Liquid metal

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Liquid gallium metal, at 30degC (86degF). Liquid gallium pouring.png
Liquid gallium metal, at 30°C (86°F).

A liquid metal is a metal or a metal alloy which is liquid at or near room temperature. [1]

Contents

The only stable liquid elemental metal at room temperature is mercury (Hg), which is molten above −38.8 °C (234.3 K, −37.9 °F). Three more stable elemental metals melt just above room temperature: caesium (Cs), which has a melting point of 28.5 °C (83.3 °F); gallium (Ga) (30 °C [86 °F]); and rubidium (Rb) (39 °C [102 °F]). The radioactive metal francium (Fr) is probably liquid close to room temperature as well. Calculations predict that the radioactive metals copernicium (Cn) and flerovium (Fl) should also be liquid at room temperature. [2]

Alloys can be liquid if they form a eutectic, meaning that the alloy's melting point is lower than any of the alloy's constituent metals. The standard metal for creating liquid alloys 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. [3] [4]

Thermal and electrical conductivity

Alloy systems that are liquid at room temperature have thermal conductivity far superior to ordinary non-metallic liquids, [5] 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 more efficiently, by electromagnetic pumps. [6] 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.

Viscosity

The viscosity of liquid metals can vary greatly depending on the atomic composition of the liquid, especially in the case of alloys. In particular, the temperature dependence of the viscosity of liquid metals may range from the standard Arrhenius law dependence, to a much steeper (non-Arrhenius) dependence such as that given empirically by the Vogel-Fulcher-Tammann equation. A physical model for the viscosity of liquid metals, which captures this great variability in terms of the underlying interatomic interactions, was also developed. [7] [8]

The electrical resistance of a liquid metal can be estimated by means of the Ziman formula, which gives the resistance in terms of the static structure factor of the liquid as can be determined by neutron or X-ray scattering measurements.

Wetting to metallic and non-metallic surfaces

Gallium wets skin, as shown here. Liquid gallium residue.png
Gallium wets skin, as shown here.

Once oxides have been removed from the substrate surface, most liquid metals will wet most metallic surfaces. At room temperature, liquid metals are often reactive and soluble to metallic surfaces, though some solid metals are resistant to attack by the common liquid metals. [9] For example gallium is corrosive to all metals except tungsten and tantalum, which have a high resistance to corrosion, more so than niobium, titanium and molybdenum. [10]

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. [11] 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

Because of their excellent characteristics and manufacturing methods, liquid metals are often used in wearable devices, medical devices, interconnected devices and so on. [3] [4]

Typical uses of liquid metals include thermostats, switches, barometers, heat transfer systems, and thermal cooling and heating designs. [12] Uniquely, they can be used to conduct heat and/or electricity between non-metallic and metallic surfaces.

Liquid metal is sometimes used as a thermal interface material between coolers and processors because of its high thermal conductivity. The PlayStation 5 video game console uses liquid metal to help cool high temperatures inside the console. [13] Liquid metal cooled reactors also use them.

Liquid metal can be used for wearable devices [4] [3] and for spare parts. [14]

Liquid metal can sometimes be used for biological applications, i.e., making interconnects that flex without fatigue. As Galinstan is not particularly toxic, wires made from silicone with a core of liquid metal would be ideal for intracardiac pacemakers and neural implants where delicate brain tissue cannot tolerate a conventional solid implant. In fact, a wire constructed of this material can be stretched to 3 or even 5 times its length and still conduct electricity, returning to its original size and shape with no loss. [15]

Due to their unique combination of high surface tension and fluidic deformability, liquid metals have been found to be a remarkable material for creating soft actuators. [16] [17] [18] The force-generating mechanisms in liquid metal actuators are typically achieved by modulation of their surface tension. [19] [20] [21] For instance, a liquid metal droplet can be designed to bridge two moving parts (e.g., in robotic systems) in such a way to generate contraction when the surface tension increases. [22] The principles of muscle-like contraction in liquid metal actuators have been studied for their potential as a next-generation artificial muscle that offers several liquid-specific advantages over other solid materials. [23]

See also

Related Research Articles

<span class="mw-page-title-main">Gallium</span> Chemical element, symbol Ga and atomic number 31

Gallium is a chemical element; it has symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, gallium is in group 13 of the periodic table and is similar to the other metals of the group.

<span class="mw-page-title-main">Glass</span> Transparent non-crystalline solid material

Glass is a non-crystalline solid that is often transparent, brittle and chemically inert. It has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics.

A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

<span class="mw-page-title-main">Metallic bonding</span> Type of chemical bond in metals

Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons and positively charged metal ions. It may be described as the sharing of free electrons among a structure of positively charged ions (cations). Metallic bonding accounts for many physical properties of metals, such as strength, ductility, thermal and electrical resistivity and conductivity, opacity, and lustre.

<span class="mw-page-title-main">Solder</span> Alloy used to join metal pieces

Solder is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.

<span class="mw-page-title-main">Amorphous metal</span> Solid metallic material with disordered atomic-scale structure

An amorphous metal is a solid metallic material, usually an alloy, with disordered atomic-scale structure. Most metals are crystalline in their solid state, which means they have a highly ordered arrangement of atoms. Amorphous metals are non-crystalline, and have a glass-like structure. But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity and can show metallic luster.

