Galinstan is a brand name and a common name for any member of a family of liquid metal eutectic alloys whose composition is mainly consisting of gallium, indium, and tin. Such eutectic alloys are liquids at room temperature, typically melting at +11 °C (52 °F), while commercial Galinstan melts at −19 °C (−2 °F).
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, galinstan finds use as a replacement for many applications that previously employed the toxic liquid mercury or the reactive NaK (sodium–potassium alloy).
- Boiling point: > 1300 °C
- Melting point: −19 °C
- Vapour pressure: < 10−8 Torr (at 500 °C)
- Density: 6.44 g/cm3 (at 20 °C)
- Solubility: Insoluble in water or organic solvents
- Viscosity: 0.0024 Pa·s (at 20 °C)
- Thermal conductivity: 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)
- Specific heat capacity: 296 J·kg−1·K−1
Galinstan tends to be "wet" and adhere to many materials, including glass, which limits its use compared to mercury.
Galinstan is commercially used as a mercury replacement in thermometers due to its nontoxic properties, but the inner tube surface must be coated with gallium oxide to prevent the alloy from wetting the glass surface.
Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them). It is also electrically conductive, and so needs to be applied more carefully than regular non-conductive compounds. Two thermal interfaces have already been developed: Thermal Grizzly Conductonaut and Coolaboratory Liquid Ultra, with thermal conductivities of 73 and 38.4 W/mK respectively. However, they must be carefully applied with a Q-tip (unlike ordinary thermal compounds, where no manual spreading is needed), and cannot be used on aluminum heatsinks as aforementioned. 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 reactors, because indium has a high absorption cross section for thermal neutrons, efficiently absorbing them and inhibiting the fission reaction. Conversely, it is being investigated as a possible coolant for fusion reactors. Unlike other liquid metals used in this application, such as lithium and mercury, the nonreactivity makes galinstan a safer material to use.
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 voxels 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.
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