Hydrogen and Deuterium Solubility, Diffusivity and Permeability from Sorption Measurements in the Ni₃₃Ti₃₉Nb₂₈ Alloy

The hydrogen/deuterium sorption properties of Ni₃₃Ti₃₉Nb₂₈ synthesized by the vacuum induction melting technique were measured between 400 and 495 °C for pressure lower than 3 bar. The Sieverts law is valid up to H(D)/M < 0.2 in its ideal form; the absolute values of the hydrogenation/deuteration enthalpy are ΔH(H₂) = 85 ± 5 kJ/mol and ΔH(D₂) = 84 ± 4 kJ/mol. From the kinetics of absorption, the diffusion coefficient was derived, and an Arrhenius dependence from the temperature was obtained, with E_a,d = 12 ± 1 kJ/mol for both hydrogen isotopes. The values of the alloy permeability, obtained by combining the solubility and the diffusion coefficient, were of the order of 10^-9 mol m^-1 s^-1 Pa^-0.5, a value which is one order of magnitude lower than that of Ni₄₁Ti₄₂Nb₁₇, until now the best Ni-Ti-Nb alloy for hydrogen purification. In view of the simplicity of the technique here proposed to calculate the permeability, this method could be used for the preliminary screening of new alloys.