<span class="mw-page-title-main">Thermal paste</span> Fluid used to maximize thermal contact

Thermal paste is a thermally conductive chemical compound, which is commonly used as an interface between heat sinks and heat sources such as high-power semiconductor devices. The main role of thermal paste is to eliminate air gaps or spaces from the interface area in order to maximize heat transfer and dissipation. Thermal paste is an example of a thermal interface material.

<span class="mw-page-title-main">Flux (metallurgy)</span> Chemical used in metallurgy for cleaning or purifying molten metal

In metallurgy, a flux is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time. They are used in both extractive metallurgy and metal joining.

<span class="mw-page-title-main">Galinstan</span> Eutectic alloy that is liquid at room temperature

Galinstan is a brand name for an alloy composed of gallium, indium, and tin which melts at −19 °C (−2 °F) and is thus liquid at room temperature. In scientific literature, galinstan is also used to denote the eutectic alloy of gallium, indium, and tin, which melts at around +11 °C (52 °F). The commercial product Galinstan is not a eutectic alloy, but a near eutectic alloy. Additionally, it likely has added flux to improve flowability, to reduce melting temperature, and to reduce surface tension.

A thermal interface material is any material that is inserted between two components in order to enhance the thermal coupling between them. A common use is heat dissipation, in which the TIM is inserted between a heat-producing device and a heat-dissipating device. There are intensive studies in developing several kinds of TIM with different target applications:

<span class="mw-page-title-main">Melt spinning</span>

Melt spinning is a metal forming technique that is typically used to form thin ribbons of metal or alloys with a particular atomic structure.

<span class="mw-page-title-main">Glass-to-metal seal</span> Airtight seal which joins glass and metal surfaces

Glass-to-metal seals are a type of mechanical seal which joins glass and metal surfaces. They are very important elements in the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass-encapsulated semiconductor diodes, reed switches, glass windows in metal cases, and metal or ceramic packages of electronic components.

<span class="mw-page-title-main">Solid</span> State of matter

Solid is one of the four fundamental states of matter along with liquid, gas, and plasma. The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural rigidity and resistance to a force applied to the surface. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire available volume like a gas. The atoms in a solid are bound to each other, either in a regular geometric lattice, or irregularly. Solids cannot be compressed with little pressure whereas gases can be compressed with little pressure because the molecules in a gas are loosely packed.

<span class="mw-page-title-main">Liquid</span> State of matter

A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a nearly constant volume independent of pressure. It is one of the four fundamental states of matter, and is the only state with a definite volume but no fixed shape.

<span class="mw-page-title-main">Glass transition</span> Reversible transition in amorphous materials

The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification.

<span class="mw-page-title-main">Soldering</span> Process of joining metal pieces with heated filler metal

Soldering is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint.

In condensed matter physics and physical chemistry, the terms viscous liquid, supercooled liquid, and glass forming liquid are often used interchangeably to designate liquids that are at the same time highly viscous, can be or are supercooled, and able to form a glass.

<span class="mw-page-title-main">Fragility (glass physics)</span>

In glass physics, fragility characterizes how rapidly the dynamics of a material slows down as it is cooled toward the glass transition: materials with a higher fragility have a relatively narrow glass transition temperature range, while those with low fragility have a relatively broad glass transition temperature range. Physically, fragility may be related to the presence of dynamical heterogeneity in glasses, as well as to the breakdown of the usual Stokes–Einstein relationship between viscosity and diffusion. Fragility has no direct relationship with the colloquial meaning of the word "fragility", which more closely relates to the brittleness of a material.

<span class="mw-page-title-main">Eutectic bonding</span>

Eutectic bonding, also referred to as eutectic soldering, describes a wafer bonding technique with an intermediate metal layer that can produce a eutectic system. Those eutectic metals are alloys that transform directly from solid to liquid state, or vice versa from liquid to solid state, at a specific composition and temperature without passing a two-phase equilibrium, i.e. liquid and solid state. The fact that the eutectic temperature can be much lower than the melting temperature of the two or more pure elements can be important in eutectic bonding.

Splat quenching is a metallurgical, metal morphing technique used for forming metals with a particular crystal structure by means of extremely rapid quenching, or cooling.

