Method for enhancing grain connectivity of PbMo6S8-based superconducting wire

Abstract

The invention discloses a method for enhancing grain connectivity of a PbMo6S8-based superconducting wire. The method comprises the following steps: 1, uniformly mixing Pb powder, Mo powder and S powder, and carrying out heat treatment to obtain mixed powder of Pb, Mo and MoS2; secondly, part of the mixed powder is ground and then sintered, and PbMo6S8 powder is obtained; thirdly, PbMo6S8 powder and the remaining mixed powder are evenly mixed and pressed into a powder rod; 4, loading the powder rod into an alloy tube and drawing the powder rod into a wire rod; and 5, heat treatment. On the basis that the high-performance PbMo6S8 superconducting powder is obtained, the mixed powder of Pb, Mo and MoS2 is added for tubing, Pb, Mo and MoS2 can react during heat treatment to form PbMo6S8 in situ, original PbMo6S8 superconducting powder grains are connected, the grain connectivity is enhanced, the core wire density is improved, the current-carrying performance of the PbMo6S8-based superconducting wire is improved, and the method is suitable for the field of high-field superconducting magnets.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material preparation technology, specifically relating to a method for enhancing the grain connectivity of 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 fabrication of high-field magnets mainly utilizes low-temperature superconducting materials NbTi and Nb3Sn. However, their intrinsic upper critical field ( H c2 The magnetic field strengths (T) are relatively low, at 18T and 25T respectively, making it difficult to prepare high-field magnets with magnetic field strengths exceeding 30T. Currently, high-temperature superconducting materials are mainly used in the form of intercalated coils to improve the magnetic field strength of magnets. Therefore, developing new 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 that molybdenum-sulfur compounds possess superconductivity. Among these, PbMo6S8 superconductors exhibit the highest superconducting transition temperature of 15 K. Simultaneously, its upper critical field is close to 60 T at 4.2 K, which is highly advantageous for its application in low-temperature, high-field environments. Furthermore, this superconducting material also possesses low anisotropy and low fabrication cost, which is beneficial for the winding and industrial production of superconducting magnets. Therefore, PbMo6S8-based superconductors hold promise as a next-generation practical superconducting material for strong magnetic fields.

[0004] In the pre-powder-packed tube method for preparing PbMo6S8 superconducting wires, high-quality PbMo6S8 precursor powder is first prepared, then packed into tubes and drawn into wires. While this method can increase the superconducting phase content and reduce the second phase in the wire core, the resulting wire exhibits poor grain connectivity. In the in-situ powder-packed tube method, the raw material powder is first packed into a metal tube to form a wire, and then heat-treated to form the phase. Although the PbMo6S8 phase can be formed in situ during heat treatment with good grain connectivity, a large amount of second phases, such as MoS2, is easily formed during the reaction. These second phases distributed at grain boundaries not only hinder superconducting current transport but also deviate from the stoichiometric ratio of the PbMo6S8 system, leading to a decrease in superconductivity. Therefore, the key to improving the current-carrying capacity of PbMo6S8 superconducting wires is to reduce the second phase and enhance grain connectivity while ensuring high superconductivity in the wire core. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for enhancing the grain connectivity of PbMo6S8-based superconducting wires. This method involves mixing high-performance PbMo6S8 superconducting powder with a mixture of Pb, Mo, and MoS2 powders to form a precursor powder, which is then packaged into a wire. During heat treatment, Pb, Mo, and MoS2 react in situ to form PbMo6S8, effectively connecting the original PbMo6S8 superconducting powder grains, enhancing grain connectivity, and thus improving the current-carrying capacity of the PbMo6S8-based superconducting wire, solving the problem of weak grain connectivity in the PbMo6S8 phase.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for enhancing the grain connectivity of PbMo6S8-based superconducting wires, characterized in that the method includes the following steps: Step 1: In an argon-protected glove box, Pb, Mo and S powders are mixed evenly according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8 to obtain mixed powder. Then, the mixed powder is vacuum sealed into a quartz tube for heat treatment to obtain mixed powder of Pb, Mo and MoS2. Step 2: After thoroughly grinding the mixed powder of Pb, Mo and MoS2 from Step 1 in a glove box, it is vacuum sealed into a quartz tube for sintering to obtain PbMo6S8 powder. Step 3: Mix the PbMo6S8 powder obtained in Step 2 with the remaining Pb, Mo and MoS2 mixed powder from Step 1 evenly, and press it into a powder rod. Step 4: Load the powder rod from Step 3 into the alloy tube and draw it into a wire; Step 5: Vacuum seal the wire obtained in Step 4 into a quartz tube for heat treatment to obtain PbMo6S8-based superconducting wire.

[0007] The method described above for enhancing the grain connectivity of PbMo6S8-based superconducting wires is characterized in that the mass of the remaining Pb, Mo, and MoS2 mixed powder in step three is 10% to 60% of the mass of the mixed Pb, Mo, and MoS2 powder obtained in step one. By controlling the mass ratio of the remaining Pb, Mo, and MoS2 mixed powder, the grain connectivity effect is ensured, while avoiding the excessive formation of a large amount of second phase, which is beneficial to improving the current-carrying capacity of PbMo6S8-based superconducting wires.

