A method for preparing PbMo6S8-based superconducting wire

Abstract

The application discloses a preparation method of a PbMo6S8-based superconducting wire, and comprises the following steps: firstly, uniformly mixing CuS, Mo and MoS2 powders, uniformly mixing the powders with molten salt KCl, and performing heat treatment to obtain mixed powders; secondly, sequentially performing water washing, acid washing and drying on the mixed powders to obtain Mo6S8 powders; thirdly, performing heat treatment on the Mo6S8 powders to remove oxygen; fourthly, loading the Mo6S8 powders into a metal tube containing a central lead rod to draw the Mo6S8 powders into a wire; and fifthly, vacuum sealing the wire into a quartz tube and performing heat sintering. The application adopts a molten salt method to prepare high-purity CuMo6S8 powders with nanometer size as precursor powders, and combines a central lead rod diffusion method, so that the central Pb element diffuses to form a PbMo6S8 phase, avoids the generation of holes and a second phase, effectively increases the number of crystal boundaries and the grain connectivity, forms an effective pinning center, improves the current carrying capacity of the PbMo6S8 superconducting wire, and is suitable for the preparation field of superconducting magnets and the like under low temperature and high magnetic field.

Description

Technical Field

[0001] This invention belongs to the field of superconducting materials 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 fabrication of high-field magnets mainly utilizes low-temperature superconducting materials NbTi and Nb3Sn, but 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 superconducting materials exhibit the highest superconducting transition temperature of 15K. Simultaneously, its upper critical field is close to 60T at 4.2K, 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 superconducting materials hold promise as next-generation practical superconducting materials for strong magnetic fields.

[0004] However, during the phase formation process of PbMo6S8 superconducting wire core powder, the second phase MoS2 easily appears and exists at grain boundaries, which can easily cause weak grain boundary connections and affect the transmission of superconducting current. Furthermore, during the reaction process, after the raw materials react completely, pores are easily formed in the core wire, reducing the connectivity between grains. In addition, the flux pinning of PbMo6S8 superconducting material is planar pinning; therefore, reducing the PbMo6S8 grain size and increasing the number of grain boundaries to form effective flux pinning centers is an effective means to improve the current carrying capacity of PbMo6S8 superconducting wires. 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 molten salt method to prepare high-purity, nano-sized CuMo6S8 powder as a precursor powder, combined with a central lead rod diffusion method. This allows the central Pb element to diffuse directly into the interstitial positions of Mo6S8, forming the PbMo6S8 phase. This not only lowers the phase formation temperature but also effectively reduces porosity and second-phase formation, effectively increases the number of grain boundaries and grain connectivity, forms effective pinning centers, and improves the current-carrying capacity of PbMo6S8 superconducting wires, thus solving the problem of poor current-carrying capacity in existing PbMo6S8 superconducting wires.

[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: Step 1: In an argon-protected glove box, mix CuS, Mo, and MoS2 powders evenly according to the atomic ratio of Cu:Mo:S in CuMo6S8 to obtain a mixed powder. Then, mix the mixed powder with molten salt KCl at a mass ratio of 1:2 and heat-treat it in an argon atmosphere to obtain a mixed powder containing KCl and CuMo6S8. Step 2: The mixed powder obtained in Step 1 is washed with water, acid-washed and dried in sequence to remove the molten salt KCl and Cu atoms from the mixed powder, so as to obtain Mo6S8 powder with nano-sized particles with a mass purity of more than 99%. Step 3: Heat-treat the Mo6S8 powder obtained in Step 2 to remove the adsorbed oxygen. Step 4: The Mo6S8 powder, after oxygen removal in Step 3, is loaded into a metal tube containing a central lead rod, and then drawn into PbMo6S8 wire. Step 5: Vacuum seal the PbMo6S8 wire obtained in Step 4 into a quartz tube and heat and sinter it to obtain PbMo6S8-based superconducting wire.

[0007] This invention first employs a molten salt method, mixing raw material powder with molten salt KCl and then heat-treating it to obtain a mixed powder containing KCl and CuMo6S8. The powder is then washed with water and acid to remove KCl and Cu atoms, yielding high-quality, nano-sized Mo6S8 powder. Using the Mo6S8 powder as a precursor, after deoxygenation, it is loaded into a metal tube containing a central lead rod and drawn to prepare PbMo6S8 wire. Utilizing the diffusion of Pb during heat treatment, Pb elements directly insert into the interstitial positions of the Mo6S8 units to form the PbMo6S8 phase, effectively avoiding the porosity caused by raw material consumption during the reaction and the second phase resulting from incomplete reaction. Finally, the PbMo6S8-based superconducting wire is obtained through heating and sintering. The method of this invention not only effectively reduces the phase formation temperature, obtains nano-sized PbMo6S8 grains, increases the number of grain boundaries, forms effective flux pinning centers, and improves its flux pinning ability, but also concentrates the pores at the center of the wire and forms a dense superconducting layer around the center of the wire, effectively reducing pores and microcracks, enhancing grain connectivity, and thus improving the current carrying capacity of PbMo6S8 superconducting wires.

