Galinstan
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Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at −19 °C (−2 °F).[1] Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed toxic liquid mercury or reactive NaK (sodium-potassium alloy). A typical composition is 68.5% Ga, 21.5% In and 10% Sn, with trace amounts of copper. Its name is a portmanteau of gallium, indium, and stannum (Latin for "tin"). Galinstan is a registered trademark of the German company Geratherm Medical AG.
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[edit] Physical properties
- Boiling point: >1300 °C
- Melting point: -19 °C
- Vapour pressure: <10−8 Torr (at 500 °C)
- Density: 6.44 g/cm3 (at 20 °C)[2]
- 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: 3.46x106 S/m (at 20 °C)[2]
- Surface tension: s = 0.718 N/m (at 20 °C)[2]
Galinstan tends to 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 must be coated with gallium oxide to prevent the alloy from wetting the glass surface.
Galinstan has higher reflectivity and lower density than mercury; it is investigated as a replacement for mercury in liquid mirror telescopes for astronomy. It is also a promising coolant, though its cost and aggressivity (it corrodes many other metals by dissolving them) are major obstacles for its use. Small amounts have begun to be sold as thermal grease to computer enthusiasts; it has a much better heat conductivity compared to more standard thermal pastes (allowing hot chips such as CPUs and GPUs to run several degrees cooler), but needs to be applied more carefully than the electrically isolating standard greases, since spills can cause short circuits. Additionally, it is unusable with the common heat sink material aluminum, which is invaded and made brittle to the point of crumbling by Galinstan.
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.[3]
[edit] See also
[edit] References
- ^ Surmann, P; Zeyat, H (Nov 2005). "Voltammetric analysis using a self-renewable non-mercury electrode.". Analytical and bioanalytical chemistry 383 (6): 1009–13. doi:10.1007/s00216-005-0069-7. PMID 16228199.
- ^ a b c "Experimental Investigations of Electromagnetic Instabilities of Free Surfaces in a Liquid Metal Drop". International Scientific Colloquium Modelling for Electromagnetic Processing, Hannover. March 24–26, 2003. http://sci-toys.com/scitoys/scitoys/thermo/liquid_metal/oscillations_in_galinstan.pdf. Retrieved 2009-08-08.
- ^ Lee C. Cadwallader (2003). "Gallium Safety in the Laboratory" (preprint). http://www.osti.gov/bridge/servlets/purl/811932-smXmM0/native/811932.pdf.
- Scharmann, F.; Cherkashinin, G.; Breternitz, V.; Knedlik, Ch.; Hartung, G.; Weber, Th.; Schaefer, J. A. (2004). "Viscosity effect on GaInSn studied by XPS". Surface and Interface Analysis 36 (8): 981. doi:10.1002/sia.1817.
- Dickey, Michael D.; Chiechi, Ryan C.; Larsen, Ryan J.; Weiss, Emily A.; Weitz, David A.; Whitesides, George M. (2008). "Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature". Advanced Functional Materials 18 (7): 1097. doi:10.1002/adfm.200701216.
