Oxidation kinetics of an AlCuFeCr approximant compound: an ellipsometric study

Using single wavelength laser ellipsometry (λ=634 nm), we have studied the oxidation kinetics of bulk polycrystalline samples of an AlCuFeCr orthorhombic approximant compound of the decagonal phase. Up to 300 °C in dry air, nearly no evolution of the ellipsometric characteristics was detected, which can be explained assuming that the growth of the oxide layer stops shortly after beginning the exposure to temperature and air. Above this temperature, the changes of the ellipsometric characteristics pointed out a higher oxidation rate and a continuous growth of the oxide layer. In boiling water, we found that the kinetics of oxidation were as fast as when above 300 °C in dry air. Taking also into account atomic force microscopy measurements of the surface roughness, plausible scenarios for the oxidation process are inferred from our data.