High-Temperature Evaporation and Thermodynamic Properties of Cm2O3

Curium oxide has been shown to vaporize congruently as Cm₂O₃. Effusion measurements have been carried out, using tungsten and molybdenum cells, over a temperature range from 1800 to 2600°K and a pressure range from 10⁻⁹ atm to 0.5 mm. The linear least‐squares fit to the total volatility, calculated as Cm₂O₃, yields the equation $\log P\mathrm{(atm)}\text{\hspace{0.17em}=\hspace{0.17em}7.32(±\hspace{0.17em}0.26)−\hspace{0.17em}29 050(±\hspace{0.17em}590)/T(°}\mathrm{K})$ . The corresponding ${\mathrm{\Delta H}}_{2200}°\mathrm{K}$ and ${\mathrm{\Delta S}}_{2200}°\mathrm{K}$ were computed to be 133.0 ± 2.7 kcal/mole of gas and 33.5 ± 1.2 cal/deg·mole of gas, respectively. The predominant vaporization process is thought to be the formation of CmO(g) and O(g), based on estimates of the heat of formation of Cm₂O₃(s), comparison of experimental and estimated entropies of vaporization, consistency between second‐ and third‐law heats of vaporization, and trends in the vaporization behavior of lighter actinide oxides. The heat of vaporization at 0°K would then be 429 ± 8 kcal/mole of Cm₂O₃.