A preparation method for preventing Bi-2223 tape from leaking

Abstract

The application discloses a preparation method for preventing Bi-2223 tapes from seepage, and comprises the following steps: 1, filling Bi-2223 precursor powder into silver pipes, heating and vacuumizing to obtain a first pipe assembly; 2, after drawing the first pipe assembly, assembling single-core wires into silver alloy pipes to obtain a second pipe assembly; 3, drawing and rolling the second pipe assembly into multi-core tapes; 4, carrying out first heat treatment on the multi-core tapes, intermediate rolling and second heat treatment to obtain multi-core Bi-2223 superconducting tapes. The application optimizes the silver super ratio of single-core and multi-core wires, combines with the optimization of rolling process, improves the roughness of the surface of the tapes, obtains the optimal thickness of the silver layer of the tapes, prevents the tapes from seepage in the heat treatment process, and the prepared multi-core Bi-2223 tapes are beneficial to the application in the fields of high-voltage cables, transformers and magnets.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material preparation technology, specifically relating to a preparation method for preventing leakage of Bi-2223 tape. Background Technology

[0002] Bi-2223 tape prepared by the powder insulator (PIT) method is characterized by its high critical current density. J c Its characteristics of being easy to process into long strips make it one of the most promising high-temperature superconducting materials for first realizing strong electrical applications in the liquid nitrogen temperature range. Its potential applications include power transmission cables, transformers, fault current limiters, and magnets.

[0003] During the heat treatment of Bi-2223 tape, the ceramic core may penetrate the silver sheath, forming seepage points on the tape surface. These seepage points can occur in Bi-2223 tape, cables, and magnets. The presence of these seepage points not only reduces the current-carrying capacity of the tape but also causes adhesion between the magnet and tape layers, leading to insulation failure and ultimately preventing the magnet from functioning properly. Therefore, leakage is a significant obstacle to improving the performance of Bi-2223 tape.

[0004] Studies have found that when the strip surface has defects such as holes and cracks and the silver layer is thin, the superconducting layers will seep out along the defects during heat treatment, forming seepage points. To prevent leakage in the strip, the thickness of the silver layer must be increased and the appearance of holes and cracks must be avoided.

[0005] Therefore, a preparation method is needed to prevent leakage of Bi-2223 tape. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a preparation method for preventing leakage of Bi-2223 tape. This method employs vacuum degassing and heating to remove most of the interstitial and adsorbed gases from the powder, preventing gas expansion during heat treatment that could cause bubbling and voids. Simultaneously, it optimizes the silver layer thickness to prevent leakage due to an insufficiently thin silver layer.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a preparation method for preventing leakage of Bi-2223 tape, characterized in that the method includes the following steps: Step 1: Using a vibrating table in air, Bi-2223 precursor powder is filled into a silver tube that is sealed at one end. Then, the other end of the silver tube is sealed with a vacuum plug, and the Bi-2223 precursor powder in the silver tube is vacuumed and heated to obtain the first tube composite. Step 2: The first tube-mounted composite obtained in Step 1 is drawn to obtain a single-core wire. Then, multiple single-core wires are bundled and assembled into a silver alloy tube according to the set core wire structure to obtain the second tube-mounted composite. Step 3: The second tube composite obtained in Step 2 is drawn and rolled to obtain a multi-core strip; Step 4: The multi-core strip obtained in Step 3 is subjected to a first heat treatment, intermediate rolling and a second heat treatment in a low oxygen atmosphere to obtain a multi-core Bi-2223 superconducting strip.

