Oxygen-free copper

Oxygen-free copper (OFC) or Oxygen-free high thermal conductivity (OFHC) 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.

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.

Oxygen-free high thermal conductivity (OFHC) 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.

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.

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