Vibration analysis of hydrogen, deuterium and tritium in metals: consequences on the isotope effect

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.

Pd-Ag Electrical Resistivity in Hydrogen and Deuterium: Temperature Effect

The electrical resistivity of Pd-Ag (silver 21 wt.%) in hydrogen and deuterium atmosphere at 100 kPa has been investigated via electrochemical impedance spectroscopy. The electrical resistivity of Pd-Ag vs. the temperature presents the characteristic S-shaped curve with a minimum and a maximum of the resistivity in different positions for the tests in hydrogen and deuterium. The results have been related to: (1) the different isotope ratios, H/M and D/M, and (2) their position in the Pd-Ag lattice. The behavior of the electrical resistivity is discussed in details by considering the hydrogen and deuterium uploading into the alloy, its effect on the conduction electrons, and the scattering of the isotopes atoms into the metal lattice. Measurements carried out in hydrogen with slow temperature ramping between 25-250 °C evidenced a hysteresis effect that can be explained by the different energy levels of isotopes in O-sites and T-sites.