[0008] The above-mentioned method for preventing leakage of Bi-2223 tape is characterized in that the vacuuming in step one is performed before heating, and the vacuum degree of the vacuuming is less than 1×10⁻⁶. -2 The heating temperature is greater than 400℃ and the time is greater than 4 hours. This invention, by controlling the heating temperature and vacuum level, effectively removes most of the adsorbed and interstitial gases from the Bi-2223 precursor powder, avoiding bubbling caused by gas expansion during subsequent heat treatment, thus preventing strip leakage. It also prevents insufficient vacuuming after tube loading due to excessively low heating temperature or excessively high vacuum, which would lead to bubbling defects on the strip surface after heat treatment, severely reducing the strip's mechanical strength and current-carrying capacity. Furthermore, it prevents these bubbles from rupturing after intermediate rolling, and thus preventing Bi-2223 grains from growing along the rupture sites during subsequent heat treatment, causing leakage.

[0009] The above-mentioned method for preventing leakage of Bi-2223 tape is characterized in that the single-core wire in step two has a hexagonal structure and a silver-to-superconductor ratio greater than 0.6. In this invention, the use of a hexagonal single-core wire facilitates seamless close-laying. By controlling the silver-to-superconductor ratio, it prevents the proportion of silver per unit area from being too small, which would be detrimental to wire processing and would also lead to a sausage effect at the silver-to-superconductor interface.

[0010] The above-mentioned method for preparing Bi-2223 strip to prevent leakage is characterized in that the silver super-ratio of the multi-core strip in step three is greater than 1.8. In this invention, by controlling the silver super-ratio, it is prevented from being too low. A low silver super-ratio is detrimental to wire processing and will result in a thin silver layer on the final wire, making leakage more likely during heat treatment.

[0011] The above-mentioned method for preparing Bi-2223 strip to prevent leakage is characterized in that, in step four, the oxygen volume content in the low-oxygen atmosphere is 7.5%~10.5%, the equilibrium gas is argon, and the intermediate rolling processing amount is less than 20%. In this invention, after the first heat treatment, the core wire density of the multi-core strip will decrease. After intermediate rolling, on the one hand, the core wire density and texture will be increased, and on the other hand, the unreacted Bi-2212 grains wrapped by Bi-2223 grains will be exposed and continue to participate in the Bi-2223 formation reaction during the second heat treatment. By controlling the processing amount of intermediate rolling, it is prevented that the processing amount of intermediate rolling is too large, which would lead to a sausage effect at the silver super-interface and make the silver layer thickness of the Bi-2223 strip too small, making leakage easy to occur in subsequent heat treatment processes.

[0012] Compared with the prior art, the present invention has the following advantages: 1. This invention removes most of the adsorbed and interstitial gases from the Bi-2223 precursor powder by heating and vacuuming the packed Bi-2223 precursor powder, thus avoiding bubbling caused by gas expansion during subsequent heat treatment and preventing strip leakage.

[0013] 2. This invention uses a vibrating table to vibrate and load the tube in the air, eliminating the need for expensive equipment such as vacuum glove boxes, which greatly reduces costs. At the same time, it is more convenient to operate in the air.

[0014] 3. By increasing the silver-to-silver ratio of single-core wires and multi-core strips, this invention not only facilitates the processing of Bi-2223 strips and the uniform deformation of the core wires, but also increases the silver layer thickness of the final Bi-2223 strip, thus preventing strip leakage.

[0015] 4. The preparation process of this invention is simple, the design is reasonable, the manufacturing cost is low, and the application scope is wide. It can be used for the industrial production of multi-core Bi-2223 superconducting tape.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in Example 1 of the present invention.

[0018] Figure 2 Metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in Comparative Example 1 of this invention.

[0019] Figure 3 This is a metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in Example 3 of the present invention.

[0020] Figure 4 Metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in Comparative Example 3 of this invention. Detailed Implementation

