U.S. patent application number 08/528538 was filed with the patent office on 2002-02-28 for superconducting wire and manufacturing method for the same.
Invention is credited to KANEKO, NORIO.
Application Number | 20020023772 08/528538 |
Document ID | / |
Family ID | 26544213 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020023772 |
Kind Code |
A1 |
KANEKO, NORIO |
February 28, 2002 |
SUPERCONDUCTING WIRE AND MANUFACTURING METHOD FOR THE SAME
Abstract
A superconducting wire having a fine line made of an oxide
superconductor which has metal material dispersed therein, the
outer periphery of which being coated with a conductive material;
and a manufacturing method for the superconducting wire, comprising
a process for drawing a metal pipe; filled with an oxide
superconductor so as to product the fine line and a process for
heating the fine line at a temperature which is higher than the
melting point of the metal material constituting the metal
pipe.
Inventors: |
KANEKO, NORIO; (ATSUGI-SHI,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26544213 |
Appl. No.: |
08/528538 |
Filed: |
September 14, 1995 |
Current U.S.
Class: |
174/125.1 ;
505/230; 505/430; 505/433; 505/813; 505/821; 505/884; 505/886 |
Current CPC
Class: |
C04B 35/4504 20130101;
Y10S 505/74 20130101; Y10T 29/49014 20150115; H01L 39/248 20130101;
Y10S 505/704 20130101 |
Class at
Publication: |
174/125.1 ;
505/230; 505/430; 505/433; 505/813; 505/821; 505/884; 505/886 |
International
Class: |
H01B 012/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1994 |
JP |
259623/1994 |
Sep 30, 1994 |
JP |
259626/1994 |
Claims
What is claimed is:
1. A superconducting wire having a fine line of an oxide
superconductor which has a metallic material therein, the outer
periphery thereof being coated with a conductive material.
2. A superconducting wire according to claim 1, wherein said
metallic material is silver or a silver alloy.
3. A superconducting wire according to claim 1, wherein said
conductive material is a metal or an alloy there which is selected
among Au, Al, Cu, Ni, Pd, Pt, Ti, Mo, W, Nb, and Mn.
4. A superconducting wire a cording to any of claims 1 to 3,
wherein said oxide superconductor is composed of the materials
represented by composition formula (I) given
below:Ln.sub.aSr.sub.bCu.sub.3-xM.sub.xO.su- b.c (I)where Ln
consists of at lease one type of element or atomic group selected
from the element group of Y element and lanthanoid element; M
consists of at least one type of element or atomic group selected
from the element group of Ti, V, Ga, Ge, Mo, W, and Re; and
2.7.ltoreq.a+b.ltoreq.3.3, 0.8.ltoreq.a.ltoreq.1.2,
6.ltoreq.c.ltoreq.9, and 0.05.ltoreq..times..ltoreq.0.7.
5. A superconducting wire a cording to any of claims 1 to 3,
wherein said oxide superconductor is composed of the materials
represented by composition formula (II) given
below:Ln.sub.aCa.sub.bSr.sub.cCu.sub.3-xM.- sub.xO.sub.d (II)where
Ln consists of at least one type of element or atomic group
selected from the element group of Y element and lanthanoid; M
consist of a least one type of element or atomic group selected
from the element group of Fe, Co, Ti, V, Ge, Mo, Re, and W; and
2.7.ltoreq.a+b+c.ltoreq.3.3, 0.8.ltoreq.a+b.ltoreq.2.1,
6.ltoreq.d.ltoreq.9, 0.05.ltoreq.b.ltoreq.1.1, and
0.05.ltoreq..times..ltoreq.1.0.
6. A superconducting wire according to any of claims 1 to 3,
wherein said oxide superconductor is composed of the materials
represented by composition formula (III) given
below:Ln.sub.aCa.sub.bSr.sub.cBa.sub.dCu.- sub.2+eO.sub.6+fC.sub.g
(III)where Ln consists of at least one type of element or atomic
group selected from the element group of Y element and lanthanide
element; and a+b+c+d=3, 0.2.ltoreq.a.ltoreq.0.8,
0.2.ltoreq.b.ltoreq.1.0, 0.5.ltoreq.c.ltoreq.2.2,
0.ltoreq.d.ltoreq.1.6, 0.ltoreq.e.ltoreq.0.8, 0<f<2, and
0.2.ltoreq.g.ltoreq.1.0.
7. A superconducting wire according to any of claims 1 to 3,
wherein said oxide superconductor is composed of the materials
represented by composition formula (IV) given
below:(Ln.sub.1-aCa.sub.a)(Sr.sub.2-bBa.su-
b.b)(Cu.sub.3-cB.sub.c)O.sub.d (IV)where Ln consists of at least
one type of element or atomic group selected from the element group
of Y element and lanthanoid element excluding Ce and Tb; and
0.1.ltoreq.a.ltoreq.0.5, 0.7.ltoreq.b.ltoreq.1.7,
0.1.ltoreq.c.ltoreq.0.5, and 6.5.ltoreq.d.ltoreq.7.5.
8. A superconducting wire according to any of claims 1 to 3,
wherein said oxide superconductor is composed of the elements of
Ln, M, Ba, Ti, Cu, and O; and the basic structure thereof is
equipped with both an octahedron or a pyramid pentahedron formed by
Cu and O and an octahedron formed by Ti and O, the octahedron or
the pyramid pentahedron and the octahedron being arranged in a
two-dimensional manner; where Ln consists of at least one type of
element or atomic group selected from the element group of Y, La,
Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; and M consists of
at least one type of element or atomic group selected from the
element group of Ca and Sr.
