A superconducting connection method for a rare earth barium copper oxide tape

Abstract

The application provides a superconducting connection method of a rare earth barium copper oxygen tape, and belongs to the technical field of superconducting material preparation.The superconducting connection method of the rare earth barium copper oxygen tape provided by the application uses a low-melting-point REBCO superconducting layer as a connecting body, and inserts the connecting body between tapes with high-melting-point REBCO superconducting layers to realize a superconducting joint.Compared with a traditional connection method, the method can reduce the influence of heat treatment temperature on the tapes, promote the formation of a connection between REBCO superconducting layer interfaces, and has a higher fault tolerance of process conditions, thereby effectively improving the performance of the superconducting joint.The preparation method is simple, has relatively low process requirements, and is easy to operate.The results of the embodiments show that the rare earth barium copper oxygen tape prepared by the method provided by the application has good superconducting performance, and the joint has higher mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of superconducting material preparation technology, and in particular to a superconducting connection method for rare earth barium copper oxide tapes. Background Technology

[0002] Based on rare earth barium copper oxide (REBa2Cu3O) 7-x REBCO (abbreviated as RE, where RE stands for rare earth elements such as Y and Gd) tapes (or coated conductors) have advantages such as high critical transition temperature (~93K, applicable to liquid nitrogen temperature range), strong current carrying capacity, high irreversible field, and good mechanical properties, and have broad application prospects in the fields of power, energy, strong magnetic fields and magnetic levitation transportation.

[0003] However, commercially available REBCO tapes are typically only in the tens to hundreds of meters range, far from meeting the needs of superconducting cables and large and medium-sized superconducting magnets. Therefore, in practical applications, they must be connected. REBCO tapes are generally composed of a metal alloy base tape (50–100 μm), a buffer layer (~200 nm), a REBCO superconducting layer (1–2 μm), a silver layer (~2 μm), and a metal protective layer (40–80 μm) in sequence. Therefore, connection technologies such as brazing based on the metal protective layer, diffusion welding of the silver layer, and fusion diffusion welding of the superconducting layer have been proposed. Most importantly, to achieve high magnetic field stability and uniformity, NMR magnets need to operate in a closed-loop continuous current mode, meaning the magnet is disconnected from the external excitation power supply to achieve lossless operation. However, due to the resistance of copper and silver, brazing based on the metal protective layer and diffusion welding of the silver layer inevitably generate joint resistance, resulting in heat loss. Therefore, only by connecting the superconducting layers to form a resistance-free superconducting joint can the application requirements of REBCO tapes in the NMR field be met.

[0004] REBCO superconducting layers are made of oxide ceramic materials, making superconducting bonding extremely difficult. Currently, fusion diffusion bonding of superconducting layers can form connections at the superconducting layer interfaces, but this requires precise control of process conditions such as temperature and vacuum level to avoid over-melting and damaging the original superconducting layer of the tape, or under-melting that prevents the formation of connections between superconducting layers, thus hindering large-scale application.

[0005] Therefore, providing a connection method that is simple to implement and whose connector has excellent superconducting and mechanical properties has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a superconducting connection method for rare earth barium copper oxide tapes. The superconducting connection method for rare earth barium copper oxide tapes provided by this invention can well retain the current carrying capacity of the original tape and has higher mechanical properties. Moreover, the connection method provided by this invention is simple and easy to operate.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a superconducting bonding method for rare-earth barium copper oxide tapes, comprising the following steps:

[0009] (1) Remove the metal protective layer and silver layer at the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed.

[0010] (2) Overlap the two sides of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to form a “sandwich” structure and obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape.

[0011] (3) Vacuum hot pressing and oxidation annealing are performed on the overlapping parts of the connected REBCO tape obtained in step (2) to obtain a superconducting rare earth barium copper oxide tape.

[0012] Preferably, the exposed length of the REBCO superconducting layer in step (1) is 1 to 4 cm.

[0013] Preferably, the preparation method of the REBCO superconducting layer connector in step (2) includes the following steps:

[0014] 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer;

[0015] 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1) to obtain a silver strip / REBCO strip.

[0016] 3) Peel off the metal alloy base and buffer layer from the silver strip / REBCO strip obtained in step 2) to obtain the silver strip / silver layer / REBCO superconducting layer;

[0017] 4) Etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector.

