Sonochemical synthesis of aragonite-type calcium carbonate with different morphologies

Aragonite, a high-pressure polymorph of CaCO3, was synthesized for the first time from simple Ca(HCO3)2 solutions by using high-power ultrasound irradiation. XRD, FT-IR and SEM techniques were used to characterize the phase composition and morphology of the products. The intensity of the ultrasound irradiation was found to have a remarkable effect on the morphology of the as-synthesized aragonite. The morphology evolved from rod-shaped to spindle-shaped when the acoustic amplitude is increased from 50% to 70% of the full amplitude. A possible mechanism for the formation of this controllable aragonite formation is proposed. The dissolved CO2 plays a crucial role in the homogeneous nucleation and growth of aragonite under sonication. Vaterite with flower- or dendrite-like structures could also be obtained by using 75% or 80% of the full acoustic amplitude, respectively. A nonequilibrium kinetics process controls the formation of unstable vaterite with unusual structures.