Surface oxidation of the Al62CU25.5Fe12.5 icosahedral quasicrystal

The surface oxidation of the Al62Cu25.5Fe12.5 icosahedral quasicrystal was studied by Auger electron microscopy. Before oxidation, a chemisorption ste p occurs, the duration of which varies with temperature and oxygen pressure . At low temperature, between room temperature and 673 K, a very thin and p assivating layer is found at the surface, where aluminium is only partially oxidized and the ratio between metal constituents remains equal to that of the nominal composition in the bulk. Above 673 K, except at very low oxyge n pressure, a segregation of aluminium takes place at the surface and leads to the: growth of a nearly purr alumina layer in which the aluminium is co mpletely oxidized. Under 2 x 10(-8) Torr of oxygen, no segregation of alumi nium occurs and almost no oxide is formed at the surface after 24 h of expo sure (1700 L).