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.

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Deficient spinel ZnMn2O4 with a hollow porous structure was prepared through a solvothermal carbon template dispersed by polyvinyl pyrrolidone.

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.