Low-cost and high-strength Bi-based superconducting wire and method for manufacturing the same

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 the priority of Chinese Patent Application No. 202310565846.9 with an application date of May 19, 2023. This application incorporates the entire text of the above - mentioned Chinese patent application by reference.

[0002] The present invention belongs to the technical field of manufacturing high - temperature superconducting wire tapes, and specifically relates to a low - cost and high - strength Bi - based superconducting wire tape and a manufacturing method thereof.

Background Art

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

[0004] Bi - based wire tapes are manufactured using the powder - in - tube method, that is, precursor ceramic oxide powder is put into a silver tube to form a single - core composite. After drawing the single - core wire, bunching / drawing or rolling of the multi - core wire, and further heat treatment, high - performance Bi - based wire tapes are manufactured. In all processes of the heat treatment, the oxygen partial pressure around the superconducting core wire must always be consistent. Otherwise, segregation problems may occur, and the current - carrying performance of the sample may be significantly reduced. During the temperature - rising process, the oxide core wire absorbs oxygen, and the superconducting core wire releases oxygen during heat preservation, which causes real - time changes in the oxygen partial pressure around the core wire. Therefore, an oxygen - permeable material is required for the clad material used to manufacture Bi - based superconducting wire tapes. Also, the clad material does not react with Bi - based precursor powder. Currently, the only clad materials that meet these two conditions are silver and silver alloys. Therefore, to manufacture Bi - based superconducting wire tapes, only Ag and Ag alloys can be used as the clad material. However, Ag and Ag alloys have the following disadvantages as clad materials.

[0005] (1) The content of pure Ag and Ag alloys (Ag alloys for Bi-based superconducting wire tapes have an Ag content exceeding 99%) is too high, resulting in too high a cost for Bi-based superconducting wire tapes. The content of Ag and Ag alloys in Bi-based superconducting tapes is close to 70%, and the content of Ag and Ag alloys in Bi-based superconducting wires even exceeds 80%. Since Ag and Ag alloys are precious metals and their prices are much higher than those of other metals, the cost of Bi-based superconducting wire tapes is high, restricting large-scale applications. Therefore, in order to realize large-scale applications of Bi-based superconducting wire tapes, it is necessary to reduce the Ag content and lower the cost.

[0006] (2) When the content of Ag and Ag alloys is high, the strength of Bi-based superconducting wire tapes is too low. The most important application of Bi-based superconducting wire tapes is in strong magnetic fields above 30 T. The strong magnetic field and the superconducting current in the superconducting wire tape generate a strong interaction, causing the superconducting wire tape to receive a large tensile stress. Also, the larger the aperture of the superconducting magnet, the gradually increasing tensile stress the superconducting tape receives. However, the strength of Ag and Ag alloys is relatively low, and it is difficult for Bi-based superconducting wire tapes with Ag and Ag alloys as the cladding material to meet the requirements of strong magnetic field magnets. Therefore, in order to realize the application of Bi-based superconducting wire tapes in ultra-strong magnetic fields, it is necessary to improve the strength of conventional Bi-based superconducting wire tapes.

[0007] (3) The critical engineering current density of the reinforced Bi-based superconducting wire tape has been significantly reduced. Conventional reinforced Bi-based superconducting wire tapes are those obtained by directly welding a high-strength metal tape to the surface of the Bi-based superconducting wire tape. Compared with the original superconducting wire tape, the thickness or diameter of this reinforced superconducting wire tape has increased significantly, thereby significantly reducing the critical engineering current density of the sample, significantly increasing the dimensions of the superconducting device manufactured with this reinforced superconducting wire tape, and significantly increasing the cooling cost and superconducting material cost of the superconducting device. Therefore, in order to realize large-scale applications of the reinforced Bi-based superconducting wire tape, it is necessary to reduce the size of the reinforced Bi-based superconducting wire tape and increase the critical engineering current density of the wire tape. Summary of the Invention

