JPH01122402A - Manufacture of oxide superconductive bulk material - Google Patents

Abstract

PURPOSE:To improve superconductive characteristics by making porosity low, by a method wherein a powder compact molded body of powder containing at least either oxide superconductive powder or precursor powder of an oxide superconductor is made a complex within a metallic sheath and the complex is heat-treated after the same has been processed through forging at specific compressed density. CONSTITUTION:A material containing an oxide superconductor and an element constituting the oxide superconductor or a mixture of them is made calcined powder by heating the same and superconductive powder is manufactured by heat-treating the calcined powder further. The superconductive powder is made a cylindrical powder compact molded body 1 by performing powder compact molding treatment of the superconductive powder and a complex 3 is manufactured by holding the same within a metallic tubular body 2 after first sintering treatment of the same. Then a rotary swaging device A is actuated, an end of the complex 3 is pushed in a gap between dies 6..., the powder compact molded body 1 is compressed while forging and compressed density is made 75% or higher of that of theoretical density. Then the final sintering treatment is performed to the exposure-treated molded body 1. With this construction, a bulk material showing favorable superconductive characteristics is obtained.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention is applicable to oxide-based superconducting joining members having relatively short lengths and large cross-sectional areas, which are used, for example, in connections between superconducting cables with large current capacity. , Josephson element, S Q U
I D (S superconducting Q
uantu+++ I interference D
The present invention relates to a method for manufacturing an oxide-based superconducting bulk material used as a plate-shaped or columnar superconducting material used as a thin-film superconducting material such as a thin-film superconducting material such as a thin film superconducting material, a printed circuit board wiring material, a magnetic shielding material, or the like.

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

This type of oxide superconducting material has the general formula A-I3-Cu
-O (However, A beam, a, Ce, Y b, S
Indicates one or more elements of group MA of the periodic table such as c, E r, etc.
B represents one or more elements of the Ua group of the periodic table, such as Ba and Sr. In order to manufacture a superconducting bulk material comprising this kind of oxide-based superconductor, it is necessary to mix the powder containing the Ma group element and the powder containing the Ia group element and copper oxide powder uniformly. Alternatively, this mixed powder is calcined to form a calcined powder into a predetermined shape, and then the resulting powder compact is heat-treated to cause each element to react in a solid phase to produce a superconducting material. I'm trying to manufacture it.

"Problems to be Solved by the Invention" However, the superconducting bulk material created as described above is simply compacted powder using compression means such as isostatic pressing, and the degree of compaction of the powder There is a problem that it is not possible to raise the level sufficiently.

Incidentally, the inventors created a powder compact by applying isostatic pressure to the above mixed powder or calcined powder, and measured the compaction density.
condition) was about 70%. Therefore, since a powder compact with insufficient compaction density is heat-treated and sintered, the resulting superconducting bulk material tends to not undergo sufficient solid phase reactions of each element. However, there is a problem that excellent critical current characteristics cannot be obtained. In addition, as mentioned above, when superconducting bulk materials are manufactured by sintering powder compacts that are not sufficiently compacted, there is a problem of large dissatisfaction in terms of strength due to the relatively large porosity inside the bulk materials. be.

For this reason, there is a risk that cracks may occur in the superconducting bulk material, especially in the vicinity of the processed part, due to the shock that is sometimes applied when processing the bulk material, such as when cutting a part of the bulk material, and the superconducting properties may deteriorate significantly. There is.

The present invention was made in view of the above problems, and provides an oxide-based superconducting bulk material that can sufficiently increase the compaction density of a powder compact, exhibits excellent superconducting properties, and has high mechanical strength. The purpose is to

"Means for Solving the Problems" The present invention provides a method for producing an oxide-based superconducting bulk material, comprising: a powder containing at least one of an oxide superconducting powder and a precursor powder of an oxide superconductor; One of the green compacts that have been subjected to powder compaction treatment is housed in a metal sheath to form a composite, and then this composite has a compaction density of 75% of the theoretical density. The solution to the problem was to carry out forging to achieve a reduction of at least %, followed by heat treatment.

