Method and system for reducing joint resistance of high-temperature superconducting strip

Abstract

The invention provides a method and system for reducing the resistance of a high-temperature superconducting tape joint, and the method comprises the steps: plating a protective layer on a whole superconducting long tape, and completing the superconducting annealing treatment; measuring the joint resistance of the superconducting tape, removing the protective layer in the joint area of the superconducting tape for the superconducting tape of which the joint resistance does not reach the standard, and re-plating the compact protective layer on the joint area of the superconducting tape; and finally, annealing treatment is performed again, so that the inside and outside of the superconducting layer reach the optimal diversion state. A perfect high-joint resistor long tape recycling mechanism is established, operation can be repeated, and the yield of superconducting tapes can be improved; the method belongs to a material resistivity optimization process, and is combined with the existing strip winding and laminating technology, so that the joint resistance can be further reduced, and the joint resistance is close to the theoretical limit.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting tape post-processing technology, and in particular to a method and system for reducing the resistance of a high-temperature superconducting tape joint. Background Art

[0002] Since the first discovery of superconductivity in 1911, superconducting materials have been regarded as the seeds of the next industrial revolution by humans due to their huge economic value without energy consumption, attracting countless scientists to invest their blood and tears. In the past decade, the first generation of high-temperature superconducting wires made mainly by the powder sheath method and the second generation of high-temperature superconducting tapes made mainly by the base tape coating method have matured successively, making it possible for people to apply superconducting materials on a large scale.

[0003] The first generation is represented by silver-coated BSCCO materials, while the second generation is represented by superconducting materials ReBCO (ReBa 2 Cu 3 O 7-δ , Re is Y, Eu and other rare earth elements) are typical. Among them, the first generation of high-temperature superconducting wires has a first-mover advantage, but the second generation of superconducting tapes has stronger current carrying capacity, better magnetic field performance and lower material cost, so it has broader development prospects in many fields such as large scientific research equipment, medical treatment, and energy.

[0004] The second generation of superconducting tapes, also known as coated conductors, has a very small coherence length of the superconducting material ReBCO, which can easily lose its superconductivity due to weak connection of grain boundaries. Therefore, in order to make long-distance current transmission wires, only a superconducting film with copper-oxygen surface alignment can be grown on a base tape coated with a stable biaxial texture buffer film layer as a superconducting current-carrying core, and then a protective layer shell is plated on the upper and lower surfaces to protect the superconducting film layer. The superconducting tape with a protective layer on the surface needs to go through an annealing process to induce the internal superconducting layer ReBCO to transform into a stable superconducting phase to make it have superconducting properties. Finally, the outermost layer is plated with a corresponding coating layer according to the needs for packaging, and the finished product can be put into use.

[0005] There are many evaluation indicators for finished superconducting tapes, such as critical current, single - root length, critical magnetic field, joint resistance, and tensile resistance. Different customers have different application scenarios and different requirements for different indicators. However, specifically in the tape post - processing stage of the subsequent process of superconducting film formation, each customer hopes that various post - processing operations will not damage the superconducting film layer itself, and the whole tape has no bad points (which will lead to low critical current), so that it still maintains existing properties such as high critical current, high critical magnetic field, and high critical - current uniformity. Although bad points can be removed by post - processing such as cutting, it results in a shorter tape length, which may not meet the application requirements. Currently, the latest technology in the superconducting field can produce long tapes with a single - root length of nearly one kilometer without low critical - current points, high critical current, and high critical magnetic field, which can meet most requirements. However, for large - scale scientific devices such as tokamak magnetic - confinement fusion, a length of nearly one kilometer is still insufficient, and several superconducting tapes must be connected end - to - end to form an ultra - long current - carrying wire coil for use. For such requirements, in addition to the single - root length, another indicator - joint resistance - must also be strictly required.

