LOW-COST AND HIGH-STRENGTH Bi-BASED SUPERCONDUCTING WIRE/TAPE AND PREPARATION METHOD THEREOF

Abstract

A low-cost and high-strength Bi-based superconducting wire/tape and a preparation method thereof, the preparation method includes: 1. subjecting a first Bi-based superconducting wire/tape to electrochemical silver reduction to remove a Ag alloy layer to obtain a second Bi-based superconducting wire/tape; and 2. subjecting the second Bi-based superconducting wire/tape to surface enhancement, such that a Cu layer is formed to obtain the low-cost and high-strength Bi-based superconducting wire/tape. An electrochemical silver reduction technology combines with an electrochemical additive method to remove a Ag alloy layer on a surface of a Bi-based superconducting wire/tape and coat a high-strength Cu layer, such that a low-cost and high-strength Bi-based superconducting wire/tape can be prepared, which reduces a preparation cost and improves a strength of a Bi-based superconducting wire/tape to meet the application requirements of large super-strong magnets.

Claims

1. A preparation method of a low-cost and high-strength Bi-based superconducting wire/tape, comprising the following steps: step 1: electrochemical silver reduction: connecting a first Bi-based superconducting wire/tape to a positive electrode of a stabilized voltage power supply, connecting a graphite electrode to a negative electrode of the stabilized voltage power supply, and arranging the first Bi-based superconducting wire/tape and the graphite electrode in parallel on a bracket; and adding an electrolyte to allow the electrochemical silver reduction, such that a Ag alloy layer on a surface of the first Bi-based superconducting wire/tape is removed to obtain a second Bi-based superconducting wire/tape; and step 2: surface enhancement: connecting the second Bi-based superconducting wire/tape obtained after the electrochemical silver reduction in the step 1 to the negative electrode of the stabilized voltage power supply, connecting a copper sheet to the positive electrode of the stabilized voltage power supply, and arranging the second Bi-based superconducting wire/tape and the copper sheet in parallel on the bracket; and adding an electrochemical additive solution to allow the surface reinforcement, such that a Cu layer is formed on a surface of the second Bi-based superconducting wire/tape to obtain the low-cost and high-strength Bi-based superconducting wire/tape.

2. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1, wherein in the step 1, a width of the graphite electrode is greater than or equal to 3 times, preferably 3 to 5 times, and more preferably 3 times a width or a diameter of the first Bi-based superconducting wire/tape; and/or the electrolyte is a deionized aqueous solution comprising a soluble silver salt at a concentration of 2 g/L to 10 g/L, and a pH of the deionized aqueous solution comprising the soluble silver salt is adjusted with a metal hydroxide to 3 to 5, wherein preferably, the concentration of the soluble silver salt in the deionized aqueous solution is 6 g/L.

3. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 2, wherein the soluble silver salt is selected from one of silver nitrate, silver fluoride, silver chlorate, and silver perchlorate; and/or the metal hydroxide is selected from one of sodium hydroxide, potassium hydroxide, barium hydroxide, and lithium hydroxide.

4. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1, wherein in the step 1, a distance between the first Bi-based superconducting wire/tape and the graphite electrode is 1 cm to 5 cm and preferably 3.5 cm; and/or a current density of a surface of the first Bi-based superconducting wire/tape is 0.1 A/dm.sup.2 to 10 A/dm.sup.2 and preferably 5 A/dm.sup.2; and/or a power-on time is 0.1 min to 30 min and preferably 3 min.

5. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1, wherein in the step 2, the electrochemical additive solution is a deionized aqueous solution comprising a soluble copper salt at a concentration of 0.1 g/L to 20 g/L and an acidic substance at a concentration of 10 g/L to 50 g/L; the concentration of the soluble copper salt is preferably 10 g/L; and the concentration of the acidic substance is preferably 30 g/L.

6. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 5, wherein the soluble copper salt is selected from one of copper sulfate, copper chloride, and copper nitrate; and/or the acidic substance is selected from one of citric acid, sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

7. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1, wherein in the step 2, a distance between the second Bi-based superconducting wire/tape and the copper sheet is 2 cm to 5 cm and preferably 3.5 cm; and/or a current density of the surface of the second Bi-based superconducting wire/tape is 0.1 A/dm.sup.2 to 10 A/dm.sup.2 and preferably 5 A/dm.sup.2; and/or the surface enhancement is conducted for 0.1 min to 20 min and preferably 10 min; and/or a thickness of the Cu layer is 10 ?m to 40 ?m and preferably 25 ?m.

8. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1, before the step 1, further comprising: surface cleaning: cleaning a surface of the first Bi-based superconducting wire/tape with ethanol to remove residual dirt on the surface of the first Bi-based superconducting wire/tape.

9. The preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1, before the step 2, further comprising: residual electrolyte removal: soaking the second Bi-based superconducting wire/tape obtained after the electrochemical silver reduction in the step 1 in ultrapure water to remove a residual electrolyte on the surface of the second Bi-based superconducting wire/tape.

10. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 1.

11. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 2.

12. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 3.

13. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 4.

14. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 5.

15. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 6.

16. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 7.

17. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 8.

18. A low-cost and high-strength Bi-based superconducting wire/tape prepared by the preparation method of the low-cost and high-strength Bi-based superconducting wire/tape according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a schematic structural diagram of a Bi-based superconducting tape adopted in Example 1 of the present disclosure;

[0033] FIG. 2 is a schematic structural diagram of a low-cost and high-strength Bi-based superconducting tape prepared in Example 1 of the present disclosure;

[0034] FIG. 3 is a schematic structural diagram of a Bi-based superconducting wire adopted in Example 2 of the present disclosure; and

[0035] FIG. 4 is a schematic structural diagram of a low-cost and high-strength Bi-based superconducting wire prepared in Example 2 of the present disclosure.

Reference Numerals

[0036] 1: superconducting core wire, 2: Ag layer, 3: Ag alloy layer, and 4: Cu layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The technical solutions in the examples of the present disclosure are clearly and completely described below with reference to the accompanying drawings of the present disclosure. Apparently, the described examples are merely a part rather than all of the examples of the present disclosure. The experimental methods in the following examples which are not specified with specific conditions are conducted according to conventional conditions or according to product instructions.

Performance Testing

[0038] The products prepared in examples and comparative examples each are tested for application performance, and test standards or methods are as follows:

1. Ag Content Test

[0039] According to the GB/T 11067.1-2006 Methods For Chemical Analysis Of SilverDetermination Of Silver ContentSilver Chloride Precipitation-Flame Atomic Absorption Spectrometric Method, a Ag content is determined.

2. Breaking Strength Test

[0040] According to the GB/T 36611-2018 Mechanical Properties MeasurementRoom Temperature Tensile Test of Ag- and/or Ag alloy-sheathed Bi-2223 and Bi-2212 Composite Superconductors, a breaking strength is tested.

3. Cost Accounting

[0041] In a cost of a conventional Bi-based superconducting wire/tape, a cost of a Ag raw material accounts for about 96%, a cost of other raw materials accounts for 2%, and a processing cost accounts for 2%. In the present disclosure, an outer Ag layer of a Bi-based superconducting wire/tape is replaced with Cu, and a half of Ag in the Bi-based superconducting wire/tape is replaced. A price of a Cu raw material is merely 1/100 of a price of a Ag raw material. A processing cost of replacing Ag with copper (including electrochemical Ag reduction and electrochemical additive processing costs) accounts for about 20% of the price of the Cu raw material. According to the standard that a cost of a conventional Bi-based superconducting wire/tape is 100%, a calculation method of a cost of the superconducting wire/tape in the present disclosure is as follows:

cost reduction rate=100%a cost of the replacement raw material Cua cost of replacement processinga remaining Ag raw material in a superconducting tapecost of other materials and processing.