"Action" Among oxide superconducting powder and oxide superconductor precursor powder,
Either one of a powder containing at least one of the powders and a compacted body obtained by subjecting this powder to a compacting process is housed in a metal sheath to form a composite, and this composite is Since the material is forged to a density of 75% or more of the theoretical density and then heat treated, a bulk material with extremely low porosity can be obtained.

The present invention will be explained in more detail below.

FIG. 1 is for explaining one embodiment of the present invention. In order to carry out the present invention and produce an oxide-based superconducting bulk material (hereinafter referred to as bulk material), first, starting materials are prepared. do.

As this starting material, an oxide superconductor, a material containing an element constituting the oxide superconductor, or a mixture thereof is used.

As the oxide superconductor, A43-C-D system (
However, A is Y, Sc, La, Ce, Pr, Nd, Pm
.

Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
B represents one or more elements of the UIa group of the periodic table such as B, Lu, etc., and B represents S r , B a , Ca
, B e , M g , Ra etc. Periodic Table I
Indicates one or more types of Group Ia elements, C is C
u, A g, A u represents Cu or two or more of the rb group elements of the periodic table and Nb, including Cu, and D is 0,
Among the elements of group Vtbrb of the periodic table such as 5ySe, Te, and Po, and the elements of group IIb of the periodic table such as F, CI, and Br, O or two or more elements containing O) are used.

In addition, materials containing elements constituting the oxide superconductor include powders containing elements of group Ila of the periodic table and nIa of the periodic table.
A mixed powder consisting of a powder containing a group element and a copper oxide powder, a powder obtained by calcining this mixed powder, or a mixed powder of the above mixed powder and calcined powder are used. The periodic table group ■a element powders used here include 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, as the periodic table group 111a element powder, Sc, Y, La, C
e, Pr, Nd, Pm.

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. Further, as the copper oxide powder, CuO, CutO, Cus'O*, CIIaOs, etc. are used.

By the way, to prepare the mixed powder, the powder method described above is usually used, but it is not limited to this method. Each element is coprecipitated as oxalate, and the precipitate is dried to form a powder. It is also possible to avoid applying the coprecipitation method to obtain a mixed powder. In addition, if alkoxide compounds, oxyketone compounds, cyclopentagenyl compounds, etc. of the above-mentioned necessary elements are mixed in a predetermined ratio to form a mixed solution, water is added to this mixed solution and hydrolyzed to form a sol. Alternatively, a sol-gel method may be applied in which this sol-like substance is heated to gel, and the gel is further heated to form a solid phase, which is then pulverized to obtain a mixed powder.

Next, add 500 to 100% of the mixed powder prepared as described above.
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 product at 1,000° C. for 1 to several tens of hours, then perform a pulverization treatment, and then perform a heat treatment in which a series of operations of pulverization, 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 classification using a sedimentation method, etc.
Preferably, powder of about 0.7 μrrI to 1.5 μm is selected and collected. Next, this superconducting powder is subjected to powder compaction treatment to form a compacted powder body 1 in the shape of a round bar. This powder compaction process is
Well-known compression processing methods such as rubber press can be used. Next, this powder compact was placed in an oxygen-containing atmosphere for 70 minutes.
0~! A first sintering process is performed by heating at 000° C. for about 24 hours.

In this first sintering process, a powder compact made of superconducting powder with a particle size of about 1 μm is heated, and the compact is sintered so that the compaction density of the compact becomes 75% or more of the theoretical density. be able to. 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. This is not preferable because it may not be possible.

Next, the compact 1 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 Ag, Cu, AI or an alloy thereof,
Or it is formed from a metal material such as stainless steel.

