Corrosion of Al-Cu-Fe quasicrystals and related crystalline phases

Corrosion of quasicrystalline and related crystalline phases in the Al-Cu-Fe system was investigated by anodic polarization in acid and alkaline solutions at room temperature. Corrosion products as well as surface morphology ware measured by means of X-ray diffraction, scanning and transmission electron microscopy. During polarization of icosahedral quasicrystals in a strong alkaline solution a two-layered film is formed: an inner layer with reduced Al content which consists of quasicrystals and a bcc phase and an nanocrystalline oxide layer with a needle-like morphology. At low pH (<2) dissolution of the quasicrystalline phases was observed to precede deposition of a porous Cu film. In a strong alkaline medium icosahedral quasicrystals have a smaller corrosion resistance than neighboring crystalline phases, e.g. the beta-phase (Al50Cu30Fe20); in strong acid solution other crystalline phases (for example Al2Cu) show less corrosion. The open circuit potentials have been observed to vary in a similar manner. (C) 1999 Elsevier Science B.V. All rights reserved.