Stirring Liquid Metals Without A Stir Bar

Heat and a magnetic field can make a liquid metal stir itself, reports a group led by Michael A. Jaworski, now at the Department of Energy's Princeton Plasma Physics Laboratory, and David N. Ruzic of the University of Illinois, Urbana-Champaign (Phys. Rev. Lett. 2010, 104, 094503). The work is the first direct experimental evidence of a flow effect that was first proposed three decades ago. Jaworski and colleagues aimed an electron beam at a pool of liquid lithium in a stainless steel tray. The beam caused a temperature gradient that in turn created an electric current between the lithium and the tray. Applying a magnetic field to the current produced a force on the liquid and caused the lithium to flow in a circular fashion, like a whirlpool. When the researchers reversed the direction of the magnetic field, the flow of lithium also reversed direction. Inserting an insulating layer of quartz between the liquid and the stainless steel nullified the effect, and the lithium remained still. This self-stirring liquid phenomenon could be used in industry to stir metals or alloys, as well as in fusion reactors, the researchers say.