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SUPER PURE OFC
Purity : About Chemical purity,  Standards and TS (technical specification), Some Examples
ABOUT  CHEMICAL

PURITY
There is a certain misunderstanding of what the purity of copper is, how it is determined and why it is needed ...
Chemical purity
Chemical purity is determined by the content of the main substance, expressed as a percentage and is defined as the difference between 100% and the sum of selected controlled chemical impurities.

Controlled (or managed) impurities - a list of chemical elements, selected from various considerations and tasks, measured in a sample and used to determine chemical purity.
In fact, "chemical purity" - "Appointed NUMBER", is obtained by subtracting from 100% the amount in% of the content of chemical elements from some selected list. If it is not obvious which list of impurities is in question, then it is worth specifying according to which list.

Obviously, to determine the chemical purity, it is necessary to know the quantitative values of these impurities.

Chemical composition of impurities - a list of controlled impurities with the quantitative value of some of them, certain groups or each of the impurities.

By choosing different lists of elements, you can get very different such numbers.
In some way it is necessary to measure, obtain quantitative values of the content of impurities from the selected list. Some "tool and rules to use it" are needed.

The concept of "Method of analysis" appears.
Analysis Methods
The method of analysis is a method of obtaining information about the chemical composition of a substance based on the use of selected chemical and physical processes and laws

The method of analysis is a sequence of preparatory activities, measurement and interpretation of the results using appropriate consumables, tools and equipment.

The method of analysis must correspond to the level of chemical purity of the tested sample and the list of measured impurities. Different methods measure the same impurities with different limits, some methods cannot, in principle, determine some impurities correctly or completely, in view of the chemical and physical processes and laws inherent in them. To test very pure samples against a list of elements, a combination of analysis methods is often needed.

Basically, the methods are characterized by the following quantitative and qualitative parameters:
 
  • Limits of detection - the minimum quantitative values of measured impurities, which can be used to determine with a given probability the presence or absence of impurities in the sumple
 
  • Limits of determination - the minimum quantitative values of the measured impurities, which can be determined with an error not exceeding the specified one
 
  • Repeatability - the closeness of measurements of the same sample by the same method under the same conditions (same analytical laboratory, same equipment, same analysts, within a short period of time)
 
  • Reproducibility - the closeness of measurements of the same sample by the same method, but under different conditions (different analytical laboratories, different equipment, different analysts, different times)
We have a certain list of elements, we have determined chemical purity by some method. What do we want? Obviously, we want to have certain characteristics and properties, we do not have the ability to determine them completely or promptly. On the basis of something, it is necessary to draw conclusions, to correlate with something.

There is a concept "Standards and TS (technical specifications)".
Standards and specifications
Standard or TS in the broad sense of the word - a sample, standard, norms, characteristics, etc., taken as initial ones for comparing other similar objects with them according to certain rules.

The features of copper are determined not so much by the copper content (chemical purity), but by the content of specific impurities and their specific amount, that is, by a specific chemical composition. Different chemical elements affect different characteristics of both the product and the technological processes themselves in different ways.
Standards and TS (technical specifications) define the following main reference parameters:

  • Chemical composition of impurities - a list of impurities with their maximum values (some, certain groups or each)
 
  • Minimum chemical purity (maximum content of all impurities) according to this list of controlled impuritie
 
  • How exactly and according to what rules is the comparison of the test object with the reference parameters
 
Several options "composition of impurities + min chemical purity" - different Grades and / or Categories according to this Standard or Specification.
Thus :

  • The chemical purity of a sample is a number assigned to a sample that is associated with a particular list of impurities. By choosing different lists of impurities, you can get very different such Numbers.
 
  • Only by chemical purity it is impossible to say about the characteristics of copper. The features and characteristics of copper are determined not so much by the copper content (chemical purity), but by the content of specific impurities and their specific amount. Knowledge of the chemical composition is required
 
  • Standards and TS define some reference parameters of chemical composition and chemical purity.
 
  • Analysis methods also affect the Purity Number, but if they measure everything from the selected list reasonably, then they have a refinement value, the base value is a list of impurities.
 
