Low-cost, high-strength Bi-based superconducting wire strip and its manufacturing method

Abstract

The present invention discloses a low-cost and high-strength Bi-based superconducting wire strip and a manufacturing method thereof. The method includes: Step 1 of subjecting the Bi-based superconducting wire strip to electrochemical silver reduction to remove the Ag alloy layer; and Step 2 of subjecting the Bi-based superconducting wire strip subjected to electrochemical silver reduction to surface strengthening treatment to form a Cu layer, thereby obtaining a low-cost and high-strength Bi-based superconducting wire strip. By combining the electrochemical silver reduction technology and the electrochemical additional processing method, the present invention removes the Ag alloy layer on the surface of the Bi-based superconducting wire strip and electroplates a high-strength Cu layer, thereby manufacturing a low-cost and high-strength Bi-based superconducting wire strip, reducing the manufacturing cost, increasing the strength of the Bi-based superconducting wire strip, meeting the requirements for application to large superconducting magnets, and enabling the manufacture of wire strips with various critical bending radii by adjusting the thickness of the Cu layer, which can be applied to small-diameter magnets. Moreover, the process is simple and suitable for mass production.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority from Chinese Patent Application No. 202310565846.9, filed May 19, 2023. This application cites the above-mentioned Chinese patent application in its entirety.

[0002] The present invention relates to the technical field of manufacturing high-temperature superconducting wire strips, and more particularly to a low-cost, high-strength Bi-based superconducting wire strip and a manufacturing method thereof. [Background technology]

[0003] Bi-based high-temperature superconducting wire strips have excellent current-carrying properties, an ultra-high upper critical magnetic field of up to 100 T, and a superconducting transition temperature of above 77 K. They have good prospects for application in both liquid nitrogen temperature power transmission and liquid helium high magnetic fields, and have already been applied in ultra-strong NMR magnetic field magnets, superconducting cables, superconducting current limiters, superconducting energy storage magnets, nuclear fusion superconducting magnets, accelerator magnets, etc.

[0004] Bi-based wire strips are manufactured using the powder-in-tube method, in which precursor ceramic oxide powders are placed inside a silver tube to form a single-filament composite. This process involves drawing single-filament wires, converging and drawing multi-filament wires, or rolling, followed by heat treatment to produce high-performance Bi-based wire strips. The oxygen partial pressure around the superconducting core must be consistent throughout the entire heat treatment process; otherwise, segregation problems may occur, significantly reducing the sample's current performance. The oxide core absorbs oxygen during temperature rise, and the superconducting core releases oxygen during warming, resulting in real-time changes in the oxygen partial pressure around the core. Therefore, oxygen-permeable cladding materials are required for Bi-based superconducting wire strips. Furthermore, the cladding materials must be non-reactive with the Bi-based precursor powder. Currently, the only cladding materials that meet these two requirements are silver and silver alloys. Therefore, only Ag and Ag alloys can be used as cladding materials to manufacture Bi-based superconducting wire strips. However, Ag and Ag alloys have the following drawbacks as cladding materials.

[0005] (1) The cost of Bi-based superconducting wire strips is too high due to the high content of pure Ag and Ag alloys (Ag alloys used in Bi-based superconducting wire strips are silver alloys with an Ag content of over 99%). The Ag and Ag alloy content in Bi-based superconducting wire strips is nearly 70%, while the Ag and Ag alloy content in Bi-based superconducting wire strips is even higher, exceeding 80%. Ag and Ag alloys are precious metals and are much more expensive than other metals, which makes Bi-based superconducting wire strips expensive and limits their large-scale application. Therefore, in order to realize large-scale application of Bi-based superconducting wire strips, it is necessary to reduce the Ag content and cost.

[0006] (2) When the Ag and Ag alloy content is high, the strength of Bi-based superconducting wire strip is too low. The most important application of Bi-based superconducting wire strip is in high magnetic fields of 30 T or higher. The strong magnetic field and the supercurrent within the superconducting wire strip interact strongly, subjecting the superconducting wire strip to large tensile stress. Furthermore, the larger the diameter of the superconducting magnet, the greater the tensile stress the superconducting wire strip experiences. However, the strength of Ag and Ag alloys is relatively low, making it difficult for Bi-based superconducting wire strips clad with Ag and Ag alloys to meet the requirements of high-field magnets. Therefore, to realize the application of Bi-based superconducting wire strips in ultra-high magnetic fields, it is necessary to improve the strength of existing Bi-based superconducting wire strips.

