Computational Study of Low-friction Quasicrystalline Coatings via Simulations of Thin Film Growth of Hydrocarbons and Rare Gases
Abstract
Quasicrystalline compounds (QC) have been shown to have lower friction compared to
other structures of the same constituents. The abscence of structural interlocking
when two QC surfaces slide against one another yields the low friction. To use QC
as low-friction coatings in combustion engines where hydrocarbon-based oil lubricant
is commonly used, knowledge of how a film of lubricant forms on the coating is required.
Any adsorbed films having non-quasicrystalline structure will reduce the self-lubricity
of the coatings. In this manuscript, we report the results of simulations on thin
films growth of selected hydrocarbons and rare gases on a decagonal Al$_{73}$Ni$_{10}$Co$_{17}$
quasicrystal (d-AlNiCo). Grand canonical Monte Carlo method is used to perform the
simulations. We develop a set of classical interatomic many-body potentials which
are based on the embedded-atom method to study the adsorption processes for hydrocarbons.
Methane, propane, hexane, octane, and benzene are simulated and show complete wetting
and layered films. Methane monolayer forms a pentagonal order commensurate with the
d-AlNiCo. Propane forms disordered monolayer. Hexane and octane adsorb in a close-packed
manner consistent with their bulk structure. The results of hexane and octane are
expected to represent those of longer alkanes which constitute typical lubricants.
Benzene monolayer has pentagonal order at low temperatures which transforms into triangular
lattice at high temperatures. The effects of size mismatch and relative strength of
the competing interactions (adsorbate-substrate and between adsorbates) on the film
growth and structure are systematically studied using rare gases with Lennard-Jones
pair potentials. It is found that the relative strength of the interactions determines
the growth mode, while the structure of the film is affected mostly by the size mismatch
between adsorbate and substrate's characteristic length. On d-AlNiCo, xenon monolayer
undergoes a first-order structural transition from quasiperiodic pentagonal to periodic
triangular. Smaller gases such as Ne, Ar, Kr do not show such transition. A simple
rule is proposed to predict the existence of the transition which will be useful in
the search of the appropriate quasicrystalline coatings for certain oil lubricants.
Another part of this thesis is the calculation of phase diagram of Fe-Mo-C system
under pressure for studying the effects of Mo on the thermodynamics of Fe:Mo nanoparticles
as catalysts for growing single-walled carbon nanotubes (SWCNTs). Adding an appropriate
amount of Mo to Fe particles avoids the formation of stable binary Fe$_3$C carbide
that can terminate SWCNTs growth. Eventhough the formation of ternary carbides in
Fe-Mo-C system might also reduce the activity of the catalyst, there are regions in
the Fe:Mo which contain enough free Fe and excess carbon to yield nanotubes. Furthermore,
the ternary carbides become stable at a smaller size of particle as compared to Fe$_3$C
indicating that Fe:Mo particles can be used to grow smaller SWCNTs.
Type
DissertationSubject
Engineering, Materials SciencePhysics, Condensed Matter
Chemistry, Physical
quasicrystal
adsorption
low friction
embedded
atom method
carbon nanotube
catalyst
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https://hdl.handle.net/10161/592Citation
Setyawan, Wahyu (2008). Computational Study of Low-friction Quasicrystalline Coatings via Simulations of Thin
Film Growth of Hydrocarbons and Rare Gases. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/592.Collections
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