Understanding nucleation and growth using computer simulation

Atomistic simulation has been used to examine two distinct problems: (1) the growth of calcium carbonate and how growth inhibitors may operate at the atomic scale and (2) the external surface properties of a zeolite and how these influence the transport of reactants or products at the surface. In the first study we have examined how the class of monophosphonate growth inhibitors disturbs the assembly of calcite at a growing surface. We show that a retarding growth inhibition mechanism is that of kink-blocking, where the poison irreversibly binds to a kink site preventing kink-kink annihilation or step assembly in the vicinity of the impurity. Secondly, we show that two models proposed by Terasaki (O. Terasaki, J. Elec. Micro. 43 (1994) 337), are stable and provide an external surface with characteristic steric and chemical properties. To assess the question of transport, we used a probe molecule of benzene to navigate the energy barrier that separates the external surface and internal surface. We find that the barrier is smaller than that in bulk which suggests that for molecules with relatively small kinetic radii, the rate determining step in the transport process will be in the host medium or crystal bulk. (C) 2001 Editions scientifiques et medicales. Elsevier SAS. All rights reserved.