Corrosion of silicate glasses in aqueous environment is common and it impacts many physical and chemical properties of these materials that have wide ranges of industrial and technological applications. However, the corrosion mechanisms of silicate glasses remain relatively poorly understood due to complicated interfacial reactions and transport behaviors. Here, we have employed molecular dynamics simulations with the recently developed reactive force field to investigate the sodium silicate glass and water interfacial reactions. Simulations up to 3 nano-seconds at four different temperatures were performed to study the key processes at the glass−water interface. The simulation results reveal three-stage interfacial reactions: (i) in the near-surface region, water diffusion and subsequent reactions with the nonbridging oxygen to form silanol groups are the dominating reactions; (ii) in the near-bulk region, the main reaction is silanol reformation through proton transfer; (iii) in the subsurface region (between the above two), both reactions were observed. It was also found that water transports in sodium silicate glasses mainly through two mechanisms: molecular water diffusion and proton transfer, with the former dominating in near-surface region and the latter dominating in all other regions. Acceleration of reactions and deeper water penetration were observed for higher temperature simulations, but by-products were observed for temperatures higher than 500 K.

The ion-exchange and associated interfacial reaction mechanisms of silicate glasses are critical in elucidating their aqueous corrosion behaviors, surface modification and property changes, hence have potential impact on both science and technology. This work reports findings of the atomic and nanoscale details of the glass–water interfacial reactions revealed by applying reactive force field (ReaxFF) based molecular dynamics (MD) simulations, from which the key mechanisms of the ion exchange, as well as the kinetics of associated interfacial reactions, are elucidated. It was found that the Na+ and H+ ion exchange can happen between two oxygen ions on a single silicon oxygen tetrahedron or adjacent tetrahedra. In addition, the clustered reaction of two non-bridging oxygens mediated by an adjacent water molecule was also identified. The latter reaction might be the main mechanism of water transport after initial surface reactions that consume the non-bridging oxygen species on the surface. Water molecules thus can play two roles: as an intermediate during the proton transfer processes and as a terminator of the clustered reactions. Statistical analyses were performed to obtain reaction kinetics and the results show that silanol formation is a more favored process than the silanol re-formation within the first 3 ns of interfacial reactions. The results obtained thus shed lights on the complex ion-exchange mechanisms during glass hydration and enable more detailed understanding of the corrosion and glass–water interactions of silicate glasses.

Reactive molecular dynamics simulations have been used to simulate the chemical mechanical polishing (CMP) process of silica glass surfaces with the ceria ( 111) and ( 100) surfaces, which are predominantly found in ceria nanoparticles. Since it is known that an alteration layer is formed at the glass surface as a consequence of the chemical interactions with the slurry solutions used for polishing, we have created several glass surface models with different degrees of hydroxylation and porosity for investigating their morphology and chemistry after the interaction with acidic, neutral, and basic water solutions and the ceria surfaces. Both the chemical and mechanical effects under different pressure and temperature conditions have been studied and clarified. According to the simulation results, we have found that the silica slab with a higher degree of hydroxylation (thicker alteration layer) is more reactive, suggesting that proper chemical treatment is fundamental to augment the polishing efficiency. The reactivity between the silica and ceria (111) surfaces is higher at neutral pH since more OH groups present at the two surfaces increased the Si−O−Ce bonds formed at the interface. Usually, an outermost tetrahedral silicate unit connected to the rest of the silicate network through a single bond was removed during the polishing simulations. We observed that higher pressure and temperature accelerated the removal of more SiO 4 units. However, excessively high pressure was found to be detrimental since the heterogeneous detachment of SiO 4 units led to rougher surfaces and breakage of the Si−O−Si bond, even in the bulk of the glass. Despite the lower concentration of Ce ions at the surface resulting in the lower amount of Si−O−Ce formed, the (100) ceria surface was intrinsically more reactive than (111). The different atomic-scale mechanisms of silica removal at the two ceria surfaces were described and discussed.

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Understanding the underlying reaction mechanisms responsible for aluminosilicate glass dissolution in aqueous environments is crucial for designing glasses for technological applications ranging from architecture windows and touch screens to nuclear waste disposal. This study investigated the glass composition effect on the interfacial reactions of sodium aluminosilicate (NAS) glasses using molecular dynamics (MD) simulations with recently developed reactive potentials. Glass–water interfacial models of six NAS glasses with varying Al2O3/Na2O ratios were investigated for up to 4 nanoseconds (ns) to elucidate the interfacial reaction mechanisms at ambient temperature. The results showed that the coordination defects, such as undercoordinated Si and Al, as well as non-bridging oxygens (NBOs) accumulated at the glass surfaces, play a crucial role in the initial hydration reaction process of the glasses. They promote the formation of silanol (Si–OH) and aluminol (Al–OH) species together with the Na+ ⇔ H+ ion-exchange reactions. The z-density profiles of H2O and H+ ions affirmed the water/H+ propagation into the glass up to 2 nanometers after 4 ns reactions. The penetration depth depends on the composition and shows a nonlinear dependence, suggesting that the subsequent water penetration, particularly into the bulk glass, is supported by the availability of random channels. Aluminol formations, including Al–OH or Al–OH2 near the surface, were found to form mainly through the hydrolysis of Al–O–Al bonds and hydration of Al+–NBO– units. While water molecules are involved in initial interfacial reactions, water penetration into the bulk glass region is primarily achieved by proton transfer. Compared to highly mobile proton transfer involving silanol groups, proton transfer associated with [AlO4]− species is much more limited, particularly in the bulk glass region. These new insights into the role of aluminum in interfacial reactions of the NAS glasses can help to understand the initial dissolution mechanisms and in designing more durable glasses.