[0006] The joint resistance is actually energy dissipation, which occurs in the overlapping part where two superconducting tapes are in contact, that is, the joint area. Since the superconducting layers do not directly contact, the current needs to pass through the protective layer - coating layer - coating layer - protective layer to reach the other superconducting layer, and this process brings energy dissipation, which is macroscopically manifested as the generation of joint resistance. The existence of joint resistance limits the lossless transmission of current by superconducting materials and will cause additional energy losses. For high - field magnet applications, a slight loss of heat at one point, under the strong magnetic - field environment and the huge energy input of the device itself, will be exponentially amplified, ultimately leading to the disconnection and detachment of the circuit. Therefore, people have been continuously exploring methods to reduce joint resistance in the past half - century. However, most of the research on reducing joint resistance has focused on the macroscopic field, that is, optimizing the winding method and tight - fitting degree of the tapes at the joint. The latest technology has achieved a direct - contact welding between the protective layers of long tapes with practicality (Patent CN107393652A), that is, the current only needs to pass through the protective layer - protective layer to reach the other superconducting layer, greatly saving the intermediate energy consumption. It can be said that the winding and fitting method of the tapes has been optimized to the extreme. However, at this stage of research, the resistivity of the protective - layer material itself has become the greatest constraint.

[0007] Currently, for the production of nearly one - kilometer high - temperature superconducting long tapes, a protective - layer coating is carried out in a high - vacuum, inert - gas environment. This conventional coating technology can ensure that almost all long tapes have no low critical - current points throughout the whole tape. However, due to process fluctuations, it is impossible to ensure that while maintaining a single - root tape without bad points, the resistivity of the protective layer is reduced to the lowest. Therefore, the general processing method is a large - scale production - inspection and classification - different - order supply mode, that is, large - batch production is carried out, and after the finished products, the joint resistance is tested. Long tapes with high joint resistance are provided for orders that do not require splicing of multiple tapes, such as cables, and long tapes with low joint resistance are supplied to contracts with strict requirements for joint resistance, such as high - field magnets.

[0008] However, as people's demand for low joint resistance long belts increases, the inventory of low joint resistance long belts is seriously insufficient, while the high joint resistance long belts are seriously overstocked and face the risk of being scrapped. This operating mode is becoming increasingly unsustainable. There is room for improvement. Summary of the invention

[0009] In view of the defects in the prior art, an object of the present invention is to provide a method and system for reducing the resistance of a high-temperature superconducting tape joint.

[0010] According to the present invention, a method for reducing the resistance of a high-temperature superconducting tape joint comprises the following steps: Step S1, coating the entire superconducting long strip with a protective layer and completing conventional superconducting annealing treatment; Step S2, measuring the joint resistance of the superconducting tape in step S1, and classifying the joint resistance into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Step S3, for superconducting tapes whose joint resistance does not meet the standard, removing the protective layer in the joint area of ​​the superconducting tape; Step S4, for the superconducting tape from which the protective layer of the joint area is removed in step S3, re-plating a dense protective layer on the joint area of ​​the superconducting tape; Step S5, performing unconventional superconducting annealing treatment on the superconducting tape re-plated with a dense protective layer in step S4; Step S6, measuring the joint resistance of the superconducting tape in step S5, and classifying the joint resistance into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; If the joint resistance of the superconducting tape in step S6 meets the joint resistance standard, the process ends; If the joint resistance of the superconducting tape in step S6 is not up to the standard, then steps S3, S4, S5 and S6 are repeated in sequence.

[0011] Preferably, in step S1, the material of the protective layer includes any one of platinum, silver and gold; In step S4, the material of the dense protective layer includes any one of platinum, silver and gold.

[0012] Preferably, for the protective layer in step S1 and the dense protective layer in step S4, the joint resistance of the dense protective layer is smaller than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is smaller than or equal to the joint resistance of the delivery standard.

[0013] Preferably, the conventional superconducting annealing treatment in step S1 is a method for inducing the superconducting material in the newly formed superconducting layer to transform into a superconducting phase; the parameters are an annealing temperature of 400 to 600° C., a time of 1.5 to 4 hours, and the strip is placed in a coil; The unconventional superconducting annealing treatment in step S5 is a method for inducing the superconducting material in the superconducting layer at the boundary between the dense coating and the conventional coating to re-convert to the superconducting phase; the parameters are an annealing temperature of 400 to 800°C, a time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed.

[0014] Preferably, the protective layer in the superconducting tape joint region is removed in step S3 by chemical etching.

