Simulations of the surfaces of soda lime aluminoborosilicate glasses exposed to water

Abstract

Molecular dynamics simulations of 7 compositionally different sodium calcium alumino‐borosilicate glasses showed formation of 4B and 5Al more consistent with experimental data without compromising the other structural features that match experimental results observed in recent simulations of these glasses. Analysis of the dry surfaces of these glasses show a lack of 4B in the top 5‐6 Å of the surface in comparison to the bulk concentration for all glasses and no 5Al. Upon exposure to water, the simulations show that the 3B in the top 5‐6 Å of the glasses are preferentially attacked, decreasing the number of B bonds to O originally from the glass, indicating a change in the glass network. Inclusion of all B–O bonds in the top 5‐6 Å (i.e., including O from water) shows a decrease in 3B but an increase in 4B that is consistent with NEXAFS analysis, which the simulations show are hydroxylated. There is an increase in the concentration of 3Al in the dry surface in comparison to the bulk, but exposure to water converts almost all of these 3Al to 4Al. Hydroxyl concentrations vary from 2.6/nm2 to 4.1/nm2, with SiOH and BOH dominating these surface hydroxyls. Upon exposure to water, network linkages to B are preferentially ruptured. This, and the preferential loss of the nonbridging oxygen sites attached to Na, provide atomistic evidence of the initial stages of removal of B and Na from glass surfaces exposed to water.

Physical boundaries within aggregates – differences between amorphous, para‐crystalline, and crystalline Structures

“…the agglomerate-agglomerate interaction and the interaction between an silica surface and a DPPC bilayer were examined using the Dreiding forcefield [25]. From a model of the bulk amorphous SiO 2 system which has been equilibrated and relaxed using the glassff force field [26] surfaces were generated by cutting the bulk structure along an arbitrary plane. For generating hydroxylated surfaces, the bonds broken by the cutting step were saturated with hydroxyl groups, followed by a geometry optimization step.…”

Molecular dynamics simulation of ballistic effects in simplified nuclear waste glasses

“…However, depending on the way the glass is prepared, these potentials can overestimate the density [36]. Several other potentials have been derived to simulate borosilicate glasses [37][38][39][40][41][42] but their use has been limited due to either their complexity or their failure to simulate some compositions. Three Buckingham-based potentials, proposed by Jolley et al [43], Deng et al [33] or Stoch et al [44] were tested in this work.…”

Atomic and micro‐structure features of nanoporous aluminosilicate glasses from reactive molecular dynamics simulations

“…This force matching algorithm was carried out for Si‐Al‐Ca‐O glasses with H 2 O and resulted in parameters for all the pair and three‐body interactions. These were further refined based on generating calcium aluminosilicate glass structures using MD simulations and comparing these to structures generated with Teter 34 and Garofalini 35 potentials. The details of the potential development process will be elaborated further in a future publication.…”