A Bi-2212 superconducting flat wire and a preparation method thereof

Abstract

The present invention belongs to the technical field of superconducting wires, and discloses a Bi-2212 superconducting flat wire and a preparation method thereof. The method comprises: S1. selecting a copper slot wire and a Ag / Mg-based Bi-2212 superconducting round wire processing piece; S2. winding the copper slot wire on a steel wheel for annealing to obtain a soft copper slot wire; S3. selecting a U-shaped mold and a rectangular mold; S4. passing the soft copper slot wire through the U-shaped mold and the rectangular mold in sequence, and embedding the Ag / Mg-based Bi-2212 superconducting round wire into the soft copper slot wire before passing through the rectangular mold, performing cold working and combining, and obtaining a nested Bi-2212 flat wire; S5. winding the nested Bi-2212 flat wire on a steel wheel, placing it in a heat treatment furnace, vacuumizing the furnace body for heat treatment, and obtaining a Bi-2212 superconducting flat wire. The Bi-2212 superconducting flat wire has high mechanical strength, good thermal stability, and low preparation cost.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting wires and relates to a Bi-2212 superconducting flat wire and a preparation method thereof. Background Art

[0002] Bi-2212 (Bi2Sr2CaCu2Ox) superconducting wire is an important high-temperature superconducting material with a wide range of applications. It has excellent current-carrying performance, with an upper critical field of up to 100T at 4.2K and an engineering critical current density of more than 1000A / mm at a magnetic field of 30T. 2 , which gives it a significant advantage in high-field magnets. At the same time, given that the Bi-2212 superconducting phase has good toughness and plasticity, it is the only high-temperature superconducting material that can be prepared into isotropic round wires. This feature makes it easier for Bi-2212 wires to be multi-core and twisted, thereby reducing AC losses and being more conducive to the preparation of complex structures such as armored cable conductors (cable-in-conduit conductor, CICC), Rutherford cables and solenoid coils. Currently, it is mainly used in high-field magnets, fusion engineering reactors, energy and other fields. In the future, with the continuous advancement of preparation technology and the promotion of industrial applications, Bi-2212 wires are expected to play an important role in more fields.

[0003] Bi-2212 superconducting wires usually use silver (Ag) as the matrix, which solves the problem that Bi-2212 wires are prone to core breakage during cold processing. The conductor structure reinforced with an intermediate Ag matrix can effectively prevent core breakage, significantly improve the processing uniformity of the wire, and increase the current carrying capacity. However, the disadvantages of the Ag matrix are also obvious: 1) The mechanical strength is low and it is easy to break during processing; 2) The production cost of using only the Ag matrix is ​​high. In the prior art, although the use of Ag / Mg alloy as the matrix or the use of aluminum bronze strip coating can enhance the mechanical strength of Bi-2212 superconducting wires, it usually leads to a decrease in electrical and thermal conductivity.

[0004] Therefore, how to prepare Bi-2212 superconducting wire that can ensure both the mechanical strength of the wire and the electrical and thermal conductivity is an urgent problem to be solved. Summary of the invention

[0005] In order to obtain Bi-2212 superconducting wire with high mechanical strength and excellent electrical and thermal conductivity, the present invention adopts the method of adding a copper layer to the Ag / Mg matrix Bi-2212 superconducting round wire to enhance the mechanical strength of the wire, ensure the excellent thermal and electrical conductivity of the wire, and greatly reduce the production cost. Based on this technical route, the present invention provides a method for preparing Bi-2212 superconducting flat wire, the method comprising:

[0006] S1. Select copper slot wire and Ag / Mg matrix Bi-2212 superconducting round wire processing parts.

[0007] S2. Winding the copper slot wire on a steel wheel for annealing to obtain a soft copper slot wire.

[0008] S3. Select a U-shaped mold and a rectangular mold.

[0009] S4. The soft copper slot wire is passed through a U-shaped die and a rectangular die in sequence, and before passing through the rectangular die, the Ag / Mg matrix Bi-2212 superconducting round wire is embedded in the soft copper slot wire for cold working and bonding to obtain a nested structure Bi-2212 flat wire.

[0010] S5. Winding the nested Bi-2212 flat wire on a steel wheel, placing it in a heat treatment furnace, evacuating the furnace body for heat treatment, and obtaining the Bi-2212 superconducting flat wire.

