WO2014126149A1 - 酸化物超電導線材 - Google Patents
酸化物超電導線材 Download PDFInfo
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- WO2014126149A1 WO2014126149A1 PCT/JP2014/053320 JP2014053320W WO2014126149A1 WO 2014126149 A1 WO2014126149 A1 WO 2014126149A1 JP 2014053320 W JP2014053320 W JP 2014053320W WO 2014126149 A1 WO2014126149 A1 WO 2014126149A1
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- oxide superconducting
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
- H01B12/02—Superconductive or hyperconductive conductors, cables, or transmission lines characterised by their form
- H01B12/06—Films or wires on bases or cores
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F6/00—Superconducting magnets; Superconducting coils
- H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N60/00—Superconducting devices
- H10N60/20—Permanent superconducting devices
- H10N60/203—Permanent superconducting devices comprising high-Tc ceramic materials
Definitions
- the present invention relates to an oxide superconducting wire. This application claims priority based on Japanese Patent Application No. 2013-028222 filed in Japan on February 15, 2013, the contents of which are incorporated herein by reference.
- One of the high-efficiency and low-current-loss electrical devices that can solve recent energy, environment, and resource problems is superconducting devices such as cables, coils, motors, and magnets that use superconductors as a low-current-loss material. It is done.
- oxide superconductors such as RE-123 series (REBa 2 Cu 3 O (7-x) : RE is a rare earth element including Y and Gd) are known. ing.
- RE-123 series REBa 2 Cu 3 O (7-x) : RE is a rare earth element including Y and Gd
- This oxide superconductor exhibits superconducting properties near the liquid nitrogen temperature and can maintain a relatively high critical current density even in a strong magnetic field. Therefore, compared with other superconductors, it is considered that it can be applied in a wide range, and is expected as a promising material for practical use.
- oxide superconductor In order to use an oxide superconductor for an electric device, it is common to process the oxide superconductor into a wire and use it as a power supply conductor or an oxide superconducting wire such as a magnetic coil.
- the oxide superconducting wire is formed by forming an oxide superconducting layer on a tape-like substrate via an intermediate layer. It is known that when an oxide superconductor is placed in a humid environment, the crystal structure is disturbed by the influence of moisture and the superconducting properties are deteriorated. Therefore, it is necessary to protect the oxide superconducting layer from moisture. For this purpose, a technology for protecting from moisture by forming a base stabilization layer containing Ag on an oxide superconducting layer is known.
- a base stabilizing layer is formed on an oxide superconducting layer of a laminate in which an oxide superconducting layer is formed on a base material via an intermediate layer, and electrolytic plating is performed on the outer periphery of the laminate including the base stabilizing layer.
- a structure is known in which a stabilizing layer of Cu or the like is formed by a method, and the outer periphery of the oxide superconducting wire is sealed from moisture.
- the current density flowing in each layer constituting the oxide superconducting wire is not equivalent because it depends on the electric resistance. Therefore, there is a problem that the thickness of the stabilization layer becomes non-uniform.
- Ni-based alloys for example, Hastelloy: trade name, manufactured by Haynes, USA
- Hastelloy trade name, manufactured by Haynes, USA
- the adhesion is poor and the Cu plating layer (stabilization layer) may be peeled off.
- Patent Document 1 completely covers the outer periphery of a laminate formed of a base material and an oxide superconducting layer formed on the base material through an intermediate layer with a base stabilization layer made of Ag, A technique for forming a stabilization layer having a uniform thickness by providing a Cu stabilization layer by plating on the base stabilization layer is disclosed.
- an object of the present invention is to provide an oxide superconducting wire that secures adhesion to a stabilizing layer while suppressing the amount of Ag used and does not deteriorate superconducting properties due to moisture.
- an oxide superconducting wire includes a base material, an intermediate layer formed on a main surface of the base material, and an oxide formed on the intermediate layer.
- An oxide superconducting laminate having a superconducting layer; a first base stabilization layer formed of Ag or an Ag alloy so as to cover at least the upper surface of the oxide superconducting layer; and an outer periphery of the oxide superconducting laminate.
- a second base stabilization layer made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component, covering at least a portion not covered with the first base stabilization layer, and the oxidation
- a base stabilization layer formed on an outer periphery of the superconductor laminate, and a base stabilization layer formed on the base stabilization layer, and at least a part of the first base stabilization layer and the second of the base stabilization layers.
- a base stabilizing layer is formed on the outer periphery of the oxide superconducting laminate, and a stabilizing layer is further formed on the base stabilizing layer.
- the base stabilization layer includes a first base stabilization layer made of Ag or an Ag alloy and a second base stabilization layer made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component.
- These first and second base stabilization layers are excellent in adhesion to plating or solder. Therefore, when a plating coating layer is provided as a stabilizing layer, it is possible to form a plating coating layer having high adhesion and a uniform film thickness.
- a metal tape is used as the stabilization layer and the metal tape is joined via a solder layer, a highly airtight stabilization layer can be formed.
- the second undercoat stabilization layer made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component is included.
- the amount used can be suppressed. Therefore, the cost can be reduced.
- the first base stabilization layer is formed on the oxide superconducting layer
- the second base stabilization layer is formed on the back surface of the base material
- the side surface of the oxide superconducting laminate The first base stabilization layer and the second base stabilization layer may be formed so as to partially overlap.
- the oxide superconducting wire according to the above aspect is a second underlayer stabilization layer made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component on the back side of the base material in the outer periphery of the oxide superconducting laminate. Is formed, and the first base stabilization layer made of Ag is not formed all around.
- the amount of Ag used can be suppressed and the cost can be reduced as compared with a structure in which the front periphery is covered with a base stabilization layer made of Ag.
- the side surface of the oxide superconducting laminate is formed and covered so that the first base stabilization layer and the second base stabilization layer partially overlap each other, moisture intrusion from the side surface is suppressed.
- the superconducting characteristics can be prevented from deteriorating.
- the second base stabilization layer may be formed so as to cover the entire exposed surface of the first base stabilization layer.
- the first base stabilization layer made of Ag or an Ag alloy is Cu, Ni, Pb, Bi, or the second base stabilization made of an alloy containing these as a main component. Covered by layers. Therefore, even if a pinhole is formed on the first base stabilization layer by performing oxygen annealing after the first base stabilization layer is formed, the pinhole is blocked by the second base stabilization layer. It is possible to prevent moisture from entering.
- the first base stabilization layer made of Ag or an Ag alloy and the solder layer are in direct contact with each other, the first base stabilization layer is eroded by the metal material constituting the solder, and the first base stabilization layer and There is a possibility that the interface resistance value with the oxide superconducting layer is increased. If this interfacial resistance value increases, the resistance when supplying current to the oxide superconducting wire from the current lead or the like becomes large, or the current in the oxide superconducting layer stabilizes when a transition occurs to the normal conducting state due to quenching. It becomes difficult to commutate to the bed. As a result, the oxide superconducting wire may be burned out.
- the oxide superconducting wire when the outer periphery of the base stabilization layer is covered with a metal tape (stabilization layer) via the solder layer, the first base stabilization layer is the second base stabilization layer. Therefore, the first base stabilization layer and the solder layer are not in direct contact with each other. Therefore, by preventing the first base stabilization layer from coming into contact with the solder layer, it is possible to suppress an increase in the interface resistance value between the first base stabilization layer and the oxide superconducting layer.
- the film thickness of the first base stabilization layer on the upper surface of the oxide superconducting layer may be not less than 0.1 ⁇ m and not more than 2 ⁇ m. According to the oxide superconducting wire according to the above aspect, pinholes are generated in the first base stabilization layer due to the heat treatment during the oxygen annealing, and a part of the oxide superconducting layer is prevented from being exposed. Since the amount used can be suppressed, the cost can be reduced.
- the stabilizing layer may be a plating coating layer or a metal tape. According to the oxide superconducting wire according to the above aspect, deterioration of superconducting characteristics due to moisture intrusion can be suppressed by having the above configuration.
