Iowa State engineers have developed micro-sized liquid-metal particles for heat-free soldering and metal processing applications.

Martin Thuo, an assistant professor of materials science and engineering at Iowa State University and an associate of the U.S. Department of Energy’s Ames Laboratory, and his researchers used a high-speed rotary tool to sheer liquid metal into droplets within an acidic liquid.

The particles are exposed to oxygen; an oxidation layer then covers the particles, essentially creating a capsule containing the liquid metal. The layer is then polished until it is thin and smooth.

Thuo’s created 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.”

The 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.