9. A manufacturing method for a superconducting wire which has a
fine line of an oxide superconductor comprising: a process for
forming a fine line by drawing a metal pipe filled with an oxide
superconductor; and a process for heating saed fine line at a
temperature which is higher than the melting point of a metal
material constituting said metal pipe.
10. A manufacturing method for the superconducting wire according
to claim 9, wherein said metal pipe has a plurality of small
holes.
11. A manufacturing method for the superconducting wire according
to claim 9, wherein said metal pipe is formed by wrapping an oxide
superconductor with a metal tape.
12. A manufacturing method for the superconducting wire according
to claim 11, herein said metal tape has a plurality of small
holes.
13. A manufacturing me hod for the superconducting wire according
to any of claims 9 to 12, wherein the outer periphery of said fine
line is coated with a conductive material.
14. A manufacturing method for the superconducting wire according
to any of claims 9 to 12, wherein the process for heating said fine
line has a step for letting said fine line pass through a melt of a
conductive material having a melting point which is higher than
that of a metal material constituting said metal pipe.
15. A manufacturing method for the superconducting wire which has a
fine line of the oxide superconductor, comprising: a process for
forming the fine line by drawing a metal pipe filled with materials
for the oxide superconductor; a process for causing said materials
to react so as to produce the oxide superconductor; and a process
for heating said metal pipe at a temperature which is higher than
the melting point of the metal material constituting said metal
pipe.
16. A manufacturing method for the superconducting wire according
to claim 15, wherein said process for causing said materials to
react so as to produce the oxide superconductor has a step for
heating said materials to a reaction temperature before and after
the process for forming said fine line.
17. A manufacturing method for the superconducting wire according
to claim 15, wherein said metal pipe has a plurality of small
holes.
18. A manufacturing method for the superconducting wire according
to claim 15, wherein metal pipe is formed by wrapping the materials
for the oxide superconductor with the metal tape.
19. A manufacturing method for the superconducting wire according
to claim 18, wherein said metal tape has a plurality of small
holes.
20. A manufacturing method for the superconducting wire according
to any of claims 15 to 19, further comprising a process for coating
the outer periphery of said fine line with the conductive
material.
21. A manufacturing method for the superconducting wire according
to any of claims 15 to 19, wherein the process for heating said
fine line has step for letting said fine line pass through the melt
of the conductive material having the melting point which is higher
than that of the metal material constituting said metal pipe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a superconducting wire
employing an oxide superconductor and a manufacturing method for
the same.
[0003] 2. Description of the Related Art
[0004] Oxide superconductors of Y base, Bi base, etc. exhibit
superconductivity at a temperature above the boiling point of
liquid nitrogen. According to a typical method for forming such a
material into a wire, a superconducting material or a material
therefor is charged in a metal pipe and subjected to wire drawing,
then the charged material is subjected to heat treatment before and
after the wire drawing as necessary. As an alternative, an oxide
superconductor is formed on a substrate by various thin film
forming means such as sputtering. The method wherein a
superconductor is charged in a metal pipe has been disclosed in
Japanese Patent Laid-Open No. 2-37623 and Japanese Patent Laid-Open
No. 1-276516. The method which employs a thin film has been
disclosed in Japanese Patent Laid-Open No. 63-241826.
[0005] These methods, however, have the following problems: the
superconductivity of an oxide superconductor varies depending on
the amount of oxygen in the materials; therefore, the amount of
oxygen in the materials must be controlled to produce the wire from
the superconductor. A superconducting wire is usually provided with
a stabilizing material which is normally a metal such as copper. In
the case of an oxide superconductor, however, copper is oxidized
during the manufacturing process due to the oxygen which is present
in the superconductor; therefore, copper cannot be used for the
stabilizing material. Further, an oxide superconductor does not
have the workability that metals have, preventing crystal grains
from deforming easily. This sometimes causes a metal pipe filled
with the superconductor material to break during a rolling process
or a stretching process which employs dies. In addition, the oxide
superconductor must be densely and uniformly charged in the metal
pipe to produce usable superconducting wire. There is still another
problem: the coefficient of thermal expansion of metal is different
from that of an oxide superconductor, presenting a serious problem
of adhesion between the metal and the oxide superconductor when
they are cooled.
[0006] To solve the problems stated above, according to Japanese
Patent Laid-Open No. 2-37623, an aluminum pipe is filled with an
oxide superconductor and the aluminum is melted and removed before
they are heated to sinter the superconductor, then they are
subjected to heat treatment at 900 to 1000 degrees centigrade with
the oxide superconductor exposed so as to control the amount of
oxygen in the material. According to Japanese Patent Laid-Open No.
1-276516, a compact of an oxide superconductor is inserted in a
silver pipe and silver powder is charged in the gap between the
silver pipe and the superconductor to secure the adhesion between
the metal pipe and the superconductor.
[0007] According to the method disclosed in Japanese Patent
Laid-Open No. 2-37623, however, the melting point of aluminum is
approximately 660 degrees centigrade and therefore, the aluminum is
very likely to be oxidized by the oxygen present in the oxide
superconductor before the aluminum is removed from the surface of
the oxide superconductor. It is especially difficult to remove the
aluminum which is in a recessed spot of the surface or in a grain
boundary of the oxide superconductor; an aluminum oxide generated
by oxidation tends to precipitate as an impurity or to react with
the oxide superconductor in some cases. Further, the Japanese
Patent Laid-Open No. 2-37623 has not disclosed anything about the
formation of a stabilizing material which is indispensable for the
application to superconductive magnet or the like. According to the
method disclosed in the Japanese Patent Laid-Open No. 1-276516, no
device has been made to improve the critical current of
superconducting wire although the presence of silver powder seems
to improve the adhesion between the metal pipe and the oxide
superconductor.
