Thermodynamic properties of uranium-aluminum alloys

Abstract

Emf measurements over the temperature range 400 to 840 °C and calorimetric data were combined to develop thermodynamic relations for the reactions U( s) + xAl( s) → UAl x ( s). The relations obtained from emf measurements are, ΔG 0( UAl 4) = −26 040+1.121 T, ΔG 0( UAl 3) = −25 190 + 0.487 T, ΔG 0( UAl 2) = −20 700 + 0.212 T. These relations are based on data obtained over the temperature spans of 401 to 639, 399 to 706, and 442 to 840 °C respectively. The standard deviations for the first and second terms (enthalpy and entropy of formation per mole of compound) are all within 140 to 160 cal/mole and 0.17 to 0.19 cal/mole·°K, respectively. The enthalpies of formation at 298 K as determined in an adiabatic calorimeter were −29.8 ± 2.0, −25.9 ± 2.0 and −22.1 ± 2.0 kcal/mole for UAl 4, UAl 3 and UAl 2 respectively. These data were combined with the emf data to yield the relations ΔG 0( UAl 4) = −32 040−7.52 T In T + 59.07 T, ΔG 0( UAl 3) = − 26 290−1.305 T In T+ 10.60 T, ΔG 0( UAl 2) = −22 790−2.326 T In T+ 18.37 T. The enthalpy change for the peritectic reaction at 732 °C UAl 4 → UAl 3 + Al (in liquid solution) was determined to be 4.0 ± 0.4 kcal/ mole. These data were employed in explaining the suppression of the formation of UAl 4by the addition of ternary components which concentrate in the UAl 3 phase.