Method of manufacturing a superconducting wire

Abstract: A superconducting wire having a fine line made of an oxide superconductor which has a metal material dispersed therein, the outer periphery of which being coated with a conductive material; and a manufacturing method for the superconducting wire, comprising a process for drawing a metal pipe filled with an oxide superconductor so as to produce the fine line and a process for heating the fine line at a temperature which is higher than the melting point of the metal material constituting the metal pipe.

Description: The present invention relates to a method of manufacturing a superconducting wire having an oxide superconductor core. Copper oxide superconductors of Y base, Bi base, etc. exhibit superconductivity at a temperature above the boiling point of liquid nitrogen. According to a typical method for forming such a material into a wire, a superconducting material or a material therefor is charged in a metal pipe and subjected to wire drawing. The charged material is subjected to heat treatment before and after the wire drawing as necessary. A method wherein a superconductor is charged in a metal pipe has been disclosed in Japanese Patent Laid-Open No. 2-37623 and Japanese Patent Laid-Open No. 1-276516. Such methods, however, have the following problems: the superconductivity of an oxide superconductor varies depending on the amount of oxygen in the materials; therefore, the amount of oxygen in the materials must be controlled to produce the wire from the superconductor. A superconducting wire is usually provided with a stabilizing material which is normally a metal such as copper. In the case of an oxide superconductor, however, copper is oxidized during the manufacturing process due to the oxygen which is present in the superconductor; therefore, copper cannot be used for the stabilizing material. Further, an oxide superconductor does not have the workability that metals have, preventing crystal grains from deforming easily. This sometimes causes a metal pipe filled with the superconductor material to break during a rolling process or a stretching process which employs dies. In addition, the oxide superconductor must be densely and uniformly charged in the metal pipe to produce usable superconducting wire. There is still another problem: the coefficient of thermal expansion of metal is different from that of an oxide superconductor, presenting a serious problem of adhesion between the metal and the oxide superconductor when they are cooled. To solve the problems stated above, according to Japanese Patent Laid-Open No. 2-37623, an aluminium pipe is filled with an oxide superconductor and the aluminium is melted and removed before they are heated to sinter the superconductor, then they are subjected to heat treatment at 900 to 1000 degrees centigrade with the oxide superconductor exposed so as to control the amount of oxygen in the material. According to Japanese Patent Laid-Open No. 1-276516, a compact of an oxide superconductor is inserted in a silver pipe and silver powder is charged in the gap between the silver pipe and the superconductor to secure the adhesion between the metal pipe and the superconductor. According to the method disclosed in Japanese Patent Laid-Open No. 2-37623, however, the melting point of aluminum is approximately 660 degrees centigrade and therefore, the aluminum is very likely to be oxidized by the oxygen present in the oxide superconductor before the aluminum is removed from the surface of the oxide superconductor. It is especially difficult to remove the aluminum which is in a recessed spot of the surface or in a grain boundary of the oxide superconductor; an aluminum oxide generated by oxidation tends to precipitate as an impurity or to react with the oxide superconductor in some cases. Further, the Japanese Patent Laid-Open No. 2-37623 has not disclosed anything about the formation of a stabilising material which is indispensable for the application to superconductive magnet or the like. According to the method disclosed in the Japanese Patent Laid-Open No. 1-276516, no device has been made to improve the critical current of superconducting wire although the presence of silver powder seems to improve the adhesion between the metal pipe and the oxide superconductor. United States Patent US-A-5204315 discloses a method of producing superconducting wire in which extrusion of oxide superconductor and silver powders and subsequent heating that results in penetration of silver into the oxide superconductor core of the wire formed by extrusion. The wire is coated with solder by dipping into a solder melt. The method disclosed therein is of the type specified in the preamble of claim 1 attached. It is an object of the present invention to provide a method for the manufacture of a practical superconducting wire which uses an oxide superconductor with high critical temperature to prevent the critical temperature and the critical current from dropping during the manufacturing process. The method of the present invention, which is of the type specified