(543e) Ni-Nb-Zr Amorphous Alloy Membranes for Hydrogen Separation

Inexpensive Ni-based metallic glasses may potentially replace Pd alloys for hydrogen separation at high temperatures in applications such as membrane reactors for the water-gas shift reaction (CO + H₂O → H₂ + CO₂). Amorphous alloy membranes based on Ni-Nb-Zr with the addition of other elements such as Ta were prepared by melt spinning and coating the surface with thin layers of Ni, Pd and Pd-alloys using physical vapor deposition. The hydrogen permeability and thermal stability of the membranes depended on the composition of the amorphous alloy and its surface coating. Long-term hydrogen permeability tests were conducted to assess membrane chemical and thermal stability. Decreases in hydrogen flux were observed over the course of 100-hour tests at 400°C. Membranes were characterized by using SEM/EDX, XRD, and AES/XPS depth profiles to study the changes in membrane microstructure and surface composition after testing. In order to further investigate membrane thermal stability, the crystallization temperature and kinetics of the Ni-Nb-Zr alloys were examined by using differential scanning calorimetry (DSC) with continuous heating rates. The decrease in hydrogen flux over time at 400°C was attributed to a combination of metallic interdiffusion between the surface coating and the membrane alloy and changes in bulk membrane structure. Exposing membranes to simulated water-gas shift (WGS) gas containing H₂, H₂O, CO and CO₂ temporarily decreased permeability.