Superconducting wire and method of manufacturing the same

Abstract: A superconducting wire is formed by an oxide superconductor in an Ag matrix. An Ag alloy containing metals for constituting the superconductor is formed in a wire. The Ag alloy wire is heat treated in an oxidising atmosphere to form the oxide superconductor in the Ag matrix.

Description: The present invention relates to a superconducting wire using a compound superconductor and a method of manufacturing the same and, more particularly, to a superconducting wire suitable for an oxide superconductor and a method of manufacturing the same. Conventionally, A15, B1, Chevrel, and Laves metal-based compound superconductors are known. Oxide ceramic-based superconductors having a crystal structure such as perovskite and layered perovskite superconductors are also known. Of these superconductors, a layered perovskite oxide superconductor such as an La-Ba-Cu-O superconductor has a critical temperature of 30K or higher at which the superconductor does not exhibit superconducting characteristics. Of a oxygen deficient perovskite oxide superconductor, e.g., a Y-Ba-Cu-O superconductor, some have critical temperatures exceeding 90K. A variety of applications have been proposed for these oxide ceramic-based superconductors since they have high critical temperatures, and these superconductors are receiving a lot of attention. High-temperature superconductors are applied to, e.g., a superconducting magnet, a transmission line, and the like. These applications are wires, and a demand has arisen for manufacturing a wire using the above-mentioned oxide ceramic-based superconductor. However, since sintering is performed in the manufacture of the oxide superconductor, pellets can only be manufactured. Therefore, the oxide superconductor can hardly be applied to a superconducting magnet and a transmission line. It is an object of the present invention to provide a superconducting wire using a compound superconductor, especially, an oxide superconductor and a method of manufacturing the same. It is another object of the present invention to provide a superconducting wire which allows a current to effectively flow therethrough, and a method of manufacturing the same. It is still another object of the present invention to provide a superconducting coil using an oxide superconducting wire. A superconducting wire according to the present invention has an Ag matrix, and an oxide superconductor dispersed in the matrix. A method of manufacturing a superconducting wire according to the present invention comprises the steps of: forming an Ag alloy which consists of metals constituting the oxide superconductor into a wire; and performing a heat treatment on the Ag alloy wire in an oxidizing atmosphere to form an oxide superconductor in an Ag matrix. According to the present invention, since an oxide superconductor is integrated with an Ag matrix to form a wire, a superconducting wire using the oxide superconductor can be very easily obtained. Since the wire can be a continuous member, a current can be effectively flowed through the wire. The superconducting wire of the present invention can be wound to obtain a superconducting coil. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a cross sectional view showing a superconducting wire of a first arrangement according to an invention described and claimed in our co-pending European Patent Application No. 88302050. 5 (EP-A-0 282 286). An embodiment of the present invention will be described below. A superconducting wire of this embodiment is formed such that an oxide superconductor is formed in an Ag matrix. An oxide superconductor having a perovskite type oxide superconductor, is used. In order to manufacture the superconducting wire, an Ag alloy containing metals for forming an oxide superconductor is processed to form a wire. Examples of elements contained in the Ag alloy are La, Ba, Sr, Y, Cu, and the like. The wire can have an arbitrary shape, and is formed into, e.g., a ribbon-like shape. Upon preparation of the alloy, Ag and other metals are charged in a reaction chamber such as a crucible to have a predetermined composition, and are melted. In this case, since La, Ba, Sr, Y, Cu, and the like as alloy components are easily oxidizable, melting is preferably performed in an inert atmosphere. A water-cooled copper crucible free from impurity contamination is preferably used as a reaction chamber. In order to process this alloy into a wire, swaging, wire drawing, or rolling is performed. This process is preferably a hot process rather than a cold process. Since the case of the cold process, elements such as La and Ag undesirably form fragile intermetallic compound, the wire is broken during working. Note that a wire may be formed by rapidly cooling a molten alloy without performing the above-mentioned process. Thereafter, the Ag alloy wire formed in the above process is subjected to an oxidizing atmosphere such as air or an oxygen gas atmosphere. With this heat treatment, oxygen in the atmosphere is diffused in the alloy, and reacts with oxide superconductor elements in the alloy. Thus, the oxide superconductor is formed in the Ag matrix. Since Ag has excellent electrical and heat conductivities, it is effective as a stabilizer for an oxide superconductor. Since Ag easily diffuses oxygen, oxygen is easily diffused in the Ag alloy during the heat treatment, and the oxide superconductor can be easily formed. In addition, since Ag itself is rarely oxidized, characteristics of a stabilizer will not be degraded. The heat treatment is preferably performed at a temperature of 400 to 940°C. If the heat treatment temperature is below 400°C, reaction of producing the oxide superconductor is very slow, resulting in inconvenience. If the temperature exceeds 940°C, an oxide superconductor undesirably becomes large in grain size and aggregated. Example 1 An alloy consisting of 8.07 wt% of La, 0.85 wt% of Sr, 8.08 wt% of Cu, and the balance of silver was prepared in a water-cooled copper crucible using a plasma arc melting furnace. The resultant alloy was subjected to hot processes, i.e., swaging and wire drawing at a temperature of 600°C, thus obtaining a wire having a diameter of 2 mm. The wire was then subjected to a heat treatment in a 1-atm oxygen atmosphere at 600°C for 96 hours. As a result, an La-Sr-Cu-O layered perovskite superconductor was formed on the surface and inside an Ag matrix. The superconducting characteristics were examined using the compound superconducting wire. A critical temperature was 35K and a critical current at 4.2 K was 10 A, demonstrating good characteristics. Example 2 An alloy consisting of 11.6 wt% of La, 2.5 wt% of Ba, 5.9 wt% of Cu, and the balance of silver was prepared in a water-cooled copper crucible using a plasma arc melting furnace. The resultant alloy was charged in a quartz vessel having a nozzle at its lower end, and was melted using a high-frequency furnace. Thereafter, the molten alloy was injected by an argon gas pressure onto a cooling Cu roll which was rotated at the lower end of the nozzle, so that the molten alloy was rapidly cooled in an argon atmosphere, thus producing a ribbon having a thickness of 0.5 mm and a width of 2 mm. The ribbon was subjected to a heat treatment in a 1-atm oxygen atmosphere at 650°C for 48 hours. As a result, an La-Ba-Cu-O layered perovskite superconductor was formed on the surface and inside an Ag matrix. The superconducting characteristics were examined using the compound superconducting wire. A critical temperature was 30K and a critical current at 4.2 K was 5 A, exhibiting good characteristics. Example 3 An alloy consisting of 4.8 wt% of Y, 14.9 wt% of Ba, 10.3 wt% of Cu, and the balance of silver was prepared in a water-cooled copper crucible using a plasma arc melting furnace. The resultant alloy was subjected to hot swaging and wire drawing processes at 800°C to obtain a wire having a diameter of 2 mm. The resultant wire was subjected to a heat treatment in a 1-atm oxygen atmosphere at 900°C for 96 hours. As a result, a Y-Ba-Cu-O oxide superconductor was formed on the surface and inside an Ag matrix. The superconducting characteristics were examined using the compound superconducting wire. A critical temperature was 83K and a critical current at 77 K was 15 A, exhibiting good characteristics.

