Kudos to the team at North Carolina State University (and the National Science Foundation for sponsoring the research) for coming up with an interesting paper and an entertaining video on 3D printing with liquid metals.
The build up of the finished part is occurring through depositing of small drops of binary eutectic alloy of gallium and indium (EGaIn, 75% Ga 25% In by weight) which is conductive and liquid at room temperature (slightly below, actually ∼15.7°C) . The 3D printer is essentially a microscope positioning stage with a third axis attached, which is carrying a syringe with the liquid alloy. The alloy is being deposited through a needle approx 250um in diameter.
Each droplet is coalescing into a sphere due to surface tension and each is quickly forming a thin protective layer (only about 1nm ) of passivating skin composed of Gallium oxide.
Be sure to check out the video for the samples of the shapes that can be printed with this technique. This is an early development stage yet and I’m sure we’ll see more interesting results come out soon. Some of the improvements that are in works have to do with devising ways to prevent the spherical droplets from further coalescing into larger diameter spheres instead of staying where they’ve been deposited.
No less intriguing are the 2D applications of the same technology – the droplets can be stretched into thin wires from 30 to 200um in diameter to build electronic circuits using CNC positioning of the depositing syringe.
Check out the 3D Printing of Free Standing Liquid Metal Microstructures paper for more details on the fascinating new technology.
On a personal note: I had no idea how affordable indium and gallium are (in quantities needed for a DIY lab, of course) – they are about $1 / gram each and eBay is full of offers. Definitely something within the reach of an adventurous DIY 3D printing enthusiast!