment is performed. The annealing temperature of the first stage is 320℃, and the holding time is 1.6h. The annealing temperature of the second stage is 460℃, and the holding time is 2.3h. Example 3

[0032] A method for preparing high-purity oxygen-free copper includes the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolysis is performed using periodic commutation current to obtain electrolytic copper; the electrolyte used is deionized water as the solvent, comprising the following components at the following concentrations: CuSO4 50 g / L, H2SO4 200 g / L, HCl 0.02 g / L, and composite additive 0.1 g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:0.3:2:0.1. Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace, and the melting is carried out under a vacuum of 3×10⁻⁶. -3 At Pa, the temperature was increased from room temperature to 800℃ at a heating rate of 6.5℃ / min, and then increased from 800℃ to 1165℃ at a heating rate of 4℃ / min. After the copper block was completely melted, the furnace temperature was maintained at 1165℃ for 0.8h. During this period, the bidirectional electromagnetic stirring device was turned on, the electromagnetic stirring current was controlled at 65A, the stirring frequency was 25Hz, and the stirring method of alternating forward rotation for 30s and reverse rotation for 30s was adopted. Step S3, Inert Gas Protected Refining: After vacuum melting and heat preservation, high-purity argon gas with a purity ≥99.999% is slowly introduced into the furnace until the furnace pressure rises to 0.11MPa. The argon gas flow rate is maintained at 17L / min. Then, a two-stage bottom-blowing refining process is performed. During the two-stage bottom-blowing process, a gradient reduction composite covering agent with a thickness of 180mm is added to the surface of the copper liquid. During the refining process, the furnace temperature is maintained at 1150℃. During this period, bidirectional electromagnetic stirring is continuously performed to ensure that the composite covering agent reacts fully with the copper liquid, achieving deep deoxidation and impurity removal. The current of the bidirectional electromagnetic stirring is 65A and the frequency is 25Hz. After refining, the mixture is allowed to stand for 8 minutes to allow the remaining impurity particles to fully float to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The copper liquid is then cooled to room temperature with the furnace to obtain preliminary copper ingots. Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode for electron beam melting; the melting vacuum degree is better than 5×10 -5Pa, electron beam power of 100kW, scanning frequency of 1300Hz, melting speed of 20kg / h, to obtain deeply purified copper liquid; Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber, which is equipped with a non-consumable tungsten electrode. The working gas is a mixture of hydrogen and argon, with hydrogen comprising 30-50% and argon as the remainder. The vacuum degree of the melting chamber is maintained at 7×10⁻⁶. -4 Pa, arc current of 350A, arc voltage of 30V, molten pool temperature controlled at 1165℃ to achieve deep deoxidation; smelting time controlled at 25min; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 180K / cm and the solidification pull-down speed v is 8mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

[0033] The electrolysis temperature in step S1 is 60℃; the polyethylene glycol in step S1 is polyethylene glycol PEG 6000; the specific parameters of the periodic commutation current in step S1 are: forward current density 300A / m², reverse current density 40A / m², and commutation period of 300s forward / 10s reverse; the electrolyte in step S1 is continuously filtered and purified with a filtration accuracy of 0.5μm and a circulation flow rate of 1L / (min·m²) to remove solid suspended particles in the electrolyte; the dual-stage bottom blowing in step S3 includes primary bottom blowing and secondary bottom blowing, wherein the primary bottom blowing tube is inserted into the copper liquid to a depth of 230mm, the argon flow rate is 18L / min, and the bottom blowing time is 18min; the secondary bottom blowing tube is inserted to a depth of 180mm, the argon flow rate is 13L / min, and the bottom blowing time is 17min.

[0034] The gradient reduction composite covering agent comprises the following components in parts by weight: 95 parts high-purity graphite particles, 2.5 parts lamp smoke carbon black, 1.5 parts acetylene black, 0.7 parts calcium fluoride, and 0.2 parts nano-alumina; the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

[0035] In the hydrogen plasma arc melting process described in step S5, electromagnetic stirring technology is used, with a stirring current frequency of 30Hz and a magnetic field strength of 0.08T. In the directional solidification process described in step S6, a steady magnetic field is applied at the front edge of the solid-liquid interface, with a magnetic induction intensity of 0.35T. In the annealing treatment described in step S7, a two-stage annealing treatment is performed. The annealing temperature of the first stage is 330℃, and the holding time is 1.8h. The annealing temperature of the second stage is 480℃, and the holding time is 2.5h. Example 4