[0008] According to the method disclosed in the Japanese Patent
Laid-Open No. 63-241826 which employs the thin film forming
process, the wire is produced beforehand and a thin film composed
of the elements for superconducting materials is formed on a
substrate, which has copper or a copper alloy deposited on the
surface thereof, prior to the heat treatment. It has been
disclosed, however, that the heat treatment must be carried out at
800 to 1000 degrees centigrade for 1 to 100 hours, depending on the
type of superconducting material used. The method requiring such an
extended heat treatment presents a problem of extremely slow
manufacture, whereas quicker manufacture of superconducting wire is
generally desirable. Moreover, the thin film producing method
requires precise control of the composition of the elements
constituting the superconductor; a slight change in the composition
results in a significant change in the superconductive
characteristics, posing a fatal problem in that a lengthy
superconducting wire cannot be produced.
[0009] Thus, although much study has been done on the manufacture
of superconducting wire which employs an oxide superconductor, no
superconducting wire for practical use has been available yet.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide a practical superconducting wire which uses an oxide
superconductor with high critical temperature to prevent the
critical temperature and the critical current from dropping during
the manufacturing process and a manufacturing method for the
same.
[0011] To this end, according to one aspect of the present
invention, there is provided a superconducting wire having a fine
line made of an oxide superconductor which has a metal material
dispersed therein, the outer periphery thereof being coated with a
conductive material.
[0012] According to another aspect of the present invention, there
is provided a manufacturing method for a superconducting wire which
has a fine line made of an oxide superconductor, comprising: a
process for forming a fine line by stretching a metal pipe filled
with an oxide superconductor; and a process for heating the fine
line at a temperature which is higher than the melting point of the
metal material constituting the metal pipe.
[0013] According to still another aspect of the present invention,
there is provided a manufacturing method for a superconducting wire
which has a fine line made of an oxide superconductor, comprising:
a process for forming a fine line by stretching a metal pipe filled
with a material for an oxide superconductor; a process for reacting
the material so as to produce an oxide superconductor, and a
process for heating the metal pipe at a temperature which is higher
than the melting point of the metal material constituting the metal
pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic cross-sectional diagram illustrative
of a superconducting wire according to the present invention;
[0015] FIG. 2 is a flowchart illustrative of a manufacturing method
according to the present invention; and
[0016] FIGS. 3, 4, 5, and 6 are schematic diagrams illustrative of
specific examples of the manufacturing method according to the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] According to the present invention, a metal material is
dispersed in a fine line made of an oxide superconductor which
constitutes a superconducting wire and the vacancies in the
superconductor are filled with the metal material. This prevents a
critical current from decreasing and improves mechanical strength
and the like. Further, a conductive material is attached closely to
the outer periphery of the fine line to maximize the function
thereof as a stabilizer; therefore, the conductive material is not
separated from the superconductor even when the superconducting
wire is subjected to heat cycles. Thus, the critical temperature
and critical current do not decrease during the manufacturing
process enabling a highly practical superconducting wire featuring
a high critical temperature and a high critical current to be
achieved.
[0018] The present invention will be described in detail by
referring to preferred embodiments of the present invention.
[0019] The superconducting wire according to the present invention
has a structure wherein a metal material such as silver or a silver
alloy is mixed in a fine line composed of an oxide superconductor
so as to prevent the critical current from decreasing, and a
particular conductive material is attached to the outer periphery
of the fine line. As the oxide superconductor constituting the
present invention, any oxide superconductor will do as long as it
has a metal material dispersed therein; it may be in the form of a
wire, a hollow tube, or a tape-shaped substrate or the like which
is provided with an oxide superconductor on the surface
thereof.
[0020] Especially desirable materials for the oxide superconductor
include the following:
[0021] a material having a formula which is expressed by
Ln.sub.aSr.sub.bCu.sub.3-xM.sub.xO.sub.c, where
2.7.ltoreq.a+b.ltoreq.3.3- , 0.8.ltoreq.a.ltoreq.1.2,
6.ltoreq.c.ltoreq.9, and 0.05.ltoreq..times..ltoreq.0.7; and Ln
consists of at least one type of element or atomic group selected
from the element group of Y element and lanthanoid element, and M
consists of at least one type of element or atomic group selected
from the element group of Ti, V, Ga, Ge, Mo, W, and Re;
[0022] a material having a formula which is expressed by
Ln.sub.aCa.sub.bSr.sub.cCu.sub.3-xM.sub.xO.sub.d, where
2.7.ltoreq.a+b+c.ltoreq.3.3, 0.8.ltoreq.a+b.ltoreq.2.1,
6.ltoreq.d.ltoreq.9, 0.05.ltoreq.b.ltoreq.1.1, and
0.05.ltoreq..times..ltoreq.1.0; and Ln consists of at least one
type of element or atomic group selected from the element group of
Y element and lanthanoid element, and M consists of at least one
type of element or atomic group selected from the element group of
Fe, Co, Ti, V, Ge, Mo, W, and Re;
[0023] a material having a formula which is expressed by
Ln.sub.aCa.sub.bSr.sub.cBa.sub.dCu.sub.2+eO.sub.6+fC.sub.g, where
a+b+c+d=3, 0.2.ltoreq.a.ltoreq.0.8, 0.2.ltoreq.b.ltoreq.1.0,
0.5.ltoreq.c.ltoreq.2.2, 0.ltoreq.d.ltoreq.1.6,
0.ltoreq.e.ltoreq.0.8, 0.ltoreq.f.ltoreq.2, and
0.2.ltoreq.g.ltoreq.1; and Ln consists of at least one type of
element or atomic group selected from the element group consisting
of Y element and lanthanide element;
[0024] a material having a formula which is expressed by
(Ln.sub.1-aCa.sub.a)(Sr.sub.2-bBa.sub.b)(CU.sub.3-cB.sub.c)O.sub.d,
where 0.1.ltoreq.a.ltoreq.0.5, 0.7.ltoreq.b.ltoreq.1.7,
0.1.ltoreq.c.ltoreq.0.5- , and 6.5.ltoreq.d.ltoreq.7.5; and Ln
consists of at least one type of element or atomic group selected
from Y element and lanthanoid element excluding Ce and Tb; and
[0025] a material which has essential component elements of Ln, M,
Ba, Ti, Cu, and O (Ln consists of at least one type of element or
atomic group selected from the element group of Y, La, Pr, Nd, Sm,
Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; and M consists of at least one
type of element or atomic group selected from the element group of
Ca and Sr); and the basic structure of which has both an octahedron
or a pyramid pentahedron formed by Cu and O and an octahedron
formed by Ti and O at the same time, the octahedron or the pyramid
pentahedron and the octahedron being arranged in a two-dimensional
manner.
