JP2727565B2 - Superconductor manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a superconductor, and more particularly to a method for manufacturing a superconductor made of a ceramic-based superconducting material.

[Prior Art] Conventionally, metal-based and ceramic-based superconductors have been known, and their application to various uses has been studied. In other words, superconductors have a zero electrical resistance when maintained at a temperature below the critical temperature. By utilizing this characteristic, it is possible to generate high magnetic fields and transmit high-capacity currents at high density. Attempted.

Recently, ceramic-based superconducting materials have been
It is in the limelight because it can raise the critical temperature that indicates superconductivity. Such a superconducting material can be used for, for example, power transmission and distribution, electrical connection between various devices or elements, AC winding, and the like by forming a long linear body. Among these ceramic-based superconducting materials, for example, ceramic-based superconducting materials exhibiting a perovskite structure or a quasi-perovskite structure represented by a Y-Ba-Cu-O-based material have been demonstrated to exhibit a high critical temperature. ing.

When applying these superconducting materials to the generation of high magnetic fields, it is necessary to make the superconductors a considerably thin wire, and when applying to high-density transmission, make the superconductors a considerably thin wire. is required. Furthermore, in applications other than the above-mentioned applications, there are quite a few cases where it is necessary to make the superconductor a thin wire.

Therefore, of the various superconductors described above, only those that can be made into a wire without deteriorating the characteristics can be applied to the above-mentioned applications. However, metal-based materials that can be easily made into a wire have a very low critical temperature (for example, lower than about 23K) and have a large restriction on the available refrigerant, so that they are used only for very limited applications. Absent.

Conversely, some ceramics have a rather high critical temperature, but it is very difficult to make a wire, and when made into a wire, it has stable electrical properties over the entire length. There is a problem that it is very difficult. More specifically, when manufacturing a wire made of a ceramic-based superconductor, a method of performing cold working at normal temperature and a method of raising the temperature to a temperature at which plastic working is easy are employed.

[Problems to be Solved by the Invention] However, when the wire is formed by the above-described method, the raw material powder is localized as the raw material of the ceramic-based superconductor is drawn, and disconnection occurs. Not only is there a problem that it is not possible to make the wire thinner than a certain extent, even when formed as a thicker wire,
There is a problem that the electrical characteristics deteriorate to some extent.

In the case of forming a wire by the above method, usually, a metal pipe is filled with a ceramic superconductor raw material, heated to a high temperature state, extruded into a wire, and if necessary, a die is formed. The wire drawing process is further performed by the above method. Therefore, the raw material of the ceramic-based superconductor is subjected to heat treatment in a state of being shielded from the external atmosphere by a metal pipe, and does not sufficiently react with oxygen and other elements necessary for the superconductor, As a result, there is a problem that a superconductor having an intended critical temperature and critical current is not generated. Further, there is a problem that it is impossible to reduce the thickness to a certain extent.

Therefore, an object of the present invention is to efficiently produce a superconductor having a dense superconducting phase, which can increase the critical temperature and critical current density, can be made into a wire without deteriorating electrical characteristics, and can be used as a superconductor. It is to provide a method that can do this.

[Means for Solving the Problems] According to the method for manufacturing a superconductor according to the present invention, first, as a raw material of a ceramic-based superconducting material, the composition ratio of yttrium, barium and copper is Y: Ba: Cu = 2: A porous sintered body containing a 1: 1 oxide and a melt of a composite oxide containing barium and copper are prepared. The porous sintered body is impregnated with a composite oxide melt. A superconductor is obtained by subjecting the impregnated sintered body to heat treatment.

According to another aspect of the method for manufacturing a superconductor according to the present invention, first, as a raw material of a ceramic-based superconducting material, the composition ratio of yttrium, barium, and copper is Y:
A powder containing an oxide in which Ba: Cu = 2: 1: 1 and a melt of a composite oxide containing barium and copper are prepared. After the powder is filled in a metal sheath tube, the metal sheath tube is reduced in diameter. By sintering the powder in the metal sheath tube, a porous sintered body is obtained. After removing the metal sheath tube, the porous sintered body is impregnated with a melt of the composite oxide. The superconductor is obtained by subjecting the impregnated sintered body to a heat treatment. In this method of manufacturing a superconductor, when the metal sheath tube is reduced in diameter, the metal sheath tube may be formed into a coil shape.

Further, in the method for manufacturing a superconductor according to the present invention, the composite oxide used as a raw material of the ceramic-based superconducting material has a barium / copper composition ratio of Ba / (Cu
+ Ba) = 10 to 50 mol% is preferred.

