Lubricity in Quasicrystals

Speaker:

Wahyu Setyawan

Date of Seminar:

Fri, 2007-11-16 12:00

Semester & Year:

Fall 2007

Seminar Location:

Hudson Hall Room 216

Seminar Contact(s):

Elizabeth Irish eri@duke.edu or Justin Jaworski jwj@duke.edu

Special Instructions:

Lunch and beverages will be served

Quasicrystalline compounds (QC) have been shown to have lower friction compared to other structures of the same constituents. The absence of structural interlocking when two QC surfaces slide against one another yields this lower friction. To use QC as a low-friction coating in combustion engines, knowledge of how a film of lubricant oil will form on the coating as well as its structure is required. Any contaminants and adsorbed films having nonquasicrystalline structure will reduce lubricity. To elucidate the effects that are due only to quasicrystallinity (as opposed to those due to chemical reaction and alloying) on an adsorbed film, adsorption of noble gases are performed. Grand canonical Monte Carlo method is employed to simulate the growth of noble gas and hydrocarbon films on a decagonal Al(73)Ni(10)Co(17) surface (d-AlNiCo). Using Lennard-Jones interatomic potentials, it is found that noble gases grow layer by layer at low temperature. Xe films undergo a first-order structural transition from 5- to 6-fold within monolayer regime. Ne, Ar, and Kr films do not show any of such transition. In these films, even though atoms are arranged in triangular patterns, a considerable amount of defect is present. The existence of the transition is sensitive to the size mismatch between noble gases and d-AlNiCo's characteristic length. A simple rule is proposed to predict the transition. The transition that occurs in Xe will reduce the lubricity of d-AlNiCo. Hydrocarbon adsorption will be simulated with interactomic potentials generated using the embbeded-atom method (EAM). Preliminary results for C-H-Al-Co-Ni EAM potentials generation will be presented.