Claims: A superconducting wire having: an Ag matrix; and an oxide superconductor dispersed in said matrix. A superconducting wire according to claim 1, characterized in that said oxide superconductor has a perovskite type crystal structure. A superconducting wire according to claim 2, characterized in that said oxide superconductor contains Cu and at least one element selected from the group consisting of: Ba, Sr, Ca, Y, Yb, Ho, Dy, Eu, Sm, Gd, Nd, La, Er, Tm and Lu. A superconducting wire according to claim 3, characterized in that said oxide superconductor contains a composition represented by (La 1-x M x ) 2 CuO 4 wherein x indicates atomic %, 0 ≤ x < 0.1, and M is an element selected from the group consisting of: Ba, Sr, and Ca. A superconducting wire according to claim 3, characterized in that said oxide superconductor contains a composition represented by ABa 2 Cu 3 O 7-δ wherein δ ≤ 0.2, and A represents an element selected from the group consisting of: Y, Yb, Ho, Dy, Eu, Sm, Gd, Nd, La, Er, Tm, and Lu. A superconducting wire according to claim 1, characterized in that the oxide superconductor is continuous. A method of manufacturing a superconducting wire comprising the steps of: forming an Ag alloy which consists of metals constituting the oxide superconductor into a wire; and performing a heat treatment on the Ag alloy wire in an oxidizing atmosphere to form an oxide superconductor in an Ag matrix. A method according to claim 7, characterized in that the heat treatment step is performed within a temperature range of 400 to 940°C. A method according to claim 7, characterized in that the heat treatment step is performed in an atmosphere of air or oxygen gas. A method according to claim 7, characterised in that the forming step is achieved by extrusing, swaging, wire drawing, or rolling. A method according to claim 7, characterized in that by the forming step, a molten Ag alloy is rapidly solidified and is directly formed into a wire or a tape. A method according to claim 7, characterised in that said oxide superconductor has a perovskite type crystal structure. A method according to claim 12, characterized in that said oxide superconductor contains Cu and at least one element selected from the group consisting of: Ba, Sr, Ca, Y, Yb, Ho, Dy, Eu, Sm, Gd, Nd, La, Er, Tm, and Lu. A method according to claim 13, characterized in that said oxide superconductor contains a composition represented by (La 1-x M x ) 2 CuO 4 , wherein x indicates atomic %, 0 ≤ x < 0.1, and M is an element selected from the group consisting of: Ba, Sr, and Ca. A method according to claim 13, characterized in that said oxide superconductor contains a composition represented by ABa 2 Cu 3 O 7-δ, wherein δ ≤ 0.2, and A represents an element selected from the group consisting of: Y, Yb, Ho, Dy, Eu, Sm, Gd, Nd, La, Er, Tm, and Lu. A superconducting coil formed by winding a superconducting wire according to any one of claims 1 to 6.

Inventors: FUKUSHIMA NOBURU, KOIZUMI MISAO, MURASE SATORU, NAKAYAMA SHIGEO, NIU HIROMI, YAMADA YUTAKA, YOSHINO HISASHI, FUKUSHIMA, NOBURU, KOIZUMI, MISAO, MURASE,, SATORU, NAKAYAMA, SHIGEO, NIU, HIROMI, YAMADA, YUTAKA, YOSHINO, HISASHI, Fukushima, Noburu, c/o Patent Division, Koizumi, Misao, c/o Patent Division, Murase,, Satoru, c/o Patent Division, Nakayama, Shigeo, c/o Patent Division, Niu, Hiromi, c/o Patent Division, Yamada, Yutaka, c/o Patent Division, Yoshino, Hisashi, c/o Patent Division
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: H01L39
IPC codes: C04B35, H01L39