Note that the constituent material of the tube body 2 is not limited to metal materials as long as they can be plastically worked, but non-oxidizing materials that do not take away oxygen from the powder compact 1 during heat treatment are particularly preferably used. . 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 body 2.

Next, the composite body 3 is forged 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 as shown. 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 dice 6
A tapered surface 6a for forging the composite body 3 is formed on the inner surface of the die, and the gap surrounded by the tapered surface 6a of each die 6 has a tapered shape.

To forge the composite body 3, the rotary swaging device A is operated and one end of the composite body 3 is pushed into the gap between the dies 6, as shown in FIG. Here, since the dies 6 are rotating while reciprocating at a predetermined interval in the direction of the arrow a in FIG. 1, the composite body 3 is sequentially forged from one end side as shown by the two-dot chain line in FIG. The composite material 13 is obtained by compressing it to a thickness. In this forging process, the composite body 13 is forged by a plurality of dies 6 that reciprocate while rotating, and the powder compact is compressed, so that no cracks occur in the composite body 3 during the forging process. Further, in this forging process, the compaction density of the compacted body in the composite can be made 75% or more of the theoretical density.

The forging process shown in Figure 1 has been completed, and the resulting composite is created! 3 has not yet reached the desired thickness, the composite I3 is processed using a rotary swaging device equipped with a die having an even smaller molding gap than the die 6 provided in the previous rotary swaging device A. Then, the composite is forged to the desired diameter.

As shown in the figure, once the composite is forged once or twice or more to obtain a desired diameter, the composite is subjected to the treatment described below to produce a bulk material.

That is, the tubular 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 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 the surface of the compact with water or neutralize it to eliminate the influence of the treatment liquid on the powder compact. In addition, when removing the metal sheath above, if there is little risk of bending the compact, it is okay to remove the metal sheath by cutting. A chemical removal method may also be used.

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 oxygen starvation, resulting in a bulk material exhibiting good superconducting properties.

Then, such a bulk material can be coated as necessary to form a protective coat layer. Examples of materials for forming this protective coat layer include tin,
Low melting point metals such as lead or alloys such as solder are preferably 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 bulk material over a long period of time.

This bulk material has a high critical current density and can be used as a large-capacity superconducting member by setting a large cross-sectional area.For example, it is used for connections between large-capacity superconducting cables. In addition to being used as a large-capacity superconducting bonding member, it can be cut into an appropriate shape and polished to form a large-area plate material.
It can be used as a thin film superconducting material, a printed circuit board wiring material, a magnetic shielding material, etc.

By the way, in the case of the bulk material manufactured as described above, the superconducting powder is subjected to powder compaction treatment, and the obtained powder compact l
After being subjected to a first sintering treatment, it is housed in a metal tube 2 to form a composite body 3, and this composite body 3 is forged by a rotary swaging device A, and then subjected to a final sintering treatment. Therefore, the produced bulk material has a low porosity and a high compaction density of more than 90% of the theoretical density, allowing sufficient solid phase reaction of each element, and in the final sintering process, the metal source of the composite is By removing the powder compact, exposing it, and heating it in an oxygen-containing atmosphere, it is possible to generate a superconductor without causing oxygen deficiency in the compact, so that the critical current density, etc. It is possible to produce bulk materials with excellent superconducting properties.

Furthermore, since it is possible to produce a dense bulk material with extremely low porosity, it is possible to produce a bulk material with high mechanical strength.

In the above example, the composite 3 was forged using the rotary swaging device A in order to manufacture a round bar-shaped bulk material, but the compaction density of the compact was 75% of the theoretical density.
As long as the forging method is as above, the forging method is not limited to this, and other forging methods such as stag forging and die forging may be used.

