JPH05251758A - Manufacture of oxide superconductive current limiting conductor - Google Patents

Abstract

PURPOSE:To get the manufacture of an oxide superconductive current limiting conductor the current limiting effect of which is large and in which the voltage between limit terminals is 100V and over. CONSTITUTION:A Y (YB2Cu3O7-x) oxide superconductive film is made on a base material by electron beam deposition method by introducing oxygen gas. After film formation, the introduction of the oxygen gas is interrupted, and then heat treatment is performed for 30 min. at 300 deg.C in vacuum environment 1.8X10<->Torr in gas pressure. Then, it is covered with silver by deposition in the same atmosphere so as to get an oxide superconductive current limiting conductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance current limiting device for use in a conductor that conducts a current using an oxide superconductor and a current limiting device capable of limiting an excessive current such as a short-circuit current. The present invention relates to a method for manufacturing a conductor.

[0002]

2. Description of the Related Art In a superconductor, when any one of the critical temperature, the critical current, and the critical magnetic field exceeds the value, the superconducting state is destroyed, and the superconducting state is established and the electric resistance is increased. In recent years, research and development on superconducting current limiting conductors (elements) that utilize this phenomenon to limit an excessive current have become active. The technology of this entire field is described in, for example, a publication {Journal of the Institute of Electrical Engineers of Japan, Volume 110, No. 9, p. 705 (1990)}. Among these, superconducting current limiting conductors utilizing oxide superconductors have recently received attention. The structure of the element used for this is a simple structure in which a pair of electrodes are formed by depositing a metal such as silver, gold or indium on a part of the superconductor by using vapor deposition or paste on the rod-shaped or plate-shaped superconductor. It is something. As a typical example, a publication {Advances in Superco
nductivity, page 691 (1988)}. This uses a sintered body of Y-Ba-Cu-based oxide superconducting powder to form a zigzag-like (meaner structure) sheet by the doctor blade method, in a normal conducting state when a current exceeding a critical current flows. The current is limited by utilizing the high resistance. However, such a sintered body (one having a linear shape, a rod shape, or a plate shape) generally has a drawback that the critical current cannot be increased, and thus the short-circuit current can be limited only in a small proportion.

Therefore, a current limiting conductor to which a film-shaped superconductor formed on a substrate is applied has been considered. Due to the progress of film forming technology, it has recently become possible to obtain an oxide superconducting thin film capable of passing a very large critical current. Further, the film-shaped one has advantages as a current limiting conductor such that it has a better cooling characteristic than the above-mentioned one such as a linear one, and can easily have a high resistance. However, the oxide superconducting thin film has a large critical current over a large area because the composition shift tends to occur when the film thickness is increased and the composition becomes inhomogeneous when formed in a large area. It was unavoidable to give rise to the major drawback of difficulty in obtaining things. In particular, the occurrence of inhomogeneity in film quality such as composition when a film is formed on a relatively large area is an unavoidable problem in the current superconducting thin film manufacturing technology, and therefore a weak portion is melted during energization, It was not possible to increase the limit terminal voltage of the current limiting conductor (equivalent to the input power or circuit voltage until the fuse is cut).

[0004]

In order to solve the above-mentioned drawbacks, a kind of thermal and electrical stabilization may be performed by coating a metal thin film on the superconducting film of the element portion by a method such as vapor deposition. Conceivable. Such a technique can be easily conceived from the conventional technique described in, for example, a publication {edited by the Physical Society of Japan, Superconductivity, p. 276, 1979 (Maruzen Co., Ltd.)}. The inventors of the present invention have made the limit terminal voltage several tens of V by the stabilization by applying such a conventional technique.
I found that it is possible to raise up to. However, it is insufficient as a practical level, and at least 100V
It is necessary to withstand the above voltage, and it is desired to further improve the stabilizing performance of the current limiting conductor.

The present invention has been made to solve the above problems, and an object thereof is to obtain a method for manufacturing an oxide superconducting current limiting conductor having a large current limiting effect and a limit terminal voltage of 100 V or more. To do.

[0006]

The method for producing an oxide superconducting current limiting conductor according to the present invention comprises the steps of forming an oxide superconducting film,
In this method, the oxide superconducting film is heat-treated in a vacuum atmosphere to coat the oxide superconducting film with silver.

