Liquid metal Silly Putty is now a thing
Gallium putties shield against EMPs, cool computer processors Metal Tech News – January 6, 2021
Last updated 1/5/2021 at 5:13pm
South Korean scientists have developed a liquid metal silicone composite material that can be stretched to a thickness of less than 50 microns when pulled really slow, snapped in half without stretching when pulled really fast, and can copy a print of the comics from a newspaper. That's right, gallium Silly Putty is now a thing.
Commercial silicone putty, better known as Crayola's trademarked Silly Putty, is one of four different materials used to create pastes and putties imbued with gallium's unique properties.
Nearly as cool as the Silly Putty that it has been mixed with, gallium is a non-toxic metal that melts at 86 degrees Fahrenheit (30 degrees Celsius), which means it is a solid material at room temperature but melts in the palm of your hand.
Gallium nitride was the breakthrough ingredient for blue light-emitting diodes, which was the final primary color needed to produce energy-efficient and long-lasting white LED lighting. This energy saving discovery earned Isamu Akasaki, Hiroshi Amano and Shuji Nakamura the 2014 Nobel Prize in Physics.
It is estimated that up to 98% of the demand for gallium originates from the semiconductor and electronics industry.
Gallium's propensity to ooze into a pool of liquid at 86 degrees, however, can make this metal troublesome for real-world applications that require a material that does not melt like butter.
A research team at the Center for Multidimensional Carbon Materials, within the Institute for Basic Science, and the Ulsan National Institute of Science and Technology in South Korea has mixed gallium with graphene, graphite, silicone carbide, diamond dust, and Silly Putty to create pastes and putties.
"We have discovered that a wide variety of particles can be incorporated into liquid gallium and have provided a fundamental understanding of how particle size plays a role in successful mixing," said Professor Rod Ruoff, a director at the Center for Multidimensional Carbon Materials who conceived of the idea of mixing such carbon fillers with liquid metals.
The South Korea research team was particularly excited about the thermal conductivity of a gallium-diamond mixture and the electromagnetic interference shielding offered by a gallium-graphene oxide composite.
Thermally conductive pastes are used as a bridge that transfers heat from computer processors to heat sinks that help to keep electronic devices cool.
A gallium-diamond dust paste created by the South Korean scientists exceeded the thermal conductivity of commercially available thermal pastes by more than 50%.
While larger diamond particles created greater thermal conductivity, testing showed that finer diamond particles demonstrated superior real-world cooling. The research team said the larger diamond particles were more prone to protrude through the bulk gallium, which creates air gaps that lessened the transfer of heat.
While mixing diamonds in graphene makes a great thermal paste, stirring some graphene into the liquid metal creates a compound that is great at blocking electromagnetic radiation that can interfere with communication systems and disable electronics. Solar flares and electromagnetic pulse (EMP) weapons are some the best-known sources of crippling electromagnetic radiation.
Graphene oxide films have proven to be highly effective at shielding electromagnetic radiation and is being considered to replace traditional metal shields aboard spacecraft.
More information on graphene shielding can be read at Out of this world 3D printed graphene in the June 10 edition of Metal Tech News.
The South Korean researchers found that a 13-micron thick – about the thickness of the clear bag liners used in office trash cans – gallium-graphene oxide coating increased graphene oxide film's electromagnetic interference shielding from 20 decibels to 75 dB. Greater than 30dB shielding is considered sufficient for most commercial uses and more than 60dB is typically needed for military uses.
The team, however, was most impressed with the gallium-graphene putty's ability to shield everyday materials from electromagnetic interference. For example, the testing showed that a similar 20-micron thick coating of this composite material painted on a sheet of paper provided more than 70 dB of shielding.
Gallium Silly Putty also has the capacity to shield against electromagnetic interference, though at a much lower rate than the gallium-graphene compound. This is because gallium Silly Putty is made by adding droplets of the liquid metal to commercial silicone putty, as opposed to mixing graphene powder into pure gallium to create the compound.
Though gallium Silly Putty needs to be 2 millimeters thick, or 100 times thicker than the gallium-graphene compound to achieve the same electromagnetic shielding, its superior stretchability and malleability offers advantages when it comes to applications such as wearable electronics.
Professor Ruoff says alloys that are liquids at lower than room temperature – indium-gallium, tin-gallium, and indium-tin-gallium – could also be used to make putties with remarkable characteristics.
The guy who came up with the idea that led to gallium Silly Putty said, "we hope our work inspires others to discover new functional fillers with exciting applications."