JPH01290730A - High purity oxygen-free copper and its application - Google Patents

Abstract

PURPOSE:To obtain the title copper having low electric resistance and excellent workability at extra low temp. by regulating from impurities, oxygen impurities and other inevitable impurities to the optimum amounts. CONSTITUTION:Iron impurities and oxygen impurities are independently regulat ed to <=1ppm and <=5ppm and the total of other inevitable impurities is regulat ed to <=10ppm to obtain high purity oxygen-free copper having <=2X10<-9>OMEGA.cm electric resistance of <=20K. The high purity oxygen-free copper furthermore has excellent heat conductivity and workability as well as electric resistance at extra low temp. and in the magnetic field. In this way, the high purity oxygen-free copper is suitable as a stabilizing material for a super conductive body used for manufacturing a super conductive magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to high-purity oxygen-free copper and its uses, and particularly to high-purity oxygen-free copper suitable as a stabilizing material for copper-coated superconducting conductors.

[Prior art] Superconducting wires that are in practical use, such as Nb-Tl and Nb
Superconducting wires such as 3Sn-based wires are compositely integrated with high-purity copper or aluminum to prevent the wires from burning out when the superconducting body collapses.

The stability of the superconducting wire increases as the electrical resistance of this superconducting stabilizing material decreases in the cryogenic region below 20°C, so it is desirable that the electrical resistance in the cryogenic temperature range be as low as possible.

However, even if high-purity copper contains iron impurities of 2 to 3 pp- or more, it tends to increase the electrical resistance at extremely low temperatures. Therefore, in recent years, there has been a demand for higher purity copper with less iron impurities.

[Problem to be Solved by the Invention 1] As stated above, conventional high-purity oxygen-free copper and its uses contain iron impurities of 2 to 3 ppm or more, and therefore have low electrical resistance at extremely low temperatures. This has the disadvantage of increasing the

[Means for Solving the Problems] The present invention has been made in view of the above, and in order to suppress the increase in electrical resistance at extremely low temperatures, iron impurities are reduced to 1 ppm or less and plastic workability is improved. Oxygen impurities for 5
ppm or less, and the total amount of other unavoidable impurities such as silver is 10 pI) or less.

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 extremely low temperatures. Therefore, its amount is limited to 1 ppm or less.

(2) Oxygen As this impurity increases, when it is combined into a superconducting wire such as Cu/Nb-Tl, its plastic workability deteriorates. Therefore, its amount is limited to 5 ppm or less.

(3) Other inevitable impurities In this case, silver is the main component. Although silver is not as strong as iron, it increases electrical resistance at extremely low temperatures. Therefore, it is desirable that the amount of other unavoidable impurities including silver is also small.
Limited to 10 pp■ or less.

Reducing these unavoidable impurities to 2 ppm or less may lead to higher costs, so it is desirable to reduce the amount to 2 to t.
ops range.

Applications of this high-purity oxygen-free copper include stabilizing materials for superconducting wires, ultra-low-temperature heat-conducting materials, etc.

[Function] By controlling the impurities to 1 ppm or less of iron, 5 ppm or less of oxygen, and 10 ppm or less of other substances, the electrical resistance at extremely low temperatures becomes small and the workability becomes excellent. Therefore, it can be widely used as a stabilizing material for superconducting wires.

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

Example 1 Electrolytic copper containing 0.05 ppm of iron impurities and a total of 3 ppm of other unavoidable impurities such as silver was used, and sufficient care was taken to prevent iron impurities from getting mixed in using fully continuous melting and casting equipment. A billet of φ 275 was cast from.

The impurity in the obtained billet was 0.5 ppm iron.
.

Oxygen: 2 ppm% Other unavoidable impurities such as silver: 5
Although the amount of impurities increased slightly to ppm, the high purity of electrolytic copper was not lost.

This billet was subjected to processing such as hot extrusion, intermediate annealing, and wire drawing to obtain a diameter of 1.0. Add this to 250'CX 3
After heating in a non-oxidizing atmosphere, the electrical resistance was measured in liquid helium in step 4.2 using the four-terminal method. As a result, the specific resistance (ρ) at 4.2 is 1.40X 1O
-9Ω·cm.

