JPH01239021A - Production of oxide-based superconducting material - Google Patents

Abstract

PURPOSE:To obtain the title material with oxide superconducting layer of dense structure formed, by forming an oxide layer of specific composition ratio externally on a metallic core followed by further forming a Cu-A alloy layer externally on said oxide layer in succession to produce a composite material which is then heat treated to effect mutual diffusion of the respective elements in said oxide layer and alloy layer. CONSTITUTION:Respective elements in a Cu-A alloy layer formed externally on a metallic core and the elements in an oxide layer of a composition A1B2Cu1 O5 are allowed to mutually diffuse by heating treatment at 800-1,300 deg.C for several hours to several hundred hours, thereby forming an oxide superconducting layer of a composition A1B1Cu3O7-delta (see, the formula). The melting point of the Cu-A alloy layer is lowered due to the addition of the A-element to effect melt diffusion-and-reaction with the elements in the oxide layer by heating in said heat treatment, thus forming the oxide superconducting layer. This melt diffusion-and-reaction causes a uniform reaction of high reaction rate, resulting in the formation of an oxide superconductor of dense structure.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to a method for producing an oxide-based superconducting material that can be applied to superconducting applied equipment such as superconducting magnets used in nuclear magnetic resonance devices and particle accelerators. It is.

"Prior Art" Recently, various oxide-based superconductors have been discovered that exhibit a critical temperature (Tc) for transition from a normal conductive state to a superconducting state or a value that exceeds the liquid nitrogen temperature.

This type of oxide superconductor has the general formula A-B-Cu-
0 (However, A represents one or more elements of group II a of the periodic table such as Mg, Ca, Sr, Ba, etc., and B represents Y, Sc
, L a , Y b .

One or more elements of group IIIa of the periodic table, such as Er, Eu, fo, Dy, etc. ), and can be used under much more convenient cooling conditions than conventional alloy-based or intermetallic compound-based superconductors, which require cooling with liquid helium. It is being researched as an extremely promising superconducting material.

By the way, the method described below is conventionally known as an example of a method for manufacturing a superconducting wire including such an oxide superconductor.

To manufacture oxide superconducting wire, A-B-Cu-0
A mixed powder is created by mixing one or more raw material powders containing each element constituting the oxide superconductor represented by , and then this mixed powder is calcined to remove unnecessary components, and then this calcined powder is The wire is filled into a metal tube, further reduced in diameter to obtain a wire with the desired diameter, and this wire is heat-treated to cause an in-phase reaction in the compacted body inside the metal tube, producing an oxide superconductor and forming a superconducting wire. This is a method of manufacturing.

``Problems that the invention is still trying to solve'' However, in the conventional method described above, it is difficult to mix the raw material powder completely uniformly, so even if heat treatment is performed, the entire superconductor has a completely uniform crystal structure. There are problems that should not be avoided, especially when manufacturing long superconducting wires.
There is a problem in that it is not possible to obtain a superconducting wire with a high critical current density because a superconductor having a uniform crystal structure cannot be produced over the entire length of the wire.

In addition, the oxide superconductor formed inside the superconducting wire mentioned above is formed by sintering a compacted compact of powder and avoiding a solid phase reaction, and there are fine pores inside it. Due to this relationship, conventional oxide superconductors manufactured using the consolidation sintering method have a polycrystalline state in which many crystals are bonded with fine pores interposed between them, and are similar to ordinary metals. Because it lacks density compared to polycrystalline materials, it has been difficult to obtain satisfactory superconducting properties such as critical current density.

The present invention was made in view of the above-mentioned problems, and it is possible to generate a superconducting layer with a dense structure without pores, the adhesion of the superconducting layer to the base material is good, the mechanical strength is high, and the superconducting layer is The object of the present invention is to provide a method for manufacturing an oxide-based superconducting material whose thickness can be controlled to a desired value.

"Means for Solving the Problems" In order to solve the above-mentioned problems, the present invention provides the general formula A -
B -Cu-0 (A is Mg, Ca, Sr, Ba
B is Y.