[0018] Preferably, in step 2), the hot pressing temperature is 400–960°C, the hot pressing pressure is 0.1–100 MPa, and the hot pressing time is 1–100 min.

[0019] Preferably, the etching solution used in step 4) is a silver etchant.

[0020] Preferably, the surface of the REBCO superconducting layer connector further includes silver nanoparticles.

[0021] Preferably, the size of the silver nanoparticles is 10–200 nm.

[0022] Preferably, in step (3), the vacuum degree of the vacuum hot pressing treatment is ≤100Pa, the pressure of the vacuum hot pressing treatment is 1~50MPa, the temperature of the vacuum hot pressing treatment is 750~950℃, and the time of the vacuum hot pressing treatment is 0.5~120min.

[0023] Preferably, the oxidation annealing temperature in step (3) is 350–600°C, and the oxidation annealing time is 0.5–20 h.

[0024] This invention provides a rare-earth barium copper oxide tape with superconducting connection prepared by the superconducting connection method described in the above technical solution.

[0025] This invention provides a superconducting connection method for rare earth barium copper oxide tapes, comprising the following steps: (1) removing the metal protective layer and silver layer at the ends of two REBCO tapes respectively, exposing the REBCO superconducting layer in the two REBCO tapes; (2) overlapping the two sides of a REBCO superconducting layer connector onto the exposed REBCO superconducting layer of the two REBCO tapes in step (1) to form a "sandwich" structure, thereby obtaining connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tapes; (3) performing vacuum hot pressing and oxidation annealing treatment sequentially on the overlapping part of the connected REBCO tapes obtained in step (2) to obtain superconducting connected rare earth barium copper oxide tapes. This invention uses a low-melting-point REBCO superconducting layer as a connector and inserts it between tapes with high-melting-point REBCO superconducting layers to achieve a superconducting joint. Compared with traditional connection methods, this reduces the impact of heat treatment temperature on the tape, promotes the formation of a connection at the REBCO superconducting layer interface, and offers higher tolerance for process conditions, thereby effectively improving the performance of the superconducting joint. The preparation method is simple, has low process requirements, and is easy to operate. Results from the embodiments show that the critical current of the rare-earth barium copper oxide tape with superconducting connection provided by this invention can approach 95% of the original connected tape, effectively preserving the current-carrying capacity of the original tape, while the joint exhibits higher mechanical strength. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation of REBCO superconducting layer connectors in Examples 1-3 of the present invention;

[0027] Figure 1In the diagram, 1 is the silver ribbon, 2 is the REBCO tape, 21 is the base tape, 22 is the buffer layer, 23 is the REBCO superconducting layer, 24 is the silver layer, 3 is the silver ribbon / silver layer / REBCO superconducting layer, and 4 is the REBCO superconducting layer connector.

[0028] Figure 2 This is a flowchart illustrating the preparation of rare-earth barium copper oxide tapes with superconducting connections in Examples 1-3 of the present invention;

[0029] Figure 2 In the diagram, 21 is the baseband, 22 is the buffer layer, 23 is the REBCO superconducting layer, 24 is the silver layer, 25 is the metal protective layer, 4 is the REBCO superconducting layer connector, and 5 is the superconducting connector of the rare earth barium copper oxide tape.

[0030] Figure 3 This is a schematic diagram of introducing nano-silver particles onto the REBCO superconducting layer connector to form a superconducting joint in the superconducting connection method provided in Embodiments 4-5 of the present invention;

[0031] Figure 3 In the diagram, 21 is the baseband, 22 is the buffer layer, 23 is the REBCO superconducting layer, 24 is the silver layer, 25 is the metal protective layer, 4 is the REBCO superconducting layer connector, 6 is the nano-silver particles, and 7 is the superconducting connector of the rare earth barium copper oxide tape.

[0032] Figure 4 The VI curve of the superconducting connector of the rare earth barium copper oxide tape prepared in Example 1 of the present invention;

[0033] Figure 5 Mechanical tensile stress-strain curves of the rare earth barium copper oxide tapes with superconducting connections prepared in Examples 1 and 5 of the present invention and the original REBCO tapes provided in Comparative Example 1. Detailed Implementation

[0034] This invention provides a superconducting bonding method for rare-earth barium copper oxide tapes, comprising the following steps:

[0035] (1) Remove the metal protective layer and silver layer at the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed.

