JPS63299012A - Superconductive fiber and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a high temperature superconductive fiber of a high critical current density value and critical temperature without deteriorating actual handling performance by forming a sintered covering layer consisting of an oxide ceramic superconductor and a binder around an inorganic fiber. CONSTITUTION:Over the periphery of an inorganic fiber 1 is formed a sintered covering layer 2 of an oxide ceramic superconductor, over which a protective film 3 is formed to constitute a fundamental body. To improve further the stability of superconductive condition of the superconductive fiber, a metallic layer 4 of normal good conductivity is preferably arranged between the sintered covering layer 2 and protective film 3. As the normal good conductivity metal, metals of good conductivity such as pure copper, silver, etc., are preferable for permitting a large superconductive critical current density. This makes it possible to obtain a superconductive fiber of a high critical current density value and critical temperature without deteriorating actual handling performance.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a superconducting fiber used as a superconducting cable, and particularly to a superconducting fiber using an oxide ceramic superconductor and a method for manufacturing the same.

<Prior art> Conventionally, superconducting conductors are Nb-Ti, Nb-Zr, Nb-
Alloy systems such as Ti-Zr and compound systems such as Nb3Sn, (Nb-Ti), and Sn%V3Ga have been proposed, but these superconducting critical temperatures (T
c) are all below 20. Also,
Although it has not been put into practical use, Nb3 Ge has the highest Tc.
Even so, it is no more than 24. Therefore, these superconducting conductors have no choice but to use liquid helium as a coolant. This liquid helium has a low boiling point <4.2K)
is very expensive and requires advanced insulation technology to keep it in a liquid state.

Recently, La-Ba-Cu-0 series, La-5r-Cu-0
A high-temperature oxide ceramic superconductor with a critical temperature (Tc) of 35K to 175 was discovered in layered perovskite ceramics such as Y-Ba-Cu-0 and 5c-Ba-Cu-0. has been done. but,
This oxide ceramic superconductor has not yet been fully developed into a conductor, and naturally the critical current density (Jc)
is also at a low level.

The first example of making wire rods is at Yozai Research Institute.
La-5r-Cu-0 powder is placed in a Cu-Ni tube and drawn to form a wire rod, with a critical temperature (Tc) of 35
K, critical current density (Jc) is 4.2, io
o'.

A/cm" is displayed.

A second example of wire rod production is the one at Tohoku University's Institute of Materials Research, in which only the La-3r-Cu-0 metal component, excluding oxygen, is made into an amorphous alloy tape using a molten metal quenching method.
After that, heat treatment is performed in an oxygen atmosphere to form an oxide ceramic. It shows a critical temperature of 40°C for a polymer-based superconducting tape.

Although the above two types of tapes have become superconducting, the critical current value is higher than that of the conventional Nb-Ti metal type or Nb
, Sn, (Nb-Ti), and Sn compound-based superconducting materials are on the order of 1/100, and there is a problem that it cannot be put into practical use unless the critical current value is increased.

In addition, the critical temperature (Tc) is lower than the boiling point of liquid nitrogen,
Not enough.

In general, the critical temperature Tc and critical magnetic field Hc2 are factors determined by the superconducting material itself, and are said to show high values in layered perovskite oxide ceramic superconductors, but the critical current depends on the structural factors of the conductor. It has a big influence and cannot be determined by the material alone. Therefore, the critical current value cannot be improved unless a stabilized conductor is created that eliminates the magnetic instability peculiar to superconductors.

From this point of view, the reason why a high critical current density (Jc) cannot be obtained with the two types of tape conductors mentioned above is that the cross-sectional condition of the two types of tape conductors mentioned above is quite porous, and the conductor is uniform in the longitudinal direction. This is thought to be because it was inferior in terms of properties, magnetic stability, and thermal stability.

By the way, when using oxide ceramic superconductors, it is possible to use liquid nitrogen (boiling point 77K) as a refrigerant because it has a high critical temperature (Tc) and is inexpensive and does not require advanced insulation technology. The overall cost is dramatically reduced compared to conventional superconducting conductors using liquid helium.

