Invar
544888
224722705
2008-07-10T03:24:41Z
Ummit
328950
missing word
[[Image:Invar-Graph-CTE-composition.png|thumb|350px|right|The coefficient of thermal expansion of nickel/iron alloys is plotted here against the nickel percentage (on a mass basis) in the alloy. The sharp minimum occurs at the Invar ratio of 36% '''Ni'''.]]
'''Invar''', also known generically as '''FeNi36''' ('''64FeNi''' in the US), is a [[nickel]] [[steel]] [[alloy]] notable for its uniquely low [[coefficient of thermal expansion]] (CTE or α). It was invented in 1896 by Swiss scientist [[Charles Edouard Guillaume]]. He received the [[Nobel Prize in Physics]] in 1920 for this discovery, which shows the importance of this alloy in scientific instruments. Like other [[nickel]]/[[iron]] compositions, Invar is a [[solid solution]]; that is, it is a single-[[Phase (matter)|phase]] [[alloy]] — similar to a dilution of common table salt mixed into water. "Invar" refers to invariable; that is, it will not react to thermal expansion.<ref name="alloying">{{cite book | last = Davis | first = Joseph R. | authorlink = | coauthors = | title = Alloying: Understanding the Basics | publisher = ASM International | date = | location = | pages = 587-589 | url = | doi = | id = | isbn = 0871707446 }}</ref>
Common grades of Invar have an α (20–100 °C) of about 1.2 × 10<sup>–6</sup> [[Kelvin|K]]<sup>–1</sup> (1.2 [[Parts-per notation|ppm]]/[[Celsius|°C]]). However, extra-pure grades (<0.1% [[Cobalt|Co]]) can readily produce values as low as 0.62–0.65 ppm/°C. Some formulations display [[negative thermal expansion]] (NTE) characteristics. It is used in precision instruments such as clocks, physics laboratory devices, seismic creep gauges, [[Shadow mask|shadow-mask]] frames,<ref>Nickel Institute: ''[http://www.nickelinstitute.org/index.cfm/ci_id/12313.htm Nickel & Its Uses]</ref> valves in motors, and [[antimagnetic watch]]es, etc.) However, it has a propensity to [[creep (deformation)|creep]].
Although Invar is today a widely used material in many industries and applications, this is a particular trademark of a French company named [[Imphy Alloys]]:{{Fact|date=March 2008}} this company originates from Aciéries d’Imphy (a small city near [[Nevers]], France) where the alloy was initially industrialised after its invention.
There are variations of the original Invar material that have slightly different coefficient of thermal expansion such as:
* Inovco, which Fe-33Ni-4.5Co and has an α (20–100 °C) of 0.55 ppm/°C.
* [[FeNi42]] (for example NILO alloy 42), has a nickel content of 42% and α ≈ 5.3 ppm/°C which matches that of [[silicon]] and therefore is widely used as lead frame material for electronic components, integrated circuits, etc.
* FeNiCo alloys — named [[Kovar]] or [[Dilver P]] — that have the same expansion behaviour as [[glass]], and because of that are used for optical parts in a wide range of temperatures and applications, such as [[satellite]]s.
==Source of Invar’s CTE properties==
A detailed explanation of Invar’s anomalously low CTE has proven elusive for physicists. All the iron-rich face centered cubic Fe-Ni alloys show Invar anomalies in their measured thermal and magnetic properties that evolve continuously in intensity with varying alloy composition. Scientists had once proposed that Invar’s behavior was a direct consequence of a high-magnetic-moment to low-magnetic-moment transition occurring in the face centered cubic Fe-Ni series (and that gives rise to the mineral [[antitaenite]]), however this has now been shown to be incorrect.<ref> K. Lagarec, D.G. Rancourt, S.K. Bose, B. Sanyal, and R.A. Dunlap. Observation of a composition-controlled high-moment/low-moment transition in the face centered cubic Fe-Ni system: Invar effect is an expansion, not a contraction. ''Journal of Magnetism and Magnetic Materials'' 236 (2001) 107-130.</ref> Instead, it appears that the low-moment/high-moment transition is preceded by a high-magnetic-moment [[Geometrically frustrated magnet|frustrated ferromagnetic state]] in which the Fe-Fe magnetic exchange bonds have a large magneto-volume effect of the right sign and magnitude to create the observed thermal expansion anomaly.<ref> D.G. Rancourt and M.-Z. Dang. Relation between anomalous magneto-volume behaviour and magnetic frustration in Invar alloys. ''Physical Review B'' 54 (1996) 12225-12231.</ref>
== References ==
<references/>
==External links==
*[http://orologeria.com/english/magazine/magazine3.htm What is Invar?, Antica Orologeria Lamberlan], retrieved Aug. 11, 2007. Properties of Invar, by Italian antique clock repair firm
*[http://asuwlink.uwyo.edu/~metal/invar.html Invar, Metalworking FAQ, Univ. of Wyoming], retrieved Aug. 11, 2007. Metallurgist Jim Kirkpatrick's notes on different Invar alloys, handling and sources.
*[http://www.imphyalloys.com/ Imphy Alloys] Commercial producer of Invar.
[[Category:Ferrous alloys]]
{{Link FA|nl}}
[[bg:Инвар]]
[[cs:Invar]]
[[de:Invar]]
[[es:Invar]]
[[fr:Invar]]
[[it:Invar]]
[[nl:Invar]]
[[ja:インバー]]
[[pl:Inwar]]
[[pt:Invar]]
[[ro:Invar]]
[[ru:Инвар (сплав)]]
[[fi:Invarteräs]]
[[sv:Invar]]
[[uk:Інвар]]
[[zh:不變鋼]]