[0015] According to the present invention, a system for reducing the resistance of a high-temperature superconducting tape joint is provided, the system comprising: Module M1 is used to coat the entire superconducting strip with a protective layer and complete superconducting annealing; Module M2 is used to measure the joint resistance of the superconducting tape in module M1, and divides it into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Module M3 is used to remove the protective layer of the joint area of ​​the superconducting tape for the superconducting tape whose joint resistance does not meet the standard; Module M4 is used for re-plating a dense protective layer on the joint area of ​​the superconducting tape from which the protective layer of the joint area is removed in module M3; Module M5, used for performing unconventional annealing treatment on the superconducting tape re-plated with a dense protective layer in module M4; Module M6 is used to measure the joint resistance of the superconducting tape in module M5, and divide it into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Module M7: If the joint resistance of the superconducting tape in module M6 is up to standard, the process ends; if the joint resistance of the superconducting tape in module M6 is not up to standard, repeat modules M3, M4, M5 and M6 in sequence.

[0016] Preferably, in the module M1, the material of the protective layer includes any one of platinum, silver and gold; In the module M4, the material of the dense protective layer includes any one of platinum, silver and gold.

[0017] Preferably, for the protective layer in the module M1 and the dense protective layer in the module M4, the joint resistance of the dense protective layer is smaller than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is smaller than or equal to the joint resistance of the delivery standard.

[0018] Preferably, the conventional superconducting annealing treatment in the module M1 is a method for inducing the superconducting material in the newly formed superconducting layer to transform into a superconducting phase; the parameters are an annealing temperature of 400 to 600° C., a time of 1.5 to 4 hours, and the strip is placed in a coil; For the unconventional superconducting annealing treatment in module M5, a method is used to induce the superconducting material in the superconducting layer at the boundary between dense coating and conventional coating to re-convert into the superconducting phase; the parameters are annealing temperature of 400 to 800°C, time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed. Preferably, the protective layer of the superconducting tape joint area in the module M3 is removed by chemical etching.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention firstly adopts a conventional method to coat the entire superconducting long strip with a protective layer. The critical current low point is less likely to occur during the plating process, and the effective length of a single superconducting strip can be ensured to be long. Then, the protective layer in the joint area of ​​the superconducting strip is removed, and a dense protective layer is re-plated using a dense coating process to obtain a lower joint resistance performance. The dense coating process will have additional stress extrusion. If the coating length is short, such as the joint area of ​​the superconducting strip, the stress can provide additional binding force to make it dense as a whole. However, for a strip of hundreds of meters, the internal stress accumulation is too large, which can easily lead to the fracture of the superconducting layer and affect the superconducting performance. The technical solution of the present application combines the two coating methods together, and at the same time obtains the advantages of the long superconducting effective length of the conventional coating method and the low joint resistance of the dense coating method, thereby improving the overall competitiveness of the product.

[0020] 2. The present invention has established a complete recycling mechanism for long strips with high joint resistance, which can be operated repeatedly and can achieve a very high yield rate; and it is a process for optimizing material resistivity. Combined with the existing strip winding and bonding technology, the technical solution of this application can further reduce the joint resistance to approach the theoretical limit.

[0021] 3. The technical solution of the present invention provides a set of reusable recycling processes for high-temperature superconducting long strips with large joint resistance due to other process fluctuations. First, the problem of increased resistance of directly bonded welded joints is solved by re-plating the joint area protective layer, and then the performance degradation of the superconducting layer caused by re-plating at the boundary of different process coatings is restored by extending the annealing time and increasing the temperature, and finally the superconducting layer reaches the best conduction state inside and outside. Based on this, a perfect recycling mechanism is established, so that such problematic strips do not face the risk of being scrapped directly, and huge economic losses are saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 The present invention mainly embodies the overall process flow chart; Figure 2 This is a schematic diagram of the recycling mechanism mainly embodied in the present invention; Figure 3The present invention mainly embodies the scanning electron micrograph of the high joint resistance long-strip silver layer under the conventional coating process; Figure 4 It is a schematic diagram of the microscopic change of the joint resistance during the implementation of the present invention; Figure 5 This is a diagram showing the boundary between the uncorroded area and the corroded area after chemical corrosion. Figure 6 This is a diagram showing the boundary between the uncorroded area and the corroded area after physical vapor deposition. Figure 7 This is a microscopic comparison diagram of the conventional coating process and the improved dense coating process mainly embodied in the present invention; Figure 8 This is a long-band critical current diagram that mainly reflects typical problems after dense coating process in the present invention; Fig. 9 The present invention mainly embodies the high-resolution transmission electron micrograph of the low point area of ​​the long band critical current of the typical problem; Fig.10 It is a schematic diagram of the phase change of superconducting material during the implementation of the present invention; Fig.11 This is a schematic diagram of the phase transition of the superconducting layer at the boundary between the conventional coating and the dense coating, which is mainly embodied in the present invention; Fig.12 This is a comparison diagram of the superconducting performance changes of the strip before and after the unconventional superconducting annealing, which mainly reflects the present invention; Fig.13 This is a comparison diagram of the joint resistance change before and after the defective strip is processed by the present invention; Fig.14 This is the resistance distribution diagram of the joint of the dense coating process mainly embodied in the present invention; Fig.15 This is the resistance distribution diagram of the joint in the conventional coating process mainly embodied in the present invention. DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0024] Embodiment 1 like Figure 1 and Figure 2 As shown, a method for reducing the resistance of a high-temperature superconducting tape joint provided by the present invention comprises the following steps: Step S1, coating the entire superconducting long strip with a protective layer and completing conventional superconducting annealing treatment.