[0036] (2) Overlap the two sides of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to form a “sandwich” structure and obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape.

[0037] (3) Vacuum hot pressing and oxidation annealing are performed on the overlapping parts of the connected REBCO tape obtained in step (2) to obtain a superconducting rare earth barium copper oxide tape.

[0038] This invention removes the metal protective layer and silver layer from the ends of two REBCO tapes, exposing the REBCO superconducting layer within the tapes. By removing the metal protective layer and silver layer, this invention exposes the REBCO superconducting layer, facilitating subsequent overlapping and splicing of the REBCO superconducting layer with REBCO superconducting layer connectors.

[0039] The present invention does not have any special limitation on the specific source of the REBCO tape; any commercially available product known to those skilled in the art can be used.

[0040] The present invention does not have any particular limitation on the method of removing the metal protective layer and the silver layer, as long as it can expose the REBCO superconducting layer without causing damage to it.

[0041] In this invention, the removal length of the metal protective layer is preferably at least 1 cm longer than the removal length of the silver layer, more preferably 2-3 cm. By removing a longer metal protective layer, this invention provides more operating space during the subsequent removal of the silver layer, thereby avoiding damage to the REBCO superconducting layer during the removal of the silver layer.

[0042] In this invention, the exposed length of the REBCO superconducting layer is preferably 1–4 cm, more preferably 2–3 cm. By controlling the exposed length of the REBCO superconducting layer, this invention facilitates a high bonding strength after overlapping with the REBCO superconducting layer connector, preventing detachment.

[0043] After exposing the REBCO superconducting layer in two REBCO tapes, the present invention overlaps the two sides of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes to form a "sandwich" structure, thereby obtaining connected REBCO tapes.

[0044] The present invention does not have any particular limitation on the specific method of overlapping, as long as both ends of the REBCO superconducting layer connector are completely overlapped with the exposed REBCO superconducting layers of the two REBCO tapes.

[0045] In this invention, the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape. By using a low-melting-point REBCO superconducting layer as the connector, this invention promotes the formation of connections at the REBCO superconducting layer interface, resulting in higher tolerance for process conditions and thus effectively improving the performance of the superconducting joint.

[0046] In this invention, the method for preparing the REBCO superconducting layer connector preferably includes the following steps:

[0047] 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer;

[0048] 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1) to obtain a silver strip / REBCO strip.

[0049] 3) Peel off the metal alloy base and buffer layer from the silver strip / REBCO strip obtained in step 2) to obtain the silver strip / silver layer / REBCO superconducting layer;

[0050] 4) Etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector.

[0051] The present invention preferably removes the metal protective layer in the REBCO tape to obtain a REBCO tape without a metal protective layer.

[0052] The present invention does not have any particular limitation on the method of removing the metal protective layer, as long as the metal protective layer can be removed without damaging the underlying silver layer.

[0053] After obtaining the REBCO tape without a metal protective layer, the present invention preferably hot-presses a silver tape onto the silver layer surface of the REBCO tape without a metal protective layer to obtain a silver tape / REBCO tape.

[0054] The present invention does not have any special limitation on the specific source of the silver strip. Commercially available products known to those skilled in the art or self-prepared products that can meet the size requirements can be used.

[0055] In this invention, the length and width of the silver strip are preferably the same as those of the REBCO strip without a metal protective layer; the thickness of the silver strip is preferably 20–100 μm, more preferably 30–80 μm, and even more preferably 50–70 μm. By controlling the dimensions of the silver strip, this invention enables the silver strip and REBCO strip to have better mechanical properties after hot pressing, facilitating the subsequent peeling and removal of the metal alloy base strip and buffer layer.

