Superconducting ceramics elongated body and method of manufacturing the same

Abstract: A superconducting ceramics elongated body comprising a flexible ceramics elongated substrate and an oxide ceramics superconducting layer formed at least on a part of the surface of the ceramics elongated substrate to longitudinally extend along the ceramics elongated substrate. The superconducting ceramics elongated body further comprises a protective layer of ceramics containing a nitride, which is provided to at least cover the surface of the superconducting layer exposed on the ceramics elongated substrate. A method of manufacturing a superconducting ceramics elongated body by forming a longitudinally continuous superconducting layer on at least a part of the surface of a flexible ceramics elongated substrate. The superconducting layer is formed on the elongated substrate by a sol-gel method, a coating/sintering method, evaporation under oxygen ions, deposition from a fluoride solution or oxidation after application of corresponding fluorides.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a superconducting ceramics elongated body comprising a longitudinally extending oxide ceramics superconducting layer and a method of manufacturing the same. Description of the Related Art In recent years, a superconducting material of oxide ceramics has been highlighted because of its high critical temperature. The range of practicable use of such a superconducting material is being widened with increase in critical temperature. For example, study has been made in order to apply the material to a power transmission medium etc. in the field of power transmission/distribution. From EP-A-0 298 866 a superconducting thin film made on a ceramic substrate and protected with a protective layer is known. Said protective layer is composed of nitride. EP-A-0 285 132 as far as it enjoys the priority date of 30/03/87 (JP application no. 79355/87) constitutes prior art in accordance with article 54(3) EPC and is directed to a superconducting elongated body comprising a flexible ceramics elongated substrate in the form of an optical fibre and a ceramics superconducting layer formed on at least part of the surface of said ceramics elongated substrate to longitudinally extend along said ceramics elongated substrate. Likewise EP-A-0 280 292 as far as it enjoys the priority date of 26/02/87 (JP application no. 44264/87) constitutes prior art in accordance with article 54(3) EPC and is directed to a method of manufacturing a superconductor with an oxide superconductive layer on a base material made of Cu or Al. In said method of manufacturing an oxide superconductive material water is added to a solution obtained by dissolving a mixture containing at least a single sort of compound within an alkoxide, a carboxylate and an acetylacetonato of a single element selected from a group of elements belonging to the groups Ia, IIa and IIIa of the periodic table and at least a single sort of compound within an alkoxide, a carboxylate and an acetylacetonato of a single element selected from a group of elements belonging to the groups Ib, IIb and IIIb of the periodic table in an appropriate organic solvent to hydrolyze the same. Alternatively, water is added to solutions of the respective compounds to separately hydrolyze the same, thereby to mix the hydrolyzed substances. Thereafter the mixture is applied onto a base material and heated, thereby to obtain a thin film of an oxide superconductive material containing the said elements. The first problem to be solved for applying an oxide ceramics superconducting material to a power transmission medium or the like is how to elongate such a superconducting material. Further, a satisfactorily elongated superconducting material must have appropriate flexibility since the same is wound on a reel or the like in practice. Thus, the second problem to be solved for applying the oxide ceramics superconducting material to a power transmission medium or the like is how to provide appropriate flexibility. SUMMARY OF THE INVENTION An object of the present invention is to provide a flexible superconducting ceramics elongated body and a method of manufacturing the same. The superconducting ceramics elongated body according to the present invention as defined in Claim 1 comprises a flexible ceramics elongated substrate in the form of a tape and an oxide ceramics superconducting layer formed on at least a part of the surface of the ceramics elongated substrate to longitudinally extend along the ceramics elongated substrate. Thus, an oxide ceramics superconducting material, forming the oxide ceramics superconducting layer which extends longitudinally along the surface of the ceramics elongated substrate, can be easily elongated with the ceramics elongated substrate serving as a matrix. Further, the superconducting ceramics elongated body can be flexibly manufactured since the oxide ceramics superconducting layer can be formed in thickness not inhibiting flexibility of the ceramics elongated substrate. The superconducting ceramics elongated body according to the present invention preferably includes a protective layer of ceramics containing a nitride, which