in the preamble of claim 1 attached, accordingly is characterised in that: said steps of heating the wire and of forming said metal or metal alloy on the outside of said wire are performed concurrently by passing the wire through a bath containing a molten metal or metal alloy of Au, Cu, Ni, Pd, Pt, Ti, Mo, Nb or Mn having a melting point higher than that of the silver or silver alloy, thereby allowing the molten metal or metal alloy to cool and solidify whilst said silver or silver alloy remains molten, then allowing the molten silver or silver alloy to solidify so as to obtain the final superconductive wire. Notably in the aforesaid method the coating conductor material is selected from metals and metal alloys including, inter alia, copper and molybdenum. It is acknowledged that European Patent Application EP-A-0351203 discloses a superconductive wire of oxide superconductor having a coating of metal selected from e.g. aluminium, aluminium alloy, copper, lead, molybdenum, zirconium or tungsten. The coating process, however, is performed without raising the temperature of the superconductor core above 200°C. The disclosed purpose of this coating is to improve mechanical strength. In the accompanying drawings: Fig. 1 is a schematic cross-sectional diagram illustrative of a superconducting wire obtainable by the method according to the present invention; Fig. 2 is a flowchart illustrative of a manufacturing method according to the present invention; and Figs. 3 and 4 are schematic diagrams illustrative of specific examples of the manufacturing method according to the present invention. In the embodiments described hereinafter the manufacturing method results in a silver or silver alloy metal material dispersed in an oxide semiconductor core of a superconducting wire and in which the vacancies in the superconductor are filled with the metal material. This prevents the critical current from decreasing and improves mechanical strength. Further, a conductive material is attached closely to the outer periphery of the wire core to maximise the function thereof as a stabiliser; therefore, the conductive material is not separated from the superconductor even when the superconducting wire is subjected to heat cycles. Thus, the critical temperature and critical current are not depressed during the manufacturing process, enabling a highly practical superconducting wire featuring a high critical temperature and a high critical current to be achieved. The present invention will be described in detail by referring to preferred embodiments of the present invention. The superconducting wire manufactured according to the present invention has a structure wherein silver or a silver alloy is dispersed in a wire core composed of an oxide superconductor so as to prevent the critical current thereof from decreasing, and a metal or metal alloy conductive material, other than the same silver or silver alloy of the core, is attached to the outer periphery of the wire core. As the oxide superconductor, any oxide superconductor will suffice as long as it has said silver or silver alloy dispersed therein. Especially desirable materials for the oxide superconductor include the following: a material having a formula (I) which is expressed by Ln a Sr b Cu 3-x M x O c , where 2.7 ≤ a + b ≤ 3.3, 0.8 ≤ a ≤ 1.2, 6 ≤ c ≤ 9, and 0.05 ≤ x ≤ 0.7; and Ln consists of at least one type of element or atomic group selected from the element group of Y element and lanthanoid element, and M consists of at least one type of element or atomic group selected from the element group of Ti, V, Ga, Ge, Mo, W and Re; a material having a formula (II) which is expressed by Ln a Ca b Sr c Cu 3-x M x O d , where 2.7 ≤ a + b + c ≤ 3.3, o.8 ≤ a + b ≤ 2.1, 6 ≤ d ≤ 9, 0.05 ≤ b ≤ 1.1, and 0.05 ≤ x ≤ 1.0; and Ln consists of at least one type of element or atomic group selected from the element group of Y element and lanthanoid element, and M consists of at least one type of element or atomic group selected from the element group of Fe, Co, Ti, V, Ge, Mo, W, and Re; a material having a formula (III) which is expressed by Ln a Ca b Sr c Ba d Cu 2+e O 6+f C g , where a + b + c + d = 3, 0.2 ≤ a ≤ 0.8, 0.2 ≤ b ≤ 1.0, 0.5 ≤ c ≤ 2.2, 0 ≤ d ≤ 1.6, 0 ≤ e ≤ 0.8, 0 < f < 2, and 0.2 ≤ g ≤ 1; and Ln consists of at least one type of element or atomic group selected from the element group consisting of Y element and lanthanide element; a material having a formula (IV) which is expressed by (Ln 1-a Ca a )(Sr 2-b Ba b )(Cu 3-c B c )O d , where 0.1 ≤ a ≤ 0.5, 0.7 ≤ b ≤ 1.7, 0.1 ≤ c ≤ 0.5, and 6.5 ≤ d ≤ 7.5; and Ln consists of at least one type of element or atomic group selected from Y element and lanthanoid element excluding Ce and Tb; and a material which has essential component elements of Ln, M, Ba, Ti, Cu, and O (Ln consists of at least one type of element or atomic group selected from the element group of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; and M consists of at least one type of element or atomic group selected from the element group of Ca and Sr); and the basic structure of which has both an