Hydration of salts as a two-step process: Water adsorption and hydrate formation

K2CO3 is a promising salt for thermochemical heat storage. For high performance, the reaction must take place as close possible to equilibrium, while ensuring sufficient rates. In this work, we studied near-equilibrium hydration kinetics of and other salts (CuCl2, MgCl2 LiCl). We proposed generic two-step mechanism salts, consisting (1) adsorption water vapour dissolution ions from initial phase (a wetting film) (2) formation hydrate crystal (crystallisation film). The two steps are assumed be in momentarious balance during process. As result, nucleation rate limiting at low supersaturations (inside metastable zone), diffusion film (outside zone). have seen that pressure stabilises zone boundary p*. driving force outside (MZ) therefore difference between atmospheric film, p ? Non-Parametric Kinetic analysis indicates plays central role inside (at supersaturations) expected. Outside MZ, suggests steady conversion rate, agreement with limitation. limited process hardly depends on temperature, but mainly difference, It further shown can characterised an apparent activation energy. However, energy fact enthalpy does not refer real barrier.