One or more elements of group IIIa of the periodic table, such as Sc, La, Yb, Er, Eu, Ho, Dy, etc. ) In the method for producing an oxide superconducting material comprising an oxide superconducting layer having a composition shown in
After forming an oxide layer with a composition ratio of 5 to form a coating material, and then forming an alloy layer made of a Cu-A alloy on the outside thereof to form a composite material, this composite material is
A heat treatment is performed at a temperature of several hours to several hundred hours to cause the elements of the oxide layer and the alloy layer to interdiffuse, thereby producing an oxide superconducting layer.

"Effect" Each element of the Cu-A alloy layer formed on the outside of the base material
Due to the heating during heat treatment, an interdiffusion reaction occurs with the elements of the oxide layer with a composition of A + B pc u, 05, resulting in A + B.
An oxide superconducting layer having a composition of tCu307-t is formed. Note that the melting point of the Cu-A alloy layer is lowered due to the effect of adding the A element, and the heating during the heat treatment causes a melt-diffusion reaction with the elements of the oxide layer to form an oxide superconducting layer.
A uniform reaction with a high reaction rate occurs due to the melt-diffusion reaction,
An oxide superconductor with a dense structure is produced.

In addition, since the elements of the oxide layer formed on the outside of the base material and the elements of the alloy layer on the outside are interdiffused to generate a superconducting layer, the generated superconducting layer is strong against the base material. Join. Furthermore, the thickness of the oxide superconducting layer can be controlled by adjusting the thickness of the oxide layer and the alloy layer.

"Example" Figures 1 to 4 show the manufacturing method of the present invention in Y-B a
This is for explaining an example applied to a method for manufacturing a -Cu-0 based oxide superconducting material.

In this example, first, melting point 80 of Ni, Zr, Ti, etc.
Pure metal at 0°C or higher, or Ni-Cu, Ti-A
1. A long tape-shaped base material 1 shown in FIG. 1 made of an alloy having a melting point of 800° C. or higher, such as stainless steel, is prepared.

Next, the outer surface of this base material 1 is coated with a thermal spraying method, a sputtering method,
By vacuum evaporation method or coating method, YtBa
A covering material 3 is manufactured by forming an oxide layer 2 having a composition of +Cut05 and having a thickness of several micrometers to several tens of micrometers as shown in FIG.

22, examples of means for forming the oxide layer 2 will be described below.

To form the oxide layer 2, Y2O3 powder and BaC0,
Powder and CuO powder Y:I3a:Cu=2:I
:I, and this mixed powder was heated to 800% in an oxidizing atmosphere such as the air or an oxygen stream.
It is sintered by heating at ~1100°C for several hours to several tens of hours.

Next, this sintered body is crushed and heated again at 800 to 1100°C.
The material is heated and sintered for several hours to several tens of hours. Next, crush this sintered body to obtain a sintered powder with a particle size of 1 to 2 μm. Next, this sintered powder is dissolved in a solvent such as ethanol to form a slurry. Then, the oxide layer 2 can be formed by applying this slurry to the outer surface of the base material 1 by spraying with a spray gun or by using a screen printing method using a screen printing machine.

Note that the means described below may be used as a means for forming the nq oxide m2. For example, a method of supplying the above sintered body to a thermal spraying gun and thermally spraying it on the outer surface of the base material I,
Alternatively, a method of forming an oxide layer by compacting the sintered body to form a bulk sintered body and sputtering this sintered body as a target, furthermore, a vapor deposition method, a CV I) method. , laser PVD method, molecular beam epitaxy method, and other film forming methods can be applied.

Once the oxide layer 2 is formed, a molar ratio of Ba is added to the outer surface of the oxide layer 2.
:Cu-(0~9):(10~l)
- Form an alloy layer 4 made of Ba alloy as shown in FIG. 3 to obtain a composite material 5. Note that a plating method, a melt dipping method, or the like can be used as a means for forming the alloy layer 4.

Next, this composite material 5 is heated to 800 to 1300°C for several hours to several tens of hours in an oxidizing atmosphere such as an oxygen stream at 1 atm, and then subjected to a final heat treatment in which it is slowly cooled to room temperature at a rate of, for example, 100°C/hour. I do.