[0007] (3) The critical engineering current density of the reinforced Bi-based superconducting wire strip is significantly reduced. Conventional reinforced Bi-based superconducting wire strips are made by directly welding a high-strength metal strip to the surface of a Bi-based superconducting wire strip. Compared with the original superconducting wire strip, the thickness or diameter of this reinforced superconducting wire strip is significantly increased, which significantly reduces the critical engineering current density of the sample and significantly increases the size of the superconducting device manufactured with this reinforced superconducting wire strip, significantly increasing the cooling costs and superconducting material costs of the superconducting device. Therefore, in order to realize large-scale application of reinforced Bi-based superconducting wire strips, it is necessary to reduce the size of the reinforced Bi-based superconducting wire strip and increase the critical engineering current density of the wire strip. Summary of the Invention [Problem to be solved by the invention]

[0008] The technical problem to be solved by the present invention is to provide a low-cost, high-strength Bi-based superconducting wire strip and a method for manufacturing the same, which overcomes the drawbacks of the prior art. The method combines electrochemical silver reduction technology and electrochemical additive processing to remove the Ag alloy layer on the surface of the Bi-based superconducting wire strip and plate a high-strength Cu layer, thereby producing a low-cost, high-strength Bi-based superconducting wire strip, reducing the cost of the Bi-based superconducting wire strip and increasing its strength, and solving the difficult problems of high cost and low strength caused by using Ag or Ag alloy cladding on the Bi-based superconducting wire strip. [Means for solving the problem]

[0009] In order to solve the above technical problems, one aspect of the present invention is to Electrochemical silver reduction: Step 1: connecting a Bi-based superconducting wire strip to the positive pole of a constant voltage power supply, connecting a graphite electrode to the negative pole of the constant voltage power supply, and then mounting the Bi-based superconducting wire strip and the graphite electrode in parallel on a holder, and then placing them in an electrolyte to perform electrochemical silver reduction, thereby removing the Ag alloy layer on the surface of the Bi-based superconducting wire strip; Surface strengthening: Step 2, in which the Bi-based superconducting wire strip that has been subjected to electrochemical silver reduction in step 1 is connected to the negative electrode of a constant-voltage power supply, tough pitch copper is connected to the positive electrode of the constant-voltage power supply, and then the Bi-based superconducting wire strip that has been subjected to electrochemical silver reduction and the tough pitch copper are attached in parallel to a holder and placed in an electrochemical additive processing solution for surface strengthening treatment, thereby forming a Cu layer on the surface of the Bi-based superconducting wire strip, thereby obtaining the low-cost, high-strength Bi-based superconducting wire strip.

[0010] In the present invention, all of the Bi-based superconducting wire strips initially used use Ag and / or Ag alloy as the cladding material.

[0011] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire ribbon, in step 1, the width of the graphite electrode is at least three times, preferably 3 to 5 times, more preferably 3 times the width or diameter of the Bi-based superconducting wire ribbon, and / or the electrolyte is a deionized aqueous solution of a soluble silver salt at a concentration of 2 g / L to 10 g / L, and the pH of the deionized aqueous solution of the soluble silver salt is adjusted to 3 to 5 with a metal hydroxide; Preferably, the concentration of the soluble silver salt deionized aqueous solution is 6 g / L. In the present invention, by controlling the pH of the electrolyte, electrochemical silver reduction is achieved without damaging the superconducting core yarn in the Bi-based superconducting wire ribbon.

[0012] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire ribbon, the soluble silver salt is selected from the group consisting of silver nitrate, silver fluoride, silver chlorate, and silver perchlorate; And / or, the metal hydroxide is selected from sodium hydroxide, potassium hydroxide, barium hydroxide, and lithium hydroxide.

[0013] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire strip, in step 1, the distance between the Bi-based superconducting wire strip and the graphite electrode is 1 cm to 5 cm, preferably 3.5 cm; and / or the current density on the surface of the Bi-based superconducting wire strip is 0.1 A / dm 2 ~10A / dm 2 , preferably 5A / dm 2 and And / or, the current application time is 0.1 to 30 minutes, preferably 3 minutes.

[0014] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire ribbon, in step 2, the electrochemical additive processing solution is a deionized aqueous solution containing 0.1 g / L to 20 g / L of a soluble copper salt and 10 g / L to 50 g / L of an acidic substance; The concentration of the soluble copper salt is preferably 10 g / L; The concentration of the acidic substance is preferably 30 g / L.

[0015] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire ribbon, the soluble copper salt is selected from copper sulfate, copper chloride, and copper nitrate; And / or, the acidic substance is selected from citric acid, sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

[0016] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire strip, in step 2, the distance between the Bi-based superconducting wire strip and the tough pitch copper is 2 cm to 5 cm, preferably 3.5 cm; and / or the current density on the surface of the Bi-based superconducting wire strip is 0.1 A / dm 2 ~10A / dm 2 , preferably 5A / dm 2 and and / or the treatment time is 0.1 min to 20 min, preferably 10 min; And / or, the thickness of the Cu layer is 10 μm to 40 μm, preferably 25 μm.

[0017] In the above-mentioned low-cost, high-strength Bi-based superconducting wire ribbon manufacturing method, before step 1, Surface wiping: The method further includes a step of cleaning the surface of the Bi-based superconducting wire band with ethanol to remove any dirt remaining on the surface of the Bi-based superconducting wire band.