[0007]

In the present invention, when the silver coating is formed after vacuum heat treatment after forming the oxide superconducting film, the conformability at the interface between the superconducting film and the silver coating becomes good, and the heat dissipation of the superconducting film during heat generation is good. Therefore, the stabilization characteristics are improved.

[0008]

EXAMPLES Example 1. A rectangular MgO substrate having a width of 5 mm and a length of 20 mm is used as a base material, and then each component metal is used as a starting material, and a Y-based (YBa ₂
Cu ₃ O _7-X) was formed of the oxide superconductor film. At this time, oxygen gas was introduced to adjust the gas pressure to 1.5 × 10 ⁻⁴ Tor.
adjusted to r, and after film formation, once in this atmosphere, 300 ° C.
After gradually cooling to 0 and cutting off the introduction of oxygen gas, the gas pressure is 1.
Heat treatment was performed at 300 ° C. for 30 minutes in a vacuum atmosphere of 8 × 10 ⁻⁶ Torr. Then, silver was vapor-deposited in the same atmosphere to obtain an oxide superconducting current limiting conductor according to an example of the present invention. Next, a central portion of the superconducting film was covered with an insulating tape, and both ends were gold-plated with no electric field to form terminal portions, and lead wires were attached to the terminals to fabricate an oxide superconducting current limiting device. The critical temperature of the superconducting film was 86 K, the thickness was 0.6 μm, and the thickness of the silver coating was about 0.3 μm.

Comparative Example 1. An oxide superconducting current limiting element was manufactured in the same manner as in Example 1, except that the silver coating was not performed in Example 1 and the film was slowly cooled to room temperature. The critical temperature of the superconductor was 86 K, which was the same as in Example 1.

Comparative Example 2. An oxide superconducting current limiting element was manufactured in the same manner as in Example 1 except that the heat treatment was not performed in vacuum. The critical temperature of the superconductor is 86
K, the same as in Example 1.

Each of the current limiting devices of Example 1, Comparative Example 1 and Comparative Example 2 was placed in liquid nitrogen and cooled, and an AC circuit (frequency of 50 Hz) was used to change the terminal voltage applied to the devices. , The limit voltage between terminals until the element was blown was investigated. As a result, the manufacturing method of Example 1 is 105 V, and the conventional method of Comparative Example 2 in which the silver coating is simply applied by vapor deposition without vacuum heat treatment is 68.
V, 8 V for the conventional method of Comparative Example 1 without any coating
Met. That is, it is considered that the conventional method cannot apply a high terminal voltage because the superconducting film is inhomogeneous and the weak portion is melted by heat during energization. On the other hand, according to one embodiment of the present invention, even if the superconducting film is inhomogeneous, the stabilization performance of the element is improved, so that it is possible to manufacture a current limiting conductor having a melting voltage of more than 100V. It was revealed. Further, in the current limiting conductor according to the embodiment of the present invention, the estimated short circuit current 35 of the used circuit is 35 in the case of the above limit terminal voltage of 105V.
It was possible to greatly limit 0A to 24A which is about 1/15 of that.

Example 2. Same rectangular MgO as in Example 1
The substrate was used as the base material. YBa ₂ by sputtering method
It was formed Cu ₃ O _7-X-based oxide superconducting film. At this time, oxygen gas was introduced to adjust the gas pressure to 1.1 × 10 ⁻⁴ Tor.
After adjusting the temperature to r, after film formation, once in this atmosphere, 200 ° C.
After gradually cooling to 0 and cutting off the introduction of oxygen gas, the gas pressure is 1.
Heat treatment was performed at 200 ° C. for 30 minutes in a vacuum atmosphere of 8 × 10 ⁻⁶ Torr. Then, silver was coated by sputtering in the same atmosphere to obtain an oxide superconducting current limiting conductor according to another embodiment of the present invention. Then, gold oxide was applied to both ends of the superconducting film without electric field to form terminals, and lead wires were attached to the terminals to fabricate an oxide superconducting current limiting device. The critical temperature of the superconducting film was 87K, the thickness was 0.5 μm, and the thickness of the silver coating was about 0.3 μm.

Comparative Example 3. An oxide superconducting current limiting device was manufactured in the same manner as in Example 2, except that the silver coating was not performed in Example 2 and the film was formed and then gradually cooled to room temperature. The critical temperature of the superconductor was 87 K, which was the same as in Example 2.