[0008] The above-mentioned method for enhancing the grain connectivity of PbMo6S8-based superconducting wires is characterized in that, in step four, powder rods are loaded into alloy tubes using a powder-pressed rod loading method.

[0009] The above-mentioned method for enhancing the grain connectivity of PbMo6S8-based superconducting wires is characterized in that the heat treatment temperature in step five is 800℃~1200℃, and the holding time is 10h~70h.

[0010] Compared with the prior art, the present invention has the following advantages: 1. This invention effectively combines the advantages of the pre-situ and in-situ powder-tube wire fabrication processes. First, high-purity, high-performance PbMo6S8 superconducting powder is prepared using solid-state sintering. Then, a certain proportion of mixed powders of Pb, Mo, and MoS2 are added to form precursor powder. This precursor powder is then packaged and drawn into tubes to prepare the wire. During heat treatment, the Pb, Mo, and MoS2 particles located between the PbMo6S8 superconducting powder grains further react, forming the PbMo6S8 phase in situ. This effectively connects the original PbMo6S8 superconducting powder grains, enhancing grain connectivity and increasing the core wire density in the PbMo6S8-based superconducting wire, thereby improving the current-carrying capacity of the PbMo6S8-based superconducting wire.

[0011] 2. The method of the present invention effectively enhances the connectivity between PbMo6S8 superconducting powder grains while ensuring the high performance of PbMo6S8 superconducting powder. Moreover, the preparation process is simple, the required equipment is readily available, the preparation difficulty is reduced, and it is easy to implement.

[0012] 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

[0013] Figure 1 The image shows the core morphology of the PbMo6S8-based superconducting wire prepared in Example 1 of this invention.

[0014] Figure 2 This is a cross-sectional view of the PbMo6S8-based superconducting wire prepared in Comparative Example 1 of this invention.

[0015] Figure 3 The image shows the core morphology of the PbMo6S8-based superconducting wire prepared in Comparative Example 1 of this invention.

[0016] Figure 4 The image shows the core morphology of the PbMo6S8-based superconducting wire prepared in Example 2 of this invention. Detailed Implementation

[0017] Example 1 This embodiment includes the following steps: Step 1: In an argon-protected glove box, according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8 of 1:6:8, select Pb, Mo and S powders with a mass purity of 99.99% or higher and pour them into a grinder for mixing and grinding for more than 30 minutes to obtain mixed powder. Then, vacuum seal the mixed powder into a quartz tube and sinter it at 700℃ for 10 hours to obtain mixed powder of Pb, Mo and MoS2. Step 2: Take 80% of the mixed powder of Pb, Mo and MoS2 from Step 1 by mass, grind it thoroughly in a glove box, and then vacuum seal it in a quartz tube and sinter it at 950°C for 48 hours to obtain PbMo6S8 powder. Step 3: Mix the PbMo6S8 powder obtained in Step 2 with the remaining 20% ​​of the mixed powder of Pb, Mo and MoS2 in Step 1 until homogeneous, and press it into a powder rod. Step 4: Using the powder rod packing method, the powder rod from Step 3 is packed into a composite sheath tube of Nb and Cu (Cu tube is wrapped around Nb tube), and then drawn into wire. Step 5: Vacuum seal the wire obtained in Step 4 into a quartz tube and heat treat it by sintering at 950℃ for 48 hours to obtain PbMo6S8-based superconducting wire.

[0018] Figure 1 The image shows the core morphology of the PbMo6S8-based superconducting wire prepared in this embodiment. Figure 1 It can be seen that the core filaments in this PbMo6S8-based superconducting wire are relatively dense. Tests show that the superconducting phase content in this PbMo6S8-based superconducting wire exceeds 99%, indicating that the Pb, Mo, and MoS2 located between the PbMo6S8 superconducting powder grains have reacted to form the PbMo6S8 phase during the heat treatment process, effectively connecting the original PbMo6S8 superconducting powder grains, enhancing grain connectivity, and thus improving the core filament density in the PbMo6S8-based superconducting wire.

[0019] Comparative Example 1 The difference between this comparative example and Example 1 is that in step three, the PbMo6S8 powder was not mixed evenly with the remaining Pb, Mo and MoS2 mixed powder from step one, but the PbMo6S8 powder was directly pressed into powder rods.

[0020] Figure 2 and Figure 3 The images show the cross-sectional view and core morphology of the PbMo6S8-based superconducting wire prepared in this comparative example. Figure 2 and Figure 3 It can be seen that, due to the use of only powder rods pressed from PbMo6S8 powder, the core wires of the prepared PbMo6S8-based superconducting wires have a large number of pores and a low density.

[0021] Will Figure 1 and Figure 3 The comparison shows that, compared with Comparative Example 1, the PbMo6S8-based superconducting wire prepared in Example 1 has a significantly increased core wire density and enhanced grain connectivity, indicating that the method of the present invention effectively improves the core wire density and enhances the grain connectivity of PbMo6S8-based superconducting wire.