octahedron or a pyramid pentahedron formed by Cu and O and an octahedron formed by Ti and O at the same time, the octahedron or the pyramid pentahedron and the octahedron being arranged in a two-dimensional manner. It is needless to say that a very small amount of an impurity may be added to these materials. In the superconducting wire manufactured according to the present invention, the conductive material to be attached to the outer periphery of the oxide superconductor wire core with silver or silver alloy dispersed therein is selected from one of the following metals or a metal alloy thereof: Au, Cu, Ni, Pd, Pt, Ti, Mo, Nb, or Mn having a melting point higher than that of the silver or silver alloy. By using the materials listed above and by dispersing a silver or silver alloy in the oxide superconductor, the critical current can be improved to a certain extent and the mechanical strength can be also improved owing to the dispersed silver or silver alloy that fills the gaps between the crystal grains. The silver/silver alloy metal material near the surface of the oxide superconductor provides good adhesion to the conductive material surrounding the outer periphery of the oxide superconductor core, thus preventing the separation of the conductive material sheath from the superconductor core even when the superconducting wire is subjected to heat cycles. According to the manufacturing method, a superconductor or a precursor thereof is charged in a silver or silver alloy metal pipe and the metal pipe is subjected to wire drawing by dies, rolling, or the like. The oxide superconductor may be heated before, after or during the wire drawing to sinter it. The heating temperature should be 500 to 950°C (degrees centigrade). The resulting wire core is placed in a container such as a crucible and it is passed through a melt of the aforesaid conductive material, thus having a melting point which is higher than that of the silver or silver alloy metal constructing the metal pipe. This causes a part of the metal of the pipe to melt into the oxide superconductor and the conductive material. By winding the fine wire using a roller or the like, the fine wire is taken out of the melt of the conductive material, with the melted conductive material and pipe metal attached to the surface of the oxide superconductor. The melt attached to the surface of the oxide superconductor is dispersed in the oxide superconductor because the metal remains in the melted state even when the conductive material solidifies, thus contributing to an improved critical current. The melt from the metal and conductive material, which has not dispersed in the oxide superconductor, remains on the surface of the oxide superconductor; therefore, the oxide superconductor can be attached without any gap when the conductive material solidifies even if the surface thereof is unsmooth. There is generally a possibility of the oxygen in the oxide superconductor being reduced while the fine wire is going through the melt of the conductive material. However, since silver or silver alloy is present, the eliminated oxygen is captured in it. Therefore, even if the conductive material is one that does not allow oxygen to permeate, the superconductivity can be restored by making use of the oxygen taken into the metal by performing heat treatment. The silver or silver alloy pipe (or cover) may be provided with a plurality of small holes so as to permit easy reaction with oxygen during the heat treatment in an oxygen atmosphere, or it may be subjected to HIP treatment or the like after wire drawing or after the conductive material is solidified. It is needless to say that an insulating material may be attached to the surface of the conductive material. An appropriate atmosphere and the like for the wire drawing, heating, winding, and delivery should be selected according to the materials used. The following describes the present invention by referring to specific embodiments. First Embodiment: Fig. 1 is a schematic cross-sectional diagram illustrative of a superconducting wire manufactured according to the present invention. Reference numeral 1 denotes an oxide superconductor. Reference numeral 2 denotes inclusions of silver or a silver alloy, which has been dispersed in the oxide superconductor, and, optionally, any material added for extra pinning; they are shown in a larger size than they really are. The silver or the silver alloy need not be dispersed evenly inside the superconductor; it may be segregated in the vicinity of the surface of the oxide superconductor. Reference numeral 3 denotes a sheath of the conductive material. The oxide superconductor used for the superconducting wire according to the present invention is generally produced by heat treatment. The density of a sintered compact is frequently lower than a theoretical density. When the sintered compact is processed into a superconducting wire, therefore, vacancies are generated in the superconducting wire. The vacancies lead to a lower critical current of the superconducting wire. To provide a preferred solution to this