Hydrogen solution in homogeneous Pd–Fe alloys

Abstract

Abstract Thermodynamic properties for H2 solution and hydride formation in Pd–Fe alloys have been determined from pressure–composition isotherms and from reaction calorimetry. The dilute phase solubility in the Pd–Fe alloys appears to be anomalous because the Sieverts’ constants for XFe≥0.0374 do not extrapolate linearly to the value for pure Pd–H. Substitution of Fe in the Pd lattice causes the unit cell size to decrease and thus this system is contracted with respect to Pd. Contracted Pd-rich alloys generally have increased plateau pressures as compared to Pd and the Pd–Fe alloys are no exception. Enthalpies for the plateau reaction have been determined by both p–c–T and reaction calorimetric methods. The enthalpy magnitudes decrease with atom fraction Fe from 19.1 kJ/mol 1 2 H 2 (XFe=0) to 13.5 (XFe=0.10) as determined from reaction calorimetry.