An analysis of the kinetics of reversible A + B(s) ⇄ C reactions on porous or powdered materials

Abstract

The kinetics of the A + B(s) ⇄ C reversible process in a powdered material was analyzed for the example of the F2 + PuF4(s) ⇄ PuF6 reaction. Two possibilities of performing this reaction were considered, with pressed and powdered plutonium tetrafluoride. The first possibility does not contain uncertainties and allows the rate constants of the forward and back reactions to be found using the known equilibrium constant values. Experiments with the powdered substance can be used to obtain data on the other details of the reaction. The most general problem was considered and all significant processes were taken into account. These were (1) the diffusion of fluorine and plutonium hexafluoride molecules in the powder, (2) the forward and back reactions on the surface of particles, and (3) the removal of plutonium hexafluoride molecules formed from the surface of the tetrafluoride powder. The reaction became equilibrium as the gas mixture moved over the reaction cell, and the product ceased to form. The optimum cell length was calculated. The theory developed is necessary for planning experiments with powdered materials and experimental data processing. The theory generalizes the results obtained by Zel’dovich to reactions with unstable final products (that is, reversible reactions).