THERMODYNAMIC PROPERTIES OF URANIUM-ALUMINUM ALLOYS

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) → UAlx(s). The relations obtained from emf measurements are, ΔG0(UAl4) = -26 040+1.121T, ΔG0(UAl3) = -25 190 + 0.487T, ΔG0(UAl2) = -20 700 + 0.212T. 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 UAl4, UAl3 and UAl2 respectively. These data were combined with the emf data to yield the relations ΔG0(UAl4) = -32 040-7.52 T In T + 59.07T, ΔG0(UAl3) = - 26 290-1.305T In T+ 10.60T, ΔG0(UAl2) = -22 790-2.326T In T+ 18.37 T. The enthalpy change for the peritectic reaction at 732 °C UAl4 → UAl3 + 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 UAl4by the addition of ternary components which concentrate in the UAl3 phase. © 1969.