JPH01105414A - Manufacture of oxide superconducting wire - Google Patents

Abstract

PURPOSE:To obtain a superconducting element wire with high critical current density and no crack by heat-treating a core wire after removing a metal sheath. CONSTITUTION:At least one of an oxide superconductor and its precursor is filled in a metal tube 2 to form a composite body 3, which is shrunk in diameter to obtain a wire 13' constituted of a core 14 and a metal sheath 15. The metal sheath 15 is then removed from this wire 13' to expose the core 14, heat treatment is applied to the core 14 to obtain a superconducting element wire 16, a cushion layer 17 is formed around this superconducting element wire 16, and a metal sheath 18 is formed around the cushion layer 17. The metal sheath is removed, the core is exposed and applied with heat treatment to form the superconducting element wire, thus the core can be heat-treated while sufficient quantity of oxygen is supplied, and the superconducting wire with high critical current density and no defective portion such as cracks is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing an oxide superconducting wire that can be used for winding a superconducting magnet or for power transmission.

"Prior Art" Recently, various oxide-based superconducting materials have been discovered whose critical temperature (Tc) for transitioning from a normal conducting state to a superconducting state is higher than the liquid nitrogen temperature.

This kind of oxide superconducting material has the general formula -B-Cu-0
(However, Δ represents one or more elements of group Ma of the periodic table such as La, Ce, Yb, Sc, and Er, and B represents one or more elements of group Ila of the periodic table such as Ba and Sr. ). In order to manufacture this type of oxide superconductor, a powder containing the 111a group element, a powder containing the MA group element, and a copper oxide powder are mixed to create a mixed powder, and this mixed powder is shaped into a predetermined shape. After molding, the obtained molded body is heat-treated and each element undergoes a solid phase reaction to produce a superconducting material.

In addition, as a method for producing a superconducting wire comprising the A-B-Cu-0 system superconductor, conventionally, the mixed powder is filled into a metal tube, or the mixed powder is heat-treated to obtain a superconducting powder. After filling, the metal tube is drawn out using a die or the like to obtain a wire rod of the desired diameter, and this wire rod is heat-treated to cause the elements in the powder compact inside to undergo a solid phase reaction. A method of obtaining a superconducting wire by producing a superconducting substance inside a metal tube is known.

"Problems to be Solved by the Invention" However, in such a method, stress is generated between the metal sheath and the superconductor inside it due to the difference in thermal expansion coefficient during heat treatment, and this stress causes numerous damage to the superconductor. Due to cracks and defective areas, it is not possible to obtain an excellent critical current density, and there is a problem in that it is not possible to obtain a superconducting wire that exhibits uniform superconducting properties along the longitudinal direction. Incidentally, when the present inventors compared the superconducting properties of this superconducting wire and the molded body, the former was found to be 172
Results have been obtained that there are some that exhibit only a value of about I15.

Is the invention a head problem? In view of this, the object of the present invention is to provide a method that can produce a superconducting wire that is free from defects such as cracks and has a high critical current density.

=3-rAnother means to solve the problem J In order to solve the above-mentioned problems, the present invention provides a method in which a metal tube is filled with at least one of an oxide superconductor and a precursor of an oxide superconductor. A composite is formed, the composite is then reduced in diameter to form a wire consisting of a core material and a metal sheath, the metal sheath is removed from the wire to expose the core material, and the core material is then heat treated. After obtaining a superconducting wire, a coating layer is formed on the outer side of the superconducting wire, and a metal sheath is further formed on the outer side of the coating layer.

``Operation'' By heat-treating the core wire after removing the metal sheath, it is possible to obtain a superconducting wire with a high critical current density and no cracks. By forming a metal coating layer, a superconducting wire can be obtained without cracking.

The present invention will be explained in more detail below.

1 to 6 are for explaining one embodiment of the present invention. In order to carry out the present invention and manufacture an oxide-based superconducting wire, starting materials are first prepared. The starting materials include oxide superconductors, materials containing elements constituting oxide superconductors (precursors), or mixtures thereof (precursors).
is used.

