A high critical current density MgB2 superconducting wire and a method for manufacturing the same

Abstract

The application belongs to the technical field of superconducting materials, and discloses a high-critical current density MgB2 superconducting wire and a preparation method thereof. The preparation method comprises the following steps: respectively performing gas desorption treatment on Mg powder and B powder in a flowing H2 atmosphere before mixing; mixing the treated Mg powder and B powder to obtain a precursor powder; loading the precursor powder into a Nb / Cu composite tube, and obtaining a composite single core rod by electron beam welding after the tube loading is completed; performing cold drawing on the composite single core rod to obtain a single core wire; assembling the single core wire into a Monel alloy tube in a bundle, and obtaining a multi-core composite wire after cold working; and performing heat treatment on the multi-core composite wire to obtain the MgB2 superconducting wire. By removing the gas adsorption of the Mg powder and the B powder, the powder gap is reduced, the ion mobility in the phase formation process and the compactness of the wire core powder are improved, and the superconducting current carrying performance of the MgB2 superconducting wire is further improved.

Description

Technical Field

[0001] This invention belongs to the field of superconducting materials technology and discloses a high critical current density MgB2 superconducting wire and its preparation method. Background Technology

[0002] MgB2 superconducting materials, with a superconducting transition temperature of 39 K, and characterized by low resistivity, low anisotropy, long coherence length, and absence of weak grain boundary connections under normal conditions, have attracted widespread attention. MgB2 wires have been applied in superconducting energy storage, superconducting cables, and superconducting magnetic resonance imaging (MRI) devices. Currently, commercially available MgB2 wires / tapes are prepared using powder-in-tube technology, specifically ex-suit PIT, in-suit PIT, and continuous powder-in-tube forming (CTFF).

[0003] Powder in tube (PIN) technology is currently the most widely used method for preparing MgB2 wires / ribbons. When using in-situ techniques, the precursor powders, Mg and B, affect the final superconducting properties of the MgB2. Because the powders used in the preparation of MgB2 wires / ribbons are all at the micrometer scale, the powder particles have a large specific surface area and readily adsorb gases. These adsorbed gases remain in the powder interstices during powder processing, reducing powder density and hindering continuous plastic deformation. The thermal expansion of the adsorbed gases under high-temperature conditions inhibits ion diffusion and migration, affecting the crystal structure of the powder after phase formation, and consequently influencing the properties of the MgB2 superconducting wires. Summary of the Invention

[0004] To overcome the problems of existing technologies, this invention provides a high critical current density MgB2 superconducting wire and its preparation method. Research has found that by desorbing the gas adsorbed on the powder surface through a redox reaction in a flowing H2 atmosphere using Mg and B powder in their initial state, and by performing continuous vacuum thermal degassing during the tube loading process, the critical current density can be further increased. By improving the continuity of powder plastic deformation and powder density during processing, the diffusion and migration between Mg and B ions during heat treatment phase formation are further driven, strengthening the intergranular connectivity of MgB2 and increasing the critical current density of the MgB2 superconducting wire.

[0005] On one hand, the present invention relates to a method for preparing a high critical current density MgB2 superconducting wire, which includes: performing gas desorption treatment on Mg powder and B powder before mixing, mixing the Mg powder and B powder after gas desorption treatment and loading them into an Nb / Cu composite tube to obtain the MgB2 superconducting wire.

[0006] Furthermore, in the preparation method of high critical current density MgB2 superconducting wire provided by the present invention, the gas desorption treatment includes: placing Mg powder and B powder in H2 atmosphere, heating to 100℃~200℃, and holding at that temperature for 1h~5h.

[0007] Furthermore, in the preparation method of high critical current density MgB2 superconducting wire provided by the present invention, the H2 atmosphere is in a flowing state and the purity of H2 is ≥99.99%.

[0008] Furthermore, in the preparation method of high critical current density MgB2 superconducting wire provided by the present invention, the flow rate of H2 in the H2 atmosphere is 50 ml / min to 250 ml / min.

[0009] Furthermore, in the preparation method of high critical current density MgB2 superconducting wire provided by the present invention, the precursor powder is loaded into an Nb / Cu composite tube under mechanical pressure, and electron beam welding is performed after the tube loading is completed.

