A preparation method of MgB2 superconducting wire and MgB2 superconducting wire

Abstract

The present application discloses a method for preparing MgB2 superconducting wire and MgB2 superconducting wire, which relates to the field of superconducting technology. The method includes: drilling a plurality of mounting holes in an oxygen-free copper ingot to obtain a porous copper ingot; loading Mg foil into an Nb tube; inserting an Mg rod inside the Nb tube; filling B powder between the Mg rod and the Mg foil to obtain a single-core rod; inserting the single-core rod into the mounting holes to obtain a multi-core composite ingot; rolling and cold drawing the multi-core composite ingot to obtain a multi-core MgB2 wire; and performing heat treatment on the multi-core MgB2 wire to obtain an MgB2 superconducting wire. In the present application, an Mg foil is coated between the Nb tube and the B powder to form a dual-region Mg diffusion with the central Mg rod, which is beneficial to preparing an MgB2 wire with high Jc. Moreover, by drilling holes in the oxygen-free copper ingot to assemble the multi-core MgB2 wire, the problem of uneven deformation of the wire core filaments caused by the incoordination of cold bonding between the sub-elements during secondary assembly is avoided.

Description

Technical Field

[0001] The present application relates to the field of superconducting technology, and in particular to a method for preparing a MgB2 superconducting wire and a MgB2 superconducting wire. Background Art

[0002] The critical transition temperature of MgB2 (magnesium diboride) superconducting material reaches 39 K. Compared with other high-temperature superconducting materials, MgB2 not only has low raw material cost, but also has low anisotropy and can be prepared into round wires. Therefore, it has great application advantages in the working environment of refrigerators or liquid hydrogen (20 K). Currently, most of the commercial MgB2 superconducting wires are PIT (Powder-InTube) MgB2 wires, because this method has a simple processing process and can achieve the preparation of kilometer-long wires. However, it is limited by the low filling rate of Mg (magnesium) powder and B (boron) powder in the tube method, resulting in many holes in the final superconducting phase, a small effective current-carrying area, and a low critical current Jc of the wire. The core of the IMD (Internal Mg Diffusion) method is to use a central Mg rod to evenly distribute the B powder around it. During heat treatment, the Mg powder melts and diffuses into the B layer, forming a dense MgB2 superconducting layer and a central hole. Therefore, the Jc of the wire produced by this method is significantly higher than that of the PIT method. However, since the Mg rod is in the center, Mg begins to diffuse from the center to the surrounding B layer during the heat treatment process. The MgB2 layer generated first at a position closer to Mg will hinder the diffusion of Mg atoms to the B layer at a farther distance. Therefore, the superconducting phase formed by the IMD method often forms a B-rich area at the position farthest from the center. This impure superconducting phase is one of the main reasons affecting the performance of IMD long wires. In addition, since multi-core MgB2 wires generally require secondary assembly, the cold bonding between the independent subcomponents causes uneven deformation of the wire core, which is also an important factor that cannot be ignored in affecting the stability of wire performance.

[0003] Therefore, how to solve the problems of B-rich MgB2 superconducting phase produced by the central Mg diffusion method and deformation uniformity of multi-core MgB2 long wires, and to prepare multi-core long wires with pure phase and stable performance, is of great significance to the promotion and application of MgB2 superconducting materials. Summary of the invention

[0004] The embodiments of the present application provide a method for preparing a MgB2 superconducting wire and a MgB2 superconducting wire, which are used to solve the problems existing in the prior art of preparing MgB2 superconducting wire by the PIT method and the IMD method.

[0005] On the one hand, the present application embodiment provides a method for preparing a multi-core MgB2 superconducting wire, comprising:

[0006] Drilling a plurality of mounting holes of the same specification on the oxygen-free copper ingot to obtain a porous copper ingot;

[0007] The Mg foil is rolled into a tube and placed into the Nb tube so that the Mg foil is in close contact with the inner wall of the Nb tube;

[0008] Insert a Mg rod inside the Nb tube;

[0009] Fill the gap between the Mg rod and the Mg foil with B powder, and compact the B powder with a die press to obtain a single core rod;

[0010] Inserting a single core rod into a mounting hole of a porous copper ingot to obtain a multi-core composite ingot;

[0011] The multi-core composite ingot is subjected to multiple rolling and cold drawing to obtain a multi-core MgB2 wire;

[0012] The multi-core MgB2 wire is heat treated to obtain a MgB2 superconducting wire.

