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The application of the molecular dynamics computer simulation technique to the problem of elucidating alkali ion migration mechanisms in alkali silicate glasses is reviewed. Some new results are presented that help to clarify the processes and their timing. In particular, it is shown that alkali ions jump into empty sites; that is, the mechanisms owe more in character to their crystalline vacancy counterpart rather than their interstitial cousins.

Addition of alumina to sodium silicate glasses considerably improves the mechanical properties and chemical durability and changes other properties such as ionic conductivity and melt viscosity. As a result, aluminosilicate glasses find wide industrial and technological applications including the recent Corning(®) Gorilla(®) Glass. In this paper, the structures of sodium aluminosilicate glasses with a wide range of Al∕Na ratios (from 1.5 to 0.6) have been studied using classical molecular dynamics simulations in a system containing around 3000 atoms, with the aim to understand the structural role of aluminum as a function of chemical composition in these glasses. The short- and medium-range structures such as aluminum coordination, bond angle distribution around cations, Q(n) distribution (n bridging oxygen per network forming tetrahedron), and ring size distribution have been systematically studied. In addition, the mechanical properties including bulk, shear, and Young's moduli have been calculated and compared with experimental data. It is found that aluminum ions are mainly four-fold coordinated in peralkaline compositions (Al∕Na < 1) and form an integral part of the rigid silicon-oxygen glass network. In peraluminous compositions (Al∕Na > 1), small amounts of five-fold coordinated aluminum ions are present while the concentration of six-fold coordinated aluminum is negligible. Oxygen triclusters are also found to be present in peraluminous compositions, and their concentration increases with increasing Al∕Na ratio. The calculated bulk, shear, and Young's moduli were found to increase with increasing Al∕Na ratio, in good agreement with experimental data.

Molecular dynamics and related atomistic computer simulations are effective ways in studying the structures and structure–property relations of glass materials. However, simulations of boron oxide (B2O3)‐containing oxide glasses pose a challenge due to the lack of reliable empirical potentials. This paper reports development of a set of partial charge pairwise composition‐dependent potentials for boron‐related interactions that enable simulations of multicomponent borosilicate glasses, together with some of the existing parameters. This set of potentials was tested in sodium borate glasses and sodium borosilicate glasses and it is shown capable to describe boron coordination change with glass composition in wide composition ranges. Structure features such as boron N4 value, density, Qn species distribution, fraction of non‐bridging oxygen around boron and silicon, total correlation function, and bond angle distribution function were calculated and compared with available experimental data. Mechanical properties of the simulated glasses calculated with the new potential also show good agreement with experiments. Therefore, this new set of potential can be used to simulate boron oxide‐containing multicomponent glasses including those with wide industrial and technology applications.

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 pH 90°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.Published in partnership with CSCP and USTB Q n distribution for network former. Bond length r x−o , cutoff used for CN calculation (r out ), cation-averaged coordination number (CN avg ) and corresponding CN distributions in ISG. X are elements in the ISG composition Structure of International Simple Glass M Collin et al.

The surface structure of silica glasses has been simulated using molecular dynamics. The surface hydroxyl concentration was estimated to be 4.5/nm 2 , based on surface defect statistics. Hydroxyl-silica potentials were developed and used to study the hydroxylation of silica surface. It is found that the energy of chemisorption of water declines in the sequence: three coordinated silicon (Si 3 ) and non-bridging oxygen (NBO) on separate sites, Si 3 and NBO on combined sites, two-and three-membered rings. Partial hydroxylation of the most reactive sites, which leads to an OH coverage of 2.5/nm 2 , was studied. Structural relaxation after hydroxylation was observed. J ournal

All materials can suffer from environmental degradation; the rate and extent of degradation depend on the details of the material composition and structure as well as the environment. The corrosion of silicate glasses, crystalline ceramics, and metals, particularly as related to nuclear waste forms, has received a lot of attention. The corrosion phenomena and mechanisms of these materials are different, but also have many similarities. This review compares and contrasts the mechanisms of environmental degradation of glass, crystalline ceramics, and metals, with the goal of identifying commonalities that can seed synergistic activities and advance the current knowledge in each area.npj Materials Degradation (2018) 2:15 ; doi:10.1038/s41529-018-0037-2 INTRODUCTIONNew research activity focused on the environmental degradation of silicate glasses, crystalline ceramics, and metals relevant to nuclear waste forms and containers has recently been described.

Strontium substitution has been found to have a beneficial effect on tissue growth in traditional bioglasses. In this paper, we have studied the effect of SrO/CaO substitution on the structure of 45S5 bioglasses in the series of 46.1SiO 2 3 24.4Na 2 O 3 (26.9Àx)CaO 3 2.6P 2 O 5 3 xSrO (x = 0, 1, 5, 10, 15) compositions using molecular dynamics (MD) simulations with effective partial charge potentials and a combination of constant temperature and pressure (NPT) and microcanomical (NVE) ensembles. The calculated neutron structure factor and neutron broadened total correlation function of the 45S5 glass were compared with experimental diffraction data and the two were found to be in reasonable agreement with each other. The SrO/ CaO substitution effects on cation local environments were analyzed by studying the partial pair distribution functions, bond angle distributions, coordination number and its distribution. Change of the medium-range structures were characterized by Q n distributions and network connectivity, cationÀcation distributions and their aggregation, as well as the preference of modifiers around the glass former cations. It was found that strontium substitution leads to a linear increase of both molar volume and density. The SrÀO bond distance is found to be around 2.59 Å, and the average strontium coordination number is around 7.0 in the substitution series. The glass network structures such as Q n distribution and network connectivity does not change much with SrO/CaO substitution. Calcium and strontium ions were found to preferentially distribute around phosphorus ions. These structural and property changes were correlated to observed glass dissolution behavior and bioactivity of strontium-containing bioactive glasses.