[Action] In the method for producing a superconductor according to the present invention, a porous material containing an oxide having a composition ratio of yttrium, barium and copper of Y: Ba: Cu = 2: 1: 1 is used as a raw material of the ceramic-based superconducting material. A quality sintered body is prepared. This porous sintered body is an insulator having a high melting point of about 1400 ° C. On the other hand, the composite oxide containing barium and copper prepared as another raw material has a lower melting point and a lower viscosity than the sintered body. Therefore, when this melt is impregnated into a porous sintered body, a superconducting phase in which the composition ratio of yttrium, barium and copper is Y: Ba: Cu = 1: 2: 3 is formed by an interfacial reaction that occurs after impregnation. Is done. Therefore, as the interfacial region between the sintered body and the melt formed by the impregnation increases with respect to the unit volume, a reaction occurring at the interface changes the whole into a superconducting phase having the above composition ratio. As described above, the melt of the composite oxide can be easily impregnated into the pores in the porous sintered body by the capillary phenomenon. After the impregnation, a heat treatment is applied to form a dense superconducting phase, so that a high critical current density (J
It becomes possible to obtain a superconductor having c).

Another method of manufacturing a superconductor according to the present invention is described.
In one aspect, a metal sheath tube is filled with a powder containing an oxide in which the composition ratio of yttrium, barium and copper is Y: Ba: Cu = 2: 1: 1. Thereafter, the powder is reduced in diameter by a known plastic working method such as swaging or drawing to obtain a powder compact having a longer composition ratio. In this case, preferably, the material of the metal sheath tube to be used may be silver or a silver alloy that hardly reacts with the powder. Next, the compact is heated while being covered with the metal sheath tube, so that the powder compact in the metal sheath tube is sintered into a porous sintered body. After sintering, the metal sheath tube is removed by a method such as pickling, and impregnation and heat treatment are performed as described above, so that the composition ratio of yttrium, barium and copper is Y: Ba: Cu = 1: 2: A long body having a superconducting phase of 3 is obtained. This elongated body is composed of a dense superconducting phase and has a high critical current density (Jc).

Furthermore, by forming the metal sheath tube into a coil shape in the diameter reduction process performed while being covered with the metal sheath tube, a coil-shaped superconductor having a high critical current density (Jc) is finally obtained. be able to. This coiled superconductor can be used for a magnet that can be operated under liquid nitrogen temperature.

In the composite oxide prepared as a raw material in the method for producing a superconductor according to the present invention, if the composition ratio of barium and copper is within a range of Ba / (Cu + Ba) = 10 to 50 mol%,
It has a melting point below 1000 ° C. Especially this composition ratio is 20 ~
When it is within the range of 40 mol%, a composite oxide having a lower melting point can be obtained. When the porous sintered body is impregnated with the melt of the composite oxide having this composition ratio, a reaction takes place at the interface between the liquid-phase composite oxide and the solid-phase sintered body, so that yttrium is produced. , A superconducting phase in which the composition ratio of barium and copper is Y: Ba: Cu = 1: 2: 3 can be easily produced. That is, a superconducting phase having the above composition ratio is hardly formed at a temperature of 1050 ° C. or higher. Further, if the above composition ratio of the composite oxide is 10 mol% or less, the melting point becomes high, and a large amount of superconducting phase having the above composition ratio cannot be easily generated by the diffusion reaction at the interface with the sintered body. is there. Further, when the composition ratio of the composite oxide is 50 mol% or more, a superconducting phase having the composition ratio cannot be generated by a diffusion reaction.

The reaction carried out at the interface between the porous sintered body and the melt of the composite oxide for the generation of the superconducting phase by the method for producing a superconductor according to the present invention is as follows:
Any reaction between the solid phase and the liquid phase or between the solid phase and the solid phase may be used.

[Example] Example 1 Y: B was prepared by using each powder composed of Y ₂ O ₃ , BaCO ₃ and CuO as a raw material.
After weighing and mixing to have a composition ratio of a: Cu = 2: 1: 1, temporary sintering was performed at a temperature of 950 ° C. for 12 hours. The obtained temporary sintered body was pulverized to prepare a powder made of Y ₂ Ba ₁ Cu ₁ O ₅ having a particle size of 1 μm. This powder was press-molded at a pressure of 2 ton / cm ² to obtain a compact having a shape of 2 mm × 30 mm. Then, the molded body at a temperature of 1000 ℃
Sintered for 12 hours. The sintered body thus obtained is
It was a porous sintered body having a porosity of 40%.

On the other hand, BaCO ₃ , each powder consisting of CuO as a raw material, Ba:
The components were weighed and mixed so as to have a composition ratio of Cu = 35: 65.
This powder was temporarily sintered at a temperature of 800 ° C. for 12 hours and then pulverized. This pre-sintered powder was melted at a temperature of 970 ° C. in a platinum crucible to obtain a melt. When the porous sintered body obtained by the above method was immersed in this melt for 1 minute,
All pores were completely impregnated with the melt. Thereafter, the sintered body was heat-treated at 960 ° C. for 6 hours in an oxygen atmosphere, and then cooled to room temperature at a cooling rate of 2 ° C./min.

