The high number of potential interstitial sites suitable for hydrogen and the favorable hydrogen-metal chemistry make quasicrystalline alloys candidates for hydrogen storage applications. Hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. The microstructure of quasicrystals in Zr69.5Cu12Ni11Al7.5 was investigated by x-ray diffraction and TEM, the kinetics of transformations by DSC and TDA.
Hydrogen was observed to exhibit a significant effect not only on the formation of Zr-based quasicrystalsfrom the glassy precursor material, but also on their stability. Ribbons with an icosahedral microstructure were found to absorb hydrogen up to H/M = 2.0. With increasing hydrogen content an expansion of the quasilattice constant was observed, followed by the formation of approximants and finally amorphization.
Only partial desorption of hydrogen can occur prior to the decomposition of the quasicrystalline phase. Desorption at lower temperatures is hindered by the formation of a thin ZrO2 barrier. Pd plating, often used to overcome such a barrier, improves the absorption kinetics as well as the desorption behavior significantly. DSC of uncoated Zr-based quasicrystals reveals that at low hydrogen contents the decomposition ofthe icosahedral quasicrystals is shifted to lower temperatures; at high hydrogen contents the formation of ZrH2-x was revealed. In the Pd-coated ribbons fully desorption is observed even below 300°C, butonly after hydrogenation up to H/M = 0.5; higher hydrogen contents lead to irreversible changes.
The micromechanism of transformations during hydrogenation as well as the decomposition during annealing of hydrogenated uncoated as well as Pd coated Zr-based quasicrystals are discussed in some detail.