JPH01206517A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor with excellent superconductive characteristics by removing a metal sheath from a compound member composed of a core member and the metal sheath so as to expose the core member and performing heat treatment on the core member and thereafter performing coating treatment. CONSTITUTION:A compound member 6 composed of a core member 4 and a metal sheath 5 is made. Next, the metal sheath 5 is removed from the compound member 6 so as to expose the core member 4 of the compound member 6. Then, the exposed member 4 is subjected to heat treatment. With this arrangement, the heat treatment is performed sufficiently supplying oxygen and the like in the atmosphere with respect to the exposed core member and as well the metal sheath is removed so that stress due to the difference of heat expansion coefficient is not loaded on the core member, and thereby the core member can become as oxide superconductor which shows uniform superconductive characteristics all along the line. Next, the oxide superconductor 7 is subjected to coating treatment so as to form a protective coat 8 on the surface of the conductor so that excellent superconductive characteristics can be made stable for a long time.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to oxides that are being developed for use in superconducting magnet coils used in nuclear magnetic resonance diagnostic equipment, particle accelerators, power transport lines, etc. The present invention relates to a method for producing a superconducting conductor. □ "Prior art and its problems" In recent years, various oxide-based superconducting materials have been discovered whose critical temperature (Tc) for transitioning from a normal conducting state to a superconducting state is higher than the liquid nitrogen temperature.

In order to manufacture a superconductor made of such an oxide-based superconducting material, for example, in the case of a Y-B a-Cu-0-based superconductor, Y,03 powder and BaO powder uO powder are mixed. A method is known in which the mixed powder is compacted into a coin-shaped bulk, and then this bulk is heat-treated.

Attempts have also been made to make wire rods from this type of oxide-based superconductor. Currently, there is a known method for obtaining a superconducting wire by filling a metal sheath made of copper, silver, etc. with the mixed powder, and then subjecting the wire to diameter reduction and heat treatment.

However, in such a method, stress is generated between the metal sheath and the oxide superconductor during heat treatment due to the difference in thermal expansion coefficient between the metal sheath and the oxide superconductor, and this stress causes clutter within the oxide superconductor. Since defective parts such as these easily occur, there is a problem in that it is difficult to obtain an oxide superconducting wire that exhibits uniform superconducting properties along the longitudinal direction. Incidentally, the present inventors have calculated the superconducting properties of this type of oxide superconducting wire and the bulk oxide superconductor by the critical current density (
When compared in terms of Jc), the former is 1/2 of the latter.
The results show that there are cases where the value is only about 115.

Therefore, there has been a desire for the development of a technology that can produce an oxide-based superconducting wire with good superconducting properties, especially a high Jc value.

The invention described in claim 1 is a method of accommodating a material made of at least one of an oxide superconductor and a material containing constituent elements of the oxide superconductor in a metal tube. to prepare a preparation,
This composite is then reduced in diameter to form a core (composed of A and a metal sheath), the metal sheath is removed from this composite to expose the core material, and then the core material is heat treated. The solution to the problem was to apply

Further, the invention described in claim 2 solves the problem in the method for manufacturing an oxide-based superconducting conductor described in claim 1, by performing a coating treatment after heat treating the core material.

The present invention will be described in detail below.

In this invention, first, a composite 1 as shown in FIG. 1 is prepared. In this example, the composite l is a housing hole 2 of a metal tube 2 made of copper or copper alloy, a precious metal such as silver, gold, platinum or an alloy of precious metal, aluminum, stainless steel, etc.
A is filled with a material 3 consisting of a material powder containing constituent elements of an oxide-based superconductor, a consolidated body thereof, a calcined product of the consolidated body, or a superconductor obtained by sintering the consolidated body. It is something. The material to be accommodated in the metal tube 2 may be in any form such as powder, granules, compacted material, or a mixture thereof.

Further, the oxide-based superorganism forming the material 3: v8. As a conductor, A-B-C-D system (however, AI!Y,
Sc.

La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, T
b, Dy, l-1o.

Periodic table 111a such as Er, 'I'm, Yb, Lu, etc.
Represents one or more of group elements, T I and Bi, and I3 represents S r, Ba, Ca, Be, ~1g, Ra
represents one or more of the elements of group 11a of the periodic table, such as Cu, A g, A u, group 1b elements of the periodic table, and Cu or two or more of Nb, including Cu. , D is 0, S, Se, Te, Po, group V+b elements of the periodic table, and F, Ca, Br, 1. Represents O or two or more elements containing O among the elements of group 1b of the periodic table of At. ), or L aCuo series, B aP
bB io 3 series, BaKBi03 series, etc. may be used. The composition ratio of each element in the above-mentioned oxide-based superconductor varies depending on the element used, the type of oxide-based superconductor, etc., but for example, in a Y-Ba-Cu-0-based superconductor, Y.

