Method for evaluating influence of epoxy resin impregnation on performance of superconducting tape

Abstract

The invention relates to the technical field of superconducting tape performance evaluation, and discloses a method for evaluating the influence of epoxy resin impregnation on the performance of a superconducting tape, which comprises the following steps: carrying out critical current test on a superconducting tape body; completely immersing the superconducting tape body into epoxy resin, and curing the epoxy resin on the surface of the superconducting tape body; cooling the superconducting tape with the epoxy resin to a temperature below a critical temperature, carrying out a critical current test on the superconducting tape with the epoxy resin, and rewarming the superconducting tape with the epoxy resin to a room temperature after the critical current test is completed; and corroding the stable layer on the surface of the superconducting tape to expose the superconducting layer of the superconducting tape, and carrying out electron microscope observation on the superconducting layer. Critical currents of a superconducting tape body before and after epoxy resin impregnation and curing are compared and analyzed to represent the performance degradation amplitude, and the surface morphology of a superconducting layer is observed through an electron microscope, so that the surface morphology of the superconducting layer corresponds to the degradation amplitude of the superconducting tape body in a quantified manner.

Description

Technical Field

[0001] The 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, including industry, power systems, motors, medical treatment, high-energy physics, transportation, aerospace, and military. High-temperature superconductors' strong power applications mainly involve large currents and high magnetic fields. Specific products include high-temperature superconducting fault current limiters, energy storage devices, transformers, generators, nuclear magnetic resonance, magnetic separation equipment, motors, magnetic levitation, cables, current leads, induction heating, high-energy accelerators, electromagnetic catapult systems, electromagnetic guns, engines, π-medium generators, etc. Among these applications, the most commonly used are coils wound with high-temperature superconducting tapes.

[0003] In high-temperature superconducting tape coils, epoxy resin is usually used to cure the coils to improve the mechanical properties, insulation properties, thermal conductivity, etc. of the superconducting magnet. Due to the multi-layer structure of the superconducting tape, its mechanical strength has significant anisotropy. During the cooling and curing process of the epoxy resin coated on the surface of the superconducting tape, stress concentration will occur between the layers of the superconducting tape due to the different cooling shrinkage rates of the layers of material. The cooling shrinkage rate of the epoxy resin is much greater than that of the superconducting tape, making the stress concentration phenomenon more serious, resulting in greater internal stress on the superconducting magnet after the epoxy resin is cured.

[0004] When the internal stress in the superconducting magnet is greater than the range that the superconducting magnet can withstand, the superconducting layer that transmits the current will be damaged, and the result is that the critical current of the superconducting magnet will decay. The related research on the performance of superconducting tapes in the prior art only tests the critical current of superconducting tapes or compares the critical current of superconducting coils before and after epoxy resin impregnation and curing, which cannot effectively characterize the degradation of the performance of superconducting tapes 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 superconducting tape performance, so as to solve the problem that the performance test of superconducting tape in the prior art cannot characterize the degradation extent 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 superconducting tape performance, comprising the following steps:

[0007] Conduct critical current test on 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, and performing a critical current test on the superconducting tape with epoxy resin. After the critical current test is completed, the superconducting tape with epoxy resin is heated back to room temperature;

[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, it is used to characterize the performance degradation amplitude of the superconducting tape body, and observing the surface morphology of the superconducting layer through an electron microscope, so that the surface morphology of the superconducting layer and the critical current degradation amplitude of the superconducting tape body are quantitatively corresponded, further guiding the improvement direction of epoxy resin, and thus avoiding the performance degradation of the superconducting magnet 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 warming 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 restoring the temperature, 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 an 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 comprises:

[0015] Taking an impregnation mold tank, and opening through openings on opposite sides of the impregnation mold tank, wherein the shape of the through openings 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 groove from the two through openings, and epoxy resin is poured into the impregnation mold groove.

[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, and 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 can be measured, and the residual strain inside the superconducting tape body and the cooling shrinkage caused by the curing of the epoxy resin can be corresponded to the degradation amplitude of the critical current. The amplitude of the critical current degradation of the superconducting tape body is quantified, which corresponds to the internal stress and strain of the superconducting tape body caused by the curing of the epoxy resin, further guiding the improvement direction of the epoxy resin, thereby avoiding the performance degradation of the superconducting magnet to a certain extent.