4. Superconducting Critical Current

[0042] According to the GB/T 18502-2018/IEC 61788-3:2006 Critical Current MeasurementDC Critical Current of Ag- and/or Ag alloy-sheathed Bi-2212 and Bi-2223 Oxide Superconductors, a superconducting critical current is tested.

5. Superconducting Critical Tensile Strength Test

[0043] A tensile force is applied to two ends of a wire/tape sample in a length direction, and a superconducting critical current of the sample is tested in situ. When a critical current of a sample drops to 95% of a critical current of the sample in a stress-free state, a corresponding tensile force is a superconducting critical tensile strength of the sample (Fischer K, Fahr T, Schlafer U, et al. Impacts of Processing Parameters and Tensile Stress on Performance of Bi-2223 Tapes (with Ag and AgMn Sheaths) [J]. IEEE transactions on applied superconductivity, 1999, 9 (2): 2625-2628) and (Mao Z H, Jin H, Qin J G, et al. Axial Tensile Stress-Strain Characteristics of Bi-2212 Round Wires under Different Heat Treatment Conditions [J]. IEEE Transactions on Applied Superconductivity, 2017, 27 (6): 6400405).

6. Critical Bend Radius

[0044] A wire/tape sample is uniformly bent in a length direction of the wire/tape sample, and a superconducting critical current of the sample is tested in situ. When a critical current of a sample drops to 95% of a critical current of a straight sample, a corresponding bend radius is a superconducting critical bend radius of the sample (Shin H S, Katagiri K. Critical Current Degradation Behaviors of Bi-2223 Superconducting Tape under Bending and Torsional Strains [J]. Superconductor Science and Technology, 2003, 16 (9): 1012-1018).

Example 1

[0045] This example includes the following steps:

[0046] Step 1: Surface scrubbing: A surface of a first Bi-based superconducting tape (as shown in FIG. 1) was scrubbed with an ethanol-moistened cotton cloth to remove the dirt left on the surface of the first Bi-based superconducting tape during a heat treatment to obtain a second Bi-based superconducting tape.

[0047] Step 2: Electrochemical silver reduction: The second Bi-based superconducting tape obtained after the surface scrubbing in the step 1 was connected to a positive electrode of a stabilized voltage power supply, a graphite electrode was connected to a negative electrode of the stabilized voltage power supply, and then the second Bi-based superconducting tape and the graphite electrode were arranged in parallel on a bracket; and then an electrolyte was added to allow the electrochemical silver reduction, such that a Ag alloy layer on a surface of the second Bi-based superconducting tape was removed to expose a silver layer on a surface of an outer superconducting core wire layer of the second Bi-based superconducting tape to obtain a third Bi-based superconducting tape and electrochemical additive manufactured Ag with a mass purity of 99.99% was produced on a surface of the graphite electrode. A width of the graphite electrode was 12 mm and a width of the second Bi-based superconducting tape was 4 mm, that is, the width of the graphite electrode was 3 times the width of the second Bi-based superconducting tape. A distance between the second Bi-based superconducting tape and the graphite electrode was 1 cm. The electrolyte was a 2 g/L AgNO.sub.3 solution, and a pH of the AgNO.sub.3 solution was adjusted with sodium hydroxide to 3. During the electrochemical silver reduction, a current density of the surface of the second Bi-based superconducting tape was adjusted to 0.1 A/dm.sup.2, and a power-on time was 30 min.

[0048] Step 3: Residual electrolyte removal: The third Bi-based superconducting tape obtained after the electrochemical silver reduction in the step 2 was soaked in ultrapure water to remove a residual electrolyte on a surface of the third Bi-based superconducting tape to obtain a fourth Bi-based superconducting tape.