Problems to be Solved by the Invention

[0008] The technical problem to be solved by the present invention is to provide a low-cost and high-strength Bi-based superconducting wire strip and a manufacturing method thereof in view of the above-mentioned drawbacks of the prior art. The method combines an electrochemical silver reduction technique and an electrochemical addition processing method to remove the Ag alloy layer on the surface of the Bi-based superconducting wire strip and electroplate a high-strength Cu layer, thereby manufacturing a low-cost and high-strength Bi-based superconducting wire strip, reducing the cost of the Bi-based superconducting wire strip, increasing the strength of the Bi-based superconducting wire strip, and solving the problems of high cost and low strength caused by the use of Ag or Ag alloy cladding for the Bi-based superconducting wire strip.

Means for Solving the Problems

[0009] To solve the above technical problems, one aspect of the present invention is Electrochemical silver reduction: After connecting the Bi-based superconducting wire strip to the positive electrode of a constant voltage power source and connecting a graphite electrode to the negative electrode of the constant voltage power source, the Bi-based superconducting wire strip and the graphite electrode are attached to a holder in parallel and placed in an electrolytic solution for electrochemical silver reduction to remove the Ag alloy layer on the surface of the Bi-based superconducting wire strip in Step 1; Surface strengthening: After connecting the Bi-based superconducting wire strip subjected to electrochemical silver reduction in Step 1 to the negative electrode of a constant voltage power source and connecting tough pitch copper to the positive electrode of the constant voltage power source, the Bi-based superconducting wire strip subjected to electrochemical silver reduction and the tough pitch copper are attached to a holder in parallel and placed in an electrochemical addition processing solution for surface strengthening treatment to form a Cu layer on the surface of the Bi-based superconducting wire strip and obtain the low-cost and high-strength Bi-based superconducting wire strip in Step 2. A manufacturing method of a low-cost and high-strength Bi-based superconducting wire strip is provided, which includes these steps.

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

[0011] In the above-mentioned low-cost and high-strength Bi-based superconducting wire strip manufacturing method, in step 1, the width of the graphite electrode is 3 times or more, preferably 3 to 5 times, and more preferably 3 times, the width or diameter of the Bi-based superconducting wire strip; 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 realized without damaging the superconducting core yarn in the Bi-based superconducting wire strip.

[0012] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire strip, 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 the group consisting of 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 min to 30 min, preferably 3 min.

[0014] In the above-mentioned method for producing a low-cost, high-strength Bi-based superconducting wire strip, 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 method for manufacturing a low-cost and high-strength Bi-based superconducting wire strip, the soluble copper salt is selected from any one of copper sulfate, copper chloride, and copper nitrate, and / or the acidic substance is selected from any one of citric acid, sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

[0016] In the above method for manufacturing a low-cost and 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 ~10 A / dm 2 preferably 5 A / 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 method for manufacturing a low-cost and high-strength Bi-based superconducting wire strip, before step 1, Surface wiping: Further including the step of cleaning the surface of the Bi-based superconducting wire strip with ethanol to remove the dirt remaining on the surface of the Bi-based superconducting wire strip.

[0018] In the above method for manufacturing a low-cost and high-strength Bi-based superconducting wire strip, before step 2, Residual liquid cleaning: Further including the step of immersing the Bi-based superconducting wire strip subjected to electrochemical silver reduction in step 1 in high-purity water and washing and removing the electrolytic solution remaining on the surface.

[0019] In another aspect of the present invention, there is further provided a low-cost and high-strength Bi-based superconducting wire strip manufactured by the above method for manufacturing a low-cost and high-strength Bi-based superconducting wire strip.

