Behaviors of sodium and calcium ions at the borosilicate glass–water interface: Gaining new insights through an ab initio molecular dynamics study

Abstract : 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 Ca$^{2+}$ 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 Ca$^{2+}$ cannot leave the surface of CNBS glass. This release is correlated with the vacancy energy of Ca$^{2+}$ and Na$^+$ cations. Here, we found that the CNBS structure with the Na$^+$ cation vacancy is energetically more favorable than the structure with the Ca$^{2+}$ 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.