Preparation method for winding Bi-2212 superconducting flat wire after reaction
By using a reaction-before-winding method, combined with the use of irregularly shaped copper flat strips and tin plating, the brittleness problem of Bi-2212 superconducting wires during the winding process was solved, achieving the preparation of Bi-2212 superconducting flat wires with high current carrying capacity and low cost, which are suitable for high-field magnet devices and superconducting cables.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN SUPERCONDUCTING WIRE TECHNOLOGIES CO LTD
- Filing Date
- 2026-01-23
- Publication Date
- 2026-04-17
AI Technical Summary
Bi-2212 superconducting wires are prone to brittle breakage during winding, resulting in a decrease in current-carrying capacity. Furthermore, traditional processes are difficult to detect defects, are costly and complex, cannot use polymer insulation materials, and require large-scale equipment for processing.
The method of reaction followed by winding is adopted. Bi-2212 superconducting round wire is placed into thin-walled copper groove wire with outer square and inner circle for plastic deformation and inlay welding. Irregular soft copper flat strip and tin plating layer are used to reduce welding difficulty. Ag matrix is electrolytically recycled to reduce cost.
The current carrying capacity of Bi-2212 superconducting flat wire was increased, manufacturing costs were reduced, the process was simplified, it is suitable for mass production, and defects were avoided through eddy current testing, thus improving welding quality.
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Figure CN121885304A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of superconducting material processing technology, and relates to a method for preparing Bi-2212 superconducting flat wire by reacting first and then winding. Background Technology
[0002] Bi-2212, a copper oxide high-temperature superconducting material, has a superconducting transition temperature of approximately 95K, higher than that of liquid nitrogen (77K). Its core advantage lies in its similarity to traditional low-temperature superconducting materials; it can be processed into flexible, isotropic circular wires and further stranded to achieve extremely high current-carrying capacity. Simultaneously, Bi-2212 maintains excellent high-field current-carrying characteristics and low AC losses even in extremely strong magnetic fields above 25K, making it suitable for applications in extremely high magnetic fields, such as high-field magnet devices, superconducting cables, and special high-field magnets for scientific research.
[0003] However, Bi-2212 wire exhibits significantly increased brittleness after reaction heat treatment, with extremely low yield strength and tensile strength. This makes it prone to superconducting phase breakage during winding, stretching, or torsion, leading to a decrease in current-carrying capacity. Therefore, traditional processes commonly employ a "winding first, then reaction" method to avoid mechanical damage to the superconducting phase during winding. However, with increasing application requirements, the limitations of this process have become increasingly apparent. Defect detection is difficult after the overall reaction heat treatment, resulting in a high risk of scrapping the finished magnet; it prevents the use of polymer insulating materials, complicating the process; and it requires complex processing of the complete magnet using large-scale heat treatment equipment, significantly increasing process difficulty and cost. In contrast, the "reaction first, then winding" process, because it avoids these problems, has become an important direction for current superconducting wire research and development.
[0004] Drawing inspiration from the nested design concept of wire-in-channel NbTi structured wires (WIC structured wires), a copper layer can be coated onto the outside of Bi-2212 superconducting round wires to create flat wires. By controlling the bending and twisting during the winding process, damage to the brittle Bi-2212 superconducting phase can be avoided, thus achieving "reaction before winding." Traditional WIC structured wires use a nested structure formed by embedding copper channel wires and Bi-2212 superconducting round wires. To ensure that long wires of tens of thousands of meters can be wound onto a single reel, the copper channel wires need to have sufficient mechanical strength, resulting in a typically large wall thickness. Even after thinning using a U-shaped die, the thickness remains high, leading to a high volumetric proportion of copper in the superconducting composite wire, which in turn reduces the overall current carrying capacity and increases manufacturing costs (traditional WIC method). Furthermore, the expensive silver matrix material used in the Bi-2212 superconducting round wires is also a significant reason for the high cost of the final wire. The welding between copper channel wire and Bi-2212 silver substrate is difficult and has many defects. Traditional methods rely on cold working combined with subsequent thermal diffusion process to solve the problem, but there are problems such as long preparation cycle and insufficient strength of the resulting wire substrate. Summary of the Invention
[0005] To address the problems and deficiencies in the existing technology, this invention provides a method for preparing Bi-2212 superconducting flat wire by reacting first and then winding.