- the oxide superconducting wire according to the above aspect is composed of the first base stabilization layer in which the entire outer periphery of the oxide superconducting laminate is made of Ag or an Ag alloy, Cu, Ni, Pb, Bi, or an alloy containing these as a main component. Since it is covered with the second underlayer stabilization layer, moisture can be prevented from entering the oxide superconducting layer of the oxide superconducting laminate, and deterioration of the superconducting characteristics can be suppressed. Further, in addition to the first base stabilization layer made of Ag or an Ag alloy, the second base stabilization layer made of Cu, Ni, Pb, Bi or an alloy containing these as a main component is used. Since the amount can be suppressed, the cost can be reduced.
- FIG. 1 is a cross-sectional perspective view schematically showing an oxide superconducting wire according to a first embodiment of the present invention.
- FIG. 5 is a cross-sectional perspective view schematically showing a modification of the oxide superconducting wire according to the first embodiment of the present invention. It is a cross-sectional perspective view which shows typically the oxide superconducting wire which concerns on 2nd Embodiment of this invention. It is a section perspective view showing typically the modification of the oxide superconducting wire concerning a 2nd embodiment of the present invention.
- FIG. 1 shows an oxide superconducting wire 1 according to a first embodiment of the present invention.
- the oxide superconducting wire 1 is configured to cover the outer periphery of the oxide superconducting conductor 15 with a plating coating layer (stabilization layer) 17.
- the oxide superconducting conductor 15 includes an oxide superconducting laminate 16 formed of a tape-like substrate 10 and an intermediate layer 11 and an oxide superconducting layer 12 laminated on the main surface 10a of the substrate 10, and And a base stabilization layer 20 laminated on the outer periphery.
- the base stabilization layer 20 includes a first base stabilization layer 13 made of Ag or an Ag alloy, a second base stabilization layer 14 made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component.
- first base stabilization layer 13 made of Ag or an Ag alloy
- second base stabilization layer 14 made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component.
- the base material 10 may be any material that can be used as a base material for a normal oxide superconducting wire, and is preferably a long tape having flexibility. Further, the material used for the base material 10 preferably has a metal having high mechanical strength, heat resistance, and easy to be processed into a wire, such as stainless steel, Hastelloy (trade name, US Haynes, Inc.). And other heat-resistant metal materials such as nickel alloys, or materials in which ceramics are arranged on these metal materials. Especially, if it is a commercial item, Hastelloy is suitable.
- Hastelloy examples include Hastelloy B, C, G, N, W, etc., which have different amounts of components such as molybdenum, chromium, iron, and cobalt, and any kind can be used in this embodiment.
- the base material 10 an oriented Ni—W alloy tape base material in which a texture is introduced into a nickel alloy can be used.
- the thickness of the substrate 10 may be appropriately adjusted according to the purpose, and is usually 10 to 500 ⁇ m, preferably 20 to 200 ⁇ m.
- An intermediate layer 11 is formed on the main surface 10 a of the substrate 10.
- the intermediate layer 11 for example, a structure in which a diffusion prevention layer, a bed layer, an alignment layer, and a cap layer are stacked in this order can be applied.
- a part of the constituent elements of the base material 10 diffuses and impurities To be mixed into the oxide superconducting layer 12 side.
- the specific structure of the diffusion prevention layer is not particularly limited as long as it has the above function, but Al 2 O 3 , Si 3 N 4 , or GZO (Gd 2 Zr 2), which has a relatively high effect of preventing impurity contamination.
- a single layer structure or a multilayer structure composed of O 7 ) or the like is desirable.
- the bed layer is used to suppress the reaction of the constituent elements at the interface between the base material 10 and the oxide superconducting layer 12 and to improve the orientation of the layer provided on the upper surface than this layer.
- the specific structure of the bed layer is not particularly limited as long as it has the above function, but Y 2 O 3 , CeO 2 , La 2 O 3 , Dy 2 O 3 , Er 2 O 3 , Eu 2 having high heat resistance. O 3, and Ho 2 O 3 single layer structure or a multilayer structure composed of a rare earth oxide such as is desirable.
- the alignment layer controls the crystal orientation of the cap layer and the oxide superconducting layer 12 formed thereon, suppresses the constituent elements of the substrate 10 from diffusing into the oxide superconducting layer 12, 10 and the oxide superconducting layer 12 are alleviated in physical characteristics such as a coefficient of thermal expansion and a lattice constant.
- the material of the alignment layer is not particularly limited as long as it has the above function, but when a metal oxide such as Gd 2 Zr 2 O 7 , MgO, ZrO 2 —Y 2 O 3 (YSZ) is used, an ion beam described later is used.
- IBAD method assisted vapor deposition method
- a layer having high crystal orientation is obtained, and the crystal orientation of the cap layer and the oxide superconducting layer 12 can be improved, which is particularly preferable. .
- the cap layer controls the crystal orientation of the oxide superconducting layer 12 to be equal to or higher than that of the oriented layer, suppresses the diffusion of elements constituting the oxide superconducting layer 12 into the intermediate layer 11, or the oxide superconducting layer 12.
- the reaction between the gas used when laminating and the intermediate layer 11 is suppressed.
- the material of the cap layer is not particularly limited as long as it has the above function, but CeO 2 , LaMnO 3 , Y 2 O 3 , Al 2 O 3 , Gd 2 O 3 , ZrO 2 , YSZ, Ho 2 O 3 , and A metal oxide such as Nd 2 O 3 is preferable from the viewpoint of lattice matching with the oxide superconducting layer 12.
- CeO 2 and LaMnO 3 are particularly suitable from the viewpoint of matching with the oxide superconducting layer 12.
- the cap layer may include a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.
- the oxide superconducting layer 12 has a function of flowing current when in the superconducting state.
- a material composed of an oxide superconductor having a generally known composition can be widely applied.
- copper such as RE-123 superconductor and Bi superconductor can be used.
- oxide superconductors examples include oxide superconductors.
- the composition of the RE-123 series superconductor is, for example, REBa 2 Cu 3 O (7-x) (RE represents a rare earth element such as Y, La, Nd, Sm, Er, Gd, and x represents oxygen deficiency).
- the material of the oxide superconducting layer 12 used in the present embodiment is a copper oxide superconductor.
- the material used for the oxide superconducting layer 12 is a copper oxide superconductor.
- the above-described base material 10, intermediate layer 11, and oxide superconducting layer 12 constitute an oxide superconducting laminate 16.
- the outer periphery of the oxide superconducting laminate 16 is covered with the base stabilization layer 20, and the main surface portion 13 b of the first base stabilization layer 13 is formed on the oxide superconducting layer 12.
- the main surface portion 14 b of the second base stabilization layer 14 is formed on the back surface 10 b of the base material 10.
- the side surface portions 13a and 14a of the first ground stabilization layer 13 and the second ground stabilization layer 14 are formed on the side surface 16a of the oxide superconducting laminate 16, and the oxide superconducting conductor 15 is configured. Yes.
- the first base stabilization layer 13 includes a main surface portion 13b formed on the oxide superconducting layer 12 of the oxide superconducting laminate 16, and a side surface portion 13a formed on the side surface 16a of the oxide superconducting laminate 16. Consists of. Further, the first base stabilization layer 13 is not formed on the back surface 10 b of the base material 10. The first base stabilization layer 13 bypasses an overcurrent generated at the time of an accident, or a chemical reaction that occurs between the oxide superconducting layer 12 and a layer provided on the upper surface of the first base stabilization layer 13. And a function of preventing deterioration of the superconducting characteristics due to the breakdown of the composition of some of the elements in one layer entering the other layer.
- the first base stabilization layer 13 makes it easy for oxygen to permeate during heating in order to make the oxide superconducting layer 12 easily take in oxygen.
- the first base stabilization layer 13 is formed of a material mainly composed of Ag such as Ag or an Ag alloy.
- the first base stabilizing layer 13 made of Ag or an Ag alloy can be formed by a film forming method such as a sputtering method.
- a film forming method such as a sputtering method.
- An example of the film formation of the first ground stabilization layer 13 by sputtering will be described below.
- a target made of Ag or an Ag alloy and the oxide superconducting laminate 16 are placed in a processing vessel into which Ar gas is introduced by reducing the pressure inside the vacuum. At this time, the oxide superconducting laminate 16 is disposed such that the oxide superconducting layer 12 faces the target.