[0025] Step S2, measuring the joint resistance of the superconducting tape in step S1, and classifying the joint resistance into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard.

[0026] Step S3: For superconducting tapes whose joint resistance does not meet the standard, remove the protective layer in the joint area of ​​the superconducting tapes.

[0027] Step S4: for the superconducting tape from which the protective layer in the joint area is removed in step S3, a dense protective layer is re-plated on the joint area of ​​the superconducting tape.

[0028] Step S5, performing unconventional superconducting annealing treatment on the superconducting tape re-plated with a dense protective layer in step S4.

[0029] Step S6, measuring the joint resistance of the superconducting tape in step S5, and classifying the joint resistance into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard.

[0030] If the joint resistance of the superconducting tape in step S6 meets the joint resistance standard, the process ends.

[0031] If the joint resistance of the superconducting tape in step S6 is not up to the standard, then steps S3, S4, S5 and S6 are repeated in sequence.

[0032] Specifically, in step S1, the material of the protective layer includes any one of platinum, silver and gold. In step S4, the material of the dense protective layer includes any one of platinum, silver and gold. The superconducting tape is a second-generation high-temperature superconducting tape with a total length of more than 100 meters. The joint area is the end area of ​​the superconducting tape, and the length is less than 10 centimeters.

[0033] Specifically, the joint resistance that meets the standard and the joint resistance that does not meet the standard are divided according to the size of the joint resistance, and the size of the joint resistance can be determined according to the delivery standard of the actual order. If the detected joint resistance is greater than the resistance of the delivery standard of the actual order, the joint resistance does not meet the standard; if the detected joint resistance is less than or equal to the resistance of the delivery standard of the actual order, the joint resistance meets the standard. The resistance of the delivery standard of the actual order can be determined by a technician in this field according to the actual situation.

[0034] Furthermore, for the protective layer in step S1 and the dense protective layer in step S4, the joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard. The specific operation is as follows: for step S1, the protective layer is plated on the entire superconducting long strip, which is a physical vapor deposition technology in a low-pressure inert gas environment; the parameters are a pressure of 5 to 10 mTorr, the inert gas filled is argon, and the flow rate is 50 to 100 sccm. For step S4, a dense protective layer is re-plated on the joint area of ​​the superconducting tape, which is a physical vapor deposition technology in a relatively low-pressure inert gas environment; the parameters are a pressure of 15 to 25 mTorr, the inert gas filled is argon, and the flow rate is 50 to 100 sccm.

[0035] Further, for the conventional superconducting annealing treatment in step S1, it is a method for inducing the superconducting material in the newly formed superconducting layer to transform into the superconducting phase; the parameters are annealing temperature of 400 to 600°C, time of 1.5 to 4 hours, and the tape is placed in a coil. For the unconventional superconducting annealing treatment in step S5, it is a method for inducing the superconducting material in the superconducting layer at the boundary between the dense coating and the conventional coating to transform into the superconducting phase again; the parameters are annealing temperature of 400 to 800°C, time of 3 to 8 hours, and the tape joint area needs to be unfolded and placed.

[0036] In step S3, the protective layer in the superconducting tape joint area is removed by chemical etching.

