New Studies of the Physical Properties of Metallic Amorphous Membranes for Hydrogen Purification

Amorphous metallic membranes display promising properties for hydrogen purification up to an ultrapure grade (purity > 99.999%). The hydrogen permeability through amorphous membranes has been widely studied in the literature. In this work we focus on two additional properties, which should be considered before possible application of such materials: the propensity to crystallize at high temperatures should be avoided, as the crystallized membranes can become brittle; the hydrogen solubility should be high, as solubility and permeability are proportional. We investigate the crystallization process and the hydrogen solubility of some membranes based on Ni, Nb, and Zr metals, as a function of Zr content, and with the addition of Ta or B. The boron doping does not significantly affect the crystallization temperature and the thermal stability of the membrane. However, the hydrogen solubility for p ~7 bar is as high as H/M ~0.31 at T = 440 °C and H/M ~0.27 at T = 485 °C. Moreover, the membrane does not pulverize even after repeated thermal cycles and hydrogenation processes up to 485 °C and 7 bar, and it retains its initial shape.