Surface nucleation and anisotropic growth models for solid-state reactions

- Kinetic analysis of solid-state reactions involving surface nucleation is discussed.
- Surface nucleation and anisotropic growth kinetic models are presented.
- Shape of the particles, direction of growth and localization of the rate-determining step are considered.
- Eighteen models are proposed according to realistic assumptions.
- Importance of particles size or particle size distribution is put in evidence.

Nucleation-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.