A Kinetic Study of the Fluorination of Silver

Abstract

IS. Supplementary Notes AbstractT h e kinetics of the reaction of fluorine with s i l v e r w e r e studied at t e m p e r a t u r e s f r o m 25' to 300' C (298 to 573 K ) and 50-t o 600-toor (6666-t o 79 993-N/m 2 ) fluorine p r e s s u r e . T h e reaction is p r e s s u r e dependent and can b e d e s c r i b e d by t h e equation yn = k r t + c. T h r e e products are identified: s i l v e r subfluoride, s i l v e r monofluoride, and s i l v e r difluoride. T h e calculated value of t h e diffusion constant is 0.10 c m 2 / s e c , and the activation energy f o r t h e diffusion p r o c e s s is 10 kcal/mole (41.8 kJ/mole).S i l v e r ion vacancy migration is proposed as t h e diffusion mechanism. Reaction-rate constants are l i s t e d . SUMMARYThe effect of the variables temperature and p r e s s u r e on the kinetics of the reaction of fluorine gas with silver w a s studied. The temperature range studied w a s 25' to 300' C (298 to 573 K ) at total fluorine p r e s s u r e s of 50 to 600 t o r r (6666 to 79 993 N/cm 2 ).The reaction was followed by the pressure-drop method and was found to b e p r e s s u r e de pendent. The applicable rate law was yn = krt + c , w h e r e y is the amount of fluorine consumed per unit area of silver surface, k r is the reaction-rate constant, t is the time in minutes, and c is a constant. The value of n w a s 1 during the initial course of the reaction, indicating a boundary controlled process. At a l a t e r time, the process be c a m e diffusion controlled, w h e r e the value of n w a s 2. The reaction is complex due to the formation of three products: s i l v e r subfluoride, s i l v e r monofluoride, and s i l v e r di fluoride. Rate constants are calculated, and activation energies are given. The reac tion appears to be cation diffusion controlled, and the diffusion through the barrier layer is by a vacancy mechanism. The calculated value of the diffusion constant is 0.10 centi m e t e r squared p e r second, and the activation energy for the diffusion is 10 kilocalories p e r mole (41.8 kJ/mole).