Cupronickel

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Cupronickel (sometimes incorrectly written as Cupernickel) or Coppernickel is an alloy of copper, nickel and strengthening impurities, such as iron and manganese. Cupronickel does not corrode in seawater, because its electrode potential 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.

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).

[edit] History

Cupronickel coin of king Pantaleon c. 170 BCE.
Obv: Bust of Dionysos with a wreath of leaves.
Rev: Panther with a small bell around the neck, touching a vine with the left leg. Greek legend: BASILEOS PANTALEONTOS "King Pantaleon".

Cupro-nickel was known to the Romans as an artificial "white" gold or silver termed "claudianum" and very possibly "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 copper-nickel alloy ^[1]

The ancient Greeks were producing it and a lower quality imitation of it in the Aegean Bronze Age and known as "orichalum". The Greco-Bactrian kings Euthydenus II dating from 180 to 170 BCE andhis younger brothers Pantaleon and Agathocles ^[2] around 170 BC.

The theory of Chinese origins of Bactrian cupro-nickel was suggested in 1868 by Flight, who found the coins, considered the oldest cupro-nickel coins yet discovered were of a very similar alloy to Chinese paktong.
^[3] Cunningham argued in 1873 the coins must be 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 only place the Bactrian alloys (copper, lead, iron, nickel and cobalt) are closely similar to Chinese paktong, and that out of nine known Asian nickel deposits, on those in China could provide such ratios.
^[4] However, this hypothesis although widely publicised, was later disproven by evidence by their perhaps over-enthusiastic oversight of the Persian arsenic-nickel mines much closer and far nearer to Bactria.^[5]

[edit] Chinese History of Cupro-Nickel

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 from the 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 exactly when 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 save [though 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"

.^[6]

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

When lu kan shih (zonc carbonate, calamine) or wo chhein (zinc metal is mixed and combined (with copper, chhih thung) on 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.

^[7]

Ko Hung of the 300 CE stated:" The Tanyang copper was created by throwing a merucric elixir into Tanyang copper and heated- gold will be formed." However, the Pha Phu Tsu and the Shen I Ching desrcibing 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.^[8]

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 Yuannanese State of Tien was founded in 334 BCE as a colony of Chhu. Most likely modern paktong was unknown to Chinese of the day- but the Yunnan ore was likely an internal trade commodity.^[9]

[edit] Western Re-Discovery

The alloy seems to have been re-discovered by the West during alchemy experiments, notably Anrdreas Libavius, in his Alchemia of 1597 where he 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 Phillippines ) and given the Spanish tintinaso.^[10]

Bishop Watson of Cambridge appears to be the first to discover cupro-nickel was an alloy of three metals. Bishop Watson of Cambridge in attempting to re-discover the secret of white-copper critiqued du Halde's History of China (1688) confuing the term paktong: Bishop Watson noted the Chinese of his day did not form it as an alloy, but smelt readily available 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 necesity 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 orichalum if it ever existed, was made"^[11]

During the peak European importation of Chinese white-copper during 1750 to 1800, increased attention was made to its' constituents whereby it was found by Peat and Cookson 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 Fyfe estimated the nickel content at 31.6%. The guessowrk ended when a Dr Dinwiddie of the Macartney Embassy of 1793 brought back some, at considerable personal risk (smuggling paktong ore was deemed a capital punishment by the CHiense Emperor) of the ore paktong was made^[12]. Cupro-nickel was now widely understood and made openly public by E.Thomason, in 1823, in his 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 ore. However, the Schneeburg district of Germany, where the famous Blufarbenwerke of cobalt blue and other pigments solely held the requisite complex cobalt-nickel-arsenic ores in Europe.
At the same time the Prussian Verein zur Beforderung des Gewerbeflessies offered a prize for the mastery of the process and unsurprisingly a Dr E.A Geitner and J.R von Gersdoff of Schneeburg won the prize and launched their German silver under the trade name Argentan or Neusilber^[13]
In 1829, Percival Norton Johnston persuaded 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% Zu.^[14]
Between 1829 and 1833- Johnson the first man to refine cupro-nickel on the British Isles was 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 BRrok 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.^[15]

[edit] Coinage

In Europe, Switzerland prioneereed the nickel billion coinage in 1850, with the addition of silver. In 1879, Switzerland adopted the far cheaper 75:25 copper to nickel ratio being used then by the Belgians, the United States and Germany.
Cupro-nickel was not used again in coinage until the 19th century. 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 1965. Currently some circulating coins like the United States Jefferson Nickel (5¢)^[16], the Swiss franc, and the South Korean 500 won^[17] are made of solid cupro-nickel (75/25 ratio).

[edit] Usage

Mineral Insulated wiring single-core thermocouple cables use a single conductor pair of thermocouple conductors such as iron-constantan, copper constantan, nickel-chromium/nickel-aluminium, have the heating element of constantan or nickel-chromium alloy within a sheath of copper, cupro-nickel or stainless steel ^[18].
Cupro-nickel has been used in many nations for coinage or as Monel metal and constantan for electrical resistances, and with Zinc for electroplated hospitality industry "silver-ware".^[19]
Beginning around the turn of the 20th century, bullet jackets were commonly made from this material. It was soon replaced with gilding metal to reduce metal fouling in the bore.

[edit] Physical properties

Cupro-nickel (70/30 ratio) melts at 1170C and has a density of 8910kg/m³ (0.322 lbs/cu in).^[20]

[edit] References

[edit] External links

• Copper.org
• Corrosion resistance - Copper Development Association UK
• National Pollutant Inventory - Copper and compounds fact sheet
• National Pollutant Inventory - Nickel and compounds fact sheet