- plasma is generated by ionizing Ar gas by applying a voltage to the target to cause discharge. Ar ions generated in the plasma sputter the target to sputter Ag sputtered particles from the target, and the sputtered particles are deposited on the oxide superconducting layer 12, whereby the first base stabilization layer 13 is formed.
- the first base stabilization layer 13 has sputtered particles (Ag particles) also on the side surfaces of the base material 10, the intermediate layer 11, and the oxide superconducting layer 12.
- the side part 13a is formed by wrapping around. This is because the sputtered particles collide with Ar in the processing container to change the direction of movement. Therefore, the side surface portion 13a of the first base stabilization layer 13 is a thinner layer than the main surface portion 13b. Further, the film thickness of the side surface portion 13a gradually decreases as the distance from the main surface portion 13b increases.
- a thin layer (not shown) of Ag is also formed on the back surface 10b side of the substrate 10.
- the first base stabilization layer 13 only needs to have at least a main surface portion 13b formed on the oxide superconducting layer 12 of the oxide superconducting laminate 16, and the side surface 16a of the oxide superconducting laminate 16 is sufficient.
- the film thickness of the main surface portion 13b formed on the oxide superconducting layer 12 of the first base stabilization layer 13 can be 10 nm or more and 10 ⁇ m or less.
- the cost can be reduced by forming the main surface portion 13b as a thin layer having a thickness of 10 ⁇ m or less.
- the film thickness formed on the oxide superconducting layer 12 of the main surface portion 13b is preferably 10 nm or more and 10 ⁇ m or less.
- the film thickness is more preferably 0.1 ⁇ m or more and 10 ⁇ m or less.
- the upper limit of the film thickness range can be set to 2 ⁇ m from the viewpoint of further cost reduction. .
- oxygen annealing treatment After the first base stabilization layer 13 is formed, heat treatment is performed at 300 to 500 ° C. for 5 to 20 hours in an oxygen atmosphere (oxygen annealing treatment). Since the oxide superconducting layer 12 has a crystal structure in which oxygen is insufficient after the film formation, oxygen can be supplied to the oxide superconducting layer 12 to adjust the crystal structure by performing the oxygen annealing treatment described above. it can.
- the second base stabilization layer 14 includes a main surface portion 14 b formed on the back surface 10 b of the base material 10 and a side surface portion 14 a formed on the side surface 16 a side of the oxide superconducting laminate 16.
- the second base stabilization layer 14 can bypass the overcurrent at the time of an accident together with the first base stabilization layer 13.
- the second base stabilization layer 14 is formed of a material made of Cu, Ni, Pb, Bi, or an alloy containing these as a main component. Examples of the Cu alloy include a Cu—Zn alloy and a Cu—Ni alloy.
- the second base stabilization layer 14 made of Cu can be formed by a sputtering method in the same manner as the first base stabilization layer 13.
- a Cu target is disposed opposite to the back surface 10 b of the substrate 10, and the second base stabilization layer 14 is formed on the substrate 10.
- the second base stabilizing layer 14 is not only applied to the back surface 10b of the base material 10 but also to the side surfaces of the base material 10, the intermediate layer 11, and the oxide superconducting layer 12 as shown in FIG. Cu particles) wrap around.
- the side surface portion 13a of the first base stabilization layer 13 is formed on the side surface of the base material 10, the intermediate layer 11, and the oxide superconducting layer 12, the side surface portion 13a of the first base stabilization layer 13 is formed. A side surface portion 14a of the second base stabilization layer 14 is formed thereon.
- the side surface portion 13a of the first base stabilization layer 13 formed on the side surfaces of the base material 10, the intermediate layer 11, and the oxide superconducting layer 12 is a thin layer, Ag is aggregated by the oxygen annealing treatment, There is a possibility that a pinhole is formed in the portion 13a.
- the pinhole is covered by forming the side surface portion 14a of the second base stabilization layer 14 on the side surface portion 13a of the first base stabilization layer 13. Therefore, the oxide superconducting laminate 16 can be completely covered with the base stabilization layer 20 formed by the first base stabilization layer 13 and the second base stabilization layer 14.
- the film thickness of the main surface portion 14b of the second base stabilization layer 14 can be 10 nm or more and 10 ⁇ m or less.
- the oxygen supplied to the oxide superconducting layer 12 by the oxygen annealing process is activated by the heat during the film formation and escapes from the oxide superconducting layer 12. There is a risk of it.
- film formation by sputtering when sputtered particles collide with the film formation body, the kinetic energy at the time of collision is converted into thermal energy, and the surface of the film formation body generates heat.
- the second base stabilization layer 14 is formed by sputtering, the back surface 10b of the substrate 10 generates heat due to the film formation.
- the amount of generated heat has a correlation with the film thickness of the second base stabilization layer 14 to be formed, and when the film thickness of the second base stabilization layer 14 is 10 ⁇ m or more, this heat is transferred to the oxide superconducting layer. 12, oxygen in the oxide superconducting layer 12 is activated and escapes. Therefore, it is desirable that the film thickness of the second base stabilization layer 14 is 10 ⁇ m or less.
- the oxide superconducting laminate 16 is formed on the oxide superconducting laminate 16. It is desirable that the thickness is 10 nm or more because it cannot be completely covered together with one base stabilization layer 13.
- the side surface portion 13 a of the first base stabilization layer 13 in FIG. 1 completely covers the side surface 16 a of the oxide superconducting laminate 16.
- the side surface portion 14 a of the second base stabilization layer 14 completely covers the side surface portion 13 a of the first base stabilization layer 13.
- any one of the side surface portion 13 a of the first base stabilization layer 13 or the side surface portion 14 a of the second base stabilization layer 14 may cover the surface of the oxide superconducting laminate 16. It is possible to cover the outer periphery of the oxide superconducting laminate 16 with the first base stabilization layer 13 and the second base stabilization layer 14 to suppress the amount of Ag used. The cost can be reduced as compared with the case where the outer periphery is covered only with one base stabilization layer 13.
- the oxide superconducting conductor 15 includes the oxide superconducting laminate 16 including the base material 10, the intermediate layer 11, and the oxide superconducting layer 12, and the oxide superconducting laminate. And a base stabilization layer 20 covering the outer periphery of the body 16.
- the foundation stabilization layer 20 includes a first foundation stabilization layer 13 and a second foundation stabilization layer 14, and the first foundation stabilization layer 13 is formed on the oxide superconducting layer 12 of the oxide superconducting laminate 16.
- the main surface portion 13b is formed, the main surface portion 14b of the second base stabilization layer 14 is formed on the back surface 10b of the substrate 10, and at least the first base stabilization is provided on the side surfaces 16a, 16a of the oxide superconducting laminate 16.
- One of the side surface portion 13 a of the stabilizing layer 13 and the side surface portion 14 a of the second base stabilization layer 14 is formed.
- the oxide superconducting wire 1 is composed of the oxide superconducting conductor 15 and a plating coating layer (stabilization layer) 17 that hermetically covers the outer periphery of the oxide superconducting conductor 15.
- the substrate 10 and the oxide superconducting layer 12 have poor plating adhesion as compared with the first base stabilization layer 13 and the second base stabilization layer 14.
- the base material 10 and the room-temperature oxide superconducting layer 12 have remarkably high electrical resistance values as compared with the first base stabilization layer 13 and the second base stabilization layer 14. Therefore, it is difficult to form a plating layer having a uniform thickness on the surface of the base material 10 and the oxide superconducting layer 12 by electrolytic plating.
- the plating coating layer 17 is the first base stabilization layer 13. Is formed only on the base stabilization layer 13 or the second base stabilization layer 14. Therefore, the plating coating layer 17 on the outer periphery of the oxide superconducting conductor 15 is excellent in adhesiveness with the oxide superconducting conductor 15. In addition, since the difference in electrical resistance between the first base stabilization layer 13 and the second base stabilization layer 14 is relatively small, the plating coating layer 17 having a more uniform film thickness can be formed. .
- the plating coating layer 17 laminated on the oxide superconducting conductor 15 is made of a highly conductive metal material.