[0006] In a first aspect, the present invention provides a method for preparing Bi-2212 superconducting flat wire by reacting and then winding, comprising: placing a Bi-2212 superconducting round wire after recovering part of the Ag matrix by electrolysis into a thin-walled copper groove wire with an outer square and inner circle shape, and simultaneously performing plastic deformation and inlay welding to obtain Bi-2212 superconducting flat wire.
[0007] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the inner diameter of the outer square and inner circle thin-walled copper groove wire is 1.03 to 1.08 times the diameter of the Bi-2212 superconducting round wire after the online recovery of part of the Ag matrix by electrolysis; The outer square and inner round thin-walled copper channel is made by bending irregularly shaped soft copper flat strips containing a tin plating layer.
[0008] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the irregular soft copper flat strip is provided with a first surface and a second surface; The first surface is a plane; The second surface is continuously and alternately provided with convex arc segments and concave arc segments along a preset extension direction. The convex arc segment is an arc-shaped structure that protrudes away from the first surface, and the concave arc segment is an arc-shaped structure that is recessed towards the first surface. The convex arc segment and the concave arc segment have a smooth transition. The thinnest part of the irregularly shaped soft copper flat strip is located in the concave arc segment, which is the shortest distance from the apex of the concave arc segment to the first surface; The tin plating layer is disposed on the first surface of the irregularly shaped soft copper flat strip.
[0009] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the thickness of the thinnest part of the irregular soft copper flat strip is 0.15~0.25mm; The angle of the convex arc segment is 90°.
[0010] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the thickness of the tin plating layer is 5~10μm; The solder for the tin plating layer is SnCu, with a Cu content of 2% to 2.5%. The temperature for preparing the tin plating layer is 260~300℃, and the speed is 50~120m / min.
[0011] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the Bi-2212 superconducting round wire after recovering part of the Ag matrix online is obtained by electrolytic recovery of part of the Ag matrix.
[0012] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the electrolyte for electrolysis is a mixed aqueous solution of AgNO3, KI and sulfosalicylic acid, the power supply is a DC constant current regulated power supply, the anode is Bi-2212 superconducting round wire, the cathode is a graphite plate, and the current is 340~750A.
[0013] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reaction and winding provided by the present invention, the preparation of the Bi-2212 superconducting flat wire specifically includes: pre-bonding Bi-2212 superconducting round wire and thin-walled copper groove wire with outer square and inner circle in a liquid solder environment through a round wire bonding mold to obtain a composite blank; and simultaneously plastically deforming and inlaying welding the composite blank in a liquid solder environment through an inlay mold to obtain the Bi-2212 superconducting flat wire.
[0014] Furthermore, in the method for preparing Bi-2212 superconducting flat wire by reacting and then winding provided by the present invention, the cross-section of the round wire combined with the mold is rectangular; The dimensions of the inlay mold are determined based on the amount of plastic deformation, which is 10% to 15% of the initial cross-sectional area of the composite blank. The temperature for the inlay welding is 260~300℃, and the speed is 20~120m / min.
[0015] Secondly, the present invention provides a Bi-2212 superconducting flat wire prepared by the above-mentioned method of preparing Bi-2212 superconducting flat wire by reacting first and then winding.
[0016] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: This invention employs a method of bending a planar tin-plated irregularly shaped copper strip to obtain a "square on the outside, round on the inside" thin-walled copper channel profile. The surface is then finished to create a thin-walled copper channel with a uniform and controllable tin layer thickness within the channel, thereby increasing the current-carrying density of the Bi-2212 superconducting flat wire. Simultaneously, the tin plating on the irregularly shaped copper strip changes the Ag-Cu welding process to Ag-Sn welding, reducing welding difficulty and significantly improving welding quality. Secondly, a large amount of Ag matrix is recovered from the surface of the Ag-based Bi-2212 superconducting round wire using an electrolytic method, reducing the manufacturing cost of the Bi-2212 superconducting flat wire. Finally, the thin-walled copper channel wire is inlaid and welded to the recovered Ag matrix Bi-2212 superconducting round wire, resulting in a low-cost pre-reaction, post-winding Bi-2212 superconducting flat wire. The preparation process is simple and controllable, suitable for mass production. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the structure of an irregularly shaped soft copper strip. In the diagram, 1 represents the first surface, 2 the second surface, 3 the thinnest part of the irregularly shaped soft copper strip, 4 the convex arc segment, and 5 the concave arc segment.
