Sampling method of superconducting layer in second generation high temperature superconducting tape

Abstract

A method for sampling a superconducting layer in a second-generation high-temperature superconducting tape belongs to the technical field of second-generation high-temperature superconducting tape testing. The sampling method comprises: a sample preparation step: splitting the second-generation high-temperature superconducting tape along the extension direction of the tape, forming a split surface on at least one of the two sides in the width direction of the tape, and partially or completely exposing the superconducting layer on the split surface; in the extension direction of the tape, the length of the split surface is consistent with the length of the tape; a soaking step: soaking the tape processed by the sample preparation step in deionized water until the buffer layer and the superconducting layer are at least partially delaminated and not completely separated; a stripping step: splitting the tape processed by the soaking step into two along the delamination position of the buffer layer and the superconducting layer to obtain a first part of the tape and a second part of the tape, at least one of which has a superconducting layer. The present invention can strip a relatively complete high-quality superconducting layer sample from the second-generation high-temperature superconducting tape without damage.

Description

Technical Field

[0001] The present invention relates to a technology in the field of second-generation high-temperature superconducting tape testing, in particular to a method for sampling a superconducting layer in a second-generation high-temperature superconducting tape. Background Art

[0002] Since the first discovery of superconductivity by Professor Kamerlingh Onnes of the Netherlands in 1911, superconducting materials and their applications have been one of the most active frontier research areas in science and technology. In recent years, with the continuous development of superconducting technology, research on power equipment based on superconductivity has also developed rapidly, especially in the fields of superconducting energy storage, superconducting motors, superconducting cables, superconducting current limiters, superconducting transformers, and superconducting synchronous condensers. In many applications, the second-generation high-temperature superconducting tapes are the core components.

[0003] The production process of the second-generation high-temperature superconducting tape is generally to polish the Hastelloy, plate a buffer layer on the Hastelloy after polishing, and then grow a superconducting layer on the buffer layer, followed by silver plating and copper plating. In some application scenarios, copper tape is also used for soldering armor, and finally the coil is wound or the conductor is prepared. During the coil winding or testing process, the superconducting tape may suffer irreversible quenching due to various reasons. At this time, analyzing the cause of the quench is crucial to the advancement of the project and the continuous optimization of the product, and the properties of the superconducting layer after the quench are the basis and key to supporting the analysis of the cause of the quench.

[0004] The biggest challenge in analyzing the properties of the superconducting layer of copper-plated and armored superconducting tapes is how to obtain high-quality superconducting layer samples. The active nature of the superconducting layer causes all acidic and alkaline liquids to corrode it, so the current method of corroding and separating the superconducting layer layer by layer is prone to "accidental damage" to the superconducting layer, affecting the analysis of the properties of the superconducting layer. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a method for sampling a superconducting layer in a second-generation high-temperature superconducting tape, which can be used to obtain a relatively complete high-quality superconducting layer sample from the second-generation high-temperature superconducting tape without damage.

[0006] The present invention relates to a method for sampling a superconducting layer in a second-generation high-temperature superconducting tape, comprising:

[0007] Sample preparation steps: at a preset splitting position, split the second-generation high-temperature superconducting tape along the tape extension direction, and form a splitting surface on at least one of the two sides in the tape width direction, and the tape width direction is perpendicular to the tape extension direction; in the tape thickness direction, the splitting surface partially or completely exposes the cross section of the superconducting layer, and when the superconducting layer is not completely exposed, the buffer layer is completely exposed, and when the superconducting layer is completely exposed, the buffer layer is at least partially exposed; in the tape extension direction, the length of the splitting surface is consistent with the length of the tape; splitting can be performed by mechanical splitting, laser splitting, ion beam splitting, etc., but no matter which method is adopted, it should be ensured that the edges after splitting are clear and complete, and no secondary fusion occurs between the layers; for example, when laser splitting is used, the laser power needs to be controlled to avoid excessive power causing the adjacent layers to melt and combine at the cutting edge;

[0008] Soaking step: Soaking the strip processed in the sample preparation step in deionized water until the buffer layer and the superconducting layer are at least partially delaminated and not completely separated; when the buffer layer and the superconducting layer are completely separated, it can be foreseen that the superconducting layer has been excessively corroded, and the superconducting layer sample prepared thereby loses the value of observation and evaluation; preferably, the at least partially delaminated and not completely separated means that the maximum size of the separated portion of the buffer layer and the superconducting layer in the width direction is one-third to two-thirds of the width; and there is no requirement for the size of the separated portion in the extending direction of the strip, because when the size in the width direction reaches the above requirement, a length suitable for stripping the strip also appears in the extending direction of the strip;

[0009] Stripping step: Divide the strip treated in the immersion step into two parts along the delamination area of ​​the buffer layer and the superconducting layer to obtain a first part of the strip and a second part of the strip, at least one of which has a superconducting layer. The stripping tool can be tweezers or a vacuum pen, but attention should be paid to the selection of the material of the contact part to ensure that no secondary damage to the sample is caused; such as blunt-tipped plastic tweezers or blunt-tipped ceramic tweezers, a vacuum pen with a silicone tip or a rubber tip. During stripping, in order to avoid causing secondary damage to the sample, the stripping angle should not be too large. It is preferred to gradually push open the upper and lower parts from the gap in the delamination area or separate them by suction from the outside; further preferably, the angle between the first part of the strip and the second part of the strip during the stripping process does not exceed 60°.

