JPH01122519A - Manufacture of oxide superconducting wire - Google Patents

Abstract

PURPOSE:To obtain an oxide superconducting wire by applying the shrink processing with the face reducing factor of specific % in one time to a composite body formed with the oxide superconducting powder and the precursor powder of the oxide superconductor to form a wire and setting the compression density of the core in the wire to the preset ratio of the theoretical density. CONSTITUTION:The compressed powder molding processing is applied to a material containing at least one of the oxide superconductor powder and the precursor powder of the oxide superconductor to form a compressed powder molding, then this molding is inserted into a metal sheath 2 to form a composite body 3. The manufacturing processing with the face reducing factor of 10-40% in one time is performed at least once with a rotary swaging device A, thus the compressed powder molding in the composite body 3 is thoroughly compressed, and a wire 13 having a core with the compression density of 75% or above against the theoretical density is obtained. After the metal sheath is removed, the wire 13 is heat-treated, thus the diffusion of elements in the core is smoothly performed at the time of the solid phase reaction of the elements, and an oxide superconducting wire with low porosity, high mechanical strength such as bending strength, and the uniform and good superconductivity in the longitudinal direction can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for manufacturing an oxide-based superconducting wire that can be used, for example, for superconducting magnet coils, power transportation, and the like.

"Prior Art" Recently, various oxide-based superconducting materials have been discovered whose critical temperature (T c ) for transitioning from a normal conducting state to a superconducting state is higher than the temperature of liquid nitrogen.

This type of oxide superconducting material has, for example, the general formula A-B
-Cu-0 (A is La, Ce, Yb, Sc, E
represents one or more elements of the ITa group of the periodic table such as r, B is B
a.

There are some elements of the Ha group of the periodic table, such as Sr, which are shown in the numerals 1 and 2). In order to manufacture this type of oxide superconductor, powder containing the 111a group element and Ila
A mixed powder is prepared by mixing a powder containing group elements and a copper oxide powder, and after molding this mixed powder into a predetermined shape, the resulting molded body is heat-treated to cause a solid phase reaction between each element to create superconductivity. It is manufactured by producing substances.

In addition, conventional methods for producing a superconducting wire comprising the Δ-B-Cu-0 system superconductor include filling a metal tube with the mixed powder, or using superconducting powder obtained by heat-treating the mixed powder. The metal tube is filled, and after filling, the metal tube is drawn using a die with a die hole to obtain a wire rod of the desired diameter, and this wire rod is heat-treated to remove the elements of the compacted powder inside into a solid phase. A method of obtaining a superconducting wire by causing a reaction to produce a superconducting substance inside a metal tube is known.

"Problems to be Solved by the Invention" In the conventional method, since the metal tube is reduced in diameter and the mixed powder is compacted by drawing using a die having a die hole, it is necessary to reduce the diameter of the metal tube to the extent that the wire does not break during the drawing process. There is a problem in that it is not possible to sufficiently increase the compaction density of the powder because it is necessary to process the powder into powders, which limits the processing rate. By the way, as a result of the present inventors measuring the compaction density of the O(:l filtered powder) after drawing using the conventional method, the compaction density was 70 to 75% of the theoretical density (state of 0% porosity). Therefore, since the powder compact, which is not sufficiently consolidated, is heat-treated and sintered, the obtained superconducting wire has a sufficient degree of solid-phase reaction of each element. There is a problem that excellent superconducting properties cannot be obtained because there is a tendency for the superconducting wire to be Because the internal porosity is relatively large, the critical current is not very large, and there are problems in terms of strength, such as insufficient bending strength of the superconducting wire.For this reason, it is used for winding wires of superconducting magnets, etc. When winding a superconducting wire around a winding drum, cracks may easily occur in the superconductor, and the superconducting properties may deteriorate significantly.