[0021] Example 1 This embodiment includes the following steps: Step 1: Using a vibration table with a vibration frequency of 40Hz in air, fill the Bi-2223 precursor powder into a silver tube sealed at one end through a metal funnel. Then, seal the other end of the silver tube with a vacuum plug. Afterward, evacuate the Bi-2223 precursor powder in the silver tube to a vacuum level of 8×10⁻⁶. -3 Pa was heated to 450℃ and held for 6 hours to obtain the first tube-packed composite. Step 2: The first tube composite obtained in Step 1 is drawn to obtain a hexagonal single-core wire with a silver-to-superior ratio of 0.62 and a side distance of 1.36mm. Then, the hexagonal single-core wire is cut and straightened in 30cm lengths. The 37 straightened hexagonal single-core wires are then bundled and assembled into a silver alloy tube to obtain the second tube composite. Step 3: The second tube composite obtained in Step 2 is drawn to obtain a 37-core wire with a silver-to-superior ratio of 1.88 and a diameter of 1.51 mm. Then, it is rolled by flat rolls to obtain a 37-core strip. Step 4: The 37-core strip obtained in Step 3 is subjected to a first heat treatment, an intermediate rolling process with a processing amount of 15%, and a second heat treatment in an argon-oxygen mixed atmosphere with an oxygen volume content of 7.5%. After furnace cooling, the 37-core Bi-2223 superconducting strip is obtained.

[0022] Figure 1 This is a metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in this embodiment. Figure 1 As can be seen from the data, the Bi-2223 superconducting tape prepared in this embodiment did not leak.

[0023] Comparative Example 1 The difference between this comparative example and Example 1 is that the silver-to-weight ratio of the 37-core wire in step three is 1.45.

[0024] Figure 2 The image shows a metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in this comparative example. Figure 2 As can be seen from this, the Bi-2223 superconducting tape prepared in this comparative example experienced leakage.

[0025] A comparison between Example 1 and Comparative Example 1 shows that Comparative Example 1 used a smaller silver-to-superconductor ratio, which led to leakage in the Bi-2223 superconducting tape. In contrast, Example 1 used a suitable silver-to-superconductor ratio, and the prepared Bi-2223 superconducting tape did not leak.

[0026] Example 2 This embodiment includes the following steps: Step 1: Using a vibration table with a vibration frequency of 40Hz in air, fill the Bi-2223 precursor powder into a silver tube sealed at one end through a metal funnel. Then, seal the other end of the silver tube with a vacuum plug. Afterward, evacuate the Bi-2223 precursor powder in the silver tube to a vacuum level of 8×10⁻⁶. -3 Pa was heated to 500℃ and held for 5 hours to obtain the first tube-packed composite. Step 2: The first tube composite obtained in Step 1 is drawn to obtain a hexagonal single-core wire with a silver-to-superior ratio of 0.65 and a side distance of 1.36mm. Then, the hexagonal single-core wire is cut and straightened in 30cm lengths. The 37 straightened hexagonal single-core wires are then bundled and assembled into a silver alloy tube to obtain the second tube composite. Step 3: The second tube composite obtained in Step 2 is drawn to obtain a 37-core wire with a silver-to-superior ratio of 1.93 and a diameter of 1.51 mm. Then, it is rolled by flat rolls to obtain a 37-core strip. Step 4: The 37-core strip obtained in Step 3 is subjected to a first heat treatment, an intermediate rolling process with a processing amount of 15%, and a second heat treatment in an argon-oxygen mixed atmosphere with an oxygen volume content of 8%. After furnace cooling, the 37-core Bi-2223 superconducting strip is obtained.

[0027] Testing showed that the 37-core Bi-2223 superconducting tape prepared in this embodiment did not leak.

[0028] Comparative Example 2 The difference between this comparative example and Example 2 is that the intermediate rolling amount in step four is 25%.

[0029] Testing revealed that the 37-core Bi-2223 superconducting tape prepared in this comparative example exhibited leakage.

[0030] A comparison between Example 2 and Comparative Example 2 shows that Comparative Example 2 used a larger intermediate rolling amount, which led to leakage in the Bi-2223 superconducting tape. In contrast, Example 1 used a suitable intermediate rolling amount, and the prepared Bi-2223 superconducting tape did not leak.

