OBSERVATION AND ATOMIZATION ENERGIES OF THE GASEOUS URANIUM CARBIDES, UC, UC2, UC3, UC4, UC5, AND UC6 BY HIGH-TEMPERATURE MASS-SPECTROMETRY

Gaseous carbides of uranium, UC, UC2, UC3, UC 4, UC5, and UC6, have been observed in a mass spectrometric investigation of the Knudsen cell effusate from a t thorium-uranium-rhodium-graphite system at high temperatures. Partial pressures of the carbide molecules were measured as a function of temperature in the 2300-2700°K range. Second and third law methods were employed to determine enthalpy changes for the reactions of the type U(g) + nC(graphite) = UC n(g), n = 1 to 6, and for additional reactions with graphite involving two gaseous carbide species and various homogeneous gas phase reactions. The experimental enthalpies when combined with thermodynamic data taken from literature yielded the following atomization energies, ΔH°at,298, and standard heats of formation, ΔH°f,298: ΔH°at,298 ΔH°f,298 kJ mol-1 or kcal mol-1 kJ mol-1 or kcal mol-1 UC 455 ± 15 108.7 ± 3.6 785 ± 26 187.6 ± 6.2 UC2 1274 ± 15 304.5 ± 3.6 682 ± 26 163.0 ± 6.2 UC3 1881 ± 20 449.6 ± 4.8 792 ± 31 189.3 ± 7.4 UC4 2564 ± 25 612.8 ± 6.0 826 ± 34 197.4 ± 8.1 UC5 3144 ± 30 751.4 ± 7.2 962 ± 38 229.9 ± 9.1 UC 6 3822 ± 30 913.5 ± 7.2 1001 ± 39 239.2 ± 9.3 © 1979 American Institute of Physics.