[0056] In this invention, the hot-pressing temperature is preferably 400–960°C, more preferably 500–800°C, and even more preferably 600–700°C; the hot-pressing pressure is preferably 0.1–100 MPa, more preferably 1–50 MPa, and even more preferably 10–30 MPa; the hot-pressing time is preferably 1–100 min, more preferably 5–80 min, and even more preferably 10–50 min; the hot-pressing atmosphere is preferably an oxygen atmosphere. By controlling the temperature and time of the hot-pressing, this invention can avoid both excessively high temperatures leading to silver melting, discontinuity or breakage of the silver strip after hot-pressing, ultimately resulting in the REBCO superconducting layer not being completely peeled off or breaking at a certain point, and excessively low temperatures leading to incomplete diffusion connections between the silver strip and the silver layer, resulting in many pores and preventing the superconducting layer from being completely peeled off.

[0057] After obtaining the silver ribbon / REBCO ribbon, the present invention preferably strips the metal alloy base strip and buffer layer from the silver ribbon / REBCO ribbon to obtain the silver ribbon / silver layer / REBCO superconducting layer.

[0058] In this invention, the preferred method of peeling is to keep the silver / REBCO strip straight and then bend and peel off the metal alloy base strip and buffer layer from one end. In this invention, the bending radius during the bend peeling is preferably >5 mm. By controlling the bending radius, this invention ensures that the REBCO superconducting layer is not damaged when the metal alloy base strip and buffer layer separate from the silver layer and REBCO superconducting layer.

[0059] After obtaining the silver strip / silver layer / REBCO superconducting layer, the present invention preferably etches the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer to obtain the REBCO superconducting layer connector.

[0060] In this invention, the etching solution used for etching is preferably a silver etchant. This invention does not impose any specific limitations on the source of the silver etchant; commercially available products well-known to those skilled in the art can be used.

[0061] This invention does not have a specific limitation on the etching time; it is sufficient to completely remove the silver band and silver layer from the silver band / silver layer / REBCO superconducting layer. By using etching to remove the silver band and silver layer, this invention avoids damage to the REBCO superconducting layer, thereby obtaining a complete REBCO superconducting layer connector.

[0062] In this invention, the surface of the REBCO superconducting layer connector preferably further includes silver nanoparticles. In this invention, the size of the silver nanoparticles is preferably 10–200 nm, more preferably 20–150 nm, and even more preferably 20–100 nm.

[0063] In this invention, the preferred method for preparing the silver nanoparticles includes magnetron sputtering or spraying.

[0064] In this invention, the preferred method of magnetron sputtering is to deposit a thin silver layer on the surface of the REBCO superconducting layer connector using magnetron sputtering, followed by annealing to form silver nanoparticles. Preferably, the silver nanoparticles are filled in recesses on the surface of the REBCO superconducting layer connector. This invention does not impose any particular limitation on the specific method for filling the recesses on the surface of the REBCO superconducting layer connector with silver nanoparticles; any method well-known to those skilled in the art can be used, such as using a template with a groove array, which is common technical knowledge.

[0065] The present invention does not impose any special limitations on the process parameters of the magnetron sputtering method; they can be determined based on the technical common sense of those skilled in the art.

[0066] In this invention, the thickness of the thin silver layer is preferably 10–50 nm. By controlling the thickness of the thin silver layer, this invention ensures that the thin silver layer agglomerates into nano-silver particles after annealing.

[0067] In this invention, the annealing temperature is preferably 400–800°C, more preferably 500–700°C, and even more preferably 600°C; the annealing time is preferably 10–60 min, more preferably 20–50 min, and even more preferably 30–40 min. By controlling the annealing parameters, this invention can transform a silver layer into nano-silver particles.

[0068] This invention prepares a thin silver layer on a REBCO superconducting layer connector by magnetron sputtering, and then anneals it to agglomerate it into silver nanoparticles. These silver nanoparticles will be in the depressions on the surface of the REBCO superconducting layer connector, acting as an interface "toughening agent" to effectively improve the oxidation annealing efficiency and mechanical strength of the superconducting joint. At the same time, most other areas of the REBCO superconducting layer connector are still exposed superconducting layers, which does not affect the connection.

[0069] In this invention, the preferred method is to spray a nano-silver suspension onto the surface of the REBCO superconducting layer connector, and then dry it to obtain nano-silver particles.

[0070] The present invention does not impose any special limitation on the concentration of the nano-silver suspension; it can be prepared according to the technical common sense of those skilled in the art.