<Problems to be Solved by the Invention> The purpose of the present invention is to solve the above-mentioned problems of the prior art, and to provide a new high-temperature superconducting fiber with a high critical current value and critical temperature, and which does not deteriorate performance in handling. The object of the present invention is to provide a manufacturing method thereof.

Another object of the present invention is to provide a new high-temperature superconducting fiber that has a high critical current value and high critical temperature, does not deteriorate handling performance, and has excellent stability, and a method for manufacturing the same. be.

Means for Solving Problems> According to a first aspect of the present invention, there is provided a superconducting fiber characterized in that a coating sintered layer of an oxide ceramic superconductor and a binder is formed around an inorganic fiber. is provided.

According to a second aspect of the present invention, a superconducting fiber is manufactured by coating the inorganic fiber with a paste of oxide ceramic superconducting powder and a binder, followed by drying and sintering. A method is provided.

Further, the oxide ceramic superconductor has a composition formula M
M'2Cu30t - (where M is Y, δSc and La, Gd, Dy, Ho%Er.

It is preferable to have at least one member selected from the group consisting of lanthanides such as Yb, Lu, and Eu; M' is at least one member selected from the group of alkaline earth metals; and δ represents deficient oxygen.

Further, it is preferable that the inorganic fiber is made of glassy ceramics.

Further, the binder preferably contains a low melting point glass having a melting point of 20° C. or less and one or more of propylene glycol, octyl alcohol, and xylyl alcohol.

Hereinafter, the present invention will be explained in detail based on preferred embodiments shown in the accompanying drawings.

In the present invention, it is important that an inorganic fiber is used as the core material of the coating sintered layer of the oxide ceramic superconductor and the binder. As a result, the mechanical strength against bending and impact is improved, and handling performance is not deteriorated, so that oxide ceramic superconducting fibers are put into practical use. Moreover, by using an inorganic fiber as a core material, it becomes possible to give the superconducting fiber a desired shape or maintain a desired shape.

The material of the inorganic fiber needs to have a melting point higher than the sintering temperature for forming the oxide ceramic superconductor coated sintered layer.

Specifically, it is preferable that the melting point is 1200°C or higher.

Further, it is preferable that the coefficient of thermal expansion of the inorganic fiber is closer to that of the oxide ceramic superconductor. This makes it possible to reduce thermal stress caused by sintering of the oxide ceramic superconductor coated sintered layer or peeling due to this.

Such inorganic fibers have a melting point of 1200°C.
The above-mentioned glassy ceramics, such as quartz glass, are preferred. The reason for this is that glassy ceramics have good thermal expansion consistency with the oxide ceramics and are economical.

The cross-sectional shape of the inorganic fiber is not limited, and can be any desired shape, such as circular, rectangular, or irregularly shaped. With only oxide ceramic superconductors, wire rods with desired cross-sectional shapes,
Although it is difficult to manufacture a strip, by forming the inorganic fiber into a desired cross-sectional shape in advance, an oxide ceramic superconducting fiber having a desired cross-sectional shape can be easily obtained.

In addition, the wire diameter of the inorganic fiber is determined by the required wire material,
Depending on the final use, wires with a wire diameter of 0.1 to 1 mm can be used. In the present invention, using such an inorganic fiber as a core material, a covering sintered layer 2 of an oxide ceramic superconductor and a binder is formed directly on the inorganic fiber surface 1 as shown in FIGS. 1 and 2. .

The oxide ceramic superconductor used in the present invention refers to a ceramic superconductor with y%ScJ and L
a, Gd%Dy%Ho.