Comparative Example 4. An oxide superconducting current limiting device was manufactured in the same manner as in Example 2 except that heat treatment was not performed in vacuum. The critical temperature of the superconductor is 87
K, the same as in Example 2.

The current limiting devices of Example 2, Comparative Example 3 and Comparative Example 4 were each placed in liquid nitrogen for cooling, and an AC circuit (frequency of 50 Hz) was used to change the terminal voltage applied to the devices. Then, the limit voltage between terminals before the element was blown was investigated. As a result, the one manufactured in Example 1 was 116 V, the conventional method in which the silver coating was simply applied by sputtering without performing the vacuum heat treatment in Comparative Example 4 was 66 V, and the conventional method in Comparative Example 3 in which no coating was applied. Was 7V. That is, it is considered that the conventional method cannot apply a high terminal voltage because the superconducting film is inhomogeneous and the weak portion is melted by heat during energization. On the other hand, according to another embodiment of the present invention, even if the superconducting film is inhomogeneous, the stability performance of the device is improved, and therefore, it is possible to manufacture a current limiting conductor which is to be blown over 100 V Became clear. Furthermore, in the current limiting conductor of Example 2, the above-mentioned limit terminal voltage 1
In the case of 16V, the estimated short circuit current 360A of the used circuit could be greatly limited to 30A which is about 1/12 of the estimated short circuit current.

By the way, as the base material used in the present invention, Al ₂ O ₃ , SiO ₂ , MgO, SrTiO ₃ and ZrO are used.
₂ , ceramics such as Y ₂ O ₃ and single crystals, metals such as gold, silver, stainless steel, copper and nickel and alloys thereof can be used.

According to the present invention, after forming the superconducting film, it is necessary to perform a heat treatment in an arbitrary vacuum atmosphere to form a silver coating having an arbitrary thickness. As this method, as shown in the embodiment, the superconducting film is formed. It is optimum to use the same method as that for forming the film. However, the present invention is not limited to this, and the silver coating layer may be formed by a film forming method different from the method of forming the superconducting film. The heat treatment temperature is not limited and can be arbitrarily selected. Although it depends on the vacuum atmosphere, it is suitable to perform the heating at about 200 to 600 ° C., and it is sufficient that oxygen on the surface of the superconducting film is removed to some extent.

In the superconducting film forming method of the present invention,
A so-called physical vapor deposition method, a chemical vapor deposition method, and an electrodeposition method utilizing electrophoresis are used. When the oxide superconducting film is formed on the substrate in the present invention, oxygen gas is generally introduced to form the film. An arbitrary value may be used as the oxygen gas pressure because it greatly differs depending on the method used. For example, in the CVD method, it is generally necessary to have a high gas pressure,
Gas pressure is low (high vacuum) with sputtering and vapor deposition
Is normal.

As a method of forming a metal coating to serve as an electrode terminal after forming the oxide superconductor current-limiting conductor according to the present invention on a substrate, vapor phase film forming method, electroless plating method, electrolytic plating method or Either crimping method may be used. Silver or gold is preferable for the electrode terminals.

By the way, in the embodiment, the Y-based material is used as an example of the oxide-based superconducting material, but the effect of the present invention is Y.
It was confirmed by the same examination as in the example that it is not limited to the system but is expressed in any oxide superconducting material such as Bi type, Tl type, Nd type and the like. Further, in the above embodiment, the case where the current limiting conductor is used for the current limiting element has been described, but the present invention is not limited to this. It goes without saying that there is no power loss and the current can be limited when an excessive current flows.

[0021]

As described above, according to the present invention, after the oxide superconducting film is formed, the oxide superconducting film is heat-treated in a vacuum atmosphere, and the oxide superconducting film is coated with silver. , The current limiting effect is large, and the voltage between limit terminals is 10
A method for producing an oxide superconducting current limiting conductor having a voltage of 0 V or higher can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sadajiro Mori 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation Central Research Institute (72) Inventor Tatsuya Hayashi 8-1-1 Tsukaguchihonmachi, Amagasaki Mitsubishi Electric Central Research Institute Co., Ltd.

Claims (1)

[Claims] 1. A method for producing an oxide superconducting current limiting conductor, wherein after forming an oxide superconducting film, the oxide superconducting film is heat-treated in a vacuum atmosphere to coat the oxide superconducting film with silver.