[0018] Figure 2 This is a schematic diagram of the structure of an irregularly shaped soft copper strip containing a tin-plated layer. In the diagram, 6 represents the tin layer, and 7 represents the irregularly shaped soft copper strip.
[0019] Figure 3 This is a schematic diagram of the thin-walled copper channel. 6 represents the tin layer, and 7 represents the irregularly shaped soft copper strip.
[0020] Figure 4 This is a schematic diagram of the Ag matrix structure on the surface of an Ag-based Bi-2212 superconducting circular wire. In the diagram, 1 represents the Ag matrix, and 2 represents the Bi-2212 superconducting phase.
[0021] Figure 5 Flowchart of the method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to the present invention. Detailed Implementation
[0022] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.
[0023] In the following embodiments, the thickness of the silver (Ag) matrix layer of the Ag-based Bi-2212 superconducting round wire can be adjusted according to actual process requirements and performance requirements, and is not limited to a specific value. Under the conditions of the aforementioned processing technology, the overall mechanical strength of the Ag-based Bi-2212 superconducting round wire can be improved by appropriately increasing the thickness of the silver matrix layer.
[0024] The calculations of the relevant machining parameters involved in the following embodiments are as follows: (1) Calculations related to thin-walled copper channel wire: Based on the diameter (D) of the Bi-2212 superconducting circular wire after partial Ag matrix recovery via electrolytic online processing, the basic structural parameters of the thin-walled copper trench wire can be determined, as shown below: The inner diameter d0 of the thin-walled copper groove wire is = k ·D, k The value is between 1.03 and 1.08. The thickness δ1 of the tin plating layer is 5~10μm; After the irregular soft copper flat strip is tin-plated, bent and shaped to form the thin-walled copper groove line, the wall thickness (δ2) of the thin-walled copper groove line is controlled at 0.1~0.2mm; The opening radius and width of the thin-walled copper channel are calculated as follows:
[0025]
[0026] In the above formula, α represents the opening arc of the thin-walled copper channel (unit: rad), W1 represents the opening width of the thin-walled copper channel, and the meaning and calculation method of r1 and d1 are given in (2) related calculation of irregular soft copper flat strip.
[0027] (2) Calculations related to irregularly shaped soft copper strips: The cross-section of the irregular soft copper strip used to prepare the thin-walled copper channel line includes a 90° convex arc segment 4 and a concave arc segment 4 that smoothly transitions to the convex arc segment 5. The thinnest part 3 is the shortest distance (t1) from the apex of the concave arc segment 5 to the first surface 1, which is 0.15~0.25mm. Its cross-sectional geometric parameters are calculated as follows: The formula for calculating the radius value r1 of the convex arc segment 4 (i.e., the R-angle radius value of the thin-walled copper channel line) is as follows:
[0028] In the above formula, d1 = d0 + 2δ1 (the inner diameter of the thin-walled copper groove without tin plating). The remaining cross-sectional parameters of the irregular soft copper strip can be calculated based on the radius r1 of the convex arc segment, the inner diameter d1 of the plating groove, and the thickness t1 at the thinnest point, using the geometric relationship of the irregular transition segment.
[0029] (3) Calculations related to the circular wire bonding mold:
[0030]
[0031] In the above formula, W3 is the width of the circular wire mold, H3 is the height of the circular wire mold, and W2=H2=d1+2δ2 (W2 is the width of the thin-walled copper channel line, and H2 is the height of the thin-walled copper channel line).
[0032] In the following embodiments, the distance between the electrolytic cell outlet and the solder bath inlet is ≤2m.
[0033] Example 1 This embodiment provides a method for preparing Bi-2212 superconducting flat wire.
[0034] like Figure 5As shown, the method for preparing Bi-2212 superconducting flat wire in this embodiment includes: S1. According to the Bi-2212 superconducting flat wire processing technology described in this embodiment, the processing parts are selected as oxygen-free copper rods with a diameter of 1.0 mm and Ag-based Bi-2212 superconducting round wires with a diameter of 0.82 mm after reaction heat treatment.
