Oxygen-free copper

Oxygen-free copper

Oxygen-free copper or Oxygen-free high
thermal conductivity copper is a group of wrought high conductivity copper
alloys that have been electrolytically refined to reduce the level of oxygen to
.001% or below. Specification
Oxygen-free copper is typically specified according to the ASTM/UNS
database. The UNS database includes many different compositions of high
conductivity electrical copper. Of these three are widely used and two are
considered oxygen-free. C10100 – also known as Oxygen-Free
Electronic. This is a 99.99%pure copper with 0.0005% oxygen content. It achieves
a minimum 101% IACS conductivity rating. This copper is finished to a final form
in a carefully regulated, oxygen-free environment. Silver is considered an
impurity in the OFE chemical specification. This is also the most
expensive of the three grades listed here.
C10200 – also known as Oxygen-Free. While OF is considered oxygen-free, its
conductivity rating is no better than the more common ETP grade below. It has
a 0.001% oxygen content, 99.95% purity and minimum 100% IACS conductivity. For
the purposes of purity percentage, silver content is counted as copper.
C11000 – also known as Electrolytic-Tough-Pitch. This is the
most common copper. It is universal for electrical applications. ETP has a
minimum conductivity rating of 100% IACS and is required to be 99.9% pure. It has
0.02% to 0.04% oxygen content. Most ETP sold today will meet or exceed the 101%
IACS specification. As with OF copper, silver content is counted as copper for
purity purposes.=Oxygen-free high thermal conductivity
Oxygen-free high thermal conductivity copper is widely used in cryogenics.
OFHC is produced by the direct conversion of selected refined cathodes
and castings under carefully controlled conditions to prevent contamination of
the pure oxygen-free metal during processing. The method of producing OFHC
copper ensures extra high grade of metal with a copper content of 99.99%. With so
small a content of extraneous elements, the inherent properties of elemental
copper are brought forth to a high degree. These characteristics are high
ductility, high electrical and thermal conductivity, high impact strength, good
creep resistance, ease of welding, and low relative volatility under high
vacuum. 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. 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 the 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. Industrial applications
For industrial applications, oxygen-free copper is valued more for its chemical
purity than its electrical conductivity. OF/OFE grade copper is used in plasma
deposition processes, including the manufacture of semiconductors and
superconductor components, as well as in high vacuum devices such as particle
accelerators. In any of these applications, the release of oxygen or
other impurities can cause undesirable chemical reactions with other materials
in the local environment. Use in home audio
The high-end speaker wire industry markets oxygen-free copper as having
enhanced conductivity or other electrical properties that are
supposedly advantageous to audio signal transmission. However, conductivity
specifications for common C11000 Electrolytic-Tough-Pitch and higher-cost
C10200 Oxygen-Free coppers are identical. Much more expensive C10100, a
highly refined copper with silver impurities removed and oxygen reduced to
0.0005%, has only a one percent higher conductivity—insignificant in audio
applications. OFC is nevertheless sold for both audio and video signals in
audio playback systems and home cinema. Oxygen-free phosphorus-containing copper
High electrical conductivity coppers are distinct from coppers deoxidized by the
addition of phosphorus in the smelting process. Oxygen-free
phosphorus-containing copper is typically used for structural and
thermal applications where the copper material will be subject to temperatures
high enough to cause hydrogen embrittlement or more exactly steam
embrittlement. Examples include welding/brazing rods and heat exchanger
tubing. Indeed, copper alloys which contain
oxygen as an impurity can be embrittled if exposed to hot hydrogen. The hydrogen
diffuses through the copper and reacts with inclusions of Cu2O, forming H2O,
which then forms pressurized water steam bubbles at the grain boundaries. This
process can cause the grains to be forced away from each other, and is
known as steam embrittlement. CuOFP has been selected as corrosion
resistant material for the overpack of spent nuclear fuel in the KBS-3 concept
developed in Sweden and Finland to dispose high-level radioactive waste in
crystalline rock formations. See also
Copper wire and cable References

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