JP2590157B2 - Manufacturing method of superconductor wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing a superconductor wire using an oxide superconductor.

(Prior Art) In recent years, since it was announced that a Ba-La-Cu-O-based layered perovskite-type oxide may have a high critical temperature, research on oxide superconductors has been carried out in various places. (Z. Phys. B Condensed Matter 64, 189-193 (1986)).
Among them, a defect perovskite type having an oxygen defect represented by a Y-Ba-Cu-O system ((LnBa ₂ Cu ₃ O _7-δ type)
(Δ represents an oxygen vacancy, usually 1 or less, and Ln is Y, La, Sc,
At least one element selected from Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu, and part of Ba can be replaced with Sr, etc.)) Has been attracting attention as a very promising material because of its high temperature of 90K or higher, which is higher than the boiling point of liquid nitrogen (Phys. Rev. Lett. Vol. 58 No. 9, 908)
−910).

By the way, since such an oxide superconductor is obtained as a sintered body of a crystalline oxide or a powder thereof, when these are used as a wire, for example, after filling the metal tube with the oxide superconductor powder, Attempts have been made to lengthen and use it by drawing.

More specifically, such a method for manufacturing a superconductor wire is described below. First, a metal tube made of silver or the like is filled with an oxide superconductor powder, which is cold-drawn to a required wire diameter and lengthened. Make a long wire. Thereafter, heat treatment is performed in an atmosphere in which oxygen can be sufficiently supplied to improve superconductivity and manufacture a superconductor wire.

(Problems to be Solved by the Invention) However, in the above-described method for manufacturing a superconductor wire, the compacted powder is processed as it is, so that the processability is poor, and the density of the powder decreases during wire drawing. However, there is a problem that a sufficiently dense material cannot be obtained even if heat treatment is performed thereafter to densify, and a sufficiently practical critical current density cannot be obtained. In addition, due to sintering of the oxide superconductor powder during heat treatment, the volume of the oxide superconductor in the metal tube is reduced, cracks are generated in the oxide superconductor, and voids are formed between the metal tube and the oxide superconductor. This causes a problem that the mechanical strength is reduced. Such a decrease in mechanical strength
This leads to an increase in the amount of strain caused by stress such as bending or pulling from the outside. Here, in the oxide superconductor having a perovskite structure described above, the superconducting properties such as critical temperature and critical current density decrease as the strain increases, so that the increase in strain caused by the generation of voids is caused by the superconductivity. Will be reduced.

In addition, the above-described oxide superconductor has a property that a superconducting current flows in the c-plane direction of the crystal. If the length of the oxide superconductor is simply increased, the arrangement direction of the crystal becomes random. It will be enough.

The present invention has been made in order to solve such a conventional problem, and improves the workability of a metal tube filled with an oxide superconductor, thereby improving the denseness, and improving the crystal of the oxide superconductor. It is an object of the present invention to provide a method for manufacturing a superconductor wire having superconductivity improved by orienting in a certain direction.

[Structure of the Invention] (Means for Solving the Problems) In a first method for manufacturing a superconductor wire, an oxide superconductor powder or a sintered body is filled in a metal tube containing silver as a main component. After drawing the metal tube as it is or after once applying heat treatment, draw it hot under a temperature condition of 500 ° C to 900 ° C, and hold it in an oxygen-containing atmosphere at a temperature range of 300 ° C to 700 ° C for several hours. It is characterized by.

Further, the second method for producing a superconducting wire is to fill an oxide superconductor powder or a sintered body into a metal tube containing silver as a main component and leave the metal tube as it is or after once performing a heat treatment. It is characterized in that wire drawing is performed at a temperature of 500 ° C. to 900 ° C. and then gradually cooled to 300 ° C. in an oxygen-containing atmosphere.

Although many oxide superconductors are known, the use of a rare earth element-containing perovskite-type oxide superconductor having a high critical temperature has a high practical effect. The oxide superconductor containing a rare earth element and having a perovskite structure may be any material capable of realizing a superconducting state. For example, an LnBa ₂ Cu ₃ O _7-δ system (δ is an oxygen defect and usually 1 or less) , Ln is Y, La, Nd, Sm, Eu, Gd,
Represents at least one element selected from rare earth elements such as Dy, Ho, Er, Tm, Yb, and Lu; a part of Ba can be replaced with Ca or the like. ) And oxides having a perovskite type in a broad sense, such as a defect perovskite type having an oxygen defect, a layered perovskite type such as an Sr—La—Cu—O system, and the like. Rare earth elements are defined in a broad sense, and include Y and La-based elements. As typical systems, in addition to Y-Ba-Cu-O systems, systems in which Y is substituted with rare earth elements such as Eu, Dy, Ho, Er, Tm, Yb, and Lu; Sr-La-Cu-O systems; Sr to Ba, Ca
And the like.