[0018] In the above-mentioned low-cost, high-strength Bi-based superconducting wire ribbon manufacturing method, before step 2, Residual Liquid Washing: The method further includes a step of immersing the Bi-based superconducting wire strip that has been subjected to electrochemical silver reduction in step 1 in high-purity water to wash and remove the electrolyte remaining on the surface.

[0019] Another aspect of the present invention further provides a low-cost, high-strength Bi-based superconducting wire strip produced by the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire strip. [Effects of the Invention]

[0020] Compared with the prior art, the present invention has the following advantages: 1. In order to address the problem of high costs due to the need to use the precious metal Ag or Ag alloy as a cladding material for Bi-based superconducting wire strips, with the Ag content reaching 66% to 82%, the present invention uses electrochemical silver reduction technology to remove the Ag alloy layer on the surface of the Bi-based superconducting wire strip, thereby reducing the effective Ag content in the Bi-based superconducting wire strip by approximately 50% and reducing the cost of the Bi-based superconducting wire strip by approximately 45%. Furthermore, a surface strengthening treatment is performed by plating a high-strength Cu layer on the surface of the Bi-based superconducting wire strip from which the Ag alloy layer has been removed, thereby producing high-strength Bi-based superconducting wire strips at low cost. This is because the Ag mass content is less than one-fold lower than that of Bi-based superconducting wire strip, yet the superconducting critical strength is more than two-fold higher. Furthermore, the electrochemical silver reduction step is a controllable Ag reduction process with extremely low or no stress, which avoids the destruction of the ceramic superconducting core caused by excessive stress in conventional mechanical silver reduction, thereby avoiding the loss of superconducting performance of the Bi-based superconducting wire strip. 2. In the present invention, the surface of a Bi-based superconducting wire strip is plated with a high-strength Cu layer instead of an Ag alloy using an electrochemical additive processing method, thereby improving the strength of the Bi-based superconducting wire strip, particularly its yield strength, and being able to withstand the strong tensile stress that occurs when the Bi-based superconducting wire strip strongly interacts with current after being subjected to a strong magnetic field. This avoids the problem that the Bi-based superconducting wire strip has little mechanical support due to the low strength of Ag and Ag alloy cladding materials, allowing the Bi-based superconducting wire strip to meet the requirements for application in large, ultra-strong magnets, promoting the development of large Bi-based ultra-strong superconducting magnetic materials and facilitating the development of nuclear fusion, accelerators and large-diameter NMR. 3. In the present invention, the Ag alloy layer on the surface of the Bi-based superconducting wire strip is removed by electrochemical silver reduction technology, while electroplating Ag is formed on the surface of the graphite electrode, and the purity of the electroplated Ag is increased to 99.9 mass% or more. This makes it possible to directly produce an Ag tube and use it in the production of Bi-based superconducting wire strip, thereby enabling the reuse of Ag, reducing waste, and further reducing the cost of Bi-based superconducting wire strip. 4. In the present invention, by using an electrochemical additive processing method to plate a high-strength Cu layer on the surface of a Bi-based superconducting wire ribbon instead of low-strength Ag or Ag alloy, the strength of the Bi-based superconducting wire ribbon is greatly improved, damage to the Bi-based superconducting wire ribbon when it is wound around a cable or magnet is avoided, and the Bi-based superconducting wire ribbon is made suitable for the production of cables and magnets. 5. In the present invention, the thickness of the Cu layer is adjusted by controlling the surface strengthening treatment process, and further the diameter and thickness of the Bi-based superconducting wire ribbon are controlled, thereby manufacturing wire ribbons with various critical bending radii, which not only reduces the cost of the Bi-based superconducting wire ribbon, but also makes it possible to manufacture Bi-based superconducting wire ribbons with smaller diameters and thicknesses, thereby reducing the critical bending radius of the Bi-based superconducting wire ribbon and making it suitable for manufacturing small-diameter magnets. 6. The present invention has a simple manufacturing process and reasonable process design, making it possible to mass-produce high-strength Bi-based wire strips at low cost, which is advantageous for promoting the industrialization and application of Bi-based superconducting wire strips. The technical solution of the present invention will be further described in detail below with reference to the drawings and examples. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a structural schematic diagram of a Bi-based superconducting band material used in Example 1 of the present invention. [Figure 2] 1 is a structural schematic diagram of a low-cost, high-strength Bi-based superconducting band material produced in Example 1 of the present invention. [Figure 3] FIG. 3 is a structural schematic diagram of a Bi-based superconducting wire used in Example 2 of the present invention. [Figure 4] FIG. 2 is a structural schematic diagram of a low-cost, high-strength Bi-based superconducting wire produced in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The technical solutions in the embodiments of the present invention will be described below clearly and completely with reference to the drawings of the present invention, but it is clear that the described embodiments are only some of the embodiments of the present invention, and are not all of the embodiments. The experimental methods without specific conditions specified in the following examples are selected according to the usual methods and conditions or product manuals.

[0023] (Performance test) The products manufactured in the examples and comparative examples were subjected to performance tests. The test standards or methods were as follows:

[0024] 1. Ag content test The Ag content was determined according to GB / T 11067.1-2006 "Methods for chemical analysis of silver, determination of silver content, silver chloride precipitation-flame atomic absorption spectrometry."