The present invention was made in view of the above-mentioned problems, and is a manufacturing technology for an oxide-based superconducting wire that can sufficiently increase the compaction density of a powder compact, exhibit excellent superconducting properties, and have high mechanical strength. The purpose is to provide

"Means for Solving the Problems" In the present invention, a powder compact is obtained by subjecting a starting material containing at least one of an oxide superconductor powder and a precursor powder of an oxide-based conductive wire powder to a powder compacting treatment. Then, the compacted compact is filled into a metal sheath to form a composite, and then the composite is subjected to diameter reduction processing with an area reduction rate of 10 to 40% at least once. The solution was to make the composite into a wire, increase the compaction density of the core wire within the wire to 75% or more of the theoretical density, and then heat treat it.

The present invention will be explained in detail below.

In the present invention, starting materials are first prepared. As this starting material, oxide superconductor powder or oxide superconductor precursor powder is used.

The oxide superconductor powders listed in ``2'' are A-B-C.
-ri system (A is Y, Sc, La, Ce, Pr, N
d, Pm.

Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
B represents one or more of the group A elements of the periodic table such as Lu, B represents S r, Ba, Ca, Be, M
C represents one or more elements of group IIa of the periodic table such as g, Ra, etc., and C represents elements of group Ib of the periodic table such as Cu, Ag, and Au and two or more of Nb including Cu or , and D is 0. Periodic table elements such as S, Se, Te, Po, etc. and periodic table elements such as F, CI, Br ■b
Powder of an oxide superconductor of O or two or more types containing O among the family members is used.

Further, as the precursor powder of the oxide superconductor, a mixed powder of a material containing elements constituting the oxide superconductor or a mixed powder of this mixed powder and the oxide superconductor powder described in 1. is used. The above material mixed powder has Tl of the periodic table.
A mixed powder consisting of a powder containing a group A element, a powder containing a group 11a element of the periodic table, copper oxide powder, etc., a powder obtained by calcining this mixed powder, or a mixed powder consisting of this calcined powder and the above mixed powder, etc. is used. The Ha group element powder of the periodic table used here is Be.

Sr, Mg, B6. These include compound powders or alloy powders such as carbonate powders, oxide powders, chloride powders, sulfide powders, and fluoride powders of each element of Ra. Further, powders of elements of the InaHa group of the periodic table include Sc, Y, La, and Ce.

P r, Nd, Pm, Sm, Eu, Gd, Tb, Dy,
T-To, Er, Tm.

Compound powders or alloy powders such as oxide powders, carbonate powders, chloride powders, sulfide powders, and fluoride powders of the elements Yb and Lu are used. Furthermore, copper oxide powder includes CuO, Cu, 09Cu302. Cu40a or the like is used.

Incidentally, in order to prepare the various mixed powders used in the present invention, a powder method is usually used, but the method is not limited to this method. It is also possible to apply a coprecipitation method in which the precipitate is dried to obtain a mixed powder. In addition, the necessary elements such as alcokind compounds, oxine ketone compounds, cyclopentadienyl compounds, acetylacetone compounds, etc. are mixed in a predetermined ratio to form a mixed solution, and water is added to this mixed solution to hydrolyze it to form a sol. At the same time, a sol-gel method may be applied in which this sol-like substance is heated to form a gel, and the gel is further heated to form a solid phase, which is then pulverized to obtain a mixed powder.

Next, the starting material thus prepared is subjected to a powder compacting treatment to produce a powder compact. The compacting process here includes, for example, cold isostatic pressing, hot isostatic pressing (HIP),
) are preferably used, but the method is not limited to these methods, and any method can be used as long as the above-mentioned starting material can be pressure-molded into a powder compact with a desired degree of compaction. be. For example, a metal tube filled with the above starting material is subjected to one or two processing methods such as drawing with a die, rotary swaging, rolling, and extrusion.
It is also possible to use a method such as applying a combination of two or more types to reduce the diameter of the metal tube and forming the starting material described in 1 above into a powder compact having a desired degree of compaction. Further, the compacting pressure in the powder compacting process is determined depending on the type of starting material, the compaction degree of the powder compact to be achieved, etc., and is usually 1.5 to 10 tons/C7.
! 'It is determined within a range of degrees.