[0008] The method for preparing a PbMo6S8-based superconducting wire, as described above, is characterized in that, in step three, the Mo6S8 powder is subjected to heat treatment under an argon-hydrogen atmosphere to remove oxygen. Typically, the heat treatment temperature for deoxygenation is 800°C, and the holding time is 3 hours. By heat-treating the Mo6S8 powder under an argon-hydrogen atmosphere to remove oxygen, the adverse effects of oxygen on the superconducting properties of PbMo6S8 are avoided.

[0009] The method for preparing a PbMo6S8-based superconducting wire described above is characterized in that, in step four, the lead rod in the metal tube containing the central lead rod is located at the center of the metal tube.

[0010] The method for preparing a PbMo6S8-based superconducting wire described above is characterized in that the heating and sintering temperature in step five is 600℃~1200℃ and the time is 5h~72h.

[0011] Compared with the prior art, the present invention has the following advantages: 1. This invention uses CuMo6S8 powder with fine grain size, high purity, and good uniformity prepared by molten salt method as precursor powder. The central Pb element diffuses directly into the interstitial position of Mo6S8 to form the PbMo6S8 phase, which effectively reduces the phase formation temperature of PbMo6S8 and avoids the formation of pores and the second phase caused by incomplete reaction, thereby improving the purity of PbMo6S8 phase.

[0012] 2. This invention uses a molten salt method combined with an acid washing process to prepare nano-sized Mo6S8 powder, thereby obtaining nano-sized PbMo6S8 phase, increasing the number of grain boundaries, forming effective flux pinning centers, and further improving the current carrying capacity of PbMo6S8 superconducting wires, laying the foundation for their application at low temperature and high magnetic field.

[0013] 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.

[0014] 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

[0015] Figure 1 This is a microscopic morphology image of the Mo6S8 powder prepared in Example 1 of the present invention.

[0016] Figure 2 The image shows a cross-sectional metallographic image of the PbMo6S8-based superconducting wire prepared in Example 1 of this invention.

[0017] Figure 3 The images show the XRD patterns of the PbMo6S8-based superconducting wire cores prepared in Example 1 and Comparative Example 1 of this invention.

[0018] Figure 4 This is a cross-sectional microstructure of the PbMo6S8-based superconducting wire core prepared in Comparative Example 2 of this invention.

[0019] Figure 5 This is a microscopic morphology image of the PbMo6S8-based superconducting wire core prepared in Comparative Example 3 of this invention.

[0020] Figure 6 The image shows the microstructure of the PbMo6S8-based superconducting wire core prepared in Example 2 of this invention.

[0021] Figure 7 The image shows the XRD pattern of the PbMo6S8-based superconducting wire core prepared in Example 3 of this invention. Detailed Implementation

[0022] Example 1 This embodiment includes the following steps: Step 1: In an argon-protected glove box, based on the atomic ratio of Cu:Mo:S in CuMo6S8 of 1:6:8, select CuS, Mo, and MoS2 powders with a mass purity of 99.99% or higher and mix them evenly to obtain a mixed powder. Then, mix the mixed powder with molten salt KCl at a mass ratio of CuMo6S8:KCl of 1:2. Pour the mixture into a mortar and grind it for at least 30 minutes. Then, sinter it at 850℃ for 60 hours in an argon atmosphere to obtain a mixed powder containing KCl and CuMo6S8. Step 2: The mixed powder obtained in Step 1 is washed with water, acid-washed and dried in sequence to remove the molten salt KCl and Cu atoms from the mixed powder, so as to obtain Mo6S8 powder with nano-sized particles with a mass purity of more than 99%. Step 3: Heat-treat the Mo6S8 powder obtained in Step 2 at 800°C under an argon-hydrogen atmosphere to remove adsorbed oxygen. Step 4: The Mo6S8 powder after oxygen removal in Step 3 is loaded into a metal tube containing a central lead rod, and then drawn into PbMo6S8 wire; the lead rod is located at the center of the metal tube. Step 5: Vacuum seal the PbMo6S8 wire obtained in Step 4 into a quartz tube and heat and sinter at 1000℃ for 12 hours to obtain PbMo6S8-based superconducting wire.

