A computational study of calcium carbonate.
Doctoral thesis, UCL (University College London).
This thesis presents the results of computer simulation studies of impurity incorporation in calcite and the aggregation of calcite particles, using a combination of classical computational techniques based on interatomic potentials, namely molecular mechanics and molecular dynamics simulations. Firstly, the atomistic simulation techniques have been employed to investigate the thermodynamics of mixing in calcite with seven divalent cationic impurities (Mg2+, Ni2+, Co2+, Zn2+, Fe2+, Mn2+ and Cd2+), based on the calculation of all inequivalent site occupancy configurations in 2 × 2 × 1 and 3 × 3 × 1 supercells of the calcite structure. In addition to the enthalpy of mixing, the configurational entropy and mixing free energy have also been calculated, providing an insight into the mixing behaviour as a function of the temperature for a series of carbonate solid solutions. The calculations have revealed that the solubility of the cationic impurities in calcite is largely related to the cationic coordination distance with oxygen. Secondly, the aggregation process has been investigated implementing classical computational techniques, and especially the interaction of a calcite nanoparticle with the major calcite surfaces, where the adhesion energy and optimised geometries of a typical calcite nanoparticle on different surfaces in vacuum and aqueous environment have been calculated. The results show the orientation of a nanoparticle is a key factor that effects the interactions, besides the size and structure of the nanoparticle. The most stable aggregated configuration occurs when the lattices of the nanoparticle and the surface are perfectly aligned. Finally, a number of symmetric calcite tilt grain boundaries have been constructed to act as models of two calcite nanoparticles, after collision has occurred but before growth has a chance to commence. Molecular dynamics simulations were then employed to study the stability of these tilt grain boundaries and the growth of a series of calcium carbonate units at the contact points in the pure and hydrated calcite tilt grain boundaries. The calculation have proved that the initial incorporation of a CaCO3 unit is preferential at the obtuse step in a grain boundary, and the growth velocity of the acute step is 1.3 to 2.1 times higher than that of the obtuse step, once the initial growth unit has been deposited on the steps. This study has evaluated the conditions required for the growth of new calcium carbonate materials in the calcite tilt grain boundaries.
|Title:||A computational study of calcium carbonate|
|Open access status:||An open access version is available from UCL Discovery|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry|
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