A method for evaluating the effect of epoxy resin impregnation on superconducting tape properties

Abstract

The present invention relates to the technical field of superconducting tape performance evaluation and discloses a method for evaluating the effect of epoxy resin impregnation on superconducting tape performance, comprising the following steps: performing a critical current test on the superconducting tape body; completely immersing the superconducting tape body in epoxy resin and allowing the epoxy resin to cure on the surface of the superconducting tape body; cooling the superconducting tape impregnated with epoxy resin to below a critical temperature, performing a critical current test on the superconducting tape impregnated with epoxy resin, and returning the superconducting tape impregnated with epoxy resin to room temperature after the critical current test; etching a stabilizing layer on the surface of the superconducting tape to expose a superconducting layer of the superconducting tape, and observing the superconducting layer under an electron microscope. The critical current of the superconducting tape body before and after epoxy resin impregnation and curing is compared and analyzed to characterize the extent of performance degradation, and the surface morphology of the superconducting layer is observed under an electron microscope to quantitatively correlate the surface morphology of the superconducting layer with the extent of degradation of the superconducting tape body.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting tape performance evaluation, and in particular to a method for evaluating the influence of epoxy resin impregnation on superconducting tape performance. Background Art

[0002] High-temperature superconductors have a wide range of applications, encompassing industry, power systems, motors, healthcare, high-energy physics, transportation, aerospace, and the military. High-voltage applications primarily involve high currents and high magnetic fields. Specific products include high-temperature superconducting fault current limiters, energy storage devices, transformers, generators, nuclear magnetic resonance (NMR) devices, magnetic separation equipment, motors, magnetic levitation, cables, current leads, induction heating, high-energy accelerators, electromagnetic catapult systems, electromagnetic guns, engines, and π-dielectric generators. Among these applications, coils made from high-temperature superconducting tape are the most common.

[0003] In high-temperature superconducting tape coils, epoxy resin is often used to cure the coils to improve the mechanical properties, insulation properties, and thermal conductivity of the superconducting magnet. Due to the multi-layer structure of the superconducting tape, its mechanical strength exhibits significant anisotropy. During the cooling and curing process of the epoxy resin coated on the surface of the superconducting tape, stress concentration occurs between the layers of the tape due to the different cooling shrinkage rates of the various layers. The epoxy resin's cooling shrinkage rate is much greater than that of the superconducting tape, exacerbating the stress concentration and resulting in significant internal stress in the superconducting magnet after the epoxy resin cures.

[0004] When the internal stress in a superconducting magnet exceeds its tolerance, it damages the superconducting layer that transmits current, resulting in a degradation of the superconducting magnet's critical current. Existing research on superconducting tape performance has limited its critical current testing to tests or comparisons of the critical current of superconducting coils before and after epoxy resin impregnation and curing. These studies fail to effectively characterize the extent of tape performance degradation caused by epoxy resin curing. Summary of the Invention

[0005] In view of this, the present invention provides a method for evaluating the effect of epoxy resin impregnation on the performance of superconducting tapes, so as to solve the problem that the performance test of superconducting tapes in the prior art cannot characterize the extent of degradation of superconducting tape performance caused by epoxy resin curing.

[0006] In a first aspect, the present invention provides a method for evaluating the effect of epoxy resin impregnation on the performance of a superconducting tape, comprising the following steps:

[0007] Conduct critical current testing on the superconducting tape body;

[0008] completely immersing the superconducting tape body into the epoxy resin and allowing the epoxy resin to solidify on the surface of the superconducting tape body;

[0009] Cooling the superconducting tape with epoxy resin to below the critical temperature, performing a critical current test on the superconducting tape with epoxy resin, and returning the superconducting tape with epoxy resin to room temperature after the critical current test is completed;

[0010] The stabilizing layer on the surface of the superconducting tape is corroded to expose the superconducting layer of the superconducting tape, and the superconducting layer is observed by electron microscopy.

[0011] By measuring the critical current of the superconducting tape body before and after epoxy resin impregnation and curing, and comparing and analyzing the critical current of the superconducting tape body before and after epoxy resin impregnation and curing, the performance degradation amplitude of the superconducting tape body is characterized. The surface morphology of the superconducting layer is observed by electron microscopy, so that the surface morphology of the superconducting layer and the critical current degradation amplitude of the superconducting tape body are quantitatively corresponded, which further guides the improvement direction of epoxy resin and thus avoids the performance degradation of superconducting magnets to a certain extent.

