JP4908566B2 - Method for manufacturing low contact resistance contacts on high transition temperature superconductors - Google Patents

Description

  The present invention relates to the development of a low contact resistance junction of an HTSC (High Transition Temperature Superconductor Compound) solid body composed of BiPbSrCaCuO for high current transport below Tc (critical temperature). This tube / rod shaped HTSC conductor, Bi (2223) (BiPbSrCaCuO), can carry very large currents at 77K and generates very low heat losses in the system due to its low thermal conductivity. In addition, if the contact resistance between the HTSC and the current conductor is low, these tube / rod conductors are ideal for any system such as a cryogen-free superconducting magnet / superconducting magnet generator etc. A large current carrying conductor.

The parameters of high current transmission in conventional conductors such as Cu, Al, etc. are mostly due to the resistance of this conductor, which results in a considerable amount of energy loss. Lossless current transport has been a key feature of superconductivity from the very beginning. Conventional superconducting materials with low Tc have been used in the manufacture of high field magnets (~ 20 Tesla), which are now readily available. The operating temperature, 4.2K (requiring a steady flow of liquid helium) has prevented large current carrying wires and cables from growing. Advances in this area with respect to large transport currents are limited only to the prototype level. With the advent of high Tc superconducting compounds (HTSC), expectations are increasing for high transport current conductors where the operating temperature can be increased to 77K. However, poor flexibility and low critical magnetic field have limited the use imminently. However, the development of Bi (2223) HTSC multifilament (multi-core) cable with a Jc of -10 ⁵ A / cm ^{2 in} a magnetic field of 77K and 0.6T showed good prospects. It wasn't exactly the traditional answer. By comparison, the tubular conductor made of this high Tc superconductor shows good potential. BSCCO tube and rod based HTC current conductors are the first application of ceramic superconductors in power engineering, as well as all traditional metal conductors that are good conductors such as Cu and Al It offers significant advantages over both conventional superconductors. Conventional low Tc superconductors embedded in copper surpass all metal conductors due to their ability to transport large currents determined by their zero resistance and critical current density Jc (˜10 ⁵ A / cm ² ). It was considered a better option. However, due to the limitation of operating at 4.2K, these materials do not necessarily replace Cu or Al.

  In addition to the higher operating temperature of 77K, this HTSC material has a low thermal conductivity, which results in a heat loss of less than 1/10 of the usual. This reduces the heat load in the cryogenic system, resulting in a significant reduction in cooling costs and enables a new and innovative cooling concept. Their other use is in the field of magnetic shielding and current limiters.

When the contact resistance of a junction made of a normal conductor (Cu, Al) that supplies a large current to the HTSC tube conductor is on the order of 10 ⁻⁴ to 10 ⁻³ Ω, all the above HTSC tubes Using conductors for high current applications (Ic> 1000A) becomes inefficient and lossy. What is required in order to make optimal use of tubular conductors is that the contact resistance of conventional conductors joined to HTSC tube conductors should be on the order of at least 10 ⁻⁶ Ω.

Reference may be made to the disclosure of Journal of Materials, Vol 43, pp21 (1991) by KH Sandhage et al., Where within the HTSC family, Y-based superconductors are used to synthesize tubular and rod-like conductors. Struggles with many crystallographic limitations, indicating that only thin film applications are commercialized. In addition, another disclosure by EH Hellstorm's Materia Research Bulletin Vol XVII, pp45, (1992) shows that Tl-based superconductors are not used for bulk applications due to health risks. ing. Supercond. By S X Dou and H K Liu. Science and Technol Vol 6, pp 297, (1993) reports that only Bi-based superconductors (Bi _{2 -X,} Pb _X Sr ₂ Ca ₂ Cu ₃ O _x ) and Bi (2212) are commercially economical. And is the preferred answer.

  This contact resistance problem for high current electrical junctions can only be solved by using silver as the normal conductor for feeding high currents to Bi based tube conductors. The major problem with this is connecting a silver feeder to the Bi (2223) ceramic surface.

  This problem has been addressed in several ways.

  US Pat. No. 5,149,686 and US Pat. No. 20030132023 sputter non-superconducting metals (Ag, Au) on small bar-shaped HTSCs on the order of micrometers to make electrical contacts. To disclose.

  Plasma spray technology of Ag / Au film onto micrometer order HTSC is disclosed by Y Yamada in Bismuth Based High Temperature Superconductors (Editor H Maeda and T Togano) pp 277 (1996).

