JP4048270B2 - MgB2 superconducting film and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a MgB ₂ superconductor useful for a wide range of applications such as linear motor cars, accelerators, high-field magnets for medical devices, accelerator magnets, power storage (SMES), and various power systems. More specifically, the present invention relates to a film superconductor made of MgB ₂ microcrystals having magnetic field characteristics in which the critical current does not decrease even in a high magnetic field.
[0002]
[Prior art and problems of the invention]
The conventional technologies related to superconductors can be broadly divided into copper oxide superconductors made of copper oxide and non-copper oxide superconductors made of other than copper oxide. The copper oxide superconductor has a two-dimensional structure composed of copper and oxygen, and the superconducting transition temperature (Tc) is higher than that of the non-copper oxide superconductor. Since is a so-called ceramic, it is difficult to process it into a conducting wire, as well as to easily form and process it, and so far it has not been possible to produce a superconductor made of copper oxide.
[0003]
On the other hand, there are two types of non-copper oxide superconductors: an intermetallic compound consisting of only a plurality of metal elements and a metal oxide not containing copper. Among non-copper oxide superconductors, superconductors made of intermetallic compounds are easy to synthesize, mold and process because they are themselves metals. As described above, each of the copper oxide superconductor and the non-copper oxide superconductor has advantages and disadvantages, but from the viewpoint of commercialization, it is easy to synthesize, form and process a metal-based superconductor. Conductors are considered to be preferable, and attempts have been made in recent years to produce metallic superconductors by combining various metals.
[0004]
As a result, MgB ₂ (magnesium diboride) having a structure in which a hexagonal surface formed of Mg (magnesium) and a hexagonal surface formed of B (boron) are laminated is used as a metallic superconductor. Has been found to have a high superconducting transition temperature. This recently developed MgB ₂ (magnesium diboride) not only has the highest superconducting transition temperature (Tc = 39K) as a metal-based superconductor, but also is inexpensive and can be synthesized, molded, It has many advantages in industrial applications, such as being relatively easy to process. As a result, development competition has started in various countries with a view to full-scale practical application. As a method for producing a superconductor using MgB ₂ as a raw material that has been clarified so far, (i) a mixture of MgB ₂ , Mg, and B powder is made linear as it is, or MgB ₂ , Mg, B powder blended into a stainless steel tube, etc., drawn, rolled, and so-called PIT (Powder In Tube) method formed into a wire body and heat treated (b) There are two methods in which boron fiber or boron film is formed on a substrate and then converted into an MgB ₂ film by diffusion reaction of Mg and boron at a high temperature in Mg vapor. However, although all the superconductors obtained by these manufacturing methods can obtain a high superconducting transition temperature (Tc), the bonding between crystal grains is insufficient or the grains are likely to be coarsened. There was a problem that the critical current (Jc) was inferior. For example, when manufactured by the PIT (Powder In Tube) method (b), a value of 100,000 A / cm ² is predicted without a magnetic field, but the temperature is 5 K (absolute temperature) and the applied magnetic field is 5 T. drops to 1000A / cm ² when the Tela. Also in the case of (b) above, when the temperature was 5K (absolute temperature) and the applied magnetic field was 5T (tera), the magnetic field current (Jc) characteristics deteriorated significantly as the applied magnetic field increased, resulting in 1000 A / cm ² .
[0005]
Literatures measuring the upper critical magnetic field (Hc2) and critical current (Jc) characteristics at high magnetic fields of single crystals and wires made of MgB ₂ have been published one after another. Currently, no material that exhibits physical properties that exceed the high magnetic field properties of superconductors.
