Layered agglomeration of primary vaterite nanoparticles during ultrasonic stirring

Abstract

Primary nanoparticles of vaterite (a metastable form of calcium carbonate) precipitated in aqueous solutions under 2.64-MHz sonication are found to experience layered agglomeration. The vaterite particles are characterized by electron microscopy and x-ray diffraction. The particle size distribution of the precipitate is determined. A mathematical model for layered agglomeration is proposed, and the conclusion is made that, under the experimental conditions used, heterogeneous nucleation of primary vaterite particles takes place.

Mechanism of the Vaterite-to-Calcite Phase Transition under Sonication

“…The likely reason is that, under the conditions of this study, the collision energy is insufficient for fragmenting vaterite particles (the proportion of the finest vaterite particles remains almost unchanged during recrystallization, at the level of the as-prepared samples). It may be that vaterite particles, which were shown previously to be layered agglomerates of finer particles [11], are flattened by collisions, which favors the formation of intergrowths of already existing and forming calcite particles. Only a small fraction of the calcite particles persist as separate spheres (Fig.…”