Surface nucleation and anisotropic growth models for solid-state reactions

International audienceNucleation-growth models for the kinetic analysis of gas–solid reactions in which nucleation proceeds at the surface of the particles are reported. The growth of the nuclei is assumed to be anisotropic, i.e. with a very fast surface rate compared to the bulk one. The nucleation and growth processes are assumed to occur with, respectively, an areic frequency γ (nb. nuclei m−2 s−1) and an areic reactivity ϕ (mol m−2 s−1), both depending only on the thermodynamic variables (such as temperature, partial pressures …) established during the reaction. Depending on the shape of the particles, the direction of growth and the localization of the rate-determining step, eighteen analytical expressions of kinetic rate are obtained. The importance of particle size is also put in evidence