[0037] Embodiment 2 Based on the first embodiment, a system for reducing the resistance of a high-temperature superconducting tape joint is provided according to the present invention, and the system includes: Module M1 is used to coat the entire superconducting strip with a protective layer and complete conventional superconducting annealing treatment; Module M2 is used to measure the joint resistance of the superconducting tape in module M1, and divides it into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Module M3 is used to remove the protective layer of the joint area of ​​the superconducting tape for the superconducting tape whose joint resistance does not meet the standard; Module M4 is used for re-plating a dense protective layer on the joint area of ​​the superconducting tape from which the protective layer of the joint area is removed in module M3; Module M5, used for performing unconventional annealing treatment on the superconducting tape re-plated with a dense protective layer in module M4; Module M6 is used to measure the joint resistance of the superconducting tape in module M5, and divide it into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Module M7: If the joint resistance of the superconducting tape in module M6 is up to standard, the process ends; if the joint resistance of the superconducting tape in module M6 is not up to standard, repeat modules M3, M4, M5 and M6 in sequence.

[0038] Preferably, in the module M1, the material of the protective layer includes any one of platinum, silver and gold. In the module M4, the material of the dense protective layer includes any one of platinum, silver and gold.

[0039] Preferably, for the protective layer in the module M1 and the dense protective layer in the module M4, the joint resistance of the dense protective layer is smaller than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is smaller than or equal to the joint resistance of the delivery standard.

[0040] Preferably, the conventional superconducting annealing treatment in the module M1 is a method for inducing the superconducting material in the newly formed superconducting layer to transform into a superconducting phase; the parameters are an annealing temperature of 400 to 600° C., a time of 1.5 to 4 hours, and the strip is placed in a coil; For the unconventional superconducting annealing treatment in module M5, a method is used to induce the superconducting material in the superconducting layer at the boundary between dense coating and conventional coating to re-convert into the superconducting phase; the parameters are annealing temperature of 400 to 800°C, time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed. Preferably, the protective layer of the superconducting tape joint area in the module M3 is removed by chemical etching.

[0041] Embodiment 3 Based on Example 1, according to a method for reducing the resistance of a high-temperature superconducting tape joint provided by the present invention, this embodiment uses conventionally coated high-temperature superconducting EuBa 2 Cu 3 O 7-δ The same remedial treatment was carried out on two typical samples with different resistance of finished joints (sample 1 is a comparative sample; sample 2 is an experimental sample, and the microscopic scanning of the silver layer of the experimental sample is shown in Fig. Figure 3 ), as the process changes microscopically, Figure 4 As shown, the following steps are included: A 1:1 ratio of ammonia and hydrogen peroxide was used to make a corrosion solution, which was then soaked in the joint area of ​​the strip, with a joint length of 7 cm. After sufficient reaction, the strip was taken out and the residual solution was rinsed with alcohol, such as Figure 5 As shown; Using the coating parameters of 20 mTorr pressure, argon inert gas, and 70 sccm flow rate, a dense silver layer was plated on the corrosion area by a DC magnetron sputtering physical vapor deposition method, such as Figure 6 As shown; The re - silvered strip is annealed at a high temperature in oxygen. The annealing temperature is 500 °C and the time is 4 hours. After the annealing is completed, it is taken out. Through direct contact welding of silver layer - silver layer, multiple strips are wound and bonded front and back, and then the joint resistance is measured.

[0042] In this embodiment, a dense coating process is adopted. Compared with the traditional conventional coating process, its pressure parameter is increased (i.e., the environmental vacuum degree is reduced). According to the principle mentioned in relevant literature that maintaining a pseudo - vacuum environment with a certain amount of inert gas is beneficial to reducing the overall sputtering effect of the thin film (Journal of Applied Surface Science, 2007, 254, 760 - 764), we extended it to the coating process field of the superconducting strip protective layer and successfully achieved a dense protective layer coating with a significant reduction in defects. The microscopic principle is explained as Figure 7 shown. An appropriate concentration of inert gas will exert a certain binding force on the periphery of the protective layer, making it densify as a whole.

