Precipitation diagram of calcium carbonate polymorphs: its construction and significance.

In order to interpret the formation mechanism of calcium carbonate polymorphs, we propose and construct a new 'precipitation diagram', which has two variables: the driving force for nucleation and temperature. The precipitation experiments were carried out by mixing calcium chloride and sodium carbonate aqueous solutions. As a result, a calcite-vaterite co-precipitation zone, a vaterite precipitation zone, a vaterite-aragonite co-precipitation zone and an aragonite precipitation zone can be defined.

Molecular dynamics simulation of the phase transition between calcite and CaCO(3)-II.

Molecular dynamics (MD) simulation of calcium carbonate at high pressure was performed to understand the phase transition between calcite [Formula: see text] and CaCO(3)-II (P 2(1)/c). In the 300-800 K temperature range, the transition of calcite to CaCO(3)-II was reproduced at a pressure of around 8 GPa. This transition is of first order and reversible in the MD calculations except for runs at 300 K where a small hysteresis exists.

Molecular dynamics simulation of the rotational order-disorder phase transition in calcite.

Molecular dynamics (MD) simulation of calcite was carried out with the interatomic potential model based on ab initio calculations to elucidate the phase relations for calcite polymorphs and the mechanism of the rotational order-disorder transition of calcite at high temperature at the atomic scale. From runs of MD calculations with increasing temperature within a pressure range of 1 atm and 2 GPa, the transition of calcite with [Formula: see text] symmetry into a high-temperature phase with [Formula: see text] symmetry was reproduced. In the high-temperature [Formula: see text] phase, CO(3) groups vibrate with large amplitudes either around the original positions in the [Formula: see text] structure or around other positions rotated ± 60°, and their positions change continuously with time.