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Galinstan (R) is a brand name for a
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
composed of gallium,
indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
, and
tin Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
which melts at and is thus liquid at room temperature. However, it is not a eutectic alloy but a near eutectic alloy. In scientific literature, galinstan is also used as an acronym denoting the eutectic composition of the alloy of Ga-In-Sn, which melts at around . The composition of both alloys is roughly the same, albeit the Galinstan (R), the technical product of a company, has likely additions of flux to improve flowability, reduce melting temperature, and reduce surface tension. The physical properties of the Galinstan (R) and the pure eutectic alloy EGaInSn thus differ slightly. Galinstan is composed of 68.5%Ga, 21.5%In, and 10.0%Sn (by weight). Due to the low toxicity and low reactivity of its component metals, in many applications, galinstan has replaced the toxic liquid mercury or the reactive NaK (
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
alloy).


Name

The name "Galinstan" is a
portmanteau A portmanteau word, or portmanteau (, ) is a blend of wordsLatin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
for "tin"). The brand name "Galinstan" is a
registered trademark The registered trademark symbol, , is a typographic symbol that provides notice that the preceding word or symbol is a trademark or service mark that has been registered with a national trademark office. A trademark is a symbol, word, or wor ...
of the German company .


Physical properties

*Boiling point: >1300°C *
Vapour pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phase ...
: <10−8
Torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one " millimeter of merc ...
(at 500°C) *Solubility: Insoluble in water or organic solvents *
Viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
: 0.0024 Pa· s (at 20°C) *
Thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
: 16.5 W·m−1· K−1 * Electrical conductivity: 3.46×106 S/m (at 20°C) * Surface tension: ''s'' = 0.535–0.718 N/m (at 20°C, dependent on producer) Unlike mercury, galinstan tends to wet and adheres to many materials, including glass, which can limit its use as a direct replacement material in some situations.


Uses

The non-toxic galinstan replaces mercury in thermometers; the tube interior must be coated with gallium oxide to prevent it from wetting the glass. Galinstan has higher reflectivity and lower density than mercury. In
astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
, it can replace mercury in
liquid-mirror telescope Liquid-mirror telescopes are telescopes with mirrors made with a reflective liquid. The most common liquid used is mercury, but other liquids will work as well (for example, low-melting alloys of gallium). The liquid and its container are rotate ...
s. Metals or alloys like galinstan that are liquids at room temperature are often used by overclockers and enthusiasts as a thermal interface for computer hardware cooling, where their higher thermal conductivity compared to thermal pastes, and thermal epoxies can allow slightly higher clock speeds and CPU processing power achieved in demonstrations and competitive overclocking. Two examples are Thermal Grizzly Conductonaut and Coolaboratory Liquid Ultra, with thermal conductivities of 73 and 38.4 W/mK respectively. Unlike ordinary thermal compounds which are easy to apply and present a low risk of damaging hardware, galinstan is electrically conductive and causes
liquid metal embrittlement Liquid metal embrittlement (LME), also known as liquid metal induced embrittlement, is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when exposed to speci ...
in many metals including aluminum which is commonly used in heatsinks. Despite these challenges the users who are successful with their application do report good results. In August 2020, Sony Interactive Entertainment patented a galinstan-based thermal interface solution suitable for mass production, for use on the PlayStation 5. Galinstan is difficult to use for cooling fission-based
nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
s, because indium has a high
absorption cross section Absorption cross section is a measure for the probability of an absorption process. More generally, the term cross section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, electromagne ...
for
thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wi ...
s, efficiently absorbing them and inhibiting the fission reaction. Conversely, it is being investigated as a possible coolant for fusion reactors. Its nonreactivity makes it safer than other liquid metals, such as
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
and mercury. Galinstan is used as a liquid, deformable conductor in soft robotics and stretchable electronics. Galinstan can be used to replace wires, interconnects, and electrodes as well as the conductive element in inductor coils and dielectric composites for soft capacitors.


X-ray equipment

Extremely high-intensity sources of 9.25 keV X-rays (gallium K-alpha line) for X-ray phase microscopy of fixed tissue (such as mouse brain), from a focal spot about 10 μm × 10 μm, and 3-D
voxel In 3D computer graphics, a voxel represents a value on a regular grid in three-dimensional space. As with pixels in a 2D bitmap, voxels themselves do not typically have their position (i.e. coordinates) explicitly encoded with their values. I ...
s of about one cubic micrometer, may be obtained with an X-ray source that uses a liquid-metal galinstan anode. The metal flows from a nozzle downward at a high speed, and the high-intensity electron source is focused upon it. The rapid flow of metal carries current, but the physical flow prevents a great deal of anode heating (due to forced-convective heat removal), and the high boiling point of galinstan inhibits vaporization of the anode.


See also

* Field's metal, has a table of low melting point alloys * Rose's metal * Wood's metal


References


Sources

* *{{cite journal , doi = 10.1002/adfm.200701216 , title = Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature , year = 2008 , last1 = Dickey , first1 = Michael D. , first2 = Ryan C. , first3 = Ryan J. , first4 = Emily A. , first5 = David A. , first6 = George M. , journal = Advanced Functional Materials , volume = 18 , pages = 1097 , last2 = Chiechi , last3 = Larsen , last4 = Weiss , last5 = Weitz , last6 = Whitesides , issue = 7, s2cid = 538906 Gallium alloys Tin alloys