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Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel
Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
 steel
Steel

Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.14% by weight , depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten....
 alloy
Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
 notable for its uniquely low coefficient of thermal expansion
Coefficient of thermal expansion

When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds....
 (CTE or a). It was invented in 1896 by Swiss scientist Charles Édouard Guillaume
Charles Edouard Guillaume

Charles ?douard Guillaume was a Swiss physicist who received the Nobel Prize in Physics in 1920 in recognition of the service he had rendered to precision measurements in physics by his discovery of anomalies in nickel steel alloys....
. He received the Nobel Prize in Physics
Nobel Prize in Physics

The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in chemistry, Nobel Prize in literature, Nobel Peace Prize, and Nobel Prize in physiology or medicine....
 in 1920 for this discovery, which shows the importance of this alloy in scientific instruments.






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Invar Graph Cte Composition
Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel
Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
 steel
Steel

Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.14% by weight , depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten....
 alloy
Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
 notable for its uniquely low coefficient of thermal expansion
Coefficient of thermal expansion

When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds....
 (CTE or a). It was invented in 1896 by Swiss scientist Charles Édouard Guillaume
Charles Edouard Guillaume

Charles ?douard Guillaume was a Swiss physicist who received the Nobel Prize in Physics in 1920 in recognition of the service he had rendered to precision measurements in physics by his discovery of anomalies in nickel steel alloys....
. He received the Nobel Prize in Physics
Nobel Prize in Physics

The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in chemistry, Nobel Prize in literature, Nobel Peace Prize, and Nobel Prize in physiology or medicine....
 in 1920 for this discovery, which shows the importance of this alloy in scientific instruments. Invar is a registered trademark of ArcelorMittal - Stainless & Nickel Alloys, formerly known as Imphy Alloys (US Trademark #63970). Like other nickel
Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
/iron
Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
 compositions, Invar is a solid solution
Solid solution

A solid solution is a solid-phase solution of one or more soluble in a solvent. Such a mixture is considered a solution rather than a Chemical compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single wiktionary:Homogeneous phase ....
; that is, it is a single-phase
Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, refractive index, and chemical composition....
 alloy
Alloy

An alloy is a partial or complete solid solution of one or more chemical element in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history....
 — similar to a dilution of common table salt mixed into water. "Invar" refers to invariable; that is, it will not react to thermal expansion.

Common grades of Invar have an a (20–100 °C) of about 1.2 × 10–6 K
Kelvin

The kelvin is a Units of measurement of temperature and is one of the seven SI base units. The Kelvin scale is a Thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero ....
–1 (1.2 ppm
Parts-per notation

?Parts-per? notation is used, especially in science and engineering, to denote Proportionality in measured quantities; particularly in low-value proportions at the parts-per-million , parts-per-billion , and parts-per-trillion level....
/°C
Celsius

Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death....
). However, extra-pure grades (<0.1% Co
Cobalt

Cobalt is a hard, lustrous, grey metal, a chemical element with symbol Co and atomic number 27. Although cobalt-based colors and pigments have been used since ancient times, and miners have long used the name kobold ore for some minerals, cobalt was only discovered in 1735 by Georg Brandt....
) can readily produce values as low as 0.62–0.65 ppm/°C. Some formulations display negative thermal expansion
Negative thermal expansion

Negative Thermal Expansion is a physical chemistry process in which some materials contract upon heating rather than thermal expansion as most materials do....
 (NTE) characteristics. It is used where high dimensional stability is required, such as precision instruments, clocks, seismic creep gauges, television shadow-mask
Shadow mask

The shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images ....
 frames, valves in motors, and antimagnetic watch
Antimagnetic watch

Anti-magnetic watches are those that are able to run with minimal deviation when exposed to a certain magnetic field. The International Organization for Standardization issued a standard for magnetic resistant watches, which many countries have adopted....
es. However, it has a propensity to creep
Creep (deformation)

Creep is the tendency of a solid material to slowly move or deform permanently under the influence of stress es. It occurs as a result of long term exposure to levels of stress that are below the yield strength of the material....
. In Land Surveying, when first-order (high-precision) elevation leveling is to be performed, the leveling rods used are made of Invar, instead of wood, fiberglass, or other metals.

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 a (20–100 °C) of 0.55 ppm/°C.
  • FeNi42 (for example NILO alloy 42), has a nickel content of 42% and a ˜ 5.3 ppm/°C which matches that of silicon
    Silicon

    Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
     and therefore is widely used as lead frame material for electronic components, integrated circuits, etc.
  • FeNiCo alloys — named Kovar
    Kovar

    Kovar is a nickel-cobalt ferrous alloy designed to be compatible with the thermal expansion characteristics of borosilicate glass in order to allow direct mechanical connections over a range of temperatures....
     or Dilver P — that have the same expansion behaviour as borosilicate glass
    Borosilicate glass

    File:Schott Duran glassware.jpgBorosilicate glass is a type of glass with the main glass-forming constituents silicon dioxide and boron oxide....
    , and because of that are used for optical parts in a wide range of temperatures and applications, such as satellite
    Satellite

    In the context of spaceflight, a satellite is an Physical body which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
    s.


Source of Invar’s thermal 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
Antitaenite

Antitaenite is a Meteorite metal alloy mineral composed of iron and nickel, 20-40% Ni that has a face centered cubic crystal structure. Its existence as a new mineral species occurring in both iron meteorites and in chondrites was first recognized in 1995....
), however this has now been shown to be incorrect. Instead, it appears that the low-moment/high-moment transition is preceded by a high-magnetic-moment 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.

See also

  • Elinvar
    Elinvar

    Elinvar is a nickel steel alloy with a modulus of elasticity which does not change much with temperature changes. The name is a contraction of the French Elasticit? invariable....


External links

  • , retrieved Aug. 11, 2007. Properties of Invar, by Italian antique clock repair firm
  • , retrieved Aug. 11, 2007. Metallurgist Jim Kirkpatrick's notes on different Invar alloys, handling and sources.