Advantages of the Invention

[0020] Compared with the prior art, the present invention has the following advantages. 1. With respect to the problem that noble metal Ag or Ag alloy must be used as the cladding material for Bi-based superconducting wire strips, and the Ag content reaches 66% - 82%, resulting in high costs, in the present invention, by removing the Ag alloy layer on the surface of the Bi-based superconducting wire strip by an electrochemical silver reduction technique, the effective Ag content in the Bi-based superconducting wire strip is reduced by about 50%, the cost of the Bi-based superconducting wire strip is reduced by about 45%, and 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 for surface strengthening treatment, a Bi-based superconducting wire strip with low cost and high strength is manufactured. The mass content of Ag is reduced by more than half compared to the Bi-based superconducting wire strip, the superconducting critical strength is improved by more than twice, and the electrochemical silver reduction step is a controllable Ag reduction process with extremely low stress or no stress, so it is possible to avoid the destruction of the ceramic superconducting core due to excessive stress in the conventional mechanical silver reduction, thereby avoiding the loss of the superconducting performance of the Bi-based superconducting wire strip. 2. In the present invention, by plating a high-strength Cu layer on the surface of the Bi-based superconducting wire strip by an electrochemical additive processing method instead of Ag alloy, the strength of the Bi-based superconducting wire strip, especially the yield strength, is improved, and it can withstand the strong tensile stress generated by strong interaction with the current after the Bi-based superconducting wire strip is placed in a strong magnetic field. Since the strength of the Ag and Ag alloy cladding materials is low, the problem of insufficient mechanical support for the Bi-based superconducting wire strip is avoided, enabling the Bi-based superconducting wire strip to meet the requirements for application in large superconducting magnets, promoting the development of large Bi-based superconducting magnets, and promoting the development of nuclear fusion, accelerators, and large-bore NMR. 3. In the present invention, while removing the Ag alloy layer on the surface of the Bi-based superconducting wire strip by an electrochemical silver reduction technique, electroplated Ag is formed on the surface of the graphite electrode, and the purity of the electroplated Ag is increased to 99.9 mass% or higher, so that an Ag tube can be directly manufactured and used for the production of Bi-based superconducting wire strips, enabling the reuse of Ag, reducing waste, and further reducing the cost of Bi-based superconducting wire strips. 4. In the present invention, by electrochemically depositing a high-strength Cu layer on the surface of a Bi-based superconducting wire strip instead of low-strength Ag or an Ag alloy, the strength of the Bi-based superconducting wire strip is significantly improved, damage to the Bi-based superconducting wire strip during winding around a cable or magnet is avoided, and it is made suitable for the manufacture of cables and magnets. 5. In the present invention, by controlling the surface strengthening treatment process to adjust the thickness of the Cu layer and further controlling the diameter and thickness of the Bi-based superconducting wire strip, wire strips with various critical bending radii are manufactured, thereby not only reducing the cost of the Bi-based superconducting wire strip but also enabling the manufacture of Bi-based superconducting wire strips with smaller diameters and thicknesses, reducing the critical bending radius of the Bi-based superconducting wire strip, and making it suitable for the manufacture of small-diameter magnets. 6. The present invention is advantageous for realizing mass production of Bi-based wire strips with a simple manufacturing process, reasonable process design, low cost, and high strength, and promoting the industrialization and application of Bi-based superconducting wire strips. Hereinafter, the technical solution of the present invention will be described in more detail with reference to the drawings and examples.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings of the present invention. It is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. For the experimental methods where specific conditions are not specified in the following embodiments, they are selected based on the normal methods and conditions or the product handling manuals.

[0023] (Performance Test) Performance tests were conducted on the products manufactured in the examples and comparative examples. The test criteria or methods are as follows.

[0024] I. Test of Ag Content The Ag content was measured 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] II. Breaking Strength Test The breaking strength test was carried out according to GB / T 36611-2018 "Measurement of Mechanical Properties - Room Temperature Tensile Test Method for Ag and / or Ag Alloy Cladded Bi-2223 and Bi-2212 Composite Superconductors".

