Interfacial Energies of Amorphous Magnesium Carbonate on Pristine and Reacted Forsterite Surfaces

Substrate reactivity can affect heterogeneous nucleation in ways that remain poorly understood. In this study, classical molecular dynamics (CMD) simulations were used to study heterogeneous nucleation of amorphous magnesium carbonate (AMC) as a function of reaction progress during forsterite (Mg2SiO4) carbonation, whereby forsterite (010) and amorphous silica surfaces were used as model pristine and fully reacted/carbonated surfaces, respectively. Interfacial energies for the nucleus–substrate, nucleus–liquid, and substrate–liquid interfaces were calculated within the framework of classical nucleation theory. AMC was predicted to favor nucleation on the pristine surface rather than on the fully reacted surface, making heterogeneous nucleation less likely as the carbonation reaction progresses. However, the calculated interfacial energies indicated that homogeneous nucleation was kinetically faster than heterogeneous nucleation, regardless of reaction progress. The CMD simulations showed that this difference resulted from the ability of both surfaces to draw water molecules out of AMC to form a partial hydration layer. These findings offer a molecular-level explanation for experimentally observed carbonate nucleation mechanisms.