A method for improving the stability of critical current testing of iron-based superconducting tapes
By forming a copper or gold additional layer on the surface of the iron-based superconducting tape, the thermal instability problem caused by the thin silver sheath was solved, the test stability and accuracy were improved, and the integrity and accuracy of the critical current test were ensured.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INST OF ELECTRICAL ENG CHINESE ACAD OF SCI
- Filing Date
- 2026-02-12
- Publication Date
- 2026-05-29
Smart Images
Figure CN122109947A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of superconducting material performance testing technology, specifically to a method for improving the stability of critical current testing of iron-based superconducting tapes. Background Technology
[0002] Since their discovery, iron-based superconducting materials have become a research hotspot in the field of practical superconducting materials due to their high superconducting transition temperature, superior high-field current-carrying capacity, and low anisotropy. After more than a decade of development, iron-based superconducting tapes have achieved significant breakthroughs in critical current density and length, marking a crucial step towards large-scale engineering applications. However, with continuous performance improvements, the fabrication process of iron-based superconducting tapes is increasingly favoring thinner silver-clad designs to enhance engineering current density, which brings new challenges to subsequent performance testing. During critical current testing, the thin silver layer is prone to thermal instability and early quench failure, leading to premature test interruption and failing to accurately reflect the material's true performance. Although various solutions exist to improve the mechanical or electromagnetic properties of superconducting tapes, such as enhancing the overall strength through multi-layer cladding structures or composite welded reinforcing layers, these improvements primarily focus on the long-term stability of the product under service conditions, rather than addressing transient thermal disturbances that occur during testing.
[0003] To meet the demands of extreme applications such as superconducting magnets, existing technologies have developed various solutions aimed at permanently enhancing the mechanical strength and operational stability of superconducting tapes. These solutions employ processes such as alloying, multilayer composite coating, and high-temperature thermal diffusion to form a reinforcing structure tightly bonded to the substrate within or on the tape during fabrication. These methods integrate the reinforcing layer as an integral part of the product, aiming to improve tape performance throughout its entire service life. Therefore, these processes are complex and costly, and their strengthening effect is deeply tied to the material preparation process. However, none of the existing technologies provide a solution specifically for "finished product testing" scenarios. Summary of the Invention
[0004] This invention provides a method to improve the stability of critical current testing for iron-based superconducting tapes, in order to solve the problem that critical current testing of silver-clad iron-based superconducting tapes that have completed final sintering is prone to inaccurate results.
[0005] In a first aspect, the present invention provides a method for improving the stability of critical current testing of iron-based superconducting tapes, comprising the following steps:
[0006] Obtain silver-clad iron-based superconducting tape that has completed final sintering; Before conducting critical transport current tests on the silver-clad iron-based superconducting tape that has undergone final sintering, an additional metal layer is formed on its surface; wherein the additional metal layer is made of at least one of copper and gold. In practical applications, copper, which is inexpensive and has excellent overall performance, is preferred as the coating material, while gold, although possessing excellent thermal and electrical conductivity, has limited its large-scale application due to its high cost.
[0007] In one alternative embodiment, the iron-based superconducting tape includes, but is not limited to, Ba. 0.6 K 0.4 Fe2As2 iron-based superconducting tape; In one optional embodiment, the final sintering conditions are a holding time of 600°C to 900°C for 0.1 to 5 hours. As an example, the final sintering temperature is 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or any range of these values (e.g., 700°C to 850°C); the holding time is 0.1 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or any range of these values (e.g., 1 hour to 4 hours).
[0008] In one alternative implementation, the additional metal layer is made of copper.
[0009] In one alternative embodiment, the thickness of the additional metal layer is 10 μm to 50 μm. As an example, the thickness of the additional metal layer is 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or within any of the above values (e.g., 15 μm to 25 μm).
[0010] In one alternative embodiment, the thickness of the additional metal layer is 15 μm to 25 μm.
[0011] In one alternative embodiment, before forming the additional metal layer, a step of cleaning the surface of the silver-clad iron-based superconducting tape is included.