[0012] In an optional embodiment, before the step of corroding the stabilization layer on the surface of the superconducting tape, the step of cooling the superconducting tape to below the critical temperature and performing a critical current test and then returning the superconducting tape to room temperature is repeated multiple times.

[0013] By repeatedly lowering the temperature of the superconducting tape to below the critical temperature and then reheating it, the actual working environment of the superconducting tape is simulated, and the critical current of the superconducting tape below the critical temperature is tested multiple times. By comparing the critical current of the superconducting tape after each cooling, it is used to characterize the current degradation amplitude of the superconducting tape body working in the epoxy resin coating environment, thereby improving the accuracy of the quantitative data of the performance degradation amplitude of the superconducting tape body.

[0014] In an optional embodiment, the step of completely immersing the superconducting tape body into the epoxy resin includes:

[0015] Taking an impregnation mold tank, and opening through-holes on opposite sides of the impregnation mold tank, wherein the shape of the through-holes matches the cross-sectional shape of the superconducting tape body perpendicular to the extension direction;

[0016] The superconducting tape body is passed through the impregnation mold tank from the two through-holes, and epoxy resin is poured into the impregnation mold tank.

[0017] In an optional embodiment, before pouring the epoxy resin into the impregnation mold tank, the method further includes: arranging a fiber grating sensor on the upper surface of the superconducting tape body, wherein the fiber grating sensor records the strain of the superconducting tape body in real time.

[0018] By recording the strain of the superconducting tape body in real time, the internal stress and strain of the superconducting tape body caused by the curing of the epoxy resin are measured. The residual strain and cooling shrinkage inside the superconducting tape body caused by the curing of the epoxy resin are corresponded to the degradation amplitude of the critical current. The amplitude of the critical current degradation of the superconducting tape body is quantified and corresponds to the internal stress and strain of the superconducting tape body caused by the curing of the epoxy resin, which further guides the improvement direction of the epoxy resin and thus avoids the performance degradation of the superconducting magnet to a certain extent.

[0019] In an optional embodiment, the step of pouring the epoxy resin into the impregnation mold includes preheating the impregnation mold containing the superconducting tape body. This ensures that the temperature of the superconducting tape body is relatively high when the epoxy resin is poured into the impregnation mold, allowing the epoxy resin to cure from the inside out, ensuring uniform curing and reducing internal stress caused by the curing process.

[0020] In an optional embodiment, the step of curing the epoxy resin on the surface of the superconducting tape body includes:

[0021] After the epoxy resin is poured into the impregnation mold tank, the temperature of the impregnation mold tank is raised to the curing temperature and kept warm to cure the epoxy resin.

[0022] In an optional embodiment, the impregnation mold tank is a silicone mold. The silicone mold has a flexible edge and will not scratch the superconducting tape. The non-sticky nature of the silicone mold facilitates demoulding after the epoxy resin is cured.

[0023] In an optional embodiment, the step of performing a critical current test on the superconducting tape body includes: fixing a voltage collection lead at each end of the superconducting tape body to be tested, performing a critical current test using a four-lead method, and defining the current value corresponding to the voltage rising to 1 μV / cm as the critical current.

[0024] In an optional embodiment, when the observed current value reaches the critical current, the power supply to the superconducting tape body is stopped to avoid critical current degradation caused by quench of the superconducting tape body.

[0025] In an optional embodiment, the electron microscopy observation is scanning electron microscopy observation, transmission electron microscopy observation, scanning tunneling microscopy observation, or atomic force microscopy observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A schematic structural diagram of an impregnation mold tank provided in an embodiment of the present invention.

[0028] Figure 2 The critical current degradation curves of four epoxy resin coated superconducting tape bodies after five thermal cycles.

[0029] Figure 3 The residual strain curves of four epoxy resin-coated superconducting tape bodies during five thermal cycles.

[0030] Figure 4 This is a surface morphology of the superconducting layer of the superconducting tape body covered with epoxy resin B.

