A magnesium diboride superconducting wire and a preparation method thereof

Abstract

The present invention discloses a magnesium diboride superconducting wire and a preparation method thereof, belonging to the technical field of superconducting wire processing. The magnesium diboride superconducting wire is prepared by the in-situ powder-in-tube method and the central Mg diffusion method. A Mg rod is loaded into a pre-pressed B tube to obtain a Mg / B composite rod. The Mg / B composite rod is loaded into a Nb / Cu composite tube, and magnesium diboride superconducting powder is loaded into the gap region between the Mg / B composite rod and the Nb / Cu composite tube to prepare the magnesium diboride superconducting wire. During the heat treatment process, the Mg element in the central region diffuses towards the surrounding B element to form MgB2. At the same time, the MgB2 powder at the edge acts as a template to induce and promote the solid-phase reaction between the Mg element and the B element, generating a MgB2 superconducting phase with higher purity, so that the wire obtains higher current-carrying performance. The present invention provides a MgB2 wire with relatively excellent current-carrying performance under low-field application conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting wire processing and relates to a magnesium diboride superconducting wire and a preparation method thereof. Background Art

[0002] Magnesium diboride (MgB2) is a new type of superconducting material with a high critical temperature and strong superconducting properties. Its critical temperature is about 39K, which is much higher than that of traditional Nb3Sn and NbTi superconducting materials. MgB2 is directly synthesized from boron and magnesium. Its ductility is better than that of oxide superconductors, and it is easy to process and shape to prepare wire strips. In addition, MgB2 has a high critical current density and strong magnetic field anti-disturbance ability, which makes it have broad application prospects in the field of superconductivity. MgB2 can be used to manufacture high-temperature superconducting transmission lines with high transmission efficiency and low energy loss, and can also be used to manufacture MRI equipment with high resolution and low energy consumption.

[0003] At present, the preparation methods of MgB2 superconducting wire strip mainly include in-situ powder sleeve method and pre-situ powder sleeve method, which have low preparation cost and simple preparation process. Since there is no weak connection between the grains of MgB2 superconducting material, preparing MgB2 into wire strip does not reduce its critical current density. However, this characteristic also makes the current carrying performance of MgB2 wire strip decay rapidly with the increase of external field. Therefore, it is of great significance to provide a MgB2 wire strip with better current carrying performance under low field application conditions. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a magnesium diboride superconducting wire and a preparation method thereof. The MgB2 superconducting wire is prepared by the pre-powder sleeve method and the central Mg diffusion method, the Mg rod is loaded into the pre-pressed B tube to obtain the Mg / B composite rod, the Mg / B composite rod is loaded into the Nb / Cu composite tube, and the gap area between the Mg / B composite rod and the Nb / Cu composite tube is loaded with MgB2 superconducting powder to prepare the magnesium diboride superconducting wire. During the heat treatment process, the Mg element in the central area diffuses to the surrounding B element and forms MgB2, while the MgB2 powder at the edge acts as a template to induce and promote the solid phase reaction of the Mg element and the B element to generate a higher purity MgB2 superconducting phase, so that the wire obtains a higher current carrying performance. The present invention provides a MgB2 wire with better current carrying performance under low-field application conditions.

[0005] To achieve the technical purpose of the present invention, on the one hand, the present invention provides a method for preparing a MgB2 superconducting wire, which specifically comprises the following steps:

[0006] S1: Use hot isostatic pressing to pre-press B powder into hollow B powder tubes. The pressing temperature is 200℃~500℃, the pressing pressure is 50Mpa~200MPa, the outer diameter range of the tube is 13mm~30mm, the inner diameter range of the tube is 11mm~25mm, and the density of the tube is 0.5g / cm 3 ~2.0g / cm 3 The masses of the Mg rod and the hollow B powder tube were calculated according to the atomic ratio Mg:B=1:2, and the Mg rod was loaded into the pre-pressed hollow B powder tube in proportion to obtain the Mg / B composite rod.