[0012] In one optional embodiment, the cleaning process includes sequential organic solvent cleaning and acid washing steps. Specifically, the organic solvent cleaning uses at least one of acetone, ethanol, or isopropanol, and the ultrasonic cleaning time is 5-15 minutes; the acid washing uses dilute nitric acid, dilute sulfuric acid, or dilute hydrochloric acid solution, and the acid washing time is 10-60 seconds. After acid washing, the solution must be thoroughly rinsed with deionized water and dried.
[0013] In one alternative embodiment, the additional metal layer is formed by electroplating or electroless plating. Specifically, electroplating may use at least one electroplating solution selected from copper sulfate, copper pyrophosphate, or copper sulfamate systems; electroless plating may use electroless copper plating or electroless gold plating processes. During the plating process, the process parameters of electroplating or electroless plating (such as current density, temperature, time, and plating solution composition) can be conventionally adjusted according to the material and thickness of the required additional metal layer.
[0014] In one alternative embodiment, when forming the additional metal layer by electroplating, the electroplating current density is 1~5 A / dm². 2 As an example, the electroplating current density is 1.0 A / dm³. 2 1.5A / dm 2 2.0A / dm 2 2.5A / dm 2 3.0A / dm 2 3.5A / dm 2 4.0A / dm 2 4.5A / dm 2 5.0A / dm 2 or within any of the above values (e.g., 1~3 A / dm). 2 2~4A / dm 2 ).
[0015] In one alternative embodiment, when forming the additional metal layer using chemical plating, the plating bath temperature is 10~70°C. As an example, the plating bath temperature is 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, or within any range of the above values (e.g., 20~50°C, 30~60°C).
[0016] In one optional embodiment, the critical transmission current test is a standard four-lead method test. Preferably, the test conditions are: cooling to 4.2K in a liquid helium bath, and increasing the DC current at a constant rate of 200A / min under a background magnetic field parallel (or perpendicular) to the strip surface. A nanovoltmeter (sensitivity 100nV) is used to monitor the potential difference between the two voltage leads of the strip. When the potential difference reaches the criterion of 1μV / cm, the corresponding current value is the critical transmission current (Ic).
[0017] The technical solution of this invention has the following advantages: A method for improving the stability of critical current testing of iron-based superconducting tapes includes the following steps: obtaining a silver-clad iron-based superconducting tape that has undergone final sintering; forming an additional metal layer on the surface of the silver-clad iron-based superconducting tape before conducting a critical current test; wherein the additional metal layer is made of at least one of copper and gold. This invention solves the technical problem of insufficient heat capacity in thin silver-clad iron-based superconducting tapes leading to localized overheating under high current testing, resulting in early thermal runaway and test interruption, by forming an additional metal layer of copper or gold on the surface of the silver-clad iron-based superconducting tape before conducting a critical current test. This additional metal layer effectively enhances heat diffusion and current shunting capabilities during the test process, thereby significantly improving the thermal stability of the test system without altering the intrinsic structure of the material, ensuring that the critical current test can be conducted to the material's true performance limit, and ultimately accurately obtaining its critical current value. Attached Figure Description
[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0019] Figure 1 This is a schematic diagram of the process of forming an additional metal layer on the surface of an iron-based superconducting tape using electroplating in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the iron-based superconducting tape coated with a copper layer in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the outer surface of the iron-based superconducting tape coated with a copper layer in Embodiment 1 of the present invention; Figure 4 This is a comparison chart showing the results of critical transport current tests performed on the copper-plated iron-based superconducting tape sample in Example 1 and the unplated iron-based superconducting tape sample in Comparative Example 1. Detailed Implementation
[0020] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.
[0021] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.
[0022] Example 1 This embodiment provides a method for improving the stability of critical current testing of iron-based superconducting tapes. The specific steps are as follows: (1) Obtaining silver-clad iron-based superconducting tapes that have completed final sintering: Provide silver-clad Ba... 0.6 K 0.4 The Fe2As2 iron-based superconducting tape has a total thickness of approximately 0.3 mm and a width of approximately 4.5 mm. The tape has undergone final sintering under an argon protective atmosphere, with a sintering temperature of 750°C for 3 hours.
