The analyze of structure of vaterite and which factors will induce vaterite formation

Calcium carbonate (CaCO3) is the most abundant mineral form of a biomineral and has important applications in industry such as nano-materials. Calcite is its most stable polymorph at ambient conditions. However, vaterite, the least stable polymorph of CaCO3, has recently been found to act as a precursor to calcite during the addition of certain organic acids. Therefore, it is increasingly important to understand the formation and properties of vaterite. In this study, we show that both the inorganic additives and the experimental setup itself may promote the formation and stabilization of vaterite. Powders of muscovite and orthoclase, but not quartz, have the ability to induce the formation of vaterite, rather than calcite, a shown by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) of the crystals formed. Empirical force-field calculations suggest that the charge distribution on the powder surfaces stabilize vaterite. Also, without any additions, polystyrene Petri dishes induce more vaterite formation than glass Petri dishes. In addition, ammonia that was used to increase solution pH and hence CaCO3 precipitation, promotes formation of vaterite rather than calcite. This shows that minor changes in experimental design can have a significant influence on the minerals precipitated. The crystal structure of the precipitating vaterite and its morphology was investigated using TEM and SEM showing that the major crystal planes of vaterite are (001) growth planes. XRD data confirmed the results of molecular dynamics simulations showing that the carbonate ions of freshly precipitated vaterite are disordered but develop long-range order after one hour of heating at 250 °C followed by quenching.