[0071] The present invention does not have a special limitation on the amount of the nano-silver suspension sprayed, as long as the size of the final nano-silver particles meets the requirements.

[0072] This invention uses a spraying method to control the size of silver nanoparticles, thereby obtaining small-sized silver nanoparticles.

[0073] This invention first removes the metal protective layer from the REBCO tape, exposing the silver layer. Then, the silver layer and tape are overlapped and hot-pressed, allowing the silver layer and tape to diffusely bond together, improving its mechanical properties. Next, the metal alloy base and buffer layer in the silver tape / REBCO tape are peeled off. During this process, the silver layer and tape act as supports, preventing damage to the REBCO superconducting layer and ensuring its complete separation from the buffer layer. Finally, the silver tape and layer in the silver tape / silver layer / REBCO superconducting layer are removed by etching, resulting in a complete low-melting-point REBCO superconducting layer connector. Nano-silver particles are then prepared on the low-melting-point REBCO superconducting layer connector, introducing nano-silver as an interface "toughening agent" between the exposed REBCO superconducting layer and the connector. This effectively improves the oxidation annealing efficiency and mechanical strength of the superconducting joint. Simultaneously, these nano-silver particles are located in the recesses on the surface of the REBCO superconducting layer connector, while most other areas remain exposed superconducting layers, without affecting the connection.

[0074] After obtaining the connected REBCO tape, the present invention performs vacuum hot pressing and oxidation annealing on the overlapping parts of the connected REBCO tape in sequence to obtain a superconducting connected rare earth barium copper oxide tape.

[0075] In this invention, the vacuum degree of the vacuum hot pressing process is preferably ≤100 Pa; the pressure of the vacuum hot pressing process is preferably 1-50 MPa, more preferably 5-40 MPa, and even more preferably 10-30 MPa; the temperature of the vacuum hot pressing process is preferably 750-950°C, more preferably 800-900°C, and even more preferably 850°C; the time of the vacuum hot pressing process is preferably 0.5-120 min, more preferably 5-100 min, and even more preferably 20-80 min. This invention, through vacuum hot pressing, enables the overlapping REBCO superconducting layers and connectors to form a unified whole, which is not easily separated.

[0076] In this invention, the temperature of the oxidation annealing treatment is preferably 350–600°C, more preferably 400–550°C, and even more preferably 450–500°C; the time of the oxidation annealing treatment is preferably 0.5–20 h, more preferably 2–10 h; and the atmosphere of the oxidation annealing treatment is preferably pure oxygen. This invention, through oxidation annealing, can restore the superconducting properties of the REBCO superconducting layer lost due to vacuum hot pressing.

[0077] This invention uses a low-melting-point REBCO superconducting layer as a connector and inserts it between strips with high-melting-point REBCO superconducting layers to achieve a superconducting joint. On the one hand, compared with traditional connection methods, it can reduce the influence of heat treatment temperature on the strip, promote the formation of a connection at the REBCO superconducting layer interface, and has a higher tolerance for process conditions, thereby effectively improving the performance of the superconducting joint. On the other hand, since nano-silver has a high oxygen diffusion coefficient and softens and becomes viscous at high temperatures, introducing nano-silver as an interface "toughening agent" between the exposed REBCO superconducting layer and the connector can effectively improve the oxidation annealing efficiency and mechanical strength of the superconducting joint.

[0078] This invention provides a superconductingly connected rare-earth barium copper oxide tape prepared by the superconducting connection method described above. The superconductingly connected rare-earth barium copper oxide tape provided by this invention exhibits excellent superconducting properties and mechanical strength.

[0079] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0080] Example 1

[0081] A superconducting bonding method for rare-earth barium copper oxide tapes comprises the following steps:

[0082] (1) Remove the metal protective layer and silver layer from the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed; the removal length of the metal protective layer is 2cm longer than the removal length of the silver layer; the exposed length of the REBCO superconducting layer is 4cm.

[0083] (2) Overlap the two ends of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape.