The superconductor thus obtained has a relative density of 98
%, And the volume fraction of the superconducting phase was 98%. This superconductor
It is a dense superconductor composed of a single phase of Y ₁ Ba ₂ Cu ₃ O _X. Its critical temperature (Tc) is 93K, and its critical current density (Jc) at liquid nitrogen temperature is 10 ⁴ A / cm ^2. Was.

Example 2 The calcined powder having a composition ratio of Y: Ba: Cu = 2: 1: 1 obtained in Example 1 was Ag-20% by weight having an inner diameter of 8 mmφ and an outer diameter of 12 mmφ.
The pipe was filled with Pd alloy. This alloy pipe was reduced in outer diameter to 2 mmφ by wire drawing. Thereafter, the alloy pipe filled with the temporarily sintered powder was subjected to a heat treatment (sintering) at a temperature of 1100 ° C. for 3 hours. After the heat treatment, the alloy pipe was pickled and removed with aqua regia. The porous sintered body thus obtained was impregnated with a melt made of an oxide having a composition ratio of Ba: Cu = 30: 70. After the impregnation, the sintered body was heat-treated at 950 ° C. for 4 hours in an oxygen atmosphere, and then cooled to room temperature at a cooling rate of 2 ° C./min. In this way, a long superconductor having an outer diameter of 1 mmφ was obtained, and the critical current density (Jc) was measured at the temperature of liquid nitrogen. As a result, 2 × 10 ⁴ A / cm ²
Met.

Example 3 The alloy pipe filled with the temporarily sintered powder in Example 2 was drawn to an outer diameter of 2 mmφ, and then cold-rolled to obtain a thickness.
It was processed into a 0.5 mm, 3 mm wide tape. This tape was wound around a magnesia pipe having an outer diameter of 50 mmφ for 50 turns. Subsequent processing was performed in the same manner as in Example 2. The superconducting coil thus obtained was able to generate a magnetic field of 5K Gauss in liquid nitrogen, and when operated in the persistent current mode, the generated magnetic field did not attenuate even after one month.

Example 4 The porous sintered body produced in Example 1 was impregnated with a melt of a composite oxide having the composition shown in Table 1. After impregnation, the sintered body was heat-treated at 960 ° C. for 4 hours in an oxygen atmosphere, and then cooled at a cooling rate of 2 ° C./min. The superconducting phase (Y: Ba: Cu) in the superconductor thus obtained
= 1: 2: 3), the relative density and the critical current density (Jc) under the temperature of liquid nitrogen were measured.
The measurement results are shown in Table 1.

According to Table 1, it is understood that a dense superconducting phase having a high critical current density (Jc) can be obtained by using a composite oxide melt having a preferable composition ratio according to the present invention as a raw material. Is done.

[Effects of the Invention] As described above, according to the present invention, a high critical current density, a dense Y-Ba-Cu-O-based superconductor can be obtained,
A long body applicable to a superconducting magnet or the like can be easily obtained. Further, by controlling the composition ratio of the composite oxide used in the production method of the present invention, a superconducting phase can be easily generated by a low-temperature reaction, and the amount of the superconducting phase can be increased. Therefore, a dense superconducting phase having a high volume ratio can be easily obtained.

Claims (5)

(57) [Claims] 1. A method of manufacturing a superconductor made of a ceramic-based superconducting material, wherein the composition ratio of yttrium, barium and copper is Y: Ba: Cu = 2: 1: 1 as a raw material of the ceramic-based superconducting material. A step of preparing a porous sintered body containing a certain oxide and a melt of a composite oxide containing barium and copper; a step of impregnating the melt with the sintered body; Subjecting the sintered body to a heat treatment. 2. A method for producing a superconductor made of a ceramic-based superconducting material, wherein the composition ratio of yttrium, barium and copper is Y: Ba: Cu = 2: 1: 1 as a raw material of the ceramic-based superconducting material. Preparing a powder containing an oxide and a melt of a composite oxide containing barium and copper; filling the metal sheath tube with the powder and reducing the diameter of the metal sheath tube; Sintering the powder in the sheath tube to obtain a porous sintered body; removing the metal sheath tube and impregnating the sintered body with the melt; and Subjecting the union to a heat treatment. 3. The method for manufacturing a superconductor according to claim 2, wherein the step of reducing the diameter of the metal sheath tube includes the step of forming the metal sheath tube into a coil shape. 4. The composite oxide, wherein a composition ratio of barium and copper is in a range of Ba / (Cu + Ba) = 10 to 50 mol%.
A method for manufacturing a superconductor according to claim 1. 5. The composite oxide, wherein a composition ratio of barium and copper is in a range of Ba / (Cu + Ba) = 10 to 50 mol%.
A method for manufacturing a superconductor according to claim 2.