JPH01115012A - Manufacture of oxide superconducting wire - Google Patents

Abstract

PURPOSE:To enable obtaining an oxide superconducting wire of high mechanical strength by housing a green compact in a metal sheath for forming a complex body and applying a diameter reduction process to the complex body and then heat treatment thereto. CONSTITUTION:A round bar-shaped green compact 1 is obtained by applying a pressed powder formation process to superconducting powder having a grain diameter of 1mum or less. The green compact 1 after sintering treatment is housed in a metal tube body 2 and a complex body 3 is prepared. The complex body 3 is reduced in diameter while being subjected to a forging process in turn from one end thereof. The diameter is reduced to a two-dot chain line and a complex body 13 is obtained. By this diameter reduction process, the compaction of the green compact 1 in the complex body 13 can be made equal to or more than 75% of theoretical compaction. Thereafter, the tube body part forming an outer metal sheath is removed and the green compact 1 is thereby exposed. And the exposed green compact 1 is subjected to final sintering treatment. According to the aforesaid process, it is possible to generate a compact superconductor of extremely low porosity and, therefore, a superconducting wire of high mechanical strength can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to superconductors and wires used for superconducting magnet coils, power transportation, etc., and relates to superconductors using oxide-based superconductors as superconductors.

"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 the general formula A-B-Cu
-0 (However, A represents one or more elements of group MA of the periodic table, such as La, Ce, Yb, Sc, Er, etc., and B represents Ba, Sr.
(indicates one or more elements of group Ma of the periodic table, such as). In order to manufacture this type of oxide superconductor, a mixed powder is prepared by mixing the powder containing the II[A group element, the powder containing the FFA group element, and the copper oxide powder,
After this mixed powder is molded into a predetermined shape, the resulting molded body is heat-treated to cause each element to react in a solid phase to produce a superconducting material.

In addition, as a method for producing a superconducting wire comprising the A-B-Cu-0 system superconductor, conventionally, the mixed powder is filled into a metal tube, or the mixed powder is heat-treated to obtain a superconducting powder. is filled into a metal tube, and after filling, the metal tube is drawn using a die with die holes to obtain a wire rod of the desired diameter, and this wire rod is heat-treated to solidify the elements of the powder compact inside. 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 pressed into powder by drawing using a die having a die hole, it is difficult to prevent wire breakage during drawing and processing. 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. Incidentally, as a result of the present inventors measuring the compaction density of the powder after drawing using the conventional method, the compaction density was about 70% of the theoretical density (state of 0% porosity) even if it was high. Therefore, since a powder compact with insufficient compaction density is heat-treated and sintered, the resulting superconducting wire tends to have insufficient solid phase reactions among the elements. However, there are cases where excellent critical current characteristics cannot be obtained. Furthermore, as mentioned above, when a superconducting wire is manufactured by sintering a powder compact with insufficient compaction density, the porosity inside the superconductor is relatively large, resulting in insufficient bending strength of the superconducting wire, etc. There is a problem with great dissatisfaction in terms of strength.

For this reason, when a superconducting wire is wound around a winding drum for use in winding a superconducting magnet, the superconductor may be prone to cracking, and the superconducting properties may deteriorate significantly.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an oxide-based superconducting wire that can sufficiently increase the compaction density of a powder compact, exhibits excellent superconducting properties, and has high mechanical strength. With the goal.

"Means for Solving the Problems" The present invention provides a method for manufacturing an oxide superconducting wire, which includes at least one of an oxide superconducting powder and an oxide superconducting precursor powder, and has a particle size of 1 μm. The following powder is subjected to powder compaction treatment to form a powder compact, then this compact is housed in a metal sheath to form a composite, and then this composite is The solution to the interlayer problem was to reduce the diameter so that the density was 75% or more of the theoretical density, and then heat treat it.

"Action" Among oxide superconducting powder and oxide superconductor precursor powder,
Powder containing at least one of the particles and having a particle size of 1 μm or less is subjected to powder compaction treatment, the obtained compact is housed in a metal sheath to form a composite, and this composite is injected with a sintered compact. Since the diameter is reduced so that the density becomes 75% or more of the theoretical density, and then heat treatment is performed, a superconductor with extremely low porosity is produced.

The present invention will be explained in more detail below.

FIG. 1 is for explaining one embodiment of the present invention.
To manufacture an oxide-based superconducting wire by carrying out the present invention, starting materials are first prepared. As this starting material, an oxide superconductor, a material containing an element constituting the oxide superconductor, or a mixture thereof is used.

The above-mentioned oxide superconductors include A-B-C-D system (where A is Y, Sc, La, Ce, Pr, Nd, P
m.