[0084] (3) The overlapping joints of the REBCO tapes obtained in step (2) are subjected to vacuum hot pressing and oxidation annealing in sequence to obtain a superconducting rare earth barium copper oxide tape; the vacuum degree of the vacuum hot pressing is 20 Pa, the pressure of the vacuum hot pressing is 20 MPa, the temperature of the vacuum hot pressing is 820 °C, and the time of the vacuum hot pressing is 20 min; the temperature of the oxidation annealing is 500 °C, the time of the oxidation annealing is 5 h, and the atmosphere of the oxidation annealing is pure oxygen.

[0085] The method for preparing the REBCO superconducting layer connector is as follows:

[0086] 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer;

[0087] 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1), to obtain a silver strip / REBCO strip; the length and width of the silver strip are the same as the length and width of the REBCO strip without a metal protective layer, and the thickness of the silver strip is 100 μm; the hot-pressing temperature is 600℃, the hot-pressing pressure is 20 MPa, the hot-pressing time is 30 min, and the hot-pressing atmosphere is an oxygen atmosphere;

[0088] 3) Keep the silver strip / REBCO strip obtained in step (2) straight, and then bend and peel off the metal alloy base strip and buffer layer from one end to obtain the silver strip / silver layer / REBCO superconducting layer; the bending radius during the bending and peeling is 20 mm.

[0089] 4) Use a silver etchant to etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector.

[0090] Example 2

[0091] A superconducting bonding method for rare-earth barium copper oxide tapes comprises the following steps:

[0092] (1) Remove the metal protective layer and silver layer from the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed; the removal length of the metal protective layer is 2cm longer than the removal length of the silver layer; the exposed length of the REBCO superconducting layer is 3cm.

[0093] (2) Overlap the two ends of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape.

[0094] (3) The overlapping joints of the REBCO tapes obtained in step (2) are subjected to vacuum hot pressing and oxidation annealing in sequence to obtain a superconducting rare earth barium copper oxide tape; the vacuum degree of the vacuum hot pressing is 100 Pa, the pressure of the vacuum hot pressing is 1 MPa, the temperature of the vacuum hot pressing is 950 °C, and the time of the vacuum hot pressing is 0.5 min; the temperature of the oxidation annealing is 600 °C, the time of the oxidation annealing is 2 h, and the atmosphere of the oxidation annealing is pure oxygen.

[0095] The method for preparing the REBCO superconducting layer connector is as follows:

[0096] 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer;

[0097] 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1), to obtain a silver strip / REBCO strip; the length and width of the silver strip are the same as the length and width of the REBCO strip without a metal protective layer, and the thickness of the silver strip is 100 μm; the hot-pressing temperature is 960℃, the hot-pressing pressure is 0.1 MPa, the hot-pressing time is 1 min, and the hot-pressing atmosphere is an oxygen atmosphere;

[0098] 3) Keep the silver strip / REBCO strip obtained in step (2) straight, and then bend and peel off the metal alloy base strip and buffer layer from one end to obtain the silver strip / silver layer / REBCO superconducting layer; the bending radius during the bending and peeling is 50 mm.

[0099] 4) Use a silver etchant to etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector.

[0100] Example 3

[0101] A superconducting bonding method for rare-earth barium copper oxide tapes comprises the following steps:

[0102] (1) Remove the metal protective layer and silver layer from the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed; the removal length of the metal protective layer is 2cm longer than the removal length of the silver layer; the exposed length of the REBCO superconducting layer is 2cm.

[0103] (2) Overlap the two ends of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape.

[0104] (3) The overlapping joints of the REBCO tapes obtained in step (2) are subjected to vacuum hot pressing and oxidation annealing in sequence to obtain a superconducting rare earth barium copper oxide tape; the vacuum degree of the vacuum hot pressing is 5 Pa, the pressure of the vacuum hot pressing is 50 MPa, the temperature of the vacuum hot pressing is 750 °C, and the time of the vacuum hot pressing is 120 min; the temperature of the oxidation annealing is 350 °C, the time of the oxidation annealing is 10 h, and the atmosphere of the oxidation annealing is pure oxygen.