[0011] Furthermore, in S1 of the above preparation method, the wall thickness of the copper slot wire is greater than 0.25 mm to ensure that the inner layer of the soft copper slot wire will not be deformed due to the heavy load of the wire on the steel wheel.

[0012] Furthermore, in S1 of the above preparation method, the Ag / Mg-based Bi-2212 superconducting round wire is preliminarily subjected to a reaction heat treatment.

[0013] Furthermore, in S2 of the above preparation method, the annealing temperature is 150-200° C., and the annealing time is 1-2 hours.

[0014] Furthermore, before performing S4, the method further includes: ultrasonically cleaning and pickling the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire to ensure that there are no oxidation spots on the contact surface between the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire.

[0015] Furthermore, in S4 of the above preparation method, the processing rate of the soft copper slot wire passing through the U-shaped die is 20-40%; and the processing rate of cold working combined is 10-20%.

[0016] Furthermore, in S5 of the above preparation method, the diameter of the steel wheel is greater than 200 mm.

[0017] Furthermore, in S5 of the above preparation method, the vacuum degree of the evacuation is less than 5×10 -3 Pa; Heat treatment conditions: heat treatment at 700~750℃ for 10~20h.

[0018] The present invention also claims protection for the Bi-2212 superconducting flat wire obtained by the above preparation method.

[0019] Compared with the prior art, the present invention "a Bi-2212 superconducting flat wire and a preparation method thereof" has at least the following beneficial effects:

[0020] The present invention performs a reaction heat treatment on a Bi-2212 superconducting round wire based on an Ag / Mg matrix, and then performs cold working and combination with an annealed copper slot wire to obtain a nested Bi-2212 flat wire, and then performs a heat treatment under a condition (700-750°C) lower than the phase reaction temperature (750-850°C) of Bi-2212, and realizes the combination of the Cu matrix and the Ag / Mg matrix of the copper slot wire through mutual diffusion to obtain the Bi-2212 superconducting flat wire. The present invention has multiple beneficial effects. First, the present invention replaces the Ag matrix with the Ag / Mg matrix, and solves the problem that the mechanical strength of the conventional Bi-2212 superconducting wire using the Ag matrix is ​​low and is prone to breakage during processing.

[0021] Secondly, the preparation method provided by the present invention introduces copper slot wires to replace part of the Ag and Ag / Mg matrix in the Bi-2212 superconducting wire, which greatly reduces the preparation cost of the wire, and also effectively improves the thermal and electrical conductivity and mechanical strength of the Bi-2212 superconducting wire.

[0022] Finally, the Bi-2212 superconducting flat wire provided by the present invention has excellent performance, and the Bi-2212 superconducting wire can still maintain good current carrying performance after reaction heat treatment, and can still maintain a relatively stable LC value after multiple windings.

[0023] The preparation method provided by the invention has simple and controllable process, low operation difficulty and is suitable for batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The flowchart is a method for preparing the Bi-2212 superconducting flat wire.

[0025] Figure 2 2 is a cross-sectional view of the copper slot line.

[0026] Figure 3 This is a cross-sectional view of the Ag / Mg-based Bi-2212 superconducting round wire. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The embodiment of the present invention provides a method for preparing Bi-2212 superconducting flat wire (see the flow chart of the preparation method Figure 1 ), the method comprising:

[0029] S1. Select copper slot wire and Ag / Mg matrix Bi-2212 superconducting round wire processing parts. The cross section of the copper slot wire is as follows Figure 2 As shown; the cross section of the Ag / Mg matrix Bi-2212 superconducting round wire is as shown Figure 3 shown.

[0030] S2. Winding the copper slot wire on a steel wheel for annealing to obtain a soft copper slot wire.

[0031] S3. Select a U-shaped mold and a rectangular mold.

[0032] S4. The soft copper slot wire is passed through a U-shaped die and a rectangular die in sequence, and before passing through the rectangular die, the Ag / Mg matrix Bi-2212 superconducting round wire is embedded in the soft copper slot wire for cold working and bonding to obtain a nested structure Bi-2212 flat wire.

[0033] S5. Winding the nested Bi-2212 flat wire on a steel wheel, placing it in a heat treatment furnace, evacuating the furnace body for heat treatment, and obtaining the Bi-2212 superconducting flat wire.

[0034] Illustratively, in S1 of the above preparation method, the wall thickness of the copper slot wire is greater than 0.25 mm to ensure that the inner layer of the soft copper slot wire will not be deformed due to the heavy load of the wire on the steel wheel.