In addition, as a pretreatment for such a powder compacting treatment, a series of treatments including calcination treatment, pulverization treatment, etc. can be repeatedly applied to the starting material twice on the same side.

Here, the above-mentioned calcination treatment is desirably performed in an atmosphere containing oxygen gas at, for example, 500 to 1000° C. for 1 to several tens of hours. This calcination treatment is performed for the purpose of removing in advance carbon dioxide gas, which is generated in the heat treatment in the subsequent step and degrades the superconducting properties of the superconductor, when carbonate is contained in the starting material. In addition, the pulverization process is performed for the purpose of making the pulverized product finer and uniform in particle size, but considering the compaction density of the compacted product obtained by the compaction process, It is desirable to keep the particle size of the pulverized product as small as possible during the pulverization process.

Furthermore, after powder compaction treatment, 800 to 1
A heat treatment may be performed in which the material is heated to 100° C. for about 1 to 100 hours and then slowly cooled. If such heat treatment is performed,
It is possible to improve the sintered density of the powder compact after treatment, and the constituent elements in the powder compact undergo a sufficient solid phase reaction with each other, thereby forming a superconductor in the powder compact. can be generated.

Furthermore, the above-mentioned starting material may be repeatedly subjected to a series of treatments consisting of the above-mentioned calcination treatment, pulverization treatment, compaction treatment, and heat treatment one or more times. By performing such a series of treatments, impurities such as carbon dioxide gas can be completely removed from the powder compact, and the sintered density of the compact can be further improved, resulting in good superconductivity. Oxide superconductors exhibiting these characteristics can be efficiently produced.

Next, as shown in FIG. 1, for example, the rod-shaped powder compact 1 obtained in the previous step is housed in a metal tube 2 to produce a composite 3. The tube body 2 used here includes Cu
, Ag, AI, an alloy thereof, or a metal material such as stainless steel. Note that the material for forming the tube body 2 is not limited to metal materials as long as they can be plastically worked, but it is necessary to select a non-oxidizing material that does not take away oxygen from the compacted compact 1 during heat treatment. be. Therefore, it is preferable to use a noble metal or an alloy containing a noble metal, but a coating layer made of a non-oxidizing material may be formed on the inner peripheral surface of the tube 2. Further, it is preferable that the inner diameter of the tubular body 2 is set to be slightly larger than the outer diameter of the powder compact 1, that the dimensional tolerance between the two is smaller, and that there is less gap between the two. This is because the powder compact 1 and the tube body 2 are
This is because if a large gap exists between the powder compact 1 and the powder compact 1, the compacting pressure is transmitted to the powder compact 1 and the compacted body 1 is likely to be inconvenient in that the diameter cannot be sufficiently reduced.

Next, in this example, the composite body 3 is subjected to a diameter reduction process using a rotary swaging device A as shown in FIG. This rotary swaging device A includes a plurality of dice 6, which are movably provided by a drive device (not shown).
・It is equipped with the following. These dice 6... are provided around a movement space when the rod-shaped composite body 3 is moved in its length direction, so as to surround this movement space, and are arranged in a direction perpendicular to the movement space (in the direction perpendicular to the movement space). It is held movably in the direction of arrow a shown in FIG. 1) and rotatably around the movement space (in the direction of arrow a shown in FIG. 1).

Further, a tapered surface 6a for performing diameter reduction processing on the composite body 3 is formed on the inner surface of each die 6, and the gap surrounded by the tapered surface 6a of each die 6 is tapered. It is shaped like a ball.

To reduce the diameter of the composite 3, the rotary swaging device A is operated and one end of the composite 3 is pushed into the gap between the dies 6, as shown in FIG. Here, since the die 6 is rotating while reciprocating at a predetermined interval in the vertical direction in FIG. The wire rod is reduced in diameter to the wire rod I3. In this diameter reduction process, the composite body 3 is reduced in diameter while being forged by a plurality of dies 6 that reciprocate while rotating, so that the composite body 3 is reduced in diameter at a large processing rate without causing wire breakage. Diameter processing is possible.