[0031] Figure 5 This is a surface morphology of the superconducting layer of the superconducting tape body covered with epoxy resin A.

[0032] Explanation of the accompanying symbols: 1. superconducting tape body; 2. impregnation mold tank; 3. fiber Bragg grating sensor; 4. voltage collection lead. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0034] The following combination Figures 1 to 5 , describing embodiments of the present invention.

[0035] According to an embodiment of the present invention, on the one hand, a method for evaluating the effect of epoxy resin impregnation on the performance of a superconducting tape is provided, comprising the following steps: first, performing a critical current test on the superconducting tape body 1. Then, the superconducting tape body 1 is completely immersed in epoxy resin, and the epoxy resin is allowed to solidify on the surface of the superconducting tape body 1. Next, the superconducting tape with epoxy resin is cooled to below the critical temperature, and a critical current test is performed on the superconducting tape with epoxy resin. After the critical current test is completed, the superconducting tape with epoxy resin is warmed to room temperature. Finally, the stabilizing layer on the surface of the superconducting tape is corroded to expose the superconducting layer of the superconducting tape, and the superconducting layer is observed under an electron microscope.

[0036] By measuring the critical current of the superconducting tape body 1 before and after epoxy resin impregnation and curing, and comparing and analyzing the critical current of the superconducting tape body 1 before and after epoxy resin impregnation and curing, the performance degradation amplitude of the superconducting tape body 1 is characterized. The surface morphology of the superconducting layer is observed by electron microscopy, so that the surface morphology of the superconducting layer and the critical current degradation amplitude of the superconducting tape body 1 are quantitatively corresponded, further guiding the improvement direction of the epoxy resin, and thus avoiding the performance degradation of the superconducting magnet to a certain extent.

[0037] In one embodiment, the critical current test step for the superconducting tape body 1 includes: fixing a voltage collection lead 4 at each end of the region to be tested of the superconducting tape body 1, performing a critical current test using a four-lead method, and defining the current value corresponding to the voltage rising to 1 μV / cm as the critical current. Specifically, the critical current of the superconducting tape body 1 that has not been cured with epoxy resin is first measured. A section of the superconducting tape body 1 is cut to a length slightly longer than the length of the test device, the region to be tested for electrical properties is determined, and two voltage collection leads 4 are soldered to both ends of the region using low-temperature solder with a melting point below 200°C. To avoid critical current degradation caused by quenching of the superconducting tape body 1, power to the superconducting tape body 1 is stopped when the current value reaches the critical current.

[0038] In one embodiment, the step of completely immersing the superconducting tape body 1 in the epoxy resin includes: taking an impregnation mold tank 2, and opening through holes on opposite sides of the impregnation mold tank 2, wherein the shape of the through holes matches the cross-sectional shape of the superconducting tape body 1 perpendicular to the extension direction; passing the superconducting tape body 1 through the two through holes through the impregnation mold tank 2, and pouring epoxy resin into the impregnation mold tank 2, as shown in FIG. Figure 1 shown.

[0039] Specifically, prepare a rectangular impregnation mold tank 2 of appropriate size, and cut slits on both sides of it that are equal to the width of the tape as through-holes. The slits should be just wide enough for the tape to pass through, but not too large to prevent the resin from being exposed. The height of the slit from the bottom of the mold is determined by the required resin thickness. Pass the reheated superconducting tape body 1 through the through-holes on both sides of the impregnation mold tank 2. During operation, do not remove the voltage collection lead 4. Place the superconducting tape body 1 from the center of the impregnation mold tank 2, and pass the two sides through the through-holes outward. Be careful not to excessively bend the superconducting tape body 1 during the process.

[0040] In one embodiment, before pouring the epoxy resin into the impregnation mold tank 2 , the method further includes: arranging a fiber Bragg grating sensor 3 on the upper surface of the superconducting tape body 1 , and the fiber Bragg grating sensor 3 records the strain of the superconducting tape body 1 in real time.

