What Copper Is
Copper is a reddish-brown metal that has been used since antiquity. It is malleable and ductile, meaning it can be bent and formed without fracturing, and it has excellent electrical and thermal conductivity, which makes it the reference material for electrical conductors and heat exchangers. A freshly exposed pure copper surface is pinkish-orange, and in air it gradually forms a protective oxide or patina that gives the metal its good atmospheric corrosion resistance.
Commercially the metal is supplied as electrolytic tough pitch copper, phosphorus-deoxidised copper or oxygen-free copper, and each of these grades is defined by a standard such as ASTM B152 for sheet, strip and plate or ASTM B75 and ASTM B88 for tube and pipe.
What Nickel Is
Nickel is a silvery-white metal with a slight golden tinge, harder than copper but still malleable enough to be struck into coins or formed into jewellery and hardware. It has a much higher melting point than copper and forms a thin passive surface film that gives it useful resistance to many corrosive media, particularly alkalis. Because of that combination, nickel is used as an alloying element rather than as a structural metal in most applications.
Head-to-Head Comparison
| Property | Copper | Nickel |
|---|---|---|
| Colour | Reddish-brown to pinkish-orange when clean | Silvery-white with a slight golden tinge |
| Chemical symbol and atomic number | Cu, 29 | Ni, 28 |
| Density | approximately 8.96 g/cm³ | approximately 8.90 g/cm³ |
| Melting point | approximately 1083 °C | approximately 1455 °C |
| Electrical conductivity | about 59.6 million S/m, the 100 % IACS reference | about 14.3 million S/m, roughly a quarter of copper |
| Thermal conductivity | approximately 390 W/(m·K) | approximately 90 W/(m·K) |
| Hardness | Soft, about 3 on the Mohs scale | Harder, about 4 on the Mohs scale |
| Corrosion behaviour | Protective oxide or patina, excellent in the atmosphere and in water | Passive film, good in alkalis, attacked by sulphur-bearing media |
| Typical uses | Wiring, busbar, plumbing, roofing, heat exchangers | Stainless steel, plating, coinage, batteries, magnets, superalloys |
The single largest practical difference is colour, which is why the two metals are easy to distinguish by eye. The second is the electrical conductivity: copper carries roughly four times the current of nickel for the same cross-section, so nickel is never used as a conductor where copper is available. The third is temperature capability: nickel keeps useful strength far above the softening range of copper.
Corrosion and Service Behaviour Compared
Copper is used outdoors and in water systems because the film that forms on its surface is stable and self-repairing. Nickel behaves differently: it depends on a passive film that is very effective in strongly alkaline environments but is less stable in sulphur-bearing atmospheres, which is why nickel-plated parts are protected with a top coating in aggressive industrial locations. In flowing seawater neither pure metal is ideal on its own, which leads directly to the alloy family described below.
The Practical Answer: Copper-Nickel Alloys
Most industrial users do not choose between copper and nickel at all; they choose a controlled mixture of the two. Adding nickel to copper raises strength and dramatically improves resistance to flowing seawater, while retaining enough thermal conductivity to be useful in heat transfer.
C70600 copper-nickel 90/10 is the standard seawater piping and condenser tube material, used in power plants, desalination plant and shipboard systems.
C71500 copper-nickel 70/30 offers higher resistance to erosion and impingement and is used where water velocity and suspended solids are higher.
Nickel silver alloys containing copper, nickel and zinc combine a silvery appearance with good formability, and are used for instrument parts, cutlery and coinage.
Nickel additions in stainless steel of the order of eight to fourteen per cent stabilise the austenitic structure of grades such as 304 and 316, which is a major use of nickel by volume.
Heat exchanger and condenser tube in the copper-nickel family is specified to ASTM B111/B111M, where the exact alloy, temper and dimensions are defined for the duty concerned.
Selection Guidance and Sustainability
Choose copper where electrical or thermal conductivity is the governing requirement.
Choose nickel or a nickel-bearing alloy where high temperature strength, alkaline service or a specific magnetic or electrochemical property is needed.
Choose a copper-nickel alloy where seawater or brackish cooling water is involved and both corrosion resistance and heat transfer are required.
Remember that both metals are produced from natural ores and can be recycled indefinitely without losing their properties, which is why both retain a high scrap value at end of life.
FAQ
Q: What is the main difference between copper and nickel?
Colour and conductivity. Copper is reddish and is the standard electrical conductor, while nickel is silvery-white, much harder, melts at a higher temperature and carries only about a quarter of the current of copper for the same cross-section.
Q: Which metal has a higher melting point?
Nickel, at approximately 1455 °C, compared with approximately 1083 °C for copper.
Q: Is nickel a better conductor than copper?
No. Copper has an electrical conductivity of about 59.6 million siemens per metre, which is the basis of the 100 % IACS reference, while nickel reaches only about 14.3 million siemens per metre.
Q: Why are copper and nickel combined in alloys?
The combination gives higher strength and much better resistance to flowing seawater than pure copper, while keeping useful thermal conductivity. Copper-nickel grades are therefore the standard choice for marine and power plant condenser tube.
Q: Which standard covers copper-nickel condenser tube?
ASTM B111/B111M covers copper and copper alloy seamless condenser tubes and ferrule stock, including the 90/10 and 70/30 copper-nickel grades.
Q: Are copper and nickel recyclable?
Yes. Both are produced from natural ore and can be recycled repeatedly without losing their properties, and both command a high value as scrap.
