JP2567402B2 - Method for manufacturing superconducting wire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a superconducting wire. More specifically, the present invention relates to a method for manufacturing a new superconducting wire having a small difference between a critical temperature and an end temperature of a phase transition as well as a high superconducting critical temperature.

In the following description, the superconducting critical temperature is Tc,
The end temperature of the phase transition at which the electrical resistance of the superconductor becomes zero
Tcf and the difference between Tc and Tcf are shown as ΔT.

Conventional technology Under the superconducting phenomenon, a substance shows complete diamagnetism, and the potential difference disappears even though a finite steady current flows inside. Therefore, various applications of superconductors as transmission media without power loss have been proposed.

That is, its application fields are power fields such as MHD power generation, power transmission, and power storage, power fields such as magnetic levitation trains and electromagnetic propulsion vessels, and NMR as a super-sensitive sensor for magnetic fields, microwaves, radiation, etc. , Pion therapy, measurement fields such as high-energy physics experimental equipment, and so on.

Further, in the field of electronics represented by Josephson devices, it is expected as a technique that can realize not only a reduction in power consumption but also an extremely fast operating device.

By the way, superconductivity was a phenomenon observed only at extremely low temperatures. That is, even in Nb ₃ Ge, which was said to have the highest superconducting critical temperature Tc as a conventional superconducting material, the extremely low temperature of 23.3 K was considered to be the limit of the superconducting critical temperature for a long time.

Therefore, conventionally, in order to realize the superconductivity phenomenon, the superconducting material has been cooled to Tc or less using liquid helium having a boiling point of 4.2K. However, the use of liquid helium has
The technical burden and cost burden of the cooling equipment including the liquefaction equipment were extremely large, which hindered the practical application of the superconducting technology.

However, in recent years, it has been reported that a sintered body containing an oxide of a Group IIa element or a Group IIIa element can become a superconductor at an extremely high Tc. Is about to be promoted. already,
In perovskite type oxides such as [La, Ba] ₂ CuO ₄ or [La, Sr] ₂ CuO ₄ , a dramatically higher Tc of 30 to 50 K was observed compared with the conventional one, and a Tc of 70 K or more was observed. There are also examples. In particular, the latter Tc-recorded superconducting material is considered to be a complex oxide having a crystal structure of, for example, an orthorombic type, which should be called a pseudo-perovskite type similar to a perovskite type oxide.

Problems to be Solved by the Invention One of the technical goals relating to superconducting materials is that liquid nitrogen can be used as a cooling medium. That is, despite the fact that liquid nitrogen is produced secondarily in large quantities in order to produce liquid oxygen required in many fields,
A large quantity and inexpensive supply is guaranteed, with few general uses and some abandonment. Liquid nitrogen has a boiling point of about 77K, so if the superconducting phenomenon can be realized at a temperature of 77K or higher, the superconducting technology can be put to practical use.

However, Tc generally indicated as a critical temperature is a temperature at which a substance starts to exhibit superconductivity, and a temperature Tcf at which the electric resistance of the substance becomes completely zero is a temperature lower than Tc.
As described above, the pseudo perovskite oxide
Although Tc close to K has been reported, currently known superconducting materials generally have a large difference between Tc and Tcf, and in some cases exhibit a ΔT of 30 ° C. or more.

Therefore, as described above, in order to put the superconducting technology using liquid nitrogen into practical use, it is essential that the Tcf of the superconducting material exceeds 77K, and a superconducting material having a higher Tc is desired.

Further, the superconductor currently expected to have a high Tc is a sintered body of several kinds of compounds such as oxides, and it is difficult to process it into a wire rod or the like. Therefore, a method of filling a metal pipe with an oxide to produce a superconducting wire has been developed.
Since the oxide was reduced, the desired composition was not obtained, and only those having bad characteristics could be produced.

Thus, the object of the present invention is to show higher Tc and Tcf,
An object of the present invention is to provide a novel method for manufacturing a superconducting wire.

Means for Solving the Problems That is, according to the present invention, one kind of element α selected from Group IIa and Group IIIa elements of the periodic table, and elements from Group IIa and Group IIIa containing the same element as α One selected element β
And a nitride containing at least one element γ selected from Group Ib, IIb, IIIb, VIIIa, and IVa elements,
Mix powders of oxides, hydroxides, carbonates, sulfates, oxalates or nitrates, pre-fire, pulverize the fired body,
A powder fired body is obtained, the powder fired body is molded, the molded body is heated at a temperature within a range of 100 ° C. with the melting point of the fired powder as an upper limit, and sintered, and the inside is Insert a thin-walled metal pipe made of at least one metal selected from the group consisting of Ag, Au, platinum group elements, and stainless steel inside, and a metal pipe different from the above metal into a double metal pipe placed outside Then, a method for producing a superconducting wire is provided, characterized in that both ends of the double metal pipe are sealed and extrusion is performed to produce an extruded material containing an oxide superconductor.

