Experiment controllably produces particles bristling with nanowires

Experiment controllably produces particles bristling with nanowires

While experimenting with sintering copper particles in air at Massachusetts Institute of Technology’s Varanasi Laboratory, assistant professor Kripa Varanasi, grad students Christopher Love and J. David Smith, and postdoc Yuehua Cui of the Laboratory for Manufacturing and Productivity created a mass of particles with long nanowires of oxidized copper. The resulting process could turn out to be an important new method for manufacturing structures that span sizes ranging down to a few nanometers, structures that could be used for managing the flow of heat in apps from power plants to electronics.

The abundance of the wires turned out to depend on the size of the original copper particles. Thus researchers can easily synthesize porous structures in bulk at various scales by selecting the particles they start out with; particles below a certain size sinter, while larger ones grow nanowires.

Field Emission SEM images show how nanowire bristles form on copper particles of different sizes. A cross-section of one of the particles (top right) reveals its hollow interior. (Courtesy of the Varanasi Lab.)

Varanasi points out that while growth of nanowires on bulk copper sheets had been observed before, this is the first time it has been observed across a variety of size scales at once, and the first time the process has been analyzed and explained. For copper particles, the bristles grow outward through diffusion, leaving the particles hollow in the middle as the metal migrates outward.

The team is now testing the same process with other materials. If it works with zirconium, it might help improve heat transfer in nuclear reactors. In addition, the results could help to optimize certain catalytic processes, Varanasi says. For further information, call Kripa K. Varanasi at 617-324-5608 or e-mail varanasi@mit.edu.

Richard Comerford