JP2574390B2 - High-purity oxygen-free copper and its uses - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to high-purity oxygen-free copper and uses thereof, and more particularly to high-purity oxygen-free copper suitable as a stabilizer for a copper-coated superconductor.

[Prior Art] Practical superconducting wires such as Nb-Ti and Nb ₃ Sn
The superconducting wire of the system or the like is integrated with high-purity copper or aluminum to prevent burning of the wire when the superconducting body collapses.

Since the stability of the superconducting wire of the superconducting stabilizer becomes smaller as the electric resistance in a cryogenic temperature region of 20 K or less becomes smaller, it is desirable that the electric resistance at a cryogenic temperature be as small as possible.
However, even in the case of high-purity copper, when iron impurities are contained in an amount of 2 to 3 ppm or more, the electric resistance at an extremely low temperature tends to increase. Therefore, recently, copper having a higher purity with less iron impurities has been required.

[Problems to be Solved by the Invention] As described above, according to the conventional high-purity oxygen-free copper and its use, since it contains iron impurities of 2 to 3 ppm or more,
There is a disadvantage that the electric resistance at a very low temperature is increased.

[Means for Solving the Problems] The present invention has been made in view of the above, and has been made to reduce the amount of iron impurities to 1 ppm or less in order to suppress an increase in electric resistance at extremely low temperatures, and to improve plastic workability. In addition, oxygen impurities are reduced to 5 ppm or less, and other unavoidable impurities including silver are reduced to 10 ppm or less in total.

That is, the high-purity oxygen-free copper of the present invention has the following configuration.

(1) Iron This impurity increases the electrical resistance at cryogenic temperatures with its increase. Therefore, its amount is limited to 1 ppm or less.

(2) Oxygen With the increase of these impurities, when they are combined with a superconducting wire such as Cu / Nb-Ti, the plastic workability is deteriorated.
Therefore, its amount is limited to 5 ppm or less.

(3) Other unavoidable impurities In this case, silver is the main component. Silver, although not as much as iron, increases its electrical resistance at cryogenic temperatures. Therefore, the amount of other unavoidable impurities including silver is desirably small, and is limited to 10 ppm or less.

Since reducing these unavoidable impurities to 2 ppm or less may increase the cost, preferably 2 to 10 ppm
Range.

Applications of this high-purity oxygen-free copper include a superconducting wire stabilizer, a cryogenic thermal conductive material, and the like.

[Action] Impurities, iron 1ppm or less, oxygen 5ppm or less, other 10ppm
By setting the content as described below, the electric resistance at an extremely low temperature is reduced, and the workability is also excellent. Therefore, it can be widely used as a stabilizing material for superconducting wires.

[Examples] Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 Iron copper containing 0.05 ppm of iron impurities and a total of 3 ppm of unavoidable impurities such as silver was used.
275 billets were cast. Impurities in the obtained billet, iron 0.5ppm, oxygen 2ppm, the total amount of other unavoidable impurities such as silver was 5ppm, the impurity amount was slightly increased,
The high purity of the electrolytic copper was not lost.

This billet was subjected to processing such as hot extrusion, intermediate annealing, drawing and drawing to obtain φ1.0. This was further heated in a non-oxidizing atmosphere at 250 ° C. × 3 hrs, and then the electric resistance was measured by a four-terminal method in 4.2 K of liquid helium. As a result, the specific resistance (ρ) at 4.2 K was 1.40 × 10 ⁻⁹ Ω · cm.

An oxygen-free copper sample of 2 ppm iron was prepared using the same electrolytic copper, and its specific resistance was measured. As a result, ρ (at 4.2 K) was 2.85 × 10 ⁻⁹ Ω · cm. It is about 1/2, indicating that the effect of reducing iron impurities is large.

