Method of producing oxide superconductor

Details Method of producing oxide superconductor Method of producing oxide superconductor

1996-11-12

2001-08-21

Arbes, Carl J. (Department: 3729)

Metal working

Method of mechanical manufacture

Electrical device making

C505S121000, C505S782000

Reexamination Certificate

active

06276048

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention p The present invention relates to a method of producing a Bi—Pb—Sr—Ca—Cu oxide superconductor, and more particularly, it relates to an improvement for attaining high critical current density.
2. Description of the Background Art
A specific material exhibits diamagnetism under a superconducting phenomenon such that no potential difference is developed although a finite stationary current flows in its interior.
This superconducting phenomenon is applied to an extremely wide range of fields such as that of electric power including MHD power generation, power transmission and magnetic energy storage and that of transportation including a magnetic levitation train and an electromagnetically thrust ship. Further, a high-sensitive sensor for a magnetic field, a high frequency, radiation or the like utilizing the superconducting phenomenon is applied to the field of measurement, and also superconductors are used in the field of nuclear magnetic resonance (NMR), &mgr;-meson remedy and a high energy physical experimental apparatus, while the superconducting phenomenon is also expected in the field of electronics, represented by the Josephson device, as a technique which can not only reduce power consumption but implement an element of extremely high-speed operation.
Superconductivity was until recently only observed under a very low temperature. Even Nb
3
Ge, which has been referred to as that having the highest critical temperature T
c
of superconductivity within conventional superconducting materials, has an extremely low critical temperature of 23.2 K and this value has been regarded as the limit critical temperature of superconduction for a long period of time.
Therefore, a superconducting material has been generally cooled to a temperature below the aforementioned critical temperature with liquid helium which boils at 4.2 K, in order to implement a superconducting phenomenon. However, such employment of liquid helium leadsto technical and economic burdens due to cooling equipment including liquefaction equipment, to hinder implementation of the technique of superconductivity.
On the other hand, it has been recently reported that a composite oxide sintered body can show superconductivity at a high critical temperature, and development of the technique of superconduction is abruptly being prompted with a superconductor whose critical temperature is not very low. It has been reported and recognized that a Y—Ba—Cu—O material superconducts at 90 K while Bi—Sr—Ca—Cu—O and Bi—Pb—Sr—Ca—Cu—O materials superconduct at 110 K respectively.
Liquid nitrogen is relatively easily obtainable at a low cost, and in fact, development of the technique of superconduction has been greatly advanced with discovery of a superconducting material which operates at the temperature of liquid nitrogen.
However, not only the critical temperature but current density is an important matter of concern for a superconducting magnet, a wiring member for a device, a power cable or the like in practice, such that current density of at least. 1000 A/cm
2
must be attained. When the superconductor is elongated, further, such current density must be substantially uniformly attained over the longitudinal direction of the elongated superconductor. The critical temperature can be increased by using a Bi superconductor or a superconductor containing Bi which is partially replaced by Pb in particular, while current density of such a Bi superconductor is 100 to 200 A/cm
2
at the most. In practice, however, the current density must be ten times or more, while such high current density must be substantially uniformly attained over the longitudinal direction of the elongated superconducting material.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing an oxide superconductor which superconducts under a temperature of at least 100 K, by far exceeding the temperature of liquid nitrogen, while exhibiting high current density.
The present invention provides a method of producing an oxide superconductor of Bi—Pb—Sr—Ca—Cu by thermally treating raw material, which method comprises a step of performing first plastic deformation on the raw material, a step of performing first heat treatment on the material subjected to the first plastic deformation, a step of performing second plastic deformation on the material subjected to the first heat treatment and a step of performing second heat treatment on the material subjected to the second plastic deformation.
FIG. 1
is a flow chart showing the inventive producing method. According to the present invention, raw material is successively subjected to first plastic deformation, first heat treatment, second plastic deformation and second heat treatment as shown in FIG.
1
.
According to the present invention, the second plastic deformation is performed after the first heat treatment, thereby to arrange orientation of superconducting phases generated by the first heat treatment. Then the second heat treatment is performed to strengthen bonding between the oriented superconducting phases, thereby to obtain an oxide superconductor having high critical current density.
According to the present invention, the raw material is preferably charged in a metal sheath to be subjected to the first plastic deformation, the first heat treatment, the second plastic deformation and the second heat treatment. However, it is not necessarily required to charge the raw material in the metal sheath. The first plastic deformation may be directly performed on raw material which is a compact of powder in a bulk state. Furthermore, the raw material may be sandwiched between metal plates. According to the present invention, the raw material may be mixed with metal powder or other oxide powder.
For example, the Bi—Pb—Sr—Ca—Cu oxide superconductor produced according to the present invention is composed of:
Bi
z
1
−x
Pb
x
Sr
z
3
Ca
z
3
Cu
y
where x, y, z
1
, z
2
and z
3
represent numbers satisfying 0.2 ≦×0.8, 1.5 ≦z
1
, z
2
, z
3
≦3.0 and 2.5 ≦y≦4.5, and oxygen.
More preferably, the inventive oxide superconductor is composed of:
Bi
a
Pb
b
Sr
c
Ca
d
Cu
e
where a, b, c, d and e represent numbers satisfying a+b :c:d:e=1.7 to 2.8:1.7 to 2.5:1.7 to 2.8: 3, and oxygen.
According to the present invention, “raw material” includes not only powder obtained by mixing compounds containing respective elements to be in prescribed composition ratios but that prepared by calcinating and sintering such mixed powder for desired times and pulverizing the same.
Therefore, either raw material powder obtained by mixing compounds each containing at least one of the respective elements or that prepared from powder simultaneously containing the said elements can be employed. Such powder maybe prepared from oxide, carbonate, sulfate, nitrate or oxalate, while a mixture thereof is also employable. The particle size may be several micrometers to 1 &mgr;m, or below 1 &mgr;m.
The metal sheath is preferably formed of silver or silver alloy, in view of permeation of oxygen and workability. However, the advantage effect of the present invention can be effectively obtained even if no metal sheath is employed or a different type of metal sheath is employed.
Examples of the first plastic deformation and the second plastic deformation performed in the present. invention may be rolling, pressing, wire drawing and the like.
According to a first embodiment of the present invention, the second plastic deformation is at least 10% in reduction of area, while the first heat treatment and the second heat treatment are carried out within a temperature range of 780 to 860° C.
The first embodiment comprises a step of performing first plastic deformation on raw material, a step of performing first heat treatment on the material subjected to the first plastic deformation within a temperature range of 780 to 860° C., a step of performing second plastic deformation of at least 10% in reduction of area on the material subjected to the firs

Affiliated with

Also associated with

Rating

Method of producing oxide superconductor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of producing oxide superconductor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing oxide superconductor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2507574