Further, in the above example, the shape of the bulk material is a round bar, but the shape of the bulk material is not limited to this, and may be in various shapes such as a square bar, a disc, or a cylinder. can. These bulk materials in shapes other than round rods can be manufactured in almost the same manner as in the above example. For example, in order to manufacture bulk materials in the shape of a square rod or plate, the superconducting powder described above is shaped into a square rod or plate. A sintered body obtained by compacting and calcining the molded body is inserted into a rectangular cylindrical metal sheath or sandwiched between metal plates to form a composite,
It can be manufactured by forging this by standing forging, removing the metal sheath, and then subjecting it to a final sintering process.

"Manufacturing example" Y, 03 powder and BaCO3 powder and CuO powder Y:B
a: Cu = 1:2:3 to obtain a mixed powder, and this mixed powder was heated to 90% in an air atmosphere.
Calcination treatment was performed by heating at 00°C for 24 hours.

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, YIB azc u30
? 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.
．． Powder of 5μI11-1μm was selected and collected.

Next, the selected superconducting powder was 2.5 tons/
Hydrostatically pressurized at cm', diameter 7 mm, length 100 mm
It was made into a round bar-shaped powder compact. Next, this powder compact was heated at 900° C. for 24 hours in an oxygen atmosphere to perform a first sintering treatment. 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.
Cold forged to 34mm.

In this forging process, the compact can be processed without cracking, and the compaction density of the compact is as follows:
The density was about 80% of the theoretical density.

Next, the forged composite was immersed in nitric acid to dissolve and remove the silver sheath to expose the powder compact. next,
850 to 95% in an oxygen atmosphere for one compacted compact
A final sintering process was performed in which the material was heated to 0°C for 12 hours and then slowly cooled to room temperature at -100°C/hour. Through this final sintering process, a bulk material in which the powder compact was densely sintered was obtained.

The consolidation density of this bulk material was about 93% of the theoretical density. ``The bulk material produced as described above has a critical temperature of 91 K and a critical current density of about 11000 A/am'' (77 K
) was shown.

In addition, when we formed a cut in a part of this bulk material with a diamond cutter, we were able to cut it well without cracking in the vicinity of the cut part due to the impact of cutting, and we found that the mechanical strength was sufficiently high. It became clear.

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

For comparison, the above-mentioned superconducting powder was compacted using a rubber press to create a compact with a compaction density of 75% or less of the theoretical density, and the same method as above was applied to this compact. A bulk material (Comparative Example 1.2) was prepared by sintering, and its critical current density was measured. Show your results! Shown below.

Table 1 [Effects of the Invention J As explained above, the present invention provides a powder containing at least one of an oxide superconducting powder and a precursor powder of an oxide superconductor, and a compact obtained by subjecting this powder to a powder compacting process. Either one of the powder compacts is accommodated in a metal sheath to form a composite, and then this composite is subjected to forging processing such that the compaction density of the compact is 75% or more of the theoretical density, Since heat treatment is performed after this, the porosity of the superconductor produced can be extremely low, and the solid phase reaction of each element can be sufficiently carried out, so oxide-based superconductors with excellent superconducting properties such as critical current density can be produced. Be able to manufacture bulk materials.

Furthermore, since a dense superconductor with extremely low porosity can be produced, an oxide-based superconducting bulk material with high mechanical strength can be produced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining one embodiment of the present invention, and for explaining a forging process. 1...Powder compact, 2...Pipe body (metal sheath), 3
...Composite, 6...Dice, A...Rotary swaging device.

Claims (3)

[Claims] (1) In the method of manufacturing an oxide-based superconducting bulk material, among the oxide superconducting powder and the precursor powder of the oxide superconductor,
Either one of a powder containing at least one of the powders and a compacted body obtained by subjecting the powder to powder compaction processing is housed in a metal sheath to form a composite, and then this composite is powder compacted. A method for manufacturing an oxide-based superconducting bulk material, which comprises performing forging processing such that the compaction density of the body becomes 75% or more of the theoretical density, followed by heat treatment. (2) The method for producing an oxide-based superconducting bulk material 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 bulk material according to claim 1, wherein the compacted powder is heat-treated at least once.