is adapted to at least cover surfaces of the superconducting layer exposed on the ceramics elongated substrate. According to such an aspect, the entire surfaces of the oxide ceramics material forming the superconducting layer are covered with the ceramics elongated substrate and the protective layer, whereby the oxide ceramics superconducting layer can be protected against moisture and humidity. The protective layer, thus serving as a water- or moisture-resistant cover for the oxide ceramics superconducting layer, can be formed in thickness not inhibiting flexibility of the ceramics superconducting substrate, similarly to the oxide ceramics superconducting layer. The oxide ceramics superconducting material for forming the oxide ceramics superconducting layer included in the inventive superconducting ceramics elongated body has perovskite-type crystal structure, for example. In more concrete terms, examples of such an oxide ceramics superconducting material are Y-Ba-Cu oxides, Y-Sr-Cu oxides, La-Ba-Cu oxides, La-Sr-Cu oxides and the like. Elements forming these oxide ceramics materials may be partially replaced by other elements. Particularly well-known composition showing superconductivity under the temperature of liquid nitrogen is YBa 2 Cu 3 O x (x = 6.3 to 6.9). Examples of ceramics for forming a flexible ceramics elongated substrate are zirconia, alumina, magnesium oxide, strontium titanate and the like. Within these, known are those containing several percent of yttrium oxide for improving flexibility. In view of strength and flexibility required for the substrate to obtain the elongated body, the thickness of a tape-type substrate is preferably within a range of 30 to 500 µm. A flexible ceramics elongated substrate in the form of a tape, for example, can be advantageously prepared by a zirconia tape having surface roughness Rmax of about 0.3 µm and rupture strength (at 25°C) of 11,000 kg/cm 2 or an alumina tape having surface roughness of about 0.3 µm and rupture strength of 3,300 kg/cm 2 , to be employed in the present invention. A protective layer employed in a preferred mode of the present invention is formed of ceramics containing a nitride. Such a nitride is selected from AlN, TiN, TiCN, Si 3 N 4 , Si 6-z Al z O z N 8-z (0 < z ≤ 4.3) and the like. The said nitirde Si 6-z Al z O z N 8-z (0 < z ≤ 4.3) is abbreviated as "sialon", which is a compound obtained by replacing part of silicon by aluminum and part of nitrogen by oxygen within Si 3 N 4 having β-type crystals. The superconducting ceramics elongated body according to the present invention must be obtained in a flexible state. Therefore, in case of employing a tape-type ceramics elongated substrate, for example, the thickness of the obtained superconducting ceramics elongated body is preferably not more than 500 µm, and more preferably, not more than 55 µm as a whole. The superconducting ceramics elongated body according to the present invention may be coated with a strong material of a relatively low temperature, e.g., a metal such as titanium or copper, oxide ceramics such as alumina or magnesia, an organic substance such as polyamide, polyimide or polyamide-imide or the like. The superconducting ceramics elongated body according to the present invention can be flexibly manufactured since the oxide ceramics superconducting layer and the protective layer can be formed while maintaining flexibility of the ceramics elongated substrate. Thus, the superconducting ceramics elongated body can be wound on a reel, for example, to be suitable for practical use. When the protective layer is provided along the preferred mode, low water or moisture resistance of the oxide ceramics superconducting material forming the oxide ceramics superconducting layer can be compensated by high water or moisture resistance of the ceramics material containing a nitride forming the protective layer. Thus, the range of application of the inventive superconducting ceramics elongated body can be further widened. In addition to the aforementioned function, the protective layer has a possible effect of increasing mechanical strength of the entire superconducting ceramics elongated body. The substrate, the superconducting layer and the protective layer forming the inventive superconducting ceramics elongated body, all of which are prepared from ceramics materials, are approximate in thermal expansion coefficient to each other, to be resistant against a thermal shock, for example. The present invention also provides a method of manufacturing a superconducting ceramics elongated body. According to the inventive manufacturing method, a longitudinally continuous superconducting layer is formed on at least a part of the surface of a flexible ceramics elongated substrate, to provide the superconducting ceramics elongated body. In the method of the present invention as defined in claim 6, the manufacturing method comprises a step of applying a solution, which is obtained by adding water to an alcohol solution of a mixture at least containing compounds of either alkoxides or acetylacetonatos of respective metal elements for composing an oxide superconducting material and hydrolyzing the same or by adding