On the role of intercrystallite diffusion in kinetics of solid-phase reactions

It has been shown that diffusion fluxes in the bulk and along the boundaries of the grains in polycrystalline layers of the products of solid phase reactions, proceeding under the conditions of quasistationary diffusion, can be considered as additive in the first approximation. The formula has been obtained which makes possible the evaluation of a mean component diffusion coefficient on the basis of bulk and boundary diffusion when their ratio remains constant during the reaction. The ratios between the parameters of bulk and boundary diffusion determined experimentally in the process of yttrium self-diffusion in yttrium ferrogarnet is (4-7)x10-2 within the temperature range from 1300-1500 deg C. According to the results of the investigation, interaction between CaO and WO3 is ensured, mainly, by a unidirectional intercrystallyte diffusion of WO3