Researchers from North Carolina State University have developed 3D printing technology and techniques to create free-standing structures made of liquid metal at room temperature.
3D Printers can use a wide range of materials, including plastics, resins, metals, ceramics and more. However the most dramatic and challenging has been printing with metal. The common method of metal printing is the direct metal laser sintering process that uses a laser beam to melt 20-40 micron layers of metal powder on top of each other to create metal parts.
Collin Ladd, Ju-Hee So, John Muth, and Michael D. Dickey have developed three-dimensional structures out of liquid metal.
Image: Michael Dickey
"It's difficult to create structures out of liquids, because liquids want to bead up. But we've found that a liquid metal alloy of gallium and indium reacts to the oxygen in the air at room temperature to form a 'skin' that allows the liquid metal structures to retain their shapes," says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State.
The researchers focus on the binary eutectic alloy of gallium and indium (EGaIn, 75% Ga 25% In by weight), but any alloy of gallium will also work, says the team. EGaIn is liquid at room temperature (m.p. ~15.7 °C) with metallic conductivity. Upon exposure to air, the metal forms a thin (~1 nm) passivating "skin" composed of gallium oxide.
They developed multiple techniques for writing metals in 3D. One technique involves stacking droplets of liquid metal on top of each other, much like a stack of oranges at the supermarket. The droplets adhere to one another, but retain their shape – they do not merge into a single, larger droplet. Video of the process is available here.
Another technique injects liquid metal into a polymer template, so that the metal takes on a specific shape. The template is then dissolved, leaving the bare, liquid metal in the desired shape. The researchers also developed techniques for creating liquid metal wires, which retain their shape even when held perpendicular to the substrate.
The team is currently exploring how to further develop these techniques, as well as how to use them in various electronics applications and in conjunction with established 3-D printing technologies.
Watch the demo video below. The paper, "3-D Printing of Free Standing Liquid Metal Microstructures," is published online in Advanced Materials.
Posted in 3D Printing Technology
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