Experimental and computational study of particle formation kinetics in UF6 hydrolysis

Abstract

The formation and growth of UO₂F₂ particles by gas-phase UF₆ hydrolysis remains of interest to actinide chemistry researchers. The total number concentration of the UO₂F₂ aerosol particles that can be produced in the reaction is regulated primarily by the availability of water molecules under our reactor conditions. An increase in water molecule concentration corresponds with a higher amount and larger size of UO₂F₂ aerosol particles produced. The growth rates of aerosol particles appear to approach a single number in the range of [0.05 ± 0.03–0.08 ± 0.04] (nm s⁻¹), as the molar ratio of water to UF₆ decreases below 1. The size of primary particles produced from the UF₆ hydrolysis under water-deprived conditions was estimated to be 3.6 ± 0.4 nm. As the molar ratio became greater than 1.7, the size of primary particles increased with increased availability of water molecules. The primary particle model developed in this work predicted a size range for the UO₂F₂ primary particles similar to that estimated based on the data from gas-phase UF₆ hydrolysis experiments. This result suggests that the volume-driven coalescence process assumption used in the derivation of the primary particle model was reasonable. The ability to precisely control the availability of water molecules and reaction time could lead to the production of nearly monodispersed aerosol particles. This finding has significant implications in the engineering and manufacturing of fuel powder materials and possibly the future development and deployment of environmental sampling apparatus.