The high current feeder is then soldered to the HTSC surface and a contact resistance on the order of 10 ⁻⁶ Ω is obtained at 77K.

  Sputtering techniques have been successful for small samples, but plasma deposition is used, especially for large samples based on bismuth (eg, tube / rod conductors).

  US Patent No. 5,506,199 and KK Michishita et al. Bismuth Based High Temperature Superconductors (edited H Maeda and T Togano) pp253 (1996) is a large sample of Ag22, sheet or wire in Bi2212 melt. Disclose the process by including.

  The main object of the present invention is to provide a method for producing a low contact resistance contact in a high transition temperature superconductor which eliminates the above-mentioned drawbacks.

  Another object of the present invention is to provide a three-layer process for producing low contact resistance joints in high transition temperature superconductors.

  Yet another object of the present invention is to provide low contact resistance for BiCaCuO superconductors.

  A further object of the present invention is to provide a contact for a tubular HTSC.

  A further object of the present invention is to provide a contact for a rod-shaped HTSC.

Another object of the present invention is to provide a contact having a contact resistance in the range of 10 ⁻⁷ to 10 ⁻⁶ Ω.

The present invention is directed to high transition temperature superconductors (HTSC), and in particular to (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} , which may or may not contain silver in the superconductor. Fig. 3 represents a three-layer process for producing contact points. This contact structure is a three-layer structure with a perforated silver foil sandwiched between two deposited silver layers by a metal spray gun, followed by heat treatment in air. This contact is made on the tube and rod. The fabricated silver contact is characterized by a low resistance of 10 ⁻⁶ Ω. In addition, this contact can carry a continuous current of 200 amps without adding a substantial heat load to the cryogen used to cool the HTSC.

In the drawings that accompany this detailed description, FIG. 1 shows the structure of the contact of an HTSC tube or rod. (1) is an HTSC tube or rod with a groove at the end, (2) is the first deposited silver layer, (3) is silver foil, (4) is silver foil perforations, ( 5) is the second deposited silver layer and (6) is the contact for the braided wire.

Therefore, in the present invention, a groove is formed at the end of the superconductor, the first silver layer is deposited by a metal spray gun at a temperature of 120 ° C., and the deposited silver layer is deposited at a temperature range of 200 to 250 ° C. Heating for a period ranging from 2 to 5 hours, winding a perforated silver foil around the heated first silver layer, depositing a second silver layer with a metal spray gun at a temperature of 120 ° C., A combination of one silver layer, a wound perforated silver foil and a second silver layer was heated in air at a temperature range of 830 to 850 ° C. for 100 to 150 hours, resulting in 10 ⁻⁷ to 10 ^−6. Obtaining a junction having a contact resistance in the range of Ω provides a method of manufacturing a low contact resistance contact on a high transition temperature superconductor.

  In an embodiment of the present invention, the high transition temperature superconductor may be a hollow cylindrical tube having a length in the range of 200 to 300 mm.

  In another embodiment of the present invention, the high transition temperature superconductor may be a solid rod having a length of 150 mm.

  In yet another embodiment of the invention, the tube wall thickness may be in the range of 2-3 mm.

  In yet another embodiment of the present invention, the outer diameter of the tube may be in the range of 12-30 mm.

In still another embodiment of the present invention, the high transition temperature superconductor may be pure (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} .

In a further embodiment of the present invention, the high transition temperature superconductor may be (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} with ₁₀ % by weight silver.

Two types of samples have been employed to make low contact resistance junctions to high transition temperature superconductors (HTSCs): tube-shaped and / or rod-shaped HTSC. FIG. 1 shows an HTSC sample (1). The tube diameter is in the range of 200-300 mm, with an outer diameter in the range of 12-30 mm, and a wall thickness in the range of 2-3 mm. The end of the tube is machined to obtain a groove (2) that is generally 20 mm long. Contacts were made in these grooves. The rod sample was 150 mm long and had a diameter in the range of 3-5 mm. The HTSC samples used were pure (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} and with 10% by weight silver.

  Methods for making the contacts are described below.

  The structure of the contact is shown in FIG. A first layer of silver (3) metal was deposited in the groove (2) with the tube temperature raised to about 120 ° C. and with the aid of a metal spray gun. The silver layer was heated in air at a temperature range of 250-300 ° C. for a time in the range of 2-5 hours. A silver foil (4) was then employed, one surface was knurled and wound around the first spray deposited silver layer. The jagged surface was kept in contact with the first layer. The foil was perforated with equally spaced holes with a diameter ranging from 1 to 1.5 mm. And up to 18 holes were drilled in 3 steps. The strip was 2 cm wide and 4-6 cm long. After completely winding the foil, leaving a small unrolled portion (6) to make the external contacts, the silver third layer (5) was maintained with the HTSC sample temperature maintained at 120 ° C. Adhered with the help of a metal spray gun. The final contact system was heated in air at a temperature range of 830-850 ° C. for a time in the range of 100-150 hours. The HTSC sample was then cooled. The external connections for all these samples were connected to a silver metal ring by braided copper wire.