[0043] The applicant needs to emphasize that: the dense coating process in the technical solution of this application can only act on the short sample, that is, the joint area, and cannot replace the conventional coating process to coat the protective layer of the entire long strip. Otherwise, the long strip is prone to the situation of low critical current, as Figure 8 shown. This is caused by the secondary effect brought by the dense coating - the residual stress of the protective layer. Under the action of the binding force of the inert gas, there will be additional stress extrusion inside the protective layer. When it is a short strip, the stress accumulation is insufficient, so there is no need to pay special attention. However, for a long strip of hundreds of meters, the internal stress accumulation is too large. If unfortunately the lower superconducting layer breaks, it will affect the superconducting performance in this area, and the macroscopic manifestation is the appearance of a low critical current at this point. The microscopic scan at the low point is as Fig. 9 shown.

[0044] In this embodiment, since the magnetron sputtering used will cause the superconducting layer to lack oxygen and degenerate into a non - superconducting tetragonal phase, it is necessary to perform annealing treatment again. The phase transition principle is as Fig.10 shown. Especially at the boundary between the corroded and uncorroded areas, the protective layer covered in this area is twice as thick as that of the primary annealing (see Fig.11 ). Oxygen needs to diffuse a longer distance to reach the superconducting layer. It is necessary to adopt an unconventional annealing method, that is, to experience a longer high - temperature annealing in oxygen than the conventional annealing to complete oxygen supplementation. It also needs to be unfolded and placed to ensure sufficient contact with oxygen. The effect after the unconventional annealing is as Fig.12 shown.

[0045] It should be emphasized that in this application, first, through the combination of chemical corrosion and magnetron sputtering, the defects deep in the silver layer of the defective joint area are eliminated, and then by changing the annealing process, the problem of oxygen deficiency in the superconducting layer at the boundary caused by the above operations is solved, and the defective products are successfully converted into qualified products. The results are as Fig.13As shown, significant economic losses were avoided (for example, CERN, the European Organization for Nuclear Research, requires that the joint resistance be less than 50nΩ. After remediation, the resistance of sample 2 was reduced from 157nΩ to 43nΩ, meeting the CERN delivery standard).

[0046] Embodiment 4 Based on Example 3, according to a method for reducing the resistance of a high-temperature superconducting tape joint provided by the present invention, according to a method for reducing the resistance of a high-temperature superconducting tape joint described in Example 3, this embodiment continuously tested several batches of high-temperature superconducting EuBa within 112 days. 2 Cu 3 O 7-δ The joint area at the end of the long strip is densely coated, and the joint resistance data measured in the first cycle are distributed as follows: Fig.14 As shown, the following steps are included: A 1:1 ratio of ammonia and hydrogen peroxide was used to make a corrosion solution, which was then soaked in the joint area of ​​the strip, with a joint length of 7 cm. After sufficient reaction, the strip was taken out and the residual solution was rinsed with alcohol. Using the coating parameters of 20 mTorr pressure, argon inert gas, and 70 sccm flow rate, a dense silver layer was plated on the corrosion area by a physical vapor deposition method using direct current magnetron sputtering; The re-silvered strip was annealed in oxygen at a high temperature of 500°C for 4 hours; After annealing, take out the strips and weld them together by direct contact between the silver layers. Then measure the joint resistance to determine whether they meet the order delivery standards. If it does not meet the requirements, the end welded joint area is cut off, and the remaining part of the long strip enters step S1 again until the end joint resistance is reduced to meet the standard.

[0047] The joint resistance of this application process is currently less than 40nΩ (336nΩ•cm 2 ) standard. It should be emphasized that this standard can be flexibly adjusted according to the requirements of recent orders.

[0048] This embodiment increases the coating pressure to ensure that the silver layer is dense and almost defect-free. A large-scale test lasting 100 days proves that before using this solution ( Fig.15 ) The connector resistance is less than 40nΩ (336nΩ•cm 2 ) ratio is 30.3%, while less than 25nΩ (210nΩ•cm 2 ) accounted for only 15.3%; but after using this solution ( Fig.13 ) The first cycle joint resistance is less than 40nΩ (336nΩ•cm 2) ratio reached an astonishing 98.4%, lower than 25nΩ (210nΩ•cm 2 ) ratio can reach 81.4%, which is enough to prove the effectiveness and repeatability of this method.