[0007] S2: Insert the Nb rod into the oxygen-free Cu tube and use hot extrusion to process it into a Nb / Cu composite rod. According to the designed ratio, a through hole is further processed in the center area of ​​the Nb / Cu composite rod by a deep hole drilling method. The diameter of the through hole is 15mm~32mm, and finally a Nb / Cu composite tube is obtained. The volume proportions of Nb and Cu in the obtained composite tube are approximately 35% and 35% respectively, and the volume proportion of the through hole is 30%.

[0008] Furthermore, the diameter of the Nb rod is 22 mm to 50 mm, the outer diameter of the oxygen-free Cu tube is 22 mm to 50 mm, and the inner diameter is 27 mm to 62 mm. The extrusion pressure of the hot extrusion is 100 MPa to 200 MPa, and the extrusion speed is 20 m / min to 40 m / min.

[0009] S3: Place the Mg / B composite rod into the center of the Nb / Cu composite tube, and then place MgB2 superconducting powder in the gap between the Mg / B rod and the Nb / Cu tube. The particle size of the MgB2 superconducting powder ranges from 1 μm to 50 μm, and the packing density of the MgB2 superconducting powder is 1.0 g / cm 3 ~3.0g / cm 3 The powder metal composite rod is plastically processed into a single core wire with a specific radial size, and then straightened and cut to obtain a single core rod.

[0010] Furthermore, the processing amount range of the plastic processing is 50%~60%, and the single-core wire with a specific radial size is a single-core wire with a size of H12.0mm~H20.0mm.

[0011] S4: The single core rods in S3 are closely packed and assembled into a monel alloy tube, and further plastic processed into a multi-core composite wire of a fixed size. The multi-core composite wire is subjected to a high-temperature phase heat treatment to obtain a multi-core MgB2 superconducting wire. The high-temperature phase heat treatment is carried out at a temperature of 500℃~900℃ for 5h~15h.

[0012] Furthermore, the processing amount of the plastic processing ranges from 50% to 60%, and the finalized size is a diameter of 1.0 mm to 2.0 mm.

[0013] On the other hand, the present invention claims protection for a MgB2 superconducting wire obtained by the above-mentioned preparation method.

[0014] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0015] (1) In the process of preparing MgB2 wire, the present invention adopts hot isostatic pressing to press B powder into tubes with different densities. On the one hand, it ensures that the mass of B powder is evenly distributed along the axial and radial directions of the wire during the processing. On the other hand, the density of the tube also provides sufficient diffusion power for the subsequent solid-phase reaction of Mg and B.

[0016] (2) The present invention adopts the pre-powder sleeve method and the central Mg diffusion method to prepare MgB2 superconducting wire. High-purity MgB2 superconducting powder is filled around the Mg / B composite rod where the central Mg diffusion occurs. The MgB2 grains act as a template to induce the phase reaction of Mg and B elements and promote the mutual diffusion reaction to be more complete, thereby generating a higher purity MgB2 superconducting phase, thereby enabling the wire to obtain higher current carrying performance. The MgB2 superconducting wire prepared by the present invention has a high current carrying capacity at 4.2K / 3T. J c 4000A / mm 2 ~5000A / mm 2 Compared with the MgB2 wire prepared directly from B powder and Mg powder at 4.2K / 3T J c 3000A / mm 2 , the critical current density is significantly improved and the current carrying performance is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention 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 in the following description are only some embodiments of the present invention.

[0018] Figure 1 MgB2 superconducting wire J c -B curve graph. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention is described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The experimental methods and detection methods described in each embodiment are conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0020] The high purity mentioned in the present invention refers to a purity greater than or equal to 99.9%.

[0021] A method for preparing a MgB2 superconducting wire comprises the following steps:

[0022] S1: High-purity B powder is pre-pressed into hollow B powder tubes with an outer diameter of 13mm~30mm and an inner diameter of 11mm~25mm by hot isostatic pressing. The pressing temperature is 200℃~500℃, the pressing pressure is 50Mpa~200MPa, and the density of the tube is 0.5g / cm 3 ~2.0g / cm 3 The masses of the Mg rod and the hollow B powder tube were calculated according to the atomic ratio Mg:B=1:2, and the high-purity Mg rod was loaded into the pre-pressed hollow B powder tube in proportion to obtain the Mg / B composite rod.

