Standards
Conductivity is generally specified relative to the 1913 International Annealed Copper Standard of 58 MS/m. Advances in the refining process now yield OF and ETP copper that can meet or exceed 101% of this standard. (Ultra-pure copper has a conductivity of 58.65 MS/m, 102.75% IACS.) Note that OF and ETP coppers have identical conductivity requirements.
Oxygen plays a beneficial role for improving copper conductivity. During the copper smelting process, oxygen is deliberately injected into the melt to scavenge impurities that would otherwise degrade conductivity.
There are advanced refining processes such as Czochralski process than can be used to reduce impurity levels to below the C10100 specification by reducing copper grain density. At this time, there are currently no UNS/ASTM classifications for these specialty coppers and the IACS conductivity of these coppers is not readily available.
Read more about this topic: Oxygen-free Copper
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—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
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—Judith Viorst (20th century)