[0023] (2) Cleaning treatment: The silver-clad iron-based superconducting tape that has undergone final sintering was immersed in an ultrasonic cleaning tank containing analytical grade acetone and ultrasonically cleaned for 10 minutes at a frequency of 40 kHz and a power of 100 W. After removal, it was allowed to air dry naturally. Subsequently, the tape was immersed in a dilute nitric acid solution prepared by mixing deionized water and concentrated nitric acid at a volume ratio of 10:1 and immersed for 30 seconds at room temperature for surface activation. After removal, it was rinsed 3 times with deionized water and dried in an oven at 80 ℃ for 30 minutes.
[0024] (3) Forming an additional metal layer: A copper layer is plated onto the surface of the strip using electroplating, as shown in the schematic diagram. Figure 1 As shown. The specific operation is as follows: Prepare the electroplating solution, containing 250g copper sulfate pentahydrate, 50g concentrated sulfuric acid, and 0.05g sodium dodecyl sulfate per liter of solution as a brightener. Use the cleaned strip as the cathode and the pure copper plate as the anode, suspending them in the electroplating solution, maintaining a cathode to anode area ratio of approximately 1:2 and an electrode spacing of approximately 8cm. Control the electroplating solution temperature at 25℃, and under stirring conditions (200r / min), use 2.5A / dm³. 2 Electroplating was performed at a constant current density for 15 minutes. After electroplating, the strip was removed, rinsed with deionized water, and dried in an 80℃ oven for 30 minutes. The coating thickness was measured to be 22 μm using a metallographic microscope. The cross-sectional structure and outer surface condition of the coated strip are shown in the figures below. Figure 2 and Figure 3 As shown.
[0025] (4) Critical Transport Current Test: The four-lead method was used, and the above-mentioned tape sample was placed in a low-temperature high magnetic field testing system. The test conditions were: liquid helium bath cooled to 4.2K, and a DC current was increased at a constant rate of 200A / min under a background magnetic field of 10T perpendicular to the tape surface. A nanovoltmeter (sensitivity 100nV) was used to monitor the potential difference between the two voltage leads of the tape. When the potential difference reached the criterion of 1μV / cm, the corresponding current value was the critical transport current (Ic). The complete voltage-current (VI) curve was recorded simultaneously. The critical transport current test results of this embodiment are as follows: Figure 4 As shown. According to Figure 4 It can be seen that its voltage-current curve exhibits typical superconducting transition behavior: in the low current region, the voltage maintains the background noise level (<100nV); after the current rises to about 300A, a detectable voltage rise begins to appear; when the current reaches 330A, the voltage reaches the criterion value of 1μV / cm, based on which the critical transport current Ic is determined to be 330A.
[0026] Example 2 This embodiment provides a method for improving the stability of critical current testing of iron-based superconducting tapes. The specific steps are as follows: (1) Obtaining silver-clad iron-based superconducting tapes that have completed final sintering: Provide silver-clad Ba... 0.6 K 0.4 The Fe2As2 iron-based superconducting tape has a total thickness of approximately 0.3 mm and a width of approximately 4.5 mm. The tape has undergone final sintering under an argon protective atmosphere, with a sintering temperature of 600°C for 5 hours.
[0027] (2) Cleaning treatment: The silver-clad iron-based superconducting tape that has undergone final sintering was immersed in an ultrasonic cleaning tank containing analytical grade acetone and ultrasonically cleaned for 10 minutes at a frequency of 40 kHz and a power of 100 W. After removal, it was allowed to air dry naturally. Subsequently, the tape was immersed in a dilute nitric acid solution prepared by mixing deionized water and concentrated nitric acid at a volume ratio of 10:1 and immersed for 30 seconds at room temperature for surface activation. After removal, it was rinsed 3 times with deionized water and dried in an oven at 80 ℃ for 30 minutes.
[0028] (3) Forming an additional metal layer: A copper layer is plated onto the surface of the strip using electroplating, as shown in the schematic diagram. Figure 1 As shown. The specific operation is as follows: Prepare the electroplating solution, containing 250g copper sulfate pentahydrate, 50g concentrated sulfuric acid, and 0.05g sodium dodecyl sulfate per liter of solution as a brightener. Use the cleaned strip as the cathode and the pure copper plate as the anode, suspending them in the electroplating solution, maintaining a cathode to anode area ratio of approximately 1:2 and an electrode spacing of approximately 8cm. Control the electroplating solution temperature at 10℃, and under stirring conditions (200r / min), use 5A / dm³. 2Electroplating was performed at a constant current density for 8 minutes. After electroplating, the strip was removed, rinsed with deionized water, and dried in an 80℃ oven for 30 minutes. The coating thickness was measured to be 10 μm using a metallographic microscope.