In such diameter reduction processing, the area reduction rate of 46 ((S, -8,)X ] 00/S,, sl: composite 3
S2: Cross-sectional area of line +, l' + 3. ] is 1
It can be determined in the range of 0 to 40%. If the area reduction rate is less than 10%, the compacting pressure applied to the compact in the composite body 3 during one processing is too small, and the pressure of the compact in the wire 13 (hereinafter referred to as core wire) is reduced. Since the density cannot be increased sufficiently, the number of diameter reduction processes must be increased, which is extremely uneconomical. In addition, if the area reduction rate exceeds 40%, 1
The molding pressure in each processing step is too high and the manufacturing time required for one processing step becomes long, resulting in inconveniences such as poor manufacturing efficiency. The processing speed in diameter reduction processing performed at such an area reduction rate is, for example, in the range of 0.1 to 10 m/min when the rotary swaging device A is used. If the processing speed is less than 0.Ii/min, it will be too slow and the manufacturing efficiency will be poor, and if it exceeds IOx/min, it will be too fast and there will be problems such as not being able to sufficiently increase the density of the core wire within the wire 13.

Such diameter reduction processing is repeated until the wire diameter of the wire vI' 13 reaches a desired wire diameter and the density of the core wire within the wire rod 13 becomes 75% or more, preferably 77% or more of the theoretical density. It will be done. If the compaction density of the core wire is less than 75% of the theoretical density, the compaction density is too small and there is a limit to the sintered density even if the core wire is subjected to post-process heat treatment. This causes the inconvenience that the characteristics become extremely poor. If the desired wire diameter and consolidation density cannot be achieved by processing using the rotary swaging device A, a rotary swaging device equipped with a die having a forming gap smaller than the forming gap of the die 6 of this device A may be used. It is necessary to repeatedly reduce the diameter using a swaging device or the like.

The wire rod 13 thus obtained is subjected to the treatment described below to produce an oxide-based superconducting wire.

That is, the tube portion serving as the outer metal source is removed from the wire 13, thereby exposing the core wire portion.

To remove the metal sheath here, a chemical method is used in which, for example, the composite is immersed in a treatment liquid such as an aqueous acid or alkali solution, and only the metal sheath is dissolved in the treatment liquid.

In this method, when copper, silver, or an alloy of these is used for the metal sheath, dilute nitric acid or the like is used as the treatment liquid.
When aluminum is used for the metal sheath, caustic soda or the like is used as the treatment liquid; when stainless steel is used for the metal sheath, aqua regia is used as the treatment liquid, but the combinations of sheath material and treatment liquid are limited to these. It is not something that will be done. And after such a removal operation,
It is desirable to immediately wash or neutralize the surface of the core wire to eliminate the effects of the treatment liquid on the core wire. Note that cutting may be used to remove the metal source (J1), but using this cutting may cause problems such as bending during the removal operation if the core wire is small in diameter. Therefore, in this example, we adopted the chemical method described above, which is less likely to cause the above disadvantages to the core wire, but if there is little risk of bending, we recommend cutting the metal sheath to remove it or removing the metal sheath. A chemical removal method may also be used.

Next, the core wire thus exposed is subjected to heat treatment. This heat treatment is preferably carried out by heating to 800 to 1100°C for about 1 to 100 hours in an oxygen atmosphere and then slowly cooling it.
During the slow cooling process, a process of holding the temperature in a temperature range of 400 to 600°C for a predetermined time may be performed to promote transformation of the crystal structure of the oxide superconductor from tetragonal to orthorhombic. Through the above heat treatment, each of the constituent elements in the core wire undergoes a sufficient solid-phase reaction with each other, and since the surface of the core wire is exposed, oxygen elements are efficiently diffused from the entire surface of the core wire into its interior. be done. Therefore, in the core wire, an oxide superconductor of the A-B-Cu-0 system, for example, which exhibits uniform superconducting properties over the entire wire is generated, and as a result, an oxide superconducting wire exhibiting good superconducting properties. is obtained.

