Nucleation of CaCO3 polymorphs from a colloidal alcoholic solution of Ca(OH)2 nanocrystals exposed to low humidity conditions

A study of the stability of calcium carbonate polymorphs formed as a result of the carbonation process from an alcoholic colloidal solution of nanocrystals of Ca(OH)(2) in low relative humidity (RH) conditions (33% and 54% RH) is presented in this research. The crystalline behavior, the time dependence of nucleation and the phases' transformations as a result of exposure to low humidity conditions are evaluated. The carbonation process is slow, starting with the nucleation of amorphous calcium carbonate, associated to an amorphization process that affects both the portlandite (Ca(OH)(2)) and the initial unstable CaCO3 polymorphs. The excess of alcohol in the solution decreases the surface tension and the nucleation is accelerated by the fast evaporation of the solvent, which avoids the particles to diffuse to their lowest energy sites, giving smaller particles with lower crystallinity as RH decreases.