[0019] In an optional embodiment, before pouring the epoxy resin into the impregnation mold tank, the step includes: preheating the impregnation mold tank in which the superconducting tape body is installed. When the epoxy resin is poured into the impregnation mold tank, the temperature of the superconducting tape body is at a relatively high level, so that the epoxy resin can be cured from the inside out, ensuring the uniformity of the epoxy resin curing process and reducing the internal stress caused by the epoxy resin curing process.

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

[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 maintained to cure the epoxy resin.

[0022] In an optional embodiment, the impregnation mold tank is a silicone mold. The silicone mold has a flexible border and will not scratch the superconducting tape, and is non-adhesive, which 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 both ends of the superconducting tape body to be tested, respectively, 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 the critical current degradation caused by the 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 implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying 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 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 image of the superconducting layer of the superconducting tape body covered with epoxy resin B.

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

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

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the 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 creative work are within the scope of protection of the present invention.

[0034] Combine the following Figures 1 to 5 , describing an embodiment 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, a critical current test is performed on the superconducting tape body 1. Then, the superconducting tape body 1 is completely immersed in the epoxy resin, and the epoxy resin is cured 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 by electron microscopy.

[0036] By measuring the critical current of the superconducting tape body 1 before and after the epoxy resin is impregnated and cured, and comparing and analyzing the critical current of the superconducting tape body 1 before and after the epoxy resin is impregnated and cured, the performance degradation amplitude of the superconducting tape body 1 is characterized, and 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 step of performing a critical current test on the superconducting tape body 1 includes: fixing a voltage collection lead 4 at both ends of the area to be tested of the superconducting tape body 1, respectively, using a four-lead method to perform a critical current test, and defining the current value corresponding to the voltage rising to 1 μV / cm as the critical current. Specifically, first measure the critical current of the superconducting tape body 1 that has not been cured with epoxy resin. Cut a section of the superconducting tape body 1 that is slightly longer than the length of the test device, determine the area to be tested for electrical properties, and use low-temperature solder with a melting point below 200°C to weld two voltage collection leads 4 at both ends of the area. In order to avoid critical current degradation caused by quenching of the superconducting tape body 1, when the current value is observed to reach the critical current, stop energizing the superconducting tape body 1.

[0038] In one embodiment, the step of completely immersing the superconducting tape body 1 into the epoxy resin comprises: 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 into the impregnation mold tank 2, and pouring the epoxy resin into the impregnation mold tank 2, such as Figure 1 shown.

[0039] Specifically, prepare a rectangular impregnation mold tank 2 of appropriate size, and open slits on both sides of it that are equal to the width of the tape as through-holes. The slits are just enough for the tape to pass through, and should not be 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, put the superconducting tape body 1 from the middle of the impregnation mold tank 2, and pass the two sides outward through the through-holes respectively. Be careful not to over-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 step further includes: arranging a fiber grating sensor 3 on the upper surface of the superconducting tape body 1, and the fiber grating sensor 3 records the strain of the superconducting tape body 1 in real time.

[0041] The prepared optical fiber sensor is passed through the through openings on both sides of the impregnation mold tank 2 above the superconducting tape body 1, and the optical fiber sensor is closely attached to the upper surface of the superconducting tape body 1. One or more optical fiber grating sensors 3 can be distributed to measure the strain distribution in the extension direction of the superconducting tape body 1. In this embodiment, three optical fiber 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 the curing of the epoxy resin are measured, and the internal residual strain and cooling shrinkage of the superconducting tape body 1 caused by the curing of the epoxy resin correspond to the degradation amplitude of the critical current, and the amplitude of the critical current degradation of the superconducting tape body 1 is quantified, which corresponds to the internal stress and strain of the superconducting tape body 1 caused by the curing of the epoxy resin, and further guides the improvement direction of the epoxy resin, thereby avoiding the performance degradation of the superconducting magnet to a certain extent.

[0042] In one embodiment, before pouring the epoxy resin into the impregnation mold tank 2, the step includes: preheating the impregnation mold tank 2 with the superconducting tape body 1 installed. The impregnation mold tank 2 with the superconducting tape body 1 installed is placed in an oven, and the two ends of the superconducting tape are led out from the top of the oven and connected to the demodulator. The oven is adjusted to the epoxy resin impregnation temperature for preheating. When the subsequent epoxy resin is poured into the impregnation mold tank 2, the temperature of the superconducting tape body 1 is at a higher level, so that the epoxy resin can be cured from the inside to the outside, ensuring the uniformity of the epoxy resin curing process and reducing the internal stress caused by the epoxy resin curing process.

