Alloy of copper containing nickel

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Two stacks of Half dollars. The coins in the stack on the right are composed of cupronickel, and can be distinguished from the silver half dollars on the left by their visible copper cores.

Cupronickel or copper–nickel (CuNi) is an alloy of copper with nickel, usually along with small quantities of other elements added for strength, such as iron and manganese. The copper content typically varies from 60 to 90 percent. (Monel is a nickel–copper alloy that contains a minimum of 52 percent nickel.)

Despite its high copper content, cupronickel is silver in colour. 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 is sometimes used for the propellers, propeller shafts, and hulls of high-quality boats. Other uses include military equipment and chemical, petrochemical, and electrical industries.[1]

Another common 20th-century use of cupronickel was silver-coloured coins. For this use, the typical alloy has 3:1 copper to nickel ratio, with very small amounts of manganese.

In the past, true silver coins were debased with cupronickel, such as coins of the pound sterling from 1947 onward having their content replaced.

Name

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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, and the romanized Cantonese term Paktong, 白銅 (the French and Cantonese terms both meaning "white copper"); cupronickel is also occasionally referred to as hotel silver, plata alemana (Spanish for "German silver"), German silver, and Chinese silver.[2]

Applications

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Marine engineering

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Cupronickel alloys are used for marine applications[3] 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.[4]

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.[5][6]
• Desalination plants: brine heaters, heat rejection and recovery, and in evaporator tubing.[7]
• Offshore oil and gas platforms and processing and FPSO vessels: systems and splash zone sheathings.[8]
• Power generation: steam turbine condensers, oil coolers, auxiliary cooling systems and high pressure pre-heaters at nuclear and fossil fuel power plants.[9]
• Seawater system components: condenser and heat exchanger tubes, tube sheets, piping, high pressure systems, fittings, pumps, and water boxes.[10][11]

Coinage

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Five Swiss francs Five Indian rupees, commemorating ILO

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.[12]

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.[13] Starting in 1860/1861, Belgium issued 5, 10 and 20 Centimes in pure cupronickel (75% copper, 25% nickel, without additional silver and zinc),[14][15] and Germany issued 5 and 10 Pfennig in the same 75:25 ratio from 1873/1874 (until 1915/1916).[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. 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[19] 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¢),[20] the Swiss franc, and the South Korean 500 and 100 won are made of solid cupronickel (75:25 ratio).[21]

Other usage

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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.[22]

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.[23][24][25] Niche applications also exist, for example the alloy's high thermal conductivity at low temperatures has made cupronickel ubiquitous in freeze branding operations.[26]

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.

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.[citation needed]

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.

Properties

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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 cryogenic temperatures and beneficial antimicrobial touch surface properties.[27]

Properties of some Cu–Ni alloys[28] Alloy UNS No. Common name European spec Ni[29] Fe[29] Mn[29] Cu Density
g/cm3 Thermal conductivity
W/(m·K) TEC
μm/(m·K) Electrical resistivity
μOhm·cm Elastic modulus
GPa Yield strength
MPa Tensile strength
MPa C70600 90–10 Cu90Ni10 9–11 1–1.8 1 Balance 8.9 40 17 19 135 105 275 C71500 70–30 Cu70Ni30 29–33 0.4–1.0 1 Balance 8.95 29 16 34 152 125 360 C71640 66–30–2–2 Cu66Ni30Fe2Mn2 29–32 1.7–2.3 1.5–2.5 Balance 8.86 25 15.5 50 156 170 435

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.

Crack in 90–10 Cu–Ni metal plate due to stresses during silver brazing

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

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Due to its ductility, cupronickel alloys can be readily fabricated in a wide variety of product forms[30] 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.[31]

Standards

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ASTM, EN, and ISO standards exist for ordering wrought and cast forms of cupronickel.[32]

Thermocouples and resistors whose resistance is stable across changes in temperature contain alloy constantan, which consists of 55% copper and 45% nickel.

History

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For more highly magnetic nickel-iron-molybdenum alloyinformation, please contact us. We will provide professional answers.

