Stock material or miscellaneous articles – All metal or with adjacent metals – Laterally noncoextensive components
Reexamination Certificate
2001-05-04
2002-08-20
Dunn, Tom (Department: 1725)
Stock material or miscellaneous articles
All metal or with adjacent metals
Laterally noncoextensive components
C428S662000, C428S660000, C428S674000, C428S930000, C505S815000, C505S919000, C505S431000
Reexamination Certificate
active
06436554
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a precursor for producing an Nb
3
Sn compound superconducting wire used for a high magnetic field superconducting magnet, a method for producing the precursor, and a method for producing an Nb
3
Sn compound superconducting wire.
FIG. 9
is a sectional view of a precursor for producing an Nb
3
Sn compound superconducting wire by a conventional internal tin diffusion method, and
FIG. 10
is a sectional view of a compound superconducting wire produced from the precursor by heat treatment. For example, the precursor and the compound superconducting wire are disclosed in JP-A-57-82911.
In
FIG. 9
, the reference numeral
17
designates an Nb
3
Sn compound superconducting wire precursor before heat treatment (hereinafter referred to as “precursor”). The precursor
17
is composed of filaments
18
of a niobium(Nb)-base metal which will be made superconductive by heat treatment, a matrix
19
of a copper(Cu)-base metal for embedding the filaments
18
, a barrier material
5
of tantalum (Ta) provided on the outer circumference of the matrix
19
, a stabilizing material
6
of oxygen-free copper provided on the outer circumference of the barrier material
5
, and a tin-base core
20
of an Sn—2%Ti alloy material embedded in the center portion of the matrix
19
.
In
FIG. 10
, the reference numeral
21
designates an Nb
3
Sn compound superconducting wire after heat treatment (hereinafter referred to as “compound superconducting wires”). The compound superconducting wire
21
is composed of superconducting filaments
22
of Nb
3
Sn produced by heat treatment, a matrix
23
of a Cu-base metal for embedding the superconducting filaments
22
, a barrier material
5
provided on the outer circumference of the matrix
23
, and a stabilizing material
6
of oxygen-free copper provided on the outer circumference of the barrier material
5
. The matrix
23
is provided as low-concentration Sn bronze because Sn in the tin-base core
20
is diffused at the time of heat treatment,
The precursor
17
shown in
FIG. 9
is produced as follows.
First, an Nb rod is inserted in a Cu pipe and the section of the Cu pipe is reduced to a predetermined size, so that a filament material of Cu-coated Nb wire is formed. The filament material is cut into a suitable length to form a large number of filament materials. A billet of Cu is filled with the large number of filament materials. A rod of Cu is arranged or a large number of Cu wires are arranged in advance in the center portion of the billet. The billet is evacuated, sealed with a cover, and then subjected to extruding. Then, a hole is mechanically formed in the center of the billet to form a hollow portion. A tin-base core material of Sn—2%Ti alloy in inserted in the hollow portion. The outside of the billet subjected to extruding is coated with a Ta pipe and with a Cu pipe successively. Further, the section of the whole is reduced, to a predetermined size. Thus, a precursor
17
shown in
FIG. 9
is produced. Incidentally, in order to make the current capacity high, the section of a Cu pipe filled with a large member of such precursors
17
may be reduced.
The precursor
17
produced as described above is twisted, and then subjected to preheat treatment and final heat treatment (generally, at a temperature in a range of from 600° C. to 800° C.) to thereby obtain the compound superconducting wire
21
shown in FIG.
10
.
By the final heat treatment, Sn in the tin-base core
20
of Sn—2%Ti alloy in the precursor
17
shown in
FIG. 9
is diffused into the ambient matrix material
19
to change the matrix
19
into a Cu—Sn alloy and, further, Sn reacts with the filaments
18
to generate Nb
3
Sn in the surfaces of the filaments
19
or in all the filaments
18
. Thus, the superconducting filaments
22
shown in
FIG. 10
are produced.