[0010] The first and second tapes obtained by the stripping step above, including the superconducting layer, can be used for the analysis and evaluation of the quality of the superconducting layer, the analysis of the cause of quenching, and the optimization and improvement of the preparation process. Specifically, the tape containing the superconducting layer is washed with deionized water and dried, and then observed and analyzed by material characterization methods such as SEM, TEM, ICP, and XRD. Affected by factors such as the preparation process and the damage of the tape, the superconducting layer may appear in one of the first and second tapes, or may appear in both the first and second tapes. For the superconducting layer appearing in both tapes, a typical situation is that the superconducting layer is a multi-layer structure, and the interlayer bonding force between the two superconducting layers is less than the interlayer bonding force between the superconducting layer and the buffer layer. Of course, this situation may also be caused by the serious damage of the superconducting layer in the tape.

[0011] For some specific implementation schemes, in the sample preparation step, on the one hand, the second-generation high-temperature superconducting tape to be sampled can be single-sided coated or double-sided coated; on the other hand, the dividing surface can be inclined to the extension direction of the tape or perpendicular to the extension direction of the tape. The dividing surface at the above angles should partially or completely expose the superconducting layer cross-section in the thickness direction of the tape.

[0012] For the second-generation high-temperature superconducting tape with double-sided coating, when the dividing plane is inclined to the extension direction of the tape, the dividing plane is composed of the copper layer cross section, silver layer cross section, superconducting layer cross section, buffer layer cross section, base tape cross section, silver layer cross section and copper layer cross section arranged in sequence, or the dividing plane is composed of the copper layer cross section, silver layer cross section, superconducting layer cross section, buffer layer cross section, silver layer cross section and copper layer cross section arranged in sequence.

[0013] For a second-generation high-temperature superconducting tape with double-sided coating, when the dividing plane is perpendicular to the extending direction of the tape, the dividing plane is composed of a copper layer section, a silver layer section, a superconducting layer section, a buffer layer section, a base tape section, a silver layer section and a copper layer section arranged in sequence; preferably, the dividing plane is located on the A and B surfaces of the tape before dividing, within 1 mm from the side edge in the width direction of the tape, that is, the preset dividing position is located within 1 mm inside the edge in the width direction of the tape.

[0014] For some specific implementation schemes, in the soaking step, the soaking time directly determines the degree of stratification and the difficulty of the stripping step, which in turn affects the stripping quality of the superconducting layer and the buffer layer. Preferably, the soaking time is 5 to 24 hours. Since deionized water will react with the REBCO material in the superconducting layer, when deionized water is used to assist in the stripping of the superconducting layer, it is also necessary to identify this effect in order to conduct a more accurate evaluation of the superconducting layer sample in the future, and even to reduce this effect while ensuring the stripping quality, so as to obtain a higher quality superconducting layer sample; the specific method is to introduce a standard sample, and then compare the superconducting layer stripped from the sample to be tested and the standard sample, and to establish a database on the soaking time in advance through experiments, so that the optimal soaking time can be determined according to the composition, thickness, preparation process, and number of superconducting layers of the superconducting layer.

[0015] For some specific implementation schemes, the second-generation high-temperature superconducting tape sample has no covering structure at both ends in the extension direction of the tape, that is, the structural layers of the second-generation high-temperature superconducting tape are in an exposed state. If the sample is covered at both ends, it needs to be cut first; if the second-generation high-temperature superconducting tape is a solder armored structure, it needs to be heated to melt the solder and remove the armor layer; preferably, the heating temperature is 180-250°C; heating at a temperature within this temperature range for a period of time to fully melt the solder, usually 10-60s, and excessive temperature and / or long-term heating should be avoided to damage the tape, especially the superconducting layer of the tape.