water to alcohol solutions of compounds of the respective metal elements for separately hydrolyzing the same and mixing the hydrolyzed alcohol solutions, to at least a part of the surface of a ceramics elongated substrate and a step of heating and firing the coating layer thus formed on the ceramics elongated substrate thereby to provide a superconducting layer. In the present invention, a sol-gel method is employed. The sol-gel method is adapted to obtain target oxide ceramics by hydrolyzing starting materials of compounds of elements for forming the oxide ceramics. According to this method, the oxide ceramics can be applied to the elongated substrate in an appropriate stage of hydrolysis since its viscosity is increased with progress of the hydrolysis. The invention is based on such recognition of the inventor. In the present invention, therefore, alkoxides or acetylacetonatos of respective metal elements for forming the target oxide superconducting material are first prepared in the form of compounds. Then, a mixture of the alkoxides and/or acetylacetonatos thus prepared is dissolved in alcohol, and water is added to the alcohol solution to hydrolyze the same. Further, dehydration/condensation reaction is caused if necessary. Thus, a sol or gel solution is obtained. The alcohol solution is applied to the surface of the elongated substrate. At this time, preferably adjusted is viscosity which is increased with progress of hydrolysis. The surface of a film thus obtained is heated to obtain an oxide superconducting layer containing the respective metal elements contained in the compounds serving as starting materials. In this case, the compounds of the respective metal elements, i.e., alcohol solutions containing the alkoxides or acetylacetonatos may be independently hydrolyzed to be thereafter mixed with each other. The alcohol solution may be applied to at least a part of the surface of the ceramics elongated substrate. It is not necessary to apply the alcohol solution to the entire surface, so far as a longitudinally continuous superconducting layer can be formed. The surface of the ceramics elongated substrate is preferably repeatedly coated with the alcohol solution and heated/fired at least twice, so that no cracking is caused in the superconducting layer after firing. The superconducting layer obtained by heating/firing in the first aspect of the present invention is excellent in adhesion to the ceramics elongated substrate and has high rupture strength, while no cracking nor disconnection is caused upon bending in prescribed curvature. As hereinabove described, the inventive method includes the step of previously mixing the solutions containing raw materials before or after hydrolysis in the first aspect, whereby the inventive method can be carried out under a lower temperature of less than 1,000°C, as compared with a method of heating/melting raw materials at a temperature exceeding 1,000°C to cause solid phase reaction. Further, the raw materials, which are mixed with each other in the form of liquids, are excellent in dispersibility, whereby a homogeneous superconducting layer is obtained as the final product. The method according to present invention is adapted to form the superconducting layer by applying the alcohol solution to the ceramics elongated substrate and heating/firing the same, whereby the superconducting ceramics elongated body can be manufactured through simple steps. Further methods for manufactoring a superconducting ceramics elongated body are claimed in co-pending applications 95 102 184.9, 95 102 180.7 and 56SU0691. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing an apparatus for illustrating an embodiment of the manufacturing method according to the present invention; Fig. 2 is a sectional view showing a first embodiment of the superconducting ceramics elongated body according to the present invention; and Fig. 3 is a sectional view showing a third embodiment of the superconducting ceramics elongated body according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Description is now made on an embodiment of the manufacturing method according to the present invention. Example 1-1 An alcohol solution containing alkoxides of respective metal elements for composing an oxide superconducting material was prepared by an isopropanol solution obtained by mixing 1 mol of yttrium-tri-3-ethyl-pentoxide: 2 mols of barium-tri-3-ethyl-pentoxide: and 3 mols of copper-tri-3-ethyl-3-pentoxide: A small amount of acetylacetone was further added to the mixed solution, which was then stirred/mixed under reflux at a temperature of 83°C. Thereafter water diluted by alcohol was added to the mixed solution to hydrolyze the same. At this time, water was added by an amount corresponding to 1.2 equivalent in mole ratio to each alkoxide. The mixed solution was further stirred under a temperature of 83°C for two hours, and then stood for cooling to the room temperature. A sol solution thus obtained was left until its viscosity was 20 poises. This sol solution was employed to manufacture a superconducting ceramics elongated body according to the method of the present invention by an apparatus shown in Fig. 1. Fig. 1 is