Method of manufacturing a ceramic superconductor

Abstract: A method of manufacturing a superconductive conductor containing a ceramics superconductive material being in composition generally expressed by a formula AaBbCc, where A represents at least a sort of element selected from a group of those belonging to the groups Ia, IIa and IIIa of the periodic table, B represents at least a single sort of element selected from a group of those belonging to the groups Ib, IIb and IIIb of the periodic table, C represents at least a single sort of element selected from a group of oxygen, carbon, nitrogen, fluorine and sulfur and a , b and c represent numbers showing composition ratios of A, B and C respectively, comprises a step of melting a material generally expressed by a formula AaBb, a step of continuously drawing out a melt (3) of AaBb from a hole provided in a frame (4), a step of solidifying the AaBb melt drawn out from the hole and a step of heating a solidified body of AaBb in an atmosphere containing C.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a superconductive conductor, and more particularly, it relates to a method of manufacturing a superconductive conductor which is suitable for manufacturing an elongated superconducting wire for a magnet or a long-distance transmission line. Description of the Related Art In recent years, a superconductive material of ceramics has been watched as that showing a higher critical temperature as described in, for example, Z. Phys. B 1986, vol. 64. p. 189-193 Phys. Rev. Lett. 1987 vol. 58, no.4, p.405-407. A superconductor of such ceramics material is prepared by press-forming ceramics powder of raw materials and thereafter sintering the same. After the press forming, temporary firing may be performed in advance to glost firing, as the case may be. In the conventional method performed by sintering the powder, it is extremely difficult to elongate the substance since the length thereof is restricted to that of a mold for the press forming. Thus, it has been difficult to apply the conventional superconductor to a device which can make the best use of its superconductivity such as a conductor for forming a coil for a high current density magnet or a long-distance transmission line. In the conventional method, further, complicated steps have been required in order to manufacture an elongated body, leading to inferior productivity. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of efficiently manufacturing a superconductive conductor by a ceramics superconductive material. The manufacturing method according to the present invention is characterized in that a ceramics material is partially heated/molten to be thereafter coupled with the remaining component under heating in an atmosphere containing said remaining component. The present invention provides a method of manufacturing a superconductive conductor containing a ceramics superconductive material being in composition generally expressed by a formula AaBbCc, where A represents at least a single sort of element selected from a group of those belonging to the groups Ia, IIa and IIIa of the periodic table, B represents at least a single sort of element selected from a group of those belonging to the groups Ib, IIb and IIIb of the periodic table, C represents at least a single sort of element selected from a group of oxygen, carbon, nitrogen, fluorine and sulfur and a , b and c represent numbers showing composition ratios of A, B and C, and the method comprises the following steps: First, a material generally expressed by a formula AaBb is molten and an AaBb melt thus obtained by such melting is continuously drawn out from a hole provided in a frame. Then the AaBb melt drawn out from the hole is solidified. Thereafter the solidified body of AaBb is heated in an atmosphere containing C. As hereinabove described, a superconductive conductor obtained according to the present invention may be, for example, in the composition expressed by AaBbCc, where A contains at least a single sort of element, preferably at least two sorts of elements selected from a group of those belonging to the groups Ia, IIa and IIIa of the periodic table. The elements belonging to the group Ia of the periodic table are H, Li, Na, K, Rb, Cs and Fr. The elements belonging to the group IIa are Be, Mg, Ca, Sr, Ba and Ra. The elements belonging to the group IIIa are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No and Lr. The elements belonging to the group Ib of the periodic table are Cu, Ag and Au and the elements belonging to the group IIb are Zn, Cd and Hg, while the elements belonging to the group IIIb are B, Al, Ga, In and Tl. Examples of the atmosphere containing C are that containing oxygen or nitrogen, a carbon monoxide atmosphere, a carbon dioxide atmosphere and a hydrogen sulfide atmosphere. According to the present