Through this final heat treatment, the alloy layer 4 made of the Cu-Ba alloy undergoes an interdiffusion melting reaction with the elements of the oxide layer 2 having a composition of YtBa at CLllOs, forming an oxide superconducting layer 6 as shown in FIG. The oxide superconducting material (superconducting tape) A is obtained. Note that C forming the alloy layer 4
u-Ba alloy has a melting point of 900℃ due to the effect of Ba addition.
Therefore, the melt-diffusion reaction becomes possible by heating during the heat treatment. Therefore, during the heat treatment, the elements of the oxide layer 2 and the elements of the alloy layer 4 undergo a melt-diffusion reaction to form the oxide superconducting layer 6. In other words, because it is possible to generate a uniform reaction with a high reaction rate by melt-diffusion reaction, it is dense and has no pores compared to conventional oxide superconductors that are manufactured by subjecting compacted bodies to solid-state reactions. It is possible to generate a superconducting layer 6 having a structure having a high critical current density.

Furthermore, if the superconducting layer 6 is formed by the melt-diffusion reaction as described above, the reaction rate of the elements is faster than in the conventional method of forming by solid phase reaction, so it is possible to form a thicker superconducting layer 6 in a shorter time. can be generated. Note that the superconducting layer 6
If heat treatment is performed at a high temperature of 1000°C or higher for a long period of time, the crystal grains of the superconducting layer 6 will become coarse, so in order to prevent this, the content of 13a in the alloy layer 4 must be adjusted to increase the melting point. It is preferable to lower the temperature at which the melt-diffusion reaction is possible, and by performing the reaction at such a low temperature for a short time, the crystal grains of the superconducting layer to be produced are made finer and the superconducting properties are improved. Can be done.

Furthermore, in the oxide superconducting material A manufactured as described above, elements undergo a melt-diffusion reaction between the oxide layer 2 and the alloy layer 4 formed on the outside of the base material 1 to form the superconducting layer 6. is generated, so the superconducting layer 6 is strongly bonded to other layers. Therefore, the superconducting layer 6 has good adhesion to the base material 1, and the superconducting material A has an excellent structure in terms of mechanical strength such as bending. Therefore, when the superconducting material A described in iη is used for a superconducting magnet, the superconducting magnet can be formed by winding it around a winding drum without producing defects such as cranks.

Moreover, the thickness of the superconducting layer 6 formed by heat treatment is
It can be controlled by adjusting the thicknesses of the oxide layer 2 and the alloy layer 4.

By the way, the superconducting material A can be used for superconducting magnet coils or for power transportation, but it can also be used, for example, by laminating a large number of sheets and storing them inside a sheath for use in large-capacity conductors. It could also be used as a superconducting conductor.

In addition, in the above example, ¥-B a-Cu-0
Although the method for producing the A-B-Cu-0 series oxide superconducting material has been described, it goes without saying that the present invention can be applied to the production of other A-B-Cu-0 series superconducting materials. In addition, Y-B a-C
When producing a superconducting material other than the u-0 type, a different type of raw material powder may be used for forming the oxide layer 2. That is, when preparing a raw material powder, Sc as a compound powder of group Ia elements of the periodic table.

Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd
, Tb, Dy.

One or more compound powders such as Ho, Er, Tm, Yb, and Lu may be used, and one or more compound powders such as Sr, Mg, Ba, and Ra may be used as compound powders of group IIa elements of the periodic table. .

Furthermore, although the tape-shaped base material 1 was used in the above embodiment, the shape of the base material 1 may be tubular or linear.

"Manufacturing example" Y 2 B a + on a Ni wire with a diameter of 0.5 mm
An oxide layer of composition CLl 105 was applied. To form this oxide layer, Y,03 powder, BaCO3 powder, and CuO powder are mixed in a ratio of Y:Ba:Cu=2:I:I, and this mixed powder is heated at 900°C in the atmosphere. Sintered by heating for 24 hours at
After crushing this sintered body, it was placed in the atmosphere again at 950°C.
A sintered body was obtained by heat treatment at ℃ for 24 hours, and this was pulverized to obtain a sintered powder. The particle size of this sintered powder is 1
It was ~2 μm.