[0049] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0050] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for reducing the resistance of a high-temperature superconducting tape joint, characterized in that: The steps include: Step S1, coating the entire superconducting long strip with a protective layer and completing conventional superconducting annealing treatment; Step S2, measuring the joint resistance of the superconducting tape in step S1, and classifying the joint resistance into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Step S3, for superconducting tapes whose joint resistance does not meet the standard, removing the protective layer in the joint area of ​​the superconducting tape; Step S4, for the superconducting tape from which the protective layer of the joint area is removed in step S3, re-plating a dense protective layer on the joint area of ​​the superconducting tape; Step S5, performing unconventional superconducting annealing treatment on the superconducting tape re-plated with a dense protective layer in step S4; Step S6, measuring the joint resistance of the superconducting tape in step S5, and classifying the joint resistance into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; If the joint resistance of the superconducting tape in step S6 meets the joint resistance standard, the process ends; If the joint resistance of the superconducting tape in step S6 is not up to the standard, then steps S3, S4, S5 and S6 are repeated in sequence.

2. The method for reducing the resistance of a high temperature superconducting tape joint according to claim 1, characterized in that: In step S1, the material of the protective layer includes any one of platinum, silver, and gold; In step S4, the material of the dense protective layer includes any one of platinum, silver and gold.

3. The method for reducing the resistance of a high temperature superconducting tape joint according to claim 1, characterized in that: For the protective layer in step S1 and the dense protective layer in step S4, the joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard.

4. The method for reducing the resistance of a high temperature superconducting tape joint according to claim 1, characterized in that: The conventional superconducting annealing treatment in step S1 is a method for inducing the superconducting material in the newly formed superconducting layer to transform into a superconducting phase; the parameters are an annealing temperature of 400 to 600° C., a time of 1.5 to 4 hours, and the strip is placed in a coil; The unconventional superconducting annealing treatment in step S5 is a method for inducing the superconducting material in the superconducting layer at the boundary between the dense coating and the conventional coating to re-convert to the superconducting phase; the parameters are an annealing temperature of 400 to 800°C, a time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed.

5. The method for reducing the resistance of a high temperature superconducting tape joint according to claim 1, characterized in that: In step S3, the protective layer in the superconducting tape joint area is removed by chemical etching.

6. A system for reducing the resistance of a high temperature superconducting tape joint, characterized in that: For realizing the method for reducing the resistance of a high-temperature superconducting tape joint according to any one of claims 1 to 5, the system comprises: Module M1 is used to coat the entire superconducting strip with a protective layer and complete conventional superconducting annealing treatment; Module M2 is used to measure the joint resistance of the superconducting tape in module M1, and divides it into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Module M3 is used to remove the protective layer of the joint area of ​​the superconducting tape for the superconducting tape whose joint resistance does not meet the standard; Module M4 is used for re-plating a dense protective layer on the joint area of ​​the superconducting tape from which the protective layer of the joint area is removed in module M3; Module M5, used for performing unconventional annealing treatment on the superconducting tape re-plated with a dense protective layer in module M4; Module M6 is used to measure the joint resistance of the superconducting tape in module M5, and divide it into two categories: the joint resistance meets the standard and the joint resistance does not meet the standard; Module M7: If the joint resistance of the superconducting tape in module M6 is up to standard, the process ends; if the joint resistance of the superconducting tape in module M6 is not up to standard, repeat modules M3, M4, M5 and M6 in sequence.

7. The system for reducing the resistance of a high temperature superconducting tape joint according to claim 6, characterized in that: In module M1, the material of the protective layer includes any one of platinum, silver, and gold; In the module M4, the material of the dense protective layer includes any one of platinum, silver and gold.

8. The system for reducing the resistance of a high temperature superconducting tape joint according to claim 6, characterized in that: For the protective layer in the module M1 and the dense protective layer in the module M4, the joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard.

9. The system for reducing the resistance of a high temperature superconducting tape joint according to claim 6, characterized in that: Conventional superconducting annealing treatment in module M1 is a method for inducing the superconducting material in the newly formed superconducting layer to transform into a superconducting phase; the parameters are annealing temperature of 400 to 600°C, time of 1.5 to 4 hours, and the strip is placed in a coil; For the unconventional superconducting annealing treatment in module M5, a method is used to induce the superconducting material in the superconducting layer at the boundary between dense coating and conventional coating to re-convert into the superconducting phase; the parameters are annealing temperature of 400 to 800°C, time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed.

10. The system for reducing the resistance of a high temperature superconducting tape joint according to claim 6, characterized in that: The protective layer of the superconducting tape joint area in module M3 is removed by chemical etching.

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