Argonne scientists discover networks of metal nanoparticles
are culprits in alloy corrosion
New alloy composition could cut costs for petrochemical
industry
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ARGONNE, Ill. (Aug. 4, 2008) – Oxide scales are supposed to protect alloys
from extensive corrosion, but scientists at U.S. Department of Energy's Argonne
National Laboratory have discovered metal nanoparticle chinks in this armor.
Oxide scales develop on the outer surface of alloys at high temperatures creating
a protective barrier that keeps destructive carbon-bearing molecules from slipping
into the alloy. The diffusion of carbon into oxide scales should be negligible,
but studies have shown that carbon can sneak through the oxide line of defense
leading to brittleness and corrosion.
"The United States loses four percent of the gross national product due
to alloy corrosion," said Argonne
Distinguished Fellow Ken Natesan, who
leads the Corrosion
and Mechanics of Materials Group in Argonne's Nuclear
Engineering Division. "A
network of continuous metal nanoparticles allows the carbon to dissolve and
diffuse through the protective oxide scales without the need of a crack or
a pore."
It was commonly believed that carbon-containing molecules escaped into cracks
or pores in the oxide scales, but using three separate techniques – nanobeam
X-ray analysis at the Advanced Photon Source, magnetic force microscopy at
the Center for Nanoscale Materials and scanning electron microscopy at the
Electron Microscopy Center– Natesan, along with Argonne scientists Zuotao
Zeng, Seth Darling and Zhonghou Cai, discovered networks of iron and nickel
nanoparticles embedded within the oxide scales.
Carbon can easily diffuse through the metals and create a path for carbon
atom transport that does not involve defects in the scale.
"By examining the oxide scale, we find the metal nanoparticles," Zeng
said. "If they are eliminated we can create a more corrosion-resistant
and longer lasting alloy."
Based on the study, Argonne has developed laboratory size batches of materials
that exhibit as much as 10 times longer life than commercial alloys with similar
chromium contents, Natesan said. At present, 50-lb batches of the alloys have
been cast successfully by an alloy manufacturer and will be commercialized
in due course. The Argonne-developed alloys are of considerable interest to
the chemical, petrochemical and refining industry.
The findings might also have broad influence on not only metal dusting and
carburization, but also in other research areas such as alloy development and
surface coatings for high-temperature fuel cell applications.
Funding for this research was provided by the U.S. Department of Energy, Office
of Energy Efficiency
and Renewable Energy, Industrial
Technologies Program.
Argonne's scientific user facilities such as the Advanced Photon Source, Electron
Microscopy Center and Center for Nanoscale Materials are supported by the U.S.
Department of Energy, Office
of Science.
A paper based on this work has been published recently in Nature
Materials.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology.
The nation's first national laboratory, Argonne conducts leading-edge basic
and applied scientific research in virtually every scientific discipline. Argonne
researchers work closely with researchers from hundreds of companies, universities,
and federal, state and municipal agencies to help them solve their specific
problems, advance America 's scientific leadership and prepare the nation for
a better future. With employees from more than 60 nations, Argonne is managed
by UChicago
Argonne, LLC for
the U.S.
Department of Energy's Office
of Science.
For more information, please
contact Brock Cooper (630/252-5565 or media@anl.gov)
at Argonne.
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