- the oxide superconducting layer 12 tries to change from the superconducting state to the normal conducting state for some reason, the base stabilization is performed.
- the oxide superconducting layer 12 functions as a stabilization layer serving as a bypass through which current flows.
- the plating coating layer 17 can completely block the oxide superconducting conductor 15 from the outside, and can more reliably prevent moisture from entering.
- the metal used for the plating coating layer 17 include copper, nickel, gold, silver, chromium, and tin, and these metals can be used singly or in combination.
- the plating coating layer (stabilizing layer) 14 is used for instantaneously suppressing an overcurrent generated when a quench occurs and the state transitions to a normal conducting state. It is done.
- the material used for the plating coating layer 17 include high-resistance metals such as Ni-based alloys such as Ni—Cr.
- the thickness of the plating coating layer 17 is not particularly limited and can be adjusted as appropriate, but can be 10 to 100 ⁇ m. When the thickness of the plating coating layer 17 is less than 10 ⁇ m, a pinhole may occur in the plating coating layer 17, and there is a possibility that moisture cannot be reliably prevented from entering. On the other hand, when the thickness of the plating coating layer 17 exceeds 100 ⁇ m, the thickness of the oxide superconducting wire 1 is enlarged and the flexibility is not preferable. Therefore, the thickness of the plating coating layer is desirably 10 ⁇ m or more and 100 ⁇ m or less.
- FIG. 2 is a schematic diagram showing an oxide superconducting wire 2 which is a modification of the above-described first embodiment of the present invention.
- symbol is attached
- the oxide superconducting wire 2 is different in the configuration covering the outer periphery of the oxide superconducting conductor 15. That is, the oxide superconducting wire 2 according to the modified example is composed of the oxide superconducting conductor 15 and a metal tape (stabilizing layer) 18 that hermetically covers the outer periphery thereof.
- the oxide superconducting wire 2 has an oxide superconducting conductor 15 disposed on the surface of the metal tape 18 provided with the solder layer 19 and wraps the peripheral surface of the oxide superconducting conductor 15 in a substantially C-shaped cross section. It is formed by bending, melting and heating the solder layer 19 and applying pressure with a roll.
- the metal tape 18 is bent into a substantially C-shaped cross section, and includes a front wall 18a, a side wall 18b, and a back wall 18c, and covers a part of the base material 10 from the oxide superconducting layer 12 of the oxide superconducting conductor 15. Yes.
- a solder layer 19 is formed on the inner peripheral surface side of the metal tape 18.
- the solder layer 19 of the metal tape 18 is formed only on the surface (inner surface) in contact with the oxide superconducting conductor 15, but the solder layer 19 may be provided on both surfaces of the metal tape 18.
- the metal tape 18 provided with the solder layer 19 on the outer periphery of the oxide superconducting conductor 15 is spirally wound or the like. It may be covered.
- the metal material constituting the metal tape 18 is not particularly limited as long as it has good electrical conductivity, but copper alloy such as copper, brass (Cu—Zn alloy), Cu—Ni alloy, stainless steel, etc. It is preferably formed of an inexpensive material, and among them, copper is preferable because it has high conductivity and is inexpensive.
- the oxide superconducting wire 2 is used for a superconducting fault current limiter
- the material used for the metal tape 18 is preferably a high resistance metal such as a Ni-based alloy such as Ni—Cr.
- the thickness of the metal tape 18 is not particularly limited and can be adjusted as appropriate, but can be 9 to 60 ⁇ m. If the thickness of the metal tape 18 is too thin, there is a risk of tearing. If it is too thick, it becomes difficult not only to form the metal tape 18 into a substantially C-shaped cross section, but also a high stress is applied during molding. Since it is necessary, the oxide superconducting layer 12 may be deteriorated.
- the solder used for the solder layer 19 is not particularly limited, and a conventionally known solder can be used.
- solder made of an alloy containing Sn as a main component, such as Sn, Sn—Ag alloy, Sn—Bi alloy, Sn—Cu alloy, Sn—Zn alloy, Pb—Sn alloy solder, Crystal solder, low-temperature solder, and the like can be mentioned, and these solders can be used singly or in combination of two or more.
- solder having a melting point of 300 ° C. or less As a result, the metal tape 18 and the first base stabilization layer 13 or the second base stabilization layer 14 can be soldered at a temperature of 300 ° C. or lower, so that the oxide superconducting layer is heated by the soldering heat. It can suppress that the characteristic of 12 deteriorates.
- the metal tape 18 functions as a stabilization layer serving as a bypass through which the current of the oxide superconducting layer 12 is commutated.
- the metal tape 18 can completely block the oxide superconducting conductor 15 from the outside, and can more reliably prevent moisture from entering.
- the outer periphery of the oxide superconducting laminate 16 is covered with the first base stabilization layer 13 or the second base stabilization layer 14 having good adhesion to the solder. Since the oxide superconducting conductor 15 is formed, the solder layer 19 and the oxide superconducting conductor 15 can be easily adhered to each other to form the oxide superconducting wire 2 having high airtightness.
- oxide superconducting wire 3 (Second embodiment of oxide superconducting wire)
- an oxide superconducting wire 3 according to a second embodiment of the present invention will be described with reference to FIG.
- symbol is attached
- the oxide superconducting wire 3 according to the second embodiment is different from the oxide superconducting wire 1 according to the first embodiment in the configuration of the base stabilization layer 21, particularly the configuration of the second base stabilization layer 24. ing. That is, as shown in FIG.
- the second base is formed so as to cover the entire outer periphery of the oxide superconducting laminate 16 on which the first base stabilizing layer 13 is formed.
- a stabilization layer 24 is formed.
- the outer periphery of the oxide superconducting conductor 25 is covered with the plating coating layer 17 to form the oxide superconducting wire 3, but the oxide superconducting wire 2 which is a modification of the first embodiment.
- a structure in which the outer periphery of the oxide superconducting conductor 25 is covered with a metal tape 18 via a solder layer 19 may be adopted.
- the second base stabilization layer 24 can be formed by a film forming method such as a sputtering method, as in the first embodiment. Similar to the side surface portion 24a, the back surface portion 24c of the second underlayer stabilization layer 24 formed on the main surface portion 13b of the first underlayer stabilization layer 13 collides with Ar in the processing vessel. By changing the direction of movement, the oxide superconducting laminate 16 is formed by wrapping around the side where the oxide superconducting layer 12 is laminated.
- the back surface portion 24c can be formed by increasing the Ar pressure (film formation pressure) in the processing container when forming the second base stabilization layer 24 by sputtering. Specifically, the back surface portion 24c can be formed by setting the film forming pressure to 0.5 Pa or more. However, if the film formation pressure is increased, the film formation rate is lowered and there is a concern about an increase in cost. Therefore, the film formation pressure is preferably 10 Pa or less.
- the film thickness of the main surface portion 24b of the second base stabilization layer 24 is 10 nm or more, similar to the film thickness of the main surface portion 14b of the second base stabilization layer 14 in the oxide superconducting wire 1 according to the first embodiment. It can be 10 ⁇ m or less. If the main surface portion 24b having a thickness exceeding 10 ⁇ m is to be formed, the oxygen supplied to the oxide superconducting layer 12 by the above-described oxygen annealing treatment may be activated and removed by heat during film formation.
- the second base stabilization layer 24 includes not only the back surface 10b of the substrate 10 and the side surface portion 13a of the first base stabilization layer 13, but also the first base stabilization layer 13. It is also formed on the main surface portion 13b. Further, the side surface portion 24a and the back surface portion 24c of the second base stabilization layer 24 formed on the side surface portion 13a and the main surface portion 13b of the first base stabilization layer 13 are formed in a processing container in film formation by sputtering. It is formed by collision with Ar inside and changing the direction of motion. Therefore, the sputtered particles lose most of the kinetic energy at the time of collision with Ar, and the thermal energy generated during lamination is small.
