The vial contains liquid-metal particles suspended in ethanol. The particles were used to demonstrate heat-free soldering. Credit: Christopher Gannon/Iowa State University
One of the latest innovations from Thuo’s lab is finding a way to make micro-scale, liquid-metal particles that can be used for heat-free soldering plus the fabricating, repairing and processing of metals – all at room temperature. He’s worked with Tevis to launch SAFI-Tech which plans to locate to the Iowa State Economic Development StartUp Factory when it opens in the ISU Research Park later this year. The project started as a search for a way to stop liquid metal from returning to a solid – even below the metal’s melting point. That’s something called undercooling and it has been widely studied for insights into metal structure and metal processing. But it had been a challenge to produce large and stable quantities of undercooled metals.
Thuo’s research team thought if tiny droplets of liquid metal could be covered with a thin, uniform coating, they could form stable particles of undercooled liquid metal. The engineers experimented with a new technique that uses a high-speed rotary tool to sheer liquid metal into droplets within an acidic liquid. The particles are exposed to oxygen and then an oxidation layer is allowed to cover the particles, essentially creating a capsule containing the liquid metal. That layer is then polished until it is thin and smooth.
Thuo’s research group proved the concept by creating liquid-metal particles containing Field’s metal (an alloy of bismuth, indium and tin) and particles containing an alloy of bismuth and tin. The particles are 10 micrometers in diameter, about the size of a red blood cell. “We wanted to make sure the metals don’t turn into solids,” Thuo said. “And so we engineered the surface of the particles so there is no pathway for liquid metal to turn to a solid. We’ve trapped it in a state it doesn’t want to be in.”
Those liquid metal particles could have significant implications for manufacturing.
“We demonstrated healing of damaged surfaces and soldering/joining of metals at room temperature without requiring high-tech instrumentation, complex material preparation or a high-temperature process,” the engineers wrote in their paper.
Thuo and the Iowa State Research Foundation Inc. have filed for a patent on the technology.
http://www.news.iastate.edu/news/2016/04/25/liquidmetal
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