The superconducting wire obtained by the method of the present invention has the general formula: (α _1-x β _x ) γ _y O _Z (where α, β and γ are the elements defined above, and x is α
The atomic ratio of β to + β is 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦ 3 when (α _1−x β _x ) is 1.
It is considered to be a mixed phase of oxides having a composition represented by the formula: 0, 1 ≦ z ≦ 5) and having a pseudo-perovskite type crystal structure mainly composed of Ba ₂ Y ₁ Cu ₃ O _7. A superconductor is built in a metal pipe.

According to a preferred embodiment of the invention, a mixture of Ba, Y and Cu nitrides, oxides, hydroxides, carbonates, sulphates, oxalates or nitrates powders, Ba, La and Cu nitrides, oxidations. Of powders of oxides, hydroxides, carbonates, sulphates, oxalates or nitrates or of Sr, La and Cu nitrides, oxides, hydroxides, carbonates, sulphates, oxalates or nitrates Pulverize any mixture of powder mixture and pre-fire, 700-1000 ℃ pre-fire
It is preferable to carry out the reaction in an O ₂ -containing atmosphere at a temperature within the range described above and an oxygen partial pressure of 0.1 to 150 atm.

Further, according to a preferred embodiment of the present invention, after the preliminary firing, the fired body is crushed to form a powder fired body, the powder fired body is molded, and the molded body is sintered. Molding is preferably carried out by the hydrostatic molding method.

Further, the sintering temperature is preferably 100 ° C or lower than the melting point of the powder fired body. Further, the atmosphere during sintering is preferably an O ₂ -containing atmosphere having an oxygen partial pressure of 0.1 to 150 atm, as in the case of preliminary firing.

Furthermore, the metal pipe into which the molded body is inserted by the method of the present invention has a thin metal pipe made of at least one metal selected from the group consisting of Ag, Au, platinum group elements and stainless steel arranged inside, and a metal pipe formed outside the thin pipe. It is a double metal pipe in which a different metal pipe is arranged. This double metal pipe is preferably one in which the above-mentioned thin metal pipe is fitted inside the outer metal pipe. A sintered body is inserted into the metal pipe, both ends are sealed, and an extrusion process is performed.

The method for producing a superconducting wire provided by the present invention comprises:
In a double metal pipe formed by fitting a thin-walled metal pipe made of at least one metal selected from the group consisting of Ag, Au, platinum group elements and stainless steel inside a pipe different from the above metals After pre-baking and crushing,
The main characteristic is that a superconducting oxide obtained by molding and sintering is inserted, both ends of the pipe are sealed, and an extrusion process is performed to obtain a superconducting wire.

As a superconducting oxide to be inserted in a metal pipe, IIa
Pre-baking after mixing powders of Group III elements, IIIa group elements and nitrides, oxides, hydroxides, carbonates, sulfates, oxalates or nitrates of any of the elements of Ib, IIb, IIIb, VIIIa It is preferable that the fired body obtained in this way is crushed, a fired body powder is molded and sintered.

According to the method of the present invention, a superconducting oxide is formed inside a double metal pipe in which a thin metal pipe made of Ag, Au, a platinum group element or stainless is arranged inside, and a pipe made of a metal different from the above metal is arranged outside. Then, the double metal pipe is sealed and extruded.

In the case of producing a wire rod in which a superconducting oxide is embedded in a metal pipe, conventionally, there has been a problem that the oxide is reduced by the metal of the pipe due to the heating during the extrusion process and the superconducting property is deteriorated. According to the method of the present invention, A
Use double metal pipes with thin-walled g, Au, platinum group element or stainless steel pipes. Since these metals are chemically stable, they do not reduce the oxide upon heating as described above and do not impair the physical properties of the oxide superconductor.

Ag, Au,
Any thin metal pipe made of at least one of a platinum group element and stainless steel may be used, but a thin metal pipe made of stainless steel is particularly preferable in terms of cost.

On the other hand, it is preferable to use Cu, Al or the like for the outer metal pipe. The use of these metals in the outer metal pipe can make up for the disadvantages in properties of the inner thin metal pipe. For example, the thin metal pipe inside
In the case of Ag, Au, or platinum group elements, Cu, Al, etc. have higher strength and lower cost, so the amount of expensive Ag, Au or platinum group elements is suppressed, and a superconducting wire with sufficient strength Can be manufactured.