a block diagram showing an apparatus for illustrating the embodiment of the first aspect of the manufacturing method according to the present invention. The apparatus shown in Fig. 1 is formed by a crucible 3 containing a sol solution 2 and a heating furnace 5. A hole 3a is defined in a central portion of the crucible 3, to pass a ceramics elongated substrate 1. First, the sol solution 2 prepared in the aforementioned manner was introduced into the crucible 3. A zirconia tape of 50 µm in thickness and 3 mm in width was employed as the ceramics elongated substrate 1, which was introduced into the crucible 3 from above and passed through the sol solution 2, to be drawn out through the hole 3a of the crucible 3. The ceramics elongated substrate 1 thus extracted from the hole 3a of the crucible 3 was provided on its surface with a coating layer 4 by the sol solution 2. The thickness of the coating layer 4 was about 1 µm. The ceramics elongated substrate 1 thus provided with the coating layer 4 was then introduced into the downwardly provided heating furnace 5, to be heated up to 800°C. The ceramics elongated substrate 1 was then drawn out in the form of a tape-type linear body from a lower portion of the heating furnace, to provide a superconducting ceramics elongated body 7 which was formed on its surface with a superconducting layer 6 of a Y-Ba-Cu-O oxide. Such coating and firing were repeated several times, to obtain the superconducting ceramics elongated body 7 which was provided with the superconducting layer 6 of about 5 µm in thickness. The superconducting layer of the superconducting ceramics elongated body obtained in the aforementioned manner was analyzed by X-ray diffraction, to recognize that the layer was in K 2 NiF 4 type layer perovskite structure, which is typical crystal structure of high-temperature superconducting ceramics. This superconducting ceramics layer superconducted at a temperature exceeding 77 K, the boiling point of liquid nitrogen. Even if the superconducting ceramics layer was bent in a radius of curvature of 30 cm, no breakage of the ceramics elongated body nor cracking in the superconducting layer was caused, while superconductivity of the elongated body was not damaged. Fig. 2 is a sectional view showing the tape-type superconducting ceramics elongated body 7 obtained in the aforementioned manner. The superconducting layer 6 is provided on the outer peripheral surface of the tape-type ceramics elongated substrate 1. Example 1-2 A sol solution was prepared similarly to Example 1-1. A tape-type ceramics elongated substrate was prepared by a zirconia tape similarly to Example 1-1 and dipped in the sol solution, to be provided with a coating layer of about 1 µm in thickness. The ceramics elongated substrate was taken out from the solution and heated up to 800°C, to be provided on its surface with a superconducting layer of a Y-Ba-Cu-O oxide. Such dipping and heating were repeated several times, to finally obtain a superconducting ceramics elongated body provided with a superconducting layer of 5µm in thickness. The superconducting ceramics elongated body superconducted at a temperature exceeding 77 K, the boiling point of liquid nitrogen, while no cracking nor disconnection was caused even if the same was bent in a radius of curvature of about 30 cm. Description is now made on an embodiment of a superconducting ceramics elongated body having a protective layer according to the present invention. Fig. 3 is an enlarged sectional view showing the embodiment of the superconducting ceramics elongated body having a protective layer. The superconducting ceramics elongated body shown in Fig. 3 comprises a tape-type elongated substrate 101, which is formed of ceramics to have flexibility. The elongated substrate 101 extends in a direction perpendicular to the plane of Fig. 3. A superconducting layer 103 is formed on one major surface 102 of the elongated substrate 101. The superconducting layer 103 is formed of oxide ceramics, anc extends longitudinally along the elongated substrate 101. Surfaces of the superconducting layer 103 exposed on the elongated substrate 101 are covered with a protective layer 104, which is formed of ceramics containing a nitride. The protective layer 104 is in contact with both side edges of the major surface 102 of the elongated substrate 101, in order to cover the entire periphery of the superconducting layer 103, i.e., not only the upper surface but also the side surfaces of the superconducting layer 103, with the elongated substrate 101. Description is now made on an experiment which was carried out in order to obtain a superconducting ceramics elongated body having the aforementioned structure. First, a zirconia tape of 5 mm in width and 100 µm in thickness was prepared as the elongated substrate 101. Then, a superconducting layer 103 composed of YBa 2 Cu 3 O x (x = 6.3 to 6.9) was formed in thickness of 5 µm on one major surface of the elongated substrate 101 by oxygen ion beam assist evaporation. Further, the protective layer 104 was formed by magnetron type reactive high-frequency sputtering under conditions of the degree of vacuum of 10 -2 to 10 -3 Torr. and making power of 