JP2016149248A - Superconducting wire rod manufacturing method and superconducting wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting wire rod manufacturing technology which, even if a joint area is smaller than that of the conventional one, can obtain a critical current value Ic equal to that of a superconducting wire rod before bonding.SOLUTION: A superconducting wire rod manufacturing method which bonds superconducting wire rods having an oxide superconducting film to each other using their ends as joint surfaces to produce a lengthened superconducting wire rod comprises: a precursor forming step of forming a precursor of an oxide superconducting material on the oxide superconducting film of the joint surface; an ultrasonic bonding step of superposing the joint surfaces, formed with the precursor, on each other and bonding them by ultrasonic bonding; and a heat bonding step of heating the precursor on the joint surfaces bonded together to generate a crystal of the oxide superconducting material on the joint surfaces, thereby forming a superconducting layer of the oxide superconducting material as a bonding layer to bond the joint surfaces to each other.SELECTED DRAWING: None

Description

  The present invention relates to a method of manufacturing a superconducting wire and a superconducting wire manufactured using the manufacturing method.

  Since the discovery of oxide superconducting materials that have superconductivity at the temperature of liquid nitrogen, the development of superconducting wires aimed at application to power devices such as cables, current limiters and magnets has been actively conducted.

  And since long superconducting wire is required for manufacture of a superconducting cable, a superconducting coil, etc. for superconducting equipment, lengthening is attained by connecting a plurality of superconducting wires sequentially (for example, (See Patent Documents 1 and 2).

  However, the oxide superconducting material that forms the superconducting film of the superconducting wire is a ceramic and has a characteristic that it has a stable phase up to the vicinity of the melting point and easily decomposes when the melting point is exceeded. Even if the superconducting wire is to be joined between the superconducting film surfaces, a method such as heat diffusion joining generally used for joining metals cannot be applied.

  For this reason, conventionally, a method of joining the protective layer and the stabilization layer formed on the superconducting film to each other by using diffusion bonding using Ag or solder has been generally used. There is a problem that a finite resistance is generated and cannot be used in the permanent current mode because it is not connected in a superconducting state.

  Therefore, the present inventors have developed a joining technique in which a superconducting layer made of an oxide superconducting material is formed on the joint surface, and the superconducting film surfaces of the superconducting wire are joined through this joint surface (see Patent Document 3). . Thereby, it can connect in the superconducting state which does not generate | occur | produce resistance.

  Specifically, the bonding technique of Patent Document 3 applies a coating pyrolysis method (MOD method: Metal Organic Deposition), and includes a metal organic compound that constitutes an oxide superconducting material on a bonding surface of a superconducting wire. By applying a solution (MOD solution) and performing a calcining heat treatment, a calcined film as a precursor of the oxide superconducting material is formed, and by performing a calcining heat treatment in a state where the calcined films are bonded together A superconducting layer of an oxide superconducting material is formed as a joining layer between the superconducting films of the two superconducting wires, and the superconducting film surfaces are joined to each other.

Japanese Patent No. 4810268 JP 2011-228065 A JP 2013-235699 A

  However, in order to obtain a critical current value Ic equivalent to that of the superconducting wire before joining in the superconducting wire joined by using the joining technique described above, it is necessary to increase the joining area between the superconducting wires, and further technical improvement can be achieved. It was sought after.

  Then, this invention makes it a subject to provide the manufacturing technique of the superconducting wire which can obtain the critical current value Ic equivalent to the superconducting wire before joining, even if it is a joining area small compared with the past.

A method for producing a superconducting wire according to an aspect of the present invention includes:
A superconducting wire manufacturing method for manufacturing an elongated superconducting wire by joining ends of superconducting wires having an oxide superconducting film as a joining surface,
A precursor forming step of forming a precursor of an oxide superconducting material on the oxide superconducting film on the bonding surface;
An ultrasonic bonding step in which the bonding surfaces on which the precursors are formed are overlapped and bonded by ultrasonic bonding;
By heating the precursor of the bonded surface bonded together to form a crystal of an oxide superconductive material on the bonded surface, a superconductive layer of the oxide superconductive material is formed as a bonded layer, and the bonded surfaces are It is a manufacturing method of the superconducting wire provided with the heating joining process which joins.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a joining area small compared with the past, the manufacturing technology of the superconducting wire which can obtain the critical current value Ic equivalent to the superconducting wire before joining can be provided.