[0043] In this embodiment, the impregnation mold tank 2 is a silicone mold. The silicone mold has a flexible border, will not scratch the superconducting tape, and is non-adhesive, which is convenient for demoulding 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: after pouring the epoxy resin into the impregnation mold tank 2, heating the impregnation mold tank 2 to a curing temperature and keeping 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 according to 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 and performing a critical current test and then returning the superconducting tape to room temperature are repeated multiple times.

[0047] Specifically, the critical current test is performed on the superconducting tape after the epoxy resin is cured. The silicone impregnation mold groove 2 is cut open to complete the demolding. During the process, care should 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 four-lead method is used to perform the critical current test. 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 after five cooling to 77K is shown in Figure 3 As shown. Epoxy resin B and epoxy resin C have almost no degradation. It can be inferred that when the total strain is around 3000με or below, it will not affect the strip. Epoxy resin A and epoxy resin D degraded by 52.5A and 35.13A respectively, and corresponding to the strain, the greater the strain, the greater the degradation. It can be inferred that when the total strain is above 10000με, it will cause the degradation of the critical current of the strip, and the greater the strain, the greater the damage caused, and the more the critical current decays.

[0049] By repeatedly lowering the temperature of the superconducting tape to below the critical temperature and then restoring the temperature, 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 a scanning electron microscope observation, a transmission electron microscope observation, a scanning tunneling microscope observation, or an atomic force microscope observation. In this embodiment, a scanning electron microscope observation is selected. Figure 4 As shown in FIG. 1 , the surface morphology of the superconducting layer of the superconducting tape body 1 covered with epoxy resin B with no degradation in critical current after the evaluation step is magnified to 650 times, 2000 times, 6500 times and 35000 times. Figure 5 As shown, the surface morphology of the superconducting layer of the superconducting tape body 1 with serious critical current degradation and the surface covered with epoxy resin A is magnified at 650 times, 2000 times, 6500 times and 35000 times. By comparing the morphology of the superconducting layer, obvious cracks can be found in the superconducting layer of the seriously degraded superconducting tape.

[0051] Although the embodiments of the present invention have been described in conjunction with 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, and 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 a superconducting tape body (1); Completely immersing the superconducting tape body (1) in epoxy resin, and allowing the epoxy resin to solidify on the surface of the superconducting tape body (1); Cooling the superconducting tape with epoxy resin to below the critical temperature, and performing a critical current test on the superconducting tape with epoxy resin. After the critical current test is completed, the superconducting tape with epoxy resin is heated back to room temperature; 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.

2. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1, characterized in that: Before the step of corroding the stabilizing 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 is repeated multiple times and then the temperature of the superconducting tape is restored to room temperature.

3. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1 or 2, characterized in that: The step of completely immersing the superconducting tape body (1) into the epoxy resin comprises: Taking an impregnation mold tank (2), and opening through holes on two 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; The superconducting tape body (1) passes through the impregnation mold groove (2) from the two through-holes, and epoxy resin is poured into the impregnation mold groove (2).

4. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 3, characterized in that: Before the step of pouring the epoxy resin into the impregnation mold groove (2), the method further comprises: arranging a fiber optic grating sensor (3) on the upper surface of the superconducting tape body (1), wherein the fiber optic grating sensor (3) records the strain of the superconducting tape body (1) in real time.

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

6. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 5, 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 to allow the epoxy resin to cure.

7. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 3, characterized in that: The dipping mold tank (2) is a mold made of silicone material.

8. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1 or 2, characterized in that: The step of testing the critical current of the superconducting tape body (1) comprises: fixing a voltage collection lead (4) at both ends of the tested area of ​​the superconducting tape body (1), respectively, using a four-lead method to test the critical current, and defining the current value corresponding to the voltage rising to 1 μV / cm as the critical current.

9. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 8, characterized in that: When the observed current value reaches the critical current, the power supply to the superconducting tape body (1) is stopped.

10. The method for evaluating the effect of epoxy resin impregnation on superconducting tape performance according to claim 1 or 2, characterized in that: The electron microscope observation is scanning electron microscope observation, transmission electron microscope observation, scanning tunneling microscope observation or atomic force microscope observation.

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