Abstract: Nano- to micron-meter CaCO₃ particles with different shape and crystal structures were prepared by adjusting the experimental conditions, including use of crystal growth inhibitors, concentrations of CaCl₂ and Na₂CO₃, and dispersing methods. CaCO₃ particles were characterized using electronic microscope, dynamic light scattering and X-ray diffraction. The results indicated that the nature and concentration of the crystal growth inhibitors had important effects on the morphology and crystal structure of the product. Without inhibitor, the product was of cubic blocks of about 4-5 μm, and cubic crystals were more uniform with ultrasonic dispersion than with mechanical stirring. However, crystal morphology and structures were easily altered by usage of crystal growth inhibitors. Using sodium triphosphate as the inhibitor, amorphous spherulites were usually formed, except at very low amount of the inhibitor where vaterite crystals were detected. With carboxymethylcellulose sodium (CMC) as the inhibitor, relatively uniform ellipsoidal particles, mostly calcite with small portion of vaterite spherulites of size about 3 μm, were observed, and the size of the spherulites changed with CaCl₂ concentration. While using sodium polystyrene sulfonate (PSS) as the inhibitor, uniform crystal spherulites were easily obtained by adjusting concentration of the inhibitors and the reactants. Opposite to the case where CMC was used, the crystalline structure was mostly vaterite with calcite in small portion. Formation mechanism of CaCO₃ particles in the presence of the inhibitors was discussed.

Key words: calcium carbonate particle, crystal growth inhibitor, dispersion method, particle size, morphology