It is sectional drawing which shows typically the elongate superconducting wire manufactured using the manufacturing method which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the ultrasonic bonding process of the manufacturing method which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the junction part of the elongate superconducting wire manufactured using the manufacturing method which concerns on one Embodiment of this invention. It is IV diagram of the elongate superconducting wire manufactured using the manufacturing method which concerns on one Embodiment of this invention. It is IV diagram of the superconducting wire before joining in the manufacturing method concerning one embodiment of the present invention. It is IV diagram of the elongate superconducting wire manufactured using the conventional manufacturing method.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

(1) A method for producing a superconducting wire according to an aspect of the present invention includes:
A superconducting wire manufacturing method for manufacturing an elongated superconducting wire by joining ends of superconducting wires having an oxide superconducting film as a joining surface,
A precursor forming step of forming a precursor of an oxide superconducting material on the oxide superconducting film on the bonding surface;
An ultrasonic bonding step in which the bonding surfaces on which the precursors are formed are overlapped and bonded by ultrasonic bonding;
By heating the precursor of the bonded surface bonded together to form a crystal of an oxide superconductive material on the bonded surface, a superconductive layer of the oxide superconductive material is formed as a bonded layer, and the bonded surfaces are It is a manufacturing method of the superconducting wire provided with the heating joining process which joins.

  In the above-described conventional bonding technique, the present inventor uses the superconducting layer of the oxide superconducting material as a bonding layer to bond the superconducting film surfaces to each other with a smaller bonding area than that of the conventional superconducting wire Ic and We intensively studied a specific method for obtaining an equivalent junction Ic.

  As a result, in the prior art applying the MOD method, a calcined film as a precursor of an oxide superconducting material was formed on the joint surface, and then the calcined films were stacked and bonded together. Is a hard ceramic and has irregularities formed on the surface, so that the calcined films are in point contact with each other even if the bonding surfaces are laminated and pasted. And since it is subjected to the main annealing heat treatment in this point contact state, even after the superconducting layer is formed from the calcined film, the superconducting layer is locally bonded, and a sufficient contact area cannot be secured. . For this reason, in order to obtain joining Ic equivalent to Ic of the superconducting wire before joining in prior art, it turned out that it is necessary to ensure the joining area of calcined films largely.

  In view of this, the present inventor has determined that the contact area between the calcined films is secured before the crystal of the oxide superconducting material is generated and is c-axis oriented, with a smaller bonding area than in the conventional heat treatment. It was considered that a superconducting layer could be formed as a bonding layer while ensuring a sufficient contact area.

  Then, as a technique for increasing the contact area between the calcined films as precursors, the inventors came up with the idea of bonding them while destroying the irregularities on the surface of the calcined film using ultrasonic bonding.

  In other words, ultrasonic bonding is a method that can heat and break the concavo-convex portion of the surface of the calcined film with ultrasonic waves that vibrate with a small amplitude to appropriately bond the bonding interface of the calcined film. As compared with the oxide superconducting film, it is possible to destroy only the uneven parts where the precursors are point-contacting, which is a much thinner film, so that the surface of the calcined film can be properly used without destroying the oxide superconducting film. Can be flattened.

As a result of further examination, the method using this ultrasonic bonding is not limited to the case where the calcined film is used as a precursor as described above, but also a process of further decomposing BaCO _{3 and the} like on the calcined film. It is understood that the present invention can be similarly applied to the case where a randomly oriented superconducting material in a microcrystalline state obtained by performing the above is used as a precursor, and further applicable to a precursor formed by a method other than the MOD method. The invention has been completed.

