A method for preparing PbMo6S8-based superconducting wire

Abstract

The application discloses a preparation method of PbMo6S8-based superconducting wire, and the method comprises the following steps: firstly, in an argon-protected glove box, Mo and S element-containing raw materials and a central Pb rod are selected, and the Mo and S element-containing raw materials are mixed and ground to obtain a precursor powder; secondly, the precursor powder is loaded into a metal composite sheath containing the central Pb rod, and then the PbMo6S8-based green wire is prepared; and thirdly, the PbMo6S8-based superconducting wire is obtained through heat treatment. The PbMo6S8-based superconducting wire is prepared by adopting the central Pb rod combined with the powder tube filling method, the central Pb element diffuses in the process of wire heat treatment, a dense superconducting layer is formed in the wire, the loose condition of the wire core wire is effectively improved, the core wire density is improved, the grain boundary connectivity is significantly enhanced, the carrying capacity of the PbMo6S8 superconducting wire is effectively improved, the process is simple, the required equipment is easy to obtain, the preparation difficulty is reduced, and the method is easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material preparation technology, specifically relating to a method for preparing PbMo6S8-based superconducting wires. Background Technology

[0002] With the rapid development of superconducting magnet technology, the steady-state magnetic field strength is increasing daily, which places new demands on the performance of superconducting materials used in magnets. Currently, the main superconducting materials for high-field magnets are the mature and stable low-temperature superconducting materials NbTi and Nb3Sn. However, the intrinsic upper critical field (H) of these two types of low-temperature superconducting materials... c2 The capacities of 18T and 25T respectively prevent their practical application in high-field magnets exceeding 30T, which are currently receiving widespread attention. While high-temperature superconducting materials can be used in the form of intercalated coils to increase the magnetic field strength of magnets, the fabrication technology for these materials is still immature, and the production cost remains high. Therefore, developing novel superconducting materials for high-field magnets is of paramount importance for the further development of superconducting magnet technology and for advancing the practical application of superconducting materials.

[0003] In the 1970s, Chevrel et al. first discovered the A species represented by the PbMo6S8 system. x Mo 6-x Superconductivity was discovered in S6 compounds, marking the first discovery of ternary superconducting compounds, leading to the designation of this molybdenum-based chalcogenide compound as the Chevrel phase. In these materials, Mo and S atoms form lattice units in the form of Mo6S8, while A-site elements such as Pb reside in the interstices of the Mo6S8 units, playing a crucial role in the superconductivity of the entire system. Systematic measurements revealed that the superconducting transition temperature (T0) of PbMo6S8-based superconducting materials... c The value is around 15K, and it has a high upper critical field (H). c2 The PbMo6S8-based superconducting material exhibits excellent properties such as (0), 60T, and very small anisotropy, which ensures its application in superconducting magnets. Therefore, PbMo6S8-based superconducting materials are expected to become the next generation of practical superconducting materials for strong magnetic fields.

[0004] Currently, the current-carrying capacity of PbMo6S8-based superconducting materials remains low due to weak grain boundary connectivity. Analysis of current fabrication techniques reveals that PbMo6S8-based superconducting wires prepared under traditional sintering conditions exhibit low core wire density and poor inter-grain connectivity, which are key factors contributing to the system's low current-carrying performance. Therefore, developing a novel fabrication technique for PbMo6S8-based superconducting wires to increase core wire density and enhance grain boundary connectivity can effectively improve the wire's current-carrying capacity. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing PbMo6S8-based superconducting wires, addressing the shortcomings of the prior art. This method uses a lead rod as the center of a metal composite cladding and fills it with precursor powder to prepare a PbMo6S8-based superconducting wire containing a central lead rod. During heat treatment, a dense superconducting layer is formed in the wire through diffusion of the central lead element. This effectively avoids the formation of pores and microcracks in the core wire of the PbMo6S8-based superconducting wire, increases the core wire density, enhances grain boundary connectivity, and effectively improves the current-carrying capacity of the PbMo6S8 superconducting wire. This solves the problem of low core wire density and poor inter-grain connectivity in existing PbMo6S8-based superconducting wires, which leads to low current-carrying capacity.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing PbMo6S8-based superconducting wires, characterized in that the method includes the following steps:

[0007] Step 1: In an argon-protected glove box, select raw materials containing Mo and S elements and a central Pb rod according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8-based superconducting wire, and mix and grind the raw materials containing Mo and S elements to obtain precursor powder.

[0008] Step 2: The precursor powder obtained in Step 1 is loaded into a metal composite sheath containing the central Pb rod selected in Step 1, and then processed to prepare PbMo6S8-based raw wire.

[0009] Step 3: Heat-treat the PbMo6S8-based raw wire processed in Step 2 to obtain PbMo6S8-based superconducting wire.