[0010] Furthermore, in the preparation method of the high critical current density MgB2 superconducting wire provided by the present invention, the Nb / Cu composite tube is obtained by mechanical composite with Cu as the outer layer and Nb as the inner layer.

[0011] Furthermore, in the preparation method of high critical current density MgB2 superconducting wire provided by the present invention, when packing the tube, the vacuum degree is maintained at 0.001 Pa to 0.1 Pa and the temperature is maintained at 200 °C to 400 °C.

[0012] Furthermore, in the preparation method of high critical current density MgB2 superconducting wire provided by the present invention, the mechanical pressure is a mechanical pressure of 100MPa to 300MPa applied to the powder in the tube along the length of the composite tube.

[0013] Furthermore, in the method for preparing high critical current density MgB2 superconducting wire provided by the present invention, the sub-bundles are cold-drawn after welding to form single-core wires.

[0014] The single-core wires are bundled together and assembled into a Monel alloy tube, and then cold-worked to obtain a multi-core composite wire.

[0015] The multi-core composite wire is heat-treated to obtain the MgB2 superconducting wire.

[0016] On the other hand, the present invention relates to a MgB2 superconducting wire, which is prepared by the above-mentioned method for preparing high critical current density MgB2 superconducting wire.

[0017] On the other hand, the present invention relates to a MgB2 superconducting wire, wherein the critical current density (Jc) of the MgB2 superconducting wire under test conditions of 4.2K and 3T is 3800A / mm². 2 ~3950A / mm 2 .

[0018] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects or advantages:

[0019] (1) First, the initial state of Mg powder and B powder is placed in H2 atmosphere. The O2, N2 and other gases adsorbed on the powder surface are desorbed during the redox reaction with H2. This prevents the O2, N2 and other gases adsorbed on the surface from reacting with Mg powder to form MgO phase during subsequent heat treatment, thus purifying the MgB2 grain boundaries and improving the strong coupling between grains.

[0020] (2) In this invention, uniformly mixed Mg and B powders are loaded into an Nb / Cu composite tube under vacuum heating. Gases adsorbed on the powder and metal tube surfaces are desorbed again under vacuum and high temperature conditions. This process reduces the gap ratio between powders caused by adsorbed gases, improves the continuity of plastic deformation during processing, reduces the degree of breakage of the Nb barrier layer caused by adsorbed gases, and increases the density of the wire core powder. More importantly, because there are no adsorbed gases, the powder does not expand during the phase-forming heat treatment, thus further enhancing the diffusion migration rate between Mg and B ions, thereby promoting the MgB2 phase-forming rate and the purity of the MgB2 phase. Furthermore, the continuous mechanical pressure applied to the powder during the powder loading process increases the powder loading density, strengthens the intergranular connectivity of MgB2, and increases the critical current density of the MgB2 superconducting wire. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The image shows the microstructure of the MgB2 core wire of the multi-core MgB2 superconducting wire of this invention without gas desorption treatment.

[0023] Figure 2 This invention describes the microstructure of the MgB2 core wire of the multi-core MgB2 superconducting wire after gas desorption.

[0024] Figure 3This is the Jc-B curve of the multi-core MgB2 superconducting wire of this invention at 4.2K. In the figure, Jc represents the critical current density and B represents the magnetic flux density. The upper curve shows the critical current density of the multi-core MgB2 superconducting wire at 4.2K under different magnetic flux densities after gas desorption treatment; the lower curve shows the critical current density of the multi-core MgB2 superconducting wire at 4.2K under different magnetic flux densities before gas desorption treatment. Detailed Implementation

[0025] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0027] This invention provides a method for preparing high critical current density MgB2 superconducting wire, which is implemented according to the following steps:

[0028] Example 1

[0029] This embodiment provides a method for preparing a high critical current density MgB2 superconducting wire.

[0030] First, the initial Mg powder and B powder were placed in an H2 atmosphere with a purity of 99.99% and a flow rate of 50 mL / min, and then heated to 100℃ and held for 1 hour. In an argon atmosphere with a purity of 99.99%, the pre-reacted Mg powder and amorphous B powder were calculated, weighed, and uniformly mixed at an atomic ratio of Mg:B = 1:2 to obtain the mixed precursor powder.