problem, silver or a silver alloy may be melted and filled in the vacancies and further, the silver or the silver alloy may be dispersed in the oxide superconductor for the purpose of pinning by making use of the filling temperature. The conductive material is attached as the stabilising material to the outer periphery of the Ag covered wire by passing it through a bath containing the molten conductive material. As first example of the manufacturing method, a silver pipe is filled with oxide superconductor powder and rolled to be formed into a wire. The wire is then heated to a temperature above 960°C (degrees centigrade) which is the melting temperature of silver. This heating causes the silver to fill the gaps among the crystal grains of the oxide superconductor or to be scattered in the oxide superconductor. The oxide superconductor is at the same time passed through a melt of the conductive material. The conductive material is thus attached to the outer periphery of the oxide superconductor at the same time as the melting of the silver, thereby producing the superconducting wire. As shown in Fig. 1, in the superconducting wire, silver or a silver alloy is dispersed in the oxide superconductor to improve its critical current density. Further, the melt of the silver or the silver alloy is also present in vacancies and recessed voids near the surface of the oxide superconductor, thus providing good adhesion to the conductive material attached around the oxide superconductor. There is no particular restrictions on the combination of the materials employed for the oxide superconductor. In this embodiment, Y 2 O 3 , SrCO 3 , WO 3 , and CuO were mixed so as to produce 10 wt% of SrY 2 O 4 with respect to YSr 2 Cu 2.8 W 0.2 O y , then the mixture was subjected to heat treatment at 950 to 1400°C (degrees centigrade) to produce the oxide superconductor. As the conductive material to be attached around the oxide superconductor, Cu was used. This same combination of the materials was employed for other -embodiments as well as this embodiment. The superconducting wire according to this embodiment obtained by using the aforesaid materials and by melting and dispersing the silver as described above showed a critical current density of approximately 10,000 A/cm 2 (5K). In contrast to this, the critical current density, which was obtained when the same oxide superconductor was employed but no silver was melted and dispersed, was approximately 2,000 A/cm 2 , which is significantly lower than that of this embodiment. Moreover, the superconductive characteristics of the superconducting wire manufactured in accordance with this embodiment remained unchanged after winding the superconducting wire by a roller having a diameter of 30 cm, whereas the comparison example, which had no silver melted and dispersed, showed a drop in conductivity to 1/100 to 1/1.000 after winding the wire by the same roller. This demonstrates that the superconducting wire manufactured in accordance with the present invention has a high mechanical strength and also a high critical current density. Second Embodiment: Fig. 3 shows the conceptual diagram of the manufacturing method for the superconducting wire. First, a silver pipe is filled with an oxide superconductor, then it is formed into a silver sheath wire by using a plurality of dies 5 (Fig. 3 shows only one die). In this case, the superconductor was charged in the silver pipe measuring 8 mm in outside diameter and 6 mm in inside diameter to produce a fine wire 4 having an outside diameter of 0.8 mm. Reference numeral 6 denotes a copper melt in a crucible, the melt being produced by a heating device which is not shown. The temperature of the copper melt is maintained at 1,100 °C (degrees centigrade). The silver sheath wire obtained as stated above is introduced into and passed through the copper melt 6. The majority of the silver is melted and dispersed in the oxide superconductor although a part of the silver mixes with the copper melt 6 since the melting point of the silver is 960°C (degrees centigrade). The wire is wound by a roller (not shown) to take the wire, with the copper attached to the surface thereof, out of the crucible. A wire 10, which has been taken out of the crucible, is cooled. The copper, which has a higher melting point and which is on the outer periphery of the oxide superconductor, starts solidifying first, whereas the inside silver solidifies more slowly than the copper. This difference in solidifying speed enables the silver to be dispersed into the gaps between the crystal grains of the oxide superconductor. The wire 10 is cooled until the solidification of the silver is completed, then the finished superconducting wire is wound using the roller (not shown). The critical current of the superconducting wire of the second embodiment thus produced is 10 4 A/cm 2 or more regardless of the composition of the superconductor materials used. No change in the superconductive characteristics was observed even when a roller having a diameter of about 300 mm was used to wind the superconducting wire. The critical