Sm, Eu, Gd, Tb, Dy, Ho, Er, Tll1
．． Represents one or more elements of group MA of the periodic table such as Yb, I, and u, and B represents S r, B a, Ca,
One of the Ua group elements of the periodic table such as B e, Mg, and Ra
C represents a group Ib element of the periodic table such as Cu, Ag, or Au, and Cu or two or more types including Nb; D represents an element such as O, S, Se, Te, or Po Periodic Table ■Group b elements and Periodic Table ■Group B elements such as F, CI, Br, etc. Indicates two or more types containing 0 or O)
are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ua of the periodic table and IIIa of the periodic table.
A mixed powder consisting of a powder containing a group element and copper oxide powder, a powder obtained by calcining this mixed powder, a mixed powder of the above mixed powder and calcined powder, etc. are used. The periodic table Ila group element powder used here includes Be,
These include compound powders or alloy powders such as carbonate powders, oxide powders, chloride powders, sulfide powders, and fluoride powders of the elements Sr, Mg, Ba, and Ra. In addition, powders of Group IIIa elements in the periodic table include Sc, Y, La, and Ce.
, Pr, Nd, Pa+.

Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
Compound powders or alloy powders such as oxide powders, carbonate powders, chloride powders, sulfide powders, and fluoride powders of the elements B and Lu are used. Furthermore, as copper oxide powder, Cu'O, CutO, Cu5O! , CL1403, etc. are used.

By the way, to prepare the mixed powder, the above-mentioned powder method is usually used, but the method is not limited to this method.Each element is co-precipitated as oxalate and the precipitate is dried. It is also free to apply a coprecipitation method to obtain a mixed powder. Further, an alkoxide compound, an oxyketone compound, a cyclopentagenyl compound, etc. of the necessary elements are mixed in a predetermined ratio to form a mixed solution,
Water is added to this mixed liquid and it is hydrolyzed to form a sol, this sol-like substance is heated to form a gel, this gel is further heated to form a solid phase, and then pulverized to form a mixed powder. A sol-gel method may be applied to obtain the sol-gel method.

Next, 500 to 100% of the mixed powder prepared as described above was added.
The superconducting powder is heated at 00° C. for about 1 to several tens of hours to obtain a calcined powder, and this calcined powder is further heat-treated to create a superconducting powder.

This heat treatment condition is appropriately set depending on the type of oxide superconductor. For example, as an oxide superconductor, Y-B a-C
When u-0 is used, the calcined powder is compacted to form a compact, and then this compact is heated to 800 to 1
It is preferable to heat the powder at 000° C. for several tens of hours, then to perform a pulverization treatment, and then to perform a heat treatment in which a series of operations of pulverization, powder compaction, and heating are repeated multiple times.

Through this heat treatment, each element constituting the superconductor causes a reaction, and a superconducting powder with a uniform composition is obtained. Note that the atmosphere during heating is not limited to an oxygen atmosphere;
An oxygen-containing atmosphere may be used, such as a mixed gas atmosphere of oxygen and an inert gas such as argon or nitrogen, or a mixed gas atmosphere of oxygen, an inert gas, and a halogen gas such as chlorine gas or fluorine gas.

Next, the superconducting powder is subjected to particle size selection, and only powders having a particle size of 1 .mu.m or less, preferably about 0.7 .mu.I11 to 1.5 .mu.m are selected and collected. To sort superconducting powder by particle size,
Selection such as sedimentation method is preferably used. Next, particle size 1μ
The superconducting powder having a particle size of 1.5 m or less is subjected to powder compaction treatment to form a round bar-shaped powder compact 1. For this powder compaction treatment, a well-known compression processing method such as hydrostatic pressing can be used. Next, this powder compact was heated to 700 to 1000°C in an oxygen-containing atmosphere.
A first sintering process is performed in which the material is heated for about 24 hours. This first
In the sintering process, by heating a compact made of superconducting powder with a particle size of 1 μm or less, it is possible to sinter the compact so that the compaction density of the compact becomes 75% or more of the theoretical density. . In this compaction and first sintering process, if superconducting powder with a particle size of 1 μm or more is used, the compaction density will be low during compaction, and even after the first sintering process, a dense compacted compact will not be obtained. Unobtainable and undesirable.

Next, the powder compact I that has undergone the first sintering process is housed in a metal tube 2 shown in FIG. 1 to create a composite 3. The tube body 2 is made of Ag5Cu, At or an alloy thereof,
Or it is formed from a metal material such as stainless steel.

The constituent material of the tubular body 2 is not limited to metal materials as long as it 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.

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.

Next, the composite body 3 is subjected to a diameter reduction process using a rotary swaging device A shown in FIG.