[0026] III. Cost Calculation In general Bi-based superconducting wire tapes, Ag raw materials account for ~96% of the cost, other materials account for 2% of the cost, and processing costs account for 2%. In this application, the Ag on the outer layer of the Bi-based superconducting wire tape was changed to Cu. The changed Ag is half of the silver content in the superconducting wire tape. The price of Cu raw material is 1 / 100 of the price of Ag raw material. When Ag is changed to copper, the processing cost (processing cost by electrochemical Ag reduction and electrochemical additional processing) is about 20% of the price of Cu raw material. Taking the cost of general Bi-based superconducting wire tapes as 100%, the cost calculation method of the superconducting wire tapes in this application is as follows. Cost reduction rate = 100% - cost of changed raw material Cu - cost of changed processing - remaining Ag raw material in the superconducting tape - other materials and processing costs.

[0027] IV. Superconducting Critical Current The superconducting critical current test was carried out in accordance with GB / T 18502-2018 / IEC 61788-3:2006, "Measurement of Critical Current, DC Critical Current of Silver and / or Silver Alloy Clad Bi-2212 and Bi-2223 Oxide Superconductors".

[0028] V. Superconducting Critical Tensile Strength Test Tension was applied to both ends of the tape in the longitudinal direction, and the superconducting critical current test of the sample was carried out in situ. When the critical current of the sample was reduced to 95% of the current in the stress-free state, this tension was the superconducting critical tensile strength of the sample [Fischer K, Fahr T, Schlafer U, et al. Influence of Processing Parameters and Tensile Stress on the Performance of Bi-2223 Tapes (with Ag and AgMn Cladding) [J]. IEEE transactions on applied superconductivity, 1999, 9(2): 2625-2628], and [Mao Z H, Jin H, Qin J G, etc. Axial Tensile Stress-Strain Characteristics of Bi-2212 Round Wires under Various Heat Treatment Conditions [J]. IEEE Transactions on Applied Superconductivity, 2017, 27(6): 6400405].

[0029] VI. Critical Bending Radius The tape was bent uniformly along its longitudinal direction, and the superconducting critical current test of the sample was carried out in situ. When the critical current of the sample decreased to 95% of the critical current in the straight sample state, the bending radius at this time was the superconducting critical bending radius of the sample [Shin H S, Katagiri K. Critical Current Degradation Behavior of Bi-2223 Superconducting Tapes under Bending and Twisting Strains [J]. Superconductor Science and Technology, 2003, 16(9): 1012-1018].