The oxide superconductor powder used in the present invention is produced, for example, as follows.

First, the constituent elements of the perovskite-type oxide superconductor such as Y, Ba, and Cu are sufficiently mixed. When mixing, Y ₂ O ₃ ,
Oxides and carbonates such as BaCO ₃ and CuO can be used as raw materials, and compounds such as nitrates and hydroxides that are converted into oxides after firing may be used. Further, an oxalate obtained by a coprecipitation method or the like may be used. The elements constituting the perovskite-type oxide superconductor are basically mixed so as to have a composition with a stoichiometric ratio, but may be slightly shifted depending on the production conditions and the like. For example, Y-Ba-
In a Cu-O system, the standard composition is 2 mol of Ba and 3 mol of Cu with respect to 1 mol of Y.
A deviation of about 3 ± 0.4 mol is not a problem.

Then, after thoroughly mixing the above-mentioned raw materials, 850-980 ° C
Bake at a temperature of about. Then, if necessary, heat treatment is performed in an oxygen-containing atmosphere, preferably in an oxygen atmosphere, or by gradually cooling to about 300 ° C. in a similar atmosphere to introduce oxygen into oxygen defects δ and improve superconductivity. be able to. This heat treatment is usually performed at about 300 to 700 ° C.

Next, the fired product is ball mill, sand grinder,
Grind by other known means. At this time, the perovskite-type oxide superconductor is divided from the cleavage plane into a fine powder. This pulverization is preferably performed so that the average particle size is 0.1 to 5 μm.

The oxide superconductor powder obtained in this manner has an oxygen-defective perovskite structure (LnBa ₂ C
u ₃ O _7−δ (δ is usually 1 or less)). In addition, Ba
Can be replaced by Sr, Ca, or the like, and a part of Cu can be replaced by Ti, V, Cr, Mn, Fe, Co, Ni, Zn, or the like. The amount of substitution can be appropriately set within a range that does not deteriorate the superconducting characteristics, but is set to 80 mol% or less because excessively large amount of substitution deteriorates the superconducting characteristics.

The method of manufacturing the superconductor wire of the present invention will be described in further detail. First, the oxide superconductor powder prepared by the above-described method, or after pressing the powder, 900
A sintered body sintered at a temperature of about ℃ to 950 ° C is filled in a metal tube containing silver as a main component, and a powder is hardened from the outside of the tube material by a swaging machine or the like. Depending on the conditions, the wire is drawn by a hot process, for example, using a roller die or a normal die, lengthened, and processed into a strip having a required shape. This wire drawing may be performed in a state where the oxide superconductor powder is filled, or a metal tube filled with the oxide superconductor powder is subjected to a heat treatment in advance at a temperature of about 850 ° C to 980 ° C. And after densifying the oxide superconductor.

Further, the metal tube containing silver as a main component used in the present invention,
It is not oxidized even at a high temperature, and has excellent oxygen supply ability and shape maintaining ability.

By performing the hot wire drawing in this manner, the workability of the oxide superconductor is increased, the compactness is improved, and the generation of voids is prevented by the progress of the compaction of the oxide superconductor. Is also possible. In addition, the plastic deformation of the oxide superconductor occurs at the time of wire drawing, and the crystal grains can be oriented in the longitudinal direction of the metal tube.

The reason for limiting the temperature condition at the time of this wire drawing to a range of 500 ° C to 900 ° C is that at less than 500 ° C, the plastic deformation of the oxide superconductor is insufficient, and the effect of improving the workability is not sufficiently obtained. If the temperature exceeds 900 ° C., the melting point of silver becomes close to that of silver, which may adversely affect the processability.

Note that cold working may be performed after this hot working. However, if the cold working is performed too much, the risk of cracks occurring in the oxide superconductor increases, so that the surface smoothing is preferably performed.

Next, the strip shape processed to the final shape by the wire drawing is subjected to a heat treatment in an oxygen-containing atmosphere where oxygen can be sufficiently supplied to improve the superconductivity. This heat treatment is suitably performed at a temperature of about 850 ° C. to 950 ° C. for about 1 hour to 50 hours. Then, after this, the superconducting properties are further improved by gradually cooling while sufficiently supplying oxygen to about 300 ° C. or maintaining the temperature at about 300 ° C. to 700 ° C. for several hours while sufficiently supplying oxygen. .