[0023] S2: Insert a high-purity Nb rod with a diameter of 22mm~50mm into a high-purity oxygen-free Cu tube with an inner diameter of 22mm~50mm and an outer diameter of 27mm~62mm, and process it into a Nb / Cu composite rod by hot extrusion. The extrusion pressure of hot extrusion is 100Mpa~200Mpa, and the extrusion speed is 20m / min~40m / min. According to the design ratio, a through hole is further processed in the center area of ​​the Nb / Cu composite rod by deep hole drilling method, and finally a Nb / Cu composite tube is obtained. The volume proportions of Nb and Cu in the obtained composite tube are about 35% and 35% respectively.

[0024] S3: Place the Mg / B composite rod into the center of the Nb / Cu composite tube, and then place high-purity MgB2 superconducting powder in the gap between the Mg / B rod and the Nb / Cu tube. The particle size of the high-purity MgB2 superconducting powder ranges from 1μm to 50μm, and the packing density of the high-purity MgB2 superconducting powder is 1.0g / cm 3 ~3.0g / cm 3 , and obtain a powder metal composite rod. The powder metal composite rod is plastically processed into a single core wire with a specific radial size, and then straightened and cut to obtain a single core rod. The processing amount of plastic processing ranges from 50% to 60%, and the specific radial size is H12.0mm to H20.0mm.

[0025] S4: The single core rods in S3 are closely packed and assembled into a monel alloy tube, and further plastic processed into a multi-core composite wire of a fixed size. The multi-core composite wire is subjected to high-temperature phase heat treatment to obtain a multi-core MgB2 superconducting wire. The high-temperature phase heat treatment is to keep the temperature at 500℃~900℃ for 5h~15h. The processing range of plastic processing is 50%~60%, and the fixed size is 1.0mm~2.0mm in diameter.

[0026] Example 1

[0027] This embodiment provides a method for preparing a MgB2 superconducting wire, which specifically includes the following steps:

[0028] S1: High-purity B powder is pre-pressed into hollow B powder tubes by hot isostatic pressing. The pressing temperature is 500℃ and the pressing pressure is 200MPa. The outer diameter and inner diameter of the tube are 13mm and 11mm respectively. The density of the tube is 2.0g / cm 3 The masses of the Mg rod and the hollow B powder tube were calculated according to the atomic ratio Mg:B=1:2, and the high-purity Mg rod was loaded into the pre-pressed hollow B powder tube in proportion to obtain the Mg / B composite rod.

[0029] S2: Insert the high-purity Nb rod (22mm in diameter) into the high-purity oxygen-free Cu tube (27mm in outer diameter and 22mm in inner diameter), and process it into Nb / Cu composite rod by hot extrusion, with an extrusion pressure of 100Mpa and an extrusion speed of 20m / min. According to the design ratio, a through hole is further processed in the center area of ​​the Nb / Cu composite rod by deep hole drilling, and the diameter of the through hole is 15mm, and finally a Nb / Cu composite tube is obtained, and the volume proportions of Nb and Cu in the obtained composite tube are about 35% and 35% respectively.

[0030] S3: The Mg / B composite rod is loaded into the center of the Nb / Cu composite tube, and then high-purity MgB2 superconducting powder with a particle size of 1 μm is loaded into the gap between the Mg / B rod and the Nb / Cu tube. The packing density is 3.0 g / cm 3 The powder metal composite rod is plastically processed (processing amount is 50%) into a single core wire with a size of H12.0 mm, and then straightened and cut to obtain a single core rod.

[0031] S4: The single core rods in S3 are closely packed and assembled into a monel alloy tube, and further plastic processed (processing amount is 50%) into a multi-core composite wire with a diameter of 2.0 mm. The multi-core composite wire is subjected to high-temperature phase heat treatment to obtain a multi-core MgB2 superconducting wire. The high-temperature phase heat treatment is carried out at a temperature of 500°C for 15 hours.

