Cupronickel

Cupronickel or copper-nickel (sometimes incorrectly referred to as "cupernickel") is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Cupronickel is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater. Because of this, it is used for piping, heat exchangers and condensers in seawater systems as well as marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats.

A more familiar common use is in silver-coloured modern circulation coins. A typical mix is 75% copper, 25% nickel, and a trace amount of manganese. In the past true silver coins were debased with cupronickel. Despite high copper content, the colour of cupro-nickel remarkably is silver.

It is used in thermocouples, and the 55% copper/45% nickel alloy constantan is used to make resistors whose resistance is stable across changes in temperature.

Monel metal is a nickel-copper alloy, containing minimum 63% nickel.

See also bronze (copper alloyed with tin), brass (copper alloyed with zinc), and nickel silver (another group of copper-nickel alloys).

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