Er% At least one element selected from the group consisting of lanthanides such as Lu and Eu, at least one element selected from the group of alkaline earth metals such as Ca, Sr, and Ba, Cu element, and 0 element. It is characterized by a significantly higher critical temperature than conventional alloy-based superconductors. Examples of such oxide ceramic superconductors include La-3r-Cu-0 soft compounds, La-5r-Cu-0 soft compounds mixed with a trace amount of Ca, and M
-B a -Cu -0 soft compound (M is Sc,
Y, and La, Gd%Dy, Ho, Er, Yb, Lu
, represents at least one member selected from the group consisting of lanthanides such as Eu, etc.), and among these, composition formula MM' 2 (:u307- (However, M Lt ditto element δ, M' is alkaline earth At least one metal selected from the group of metals (δ represents deficient oxygen), etc. Here, as the alkaline earth metal, Ca
, Sr, or Ba are preferable, and Ba is particularly preferable.

These are generally manufactured from elements or their oxides as raw materials by methods such as sintering, electron beam evaporation, and sputtering.

Furthermore, the binder used when forming the sintered coating layer of oxide ceramic superconductor around the outer periphery of the inorganic fiber is preferably a mixture of an inorganic binder that does not volatilize during sintering and an organic binder that radiates during sintering. Any inorganic binder with a low melting point may be used as the inorganic binder, but a low melting point glass with a melting point of 1000°C or less is preferable. A material that matches the coefficient of thermal expansion is used. Specifically, borosilicate glass, lead glass, soda lime glass, zinc glass, etc. can be mentioned, and among these, borosilicate glass whose main component is B2O3 is particularly preferable because it has good thermal expansion consistency. Any organic binder may be used as long as it radiates during sintering, but propylene glycol, octyl alcohol, xylyl alcohol, and mixtures thereof are preferred.

This is also because the thickness of the covering sintered layer is generally preferably 5 to 100 Jffi, although it depends on the use of the wire or strip. The reason for this is that a uniform superconductor layer with the required thickness can be obtained.

As shown in FIG. 1, the superconducting fiber of the present invention has a protective coating 3 on the outermost layer that insulates and protects a coating sintered layer 2 of an oxide ceramic superconductor. The protective coating 3 may be anything that insulates and protects the sintered coating layer 2, for example, any coating used for ordinary cables, etc., and a coating made of resin or plastic material such as nylon is particularly preferred.

Further, the thickness of the protective liquid @3 is not particularly limited, as long as it has a thickness that can insulate the covering sintered layer 2 and improve the resistance to external damage.

As described above, the superconducting fiber of the present invention is basically one in which a sintered coating layer of an oxide ceramic superconductor is formed around the outer periphery of an inorganic fiber, and a protective film is formed on the sintered coating layer. However, in order to further improve the stabilization of the superconducting state of the superconducting fiber, it is preferable to provide a normal-conducting, good-conductor metal layer 4 between the sintered covering layer 2 and the protective coating 3, as shown in FIG. At this time, pure copper, silver, aluminum, indium, tin, and alloys thereof are preferable as the normally conductive metal. The reason for this is that these metals have low resistivity and good electrical conductivity, which improves the stability of the superconducting state and allows for a large superconducting critical current density. This is because it can impart brazing properties and is also useful for preventing external damage.

The superconducting fiber according to the present invention is basically constructed as described above, and the manufacturing method thereof will be explained in detail below.

A flowchart of an embodiment of the method for manufacturing a superconducting fiber of the present invention is shown in FIG.

The oxide ceramic superconductor powder used in the present invention may be a fine powder obtained by preliminary sintering and pulverization of raw material powder, but fine powder obtained by main sintering and subsequent pulverization may also be used. .

The raw material powders include Y, Sc and La%Gd, H
o, Er.

A mixed powder of a compound containing at least II4 selected from the group consisting of lanthanides such as Yb, Lu, Eu, etc., at least one selected from the group consisting of Ca, Sr, and Ba, the Cu element, or oxides or oxygen of these elements. Good to have.

In particular, one or more of (i) copper oxide powder, (ii) barium carbonate powder and (iii) strontium oxide powder, yttrium oxide powder, lanthanum oxide powder, and scandium oxide powder. It is preferable to form an oxide ceramic superconductor by sintering a mixed powder containing two or more types. The reason for this is that the reproducibility of superconducting properties is good and the production efficiency is good.

