Cupronickel

Cupronickel or copper-nickel or "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.

Other names

Aside from cupro-nickel, many other terms exist which describe the same material. Still registered as tradenames are Alpaka or Alpacca (registered trademark), Argentan Minargent, the French term name Cuivre blanc Occasionally cupro-nickel is also referred to as "hotel silver", plata alemana (Spanish for "German Silver"), "German silver" and "Chinese silver".

History

Cupro-nickel was known to the Romans as an artificial "white" gold or silver termed "claudianum" and very possibly the "molybdochalcum" of the Alexandrians.

The cupro-nickel alloy was known by Chinese since circa 3rd century BCE as "white copper" (some weapons from the Warring States Period were in Cu-Ni alloy).

The ancient Greeks were producing cupronickel and a lower quality imitation of it in the Aegean Bronze Age and known as "orichalcum". The Greco-Bactrian kings issued the first cupro-nickel coins, with Euthydemus II, dating from 180 to 170 BCE, and his younger brothers Pantaleon and Agathocles around 170 BCE.

The theory of Chinese origins of Bactrian cupro-nickel was suggested in 1868 by Flight, who found the coins and considered the oldest cupro-nickel coins yet discovered were of a very similar alloy to Chinese paktong. Cunningham in 1873 argued the coins must have been the result of overland trade from China, through India to Greece — highly controversial at the time and much derided. In 1973, Cheng and Schwitter in their new analyses argued the Bactrian alloys (copper, lead, iron, nickel and cobalt) were closely similar to Chinese paktong, and that out of nine known Asian nickel deposits, only those in China could provide same identical chemical content ratios. However this hypothesis, although widely publicised, was later disproven by a perhaps over-enthusiastic oversight of the well-known Persian arsenic-nickel mines much closer to Bactria and known to be exploited by the Greeks and Persians.

Chinese history of cupronickel

The author-scholar Ho Wei describes most exactly the process in circa 1095 CE, which suggest the Chinese were not aware that nickel was a metal in its own right. The paktong alloy was described as being made from adding small pills of naturally-occurring "Yunnan" ore to a bath of molten copper. When a crust of slag formed, saltpeter was added, the alloy stirred and the ingot immediately cast. Zinc is mentioned as an ingredient — but not detailed when exactly it was added. The ore used is noted as solely available from Yunnan, related from the story:

San Mao Chun were at Tanyang during a famine year when many people died, so taking certain chemicals, Ying projected them onto silver, turning it into gold, and he also transmuted iron into silver — thus enabling the lives of many to be saved [through purchasing grain through this fake silver and gold] Thereafter all those who prepared chemical powders by heating and transmuting copper by projection called their methods "Tanyang techniques".

The late Ming and Ching literature have very little information about paktong. However, it is first mentioned specifically by name in the Thien Kung Khai Wu of circa 1637:

When lu kan shih (zinc carbonate, calamine) or wo chhein (zinc metal) is mixed and combined with chih thung (copper), one gets 'yellow bronze' (ordinary brass). When phi shang and other arsenic substances are heated with it, one gets 'white bronze' or white copper: pai thong. When alum and niter and other chemicals are mixed together one gets ching thung: green bronze.

Ko Hung of the 300 CE stated:" The Tanyang copper was created by throwing a mercuric elixir into Tanyang copper and heated- gold will be formed." 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.

Needham et al. argue that cupro-nickel was at least known as a unique alloy by the Chinese during the reign of Liu An in 120 BCE in Yunnan. Moreover the Yunnanese State of Tien was founded in 334 BCE as a colony of the Chu. Most likely modern paktong was unknown to Chinese of the day — but the naturally occurring Yunnan ore cupro-nickel alloy was likely a valuable internal trade commodity.

Western re-discovery

The alloy seems to have been re-discovered by the West during alchemy experiments. Notably Andreas Libavius, in his Alchemia of 1597 mentions a surface-whitened copper aes album by mercury or silver; but in De Natura Metallorum in Singalarum Part 1, of 1599 the same term was applied to '"tin" from the East Indies (modern-day Indonesia and the Philippines) and given the Spanish name: tintinaso.

Richard Watson of Cambridge appears to be the first to discover cupro-nickel was an alloy of three metals. In attempting to re-discover the secret of white-copper, Watson critiqued Jean-Baptiste Du Halde's History of China (1688) as confusing the term paktong, He noted the Chinese of his day did not form it as an alloy, but smelted readily available unprocessed ore:

appeared from a vast series of experiments made at Peking- that it occurred naturally as an ore mined at the region, the most extraordinary copper is pe-tong or white copper: it is white when dug out of the mine and even more white within than without. It appears , by a vast number of experiments made at Peking, that its colour is owing to no mixture; on the contrary, all mixtures diminish its beauty, for, when it is rightly managed it looks exactly like silver and were there not a necessity of mixing a little tutenag or such metal to soften it, it would be so much more the extraordinary as this sort of copper is found no where but in China and that only in the Province of Yunnan". Notwithstanding what is here said, of the colour of the copper being owing to no mixture, it is certain the Chinese white copper as brought to us, is a mixt [sic: mixed] metal; so that the ore from which it was extracted must consist of various metallic substances; and from such ore that the natural orichalcum if it ever existed, was made".

During the peak European importation of Chinese white-copper during 1750 to 1800, increased attention was made to its discovering its constituents—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%".

Another trial by Andrew Fyfe estimated the nickel content at 31.6%. Guesswork ended when James Dinwiddie of the Macartney Embassy of 1793 brought back, at considerable personal risk (smuggling of paktong ore was a capital crime by the Chinese Emperor) some of the ore from which paktong was made. Cupro-nickel became widely understood, as published by E. Thomason, in 1823, in a submission, later rejected for not being new knowledge, to the Royal Society of Arts.

Efforts to duplicate exactly the Chinese paktong failed in Europe due to a general lack of requisite complex cobalt-nickel-arsenic naturally occurring ore. However, the Schneeburg 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 and unsurprisingly, Dr E.A. Geitner and J.R. von Gersdoff of Schneeburg duly won the prize and launched their German silver under the trade name Argentan and Neusilber ("new Silver")

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 of 18% Ni, 55% Cu and 27% Zn. Between 1829 and 1833—Percival Norton Johnson was the first man to refine cupro-nickel on the British Isles: and became a wealthy man producing in excess of 16.5 tonnes per year, mainly made into cutlery by the Birmingham firm William Hutton and sold under the trade-name "Argentine". Johnsons' most serious competitor, 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: British Plate.

Coinage

File:5CHFr.jpg

Five Swiss francs

In Europe, Switzerland pioneered the nickel billion coinage in 1850, with the addition of silver. In 1879, Switzerland adopted the far cheaper 75:25 copper to nickel ratio then being used by the Belgians, the United States, and Germany.

In part due to silver hoarding in the Civil War, the United States Mint first used cupro-nickel for circulating coinage in three cent pieces starting in 1865 and then for five cent pieces starting in 1866. Prior to these dates, both denominations had been made only in silver in the United States. Cupro-nickel is the cladding on either side of United States Half Dollars (50¢) since 1971, and all quarters (25¢) and dimes (10¢) made after 1964. Currently some circulating coins like the United States Jefferson Nickel (5¢), the Swiss franc, and the South Korean 500 and 100 won are made of solid cupro-nickel (75/25 ratio).

See also

• bronze (copper alloyed with tin)
• brass (copper alloyed with zinc)
• nickel silver (another group of Cu-Ni alloys).

External links

• National Pollutant Inventory – Copper and compounds fact sheet
• National Pollutant Inventory – Nickel and compounds fact sheet