PHYSICAL PROPERTIES OF COPPER AND COPPER ALLOYS

Pure Copper

With atomic number 29, copper is a member of subgroup IB on the periodic table of the elements. Other ‘‘noble metals’’ in this subgroup include silver and gold, with which copper shares properties such as high ductility and chemical stability. Copper’s atomic structure is 1s2 2s2 2p6 3s2 3p6 3d10 4s1. Its filled 3d state and loosely bound 4s electrons and the optical transitions between filled 3d and empty 4s states are responsible for copper’s high electrical and thermal conductivity and its distinctive red color.

Copper’s atomic weight is 63.546. Almost all copper found in nature exists as one of two stable isotopes, Cu (occurring 69.09%) and Cu (30.91%). Unstable isotopes, ranging from Cu to Cu, are -emitters, although naturally occurring copper is not thought of as radioactive.

Table 36 contains a compilation of physical properties for the pure metal. Most important among these from an engineering standpoint are its high electrical and thermal conductivities. Copper is, in fact, the standard for electrical conductivity against which all other metals are compared. The International Annealed Copper Standard (IACS) is defined as the volume conductivity of an annealed pure copper wire 1 m long, weighing 1 g, having a density of 8.89 g/cm3 at 298 K (25 C) and a conductivity of exactly 58 m/ mm2 (i.e., having a resistance of exactly 0.15328 ). This value is designated ‘‘100% IACS’’ and corresponds to a volume resistivity of 16.70 n m. The conductivity of copper produced today often exceeds that of metal available at the time the international standard was established, and it is not unusual for today’s electrical and electronic grades of copper to exhibit IACS values of at least 101%.

Copper’s electrical conductivity is conventionally given on a volume basis. In these terms, aluminum’s conductivity is about 62% IACS, but because of the large density difference in density between the two metals, it is roughly twice that of copper on a weight basis.

The lighter metal is thus used for overhead transmission lines while copper is preferred for high-voltage underground lines to conserve space inside conduits and where reliable connectivity and corrosion resistance are important.

Copper’s high thermal conductivity is useful in applications such as heat exchangers and thermal buffers in superconducting cables (copper itself is not a superconductor). Thermal conductivity decreases only about 7% between room temperature and the melting point. Alloying reduces thermal conductivity but improves strength and corrosion resistance.

COPPER AND COPPER ALLOYS
Konrad J. A. Kundig
Metallurgical Consultant
Tucson, Arizona
John G. Cowie
Copper Development Association
New York, New York



Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright  2006 by John Wiley & Sons, Inc.

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