  • The obvious goal is to obtain predictable characteristics of copper by "Chemical Purity Number" with compliance with some Standard or Specification. There may be fluctuations in the values of characteristics, but it is quite natural to expect certain values, in particular, no worse than they can be. The required characteristics of copper are determined by the scope and task.
COMMONLY ACCEPTED

STANDARDS AND TS
Standard or TS in the broad sense of the word - a sample, standard, norms, characteristics, etc., taken as initial ones for comparing other similar objects with them according to certain rules
All globally accepted standards describe copper up to a maximum purity of "at least 99.99%". The most famous standards are ASTM B170 (USA) and GOST 859-2001 (Russia). There are other similar standards in other countries: Japan, Great Britain, Germany, etc. The standards take into account the possibility of mass production using certain technologies. For special tasks, in particular, copper shells of superconductors, copper of ~99.995% purity according to GOST 859 with RRR 400+ characteristic is produced in batches, which is quite sufficient for these purposes.

There are no generally accepted universal standards that describe the requirements for purity above 99.99%, at least at the state level. For purity of 99.995-99.999% and higher for impurities from ASTM B170 and GOST 859, it is already difficult to obtain "these beautiful numbers". There are other, non-mass technologies, but they also have a number of limitations and difficulties. For a purity of 99.999% and higher, there are still difficulties in available verification: different analytical methods either do not have sufficient sensitivity, or are not quite suitable ...

Therefore, manufacturers often set their own specifications for copper 99.995-99.999% and higher, describing their list of elements for determining purity, often very different from GOST 859-2001 and ASTM B170, and sometimes rules how "calculate purity ..." Such approach does not make it possible to predict the main characteristics and properties of such copper. Such copper of 99.995-99.999% and higher can have both a large spread in characteristics, and have a "guaranteed minimum level" of characteristics worse than ordinary classical copper, even with a purity of 99.95% according to generally accepted standards.

Perhaps, for some tasks, "such manipulations" are acceptable - reducing the number of elements for determining purity, choosing elements that are not included in GOST and ASTM, etc. Such tasks must be distinguished. We are not aware of such special applications where such copper would be significantly better than classical 99.99%, and for most, if not all, serious tasks related to physical characteristics, at least in vacuum and cryogenics, there will usually be consequences.
Controlled impurities according to GOST 859, ASTM B170 and some specifications :
Total different
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
chemical elements
26
O
S
P
Ni
Zn
As
Se
Sn
Sb
Te
Pb
Bi
Fe
Ag
Mn
Cd
Si
Cr
Co
Al
Mg
Ti
Mo
Ca
K
W
Standards
Cu
1
ГОСТ   859-2001
cathode copper 
2N-4N
19
O
S
P
Ni
Zn
As
Se
Sn
Sb
Te
Pb
Bi
Fe
Ag
Mn
Cd
Si
Cr
Co
2
ГОСТ 859-2001
cast copper
2N-4N
12+2
*
O
S
P
Ni
Zn
As
Se
Sn
Sb
Te
Pb
Bi
Fe
Ag
3
ASTM B170
cast copper
2N-4N
16
O
S
P
Ni
Zn
As
Se
Sn
Sb
Te
Pb
Bi
Fe
Ag
Mn
Cd
TS
Cu
4
Sibneotech
cast copper
5N5-7N
16
O
S
P
Ni
Zn
As
Se
Sn
Sb
Te
Pb
Bi
Fe
Ag
Mn
Cd
5
Umicore Ltd
cast copper
4N5-6N
12+2
*
O
S
P
Ni
Zn
As
-
Sn
Sb
-
Pb
Bi
Fe
Ag
Mn
Cd
6
Acrotec Ltd
cast copper
6N-9N
10
-
S
-
Ni
-
As
Se
-
Sb
-
Pb
-
Fe
Ag
-
-
Si
Al
7
Sigma-Aldriich  Corp
Bars
5N
15
-
-
-
Ni
Zn
As
-
Sn
Sb
-
-
Bi
Fe
Ag
-
Cd
Cr
Al
Ti
Ca
K
W
8
Sigma-Aldriich  Corp
Powder
5N
13
-
-
-
Ni
Zn
As
-
Sn
Sb
-
-
Bi
Fe
Ag
-
Cd
Cr
Al
Ti
Ca
K
W
9
TS №1
Powder
4N?
9
-
-
-
Ni
Zn
-
-
-
Sb
-
-
-
Fe
-
Mn
Cd
Al
Ti
Mo
10
TS №2
Powder?
4N?
6
-
-
P
-
-
-
-
-
-
-
-
-
-
-
-
Cd
Al
Mg
Ti
Mo
*
Se, Te in GOST 859 cast and O, S in Umocore are not calculated, but are indicated and limited
EXAMPLE 1

COPPER M1 99.999+%?
Chemical purity - "Appointed NUMBER", is obtained by subtracting from 100% the amount in% of the content of chemical elements from some selected list. If it is not obvious which list of impurities is in question, then it is worth specifying according to which list. By choosing different lists of impurities and methods of analysis, one can obtain very different such Numbers.
Copper grade M1 according to GOST 859 must have a purity of "Cu + Ag not less than 99.90%" and the corresponding chemical composition: each controlled impurity must not exceed the established limit. Can M1 copper be 99.999+% pure?

