Elucidating the Atomic Structures of the Gel Layer Formed during Aluminoborosilicate Glass Dissolution: An Integrated Experimental and Simulation Study

Altered glasses produced during the aqueous dissolution of silicate and borosilicate glasses are among the most complex structures to understand at the atomic level due to their amorphous nature, random porosity, and various levels of hydration. In this study, we gained insights into the complex atomic structures of altered aluminoborosilicate glasses by combining a range of experimental and computational approaches. The altered glasses were prepared by the dissolution of three glasses with varying levels of alumina in an acid for 7 days. A comprehensive set of experimental [elemental analysis, high-energy X-ray diffraction, 29Si and 27Al solid-state nuclear magnetic resonance (NMR), and O 1s X-ray photoelectron spectroscopy (XPS)] and modeling (molecular dynamics (MD) simulations using nonreactive and reactive force fields) approaches were used to study the atomic structures of these altered glasses. Elemental analysis showed that most of the B in the pristine glasses was leached into the solution and was not contained in the altered glass. The 29Si and 27Al solid-state NMR spectra revealed that the altered glasses have more polymerized silicate networks as compared to those in the pristine glasses due to the reformation of linkages among Si and Al oxygen polyhedral in the altered glasses. The bridging and nonbridging (or hydroxyl O) atoms in the altered glasses were also quantified from their O 1s XPS spectra. Atomic structure models of the altered glasses were constructed using MD simulations using the reactive force field based on the compositional information obtained from experiments. Various pore structures were generated using the charge-scaling (CS) method using different initial densities and CS temperatures; the best CS parameters of each altered glass were then determined by comparing with the experimental structure factors obtained from high-energy X-ray diffraction. Pore and atomic structures and vibrational properties around these pore surfaces were analyzed. These results from this comprehensive study thus provide a realistic insight into the pore morphology, atomic structure, and vibrational properties of altered glasses.