When performing sintering, it is preferable to make the particles of the raw material powder as small as possible, and the preliminary sintering temperature is 850~850℃.
1000℃, preliminary sintering time 4 to 20 hours, main sintering temperature 8
5ON12o.

℃, and the main sintering time is preferably 2 to 10 hours, and both the main sintering and the preliminary sintering may be performed in the atmosphere.

The particles of the oxide ceramic superconductor powder are preferably as small as possible, and after sintering the raw material powder, it is preferable to grind it into a fine powder using a pulverizer such as a disk mill, ball mill, drum mill, or jet mill.

As shown in FIG. 3, in the method of the present invention, the oxide ceramic superconductor powder and the low melting point (i
ooo°C or less) An inorganic binder such as glass and the above-mentioned organic binder were mixed to form a paste-like mixture.

The paste-like mixture thus obtained is coated (applied) around the outer periphery of the above-mentioned inorganic fiber and dried.
This outer periphery coating is repeated several times to obtain a predetermined thickness.

After this, after sufficiently drying and heating to 300 to 400°C to burn out the organic binder component, main sintering is performed to coat and sinter the oxide ceramic superconductor and inorganic binder. A layer is formed around the inorganic fiber.

Here, as mentioned above, the main sintering is performed in the atmosphere at a temperature of 850°C.
What is necessary is just to carry out at 1200 degreeC for 2 to 10 hours.

At this time, the inorganic fiber is a glassy ceramic with a melting point of 1200°C or higher, and the inorganic binder is a glassy ceramic with a melting point of 1000°C or higher.
If the glass has a low melting point below, the inorganic binder will melt during main sintering, so the oxide ceramic superconductor will be in close contact with the inorganic binder, and the inorganic binder will be very different from the inorganic fiber. Adheres well.

Therefore, the oxide ceramic superconductor can be closely attached to an inorganic fiber via an inorganic binder and suitably made into a wire. In this way, it is possible to improve the superconducting properties.

Thereafter, the superconducting fiber of the present invention is manufactured by covering the outer periphery of the formed sintered covering layer with the above-mentioned insulation protection material to form a protective film. As described above, the insulation protection material is preferably a resin such as nylon or a plastic material, and the coating method may be any conventional method, such as coating and baking, extrusion, tape wrapping, etc.

The method for manufacturing a superconducting fiber of the present invention is basically configured as described above, but in order to improve the stability of the superconducting state and the critical current density, a method is added between the sintered coating layer and the protective film. When forming a normal-conducting, good-conducting metal layer, after main sintering, the above-mentioned metal material is applied directly onto the sintered coating layer of the oxide ceramic superconductor by electroless plating, thermal spraying, vapor deposition, or metal coating. The metal layer is formed by seam welding the strips or the like.

Thereafter, the above-described protective coating is formed to produce the superconducting fiber of the present invention.

Although the superconducting fiber and the method for manufacturing the same according to the present invention are basically constructed as described above, the present invention is not limited thereto, and improvements and designs may be made without overcoming the gist of the present invention. Of course, changes are possible.

<Example> The present invention will be specifically described below based on Examples.

(Example 1) Superconductor raw material powders include Y2O3, BaCO3, C
Use uO powder (particle size 5- or less) and convert it into (Y r B
B2) Cu307-6 (δ represents deficient oxygen)
The mixture was mixed in such a manner that the composition ratio was as follows, and the powder was pre-sintered in the atmosphere at a sintering temperature of 850 to 950°C for 4 to 20 hours. Thereafter, they were crushed and mixed, and sintered again under the same conditions, and the crushed and mixed mixture was used as a pre-sintered oxide ceramic superconductor fine powder. The oxide ceramic superconductor powder was mixed with an organic binder and an inorganic binder to form a paste, and the paste was repeatedly coated and dried around a quartz glass fiber having a diameter of too#m to a thickness of 257 Jl.
After that, it is dried at 300-400℃ to burn out the organic binder component, and then sintered at a temperature of 950-1050℃.
Main sintering was carried out in the atmosphere at ℃ for 2 to 5 hours in order to improve the superconducting properties. Furthermore, the periphery was coated with a nylon insulating material to obtain a 300-diameter superconducting fiber.

