Thermodynamic properties of Uranium-Bismuth alloys

Abstract

Thermodynamic properties of uranium-bismuth alloys were determined by measuring the vapor pressure of bismuth in equilibrium with the condensed phase. Classical methods based on the rate of sublimation, rate of evaporation or rate of effusion could not be used since each method requires an accurate knowledge of the molecular weight of the vapor. The molecular weight of bismuth is not accurately known, but the presence of Bi and Bi2 species has been established.An optical absorption technique was used to determine the concentration of each species independently. Briefly, this method consists of measuring concentrations in a vapor by the quantity of light absorbed at certain characteristic frequencies by the species in the vapor. The amount of each species present, which is related to the pressure, was determined by measuring the diminution of intensity at 3067 and 2731 A. The amount of radiation absorbed was found to be dependent on the thickness of the vapor space and the concentration of the bismuth vapor.The thermodynamic activity of bismuth was measured at temperatures from 725 to 875[deg]C in the regions: U3Bi4 + UBi2, UBi2 + liquid and the one-phase, liquid region. In order to obtain measurable quantities in the regions UBi + U and UBi + U3Bi4 it was necessary to work at temperatures from 800 to 1000[deg]C. From a measure of the activity of bismuth, the activity of uranium was calculated for the entire system. The liquid uranium--bismuth alloys were found not to be regular solutions. The Henry's law parameter (3.49 x 10-3 at 1064[deg]K) was found to be valid for uranium concentrations of less than 2 mole % uranium. From a complete knowledge of the activities of uranium and bismuth in the system the partial molar quantities and integral molar quantities were calculated at five temperatures: 1018, 1041, 1064, 1089 and 1115[deg]K.