- the thermal influence due to the formation of the back surface portion 24c is minute, and oxygen escapes if the film thickness of the main surface portion 24b is 10 ⁇ m or less as in the second undercoat stabilization layer 14 of the first embodiment liquid. It is desirable without fear. Further, when the film thickness of the second base stabilization layer 24 formed on the base material 10 is less than 10 nm, the first base stabilization layer 13 formed on the oxide superconducting laminate 16 and Since it becomes impossible to completely cover the oxide superconducting laminate 16 with the second base stabilization layer 24, the thickness is preferably 10 nm or more.
- the step of forming the main surface portion 24b and the step of forming the back surface portion 24c are performed separately in addition to the formation of the back surface portion 24c of the second base stabilization layer 24 by the wraparound of the sputtered particles. You can also. That is, after the rear surface 10b of the base material 10 of the oxide superconducting laminate 16 is arranged to face the target to form the main surface portion 24b, the first ground stabilizing layer 13 of the oxide superconducting laminate 16 is formed.
- the back surface portion 24c may be formed by disposing the main surface portion 13b side facing the target.
- the first base stabilization layer 13 is heated by the oxygen annealing treatment, Ag atoms of the first base stabilization layer 13 are locally aggregated on the surface of the oxide superconducting layer 12 and are isolated and dispersed. In some cases, Ag particles may be aggregated. As a result, pinholes may be formed in the first base stabilization layer 13 and the oxide superconducting layer 12 may be exposed.
- the plating coating layer 17 is formed on the first underlayer stabilization layer 13, since the acidic plating solution and the oxide superconducting layer 12 are in contact with each other in the exposed portion, the oxide superconducting layer 12 is corroded and has superconducting properties. There is a risk of causing deterioration.
- the first base stabilization layer 13 is completely covered by the second base stabilization layer 24. Therefore, even if pinholes are formed on the first ground stabilization layer 13, the superconducting characteristics are not deteriorated by forming the plating coating layer 17.
- the outer periphery of the oxide superconducting conductor 25 in this embodiment is completely covered with the second base stabilization layer 24, and the plating coating layer 17 is formed on the second base stabilization layer 24. Therefore, the plating coating layer 17 on the outer periphery of the oxide superconducting conductor 25 is excellent in adhesion with the oxide superconducting conductor 25 and has a more uniform film thickness.
- FIG. 4 is a schematic diagram showing an oxide superconducting wire 4 which is a modification of the above-described second embodiment of the present invention, and is composed of an oxide superconducting conductor 25 and a metal tape 18 that covers the outer periphery thereof in an airtight manner. ing.
- symbol is attached
- the outer periphery of the oxide superconducting conductor 25 is covered with the second base stabilizing layer 24 having good adhesion to the solder, and the metal tape 18 can be easily adhered through the solder layer 19, and the oxide superconducting wire 4. Can be formed.
- the metal tape 18 can be easily adhered through the solder layer 19, and the oxide superconducting wire 4. Can be formed.
- a metal tape is directly soldered on the first base stabilization layer, if a pinhole is formed on the first base stabilization layer 13, a reaction between the solder and the oxide superconducting layer 12 occurs. Superconducting properties may be reduced.
- pinholes are formed on the first base stabilization layer 13.
- the thickness of the back surface 24c of the second base stabilization layer 24 is 0.1 ⁇ m or more and 5 ⁇ m or less. It is preferable to do.
- the film thickness of the back surface portion 24c of the second base stabilization layer 24 is smaller than 0.1 ⁇ m, the Cu of the second base stabilization layer 24 and Sn of the solder layer 19 are alloyed to form the first base stabilization layer. There is a risk that the adhesion between the base 13 and the second undercoat stabilization layer 24 will deteriorate.
- the metal (for example, Sn) constituting the solder layer 19 erodes the first base stabilization layer 13, and the first base stabilization is performed.
- the layer 13 is an alloy of Ag and a metal constituting the solder.
- the erosion of the metal constituting the solder layer 19 is limited to the vicinity of the interface with the solder layer 19 in the first base stabilization layer 13, but the first base stabilization layer 13 is formed thin (for example, 2 ⁇ m or less). ), The entire thickness of the first base stabilization layer 13 is alloyed.
- Table 1 shows a sample 1 in which a first underlayer stabilization layer is formed on an oxide superconducting layer, and a Sn solder layer is further formed on the first underlayer stabilization layer, and a first underlayer on the oxide superconducting layer.
- the first base stabilization layer is formed on the sample 2 in which only one base stabilization layer is formed, and the first base stabilization layer formed on the oxide superconducting layer, and then the second base stabilization
- substrate stabilization layer in the sample 3 which formed the solder layer by Sn on the formation layer is shown.
- variety of a wire is 10 mm
- region which measured the interface resistance value is 20 mm.
- the thickness of the first ground stabilization layer of Samples 1 to 3 is 2 ⁇ m
- the thickness of the second ground stabilization layer of Sample 3 is 1 ⁇ m.
- the interface resistance value with the base stabilization layer 13 is significantly increased. This is because Sn penetrates into the first base stabilization layer 13 and the first base stabilization layer 13 becomes an Ag—Sn alloy, and the interface state between the first base stabilization layer 13 and the oxide superconducting layer 12 changes. It is thought that it is to do.
- the second base stabilization layer 24 is provided between the first base stabilization layer and the solder layer, the first base stabilization layer 13 may be as thin as 2 ⁇ m or less. However, it can be seen that the interface resistance value between the oxide superconducting layer 12 and the first base stabilization layer 13 does not increase.
- the first base stabilization layer 13 is completely covered with the second base stabilization layer 24. Therefore, the solder layer 19 is not in contact with the first base stabilization layer 13. Therefore, since solder does not penetrate into the first base stabilization layer 13 and become an alloy with Ag, the interface resistance value between the first base stabilization layer 13 and the oxide superconducting layer 12 can be seen from Table 1. Can be prevented from rising. Further, when the film thickness of the first base stabilization layer 13 is as thin as 2 ⁇ m or less, Ag is eroded by Sn of the solder layer, so that the entire first base stabilization layer 13 becomes an Ag—Sn alloy. End up.
- the metal tape 18 is peeled off.
- the second base stabilization layer 24 provided between the first base stabilization layer 13 and the solder layer 19 functions as an Sn diffusion prevention layer, Ag is Sn in the solder layer. Therefore, the adhesion of the metal tape 18 can be secured.
- Example preparation First, the surface of a tape-shaped substrate made of Hastelloy C-276 (trade name of Haynes, USA) having a width of 10 mm, a thickness of 0.1 mm, and a length of 1000 mm was polished using alumina having an average particle diameter of 3 ⁇ m. Next, the surface of the substrate was degreased and washed with acetone.
- Hastelloy C-276 trade name of Haynes, USA
- Al 2 O 3 (diffusion prevention layer; film thickness 100 nm) is formed on the main surface of the base material by sputtering, and Y 2 O 3 (bed layer; film thickness 30 nm) is formed thereon by ion beam sputtering.
- MgO metal oxide layer; film thickness: 5 to 10 nm
- 500 nm thick is formed thereon by pulsed laser deposition (PLD method).
- CeO 2 (cap layer) was formed.
- a 2.0 ⁇ m thick GdBa 2 Cu 3 O 7- ⁇ oxide superconducting layer was formed on the CeO 2 layer by the PLD method.
- a first ground stabilization layer made of Ag having a thickness of 2 ⁇ m is formed on the oxide superconducting layer by sputtering from the oxide superconducting layer side, and oxygen annealing is performed in an oven at 500 ° C. for 10 hours in an oxygen atmosphere. Further, after cooling in a furnace for 26 hours, the product was taken out.
- a second base stabilization layer made of Cu having a thickness of 1 ⁇ m was formed on the base material by sputtering from the back surface side of the base material to obtain an oxide superconductor. This oxide superconductor is commonly used in Examples 1 and 2 below.
- Example 1 A plating coating layer was formed by plating on the outer periphery of the oxide superconducting conductor obtained through the above-described procedure, and the oxide superconducting wire of Example 1 having the same structure as that of the oxide superconducting wire 1 shown in FIG.
- the procedure of the plating method is to immerse the oxide superconducting conductor in an aqueous copper sulfate solution during the process of unwinding the above-described oxide superconducting conductor wound from the coil and winding it again with the winding coil.
