Cupronickel

Cupronickel, as the German kupfernickel, originally referred to the mineral form of nickel arsenide; natural deposits had superficial similarities to copper ores, and local folklore blamed the sprite Nickel (compare Old Nick) for the absence of usable copper and health issues from arsenic exposure. 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. The mineral was given its modern names, nickeline and niccolite, by the mid-19th century. Aside from cupronickel and copper–nickel, several other terms have been used to describe the material: the tradenames Alpaka or Alpacca, Argentan Minargent, the registered French term cuivre blanc, Chinese silver, and the romanized Cantonese term Paktong, 白銅 (the French and Cantonese terms both meaning "white copper"). Cupronickel alloys containing zinc are referred to as nickel silver, also sometimes hotel silver, German silver, plata alemana (Spanish for "German silver"). ==Applications==

Marine engineering Cupronickel alloys are used for marine applications due to their resistance to seawater corrosion, good fabricability, and their effectiveness in lowering macrofouling levels. Alloys ranging in composition from 90% Cu–10% Ni to 70% Cu–30% Ni are commonly specified in heat exchanger or condenser tubes in a wide variety of marine applications. Important marine applications for cupronickel include: • Shipbuilding and repair: hulls of boats and ships, seawater cooling, bilge and ballast, sanitary, fire fighting, inert gas, hydraulic and pneumatic chiller systems. • Desalination plants: brine heaters, heat rejection and recovery, and in evaporator tubing. • Offshore oil and gas platforms and processing and FPSO vessels: systems and splash zone sheathings. • Power generation: steam turbine condensers, oil coolers, auxiliary cooling systems and high pressure pre-heaters at nuclear and fossil fuel power plants. • Seawater system components: condenser and heat exchanger tubes, tube sheets, piping, high pressure systems, fittings, pumps, and water boxes. Coinage The successful use of cupronickel in coinage is due to its corrosion resistance, electrical conductivity, durability, malleability, low allergy risk, ease of stamping, antimicrobial properties and recyclability. In Europe, Switzerland pioneered cupronickel-based billon coinage in 1850, with the addition of silver and zinc, for coins of 5, 10 and 20 Rappen. Starting in 1860/1861, Belgium issued 5, 10 and 20 Centimes in pure cupronickel (75% copper, 25% nickel, without additional silver and zinc), and Germany issued 5 and 10 Pfennig in the same 75:25 ratio from 1873/1874 (until 1915/1916). In 1879, Switzerland, for 5 and 10 Rappen coins, also adopted that cheaper 75:25 copper to nickel ratio then being used in Belgium, the United States and Germany. From 1947 to 2012, all "silver" coinage in the UK was made from cupronickel (but from 2012 onwards the two smallest UK cupronickel denominations were replaced with lower-cost nickel-plated steel coins). Moreover, when silver prices rose in the 1960s/1970s also some other European countries replaced remaining silver denominations by cupronickel, e.g. the 1/2 to (pictured) 5 Swiss franc coins starting 1968 and German 5 Deutsche Mark 1975–2001. Since 1999, cupronickel is also used for the inner segment of the 1 euro coin and the outer segment of the 2 euro coin. In part due to silver hoarding in the Civil War, the United States Mint first used cupronickel 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. Cupronickel 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, such as the United States Jefferson nickel (5¢), the Swiss franc, and the South Korean 500 and 100 won are made of solid cupronickel (75:25 ratio). Decorative housewares Nickel silver cupronickels are used extensively as a substitute for silver in tableware and other decorative housewares. Nickel silver is also used as a base for silver plating, where the product is known as electro-plated nickel silver, or EPNS. Other usage A thermocouple junction is formed from a pair of thermocouple conductors such as iron-constantan, copper-constantan or nickel-chromium/nickel-aluminium. The junction may be protected within a sheath of copper, cupronickel or stainless steel. Cupronickel is used in cryogenic applications. It retains high ductility and thermal conductivity at very low temperatures. Where other metals like steel or aluminum would shatter and become thermally inert, cupronickel's unusual thermal and mechanical performance at these low temperatures facilitate a number of niche uses. Machinery that must perform many duty cycles at continuously low-temperatures and heat exchangers at cryogenic plants are the main industrial destinations of cupronickel in cryogenic applications. Niche applications also exist, for example the alloy's high thermal conductivity at low temperatures has made cupronickel ubiquitous in freeze branding operations. In the early 20th century, this material was used to make bullet jackets. But it was soon replaced by gilding metal to reduce metal contamination of the barrel bore. Currently, cupronickel and nickel silver remain the basic material for silver-plated cutlery. It is commonly used for mechanical and electrical equipment, medical equipment, zippers, jewelry items, and both for strings for instruments in the violin family, and for guitar frets. Fender Musical Instruments used "CuNiFe" magnets in their "Wide Range Humbucker" pickup for various Telecaster and Starcaster guitars during the 1970s. For high-quality cylinder locks and locking systems, cylinder cores are made from wear-resistant cupronickel. Cupronickel has been used as an alternative to traditional steel hydraulic brake lines (the pipes containing the brake fluid), as it does not rust. 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. ==Physical and mechanical properties==