The compound superconducting wire
21
according to the internal tin diffusion method an shown in
FIG. 10
has a structure in which superconducting filaments
22
of Nb
3
Sn generated by heat treatment are embedded in the matrix
23
as densely a possible while being prevented from being in contact with one another in order to increase as large as possible, the critical current density (Jc) which is ong of superconducting properties.
Further, in order to improve the Jc property in a high magnetic field through improvement of an upper critical magnetic field which is one of the superconducting properties, Ti is added to the superconducting filaments
22
of Nb
3
Sn. There are various methods for adding Ti as follows.
In an internal tin diffusion method, employed are a method of adding Ti as an alloy to a tin-base core
20
as shown in
FIG. 8
(JP-A-62-174354), a method of adding Ti as an alloy to filaments
18
shown in
FIG. 8
(JP-A-60-170113), and a method in which both the two methods mentioned above are used in combination.
In a so-called bronze method using a precursor which is configured such that an Nb-base metal material is embedded in the matrix
19
provided as a Cu—Sn alloy, employed are a method of adding Ti as an alloy to filaments
18
(JP-A-57-54260), and a method of adding Ti as an alloy to the matrix
19
(JP-A-58-23110).
In a so-called jelly roll method using a precursor which is configured such that rolls of Nb foil used instead of the Nb rods are embedded in the matrix
19
, employed is a method of adding Ti as an alloy to the Nb foil (PCT Application: PCT/US 90/054/08).
The methods of adding Ti as an alloy in the conventional internal tin diffusion method, bronze method, and jelly roll method have the following problems (1) to (6) in production and use of the alloy.
(1) It is difficult to produce a Ti-added alloy because of generation of a Ti intermetallic compound or work-hardening. Accordingly, a good-quality alloy material free from breaking cannot be obtained.
(2) When any other metal such as Mn, etc. than Ti is added simultaneously with Ti, an intermetallic compound is generated to make it difficult to process a Ti-added alloy.
(3) In production (vacuum melting) of a Ti-added alloy, oxygen impurities such as Ti oxide, etc. increase because the vapor pressure of Ti is so high that the degree of vacuum at the time of vacuum melting cannot be increased. Accordingly, the superconducting property of the superconducting filaments
22
is worsened by the oxygen impurities.
(4) In production of a Ti-added Sn alloy, the size of the Ti intermetallic compound varies in accordance with the cooling speed. Accordingly, when the size of the Ti intermetallic compound is large, Jc in the superconducting filaments
22
varies.
(5) The cost for production of a Ti-added Nb alloy increases because vacuum melting is required.
(6) In the internal tin diffusion method, the tin-base core
20
of Sn—Ti is emedded in the center portion of the matrix
19
. Accordingly, in preheat treatment for diffusing Sn and Ti, the concentration gradient of Ti is generated between the inner and outer arrays of filaments
18
. After final heat treatment, the outer array of filaments
18
are inferior in Jc property to the inner array of filaments
18
and lower in n-value which is one of the superconducting properties (the n-value is an index for indicating uniformity in the longitudinal direction of a superconducting wire, that is, the superconducting property becomes excellent as the n-value increases).
SUMMARY OF THE INVENTION
The present invention is designed to solve the aforementioned problems and an object thereof is to provide an Nb
3
Sn compound superconducting wire in which Ti can be added to superconducting filaments without using an Sn—Ti alloy, a Cu—Ti alloy, a Cu—Sn—Ti alloy or an Nb—Ti alloy as a conventional Ti-added alloy to thereby attain easy production, low cost, stable quality and improvement in superconducting properties Jc and n-value, that is, to provide a compound superconducting wire precursor, a method for producing the same, and a method for producing a compound superconducting wire.
In order to achieve the above object, according to an aspect of the p
Cooke Colleen P.
Dunn Tom
Leydig & Voit & Mayer
Mitsubishi Denki & Kabushiki Kaisha
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