INVESTIGA??O DA OXIDA??O DO QUASICRISTAL Al62,2Cu 25,3Fe12,5 NA FASE ICOSAEDRAL INVESTIGATION OF THE OXIDATION OF THE QUASICRYSTAL Al62,2Cu 25,3Fe12,5 PHASE ICOSAHEDRAL

摘要

The oxidation of the icosahedral phase Al62,2Cu25,3Fe12,5 is investigated by means of X-ray diffraction(XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The stages ofthe oxidation take place under very low pressure, which cause the nucleation and growth of the oxidelayer on the surface of the quasicrystalline. The quasicrystalline alloy was characterized at ambienttemperature, before and after oxidation. Oxidation leads to a long range diffusion of aluminum atomson the lattices, which forms an amorphous oxide layer on top of the grains. When the aluminum losesinside the grains, there is an icosahedral phase transformed into intermetallic phase of the crystallinetype. Oxidation of quasicrystalline Al62,2Cu25,3Fe12,5 alloy was analyzed under different conditions ofheat treatment duration. This change no longer occurs when the grain size is larger than a critical value.In the icosahedral phase, aluminium oxidation forms a dense, passivating layer at the outermost surfaceof the quasicrystal which causes depletion of both copper and iron. The presence of hematite wasobserved as well as alumina in the dense layer.