Oxygen isotope exchange in oxygen-bearing compounds of uranium

Isotope exchange is reported for gaseous oxygen in contact with the following uranium compounds: -Na₂UO₄, -Na₂UO₄, Na₂U₂O₇, UO₃(A), -UO₃, -UO_2.94 and U₃O₈.; qualitative tests have also been done with UO₂F₂ and Cs₂UO₂Cl₄. The times of half-exchange have been determined as functions of temperature for U₃O₈, -UO_2.94, Na₂U₂O₇ and -Na₂UO₄; diffusion coefficients for oxygen have been calculated for UO₃(A), -UO₃, Na₂U₂O₇, -Na₂UO₄ and -Na₂UO₄. Activation energies have been deduced for diffusion and surface exchange. All the oxygen atoms in these compounds are equivalent as regards isotope exchange; the above activation energies increase with the UO ratio in some cases. Diffusion-limited exchange tends to show periodic oscillations in rate not ascribable to errors of measurement; a mechanism is proposed for this.