[0105] The method for preparing the REBCO superconducting layer connector is as follows:

[0106] 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer;

[0107] 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1), to obtain a silver strip / REBCO strip; the length and width of the silver strip are the same as the length and width of the REBCO strip without a metal protective layer, and the thickness of the silver strip is 100 μm; the hot-pressing temperature is 400℃, the hot-pressing pressure is 100 MPa, the hot-pressing time is 100 min, and the hot-pressing atmosphere is an oxygen atmosphere;

[0108] 3) Keep the silver strip / REBCO strip obtained in step (2) straight, and then bend and peel off the metal alloy base strip and buffer layer from one end to obtain the silver strip / silver layer / REBCO superconducting layer; the bending radius during the bending and peeling is 50 mm.

[0109] 4) Use a silver etchant to etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector.

[0110] Example 4

[0111] A superconducting bonding method for rare-earth barium copper oxide tapes comprises the following steps:

[0112] (1) Remove the metal protective layer and silver layer from the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed; the removal length of the metal protective layer is preferably 2cm longer than the removal length of the silver layer; the exposed length of the REBCO superconducting layer is 1cm.

[0113] (2) Overlap the two ends of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape.

[0114] (3) The overlapping joints of the REBCO tapes obtained in step (2) are subjected to vacuum hot pressing and oxidation annealing in sequence to obtain a superconducting rare earth barium copper oxide tape; the vacuum degree of the vacuum hot pressing is 20 Pa, the pressure of the vacuum hot pressing is 20 MPa, the temperature of the vacuum hot pressing is 820 °C, and the time of the vacuum hot pressing is 20 min; the temperature of the oxidation annealing is 500 °C, the time of the oxidation annealing is 5 h, and the atmosphere of the oxidation annealing is pure oxygen.

[0115] The method for preparing the REBCO superconducting layer connector is as follows:

[0116] 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer;

[0117] 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1), to obtain a silver strip / REBCO strip; the length and width of the silver strip are the same as the length and width of the REBCO strip without a metal protective layer, and the thickness of the silver strip is 100 μm; the hot-pressing temperature is 600℃, the hot-pressing pressure is 20 MPa, the hot-pressing time is 30 min, and the hot-pressing atmosphere is an oxygen atmosphere;

[0118] 3) Keep the silver strip / REBCO strip obtained in step (2) straight, and then bend and peel off the metal alloy base strip and buffer layer from one end to obtain the silver strip / silver layer / REBCO superconducting layer; the bending radius during the bending and peeling is 20 mm.

[0119] 4) Use a silver etchant to etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector. Then, use magnetron sputtering to deposit a 50 nm thick silver layer on the surface of the REBCO superconducting layer connector, and then anneal at 400 °C for 60 min to form silver nanoparticles. The size range of the silver nanoparticles is 30–200 nm.

[0120] Example 5

[0121] In step 4), a 10 nm thick silver layer is deposited on the surface of the REBCO superconducting layer connector using magnetron sputtering, and then annealed at 800 °C for 10 min to form silver nanoparticles; the size range of the silver nanoparticles is 10–50 nm.

[0122] Other conditions are the same as in Example 4.

[0123] Comparative Example 1

[0124] The original REBCO tape, i.e. the REBCO tape in step (1) of Example 1.

[0125] The flowcharts for preparing REBCO superconducting layer connectors in Examples 1-3 are as follows: Figure 1 As shown; Figure 1 In the diagram, 1 represents the silver ribbon, 2 represents the REBCO tape, 21 represents the base tape, 22 represents the buffer layer, 23 represents the REBCO superconducting layer, 24 represents the silver layer, 3 represents the silver ribbon / silver layer / REBCO superconducting layer connector, and 4 represents the REBCO superconducting layer connector. Figure 1 As can be seen, after removing the metal protective layer on the surface of the REBCO tape, the silver tape and silver layer are hot-pressed together, and then the base tape and buffer layer are separated and removed. Finally, the silver tape / silver layer is removed by silver etching solution, and a complete REBCO superconducting layer is obtained as the connector.

[0126] The flowcharts for the preparation of superconducting rare-earth barium copper oxide tapes in Examples 1-3 are as follows: Figure 2 As shown; Figure 2 In the diagram, 21 is the baseband, 22 is the buffer layer, 23 is the REBCO superconducting layer, 24 is the silver layer, 25 is the metal protective layer, 4 is the REBCO superconducting layer connector, and 5 is the superconducting joint of the rare earth barium copper oxide tape.