[0049] Step 4: Surface enhancement: The fourth Bi-based superconducting tape obtained after the residual electrolyte removal in the step 3 was connected to the negative electrode of the stabilized voltage power supply, a copper sheet was connected to the positive electrode of the stabilized voltage power supply, and then the fourth Bi-based superconducting tape and the copper sheet were arranged in parallel on the bracket; and an electrochemical additive solution was added to allow the surface enhancement, such that a Cu layer with a thickness of 20 ?m was formed on a surface of the fourth Bi-based superconducting tape to obtain a low-cost and high-strength Bi-based superconducting tape (as shown in FIG. 2). A distance between the fourth Bi-based superconducting tape and the copper sheet was 2 cm. The electrochemical additive solution included 0.1 g/L copper sulfate and 10 g/L citric acid. During the surface enhancement, a current density of the surface of the fourth Bi-based superconducting tape was adjusted to 0.1 A/dm.sup.2; and the surface enhancement was conducted for 20 min.

[0050] According to test results, for the low-cost and high-strength Bi-based superconducting tape prepared in this example, a Ag mass content is reduced from 66% in the first Bi-based superconducting tape to 33%, a breaking strength is increased from 90 MPa to 94 MPa of the first Bi-based superconducting tape to 102 MPa to 104 MPa, and a superconducting critical tensile strength at 77 K is increased from 5 kg of the first Bi-based superconducting tape to 14 kg, indicating enhanced mechanical properties. The low-cost and high-strength Bi-based superconducting tape prepared in this example and the first Bi-based superconducting tape exhibit completely-consistent superconducting critical current-carrying performance, and both have a superconducting critical current of 53 A at self-field 77 K, which further confirms that the electrochemical Ag reduction and electrochemical copper deposition processes have no impact on the performance of a superconducting core wire.

TABLE-US-00001 Cost of the Cost Cost of a total Cost of a remaining Ag Cost of other of an Ag material in copper Cost of material in a materials Cost original the original raw replacement superconducting and reduction tape tape material processing tape processing rate 100% 96.0% 0.48% 0.096% 48% 4.0% 47.424%

[0051] In this example, copper is used instead of nearly a half of the precious metal Ag in the first Bi-based superconducting tape, such that a cost reduction rate for the first Bi-based superconducting tape reaches 47.424% without reducing the current-carrying performance. The enhanced mechanical properties allow the low-cost and high-strength Bi-based superconducting tape to be used under severe magnetic field or pressure conditions, which broadens an application range of the Bi-based superconducting tape.

[0052] FIG. 1 is a schematic structural diagram of the first Bi-based superconducting tape adopted in Example 1, including: superconducting core wire 1, a Ag layer wrapping around the superconducting core wire 1, and outermost Ag alloy layer 3. FIG. 2 is a schematic structural diagram of the low-cost and high-strength Bi-based superconducting tape prepared in Example 1, including: superconducting core wire 1, a Ag layer wrapping around the superconducting core wire 1, and outermost Cu layer 4. It can be seen from the comparison between FIG. 1 and FIG. 2 that the present disclosure adopts an electrochemical silver reduction technology and an electrochemical additive method to remove a Ag alloy layer on a surface of a Bi-based superconducting wire/tape and coat a high-strength Cu layer instead.

Example 2

[0053] This example includes the following steps:

[0054] Step 1: Surface scrubbing: A surface of a first Bi-based superconducting wire (as shown in FIG. 3) was scrubbed with an ethanol-moistened cotton cloth to remove the dirt left on the surface of the first Bi-based superconducting wire during a heat treatment to obtain a second Bi-based superconducting wire.

