Nichrome (also known as NiCr, nickel-chromium or chromium-nickel) is a family of

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

s of

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

and

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

(and occasionally

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

) commonly used as resistance wire, heating elements in devices like toasters, electrical kettles and space heaters, in some dental restorations (fillings) and in a few other applications. Patented in 1906 by Albert Marsh (US patent 811,859), nichrome is the oldest documented form of resistance heating alloy. The A Grade nichrome alloy is 80% nickel and 20% chromium by mass, but there are many other combinations of metals for various applications.

Properties

C Grade Nichrome is consistently silvery in color, is corrosion-resistant, has a high

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

of approximately , and has an

electrical resistivity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

of around 1.12 μΩ·m, which is around 66 times higher resistivity than copper of 16.78 nΩ·m. Some nichrome formulations have a resistivity as low as 1.0 μΩ·m or as high as 1.5 μΩ·m. Almost any conductive wire can be used for heating, but most metals conduct electricity with great efficiency, requiring them to be formed into very thin and delicate wires to create enough resistance to generate heat. When heated in air, most metals then oxidize quickly, become brittle and break. Nichrome wire, when heated to red-hot temperatures, develops an outer layer of chromium oxide, which is thermodynamically stable in air, is mostly impervious to oxygen, and protects the heating element from further oxidation. Nichrome alloys are known for their high mechanical strength and their high creep strength. The properties of nichrome vary depending on its alloy. Figures given are representative of typical material and are accurate to expressed significant figures. Any variations are due to different percentages of nickel or chromium.

Standard compositions

Nichrome alloys for use in resistance heating are described by both ASTM and DIN standards. These standards specify the relative percentages of

and

that should be present in an alloy. In ASTM three alloys that are specified contain, amongst other trace elements: * 80% Ni, 20% Cr * 60% Ni, 16% Cr * 35% Ni, 20% Cr

Properties by composition

Each standard composition of nichrome has unique material properties. Some general ones are given as follows:

Uses

Because of its low cost of manufacture, strength, ductility, resistance to

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

, stability at high temperatures, and electrical resistance, nichrome is widely used in electric heating elements in applications such as hair dryers and heat guns. Typically, nichrome is wound in coils to a certain

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual paral ...

, and when current is passed through it the

Joule heating Joule heating (also known as resistive heating, resistance heating, or Ohmic heating) is the process by which the passage of an electric current through a conductor (material), conductor produces heat. Joule's first law (also just Joule's law), ...

produces heat. Nichrome is used in the

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...

s and

fireworks Fireworks are Explosive, low explosive Pyrotechnics, pyrotechnic devices used for aesthetic and entertainment purposes. They are most commonly used in fireworks displays (also called a fireworks show or pyrotechnics), combining a large numbe ...

industry as a bridgewire in electric ignition systems, such as electric matches and

model rocket A model rocket is a small rocket designed to reach low altitudes (e.g., for a model) and #Model rocket recovery methods, be recovered by a variety of means. According to the United States National Association of Rocketry, National Associati ...

igniters. Industrial and hobby hot-wire foam cutters use nichrome wire. Nichrome wire is commonly used in

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

as an internal support structure to help some elements of

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

sculptures hold their shape while they are still soft. Nichrome wire is used for its ability to withstand the high temperatures that occur when clay work is fired in a

kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or Chemical Changes, chemical changes. Kilns have been used for millennia to turn objects m ...

. Nichrome wire can be used as an alternative to

platinum Platinum is a chemical element; it has Symbol (chemistry), symbol Pt and atomic number 78. It is a density, dense, malleable, ductility, ductile, highly unreactive, precious metal, precious, silverish-white transition metal. Its name origina ...

wire for flame testing by colouring the non-luminous part of a flame to detect cations such as sodium, potassium, copper, calcium, etc. Other areas of usage include motorcycle mufflers, in certain areas in the microbiological lab apparatus, as the heating element of plastic extruders by the

RepRap RepRap (a contraction of ''replicating rapid prototyper'') is a project to develop low-cost 3D printers that can print most of their own components. As open designs, all of the designs produced by the project are released under a free software l ...

3D printing community, in the solar panel deployment mechanism of spacecraft LightSail-A, and as the heating coils of electronic cigarettes. The

price is controlled by the more expensive

content. Distributor pricing is typically indexed to market prices for nickel. Nickel allergies are common; while the wire in heating elements is rarely directly touched by users of devices, some uses of nichrome are, and a 1984 study by the University of Puerto Rico showed that 28.5% of people tested had some kind of allergic reaction following contact with nickel.Blanco-Dalmau, L., Carrasquillo-Alberty, H., & Silva-Parra, J. (1984)
A study of nickel allergy
''The Journal of prosthetic dentistry'', ''52''(1), 116-119.

References

{{refs Nickel–chromium alloys Refractory metals Fire making Nickel alloys Electric heating

Properties

Standard compositions

Properties by composition

Uses

See also

References