[0035] Illustratively, in S1 of the above preparation method, the Ag / Mg-based Bi-2212 superconducting round wire is pre-treated by reaction heat treatment.

[0036] Illustratively, in S2 of the above preparation method, the annealing temperature is 150-200° C., and the annealing time is 1-2 h.

[0037] Exemplarily, before performing S4, the step further includes: ultrasonically cleaning and pickling the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire to ensure that there are no oxidation spots on the contact surface between the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire.

[0038] Illustratively, in S4 of the above preparation method, the processing rate of the soft copper slot wire passing through the U-shaped die is 20-40%; and the processing rate of cold working combined is 10-20%.

[0039] Illustratively, in S5 of the above preparation method, the diameter of the steel wheel is greater than 200 mm.

[0040] For example, in S5 of the above preparation method, the vacuum degree of the evacuation is less than 5×10 -3Pa; Heat treatment conditions: heat treatment at 700~750℃ for 10~20h.

[0041] Example 1

[0042] This embodiment provides a method for preparing a Bi-2212 superconducting flat wire.

[0043] S1. Select copper slot wire and Ag / Mg matrix Bi-2212 superconducting round wire processed parts after reaction heat treatment; in this embodiment, the copper slot wire width is 2.6mm, the height is 2.0mm, the slot width is 1.4mm, and the copper slot wire wall thickness is 0.6mm; the diameter of the Ag / Mg matrix Bi-2212 superconducting round wire is 1.5mm.

[0044] S2. The copper slot wire is wound on a steel wheel for annealing at a temperature of 200° C. for 1 h to obtain a soft copper slot wire.

[0045] S3. Select U-shaped mold 1 with a width of 2.45 mm, a height of 1.88 mm, and a groove width of 1.47 mm; U-shaped mold 2 with a width of 2.35 mm, a height of 1.8 mm, and a groove width of 1.55 mm; and a rectangular mold with a width of 2.2 mm and a height of 1.68 mm.

[0046] The soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire are ultrasonically cleaned and pickled to ensure that there are no oxidation spots on the contact surface between the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire. Ultrasonic cleaning conditions: ultrasonic cleaning temperature is 70°C, ultrasonic cleaning length is 40m; pickling conditions: H + The concentration of nitric acid is 1.5 mol / L and the pickling length is 2 m.

[0047] S4. The soft copper slot wire is passed through the U-shaped mold 1, the U-shaped mold 2 and the rectangular mold in sequence, and before passing through the rectangular mold, the Ag / Mg matrix Bi-2212 superconducting round wire is embedded in the soft copper slot wire, and cold working and bonding are performed to obtain a nested structure Bi-2212 flat wire. The processing rate of the soft copper slot wire passing through the U-shaped mold 1 is 29.7%, and the processing rate of passing through the U-shaped mold 2 is 29.5%; the processing rate of cold working and bonding is 16.5%.

[0048] S5. The nested Bi-2212 flat wire is wound on a steel wheel with a diameter of 350 mm, placed in a heat treatment furnace, and the furnace is evacuated for heat treatment, with a vacuum degree of less than 5×10 -3 Pa; Heat treatment conditions: 750℃ heat treatment for 20h to obtain Bi-2212 superconducting flat wire.

[0049] Example 2

[0050] This embodiment provides a method for preparing a Bi-2212 superconducting flat wire.

[0051] S1. Select copper slot wire and Ag / Mg matrix Bi-2212 superconducting round wire processed parts after reaction heat treatment; in this embodiment, the copper slot wire width is 1.6mm, the height is 1.2mm, the slot width is 0.77mm, and the copper slot wire wall thickness is 0.43mm; the diameter of the Ag / Mg matrix Bi-2212 superconducting round wire is 0.80mm.

[0052] S2. The copper slot wire is wound on a steel wheel for annealing at a temperature of 100° C. for 2 hours to obtain a soft copper slot wire.

[0053] S3. Select a U-shaped mold with a width of 1.5 mm, a height of 1.1 mm, and a groove width of 0.82 mm and a rectangular mold with a width of 1.4 mm and a height of 1.03 mm.

[0054] The soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire are ultrasonically cleaned and pickled to ensure that there are no oxidation spots on the contact surface between the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire. Ultrasonic cleaning conditions: ultrasonic cleaning temperature is 70°C, ultrasonic cleaning length is 40m; pickling conditions: H + The concentration of nitric acid is 1.5 mol / L and the pickling length is 2 m.