200 W. The protective layer 104 was prepared by Si 3 N 4 or "sialon". In the sputtering process, the ratio of N to Ar in the atmosphere was 0.5 when Si 3 N 4 was employed, while the ratio of (N + O) to Ar was 0.5 when "sialon" was employed. The superconducting ceramics elongated body thus obtained was introduced into a constant temperature/constant humidity bath having a temperature of 50°C and relative humidity of 95 %, to examine its moisture resistance. A reference example was prepared by an elongated body provided with no protective layer. Both of the Example and reference example superconducted at the temperature of liquid nitrogen immediately after formation. In the reference example provided with no protective layer, however, the superconducting layer was partially peeled off in the so-called disconnected state after introduction into the constant temperature/constant humidity bath for 24 hours. On the other hand, the superconducting ceramics elongated body provided with the protective layer maintained its superconductivity, which was attained immediately after formation, even if 48 hours were passed in the constant temperature/constant humidity bath. Then, the samples were bent in a prescribed radius of curvature, for evaluation of flexibility. In both of the samples, no disconnection was caused in the superconducting layers upon bending in a radius of curvature of 30 cm, and the superconducting states were maintained in the superconducting layers. In the sample provided with the protective layer, no disconnection was caused in the superconducting layer 103 even if the same was bent in a radius of curvature of 20 cm. Thus, it has been confirmed that the protective layer 104 was also adapted to improve mechanical strength of the superconducting ceramics elongated body. As hereinabove described, the superconducting ceramics elongated body according to the present invention is flexible since the superconducting layer is formed on at least a part of the surface of the flexible ceramics elongated substrate. Thus the superconducting ceramics elongated body according to the present invention, which can be wound on a reel, for example, is highly practicable. The superconducting ceramics elongated body according to the present invention is not restricted to a power transmission medium in the field of energy, but is also applicable to a switching element, a storage device, a magnetic flux sensor, an amplifying element or the like, which is employed as a device in the field of electronics. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A superconducting ceramics elongated body comprising: a flexible ceramics elongated substrate and a tape (1; 101) and a ceramics superconducting layer (6; 103) formed on at least a part of the surface of said ceramics elongated substrate to longitudinally extend along said ceramics enlongated substrate. A superconducting ceramics elongated body in accordance with claim 1, wherein the tickness of said superconducting ceramics (1; 101) elongated body is not more than 500 µm. A superconducting ceramics elongated body in accordance with claim 1, wherein the thickness of said superconducting ceramics (101; 1) elongated body is not more than 55 µm. A superconducting ceramics elongated body in accordance with claim 1, wherein a protective layer of ceramics (104) containing nitride, being provided to at least cover the surface of said superconducting layer exposed on said ceramics elongated substrate (101). A superconducting ceramics elongated body in accordance with claim 4, wherein said nitride is selected from a group of AlN, TiN, TiCN, Si 3 N 4 and Si 6-z Al z O z N 8-z (0 < z ≤ 4.3). A method of manufacturing a superconducting ceramics elongated body by forming a longitudinally continuous superconducting layer at least on a part of the surface of a flexible ceramics elongated substrate in the form of a tape, said method comprising: a step of applying a solution, being obtained by adding water to an alcohol solution of a mixture containing at least compounds of either alkoxides or acetylacetonatos of respective metal elements for composing an oxide superconducting material and hydrolyzing the same, or a solution, being obtained by respectively adding water to alcohol solutions of said compounds of said respective metal elements for separately hydrolyzing the same and mixing said hydrolyzed solutions with each other, to at least a part of the surface of said ceramics elongated substrate; and a step of heating and firing said coating layer formed on said ceramics elongated substrate to provide said superconducting layer.

Inventors: HAYASHI NORIKI, INAZAWA SHINJI, MIYAZAKI KENJI, TAKAHASHI KENICHI, TAKANO SATOSHI, YOSHIDA NORIYUKI, HAYASHI, NORIKI, INAZAWA, SHINJI, MIYAZAKI, KENJI, TAKAHASHI, KENICHI, TAKANO, SATOSHI, YOSHIDA, NORIYUKI, HAYASHI, NORIKI C/O OSAKA WORKS, INAZAWA, SHINJI C/O OSAKA WORKS, MIYAZAKI, KENJI C/O OSAKA WORKS, TAKAHASHI, KENICHI C/O OSAKA WORKS, TAKANO, SATOSHI C/O OSAKA WORKS, YOSHIDA, NORIYUKI C/O OSAKA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1988
Main classification: H01L39
IPC codes: B32B18, C04B41, H01B12, C01G1, C04B35, H01L39, C01B13, H01B13, H01L23, C01G3, B28B1