Chinese history

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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.[33] 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.[34]

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".[34]

The late Ming and Qing 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."[34]

Ko Hung stated in 300 AD: "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.[34]

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. Moreover, the Yunnanese State of Tien was founded in 334 BC as a colony of the Chu. 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.[34]

Greco-Bactrian coinage

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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. Coins of a similar alloy with busts of his younger brothers, Pantaleon and Agathocles, were minted around 170 BCE. The composition of the coins was later verified using the traditional wet method and X-ray fluorescence spectrometry.[34] 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. Cammann.[34]

In 1973, Cheng and Schwitter in their new analyses suggested that the Bactrian alloys (copper, lead, iron, nickel and cobalt) were closely similar to the Chinese paktong, and of nine known Asian nickel deposits, only those in China could provide the identical chemical compositions.[34] 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. If the Bactrian nickel theory were true, according to Cammann, the Silk Road would have increased the supply of cupronickel. However, the end of Greco-Bactrian cupronickel currency could be attributed to other factors such as the end of the House of Euthydemus.[34]

European history

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The alloy seems to have been rediscovered 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, 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.[34]

Richard Watson of Cambridge appears to be the first to discover that cupronickel was an alloy of three metals. In attempting to rediscover 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 rather 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."[34]

During the peak European importation of Chinese white-copper from 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 brought back in 1793, 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.[35] 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).[35]

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.[35]

Between 1829 and 1833, Percival Norton Johnson was the first person to refine cupronickel on the British Isles. He became a wealthy man, producing in excess of 16.5 tonnes per year. The alloy was mainly made into cutlery by the Birmingham firm William Hutton and sold under the trade-name "Argentine".

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".[35]

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.

See also

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References

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Copper Nickel Alloy Wire Heating

CopperNickel (also known as copper-nickel) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Despite its high copper content, copper-nickel is silver in colour. Due to the specific properties of nickel and copper alloys, they are applied in various domains of industry e.g. mint industry, armaments industry, desalination industry, marine engineering, extensively used in the chemical, petrochemical and electrical industries. copper-nickel is highly resistant to corrosion in seawater because its electrode potential is adjusted to be neutral with regard to seawater. For this reason, it is used for piping, heat exchangers and condensers in seawater systems, marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats. Another common use of copper-nickel is in silver-coloured modern-circulated coins. A typical mix is 75% copper, 25% nickel, and a trace amount of manganese. In the past, true silver coins were debased with copper-nickel. Single-core thermocouple cables use a single conductor pair of thermocouple conductors such as iron-constantan, copper constantan or nickel-chromium/nickel-aluminium. These have the heating element of constantan or nickel-chromium alloy within a sheath of copper, copper-nickel or stainless steel.

Copper Nickel Resistance Alloys

Copper Nickel (CuNi) alloys are medium to low resistance materials typically used in applications with maximum operating temperatures up to 600°C (1,110°F).

With low temperature coefficients of electrical resistance, resistance, and thus performance, is consistent regardless of temperature. Copper Nickel alloys mechanically boast good ductility, are easily soldered and welded, as well as have outstanding corrosion resistance. These alloys are typically used in high current applications requiring a high level of precision.

Copper Nickel Alloy Wires for the manufacturing of low temperatures electric resistances so as heating principally destined cables, shunts, resistances for automobile, they have a maximum operating temperature of 400 °C. They do not therefore intervene in the field of resistances for industrial furnaces. The most known, CuNi 44 (also called Constantan) presents the advantage of a very low temperature coefficient.

There are also CuMnNI alloys of chemical composition copper and nickel with addition of manganese with a low resistivity (from 0.49 to 0.05 Ohm mm²/m).

Common Name: Alloy 294, Alloy 49, Cu-Ni 44
Motor control, heating wires and cables; precision and vitreous resistors, potentiometers.
Datasheet

Common Name: Alloy 30, Cu-Ni 23, Cu-Ni 23, Alloy 260
Alloy exhibits low resistivity and high temperature coefficient of resistance. Typical applications include voltage regulators, timing devices, temperature sensitive resistors, temperature compensating devices, motor control, heating wires and cables, precision and vitreous resistors, potentiometers, and low temperature heating applications.
Datasheet

Common Name: Alloy 95, 90 Alloy, Cu-Ni 10, Cu-Ni 10, Alloy 320
Alloy exhibits low resistivity and high temperature coefficient of resistance. Typical applications include voltage regulators, timing devices, temperature sensitive resistors, temperature compensating devices, motor control, heating wires and cables, precision and vitreous resistors, potentiometers, and low temperature heating applications.
Datasheet

Common Name: Alloy 180, 180 Alloy, Cu-Ni 23, Nickel Alloy 180
Alloy exhibits low resistivity and high temperature coefficient of resistance. Typical applications include voltage regulators, timing devices, temperature sensitive resistors, temperature compensating devices, motor control, heating wires and cables, precision and vitreous resistors, potentiometers, and low temperature heating applications.
Datasheet

Copper Nickel Resistance Heating Wire

Copper Nickel Resistance Heating Wire are principally destined for the manufacturing of low temperatures electric resistances so as heating cables, shunts, resistances for automobile, they have a maximum operating temperature of 752°F. They do not therefore intervene in the field of resistances for industrial furnaces. Those are alloys of chemical composition copper + nickel with addition of manganese with a low resistivity (from 231.5 to 23.6 Ohm.mm2/ft). The most known, CuNi 44 (also called Constantan) presents the advantage of a very low temperature coefficient.

