Understanding the Hydration Process of Salts: The Relation between Surface Mobility and Metastability

In this work, the relation between mobility and metastability is investigated. This is done under pure water vapor vacuum conditions. First, the properties of the metastable zone under pure water vapor conditions are investigated and compared to those under atmospheric conditions. Second, mobility is investigated using electrochemical impedance spectroscopy, whereby we differentiate between bulk and surface mobility. Using surface mobility, we showed that mobility is a prerequisite for the nucleation of K2CO3. Sufficient mobility must be introduced for the diffusion of ions and water, whereby an increase of almost two orders of magnitude (800 times) is observed on a hydrated sample. It has been shown that the metastable zone is both a consequence of the energy barrier for nucleation and the low ion mobility at low vapor pressures.