Nichrome
Nichrome(also known asNiCr,nickel-chromiumorchromium-nickel) is a family ofalloysofnickelandchromium(and occasionallyiron[1]) commonly used asresistance wire,heating elementsin devices liketoasters,electrical kettlesandspace heaters,in somedental restorations(fillings) and in a few other applications.
Patented in 1906 byAlbert Marsh(US patent 811,859[2]), 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
[edit]C Grade Nichrome is consistently silvery incolour,is corrosion-resistant, has a highmelting pointof about 1,400°C(2,550°F), and has anelectrical resistivityof around 1.12 μΩ·m, which is around 66 times higher resistivity than copper of 16.78 nΩ·m.[3]Some nichrome formulations have a resistivity as low as 1.0 μΩ·m or as high as 1.5 μΩ·m.[4]
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 ofchromium oxide,[5]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.[6]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
[edit]Nichrome alloys for use in resistance heating are described by both ASTM and DIN standards.[7][8]These standards specify the relative percentages ofnickelandchromiumthat 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
[edit]Each standard composition of nichrome has unique material properties. Some general ones are given as follows:[9]
| Alloy | % Content | Density
[g/cm3] | ||
|---|---|---|---|---|
| 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
[edit]Because of its low cost of manufacture, strength, ductility, resistance tooxidation,stability at high temperatures, and resistance to the flow of electrons, nichrome is widely used in electricheating elementsin applications such as hair dryers and heat guns. Typically, nichrome is wound in coils to a certainelectrical resistance,and when current is passed through it theJoule heatingproduces heat.
Nichrome is used in theexplosivesandfireworksindustry as abridgewirein electric ignition systems, such aselectric matchesandmodel rocketigniters.
Industrial and hobby hot-wire foam cutters use nichrome wire.
Nichrome wire is commonly used inceramicas an internal support structure to help some elements ofclaysculptures 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 akiln.
Nichrome wire can be used as an alternative toplatinumwire forflame testingby colouring the non-luminous part of a flame to detectcationssuch as sodium, potassium, copper, calcium, etc.
Other areas of usage include motorcyclemufflers,in certain areas in the microbiological lab apparatus, as the heating element of plastic extruders by theRepRap3D printing community, in the solar panel deployment mechanism of spacecraftLightSail-A,and as the heating coils ofelectronic cigarettes.
Thealloyprice is controlled by the more expensivenickelcontent. Distributor pricing is typically indexed tomarket prices for nickel.
Toxicity
[edit]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.[10]
See also
[edit]References
[edit]- ^Flournoy, Blake."What Is Nichrome Wire Used for?".sciencing.Retrieved28 October2019.
- ^"US Patent 811,858"
- ^"Resistivity of some common materials". MWS Wire Industries, Inc.
- ^"Resistivity of Nichrome". hypertextbook
- ^""Advanced Topic: Oxidation Resistant Materials" (PDF). Sciences Education Foundation. General Atomics. 2002 "(PDF).Archived fromthe original(PDF)on 2016-03-04.Retrieved2016-01-05.
- ^"Nichrome - Union City Filament".Union City Filament.Retrieved2017-10-02.
- ^B02 Committee.Specification for Drawn or Rolled Nickel-Chromium and Nickel-Chromium-Iron Alloys for Electrical Heating Elements(Report). ASTM International.doi:10.1520/b0344-20.
{{cite report}}:CS1 maint: numeric names: authors list (link) - ^DIN 17470:1984-10, Heizleiterlegierungen; Technische Lieferbedingungen für Rund- und Flachdrähte(Report). Beuth Verlag GmbH.doi:10.31030/1164343.
- ^Hegbom, Thor (2017-12-19).Integrating Electrical Heating Elements in Product Design.CRC Press.ISBN978-1-4822-9220-6.
- ^Blanco-Dalmau, L., Carrasquillo-Alberty, H., & Silva-Parra, J. (1984).A study of nickel allergy.The Journal of prosthetic dentistry,52(1), 116-119.