[0016] Compared with the prior art, the present invention has the following technical effects:

[0017] Deionized water can react relatively slowly with the REBCO material in the superconducting layer to generate Ba(OH)2, BaCO3, RE2BaCuO5, CuO and other substances, thereby causing the interlayer bonding force between the superconducting layer and the buffer layer to gradually decay; the weakening of the interlayer bonding force begins first from the edge; when separation points appear at the edge, water vapor gradually invades between the superconducting layer and the buffer layer, causing the above-mentioned attenuation area to gradually expand, so that the two are gradually delaminated; on this basis, the stripping of the superconducting layer and the buffer layer reduces the difficulty of stripping; and because the expansion speed of the above-mentioned corrosion process along the extension direction and width direction of the strip is much faster than the expansion speed in the thickness direction of the strip, a higher quality superconducting layer can be obtained after stripping. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the overall structure of the second-generation high-temperature superconducting tape to be prepared in Example 1;

[0019] Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure of the second generation high temperature superconducting tape after the end is cut;

[0020] Figure 3 for Figure 2 Schematic diagram of the cross-sectional structure of the second generation high temperature superconducting tape after removing the armor layer;

[0021] Figure 4 for Figure 3 Schematic diagram of the cross-sectional structure of the second generation high temperature superconducting tape after being cut on both sides in the width direction;

[0022] Figure 5 This is a photo of the sample to be peeled in Example 1 after being immersed in deionized water for 10 hours;

[0023] Figure 6 This is a photo of the sample to be peeled in Example 1 after being immersed in deionized water for 20 hours;

[0024] Figure 7 is the XRD diffraction pattern of the first part of the strip in Example 1;

[0025] Figure 8 is the XRD diffraction pattern of the second portion of the strip in Example 1;

[0026] Fig. 9 is a schematic diagram of the cross-sectional structure of the first portion of the strip without a buffer layer in Example 1;

[0027] Fig.10 is a schematic diagram of the cross-sectional structure of the second portion of the strip having a buffer layer in Example 1;

[0028] Fig.11 This is a SEM electron microscope image of the superconducting layer in the first part of the tape at a magnification of 5K times;

[0029] Fig.12 This is the SEM electron microscope image of the superconducting layer in the standard sample at 5K times magnification;

[0030] Fig.13 The XRD diffraction pattern of the superconducting layer sample obtained using the acid solution in Example 1;

[0031] In the figure: 001, second-generation high-temperature superconducting tape; 100, metal base tape; 200, buffer layer; 300, superconducting layer; 400, silver layer; 500, copper layer; 600, solder; 700, armor layer. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The experimental methods without specific conditions in the examples are carried out according to conventional methods and conditions.

[0033] Example 1

[0034] like Figure 1The figure shows a second-generation high-temperature superconducting tape 001, whose cross-section (cross-section in the width direction of the tape) has a structure as shown in FIG. Figure 2 As shown, it includes a unit structure, which includes a metal base tape 100, a buffer layer 200 and a superconducting layer 300 stacked in sequence, the outer side of the unit structure is wrapped with a silver layer 400, the outer side of the silver layer 400 is plated with a copper layer 500, and the copper layer 500 and the armor layer 700 are fixedly connected by solder 600. Of course, in addition to Figure 1 In addition to the second-generation high-temperature superconducting tape 001 with an armor layer, some second-generation high-temperature superconducting tapes do not contain an armor layer or solder. Such superconducting tapes can also be stripped of the superconducting layer using the method of the present invention.

[0035] The second generation high temperature superconducting tape 001 with armor layer was wound into a coil. After the coil was excited several times, it was found that the superconducting tape had quenching phenomenon. After unwinding, the critical current was checked. Finally, it was determined that the critical current of a section of 0.5m in length had obvious degradation, and it was necessary to analyze this section of superconducting tape.

[0036] Along the extension direction of the strip, two samples with a length of 5 cm are cut in this section, and the cuts are required to be neat; after cutting, they are baked at 220℃ for 40s, and the armor layer is removed after the solder melts, and a sample with the following characteristics is obtained: Figure 3 A sample with the cross-sectional structure shown in the figure; another sample with a length of 5 cm is taken outside this section as a standard sample.

[0037] For one of the samples to be analyzed and the standard sample, a superconducting layer sample is prepared by the method of the present invention, and the specific process is as follows:

[0038] The sample is cut from top to bottom (i.e. thickness direction) along the strip extension direction (i.e. length direction). The cut is required to be neat and the direction of the cut surface is perpendicular to the strip extension direction and width direction. The distance between the cutting position and the nearest side edge in the strip width direction is 0.5 mm, and both sides are cut. After the cutting is completed, the following is obtained: Figure 4 The sample has a cross-sectional structure shown; the sample has a total of 4 sections in the length and width directions, and each layer of the sample is exposed in these 4 sections.

[0039] The cut samples were immersed in deionized water for 10 hours and the following Figure 5 The sample to be analyzed is shown in the figure. At this time, some separation points appear at the edge of the sample. After soaking for 10 hours, the following Figure 6 The sample to be analyzed is shown in Figure 1. At this time, the sample has obvious stratification but is not completely separated.

