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{{Short description|Family of alloys of mainly nickel and chromium}}
'''Nichrome''' (also known as '''NiCr''', '''nickel-chromium''' or '''chromium-nickel''') is a family of [[alloy]]s of [[nickel]] and [[chromium]] (and occasionally [[iron]]<ref name="sciencing">{{cite web |last1=Flournoy |first1=Blake |title=What Is Nichrome Wire Used for? |url=https://sciencing.com/nichrome-wire-used-for-5871336.html |website=sciencing.com |access-date=28 October 2019}}</ref>) commonly used as [[resistance wire]], [[Heating element|heating elements]] in devices like [[Toaster|toasters]], [[Electric water boiler|electrical kettles]] and [[Space heater|space heaters]], in some [[dental restoration]]s (fillings) and in a few other applications.

Patented in 1906 by [[Albert L. Marsh|Albert Marsh]] (US patent 811,859<ref>[https://patents.google.com/patent/US811859A/en?oq=811859"US Patent 811,858"]</ref>), 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 [[colour]], is corrosion-resistant, has a high [[melting point]] of about {{convert|1400|C|F|lk=on}}, and has an [[Electrical resistivity and conductivity|electrical resistivity]] of around 112&nbsp;μΩ–cm, which is around 66 times higher resistivity than copper of 1.678&nbsp;μΩ–cm.<ref>[https://mwswire.com/resistance-wire-2/ "Resistivity of some common materials".  MWS Wire Industries, Inc.]</ref>

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]],<ref>{{Cite web |url=http://www.sci-ed-ga.org/websites/gasef/images/pdf/light/section_13.pdf |title="Advanced Topic: Oxidation Resistant Materials" (PDF). Sciences Education Foundation. General Atomics. 2002 |access-date=2016-01-05 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304083053/http://www.sci-ed-ga.org/websites/gasef/images/pdf/light/section_13.pdf |url-status=dead }}</ref> 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.<ref>{{Cite news|url=https://ucfilament.com/materials/nichrome/|title=Nichrome - Union City Filament|work=Union City Filament|access-date=2017-10-02|language=en-US}}</ref> 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.<ref>{{Cite report |url=http://www.astm.org/cgi-bin/resolver.cgi?B344-20 |title=Specification for Drawn or Rolled Nickel-Chromium and Nickel-Chromium-Iron Alloys for Electrical Heating Elements |last=B02 Committee |publisher=ASTM International |doi=10.1520/b0344-20 |language=en}}</ref><ref>{{Cite report |url=https://www.beuth.de/de/-/-/1151382 |title=DIN 17470:1984-10, Heizleiterlegierungen; Technische Lieferbedingungen für Rund- und Flachdrähte |publisher=Beuth Verlag GmbH |doi=10.31030/1164343}}</ref> These standards specify the relative percentages of [[nickel]] and [[chromium]] 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:<ref name=":1">{{Cite book |last=Hegbom |first=Thor |url=https://books.google.com/books/about/Integrating_Electrical_Heating_Elements.html?id=LDsPEAAAQBAJ |title=Integrating Electrical Heating Elements in Product Design |date=2017-12-19 |publisher=CRC Press |isbn=978-1-4822-9220-6 |language=en}}</ref> 
{| class="wikitable"
|+Table of nichrome alloys
! rowspan="2" |Alloy
! colspan="3" |% Content
! rowspan="2" |Density
[g/cm<sup>3</sup>]
|-
!Ni
!Cr
!Fe
|-
|NiCr 80/20
|80
|20
|0
|8.3
|-
|NiCr 70/30
|70
|30
|0
|8.1
|-
|NiCr 60/16
|60
|16
|Remainder
|8.2
|-
|NiCr 35/20
|35
|20
|Remainder
|7.9
|}

== Uses ==

Because of its low cost of manufacture, strength, ductility, resistance to [[oxidation]], stability at high temperatures, and resistance to the flow of electrons, nichrome is widely used in electric [[heating element]]s in applications such as hair dryers and heat guns. Typically, nichrome is wound in coils to a certain [[electrical resistance]], and when current is passed through it the [[Joule heating]] produces heat.

Nichrome is used in the [[explosive]]s and [[fireworks]] industry as a [[bridgewire]] in electric ignition systems, such as [[electric match]]es and [[model rocket]] igniters.

Industrial and hobby hot-wire foam cutters use nichrome wire.

Nichrome wire is commonly used in [[ceramic]] as an internal support structure to help some elements of [[clay]] 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]].

Nichrome wire can be used as an alternative to [[platinum]] wire for [[flame test]]ing 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 [[muffler]]s, in certain areas in the microbiological lab apparatus, as the heating element of plastic extruders by the [[RepRap]] 3D printing community, in the solar panel deployment mechanism of spacecraft [[LightSail-A]], and as the heating coils of [[electronic cigarette]]s.

The [[alloy]] price is controlled by the more expensive [[nickel]] content. Distributor pricing is typically indexed to [[Nickel#Market value|market prices for nickel]].

== Toxicity ==
{{Further|Nickel allergy}}Nickel is a common allergen, 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.<ref>Blanco-Dalmau, L., Carrasquillo-Alberty, H., & Silva-Parra, J. (1984). [http://www.laserandholisticdental.com/wp-content/uploads/2016/03/a-study-of-nickel-allergy.pdf A study of nickel allergy]. ''The Journal of prosthetic dentistry'', ''52''(1), 116-119.</ref>

== See also ==

* [[Chromel]]
* [[Constantan]]
* [[Hastelloy]]
* [[Inconel]]
* [[Kanthal (alloy)|Kanthal]]

== References ==

{{refs}}

[[Category:Nickel–chromium alloys]]
[[Category:Refractory metals]]
[[Category:Fire making]]
[[Category:Nickel alloys]]
[[Category:Electric heating]]