Switching between kinetic and thermodynamic control: calcium carbonate growth in the presence of a simple alcohol

Calcium carbonate was grown by diffusion of gaseous carbon dioxide into aqueous calcium chloride-alcohol solutions and the relationship between the alcohol additive and the growing crystal was investigated. There was no evidence that crystal growth was controlled through any specific molecular interaction between the growing calcium carbonate facets and the alcohol. Under control conditions, both calcite and vaterite were grown in a ratio of 1 : 3, respectively. However, the overall trend for all the alcohols investigated was preferential precipitation of calcite, as compared to the control. In addition to this primary alcohol effect, a morphological variant of perfect calcitic rhombohedra, a hopper crystal, was observed. This morphological form was present in all growth solutions, but made up an increasing proportion of the calcite fraction for solutions with viscosities above approximately 1.6 mPa s, irrespective of the absolute alcohol concentration. The different morphological and polymorphic forms of the calcium carbonate crystals were examined by scanning electron microscopy and powder X-ray diffraction, respectively.