B arc u307-6, and δ is in the range of 0≦δ≦5. In addition, in the Bix5ry CazCuwO-based superconductor, 1≦X≦3, l≦y≦3.0≦Z≦3
,! Range of ≦8≦4, TIX Cay Baz Cuw
In O-based superconductors, l≦X≦3, l≦y≦3
．． Let the range be 0≦Z≦3.1≦8≦4. In addition, to give an example of a typical composition in the above-mentioned system, B
its r+Carc u20 y SB i2S r
2Ca2Cu30 XSB 12s rtca+cu2
0 X ST l+ca3BatcutOx, T
ItCatBa, CUsOXST 1tcal13a2
cu20x, La5Cu+04-x1BaKBiO3
, I3 aP bB io3, etc.

The material 3 used here includes a powder of one or more elements of Group 1 of the periodic table (group 1o elements, TI, and Bi) and elements of group 11a of the periodic table. 1 type or 2B or more element powder, Cu or 2 or more element powders containing Cu among the elements of group 1b of the periodic table, elements of group 11'lb of the periodic table, and group 1b of the periodic table. Of the elements, O or two or more element powders containing O were mixed. Compound powders such as carbonate powders, oxide powders, chloride powders, sulfide powders, fluoride powders, etc., are used.

Next, by subjecting the thus-obtained compound l to i-extent processing, a composite material 6 consisting of a core material 4 and a metal sheath 5 is produced as shown in FIG. Various methods such as wire drawing using a die, rolling, and forging such as rotary swaging may be appropriately used for this diameter reduction process.

Next, the outer metal sheath 5 is removed from this composite material 6, thereby exposing the core material 4 of the composite material 6. To remove the metal sheath 5 here, for example, a method is used in which the composite material 6 is immersed in a treatment liquid such as an acid or alkali aqueous solution, and only the metal sheath 5 of the composite material 6 is dissolved in the treatment liquid. .

In this method, when copper, silver or an alloy thereof is used for the metal sheath 5, dilute nitric acid or the like is used as the treatment liquid, and when aluminum is used for the metal sheath 5, caustic soda or the like is used as the treatment liquid. When stainless steel is used for the metal sheath 5, aqua regia or the like is used as the treatment liquid, but 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 perform a water washing treatment or a neutralization treatment on the surface of the core material 4 to eliminate the influence of the treatment liquid on the core material 4. Note that another method for removing the metal sheath 5 is to use cutting, but if this cutting is used, the core material 4 may be damaged during the removal operation if the composite material 6 has a small diameter. It is necessary to do this in a way that does not cause any inconveniences such as bending. From this point of view, in the present invention, a melting method that does not easily cause the above-mentioned disadvantages to the core material 4 is preferably used. Furthermore, as a method for removing the metal sheath 5, a method may be selected in which only the metal sheath 5 is selectively melted and removed using a high frequency melting method.

Next, the thus exposed core ÷44 is subjected to heat treatment. This heat treatment is performed at a treatment temperature of 700 to 10
The treatment is carried out at 00°C for a treatment time of 0.1 to several hundred hours. The atmosphere during this heat treatment is normally an oxygen atmosphere, but if necessary, Sulfur is added to the oxygen atmosphere.
, Se, etc.: gases of group Vtb elements of the g1 table and I
', CLBr, etc., can be included in the gases of Group Ⅰb of the Circular +01 Table.

These elements are introduced into some of the constituent elements of the finally obtained oxide-based conductive wire and contribute to improving the superconducting properties. By heat treatment in such an atmosphere,
When the constituent elements in the core material 4 are sufficiently reacted with each other, oxygen or the components of oxygen and the additive gas are efficiently diffused from the exposed surface of the core material 4 into the interior thereof.

Therefore, an oxide-based superconductor exhibiting uniform superconducting properties along the longitudinal direction of the core material 4 is generated in the core material 4, and as a result, the core material 4 exhibits good superconducting properties as shown in FIG. An oxide-based superconducting conductor 7 shown in the figure is obtained.

Then, the oxide-based superconducting conductor 7 obtained in this way
A coating treatment is performed as necessary to form a protective coating layer 8 on the surface of the oxide-based superconducting conductor 7 as shown in FIG. As the material for forming the protective coat layer 8, for example, a low melting point metal such as tin or lead, or an alloy such as solder is used, but an amorphous carbon film,
The protective coat layer 8 may be formed by forming a ceramic film, an enamel film, a copper alloy film, or the like. As a method for forming the protective coat layer 8, for example, electroplating, melt plating, solder plating, or the like is preferably used. Alternatively, after depositing the low melting point metal powder, the alloy powder, or the ceramic powder on the surface of the oxide-based superconducting conductor 7 to a predetermined thickness,
A method of sintering the powder can also be used.