Example

[0030] This example includes the following steps. Step 1 Surface wiping: The surface of the Bi-based superconducting tape (see Figure 1) was wiped with a cotton cloth moistened with ethanol to remove the dirt remaining on the surface of the Bi-based superconducting tape in the heat treatment process. Step 2 Electrochemical silver reduction: The Bi-based superconducting tape wiped in Step 1 was connected to the positive electrode of a constant voltage power supply, and the graphite electrode was connected to the negative electrode of the constant voltage power supply. The width of the graphite electrode was 12 mm, the width of the Bi-based superconducting tape was 4 mm, and the width of the graphite electrode was three times the width of the Bi-based superconducting tape. Next, the wiped Bi-based superconducting tape and the graphite electrode were attached to a holder in parallel and placed in an electrolytic solution for electrochemical silver reduction. The distance between the Bi-based superconducting tape and the graphite electrode was 1 cm, the electrolytic solution was a 2 g / L AgNO3 solution, and the pH of the AgNO3 solution was adjusted to 3 with sodium hydroxide. During the electrochemical silver reduction, the current density on the surface of the Bi-based superconducting tape was adjusted to 0.1 A / dm 2 and the energization time was 30 min to remove the Ag alloy layer on the surface of the Bi-based superconducting tape, expose the silver layer on the surface of the superconducting core wire in the outer layer of the Bi-based superconducting tape, and form electroplated Ag with a purity of 99.99 mass% on the surface of the graphite electrode. Step 3 Residual liquid washing: The Bi-based superconducting tape subjected to electrochemical silver reduction in Step 2 was immersed in high-purity water to wash and remove the electrolytic solution remaining on the surface. Step 4 Surface strengthening: The Bi-based superconducting tape washed in Step 3 was connected to the negative electrode of a constant voltage power supply, and tough pitch copper was connected to the positive electrode of the constant voltage power supply. Next, the washed Bi-based superconducting tape and the tough pitch copper were attached to a holder in parallel and placed in an electrochemical addition processing solution for surface strengthening treatment. The distance between the washed Bi-based superconducting wire tape and the tough pitch copper was 2 cm, the electrochemical addition processing solution contained 0.1 g / L of copper sulfate and 10 g / L of citric acid, and the current density on the surface of the Bi-based superconducting tape was adjusted to 0.1 A / dm 2 during the surface strengthening treatment, and the treatment time was 20 min. Thereby, a Cu layer with a thickness of 20 μm was formed on the surface of the Bi-based superconducting tape, and a Bi-based superconducting tape with low cost and high strength (see Figure 2) was obtained. As a result of the detection, the low-cost and high-strength Bi-based superconducting tape manufactured in this example has an Ag mass content that has decreased from 66% to 33% of the original Bi-based superconducting tape, a breaking strength that has increased from 90 MPa to 94 MPa of the original Bi-based superconducting tape to 102 MPa to 104 MPa, a superconducting critical tensile strength at 77 K that has increased from 5 kg to 14 kg, and its mechanical properties have been enhanced. The low-cost and high-strength Bi-based superconducting tape manufactured in this example shows completely the same performance as the original Bi-based superconducting tape in terms of superconducting critical current-carrying performance. The superconducting critical current at a self-field of 77 K is 53 A for both. This demonstrates that the processes of electrochemical Ag reduction and electrochemical copper deposition have no impact on the performance of the superconducting core wire.

Table 1

Example

[0031] This example includes the following steps. Step 1 Surface wiping: The surface of the Bi-based superconducting wire (see Figure 3) was wiped with a cotton cloth wetted with ethanol to remove the 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 electrode of a constant voltage power supply, and the graphite electrode was connected to the negative electrode of the constant voltage power supply. The width of the graphite electrode was 16 mm, the diameter of the Bi-based superconducting tape was 4 mm, and the width of the graphite electrode was 4 times the diameter of the Bi-based superconducting tape. Next, the wiped Bi-based superconducting wire and the graphite electrode were attached to a holder in parallel and placed in an electrolytic solution for electrochemical silver reduction. The distance between the Bi-based superconducting wire and the graphite electrode was 1 cm, the electrolytic solution was a 2 g / L AgNO3 solution, and the pH of the AgNO3 solution was adjusted to 3 with sodium hydroxide. During the electrochemical silver reduction, the current density on the surface of the Bi-based superconducting wire was adjusted to 10 A / dm 2 and the energization time was 15 min to remove the Ag alloy layer on the surface of the Bi-based superconducting wire, expose the silver layer on the surface of the superconducting core filaments in the outer layer of the Bi-based superconducting wire, and form electroplated Ag with a purity of 99.99 mass% on the surface of the graphite electrode. Step 3 It is the same as Example 1. Step 4 Compared with Example 1, the following points are different. The electrochemical additional 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 is adjusted to 3 A / dm 2 during the surface strengthening treatment, and the treatment time is 15 min. Thereby, a Cu layer with a thickness of 40 μm was formed on the surface of the Bi-based superconducting wire, and a Bi-based superconducting wire with low cost and high strength (see Figure 4) was obtained. As a result of the detection, the low-cost and high-strength Bi-based superconducting wire manufactured in this example has an Ag mass content that has decreased from 80% to 40% of the original Bi-based superconducting wire, a breaking strength that has increased from 100 MPa to 135 MPa of the original Bi-based superconducting wire, a superconducting critical tensile strength at 77 K that has increased from 7 kg to 17 kg, and its mechanical properties have been enhanced. The low-cost and high-strength Bi-based superconducting wire manufactured in this example shows exactly the same performance as the original Bi-based superconducting wire in terms of superconducting critical current-carrying performance. The superconducting critical current at a self-field of 77 K is 17 A for both. This demonstrates that the processes of electrochemical Ag reduction and electrochemical copper deposition have no effect on the performance of the superconducting core wire.