We carried out a chemical analysis of 3 samples of copper grade M1. The first two samples of copper M1 had a purity in the range of 99.92% - 99.93%, the third sample of copper M1 had a purity of 99.95%. It should be noted that samples No. 1 and No. 2 of copper M1 did not meet the requirements of GOST 859 for the maximum content of specific impurities: they had an excess of one of the elements by 15-20 times, up to 300-400 ppm instead of 20 ppm. Some even low characteristics for M1 should not be expected from these samples, although it is not intended for special tasks and conditions where high physical characteristics are required.

According to the data given in the table below, it is easy to see that the chemical purity (as a certain number) of any sample depends on the selected list of controlled impurities and analysis methods. The higher the chemical purity, the more controlled impurities differ from generally accepted standards and counting rules. The purity determined by the standards is almost the same as the purity determined by all 26 elements, and will not differ significantly from that determined by the entire periodic table. Differences throughout the periodic table will be mainly due to the sum of detection limits or impurity values close to them - they must be counted as impurities in the number of detection limits .

That is, for the same sample we have different chemical purity (as a certain number). The physical characteristics of each copper sample do not change. Without knowing from which list of elements and by which method of analysis the purity was determined, nothing can be said about the expected characteristics of copper samples. Moreover, copper samples with the same chemical purity, determined from the same list of impurities and the same analysis method, can also differ greatly in characteristics due to the difference in the specific chemical composition. The sum of impurities in the samples may be the same, but the quantitative values of various impurities may differ, and they affect the physical characteristics in different ways. The specific chemical composition is important, and for this, impurity limits are introduced in the standards in order to determine a certain range of expected characteristics.
Chemical purity of 3 samples of copper grade M1 and 2 of our median samples of grades Standard and Extra, depending on the lists of impurities and on the methods of analysis:
Standards
TS (specifications)
1
2
3
4
5
6
7
8
9
10
Copper sample
Method
All (26)
ГОСТ 859
cathode
ГОСТ 859
cast
ASTM B170
cast
Сибнеотэк
cast
Umicore
cast  
Acrotec
cast  
Sigma
cast
Sigma
powder
ТУ №1
powder
ТУ №2
powder
2N-4N
2N-4N
2N-4N
5N5-7N
2N5-6N
6N-9N
5N
5N
4N-5N?
4N-5N?
М1 GOST 859
1
М1
LMS
3 N 2
3 N 2
3 N 2
3 N 2
3 N 2
3 N 4
4 N
3 N 5
4 N
4 N
4 N 8
2
M1
LMS
3 N 3
3 N 3
3 N 3
3 N 3
3 N 3
3 N 6
4 N
3 N 6
4 N
4 N
4 N 6
3
M1
LMS
3 N 5
3 N 5
3 N 5
3 N 5
3 N 5
4 N 8
5 N
5 N
5 N
5 N
5 N 4
Sibneotech
4
Standard - med
LMS
5 N
5 N 1
5 N 2
5 N 2
5 N 2
5 N 7
5 N 5
5 N 7
5 N 7
5 N 8
6 N
5
Extra - med
LMS
5 N 1
5 N 1
5 N 2
5 N 2
5 N 2
5 N 8
5 N 5
5 N 8
5 N 8
5 N 8
6 N
4
Standard - med
LMS+GDMS
5 N 6
5 N 7
5 N 7
5 N 7
5 N 7
6 N
6 N
6 N
6 N
6 N 6
7 N +
5
Extra - med
LMS+GDMS
5 N 7
5 N 7
5 N 8
5 N 8
5 N 8
6 N 7
6 N 3
6 N 7
6 N 7
7 N
7 N +
From the table, we take specific examples of the chemical purity of 2 samples highlighted in color. What will we have?
Example of different chemical purity for 2 different samples with the same method of analysis and different controlled impurities :
1
2
3  (Characteristics)
Sample
Method
Chemical purity
List of impurities
% IACS
RRR 4.2K=R 293K /R 4.2K
λ 4.2K / λ 293K
М1 №3
LMS
5N4
ТУ №2
<100
50-100
1
Standard - med
LMS
5N1
ГОСТ 859
104-105
2000
25-30
Based only on chemical purity, in this case determined by one method, and not taking into account the list of controlled impurities, we have that, as it were, sample No. 3 of copper M1 looks "more beautiful ...", that is, "as it were, better" ... Sample M1 copper can have 99.999+% pure...

