Hydrogen permeability and crystallization kinetics in amorphous Ni–Nb–Zr alloys

Abstract

Amorphous Ni-based alloys show great promise as inexpensive, hydrogen-selective membrane materials. One of the main barriers to the commercial uptake of these materials is their tendency to crystallize during a long-term operation at elevated temperatures, a process which decreases both strength and permeability. In this study, the crystallization kinetics of a series of Ni100−xZrx (where x = 36.3 or 70 at.%) and (Ni0.6Nb0.4)100−xZrx (where x = 0, 10, 20 or 30 at.%) amorphous alloy membranes were examined by thermal analyses under isothermal and non-isothermal conditions. The activation energy of crystallization and the crystallization mechanism for binary Ni–Zr alloys were determined using the Johnson-Mehl-Avrami (JMA) equation. The Kissinger and Ozawa methods were applied to the non-isothermal kinetics derived from the heating rate dependence of the crystallization temperature. The hydrogen permeation properties of the Ni–Nb–Zr membranes were investigated over the 573–673 K temperature range at different hydrogen partial pressures. The linear relationship between the hydrogen permeation flux and the hydrogen partial pressure difference across the membrane indicates that permeation was controlled by diffusion through the bulk membrane. The effect of Zr concentration on the hydrogen permeability and the thermal stability was also investigated. The hydrogen permeability improved while the thermal stability decreases with the addition of Zr.