Kinetics of the uranium-hydrogen system

Abstract

The reaction kinetics of $\mathrm{U}\text{+ 3/2\hspace{0.17em}}{\mathrm{H}}_2\rightleftarrows {\mathrm{UH}}_3$ was studied with fine powders on an ultrahigh‐vacuum microbalance. The kinetics were found to be first order with respect to uranium for the hydriding reaction and nearly zero order with respect to uranium hydride for dehydriding. A new reaction mechanism is proposed to account for the experimental observations which involves diffusion in the reactant phase by hydrogen before nucleation to form the hydride phase. This reactant phase diffusion and phase transformation reaction with its associated solid state mathematics accounts for all the observations made to date on the kinetics of this system.