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 UC_1.1 was formed. Rates of evaporation of this composition, measured from 2190° to 2525° by the Langmuir method, are described by ${\log }_{10}\mathrm{m(}{\mathrm{UC}}_{\text{1.1(}\mathrm{s})}{\text{)\hspace{0.17em}=\hspace{0.17em}9.148\hspace{0.17em}−\hspace{0.17em}3.574\hspace{0.17em}×\hspace{0.17em}10}}^4{T}^{\text{−1}}({\mathrm{g\; cm}}^{\text{−2}}·{\sec }^{\text{−1}})$ . Based on the decomposition process, ${\mathrm{UC}}_{\text{1.1(}\mathrm{s})}\mathrm{\hspace{0.17em}\to \hspace{0.17em}}{\mathrm{U}}_{(\mathrm{g})}{\mathrm{\hspace{0.17em}+\hspace{0.17em}n}}_1{\mathrm{C}}_{\text{1(}\mathrm{g})}{\mathrm{\hspace{0.17em}+\hspace{0.17em}n}}_2{\mathrm{C}}_{\text{2(}\mathrm{g})}{\mathrm{\hspace{0.17em}+\hspace{0.17em}n}}_3{\mathrm{C}}_{\text{3(}\mathrm{g})}$ , the partial pressure of uranium is given by ${\log }_{10}{\mathrm{PU}}_{(\mathrm{g})}(\mathrm{atm}{\text{)\hspace{0.17em}=\hspace{0.17em}8.191\hspace{0.17em}−\hspace{0.17em}3.624\hspace{0.17em}×\hspace{0.17em}10}}^4{T}^{\text{−1}}$ . The partial pressure of carbon, expressed as effective monatomic pressure, is ${\log }_{10}{P}_c{\text{\hspace{0.17em}=\hspace{0.17em}8.341\hspace{0.17em}−\hspace{0.17em}3.608\hspace{0.17em}×\hspace{0.17em}10}}^4{T}^{\text{−1}}$ . 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 UC_1.1(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.