[0026] It is needless to say that a very small amount of an
impurity may be added to these materials.
[0027] In the superconducting wire according to the present
invention, any conductive material may be used as the conductive
material to be attached to the outer periphery of the oxide
superconductor with a metallic material dispersed therein;
especially desirable materials include a metal or a metal alloy
such as Au, Al, Cu, Ni, Pd, Pt, Ti, Mo, W, Nb, and Mn.
[0028] By using the materials listed above and by dispersing a
metallic material such as silver in the oxide superconductor, the
critical current can be improved to a certain extent and the
mechanical strength and the like can be also improved owing to the
metal material that fills the gaps among the crystal gains. The
metal material near the surface of the oxide superconductor
provides good adhesion to the conductive material surrounding the
outer periphery of the oxide superconductor, thus preventing the
separation of the conductive material from the superconductor even
when the superconducting wire is subjected to heat cycles.
[0029] The present invention also provides a manufacturing method
for the superconducting wire described above. According to the
manufacturing method, a superconductor or a material therefor is
charged in a metal pipe and the metal pipe is subjected to wire
drawing by dies, rolling, or the like. The oxide superconductor may
be heated before, after or during the wire drawing to sinter it.
The heating temperature should be 500 to 950 degrees centigrade.
The resulting fine line is placed in a container such as a crucible
and it is let pass through a melt of a conductive material having a
melting point which is higher than that of the metal constructing
the metal pipe. This causes a part of the metal of the pipe to melt
into the oxide superconductor and the conductive material. By
winding the fine wire using a roller or the like, the fine line is
taken out of the melt of the conductive material, with the melted
conductive material and pipe metal attached to the surface of the
oxide superconductor.
[0030] The melt attached to the surface of the oxide superconductor
is dispersed in the oxide superconductor because the metal remains
in the melted state even when the conductive material solidifies,
thus contributing to an improved critical current. The melt from
the metal and conductive material, which has not dispersed in the
oxide superconductor, remains on the surface of the oxide
superconductor; therefore, the oxide superconductor can be attached
without any gap when the conductive material solidifies even if the
surface thereof is unsmooth. There is generally a possibility of
the oxygen in the oxide superconductor being reduced while the fine
line is going through the melt of the conductive material.
According to the present invention, however, the eliminated oxygen
is captured in the silver or silver alloy; therefore, even if the
conductive material is the one that does not allow oxygen to
permeate, the superconductivity can be restored by making use of
the oxygen taken into the metal by performing heat treatment.
[0031] The means for producing the conductive material is not
limited to the one wherein the fine line is allowed to pass through
the melt. For instance, in the case of a material like W which has
a high melting point, not only the metal constituting the pipe but
also the oxide superconductor melt or decompose in some cases. In
the case of a material like Al which has a low melting point, a
metal such as silver does not melt even when it passes through the
melt. In such a case, the metal constituting the pipe is melted
before the conductive material is attached by an appropriate means
according to the type of material used. Methods for attaching the
conductive material include the one whereby the conductive material
is applied and subjected to heat treatment, the one utilizing
vacuum deposition, and the one utilizing chemical deposition.
[0032] The metal pipe may be provided with a plurality of small
holes so as to permit easy reaction with oxygen during the heat
treatment in an oxygen atmosphere, or it may be subjected to HIP
treatment or the like after wire drawing or after the conductive
material is solidified. It is needless to say that an insulating
material may be attached to the surface of the conductive material.
There is a possibility of the solving of the conductive material
and the metal when the conductive material passes through the melt;
however, no problem occurs according to the present invention even
if they solve. An appropriate atmosphere and the like for the wire
drawing, heating, winding, and delivery should be selected
according to the type of material used.
[0033] The following describes the present invention by referring
to specific embodiments.
[0034] First Embodiment
[0035] FIG. 1 is a schematic cross-sectional diagram illustrative
of a superconducting wire according to the present invention.
Reference numeral 1 denotes an oxide superconductor. Reference
numeral 2 denotes silver or a silver alloy, which has been
scattered in the oxide superconductor, and/or a material added for
pinning; they are shown in a larger size than they really are. The
silver or the silver alloy need not be scattered evenly inside the
superconductor; it may be segregated in the vicinity of the surface
of the oxide superconductor. Reference numeral 3 denotes a
conductive material.
