Controlling the kinetic versus thermodynamic crystallisation of calcium carbonate

Calcium carbonate was grown by diffusion of gaseous carbon dioxide into an aqueous solution of calcium chloride. The interplay between kinetic and thermodynamic control of the growth was investigated. It was found that the calcium ion is the dominant species in producing thermodynamic growth of rhombohedral calcite, while kinetic growth is preferentially controlled by carbon dioxide. This was evidenced by the formation of vaterite as the partial pressure of carbon dioxide increased for a given calcium ion concentration. The different morphological and polymorphic forms grown were examined by scanning electron microscopy and powder X-ray diffraction, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.