[0055] Step 2: Electrochemical silver reduction: The second Bi-based superconducting wire obtained after the surface scrubbing in the step 1 was connected to a positive electrode of a stabilized voltage power supply, a graphite electrode was connected to a negative electrode of the stabilized voltage power supply, and then the second Bi-based superconducting wire and the graphite electrode were arranged in parallel on a bracket; and then an electrolyte was added to allow the electrochemical silver reduction, such that a Ag alloy layer on a surface of the second Bi-based superconducting wire was removed to expose a silver layer on a surface of an outer superconducting core wire layer of the second Bi-based superconducting wire to obtain a third Bi-based superconducting wire and electrochemical additive manufactured Ag with a mass purity of 99.99% was produced on a surface of the graphite electrode. A width of the graphite electrode was 16 mm and a diameter of the second Bi-based superconducting tape was 4 mm, that is, the width of the graphite electrode was 4 times the diameter of the second Bi-based superconducting tape. A distance between the second Bi-based superconducting wire and the graphite electrode was 1 cm. The electrolyte was a 2 g/L AgNO.sub.3 solution, and a pH of the AgNO.sub.3 solution was adjusted with sodium hydroxide to 3. During the electrochemical silver reduction, a current density of the surface of the second Bi-based superconducting wire was adjusted to 10 A/dm.sup.2, and a power-on time was 15 min.

[0056] Step 3: This step was the same as in Example 1.

[0057] Step 4: This step was different from Example 1 in that: The electrochemical additive solution included 2 g/L copper sulfate and 10 g/L citric acid. During the surface enhancement, a current density of the surface of the fourth Bi-based superconducting wire was adjusted to 3 A/dm.sup.2; and the surface enhancement was conducted for 15 min. A Cu layer with a thickness of 40 ?m was formed on the surface of the fourth Bi-based superconducting wire to obtain a low-cost and high-strength Bi-based superconducting wire (as shown in FIG. 4)

[0058] According to test results, for the low-cost and high-strength Bi-based superconducting wire prepared in this example, a Ag mass content is reduced from 80% in the first Bi-based superconducting wire to 40%, a breaking strength is increased from 100 MPa of the first Bi-based superconducting wire to 135 MPa, and a superconducting critical tensile strength at 77 K is increased from 7 kg of the first Bi-based superconducting wire to 17 kg, indicating enhanced mechanical properties. The low-cost and high-strength Bi-based superconducting wire prepared in this example and the first Bi-based superconducting wire exhibit completely-consistent superconducting critical current-carrying performance, and both have a superconducting critical current of 17 A at self-field 77 K, which further confirms that the electrochemical Ag reduction and electrochemical copper deposition processes have no impact on the performance of a superconducting core wire.

TABLE-US-00002 Cost of the Cost Cost of a total Cost of a remaining Ag Cost of other of an Ag material in copper Cost of material in a materials Cost original the original raw replacement superconducting and reduction tape tape material processing tape processing rate 100% 96.5% 0.48% 0.096% 48% 3.5% 47.924%

[0059] In this example, copper is used instead of the precious metal Ag in the first Bi-based superconducting wire, such that a cost reduction rate for the first Bi-based superconducting wire reaches 47.924% without reducing the current-carrying performance. The enhanced mechanical properties allow the low-cost and high-strength Bi-based superconducting wire to be used under a magnetic field or a pressure increased by 30% or more, which broadens an application range of the Bi-based superconducting wire.

[0060] FIG. 3 is a schematic structural diagram of the first Bi-based superconducting tape adopted in Example 1, including: superconducting core wire 1, a Ag layer wrapping around the superconducting core wire 1, and outermost Ag alloy layer 3. FIG. 4 is a schematic structural diagram of the low-cost and high-strength Bi-based superconducting tape prepared in Example 2, including: superconducting core wire 1, a Ag layer wrapping around the superconducting core wire 1, and outermost Cu layer 4. It can be seen from the comparison between FIG. 3 and FIG. 4 that the present disclosure adopts an electrochemical Ag reduction technology and an electrochemical additive method to remove a Ag alloy layer on a surface of a Bi-based superconducting wire/tape and coat a high-strength Cu layer instead.

Example 3

[0061] This example includes the following steps:

[0062] Step 1: Surface scrubbing: A surface of a first Bi-based superconducting tape was scrubbed with an ethanol-moistened cotton cloth to remove the dirt left on the surface of the first Bi-based superconducting tape during a heat treatment to obtain a second Bi-based superconducting tape.