[0035] S2. After straightening the oxygen-free copper rod, it is flattened into a copper flat strip with a width of 2.39 mm and a thickness of 0.26 mm. The copper flat strip is then rolled in three passes to produce a shaped copper flat strip with a length of 2.39 mm, a minimum thickness of 0.15 mm, a concave radius of 0.24 mm, an angle of 70.2°, a convex radius of 0.275 mm, and an angle of 90°. The shaped copper flat strip is then annealed, cooled, cleaned, and subjected to anti-oxidation treatment to obtain a shaped soft copper flat strip. (Example:) Figure 1 As shown, the irregularly shaped flexible copper strip has a first surface 1 and a second surface 2. The first surface 1 is a plane; the second surface 2 has alternating convex arc segments 4 and concave arc segments 5 along a predetermined extension direction. The convex arc segment 4 is an arc-shaped structure that protrudes away from the first surface 1, and the concave arc segment 5 is an arc-shaped structure that is recessed towards the first surface 1, with a smooth transition between the convex arc segment 4 and the concave arc segment 5. The thinnest point is located in the concave arc segment 5, which is the shortest distance from the apex of the concave arc segment 5 to the first surface 1.
[0036] S3. After removing the oxide from the surface of the irregularly shaped soft copper strip, tin plating is performed on the first surface of the irregularly shaped soft copper strip, and the thickness of the tin plating layer is 5μm. Figure 2 The tin-based solder used for tin plating is Sn2.5Cu, the soldering temperature is 300℃, and the soldering speed is 120m / min.
[0037] S4. After bending and shaping the irregularly shaped soft copper strip containing a tin plating layer, a thin-walled copper groove line with an outer square and inner circle shape is formed, with a width of 1.05mm, a height of 1.05mm, an inner diameter of 0.84mm, a radius of 0.27mm, an upper opening angle of 1.34rad, an opening width of 0.53mm, and a wall thickness of 0.1mm. Figure 3 It consists of a tin-plated layer 6 and an irregularly shaped soft copper flat strip 7. The thin-walled copper channel wire is treated with a flux to remove oxides. A water-based, no-clean flux is added to the flux.
[0038] S6. Electrolytic treatment of Ag-based Bi-2212 superconducting round wires in an electrolytic cell (10m long) is performed to dissolve and recover Ag from the surface of the Ag-based Bi-2212 superconducting round wires. Figure 4The process yielded a 0.8 mm Bi-2212 superconducting round wire. The electrolytic cell contained 500 L of electrolyte, a mixed aqueous solution of AgNO3, KI, and sulfosalicylic acid (AgNO3 concentration 30 g / L, KI concentration 200 g / L, sulfosalicylic acid concentration 40 g / L). The electrolysis was powered by a DC constant current regulated power supply. The anode was the Bi-2212 superconducting round wire, and the cathode consisted of multiple parallel graphite plate electrodes (1 m² area). 2 The electrolysis current is 480A.
[0039] S7. Thin-walled copper channel wire and electrolytically treated Bi-2212 superconducting round wire are simultaneously introduced into a solder bath (liquid Sn2Cu). Using a circular wire bonding mold (rectangular, 1.32mm × 1.31mm) immersed in Sn2Cu solder, the Bi-2212 superconducting round wire and thin-walled copper channel wire are pre-bonded to obtain a composite blank. In Sn2Cu solder, the composite blank is further passed through a 1.01mm × 0.91mm rectangular embedding mold. Simultaneously with plastic deformation (15% processing amount), embedding welding is completed in the solder medium to obtain a Bi-2212 superconducting flat wire, denoted as Superconducting Wire-1. The embedding welding temperature is 300℃, and the embedding welding speed is 120m / min. After welding, the Ag layer on the cathode graphite plate electrode is collected.