[0029] (4) Critical Transport Current Test: The four-lead method was used, and the above-mentioned tape sample was placed in a low-temperature high magnetic field testing system. The test conditions were: cooling to 4.2K in a liquid helium bath, and increasing the DC current at a constant rate of 200A / min under a background magnetic field of 10T perpendicular to the tape surface. A nanovoltmeter (sensitivity 100nV) was used to monitor the potential difference between the two voltage leads of the tape. When the potential difference reached the criterion of 1μV / cm, the corresponding current value was the critical transport current (Ic). In this embodiment, the critical transport current Ic was measured to be 309A.
[0030] Example 3 This embodiment provides a method for improving the stability of critical current testing of iron-based superconducting tapes. The specific steps are as follows: (1) Obtaining silver-clad iron-based superconducting tapes that have completed final sintering: Provide silver-clad Ba... 0.6 K 0.4 The Fe2As2 iron-based superconducting tape has a total thickness of approximately 0.3 mm and a width of approximately 4.5 mm. The tape has undergone final sintering under an argon protective atmosphere, with a sintering temperature of 900°C for 6 minutes.
[0031] (2) Cleaning treatment: The silver-clad iron-based superconducting tape that has undergone final sintering was immersed in an ultrasonic cleaning tank containing analytical grade acetone and ultrasonically cleaned for 10 minutes at a frequency of 40 kHz and a power of 100 W. After removal, it was allowed to air dry naturally. Subsequently, the tape was immersed in a dilute nitric acid solution prepared by mixing deionized water and concentrated nitric acid at a volume ratio of 10:1 and immersed for 30 seconds at room temperature for surface activation. After removal, it was rinsed 3 times with deionized water and dried in an oven at 80 ℃ for 30 minutes.
[0032] (3) Forming an additional metal layer: A copper layer is plated onto the surface of the strip using electroplating, as shown in the schematic diagram. Figure 1 As shown. The specific operation is as follows: Prepare the electroplating solution, containing 250g copper sulfate pentahydrate, 50g concentrated sulfuric acid, and 0.05g sodium dodecyl sulfate per liter of solution as a brightener. Use the cleaned strip as the cathode and the pure copper plate as the anode, suspending them in the electroplating solution, maintaining a cathode to anode area ratio of approximately 1:2 and an electrode spacing of approximately 8cm. Control the electroplating solution temperature at 70℃, and under stirring conditions (200r / min), use 1A / dm³. 2 Electroplating was performed at a constant current density for 60 minutes. After electroplating, the strip was removed, rinsed with deionized water, and dried in an 80℃ oven for 30 minutes. The coating thickness was measured to be 25 μm using a metallographic microscope.
[0033] (4) Critical Transport Current Test: The four-lead method was used, and the above-mentioned tape sample was placed in a low-temperature high magnetic field testing system. The test conditions were: cooling to 4.2K in a liquid helium bath, and increasing the DC current at a constant rate of 200A / min under a background magnetic field of 10T perpendicular to the tape surface. A nanovoltmeter (sensitivity 100nV) was used to monitor the potential difference between the two voltage leads of the tape. When the potential difference reached the criterion of 1μV / cm, the corresponding current value was the critical transport current (Ic). In this embodiment, the critical transport current Ic was measured to be 327A.
[0034] Comparative Example 1 This comparative example provides a method for testing the stability of the critical current of an iron-based superconducting tape. The only difference between this method and Example 1 is that steps (2) and (3) are not performed, i.e., no cleaning or plating treatment is performed on the surface. Other conditions are the same as in Example 1.
[0035] The critical transmission current test results of this comparative example are as follows: Figure 4 As shown. According to Figure 4 It can be seen that when the current of the uncoated sample in this comparative example increases to about 260A, the voltage signal jumps sharply from the background noise level to more than 10mV within a few seconds, exhibiting typical quench characteristics. The test system automatically cuts off the current, and the complete superconducting transition curve cannot be obtained. Therefore, the true critical transport current value cannot be measured.