Table 2

Example

[0032] This example includes the following steps. Step 1 Surface wiping: The surface of the Bi-based superconducting tape was wiped with a cotton cloth wetted with ethanol to remove the dirt remaining on the surface of the Bi-based superconducting tape in the heat treatment process. Step 2 Electrochemical silver reduction: The Bi-based superconducting tape wiped in Step 1 was connected to the positive electrode of a constant voltage power supply, and the graphite electrode was connected to the negative electrode of the constant voltage power supply. The width of the graphite electrode is 20 mm, the width of the Bi-based superconducting tape is 4 mm, and the width of the graphite electrode is 5 times the width of the Bi-based superconducting tape. Next, the wiped Bi-based superconducting tape and the graphite electrode were attached to the holder in parallel and placed in the electrolytic solution for electrochemical silver reduction. The distance between the Bi-based superconducting tape and the graphite electrode is 5 cm, the electrolytic solution is a 10 g / L AgNO3 solution, and the pH of the AgNO3 solution is adjusted to 5 with sodium hydroxide. During the electrochemical silver reduction, the current density on the surface of the Bi-based superconducting tape was adjusted to 10 A / dm 2 and the energization time was 0.1 min to remove the Ag alloy layer on the surface of the Bi-based superconducting tape, expose the silver layer on the surface of the superconducting core wire in the outer layer of the Bi-based superconducting tape, and form electroplated Ag with a purity of 99.99 mass% on the surface of the graphite electrode. Step 3 It is the same as Example 1. Step 4 Compared with Example 1, the following points are different. The distance between the washed Bi-based superconducting tape and the tough pitch copper is 5 cm, the electrochemical additional processing solution contains 20 g / L of copper chloride and 50 g / L of sulfuric acid, and the current density on the surface of the Bi-based superconducting tape during the surface strengthening treatment is adjusted to 10 A / dm 2 and the treatment time is 0.1 min. Thereby, a Cu layer with a thickness of 10 μm was formed on the surface of the Bi-based superconducting tape, and a Bi-based superconducting tape with low cost and high strength was obtained.

Table 3

Example

[0033] This example includes the following steps. Step 1 It is the same as Example 1. Step 2 Electrochemical silver reduction: The Bi-based superconducting tape wiped in Step 1 was connected to the positive electrode of a constant-voltage power supply, and the graphite electrode was connected to the negative electrode of the constant-voltage power supply. The width of the graphite electrode is 12 mm, the width of the Bi-based superconducting tape is 4 mm, and the width of the graphite electrode is three times the width of the Bi-based superconducting tape. Next, the wiped Bi-based superconducting tape and the graphite electrode were attached to the holder in parallel and placed in the electrolyte for electrochemical silver reduction. The distance between the Bi-based superconducting tape and the graphite electrode is 3.5 cm, the electrolyte is a 6 g / L AgNO3 solution, and the pH of the AgNO3 solution is adjusted to 4 with sodium hydroxide. During the electrochemical silver reduction, the surface current density of the Bi-based superconducting tape was adjusted to 5 A / dm 2 and the energization time was 3 min to remove the Ag alloy layer on the surface of the Bi-based superconducting tape, expose the silver layer on the surface of the superconducting core wire in the outer layer of the Bi-based superconducting tape, and form electroplated Ag with a purity of 99.99 mass% on the surface of the graphite electrode. Step 3 It is the same as Example 1. Step 4 Compared with Example 1, the following points are different. The distance between the washed Bi-based superconducting tape and tough pitch copper is 3.5 cm. The electrochemical additive processing solution contains 10 g / L of copper sulfate and 30 g / L of citric acid. During the surface strengthening treatment, the surface current density of the Bi-based superconducting tape is adjusted to 5 A / dm 2 and the treatment time is 10 min. As a result, a Cu layer with a thickness of 40 μm is formed on the surface of the Bi-based superconducting tape, and a low-cost and high-strength Bi-based superconducting tape is obtained.

