Cupronickel

Two stacks of half dollars, one silver, one clad - effects of the Coinage Act 1965

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Crack in CuNi metal due to silver brazing

Cupronickel or copper-nickel is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. The copper content typically varies from 60 to 90 percent. The invention of cupronickel is dated back to the 19th century and it has been used for various applications due to its corrosion resistance, especially in marine environments, and its distinctive silver color.

Properties

Cupronickel alloys are known for their high resistance to corrosion in seawater, making them an ideal material for marine hardware, coinage, and seawater piping systems. The addition of nickel to copper improves its strength, durability, and resistance to corrosion and wear. These alloys also exhibit good thermal and electrical conductivity, though less than that of pure copper.

Composition and Grades

The most common grades of cupronickel are 90/10 (90% copper, 10% nickel) and 70/30 (70% copper, 30% nickel). The 90/10 alloy is commonly used where corrosion resistance is needed more than strength, while 70/30 is preferred for its higher strength and slightly better corrosion resistance. Other elements like manganese, iron, and zinc can be added to enhance specific properties.

Applications

Cupronickel's resistance to corrosion by seawater, as well as its aesthetic appeal, makes it a popular choice for coins. Many countries use cupronickel alloys in their higher-value coins. It is also used in marine engineering for piping, heat exchangers, and condensers because of its ability to withstand the corrosive effects of seawater. Additionally, it finds applications in desalination plants, offshore oil and gas platforms, and power generation.

History

The use of cupronickel can be traced back to the Chinese Qing dynasty and was later adopted by the British Admiralty in the 19th century for marine applications. The introduction of cupronickel in coinage began in the 20th century, with various countries adopting the alloy for its durability and resistance to wear and corrosion.

Environmental Impact

Cupronickel alloys are non-toxic and have a minimal environmental impact when used in marine environments. Their corrosion resistance ensures that they do not release harmful levels of copper or nickel into seawater, making them a sustainable choice for marine applications.

See Also

• Alloy
• Copper
• Nickel
• Corrosion resistance
• Coinage

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