THE ROLE OF SODIUM IN THE MECHANISM OF INTERACTION OF SODIUM SILICATE MELT WITH AQUEOUS FLUID: EVIDENCE FROM 1H AND 23NA NMR

Abstract

Sodium silicate melts of the composition Na2O · RSiO2 (R = 3, 4) with varying water contents were studied by 1H and 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 dissociation 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.