invention, the material AaBb substantially enters an alloy state when being cooled/solidified, to have flexibility. Therefore, the material AaBb thus cooled/solidified is superior in workability to ceramics. Thus, a superconductive conductor can be easily obtained in an arbitrary final configuration by providing the material AaBb with such a configuration to be obtained in the stage after cooling/solidification. The raw material AaBb employed in the present invention hardly reacts with a part or an apparatus such as a crucible, with which the same is brought into contact in manufacturing, as compared with AaBbCc in general, whereby the melting/solidification method can be easily industrially carried out. Further, AaBb is generally superior in thermal conductivity to AaBbCc, whereby it is possible to increase the speed for drawing out the same, which is in a molten state. In a preferred embodiment according to the present invention, a material generally expressed by a formula AaBb is molten to be drawn out through a hole provided in a frame of a high temperature exceeding a melting point of AaBb. The frame of such a high temperature is so employed that a conductor being circular in section, a deformed conductor or a strip-shaped conductor can be easily obtained by devising the configuration of the frame, i.e., the sectional configuration of a portion for passing a melt of AaBb. The AaBb melt thus drawn out may be solidified by forcible cooling or natural standing. The AaBb solidified body may be heated in an atmosphere containing C through the heat in melting of AaBb itself. Thus, it is not necessary to re-heat the same by specific heating means. In this case, the atmosphere containing C is preferably provided in continuation to the high-temperature frame, so that C can be more efficiently coupled to AaBb. The AaBb solidified body may be temporarily cooled to be not more than a prescribed temperature and then re-heated, to be coupled with C under the atmosphere containing C in this state. The AaBb solidified body is preferably solidified to provide a unidirectional solidified member or a monocrystal member, whereby there is a possibility that a superconductive conductor having excellent superconductivity may be obtained. Further, preferably at least copper is contained as B and at least oxygen is contained as C in the aforementioned composition formula, in order to increase the critical temperature. According to this embodiment, an elongated body of an arbitrary sectional configuration can be drawn out with relatively small force by employing the high-temperature frame as hereinabove described. When the AaBb solidified body is provided as a unidirectional solidified member or a monocrystal body, more effective use of superconductivity may be made in the form of an elongated superconductive conductor. Such a unidirectional solidified member or monocrystal body can be easily obtained since the AaBb melt is drawn out through the high-temperature frame. According to this embodiment, further, the melt is drawn out through the frame of a high temperature, whereby an elongated body which is varied in sectional configuration can be easily obtained to provide a superconductive conductor in the form of a fine wire or a tape-like superconductive conductor by devising the sectional configuration of the high-temperature frame. Thus, an elongated superconductive conductor can be efficiently produced with no complicated mold or apparatus and through no troublesome steps. Thus, it is possible to industrially produce an elongated superconductive conductor being most applicable to form a long-distance transmission line or a coil for a high current density magnet, which can make the most effective use of superconductivity. It is pointed out here that the inventive manufacturing method is also applicable to manufacturing of a superconductive conductor being in the form other than an elongated body. In another preferred embodiment of the present invention, the material AaBb is molten and drawn out through a hole provided in a frame and then immediately brought into conatact with a cooling medium to be cooled/solidified. Thereafter the substance is heated in an atmosphere containing C. In the aforementioned step, the cooling medium is preferably prepared by a liquid such as water. Further, the substance obtained through the said cooling/solidifying step is preferably provided in an amorphous state, so that deeper infiltration of C is facilitated in a later heating step or superior flexibility is provided in this state, as the case may be. The outer diameter or thickness of the substance after cooling/solidification is preferably selected to be not more than 100 µm, in order to facilitate infiltration of C as deep as possible in the later heating step, as well as to further stabilize a superconductive state of a