Table 4

Example

[0034] In this embodiment, compared with Embodiment 2, the following points are different. In Step 4, the distance between the washed Bi-based superconducting wire and tough pitch copper is 2 cm, the electrochemical addition processing solution contains 3 g / L of copper sulfate and 10 g / L of citric acid, and the surface strengthening treatment time is 10 min. Thereby, a Cu layer with a thickness of 25 μm was formed on the surface of the Bi-based superconducting wire.

Table 5

[0035] The strengthening method of welding a copper tape by adopting mechanical Ag reduction and soldering specifically includes the following steps. First, using a CNC machining center planner, a mechanical Ag reduction operation was performed with a cutting amount of 5 microns. After 10 times of processing, the Ag on the surface of the Bi-based superconducting tape can be completely removed. However, although such a method can obtain high-purity Ag by-products, stress and further strain occur each time of processing, which causes damage to the ceramic superconducting core. Also, each time of mechanical processing, the critical current of the superconducting tape decreases by 5 - 10%. Similar to Example 1, in such a mechanical Ag reduction method, although the Ag content in the superconducting tape decreased by half, the current-carrying performance of the superconducting tape decreased by about 70%. On the other hand, in the electrochemical Ag reduction method of Patent Example 1, the Ag content could be reduced to the same level, but it had no effect on the current-carrying performance of the superconducting tape. Next, the Ag content in the superconducting tape subjected to mechanical Ag reduction was reduced by half, and the copper tape was strengthened by soldering. In this way, the strength of the tape can be strengthened to 150 Mpa. However, during welding, if natural welding is completely adopted, the soldering thickness is too large, and the cross-sectional area of the tape increases approximately twice, which not only affects the dimensional uniformity of the tape but also reduces the critical engineering current density of the tape by half.

[0036] If pressure-assisted soldering is adopted, it is possible to discharge the solder between the reinforcing tape and the superconducting tape as much as possible under the action of external pressure, and maintain the soldering firmness between the two tapes and the dimensional uniformity of the final reinforced tape. However, under the action of external pressure, the ceramic core of the Bi-based superconducting tape may also be damaged, and the current-carrying performance of the superconducting tape may decrease by about 20%.

[0037] On the other hand, in Patent Example 1, electrochemical addition processing was performed on the superconducting tape with the same Ag content after Ag reduction. Since almost no stress is introduced in the electrochemical addition processing, the ceramic superconducting core of the superconducting tape is hardly affected before and after the electrochemical addition processing, and the current-carrying performance of the final tape is also not affected.

[0038] As a result of the comparison, although mechanical Ag reduction and strengthening by copper tape welding can achieve a decrease in the nominal Ag content of the Bi-based superconducting tape and an improvement in mechanical strength, the superconducting performance of the superconducting tape decreased by about 90%. On the other hand, the electrochemical Ag reduction and electrochemical addition processing technology of the present invention can reduce the Ag content by about 50% without degrading the superconducting performance, and improve the mechanical properties by at least 30% or more.

[0039] The above are only preferred embodiments of the present invention and do not 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 all fall within the protection scope of the technical solution of the present invention.