This rotary swaging device A includes a plurality of dies 6 that are movably provided by a drive device along the path shown in the figure. These dice 6 are provided around a movement space when the round rod-shaped composite body 3 is moved in its length direction, and are provided in a direction perpendicular to the movement space (first direction). It is held movably in the direction of the arrow a shown in the figure) and rotatably around the movement space (in the direction of the arrow shown in FIG. 1). Also, each die 6
A tapered surface 6a for reducing the diameter of the composite body 3 is formed on the inner surface of the die, and the gap surrounded by the sixth tapered surface 6a of each die becomes tapered.

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 dice 6 are rotating while reciprocating at a predetermined interval in the direction of the arrow a in FIG.
is sequentially forged from one end side and reduced in diameter to the wire diameter shown by the two-dot chain line in FIG. 1 to obtain a composite body 13. In this diameter reduction process, in order to reduce the diameter while forging the composite body 13 using a plurality of rotating and reciprocating dies 6, the composite body 3 is reduced in diameter at a large processing rate without causing wire breakage in the composite body 3 during the diameter reduction process. Diameter processing is possible. Moreover, in this diameter reduction process, the compaction density of the compacted body in the composite can be made 75% or more of the theoretical density.

When the diameter reduction process shown in FIG. 1 has been completed and the wire diameter of the composite body 13 thus created has not yet reached the desired wire diameter, the composite body 13 is placed in the rotary swaging device A. A diameter reduction process is performed using a rotary swaging device equipped with a die having a molding gap smaller than that of the die 6 that was used to form the wire, thereby forming a composite having a desired wire diameter.

As mentioned above, once the diameter of the composite is reduced to the desired wire diameter by performing diameter reduction processing one or more times, the composite after diameter reduction is subjected to the treatment described below to form a superconducting wire. Manufacture.

That is, the tube portion serving as the outer metal sheath is removed from the composite, thereby exposing the powder compact portion. To remove the metal sheath, for example, the composite is immersed in a treatment solution such as an acid or alkali aqueous solution.
A chemical method or the like is used in which only the metal sheath is dissolved in the processing liquid. This method includes copper in a metal sheath,
When silver or alloys of these are used, dilute nitric acid is used as the treatment liquid, when aluminum is used for the metal sheath, caustic soda is used as the treatment liquid, and when stainless steel is used for the metal sheath, the treatment liquid is Although aqua regia or the like is used, the combination of the sheath material and the treatment liquid is not limited to these. After such a removal operation, it is desirable to immediately wash or neutralize the surface of the molded article to eliminate the influence of the treatment liquid on the molded article. Note that cutting may be another method for removing the metal sheath, but
If this cutting process is used, if the molded object is small in diameter, there is a risk of inconveniences such as bending during the removal operation. It was adopted. however,
If there is little risk of bending, the metal sheath may be removed by cutting, and a method of removing the metal sheath by cutting and a method of chemically removing the metal sheath may be used in combination.

Next, the powder compact thus exposed is subjected to a final sintering treatment. This final sintering treatment is preferably carried out by heating at 800 to 1100° C. for about 1 to 100 hours in an oxidizing atmosphere, and then slowly cooling at, for example, -100° C./hour.

Here, during the slow cooling process, a process of holding the temperature in the temperature range of 400 to 600°C for a predetermined period of time is performed to promote the transformation of the crystal structure of the oxide superconductor from a tetragonal product to an orthorhombic one. It's okay.

Through this final sintering process, the powder compact is further densified to a compaction density of about 90 to 95% of the theoretical density, and since the surface of the compact is exposed, the compact The powder compact is sintered without causing oxygen deficiency, thereby obtaining an oxide-based superconducting wire exhibiting good superconducting properties.

Then, such an oxide-based superconducting wire can be coated as necessary to form a protective coat layer. 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. Alternatively, a method may be used in which the powder of the low melting point metal or the alloy powder is applied to the surface of the oxide superconducting wire to a predetermined thickness and then the powder is sintered. 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.

By the way, in the case of the oxide-based superconducting wire manufactured as described above, superconducting powder with a particle size of 1 μm or less was subjected to a powder compaction treatment, and the obtained compacted powder body 1 was subjected to a first sintering treatment. rear,
It is housed in a metal sheath 2 to form a composite body 3, and this composite body 3
The wire is forged and reduced in diameter using rotary swaging device A, and then subjected to a final sintering process, so the resulting oxide-based superconducting wire has a low porosity and a high pressure of over 90% of its theoretical density. A product with high density and mechanical strength can be obtained.

In the above-mentioned example, the diameter of the composite 3 was reduced by forging using the rotary swaying device A, but if the compaction density of the compact is 75% or more of the theoretical density, However, the diameter may be reduced by other diameter reduction processes, such as rolling.

