Method of manufacturing a superconducting ceramics elongated body

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 The present invention relates to a method of manufactoring a superconducting ceramics elongated body comprising a longitudinally extending oxide ceramics superconducting layer. This is divisional application of European patent application No. 0 304 061 directed to a superconducting elongated body and a method of manufactoring the same. Further methods of manufactoring superconducting ceramics elongated bodies are claimed in co-pending applications EP-A-0 657 949 and EP-A-0 725 448. Description of 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. See in this respect Applied Physics letters, volume 51, July - December 1987, pages 203 to 204, "High T c superconductors-composite wire fabrication" by S. Jin et. al. From EP-A-0 303 412 forming prior art in accordance with Art. 54(3) EPC superconductor-coated carbon fiber composite is known comprising a carbon fiber base coated with a superconducting layer. 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 method of manufacturing a flexible superconducting ceramics elongated body. The superconducting ceramics elongated body manufactured according to the method as claimed in claim 1 comprises a flexible ceramics elongated substrate 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 oxide ceramics superconducting material for forming the oxide ceramics superconducting layer in the inventive method of manufactoring 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. The ceramics elongated substrate is not particularly restricted in configuration, but the same may be provided in the form of a tape or a round wire. 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 while the diameter of a round-wire type substrate is also 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. The superconducting ceramics elongated body manufactored 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. When, on the other hand, a round-wire type ceramics superconducting substrate is employed, for example, the entire diameter of the obtained superconducting ceramics elongated body is preferably selected to be not more than 500 µm, and more preferably, not more than 55 µm. The substrate and the superconducting layer in the inventive method of manufactoring 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. 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. According to the present invention as claimed in claim 1, the manufacturing method comprises a step of applying superconducting ceramics powder to the surface of a ceramics elongated substrate followed by a step of compression-moulding said ceramics powder on the substrate and a step of heating and firing the superconducting ceramics powder thus applied, thereby to provide a superconducting layer. The superconducting ceramics powder may be applied to at least a part of the surface of the ceramics elongated substrate. It is not necessary to apply the superconducting ceramics powder to the entire surface of the ceramics elongated substrate, so far as a longitudinally continuous superconducting layer can be formed. In order to ensure continuity of the superconducting layer after firing, fine particles are preferably compression-molded to be adhered to the surface of the ceramics elongated substrate. Heat treatment is performed to sinter the fine particles on the ceramics elongated substrate, thereby to provide a continuous superconducting layer. The fine particles are sintered by the heat treatment to ensure continuity of the superconducting layer, while rupture strength is supplied to the superconducting layer, thereby to prevent occurrence of cracking or disconnection upon bending in prescribed curvature. It is well known that an oxide superconducting material having perovskite structure is improved in superconductivity by heat treatment in oxygen. When such an oxide superconducting material of perovskite structure is adapted to prepare superconducting ceramics fine particles, therefore, heat treatment is preferably performed under an oxygen gas atmosphere. In this case, oxygen gas partial pressure is preferably 27 (200) to 133 kPa (1,000 mmHg), and more preferably, 101 kPa (760 mmHg). If the oxygen gas partial pressure is lower than 101 kPa (760 mmHg), nitrogen gas may be mixed to substantially equalize the pressure of the mixed gas to the atmospheric pressure. The method according to the present invention is adapted to form the superconducting layer by applying the superconducting ceramics fine particles to the ceramics elongated substrate and heating/sintering the same, whereby the superconducting ceramics elongated body can be manufactured through simple steps. 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 a second aspect of the manufacturing method according to the present invention; Fig. 2 is a front elevational view showing an apparatus for illustrating another embodiment of the second aspect of the manufacturing method according to the present invention; Fig. 3 is a plan view showing the apparatus for illustrating the embodiment of the second aspect of the manufacturing method according to the present invention shown in Fig. 2; DESCRIPTION OF THE PREFERRED EMBODIMENTS Description is now made on an embodiment of the manufacturing method according to the present invention. Example 1 Fine particles of superconducting ceramics were first prepared as follows: Raw materials were prepared from Y 2 O 3 powder, BaCO 3 powder and CuO powder, which were mixed and compression-molded under pressure of 9810 kPa (100 atm.) at the room temperature under the atmosphere. A compression-molded body thus obtained was preliminarily sintered in an atmosphere containing 101 kPa (760 mmHg) of oxygen gas at 940°C for 24 hours. A preliminarily sintered ceramics body thus obtained was pulverized in a ball mill to be 0.5 to 1 µm in particle size. The pulverized fine particles were again compression-molded to repeat preliminary sintering. Such a series of steps were repeated until the ceramics powder was in composition of YBa 2 Cu 3 O 6.8 in X-ray diffraction. The most preferable condition for the gas atmosphere in preliminary sintering is oxygen gas partial pressure of 760 mmHg, as hereinabove described. However, the oxygen gas partial pressure may be within a range of 27 to 133 kPa (200 to 1,000 mmHg). If the oxygen partial pressure is lower than 101 kPa (760 mmHg), nitrogen gas may be mixed to equalize the pressure of the mixed gas to the atmospheric pressure. The superconducting ceramics powder obtained in the aforementioned manner was employed to manufacture a superconducting ceramics elongated body according to the present invention, by an apparatus shown in Fig. 1. Referring to Fig. 1, a ceramics elongated substrate 21 was inserted between rollers 25a and 25b and rightwardly moved in Fig. 1, to pass through a heating furnace 26. The ceramics elongated substrate 21 was prepared by a zirconia-tape type wire rod of 3 mm in width and 50 µm in thickness. Superconducting ceramics fine particles 22 were supplied to the upper surface of the ceramics elongated substrate 21 and rolled by the rollers 25a and 25b, to define a layer of 5 µm in thickness by compression molding on the ceramics elongated substrate 21. Thus, a compression-molded layer 23 was formed by the superconducting ceramics fine particles 22 on the ceramics elongated substrate 21. The ceramics elongated substrate 21 thus provided with the compression-molded layer 23 was introduced into the heating furnace 26, in the form of an elongated body 29 coated with the fine particles. A heater 27 was provided around the heating furnace 26 to heat the same. Further, the heating furnace 26 was provided with an oxygen gas supply port 28a and an oxygen gas exhaust port 28b. Oxygen gas was supplied from the oxygen gas supply port 28a and exhausted from the oxygen gas exhaust port 28b, to provide an oxygen gas atmosphere in the heating furnace 26. The pressure of the oxygen gas was controlled to be identical to the atmospheric pressure of 101 kPa (760 mmHg). It took 30 minutes for the elongated body 29, coated with the fine particles, to pass through the heating furnace 26. The compression-molded layer 23 was sintered in the heating furnace 26, to provide a superconducting layer 24. The ceramics elongated substrate 21 provided with the superconducting layer 24 on its one surface was delivered as a superconducting ceramics elongated body 30. The temperature-resistance characteristic of the superconducting ceramics elongated body obtained in the aforementioned manner was measured to confirm that it superconducted at a temperature exceeding 77 K, the boiling point of liquid nitrogen. It has been also confirmed that no cracking nor disconnection was caused even if the superconducting ceramics elongated body thus obtained was bent in a radius of curvature of 30 cm, while its superconductivity was not damaged. However, cracking or disconnection was caused by bending in the elongated body 29 coated with the fine particles before introduction into the heating furnace 26. This suggests that the sintering step contributed to improvement in strength of the superconducting layer against bending. Example 2 Superconducting ceramics fine particles were prepared similarly to Example 1 and compression-molded by rolling as shown in Fig. 2, to be applied to the surface of a zirconia wire of 0.1 mm in diameter. Referring to Fig. 2, numeral 31 indicates a ceramics elongated substrate in the form of a round wire and numeral 33 indicates a compression-molded layer. The superconducting ceramics fine particles were supplied between rollers 35 and 36 and compressed by the same to form the compression-molded layer 33, thereby to obtain an elongated body 39 coated with the fine particles. Fig. 3 is a top plan view showing the rollers 35 and 36. In addition to the pair of rollers 35 and 36, other rollers are preferably provided at various angles with respect to the ceramics elongated substrate 31, in order to uniformly compress the periphery thereof. Fig. 3 illustrates an exemplary roller 37, which is provided perpendicularly to the rollers 35 and 36. The roller 37 forms a counterpart to another roller (not shown), to compress the peripheral surface of the elongated body 39 coated with the fine particles as well as to deliver the same. The elongated body 39 coated with the fine particles may be supplied in a twisted manner to pass through a plurality of rollers, so that its peripheral surface is uniformly compressed. The compression-molded layer 33 of about 3 µm in thickness was thus formed by the superconducting ceramics fine particles on the ceramics elongated substrate 31, which was then introduced into a heating furnace under an oxygen atmosphere similarly to that shown in Fig. 1 to sinter the compression-molded layer 33 for providing a superconducting layer, thereby to manufacture a superconducting ceramics elongated body. The superconducting ceramics elongated body obtained in the aforementioned manner superconducted at a temperature exceeding 77 K, the boiling point of liquid nitrogen, while no cracking nor disconnection was caused even if the elongated body was bent in a radius of curvature of about 30 cm.

