RRR ( R 293K  / R T )  and  THERMAL CONDUCTION  in cryogenics

For classical mass-produced copper, these characteristics are more or less investigated. The structure of mass-produced copper is usually close.

For purer copper the data are fragmentary, they can be very different and there are difficulties in comparing. Partly due to the fact that even laboratory samples with a purity of 5N5 and especially above, in accordance with generally accepted standards with a controlled impurity composition and crystal structure, are not easy to produce. Often, some general purity is reported, but not a specific chemical composition, or it is simply mentioned that they are measured and belong to the most pure and perfect samples. At low temperatures, the characteristics strongly depend on the impurities, on the degree of perfection of the crystal and other defects.

Below we present some data not for engineering calculations, but for a general picture. The data for Some Pure Copper 1, 2 and 3 are from sources trustworthy, and given the difficulty of measuring such quantities, it can be  accepted. Data for Some pure copper 1 is given for a very pure sample, the crystal structure is unknown. Some pure copper 2  was obtained in one of the research works as copper of 99.999% purity in the form of a single crystal with RRR 273K / 4.2K ~ 2000. Data for Some pure copper 3 are given for both the very pure and perfect sample with a residual resistance of 0.589 * 10 (-9) ohm * cm. Unfortunately, we have no data and clarity on how pure and perfect the samples are, that is, whether the characteristics of the Pure Copper 3 are the max for copper.

99,95 - 99,97%, 100% IACS

М0б/М0 (RF), С10200 (USA),
Cu-OF/C110 (UK), C1020 (Japan)

80-120

400

1000

1300

1800

2000

2000

1900

1500

min  99,99%,  101-102% IACS

М00б/М00 (RF), С10100 (USA),
Cu-OFE/C103 (UK), C1011 (Japan)

200-300

1200-2000

2500-4000

3500-4500

4500-5000

4500-5000

3500-4000

2600-3100

1500-1700

Special grade copper for use in cryogenics   :

CG-OFG, Hitachi Cable Ltd

500

240-250

220

160

120

100

90

80

3000

5000

6500

7700

7000

6000

4000

2000

Some Pure Copper 1

---

7500

12500

14000

12500

9000

7000

5500

2600

Some Pure Copper 2

2100-2200

---

Produced Copper

Forecast

Some Pure Copper 3

2900-3000

16200

24000

10800

From considerations arising from our Technology and some test results of our copper, we are sure that we have already produced a product close to Some pure copper 3. In any case, such results can be obtained.

P.S. RRR can be increased up to 1000 by annealing and "oxygenation" of copper with a purity of 99.99%, when the formation of oxides leads to a decrease in resistance. But this is not for very pure copper (impurities remain, increased oxygen content) with the ensuing consequences for other characteristics and properties: "hydrogen disease", reduction of plasticity, etc. For very pure copper 99.99999% (?) with RRR 2000 dissolving of oxygen 25 ppm leads to a decrease RRR to 50. Therefore, with copper 5N and higher under not standards must be handled, depending on the tasks: if RRR is needed, RRR may be worse than C10200 or worse, ect.
In some tasks, very high characteristics for RRR and Thermal Conductivity may be in conflict, in some cases vice versa. Super purety and perfect structure are not also a simultaneous requirement for some other tasks, but in some tasks are necessary. We proceed from the fact that for those tasks where maximum purity and structure are needed, with consequent characteristics and properties, when it is needed as such, then it is better that copper already exists, and we have produced it. Especially since it is not easy and it could be a limitation in the planning of tasks with use of such quality. In general, it is also useful for many existing tasks, but each must be looked at by evaluating the necessary parameters and benefits, and not just the mentioned characteristics.