Amorphous Membranes for Hydrogen Separation Based On Ni-Nb-Zr Alloys

Inexpensive metallic glass membranes based on Ni-Nb-Zr may replace Pd alloy membranes for hydrogen separations and in membrane reactors for hydrogen production from gasified coal and biomass. Amorphous Ni₄₂Nb₂₈Zr₃₀ alloy membranes with the substitution of other elements such as Co or other elements for Ni (Ni₃₂Nb₂₈Zr₃₀Co₁₀) were prepared by melt spinning and then sputtered with a thin (500 nm) layer of Pd surface catalyst. Decreases in hydrogen flux were observed at higher temperatures (up to 450°C) during long-term hydrogen permeability tests. For example, Co increased the thermal stability of the membrane, but decreased its hydrogen permeability. Membranes were characterized by using SEM/EDX, XRD, TEM and AES sputter depth profiles to study the changes in surface and bulk microstructure and composition after testing. The decrease in hydrogen flux over time was attributed to a combination of metallic interdiffusion between the surface coating and the underlying membrane alloy and changes in membrane structure.