[0041] The prepared optical fiber sensors are passed through the through-holes on both sides of the impregnation mold tank 2 above the superconducting tape body 1, with the optical fiber sensors in close contact with the upper surface of the superconducting tape body 1. One or more optical fiber Bragg grating sensors 3 can be distributed to measure the strain distribution along the extension direction of the superconducting tape body 1. In this embodiment, three optical fiber Bragg grating sensors 3 are arranged on the superconducting tape body 1. By recording the strain of the superconducting tape body 1 in real time, the internal stress and strain of the superconducting tape body 1 caused by epoxy resin curing are measured. The residual strain and cooling shrinkage caused by epoxy resin curing are correlated with the degradation of critical current. The degradation of critical current of the superconducting tape body 1 is quantified and correlated with the internal stress and strain caused by epoxy resin curing. This provides guidance for epoxy resin improvement and, to a certain extent, prevents the performance degradation of superconducting magnets.

[0042] In one embodiment, before pouring the epoxy resin into the impregnation mold 2, the step includes preheating the impregnation mold 2 containing the superconducting tape body 1. The impregnation mold 2 containing the superconducting tape body 1 is placed in an oven, with both ends of the superconducting tape drawn out of the oven top and connected to a demodulator. The oven is preheated to the epoxy resin impregnation temperature. This ensures that when the epoxy resin is subsequently poured into the impregnation mold 2, the temperature of the superconducting tape body 1 is at a relatively high level, allowing the epoxy resin to cure from the inside out, ensuring uniformity during the epoxy resin curing process and reducing internal stress caused by the epoxy resin curing process.

[0043] In this embodiment, the impregnation mold tank 2 is made of silicone material. The silicone mold has a flexible edge and will not scratch the superconducting tape. It is also non-adhesive and easy to demould after the epoxy resin is cured.

[0044] In one embodiment, the step of curing the epoxy resin on the surface of the superconducting tape body 1 includes: pouring the epoxy resin into the impregnation mold tank 2, heating the impregnation mold tank 2 to a curing temperature and maintaining the temperature to cure the epoxy resin.

[0045] Specifically, epoxy resin is prepared in a flask according to the component ratio. The flask is placed in a magnetic stirrer for heating and stirring, and a vacuum pump is connected to degas the epoxy resin colloid. The prepared and evenly stirred epoxy resin is poured into the installed impregnation mold tank 2, and it is ensured that the epoxy resin covers the superconducting tape body 1 and the fiber grating sensor 3. The height of the epoxy resin exceeding the superconducting tape body 1 is determined by the required epoxy resin thickness. The oven heating program is set, the resin begins to solidify, and the fiber grating sensor 3 records the strain of the superconducting tape body 1 in real time.

[0046] In one embodiment, before the step of etching the stabilization layer on the surface of the superconducting tape, the steps of cooling the superconducting tape to below the critical temperature, performing a critical current test, and then returning the superconducting tape to room temperature are repeated multiple times.

[0047] Specifically, a critical current test is performed on the superconducting tape after the epoxy resin is cured. The silicone impregnation mold tank 2 is cut open to complete the demolding. During the process, care must be taken not to damage the superconducting tape and the fiber grating sensor 3. The temperature of the superconducting tape is lowered to below the critical temperature. For high-temperature superconducting tapes, the sample is immersed in liquid nitrogen. During the cooling process, the fiber grating sensor 3 records the internal strain in real time. The critical current test is performed using the four-lead method. After the measurement, the sample is warmed to room temperature and then placed in liquid nitrogen for testing, completing a thermal cycle. A total of several thermal cycles are performed and the critical current is measured.

[0048] In this embodiment, four different epoxy resins are used to coat the same superconducting tape. The critical current degradation of the superconducting tape bodies 1 coated with the four epoxy resins after five thermal cycles is shown in FIG. Figure 2 As shown in the figure, the sum of the residual strain of the four epoxy resin coated superconducting tape bodies 1 during the five thermal cycles and the strain value of the five cooling times to 77K is shown in the figure. Figure 3 As shown in the figure, Epoxy Resins B and C show almost no degradation, suggesting that total strains of approximately 3000 με or less will not affect the strip. Epoxy Resins A and D, on the other hand, degraded by 52.5 A and 35.13 A, respectively. Corresponding to the strain, the greater the strain, the greater the degradation. It can be inferred that total strains above 10000 με will cause degradation of the strip's critical current, and that greater strains will cause greater damage and greater critical current attenuation.