Further, when the inner thin metal pipe is a stainless steel pipe, Cu, Al and the like have higher workability, so that the heating temperature during extrusion can be set lower. Therefore, unnecessary thermal cycling is not given to the oxide, and processing is easy and the degree of freedom is high. Therefore, the method of the present invention is often superior to the case where an oxide is simply inserted into a stainless steel pipe.

The double metal pipe used in the method of the present invention is preferably formed by fitting a thin metal pipe of the above metal into a metal pipe different from the metal of the thin metal pipe.

The sintering temperature at the time of producing the oxide superconductor used in the method of the present invention is preferably a temperature within which the difference between the melting temperature of the fired powder and the melting temperature is within 100 ° C. This is because if the sintering temperature is lower than the above range, the sintering reaction of the fired body powder does not proceed, and the strength of the obtained sintered body becomes extremely low. On the other hand, if the sintering temperature exceeds the above range, a liquid phase is generated during sintering, and the fired body is melted or decomposed. The Tc of the sintered body that has undergone such a reaction is greatly reduced.

Atmosphere during sintering, O ₂ containing atmosphere having an oxygen partial pressure of 0.1 to 150 atmospheres are preferred, oxygen defects and crystal structure of the sintered body the oxygen partial pressure is out of this range, different from the desired one Therefore, Tc is greatly reduced.

In the sintered body manufactured as described above, a substance having a high superconducting critical temperature is likely to be formed particularly at a crystal grain boundary in the sintered body. Therefore, when producing a superconducting material by sintering, the crystal grain size of the final sintered body is small,
It should be considered so that the grain boundary area is as large as possible.

Therefore, first, the average particle size of the raw material powder is preferably 20 μm or less, and particularly, the fired body powder after the preliminary firing is preferably ground to 10 μm or less. That is, as the particle size of the raw material powder subjected to sintering increases, the crystal grain size of the obtained sintered body immediately increases. However, excessively performing the pulverizing step is not preferable in terms of efficiency due to an increase in working time. Therefore, it is sufficient to satisfy the above range to obtain a superconducting wire having superconducting properties which is the object of the present invention.

By these operations, the superconductor crystals formed according to the method of the present invention are microstructured and formed as a superconducting material having an extremely high critical temperature.

According to a preferred embodiment of the present invention,
As a method of forming the pulverized fired body powder, it is preferable to use an isostatic pressing method. When isostatic pressing is used, isotropic pressure is applied to the compact, and unnecessary stress does not remain, so the compact does not break during subsequent sintering or extrusion, and The characteristics of the superconducting material obtained in the above are also improved.

Hereinafter, the present invention will be specifically described with reference to Examples, but the technical scope of the present invention is not limited by the following disclosure.

Example BaCO ₃ , Y ₂ O ₃ and CuO powder having a purity of 3 N or more and an average particle size of 5 μm or less were mixed with a ball mill at a ratio of 0.6: 0.4: 1. This raw material mixture powder was placed in the atmosphere at 900 ° C for 24 hours.
Burned for hours. The cake-like solidified fired powder obtained is pulverized to a powder of 100 mesh or less in a mortar, filled in a rubber mold, and hydrostatically molded at a pressure of 1.2 ton / cm ² to obtain φ48 ×.
It was molded into a column of 100 mm. Oxygen partial pressure 0.1To
Sintering was performed at 900 ° C. for 10 hours in an oxygen-containing atmosphere of rr.

Insert the oxide superconductor obtained by sintering into a Cu pipe with an outer diameter of 70 mmφ, an inner diameter of 50 mmφ, and a length of 100 mm, in which a thin-walled stainless steel (SUS316) pipe with a wall thickness of 0.5 mm is press-fitted, and insert Cu of φ70 × 10 mm at both ends of the pipe. A disc was attached and extruded. The extrusion ratio was 22 and the temperature was 500 ° C. during the extrusion process.

As a comparative example, similarly processed oxide molded bodies were inserted into common copper pipes, iron pipes, and stainless steel pipes used in the conventional method, and extrusion processing was also performed at an extrusion ratio of 22. The respective extrusion conditions are shown in Table 1.

A member of φ15 × 100 mm was cut out from the center of each of the obtained φ15 × 2000 mm extrudates to obtain a sample.