By forming the protective coat layer 8 in this manner, it is possible to prevent constituent elements such as oxygen from dissipating from the crystals of the oxide-based superconducting conductor 7, thereby maintaining good superconducting properties of the oxide-based superconducting conductor 7 for a long period of time. It becomes possible to stabilize it.

According to such a manufacturing method, the accommodation hole 2 of the metal vibrator 2
The diameter of a composite l filled with an oxide superconductor material 3 is reduced to form a composite material 6, and then the metal sheath 5 is removed from this composite material 6 to expose the core material 4, and then this Since the core material 4 is heat-treated, it is possible to heat-treat the exposed core material 4 while supplying sufficient oxygen, etc., thereby achieving uniform superconducting properties over the entire length of the core material 4. An oxide-based superconductor exhibiting this can be produced, and thereby an oxide-based superconducting conductor 7 exhibiting good superconducting properties can be manufactured from the core material 4.

Then, the oxide-based superconducting conductor 7 obtained in this way
By coating the oxide-based superconducting conductor 7 as necessary to form a protective coating layer 8 on its surface, it is possible to prevent constituent elements such as oxygen from dissipating from the superconductor in the oxide-based superconducting conductor 7. It becomes possible to stabilize the good superconducting properties of the superconducting conductor 7 over a long period of time.

In this example, a powder material 3 was used, but for example, a material powder containing constituent elements of an oxide superconductor is compacted to form a cylindrical compact, and this compact is used as the metal tube 2. The composite body 1 may be produced by inserting it into the accommodation hole 2a. In this case, the powder particles in the material 3 are brought into a compacted state by compaction, and therefore a denser core material 4 can be obtained by further compressing the material 3 in the diameter reduction process of the rear ball F. Therefore, excellent effects such as less occurrence of defects such as clutter in the oxide superconducting conductor 7 obtained by heat treatment of the core material 4 can be obtained.

In the above example, the case where the superconducting conductor 7 with a round cross section is formed has been described, but the cross-sectional shape of the superconducting conductor may be any shape such as a square, an ellipse, or an irregular cross-section.

"Example 1" Y2O3 powder, BaO powder, and CaO powder were mixed into Y:Ba:C
A material powder was prepared by mixing at a ratio of u=l:2:3. Next, this material powder was filled into a silver pipe to produce a composite.

Next, this composite was subjected to diameter reduction processing to obtain a composite consisting of a cylindrical silver sheath with an outer diameter of 1.5zz and a core material with a diameter of 0.8!1 m. Next, this composite material was immersed in dilute nitric acid to dissolve and remove the silver sheath to expose the core material.

Next, heat treatment temperature 8 for this core (4) in oxygen atmosphere
Heat treatment is performed at 50 to 950°C for 12 hours to form Y + B at Cu + o ? over the entire length of the core material. −δ(0≦
An oxide-based superconductor having a composition of δ≦5) was produced to obtain an oxide-based superconductor. Next, the surface of this oxide-based superconductor was soldered to form a protective coating layer having a thickness of 11 mm.

The critical temperature (Tc) and critical current density (Jc) of the oxide superconducting conductor manufactured in this way were measured and found that Tc = 90K.

A value of J c = l x 10 'A/cM'' (at 77K) could be confirmed.

"Example 2" BaCO3 powder and CuO powder were mixed at a ratio of 2:3,
BatCu is calcined in the atmosphere at 880℃ for 10 hours.
A calcined powder having a composition of +Os was obtained, and this calcined powder was further ground and mixed with TlyOs powder and CaO powder. During this mixing, (calcined powder): (T
A mixed powder was obtained by mixing at a ratio of LO3 powder: CaO powder = 1:2:3.

Subsequently, the mixed powder was compacted and then heat-treated in oxygen gas at 870°C for 1 hour, followed by slow cooling at a rate of 200°C/hour to form T1. Ca2BatCus
An intermediate sintered body was obtained by producing an oxide superconductor having a composition of Ox.

Next, the Moeki intermediate sintered body was inserted into an Ag pipe having an outer diameter of 10 mm and a wall thickness of 1.5 mm, and the pipe was reduced to a diameter of 0.5 mm using a rotary swaging device to obtain a composite material. Next, this composite material is immersed in dilute nitric acid to dissolve and remove the Ag sheath, exposing the internal core material, and heat-treating the core material by heating it at 870 ° C. for 30 minutes in an oxygen gas flow at a flow rate of 2 Q/min. T lzc atB atc
An oxide superconductor comprising an oxide superconductor having a composition of u, o x was obtained. This oxide superconductor has Tc=120K.