Cupronickel lacks a copper color due to nickel's high electronegativity, which causes a loss of one electron in copper's d-shell (leaving 9 electrons in the d-shell versus pure copper's typical 10 electrons). 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 antimicrobial touch surface properties. Subtle differences in corrosion resistance and strength determine which alloy is selected. Descending the table, the maximum allowable flow rate in piping increases, as does the tensile strength. In seawater, the alloys have excellent corrosion rates which remain low as long as the maximum design flow velocity is not exceeded. This velocity depends on geometry and pipe diameter. They have high resistance to crevice corrosion, stress corrosion cracking and hydrogen embrittlement that can be troublesome to other alloy systems. Copper–nickels naturally form a thin protective surface layer over the first several weeks of exposure to seawater and this provides its ongoing resistance. Additionally, they have a high inherent biofouling resistance to attachment by macrofoulers (e.g. seagrasses and molluscs) living in the seawater. To use this property to its full potential, the alloy needs to be free of the effects of, or insulated from, any form of cathodic protection. However, Cu–Ni alloys can show high corrosion rates in polluted or stagnant seawater when sulfides or ammonia are present. It is important, therefore, to avoid exposure to such conditions, particularly during commissioning and refit while the surface films are maturing. Ferrous sulfate dosing to sea water systems can provide improved resistance. As copper and nickel alloy with each other easily and have simple structures, the alloys are ductile and readily fabricated. Strength and hardness for each individual alloy is increased by cold working; they are not hardened by heat treatment. Joining of 90–10 (C70600) and 70–30 (C71500) is possible by both welding or brazing. They are both weldable by the majority of techniques, although autogenous (welding without weld consumables) or oxyacetylene methods are not recommended. The 70–30 rather than 90–10 weld consumables are normally preferred for both alloys and no after-welding heat treatment is required. They can also be welded directly to steel, providing a 65% nickel–copper weld consumable is used to avoid iron dilution effects. The C71640 alloy tends to be used as seamless tubing and expanded rather than welded into the tube plate. Brazing requires appropriate silver-base brazing alloys. However, great care must be taken to ensure that there are no stresses in the Cu–Ni being silver brazed, since any stress can cause intergranular penetration of the brazing material, and severe stress cracking (see image). Thus, full annealing of any potential mechanical stress is necessary. 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. They have also been used as splash zone cladding on offshore structures and protective cladding on boat hulls, as well as for solid hulls themselves. ==Fabrication==

Due to its ductility, cupronickel alloys can be readily fabricated in a wide variety of product forms and fittings. Cupronickel tubing can be readily expanded into tube sheets for the manufacturing of shell and tube heat exchangers. Details of fabrication procedures, including general handling, cutting and machining, forming, heat treatment, preparing for welding, weld preparations, tack welding, welding consumables, welding processes, painting, mechanical properties of welds, and tube and pipe bending are available. ==Standards==

ASTM, EN, and ISO standards exist for ordering wrought and cast forms of cupronickel. Thermocouples and resistors whose resistance is stable across changes in temperature contain alloy constantan, which consists of 55% copper and 45% nickel. ==History==

Obverse: Bust of Dionysos with a wreath of leaves. Reverse: Panther with a small bell around the neck, touching a vine with the left leg. Greek legend: BASILEOS PANTALEONTOS "King Pantaleon". --> Chinese history Cupronickel alloys were known as "white copper" to the Chinese since about the third century BC. Some weapons made during the Warring States period were made with Cu-Ni alloys. The theory of Chinese origins of Bactrian cupronickel was suggested in 1868 by Flight, who found that the coins considered the oldest cupronickel coins yet discovered were of a very similar alloy to Chinese paktong. The author-scholar, Ho Wei, precisely described the process of making cupronickel in about 1095 AD. The paktong alloy was described as being made by 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 was stirred and the ingot was immediately cast. Zinc is mentioned as an ingredient but there are no details about when it was added. The ore used is noted as solely available from Yunnan, according to 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". Cupronickel 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 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. Unsurprisingly, Dr E.A. Geitner and J.R. von Gersdoff of Schneeberg won the prize and launched their "German silver" brand under the trade names Argentan and Neusilber (new silver). In 1866, the US Congress passed a law authorizing the creation of a 3-cent coin consisting of 75% copper and 25% nickel, and the nickel, as it became known, was created. Brazil adopted the alloy for coin in 1870, and Imperial Germany followed in 1873. France and Greece adopted of this technology in the 20th century. After the unification of Germany cupronickel coinage was introduced by the German Coinage Act, and sudden demand of nickel for tens of millions of 5 and 10 pfennig coins minted in 1873-1876 caused such a shock on the previously tranquil market that price more than tripled, leading to a significant expansion of supply. By 1902 the alloy was used in the UK for bullet jackets. By the 1920s, a 70–30 copper–nickel grade was developed for naval condensers. Soon afterwards, a 2% manganese and 2% iron alloy now known as alloy C71640 was introduced for a UK power station which needed better erosion resistance because the levels of entrained sand in the seawater. A 90–10 alloy first became available in the 1950s, initially for seawater piping, and is now the more widely used alloy for this purpose. ==See also==