- a plating coating layer made of Cu and having a thickness of 75 ⁇ m was formed.
- the electrolytic plating was set so that the current density of the object to be plated (oxide superconducting conductor) was 5 A / dm 2, and the plating conditions were set to a plating bath temperature of 25 ° C. and an immersion time of 18 minutes.
- Example 2 The outer periphery of the oxide superconducting conductor obtained through the above-described procedure was covered with a metal tape via a solder layer to produce an oxide superconducting wire having the same structure as that of the oxide superconducting wire 2 of Example 2 shown in FIG. .
- a metal tape made of Cu having a width of 10 mm, a thickness of 50 ⁇ m, and a length of more than 1000 mm, on which Sn plating (melting point: 230 ° C., solder layer) having a thickness of 5 ⁇ m is formed on one side is prepared.
- the oxide superconducting conductor On the surface of the metal tape that has been subjected to Sn plating, the oxide superconducting conductor has the same length as that of the metal tape, and the first base stabilization layer and the surface of the metal tape that has been subjected to Sn plating are opposed to each other.
- the solder is formed by melting Sn on the metal tape by passing it through a heating / pressurizing roll, and the first base stabilization layer of the oxide superconductor is bonded to the metal tape. It was. Next, both ends of the metal tape in the width direction were bent into a U-shape, and both ends of the metal tape were bent toward the back side of the substrate to form a metal tape so as to have a substantially C-shaped cross section.
- the heating / pressurizing roll was a silicon roll, and the heating / pressurizing treatment was performed at a heating temperature of 240 ° C., a pressing force of 10 to 20 MPa, and a wire conveying speed of 100 m / h.
- a pressure cooker test was performed for Examples 1 and 2 in a high temperature (120 ° C.), high humidity (100%), and high pressure (2 atm) environment for 100 hours, and the ratio of critical current values before and after the test. was measured.
- Ic 0 critical current value after being left for the ratio
- Ic critical current
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Abstract
Description
本願は、2013年2月15日に、日本に出願された特願2013-028222号に基づき優先権を主張し、その内容をここに援用する。
酸化物超電導体は多湿環境下に置かれると水分の影響を受けて結晶構造が乱れ、超電導特性が劣化することが知られている。従って酸化物超電導層を水分から保護する必要がある。このためにAgを含む下地安定化層を、酸化物超電導層上に形成することにより、水分から保護する技術が知られている。
例えば、基材上に中間層を介して酸化物超電導層を成膜した積層体の酸化物超電導層上に下地安定化層を形成し、下地安定化層を含む積層体の外周に、電解めっき法によりCu等の安定化層を形成し、酸化物超電導線材の外周を水分から封止した構造が知られている。
そこで、特許文献1には、基材と基材上に中間層を介して形成された酸化物超電導層とで形成される積層体の外周を、Agからなる下地安定化層で完全に覆い、この下地安定化層上にめっき法によりCuの安定化層を設けることで、均一な厚さの安定化層を形成する技術が開示されている。
上記態様に係る酸化物超電導線材は、酸化物超電導積層体の外周に下地安定化層が形成され、さらにこの下地安定化層上に安定化層が形成されている。下地安定化層は、Ag又はAg合金からなる第1の下地安定化層とCu、Ni、Pb、Bi又はこれらを主成分とする合金からなる第2の下地安定化層から構成されている。これらの第1及び第2の下地安定化層は、めっきまたは半田との密着性に優れている。
したがって、安定化層としてめっき被覆層を設ける場合は、密着性が高く均一な膜厚を有するめっき被覆層を形成することが可能である。
また、安定化層として金属テープを用い、当該金属テープを半田層を介して接合する場合においては、気密性の高い安定化層を形成することができる。
さらに、Ag又はAg合金からなる第1の下地安定化層に加えて、Cu、Ni、Pb、Bi、又はこれらを主成分とする合金からなる第2の下地安定化層を有するため、Agの使用量を抑制することが可能である。従って、コストを削減することができる。
上記態様に係る酸化物超電導線材は、酸化物超電導積層体の外周のうち、基材の裏面側はCu、Ni、Pb、Bi又はこれらを主成分とする合金からなる第2の下地安定化層が形成されており、Agからなる第1の下地安定化層が全周に形成されていない。そのため、前周をAgからなる下地安定化層で覆う構造と比較してAgの使用量を抑制しコストを抑えることができる。また、酸化物超電導積層体の側面が第1の下地安定化層と第2の下地安定化層が部分的に重なるように形成されて被覆されているため、側面からの水分の浸入を抑制し、超電導特性が劣化することを抑制できる。
上記態様に係る酸化物超電導線材によれば、Ag又はAg合金からなる第1の下地安定化層が、Cu、Ni、Pb、Bi又はこれらを主成分とする合金からなる第2の下地安定化層によって覆われている。そのため、第1の下地安定化層成膜後に酸素アニール処理を行って、第1の下地安定化層上にピンホールが形成されていても、第2の下地安定化層によって係るピンホールを塞ぐことが可能となり、水分の浸入を確実に防ぐことができる。
また、Ag又はAg合金からなる第1の下地安定化層と半田層とが直接接触すると、第1の下地安定化層が半田を構成する金属材料に浸食され、第1の下地安定化層と酸化物超電導層との界面抵抗値が上昇する虞がある。この界面抵抗値が上昇した場合、電流リード等から酸化物超電導線材に電流を供給する際の抵抗が大きくなったり、またはクエンチが起こり常電導状態に転移した時に酸化物超電導層の電流が安定化層へ転流しにくくなったりする。その結果、酸化物超電導線材が焼損するおそれがある。
一方、上記態様に係る酸化物超電導線材によれば、下地安定化層の外周を半田層を介して金属テープ(安定化層)で覆う場合においては、第1の下地安定化層が、第2の下地安定化層によって覆われているため、第1の下地安定化層と半田層が直接接触することが無い。したがって、第1の下地安定化層が半田層と接触させないことで、第1の下地安定化層と酸化物超電導層との界面抵抗値の上昇を抑制できる。