[0010] The preparation method of the PbMo6S8-based superconducting wire described above is characterized in that the precursor powder in step one is a mixture of elemental Mo and S powder or a mixture of Mo and MoS2 powder.

[0011] The above-mentioned method for preparing a PbMo6S8-based superconducting wire is characterized in that the metal composite sheath in step two is arranged in a barrier layer / outer sheath structure, including Mo / Cu, Nb / Cu, or Ta / Cu tubes.

[0012] The method for preparing a PbMo6S8-based superconducting wire described above is characterized in that, in step two, during the loading of the precursor powder, a central lead rod is used as the center of the target product, the PbMo6S8-based superconducting wire.

[0013] The method for preparing a PbMo6S8-based superconducting wire described above is characterized in that the heat treatment temperature in step three is 700℃~1000℃ and the heat treatment time is 10h~100h.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. This invention replaces the Pb powder or Pb compound in the traditional powder-packed tube method with a central lead rod, allowing the lead element in the central lead rod to diffuse outward during heat treatment, forming a dense superconducting layer with the precursor powder in the wire. Furthermore, the pores formed are concentrated in the center of the wire, effectively preventing the formation of pores and microcracks in the superconducting layer of the wire core. This increases the core wire density, enhances grain boundary connectivity, and effectively improves the current-carrying capacity of the PbMo6S8 superconducting wire. It solves the problem of low core wire density and poor grain connectivity caused by the in-situ formation of pores due to the diffusion of Pb element in the precursor powder during the heat treatment phase formation process of the traditional powder-packed tube method.

[0016] 2. The central lead rod used in this invention has good plasticity and ductility, which effectively improves the processing performance of PbMo6S8 wire.

[0017] 3. The preparation process of the present invention is simple, the required equipment is readily available, the preparation difficulty is reduced, and it is easy to implement and apply.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1a This is a schematic diagram of the tube loading process of the present invention.

[0020] Figure 1b This is a schematic diagram of the tube assembly structure of the present invention.

[0021] Figure 2a This is a cross-sectional view of the PbMo6S8-based raw wire prepared in Example 1 of the present invention.

[0022] Figure 2b This is a cross-sectional view of the PbMo6S8-based superconducting wire prepared in Example 1 of the present invention.

[0023] Figure 3 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in Example 1 of the present invention.

[0024] Figure 4 This is a cross-sectional view of the PbMo6S8-based superconducting wire prepared in Comparative Example 1 of this invention.

[0025] Figure 5 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in Comparative Example 1 of this invention.

[0026] Figure 6 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in Example 2 of the present invention.

[0027] Figure 7 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in Example 3 of the present invention. Detailed Implementation

[0028] Example 1

[0029] This embodiment includes the following steps:

[0030] Step 1: In an argon-protected glove box, select MoS2 and Mo powder raw materials with a purity of 99.99% or higher and a particle size greater than 200 mesh, and a central Pb rod with a purity of 99.99%, according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8-based superconducting wire of 1:6:8. Pour the MoS2 and Mo powder raw materials into a grinder and mix and grind for more than 30 minutes to obtain the precursor powder.

[0031] Step Two, as follows Figure 1a As shown, the central Pb rod selected in step one is placed at the center of the Nb tube. The precursor powder obtained in step one is then loaded into the barrier layer of the Nb tube containing the central Pb rod. Finally, the powder-loaded Nb tube is inserted into the outer sheath of the Cu tube, as shown. Figure 1b As shown, PbMo6S8-based raw wires were prepared by drawing.

[0032] Step 3: Sinter the PbMo6S8-based raw wire processed in Step 2 at 950°C for 72 hours in an argon atmosphere to obtain PbMo6S8-based superconducting wire.

[0033] Figure 2a This is a cross-sectional view of the PbMo6S8-based green wire prepared in this embodiment. Figure 2a It can be seen that the structure of the PbMo6S8-based wire is clear, consisting of a Cu cladding, an Nb barrier layer, powder, and a central lead rod from the outside in. Figure 2b This is a cross-sectional view of the PbMo6S8-based superconducting wire prepared in this embodiment. Figure 2b It can be seen that a dense superconducting layer is formed in the wire after heat treatment.

[0034] Figure 3 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in this embodiment. Figure 3 It can be seen that the PbMo6S8-based superconducting wire core prepared in this embodiment has a high density.

[0035] Combination Figures 2a-2b and Figure 3 It can be seen that the central lead diffusion method of this invention can prepare well-structured PbMo6S8-based superconducting wires.

[0036] Comparative Example 1

[0037] The difference between this comparative example and Example 1 is that a central lead rod was not used in step two; instead, the mixed powders of Pb, Mo, and MoS2 were directly packed into the tube.