But if you need a high RRR characteristic and Thermal conductivity in cryogenics, then you will not get anything, and as they say: "If you put a quinoa in a mill, you should not wait for flour to come out ...".
P.S.  In some tasks, for characteristics, not only chemical purity and chemical composition according to the most serious standard matter ... and even the exact chemical composition of the entire periodic table does not determine the real level of the characteristic, it determines only a certain lower limit ... often significantly lower than theoretically achievable , which can be achieved based not only on chemical purity ... There are other parameters that can lead to a significant improvement in performance for some tasks. See "Characteristics" section.
EXAMPLE 2

Cu 4N5 - 9N? World leaders?
...that is why manufacturers often set their own specifications for copper 99.995-99.999% and higher, describing their lists of elements for determining purity, and sometimes even rules "calculate purity ...".
The list of controlled impurities differs from ASTM B170. O, P, Zn, Sn, Te, Bi are excluded - very important elements ... Si, Al are added - important elements, but in fact there are always few of them at any level of purity, and in general, if the raw material is not recycled, by the value of the final cleanliness has little effect...

Changed scoring rules - detection limits for 9N are not taken into account when specifying purity. Is it guaranteed purity? Also, if not a typo, is it offer some piece of 2 * 2 * 2 mm?

If we apply the classical rules and the indicated impurity values, then according to the indicated impurity values:

  • the proposed 6N corresponds to the declared
  • suggested 9N corresponds to 7N7, cube 2*2*2mm?

This is a technical proposal. We do not know for what purpose such a list of controlled impurities. If you do not check the excluded elements, then nothing can be said about the characteristics, 9N can be easy to be worse than significant characteristics 4N according to ASTM ... The indicated measurement limits and a number of values some impurities suggest that many other impurities it should also be at a high level , but it has to been check... Also, if not a typo, then a standard form of 2 * 2 * 2mm is proposed....

* * *
According to these technical conditions, we also have something to offer as such 9N, in fact 7N7 ..., and even for a much larger list of elements and taking into account the important .... No one can measure and we do not know where it can do.

Also, we offer not 2 * 2 * 2 mm cubes, but full-fledged ingots similar to a single crystal, from which it is already possible to make a product ...
The list of controlled impurities is practically the same as ASTM B170. Se and Te are excluded. These elements rarely occur in significant quantities in terms of their influence on some characteristics, but even so, if we are talking about limiting characteristics ... C was added, for which task we do not know

Counting rules have been changed - O, S, C are not taken into account. Typical analyzes are indicated. A typical analysis is what  the percentage of product? What are the guaranteed purity and chemical composition?

Applying the classical rules and the specified impurity values, the claimed best grade 6N copper has a TYPICAL PURITY:

  • OFC 5N7
  • "Cu 6N metals basis, OF" 

This is a proposal for technical specifications, although it is correct - the calculation rules have been changed, but the most significant impurities are taken into account. This approach can be accepted, since O and S, as a rule, are cleaned and measured with much worse limits and by far not all methods of analysis. If the rest are an order of magnitude better, and something happens to them, then the figure as purity, if you count O and S, will not change. A separate count of traces of metallic impurities gives some guidance on what and how. We have the same problem.

* * *
The typical purity of the proposed best grade 6N is actually OFC 5N7="Cu 6N metals basis, OF" and no minimum guaranteed purity level is specified. Our brand Standard has such purity as median purity, and the minimum guaranteed purity level is indicated - OFC 5N5 = "Cu 5N7 metals basis, OF". This is for the entire batch and, if you remove a couple of ingots with Ag, then min for the experimental grade Standard - purity OFC 5N7 = "Cu 6N metals basis, OF"

For our brand Extra:

  • min            OFC 5N7="Cu 6N metals basis, OF"
  • median   OFC 5N7="Cu >6N5 metals basis, OF"
Be careful "seeing beautiful numbers" even among the world's leading companies - everything is in the details. We rightfully claim that the quality we offer is one of the best in the world, and possibly the best in this form. The chemical purity declared by us is even slightly underestimated, everything is indicated correctly and according to all the rules, and checked. For such purity, the shape is not small, it is convenient for some tasks, and the structure is similar to a single crystal ...
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