[0023] Figure 1 The image shows the microstructure of the Mo6S8 powder prepared in this embodiment. Figure 1 It can be seen that the Mo6S8 powder has a grain size of less than 500 nm, which is nanoscale.

[0024] Figure 2 The image shows a cross-sectional metallographic image of the PbMo6S8-based superconducting wire prepared in this embodiment. Figure 2 It can be seen that a dense superconducting layer exists in the PbMo6S8-based superconducting wire, indicating that the method of the present invention utilizes the diffusion of Pb element to gather all the pores at the center of the wire, forming a dense superconducting layer in the wire, and thus preparing the PbMo6S8-based superconducting wire.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that the heat treatment process of Mo6S8 powder to remove oxygen in step three was not performed. Instead, the Mo6S8 powder obtained in step two was directly subjected to the tube loading, drawing, and tube sealing and heating sintering processes in step four and step five, respectively.

[0026] Figure 3 The images show the XRD patterns of the PbMo6S8-based superconducting wire cores prepared in Example 1 and Comparative Example 1 of this invention. Figure 3It can be seen that the Mo6S8 powder in Comparative Example 1 was not subjected to heat treatment to remove oxygen, so the PbMo6S8 phase formed contained the MoO2 phase. However, in Example 1, after heat treatment to remove oxygen from the Mo6S8 powder, the diffraction peak of MoO2 disappeared, and a single PbMo6S8 phase was obtained. This shows that oxygen has an important influence on the superconductivity of PbMo6S8 superconducting materials. Heat treatment to remove oxygen from the Mo6S8 powder ensured the formation of a high content of PbMo6S8 phase.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that the traditional powder packing method is used, and the mixed powder of Mo6S8 powder and Pb powder is directly packed into the metal tube for the packing, drawing and sealing processes in step four and the heating and sintering processes in step five.

[0028] Figure 4 This is a cross-sectional microstructure image of the PbMo6S8-based superconducting wire core prepared in Comparative Example 2 of this invention. Figure 4 It can be seen that there are obvious large pores formed by the reaction of Pb powder in the core wire of this PbMo6S8-based superconducting wire. Figure 2 and Figure 4 Comparison shows that this embodiment places the Pb element in the form of a lead rod at the center of the wire, so that the pores after the complete diffusion and reaction of the Pb element are concentrated in the center of the wire, which greatly enhances the connectivity between grains and forms a dense superconducting layer around it. This avoids the problem of leaving pores in the core wire superconducting layer after the complete reaction of the Pb element during the sintering process of traditional powder-packed tubes, which causes the core wire density to decrease and the grain connectivity to deteriorate.

[0029] Comparative Example 3 The difference between this comparative example and Example 1 is that steps one through three were not performed. Instead, the mixed powder of Mo and MoS2 was directly loaded into a metal tube containing a central lead rod for the tube loading, drawing, sealing, and heating sintering processes in step four and step five, respectively.

[0030] Figure 5 The image shows the microstructure of the PbMo6S8-based superconducting wire core prepared in this comparative example. Figure 5 It can be seen that in the process of preparing PbMo6S8-based superconducting wires using a mixture of Mo and MoS2 powders as precursor powders, incomplete reaction is easily caused, resulting in a large amount of unreacted MoS2 remaining in the core wire of the PbMo6S8-based superconducting wire, which affects the purity of the PbMo6S8 superconducting phase and is therefore not conducive to improving the current carrying capacity of the PbMo6S8-based superconducting wires.

[0031] Example 2 This embodiment includes the following steps: Step 1: In an argon-protected glove box, based on the atomic ratio of Cu:Mo:S in CuMo6S8 of 1:6:8, select CuS, Mo, and MoS2 powders with a mass purity of 99.99% or higher and mix them evenly to obtain a mixed powder. Then, mix the mixed powder with molten salt KCl at a mass ratio of CuMo6S8:KCl of 1:2. Pour the mixture into a mortar and grind it for at least 30 minutes. Then, sinter it at 850℃ for 60 hours in an argon atmosphere to obtain a mixed powder containing KCl and CuMo6S8. Step 2: The mixed powder obtained in Step 1 is washed with water, acid-washed and dried in sequence to remove the molten salt KCl and Cu atoms from the mixed powder, so as to obtain Mo6S8 powder with nano-sized particles with a mass purity of more than 99%. Step 3: Heat-treat the Mo6S8 powder obtained in Step 2 at 800°C under an argon-hydrogen atmosphere to remove adsorbed oxygen. Step 4: The Mo6S8 powder after oxygen removal in Step 3 is loaded into a metal tube containing a central lead rod, and then drawn into PbMo6S8 wire; the lead rod is located at the center of the metal tube. Step 5: Vacuum seal the PbMo6S8 wire obtained in Step 4 into a quartz tube and heat and sinter at 1200℃ for 5 hours to obtain PbMo6S8-based superconducting wire.

