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 degrees 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 Delta H(H-2) = 85 +/- 5 kJ/mol and Delta H(D-2) = 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,E-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.