[0127] Schematic diagrams of the superconducting connection methods provided in Examples 4 and 5, in which nano-silver particles are introduced onto the REBCO superconducting layer connector to form a superconducting joint, are shown below. Figure 3 As shown; Figure 3 In the diagram, 21 is the baseband, 22 is the buffer layer, 23 is the REBCO superconducting layer, 24 is the silver layer, 25 is the metal protective layer, 4 is the REBCO superconducting layer connector, 6 is the nano-silver particles, and 7 is the superconducting connector for the rare-earth barium copper oxide tape. Figure 3 It can be seen that the nano-silver particles are coated on the surface of the REBCO superconducting layer connector, and then act as an interface "toughening agent" to improve the oxidation annealing efficiency and mechanical strength of the superconducting joint.

[0128] Figure 4 The VI curve is shown for the superconducting joint of the rare-earth barium copper-oxygen tape prepared in Example 1. Figure 4 It can be seen that the critical current of the original tape is 118A, and the critical current at the joint of the superconducting rare earth barium copper oxide tape prepared by the method of the present invention is 112A, which is about 95% of that of the original tape. This shows that the superconducting joint prepared by the method of the present invention can retain the critical current of the original tape to a great extent, and the current carrying capacity of the joint is excellent.

[0129] Figure 5 Mechanical tensile stress-strain curves of the superconducting rare-earth barium copper oxide tapes prepared in Examples 1 and 5, and the original REBCO tape provided in Comparative Example 1. Figure 5 It can be seen that the joint with silver nanoparticles obtained by adding nano-silver has higher mechanical strength than the joint without nano-silver assisted welding.

[0130] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A superconducting bonding method for rare-earth barium copper oxide tapes, comprising the following steps: (1) Remove the metal protective layer and silver layer at the ends of the two REBCO tapes respectively, so that the REBCO superconducting layer in the two REBCO tapes is exposed. (2) Overlap the two sides of a REBCO superconducting layer connector onto the exposed REBCO superconducting layers of the two REBCO tapes in step (1) to form a "sandwich" structure and obtain connected REBCO tapes; the melting point of the REBCO superconducting layer connector is lower than the melting point of the REBCO superconducting layer in the REBCO tape. (3) Vacuum hot pressing and oxidation annealing are performed on the overlapping parts of the connected REBCO tape obtained in step (2) to obtain a superconducting rare earth barium copper oxide tape. The preparation method of the REBCO superconducting layer connector in step (2) includes the following steps: 1) Remove the metal protective layer from the REBCO tape to obtain a REBCO tape without a metal protective layer; 2) Hot-press a silver strip onto the silver layer surface of the REBCO strip without a metal protective layer obtained in step 1) to obtain a silver strip / REBCO strip; 3) Peel off the metal alloy base and buffer layer from the silver strip / REBCO strip obtained in step 2) to obtain the silver strip / silver layer / REBCO superconducting layer; 4) Etch the silver strip and silver layer in the silver strip / silver layer / REBCO superconducting layer obtained in step 3) to obtain the REBCO superconducting layer connector; In step 2), the hot pressing temperature is 400~960℃, the hot pressing pressure is 0.1~100MPa, and the hot pressing time is 1~100min.

2. The superconducting connection method according to claim 1, characterized in that, In step (1), the exposed length of the REBCO superconducting layer is 1~4cm.

3. The superconducting connection method according to claim 1, characterized in that, The etching solution used in step 4) is a silver etchant.

4. The superconducting connection method according to claim 1, characterized in that, The surface of the REBCO superconducting layer connector also includes silver nanoparticles.

5. The superconducting connection method according to claim 4, characterized in that, The size of the silver nanoparticles is 10~200nm.

6. The superconducting connection method according to claim 1, characterized in that, In step (3), the vacuum degree of vacuum hot pressing is ≤100Pa, the pressure of vacuum hot pressing is 1~50MPa, the temperature of vacuum hot pressing is 750~950℃, and the time of vacuum hot pressing is 0.5~120min.

7. The superconducting connection method according to claim 1, characterized in that, The oxidation annealing temperature in step (3) is 350~600℃, and the oxidation annealing time is 0.5~20h.

8. The superconducting rare-earth barium copper oxide tape prepared by the superconducting connection method according to any one of claims 1 to 7.

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