Next, after dissolving this sintered powder in ethanol to form a slurry, the Ni wire rod was immersed in this slurry, and Y 2B at CL with a thickness of about 10 μm was coated around the outer periphery of the wire rod.
A coating material was obtained by forming an oxide layer having a composition represented by l+Os.

Next, pure copper and BaCO3 powder were mixed into Cu:Ba=1:
I, and heated at 800°C for 24 hours in a vacuum of 10-3 Torr or less, then dissolved in ethanol to form a slurry, which was applied to the outer surface of the above-mentioned coating material to form a composite material. Obtained. The thickness of the coating layer in this composite material was approximately 20 μm.

Next, this composite material was heated at 950°C for 24 hours in an oxygen atmosphere.
A heat treatment of heating for a period of time and then slowly cooling to room temperature was performed to cause the elements of the oxide layer and the alloy layer to interdiffuse to form an oxide superconducting layer, thereby obtaining an oxide superconducting material.

When the critical temperature of this oxide superconducting material was measured, it was possible to obtain an onset of 92K and an offset of 90K, confirming that it is an excellent oxide superconducting material. Furthermore, when we observed the cross section of this oxide superconducting material using a microscope, we were able to confirm the presence of an interdiffused layer with a thickness of approximately 15 μm.
As a result of X-ray diffraction analysis of this interdiffusion layer, Y, B a
It was confirmed that orthorhombic crystals having a composition of , Cu307-δ were formed.

``Effects of the Invention'' As explained above, the present invention provides a uniform reaction rate in which the alloy layer whose melting point has been lowered by the effect of adding elements is heated during heat treatment to melt and react with the elements of the oxide layer. It is possible to generate an oxide superconductor by causing a fast melting reaction of , and there is an effect that a homogeneous and dense oxide superconductor layer having a composition ratio of A+B2Cu307-δ can be generated. Furthermore, if the formation of the oxide superconducting layer is avoided by the melt-diffusion reaction, the diffusion rate of the elements can be made faster compared to the conventional in-phase reaction, which has the effect of generating a thick oxide superconducting layer in a shorter time. be.

In addition, since the oxide superconducting layer is generated by mutually diffusing the elements of the oxide layer and the alloy layer, the thickness of the superconducting layer can be controlled by adjusting the thickness of the oxide layer and the alloy layer. In addition, it is possible to generate a superconducting layer according to the composition of the elements contained in the mixed layer. Furthermore, since the elements of the oxide layer and the alloy layer undergo a mutual diffusion reaction, a uniform superconducting layer can be produced over the entire length of the base material.

[Brief explanation of the drawing]

Figures 1 to 4 are for explaining one embodiment of the present invention; Figure 1 is a sectional view of the base material, Figure 2 is a sectional view of the covering material, and Figure 3 is a sectional view of the composite material. Cross-sectional view, FIG. 4 is a cross-sectional view of the superconducting material. 1... Scrap material, 2... Oxide layer, 91 ・
Alloy layer, 6. Superconducting layer, A. Superconducting material.

Claims (1)

[Claims] General formula AB-Cu-O (where A is Mg, Ca, S
r, represents one or more elements of group IIa of the periodic table such as Ba, and B
represents one or more elements of group IIIa of the periodic table, such as Y, Sc, La, Yb, Er, Eu, Ho, and Dy. ) In the method for manufacturing an oxide-based superconducting material comprising an oxide superconducting layer having a composition represented by A_1 on the outside of a metal core material,
After forming an oxide layer with a composition ratio of B_2Cu_1O_5 to form a coating material, and then forming an alloy layer made of a Cu-A alloy on the outside thereof to form a composite material, this composite material was heated at 800 to 1300°C. 1. A method for producing an oxide-based superconducting material, which comprises performing heat treatment for several hours to hundreds of hours to cause elements in the oxide layer and the alloy layer to interdiffuse to form an oxide superconducting layer.