[0025] 2. Breaking strength test The fracture strength test was carried out in accordance with GB / T 36611-2018 "Measurement of mechanical properties, room temperature tensile test method for Ag and / or Ag alloy clad Bi-2223 and Bi-2212 composite superconductors."

[0026] 3. Cost calculation In a typical Bi-based superconducting wire strip, Ag raw material accounts for approximately 96% of the cost, other materials account for 2%, and processing costs account for 2%. In this application, the Ag in the outer layer of the Bi-based superconducting wire strip is changed to Cu. The changed Ag is half the silver content of the superconducting wire strip. The price of the Cu raw material is 1 / 100 of the price of the Ag raw material. When Ag is changed to copper, the processing cost (processing cost by electrochemical Ag reduction and electrochemical additional processing) is approximately 20% of the price of the copper raw material. The cost of a typical Bi-based superconducting wire strip is set to 100%, and the method for calculating the cost of the superconducting wire strip in this application is as follows: Cost reduction rate = 100% - cost of modified raw material Cu - modified processing cost - remaining Ag raw material in the superconducting strip - other material and processing costs.

[0027] 4. Superconducting critical current Superconducting critical current tests were conducted in accordance with GB / T 18502-2018 / IEC 61788-3:2006 "Critical current measurements, DC critical current of silver and / or silver alloy clad Bi-2212 and Bi-2223 oxide superconductors."

[0028] 5. Superconducting critical tensile strength test In-situ testing of the superconducting critical current of wire ribbon samples was performed by applying tension to both longitudinal ends. The tension that reduces the critical current of the sample to 95% of the current in the unstressed state is the superconducting critical tensile strength of the sample [Fischer K, Fahr T, Schlafer U, et al. Effect of processing parameters and tensile stress on the performance of Bi-2223 ribbon (with Ag and AgMn cladding) [J]. IEEE Transactions on Applied Superconductivity, 1999, 9(2): 2625-2628], and [Mao ZH, Jin H, Qin JG, et al. Axial tensile stress-strain properties of Bi-2212 round wire under various heat treatment conditions [J]. IEEE Transactions on Applied Superconductivity, 2017, 27(6): 6400405].

[0029] 6. Critical bending radius The wire ribbon was uniformly bent along its length, and the superconducting critical current of the sample was tested in situ. The bending radius at which the critical current of the sample dropped to 95% of the critical current of the straight sample was the critical bending radius of the sample [Shin HS, Katagiri K. Critical current degradation behavior of Bi-2223 superconducting ribbon under bending and torsional strain [J]. Superconductor Science and Technology, 2003, 16(9): 1012-1018]. [Example]

