Liquid metal

For other uses, see Liquid metal (disambiguation).

Liquid metal consists of gallium-containing alloys with very low melting points which form a eutectic which is liquid at room temperature.[1] The standard metal used to be mercury, but gallium-based alloys are being used as a replacement in various applications. Mercury is toxic, and has a high vapor pressure at room temperature.[2] Gallium alloys have reduced toxicity and a lower vapor pressure than mercury.

Thermal and electrical conductivity

Alloy systems that are liquid at room temperature have a high degree of thermal conductivity far superior to ordinary non-metallic liquids.[3] The high degree of thermal conductivity allows liquid metal to efficiently transfer energy from the heat source to the liquid. Alloy system's also has a high electrical conductivity compared to other non-metallic liquid. The property of high electrical conductivity 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. Other advantages of liquid alloy systems are their inherent high densities and electrical conductivities.

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 interestingly mercury.[5] Gallium is corrosive to all metals except tungsten and tantalum, which have a high resistance to corrosion. Niobium, titanium and molybdenum have resistance to corrosion, but less so than tungsten and tantalum.[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 gallium-containing 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 glass 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 C. J. Kim's group at UCLA debunked the above myth by testing Galinstan, a gallium-based alloy that is liquid at room temperature, in a completely 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 applications for 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.

Packaging

Liquid metal is usually packed in polyethylene bottles.

Storage/shelf life

Unopened bottles of liquid metal generally have a one-year shelf life. It is recommended that, as the liquid metal is removed from the bottle, the volume be replaced with dry argon gas. This will minimize the possibility of oxidation at the surface of the alloy. If the liquid metal has been stored below its melting point and has solidified, it should be re-melted and thoroughly shaken or mixed before use. Care should be taken in reheating the liquid metal in the original packaging provided. Temperatures should not exceed 65 °C (149 °F).

General handling guidelines

In popular culture

A fictional "mimetic polyalloy" is a form of liquid metal consisting entirely of microscopic nanobots, which are used for production of a Series 1000 Terminator in Terminator 2: Judgment Day.

See also

References

  1. ↑ Indalloy Alloys Liquid at Room Temperature
  2. ↑ Thermal Interface Materials
  3. ↑ Kunquan, Ma; Jing, Liu (October 2007). Liquid metal cooling in thermal management of computer chips. Frontiers of Energy and Power Engineering in China (Review Article) 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. 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, ASIN B0007AXLOA 12. External link in |title= (help)
  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 (Journal Article) 21 (IEEE). pp. 443–450. doi:10.1109/JMEMS.2011.2174421.
  8. ↑ Liquid Metal Thermal Interface Materials
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