The Role of Sodium in the Mechanism of Interaction of Sodium Silicate Melt with Aqueous Fluid: Evidence from ~1H and ~23Na NMR

摘要

Sodium silicate melts of the composition Na_2O centre dot RSiO_2 (R = 3,4)with varying water contents were studied by ~1H adn~23Na NMR. It was found that Na~+ occurs in sodium silicate melt in two coordinations: (1) covalently bonded to oxygen in the fragment Si-O-Na and (2) incorporated into an oxygen niche formed by bridging oxygens with their unshared electron pairs. Water-melt interaction results in at least the partial disso-ciation of water molecules. Owing to its higher acidity, a hydrogen ion, H~+, replaces Na~+ from the bond Si-O-Na into an oxygen niche forming the bond Si-OH. Comparison of the NMR spectra of hydrous quartz and sodium silicate glasses allows us to suppose that Na~+ defines the mechanism of interaction of the sodium silicate melt and aqueous fluid. The Na~+ ions of the second type serve as coordination centers for water molecules.