[0049] By repeatedly lowering the temperature of the superconducting tape to below the critical temperature and then reheating it, the actual working environment of the superconducting tape is simulated, and the critical current of the superconducting tape below the critical temperature is tested multiple times. By comparing the critical current of the superconducting tape after each cooling, it is used to characterize the current degradation amplitude of the superconducting tape body 1 working in the epoxy resin coating environment, thereby improving the accuracy of the quantitative data of the performance degradation amplitude of the superconducting tape body 1.

[0050] The electron microscope observation step can be scanning electron microscope observation, transmission electron microscope observation, scanning tunneling microscope observation, or atomic force microscope observation. In this embodiment, scanning electron microscope observation is selected. Figure 4 As shown in FIG, the surface morphology of the superconducting layer of the superconducting tape body 1 covered with epoxy resin B with no degradation of critical current after the evaluation step is magnified to 650 times, 2000 times, 6500 times and 35000 times. Figure 5 The following images show the surface topography of the superconducting layer of a superconducting tape body 1 coated with epoxy resin A, exhibiting severe critical current degradation, at magnifications of 650x, 2000x, 6500x, and 35,000x. Comparing the superconducting layer topography reveals obvious cracks in the severely degraded superconducting tape.

[0051] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for evaluating the effect of epoxy resin impregnation on superconducting tape performance, characterized in that: The following steps are involved: Performing a critical current test on the superconducting tape body (1); A fiber Bragg grating sensor (3) is arranged on the upper surface of the superconducting tape body (1), and the fiber Bragg grating sensor (3) records the strain of the superconducting tape body (1) in real time. Then, the superconducting tape body (1) is completely immersed in epoxy resin, and the epoxy resin is solidified on the surface of the superconducting tape body (1); Cooling the superconducting tape with epoxy resin to below the critical temperature, performing a critical current test on the superconducting tape with epoxy resin, and returning the superconducting tape with epoxy resin to room temperature after the critical current test is completed; The superconducting tape is cooled to below the critical temperature and tested for critical current multiple times, and then the superconducting tape is heated to room temperature. The stabilizing layer on the surface of the superconducting tape is corroded to expose the superconducting layer of the superconducting tape. The superconducting layer is observed under an electron microscope to quantitatively correspond the surface morphology of the superconducting layer to the critical current degradation amplitude of the superconducting tape body. The residual strain and cooling shrinkage inside the superconducting tape body caused by the curing of the epoxy resin are corresponded to the degradation amplitude of the critical current. The amplitude of the critical current degradation of the superconducting tape body is quantified and corresponds to the stress and strain inside the superconducting tape body caused by the curing of the epoxy resin.

2. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1, characterized in that: The step of completely immersing the superconducting tape body (1) in the epoxy resin comprises: Taking an impregnation mold tank (2), and openings on opposite sides of the impregnation mold tank (2), wherein the shape of the openings matches the cross-sectional shape of the superconducting tape body (1) perpendicular to the extension direction; The superconducting tape body (1) is passed through the impregnation mold tank (2) from the two through-holes, and epoxy resin is poured into the impregnation mold tank (2).

3. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 2, characterized in that: Before the step of pouring the epoxy resin into the impregnation mold tank (2), the impregnation mold tank (2) in which the superconducting tape body (1) is installed is preheated.

4. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 3, characterized in that: The step of curing the epoxy resin on the surface of the superconducting tape body (1) comprises: After the epoxy resin is poured into the impregnation mold tank (2), the temperature of the impregnation mold tank (2) is raised to a curing temperature and kept warm, so that the epoxy resin is cured.

5. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 2, characterized in that: The dipping mold tank (2) is a mold made of silicone material.

6. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1, characterized in that: The step of performing a critical current test on the superconducting tape body (1) comprises: fixing a voltage collection lead (4) at both ends of the test area of ​​the superconducting tape body (1), performing a critical current test using a four-lead method, and defining the current value corresponding to the voltage rising to 1µV / cm as the critical current.

7. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 6, characterized in that: When the observed current value reaches the critical current, the power supply to the superconducting tape body (1) is stopped.

8. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1, characterized in that: The electron microscopy observation is scanning electron microscopy observation, transmission electron microscopy observation, scanning tunneling microscopy observation or atomic force microscopy observation.

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