current of the silver sheath wire with no silver melted was about 10 2 A/cm 2 . The oxide superconductor broke when the wire was wound using the roller having the 300mm diameter. This superconducting wire showed almost no change in the critical temperature of the superconductor before it was charged in the silver pipe and after it was formed into the superconducting wire. Third Embodiment: Fig. 4 shows the conceptual diagram of the manufacturing method for the superconducting wire of the third embodiment. First, a silver pipe with a bore of approximately 0.1 to 0.5 mm diameter is produced from silver tape. It is filled with materials for producing the superconductor. These materials may be introduced during production of the pipe at a stage when the tape has been formed into a U-shape cross-section, or they may be introduced after the pipe has been produced. The filled silver pipe is formed into a wire having a diameter of 1 mm by using the die 5. At this time, as shown in Fig. 4, the silver pipe is heated by heaters 8 before and after it is drawn by the die so as to produce the oxide superconductor. In general, a carbonate or nitrate, or an oxide of a constituent metal element is used as the material for producing the oxide superconductor. The hole formed in the silver pipe makes it possible to supply oxygen to the central part of the silver pipe and also to discharge a gas such as carbon dioxide which is generated when the materials are decomposed. Thus, according to this embodiment, a superconductor with good characteristics can be produced by the heat treatment using the heaters 8. The wire 4 thus obtained is placed in a crucible to let it go through melted gold 6. The temperature of the gold melt 6 is maintained at 1,065 to 1,080°C (degrees centigrade). Since the melting point of silver is 960°C (degrees centigrade),the silver melts and disperses in the oxide superconductor when the wire 4 is passed through the gold melt 6. When the wire is pulled out of the crucible, it has the gold on the surface thereof. The gold and silver are partially mixed before they solidify; the mixing ratio can be controlled by the time during which the wire is in contact with the gold melt 6 and the winding speed. There should be no problem as long as the mixing ratio stays constant to a certain level throughout the wire which has been wound. The superconducting wire of the third embodiment thus produced exhibits high resistance to mechanical deformation; it can be produced in a length of about 1,000 m even when the roller 7 has a diameter of 200 mm. Fourth Embodiment: Fig. 2 shows the flow of the manufacturing method in accordance with the present invention. First, a silver or silver alloy flat tape is prepared and bent so that the cross-sectional area thereof is U-shaped. Oxide superconductor powder or a material mixture for the oxide superconductor powder is supplied to the inner side of the U-shaped tape, then it is formed so that the cross-sectional area is O-shaped. At this time, the both ends of the silver or silver alloy tape may be in contact or overlapped or they may even have a gap, provided the powder inside does not fall out. After that, the tape is subjected to wire drawing by appropriate figuring. Heat treatment is performed before and after or during the wire drawing as necessary. The wire is then led into the crucible to melt the silver or silver alloy thereby to disperse the silver or silver alloy in the superconductor, and the conductive material, which serves as the stabilizer, is attached to the surface of the superconductor. The melting of the silver or silver alloy and the attaching of the conductive material conducted at the same time. Fig. 3 shows the principle for melting the silver or silver alloy and attaching the conductive material at the same time. Reference numeral 1 denotes the oxide superconductor powder charged in the silver or silver alloy tape 3 which has been formed to have the O-shaped cross section. Reference numeral 5 indicates the die. The drawing shows'only one cycle of process; however, a plurality of dies may be used as necessary to implement a plurality of regressive process cycles. Reference numeral 4 indicates the material wire which has been formed into a desired shape by the method stated above; the wire is led into the crucible 12 to let it pass through the melt 6 of the conductive material. This causes the silver or silver alloy on the surface of the superconductor to melt. The majority of the melted silver or silver alloy moves into the vacancies or the like in the superconductor although a part thereof is mixed with the melt 6. As a result, when the wire is pulled out of the crucible 12 holding the melt 6 of the conductive material, the conductive material is applied to the surface of the wire. At this time, since the melting point of the conductive material is higher than that of the silver or silver alloy, the conductive material solidifies first, and then the silver or the silver alloy dispersed in the superconductor solidifies. Thus, the silver or the silver alloy dispersed and solidified in