[0036] A method for preparing high-purity oxygen-free copper includes the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolysis is performed using periodic commutation current to obtain electrolytic copper; the electrolyte used is deionized water as the solvent, comprising the following components at the following concentrations: CuSO4 53 g / L, H2SO4 210 g / L, HCl 0.025 g / L, and composite additive 0.11 g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:0.35:2:0.1. Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace, and the melting is carried out under a vacuum of 2×10⁻⁶. -3 At Pa, the temperature was increased from room temperature to 800℃ at a heating rate of 7.5℃ / min, and then increased from 800℃ to 1175℃ at a heating rate of 4.5℃ / min. After the copper block was completely melted, the furnace temperature was maintained at 1175℃ for 0.9h. During this period, the bidirectional electromagnetic stirring device was turned on, the electromagnetic stirring current was controlled at 75A, the stirring frequency was 28Hz, and the stirring method was adopted by alternating forward rotation for 30s and reverse rotation for 30s. Step S3, Inert Gas Protection Refining: After vacuum melting and heat preservation, high-purity argon gas with a purity ≥99.999% is slowly introduced into the furnace until the furnace pressure rises to 0.12MPa. The argon gas flow rate is maintained at 19L / min. Then, a two-stage bottom-blowing refining process is performed. During the two-stage bottom-blowing process, a gradient reduction composite covering agent is added to the surface of the copper liquid, with a covering thickness of 190mm. During the refining process, the furnace temperature is maintained at 1155℃. During this period, bidirectional electromagnetic stirring is continuously performed to ensure that the composite covering agent reacts fully with the copper liquid, achieving deep deoxidation and impurity removal. The current of the bidirectional electromagnetic stirring is 75A, and the frequency is 28Hz. After refining, the mixture is allowed to stand for 9 minutes to allow the remaining impurity particles to fully float to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The copper liquid is then cooled to room temperature with the furnace to obtain preliminary copper ingots. Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode for electron beam melting; the melting vacuum degree is better than 5×10 -5Pa, electron beam power of 110kW, scanning frequency of 1400Hz, melting speed of 23kg / h, to obtain deeply purified copper liquid; Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber, which is equipped with a non-consumable tungsten electrode. The working gas is a mixture of hydrogen and argon, with hydrogen comprising 45% and argon as the remainder. The vacuum degree of the melting chamber is maintained at 6 × 10⁻⁶. -4 Pa, arc current of 380A, arc voltage of 33V, molten pool temperature controlled at 1175℃ to achieve deep deoxidation; smelting time controlled at 28min; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 190K / cm and the solidification pull-down speed v is 9mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

[0037] The electrolysis temperature in step S1 is 63℃; the polyethylene glycol in step S1 is polyethylene glycol PEG 6000; the specific parameters of the periodic commutation current in step S1 are: forward current density 310A / m², reverse current density 45A / m², and commutation period of 300s forward / 10s reverse; the electrolyte in step S1 is continuously filtered and purified with a filtration accuracy of 0.55μm and a circulation flow rate of 1.1L / (min·m²) to remove solid suspended particles in the electrolyte; the dual-stage bottom blowing in step S3 includes primary bottom blowing and secondary bottom blowing, wherein the primary bottom blowing tube is inserted into the copper liquid to a depth of 240mm, the argon flow rate is 19L / min, and the bottom blowing time is 19min; the secondary bottom blowing tube is inserted to a depth of 190mm, the argon flow rate is 14L / min, and the bottom blowing time is 19min.

[0038] The gradient reduction composite covering agent comprises the following components in parts by weight: 95.5 parts high-purity graphite particles, 2.8 parts lamp smoke carbon black, 1.8 parts acetylene black, 0.9 parts calcium fluoride, and 0.25 parts nano-alumina; the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

[0039] In the hydrogen plasma arc melting process described in step S5, electromagnetic stirring technology is used, with a stirring current frequency of 40Hz and a magnetic field strength of 0.09T. In the directional solidification process described in step S6, a steady magnetic field is applied at the front of the solid-liquid interface, with a magnetic induction intensity of 0.45T. In the annealing treatment described in step S7, a two-stage annealing treatment is performed. The annealing temperature of the first stage is 340℃, and the holding time is 1.9h. The annealing temperature of the second stage is 490℃, and the holding time is 2.8h. Example 5