Claims: A method of manufacturing a superconducting oxide ceramics elongated body (30) by forming a longitudinally extending oxide ceramics superconducting layer (23; 33) on at least a part of the surface of a flexible ceramics elongated substrate (21; 31), said method comprising: a first step of applying superconducting oxide ceramics powder (22) on the surface of said ceramics elongated substrate (21; 31); a second step of compression-moulding said superconducting ceramics powder (22) on said substrate ; and a third step of heating and sintering applied to said compression-moulded superconducting ceramics powder (22) to thereby provide said superconducting layer (23; 33); A method of manufacturing a superconducting ceramics elongated body in accordance with claims 1, wherein said ceramics elongated substrate is in the form of a tape (21). A method of manufacturing a superconducting ceramics elongated body in accordance with claim 2, wherein said superconducting ceramics powder (22) is compression-molded to a thickness 5 µm. A method of manufacturing a superconducting ceramics elongated body in accordance with claims 1, wherein said ceramics elongated substrate is in the form of a round wire (31). A method of manufacturing a superconducting ceramics elongated body in accordance with claim 4, wherein said superconducting layer (33) is compression-molded to a thickness of 3 µm. A method of manufacturing a superconducting ceramics elongated body in accordance with anyone of the preceding claims, wherein said step of heating and sintering applied to said superconducting ceramics powder (22) is carried out in the presence of oxygen. A method of manufacturing a superconducting ceramics elongated body in accordance with anyone of the preceding claims, wherein said step of heating and sintering applied to said superconducting ceramics powder (22) is carried out under atmospheric pressure.

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