Morphological study of micropits formed by anodic etching of an Al-Pd-Mn icosahedral quasicrystal

Faceted micropits obtained by electrochemical etching of a single quasicrystal of an Al-Pd-Mn icosahedral phase have been examined by optical and electron microscopy. Anodic etching of the flat surface of a fivefold plane in a solution composed of CH3OH and HNO3(3:1 in volume ratio) reveals a variety of icosahedrally faceted micropits which originated from pre-existing microvoids and etch pits of pentagonal pyramid shape due to the other origins, probably structural defects inside the specimen. As the dissolution progresses, the micropits make successive changes in their shapes, ending in pentagonal pyramids before they vanish.