[0022] Example 2 This embodiment includes the following steps: Step 1: In an argon-protected glove box, according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8 of 1:6:8, select Pb, Mo and S powders with a mass purity of 99.99% or higher and pour them into a grinder for mixing and grinding for more than 30 minutes to obtain mixed powder. Then, vacuum seal the mixed powder into a quartz tube and sinter it at 700℃ for 10 hours to obtain mixed powder of Pb, Mo and MoS2. Step 2: Take 40% of the mixed powder of Pb, Mo and MoS2 from Step 1 by mass, grind it thoroughly in a glove box, and then vacuum seal it in a quartz tube and sinter it at 950°C for 48 hours to obtain PbMo6S8 powder. Step 3: Mix the PbMo6S8 powder obtained in Step 2 with the remaining 60% of the mixed powder of Pb, Mo and MoS2 in Step 1 until homogeneous, and press it into a powder rod. Step 4: Using the powder rod packing method, the powder rod from Step 3 is packed into a composite sheath tube of Nb and Cu (Cu tube is wrapped around Nb tube), and then drawn into wire. Step 5: Vacuum seal the wire obtained in Step 4 into a quartz tube and heat treat it by sintering at 800℃ for 70 hours to obtain PbMo6S8-based superconducting wire.

[0023] Figure 4 The image shows the core morphology of the PbMo6S8-based superconducting wire prepared in this embodiment. Figure 4 It can be seen that the core wire of this PbMo6S8-based superconducting wire is dense, the porosity is greatly reduced, and the grain connectivity is significantly enhanced.

[0024] Example 3 This embodiment includes the following steps: Step 1: In an argon-protected glove box, according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8 of 1:6:8, select Pb, Mo and S powders with a mass purity of 99.99% or higher and pour them into a grinder for mixing and grinding for more than 30 minutes to obtain mixed powder. Then, vacuum seal the mixed powder into a quartz tube and sinter it at 700℃ for 10 hours to obtain mixed powder of Pb, Mo and MoS2. Step 2: Take 90% of the mixed powder of Pb, Mo and MoS2 from Step 1 by mass, grind it thoroughly in a glove box, and then vacuum seal it in a quartz tube and sinter it at 950°C for 48 hours to obtain PbMo6S8 powder. Step 3: Mix the PbMo6S8 powder obtained in Step 2 with the remaining 10% of the mixed powder of Pb, Mo and MoS2 in Step 1 until homogeneous, and press it into a powder rod. Step 4: Using the powder rod packing method, the powder rod from Step 3 is packed into a composite sheath tube of Nb and Cu (Cu tube is wrapped around Nb tube), and then drawn into wire. Step 5: Vacuum seal the wire obtained in Step 4 into a quartz tube and heat treat it by sintering at 1200℃ for 10 hours to obtain PbMo6S8-based superconducting wire.

[0025] Testing revealed that the PbMo6S8-based superconducting wire prepared in this embodiment exhibited high core wire density and good grain connectivity; compared to Comparative Example 1, its critical current density under a self-field at 4.2K ( J c From 10 4 A / cm 2 Increased to 10 5 A / cm 2 above.

[0026] 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 enhancing the grain connectivity of PbMo6S8-based superconducting wires, characterized in that, The method includes the following steps: Step 1: In an argon-protected glove box, Pb, Mo and S powders are mixed evenly according to the atomic ratio of Pb:Mo:S in the target product PbMo6S8 to obtain mixed powder. Then, the mixed powder is vacuum sealed into a quartz tube for heat treatment to obtain mixed powder of Pb, Mo and MoS2. Step 2: After thoroughly grinding the mixed powder of Pb, Mo and MoS2 from Step 1 in a glove box, it is vacuum sealed into a quartz tube for sintering to obtain PbMo6S8 powder. Step 3: Mix the PbMo6S8 powder obtained in Step 2 with the remaining Pb, Mo and MoS2 mixed powder from Step 1 evenly, and press it into a powder rod. Step 4: Load the powder rod from Step 3 into the alloy tube and draw it into a wire; Step 5: Vacuum seal the wire obtained in Step 4 into a quartz tube for heat treatment to obtain PbMo6S8-based superconducting wire.

2. The method for enhancing grain connectivity of PbMo6S8-based superconducting wires according to claim 1, characterized in that, The mass of the remaining Pb, Mo and MoS2 mixed powder in step three is 10% to 60% of the mass of the Pb, Mo and MoS2 mixed powder obtained in step one.

3. The method for enhancing the grain connectivity of PbMo6S8-based superconducting wires according to claim 1, characterized in that, In step four, the powder rods are loaded into the alloy tubes using a powder pressing and tube loading method.

4. The method for enhancing the grain connectivity of PbMo6S8-based superconducting wires according to claim 1, characterized in that, The heat treatment temperature in step five is 800℃~1200℃, and the holding time is 10h~70h.

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