上記態様に係る酸化物超電導線材によれば、酸素アニール時の熱処理によって第1の下地安定化層にピンホールが発生し、酸化物超電導層の一部が露出することを回避しつつ、Agの使用量を抑えることができるためコストを低減できる。
上記態様に係る酸化物超電導線材によれば、上記の構成を有することにより水分浸入による超電導特性の劣化を抑制できる。
また、Ag又はAg合金からなる第1の下地安定化層に加えて、Cu、Ni、Pb、Bi又はこれらを主成分とする合金からなる第2の下地安定化層を有するため、Agの使用量を抑制することが可能であるため、コストを削減することができる。
図1に本発明の第1実施形態に係る酸化物超電導線材1を示す。酸化物超電導線材1は、酸化物超電導導体15の外周をめっき被覆層(安定化層)17で覆うように構成されている。また、酸化物超電導導体15は、テープ状の基材10と基材10の主面10aに積層された中間層11及び酸化物超電導層12とで形成される酸化物超電導積層体16と、その外周に積層された下地安定化層20と、から構成される。下地安定化層20は、Ag又はAg合金からなる第1の下地安定化層13と、Cu、Ni、Pb、Bi、又はこれらを主成分とする合金からなる第2の下地安定化層14とを有する。
以下、図1を基に、酸化物超電導線材1の各構成要素について詳しく説明する。
拡散防止層は、その上面に他の層を形成するために加熱処理した結果、基材10や他の層が熱履歴を受ける場合に、基材10の構成元素の一部が拡散し、不純物として酸化物超電導層12側に混入することを抑制する。拡散防止層の具体的な構造としては、上記機能を有すれば特に限定されないが、不純物の混入を防止する効果が比較的高いAl2O3、Si3N4、又はGZO(Gd2Zr2O7)等から構成される単層構造あるいは複層構造が望ましい。
ここで、キャップ層にCeO2を用いる場合、キャップ層は、Ceの一部が他の金属原子又は金属イオンで置換されたCe-M-O系酸化物を含んでいても良い。
また、本実施形態において用いられる酸化物超電導層12の材料は、銅酸化物超電導体であり、以下、特に指定がなければ、酸化物超電導層12に用いる材料を銅酸化物超電導体とする。
第1の下地安定化層13は、事故時に発生する過電流をバイパスしたり、酸化物超電導層12と第1の下地安定化層13よりも上面に設けられる層との間で起こる化学反応を抑制し、一方の層の元素の一部が他方の層側に侵入して組成がくずれることによる超電導特性の低下を防いだりするなどの機能を有する。また、第1の下地安定化層13は、酸化物超電導層12に酸素を取り込ませやすくするために、加熱時には酸素を透過しやすくさせる。第1の下地安定化層13は、AgあるいはAg合金のようなAgを主成分とする材料から形成される。
まず、Ag又はAg合金からなるターゲットと酸化物超電導積層体16を、内部を真空状態に減圧しArガスを導入した処理容器内に配置する。このとき、酸化物超電導積層体16は、酸化物超電導層12がターゲットに対向するように配置する。次に前記ターゲットに電圧を印加し放電させることでArガスをイオン化してプラズマを生成する。プラズマ中に生成されたArのイオンが、前記ターゲットをスパッタしてターゲットからAgのスパッタ粒子がはじき出され、当該スパッタ粒子が酸化物超電導層12上に堆積することで、第1の下地安定化層13が成膜される。
なお、第1の下地安定化層13は、少なくとも酸化物超電導積層体16の酸化物超電導層12上に形成される主面部13bを有していればよく、酸化物超電導積層体16の側面16aに形成される側面部13aは形成されていなくても良い。
また、第1の下地安定化層13のAgが後述の半田層のSnによって溶食されるおそれがない場合は、さらなるコスト低減の観点から上記膜厚範囲の上限値を2μmとすることもできる。
第2の下地安定化層14は、前記第1の下地安定化層13と共に、事故時の過電流をバイパス可能である。第2の下地安定化層14は、Cu、Ni、Pb、Bi、又はこれらを主成分とする合金からなる材料から形成される。Cu合金としては、Cu-Zn合金、Cu-Ni合金等が例示される。
スパッタ法による成膜において、スパッタ粒子が被成膜体に衝突すると衝突時の運動エネルギーが熱エネルギーに変換され、被成膜体の表面が発熱する。スパッタ法によって第2の下地安定化層14を成膜する際も、成膜によって基材10の裏面10bが発熱する。
発熱量は、成膜する第2の下地安定化層14の膜厚と相関関係を有し、第2の下地安定化層14の膜厚が10μm以上であると、この熱が酸化物超電導層12に伝わり酸化物超電導層12の酸素が活性化して抜け出てしまう。したがって、第2の下地安定化層14の膜厚は10μm以下であることが望ましい。
また、第2の下地安定化層14の基材10上に形成される膜厚が10nm未満であると、酸化物超電導積層体16を、当該酸化物超電導積層体16上に成膜された第1の下地安定化層13と共に完全に被覆することができなくなるため、10nm以上であることが望ましい。
酸化物超電導積層体16を第1の下地安定化層13と第2の下地安定化層14とによって、外周を覆い、Agの使用量を抑制することが可能となり、Agを主成分とする第1の下地安定化層13のみによって外周を覆う場合と比較して、コストを削減することができる。
基材10及び酸化物超電導層12は、第1の下地安定化層13や第2の下地安定化層14と比較してめっきの密着性が悪い。また、基材10及び常温の酸化物超電導層12は、第1の下地安定化層13及び第2の下地安定化層14と比較して著しく電気抵抗値が高い。そのため、電解めっきにより、基材10及び酸化物超電導層12の表面に均一な厚みを有するめっき層を形成することは困難である。
しかしながら、本実施形態に係る酸化物超電導積層体16は、第1の下地安定化層13と第2の下地安定化層14によって、完全に被覆されているため、めっき被覆層17は、第1の下地安定化層13又は第2の下地安定化層14との上にのみ形成される。したがって、酸化物超電導導体15の外周のめっき被覆層17は、酸化物超電導導体15との密着性に優れる。加えて、第1の下地安定化層13と第2の下地安定化層14との電気抵抗値の差は、比較的小さいためより均一な膜厚を有するめっき被覆層17を形成することができる。
また、めっき被覆層17により、酸化物超電導導体15を外部から完全に遮断することが可能となり、より確実に水分の浸入を防ぐことができる。
めっき被覆層17に使用する金属としては、銅、ニッケル、金、銀、クロム、及び錫などを挙げることができ、これらの金属のうち一種又は二種以上を組み合わせて用いることができる。
また、酸化物超電導線材1を超電導限流器に使用する場合、めっき被覆層(安定化層)14は、クエンチが起こり常電導状態に転移した時に発生する過電流を瞬時に抑制するために用いられる。この用途の場合、めっき被覆層17に用いられる材料は、例えば、Ni-Cr等のNi系合金等の高抵抗金属が挙げられる。
図2は、上述した本発明の第1実施形態の変形例である酸化物超電導線材2を表す模式図である。なお、上述の実施形態と同一の構成要素については、同一符号を付し、その説明を省略する。
酸化物超電導線材2は、上述した第1実施形態に係る酸化物超電導線材1と比較すると、酸化物超電導導体15の外周を覆う構成が異なっている。
即ち、変形例の酸化物超電導線材2は、酸化物超電導導体15とその外周を気密に覆う金属テープ(安定化層)18とにより構成されている。
金属テープ18は、横断面略C字型に折り曲げられ、表面壁18aと側壁18bと裏面壁18cとからなり、酸化物超電導導体15の酸化物超電導層12から基材10の一部を覆っている。また、金属テープ18の内周面側には半田層19が形成される。
以上のように、金属テープ18によって酸化物超電導導体15を被覆することで、内部に水分を浸入させない気密な構造を実現できる。
なお、変形例において金属テープ18の半田層19は、酸化物超電導導体15と接する面(内側面)のみに形成されているが、金属テープ18の両面に半田層19を設けていても良い。
また、酸化物超電導導体15を金属テープ18によって略C字型に被覆する以外にも、酸化物超電導導体15の外周に半田層19を設けた金属テープ18を螺旋巻きにするなどして気密に被覆しても良い。
金属テープ18の厚さは特に限定されず、適宜調整可能であるが、9~60μmとすることができる。金属テープ18の厚さが薄すぎると破れが生じる虞があり、また厚すぎると、金属テープ18を横断面略C字型に成形することが困難となるのみならず、成形時に高い応力を加える必要があるため酸化物超電導層12が劣化する虞がある。
変形例として示した酸化物超電導線材2において、酸化物超電導積層体16の外周は、半田と密着性の良い、第1の下地安定化層13又は第2の下地安定化層14によって覆われて酸化物超電導導体15を形成しているため、半田層19と酸化物超電導導体15は、容易に密着し気密性の高い酸化物超電導線材2を形成することができる。
以下、本発明の第2実施形態に係る酸化物超電導線材3について図3に基づいて説明する。なお、上述の第1実施形態と同一の構成要素については、同一符号を付し、その説明を省略する。
