Alan E. Florin

Preparation and properties of plutonium hexafluoride and identification of plutonium(VI) oxyfluoride

Abstract The compound plutonium hexafluoride has been identified and characterized. A method of preparation by the fluorination of plutonium tetrafluoride is outlined. The vapour pressure, which corresponds closely to that of uranium hexafluoride, has been measured between 0 and 63°C. The vapour pressure is represented by the equations: Log 10 P liquid ( mm ) = 7·6923 − 1614·3 T Log 10 P solid ( mm ) = 10·841 − 2634·3 T The boiling-point is 62·3°C. The heat of sublimation is calculated to be 12·1 kcal/mole. The melting-point is 50·7°C. The heat of vaporization is 7·4 kcal/mole. The heat of fusion is 4·7 kcal/mole, and the corresponding entropy of fusion is 14·5 cal/mole °C. A study of the equilibrium, PuF 4 + F 2 ⇌ PuF 6 has resulted in values of 11·5 kcal/mole and 7·8 e.u. for ΔH and ΔS in the temperature range from 167 to 308°C. Respective values of 6·77 and −0·3 were obtained in the range from 308 to 600°. The rates of thermal decomposition and radio-decomposition have been considered. A solid compound produced when plutonium hexafluoride was exposed to moist air was identified as plutonium(VI) oxyfluoride, PuO 2 F 2 .