superconductive conductor, which may be obtained through performance of no specific working thereafter. According to this embodiment, the material AaBb is molten and then drawn out into the cooling medium through the hole to be cooled/solidified in a prescribed configuration. AaBb is easily cooled and solidified since the same is generally superior in thermal conductivity to AaBbCc. Thus, AaBb can be easily and uniformly quenched/solidified, to be readily provided in amorphous structure after cooling/solidification. Further, AaBb hardly reacts with ceramics forming a crucible or a nozzle as compared with AaBbCc in general, and hence the same can be easily industrially handled in a molten state. Thus, industrialization is facilitated with importance in industry. In addition, AaBb can be drawn out into the cooling medium through the hole in the molten state and cooled/solidified, to be extremely easily elongated. Thus, the elongated substance is thereafter heated in the atmosphere containing C, so that a superconductive conductor containing a ceramics superconductive material can be easily obtained. Namely, an elongated wire, particularly a fine wire, or a thin tape-like substance can be easily obtained to further widen the range of application of such a superconductive conductor. 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 sectional view schematically showing an apparatus employed for carrying out first Example of the present invention; and Fig. 2 is a sectional view schematically showing an apparatus employed for carrying out second Example of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 An elongated superconductive conductor was obtained through an apparatus as shown in Fig. 1. Referring to Fig. 1, this apparatus has a crucible 2 provided on its exterior with a heater 1, a high temperature frame 4 provided in a side wall portion of the crucible 2, an oxygen atmosphere furnace 5 outwardly adjacent to the high temperature frame 4 and rolls 6 and 7 for drawing out a solidified body. The atmosphere furnace 5 is also provided with a heater 8 on its periphery. YBa₂Cu₃ was heated/molten in the crucible 2 to obtain a melt 3, which was then drawn out from the high temperature frame 4 of 1.0 mm in inner diameter and immediately passed through the oxygen atmosphere furnace 5 under oxygen partial pressure of 2.00 x 10⁴ Pa (150 mmHg) at a temperature of 800°C, thereby to obtain a ceramics elongated body of YBa₂Cu₃O 7-x . This ceramics elongated body presented superconductivity at 90 K. Example 2 An elongated ceramics superconductive conductor was prepared through an apparatus as shown in Fig. 2. Referring to Fig. 2, numeral 1 indicates a heater and numeral 2 indicates a crucible, while numeral 3 indicates a melt and numeral 4 indicates a high temperature frame provided on the melt 3. An oxygen atmosphere furnace 5 is provided above the high temperature frame 4, and a pair of rolls 6 and 7 are provided above the atmosphere furnace 5, to be rotated in directions shown by arrows in the figure for drawing out a solidified ceramics body. The atmosphere furnace 5 is also provided with a heater 8 on its periphery. A material being in composition of (La 0.925 Sr 0.075 )₂Cu was heated/molten in the crucible 1 to be drawn out from the high temperature frame 4 having a passage portion of 0.5 mm in thickness and 10 mm in width to be immediately passed through the oxygen atmosphere furnace 5 under oxygen partial pressure of 2.00 x 10⁴ Pa (150 mmHg) at a temperature of 780°C, thereby to obtain a ceramics body having layer perovskite structure of (La 0.925 Sr 0.075 )₂CuO₂. This ceramics body presented superconductivity at 40 K. Example 3 Y 0.4 Ba 0.6 Cu containing 0.7 atomic percent of Be as an impurity was heated/molten in a crucible and drawn out into flowing water through a nozzle of 100 µm in pore diameter by Ar gas pressure, to be solidified in the form of a fine wire. This substance was heated in a furnace under oxygen partial pressure of 2.67 x 10⁴ Pa (200 Torr). at 1100°C for two hours, to obtain a superconductive conductor containing a ceramics superconductive material of Be 0.007 Y 0.4 Ba 0.6 CuO₃. This superconductive conductor presented superconductivity at 90 K. Example 4 La 1.66 Sr 0.34 Cu was heated/molten in a crucible to prepare a tape-like body of 30 µm in thickness and 60 mm in width by the so-called roll quench method. This substance was heated in a furnace of 1000° under oxygen partial pressure off 2.67 x 10⁴ Pa (200 Torr). for two hours, to obtain a superconductive conductor containing a ceramics superconductive material having layer perovskite structure of La 1.66 Sr 0.34 CuO₄. This superconductive conductor presented superconductivity at 30 K. Example 5 Bi₂Sr₂Ca₂Cu₃ was heated/molten in a crucible to prepare a tape-like body of 100 µm in thickness and 5 mm in width by the so-called roll quench method. This substance was heated in a furnace of 830°C under oxygen pressure of 1.01 x 10⁵ Pa (1 atm). for two hours, to obtain a superconductive conductor containing a ceramics superconductive material having layer structure of Bi₂Sr₂Ca₂Cu₃O X . This superconductive conductor presented superconductivity at 105 K. 