As the binder for applying the pre-sintered oxide ceramic superconductor fine powder to the quartz glass fiber, the organic binder was a mixture of propylene glycol, octyl alcohol, and xylyl alcohol, and the inorganic binder was B20. A low melting point glass containing as the main component was used.

At this time, the melting point of the core quartz glass fiber is 1200℃
In contrast, the melting point of the binder glass is 100
It had a low melting point of 0°C or less.

When the characteristics of the obtained superconducting fiber were measured, it was found that the critical temperature at which the electrical resistance becomes zero is 83K.

Also, the critical current density value is 4.2 and 2000 A
/cm2 values were shown.

<Effects of the Invention> As detailed above, according to the present invention, an oxide ceramic superconductor can be easily made into a wire, can be used as a conductor, has a high critical current density value and a high critical temperature,
It is possible to provide a new superconducting fiber whose performance does not deteriorate during handling.

Further, according to the present invention, in addition to the above-mentioned effects, the stability of the superconducting state is improved by forming a normal-conducting, good-conducting metal layer on the covering sintered layer of the wire-shaped oxide ceramic superconductor. An improved superconducting fiber can be provided.

Further, according to the present invention, since the oxide ceramic superconductor powder, the low melting point inorganic binder, and the organic binder are made into a paste, applied to the inorganic fiber, dried, and then sintered, the wire of the oxide ceramic superconductor is It is possible to easily and inexpensively produce a superconducting fiber that is not only easy to fabricate, but also has high adhesion to the inorganic fiber that is the core material.

Therefore, it becomes possible to use the oxide ceramic superconductor in a high temperature range (temperature range where liquid nitrogen can be used), and it has the effect of expanding its use as a power cable.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of a superconducting fiber according to the present invention. FIG. 2 is a cross-sectional view of another embodiment of the superconducting fiber according to the present invention. FIG. 3 is a flowchart showing an embodiment of the method for manufacturing a superconducting fiber according to the present invention. Explanation of symbols 1... Inorganic fiber, 2... Covering sintered layer,
3...Protective film, 4...Metal layer Patent applicant: Hitachi Cable Co., Ltd. Representative: Patent attorney Nobutoshi Watanabe, 1') FIG, IFIG, 2 Fig. 3

Claims (8)

[Claims] (1) A superconducting fiber characterized by forming a coating sintered layer of an oxide ceramic superconductor and a binder around an inorganic fiber. (2) The oxide ceramic superconductor has a composition formula M
M'_2Cu_3O_7_-_δ (However, M is Y, Sc
and La, Gd, Dy, Ho, Er, Yb, Lu, E
At least one selected from the group consisting of lanthanides such as u
The superconducting fiber according to claim 1, wherein M' is at least one selected from the group of alkaline earth metals, and δ represents deficient oxygen. (3) The superconducting fiber according to claim 1 or 2, wherein the inorganic fiber is a glassy ceramic. (4) Claims 1 to 3, wherein the binder contains a low melting point glass having a melting point of 1000°C or less.
The superconducting fiber according to any of paragraphs. (5) A method for producing a superconducting fiber, which comprises coating the periphery of an inorganic fiber with a paste of oxide ceramic superconductor powder and a binder, followed by drying and sintering. (6) The oxide ceramic superconductor has a composition formula M
M'_2Cu_3O_7_-_δ (However, M is Y, Sc
and La, Gd, Dy, Ho, Er, Yb, Lu, E
At least one selected from the group consisting of lanthanides such as u
6. The method for producing a superconducting fiber according to claim 5, wherein M' is at least one selected from the group of alkaline earth metals, and δ represents deficient oxygen. (7) The method for manufacturing a superconducting fiber according to claim 5 or 6, wherein the inorganic fiber is a glassy ceramic. (8) The superconductor according to any one of claims 5 to 7, wherein the binder contains a low-melting glass having a melting point of 1000°C or less and one or more of propylene glycol, octyl alcohol, and xylyl alcohol. Fiber manufacturing method.