Abstract
Crystalline Pd/Pd-Ag membranes are widely used for hydrogen separation from CO2 and other gases in power generation applications. To substitute these high cost noble metal alloy membranes, the Ni-Nb-Zr amorphous alloys are being developed that exhibit relatively high permeability of hydrogen between 200–400 °C. Atom probe tomography (APT) experiments performed on these ribbons revealed nm-scale Nb-rich and Zr-rich regions (clusters) embedded in a ternary matrix, indicating phase separation within the Ni-Nb-Zr amorphous alloy. Density functional theory (DFT) simulations have predicted that these clusters are composed of icosahedral coordination polyhedra. The interatomic distances and correlation lengths of the short range order of these alloys were determined by neutron total scattering which match well with our DFT based molecular dynamics (DFT-MD) simulations.
Highlights
Ni-based amorphous alloys have been developed to replace crystalline Pd/Pd-23Ag (23% Ag) noble metal alloy membranes which are commercially available for hydrogen separation from CO2 and other gases in power generation applications
Phase separation in Ni-Nb-Zr amorphous membranes, without prior annealing to crystallization and cluster effects on glass formability, mechanical, electrical and dynamic properties have not been reported earlier to the best of our knowledge. To address these issues we performed a combination of atom probe tomography (APT) and neutron scattering (HIPD) experiments coupled with the density functional theory (DFT) based molecular dynamics (MD) simulations on the membrane alloy ribbons of (Ni0.60Nb0.40)70Zr30
We present the local atomic order of the (Ni0.60Nb0.40)70Zr30 glassy alloy membrane ribbon and discuss cluster formation obtained from the APT experiments and interatomic distances between atoms measured by neutron scattering experiments and DFT simulations
Summary
Ni-based amorphous alloys have been developed to replace crystalline Pd/Pd-23Ag (23% Ag) noble metal alloy membranes which are commercially available for hydrogen separation from CO2 and other gases in power generation applications. Phase separation (chemical heterogeneity) in Ni-Nb-Zr amorphous membranes, without prior annealing to crystallization and cluster effects on glass formability, mechanical, electrical and dynamic properties have not been reported earlier to the best of our knowledge. To address these issues we performed a combination of atom probe tomography (APT) and neutron scattering (HIPD) experiments coupled with the density functional theory (DFT) based molecular dynamics (MD) simulations on the membrane alloy ribbons of (Ni0.60Nb0.40)70Zr30. We present the local atomic order of the (Ni0.60Nb0.40)70Zr30 glassy alloy membrane ribbon and discuss cluster formation obtained from the APT experiments and interatomic distances between atoms measured by neutron scattering experiments and DFT simulations
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