Description of Reference Numerals

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

Claims

1. A method for manufacturing a Bi-based superconducting wire strip with low cost and high strength, comprising: Electrochemical silver reduction: After connecting the Bi-based superconducting wire strip to the positive electrode of a constant voltage power supply and connecting a graphite electrode to the negative electrode of the constant voltage power supply, mounting the Bi-based superconducting wire strip and the graphite electrode in parallel on a holder, placing them in an electrolytic solution for electrochemical silver reduction to remove the Ag alloy layer on the surface of the Bi-based superconducting wire strip, which is Step 1; Surface strengthening: After connecting the Bi-based superconducting wire strip subjected to electrochemical silver reduction in Step 1 to the negative electrode of a constant voltage power supply and connecting tough pitch copper to the positive electrode of the constant voltage power supply, mounting the Bi-based superconducting wire strip subjected to electrochemical silver reduction and the tough pitch copper in parallel on a holder, placing them in an electrochemical addition processing solution for surface strengthening treatment to form a Cu layer on the surface of the Bi-based superconducting wire strip, thereby obtaining the Bi-based superconducting wire strip with low cost and high strength, which is Step 2. The manufacturing method is characterized by including these steps.

2. In Step 1, the width of the graphite electrode is 3 times or more, preferably 3 - 5 times, more preferably 3 times the width or diameter of the Bi-based superconducting wire strip; and / or the electrolytic solution is a deionized aqueous solution of a soluble silver salt with a concentration of 2 g / L - 10 g / L, and the pH of the deionized aqueous solution of the soluble silver salt is adjusted to 3 - 5 with a metal hydroxide; preferably, the concentration of the deionized aqueous solution of the soluble silver salt is 6 g / L. The manufacturing method of the Bi-based superconducting wire strip with low cost and high strength according to Claim 1 is characterized by this.

3. The soluble silver salt is selected from any one of silver nitrate, silver fluoride, silver chlorate, and silver perchlorate; and / or the metal hydroxide is selected from any one of sodium hydroxide, potassium hydroxide, barium hydroxide, and lithium hydroxide. The manufacturing method of the Bi-based superconducting wire strip with low cost and high strength according to Claim 2 is characterized by this.

4. In Step 1, the distance between the Bi-based superconducting wire strip and the graphite electrode is 1 cm - 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 to 10 A / dm ２ , preferably 5 A / dm ２ and and / or the energization time is 0.1 min - 30 min, preferably 3 min. The manufacturing method of the Bi-based superconducting wire strip with low cost and high strength according to Claim 1 is characterized by this.

5. In Step 2, the electrochemical addition processing solution is a deionized aqueous solution containing 0.1 g / L - 20 g / L of a soluble copper salt and 10 g / L - 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. The method for manufacturing a low-cost and high-strength Bi-based superconducting wire and strip according to claim 1 is characterized by this.

6. The soluble copper salt is selected from any one of copper sulfate, copper chloride, and copper nitrate, And / or, the acidic substance is selected from any one of citric acid, sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. The method for manufacturing a low-cost and high-strength Bi-based superconducting wire and strip according to claim 5 is characterized by this.

7. In step 2, the distance between the Bi-based superconducting wire and 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 to 10 A / dm ２ , preferably 5 A / 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. The method for manufacturing a low-cost and high-strength Bi-based superconducting wire and strip according to claim 1 is characterized by this.

8. Before step 1, Surface wiping: The method for manufacturing a low-cost and high-strength Bi-based superconducting wire and strip according to claim 1 further includes a step of cleaning the surface of the Bi-based superconducting wire and strip with ethanol to remove the dirt remaining on the surface of the Bi-based superconducting wire and strip.

9. Before step 2, Residual liquid cleaning: The method for manufacturing a low-cost and high-strength Bi-based superconducting wire and strip according to claim 1 further includes a step of immersing the Bi-based superconducting wire and strip subjected to electrochemical silver reduction in step 1 in high-purity water and washing and removing the electrolytic solution remaining on the surface.

10. A low-cost and high-strength Bi-based superconducting wire and strip, characterized in that it is manufactured by the method for manufacturing a low-cost and high-strength Bi-based superconducting wire and strip according to any one of claims 1 to 9.

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