Liquid metal

Liquid metal consists of alloys with very low melting points which form a eutectic that is liquid at room temperature.[1] The standard metal used to be mercury, but gallium-based alloys, which are lower both in their vapor pressure at room temperature and toxicity, are being used as a replacement in various applications.[2]

A few elemental metals are liquid at or near room temperature. The most well known is mercury, which is molten above −38.8 °C (234.3 K, −37.9 °F). Others include caesium, which has a melting point of 28.5 °C (83.3 °F), rubidium (39 °C [102 °F]), francium (estimated at 27 °C [81 °F]), and gallium (30 °C [86 °F]); bromine is also liquid at room temperature (melting at −7.2 °C, 19 °F), but it is a halogen, not a metal.

Thermal and electrical conductivity

Alloy systems that are liquid at room temperature have thermal conductivity far superior to ordinary non-metallic liquids,[3] allowing liquid metal to efficiently transfer energy from the heat source to the liquid. They also have a higher electrical conductivity that allows the liquid to be pumped by more efficient, electromagnetic pumps.[4] This results in the use of these materials for specific heat conducting and/or dissipation applications.

Another advantage of liquid alloy systems is their inherent high densities.

Wetting to metallic and non-metallic surfaces

Once oxides have been removed from the substrate surface, most liquid metals will wet to most metallic surfaces. Specifically though, room-temperature liquid metal can be very reactive with certain metals. Liquid metal can dissolve most metals; however, at moderate temperatures, only some are slightly soluble, such as sodium, potassium, gold, magnesium, lead, nickel and mercury.[5] Gallium is corrosive to all metals except tungsten and tantalum, which have a high resistance to corrosion, more so than niobium, titanium and molybdenum.[6]

Similar to indium, gallium and gallium-containing alloys have the ability to wet to many non-metallic surfaces such as glass and quartz. Gently rubbing the alloy into the surface may help induce wetting. However, this observation of "wetting by rubbing into glass surface" has created a widely spread misconception that the gallium-based liquid metals wet glass surfaces, as if the liquid breaks free of the oxide skin and wets the surface. The reality is the opposite: the oxide makes the liquid wet the glass. In more details: as the liquid is rubbed into and spread onto the glass surface, the liquid oxidizes and coats the glass with a thin layer of oxide (solid) residues, on which the liquid metal wets. In other words, what is seen is a gallium-based liquid metal wetting its solid oxide, not glass. Apparently, the above misconception was caused by the super-fast oxidation of the liquid gallium in even a trace amount of oxygen, i.e., nobody observed the true behavior of a liquid gallium on glass, until research at the UCLA debunked the above myth by testing Galinstan, a gallium-based alloy that is liquid at room temperature, in an oxygen-free environment.[7] Note: These alloys form a thin dull looking oxide skin that is easily dispersed with mild agitation. The oxide-free surfaces are bright and lustrous.

Applications

Typical uses of liquid metals include thermostats, switches, barometers, heat transfer systems, and thermal cooling and heating designs.[8] Uniquely, they can be used to conduct heat and/or electricity between non-metallic and metallic surfaces.

Liquid metal is used extensively by overclockers and computer enthusiasts to replace the original thermal interface on CPU and/or GPU dies to improve cooling efficiency and performance.[9]

    See also

    References

    1. ↑ http://www.quadsimia.com/, Quadsimia Internet Solutions -. "Indium Corporation Global Solder Supplier Electronics Assembly Materials". Indium Corporation. Retrieved 2017-11-26.
    2. ↑ Thermal Interface Materials
    3. ↑ Kunquan, Ma; Jing, Liu (October 2007). Liquid metal management of computer chips. Frontiers of Energy and Power Engineering in China. 1. Higher Education Press, co-published with Springer-Verlag GmbH. pp. 384–402. doi:10.1007/s11708-007-0057-3. ISSN 1673-7504.
    4. ↑ Miner, A.; Ghoshal, U. (2004-07-19). "Cooling of high-power-density microdevices using liquid metal coolants". Applied Physics Letters. 85 (3): 506–508. Bibcode:2004ApPhL..85..506M. doi:10.1063/1.1772862. ISSN 0003-6951.
    5. ↑ Wade, K.; Banister, A. J. (1975). The Chemistry of Aluminum, Gallium, Indium, and Thallium, Pergamon Texts in Inorganic Chemistry. 12. ASIN B0007AXLOA.
    6. ↑ Lyon, Richard N., ed. (1952). Liquid Metals Handbook (2 ed.). Washington, D.C.
    7. ↑ Liu, T.; S., Prosenjit; Kim, C.-J. (April 2012). Characterization of Nontoxic Liquid-Metal Alloy Galinstan for Applications in Microdevices. Journal of Microelectromechanical Systems. 21. IEEE. pp. 443–450. doi:10.1109/JMEMS.2011.2174421.
    8. ↑ Liquid Metal Thermal Interface Materials
    9. ↑ "Thermal Grizzly High Performance Cooling Solutions - Conductonaut". Thermal Grizzly. Retrieved 2018-06-01.
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