Effect of Leaching on Surface Microstructure and Chemical Composition of Al-Based Quasicrystals

Abstract

We have studied the effect of leaching treatments on the surface microstructure and chemical composition of Al-based quasicrystals. The high symmetry surfaces of single grain icosahedral (i-) Al–Cu–Fe and decagonal (d-) Al–Ni–Co quasicrystals and a polygrain i-Al–Pd–Re quasicrystal with random surface orientation were leached with NaOH solution at varying times and the resulting surfaces were characterized by scanning electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy. The leaching treatments preferentially remove Al producing nanoparticles of the transition metals and their oxides. The leached fivefold surface of i-Al–Cu–Fe exhibits micron sized dodecahedral cavities on which the nanoparticles are precipitated. However, no specific microstructure has been observed on the tenfold surface of d-Al–Ni–Co and the polygrain i-Al–Pd–Re. The quasicrystalline surface can be regained after polishing the leached layer, indicating that leaching occurs only in a limited depth from the surface. This was revealed by low energy electron diffraction after the surface was prepared under ultra high vacuum conditions. These results provide important information for preparation of model catalysts of nanoparticles of catalytically active metals on quasicrystal surfaces.