Cupronickel
|
|
Cupronickel is an alloy of copper, nickel and stengthening impurities, such as iron and manganese.
Cupronickel does not corrode in seawater, because its electronegativity is adjusted to be neutral with regard to seawater. Because of this it is used for marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats.
The most ubiquitous use, from the point of view of the average person, is that most of the silver-coloured modern circulation coins are cupronickel. A typical mix is 75% copper, 25% nickel, and a trace amount of manganese. In the past true silver coins were debased with cupronickel.
It is used in thermocouples, and a 55% copper/45% nickel alloy is used to make very accurate resistors.
Monel metal is a copper-nickel alloy.
See also bronze (copper alloyed with tin), brass (copper alloyed with zinc), and nickel silver (another group of copper-nickel alloys).
History
The cupronickel alloy technology has been known by the Chinese since the 3rd century BCE under the name "White copper" (some weapons from the Warring States Period were in copper-nickel alloy 1).
The Greco-Bactrian kings Agathocles and Pantaleon were the first in the world to issue copper-nickel (75/25 ratio) coins 2 around 170 BCE, suggesting that exchanges of the metallic alloy, or possibly exchanges of technicians, were happening at the time between China and the region of Bactria. The practice of exporting Chinese metals, in particular iron, for trade is attested around that period.
The cupro-nickel technology was not used again in coinage until the 19th century.
External links
1 Ancient Chinese weapons (http://www.chinatoday.com.cn/English/e20026/sunzi1.htm) & A halberd of copper-nickel alloy, from the Warring States Period. (http://www.chinatoday.com.cn/English/e20026/images/t20026/p581.jpg)
2 Copper-Nickel coinage in Greco-Bactria. (http://dougsmith.ancients.info/feac58bak.html)
it:Cupronichel
