[meteorite-list] A Stellar, Metal-Free Way to Make Carbon Nanotubes

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 23 Feb 2010 11:25:03 -0800 (PST)
Message-ID: <201002231925.o1NJP3PY022010_at_zagami.jpl.nasa.gov>

http://www.nasa.gov/topics/technology/features/metal-free-nanotubules.html

A Stellar, Metal-Free Way to Make Carbon Nanotubes
Elizabeth Zubritsky
Goddard Space Flight Center
February 22, 2010
 
Space apparently has its own recipe for making carbon nanotubes, one of the
most intriguing contributions of nanotechnology here on Earth, and metals are
conspicuously missing from the list of ingredients.

The finding is the surprising by-product of lab experiments designed by
Joseph Nuth at NASA's Goddard Space Flight Center, Greenbelt, Md. and
his colleagues to address the astronomical question of how carbon gets
recycled in the regions of space that spawn stars and planets. The work
also could help researchers understand puzzling observations about some
supernovas.

In a recent paper in Astrophysical Journal Letters, Nuth's team
describes the modest chemical reaction. Unlike current methods for
producing carbon nanotubes tiny yet strong structures with a range of
applications in electronics and, ultimately, perhaps even medicine - the
new approach does not need the aid of a metal catalyst. "Instead,
nanotubes were produced when graphite dust particles were exposed to a
mixture of carbon monoxide and hydrogen gases," explains Nuth.

"I am amazed at the implications of this paper, not only for
astrophysics but also for materials science," says Dick Zare, the chair
of the chemistry department at Stanford University, Stanford, Calif.
"Could Nature know a new chemistry for making carbon nanotubes that we
have yet to discover?"

One indication of that possibility came in 2008, when the long, thin
carbon structures known as graphite whiskers - essentially, bigger cousins
of carbon nanotubes - were identified in three meteorites. That finding
offered the tantalizing prospect that a haze of graphite whiskers in
space could explain why some supernovas appear dimmer, and therefore
farther away, than they should be, according to current models. Yet,
"very little is known about graphite whisker formation, and so it is
difficult to adequately interpret their discovery," says Marc Fries of
NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Fries and Andrew Steele at the Carnegie Institution for Science,
Washington, reported the meteorite findings.

Now, the experiments by Nuth's team suggest a possible route for forming
such structures. This "is exactly the sort of fundamental approach
needed for a meaningful understanding of what graphite whiskers are and
what their presence means in the larger context of solar system
formation and astronomical observations," Fries explains.

Nuth's approach is a variation of a well-established way to produce
gasoline or other liquid fuels from coal. It's known as Fischer-Tropsch
synthesis, and researchers suspect that it could have produced at least
some of the simple carbon-based compounds in the early solar system.
Nuth proposes that the nanotubes yielded by such reactions could be the
key to the recycling of the carbon that gets released when carbon-rich
grains are destroyed by supernova explosions.

The structure of the carbon nanotubes produced in these experiments was
determined by Yuki Kimura, a materials scientist at Tohoku University,
Japan, who examined the samples under a powerful transmission electron
microscope. He saw particles on which the original smooth graphite
gradually morphed into an unstructured region and finally to an area
rich in tangled hair-like masses. A closer look with an even more
powerful microscope showed that these tendrils were in fact cup-stacked
carbon nanotubes, which resemble a stack of Styrofoam cups with the
bottoms cut out.

These observations surprised Kimura because carbon nanotubes are
typically grown with platinum or another metal as a catalyst, yet Nuth's
reaction had used no metals. Kimura checked for contamination but "did
not find the presence of metallic particles accompanying the nanotube in
the sample," he says.

If further testing indicates that the new method is suitable for
materials-science applications, it could supplement, or even replace,
the familiar way of making nanotubes, explains Kimura. That possibility
"is most exciting and invites yet more study," says Zare.

The findings also might open a new realm of investigation in astronomy,
because "we can take the whiskers produced by Joe and interrogate their
properties," says Steele.

In particular, researchers can evaluate whether graphite whiskers absorb
light, he notes. A positive result would lend credence to the
proposition that the presence of these molecules in space affects the
observations of some supernovas. The ability to test this hypothesis
could start a reaction of its own.
 
 
Received on Tue 23 Feb 2010 02:25:03 PM PST