Reaction mechanism of aluminosilicate glasses in aqueous solution from reactive molecular dynamics simulations

Reactive molecular dynamics simulations were performed to investigate interfacial reaction mechanisms of sodium aluminosilicate (NAS) glass with water. Six NAS glass-water interfacial models for glasses with varying Al2O3/Na2O ratios were simulated using the Diffusive Charge Reactive Potential (DCRP) at different temperatures (298 K, 323 K, 343 K, 363 K) for up to 4 ns. Hydrolysis, ion-exchange, and proton transfer reactions at the interfaces were observed and analyzed. It was found that the hydrolysis of Al-O-Si and Al-O-Al happens more easily than that of Si-O-Si. Formation of Al-(OH)-Si or Al-(OH)-Al intermediates or penta-coordinated Al was found to precede the Al-O-Al/Si bond breakage. Proton transfer facilitates water diffusion into the glass bulk mainly through Si-OH rather than Al-OH. Surface silanol concentration depends both on the temperature and alumina content. The initial reaction rates (t < 500 ps) for silanol formation at different temperatures were calculated and showed a decrease in reaction rate for glasses with higher alumina at all temperatures.