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Simpler Nanowires

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A dime-size crucible sits on a protective felt pad and a small amount of metal is placed inside with a long pair of tweezers. The crucible has wires connected to a braided cord that wraps around it.
The same image as before but now the crucible is glowing orange with heat

A closeup image of the glowing orange crucible

Fabrication of oxide nanowires begins with creating a bimetallic alloy, in this case aluminum and lithium, by heating in a crucible.

By John Toon

A simple technique for producing oxide nanowires directly from bulk materials could dramatically lower the cost of producing the one-dimensional (1-D) nanostructures. That could open the door for their use in lightweight structural composites, advanced sensors, and electronic devices — as well as thermally stable and strong battery membranes able to withstand temperatures of more than 1,000 degrees Celsius.

The technique uses a solvent reaction with a bimetallic alloy — in which one of the metals is reactive — to form bundles of nanowires using reactive metal dissolution. The process takes place at ambient temperature and pressure without the use of catalysts, toxic chemicals, or costly processes such as chemical vapor deposition.

“This technique could open the door for a range of synthesis opportunities to produce low-cost 1-D nanomaterials in large quantities,” said Gleb Yushin, a professor in Georgia Tech’s School of Materials Science and Engineering. “You can essentially put the bulk materials into a bucket, fill it with a suitable solvent, and collect nanowires after a few hours, which is way simpler than how many of these structures are produced today.”

The resulting alloy sample is then placed in a test tube containing a solvent such as ethanol, where the reactive lithium dissolves out into solution.

The aluminum nuclei left behind seed the growth of aluminum alkoxide nanowires, which can be heated in the open air to form paper-like sheets.

A microscope image shows the fibers.

Yushin’s research team has produced oxide nanowires from lithium-magnesium and lithium-aluminum alloys using a variety of solvents, including simple alcohols. The research, reported in the journal Science, was supported by the National Science Foundation and California-based Sila Nanotechnologies.

Fabrication of the nanowires begins with formation of alloys composed of one reactive and one non-reactive metal, such as lithium and aluminum. The alloy is then placed into a suitable solvent, which could include a range of alcohols, such as ethanol. The reactive metal (lithium) dissolves from the surface into the solvent, initially producing aluminum nuclei (nanoparticles).

Though bulk aluminum is normally not reactive with alcohol due to the formation of a passivation layer, the continuous dissolution of lithium prevents the passivation and allows gradual formation of aluminum alkoxide nanowires, which grow perpendicular to the surface of the particles starting from the nuclei until the particles are completely converted. The alkoxide nanowires can then be heated in open air to form aluminum oxide nanowires and may be formed into paper-like sheets.

Related: New Low-Cost Technique Converts Bulk Alloys to Oxide Nanowires, January 19, 2017

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