A model is developed that described the growth kinetics of a compound layer during a reaction-diffusion process. The compound layer formation occurs at the interfaces of two insoluble solid layers. The compound layer is formed as a result of chemical reaction
between the diffusing species and surface atoms. The layer growth occurs in two stages; the first growth stage is controlled by chemical reaction while the second growth stage is controlled by diffusion. A critical thickness and time are obtained at the transition point
between the two growth stages. The result of this model shows a layer growth kinetics that is complex than linear and parabolic laws. The complexity of the growth kinetics is ascribed to the simultaneous diffusion of two kinds of atomic species in the compound layer.