The above-mentioned oxide superconductor is based on the A-B-C-D system (where A represents one or more elements of Group IIfa of the periodic table such as La, Ce, Y, Yb, Dy, and 14o, and B represents S
R, represents one or more elements of group ITa of the periodic table such as Ba, and C represents elements of group 1b of the periodic table such as Cu, Ag, Au, and N.
b represents Cu or two or more elements containing Cu, and D represents elements of group ■b of the periodic table such as O, S, and Se, and F'
, C.I.

Indicates O or two or more elements containing O among elements in group IIb of the periodic table such as Br. ) are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ua of the periodic table and elements of group 11Ta of the periodic table.
A mixed powder consisting of a powder containing a group element and copper oxide powder, a powder obtained by calcining this mixed powder, a mixed powder of the above mixed powder and calcined powder, etc. are used. The Ha group element powder of the periodic table used here includes Be, S
These include compound powders or alloy powders such as carbonate powders, oxide powders, chloride powders, sulfide powders, and fluoride powders of each element of r, Mg, Ba, and Ra. Also, periodic table I
Group Ia element powders include Sc, Y, La, Ce, and P.
r, Nd, Pm.

Sm, Eu, Gd, Tb, Dy, I(o, Er, Tm,
Compound powders or alloy powders such as oxide powders, carbonate powders, chloride powders, sulfide powders, and fluoride powders of the elements Yb and Lu are used. Further? The copper oxide powders include CuO, Cu, ○, and CL1302. C14
03 etc. are used.

By the way, in order to prepare the mixed powder, Moe's powder method is usually used, but the method is not limited to this method.Each element can be coprecipitated as a sulfuric acid salt, and the precipitate can be dried. It is also free to apply a coprecipitation method to obtain a mixed powder.

In addition, the above-mentioned necessary elements such as alcokind compounds, oquinoketone compounds, cyclopentadienyl compounds, etc. are mixed in a predetermined ratio to form a mixed solution, and water is added to this mixed solution to hydrolyze it to form a sol, A sol-gel method may be applied in which this sol-like substance is heated to gel, and the gel is further heated to make the same phase, and then pulverized to obtain a mixed powder.

Next, the powder 1 prepared as described above is filled into a metal tube 2 shown in FIG. 1 to create a composite 3. Said tube body 2
is made of a metal material such as Cu, Ag, AI, an alloy thereof, or stainless steel. The material to be filled in the tube body 2 may be a superconductor obtained by calcining the powder or sintering the powder, superconducting powder obtained by crushing this superconductor, or superconducting granules. .

Next, the composite body 3 is subjected to a diameter reduction process using a rotary swaging device A shown in FIG. This rotary swaging device A includes a plurality of dies 6 that are movably provided by a drive device along the path shown in the figure. These dice 6 are provided around a movement space when the rod-shaped composite body 3 is moved in its length direction, so as to surround this movement space, and are arranged in a direction perpendicular to the movement space (see Fig. 1). It is held movably in the direction of the arrow a shown in FIG. 1) and rotatably around the movement space (in the direction of the arrow shown in FIG. 1). Further, a taper 6a for reducing the diameter of the composite body 3 is formed on the inner surface of each die 6, so that the gap surrounded by the taper 6a of each die 6 becomes tapered. ing.

To reduce the diameter of the composite 3, the surface rotary swaging device A is operated and one end of the composite 3 is pushed into the gap between the dies 6, as shown in FIG. Here, since the dies 6 are rotating while reciprocating at a predetermined interval in the vertical direction of FIG. 1, the composite body 3 is sequentially forged from one end and is reduced in diameter to two points in FIG. 1. The wire diameter is reduced to the wire diameter shown by the chain line, and a wire rod 13 consisting of a core material 14 and a metal sheath I5 is obtained. In this diameter reduction process,
In order to reduce the diameter of the composite body 3 while forging it with a plurality of dies 6 that reciprocate while rotating, the composite body 3 that is undergoing diameter reduction processing is
Diameter reduction processing can be performed at a large processing rate without causing wire breakage. The composite body 3 is repeatedly reduced in diameter by the rotary softening device A until it reaches a desired wire diameter, thereby obtaining a wire rod having the desired wire diameter of 13° as shown in FIG.

