JPS6241303B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cryogenic copper conductor with excellent conductivity at cryogenic temperatures and a method for manufacturing the same. Note that the extremely low temperature referred to here refers to a temperature of approximately -150° C. or lower, such as the temperature of liquid helium or liquid nitrogen. In recent years, conductors with excellent electrical conductivity at extremely low temperatures, such as stabilizers for superconducting materials, are often required. Generally, when impurities are dissolved in a metal, the electrical resistance is higher than that of a pure metal, and the conductivity is impaired.
In addition, even if the amount of impurities is small and has almost no effect on conductivity at room temperature, the contribution of thermal vibration to electrical resistance becomes extremely small at extremely low temperatures, so impurities affect conductivity. The degree of influence is likely to be very large. In addition, especially when the copper conductor is oxygen-free, the impurities contained therein are not precipitated as oxides, so there is a problem that the impurities are more likely to impair conductivity at extremely low temperatures. -ing For this reason, ordinary conductive copper materials use raw materials that have undergone electrolytic refining and have a fairly low amount of impurities, but even then, trace amounts of impurities may still be mixed in or remain, resulting in poor conductivity at low temperatures. This often resulted in harm. As a means to improve conductivity at low temperatures and to further reduce the amount of impurities than ordinary electrolytic copper, ordinary electrolytic copper must be refined by electrolytic refining or so-called zone melting. However, the raw materials obtained by these purification methods are expensive and therefore industrially difficult. Furthermore, even if such particularly high-purity raw materials were used, the desired effect would not be obtained due to impurities such as S and Fe mixed in during manufacturing processes such as melting and casting. In contrast, the present invention was developed as a result of various studies on improving the conductivity of copper conductors at extremely low temperatures using raw materials containing trace amounts of impurities that were electrolytically refined using industrially available ordinary methods. With this, it is intended to easily provide conductors for cryogenic temperatures. That is, the cryogenic copper conductor of the present invention contains Pb5 to 40ppm.
It is characterized in that it contains almost no oxygen, or if it does contain it, it is less than 500 ppm, and the remainder consists essentially of Cu. The S content as an impurity in this copper conductor is preferably 30 ppm or less. Further, it is desirable that the total content of impurities including S is 100 ppm or less. Furthermore, the present invention provides that in the manufacturing process for obtaining the copper conductor as described above, after hot treatment of the material, before processing into a desired shape and/or after processing, at least once at 450 to 750°C for 30 minutes. It is characterized in that it is heated and maintained for the above period. The reason why Pb is defined as 5 to 40 ppm in the present invention is that less than 5 ppm has little effect on improving conductivity at extremely low temperatures, and adding 40 ppm or more does not result in any better improvement, and on the contrary, Pb This is because there is a risk of impairing the hot workability of the material. In addition, in the present invention, the content of S as an impurity is
The reason why the total content of impurities excluding Pb, Ag, and O ₂ is set to be 30 ppm or less and 100 ppm or less is that the present invention aims to use raw materials with purity that can be easily obtained industrially. , at this time S
contains more than 30ppm, Pb, Ag, O ₂
This is because if the total content of impurities excluding Pb exceeds 100 ppm, excellent conductivity at extremely low temperatures can no longer be expected even if Pb is added within the above range to the raw material. In the present invention, the amount of O ₂ and Ag is excluded from the total content of impurities because the presence of both elements hardly affects the conductivity at low temperatures. Therefore, in order to obtain the cryogenic copper conductor according to the present invention, in addition to oxygen-free copper, 200 to 500 ppm of copper is used as raw material.
Toughpitch copper containing O ₂ can also be used. Next, using a Cu material containing Pb and impurities within the above range, it is processed into the desired shape after normal heat treatment. The reason for specifying the range is that it takes an extremely long time to improve conductivity at extremely low temperatures below 450℃, and
This is because at temperatures exceeding 750°C, the amount of solid solution of added Pb increases, which may conversely impair conductivity at extremely low temperatures. The time for maintaining this heating temperature may be 30 minutes or more. The present invention will be explained in detail below with reference to Examples. Example 1 Fe6ppm, Ni3ppm, as main impurities
Electrolytic copper containing less than 1 ppm of Ag16ppm, S5ppm, and other elements is dissolved in a protective atmosphere, and an appropriate amount of Pb is added to the solution so that the final product contains Pb in the range of 5 to 40 ppm. An oxygen-free copper ingot was obtained by continuous casting. This ingot was hot rolled into a rough drawn wire of 8 mm diameter, and further cold wire drawn to obtain a copper conductor of 2.6 mm diameter. Next, this copper conductor was heated and held in a vacuum at 600°C for 10 hours to obtain a copper conductor for cryogenic use. The electrical resistance of the thus obtained cryogenic copper conductors with different Pb contents at room temperature and liquid helium temperature (-269°C) was measured, and the electrical resistance ratio (R ₂₉₃ /R _4.2 ) _was found. The results shown in Table 1 were obtained. The electrical resistance ratio (R ₂₉₃ / _{R 4.2} ) is expressed as the electrical resistance value at room temperature/the electrical resistance value at liquid helium temperature, and is often used as a measure of conductivity at extremely low temperatures. The higher the value, the better the conductivity at extremely low temperatures.