[0040] A method for preparing high-purity oxygen-free copper includes the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolytic copper is obtained by periodic commutation current electrolysis; the electrolyte used is deionized water as solvent, including the following components at the following concentrations: CuSO4 55 g / L, H2SO4 220 g / L, HCl 0.03 g / L, and composite additive 0.12 g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:0.4:2:0.1. Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace, and the melting is carried out under a vacuum of 1×10⁻⁶. -3 At Pa, the temperature was increased from room temperature to 800℃ at a heating rate of 8℃ / min, and then increased from 800℃ to 1180℃ at a heating rate of 5℃ / min. After the copper block was completely melted, the furnace temperature was maintained at 1180℃ for 1 hour. During this period, the bidirectional electromagnetic stirring device was turned on, the electromagnetic stirring current was controlled at 80A, the stirring frequency was 30Hz, and the stirring method was adopted by alternating forward rotation for 30s and reverse rotation for 30s. Step S3, Inert Gas Protected Refining: After vacuum melting and heat preservation, high-purity argon gas with a purity ≥99.999% is slowly introduced into the furnace until the furnace pressure rises to 0.12MPa. The argon gas flow rate is maintained at 20L / min. Then, a two-stage bottom-blowing refining process is performed. During the two-stage bottom-blowing process, a gradient reduction composite covering agent with a thickness of 200mm is added to the surface of the copper liquid. During the refining process, the furnace temperature is maintained at 1160℃. During this period, bidirectional electromagnetic stirring is continuously performed to ensure that the composite covering agent reacts fully with the copper liquid, achieving deep deoxidation and impurity removal. The current of the bidirectional electromagnetic stirring is 80A and the frequency is 30Hz. After refining, the mixture is allowed to stand for 10 minutes to allow the remaining impurity particles to fully float to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The copper liquid is cooled to room temperature with the furnace to obtain preliminary copper ingots. Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode for electron beam melting; the melting vacuum degree is better than 5×10 -5Pa, electron beam power of 120kW, scanning frequency of 1500Hz, melting speed of 25kg / h, to obtain deeply purified copper liquid; Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber, which is equipped with a non-consumable tungsten electrode. The working gas is a mixture of hydrogen and argon, with hydrogen comprising 50% and argon as the remainder. The vacuum degree of the melting chamber is maintained at 5 × 10⁻⁶. -4 Pa, arc current of 400A, arc voltage of 35V, molten pool temperature controlled at 1180℃ to achieve deep deoxidation; smelting time controlled at 30min; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 200K / cm and the solidification pull-down speed v is 10mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

[0041] The electrolysis temperature in step S1 is 65℃; the polyethylene glycol in step S1 is polyethylene glycol PEG 6000; the specific parameters of the periodic commutation current in step S1 are: forward current density 320A / m², reverse current density 50A / m², and commutation period of 300s forward / 10s reverse; the electrolyte in step S1 is continuously filtered and purified with a filtration accuracy of 0.6μm and a circulation flow rate of 1.2L / (min·m²) to remove solid suspended particles in the electrolyte; the dual-stage bottom blowing in step S3 includes primary bottom blowing and secondary bottom blowing, wherein the primary bottom blowing tube is inserted into the copper liquid to a depth of 250mm, the argon flow rate is 20L / min, and the bottom blowing time is 20min; the secondary bottom blowing tube is inserted to a depth of 200mm, the argon flow rate is 15L / min, and the bottom blowing time is 20min.

[0042] The gradient reduction composite covering agent comprises the following components in parts by weight: 96 parts high-purity graphite particles, 3 parts lamp smoke carbon black, 2 parts acetylene black, 1 part calcium fluoride, and 0.3 parts nano-alumina; the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

[0043] In the hydrogen plasma arc melting process described in step S5, electromagnetic stirring technology is used, with a stirring current frequency of 50Hz and a magnetic field strength of 0.1T; in the directional solidification process described in step S6, a steady magnetic field is applied at the front of the solid-liquid interface, with a magnetic induction intensity of 0.5T; in the annealing treatment described in step S7, a two-stage annealing treatment is performed, with the annealing temperature of the first stage at 350℃ and the holding time at 2h; and the annealing temperature of the second stage at 500℃ and the holding time at 3h.

[0044] Comparative Example 1 This example provides a method for preparing high-purity oxygen-free copper, which is basically the same as that in Example 1, except that an equal amount of thiazolidin-2-thione is used instead of pyridine hydroxypropanesulfonic acid salt.

[0045] Comparative Example 2 This example provides a method for preparing high-purity oxygen-free copper, which is basically the same as that in Example 1, except that an equal amount of pyridinium hydroxypropanesulfonic acid salt is used instead of thiazolidin-2-thione.