[0030] This embodiment includes the following steps. Step 1 Surface wiping: The surface of the Bi-based superconducting band material (see FIG. 1) was wiped with a cotton cloth wetted with ethanol to remove any dirt remaining on the surface of the Bi-based superconducting band material during the heat treatment process. Step 2 Electrochemical silver reduction: The Bi-based superconducting strip wiped in step 1 was connected to the positive pole of a constant-voltage power supply, and the graphite electrode was connected to the negative pole of the constant-voltage power supply. The width of the graphite electrode was 12 mm, the width of the Bi-based superconducting strip was 4 mm, and the width of the graphite electrode was three times the width of the Bi-based superconducting strip. Next, the wiped Bi-based superconducting strip and the graphite electrode were attached in parallel to a holder and placed in an electrolyte to perform electrochemical silver reduction. The distance between the Bi-based superconducting strip and the graphite electrode was 1 cm, and the electrolyte was a 2 g / L AgNO3 solution, the pH of which was adjusted to 3 with sodium hydroxide. During electrochemical silver reduction, the current density on the surface of the Bi-based superconducting strip was 0.1 A / dm 2 The current was adjusted to 500 W, and the current was applied for 30 minutes. This removed the Ag alloy layer on the surface of the Bi-based superconducting band material, exposing the silver layer on the surface of the superconducting core yarn in the outer layer of the Bi-based superconducting band material, and electroplated Ag with a purity of 99.99% by mass was formed on the surface of the graphite electrode. Step 3 Residual liquid washing: The Bi-based superconducting strip material that had been subjected to electrochemical silver reduction in step 2 was immersed in high-purity water to wash away the electrolyte remaining on the surface. Step 4 Surface strengthening: The Bi-based superconducting strip cleaned in step 3 was connected to the negative pole of a constant voltage power supply, and the tough pitch copper was connected to the positive pole of the constant voltage power supply. Next, the cleaned Bi-based superconducting strip and the tough pitch copper were attached in parallel to a holder and placed in an electrochemical additive processing solution for surface strengthening. The distance between the cleaned Bi-based superconducting wire strip and the tough pitch copper was 2 cm, and the electrochemical additive processing solution contained 0.1 g / L copper sulfate and 10 g / L citric acid. During the surface strengthening treatment, the current density on the surface of the Bi-based superconducting strip was 0.1 A / dm 2 The treatment time was adjusted to 20 min. As a result, a 20 μm thick Cu layer was formed on the surface of the Bi-based superconducting band material, and a low-cost, high-strength Bi-based superconducting band material (see Figure 2) was obtained. The results showed that the Ag mass content of the low-cost, high-strength Bi-based superconducting strip produced in this example was reduced from 66% to 33% of that of the original Bi-based superconducting strip, its breaking strength increased from 90-94 MPa of the original Bi-based superconducting strip to 102-104 MPa, and its superconducting critical tensile strength at 77 K increased from 5 kgf / cm2 to 14 kgf / cm2, thereby enhancing its mechanical properties. The low-cost, high-strength Bi-based superconducting strip produced in this example exhibited superconducting critical current performance that was completely consistent with that of the original Bi-based superconducting strip, with both having a superconducting critical current of 53 A in a self-field at 77 K. This demonstrates that the electrochemical Ag reduction and electrochemical copper deposition processes have no effect on the performance of the superconducting core yarn. [Table 1] In this embodiment, copper is used in place of approximately half of the precious metal Ag in the Bi-based superconducting band material, thereby achieving a cost reduction rate of 47.424% without reducing the current-carrying performance of the Bi-based superconducting band material. Meanwhile, the strengthened mechanical properties make the Bi-based superconducting band material applicable to conditions of even more severe magnetic fields and pressures, thereby expanding the range of applications for the Bi-based superconducting band material. Fig. 1 is a schematic diagram of the structure of the Bi-based superconducting band used in Example 1. This Bi-based superconducting band includes a superconducting core yarn 1, an Ag layer covering the outside of the superconducting core yarn 1, and an Ag alloy layer 3 covering the outermost layer. Fig. 2 is a schematic diagram of the structure of the low-cost, high-strength Bi-based superconducting band produced in this example. This Bi-based superconducting band includes a superconducting core yarn 1, an Ag layer covering the outside of the superconducting core yarn 1, and a Cu layer 4 covering the outermost layer. A comparison of Figs. 1 and 2 reveals that in this invention, the Ag alloy layer on the surface of the Bi-based superconducting wire band is removed using electrochemical silver reduction technology and electrochemical additive processing, and a high-strength Cu layer is plated in its place. [Example]

[0031] This embodiment includes the following steps. Step 1 Surface wiping: The surface of the Bi-based superconducting wire (see FIG. 3) was wiped with a cotton cloth wetted with ethanol to remove dirt remaining on the surface of the Bi-based superconducting wire during the heat treatment process. Step 2 Electrochemical silver reduction: The Bi-based superconducting wire wiped in step 1 was connected to the positive pole of a constant-voltage power supply, and the graphite electrode was connected to the negative pole of the constant-voltage power supply. The width of the graphite electrode was 16 mm, the diameter of the Bi-based superconducting band was 4 mm, and the width of the graphite electrode was four times the diameter of the Bi-based superconducting band. Next, the wiped Bi-based superconducting wire and the graphite electrode were attached in parallel to a holder and placed in an electrolyte to perform electrochemical silver reduction. The distance between the Bi-based superconducting wire and the graphite electrode was 1 cm, and the electrolyte was a 2 g / L AgNO3 solution, the pH of which was adjusted to 3 with sodium hydroxide. During electrochemical silver reduction, the current density on the surface of the Bi-based superconducting wire was 10 A / dm 2 The current flow time was adjusted to 15 minutes, and the Ag alloy layer on the surface of the Bi-based superconducting wire was removed, exposing the silver layer on the surface of the superconducting core yarn in the outer layer of the Bi-based superconducting wire, and electroplated Ag with a purity of 99.99% by mass was formed on the surface of the graphite electrode. Step 3 This is the same as in the first embodiment. Step 4 The following points are different from Example 1: The electrochemical additive processing solution contains 2 g / L of copper sulfate and 10 g / L of citric acid, and the current density on the surface of the Bi-based superconducting wire during the surface strengthening treatment is 3 A / dm 2 The treatment time was 15 minutes. As a result, a 40 μm thick Cu layer was formed on the surface of the Bi-based superconducting wire, and a low-cost, high-strength Bi-based superconducting wire (see Figure 4) was obtained. The results showed that the Ag mass content of the low-cost, high-strength Bi-based superconducting wire produced in this example was reduced from 80% to 40% of that of the original Bi-based superconducting wire, its breaking strength was increased from 100 MPa of the original Bi-based superconducting wire to 135 MPa, and its superconducting critical tensile strength at 77 K was increased from 7 kg to 17 kg, thereby improving its mechanical properties. The low-cost, high-strength Bi-based superconducting wire produced in this example exhibited superconducting critical current performance that was completely consistent with that of the original Bi-based superconducting wire, with both having a superconducting critical current of 17 A in a self-field at 77 K. This demonstrates that the electrochemical Ag reduction and electrochemical copper deposition processes have no effect on the performance of the superconducting core yarn. [Table 2] In this embodiment, copper is used instead of the precious metal Ag in the Bi-based superconducting wire, thereby achieving a cost reduction rate of 47.924% without reducing the current-carrying performance of the Bi-based superconducting wire. Meanwhile, the improved mechanical properties make the Bi-based superconducting wire applicable to conditions where the magnetic field or pressure increases by 30% or more, thereby expanding the range of applications for the Bi-based superconducting wire. Fig. 3 is a schematic diagram of the structure of the Bi-based superconducting band used in Example 1, which includes a superconducting core yarn 1, an Ag layer covering the outside of the superconducting core yarn 1, and an Ag alloy layer 3 covering the outermost layer. Fig. 4 is a schematic diagram of the structure of the low-cost, high-strength Bi-based superconducting band produced in this example, which includes a superconducting core yarn 1, an Ag layer covering the outside of the superconducting core yarn 1, and a Cu layer 4 covering the outermost layer. A comparison of Figs. 3 and 4 reveals that in the present invention, the Ag alloy layer on the surface of the Bi-based superconducting wire band is removed by electrochemical Ag reduction technology and electrochemical additive processing method, and a high-strength Cu layer is plated in its place. [Example]