Their advantages are the following:

• Very good resistance to corrosion
• Very good malleability
• Very good solderability

Copper–manganese alloys (~84% Cu, 12% Mn with nickel, aluminium or germanium as the remaining constituent). These Cu-Mn-Ni alloys are sold under various proprietary names, and manganin, the pioneer alloy of this group, was for many years the traditional material for high-grade standard resistors. The resistivity is about 40 × 10−8 Ω m and varies approximately parabolically with temperature over the range 0 to 50 °C, with a maximum close to 20 °C. The temperature coefficient can be as low as 3 × 10−6 °C−1 over the range 15 °C to 20 °C. Its secular stability is very good and, if wires are supported in strain-free conditions, can be less than 1 in 107 per year. The thermo-e.m.f. of the alloys against copper is close to zero and may be positive or negative according to composition and heat treatment. Joints between the copper manganese alloys and copper are made most effectively by welding in an atmosphere of argon, and by hard soldering if welding is impracticable.

Copper–nickel alloys (~55% Cu, 45% Ni). These alloys are manufactured commercially under a wide range of proprietary names, and are used in the construction of standard resistors. The resistivity is about 50 × 10−8 Ω m with a temperature coefficient which may lie between ±0.000 04 °C−1. The alloys can be soft-soldered with ease, but their high thermo-e.m.f. against copper (~40 μV °C−1) is a disadvantage in d.c. resistors, although the effect is usually negligible in a.c. resistors dropping 1 volt or more. These alloys are also used for current controlling resistors when constancy is more important than low cost.

Copper-nickel alloy is designed for specialized electrical and electronic applications. It has a very low temperature coefficient of resistance and medium-range electrical resistivity. Used for wire-wound precision resistors and bimetal contacts which change on heating by electrical resistance.

Copper Nickel Low Resistance Alloy is used in Heat Exchangers and Condensers. Good thermal conductivity and corrosion resistance to the sea water flow rates required have allowed copper-nickel tubing to remain an established alloy where high reliability is called for. A copper-nickel alloy of the 70-30 type having superior weldability. It is resistant to corrosion and biofouling in seawater, has good fatigue strength, and has relatively high thermal conductivity. Used for seawater condensers, condenser plates, distiller tubes, evaporator and heat exchanger tubes, and saltwater piping.

Copper Nickel Alloy Properties

• Low General Corrosion Rates in Sea Water General corrosion rates of copper nickel alloys are normally in the order of 0.0025-0.025mm/yr, which makes the alloy suitable for requirements in most marine applications.
• Resistance to Stress Corrosion Cracking Due to Ammonia in Sea Water  Copper based alloys (e.g. brass) can be susceptible to ammoniacal stress corrosion cracking. However copper-nickel has the highest resistance to this and stress corrosion in sea water is not known to be a problem.
• High Resistance to Crevice Corrosion & Stress Corrosion due to Chlorides Copper-nickel is not susceptible to the type of crevice corrosion and stress corrosion cracking found in stainless steels. As such there is not a related temperature limitation for use in chloride environments.
• Good Pitting Resistance  The resistance to pitting in clean sea water is good and if pits do occur they tend to be broad and shallow in nature rather than undercut.
• Readily Weldable and No Post Weld Heat Treatment Required Copper-nickel is straightforward to weld by conventional welding techniques.The alloy can also be welded to steel.
• Easy to Fabricate Hot and cold working techniques can be used but because of the good ductility of the alloy, cold working is normally preferred.

Copper-Nickel Foil For Heating Elements

Cu-Ni Foil is an extremely good combination property that is used in the largest amount and most widely as a corrosion resistance alloy. This alloy in hydrofluoric acid and fluoride gas medium with excellent corrosion resistance, as well as to the hot concentrated alkali. At the same time, it is corrosion resistant to neutral solution, sea water, air, organic compounds. An important feature of this copper nickel alloy is generally not to generate stress corrosion cracking and have good cutting performance. Cu-Ni Foil alloy is high-intensity single-phase solid solution.