Then, such an oxide-based superconducting wire can be subjected to a coating treatment to form a protective coat layer, if necessary. As the material for forming this protective coat layer, for example, low melting point metals such as tin and lead, alloys such as solder, etc. are suitably used.

As a method for forming this protective coat layer, methods such as electroplating, melt plating, and solder plating are suitably used. In addition, as another method, a method can be used in which the powder of the low melting point metal described in "-" or the alloy powder described in "1" is adhered to the surface of the oxide superconducting wire to a predetermined thickness, and then the powder described in "1" is sintered. I can do all kinds of things. By forming the protective coat layer in this manner, it becomes possible to stabilize the good superconducting properties of the oxide-based superconducting wire over a long period of time.

According to this manufacturing method, the rotary swaging device A performs at least one forging process with an area reduction rate of 10 to 40%.
By repeating the rotation, the compacted body in the composite body 3 is sufficiently consolidated, and a wire rod 13 having a core wire with a consolidation density of 75% or more of the theoretical density is obtained, and then the wire rod 13 is heat-treated after the metal sheath is removed. This enables smooth diffusion of elements when each element in the core wire reacts in phase, resulting in low porosity, high mechanical strength such as bending strength, and uniform and good superconducting properties in the longitudinal direction. Oxide-based superconducting wires can be manufactured. Therefore, the oxide-based superconducting wire obtained in this way is resistant to bending and has good flexibility, so it can be wound without cracking and is suitable for winding wires for superconducting magnets. Become.

Moreover, if the composite body 3 is produced after heat-treating the compacted body 1, the sintered density of the compacted body 1 can be significantly improved by the heat treatment, so the diameter reduction process for the composite body 3 can be performed. As a result, a wire rod having a core wire with an extremely high degree of consolidation can be obtained.

Therefore, an oxide-based superconducting wire exhibiting good superconducting properties can be manufactured by removing the tube portion of this wire to expose the core wire portion and then heat-treating the wire in an oxygen atmosphere.

In this example, rotary swaging was used to reduce the diameter of the composite 3, but the present invention is not limited to this, and processing methods such as rolling may also be suitably used.

Examples are shown below to clarify the effects of the present invention.

"Example" A mixed powder was obtained by mixing Y2O3 powder with an average particle size of 4 μm, Ba CO3 powder with 171i, and CuO powder with the same size of 1 μm so that Y:Ba:Cu = 1 + 2.37. . Next, this mixed powder was calcined in an oxygen stream at 900°C for 24 hours, pulverized in a ball mill, and the molding pressure was increased to 2.5°C.
A compacting process was carried out using a rubber press at a pressure of ton/am2 to obtain a rod-shaped powder compact. Next, this green compact was heat-treated at 900° C. for 124 hours in an oxygen stream. Such calcining treatment, crushing treatment,
A series of treatments consisting of powder compaction treatment and heat treatment was repeated to obtain a powder compact with an outer diameter of about 6.9 m. By the way, the compaction density of this powder compact is 78% of the theoretical density,
Its critical current density was about 40 A/1Z71'.

Next, this powder compact was filled into a silver tube having an outer diameter of Ions and an inner diameter of 71+z to form a composite. Next, using a rotary swaging device equipped with a die having a configuration similar to that shown in FIG.
The wire was cold forged and reduced in diameter in stages until it became a 1x wire rod. In addition, in order to obtain a wire rod by reducing the diameter while forging the composite in stages, prepare multiple dies with different gaps between the dies, and set the area reduction rate in one diameter reduction process to approximately 20%. The forging operation was performed multiple times to reduce the diameter, and the processing speed was set to In/min.