[0032] This embodiment includes the following steps. Step 1 Surface wiping: The surface of the Bi-based superconducting band material was wiped with a cotton cloth wetted with ethanol to remove dirt remaining on the surface of the Bi-based superconducting band material during the heat treatment process. Step 2 Electrochemical silver reduction: The Bi-based superconducting strip wiped in step 1 was connected to the positive pole of a constant-voltage power supply, and the graphite electrode was connected to the negative pole of the constant-voltage power supply. The width of the graphite electrode was 20 mm, the width of the Bi-based superconducting strip was 4 mm, and the width of the graphite electrode was five times the width of the Bi-based superconducting strip. Next, the wiped Bi-based superconducting strip and the graphite electrode were attached in parallel to a holder and placed in an electrolyte to perform electrochemical silver reduction. The distance between the Bi-based superconducting strip and the graphite electrode was 5 cm, and the electrolyte was a 10 g / L AgNO3 solution, the pH of which was adjusted to 5 with sodium hydroxide. During electrochemical silver reduction, the current density on the surface of the Bi-based superconducting strip was 10 A / dm 2 The current flow time was adjusted to 0.1 min, and the Ag alloy layer on the surface of the Bi-based superconducting band material was removed, exposing the silver layer on the surface of the superconducting core yarn in the outer layer of the Bi-based superconducting band material, and electroplated Ag with a purity of 99.99% by mass was formed on the surface of the graphite electrode. Step 3 This is the same as in the first embodiment. Step 4 The following points are different from Example 1: the distance between the cleaned Bi-based superconducting wire strip and the tough pitch copper was 5 cm, the electrochemical additive processing solution contained 20 g / L copper chloride and 50 g / L sulfuric acid, and the current density on the surface of the Bi-based superconducting strip during the surface strengthening treatment was 10 A / dm 2 The treatment time was adjusted to 0.1 min. As a result, a Cu layer with a thickness of 10 μm was formed on the surface of the Bi-based superconducting band material, and a high-strength Bi-based superconducting band material was obtained at low cost. [Table 3] The results showed that the Ag mass content of the low-cost, high-strength Bi-based superconducting strip produced in this example was reduced from 66% to 45% of that of the original Bi-based superconducting strip, resulting in a cost reduction of 30.179%, and the breaking strength was increased from 90-94 MPa of the original Bi-based superconducting strip to 98 MPa, and the superconducting critical tensile strength at 77 K was increased from 5 kg to 5.5 kg. The low-cost, high-strength Bi-based superconducting strip produced in this example exhibited superconducting critical current performance that was completely consistent with that of the original Bi-based superconducting strip, with both having a superconducting critical current of 56 A in a self-field at 77 K. This demonstrates that the electrochemical Ag reduction and electrochemical copper deposition processes have no effect on the performance of the superconducting core yarn. Although the low-cost, high-strength Bi-based superconducting strip did not show any significant improvement in mechanical properties, the critical bending radius was reduced from the original 3 cm to 2.5 cm, making it applicable to fields requiring a smaller bending radius. [Example]

