(356c) Hydrogen Permeability, Thermal Stability and Mechanical Strength of Melt-Spun (Ni1-xNbx)80Zr20 (for x = 0.3 to 0.6) Amorphous Alloy Membranes

Amorphous Ni-based alloys are inexpensive hydrogen-selective membrane materials. One of the main barriers to the greater commercial use of these materials is their tendency to absorb hydrogen and embrittle, a process which decreases strength and causes membrane failure. The material also has a tendency to crystallize during a long-term operation at elevated temperatures,

a process which decreases both strength and hydrogen permeability. In this study, the hydrogen permeability and solubility of a series of (Ni_1-xNb_x)₈₀Zr₂₀(for x = 0.3 to 0.6) amorphous alloy membranes was studied. Amorphous membrane ribbons with thicknesses of 40-60 µm were fabricated by melt spinning and coated with a thin (500 nm) layer of Pd surface catalyst by magnetron sputtering.

The hydrogen permeation properties of the membranes were investigated over the 350-450°C temperature range at different hydrogen partial pressures. The effect of Ni concentration on the hydrogen permeability and the thermal stability was also investigated; the hydrogen permeability decreases with the addition of Ni.

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 glass transition and crystallization kinetics of melt-spun Ni₆₀Nb₂₀Zr₂₀ amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The activation energies of crystallization, Ex, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics indicating a diffusion-controlled three-dimensional growth mechanism. In addition, the inter-metallic phases and morphology after membrane testing have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM).