JP2583565B2 - Method for producing oxide-based superconducting material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an oxide-based superconducting material applicable to superconducting applied devices such as a superconducting magnet used in a nuclear magnetic resonance apparatus or a particle accelerator. is there.

"Prior art" Recently, various oxide superconductors have been discovered in which a critical temperature (Tc) at which a transition from a normal conducting state to a superconducting state is higher than the temperature of liquid nitrogen. This type of oxide superconductor has a general formula AB-Cu-O (where A is Y, Sc, La, Yb, E
R represents at least one kind of group IIIa element of the periodic table such as Eu, Ho, and Dy, and B represents at least one kind of group IIa element of the periodic table such as Mg, Ca, Sr, and Ba. ), Which can be used under significantly more advantageous cooling conditions than conventional alloy-based or intermetallic compound-based superconductors, which had to be cooled with liquid helium. Research is being carried out as a promising superconducting material.

Incidentally, conventionally, as an example of a method for manufacturing such an oxide superconductor, a method described below has been known.

In order to manufacture an oxide superconductor, a mixed powder is prepared by mixing a plurality of raw material powders containing each element constituting the oxide superconductor represented by AB-Cu-O, and then the mixed powder is mixed. After removing the unnecessary components by calcination, the calcined powder is heat-treated into a superconducting powder, and then compacted into a predetermined shape, or filled with a superconducting powder in a metal tube, and further reduced in diameter to a desired size. This is a method of producing an oxide superconductor by performing a heat treatment after forming into a wire having a diameter.

[Problems to be Solved by the Invention] However, in the above-described conventional method, it is difficult to completely and uniformly mix the raw material powders. There is a problem that does not become a structure, especially when a long superconducting wire is manufactured, a superconductor having a high critical current density cannot be obtained because a superconductor having a uniform crystal structure cannot be generated over the entire length of the wire. there were.

In addition, the oxide superconductor formed inside the above-described superconducting wire is formed by sintering a compacted powder and subjecting it to a solid-phase reaction, in which fine pores are present. Therefore, conventional oxide superconductors manufactured by the compaction sintering method form a polycrystalline state in which a large number of crystals are joined together with fine pores interposed between them. There is a problem that satisfactory superconductivity such as critical current density cannot be obtained because of lack of denseness as compared with polycrystals such as materials.

The present invention has been made in view of the above problems, and enables formation of a superconducting layer having a dense structure without voids, and oxidation capable of controlling the thickness of the superconducting layer with respect to a substrate to a desired value. It is an object of the present invention to provide a method for manufacturing a material-based superconducting material.

"Means for Solving the Problems" The present invention provides a compound represented by the general formula AB
-Cu-O (where A represents one or more elements of Group IIIa of the Periodic Table III such as Y, Sc, La, Yb, Er, Eu, Ho, Dy, and B represents Mg, Ca, Sr,
One or more elements of Group IIa of the Periodic Table II such as Ba. In the method for producing an oxide-based superconducting material having the composition shown in (1), a pure copper layer was formed outside a metal base material, and then a layer containing the B element was formed on the outer periphery thereof to form a laminated material. Thereafter, the laminated material is heated in a vacuum or an inert gas atmosphere to form a first mixed material layer in which the pure copper and the B element are interdiffused to form a composite material. After forming a second composite material layer having a composition ratio of A ₂ B ₁ Cu ₁ O _{5 on} the outside of the superconducting material to form a superconducting material,
First heat treatment at 300 ° C for several hours to several hundred hours
And an element of the second mixed material are interdiffused to form an oxide superconducting layer.

[Operation] The elements of the first mixed material layer formed outside the base material and the second mixed material layer formed outside the base material undergo a mutual diffusion reaction by heating during heat treatment, and An oxide superconducting layer having a composition of A ₁ B ₂ Cu ₃ O _7-X is formed in an intermediate portion of the mixed material layer.

"Example" FIGS. 1 to 5 show that the production method of the present invention is Y-Ba-
The purpose of the present invention is to describe an example applied to a method for producing a Cu-O-based oxide superconductor.

In this embodiment, first, a tape-shaped metal such as Ni, Zr, and Ti having a melting point of 800 ° C. or more, or an alloy having a melting point of 800 ° C. or more such as Ni-Cu, Ti-Al, and stainless steel is used. A long base material 1 is prepared.

Next, a pure copper layer 2 having a thickness of several μm to several tens μm is formed on the outer surface of the substrate 1. As a method of forming the pure copper layer 2 on the outer surface of the substrate 1, a method such as an electrolytic plating method using a copper sulfate electrolytic bath, a vacuum evaporation method, or the like is suitably used.

Next, a Ba-containing layer 3 made of metal Ba or a compound of Ba and having a thickness of several μm to several tens μm is formed on the outer surface of the pure copper layer 2 to produce a laminated material 4 shown in FIG. As the compound of Ba, one or more of Ba carbonate, oxide, nitrate, oxalate, chloride, fluoride and the like can be used.
In addition, as a method of forming the Ba-containing layer 3 on the outer surface of the pure copper layer 2, a slurry such as a method of adding a solvent such as ethanol to the Ba compound powder is used in addition to a film forming means such as a thermal spraying method, a sputtering method, and a vacuum evaporation method. A method of preparing a coating material and applying the coating material to the outer surface of the pure copper layer 2 is used.

Next, the laminated material 4 is placed in a vacuum or argon gas,
In an atmosphere of inert gas such as helium gas, 600
A heat treatment of heating at で 900 ° C. for several hours to tens of hours is performed. By this heat treatment, the elements of the pure copper layer 2 and the Ba-containing layer 3 diffuse into each other, and as shown in FIG.
The composite material 6 in which the first mixed material layer 5 containing each element of Ba is obtained.

Next, a second mixed material layer 7 having a composition of Y ₂ Ba ₁ Cu ₁ O _{5 and} a thickness of about several μm to several tens μm is formed on the outer surface of the composite material 4.
The superconducting material 8 is manufactured by forming as shown in the figure.

Here, an example of means for forming the second mixed material layer 7 will be described below.

In order to form the second mixed material layer 7, Y ₂ O ₃ powder and BaCO 3
₃ powder and CuO powder are mixed at a ratio of Y: Ba: Cu = 2: 1: 1 (molar ratio), and the mixed powder is heated to 800 to 1100 ° C. in an oxidizing atmosphere such as air or an oxygen stream. For several hours to several tens of hours for sintering. Next, the sintered body is pulverized and heated again at 800 to 1100 ° C. for several hours to several tens of hours to be sintered. Next, this sintered body is pulverized to obtain a sintered powder having a particle size of 1 to 2 μm. Next, a solvent such as ethanol is added to the sintered powder to form a slurry. Then, the second mixed material layer 7 can be formed by applying the slurry to the outer surface of the composite material 6 by a spraying method using a spray gun or a screen printing method using a screen printing machine.

In addition, as a means for forming the second mixed material layer 7, a means described below may be performed. For example,
A method in which the sintered body is supplied to a thermal spraying gun and sprayed on the outer surface of the composite material 6, or the sintered body is compacted to form a bulk sintered body, and sputtering is performed using the sintered body as a target. To form the second mixed material layer 7, furthermore, a vacuum deposition method, a chemical vapor deposition method, a laser PVD method,
A film forming means such as a molecular beam epitaxy method can be applied.

Next, the superconducting material 8 is heated at 800 to 1300 ° C. for several hours to several tens of hours in an oxidizing atmosphere such as an oxygen gas stream of 1 atm, and then gradually cooled to room temperature, for example, at a rate of 100 ° C./hour. A final heat treatment is performed.

By this final heat treatment, the elements of the first mixed material layer 5 and the elements of the second mixed material layer 7 undergo an interdiffusion reaction, and as shown in FIG. 5, the composition of Y ₁ Ba ₂ Cu ₃ O _7-X A superconducting layer 9 made of a dense oxide superconductor having a specific ratio is generated, and an oxide-based superconducting material (superconducting tape) A is obtained.

In the method of manufacturing the oxide-based superconducting material A according to this example, Cu
Y ₂ Ba ₁ C is formed on the outer surface of the first mixed material layer 5 containing oxides of Ba and Ba.
A superconducting material 8 is formed by forming a second mixed material layer 7 made of an oxide having a composition of u ₁ O ₅ , and the superconducting material 8 is subjected to a heat treatment, whereby each element of each of the mixed material layers 5 and 7 is formed. To cause a superconducting layer 9 made of an oxide superconductor in the intermediate portion of each of the mixed material layers 5 and 7, so that a heat treatment is performed on the mixed powder obtained by mixing the raw material powders as compared with the conventional method. A superconductor can be generated by causing a uniform reaction, and a dense superconducting layer 9 having a composition ratio of Y ₁ Ba ₂ Cu ₃ O _7-X with a uniform and uniform crystal direction can be generated. it can.

When metal Ba is used as the material of the Ba-containing layer 3 and the first mixed material layer 5 is made of a Cu—Ba alloy, the Cu—Ba alloy that forms the first mixed material layer 5 is made of Ba—Ba alloy. The melting point can be lowered to about 900 ° C. by the effect of the addition of, so that the melt-diffusion reaction becomes possible by heating during the final heat treatment. Therefore, at the time of the final heat treatment, the elements of the first mixed material layer 5 and the elements of the second mixed material layer 7 undergo a melt diffusion reaction to form the superconducting layer 9. That is, a uniform reaction having a higher reaction rate can be generated by the melt diffusion reaction than in the case of the solid phase diffusion reaction as in the conventional method. In addition, if the superconducting layer 9 is generated by the above-described melt diffusion reaction, the reaction speed of the elements is high, so that the thick superconducting layer 9 can be generated in a short time. When the superconducting layer 9 is formed, if the heat treatment is performed at a high temperature of 1000 ° C. or more for a long time, the crystal grains of the superconducting layer 9 are coarsened. It is preferable to adjust the content to lower the melting point and lower the temperature at which the melt diffusion reaction is possible. By performing the reaction at such a low temperature for a short time, the crystal grains of the superconducting layer 9 to be generated can be finely divided. To improve superconductivity.

Further, in the case of the oxide-based superconducting material A manufactured as described above, a pure copper layer 2 and a Ba-containing layer 3 are formed on the outer surface of the substrate 1 and then heat-treated to exchange Ba and Cu. Elements diffuse between the first mixed material layer 5 formed by diffusion and the second mixed material layer 7 formed on the outer surface of the mixed material layer 5 to generate a superconducting layer 9. Strongly bonded to layers. For this reason, the superconducting layer 9 has good adhesion to the substrate, and the oxide superconducting material A has an excellent structure in terms of mechanical strength such as bending. Therefore, when the oxide-based superconducting material A is used for a superconducting magnet, the superconducting magnet can be formed by being wound around a winding drum without causing defects such as cracks.

The thickness of superconducting layer 9 formed by the heat treatment can be controlled by adjusting the thickness of pure copper layer 2, Ba-containing layer 3, and second mixed material layer 7.

By the way, the oxide-based superconducting material A can be used alone for a superconducting magnet coil or for power transport, but in addition, for example, a large number of sheets may be stacked and stored in a sheath to be used for a large capacity. Can be used as a superconductor.

In addition, in the said Example, although the manufacturing method of the oxide superconducting material of Y-Ba-Cu-O system was demonstrated, this invention is applied to the manufacturing method of other AB-Cu-O superconducting material. Of course, it can be applied. That is, among the elements constituting the first mixed material layer 5 and the second mixed material layer 7, Sc, La, Y, Ce, Pr, Nd, Pm, Sm, Eu, G
One or more of d, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. may be used, and one or more of Sr, Mg, Ba, Ra, etc. may be used as Group IIa elements of the periodic table.

In the above embodiment, the tape-shaped substrate 1
However, the substrate 1 may have various shapes such as a tubular shape, a linear shape, and a plate shape.

(Production Example) A 2 mm wide, 0.2 mm thick tape material made of Ni was plated with copper by electroplating to form a pure copper layer having a thickness of 10 μm. Next, a slurry was prepared by adding ethanol to the barium carbonate powder, and the outer surface of the pure copper layer of the tape material was spray-coated to form a Ba-containing layer having a thickness of about 10 μm, thereby producing a laminated material. Next, this laminated material is heated at 800 ° C. for 30 hours in a vacuum atmosphere of 10 ⁻³ Torr to form a first mixed material layer in which Cu and Ba in the pure copper layer and the Ba-containing layer are mutually diffused. To produce a composite. On the other hand, Y ₂ O ₃ and BaCO ₃
And each powder of CuO is uniformly pulverized and mixed so that Y: Ba: Cu = 2: 1: 1 (molar ratio).
Heat-treated at 900 ° C for 30 hours, then mixed with powder, and further heat-treated at 950 ° C for 30 hours in air atmosphere to obtain Y ₂ Ba ₁ Cu
An oxide powder having a composition of ₁ O ₅ was prepared, and then this powder was added with ethanol to prepare a slurry-like coating material.

Next, the composite material was immersed in the coating material, and a second mixed material having a thickness of about 20 μm was formed on the outer surface of the composite material to produce a superconducting material. Next, the superconducting material was heated in an oxygen stream at 950 ° C. for 24 hours, and then subjected to a final heat treatment of gradually cooling to room temperature, thereby obtaining a long tape-shaped oxide-based superconducting material.

When the critical temperature (Tc) of the obtained oxide superconductor was measured, an onset of 90 K and an offset of 88 K were obtained, and it was confirmed that the oxide superconductor was an excellent oxide superconductor. Further, when the cross section of this oxide-based superconducting material was observed with a microscope, the existence of an interdiffusion layer (superconducting layer) having a thickness of about 15 μm could be confirmed. As a result of X-ray diffraction analysis of this interdiffusion layer, Y It was confirmed that an orthorhombic crystal having a composition of ₁ Ba ₂ Cu ₃ O _7-X was generated.

[Effects of the Invention] As described above, the method for manufacturing an oxide-based superconducting material according to the present invention provides a method for producing a first mixed material containing element B (group IIa element in the periodic table II) and Cu outside the substrate. A heat treatment is applied to the material and the oxide superconducting material forming the second mixed material having a composition ratio of A ₂ B ₁ Cu ₁ O ₅ to cause the elements of each mixed material layer to undergo an interdiffusion reaction, so that a uniform reaction occurs. The oxide superconducting layer can be generated by the generation, and there is an effect that a uniform and dense oxide superconducting layer having a composition of A ₁ B ₂ Cu ₃ O _7-X can be generated. Further, if an alloy of element B and Cu is used for the first mixed material layer, and an element of the first mixed material layer and an element of the second mixed material layer are subjected to a melt diffusion reaction to form an oxide superconducting layer, Since the diffusion rate of the element can be increased as compared with the solid-state reaction as in the conventional method, there is an effect that a thick oxide superconducting layer can be formed in a shorter time.

Further, since the elements of the first mixed material layer and the second mixed material layer are interdiffused to generate the oxide superconducting layer, the thickness of the oxide superconducting layer is adjusted by adjusting the thickness of each mixed material layer. And the oxide superconducting layer according to the composition of the element contained in each mixed material layer can be produced. Further, since the elements of the first mixed material layer and the second mixed material layer undergo an interdiffusion reaction, there is an effect that a uniform oxide superconducting layer can be formed over the entire length of the base material.

Further, after laminating a pure copper layer and a layer containing element B on the outer side of the base material, a first mixed material layer formed by performing heat treatment and a second mixed material layer formed on the outer surface thereof are formed. Since the element undergoes a diffusion reaction to form an oxide superconducting layer,
The oxide superconducting layer is strongly bonded to other layers, and an oxide superconducting material having high mechanical strength can be obtained.

[Brief description of the drawings]

1 to 5 are views for explaining an example of the method of the present invention. FIG. 1 is a sectional view of a base material, FIG. 2 is a sectional view of a laminated material, and FIG. 3 is a sectional view of a composite material. FIG. 4 is a sectional view of a superconducting material, and FIG. 5 is a sectional view of an oxide superconducting material. DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Pure copper layer, 3 ... Ba containing layer, 4 ... Laminated material, 5 ... First mixed material layer, 6 ... Composite material, 7 ...
Second mixed material layer, 8: superconducting material, 9: superconducting layer, A: oxide-based superconducting material.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshimitsu Ikeno 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd. (72) Inventor Nobuyuki 1-5-1 Kiba 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Inside the Electric Wire Co., Ltd. (72) Inventor Shinya Aoki 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd. (72) Inventor Kyoji Tachikawa 3--13-29, Seijo, Setagaya-ku, Tokyo

Claims (1)

(57) [Claims] A compound of the formula AB--Cu--O wherein A is Y, S
c, La, Yb, Er, Eu, Ho, Dy, etc., at least one kind of group IIIa element of the Periodic Table III, and B represents one of Group IIa elements of the Periodic Table II, such as Mg, Ca, Sr, Ba, etc. Shows more than species. In the method for producing an oxide-based superconducting material having the composition shown in (1), a pure copper layer was formed outside a metal substrate, and then a layer containing the B element was formed on the outer periphery thereof to form a laminated material. Thereafter, the laminated material is heated in a vacuum or an inert gas atmosphere to form a first mixed material layer in which the pure copper and the B element are interdiffused to form a composite material. After forming a superconducting material by forming a second mixed material layer having a composition ratio of A ₂ B ₁ Cu ₁ O ₅ outside the superconducting material,
An oxide-based material comprising performing a heat treatment of heating at 800 to 1300 ° C. for several hours to several hundred hours to mutually diffuse elements of the first mixed material and the second mixed material to form an oxide superconducting layer. Manufacturing method of superconducting material.