Molecular dynamics simulation of ballistic effects in mesoporous silica

Accumulation of ion displacement cascades in mesoporous silica material have been modeled using molecular dynamics (MD). For nuclear energies exceeding 30 keV/nm³, the volume and structural properties (Si-O-Si bond angle, coordination of O and Si) of the mesoporous silica material are modified thereby resulting in the complete collapse of the structure. Similar results were obtained from Au⁺ ion-irradiation (E = 0.5 MeV) experiments on mesoporous silica samples in which the density of the samples was shown to increase upon irradiation before saturating at deposited nuclear energies exceeding 30 keV/nm³. Both ion-irradiation experiments and MD simulations have shown that the ballistic effects are responsible for inducing densification of the mesoporous silica material. The mechanism underlying this densification is discussed in terms of irradiation induced sintering.