Oxidation and hydrogenation of quasicrystals

Quasicrystals are often regarded as Hume-Rothery phases stabilized at different electron concentrations e/a. Concentration changes during oxidation or hydrogenation are expected to displace the electron concentration out of the stability range. Therefore, these processes might be accompanied by phase transformations. Oxidation experiments with Al₆₃Cu₂₅Fe₁₂ 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 quasicrystalline structure could be detected. During further oxidation the formation of oxide nodules has been observed rather than a homogeneous thickening of the oxide layer. Heterogeneous phase transformation into λ-Al₁₃Fe₄ indicates additional segregation effects. i-Zr_69.5Ni₁₂Cu₁₁Al_7.5 quasicrystals can absorb large amounts of hydrogen which leads to an increase of the quasilattice constant by 10% and microstructural changes of so far unknown character: weakening of the contrast of quasicrystals in transmission electron microscopy (TEM) as well as a disappearance of the weak diffraction spots in the corresponding diffraction pattern.