Abstract
AbstractAn experimental comparison has been made between the properties of the surfaces of an Al70Pd21Mn9 quasicrystal and its Al48Pd42Mn10 approximant. The Al70Pd21Mn9 sample was a single grain icosahedral quasicrystal cut to expose its five-fold symmetric (000001) surface. The approximant was polycrystalline β-phase Al48Pd42Mn10, which has a CsCl-type cubic structure. Surfaces of both were prepared under ultra-high vacuum (UHV) conditions and then used for comparative measurements of their frictional properties and oxidation rates. Both materials are oxidized by reaction with O2 to form a thin film of aluminum oxide that ultimately passivates their surfaces. The interesting difference between the two is that the rate of oxidation of the approximant is significantly higher than that of the quasicrystal in spite of the fact that the bulk Al concentration of the approximant is lower than that of the quasicrystal. Friction measurements were made under UHV conditions between pairs of quasicrystals and pairs of approximants whose surfaces were either clean or oxidized to varying degrees. The friction between pairs of the approximant surfaces is significantly higher than that measured between the quasicrystal surfaces under all conditions of surface oxidation.
Highlights
The extraordinary structural properties of quasicrystals have motivated numerous measurements of materials properties that might exhibit anomalous behavior that is a direct result of quasicrystallinity
In the work described here we have studied the oxidation of the clean surface of the Al48Pd42Mn10 approximant and compared that to our prior observations of the oxidation of the Al70Pd21Mn9 quasicrystal surface
Oxidation of the alloy surfaces has been studied using Auger electron spectroscopy (AES) to monitor the uptake of oxygen during exposure to both O2 and to H2O
Summary
The extraordinary structural properties of quasicrystals have motivated numerous measurements of materials properties that might exhibit anomalous behavior that is a direct result of quasicrystallinity. Friction measurements were made under UHV conditions between pairs of quasicrystals and pairs of approximants whose surfaces were either clean or oxidized to varying degrees. The friction between pairs of the approximant surfaces is significantly higher than that measured between the quasicrystal surfaces under all conditions of surface oxidation.
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