[0013] On the other hand, an embodiment of the present application further provides a MgB2 superconducting wire, which is prepared by the above method.

[0014] The preparation method of a MgB2 superconducting wire and the MgB2 superconducting wire in the present application have the following advantages:

[0015] 1. A layer of metal Mg foil is coated between the Nb tube and the B powder, and a double-zone Mg diffusion method is used to prepare MgB2 superconducting wire with the central Mg rod. This not only forms a dense superconducting layer during heat treatment, but also avoids the problem of residual B powder due to inadequate diffusion at the far Mg end, which is beneficial to improving the purity of the superconducting phase and preparing MgB2 wire with high Jc.

[0016] 2. Drilling holes directly on the oxygen-free copper ingot to assemble multi-core MgB2 wires avoids the problem of uneven deformation of the wire core wires caused by the lack of coordination in cold bonding between the subcomponents during secondary assembly, which is beneficial to improving the uniformity of deformation of the wire core wires and stabilizing the performance of the MgB2 long wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of a porous copper ingot provided in an embodiment of the present application.

[0019] Figure 2 A schematic diagram of the structure of a single core rod provided in an embodiment of the present application.

[0020] Description of the accompanying drawings: 100, porous copper ingot; 110, oxygen-free copper ingot; 120, mounting hole; 200, single core rod; 210, Mg rod; 220, B powder; 230, Mg foil; 240, Nb tube. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] Figure 1-2 The present invention provides a method for preparing a MgB2 superconducting wire, which includes:

[0023] S100 , drilling a plurality of mounting holes 120 of the same specification on the oxygen-free copper ingot 110 to obtain a porous copper ingot 100 .

[0024] For example, Figure 1 As shown, multiple mounting holes can be evenly drilled along the axial direction on the oxygen-free copper ingot 110, and the mounting holes 120 cover as much area as possible on the cross section of the oxygen-free copper ingot 110. When drilling, it is necessary to ensure that the mounting holes 120 meet certain straightness requirements and the hole walls are smooth.

[0025] Furthermore, the purity of the oxygen-free copper ingot 110 is greater than 99.9%, and the oxygen-free copper ingot 110 is also cylindrical, with a diameter of 45-75 mm and a length of 1000 mm. The diameter of the mounting holes 120 is 15.5 mm, and the number is 6-36.

[0026] S110 , the Mg foil 230 is rolled into a tube shape and placed into the Nb (niobium) tube 240 , so that the Mg foil 230 is in close contact with the inner wall of the Nb tube 240 .

[0027] Exemplarily, the mounting hole 120 is cylindrical, so when the Mg foil 230 is rolled, it is rolled into a cylindrical tube structure.

[0028] Furthermore, the purity of the Nb tube 240 is greater than 99.9%, the outer diameter is 15 mm, and the wall thickness is 1.5 mm to 2.0 mm. The purity of the Mg foil 230 is 99.99%, the thickness is 0.1 mm to 0.5 mm, and the diameter of the roll formed by the Mg foil 230 is smaller than the inner diameter of the Nb tube 240 by 0.3 mm to 0.5 mm.

[0029] S120 , inserting the Mg rod 210 into the Nb tube 240 .

[0030] For example, before the Mg foil 230 is loaded into the Nb tube 240, one end of the Nb tube 240 is sealed with a plug, the center of the plug has a groove with the same diameter as the diameter of the Mg rod 210, and after the Mg rod 210 is inserted into the Nb tube 240, the lower end of the Mg rod 210 is inserted into the groove. By providing the groove, after the Mg rod 210 is loaded into the Nb tube 240, the center of the lower end of the Mg rod 210 coincides with the center of the Nb tube 240, thereby preventing the Mg rod 210 from being eccentric inside the Nb tube 240.

[0031] Furthermore, the diameter of the Mg rod 210 is 6 mm to 8 mm, and the length is 1000 mm.