In the above processing, it was possible to process the wire up to the final wire diameter without any troubles such as wire breakage. When we measured the compaction density of the core wire inside the wire produced in this way, we found that it was 82% of the theoretical density, which was much improved compared to the wire that had been reduced in diameter by drawing with dies. Ta.

Next, this wire was immersed in nitric acid to dissolve and remove the silver source to expose the core wire.

Next, this core wire is heated to 890°C in an oxygen stream for 17 hours, and then heat-treated to slowly cool it to room temperature at -100°C/hour to form an oxide-based material over the entire core wire. A superconductor was produced and a superconducting core wire was obtained. When the sintered density of this superconducting core wire was measured, it was found to be 915% of the theoretical density. Next, the surface of this superconducting core wire was solder-plated to form a protective coating layer having a thickness of lsx, thereby producing an oxide-based superconducting wire.

The oxide superconducting wire produced in this way has a critical temperature
91 has a critical current density of approximately 11000 A/cm2 (77K
) was shown.

On the other hand, powder compacts were produced in which the compaction density was set to 65% and 74% of the theoretical density (Comparative Example 1.2). The compacted bodies of Comparative Examples 1 and 2 were made into composite bodies in the same manner as in the above examples, and then these composite bodies were forged by rotary swaging and reduced in diameter to 1.5u. Next, the metal sheath of the wire obtained by reducing the diameter was dissolved and removed to expose the core wire, and then the core wire was heat-treated under the same conditions as in the example to obtain a superconducting core wire. The sintered density (percentage of theoretical density) and critical current density (measurement temperature 77K) of these two types of superconducting core wires were measured, and the results are shown in Table 1.

(Space below) =20= From the above in Table 1, the oxide-based superconducting wire manufactured by implementing the present invention has higher mechanical strength than the oxide-based superconducting wire manufactured by the conventional method. It became clear that the superconducting properties were also excellent.

"Effects of the Invention" As explained above, according to the manufacturing method of the present invention, a compacted product is obtained by subjecting a starting material containing at least one of an oxide superconductor powder and its precursor powder to a compacting process. A composite obtained by filling a metal sheath is subjected to diameter reduction processing with an area reduction rate of 10 to 40% at least once to make the composite into a wire and to reduce the core wire within the wire. Since the heat treatment is performed after the consolidation density of the wire is set to 75% or more of the theoretical density, the consolidation density of the core wire within the wire can be made higher than, for example, by conventional drawing processing. Therefore, since the heat treatment allows the constituent elements to diffuse smoothly and easily inside the high-density core wire, it is possible to manufacture an oxide-based superconducting wire that has excellent mechanical strength and superconducting properties. Moreover, when the oxide-based superconducting wire manufactured according to the present invention is wound around a winding drum to be used as a winding wire for a superconducting magnet, it can be wound without producing a crank.

[Brief explanation of the drawing]

FIG. 1 is for explaining one embodiment of the present invention.
It is a sectional view for explaining diameter reduction processing. 1... Powder compact, 2... Tube body (metal W), 3...
・Complex, 6... Tice, 13... Line side, A...
Rotary swaging device. Jaw person Fujikura Electric Cable Co., Ltd. Figure 1

Claims (3)

[Claims] (1) A starting material containing at least one of an oxide superconductor powder and an oxide superconductor precursor powder is subjected to a powder compaction treatment to form a compact, and then the compact is placed in a metal sheath. After filling the composite to form a composite, the composite is subjected to diameter reduction processing at least once with an area reduction rate of 10 to 40% to make the composite into a wire rod, and the inside of the wire is reduced. A method for producing an oxide-based superconducting wire, which comprises heat-treating the core wire after the core wire has a compaction density of 75% or more of the theoretical density. (2) The method for manufacturing an oxide superconducting wire according to claim 1, wherein the precursor powder is a calcined powder of a material containing constituent elements of an oxide superconductor. (3) The method for producing an oxide-based superconducting wire according to claim 1, wherein the powder compact is heat-treated at least once.