Autoacceleration of the free-radical chain luminescent oxidation of U(IV) with xenon trioxide in aqueous HClO4

autoacceleration is observed in the chemiluminescent radical chain oxidation of U(IV) with xenon trioxide in aqueous perchloric acid in a Teflon (not conventional glass) reactor. The decay of chemiluminescence accompanying the reaction between U(IV) and XeO3 in the case of excess oxidizer obeys a first-order kinetic equation only at low U(IV) concentrations of 10(-5)-10(-6) mol/l. Autoacceleration takes place at comparatively high reactant concentrations when the contribution from the heterogeneous loss of radicals on the reactor walls into chain termination is comparatively small and the role of degenerate chain branching reactions is significant. It is inferred that a critical phenomenon rare for liquid-phase radical chain processes takes place in U(IV) oxidation with xenon trioxide: a comparative small increase in the reactant concentrations causes this chemiluminescent redox process to pass from the quasi-steady-state regime to autoacceleration.