[0006]
Accordingly, the invention of this application provides an MgB ₂ superconductor that solves the above-described problems and has not only a high superconducting transition temperature but also an excellent critical current in a high magnetic field and a method for producing the same. It is something to try.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the invention of this application is provided with a buffer layer in order to suppress the chemical reaction between Mg-B and the metal substrate surface on the metal substrate surface. After forming an Mg-B amorphous precursor film with excess Mg on the surface of the buffer layer, the precursor film is heated at a temperature increase rate of 80 to 150 ° C./min in the atmospheric pressure of an inert gas . , MgB _2, characterized in that to form a superconducting film-like body of MgB ₂ heating retention of 10 to 30 minutes, after cooling at a cooling rate of 50 to 150 ° C. / min from MgB amorphous precursor A method for producing a superconducting film is provided. And secondly, in the above method, prior to forming the Mg-excess Mg-B amorphous precursor film on the surface of the metal substrate, it is selected from the group of ZrO ₂ , Y ₂ O ₃ and YSZ. is intended to provide a method of providing a buffer layer composed of at least one, and in the third, in the above method, to provide a manufacturing method, wherein the metal substrate is a Ni-based alloy metal, Fourth, a buffer layer made of at least one selected from the group consisting of ZrO ₂ , Y ₂ O ₃ , and YSZ is provided on the surface of the metal substrate, and a superconducting film of MgB ₂ is formed on the surface of the buffer layer. wherein the but provides MgB ₂ superconductor film like body, characterized in that it is formed, the fifth, the MAB ₂ superconductor film-like body of the metal substrate is a Ni-based alloy Kyosu Hisage the MAB ₂ superconducting film-like material to It is intended.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the feature of the invention of this application is to dramatically improve the high magnetic field characteristics by forming MgB ₂ on the metal substrate as described above. The invention of this application will be described in detail below. Summary of the Invention This application is on the metal substrate of the N i-based alloy gold, to form an amorphous precursor of Mg-B which is contained excessively Mg in laser deposition or the like, the precursor coated metal substrate It is heated to 350 to 650 ° C. at a temperature rising rate of 80 to 150 ° C./min in an atmospheric pressure of an inert gas such as argon without using oxygen. Then, after maintaining the heating state for about 10 to 30 minutes, for example, rapid cooling at about 50 to 150 ° C./min causes crystallization of MgB ₂ nano-sized microcrystals on the metal substrate. With this heating, excess Mg volatilizes, and at the same time, decomposition and volatilization of MgB ₂ proceed. In order to produce MgB _{2 in} the competitive state, it is necessary to set the temperature range to 350 to 650 ° C. In addition, in the method for producing MgB ₂ nanosize microcrystals of the present invention, it is impossible to completely remove oxygen from the atmosphere and from the raw materials, and the oxygen-free state in the invention of this application Does not mean a state in which oxygen is completely removed, but a superconductor is produced in which fine precipitates formed by combining oxygen with Mg and B are finely dispersed in MgB ₂ nano-sized microcrystals. It means that the state is included.
[0009]
The invention of this application is Ru to form a pre-buffer layer before forming the amorphous precursor of Mg-B which is contained excessively Mg on a metal substrate by laser deposition or the like. The reason for disposing this buffer layer is to widen an appropriate range of heat treatment conditions when performing heat treatment after forming the Mg-B amorphous precursor on the metal substrate. Embodiment of the second invention providing the buffer layer, on a metal substrate of N i-based alloy gold, excess Mg after providing a buffer layer of _{ZrO 2, Y 2 O 3,} YS Z which do not react with Mg-B An amorphous precursor of Mg-B contained in the material is formed by laser vapor deposition or the like. The metal substrate coated with the precursor film is 350 to 650 ° C. at a temperature rising rate of 80 to 150 ° C./min in the atmospheric pressure of an inert gas such as oxygen-free argon as in the first invention. Heating to a relatively low temperature, heating and holding for about 10 to 30 and then rapidly cooling to rapidly heat at atmospheric pressure, hold for a short time, and rapidly cool to form MgB ₂ nano-sized microcrystals on the metal substrate. It is something to be issued.
