Vaporization study on fission-produced noble metal alloys by mass-spectrometric method

Abstract

Abstract The vapor pressures over the ϵ-phase of the MoxRuyPdz alloys (x = 0.20-0.45, y = 0.15–0.60, z = 0.20–0.40) were measured by means of mass spectrometry in the temperature range 1536–1791 K. Palladium vapor was observed as the only gaseous species. The chemical activities of palladium in the alloys, determined from the vapor pressures of Pd(g), were compared with those calculated on the basis of the regular solution model using the Kaufman and Bernstein parameters. Applying a least-squares fit to the chemical activity of palladium obtained experimentally in this study, the interaction parameters and the free energy of formation were determined for the regular solution model and the Hillert model. The vapor pressures of Mo(g) and Ru(g) over the Mo-Ru-Pd alloys were calculated using the regular solution model. Thermodynamic quantities such as the partial molar free energy of mixing, the excess partial molar free energy of palladium and the partial molar enthalpy and entropy of Pd(g) over the Mo-Ru-Pd alloys were also calculated from the palladium vapor pressures.