CPM Seminar

The high number of tetrahedrally coordinated sites for interstitial hydrogen and the favorable hydrogen-metal chemistry make glassy and quasicrystalline Zr-Cu-Ni-Al alloys a candidate for hydrogen storage applications. Quasicrystals are often regarded as Hume-Rothery phases stabilized at particular electron concentrations e/a. Concentration changes during the hydrogenation are expected to displace the electron concentration out of the stability range. Therefore, this process might be accompanied by phase transformations. Zr- as well as Ti-based quasicrystals have been observed recently to store hydrogen up to a content close to the best crystalline materials, thus opening a promising new field for application.

Hydrogen charging was performed electrochemically in a glycerin-phosphoric acid electrolyte. Hydrogen absorption/desorption as well as the influence of hydrogen on the formation and stability of quasicrystals were studied by means of x-ray diffraction, electron microscopy, DSC and TDA. Absorption kinetics and storage capacity were found to be far better for the quasicrystalline than for the associated amorphous phase in Zr_69.5Cu₁₂Ni₁₁Al_7.5. The interstitial hydrogen was observed to play an important role not only in the stability of the quasicrystals, but also in their formation from amorphous precursor material. Even low hydrogen contents lead to changes of the crystallization behavior above the glass transition.

Friday, November 27th 1998, 10:30
Ernest Rutherford Physics Building, room 115