[0063] Step 2: Electrochemical silver reduction: The second Bi-based superconducting tape obtained after the surface scrubbing in the step 1 was connected to a positive electrode of a stabilized voltage power supply, a graphite electrode was connected to a negative electrode of the stabilized voltage power supply, and then the second Bi-based superconducting tape and the graphite electrode were arranged in parallel on a bracket; and then an electrolyte was added to allow the electrochemical silver reduction, such that a Ag alloy layer on a surface of the second Bi-based superconducting tape was removed to expose a silver layer on a surface of an outer superconducting core wire layer of the second Bi-based superconducting tape to obtain a third Bi-based superconducting tape and electrochemical additive manufactured Ag with a mass purity of 99.99% was produced on a surface of the graphite electrode. A width of the graphite electrode was 20 mm and a width of the second Bi-based superconducting tape was 4 mm, that is, the width of the graphite electrode was 5 times the width of the second Bi-based superconducting tape. A distance between the second Bi-based superconducting tape and the graphite electrode was 5 cm. The electrolyte was a 10 g/L AgNO.sub.3 solution, and a pH of the AgNO.sub.3 solution was adjusted with sodium hydroxide to 5. During the electrochemical silver reduction, a current density of the surface of the second Bi-based superconducting tape was adjusted to 10 A/dm.sup.2, and a power-on time was 0.1 min.

[0064] Step 3: This step was the same as in Example 1.

[0065] Step 4: This step was different from Example 1 in that: A distance between the fourth Bi-based superconducting wire/tape and the copper sheet was 5 cm. The electrochemical additive solution included 20 g/L copper chloride and 50 g/L sulfuric acid. During the surface enhancement, a current density of the surface of the fourth Bi-based superconducting tape was adjusted to 10 A/dm.sup.2; and the surface enhancement was conducted for 0.1 min. A Cu layer with a thickness of 10 ?m was formed on the surface of the fourth Bi-based superconducting tape to obtain a low-cost and high-strength Bi-based superconducting tape.

TABLE-US-00003 Cost of the Cost Cost of a total Cost of a remaining Ag Cost of other of an Ag material in copper Cost of material in a materials Cost original the original raw replacement superconducting and reduction tape tape material processing tape processing rate 100% 96.0% 0.31% 0.061% 65% 4.0% 30.179%

[0066] According to test results, for the low-cost and high-strength Bi-based superconducting tape prepared in this example, a Ag mass content is reduced from 66% in the first Bi-based superconducting tape to 45%, a cost reduction rate reaches 30.179%, a breaking strength is increased from 90 MPa to 94 MPa of the first Bi-based superconducting tape to 98 MPa, and a superconducting critical tensile strength at 77 K is increased from 5 kg of the first Bi-based superconducting tape to 5.5 kg. The low-cost and high-strength Bi-based superconducting tape prepared in this example and the first Bi-based superconducting tape exhibit completely-consistent superconducting critical current-carrying performance, and both have a superconducting critical current of 56 A at self-field 77 K, which further confirms that the electrochemical Ag reduction and electrochemical copper deposition processes have no impact on the performance of a superconducting core wire. Although mechanical properties of the low-cost and high-strength Bi-based superconducting tape have not been improved significantly, a critical bend radius of the low-cost and high-strength Bi-based superconducting tape has been reduced from the original 3 cm to 2.5 cm, and thus the low-cost and high-strength Bi-based superconducting tape can be used in the field requiring small bend radii.

Example 4

[0067] This example includes the following steps:

[0068] Step 1: This step was the same as in Example 1.

