Liquid metal
Liquid metal consists of gallium-contained alloys with very low melting points. These low melting point alloys are liquid at room temperature.[1] The standard used to be mercury but gallium-based alloys are being used as a replacement in various applications. Mercury has a high vapor pressure at room temperature.[2] These alloys have reduced toxicity and a lower vapor pressure than mercury.
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[edit] 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] 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.
[edit] 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 Na, K, Au, Mg, Pb, Ni and interestingly Hg.[4] As stated, 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 than tungsten and tantalum.[5] 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. 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.
[edit] Applications
Typical applications for liquid metals include thermostats, switches, barometers, heat transfer systems, and thermal cooling and heating designs.[6] Uniquely, they can be used to conduct heat and/or electricity between non-metallic and metallic surfaces.
[edit] Packaging
Liquid metal is usually packaged in polyethylene bottles.
[edit] 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. 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 65.6°C.
[edit] General handling guidelines
- Liquid metal should be frozen prior to shipping and shipped in an unrefrigerated solid state.
- Materials may be stored at room temperatures.
- Gallium-contained alloys have a specific shelf life and should be managed as a first-in, first-out (FIFO) product. Packaging should be labeled with date and time of opening.
- Liquid metal should be shipped in accordance with the applicable international regulations and reported as a corrosive liquid. Due to their corrosive nature, they should not be put in contact with most other metals.
- Liquid metal should be stored in a cool, dry area away from incompatible materials, including hydrogen peroxide, hydrochloric acid, and halogenated chemicals.
- Prior to use, liquid metal should be allowed to reach room temperature and liquefy. Shake or mix before use.
- Allow up to four hours for solidified liquid metal to reach room temperature. Remove from storage one day before use.
- Rapid warming of liquid metal on top of an oven or by any other method is not recommended.
- A temperature-controlled water bath may be used. Gallium-containing alloys are very corrosive when hot. Its temperature should not exceed 65°C.
- Gallium may be absorbed through the skin. Rubber or vinyl gloves should be worn at all times when handling gallium-containing alloys.
- It is not recommended to repackage gallium-containing alloys from their original packaging.
- As the liquid metal is removed from the packaging, it is recommended that the volume be replaced with dry argon to minimize the possibility of oxidation on the surface of the alloy.
[edit] See also
[edit] References
- ^ Indalloy Alloys Liquid at Room Temperature
- ^ Thermal Interface Materials
- ^ Kunquan, Ma; Jing, Liu (October 2007) (Review Article). Liquid metal cooling in thermal management of computer chips. 1. Higher Education Press, co-published with Springer-Verlag GmbH. 384–402. doi:10.1007/s11708-007-0057-3. ISSN 1673-7504.
- ^ Wade, K.; Banister, A. J. (1975). The Chemistry of ALUMINUM, GALLIUM, INDIUM, and THALLIUM, Pergamon Texts in Inorganic Chemistry, ASIN #B0007AXLOA. 12.
- ^ Lyon, Richard N., ed. (1952). Liquid Metals Handbook (2 ed.). Washington, D.C..
- ^ Liquid Metal Thermal Interface Materials