[0055] S4. The soft copper slot wire is passed through the U-shaped die and the rectangular die in sequence, and before passing through the rectangular die, the Ag / Mg matrix Bi-2212 superconducting round wire is embedded in the soft copper slot wire, and cold working and bonding are performed to obtain the nested structure Bi-2212 flat wire. The processing rate of the soft copper slot wire passing through the U-shaped die is 35.7%; the processing rate of cold working and bonding is 14.4%.

[0056] S5. The nested Bi-2212 flat wire is wound on a steel wheel with a diameter of 200 mm, placed in a heat treatment furnace, and the furnace is evacuated for heat treatment, with a vacuum degree of less than 5×10 -3 Pa; Heat treatment conditions: 700℃ heat treatment for 10h to obtain Bi-2212 superconducting flat wire.

[0057] Example 3

[0058] This embodiment provides a method for preparing a Bi-2212 superconducting flat wire.

[0059] S1. Select copper slot wire and Ag / Mg matrix Bi-2212 superconducting round wire processed parts that have undergone reaction heat treatment; in this embodiment, the copper slot wire width is 2.08mm, the height is 1.52mm, the slot width is 0.90mm, and the copper slot wire wall thickness is 0.59mm; the Ag / Mg matrix Bi-2212 superconducting round wire has a diameter of 1.0mm.

[0060] S2. The copper slot wire is wound on a steel wheel for annealing at a temperature of 180° C. for 1.5 h to obtain a soft copper slot wire.

[0061] S3. Select U-shaped mold 1 with a width of 1.95 mm, a height of 1.41 mm, and a groove width of 0.98 mm; U-shaped mold 2 with a width of 1.85 mm, a height of 1.33 mm, and a groove width of 1.04 mm; and a rectangular mold with a width of 1.75 mm and a height of 1.25 mm.

[0062] The soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire are ultrasonically cleaned and pickled to ensure that there are no oxidation spots on the contact surface between the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire. Ultrasonic cleaning conditions: ultrasonic cleaning temperature is 70°C, ultrasonic cleaning length is 40m; pickling conditions: H + The concentration of nitric acid is 1.5 mol / L and the pickling length is 2 m.

[0063] S4. The soft copper slot wire is passed through the U-shaped mold 1, the U-shaped mold 2 and the rectangular mold in sequence, and before passing through the rectangular mold, the Ag / Mg matrix Bi-2212 superconducting round wire is embedded in the soft copper slot wire, and cold working and bonding are performed to obtain a nested structure Bi-2212 flat wire. The processing rate of the soft copper slot wire passing through the U-shaped mold 1 is 30%, and the processing rate of passing through the U-shaped mold 2 is 28.8%; the processing rate of cold working and bonding is 12.5%.

[0064] S5. The nested Bi-2212 flat wire is wound on a steel wheel with a diameter of 300 mm, placed in a heat treatment furnace, and the furnace is evacuated for heat treatment, with a vacuum degree of less than 5×10 -3 Pa; Heat treatment conditions: 700℃ heat treatment for 10h to obtain Bi-2212 superconducting flat wire.

[0065] Example 4

[0066] This example describes the performance test of the Bi-2212 superconducting flat wire prepared in Examples 1 to 3, including critical current (Ic value) and cross-sectional observation.

[0067] 1.Ic value

[0068] The Ic value test of the Bi-2212 superconducting flat wire prepared in Examples 1 to 3 is as follows:

[0069] 1) Take the Bi-2212 superconducting flat wire obtained in S5 and name it "superconducting wire-1";

[0070] 2) The Bi-2212 superconducting flat wire obtained from S5 was repeatedly wound on a steel wheel twice and then sampled. The diameter of the winding steel wheel was the same as that of S5 and was named "superconducting wire-2";

[0071] 3) Repeat winding the "superconducting wire-2" sample twice and then take a sample. The diameter of the winding steel wheel is the same as S5 and it is named "superconducting wire-3".

[0072] 4) The Ic values ​​(4.2K, 12T) of the “superconducting wire-1”, “superconducting wire-2” and “superconducting wire-3” samples were measured respectively. The results are shown in Table 1.