Next, the metal sheath I5 is removed from the wire 13' to expose the core 14 of the wire 13' as shown in FIG.

To remove the metal sheath I5, for example, the core material 6 is immersed in a treatment liquid such as an aqueous acid or alkali solution, and only the metal sheath 15 is dissolved in the treatment liquid. Here, when copper, silver, or an alloy of these is used as the metal sheath 15, dilute nitric acid or the like is used as the treatment liquid, and when aluminum or the like is used as the metal sheath 15, caustic soda or the like is used. When stainless steel is used as the material, aqua regia or the like is used as the treatment liquid, but the treatment liquid is not limited to these.

After removing the metal sheath I5 and exposing the core material 14, the core material 4 is subjected to heat treatment. This heat treatment is preferably performed by heating at 800 to 1100° C. for about 1 to 100 hours in an oxidizing atmosphere and then slowly cooling. Through this heat treatment, each element undergoes a solid phase reaction inside the core material 14, resulting in A -
A B-Cu-0 based superconducting material is produced, and a superconducting strand I6 shown in FIG. 4 is obtained.

By the way, in the superconducting wire 16 manufactured as described above, the core material 14 is manufactured by being forged and reduced in diameter multiple times using a rotary swaging device, and the core material 14 is sufficiently compacted. is formed, so that the elements can diffuse smoothly when each element undergoes an in-phase reaction by heat treatment. Therefore, the produced superconducting wire (6) has a low porosity and high mechanical strength.

Next, a cushion layer 17 is formed on the outer surface of the superconducting wire 16 as shown in FIG. This cushion layer 17 is made of a low melting point metal such as solder, a soft metal such as indium, or a material having an expansion coefficient intermediate between the thermal expansion coefficient of the superconducting wire 16 and that of the metal north 18 described later. It consists of In order to form this cushion layer 17, a method such as preparing a tape made of a metal material constituting the cushion layer 17 and attaching or wrapping this tape around the superconducting wire 16 vertically, or
Alternatively, it can be formed by means such as a welding method, a vapor deposition method, and a depth forming method.

Once the cushion layer 17 is formed, the superconducting wire B can be obtained by subsequently covering the outside with a metal sheath 18 made of aluminum, copper, or the like.

In order to form this metal sheath I8, it is sufficient to prepare a tape or a thin plate made of a metal material constituting the metal sheath 18, form it into a tubular shape, and cover the outside of the cushion layer 17. This coating is preferably carried out by applying a known tube forming method using dies or forming rolls. Here, a metal sheath 1 is provided on the outer surface of the cushion layer 17.
8, a metal sheath 18 and a cushion layer 17
Covering with the metal sheath 18 can be performed without creating a gap or the like.

The superconducting wire B produced as described above is wound around a drum for use as a winding wire for a superconducting magnet, and is used after being cooled with a refrigerant such as liquid nitrogen, as well as being used for power transportation. .

In addition, in the superconducting wire B, since the coefficient of thermal expansion of the superconducting wire 16 and the thermal expansion coefficient of the metal sheath 18 are different, when the superconducting wire A is cooled from room temperature to liquid nitrogen temperature, or from liquid nitrogen temperature to When the superconducting wire 16 is returned to room temperature, stress due to the difference in coefficient of thermal expansion may act on the superconducting wire 16. However, in this respect, in the superconducting wire B, since the cushion layer 17 formed between the superconducting wire I6 and the metal sheath 18 relieves the thermal stress, cracks do not occur in the superconducting wire 16. Furthermore, if there is a gap between the cushion layer 17 and the metal sheath I8, there is a concern that the stress will be concentrated in this area, but as mentioned above, there is no gap in the superconducting wire A. No such stress concentration occurs.

