Molecular modelling studies of calcium carbonate and its nanoparticles

Abstract

Molecular dynamics (MD), simulations have been carried out of crystalline aragonite and calcite, and of finely dispersed calcium carbonate in the form of nanosized inorganic core- organic shell particles. The latter, called overbased detergents commercially, are used as acid-consuming components in automotive and marine engine oils. We have modelled several types of these particles using different surfactant types. We compare the internal structure of the calcium carbonate in these particles with calcite and aragonite crystalline forms using MD in each case. The atomic force-field adopted accounts reasonably well for the crystalline phases, although under unconstrained (constant stress) conditions some distortion of the aragonite structure was noticed. The microstructure of the nanoparticles appears to be quite different to the crystals, and seemingly amorphous. For these small clusters it appears that there is probably no thermodynamic benefit in forming local crystalline order in the cores. The relatively large surface to volume ratio found in these particles lends itself to a more amorphous microstructure.

Keywords:

• Aragonite
• Calcite
• Nanoparticles