[0040] In this embodiment, superconducting wire-1 was rewound and subjected to eddy current testing twice, designated as superconducting wire-2. Superconducting wire-2 was rewound and subjected to eddy current testing twice, designated as superconducting wire-3. The performance of superconducting wire-1, superconducting wire-2, and superconducting wire-3 were tested sequentially. The critical current Ic (4.2K, 12T) of superconducting wire-1 was 186.2A, the critical current Ic (4.2K, 12T) of superconducting wire-2 was 185.8A, and the critical current Ic (4.2K, 12T) of superconducting wire-3 was 187.1A. The above experimental results show that multiple rewinding did not significantly affect the critical current Ic of the Bi-2212 superconducting flat wire. At the same time, the solder on the surface of the Bi-2212 superconducting flat wire was uniform and smooth, and no defect signals related to missing solder joints were found during the rewinding process by eddy current testing.
[0041] Example 2 This embodiment provides a method for preparing Bi-2212 superconducting flat wire.
[0042] Similar to Example 1, the preparation method of the Bi-2212 superconducting flat wire in this example includes: S1. According to the Bi-2212 superconducting flat wire processing technology described in this embodiment, the processing parts are selected as oxygen-free copper rods with a diameter of 1.9 mm and Ag-based Bi-2212 superconducting round wires with a diameter of 1.74 mm after reaction heat treatment.
[0043] S2. After straightening the oxygen-free copper rod, roll it flat into a copper flat strip of 4.84mm × 0.48mm; after rolling the copper flat strip in 3 passes, it is made into an irregular copper flat strip with a length of 4.84mm, a thickness of 0.25mm at the thinnest point, a concave arc radius of 0.56mm, an angle of 72.8°, a convex arc radius of 0.51mm, and an angle of 90°; after annealing, cooling, cleaning, and anti-oxidation treatment, the irregular soft copper flat strip is obtained.
[0044] S3. After removing the oxide from the surface of the irregularly shaped soft copper strip, tin plating is performed on the first surface of the irregularly shaped soft copper strip to obtain an irregularly shaped soft copper strip with a tin plating layer, the thickness of which is 5μm. The tin-based solder used for tin plating is Sn2Cu, the soldering temperature is 260℃, and the soldering speed is 50m / min.
[0045] S4. The irregularly shaped soft copper strip containing a tin plating layer is sequentially bent and shaped to form a thin-walled copper channel line with an outer square and inner circle shape, measuring 2.15mm in width, 2.15mm in height, 1.74mm in inner diameter of the channel, 0.51mm in radius, 1.37rad in top opening angle, 1.10mm in opening width, and 0.2mm in wall thickness. The thin-walled copper channel line is then subjected to a fluxing machine to remove oxides. A water-based, no-clean flux is added to the fluxing machine.
[0046] S6. Ag-based Bi-2212 superconducting round wire was electrolyzed in a 10m long electrolytic cell to dissolve and recover the Ag on the surface of the wire, yielding a 1.7mm Bi-2212 superconducting round wire. The electrolytic cell contained 500L of electrolyte, a mixed aqueous solution of AgNO3, KI, and sulfosalicylic acid (AgNO3 concentration 30g / L, KI concentration 200g / L, sulfosalicylic acid concentration 40g / L). The electrolysis was powered by a DC constant current regulated power supply. The anode was the Bi-2212 superconducting round wire, and the cathode consisted of multiple graphite plate electrodes connected in parallel (area 1.5m²). 2 The electrolysis current is 340A.
[0047] S7. Thin-walled copper channel wire and electrolytically treated Bi-2212 superconducting round wire are simultaneously passed into a solder bath (Sn0.7Cu). Using a round wire bonding mold (rectangular, 2.75mm × 2.32mm) immersed in Sn0.7Cu solder, the Bi-2212 superconducting core material is pre-bonded to the thin-walled copper channel wire to obtain a composite blank. In Sn2Cu solder, the composite blank is further passed through a 2.1mm × 1.9mm embedding mold (rectangular). Simultaneously with plastic deformation (10% processing amount), embedding welding is completed in the solder medium to obtain a Bi-2212 superconducting flat wire, denoted as Superconducting Wire-1. The embedding welding temperature is 260℃, and the embedding welding speed is 20m / min. After welding, the Ag layer on the cathode graphite plate electrode is collected.