[0032] The multi-core MgB2 superconducting wire prepared in this embodiment J c -B curve as Figure 1 As shown. Figure 1 It can be seen that the MgB2 wire prepared in this embodiment is J c 5000A / mm 2 .

[0033] Example 2

[0034] This embodiment provides a method for preparing a MgB2 superconducting wire, which specifically includes the following steps:

[0035] S1: High-purity B powder is pre-pressed into hollow B powder tubes by hot isostatic pressing. The pressing temperature is 350℃, the pressing pressure is 125MPa, the outer diameter and inner diameter of the tube are 20mm and 17mm respectively, and the density of the tube is 1.25g / cm 3 The masses of the Mg rod and the hollow B powder tube were calculated according to the atomic ratio Mg:B=1:2, and the high-purity Mg rod was loaded into the pre-pressed hollow B powder tube in proportion to obtain the Mg / B composite rod.

[0036] S2: Insert the high-purity Nb rod (33mm in diameter) into the high-purity oxygen-free Cu tube (41mm in outer diameter and 33mm in inner diameter), and process it into Nb / Cu composite rod by hot extrusion, with an extrusion pressure of 150Mpa and an extrusion speed of 30m / min. According to the design ratio, a through hole is further processed in the center area of ​​the Nb / Cu composite rod by deep hole drilling, and the diameter of the through hole is 22mm, and finally a Nb / Cu composite tube is obtained, and the volume proportions of Nb and Cu in the obtained composite tube are about 35% and 35% respectively.

[0037] S3: Load the Mg / B composite rod into the center of the Nb / Cu composite tube, and then load high-purity MgB2 superconducting powder with a particle size of 25 μm into the gap between the Mg / B rod and the Nb / Cu tube. The packing density is 2.0 g / cm 3 The powder metal composite rod is plastically processed (processing amount is 55%) into a single core wire with a size of H16.0 mm, and then straightened and cut to obtain a single core rod.

[0038] S4: The single core rods in S3 are closely packed and assembled into a monel alloy tube, and further plastic processed into a multi-core composite wire with a diameter of 1.5 mm. The multi-core composite wire is subjected to high-temperature phase heat treatment to obtain a multi-core MgB2 superconducting wire. The high-temperature phase heat treatment is carried out at a temperature of 700°C for 10 hours.

[0039] The multi-core MgB2 superconducting wire prepared in this embodiment J c -B curve as Figure 1 As shown. Figure 1 It can be seen that the MgB2 wire prepared in this embodiment is J c 4500A / mm 2 .

[0040] Example 3

[0041] This embodiment provides a method for preparing a MgB2 superconducting wire, which specifically includes the following steps:

[0042] S1: High-purity B powder is pre-pressed into hollow B powder tubes by hot isostatic pressing. The pressing temperature is 200℃, the pressing pressure is 50MPa, the outer diameter and inner diameter of the tube are 30mm and 25mm respectively, and the density of the tube is 0.5g / cm 3 The masses of the Mg rod and the hollow B powder tube were calculated according to the atomic ratio Mg:B=1:2, and the high-purity Mg rod was loaded into the pre-pressed hollow B powder tube in proportion to obtain the Mg / B composite rod.

[0043] S2: Insert the high-purity Nb rod (50mm in diameter) into the high-purity oxygen-free Cu tube (62mm in outer diameter and 50mm in inner diameter), and process it into Nb / Cu composite rod by hot extrusion, with an extrusion pressure of 200Mpa and an extrusion speed of 40m / min. According to the design ratio, a through hole is further processed in the center area of ​​the Nb / Cu composite rod by deep hole drilling, and the diameter of the through hole is 32mm, and finally a Nb / Cu composite tube is obtained, and the volume proportions of Nb and Cu in the obtained composite tube are about 35% and 35% respectively.