(2) The oxide superconducting material constituting the bonding layer is an oxide superconducting material in which crystals grow at the same temperature as the oxide superconducting material constituting the oxide superconducting film of the superconducting wire or at a lower temperature. Preferably there is.

  Thus, by forming the bonding layer with an oxide superconducting material in which crystals grow at the same temperature as or lower than that of the oxide superconducting film, the bonding layer and the oxide can be oxidized without destroying the structure of the oxide superconducting film. Adhesiveness with a physical superconducting film can be improved, and a superconducting wire can be joined more appropriately.

(3) Moreover, it is preferable that the formation method of the said joining layer is the application | coating pyrolysis method using the solution containing the organic compound of the metal which comprises an oxide superconducting material.

  As a method for forming the bonding layer, the surface of the superconducting wire before bonding is smoothed by using a coating pyrolysis method in which a solution of an organometallic complex dissolved in an organic solvent is applied and heat-treated. And a sufficient contact area can be secured.

(4) It is preferable to use an organometallic compound containing no fluorine as the organic compound of the metal.

  When a solution in which an organometallic compound containing fluorine is dissolved in an organic solvent is used, the fluorine dissolves the superconducting layer on the bonding surface, and good crystallinity cannot be obtained from the film of the solution. Can not be suppressed. When a solution in which an organometallic compound not containing fluorine is dissolved in an organic solvent is used, these problems do not occur, which is preferable.

[Details of the embodiment of the present invention]
Hereinafter, the present invention will be described based on embodiments with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

1. Superconducting wire according to this embodiment First, the superconducting wire according to this embodiment will be described. FIG. 1 is a cross-sectional view schematically showing a long superconducting wire manufactured using the manufacturing method according to the present embodiment. FIG. 2 is a cross-sectional view schematically showing the ultrasonic bonding process of the manufacturing method according to the present embodiment, and (a) and (b) show the states before and after the start of ultrasonic bonding, respectively. ing. Moreover, FIG. 3 is sectional drawing which shows typically the junction part of the elongate superconducting wire manufactured using the manufacturing method which concerns on this embodiment.

  As shown in FIG. 1, in this embodiment, the oxide superconducting films 14 and 24 of the two superconducting wires 11 and 21 are joined via the joining layer 31, and the elongate superconducting wire 1 is manufactured. Is done. Specifically, a superconducting layer of an oxide superconducting material is formed as a joining layer 31 on a joining surface where the oxide superconducting film 14 of the superconducting wire 11 and the oxide superconducting film 24 of the superconducting wire 21 are opposed to each other. ing. In FIG. 1, 12 and 22 are metal substrates, and 13 and 23 are intermediate layers. And such an elongate superconducting wire 1 is manufactured by joining the two superconducting wires 11 and 21 using the following method.

2. Method for Producing Superconducting Wire According to this Embodiment In this embodiment, a superconducting layer of an oxide superconducting material is formed as the bonding layer 31 shown in FIG. 1 through a precursor forming step, an ultrasonic bonding step, and a heating bonding step. Thus, the oxide superconducting films 14 and 24 of the two superconducting wires 11 and 21 are joined to each other via the joining layer 31. Hereinafter, the case where the MOD method is used for forming the bonding layer 31 will be described as an example in the order of steps.

(1) Precursor formation step First, the oxide superconducting material precursors 15 and 25 are formed on the oxide superconducting films 14 and 24 at both ends in the longitudinal direction of the two superconducting wires 11 and 21 to be bonded surfaces. (See FIG. 2).

  Specifically, a solution (MOD solution) containing a metal organic compound constituting the oxide superconducting material is applied on the oxide superconducting films 14 and 24 at both ends of the superconducting wires 11 and 21, and then dried. A coating film is formed, and the dried coating film is thermally decomposed by heat treatment to form a precursor of the oxide superconducting material.