[0048] In this embodiment, superconducting wire-1 was rewound and subjected to eddy current testing twice, designated as superconducting wire-2. Superconducting wire-2 was rewound and subjected to eddy current testing twice, designated as superconducting wire-3. The performance of superconducting wire-1, superconducting wire-2, and superconducting wire-3 was tested sequentially. The critical current Ic (4.2K, 12T) of superconducting wire-1 was 835.9A, the critical current Ic (4.2K, 12T) of superconducting wire-2 was 836.9A, and the critical current Ic (4.2K, 12T) of superconducting wire-3 was 834.5A. The above experimental results show that multiple rewinding did not significantly affect the critical current Ic of the Bi-2212 superconducting flat wire. At the same time, the solder on the surface of the Bi-2212 superconducting flat wire was uniform and smooth, and no defect signals related to missing solder joints were found during eddy current testing during the rewinding process.
[0049] Example 3 This embodiment provides a method for preparing Bi-2212 superconducting flat wire.
[0050] Similar to Example 1, the preparation method of the Bi-2212 superconducting flat wire in this example includes: S1. According to the Bi-2212 superconducting flat wire processing technology described in this embodiment, the processing parts are selected as oxygen-free copper rods with a diameter of 1.2 mm and Ag-based Bi-2212 superconducting round wires with a diameter of 1.10 mm after reaction heat treatment.
[0051] S2. After straightening the oxygen-free copper rod, roll it flat into a copper flat strip of 3.03mm × 0.30mm; after rolling the copper flat strip in 3 passes, it is made into an irregular copper flat strip with a length of 3.03mm, a thickness of 0.15mm at the thinnest point, a concave arc radius of 0.36mm, an angle of 73.2°, a convex arc radius of 0.31mm, and an angle of 90°; after annealing, cooling, cleaning, and anti-oxidation treatment, the irregular soft copper flat strip is obtained.
[0052] S3. After removing the oxide from the surface of the irregularly shaped soft copper strip, tin plating is performed on the first surface of the irregularly shaped soft copper strip to obtain an irregularly shaped soft copper strip with a tin plating layer, the thickness of which is 10μm. The tin-based solder used for tin plating is Sn2Cu, the soldering temperature is 280℃, and the soldering speed is 80m / min.
[0053] S4. The irregularly shaped soft copper strip containing a tin plating layer is sequentially bent and shaped to form a thin-walled copper channel line with an outer square and inner circle shape, measuring 1.30mm in width, 1.30mm in height, 1.08mm in inner diameter of the channel, 0.31mm in radius, 1.37rad in top opening angle, 0.7mm in opening width, and 0.1mm in wall thickness. The thin-walled copper channel line is then subjected to a fluxing machine to remove oxides. A water-based, no-clean flux is added to the fluxing machine.
[0054] S6. Ag-based Bi-2212 superconducting round wire was electrolyzed in a 10m long electrolytic cell to dissolve and recover the Ag on the surface of the wire, yielding a 1.07mm Bi-2212 superconducting round wire. The electrolytic cell contained 500L of electrolyte, a mixed aqueous solution of AgNO3, KI, and sulfosalicylic acid (AgNO3 concentration 30g / L, KI concentration 200g / L, sulfosalicylic acid concentration 40g / L). The electrolysis was powered by a DC constant current regulated power supply. The anode was the Bi-2212 superconducting round wire, and the cathode consisted of multiple graphite plate electrodes connected in parallel (area 1.5m²). 2 The electrolysis current is 640A.
[0055] S7. Thin-walled copper channel wire and electrolytically treated Bi-2212 superconducting round wire are simultaneously passed into a solder bath (Sn0.7Cu). Using a round wire bonding mold (rectangular, 1.60mm × 1.40mm) immersed in Sn0.7Cu solder, the Bi-2212 superconducting core material is pre-bonded to the thin-walled copper channel wire to obtain a composite blank. In Sn2Cu solder, the composite blank is further passed through a 1.45mm × 0.95mm embedding mold (rectangular). Simultaneously with plastic deformation (13% processing amount), embedding welding is completed in the solder medium to obtain a Bi-2212 superconducting flat wire, denoted as Superconducting Wire-1. The embedding welding temperature is 280℃, and the embedding welding speed is 80m / min. After welding, the Ag layer on the cathode graphite plate electrode is collected.