[0033] This embodiment includes the following steps. Step 1 This is the same as in the first embodiment. Step 2 Electrochemical silver reduction: The Bi-based superconducting strip wiped in step 1 was connected to the positive pole of a constant-voltage power supply, and the graphite electrode was connected to the negative pole of the constant-voltage power supply. The width of the graphite electrode was 12 mm, the width of the Bi-based superconducting strip was 4 mm, and the width of the graphite electrode was three times the width of the Bi-based superconducting strip. Next, the wiped Bi-based superconducting strip and the graphite electrode were attached in parallel to a holder and placed in an electrolyte to perform electrochemical silver reduction. The distance between the Bi-based superconducting strip and the graphite electrode was 3.5 cm, and the electrolyte was a 6 g / L AgNO3 solution, the pH of which was adjusted to 4 with sodium hydroxide. During electrochemical silver reduction, the current density on the surface of the Bi-based superconducting strip was 5 A / dm 2 The current was adjusted to 500 W, and the current flow time was set to 3 minutes, removing the Ag alloy layer on the surface of the Bi-based superconducting band material, exposing the silver layer on the surface of the superconducting core yarn in the outer layer of the Bi-based superconducting band material, and forming electroplated Ag with a purity of 99.99% by mass on the surface of the graphite electrode. Step 3 This is the same as in the first embodiment. Step 4 The following points are different from Example 1: the distance between the cleaned Bi-based superconducting wire strip and the tough pitch copper was 3.5 cm, the electrochemical additive processing solution contained 10 g / L of copper sulfate and 30 g / L of citric acid, and the current density on the surface of the Bi-based superconducting strip during the surface strengthening treatment was 5 A / dm 2 The treatment time was 10 minutes. As a result, a 40 μm thick Cu layer was formed on the surface of the Bi-based superconducting band material, and a low-cost, high-strength Bi-based superconducting band material was obtained. [Table 4] The results showed that the Ag mass content of the low-cost, high-strength Bi-based superconducting strip produced in this example was reduced from 60% to 40% of that of the original Bi-based superconducting strip, resulting in a cost reduction of 31.451%. The fracture strength increased from 90-94 MPa of the original Bi-based superconducting strip to 124 MPa, and the superconducting critical tensile strength at 77 K increased from 5 kgf / cm2 to 16 kgf / cm2, improving its mechanical properties. The low-cost, high-strength Bi-based superconducting strip produced in this example exhibited superconducting critical current performance that was completely consistent with that of the original Bi-based superconducting strip, with both having a superconducting critical current of 52 A at 77 K. This demonstrates that the electrochemical Ag reduction and electrochemical copper deposition processes have no effect on the performance of the superconducting core yarn. In this embodiment, copper is used instead of the precious metal Ag in the Bi-based superconducting band material, thereby reducing the raw material cost by 49% without reducing the current-carrying performance of the Bi-based superconducting band material. On the other hand, due to the strengthening of the mechanical properties, the Bi-based superconducting band material can be applied to more severe conditions, with magnetic fields and pressures improved by 30% or more, thereby expanding the range of applications of the Bi-based superconducting band material. [Example]

[0034] This example differs from Example 2 in the following respects: In Step 4, the distance between the cleaned Bi-based superconducting wire and the tough pitch copper was 2 cm, the electrochemical additive processing solution contained 3 g / L copper sulfate and 10 g / L citric acid, and the surface strengthening treatment time was 10 minutes, thereby forming a Cu layer with a thickness of 25 μm on the surface of the Bi-based superconducting wire. [Table 5] Testing results showed that the Ag mass content of the low-cost, high-strength Bi-based superconducting wire produced in this example was reduced from 80% to 50% of that of the original Bi-based superconducting wire, thereby reducing the raw material cost by 30% without reducing current-carrying performance. The low-cost, high-strength Bi-based superconducting wire produced in this example exhibited superconducting critical current performance identical to that of the original Bi-based superconducting wire, with both having a superconducting critical current of 16 A at a self-field of 77 K. This demonstrates that the electrochemical Ag reduction and electrochemical copper deposition processes have no effect on the performance of the superconducting core yarn. The low-cost, high-strength Bi-based superconducting wire showed no change in fracture strength or superconducting critical tensile strength at a self-field of 77 K, but its critical bending radius was reduced from 12.5 cm to 10 cm, making it advantageous for applications requiring a smaller bending radius. Comparative Example 1

[0035] The strengthening method of welding copper strips by mechanical Ag reduction and soldering specifically includes the following steps: First, a CNC machining center planer was used to perform a mechanical Ag reduction operation with a cutting depth of 5 microns. After 10 passes, the Ag on the surface of the Bi-based superconducting strip was completely removed. However, while this method produces high-purity Ag by-products, stress and distortion occur with each machining operation, causing damage to the ceramic superconducting core. Furthermore, the critical current of the superconducting strip decreases by 5 to 10% with each machining operation. As in Example 1, this mechanical Ag reduction method reduced the Ag content in the superconducting band by half, but reduced the current-carrying performance of the superconducting band by approximately 70%. On the other hand, the electrochemical Ag reduction method of Example 1 of the present patent was able to reduce the Ag content to the same level, but did not affect the current-carrying performance of the superconducting band. Next, the Ag content in the superconducting strip was reduced by half through mechanical Ag reduction, and the copper strip was strengthened by soldering. In this way, the strength of the strip could be increased to 150 MPa. However, if natural welding was fully adopted during welding, the soldering thickness would be too large, increasing the cross-sectional area of ​​the strip by approximately 100%. This not only affected the dimensional uniformity of the strip, but also reduced the critical engineering current density of the strip by 100%.

