Controllable synthesis of calcium carbonate polymorphs at different temperatures

Calcium carbonate with various structures and morphologies were prepared by double injection of the CaCl2 and NH4HCO3 solutions with molar ratio of 1:1 at 30-80 degrees C. The lamellar vaterite particles, the mixture composed of vaterite, aragonite and calcite, and the aragonite whiskers were formed at 30-40 degrees C, 50-70 degrees C and 80 degrees C, respectively. Thermodynamic calculation showed that the value of [CO32-]/[Ca2+] decreased with the increase of temperature, which may be one of the reasons for the formation of the lamellar vaterite at 30-40 degrees C and the aragonite whiskers at 80 degrees C. (C) 2008 Elsevier B.V. All rights reserved.