Oxygen-free copper (OFC) or oxygen-free high thermal conductivity (OFHC) copper is a group of wrought high-conductivity

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

alloys that have been electrolytically refined to reduce the level of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

to 0.001% or below. Oxygen-free copper is a premium grade of copper that has a high level of conductivity and is virtually free from oxygen content. The oxygen content of copper affects its electrical properties and can reduce conductivity.

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'' (OFE). 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 (Ag) 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'' (OF). 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 (Ag) content is counted as copper (Cu). * C11000 – also known as ''electrolytic-tough-pitch'' (ETP). This is the most common copper. It is ubiquitous in 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 (typical). Most ETP sold today meets or exceeds the 101% IACS specification. As with OF copper, silver (Ag) content is counted as copper (Cu) for purity purposes.

Oxygen-free high thermal conductivity

''Oxygen-free high thermal conductivity'' (OFHC) copper is widely used in

cryogenics In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a universa ...

. OFHC is produced by the direct conversion of selected refined

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

s and castings under carefully controlled conditions to prevent

contamination Contamination is the presence of a constituent, impurity, or some other undesirable element that renders something unsuitable, unfit or harmful for the physical body, natural environment, workplace, etc. Types of contamination Within the scien ...

of the pure oxygen-free metal during processing. The method of producing OFHC copper ensures an 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. In practice the oxygen content is typically 0.001 to 0.003% with a total maximum impurity level of 0.03%. These characteristics are high

ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...

, high

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

and

thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...

, high

impact strength In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.creep resistance, ease of

welding Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melting, melt the parts together and allow them to cool, causing Fusion welding, fusion. Co ...

, and low

relative volatility Relative volatility is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals. This quantity is widely used in designing large industrial distillation processes. In effect, it indicates the ease or difficulty of ...

under

ultra-high vacuum Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressures lower than about . UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of ...

Standards

Conductivity is generally specified relative to the 1913 International Annealed Copper Standard of S/ 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 S/m, 102.75% IACS.) Note that OF and ETP coppers have identical conductivity requirements.

Oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

plays a beneficial role for improving copper conductivity. During the copper

smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron-making, iron, copper extraction, copper ...

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 The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, plati ...

than can achieve impurity levels 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 (

sputtering In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and c ...

) processes, including the manufacture of

semiconductors A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping levels ...

and superconductor components, as well as in other

devices such as

particle accelerators A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies to contain them in well-defined particle beam, beams. Small accelerators are used for fundamental ...

. 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 Speaker wire is used to make the electrical connection between loudspeakers and audio amplifiers. Modern speaker wire consists of two or more electrical conductors individually Electrical insulation, insulated by plastic (such as polyvinyl chlor ...

industry markets oxygen-free copper as having enhanced conductivity or other electrical properties that are supposedly advantageous to

audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals or a series of binary numbers for Digital signal (signal processing), digital signals. Audio signals have frequencies i ...

transmission. In fact, conductivity specifications for common C11000 (ETP) and higher-cost C10200 oxygen-free (OF) coppers are identical; and even the much more expensive C10100 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 A home cinema, also called home theater, is a home entertainment audio-visual system that seeks to reproduce a movie theater experience and mood using consumer grade electronic video and audio equipment and is set up in a private home. In ...

Oxygen-free phosphorus-containing copper

High-electrical-conductivity coppers are distinct from coppers deoxidized by the addition of

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

in the smelting process. ''Oxygen-free phosphorus-containing copper'' (CuOFP) is typically used for structural and thermal applications where the copper material will be subject to temperatures high enough to cause

hydrogen embrittlement Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can Permeation, permeate solid metals. O ...

or more exactly steam embrittlement. Examples include

/ brazing rods and

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

tubing. Copper alloys containing oxygen as an impurity (in the form of residual oxides present in the metal matrix) can be embrittled if exposed to hot

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

. The hydrogen diffuses through the copper and reacts with inclusions of Cu₂O, forming H₂O, which then forms pressurized water

steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...

bubbles at the

grain boundaries In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional crystallographic defect, defects in the crystal structure, and tend to decrease the ...

. This process can cause the grains to be forced away from each other and is known as ''steam embrittlement'' (because the problem is caused through production of

, not exposure to it). CuOFP has been selected as corrosion-resistant material for the overpack of

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...

in the KBS-3 concept developed in Sweden and Finland to dispose of high-level radioactive waste in crystalline rock formations.

References

{{reflist Copper