An oxygen-free copper sample containing 2 ppm of iron was prepared using the same electrical steel, and its specific resistance was measured.

p (at 4.2K) = 2.85X10-”ΩI(
Jll, and the material of the present invention is approximately 1/2 that of the conventional material, which indicates that it has a large effect of reducing iron impurities.

Example 2 The billet of φ 275 obtained in Example 1 was processed into a steel pipe with an outer diameter of about 10 On+m and a wall thickness of about 20 mm by hot extrusion, and then cold expansion drawing and annealing were repeated to obtain an outer diameter of 140 mm.
A large diameter steel pipe with a wall thickness of 10 mm and a wall thickness of 10 mm was obtained. A superconducting material of Nb-46, 5vt%Ti with an outer diameter of 118 mm is inserted into this steel pipe to form a billet for hydrostatic extrusion, and this billet is extruded and cold drawn to produce so-called Cu/Nb-Tl.
It was made into a composite single line. A plurality of these single wires were inserted into a large-diameter copper tube produced in the same manner as above to obtain a billet for extruding multi-superconducting wires. This billet is extruded, cold drawn,
A superconducting wire having an outer diameter of 1.2+am, a copper ratio of 2.0, and an Nb-Ti filament diameter of 20 μm and 1200 filaments was obtained by aging heat treatment.

This superconducting wire was heated at 250° C. for 3 hrs to soften the stabilizing copper portion without deteriorating the superconducting properties, and then the electrical resistance of the superconducting wire at extremely low temperatures was measured. As a result, the specific resistance (at 4.2K) of the obtained superconducting wire was 2. IX 10 = Ω' (m. On the other hand, that of the superconducting wire in which oxygen-free steel containing 2 ppm of iron impurities was applied as a stabilizing material was 4.3X lo = Ω・cm, which indicates that the material of the present invention has a significant The properties did not change even in composite materials.

Also, assuming a superconducting magnet, in 4.2, 5T
(Tesla) electrical resistance was also determined to be 1411J. As a result, the present invention material was found to be 2. IX 10-8 Ω" cm, and the conventional material was 2.5 x 10-8 Ω. Although the effect is weaker than in zero magnetic field, it is smaller by more than 2°5.

Note that the same effect can be expected even when the stabilized copper for superconducting wire of the present invention is applied to a Nb3Sn wire produced by the so-called bronze method.

In addition, when applied to Cu/Nb-Tlm metal core wire, especially when the filament diameter is 108 m or less, the reaction between Cu and Nb-Ti becomes intense during aging heat treatment, and Nb-
Particularly Ti in Ti contaminates Cu, which may reduce the effect of the present invention. In order to prevent this, the cross-sectional structure of the single wire should be changed to Cu/Nb/Nb-Ti SCu/
V/Nb-Ti or Cu/Ta/Nb-Tl, etc., and it is desirable to use Nb, V, or Ta as a reaction-suppressing diffusion barrier between Cu and Ti.

Furthermore, since the oxygen-free copper of the present invention has high thermal conductivity at extremely low temperatures, it is also effective as a heat transfer material for extremely low temperatures.

[Effects of the Invention] As explained above, the present invention provides a stable superconducting wire that has excellent electrical resistance and thermal conductivity at extremely low temperatures and in a magnetic field by reducing impurities, and has excellent workability. It has the advantage of providing highly pure oxygen-free copper suitable for chemical processing.

Agent: Patent attorney 1: Buddha Fujime

Claims (3)

[Claims] (1) Iron impurities and oxygen impurities are 1 ppm or less and 5 ppm or less by weight, respectively, and the total amount of other unavoidable impurities is 10 ppm or less, and the electrical resistance at 20K or less is 2 x 10^-^9 Ω・cm or less. High purity oxygen-free copper characterized by: (2) A superconducting conductor characterized in that the high purity oxygen-free copper described in item 1 is used as a stabilizing material. (3) A superconducting magnet characterized in that the superconducting conductor described in item 2 is used in a coil.