[0036] The oxide superconductor used for the superconducting wire
according to the present invention is generally produced by heat
treatment. The density of a sintered compact is frequently lower
than a theoretical density. When the sintered compact is processed
into a superconducting wire, therefore, vacancies are generated in
the superconducting wire. The vacancies lead to a lower critical
current of the superconducting wire. To solve this problem, silver
or a silver alloy is melted and filled in the vacancies and
further, the silver or the silver alloy is dispersed in the oxide
superconductor for the purpose of pinning by making use of the
filling temperature. A conductive material is attached as the
stabilizing material to the outer periphery of the
superconductor.
[0037] The superconducting wire in accordance with the present
invention may be manufactured by any method: for example, a silver
pipe is filled with oxide superconductor powder and rolled to be
formed into a wire. The wire is then heated to a temperature above
960 degrees centigrade which is the melting temperature of silver.
This heating causes the silver to fill the gaps among the crystal
grains of the oxide superconductor or to be scattered in the oxide
superconductor. The conductive material is attached to the outer
periphery of the oxide superconductor at the same time as or after
the melting of the silver, thereby producing the superconducting
wire. There is no particular established way to attach the
conductive material; several methods may be employed: for example,
the oxide superconductor is allowed to pass through the melt of a
conductive material, or various deposition processes may be used,
or an organometal may be applied and subjected to heat treatment. A
suitable method for attaching the conductive material should be
selected depending on the type of materials used.
[0038] As shown in FIG. 1, in the superconducting wire according to
the present invention, silver or a silver alloy is scattered in the
oxide superconductor to improve the critical current density.
Further, the melt of the silver or the silver alloy is also present
in vacancies and the recessed spots near the surface of the oxide
superconductor, thus providing good adhesion to the conductive
material attached around the oxide superconductor.
[0039] There is no particular restrictions on the combination of
the materials employed for the present invention. In this
embodiment, Y.sub.2O.sub.3, SrCO.sub.3, WO.sub.3, and CuO were
mixed so as to produce 10 wt % of SrY.sub.2O.sub.4 with respect to
YSr.sub.2Cu.sub.2.8W.sub.0.2O- .sub.y. then the mixture was
subjected to heat treatment at 950 to 1400 degrees centigrade to
produce the oxide superconductor. As the conductive material to be
attached around the oxide superconductor, Cu was used. The same
combination of the materials was employed for other embodiments as
well as the first embodiment to produce the superconducting wire in
accordance with the present invention.
[0040] The superconducting wire according to this embodiment
obtained by using the aforesaid materials and by melting and
dispersing the silver as described above showed a critical current
density of approximately 10,000 A/cm.sup.2 (5K). In contrast to
this, the critical current density, which was obtained when the
same oxide superconductor was employed but no silver was melted and
dispersed was approximately 2,000 A/cm.sup.2, which is extremely
smaller than that of this embodiment.
[0041] Moreover, the superconductive characteristics of the
superconducting wire in accordance with this embodiment remained
unchanged after winding the superconducting wire by a roller having
a diameter of 30 cm, whereas the comparison example, which had no
silver melted and dispersed, showed a drop in conductivity to 1/100
to 1/1,000 after winding the wire by the same roller. This proves
that the superconducting wire in accordance with the present
invention provides high mechanical strength and also high critical
current density.
[0042] Second Embodiment
[0043] FIG. 3 shows the conceptual diagram of the manufacturing
method for the superconducting wire. First, a silver pipe is filled
with an oxide superconductor, then it is formed into a silver
sheath wire by using a plurality of dies 5 (FIG. 3 shows only one
die). In this case, the superconductor was charged in the silver
pipe measuring 8 mm in outside diameter and 6 mm in inside diameter
to produce a fine line 4 having an outside diameter of 0.8 mm.
Reference numeral 6 denotes a copper melt in a crucible, the melt
being produced by a heating device which is not shown. The
temperature of the copper melt is maintained at 1,100 degrees
centigrade. The silver sheath wire obtained as stated above is
placed in and let pass through the copper melt 6. The majority of
the silver is melted and dispersed in the oxide superconductor
although a part of the silver mixes with the copper melt 6 since
the melting point of the silver is 960 degrees centigrade. The wire
is wound by a roller (not shown) to take the wire, with the copper
attached to the surface thereof, out of the crucible. A wire 10,
which has been taken out of the crucible, is cooled. The copper,
which has a higher melting point and which is on the outer
periphery of the oxide superconductor, starts solidifying first,
whereas the inside silver solidifies more slowly than the copper.
This difference in solidifying speed enables the silver to be
scattered into the gaps and crystals of the oxide superconductor.
The wire 10 is cooled until the solidification of the silver is
completed, then the finished superconducting wire is wound using
the roller (not shown).
[0044] The critical current of the superconducting wire of the
second embodiment thus produced is 10.sup.4 A/cm.sup.2 or more
regardless of the composition of the superconductor materials used.
No change in the superconductive characteristics was observed even
when a roller having a diameter of about 300 mm was used to wind
the superconducting wire. The critical current of the silver sheath
wire with no silver melted was about 10.sup.2 A/cm.sup.2. The oxide
superconductor broke when the wire was wound using the roller
having the 300 mm diameter. The superconducting wire in accordance
with the present invention showed almost no change in the critical
temperature of the superconductor before it was charged in the
silver pipe and after it was formed into the superconducting
wire.
