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

Abstract

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.