3, 4 The formation of this alteration layer is usually associated with a drop in the corrosion rate-a behavior known as the passivation effect. 1, 2, 3 In most cases, the leaching of the mobile cations initially present in the silicate phase (e.g., B and alkali), their replacement by hydrated species, and the restructuring of the leached material results in the formation of a disordered, porous, and hydrated “gel” layer on the surface of the dissolving phase. When exposed to water, silicate glasses and minerals tend to dissolve via several mechanisms, including hydration, hydrolysis, and ion-exchange. Rather, we establish that the propensity for passivation is intrinsically governed by the reorganization of the medium-range order structure of the gel upon aging and, specifically, the formation of small silicate rings that hinder water mobility. Based on these results, we demonstrate that the passivation effect cannot be solely explained by the repolymerization of the hydrated gel upon aging. Nevertheless, only select glass compositions are found to exhibit some passivation. We show that, upon the aging of the gel, the passivation effect manifests itself as a drop in hydrogen mobility. Here, based on reactive molecular dynamics simulations, we investigate the hydration of a series of modified borosilicate glasses with varying compositions. ![]() When exposed to water, silicate glasses and minerals can form a hydrated gel surface layer concurrent with a decrease in their dissolution kinetics-a phenomenon known as the “passivation effect.” However, the atomic-scale origin of such passivation remains debated.
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