the oxide superconductor enables a higher critical current density. Moreover, the vacancies in the oxide superconductor and the recessed spots near the surface thereof are also filled primarily with the melt of the silver or the silver alloy, thus ensuring good adhesion of the conductive material attached to the outer periphery of the oxide superconductor. All steps including the step for making the silver or silver alloy tape into a pipe and the step for supplying the superconductor powder can be implemented in succession by using a supplying reel and a winding reel (not illustrated in Fig. 3). There is no particular restrictions on the combination of the materials used in the present invention. In the fourth embodiment, Y 2 O 3 , SrCO 3 , WO 3 , and CuO were mixed so as to produce 10wt% of SrY 2 O 4 with respect to YSr 2 Cu 2.8 W 0.2 O y , then the mixture was subjected to heat treatment at 950 to 1400°C (degrees centigrade) to produce the oxide superconductor. As the conductive material wrapping around the oxide superconductor, Cu was used. The same combination of the materials was employed for other embodiments as well as the fourth embodiment to produce the superconducting wire. The superconducting wire of this embodiment obtained by using the aforesaid materials and by melting and dispersing the silver as described above exhibited a critical current density of approximately 10,000 A/cm 2 (5K). In contrast to this, the critical current density, which was obtained when the same oxide superconductor was employed but no silver was melted and dispersed, was approximately 2,000 A/cm 2 , which is significantly lower than that of this embodiment. Furthermore, the superconductive characteristics of the superconducting wire manufactured in accordance with this embodiment remained unchanged after winding the superconducting wire by the roller having the 30cm diameter, whereas the comparison example, which had no silver melted and dispersed, showed a drop in conductivity to 1/100 to 1/1,000 after winding the wire by the same roller. This demonstrates that superconducting wire manufactured in accordance with the present invention has a high mechanical strength and also a high critical current density. Fifth Embodiment: Fig. 3 shows the conceptual diagram illustrative of the process for melting the silver and attaching the conductive material in the fifth embodiment. First, a silver sheath material which has an oxide superconductor therein and which has been formed into a pipe is processed into a fine line by a plurality of dies 5 (only one die is shown in Fig. 3). In this embodiment, a silver sheath material measuring 8 mm in outside diameter and 6 mm in inside diameter was formed into the fine line 4 having an outside diameter of 0.8 mm. Reference numeral 6 denotes a copper melt in the crucible 12 produced by melting copper by a heating device which is not shown; the temperature of the melt is maintained at 1,090°C (degrees centigrade). The silver sheath material obtained as stated above is placed in the copper melt 6 and passed through the copper melt 6. At this time, the majority of the silver is melted and dispersed in the oxide superconductor although a part of the silver mixes with the copper melt 6 since the melting point of the silver is 960°C (degrees centigrade ). Then, the wire is wound by a roller, not shown, to take the wire, which has the copper attached to the surface thereof, out of the crucible 12. The wire 10 taken out of the crucible 12 starts solidifying from the outer periphery; it is cooled until the solidification of the silver inside is completed before the finished superconducting wire is wound using the roller which is not shown. Oxygen may be blown into the melted silver so that the oxide superconductor with oxygen reduced may restore the superconductive characteristics. Heat treatment may be performed again after the silver on the outer periphery solidifies. The critical current of the superconducting wire thus produced was 10 4 A/cm 2 or more regardless of the composition of the oxide superconductor material used and no change in the superconductive characteristics was observed even when the diameter of the roller winding the superconducting wire was about 300 mm. A wire which has the same performance was obtained when a silver tape with a hole having a diameter of 0.5 mm or less was employed to make the superconducting wire in the same manner as stated above. When, however, the speed for winding the wire was too high for the silver of the silver tape to fully melt, the critical current of the resulting wire was about 10 2 A/cm 2 and the observation of the cross section of the obtained wire revealed the presence of a gap over the whole surface between the silver and the superconductor. Such a gap was not observed in the superconducting wire manufactured according to the present invention. This demonstrates that, in the method of the present invention, the silver melts and fully covers the irregular surface of the superconductor, thereby ensuring close contact with the conductive material on the outer periphery.