The critical temperature Tc and Tcf of the sample thus obtained were measured by attaching electrodes with Ag conductive paste to both ends of the sample according to a standard method, immersing it in liquid helium in a cryostat and once cooling it to 10 K, and showing that the sample shows superconductivity. After confirmation, the temperature is gradually raised by the heater, the temperature at which the sample begins to lose superconductivity and begins to show electrical resistance (Tcf), and the temperature at which the sample starts to lose superconductivity and shows the same electrical resistance as normal (Tcf).
c) was measured. The temperature was measured using a calibrated Au (Fe) -Ag thermocouple, and the electrical resistance was measured by a DC 4-point probe method. The results of this measurement are also shown in Table 1.

The examples according to the method of the present invention have higher Tc and Tcf than any of the comparative examples. This is presumably because when a copper or iron pipe is used without stainless powder, the oxide is reduced during extrusion. In addition, when a stainless steel pipe is used, reduction of oxides does not occur, but since the extrusion process is performed at high temperature, it adversely affects the superconductor,
In particular, ΔT becomes large.

From the above, it was proved that the method of the present invention is effective in obtaining a superconducting wire having excellent properties because it can prevent the reduction of oxide during extrusion and enables extrusion at a low temperature.

Effects of the Invention As described above in detail, the superconducting wire obtained by the method of the present invention exhibits high Tc and Tcf which can also use liquid nitrogen as a cooling medium, and its high critical temperature for a long period of time. maintain.

This is obtained by configuring conditions for generating an oxide having a pseudo-perovskite-type crystal structure which is considered to be responsible for superconductivity according to the characteristic manufacturing method of the present invention.

As described above, since high and stable Tc and Tcf can be obtained, liquid nitrogen can be used as a cooling medium for generating superconductivity, and the practical application of superconductivity technology is greatly promoted.

Also, by applying the present invention, conductive materials such as wires and coils can be manufactured, and can be applied to various fields such as various wiring materials, motors and generators.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsuji Ueshiro 1-1-1, Kunyokita, Itami-shi Itami Works, Sumitomo Electric Industries, Ltd. (56) References JP-A-63-279523 (JP, A)

Claims (11)

(57) [Claims] 1. A single element α selected from Group IIa and IIIa elements of the Periodic Table, a single element β selected from elements of Group IIa and IIIa elements containing the same as α and a period. Powders of nitrides, oxides, hydroxides, carbonates, sulfates, oxalates or nitrates containing at least one element γ selected from Group Ib, IIb, IIIb, VIIIa and IVa elements Mixing, preliminary firing, crushing the fired body to obtain a powder fired body, molding the powder fired body, the molded body, the melting point of the fired body powder as an upper limit, the difference from the melting point is within 100 ℃ And sintered at a temperature in the range of, and a thin metal pipe made of at least one metal selected from the group consisting of Ag, Au, platinum group elements and stainless steel is provided inside Insert the pipe into the double metal pipe located on the outside and attach both ends of the double metal pipe. A method for producing a superconducting wire, which comprises producing an extruded material containing an oxide superconductor by sealing and extruding. 2. The oxide superconductor has the general formula: (α _1-x β _x ) γ _y O _Z (where α, β and γ are the elements defined above, and x is α).
The atomic ratio of β to + β is 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦ when (α _1-x β _x ) is 1.
3.0, the atomic ratio is such that 1 ≦ z ≦ 5). The method for producing a superconducting wire according to claim 1, wherein the oxide has a composition represented by: 3. In the above general formula, α is Ba and β is Y
3. The method for manufacturing a superconducting wire according to claim 1, wherein γ is Cu. 4. In the above general formula, α is Ba, and β is La
3. The method for manufacturing a superconducting wire according to claim 1, wherein γ is Cu. 5. In the general formula, α is Sr and β is La
3. The method for manufacturing a superconducting wire according to claim 1, wherein γ is Cu. 6. The powder of the nitrides, oxides, hydroxides, carbonates, sulfates, oxalates or nitrates of the elements α, β and γ has an average particle size of 20 μm or less, respectively. The method for manufacturing a superconducting wire according to any one of claims 1 to 5, wherein 7. The method for manufacturing a superconducting wire according to claim 1, wherein the pre-firing is performed at a temperature in the range of 700 to 1000 ° C. 8. The method for producing a superconducting wire according to claim 1, wherein the fired body after the preliminary firing is pulverized to an average particle size of 10 μm or less. 9. The method for manufacturing a superconducting wire according to claim 1, wherein the forming of the formed body is performed by an isostatic pressing method. 10. The superconducting wire according to claim 1, wherein the metal pipe outside the double metal pipe is a copper pipe. Method. 11. The method according to claim 1, wherein the preliminary firing and / or sintering is performed in an O ₂ -containing atmosphere having an oxygen partial pressure of 0.1 to 150 atm. 1
13. The method for producing a superconducting wire according to item 10.