J c = 2 x 10 'A/am'' (at 77K).

"Example 3" BaCO3 powder and CaO powder were mixed at a ratio of 1:3,
It was calcined at 880° C. for 12 hours to obtain a calcined powder having a composition of BaCO3 powder. Next, this calcined powder is pulverized and T LO
3 powder and CaO powder, and subjected to a sintered heat treatment at 880° C. for 2 hours in a closed heating furnace at 1 atm filled with oxygen gas to obtain an intermediate sintered body. Next, the intermediate sintered body was inserted into a pipe made of Ag and subjected to diameter reduction processing under the same conditions as in Example 1 described above to obtain a composite material. Next, the Ag sheath of this composite material was dissolved and removed with dilute nitric acid to obtain the core material, which was then heated at 880'C for 30 minutes in a closed heating furnace at 1 atm filled with oxygen gas, and then cooled. Perform heat treatment, T I2c a+B a2c ut
An oxide superconducting wire including an oxide superconductor having a composition of ox was obtained. This oxide superconducting wire has Tc=lO8K.

It showed Jc=I X I O'A/am' (at 77K).

"Actual emergency case 1" Each nitrate solution of Bi, Pb, Sr, Ca, and Cu was prepared as Bi:Pb:Sr:Ca:Cu=1.4:0.
(i:2:2:3, and oxalate as a superconductor raw material was coprecipitated with ammonium oxalate, and this coprecipitate was avoided to dry to obtain a mixed powder.This mixed powder was The calcined powder obtained by calcining at 820° C. for 12 hours was filled into an Ag pipe to produce a composite.

Next, this composite was subjected to diameter reduction processing to obtain a composite consisting of a cylindrical Ag sheath with an outer diameter of 1.5 mm and a core material with a diameter of 0.8 mm. Next, this composite material was passed between high-frequency coils to selectively dissolve and remove only the silver sheath, exposing the core material.

Next, this core material was heated to 850℃ in the atmosphere for 50 minutes.
Heat treatment is performed to heat the core material for a long time to achieve B
An oxide-based superconductor consisting of 12P by S r and Carc uso x was produced to obtain an oxide-based superconductor. Next, the surface of this oxide-based superconducting conductor was soldered to form a protective coating layer having a thickness of I Rm.

The critical temperature (Tc) and critical current density (Jc) of the oxide-based superconductor produced in this way were measured and found to be 1"c=IO6K Jc=I x I O'A/cm" (at 77K) I was able to confirm that.

"Effects of the Invention" As explained above, according to the present invention, the metal sheath is removed from a composite material consisting of a core material and a metal sheath to expose the core material, and then the core material is subjected to heat treatment. So,
It is possible to heat-treat the exposed core material while supplying sufficient oxygen, etc. in the atmosphere, and since the metal sheath is removed, stress due to the difference in coefficient of thermal expansion is not applied to the core material. Therefore, it is possible to produce an oxide-based superconductor that exhibits uniform superconducting properties over the entire core material, thereby making it possible to manufacture an oxide-based superconductor that exhibits good superconducting properties.

When the oxide superconducting conductor obtained in this way is coated to form a protective coat layer on the surface of the oxide superconducting conductor, this protective coat layer protects the superconductor in the oxide superconducting conductor. It is possible to prevent dissipation of constituent elements such as oxygen, and therefore it is possible to stabilize the good superconducting properties of the above-mentioned oxide-based superconducting conductor over a long period of time.

[Brief explanation of the drawing]

1 to 4 are for explaining an example of the manufacturing method of the present invention. FIG. 1 is a cross-sectional view showing a composite body suitably used in the present invention, and FIG. Figure 3 is a cross-sectional view showing the composite material shown in Fig. 2 with a reduced diameter. FIG. 4 is a cross-sectional view showing the state in which the oxide-based superconducting wire shown in FIG. 3 has been subjected to a coating treatment. l...Composite, 3...Material, 4...Core material, 5...
Metal sheath, 6... Wire rod, 7... Oxide superconducting conductor, 8... Protective coat layer.

Claims (2)

[Claims] (1) A composite is produced by housing at least one of an oxide superconductor and a material containing constituent elements of the oxide superconductor in a metal tube, and then the composite is reduced in diameter. An oxide-based superconducting conductor characterized by forming a composite material consisting of a core material and a metal sheath, then removing the metal sheath from this composite material to expose the core material, and then subjecting the core material to heat treatment. manufacturing method. (2) The method for producing an oxide-based superconducting conductor according to claim 1, wherein the core material is subjected to a coating treatment after being heat-treated.