Can agitation determine the polymorphs of calcium carbonate during the decomposition of calcium bicarbonate?

Abstract

The influence of agitation on the polymorphs and morphologies of calcium carbonate (CaCO₃) during the decomposition of calcium bicarbonate (Ca(HCO₃)₂) was semi-quantitatively investigated in the present work. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the polymorphs and morphologies of CaCO₃ in the presence and the absence of polyethylene glycol (PEG). In the absence of PEG, the amount of calcite increases with the strengthening of agitation, while the amount of vaterite decreases and even completely disappears. We believe that agitation contributes to the crystallization of the thermodynamically stable phase and limits crystallization of the thermodynamically least stable. This belief was verified by the XRD results under the same agitation conditions in the presence of PEG. The influence of agitation on the polymorphs of CaCO₃ was discussed from the view of the arrangement of Ca²⁺ ions under static and stirring conditions.