RRR ( R 293K / R T ) and THERMAL CONDUCTION in cryogenics
For classical mass-produced copper, that is, copper of 99.9-99.99% purity by generally accepted standards, these characteristics are more or less investigated. For specific brands with regard to standards there may be some differences due to requirements for the content of some impurities. If copper is made in the classical way, then other “harmful” impurities outside of generally accepted standards are contained in much smaller quantities and do not actually have an effect compared to those to be controlled, for which the maximum content is determined. 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. With this in mind, below we present some data not for engineering calculations, but for a general picture.
Some Pure Copper
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.
Some different sources state that for high-quality copper 99.999% electrical conductivity is no less than ~ 103.4-6% IACS and RRR > 1000. 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.
RRR for our copper expected > 1500 - 2000 - ...? ( for Extra completely > 2000 - ...? ), Thermal conductivity is expected at the same high level. Taking into account the data for Some copper 2, characteristics can be higher, in particular, RRR and for Basic can be > 2000. We cannot say it exactly, the exact chemical composition of Some cooper 2 is not known for us. In general, RRR and thermal conductivity are expected to be ~ 60-95 % of max for copper (C10100: RRR ~ 200-300 or < 7-10%). Forecast expectations of 60-95% of max are reasonable, fully justified and the question
is rather in the statistical interval distribution of this forecast for the current product.
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.
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.