[0031] After cleaning, Nb and Cu tubes are mechanically combined to obtain an Nb / Cu composite tube. Precursor powder is then loaded into the Nb / Cu composite tube under gravity at a vacuum of 0.001 Pa and a temperature of 200°C, while a mechanical pressure of 100 MPa is applied to the powder along the length of the metal tube. After loading, the top of the Nb / Cu composite tube is electron-beam welded to obtain a composite single-core rod. The composite single-core rod is then cold-worked to a fixed-size composite single-core wire using a 20% machining allowance. The cleaned composite single-core wires are bundled and assembled into a Monel alloy tube to obtain a composite multi-core rod. After cold working, the composite multi-core rod is finally formed into a multi-core composite wire with a diameter of 1.0 mm.

[0032] In a flowing argon atmosphere, the multi-core composite wire was held at 500℃ for 3 hours to obtain a multi-core MgB2 superconducting wire. The resulting wire achieved a critical current density of 3800 A / mm² at 4.2 K and 3 T. 2 .

[0033] Example 2

[0034] This embodiment provides a method for preparing a high critical current density MgB2 superconducting wire.

[0035] First, the initial Mg powder and B powder were placed in an H2 atmosphere with a purity of 99.99% and a flow rate of 150 mL / min, and then heated to 150℃ and held for 3 hours. In an argon atmosphere with a purity of 99.99%, the pre-reacted Mg powder and amorphous B powder were calculated, weighed, and uniformly mixed at an atomic ratio of Mg:B = 1:2 to obtain the mixed precursor powder.

[0036] After cleaning, Nb and Cu tubes are mechanically combined to obtain an Nb / Cu composite tube. Precursor powder is then loaded into the Nb / Cu composite tube under gravity at a vacuum of 0.01 Pa and a temperature of 300°C, while a mechanical pressure of 200 MPa is applied to the powder along the length of the metal tube. After loading, the top of the Nb / Cu composite tube is electron-beam welded to obtain a composite single-core rod. The composite single-core rod is then cold-worked to a fixed-size composite single-core wire using a 30% machining allowance. The cleaned composite single-core wires are then bundled and assembled into a Monel alloy tube to obtain a composite multi-core rod. This composite multi-core rod is then cold-worked to finally form a multi-core composite wire with a diameter of 1.5 mm.

[0037] In a flowing argon atmosphere, the multi-core composite wire was held at 650℃ for 5 hours to obtain a multi-core MgB2 superconducting wire. The resulting wire achieved a critical current density of 3900 A / mm² at 4.2 K and 3 T. 2 .

[0038] Example 3

[0039] This embodiment provides a method for preparing a high critical current density MgB2 superconducting wire.

[0040] First, the initial Mg powder and B powder were placed in an H2 atmosphere with a purity of 99.99% and a flow rate of 250 mL / min, and then heated to 200℃ and held for 5 hours. In an argon atmosphere with a purity of 99.99%, the pre-reacted Mg powder and amorphous B powder were calculated, weighed, and uniformly mixed at an atomic ratio of Mg:B = 1:2 to obtain the mixed precursor powder.

[0041] After cleaning, Nb and Cu tubes are mechanically combined to obtain an Nb / Cu composite tube. Precursor powder is then loaded into the Nb / Cu composite tube under gravity at a vacuum of 0.01 Pa and a temperature of 400℃, while a mechanical pressure of 300 MPa is applied to the powder along the length of the metal tube. After loading, the top of the Nb / Cu composite tube is electron-beam welded to obtain a composite single-core rod. The composite single-core rod is then cold-worked to a fixed-size composite single-core wire using a 40% machining allowance. The cleaned composite single-core wires are then bundled and assembled into a Monel alloy tube to obtain a composite multi-core rod. This composite multi-core rod is then cold-worked to finally form a multi-core composite wire with a diameter of 2.0 mm.

[0042] In a flowing argon atmosphere, the multi-core composite wire was held at 900℃ for 10 hours to obtain a multi-core MgB2 superconducting wire. The resulting wire achieved a critical current density of 3950 A / mm² at 4.2 K and 3 T. 2 .

[0043] Comparative Example 1

[0044] This comparative example provides a method for preparing high critical current density MgB2 superconducting wires.