  The MOD solution is a solution in which an REBCO (RE: rare earth element) -based oxide superconducting material, that is, an organic compound (organic metal compound) of RE, Ba, and Cu such as Y and Gd, is dissolved in an organic solvent. Is used.

  The organometallic compound is preferably a fluorine-free organometallic compound such as acetylacetonate of these metals, and the MOD solution is prepared by dissolving these organometallic compounds in an organic solvent such as alcohol. be able to.

  Examples of the method for applying the solution to the oxide superconducting film include a die coating method and an ink jet method, but other application methods may be employed. The application is performed on the entire surface of the oxide superconducting films 14 and 24 to be the bonding surfaces, and the application thickness is appropriately set.

As the heat treatment, a heat treatment (calcination heat treatment) is performed on the dried coating film at a temperature higher than the decomposition temperature of the organometallic compound and lower than the generation temperature of the oxide superconducting material. As a result, the organometallic compound of the coating film is thermally decomposed, and is composed of BaCO ₃ which is a carbonic acid compound of Ba and rare earth element oxides such as Y ₂ O ₃ and CuO as a precursor of the oxide superconducting material. The film is formed as a calcined film.

  The specific heating temperature is preferably about 500 ° C., and the heating rate is preferably about 10 to 20 ° C./min. The treatment atmosphere is preferably an atmosphere having a dew point of 15 to 20 ° C. and an oxygen concentration of 20% or more. The heat treatment time is preferably about 20 minutes.

In the above precursor formation step, the calcined film formed is further heat-treated at a temperature equal to or higher than the decomposition temperature of the calcined film in an oxygen concentration atmosphere of 1 to 100%. BaCO ₃ or the like may be decomposed to form a randomly oriented microcrystalline precursor.

(2) Ultrasonic bonding step Next, the bonding surfaces on which the precursors 15 and 25 are formed are overlapped and bonded together by ultrasonic bonding.

  As shown in FIG. 2A, a large number of irregularities are formed on the surfaces of the precursors 15 and 25 formed in the precursor forming step. For this reason, even if the joining surfaces on which the precursors 15 and 25 are formed are overlapped and fixed using a jig, the precursors 15 and 25 are in point contact with each other at the convex portion.

  In such a point contact state, the superconducting layer cannot secure a sufficient contact area even after a heat bonding step described later. In this embodiment, the surface of the fixed precursors 15 and 25 is fixed. By applying ultrasonic vibration, the projections are destroyed and the surfaces of the precursors 15 and 25 are flattened. Thereby, as shown in FIG.2 (b), the precursors 15 and 25 can be contacted by a surface and can be bonded together appropriately.

  Specific bonding conditions such as the frequency, amplitude, application time, and pressing force by the jig are appropriately set according to the material and thickness of the precursor.

(3) Heat bonding step Next, the bonded superconductors 15 and 25 are heated to generate crystals of the oxide superconducting material on the bonding surface, whereby the superconducting layer of the oxide superconducting material is bonded to the bonding layer 31. The joining surfaces are joined together.

  Specifically, the precursors 15 and 25 are subjected to heat treatment (main heat treatment) at a temperature equal to or higher than the temperature at which the oxide superconducting material crystal is formed. More specifically, in a low oxygen concentration Ar atmosphere with an oxygen concentration of about 100 ppm, the temperature is raised to about 800 ° C. at a temperature raising rate of about 100 ° C./min, and then the temperature is lowered to room temperature at the same temperature lowering rate. .

  As a result, the precursors 15 and 25 of the joint surfaces are c-axis oriented and coarsened so as to straddle the joint surfaces, and grow as crystals of the oxide superconducting material. As a result, as shown in FIG. 3, the joining layer 31 can be formed by integrating the superconducting layers of the oxide superconducting material. Since the oxide superconducting films 14 and 24 can be joined via the joining layer 31, the superconducting wire 1 that is elongated by joining in the superconducting state can be manufactured.