[0032] S130 , filling the gap between the Mg rod 210 and the Mg foil 230 with B powder 220 , and compacting the B powder 220 with a molding machine to obtain a single core rod 200 .

[0033] Exemplarily, before filling the gap between the Mg rod 210 and the Mg foil 230 with the B powder 220, the B powder 220 is weighed according to a preset mass ratio of Mg to B. The mass ratio is specifically Mg:B=1.05:2. The B powder 220 used is a spherical amorphous B powder with an average particle size of less than 200 nm and a purity of more than 99.9%.

[0034] Further, B powder 220 is weighed in a protective atmosphere, and the B powder 220 is filled in the gap between the Mg rod 210 and the Mg foil 230 in the protective atmosphere. Specifically, the protective atmosphere may be argon gas.

[0035] After the B powder 220 is compacted by the molding machine, a plug is also used to seal the other end of the Nb tube 240. This step is also performed in a protective atmosphere to prevent air from entering the Nb tube 240. The plugs at both ends of the Nb tube 240 are made of Cu (copper) or Al (aluminum), and the purity is greater than 99.9%.

[0036] S140, inserting the single core rod 200 into the mounting hole 120 of the porous copper ingot 100 to obtain a multi-core composite ingot, and performing multiple rolling and cold drawing on the multi-core composite ingot to obtain a multi-core MgB2 wire.

[0037] Exemplarily, the processing amount of the rolling process is 15-25%, and the cold drawing process is performed after the diameter of the multi-core MgB2 wire is less than 6.00 mm, and the processing amount of each pass of the cold drawing process is 8-15%.

[0038] S150, heat treating the multi-core MgB2 wire to obtain a MgB2 superconducting wire.

[0039] Exemplarily, when the multi-core MgB2 wire is heat treated, the temperature is 600°C to 700°C, and the holding time is 1h to 4h.

[0040] After heat treatment, the Mg foil 230 can provide B diffusion of Mg atoms from the outside to the inside, forming a bidirectional diffusion with the Mg atoms provided by the central Mg rod 210, so as to compensate for the B-rich problem caused by the long diffusion distance of the simple central Mg diffusion method.

[0041] The embodiment of the present application also provides a MgB2 superconducting wire, which is prepared by the above method.

[0042] Example 1

[0043] Step 1: Drill 6 cylindrical mounting holes 120 of the same specification with a diameter of 15.5 mm and a depth of 1000 mm on an oxygen-free copper ingot 110 with a diameter of 50 mm, a length of 1000 mm and a purity of 99.9%. The mounting holes 120 are arranged in a circular array to ensure that the straightness of the mounting holes 120 is ≤1 mm / 1000 mm and the inner wall is smooth.

[0044] Step 2: Close one end of a 99.9% pure Nb tube 240 with a Cu plug having a groove in the center, and then roll a piece of 0.2 mm thick 99.99% pure Mg foil 230 into a cylindrical tube with a diameter of 15 mm and a length of 1000 mm and insert it into the Nb tube 240 so that it is close to the inner wall of the Nb tube 240.

[0045] Step 3: Insert a Mg rod 210 with a purity of 99.99%, a diameter of 8 mm and a length of 1000 mm into the center of the Nb tube 240 so that one end of the Mg rod 210 is fixed in the groove of the plug to ensure that the position of the Mg rod 210 in the Nb tube 240 is in the center of the Nb tube 240.

[0046] Step 4: In a circulating argon atmosphere with a purity of 99.99%, weigh amorphous B powder 220 with a purity of 99.9% according to a mass ratio of Mg:B=1.05:2, fill it into the gap between the Mg foil 230 and the Mg rod 210 and compact it with a molding machine, and after the powder filling is completed, seal the end of the Nb tube 240 with a Cu plug to obtain a single core rod 200.

[0047] Step five, insert the six single-core rods 200 obtained in step four into the mounting holes 120 on the porous copper ingot 100 processed in step one to obtain a six-core MgB2 composite ingot, which is cold rolled 15 times with a processing amount of 25% to a diameter of 6.00 mm. When the outer diameter of the wire is less than 6.00 mm, it is cold drawn with a processing amount of 10% to a diameter of 1.00 mm, thereby obtaining a six-core MgB2 wire.

