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We study reactivity and leaching at the calcium sodium borosilicate (CNBS)–water interface by means of a Car–Parrinello ab initio molecular dynamics simulation over a simulation time of 100 ps. With an emphasis on the comparison between the behaviors of Ca2+ and Na+ cations at the CNBS glass–water interface, different mechanism events during the trajectory are revealed, discussed, and correlated with other density functional theory calculations. We show that Na+ ions can be released in solution, while Ca2+ cannot leave the surface of CNBS glass. This release is correlated with the vacancy energy of Ca2+ and Na+ cations. Here, we found that the CNBS structure with the Na+ cation vacancy is energetically more favorable than the structure with the Ca2+ cation vacancy. The calcium adsorption site has been shown to have a greater affinity for water than can be found in the case of the sodium site, demonstrating that affinity may not be considered a major factor controlling the release of cations from the glass to the solution. [ABSTRACT FROM AUTHOR]

Predicting the chemical durability of glass materials is important for various applications from daily life such as cell phone screens and kitchenware to advanced technologies such as nuclear waste disposal and biomedicine. In this work, we explored the prediction of the initial glass dissolution rates using structural features from molecular dynamics (MD) simulations for a series of glass compositions (total 28), including ZrO2‐ and V2O5‐containing boroaluminosilicate, borosilicate, and aluminosilicate glasses. The initial dissolution rates (r0) measured experimentally at 90°C with varying solution conditions were correlated with structural features (e.g., polyhedral linkages and non‐bridging oxygen species) obtained from MD simulations, either from this study or from literature. As hydrolysis of the glass network through breaking of the network former linkages (e.g., Si–O–Si, Si–O–Al, etc.) is a critical step of network glass dissolution, the statistics of these linkages obtained from MD were also correlated to r0 through linear regression, where the coefficients of determination (R2) and root mean square error are found to be 0.949 and 0.681, respectively. This model was compared and discussed with existing models developed by various approaches, including machine learning, the kinetic rate equation, topological constraint theory, and other descriptors from MD simulations. The discussion provides insights on future model improvements to predict glass dissolution. In addition, as the effect of V2O5 on glass dissolution was not well studied comparing to ZrO2, the impact of V2O5 was emphasized in this paper, suggesting that the impact is not the same across all glass compositions and test conditions. [ABSTRACT FROM AUTHOR]

Quantitative Structure Property Relationship (QSPR) analysis based on molecular dynamics (MD) simulations is a promising approach for establishing the composition‐property relationships of glasses and other materials with complex structures. A series of 20 borosilicate, aluminosilicate, and boroaluminosilicate glasses have been modeled using MD simulations with recently developed effective potentials. Short‐ and medium‐range structures of these glasses were analyzed and, based on the structural information, QSPR analysis of the initial dissolution rates (r0) of these glasses that were measured at 90°C and pH 9 by using various structural descriptors such as percentage of bridging oxygen species, network connectivity, and average ring size. The structural descriptor, Fnet, which contains both energetic information such as single bond strength and structural information such as cation coordination number and Qn distribution, was also used. It was found that while the overall network connectivity, average ring size and Fnet provide reasonable correlations with r0 of studied glasses, Fnet gives the best correlation among the descriptors. For glasses that show incongruent dissolution, it was found that modification of glass compositions to account for preferential release of modifier cations is necessary to achieve best correlations. The findings were discussed with results of recent studies on evaluating the compositional dependence of glass dissolution behavior using the topological‐constraints‐based models. [ABSTRACT FROM AUTHOR]

Hydrogen bonding interactions play an important role in many chemical and physical processes occurring in bulk liquids and at interfaces. In this study, hydrous species (H2O and Si-OH) on nano-porous alteration layers (gels) formed on a boroaluminosilicate glass called International Simple Glass corroded in aqueous solutions at pH 7 and pH 9, and initially saturated with soluble silicon-containing species were analyzed using linear and non-linear vibrational spectroscopy in combination with molecular dynamics simulations. The simulation results revealed various possible types of hydrogen bonds among these hydrous species in nanoconfinement environments with their populations depending on pore-size distribution. The nano-porous gels formed on corroded glass surfaces enhance hydrogen bond strength between hydrous species as revealed by attenuated total reflectance infrared spectroscopy. Sum frequency generation spectroscopy showed some significant differences in hydrogen bonding interactions on alteration layers formed at pH 7 and pH 9. The glass dissolution under the leaching conditions used in this study has been known to be ten times faster at pH 7 in comparison to that at pH 9 due to unknown reasons. The simulation and experimental results obtained in this study indicate that the water mobility in the gel formed at pH 9 could be slower than that in the gel formed at pH 7, and as a result, the leaching rate at pH 9 is slower than that at pH 7. [ABSTRACT FROM AUTHOR]