  In the manufacturing method according to the present embodiment, as described above, the ultrasonic bonding step is performed before the heat bonding step to destroy and flatten the portion where the precursors 15 and 25 are in point contact. Since they are bonded together, a sufficient contact area can be ensured when the precursors 15 and 25 are bonded to each other by the heat bonding process to form the superconducting layer. As a result, even if the joining area of the two superconducting wires is smaller than the conventional one, it is possible to appropriately suppress the decrease in Ic in the superconducting wire after joining.

  In the above description, the MOD method has been described as an example of the method for forming the precursor. However, as a method for forming the precursor, a gas phase method or the like is adopted in addition to the MOD method as the liquid phase method. You can also. Specific vapor deposition methods include physical vapor deposition (PVD) methods such as pulsed laser deposition (PLD) and electron beam deposition, metal organic chemical vapor deposition (MOCVD), and metal organic chemical vapor deposition (MOCVD). A chemical vapor deposition (CVD) method such as a deposition method can be preferably used.

  At this time, the oxide superconducting material in the superconducting layer formed as the bonding layer does not necessarily have to be the same oxide superconducting material as the oxide superconducting films 14 and 24, but is the same as the oxide superconducting films 14 and 24. An oxide superconducting material that crystallizes at a temperature or lower temperature is preferable.

[Experimental example]
Next, the present invention will be described more specifically based on experimental examples.

(Experimental example 1)
1. Fabrication of superconducting wire After forming 600 nm thick intermediate layers 13 and 23 on metal substrates 12 and 22 made of Ni / Cu / SUS having a thickness of 150 μm, YBCO-based oxidation having a thickness of 3 μm using the FF-MOD method. Superconducting wires 11 and 21 having a width of 4 mm and a length of 100 mm were produced by forming the physical superconducting films 14 and 24.

2. Superconducting Wire Joining Next, superconducting wires 11 and 21 were joined in accordance with the following procedure to produce elongated superconducting wire 1.

(1) Precursor formation step First, a Y: Ba: Cu molar ratio is 1: 2: 3, and the total ion concentration of Y + Ba + Cu is 1 mol / L, and an acetylacetonate complex of Y, Ba, and Cu is included. Prepare an alcohol solution, apply the solution to the surface of the oxide superconducting films 14 and 24 at both ends of the superconducting wires 11 and 21 to a thickness of about 25 μm, and dry the film at 150 ° C. for 10 minutes in the air. Formed.

  Thereafter, the coating film is placed in an atmosphere having a dew point of 15 ° C. to 20 ° C. and an oxygen concentration of 20%, and the temperature is raised to 500 ° C. at a rate of 2.5 ° C./min. The bodies 15 and 25 were formed as films.

(2) Ultrasonic bonding process Next, the bonding surfaces of the oxide superconducting films 14 and 24 on which the precursors 15 and 25 were formed were superposed and bonded together by ultrasonic bonding.

Specifically, the joining surfaces of the oxide superconducting films 14 and 24 on which the precursors 15 and 25 are formed are overlapped so that the joining area becomes 10 mm ² and pressed with a pressure of 1 MPa using a jig. However, an ultrasonic wave having a frequency of 20 kHz and an amplitude of 0.1 mm was applied, and the bonding surfaces of the oxide superconducting films 14 and 24 were ultrasonically bonded to each other for bonding.

(3) Heat Bonding Step Next, the bonded joint surface precursors 15 and 25 are heated to generate crystals of the oxide superconducting material on the joint surface, thereby forming the oxide superconducting material bonding layer 31. As a result, the superconducting wires 11 and 21 were joined together to produce the elongated superconducting wire 1.

Specifically, the precursors 15 and 25 were placed in an Ar atmosphere with 1 atm and an O ₂ concentration of 100 ppm, and the temperature was raised to about 800 ° C. at a rate of temperature increase of 1000 ° C./min or less and held for about 20 minutes. After the temperature holding was completed, the temperature was lowered to about 500 ° C., then the atmosphere was switched to a 100% oxygen atmosphere and the temperature was lowered to room temperature.