[0036] Comparative Example 2 This comparative example provides a method for testing the critical current stability of iron-based superconducting tapes. The only difference between this method and Example 1 is the material of the additional metal layer. Specifically, in step (3), copper is not used as the additional metal layer; instead, the same process conditions are applied (the electroplating solution is a nickel sulfamate system, and the current density is 2.5 A / dm³). 2 (Time: 15 minutes) A nickel layer with a thickness of approximately 22 μm was plated onto the cleaned silver-clad strip surface. Nickel has significantly lower room temperature thermal conductivity (approximately 90 W / (m·K)) and electrical conductivity than copper. Other steps and conditions were the same as in Example 1.
[0037] Critical transport current (CRT) testing revealed that while the nickel-plated sample did not experience early quenching near 260 A, its complete superconducting transition curve showed that the voltage reached the criterion value of 1 μV / cm when the current reached approximately 276 A, indicating a CRT Ic of approximately 276 A. This value is higher than the unplated sample in Comparative Example 1 (<260 A), but significantly lower than the copper-plated sample in Example 1 (330 A). This indicates that while using a metal with insufficient thermal and electrical conductivity (such as nickel) as an additional layer can provide some mechanical support and partially improve heat dissipation, it cannot fully utilize the true current-carrying potential of the strip due to the inability to achieve efficient heat dissipation and current shunting, thus limiting the improvement in test stability and accuracy.
[0038] Comparative Example 3 This comparative example provides a method for testing the critical current stability of a superconducting tape, differing from Example 1 only in the substrate material. Specifically, instead of using an iron-based superconducting tape, a second-generation yttrium barium copper oxide high-temperature superconducting tape with a silver stabilizing layer and fully fabricated is provided. This tape exhibits a typical REBCO-coated conductor structure, with a total thickness of approximately 100 μm and a width of approximately 4 mm. Under the exact same conditions as in Example 1 (including cleaning, copper plating process and thickness (22 μm), and standard four-lead method testing at 4.2 K and 10 T), the critical transport current of this copper-plated second-generation high-temperature superconducting tape sample was tested.
[0039] The following control group was also included in this comparative example: Second-generation high-temperature superconducting tapes of the same batch and specifications were taken and subjected to critical transport current tests under identical test conditions without any plating treatment.
[0040] Tests revealed that the critical transport current (CVT) of the copper-plated second-generation high-temperature superconducting tape sample was 154 A, while that of the unplated sample from the same batch was 151 A, with the difference falling within the measurement error range. Although the added copper layer had no adverse effect on the testing process, no significant increase in the CVT was observed compared to the unplated version. This is presumably because the tape itself has a sufficiently thick baseband and silver layer as a heat sink, and the testing bottleneck primarily stems from the intrinsic pinning characteristics or grain boundary connectivity within the material.
[0041] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A method for improving the stability of critical current testing of iron-based superconducting tapes, characterized in that, Includes the following steps: Obtain silver-clad iron-based superconducting tape that has completed final sintering; Before conducting the critical transport current test on the silver-clad iron-based superconducting tape that has completed final sintering, an additional metal layer is formed on its surface; wherein the material of the additional metal layer is at least one of copper and gold.
2. The method according to claim 1, characterized in that, The additional metal layer is made of copper.
3. The method according to claim 1 or 2, characterized in that, The thickness of the additional metal layer is 10μm to 50μm.
4. The method according to claim 3, characterized in that, The thickness of the additional metal layer is 15μm~25μm.
5. The method according to claim 1 or 2, characterized in that, Before forming the additional metal layer, the process also includes a step of cleaning the surface of the silver-clad iron-based superconducting tape.
6. The method according to claim 5, characterized in that, The cleaning process includes sequential organic solvent cleaning and acid washing steps.
7. The method according to claim 1 or 2, characterized in that, The additional metal layer is formed by electroplating or chemical plating.
8. The method according to claim 7, characterized in that, When forming the additional metal layer by electroplating, the electroplating current density is 1~5 A / dm. 2 .
9. The method according to claim 7, characterized in that, When forming an additional metal layer using chemical plating, the plating bath temperature is 10~70℃.
10. The method according to claim 1 or 2, characterized in that, The critical transmission current test is performed using the four-lead method.