[0073] Table 1. Ic values ​​of Bi-2212 superconducting flat wires prepared in Examples 1 to 3 (4.2K, 12T)

[0074]

[0075] As can be seen from Table 1, in Examples 1 to 3, the Ic values ​​of the "superconducting wire-1", "superconducting wire-2" and "superconducting wire-3" samples are basically the same, and they can still maintain a relatively stable Ic value after repeated winding, indicating that the Bi-2212 superconducting flat wire has excellent thermal stability.

[0076] 2. Cross-sectional observation

[0077] In addition, the cross sections of the samples of each embodiment were cut to observe whether there was no gap between the soft copper groove wire and the Ag / Mg matrix Bi-2212 superconducting round wire. By observing the cross sections of the Bi-2212 superconducting flat wires prepared in Examples 1 to 3, it was confirmed that there was no gap between the soft copper groove wire and the Ag / Mg matrix Bi-2212 superconducting round wire, and the combination was stable.

[0078] In summary, the present invention achieves the enhancement of the mechanical strength of the wire by adding a copper layer to the outside of the Ag / Mg matrix Bi-2212 superconducting round wire, ensures the excellent thermal and electrical conductivity of the wire, and greatly reduces the production cost of the Bi-2212 superconducting flat wire. The Ag / Mg matrix Bi-2212 superconducting round wire is subjected to reaction heat treatment and then cold-processed and combined with the annealed copper slot wire to obtain a nested structure Bi-2212 flat wire, which is heat-treated at a temperature lower than the phase reaction temperature of Bi-2212 (750~850℃) (700~750℃), and the Cu matrix of the copper slot wire and the Ag / Mg matrix are combined by mutual diffusion to obtain a Bi-2212 superconducting wire with low preparation cost.

[0079] The technical solution provided by the present invention solves the problems of low mechanical strength, easy fracture during processing and high preparation cost of the conventional Bi-2212 superconducting wire using Ag matrix. In addition, the present invention ensures higher thermal stability of the wire, and realizes that the Bi-2212 superconducting wire can still maintain good current carrying performance after reaction heat treatment, and can still maintain a relatively stable lc value after multiple windings. The preparation method of the present invention is simple and controllable, has low operation difficulty, and is suitable for mass production.

[0080] The embodiments described above are only some embodiments of the present invention, not all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but only represents selected embodiments of the present invention. All other embodiments obtained without creative work and related deductions and substitutions made by ordinary technicians in the field under the conditions of the concept of the present invention belong to the scope of protection of the present invention.

Claims

1. A method for preparing Bi-2212 superconducting flat wire, characterized in that: The method comprises: S1. Select copper slot wire and Ag / Mg matrix Bi-2212 superconducting round wire processing parts; S2. The copper slot wire is wound on a steel wheel and annealed to obtain a soft copper slot wire; S3. Select a U-shaped mold and a rectangular mold; S4. The soft copper groove wire is passed through a U-shaped die and a rectangular die in sequence, and the Ag / Mg matrix Bi-2212 superconducting round wire is embedded in the soft copper groove wire before passing through the rectangular die, and cold-worked and combined to obtain a nested structure Bi-2212 flat wire; S5. Winding the nested Bi-2212 flat wire on a steel wheel, placing it in a heat treatment furnace, evacuating the furnace body for heat treatment, and obtaining the Bi-2212 superconducting flat wire.

2. The preparation method according to claim 1, characterized in that: In S1, the copper slot line wall thickness is greater than 0.25 mm.

3. The preparation method according to claim 1, characterized in that: In S1, the Ag / Mg-based Bi-2212 superconducting round wire is preliminarily subjected to a reaction heat treatment.

4. The preparation method according to claim 1, characterized in that: In S2, the annealing temperature is 150~200°C, and the annealing time is 1~2h.

5. The preparation method according to claim 1, characterized in that: Before performing S4, the method further includes: ultrasonically cleaning and pickling the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire to ensure that there are no oxidation spots on the contact surface between the soft copper slot wire and the Ag / Mg-based Bi-2212 superconducting round wire.

6. The preparation method according to claim 1, characterized in that: In S4, the processing rate of the soft copper slot wire passing through the U-shaped die is 20~40%; the processing rate of cold working combined is 10~20%.

7. The preparation method according to claim 1, characterized in that: In S5, the diameter of the steel wheel is greater than 200 mm.

8. The preparation method according to claim 1, characterized in that: In S5, the vacuum degree of the evacuation is less than 5×10 - 3 Pa; Heat treatment conditions: heat treatment at 700~750℃ for 10~20h.

9. Bi-2212 superconducting flat wire prepared by the preparation method of claim 1.

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