Neutron diffraction study of the Pd0.772Ag0.228Dν membrane for hydrogen separation

Abstract

Experiments of deuterium absorption/desorption were performed on a foil of Pd77Ag23 (wt%) alloy in the 78–196 °C temperature and 1–4 bar pressure ranges under the neutron beam at ILL (Grenoble). Powder diffraction patterns were collected on the D1B diffractometer (λ = 1.2871 Å) on the Pd0.772Ag0.228Dν deuterated alloy, and the face-centred-cubic structure was Rietveld-refined locating the D atom in the octahedral site with a variable occupancy ν (=D/M ratio). The results of ν(T) curves at different p(D2) pressures are discussed in comparison with literature data on H and D absorption into PdAg alloys from thermodynamic measurements. A negative deviation from predictions of Sieverts' law is shown by the dependence of D occupancy on pressure. This effect relates the behaviour of the activity coefficient γD to D–D and D–M interactions in the solid solution phase.