Gas Chromatographic and Gravimetric Studies of Uranium Oxidation Mechanism

New insights into the mechanism off uranium oxidation in moist gases at 75 C (167 F) were made possible by concurrent studies employing gas chromatographic, volumetric, barometric, gravimetric, metallographic and X-ray methods. Presence of uranium hydride beneath the oxide was verified. A “hydride fracture” mechanism is proposed in which growth and fracture of uranium hydride play vital roles in determining the oxidation rate. The hydride phase is transitory which may explain why little importance has been attached heretofore to hydride formation. Hydrogen stimulates attack in the presence of moisture through formation of hydride. Oxygen’s inhibitive action is related to retardation of hydride growth and cracking. Oxidation proceeds in at least two stages: the early stage obeys the relationship ΔW = k₁tⁿ where n ≅ 1.5, whereas the later stage is pseudo-linear. Oxygen diffusion to the oxide-hydride interface may be rate controlling. The activation energy is low, 7-12 kcal/mole.