Mass Spectrometric Study of the Vaporization of Uranium Monophosphide

The vaporization of uranium monophosphide, UP, and its mixtures with uranium oxide, UO2, have been investigated by Knudsen effusion techniques in combination with a mass spectrometer. The vaporization of UP occurs by decomposition according to UP(s)=U(g)+(1/x)Px(g) (x is either 1 or 2).If UO2 is present approximately in equimolar ratio with UP the principal reaction is according to UP(s)+UO2(s)=2UO(g)+(1/x)Px(g) (x is either 1 or 2).The partial pressures of P, P2, and U over UP have been obtained from the silver calibration for the temperature range of 1750°—2250°K. The temperature dependence of logKp for Reaction (1), where x=1 was determined to be the following: logKp=−(54888/T)+14.6056±0.1392.From the second-law treatment, the heat of vaporization in kcal/mole of UP is obtained for Reaction (1) as 251.17±4.88 when x=1. Vapor pressures derived from other methods, such as (a) from known dissociation energy of P2 and thermodynamic functions of P and P2, and (b) from the amounts of sample evaporated are discussed.