[0010]
【Example】
Hereinafter, the invention of this application will be described in detail by way of examples. In addition, although what is described in the following Example 1 shows the preferable aspect of this invention, it cannot be overemphasized that it is not limited to the following Example.
Example 1 YSZ was coated as a buffer layer of about 1 μm by sputtering on 30 mm × 4.0 mm × 0.3 mm of Hastelloy tape (Ni-base heat-resistant alloy). A Mg-excess Mg—B amorphous precursor film was formed thereon at room temperature in a reduced pressure Ar gas atmosphere using a laser deposition method (PLD) using an Mg-excess MgB ₂ target. Thereafter, heat treatment was performed under 1 atm of Ar gas not containing O ₂ and H ₂ O as impurities. In the heat treatment, the temperature was raised at about 100 ° C./min, held at 580 ° C. for 20 minutes, and then rapidly cooled. As a result, a glossy MgB ₂ superconducting conductor of about 0.5 μm in black or blue-black color was obtained. The film transitioned to zero resistance at 24K (absolute temperature). The result of the critical current (Jc) characteristic in the high magnetic field by the transport method in the high magnetic field of the obtained conductor (1) is shown as Nb-Ti practical wire (2), stainless steel tape (3), cupronickel core wire (4 ), A product formed by the boron fiber method measured at 5K (5) and a cupronickel tape (6) are compared in FIG. As is apparent from FIG. 1, the superconductor (1) obtained by the method of the present invention is 10T, while the critical current decreases as the applied magnetic field increases in those molded by other methods. Even in a high magnetic field of (Tera), a critical current (Jc) of 10 ⁵ A / cm ² is flowing. This not only shows the critical current (Jc) characteristic in a high magnetic field as compared with the conventional MgB ₂ wire, but also the most frequently used Nb—Ti wire (2) is 8T (tera). From this, it can be seen that the high magnetic field characteristics are excellent even when the critical current rapidly decreases .
[0011]
【The invention's effect】
As explained in detail above, the MgB ₂ superconducting film of the invention of this application has good high magnetic field characteristics, and Mg (magnesium) and B (boron) constituting MgB ₂ are rich in resources and inexpensive. Compared with conventional superconductor materials, the manufacturing cost can be greatly reduced. In addition, there is a possibility that it can be used at 20K where the refrigerator can be cooled, and a reduction in cooling cost can be expected.
[Brief description of the drawings]
FIG. 1 is a magnetic field characteristic comparison diagram of critical current density of MgB ₂ wire.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Superconducting membrane body manufactured by this invention 2 Nb-Ti practical wire 3 Stainless steel tape 4 Cupronickel (white copper) core wire 5 Boron fiber method (5K)
6 Cupronickel (white copper) tape

Claims (5)

The metal substrate surface, the buffer layer is provided in order to suppress the chemical reaction between the Mg-B and the metal substrate surface, an amorphous precursor film of Mg excess Mg-B on the surface of the buffer layer Later, the precursor film is heated in an inert gas at atmospheric pressure at a heating rate of 80 to 150 ° C./min , heated and held for 10 to 30 minutes, and cooled at a cooling rate of 50 to 150 ° C./min. method of manufacturing a MgB ₂ superconductor film like body, characterized in that to form a superconducting film-like body of MgB ₂ from MgB amorphous precursor through. The production method according to claim 1, wherein the buffer layer is made of at least one selected from the group consisting of ZrO ₂ , Y ₂ O ₃ , and YSZ . The method according to claim 1 or 2, wherein the metal substrate is a Ni-based alloy . ZrO on the metal substrate surface ₂ , Y ₂ O ₃ , A buffer layer made of at least one selected from the group of YSZ is provided, and MgB is formed on the surface of the buffer layer. ₂ MgB characterized in that a superconducting film is formed ₂ Superconducting membrane. The MgB according to claim 4, wherein the metal substrate is a Ni-based alloy. ₂ Superconducting membrane.

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