  The resistivity of the contacts made by this procedure was measured by the 4-point probe method and summarized in Table-1.

  For the 4-point probe method, the voltage tap was soldered directly to the superconductor near the current contact. Two wires were attached to the current contact, one for flowing current and the other for detecting the voltage at the surface of the contact. The other voltage tap was soldered directly to the superconductor near the current contact. The measurement accuracy was about ± 10%. Measurements were taken with sample temperatures of 77K and 4.2K, both with and without a magnetic field.

A two-layer structure consisting essentially of a first layer deposited by a metal spray gun and perforated silver foil was also optionally provided. The final assembly was heated in air at a temperature range of 830-850 ° C. for a time in the range of 100-150 hours. However, the contact resistance was observed to be in the range of 10 ⁻⁵ Ω.

Low resistivity materials and HTSC cables can be used to energize superconducting magnets and other non-superconducting devices that require high current transport at 77K. The specific resistance of copper is on the order of 10 ⁻⁹ Ω-m. The characteristics of the tubular conductor are due to the zero loss of the material and the low thermal conductivity.

  In particular, devices that require very low power loss or low heat load in current transport, ie low contact resistance tube conductors, are essential. Any heat load greater than 1 W is detrimental, such as in the case of a cryogen-free magnetic system whose closed circuit system emits a temperature of 10K, and only a tubular conductor is used.

  The importance of low contact resistance joints is critical in these devices. In addition, the low thermal conductivity is 1/10 that of copper, which is a first candidate for avoiding the loss of the freezing agent when a large transport current is used as usual.

The novelty of the present invention lies in the low contact resistance of 10 ⁻⁷ to 10 ⁻⁶ Ω and the ability to carry a current of 200 amps continuously for at least 2 hours without any heat load on the cryogen.

  The novelty is obtained by the unobvious inventive step of adopting the process of assembling three layers and using perforated silver foil sandwiched between deposited silver layers by a metal spray gun.

  The following examples are given for illustrative purposes only and should not be construed to limit the scope of the invention.

Example 1
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor with 10% by weight of silver was employed and a groove was made at the end. The length of the tube was 305 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 2.4 mm. A first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was knurled. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance at zero applied magnetic field at 77 K was measured and the value obtained was 5.1 × 10 ⁻⁶ Ω.

Example 2
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor with 10% by weight of silver was employed and a groove was made at the end. The length of the tube was 300 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 2.4 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance at zero applied magnetic field at 77 K was measured and the value obtained was 2.02 × 10 ⁻⁷ Ω.

Example 3
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor with 10% by weight of silver was employed and a groove was made at the end. The length of the tube was 300 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 2.4 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured with a zero applied magnetic field at 4.2 K was 1.5 × 10 ⁻⁸ Ω.

Example 4
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor with 10% by weight of silver was employed and a groove was made at the end. The length of the tube was 300 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 2.4 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured at 77 K with an applied magnetic field of 0.09 Tesla was 4.8 × 10 ⁻⁷ Ω.

Example 5
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor without silver was employed and a groove was made at the end. The length of the tube was 300 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 2.4 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured at 77 K with zero applied magnetic field was 6.09 × 10 ⁻⁷ Ω.

Example 6
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor without silver was employed and a groove was made at the end. The length of the tube was 300 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 2.4 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured with a zero applied magnetic field at 4.2 K was 8.5 × 10 ⁻⁸ Ω.

Example 7
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor without silver was employed and a groove was made at the end. The length of the tube was 305 mm and the outer diameter of the tube was 12.4 mm and the wall thickness was 1 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured at 77 K with an applied magnetic field of 0.03 Tesla was 9.5 × 10 ⁻⁷ Ω.

Example 8
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor with 10% by weight of silver was employed and a groove was made at the end. The length of the tube was 200 mm and the outer diameter of the tube was 30.8 mm and the wall thickness was 2.8 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured at 77 K with zero applied magnetic field was 3.8 × 10 ⁻⁷ Ω.