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 spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims: A method of manufacturing a superconductive conductor formed by a ceramics superconductive material being in composition generally expressed by a formula AaBbCc, where A represents at least a single sort of element selected from a group consisting of: H, Li, Na, K, Rb, Cs, Fr; Be, Mg, Ca, Sr, Ba, Ra; Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr; and Bi; B represents at least a single sort of element selected from a group consisting of: Cu, Ag, Au; Zn, Cd, Hg; B, Al, Ga, In, Tl; C represents at least a single sort of element selected from a group consisting of: oxygen, carbon, nitrogen, fluorine and sulfur; and a, b and c represent numbers showing composition ratios of A, B and C respectively, said method comprising: a step of melting a material generally expressed by a formula AaBb, where A, B, a and b represent those described above; a step of continuously drawing out a melt of said AaBb through a hole provided in a frame; a step of solidifying said AaBb melt drawn out from said hole; and a step of heating a solidified body of said AaBb in an atmosphere containing said C. A method of manufacturing a superconductive conductor in accordance with claim 1, wherein said drawing out step comprises a step of heating said frame to a high temperature exceeding a melting point of said AaBb. A method of manufacturing a superconductive conductor in accordance with claim 1 or 2, wherein said A contains at least two sorts of elements selected from said group as defined in claim 1. A method of manufacturing a superconductive conductor in accordance with claim 3, wherein at least copper is contained as said B and at least oxygen is contained as said C. A method of manufacturing a superconductive conductor in accordance with claim 2, wherein said AaBb solidified body is either a unidirectionally elongated solidified member or a monocrystal body. A method of manufacturing a superconductive conductor in accordance with claim 2, wherein said AaBb solidified body is brought into a prescribed temperature through heat in melting of said AaBb, to be coupled with said C in said atmosphere containing said C. A method of manufacturing a superconductive conductor in accordance with claim 6, wherein said atmosphere containing said C is provided in continuation to said frame of a high temperature. A method of manufacturing a superconductive conductor in accordance with claim 2, wherein said AaBb solidified body is re-heated to be coupled with said C under said atmosphere containing said C in this state. A method of manufacturing a superconductive conductor in accordance with claim 1, wherein said solidifying step comprises a step of bringing said AaBb melt obtained by said drawing out step into contact with a cooling medium. A method of manufacturing a superconductive conductor in accordance with claim 9, wherein at least copper is contained as said B and at least oxygen is contained as said C. A method of manufacturing a superconductive conductor in accordance with claim 9, wherein said cooling medium is a liquid. A method of manufacturing a superconductive conductor in accordance with claim 9, wherein said AaBb solidified body is in amorphous structure after cooling/solidification. A method of manufacturing a superconductive conductor in accordance with claim 9, wherein the outer diameter or thickness of said cooled/solidified substance is not more than 100 µm. A superconductive conductor obtainable by a method according to claim 1. A superconductive conductor in accordance with claim 14, wherein said A contains at least two sorts of elements selected from said group as defined in claim 1. A superconductive conductor in accordance with claim 15, wherein at least copper is contained as said B and at least oxygen is contained as said C. A superconductive conductor in accordance with claim 16, wherein at least yttrium and barium are contained as said A.

Inventors: HAYASHI KAZUHIKO C O OSAKA WOR, HITOTSUYANAGI HAJIME C O OSAKA, NAKAI YOSHIHIRO C O OSAKA WORK, OHKURA KENGO C O OSAKA WORKS O, SAWADA KAZUO C O OSAKA WORKS O, HAYASHI, KAZUHIKO C/O OSAKA WORKS OF SUMITOMO EL., HITOTSUYANAGI, HAJIME C/O OSAKA WORKS SUMITOMO EL., NAKAI, YOSHIHIRO C/O OSAKA WORKS OF SUMITOMO EL., OHKURA, KENGO C/O OSAKA WORKS OF SUMITOMO EL.IND., SAWADA, KAZUO C/O OSAKA WORKS OF SUMITOMO EL.IND.
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1988
Main classification: H01L39
IPC codes: C04B35, H01L39