【table】

[Table] From Table 1 above, the copper conductor of the present invention is the comparative example (No.
Compared to the conventional copper conductor shown in No. 6 and No. 7), the electrical resistance at cryogenic temperatures is smaller (R ₂₉₃ /R _4.2 is _larger ), and the copper conductor using high-purity copper in Comparative Example 9 It was found that the conductivity at low temperatures was improved to near the value of the electrical resistance ratio. Furthermore, when the Pb content in the copper conductor is less than 5 ppm, the effect of Pb inclusion is insufficient (Comparative Examples 6 and 7), and even when using 40 ppm or more as in Comparative Example 8, there is no effect on electrical resistance at low temperatures. The above improvement effect was not observed, and on the contrary, hot workability worsened. Example 2 Electrolytic copper with different impurity contents as shown in Table 2 was melted in the atmosphere, Pb was added thereto, and then cast to obtain a copper ingot with an oxygen content of approximately 200 to 300 ppm. . This was drawn in the same manner as in Example 1,
A copper conductor with a diameter of 1.8 mm was obtained. Next, this copper casting was 650
A cryogenic copper conductor was obtained by heating and holding at ℃ for 8 hours. The electrical resistance ratios of the obtained copper conductors were measured in the same manner as in Example 1 and were as shown in Table 2.

【table】

[Table] From the above table, it was demonstrated that the copper conductor of the present invention is extremely effective in improving conductivity at low temperatures within the range of impurity amounts mentioned above. On the other hand, when the amount of impurities exceeds a certain amount and is contained in a large amount as in Comparative Examples No. 6 and 7, even the addition of Pb has little effect on improving conductivity at extremely low temperatures. I couldn't see it. Example 3 Impurities: Fe4ppm, Sn6ppm, Ni2ppm,
Ag11ppm, S5ppm and other elements are respectively
Example 1 After melting electrolytic copper containing 1 ppm or less in a protective atmosphere and adding the required amount of Pb,
A 2.6 mmφ copper conductor was prepared in the same manner as above. Next, this copper conductor was heated and held in vacuum at various temperatures of 400 to 800°C as shown in Table 3 for 10 hours to obtain cryogenic copper conductors. The electrical resistance ratios measured for these are shown in Table 3.

【table】

[Table] The above table demonstrates that the conductivity of the copper conductor of the present invention at low temperatures can be significantly improved by heating and maintaining it within the range of 450 to 750°C. Example 4 Impurities: Fe7ppm, Sn5ppm, Ni7ppm,
Ag8ppm, S6ppm and other elements are dissolved by melting electrolytic copper consisting of approximately 1ppm or less in a protective atmosphere to remove Pb.
After adding 20 ppm, 2.6 was added in the same manner as in Example 1.
A copper conductor of mmφ was obtained. The Pb content in this copper conductor was 14 ppm. Next, this copper conductor was heated and held in a vacuum at temperatures of 550° C. and 700° C. for the times shown in Table 4, respectively, to obtain cryogenic copper conductors. The electrical resistance ratio of the obtained copper conductor is shown in Table 4.

【table】

[Table] From the results in Table 4 and Table 3 above, the heating and holding conditions for obtaining the cryogenic copper conductor of the present invention are 450 to 750 in order to further exhibit the conductivity effect at cryogenic temperatures. It was confirmed that 30 minutes or more at ℃ is preferable. In addition, the amount of Pb added in each example of the present invention described above is the amount contained in the copper conductor as a final product.
It is sufficient that the amount is about 20 to 50% higher than the amount of Pb. As detailed above, the cryogenic copper conductor of the present invention has an S content as an impurity of 30 ppm or less,
The total content of impurities excluding O ₂ , Ag and Pb is
Since it is a copper conductor containing 5 to 40 ppm of Pb and less than 100 ppm, it is possible to industrially produce a copper conductor that has excellent conductivity at extremely low temperatures whether using oxygen-free copper or tough pitch copper. It can be easily provided. In particular, in addition to using the above-mentioned materials, the cryogenic copper conductor of the present invention is heated at 450 to 750°C at least once before and/or after processing into the desired shape after hot treatment. Further effects can be obtained by heating and holding for 30 minutes or more. The obtained copper conductor can be used in a wide range of applications, such as as a stabilizing material for superconducting conductors, and has great effects.

Claims (1)

[Claims] 1. A copper conductor for cryogenic use, characterized in that it contains 5 to 40 ppm of Pb, and the remainder consists essentially of copper. 2. The cryogenic copper conductor according to claim 1, wherein the copper is oxygen-free copper. 3 Claim 1 in which the copper is tough pitch copper
Copper conductor for cryogenic temperatures as described in section. 4. The cryogenic copper conductor according to claim 2, which contains 30 ppm or less of S as an impurity. 5. The cryogenic copper conductor according to claim 3, which contains 30 ppm or less of S as an impurity. 6 Total content of impurities excluding Pb and Ag is 100ppm
A cryogenic copper conductor according to claim 2 or 4 as follows. 7 The total content of impurities excluding Pb, Ag and _O2 is
The cryogenic copper conductor according to claim 3 or 5, which has a content of 100 ppm or less. 8 At least once before and/or after processing a material containing 5 to 40 ppm of Pb, the remainder of which is essentially copper, after hot treatment and processing into the desired shape.
A method for producing a copper conductor for cryogenic use, characterized by heating and holding at 450 to 750°C for 30 minutes or more. 9. The method for producing a cryogenic copper conductor according to claim 8, wherein the copper is oxygen-free copper. 10. The method for producing a cryogenic copper conductor according to claim 8, wherein the copper is tough pitch copper. 11. The method for producing a cryogenic copper conductor according to claim 9, which contains 30 ppm or less of S as an impurity. 12. The method for producing a cryogenic copper conductor according to claim 10, which contains 30 ppm or less of S as an impurity. 13 The total content of impurities excluding Pb and Ag is
A method for producing a copper conductor for cryogenic use according to claim 9 or 11, wherein the content is 100 ppm or less. 14. The method for producing a cryogenic copper conductor according to claim 10 or 12, wherein the total content of impurities excluding Pb, Ag and _O2 is 100 ppm or less.