[0045] Third Embodiment
[0046] FIG. 4 shows the conceptual diagram of the manufacturing
method for the superconducting wire of the third embodiment. First,
a silver pipe with a hole having a diameter of approximately 0.1 to
0.5 mm is filled with materials for producing the superconductor
and it is formed into a wire having a diameter of 1 mm by using the
die 5. At this time, as shown in FIG. 4, the silver pipe is heated
by heaters 8 before and after it is drawn by the die so as to
produce the oxide superconductor. In general, a carbonate or
nitrate, or an oxide of a constituent metal element is used as the
material for producing the oxide superconductor. The hole formed in
the silver pipe makes it possible to supply oxygen to the central
part of the silver pipe and also to discharge a gas such as carbon
dioxide which is generated when the materials are decomposed. Thus,
according to this embodiment, a superconductor with good
characteristics can be produced by the heat treatment using the
heaters 8.
[0047] The wire 4 thus obtained is placed in a crucible to let it
go through melted gold 6. The temperature of the gold melt 6 is
maintained at 1,065 to 1,080 degrees centigrade. Since the melting
point of silver is 960 degrees centigrade, the silver melts and
disperses in the oxide superconductor when the wire 4 is passed
through the gold melt 6. When the wire is pulled out of the
crucible, it has the gold on the surface thereof. The gold and
silver are partially mixed before they solidify; the mixing ratio
can be controlled by the time during which the wire is in contact
with the gold melt 6 and the winding speed. There should be no
problem as long as the mixing ratio stays constant to a certain
level throughout the wire which has been wound.
[0048] The superconducting wire of the third embodiment thus
produced exhibits high resistance to mechanical deformation; it can
be produced in a length of about 1,000 m even when the roller 7 has
a diameter of 200 mm.
[0049] Fourth Embodiment
[0050] FIG. 5 shows the conceptual diagram of the manufacturing
method for the superconducting wire according to the fourth
embodiment. A pipe made of an alloy of silver with 3 wt % of
palladium added is filled with an oxide superconductor and formed
into a desired sheath wire by using the die 5. The sheath wire is
then heated by the heating device 11 so as to melt the silver
alloy. After the melted alloy solidifies, the conductive material
is formed on the surface of the sheath wire by using a thin film
forming device 9 to make the superconducting wire of this
embodiment. Any heating device may be used for the heating device
11 as long as it is capable of heating the sheath wire to a
temperature at which the silver alloy is melted; infrared rays were
concentrated for heating in this embodiment. Likewise, any device
may be used for the thin film forming device 9 as long as it is
capable of forming a conductive material of the desired thickness;
organopalladium was applied and subjected to heat treatment to
produce a palladium film in this embodiment.
[0051] The superconducting wire according to this embodiment thus
produced exhibits extremely good adhesion between the silver and
palladium, minimizing the chance of cracking or the like when the
wire is subjected to mechanical deformation. Further, the silver
and palladium dispersed in the superconductor have caused the
critical current density to increase to a value which is two orders
of magnitude or more larger than that of the superconducting wire
with no dispersed silver alloy.
[0052] Fifth Embodiment
[0053] FIG. 6 is the conceptual diagram illustrative of the
manufacturing method for the superconducting wire according to the
fifth embodiment. In this embodiment, a mixture material, i.e. the
composite material, for the oxide superconductor was charged in a
silver alloy pipe which is composed of silver with 1 wt % of
magnesium added and which is provided with a plurality of small
holes. Before the wire drawing by the die 5, the silver alloy pipe
was heated by the heater 8 to remove the gases including the
cracked gas, moisture, etc. discharged from the material, thus
producing the superconductor of the fifth embodiment. The silver
alloy pipe filled with the produced oxide superconductor was drawn
to a desired size by the die 5 before it was cooled to room
temperature. In this embodiment, ten different dies were used for
the wire drawing and the temperature was decreased from 500 to 100
degrees centigrade as the wire diameter decreased, then heat
treatment was carried out again by the heater 8. The atmosphere for
the heat treatment before and after the wire drawing by the dies 5
is selected according to the type of the superconductor employed.
The conditions for the heat treatment are set so that the oxide
superconductor is furnished with the best possible superconductive
characteristics by the heat treatment carried out before and after
the wire drawing carried out by the dies 5. In this embodiment, the
heat treatment was performed at 930 degrees centigrade.
[0054] After that, the wire formed by the drawing was heated by the
heating device 11 to melt the silver alloy on the surface. In this
embodiment, an electric furnace having a kanthal super wire as the
heating element was used as the heating device 11. After the melted
silver alloy was scattered in the oxide superconductor, the oxide
superconductor was cooled and the conductive material was formed on
the surface thereof by the thin film forming device 9. In this
embodiment, the conductive material was attached by passing the
wire through an aluminum melt in a crucible.
[0055] The superconducting wire according to the fifth embodiment
thus produced provided high resistance to mechanical deformation
and had a critical current density which is two orders of magnitude
larger than that of the superconducting wire with no silver alloy
melted and dispersed.
[0056] Sixth Embodiment
[0057] FIG. 2 shows the flow of the manufacturing method in
accordance with the present invention. First, a silver or silver
alloy flat tape is prepared and bent so that the cross-sectional
area thereof is U-shaped. Oxide superconductor powder or a material
mixture for the oxide superconductor powder is supplied to the
inner side of the U-shaped tape, then it is formed so that the
cross-sectional area is O-shaped. At this time, the both ends of
the silver or silver alloy tape may be in contact or overlapped or
they may even have a gap, provided the powder inside does not fall.