[0031] Example 3 This embodiment includes the following steps: Step 1: Using a vibration table with a vibration frequency of 40Hz in air, fill the Bi-2223 precursor powder into a silver tube sealed at one end through a metal funnel using a vibratory filling method. Then, seal the other end of the silver tube with a vacuum plug. Afterward, evacuate the Bi-2223 precursor powder in the silver tube to a vacuum level of 6.2 × 10⁻⁶. -3 Pa was heated to 520℃ and held for 4 hours to obtain the first tube-packed composite. Step 2: The first tube composite obtained in Step 1 is drawn to obtain a hexagonal single-core wire with a silver-to-superior ratio of 0.65 and a side distance of 1.36mm. Then, the hexagonal single-core wire is cut and straightened in 30cm lengths. The 37 straightened hexagonal single-core wires are then bundled and assembled into a silver alloy tube to obtain the second tube composite. Step 3: The second tube composite obtained in Step 2 is drawn to obtain a 37-core wire with a silver-to-superior ratio of 1.97 and a diameter of 1.51mm. Then, it is rolled by flat rolls to obtain a 37-core strip. Step 4: The 37-core strip obtained in Step 3 is subjected to a first heat treatment, an intermediate rolling process with a processing amount of 17%, and a second heat treatment in an argon-oxygen mixed atmosphere with an oxygen volume content of 10.5%. After furnace cooling, the 37-core Bi-2223 superconducting strip is obtained.

[0032] Figure 3 This is a metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in this embodiment. Figure 3 As can be seen from the data, the Bi-2223 superconducting tape prepared in this embodiment did not leak.

[0033] Comparative Example 3 The difference between this comparative example and Example 3 is that the heating and vacuuming in step one are not performed.

[0034] Figure 4 The image shows a metallographic image of the cross-section of the Bi-2223 superconducting tape prepared in this comparative example. Figure 4 As can be seen from this, the Bi-2223 superconducting tape prepared in this comparative example experienced leakage.

[0035] Testing revealed that in Comparative Example 3, numerous bubbles appeared on the surface of the 37-core strip after the first heat treatment, and leakage occurred at the bubble locations after intermediate rolling and the second heat treatment.

[0036] A comparison of Example 3 and Comparative Example 3 shows that Comparative Example 3 did not involve heating or vacuuming after powder loading, which led to leakage in the Bi-2223 superconducting tape. In contrast, Example 1 involved heating and vacuuming after powder loading, and the prepared Bi-2223 superconducting tape did not leak.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing Bi-2223 tape to prevent leakage, characterized in that, The method includes the following steps: Step 1: Using a vibration table in air, Bi-2223 precursor powder is filled into a silver tube sealed at one end. The other end of the silver tube is then sealed with a vacuum plug. The Bi-2223 precursor powder inside the silver tube is then evacuated and heated to obtain the first tube-filled composite. The vacuum level is less than 1 × 10⁻⁶. -2 Pa; The heating temperature is 450℃~520℃, and the time is greater than 4 hours; Step 2: The first tube-mounted composite obtained in Step 1 is drawn to obtain a single-core wire. Then, multiple single-core wires are bundled and assembled into a silver alloy tube according to the set core wire structure to obtain a second tube-mounted composite. The single-core wire has a hexagonal structure and a silver-to-superconducting ratio greater than 0.

6. Step 3: The second tube composite obtained in Step 2 is drawn and rolled to obtain a multi-core strip; the multi-core strip has 37 cores and a silver-to-super-silver ratio greater than 1.8; Step 4: The multi-core strip obtained in Step 3 is subjected to a first heat treatment, intermediate rolling and a second heat treatment in a low oxygen atmosphere to obtain a multi-core Bi-2223 superconducting strip.

2. The preparation method for preventing leakage of Bi-2223 tape according to claim 1, characterized in that, The vacuuming described in step one is performed before heating and takes more than 12 hours.

3. The preparation method for preventing leakage of Bi-2223 tape according to claim 1, characterized in that, In step four, the oxygen volume content in the low-oxygen atmosphere is 7.5%~10.5%, the balance gas is argon, and the intermediate rolling processing amount is less than 20%.

Images