Editing Heating element (section)

===Metal alloys===
Resistance heating [[alloy]]s are metals that can be used for electrical heating purposes above 600&nbsp;°C in air. They can be distinguished from resistance alloys which are used primarily for resistors operating below 600&nbsp;°C.<ref name=":1">{{Cite book |last=Hegbom |first=Thor |url=https://books.google.com/books?id=LDsPEAAAQBAJ |title=Integrating Electrical Heating Elements in Product Design |date=2017-12-19 |publisher=CRC Press |isbn=978-1-4822-9220-6 |pages= |language=en}}</ref>

While the majority of atoms in these alloys correspond to the ones listed in their name, they also consist of trace elements. Trace elements play an important role in resistance alloys, as they have a substantial influence on mechanical properties such as work-ability, form stability, and oxidation life.<ref name=":1" /> Some of these trace elements may be present in the basic raw materials, while others may be added deliberately to improve the performance of the material. The terms ''contaminates'' and ''enhancements'' are used to classify trace elements.<ref name=":6" /> Contaminates typically have undesirable effects such as decreased life and limited temperature range. Enhancements are intentionally added by the manufacturer and may provide improvements such as increased oxide layer adhesion, greater ability to hold shape, or longer life at higher temperatures.

The most common alloys used in heating elements include:

==== Ni-Cr(Fe) alloys (AKA nichrome, Chromel) ====
Ni-Cr(Fe) resistance heating alloys, also known as [[nichrome]] or [[Chromel]], are described by both ASTM and DIN standards.<ref name=":3">{{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|url-access=subscription }}</ref><ref name=":5">{{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|url-access=subscription }}</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

Nichrome 80/20 is one of the most commonly used resistance heating alloys because it has relatively high resistance and forms an adherent layer of [[chromium oxide]] when it is heated for the first time. Material beneath this layer will not oxidize, preventing the wire from breaking or burning out.

==== Fe-Cr-Al alloys (AKA Kanthal®) ====
Fe-Cr-Al resistance heating alloys, also known as [[Kanthal (alloy)|Kanthal®]], are described by an ASTM standard.<ref name=":4">{{Cite report |url=http://www.astm.org/cgi-bin/resolver.cgi?B603-07R18 |title=Specification for Drawn or Rolled Iron-Chromium-Aluminum Alloys for Electrical Heating Elements |last=B02 Committee |publisher=ASTM International |doi=10.1520/b0603-07r18 |language=en|url-access=subscription }}</ref> Manufacturers may opt to use this class of alloys as opposed to Ni-Cr(Fe) alloys to avoid the typically relatively higher cost of nickel as a raw material compared to aluminum. The tradeoff is that Fe-Cr-Al alloys are more brittle and less ductile than Ni-Cr(Fe) ones, making them more delicate and prone to failure.<ref name=":2">{{Cite web |date=2021-09-27 |title=Why Your Toaster Will Eventually Fail You |url=https://www.nytimes.com/wirecutter/blog/your-toaster-will-eventually-fail/ |access-date=2023-12-29 |website=Wirecutter: Reviews for the Real World |language=en-US}}</ref>

On the other hand, the aluminum oxide layer that forms on the surface of Fe-Cr-Al alloys is more thermodynamically stable than the chromium oxide layer that tends to form on Ni-Cr(Fe), making Fe-Cr-Al better at resisting corrosion.<ref name=":2" /> However, humidity may be more detrimental to the wire life of Fe-Cr-Al than Ni-Cr(Fe).<ref name=":1" />

Fe-Cr-Al alloys, like stainless steels, tend to undergo [[embrittlement]] at room temperature after being heated in the temperature range of 400 to 575&nbsp;°C for an extended duration.<ref>{{Cite journal |last1=Nichol |first1=T. J. |last2=Datta |first2=A. |last3=Aggen |first3=G. |date=April 1980 |title=Embrittlement of ferritic stainless steels |url=https://link.springer.com/10.1007/BF02670694 |journal=Metallurgical Transactions A |language=en |volume=11 |issue=4 |pages=573–585 |doi=10.1007/BF02670694 |issn=0360-2133|url-access=subscription }}</ref>

==== Other alloys ====
* Cu-Ni alloys ([[cupronickel]]): Used for low temperature heating
* Heating elements for high-temperature [[Industrial furnace|furnace]]s are often made of exotic materials, including [[platinum]], [[tungsten disilicide]]/[[molybdenum disilicide]], and [[molybdenum]] ([[vacuum furnace]]s).