[0045] The difference between this comparative example and Example 3 is that the temperature of the H2 atmosphere was 300°C during the degassing treatment of the initial Mg and B powders, resulting in a multi-core MgB2 superconducting wire with a critical current density of 3300 A / mm at 4.2 K and 3 T. 2 Compared to Example 3, the critical current density decreased by 16.5% at temperatures exceeding 200°C.

[0046] Comparative Example 2

[0047] This comparative example provides a method for preparing high critical current density MgB2 superconducting wires.

[0048] The difference between this comparative example and Example 1 is that the temperature of the H2 atmosphere was 50°C during the degassing treatment of the initial Mg and B powders, resulting in a multi-core MgB2 superconducting wire with a critical current density of 3100 A / mm at 4.2 K and 3 T. 2 Compared to Example 1, the critical current density decreased by 18.4% at temperatures below 100°C.

[0049] Comparative Example 3

[0050] This comparative example provides a method for preparing high critical current density MgB2 superconducting wires.

[0051] The difference between this comparative example and Example 3 is that the initial Mg powder and B powder were first mixed in an argon atmosphere with a purity of 99.99%, followed by degassing. This resulted in a multi-core MgB2 superconducting wire with a critical current density of 3200 A / mm² at 4.2 K and 3 T. 2 Compared with Example 3, in which the initial Mg powder and B powder were subjected to gas desorption before mixing, the critical current density of the MgB2 superconducting wire prepared in this comparative example was reduced by 19.0%.

[0052] Comparative Example 4

[0053] This comparative example provides a method for preparing high critical current density MgB2 superconducting wires.

[0054] The difference between this comparative example and Example 3 is that the Mg powder and B powder that have not undergone degassing were mixed in an environment with argon purity of 99.99%, ultimately resulting in a multi-core MgB2 superconducting wire with a critical current density of 2950 A / mm² at 4.2 K and 3 T. 2 Compared to the results in Example 3, where the initial Mg powder and B powder were subjected to gas desorption treatment before mixing, the critical current density decreased by 25.3%.

[0055] By comparing the microstructure of the MgB2 core wire obtained in the final MgB2 superconducting wire, such as... Figure 1 , Figure 2 As shown, compared to wires prepared without gas desorption treatment, the porosity of the MgB2 core wires prepared by gas adsorption treatment is significantly reduced, and the density is significantly increased; the critical current density of the MgB2 superconducting wires prepared by gas desorption treatment is significantly improved, such as... Figure 3 As shown.

[0056] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for preparing a high critical current density MgB2 superconducting wire, comprising mixing Mg powder and B powder and loading the mixture into an Nb / Cu composite tube to obtain the MgB2 superconducting wire, characterized in that, include: Mg powder and B powder are subjected to gas desorption treatment separately before being mixed; The gas desorption treatment includes: placing Mg powder and B powder separately in an H2 atmosphere, heating to 100℃~200℃, and holding at that temperature for 1h~5h; the H2 atmosphere is in a flowing state, and the purity of H2 is ≥99.99%; the flow rate of H2 in the H2 atmosphere is 50mL / min~250mL / min. Mg powder and B powder are mixed to obtain precursor powder, which is then loaded into an Nb / Cu composite tube under mechanical pressure. After loading, the tube is welded by electron beam. The outer layer of the Nb / Cu composite tube is Cu, and the inner layer is Nb. During loading, the vacuum degree is maintained at 0.001 Pa to 0.1 Pa, and the temperature is maintained at 200℃ to 400℃. The mechanical pressure is 100 MPa to 300 MPa applied to the powder in the tube along the length of the composite tube.

2. The method for preparing high critical current density MgB2 superconducting wire according to claim 1, characterized in that, After electron beam welding, the wire is cold-drawn to form a single-core wire. The single-core wires are bundled together and assembled into a Monel alloy tube, and then cold-worked to obtain a multi-core composite wire. The multi-core composite wire is heat-treated to obtain the MgB2 superconducting wire.

3. A MgB2 superconducting wire, characterized in that, It is prepared by the method for preparing high critical current density MgB2 superconducting wire according to any one of claims 1 to 2.

4. The MgB2 superconducting wire according to claim 3, characterized in that, The critical current density of the MgB2 superconducting wire under test conditions of 4.2K and 3T is 3800A / mm². 2 ~3950A / mm 2 .

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