[0048] Step 6: Place the 6-core MgB2 wire with a diameter of 1.00 mm obtained in step 5 into a vacuum heat treatment furnace for heat treatment. -3 When the temperature is below 4.2K, the temperature is raised to 600℃ at a rate of 10℃ / min, kept at 600℃ for 1h, and then cooled to room temperature with the furnace to complete the heat treatment to obtain a 6-core MgB2 superconducting wire. The current carrying performance of the 6-core MgB2 superconducting wire is tested, and its Jc at 4.2K and 3T is 1.6×10 4 A / mm 2 .

[0049] Example 2

[0050] Step 1: Drill 7 cylindrical mounting holes 120 of the same specification with a diameter of 15.5 mm and a depth of 1000 mm on an oxygen-free copper ingot 110 with a diameter of 50 mm, a length of 1000 mm and a purity of 99.9%. The mounting hole 120 includes a center hole and edge holes arranged in a circular array around the center hole, ensuring that the straightness of the mounting hole 120 is ≤1 mm / 1000 mm and the inner wall is smooth.

[0051] Step 2: Close one end of a 99.9% pure Nb tube 240 with a Cu plug having a groove in the center, and then roll a piece of 0.2 mm thick 99.99% pure Mg foil 230 into a cylindrical tube with a diameter of 15 mm and a length of 1000 mm and insert it into the Nb tube 240 so that it is close to the inner wall of the Nb tube 240.

[0052] Step 3: Insert a Mg rod 210 with a purity of 99.99%, a diameter of 8 mm and a length of 1000 mm into the center of the Nb tube 240 so that one end of the Mg rod 210 is fixed in the groove of the plug to ensure that the position of the Mg rod 210 in the Nb tube 240 is in the center of the Nb tube 240.

[0053] Step 4: In a circulating argon atmosphere with a purity of 99.99%, weigh amorphous B powder 220 with a purity of 99.9% according to a mass ratio of Mg:B=1.05:2, fill it into the gap between the Mg foil 230 and the Mg rod 210 and compact it with a molding machine, and after the powder filling is completed, seal the end of the Nb tube 240 with a Cu plug to obtain a single core rod 200.

[0054] Step five, insert the seven single-core rods 200 obtained in step four into the mounting holes 120 on the porous copper ingot 100 processed in step one to obtain a seven-core MgB2 composite ingot, which is cold-rolled through 18 passes with a processing amount of 20% to a diameter of 6.00 mm. When the outer diameter of the wire is less than 6.00 mm, it is cold-drawn with a processing amount of 10% to a diameter of 1.00 mm, thereby obtaining a seven-core MgB2 wire.

[0055] Step 6: Place the 7-core MgB2 wire with a diameter of 1.00 mm obtained in step 5 into a vacuum heat treatment furnace for heat treatment. -3 When the temperature is below 4.2K, the temperature is raised to 650℃ at a rate of 10℃ / min, kept at 650℃ for 2.5h, and then cooled to room temperature with the furnace to complete the heat treatment to obtain a 7-core MgB2 superconducting wire. The current carrying performance of the 7-core MgB2 superconducting wire is tested, and its Jc at 4.2K and 3T is 1.5×10 4 A / mm 2 .

[0056] Example 3

[0057] Step 1: Drill 18 cylindrical mounting holes 120 of the same specification with a diameter of 15.5 mm and a depth of 1000 mm on an oxygen-free copper ingot 110 with a diameter of 75 mm, a length of 1000 mm and a purity of 99.9%. The mounting holes 120 are arranged in a circular array to ensure that the straightness of the mounting holes 120 is ≤1 mm / 1000 mm and the inner wall is smooth.

[0058] Step 2: Close one end of a 99.9% pure Nb tube 240 with a Cu plug having a groove in the center, and then roll a piece of 0.3 mm thick 99.99% pure Mg foil 230 into a cylindrical tube with a diameter of 15 mm and a length of 1000 mm and insert it into the Nb tube 240 so that it is close to the inner wall of the Nb tube 240.