[0032] Figure 6 The image shows the microstructure of the PbMo6S8-based superconducting wire core prepared in this embodiment. Figure 6 It can be seen that the PbMo6S8-based superconducting wire forms a phase rapidly and uniformly, with no large pores appearing in the core wire, and the core wire is relatively dense; further testing revealed that the superconducting transition temperature of the PbMo6S8-based superconducting wire is 13K.

[0033] Example 3 This embodiment includes the following steps: Step 1: In an argon-protected glove box, based on the atomic ratio of Cu:Mo:S in CuMo6S8 of 1:6:8, select CuS, Mo, and MoS2 powders with a mass purity of 99.99% or higher and mix them evenly to obtain a mixed powder. Then, mix the mixed powder with molten salt KCl at a mass ratio of CuMo6S8:KCl of 1:2. Pour the mixture into a mortar and grind it for at least 30 minutes. Then, sinter it at 850℃ for 60 hours in an argon atmosphere to obtain a mixed powder containing KCl and CuMo6S8. Step 2: The mixed powder obtained in Step 1 is washed with water, acid-washed and dried in sequence to remove the molten salt KCl and Cu atoms from the mixed powder, so as to obtain Mo6S8 powder with nano-sized particles with a mass purity of more than 99%. Step 3: Heat-treat the Mo6S8 powder obtained in Step 2 at 800°C under an argon-hydrogen atmosphere to remove adsorbed oxygen. Step 4: The Mo6S8 powder after oxygen removal in Step 3 is loaded into a metal tube containing a central lead rod, and then drawn into PbMo6S8 wire; the lead rod is located at the center of the metal tube. Step 5: Vacuum seal the PbMo6S8 wire obtained in Step 4 into a quartz tube and heat and sinter at 600℃ for 72 hours to obtain PbMo6S8-based superconducting wire.

[0034] Figure 7 The image shows the XRD pattern of the PbMo6S8-based superconducting wire core prepared in this embodiment. Figure 7 It can be seen that the main phase of the PbMo6S8-based superconducting wire core is the PbMo6S8 phase, and the content of the superconducting phase is calculated to be more than 95%. Therefore, it can be seen that the technical solution of the present invention can be used to prepare PbMo6S8-based superconducting wires with high superconducting phase content.

[0035] 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, mix CuS, Mo, and MoS2 powders evenly according to the atomic ratio of Cu:Mo:S in CuMo6S8 to obtain a mixed powder. Then, mix the mixed powder with molten salt KCl at a mass ratio of 1:2 and heat-treat it in an argon atmosphere to obtain a mixed powder containing KCl and CuMo6S8. Step 2: The mixed powder obtained in Step 1 is washed with water, acid-washed and dried in sequence to remove the molten salt KCl and Cu atoms from the mixed powder, so as to obtain Mo6S8 powder with nano-sized particles with a mass purity of more than 99%. Step 3: Heat-treat the Mo6S8 powder obtained in Step 2 to remove the adsorbed oxygen. Step 4: The Mo6S8 powder, after oxygen removal in Step 3, is loaded into a metal tube containing a central lead rod, and then drawn into PbMo6S8 wire. Step 5: Vacuum seal the PbMo6S8 wire obtained in Step 4 into a quartz tube and heat and sinter it to obtain PbMo6S8-based superconducting wire.

2. The method for preparing a PbMo6S8-based superconducting wire according to claim 1, characterized in that, In step three, the Mo6S8 powder is heat-treated to remove oxygen under an argon-hydrogen atmosphere. The heat treatment temperature is 800℃ and the holding time is 3h.

3. The method for preparing a PbMo6S8-based superconducting wire according to claim 1, characterized in that, In step four, the lead rod in the metal tube containing the central lead rod is located at the center of the metal tube.

4. The method for preparing a PbMo6S8-based superconducting wire according to claim 1, characterized in that, The heating and sintering temperature in step five is 600℃~1200℃, and the time is 5h~72h.

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