References

  1. ↑ Neumann, Taylor V.; Dickey, Michael D. (2020). "Liquid Metal Direct Write and 3D Printing: A Review". Advanced Materials Technologies. 5 (9): 2000070. doi: 10.1002/admt.202000070 . ISSN   2365-709X.
  2. ↑ Mewes, Jan-Michael; Schwerdtfeger, Peter (11 February 2021). "Exclusively Relativistic: Periodic Trends in the Melting and Boiling Points of Group 12". Angewandte Chemie. 60 (14): 7703–7709. doi: 10.1002/anie.202100486 . PMC   8048430 . PMID   33576164.
  3. 1 2 3 Kleiner, Kurt (3 May 2022). "Gallium: The liquid metal that could transform soft electronics". Knowable Magazine. doi: 10.1146/knowable-050322-2 . Retrieved 31 May 2022.
  4. 1 2 3 Tang, Shi-Yang; Tabor, Christopher; Kalantar-Zadeh, Kourosh; Dickey, Michael D. (26 July 2021). "Gallium Liquid Metal: The Devil's Elixir". Annual Review of Materials Research. 51 (1): 381–408. Bibcode:2021AnRMS..51..381T. doi: 10.1146/annurev-matsci-080819-125403 . ISSN   1531-7331. S2CID   236566966.
  5. ↑ Kunquan, Ma; Jing, Liu (October 2007). "Liquid metal management of computer chips". Frontiers of Energy and Power Engineering in China. 1 (4): 384–402. doi:10.1007/s11708-007-0057-3. ISSN   1673-7504. S2CID   195071023.
  6. ↑ 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.
  7. ↑ Krausser, J.; Samwer, K.; Zaccone, A. (2015). "Interatomic repulsion softness directly controls the fragility of supercooled metallic melts". Proceedings of the National Academy of Sciences of the USA. 112 (45): 13762–13767. arXiv: 1510.08117 . Bibcode:2015PNAS..11213762K. doi: 10.1073/pnas.1503741112 . PMC   4653154 . PMID   26504208.
  8. ↑ Fu, Yu; Li, Hongxia; Tang, Kai; Yang, Shenglan; Shi, Yue; Liu, Bin; Luo, Qun; Zhang, Lijun; Li, Qian; Pan, Fusheng (2024-06-01). "Melt viscosity of light alloys: Progress and challenges". Journal of Materials Science & Technology. 183: 72–88. doi:10.1016/j.jmst.2023.11.002. ISSN   1005-0302. S2CID   265424554.
  9. ↑ Wade, K.; Banister, A. J. (1975). The Chemistry of Aluminum, Gallium, Indium, and Thallium. Pergamon Texts in Inorganic Chemistry. Vol. 12. ASIN   B0007AXLOA.
  10. ↑ Lyon, Richard N., ed. (1952). Liquid Metals Handbook (2 ed.). Washington, D.C.{{cite book}}: CS1 maint: location missing publisher (link)
  11. ↑ 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 (2): 443–450. CiteSeerX   10.1.1.703.4444 . doi:10.1109/JMEMS.2011.2174421. S2CID   30200594.
  12. ↑ Liquid Metal Thermal Interface Materials
  13. ↑ Grubb, Jeff (October 7, 2020). "PlayStation 5 uses liquid metal — here's why that's cool". VentureBeat . Retrieved December 19, 2020.
  14. ↑ "Liquid Metal 3D Printing Makes Its Debut". Automation World. 2021-02-18. Retrieved 2022-07-23.
  15. ↑ Zhang, Mingkuan; Wang, Xiaohong; Huang, Zhiping; Rao, Wei (2020). "Liquid Metal Based Flexible and Implantable Biosensors". Biosensors. 10 (11): 170. doi: 10.3390/bios10110170 . PMC   7696291 . PMID   33182535.
  16. ↑ 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): 1097–1104. doi:10.1002/adfm.200701216. S2CID   538906.
  17. ↑ Liao, Jiahe (2022). Liquid metal actuators (Ph.D. thesis). Carnegie Mellon University.
  18. ↑ Majidi, Carmel (2021). "Fluid-like soft machines with liquid metal". Matter. 4 (2): 336–337. doi: 10.1016/j.matt.2021.01.009 .
  19. ↑ Liao, Jiahe; Majidi, Carmel (2021). "Soft actuators by electrochemical oxidation of liquid metal surfaces". Soft Matter. 17 (7): 1921–1928. Bibcode:2021SMat...17.1921L. doi:10.1039/D0SM01851A. PMID   33427274. S2CID   231577619.
  20. ↑ Russell, Loren; Wissman, James; Majidi, Carmel (18 December 2017). "Liquid metal actuator driven by electrochemical manipulation of surface tension". Applied Physics Letters. 111 (25): 254101. Bibcode:2017ApPhL.111y4101R. doi: 10.1063/1.4999113 .
  21. ↑ Khan, Mohammad Rashed; Eaker, Collin B; Bowden, Edmond F; Dickey, Michael D (2014). "Giant and switchable surface activity of liquid metal via surface oxidation". Proceedings of the National Academy of Sciences. 111 (39): 14047–14051. Bibcode:2014PNAS..11114047K. doi: 10.1073/pnas.1412227111 . PMC   4191764 . PMID   25228767.
  22. ↑ Liao, Jiahe; Majidi, Carmel (2022). "Muscle-Inspired Linear Actuators by Electrochemical Oxidation of Liquid Metal Bridges". Advanced Science. 9 (26): 2201963. doi:10.1002/advs.202201963. PMC   9475532 . PMID   35863909.
  23. ↑ Liao, Jiahe; Majidi, Carmel; Sitti, Metin (2023). "Liquid Metal Actuators: A Comparative Analysis of Surface Tension Controlled Actuation". Advanced Materials. 36 (1): 2300560. doi:10.1002/adma.202300560. hdl: 20.500.11850/641439 . PMID   37358049.
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