Knowing the structure of a material is necessary to understand its evolution under various influences; here, the alteration by water of a reference glass of nuclear interest, called International Simple Glass (ISG), is studied. The ISG atomic structure has not yet been thoroughly characterized. Short- and medium-range order in this six-oxide glass was investigated by molecular dynamics (MD) methods. Combining the simulated data with experimental observations acquired from both pristine and altered ISG provided new insight into the formation of surface layers and passivation of the underlying glass. In the tested conditions of 90 °C, silica-saturated solution, and pH90°C 7, the passivating layer partly inherits the structure of the pristine glass network despite the release of mobile elements (Na, B, and some Ca), with a reorganization of the silicate network following B release. The layer appears to minimize its internal energy by relaxing strain accumulated during glass quenching. The resulting passivated glass shows a strong resistance to hydrolysis. The nanopores of this hydrated material, displaying a mean pore size of ∼1 nm, are filled with various water species. Water speciation determination inside the nanopores is therefore an achievement for future water dynamic study in the passivated glass. Nuclear glass: developing a new layer of understanding A combination of experiments and simulations has provided insight into the structural changes of a glass of nuclear interest in solution. Borosilicate glasses are used as containment matrices for the highly radioactive waste that results from spent-nuclear-fuel reprocessing. They are stored in deep geological repositories and while this is seen as a relatively long-term solution, how they respond to their environment is of obvious importance. A team, led by Stéphane Gin at the CEA, Marcoule, France, have now studied the changes that a reference glass known as International Simple Glass (ISG) undergoes when exposed to water. Their simulations and analytical experiments provide insight into the structure of pristine ISG while also observing the generation of a passivating layer, which partly inherits the structure of the pristine glass but is less reactive with water. [ABSTRACT FROM AUTHOR]

Abstract Ballistic effects in simple sodium borosilicate ( Na 2 O B 2 O 3 = 1) and sodium alumino-borosilicate glasses ( Na 2 O − Al 2 O 3 B 2 O 3 = 1) were investigated using molecular dynamics simulations. Specifically, the glasses were irradiated with heavy projectiles that caused atomic displacements by elastic collisions (displacement cascades) and progressively damaged the bulk glass. The accumulated pressure and internal energy inside the glass were found to saturate with deposited energy. Furthermore, structural analysis of the irradiated glasses revealed several important ballistic effects including a decrease in glass density, depolymerization of the borosilicate network, and increase in chemical mixing, short range and intermediate disorder. The magnitude of radiation damage was found to depend on the glass composition and, in general, alumino-borosilicate glasses were found to be slightly less damaged, after irradiation, as compared to borosilicate glasses. Highlights • Simulated borosilicate and alumino-borosilicate glasses were irradiated by recoil nuclei. • Irradiation damage was quantified in terms of short- and medium-range disorder, density, randomness, and chemical mixing. • Alumino-borosilicate glasses were predicted to be less damaged than borosilicate glasses. [ABSTRACT FROM AUTHOR]

• The pore size of the simulated gels as well as the total porosity increases with increasing soluble element content in the initial glass. The gels with the largest pore size seems to present a more connected porosity. • The initial destabilization of the glass with the increasing departure of the soluble elements induces a larger and longer reorganization of the gels. The gels presenting the larger reorganization displays a linear evolution between both Al and Ca coordination numbers and the mean pore radius. • The structural defects of the "dry" gels are mainly borne by the aluminum, with a high 3-fold coordinated Al proportion, mostly at the pore surface, which can be due to a surface effect and/or the lack of availability of charge compensators. In fact these latter also accumulate at the pore surface. In contact with water, glass transforms into amorphous and porous structures called gels. A simulation method based on classical molecular dynamics is proposed here to mimic "dry" gels forming from initial oxide glass structures. Six glass compositions were investigated. Two behaviours were evidenced depending on the initial glass composition, and in particular on the quantity of elements removed. If a large quantity of soluble elements (B, Na) was removed, it induced an increase in the average pore size within the gels, and the time needed to stabilise the gel structure increased because more local atomic rearrangements occurred. The gel network displayed a higher proportion of Si-Q 4 at the expense of Si-Q 3 and a lower average ring size compared to the glass network, irrespective of the glass composition. Surface effects were also highlighted in the dry gels, such as the presence of 3-coordinated Al and a decrease in the average angle Si-O-Si and Al-O-Al. These findings will be compared to both wet gels and experimental data in further studies, to help find the best procedure to simulate such structures. [ABSTRACT FROM AUTHOR]

• A force matching procedure is used to fit a classical potential for dry and hydrated calcium aluminosilicate glasses. • The classical potential is refined by structural matching to improve the simulation of the glass structure. • The Ca environment and diffusion coefficient in water are well reproduced while the Al environment in water is less well reproduced. Potential development and refinement to improve the applicability and transferability of the forcefield is important to atomistic simulations of glass materials and their interactions with the environment. In this paper, we demonstrate potential development of calcium aluminosilicate glasses with and without water using a reactive potential framework by adopting the force matching technique and subsequent refinement. Accordingly, we have reproduced the forces on atoms of the system from a DFT based ab-initio molecular dynamics (AIMD) simulations by adjusting the potential parameters. We chose the diffuse charge reactive potential (DCRP) as the classical potential as it has been previously demonstrated to accurately and efficiently simulate interactions between water and silicate-glasses. The obtained force matched parameters were further refined to accurately reproduce the structures and dynamics of dry and hydrated calcium alumino silicate glass and gel structures. The Ca2+ behavior in solution was correctly reproduced with an average local coordination equal to 6.12 and a diffusion coefficient close to the experimental values. This force field also correctly reproduces the local environment of Al3+ in glass, but it falls short in describing Al3+ ion coordination in solutions as compared to AIMD results, suggesting a direction of future improvement. This set of potential can thus be used for simulations of calcium aluminosilicate glasses with various technological applications and hydrated gel structures resulted from corrosions of boroaluminosilicate glasses. [ABSTRACT FROM AUTHOR]