Cupronickel

Cupronickel is highly resistant to corrosion by salt water, and is therefore used for piping, heat exchangers and condensers in seawater systems, as well as for marine hardware.

It was from a sample of this kupfernickel that Baron Axel Fredrik Cronstedt first isolated elemental nickel in 1751, naming the new metal for the sprite.

[2] Cupronickel alloys are used for marine applications[3] due to their resistance to seawater corrosion, good fabricability, and their effectiveness in lowering macrofouling levels.

[16] In 1879, Switzerland, for 5 and 10 Rappen coins, also adopted that cheaper 75:25 copper to nickel ratio[17][18] then being used in Belgium, the United States and Germany.

Currently, some circulating coins, such as the United States Jefferson nickel (5¢),[20] the Swiss franc, and the South Korean 500 and 100 won are made of solid cupronickel (75:25 ratio).

[24][25][26] Niche applications also exist, for example the alloy's high thermal conductivity at low temperatures has made cupronickel ubiquitous in freeze branding operations.

Since cupronickel is much softer than steel, it bends and flares more easily, and the same property allows it to form a better seal with hydraulic components.

Important properties of cupronickel alloys include corrosion resistance, inherent resistance to macrofouling, good tensile strength, excellent ductility when annealed, thermal conductivity and expansion characteristics amenable for heat exchangers and condensers, good thermal conductivity and ductility at cryogenic temperatures and beneficial antimicrobial touch surface properties.

In seawater, the alloys have excellent corrosion rates which remain low as long as the maximum design flow velocity is not exceeded.

Copper–nickels naturally form a thin protective surface layer over the first several weeks of exposure to seawater and this provides its ongoing resistance.

Applications for Cu–Ni alloys have withstood the test of time, as they are still widely used and range from seawater system piping, condensers and heat exchangers in naval vessels, commercial shipping, multiple-stage flash desalination and power stations.

The paktong alloy was described as being made by adding small pills of naturally occurring yunnan ore to a bath of molten copper.

However, the Pha Phu Tsu and the Shen I Ching describing a statue in the Western provinces as being of silver, tin, lead and Tanyang copper – which looked like gold, and could be forged for plating and inlaying vessels and swords.

[36] Joseph Needham et al. argue that cupronickel was at least known as a unique alloy by the Chinese during the reign of Liu An in 120 BC in Yunnan.

Most likely, modern paktong was unknown to Chinese of the day – but the naturally occurring Yunnan ore cupronickel alloy was likely a valuable internal trade commodity.

[36] In 1868, W. Flight discovered a Greco-Bactrian coin comprising 20% nickel that dated from 180 to 170 BCE with the bust of Euthydemus II on the obverse.

[36] Cunningham in 1873 proposed the "Bactrian nickel theory," which suggested that the coins must have been the result of overland trade from China through India to Greece.

Cunningham's theory was supported by scholars such as W. W. Tarn, Sir John Marshall, and J. Newton Friend, but was criticized by E. R. Caley and S. van R.

[36] Cammann criticized Cheng and Schwitter's paper, arguing that the decline of cupronickel currency should not have coincided with the opening of the Silk Road.

But in De Natura Metallorum in Singalarum Part 1, published in 1599, the same term was applied to "tin" from the East Indies (modern-day Indonesia and the Philippines) and given the Spanish name, tintinaso.

Peat and Cookson found that "the darkest proved to contain 7.7% nickel and the lightest said to be indistinguishable from silver with a characteristic bell-like resonance when struck and considerable resistance to corrosion, 11.1%".

Efforts in Europe to exactly duplicate the Chinese paktong failed due to a general lack of requisite complex cobalt–nickel–arsenic naturally occurring ore.

However, the Schneeberg district of Germany, where the famous Blaufarbenwerke made cobalt blue and other pigments, solely held the requisite complex cobalt–nickel–arsenic ores in Europe.

At the same time, the Prussian Verein zur Beförderung des Gewerbefleißes (Society for the Improvement of Business Diligence/Industriousness) offered a prize for the mastery of the process.

[37] In 1829, Percival Norton Johnston persuaded Dr. Geitner to establish a foundry in Bow Common behind Regents' Park Canal in London, and obtained ingots of nickel-silver with the composition 18% Ni, 55% Cu and 27% Zn.

Johnsons' most serious competitors, Charles Askin and Brok Evans, under the brilliant chemist Dr. EW Benson, devised greatly improved methods of cobalt and nickel suspension and marketed their own brand of nickel-silver, called "British Plate".