"Example" Y2O3 powder and B a CO, powder and CuO powder Y
A mixed powder was obtained by mixing Ba:Cu=1, 2, and 3, and this mixed powder was heated at 700°C for 24 hours and then calcined at 900°C for 24 hours. Next, this calcined powder was made into a powder with an outer diameter of 10 mm and an inner diameter of 7 mm.
A composite was obtained by filling a silver tube. Next, using a rotary swaging device equipped with a die having the same configuration as the die shown in FIG. 1, the composite was cold-forged to a diameter of 1.4 mm while being reduced in diameter in stages to form a powder compact. A wire rod was obtained consisting of a core wire made of the material and a sheath made of the constituent material of the tube body. In addition, in order to reduce the diameter of the composite in stages, prepare multiple dies with different gaps between the dies, set the cross-section reduction rate of the 1-pass to approximately 20%, and change the direction of diameter reduction for each I-pass. The diameter was reduced by forging multiple times, and the processing speed was 1 m/min.

In the above processing, it was possible to process the wire up to the final wire diameter without any problems such as wire breakage.

In the wire rod manufactured as described above, the compaction density of the powder is improved compared to a wire rod whose diameter is reduced by drawing using a die. The diameter of the core part of this wire is 0.8r
It was tt11.

Next, this wire was immersed in nitric acid to dissolve and remove the silver sheath to expose the core material.

Next, this core material is heated to 850 to 950 in an oxygen atmosphere.
A heat treatment of heating at .degree. C. for 24 hours was performed to generate an oxide-based superconductor over the entire core wire, thereby obtaining a superconducting strand.

Next, a layer of Pb-9n alloy with a thickness of 0.100 mm was applied to the surface of this superconducting wire by a dip forming method.
A cushion layer with a thickness of 0 mm is formed on the outer periphery.
．． An oxide-based superconducting wire was manufactured by covering a 5 mm Cu metal sheath by a tape forming method.

The superconducting wire manufactured as described above has a critical temperature of 91 and a critical current density of about 10,000 A/cm' (77 K
) was shown.

Furthermore, when this superconducting wire was wound around a winding drum, it was found that the wire could be wound without cracking, and that its mechanical strength was sufficiently high.

From the above, it has been revealed that the superconducting wire manufactured by implementing the present invention exhibits particularly excellent critical current density and has high mechanical strength.

"Effects of the Invention" As explained above, the present invention removes the metal sheath, exposes the core material, performs heat treatment, and supplies a sufficient amount of oxygen etc. to the core material in order to form a superconducting wire. Since the heat treatment can be performed while the wire is heated, it is possible to obtain a superconducting wire that exhibits good superconducting properties and exhibits uniform superconducting properties over its entire length. In addition, since the superconducting wire is coated with a metal sheath via a cushion layer, when the superconducting wire is cooled to a low temperature or returned from a low temperature to room temperature, the difference in thermal expansion coefficient between the metal sheath and the superconducting wire may occur. Since the cushion layer relieves this stress, it is possible to process the oxide superconducting wire so as not to cause cracks.

[Brief explanation of the drawing]

1 to 6 are for explaining one embodiment of the present invention. FIG. 1 is a sectional view for explaining a rotary swaging device, FIG. 2 is a sectional view of a wire rod, and FIG. 3 is a sectional view for explaining a rotary swaging device. 4 is a cross-sectional view of the core material, FIG. 4 is a cross-sectional view of the superconducting wire, FIG. 5 is a cross-sectional view of the wire with a cushion layer formed thereon, and FIG. 6 is a cross-sectional view of the superconducting wire. 1...Powder, 2...Tube, 3...
... Composite, 13.13° ... Wire rod, 14 - Core material, 15 ... Metal sheath,
16... Superconducting wire, I7... Crack layer, 18... Metal sheath, A... Superconducting wire.

Claims (1)

[Claims] At least one of the oxide superconductor and the oxide superconductor precursor is filled into a metal tube to form a composite, and this composite is then reduced in diameter to form a wire consisting of a core material and a metal sheath. The metal sheath is removed from this wire to expose the core material, and then the core material is heat treated to obtain a superconducting wire, and then a low melting point material or soft metal is formed on the outside of the superconducting wire. A method for producing an oxide superconducting wire, comprising forming a cushion layer and further covering the outside of the cushion layer with a metal sheath.