(Operation) In the method for producing a superconductor wire of the present invention, since the hot wire drawing is performed, the workability of the oxide superconductor is increased, and the processing reduces the denseness of the oxide superconductor. In addition, since the density of the oxide superconductor advances to some extent during the wire drawing, the generation of voids between the metal tube and the oxide superconductor is prevented even in the final heat treatment. Also, at the time of wire drawing, the oxide superconductor is stretched in the longitudinal direction of the wire while causing plastic deformation,
The c-plane of the crystal grain is oriented in the longitudinal direction of the metal tube. Then, at the time of the final heat treatment, crystal grains grow further along this orientation state, so that the resulting superconductor wire has the c-plane of the crystal oriented in the longitudinal direction of the wire, and has an excellent critical current density. .

(Example) Next, an example of the present invention is described.

Example Y ₂ O ₃ powder having a particle size of 1 to 5 μm, BaCO ₃ powder and CuO powder were weighed in a predetermined amount so as to be 0.5 mol of Y ₂ O ₃ , 2 mol of BaCO _{3 and 3} mol of CuO, and after sufficient mixing, After firing at 900 ° C. in the air for 48 hours and reacting, then firing this product at 800 ° C. for 24 hours in an oxygen atmosphere and reacting to introduce oxygen into the oxygen vacant space, then pulverizing using a ball mill, Average particle size
A 0.5 μm perovskite oxide superconductor powder was obtained.

Next, this oxide superconductor powder was prepared for an outer diameter of 20 mm and an inner diameter of 16 mm.
× One end of a length of 70 mm was placed in a silver tube sealed with a silver material, and after being pressed with a press pressure of 1 ton / cm ² , a silver stopper was attached to the other end, and welding was performed while leaving a vent hole.

Subsequently, the metal tube was drawn while being heated to 700 ° C. in a heating furnace, thereby producing a strip having an outer diameter of 1 mm.

Thereafter, the linear body is heated at 900 ° C. in an oxygen atmosphere.
Heat treatment under the conditions of × 24 hours, 400 ° C × 48 hours,
The target superconductor wire was obtained.

When the superconducting properties of the superconducting wire thus obtained were measured, good results were obtained with a critical temperature of 90 K and a critical current density of 2000 A / cm ² in the longitudinal direction of the wire.

When the density of the superconductor wire was determined from the cross-sectional structure, it was as good as 98%. Further, when the degree of orientation of the oxide superconductor was examined by X-ray diffraction, it was found that the c-plane of the crystal was oriented 70% in the longitudinal direction of the line.

On the other hand, for comparison with the present invention, except that the wire drawing in the above example was performed cold, a superconductor wire was produced under the same conditions, and the characteristics of the superconductor wire were similarly measured. Critical temperature 90K, critical current density 1000A
/ cm ² , density 85%, and no c-plane orientation of the crystal was observed.

[Effects of the Invention] As is clear from the above examples, according to the method for manufacturing a superconductor wire of the present invention, the wire drawing is performed hot at a temperature of 500 ° C to 900 ° C. The denseness of the oxide superconductor is improved, the generation of voids between the metal tube and the oxide superconductor is prevented, and the oxide superconductor undergoes plastic deformation by hot working. It becomes possible to orient the c-plane. Therefore, the critical current density is greatly improved, and a practical superconductor wire can be obtained.

Claims (5)

(57) [Claims] An oxide superconductor powder or a sintered body is filled in a metal tube containing silver as a main component, and the metal tube is subjected to a temperature condition of 500 ° C. to 900 ° C. as it is or once subjected to a heat treatment. A method for producing a superconducting wire, comprising: performing wire drawing by hot working under a temperature of 300 ° C. to 700 ° C. in an oxygen-containing atmosphere for several hours. 2. The method according to claim 1, wherein said oxide superconductor is a perovskite-type oxide superconductor containing a rare earth element. 3. The superconductor according to claim 1, wherein said oxide superconductor contains a rare earth element, Ba and Cu in an atomic ratio of substantially 1: 2: 3. Manufacturing method of body wire. 4. The oxide superconductor comprises LnBa ₂ Cu ₃ O _7-δ.
2. The superconducting wire according to claim 1, wherein the superconducting wire has an oxygen-defective perovskite structure represented by (Ln represents at least one selected from rare earth elements, and δ represents oxygen vacancy). Method. 5. An oxide superconductor powder or a sintered body is filled in a metal tube containing silver as a main component, and the metal tube is subjected to a temperature condition of 500 ° C. to 900 ° C. as it is or once subjected to a heat treatment. A method for producing a superconducting wire, comprising: drawing a wire by hot working according to (1), and gradually cooling to 300 ° C. in an oxygen-containing atmosphere.