OXIDATION AND HYDROGENATION OF QUASI-CRYSTALS

Quasicrystals are often regarded as Hume-Rothery phases stabilized at different electron concentrations e/a. Concentration changes during ox idation or hydrogenation are expected to displace the electron concent ration out of the stability range. Therefore. these processes might be accompanied by phase transformations. Oxidation experiments with Al63 Cu25Fe12 icosahedral quasicrystals reveal only in the early stages the formation of a smooth oxide layer accompanying reconstruction of the surface. No phase transformation due to oxygen diffusion into the quas icrystalline structure could be detected. During further oxidation the formation of oxide nodules has been observed rather than a homogeneou s thickening of the oxide layer. Heterogeneous phase transformation in to lambda-Al13Fe4 indicates additional segregation effects. i-Zr69.5Ni 12Cu11Al7.5 quasicrystals can absorb large amounts of hydrogen which l eads to an increase of the quasilattice constant by 10% and microstruc tural changes of so far unknown character: weakening of the contrast o f quasicrystals in transmission electron microscopy (TEM) as well as a disappearance of the weak diffraction spots in the corresponding diff raction pattern. (C) 1997 Elsevier Science S.A.