[0036] The use of pressure-assisted soldering allows the solder between the reinforcing band and the superconducting band to be expelled as much as possible under the action of external pressure, maintaining the strength of the solder joint between the two bands and the dimensional uniformity of the final reinforcing band. However, the ceramic core of the Bi-based superconducting band may also be destroyed under the action of external pressure, resulting in a decrease of approximately 20% in the electrical conductivity of the superconducting band.

[0037] On the other hand, in Example 1 of the present patent, electrochemical additive processing was performed on a superconducting band after Ag reduction but with the same Ag content. Because almost no stress is introduced in the electrochemical additive processing, the ceramic superconducting core of the superconducting band material is hardly affected before and after the electrochemical additive processing, and the current-carrying performance of the final band material is also not affected.

[0038] The comparison showed that mechanical Ag reduction and strengthening by copper band welding could reduce the nominal Ag content of Bi-based superconducting strips and improve mechanical strength, but reduced the superconducting performance of the superconducting strips by approximately 90%. On the other hand, the electrochemical Ag reduction and electrochemical additive processing technology of the present invention reduces the Ag content by approximately 50% and improves mechanical properties by at least 30% without reducing superconducting performance.

[0039] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. All simple modifications, changes and equivalent changes made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the technical solutions of the present invention. [Explanation of symbols]

[0040] 1-Superconducting core yarn 2-Ag layer 3-Ag alloy layer 4-Cu layer

Claims

1. A method for producing a low-cost, high-strength Bi-based superconducting wire strip, comprising: Electrochemical silver reduction: Step 1: connecting a Bi-based superconducting wire strip to the positive electrode of a constant voltage power supply, connecting a graphite electrode to the negative electrode of the constant voltage power supply, and then mounting the Bi-based superconducting wire strip and the graphite electrode in parallel on a holder, and placing them in an electrolyte to perform electrochemical silver reduction, thereby removing the Ag alloy layer on the surface of the Bi-based superconducting wire strip; surface strengthening: Step 2 of connecting the Bi-based superconducting wire strip that has been subjected to electrochemical silver reduction in Step 1 to the negative electrode of a constant-voltage power supply, connecting tough pitch copper to the positive electrode of the constant-voltage power supply, and then mounting the Bi-based superconducting wire strip that has been subjected to electrochemical silver reduction and the tough pitch copper in parallel on a holder and immersing them in an electrochemical additive processing solution to perform surface strengthening treatment, thereby forming a Cu layer on the surface of the Bi-based superconducting wire strip, thereby obtaining the low-cost, high-strength Bi-based superconducting wire strip.

2. In step 1, the width of the graphite electrode is three times or more the width or diameter of the Bi-based superconducting wire ribbon material, and / or the method for producing a low-cost, high-strength Bi-based superconducting wire ribbon according to claim 1, wherein the electrolytic solution is a deionized aqueous solution of a soluble silver salt of 2 g / L to 10 g / L, and the pH of the deionized aqueous solution of the soluble silver salt is adjusted to 3 to 5 with a metal hydroxide.

3. the soluble silver salt is selected from silver nitrate, silver fluoride, silver chlorate, and silver perchlorate; and / or the metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, and lithium hydroxide.

4. In step 1, the distance between the Bi-based superconducting wire strip and the graphite electrode is 1 cm to 5 cm; And / or, the current density on the surface of the Bi-based superconducting wire strip is 0.1 A / dm ２ ∼10 A / dm2, 2. The method for producing a low-cost, high-strength Bi-based superconducting wire strip according to claim 1, wherein the current application time is 0.1 to 30 minutes.

5. In step 2, the electrochemical additive processing solution is a deionized aqueous solution containing 0.1 g / L to 20 g / L of a soluble copper salt and 10 g / L to 50 g / L of an acidic substance; The concentration of the soluble copper salt is 10 g / L; 2. The method for producing a low-cost, high-strength Bi-based superconducting wire ribbon according to claim 1, wherein the concentration of the acidic substance is 30 g / L.

6. the soluble copper salt is selected from copper sulfate, copper chloride, and copper nitrate; and / or the acidic substance is selected from the group consisting of citric acid, sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

7. In step 2, the distance between the Bi-based superconducting wire band material and the tough pitch copper is 2 cm to 5 cm; And / or, the current density on the surface of the Bi-based superconducting wire strip is 0.1 A / dm ２ ∼10 A / dm2, and / or the treatment time is 0.1 min to 20 min; and / or the Cu layer has a thickness of 10 μm to 40 μm.

8. Before step 1, 2. The method for producing a low-cost, high-strength Bi-based superconducting wire strip according to claim 1, further comprising the step of: surface wiping: washing the surface of the Bi-based superconducting wire strip with ethanol to remove any dirt remaining on the surface of the Bi-based superconducting wire strip.

9. Before step 2, 2. The method for producing a low-cost, high-strength Bi-based superconducting wire ribbon according to claim 1, further comprising the step of: washing away residual liquid; immersing the Bi-based superconducting wire ribbon that has been subjected to electrochemical silver reduction in step 1 in high-purity water to wash away the electrolytic solution remaining on the surface.

Images