Claims: A method of manufacturing a superconductive wire comprising steps of: producing a wire having an oxide superconductor core and a covering of silver or silver alloy; heat treating the wire to cause the silver or silver alloy of said covering to penetrate said wire; and forming a metal or metal alloy, different from said silver or silver alloy on the outside of said core, using a bath of the molten metal or metal alloy; characterised in that : said steps of heating the wire and of forming said metal or metal alloy on the outside of said wire are performed concurrently by passing the wire through a bath containing a molten metal or metal alloy of Au, Cu, Ni, Pd, Pt, Ti, Mo, Nb or Mn having a melting point higher than that of the silver or silver alloy, thereby allowing the molten metal or metal alloy to cool and solidify whilst said silver or silver alloy remains molten, then allowing the molten silver or silver alloy to solidify so as to obtain the final superconductive wire. A method according to claim 1, wherein said step of producing a wire is performed by compacting a powder of said oxide superconductor into a pipe of said silver or silver alloy and drawing a wire from the filled pipe by rolling or by extrusion through dies. A method according to claim 1, wherein said step of producing a wire is performed by filling a U-shaped tape of silver or silver alloy with a powder of said oxide superconductor, forming said U-shaped tape into a pipe and compacting the oxide superconductor powder, and drawing a wire from the filled pipe by rolling or by extrusion through dies. A method according to claim 1, wherein said step of producing a wire is performed by compacting, into a pipe of said silver or silver alloy, a mixed powder for forming said oxide superconductor which mixed powder comprises powders of ingredient nitrates, carbonates or oxides of the constituent metal elements of said oxide superconductor, and drawing a wire from the filled pipe by rolling or by extrusion through dies, and which method includes heating the mixed powder before, after, or both before and after, drawing, to convert the mixed powder to said oxide superconductor. A method according to claim 1, wherein said step of producing a wire is performed by filling a U-shaped tape of silver or silver alloy with a mixed powder for forming said oxide superconductor, which mixed powder comprises powders of ingredient nitrates, carbonates, or oxides of the constituent metal elements of said oxide superconductor, forming said U-shaped tape into a pipe and compacting the mixed powder, and drawing a wire from the filled pipe by rolling or by extrusion through dies, and which method includes heating the mixed powder before, after, or both before and after, drawing, to convert the mixed powder to said oxide superconductor. A method according to any preceding claim wherein said oxide superconductor is composed of the materials represented by composition formula (I) given below: Ln a Sr b Cu 3-x M x O c where Ln consists of at least one type of element or atomic group selected from the element group of Y element and lanthanoid element; M consists of at least one type of element or atomic group selected from the element group of Ti, V, Ga, Ge, Mo, W, and Re; and 2.7 ≤ a + b ≤ 3.3, 0.8 ≤ a ≤ 1.2, 6 ≤ c ≤ 9, and 0.05 ≤ x ≤ 0.7. A method according to any preceding claim 1 to 5, wherein said oxide superconductor is composed of the materials represented by composition formula (II) given below: Ln a Ca b Sr c Cu 3-x M x O d wherein Ln consists of at least one type of element or atomic group selected from the element group of Y element and lanthanoid; M consists of at least one type of element or atomic group selected from the element group of Fe, Co, Ti, V, Ge, Mo, Re, and W; and 2.7 ≤ a + b + c ≤ 3.3, 0.8 ≤ a + b ≤ 2.1, 6 ≤ d ≤ 9, 0.05 ≤ b ≤ 1.1, and 0.05 ≤ x ≤ 1.0. A method according to any preceding claim 1 to 5, wherein said oxide superconductor is composed of the materials represented by composition formula (III) given below: Ln a Ca b Sr c Ba d Cu 2+e O 6+f C g wherein Ln consists of at least one type of element or atomic group selected from the element group of Y element and lanthanide element; and a + b + c + d = 3, 0.2 ≤ a ≤ 0.8, 0.2 ≤ b ≤ 1.0, 0.5 ≤ c ≤ 2.2, 0 ≤ d ≤ 1.6, 0 ≤ e ≤ 0.8, 0 〈 f 〈 2, and 0.2 ≤ g ≤ 1.0. A method according to any preceding claim 1 to 5, wherein said oxide superconductor is composed of the materials represented by composition formula (IV) given below: (Ln 1-a C a )(Sr 2-b Ba b )(Cu 3-c B c )0 d where Ln consists of at least one type of element or atomic group selected from the element group of Y element and lanthanoid element excluding Ce and Tb; and 0.1 ≤ a ≤ 0.5, 0.7 ≤ b ≤ 1.7, 0.1 ≤ c ≤ 0.5, and 6.5 ≤ d ≤ 7.5. A method according to any preceding claim 1 to 5, wherein said oxide superconductor is composed of the elements of Ln, M, Ba, Ti, Cu and O; and the basic structure thereof is equipped with both an octahedron or a pyramid pentahedron formed by Cu and O and an octahedron formed by Ti and O, the octahedron or the pyramid pentahedron and the octahedron being arranged in a two-dimensional manner; where Ln consists of at least one type of element or atomic group selected from the element group of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; and M consists of at least one type of element or atomic group selected from the element group of Ca and Sr.

Inventors: KANEKO NORIO, KANEKO, NORIO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: H01B12
IPC codes: H01L39, C04B35