"Production example" Y2O powder, BaCO3 powder and CuO powder Y:B
A mixed powder was obtained by mixing so that arc u = 1:2 +3, and a calcination treatment was performed by heating this mixed powder at 900° C. for 24 hours in an air atmosphere.

Next, this calcined powder was compacted into a rod shape, heated at 900° C. for 24 hours in an oxygen atmosphere, and then pulverized. Furthermore, by repeating this series of operations of crushing, compacting, and heating three times, Y, Ba, Cu30□-
A superconducting powder having a composition indicated by X was obtained.

Next, this superconducting powder is sorted for particle size by the sedimentation method, and the particle size is 0.
．． Powders of 5 μm to 1 μm were selected and collected.

Next, the selected superconducting powder was heated at a rate of 2.5 tons/c.
m" to form a round bar-shaped powder compact with a diameter of 6.5 mm. Next, this powder compact was heated in an oxygen atmosphere for 90 minutes.
The first sintering treatment was performed by heating at 00°C for 24 hours. The compaction density of the powder compact after the first sintering process was approximately 75% of the theoretical density.

Next, this molded body was inserted into a silver tube having an outer diameter of 10 mm and an inner diameter of 7 mm to obtain a composite body. Next, using a rotary swaging device equipped with a die having the same configuration as the die shown in FIG. 1, the surface composite was cold forged to a diameter of 1.5 mm and reduced in diameter in stages. In addition, in order to reduce the diameter of the composite in stages, prepare multiple dies with different gaps between the dies, set the cross-sectional reduction rate of the l pass to about 20%,
The forging operation was performed multiple times to reduce the diameter, and the processing speed was 1 m7 minutes.

In the above processing, the wire could be processed to the final wire diameter without any troubles such as wire breakage, and the compaction density of the molded body was about 80% of the theoretical density.

Next, this wire rod was impregnated in nitric acid, and the silver sheath was dissolved and removed to expose the powder compact. Next, this green compact was heated at 850 to 950°C for 12 hours in an oxygen atmosphere, and then subjected to a final sintering process in which it was slowly cooled to room temperature at -100°C/hour. Through this final sintering process, a superconducting core wire in which the powder compact in the reduced diameter wire was densely sintered was obtained. The compaction density of this superconducting core wire is 9 of the theoretical density.
It was around 3%.

Next, the surface of this superconducting core wire is soldered to a thickness of l1.
A superconducting wire was manufactured by forming a shoulder protective coating layer.

The superconducting wire manufactured as described above has a critical temperature of 91 K and a critical current density of approximately 10,000 A/cII+" (7
7K).

Furthermore, when this superconducting wire was wound around a winding drum, it was found that the wire could be wound without cracking, and that its mechanical strength was sufficiently high.

From the above, it has been revealed that the superconducting wire manufactured by implementing the present invention has excellent superconducting properties and high mechanical strength.

For comparison, the above-mentioned superconducting powder was filled into a silver tube, and this was drawn using a die with a die hole, so that the compaction density inside the tube was 75% or less of the theoretical density. A diameter-reduced wire rod was created, and this wire rod was subjected to the same sintering treatment as described above to create superconducting wires (Comparative Examples 1 and 2), and their critical current densities were measured. The results are shown in Table 1.

(Margins below) Table 1 "Effects of the Invention" As explained above, the present invention includes at least one of an oxide superconducting powder and an oxide superconductor precursor powder,
Powder having a particle size of 1 μm or less is subjected to powder compaction treatment to form a compact, then subjected to diameter reduction processing such that the compaction density of the compact is 75% or more of the theoretical density, and then heat treated. The porosity of the superconductor produced can be extremely low, and the solid-state reaction of each element can be sufficiently carried out, making it possible to manufacture oxide superconducting wires with excellent superconducting properties such as critical current density. Can be done.

Furthermore, since a dense superconductor with extremely low porosity can be produced, a superconducting wire with high mechanical strength can be produced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining an embodiment of the present invention, and for explaining diameter reduction processing. l...Powder compact, 2...tube (metal tube), 3...
- Complex, 6...Dice, A...Rotor i north swaging device.

Claims (3)

[Claims] (1) In the method for manufacturing an oxide superconducting wire, a powder containing at least one of an oxide superconducting powder and an oxide superconducting precursor powder and having a particle size of 1 μm or less is subjected to a powder compacting treatment. The compact is made into a powder compact, and then this compact is housed in a metal sheath to form a composite, and this composite is subjected to diameter reduction so that the compaction density of the compact is 75% or more of the theoretical density. A method for producing an oxide-based superconducting wire, the method comprising processing and then heat-treating. (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.