Example 2 After processing the billet of φ275 obtained in Example 1 into a copper tube having an outer diameter of about 100 mm and a wall thickness of about 20 mm by hot extrusion, cold expanding and drawing and annealing were repeated to obtain an outer diameter of 140 mm. 10mm thickness
Was obtained. Nb-46.5wt with 118mm outside diameter
% Ti superconducting material is inserted into a billet for hydrostatic extrusion,
This billet is extruded and cold drawn to form a so-called Cu
/ Nb-Ti composite single wire. A plurality of the single wires were inserted into a large-diameter copper tube manufactured in the same manner as above to obtain a billet for extruding a multi-superconducting wire. The billet was subjected to extrusion, cold drawing, and aging heat treatment to obtain a superconducting wire having an outer diameter of 1.2 mm, a copper ratio of 2.0, an Nb-Ti filament diameter of 20 μm, and a number of filaments of 1200.

After heating the superconducting wire at 250 ° C. × 3 hrs, at which the stabilized copper portion softens without deteriorating the superconducting characteristics, the electric resistance of the superconducting wire at a cryogenic temperature was measured. as a result,
The specific resistance (at4.2K) of the obtained superconducting wire is 2.1 × 10 ^-9 Ω · c
m. On the other hand, that of superconducting wire using oxygen-free copper containing 2 ppm of iron impurities as a stabilizing material is 4.3 × 10 ^-9 Ω
Cm, and the significance of the material of the present invention was not changed in the composite material.

Assuming a superconducting magnet, the electrical resistance at 4.2K and 5T (tesla) was also measured. As a result, the material of the present invention is 2.
1 × 10 ⁻⁸ Ω · cm and 2.5 × 10 ⁻⁸ Ω · cm for the conventional material, the effect is weaker than in a zero magnetic field, but is reduced by more than 20%.

The same effect can be expected when the stabilized copper for a superconducting wire of the present invention is applied to an Nb ₃ Sn wire produced by a so-called bronze method.

In addition, when applied to a Cu / Nb-Ti composite multifilamentary wire, particularly when the filament diameter is 10 μm or less, it is not possible to form Cu and
There is a possibility that the reaction between Nb-Ti becomes violent, and particularly Ti in Nb-Ti contaminates Cu, and the effect of the present invention is weakened. In order to prevent this, the cross-sectional structure of the single wire should be Cu / Nb / Nb-T
i, Cu / V / Nb-Ti or Cu / Ta / Nb-Ti etc., Nb, V or Ta
Is desirably a diffusion barrier for suppressing the reaction between Cu and Ti.

Further, the oxygen-free copper of the present invention has a high thermal conductivity at cryogenic temperatures, and thus is effective as a cryogenic heat transfer material.

[Effects of the Invention] As described above, according to the present invention, by reducing impurities, the stability for superconducting wires excellent in electric resistance and thermal conductivity at cryogenic temperatures and in a magnetic field and also excellent in workability is obtained. There is an advantage that high-purity oxygen-free copper suitable for a chemical material can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuji Sakai 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Inside the Metal Research Laboratory, Hitachi Cable, Ltd. (72) Kazuo Sugaya 3550 Kida Yomachi, Tsuchiura City, Ibaraki Hitachi Line Inside the Tsuchiura Plant Co., Ltd. (72) Inventor Yutaka Ouchi 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Inside the Tsuchiura Plant Hitachi Cable Co., Ltd. (56) References JP-A-62-111455 (JP, A) JP-A-60 -62009 (JP, A) JP-A-56-133963 (JP, A)

Claims (3)

(57) [Claims] An iron impurity and an oxygen impurity are each 1 ppm by weight.
Not more than 5 ppm, and the total of unavoidable impurities including silver is 10 ppm or less, and the electric resistance of 20K or less is 2 × 10 ⁻⁹ Ω.
-High purity oxygen-free copper characterized by being less than cm. 2. An iron impurity and an oxygen impurity each containing 1 ppm by weight.
Not more than 5 ppm, and the total of unavoidable impurities including silver is 10 ppm or less, and the electric resistance of 20K or less is 2 × 10 ⁻⁹ Ω.
-A superconducting conductor characterized by using high-purity oxygen-free copper having a size of not more than cm as a stabilizer. 3. An iron impurity and an oxygen impurity each containing 1 ppm by weight.
Not more than 5 ppm, and the total of unavoidable impurities including silver is 10 ppm or less, and the electric resistance of 20K or less is 2 × 10 ⁻⁹ Ω.
-A superconducting magnet characterized in that a superconducting conductor using high-purity oxygen-free copper of less than cm as a stabilizer is used for the coil.