[0059] Step 3: Insert a Mg rod 210 with a purity of 99.99%, a diameter of 8 mm and a length of 1000 mm into the center of the Nb tube 240 so that one end of the Mg rod 210 is fixed in the groove of the plug to ensure that the position of the Mg rod 210 in the Nb tube 240 is in the center of the Nb tube 240.

[0060] Step 4: In a circulating argon atmosphere with a purity of 99.99%, weigh amorphous B powder 220 with a purity of 99.9% according to a mass ratio of Mg:B=1.05:2, fill it into the gap between the Mg foil 230 and the Mg rod 210 and compact it with a molding machine, and after the powder filling is completed, seal the end of the Nb tube 240 with a Cu plug to obtain a single core rod 200.

[0061] Step five, insert 18 single core rods 200 obtained in step four into the mounting holes 120 on the porous copper ingot 100 processed in step one to obtain an 18-core MgB2 composite ingot, which is cold rolled 15 times with a processing amount of 25% to a diameter of 6.00 mm. When the outer diameter of the wire is less than 6.00 mm, it is cold drawn with a processing amount of 10% to a diameter of 1.00 mm, thereby obtaining an 18-core MgB2 wire.

[0062] Step 6: Place the 18-core MgB2 wire with a diameter of 1.00 mm obtained in step 5 into a vacuum heat treatment furnace for heat treatment. -3 When the temperature is below 400℃, the temperature is raised to 700℃ at a rate of 10℃ / min, kept at 700℃ for 4h, and then cooled to room temperature with the furnace to complete the heat treatment to obtain 18-core MgB2 superconducting wire. The current carrying performance of the 18-core MgB2 superconducting wire is tested, and its Jc at 4.2K and 3T is 1.48×10 4 A / mm 2 .

[0063] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0064] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for preparing a MgB2 superconducting wire, characterized in that: include: Drilling a plurality of mounting holes (120) of the same specification on an oxygen-free copper ingot (110) to obtain a porous copper ingot (100); The Mg foil (230) is rolled into a tube shape and loaded into the Nb tube (240), so that the Mg foil (230) is closely attached to the inner wall of the Nb tube (240); Inserting a Mg rod (210) with a purity of 99.99% into the Nb tube (240); Filling the gap between the Mg rod (210) and the Mg foil (230) with B powder (220), and compacting the B powder (220) with a molding machine to obtain a single core rod (200); Inserting the single core rod (200) into the mounting hole (120) of the porous copper ingot (100) to obtain a multi-core composite ingot; The multi-core composite ingot is subjected to multiple rolling and cold drawing to obtain a multi-core MgB2 wire; The multi-core MgB2 wire is heat treated to obtain a MgB2 superconducting wire.

2. The method for preparing a MgB2 superconducting wire according to claim 1, characterized in that: Before the Mg foil (230) is loaded into the Nb tube (240), one end of the Nb tube (240) is closed with a plug, the center of the plug has a groove with the same diameter as the diameter of the Mg rod (210), and after the Mg rod (210) is inserted into the Nb tube (240), the lower end of the Mg rod (210) is inserted into the groove.

3. The method for preparing a MgB2 superconducting wire according to claim 2, characterized in that: After the B powder (220) is compacted by a molding machine, the other end of the Nb tube (240) is also sealed by the plug.

4. The method for preparing a MgB2 superconducting wire according to claim 1, characterized in that: Before the B powder (220) is filled into the gap between the Mg rod (210) and the Mg foil (230), the B powder (220) is weighed according to a preset mass ratio of Mg to B.

5. The method for preparing a MgB2 superconducting wire according to claim 4, characterized in that: The B powder (220) is weighed in a protective atmosphere, and the B powder (220) is filled in a gap between the Mg rod (210) and the Mg foil (230) in the protective atmosphere.

6. The method for preparing a MgB2 superconducting wire according to claim 4, characterized in that: The mass ratio is Mg:B=1.05:

2.

7. The method for preparing a MgB2 superconducting wire according to claim 1, characterized in that: When the multi-core MgB2 wire is heat treated, the temperature is 600°C to 700°C and the insulation time is 1h to 4h.

8. A MgB2 superconducting wire, characterized in that: The MgB2 superconducting wire is prepared by the method described in any one of claims 1-7.

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