[0069] Step 2: Electrochemical silver reduction: The second Bi-based superconducting tape obtained after the surface scrubbing in the step 1 was connected to a positive electrode of a stabilized voltage power supply, a graphite electrode was connected to a negative electrode of the stabilized voltage power supply, and then the second Bi-based superconducting tape and the graphite electrode were arranged in parallel on a bracket; and then an electrolyte was added to allow the electrochemical silver reduction, such that a Ag alloy layer on a surface of the second Bi-based superconducting tape was removed to expose a silver layer on a surface of an outer superconducting core wire layer of the second Bi-based superconducting tape to obtain a third Bi-based superconducting tape and electrochemical additive manufactured Ag with a mass purity of 99.99% was produced on a surface of the graphite electrode. A width of the graphite electrode was 12 mm and a width of the second Bi-based superconducting tape was 4 mm, that is, the width of the graphite electrode was 3 times the width of the second Bi-based superconducting tape. A distance between the second Bi-based superconducting tape and the graphite electrode was 3.5 cm. The electrolyte was a 6 g/L AgNO.sub.3 solution, and a pH of the AgNO.sub.3 solution was adjusted with sodium hydroxide to 4. During the electrochemical silver reduction, a current density of the surface of the second Bi-based superconducting tape was adjusted to 5 A/dm.sup.2, and a power-on time was 3 min.

[0070] Step 3: This step was the same as in Example 1.

[0071] Step 4: This step was different from Example 1 in that: A distance between the fourth Bi-based superconducting wire/tape and the copper sheet was 3.5 cm. The electrochemical additive solution included 10 g/L copper sulfate and 30 g/L citric acid. During the surface enhancement, a current density of the surface of the fourth Bi-based superconducting tape was adjusted to 5 A/dm.sup.2; and the surface enhancement was conducted for 10 min. A Cu layer with a thickness of 40 ?m was formed on the surface of the fourth Bi-based superconducting tape to obtain a low-cost and high-strength Bi-based superconducting tape.

TABLE-US-00004 Cost of the Cost Cost of a total Cost of a remaining Ag Cost of other of an Ag material in copper Cost of material in a materials Cost original the original raw replacement superconducting and reduction tape tape material processing tape processing rate 100% 95.5% 0.32% 0.064% 64% 4.5% 31.451%

[0072] According to test results, for the low-cost and high-strength Bi-based superconducting tape prepared in this example, a Ag mass content is reduced from 60% in the first Bi-based superconducting tape to 40%, a cost reduction rate reaches 31.451%, a breaking strength is increased from 90 MPa to 94 MPa of the first Bi-based superconducting tape to 124 MPa, and a superconducting critical tensile strength at 77 K is increased from 5 kg of the first Bi-based superconducting tape to 16 kg, indicating enhanced mechanical properties. The low-cost and high-strength Bi-based superconducting tape prepared in this example and the first Bi-based superconducting tape exhibit completely-consistent superconducting critical current-carrying performance, and both have a superconducting critical current of 52 A at self-field 77 K, which further confirms that the electrochemical Ag reduction and electrochemical copper deposition processes have no impact on the performance of a superconducting core wire.

[0073] In this example, copper is used instead of the precious metal Ag in the first Bi-based superconducting tape, such that a raw material cost of the first Bi-based superconducting tape is reduced by 49% without reducing the current-carrying performance. The enhanced mechanical properties allow the low-cost and high-strength Bi-based superconducting tape to be used under a magnetic field or a pressure increased by 30% or more, which broadens an application range of the Bi-based superconducting tape.

Example 5

[0074] This example was different from Example 2 in that: a distance between the fourth Bi-based superconducting wire and the copper sheet was 2 cm; the electrochemical additive solution included 3 g/L copper sulfate and 10 g/L citric acid; the surface enhancement was conducted for 10 min; and a Cu layer with a thickness of 25 ?m was formed on the surface of the fourth Bi-based superconducting wire.