Example 9
A tube of (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor with 10% by weight of silver was employed and a groove was made at the end. The length of the tube was 200 mm and the outer diameter of the tube was 30.8 mm and the wall thickness was 2.8 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured with a zero applied magnetic field at 4.2 K was 2.3 × 10 ⁻⁸ Ω.

Example 10
A (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor rod with 10% by weight silver was employed and a groove was made at the end. The rod length was 150 mm and the outer diameter was 3 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured at 77K and zero applied magnetic field was 3.7 × 10 ⁻⁷ Ω.

Example 11
A (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor rod with 10% by weight silver was employed and a groove was made at the end. The rod length was 150 mm and the outer diameter was 3 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured with a zero applied magnetic field at 4.2 K was 4.05 × 10 ⁻⁸ Ω.

Example 12
A (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor rod with 10% by weight silver was employed and a groove was made at the end. The rod length was 150 mm and the outer diameter was 5 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured at 77 K with a zero applied magnetic field was 3.0 × 10 ⁻⁷ Ω.

Example 13
A (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} high transition temperature superconductor rod with 10% by weight silver was employed and a groove was made at the end. The rod length was 150 mm and the outer diameter was 5 mm. The first silver layer was deposited in this groove by a hot metal spray gun at a temperature of 120 ° C. and subsequently heated at a temperature of 250 ° C. for 2 hours. A silver metal foil with a width of 2 cm was employed, and 18 holes with a hole diameter of 1 mm were drilled in each of the three stages. One surface of this foil was jagged. The foil was then wrapped around the first silver layer with the jagged surface of the silver foil in contact with the first silver layer. This second silver layer was then adhered to a combination of the first silver layer and the wound perforated silver foil at a temperature of 120 ° C. with a hot metal spray gun. The entire three-layer structure was sintered in air at 830 ° C. for 100 hours. In order to establish an electrical contact to this silver contact, a hole was drilled at the end of the silver foil drilled at the end and a high current conductor was connected. The contact resistance measured with a zero applied magnetic field at 4.2 K was 4.7 × 10 ⁻⁸ Ω.

  The resistivity of the contacts made by the procedure described in the previous example was measured by the 4-point probe method and summarized in Table-1.

  For the 4-point probe method, the voltage tap was soldered directly to the superconductor near the current contact. Two wires were attached to the current contact, one for flowing current and the other for detecting the voltage at the surface of the contact. The other voltage tap was soldered directly to the superconductor near the current contact. The measurement accuracy was about ± 10%.

  The external connections for all these samples were connected to a silver metal ring by braided copper wire.

Claims (9)

A method of manufacturing a contact having a low contact resistance on a high transition temperature superconductor, wherein a groove is formed at an end of the superconductor, and a first silver layer is formed on the groove by a metal spray gun at 120 ° C. Adhering at a temperature, heating the adhering silver layer at a temperature range of 200-250 ° C. for a period of 2-5 hours, adopting a perforated silver foil, one of the perforated silver foils The surface of the silver foil is jagged, the perforated silver foil is wound around the heated first silver layer while the jagged surface of the silver foil is in contact with the first silver layer, and the second silver layer is coated with a metal spray gun. be deposited with Ri by the time the heating in the range of 100 to 150 hours in air at a temperature range of the the first silver layer rolled and perforated silver foil and a combination of a second silver layer from 830 to 850 ° C. Resulting in a junction with the superconductor. How to be in.   The method of claim 1, wherein the high transition temperature superconductor is a hollow tubular tube having a length in the range of 200-305 mm.   The method according to claim 2, wherein the wall thickness of the tube is in the range of 1 to 3 mm.   The method according to claim 2, wherein the outer diameter of the tube is in the range of 10 to 20 mm.   The method of claim 1, wherein the high transition temperature superconductor is a solid rod in the range of 200 to 305 mm in length. The method according to any one of claims 1 to 5, wherein the high transition temperature superconductor is pure (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} . High transition temperature superconductors with 10% silver (Bi, Pb) is _{2 Sr 2 Ca 2 Cu 3 O} 10 + x, the method according to any one of claims 1 to 5. The contact manufactured by the method according to claim 1, wherein the contact resistance is in a range of 3.07 × 10 ^{−6 to} 3.0 × 10 ⁻⁷ Ω at 77 K with a zero applied magnetic field. The contact according to claim 8, wherein the contact resistance is in the range of 1.5 × 10 ^{−8 to} 8.5 × 10 ⁻⁸ Ω at 4.2 K with zero applied magnetic field.

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