[0056] In this embodiment, superconducting wire-1 was rewound and subjected to eddy current testing twice, designated as superconducting wire-2. Superconducting wire-2 was rewound and subjected to eddy current testing twice, designated as superconducting wire-3. The performance of superconducting wire-1, superconducting wire-2, and superconducting wire-3 was tested sequentially. The critical current Ic (4.2K, 12T) of superconducting wire-1 was 320.4A, that of superconducting wire-2 was 316.7A, and that of superconducting wire-3 was 318.8A. The above experimental results show that multiple rewindings did not significantly affect the critical current Ic of the Bi-2212 superconducting flat wire. Furthermore, the solder on the surface of the Bi-2212 superconducting flat wire was uniform and smooth, and no defect signals related to solder joint leakage were found during eddy current testing during the rewinding process.
[0057] Example 4 This embodiment provides a method for preparing Bi-2212 superconducting flat wire.
[0058] Similar to Example 1, the preparation method of the Bi-2212 superconducting flat wire in this example includes: S1. According to the Bi-2212 superconducting flat wire processing technology described in this embodiment, the processing parts are selected as oxygen-free copper rods with a diameter of 1.8 mm and Ag-based Bi-2212 superconducting round wires with a diameter of 1.54 mm after reaction heat treatment.
[0059] S2. After straightening the oxygen-free copper rod, roll it flat into a copper flat strip of 4.37mm × 0.46mm; after rolling the copper flat strip in 3 passes, it is made into an irregular copper flat strip with a length of 4.37mm, a thickness of 0.25mm at the thinnest point, a concave arc radius of 0.47mm, an angle of 71.6°, a convex arc radius of 0.48mm, and an angle of 90°; after annealing, cooling, cleaning, and anti-oxidation treatment, the irregular soft copper flat strip is obtained.
[0060] S3. After removing the oxide from the surface of the irregularly shaped soft copper strip, tin plating is performed on the first surface of the irregularly shaped soft copper strip to obtain an irregularly shaped soft copper strip with a tin plating layer, the thickness of which is 10μm. The tin-based solder used for tin plating is Sn2Cu, the soldering temperature is 280℃, and the soldering speed is 100m / min.
[0061] S4. The irregularly shaped soft copper strip containing a tin plating layer is sequentially bent and shaped to form a thin-walled copper channel line with an outer square and inner circle shape, measuring 1.97mm in width, 1.97mm in height, 1.55mm in inner diameter of the channel, 0.48mm in radius, 1.35rad in top opening angle, 0.98mm in opening width, and 0.2mm in wall thickness. The thin-walled copper channel line is then subjected to a fluxing machine to remove oxides. A water-based, no-clean flux is added to the fluxing machine.
[0062] S6. Ag-based Bi-2212 superconducting round wires were electrolyzed in a 10m long electrolytic cell to dissolve and recover the Ag on the surface of the wires, yielding 1.50mm Bi-2212 superconducting round wires. The electrolytic cell contained 500L of electrolyte, a mixed aqueous solution of AgNO3, KI, and sulfosalicylic acid (AgNO3 concentration 30g / L, KI concentration 200g / L, sulfosalicylic acid concentration 40g / L). The electrolysis was powered by a DC constant current regulated power supply. The anode was the Bi-2212 superconducting round wire, and the cathode consisted of multiple graphite plate electrodes connected in parallel (area 1.5m²). 2 The electrolysis current is 750A.
[0063] S7. Thin-walled copper channel wire and electrolytically treated Bi-2212 superconducting round wire are simultaneously introduced into a solder bath (Sn0.7Cu). Using a round wire bonding mold (rectangular, 2.48mm × 2.12mm) immersed in Sn0.7Cu solder, the Bi-2212 superconducting core material is pre-bonded to the thin-walled copper channel wire to obtain a composite blank. In Sn2Cu solder, the composite blank is further passed through a 2.10mm × 1.58mm rectangular embedding mold. Simultaneously with plastic deformation (10% processing amount), embedding welding is completed in the solder medium to obtain a Bi-2212 superconducting flat wire, denoted as Superconducting Wire-1. The embedding welding temperature is 280℃, and the embedding welding speed is 50m / min. After welding, the Ag layer on the cathode graphite plate electrode is collected.