TABLE-US-00005 Cost of the Cost Cost of a total Cost of a remaining Ag Cost of other of an Ag material in copper Cost of material in a materials Cost original the original raw replacement superconducting and reduction tape tape material processing tape processing rate 100% 97.0% 0.36% 0.073% 61% 3.0% 35.939%

[0075] According to test results, for the low-cost and high-strength Bi-based superconducting wire prepared in this example, a Ag mass content is reduced from 80% in the first Bi-based superconducting wire to 50%, such that a raw material cost of the first Bi-based superconducting tape was reduced by 30% without reducing the current-carrying performance. The low-cost and high-strength Bi-based superconducting wire prepared in this example and the first Bi-based superconducting wire exhibit completely-consistent superconducting critical current-carrying performance, and both have a superconducting critical current of 16 A at self-field 77 K, which further confirms that the electrochemical Ag reduction and electrochemical copper deposition processes have no impact on the performance of a superconducting core wire. Although the breaking strength and the superconducting critical tensile strength at 77 K of the low-cost and high-strength Bi-based superconducting wire have not been improved significantly, a critical bend radius of the low-cost and high-strength Bi-based superconducting wire has been reduced from the original 12.5 cm to 10 cm, and thus the low-cost and high-strength Bi-based superconducting wire can be used in the field requiring small bend radii.

Comparative Example 1

[0076] Mechanical Ag reduction and tin-soldering of a copper strip for enhancement were adopted. Specific steps were as follows:

[0077] An electric planer of a computer numerical control (CNC) machining center was used to allow the mechanical Ag reduction with a cutting amount of 5 ?m. 10 times of the mechanical Ag reduction could successfully remove Ag on a surface of a Bi-based superconducting tape. However, although this method could lead to a high-purity Ag by-product, each pass of the mechanical Ag reduction would lead to a stress and even a strain, thereby causing a damage to a ceramic superconducting core. In addition, each pass of the mechanical Ag reduction caused a critical current of the superconducting tape to be reduced by 5% to 10%.

[0078] Similar to Example 1, a Ag content in the superconducting tape was reduced by half through this mechanical Ag reduction method, but the current-carrying performance of the superconducting tape was reduced by nearly 70%. In contrast, the electrochemical Ag reduction method in Example 1 of the present disclosure made the Ag content reduced to a same level without affecting the current-carrying performance of the superconducting tape.

[0079] After the Ag content in the superconducting tape was reduced by half through the mechanical Ag reduction, an enhancing copper strip was tin-soldered to a resulting superconducting tape, which could increase a strength of the superconducting tape to 150 Mpa. However, during the soldering, if complete natural soldering is adopted, a too-large soldering tin thickness will increase a cross-sectional area of the superconducting tape by nearly 1 time, which not only affects the dimension uniformity of the superconducting tape, but also reduces a critical engineering current density of the superconducting tape by half.

[0080] If pressure-assisted tin-soldering is adopted, soldering tin between the enhancing copper strip and the superconducting tape can be discharged as much as possible under an action of an external pressure while ensuring the soldering firmness between the enhancing copper strip and the superconducting tape and finally enhancing the dimension uniformity of the superconducting tape. However, under an action of an external pressure, a ceramic core of the Bi-based superconducting tape would also be destroyed, making the current-carrying performance of the superconducting tape reduced by about 20%.

[0081] In contrast, an electrochemical additive process was adopted for a Ag-reduced superconducting tape with the same Ag content in Example 1 of the present disclosure. Since almost no stress was introduced during the electrochemical additive process, a ceramic superconducting core of the superconducting tape was almost not affected before and after the electrochemical additive process, and thus the final current-carrying performance of the superconducting tape was not affected.

[0082] Although the mechanical Ag reduction and the copper strip soldering enhancement can nominally reduce a Ag content in a Bi-based superconducting tape and enhance a mechanical strength of the Bi-based superconducting tape, but the superconducting performance of the superconducting tape is reduced by nearly 90%. However, the electrochemical Ag reduction and electrochemical additive technologies of the present disclosure can reduce a Ag content by nearly 50% and improve mechanical properties by at least 30% or more without reducing the superconducting performance.

[0083] The above are merely preferred examples of the present disclosure, and are not intended to limit the present disclosure in any form. Any simple modifications, changes, and equivalent variations made to the above examples according to the technical essence of the present disclosure should fall within the protection scope of the technical solutions of the present disclosure.