Enthalpies of formation of UNi₅, UNi₂ and UFe₂ by solution calorimetry

Abstract

The enthalpies of formation of the intermetallic compounds UNi₅, UNi₂ and UFe₂ at room temperature were determined by high temperature solution calorimetry in which liquid aluminium was used as the solvent. The "thermal effects of dissolution" of Ni, Fe, UNi₅, UNi₂ and UFe₂ in liquid aluminium were measured in separate experiments by dropping the samples, held at ambient temperature, into liquid aluminium maintained at 994 K in a high temperature differential calorimeter. The thermal effects of dissolution of the samples in liquid aluminium at infinite dilution were derived from these measurements, and based on these data, the enthalpies of formation of UNi₅, UNi₂ and UFe₂ at room temperature were computed as -(39.54 ± 8.6), -(37.89 ± 4.4) and -(38.73 ± 5.4) kJ (g-atom)-1, respectively. The partial enthalpies of solution at infinite dilution, ( ΔH^-∞) for Ni and Fe in liquid aluminium were also derived from the measured data as -(147.26 ± 1) and -(114.71 ± 1.2) kJ mol^-1, respectively.