Oxygen-free copper

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The CuOFP capsule used as overpack for spent nuclear fuel disposal in the KBS-3 concept (Swedish version) Loppusijoituskapseli.jpg
The CuOFP capsule used as overpack for spent nuclear fuel disposal in the KBS-3 concept (Swedish version)

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. [1] [2]

Copper Chemical element with atomic number 29

Copper is a chemical element with symbol Cu 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-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

Oxygen Chemical element with atomic number 8

Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.



Oxygen-free copper is typically specified according to the ASTM/UNS database. [3] The UNS database includes many different compositions of high conductivity electrical copper. Of these three are widely used and two are considered oxygen-free.

The unified numbering system (UNS) is an alloy designation system widely accepted in North America. It consists of a prefix letter and five digits designating a material composition. For example, a prefix of S indicates stainless steel alloys, C indicates copper, brass, or bronze alloys, T indicates tool steels, and so on. The first 3 digits often match older 3-digit numbering systems, while the last 2 digits indicate more modern variations. For example, Stainless Steel Type 310 in the original 3-digit system became S31000 in the UNS System. The more modern low-carbon variation, Type 310S, became S31008 in the UNS System. Often, the suffix digit is chosen to represent a material property specification. For example, "08" was assigned to UNS S31008 because the maximum allowed carbon content is 0.08%. The UNS is managed jointly by the ASTM International and SAE International. A UNS number alone does not constitute a full material specification because it establishes no requirements for material properties, heat treatment, form, or quality.

The International Annealed Copper Standard (IACS) is a standard established in 1914 by the United States Department of Commerce. It is an empirically derived standard value for the electrical conductivity of commercially available copper.

Oxygen-free high thermal conductivity

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. [4]

Cryogenics study of the production and behaviour of materials at very low temperatures

In physics, cryogenics is the production and behaviour of materials at very low temperatures. A person who studies elements that have been subjected to extremely cold temperatures is called a cryogenicist.

A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic cathode current departs also means that electrons flow into the device's cathode from the external circuit.

Contamination is the presence of a constituent, impurity, or some other undesirable element that soils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc.


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. [5]

The siemens is the derived unit of electric conductance, electric susceptance, and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance, reactance, and impedance respectively; hence one siemens is redundantly equal to the reciprocal of one ohm, and is also referred to as the mho. The 14th General Conference on Weights and Measures approved the addition of the siemens as a derived unit in 1971.

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. [6]

Smelting Use of heat and a reducing agent to extract metal from ore

Smelting is a process of applying heat to ore in order to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind. The reducing agent is commonly a source of carbon, such as coke—or, in earlier times, charcoal.

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. [7] [8] [9] [10] 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) 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. [11]

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 (ETP) and higher-cost C10200 Oxygen-Free (OF) coppers are identical. [12] 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. [12] OFC is nevertheless sold for both audio and video signals in audio playback systems and home cinema. [12]

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 (CuOFP) 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. [13]

Copper alloys which contain oxygen as an impurity (in the form of residual oxides present in the metal matrix) can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of Cu2O, forming H2O (water), 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 (because steam is produced, not because exposure to steam causes the problem).

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

Related Research Articles

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Cupronickel or copper-nickel (CuNi) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. The copper contents typically varies from 60 to 90 percent.

Electrical conductor object or material which permits the flow of electricity

In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge in one or more directions. Materials made of metal are common electrical conductors. Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.

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Phosphor bronze

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Monel group of nickel alloys; trademark name

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Hydrogen embrittlement

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Glass-to-metal seal

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Oxygen-free may refer to the absence of oxygen in an environment or in a material.

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2014 aluminium alloy (aluminum) is an aluminium-based alloy often used in the aerospace industry.

1050 aluminium alloy is an aluminium-based alloy in the "commercially pure" wrought family. As a wrought alloy, it is not used in castings. Instead, it is usually formed by extrusion or rolling. It is commonly used in the electrical and chemical industries, on account of having high electrical conductivity, corrosion resistance, and workability. 1050 alloy is also sometimes used for the manufacture of heat sinks, since it has a higher thermal conductivity than other alloys. It has low mechanical strength compared to more significantly alloyed metals. It can be strengthened by cold working, but not by heat treatment.

1100 aluminium alloy is an aluminium-based alloy in the "commercially pure" wrought family. With a minimum of 99.0% aluminum, it is the most heavily alloyed of the 1000 series. It is also the mechanically strongest alloy in the series, and is the only 1000-series alloy commonly used in rivets. At the same time, it keeps the benefits of being relatively lightly alloyed, such as high electrical conductivity, thermal conductivity, corrosion resistance, and workability. It can be strengthened by cold working, but not by heat treatment.

5154 aluminium alloy is an alloy in the wrought aluminium-magnesium family. As an aluminium-magnesium alloy, it combines moderate-to-high strength with excellent weldability. 5154 aluminium is commonly used in welded structures such as pressure vessels and ships. As a wrought alloy, it can be formed by rolling, extrusion, and forging, but not casting. It can be cold worked to produce tempers with a higher strength but a lower ductility. It is generally not clad.

5454 aluminium alloy is an alloy in the wrought aluminium-magnesium family. It is closely related to 5154 aluminium alloy. As an aluminium-magnesium alloy, it combines moderate-to-high strength with excellent weldability. Like 5154, 5454 aluminium is commonly used in welded structures such as pressure vessels and ships. As a wrought alloy, it can be formed by rolling, extrusion, and forging, but not casting. It can be cold worked to produce tempers with a higher strength but a lower ductility. It is generally not clad.

5456 aluminium alloy is an alloy in the wrought aluminium-magnesium family. While it is closely related to 5356 aluminium alloy, it is used in structural applications, like most other aluminium-magnesium alloys, and not as filler for welding. As a wrought alloy, it can be formed by rolling, extrusion, and forging, but not casting. It can be cold worked to produce tempers with a higher strength but a lower ductility. It is susceptible to exfoliation corrosion when held at temperatures above 65 °C (150 °F) for extended periods of time.

6005A aluminium alloy is an alloy in the wrought aluminium-magnesium-silicon family. It is closely related, but not identical, to 6005 aluminium alloy. Between those two alloys, 6005A is more heavily alloyed, but the difference does not make a marked impact on material properties. It can be formed by extrusion, forging or rolling, but as a wrought alloy it is not used in casting. It cannot be work hardened, but is commonly heat treated to produce tempers with a higher strength at the expense of ductility.


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