第2実施形態に係る酸化物超電導線材3は、第1実施形態に係る酸化物超電導線材1と比較して下地安定化層21の構成、特に第2の下地安定化層24の構成が相違している。即ち、図3に示すように、第2実施形態に係る酸化物超電導線材3では、第1の下地安定化層13を成膜した酸化物超電導積層体16の外周全体を覆うよう第2の下地安定化層24が形成されている。
なお、本実施形態において、酸化物超電導導体25の外周は、めっき被覆層17によって被覆されて酸化物超電導線材3を構成しているが、第1実施形態の変形例である酸化物超電導線材2(図2参照)に示すように、酸化物超電導導体25の外周を半田層19を介して金属テープ18によって覆った構造としても良い。
また、第2の下地安定化層24の基材10上に形成される膜厚が10nm未満であると、当該酸化物超電導積層体16上に成膜された第1の下地安定化層13と第2の下地安定化層24とで、酸化物超電導積層体16を完全に被覆することができなくなるため、10nm以上であることが望ましい。
第1の下地安定化層13上にめっき被覆層17を形成する場合、この露出した部分において酸性であるめっき液と酸化物超電導層12が接触するため、酸化物超電導層12が腐食し超電導特性の劣化を引き起こす虞がある。
本実施形態においては、第1の下地安定化層13が第2の下地安定化層24によって完全に被覆されている。そのため、第1の下地安定化層13上にピンホールが形成されている場合であっても、めっき被覆層17を形成することによる、超電導特性の劣化が生じない。
第2実施形態の酸化物超電導線材3において、めっき被覆層17にかえて半田層19を介して金属テープ18によって被覆することもできる。
図4は、上述した本発明の第2実施形態の変形例である酸化物超電導線材4を表す模式図であり、酸化物超電導導体25とその外周を外部と気密に覆う金属テープ18により構成されている。なお、上述の実施形態と同一の構成要素については、同一符号を付し、その説明を省略する。
また、第1の下地安定化層上に金属テープを直接半田付けする際に、第1の下地安定化層13上にピンホールが形成されていると半田と酸化物超電導層12との反応によって超電導特性が低下するおそれがある。酸化物超電導線材4では、第1の下地安定化層13が第2の下地安定化層24によって完全に被覆されているため、第1の下地安定化層13上にピンホールが形成されている場合であっても、半田を使用することによる、超電導特性の劣化が生じない。
なお、酸化物超電導層12と第1の下地安定化層13との界面抵抗値を抑制する観点から、第2の下地安定化層24の裏面部24c膜厚は、0.1μm以上5μm以下とすることが好ましい。第2の下地安定化層24の裏面部24c膜厚が0.1μmより薄い場合、第2の下地安定化層24のCuと半田層19のSnとが合金化し、第1の下地安定化層13と第2の下地安定化層24との密着性が悪くなる虞がある。
また、第1の下地安定化層と半田層との間に第2の下地安定化層24が設けられていれば、第1の下地安定化層13の膜厚が2μm以下と薄い場合であっても、酸化物超電導層12と第1の下地安定化層13との界面抵抗値は上昇しないことがわかる。
さらに、第1の下地安定化層13の膜厚が2μm以下と薄い場合、Agが半田層のSnによって溶食されることで第1の下地安定化層13全体がAg-Sn合金となってしまう。この場合、Snと酸化物超電導層12との密着性が悪いため、金属テープ18が剥離してしまう。しかしながら、本構成では、第1の下地安定化層13と半田層19との間に設けられる第2の下地安定化層24がSn拡散防止層としての機能を果たすため、Agが半田層のSnによって溶食されず、金属テープ18の密着性を確保することができる。
(試料の作製)
まず、ハステロイC-276(米国ヘインズ社商品名)からなる幅10mm、厚さ0.1mm、長さ1000mmのテープ状の基材の表面を平均粒径3μmのアルミナを使用して研磨した。次に、前記基材の表面をアセトンにより脱脂、洗浄した。
この基材の主面上にスパッタ法によりAl2O3(拡散防止層;膜厚100nm)を成膜し、その上に、イオンビームスパッタ法によりY2O3(ベッド層;膜厚30nm)を成膜した。
次いで、このベッド層上に、イオンビームアシスト蒸着法(IBAD法)によりMgO(金属酸化物層;膜厚5~10nm)を形成し、その上にパルスレーザー蒸着法(PLD法)により500nm厚のCeO2(キャップ層)を成膜した。次いでCeO2層上にPLD法により2.0μm厚のGdBa2Cu3O7-δ(酸化物超電導層)を形成した。
さらに酸化物超電導層側からスパッタ法により酸化物超電導層上に2μm厚のAgからなる第1の下地安定化層を形成し、炉の中で500℃で10時間、酸素雰囲気中において酸素アニールし、さらに炉の中で26時間冷却した後に取り出した。
次に基材の裏面側からスパッタ法により基材上に1μm厚のCuからなる第2の下地安定化層を形成し、酸化物超電導導体を得た。この酸化物超電導導体を以下の実施例1、2で共通して使用する。
上述の手順を経て得た酸化物超電導導体の外周にめっき法によりめっき被覆層を形成し、図1に示す酸化物超電導線材1と同構造の実施例1の酸化物超電導線材を作製した。
めっき法の手順は、コイル巻きした上述の酸化物超電導導体を、コイルから巻出し、巻き取りコイルにより再びコイル巻きする行程の最中に、硫酸銅水溶液に酸化物超電導導体を浸漬させ、電解めっきを行い、Cuからなる75μmの厚みを有するめっき被覆層を形成した。なお、電解めっきは、被めっき体(酸化物超電導導体)の電流密度が5A/dm2となるように設定し、めっき処理条件はめっき浴温度25℃、浸漬時間18分に設定した。
上述の手順を経て得た酸化物超電導導体の外周を、半田層を介して金属テープにより被覆し、図2に示す実施例2の酸化物超電導線材2と同構造の酸化物超電導線材を作製した。
まず、片面に厚さ5μmのSnめっき(融点230℃、半田層)が形成された幅10mm、厚さ50μm、長さ1000mm超のCuからなる金属テープを用意する。この金属テープのSnめっきが施された面上に、前記酸化物超電導導体を金属テープと長手方向が一致しかつ第1の下地安定化層と金属テープのSnめっきが施された面とが対向するように載置し、加熱・加圧ロールに通過させて金属テープ上のSnを溶融させて半田層を形成し、酸化物超電導導体の第1の下地安定化層と金属テープとを接合させた。
次に、金属テープの幅方向両端側を曲げてコ字型に加工し、さらに金属テープの両端側を基材裏面側に折り曲げて横断面略C字型をなすよう金属テープを成形した。
次に、再度、加熱・加圧ロールに通過させて、金属テープ上のSnを溶融させて半田層を形成し、酸化物超電導導体の側端部及び基材側の一部を金属テープと接合させた。この加熱・加圧ロールによる加熱・加圧処理により、金属テープとその内側に設けられた酸化物超電導導体との間の隙間をSnで埋め、図2の実施例2と同構造の酸化物超電導線材を得た。
なお、加熱・加圧ロールは、シリコン製ロールを用い、加熱温度240℃、加圧力10~20MPa、線材搬送速度100m/hで加熱・加圧処理を行った。
Claims (5)
- 基材と、前記基材の主面上に形成される中間層と、前記中間層の上に形成される酸化物超電導層とを有する酸化物超電導積層体と、
少なくとも前記酸化物超電導層の上面を覆うように形成されAg又はAg合金からなる第1の下地安定化層と、前記酸化物超電導積層体の外周のうち少なくとも前記第1の下地安定化層で覆われていない部分を覆いCu、Ni、Pb、Bi、又はこれらを主成分とする合金からなる第2の下地安定化層とを有し、前記酸化物超電導積層体の外周に形成される下地安定化層と、
前記下地安定化層上に形成され、前記下地安定化層のうち少なくとも、前記第1の下地安定化層の一部及び前記第2の下地安定化層の一部を覆う安定化層と、を備える酸化物超電導線材。 - 前記酸化物超電導層上に前記第1の下地安定化層が形成され、
前記基材の裏面上に前記第2の下地安定化層が形成され、
前記酸化物超電導積層体の側面において前記第1の下地安定化層と前記第2の下地安定化層とが部分的に重なるように形成されている請求項1に記載の酸化物超電導線材。 - 前記第2の下地安定化層が前記第1の下地安定化層の露出する面全体を覆うように形成されている請求項1又は2に記載の酸化物超電導線材。
- 前記酸化物超電導層の上面における前記第1の下地安定化層の膜厚が0.1μm以上2μm以下である請求項3に記載の酸化物超電導線材。
- 前記安定化層がめっき被覆層又は金属テープである請求項1から4の何れか一項に記載の酸化物超電導線材。
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EP2958115B1 (en) | 2017-08-30 |
US20150357092A1 (en) | 2015-12-10 |
EP2958115A4 (en) | 2016-10-19 |
US10163549B2 (en) | 2018-12-25 |
EP2958115A1 (en) | 2015-12-23 |
RU2606959C1 (ru) | 2017-01-10 |
JP5684961B2 (ja) | 2015-03-18 |
JPWO2014126149A1 (ja) | 2017-02-02 |
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