(Experimental example 2)
The superconducting wire was joined by the same method as in Experimental Example 1 except that the superconducting wires were joined together by heating without performing ultrasonic joining, thereby producing a lengthened superconducting wire.

(Experimental example 3)
The superconducting wire was joined by the same method as in Experimental Example 2 except that the joining area between the precursors was 20 mm ² , thereby producing a long superconducting wire.

(Experimental example 4)
The superconducting wire was joined by the same method as in Experimental Example 2 except that the joining area between the precursors was 30 mm ² , thereby producing a lengthened superconducting wire.

2. Evaluation (1) IV characteristics The IV characteristics of the long superconducting wire produced in Experimental Example 1 were measured (FIG. 4) and compared with the IV characteristics (FIG. 5) of the superconducting wire before joining.

As shown in FIGS. 4 and 5, in Experimental Example 1, Ic was almost the same value after bonding. Further, when bonding is performed without performing ultrasonic bonding as in Example 4, from Table 1 and FIG. 6, in order to obtain suitable IV characteristics even after bonding, the bonding area between the precursors is 30 mm. It was confirmed that about ² needs to be secured.

(2) Change in Ic before and after bonding For each of the long superconducting wires produced in Experimental Examples 1 to 4, Ic was measured at a liquid nitrogen temperature (77 K) using the four-terminal method, and Ic before bonding. The degree of change was calculated. The results are shown in Table 1.

  From Table 1, it can be seen that in Experimental Example 1 in which ultrasonic bonding was performed, Ic similar to that before bonding was maintained even after the superconducting layer was formed by the heat bonding process and the superconducting wires were bonded to each other.

  On the other hand, in the conventional method in which ultrasonic bonding is not performed, in Example 2 in which the bonding area is set to be the same as in Example 1, Ic is lower than that before bonding, and in order to obtain Ic similar to that before bonding. It can be seen that, as in Experimental Example 4, it is necessary to set the bonding area sufficiently wide.

  From the above results, superconducting wire rods can be obtained by performing ultrasonic bonding before performing the heat bonding step, thereby ensuring a sufficient contact area even if the bonding area is set small and obtaining the same Ic as before bonding. It was confirmed that they could be connected properly in a superconducting state.

  The present invention relates to a superconducting cable used in the permanent current mode by joining oxide superconducting films using an oxide superconducting material in joining superconducting wires having an oxide superconducting film. It is possible to provide a superconducting wire having a scale.

DESCRIPTION OF SYMBOLS 1 Elongated superconducting wire 11, 21 Superconducting wire 12, 22 Metal substrate 13, 23 Intermediate layer 14, 24 Oxide superconducting film 15, 25 Precursor 31 Bonding layer

Claims (4)

A superconducting wire manufacturing method for manufacturing an elongated superconducting wire by joining ends of superconducting wires having an oxide superconducting film as a joining surface,
A precursor forming step of forming a precursor of an oxide superconducting material on the oxide superconducting film on the bonding surface;
An ultrasonic bonding step in which the bonding surfaces on which the precursors are formed are overlapped and bonded by ultrasonic bonding;
By heating the precursor of the bonded surface bonded together to form a crystal of an oxide superconductive material on the bonded surface, a superconductive layer of the oxide superconductive material is formed as a bonded layer, and the bonded surfaces are The manufacturing method of the superconducting wire provided with the heating joining process which joins.   The oxide superconducting material constituting the bonding layer is an oxide superconducting material in which crystals grow at the same temperature as or lower than the oxide superconducting material constituting the oxide superconducting film of the superconducting wire. A method for producing a superconducting wire according to 1.   The method for producing a superconducting wire according to claim 1 or 2, wherein the bonding layer is formed by a coating pyrolysis method using a solution containing a metal organic compound constituting the oxide superconducting material.   The method for producing a superconducting wire according to any one of claims 1 to 3, wherein an organic metal compound containing no fluorine is used as the metal organic compound.

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