After that, the tape is subjected to wire drawing by appropriate
figuring. Heat treatment is performed before and after or during
the wire drawing as necessary. The wire is then led into the
crucible to melt the silver or silver alloy thereby to disperse the
silver or silver alloy in the superconductor, and the conductive
material, which serves as the stabilizer, is attached to the
surface of the superconductor. The melting of the silver or silver
alloy and the attaching of the conductive material may be done at
the same time or in succession; they were conducted at the same
time in the sixth embodiment.
[0058] FIG. 3 shows the principle for melting the silver or silver
alloy and attaching the conductive material at the same time.
Reference numeral 1 denotes the oxide superconductor powder charged
in the silver or silver alloy tape 3 which has been formed to have
the O-shaped cross section. Reference numeral 5 indicates the die.
The drawing shows only one cycle of process; however, a plurality
of dies may be used as necessary to implement a plurality of
regressive process cycles. Reference numeral 4 indicates the
material wire which has been formed into a desired shape by the
method stated above; the wire is led into the crucible 12 to let it
pass through the melt 6 of the conductive material. This causes the
silver or silver alloy on the surface of the superconductor to
melt. The majority of the melted silver or silver alloy moves into
the vacancies or the like in the superconductor although a part
thereof is mixed with the melt 6.
[0059] As a result, when the wire is pulled out of the crucible 12
holding the melt 6 of the conductive material, the conductive
material is applied to the surface of the wire. At this time, since
the melting point of the conductive material is higher than that of
the silver or the like, the conductive material solidifies first,
and then the silver or the silver alloy dispersed in the
superconductor solidifies. Thus, the silver or the silver alloy
dispersed and solidified in the oxide superconductor enables a
higher critical current density. Moreover, the vacancies in the
oxide superconductor and the recessed spots near the surface
thereof are also filled primarily with the melt of the silver or
the silver alloy, thus ensuring good adhesion of the conductive
material attached to the outer periphery of the oxide
superconductor. All steps including the step for making the silver
or silver alloy tape into a pipe and the step for supplying the
superconductor powder can be implemented in succession by using a
supplying reel and a winding reel (not illustrated in FIG. 3).
[0060] There is no particular restrictions on the combination of
the materials used in the present invention. In the sixth
embodiment, Y.sub.2O.sub.3, SrCO.sub.3, WO.sub.3, and CuO were
mixed so as to produce 10 wt % of SrY.sub.2O.sub.4 with respect to
YSr.sub.2Cu.sub.2.8W.sub.0.2O- .sub.y, then the mixture was
subjected to heat treatment at 950 to 1400 degrees centigrade to
produce the oxide superconductor. As the conductive material
wrapping around the oxide superconductor, Cu was used. The same
combination of the materials was employed for other embodiments as
well as the sixth embodiment to produce the superconducting
wire.
[0061] The superconducting wire of this embodiment obtained by
using the aforesaid materials and by melting and dispersing the
silver as described above exhibited a critical current density of
approximately 10,000 A/cm.sup.2 (5K). In contrast to this, the
critical current density, which was obtained when the same oxide
superconductor was employed but no silver was melted and dispersed,
was approximately 2,000 A/cm.sup.2, which is extremely smaller than
that of this embodiment.
[0062] Furthermore, the superconductive characteristics of the
superconducting wire in accordance with this embodiment remained
unchanged after winding the superconducting wire by the roller
having the 30cm diameter, whereas the comparison example, which had
no silver melted and dispersed, showed a drop in conductivity to
1/100 to 1/1,000 after winding the wire by the same roller. This
proves that the superconducting wire in accordance with the present
invention provides high mechanical strength and also high critical
current density.
[0063] Seventh Embodiment
[0064] FIG. 3 shows the conceptual diagram illustrative of the
process for melting the silver and attaching the conductive
material in the seventh embodiment. First, a silver sheath material
which has an oxide superconductor therein and which has been formed
into a pipe is processed into a fine line by a plurality of dies 5
(only one die is shown in FIG. 3). In this embodiment, the silver
sheath material measuring 8 mm in outside diameter and 6 mm in
inside diameter was formed into the fine line 4 having an outside
diameter of 0.8 mm. Reference numeral 6 denotes a copper melt in
the crucible 12 produced by melting copper by a heating device
which is not shown; the temperature of the melt is maintained at
1,090 degrees centigrade. The silver sheath material obtained as
stated above is placed in the copper melt 6 and let pass through
the copper melt 6. At this time, the majority of the silver is
melted and dispersed in the oxide superconductor although a part of
the silver mixes with the copper melt 6 since the melting point of
the silver is 960 degrees centigrade. Then, the wire is wound by a
roller, not shown, to take the wire, which has the copper attached
to the surface thereof, out of the crucible 12. The wire 10 taken
out of the crucible 12 starts solidifying from the outer periphery;
it is cooled until the solidification of the silver inside is
completed before the finished superconducting wire is wound using
the roller which is not shown. Oxygen may be blown into the melted
silver so that the oxide superconductor with oxygen reduced may
restore the superconductive characteristics. Heat treatment may be
performed again after the silver on the outer periphery
solidifies.
[0065] The critical current of the superconducting wire thus
produced was 10.sup.4 A/cm.sup.2 or more regardless of the
composition of the superconductor material used and no change in
the superconductive characteristics was observed even when the
diameter of the roller winding the superconducting wire was about
300 mm. A wire which has the same performance was obtained when a
silver tape with a hole having a diameter of 0.5 mm or less was
employed to make the superconducting wire in the same manner as
stated above.
