Dissociation Behavior of Uranium Monocarbide

Abstract

Uranium monocarbide was found to lose uranium preferentially in the temperature range 2250°–2525°K until a constant vaporizing, nonstoichiometric composition approaching UC1.1 was formed. Rates of evaporation of this composition, measured from 2190° to 2525° by the Langmuir method, are described by log10m(UC1.1(s)) = 9.148 − 3.574 × 104T−1(g cm−2·sec−1). Based on the decomposition process, UC1.1(s) → U(g) + n1C1(g) + n2C2(g) + n3C3(g), the partial pressure of uranium is given by log10PU(g)(atm) = 8.191 − 3.624 × 104T−1. The partial pressure of carbon, expressed as effective monatomic pressure, is log10Pc = 8.341 − 3.608 × 104T−1. These data yield a heat of vaporization at 298°K of 235.1 ± 2.7 kcal/mole for the above vaporization process. The resultant standard heat of formation of UC1.1(s) at 298°K is −21.2 ± 4.1 kcal/mole if 125 ± 3 kcal/mole is taken as the heat of sublimation of uranium.