Modelling the thermal stability of precursor nanoparticles in zeolite synthesis

We have modelled the thermal stability of silica nanoparticles commonly observed as precursors in the synthesis of zeolites. We performed canonical Monte Carlo and parallel tempering simulations on a lattice model that describes the self-assembly of nanoparticles under conditions at which they are observed experimentally. The effect of heating on the relative stability of the phases of the model was analysed by running simulations at various temperatures. At low temperature, the model yields a metastable multi-particle phase with a characteristic size distribution, which is separated by an energy barrier from the true equilibrium phase, a dense silica solid. As temperature increases, the system enters a transition region and eventually reaches the bulk phase. This transition is reminiscent of the experimentally observed transition from nanoparticles to zeolite. The transition temperature scales with the inverse of the system volume, approaching an asymptotic value for large system sizes. This indicates the transition temperature is a reproducible macroscopic property of the system. The transition temperature in the model is within the range of temperatures at which nanoparticles form zeolite crystals in experiments.