[0064] In this embodiment, superconducting wire-1 was rewound and subjected to eddy current testing twice, designated as superconducting wire-2. Superconducting wire-2 was rewound and subjected to eddy current testing twice, designated as superconducting wire-3. The performance of superconducting wire-1, superconducting wire-2, and superconducting wire-3 were tested sequentially. The critical current Ic (4.2K, 12T) of superconducting wire-1 was 648.1A, the critical current Ic (4.2K, 12T) of superconducting wire-2 was 652.2A, and the critical current Ic (4.2K, 12T) of superconducting wire-3 was 655.7A. The above experimental results show that multiple rewinding did not significantly affect the critical current Ic of the Bi-2212 superconducting flat wire. At the same time, the solder on the surface of the Bi-2212 superconducting flat wire was uniform and smooth, and no defect signals related to missing solder joints were found during eddy current testing during the rewinding process.
[0065] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.
Claims
1. A method for preparing Bi-2212 superconducting flat wire by first reacting and then winding, characterized in that, include: Bi-2212 superconducting round wires, after partial Ag matrix recovery via electrolysis, are placed into thin-walled copper grooves with an outer square and inner circle shape. Simultaneous plastic deformation and inlay welding are performed to obtain Bi-2212 superconducting flat wires.
2. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 1, characterized in that, The inner diameter of the outer square and inner circular thin-walled copper groove wire is 1.03 to 1.08 times the diameter of the Bi-2212 superconducting circular wire after partial Ag matrix recovery by electrolysis. The outer square and inner round thin-walled copper channel is made by bending irregularly shaped soft copper flat strips containing a tin plating layer.
3. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 2, characterized in that, The irregularly shaped soft copper flat strip is provided with a first surface and a second surface; The first surface is a plane; The second surface is continuously and alternately provided with convex arc segments and concave arc segments along a preset extension direction. The convex arc segment is an arc-shaped structure that protrudes away from the first surface, and the concave arc segment is an arc-shaped structure that is recessed towards the first surface. The convex arc segment and the concave arc segment have a smooth transition. The thinnest part of the irregularly shaped soft copper flat strip is located in the concave arc segment, which is the shortest distance from the apex of the concave arc segment to the first surface; The tin plating layer is disposed on the first surface of the irregularly shaped soft copper flat strip.
4. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 3, characterized in that, The thinnest part of the irregularly shaped soft copper strip has a thickness of 0.15~0.25mm; The angle of the convex arc segment is 90°.
5. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 2, characterized in that, The thickness of the tin plating layer is 5~10μm; The solder for the tin plating layer is SnCu, with a Cu content of 2% to 2.5%. The temperature for preparing the tin plating layer is 260~300℃, and the speed is 50~120m / min.
6. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 1, characterized in that, The Bi-2212 superconducting round wire with partial Ag matrix recovery in the online process is obtained by electrolytically recovering a portion of the Ag matrix from the Bi-2212 superconducting round wire with Ag matrix.
7. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 6, characterized in that, The electrolyte for the electrolysis is a mixed aqueous solution of AgNO3, KI and sulfosalicylic acid. The power supply is a DC constant current regulated power supply. The anode is Bi-2212 superconducting round wire, the cathode is a graphite plate, and the current is 340~750A.
8. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 1, characterized in that, The preparation of the Bi-2212 superconducting flat wire specifically includes: pre-bonding the Bi-2212 superconducting round wire and the outer square inner round thin-walled copper groove wire in a liquid solder environment through a round wire bonding mold to obtain a composite blank; and then simultaneously plastically deforming and inlaying the composite blank in a liquid solder environment through an inlay mold to obtain the Bi-2212 superconducting flat wire.
9. The method for preparing Bi-2212 superconducting flat wire by reacting first and then winding according to claim 8, characterized in that, The cross-section of the circular wire mold is rectangular; The dimensions of the inlay mold are determined based on the amount of plastic deformation, which is 10% to 15% of the initial cross-sectional area of the composite blank. The temperature for the inlay welding is 260~300℃, and the speed is 20~120m / min.
10. The Bi-2212 superconducting flat wire prepared by the method of reacting and then winding Bi-2212 superconducting flat wire as described in any one of claims 1 to 9.