Controlled growth of nanocrystalline rods, hexagonal plates and spherical particles of the vaterite form of calcium carbonate

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Pure vaterite (hexagonal) phase of calcium carbonate has been obtained at room temperature (20 °C) using a microemulsion route. The process resulted in uniform micron-sized hexagonal plates (∼1 µm) of vaterite where 9.375 µmol of Ca2+ and CO32− ions was used while at lower concentration (0.625 μmol) cubes of calcite phase were obtained. High magnification TEM images of the hexagonal plates shows an assembly of spherical nanoparticles (∼50 nm). At an optimal concentration, rod-shaped vaterite particles were obtained at 40 °C. This is the first report of the rod-shaped morphology of the vaterite phase. The length and diameter of the rods have been found to be ∼250 and ∼30 nm, respectively. The surface charge of the vaterite phase (rod-shaped) was found to be +31 mV which is consistent with the high ionic concentration used in the synthesis.