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Nonequilibrium Interface and Surface Dynamics 2007
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Using Impurities to Tailor Mesoporous Metals:
A KMC Study of Dealloying
CSIC Building (#406),
Seminar Room 4122.
Directions: home.cscamm.umd.edu/directions
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Using Impurities to Tailor Mesoporous Metals: A KMC
Study of Dealloying
Professor
Jonah Erlebacher
Johns Hopkins
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Abstract:
Dealloying, the selective dissolution of one or more
component from a multi-component alloy, was
originally studied in the context of corrosion,
where it can lead to undesirable materials failure (e.g,
dissolution of Zn from CuZn brass can lead to
stress-corrosion cracking). More recently,
dealloying has been used to form beautiful and
functional mesoporous metals; for instance,
dealloying of Ag from Ag/Au yields a nanoporous gold
with average pore size ~15 nm in diameter. For some
applications, 15 nm pores is good enough, but to
really produce metals with extraordinary
surface/volume ratios, one would prefer smaller pore
sizes, like 2-5 nm. We have been studying the
evolution of (nano)porosity during dealloying using
Kinetic Monte Carlo simulation. A
crystallographically appropriate model incorporating
surface diffusion in competition with
potential-dependent dissolution rate of silver from
an fcc gold/silver lattice is a minimal model that
reproduces the important experimental aspects of
dealloying. These include the observation of
compositional parting limits, critical potentials,
dealloying and porosity evolution at sufficiently
high potential, and passivation at sufficiently low
potential. The model also explains that the ~15 nm
pores in silver/gold is a lower limit in this
system, due to the intrinsically fast mobility of Au
in acidic environments, which leads to a coarsened
microstructure. Here we show that the KMC model
shows that pore size and critical potential are also
highly dependent on step edge mobility, and this can
be slowed significantly by the presence of
impurities. This effect explains the corrosion
protection afforded to brass by the addition of ~1%
As to the alloy. It also predicts that the addition
of small amounts of lower-mobility Pt (<5%) to Ag/Au
alloys should lead not only to smaller pore sizes,
but Pt segregation to step edges during dissolution
will also lead to a ?core/shell? mesoporous metal ?
a kinetically stabilized mesporous metal with ~2 nm
pores. We will introduce experiments showing this is
indeed the case.
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