Kinetics of the hydrofluorination of thorium dioxide

Abstract

Uniformly colored and optically isotropic interference films of thorium tetrafluoride were formed on the polished trigonal faces of single crystals of thorium dioxide by reaction with gaseous hydrogen fluoride. The kinetics were determined spectrophotometrically at six temperatures in the interval 218°-327°C. The reaction is diffusion controlled with the film thickness proportional to the square roots of pressure of HF(g) and time corrected for an incubation period. The rate constant is β = 7.0×102 exp (-6630/RT) A/(sec·Torr)1/2 within an error (75% confidence) of ±280 cal/mole for the heat of activation.