Reactions between RbI and Ag4RbI5 were studied. Following the formation of product phases, local thermodynamic equilibrium was established, and further reaction occurred via the cation interdiffusion of Ag+ and Rb+. The reaction rate was controlled by the Rb+ diffusion coefficient. By analyzing the reaction kinetics, the diffusion coefficients were calculated for temperatures of 120 to 190C. The results could be described by:

D (m2/s) = 3 x 10-10 exp[-39(kJ/mol)/RT]

Solid State Reactions and Transport Properties in the Quasibinary System AgI/RbI. B.Schröder, V.Leute: Journal of Physics and Chemistry of Solids, 1980, 41[8], 827-35