High-Temperature Vapor-Pressure Studies of UO2 by the Effusion Method and Its Thermodynamic Interpretation

A high‐temperature effusion investigation under vacuum of the vapor pressure of UO₂ is presented over the temperature range from 2200° to 2800°K. A least‐square analysis of the experimental results yielded the equation $$\log {\text{p\hspace{0.17em}(mm)=12.426–3.318(10}}^4\mathrm{/T).}$$ The latent heat of sublimation ΔH°₂₉₈=148.6 kcal/mole was determined by applying the third‐law method of thermodynamics. Blackbody hole readings, corrected for both the transmissivity of interposed windows and the cavity temperature, were checked by measuring the spectral emissivity of the optically smooth polished tungsten surface at 0.65 μ, which decreased from 0.44 at 2300°K to 0.416 at 2850°K. Compatibility tests at 2800°K revealed no signs of a noticeable reaction between UO₂ and the tungsten effusion cell.