[0066] When, however, the speed for winding the wire was too high
for the silver of the silver tape to fully melt, the critical
current of the resulting wire was about 10.sup.2 A/cm.sup.2 and the
observation of the cross section of the obtained wire revealed the
presence of a gap over the whole surface between the silver and the
superconductor. Such a gap was not observed in the superconducting
wire according to the present invention. This demonstrates that,
according to the present invention, the silver melts and fully
covers the irregular surface of the superconductor, thereby
ensuring close contact with the conductive material on the outer
periphery.
[0067] Eighth Embodiment
[0068] FIG. 4 is the conceptual diagram showing the manufacturing
method for the superconducting wire of the eight embodiment. First,
a silver tape with a hole of a diameter of about 0.1 mm to about
0.5 mm is formed into a U-shape by continuous rolling. The
materials for producing the superconductor are supplied to the
recessed section of the tape, then the tape is shaped into a pipe
by further rolling. The wire material is formed into a wire having
a diameter of 1 mm by the die 5. At this time, as shown in FIG. 4,
the silver pipe is heated before and after the die to make the
oxide superconductor. In general, a carbonate or nitrate, or an
oxide of a constituent metal element is used as the material for
making the oxide superconductor. The hole formed in the silver pipe
makes it possible to supply oxygen to the central part of the
silver pipe and also to discharge a gas such as carbon dioxide
which is generated when the e materials are decomposed. T thus,
according to this embodiment, a superconductor with good
characteristics can be produced by the heat treatment using the
heaters 8. The wire 4 thus obtained is placed in the crucible 12 to
let it go through the melted gold 6. The temperature of the gold
melt 6 is maintained at 1,065 to 1,080 degrees centigrade. Since
the melting point of silver is 960 degrees centigrade, the silver
melts and disperses in the oxide superconductor when the wire 4 is
passed through the gold melt 6. When the wire is pulled out of the
crucible 12, it has the gold on the surface thereof. The gold and
silver are partially mixed before they solidify; the mixing ratio
can be controlled by the time during which the wire is in contact
with the gold melt 6 and the winding speed.
[0069] The superconducting wire thus produced exhibits high
resistance to mechanical deformation; it can be produced in a
length of about 1,000 m even when the diameter of the roller 7 is
200 mm.
[0070] Ninth Embodiment
[0071] FIG. 5 is the conceptual diagram illustrative of the
manufacturing method for the superconducting wire of the ninth
embodiment. A tape made of an alloy of silver with 3 wt % of
palladium added is made into a pipe and an oxide superconductor is
charged therein, then the pipe is formed into a desired sheath wire
by using the die 5. The sheath wire is then heated by the heating
device 11 so as to melt the silver alloy. After the melted alloy
solidifies, the conductive material is formed on the surface of the
sheath wire by using the thin film forming device 9 to make the
superconducting wire. Any heating device may be used for the
heating device 11 as long as it is capable of heating the sheath
wire to a temperature at which the silver alloy is melted; infrared
rays were concentrated for the heat treatment in this embodiment.
Likewise, any device may be used for the thin film forming device 9
as long as it is capable of forming a conductive material of the
desired thickness; organopalladium was applied and subjected to
heat treatment to produce a palladium film in the ninth
embodiment.
[0072] The superconducting wire according to this embodiment thus
produced exhibits extremely good adhesion between the silver and
palladium, minimizing the chance of cracking or the like when the
wire is subjected to mechanical deformation. Further, the silver
and palladium dispersed in the superconductor caused the critical
current density to increase to a value which is two orders of
magnitude or more larger than the critical current density of the
superconducting wire with no dispersed silver alloy.
[0073] Tenth Embodiment
[0074] FIG. 6 is the conceptual diagram showing a part of the
manufacturing method for the superconducting wire according to the
tenth embodiment. In this embodiment, the oxide superconductor was
charged in a silver alloy tape, which is composed of silver with 1
wt % of magnesium added and which is provided with a plurality of
small holes, while shaping the tape into a pipe. Before the wire
drawing by the die 5, the silver alloy pipe was heated by the
heater 8 to remove the gases including the cracked gas, moisture,
etc. discharged from the material, thus producing the
superconductor. The silver alloy pipe filled with the produced
oxide superconductor was drawn to a desired size by the die 5
before it was cooled to room temperature. In the present invention,
the wire drawing was carried out at 500 to 100 degrees centigrade,
then heat treatment was implemented again by the heater 8. The
atmosphere for the heat treatment before and after the wire drawing
by the die 5 is selected according to the type of the
superconductor employed.
[0075] After that, the wire formed by the drawing was heated by the
heating device 11 to melt the silver alloy on the surface. In this
embodiment, the electric furnace employing the kanthal super wire
as the heating element was used as the heating device 11. After the
melted silver alloy was scattered in the oxide superconductor, the
oxide superconductor was cooled and the conductive material was
formed on the surface thereof by the thin film forming device 9. In
this embodiment, the conductive material was attached by passing
the wire through the aluminum melt in the crucible. The heat
treatment prior to the wire drawing step may be omitted if the
oxide superconductor powder is supplied to the silver alloy
tape.
[0076] The superconducting wire thus produced provided high
resistance to mechanical deformation and had a critical current
density which is two orders of magnitude larger than that of the
superconducting wire with no silver alloy melted and dispersed.
[0077] Thus, according to the present invention, there is provided
a highly reliable, practical superconducting wire which is capable
of fully displaying the characteristics of an oxide superconductor
employed for the superconducting wire without incurring a drop in
the critical temperature or the critical current during the
manufacturing process and which also provides high resistance to
mechanical deformation.
* * * * *