Plutonium oxide transformation kinetics and diffusion coefficient measurement

When subjected to ultra high vacuum (UHV) conditions, a thin surface dioxide covering on a plutonium metal substrate will undergo a spontaneous, thermodynamically driven, reduction to the trivalent sesqui-oxide, Pu2O3. Kinetic information about this surface transformation, from PuO2 to Pu2O3, is gained by following the changing depths of these two oxide layers, using X-ray photoelectron spectroscopy (XPS) as a probe. A mathematical model is proposed to follow this auto-reduction reaction, based on a simple 2D layered structure. The rate of this plutonium oxide inter-conversion is controlled by diffusion of oxygen across the steadily expanding Pu2O3 layer. Through investigating the kinetics of this auto-reduction reaction, a value of 1.4 × 10−16 cm2 s−1 is obtained for the diffusion coefficient of oxygen through α-Pu2O3.