Cu - Ni Foil alloy in fluoride gas, hydrochloric acid, sulfuric acid, hydrofluoric acid and their derivatives have a very good corrosion resistance property, and possess better corrosion resistance more than copper alloy in the sea water. Acid medium: Cu-Ni Alloy Foil have corrosion resistance in less than 85% consistency of sulfuric acid. Cu-Ni Foil alloy is an important material that resistant to hydrofluoric acid. Water corrosion: Cu-Ni Foil alloy in most corrosion cases of water, not only excellent corrosion resistance, but also less pitting, stress corrosion, the corrosion rate less than 0.025mm. High temperature corrosion: Cu-Ni Alloy Foil for the work of the highest temperature at about 600 °C in general in the air, in the high temperature steam, the corrosion rate less than 0.026mm. Ammonia: Cu-Ni Alloy Foil can be resistant to an hydrous ammonia and aminate conditions corrosion below 585 °C due to the high nickel.

Cu-Ni Foil copper nickel alloy is a multi-purpose material in many industrial applications: 

1. Seamless water pipe in the power factory
2. Sea-water exchanger and evaporator
3. Sulfuric acid and hydrochloric acid environment
4. Crude distillation
5. Sea-water in the use of equipment and propeller shaft
6. Nuclear industry and used in the manufacture of uranium enrichment isotope separation equipmen
7. Manufacturing hydrochloric acid equipment used in the production of pump and valve. 

Heater utilizing copper-nickel alloy

An electrical resistance heater which utilizes a copper-nickel alloy heating cable. This metallurgy heating cable is significantly less prone to failure due to localized overheating because the alloy has a low temperature coefficient of resistance. Used as a well heater, the heating cable permits heating of long segments of subterranean earth formation with a power supply of 400 to 1200 volts.

Copper Nickel Electrical low resistance heaters suitable for heating long intervals of subterranean earth formations have been under development for many years. These heaters have been found to be useful for carbonizing hydrocarboncontaining zones for use as electrodes within reservoir formations, for enhanced oil recovery and for recovery of hydrocarbons from oil shales. One process is to create electrodes utilizing a subterranean heater. The heater utilized is capable of heating an interval of 20 to 30 meters within subterranean oil shales to temperatures of 500°C. to 1000°C. Iron or chromium alloy resistors are utilized as the core heating element. These heating elements have a high resistance and relatively large voltage is required for the heater to extend over a long interval with a reasonable heat flux. It would be preferable to utilize lower resistance material. Further, it would be preferable to use a material which is malleable to permit more economical fabrication of the heater.

Subterranean heaters having copper core heating elements are disclosed. This core has a low resistance, which permits heating long intervals of subterranean earth with a reasonable voltage across the elements. Further, because copper is a malleable material, this heater is much more economical to fabricate. These heaters can heat 1000-foot intervals of earth formations to temperatures of 600° C. to 1000° C. with 100 to 200 watts per foot of heating capacity with a 1200 volt power source. But copper also has shortcomings as a material for a heating element. As the temperature of a copper heating element increases, the electrical resistance increases at a rate which is undesirably high. If a segment of the heating coil becomes excessively hot, the increase in electrical resistance of the hot segment causes a cascading effect which can result in failure of the element.

A subterranean heater utilizing an electric resistant heater element having a lower temperature coefficient of resistance would not only improve temperature stability, but would simplify the power supply circuitry. It is therefore the object to provide an improved heater capable of heating long intervals of subterranean earth wherein the heating element has a low temperature coefficient of resistance, a low electrical resistance, and utilizes a core of a malleable metal material.

When this copper-nickel alloy is incorporated into such a heater cable the benefits of a low resistance heater are obtained along with the benefit of having a low temperature coefficient of resistance. The heater cable material is also malleable. Such a heater can therefore be utilized to heat subterranean intervals of earth to temperatures of 500° C. to 1000° C. utilizing voltages in the range of 400 to 1000 Volts.

These copper nickel alloy heater coils are less likely to fail prematurely because the resistance of the cable in hot segments is much nearer to the resistance of the remaining coil. Hot spots therefore have less tendency to continue to increase in temperature due to higher electrical resistance, causing premature failure. The electrical resistance of the copper nickel alloy element also varies less between the initial cool state and the service temperatures which simplifies the power supply circuitry. The benefits of the low resistance and low temperature coefficient of resistance copper nickel alloy heater element are most significant when the heater is one which applies heat over large intervals of subterranean earth and at a temperature level of 600° C. to 1000° C. lntervals of 1000 feet or more can be heated with these heaters.

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Article courtecy of Copper Development Association Inc. Applications include heating cords and mats. Copper Nickel CuproNickel or Alloy 60 is characterised by low resistivity, with a medium resistance to oxidation and chemical corrosion. The maximum working temperature is 300 used in heating cables and in electrical welded fittings.