[0038] Figure 4 This is a cross-sectional view of the PbMo6S8-based superconducting wire prepared in this comparative example. Figure 4 It can be seen that the structure of this PbMo6S8-based wire, from the outside in, consists of a Cu cladding, an Nb barrier layer, and a superconducting core wire. The core wire is very loosely packed. This can be seen from its local SEM. Figure 5 Numerous pores can be clearly observed in the wire core.

[0039] Example 2

[0040] This embodiment includes the following steps:

[0041] Step 1: In an argon-protected glove box, select Mo and S elemental powder raw materials with a purity of 99.99% or higher and a particle size greater than 200 mesh, and a central Pb rod with a purity of 99.99%, according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8-based superconducting wire of 1:6:8. Pour the Mo and S elemental powder raw materials into a grinder and mix and grind for more than 30 minutes to obtain the precursor powder.

[0042] Step Two, as follows Figure 1a As shown, the central Pb rod selected in step one is placed at the center of the Mo tube. The precursor powder obtained in step one is then loaded into the barrier layer of the Mo tube containing the central Pb rod. Finally, the powder-loaded Nb tube is inserted into the outer sheath of the Cu tube, as shown. Figure 1b As shown, PbMo6S8-based raw wires were prepared by drawing.

[0043] Step 3: Sinter the PbMo6S8-based raw wire processed in Step 2 at 700°C for 100 hours in an argon atmosphere to obtain PbMo6S8-based superconducting wire.

[0044] Figure 6 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in this embodiment. Figure 6 It can be seen that, compared to Comparative Example 1 Figure 5 In this embodiment, the PbMo6S8-based superconducting wire prepared by changing the powder in the tube and using the central lead diffusion method still shows a significant increase in core wire density.

[0045] Example 3

[0046] This embodiment includes the following steps:

[0047] Step 1: In an argon-protected glove box, select MoS2 and Mo powder raw materials with a purity of 99.99% or higher and a particle size greater than 200 mesh, and a central Pb rod with a purity of 99.99%, according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8-based superconducting wire of 1:6:8. Pour the MoS2 and Mo powder raw materials into a grinder and mix and grind for more than 30 minutes to obtain the precursor powder.

[0048] Step Two, as follows Figure 1a As shown, the central Pb rod selected in step one is placed at the center of the Ta tube. The precursor powder obtained in step one is then loaded into the barrier layer of the Ta tube containing the central Pb rod. Finally, the powder-loaded Nb tube is inserted into the outer sheath of the Cu tube, as follows. Figure 1b As shown, PbMo6S8-based raw wires were prepared by drawing.

[0049] Step 3: Sinter the PbMo6S8-based raw wire processed in Step 2 at 1000℃ for 10 hours in an argon atmosphere to obtain PbMo6S8-based superconducting wire.

[0050] Figure 7 This is a partial SEM image of the PbMo6S8-based superconducting wire core prepared in this embodiment. Figure 7 It can be seen that, compared to Comparative Example 1 Figure 5 In this embodiment, the number of pores in the PbMo6S8-based superconducting wire core is significantly reduced, and the core density is significantly increased. This indicates that the present invention effectively increases the core density of PbMo6S8-based superconducting wire and improves grain connectivity by in-situ forming a high-density PbMo6S8 phase through diffusion of the central Pb element.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing PbMo6S8-based superconducting wire, characterized in that, The method includes the following steps: Step 1: In an argon-protected glove box, select raw materials containing Mo and S elements and a central Pb rod according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8-based superconducting wire, and mix and grind the raw materials containing Mo and S elements to obtain precursor powder. Step 2: The precursor powder obtained in Step 1 is loaded into a metal composite sheath containing the central Pb rod selected in Step 1, and then processed to prepare PbMo6S8-based raw wire. During the process of loading the precursor powder, the central lead rod is used as the center of the target product PbMo6S8-based superconducting wire. Step 3: Heat-treat the PbMo6S8-based raw wire processed in Step 2 to obtain PbMo6S8-based superconducting wire.

2. The method for preparing a PbMo6S8-based superconducting wire according to claim 1, characterized in that, The precursor powder mentioned in step one is a mixture of elemental Mo and S powder or a mixture of Mo and MoS2 powder.

3. The method for preparing a PbMo6S8-based superconducting wire according to claim 1, characterized in that, The metal composite sheath described in step two is arranged in a barrier layer / outer sheath structure, including Mo tube / Cu tube, Nb tube / Cu tube, or Ta tube / Cu tube.

4. The method for preparing a PbMo6S8-based superconducting wire according to claim 1, characterized in that, The heat treatment temperature in step three is 700℃~1000℃, and the heat treatment time is 10h~100h.

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