[0046] Comparative Example 3 This example provides a method for preparing high-purity oxygen-free copper, which is basically the same as that in Example 1, except that the hydrogen plasma arc melting step is omitted.

[0047] Comparative Example 4 This example provides a method for preparing high-purity oxygen-free copper, which is basically the same as that in Example 1, except that there is no electron beam melting step.

[0048] To further illustrate the beneficial technical effects of the high-purity oxygen-free copper preparation methods involved in the various embodiments of the present invention, the high-purity oxygen-free copper prepared by the high-purity oxygen-free copper preparation methods involved in Example 1 and Comparative Examples 1-4 was subjected to compositional analysis, and the resistivity was measured using a resistivity measuring instrument in accordance with GB / T 351-2019 "Methods for Measuring the Resistivity of Metallic Materials", and then the conductivity (in IACS units) was calculated. The results are shown in Table 1.

[0049] Table 1 Test Results of High-Purity Oxygen-Free Copper project conductivity Copper content Oxygen content unit %IACS % ppm Example 1 102.3 ≥99.9999 ＜1.0 Comparative Example 1 100.7 99.99950 3.8 Comparative Example 2 101.0 99.99957 3.2 Comparative Example 3 99.1 99.99875 8.3 Comparative Example 4 99.8 99.99917 6.5 As can be seen from the table above, the high-purity oxygen-free copper prepared in Example 1 exhibits the best overall performance, with a conductivity of 102.3% IACS, a copper content ≥99.9999%, and an oxygen content <1.0 ppm. Comparative Examples 1-2, due to the lack of composite additive components, Comparative Example 3, due to the lack of hydrogen plasma arc melting, and Comparative Example 4, due to the lack of electron beam melting, all showed decreased conductivity, reduced copper content, and increased oxygen content. The combined use of thiazolidin-2-thione, pyridinium hydroxypropanesulfonate, hydrogen plasma arc melting, and electron beam melting is beneficial for improving the aforementioned properties of the product.

[0050] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity oxygen-free copper, characterized in that, Includes the following steps: Step S1, Multi-stage electrolytic refining: Using 4N grade cathode copper as the anode and pure copper starting sheet as the cathode, electrolytic copper is obtained by periodic commutation current electrolysis; the electrolyte used is deionized water as solvent, including the following components at the following concentrations: CuSO4 45-55 g / L, H2SO4 180-220 g / L, HCl 0.01-0.03 g / L, and composite additive 0.08-0.12 g / L; the composite additive is composed of gelatin, thiazolidin-2-thione, polyethylene glycol, and pyridinium hydroxypropanesulfonate in a mass ratio of 1:(0.2-0.4):2:0.

1. Step S2, Gradient Heating Vacuum Melting: Electrolytic copper is added to a vacuum melting furnace for gradient heating vacuum melting; Step S3, Inert Gas Protection Refining: After vacuum melting and heat preservation, inert gas protection refining is carried out, and then the copper liquid is cooled to room temperature with the furnace to obtain preliminary copper ingots; Step S4, Electron Beam Melting: After mechanically grinding the surface of the initial copper ingot to remove the oxide scale, it is placed in an electron beam cold hearth melting furnace as a consumable electrode to obtain deeply purified copper liquid. Step S5, Hydrogen Plasma Arc Melting: The deeply purified copper liquid is guided to the hydrogen plasma arc melting chamber for hydrogen plasma arc melting; Step S6, Directional solidification: The copper liquid processed in step S5 is poured into a pull-down directional solidification crucible. The crucible is made of tantalum-plated graphite and has a water-cooled copper crystallizer at the bottom. The solid-liquid interface temperature gradient G is controlled to be 150-200K / cm and the solidification pull-down speed v is 5-10mm / h to obtain a high-purity oxygen-free copper ingot. Step S7, Post-processing: The high-purity oxygen-free copper ingot is annealed in an argon atmosphere to finally obtain the high-purity oxygen-free copper product.

2. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, The electrolysis temperature in step S1 is 55-65℃; the polyethylene glycol is polyethylene glycol PEG 6000.

3. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, The specific parameters of the periodic commutation current in step S1 are: forward current density 280-320A / m², reverse current density 30-50A / m², and commutation period of 300s forward / 10s reverse; the electrolyte is continuously filtered and purified with a filtration accuracy of 0.4-0.6μm and a circulation flow rate of 0.8-1.2L / (min·m²) to remove solid suspended particles in the electrolyte.

4. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, The gradient heating vacuum melting described in step S2 specifically involves: at a vacuum degree of 5×10 -3 -1×10 -3 Under Pa conditions, the temperature is increased from room temperature to 800℃ at a heating rate of 5-8℃ / min, and then increased from 800℃ to 1150-1180℃ at a heating rate of 3-5℃ / min. After the copper block is completely melted, the furnace temperature is maintained at 1150-1180℃ for 0.5-1h. During this period, the bidirectional electromagnetic stirring device is turned on, with the electromagnetic stirring current controlled at 50-80A and the stirring frequency at 20-30Hz, using an alternating stirring method of 30s forward and 30s reverse.

5. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, The inert gas protected refining process in step S3 specifically involves: slowly introducing high-purity argon gas (≥99.999%) into the furnace until the furnace pressure reaches 0.10-0.12 MPa, maintaining an argon flow rate of 15-20 L / min. Then, a two-stage bottom-blowing refining process is performed. During this process, a gradient reduction composite covering agent is added to the surface of the molten copper, with a covering thickness of 150-200 mm. During the refining process, the furnace temperature is maintained at 1140-1160℃, and continuous bidirectional electromagnetic stirring is used to ensure the composite covering agent fully reacts with the molten copper, achieving deep deoxidation and impurity removal. The bidirectional electromagnetic stirring... The current is 50-80A and the frequency is 20-30Hz. After refining, let it stand for 5-10 minutes to allow the remaining impurity particles to float fully to the covering agent layer. After slag removal, the copper liquid and impurities are completely separated. The dual-stage bottom blowing includes a first-stage bottom blowing and a second-stage bottom blowing. The bottom blowing tube of the first-stage bottom blowing is inserted into the copper liquid to a depth of 200-250mm, the argon flow rate is 15-20L / min, and the bottom blowing time is 15-20min. The bottom blowing tube of the second-stage bottom blowing is inserted to a depth of 150-200mm, the argon flow rate is 10-15L / min, and the bottom blowing time is 15-20min.

6. The method for preparing high-purity oxygen-free copper according to claim 5, characterized in that, The gradient reduction composite covering agent comprises the following components in parts by weight: 94-96 parts high-purity graphite particles, 2-3 parts lamp smoke carbon black, 1-2 parts acetylene black, 0.5-1 parts calcium fluoride, and 0.1-0.3 parts nano-alumina; the high-purity graphite particles have a purity ≥99.99% and a particle size of 1-3 mm; the lamp smoke carbon black has a particle size of 100-200 μm; the acetylene black has a particle size of 200-500 μm; the calcium fluoride has a particle size of 100-300 μm; and the nano-alumina has a particle size of 50-100 nm.

7. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, The specific parameters for electron beam melting in step S4 are: melting vacuum degree better than 5×10 -5 Pa, electron beam power of 80-120kW, scanning frequency of 1000-1500Hz, melting speed of 15-25kg / h.

8. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, The specific parameters for hydrogen plasma arc melting in step S5 are as follows: the melting chamber is equipped with a non-consumable tungsten electrode; the working gas is a mixture of hydrogen and argon, wherein the hydrogen component is 30-50% and the remainder is argon; the vacuum degree of the melting chamber is maintained at 1×10⁻⁶. -3 -5×10 -4 The electric arc current is 300-400A, the electric arc voltage is 25-35V, and the molten pool temperature is controlled at 1150-1180℃ to achieve deep deoxidation; the melting time is controlled at 20-30min; during the hydrogen plasma arc melting process, electromagnetic stirring technology is used, with a stirring current frequency of 10-50Hz and a magnetic field strength of 0.05-0.1T.

9. The method for preparing high-purity oxygen-free copper according to claim 1, characterized in that, During the directional solidification process described in step S6, a steady magnetic field with a magnetic induction intensity of 0.2-0.5T is applied at the front edge of the solid-liquid interface. The annealing treatment described in step S7 is a two-stage annealing treatment. The annealing temperature of the first stage is 300-350℃, and the holding time is 1.5-2h. The annealing temperature of the second stage is 450-500℃, and the holding time is 2-3h.

10. The method for preparing high-purity oxygen-free copper according to any one of claims 1-9, characterized in that, The high-purity oxygen-free copper has a conductivity of 102.3% IACS, a copper content of 99.999989%, and an oxygen content of ≤1.0ppm.