[0040] Use tweezers to separate the sample to be analyzed along the layered structure to obtain the first part of the strip (the schematic diagram of the cross-sectional structure is shown in Fig. 9 as shown) and the second strip (cross-sectional structure diagram as shown Fig.10 As shown in Figure 2), XRD analysis was performed on the two parts of the tape and it was found that the first part of the tape contained a superconducting layer but no buffer layer, as shown in Figure 2. Figure 7 As shown; the second portion of the tape contains a buffer layer without a superconducting layer, such as Figure 8 shown.

[0041] For another sample to be analyzed, the superconducting layer sample was prepared by acid corrosion. The specific process is as follows: a nitric acid solution with a mass percentage concentration of 10% was used for corrosion to gradually remove the solder, copper layer and silver layer. Fig.13 As shown, this is the XRD diffraction pattern after using 10% concentration nitric acid to remove the metal covering layer. From the spectrum, it can be found that the superconducting layer has been destroyed and the buffer layer has been exposed.

[0042] Based on the above research, by comparing the superconducting layer samples obtained by stripping the sample to be analyzed by the method of the present invention and by etching the sample to be analyzed by acid solution, it can be found that the superconducting layer sample obtained by the method of the present invention has a complete structure;

[0043] based on Fig.11 and Fig.12 The SEM electron microscope image shown compares the superconducting layer samples peeled off from the sample to be analyzed and the standard sample. It can be found that at a magnification of 5000 times, the superconducting layer sample peeled off from the sample to be analyzed has cracks, while the superconducting layer sample peeled off from the standard sample has no defects such as cracks, which proves that the superconducting layer sample peeled off by the method of the present invention is almost not damaged by operations such as shearing the sample and immersing in deionized water. It is possible to separate and obtain high-quality samples that reflect the true properties of the superconducting layer and have high analytical value.

[0044] Through further testing and analysis of the superconducting layer samples, it was finally determined that the superconducting layer of the superconducting tape of the coil was broken due to external force after multiple excitations, which led to the quenching of the coil. Starting from this direction, the coil winding process and testing process were checked, and it was finally determined that it was due to uneven winding tension and excessive tension on the superconducting tape after shrinking at low temperature, which damaged the superconducting layer and caused cracks, leading to the quenching of the superconducting coil.

[0045] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for sampling a superconducting layer in a second-generation high-temperature superconducting tape, characterized in that: include: Sample preparation steps: at a preset splitting position, splitting the second-generation high-temperature superconducting tape along the tape extension direction, forming a splitting surface on at least one of the two sides in the tape width direction, the tape width direction is perpendicular to the tape extension direction; in the tape thickness direction, the splitting surface partially or completely exposes the superconducting layer, when the superconducting layer is not completely exposed, the buffer layer is completely exposed, and when the superconducting layer is completely exposed, the buffer layer is at least partially exposed; in the tape extension direction, the length of the splitting surface is consistent with the length of the tape; Soaking step: Soaking the tape processed in the sample preparation step in deionized water until the buffer layer and the superconducting layer are at least partially delaminated but not completely separated; Stripping step: dividing the tape treated in the soaking step into two along the delamination portion between the buffer layer and the superconducting layer to obtain a first tape portion and a second tape portion, at least one of which has a superconducting layer.

2. The sampling method according to claim 1, characterized in that: In the sample preparation step, the dividing surface is inclined to the extending direction of the strip or perpendicular to the extending direction of the strip.

3. The sampling method according to claim 2, characterized in that: When the dividing surface is perpendicular to the extending direction of the strip, the preset dividing position is located within 1 mm inward from the edge in the width direction of the strip.

4. The sampling method according to claim 1, characterized in that: The strip is divided into two separate dividing surfaces on both sides in the width direction.

5. The sampling method according to claim 1, characterized in that: In the sample preparation step, segmentation is performed by mechanical segmentation, laser segmentation or ion beam segmentation.

6. The sampling method according to claim 1, characterized in that: In the soaking step, the soaking time is 5 to 24 hours.

7. The sampling method according to claim 1, characterized in that: In the peeling step, the upper and lower parts are gradually pushed apart from the gap in the delaminated area or separated by suction from the outside.

8. The sampling method according to claim 7, characterized in that: During the process of pushing open or separating, the angle between the first portion of the strip and the second portion of the strip does not exceed 60°.

9. The sampling method according to claim 7, characterized in that: In the stripping step, a vacuum pen or tweezers is used as a stripping tool, wherein the vacuum pen has a silicone tip or a rubber tip, and the tweezers are blunt-tip tweezers.

10. The sampling method according to claim 1, characterized in that: The method also includes the step of heating the armored second-generation high-temperature superconducting tape; the heating temperature is 180 to 250° C., the heating time is 10 to 60 seconds, and the solder is melted to remove the armor layer.

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