[0044] S3: Load the Mg / B composite rod into the center of the Nb / Cu composite tube, and then load high-purity MgB2 superconducting powder with a particle size of 50 μm into the gap between the Mg / B rod and the Nb / Cu tube. The packing density is 1.0 g / cm 3 The powder metal composite rod is plastically processed (processing amount is 60%) into a single core wire with a size of H20.0 mm, and then straightened and cut to obtain a single core rod.

[0045] S4: The single core rods in S3 are closely packed and assembled into a monel alloy tube, and further plastic processed into a multi-core composite wire with a diameter of 1.0 mm. The multi-core composite wire is subjected to high-temperature phase heat treatment to obtain a multi-core MgB2 superconducting wire. The high-temperature phase heat treatment is carried out at a temperature of 900°C for 5 hours.

[0046] The multi-core MgB2 superconducting wire prepared in this embodiment J c -B curve as Figure 1 As shown. Figure 1 It can be seen that the MgB2 wire prepared in this embodiment is J c 4000A / mm 2 .

[0047] Comparative Example 1

[0048] Compared with Example 1, the present comparative example differs in that: in S1, the Mg / B composite rod is directly prepared using high-purity B powder and high-purity Mg powder as raw materials, in S2, the diameter of the through hole in the central area of ​​the Nb / Cu composite rod is 20 mm, and in S3, high-purity MgB2 superconducting powder is not loaded in the gap area.

[0049] MgB2 superconducting wire J c -B curve as Figure 1 As shown. Figure 1 It can be seen that the MgB2 wire prepared in this comparative example is J c 3000A / mm 2 .

[0050] The embodiments described above are part of the embodiments of the present invention, rather than all of the 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 merely 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 a magnesium diboride superconducting wire, characterized in that: include: The Mg rod is loaded into the B tube to obtain the Mg / B composite rod; The Mg / B composite rod is loaded into a Nb / Cu composite tube, and MgB2 superconducting powder is loaded into the gap between the Mg / B composite rod and the Nb / Cu composite tube, and a single core wire is obtained after a first plastic working; The single core wires are closely packed and assembled into a monel alloy tube, and a multi-core composite wire is obtained after a second plastic working; The multi-core composite wire is subjected to high-temperature phase-forming heat treatment to obtain the magnesium diboride superconducting wire; The B tube is obtained by pre-pressing B powder; The pre-pressing adopts hot isostatic pressing method; The outer diameter of the B tube ranges from 13 mm to 30 mm; The density of the B tube is 0.5 g / cm 3 ~2.0g / cm 3 ; Inserting a Nb rod into an oxygen-free Cu tube, obtaining a Nb / Cu composite rod through hot extrusion, and deep drilling the Nb / Cu composite rod to obtain the Nb / Cu composite tube; The volume proportion of Nb in the Nb / Cu composite tube is 35%, and the volume proportion of Cu in the Nb / Cu composite tube is 35%; The diameter of the through hole in the Nb / Cu composite tube is 15 mm to 32 mm; The packing density of MgB2 superconducting powder is 1.0g / cm 3 ~3.0g / cm 3 .

2. The preparation method according to claim 1, characterized in that: The atomic number ratio of Mg to B in the Mg / B composite rod is 1:

2.

3. The preparation method according to claim 1, characterized in that: The pressing temperature of the hot isostatic pressing method is 200° C. to 500° C., and the pressing pressure of the hot isostatic pressing method is 50 MPa to 200 MPa.

4. The preparation method according to claim 1, characterized in that: The extrusion pressure of the hot extrusion is 100Mpa~200Mpa, and the extrusion speed of the hot extrusion is 20m / min~40m / min.

5. The preparation method according to claim 1, characterized in that: The particle size of the MgB2 superconducting powder ranges from 1 μm to 50 μm.

6. The preparation method according to claim 1, characterized in that: The processing amount of the first plastic processing is 50% to 60%; The processing amount of the second plastic processing is 50%~60%.

7. The preparation method according to claim 1, characterized in that: The high temperature phase forming heat treatment is carried out at a temperature of 500° C. to 900° C. for 5 h to 15 h.

8. A magnesium diboride superconducting wire, characterized in that: Obtained by the preparation method according to any one of claims 1 to 7.

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